Dechlorination Kinetics Research Articles

Preparation of functionalized Pd/Fe-Fe3O4@MWCNTs nanomaterials for aqueous 2,4-dichlorophenol removal: Interactions, influence factors, and kinetics

Magnetic multi-walled carbon nanotubes (MWCNTs) were prepared to support Pd/Fe nanoparticles, inhibit the aggregation and passivation, and achieve magnetic separation to avoid the environmental risk of nanoparticles. Rapid adsorption of initial contaminant, steady dechlorination, and gradual desorption of final product was observed. The micromorphology, chemical structure, and components of the nanohybrids were comprehensively characterized by a series of analysis technologies, such as EDX, XRD, SEM, TEM, and XPS. The interactions between the nanohybrids compositions were discussed according to the characterization and experimental data. The whole insight of 2,4-dichlorophenol (2,4-DCP) adsorption- dechlorination-desorption was studied in detail, including the pathways, influence factors, dechlorination kinetics and selectivity. Weak acidity (pH=5.0 and 6.5) favored the 2,4-DCP removal. Satisfactory reactivity of the Pd/Fe-Fe3O4@MWCNTs nanohybrids was observed in five consecutive runs, and 99.2%, 89.6%, 92.1%, 99.8%, and 99.9% of 2,4-DCP was removed, respectively. Most of the final product (phenol) was steadily desorbed to the liquid phase, resulted in the re-exposure of active sites on the nanohybrids and maintained a longer activity.

Beyaz Çürükçül Mantar Trametes versicolor’dan Elde Edilen Lakkaz Enzimi İle 2,4,6-Triklorofenol’ün Enzimatik Deklorinasyonunun Kinetik Modellemesi

This study examined kinetic modeling of the detoxification induced by dechlorination of laccase enzyme obtained from Trametes versicolor which is a white rot fungi strain and 2,4,6-trichlorophenol which is a toxic chlorinated phenolic compound. In the evaluation of the kinetics of detoxification induced by dechlorination of 2,4,6-trichlorophenol used as substrate, the Systat 10 software package which is a statistics program was used while two-substrate solution environment was used to explain the kinetic behavior of the dechlorination. It was observed as a result of experiments and statistical analysis that Moser equation is the optimal kinetic model. Given the statistical data obtained and the graph, the dual-substrate model was found to be compatible with the experimental data. The bio-kinetic parameter values obtained for the model that identifies enzymatic dechlorination kinetics were calculated as Vmax =9.341 ppmO2/min, Ks =38.254 g/L, Ko =20.747 ppm, R = 1.895 and N = 1.233. In the literature, no studies were found on kinetic modeling for the degradation of 2,4,6-trichlorophenol, and through this study, we have been first to conduct a study on kinetic modeling of the degradation induced by enzymatic dechlorination of 2,4,6-trichlorophenol. The GC/MS analysis results showed that the chlorophenolic compound used throughout the enzymatic dechlorination performed with laccase enzyme was degraded 80% to 100%. Based on the GC/MS analysis results, the conclusion that the enzyme responsible for the dechlorination was laccase was also found to support the findings available in literature.

Chromatographic speciation of Cr(III)-species, inter-species equilibrium isotope fractionation and improved chemical purification strategies for high-precision isotope analysis

Chromatographic purification of chromium (Cr), which is required for high-precision isotope analysis, is complicated by the presence of multiple Cr-species with different effective charges in the acid digested sample aliquots. The differing ion exchange selectivity and sluggish reaction rates of these species can result in incomplete Cr recovery during chromatographic purification. Because of large mass-dependent inter-species isotope fractionation, incomplete recovery can affect the accuracy of high-precision Cr isotope analysis. Here, we demonstrate widely differing cation distribution coefficients of Cr(III)-species (Cr3+, CrCl2+ and CrCl2+) with equilibrium mass-dependent isotope fractionation spanning a range of ∼1‰/amu and consistent with theory. The heaviest isotopes partition into Cr3+, intermediates in CrCl2+ and the lightest in CrCl2+/CrCl3°. Thus, for a typical reported loss of ∼25% Cr (in the form of Cr3+) through chromatographic purification, this translates into 185ppm/amu offset in the stable Cr isotope ratio of the residual sample. Depending on the validity of the mass-bias correction during isotope analysis, this further results in artificial mass-independent effects in the mass-bias corrected 53Cr/52Cr (μ53Cr* of 5.2ppm) and 54Cr/52Cr (μ54Cr* of 13.5ppm) components used to infer chronometric and nucleosynthetic information in meteorites. To mitigate these fractionation effects, we developed strategic chemical sample pre-treatment procedures that ensure high and reproducible Cr recovery. This is achieved either through 1) effective promotion of Cr3+ by >5 days exposure to HNO3H2O2 solutions at room temperature, resulting in >∼98% Cr recovery for most types of sample matrices tested using a cationic chromatographic retention strategy, or 2) formation of Cr(III)-Cl complexes through exposure to concentrated HCl at high temperature (>120°C) for several hours, resulting in >97.5% Cr recovery using a chromatographic elution strategy that takes advantage of the slow reaction kinetics of de-chlorination of Cr in dilute HCl at room temperature. These procedures significantly improve cation chromatographic purification of Cr over previous methods and allow for high-purity Cr isotope analysis with a total recovery of >95%.

Dechlorination and decomposition of chloroform induced by glow discharge plasma in an aqueous solution

In this study, efficient dechlorination and decomposition of chloroform (CF) induced by glow discharge plasma (GDP) in contact with a sodium sulfate solution was investigated. Intermediate byproducts were determined by ionic chromatography and headspace gas chromatography, respectively. Results showed that CF can be effectively dechlorinated and decomposed under the action of GDP. Both removal and dechlorination of CF increased with increasing pH and with addition of hydroxyl radical scavengers to the solution. Addition of H2O2 to the solution slightly decreased the CF removal. Formic acid, oxalic acid and dichloromethane were determined as the major intermediate byproducts. Final products were carbon dioxide and hydrochloric acid. Hydrated electrons were the most likely active species responsible for initiation of the dechlorination, and hydroxyl radicals may be the ones for the oxidation of the organic intermediate byproducts. Hydrolyses of the chloromethyl radicals contributed much in the mineralization of the organic chlorine. Reaction mechanism was proposed based on the dechlorination kinetics and the distribution of intermediate byproducts.

Study on dechlorination kinetics from zinc oxide dust by clean metallurgy technology

Abstract Cavity perturbation method was used to determine the dielectric properties (ε′, ε″, and tan δ) of zinc oxide dust. The process of dechlorination from zinc oxide dust by microwave roasting was evaluated considering the effect of different roasting temperatures and holding times. The research results showed that the ZnCl2 and PbCl2 with high-loss factor were heated preferentially by microwave, and the dechlorination rate can reach 97.22% after microwave roasting at 650°C for 40 min. The phases of zinc oxide dust before and after microwave roasting were observed and characterized by X-ray diffraction (XRD) analysis. The kinetics of dechlorination from zinc oxide dust was investigated. The three kinetic factors were obtained by the dynamic isothermal method, which provided a theoretical basis for dechlorination from zinc oxide dust. Thermodynamic analysis showed that the volatilization of chlorides was mainly ionic crystal phase transition process. The volatile kinetics of zinc oxide dust were controlled by the solid state diffusion and interface chemical reaction, during the microwave heating, with an activation energy E=46.6 KJ/mol and the reaction order n is level 1.

Kinetics of 2-chlorobiphenyl Reductive Dechlorination by Pd-fe0Nanoparticles

Kinetics of 2-chlorobiphenyl (2-Cl BP) catalytic reductive dechlorination by Pd-Fe 0 nanoparticles were investigated. Experimental results showed that ultrafine bimetallic Pd-Fe 0 e nanoparticles were synthesized in the presence of 40 kHz ultrasound in order to enhance disparity and avoid agglomeration. The application of ultrasonic irradiation during the synthesis of Pd-Fe 0 nanoparticles further accelerated the dechlorinated removal ratio of 2-Cl BP. Up to 95.0% of 2-Cl BP was removed after 300 min reaction with the following experimental conditions: initial 2-Cl BP concentration 10 mg L -1 , Pd content 0.8 wt. %, bimetallic Pd-Fe 0 nanoparticles prepared in the presence of ultrasound available dosage 7g L -1 , initial pH value in aqueous solution 3.0, and reaction temperature 25°C. The catalytic reductive dechlorination of 2-Cl BP followed pseudo-first-order kinetics and the apparent pseudo-first-order kinetics constant was 0.0143 min -1 .

Glow Discharge Plasma Induced Dechlorination and Decomposition of Dichloromethane in an Aqueous Solution

In the present study, efficient dechlorination and decomposition of dichloromethane (DCM) induced by glow discharge plasma (GDP) in contact with an aqueous solution was investigated. Experimental results showed that DCM underwent effective dechlorination and decomposition under the action of GDP. Both the removal and the dechlorination of DCM increased with increasing pH and with the presence of hydroxyl radical scavengers and decreased with quenchers of hydrated electrons. Formic acid and formaldehyde were the major intermediate byproducts. Final products were carbon dioxide and chloride ion. Hydrated electrons were the most important active species responsible for initiation of the reaction. Hydrolysis of the resulting chloromethyl radicals played an important role in mineralization of chlorine atoms of the molecule. Hydroxyl radicals were mainly involved in the oxidation of the intermediate byproducts. Reaction mechanism was proposed based on the dechlorination kinetics and the distribution of intermediate byproducts.

Cooperative adsorption based kinetics for dichlorobenzene dechlorination over Pd/Fe bimetal

Pd/Fe bimetal has been used in dichlorobenzene treatment with high efficiency. In order for an industrial application of this process, the dechlorination kinetics was studied. As a catalytic reaction, the overall dechlorination process can be characterized by the step of adsorption and surface reaction. A cooperative adsorption theory was applied to describe the adsorption behaviors in this system. Four chemicals: dichlorobenzene, chlorobenzene, benzene and hydrogen, are adsorbed on the catalyst surface, where active centers provide the space for adhesion. Two groups of active centers, “σ” and “σ*”, are divided by size in order to distinguish the capability of capturing aromatic compounds. Apparent multilayer adsorption was used to model the cooperative adsorption behaviors in this system. The adsorption sites were characterized by two energy levels. Based on the cooperative adsorption theory, a kinetic model was built for the dechlorination process under adsorption limitation. There are five parameters in the final model including the concentration of active sites, Cσ, one reaction rate constant: kDCB and three equilibrium constants: K1,K2 and Ke. The resultant model was found to describe the experimental data well.

Enhanced reductive dechlorination of tetrachloroethene by nano-sized mackinawite with cyanocobalamin in a highly alkaline condition

In this study, we characterize the reductive dechlorination of tetrachloroethene (PCE) by nano-sized mackinawite (nFeS) with cobalamin (Cbl(III)) at a high pH and investigate the effects of environmental factors, including the concentrations of the target contaminant, reductant, and catalyst and suspension ions on the dechlorination kinetics of PCE. Ninety five percent of the PCE was degraded by nFeS with Cbl(III) in 15 h. Cyclic voltammetry conducted with regard to the reductive dechlorination showed a higher redox potential of mackinawite under a high-pH condition (−1.01 V), suggesting that the oxidation state of the central cobalt ion in the cobalamin could be reduced to Cbl(I). The change of cobalamin species on the nFeS surface was verified under different pH conditions by UV–vis spectroscopy. The rate constant of PCE dechlorination increased from 0.1582 to 0.4284 h−1 due to the increase in the nFeS content (2.085–20.85 g/L). As the concentration of Cbl(III) increased from 0 to 0.5 mM, the dechlorination kinetics of PCE was accelerated (0–1.4091 h−1) but reached a state of equilibrium from 0.5 to 1 mM. The increase in the initial PCE concentration (0.035–1.0 mM) slowed down the dechlorination kinetics (0.2036–0.0962 h−1). The dechlorination kinetics was enhanced by 1.5–11 times when 10 mM of ions (Na+, K+, Mg2+, Ca2+, CO32−, SO42−, and NO3−) were added, while an addition of HCO3 decelerated it by 10 times. This study can provide background knowledge pertaining to the PCE dechlorination by a natural reductant under a high-pH condition and the effect of environmental factors on the dechlorination kinetics for the development of novel remediation technologies.

The reactivity of well-dispersed zerovalent iron nanoparticles toward pentachlorophenol in water

In order to prevent the aggregation of nanoparticles (NPs), surface modification or the addition of a stabilizer are used for stabilization. However, the real reactivity of NPs is still unclear because of the surface coating. For different physical dispersion methods, the particle stabilization for nanoscale zerovalent iron (NZVI) particles and their reactivity are studied. The particle properties of different preparations and their reactivity toward one polychlorinated aromatic compound, pentachlorophenol (PCP), with different electrolytes are also evaluated. Ultrasonication (US) with magnetic stirring disperses NZVI and Pd/Fe NPs well in water and does not affect the surface redox property a lot under the operating conditions in this study. The well-suspended NZVI cannot dechlorinate PCP but adsorption removal is observed. Compared to shaking, which gives limited removal of PCP (about 43%), Pd/Fe NPs remove 81% and 93% of PCP from water in the US and the US/stirring systems, respectively, which demonstrates that a greater surface area is exposed because of effective dispersion of Pd/Fe NPs. As the Pd doping increases, the dechlorination kinetics of PCP is improved, which shows that a catalyst is needed. With US/stirring, chloride ions do not significantly affect the removal kinetics of PCP, but the removal efficiency increases in the presence of nitrate ions because PCP anions were adsorbed and coagulated by the greater amount of iron (hydro)oxides that are generated from the reduction of nitrate on Pd/Fe. However, bicarbonate ions significantly block the adsorption and reaction sites on the Pd/Fe NP surface with US/stirring. The US/stirring method can be used to evaluate the actual activity of NPs near the nanoscale. The use of Pd/Fe NPs with US/stirring removes PCP from water effectively, even in the presence of common anions expect a high concentration of bicarbonate.

Electrically conductive magnetite particles enhance the kinetics and steer the composition of anaerobic TCE-dechlorinating cultures

The interaction of anaerobic dechlorinating cultures with soil and aquifer geochemical components is largely unknown, although this has potentially a major impact on the bioremediation of chlorinated solvent-contaminated sites. In this study, we found that addition of magnetite (Fe3O4) – the end-product of Fe(III)-reduction by dissimilatory iron reducing bacteria – to anaerobic dechlorinating cultures enhances the kinetics of trichloroethene dechlorination up to 1.5-times, compared to unamended controls. Specifically, a low concentration (approx. 10mg/L as total Fe) of small size particles (200nm-filtered) resulted in a greater stimulatory effect compared to the addition of a higher concentration (approx. 300mg/L as total Fe) of unfiltered particles. Notably, Desulforomonas spp. were substantially enriched in microcosms supplemented with magnetite, whereas Dehalococcoides mccartyi spp. was found to be markedly inhibited or outcompeted. Multiple lines of evidence, including the direct visualization of microbial cells and magnetite particles via Confocal Laser Scanning Microscopy (CLSM), suggest that electrically conductive particles promoted the establishment of a cooperative metabolism, based on direct interspecies electron transfer, between dechlorinating and non-dechlorinating microorganisms.

Base-catalyzed decomposition of hexachlorobenzene: effect on dechlorination efficiency of different hydrogen donors, alkalis and catalysts

The effect of different hydrogen donors, alkalis, and catalysts on the dechlorination efficiency of hexachlorobenzene (HCB) by base-catalyzed decomposition (BCD) technology was investigated. According to an orthogonal experiment, all three factors have notable influence on the dechlorination of HCB, and four different combinations of reagents were suitable for the treatment of HCB at high concentrations: polyethylene glycol (PEG) + hydroxide, octadecane + KOH, glycerin + hydroxide, and glycerin + carbonate. Further research regarding the effects of catalysts determined that ∼100% dechlorination of HCB can be achieved in 3 h at 250 °C in the presence of PEG and hydroxide without any catalyst, and iron rather than nickel was recommended as catalyst when octadecane and KOH were used for HCB dechlorination. In addition, an investigation of the HCB dechlorination kinetics in the presence of PEG and various alkalis determined that the HCB dechlorination rate constant increased linearly with the decreasing of the ionic potential of the metal cation in the hydroxide.

Kinetics of dechlorination by Dehalococcoides mccartyi using different carbon sources

Stimulated anaerobic dechlorination is generally considered a valuable step for the remediation of aquifers polluted with chlorinated ethenes (CEs). Correct simulation and prediction of this process in situ, however, require good knowledge of the associated biological reactions. The aim of this study was to evaluate the dechlorination reaction in an aquifer contaminated with trichloroethene (TCE) and its daughter products, discharging into the Zenne River. Different carbon sources were used in batch cultures and these were related to the dechlorination reaction, together with the monitored biomarkers. Appropriate kinetic formulations were assessed. Reductive dechlorination of TCE took place only when external carbon sources were added to microcosms, and occurred concomitant with a pronounced increase in the Dehalococcoides mccartyi cell count as determined by 16S rRNA gene-targeted qPCR. This indicates that native dechlorinating bacteria are present in the aquifer of the Zenne site and that the oligotrophic nature of the aquifer prevents a complete degradation to ethene. The type of carbon source, the cell number of D. mccartyi or the reductive dehalogenase genes, however, did not unequivocally explain the observed differences in degradation rates or the extent of dechlorination. Neither first-order, Michaelis-Menten nor Monod kinetics could perfectly simulate the dechlorination reactions in TCE spiked microcosms. A sensitivity analysis indicated that the inclusion of donor limitation would not significantly enhance the simulations without a clear process understanding. Results point to the role of the supporting microbial community but it remains to be verified how the complexity of the microbial (inter)actions should be represented in a model framework.

Kinetics of electrochemical dechlorination of 2-chlorobiphenyl on a palladium-modified nickel foam cathode in a basic medium: From batch to continuous reactor operation

A kinetic model for the electrochemical dechlorination of polychlorinated biphenyls (PCBs) will be an important contribution to the design and optimization of a continuous reactor. Initially, the electrocatalytic hydrodechlorination of 2-chlorobiphenyl (2-ClBP) to biphenyl at a palladium-modified nickel foam (Pd/Ni) cathode in a batch reactor was used as a model reaction for a quantitative study of the influences of the operating parameters, including temperature, the initial concentrations of PCBs, current density and the amount of Pd loading, on the apparent reaction rate. The dechlorination was found to follow pseudo first-order kinetics with respect to the 2-ClBP concentration. It was also found that a simple global power law rate equation, with Arrhenius dependency, can be used to describe the correlation between the pseudo first-order reaction rate constants and the reaction conditions. Subsequently, a mathematical model for predicting the performance of reductive dechlorination of 2-ClBP on Pd/Ni electrodes in a continuous stirred tank reactor was constructed, based on the batch-reaction kinetics. The suitability of the model was validated by performing experiments in and out of the range of reaction conditions applied in the batch reactor. The results show that the calculated values are a good fit to the experimental data.

Study on the physicochemical properties of poly(methylmethacrylate) (PMMA) modified Pd/Fe nanocomposites: Roles of PMMA and PMMA/ethanol

To probe the roles of poly(methylmethacrylate) (PMMA) and PMMA/ethanol in controlling the physicochemical properties of Pd/Fe nanoparticles (NPs) and explore a feasible approach to fabricating highly reactive Pd/Fe NPs, we modified Pd/Fe NPs with PMMA and PMMA/ethanol via aqueous chemical reduction. The particle dispersion and resisting oxidation ability were enhanced by modification with PMMA and PMMA/ethanol, and the 2,4-dichlorophenol dechlorination efficiency increased with the increased molar ratio of PMMA to iron and ethanol to iron. During the preparation, the roles of PMMA and PMMA/ethanol were to control particle agglomeration and oxidation, while those for the dechlorination process were to offer more reactive surfaces and access of active reaction sites to contaminants. Compared to the unmodified process, the modification process resulted in a different dechlorination process mainly resulted from the roles of PMMA and PMMA/ethanol in regulating properties of Pd/Fe NPs. In addition, the roles of PMMA and PMMA/ethanol in 2,4-dichlorophenol dechlorination kinetics using Pd/Fe NPs were revealed. The ethanol introduced enhanced the particle resisting oxidation ability and prolonged its longevity. These results demonstrated that the PMMA and ethanol had played a favorable role in promoting colloidal stability and improving dechlorination ability of Pd/Fe NPs.

Microbially enhanced dissolution and reductive dechlorination of PCE by a mixed culture: Model validation and sensitivity analysis

Reductive dechlorination catalyzed by organohalide-respiring bacteria is often considered for remediation of non-aqueous phase liquid (NAPL) source zones due to cost savings, ease of implementation, regulatory acceptance, and sustainability. Despite knowledge of the key dechlorinators, an understanding of the processes and factors that control NAPL dissolution rates and detoxification (i.e., ethene formation) is lacking. A recent column study demonstrated a 5-fold cumulative enhancement in tetrachloroethene (PCE) dissolution and ethene formation (Amos et al., 2009). Spatial and temporal monitoring of key geochemical and microbial (i.e., Geobacter lovleyi and Dehalococcoides mccartyi strains) parameters in the column generated a data set used herein as the basis for refinement and testing of a multiphase, compositional transport model. The refined model is capable of simulating the reactive transport of multiple chemical constituents produced and consumed by organohalide-respiring bacteria and accounts for substrate limitations and competitive inhibition. Parameter estimation techniques were used to optimize the values of sensitive microbial kinetic parameters, including maximum utilization rates, biomass yield coefficients, and endogenous decay rates. Comparison and calibration of model simulations with the experimental data demonstrate that the model is able to accurately reproduce measured effluent concentrations, while delineating trends in dechlorinator growth and reductive dechlorination kinetics along the column. Sensitivity analyses performed on the optimized model parameters indicate that the rates of PCE and cis-1,2-dichloroethene (cis-DCE) transformation and Dehalococcoides growth govern bioenhanced dissolution, as long as electron donor (i.e., hydrogen flux) is not limiting. Dissolution enhancements were shown to be independent of cis-DCE accumulation; however, accumulation of cis-DCE, as well as column length and flow rate (i.e., column residence time), strongly influenced the extent of reductive dechlorination. When cis-DCE inhibition was neglected, the model over-predicted ethene production ten-fold, while reductions in residence time (i.e., a two-fold decrease in column length or two-fold increase in flow rate) resulted in a more than 70% decline in ethene production. These results suggest that spatial and temporal variations in microbial community composition and activity must be understood to model, predict, and manage bioenhanced NAPL dissolution.

Comparison of Reaction Rates and Relative Efficiencies for Various Dechlorination Chemicals

Dechlorination of chlorinated water and wastewater is most often achieved by chemical reduction through the addition of sulfur-IV compounds before discharge into the aquatic receiving environment or upon entry in the distribution system. However, reasonable doubts subsist about the efficiency of sulfur-IV compounds as dechlorination mediators for the reduction of chlorine and organic chloramines. As a consequence, alternative treatments have been investigated over the past few years but little information remains available on the kinetics of dechlorination at different dosages. In this study, the kinetics of dechlorination promoted by five selected dechlorination agents were observed at different stoichiometric ratios (1x, 3x, and 10x), and ANOVA was applied to the results in order to assess their statistical significance. Hydrogen peroxide (HP) was shown to promote faster than expected dechlorination; ascorbic acid and calcium thiosulfate also presented viable alternatives to treatment by sulfur-IV compounds represented by sodium sulfite and bisulfite in this study. This study challenges the common perception that HP dechlorination is slow and provides a comparative analysis for dechlorination kinetics using regression analysis, half-life values, and rate constants.

Electron donor limitations reduce microbial enhanced trichloroethene DNAPL dissolution: A flux-based analysis using diffusion-cells

Electron donor limitations likely reduce microbial enhanced trichloroethene (TCE) dense non-aqueous phase liquid (DNAPL) dissolution. This study quantitatively examined the relation between the DNAPL dissolution enhancement and the electron donor supply rate. An experiment used diffusion-cells with a 5.5cm central sand layer, separating a DNAPL layer from an aqueous top layer. Top layers were amended with different concentrations of formate (0–16mM). The TCE DNAPL dissolution rate increased from no enhancement compared to abiotic dissolution without formate, to a 2.4 times dissolution enhancement with 16mM formate amended to the top layer. With 2, 4 and 8mM formate amended the top layer, the TCE diffusion flux out of the DNAPL layer equaled the formate diffusion flux out of the top layer, which illustrates their stoichiometric interdependence under electron donor limiting conditions. In contrast, with 16mM formate amended to the top layer, the TCE diffusion flux was lower than the formate diffusion flux, demonstrating that the dechlorination kinetics limited the DNAPL dissolution enhancement. The DNAPL dissolution flux under electron donor limiting conditions was readily predicted from the electron donor concentration in the top layer.

Kinetic study of cis-dichloroethylene (cis-DCE) and vinyl chloride (VC) dechlorination using green rusts formed under varying conditions

Abiotic degradation of cis-dichloroethylene (cis-DCE) and vinyl chloride (VC) was investigated using Fe hydroxides obtained by hydrolyzing Fe(II) salts over a pH range of 7.7–8.0. Within this narrow pH range, a green rust (GR) precipitated. The dechlorination reactivity of the resulting GR precipitates increased with the dissolved Fe(II) concentration remaining in solution after precipitation. Controls run using only the dissolved Fe(II) supernatant were not reactive, suggesting the relative amount of Fe(II) on the surface of precipitated GRs was the causative agent in the relative reactivity. To test this, a series of GR batches with varying dissolved Fe(II) concentrations were prepared by acid-base titration and examined for cis-DCE and VC dechlorination kinetics under reducing conditions. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses of these batches were performed to characterize the bulk mineralogy and the excess surface Fe(II), respectively. Cis-DCE and VC dechlorination results along with solid phase characterization show that different surface Fe(II)/Fe(III) compositions are responsible for the different reactivity of GRs formed within the GR precipitation zone.

Preparation and dechlorination of a poly(vinylidene difluoride)-grafted acrylic acid film immobilized with Pd/Fe bimetallic nanoparticles for monochloroacetic acid

A poly(vinylidene fluoride) (PVDF) film was successfully modified to have hydrophilicity by three modification steps: (1) alkaline treatment to defluorinate the original PVDF film, (2) nucleophilic addition to hydrophilize the PVDF film, and (3) grafting acrylic acid (g-AA) to change the hydrophilization extent of the modified support film in order to facilitate the uniform distribution of metallic nanoparticles (NPs) immobilized on the modified film. Pd/Fe NPs were prepared and immobilized on the PVDF film grafted with AA (g-AA). The PdFe/PVDF-g-AA NPs were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, contact angle analysis, and X-ray photoelectron spectroscopy. The PdFe/PVDF-g-AA NPs exhibited high reactivity in the dechlorination of monochloroacetic acid (MCAA). The effects of acrylic acid concentration and Pd loading content on the MCAA dechlorination process were investigated. The kinetics of MCAA dechlorination by PdFe/PVDF-g-AA NPs was discussed, and a conceptual model was proposed.