![[logo] US EPA](http://www.epa.gov/epafiles/images/logo_epaseal.gif){kind=logo}
![[logo] Nanotechnology Conference Logo](images/header.gif)
Conference Abstracts (S-Z)
Sequestration of Heavy Metals with Nanoscale Zero-Valent
Iron (nZVI)
Wei-xian Zhang, Weile Yan, Xiao-qin Li. Department of
Civil and Environmental Engineering, Lehigh University, Bethlehem, Pennsylvania, USA
Research on environmental applications of nZVI in the past decade has been focusing primarily on the reductive remediation of halogenated hydrocarbons. Recent work in our lab suggests that nZVI is also an efficient nanomaterial for the treatment and remediation of heavy metals in water. The core-shell structure of nZVI nanoparticles has been confirmed with spectroscopic and microscopic characterizations (XPS/HR-TEM/STEM) to comprise of a metallic core surrounded by a thin shell of amorphous iron oxide. The unique structure allows nZVI to interact with metal ions in dual modes. Metals such as Zn(II) and Cd(II) with standard potential E0 close to or more negative than that of iron are removed by surface complex formation with the iron hydroxide shell. For metals with E0 substantially higher than that of iron, such as Cu(II), Ag(I) and Hg(II), the removal mechanism is predominantly reduction. Metals with E0 comparable to that of iron, e.g. Ni(II) and Pb(II), are sequestrated via both reduction and sorption.
The dual mechanisms and the large surface area afforded by the minute size of the nanoparticles provide significant advantages relative to the conventional treatment options. For example, the capacity of Ni(II) removal is more than 100% higher than the best inorganic sorbents. For Cu(II), removal capacity of 922mg-Cu/g-nZVI was observed, at least 10 times higher than that of goethite. Consistent Cu(II) sequestration performance (>95%) was observed with nZVI over a broad pH range of 3.0 to 8.5, whereas iron-oxide based sorbents were ineffective at pH < 4. With reference to commercial micro-scale iron powders, nZVI exhibited 2 orders of magnitude increase in reaction rate constants (Km). In addition to the promising potential for heavy metals remediation, the results presented here offer new insights into the structure, reactivity and longevity of iron and iron-based bimetallic nanoparticles.
Status of nZVI Technology: Lessons Learned from North
American and International Field Implementations
F. Gheorghiu1, M. Borda1, A.
Kane, P. Swinick1, S. Finn1, F. He1, J. Paul1,
S. Hains2, M. Barbeau2, M. Pupeza3, J.P.
Davit3. (1) Golder Associates–United States; (2) Golder
Associates–Canada; (3) Golder Associates–Europe
With nearly 10 years of experience, Golder Associates Inc. (Golder) is a leader in the manufacture and implementation of nano-scale zero-valent iron (nZVI) for environmental remediation applications. Golder has designed and implemented nZVI injections in the United States, Canada, Europe and Australia including, ten (10) pilot-scale studies, ten (10) bench-scale studies and one (1) full-scale implementation. Golder’s global experience has led to several significant advancements in the technology including, verifying the need to include palladium (Pd) as a catalyst for in situ treatment using mechanically crushed material, verifying the need to include a surface modifier (e.g., soy powder) to enhance the mobility of nZVI in the subsurface, and establishing the enhanced treatment potential of combined nZVI/enhanced bioremediation alternatives. In addition to these advances in implementation, Golder is also advancing the types of nZVI used in the field including the manufacture of mechanically crushed nZVI through licensing with Lehigh University and in-well precipitated nZVI.
Advances in nZVI Delivery
The reactivity of nZVI toward contaminants of concern (COCs) has been thoroughly researched with successful results, leaving the delivery of nZVI to impacted zones as the most critical path to successful site remediation. To this end, Golder has utilized several surface modifiers to diminish the attractive forces between nano-particles which cause agglomeration and limit mobility in the subsurface. Recent research (Lowery, pers. comm.) is showing that agglomeration, rather than interaction with aquifer materials, is the single greatest cause of limited mobility in nZVI application. At several project sites, Golder has surface-modified nZVI particles using Soy Protein to establish a negative surface charge on particles and increase the degree of particle-particle repulsion allowing for injection with up to a 15 ft radius of influence (ROI). Future development of “green” polymers will continue to advance this ability to improve the mobility of nZVI and achieve better COC targeting in the subsurface.
Necessity of Catalysts
Precipitated nZVI has reactivity unparalleled by its mechanically crushed counterpart. However, by exploiting the chemistry of noble metals the reactivity of mechanically crushed nZVI can be restored. This process involves the addition of a small concentration of palladium ([Pd] as Pd acetate) to the mechanically crushed material. Palladium irreversible adsorbs to the nZVI surface and exhibits catalytic activity as the non-reactive palladium is in contact with the highly reactive Fe0 surface causing enhanced corrosion of the Fe0. This process provides a driving force for the production of electrons which are subsequently used to reduce chlorinated aliphatic hydrocarbons (CAHs) to non-toxic daughter products. Golder has successfully performed several pilot- and full-scale applications using bi-metallic nano particles (BNPs).
Advances in nZVI Couple with Enhanced Bioremediation
During the largest pilot-scale nZVI injection performed to date (~4,500 kg nZVI injected) a thorough microbiological assessment was performed illustrating the transition of abiotic CAH degradation to enhanced bioremediation of CAHs. This transition appears to driven by the redox condition of the aquifer due to nZVI reactivity (ORP values changed from +200 mV to -500 mV upon injection) coupled with the addition of complex source of soluble and sparring soluble carbon (Soy Protein) which acts as an electron donor. This transition and continued degradation of CAHs continued for over one (1) year and achieved a groundwater concentration target of 5 ppb for trichloroethylene (TCE) without build-up of intermediate degradation products. This suggests that a combined remedy of nZVI injection and long-term enhanced bioremediation may be a very strong candidate technology for a number of CAH impacted sites.
Structure of Iron Oxide Nanoparticles;
Influence of pH and Organic Matter Effects
Susan Cumberland, Department of Environmental Health, GEES, University of Birmingham,
UK
Metal oxide nanoparticles (where at least one dimension is between 1 and 100 nm) are currently being exploited for use in the remediation of ground water and drinking water. Iron oxides in particular are being used in vast quantities in a variety of processes. However, due to the small size, increased surface area and related effects nanoparticles differ from their bulk counterparts in significant and unexpected ways. A number of studies have highlighted that there may also be a risk to the environment due to their potential hazard and increased exposure as the nanoparticle industry grows. As nanoparticles are almost certainly entering the environment, knowledge of fate and transportation in ground and surface waters is essential.
Synthesized iron oxide nanoparticles were mixed with an aquatic fulvic acid and a peat humic acid at different concentrations (0-25 ppm) and pH values (2-10). The suspensions were analysed by particle size using flow –field flow fractionator, dynamic light scattering and electrophoresis. Primary particle size increased with both increased NOM concentration and with pH. Particle aggregation occurred immediately and was extensive at pH 6 and higher. Aggregation occurred as surface charge approached zero, as no stabilising agents were added in this system. Humic substances were found to form surface coatings on the iron oxide nanoparticles which were only 1-2 nm in thickness. The influence of pH and NOM concentration will affect the fate and bioavailability of nanoparticles in the aquatic environment due to these changes in surface properties, aggregation and subsequent sedimentation.
Surface Chemistry of Nanoscale Zero-valent Iron (nZVI)
Wei-xian Zhang. Department of Civil and Environmental
Engineering, Lehigh University, Bethlehem, PA, USA
Zero-valent iron nanoparticle technology is becoming an increasingly popular choice for treatment of hazardous and toxic wastes, and for remediation of contaminated sites. In the U.S. alone, more than 30 projects have been documented since 2001. More are planned or ongoing in North America, Europe and Asia. The diminutive size of the iron nanoparticles helps to foster effective subsurface dispersion while their large specific surface area corresponds to enhanced reactivity for rapid contaminant transformation. Recent innovations in nanoparticle synthesis and production have resulted in substantial cost reductions and increased availability of nanoscale zero-valent iron for large scale applications. In this presentation, methods of nZVI synthesis and characterization will be reviewed. Applications of nZVI for treatment of both organic and inorganic contaminants will be discussed. Key issues related to field applications such as fate/transport, toxicity and potential environmental impact are also explored.
Surfactive Stabilization of Multi-walled Carbon Nanotube
Dispersions with Dissolved Humic Substances
Mark. A. Chappell1, Aaron J. George2,
Beth E. Porter2, Cynthia L. Price1, Katerina M. Dontsova2,
Alan J. Kennedy1, Jeffery A. Steevens1. (1) Environmental
Laboratory, Engineering Research & Development Center, US Army Corps of
Engineers, Vicksburg, MS, USA; (2) SpecPro, Inc., Vicksburg, MS, USA
Soil humic substances (HS) have been shown to stabilize carbon nanotube (CNT) dispersions in solution yet the mechanisms by which this occurs are widely misunderstood. For this paper, we hypothesize that this behavior is a property of the surfactive nature of HS. Experiments were conducted by dispersing multi-walled CNT in solutions containing a range of dissolved HS concentrations obtained from the commercial Aldrich humic acid or water-extractable HS from Catlin silt loam soil (fine-silty, mixed, mesic, superactive Oxyaquic Argiudolls). CNT dispersions demonstrated enhanced stability at 50 and 300 mg L-1 added HS from Aldrich HA and Catlin HS, respectively. Dynamic light-scattering data showed that increasing the concentration of HS decreased CNT mean particle diameter (MPD) to approx. 250 nm for Aldrich HA and to approx. 450 nm for the Catlin HS. CNT particle size polydispersivity (PD) also reached a minimum at approx. 0.3 and 0.35 with increasing Aldrich HA and Catlin HS, respectively, indicating enhanced homogeneity of particle sizes but with significant differences between the two humic materials. HS adsorption isotherms revealed that maximum dispersion stability and minimization of MPD and PD corresponded with saturation of CNT particles with HS – a behavior indicative of surfactants. To verify this conclusion, CNT dispersion potential was studied in the presence of two nonionic (Brij 35 and Triton X) and one anionic (SDS) surfactants. Trends in CNT MPD and PD minimas, and surfactant adsorption were observed with increasing dispersion stability. Results showed that the highly surfactive nature of dissolved HS readily stabilized CNT dispersions. It is our opinion that natural levels of HS present in most waters is sufficient to readily disperse CNT in the environment.
The Testing Of A Nanomembrane Filtration Unit For The
Production Of Potable Water From A Brackish Groundwater Source
A brackish groundwater desalination study was carried out in
North West Province of South Africa which is situated on a semiarid region. The
province is essentially rural and comprises 80% of the population who solely
depend on untreated groundwater or borehole water for their livelihood. A
nanomembrane technology unit was tested for the treatment of brackish
groundwater at Batlhaping Primary School in Madibogo village. This technology
was chosen for two reasons: its low cost; ease of operation and maintenance.
The research site, Batlhaping Primary School, is 100 kilometers north-east of Mafikeng, the capital city of the province. The major contaminants in the brackish
groundwater at the school are nitrate, chloride, sulphate, calcium and
magnesium ions. The groundwater was also spiked with fluoride ion which is a
common pollutant in the province, particularly in the north eastern parts. Six
nanomembranes (three nanofiltration and three reverse osmosis) were tested for
the treatment of the brackish groundwater. The nanomembranes were initially
characterized on a dead-end module reactor using the water permeability and
retention coefficient methods. The Batlhaping Primary School brackish
groundwater, the raw or feedwater, was successively treated using the different
nanomembrane processes to determine the most appropriate one. The raw water was
finally treated on a cross-flow module reactor pilot water treatment plant
using the six nanomembranes at the research site. The pressures at which the
raw water was permeated through the nanomembrane were 16, 18, 20 and 22 bars. A
reverse osmosis membrane was found to be the most effective for the removal of
excess pollutant concentrations of the determinands. However, a nanofiltration
membrane was found to be appropriate for the treatment of the brackish
groundwater since it retained the appropriate nutrient concentrations of the
determinands which are required for the normal development of the human body,
namely, calcium and magnesium ions.
Toxicity of C60 fullerenes and co-contaminants in fish
Establishing the toxicity of nanomaterials is essential to
protect human and ecosystem health and to appropriately guide the development
of nanotechnology. The fullerene C60 is a manufactured nanoparticle
(NP, diameter ~1 nm) that has unique and beneficial physicochemical properties,
and future production projections indicate that C60 may be released
into the environment with potential for exposure in organisms. Ultimately,
aquatic environments may be contaminated and aquatic organisms (e.g. fish)
exposed with potential negative effects on their survival. Information on the
toxicity of C60 is conflicting and some research indicates the NP is
toxic while other research indicates little or no toxicity. In the present
research, we have investigated the toxicity of C60 in larval
zebrafish and applied techniques of global gene expression (Affymetrix GeneChip® Zebrafish Genome Array) and real-time reverse transcriptase PCR to evaluate
toxicological effects. The Affymetrix zebrafish array was used to assess
changes in gene expression (14,900 gene transcripts) in larval zebrafish after
75-h exposure to the following treatments: 1) C60 aggregates
generated by stirring and sonciation (72 h) of C60 in water (12.5 mg
C60/500 mL water), 2) C60 aggregates generated by established
methods with THF vehicle, 3) THF vehicle (i.e., method 2 without C60 added), and 4) “fish water” control. Results indicated that changes in global
gene expression were related to decomposition products of the THF vehicle
rather than C60 itself. C60 aggregates prepared without
THF were not toxic in larval zebrafish; however, the interaction of the NP
aggregates with other contaminants was recognized to be toxicologically
important. Subsequently, we investigated the interaction of other contaminants
with C60 aggregates and have determined that aggregate
characteristics (e.g. size, charge) can change in the presence of a
co-contaminant and that C60 can alter contaminant bioavailability in
fish. Evidence indicates that while the toxicity of pristine C60 may be limited under some exposure scenarios (e.g. larval fish, aqueous
exposure), the interaction of C60 with other contaminants present in
the environment or co-released into the environment is a potential
environmental problem.
Transport and Reactivity of Lactate-Modified Nanoscale
Iron Particles in PCP-Contaminated Field Sand
Krishna R. Reddy2, Amid P.
Khodadoust1, Kenneth Darko-Kagya3. (1) Professor,
Department of Civil & Materials Engineering, University of Illinois at
Chicago, Chicago, IL, USA; (2) Associate Professor, Department of Civil &
Materials Engineering, University of Illinois at Chicago, Chicago, IL, USA; (3)
Graduate Research Assistant, Department of Civil & Materials Engineering,
University of Illinois at Chicago, Chicago, IL, USA
Nanoscale iron particles have great potential for in-situ remediation of subsurface soils. The transport of reactive nanoscale iron particles (RNIPs) into the contaminated subsurface is essential for the success of this remediation technology. RNIP cannot be transported through porous media effectively without surface modification. In this study, the transport of RNIP modified with lactate was investigated in column experiments using field sand contaminated with pentachlorophenol (PCP). Bare and lactate-modified RNIP were investigated at two different slurry concentrations of 1 g/L and 4 g/L. Lactate was found to prevent agglomeration of nanoscale iron particles, making them dispersed in slurry for a longer period of time. The RNIP was introduced at the inlet of the soil column under a constant, low hydraulic gradient. Visual observations were made on the transport of RNIP during the experiments. The distribution of RNIP was found to be more uniform in the 4 g/L modified RNIP experiment compared to all other experiments. Hydraulic conductivity of the soil was measured during the course of each experiment- it remained approximately the same in tests with bare RNIP at low concentration and those with modified RNIP at different concentrations; however, it reduced in the test with bare RNIP at higher concentration. The pH, total dissolved solids, electrical conductivity, and iron and PCP concentrations in the outflow were measured. At the end of testing, the soil was extruded from the column and the concentrations of iron and PCP in the soil were measured. Degradation of PCP was found to be lower with bare RNIP as compared to modified RNIP due to limited and non-uniform transport of RNIP in the soil. Degradation and the total removal of the PCP were found higher (61.2% and 9.7%, respectively) for the 1 g/L modified RNIP; while the degradation and removal were lower (51.6% and 6.4%, respectively) for the 4 g/L modified RNIP. Overall, the results showed that lactate-modified RNIP favors relatively uniform distribution of RNIP in the soil, but the extent of PCP reduction is lowered by the surface modification. Further research is being performed to optimize the lactate-modified RNIP that provides efficient delivery as well as enhance reduction of PCP in the soil.
Treatment of Hi-Tech Industrial Wastewaters using Iron
Nanoparticles
Gordon C.C. Yang, Chia-Heng Yen. Institute of
Environmental Engineering, National Sun Yat-Sen University, Kaohsiung, Taiwan
In this work laboratory-prepared nanoscale zero-valent iron (also known as nanoiron) was used for the treatment of two wastewaters from the semiconductor industry and optoelectronics industry. These two industrial wastewaters were from the manufacturing processes of Cu-CMP (chemical mechanical polishing of copper layer) and STN-LCD (super twisted nematic- liquid crystal display), respectively. In general, CMP wastewater has the nature of high alkalinity, total solids content, and turbidity (ca. 100–300 NTU). The inorganic contaminants in CMP wastewater may include suspended solids (in the range of nanometers to micrometers). On the other hand, the organic contaminants may include metal complexing agents, surfactants, stabilizers and rheology control agents. With the large-scale introduction of copper metallization in the semiconductor manufacturing industry in recent years, the resulting CMP effluent was expected to contain a higher concentration of copper. Such a wastewater stream needs proper treatment(s) to comply with the local discharge regulations for suspended solids and possibly other contaminants. Among various technologies reported, coagulation, electrocoagulation, and filtration were found to be effective in removing the suspended solids and copper from Cu-CMP wastewater. As for LCD wastewaters, many refractory organic compounds, sulfur-containing compounds, and nitrogenous compounds would be found as a result of the array process, cell process, and module assembly process. Currently, LCD wastewaters are mainly treated by biological processes. Ozone or reverse osmosis (RO) process coupled with biological process were also reported for treating LCD wastewaters. The above biological related processes, however, would result in an increased nitrate concentration in the system. Therefore, in this work an attempt was made to employ nanoscale zero-valent iron for the treatment of these concerned hi-tech industrial wastewaters. The treatment results appear to be promising and satisfactory. Under ambient conditions the concentrations of chemical oxygen demand (COD) for both wastewaters were reduced to the levels lower than the local discharge standards for effluents. Experimental results also showed that nanoiron was capable of chemically reducing the contained nitrates in STN-LCD wastewater and Cu-CMP wastewater resulting in treatment efficiencies of 99% and over 70%, respectively. Additionally, due to the mechanism of metal replacement, 99% of copper ions in Cu-CMP wastewater were removed as a result of nanoiron application.
Tuning the Properties of Iron Nanoparticles: Doping
Effects on Reactivity and Aging
DR Baer1, PG Tratnyek2, JE
Amonette1, CL Chun3, P Nachimuthu1, JT Numri2,
RL Penn3, Y Qiang4, A Sharma4. (1) Pacific
Northwest National Laboratory, USA; (2) Oregon Health and Sciences University, USA; (3) University of Minnesota, USA; (4) University of Idaho, USA
Predicting and controlling the behaviors of nanoparticles in the environment must include understanding the effects of trace elements and impurities (i.e., dopants) on their properties. The overall impact of many trace elements on the redox activity of iron metal and iron oxide nanoparticles in natural and engineering systems is well established. However, the fundamental mechanisms that are responsible for specific behaviors and the relationship of these mechanisms to the structural characteristics of the particles and dopants are not well understood. In addition, the role of trace elements on particle aging and the overall reaction lifetime has not yet received much attention. In current studies, we are examining the impact of Al, Cu, Ni, Pd, and S on the reactivity and aging behaviors of iron metal-core oxide-shell nanoparticles with the objectives of understanding their reaction pathways and engineering/designing particles with desired reaction pathways and lifetimes. For these studies dopants have been added as a component during particle formation (hydrogen-reduction or sputter-gas-aggregation) or to already (solution-deposition). The materials have been characterized by a variety of methods including: trace elements analysis by inductively coupled plasma mass spectrometry, transmission electron microscopy [with a particular focus on locating the trace elements], phase identification by x-ray diffraction (XRD), and surface chemical state by x-ray photoelectron spectroscopy (XPS). Reaction studies have been conducted to determine the reactivity and branching ratio of products for the reductive degradation of carbon tetrachloride. A current focus of the work is on determining how trace elements impact corrosion reactions and particle lifetimes. These studies include in situ real-time methods such as electrochemistry and in aquo XRD. Although some of these measurements are still in progress, with current results we can conclude that the nature (location) of the trace-element addition affects the reaction process and that some impurities significantly alter the aging process. This type of information is essential to optimizing the design and synthesis of nanoparticles and to predicting their reactivity and longevity.
This work has been supported by the US Department of Energy (DOE) Office of Science, Offices of Basic Energy Science and Biological and Environmental Research. Portions of the work were conducted in the Environmental Molecular Sciences Laboratory (EMSL), a DOE national user facility.
Using microarrays to test the effects of acute exposure
to multiwalled carbon nanotubes (MWCNTs) on gene expression in fathead minnows
(Pimephales promelas)
Barbara J. Carter1,
(1) EcoArray, Inc., Gainesville, FL, USA
Concerns regarding the release of nanomaterials, in general, and nanotubes, in particular, into the environment and their potential effects on fish and wildlife have been increasing. However, the evaluation of the potential for exposure and adverse effects of nanoparticles on fish and wildlife has begun to be addressed only recently through toxicological testing, and data are extremely limited. Under an EPA Phase 1 SBIR grant, we were given the opportunity to use state-of-the-art oligonucleotide microarrays to examine gene expression patterns in male fathead minnows (Pimephales promelas) exposed to two different sizes of multiwalled carbon nanotubes (MWCNTs).
Adult male fathead minnows were exposed for 48-hours using five different graded concentrations of each nanotube and a control under static renewal conditions. The toxicities of the nanotubes were evaluated using standard toxicity testing protocols. Sampling of the tissues for acute gene expression and histology was done 48-hours post exposure. Gills were subjected to histopathological analysis. Gill, gonad and liver tissues were harvested to run on microarrays. Selection of the animals used for the microarray analysis was based on the mortality observed in each of the treatment groups: the lowest dose to elicit significant mortality (lowest observable adverse effect level, LOAEL), the highest dose in which no mortality was observed (no observable adverse effect level, NOAEL), and the control treatment group. We measured gene expression using a fully annotated 15,208 gene oligonucleotide microarray and a 2-color reference design for the experiment. The data were normalized and examined for significance using standard software.
The data were analyzed to determine what, if any, pathways are affected in the fathead minnow after acute exposure to MWCNTs. This information should enable us to identify “genetic fingerprints” and to use the database as a tool for identifying contaminants in unknown situations (class prediction), which may lead to an interpretation of human health issues. The research undertaken in the Phase 1 study of nanotubes should help validate the expediency and affordability of the high-density fathead minnow microarrays for compound screening and use in environmental toxicology.
Using Nanoscale Zero-Valent Iron for in situ Groundwater
Remediation of Chlorinated Organic Solvents in Taiwan
Yu-Ting
Wei1, Shian-Chee Wu1, De-Huang Huang2, Hsing-Lung
Lien3. (1) Graduate Institute of Environmental Engineering, National
Taiwan University, Taipei, Taiwan, ROC; (2) Chinese Petroleum Corporation,
Kaohsiung, Taiwan, ROC; (3) Department of Civil and Environmental
Engineering, National University of Kaohsiung, Kaohsiung, Taiwan, ROC
A 40-m2 pilot-scale field study was conducted to investigate the use of palladized nanoscale zero-valent iron (NZVI) for remediation of groundwater contaminated with a variety of chlorinated organic solvents including vinyl chloride (VC), dichloroethanes and dichloroethylenes in southern Taiwan. Major contaminant is VC that has a concentration ranging from 10 to 5000 mg/L. The concentration distribution is depth-dependent at the site where contaminant concentrations increased with depth. A total iron mass of about 20 kg on-site synthesized NZVI (Pd 0.05wt%) suspended in 8,500 L water was injected via gravity into the sandy aquifer. Twelve multi-level monitoring wells allowing to collect samples from three different depths (6, 12, 18 m) were installed. For a monitoring period of 2 months, a spatial and temporal decrease in VC concentrations was observed. VC concentrations in upper and medium levels were relatively lower (< 100 mg/L) than those in the bottom level (>1000 mg/L). The degradation efficiency was greater than 90% at both upper and medium levels but was about 60-85% at the bottom level. Oxidation-reduction potential (ORP) measurements indicated a homogeneous reducing condition (ORP -450 ~ -280 mV) was achieved in the testing field. Analysis of total iron concentrations found iron was mainly trapped at the upper level. No strong correlation among ORP, total iron concentration and the VC degradation efficiency was observed. Nevertheless, the former two parameters suggested NZVI is mobile.
Water Pollution Control Using Functional Nanomaterials
Glen E. Fryxell, Richard Skaggs, Shas V. Mattigod, Dawn Wellman, Kent Parker, Wassana Yantasee, R. Shane Addleman, Xiaohong S. Li, Yongsoon Shin, Pacific Northwest Laboratory, U.S. Department of Energy, USA
In the course of the last decade, there has been an explosion in the amount of research performed in the area of nanostructured materials. Of central importance in this arena is the multitude of reports dealing with the surfactant templated synthesis of mesoporous ceramic materials. Porosity in the “meso-“ range (i.e. between about 2 nm and 200 nm) provides a huge amount of surface area in a very small volume. Surface area is a key consideration when designing and building a sorbent material since all sorption events take place at a surface. Another advantage provided by these mesoporous ceramics is the rigid nature of the ceramic backbone alleviates the problems associated with solvent swelling and particle attrition encountered with typical polymer-based ion exchange resins.
This presentation will discuss the functionalization of these mesoporous materials with functionalized organosilanes that are tailored to bind heavy metals to remove them from contaminated waters. For example, Hg is a “soft” Lewis acid, therefore we targeted the installation of “soft” Lewis bases, in this case alkyl thiols, to take advantage of sulfur’s legendary affinity for mercury. Preparation of thiol terminated self-assembled monolayers in mesoporous supports (SAMMS®) is readily accomplished in an environmentally friendly (“green”) fashion, and creates a powerful new class of mercury sorbent. These functional nanoporous materials are now commercially available from Steward Environmental Solutions (of Chattanooga, TN). Laboratory tests have shown that Hg is captured quickly and efficiently from a variety of media, including groundwater, contaminated oils, and even contaminated chemical warfare agents. Once bound, the Hg is held fast and does not leach off. Other classes of SAMMS have been tailored to bind other targets, like arsenate, chromate, uranium, and cesium.