&EPA
     United States
     Environmental Protection
     Agency
               United States
               Environmental Protection Agency
Office of Radiation and Indoor Air
Radiation Protection Division (6608J)
EPA 402-R-09-002
January 2009

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                      January 2009 EPA/402/R-09/002
Potential Nano-Enabled
Environmental
Applications for
Radionuclides
By
EnDyna, Inc.
McLean, VA 22102

EPA Contract No. 07-HQ-02407

Project Officer
Madeleine Nawar
Radiation Protection Division
U.S. Environmental Protection Agency
Washington, DC 20460
 1 Office of Radiation and Indoor Air
 I Radiation Protection Division

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Preface

"Potential  Nano-Enabled  Environmental  Applications  for  Radionuclides"  is   an
informational document designed to  familiarize interested parties with some of the
emerging nanotechnologies, and to recognize their potential environmental applications
and  implications.  Specifically, it  is  developed to  assist  in decision  making  for
incorporating nano-enabled technologies in mitigation of environmental contaminants
including radionuclides. The document represents a snapshot in time to elucidate some of
the base knowledge of nano-science which has evolved over the last 5-10 years. For the
purposes of this  document, "nano-enabled technologies  and/or  processes" refer  to
technologies which are enabled by a nano subsystem.

This document may be updated in the  future, and if you  have any comments on the
document or suggestions  for  incorporation  in future  updates,  please contact:  Ms
Madeleine Nawar,  USEPA, ORIA, RPD, 1200 Pennsylvania Ave., NW (MC 6608J),
Washington DC 20460-0001, USA, Phone: 202-343-9229, Fax: 202-343-2306, Email:
nawar.madeleine@epa.gov

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                                                                Disclaimer

The opinions expressed within this report do not necessarily represent the views of the
U.S.  Environmental Protection Agency (EPA). Mention of trade names or commercial
products  does  not  constitute  endorsement or  recommendation  for  use.  Similarly,
exclusions or absence of specific references is merely an indication that information
related to that  entity  was  not readily  available  during the development of this
informational document.

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Acknowledgements

This report was developed by the Radiation Protection Division  (RPD) of the U.S.
Environmental Protection Agency's (EPA's) Office of Radiation and Indoor Air (ORIA).
Ms. Madeleine Nawar served as the EPA Project Manager. Several individuals provided
valuable  input on  the  content of this  report throughout its development. Special
acknowledgement and appreciation is extended to RPD management and colleagues for
their support and encouragement.

A multi-disciplinary set of individuals provided peer review are:
   •  Jim Alwood, Chemical Control Division, Office of Pollution Prevention  Toxic
      Substances. U.S. EPA
   •  Terry  Barton,  Senior Environmental  Scientist,  Superfund and Technology
      Liaison Program, U.S. EPA Region 6
   •  J.  Michael  Davis,  Ph.D.,  Senior Science  Advisor, National  Center  for
      Environmental Assessment, Office of Research and Development, U.S. EPA
   •  Brendlyn Faison, Ph.D., Office of Science and Technology, U.S. EPA
   •  Richard Mattick, [in collaboration with U.S.  EPA regional superfund  staff],
      Policy Analysis and Regulatory Management Staff, Office of Solid Waste and
      Emergency Response, U.S. EPA
   •  Najm Shamim,  Ph.D., Office of Pesticide Programs, Antimicrobials Division,
      U.S. EPA
   •  Richard Wiggins,  Ph.D., Senior  Science  Advisor; Research Planning and
      Coordination  Staff/National  Health  and  Environmental   Effects  Research
      Laboratory Office of Research and Development, U.S. EPA
   •  Ronald Wilhelm, Senior Scientist, RPD, ORIA, U.S. EPA

This document was prepared under Contract No. 07-HQ-02407, EnDyna, Inc., and under
the sponsorship of ORIA. Madeleine Nawar of EPA's RPD served as the Project Officer.
The primary authors were Dr. Smita Siddhanti and Dr. Ian Tasker, assisted by Daniel
Ruedy,  of EnDyna, Inc.   The  EnDyna project team wishes to acknowledge  the
contribution of the following individuals for  their valuable  comments, input, and
suggestions for this document's improvement.

   •  Rafaela Ferguson, RPD, ORIA, U.S. EPA
   •  Dr. Eric Nuttall, the University of New Mexico
   •  Dr. Igor Linkov, U.S. Army Corps of Engineers

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                                                   Table of Contents

Executive Summary	vii

1.0  Introduction	1
  1.1   Definition of Nanotechnology	1
  1.2   Purpose of This Report	1
  1.3   Background of Nanotechnology	2
  1.4   Application of Nanotechnology	3
  1.5   Risk Associated with Nanoparticles in the Environment	4
    1.5.1   Nanomaterial Properties Associated with Risk	5
    1.5.2   Possible Approaches to Nanotechnology Risk Assessment	6
    1.5.3   Data Gaps and Limitations for Nanomaterials Risk Assessment	7
    1.5.4   Approaches to Managing Nanotechnology Risk	9
  1.6   Nanotechnology for Environmental Remediation	12
    1.6.1   Current Applications	12
    1.6.2   Awareness of Potential Environmental Benefits	13
    1.6.3   EPA's Involvement in Nanotechnology	14
    1.6.4   International Involvement  in Nanotechnology	18
  1.7   Nanotechnology for Environmental Remediation of Radionuclides	19
    1.7.1   Technical Status	19
    1.7.2   Rational Approach to Design in Nanotechnology	20
  1.8   Structure of This Report and Summary of Examined Technologies	21
  1.9   References	25

2.0  Nano-Enabled Remediation Technologies	30
  2.1   Introduction	30
  2.2   Zero-valent Iron Nanoparticles	32
    2.2.1   Background	32
    2.2.2   Description	32
    2.2.3   Summary of Environmental Potential	37
    2.2.4   References	37
  2.3   Self-Assembled Monolayers on Mesoporous Supports	39
    2.3.1   Description	39
    2.3.2   Operational Considerations	43
    2.3.3   Summary of Environmental Potential	43
    2.3.4   References	44
  2.4   Membranes: Nanofiltration  and Affinity	46
    2.4.1   Background	46
    2.4.2   Nanofiltration Membranes	46
    2.4.3   Summary of Environmental Potential	50
    2.4.4   Electrospun Fibers	50
    2.4.5   Surface Modified Membranes	52
    2.4.6   References	55
  2.5   Zeolites	58
    2.5.1   Introduction	58
    2.5.2   Description	58

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    2.5.3   Potential Applications	59
    2.5.4   Impacts, Hazards, Efficacy, and Limitations	62
    2.5.5   Management of Zeolite Wastes	62
    2.5.6   Summary of Environmental Potential	64
    2.5.7   References	65
  2.6   Other Nanoparticles	69
    2.6.1   Nanodiamonds	69
    2.6.2   Dendrimers	72
    2.6.3   Argonne Supergel	74
    2.6.4   Summary of Environmental Potential	75
    2.6.5   References	75
  2.7   Uranium Reduction by Bacteria	77
    2.7.1   References	83
  2.8   Carbon Nanotubes (Fullerenes)	85
    2.8.1   Background	85
    2.8.2   Description	85
    2.8.3   Operational Considerations	89
    2.8.4   Summary of Environmental Potential	89
    2.8.5   References	90

3.0  Nano-Enabled Sensor Technologies	94
  3.1   Introduction	94
    3.1.1   Basics	94
    3.1.2   Chemical Sensors	95
    3.1.3   The Trend towards Miniaturization	96
    3.1.4   Opportunities	97
    3.1.5   References	98
  3.2   "Lab-on-a-Chip"	99
    3.2.1   Summary of Environmental Potential	102
    3.2.2   References	102
  3.3   Microcantilever Sensors	103
    3.3.1   Summary of Environmental Potential	107
    3.3.2   References	107
  3.4   Spectroscopic Sensors	109
    3.4.1   Probe Encapsulated by Biologically Localized Embedding	Ill
    3.4.2   Surface Plasmon Resonance	112
    3.4.3   Summary of Environmental Potential	114
    3.4.4   References	114
  3.5   Nanowire Sensors	117
    3.5.1   Background	117
    3.5.2   Description	117
    3.5.3   Summary of Environmental Potential	120
    3.5.4   References	120
  3.6   Nanobelts and Nanorods	122
    3.6.1   Nanobelts	122
    3.6.2   Nanorods	123
    3.6.3   References	126

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4.0  Observations and Conclusions	128

Appendix A: Acronyms	131
Appendix B: Glossary	133
References for Figures	138

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Executive Summary

The remediation of radionuclides and heavy metals using current technology is generally
a costly and challenging proposition. Though funds for new technology development are
limited, the need for innovative technologies and transformational approaches continues
to be strong. In recent  years,  nanotechnology has risen to the forefront  and the  new
properties and enhanced reactivities offered by nanomaterials may offer a new, low-cost
paradigm  to solving  complex  environmental  and engineering problems.  Many U.S.
federal  agencies,  including the U.S. Environmental Protection  Agency  (EPA), are
strongly supporting  a wide range of nanotechnology research. Similarly, other countries
are also promoting research in this new field.

Environmental technologies frequently emerge as  an offshoot of other technological
developments or scientific advances. They can also be further enabled by changes in
regulatory  approach  or stakeholder  acceptance.  Technologies such  as  real-time
contaminant measurements within the EPA Triad framework, bioremediation, permeable
reactive barriers,  in-situ chemical oxidation, and enhanced attenuation have all been
added to the toolbox of environmental technologies over the past decade. During roughly
the same period, nanotechnology has evolved from an interesting (albeit arcane) area of
manufacturing science, to being heralded as a paradigm-shifting technological revolution
in the mold comparable to that of information technology or biotechnology. Coupled with
this  broad  evolution,  there   has   been  a  considerable amount  of  interest in
nanotechnologies  for a wide variety of applications in  environmental remediation and
waste reduction. For example, zero-valent iron (ZVI) nanoparticles for the remediation of
chlorinated organics have effectively become a commercially-available technology. A
number of  other  technologies,  such  as nano-scale  photocatalysts  and  improved
nanofiltration membranes, are also nearing commercialization.

Nanotechnologies applied to the remediation of radionuclides have been a slower area to
develop; this may well have been predictable since experience shows that the pathway for
development of radionuclide  remediation technologies  is generally burdened with
difficulties. However,  it is important to realize that—although our conceptual awareness
of nanotechnology is relatively  new—nanotechnologies have in fact been used safely and
effectively in the management  of radioactive waste almost from the start of the nuclear
age; zeolites, now recognized as a nanotechnology due to their nanostructure, have been
used as ion exchangers to remove radioactive components from aqueous waste solutions
for half a century.

In this report, the current, early  stages of development of nanotechnology applications for
remediation  of radionuclides  and heavy metals  are  divided into  two  areas:  new
remediation  methods and advancements in  sensors. Though developments in these fields
still remain  in  their early  stages, this report  describes some  of the more promising
remediation  nanotechnologies  and new sensors, and attempts to extrapolate general
developments  in  nanotechnologies  to  advances  in  radionuclide  remediation  and
monitoring.  Some emerging examples already exist in both radionuclide remediation and
monitoring.  For example, the  "Lab-on-a-Chip" (LOG)  device for analyzing solutions

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containing  radionuclides and  heavy metals  is a  promising development. Though  a
recently-emerged technology, the LOG device is being actively investigated in the United
States and overseas for modification to radionuclide sensing, is advancing quickly, and is
already being applied to radionuclides and heavy metals. Examples of other new sensor
advances are reviewed and presented in this report.

There is considerable potential for nanotechnology to assist with the remediation of
radionuclide-contaminated  sites. For  example, ZVI nanoparticles,  a  reducing agent
already implemented for the remediation of chlorinated organics in groundwater, are an
excellent prospect for use as a reducing agent to precipitate uranium from contaminated
groundwater.   ZVI  nanoparticles  are  commercially  available,  and  field tests  for
remediation of  heavy  metals  such  as chromium (IV)  have shown promise.  Two
advantages of ZVI are the greater aerial distribution in saturated porous media and a high
degree of reactivity  due to the greater surface area of these very fine  particles. Another
example  is the Self Assembled  Monolayers on Mesoporous  Supports (SAMMS)
technology, originally developed by the Department  of Energy  (DOE)  primarily for
mercury  but also with  radionuclides  in  mind, which  has recently  had  its first  field
implementation.

There are strong scientific basis and solid research demonstrating that nanotechnologies
will make  significant advances over a wide range of technological fields.  Government
agencies around the world and the commercial sector now invest billions of dollars into
nanoscience and technology research and development. However, the amount of funding
environmental  nanoscience  research and development receives represents only a fraction
of this massive overall effort. Hence, environmental nanoscience has lagged significantly
behind other application and development areas in the nanoscience  field.  Because of
growing  national and international interest  in the environment,  it is expected that
environmental  nanoscience will grow.

This report presents a general introduction to nanotechnology, providing a broad context
to its narrower  focus on  nanotechnology for environmental remediation and waste
management.   The  introduction also  addresses  some  risk  considerations involving
nanotechnology, and discusses nanotechnology   as  applied  to  both  environmental
remediation (in general)   and the environmental remediation of  radionuclides (in
particular).  The  body of the document  consists of two main sections, one surveying
nanotechnologies for remediation, the other  surveying nanotechnologies  for  sensors.
These two  sections are divided into chapters which describe a nanotechnology or group
of related nanotechnologies, and include a brief summary of the environmental potential
of each.

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1.0  Introduction

1.1    Definition of Nanotechnology

Nanotechnology is the art and science of manipulating matter at the atomic or molecular
scale and holds the promise of providing significant improvements in technologies for
protecting the environment. While many definitions for nanotechnology exist, the U.S.
Environmental Protection Agency (EPA) uses the definition developed by the National
Nanotechnology Initiative (NNI),  a U.S. Government research and development (R&D)
program established to coordinate multi-agency efforts in nanoscale science, engineering,
and technology.  The NNI is comprised of 26 federal agencies, 13 of which have R&D
budgets in nanotechnology.  The NNI (NNI 2007) requires nanotechnology to involve all
of the following:

    1.  Research   and   technology  development  at   the   atomic,   molecular,   or
       macromolecular levels, in the length  scale of approximately 1-100 nanometer
       (nm) range in any direction;
   2.  Creating and using structures, devices, and systems that have novel properties and
       functions as a result of their small and/or intermediate size; and
   3.  Ability to control or manipulate on the atomic scale.

Nanotechnology is thus the technology of the extremely small; one nm is defined as one
billionth of  a meter. In comparison, 1 nm is  one fifty-thousandth of the diameter of a
human hair, or, if a nanometer was scaled  to the diameter of a child's marble, then a
meter would have to be scaled to the diameter of the Earth. Nanotechnology is often
regarded as  being  a product of the latter part of the twentieth century, a product of the
drive towards miniaturization led by the semiconductor industry. However, in a broader
sense, nanotechnology has been around, albeit unrealized  as such, for a long time. Two
thousand years ago the ancient Greeks used a permanent hair-dying recipe that worked by
depositing 5 nm lead sulfide crystals inside hair. High-quality steel made in India before
the  turn of the first millennium has been  shown to  contain—and owe its outstanding
properties to—carbide structures similar to  modern carbon nanotubes. Medieval artists
colored stained glass using metal nanoparticles.  The difference between these ancient
examples of "nanotechnology"  and the current situation is the ability to understand—or at
least embark on a path towards understanding—the fundamental principles underlying
nanotechnological  behavior, the ability to assess the current state of knowledge, and the
ability to systematically plan for the future based on that knowledge.

1.2    Purpose of This Report

The  purpose of this report is to assist EPA in its exploration  of the potential for using
nano-enabled technologies in the cleanup of radioactive contamination, and in decisions
to assist with the development of viable technologies in this area.  For the purposes of this
report, "nano-enabled technologies" refers to technologies that  are enabled by a nano
sub-system.  This report will be used to identify and evaluate emerging applications and

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implications  (both  health and ecological)  of  nano-enabled technologies for  the
remediation of sites contaminated with radionuclides.

1.3    Background of Nanotechnology

The history of nanotechnology is generally understood to have begun in December 1959
when physicist Richard Feynman gave a speech, "There's Plenty of Room at the Bottom"
(Feynman 1959), at an American Physical Society meeting at the California Institute of
Technology in which he identified the potential  of  nanotechnology. Feynman  said it
should be possible to build machines small enough to manufacture objects with  atomic
precision, and that if information could be  written on  an atomic scale,  "all  of the
information that man  has carefully accumulated in all  the  books in the world  can be
written ... in a cube of material one two-hundredths of an inch wide—about the  size of
the smallest piece  of dust visible  to the  human eye."  He claimed that there were no
physical laws preventing such achievements, while noting that physical properties would
change in importance (e.g., gravity  becoming less important), though surface  phenomena
would begin to dominate behavior.

In 1974, Norio Taniguchi first used the  word "nanotechnology" (Taniguchi 1974), in
regard to an ion sputter machine, to refer to "production technology to get the extra-high
accuracy and ultra-fine dimensions, i.e.  the preciseness and fineness on the order of one
nanometer." In the 1980s, Eric Drexler  authored the landmark book on nanotechnology,
"Engines of Creation" (Drexler 1986), in which the concept  of molecular manufacturing
was  introduced to  the public at large.  It is due to Drexler that much of the public's
imagination  has   been  captured  by    the   potential   of  nanotechnology  and
nanomanufacturing. In  1985, fullerenes, or "buckyballs," were discovered (Kroto et al.
1985). By the 1990s, nanotechnology was advancing rapidly. In 1990, the first academic
nanotechnology journal was published, in 1993 the first Feynman Prize was awarded, and
by 2000 President Bill Clinton announced the U.S. National Nanotechnology Initiative
(NNI).  NNI and other nanotechnology proponents now anticipate  the development of
nano-enabled tools to help address many current challenges facing the United States and
the international community, including:

   •   Clean, secure, affordable energy;
   •   Stronger, lighter, more durable materials;
   •   Low-cost filters to provide clean drinking water;
   •   Medical devices and drugs to detect and treat diseases more effectively with fewer
       side effects;
   •   Lighting that uses  a fraction of the energy associated with conventional systems;
   •   Sensors to detect and identify harmful chemical and biological agents;  and
   •   Techniques to clean up harmful chemicals in the environment.

This document focuses on the  last  of these challenges—techniques  to clean  up harmful
chemicals  in  the  environmental.  Nanotechnologies  offer  new   and  previously
unanticipated possibilities due to new properties and behaviors that occur at the nano
scale, which can be harnessed in a structured and planned manner. The growing ability to

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design and tailor technologies to specific ends indicates that problems that were  once
regarded as impossible to solve can now be addressed in a rational manner. The size of
nanoparticles allows  nanoscale  behavior to be introduced into areas inaccessible to
conventional  technologies. When material exists in the nanoparticulate form, it exhibits
unusual behavior that has made it the subject of great interest. This unusual behavior is
the result of two phenomena. First, the surface area-to-volume  ratio of nanoparticles is
much greater than that of larger particles. Nanoparticles in the 10 nm range can have 50%
of their molecular structure exposed to the surface, a percentage that is millions of times
greater than that of typical powdered materials.  Since chemical reactivity and catalytic
ability is directly related to surface area,  chemical  properties are greatly  enhanced.
Second,  at the  nanoparticle  scale, quantum behavior that is typically masked in larger
particles can be readily displayed.

1.4    Application of Nanotechnology

Descriptions of nanotechnology that characterize it purely in terms of the minute size of
the physical features with which it is concerned—assemblies between the size of an  atom
and about 100 molecular diameters—make it sound as though nanotechnology is merely
using infinitely smaller parts than conventional engineering. However, working matters
are truly more complex; rearranging the atoms and molecules leads to new properties and
unusual  behaviors.  A transition is apparent between the fixed behavior  of individual
atoms and molecules and the adjustable behavior of collectives.  Many scientists are now
investigating  the fundamental nature of nanotechnology in a wide spectrum of academic
fields—from  the basic sciences  to engineering.  Much of known science  (e.g., colloid
science,  electronics, chemistry, physics, and genetics) will be applicable, but augmented
with exciting new breakthroughs.

The potential applications of nanotechnology range across a broad scale. For example, in
medical  systems, it could be possible to improve the tissue compatibility of implants to
create scaffolds for tissue regeneration, or perhaps even to build artificial organs. Further,
new types of genetic therapies and anti-aging treatments could be possible.

Nanotechnology  is  currently used  by  leading  businesses  and  industrial  research
companies for a variety of technical and innovative applications. Examples include:

    •   ExxonMobil is using zeolites, minerals with pore sizes  of less than  1  nm, as a
       more  efficient catalyst to break down or crack large hydrocarbon  molecules to
       form gasoline.
    •   IBM  has added  nanoscale layering to disk drives, thus  exploiting the  giant
       magnetoresistive effect to attain highly dense data storage.
    •   Gilead Sciences is using nanotechnology in the form of lipid spheres, also known
       as liposomes, which  measure about 100 nm in diameter, to encase  an anticancer
       drug to treat the AIDS-related Kaposi's sarcoma.
    •   Carbon  Nanotechnologies, a  company  co-founded  by  buckyball  discoverer
       Richard E. Smalley, is making carbon nanotubes more affordable by using a new
       and more efficient manufacturing process.

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    •   Nanophase Technologies is utilizing nanocrystalline particles, incorporated into
       other materials, to produce tough ceramics, transparent sun blocks, and catalysts
       for environmental uses, among other applications.

Though  vastly  different  in  the  outputs they  produce, these  companies all use
nanotechnology   to  develop   more  efficient,   affordable,   and,   most   recently,
environmentally-safe products.

1.5    Risk Associated with Nanoparticles in the Environment

As  previously  noted,  the  potential  widespread  application of  nanomaterials  in
environmental remediation is made possible by the miniaturization of materials down to
the nano-scale.  However, this  same enabling characteristic  also  influences risk by
changing  the  particles' potential  for mobility,  exposure, absorption,  reactivity, and
toxicity. When a nanomaterial is used for  environmental remediation, it is intentionally
introduced into the environment to exploit its unique properties. For example, nano-sized
colloidal iron nanoparticles can act as catalysts in redox reactions.  Of particular concern
is the  potential  mobility  of nanoparticles  out of targeted sites or tissues, or whether
intentional or unintentional releases of highly mobile nano-particles into the environment
could be controlled (CRS 2008).

Nevertheless,  nanomaterials  can  have side  effects,  and a risk  assessment requires
knowledge of their distribution in the environment and food chain. Risk assessment is
required for understanding  the nanoparticles'  behavior to evaluate  potential risks
associated with nanomaterial use for remediation. Side effects associated with the use of
nanotechnology, especially environmental  risks associated with residual nanomaterials'
fate and transport  in the environment, are  not yet fully  explored and  understood.
Uncertainties of the nature and interaction of nanomaterials in the following areas add to
the complexity of risk concerns.  These include: uncertainty in relationship between size,
surface area, and surface reactivity; and uncertainty in relationship of radionuclides and
nanomaterials. A clear understanding of the relationship between these parameters is still
evolving  and is  not  yet  clearly understood. Additionally, the  relation  between
radionuclides and nanomaterials is not yet determined.

Risk assessment is practiced by EPA and other federal agencies as a tool to evaluate risks
associated  with  chemicals  and radionuclides in  the environment. Risk assessment
approaches and procedures have been formulated by the National Academy  of Sciences,
and have been subsequently tailored to specific applications by EPA and other federal
agencies.  EPA  risk assessment has four components:  hazard identification, toxicity
assessment,  exposure  assessment, and risk characterization. Although the risk assessment
paradigm has been used successfully by the scientific community since the early  1980s,
its  application  to  nanotechnology  requires  incorporating an uncertainty  in  basic
knowledge that is very large when compared  to the uncertainty for other materials and
Pharmaceuticals. To do so requires an understanding of product life-cycle and the ability
to communicate  effectively with personnel,  stakeholders, and regulators.

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Although risk assessment/management of conventional  chemicals is well  established,
nanotechnology  risk  assessment is an emerging field; there is a growing body of
scientific literature dealing with potential associated risks, including:
   •   Effects of nano-particle introduction on soil chemistry /fertility /texture;
   •   Fate and transport  (e.g., zero-valent iron  (ZVI) or ZVI-uranium-contaminated
       nano-particles);
   •   Exposure pathways and assessment (including environmental and  occupational
       exposures, both chronic  and acute);
   •   Dose-response  relationship  and toxicity (including effects on  organs such as
       lungs, gills, liver, kidneys, and immune systems);
   •   Bioaccumulation and biomagnification (e.g., food chain); and
   •   Effects on  humans  as well  as  effects on ecosystems, ranging from impacts at
       molecular (nano) scale  through the microbial (microorganisms) and  the meso
       (small animals) to the macro (large animal communities).

The following sections provide a brief overview of: nanomaterial properties potentially
associated  with  risk  (1.5.1), possible approaches  to nanotechnology  risk assessment
(1.5.2), data gaps and limitations for assessing nanomaterial risk (1.5.3), and an overview
of the proposed frameworks for risk management (1.5.4).

1.5.1  Nanomaterial Properties Associated with Risk

Characteristics  of nanomaterials potentially leading  to increased toxicity, risks  and
associated  modifying factors have been discussed in recent literature (Biswas and Wu
2005, Borm and Muller-Schulte 2006, Borm et al. 2006, Gwinn and Vallyathan 2006,
Kreyling et al. 2006, Medina et  al. 2007, Nel et al. 2006, Oberdorster et al. 2007, Thomas
and Sayre 2005). In general, the following properties of nanomaterials are discussed as
potential risk drivers:

   •   Chemical composition is one of the key factors discussed.  Nanomaterials may be
       derived  from bulk  materials with known toxic properties. Moreover, in many
       cases a given  nanomaterial  can be  produced by  different  processes yielding
       several derivatives of the same  material. It is important to note that the chemical
       properties of particles at the nanometer size can  differ  significantly  from the
       chemical  properties  of  larger particles  consisting  of the   same  chemical
       composition.
   •   Toxicity potential can be  caused by either chemical toxicity based on chemical
       composition or stress or stimuli caused by the surface, size, and/or shape  of the
       particle. Differentiation  between these two toxic effects  is not straightforward
       (Brunner et al. 2006), but the  size of the  particle  may indirectly dominate the
       uptake of particles into cells (Limbach et al. 2005, Kreyling et al. 2006).
   •   Surface reactivity can increase  the harm caused  by nanomaterial in a cell and
       reduce  the  potential  for environmental  degradation  (Limbach et al.  2007).
       Materials with active surfaces are deemed more harmful than the materials that lack
       such surfaces. It should be noted that  smaller particle size also means higher
       surface reactivity because more of the atoms are in the surface of the particle.

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   •   Solubility and environmental mobility have been proven to greatly affect the risk
       associated with nanomaterials (Brunner et al. 2006). Higher mobility results in
       higher risk, and insoluble materials or materials with nanoparticles embedded in
       a bulk material matrix may be less bioavailable.
   •   Agglomeration affects the toxicity as well. Particles that naturally agglomerate into
       larger units  can be interpreted  as  less toxic. Three agglomeration classes (low,
       medium,   and  high)  have  been  defined.  In  these,  highest  agglomeration
       corresponds to lowest risk.

1.5.2  Possible Approaches to Nanotechnology Risk Assessment

Though multiple  frameworks for nanomaterials risk assessment and  risk management
have been proposed, none has  been formally adopted as regulatory tool (Linkov et  al.
2008). Two examples of the representative risk assessment frameworks are presented in
this  section,  while multiple risk assessment and  risk  management frameworks  are
summarized in Section 1.5.5.

NanoRisk Framework

The NanoRisk Framework (www.NanoRiskFramework.com) was developed  by DuPont
Corporation and the Environmental Defense Fund to address the environmental, health,
and safety risks of nanomaterials across all stages of product life cycle.  It recommends
six distinct steps:

   •   Step 1. Describe Material and Application. Develop a general description of the
       nanomaterial and its intended uses, based on information in the possession of the
       developer or in the literature. The user also identifies analogous materials and
       applications that may help fill data gaps in this and other steps.
   •   Step 2. Profile Lifecycle(s). The second step defines a process to develop three
       sets of profiles—of the nanomaterial's properties, its inherent hazards, and its
       associated exposures throughout the material's lifecycle.  The properties profile
       identifies and characterizes a nanomaterial's physical and chemical properties.
       The hazard profile identifies and characterizes the nanomaterial's potential safety,
       health, and environmental hazards.
   •   Step 3. Evaluate Risks. In this step, all the information generated in the profiles is
       reviewed in order to identify and characterize the nature, magnitude, and
       probability of risks presented by this particular nanomaterial and its anticipated
       application. In so doing,  the user considers gaps in the lifecycle profiles,
       prioritizes those gaps, and determines  how to address them—either by generating
       data or by using, in place of such data," reasonable worst case" assumptions or
       values.
   •   Step 4. Assess Risk Management. Here the user evaluates the available options
       for managing the risks identified in Step 3 and recommends a course of action.
       Options include engineering controls,  protective equipment, risk communication,
       and product or process modifications.

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   •   Step 5. Decide, Document and Act. In this step, appropriate to the product's
       stage of development, the user consults with the appropriate review team and
       decides whether or in what capacity to continue development and production.
       Consistent with a transparent decision-making process, the user documents those
       decisions and their rationale and shares appropriate information with the relevant
       stakeholders, both internal and external.
   •   Step 6. Review and Adapt. Through regularly scheduled reviews as well as
       triggered reviews, the user updates and re-executes the risk evaluation, ensures
       that risk-management systems are working as expected, and adapts those systems
       in the face of new information (e.g., regarding hazard data) or new conditions
       (such as new or altered exposure patterns).

Through these six steps, the framework seeks to guide  a process for risk evaluation and
management that is practical, comprehensive, transparent, and flexible.

Comprehensive  Environmental Assessment Approach (Davis 2007):

The  Comprehensive Environmental Assessment (CEA) approach  combines life-cycle
perspective with the risk assessment paradigm.  This systematic approach could guide
research strategy for assessing the risks  of nanotechnology and avoid  unintended
consequences (Davis 2007). The CEA approach begins with assessing product life cycle
stages including  material  production or extraction, manufacturing processes, distribution,
storage, use,  and disposal (including recycling). At  any given stage of the life cycle,
nanoscale substances and/or associated materials (e.g., manufacturing by-products) might
enter one or more of the  environmental media—air, water,  soil—and affect humans and
ecological receptors through multiple pathways, including  food web. It is important to
identify nanomaterials in their primary form and, further, to consider the transport and
transformation processes they may undergo during the product life cycle.

To evaluate exposure in a comprehensive manner, it is important to consider,  among
other things,  both aggregate exposure across routes  (inhalation, ingestion,  and  dermal
absorption) and cumulative exposure to multiple (primary and secondary) pollutants. The
CEA approach tends to  focus on the range of exposure scenarios, including  micro-
environmental and high-end exposures, not just "typical" or "average" exposure levels.
The human health and ecological hazards associated with respective contaminants can be
described qualitatively and, if possible, quantitatively.

±5.3  Data Gaps and Limitations for Nanomaterials Risk Assessment

Though the use of nanomaterials is increasing, understanding the environmental fate and
transport,  toxicity, and  potential human health and ecological risks  associated with
nanomaterial use remains extremely limited.  This is  due to a variety of barriers, including
proprietary nature of information; and lack of standardization  in nomenclature, metrics,
and materials (CRS 2008).

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Risk assessment requires information related to the following four components: hazard
identification, toxicity assessment, exposure assessment,  and risk characterization.  For
human health and environmental risk assessment of nanomaterials, the current knowledge
base contains data gaps.  The literature has established these knowns (things we know that
we know) and unknowns (things we know that we don't know) in the nanotechnology
context for the four components (Davis 2007). Some of the data gaps for each of the risk
assessment components  are described below.

    •   Predicting the environmental fate of nanomaterials: At present there  are  few
       available studies on the environmental fate of nanomaterials but they are not
       adequate  to  predict the  fate  of nanomaterials based on  their fundamental
       properties. Nanomaterials released to soil  and ground water as part of remedial
       activities can be strongly sorbed into soil due to their high  surface  areas,  and
       therefore become immobile. On the other hand, nanomaterials are small enough to
       fit into the smaller spaces between soil particles, and therefore might travel farther
       than larger particles before becoming trapped in the soil matrix. In addition to the
       nanomaterial properties discussed above,  types and properties of the  soil  and
       water  can  affect nanomaterial mobility.  Since nanoparticles are likely  to be
       transported as colloids,  the mobility of mineral colloids in soils and sediments and
       the availability of humic substances are important considerations. Additionally, in
       the  presence of   various  soils  having different pH, and  radionuclides,
       nanomaterials may  form different byproducts. The fate  of nanomaterials in
       aqueous  environments  is  controlled  by solubility or dispersability; interactions
       between the nanomaterial and natural and anthropogenic chemicals in the system;
       and biological and abiotic  processes. Light-induced photoreactions are often
       important in determining the environmental fate of chemical substances.

    •   Nanomaterial toxicity and bioaccumulation potential: Past literature provides some
       evidence of toxicity and bioaccumulation  potential, but the results are generally
       inconclusive. Laboratory testing of nanomaterial uptake has shown a wide  range of
       potential  affects on tested organisms,  including  bioaccumulation potential,
       mortality, and biomarker-response. Nevertheless, the concentration of nanoparticles
       used in this and other studies may far exceed concentrations that could potentially
       result from those that would be associated with site remediation.

    •   Exposure estimation:  When  a  nanomaterial  is  used  for  an  environmental
       application,  exposure estimation might not be straightforward. Multiple variables
       could influence nanomaterial exposure assessment, including the characterization
       of the effectiveness  of variations in biological reactivity, size,  shape, and charge,
       as well as factors that complicate the straightforward  estimation of exposure such
       as metabolism, excretion, and adduction to biological molecules.  For example,
       several studies on carbon nanotubes have shown that  the toxicity and distribution
       of nanoparticles  is dependent upon the presence of functional groups, impurities,
       fiber length, and  aggregation status.

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   •   Risk Characterization: Given estimates of exposure and toxicity, the final step
       involved in estimating the hazard of contaminant exposure is risk characterization
       (i.e., the likelihood  of  adverse environmental impact  at varying  degrees  of
       exposure).  Risk  characterization  must  be  developed  separately  for  each
       nanomaterial, or even for the same nanomaterials with different functions  or at
       different environmental life-cycle stages. Given the required effort, detailed risk
       characterization may not be  possible.  Decision tools and databases could be
       developed to allow the use of all available information, as well as proxy data for
       making the best judgment on risk characterization.

±5.4  Approaches to Managing Nanotechnology Risk

As a field of science, nanotechnology is still young and uncertainty in basic knowledge
does not lend itself to fully informed and accurate risk assessments, but scientific
evidence does exist that suggest some nanoparticles may be hazardous.  Some regulatory
and industry representatives caution that inadequate government  oversight, or  even  a
perceived lack  of oversight, could lead to  consumer rejection of an entire  range  of
products incorporating  nanotechnology.  Such a  reaction would significantly  hinder
development and industry growth. To prevent a loss of consumer confidence, academic
researchers, policy analysts, and some nanotechnology entrepreneurs have been working
with federal agencies that are responsible for protecting the environment, workers, and
consumers (CRS 2008).

Assessment and management of the potential risks associated with nanotechnology is a
challenge with  which U.S.  agencies and  countries in the European Union (EU) are
beginning to come to terms. Despite all the limitations, some progress in approaching
risk-based  nanotechnology regulation  is being  made.  In the  EU for example, the
European Commission (EC) has adopted the opinion of the Scientific  Committee on
Emerging  and  Newly  Identified  Health  Risks  (SCENIHR)  on  definitions  for
nanotechnology.  This advance takes one of the first steps towards risk assessment and
regulation:  standardizing nomenclature, metrics, and materials.  In addition, the EU is
currently conducting research to compare nanotechnology regulatory policies in the EU
with those in the United  States.  Similar to previous efforts  to reach coordination on
regulation (including beef, chemicals, and genetically modified organism regulations),
those involved are hopeful that this  research will improve transatlantic regulatory
cooperation of nanotechnology in the future (NanoReg News 2008).

A review of current nanomaterial risk management frameworks and related documents is
summarized in Table 1. Details of these can be found in the references provided.

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                Table 1: Current nanomaterial risk frameworks 1
Agency
               Focus
     Citation
U.S. Environmental
Protection Agency
(EPA) White Paper
Comprehensive framework intended to
set forth current scientific knowledge
and its gaps related to possible
environmental benefits of
nanotechnology, as well as potential
risks from environmental exposure to
nanomaterials.
  (US EPA 2007)
Federal Drug
Administration
(FDA)
Report intended to help assess questions
regarding the adequacy and application
of the FDA's regulatory authority to
nanomaterials, and to provide findings
and recommendations to the FDA
Commissioner.
  (US FDA 2007)
Woodrow Wilson
Center
Paper intended to describe the
possibilities for government action to
deal with the adverse effects of
nanotechnology, and to provide
evidence relevant for determining what
needs to be done to manage
nanotechnology.	
   (Davies 2006)
Environmental
Defense (EDF)-
DuPont
Comprehensive framework for the
responsible development, production,
use, and end-of-life disposal of
nanomaterials, intended for use by
companies and other organizations.
(EDF-DuPont 2007)
Quebec Commission
Comprehensive discussion of the
scientific, legal, and ethical implications
of nanotechnology, intended to help
uphold the protection of health and the
environment, as well as respect for
many values such as dignity, liberty,
integrity, justice, transparency, and
democracy.	
    (QC 2006)
Royal Society
Comprehensive framework intended to
summarize current scientific knowledge
and applications of nanotechnology, and
 (RS & RAE 2004)
   1 Linkov, I., Satterstrom, K., (2008). "Nanomaterial Risk Assessment and Risk
   Management: Review of Regulatory Frameworks." In: Linkov, I, Ferguson, E.,
   Magar, V. (in press). "Real Time and Deliberative Decision Making: Application to
   Risk Assessment for Non-chemical Stressors. Springer, Amsterdam.

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Agency
               Focus
     Citation
                      to identify possible health and safety,
                      environmental, ethical, and societal
                      implications or uncertainties.	
Department for
Environment, Food,
and Rural Affairs
(DEFRA)
Trial Voluntary Reporting Scheme to
collect data from organizations in the
nanotechnology  industry to help the
United Kingdom develop appropriate
controls for risks to the environment and
human health from nanomaterials.
(UK DEFRA 2006)
Responsible
NanoCode
Paper intended to highlight key issues
that emerged from a business workshop
on nanotechnology, including
development of a responsible
nanotechnology code.	
   (RNC 2006)
European
Commission
Scientific
Commission on
Emerging and Newly
Identified Health
Risks (SCENIHR)
Technical document intended to assess
the appropriateness of current risk
assessment methodologies for the risk
assessment of nanomaterials, and to
provide suggestions for improvements
to the methodologies.
  (EC SCENIHR
      2007)
European
Commission Action
Plan
Plan intended to help Europe build on
its strengths and advances to ensure that
nanotechnology research is carried out
with maximum impact and
responsibility, and that the resulting
knowledge is applied in products that
are useful, safe, and profitable.	
    (EC 2005)
International Risk
Governance Council
(IRGC) Policy Brief
Brief intended to assist policy makers in
developing the processes and
regulations to enable the development
and public acceptance of
nanotechnology.	
   (IRGC 2007)
IRGC White Paper 1
Comprehensive framework intended to
advance the development of an
integrated, holistic, and structured
approach for the investigation of risk
issues and the governance processes and
structures pertaining to them.	
   (IRGC 2005)
IRGC White Paper 2
Comprehensive framework which
applies general IRGC risk governance
framework to the field of
nanotechnology.	
   (IRGC 2006)

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In response to public concern for the protection of the environment and human health
from the potential hazards of nanomaterials, EPA has released a nanotechnology research
strategy to protect the environment (EPA 2008).  In addition,  EPA has also recently
completed  the Basic Program  phase of the EPA's  Nanoscale Materials  Stewardship
Program (NMSP), where some  organizations are showing their support for a successful
beginning of a voluntary information collection program (NanoReg News 2008).

Currently, the main challenge facing EPA is minimizing nanotechnology's  potential for
unintended, harmful  consequences, while pursuing the positive aspects of nanomaterial
use,  including potential  of  environmental remediation applications. In the Office of
Research and Development's (ORD) recently released Draft Nanomaterial Strategy (EPA
2008), EPA both builds on and is consistent with the NNI's previous reports,  as well as its
own Nanotechnology White  Paper (EPA 2007). In Draft Nanomaterial Strategy, EPA
gives special attention to its mission to protect the environment and its specific needs for
being able to regulate nanotechnology (NanoReg News 2008).  It also identifies four
major areas for future research:

   •   environmental fate and transport,
   •   human health implications,
   •   risk assessment methodology, and
   •   risk mitigation strategies.

Initially, EPA's  research will focus  on nanoscale titanium dioxide,  ZVI, nanosilver,
carbon  nanotubes, and cerium  oxide, with the intention  that the resulting body of
knowledge can be extrapolated for classes of nanomaterials in the future, particularly as
nomenclature, metrics, and materials become standardized.  Anticipated outcomes from
this research  program  are expected to be focused research products  that  address  risk
assessment and  risk management needs for nanomaterials in  support of the various
environmental statutes for which EPA is responsible (NanoReg News 2008).

1.6    Nanotechnology for Environmental Remediation

±6.1  Current Applications

Recent  advances  in  the  design, production, and fundamental understanding  of
nanomaterials have  led to preliminary investigations  of their use in the remediation of
chlorinated organics in the  subsurface,  and to a wide range of suggestions for their
potential use in the remediation of other environmental contaminants, including those at
radiologically-contaminated sites. The potential for innovative use is directly related to
the enhanced chemical  activity  resulting  from the  increased  surface area and  the
manifestation of quantum effects, yet it also  takes advantage of a third  feature of
nanoparticles,  namely  their  ability to be transported to  areas inaccessible to other
remediation approaches. For example, if we consider bioremediation, part of the promise
lies in the  fact that microbes capable of destroying  organic contaminants  can directly
access subsurface pore structure that is too small for regular particles to access. However,
there  is still  much  of the pore  structure in  the subsurface that is too small even for

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microbes. Nanoparticles are typically two orders of magnitude smaller than bacteria and
can thus be transported to an occluded contaminant that is hidden from direct bacterial
contact.  Current applications, discussed  in  more  detail  in  Sections 2  and 3 of this
document, include zeolites and nanoparticulate ZVI.

1.6.2  Awareness of Potential Environmental Benefits

Since nanotechnology  and nanomaterials are comparatively new technologies,  only
partial knowledge of the environmental fate,  transport, effects, and risks associated with
them is available, and some of this information appears to be contradictory. Ultimately,
this knowledge will be crucial in deciding whether a technology involving nanomaterials
is an appropriate remedy. Concerns in this regard have been so strong that a report by the
Royal  Society  (RS)  and  the Royal Academy  of Engineering (RAE)  in  the United
Kingdom has recommended  "that  the use  of free  (that is,  not fixed  in a matrix)
manufactured nanoparticles in environmental applications, such as remediation, should
be prohibited until appropriate research has been undertaken and it can be demonstrated
that the  potential benefits outweigh the  potential risks (RS/RAE 2004)."  Thus,  it is
important to conduct a comprehensive review and evaluation of both the effectiveness
and the potential impacts of available treatment options.

Within all  of the discussion  about  nanotechnology opportunities, consideration of the
application  of  nanotechnology  to  environmental  problems  seems  to  have   been
subordinated to consideration  of risks of nanotechnology. Though the potential has  been
recognized, often it is the risks posed to human health and  the environment that  have
dominated  discussion of nanotechnology  and the environment.  The term  "disruptive
technology" was introduced in 2003 (Uldrich and Newberry 2003) to  describe a new
technology that is  significantly cheaper (or performs  better)  than a current technology,
and will revolutionize worldwide markets by superseding the existing technology. The
industries on which nanotechnology will  likely have  a disruptive  effect were analyzed
and at the high-end (i.e., largest impact) included:
   •   Healthcare
   •   Long-term care
   •   Electronics
   •   Telecom
   •   Packaging
   •   United States Chemical
   •   Plastics
   •   Apparel
   •   Pharmaceutical
   •   Semiconductor

At the low-end, the industries included:
   •   Cosmetics
   •   Chocolate
   •   Batteries
   •   Blue jeans

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   •   Khakis
   •   Fluorescent tagging
   •   Mouthwash

At the time of Uldrich and Newberry 2003, the environmental industry was not classified
on the list.

±6.3  EPA's Involvement in Nanotechnology

Fortunately, nanotechnology in the environmental industry  is progressing,  gradually
becoming more  advanced and better recognized.  EPA is  obligated to protect human
health and  safeguard the  environment by better understanding and addressing potential
risks from  exposure to nanoscale materials, but it is also interested in researching and
developing the  possible benefits of nanotechnology.   Since  2001, EPA has played a
leading  role in  funding research  and setting   research directions  for  developing
environmental applications of nanotechnology. Two recent examples demonstrate EPA's
commitment:  the   "Nanotechnology   White  Paper"   and  the   "Workshop  for
Nanotechnology on Site Remediation."

In February 2007, EPA published the "Nanotechnology White Paper" (EPA 2007) based
on the work of a cross-Agency workgroup created  in December 2004 by EPA's Science
Policy Council. It describes key science issues EPA should consider to ensure that society
accrues the important environmental protection benefits that nanotechnology may offer.
The document notes that  since 2001, EPA's Science To Achieve Results (STAR) grant
program has funded 36 research grants—totaling nearly $12 million—in the application
of nanotechnology to protect the environment, including the development of:  1) low-cost,
rapid, and  simplified methods  of removing toxic contaminants  from  water; 2) new
sensors  that  are more sensitive  for  measuring  pollutants;   3)  green manufacturing
nanomaterials; and 4) more efficient, selective catalysts.  Additional projects have been
funded through the Small Business Innovation Research (SBIR) program, and there are
14 recent STAR program projects focused on studying the possible harmful effects, or
implications, of engineered nanomaterials.

This  white paper  also  describes  the  benefits,  risk  assessment,  and  responsible
development  of nanotechnology, and outlines the involvement in nanotechnology  by
various EPA Offices including:

   •   Office of Pollution Prevention and Toxics (OPPT)  — activities include reviewing
       premanufacture notifications for  a number of nanoscale materials that have been
       received  under the Toxics  Substances Control Act,  initiating a  Nanoscale
       Materials  Stewardship Program  to encourage  submission and  development of
       information          for         nanoscale          materials         (see
       http://www.epa.gov/oppt/nano/stewardship. htm),     public    outreach,     and
       international engagement on nanotechnology  issues with  the  Organization of
       Economic Cooperation and  Development and  International Organization for
       Standardization (ISO).

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   •   Office  of  Air and  Radiation/Office  of Transportation  and  Air  Quality
       (OAR/OTAQ) — activities include reviewing an application for registration of a
       diesel additive containing cerium oxide. Cerium oxide nanoparticles are being
       marketed in  Europe  as  on- and  off-road diesel fuel additives  to  decrease
       emissions, and some manufacturers claim fuel economy benefits.
   •   Office of Pesticide Programs (OPP) — activities include working with members
       of the  pesticide  industry  regarding  licensing/registration   requirements  for
       pesticide products that utilize nanotechnology.
   •   Office of Solid Waste and Emergency Response (OSWER) — activities include
       investigating potential implications and applications of nanotechnology by  such
       means as: an October 2005 workshop  on "Nanotechnology for Site Remediation"
       organized with EPA's ORD and several other federal agencies; and a July 2006
       symposium entitled,  "Nanotechnology and OSWER: New  Opportunities and
       Challenges."
   •   Office of Enforcement and Compliance Assurance (OECA) — activities include
       reviewing Agency  information  on  nanotechnology  (e.g., studies, research);
       evaluating  existing   statutory  and regulatory frameworks  to  determine  the
       enforcement issues associated with nanotechnology; evaluating the science issues
       for  regulation/enforcement  that  are associated  with  nanotechnology,   and;
       considering what information OECA's National  Enforcement  Investigations
       Center (NEIC) may need to consider to support the Agency.

Importantly, EPA's white paper presents a set of key nanotechnology recommendations,
including:

   •   Environmental  Applications Research.  The  Agency  should  continue  to
       undertake, collaborate on, and support research to better  understand and apply
       information regarding environmental applications of nanomaterials.
   •   Risk Assessment Research. To ensure that research best  supports  Agency
       decision-making, EPA should conduct case studies to further identify unique risk
       assessment considerations for nanomaterials. The Agency should also continue to
       undertake, collaborate on, and support research to better  understand and apply
       information regarding nanomaterials':
          o chemical and physical identification and characterization,
          o environmental fate,
          o environmental detection and analysis,
          o potential releases and human exposures,
          o human health effects assessment, and
          o ecological effects assessment.
   •   Pollution Prevention, Stewardship, and  Sustainability. The Agency should
       engage resources and expertise to  encourage, support, and develop approaches
       that promote  pollution prevention, sustainable resource use,  and good  product
       stewardship in the production, use, and end-of-life management of nanomaterials.
       Additionally,   the  Agency   should  draw   on   new,  "next   generation"
       nanotechnologies  to  identify  ways  to  support  environmentally beneficial

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       approaches such as green  energy,  green  design, green  chemistry, and  green
       manufacturing.
   •   Collaboration and Leadership. The Agency should continue  and expand  its
       collaborations regarding nanomaterial applications and potential human health
       and environmental implications.
   •   Intra-Agency Workgroup. The Agency should continue  to convene a standing
       intra-Agency group to foster information sharing on nanotechnology science and
       policy issues.
   •   Training. The Agency should continue and expand  its nanotechnology training
       activities for scientists  and managers.

Another  recent  example  of  EPA's  involvement  in  using nanotechnology  for  better
environmental remediation is  the October 2005 "Workshop on Nanotechnology for Site
Remediation" (EPA 2005). This workshop explored the place of nanotechnology among
existing remedial techniques,  considered the overall state of the science, and examined
some case studies (primarily of  nanoparticulate ZVI). Workshop participants also
discussed research needs and data gaps.  Their findings  may  be  summarized into four
broad categories (i.e., performance;  toxicity; basic nanoscience; and fate and transport) as
follows:

Performance
   •   Better  understanding  of  injection  techniques  and  control  of nanoparticle
       movement  in the  subsurface; better  ways to overcome other  limitations  on
       material emplacement such as permeability changes over time with injections;
   •   Development of a set of performance-assisting tools  such  as validation methods,
       modeling, scale-up  equations, statistics, and QA/QC approaches;
   •   Development  of performance metrics/standards of the nanoparticles, including
       manufacturing, size, shape, storage,  and property and reactivity  standards for
       nanoparticles;
   •   Development of performance assessment and performance prediction tools for the
       contaminants being remediated;
   •   Development of in-situ sensors, real-time techniques, and  analytical methods for
       detecting nanoparticles;
   •   Better understanding of the effects of treatment trains (options and optimization
       of combinations) and synergies of multiple contaminants "cocktail treatment";
   •   Need national test sites covering major geologic settings to permit rigorous field
       demonstration; and
   •   Need  for contingency ability to remove  nanoparticles  from wastewater and
       drinking water.

Toxicity
   •   Recognizing gaps in data and in  the understanding of toxicological effects  on
       humans,  flora, and fauna and how low risk  toxicity can be measured in the
       environment;
   •   Recognizing lack of information on fate, stability, and potential for transformation
       (for example heavy metal sequestration);

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    •   Understanding  the  difference  between  maximizing  remedial  effects  while
       minimizing toxicological problems;
    •   Integrating toxicological behavior into risk-based decision making; and
    •   Better understanding of macro-scale  toxicity  properties and whether it can be
       extrapolated to nano-scale using knowledge of size, shape, chemistry.

Basic Nanoscience
    •   Discovering the existence of intrinsic nano-scale processes and mechanisms (such
       as surface area versus electronic effects and bulk properties versus surface effect);
    •   Discovering the difference between extrapolating macro-scale and micro-scale to
       nano-scale, or determining if there is there a unique nano-scale physico-chemistry
       that cannot be identified at the macro-scale;
    •   Better understanding needed of agglomeration behavior to control both  in-situ
       reactivity and transport; and
    •   Recognizing the need for better information products and information synthesis.

Fate and Transport
    •   Major risks and uncertainties seen in fractured media and in  the transport  of
       sequestered contaminants;
    •   Better monitoring  and detection techniques are needed for fate  and transport  as
       well as for performance studies; and
    •   Need  much better information  on  site-to-site  variability of fate  and transport
       rather than assuming that behavior identified at one site can be applied widely;

Investigation of fate and transport  of  nanoparticles  for environmental applications  is
important since an understanding in this area is critical to evaluating performance (the
need  to  know how  far and in  what form the nanoparticle will travel to  perform its
function), toxicity (the risk  of the nanoparticle traveling unanticipated distances in very
toxic  forms),  and  cost   (directly  related  to performance).  Though  the fate of the
nanoparticle will  depend heavily on the characteristics and material of the nanoparticle,
recent work has indicated  that transport may not be as grave a concern as once thought. It
has been noted that the common assumption  that nanoparticles will be highly mobile  in
porous  media  due to  their  tiny  size  in comparison  with  pore  spaces,  is  an
oversimplification (Tratynek 2006). The  mobility  of nanoparticles  in  the saturated
subsurface is the product of the number of nanoparticle  collisions  with  the porous
medium  per unit transport  distance (where  collisions  arise from Brownian  diffusion,
interception and gravitational sedimentation) and the sticking coefficient. Calculations for
a typical subsurface using a range  of sticking coefficients indicates that  transport will
range from millimeters to a few tens of meters.  These calculations  seem to have been
borne out in field tests with iron nanoparticles used to remediate chlorinated organics.

In fact, an area of current interest is how to coat particles so that they will not stick and
will travel further to attain their remedial purpose. This indication of limited travel only
applies in porous  media and would not be expected to hold in fractured geologic media or
in surface  water. As a  result, EPA is continuing investigations of fate  and transport

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through research2  such as that on  the  environmental  fate  of single-walled carbon
nanotubes in the estuarine environment at the University of South Carolina. Similar work
on environmental fate and transport is  also being conducted at a number of academic
centers, such as the Center for Biological and Environmental Nanotechnology (CBEN) at
Rice University, which aims to understand and manipulate the wet/dry interface between
nanosystems  and biological  systems,  and  the  Nanomaterials in  the  Environment,
Agriculture, and Technology Organized Research Unit (NEAT-ORU) at the University of
California Davis, which emphasizes  research on the  interaction of materials and  the
natural and man-made environment.

±6.4  International Involvement in Nanotechnology

The  United States  is not alone  in exploring  the benefits  of  nanotechnology  for
environmental  remediation  and  its implications  on human health, welfare, and  the
environment. Two recent reports from Europe help paint a picture of current thinking.

A 2007 report from the United Kingdom's Department for Environment, Food and Rural
Affairs  (DEFRA) titled "Environmentally Beneficial Nanotechnologies:  Barriers and
Opportunities" (Walsh 2007), was commissioned to provide an overview of the  areas
where  nanotechnology could have a beneficial  environmental impact above current
technology and the barriers preventing its  adoption. Five  nanotechnological applications
were subject to detailed investigation: fuel additives, solar cells, the hydrogen economy,
batteries, and insulation.

A workshop  on "Nanotechnologies  for  Environmental  Remediation"  (Rickerby and
Morrison 2007) was convened at the  Joint Research Center in Ispra, Italy in  2007. This
workshop brought leading scientists together from across the EU to present  their  latest
work in environmental remediation and discuss issues including:

   •   The most effective nanotechnologies for pollution prevention or cleanup;
   •   The dependability and proximity to market of remediation techniques based on
       nanotechnologies;
   •   The additional research needed to exploit the full potential of nanotechnology for
       remediation;
   •   The most promising environmental  nanotechnologies and those that should be
       further explored;
   •   The potential risks of using nanotechnologies in remediation applications.
   •   Whether there is a need for targeted funding for infrastructure to support
       nanotechnologies for environmental remediation; and
   •   The opportunities for setting up EU collaborative projects on environmental
       nanotechnologies.

The  issues of  environmental  remediation were considered to be quite substantial and
poorly addressed by  conventional technologies.  They include access to clean drinking
2 ORD STAR

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water; removal of airborne pollutants; and the cleanup of industrially-contaminated sites
(in  particular ex-military  sites). Although there have  been a  number  of laboratory
demonstrations of nanotechnology applications for environmental cleanup, there remains
the  issue of translating these into industrial-level processes. The  workshop consisted of
two principal sessions:  "Water Treatment  and Purification," and "Air, Water and Soil
Decontamination." Participants discussed the following important issues:

    •   Photocatalytic treatment of water for degradation of pollutants and the destruction
       of microorganisms;
    •   Titanium dioxide (TiO2) nanopowder immobilization on substrates to produce a
       photogalvanic system with a photoanode for photodegradation of organic
       pollutants;
    •   Photocatalytic inactivation of bacterial spores and photocatalytic disinfection of
       water;
    •   Membrane nanofiltration for the treatment of process and wastewater;
    •   Colloidal and interface chemistry;
    •   Development of a system utilizing iron-precipitating bacteria to co-precipitate;
    •   Organic and inorganic pollutants,  such as arsenic;
    •   Sol-gel synthesis of nanosized TiC>2 particles on polypropylene fibers for the
       photocatalytic degradation of organic pollutants;
    •   Ultra nanocrystalline diamond used as an electrode for water treatment and
       disinfection;
    •   Feasibility of a Lab-on-a-Chip (LOG) device for analyzing highly radioactive
       solutions;
    •   Development of catalytic trap technology and advanced systems for particulate
       matter;
    •   Incorporating TiC>2 in building materials or surface coatings to impart self-
       cleaning and de-polluting properties; and
    •   A double skin sheet reactor (DSSR) for water purification.

1.7    Nanotechnology for Environmental Remediation of Radionuclides

1.7.1  Technical Status

Discussion in Section 1.6 has illustrated that research  of radionuclide remediation is
lacking in the growing interest of environmental nanotechnology. The mention in Section
1.6.4  of investigating the  feasibility of an LOG device for analyzing highly radioactive
solutions is  an encouraging exception. In spite of this current situation, the potential for
nanotechnology to  assist with  the remediation of radionuclide-contaminated  sites is
considerable. For example,  zeolites, nanostructured materials that can also be made as
nanoparticles, already have a  long  history  of use  in the treatment of liquid radioactive
waste. ZVI  nanoparticles, a reducing agent already implemented for the remediation of
chlorinated organics in groundwater, are an excellent prospect for use as a reducing agent
to precipitate uranium  form  contaminated groundwater. LOG is  a recently emerged
sensing technology that is being actively investigated for modification to radionuclide
sensing. The Self-Absorbed Monolayers on Mesoporous Supports (SAMMS) technology,

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originally developed by DOE primarily for mercury, but also with radionuclides in mind,
has recently had its first field implementation.

In addition to these examples of current or near-term applications of nanotechnology to
radionuclides, it is clear from the analysis of the scientific and engineering principles that
other technologies  can  be developed,  and it is  clear  from analysis  of  broader
governmental and industrial issues and initiatives that a rational approach to design of
nanomaterials  and nanotechnologies is being pursued.  Two examples, one technical
(rational design of organic ligands) and the other programmatic (Chemical Industry R&D
Roadmap for Nanomaterials by Design) demonstrate the potential of a rational design
approach.

± 7.2  Rational Approach to Design in Nanotechnology

The rational  design  of complexants or  sequestrants in organic chemistry  draws on
expertise from a number of areas of chemistry, including  supramolecular chemistry,
molecular  recognition,  host-guest  chemistry,  molecular mechanics,  and  molecular
modeling. The conceptual origins go back over 100  years to the idea developed by Emil
Fischer, who proposed that enzyme-substrate interactions occur through a "lock and key"
mechanism. Subsequent research was stimulated by work such as the elucidation of DNA
structure,  where non-bonding interactions  were critical to understanding the three-
dimensional structure.  As far back as the mid to late 1990s, government and industry
began shifting their focus in the area of separations from complexants and sequestrants to
separations platforms such as membranes. The U.S. chemical industry presents one of the
best examples of this structured approach.  The  U.S.  chemical industry is the world's
largest, accounting for over 26%  of global  chemical production (over $450 billion per
year) (DOE 2007). The chemical industry worldwide is the largest component of the
nanotechnology industry; worldwide the nanotechnology industry is estimated  at $130
billion  (Cientifica 2007), of which the chemical industry accounts for approximately $69
billion  (53%). With its enormous scientific and engineering basis (accounting for one out
of every four U.S. patents) and knowledge of varied product requirements, the chemical
industry  is well  positioned  and  motivated  to   explore a  rational  approach  to
nanotechnology.

Currently, much nanomaterial development occurs through empirical or Edisonian R&D,
in which  a nanomaterial structure with interesting properties is discovered, an application
is subsequently sought  and development of a  product retaining  the nanoproperty is
attempted. This approach is hit  or miss. As a result, a smaller-than-optimal number of
products are produced even though time-to-market can be rapid. Against this background,
in 2003, the Chemical Industry Vision2020 Technology Partnership (Vision2020) issued
its  technology roadmap, "Chemical Industry  R&D Roadmap for  Nanomaterials by
Design: From Fundamentals to Function (Chemical Industry Vision2020 2003)."

Vision2020 is an  industry-led  partnership process among  public and  private sector
stakeholders in the chemical and allied industries. The chemical industry has recognized
both the  significance of nanomaterials to its operations and markets and a solution-

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 oriented approach to materials  development, or "nanomaterials by  design", is needed.
 Conceptually, nanomaterials by design is the ability to employ scientific principles in
 deliberately  creating structures with  nanoscale features (e.g., size, architecture) that
 deliver unique capabilities for target applications and require detailed understanding of
 science at the nanoscale. The general concept  of rational design  originated within the
 chemical  community  after  it  found early applications  in pharmaceutical  design.
 Vision2020's  roadmap  presented  four  major research  areas  for  nanotechnology
 development:

    •  Manufacturing and Processing—developing unit operations and robust scale-up
       and scale-down methodologies for manufacturing, with emphasis on synthesis,
       separation, purification, stabilization, and assembly.
    •  Characterization  Tools—developing   analytical   tools   for  measuring  and
       characterizing nanomaterials both  in scientific research and in numerous areas of
       production.
    •  Fundamental Understanding and Synthesis—developing new paradigms for the
       creation and  controlled  assembly of nanoscale building  blocks, based  on  an
       understanding of physics and chemistry at the nanoscale.
    •  Modeling  and  Simulation—developing  computational tools  to predict bulk
       properties of materials that contain nanomaterials and can bridge between scales
       from atoms, to self-assembly, to devices.

 Once these developments are achieved, large numbers of diverse products could rapidly
 enter global  markets to solve long-standing problems and stimulate economic growth for
 decades to  come. A  library  of  nanomaterials and  synthesis  techniques  could  be
 established by 2020  for use  by material producers and end-users worldwide, offering
 diverse, high-quality nanomaterial building blocks with well-characterized compositions,
 stable architectures,  and predicted properties.  Safe, reproducible,  cost-effective, and
 clearly-defined manufacturing and assembly methods would be available to incorporate
 nanomaterials into systems and devices  designed to  perform  specified functions, while
 retaining nanoscale attributes.  The  roadmap  suggests a twenty-year  period for  the
 completion of this development.

 1.8   Structure of This Report and Summary of Examined Technologies

 The remainder of this report is organized into three sections listed below:

    •  Section 2: Nano-Enabled Remediation Technologies (each technology description
       is followed by references specific to that technology)
    •  Section 3: Nano-Enabled Sensor  Technologies (each  technology description is
       followed by references specific to that technology)
    •  Section 4: Observations and Conclusions
IB*

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Table 2 below provides a summary of the technologies examined in this document and
includes a reference to the section in which the technology is discussed, a brief summary
of the technology, an estimate of  the maturity level  for the  technology and the main
medium in which the technology operates.

        Table 2: Summary of Examined Nanotechnologies and Nanosensors
Technology
Zero-valent
Iron (ZVI)
Nanoparticles







Self-Absorbed
Monolayers on
Mesoporous
Supports
(SAMMS)







Nanofiltration
Membranes










Zeolites








Section
Section
2.2
Page 32
-L dg^t ~J Z,






Section
20
.3
Papp 39
-L cisit' j y








Section
2.4
T>Q(Tp
J^agC
46







Section
2.5
Patrp S8
A d ftt- -^ O





Summary
ZVI nanoparticles are a
nanotechnology modification
of the established ZVI
technology in which the ZVI
undergoes oxidation and
consequently is able to reduce
species, such as chlorinated
organics and higher valency
toxic metals (e.g., uranium and
chromium).
SAMMS is a separations
technology designed for the
removal of soluble species in
aqueous solution. It is likely to
be a strong competitor to
conventional ion exchangers,
solid-supported complexants,
or other solid sorbents. The
fundamental scientific
underpinnings make SAMMS
an extremely flexible
separations technology.
Nanofiltration and reverse
osmosis membranes are a
mature separation technology
designed for the removal of
paniculate and soluble species
in aqueous solution. They
occupy the part of the
spectrum of filtration
technologies where extremely
small particulates and soluble
species can be removed from
aqueous solution.
Zeolites are a well-established
ion exchange technology that
is used, among a wide range of
other, non-separatory
industrial applications, for the
treatment aqueous waste
streams containing radioactive
solutes. Zeolites are a
nanotechnology that had
Maturity
The use of macro-scale ZVI
in subsurface permeable
reactive barriers is a well-
established technology.
Nano-scale ZVI has already
undergone field
demonstrations.



Commercially available and
being used in the field for
mercury remediation, with
ongoing development for a
wide range of toxic and
radioactive metals.






Conventional nanofiltration
and reverse osmosis
membranes are well-
established. The use of
insights from recent
nanotechnology
developments for improved
membranes is well
underway and commercial
products are expected to be
available in the near future.

A mature, long-established
technology, widely used for
the treatment of radioactive
waste streams and under
ongoing development.




Media
Aqueous









Aqueous











Aqueous











Aqueous/
soils








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Technology



Other
Nanoparticles










Uranium
Reduction by
Bacteria



Carbon
nanotubes
(fullerenes)








Lab-on-a-Chip
(LOC)









Microcantilever
Sensors



Section



Section
2.6

Page
69







Section
2.7
Page 77



Section
2.8
"Pflpp
J^agC
85






Section
3.2
Papp 99
-L ci sit ^ y







Section
3.3
Page 103
-L Clgt _LV/^J

Summary
established uses predating the
general concept of
nanotechnology.
Nanodiamonds, dendrimers,
and the Argonne Supergel are
presented to demonstrate the
range of possibilities offered
by nanoparticles — particularly
the ease with which a
nanoparticle can be
incorporated into another
technology application and the
ability to engineer specific
properties into a nanoparticle
at the atomic level.
By using the appropriate
micro-organism and nutrient
addition, soluble uranium (VI)
can be converted in-situ to
much less soluble uranium
(IV) by enzymatic reduction.
A class of hollow, spherical, or
ellipsoidal molecules
composed entirely of carbon
atoms in a cage-like structure.
They have a range of potential
applications, from sensing
elements, to components of
advanced nano-composite
materials that may enable
better membranes for reverse
osmosis and nanofiltration.
LOC is a platform that can
integrate a number of
laboratory analytical functions,
such as separations and
analysis of components of a
mixture, on a single
microprocessor chip using
fluid volumes in the nanoliter
and lower range, thus allowing
realization of small, portable
equipment.
A microcantilever is an
extremely small beam
supported at one end and
capable of well-defined
bending and vibrational
Maturity



Various depending on
specific technology.










The technology concept is
mature and commercially
available.



Nanotubes are now
commercially available in
"tons-per-year" quantities.
Applications are in the
laboratory stage with future
development likely to speed
up now that availability has
been increased and cost
decreased.


The technology is
commercially available for
biological research.








The technology concept is
mature and commercially
available.


Media



Various
depen-
ding on
specific
techno-
logy.






Aqueous,
soil, sub-
surface



Aqueous










Aqueous










Aqueous





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Technology









Spectroscopic
Sensors















Nanowire
Sensors









Nanobelts and
Nanorods










Section









Section
3.4
Page 109














Section
3.5
Page

117






Section
3.6
Doo-p
rage
122







Summary
behavior that can be accurately
monitored. When the
microcantilever surface is
modified so as to be able to
bind a target species, the
changes in vibrational
behavior allow concentration
of the target species to be
determined.
Spectroscopic measurements,
particularly fluorescence
spectroscopy, are one of the
most sensitive conventional
detection technologies,
routinely going to the single
molecule level in the
laboratory. Nano-enabled
technologies promise to
expand the availability and
application of these
techniques. Probe
Encapsulated by Biologically
Localized Embedding
(PEBBLE), surface plasmon
resonance, nanobelts and
nanorods are discussed as
examples.
Nanowires are solid, rod-like
materials with diameters in the
5-100 nm range and are most
often made from metals or
semi-conducting metal oxides.
Their main application is
expected to be in sensors, with
the underlying phenomenon
that is exploited being the field
effect upon which field effect
transistors are based.
Nanobelts are a class of
nanostructure often viewed as
a type of nanowire. Nanobelts
form ribbon-like structures
with widths of 30-300 nm,
thicknesses of 10-30 nm, and
lengths in the millimeter
range. Nanorods are solid
nanostructures
morphologically similar to
nanowires but with aspect
ratios of approximately 3-to-5.
Maturity









Various, depending on
specific technology.















Early stage of development.










Under investigation for
various applications.










Media









Primarily
aqueous















Aqueous










Various
depen-
ding on
specific
techno-
logy.







-------
This report does not address technologies complementary to radionuclide remediation or
sensing. For example, if a subsurface plume were to contain both Resource Conservation
and Recovery Act (RCRA) organics and radionuclides as contaminants, the material was
brought to the surface, and a problematic mixed waste was produced;  a nanotechnology
that  could  destroy  the RCRA  organic  would accomplish much  in  assisting with  the
management of the  radionuclide. Though this type of consideration is beyond the scope
of this report, it represents yet another approach by which nanoparticles can assist in the
management of radionuclide problems.

In addition to the technologies  that are presented in this report, there are a number of
other technologies  or scientific concepts that over the short term, as nanotechnology
advances, may have remedial  potential for radionuclides. The prediction of future
technology success  is a task always fraught with risks, particularly as the time period of
the prediction grows. It is often pointed out that at the end of the nineteenth century many
scientists believed that all  of the basic fundamental  principles governing  physics and
chemistry were known, and that few big discoveries left with only details remaining. The
difficulties  in technical  prediction still remain. Some of the choices  for the following
sections are obvious. For instance, technologies such as ZVI nanoparticles, SAMMS, and
zeolites have already found commercial or near-commercial applications in the treatment
of radionuclides. Others are included since they are being actively  researched for closely
similar applications. For instance, dendrimers are  being examined for application in the
treatment of heavy metals and the transfer of understanding from heavy  metals  to
radioactive metals is usually fairly straightforward; it is very common in research to use
the lanthanides as models for the actinides since the non-radioactive lanthanides are much
easier  to  work  with than the  radioactive actinides and  useful predictions  and
extrapolations of behavior from one class to the other can be made. For the rest of the
technologies common factors employed in the analysis of technology potential were used.
For example, factors such as the existence of a standardized  framework  or platform
within which to work, the existence of a wealth  of related knowledge and supporting
research, the technology  offering  a technically  elegant or conceptually  compelling
solution to a problem, or the robustness and  flexibility  of a technology are all positive
indicators of its likely success. The reader should  of course understand that, particularly
in a rapidly  developing  field,   there  is  always   inherent  uncertainty  in  making
extrapolations of likely technology success.

1.9   References

Biswas, P. and C.-Y Wu. 2005. Nanoparticles and the environment. Journal of the Air
& Waste Management Association: 55, 708-746.

Borm, P., and D. Muller-Schulte. 2006. Nanoparticles in drug delivery and  environ-
mental exposure: same size, same risks? Nanomedicine: 1(2), 235-249.

Borm, P., D. Robbins, S. Haubold,  T. Kuhlbusch, H. Fissan, K. Donaldson, R.  Schins, V.
Stone, W. Kreyling, J. Lademann, J. Krutmann, D. Warheit, E. Oberdorster. 2006. The

-------
potential risks of nanomaterials: a review carried out for ECETOC. Particle and Fibre
Toxicology: 3(11).

Brunner, T., P. Wick, P. Manser, P. Spohn, R. Grass, L. Limbach, A. Bruinink, W. Stark.
2006. In vitro cytotoxicity of oxide nanoparticles: Comparison to asbestos, silica, and the
effect of particle solubility. Environmental Science & Technology: 40(14): 4374-4381.

Chemical Industry Vision2020 Technology Partnership. 2003. Chemical Industry R&D
Roadmap for Nanomaterials by Design: From Fundamentals to Function.

Cientifica. 2007. Halfway to the trillion Dollar market? A Critical Review of the
Diffusion of Nanotechnologies. London, April 2007.

Congressional Research Service (CRS). 2008. Engineered Nanoscale Materials and
Derivative Products: Regulatory Challenges. CRS Report for Congress. January 22, 2008.
Order Code RL34332.

Davis, J.M., 2007. How to Assess the Risks of Nanotechnology: Learning from Past
Experience. Journal of Nanoscience and Nanotechnology. Vol. 7, 402-409, 2007.

Davies, J. Clarence, 2006. Managing the Effects of Nanotechnology. Woodrow Wilson
International Center for Scholars Project on Emerging Nanotechnologies. Washington
DC 20004-3027.
http://www.nanotechproject.org/process/files/2708/30_pen2_mngeffects.pdf

Department of Energy (DOE). 2007. Industrial Technologies Program: Chemicals
Industry of the Future. Website. Accessed December 2007.
http://wwwl.eere.energy.gov/industry/chemicals/.

Drexler, K.E. 1986. Engines of Creation • The Coming Era of Nanotechnology. Anchor
Books, New York.

Environmental Protection Agency (EPA).  2005-B. U.S. EPA Workshop on
Nanotechnology for Site Remediation U.S. Department of Commerce, Washington, DC.
October 20-21,2005.
es.epa.gov/ncer/publications/workshop/pdf/10_20_05_nanosummary.pdf

EPA 2007. U.S. EPA Nanotechnology White Paper; EPA 100/B-07/001. EPA Science
Policy Council,  Washington, DC.
es.epa.gov/ncer/nano/publications/whitepaperl2022005.pdf

EPA. 2008. Draft Nanotechnology Research Strategy; EPA/600/S-08/002. United States
Environmental Protection Agency, Office  of Research and Development, Washington
DC.

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European Commission (EC). 2005. Communication from the Commission to the Council,
the European Parliament and the Economic and Social Committee: Nanosciences and
nanotechnologies: An action plan for Europe 2005-2009. B-1050, Brussels, Belgium.
http://ec.europa.eu/research/industrial_technologies/pdf/nano_action_plan_en.pdf

EC Scientific Committee on Emerging and Newly-Identified Health Risks (EC
SCENIHR), 2007. Opinion on the appropriateness of the risk assessment methodology in
accordance with the technical guidance documents for new and existing substances for
assessing the risks of nanomaterials. B-1049 Brussels, Belgium.
http://ec.europa.eu/heal th/ph_risk/committees/04_scenihr/docs/scenihr_o_010.pdf.

Environmental Defense-DuPont Nano Partnership (ED-DuPont). 2007. Nano Risk
Framework, http://www.environmentaldefense.org/documents/
6496_Nano%20Risk%20Framework.pdf.

Feynman, R. 1959. There's Plenty of Room at the Bottom. Speech given at American
Physical Society Meeting, California Institute of Technology, December. Accessed at
http://nanoparticles.org/pdf/Feynman.pdf.

Gwinn, M.  and V.  Vallyathan. 2006. Nanoparticles: Health effects—pros and cons.
Environmental Health Perspectives:  114(2): 1818-1825.

International Risk Governance Council (IRGC). 2005. White Paper on Risk Governance:
Towards an Integrative Approach. By Ortwin Renn with Annexes by Peter Graham. CH-
1219 Geneva, Switzerland. http://www.irgc.org/IMG/pdf/
IRGC_WP_No_l_Risk_Governance	reprinted_version_.pdf.

International Risk Governance Council (IRGC). 2006. White Paper on Nanotechnology
Risk Governance. By Ortwin Renn and Mike Roco with Annexes by Mike Roco and
Emily Litten. CH-1219 Geneva, Switzerland.
http://www.irgc.org/IMG/pdf/IRGC_white_paper_2_PDF_fmal_version-2.pdf.

International Risk Governance Council (IRGC). 2007. Policy Brief: Nanotechnology
Risk Governance: Recommendations for a global, coordinated approach to the
governance of potential risks. CH-1219 Geneva, Switzerland.
http://www.irgc.org/IMG/pdf/PB_nanoFIN AL2_2_.pdf

Kreyling, W., M.  Semmler-Behnke, W. Mbller. 2006. Health implications of nanoparticles.
Journal of Nanomaterial Research: 8: 543-562.

Kroto, H.W., J.R. Heath, S.C. O'Brien, R.F. Curl andR.E. Smalley. 1985. C60:
Buckminsterfullerene. Nature. 318(6042): 162-163.

Limbach, L., Y. Li, R.  Grass, T. Brunner, M. Hintermann, M. Muller, D. Gunther, W.
Stark. 2005. Oxide nanoparticle uptake in  human lung fibroblasts: Effects of particle size,

-------
agglomeration, and diffusion at low concentrations. Environmental Science & Technology:
39(23): 9370-9376.

Limbach, L., P.  Wick, P. Manser, RGrass, A. Bruinink, W. Stark. 2007. Exposure of
engineered nanoparticles to human lung epithelial cells: Influence of chemical
composition and catalytic activity on oxidative stress. Environmental Science &
Technology: 41(11): 4158-4163.

Linkov, L, E. Ferguson, V. Magar. In press. Real Time and Deliberative Decision
Making: Application to Risk Assessment for Non-chemical Stressors. Springer,
Amsterdam.

Linkov, L, K. Satterstrom, J. Steevens, E. Ferguson, R. Pleus. 2007. Multi-criteria
decision analysis and environmental risk assessment for nanomaterials. Journal of
Nanoparticle Research. 9: 543-554.

Medina,  C., M. Santos-Martinez, A. Radomski, O. Corrigan, M. Radomski. 2007.
Nanoparticles: pharmacological and toxicological significance. British Journal of
Pharmacology: 150: 552-558.

NanoReg News. 2008. NanoReg Report: Policy News for the Nanotechnology Value
Chain. February 15, 2008. Volume 5, Issue 3. Accessed March, 2008.
http ://www.nanoregnews. com/.

National Nanotechnology Initiative (NNI).  2007. Website. Accessed December 2007.
http://www.nano.gov/.

Nel, A., T. Xia, L.Madler, N. Li. 2006. Toxic potential of materials at the nanolevel.
Science.  311:622-627.

Oberdbrster, G., V. Stone, K. Donaldson. 2007. Toxicology of nanoparticles: A historical
perspective. Nanotoxicology. 1(1): 2-25.

Quebec Comision de 1'ethique de la science et de la technologie (QC), 2006. Position
Statement: Ethics and Nanotechnology: A Basis for Action.  Quebec Gl V 4Z2.
http://www.ethique.gouv.qc.ca/IMG/pdf/Avis-anglaisfmal-2.pdf

Responsible NanoCode (RNC). 2006. Workshop report: How can business respond to the
technical, social  and commercial uncertainties of nanotechnology?
http://www.responsiblenanocode.org/documents/Workshop-Report_07112006.pdf

Rickerby, D. and M. Morrison. 2007. Report from the Workshop on Nanotechnologies
for Environmental Remediation, JRC Ispra  16-17 April 2007. Institute for Environmental
Sustainability.

-------
Royal Society and Royal Academy of Engineering (RS & RAE), 2004. Nanoscience and
nanotechnologies: opportunities and uncertainties. Science Policy Section, The Royal
Society, London. http://www.nanotec.org.uk/fmalReport.htm.

Taniguchi, N. 1974. On the Basic Concept of 'Nano-Technology.' Proceedings of the
International Conference on Production Engineering, Tokyo, Part II, Japan Society of
Precision Engineering.

Thomas, K. and P. Sayre. 2005. Research strategies for safety evaluation of nanomaterials,
part i: Evaluating the human health implications of exposure to nanoscale materials.
lexicological Sciences. 87(2): 316-321.

Tratynek, P.G. and R.L. Johnson.  2006. Nanotechnologies for Environmental  Cleanup.
Nanotoday. 1(2). May 2006.

Uldrich, J. and D. Newberry. 2003. Next Big Thing Is Really Small: How
Nanotechnology Will Change the Future of Your Business. Crown Publishing Group,
New York.

UK Department for Environment Food and Rural Affairs (UK DEFRA). 2006. UK
Voluntary Reporting Scheme for Engineered Nanoscale Materials. London SW1P 3 JR.
Available at: http://www.defra.gov.uk/environment/nanotech/policy/pdf/vrsnanoscale.pdf

U.S. Food and Drug Administration (US FDA). 2007. Nanotechnology: a report  of the
U.S. Food and Drug Administration Nanotechnology Task Force. July 25, 2007.
Available via DIALOG http://www.fda.gov/nanotechnology/taskforce/report2007.html

Walsh, B. 2007. Environmentally Beneficial Nanotechnologies: Barriers and
Opportunities. Report prepared for the United Kingdom Department for Environment,
Food and Rural Affairs. Oakdene Hollins, Aylesbury, The United Kingdom.

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2.0        Nano-Enabled Remediation Technologies

2.1    Introduction

In dealing with the remediation of environmental contamination or the closely-related
concern of managing wastes, options for treating non-radiological (though potentially
very hazardous)  materials can be divided into two broad categories:  separation of the
contaminant and  transformation of the contaminant. For example, if an aqueous stream is
contaminated with trichloroethylene  (TCE), the stream could be cleaned by passage
through a bed of activated charcoal to separate the TCE from the stream, or by passage
over a bed of ZVI, in which case the ZVI would transform  the  TCE. In the  case of
radionuclide contamination, the situation is complicated by the fact that no amount of
transformation will ever remove the radiological characteristic of the waste—a uranium
atom will always remain  a  uranium  atom no matter how  it  speciates chemically.
Transformations  may be useful, but only to the extent that they assist in bringing about a
separation. For radiological contamination, the separations of interest may be the removal
of the radioactive species from its host matrix (i.e., an extraction), or  it may  involve
processes such as fixation or stabilization, in which the radioactive material is separated
from any mobilization and/or transport pathways so that the risk it poses is reduced or
eliminated altogether by preventing it from being made available to a receptor.

The  remediation of radionuclide-contaminated  sites has  been  problematic for decades.
Radionuclides typically remain a matter of concern even at concentrations that are orders
of magnitude lower than those  for  most non-radiological  materials.  Further, the
geological matrix can present considerable heterogeneities even over small distances and
is inherently difficult to characterize. The situation is further complicated by the timeline
for developing remedial technologies. In  contrast to  enabling technologies such as
sensors, remedial technologies are generally much more time-consuming  and  involve
considerably higher costs and risks. These problems are amplified when radionuclides are
involved. Though the novel chemical and  physical properties offered by nanoparticles
may yield  new  approaches  to  remediation,  the  fundamental difficulties  posed  by
radionuclides will  not disappear.  This does  not mean that  nanoparticles offer little
promise for environmental remediation. On the contrary, the potential appears to be great,
but it is more likely to come in the areas of remediation of non-radiological contaminants,
pollution prevention through the development of greener manufacturing processes, better
waste  treatment  of non-radiological  contaminants, and sensors than in  the area of
remediation of radiological material.

Having provided this cautionary background,  the  research involved  in preparing this
report indicates that nanotechnology is likely to provide some useful tools for the toolbox
of remediation technologies applicable  to radionuclide-contaminated sites. For the past
two  decades, it has been recognized that environmental contamination by radionuclides
constitutes one the most difficult environmental problems.  The  cost of remediation of
such sites may be enormous. Major decreases in anticipated costs do not seem to be likely
through  incremental  improvements  to   existing  approaches  and  transformational
alternatives that have been actively sought.  Since nanotechnology is still in its infancy,

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the possibility of transformational approaches arising should not be  dismissed, even if
there is little indication at present regarding how this will come about.

Already, nanotechnology does offer some intriguing possibilities. One example is that
macroscale ZVI has been used successfully for years as a means of treating chlorinated
organics in groundwater via use of permeable reactive barriers (PRBs). Nanoscale ZVI is
currently  being investigated for the  same  application,  exploiting the  fact  that its
rheological properties  allow it to  be  injected.  ZVI  has also  been investigated as a
reductant to transform  materials of concern,  such as chromium and uranium, from their
higher valency, more  soluble forms, to  lower valency,  and soluble forms  possessing
lower risk. It seems  likely that nanoscale ZVI may offer the same chemical reductant
properties, possibly even enhanced, with the flexibility of injectability. This  conclusion
involves an extrapolation, but it is a fairly small one. A  second example, and one that
does  not  involve  an  extrapolation,  is  zeolites—nanostructured,  ion-exchanging
separations materials that have been used in  radioactive material waste management for
half a century. A third example is the Self-Assembled Monolayers  on Mesoporous
Supports (SAMMS) technology, which offers a new platform for separations agents. This
technology is currently being demonstrated  for  mercury removal and, in combination
with the fundamental understanding already available, the extrapolation to a technology
for the separation  of radionuclides is small.

Separations may  be the area where nanotechnology makes  its  biggest  impact  in
remediation.  Carbon  nanotubes  can  be incorporated  into membranes and  permit
extremely  fast fluid  flow;  they are under active  investigation  as  a desalination
technology. The  combination of existing knowledge on  ligand  design—an  area  of
fundamental  importance to  separations science—with  new nanostructures,  such  as
dendrimers, may offer greatly improved separations performance. The following sections
describe technologies  or technology concepts that have  either been demonstrated  for
radionuclide treatment, such as zeolites, or that can be comfortably extrapolated  to
radionuclides,  such  as ZVI. Since a certain  degree of extrapolation  is necessarily
involved, the survey in this report is not intended to be comprehensive, but rather seeks to
provide information  on reasonable possibilities that may  yield technologies in the near
future. The technologies examined in this report are:

    •   ZVI nanoparticles
    •   SAMMS
    •   Membranes: nanofiltration and affinity
    •   Zeolites
    •   Other nanoparticles
    •   Uranium reduction by bacteria
    •   Carbon nanotubes

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2.2    Zero-valent Iron Nanoparticles

2.2.1  Background

The  massive surface area and unique  properties  of nanoparticles have led to much
research on their application to environmental remediation. Across the broad array of
environmental  concerns,  research  ranges  from  the use  of TiO2  nanoparticles for
photocatalytic treatment of nitrous oxides  in plant emissions, to  the use of naturally
occurring metal  oxide nanoparticles for  the treatment of organic  contaminants in
groundwater. There are, however,  few examples of commercial-scale  technologies that
use nanoparticles for environmental remediation of non-radiological materials, and even
fewer for remediation of radionuclides. The closest example to a commercial technology
is the use of iron nanoparticles as a reductant for the remediation of chlorinated organics
in water; this is a direct modification of the  use of iron filings or microscale iron powder
for  the  remediation of chlorinated organics in water. In addition, one  company  (Pars
Environmental  Inc.) has  successfully used iron nanoparticles  at several chromium-
contaminated sites for reducing soluble and carcinogenic chromium in  the +6 valence
state to insoluble and non-carcinogenic chromium in the +3 valence state.

In general,  nanoiron  particles can  treat the following contaminates  in a  range of
geological settings:

   •   Contaminants:
       o  Halogenated aliphatics (PCE, TCE, 1,1,1 -TCA, 1,1,2,2-TeCA)
       o  Halogenated aromatics
       o  PCBs
       o  Halogenated herbicides and pesticides
       o  Nitroaromatics
       o  Metals (e.g., Cr6+, As)
   •   Geologic Conditions:
       o  Sand
       o  Silt
       o  Fractured rock
       o  Landfills
       o  Fill materials
       o  Sediments

Additionally, EPA is  preparing a fact sheet on the use  of nanotechnology for site
remediation and will  include  information  about sites where the technology  has been
tested.

2.2.2  Description

Iron nanoparticles represent the only field application of free-released nanoparticles for
environmental remediation. First suggested  in 1996 and now the subject of a number of

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reviews (Kumar  2006,  Zhang and  Elliott  2006,  Lo  et  al. 2006), the  use  of iron
nanoparticles is a variation on the use  of ZVI as a PRB.

The  non-nanoparticle ZVI PRB technology  has  been used to remediate contaminated
groundwater for almost 20 years (Senzaki and Kumagai 1988) and has been demonstrated
in the field and  in  the  laboratory for  a wide  range  of  contaminants, including the
reduction of nitrates, bromates, chlorates, nitroaromatic compounds, chlorinated ethanes,
chlorinated methanes, and brominated or carbarylated pesticides,  and  the removal of
arsenic, lead, uranium, mercury, and  hexavalent  chromium (Nuxoll et al. 2003, Arnold
and Roberts 2000). Typically, iron filings or microscale iron powder have been used to
create a barrier a few meters wide, contained by gravel supporting beds. The chemistry is
well  understood as the corrosion of iron based on the following reactions:

                           aq) + O2(aq) -> 2Fe2+(aq) + 2H2O(\)
                        4H+(aq) + O2(aq) -> 4FeYaqJ + 2H.2O([)

                        2H2O(\)
As ZVI is oxidized to ferrous and/or ferric iron, pH increases, hydrogen  is evolved,
oxidizable  materials are consumed, and  the  strong reducing  conditions created are
favorable  for the pathways (oxide-mediated electron transfer  from the metal to the
chlorinated organic, reduction of the chlorinated organic by the ferrous iron and reduction
by evolved hydrogen) — leading to complete dechlorination. Eventually, ferric or ferrous
iron  may precipitate as a solid or remain  in solution, depending on the pH and  redox
conditions. Mineral precipitates of carbonates, sulfides, and/or oxides may form coatings
on the reactive  grains, inhibit the performance of the iron, and reduce the porosity and
permeability of the aquifer, but analysis of the evidence suggests  that destruction of
chlorinated solvents  can  still continue to  completion. Additionally, the  generation of
strong reducing conditions and hydrogen gas foster anaerobic microbial growth  and
increase natural biological degradation in the field (Henn and Waddill  2006).

The first field-scale application  of conventional ZVI for groundwater remediation was at
the Canadian Forces Base in Borden, Ontario in 1991. A treatment zone was excavated,
isolated by sheet pile; filled with a mixture of granular iron and sand; and the sheet piles
were  removed.  Contaminated groundwater flowed through the treatment zone  and the
chlorinated ethenes (perchloroethylene and trichloroethylene) were  almost  completely
removed. The approach is now a standard, and regulatory guidance for the general use of
PRBs (including those involving iron) is available (ITRC  1999a), together with design
guidance (ITRC 1999b), and recently learned lessons and new directions (ITRC 2005).

The concept of using nanoparticle iron to remediate chlorinated organics  follows almost
immediately from the conventional ZVI treatment. The small size of the particles (-10
nm) would allow them to be injected into a geologic matrix and reach areas unavailable
even to the microbes (-1,000 nm) used in bioremediation. Since reactivity appears to be

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a direct function of total iron particle surface area, their performance is expected to be
superior to that of larger particles. Production of ZVI nanoparticles is relatively easy,
involving the reduction of ferric ion by sodium borohydride (Wang and Zhang 1997):
4Fe3+ + 3BH 4+ 9H2O -> 4Fe°j +3H2BO 3
                                                        12H+ + 6H2
A successful, pilot-scale study  has  already been performed (Henn and Waddill 2006)
using 300 pounds of palladium-catalyzed and polymer-coated nanoscale ZVI particle
suspension at the Naval Air Station in Jacksonville, Florida.  The particle suspension was
injected via a gravity feed and recirculated through a source area containing chlorinated
volatile organic  compounds (VOCs).  Between  65  and  99% aqueous-phase VOC
concentration reduction  occurred, due to abiotic degradation, within five weeks  of the
injection and  then yielded to  slower  biological  degradation.  Aqueous-phase VOC
concentrations were reduced up to 99 % and were near or  below applicable regulatory
criteria. Though there are still considerable knowledge gaps, the technology appears to
have great potential.

Recently,  Pars  Environmental,  Inc.  has developed a ZVI particle which, over time,
encapsulates  the   metal  contaminant;  it  is  reported  that  this  encapsulated layer
immobilizes the contaminant for up to 30 years. This stepwise process resulting in the
reduction of Cr(VI) to Cr(IV) and encapsulation of Cr(IV) in an onion-like skin around a
nano ZVI particle is illustrated in Figure 1.
                1.ZVI
                             2. Adsorption of nano iron
                                          3. Reduction of Cr(VI)
                                                           4. Formation of
                                                           Cr-Fe alloy
                                                           (hydroxide)
                                                           \
              Figure 1. Encapsulation stabilization of the contaminant

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The key features of this process as illustrated for Cr(IV) are:
   1.  Nano Cr-Fe layer
          a.  Thickness - 10 nm
          b.  -40 atoms
   2.  2/3 of the mass from Cr(VI)
          a.  Cr 0.667 Fe 0.333 OOH
   3.  Insoluble
   4.  Reducing power (FeO)

The same reducing ability of ZVI is suggested for the remediation of radionuclides and
heavy metals to bring about a reduction of the metal to a less soluble, lower oxidation
state. For chromium, a conventional ZVI PRB consisting of 450 tons of granular ZVI was
installed  in 1996 at the United States Coast  Guard Support Center in Elizabeth City,
North Carolina, and has been subject to considerable  documentation (Puls et  al. 1998,
Blowes et al. 1997, Blowes et al.  1999, FRTR 1998). The PRB was a continuous trench
approximately 46 m long, 7 m deep, and 0.6 m thick. Concentrations of Cr(VI)  had been
as high  as  5  mg/L,  but  decreased to  non-detectable levels  (<0.0025 mg/L) after
installation  of the PRB. The removal mechanism  for  Cr(VI)  was determined to be
precipitation as Cr(III) oxyhydroxide or co-precipitation with iron oxyhydroxide. Despite
this success, a similar ZVI PRB at the Haardkrom site  electroplating facility in  Kolding,
Denmark, was not effective, with  speculation being  that the TCE present may have
depleted the chromium-reducing ability of portions of the barrier (Roehl et al. 2005).

For uranium, a number of conventional  ZVI  barriers  (Bronstein 2005)  have been
demonstrated, including:

   •   Bodo Canyon Disposal Site, La Plata County, Colorado—a number  of PRBs
       (composed of ZVI, copper wool,  and steel wool) were used  to treat arsenic,
       molybdenum, selenium, uranium, vanadium, and zinc. The barrier containing ZVI
       operated from August 1999 until June 2004 (when flow ceased from the  seep and
       remediation was no longer needed). It maintained effluent uranium concentrations
       of less than 0.01 mg/L, and was highly effective in treating contaminants.
   •   Cotter Corporation Uranium Mill, Canon  City,  Colorado—a ZVI PRB was used
       to treat  molybdenum and  uranium. Though the barrier eventually failed  for
       molybdenum, uranium concentrations remained at less than 0.006 mg/L.  It was
       found that the ZVI was clogged by mineral precipitants. Modifications, including
       a pretreatment zone composed of coarse gravel and ZVI, were suggested.
   •   Fry  Canyon Site, Fry  Canyon, Utah—a  PRB  of ZVI, amorphous ferric oxide
       (AFO), and phosphate rock was used to treat uranium. The  ZVI barrier  has been
       the most effective, removing 99.9% of uranium.
   •   Mecsek  Ore Site, Pecs, Hungary—a PRB composed of  ZVI and shredded cast
       iron was used  to treat uranium, and concentrations within the groundwater in
       2003 were reduced to less than 1% of the  influent value after passing through the
       barrier.

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   •   Monticello Mill Tailings Site, Monticello, Utah—a ZVI PRB was used to treat
       uranium, arsenic, manganese, molybdenum, selenium, vanadium, and nitrates.
       Results show that the barrier was effective in treating the contaminants. Nearly all
       of the uranium, arsenic, manganese, molybdenum, selenium, and vanadium were
       removed from the groundwater, and nitrate, molybdenum, and manganese were
       greatly reduced. Since 2000, contaminants have been reduced to below detectable
       levels.
   •   Rocky  Flats Environmental Technology Site (Solar Ponds Plume),  Golden,
       Colorado—a barrier composed  of ZVI and wood chips was used to treat nitrate
       and uranium. Remediation  goals required  a reduction of uranium from 20-28
       pCi/L to 10 pCi/L.  Surface stream samples below 10 pCi/L for uranium indicate
       that the PRB is working properly.
   •   Y-12 Site, Oak Ridge, Tennessee—a barrier composed of ZVI and peat materials
       is being used to treat uranium, technetium, and  nitric acid. A funnel and gate
       barrier failed due to leaking. A  continuous trench was subsequently installed and
       has shown  that  uranium and  technetium  concentrations have  decreased, but
       because of reactions with groundwater constituents, the lifespan of the ZVI wall
       may be significantly shorter than expected.

Overall, these  results strongly support the case for using conventional ZVI as an effective
reductant for radionuclides, such as uranium. Thus, the potential  for iron nanoparticles is
considerable. Extensive research is ongoing, including studies  on formulation of the iron
nanoparticles,  delivery vehicles and methods of in-situ stabilization. A potential remedial
scheme using ZVI nanoparticles is shown in Figure 2.
        Contaminant
          Source
           Dechlorination of Organic
           Solvent (e.g., COj, C;C14)
                Injection of Iron
                Nanoparticles
                                             Transformation of
                                             Fertilizers (e.g., NO,-)
Detoxification, of Pesiticides
(e.g., Undone, DDT)
                                                         Immobilization of
                                                         Metals fc.g., Pb, Cr, As)
            Figure 2. Potential remedial scheme using ZVI nanoparticles
Obviously, a  considerable  amount  of further work must be performed to establish
baseline  performance and to develop  the knowledge base required to gain regulatory

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acceptability  for the technology as applied to uranium. However, iron  nanoparticles
remain a leading contender for application to the remediation of radionuclides.
2.2.3  Summary of Environmental Potential

ZVI nanoparticles  are  the  first  field application  of  free-released  nanoparticles  for
environmental remediation. The use of macro-scale  ZVI in subsurface PRBs is a well-
established technology for the reduction of both chlorinated hydrocarbons and toxic
metals in contaminated ground water; ZVI nanoparticles use exactly the same chemistry,
but take  advantage of  the  increased  surface  area  and  the  rheological  ability  of
nanoparticles to flow in the subsurface and permeate crevices where contaminants may
reside. The technology is potentially applicable in most circumstances where macro-scale
ZVI would be employed. Where mixed contaminants, such as chlorinated organics and
higher valency toxic metals, are present, ZVI nanoparticles may be able to accomplish
the remediation of both types of material. The demonstrated ability of ZVI to encapsulate
a  heavy metal contaminant  (chromium)  through  a combination of  adsorption and
reduction processes, and the ability of ZVI to act as a reducing agent offers significant
potential for the remediation of radioactive species such as uranium or plutonium where
the reduced form of the metal is of much lower solubility and can be effectively removed
from solution. Risk issues are not expected to be significant since data, to date, show that
the iron nanoparticles do not travel extensively, and nanoparticles of iron oxides (into
which nanoparticulate iron will eventually transform) are ubiquitous in groundwater.

2.2.4  References

Arnold, W.A., and A.L. Roberts. 2000. Pathways and kinetics of chlorinated ethylene and
chlorinated acetylene reaction with Fe(0) particles. Environmental Science &
Technology. 34: 1794-1805.

Blowes, D.W., CJ. Ptacek, J.L. Jambor. 1997. In situ remediation of Cr(VI)
contaminated groundwater using permeable reactive walls: Laboratory studies.
Environmental Science and Technology. 31  (12): 3348-3357.

Blowes, D.W., R.W. Puls, R.W. Gillham, CJ. Ptacek, T. Bennett, J.G. Bain, CJ. Hanton-
Fong, C J. Paul. 1999. An In situ Permeable Reactive Barrier for the
Treatment of Hexavalent Chromium and Trichloroethylene in Ground Water:
Volume 2 Performance Monitoring. EPA/600/R-99/095b. Cincinnati, OH: United States
Environmental Protection Agency.

Bronstein, Kate. 2005. Permeable Reactive Barriers for Inorganic and Radionuclide
Contamination. Prepared for U.S. EPA, Washington DC. Website. Accessed October
2007. http://clu-in.org/download/studentpapers/bronsteinprbpaper.pdf

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Federal Remediation Technologies Roundtable (FRTR). 1998. In Situ Permeable
Reactive Barrier for Treatment of Contaminated Groundwater at the U.S. Coast Guard
Support Center, Elizabeth City, North Carolina. Website. Accessed October 2007.
http://costperformance.org/profile.cfm?ID=287&CaseID=287.

Henn, K.W. and D.W. Waddill. 2006. Utilization of nanoscale zero-valent iron for source
remediation-A case study. Remediation Journal. 16(2): 57-77'.

Interstate Technology & Regulatory Council (ITRC). 1999a. Regulatory Guidance for
Permeable Reactive Barriers Designed to Remediate Chlorinated Solvents, 2nd Edition,
PBW-1. Washington, DC: ITRC Permeable Reactive Barriers Team.

ITRC.  1999b. Design Guidance for Application of Permeable Reactive Barriers for
Groundwater Remediation, PBW-2. Washington, DC: ITRC Permeable Reactive Barriers
Team.

ITRC.  2005. Permeable Reactive Barriers: Lessons Learned/New Directions, PRB-4.
Washington, DC: ITRC Permeable Reactive Barriers Team.

Kumar, C.S.S.R. 2006. Nanomaterials: Toxicity, Health and Environmental Issues.
Wiley-VCH, Germany.

Lo, I.M.-C., R.Y. Surampalli, and K.C.K. Lai (Eds.). 2006. Zero-Valent Iron Reactive
Materials for Hazardous Waste and Inorganics Removal. ASCE Publications, Reston,
VA.

Nuxoll, E.E.,  T. Shimotori, W.A. Arnold, E.L. Cussler. 2003. Iron Nanoparticles in
Reactive Environmental Barriers. Presentation at the AIChE Annual Meeting, November
20,2003.

Puls, R. W., D.W. Blowes, R.W. Gillham. 1998. "Emplacement verification and long-
term performance monitoring of a permeable reactive barrier at the USCG Support
Center, Elizabeth City, North Carolina." In Groundwater quality: remediation and
protection, Vol. 250. M. Herbert, and K. Kovar, eds. Amherst, Mass: International
Association of Healthy Soils Publication, 459-466.

Roehl, K.E., K. Czurda, T. Meggyes, F. Simon, D.I. Stewart. 2005. Long-term
Performance of Permeable Reactive Barriers. Elsevier, New York.

Senzaki, T. and Y. Kumagai.  1988. Treatment of 1,1,2,2-Tetrachloroethane with iron
powder. Kogyo Yosui. 357(1): 2-7.

Wang, C. and W. Zhang.  1997. Nanoscale metal particles for dechlorination of PCE and
PCBs. Environmental Science and Technology. 31(7), 2154-2156.

Zhang, W.-X. and D.W. Elliott. 2006. Applications of iron nanoparticles for groundwater
remediation; Remediation Journal.  16(2): 7-21.

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2.3    Self-Assembled Monolayers on Mesoporous Supports

SAMMS is an award-winning (PNNL 2007) hybrid of two active areas  in materials
science—mesoporous materials and molecular self-assembly on the mesoporous material
surface—that combine to create a material capable of efficiently removing target species
from aqueous solutions and other liquids.

A highly developed, engineering-scale technology that is entering the market, SAMMS
reached the commercial threshold  in  2006 for mercury  remediation. The conceptual
developer,  Pacific Northwest  National  Laboratory  (PNNL)  states   that currently
demonstrated laboratory production  capacity is approximately 5 kg. Battelle (the operator
of PNNL)  and Mobil  Oil Corporation (developer of the  original mesoporous support,
now ExxonMobil) are  establishing commercial  production capacity  for the  manufacture
of these materials. Mobil has demonstrated the ability to produce mesoporous substrates
in batch quantities of one ton or more; scale-up of the functionalization process to these
production levels is underway. Costs for these materials are expected to  fall into the
range of selective anion ion exchange resins. PNNL maintains a Web  site devoted to
SAMMS. In  addition to excellent descriptions  of the technology (SAMMS 2006), the
Web site provides links to information on:

   •   current R&D activities;
   •   publications;
   •   general articles;
   •   lanthanide and actinide investigations; and
   •   Other forms (thiol, chelate, anion, and actinide) of SAMMS.

The  following descriptions have  drawn heavily from the information contained in the
PNNL Web site and its links.

2.3.1  Description

Mesoporous materials, one  component of the  SAMMS hybrid, are porous substances
with pore diameters in the range of 2-50 nm; materials below this  size range are called
"microporous"  (and usually  include  materials  such  as zeolites,  aluminophosphates
(AlPOs), clathrasils, pillared and non-pillared clays) and above this range  they are called
"macroporous". Mesoporous materials are thus within the 1-100 nm length scale that
typically defines nanotechnology. The term "mesoporous" can apply  to any material with
pore size in the appropriate range, but in the case of the SAMMS technology, structured
mesoporous  ceramics  are  usually involved.  In  1992,  researchers  at  Mobil, while
exploring novel microporous  materials for new catalysts, synthesized  a new  type of
silica-based material, named the M41S family, which possessed uniform, mesoporous-
scale pores regularly  distributed throughout the solid  material.  The  synthesis  used
cylindrical  surfactant micelles to direct (create) the structure formation of the pores in the
sol-gel preparation process. The larger pores allow bulk solution  to enter and easily
explore the interior's entire  surface;  this is in contrast to the behavior of the smaller pores

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typical of zeolites (typically 0.5-1 nm), where size exclusion is often a dominant effect.
Fryxell (SAMMS 2006) has described the structure as follows:
     "To envision what mesoporous ceramic look like, think of a glass honeycomb
     in which  the holes in the honeycomb  are very uniform and are only 60
     Angstroms across (roughly twice the width of a double-helix strand of DNA),
     and the walls are only 10 Angstrom thick (about the size of a "typical" amino
     acid molecule). These parallel, open-ended pores result in a material that has
     extremely high surface area, all of which is accessible to solution. "

SAMMS are created by attaching a monolayer of molecules to mesoporous ceramic
supports. The method uses linear molecules possessing different chemical functionalities
at each end.  The  chemical  functionality at one end has an affinity for the mesoporous
surface, while the chemical functionality at the other end has an affinity for the target
species to be bound  by  the  SAMMS  material.  A  combination of intermolecular and
intramolecular  forces drive the bi-functional  molecules to assemble along  the entire
length  of the pore as  a close-packed monolayer,  completely covering the surface of the
mesoporous support, thus exposing a new chemical surface and interface to bulk solution.
Figure 3 (SAMMS 2006) presents a graphical representation of the process.
         Self-assembled monolayer
                                                    SAMMS
                           •^
                           *j
           Mesoporous support
                         Figure 3. Formation of SAMMS

Possessing physical  characteristics  similar to activated carbon, mesoporous materials
have very high surface area to mass ratios. SAMMS powder can have a specific surface
area of approximately  1000 m2/g.  For comparison,  the  surface of  a tennis court is
approximately 260 m2. Monolayer molecules fully cover the available surface and thus
present a  large area  for binding target species. The large surface area, combined with
large pore sizes that  allow entry of  solution, create a hybrid material with fast kinetics,
high material loading, and excellent selectivity. Both the properties  of the molecules in
the monolayer and the pore size of the mesoporous support can be tailored for a specific

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application.  The functional group facing the interior of the pore can be designed to
selectively bind targeted molecules while the pore size, monolayer length, and density
can be adjusted to give the material specific diffusive and kinetic properties.

SAMMS is  developing in several engineered forms (such as beads, membranes, and
membrane cartridges) and  can  be delivered  with  a variety  of  chemically  active
substances.  In  addition, the  SAMMS technology  is  developing systematically in a
number of functional forms including:
       Thiol-SAMMS, primarily targeting Hg, Ag, Au, Cu, Cd, and Pb;
       Chelate-SAMMS, primarily targeting Cu, Ni, Co, and Zn;
       Anion-SAMMS   primarily   targeting   chromate,  arsenate,   selenite,
       pertechnetate; and
       Actinide-SAMMS primarily targeting Am, Pu, Th, Np, and U.
and
    a. Thiol-SAMMS.  Thiol-SAMMS was the  first  and  is  the  most  extensively
    investigated functional form, having been specifically developed for the removal of
    mercury from liquid media (Chen et al. 1999, Mattigod et al. 1997).  Thiol-SAMMS
    is  also  the  first   commercial  application  of  the   SAMMS  technology
    (ChemicalProcessing.com  2006).  The  Thiol-SAMMS  functional  form   takes
    advantage of the  fact that the thiol functional group has a very strong affinity for
    mercury (in fact "mercaptans", an  alternate name for thiols, derives from the Latin
    "met-curium captans" meaning mercury capturers). In Thiol-SAMMS, a monolayer
    of mercaptopropyl  siloxane coats the mesoporous surface with  the thiol groups
    pointing towards  the pore  center,  presenting a thiol surface to the  solution in the
    lined  pores. This  surface is able to bind cationic, organic, metallic,  and complexed
    forms of mercury with great affinity (distribution coefficient, or Kd, ~1 x 108) and
    rapid  kinetics. A graphical representation is shown in Figure 4.
  Figure 4. Thiol-SAMMS showing mercury atoms (blue) binding to sulfur atoms
                            (yellow) from thiol groups

   b. Chelate-SAMMS.  In Chelate-SAMMS (SES 2007, SAMMS  2006),  chelating
   functional groups (such as ethylenediamine, ethylenediamine triacetic acid, pyridine,
   etc.) are attached to the surface of the mesoporous materials using a similar chemistry

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to that used for preparation of the thiol-SAMMS. The chelating group is tailored for
the  targeted  metal (e.g.,  ethylenediamine for copper  and 1,2-hydroxypyridinone
(HOPO) for  the  actinides). Results are promising  and research  is  continuing to
optimize the synthesis and metal loadings.

An intriguing aspect of Chelate-SAMMS, and one that demonstrates the versatility of
the technology, is through a synthesis modification, which is a functional form of
SAMMS that is  able to  bind  cesium (Lin et al. 2001). The basis is that metal
ferrocyanides  have been  widely  investigated  as  ion exchangers for cesium, with
potassium cobalt ferrocyanide having the advantages  of high capacity and selectivity
for cesium, but the drawback of being a very fine powder that is difficult to coax into
an effective  engineered  form. In  the SAMMS  approach,  mesoporous  silica is
functionalized with an ethylenediamine terminated silane. Copper(II) ions are then
incorporated simply by stirring a copper(II) chloride solution with the functionalized
mesoporous support for a few hours, and refluxing in toluene to produce  Cu-EDA-
SAMMS. This is converted to Cu-Ferrocyanide-EDA  SAMMS simply by mixing Cu-
EDA-SAMMS with sodium ferrocyanide. The conclusion of the work was that:

   "The synthesis of the  cesium selective SAMMS is a simple,  direct, and
  convergent synthesis. These  nanocomposite materials are easily  made from
  commercially available bulk materials and are highly selective for cesium from
  various high-salt and acid solutions. The high surface area of the mesoporous
  silica creates a high loading capacity for cesium sorption.  The fast binding
  kinetics and high loading capacity of SAMMS sorbent materials are due to the
  rigidly  open pore  structure and rapid interfacial chemistry.  The chemical
  specificity  results from  the selectivity of the copper(II) ferrocyanide interface
  within the nanoporous structure.  This unique combination of properties makes
  SAMMS-based methodology a strong candidate for  the cleanup  of cesium-
  containing nuclear wastes and contaminatedgroundwater" (Lin et al. 2001).

c. Anion-SAMMS. Anion-SAMMS  functional forms  (SAMMS 2006,  SES  2007) are
being investigated since there is a great need for effective anion binders (e.g., in the
cleanup of pertechnetate contamination at DOE sites). While organic ion  exchange
resins  based  on  quaternary ammonium ion exchange chemistry  and  inorganic
materials,  such as alumina, are available, they are orders of magnitude less effective
than  state-of-the-science  cation exchangers. The SAMMS  approach mimics the
strategy used for  Cu-Ferrocyanide-EDA  SAMMS  by lining the   pores  of the
mesoporous material with cationic transition metals complexes specifically targeting
those complexes  that would allow for  a  direct interaction between the cationic
receptor and  the  target anion. Research (Fryxell 2001) has  shown  that copper or
nickel  ethylenediamine complexes immobilized on mesoporous silica are extremely
efficient ion binding materials for chromate, comparable in terms of loading to the
best  cation  exchangers.  By  exploiting  variations  in transition-metal  complex
chemistry, the promise is held that effective ion exchangers for tetrahedral anions can
be developed. It is also worthy of note that Thiol-SAMMS capped with soft metals,

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    such as silver or mercury, have shown promise as "getters" for radioiodine (Mattigod
    et al. 2003a, Mattigod et al. 2003b).

    d. Actinide-SAMMS. Actinide-SAMMS (Fryxell 2001, Lin  et al. 2005,  SAMMS
    2006, SES 2007) is the least developed area of the SAMMS technology. There exists
    a  body of research on SAMMS applied to lanthanide separations (Fryxell  2001,
    Fryxell 2004, Yantasee  2005, Lin  et al. 2005),  and parallels between lanthanide
    chemistry  and  actinide  chemistry  are  fairly well understood.  In  addition,  the
    theoretical basis has been explored (Fryxell 2001) and laboratory experiments suggest
    that by examining potent actinide binding ligands from prior studies and synthesizing
    functional  forms such as amidophosphonic acid-SAMMS  and hydroxypyridinone-
    SAMMS, excellent actinide sorbents can be developed.

At the present time no studies have been conducted on the fate and transport of SAMMS
material.

2.3.2  Operational Considerations

PNNL staff assert that SAMMS is clearly superior to commercially-available sorbents,
with 99% of  Thiol-SAMMS'  mercury-adsorbing action taking place in  the  first five
minutes;  tests at PNNL show  that  the material  can remove  99.9% of mercury in  a
simulated wastewater,  reducing the  mercury level to well below EPA discharge  limits
(ChemicalProcessing.com 2006).  Treatment costs appear to be an order  of magnitude
lower than those of the best available alternative technologies.

From ChemicalProcessing.com: "...says Shas Mattigod, a staff scientist at PNNL. 'There
is no comparison.' Mattigod calls treatment costs an order of magnitude lower than those
of the best available alternative technologies. 'We estimate that it will cost about $200,
including material, analysis and labor, to treat similar volumes of this waste solution,' he
says. 'This would save $3,200 over the more-traditional disposal methods.'"

2.3.3  Summary of Environmental  Potential

The SAMMS technology is  one of the  most  promising  nano-enabled environmental
technologies. It is probably  the only nanotechnology so far that was both specifically
designed  for,  and has already found  commercial  application in, environmental
management. It is a technology used for separating aqueous solutions,  but is more likely
to  find application in sorbent units as opposed to being released into the environment to
perform its separately behavior. Technologically, it combines rational ligand design for
targeting  species in solution  with  molecular  self  assembly  on mesoporous support
structures.  Rational ligand design  is well  understood; molecular self assembly  and
mesoporous material  behavior are  firmly  enough  understood  to allow commercial
application.  Yet both  are benefiting greatly from further developments, many coming
from  various areas  of  nanotechnology  research. The technology  is extremely flexible,
allowing  a wide variety of aqueous species to  be targeted for removal. The  SAMMS
material offers the benefit of high capacity, and also appears to be a strong candidate as a

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waste form that may be disposed of directly, thus significantly easing further processing
requirements.

2.3.4  References

ChemicalProcessing.com. "Nanosponge soaks up mercury". 2006. Website. Accessed
October, 2007. http://www.chemicalprocessing.com/industrynews/2006/052.html.

Chen, Xiaobing, X. Feng, J. Liu, G. Fryxell, M. Gong. 1999. Mercury Separation and
Immobilization using Self-Assembled Monolayers on Mesoporous Supports (SAMMS).
Separation Science and Technology. 34 (6-7): 1121-1132.

Fryxell, G.E. 2001. Actinide-Specific Interfacial Chemistry of Monolayer Coated
Mesoporous Ceramics Number 65370. FINAL REPORT U.S. Department of Energy
Environmental Management Science Program. Website. Accessed October 2007.
http://www.osti.gov/em52/2000projsum/65370.pdf.

Fryxell, GE, H. Wu, Y. Lin, W.J. Shaw, J.C. Birnbaum, J.C. Linehan, Z. Me, K.
Kemner, S. Kelly. 2004. Lanthanide selective sorbents: self-assembled monolayers on
mesoporous supports (SAMMS). Journal of Materials Chemistry. 14 (200): 3356-3363.

Lin, Y., G. Fryxell, H. Wu, M. Engelhard. 2001. Selective Sorption of Cesium Using
Self-Assembled Monolayers on  Mesoporous Supports. Environmental Science
Technology. 35(19): 3962 -3966.

Lin, Y., S.K Fiskum, W. Yantasee, H. Wu, S.V. Mattigod, G.E. Fryxell, K.N. Raymond,
J.Xu. 2005. Incorporation of Hydroxypyridinone (HOPO) Ligands into Self-Assembled
Monolayers on Mesoporous Supports (SAMMS) for Selective Actinide Sequestration.
Environmental Science and Technology. 39:1332-1337.

Mattigod,  S. V., Feng, X., Fryxell, G. E., Liu, J., Gong, M., Ghormley, C., Baskaran, S.,
Me, Z., Klasson, K. T. 1997. Mercury  Separation from Concentrated Potassium
Iodide/Iodine Leachate Using Self-Assembled Mesoporous Mercaptan Support
(SAMMS) Technology. PNNL-11714. Prepared for the U.S. DOE, Washington DC.

Mattigod,  S.V., R. Skaggs, G.E. Fryxell. 2003a. Removal of Heavy Metals from
Contaminated Waters Using Novel Nanoporous Adsorbent Materials. PNWD-SA-5955,
Battelle, Pacific Northwest Division, Richland, WA.

Mattigod,  S. V., G. E. Fryxell, R. J. Serne, K. E. Parker, F. M. 2003b. Evaluation of
Novel Getters for Adsorption of Radioiodine from Groundwater and Waste Glass
Leachates. RadiochimicaActa. 91: 539-545.

Pacific Northwest National Laboratory (PNNL). R&D100 Awards. Website. Accessed
October, 2007. http://www.pnl.gov/about/rd 1 OOawards.asp.

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Self Assembled Monolayers on Mesoporous Supports (SAMMS). 2006. Website.
Accessed October, 2007. http://samms.pnl.gov.

Steward Environmental  Solution (SES). 2007. Website. Accessed November 2007.
http://www.stewardsolutions.com.

Yantasee W., G.E. Fryxell, Y. Lin, H. Wu, K.N. Raymond, J. Xu. 2005.
Hydroxypyridinone (HOPO) Functionalized Self-Assembled Monolayers on Mesoporous
Supports (SAMMS) for  Sequestering Rare Earth Cations. Journal of Nanoscience and
Nanotechnology.  5(4): 527-535.

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2.4    Membranes: Nanofiltration and Affinity

2.4.1  Background

The term "membrane" covers a wide range of processes, including those used for gas/gas,
gas/liquid, liquid/liquid, gas/solid, and liquid/solid separations. Membrane technology is
well-established and is used in many processes. Membrane production is a  large-scale
operation. Membranes are used for the separation of radionuclides  as  well  as  other
contaminants.  This  section discusses three nanotechnologies that are  often used in the
filtering processes and show great potential for applications in remediation.

   1.  Nanofiltration (and its sibling technologies: reverse osmosis, ultrafiltration, and
       microfiltration),   is  a   fully-developed,  commercially-available  membrane
       technology with a large number of vendors. Nanofiltration relies on the ability of
       membranes to discriminate  between the physical size of particles or species in a
       mixture or solution and is primarily used for water pre-treatment, treatment, and
       purification (Van der Bruggen and Vandecasteele 2003, Rautenbach and Groeschl
       1990, Rautenbach et al.  1997, Atkinson 2002, Costa and de  Pinho 2006). There
       are approximately 600 companies worldwide offering membrane systems.

   2.  Electrospinning is a process utilized by the nanofiltration process, in which fibers
       are stretched and elongated down to a diameter of about  10 nm.  The modified
       nanofibers that are produced are particularly useful in the filtration process as an
       ultra-concentrated filter with  a very large surface area. Studies have found that
       electrospun  nanofibers  can capture metallic ions and are continually  effective
       through re-filtration.

   3.  Surface modified membrane is a term used for membranes with altered makeup
       and  configuration,  though  the basic properties  of their underlying materials
       remain intact.

With the global water market valued at over $300 billion, and water supplies becoming
an important international issue, nanofiltration is anticipated to have a very important role
in the future. In contrast to the types of filtration that rely  on size discrimination, affinity
membranes  use chemical recognition between  the components  of  the membrane and
components of solution to effect separation. Affinity membranes and  related technologies
are well-established and find their primary markets in the biomedical and biotechnology
industries.

2.4.2  Nanofiltration Membranes

Nanofiltration   is one of  a group  of similar membrane processes (including reverse
osmosis, ultrafiltration,  and microfiltration) used to separate components of a liquid
mixture. These four processes are best understood together and as a  continuum in terms
of the size of particles that can be removed from a mixture.

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In the regular  particle  filtration  of a liquid containing entrained  particles, the liquid
mixture is forced (by gravity or applied pressure) through a filter medium that has pores
or passages of a size  that allows the liquid and small particles  to  pass  through, but
prevents passage of larger particles.  A paper coffee filter is an example of a regular
particle filtration. The  paper filter allows passage of the water  containing dissolved or
extremely small material, but prevents passage  of the larger coffee grounds. Smaller
pores or passages in the filter medium prevent larger particles from passing through with
the liquid. Figure  5 provides a  graphical representation of the  generalized filtration
process.
                                0o  %   m   •
                                     ' n  n  9  £>  o
              Figure 5. General representation of the filtration process

There are two basic types of filters: depth filters and membrane filters. Depth filters have
a significant physical depth and the particles to be retained are captured through out the
depth of the  filter.  Depth filters often have a labyrinthine three-dimensional structure,
with multiple channels and heavy branching so that there is a large pathway through
which the liquid must flow and by which the filter can retain particles. Depth filters have
the advantages of low cost, high throughput,  large particle retention capacity, and the
ability to retain a variety of particle sizes. However, they can suffer from entrainment of
the filter medium, uncertainty regarding effective pore size, some uncertainty regarding
the overall integrity of the  filter,  and the risk of particles being mobilized when the
pressure differential across the filter is large.

The second type of filter is  the membrane filter,  in which depth  is not  considered
important.  The  membrane filter uses a  relatively  thin material with  a  well-defined
maximum pore size and the particle  retaining effect takes place almost entirely at the
surface. Membranes offer the advantage of having well-defined effective pore sizes, can
be integrity tested more easily  than depth filters, and can achieve more filtration of much
smaller  particles. They tend to be more expensive than depth filters and usually cannot
achieve the throughput of a depth filter. Filtration  technology has developed a well-
defined  terminology that has been well addressed by commercial  suppliers; the American
Standard Test Method (ASTM) has developed a  standard (ASTM D6161-05) (ASTM

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2007)   that  addresses  the  terminology  used   for   microfiltration,   ultrafiltration,
nanofiltration, and reverse osmosis membrane processes.

Reverse osmosis, nanofiltration,  ultrafiltration,  and  microfiltration are  all membrane
processes able to remove small particles or soluble species. They all work on exactly the
same principle as regular particle filtration, but the distinguishing feature between them is
their effective pore size, and thus, the minimum size  of particle that will  be rejected by
the membrane; reverse osmosis membranes reject all but the very smallest species (small
soluble organic  species that are not otherwise considered even to be "particles"),  while
microfiltration allows considerably larger particles to pass through. Figure 6 provides a
graphic representation of the process characteristics of the four membrane  processes, and
Figure  7  provides a graphic representation  showing the size range  and approximate
molecular weight range where each of the four membrane filtration technologies finds its
application.

Regular particle filtration will reject particles down to about the one micron (1,000 nm)
size range. If filtration to reject particles smaller than this  limit is required,  microfiltration
should  first be considered.  Microfiltration operates at the low end  of familiar particle
filtration, being at the  limit able to retain particles above the 100 nm  size range.  Its
separating  abilities  thus  cease  at  the   100  nm  limit usually  associated   with
nanotechnology. Microfiltration can remove most  suspended solids and living material,
such as bacteria, but will not retain any type of dissolved solute or smaller biological
material,  such  as viruses. Ultrafiltration  is  effective only to the  10 nm  size range,
allowing it to reject most proteins,  viruses, and groundwater colloids. Nanofiltration is
usually used to remove  material in the 0.5-10 nm range and will reject most of the  larger
organic molecules, sugars, and  multivalent ions, with only monovalent ions and  water
being able to pass through. To remove the monovalent ions, reverse osmosis membranes
are required; these will reject almost all material, except water and simple organic species
(such as very short chain alcohols and acids).
               Microfiltration
               Ultrafiltration
               Nanofiltration
              Reverse Osmosis
                             Water   Monovalent   MuUsifsk'nt
                                    ISM     le>M
                             Water   Mofiovalent   MutUvalem   Vir
                                    ioiH     loni
                    Figure 6. Membrane process characteristics

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                      100  2DD 1,000 20,000 100,000 500,000 IMP/  5 MM
        Note: 1 micron (micromotor) -4x10-5 inches - 1 x 104 Angstrom unite    © 2004 - Koch Memftrane Systems

               Figure 7. Size range for filtration separation processes

Benefits of water treatment nanofiltration include:

    •   Lower operating costs,
    •   Lower energy costs,
    •   Lower discharge and less wastewater than reverse osmosis,
    •   Reduction of total dissolved solids (TDS) content of slightly brackish water,
    •   Reduction of pesticides and VOCs (organic chemicals),
    •   Reduction of heavy metals,
    •   Reductions of nitrates and sulfates,
    •   Reduction color, tannins, and turbidity,
    •   Hard water softening,
    •   Being chemical-free (i.e., does not use salts or chemicals), and
    •   Water pH after nanofiltration is typically non aggressive.

For radionuclide treatment  applications,  nanofiltration  and  ultrafiltration  have been
investigated as an ultra low-level analytical tool to separate actinides from  other ionic
species in high-level  radioactive waste solutions, and  as a possible treatment option for
waste streams from the Los  Alamos National Laboratory  Plutonium Treatment Facility
(Smith  1993). In these applications, the nanofiltration and ultrafiltration membranes are
coupled with  water-soluble  chelating  polymers  (WSCP).  WSCPs  are  polymers
engineered to contain both highly selective chelating functionalities to bind with targeted
metal ions, and solubilizing functionalities to  allow  the polymer to dissolve  in water
(Smith  et  al.  1995). The polymer's overall size  is  large enough that  it exceeds  the
rejection  limit  for  an  ultrafiltration  membrane.  When  the  unchelated  polymer is
introduced into  a solution that contains the target ions for which the chelating  groups

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were designed, the polymer binds with these target ions and nothing else.  The chelated
polymer can then be separated from the solution (and all other ions in the solution) by
ultrafiltration; the chelated target ions can be separated from the polymer by adjusting the
solution chemistry; and the regenerated water-soluble chelating polymer can be recycled
(Jarvinen  1995).  In  these  applications, ultrafiltration  combined  with WSCP has the
advantage of being aqueous-based (such as ion exchange resins), has a high throughput
and rapid kinetics (like two-phase liquid-liquid  extraction systems), but does not have the
disadvantage of using organic solvent-based extractants.

WSCPs with molecular weights in the 100,000  range have been prepared  based on
polyacrylic  acid  or  polyethyleneimine with  functional groups  of phosphonic acid,
acylpyrazolone acid,  and hydroxamic acid. In acidic nitrate and acidic chloride solutions,
these functional groups have a high affinity for actinides and a low affinity  for alkali
metals and alkaline  earths. The concentration  of polymer is typically 1-2%,  with the
ultrafiltration membrane typically having 10-100 |im pores (Gibson 1994,  Smith  1993).
This technology has been tested at bench scale  for the removal of heavy metal ions from
electroplating  waste streams. Development continues (Moreno-Villoslada and  Rivas
2002, Rivas et al. 2003,  Rivas et al. 2006, Tomida et al. 1994, Kawano et al.  2002),
though  dendrimers  may  compete as a chelating  moiety in the future  if their costs
decrease.

Summary of Environmental Potential

Nanofiltration  is an established technology  with  numerous  equipment developers,
manufacturers,  and vendors. The major application is in reverse osmosis for desalination
and  production of  high purity water  for specialized  industrial  uses,  with  small
applications for wastewater treatment. While  current and past development has relied
predominantly on size exclusion effects, the promise of nanotechnology is that specific
chemical and physical behavior can be engineered into the materials, and  that the slow
flow rates typical of reverse osmosis and nanofiltration can be overcome—allowing the
energy requirements  and production costs for the production of pure water to be greatly
reduced. The general industrial uses  of filtration technology should support developments
that will allow  spin-off applications for environmental uses; a significant effort is being
made to apply nanotechnology developments of filtration technology to the production of
potable water  in economically  challenged arid  regions. The primary environmental
applications are likely to be "end-of-pipe"  and polishing  uses. Nanofiltration combined
with water-soluble  chelating polymers  has  been  investigated  for the removal of
radioactive species from aqueous waste streams (Smith 1993, Smith et al. 1995).

2.4.4  Electrospun Fibers

Electrospinning is a process for making nanofibers with diameters down to  about 10 nm.
The technology produces the nanofibers  from polymer solutions  or melts, with the
extreme elongation and narrowing  of the fiber occurring as a result of electrostatic
repulsion. Electrospinning has the characteristics of both the commercial electrostatic
spraying technique  and the commercial  spinning of fibers,  each of which is a long
established technology in its  own right. Electrostatic spraying is a coating technology,

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over a century old, involving atomizing a  liquid from  a spray gun and imparting an
electrical  charge to the droplets by using an electrode placed at the end of a spray gun.
The electrode typically operates in the 30 to  140 kilovolt range with a current of 0 to 225
microamperes. The droplets are attracted toward a target  that is either grounded or has a
positive  charge,  and  produces  a uniform  coating of  liquid  (frequently paint).  The
electrostatic spraying approach can also be used  as a surface modification technique to
introduce nanoparticles onto fibers or other surfaces by  spraying solutions that contain
only about one particle per droplet.

In comparison, electrospinning (first patented by Antonin Formhals in 1934) uses the
electrical  charge to form a mass of fine polymer filaments. In electrospinning, a polymer
solution or melt is driven through a spray gun nozzle and forms a droplet at the tip. When
the voltage is applied to the nozzle, the droplet is stretched; if the viscosity of the material
is sufficiently high, the breakup encountered  in  electrostatic spraying does not occur.
Instead,  a thin,  charged  liquid jet  is  formed.  The jet  elongates  and is  whipped
continuously by  electrostatic repulsion, forcing  it  to  follow a spiral  path  toward the
oppositely charged or  grounded collector. The whipping  action helps to elongate the jet
much further to a diameter on the order of tens  of nanometers. Figure  8  illustrates the
basic process. Fibers are formed either by the melt cooling or the solvent evaporating
from the polymer solution. Nanoparticles can be mixed into, or produced directly in, the
polymer solution and spun with the fibers (Lee et al. 2005). Nanofibers produced in this
way have many  potential  applications,  including high efficiency  filter media,  as
nanocomposite materials for water treatment membranes,  catalysis, hydrogen storage, or
in biomedical  applications (such as drug release carriers or artificial tissue).
                   Precursor
               Pendant drop of polymer
                                                            Power supply
           Jet initiation and
           extension
Bending instability and
further elongation
Solidification of the jet
into fibers
                     Figure 8. Basic principle of electrospinning

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Investigations into the potential  of electrospun fibers for water treatment have mainly
focused on their use in membranes, where the massive surface area (illustrated in Figure
9) offers  special  advantages.  Ki  et al.  (Ki  et al. 2007)  examined  membranes of a
nanofibrous blend of silk fibroin and wool keratose and found that it had an exceptional
performance for the adsorption of metal ions, that its adsorption capacity was maintained
after several desorption and re-adsorption cycles, and that it is very suitable for removing
and recovering heavy metal ions from water, potentially as an affinity membrane.

Ramakrishna et al. (Ramakrishna et al. 2006) reviewed electrospun nanofibers from the
perspective  that their porous nature  and large  surface-to-volume ratio gives them the
potential for use in various applications where high porosity is desirable. They noted that
electrospinning has  an  advantage of  comparatively  low  cost  with relatively high
production rate, that the unique  ability  to produce nanofibers of different materials in
various fibrous assemblies,  and  that the ability to form porous fibers means that the
surface area of the fiber mesh can be increased tremendously. Since  the fibers can be
surface functionalized, affinity membranes can easily be formed with the potential for
application  in the removal of heavy  metals from  wastewater. They concluded that
electrospinning may well be one of the most significant  nanotechnologies of the 21st
century.
          Figure 9. An electrospun polysulphone membrane: (a) surface;
              (b) cross-section; and (c) magnified cross-section images

Sang et al. (Sang et al. 2008) examined various filtration modes for using an electrospun
chloridized polyvinyl chloride nanofiber membrane (including static adsorption, direct
filtration,  soil-addition filtration, diatomite-addition filtration, and micellar  enhanced
filtration), and they concluded that the membrane,  when used with micellar  enhanced
filtration, can be used for the treatment of the groundwater containing heavy metals (such
as copper, lead, and cadmium) with high efficiency.

2.4.5  Surface Modified Membranes
Electron-beam-induced grafting  is  one of two methods  in  the  category  of ionizing
radiation—gamma  radiation  from  cobalt-60  is the  other.  Electron-beam-induced
technology provides a pathway for customizing surfaces such as membranes; hence, the
commercial  name eMembranes  (developed by  the  Japan Environmental  Purification
Research  Institute). The technology  allows  membrane  surface alternation without

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changing the basic properties of the underlying bulk materials. Electron-beam machines
are currently available and  play  a significant role in processing  specialty polymeric
materials.  For example, electron-beam-induced grafting has existed in some  form for
decades; nuclear power plants have used ion exchange resins enhanced by electron-beam-
induced grafting to cleanse uranium from coolants. The future materials generated with
this technology is based on over 50 years of scientific  research.  The technology is
stimulating the development of new and promising membranes. Electron-beam-induced
grafting is being used by laboratories throughout the world to create surfaces, including
chemical resistance, wet ability, biocompatibility,  antithrombo, dyability, and  antistatic
properties.  Grafting has also been used to produce ion exchange membranes for the
removal of heavy-metal for aqueous waste streams. An emerging application is biological
separations, but the basic concept also has targeted the removal of heavy  metals  from
industrial wastewaters. There is little doubt that many new and improved products will be
created to aid in the cleanup of radionuclides.

eMembrane technology is being  extended  to create  specialized membranes for  many
potential applications. The  ability  to create specialized  nano-engineered membranes
opens up  many envisioned possible  future applications.  An  example of developing
applications is a new water remediation technology, which could remove—in one pass—
multiple contaminants such as viruses, radionuclides, heavy  metals, and chlorinated
solvents. A membrane could be tailored for a specific cleanup application. This would
greatly reduce remediation costs and accelerate the cleanup process.

The following example of eMembrane development gives an indication of the broad and
varied  possibilities for developing customized membranes and material surfaces, and
draws heavily from company provided literature. eMembrane's technology  involves the
nano-grafting of polymer  chains containing selective binding  functionalities.  This
technology can impart new  and multiple polymeric material on existing materials and
membranes. At the heart of the technology is the technique of electron-beam induced
polymer grafting. Figure 10 provides a graphical representation of the technique showing
the attachment of polymeric material.
                                x>>>>x>>                «.
                 nano-grafting   -
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An electron beam irradiates a base membrane that can be made from  any polymeric
material. Other radiation sources,  such as gamma rays,  can also be used for similar
radiation induced polymer  grafting (Ramakrishna  et al. 2005). The  electron beam
irradiation generates active species, or radicals, on the surface of the polymer. The active
species are the sites at which other long polymer chains or brushes can be attached. The
polymer brushes  may contain the binding functionalities at the time of attachment, or
they may  be chemically functionalized after attachment has occurred.  Electron beam
irradiation is seen as an advantageous method of surface modification since it can occur
after the basic polymer has been fabricated and does not affect the shape; by varying the
electron beam  energy  and other process  characteristics,  the  depth  and  degree  of
functionalization can be controlled.

eMembrane's electron-beam technology permits a density of polymer brush attachment
that is extraordinary—up to 10 trillion polymer brushes  per  square  centimeter can  be
attached giving a surface spacing of about 4 nm between  each brush, a density far
exceeding any other technique. The brushes can range from 10 to 300 nm long and can
contain a variety of functionalities, allowing the production of highly tailored separation
material. For example, a microporous  membrane with grafted functionalized  polymer
brushes not only  performs microfiltration (by molecular size cutoff),  but the functional
groups on  its brushes  can  also  simultaneously capture and remove toxic  metal ions,
soluble proteins, viruses, or cells from the filtrate. In effect, it has become  an affinity
membrane (Ofsthun et al. 1999, Zou et al. 2001, Nasef 2004, Klein 1991). Materials in a
variety of  shapes (e.g., film,  hollow  fiber,  non-woven  cloth,  etc.) are grafted with
polymer brushes that extend off the surface of the starting material. Figure 11 provides a
graphical representation of the functionalized polymer surface with a  variety of brushes
attached to facilitate a number of separations.
                                                    P O LYME R B RUS H
              POLYMER SURFACE;
                   Figure 11. eMembrane-functionalized surface

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Environmentally-related applications currently under investigation by eMembrane, Inc.
include:

Ion
   •   Removal, collection of heavy metal ions from fluids,
   •   Ultra-pure water production
   •   Immobilized metal affinity membrane

Gas
   •   Removal of odors or toxic gases via neutralization

Biological
   •   Tools for proteomics
   •   Display of multilayer of various proteins for protein-protein interaction studies
   •   Immobilized enzymes for proteomics, biosensors, and bioreactors
   •   Large-scale biologies purification

Cell
   •   Immobilized cells for proteomics studies
   •   Removal of bacteria
   •   Bioreactors, artificial organs

Radiation cross-linking of naturally occurring polymers, such as polysaccharides, is being
investigated  for  the  production  of  biodegradable   hydrogel/nanogel.  This  new
nanomaterial consists of individual  macromolecules that are internally cross-linked by
irradiation ionizing radiation.

Specifically modified  nanogels  are  being  studied for  wastewater  filtration.  Gels
containing  acid groups have to bind ions, including uranium and nickel, for use in the
removal of metals from aqueous media. These gels can be formulated and customized to
remove most contaminants found in water.

No fate and transport studies have been  conducted, nor are anticipated, since this is a
process unit rather than a material. Because the technology is in the development state, no
operational or maintenance  parameters have been  determined, and no information on
impacts,  hazards,  efficacy, limitations, and  waste management approaches is available.
One of the greatest, unknown concerns is what could happen if the fibers dislodge from
the surface and enter the drinking water supply.

2.4.6  References

ASTM International. 2007. Standard Terminology Used for Microfiltration,
Ultrafiltration, Nanofiltration and Reverse Osmosis Membrane Processes. Website.
Accessed October 2007.
http://www.astm.org/cgibin/SoftCart.exe/DATABASE.CART/REDLINE PAGES/D616
1 .htm?E+mystore.

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Atkinson, S. 2002. Nanofiltration concentrates coloured wastewater and produces potable
water. Membrane Technology. 2002(7): 11-12.

Costa, A.R. and M.N. de Pinho. 2006. Comparison of the performance of ultrafiltration
and nanofiltration in surface water treatment. Desalination. 199(1-3): 73-75.

Gibson, R.R., B.F. Smith, G.D. Jarvinen, T.W. Robinson, R.E. Barrans, K.V. Wilson.
1994. The Use of Water-Soluble Chelating Polymers as an Analytical Method for the
Separation of Actinides in Aqueous Systems. Presentation at the Eighteenth Annual
Actinide Separations Conference, Durango, CO, May 23-26, 1994.

Jarvinen, G.D., R.E. Barrans, N.C.  Jr., Schroder, K.L. Wade, M.M. Jones, B.F. Smith,
J.L. Mills, G. Howard, H. Freiser, S. Muralidharan. 1995. Selective Extraction of
Tetravalent Actinides from Lanthanides with Dithiophosphonic Acids and
Tributylphosphate. In Separations of Elements. K.L. Nash and G.R. Choppin, eds.
Plenum Press, New York, 43-62.

Kawano, K., K. Hamaguchi, S. Masuda, T. Tomida. 2002. Binding Properties of a Water-
Soluble Chelating Polymer with Divalent Metal Ions Measured by Ultrafiltration. Poly(K-
acethylaminoacrylic acid). Industrial and Engineering Chemical Research. 41(20): 5079-
5084.

Ki, C.S., E.H. Gang, 1C Urn, Y.H.  Park. 2007. Nanofibrous membrane of wool
keratose/silk fibroin blend for heavy metal ion adsorption. Journal of Membrane Science.
302(1-2): 20-26.

Klein, E. 1991. Affinity Membranes: Their Chemistry and Performance in Adsorptive
Separation Processes. Wiley-Interscience, Hoboken, NJ.

Lee, H.K., E.H. Jeong, C.K. Baek, J.H. Youk. 2005. One-step  preparation of ultrafine
poly(acrylonitrile) fibers containing silver nanoparticles. Materials Letters. 59(23):2977-
2980.

Moreno-Villoslada I. and B.L. Rivas. 2002. Metal ion enrichment of a water-soluble
chelating polymer studied by ultrafiltration. Journal of Membrane Science. 208(1-2): 69-
73.

Nasef, M.M. 2004. Application of Electron Beam for Preparation of Membranes. Nippon
Genshiryoku Kenkyujo JAERI, Conf Journal. 37-54.

Ofsthun, N. J., P.J. Soltys, G.A. Kunas. 1999. Affinity membrane system and method of
using same. U.S. Patent No. 5,871,649.

Ramakrishna, S. W.-E. Teo, T.-C. Lim (Eds). 2005. Introduction to Electrospinning and
Nanofibers. World Scientific Publishing Company, Singapore.

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Ramakrishna, S., K. Fujihara, W.-E. Teo, T. Yong, Z. Ma, R. Ramaseshan. 2006.
Electrospun nanofibers: solving global issues. Materials Today. 9(3): 40-50.

Rautenbach R. and A. Groeschl. 1990. Separation Potential of Nanofiltration Membranes.
Desalination. 77(1-3): 73-84.


Rivas, B.L., E.D. Pereira, I. Moreno-Villoslada. 2003. Water-soluble polymer-metal ion
interactions. Progress in Polymer Science. 28(2): 173-208.

Rivas, B.L., S.A. Pooley, E.D. Pereira, A. Maureira. 2006. Water-Soluble
Polyelectrolytes with Metal Ion Removal Ability by Using the Liquid Phase Based
Retention Technique.  World Polymer Congress-MACRO 2006. 245-246(1): 116-122.


Sang, Y., F. Li, Q. Gu, C. Liang, J. Chen. 2008. Heavy metal contaminated groundwater
treatment by a novel nanofiber membrane. Desalination. 223:349-360.

Smith B.F.  1993. Actinide separations for advanced processing of nuclear waste: Annual
Report 1993. Report LA-UR-93-4017, Los Alamos National Laboratory.

Smith, B.F., T.W. Robinson, J.W.  Gohdes. 1995. Water-Soluble Polymers and
Composition Thereof. U.S. Patent DOE No. S-78, 350.

Tomida T.,  T. Inoue, K. Tsuchiya, S. Masuda. 1994. Concentration and/or removal of
metal ions using a water-soluble chelating polymer and a microporous hollow fiber
membrane.  Industrial and Engineering Chemistry Research. 33:904-906.

Van der Bruggen B. and C. Vandecasteele. 2003. Removal of pollutants from surface
water and groundwater by nanofiltration: overview of possible applications in the
drinking water industry. Environmental Pollution. 122(3): 435-445.

Zou, H., Q.  Lou, D. Zhou. 2001. Affinity membrane chromatography for the analysis and
purification of proteins. Journal of Biochemical and Biophysical Methods. 49(1-3):199-
240.

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2.5    Zeolites

2.5.1  Introduction

Zeolites are a well-established technology used in a range of processes and industries.
Zeolites are not new materials—they have been  investigated for over two  and  a  half
centuries,  with  stilbite  and natrolite both  being identified in the 1750s. Industrial
applications include catalysis in the petroleum industry (Venuto and Dekker 1979, Chen
et al. 1994), various uses in agriculture (St. Cloud 2007,  BRZ Zeolite 2007, Zeolite
Australia 2007), horticulture (ZeoPro 2007), gas  separations (Yang 1994, Kerry 2007,
Kanellopoulos 2000), domestic water treatment (McKetta 1999,  Kawamura 2000, Faust
1998); and nuclear waste processing (Auerback et al. 2003, Choppin and Khankhasayev
1999). The value of zeolite catalysis to petroleum cracking is well in excess  of $200
billion  (MassNanoTech  2007). About  50 naturally  occurring zeolites  have been
identified; over 150 synthetic zeolites have been prepared and characterized; and further
thousands of combinations of framework and composition are available (MassNanoTech
2007, Baerlocher and McCusker 1996). Zeolites have long been used in the nuclear
industry  (Auerback  et al.  2003,  Choppin and  Khankhasayev  1999)  owing  to their
properties as ion exchangers. The planned siting of the United States' first deep geologic
radioactive waste repository at Yucca Mountain  in Nevada, where design philosophy
called for both engineered and natural barriers (Ahn et al. 1981) to inhibit the transport of
any  potentially  leaking radionuclides,  was  influenced  considerably  by the local
abundance of the natural zeolites mordenite and clinoptilolite, both of which have large
cationic exchange capacities.

2.5.2  Description

Zeolites are crystalline aluminosilicates, compositionally similar to clay minerals, but
differing in their  well-defined  three-dimensional nano- and micro-porous structure.
Aluminum, silicon, and oxygen are arranged in a regular structure of [SiC^]" and [AlO/t]"
tetrahedral units that form a framework with small pores (also called tunnels, channels, or
cavities) of about 0.1-2 nm diameter running through the material.  Figure 12  shows a
representation of a typical zeolite framework. It should be clearly noted that this  is  just
one of a large and growing number of types of zeolite framework. In 1970, the Atlas of
Zeolite Framework Types (Baerlocher and McCusker 1996) listed 27 known frameworks,
but by 2003, the number had grown to 145. The  variety of size  and  shape available for
the pore structure is  the source of  zeolites' catalytic activity that is  so important to the
petrochemical industry.

A second consequence of the framework being built from negatively charged units is that
it possesses a  net negative  charge  that must be balanced by the presence of positively
charged cations. Most naturally occurring zeolites have the environmentally predominant
sodium ion as a loosely bound counter ion. These  can be readily displaced by other  ions
for which  a particular  framework has a much  greater affinity, thus giving zeolites
significant ion exchange properties.

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                       Figure 12. A typical zeolite structure

It  should  be noted that the ion exchange  and the pore size properties of zeolites are
partially linked. When the zeolite is in the sodium form (i.e., it has positively charged
sodium ions balancing the net negative charge on the aluminosilicate framework), the
sodium ions are associated with the tetrahedral aluminum or silicon atoms at the entrance
to the pores and, because  of their finite size, they effectively reduce the diameter of the
pore opening slightly. If the sodium ions are replaced by potassium ions, which are larger
than the sodium ions, then the opening of the pore is effectively reduced even further.
This behavior permits a degree of control over the size of material that can enter the
pores.

Zeolites are usually aluminosilicates, but other tetrahedral  atoms such as phosphorus,
gallium, germanium, boron, and beryllium can exist in the framework as well.

2.5.3  Potential Applications

General Applications. Zeolites have a  wide range of commercial uses (InterSun 2007),
including:

    Aquaculture
       •  Ammonia filtration in fish hatcheries
       •  Biofilter media
    Agriculture
       •  Odor control
       •  Confined animal environmental control
       •  Livestock feed  additives

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   Horticulture
       •  Nurseries, greenhouses
       •  Floriculture
       •  Vegetables/herbs
       •  Foliage
       •  Tree and shrub transplanting
       •  Turf grass soil amendment
       •  Reclamation, revegetation, and landscaping
       •  Silviculture (forestry, tree plantations)
       •  Medium for hydroponic growing
   Household Products
       •  Household odor control
       •  Pet odor control
   Industrial Products
       •  Absorbents for oil and spills
       •  Gas separations

Environmental Applications. Although environmental applications of zeolites are small
compared with applications of their catalytic properties, considerable research and some
implementations have taken place including:

   Radioactive Waste
        •     Site remediation/decontamination
   Water Treatment
        •     Water filtration
        •     Heavy metal removal
        •     Swimming pools
   Wastewater Treatment
         •    Ammonia removal in municipal sludge/wastewater
         •    Heavy metal removal
         •    Septic leach fields

Pasini (Pasini 1996) has described the state-of-the-art technology with regard to the use
of natural zeolites in the protection of the environment.  He focuses on the possible cation
exchange procedures and principles that can be operated at an industrial level; the
removal  of NH4+ from municipal  and  industrial wastewater; the possibilities for use of
natural zeolites for removal of heavy metals from water after laboratory experiments; and
how  chemical  and  structural  features  make  zeolites   a  powerful  tool  for  the
decontamination of waters containing  radionuclides. The compendium by Misaelides et
al. (1999) dealt with general environmental applications and contained much information
on the use of zeolites as radionuclide  sorbents (Macasek 1999,  Bish  1999, Rajec et al.
1999, Colella 1999), including consideration of the  sorption and leaching  properties of
the composites and complexes of natural microporous materials; investigation of natural
zeolites and nuclear waste management in the case of Yucca  Mountain,  Nevada; the
sorption  of heavy metals and radionuclides on zeolites and  clays; and environmental

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applications of natural zeolitic materials based on their ion exchange properties. As an
example of the depth to which these studies can  go,  Komarneni (Komarneni 1985)
investigated  the  use  of one  zeolite, phillipsite,  in  cesium decontamination  and
immobilization, citing:

    "The use of zeolites such as clinoptilolite in nuclear waste decontamination is a
    common practice (IAEA  1972). Zeolites and zeolitic tufts have also been used to
    decontaminate low and intermediate-level liquid nuclear wastes (Mercer and
    Ames 1978) and to separate 37Cs from high-level radioactive defense wastes at
    Hanford, Washington (Nelson and Mercer 1963, Brandt 1970, Buckingham
    1970). Zeolitic  ion ex-changers, such  as lonsiv IE-95 (USNRC 1980)  which
    consists  of a mixture of natural chabazite and erionite from Bowie, Arizona and
    lonsiv IE-96 (which  consists of chabazite)  + Linde A-51 (Hofstetter  and Hitz
    1983)  are currently  used to clean up  accident  wastewater at the  Three Mile
    Island-Unit II reactor, Middletown, Pennsylvania.  "

Radionuclide Applications. Zeolites are one of the few nanotechnologies that have been
investigated for environmental  remediation purposes. Because of their ion  exchange
properties, and  the fact that  they are a seemingly benign natural product that  can bring
certain  improvements  (such as increasing  the  soil  cation-exchange capacity and soil
moisture,  improving hydraulic  conductivity, increasing  yields in acidified soils, and
reducing plant uptake of metal contaminants) to  soil  properties (Allen and Ming 1995),
zeolites have been examined for their ability to remediate heavy metals in soil (Weber et
al.  1984). Based on  this work, Campbell  and  Davies  (Campbell and Davies 1997)
performed an experimental investigation of plant uptake of cesium from soils  amended
with clinoptilolite and calcium carbonate.

The origin of this work was the observation that  radioactive cesium (137Cs)  from the
Chernobyl accident of 1986 has unexpectedly remained in a bioavailable form in upland,
sheep-grazing soils of Great  Britain. As  a potential  remedial  measure, the  zeolite
clinoptilolite was tested in a greenhouse pot  experiment for its effectiveness in selectively
taking up cesium from two British soils: a lowland loam  and an upland peat. Rye-grass
grown  on  10%  clinoptilolite-treated  soils  resulted  in  grass  leaf  tissue  cesium
concentrations below 30  mg Cs kg"1 grass in all cases. Where no clinoptilolite had been
added, cesium in grass leaf-tissue reached 1,860  mg  kg"1  in rye grown on peat and 150
mg kg"1 in rye grown  on loam. In contrast,  the addition of calcium carbonate to the Cs-
treated,  clinoptilolite-free  peat  soil  enhanced the grass   concentration of Cs by
approximately five times, but this effect was not observed with the concentration of Cs in
grass grown from loam soils with the same treatments.

However, despite this apparent beneficial result of adding the zeolite, adverse side effects
were observed.  Since the zeolite is in the sodium form, sodium ions are released and the
risk of  sodium  toxicity to plants increases  as cation exchange proceeds. Further, since
clinoptilolite binds heavy metals in general, essential  heavy metals  (such as zinc) would
be  markedly decreased  by  the  application of zeolite,  which  in  turn could  result  in
deficiency problems in animals. It  was also noted that since grazing animals consume a

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considerable amount of soil in their diet, the consumption of radionuclide-laden zeolites
could itself bring risks.

In general, it has been noted that the main research behind the use of natural zeolites as a
remediation tool for contaminated soil has been conducted largely through laboratory and
greenhouse trials. There is very little evidence in the literature to support the long-term
use of natural  zeolites in real remediation projects (Stead et al. 2000). It was also noted
that the future potential  of using zeolites has not been fully appreciated, and that there is
an urgent need  to undertake field trials  and evaluate  the in-situ efficiency  for these
remediation purposes.

Since zeolites are natural  materials and are  mainly used  in industrial processes, little
research is focused on their fate and transport, though an extensive volume of work exists
on  their  geological origin and behavior. Extensive  data exists  on  operation  and
maintenance parameters. As would be expected,  specific details are highly dependent on
waste  streams involved.  Three  references (IAEA 1967,  IAEA 1984,  IAEA  2002)
discussed below provide an excellent overview of the issues involved.

2.5.4  Impacts, Hazards, Efficacy, and Limitations

Zeolites are a  bulk commodity. World production is on the order of 4 million tons per
year, with China producing and using about 2.5 million tons (primarily as a low-grade
additive to pozzolan cement); U.S. consumption is  about 0.5 million tons. The primary
industrial use  is as a petrochemical catalyst and  the second largest use is as a  detergent
builder. Thus,  the use of zeolites in radionuclide remediation would be expected to have
little impact. Most zeolites, particularly those with current widespread uses, are regarded
as a safe material; they  are currently being marketed as a health food and references to
their medicinal use date  back thousands of years. Zeolites are also used as a feed additive
for cattle, pigs, chicken, and fish. It should be noted, however, that one zeolite, erionite,
is regarded as  a carcinogen due to its fibrous nature and high iron  content.

Regarding efficacy, though zeolites have had limited uses in environmental remediation
outside of their use in  the nuclear industry as an ion  exchanger for  liquid radioactive
waste management, they are seen as  having significant potential.  Even  the drawbacks
mentioned in the work of Campbell and Davies (Campbell  and Davies 1997) (discussed
in Section 2.5.3) should be surmountable. To  eliminate the sodium toxicity risk to soil,
the zeolite could be preconditioned into the ammonium form, which would likely lead to
plant  growth  improvements. Overcoming the concern of nutritionally  important  soil
nutrients binding together would require that the zeolite used (possibly synthetic) would
be designed to have a  very high specificity  for the target radionuclide  and little else.
Alternatively,  soil quality could easily be monitored and appropriate amendments made.

2.5.5  Management of Zeolite Wastes

Ion exchange  in general  is one of the most well-developed,  common,  and  effective
treatment methods for  liquid radioactive waste, and  is  widely  used in the nuclear
industry. Zeolites are a large component of the inorganic  ion exchangers used and an

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extensive amount of literature exists on various aspects of their treatment and disposal.
Among the  best overviews  of this technology base are the series of technical reports
issued by the International  Atomic Energy Agency (IAEA) in 1967,  1984 and 2002
(IAEA 1967, IAEA  1984, IAEA 2002). The information below draws  largely from the
most recent of these reports (IAEA 2002).

Prior to treatment for disposal, two pre-treatments—dewatering and size reduction—may
be needed.  Dewatering is generally  accomplished by  pressure,  vacuum filtration,  or
centrifugation. If drying is needed,  hot air is usually used as the drying medium with a
shallow bed of spent  materials. Types of  drying units include  fluidized bed dryers,
vertical thin film dryers, and cone dryers.

Since inorganic ion exchange materials (such  as  zeolites) are generally resistant to
degradation  by radiation  or biological  actions,  they are  treated by the  use  of  direct
immobilization,  or  by   high  temperature  processes (such  as  vitrification).  The
immobilization  matrices  currently  used  include   vitrification,   cement,  bitumen
encapsulation, polymer encapsulation, and disposal in high-integrity containers.

Vitrification has been widely evaluated for the immobilization of highly-active waste,
such as waste from the reprocessing of spent nuclear fuel, and has been evaluated for the
treatment of ion exchange resins (Jantzen et al. 1995, Cicero-Herman et al.  1998). The
excellent leach resistance property of the  resulting glass waste  form is the  principal
advantage of vitrification. Vitrification processes are capital-intensive, and the melters
have a relatively short operational  life (approximately 5 years). Vitrification processes
operate at  temperatures ranging from  1100°C to 3000°C,  depending on the  waste
composition and glass forming additives used.

Cement immobilizing radioactive  waste has been used in the  nuclear industry and at
nuclear research centers for more than 40 years. Detailed descriptions of the process can
be found in  references from the IAEA in 1993 and the Los Alamos National Laboratory
in 1997.  Cement has many characteristics in its favor: it is readily available and widely
used in civil engineering, the raw material is inexpensive, and the processing equipment
can be based  on conventional technology.  The  resulting  waste forms are strong;
noncombustible  and radiation  resistant,  have  a  high density (providing  radiation
shielding), have a reasonable chemical stability, and have a moderate resistance to the
release of radionuclides. The high pH conditions typical for cement results  in a low
solubility for many radionuclides  by the formation of hydrolyzed species,  carbonates,
etc.,  which  provides a good resistance to leaching.  The  main disadvantage  of the
cementation of spent ion exchange materials is that  the final  waste volume is high
compared with the initial volume,  owing to the low waste loadings that are  achievable.
The loadings can be increased  by a pretreatment (such as grinding) of the spent ion
exchange materials before cementation, which improves the quality of the final cemented
products.

Bitumen is  a generic term  used to cover a  wide range  of high molecular weight
Hydrocarbons. Bitumen  encapsulation is  currently not used in the United  States for

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disposal, although several bitumen varieties are commercially available overseas for the
immobilization of radioactive  waste,  including spent ion exchange resins. The main
characteristics that make bitumen suitable as a matrix material are:

    •   Its insolubility in water;
    •   Its high resistance to the diffusion of water;
    •   Its chemical inertness;
    •   Its plasticity and good rheological properties;
    •   Its good aging characteristics;
    •   Its high incorporation capacity, which leads to high volume reduction factors; and
    •   Its instant availability at a reasonable cost.

However, since it is an organic material, bitumen has the following disadvantages:

    •   It decreases in viscosity as a function of temperature, leading to a softening of the
       matrix, which melts at temperatures of about 70°C;
    •   It is combustible, although not easily flammable (the flash point and flammability
       temperatures  are higher than 290°C to 350°C, depending on the type  of bitumen);
    •   It has a lower stability against radiation than cement, especially under the higher
       radiation fields often associated with spent ion exchange media; and
    •   It reacts with  oxidizing materials such as sodium nitrate.

The immobilization  of spent ion exchange resins  in  polymers is  practiced  at many
installations worldwide. Different types of polymers are  used and further studies to
improve cost effectiveness, process simplicity, and product quality are being carried out
in many  countries.  Among the many polymers  used are  epoxy  resins, polyesters,
polyethylene,  polystyrene and copolymers, urea formaldehyde,  polyurethane, phenol-
formaldehyde, and polystyrene.

2.5.6  Summary of Environmental Potential

Zeolites are a well-established technology with a variety of industrial uses  ranging from
construction materials and detergent builders, to catalysts and  separation agents.  They are
one of the oldest separation technologies for the removal of radioactive components from
aqueous waste streams. The  flexible  tectonic structure and ability to be chemically
"tailored" to specific target species continues to stimulate their development. In addition
to their use as an "end-of-pipe" treatment for aqueous streams, zeolites are one of the few
materials  offering  the  possibility  of being an  inexpensive  amendment  to  soils
contaminated  with radioactive  species, since extremely high species  selectivity and
binding strength can  be designed into the material. Continued investigation  of zeolites in
general is expected due to their catalytic properties; research  in this area should support
further developments, potentially leading to environmental applications.

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2.5.7  References

Ahn, T.M., R. Dayal, RJ. Wilke. 1981. Evaluation of backfill as a barrier to radionuclide
migration in a high level waste repository. Technical Report BNL-NUREG-30107;
CONF-810499-2, Brookhaven National Laboratory. Website. Accessed November 2007.
http://www.osti.gov/energycitations/product.biblio.jsp?osti_id=5158859.

Allen, E. R. and D. W. Ming. 1995. Recent Progress in the Use of Natural Zeolites in
Agronomy and Horticulture. Natural Zeolites '93, Occurrence, Properties, Use; D. W.
Ming and F. A. Mumpton, (Eds.); International Committee on Natural Zeolites.
Brockport, New York.

Auerback, S.M., K.M.  Carrado, P.K. Dutta. 2003. Handbook of Zeolite Science and
Technology. Marcel  Dekker, Inc., New York.

Baerlocher Ch. and L.B. McCusker.  1996. Database of Zeolite Structures. Website.
Accessed November 2007. http://www.iza-structure.org/databases/.

Bish, D.L. 1999. Natural Zeolites and Nuclear Waste Management; The Case of Yucca
Mountain, Nevada, USA. In Natural Microporous Materials in Environmental
Applications. P.Misaelides, F. Macasek, TJ. Pinnavaia, and C. Colella (Eds.). Kluwer
Academic Publishers, The Netherlands.

Brandt, H.L. 1970. B-plant recovery of cesium from Purex supernatant. Report ARH-
1639. United States Atomic Energy Commission, Hanford, Washington.

BRZ Zeolite. 2007. Website. Accessed October 2007.
http://www.zeolite.ca/agriculture.htm

Buckingham, J. S. 1970. Laboratory evaluation of zeolite material for removing
radioactive cesium from alkaline waste solutions. Report ARH-SA-49. United States
Atomic Energy Commission, Hanford, Washington.

Campbell, L.S., and B.E. Davies. 1997'. Plant andSoil. 189(l):65-74.

Chen, N.Y., T.F. Degnan, C.M. Smith. 1994. Molecular Transport and Reaction in
Zeolites: Design and Application of Shape Selective Catalysis. Wiley, VCH, Hoboken,
NJ.

Choppin, G.R. and M.K. Khankhasayev.  1999. Chemical Separation Technologies and
Related Methods of Nuclear Waste Management: Applications, Problems, and Research
Needs (NATO Science Partnership Sub-Series: 2). Springer, New York.

Cicero-Herman, C.A., P. Workman., K. Poole, D. Erich, J. Harden. 1998. Commercial
Ion Exchange Resin  Vitrification in Borosilicate Glass. Westinghouse Savannah River
Co., Aiken, SC.

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Coleila, C. 1999. Environmental Applications of Natural Zeolitic Materials Based on
Their Ion Exchange Properties. In Natural Microporous Materials in Environmental
Applications. P.Misaelides, F. Macasek, TJ. Pinnavaia, and C. Colella (Eds.). Kluwer
Academic Publishers, The Netherlands.

Faust, S.D. 1998. Chemistry of Water Treatment. ISBN-10: 1575040115; ISBN-13: 978-
1575040110.

Hofstetter, K. J. and Hitz, C. G. 1983. The use of the submerged demineralizer system.
Separation Science Technology. 18:1747-1764.

International Atomic Energy Agency (IAEA). 1967. Operation and Control of Ion
Exchange Processes for Treatment of Radioactive Wastes, Technical Reports Series No.
78.

International Atomic Energy Agency (IAEA). 1972. Use of local minerals in the
treatment of radioactive wastes: Technical Report Series 136.

International Atomic Energy Agency (IAEA). 1984. Treatment of Spent Ion-exchange
Resins for Storage and Disposal, Technical Reports Series No. 254.

International Atomic Energy Agency (IAEA). 2002. Application of Ion Exchange
Processes for the Treatment of Radioactive Waste and Management of Spent
Ion Exchangers, Technical Reports Series No. 408.

InterSun. 2007. Zeolite Applications. Website. Accessed October 2007.
http://www.siberg.com/zeolite.htm.

Jantzen, C.M., D.K. Peeler, C.A. Cicero. 1995. Vitrification of Ion-exchange (IEX)
Resins: Advantages and Technical Challenges. Westinghouse Savannah River Co.,
Aiken, SC.

Kanellopoulos, N.K. (ed.). 2000. Recent Advances in Gas Separation by Microporous
Ceramic Membranes. Elsiever, New York.
Kawamura, S. 2000. Integrated Design and Operation of Water Treatment Facilities.
Wiley, Hoboken, NJ.

Kerry, F. G. 2007. Industrial Gas Handbook: Gas Separation and Purification. CRC
Press, Boca Raton, FL.

Komarneni, S. 1985. Philipsite In Cs Decontamination and Immobilization. Clays and
Clay Minerals. 33(2): 145-151.

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Los Alamos National Laboratory. 1997. Cement Waste-form Development for Ion-
exchange Resins at the Rocky Flats Plant. Rep. LA-13226.

Macasek, TJ. 1999. Sorption and Leaching Properties of the Composites and Complexes
of Natural Microporous Materials. In Natural Microporous Materials in Environmental
Applications. P. Misaelides, F. Macasek, TJ. Pinnavaia, and C. Colella (Eds.). Kluwer
Academic Publishers, The Netherlands.

MassNanoTech. 2007. University of Massachusetts Nanoscale Science and Engineering.
Website. Accessed October 2007.
http://www.umass.edu/massnanotech/faculty _auerbach.htm.

McKetta, JJ. 1999. Encyclopedia of Chemical Processing and Design: Volume 67 -
Water and Wastewater Treatment: Protective Coating Systems to Zeolite, 1st Edition.
CRC Press, Boca Raton, FL.

Mercer, B. W. and L.L. Ames. 1978. Zeolite ion exchange in radioactive and municipal
wastewater treatment. In Natural Zeolites: Occurrence, Properties, Use.  L. B.  Sand and
F. A. Mumpton (eds.). Pergamon Press, Elmsford, New York, 451-462.

Misaelides, P., F. Macasek, TJ. Pinnavaia, C. Colella (Eds.). 1999. Natural Microporous
Materials in Environmental Applications. Kluwer Academic Publishers, The Netherlands.

Nelson, J.  L. and Mercer, B. W. 1963. Ion exchange separation of cesium from alkaline
waste supernatant solutions. United  States Atomic Energy Commission, Hanford,
Washington.

Pasini, M. 1996. Natural zeolites as  cation exchangers for environmental protection.
Mineralium Deposita. 31(6):563-575.

Rajec, P., F. Macasek, P.Misaelides. 1999. Sorption of Heavy Metals and Radionuclides
on Zeolites and Clays. In Natural Microporous Materials in Environmental Applications.
P. Misaelides, F. Macasek, T J. Pinnavaia, and C. Colella (Eds.). Kluwer Academic
Publishers, The Netherlands.

St. Cloud.  2007. Zeolite. Website. Accessed October, 2007.
http://www.stcloudmining.com/agriculture.html.

Stead, K.,  S.K. Ouki, N.Ward. 2000. Natural Zeolites—Remediation technology for the
21st Century. Eurosoil 2000, British Society of Soil Science, University of Reading,
September 4-6, 2000.

United States Nuclear Regulatory Commission (USNRC).  1980. Draft Programmatic
environment impact statement related to decontamination and disposal of radioactive
wastes resulting from March 1979 accident. Three Mile Island Nuclear Station, Unit 2:
U.S. Nuclear Regulatory Commission Report NUREG- 0683, Washington, DC.

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Venuto, P.B. and M. Dekker. 1979. Fluid Catalytic Cracking with Zeolite Catalysts.
ISBN-10: 0824777824; ISBN-13: 978-0824777821. Washington, ReportHW-76449, p.3.

Weber, M. A., K. A. Barbarick, and D. G. Westfall.  1984. Application of clinoptilolite to
soil amended with sewage sludge. Zeo-Agriculture: Use of Natural Zeolites in
Agriculture and Aquaculture. W. F. Pond and F. A. Mumpton (Eds.) Westview Press,
Boulder, CO.

Yang, R.T.  1994. Gas Separation by Adsorption Processes. World Scientific Publishing
Company, Imperial College Press, Singapore.

Zeolite Australia PTY LTD. 2007. Website. Accessed October 2007.
http://www.zeolite.com.au/products/agriculture.html.

ZeoPro. 2007. Website. Accessed October 2007. http://www.zeoponix.com/zeolite.htm.

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2.6    Other Nanoparticles

Though iron nanoparticles presented in Section 2.2 are the most fully developed type of
nanoparticle for environmental  remediation, they  are not the only type of nanoparticle
that  has  been suggested for  environmental remediation. Some additional possibilities
include the use  of TiO2 nanoparticles as photocatalysts for the destruction  of organic
pollutants (Rajh et  al.  2003),  the   separation  of ionic solutes  using nanoparticle-
crosslinked polymer hydrogels (Thomas et al. 2003), or the use of coated magnetic
nanoparticles in high-gradient magnetic separations (Moeser et al. 2004). The subsections
below present  information  on three possibilities: nanodiamonds,  dendrimers,  and
Argonne Supergel.

Nanodiamonds are the subject of much research due to their potential in electronic and
bio-imaging applications, and because they can  be prepared directly, simply, and in
potentially large amounts.  They are apparently biologically benign, and their ease of
surface functionalization and magnetic properties  make  them a  potential  separation
platform.

Dendrimers are a new class of polymer with tailorable properties, both at the surface and
in the interior of the particle.  They have been of great interest in the area of separations,
and  are  potential complements to  separation processes involving  nanofiltration or
microfiltration.

Argonne Supergel is presented as a nano-enabled  technology developed specifically for
radionuclide  decontamination. These  three examples  (nanodiamonds, dendrimers, and
Supergel) are presented to provide a sense of the range of possibilities that nanoparticles
can offer for separation-based remediation.

2.6.1  Nanodiamonds

Nanodiamond is a term used for a group  of diamond-related materials with nanoscale
dimensions, including diamond films and diamond nanoparticles. These are prepared by a
variety  of methods,  including  high-pressure gas-phase nucleation  and application of
shock waves to graphite (Dolmatov 2001). Within this group  of diamond materials lies a
subgroup  called detonation  Nanodiamond (DND), or  ultrananocrystalline  diamond
(UNCD).  These materials  were discovered in Russia in 1963, and produced by the
detonation of oxygen deficient  explosives,  such as  a  3-to-2  mixture  of 2,4,6-
Trinitrotoluene  (TNT) and Hexahydro-Trinitro-Triazine (RDX).  Figure  13  shows  a
Transmission Electron Microscope (TEM) image of DNDs.

DNDs were unknown in the West until recently, and have attracted much interest (Petrov
et al. 2006,  Gruen et al.  2005) because  of their  unusually uniform shape  and  size
distribution and  the fact that they can be  produced in large quantities (Osawa 2003).
Before DND was widely known, Western industry produced microdiamonds by  applying
an externally produced Shockwave to heated graphite at high pressures. This produced a
polycrystalline material with a wide  size  distribution and very few particles  reaching

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down to the 10-20 nm size range. In contrast, DND has a fairly tight size distribution in
the 3-5 nm range, consisting of about 5,000 carbon atoms, and has a regular octahedral
shape (Figure 14).
                         Figure 13. TEM image of DND
  Figure 14. Model of nanodiamonds demonstrating their regular octahedral shape
Nanodiamond  production  from  a  detonation  produces  a  sooty  product that  is
approximately 50% DND. To obtain the nanodiamonds from this mixture, two challenges
must be overcome—the presence of graphitic impurities and the fact that the diamonds
tend to aggregate into clusters with average sizes of 30 |j,m, 3 |j,m, and 100-200 nm. The
aggregates can be broken up by a combination of ultrasound and high-speed zirconia
bead milling.

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Nanodiamonds possess interesting properties. Their surfaces have a tendency to change
from  the  regular diamond structure to a fullerene (buckyball) structure (Figure 15),
resulting in a  material that appears  to have a diamond within a fullerene cage and has
some of the physical properties of the nanodiamond combined with the rich chemistry of
the fullerene.
     Figure 15. Structure with nanodiamond center and fullerene-like surface

The potential for surface chemical functionalization opens up a wide range of possible
applications  for  derivatized  material.  Even  without  chemical  functionalization,
nanodiamonds have been suggested for a range of applications, including:

    •   Lapping and polishing applications
    •   All-rigid memory disk substrate
    •   Polycarbonate and CR-39 eyeglass lenses
    •   Miniature and precision ball bearings
    •   Optical and laser optical components
    •   Ceramics
    •   Precious stones
    •   Metallic mirrors and precision metal polishing
    •   Ferrite surface preparation
    •   Mechanical seal lapping
    •   Superhard and soft nanoabrasives

Other applications include:

    •   Surface germination for following growth of diamond-like films
    •   Ni-Diamond and Cr-Diamond electroplated hard coatings
    •   Molecular sieves
    •   Lubricant additive to engine oil
    •   Dry lubricants for metal industry (drawing of W-, Mo-, V-, Rh-wires)
    •   Reinforcing fillers for plastics and rubbers
    •   Chromatographic carriers

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A major area that is being investigated is the biomedical potential of nanodiamonds,
including their  roles  as drug  carriers,  implant coatings,  and  medical nanorobots.
Nanodiamonds are soluble in water, can be functionalized, and appear to be biologically
benign. Cytotoxicity research findings from the University of Dayton indicate that
nanodiamonds are biologically compatible materials across a range of sizes with regard to
a variety of cell types, with or without surface modifications (Schrand et al. 2007).

Nanodiamonds have also been suggested as sorbent materials (Dolmatov 2001, Gruen et
al. 2005), giving rise to the possibility  of environmental remediation applications. Their
observed magnetic properties (Talapatra 2005) also open the possibility  of their use in
magnetic separations. The radiation stability of the carbon also opens up the possibility as
a disposal waste form.

2.6.2  Dendrimers
A dendrimer is a highly and repetitively branched, three-dimensional polymer created by
a sequence of iterative chemical reactions starting from a central core. Each iteration is
known as a generation and  has twice the complexity of the prior generation. The term
comes from dendron (the Greek word for tree), with the analogy being the branch-like
structure of the dendrimer. Dendrimers have been  called the fourth major class of
polymeric architecture (after linear, cross-linked, and branched polymers), but unlike
other polymers where atom-by-atom control is not feasible and polydispersity (and the
variability  it brings) is an inherent  characteristic,  dendrimers  are characterized  by
monodispersity (i.e., all dendrimer molecules are of a uniform and controllable size) and
well-defined properties. Figure 16 provides a  graphical representation of a generalized
dendrimer structure.
                                      generation
                                      numbers
  branching
  points
termini
focal point'
(chemically addressable group)
                   DENDRIMER                             DENDRON

                   Figure 16. A generalized dendrimer structure

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Figure 16 allows some of the special chemical properties of dendrimers to be explained.
Starting at the core (GO) and moving through branching points Gl and G2, it can be seen
that as the dendrimer branches out in a predictable manner, large voids can exist within
the dendrimer internal structure. Both the size and the physical nature (e.g., hydrophobic
or hydrophilic characteristics)  of these  voids can be controlled  during  synthesis by
judicious  selection of both the  length and composition of the branch backbone. These
voids can be used to store material (metals,  organic and inorganic  molecules, and even
other nanoparticles), and together with the fact that dendrimers can easily move across
biological membranes,  the controllable nature  of the voids has  led to  suggested
applications of dendrimers as carriers of genetic material into cells (Kukowska-Latallo et
al. 1996), drug delivery agents (Lim and  Simanek 2005), and diagnostic imaging agents
(Tomalia  2003). The voids can also be used to hold material undergoing reactions and
has led to investigations of dendrimers as nanoreactors (Chung and Rhee 2003).

A second feature that is illustrated in Figure  16 is the surface formed by the terminal
groups.  As  the  number  of generations of the dendrimer increases, the total external
surface area rises dramatically. If the terminal groups are designed to be binding moieties
for other  species, then it is apparent that a dendrimer, compared to say a macroscopic
bead  of  ion exchange resin (which will have a  much smaller surface area than an
equivalent amount  of dendrimer),  can  potentially bind up  a  large amount of target
material.  It  is this  aspect of dendrimers that is  of prime  concern  for environmental
applications. Current expertise in dendrimer synthesis also allows for more than one type
of terminal  group to be attached  to the dendrimer,  thus  offering  the possibility of
multifunctional molecules. Terminal groups can be attached to modify solubility, modify
binding capacity and specificity, and to allow further reaction with or attachment to other
surfaces or  nanoparticles. It has been suggested that amphipathic  dendrimers could be
synthesized  with one half of the molecule (or one hemisphere)  covered in hydrophobic
groups, and  the other half containing hydrophilic groups.

Due to the degree of structural  control  that dendrimers make possible, and the fact that
their  highly customizable properties  should make them  building blocks  for  other
nanomaterials, they have been the subject of much research, with the number of academic
publications approaching ten thousand. Commercial development has been slower than
once anticipated because of their  high cost (on the order of  $10 per milligram) and the
complexity  of scaling-up production. Though these factors  are themselves subject of
much research, dendrimers already have a market or near-market presence:

    •   Dade Behring, one of the world's largest medical diagnostic firms, is developing a
       dendrimer-based, rapidly responding tool for detecting heart attacks and cardiac
       damage.
    •   The  U.S. Army  Research Laboratory is developing  a dendrimer-based anthrax
       detection agent.
    •   Starpharma is developing the world's first dendrimer-based drug, Vivagel, to fight
       sexually transmitted infections. It has been  awarded $20 million by the National
       Institutes of Health (NIH) to develop its HIV indication; given further awards to

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       develop its genital herpes indication; and was granted Fast Track status by the
       U.S. FDA in 2006 as a product for preventing HIV infection.

Dendrimers are currently under investigation as  metal sequestering agents for waste
remediation technologies (Cohen et al. 2001), and for the removal of uranium  from
aqueous streams  (Diallo  2007). In the latter work,  dendrimers may be compared with
chelating agents, which are widely used in uranium separation processes, such as solvent
extraction or ion exchange resins. Ion exchange resins with amino groups typically bind
on  the order  of 100  mg of  uranium per  gram of resin,  while the  work  with
poly(amidoamine) and poly(propyleneimime)  dendrimers, which contain nitrogen and
oxygen donors,  can bind up to  2500 mg of uranium  per gram of dendrimer without
reaching saturation in either acid or basic solutions. Further, the binding kinetics of the
dendrimers to uranium is very fast and reaches equilibrium in less than 20 minutes. Rapid
equilibration, high loading capacity, and selectivity mean that such dendrimers could thus
serve as high  capacity and  selective  chelating agents for uranium. The dendrimer-
uranium complexes could be easily separated by ultrafiltration and then regenerated, thus
avoiding the need to add further reagents and simplifying the overall process.

2.6.3  Argonne Supergel

Argonne National Laboratory (ANL) has  developed a system,  called the "Supergel"
technique,  to safely capture and  dispose of radioactive elements in porous structures
outdoors (such  as buildings and monuments), using a spray-on, super-absorbent gel and
engineered nanoparticles (ANL 2006). Porous structures are notoriously hard to clean. In
decommissioning and decontamination operations,  it is common practice to demolish
contaminated structures or completely remove a significant surface layer rather than
attempt to  remove radioactivity. ANL's Supergel  technique preserves surfaces, which
means that monuments or buildings would  not have to be defaced to remove radiation.
The Supergel was developed with funding from the Department of Homeland Security to
help fill a technology gap in preparedness for  a terrorist attack with a "dirty bomb" or
other  radioactive dispersal  device,  but   it   could  also  be  used  in  more  general
decontamination situations.

The Supergel technique uses commercially available equipment in a simple  procedure.
First, a wetting agent and a  super-absorbent gel are sprayed onto the  contaminated
surface. The polymer gel used to absorb  the  radioactivity is  similar to the absorbent
material found  in  disposable diapers.  When  exposed to water, the  polymers  form
something similar to a structural scaffold that allows the gel to absorb a large amount of
liquid. When sprayed on concrete, the wetting agent causes the bound radioactivity to re-
suspend in the concrete pores and the superabsorbent polymer gel then draws the liquid
out, along  with the  resuspended  radioactivity.  Inside the  gel, the radioactive  material
becomes fixed by engineered nanoparticles  that also reside in the gel. After a period of
standing, the gel is vacuumed and recycled, leaving behind a relatively small amount of
radioactive waste for disposal.

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2.6.4  Summary of Environmental Potential

These three technologies—nanodiamonds,  dendrimers, and Supergel—demonstrate the
broad potential of nanoparticles. Nanodiamonds, though relatively new, offer  a wide
range of potential applications and  can be  produced in bulk at reasonable  prices.
Dendrimers are a new class of polymer architecture that has caused much excitement due
to the potential of engineering properties at the molecular level into materials of uniform
and controllable size. The Argonne Supergel shows the ease with which nanoparticles
can be incorporated into other applications to address highly specific technology needs.

2.6.5  References

Argonne National Laboratory (ANL). 2006. 'Supergel' Systems Cleans Radioactively
Contaminated  Structures. Website. Accessed October 2007.
http://www.anl.gov/National  Securitv/docs/factsheet  Supergel.pdf.

Chung, Y.-M., and H.-K. Rhee. 2003. Pt-Pd Bimetallic Nanoparticles Encapsulated in
Dendrimer Nanoreactor. Catalysis Letters. 85(3-4): 159-164.

Cohen, S.M., S. Petoud, K.N. Raymond. 2001. Synthesis and Metal Binding Properties of
Salicylate-, Catecholate-, and Hydroxypyridinonate-Functionalized Dendrimers.
Chemistry.  7(1): 272-279.

Dolmatov, V.Y. 2001. Detonation synthesis ultradispersed diamonds: properties and
applications. Russian Chemical Reviews. 70: 607.

Diallo, M.S. 2007. Dendrimer Based Chelating Agents and Separation Systems for
U(VI): Fundamental Investigations and Applications to In situ Leach Mining.
Presentation at the Global Uranium Symposium, Corpus Christi, TX, May 2007.

Gruen, D.M., A.O.  Shenderova, A.Y. Vul (Eds.). 2005. Synthesis. Properties and
Applications of Ultrananocrystalline Diamond: Proceedings of the NATO Advanced
Research Workshop on Synthesis, Properties and Applications of Ultrananocrystalline
Diamond. St. Petersburg, Russia, 7-10 June 2004. Springer, New York.

Kukowska-Latallo, J.F., A.U. Bielinska, J. Johnson, R. Spindler, D.A. Tomalia, J.R.
Baker, Jr. 1996. Efficient transfer of genetic material into mammalian cells using
Starburst polyamidoamine dendrimers. National Academy of Science. 93(10): 4897-
4902.

Lim, J. and E.E. Simanek. 2005. Toward the Next-Generation Drug Delivery Vehicle:
Synthesis of a Dendrimer with Four Orthogonally Reactive Groups. Molecular
Pharmaceutics. 2 (4), 273 -277.

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Moeser, G.D., K.A. Roach, W.H. Green, T.A.Hatton, P.E. Laibinis. 2004. High-gradient
magnetic separation of coated magnetic nanoparticles. A.I.Ch/E. Journal. 50 (11): 2835-
2848.

Osawa, Eiji. 2003. Detonation Nanodiamond-Potential Material For FED. American
Physical Society, Annual APS March Meeting 2003, March 3-7, 2003.

Petrov, I, P. Detkov, J. Walch and O. Shenderova. 2006. Polydispersed Detonation
Nanodiamond and Approaches for its Fractioning. In Technical Proceedings of the 2006
NSTI Nanotechnology Conference and Trade Show, Volume 1. NSTI, Cambridge,
Massachusetts: 150-153.

Rajh, T., O. V. Makarova, M. C. Thurnauer, andD. Cropek. 2003. Surface Modification
of TiO2: a Route for Efficient Semiconductor Assisted Photocatalysis; Chapter 9 in
Synthesis, Functionalization and Surface Treatment of Nanoparticles. M.-I. Baraton
(Ed.), American Scientific Publishers, California: 147-171.

Schrand, A.M., H. Huang, C. Carlson, JJ. Schlager, E.O. Sawa, S.M. Hussain, L. Dai.
2007. Are Diamond Nanoparticles Cytotoxic? Journal of Physical Chemistry B. 111:2-7.

Thomas, P., B. Cipriano and S. Srinivasa Raghavan.  2003. Separation of Ionic Solutes
Using Nanoparticle-Crosslinked Polymer Hydrogels; Presentation at the American
Physical Society March Meeting, Denver,  CO, March 6.

Tomalia, D. 2003. Dendrimers as multi-purpose nanodevices for oncology drug delivery
and diagnostic imaging. Nanomedicine: Nanotechnology, Biology and Medicine. 2(4):
309.

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2.7    Uranium Reduction by Bacteria

Bioreductive immobilization  of uranium is a quasi  nanotechnology.  The precipitated
uranium and other minerals are in the form of nano size particles, whereas the bacteria
are about  1  |j,m. In this section, the process  is described, equations are provided, and
photographs presented showing the nanoscale uraninite particles.

The large  number of contaminated sites and volumes of contaminated  groundwater and
soil call for innovative and economically attractive remediation technologies. To date,
pump-and-treat is the most widely used technology. Frequently, pump-and-treat has been
ineffective in permanently lowering contaminant concentrations in groundwater (Travis
and Doty  1990). A recent study by Quinton et al. (Quinton et al.  1997) showed that
groundwater cleanup technologies (such as  pump and treat, permeable reactive barriers
with ZVI,  and bio-barriers) are more expensive than in-situ bioremediation.

Microorganisms can reduce uranium indirectly by producing hydrogen sulfide (H2S) or
pure hydrogen (H^) in the course of other processes (abiotic reduction) or directly using
enzymes (enzymatic reduction). The first microorganisms identified  to  enzymatically
reduce  U(VI)  were  the  dissimilatory Fe(III)-reducing  microorganisms,   Geobacter
metallireducens and Shewanellaputrefaciem (Lovley et al.  1991). These microorganisms
used uranium as an electron acceptor, H2  or acetate as an electron donor  to  support
growth, and tolerated U(VI) concentrations as high as 8 mM.  Several authors  studied the
enzymatic reduction of U(VI) by various pure  or mixed cultures of microorganisms,
including metal- and sulfate-reducing bacteria (a summary of previous work can be found
in Abdelouas et al. 1999a). These authors reviewed the literature on microbial reduction
of uranium and the significance of biogeochemical processes related  to uranium mining,
tailings, and groundwater remediation. In Figure 17, the  key reductive  and oxidative
reactions are shown for this process; in Figure 18, a bacterium is shown surrounded by
nanosize uraninite particles.

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           1/4O2(g) + H++e
     1/5NO3- + 6/5H++e
1/2 MnO2+1/2 HCCV + 3/2H+ + e
    1/2 UO2(CO3)22-
  FeOOH(s) + HCCV + 2 H++ e

      1/8SO42-+9/8H+ + e  -
    Oxidation of ethanol
      1/5C2H5OH + 1/4H2O
 ->  1/2 H2O
1/10N2(g) + 3/5H2O
      1/2 MnCO3(s) + H2O
  1/2 UO2(s) + HCO3-
     FeCO3(s) + 2 H2O
  1/8HS- + 1/2H2O
   1/6CO2 + H++e
            Figure 17. Reductive and oxidative reactions
                      Decreasing
                    redox intensity
                                  Bacterium
                                    r>-<
Figure 18. Microphotographs showing a bacterium surrounded with uraninite
                        nanoparticles

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The first demonstration of a feasible process for the in-situ immobilization of uranium as
a bioremediation strategy was conducted by a team of scientists from the University of
Massachusetts,  PNNL,  the  University  of Tennessee, and  several  other institutions
(Anderson 2003). The team conducted a two-month field study and demonstrated that by
adding acetate  to the subsurface, they could stimulate the growth and proportion of
Geobacter species  within the subsurface microbial community. At the same time, the
concentration of uranium in the ground water was greatly reduced.

The observation of bacteria able to immobilize uranium is an area of active study, both
from biochemical and nano-geological perspectives. Comparatively little is known about
either the bacteria or the processes they use; even  questions over the long-term  stability
of the immobilized  uranium have  yet  to achieve  a  comprehensive answer. Recent
research  at  Virginia Polytechnic  Institute  (Virginia  Tech  2006)  with  Shewanella
oneidensis MR-1 (one of the most common bacteria in the Earth) has shown that particle
size is important, with smaller nanoparticles of the iron (III) oxide hematitie showing a
lower rate of reduction than larger nanoparticles. Research on the  same bacterium at
PNNL (Marshall 2006) has demonstrated that much of Shewanella's biochemistry of
immobilization  occurs outside the cell, producing uniform, 5-nm particles of uraninite
trapped as strings of particles in a glue-like extracellular polymeric substance (Figure 19).
 Figure 19. Uraninite nanoparticles trapped in an extracellular polymeric substance
                              exuded by Shewanella

A current five-year, $15-million U.S. Department of Energy (DOE) project led by Oak
Ridge  National Laboratory  (ORNL)  (Edwards  2007) is trying to provide a further
understanding of the  coupled microbiological  and  geochemical processes  limiting
radionuclide bioremediation, and through an examination of terminal-electron accepting
processes involving geobacteraceae has shown that  due to the stress imposed by low pH
on microbial  metabolism, the terminal-electron  accepting processes of acidic subsurface
sediment  are inherently  different  from  those  of  neutral  pH  environments  and

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neutralization will be necessary to achieve sufficient metabolic rates for radionuclide
remediation.

In addition to direct bacterial processes for the reduction of uranium, indirect processes
may occur where bacteria or other microbes assist in the reduction processes by control
of the chemical environment. The dissimilatory iron reducing bacteria mentioned above
metabolically couple the oxidation of organic  compounds with the reduction of Fe (III)
generating energy and Fe(II) complexes, the latter of which in turn lead to the production
of a range of Fe(II) minerals such as magnetite, siderite, vivianite, ferruginous smectite,
and green rust.  In fact, the oxidation/reduction behavior of uranium, together with the
ability of micro-organisms to take advantage of such oxidation/reduction behavior, may
well play a significant role in the formation of uranium ore deposits (Dexter-Dyer 1984).
This behavior is being exploited in the concept of microbial mining of uranium, and may
be of importance to remediation. An example is "green rust", a class of iron (II)/iron (III)
hydroxide  compounds having  a pyroaurite-type  structure  consisting of  alternating
positively  charged hydroxide layers and hydrated anion layers. Green rusts are products
of both abiotic and microbially induced corrosion of iron, and occur in both microbially
mediated  and abiotic reductive dissolution of ferric oxyhydroxides.  Extended X-Ray
Absorption Fine Structure (EXAFS) studies have shown that uranyl ion can be reduced to
UO2 (U(IV)) by green rust (O'Loughlin 2003), with the uraninite forming nanoparticles
on the green rust crystal surface (Figure 20).
                                   Uraninite nanopartieles^l
                                                        f
                                                   .si?
                                                   - -*>
                                                  :\
                                                       • .-
                                                  •>""
                                             " - t', ,          50 nm
                                          w
               ireen Rust particle
                                                           A
            Figure 20. Uraninite nanoparticles on a green rust particle

The DOE has funded a project through its Environmental Management Science Program
(EMSP) to examine the processes underlying the potential use of dissimilatory  metal-
reducing bacteria (DMRB) to create subsurface redox barriers for immobilizing uranium

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and other redox-sensitive metal/radionuclide contaminants (Roden 2005). The results of
these studies suggest that:

   •   the efficiency of dissolved U(VI) scavenging may be influenced by the kinetics of
       enzymatic U(VI) reduction in systems with relative short fluid residence times;
   •   association of U(VI) with diverse surface sites in natural soils and sediments has
       the potential to limit the rate and extent of microbial U(VI) reduction, and in turn
       modulate the effectiveness of in-situ U(VI) bioremediation; and
   •   abiotic, ferrous iron (Fe(II))-driven U(VI) reduction is likely to be less efficient in
       natural soils and sediments  than would be inferred from  studies with  synthetic
       Fe(III) oxides.

A key implication of these findings is that production of Fe(II)-enriched sediments during
one-time (or  periodic) stimulation of DMRB activity is not likely to  permit  efficient,
long-term abiotic conversion of U(VI) to U(IV) in biogenic redox barriers designed to
prevent far-field subsurface U(VI) migration. Instead, ongoing DMRB  activity will be
required to achieve maximal U(VI) reduction efficiency.

The  study of dissimilatory metal reducing bacteria (DMRB, the general class  of which
dissimilatory  iron reducing  bacteria  are part)  has  recently  led to some interesting
nanoscience discoveries that  may offer new directions for nanotechnology. While most
biological oxidation-reduction reactions take place in the liquid phase using water soluble
species, dissimilatory reductions require a process where the electron acceptor is a solid
phase material. Understanding  the  details of this process has been the topic  of much
research,  with  the  focus  largely being  on  c-type  (monomeric) cyctochromes (heme
proteins  generally bound in cell membranes) which are  known to perform  electron
transport. In 2005, Derek Lovley, who discovered Geobacter in 1987, published research
showing that  conductive structures (known as pili or "microbial nanowires") only a  few
nanometers  wide  but microns  long, are  produced by  Geobacter,   are  electrically
conductive, and are indicated as being involved in electron transport  (Reguera 2005).
Subsequently, an international  group  (Gorby 2006) showed that other bacteria can be
induced to produce nanowires (as small as 10 nm in diameter, but can reach hundreds of
microns in length) when kept in an oxygen-starved state, are electrically conductive,  and
that this behavior is not limited to DMRB but might be a common bacterial strategy for
efficient electron transfer and energy  distribution. When in a community, the bacterial
nanowires can cross and touch,  and may allow for sharing of electrons among a network
of bacteria. Figure 21 illustrates the bacterial nanowire reaching  across organisms,  and
Figure 22 depicts a close-up image of a  nanowire.  The nanowires have been  of great
interest as a potential production and supply method of nanowires for other applications
(such as  sensors,  nano-electronic components), as the  basis of a possible  remedial
treatment approach, or as a component of microbial fuel cells.

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              Figure 21. Scanning electron microscope image of
                     Shewanetta ddeinensis strain MR-1
 Figure 22. Scanning Tunneling Microscope (STM) images of isolated nanowires
from wild-type MR-1, with lateral diameter of 100 nm and a topographic height of
between 5 and 10 nm. Arrows indicate the location of a nanowire and a step on the
                                 graphite

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In summary, the literature on microbially mediated reduction of U(VI) showed that U(VI)
can be reduced to U(IV) by enzymatic activity of microorganisms, including:

    •   metal- and sulfate-reducing bacteria;
    •   U(VI) can be reduced either by pure cultures or by mixed indigenous cultures;
    •   U(IV) precipitates as uraninite (UO2);
    •   complexation of  U(VI) with  organic  and  inorganic  ligands can  inhibit its
       reduction by microorganisms; and
    •   complexation of U(IV) may inhibit its precipitation.

Uranium reduction by bacteria is an example of bioremediation. As its advocates point
out, bioremediation may be regarded as the oldest environmental  technology  of  all,
having existed virtually as long as the human species. Prior to 1989, bioremediation as a
formal environmental technology was  not widely  known;  it had a small number of
advocates, though its claims were backed by considerable laboratory and academic work.
The March  1989 Exxon  Valdez  disaster  in  Alaska and  the subsequent  use of
bioremediation using naturally occurring marine organisms together with added nutrients,
opened the way for bioremediation to become an  established environmental remediation
option. Economically, bioremediation usually offers great overall cost savings compared
to competing technologies. In addition, risks tend to be smaller since contaminants  are
not transferred from one medium to another for  processing, and  there is  no waste
transportation involved. On the other hand, the bioremediation process may  take much
longer than chemical or physical treatment alternatives, requiring ongoing monitoring to
ensure that progress  is  being  made.  When geological  conditions  are  suitable and
sufficient time is available, bacterial reduction of uranium is likely to be an attractive
remedial alternative.

2.7.1  References

Abdelouas, A., W. Lutze, H. E. Nuttall. 1999a. Chapter 9: Uranium Contamination in the
Subsurface: Characterization and Remediation. In Uranium: Mineralogy, Geochemistry,
and Environment. P. C. Burns and R. Finch, (Eds.). Reviews in Mineralogy. 38: 433-473.

Anderson, R.T., H.A. Vrionis, I. Ortiz-Bernad, .T.  Resch, .E. Long, R. Dayvault, K.
Karp, S. Marutzky, D.R. Metzler, A. Peacock, D.C. White, M.Lowe, D.R. Lovley. 2003.
Stimulated in situ removal of U(VI) from groundwater of a uranium-contaminated
aquifer. Applied and Environmental Microbiology. 69(10): 5884-5891.

Dexter-Dyer, B., M. Kretzschmar, W.E. Krumbein.1894. Possible microbial pathways in
the formation of Precambrian ore deposits. Journal of the Geological Society. 141 (2):
251-262.

Edwards L., K. Kiisel, H. Drake, I.E. Kostka. 2007. Electron flow in acidic subsurface
sediments co-contaminated with nitrate and uranium. Geochimica et Cosmochimica Ada.
71(3): 643-654.

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Gorby, Y.A.,  S. Yanina, J.S. McLean, K.M. Rosso, D.Moyles, A. Dohnalkova, TJ.
Beveridge, IS. Chang, B.H. Kim, K.S. Kim, D.E. Culley, S.B. Reed, M.F. Romine, D.A.
Saffarini|, E.A. Hill, L. Shi, D.A. Elias, D.W. Kennedy, G. Pinchuk, K. Watanabe,  S.
Ishii, B. Logan, K.H. Nealson, J.K. Fredrickson. 2006. Electrically conductive bacterial
nanowires produced by Shewanella oneidensis strain MR-1 and other microorganisms.
Proceedings of the National Academy of Science.  103(30): 11358-63.

Lovley D.R., E.J.P. Phillips, Y. Gorby, E. Landa.  1991.  Microbial reduction of uranium.
Nature.  350: 413-416.

O'Loughlin, E.J., S.D. Kelly, R.E. Cook, R. Csencsits, K.M. Kemner. 2003. Reduction
of uranium(VI) by mixed iron(II)/iron(III) hydroxide (green rust): formation of UO2
Nanoparticles. Environmental Science and Technology. 37: 721-727.

Quinton, G. E., R. J. Buchanan, D.  E. Ellis, S. H. Shoemaker. 1997. A Method to
Compare Groundwater Cleanup Technologies. Remediation. 7-16.

Marshall, M.J., A.S. Beliaev, A.C. Dohnalkova, D.W. Kennedy, L. Shi, Z. Wang, M.I.
Boyanov, B. Lai, K.M. Kemner, J.S. McLean, S.B. Reed, D.E. Culley, V.L. Bailey, C.J.
Simonson, D.A. Saffarini, M.F. Romine, J.M. Zachara, J.K. Fredrickson. 2006. c-type
cytochrome-dependent formation of U(IV) nanoparticles by Shewanella oneidensis.
Biology. 4(8): 1324-1333.

Reguera, G., K.D. McCarthy, T. Mehta, J.S. Nicoll, M.T. Tuominen, D.R. Lovley.  2005.
Extracellular electron transfer via microbial nanowires. Nature. 435: 1098-1101.

Roden, E.E., and M.O. Barnett. 2002. Reductive immobilization of U(VI) in Fe(III)
oxide-reducing subsurface sediments: Analysis of coupled microbial-geochemical
processes in experimental reactive transport systems. Final Scientific/Technical Report—
EMSP 73914, U.S.  Department of Energy, Washington, DC.

Talapatra, S., P.G. Ganesan,  T. Kim, R. Vajtai, M.  Huang, M. Shima, G. Ramanath, D.
Srivastava, S.C.  Deevi  , P.M.  Ajayan.  2005. Irradiation-Induced Magnetism  in Carbon
Nanostructure^1. Physical Review Letters. 95:  097201.

Travis, C. C.  and C. B. Doty. 1990.  Can Contaminated Aquifers at  Superfund Sites be
Remediated?  Environmental Science Technology.  24: 1464-1466.

Virginia  Tech (2006, September  21). Particle  Size Matters To Bacteria  Ability To
Immobilize  Heavy  Metals.  ScienceDaily.  Website.   Accessed  December  2007.
http://www.sciencedaily.com/releases/2006/09/060915203321.htm.

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2.8    Carbon Nanotubes (Fullerenes)

2.8.1  Background

After long being  available only in research-level quantities, commercial-scale C-60
fullerene production at the "tons-per-year" level is now available. The price of larger
fullerenes  is  still  high  and  quantities available  are still  small. Commercial-scale
production at affordable prices is the target of intense research; over 1,500 patents have
been filed on various potential  production technologies.  No  radionuclide remediation
technology is currently available or apparently under  consideration, though the concept
has been discussed. Carbon nanotubes and fullerenes are of special interest  since they
have been subject of much research both as components in remediations systems (either
as part of nano-composite membranes or as functionalized separation platforms), and as
sensors (primarily through a field effect transition mechanism). They are also one of the
icons of the nanotechnology age.

2.8.2  Description

Fullerenes (first discovered in 1985 by Robert Curl, Harold Kroto, and Richard Smalley),
are a class of hollow, spherical, or ellipsoid  molecules—composed entirely of carbon
atoms—in a cage-like structure composed of pentagonal and hexagonal faces. They were
named  after  the  architect  Richard Buckminster Fuller due to their similarity to his
geodesic dome design, and are  often referred to as "buckyballs". Fullerenes were the
seventh allotropic form of carbon to be discovered  (together with the two forms of
diamond, the two forms of graphite, chaoit, and carbon (IV)). Their discovery led to Curl,
Kroto, and Smalley receiving the Nobel  Prize for Chemistry in 1996. Figure 23 provides
a graphical representation of the 60-carbon atom containing C-60  fullerene, and Figure
24  illustrates  a graphical  representation of  the  540-carbon atom containing C-540
fullerene.
                             Figure 23. C-60 fullerene

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                            Figure 24. C-540 fullerene

An infinite number of spherical fullerenes are believed to be able to exist. Known forms
include C-60,  C-70, C-76,  C-84, C-240,  and  C-540. All  fullerenes  consist  of 12
pentagonal faces and a varying number of hexagonal faces. In general, for a fullerene C-n
there will be 12 pentagonal faces and half of n  minus 10 (n/2-10) hexagonal faces; thus,
the C-60 fullerene has 12 pentagonal faces and 20 hexagonal faces.

Fullerenes have a rich and  complex chemistry (Stevens 1994, Kadish and Roff 2000,
Taylor 1995, Andreoni 2000, Hirsch et al. 2005) that led to the publication of over 15,000
academic papers within 15 years  of  their discovery.  C-60  behaves like an electron
deficient  alkene,  reacts  readily with electron  rich  species, and participates in many
reactions   (including  oxidations,  reductions,  nucleophilic   additions,  electrophilic
additions,  Diels-Alder reactions,  and  Friedel-Craft  alkylations).  This  rich chemistry
permits a wide range of fullerene functionalization and opens the  way to designing
functionalized fullerene for specific properties and purposes.

A large  number  of applications have been suggested  for basic fullerenes  and their
functionalized derivatives. Potential applications include organic photovoltaics, polymer
electronics, antioxidants, biopharmaceuticals, antibacterials, HIV inhibition,  catalysts,
water purification,  MRI agents,  optical devices,  scanning  tunneling  microscopy, and
atomic force microscopy (Nano-C 2006, Tang 2005, Da Ros et al. 2001).

Fullerenes have also been the subject  of many studies related to radioactive materials.
They are  being extensively  investigated as carrier species for medical radionuclides in
cancer therapy  (Saha et al. 2006, Dagani 2002, Braun 1999, Medical News Today 2005).
It has been observed that in the combustion of coal, which contains small  amounts of
uranium, nanocrystals of the mineral uranitite are encased in fullerene-type cages. This

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potentially provides an unanticipated pathway for radiation exposure (Utsunomiya et al.
2002). They have also been explored as a technology for radioactive waste management.
DOE has determined that there are three major isotopes contributing to public radiation
dose  as a  consequence  of  radionuclide releases—iodine-129,  technetium-99,  and
neptunium-237—and fullerenes have been investigated as a sorbent for iodine (Schmett
2002). It is  also worth noting that a structure closely  related to fullerenes, the carbon
nanohorn (Figure 25), has been suggested as a possibility for radioactive waste disposal.
                         Figure 25. The carbon nanohorn

Though a vast amount of research has already been performed on basic carbon fullerenes,
the real potential may lie in the fact that the work performed to date may only represent
the tip of the iceberg. Many structures related to  the  basic fullerenes and the carbon
nanohorn have been discovered. For example, the carbon nanocone (Figure 26) and
"NanoBuds" (Figure 27) are relatively new materials developed by the Finnish company
Canatu  Oy  (Canatu  2004,  Nanowerk 2007)  by combining  carbon nanotubes  and
fullerenes.  The  resulting nanobuds possess properties  of both  materials  (e.g., the
electrical conductivity of carbon nanotubes with the chemical flexibility of fullerenes).
Fullerene composites (Ltaief et al. 2006, Calleja et al. 1996, Barrera et al. 1994, Brabec et
al. 1998, Eklund and Rao 2000, Prassides 2004) and hybrid materials, such as a fullerene-
dendrimer-mesoporous silica hybrid (Nierengarten et al.  2004), have been described.

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                         Figure 26. The carbon nanocone
                                                          Energy, eV
£*,V  ft^^?
 c'"                       IP'
                                                              ^ -6.66

                                                              §| -6.76

                                                              fc -6.S6
                                                              C -7'06

                                                              fc -7.16

                                                              C, -7,26

                                                              t -7,36

                                                              fc -7.46

                                                              C -7.56

                                                              • -7.66
                           Figure 27. Carbon nanobuds

Further,  there  exists a  potentially  enormous  class  of "inorganic fullerenes".  First
described in 1992 (Materials  Science  Resource  2005),  over  50 different types of
inorganic fullerenes, and nanotubes have been  reported in the technical and scientific
literature, and  include molybdenum  sulfide, molybdenum  selenide, tungsten  sulfide,
tungsten selenide, transition-metal  chalcogenides, transition-metal oxides,  transition-
metal halides, in addition to mixed-phase, metal-doped, boron-based, silicon-based, and
pure metal nanotubes (Sano et al. 2003, Lvayen et al. 2007, Fu et al. 2005, Parilla et al.
2004, Xia et al.  2004, Remskar et al. 2001, Parilla et al. 1999, Halford 2005), and "onion-
like" fullerenes  consisting of cages nested within other cages like Russian dolls (Cabio'h
et al. 2005, Golberg et al. 1999).

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2.8.3  Operational Considerations

As  one of the longest known and  most intensely investigated type  of nanoparticle,
fullerenes have been the subject of much study in terms of fate and transport. However,
there  is little consensus, other than the need for more research  (Zepp and Westerhoff
2007, Wenger 2007, EIMS 2006, Handy and Owen 2006, Boxall 2007, Baalusha 2007,
SETAC 2007, Drobne 2007). Recently, the results on investigations into the role of C-60
nanoparticles  in  relation  to  toxicity  and  bioaccumulation of xenobiotic  organic
compounds in Daphnia magna were presented (Johansen et al. 2007). The hypothesis
was that  C-60 nanoparticles  may  act  as  carriers  of xenobiotic  organic chemicals
(nanovectors), but mixed results were observed and are detailed below.

    •   There was an increase in algal toxicity of atrazine with C-60 present; no changes
       in toxicity of methylparathion towards algae and daphnia.
    •   There was a decrease in the toxicity of pentachlorophenol (PCP)  towards algae
       and daphnia after addition to C-60 suspensions.
    •   There was an increase in the toxicity of phenanthrene towards algae and daphnia
       in C-60 suspensions since the sorbed phenanthrene is bioavailable.
    •   The uptake and excretion  rates  of phenanthrene and PCP were not significantly
       affected by addition to C-60 suspensions.

Also,  results  on investigations into the effects of C-60 fullerene nanoparticles  on soil
bacteria and protozoa (Johansen et al. 2007) showed that fullerenes seem  to have no, or
only moderate, effects  on the  soil microbial community (regarding the number and
viability of bacteria and protozoa). The genetic diversity of bacteria and protozoa seems
to be  altered  slightly, but the mechanism behind  the diversity changing effect is unclear
(possible  direct toxic  effects on some of the microorganisms  or  indirect effects by
sorption of nutrient  or inhibiting factors in the soil). The  conclusion was that  since
various fullerenes are very recalcitrant, and their production is expected  to increase to
very large quantities,  it is important that their fate and ecotoxicology  in complex
environmental matrices be evaluated thoroughly in regards to transport, degradation,
toxicology, and interactions with  xenobiotics, and that there is a need for standardized
methods  for  exposure  of nanomaterials to organisms in vitro and in more complex
systems.

2.8.4  Summary of Environmental Potential

Carbon nanotubes, and closely related  materials, such as  carbon  nanohorns and carbon
nanobuds, combine unique properties per se (such as greatly enhanced flow rates of water
through the inside of the tubes over what would be expected from current theories) with
the  broad potential  that results  from  a rich and  complex chemistry.  The  range of
applications is similarly wide, including both the development of advanced separately
processes  (such as nanofiltration and reverse osmosis) and  the  development of nano-
enabled sensors with  the carbon nanotube acting as the sensing  element. Carbon
nanotubes have already been investigated for application to DOE's three major problem
isotopes (iodine-129, technetium-99 and neptunium-237) contributing to public radiation

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dose. Carbon nanotubes are one of the longest known and most widely investigated type
of nanoparticle, with  research  including  hybrid  products formed  with other nano-
structured  materials  (such  as  dendrimers).  Given  the  extremely  broad  range  of
possibilities  and the  level  of  research  interest, the  likelihood  of  environmental
technologies resulting from carbon nanotubes is assessed as very high.

2.8.5  References

Andreoni, W. (Ed.). 2000. The Physics of Fullerene-Based and Fullerene-Related
Materials. Klewer Academic Publishers, The Netherlands.

Baalusha, M. 2007. The existing toxicity test with a terrestrial isopod Porcellio scaber is a
satisfactory starting point for assessing effects of nanoparticles. Presented at the SET AC
Europe Annual Meeting. May 18, 2007.
Accessed at http://se.setac.org/files/setac-eu-0121-2007.pdf.

Barrera, E.V., J.  Sims, D.L. Callahan, V. Provenzano, J.  Milliken, R.L. Holtz. 1994.
Processing of fullerene-reinforced composites. Journal of Materials Resources. 9(10):
2662-2669.

Boxall, Alistair. 2007. Current and predicted environmental exposure arising from
engineered nanomaterials. Presented at SET AC Europe Annual Meeting. June  15, 2007.
http://se.setac.org/files/setac-eu-0273-2007.pdf.

Brabec, C.J., V. Dyakonov, N.S.  Sariciftci, W. Graupner, G. Leising, J.C. Hummelen.
1998. Investigation of photoexcitations of conjugated polymer/fullerene composites
embedded in conventional polymers. Journal of Chemical Physics.  109(3):  1185-1195.

Cabio'h, T., J.P.  Riviere and J. Delafond. 2005. A new technique for fullerene onion
formation. Journal of Materials Science. 30(19):  4787-4792.

Calleja, F.J., L. Giri, T. Asano, Ti. Mieno, A. Sakurai, M. Ohnuma, and C.  Sawatari.
1996. Structure and mechanical properties of polyethylene-fullerene composites. Journal
of Materials Science. 31(19):5153-5157.

Canatu. 2007. Nanobuds. Website. Accessed October 2007.
http://www.canatu.com/nanobuds.html.

Da Ros, T., G. Spalluto, M. Prato. 2001. Biological Applications of Fullerene
Derivatives: A Brief Overview. Website. Accessed October 2007.
http://www.vnovak.hr/ccacaa/CCA-PDF/cca2001/v74-n4/cca 74 2001 743-755  Da-Ros.pdf.

Dagani, Ron. 2002. Exotic Fullerene: Synthesis of metallofullerene derivative brings
medical applications closer. Chemical and Engineering News. 80(4): 15. Website.
Accessed October 2007. http://pubs.acs.org/cen/topstory/8004/8004notw7.html.

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Drobne, Damjana. 2007. Toxicity of nanoparticles to embryos of the marine macroalgae
Fucus serratus. Presented at SET AC Europe Annual Meeting. June 15, 2007. Website.
Accessed October 2007. http://se.setac.org/files/setac-eu-0274-2007.pdf

EIMS Metadata Report. 2006. Fate and transport of carbon nanomaterials in
unsaturdayted and saturated soils. 2006 Progress Report. Website. Accessed at
http://oaspub.epa.gov/eims/eimsapi.dispdetail?deid= 143629.

Eklund, P.C. and A.M. Rao (Eds.). 2000. Fullerene Polymers and Fullerene Polymer
Composites. Springer, Berlin.

Fu, X., D. Wu, X. Zhou, H. Shi, Z. Hu. 2005. Solvothermal synthesis of molybdenum
disulfide hollow spheres modified by Cyanex 301 in water-ethanol medium. Journal of
Nanoparticle Research. 9(4): 675-681.

Golberg, D. Y. Bando, K. Kurashima, T. Sasaki. 1999. Fullerene and onion formation
under electron irradiation of boron-doped graphite. Carbon. 37(2): 293-299.

Halford, Bethany. 2005. Unusual properties of nanotubes made from inorganic materials
offer intriguing possibilities for applications. Chemical and Engineer ing News. 83(35):
30-33.

Handy, Richard, and Richard Owen. 2006. Environmental Effects of Nanoparticles and
Nanomaterials Conference. September 18, 2006. Website. Accessed November 2007.
http://www.setac-uk.org.uk/nano.pdf.

Hirsch, A., M. Brettreich, F. Wudl. 2005. Fullerenes: Chemistry and Reactions. Wiley-
VCH, Germany.

Johansen, A., A. Pedersen,  J.  Scott-Fordsmand, A. Winding. 2007. Effects of C60
fullerene nanoparticles on soil bacteria and protozoa. Presented at SETAC Europe
Annual Meeting. June 15, 2007. Website. Accessed November 2007.
http://se.setac.org/files/setac-eu-0275-2007.pdf.

Kadish, K.M., and R.S.  Roff (Eds.). 2000. Fullerenes: Chemistry. Physics, and
Technology. Wiley-Interscience, Hoboken, New Jersey.

Ltaief, A., A. Bouazizi, J. Davenas, P. Alcouffe, R. Ben Chaabane. 2006.  Dielectric
behaviour of polymer-fullerene composites for organic solar cells. Thin Solid Films. 511-
512:498-505.

Lvayen, V., E. Benavente, C.M. Sotomayor Tores, G. Gonzalez. 2007. Inorganic
Fullerenes: From lamellar Precursors to Functionalized Nanotubes. Sold State
Phenomena. 121-123: 1-4.

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Materials Science Resource. 2005. Reshef Tenne Named 2005 MRS Medalist for
Inorganic Fullerenes. Website. Accessed October 2007.
http://www.mrs.org/s_mrs/doc.asp?CID=2079&DID=166552

Medical News Today. 2005. Nanoparticle created as diagnostic, therapeutic agent;
brain tumors targeted. Oct. 19, 2005. Website. Accessed October 2007.
http://www.medicalnewstoday.com/articles/32245.php.

Nano-C. 2006. Fullerene Applications. Website. Accessed October 2007.
http://nano-c.com/fullereneapp.html.

Nanowerk. 2007. Novel carbon nanomaterial combines benefits of fullerenes and
nanotubes. Website. Accessed October 2007.
http ://www. nanowerk. com/spotlight/spotid= 1561. php.

Nierengarten, J., M. Guttierez-Nava, S. Zhang, P. Masson, L. Oswald, C. Bourgogne, Y.
Rio, G. Accorsi, N. Armaroli, S.  Setayesh. 2004. Fullerene-containing macromolecules
for materials science applications. Carbon. 42(5-6).

ParillaP.A., A. C. Dillon, K. M. Jones, G. Riker, D. L. Schulz, D. S. Ginley, M. J. Heben.
1999. The first true inorganic fullerenes? Nature. 397(114).

Parilla, P., A.C. Dillon, B. A. Parkinson, K.M. Jones, J. Alleman, G. Riker, D. S.  Ginley,
M. J. Heben. 2004. Formation of nanooctahedra in molybdenum disulfide and
molybdenum diselenide using pulsed laser vaporization. Journal of Physical Chemistry
B. 108(20): 6197-6207.

Prassides,  K. (2004). Fullerene-Based Materials. Springer, New York.

Remskar, M., A. Mrzel, Z. Skraba, A. Jesih, M. Ceh, J. Demlar, P. Stadelmann, F. Levy,
D. Mihailovic. 2001. Self-Assembly of Subnanometer-Diameter Single-Wall MoS2
Nanotubes. Science. 292(5516): 479-481.

Saha, S.K., D.P. Chowdhury, S.K. Das, R. Guin. 2006. Encapsulation of radioactive
isotopes into Ceo fullerene cage by recoil implantation technique. Nuclear Instruments
and Methods in Physics Research Section B: Beam Interactions with Materials and
Atoms. 243(2): 277-281.

Sano, N., H. Wang, M. Chhowalla, I. Alexandrou, G.A.J.  Amaratunga, M. Naito, T.
Kanki. 2003. Fabrication of inorganic molybdenumdisulfide fullerenes by arc in water.
Chemical Physics Letters. 368(3):331-337.

Schmett, G.T. 2002. Immobilization of fission iodine by reaction with fullerene
containing carbon compounds or insoluble natural organic matter. Dissertation. Website.
Accessed October 2007. http://aaa.nevada.edu/pdffiles/thesisschmett.pdf.

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SET AC. 2007. SET AC Europe 17th Annual Meeting Presentations. Website. Accessed
October 2007. http://se.setac.org/

Stevens, P.W. 1994. Physics and Chemistry of Fullerenes. World Scientific Publishing
Company, Singapore.

Tang, J. 2005. The Discovery and Applications of Fullerenes. Literature Seminar.
October 4, 2005, University of Alabama. Website. Accessed October 2007.
http://bama.ua.edu/~chem/seminars/student_seminars/fall05/papers-f05/tang-sem.pdf

Taylor, R. 1995. The Chemistry of Fullerenes. World Scientific Publishing Company,
Singapore.

Utsunomiya,  S., K.A. Jense, GJ. Keeler, R.C. Ewing. 2002. Uraninite and Fullerene in
Atmospheric  Particulates. Environmental Science & Technology. 36(23): 4943-4947.

Wenger, Y. 2007. Toxicity at the nanoscale level in trout hepatocytes exposed to
quantum dots- exploring a new realm of toxicity. Presented at SET AC Europe Annual
Meeting. May 9, 2007. Website. Accessed November 2007.
http://se.setac.org/files/setac-eu-0006-2007.pdf

Xia, J., Z. Xu, W. Chen,  Q. Me, G. Li. 2004. Preparation and characterization of
tungsten-substituted molybdenum disulfide nanorods. Chemistry Letters. 33(6): 766.

Zepp, R. and  P.  Westerhoff 2007. Nanotechnology Fate and Transport of Engineered
Nanomaterials. Sponsored by National Institutes for Health, National Institute of
Environmental Health Sciences, Superfund Basic Research Program. Presented August
16, 2007. Website. Accessed October 2007.
http://www.clu-in.org/conf/tio/nano6 081607/prez/nano6 08 16  07 modifiedpdf.pdf

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3.0  Nano-Enabled Sensor Technologies

3.1    Introduction

3.1.1  Basics

Nanosensors are chemical sensors possessing a nanoscale sensing element. A chemical
sensor is a device capable of providing quantitative or semi-quantitative information on a
chemical species  (or analyte) through calibration, and then brought into direct contact
with the species in its environment. According to the definition given by the International
Union of Pure and Applied Chemistry (IUPAC), a  chemical sensor is:

       "A device  that  transforms  chemical  information,  ranging from  the
       concentration of  a specific  sample component  to  total composition
       analysis,  into an  analytically useful signal. The chemical information,
       mentioned above, may originate from a chemical reaction of the analyte or
       from a physical property of the system investigated. Chemical  sensors
       contain two basic functional units:  a receptor and a transducer part.  Some
       sensors may  include a  separator which  is,  for example  a  membrane
       (IUPAC 1997)."

The receptor part of a sensor is defined by IUPAC  as:

       "The chemical information  is  transformed in  it into  a  form  of energy,
       which maybe measured by the transducer.  The  receptor part maybe  based
       upon various principles: physical,  chemical  or  biochemical  (IUPAC
       1997)."

The transducer part of a sensor is defined by IUPAC as a:

       "Device capable of transforming energy carrying the chemical information about
       the sample into a useful analytical signal (IUPAC 1997)."

In addition, a sensor may  include an output system, which processes the transducer
output into a useable form and relays it to the outside world. In contrast to a sensor, a
chemical analysis (or assay) method or system requires many more processing steps than
simply bringing a device into contact with the analyte,  and frequently involves the use of
additional reagents. It is important that the receptor and transducer parts of a sensor are
closely integrated. As an  example of a receptor and transducer combination, imagine a
very small, reed-like beam with a  reflective surface,  capable of vibration that can be
measured by a laser. In its basic state, the beam will vibrate with one frequency. If part of
the surface of the beam is covered with a ligand that will bind highly selectively with a
target analyte, then in the absence of the analyte,  it will vibrate with a second,  different
frequency; in the  presence of the analyte,  it will vibrate with  a third, yet again  different
frequency that is a function of the analyte concentration. In this scheme the ligand is the
receptor  and the  beam/laser system  is the  transducer;  the sensor operates by optical

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transduction  of a chemical binding  event. Receptor events may  be transduced by
electrical, electrochemical, piezoelectrical, optical, magnetic thermal, mass sensitive, or
other means.

3.1.2  Chemical Sensors

Chemical sensors are used in many settings, including:

    •  Medical and health care arena for clinical diagnosis, drug screening, etc.;
    •  Pharmaceutical development, biotechnology, microbiology, bacteriology,
       virology, genomics, and proteomics research;
    •  A vast range of industrial process control;
    •  Industrial effluent and pollution control;
    •  Safety;
    •  Environmental monitoring; and
    •  Defense and security (chemical and biological weapons, explosives, and narcotics
       detection).

The United States chemical  sensor market is valued at approximately $3 billion per year,
of which between one half and two thirds is for medical diagnostics, and much of the
remainder is for gas sensors.  The market is growing;  this is a result of past sensor
development research and, in turn, is contributing to current and future research for even
better sensors. The characteristics of an ideal chemical sensor include:

    •  Inexpensive—advantageous on its own merits and allows use of multiple
       detectors in arrays;
    •  Low operating costs;
    •  Robust;
    •  Reliable;
    •  Reversible;
    •  Continuously useable;
    •  High specificity;
    •  High selectivity;
    •  High sensitivity;
    •  High accuracy;
    •  Repeatability;
    •  Fast speed of response;
    •  Broad dynamic range;
    •  Insensitivity to (or ability to compensate for) interference by factors such as
       temperature, pH, ionic strength, electrical and magnetic fields, etc.;
    •  Small size for in-situ (biological or geological use); and
    •  Minimal perturbation of the  sample.

Nanotechnology offers the promise of providing nanosensors capable of achieving many
of  these  ideal  characteristics,  particularly  those  associated with  speed,  selectivity,

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sensitivity, and size reduction. As a consequence, nanosensor development is one of the
most active areas in the whole of nanotechnology. There are a number of major drivers
for this activity. The  first is miniaturization of sensors,  which has been a pronounced
trend in sensor development for the past 50 years. Some advantages of miniaturization
are obvious. Smaller size:

    •   leads to less material used in fabrication, enabling mass production contributing to
       lower cost and broadening market availability.
    •   leads to reductions in weight and power consumption, which dramatically
       increase the versatility and range of options for use, and
    •   permits reduction of sample size and decrease in any  reagent consumption.

3.1.3  The Trend towards Miniaturization

All of the preceding factors have  encouraged the trend towards microsensors over the
past decades,  but the move  to  the  nanoscale invites  factors beyond  the  simple
continuation of miniaturization.

    •   First,  the new properties that are realized at the nanoscale and that have been
       partly discussed in earlier sections can be used in either the receptor or transducer
       parts of the sensor.
    •   A  second nanoscale factor is that there are some inherent benefits  in working
       directly at the molecular level where the sensing phenomena take place.

A study that directly asked the  question of whether  smaller  is better for  sensors
(Kopelman and Dourado  1996) examined optical sensors  and formalized the specific
advantages of having nanoscale dimension sensors. In most  instances, there is an explicit
functional dependence of optode characteristics on the sensor radius (r), with the absolute
detection  limit decreasing with the  cube of the radius  (r3),  and the response time
decreasing with the square of the radius (r2). Other features that improve, as sensors get
smaller, include sample volume, sensitivity, invasiveness, spatial  resolution, dissipation
of heat in sensor  and/or sample,  and materials  cost.  A third nanoscale factor is that
fabrication advances  in  the semiconductor  and related industries, together with the
coming of control of fluids on the microscale,  has allowed the integration of many
laboratory  processing  steps  into a single  device, and given rise to the concept and
implementation of the LOG discussed in Section 3.2.

The development of the LOG is directly related to a second major driver of nanosensor
development—the analytical needs of the biotechnological and biomedical  industries.
Across many areas of biologically-related research, including the enormous areas of
pharmaceutical and proteomic research, there is a need for cellular-level and massive-
throughput analytical  and sensing  capabilities. The large-scale, low-cost manufacturing
potential for nanosensors,  and  the  greatly reduced reagent demands associated with
sample preparation in their use, make them extremely attractive tools. In the medical
field, early detection and diagnosis can greatly reduce the cost of patient care associated

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with advanced stages of many diseases. Similarly, point-of-care sample analysis and real-
time diagnosis can provide major savings for treatment of less serious conditions.

An additional issue, not so much a driver for sensor development, but rather an enabling
aspect in comparison with the development of remedial technologies, is the comparative
ease of  sensor  development.  Past experience,  particularly  in federal agencies with
environmental responsibilities (such as EPA, DOE, and Department of Defense (DoD)),
indicates that,  generally, the time to maturity for a sensor development project (i.e., the
duration  of the  entire  effort from  initial  idea, through  proof-of-concept, scientific
development, engineering development, prototyping,  demonstration, and deployment) is
considerably shorter and less complex than the time to maturity for a remedial technology
development project. Further, in terms  of market penetration,  or the transition from first
being commercially available to  being widely deployed, the timeline is shorter and the
regulatory hurdles are much lower. Since the risks  associated with sensors are  much
smaller than with remedial  technologies and the development costs are smaller, even
when allowance is made for the  shorter development time,  environmental sensors are a
much more attractive investment  than  remedial technologies. This situation  is likely to
apply to nanotechnologies, as well as to conventional technologies.

3.1.4  Opportunities

In  the environmental area (in  general)  and  the  remediation  of radionuclides  (in
particular), there is a marked need for sensors with:

    •   lower fixed and operating costs;
    •   better performance in terms of sensitivity and specificity; and
    •   more versatility in terms of portability and field operability.

Control  of remedial  processes,  contaminant detection, compliance monitoring, and
environmental decision-making should all benefit from sensors  with molecular level
detection and improved overall performance. Current methods are costly, time-intensive,
and limited (Sandia 2005).  The use of in-situ or field operable sensors eliminates risks
and costs associated with sample  collection,  handling, custody, transport, and storage.
DOE's Savannah River Site requires  manual collection of nearly 40,000 groundwater
samples per year, with a cost of between $100 and $1,000 per sample for off-site analysis
(Looney  and Falta 2000).

It is anticipated that nanotechnology will have a bigger impact in providing  sensors for
radionuclide remediation than it will in providing remedial technologies, due to:

    •   the well-structured basic understanding of sensor technology development;
    •   the shorter, less expensive timelines for sensor development; and
    •   the existing level of activity surrounding nanoscale sensor development.

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The number of development efforts for radionuclide sensors is still very small, but this is
because most efforts are being put into the medical and biotechnology areas, where there
is a much larger potential market. Given our level of understanding of how receptors are
integral to sensors and  our  level of understanding of how to design receptors for
radionuclide species, it is a small extrapolation from the current, biologically oriented
state-of-the-science to a future  state-of-the-science,  where radionuclide  sensors can be
easily  realized. The following  sections describe sensor  technologies,  or technology
concepts,  that can be comfortably extrapolated to radionuclides. As with  Section 2 on
remedial  technologies,   since   extrapolation  is  involved,  the  survey  cannot  be
comprehensive but rather seeks  to provide information  on reasonable possibilities  that
may yield sensor technologies in the near future.

3.1.5  References

IUPAC. 1997. Compendium of Analytical Nomenclature—Definitive Rules  1997, 3rd
Edition. Chapter 7, Section 4. Prepared for Publication by Janos Inczedy, Tamas Lengyel,
and Allan M. Ure (Eds.). International Union of Pure and  Applied Chemistry, Research
Triangle Park, North Carolina, USA. Website. Accessed November 2007.
http://www.iupac.org/publications/analytical_compendium/Cha07sec4.pdf

Kopelman, R.  and S. Dourado. 1996. Is smaller better? - Scaling of characteristics with
size of fiber-optic chemical and biochemical sensors. Proceedings in Society of Photo-
Optical Instrumentation Engineers (SPIE). 2836, 2-11.

Sandia. 2005. Micro-Chemical Sensors for In situ Monitoring and Characterization of
Volatile Contaminants. Website. Accessed December 2007.
http://www.sandia.gov/sensor/MainPage.htmtfDescription.

Looney, B.B. and R.W. Falta (eds.). 2000. Vadose Zone Science and Technology
Solutions. Battelle Press, Columbus Ohio.

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3.2    "Lab-on-a-Chip"

A Lab-on-a-Chip  (LOG)  device,  also  known  as  a  micro-total-analytical  system
(microTAS) or microfluidics device, is a device that can integrate miniaturized laboratory
functions  (such  as  separation and analysis  of components  of a  mixture)  on a single
microprocessor chip using extremely small fluid volumes on the  order of nanoliters to
picoliters. From a technology categorization perspective, LOCs can be viewed as a subset
of microelectromechanical systems (MEMS) and combine miniaturized or novel sensing
systems, fluid flow control  concepts from  microfluidics, and the suite  of fabrication
techniques (such as  material  deposition,  material  removal,  surface patterning, and
electrical property modification) used by the semiconductor industry.

Currently,  the  main  commercial  applications of  LOCs  are   in  the  medical  and
biotechnological fields, where it is anticipated that developments so far are the heralds of
a technological revolution. In the same way that miniaturization changed computers from
machines  of limited capabilities occupying large rooms to small and easily  portable yet
powerful technology of today, over a period of a few decades, medical, biotechnological,
and chemical analysis is expected to move from room-sized laboratories to microchip-
based devices housed in hand-held or small  portable readout consoles. Figure  28 shows
an example of an LOG device that was tested on the International Space Station in 2007.
      Figure 28: LOC device tested on the International Space Station in 2007

At the heart of LOC devices are "chips", ranging in size from a fingernail to a credit card,
fabricated using processes adapted from the printed circuit industry such as lithography,
chemical etching, and laser machining. Figure 29 illustrates an impression of the size of
the chip. Figure 30 provides a functional diagram of LOCs.

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                    Figure 29. A comparison of the size of LOCs
                      Sons or
                      Healer

              EC-Elution Cham be
                 R5- Waste
      R7- DEP Fluid Carrier

R6- PCR Reagents
                          PCR
         R1 Sample

         R2- Lysi» Buffer &
         Magnetic Scads

         R3- Washing Buffer
         R4- Resuspension Buffer
                                                             ieleclmphorelic
                                                            Sorting Electrode
                                                            Arrays
                    PCR Product Detectors

              Electromagnet
     LC- Lyais Chamber
R: Reservoir
P: Micropump
                      Figure 30. Functional diagram of LOCs
In a manner similar to the production of printed circuit boards using techniques such as
embossing and molding, microstructures (such as channels for liquid flow and pits for
mixing and reactions) are made on the chip by depositing layers of material on top of one
another on a surface, then patterning and selectively removing material to form a feature.
A flat top surface or lid is attached to enclose the channels or mixing pits, and reagents
can be driven around the system by pneumatic, electromotive, or capillary systems.

The LOG was first conceived by Michael Widner at Ciba-Geigy (now Novartis) in the
1980s, described conceptually in 1990 (Manz et al.  1990) with a groundbreaking work
being published in 1992 (Harrison et al. 1992). Further development occurred as a new
area of discovery—microfluidics—was developed  in the 1990s.  Microfluidics  is  an

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interdisciplinary field dealing with the behavior and control of extremely small volumes
of fluids and the design of systems that use these small volumes. Though most commonly
encountered in ink-jet printers, the vast majority of microfluidics applications have been
in biotechnology research, and some experts even regard it as a branch of biotechnology.
In some ways, Microfluidics parallels nanotechnology in that the behavior of fluids at the
microscale can differ substantially from the behavior at the macroscale; phenomena such
as surface tension, heat conduction, and fluidic resistance start to become important, and
issues such as evaporation, absence of turbulent flow, and the threat posed by presence of
air bubbles are critical to system design.

Initially, much of the impetus for continued development of LOCs came from the Human
Genome Project, a 13-year project coordinated by  DOE and the National Institutes of
Health (NIH) that began in 1990 and was completed  in 2003. Currently, much of the
impetus for the continued  development of LOCs comes from the  desire for point-of-care
medical diagnostics, whether in the doctor's office, on a spacecraft, or  other remote
location. Additionally,  development  research  is  driven by  the  continued need  for
miniaturization,  both to reduce  the  costs  and  the  environmental  impacts of research
(green analytical chemistry). The LOG concept, already significant, is still considered to
be  in its  infancy.  Development research continues  in many  areas. In the  area  of
fabrication materials, LOCs constructed  using soft lithography techniques, rather than
silicon microchip fabrication processes,  are being  investigated.  Soft lithography is  an
alternative  to  silicon-based micromachining that uses replica  molding of nontraditional
elastomeric materials to fabricate stamps and microfluidic channels. In an extension to the
soft lithography  approach, multilayer soft lithography, with which devices consisting of
multiple layers  may be fabricated from soft materials, is being used to build active
microfluidic systems containing on/off valves, switching valves, and pumps entirely  out
of elastomer.  The softness of these materials allows the device areas to be reduced by
more than  two  orders of magnitude compared  with silicon-based devices. The other
advantages of soft lithography  (such  as  rapid prototyping,  ease of fabrication, and
biocompatibility) are retained (Unger et al. 2000).

Environmental LOCs are also being investigated. An environmental LOG project is being
funded  by EPA with objectives  to create a  novel,  nanomaterial-based  submersible
microfluidic  device, exploiting unique  properties  of  metal  nanoparticles and carbon
nanotubes for rapidly, continuously, and economically monitoring different classes of
priority  pollutants.  The project also seeks to understand the  relationship between  the
physical and chemical properties of these  nanomaterials and their observed behavior. The
challenge addressed is to help transform the LOG concept to an effective environmental
monitoring system, and involves the examination of nanoparticle  and  nanotube materials
for the  separation and detection processes, respectively (Wang 2007). In addition,  the
NIH is  supporting the development of a point  detection disposable  LOG with built-in
mercury precursor electrodes for heavy metal detection (Ahn 2006).

Within these  development efforts, it is also  recognized that for novel and innovative
technologies, even those that have an established market presence, close communication
between developers and future users is essential. For example, in the United Kingdom,

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research  collaboration between  five leading universities in the healthcare  technology
assessment arena  and a  group of industrial partners—Multidisciplinary Assessment of
Technology Centre for Healthcare (MATCH) —is conducting a survey of LOG point-of-
care device manufacturers. Point-of-care in this context is defined  as "analytical testing
performed outside the central pathology laboratory using a device or devices that can be
easily transported to the vicinity of the patient" (MATCH 2006). The aim is to assess the
value of LOG for the diagnosis of cardiac-related problems using case studies, and to
develop methods to shorten the time and decrease the costs of LOG development.

3.2.1  Summary of Environmental Potential

The LOG  has  great potential for addressing  environmental needs.  The  technology
platform is mature and well-established, and as other nano-enabled sensing technologies
are developed, integration into the LOG should be facile.  The twin features of rapid
sample throughput and field portability should  make the LOG a valuable tool in filed
operations, particularly in circumstances such as the EPA Triad approach, where real-
time monitoring is required to guide the progress of remedial  work.

3.2.2  References

Ahn, C.H. 2006. A Point Detection Disposable Lab-on-a-Chip With Built-in Mercury
Precursor Electrodes For Heavy Metal Detection. Website. Accessed December 2007.
www.biomems.uc.edu/sponsors/_index.html.

Harrison, D.J., A. Manz,  Z. Fan, H. Liidi, H. M. Widmer.  1992. Capillary Electrophoresis
and Sample Injection Systems Integrated on a Planar Glass Chip. Analytical Chemistry.
64:1926-1932.

Manz, A., N. Graber, H.M. Widmer. 1990. Miniaturized total chemical analysis systems:
A novel concept for chemical sensing. Sensors and Actuators B: Chemical. 1(1-6): 244-
248.

Multidisciplinary Assessment of Technology Centre for Healthcare (MATCH). 2006.
Industrial Survey on Cardiac Point-of-care. Website. Accessed December 2007.
http://www.match.ac.uk/POCT industrial survev/index.jsp.

Unger, M.A, H.-P. Chou, T. Thorsen, A. Scherer, S.R. Quake. 2000. Monolithic
Microfabricated Valves and Pumps by Multilayer Soft Lithography.  Science. 288(5463):
113-116.

Wang, J. 2007. Nanomaterial-Based Microchip Assays for Continuous Environmental
Monitoring. Grant number RD - 83090002-0. US E.P.A, Washington D.C.
http://vosemite.epa.gov/oarm/igms egfnsf/fca67bald90470b585256fb6006df291/0a3daa
8868al9a7c85256f90002109b9!OpenDocumentwww.nibib.nih.gov/.../1112April2006%
20POCT/FINAL%20book%20for%20NIBIB after.pdf

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3.3    Microcantilever Sensors

Microcantilever sensors are a technology which may develop into sensing systems for
radionuclides, or is at least an example showing the potential and emergence of a new
generation of highly sophisticated but flexible sensors.  From a mechanical engineering
perspective,  a cantilever is simply a beam supported at one end and capable  of defined
bending and vibrational behavior. A microcantilever is simply a very small cantilever, the
properties of which can be understood from basic engineering principles.

The microcantilever was first developed in 1986 (Binnig et al.  1986) for use  in Atomic
Force Microscopy (AFM),  the  premier tool for nanoscale imaging and measuring. In
AFM,  an extremely sharp microscale tip, (with a tip radius of a few  nanometers)
connected to the end of a microcantilever (up to 10 nm thick,  about 500 nm wide and
about 2,500  nm long, and fabricated from Si or SisN/t),  is positioned extremely close to
the surface  of a sample and the sample, is  then moved  beneath the tip. Interactions
between the  surface of the sample and the end of the tip  arising from atomic forces (such
as Van der Waals force, electrostatic force, magnetic force, or capillary force) attract or
repel the tip  (depending on mode of operation) and bend  the microcantilever. Reflecting a
laser beam  off the cantilever and monitoring the beam's deflection with photodiode
arrays measures the amount of bending. A graphical representation of the AFM sensing
components   is provided in Figure  31,  and  a Scanning  Electron Micrograph  of  a
microcantilever biosensor used for DNA detection is shown in Figure 32.

                   Sample Surface
                                                Cantilever & Tip
                                           PZT Scanner
          Figure 31. Principle of operation of the atomic force microscope

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         Mag= 1.63KX
                                  EHT = 13.00kV
                                  WD= 35mm
Signal A = MPSE  Date :27 Oct 2005
Photo No. = 2180  Time :22:28:07
  Figure 32. Scanning electron micrograph of fabricated microcantilever biosensor
                              used for DNA detection

The microcantilever is the simplest MEMS device. Early work  soon demonstrated the
versatility of the device in AFMs, with the microcantilever able to perform in air, liquid,
or vacuum  and  across  a range  of temperatures.  It  also  demonstrated the  extreme
sensitivity of the AFM to environmental effects and impurities, and the need to control
these in making accurate measurements. However, studies on overcoming these issues
also showed that the sensitivity of AFM to these environmental factors could be turned
around, allowing  the AFM  to be a  sensor for  these same  factors.  For  example,  a
microcantilever  fabricated from  silicon  and  coated  with  an  aluminum  surface for
reflection of the laser beam  can act as a "bimetallic strip" and respond to temperature
changes. If a thermal  event takes place  on  the cantilever surface,  the  silicon  and
aluminum expand to different extents and the cantilever bends, allowing the cantilever to
act as a calorimeter of near-ultimate sensitivity. Similarly, if the microcantilever is given
an absorbent coating that can attract water and is allowed to vibrate in dry air, it will have
a  natural frequency of vibration; changes  in  humidity  change  the  mass of the
microcantilever, and thus  change the frequency  of  vibration, allowing it to act as  a
humidity sensor. From this, it is a short step to the  concept of coating the microcantilever
with a chemical functionality that binds selectively with a target  analyte. In the absence
of the analyte, the microcantilever vibrates with one frequency, while in the  presence of
the analyte, binding with the microcantilever coating occurs and vibration takes place at a
frequency directly related to the degree of analyte binding—hence concentration.
A related sensing mode is that the surface of the microcantilever can be coated with a
layer of material  that contains the chemical functionality able to bind selectively with a

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target analyte. If this layer expands or contracts as the analyte is bound, then bending of
the microcantilever occurs in a manner analogous to that of the bimetallic strip used for
thermal sensing. The degree of bending is directly related to analyte concentration. This
behavior was the basis of a microcantilever radionuclide  sensor development project at
ORNL. As described in  Section 2.3 on SAMMS, if a head group  at the end of a long
organic chain molecule  can interact strongly with a  substrate, then a  closely packed
molecular monolayer of  the chain molecules aligned with the chains pointing outwards
from the substrate surface can form spontaneously when the two are brought into contact.
The tail end of the organic chain can be functionalized prior to, or after, self-assembly
using chemical functionalities selective for a targeted  species. Thiol (S-H) head groups
and a  gold substrate  form an excellent pairing for this type  of behavior, and the self
assembly of alkanethiols  has been observed to produce surface stress in the gold substrate
(Bergeretal.  1997).

Silicon and closely-related materials have been the main materials of construction for
microcantilevers. Silicon has been recognized as an outstanding mechanical  material for
over a quarter of a century (Petersen 1982).  However,  silicon is not the only fabrication
material under investigation. Chemical sensing with micromolded plastic cantilevers and
production issues have been explored (McFarland and Colton 2005).

In  addition to  microcantilevers  based  on silicon,  plastics;  and  related  materials,
nanostructures (such as single-walled carbon nanotubes (SWCNT)) have been explored
for gas-sensing applications (Hsu 2007). The approach uses the fact that SWCNTs are
capable  of interacting  with the  gaseous  species—either directly  through  surface
adsorbtion, or indirectly by using a polymer analyte coated on its surface—and the higher
surface-to-bulk ratio available with a nanostructure leads to higher sensitivity and shorter
response time. As with other microcantilevers, the effect of bound or adsorbed species is
manifested either as a change in resonant frequency (which can be detected by using a
Wheatstone bridge circuit), or as an increased surface stress (which can be  detected by
measuring  the  change in the  capacitance value through comparison  with a specific
reference  capacitor).  Hsu's work  involved  successful  simulation,  fabrication,  and
manipulation of the SWCNT; development and simulation of a capacitive sensing circuit
layout; and consideration of  packaging and  integration issues,  including  use of  a
"nanoglue" developed at Rensselaer Polytechnic Institute, based on the processing of a
self-assembled  molecular monolayer and capability of bonding completely  dissimilar
materials.

Among the drivers for further development  was the widespread need for portable, real-
time,  in-situ  chemical, physical,  and radiological sensors in  a variety  of  applications
including  the  characterization  and  monitoring  of mixed waste,   ground  water,
contaminated soil, and process streams. Microcantilever-based sensors were recognized
as a potential solution for this need. They also provide  excellent sensitivity for important
metal  ions in  solution  such as Hg2+,  CrC>42",  Sr2+,  and  TcO4".  The ability  of  the
microcantilever  to  detect cesium (Thundat  et al.  1999, Ji et  al.  2000a) (though
irreversibility problems were observed) and chromate (Ji et al. 2000b) was demonstrated;

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concentrations below the parts per billion level were obtained with exceptional selectivity
even in the presence of other interferences.

Fundamental microcantilever research at ORNL showed that adsorption-induced changes
in the spring constant of a cantilever, leading to errors in the calculation of adsorbed mass
from  shifts in resonance  frequency  (Thundat  2002). Simultaneous  measurement of
resonance frequency and adsorption-induced bending was shown to allow the change in
spring constant to be determined. A silicon microcantilever with gold coating on one side
was found to respond  selectively and sensitively to Hg(II) ions in solution, and while
modification of the Si  surface with a  silane reagent did not change the response to Hg,
modification of the gold surface with octanethiol greatly retarded the rate of deflection,
indicating the Hg(II) is reacting with  the gold surface. The surface charge on the  gold-
solution interface is postulated to reduce Hg(II) to a surface  amalgam. Modification of
the gold surface with  a monolayer 1,6-hexanedithiol  makes the surface sensitive and
selective for (CH3)Hg+ adsorption-induced deflection.  Na+, K+, Pb2+, Zn2+, Cd2+,  Ca2+,
and Ni2+ in solution do not interfere with the response of the microcantilever to Hg. Gold
coated cantilevers with chemically modified surfaces respond sensitively to Ca2+ ions at a
concentration of 10"9 M. The sorption of a monolayer  of 2-(4-mercaptophenoxy)-N, N-
diethyl-acetamide, as well as the agent bis (11-mercaptoundecyl) phosphate were shown
to detect Ca2+ ions, although the former was more selective. A self-assembled monolayer
of L-cysteine on a cantilever  coated with gold on one side was shown to be effective for
the detection of a  concentration of 10"10 M  Cu2+. Both the Ca2+ and the Cu2+  were
relatively free from interference by  each other and Na+, K+, Pb2+,  Zn2+, Cd2+, and Ni2 in
solution (Thundat 2002).

Subsequent work showed that electrochemically-active metal ions (Cu, Cr, Hg and Pb)
could be detected by the novel approach of using a cantilever as  a working electrode
since  electrodeposition of electro-active metal ions  on cantilever surface results in
cantilever bending. Together with  the observation that  that the cantilever bending is
extremely  sensitive  to electrochemical  current  in the  solution, this has led to  the
development of a technique where the cantilever serves as  a reference/counter electrode
for electrochemical reactions occurring on another working electrode (Thundat  et al.
2006), with work continuing towards the development of field-deployable, miniature
sensors with extremely high  sensitivity, exceptional  selectivity,  and the ability to be
integrated into  a wireless communication  system that will allow real-time data to be
provided on concentration  and speciation of multiple  contaminants and  their variation
with time.

Work has also continued on microcantilevers functionalized with metal-binding moieties.
Gold-coated sides  of  silicon nitride  microcantilevers functionalized with the metal-
binding protein AgNt84-6  have been  demonstrated to be  sensors  for the detection of
heavy metal ions, such as Hg2+ and Zn2+ (Cherian et al.  2003). On exposure to HgCb and
ZnCb  solutions, the microcantilevers underwent bending corresponding to an expanding
gold side, while exposure to MnCb solution did not result in a similar bending, indicating
a  weak or lacking   interaction  of  Mn2+  ions  with  the  AgNt84-6  protein.   The
microcantilever bending data were consistent with data  from electrophoresis that showed

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protein  interaction with  Zn2+  ions  but  not  with  Mn2+  ions,  demonstrating that
microcantilever bending can be used to discriminate between metal ions that bind and do
not bind to AgNt84-6 protein in real time.

3.3.1 Summary of Environmental Potential

Microcantilever sensors are one  of the few nano-sensor technologies that have already
been investigated with the  detection of radioactive species in mind. The technology is
very flexible; all that  is needed for  detection of a species is a coating with a chemical
functionality capable of binding  the target species. The technology is well-established,
reliable, and sensitive—its origin in the  AFM  makes it a gateway technology for the
nanotechnology age—and is easily integrated into the LOG platform. The versatility of
the technique is further expanded by the  fact that many materials, including innovative
nanomaterials such as carbon nanotubes, may be  usable as the cantilever.

3.3.2 References

Berger, R., E. Delamarche, H.P. Lang, Ch. Gerber, J.K. Gimzewski, E. Meyer, H.-J.
Giintherodt. 1997. Surface stress in the self-assembly of alkanethiols on gold. Science.
276: 2021-2024.

Binnig, G., C.F. Quate, C. Gerber. 1986. Physics Review Letters. 56: 930-933.

Cherian, S., R. K. Gupta, B. C. Mullin and T. Thundat. 2003. Detection of heavy metal
ions using protein-functionalized  microcantilever sensors. Biosensors andBioelectronics.
19(15)411-416.

Hsu. J.C. 2007. Fabrication of Single Walled Carbon Nanotube (SW-CNT) Cantilevers
for Chemical Sensing. Thesis for Master of Science in Electrical Engineering (etd-
11082007-103811), Louisiana State University, May 2007.

Ji, H.-F., E. Finot, R. Dabestani, T. Thundat, G. M. Brown, P. F. Britt. 2000a. A Novel
Self-Assembled Monolayer (SAM) Coated Microcantilever for Low Level Cesium
Detection. Chemical Communications. 457-458.
Ji, H-F., T. G. Thundat, R. Dabestani, G. M. Brown, P. F. Britt, P. V. Bonnesen. 2000b.
Ultrasensitive I
73: 1572-1576.
Ultrasensitive Detection of CrC>42" Using a Microcantilever Sensor. Analytical Chemistry.
McFarland, A.W. and J.S. Colton. 2005. Chemical sensing with micromolded plastic
microcantilevers. Journal ofMicroelectromechanicalSystems. 14: 1375-85.

Petersen, K. E. 1982. Silicon as a mechanical material. Proceedings of IEEE. 70: 420-
457.

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Thundat, T., E. Finot, H-F. Ji, R. Dabestani, P. F. Britt, P. V. Bonnesen, G. M. Brown, R.
J. Warmack. 1999. Highly Selective Microcantilever Sensor for Cesium Ion Detection.
Proceedings of Electrochemical Society.  99(123)314-319.

Thundat, T.G. 2002. Microsensors for In situ Chemical, Physical, and Radiological
Characterization of Mixed Waste. EMSP-73 808-2002. U.S. DOE Environmental
Management Science Program Report, Washington DC.

Thundat, T.G., Z. Hu, G.M. Brown, B. Gu. 2006. Microcantilever Sensors for In situ
Subsurface Characterization. 2006 ERSD Annual Report. Oak Ridge National
Laboratory, Tennessee.

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3.4    Spectroscopic Sensors

Spectroscopy  is  the  scientific  study  of the  absorption,  emission,  or  scattering  of
electromagnetic  radiation by  atoms, molecules, ions,  solids,  liquids,  or gases.  The
underlying and  unifying  phenomenon  behind all  types  of spectroscopy is that  the
interaction of electromagnetic radiation with any type of matter can cause transitions
between quantized energy levels (often, though not  always, electronic energy levels) of
the atoms  or molecules.  Since so many of these transitions  can occur and can  be
influenced and modified by other phenomena,  spectroscopy  provides the potential for
enhanced  chemical analysis and sensing. The list of spectroscopic techniques and  sub-
techniques is large and continually increasing.  A partial sampling of these techniques
includes:
       Absorption spectroscopy
       Atomic absorption spectroscopy
       Atomic emission spectroscopy
       Atomic fluorescence spectroscopy
       Attenuated total reflectance spectroscopy
       Auger electron spectroscopy
       Cavity-ringdown laser absorption spectroscopy
       Electron paramagnetic spectroscopy
       Electron spectroscopy
       Electron spin resonance spectroscopy
       Extended x-ray absorption fine structure spectroscopy
       Fluorescence spectroscopy
       Fluorescence correlation spectroscopy
       Gamma-ray spectroscopy
       Image correlation spectroscopy
       Infrared spectroscopy
       Intracavity-absorption spectroscopy
       Laser spectroscopy
       Laser-induced fluorescence
       Mass spectrometry
       Mossbauer spectroscopy
       Nuclear magnetic resonance spectroscopy
       Multiplex or frequency-modulated spectroscopy
       Raman spectroscopy
       Resonance-ionization spectroscopy
       Tunable diode laser  absorption spectroscopy
       Surface-enhanced raman spectroscopy
       UV-vis absorption spectroscopy
       X-Ray  spectroscopy

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Phenomena based on nanoscale effects are being examined in and by many of these types
of spectroscopy. Some examples include:

   •   Nanosensors for nitric oxide using cytochromes have been examined and show a
       fast, reversible, and linear response up to 1 mM nitric oxide with a detection limit
       of 20 nM (Barker et al. 1998).
   •   A fluorescence nanosensor for Cu2+ ions using surface functionalization of silica
       particles with trialkoxysilane derivatized ligand and fluorescent dye has been
       investigated (Brasola et al. 2003).
   •   PEBBLE nanosensors, in the 20 to 200 nm size range, have been made for zinc
       detection using two fluorescent dyes (one sensitive to zinc and the other as a
       reference) localized in a polymer matrix by a microemulsion (Sumner et al.  2002).
   •   A simple colorimetric technique for the detection of small concentrations of lead,
       cadmium, and mercury) using reversible chelation/aggregation process for
       functionalized gold nanoparticles has been developed (Kim et al. 2001).
   •   A distributed Bragg reflector (a high-quality reflector used in waveguides and
       formed from multiple alternating layers of materials with varying refractive
       index) optical sensing element for organic solvents has been developed using
       stacks of Teflon®-like and gold nanoparticles. Absorption of organic vapors
       causes swelling of the composite and affects the reflectivity (Convertino et al.
       2004).
   •   The first nanometer-scale anion sensing fluorescent spherical nanosensors have
       been developed (Brasuel et al. 2003).
   •   A rapid  and sensitive fluorescence immunoassay has been developed for the
       simultaneous detection and identification of multiple harmful microorganisms
       using dye-doped silica nanoparticle-antibody conjugates (Zhao et al. 2004).
   •   The fabrication of submicron optical-fiber fluorescent sensors and particle-based
       fluorescent nanosensors has been reviewed, and the functional  characteristics of
       miniaturized fluorescent sensors and their applications for quantitative
       measurement of intracellular analytes have been discussed (Lu and Resenzweig
       2004).
   •   A nanoscale fluoroimmunoassay for the herbicide atrazine in an LOG has been
       developed using lanthanide oxide nanoparticle labels (Koivunen et al. 2004).

As these examinations indicate, most spectroscopic sensing methods detect the binding of
a target species to  a receptor by incorporating a fluorescent moiety into the receptor and
then examining the fluorescence behavior.  Fluorescence spectroscopy analyzes the
fluorescence  of  a  material,  where  fluorescence is  a non-thermally  originating
luminescence phenomenon in which a molecule or other species absorbs a photon at one
wavelength (usually in the visible range), and then re-emits another photon with a longer
wavelength (usually in the ultraviolet range), with the difference in energy between the
two photons becoming thermal energy through vibrational relaxation. Fluorescence can
now reach down to the single molecule detection level and is such a  powerful technique
that, over the past decade, it has become the dominant tool in biotechnology and medical
imaging (Geddes 2005).  The following two examples demonstrate nanotechnologies that

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incorporate  the  fluorescence  spectroscopy tool,  PEBBLE  and  Surface  Plasmon
Resonance.

3.4.1  Probe Encapsulated by Biologically Localized Embedding

A nanotechnology  that  incorporates  the fluorescence  tool  is  PEBBLE.  PEBBLE
nanosensors are  sub-micron  sized optical sensors designed  specifically  for minimally
invasive  analyte monitoring  in viable, single cells. PEBBLE is a general  term that
describes a family of matrices and nano-fabrication techniques used to miniaturize many
existing optode technologies. The main classes of PEBBLE nanosensors are based on
matrices of polyacrylamide hydrogel, sol gel silica, and cross-linked decyl methacrylate.
These matrices have been used to fabricate sensors for H4", Ca2+, K+, Na+, Mg2+, Zn2+, Cl",
NCV, O2, NO, and  glucose that range from 30 to 600 nm in size. A host of delivery
techniques have been used to successfully deliver PEBBLE nanosensors into mouse cells
(Monson et al. 2003, Park et al. 2003, Xu et al. 2001, Buck et al. 2004, Xu et al.  2002,
Clark et al. 1999, Sumner et  al. 2002). The PEBBLE nanosensor format offers the twin
benefits  of protecting  fluorescent  indicator dyes from interferents  and  allowing
combination of multiple dyes, ionophores, and other  components to create  complex
sensing schemes. It is  the multifunctionality that is the main advantage of PEBBLE
nanosensors for biological research. A conceptual representation is shown in Figure 33.
     Figure 33. Conceptual representation of the multifunctionality of PEBBLE
                                  nanosensors

PEBBLE nanosensors were specifically developed for biological work since they have
the advantages of a small size that permits intra-cellular biological measurements to be

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made without causing cell mortality; a polymeric matrix able to contain a combination of
indicator dyes, reference dyes, and catalysts (including some that might normally be toxic
to the cell); fast response time; and the option of being calibrated by either ex-vivo or ex-
vitro means.  The use of both  indicator dyes and reference dyes enables ratiometric
fluorescent detection, which can correct for variations in excitation source intensity and
minimizes the effects of photobleaching on quantitative measurements.

3.4.2  Surface P/asmon Resonance

While PEBBLE nanosensors offer a platform on which existing spectroscopic techniques
can be mounted, a spectroscopy that offers great potential for chemical sensing and has
achieved a much  deeper understanding as a result  of nanotechnology  (specifically
through the development of the new field of nanoparticle optics) is surface plasmon
resonance (SPR) spectroscopy.

Comprehension of SPR first requires an understanding  of the plasmon phenomenon. In
physics, photons are  regarded as the particle equivalent of quantized electromagnetic
waves. From solid-state physics, it is also commonly understood that the electrons in a
metallic crystal can be successfully modeled as a quasi-ideal gas, or plasma.. Oscillations
in the charge density of this quasi-ideal gas can occur, and when waves are quantized as
standing waves then the particle equivalent is known as a plasmon. Surface plasmons are
plasmons confined to the surface  of a material  or the interface  of  plasma-containing
material with some other material. They propagate parallel to the material surface and are
evanescent waves that decay exponentially with distance from that surface; they are thus
very sensitive to any  changes at the surface. Plasmons can be excited by coupling with
incident light to give the phenomenon of surface plasmon resonance.

Gold and silver are the classic metals for supporting surface plasmons,  but metals such as
copper, chromium, and  titanium also support the phenomenon. When surface plasmon
resonance is achieved on macroscale or mesoscale surfaces using very thin metal films,
the  plasmon wave can propagate across the surface  for a distance of tens or hundreds of
thousands of nanometers, but decays quickly as it moves outward from the surface. This
is known as propagating surface plasmon resonance. Surface plasmon resonance can also
be achieved on the nanoscale using metal nanoparticles, even though they are smaller
than the wavelength of the light involved. In this case the plasmon wave oscillates locally
around the nanoparticle. This manifestation of the phenomenon is called localized surface
plasmon resonance (LSPR). A comprehensive review of LSPR spectroscopy and sensing
is available (Willets and Van Duyne 2007).

The primary consequences of LSPR resonance include (1) localized electromagnetic field
enhancement that is  responsible for the intense  signals observed in surface-enhanced
spectroscopies,  and (2)  selective  photon absorption and scattering (collectively  called
extinction), which  can be easily monitored using UV-vis spectroscopy (Haes and Van
Duyne 2002). Regarding the extinction behavior, theoretical considerations of the optical
properties of nanoparticles (Haes et al. 2004) indicates that there are at least four different
nanoparticle-based sensing  mechanisms for transducing chemical-binding  events into

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optical signals: (1) resonant Rayleigh scattering from nanoparticle labels (analogous to
fluorescent  dye labels);  (2)  nanoparticle  aggregation  behavior;  (3)  charge-transfer
interactions at nanoparticle surfaces; and (4) local refractive index changes. The plasmon
resonance phenomenon thus provides a variety of approaches for measuring its behavior
that can be exploited in the development of sensors.

Changes to the surface have major effects on this  resonance. It  has been observed that
solutions of certain nanoparticles (e.g., gold) can give rise to intense colors; as far back as
the medieval period, artists working in stained glass used this effect (see Figure 34). The
origin of this effect, which  is not  manifested in the bulk material, is the absorption of
energy in the ultra-violet region of the spectrum as a result of surface plasmon resonance.
Changes to  the  surface of the gold  particles (e.g., the binding of DNA or other  bio
material) have noticeable  and  easily measurable effects  on  the frequency of the surface
plasmon resonance, and can be used as a sensing mechanism.
  Figure 34. The colors in medieval stained glass are the result of surface plasmon
                                    resonance

The most acclaimed use of LSPR spectroscopy using nanoparticles has been the detection
of a biomarker for Alzheimer's disease from synthetic and clinical samples (Haes and
Van Duyne 2004,  Haes et al. 2005). It has also been shown to detect small molecules,
such as camphor (Zhao et al. 2006b). Further, with the appropriate recognition moiety,
LSPR  should be  easily modifiable to detect  metals and radionuclides.  In fact,  the
feasibility of developing an SPR spectroscopy-based sensor, a  technique very closely
related,  for  a  radioactive  material  (pertechnetate)  has already  been demonstrated
(Anderson 2000). A previously  developed fiber optic SPR sensor used for gas phase dew
point determination  was  modified to liquid-phase  sensing  by placing a coating  of
polyethylene glycol  (PEG,  which has been used in aqueous  biphasic extraction for
removal  of pertechnetate from  Hanford and Oak Ridge tank waste) on  an  SPR system

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consisting of a sapphire hemisphere coated with a thin gold film.  The SPR sensor
generated high-resolution, low-noise SPR spectra suitable for high sensitivity sensing of
analyte  adsorption onto the sensor  surface,  and  was able to discriminate very small
changes in refractive index and show a unique response to 10 ppm perrhenate in NaOH
solution.

3.4.3 Summary of Environmental Potential

As a class,  spectroscopic techniques (such as PEBBLEs,  surface plasmon resonance, or
sensing  technologies based on nanobelts and nanorods) offer the possibility of detection
capabilities down to the single molecule level. Sensing technologies for characterization
and monitoring uses are of extreme importance  in the environmental field—both for
remediation  and  for process monitoring for  pollution  prevention  applications. The
flexibility that can be imparted to nano-enabled sensors means that a wide variety of
species can be detected at the lowest levels, and creates a potentially large opportunity for
these and similar technologies.

3.4.4 References

Anderson, B.B.  2000.  Feasibility Study for the Development of a  Surface Plasmon
Resonance spectroscopy-based Sensor for the BNFL-Hanford. BNF-003-98-0308. U.S.
Department of Energy Savannah River Site, Technical Report.

Barker,   S.L.R.,  R.  Kopelman, M.A. Cusanovich.  1998. Fiber-Optic Nitric  Oxide-
Selective Biosensors and Nanosensors. Analytical Chemistry. 70(5): 971-976.

Brasola  E., F. Mancin, E. Rampazzo, P. Tecilla, U.  Tonellato. 2003. A Fluorescence
Nanosensor for Cu2+ on Silica Particles. Chemical Communications. 24: 3026-3027.

Brasuel,  M.G., TJ.  Miller,  R. Kopelman, M.A. Philbert. 2003. Liquid Polymer Nano-
PEBBLEs for Cl- Analysis and Biological Applications. Analyst. 128(10): 1262-1267.

Buck, S.M., Y.E.  Koo, E.J Park, H. Xu, M.A. Philbert, M. Brasuel, R.  Kopelman. 2004.
Optochemical nanosensor PEBBLEs: photonic explorers for bioanalysis with biologically
localized embedding. Current Opinion Chemical Biology. 8(5):540-546.

Clark, H.A., R. Kopelman,  R. Tjalkens, M.A.  Philbert.   1999. Optical nanosensors for
chemical analysis inside single living cells. 2. Sensors for  pH and  calcium and the
intracellular application of PEBBLE sensors. Analytical Chemistry. 71(21): 4837-4843.

Convertino, A., A. Capobianchi, A.  Valentini,  E.N.M. Cirillo. 2004. High Reflectivity
Bragg Reflectors  Based on a Gold Nanoparticle/Teflon-Like Composite  Material as a
New Approach to the Organic Solvent Detection. Sensors and Actuators B: Chemical.
100(1-2): 212-215.

Geddes, C.D.  2005. Advanced Concepts in Fluorescence Sensing. Springer, New York.

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Haes, A. J.  and R.  P.  Van Duyne.  2002.  A Highly Sensitive and  Selective  Surface-
Enhanced Nanobiosensor. Materials Research  Society Symposium Proceedings. 723:
O3.1.1-O3.1.6.

Haes, AJ. and R. P. Van Duyne. 2004. A Unified View of Propagating and Localized
Surface Plasmon Resonance Biosensors. Analytical and Bioanalytical Chemistry. 379:
920-930.

Haes, A. J., L. Chang, W.L. Klein, R. P. Van Duyne. 2005. Detection of a biomarker for
Alzheimer's disease from synthetic and clinical  samples  using  a nanoscale optical
biosensor. Journal of the American Chemical Society. 127:2264-2271.

Kim,   Y.,   R.C.  Johnson,   J.T.   Hupp.  Gold  Nanoparticle-Based   Sensing  of
"Spectroscopically Silent" Heavy Metal Ions. Nano Letters. 1(4): 165-167.

Koivunen, M.E., M.E., SJ.  Gee, I.M.  Kennedy, B.D. Hammock.  2004. Nanoscale
Fluoroimmunoassays   with   Lanthanide   Oxide   Nanoparticles:    'Lab-on-a-Chip'.
Presentation (Abstract ANYL 194) at the 227th ACS National Meeting, Anaheim, CA.

Lu, J. and  Z.  Rosenzweig. 2000.  Nanoscale Fluorescent Sensors for Intracellular
Analysis. Journal of Analytical Chemistry. 366(6-7): 569-575.

Monson, E., M. Brasuel, M. Philbert, R. Kopelman. 2003. PEBBLE Nanosensors for in
vitro Bioanalysis. In Biomedical Photonics Handbook. T. Vo-Dinh (Ed.) CRC Press,
Boca Raton, Florida.

Park,  E.J., M. Brasuel, C. Behrend, M.A. Philbert, R. Kopelman.  2003. Ratiometric
optical PEBBLE nanosensors for real-time  magnesium  ion concentrations inside viable
cells. Analytical Chemistry. 75(15): 3784-91.

Sumner,  J.P., J.W.Aylott,  E.  Monson, R.  Kopelman.  2002. A  fluorescent  PEBBLE
nanosensor for intracellular free zinc. The Analyst. 127(1): 11-16.

Willets, K.A.  and R.P. Van Duyne.  2007. Localized Surface  Plasmon Resonance
Spectroscopy and Sensing. Annual Review of Physical Chemistry. 58:267-297.

Xu, H.,  J.W.  Aylott,  R. Kopelman,  TJ.  Miller, M.A.  Philbert. 2001. A  real-time
ratiometric method for the determination of molecular oxygen inside living cells using
sol-gel-based spherical optical nanosensors with applications to rat C6 glioma. Analytical
Chemistry. 73(17): 4124-4133.

Xu, H., J.W.Aylott, R. Kopelman. 2002. Fluorescent nano-PEBBLE sensors designed for
intracellular glucose imaging. The Analyst. 127(11): 1471-1477.

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Zhao, X., L.R. Billiard, SJ. Mechery, Y. Wang, S. Jin, W. Tan. 2004. A rapid bioassay
for single bacterial cell quantitation using bioconjugated nanoparticles.  Proceedings of
the National Academy of Sciences USA. 101(42): 15027-15032

Zhao, Y.-P., S.-H. Li, S.B. Chaney, S. Shanmukh, J.-G. Fan, R.A. Dluhy, W. Kisaalita.
2006.  Designing  Nanostructures  for  Sensor  Applications.  Journal of Electronic
Materials. 35(5): 846.

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3.5    Nanowire Sensors

3.5.1  Background

Nanowires are solid, rod-like materials with diameters in the 5-100 nm range, and are
most often made from metals or semiconducting metal oxides.  Nanowires are different
from molecular wires (also sometimes  referred to as "molecular nanowires"), which are
molecular entities with diameters typically less than 3 nm and repeating subunits. DNA is
the premier example of a  molecular nanowire, with the repeating  subunits being the
constituent nucleotides; inorganic examples include Li2Mo6Se6  and MoeSg-xIx. Research
on nanowires is often  conducted along with  parallel research on  carbon nanotubes.
Though these materials are different, the sensing mechanisms and underlying behavior
are usually very  similar. However, it should be noted that there are significant differences
in processing and scale-up potential; though similar devices may  be made from these
nanostructures, this does not mean that similar commercial products will eventually be
available.

3.5.2  Description

Nanowire sensors have attracted much attention for two reasons. First, their large surface
area to volume ratio promises high sensitivity. Second, the size of the nanostructures is
similar to the size of species being sensed, thus the  nanostructures make good candidate
transducers for producing the  signals that are then read  and recorded by conventional
instruments. The underlying phenomenon exploited in using nanowires is the field effect
on which field effect transistors (FETs)  are based. The wire acts  as the channel from
source to drain for  the FET. If functional groups attached to the nanowire  can act as a
receptor  to bind with a target species  (particularly a biological entity that possesses a
charge), then the charge on the surface  of the nanowire changes. Since this can influence
electronic behavior  into the depth of the nanowire, a gating effect occurs that can be used
in sensing. Figure 35 provides a representation of a nanowire configured as an FET.
                              Gate Layer
                            {e.g., p-Doped Si)
Nanowire
        Figure 35. Nanowire in a field effect transistor (FET) configuration

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Since they were  discovered, silicone nanowires have primarily been  investigated  for
sensing applications in biological systems (Cui et al. 2001). This is because the field
effects on a nanowire functionalized with receptors are considerably larger with charged
biological  species   than  with  ions.   Nanowires  have  been  viewed  as  one  of
nanotechnology's  most promising current products for biomedical research (Hood et al.
2004). Techniques  for generating  various  types  of important nanowires, nanorods,
nanobelts, and nanotubes, synthetic strategies, research activities unique properties (e.g.,
thermal,  mechanical, electronic,  optoelectronic, optical,  nonlinear optical, and field
emission), and methods for assembling nanostructures into functional devices have been
well reviewed (Xia et al. 2003). A comprehensive review of current research activities on
chemical sensors  based on nanotubes, nanorods, nanobelts, and nanowires, focusing on
experimental  principle, design of sensing devices, and sensing mechanism has recently
been published (Huang and Choi 2007). Other sensing  properties of silicon nanowires
have been explored, such as gas sensing, where it has been observed that upon exposure
to ammonia gas and water vapor, the electrical resistance of the HF-etched relative to
non-etched silicon nanowires sample is found to dramatically decrease—even at room
temperature (Zhou et al. 2003).

These  materials  have recently  sparked considerable interest in nanoelectronics, in
composite  nanomaterials,  and as conducting  polymer nanowire  sensors. Sensors and
actuators assembled with conductive polymers nanowires are claimed to have superior
responding  characteristics  to  their   conventional  counterparts  (Liu  et  al.  2004,
Ramanathan  et  al.  2004,  Alam et  al. 2005).  Conjugated  polymers  are organic
macromolecules which consist at least of one backbone  chain of alternating double and
single  bonds. This  electronic  structure allows a pi (TC)  orbital system, modifiable by
intermolecular interactions and other functionalization, to extend along the entire  length
of the  backbone,  bestowing  one-dimensional conductivity on the polymer. Sensors and
sensor  arrays  based  on conjugated   polymers  and  carbon  nanotubes  have  been
investigated. The four basic electrical transduction modes—conductometry (monitoring
the conductivity changes), potentiometric (monitoring the open circuit potential at zero
current), amperometry (monitoring  the change in current while the potential is kept
constant), and voltammetric  (monitoring the change in current while varying the applied
potential)—have already been investigated (Dai et al. 2002). Heavy metal-ion sensing for
drinking water analysis (Cu2+ and Ni2+ at parts per trillion range) have been demonstrated
using a conducting polymer nanojunction array. Each nanojunction is formed by bridging
a pair of nanoelectrodes  separated with a  small  gap with  electrodeposited,  peptide-
modified polyanilines and signal  transduction sensing mechanism using the change in
conductance due to  polymer conformational changes induced by the metal-ion chelating
peptide  (Aguilar   et   al.   2005).   Dielectrophoretically  assembled  poly   (3,4-
ethylenedioxythiophene)/ poly (styrenesulfonate) have been investigated as sensors  for
acetone, methanol, and ethanol (Dai et al. 2002).

Conducting polymer  nanowire sensors have  even been formed directly in place in
microfluidics devices (Wang et al. 2006). Such an approach has a number of advantages,
including:

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  4.
the monomeric precursor polymerizes directly on the electrode surface, producing
high-quality ohmic contacts;
addressability  is inherent to this method because nanowires can be grown across
individual electrode junctions;
the introduction and  delivery of  small  amounts  of precursor monomers and
analytes are highly controllable and enable the rapid exchange of nanoliter-level
solutions on the same;
the turbulence-free environment within a microchannel helps the  formation  of
well-defined conducting polymer  nanowires during the  electropolymerization
process; and
once the nanowires are grown, the entire device is ready for use, without the
necessity of any postfabrication processing. Figure 36 provides a representation of
an actual device.
                                             Working Electrodes
                                                      '
                                        OuifHit i1 Reference Elecuotle
                  (C)
Figure 36. Conducting polymer nanowire sensor formed directly in microfluidics
  device showing (a) actual view of fabricated device, (b) optical micrograph of
     microfluidics device and (c) schematic with polyaniline and polypyrrole

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Various types of nanowire have been studied for environmental applications other than
sensors.  For example,  natural nanowires  in  electricigens  (microorganisms able to
completely oxidize organic compounds to carbon dioxide with the sole electron acceptor
being an electrode) (Reguera et al. 2005, Reguera et al. 2006,  Reguera et al. 2007); ZVI,
iron-nickel,  and iron-palladium nanowires have been studied as  an  alternative to iron
nanoparticles  in  the  remediation  of  chlorinated  organics  (Yoo  et  al. 2007);  and
regenerable  gold nanowires have been studied as sensors for mercury (Keebaugh et al.
2007).

3.5.3  Summary of Environmental Potential

Sensors based on nanowires are at an early stage of development.  Their large surface
area-to-volume ratio promises high sensitivity. Functionalization of the nanowire will
allow a variety of species to be sensed.

3.5.4  References

Aguilar, A.D., E. S. Forzani, X. Li, N. Tao, L.A. Nagahara, I. Amlani, R. Tsui. 2005.
Chemical sensors using peptide-functionalized conducting polymer nanojunction arrays.
Applied Physics Letters. 87: 193108.

Cui, Y., Q. Wei, H. Park, and C. M. Lieber. 2001. Science. 293: 1289.

Dai, L., P. Soundarrajan, T. Kim. 2002. Sensors and sensor arrays based on conjugated
polymers and carbon nanotubes. Pure Applied Chemistry. 74(9): 1753-1772.

Hood, L., J.R. Heath, M.E. Phelps, B. Lin. 2004. Systems biology and new technologies
enable predictive and preventative medicine.  Science. 306: 640-643.

Huang, XJ.  and Y.-K. Choi. 2007. Chemical sensors based on  nanostructured materials.
Sensors and Actuators B: Chemical. 122 (2):  659-671.

Keebaugh, S., WJ. Nam, SJ. Fonash. 2007. Manufacturable, Highly Responsive
Nanowire Mercury Sensors. Presentation at Nanotech 2007 Conference, Santa Clara, CA,
May 21,20070

Liu, H.Q., J. Kameola, D.A Czaplewski, H.G. Craighead. 2004. Polymeric nanowire
chemical sensor. Nanotechnology Letters. 4: 671-675.

Reguera, G., K. D. McCarthy, T. Mehta, J. S. Nicoll, M. T. Tuominen, D. R. Lovley.
2005. Extracellular electron transfer via microbial nanowires. Nature. 435:1098-1101.

Reguera, G., K. P. Nevin, J. S. Nicoll, S. F. Covalla, T. L. Woodard, D. R. Lovley. 2006.
Biofilm and Nanowire Production Leads to Increased Current in Geobacter
sulfurreducens Fuel  Cells. Applied and Environmental Microbiology. 72(11): 7345-7348.

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Reguera, G., R.B. Pollina, IS. Nicoll, D.R. Lovley. 2007. Possible Nonconductive Role
of Geobacter sulfurreducens Pilus Nanowires in Biofilm Formation. Journal of
Bacteriology. 189: 2125-2127.

Wang, I, Y. L. Bunimovich, G. Sui, S. Savvas, Y. Guo, J. R. Heath, H.-R. Tseng. 2006.
Electrochemical Fabrication of Conducting Polymer Nanowires in an Integrated
Microfluidic System. Chemical Communications. 3075-3077.

Xia, Y., P. Yang, Y. Sun, Y. Wu, B. Mayers, B. Gates, Y. Yin, F. Kim, H. Yan. 2003.
One-dimensional nanostructures: Synthesis, characterization, and applications. Advanced
Materials. 15(5): 353-389.

Yoo, B.-Y., S.C. Hernandez, B. Koo, Y. Rheem, N.V. Myung. 2007. Electrochemically
fabricated zero-valent iron, iron-nickel, and iron-palladium nanowires for environmental
remediation applications. Water Science and Technology. 55:  149-156.

Zhou, X.T., J. Q. Hu, C. P.  Li, D. D. D. Ma, C. S. Lee, S. T. Lee. 2003. Silicon nanowires
as chemical sensors. Chemical Physics Letters. 369(1-2): 220-224.

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3.6    Nanobelts and Nanorods

3.6.1  Nanobelts

Nanobelts are a class of nanostructure often viewed as a type of nanowire, usually made
from semiconducting metal oxides (such as SnC>2, ZnO, In2O3 or CdO, or selenides such
as CdSe). Nanobelts form ribbon-like structures with widths of 30-300 nm, thicknesses of
10-30 nm, and lengths in the millimeter range. They are chemically-pure and structurally-
uniform  single crystals, possessing rectangular cross sections,  clean edges, and smooth
surfaces.
                            Figure 37. SnO2 nanobelts

Much research has been conducted on the use of nanobelts as gas sensors. Current gas
sensors typically use metal oxides (such as SnO2) as the sensing element, and operate by
measuring changes in electrical conductance of the surface as it undergoes reduction or
oxidation reactions with the gas. Though the exact mechanism is not fully understood,  it
appears that at high  temperatures in the absence of oxygen, free  electrons move easily
through the oxide and across the  boundaries  between crystal grains. When  oxygen  is
present, it is adsorbed on the oxide surfaces and at the grain boundaries, and (due to its
affinity for electrons) it removes free electrons from the underlying material, creating an
electron-depleted  region  and  a  potential barrier at the grain  boundaries.  This  is
manifested as an increase in resistance. In contrast, when a reducing gas is present, it too
is  adsorbed on the oxide surfaces  and at the grain boundaries, where it can react with
oxygen, and thus lower the oxygen-generated potential barrier. This is manifested as a
reduction in resistance, allowing the sensor to act as a variable resistor dependent on gas
concentration.

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By virtue of their unique geometry, nanobelts have enormous surface areas per unit mass
and most of the material is at the surface. When gases are adsorbed onto the nanobelt
surface, the electron depletion or accumulation behavior becomes pronounced (as is the
effect on the current flowing along the nanobelt) allowing them to act in a fashion similar
to FETs. Further, their small size makes for greatly reduced  power consumption  over
macroscale sensors. Research  (Fields et al. 2006, Comini et  al. 2002) has  shown this
behavior to be the basis for effective nanobelt gas sensors,  and  similar sensors have been
made for nerve gas detection (Yu et al.  2005), ethanol sensing (Wan et al. 2004, Xue et
al. 2005), and hydrogen sensing (Wang et al. 2005).

Nanobelts possess essentially similar properties to nanowires; they  can exhibit  FET
behavior and have functionalizable surfaces, thus making  sensor development strategies
for nanowires also available to nanobelts.

3.6.2  Nanorods

Nanorods are solid nanostructures morphologically similar to nanowires but with aspect
ratios of approximately 3-to-5. They are  formed from a variety of materials including
metals, semiconducting oxides, diamonds  (aggregated diamond nanorods produced from
fullerenes are the hardest material so far  discovered), and organic materials. Figure 38
provides an image of ZnO nanorods grown from aqueous solution.
               Figure 38. ZnO nanorods grown in aqueous solution

Nanorods are produced  by a number of techniques,  including: a vapor-liquid-solid
approach; mechanical alloying; direct chemical synthesis using ligands for shape control;

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plasma  arc discharge;  laser ablation; and  catalytic decomposition (Ayala-Sistos et al.
2005, He et al. 2002, Chopra et al.  1995,  Goldberg et al. 1996, Goldberg et al. 2002,
Hamilton et al. 1993). They are under considerable investigation for applications such as
gas  sensors;  video   displays;  computer components;  nanoelectronic  and   nano-
optoelectronic components; MEMS  devices; and solar energy conversion. One of the
factors in their investigation is that both the size and shape can be controlled by use of
additives during synthesis  so that  scaling—as well as  basic properties—can be studied
(Garcia and  Semancik 2007), and  flexibility  is available  for component integration
(Benkstein et  al. 2006). By functionalizing the nanorods, amphiphilic entities that can
self-assemble  and form convex curvature can be created—a capability of importance in
nanoelectronic and biomedical applications  (Park et al. 2004, Chen et al. 2007). Figure 39
provides a graphic representation of a potential structure.
     Figure 39. Self-assembly of gold-polymer nanorods into a curved structure

The particular morphology of nanorods also leads to properties that may have unusual,
niche applications. For example, the light emitted from or scattered off of gold nanorods
is  strongly  polarized along  the  rod length  axis, an  excellent property for an  ideal
orientation probe (Kou et al. 2006).

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Nanorods have recently  been  subject of  a newly  demonstrated  technique  for the
fabrication of nanostructures  (Zhao et al.  2006).  An  ideal nanostructure fabrication
method would have four desirable features: (1) the ability to control the size, aspect ratio,
and shape of the nanostructures; (2) the ability to grow the desired nanostructure at low
temperature and onto a particular substrate geometry (e.g., flat, cylindrical, or tapered);
(3) the  ability  to fabricate  metallic  and dielectric  nanostructures  with  multilayer
structures; and (4) the ability to seamlessly integrate the fabrication process with other
conventional microfabrication techniques. The following four general approaches  have
been employed to date:

   •   nanolithography-based methods which  use advanced lithographic techniques,
       such  as  electron  beam  lithography, x-ray  lithography, and  proximal probe
       lithography with deposition and plasma etching processes;
   •   solution-based approaches which use very complicated,  controlled wet chemical
       reactions to synthesize nanostructures and require a detailed understanding of the
       chemical reaction and crystal growth mechanisms;
   •   vapor-based methods, such as the vapor-liquid-solid method used since the 1960s,
       which usually  require higher  temperatures  and  a specific catalyst for  each
       structure; and
   •   template-based methods using host nanoporous materials as forms.

None of these fabrication methods are desirable features of an ideal method of fabricating
nanostructured substrates,  but Zhao et al.  have investigated  a novel nanostructure
fabrication technique in the production of nanorods called  glancing angle  deposition
(GLAD). GLAD is a physical vapor deposition technique in which the substrate is rotated
in the polar and azimuthal directions  by two stepper motors programmed by a computer.
The  experimental  results  have demonstrated that the  GLAD technique offers  several
strategic  advantages compared to  other nanofabrication techniques—most particularly
that the structures of the nanorods can be well  designed by  computer programming, a
feature that cannot be achieved by any other fabrication technique. Control  of this type,
by whatever method is important since a novel, tapered form of nanorod,  known as
"nanorice",  has been shown to  be the most sensitive  surface  plasmon  resonance
nanosensor yet devised (Wang et al. 2006, Srivastava and Lee 2006).

Exploratory work on the use of nanorods for sensors is well underway. A biosensor for
determination of heavy metals based on hydrothermally-grown ZnO nanorod/nanotube
and metal-binding peptides has been presented. The ZnO acts as  an FET and heavy metal
binding with a peptide causes an electrical  signal change,  which can be measured and
correlated to the concentration of heavy metals (Jia et al. 2007). A gold nanorod sensor
for mercury is able to determine mercury in tap water  samples at the parts-per-trillion
level  has  also been developed.  The selectivity  and  sensitivity result  from  the
amalgamation of mercury  and gold, and the entire sensing procedure takes  less than  10
minutes,  with no sample separation and/or sample pre-concentration requirements. The
only step prior to mercury  determination consists of mixing the water sample with a gold
nanorod solution in sodium borohydride. The limit of detection (6.6xlO"13 g.L"1) shows
excellent  potential for monitoring  ultra-low  levels  of  mercury  in  water  samples

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(Hernandez et al. 2007). In work on the control of homogeneity in shape, size, and the
organization of gold nanorods, the possibility of a copper sensor has been suggested. The
basis of the idea is the strong dependence of surface plasmon resonance peaks on the size
of gold nanorods, and the detection mechanism is based  on the color change due to
plasmon-plasmon interaction between adjacent gold nanorods. The gold nanorods were
successfully functionalized with glutathione, and the addition of Cu2+ ions considerably
improves the assembly, opening the possibility of making a copper sensor (Afshar 2007).

3.6.3  References

Afshar, R. 2007.  Gold nanorods: Synthesis and self assembly. Master Project Micro- and
Nanotechnology, University of Neuchatel, Switzerland, February 2007.

Ayala-Sistos, J., G. Rosas,  R. Esparza, R. Perez. 2005. BN Nanorod Production Using
Mechanical Alloying. Advances in Technology of Materials and Materials Processing.
7(2): 175-180.

Benkstein, K.D.,  C. J. Martinez, G. Li, D. C. Meier, C., B. Montgomery, S. Semancik.
2006. Integration of Nanostructured Materials with MEMS Microhotplate Platforms to
Enhance Chemical Sensor Performance. Journal ofNanoparticle Research. 8(6): 809-
822.

Chen, T., Z. Zhang, S. C. Glotzer. 2007. A precise packing sequence for self-assembled
convex structures. Proceedings of the National Academy of Sciences. 104: 717-722.

Chopra, N. G., R. J. Luyken, K. Cherrey, V. H. Crespi, M. L. Cohen, S. G. Louis, A.
Zettl.  1995. Boron Nitride Nanotubes. Science. 269: 966-967.

Comini, E., G. Faglia,  G. Sberveglieri, Z. Pan, Z.L. Wang. 2002. Stable and highly
sensitive gas sensors based on semiconducting  oxide nanobelts. Applied Physics Letters.
81:1869.

Fields, L.L., J. P. Zheng, Y. Cheng, P. Xiong. 2006. Room-temperature low-power
hydrogen sensor based on a single tin dioxide nanobelt. Applied Physics Letters. 88:
263102.

Garcia, S.P. and S. Semancik. 2007. Controlling the Morphology of Zinc Oxide
Nanorods Crystallized from Aqueous Solutions: The Effect of Crystal Growth Modifiers
on Aspect Ratio.  Chemistry of Materials.  19(16), 4016-4022.

Goldberg, D., Y.  Bando, M. Eremets, K. Takemura, H. Yusa. 1996. Nanotubes in boron
nitride laser heated at high  pressure. Applied Physics Letters. 69: 2045-2047.

Goldberg, D., Y.  Bando, M. Mitote, K. Kurashima, T. Sato, N. Grobert, M. Reyes, H.
Terrones, M. Terrones. 2002. Preparation of aligned multi-walled BN and B/C/N
nanotubular arrays and their characterization using HRTEM, EELS and energy-filtered
TEM. Physica. B. 323: 60-66.

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Hamilton, E. J. M., S. E. Dolan, C. M. Mann, H. O. Colijn, C. A. MacDonald, S. G.
Shore. 1993. Preparation of Amorphous Boron-Nitride and its Conversion to a
Turbostratic Tubular Form. Science. 260:659-663.

He, H., T.H. Wu, C.L. Hsin, K.M. Li, LJ. Chen, Y.L. Chueh, L. J. Chou, Z.L. Wang.
2002. Beaklike SnO(2) Nanorods with Strong Photoluminescent and Field-Emission
Properties. Small. 2(1), 116-120.

Hernandez, F.E., M. Rexand and A.D. Campiglia. 2007. Pushing the Limits of Mercury
Sensors with Gold Nanorods. Presentation atNanotech 2007 Conference,  Santa Clara,
California, May 22, 2007.

Jia, W., E.T. Reitz, Y. Lei. 2007. Biosensor for heavy metals using hydrothermally grown
ZnO nanorods and metal binding peptides. Presentation at Nanotech 2007 Conference,
Santa Clara, California, May 22, 2007.

Kou, S.Z.X., C.-K. Tsung, M.H. Yeung, Q. Shi, G.D. Stucky, L. Sun, J. Wang, C. Yan.
2006. Growth of Gold Nanorods and Bipyramids Using CTEAB Surfactant. Journal of
Physical Chemistry B. 110: 16377-16383.

Park, S., J.-H. Lim, S.-W. Chung,  C.A. Mirkin. 2004. Self-Assembly of Mesoscopic
Metal-Polymer Amphiphiles. Science. 303(5656): 348-351.

Srivastava, D. and I. Lee. 2006. Nanorice and Nanospears from Polymer Nanospheres.
Advanced Materials. 18: 2471-2475.

Wan, Q., H. Li, Y. J. Chen, T. H. Wang, X. L. He, J. P. Li, C. L. Lin. 2004. Fabrication
and ethanol sensing characteristics of ZnO nanowire gas sensors. Applied Physics Letters.
84: 3654-3656.

Wang, H. T., B. S. Kang, F. Ren, L.  C. Tien, P. W. Sadik, D. P. Norton, S. J. Pearton, J.
Lin. 2005. Hydrogen-selective sensing at room temperature with ZnO nanorods; Applied
Physics Letters.  86: 243503.

Wang, H., D. W. Brandl, F. Le, P. Nordlander, N. J. Halas. 2006. Nanorice: a hybrid
nanostructure. Nano Letters. 6: 827.

Xue, X. Y., Y. J. Chen, Y. G. Wang, T. H. Wang. 2005. Synthesis and ethanol sensing
properties ofZnSnO3 nanowires. Applied Physics Letters. 86: 233101.

Yu, C., Qing Hao, S. Saha, L. Shi, Xiangyang Kong, Z. L. Wang. 2005. Integration of
metal oxide nanobelts with microsystems for nerve agent detection; Applied Physics
Letters. 86:063101.

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4.0  Observations and Conclusions

This document has  synthesized  a review of information on  existing and  potential
applications of nano-enabled technologies for remediation and sensing of environmental
pollutants,  including radionuclides at  contaminated sites.  Since most  environmental
nanotechnologies  are just emerging and  cover a  very  broad spectrum  of  potential
applications, the approach used in this document is to first present nanotechnologies that
are currently being field tested followed by those that are still in the research and/or
development stage. A wide  range of promising nano-enabled technologies have been
presented and discussed to the extent feasible.

It is important to note that the majority of mature (tested and tried) nanotechnologies are
dominant in the electronics and biomedical fields. Which nanotechnologies will actually
migrate into environmental sensor (and possibly remediation) is challenging to determine
at  this time with  significant accuracy,  but comments were made in the document on
extrapolation of nanotechnologies across scientific fields where appropriate. In addition
to  gathering the information presented here, the process of searching and examining the
technical literature allowed  some broad  observations to be  made. These collective
findings may be summarized as follows:

    1.  Nano-enabled  technologies may  be  classified  into  two  broad  categories:
       remediation and sensing  technologies.    Remediation  includes  detecting,
       sequestration, and destruction of materials that constitute a threat to pubic health,
       welfare, and the environment. Sensing technologies, with enhanced sensors using
       nanomatrials, are used for detecting the presence of pollutants and could be used
       in monitoring releases for regulatory compliance.

    2.  The classification in (1) above is most useful in presenting the overall  state-of-
       the-science if: a) a reasonable extrapolation is allowed from related behavior (e.g.,
       it is accepted as reasonable that the  success of a technology in the  remediation of
       heavy  metals  signals the  technology's  expected  success  for remediation  of
       radionuclides), and b) the concept of environmental remediation is  expanded to
       include  radioactive  waste  management  and radiological decontamination  c)
       sensing of foreign substance or element may also serve as a prerequisite for
       furthering the development of environmental contaminant detection.

    3.  In general, our understanding of nanotechnology risk  is still developing. More
       information is needed on  both the appropriate framework and on the basic
       information to be used within  that framework. Additionally, the  relationship
       between radionuclides  and nanotechnology  risk is  even more elementary.  A
       growing body of information and knowledge of the fate and transport of various
       nanomaterials should aid in the assessment of potential risks and mitigation of
       hazards to public health  and  the environment posed  by  nanotechnologies
       applications.

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4.  The physical and chemical properties (i.e., high surface area, high reactivity, easy
   dispersability,  rapid diffusion,  etc.)  of nanomaterials  provide  the  unique
   properties/capabilities for various environmental nanotech applications. The term
   "nanomaterial" is very broad and includes nanoparticles (based on overall size or
   gross  dimensions),  nanostructured  materials  (which  may   be  microscale,
   mesoscale,  or even macroscale particles,  but still  have nanoscale  structural
   features, such as the channels in zeolites), and nanocomposite materials.

5.  A number of nano-enabled remediation technologies have either been field tested,
   trial demonstrated, or are close to and/or awaiting, full-scale  implementation.
   These include ZVI nanoparticles (ZVI microparticles have already been used to
   remediate  uranium  contamination  of ground water),  zeolites (nanostructured
   materials that have been used in radioactive waste treatment for half a century and
   have been investigated for the remediation of radioactive cesium in soils,  and are
   now  available  as  nanoparticles),  and  a  radiological  decontamination   gel
   (developed  at ANL and employing a nanoparticulate radionuclide sorbent). As
   more nanotechnologies are applied in the field, performance data to include cost,
   operation and maintenance should be collected  real-time to aid in  further
   evaluation,   and   validating   the   sustainability   of  the   environmental
   nanotechnologies applied to radionuclides.

6.  Based on analysis of the underlying technical and and scientific framework  of a
   number  of  available nano-enabled  remedial  technologies, it is anticipated  that
   nano-enabled technologies will have significant impact in the sensor development
   area. This is due to well-established fundamentals of sensor behavior that allow
   distinct advantages to be realized when the sensing events are  measured at the
   molecular level.  Despite the great potential for nano-enabled sensors, there are
   still some major hurdles to overcome in terms of reliable large volume production
   of nanoscale sensing elements, effective nanoscale manipulation, and integration
   of the nanoscale sensing elements with the external world.

7.  The electronics/biotechnological/biomedical driver for  nano-enabled subsystem
   development has  a two-fold benefit.  It  helps the cause of  radionuclide  site
   remediation by maintaining a development impetus, the benefit of which can be
   taken by those concerned with radionuclides. In doing so, this driver also  puts
   limits on its own utility to radionuclides  since  biosensing  has become  the
   dominant paradigm and many developers are  unaware  of the  needs of  the
   environmental community.

8.  The issue of low visibility  of environmental needs to the nano-enabled  sensing
   community could easily be addressed by a straightforward communications effort,
   using avenues such as the Vision 2020 technology  partnership or the MATCH
   Programme in the United Kingdom.

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As can be ascertained from this report, nanotechnology is strongly supported by many
federal  agencies,  though  relatively  little  support by  comparison is  available for
environmental applications. In addition, the market for environmental applications is
perceived limited in compared to other fields such as biomedical and/or  electronics to
name a  few.  This may be  a barrier to the rapid development  and  deployment of
nanotechnologies for environmental applications.

As discussed, there  are many  possible risk concerns  associated with nanotechnology.
Further, in the case of nanoparticle  in situ applications there are risk concerns voiced in
the  literature and  there is no  regulatory guidance at this time. Risk  concerns are a
potential barrier to the acceptance and widespread deployment of nanoparticle based
environmental technologies. Further, barriers may include the relatively limited market in
environmental nanotechnologies. It seems most likely that nanotechnology-based sensors
will be advanced further and will be  more widely accepted, with nanotechnologies for
remediation developing more gradually.

As explained earlier, the  purpose of this document is to  provide  an overview of the
potential applications of nano-enabled technologies and subsystems to radionuclides in
the environment, and to further an investigation  of case studies to evaluate and validate
the sustainability of various applications as they emerge.

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Appendix A
Acronyms
AFM           Atomic Force Microscopy
AFO           Amorphous Ferric Oxide
ANL           Argonne National Laboratory
AlPOs          Aluminophosphates
ASTM         American Standard Test Method
CBEN          Center for Biological and Environmental Nanotechnology
DEFRA        Department for Environment, Food, and Rural Affairs
DMRB         Dissimilatory Metal-Reducing Bacteria
DND           Detonation Nanodiamonds
DoD           U.S. Department of Defense
DOE           U.S. Department of Energy
DSSR          Double Skin Sheet Reactor
EC            European Commission
EDA           Ethylenediamine
EOF           Environmental Defense Fund
EMSP          Environmental Management Science Program
EPA           U.S. Environmental Protection Agency
EU            European Union
EXAFS        Extended X-Ray Absorption Fine Structure
FDA           Federal Drug Administration
FET           Field Effect Transistor
GLAD         Glancing Angle Deposition
HOPO          Hydroxypyridinone
IAEA          International Atomic Energy Agency
IRGC          International Risk Governance Council
IR             Infrared
ITRC           Interstate Technology & Regulatory Council
ITRS           International Technology Roadmap for Semiconductors
ISO            International Organization for Standardization
IUPAC         International Union of Pure and Applied Chemistry
LOG           Laboratory-on-a-Chip
LSPR          Localized Surface Plasmon Resonance
MATCH        Multidisciplinary Assessment of Technology Centre for Healthcare
MCDA         multi-criteria decision analysis
MEMS         Microelectromechanical Systems
microTAS      Micro-Total Analytical System
NEAT-ORU    Nanomaterials in the Environment, Agriculture, and Technology Organized Research
               Unit
NEIC           National Enforcement Investigations Center
NIH           National Institutes of Health
nm            nanometer
NMSP          Nanoscale Materials Stewardship Program
NNI           National Nanotechnology Initiative
NODE         Nanowire-based One-Dimensional Electronics
OAR/OTAQ    Office of Air and Radiation/Office of Transportation and Air Quality
OECA         Office of Enforcement and Compliance Assurance
OPP           Office of Pesticide Programs
OPPT          Office of Pollution Prevention and Toxics
ORD           Office of Research and Development
ORNL          Oak Ridge National Laboratory
OSWER        Office of Solid Waste and Emergency Response

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PCB           Polychlorinated Biphenyls
PCE           Perchloroethylene
PEBBLE       Probe Encapsulated By Biologically Localized Embedding
PEG           Polyethylene Glycol
PNNL          Pacific Northwest National Laboratories
PRB           Permeable Reactive Barrier
R&D           Research and Development
RCRA          Resource Conservation and Recovery Act
RDX           Hexahydro-Trinitro-Triazine
RO            Reverse Osmosis
RS/RAE        Royal Society/Royal Academy of Engineering
SAMMS        Serf-Assembled Monolayers on Mesoporous Supports
SBIR           Small Business Innovation Research
SCENIHR      Scientific Committee on Emerging and Newly Identified Health Risks
SES           Steward Environmental Solutions
SET AC        Society of Environmental Toxicology and Chemistry
SPR           Surface Plasmon Resonance
STAR          Science To Achieve Results
STM           Scanning Tunneling Microscope
SWCNT        Single-Walled Carbon Nanotubes
TCA           Trichloroethane
TCE           Trichloroethylene
TDS           Total Dissolved Solids
TNT           2,4,6-Trinitrotoluene
UNCD          Ultrananocrystalline diamonds
USNRC        U.S. Nuclear Regulatory Commission
VOC           Volatile Organic Compound
WSCP          Water-Soluble Chelating Polymers
ZVI           Zero-Valent Iron

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Appendix B
Glossary

Array: An arrangement of sensing elements in repeating or non-repeating units that are
arranged for increased sensitivity or selectivity.

Assembler: A general-purpose device for molecular manufacturing capable of guiding
chemical reactions by positioning molecules.

Atomic force microscope (AFM): An instrument able to image surfaces to molecular
accuracy by mechanically probing their surface contours.  A kind of proximal probe.

Buckyball/C-60: see Fullerenes, of which "buckyballs" is a subset. The term
"buckyball" refers only to the spherical fullerenes and is derived from the word
"Buckminsterfullerene," which is a geodesic dome/soccer ball-shaped C-60 molecule. C-
60 was the first buckyball to be discovered and remains the most common and  easy to
produce.

Cantilever: A beam supported at one end and capable of defined bending and vibrational
behavior.

Catalyst:  A substance, usually used in small amounts relative to the reactants,  that
modifies and increases the rate of a reaction without being consumed or changed in the
process.

Chemical Sensor: A device capable of providing quantitative or semi-quantitative
information on a chemical species (or analyte) through calibration, and then brought into
direct contact with the species in its environment.

Conjugated Polymers: Organic macromolecules that consist at least of one backbone
chain of alternating double and single bonds.

Dendrimers: Artificially-engineered or manufactured molecules built up from branched
unites called monomers. Technically, a dendrimer is a branched polymer, which is a large
molecule comprised of many smaller ones linked together.

Depth Filters: A type of filter in which the filter medium has a significant physical depth
and the particles to be retained are captured throughout the depth of the filter.

Disruptive Technology: Introduced in 2003, this term is used to describe a new
technology that is significantly cheaper (or performs better) than a current technology.

Electron beam lithography: Lithographic patterning using an electron beam, usually to
induce a change in solubility in polymer films. The resulting patterns can be subsequently
transferred to other metallic, semiconductor, or insulating films.

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Electrospinning: A process for making nanofibers with diameters down to about 10 nm
using an electrical charge to elongate and narrow fibers formed by an added melt.

Enabling science and technologies: Areas of research relevant to a particular goal, such
as nanotechnology.

Engineered/manufactured nanomaterials: Nanosized materials that are purposefully
made. These are in contrast to incidental and naturally-occurring nanosized materials.
Engineering/manufacturing may be done through certain chemical and/or physical
processes to create materials with specific properties. There are both "bottom-up"
processes (such as self-assembly) that create nanoscale materials from atoms and
molecules, as well as "top-down" processes (such as milling) that create nanoscale
materials from their macro-scale counterparts. Nanoscale materials that have macro-scale
counterparts frequently display different or enhanced properties compared to the macro-
scale form.

Exploratory  engineering: Design and analysis of systems that are theoretically possible
but cannot be built yet, owing to limitations in available tools.

Exposure assessment: The determination or estimation (qualitative or quantitative) of
the magnitude, frequency, duration, route, and extent (number of people) of exposure to a
chemical, material, or microorganism.

Fullerenes: Pure carbon, cage-like molecules composed of at least 20 atoms of carbon.
The word "fullerene" is derived from the word "Buckminsterfullerene," which refers
specifically to the C-60 molecule and is named after Buckminster Fuller, an architect who
described and made famous the geodesic dome. C-60 and C-70 are the most common and
easy to produce fullerenes.

Green Rust:  A class of Iron II/Iron III hydroxide compounds having a pyroaurite-type
structure consisting of alternating positively charged hydroxide layers and hydrated anion
layers.

Incidental nanosized materials: Nanomaterials that are the byproducts of human
activity, such as combustion, welding, or grinding.

Lab-on-a-Chip (LOC): Also known as a micro-total-analytical system (microTAS), or
microfluidics device, is a device that can integrate miniaturized laboratory functions,
such as separation and analysis of components of a mixture, on a single microprocessor
chip using extremely small fluid volumes on the order of nanoliters to picoliters.

Limited assembler: Assembler capable of making only certain products;  faster, more
efficient, and  less liable to abuse than a general-purpose assembler.

Macroporous: Mesoporous materials with a pore diameter range greater than 50 nm.

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Membrane filter: A filter that uses relatively thin material with a well-defined maximum
pore size, with particle retaining effects taking place almost entirely at the surface.

Mesoporous materials: Porous substances with pore diameters in the range of 2-50 nm.

Microcantilever: A very  small cantilever, the properties of which can be understood
from basic engineering principles.

Microfluidics: An interdisciplinary field dealing with the behavior and control of
extremely small volumes of fluids and the design of systems that use these small
volumes.

Microporous: Mesoporous materials with a pore diameter range less than 2 nm.

Molecular manufacturing: Manufacturing using molecular machinery, giving molecule-
by-molecule control of products and by-products via positional chemical synthesis.

Molecular nanotechnology: Thorough, inexpensive control of the structure of matter
based on molecule-by-molecule control of products and byproducts; the products and
processes of molecular manufacturing, including molecular machinery.

Molecular recognition: A chemical term referring to processes in which molecules
adhere in a highly specific way, forming a larger structure; an enabling technology for
nanotechnology.

Nano-: A prefix meaning  one billionth (1/1,000,000,000).

Nanobelts: A class of nanostructure often viewed as a type of nanowire, usually made
from semiconducting metal oxides, such as SnO2, ZnO, In2O3 or CdO, or selenides such
as CdSe. Nanobelts form ribbon-like structures with widths of 30-300 nm, thicknesses of
10-30 nm, and lengths in the millimeter range.

Nanoelectronics: Electronics on a nanometer scale, whether by current techniques or
nanotechnology; includes both molecular electronic and nanoscale devices resembling
today's semiconductor devices.

Nanomanufacturing: Same as molecular manufacturing.

Nanometer: One billionth of a meter.

Nanoparticle: Free standing nanosized material, consisting of between tens to thousands
of atoms.

Nanorods:  Solid nanostructures morphologically similar to nanowires but with aspect
ratios of about 3-to-5. They are formed from a variety of materials including metals,

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semiconducting oxides, diamonds (aggregated diamond nanorods produced from
fullerenes are the hardest material so far discovered), and organic materials.

Nanoscale: Having dimensions measured in nanometers.

Nanoscience: The interdisciplinary field of science devoted to the advancement of
nanotechnology.

Nanosensors: Chemical sensors possessing a nanoscale  sensing element.

Nanostructures: Structures at the nanoscale; that is, structures of an intermediate size
between molecular and microscopic (micrometer-sized) structures.

Nanotechnology: Research and technology development at the atomic, molecular or
macromolecular levels, in the length scale of approximately 1-100 nm range; creating and
using structures, devices, and systems that have novel properties and functions because of
their small and/or intermediate size; and the ability to control or manipulate on the atomic
scale.

Nanotube: Tubular structure, carbon and non-carbon based, with dimensions in the
nanometer regime.

Nanowire: High aspect ratio structures with nanometer diameters that can be filled
(nanorods) or hollow (nanotubes).

PEBBLE (Probe Encapsulated by Biologically Localized Embedding): sub-micron
sized optical sensors designed specifically for minimally invasive analyte monitoring in
viable, single cells.

Point-of-Care:  Analytical testing performed outside the central pathology laboratory
using a device or devices that can be easily transported to the vicinity of the patient.

Quantum dot: A closely packed semiconductor crystal comprised of hundreds or
thousands of atoms, and whose size is on the order of a few nanometers to a few hundred
nanometers. Changing the size of quantum dots changes  their optical properties.

Scanning Tunneling Microscope (STM): An instrument able to image  conducting
surfaces to atomic accuracy; has been used to pin molecules to a surface.

Sealed assembler lab: A general-purpose assembler system in a container permitting
only energy and information to be exchanged with the environment.

Self-Assembled Monolayers on Mesoporous Supports (SAMMS): Nanoporous
ceramic materials that have been developed to remove contaminants from environmental
media.

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Self-assembly: The ability of objects to assemble themselves into an orderly structure.
Routinely seen in living cells, this is a property that nanotechnology may extend to
inanimate matter.

Self-replication: The ability of an entity such as a living cell to make a copy of itself.

Spectroscopy: The scientific study of the absorption, emission, or scattering of
electromagnetic radiation by atoms, molecules, ions, solids, liquids, or gases.

Sticking Coefficient: A standard term in surface chemistry and surface physics. It is the
ratio of the number of adsorbate molecules that adsorb, or "stick", to a surface, to the total
number of molecules that impinge upon that surface during the same period of time. A
value of 1.00 means all impinging molecules stick, while a value of 0.00 means none
stick. The concept is used in investigations of nanoparticle mobility in the subsurface.

Superlattice: Nanomaterials composed of thin crystal layers. The properties (thickness,
composition) of these layers repeat periodically.

Surface Modified  Membranes: Using technology to change the surface of the
membrane, but not the underlying bulk material.

Water-Soluble Chelating Polymers (WSCP): Polymers engineered to contain both
highly elective chelating functionalities to bind with targeted metal ions, and solubilizing
functionalities to allow the polymer to dissolve in water.

Zeolite: A mineral with a pore size of less than 1 nm.

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                                                             Appendix C
                                              References for Figures

Figure 2 accessed at http://www.nsf.gov/od/lpa/news/03/images/figure 1 zhang.jpg

Figure 3 accessed at http://samms.pnl.gov/sammstech summary.pdf

Figure 4 accessed at http://sammsadsorbents.com/page/what-is-samms

Figure 5 accessed at
     http://upload.wikimedia.org/wikipedia/commons/thumb/8/86/Filtration_diagram.sv
     g/4llpx-Filtration  diagram.svg.png

Figure 6 and 7 accessed at http://www.kochmembrane.com/sep nf.html

Figure 8 accessed at
     http://www.sciencedirect.com/science?_ob=MiamiCaptionURL&_method=retrieve
     & udi=B6XU-4J95TSY-
     P&_image=fig3&_ba=3&_user=10&_coverDate=03%2F31%2F2006&_rdoc=l&_f
     mt=full& orig=search& cdi=7244&view=c&  acct=C000050221&  version=l& u
     iiVersion=0& userid=10&md5=78742dc3860626aacbd253add60720d7
Figure 9 accessed at
     http://www.sciencedirect.com/science?_ob=MiamiCaptionURL&_method=retrieve
     & udi=B6XU-4J95TSY-
     P&_image=figl 1& ba=l 1& user=10& coverDate=03%2F31%2F2006& rdoc=l
     & fmt=full& orig=search& cdi=7244&view=c& acct=C000050221& version=l
     & urlVersion=0&  userid=10&md5=941b7370b30b83fabl7bcl94218a4570

Figure 10 accessed at http://www.foresight.org/conference2005/presentations/lee.pdf

Figure 11 accessed at http://www.emembrane.com/tech.html

Figure 12 accessed at http://en.wikipedia.Org/wiki/Image:Zeolite-ZSM-5-3D-vdW.png

Figure 13 accessed at http://upload.wikimedia.Org/wikipedia/en/7/72/Nanodiamonds.jpg

Figure 14 accessed at http://www.nanonet.go.jp/english/mailmag/2007/091a.html

Figure 15 accessed at http://focus.aps.org/story/vl l/st4

Figure 16 accessed at http://upload.wikimedia.Org/wikipedia/en/e/e8/Graphs.jpg

Figure 18 created by Dr.  Eric Nuttall, University of New Mexico

Figure 19 accessed at http://www.pnl.gov/news/release.asp?id=175

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Figure 20 accessed at http://www.mesg.anl.gov/

Figure 21 accessed at http://www.whatsnextnetwork.com/technology/index.php/2006/07/

Figure 23 accessed at http://en.wikipedia.org/wiki/Nanomaterials

Figure 24 accessed at
     http://upload.wikimedia.Org/wikipedia/commons/c/c5/Fullerene c540.png

Figure 25 accessed at http://theor.jinr.ru/disorder/carbon.html

Figure 26 accessed at http://theor.jinr.ru/disorder/carbon.html

Figure 27 accessed at
     http://upload.wikimedia.org/wikipedia/commons/6/62/NanobudComputations70%2
     5.jpg

Figure 28 (L) accessed at http://www.physorg.com/news95082478.html

Figure 28 (R) accessed at http://science.nasa.gov/headlines/v2006/16nov locad.htm

Figure 29 accessed at http://www.tastechip.com/labchip/nano biochip.html

Figure 30 accessed at http://www.brunel.ac.uk75118/esrg%20images/chip.jpg

Figure 31 accessed at http://www.answers.com/topic/atomic-force-microscope

Figure 32 accessed at http://www.eng.umd.edu/media/pressreleases/pr072506  crab-
     detector.html

Figure 33 accessed at http://nano.cancer.gov/news_center/monthly_feature_2005_dec.asp

Figure 34 accessed at http://picasaweb.google.com/lh/photo/OSEZilSwhpJgPv3-qpUfxg

Figure 35 accessed at http://www.defensetechbriefs.com/content/view/1023/34/

Figure 36 accessed at
     http://www.rsc.org/deliverv/ArticleLinking/DisplavHTMLArticleforfree.cfm7Jour
     nalCode=CC&Year=2006&ManuscriptID=b604426c&Iss=29

Figure 37 accessed at http://www.nanoscience.gatech.edu/zlwang/paper/HIpapers.html

Figure 38 accessed at http://www.phy.bris.ac.uk/groups/electron_microscopy/index.html

Figure 39 accessed at http://nanotechnologytoday.blogspot.com/2007/ll/gold-nanorods-
     shed-light-on-new.html

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