James Farrell

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Courses

Scholarly Contributions

Chapters

• Farrell, J., Wang, J., & LeBlanc, R. (2003). Electrochemical Destruction of Triclosan. In Book(pp 99-112). American Chemical Society. doi:10.1021/bk-2004-0863.ch008
• Farrell, J., Melitas, N., & Conklin, M. (2002). Understanding the Mechanisms Controlling the Kinetics of Arsenate and Chromate Removal from Solution Using Zero Valent Iron. In Book(pp 165-180). American Chemical Society. doi:10.1021/bk-2002-0837.ch012
• Li, T., & Farrell, J. (2002). Mechanisms Controlling Chlorocarbon Reduction at Iron Surfaces.
• Grathwohl, P., Farrell, J., & Reinhard, M. (1990). Desorption kinetics of volatile organic contaminants from aquifer materials. In Contaminated Soil’90(pp 343--350). Springer.
• Grathwohl, P., Farrell, J., & Reinhard, M. (1990). Desorptionskinetik Fl\"uchtiger Organischer Verbindungen bei Aquifer Material. In Altlastensanierung’90(pp 401--408). Springer.

Journals/Publications

• Farrell, J., Hickenbottom, K., Achilli, A., Phakdon, T., & Xu, J. (2022). Pretreatment of Reverse Osmosis Concentrate from Reclaimed Water for Conventional and High-Efficiency Reverse Osmosis and Evaluation of Electrochemical Production of Reagents. ACS ES&T Water, 2(6), 1022-1030. doi:10.1021/acsestwater.2c00015
• Farrell, J., Martinez, R. J., Chen, Y., Baygents, J. C., & Gervasio, D. (2020). Alkaline Stability of Novel Aminated Polyphenylene-Based Polymers in Bipolar Membranes. J. Membrane Sci. Res..
• Farrell, J., Snyder, S. A., Achilli, A., Lopez-Prieto, I. J., Park, M., & AzadiAghdam, M. (2020). Pretreatment for water reuse using fluidized bed crystallization. Journal of Water Process Engineering.
• Farrell, J., & Martinez, R. J. (2019). Understanding Hydroxide Reactions with Guanidinium-based Anion Exchange Polymers under Conditions Relevant to Bipolar Membrane Electrodialysis. J Computational and Theoretical Chemistry, 1155, 75-81. doi:10.1016/j.comptc.2019.03.020
• Farrell, J., Martínez‐Huitle, C. A., Brillas, E., & Einaga, Y. (2019). Trends in Synthetic Diamond for Electrochemical Applications. ChemElectroChem, 6(17), 4330-4331. doi:10.1002/celc.201901088
• Chen, Y., Baygents, J. C., & Farrell, J. (2017). Evaluating electrocoagulation and chemical coagulation for removing dissolved silica from high efficiency reverse osmosis (HERO) concentrate solutions. Journal of Water Process Engineering, 16, 50-55. doi:10.1016/j.jwpe.2016.12.008
• Chen, Y., James, B. C., & Farrell, J. (2017). Removing Phosphonate Antiscalants from Membrane Concentrate Solutions using Ferric Hydroxide Adsorbents. Journal of Water Process Engineering, 19, 18-25.
• Chen, Y., James, B. C., & Farrell, J. (2017). Understanding Competitive Adsorption of NTMP and Silica on Ferric Hydroxide. Environmental Engineering Science, 34(6), 401-409. doi:10.1089/ees.2016.0441
• Farrell, J. (2017). Tridentate arsenate complexation with ferric hydroxide and its effect on the kinetics of arsenate adsorption and desorption. Chemosphere, 184, 1209-1217. doi:10.1016/j.chemosphere.2017.06.099
• Martinez, R., & Farrell, J. (2017). Understanding Nitrilotris(methylenephosphonic acid) Reactions with Ferric Hydroxide. Chemosphere, 175, 490-496.
• Aghdam, M. A., Zraick, F., Simon, J., Farrell, J., & Snyder, S. A. (2016). A novel brine precipitation process for higher water recovery. DESALINATION, 385, 69-74.
• Chen, Y., Davis, J., Nguyen, C., Baygents, J. C., & Farrell, J. (2016). Electrochemical Ion Exchange Regeneration and Fluidized Bed Crystallization for Zero Liquid Discharge Water Softening. Environmental Science and Technology, 50, 5900-5907.
• Farrell, J., Nguyen, C. H., Chen, Y., Davis, J. R., & Baygents, J. C. (2016). Electrochemical Ion-Exchange Regeneration and Fluidized Bed Crystallization for Zero-Liquid-Discharge Water Softening. Environmental Science & Technology, 50(11), 5900-5907. doi:10.1021/acs.est.5b05606
• Davis, J. R., Chen, Y., Baygents, J. C., & Farrell, J. (2015). Production of Acids and Bases for Ion Exchange Regeneration from Dilute Salt Solutions Using Bipolar Membrane Electrodialysis. ACS SUSTAINABLE CHEMISTRY & ENGINEERING, 3(9), 2337-2342.
• Farrell, J., Chen, Y., Davis, J. R., & Baygents, J. C. (2015). Production of Acids and Bases for Ion Exchange Regeneration from Dilute Salt Solutions Using Bipolar Membrane Electrodialysis. ACS Sustainable Chemistry & Engineering, 3(9), 2337-2342. doi:10.1021/acssuschemeng.5b00654
• Chaudhary, B. K., & Farrell, J. (2014). Preparation and Characterization of Homopolymer Polyacrylonitrile-Based Fibrous Sorbents for Arsenic Removal. Environmental engineering science, 31(11), 593--601.
• Davis, J. R., Baygents, J. C., & Farrell, J. (2014). Effect of current density and sulfuric acid concentration on persulfuric acid generation by boron-doped diamond film anodes. Journal of Applied Electrochemistry, 44(7), 841--848.
• Davis, J., Baygents, J. C., & Farrell, J. (2014). Understanding Persulfate Production at Boron Doped Diamond Film Anodes. Electrochimica Acta, 150, 68--74.
• Farrell, J., & Chaudhary, B. (2015). Understanding Regeneration of Arsenate Loaded Ferric Hydroxide-based Adsorbents. Environmental Engineering Science, 32, 1-5.
• Farrell, J., & Chaudhary, B. K. (2014). Preparation and Characterization of Homopolymer Polyacrylonitrile-Based Fibrous Sorbents for Arsenic Removal. Environmental Engineering Science, 31(11), 593-601. doi:10.1089/ees.2014.0169
• Hubler, D. K., Baygents, J. C., Chaplin, B. P., & Farrell, J. (2014). Understanding Chlorite, Chlorate and Perchlorate Formation When Generating Hypochlorite Using Boron Doped Diamond Film Electrodes. ECS Transactions, 58(35), 21--32.
• Hubler, D., Baygents, J., Chaplin, B., & Farrell, J. (2014). Understanding Chlorite and Chlorate Formation Associated with Hypochlorite Generation at Boron Doped Diamond Film Anodes. Journal of The Electrochemical Society, 161(12), E182--E189.
• Chaplin, B. P., Hubler, D. K., & Farrell, J. (2013). Understanding anodic wear at boron doped diamond film electrodes. Electrochimica Acta, 89, 122-131.
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  Abstract: This research investigated the mechanisms associated with anodic wear of boron-doped diamond (BDD) film electrodes. Cyclic voltammetry (CV), x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and electrochemical impedance spectroscopy (EIS) were used to measure changes in electrode response and surface chemistry as a function of the charge passed and applied current density. Density functional theory (DFT) modeling was used to evaluate possible reaction mechanisms. The initial hydrogen-terminated surface was electrochemically oxidized at lower potentials than water oxidation (≤ 1.83 V/SHE), and was not catalyzed by the hydrogen-terminated surface. In the region where water oxidation produces hydroxyl radicals (OH), the hydrogen-terminated surface may also be oxidized by chemical reaction with OH. Oxygen atoms became incorporated into the surface via reaction of carbon atoms with OH, forming both C O and C-OH functional groups, that were also detected by XPS measurements. Experimental and DFT modeling results indicate that the oxygenated diamond surface lowers the potential for activationless water oxidation from 2.74 V/SHE for the hydrogen terminated surface to 2.29 V/SHE for the oxygenated surface. Electrode wear was accelerated at high current densities (i.e., 500 mA cm-2), where SEM results indicated oxidation of the BDD film resulted in significant surface roughening. These results are supported by EIS measurements that document an increase in the double-layer capacitance as a function of the charge passed. DFT simulations provide a possible mechanism that explains the observed diamond oxidation. DFT simulation results indicate that BDD edge sites (=CH2) can be converted to COOH functional groups, which are further oxidized via reactions with OH to form H 2CO3(aq.) with an activation energy of 58.9 kJ mol -1. © 2012 Elsevier Ltd. All Rights Reserved.
• Farrell, J. (2013). 43535-AC5 Understanding Water and Organic Compound Oxidation at Boron Doped Diamond Film Electrodes.
• Farrell, J., & Chaudhary, B. K. (2013). Understanding arsenate reaction kinetics with ferric hydroxides. Environmental Science and Technology, 47(15), 8342-8347.
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  PMID: 23806140;Abstract: Understanding arsenic reactions with ferric hydroxides is important in understanding arsenic transport in the environment and in designing systems for removing arsenic from potable water. Many experimental studies have shown that the kinetics of arsenic adsorption on ferric hydroxides is biphasic, where a fraction of the arsenic adsorption occurs on a time scale of seconds while full equilibrium may require weeks to attain. This research employed density functional theory modeling in order to understand the mechanisms contributing to biphasic arsenic adsorption kinetics. The reaction energies and activation barriers for three modes of arsenate adsorption to ferric hydroxides were calculated. Gibbs free energies of reaction depended on the net charge of the complexes, which is a function of the system pH value. Physical adsorption of arsenate to ferric hydroxide proceeded with no activation barrier, with Gibbs free energies of reaction ranging from -21 to -58 kJ/mol. The highest Gibbs free energies of reaction for physical adsorption resulted from negative charge assisted hydrogen bonding between H atoms on the ferric hydroxide and O atoms in arsenate. The conversion of physically adsorbed arsenate into monodentate surface complexes had Gibbs free energies of activation ranging from 62 to 73 kJ/mol, and Gibbs free energies of reaction ranging from -23 to -38 kJ/mol. The conversion of monodentate surface complexes to bidentate, binuclear complexes had Gibbs free energies of activation ranging from 79 to 112 kJ/mol and Gibbs free energies of reaction ranging from -11 to -55 kJ/mol. For release of arsenate from uncharged bidentate complexes, energies of activation as high as 167 kJ/mol were encountered. Increasingly negative charges on the complexes lowered the activation barriers for desorption of arsenate, and in complexes with -2 charges, the highest activation barrier was 65 kJ/mol. This study shows that the slow kinetics associated with arsenic adsorption and desorption can be attributed to the high Gibbs free energies of activation for forming and breaking bonds with the ferric hydroxide. © 2013 American Chemical Society.
• Farrell, J., Farrell, J. -., Luo, J., & Farrell, J. -. (2013). Understanding pH Effects on Trichloroethylene and Perchloroethylene Adsorption to Iron in Permeable Reactive Barriers for Groundwater Remediation. International journal of environmental science and technology : IJEST, 10(1).
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  Metallic iron filings are becoming increasing used in permeable reactive barriers for remediating groundwater contaminated by chlorinated solvents. Understanding solution pH effects on rates of reductive dechlorination in permeable reactive barriers is essential for designing remediation systems that can meet treatment objectives under conditions of varying groundwater properties. The objective of this research was to investigate how the solution pH value affects adsorption of trichloroethylene (TCE) and perchloroethylene (PCE) on metallic iron surfaces. Because adsorption is first required before reductive dechlorination can occur, pH effects on halocarbon adsorption energies may explain pH effects on dechlorination rates. Adsorption energies for TCE and PCE were calculated via molecular mechanics simulations using the Universal force field and a self-consistent reaction field charge equilibration scheme. A range in solution pH values was simulated by varying the amount of atomic hydrogen adsorbed on the iron. The potential energies associated TCE and PCE complexes were dominated by electrostatic interactions, and complex formation with the surface was found to result in significant electron transfer from the iron to the adsorbed halocarbons. Adsorbed atomic hydrogen was found to lower the energies of TCE complexes more than those for PCE. Attractions between atomic hydrogen and iron atoms were more favorable when TCE versus PCE was adsorbed to the iron surface. These two findings are consistent with the experimental observation that changes in solution pH affect TCE reaction rates more than those for PCE.
• Gao, X., Root, R. A., Farrell, J., Ela, W., & Chorover, J. (2013). Effect of silicic acid on arsenate and arsenite retention mechanisms on 6-L ferrihydrite: A spectroscopic and batch adsorption approach. Applied Geochemistry, 38, 110-120.
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  Abstract: The competitive adsorption of arsenate and arsenite with silicic acid at the ferrihydrite-water interface was investigated over a wide pH range using batch sorption experiments, attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, extended X-ray absorption fine structure (EXAFS) spectroscopy, and density functional theory (DFT) modeling. Batch sorption results indicate that the adsorption of arsenate and arsenite on the 6-L ferrihydrite surface exhibits a strong pH-dependence, and the effect of pH on arsenic sorption differs between arsenate and arsenite. Arsenate adsorption decreases consistently with increasing pH; whereas arsenite adsorption initially increases with pH to a sorption maximum at pH 7-9, where after sorption decreases with further increases in pH. Results indicate that competitive adsorption between silicic acid and arsenate is negligible under the experimental conditions; whereas strong competitive adsorption was observed between silicic acid and arsenite, particularly at low and high pH. In situ, flow-through ATR-FTIR data reveal that in the absence of silicic acid, arsenate forms inner-sphere, binuclear bidentate, complexes at the ferrihydrite surface across the entire pH range. Silicic acid also forms inner-sphere complexes at ferrihydrite surfaces throughout the entire pH range probed by this study (pH 2.8-9.0). The ATR-FTIR data also reveal that silicic acid undergoes polymerization at the ferrihydrite surface under the environmentally-relevant concentrations studied (e.g., 1.0. mM). According to ATR-FTIR data, arsenate complexation mode was not affected by the presence of silicic acid. EXAFS analyses and DFT modeling confirmed that arsenate tetrahedra were bonded to Fe metal centers via binuclear bidentate complexation with average As(V)-Fe bond distance of 3.27. Å. The EXAFS data indicate that arsenite forms both mononuclear bidentate and binuclear bidentate complexes with 6-L ferrihydrite as indicated by two As(III)-Fe bond distances of ~2.92-2.94 and 3.41-3.44. Å, respectively. The As-Fe bond distances in both arsenate and arsenite EXAFS spectra remained unchanged in the presence of Si, suggesting that whereas Si diminishes arsenite adsorption preferentially, it has a negligible effect on As-Fe bonding mechanisms. © 2013 .
• Abe, K., Ahmad, S., Akhavan-Tabatabaei, R., Akhtar, J., Allen, R., Anis, M., Backe, O., Baly, R., Bang, J., Baygents, J., & others, . (2012). 2012 Index IEEE Transactions on Semiconductor Manufacturing Vol. 25. IEEE TRANSACTIONS ON SEMICONDUCTOR MANUFACTURING, 25(4), 673.
• Dakubo, F., Baygents, J. C., & Farrell, J. (2012). Hydrogen Peroxide Removal From Chemical--Mechanical Planarization Wastewater. Semiconductor Manufacturing, IEEE Transactions on, 25(4), 623--629.
• Dakubo, F., Baygents, J. C., & Farrell, J. (2012). Peroxodisulfate assisted leaching of chalcopyrite. Hydrometallurgy, 121, 68--73.
• Dakubo, F., Baygents, J. C., & Farrell, J. (2012). Peroxodisulfate assisted leaching of chalcopyrite. Hydrometallurgy, 121-124, 68-73.
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  Abstract: This research investigated the effectiveness of peroxodisulfate (S 2O 82-) for enhancing copper leaching rates from chalcopyrite. Batch and column experiments were performed using sulfuric acid leach solutions at pH = 2, with and without Na 2S 2O 8. The presence of peroxodisulfate greatly increased copper leaching rates. Tafel analysis and electrochemical impedance spectroscopy experiments performed using chalcopyrite powder electrodes indicated that peroxodisulfate increased the corrosion rate by decreasing the charge transfer resistance for chalcopyrite oxidation. In contrast to the preferential leaching of iron that has been observed for other oxidants added to chalcopyrite leach solutions, peroxodisulfate assisted leaching resulted in the release 1 mol of Cu per mole of Fe, which is identical to their stoichiometric ratio in chalcopyrite. Rates of Cu leaching from chalcopyrite followed a surface reaction rate limited, shrinking-core model with an apparent activation energy of 41 kJ/mol. © 2012 Elsevier B.V. All rights reserved.
• Farrell, J., Megdal, S. B., Hubler, D. K., Baygents, J. C., & Mackay, C. (2012). Evaluating economic effects of semiconductor manufacturing in water-limited regions. Journal - American Water Works Association, 104(2), E100-E106. doi:10.5942/jawwa.2012.104.0024
• Hubler, D. K., Baygents, J. C., & Farrell, J. (2012). Sustainable Electrochemical Regeneration of Copper-Loaded Ion Exchange Media. Industrial \& Engineering Chemistry Research, 51(40), 13259--13267.
• Hubler, D. K., Baygents, J. C., & Farrell, J. (2012). Sustainable electrochemical regeneration of copper-loaded ion exchange media. Industrial and Engineering Chemistry Research, 51(40), 13259-13267.
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  Abstract: An electrochemical method for regenerating copper-loaded ion exchange media was investigated. The method involved circulating a moderate pH regenerant solution between a bed of ion exchange media and an electrochemical cell. The electrochemical regeneration process eliminates more than 99% of the acid and base use associated with conventional regeneration, consumes no water, produces metallic copper, and eliminates the production of a copper-laden sludge. Experiments were performed measuring copper plating rates as a function of the aqueous copper concentration, cell current, and flow rate. Experiments were also performed to determine the equilibrium partitioning of copper ions between the solution and the ion exchange media under loading and regeneration conditions. A mathematical model was developed and calibrated using experimental data, to provide guidance for the design of electrochemical ion exchange regeneration systems. The model incorporates the plating kinetics, the stripping of copper from the resin, and the equilibrium isotherm and predicts aqueous and adsorbed copper concentrations during the regeneration process. The model indicates that, in 789 min, 90% of copper can be removed from a resin loaded with 50 mg(Cu)/g(resin). An economic analysis indicates that energy costs for plating are less than 1% of chemical costs for conventional ion exchange regeneration. © 2012 American Chemical Society.
• Hubler, D. K., Baygents, J. C., Mackay, C., Megdal, S. B., & Farrell, J. (2012). Evaluating economic effects of semiconductor manufacturing in water-limited regions. Journal - American Water Works Association, 104(2), 47-48.
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  Abstract: High-volume semiconductor manufacturing (HVSM) with high demands for freshwater is often located in regions with limited water resources. This nexus of water demand and water scarcity has raised concerns among municipal governments, prompting several to consider water supply restrictions as they plan for economic growth and development. Drawing upon water-use data and economic valuations of land use from Chandler, Ariz., this study compares the fiscal effect of HVSM with three alternative water uses: office, retail, and general manufacturing. Normalizing the economic benefit to net water use (after reclamation) has a marked effect on the fiscal consequences of water uses. The effects generated by mostly nonconsumptive water uses-e.g., HVSM and general manufacturing-increase significantly relative to less water-intensive but more consumptive water uses. Results showed that water-intensive land uses need not be avoided in communities where water is scarce, provided that the community has the facilities to reclaim the wastewater.
• Hubler, D. K., Baygents, J. C., Mackay, C., Megdal, S. B., & Farrell, J. (2012). Evaluating economic effects of semiconductor manufacturing in water-limited regions.. Journal: American Water Works Association, 104(2).
• Hubler, D. K., Baygents, J. C., Mackay, C., Megdal, S. B., Farrell, J., & others, . (2012). Evaluating Economic Effects of Semiconductor Manufacturing in Water-Limited Regions (PDF). Journal-American Water Works Association, 104(2), E100--E106.
• Azizi, O., Hubler, D., Schrader, G., Farrell, J., & Chaplin, B. P. (2011). Mechanism of perchlorate formation on boron-doped diamond film anodes. Environmental science \& technology, 45(24), 10582--10590.
• Chaplin, B. P., Wyle, I., Zeng, H., Carlisle, J. A., & Farrell, J. (2011). Characterization of the performance and failure mechanisms of boron-doped ultrananocrystalline diamond electrodes. Journal of Applied Electrochemistry, 41(11), 1329--1340.
• Chaplin, B. P., Wyle, I., Zeng, H., Carlisle, J. A., & Farrell, J. (2011). Characterization of the performance and failure mechanisms of boron-doped ultrananocrystalline diamond electrodes. Journal of Applied Electrochemistry, 41(11), 1329-1340.
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  Abstract: This research investigated the anodic stability of boron-doped ultrananocrystalline diamond (BD-UNCD) film electrodes on a variety of substrates (Si, Ta, Nb, W, and Ti) at a current density of 1 A cm-2. At an applied charge of 100 A h cm-2, measurable BD-UNCD film wearwas not observed using SEM cross-sectional measurements. However, anodic treatment of the electrodes resulted in surface oxidation and film delamination, which caused substantial changes to the electrochemical properties of the electrodes. The substrate roughness, substrate electroactivity, and compactness of the substrate oxide were key parameters that affected film adhesion, and the primary mechanism of electrode failure was delamination of the BD-UNCD film. Substrate materials whose oxides had a larger coefficient of thermal expansion relative to the reduced metal substrates resulted in film delamination. The approximate substrate stability followed the order of: Ta> Si>Nb> W> Ti© 2011 Springer Science+Business Media B.V.
• Farrell, J., Schrader, G., Azizi, O., Hubler, D., & Chaplin, B. P. (2011). Mechanism of Perchlorate Formation on Boron-Doped Diamond Film Anodes. Environmental Science & Technology, 45(24), 10582-10590. doi:10.1021/es202534w
• Carter, K. E., & Farrell, J. (2010). Removal of perfluorooctane and perfluorobutane sulfonate from water via carbon adsorption and ion exchange. Separation Science and Technology, 45(6), 762--767.
• Carter, K. E., & Farrell, J. (2010). Removal of perfluorooctane and perfluorobutane sulfonate from water via carbon adsorption and ion exchange. Separation Science and Technology, 45(6), 762-767.
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  Abstract: This research investigated the removal of perfluorooctane sulfonate (PFOS) and perfluorobutane sulfonate (PFBS) from water by Filtrasorb®400 granular activated carbon (GAC) and Amberlite®IRA-458 ion exchange resin. Kinetic experiments showed that the time required for the uptake equilibrium was ~50 hours for the GAC and ~10 hours for the resin. Sorption isotherms showed that PFOS and PFBS uptake was endothermic and was promoted by hydrophobic effects on the GAC, and by a combination of hydrophobic adsorption and ion exchange on the resin. The aqueous solubility of PFOS was highly dependent on the ionic composition of the solution. PFOS and PFBS uptake by the resin was hysteretic and nearly irreversible using conventional regeneration methods. © Taylor & Francis Group, LLC.
• Chaplin, B. P., Farrell, J., Carlisle, J., Zeng, H., Chaplin, B. P., Farrell, J., Carlisle, J., & Zeng, H. (2010). Characterization of performance and wear mechanism of diamond electrodes used for electrochemical oxidation of TCE. ACS National Meeting Book of Abstracts.
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  Abstract: Boron-doped diamond (BDD) electrodes have shown tremendous promise for the oxidation of recalcitrant and complex waste streams through a combination of direct electron transfer at the electrode surface and indirect electron transfer mediated by hydroxyl radicals produced by water oxidation. However, little research has been dedicated to understanding the mechanisms associated with electrode wear and the effects of electrode wear on the mechanisms (direct vs. indirect) of contaminant oxidation. In this work, TCE is used as a model organic contaminant to investigate the relationship between electrode wear and the mechanisms of contaminant oxidation. Surface characterization (XPS, SEM, AFM) of the electrodes along with electrochemical impedance spectroscopy are used to correlate the electrode structure with measured TCE oxidation rates. This information will help to obtain a better understanding of the mechanisms associated with BDD electrode wear and will aid in the design of long-life electrodes.
• Chaplin, B. P., Schrader, G., & Farrell, J. (2010). Electrochemical destruction of N-nitrosodimethylamine in reverse osmosis concentrates using boron-doped diamond film electrodes. Environmental science \& technology, 44(11), 4264--4269.
• Farrell, J., Schrader, G., & Chaplin, B. P. (2010). Electrochemical Destruction of N-Nitrosodimethylamine in Reverse Osmosis Concentrates using Boron-doped Diamond Film Electrodes. Environmental Science & Technology, 44(11), 4264-4269. doi:10.1021/es903872p
• Tamilmani, S., Huang, W., Raghavan, S., & Farrell, J. (2010). REMOVAL OF DISSOLVED COPPER FROM CMP WASTE WATER BY DIRECT ELECTROREDUCTION.
• Carter, K. E., & Farrell, J. (2009). Electrochemical oxidation of trichloroethylene using boron-doped diamond film electrodes. Environmental Science and Technology, 43(21), 8350-8354.
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  PMID: 19924968;Abstract: This research investigated the oxidation of trichloroethene (TCE) at boron-doped diamond film electrodes. Flow-through experiments in gastight reactors were performed to determine trichloroethene oxidation products, and rotating disk electrode (RDE) experiments were used to determine TCE oxidation kinetics. RDE experiments were performed over a range in current densities and temperatures in order to elucidate the rate-limiting mechanisms for TCE oxidation. Density functional theory (DFT) simulations were used to investigate the activation barriers for oxidation by direct electron transfer and hydroxyl radicals. Oxidation of TCE produced formate, carbon dioxide, chlorate, and chloride. DFT simulations, experimentally measured apparent activation energies, and linear sweep voltammetry scans indicated that TCE oxidation occurred via direct electron transfer at electrode potentials
• Carter, K. E., & Farrell, J. (2009). Electrochemical oxidation of trichloroethylene using boron-doped diamond film electrodes. Environmental science \& technology, 43(21), 8350--8354.
• Chaplin, B. P., Schrader, G., & Farrell, J. (2009). Electrochemical oxidation of N-nitrosodimethylamine with boron-doped diamond film electrodes. Environmental science \& technology, 43(21), 8302--8307.
• Farrell, J., Davis, J. R., Gu, Z., Liao, Z., Schulz, M. C., & Baygents, J. C. (2009). Treatment of cooling tower blowdown water containing silica, calcium and magnesium by electrocoagulation. Water Science and Technology, 60(9), 2345-2352. doi:10.2166/wst.2009.675
• Farrell, J., Farrell, J. -., Carter, K. E., & Farrell, J. -. (2009). Electrochemical oxidation of trichloroethylene using boron-doped diamond film electrodes. Environmental science & technology, 43(21).
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  This research investigated the oxidation of trichloroethene (TCE) at boron-doped diamond film electrodes. Flow-through experiments in gastight reactors were performed to determine trichloroethene oxidation products, and rotating disk electrode (RDE) experiments were used to determine TCE oxidation kinetics. RDE experiments were performed over a range in current densities and temperatures in order to elucidate the rate-limiting mechanisms for TCE oxidation. Density functional theory (DFT) simulations were used to investigate the activation barriers for oxidation by direct electron transfer and hydroxyl radicals. Oxidation of TCE produced formate, carbon dioxide, chlorate, and chloride. DFT simulations, experimentally measured apparent activation energies, and linear sweep voltammetry scans indicated that TCE oxidation occurred via direct electron transfer at electrode potentials
• Farrell, J., Farrell, J. -., Chaplin, B. P., Schrader, G., & Farrell, J. -. (2009). Electrochemical oxidation of N-nitrosodimethylamine with boron-doped diamond film electrodes. Environmental science & technology, 43(21).
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  This research investigated NDMA oxidation by boron-doped diamond (BDD) film electrodes. Oxidation rates were measured as a function of electrode potential, current density, and temperature using rotating disk and flow-through reactors. Final NDMA reaction products were carbon dioxide, ammonium, and nitrate, with dimethylamine and methylamine as intermediate products. Reaction rates were first-order with respect to NDMA concentration and surface area normalized oxidation rates as high as 850 +/- 50 L/m(2)-hr were observed at a current density of 10 mA/cm(2). The flow-through reactor yielded mass transfer limited reaction rates that were first-order in NDMA concentration, with a half-life of 2.1 +/- 0.1 min. Experimental evidence indicates that NDMA oxidation proceeds via a direct electron transfer at potentials >1.8 V/SHE with a measured apparent activation energy of 3.1 +/- 0.5 kJ/mol at a potential of 2.5 V/SHE. Density functional theory calculations indicate that a direct two-electron transfer can produce a stable NDMA((+2)) species that is stabilized by forming an adduct with water. The transfer of two electrons from NDMA to the electrode allows an activation-less attack of hydroxyl radicals on the NDMA((+2)) water adduct. At higher overpotentials the oxidation of NDMA occurs by a combination of direct electron transfer and hydroxyl radicals produced via water electrolysis.
• Farrell, J., Schrader, G., & Chaplin, B. P. (2009). Electrochemical Oxidation of N-Nitrosodimethylamine with Boron-doped Diamond Film Electrodes. Environmental Science & Technology, 43(21), 8302-8307. doi:10.1021/es901582q
• Gu, Z., Liao, Z., Schulz, M., Davis, J. R., Baygents, J. C., & Farrell, J. (2009). Estimating dosing rates and energy consumption for electrocoagulation using iron and aluminum electrodes. Industrial \& Engineering Chemistry Research, 48(6), 3112--3117.
• Liao, Z., & Farrell, J. (2009). Electrochemical oxidation of perfluorobutane sulfonate using boron-doped diamond film electrodes. Journal of Applied Electrochemistry, 39(10), 1993-1999.
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  Abstract: This research investigated oxidation of perfluorobutane sulfonate (PFBS) at a boron-doped diamond (BDD) film anode. PFBS oxidation produced carbon dioxide, sulfate, fluoride, and trace amounts of trifluoroacetic acid (TFA). Rate constants for PFBS oxidation as a function of current density and temperature were measured using a rotating disk electrode (RDE) reactor. Reaction rates in the RDE reactor were zeroth order with respect to PFBS concentration, which is indicative of a reaction limited by the availability of reactive sites. The apparent electron transfer coefficient and apparent activation energy were used to evaluate the rate-limiting step for PFBS oxidation. Density functional simulations were used to calculate the reaction energies and activation barriers for PFBS oxidation by hydroxyl radicals and by direct electron transfer. Simulation results indicated that the experiments were performed at sufficiently high overpotentials that the rate-limiting step was an activationless direct electron transfer reaction. © 2009 Springer Science+Business Media B.V.
• Liao, Z., & Farrell, J. (2009). Electrochemical oxidation of perfluorobutane sulfonate using boron-doped diamond film electrodes. Journal of applied electrochemistry, 39(10), 1993--1999.
• Liao, Z., Gu, Z., Schulz, M. C., Davis, J. R., Baygents, J. C., & Farrell, J. (2009). Treatment of cooling tower blowdown water containing silica, calcium and magnesium by electrocoagulation. Water Science and Technology, 60(9), 2345-2352.
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  PMID: 19901466;Abstract: This research investigated the effectiveness of electrocoagulation using iron and aluminium electrodes for treating cooling tower blowdown (CTB) waters containing dissolved silica (Si(OH)4), Ca2+ and Mg 2+. The removal of each target species was measured as a function of the coagulant dose in simulated CTB waters with initial pH values of 5, 7, and 9. Experiments were also performed to investigate the effect of antiscaling compounds and coagulation aids on hardness ion removal. Both iron and aluminum electrodes were effective at removing dissolved silica. For coagulant doses ≤3mM, silica removal was a linear function of the coagulant dose, with 0.4 to 0.5 moles of silica removed per mole of iron or aluminium. Iron electrodes were only 30% as effective at removing Ca2+ and Mg2+ as compared to silica. There was no measurable removal of hardness ions by aluminium electrodes in the absence of organic additives. Phosphonate based antiscaling compounds were uniformly effective at increasing the removal of Ca2+ and Mg2+ by both iron and aluminium electrodes. Cationic and amphoteric polymers used as coagulation aids were also effective at increasing hardness ion removal. © IWA Publishing 2009.
• Liao, Z., Gu, Z., Schulz, M., Davis, J., Baygents, J., Farrell, J., & others, . (2009). Treatment of cooling tower blowdown water containing silica, calcium and magnesium by electrocoagulation. Water Science and Technology, 60(9), 2345.
• SCHULZ, M., BAYGENTS, J., & FARRELL, J. (2009). Paper: LABORATORY AND PILOT TESTING OF ELECTROCOAGULATION FOR REMOVING SCALEFORMING SPECIES FROM INDUSTRIAL PROCESS WATERS.
• Schulz, M. C., Baygents, J. C., & Farrell, J. (2009). Laboratory and pilot testing of electrocoagulation for removing scaleforming species from industrial process waters. International Journal of Environmental Science and Technology, 6(4), 522-526.
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  Abstract: This study investigated the performance of electrocoagulation using iron and aluminum electrodes for removing silica, calcium and magnesium from cooling tower blowdown and reverse osmosis reject waters. Experiments were conducted at both the bench and pilot scales to determine the levels of target species removal as a function of the coagulant dose. At the bench scale, aluminum removed the target compounds from both cooling tower blowdown and reverse osmosis reject more efficiently than iron. A 2 mM aluminum dose removed 80% of the silica and 20 to 40% of the calcium and magnesium. The same iron dose removed only 60% of the silica and 10 to 20% of the calcium and magnesium. When operated with iron electrodes, pilot unit performance was comparable to that of the bench unit, which suggests that such systems can be scaled-up on the basis of coagulant dose. However, when operated with aluminum electrodes the pilot unit underperformed the bench unit due to fouling of the electrode surfaces after a few hours of operation. This result was completely unexpected based on the short-term experiments performed using the bench unit. © IRSEN, CEERS, IAU.
• Schulz, M., Baygents, J., & Farrell, J. (2009). Laboratory and pilot testing of electrocoagulation for removing scale-forming species from industrial process waters Article 1: Volume 6, Number 4, Pages 521-526 (6), Autumn 2009 XML PDF (186 K).
• Schulz, M., Baygents, J., & Farrell, J. (2009). Laboratory and pilot testing of electrocoagulation for removing scale-forming species from industrial process waters. International Journal of Environmental Science \& Technology, 6(4), 521--526.
• Zheng, G. u., Liao, Z., Schulz, M., Davis, J. R., Baygents, J. C., & Farrell, J. (2009). Estimating dosing rates and energy consumption for electrocoagulation using Iron and aluminum electrodes. Industrial and Engineering Chemistry Research, 48(6), 3112-3117.
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  Abstract: The effect of current density on dosing rates and energy requirements for iron and aluminum electrodes in a bench-scale electrocoagulation (EC) reactor have been investigated. Dissolution rates of the iron and aluminum anodes were independent of bulk solution pH values. Iron dosing rates followed Faraday's law, but aluminum dosing rates averaged 83% greater than those predicted by Faraday's law. Chemical corrosion of both the anode and cathode contributed to the extra-faradaic aluminum dosing. A method was developed to determine the faradaic power consumption as a function of the current density. An equation describing power dissipation by ohmic and faradaic mechanisms was derived and used to estimate energy consumption per unit coagulant dose for EC reactors operating over a wide range of conditions. The derived equation can be used to compare the operational costs for EC with those using chemical additives, such as alum or ferric chloride. © 2009 American Chemical Society.
• Carter, K. E., & Farrell, J. (2008). Oxidative destruction of perfluorooctane sulfonate using boron-doped diamond film electrodes. Environmental Science and Technology, 42(16), 6111-6115.
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  PMID: 18767674;Abstract: This research investigated the oxidative destruction of perfluorooctane sulfonate at boron-doped diamond film electrodes. Experiments measuring oxidation rates of PFOS were performed over a range in current densitiesand temperatures using a rotating disk electrode (RDE) reactor and a parallel plate flow-through reactor. The oxidation of PFOS yielded sulfate, fluoride, carbon dioxide, and trace levels of trifluoroacetic acid. Reaction rates in the RDE reactor were zeroth order in PFOS concentration. Reaction rates in the flow-through reactor were mass-transfer-limited and were pseudo-first-order in PFOS concentration, with a half-life of 5.3 min at a current density of 20 mA/cm2. Eyring analysis of the zeroth order rate constants at a fixed electrode potential yielded an apparent activation energy of 4.2 kJ/mol for PFOS oxidation. Oensity functional theory (OFT) simulations were used to calculate activation barriers for different possible reaction mechanisms, including oxidation by hydroxyl radicals at different sites on the PFOS molecule, and direct electron transfer. A comparison of the experimentally measured apparent activation energy with those calculated using DFT indicated that the most likely rate-limiting step for PFOS oxidation was direct electron transfer. © 2008 American Chemical Society.
• Carter, K. E., & Farrell, J. (2008). Oxidative destruction of perfluorooctane sulfonate using boron-doped diamond film electrodes. Environmental science \& technology, 42(16), 6111--6115.
• Farrell, J., Farrell, J. -., Carter, K. E., & Farrell, J. -. (2008). Oxidative destruction of perfluorooctane sulfonate using boron-doped diamond film electrodes. Environmental science & technology, 42(16).
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  This research investigated the oxidative destruction of perfluorooctane sulfonate at boron-doped diamond film electrodes. Experiments measuring oxidation rates of PFOS were performed over a range in current densities and temperatures using a rotating disk electrode (RDE) reactor and a parallel plate flow-through reactor. The oxidation of PFOS yielded sulfate, fluoride, carbon dioxide, and trace levels of trifluoroacetic acid. Reaction rates in the RDE reactor were zeroth order in PFOS concentration. Reaction rates in the flow-through reactor were mass-transfer-limited and were pseudo-first-order in PFOS concentration, with a half-life of 5.3 min at a current density of 20 mA/cm2. Eyring analysis of the zeroth order rate constants at a fixed electrode potential yielded an apparent activation energy of 4.2 kJ/mol for PFOS oxidation. Density functional theory (DFT) simulations were used to calculate activation barriers for different possible reaction mechanisms, including oxidation by hydroxyl radicals at different sites on the PFOS molecule, and direct electron transfer. A comparison of the experimentally measured apparent activation energy with those calculated using DFT indicated that the most likely rate-limiting step for PFOS oxidation was direct electron transfer.
• Farrell, J., Farrell, J. -., Mishra, D., Liao, Z., & Farrell, J. -. (2008). Understanding reductive dechlorination of trichloroethene on boron-doped diamond film electrodes. Environmental science & technology, 42(24).
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  This research investigated reduction of trichloroethylene (TCE) at boron-doped diamond (BDD) film cathodes using a rotating disk electrode reactor. Rates of TCE reduction were determined as functions of the electrode potential and TCE concentration over a temperature range between 2 and 32 degrees C. Reduction of TCE resulted in production of acetate and chloride ions with no detectable intermediate products. At a current density of 15 mA/cm2 and concentrations below 0.75 mM, reaction rates were first order with respect to TCE concentration, with surface area normalized rate constants 2 orders of magnitude greater than those for iron electrodes. Density functional theory (DFT) simulations were used to evaluate activation barriers for reduction by direct electron transfer, and for reaction with four functional groups commonly found on BDD surfaces. The DFT calculated activation barrier for direct electron transfer was more than 4 times greater than the experimentally measured value of 22 kJ/mol. In contrast, the DFT activation barrier for reaction at a deprotonated hydroxyl site on a tertiary carbon atom (triple bond C-O(-)) of 24 kJ/mol was in close agreement with the experimental value. Both experiments and quantum mechanical simulations support a TCE reduction mechanism that involves chemically adsorbed intermediates.
• Farrell, J., Farrell, J. -., Zhang, N., Luo, J., Blowers, P., & Farrell, J. -. (2008). Understanding trichloroethylene chemisorption to iron surfaces using density functional theory. Environmental science & technology, 42(6).
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  This research investigated the thermodynamic favorability and resulting structures for chemical adsorption of trichloroethylene (TCE) to metallic iron using periodic density functional theory (DFT). Three initial TCE positions having the plane defined by HCC atoms parallel to the iron surface resulted in formation of three different chemisorption complexes between carbon atoms in TCE and the iron surface. The Cl-bridge initial configuration with the HCC plane of TCE perpendicular to the iron surface did not result in C-Fe bond formation. The most energetically favorable complex formed at the C-bridge site where the initial configuration had the C=C bond in TCE at a bridge site between adjacent iron atoms. In the C-bridge complex, one C atom formed two a bonds to different Fe atoms, while the second C atom formed a sigma bond with a second Fe atom. Surface complexation atthe C-bridge site resulted in scission of all three C-Cl bonds and also resulted in a shortening of the C==C bond to a distance intermediate between a double and a triple bond. Initial configurations with the C==C bond adsorbed at top or hollow sites on the iron surface resulted in formation of C-Fe a bonds between a single C and two adjacent Fe atoms, and the scission of only two C==Cl bonds. Bond angles and bond lengths indicated that there were no changes in bond order of the C==C bond for top and hollow adsorption. Chemisorption at the C-bridge site had an activation energy of 49 kJ/mol and an early transition state where all three C-CI bonds were activated. The early transition state and the loss of all three Cl atoms upon chemisorption are consistent with most experimental observations that TCE undergoes complete dechlorination in one interaction with the iron surface. The absence of chemisorption and scission of only two C--Cl bonds at the Cl-bridge site is consistent with experimental observations that trace amounts of chloroacetylene may also be produced from reactions of TCE with iron.
• Mishra, D., Liao, Z., & Farrell, J. (2008). Understanding reductive dechlorination of trichloroethene on boron-doped diamond film electrodes. Environmental Science and Technology, 42(24), 9344-9349.
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  PMID: 19174914;Abstract: This research investigated reduction of trichloroethylene (TCE) at boron-doped diamond (BDD) film cathodes using a rotating disk electrode reactor. Rates of TCE reduction were determined as functions of the electrode potential and TCE concentration over a temperature range between 2 and 32°C. Reduction of TCE resulted in production of acetate and chloride ions with no detectable intermediate products. At a current density of 15 mA/cm2 and concentrations below 0.75 mM, reaction rates were first order with respectto TCE concentration, with surface area normalized rate constants 2 orders of magnitude greater than those for iron electrodes. Density functional theory (DFT) simulations were used to evaluate activation barriers for reduction by direct electron transfer, and for reaction with four functional groups commonly found on BDD surfaces. The DFT calculated activation barrier for direct electron transfer was more than 4 times greater than the experimentally measured value of 22 kJ/mol. In contrast the DFT activation barrier for reaction at a deprotonated hydroxyl site on a tertiary carbon atom (≡C-0-) of 24 kJ/mol was in close agreement with the experimental value. Both experiments and quantum mechanical simulations support a TCE reduction mechanism that involves chemically adsorbed intermediates. © 2008 American Chemical Society.
• Mishra, D., Liao, Z., & Farrell, J. (2008). Understanding reductive dechlorination of trichloroethene on boron-doped diamond film electrodes. Environmental science \& technology, 42(24), 9344--9349.
• Zhang, N., Luo, J., Blowers, P., & Farrell, J. (2008). Understanding trichloroethylene chemisorption to iron surfaces using density functional theory. Environmental Science and Technology, 42(6), 2015-2020.
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  PMID: 18409630;PMCID: PMC3700525;Abstract: This research investigated the thermodynamic favorability and resulting structures for chemical adsorption of trichloroethylene (TCE) to metallic iron using periodic density functional theory (DFT). Three initial TCE positions having the plane defined by HCC atoms parallel to the iron surface resulted in formation of three different chemisorption complexes between carbon atoms in TCE and the iron surface. The Cl-bridge initial configuration with the HCC plane of TCE perpendicular to the iron surface did not result in C-Fe bond formation. The most energetically favorable complex formed at the C-bridge site where the initial configuration had the C=C bond in TCE at a bridge site between adjacent iron atoms. In the C-bridge complex, one C atom formed two σ bonds to different Fe atoms, while the second C atom formed a σ bond with a second Fe atom. Surface complexation at the C-bridge site resulted in scission of all three C-Cl bonds and also resulted in a shortening of the C=C bond to a distance intermediate between a double and a triple bond. Initial configurations with the C=C bond adsorbed at top or hollow sites on the iron surface resulted in formation of C-Fe σ bonds between a single C and two adjacent Fe atoms, and the scission of only two C-Cl bonds. Bond angles and bond lengths indicated that there were no changes in bond order of the C=C bond for top and hollow adsorption. Chemisorption at the C-bridge site had an activation energy of 49 kJ/mol and an early transition state where all three C-Cl bonds were activated. The early transition state and the loss of all three Cl atoms upon chemisorption are consistent with most experimental observations that TCE undergoes complete dechlorination in one interaction with the iron surface. The absence of chemisorption and scission of only two C-Cl bonds atthe Cl-bridge site is consistent with experimental observations that trace amounts of chloroacetylene may also be produced from reactions of TCE with iron. © 2008 American Chemical Society.
• Zhang, N., Luo, J., Blowers, P., & Farrell, J. (2008). Understanding trichloroethylene chemisorption to iron surfaces using density functional theory. Environmental science \& technology, 42(6), 2015--2020.
• Mishra, D., & Farrell, J. (2007). Reductive dechlorination of trichloroethylene using boron doped diamond film electrode. American Water Works Association - AWWA Annual Conference and Exposition, ACE 2007.
• Farrell, J., Zhang, N., & Blowers, P. (2006). Density functional study of chloroethene reactions with iron surfaces. ACS National Meeting Book of Abstracts, 231.
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  Abstract: The reactions involved in reduction of trichloroethylene (TCE) and tetrachloroethylene (PCE) at metallic iron surfaces were studied. The Perdew-Burke-Enzerhof functional was used to model both physical and chemical adsorption of TCE and PCE at different sites on the iron surface. Initial configurations with the C=C bond physically adsorbed at bridge sites between adjacent iron atoms resulted in di-sigma bond formation between two C and two Fe atoms and activation of all three C-Cl bonds. Initial configurations with the C=C bond physically adsorbed at a top site above a single Fe atom, or at a hollow site between four Fe atoms, resulted in only one C atom binding to the iron and activation of only two C-Cl bonds. Chemisorbed structures formed at bridge sites were the most energetically favorable and had early transition states with activation energies of ∼ 50 kJ/mole. This is an abstract of a paper presented at the 231th ACS National Meeting (Atlanta, GA 3/26-30/2006).
• Farrell, J., Zhang, N., & Blowers, P. (2006). Density functional study of chloroethene reactions with iron surfaces. ACS, Division of Environmental Chemistry - Preprints of Extended Abstracts, 46(1), 101-1012.
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  Abstract: The thermodynamic favorability and resulting structures for chemical adsorption of trichloroethylene (TCE) and tetrachloroethylene (PCE) to iron surfaces were studied using periodic density functional theory (DFT). DFT modeling of adsorbed species was performed using the non-local Perdew-Burke-Enzerhof functional. Chemisorption structures were obtained for the four physically adsorbed initial configurations. Three of the initial configurations placed the plane of the TCE molecule parallel to the Fe [100] surface at bridge, top, and hollow sites. In the fourth initial structure the plane of the TCE molecule was perpendicular to the Fe[100] surface with two Cl atoms at bridge sites between adjacent Fe atoms. TCE and PCE underwent complete dechlorination in one interaction with the iron surface. Trace amounts of mono- and dichloroacetylene may be produced from reactions of TCE and PCE with zerovalent iron. This is an abstract of a paper presented at the 231st ACS National Meeting (Atlanta, GA 3/26-30/2006).
• Wang, J., & Farrell, J. (2006). Determining the atomic hydrogen surface coverage on iron and nickel electrodes under water treatment conditions. Journal of Applied Electrochemistry, 36(3), 369-374.
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  Abstract: Reductive methods for removing, detoxifying, or inactivating contaminants in water often involve reactions with atomic hydrogen produced from water reduction. Knowledge of how the solution pH value and electrode potential affect the concentration of atomic hydrogen on the reactive surface will be useful for evaluating possible reaction mechanisms and in optimizing treatment schemes. Presently, there are no simple methods for determining the atomic hydrogen surface coverage on the base metals that are typically used as cathodes or sacrificial reactants in water treatment operations. This research develops and evaluates an iterative, coulometric method for determining the fractional atomic hydrogen surface coverage (θH) on iron and nickel electrodes under water treatment conditions. The method is applicable at pH values and potentials where proton discharge is the rate-limiting step for the hydrogen evolution reaction (HER), and is valid under conditions where the metals are covered by oxide layers that lower the apparent electron transfer coefficients by up to 40% as compared to oxide-free conditions at low pH values. The method is also able to determine the exchange current density and the rate constants for the Volmer discharge and Tafel recombination steps of the HER. © Springer 2005.
• Wang, J., & Farrell, J. (2006). Determining the atomic hydrogen surface coverage on iron and nickel electrodes under water treatment conditions. Journal of applied electrochemistry, 36(3), 369--374.
• Blowers, P., Zhang, N., & Farrell, J. (2005). Dft Study of Trichloroethylene Chemisorption to Iron Surfaces Using Density Functional Theory. The 2005 Annual Meeting.
• Blowers, P., Zhang, N., & Farrell, J. (2005). Dft study of trichloroethylene chemisorption to iron surfaces using density functional theory. AIChE Annual Meeting Conference Proceedings, 2005.
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  Abstract: The mechanisms for chemical adsorption of trichloroethylene (TCE) to iron surfaces were studied using periodic density functional theory (DFT). DFT modeling of adsorbed species was performed using the generalized gradient approximation with the Perdew-Burke-Enzerhof (PBE) functional. Chemisorption structures were obtained for four adsorbed initial configurations. Di-sigma C-Fe and Cl-Fe complexes were formed by initial configurations with two carbon (C-bridge) or two chlorine atoms (Cl-bridge) adsorbed at bridge sites between adjacent iron atoms, respectively. Calculated binding energies indicated that chemisorption was highly exothermic, with the complex formed at the C-bridge site being the most energetically favorable. Chemisorption at the C-bridge site had an early transition state in which all three C-Cl bonds were activated from ∼ 1.7 to ∼ 2.2 Å, with an activation energy of 50 kJ/mole. The early transition state and the loss of all three Cl atoms upon chemisorption were consistent with most experimental observations that TCE undergoes complete dechlorination in one interaction with the iron surface. This is an abstract of a paper presented at the AIChE Annual Meeting and Fall Showcase (Cincinnati, OH 1/04/2005).
• Blowers, P., Zhang, N., & Farrell, J. (2005). Dft study of trichloroethylene chemisorption to iron surfaces using density functional theory. AIChE Annual Meeting, Conference Proceedings, 10734-.
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  Abstract: Zero-valent iron has been widely utilized as a reactive agent for reductive dechlorination of solvents in contaminated groundwaters. Prior research has suggested that chemical adsorption may be involved in chloroalkene reduction via an inner-sphere electron transfer mechanism. This research investigated the mechanisms for chemical adsorption of trichloroethylene (TCE) to iron surfaces using periodic density functional theory (DFT). DFT modeling of adsorbed species was performed using the generalized gradient approximation with the Perdew-Burke-Enzerhof (PBE) functional. Chemisorption structures were obtained for four adsorbed initial configurations. Di-sigma C-Fe and Cl-Fe complexes were formed by initial configurations with two carbon (C-bridge) or two chlorine atoms (Cl-bridge) adsorbed at bridge sites between adjacent iron atoms, respectively. Sigma bond formation between two C or Cl atoms and two iron atoms resulted in activation of all three C-Cl bonds. This also resulted in a shortening of the C=C bond by an amount consistent with an intermediate between a double and a triple bond. Optimizations of initial configurations with the C=C bond adsorbed at top or hollow sites on the iron surface resulted in the formation of two C-Fe sigma bonds between a single C and two Fe atoms, and only two C-Cl bonds became activated. Bond angles and bond lengths indicated that there were no changes in bond order of the C=C bond upon top and hollow adsorption. Calculated binding energies indicated that chemisorption was highly exothermic, with the complex formed at the C-bridge site being the most energetically favorable. Chemisorption at the C-bridge site had an early transition state in which all three C-Cl bonds were activated from ∼1.7 to ∼2.2 Å, with an activation energy of 50 kJ/mol. The early transition state and the loss of all three Cl atoms upon chemisorption are consistent with most experimental observations that TCE undergoes complete dechlorination in one interaction with the iron surface. The sigma bonded structures where only two C-Cl bonds were activated upon adsorption is consistent with experimental observations that trace amounts of chloroacetylene may be produced from reactions of TCE with iron.
• Farrell, J., & Blowers, P. (2005). Ab lnitio Study of Carbon--Chlorine Bond Cleavage in Carbon Tetrachloride. Environmental science \& technology, 612--617.
• Farrell, J., Farrell, J. -., Mishra, D., & Farrell, J. -. (2005). Understanding nitrate reactions with zerovalent iron using tafel analysis and electrochemical impedance spectroscopy. Environmental science & technology, 39(2).
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  This study investigated the reaction mechanisms of nitrate (NO3-) with zerovalent iron (ZVI) media under conditions relevantto groundwatertreatment using permeable reactive barriers (PRB). Reaction rates of NO3- with freely corroding and with cathodically or anodically polarized iron wires were measured in batch reactors. Tafel analysis and electrochemical impedance spectroscopy (EIS) were used to investigate the reactions occurring on the iron surfaces. Reduction of NO3- by corroding iron resulted in near stoichiometric production of NO2-, which did not measurably react in the absence of added Fe(II). Increasing NO3- concentrations resulted in increasing corrosion currents. However, EIS and Tafel analyses indicated that there was little direct reduction of NO3- at the ZVI surface, despite the presence of water reduction. This behavior can be attributed to formation of a microporous oxide on the iron surfaces that blocked reduction of NO3- and NO2- but did not block water reduction. This finding is consistent with previous observations that NO3- impedes reduction of organic compounds by ZVI. Nitrite concentrations greater than 4 mM resulted in anodic passivation of the iron, but passivation was not observed with NO3- concentrations as high as 96 mM. This indicates that the passivating oxide preventing NO3- reduction was permeable toward cation migration. Since reaction with Fe(0) can be excluded asthe mechanism for NO3- and NO2- reduction, reaction with Fe(II)-containing oxides coating the iron surface is the most likely reaction mechanism. This suggests that short-term batch tests requiring little turnover of reactive sites on the iron surface may overestimate long-term rates of NO3- removal because the effects of passivation are not apparent in batch tests conducted with high initial Fe(II) to NO3- ratios.
• Farrell, J., Farrell, J. -., Zhang, N., Blowers, P., & Farrell, J. -. (2005). Ab initio study of carbon-chlorine bond cleavage in carbon tetrachloride. Environmental science & technology, 39(2).
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  Chlorinated solvents in groundwater are known to undergo reductive dechlorination reactions with Fe(ll)-containing minerals and with corroding metals in permeable-barrier treatment systems. This research investigated the effect of the reaction energy on the reaction pathway for C-Cl bond cleavage in carbon tetrachloride (CCl4). Hartree-Fock, density functional theory, and modified complete basis set ab initio methods were used to study adiabatic electron transfer to aqueous-phase CCl4. The potential energies associated with fragmentation of the carbon tetrachloride anion radical (CCl4-) into a trichloromethyl radical (CCl3) and a chloride ion (Cl-) were explored as a function of the carbon-chlorine bond distance during cleavage. The effect of aqueous solvation was investigated using a continuum conductor-like screening model. Solvation significantly lowered the energies of the reaction products, suggesting that dissociative electron transfer was enhanced by solvation. The potential energy curves in an aqueous medium indicate that reductive cleavage undergoes a change from an inner-sphere to an outer-sphere mechanism as the overall energy change for the reaction is increased. The activation energy for the reaction was found to be a linear function of the overall energy change, and the Marcus-Hush model was used to relate experimentally measured activation energies for CCl4 reduction to overall reaction energies. Experimentally measured activation energies for CCl4 reduction by corroding iron correspond to reaction energies that are insufficiently exergonic for promoting the outer-sphere mechanism. This suggests that the different reaction pathways that have been observed for CCl4 reduction by corroding iron arise from different catalytic interactions with the surface, and not from differences in energy of the transferred electrons.
• Farrell, J., Farrell, J. -., Zhang, N., Blowers, P., & Farrell, J. -. (2005). Evaluation of density functional theory methods for studying chemisorption of arsenite on ferric hydroxides. Environmental science & technology, 39(13).
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  Understanding adsorption of arsenic on ferric hydroxide surfaces is important for predicting the fate of arsenic in the environment and in designing treatment systems for removing arsenic from potable water. This research investigated the binding of arsenite to ferric hydroxide clusters using several density functional theory methods. Comparison of calculated and experimentally measured As-O and As-Fe bond distances indicated that As(III) forms both bidentate and monodentante corner-sharing complexes with Fe(III) octahedra. Edge-sharing As(III) complexes were less energetically favorable and had As-O and As-Fe distances that deviated more from experimentally measured values than corner-sharing complexes. The hydrated bidentate complex was the most energetically favorable in the vacuum phase, while the monodentate complex was most favored in the aqueous phase. Structures optimized using the Harris and Perdew-Wang local functionals were close to both experimental data and structures optimized using the nonlocal Becke-Lee-Yang-Parr (BLYP) functional. Binding energies calculated with the gradient-corrected BLYP functional were only weakly dependent on the method used for geometry optimization. The approach of using low-level structures coupled with higher level single-point energies was found to reduce computational time by 75% with no loss in accuracy of the computed binding energies.
• Farrell, J., Martin, F. J., Martin, H. B., O'Grady, W. E., & Natishan, P. (2005). Anodically generated short-lived species on boron-doped diamond film electrodes. Journal of the Electrochemical Society, 152(1), E14-E17.
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  Abstract: Electrodes composed of boron-doped diamond (BDD) films on metal and semiconductor substrates have a wide range of applications in electrochemistry. This research investigated short-lived species (SLS) produced by anodic polarization of BDD electrodes in 1.0 M HClO4 solutions. Normal pulse voltammetry experiments were performed to identify anodically produced SLS with lifetimes of less than 50 ms under open-circuit conditions. Potential step chronoamperometry experiments were performed to investigate the steady-state concentrations of SLS at the electrode-solution interface as a function of potential. Anodic potentials greater than 1.5 V with respect to the standard hydrogen electrode (SHE) were required to generate the SLS. Increasing anodic potentials between 1.5 and 3.0 V/SHE resulted in increasing concentrations of the SLS, until a saturation point was reached. Past work by other investigators suggests that the SLS likely consist primarily of HO* radicals produced from water oxidation. © 2004 The Electrochemical Society. All rights reserved.
• Farrell, J., Martin, F. J., Martin, H. B., O’Grady, W. E., & Natishan, P. (2005). Anodically generated short-lived species on boron-doped diamond film electrodes. Journal of the Electrochemical Society, 152(1), E14--E17.
• Farrell, J., Mishra, D., Farrell, J. -., & Farrell, J. -. (2005). Evaluation of mixed valent iron oxides as reactive adsorbents for arsenic removal. Environmental science & technology, 39(24).
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  The objective of this research was to determine if Fe(II)-bearing iron oxides generate ferric hydroxides at sufficient rates for removing low levels of arsenic in packed-bed reactors, while at the same time avoiding excessive oxide production that contributes to bed clogging in oxygenated waters. Column experiments were performed to determine the effectiveness of three media for arsenic removal over a range in empty bed contact times, influent arsenic concentrations, dissolved oxygen (DO) levels, and solution pH values. Corrosion rates of the media as a function of the water composition were determined using batch and electrochemical methods. Rates of arsenic removal were first order in the As(V) concentration and were greater for media with higher corrosion rates. As(V) removal increased with increasing DO levels primarily due to faster oxidation of the Fe2+ released by media corrosion. To obtain measurable amounts of arsenic removal in 15 mM NaCl electrolyte solutions containing 50 microg/L As(V), the rate of Fe2+ released by the media needed to be at least 15 times greater than the As(V) feed rate into the column. In waters containing 30 mg/L of silica and 50 microg/L of As(V), measurable amounts of arsenic removal were obtained only for Fe2+ release rates that were at least 200 times greater than the As(V) feed rate. Although all columns showed losses in hydraulic conductivity overthe course of 90 days of operation, the conductivity values remained high, and the losses could be reversed by backwashing the media. The reaction products produced by the media in domestic tap water had average As-to-Fe ratios that were approximately 25% higher than those for a commercially available adsorbent.
• Farrell, J., Zhang, N., & Blowers, P. (2005). Evaluation of Density Functional Theory Methods for Studying Chemisorption of Arsenite on Ferric Hydroxides. Environmental Science & Technology, 39(13), 4816-4822. doi:10.1021/es050271f
• Mishra, D., & Farrell, J. (2005). Evaluation of mixed valent iron oxides as reactive adsorbents for arsenic removal. Environmental Science and Technology, 39(24), 9689-9694.
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  PMID: 16475353;Abstract: The objective of this research was to determine if Fe(II)-bearing iron oxides generate ferric hydroxides at sufficient rates for removing low levels of arsenic in packed-bed reactors, while at the same time avoiding excessive oxide production that contributes to bed clogging in oxygenated waters. Column experiments were performed to determine the effectiveness of three media for arsenic removal over a range in empty bed contact times, influent arsenic concentrations, dissolved oxygen (DO) levels, and solution pH values. Corrosion rates of the media as a function of the water composition were determined using batch and electrochemical methods. Rates of arsenic removal were first order in the As(V) concentration and were greater for media with higher corrosion rates. As(V) removal increased with increasing DO levels primarily due to faster oxidation of the Fe2+ released by media corrosion. To obtain measurable amounts of arsenic removal in 15 mM NaCl electrolyte solutions containing 50 μg/L As(V), the rate of Fe2+ released by the media needed to be at least 15 times greater than the As(V) feed rate into the column. In waters containing 30 mg/L of silica and 50 μg/L of As(V), measurable amounts of arsenic removal were obtained only for Fe2+ release rates that were at least 200 times greater than the As(V) feed rate. Although all columns showed losses in hydraulic conductivity over the course of 90 days of operation, the conductivity values remained high, and the losses could be reversed by backwashing the media. The reaction products produced by the media in domestic tap water had average As-to-Fe ratios that were ∼25% higher than those for a commercially available adsorbent. © 2005 American Chemical Society.
• Mishra, D., & Farrell, J. (2005). Evaluation of mixed valent iron oxides as reactive adsorbents for arsenic removal. Environmental science \& technology, 39(24), 9689--9694.
• Mishra, D., & Farrell, J. (2005). Understanding nitrate reactions with zerovalent iron using tafel analysis and electrochemical impedance spectroscopy. Environmental Science and Technology, 39(2), 645-650.
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  PMID: 15707067;Abstract: This study investigated the reaction mechanisms of nitrate (NO 3-) with zerovalent iron (ZVI) media under conditions relevant to groundwater treatment using permeable reactive barriers (PRB). Reaction rates of NO3- with freely corroding and with cathodically or anodically polarized iron wires were measured in batch reactors. Tafel analysis and electrochemical impedance spectroscopy (EIS) were used to investigate the reactions occurring on the iron surfaces. Reduction of NO 3- by corroding iron resulted in near stoichiometric production of NO2-, which did not measurably react in the absence of added Fe(II). Increasing NO3- concentrations resulted in increasing corrosion currents. However, EIS and Tafel analyses indicated that there was little direct reduction of NO3- at the ZVI surface, despite the presence of water reduction. This behavior can be attributed to formation of a microporous oxide on the iron surfaces that blocked reduction of NO3- and NO2- but did not block water reduction. This finding is consistent with previous observations that NO3- impedes reduction of organic compounds by ZVI. Nitrite concentrations greater than 4 mM resulted in anodic passivation of the iron, but passivation was not observed with NO 3- concentrations as high as 96 mM. This indicates that the passivating oxide preventing NO3- reduction was permeable toward cation migration. Since reaction with Fe(0) can be excluded as the mechanism for NO3- and NO2- reduction, reaction with Fe(II)-containing oxides coating the iron surface is the most likely reaction mechanism. This suggests that short-term batch tests requiring little turnover of reactive sites on the iron surface may overestimate long-term rates of NO3- removal because the effects of passivation are not apparent in batch tests conducted with high initial Fe(II) to NO3- ratios.
• Mishra, D., & Farrell, J. (2005). Understanding nitrate reactions with zerovalent iron using tafel analysis and electrochemical impedance spectroscopy. Environmental science \& technology, 39(2), 645--650.
• Wang, J., & Farrell, J. (2005). Feasibility study for reductive destruction of carbon tetrachloride using bare and polymer coated nickel electrodes. Journal of Applied Electrochemistry, 35(3), 243-248.
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  Abstract: This research investigated the feasibility of an electrochemical reductive dechlorination method for removing carbon tetrachloride (CT) from contaminated waters. Reaction rates and Faradaic current efficiencies were measured for CT dechlorination in small flow-through reactors utilizing bare and silicone polymer coated nickel cathodes. CT dechlorination resulted in near stoichiometric production of methane. Rates of CT reduction were found to follow a first-order kinetic model for all CT concentrations investigated. CT disappearance was limited by its reaction rate and the performance of the reactor could be approximated with an ideal plug-flow reactor model. Destruction half-life values for CT with the bare nickel electrode ranged from 3.5 to 5.8∈min for electrode potentials ranging from -652 to -852∈mV with respect to the standard hydrogen electrode (SHE). The apparent electron transfer coefficient for CT reduction was only 0.06. The low transfer coefficient can be attributed to oxides coating the electrode surface that contributed to mass transfer resistance for CT reduction. Faradaic current efficiencies for CT reduction were found to decline with decreasing electrode potential. This can be attributed to an electron transfer coefficient for water reduction of 0.33 that was significantly greater than that for CT reduction. Faradaic current efficiencies could be increased by 100-360% by coating the electrode with a silicone polymer. In addition to decreasing the rate of water reduction by acting as hydrophobic mass transfer barrier the polymer coating resulted in small increases in CT reaction rates. The energy cost per volume of water treated was strongly dependent on the electrode potential but only weakly dependent on the influent CT concentration over the range of practical interest. The energy costs for reductive dechlorination appear to be lower than the carbon costs for adsorptive treatment of CT. This indicates that low current efficiencies at low CT concentrations are not a significant obstacle for developing a practical treatment process. The main impediment to electrochemical treatment for removing CT from water is the slow reaction rate that requires large reactors for obtaining sufficient hydraulic detention time to meet effluent water standards. © Springer 2005.
• Wang, J., & Farrell, J. (2005). Feasibility study for reductive destruction of carbon tetrachloride using bare and polymer coated nickel electrodes. Journal of applied electrochemistry, 35(3), 243--248.
• Zhang, N., Blowers, P., & Farrell, J. (2005). Ab initio study of carbon-chlorine bond cleavage in carbon tetrachloride. Environmental Science and Technology, 39(2), 612-617.
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  PMID: 15707062;Abstract: Chlorinated solvents in groundwater are known to undergo reductive dechlorination reactions with Fe(II)-containing minerals and with corroding metals in permeable-barrier treatment systems. This research investigated the effect of the reaction energy on the reaction pathway for C-Cl bond cleavage in carbon tetrachloride (CCl4). Hartree-Fock, density functional theory, and modified complete basis set ab initio methods were used to study adiabatic electron transfer to aqueous-phase CCl4. The potential energies associated with fragmentation of the carbon tetrachloride anion radical ( .CCl4-) into a trichloromethyl radical ( .CCl3) and a chloride ion (Cl-) were explored as a function of the carbon-chlorine bond distance during cleavage. The effect of aqueous solvation was investigated using a continuum conductor-like screening model. Solvation significantly lowered the energies of the reaction products, suggesting that dissociative electron transfer was enhanced by solvation. The potential energy curves in an aqueous medium indicate that reductive cleavage undergoes a change from an innersphere to an outer-sphere mechanism as the overall energy change for the reaction is increased. The activation energy for the reaction was found to be a linear function of the overall energy change, and the Marcus-Hush model was used to relate experimentally measured activation energies for CCl4 reduction to overall reaction energies. Experimentally measured activation energies for CCl4 reduction by corroding iron correspond to reaction energies that are insufficiently exergonic for promoting the outer-sphere mechanism. This suggests that the different reaction pathways that have been observed for CCl4 reduction by corroding iron arise from different catalytic interactions with the surface, and not from differences in energy of the transferred electrons.
• Zhang, N., Blowers, P., & Farrell, J. (2005). Ab initio study of carbon-chlorine bond cleavage in carbon tetrachloride. Environmental science \& technology, 39(2), 612--617.
• Zhang, N., Blowers, P., & Farrell, J. (2005). Evaluation of density functional theory methods for studying chemisorption of arsenite on ferric hydroxides. Environmental Science and Technology, 39(13), 4816-4822.
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  PMID: 16053079;Abstract: Understanding adsorption of arsenic on ferric hydroxide surfaces is important for predicting the fate of arsenic in the environment and in designing treatment systems for removing arsenic from potable water. This research investigated the binding of arsenite to ferric hydroxide clusters using several density functional theory methods. Comparison of calculated and experimentally measured As-O and As-Fe bond distances indicated that As(III) forms both bidentate and monodentante corner-sharing complexes with Fe(III) octahedra. Edge-sharing As(III) complexes were less energetically favorable and had As-O and As-Fe distances that deviated more from experimentally measured values than corner-sharing complexes. The hydrated bidentate complex was the most energetically favorable in the vacuum phase, while the monodentate complex was most favored in the aqueous phase. Structures optimized using the Harris and Perdew-Wang local functionals were close to both experimental data and structures optimized using the nonlocal Becke-Lee-Yang-Parr (BLYP) functional. Binding energies calculated with the gradient-corrected BLYP functional were only weakly dependent on the method used for geometry optimization. The approach of using low-level structures coupled with higher level single-point energies was found to reduce computational time by 75% with no loss in accuracy of the computed binding energies. © 2005 American Chemical Society.
• Zhang, N., Blowers, P., & Farrell, J. (2005). Evaluation of density functional theory methods for studying chemisorption of arsenite on ferric hydroxides. Environmental science \& technology, 39(13), 4816--4822.
• Blowers, P., Wang, J., & Farrell, J. (2004). Understanding Reduction of Carbon Tetrachloride at Nickel Surfaces. Environmental science \& technology, 1576--1581.
• Farrell, J., & Luo, J. (2004). Understanding chloroethene chemisorption to iron surfaces using molecular mechanics and density functional theory. ACS, Division of Environmental Chemistry - Preprints of Extended Abstracts, 44(2).
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  Abstract: The thermodynamic favorability and resulting structures for chemical desorption of trichloroethylene (TCE) and tetrachloroethylene (PCE) to iron surfaces were studied using molecular mechanics and periodic density functional theory. PCE chemisorbed via pi and di-sigma bond formation between Fe and C atoms, while TCE chemisorbed via sigma and di-sigma bonds. Upon sigma and pi-bond formation, all C-Cl bonds became activated and the Cl atoms formed bonds with the iron surface. Sigma and pi bond formation also resulted in a shortening of the carbon-carbon bond by an amount consistent with the conversion of a double to a triple bond. Upon di-sigma bond formation, only one C-Cl bond on each C atom became activated, while the remaining bonds remained unchanged. Both angles and bond lengths indicated that there was no change in bond order of the carbon-carbon double bond upon di-sigma bond formation. This is an abstract of a paper presented at the 228th ACS National Meeting (Philadelphia, PA 8/22-26/2004).
• Farrell, J., & Wang, J. (2004). Electrochemical inactivation of Triclosan with Boron Doped Diamond Film Electrodes. Environmental science \& technology, 5232--5237.
• Farrell, J., Farrell, J. -., Wang, J., & Farrell, J. -. (2004). Electrochemical inactivation of triclosan with boron doped diamond film electrodes. Environmental science & technology, 38(19).
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  This research investigated an electrochemical method for inactivating contaminated stockpiles of the biocidal agent, triclosan. The goal of the electrolysis was to produce products that were amenable to treatment in conventional activated sludge treatment systems. Triclosan oxidation in electrochemical cells with boron doped diamond (BDD) film anodes was investigated in aqueous solutions at a pH value of 12. Chronoamperometry experiments showed that direct oxidation of triclosan occurred at potentials below those for H2O, Cl-, or OH- oxidation. Measurable rates of triclosan oxidation began at potentials above 0.4 V with respect to the standard hydrogen electrode (SHE), while potentials of 0.5, 1.3, and 1.8 V were required to obtain measurable oxidation rates of H2O, Cl-, and OH-, respectively. At anode potentials below 2 V, the dominant electrode reaction involved direct triclosan oxidation, while indirect oxidation was the dominant pathway at higher potentials. However, cyclic voltammetry experiments showed that direct oxidation of triclosan resulted in the formation of a passivating film on the electrode that could only be removed by oxidation at potentials above 3 V. Direct triclosan oxidation showed a very weak potential dependence, suggesting that its oxidation was limited by chemical dependent factors rather than by an outer-sphere electron transfer reaction. Organic triclosan oxidation products consisted primarily of chlorinated acetic acids and chlorinated phenolic compounds. Although the byproducts of triclosan oxidation became increasingly less reactive with increasing electrolysis time, triclosan could be completely oxidized to CO2 at current densities above 2 mA/cm2. Microtox testing indicated that residual triclosan accounted for nearly all the toxicity in the treated water, despite the fact that chlorinated byproduct concentrations were significantly higher than those of triclosan itself.
• Farrell, J., Farrell, J. -., Wang, J., Blowers, P., & Farrell, J. -. (2004). Understanding reduction of carbon tetrachloride at nickel surfaces. Environmental science & technology, 38(5).
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  Nickel has been found to be an effective cathode material and catalyst for reductive destruction of chlorinated solvents in contaminated water. This study investigated reductive dechlorination of carbon tetrachloride (CT) at a nickel rotating disk electrode using chronoamperometry and electrochemical impedance spectroscopy. Chronoamperometry experiments were performed to determine rates of CT reduction as a function of the electrode potential, pH, CT concentration, and temperature. The reaction products of CT dechlorination were 95 +/- 4% methane and 4.1 +/- 2.5% chloroform. Only trace levels of methylene chloride and chloromethane were produced, indicating that sequential hydrogenolysis was not the predominant pathway for methane production. Electrochemical impedance spectroscopy showed that the rate-limiting step for methane production was the transfer of the first electron to a physically adsorbed CT molecule. The temperature independence of the electron transfer coefficient and the decreasing activation energy with decreasing electrode potential indicated that the rate-limiting step involved an outer-sphere electron transfer. At neutral pH values, oxides inactivated much of the electrode surface for both CT reduction and hydrogen evolution. At lower pH values, oxide dissolution served to increase the electroactive surface area of the disk electrode. Anson analysis and kinetic modeling showed that CT adsorption to electroactive sites was a nonlinear function of the CT concentration and was in equilibrium with the bulk solution. CT dechlorination rates on nickel electrodes were 16 times slower than those on iron electrodes under similar conditions. However, CT reactions at nickel surfaces produced predominantly methane as the first detectable product, while reduction at iron surfaces produced chloroform. These results suggest that, although nickel is not a catalyst for the rate-limiting step for CT dechlorination, it may serve a catalytic role in subsequent reaction steps.
• Farrell, J., Wang, J., LeBlanc, R., Gan, J., Zhu, P., Aust, S., Lemley, A., & others, . (2004). Electrochemical destruction of triclosan.. Pesticide decontamination and detoxification, 99--112.
• Farrell, J., Zhang, N., & Blowers, P. (2004). Ab Initio Study of Carbon−Chlorine Bond Cleavage in Carbon Tetrachloride. Environmental Science & Technology, 39(2), 612-617. doi:10.1021/es049480a
• Tamilmani, S., Huang, W. H., Raghavan, S., & Farrell, J. (2004). Electrochemical treatment of simulated copper CMP wastewater using boron doped diamond thin film electrodes-a feasibility study. Semiconductor Manufacturing, IEEE Transactions on, 17(3), 448--454.
• Tamilmani, S., Huang, W., Raghavan, S., & Farrell, J. (2004). Ultraclean and Environmentally Benign Manufacturing-Electrochemical Treatment of Simulated Copper CMP Wastewater Using Boron Doped Diamond Thin Film Electrodes--A Feasibility Study. IEEE Transactions on Semiconductor Manufacturing, 17(3), 448--454.
• Wang, J., & Farrell, J. (2004). Electrochemical inactivation of triclosan with boron doped diamond film electrodes. Environmental Science and Technology, 38(19), 5232-5237.
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  PMID: 15506222;Abstract: This research investigated an electrochemical method for inactivating contaminated stockpiles of the biocidal agent, triclosan. The goal of the electrolysis was to produce products that were amenable to treatment in conventional activated sludge treatment systems. Triclosan oxidation in electrochemical cells with boron doped diamond (BDD) film anodes was investigated in aqueous solutions at a pH value of 12. Chronoamperometry experiments showed that direct oxidation of triclosan occurred at potentials below those for H2O, CI-, or OH- oxidation. Measurable rates of triclosan oxidation began at potentials above 0.4 V with respect to the standard hydrogen electrode (SHE), while potentials of 0.5, 1.3, and 1.8 V were required to obtain measurable oxidation rates of H2O, CI-, and OH-, respectively. At anode potentials below 2 V, the dominant electrode reaction involved direct triclosan oxidation, while indirect oxidation was the dominant pathway at higher potentials. However, cyclic voltammetry experiments showed that direct oxidation of triclosan resulted in the formation of a passivating film on the electrode that could only be removed by oxidation at potentials above 3 V. Direct triclosan oxidation showed a very weak potential dependence, suggesting that its oxidation was limited by chemical dependent factors rather than by an outer-sphere electron transfer reaction. Organic triclosan oxidation products consisted primarily of chlorinated acetic acids and chlorinated phenolic compounds. Although the byproducts of triclosan oxidation became increasingly less reactive with increasing electrolysis time, triclosan could be completely oxidized to COz at current densities above 2 mA/cm2. Microtox testing indicated that residual triclosan accounted for nearly all the toxicity in the treated water, despite the fact that chlorinated byproduct concentrations were significantly higher than those of triclosan itself.
• Wang, J., & Farrell, J. (2004). Electrochemical inactivation of triclosan with boron doped diamond film electrodes. Environmental science \& technology, 38(19), 5232--5237.
• Wang, J., Blowers, P., & Farrell, J. (2004). Understanding Reduction of Carbon Tetrachloride at Nickel Surfaces. Environmental Science and Technology, 38(5), 1576-1581.
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  PMID: 15046362;Abstract: Nickel has been found to be an effective cathode material and catalyst for reductive destruction of chlorinated solvents in contaminated water. This study investigated reductive dechlorination of carbon tetrachloride (CT) at a nickel rotating disk electrode using chronoamperometry and electrochemical impedance spectroscopy. Chronoamperometry experiments were performed to determine rates of CT reduction as a function of the electrode potential, pH, CT concentration, and temperature. The reaction products of CT dechlorination were 95 ± 4% methane and 4.1 ± 2.5% chloroform. Only trace levels of methylene chloride and chloromethane were produced, indicating that sequential hydrogenolysis was not the predominant pathway for methane production. Electrochemical impedance spectroscopy showed that the rate-limiting step for methane production was the transfer of the first electron to a physically adsorbed CT molecule. The temperature independence of the electron transfer coefficient and the decreasing activation energy with decreasing electrode potential indicated that the rate-limiting step involved an outer-sphere electron transfer. At neutral pH values, oxides inactivated much of the electrode surface for both CT reduction and hydrogen evolution. At lower pH values, oxide dissolution served to increase the electroactive surface area of the disk electrode. Anson analysis and kinetic modeling showed that CT adsorption to electroactive sites was a nonlinear function of the CT concentration and was in equilibrium with the bulk solution. CT dechlorination rates on nickel electrodes were 16 times slower than those on iron electrodes under similar conditions. However, CT reactions at nickel surfaces produced predominantly methane as the first detectable product, while reduction at iron surfaces produced chloroform. These results suggest that, although nickel is not a catalyst for the rate-limiting step for CT dechlorination, it may serve a catalytic role in subsequent reaction steps.
• Wang, J., Blowers, P., & Farrell, J. (2004). Understanding reduction of carbon tetrachloride at nickel surfaces. Environmental science \& technology, 38(5), 1576--1581.
• Farrell, J. (2003). Investigating the Role of Atomic Hydrogen on Chloroethene Reactions with Iron Using Tafel Analysis and Electrochemical Impedance Spectroscopy. Environmental science \& technology, 3891--3903.
• Farrell, J., & Wang, J. (2003). Investigating the Role of Atomic Hydrogen on Chloroethene Reactions with Iron Using Tafel Analysis and Electrochemical Impedance Spectroscopy. Environmental Science & Technology, 37(17), 3891-3896. doi:10.1021/es0264605
• Farrell, J., Farrell, J. -., Luo, J., & Farrell, J. -. (2003). Examination of hydrophobic contaminant adsorption in mineral micropores with grand canonical Monte Carlo simulations. Environmental science & technology, 37(9).
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  A molecular level understanding of the interactions between hydrophobic organic contaminants (HOCs) and sediments is needed in order to assess contaminant fate in the environment. Grand canonical Monte Carlo simulations were performed to investigate water and trichloroethylene (TCE) adsorption in slit micropores confined by charged and uncharged silica surfaces. Gas-phase single-sorbate simulations with water or TCE were performed as well as mixture simulations of bulk water containing TCE at 1% of its saturation concentration. Gas-phase isosteric heats for water adsorption in the uncharged pores ranged from -40 to -52 kJ/mol, and the densities of the adsorbed water phases were always less than that for bulk water. Gas-phase isosteric heats for water adsorption in the charged pores ranged from -79 to -170 kJ/mol, and the densities of the adsorbed water phases were close to that for bulk water. The isosteric heats and water densities indicated that the uncharged pores were mildly hydrophobic, and the charged pores were very hydrophilic. In mixture simulations of adsorption from solution, the presence of water promoted TCE adsorption in uncharged pores with widths between 14 and 20 A. The isosteric heats for TCE adsorption from solution ranged from -14 to -27 kJ/mol in the uncharged pores and from -9.3 to -50 kJ/mol in the charged pores. Strong attractions to the pore surfaces were significantly diminished after adsorption of the first two monolayers of either adsorbate. Aqueous-phase TCE at a concentration equal to 1% of its saturation concentration was able to completely displace adsorbed water in uncharged pores. Even in highly hydrophilic pores, TCE at this concentration was able to displace up to 50% of the adsorbed water. Apparent differential enthalpies of adsorption determined from the temperature dependence of TCE adsorption isotherms underestimated the magnitude of the true isosteric heats of adsorption by up to 30 kJ/mol. This shows that HOC adsorption enthalpies determined from the temperature dependence of their adsorption isotherms underestimate the true strength of HOC-adsorbent interactions.
• Farrell, J., Farrell, J. -., Wang, J., & Farrell, J. -. (2003). Investigating the role of atomic hydrogen on chloroethene reactions with iron using tafel analysis and electrochemical impedance spectroscopy. Environmental science & technology, 37(17).
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  Metallic iron filings are commonly employed as reducing agents in permeable barriers used for remediating groundwater contaminated by chlorinated solvents. Reactions of trichloroethylene (TCE) and tetrachloroethylene (PCE) with zerovalent iron were investigated to determine the role of atomic hydrogen in their reductive dechlorination. Experiments simultaneously measuring dechlorination and iron corrosion rates were performed to determine the fractions of the total current going toward dechlorination and hydrogen evolution. Corrosion rates were determined using Tafel analysis, and dechlorination rates were determined from rates of byproduct generation. Electrochemical impedance spectroscopy (EIS) was used to determine the number of reactions that controlled the observed rates of chlorocarbon disappearance, as well as the role of atomic hydrogen in TCE and PCE reduction. Comparison of iron corrosion rates with those for TCE reaction showed that TCE reduction occurred almost exclusively via atomic hydrogen at low pH values and via atomic hydrogen and direct electron transfer at neutral pH values. In contrast, reduction of PCE occurred primarily via direct electron transfer at both low and neutral pH values. At low pH values and micromolar concentrations, TCE reaction rates were faster than those for PCE due to more rapid reduction of TCE by atomic hydrogen. At neutral pH values and millimolar concentrations, PCE reaction rates were faster than those for TCE. This shift in relative reaction rates was attributed to a decreasing contribution of the atomic hydrogen reaction mechanism with increasing halocarbon concentrations and pH values. The EIS data showed that all the rate limitations for TCE and PCE dechlorination occurred during the transfer of the first two electrons. Results from this study show that differences in relative reaction rates of TCE and PCE with iron are dependent on the significance of the reduction pathway involving atomic hydrogen.
• Farrell, J., Manspeaker, C., & Luo, J. (2003). Understanding competitive adsorption of water and trichloroethylene in a high-silica Y zeolite. Microporous and Mesoporous Materials, 59(2-3), 205-214.
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  Abstract: In this study, the adsorption of trichloroethylene (TCE) and water was investigated on a hydrophobic Y zeolite with an Si to Al ratio of 80. Single adsorbate isotherms for water or TCE, and TCE isotherms under conditions of 100% relative humidity (RH) were measured over the temperature range from 5 to 47 °C. Water adsorption isotherms were well described by the Freundlich isotherm model with isotherm exponents of 1.5. Isosteric heats for water adsorption were less exothermic than the enthalpy for water condensation, and ranged from -34 to -39 kJ/mol. Entropy changes associated with water adsorption were less negative than those for condensation of bulk water, indicating that the adsorbed phase had less structure than bulk water. Type V isotherms were observed for TCE adsorption under conditions of 0% RH. Isosteric heats for TCE adsorption on the dry zeolite ranged from -40 to -56 kJ/mol, and showed regions where the heats of adsorption both increased and decreased with increasing TCE loading. The Henry's law asymptote for TCE adsorption on the dry zeolite was not experimentally accessible at the lowest vapor concentrations investigated. Type V isotherms with a linear region were observed for TCE adsorption under conditions of 100% RH. The isosteric heats for TCE adsorption on the wet zeolite depended strongly on the adsorbed phase concentration, and ranged from -35 to -64 kJ/mol. At adsorbed phase TCE concentrations below 0.01 g/g, the presence of water increased TCE uptake by the zeolite. However, at all other TCE loadings the presence of water decreased TCE adsorption by up to 83%. © 2003 Elsevier Science Inc. All rights reserved.
• Farrell, J., Manspeaker, C., & Luo, J. (2003). Understanding competitive adsorption of water and trichloroethylene in a high-silica Y zeolite. Microporous and mesoporous materials, 59(2), 205--214.
• Luo, J., & Farrell, J. (2003). Examination of hydrophobic contaminant adsorption in mineral micropores with grand canonical Monte Carlo simulations. Environmental Science and Technology, 37(9), 1775-1782.
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  PMID: 12775048;Abstract: A molecular level understanding of the interactions between hydrophobic organic contaminants (HOCs) and sediments is needed in order to assess contaminant fate in the environment. Grand canonical Monte Carlo simulations were performed to investigate water and trichloroethylene (TCE) adsorption in slit micropores confined by charged and uncharged silica surfaces. Gas-phase single-sorbate simulations with water or TCE were performed as well as mixture simulations of bulk water containing TCE at 1% of its saturation concentration. Gas-phase isosteric heats for water adsorption in the uncharged pores ranged from -40 to -52 kJ/mol, and the densities of the adsorbed water phases were always less than that for bulk water. Gas-phase isosteric heats for water adsorption in the charged pores ranged from -79 to -170 kJ/mol, and the densities of the adsorbed water phases were close to that for bulk water. The isosteric heats and water densities indicated that the uncharged pores were mildly hydrophobic, and the charged pores were very hydrophilic. In mixture simulations of adsorption from solution, the presence of water promoted TCE adsorption in uncharged pores with widths between 14 and 20 Å. The isosteric heats for TCE adsorption from solution ranged from -14 to -27 kJ/mol in the uncharged pores and from -9.3 to -50 kJ/mol in the charged pores. Strong attractions to the pore surfaces were significantly diminished after adsorption of the first two monolayers of either adsorbate. Aqueous-phase TCE at a concentration equal to 1% of its saturation concentration was able to completely displace adsorbed water in uncharged pores. Even in highly hydrophilic pores, TCE at this concentration was able to displace up to 50% of the adsorbed water. Apparent differential enthalpies of adsorption determined from the temperature dependence of TCE adsorption isotherms underestimated the magnitude of the true isosteric heats of adsorption by up to 30 kJ/ mol. This shows that HOC adsorption enthalpies determined from the temperature dependence of their adsorption isotherms underestimate the true strength of HOC-adsorbent interactions.
• Luo, J., & Farrell, J. (2003). Examination of hydrophobic contaminant adsorption in mineral micropores with grand canonical Monte Carlo simulations. Environmental science \& technology, 37(9), 1775--1782.
• Melitas, N., Conklin, M., & Farrell, J. (2003). Understanding the mechanisms controlling the kinetics of arsenate and chromate removal from solution using zero valent iron. CHLORINATED SOLVENT AND DNAPL REMEDIATION, 837, 165--180.
• Wang, J., & Farrell, J. (2003). Investigating the role of atomic hydrogen on chloroethene reactions with iron using Tafel analysis and electrochemical impedance spectroscopy. Environmental Science and Technology, 37(17), 3891-3896.
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  PMID: 12967110;Abstract: Metallic iron filings are commonly employed as reducing agents in permeable barriers used for remediating groundwater contaminated by chlorinated solvents. Reactions of trichloroethylene (TCE) and tetrachloroethylene (PCE) with zerovalent iron were investigated to determine the role of atomic hydrogen in their reductive dechlorination. Experiments simultaneously measuring dechlorination and iron corrosion rates were performed to determine the fractions of the total current going toward dechlorination and hydrogen evolution. Corrosion rates were determined using Tafel analysis, and dechlorination rates were determined from rates of byproduct generation. Electrochemical impedance spectroscopy (EIS) was used to determine the number of reactions that controlled the observed rates of chlorocarbon disappearance, as well as the role of atomic hydrogen in TCE and PCE reduction. Comparison of iron corrosion rates with those for TCE reaction showed that TCE reduction occurred almost exclusively via atomic hydrogen at low pH values and via atomic hydrogen and direct electron transfer at neutral pH values. In contrast, reduction of PCE occurred primarily via direct electron transfer at both low and neutral pH values. At low pH values and micromolar concentrations, TCE reaction rates were faster than those for PCE due to more rapid reduction of TCE by atomic hydrogen. At neutral pH values and millimolar concentrations, PCE reaction rates were faster than those for TCE. This shift in relative reaction rates was attributed to a decreasing contribution of the atomic hydrogen reaction mechanism with increasing halocarbon concentrations and pH values. The EIS data showed that all the rate limitations for TCE and PCE dechlorination occurred during the transfer of the first two electrons. Results from this study show that differences in relative reaction rates of TCE and PCE with iron are dependent on the significance of the reduction pathway involving atomic hydrogen.
• Wang, J., & Farrell, J. (2003). Investigating the role of atomic hydrogen on chloroethene reactions with iron using Tafel analysis and electrochemical impedance spectroscopy. Environmental science \& technology, 37(17), 3891--3896.
• Wang, J., & Farrell, J. (2003). Mechanistic and kinetic study of carbon tetrachloride reduction at nickel surfaces. ACS Division of Environmental Chemistry, Preprints, 43(2).
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  Abstract: There has been considerable interest in developing destructive treatment methods for removing chlorinated organic solvents from contaminated waters. A study investigated the mechanism and kinetics of carbon tetrachloride (CT) reduction at nickel cathodes. Either competition between CT molecules for reactive sites on the electrode surface, or adsorption of CT onto the electrode followed a nonlinear isotherm. The rates of subsequent reaction steps did not affect the overall rate of hydrogen evolution. Transfer of the first electron to a CT molecular was the rate-limiting step for CT reduction to CH4. The rate-limiting step for complete CT dechlorination to CH4 involved an outer sphere electron transfer.
• Wang, J., & Farrell, J. (2003). Understanding the role of atomic hydrogen on chloroethene reactions at iron surfaces. ACS Division of Environmental Chemistry, Preprints, 43(2).
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  Abstract: There has been increasing interest in using metallic iron fillings for remediating groundwater contaminated by chlorinated solvents. The role of atomic hydrogen in reductive dechlorination of trichloroethylene (TCE) and tetrachloroethylene (PCE) was studied. At pH = 7, TCE reaction rates were 2 ± 0.26 times faster than those for PCE when each was present at 6 μM concentration, and were 1.5 ± 0.15 times faster at 30 μM concentration. The reaction mechanism involving atomic hydrogen could be saturated at low TCE concentrations. Thus, at neutral pH values reduction by atomic hydrogen could be the dominant TCE reduction pathway only at very low TCE concentrations.
• Curry, J., Farrell, J., Luo, J., & Blowers, P. (2002). Experimental and Molecular Mechanics and Ab Initio Investigation of Activated Adsorption and Desorption of Trichloroethylene in Mineral Micropores. Environmental Science & Technology, 36(7), 1524-1531. doi:10.1021/es011172e
• Farrell, J. (2002). Assessing arsenic removal technologies. Southwest Hydrology, 20.
• Farrell, J., & Luo, J. (2002). Grand Canonical Monte Carlo study of sediment-contaminant interactions. ACS Division of Environmental Chemistry, Preprints, 42(2), 123-126.
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  Abstract: Contamination of aquifer and river sediments by hydrophobic organic compounds is a widespread problem that affects both the quality of potable water supplies, and the bioaccumulation of toxic compounds in aquatic organisms. Grand canonical Monte Carlo simulations were used to investigate the molecular-scale interactions between trichloroethylene (TCE) and sediment micropores. The energy changes accompanying TCE adsorption in the charged pore followed the same trend as those in the uncharged pore. Increasing pore widths were associated with an increasing contribution of entropically promoted adsorption. The negative entropy change accompanying TCE adsorption for pores widths of 12 Å and below was attributed to more restricted molecular motion in the charged pore due to the strong force field associated with the uncompensated charges. In the uncharged pore, the negative adsorption of water was promoted primarily by entropy effects. The lower entropy of adsorbed water resulted in lower water densities in the pore phase as compared to the bulk phase. In the charged pore, water adsorption was promoted by the highly exothermic heats of adsorption, but was nearly equally opposed by the loss in entropy upon adsorption. The net result was that the water density in the charged pores was similar to that in the bulk solution phase. The decrease in entropy accompanying water adsorption arises from the orienting effect of the charged surface sites. This is an abstract of a paper presented at the 224th ACS National Meting (Boston, MA 8/18-22/2002).
• Farrell, J., Farrell, J. -., Melitas, N., & Farrell, J. -. (2002). Understanding chromate reaction kinetics with corroding iron media using Tafel analysis and electrochemical impedance spectroscopy. Environmental science & technology, 36(24).
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  The kinetics of chromate removal from contaminated water by zerovalent iron media are not well understood. This study investigated the reactions occurring on iron surfaces in chromate solutions in order to understand the removal kinetics and to assess the long-term ability of zerovalent iron for removing Cr(VI) from contaminated water. Tafel polarization analysis and electrochemical impedance spectroscopy were used to determine the corrosion rates and charge-transfer resistances associated with Cr(VI) removal by iron wires suspended in electrolyte solutions with initial Cr(VI) concentrations of 10,000 microg/L. The condition of the iron surfaces at the time of their exposure to chromate determined the effectiveness of the iron for chromate removal. Both iron coated with a water-formed oxide and initially oxide-free iron were effective for chromate removal. However, iron coated with an air-formed oxide was an order of magnitude less effective for removing soluble chromium. Although iron with the air-formed oxide was largely passivated with respect to chromate removal, its overall rate of corrosion was similar to that for iron with the other initial surface conditions. This indicates that water, but not chromate, was able to penetrate the air-formed oxide coating and access cathodic sites. For all initial surface conditions, addition of chromate decreased the corrosion rate by increasing the corrosion potential and the anodic charge transfer resistance. Although Cr(VI) is a strong oxidant rates of iron corrosion were not proportional to the aqueous Cr(VI) concentrations due to anodic control of iron corrosion. Under anodically controlled conditions, the rate of corrosion was limited by the rate at which Fe2+ could be released at anodic sites and not by the rate at which oxidants were able to accept electrons. This study shows that the zero order removal kinetics of Cr(VI) by iron media can be explained by anodic control of iron corrosion and the concomitant anodic control of Cr(VI) reduction.
• Farrell, J., Luo, J., Blowers, P., & Curry, J. (2002). Experimental and molecular mechanics and Ab initio investigation of activated adsorption and desorption of trichloroethylene in mineral micropores. Environmental Science and Technology, 36(7), 1524-1531.
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  PMID: 11999061;Abstract: This research investigated activated adsorption of a hydrophobic organic contaminant (HOC) in mineral micropores using experimental and molecular modeling techniques. Adsorption of trichloroethylene (TCE) on a silica gel adsorbent was measured using a frontal analysis chromatography technique at atmospheric and elevated fluid pressures. Increasing the fluid pressure yielded increased TCE uptake that was not released upon lowering the pressure back to atmospheric conditions. This showed that the increase in pressure was able to rapidly induce the formation of a desorption-resistant fraction that previous investigations have shown requires months to develop at atmospheric pressure. Grand Canonical Monte Carlo (GCMC) modeling was then used to elucidate the nature of water and TCE behavior within silica micropores. The GCMC modeling showed that molecular scale packing restrictions resulted in pore fluid densities that ranged from 0.28 to 0.78 of those in the bulk solution. The modeling also showed that TCE was able to displace water from hydrophilic mineral pores due to molecular scale packing restrictions. Exothermic isosteric heats for TCE adsorption up to -27 kJ/mol were observed and were greatest in pores of 7 and 8 Å. This indicated that TCE adsorption was energetically most favorable in pores that were minimally large enough to accommodate a TCE molecule. The pressure-induced uptake appeared to result primarily from an increase in the packing density in the smallest pores. Ab initio calculations showed that small distortions of a TCE molecule from its low energy conformation require high activation energies. Results from this study indicate that activated adsorption requiring bond angle distortions in the adsorbate may be responsible for the slow attainment of adsorptive equilibrium of HOCs on microporous solids. Likewise, activated desorption from molecular-sized adsorption sites may contribute to the slow release of HOCs from aquifer sediments.
• Farrell, J., Luo, J., Blowers, P., & Curry, J. (2002). Experimental and molecular mechanics and ab initio investigation of activated adsorption and desorption of trichloroethylene in mineral micropores. Environmental science \& technology, 36(7), 1524--1531.
• Farrell, J., Melitas, N., Conklin, M., Farrell, J. -., & Farrell, J. -. (2002). Electrochemical study of arsenate and water reduction on iron media used for arsenic removal from potable water. Environmental science & technology, 36(14).
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  Zerovalent iron filings have been proposed as a filter medium for removing As(III) and As(V) compounds from potable water. The removal mechanism involves complex formation of arsenite and arsenate with the iron surface and with iron oxides produced from iron corrosion. There is conflicting evidence in the literature on whether As(V) can be reduced to As(III) by iron filter media. This research uses electrochemical methods to investigate the redox reactions that occur on the surface of zerovalent iron in arsenic solutions. The effect of arsenic on the corrosion rate of zerovalent iron was investigated by analysis of Tafel diagrams for iron wire electrodes in anaerobic solutions with As(V) concentrations between 100 and 20,000 microg/L. As(V) reduction in the absence of surface oxides was investigated by analysis of chronoamperometry profiles for iron wire electrodes in solutions with As(V) concentrations ranging from 10000 to 106 microg/L. The effect of pH on As(V) reduction was investigated by analyses of chronopotentiometry profiles for iron wire electrodes at pH values of 2, 6.5, and 11. For freely corroding iron, the presence of As(III) and As(V) decreased the iron corrosion rate by a factor of 5 as compared to that in a 3 mM CaSO4 blank electrolyte solution. The decrease in corrosion rate was independent of the arsenic concentration and was due to the blocking of cathodic sites for water reduction by arsenic compounds chemisorbed to the iron surface. The chronoamperometry and chronopotentiometry experiments showed that elevated pH and increased As(III) to As(V) ratios near the iron surface decreased the thermodynamic favorability for As(V) reduction. Therefore, reduction of As(V) occurred only at potentials that were significantly below the apparent equilibrium potentials based on bulk solution pH values and As(III) to As(V) ratios. The potentials required to reduce more than 1% of the As(V) to As(III) were below those that are obtainable in freely corroding iron media. This indicates that there will be minimal or no reduction of As(V) in iron media filters under conditions relevant to potable water treatment.
• Farrell, J., Melitas, N., Wang, J., Conklin, M., O'Day, P., Farrell, J. -., & Farrell, J. -. (2002). Understanding soluble arsenate removal kinetics by zerovalent iron media. Environmental science & technology, 36(9).
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  Zerovalent iron filings have been proposed as a filter medium for removing arsenic compounds from potable water supplies. This research investigated the kinetics of arsenate removal from aqueous solutions by zerovalent iron media. Batch experiments were performed to determine the effect of the iron corrosion rate on the rate of As(V) removal. Tafel analyses were used to determine the effect of the As(V) concentration on the rate of iron corrosion in anaerobic solutions. As(V) removal in column reactors packed with iron filings was measured over a 1-year period of continuous operation. Comparison of As(V) removal by freely corroding and cathodically protected iron showed that rates of arsenate removal were dependent on the continuous generation of iron oxide adsorption sites. In addition to adsorption site availability, rates of arsenate removal were also limited by mass transfer associated with As(V) diffusion through iron corrosion products. Steady-state removal rates in the column reactor were up to 10 times faster between the inlet-end and the first sampling port than between the first sampling port and the effluent-end of the column. Faster removal near the influent-end of the column was due to a faster rate of iron oxidation in that region. The presence of 100 microg/L As(V) decreased the iron corrosion rate by up to a factor of 5 compared to a blank electrolyte solution. However, increasing the As(V) concentration from 100 to 20,000 microg/L resulted in no further decrease in the iron corrosion rate. The kinetics of arsenate removal ranged between zeroth- and first-order with respect to the aqueous As(V) concentration. The apparent reaction order was dependent on the availability of adsorption sites and on the aqueous As(V) concentration. X-ray absorption spectroscopy analyses showed the presence of iron metal, magnetite (Fe3O4), an Fe(III) oxide phase, and possibly an Fe(II,III) hydroxide phase in the reacted iron filings. These mixed valent oxide phases are not passivating and permit sustained iron corrosion and continuous generation of new sites for As(V) adsorption.
• Melitas, N., & Farrell, J. (2002). Understanding chromate reaction kinetics with corroding iron media using Tafel analysis and electrochemical impedance spectroscopy. Environmental science \& technology, 36(24), 5476--5482.
• Melitas, N., Conklin, M., & Farrell, J. (2002). Electrochemical study of arsenate and water reduction on iron media used for arsenic removal from potable water. Environmental Science and Technology, 36(14), 3188-3193.
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  PMID: 12141502;Abstract: Zerovalent iron filings have been proposed as a filter medium for removing As(III) and As(V) compounds from potable water. The removal mechanism involves complex formation of arsenite and arsenate with the iron surface and with iron oxides produced from iron corrosion. There is conflicting evidence in the literature on whether As(V) can be reduced to As(III) by iron filter media. This research uses electrochemical methods to investigate the redox reactions that occur on the surface of zerovalent iron in arsenic solutions. The effect of arsenic on the corrosion rate of zerovalent iron was investigated by analysis of Tafel diagrams for iron wire electrodes in anaerobic solutions with As(V) concentrations between 100 and 20,000 μg/L. As(V) reduction in the absence of surface oxides was investigated by analysis of chronoamperometry profiles for iron wire electrodes in solutions with As(V) concentrations ranging from 10 000 to 106 μg/L. The effect of pH on As(V) reduction was investigated by analyses of chronopotentiometry profiles for iron wire electrodes at pH values of 2, 6.5, and 11. For freely corroding iron, the presence of As(III) and As(V) decreased the iron corrosion rate by a factor of 5 as compared to that in a 3 mM CaSO4 blank electrolyte solution. The decrease in corrosion rate was independent of the arsenic concentration and was due to the blocking of cathodic sites for water reduction by arsenic compounds chemisorbed to the iron surface. The chronoamperometry and chronopotentiometry experiments showed that elevated pH and increased As(III) to As(V) ratios near the iron surface decreased the thermodynamic favorability for As(V) reduction. Therefore, reduction of As(V) occurred only at potentials that were significantly below the apparent equilibrium potentials based on bulk solution pH values and As(III) to As(V) ratios. The potentials required to reduce more than 1% of the As(V) to As(III) were below those that are obtainable in freely corroding iron media. This indicates that there will be minimal or no reduction of As(V) in iron media filters under conditions relevant to potable water treatment.
• Melitas, N., Conklin, M., & Farrell, J. (2002). Electrochemical study of arsenate and water reduction on iron media used for arsenic removal from potable water. Environmental science \& technology, 36(14), 3188--3193.
• Melitas, N., Wang, J., Conklin, M., O'Day, P., & Farrell, J. (2002). Understanding soluble arsenate removal kinetics by zerovalent iron media. Environmental Science and Technology, 36(9), 2074-2081.
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  PMID: 12026995;Abstract: Zerovalent iron filings have been proposed as a filter medium for removing arsenic compounds from potable water supplies. This research investigated the kinetics of arsenate removal from aqueous solutions by zerovalent iron media. Batch experiments were performed to determine the effect of the iron corrosion rate on the rate of As(V) removal. Tafel analyses were used to determine the effect of the As(V) concentration on the rate of iron corrosion in anaerobic solutions. As(V) removal in column reactors packed with iron filings was measured over a 1-year period of continuous operation. Comparison of As(V) removal by freely corroding and cathodically protected iron showed that rates of arsenate removal were dependent on the continuous generation of iron oxide adsorption sites. In addition to adsorption site availability, rates of arsenate removal were also limited by mass transfer associated with As(V) diffusion through iron corrosion products. Steady-state removal rates in the column reactor were up to 10 times faster between the inlet-end and the first sampling port than between the first sampling port and the effluent-end of the column. Faster removal near the influent-end of the column was due to a faster rate of iron oxidation in that region. The presence of 100 μg/L As(V) decreased the iron corrosion rate by up to a factor of 5 compared to a blank electrolyte solution. However, increasing the As(V) concentration from 100 to 20 000 μg/L resulted in no further decrease in the iron corrosion rate. The kinetics of arsenate removal ranged between zeroth- and first-order with respectto the aqueous As(V) concentration. The apparent reaction order was dependent on the availability of adsorption sites and on the aqueous As(V) concentration. X-ray absorption spectroscopy analyses showed the presence of iron metal, magnetite (Fe3O4), an Fe(III) oxide phase, and possibly an Fe(II,III) hydroxide phase in the reacted iron filings. These mixed valent oxide phases are not passivating and permit sustained iron corrosion and continuous generation of new sites for As(V) adsorption.
• Melitas, N., Wang, J., Conklin, M., O'Day, P., & Farrell, J. (2002). Understanding soluble arsenate removal kinetics by zerovalent iron media. Environmental science \& technology, 36(9), 2074--2081.
• Tie, L. i., & Farrell, J. (2002). Mechanisms controlling chlorocarbon reduction at iron surfaces. ACS Symposium Series, 806, 397-410.
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  Abstract: This research investigated whether rates of carbon tetrachloride (CT) and trichloroethylene (TCE) dechlorination on iron surfaces are limited by rates of electron transfer. The contributions of direct electron transfer and indirect reduction via atomic hydrogen to the overall dechlorination rates were also investigated. Electron transfer coefficients for CT and TCE were determined from measurements of dechlorination rates over a potential range from -600 to -1200 mV (SHE), and a temperature range of 2 to 42 °C. The transfer coefficient for CT was found to be independent of temperature, and the apparent activation energy was found to decrease with increasingly negative electrode potentials. These observations indicate that the rate of electron transfer controlled the observed rate of CT dechlorination. In contrast, the transfer coefficient for TCE was temperature dependent, and increased with increasingly negative electrode potentials. This indicated that TCE dechlorination was not controlled by an electron transfer step. Comparison of analytically and amperometrically measured reaction rates showed that CT reduction occurred primarily via direct electron transfer, while TCE reduction involved both direct electron transfer, and an indirect mechanism involving atomic hydrogen. Comparison of amperometrically and analytically measured reaction rates for TCE and perchloroethylene (PCE) also supports an indirect mechanism for chloroethene reduction.
• Wang, J., & Farrell, J. (2002). Direct and indirect electron transfer mechanisms involved in chlorocarbon reduction. ACS Division of Environmental Chemistry, Preprints, 42(2), 493-495.
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  Abstract: The electron transfer reactions involved in reductive dechlorination of carbon tetrachloride (CT), trichloroethylene (TCE), and perchloroethylene (PCE) were studied. Increasing CT concentrations were associated with increasing iron corrosion rates, showing that CT was able to directly oxidize the iron wire. However, the current going towards CT reduction was always greater than the measured corrosion current. Since the measured corrosion currents only account for the oxidation of Fe(0) to Fe(II), this indicated that CT reduction also occurred via oxidation of Fe(II) to Fe(III). TCE reduction occurred primarily by reaction with atomic hydrogen produced from reduction of water. At a pH 7 rates of TCE reduction were less than those for PCE. However, at pH 3, the rates for TCE reduction were greater than those for PCE. This difference in relative reaction rates could be attributed to different rates of reaction with atomic hydrogen for TCE and PCE. The fraction of the iron surface covered with atomic hydrogen was much greater at pH value of 3 as compared to pH 7. Thus, the faster rate of TCE reduction at low pH could likely be attributed to its faster rate of reaction with atomic hydrogen. This is an abstract of a paper presented at the 224th ACS National Meeting (Boston, MA 8/18-22/2002).
• Farrell, J., & Li, T. (2001). Electrochemical Investigation of the Rate-Limiting Mechanisms for Trichloroethylene and Carbon Tetrachloride Reduction at Iron Surfaces. Environmental Science & Technology, 35(17), 3560-3565. doi:10.1021/es0019878
• Farrell, J., Wang, J. P., O'Day, P., & Conklin, M. (2001). Electrochemical and spectroscopic study of arsenate removal from water using zero-valent iron media. Environmental Science and Technology, 35(10), 2026-2032.
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  PMID: 11393984;Abstract: This study investigated the mechanisms involved in removing arsenate from drinking water supplies using zero-valent iron media. Batch experiments utilizing iron wires suspended in anaerobic arsenate solutions were performed to determine arsenate removal rates as a function of the arsenate solution concentration. Corrosion rates of the iron wires were determined as a function of elapsed time using Tafel analysis. The removal kinetics in the batch reactors were best described by a dual-rate model in which arsenate removal was pseudo-first-order at low concentrations and approached zero-order in the limit of high arsenate concentrations. The presence of arsenate decreased iron corrosion rates as compared to those in blank 3 mM CaSO4 background electrolyte solutions. However, constant corrosion rates were attained after approximately 10 days elapsed, indicating that the passivation processes had reached steady state. The cathodic Tafel slopes were the same in the arsenate and the blank electrolyte solutions. This indicates that water was the primary oxidant for iron corrosion and that arsenate did not directly oxidize the iron wires. The anodic Tafel slopes were greater in the arsenate solutions, indicating that arsenate formed complexes with iron corrosion products released at anodic sites on the iron surfaces. Ion chromatography analyses indicated that there was no measurable reduction of As(V) to As(III). X-ray absorption spectroscopy analyses indicated that all arsenic associated with the zero-valent iron surfaces was in the +5 oxidation state. Interatomic arsenic - iron distances determined from EXAFS analyses were consistent with bidentate corner-sharing among arsenate tetrahedra and iron octahedra. Results from this study show that under conditions applicable to drinking water treatment, arsenate removal by zero-valent iron media involves surface complexation only and does not involve reduction to metallic arsenic.
• Farrell, J., Wang, J., O'Day, P., & Conklin, M. (2001). Electrochemical and spectroscopic study of arsenate removal from water using zero-valent iron media. Environmental science \& technology, 35(10), 2026--2032.
• Li, T., & Farrell, J. (2001). Electrochemical investigation of the rate-limiting mechanisms for trichloroethylene and carbon tetrachloride reduction at iron surfaces. Environmental science \& technology, 35(17), 3560--3565.
• Melitas, N., Chuffe-Moscoso, O., & Farrell, J. (2001). Kinetics of soluble chromium removal from contaminated water by zerovalent iron media: Corrosion inhibition and passive oxide effects. Environmental Science and Technology, 35(19), 3948-3953.
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  PMID: 11642457;Abstract: Permeable reactive barriers containing zerovalent iron are being increasingly employed for in situ remediation of groundwater contaminated with redox active metals and chlorinated organic compounds. This research investigated the effect of chromate concentration on its removal from solution by zerovalent iron. Removal rates of aqueous Cr(VI) by iron wires were measured in batch experiments for initial chromium concentrations ranging from 100 to 10 000 μg/L. Chromate removal was also measured in columns packed with zerovalent iron filings over this same concentration range. Electrochemical measurements were made to determine the free corrosion potential and corrosion rate of the iron reactants. In both the batch and column reactors, absolute rates of chromium removal declined with increasing chromate concentration. Corrosion current measurements indicated that the rate of iron corrosion decreased with increasing Cr(VI) concentrations between 0 and 5000 μg/L. At a Cr(VI) concentration of 10 000 μg/L, Tafel polarization diagrams showed that chromium removal was affected by its diffusion rate through a passivating oxide film and by the ability of iron to release Fe2+ at anodic sites. In contrast, water reduction was not mass transfer limited, but chromium did decrease the exchange current for the hydrogen evolution reaction. Even at the most passivating concentration of 10 000 μg/L, effluent Cr(VI) concentrations in the column reactors reached a steady state, indicating that passivation had also reached a steady state. Although chromate contributes to iron surface passivation, the removal rates are still sufficiently fast for in situ iron barriers to be effective for Cr(VI) removal at most environmentally relevant concentrations.
• Melitas, N., Chuffe-Moscoso, O., & Farrell, J. (2001). Kinetics of soluble chromium removal from contaminated water by zerovalent iron media: corrosion inhibition and passive oxide effects. Environmental science \& technology, 35(19), 3948--3953.
• Tie, L. i., & Farrell, J. (2001). Electrochemical investigation of the rate limiting mechanisms for trichloroethylene and carbon tetrachloride reduction at iron surfaces. ACS Division of Environmental Chemistry, Preprints, 41(2), 739-744.
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  Abstract: The rate limiting mechanisms for reductive dechlorination of carbon tetrachloride (CT) and tetraethylene chloride (TCE) involve electron transfer were determined. The apparent Ea for CT reduction decreased with increasingly negative electrode potentials, suggesting that the rate of CT dechlorination is controlled by an electron transfer step. In contrast to CT, the Ea values for TCE exhibited a slight increase with decreasing E. Rates of CT reduction at iron surfaces were limited by the rate of electron transfer, while rates of TCE reduction were limited by chemical dependent factors. Reduction via an outer sphere mechanism might explain why halogenated alkanes undergo stepwise reductive dechlorination and produce chlorinated byproducts. In contrast, inner sphere reactions, which might involve chemisorption and thus produce longer interactions with the iron surface, might explain why the primary pathway for chlorinated alkene reduction produces few detectable chlorinated byproducts. This is an abstract of a paper presented at the 222nd ACS National Meeting (Chicago, IL 8/26-30/2001).
• Tie, L. i., & Farrell, J. (2001). Electrochemical investigation of the rate limiting mechanisms for trichloroethylene and carbon tetrachloride reduction at iron surfaces. ACS National Meeting Book of Abstracts, 41(2), 739-744.
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  Abstract: Permeable reactive barrier containing zero valent iron has become a popular technology for in situ bioremediation of groundwater contaminated with chlorinated organic compounds. The electrochemical investigation of the rate limiting mechanisms for trichloroethylene (TCE) and carbon tetrachloride (CT) reduction at iron surfaces was conducted. The transfer coefficient for CT reduction was independent of temperature, while that for TCE reduction was temperature dependent. This indicated that the rate of CT reduction was limited by an electron transfer step, while that for TCE was limited by chemical dependent factors. The apparent activation energies (Ea) for CT reduction decreased with increasingly negative electrode potentials. In contrast to CT, the Ea values of TCE exhibited a slight increase with decreasing E. The rates of CT reduction at iron surfaces were limited by the rate of electron transfer, while rates of TCE reduction were limited by chemical dependent factors.
• Tie, L. i., & Farrell, J. (2001). Electrochemical investigation of the rate-limiting mechanisms for trichlomethylene and carbon tetrachloride reduction at iron surfaces. Environmental Science and Technology, 35(17), 3560-3565.
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  PMID: 11563664;Abstract: The mechanisms involved in reductive dechlorination of carbon tetrachloride (CT) and trichloroethylene (TCE) at iron surfaces were studied to determine if their reaction rates were limited by rates of electron transfer. Chronoamperometry and chronopotentiometry analyses were used to determine the kinetics of CT and TCE reduction by a rotating disk electrode in solutions of constant halocarbon concentration. Rate constants for CT and TCE dechlorination were measured as a function of the electrode potential over a temperature range from 2 to 42 °C. Changes in dechlorination rate constants with electrode potential were used to determine the apparent electron-transfer coefficients at each temperature. The transfer coefficient for CT dechlorination was 0.22 ± 0.02 and was independent of temperature. The temperature independence of the CT transfer coefficient is consistent with a rate-limiting mechanism involving an outer-sphere electron-transfer step. Conversely, the transfer coefficient for TCE was temperature dependent and ranged from 0.06 ± 0.01 at 2 °C to 0.21 ± 0.02 at 42 °C. The temperature-dependent TCE transfer coefficient indicated that its reduction rate was limited by chemical dependent factors and not exclusively by the rate of electron transfer. In accord with a rate-limiting mechanism involving an electron-transfer step, the apparent activation energy (Ea) for CT reduction decreased with decreasing electrode potential and ranged from 33.0 ± 1.6 to 47.8 ± 2.0 kJ/mol. In contrast, the E, for TCE reduction did not decline with decreasing electrode potential and ranged from 29.4 ± 3.4 to 40.3 ± 3.9. The absence of a potential dependence for the TCE Ea supports the conclusion that its reaction rate was not limited by an electron-transfer step. The small potential dependence of TCE reaction rates can be explained by a reaction mechanism in which TCE reacts with atomic hydrogen produced from reduction of water.
• Tie, L. i., & Farrell, J. (2001). Rate-limiting mechanisms for carbon tetrachloride and trichloroethylene reactions at iron surfaces. ACS Division of Environmental Chemistry, Preprints, 41(1), 1154-1159.
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  Abstract: The rate limiting mechanisms for reductive dechlorination of carbon tetrachloride (CT) and trichloroethylene (TCE) involve electron transfer were studied. The temperature dependencies of the transfer coefficients and reaction rates were used to assess whether the rate limiting mechanisms for TCE and CT reduction involved electron transfer. The transfer coefficient for CT reduction was independent of temperature, while that for TCE reduction was temperature dependent, indicating that the rate of CT reduction was limited by an electron transfer step, while that for TCE was limited by chemical dependent factors. The apparent activation energies for CT reduction decreased with increasingly negative electrode potentials. This suggested that the rate of CT dechlorination is controlled by an electron transfer step. The rate-limiting step for TCE dechlorination did not involve electron transfer. This is an abstract of a paper presented at the 221st ACS National Meeting (San Diego, CA 4/1-5/2001).
• Tie, L. i., & Farrell, J. (2001). Rate-limiting mechanisms for carbon tetrachloride and trichloroethylene reactions at iron surfaces. ACS National Meeting Book of Abstracts, 41(1), 1154-1159.
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  Abstract: Permeable reactive barriers containing zerovalent iron are becoming increasingly popular for in situ remediation of groundwater contaminated with chlorinated organic compounds, e.g., trichloroethylene (TCE). A study was carried out to determine if the rate limiting mechanisms for reductive dechlorination of carbon tetrachloride (CT) and TCE involve electron transfer. The reaction rate of TCE might not be limited by an electron step. The transfer coefficient for CT reduction was independent of temperature, while that for TCE reduction was temperature dependent, indicating that the rate of CT reduction was limited by an electron transfer step, while that for TCE was limited by chemical dependent factors. The apparent activation energy (Ea) for CT reduction decreased with increasingly negative electrode potentials. This suggested that the rate of CT dechlorination was controlled by an electron transfer step. In an outer sphere reaction, a fraction of the polarization energy went towards changing the chemical activation energy. Cathodic polarizations resulted in negative overpotentials, and thus resulted in decreasing Ea values with decreasing electrode potential. In contrast to CT, the weak interdependence of Ea for TCE reduction and E further supported the conclusion that the rate-limiting step for TCE dechlorination does not involve electron transfer.
• Farrell, J., Chuffe-Moscoso, O., & Melitas, N. (2000). Investigation of the factors controlling chromate removal by zerovalent iron. ACS Division of Environmental Chemistry, Preprints, 40(2), 742-744.
• Farrell, J., Kason, M., Melitas, N., & Li, T. (2000). Investigation of the long-term performance of zero-valent iron for reductive dechlorination of trichloroethylene. Environmental Science \& Technology, 34(3), 514--521.
• Farrell, J., Kason, M., Melitas, N., & Tie, L. i. (2000). Investigation of the long-term performance of zero-valent iron for reductive dechlorination of trichloroethylene. Environmental Science and Technology, 34(3), 514-521.
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  Abstract: This research investigated the long-term performance of zero-valent iron for mediating the reductive dechlorination of trichloroethylene (TCE). Over a 2-year period, rates of TCE dechlorination in columns packed with iron filings were measured in simulated groundwaters containing either 3 mM CaSO4, 5 mM CaCl2, or 5 mM Ca(NO3)2. At early elapsed times, TCE reaction rates were pseudo-first-order in TCE concentration and were independent of the solution pH. With increasing elapsed time, reaction rates deviated from pseudo-first-order behavior due to reactive site saturation and increased iron surface passivation toward the influent end of each column. The extent of passivation was dependent on both the TCE concentration and the background electrolyte solution. For most of the investigation, TCE reaction rates in 3 mM CaSO4 and 5 mM CaCl2 solutions were statistically identical at the 0.05 confidence level. However, TCE reaction rates in 5 mM Ca(NO3)2 were slower. In columns operated using chloride- and sulfate-containing waters, the effective half-life for TCE dechlorination increased from approximately 400 min after 10 days elapsed to approximately 2500 min after 667 days. The effective TCE half-life in the nitrate-containing water increased from approximately 1500 min after 10 days to approximately 3500 min after 667 days. Measurements of iron corrosion rates in nitrate and chloride solutions showed that nitrate contributed to increased iron surface passivation and decreased rates of iron corrosion. Corrosion current measurements indicated that halocarbon reduction on fresh iron surfaces was cathodically controlled, whereas on aged iron surfaces, iron corrosion was anodically controlled. Anodic control of iron corrosion contributed to the development of reactive site saturation with time and to similar reaction rates for TCE and perchloroethylene. Passivation of the iron surfaces was found to be dependent on the adhering tendency of the corrosion products and not on the overall mass of corrosion products in the columns. The decrease in TCE reaction rates over time can be attributed to anodic control of iron corrosion and not to increasing reactant mass transfer limitations associated with diffusion through porous corrosion products.
• Farrell, J., Luo, J., Blowers, P., & Curry, J. (2000). Square pegs, round holes and slow desorption. ACS Division of Environmental Chemistry, Preprints, 40(2), 142-144.
• Farrell, J., Luo, J., Blowers, P., & Curry, J. (2000). Square pegs, round holes and slow desorption. ACS National Meeting Book of Abstracts, 40(2), 142-144.
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  Abstract: Predicting the transport and fate of hydrophobic organic contaminants in underground aquifers requires a mechanistic understanding of sediment-contaminant interactions. A rapid, pressure induced formation of a desorption resistant fraction of trichloroethylene (TCE) on three model adsorbents, i.e., silica gel, hydrophobic Y-zeolite, and polyvinyl chloride beads, was studied. Quantum mechanical calculations were performed to determine the energy associated with distorting the bond angles in a TCE molecule from their equilibrium configuration. Atomistic simulations were performed to determine the effect of separation distance on intermolecular repulsions between a TCE molecule and a silica surface. The effect of pressure on TCE adsorption was small or negligible after the first pressure step. TCE adsorption and desorption on this silica gel were completely reversible for short equilibration times, but a desorption resistant fraction could be induced by equilibration times longer than 1 day. The TCE pressure induced adsorption occurred in pores smaller than the effective size of a TCE molecule at 1 bar. The energies associated with even small molecular distortions could lead to high activation energies for desorption. Increasing contaminant sequestration with increasing contact time might be attributed to the activation energy required for penetrating pores smaller than the equilibrium size of the adsorbate molecule. The rapid development of desorption resistant TCE on the silica gel suggested that the diffusional distances associated with this mechanisms were small.
• Farrell, J., Melitas, N., & Tie, L. i. (2000). Mechanisms controlling halocarbon reduction rates by zerovalent iron. ACS Division of Environmental Chemistry, Preprints, 40(2), 787-788.
• Farrell, J., Melitas, N., & Tie, L. i. (2000). Mechanisms controlling halocarbon reduction rates by zerovalent iron. ACS National Meeting Book of Abstracts, 40(2), 787-789.
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  Abstract: Metallic iron filings could be used in passive groundwater remediation schemes. A study was carried out to investigate the long-term effectiveness of three types of zerovalent iron material for reductive dechlorination of trichloroethylene (TCE) and perchloroethylene (PCE). The effects of water chemistry, elapsed time, and influent halocarbon concentration on reaction rates and rate limiting mechanisms were studied. In the presence of nitrate, the iron corrodes at a slower rate due to anodic inhibition. Reaction rates were initially first order in reactant concentration, but showed increasing deviation from first order behavior with increasing elapsed time. Deviation from first order behavior was attributed to iron surface passivation leading to anodic control of iron corrosion. TCE concentrations near aqueous saturation rapidly passivated the iron. On fresh iron surfaces, the corrosion rate increased with TCE concentration, up to a concentration of 6 mM. However, increasing the TCE concentration above 6 mM resulted in a decreased rate of iron corrosion. Although corrosion rates in the blank electrolyte solutions were similar for the fresh and magnetite coated iron, increasing TCE concentrations had little effect on the corrosion rate of the magnetite coated iron. There were two mechanisms involved in halocarbon reduction, i.e., the chronoamperometry and corrosion current measurements detected the rate of direct electron transfer, while the analytical measurements detect both the direct and indirect mechanisms. The rate of indirect reduction was faster for TCE, while the rate of direct reduction was faster for PCE.
• Farrell, J., Melitas, N., Kason, M., & Li, T. (2000). Electrochemical and Column Investigation of Iron-Mediated Reductive Dechlorination of Trichloroethylene and Perchloroethylene. Environmental Science & Technology, 34(12), 2549-2556. doi:10.1021/es991135b
• Farrell, J., Melitas, N., Kason, M., & Li, T. (2000). Electrochemical and column investigation of iron-mediated reductive dechlorination of trichloroethylene and perchloroethylene. Environmental science \& technology, 34(12), 2549--2556.
• Farrell, J., Melitas, N., Kason, M., & Tie, L. i. (2000). Electrochemical and column investigation of iron-mediated reductive dechlorination of trichloroethylene and perchloroethylene. Environmental Science and Technology, 34(12), 2549-2556.
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  Abstract: This research investigated the long-term performance of zero-valent iron aggregates for reductive dechlorination of trichloroethylene (TCE) and perchloroethylene (PCE). The effects of elapsed time, mass transfer limitations, and influent halocarbon concentration on reductive dechlorination rates were investigated using groundwater obtained from a field site contaminated with chlorinated organic compounds. Over the first 300 days of operation, reaction rates for TCE and PCE gradually increased due to increasing porosity of the iron aggregates. Although there was microbial growth in the column, biological activity did not measurably contribute to reductive dechlorination. Dechlorination rates were pseudo-first-order in reactant concentration for submillimolar halocarbon concentrations. TCE concentrations near aqueous saturation resulted in passivation of the iron surfaces and deviation from first-order reaction kinetics. However, this passivation was slowly reversible upon lowering the influent TCE concentration. Tafel polarization diagrams for an electrode constructed from the iron aggregates indicated that corrosion of the aggregates was anodically controlled. At all halocarbon concentrations, aggregate oxidation by water accounted for more than 80% of the corrosion. Throughout the course of the 3- yr column investigation, reaction rates for TCE were 2-3 times faster than those for PCE. However, current measurements with the aggregate electrode indicated that direct PCE reduction was faster than that for TCE. This disparity between amperometrically measured reaction rates and those measured in the column reactor indicated that halocarbon reduction may occur via direct electron transfer or may occur indirectly through reaction with atomic hydrogen adsorbed to the iron. Comparison of aggregate corrosion rates with those of fresh iron suggested that anodic control of corrosion leads to predominance of the indirect reduction mechanism. The faster reaction rate for TCE under anodically controlled conditions can therefore be attributed to its faster rate of indirect reduction as compared to PCE.
• Farrell, J., Wang, J., O'Day, P., & Conklin, M. (2000). Iron mediated reductive precipitation of arsenic from contaminated groundwater. ACS Division of Environmental Chemistry, Preprints, 40(2), 794-796.
• Li, T., & Farrell, J. (2000). Kinetic and mechanistic investigation of halocarbon reduction at iron cathodes.. Second International Conference on Remediation of Chlorinated and Racalcitrant Compounds, 353--359.
• Li, T., & Farrell, J. (2000). Reductive dechlorination of trichloroethene and carbon tetrachloride using iron and palladized-iron cathodes. Environmental science \& technology, 34(1), 173--179.
• Tie, L. i., & Farrell, J. (2000). Reductive dechlorination of trichloroethene and carbon tetrachloride using iron and palladized-iron cathodes. Environmental Science and Technology, 34(1), 173-179.
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  Abstract: This research investigated the effectiveness of electrochemical reduction for removing trichloroethylene (TCE) and carbon tetrachloride (CT) from dilute aqueous solutions. The kinetics, reaction mechanisms, and current efficiencies for TCE and CT reduction were investigated using flow-through, iron electrode reactors and with amperometric measurements of reduction rates. The electrode reactors were operated over a range of flow rates, pH, ionic strength, dissolved oxygen concentration, and working electrode potentials. Typical reduction half-lives for TCE and CT in the iron reactor were 9.4 and 3.7 min, respectively. The addition of palladium as an electrocatalyst at a level of 1 mg of Pd per m2 of electrode surface area increased the reaction rates by a factor of 3. When operated continuously, reaction rates in the palladized-iron reactor were stable over a 9-month period of operation, indicating that there was no loss of palladium from the electrode. In both the iron and Pd-iron reactors, TCE was reduced primarily to ethane and ethene, while CT was reduced almost exclusively to methane. Under all operating conditions, chlorinated compounds accounted for less than 2% of the total reaction byproducts. Comparisons of amperometrically measured current efficiencies with those measured in the flow-through reactors and the weak effect of electrode potential on TCE reaction rates indicated that the primary pathway for TCE reduction by iron and palladized-iron electrodes is indirect and involves atomic hydrogen as the reducing agent. Direct reduction of TCE appeared to be inhibited by the preferential reduction of water. The finding that electrodes coated with a hydrophobic polymer to inhibit water reduction showed current efficiencies greater than 90% for direct TCE reduction supports this hypothesis. For CT, similar ampermetric and analytically measured current efficiencies indicated that the primary mechanism for CT reduction is direct electron transfer. Carbon dioxide and bisulfide, which have been found to foul palladium in other catalytic systems, did not deactivate the catalyst. The fast reaction kinetics and electrode stability indicate that electrochemical reduction may be feasible for treating waters contaminated with chlorinated organic compounds.
• Farrell, J., & Li, T. (1999). Reductive Dechlorination of Trichloroethene and Carbon Tetrachloride Using Iron and Palladized-Iron Cathodes. Environmental Science & Technology, 34(1), 173-179. doi:10.1021/es9907358
• Farrell, J., Bostick, W. D., Jarabek, R. J., & Fiedor, J. N. (1999). Electrosorption and reduction of pertechnetate by anodically polarized magnetite. Environmental Science and Technology, 33(8), 1244-1249.
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  Abstract: The radionuclide technetium is a common surface and groundwater contaminant at many nuclear fuels processing facilities. This research investigated a new method for removing pertechnetate from contaminated waters based on the low aqueous solubility of reduced technetium species. The removal method involved electrostatic adsorption of pertechnetate at an anodically polarized magnetite electrode, followed by reduction of the adsorbed Tc(VII). This method was capable of reducing technetium associated β activity below the 900 pCi/L drinking water maximum contaminant level set by the US EPA for manmade β activity. Upon termination of the applied polarization, the reduced technetium species remained adhered to the magnetite electrode under anaerobic conditions. Under aerobic conditions, the technetium was slowly released back into solution, indicating that the reduced technetium is afforded a degree of cathodic protection due to preferential oxidation of the magnetite. The advantages of this electrosorption/reduction technique over direct cathodic reduction are an increase in the stability of the reduced technetium, removal to lower aqueous concentrations, and greatly increased removal kinetics.
• Farrell, J., Bostick, W. D., Jarabek, R. J., & Fiedor, J. N. (1999). Electrosorption and reduction of pertechnetate by anodically polarized magnetite. Environmental science \& technology, 33(8), 1244--1249.
• Farrell, J., Bostick, W. D., Jarabek, R. J., & Fiedor, J. N. (1999). Uranium removal from ground water using zero valent iron media. Ground Water, 37(4), 618-624.
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  Abstract: Removal of uranium from contaminated ground water using zero valent iron is currently under evaluation at several U.S. Department of Energy (DOE) facilities. Uranium removal by zero valent iron may occur via adsorption onto iron corrosion products, and by reduction to less soluble valence states by reactions with elemental iron. This research investigated the effects of water chemistry and surface precipitate buildup on the removal of soluble uranium by zero valent iron. Batch testing was performed to assess solution chemistry effects on uranium adsorption to the potential iron corrosion products, magnetite and a mixed valent amorphous iron oxide. Uranium adsorption to the simulated iron corrosion products was highly dependent on pH, and the concentration and speciation of the background electrolyte solution. Uranium removal via reduction by elemental iron closely approximated pseudo-first-order removal kinetics, despite the buildup of up to 40,000 monolayers of precipitated uranium on the iron surfaces. This indicates that the rate of uranium removal is not strongly dependent on the thickness of the adsorbed uranium layer. Short-term rates of uranium reduction were similar for all solutions tested, but long-term rates were highly dependent on water chemistry. Compared to deionized water, uranium removal rates were increased in sodium chloride containing solutions and reduced in sodium nitrate solutions. The strong influence of water chemistry on long-term reduction rates indicates that system design will require extended testing with the ground water of interest.
• Farrell, J., Bostick, W. D., Jarabek, R. J., & Fiedor, J. N. (1999). Uranium removal from ground water using zero valent iron media. Groundwater, 37(4), 618--624.
• Farrell, J., Grassian, D., & Jones, M. (1999). Investigation of Mechanisms Contributing to Slow Desorption of Hydrophobic Organic Compounds from Mineral Solids. Environmental Science & Technology, 33(8), 1237-1243. doi:10.1021/es980732f
• Farrell, J., Grassian, D., & Jones, M. (1999). Investigation of mechanisms contributing to slow desorption of hydrophobic organic compounds from mineral solids. Environmental Science and Technology, 33(8), 1237-1243.
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  Abstract: This research investigates the mechanisms contributing to the slow desorption of hydrophobic organic compounds from water-saturated mineral solids. The mechanisms investigated were adsorption-retarded aqueous diffusion, micropore diffusion, high-energy micropore adsorption, and micropore blockage by precipitated minerals. To reduce the potential confounding effects of adsorbent heterogeneity, a set of homogeneous silica gel and glass bead adsorbents were used in the investigation. Desorption rates for the slow-desorbing fractions of chloroform [CF), trichloroethylene (TCE), and perchloroethylene (PCE) from silica gel did not conform to the pore-diffusion model for adsorption-retarded aqueous diffusion. This indicated that diffusion through adsorbent mesopores was not responsible for slow desorption from silica gel. Micropore-diffusion modeling of TCE desorption from three silica gels and microporous glass beads indicated that pores less than 2 nm in diameter were responsible for slow desorption. Desorption rates for CF, TCE, and PCE from silica gel were also measured in methanol solutions. Under methanol extraction conditions, desorption rates for all three compounds were 1-2 orders of magnitude less than under watersaturated conditions. This indicated that high-energy adsorption was not responsible for the slow-desorbing fraction, and suggested that mineral precipitation leads to blockage of intragranular micropores. The activation energy for TCE desoration from water-saturated silica gel was measured using temperature-programmed desorption. The TCE desorption activation energy of 15 kJ/mol was close to the dissolution enthalpy for silica gel of 13 kJ/mol. This supported the hypothesis that micropore blockage by precipitated minerals may be limiting contaminant desorption rates under water-saturated conditions.
• Farrell, J., Grassian, D., & Jones, M. (1999). Investigation of mechanisms contributing to slow desorption of hydrophobic organic compounds from mineral solids. Environmental science \& technology, 33(8), 1237--1243.
• Farrell, J., Hauck, B., & Jones, M. (1999). Thermodynamic investigation of trichloroethylene adsorption in water- saturated microporous adsorbents. Environmental Toxicology and Chemistry, 18(8), 1637-1642.
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  Abstract: Adsorption of trichloroethylene (TCE) in adsorbents containing hydrophilic and hydrophobic micropores was investigated in order to determine the mechanisms responsible for TCE adsorption on mineral solids. A high- pressure liquid chromatography method was used to measure TCE adsorption isotherms on three microporous adsorbents. Silica gel and zeolite type NaX were used as hydrophilic model adsorbents, and hexamethyldisilazane (HMDS)- treated silica gel was used as a model hydrophobic adsorbent. Batch uptake and desorption isotherms were also measured on the hydrophilic silica gel. Uptake of TCE by all three adsorbents was linear over the concentration range investigated. However, the silica gel desorption isotherm was highly nonlinear, as indicated by its Freundlich isotherm exponent of 0.58. Capillary phase separation into hydrophobic micropores was postulated as being responsible for the isotherm hysteresis. Supporting this hypothesis was the conformance of the TCE adsorption isotherm to Dubinin-Radushkevitch volume filling of micropores theory. The enthalpies for TCE adsorption on all three solids were determined by van't Hoff analysis of distribution coefficients measured over a temperature range from 5 to 90°C. The TCE adsorption enthalpies on the silica gel and HMDS silica gel were exothermic, but on the zeolite adsorption was endothermic. High exothermic adsorption enthalpies on the silica gel adsorbents indicated that TCE adsorption was occurring in hydrophobic micropores, and that adsorption on surfaces with large radii of curvature contributed only minimally to the total uptake. This indicates that the predominant mechanism for TCE adsorption on these mineral solids is not partitioning into the vicinal water layer.
• Farrell, J., Hauck, B., & Jones, M. (1999). Thermodynamic investigation of trichloroethylene adsorption in water-saturated microporous adsorbents. Environmental toxicology and chemistry, 18(8), 1637--1642.
• Fiedor, J. N., Bostick, W. D., Jarabek, R. J., & Farrell, J. (1998). Understanding the mechanism of uranium removal from groundwater by zero- valent iron using X-ray photoelectron spectroscopy. Environmental Science and Technology, 32(10), 1466-1473.
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  Abstract: The contaminant of most concern in groundwater at the Oak Ridge Y-12 Plant's Bear Creek Valley Characterization Area is soluble uranium. The removal mechanism of soluble uranium from groundwater by zero-valent iron (ZVI, Fe0) was investigated. X-ray photoelectron spectroscopy (XPS, ESCA) was used to determine the uranium oxidation state at the Fe0 or iron oxide surface. Product speciation and relative reaction kinetics for the removal of soluble uranium under aerobic and anaerobic conditions with ZVI are presented. Under aerobic conditions, U6+ is rapidly and strongly sorbed to hydrous ferric oxide particulates ('rust'), whereas U6+ is slowly and incompletely reduced to U4+ under anaerobic conditions.
• Fiedor, J. N., Bostick, W. D., Jarabek, R. J., & Farrell, J. (1998). Understanding the mechanism of uranium removal from groundwater by zero-valent iron using X-ray photoelectron spectroscopy. Environmental science \& technology, 32(10), 1466--1473.
• Farrell, J., & Grassian, D. (1997). Adsorption of hydrophobic organic compounds in in water-saturated microporous materials. ACS Division of Environmental Chemistry, Preprints, 37(2), 195-196.
• Hauck, B., & Farrell, J. (1997). High performance liquid chromatography measurements of capillary phase separation in water-saturated adsorbents. ACS Division of Environmental Chemistry, Preprints, 37(2), 160-161.
• Corley, T. L., Farrell, J., Hong, B., & Conklin, M. H. (1996). VOC accumulation and pore filling in unsaturated porous media. Environmental Science and Technology, 30(10), 2884-2891.
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  Abstract: A series of unsaturated column experiments was conducted to study different grain-scale accumulation mechanisms affecting total uptake of volatile organic compounds (VOCs) onto a model solid and subsequent removal of VOCs from the porous media. Experimental variables included VOC (benzene, methylbenzene, 1,4-dimethylbenzene, and 1,3,5-trimethylbenzene), moisture content (primarily water-unsaturated conditions), and influent VOC concentration. Calculations of the mass distributions of benzene indicated that it was primarily in the aqueous and air phases with a small fraction at the airwater interface. Similar calculations for the other VOCs indicated that greater than 50% of the accumulated mass of these VOCs was located within intraparticle pores and on the substrate surface. Analysis of the sorption data in terms of a pore-filling model support the hypothesis that a capillary phase separation (CPS) process occurred within the pores and produced a neat, separate VOC phase. We suggest that CPS will become more critical in materials with small mesopores or micropores, and that it is partly responsible for the existence of a resistant fraction of VOCs present within water-filled intraparticle pores.
• Corley, T. L., Farrell, J., Hong, B., & Conklin, M. H. (1996). VOC accumulation and pore filling in unsaturated porous media. Environmental science \& technology, 30(10), 2884--2891.
• Farrell, J., Corley, T. L., Hong, B., & Conklin, M. H. (1996). VOC Accumulation and Pore Filling in Unsaturated Porous Media. Environmental Science & Technology, 30(10), 2884-2891. doi:10.1021/es950644k
• Farrell, J., & Reinhard, M. (1994). Desorption of halogenated organics from model solids, sediments, and soil under unsaturated conditions. 1. Isotherms. Environmental Science and Technology, 28(1), 53-62.
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  Abstract: Desorption isotherms spanning 4-5 orders of magnitude in vapor concentration were measured for chloroform, trichloroethylene, and tetrachloroethylene under unsaturated conditions at 100% relative humidity. The mechanisms affecting isotherm shape were investigated using model solids, aquifer materials, and soil spanning a range in physical properties. Uptake from the vapor phase was examined in terms of four sorption mechanisms: (1) mineral surface adsorption, (2) partitioning into natural organic matter, (3) partitioning into surface-bound water, and (4) adsorption in micropores. Evidence is presented that a heretofore overlooked mechanism-adsorption in micropores-contributes significantly to sorbate uptake and contributes to isotherm nonlinearity on solids with low natural organic matter contents. Micropores are those pores less than several adsorbate diameters in width and are implicated as showing enhanced adsorption as compared to pores of larger dimension. Isotherm shape on solids with low natural organic matter appears to be dominated by intraaggregate microporosity.
• Farrell, J., & Reinhard, M. (1994). Desorption of halogenated organics from model solids, sediments, and soil under unsaturated conditions. 1. Isotherms. Environmental science \& technology, 28(1), 53--62.
• Farrell, J., & Reinhard, M. (1994). Desorption of halogenated organics from model solids, sediments, and soil under unsaturated conditions. 2. Kinetics. Environmental Science and Technology, 28(1), 63-72.
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  Abstract: The mechanisms controlling desorption rates from soils and sediments were investigated by measuring TCE desorption kinetics from model solids, sediments, and soil under unsaturated conditions at 100% relative humidity. A new experimental methodology enabled measurement of desorption rates over more than 7 orders of magnitude and revealed that intraparticle pores of molecular dimensions may be responsible for the slow release of sorbed contaminants. Desorption kinetics proceeded on two distinct time scales, and all solids had both a fast and slowly released fraction. The amount of slow desorbing TCE was found to depend on the initial vapor concentration, but not in direct proportion. At TCE vapor concentrations near saturation, the fast fraction comprised the majority of the sorbed TCE and required less than 10 min for desorption, whereas the slow desorbing fraction was released over periods of months to years. Although model solids with uniform pore and particle sizes were used, a pore diffusion model was not adequate to describe both the fast and slow desorbing fractions. The measured physical properties of the solids were not useful for making a priori predictions and, in comparisons among the solids, did not correlate with the amount and the rate of slowly released TCE. The Freundlich isotherm exponents correlated with the fraction of slowly released TCE, but isotherm nonlinearity was not sufficient to account for the dual rate behavior.
• Farrell, J., & Reinhard, M. (1994). Desorption of halogenated organics from model solids, sediments, and soil under unsaturated conditions. 2. Kinetics. Environmental science \& technology, 28(1), 63--72.
• Farrell, J., & Reinhard, M. (1992). Measurement of Organic Vapor Isotherms on Wet Soils and Aquifer Materials. Current Practices in Ground Water and Vadose Zone Investigations, 1118, 140.
• Farrell, J., & Reinhard, M. (1992). Measurement of organic vapor isotherms on wet soils and aquifer materials. ASTM Special Technical Publication, 140-150.
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  Abstract: A technique for measuring organic vapor sorption onto water coated soils and aquifer materials is presented. The method has several advantages over other techniques such as microbalance, extraction, and headspace method. The solids used are coated with a surface layer of water and are in equilibrium with a gas phase at 100% relative humidity, simulating conditions in the unsaturated zone. Advantages of the method include the ability to measure isotherms over at least 5 orders of magnitude in organic vapor concentration, the ability to measure sorption onto very low sorbing solids, and the ability to allow an indefinite time for equilibrium to be reached.
• Grathwohl, P., Farrell, J., & Reinhard, M. (1991). Desorption kinetics of volatile organic contaminants from aquifer materials. Contaminated soil '90. Third KfK/TNO conference, Karlsruhe, 1990. Vol. I, 343-350.
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  Abstract: Sorption and desorption of volatile, halogenated hydrocarbons from aquifer material are investigated using a frontal gas chromatography technique. One of the aquifer materials studied was silty sand with 0.15% organic C from the Santa Clara Valley, California; the other was a fine grained sand containing 0.02% organic C from Borden, Ontario. The time to recover 90% of the hydrocarbon was significantly higher for the water containing samples than for the dry solids despite the fact that the dry solids sorbed much more strongly. These findings suggest that mass transfer limitations are due to diffusion through the aqueous phase in the intraparticle domain, and that remediation of contaminated soil using soil air extraction techniques is typically operated under nonequilibrium conditions. Removal of the solid-bound contaminants is much slower than the concentration decrease in the mobile phase. -from Authors

Proceedings Publications

• Farrell, J., Davis, J., & Baygents, J. C. (2013). Electrochemical generation of persulfate using boron-doped diamond film electrodes. In ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 246.
• Farrell, J., Hubler, D. K., Baygents, J. C., & Chaplin, B. C. (2013). Understanding Chlorite, Chlorate and Perchlorate Formation When Generating Hypochlorite Using Boron Doped Diamond Film Electrodes. In 224th ECS Meeting (October 27--November 1, 2013).
• Farrell, J., Hubler, D. K., Baygents, J. C., & Chaplin, B. P. (2013). Understanding chlorite and chlorate production by boron-doped diamond film anodes during electrochemical hypochlorite generation. In ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 246.
• Farrell, J. (2012). Molecular modeling of reactions in electrochemical water treatment. In ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 243.
• Chaplin, B. P., Farrell, J., Carlisle, J., & Zeng, H. (2010). Characterization of performance and wear mechanism of diamond electrodes used for electrochemical oxidation of TCE. In ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 240.
• Chaplin, B. P., Duncan, C., Schrader, G., & Farrell, J. (2009). ENVR 226-Electrochemical destruction of reverse osmosis brines: A sustainable technology to enhance water reuse. In ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 238.
• Chaplin, B. P., Duncan, C., Schrader, G., & Farrell, J. (2009). Oxidation of N-nitrosodimethylamine (NDMA) using boron-doped diamond film electrodes. In ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 237.
• Baygents, J. C., & Farrell, J. M. (2008). COLL 30-Electrocoagulation and water sustainability: Silica and hardness control. In ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 235.
• Chaplin, B. P., Gu, Z., Baygents, J. C., & Farrell, J. (2008). ENVR 21-Electrochemical regeneration of ion exchange. In ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 236.
• Farrell, J. (2007). Removal of hexavalent chromium from groundwater using zero-valent iron media. In Zero-Valent Iron Reactive Materials for Hazardous Waste and Inorganics Removal, 61--76.
• Farrell, J., Zhang, N., & Blowers, P. (2006). Density functional study of chloroethene reactions with iron surfaces. In ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 231.
• Farrell, J., & Luo, J. (2004). Understanding chloroethene chemisorption to iron surfaces using molecular mechanics and density functional theory.. In ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 228, U691--U691.
• Farrell, J., & Mishra, D. (2004). Reactive iron oxide-based adsorbent media for removing arsenic from drinking water.. In ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 228, U611--U611.
• Farrell, J., & Mishra, D. (2004). Understanding nitrate reactions with zerovalent iron media in permeable reactive barriers.. In ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 228, U607--U607.
• Zhang, N., Farrell, J., & Blowers, P. (2004). Density functional theory study of arsenite binding to ferric oxides.. In ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 228, U550--U550.
• Wang, J., & Farrell, J. (2003). Electrochemical oxidation of triclosan at boron doped diamond surfaces.. In ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 226, U496--U496.
• Wang, J., & Farrell, J. (2003). Mechanistic and kinetic study of carbon tetrachloride reduction at nickel surfaces.. In ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 226, U511--U511.
• Wang, J., & Farrell, J. (2003). Understanding the role of atomic hydrogen on chloroethene reactions at iron surfaces.. In ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 226, U477--U477.
• Farrell, J., & Luo, J. (2002). Grand canonical Monte Carlo study of sediment-contaminant interactions. In ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 224, U537--U537.
• Melitas, N., Farrell, J., & Conklin, M. (2002). Investigation of arsenate reduction in iron media filters.. In ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 224, U527--U528.
• Raghavan, S., Tamilmani, S., & Farrell, J. (2002). Electrochemical treatment of wastewater generated from chemical mechanical planarization of silicon wafers.. In ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 224, U530--U530.
• Wang, J., & Farrell, J. (2002). Direct and indirect electron transfer mechanisms involved in chlorocarbon reduction.. In ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 224, U525--U526.
• Li, T., & Farrell, J. (2001). Rate limiting mechanisms for carbon tetrachloride and trichloroethylene reactions at iron surfaces.. In ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 221, U471--U471.
• Melitas, N., Conklin, M., & Farrell, J. (2001). Electrochemical investigation of chromate and arsenate removal from water using zerovalent iron media.. In ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 221, U470--U470.
• Farrell, J., Chuffe-Moscoso, O., & Melitas, N. (2000). Investigation of the factors controlling chromate removal by zerovalent iron.. In ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 220, U366--U367.
• Farrell, J., Luo, J., Curry, J., & Blowers, P. (2000). Square pegs, round holes, and slow desorption.. In ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 220, U320--U320.
• Farrell, J., Melitas, N., & Li, T. (2000). Mechanisms controlling halocarbon reduction rates by zero valent iron.. In ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 220, U372--U373.
• Farrell, J., Wang, J., O'Day, P., & Conklin, M. (2000). Iron mediated reductive precipitation of arsenic from contaminated groundwater.. In ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 220, U373--U373.
• Grassian, D., & Farrell, J. (1997). Adsorption of hydrophobic organic compounds in water-saturated microporous materials.. In ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 214, 99--ENVR.
• Hauck, B., & Farrell, J. (1997). HPLC measurements of hydrophobic organic compound adsorption in water-saturated microporous materials.. In ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 214, 63--ENVR.
• Kason, M., & Farrell, J. (1997). Electrochemical removal of uranium, technetium, and trichloroethylene. In ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 214, 10--NUCL.
• WERTH, C., FARRELL, J., & REINHARD, M. (1994). DESORPTION ISOTHERMS AND KINETICS OF TRICHLOROETHYLENE FROM LIVERMORE SEDIMENTS. In ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 207, 86--ENVR.

Presentations

• Farrell, J., Phakdon, T., & Xu, J. (2022). Electrolytic Coagulation & Disinfection for Treating Flowback and Produced Water (FPW) for Reuse. National Energy Technology Laboratory Resource Sustainability Annual Project Review Meeting. Pittsburgh, PA: National Energy Technology Laboratory.
• Xu, J., Phakdon, T., Achilli, A., Hickenbottom, K., & Farrell, J. (2022). Electrochemically Enhanced Reverse Osmosis to Achieve Minimal Discharge in Water Reclamation. 2022 Spring National Meeting of the American Chemical Society. San Diego, CA: American Chemical Society.
• Farrell, J., & Azadi-Aghdam, M. (2019, November). Increasing Water Recovery from Nanofiltration and Reverse Osmosis using Bipolar Membrane Electrodialysis and Electrochemically Promoted Fluidized Bed Crystallization. Water and Energy Sustainable Technology Center Annual Meeting. Tucson, AZ: Water and Energy Sustainable Technology Center.
• Farrell, J., & Chen, Y. (2016, Summer). Electrochemical Ion Exchange Regeneration and Fluidized Bed Crystallization for Zero Liquid Discharge Water Softening. AZ Water Conference.
• Farrell, J., Davis, J., Chen, Y., & Nguyen, C. (2015, May). Electrochemical Ion Exchange Regeneration and Rapid Electrochemical Crystallization Softening. AZ Water Conference. Phoenix, AZ: AZ Water.

Others

• Farrell, J., & Chen, Y. (2017, January). Selective Leaching of Mg from Phosphorous Concentrate with Sulfurous acid, Magnesium Bisulfite and Sulfuric Acid. Neylon Consulting.
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  Technical report for research project.
• Farrell, J., & Chen, Y. (2017, November). Selective Mg Removal from Phosphate Ore using Magnesium Bisulfite and Sulfurous Acid. Neylon Consulting.
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  Technical report for completion of research project.
• Farrell, J. (1996). Iron mediated reductive transformations of chlorinated organic compounds in aqueous systems.
• Farrell, J. (1993). Desorption equilibrium and kinetics of chlorinated solvents on model solids, aquifer sediments, and soil.