Final Report: Synthesis and Application of a New Class of Stabilized Nanoscale Iron Particles for Rapid Destruction of Chlorinated Hydrocarbons in Soil and Groundwater

EPA Grant Number: GR832373
Title: Synthesis and Application of a New Class of Stabilized Nanoscale Iron Particles for Rapid Destruction of Chlorinated Hydrocarbons in Soil and Groundwater
Investigators: Zhao, Dongye , Roberts, Christopher B. , He, Feng
Institution: Auburn University Main Campus
EPA Project Officer: Hahn, Intaek
Project Period: August 1, 2005 through July 31, 2008 (Extended to July 31, 2009)
Project Amount: $280,215
RFA: Greater Research Opportunities: Research in Nanoscale Science Engineering and Technology (2004) RFA Text |  Recipients Lists
Research Category: Hazardous Waste/Remediation , Nanotechnology , Safer Chemicals

Objective:

The main objectives of the study were to: 1) develop an optimized protocol to synthesize highly dispersed zero-valent iron (ZVI) nanoparticles for the rapid destruction of chlorinated hydrocarbons in soil and groundwater; 2) determine the factors affecting the size, delivery, transportability, and reactivity of the new stabilized Fe-Pd nanoparticle for in situ dechlorination in the subsurface; 3) investigate the feasibility of this stabilized Fe-Pd nanoparticles for soil-sorbed TCE degradation; and 4) evaluate the in-situ application of Fe-Pd bimetallic nanoparticles for groundwater treatment in a field demonstration.

Summary/Accomplishments (Outputs/Outcomes):

In accord with the research objectives, this project achieved the following major results:

  1. Developed a new method for synthesizing a new class of starch- or carboxymethyl cellulose stabilized ZVI nanoparticles of controllable size and transportability. The strategy has been widely cited and turned out to be highly useful for preparing dispersible nanoparticles for a variety of environmental remediation uses (e.g., in situ immobilization of toxic metals in soils and sediments)
  2. Produced one patented technology for in situ remediation of chlorinated hydrocarbons in soils and groundwater using polysaccharide stabilized ZVI nanoparticles. The project also was indirectly responsible for two other U.S. patents involving in situ remediation of toxic metals in water, soils, and sediments using polysaccharide stabilized nanoparticles.
  3. Explored the feasibility of the technology for in situ dechlorination of soil-sorbed chlorinated solvents and quantified factors that affect the degradation efficiency.
  4. Carried out two pilot tests at one California site and one Alabama site, both indicating tremendous practical potential in terms of technical effectiveness and cost competitiveness.

Complete details of technical aspects.
This research resulted in more than 19 journal papers and more than 30 presentations and invited seminars. Some of the primary findings and results are summarized as follows.

Stabilization of palladized iron (Fe-Pd) nanoparticles with sodium carboxymethyl cellulose (CMC).
We investigated the feasibility of using CMC as a novel stabilizer for preparing more stable and chemically reactive Fe-Pd nanoparticles for the dechlorination process. Compared to nonstabilized Fe-Pd particles, the CMC-stabilizednanoparticles displayed markedly improved stability against aggregation, chemical reactivity, and soil transport. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) analyses indicated that the CMC-stabilized nanoparticles with a diameter <17.2 nm are highly dispersed in water. Fourier transform infrared (FTIR) spectroscopy results suggested that CMC molecules were adsorbed to iron nanoparticles primarily through the carboxylate groups through monodentate complexation. In addition, -OH groups in CMC were also involved in interactions with iron particles. Batch dechlorination tests demonstrated that the CMC-stabilized nanoparticles degraded trichloroethene (TCE) 17 times faster than their nonstabilized counterparts based on the initial pseudo-first-order rate constant. Last, column tests showed that the stabilized nanoparticles can be readily transported in a loamy-sand soil and then eluted completely with three bed volumes of deionized (DI) water.

Manipulating the size and dispersibility of ZVI naoparticles by use of carboxymethyl cellulose stabilizers.
The factors that affect the size and size distribution of sodium carboxymethyl cellulose (NaCMC) stabilized Fe nanoparticles were investigated, including the CMC/Fe2+ molar ratio and initial Fe2+ concentration, CMC structure, such as molecular weight and degree of substitution, synthesizing temperature, NaBH4 adding rate and mixing, synthesizing pH and cations in water. At an initial Fe2+ concentration of 0.1 g/L and with 0.2% (w/w) of CMC (Mr ) 90 000), nanoparticles with a hydrodynamic diameter of 18.6 nm were obtained. Smaller nanoparticles were obtained as the CMC/Fe2+ molar ratio was increased. When the initial Fe2+ concentration was increased to 1 g/L, only 1/4 of the CMC was needed to obtain similar nanoparticles. On an equal weight basis, CMC with a greater Mr or higher D.S. (degree of substitution) gave smaller nanoparticles, and lower the synthesizing temperature favored the formation of smaller nanoparticles. It is proposed that CMC stabilizes the nanoparticles through the accelerating nucleation of Fe atoms during the formation of ZVI nanoparticles and, subsequently, forms a bulky and negatively charged layer via sorption of CMC molecules on the ZVI nanoparticles, thereby preventing the nanoparticles from agglomeration through electrosteric stabilization. NaBH4 adding rate as low as 1 ml/min caused the obvious aggregation of Fe nanoparticles. Further increase of adding rate to 10ml/min reduced the primary particle size to 16.2nm. However, a faster adding rate 20 ml/min caused the particle size increase back to 18.5nm due to inefficient dispersion of the fast generated nuclei. In agreement with the classical coagulation theory, the presence of high concentrations of cations (Na+ and Ca2+) promoted agglomeration of the nanoparticles. The strategy for manipulating the size of the ZVI nanoparticles may facilitate more effective applications of ZVI nanoparticles for in situ dechlorination in soils and groundwater.

Hydrodechlorination of TCE using stabilized Fe-Pd nanoparticles: Reaction mechanism and effects of stabilizers, catalysts and reaction conditions.
Another study was conducted to investigate the effect of carboxymethyl cellulose as a stabilizer on the reactivity of CMC-stabilized Fe-Pd nanoparticles toward trichloroethylene (TCE). The pseudo-first-order TCE degradation rate increased from 0.86 h-1 to 6.8 h-1 as the CMC-to-Fe molar ratio increased from 0 to 0.0124. However, a higher CMC-to-Fe ratio inhibited the TCE degradation. Within the same homologous series, CMC of greater molecular weight resulted in more reactive nanoparticles for TCE hydrodechlorination. Hydrogen (either residual hydrogen from zero-valent iron (ZVI) nanoparticle synthesis or hydrogen evolved from ZVI corrosion) can serve as effective electron donors for TCE dechlorination in the presence of Pd (either coated on ZVI or as separate nanoparticles). Decreasing reaction pH from 9.0 to 6.0 increased the TCE reduction rate by 11.5 times, but enhanced the Fe corrosion rate by 31.4 times based on the pseudo-first order rate constant. Decreasing pH shifted the rate controlling step of TCE reduction from Fe corrosion to hydrodechlorination. Ionic strength (<0.51 M) did not significantly affect TCE reduction.

Transport of carboxymethyl cellulose stabilized iron nanoparticles in porous media: Column experiments and modeling.
This work investigated transport of CMC-stabilized ZVI nanoparticles (CMC-Fe) using column breakthrough experiments and model simulations. The nanoparticles (18.1 ± 2.5 nm) were transportable through four saturated model porous media: coarse and fine glass beads, clean sand, and sandy soil. The transport data were interpreted using both classical filtration theory and a modified convection–dispersion equation with a first-order removal rate law. At full breakthrough, a constant concentration plateau (Ce/C0) was reached, ranging from 0.99 for the glass beads to 0.69 for the soil. Although Brownian diffusion was the predominant mechanism for particle removal in all cases, gravitational sedimentation also played an important role, accounting for 30% of the overall single-collector contact efficiency for the coarse glass beads and 6.7% for the soil. The attachment efficiency for CMC-Fe was found to be 1–2 orders of magnitude lower than reported for ZVI nanoparticles stabilized with other commercial polymers. The particle removal and travel distance are strongly dependent on interstitial flow velocity, but only modestly affected by up to 40 mM of calcium. Simulation results indicate that once delivered, 99% of the nanoparticles will be removed by the soil matrix within 16 cm at a groundwater flow velocity of 0.1 m/day, but may travel over 146 m at flow velocity of 61 m/day.

Degradation of soil-sorbed TCE by stabilized zero valent iron nanoparticles: Effects of sorption, surfactants, and natural organic matter.
This work followed our previous experimental work and focused on soil-sorbed TCE remediation. Abiotic reductive dechlorination of trichloroethylene in 2 soils by CMC-stabilized ZVI nanoparticles was characterized in batch tests, with and without surfactant.  Four representative surfactants were tested in the aqueous degradation and TCE desorption experiments, including two anionic surfactants SDS (sodium dodecyl sulfate) and SDBS (sodium dodecyl benzene sulfonate), a cationic surfactant hexadecyltrimethylammonium (HDTMA) bromide, and a non-ionic surfactant Tween 80. All four surfactants were observed to enhance the extent and rate of TCE desorption at a concentration below or above cmc (critical micelle concentration), with the anionic surfactant SDS being the most effective. TCE degradation in the water phase with surfactants at a range of concentrations (i.e., sub- and supra-critical micelle concentration) was also examined. Dechlorination kinetics was adequately described as pseudo-first-order reaction. The kinetics rate constant increased to 0.16min-1 with addition of 1xcmc SDS in the reactor, much higher than 0.063 min-1 without a surfactant. Soil-sorbed TCE degradation in 2 soils in the presence of SDS was investigated. After 40 hours of dechlorination with ZVI nanoparticles, the soil-sorbed TCE was degraded by 49% with 5cmc SDS and 39% with 1 cmc SDS, respectively. The same experiment without surfactant, 44% of total TCE was degraded.  Evidently, SDS was able to enhance the rate and extent of TCE degradation in the soil only at high concentrations (≥5 xcmc). SDS was much more effective for degradation of TCE sorbed in the smith farm soil. In the absence of surfactant, nearly 80% of soil-sorbed TCE was degraded within 8h, and finally 83% of total TCE was removed after 47.5 hours. When 1xcmc SDS was added, >90% of TCE was degraded in <30h. The natural organic matter from the soil matrix inhibited the TCE degradation. The observed pseudo-first order rate constant was reduced from1.224 hr-1 when no soil exudates were added to 0.8092 and 0.4056 hr-1, respectively, when 40 ppm and 350 ppm TOC was present.

Field assessment of carboxymethyl cellulose stabilized iron nanoparticles for in situ destruction of chlorinated solvents in source zone.
This study pilot-tested carboxymethyl cellulose (CMC) stabilized zero-valent-iron (ZVI) nanoparticles for in-situ destruction of chlorinated ethenes such as perchloroethylene (PCE) and trichloroethylene (TCE) and polychlorinated biphenyls (PCBs) that had been in groundwater for decades. The test site was located in a well-characterized secondary source zone of PCBs and chlorinated ethenes. Four test wells were installed along the groundwater flow direction (spaced 5 ft apart), including one injection well (IW), one up-gradient monitoring well (MW-3) and two downgradient monitoring wells (MW-1 and MW-2). Stabilized nanoparticle suspension was prepared on site and injected into the 50-ft deep, unconfined aquifer. Approximately 150 gallons of 0.2 g/L Fe-Pd (CMC = 0.1 wt%, Pd/Fe = 0.1 wt%) was gravity-fed through IW-1 over a 4-h period (Injection #1). One month later, another 150 gallons of 1.0 g/L Fe-Pd (CMC = 0.6 wt%, Pd/Fe = 0.1 wt%) was injected into IW-1 at an injection pressure < 5 psi (Injection #2). When benchmarked against the tracer, approximately 37.4% and 70.0% of the injected Fe was detected in MW-1 during injection #1 and #2, respectively, confirming the soil mobility of the nanoparticles through the aquifer, and higher mobility of the particles was observed when the injection was performed under higher pressure. Rapid degradation of PCE and TCE was observed in both MW-1 and MW-2 following each injection, with the maximum degradation being observed during the first week of the injections. The chlorinated ethenes concentrations gradually returned to their pre-injection levels after ~2 weeks, indicating exhaustion of the ZVI's reducing power. However, the injection of CMC-stabilized nanoparticle and the abiotic reductive dechlorination process appeared to have boosted a long-term in situ biological dechlorination thereafter, which was evidenced by the fact that PCE and TCE concentrations showed further reduction after two weeks. After 596 days from the first injection, the total chlorinated ethenes concentration decreased by about 40% and 61% in MW-1 and MW-2, respectively. No significant longterm reduction of PCB 1242 was observed in MW-1, but a reduction of 87% was evident in MW-2. During the 596 days of testing, the total concentrations of cis-DCE (dichloroethylene) and VC (vinyl chloride) decreased by 20% and 38% in MW-1 and MW-2, respectively. However, the combined fraction of cis-DCE and VC in the total chlorinated ethenes (PCE, TCE, cis-DCE and VC) increased from 73% to 98% and from 62% to 98%, respectively, which supports the notion that biological dechlorination of PCE and TCE was active. It is proposed that CMC-stabilized ZVI-Pd nanoparticles facilitated the early stage rapid abiotic degradation. Over the long run, the existing biological degradation process was boosted with CMC as the carbon source and hydrogen from the abiotic/biotic processes as the electron donor, resulting in the sustained enhanced destruction of the chlorinated organic chlorinated ethenes in the subsurface.

Push-pull tests to field demonstrate the mobility and reactivity of carboxymethyl cellulose stabilized iron nanoparticles in saturated zone.
This paper describes the results of the first single well push-pull tests conducted to evaluate the migration of carboxymethyl cellulose (CMC) stabilized nanoscale zero-valent iron (ZVI) in a saturated zone and their reactivity toward chlorinated ethenes. CMC-stabilized nanoscale ZVI particles were synthesized on site by reducing ferrous ions with borohydride in water in presence of CMC. The mono nanoscale ZVI or bimetallic Fe-Pd nanoparticle suspension were then injected into the well at different screen intervals during three push-pull tests. After different time intervals, the groundwater-suspension mixture was recovered by pumping from the well.  The comparison between tracer Br- and iron concentrations indicated that the CMC-stabilized nanoscale ZVI particles were mobile in the aquifer but appeared to lose mobility with time due to the interactions between particles and soil grain surface. After 13 hours in the aquifer, the iron particles became essentially immobilized. During push-pull test with injection of Fe-Pd nanoparticles, ethane concentrations increased from undetectable to 65 ppb in extracted groundwater and then gradually decreased, indicating the abiotic degradation of chlorinated ethenes. Meanwhile, ethene concentration continuously increased from 10 to 45 ppb during the whole extraction period. These results may imply an incomplete abiotic degradation and/or a biologically enhanced reductive dechlorination of VOCs in the presence of nanoscale ZVI.

One-step “green” synthesis of Pd nanoparticles of controlled size and their catalytic activity for trichloroethene hydrodechlorination.
One promising technology to remediate TCE contaminated groundwater is using Pd particles to catalyze the hydrodechlorination of TCE by H2 to readily biodegradable ethane. A straightforward, one-step “green” approach for preparing Pd nanoparticles of controlled size and size distribution. The new catalysts were synthesized using a low-cost, biocompatible cellulose, sodium carboxymethyl cellulose (CMC), as a stabilizer and ascorbic acid as a reducing agent at temperatures ranging from 22 to 95 °C. The mean size and polydispersivity (expressed as standard deviation, SD) of the Pd nanoparticles was exponentially reduced by increasing the preparation temperature from 22 to 95 °C. At 95 °C, nearly monodisperse Pd nanoparticles were obtained with a mean diameter of 3.6 nm (SD ) 0.5 nm). The Pd nanoparticles exhibited high catalytic reactivity when tested for hydrodechlorination of trichloroethene in the presence of H2. The observed pseudo-first-order reaction rate constant, kobs, was up to 692 L g-1 min-1, which is comparable to the Pd nanoparticles synthesized per the conventional borohydride reduction method. This new approach not only offers a simple way to manipulate particle size and size distribution but also eliminates the need of borohydride, which is much more costly and less environmentally friendly than the ascorbic acid used in this work.

Polysugar-stabilized Pd nanoparticles exhibiting high catalytic activities for hydrodechlorination of TCE.
We present a straightforward and environmentally friendly aqueous-phase synthesis of small Pd nanoparticles (approximately 2.4 nm under the best stabilization) by employing a “green,” inexpensive, and biodegradable/biocompatible polysugar, sodium carboxymethylcellulose (CMC), as a capping agent. The Pd nanoparticles exhibited rather high catalytic activity (observed pseudo-first-order reaction kinetic rate constant, kobs, is up to 828 L g-1 min-1) for the hydrodechlorination of environmentally deleterious trichloroethene (TCE) in water. Fourier transform IR (FT-IR) spectra indicate that CMC molecules interact with the Pd nanoparticles via both carboxyl (−COO-) and hydroxyl (−OH) groups, thereby functioning to passivate the surface and suppress the growth of the Pd nanoparticles. Hydrodechlorination of TCE using differently sized CMC-capped Pd nanoparticles as catalyst was systematically investigated in this work. Both the catalytic activity (kobs) and the surface catalytic activity (turnover frequency, TOF) of these CMC-capped Pd nanoparticles for TCE degradation are highly size-dependent. This point was further verified by a comparison of the catalytic activities and surface catalytic activities of CMC-capped Pd nanoparticles with those of β-d-glucose-capped Pd and neat Pd nanoparticles for TCE degradation.

An evaluation of the new technology.
Based on our lab and field test data, the nanoparticle cost for destroying TCE is ~$100/lb-TCE, compared to ~$10,000/lb with pump-and-treat, and $310~530 for excavating one cubic yard of a shallow soil. With respect to cleanup timeframe, the technology can potentially reduce the timeframe from >500 for pump-and-treat or PRB to <20 years.  When with other in situ methods, such as thermal or chemical oxidation, our technology offers a great advantage of much reduced risk in terms of worker risk, contaminant migration, and environmental perturbation. Because this approach can significantly accelerate the cleanup of contaminated groundwater, it may reduce life-cycle treatment costs by as much as 90%, and can save billions of dollars to treat the large volumes of contaminated groundwater at thousands of sites containing chlorinated solvents. This technology also enables to in situ attack contaminant plumes sitting in deep aquifers, which had been impossible with traditional technologies.


Journal Articles on this Report : 18 Displayed | Download in RIS Format

Other project views: All 35 publications 19 publications in selected types All 19 journal articles
Type Citation Project Document Sources
Journal Article Bennett P, He F, Zhao D, Aiken B, Feldman L. In situ testing of metallic iron nanoparticle mobility and reactivity in a shallow granular aquifer. Journal of Contaminant Hydrology 2010;116(1-4):35-46.
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GR832373 (Final)
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  • Journal Article He F, Zhao D, Liu J, Roberts CB. Stabilization of Fe-Pd nanoparticles with sodium carboxymethyl cellulose for enhanced transport and dechlorination of trichloroethylene in soil and groundwater. Industrial & Engineering Chemistry Research 2007;46(1):29-34.
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  • Journal Article He F, Zhao D. Manipulating the size and dispersibility of zerovalent iron nanoparticles by use of carboxymethyl cellulose stabilizers. Environmental Science & Technology 2007;41(17):6216-6221.
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  • Journal Article He F, Zhao D. Hydrodechlorination of trichloroethene using stabilized Fe-Pd nanoparticles: reaction mechanism and effects of stabilizers, catalysts and reaction conditions. Applied Catalysis B: Environmental 2008;84(3-4):533-540.
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  • Journal Article He F, Zhao D. Response to comment on "Manipulating the size and dispersibility of zerovalent iron nanoparticles by use of carboxymethyl cellulose stabilizers." Environmental Science & Technology 2008;42(9):3480.
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  • Journal Article He F, Liu JC, Roberts CB, Zhao D. One-step "green" synthesis of Pd nanoparticles of controlled size and their catalytic activity for trichloroethene hydrodechlorination. Industrial & Engineering Chemistry Research 2009;48(14):6550-6557.
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  • Journal Article He F, Zhang M, Qian T, Zhao D. Transport of carboxymethyl cellulose stabilized iron nanoparticles in porous media: column experiments and modeling. Journal of Colloid and Interface Science 2009;334(1):96-102.
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  • Journal Article Joo SH, Zhao D. Destruction of lindane and atrazine using stabilized iron nanoparticles under aerobic and anaerobic conditions: effects of catalyst and stabilizer. Chemosphere 2008;70(3):418-425.
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  • Journal Article Kanel SR, Goswami RR, Clement TP, Barnett MO, Zhao D. Two dimensional transport characteristics of surface stabilized zero-valent iron nanoparticles in porous media. Environmental Science & Technology 2008;42(3):896-900.
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  • Journal Article Liu J, He F, Durham E, Zhao D, Roberts CB. Polysugar-stabilized Pd nanoparticles exhibiting high catalytic activities for hydrodechlorination of environmentally deleterious trichloroethylene. Langmuir 2008;24(1):328-336.
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  • Journal Article Liu JC, He F, Gunn TM, Zhao D, Roberts CB. Precise seed-mediated growth and size-controlled synthesis of palladium nanoparticles using a green chemistry approach. Langmuir 2009;25(12):7116-7128.
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  • Journal Article Liu R, Zhao D. In situ immobilization of Cu(II) in soils using a new class of iron phosphate nanoparticles. Chemosphere 2007;68(10):1867-1876.
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  • Journal Article Pan G, Li L, Zhao D, Chen H. Immobilization of non-point phosphorus using stabilized magnetite nanoparticles with enhanced transportability and reactivity in soils. Environmental Pollution 2010;158(1):35-40.
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  • Journal Article Xiong Z, Zhao D, Pan G. Rapid and complete destruction of perchlorate in water and ion-exchange brine using stabilized zero-valent iron nanoparticles. Water Research 2007;41(15):3497-3505.
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  • Journal Article Xiong Z, He F, Zhao D, Barnett MO. Immobilization of mercury in sediment using stabilized iron sulfide nanoparticles. Water Research 2009;43(20):5171-5179.
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  • Journal Article Xiong Z, Zhao D, Pan G. Rapid and controlled transformation of nitrate in water and brine by stabilized iron nanoparticles. Journal of Nanoparticle Research 2009;11(4):807-819.
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  • Journal Article Xu Y, Zhao D. Reductive immobilization of chromate in water and soil using stabilized iron nanoparticles. Water Research 2007;41(10):2101-2108.
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  • Journal Article Zhang M, Wang Y, Zhao D, Pan G. Immobilization of arsenic in soils by stabilized nanoscale zero-valent iron, iron sulfide (FeS), and magnetite (Fe3O4) particles. Chinese Science Bulletin 2010;55(4-5):365-372.
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  • Supplemental Keywords:

    RFA, Scientific Discipline, Waste, Water, TREATMENT/CONTROL, Sustainable Industry/Business, Contaminated Sediments, Treatment Technologies, Sustainable Environment, Environmental Chemistry, Technology for Sustainable Environment, Environmental Engineering, dechlorination, decontamination, nanoparticle remediation, groundwater rememdiation, contaminated sediment, nanotechnology, chlorinated aromatic hydrocarbons (CAHs), chlorinated hydrocarbons (CHCs), nanomaterials, contaminated groundwater

    Progress and Final Reports:

    Original Abstract
  • 2006 Progress Report
  • 2007 Progress Report
  • 2008