Dechlorination Of Carbon Tetrachloride Research Articles

Graphene oxide-mediated rapid dechlorination of carbon tetrachloride by green rust

Graphene-based nanomaterials can mediate environmentally relevant abiotic redox reactions of chlorinated aliphatic hydrocarbons. In this study as low amounts as ∼0.007 % of graphene oxide (GO) was found to catalyze the reduction of carbon tetrachloride by layered Fe(II)-Fe(III) hydroxide (Green Rust, GR) in aqueous solutions with chloroform being the reduction product. On the basis of sorption studies of carbon tetrachloride onto the GO surface it is suggested that it is the amphiphilicity of GO, which initiates the reaction by providing a suitable reaction platform for the reagents. This study indicates that traces of graphene oxide can affect reaction pathways as well as kinetics for dechlorination processes in anoxic sediments by facilitating a partial dechlorination.

Carbon dioxide radical anion-based UV/S2O82−/HCOOH reductive process for carbon tetrachloride degradation in aqueous solution

Abstract The reduction performance of carbon tetrachloride (CT) mediated by carbon dioxide radical anion (CO 2 − ) was investigated in this study, and CO 2 − was generated by the reaction of formic acid and sulfate radical produced in the UV/S 2 O 8 2− process. The effects of various factors including persulfate and formic acid concentrations, solution pH, and anions such as Cl − , HCO 3 − , NO 3 − , and SO 4 2− were evaluated. The experimental results showed that CT could be almost completely removed in 60 min with 1.50 mM persulfate and 2.25 mM formic acid. CT degradation efficiency was found to increase with increasing persulfate (0.75−4.50 mM) and formic acid (0.75−2.25 mM) concentrations. In the pH adjusted solutions (from pH 6–8), maximum CT degradation occurred at pH 6. Both Cl − and NO 3 − (1−100 mM), as well as HCO 3 − at high concentrations (10 and 100 mM), adversely affected CT degradation performance. The addition of methyl viologen as CO 2 − scavengers proved the presence of CO 2 − in this UV/S 2 O 8 2− /HCOOH process, and the dechlorination of CT was not complete as Cl − release rate was 80.6% after 240 min.

Iron-Sulfide-Associated Products Formed during Reductive Dechlorination of Carbon Tetrachloride.

This paper investigated the mackinawite (FeS)-associated products formed during reaction between FeS and carbon tetrachloride (CT) at pH 7 and 8. At pH 8, reaction of FeS with CT led to formation of abundant spherical particles with diameters between 50 and 400 nm on the FeS surface and in solution; far fewer such particles were observed at pH 7. Analysis of the FeS surface by energy dispersive X-ray spectroscopy after reaction with CT at pH 8 showed decreased sulfur and elevated oxygen compared to unreacted FeS. The spherical particles that formed upon FeS reaction with CT were mostly amorphous with localized areas of poorly crystalline two-line ferrihydrite. X-ray photoelectron spectroscopy indicated that the predominant Fe surface species after reaction with CT at pH 8 was Fe(III)-O, consistent with ferrihydrite and other amorphous iron (hydr)oxides as major products. Powder X-ray diffraction analysis suggested formation of greigite upon reaction of FeS with CT at pH 7. Both ferrihydrite and Fe(2+), which is a product of greigite dissolution, can react with dissolved HS(-) to form FeS, suggesting that, after oxidation by chlorinated aliphatics, FeS can be regenerated by addition or microbial generation of sulfide.

Zero-valent iron nanoparticles with sustained high reductive activity for carbon tetrachloride dechlorination

Fe oxide shell breakdown and new oxyhydroxide formation during CT dechlorination contribute to pH self-buffering and sustained nZVI reactivity.

Catalytic dechlorination of carbon tetrachloride in liquid phase with methanol as H-donor over Ag/C catalyst.

Catalytic hydrodechlorination of carbon tetrachloride (CCl4) is an effective measure to remove CCl4 due to its pollutant character. The dechlorination of CCl4 to dichloromethane (CH2Cl2) and chloroform (CHCl3) with a molar ratio of 3:2 was catalyzed by carbon-supported silver (Ag/C) catalyst in methanol solution. It was proposed from the catalytic results and characterization (X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy) data that, the chloride ion is abstracted from adsorbed CCl4 by Ag to form CCl3 and CCI2 radicals and silver chloride (AgCl), and meanwhile the dehydrogenation of methanol over Ag domains intrigues initial active Ag-H species and formaldehyde (HCHO); then the CCI3 and CCI, radicals are combined with Ag-H to generate reaction products (CHCl3 and CH2Cl2) and Ag, and the dehydrogenated product HCHO facilitates the regeneration of formed AgCl to Ag with formation of carbon monoxide and hydrogen chloride. The catalyst can be recovered and recycled, and there was no significant decrease in catalytic activity and selectivity after 4th recycling.

Simultaneous adsorption and dechlorination of carbon tetrachloride using copper nanoparticles@graphene oxide composites

Cu nanoparticles@graphene oxide composites (CGC) were synthesized by a simplistic and effective chemical reduction method. The resulting CGC composites were characterized by X-ray diffraction, scanning electron microscopy with energy dispersive X-ray analysis, transmission electron microscopy, Fourier transform infrared spectroscopy and thermogravimetric analysis. The performance of the CGC composites for dechlorination of carbon tetrachloride was evaluated. The batch investigations indicated that carbon tetrachloride could be almost completely removed by CGC after 75 min. The adsorption isotherm was also discussed. The high removal capacities of CGC with respect to the bare nanoscale zerovalent copper owe to the increased adsorption sites in the composites that are resulted from aggregation inhibition, which leads to the reduced Cu nanoparticles size.

Enhanced dechlorination of carbon tetrachloride by Geobacter sulfurreducens in the presence of naturally occurring quinones and ferrihydrite

The effect of naturally occurring quinones including lawsone (LQ), ubiquinone (UQ), juglone (JQ), and 1,4-naphthoquinone (NQ) on the biotransformation of carbon tetrachloride (CT) in the presence of Geobacter sulfurreducens and ferrihydrite was investigated. AQDS was used as the model compound for comparison. The reductive dissolution of ferrihydrite by G. sulfurreducens was enhanced by AQDS, NQ, and LQ. However, addition of UQ and JQ had little enhancement effect on Fe(II) production. The bioreduction efficiency and rate of ferrihydrite was highly dependent on the natural property and concentration of quinone compounds and the addition of low concentrations of LQ and NQ significantly accelerated the biotransformation rate of CT. The pseudo-first-order rate constants for CT dechlorination (kobsCT) in AQDS-, LQ- and NQ-amended batches were 5.4–5.8, 4.6–7.4 and 2.4–5.8 times, respectively, higher than those in the absence of quinone. A good relationship between kobsCT for CT dechlorination and bioreduction ratio of ferrihydrite was observed, indicating the important role of biogenic Fe(II) in dechlorination of CT under iron-reducing conditions. Spectroscopic analysis showed that AQDS and NQ could be reduced to semiquinones and hydroquinones, while only hydroquinones were generated in LQ-amended batches.

Carbon Tetrachloride Degradation by Alkaline Ascorbic Acid Solution

Ascorbic acid (AA) mediated electron transfer may induce reductive dechlorination of carbon tetrachloride (CCl(4)). This study investigated the role of AA in conjunction with the presence of iron minerals over a wide pH range for the reduction of CCl(4) in aqueous systems. The results indicate that CCl(4) was reduced by AA at a pH of 13 (>pKa(2, AA) of 11.79) and chloroform (CHCl3) was a transformation byproduct of CCl(4). When CCl(4) levels were reduced to near complete disappearance, the decrease of CHCl(3) was then observed. The degradation rate of CCl(4) and also the formation rate of CHCl(3) increased with increased AA concentrations. Analysis of reaction kinetics between CCl(4) and AA revealed an overall second-order reaction with a rate constant of 0.253 ± 0.018 M(-1) s(-1). Furthermore, the reduction rate of CCl(4) by AA at pH of 13 could be enhanced with the presence of iron minerals (Fe(3)O(4), Fe(2)O(3), FeOOH, and FeS2). In the absence or presence of iron minerals, the fraction of CCl(4) transformed to CHCl(3) was less than 1, indicating simultaneous one- and two-electron transfer processes. The end-products of AA at a pH of 13 included threonic acid and oxalic acid. This study highlights the potential of an alkaline AA solution for remediating chlorinated solvents.

Kinetics during the redox biotransformation of pollutants mediated by immobilized and soluble humic acids

The aim of this study was to elucidate the kinetic constraints during the redox biotransformation of the azo dye, Reactive Red 2 (RR2), and carbon tetrachloride (CT) mediated by soluble humic acids (HAs) and immobilized humic acids (HAi), as well as by the quinoid model compounds, anthraquinone-2,6-disulfonate (AQDS) and 1,2-naphthoquinone-4-sulfonate (NQS). The microbial reduction of both HAs and HAi by anaerobic granular sludge (AGS) was the rate-limiting step during decolorization of RR2 since the reduction of RR2 by reduced HAi proceeded at more than three orders of magnitute faster than the electron-transferring rate observed during the microbial reduction of HAi by AGS. Similarly, the reduction of RR2 by reduced AQDS proceeded 1.6- and 1.9-fold faster than the microbial reduction of AQDS by AGS when this redox mediator (RM) was supplied in soluble and immobilized form, respectively. In contrast, the reduction of NQS by AGS occurred 1.6- and 19.2-fold faster than the chemical reduction of RR2 by reduced NQS when this RM was supplied in soluble and immobilized form, respectively. The microbial reduction of HAs and HAi by a humus-reducing consortium proceeded 1,400- and 790-fold faster than the transfer of electrons from reduced HAs and HAi, respectively, to achieve the reductive dechlorination of CT to chloroform. Overall, the present study provides elucidation on the rate-limiting steps involved in the redox biotransformation of priority pollutants mediated by both HAs and HAi and offers technical suggestions to overcome the kinetic restrictions identified in the redox reactions evaluated.

Correction to “Efficient Dechlorination of Carbon tetrachloride by Hydrophobic Green Rust Intercalated with Dodecanoate Anions”

Correction to “Efficient Dechlorination of Carbon tetrachloride by Hydrophobic Green Rust Intercalated with Dodecanoate Anions”

Efficient Dechlorination of Carbon Tetrachloride by Hydrophobic Green Rust Intercalated with Dodecanoate Anions

The reductive dechlorination of carbon tetrachloride (CT) by Fe(II)-Fe(III) hydroxide (green rust) intercalated with dodecanoate, Fe(II)(4)Fe(III)(2)(OH)(12)(C(12)H(23)O(2))(2) · yH(2)O (designated GR(C12)), at pH ~ 8 and at room temperature was investigated. CT at concentration levels similar to those found in heavily contaminated groundwater close to polluted industrial sites (14-988 μM) was reduced mainly to the fully dechlorinated products carbon monoxide (CO, yields >54%) and formic acid (HCOOH, yields >6%). Minor formation of chloroform (CF), the only chlorinated degradation product, was also detected (yields <6.3%). Reactions carried out with excess GR followed pseudo first-order kinetics with respect to CT with rate constants ranging from 6.5 × 10(-2) to 0.47 h(-1). These rate constants are comparable to those measured for CT dechlorinations mediated by zerovalent iron. Reduction of the highest concentration of CT (1.4 mM) proceeds until 56% of the Fe(II) sites of GR(C12) was consumed. This reaction ceased after 10 h due to surface passivation of GR(C12).

Enhanced reductive degradation of carbon tetrachloride by biogenic vivianite and Fe(II)

We demonstrated that reductive dechlorination of carbon tetrachloride (CT) can be enhanced by iron-bearing soil minerals (IBSMs) in the presence of Shewanella putrefaciens CN32 (CN32) due to the formation of biogenic vivianite and Fe(II). The bioreduction efficiency of magnetite was the highest (51.1%), followed by lepidocrocite (25.7%), goethite (3.6%), and hematite (1.8%). The dechlorination kinetic of CT by lepidocrocite (0.043d−1) in the presence of CN32 was three times faster than that by microbial transformation with CN32 (0.014d−1). Chloroform (16.1–29.4%), carbon monoxide (2.4–23.8%), and formate (0–58.0%) were measured as main products for the degradation of CT by magnetite and lepidocrocite in the presence of CN32. X-ray diffraction and electron microscope analyses revealed that the biogenic vivianite can form during the CT degradation in magnetite and lepidocrocite suspensions with CN32. The dechlorination kinetics of CT by chemogenic vivianite was much faster than that by magnetite and lepidocrocite with CN32. The highest formate production (84.2%) was observed during a full degradation of CT by the chemogenic vivianite. The experimental results showed that biogenic vivianite and sorbed Fe(II) formed during the bioreduction of IBSMs played a pivotal role for the reductive dechlorination of CT.

Simultaneous biodegradation of phenol and carbon tetrachloride mediated by humic acids

The capacity of an anaerobic sediment to achieve the simultaneous biodegradation of phenol and carbon tetrachloride (CT) was evaluated, using humic acids (HA) as redox mediator. The presence of HA in sediment incubations increased the rate of biodegradation of phenol and the rate of dehalogenation (2.5-fold) of CT compared to controls lacking HA. Further experiments revealed that the electron-accepting capacity of HA derived from different organic-rich environments was not associated with their reducing capacity to achieve CT dechlorination. The collected kinetic data suggest that the reduction of CT by reduced HA was the rate-limiting step during the simultaneous biodegradation of phenol and CT. To our knowledge, the present study constitutes the first demonstration of the simultaneous biodegradation of two priority pollutants mediated by HA.

Degradation of carbon tetrachloride in modified Fenton reaction

We showed that the dechlorination of carbon tetrachloride (CT) can be significantly enhanced at nearneutral pH by modified Fenton reaction in the presence of Fe(II) chelated by cross-linked chitosan (CS) with glutaraldehyde (GLA). CT dechlorination was verified by monitoring the release of chloride and detection of intermediates such as trichloromethane and dichloromethane in the modified Fenton system with Fe(II) chelated by cross-linked CS with GLA (Fe(II)-CS/GLA). Measured chlorine mass balance of each sample was greater than 91% of total chlorine mass corresponding to initial CT concentration throughout the reaction. Addition of hydroxyl radical scavenger (2-propanol) enhanced the CT degradation in 5 h at near-neutral pH (removal efficiency from 57.2% to 92.4%), while the addition significantly inhibited trichloroethylene (TCE) degradation at the same condition (74.7% to 19.9%). This implies that, in contrast to the dechlorination of TCE, that of CT did not follow an oxidative dechlorination pathway but a reductive dechlorination pathway in the modified Fenton system with Fe(II)-CS/GLA. Dechlorination kinetics of CT in the modified Fenton system was affected by the concentrations of H2O2, Fe(II), and CT. The formation of surface Fe(II)-CS/GLA complex and its valence change from Fe(II) to Fe(III) observed during the modified Fenton reaction gave a clue to identify the proposed reaction mechanism properly.

Dechlorination of Environmental Contaminants Using a Hybrid Nanocatalyst: Palladium Nanoparticles Supported on Hierarchical Carbon Nanostructures

This paper demonstrates the effectiveness of a new type of hybrid nanocatalyst material that combines the high surface area of nanoparticles and nanotubes with the structural robustness and ease of handling larger supports. The hybrid material is made by fabricating palladium nanoparticles on two types of carbon supports: as-received microcellular foam (Foam) and foam with carbon nanotubes anchored on the pore walls (CNT/Foam). Catalytic reductive dechlorination of carbon tetrachloride with these materials has been investigated using gas chromatography. It is seen that while both palladium-functionalized carbon supports are highly effective in the degradation of carbon tetrachloride, the rate of degradation is significantly increased with palladium on CNT/Foam. However, there is scope to increase this rate further if the wettability of these structures can be enhanced in the future. Microstructural and spectroscopic analyses of the fresh and used catalysts have been compared which indicates that there is no change in density or surface chemical states of the catalyst after prolonged use in dechlorination test. This implies that these materials can be used repeatedly and hence provide a simple, powerful, and cost-effective approach for dechlorination of water.

Dechlorination of chlorinated hydrocarbons by bimetallic Ni/Fe immobilized on polyethylene glycol-grafted microfiltration membranes under anoxic conditions

In this study, the dechlorination of chlorinated hydrocarbons including trichloroethylene (TCE), tetrachloroethylene (PCE) and carbon tetrachloride (CT) by bimetallic Ni/Fe nanoparticles immobilized on four different membranes was investigated under anoxic conditions. Effects of several parameters including the nature of membrane, initial concentration, pH value, and reaction temperature on the dechlorination efficiency were examined. The scanning electron microscopic images showed that the Ni/Fe nanoparticles were successfully immobilized inside the four membranes using polyethylene glycol as the cross-linker. The agglomeration of Ni/Fe were observed in poly(vinylidene fluoride), Millex GS and mixed cellulose ester membranes, while a relatively uniform distribution of Ni/Fe was found in nylon-66 membrane because of its hydrophilic nature. The immobilized Ni/Fe nanoparticles exhibited good reactivity towards the dechlorination of chlorinated hydrocarbons, and the pseudo-first-order rate constant for TCE dechlorination by Ni/Fe in nylon-66 were 3.7–11.7 times higher than those in other membranes. In addition, the dechlorination efficiency of chlorinated hydrocarbons followed the order TCE > PCE > CT. Ethane was the only end product for TCE and PCE dechlorination, while dichloromethane and methane were found to be the major products for CT dechlorination, clearly indicating the involvement of reactive hydrogen species in dechlorination. In addition, the initial rate constant for TCE dechlorination increased upon increasing initial TCE concentrations and the activation energy for TCE dechlorination by immobilized Ni/Fe was 34.9 kJ mol −1, showing that the dechlorination of TCE by membrane-supported Ni/Fe nanoparticles is a surface-mediated reaction.

Enhanced Dechlorination of Carbon Tetrachloride by Immobilized Fulvic Acids on Alumina Particles

Fulvic acids (FA) were immobilized on alumina particles in order to evaluate their catalytic effect as solid-phase redox mediator (RM) during the reductive dechlorination of carbon tetrachloride (CT) by anaerobic sludge. FA were extracted from three different soil samples and two commercial composts. Electron carrying capacity (ECC) was determined in all FA samples in order to select the appropriate source of redox-mediating compounds for CT dechlorination. TiO2, Al(OH)3, and γ-Al2O3 particles were tested as immobilizing materials for the extracted FA. FA extracted from a temperate pine forest soil showed the highest ECC (291.72 μmol g−1). The highest adsorption capacity of FA, measured as total organic carbon (TOC), was achieved by alumina (γ-Al2O3) particles (12 mg TOC-FA g−1). Results suggest that the transfer of electrons rather than their microbial generation through glucose fermentation was the rate-limiting factor during dechlorination of CT. Immobilized FA increase up to 10.4-fold the rate of CT dechlorination as compared with the control lacking FA. Immobilization of FA on alumina particles was very stable, and spectrophotometric screening did not detect any detachment of FA during dechlorination of CT, thus confirming that the enhanced dechlorination achieved could exclusively be linked to the redox-mediating capacity of immobilized FA. The present study constitutes the first demonstration that immobilized FA on alumina particles could serve as a solid-phase RM in dechlorination reactions.

Facile fabrication of nanostructured Pd–Fe bimetallic thin films and their electrodechlorination activity

A series of nanostructured Pd–Fe bimetallic thin films with the performance of fast and high-efficiency electrochemical reductive dechlorination were directly formed on glassy carbon electrodes (GCEs) through galvanic replacement of partial Fe 0 nanoparticles by Pd(II) ions. The composition and morphology of such Pd–Fe thin films are strongly dependent on the sacrificial Fe film templates fabricated by a template-free, double-potential step electrodeposition technique. The size, shape and morphology of the Fe nanoparticles that constitute the Fe thin films can be controlled well by adjusting the concentration of Fe 2+ ions in electrolyte solutions. Due to the good synergistic effect between Pd and Fe, the as-prepared Pd–Fe thin films with the novel microstructure display a high reactivity towards the electrochemical reductive dechlorination of carbon tetrachloride (CT), which closely related to the composition of Pd–Fe thin films, applied potential and temperature. The dechlorination reaction of CT complied with pseudo-first-order kinetics.

Ligand-assisted degradation of carbon tetrachloride by microscale zero-valent iron

Degradation of carbon tetrachloride (CT) by microscale zero-valent iron (ZVI) was investigated in batch systems with or without organic ligands (ethylenediaminetetraacetic acid (EDTA), citric acid, tartaric acid, malic acid and oxalic acid) at pHs from 3.5 to 7.5. The results demonstrated that at 25°C, the dechlorination of CT by microscale ZVI is slow in the absence of organic ligands, with a pseudo-first-order rate constant of 0.0217h−1 at pH 3.5 and being further dropped to 0.0052h−1 at pH 7.5. However, addition of organic ligands significantly enhanced the rates and the extents of CT removal, as indicated by the rate constant increases of 39, 31, 32, 28 and 18 times in the presence of EDTA, citric acid, tartaric acid, malic acid and oxalic acid, respectively, at pH 3.5 and 25°C. The effect of EDTA was most significant; the dechlorination of CT at an initial concentration of 20mgl−1 increased from 16.3% (no ligands) to 89.1% (with EDTA) at the end of 8h reaction. The enhanced CT degradation in the presence of organic ligands was primarily attributed to the elimination of a surface passivation layer of Fe(III) (hydr)oxides on the microscale ZVI through chelating of organic ligands with Fe(III), which maintained the exposure of active sites on ZVI surface to CT.

Reductive dechlorination of carbon tetrachloride in acidic soil manipulated with iron(II) and bisulfide ion

Batch and column tests were conducted to investigate the effect of reductant concentration, reductant contact time, and suspension pH on reductive dechlorination of carbon tetrachloride (CT) by soil manipulated with Fe(II) and HS −. Kinetic rate constants for the reductive dechlorination increased as the reductant concentrations increased. Fe(II) was more effective reductant than HS −, resulting in higher rate constants. The contact time of 1 day for the soil with HS − and that of 4 h with Fe(II) showed the highest reaction rates, respectively. The kinetic rate constants increased as the pH of soil suspensions with Fe(II) (5.2–8.0) and HS − (8.3–10.3) increased. Soil column with Fe(II) showed larger bed volumes (13.8) to reach a column breakthrough than that with HS − (4.0). Fe(II) treatment showed better removal of CT in the soil column with the addition of CaO than HS − treatment did. In contrast, HS − treatment not producing toxic products could be considered as an environmentally favorable reductant.