Reduction Of Carbon Tetrachloride Research Articles

Efficient Reduction of Carbon Tetrachloride in an Electrochemical Reactor with a Three-Dimensional Electrode

A selective electrochemical synthesis of chloroform from carbon tetrachloride (CT) in a laboratory-scale electrochemical reactor using a carbon felt three-dimensional electrode is studied. The characterization of the electrochemical reactor from the point of view of material transport was carried out, obtaining good correlations both in the adjustment to a simple bath reactor model and the adjustment to a piston-flow model, and the operating parameters were obtained, such as the material transport coefficient or the limiting intensity. The galvanostatic electrolysis of CT in the filter-press reactor obtained good values for current efficiency and selectivity, so that only hydrogen was obtained as a by-product. With respect to the use of flat electrodes, the three-dimensional carbon felt electrode improves the results in all the studied parameters under identical experimental conditions.

Quantitative Assessment of Monitoring Natural Attenuation on Carbon Tetrachloride Reduction at a Groundwater-Contaminated Site in Eastern China

Quantitative Assessment of Monitoring Natural Attenuation on Carbon Tetrachloride Reduction at a Groundwater-Contaminated Site in Eastern China

Toward rapid reduction of carbon tetrachloride in water by zero-valent aluminum/persulfate system.

The oxidation performance of the zero-valent aluminum (ZVAl)/persulfate (PS) combined system had been studied by researchers in the past, which relied on the activation of PS by ZVAl to generate potent oxidizing radicals (•OH and SO4•-) to degrade pollutants. However, ZVAl is a strong reductant and its reduction effect cannot be ignored. The reductive performance of the ZVAl/PS combined system is still unknown. Therefore, carbon tetrachloride (CT), an antioxidant organic pollutant, was selected as the target pollutant to test the reductive performance of the ZVAl/PS system in this study. We found a significant synergistic effect between ZVAl and PS, and the ZVAl/PS combined system could rapidly degrade CT in a wide pH range of 3-11 after an induction period. By SEM-EDS, TEM, XPS, and XRD analysis, it was found that PS could promote the corrosion of the oxide film on the ZVAl surface. The quenching experiment proved that PS could accept the electrons released from ZVAl to produce superoxide radical anion (O2•-), which led to the degradation of CT rather than the oxidative process by •OH and SO4•-. The hydrogen evolution experiment indicated that electronic reduction might play a secondary role in CT degradation. In conclusion, our study further explored the reductive performance of the ZVAl/PS combined system and expanded the pathway of CT degradation without any organic solvent addition, which provides a new strategy for the efficient degradation of refractory halogenated organic pollutants.

Mechanism of carbon tetrachloride reduction in Fe(II) activated percarbonate system in the environment of sodium dodecyl sulfate

This work innovatively found that Fe(II) activated sodium percarbonate (SPC) process could successfully degrade carbon tetrachloride (CT) in the environment of sodium dodecyl sulfate (SDS). CT degradation was remarkably accelerated to 87.2% at the optimum SPC/Fe(II)/CT molar ratio of 5/10/1 with the environment of 0.2 critical micelle concentration (CMC) SDS concentration. Fe(II) could effectively catalyze the decomposition of SPC to generate reactive oxygen species (ROSs). The results demonstrated that SDS enhanced the Fenton system and developed ROSs genertion. Hydroxyl radical (HO•), superoxide radical (O2−•), carbon dioxide radical (CO2−•), and singlet oxygen (1O2) were mainly generated in SPC/Fe(II) system under the condition of 0.2 CMC SDS, while CO2−• and 1O2 were the dominant active substances at 2.0 CMC SDS presence. The SPC/Fe(II) process performed much effective for the efficient degradation of CT at the acidic pH condition. The specific redox degradation pathway of CT started from the reduction of CT to •CCl3 through CO2−• and O2−• to form intermediates that were further dechlorinated by ROSs. In conclusion, the application of Fe(II) catalyzed SPC in the environment of SDS is a promising technology in converting the oxidation process into the simultaneous existence of oxidation and reduction process.

Aqueous micellar solutions of surface active ionic liquids as eco-green solvents for electrodexoification of halocarbons: A case study of dodecylmethylimidazolium chloride micelle solubilized carbon tetrachloride

The electrochemical reduction of carbon tetrachloride (CCl4) in aqueous micellar solutions of imidazolium based surface active ionic liquid (SAIL), dodecyl-3-methylimidazolium chloride (DDMIMCl) was investigated. Detailed analysis of the transient current-potential records suggests that the electroreductive dehalogenation of DDMIMCl micelle solubilized CCl4 proceeds through sticky dissociative pathway. Quantification of the associated thermodynamic and kinetic parameters reveals that some strong modifications are required to extend the validity of the conventional sticky dissociative electron transfer model otherwise suited for isotropic/continuum solvents, to electrochemical reactions in micro-heterogeneous micellar systems. The characteristic voltammetric features and the estimated kinetic/thermodynamic parameters suggest that the significant interaction between the electrogenerated Cl− and CCl3. fragments in the very complex water/micellar interface significantly facilitates the electroreduction of CCl4. Present work is first of its kind to highlight the technical/mechanistic advantages associated with the use of SAIL based micelles for the electrochemical detoxification of halocarbons. The presented results strongly support the use of SAIL aqueous based micellar systems for safe, economical, eco-friendly and efficient dehalogenation of halocarbons.

Mechanism of carbon tetrachloride reduction in ferrous ion activated calcium peroxide system in the presence of methanol

This study investigated the reductive initiation for the depletion of highly oxidized/perhalogenated pollutants, specifically the degradation of carbon tetrachloride (CT) was induced by adding methanol (MeOH) into a ferrous ion (Fe(II)) activated calcium peroxide (CaO2) system. The results indicated that CT could be completely degraded within 20 min at CaO2/Fe(II)/MeOH/CT molar ratio of 30/40/10/1 in this system. Scavenging tests suggested that both superoxide radical anion (O2−) and carbon dioxide radical anion (CO2−) were predominant reactive species responsible for CT destruction. Hydroxymethyl radicals (CH2OH), an intermediate in the transformation of MeOH, could also initiate CT degradation by reducing CCl bond. GC/MS analysis identified CHCl3, C2Cl4, and C2Cl6 as the intermediates accompanied by CT destruction, and a reduction mechanism for CT degradation was proposed accordingly. In addition, the impact of solution matrix and initial solution pH were evaluated, and the results showed that Cl−, NO3−, and HCO3− had adverse effects on CT degradation. Moreover, the alkaline condition was unfavorable to CT depletion. In conclusion, the results obtained in the actual groundwater tests encouragingly demonstrated that the CaO2/Fe(II)/MeOH process is a highly promising technique for the remediation of CT-contaminated groundwater.

A Silicate/Glycine Switch To Control the Reactivity of Layered Iron(II)–Iron(III) Hydroxides for Dechlorination of Carbon Tetrachloride

Layered FeII-FeIII hydroxide chloride (chloride green rust, GRCl) has high reactivity toward reducible pollutants such as chlorinated solvents. However, this reactive solid is prone to dissolution, and hence loss of reactivity, during storage and handling. In this study, adsorption of silicate (Si) to GRCl was tested for its ability to minimize GRCl dissolution and to inhibit reduction of carbon tetrachloride (CT). Silicate adsorbed with high affinity to GRCl yielding a sorption maximum of 0.026 g of Si/g of GRCl. In the absence of Si, the pseudo-first-order rate constant for CT dehalogenation by GRCl was 2.1 h-1, demonstrating very high reactivity of GRCl but with substantial FeII dissolution up to 2.5 mM. When Si was adsorbed to GRCl, CT dehalogenation was blocked and FeII dissolution extent was reduced by a factor of 28. The addition of glycine (Gly) was tested for reactivation of the Si-blocked GRCl for CT dehalogenation. At 30 mM Gly, partial reactivation of the GRCl was observed with pseudo-first-order rate constant for CT reduction of 0.075 h-1. This blockage and reactivation of GRCl reactivity demonstrates that it is possible to design a switch for GRCl to control its stability and reactivity under anoxic conditions.

Reduction of carbon tetrachloride by nanoscale palladized zero-valent iron@ graphene composites: Kinetics, activation energy, effects of reaction conditions and degradation mechanism

Herein, we reported a study on using the catalytic performance of nanoscale palladized zero-valent iron@ graphene composites (PFGC) synthesized by using coprecipitation method to significantly enhance carbon tetrachloride (CT) dechlorination in the laboratory, and then the nanocomposite was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunner-Emmet-Teler (BET), and X-ray photoelectron spectroscopy (XPS). The catalytic activity was investigated in consideration of several operation parameters including the initial pH, temperature, the dosage of nanocatalyst and the optimal content of palladium metal. The results showed that 50.4% and 93.5% CT (Cinitial=3mgL−1) were removed from aqueous solution by nZVI (Nanoscale zero-valent iron, 0.5gL−1) and PFGC (Nanoscale palladized zero-valent iron@ graphene composites, using Fe/GO=2:1 and Pd/Fe=0.75%, 0.5gL−1), respectively. The degradation kinetics of CT in all experiments followed pseudo first-order reaction kinetics. Moreover, it has been found that palladium metal (Pd0) accelerated hydrogen formation and activation to generate atomic hydrogen (·H) which in turn behaved as the reducing agents responsible for the dechlorination reactions as presented in the conceptual model. And the activation energies reduced from 44.42 to 30.18kJ/mol. However, it was very easy to agglomerate and form large-sized particles due to the high specific surface energy, hence, graphene as the supporting matrix graphically depicted in the SEM images increased specific surface areas to improve the dispersibility of bimetallic nanoparticles. After five successive runs, there was no significant reduction in the removal efficiency indicating a good reusability and stability of PFGC.

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.

Self-Templated Synthesis of Mesoporous Carbon from Carbon Tetrachloride Precursor for Supercapacitor Electrodes.

A high-surface-area mesoporous carbon material has been synthesized using a self-templating approach via reduction of carbon tetrachloride by sodium potassium alloy. The advantage is the reduction-generated salt templates can be easily removed with just water. The produced mesoporous carbon has a high surface area and a narrow pore size distribution. When used as a supercapacitor electrode, this material exhibits a high specific capacitance (259 F g(-1)) and excellent cycling performance (>92% capacitance retention for 6000 cycles).

Reductive dechlorination of carbon tetrachloride using buffered alkaline ascorbic acid

Alkaline ascorbic acid (AA) was recently discovered as a novel in-situ chemical reduction (ISCR) reagent for remediating chlorinated solvents in the subsurface. For this ISCR process, the maintenance of an alkaline pH is essential. This study investigated the possibility of the reduction of carbon tetrachloride (CT) using alkaline AA solution buffered by phosphate and by NaOH. The results indicated that CT was reduced by AA, and chloroform (CF) was a major byproduct at a phosphate buffered pH of 12. However, CT was completely reduced by AA in 2M NaOH without CF formation. In the presence of iron/soil minerals, iron could be reduced by AA and Fe2+ tends to precipitate on the mineral surface to accelerate CT degradation. A simultaneous transfer of hydrogenolysis and dichloroelimination would occur under phosphate buffered pH 12. This implies that a high alkaline environment is a crucial factor for maintaining the dominant pathway of two electron transfer from dianionic AA to dehydroascorbic acid, and to undergo dichloroelimination of CT. Moreover, threonic acid and oxalic acid were identified to be the major AA decomposition products in alkaline solutions.

Solvothermal Preparation of an Electrocatalytic Metalloporphyrin MOF Thin Film and its Redox Hopping Charge-Transfer Mechanism

A thin film of a metalloporphyrin metal-organic framework consisting of [5,10,15,20-(4-carboxyphenyl)porphyrin]Co(III) (CoTCPP) struts bound by linear trinuclear Co(II)-carboxylate clusters has been prepared solvothermally on conductive fluorine-doped tin oxide substrates. Characterization of this mesoporous thin film material, designated as CoPIZA/FTO, which is equipped with large cavities and access to metal active sites, reveals an electrochemically active material. Cyclic voltammetry displays a reversible peak with E(1/2) at -1.04 V vs ferrocyanide attributed to the (Co(III/II)TCPP)CoPIZA redox couple and a quasi-reversible peak at -1.45 V vs ferrocyanide, which corresponds to the reduction of (Co(II/I)TCPP)CoPIZA. Analysis of the spectroelectrochemical response for the (Co(II/I)TCPP)CoPIZA redox couple revealed non-Nernstian reduction with a nonideality factor of 2 and an E(1/2) of -1.39 V vs ferrocyanide. The film was shown to retain its structural integrity with applied potential, as was demonstrated spectroelectrochemically with maintenance of isosbestic points at 430, 458, and 544 nm corresponding to the (Co(III/II)TCPP)CoPIZA transition and at 390 and 449 nm corresponding to the (Co(II/I)TCPP)CoPIZA transition. The mechanism of charge transport through the film is proposed to be a redox hopping mechanism, which is supported by both cyclic voltammetry and spectroelectrochemistry. A fit of the time-dependent spectroelectrochemical data to a modified Cottrell equation gave an apparent diffusion coefficient of 7.55 (±0.05) × 10(-14) cm(2)/s for ambipolar electron and cation transport throughout the film. Upon reduction of the metalloporphyrin struts to (Co(I)TCPP)CoPIZA, the CoPIZA thin film demonstrated catalytic activity for the reduction of carbon tetrachloride.

Size controlled synthesis of carbon quantum dots using hydride reducing agents

Highly luminescent carbon quantum dots (CQDs) are synthesized at room temperature by hydride reduction of carbon tetrachloride within inverse micelles.

High Performance Photocatalysts Based on N-doped Graphene-P25 for Photocatalytic Reduction of Carbon Tetrachloride

Carbon tetrachloride (CCl4) is a kind of toxic and persistent groundwater contaminant. Considering keeping drinking water safe, a novel kind of N-doped graphene (NGS)-P25 TiO2 photocatalyst was prepared by a facile one-step hydrothermal method for the removal of CCl4 from contaminated water. Simultaneously, nitrogen-doping and the reduction of graphene oxide, and loading of P25 were finished during the same process. The photocatalytic efficiency of resulted NGS-P25 nanoparticles was studied for the degradation of CCl4. The results indicated that NGS-P25 exhibited the highest photocatalytic activity under UV light irradiation, outperforming graphene-P25, bare P25 or NGS. The effects of NGS-P25 dosage, irradiation time, CCl4 concentration and pH on CCl4 photocatalytic degradation efficiency were discussed in detail. Accordingly, the optimum experimental conditions were obtained. Moreover, the high performance photocatalyst of NGS-P25 can be extended to environmental pollution control and remediation towards various pollutants.

Zero-Valent Iron: Impact of Anions Present during Synthesis on Subsequent Nanoparticle Reactivity

Zero-valent iron particles are an effective remediation technology for ground water contaminated with halogenated organic compounds. In particular, nanoscale zero-valent iron is a promising material for remediation because of its high specific surface area, which results in faster rate constants and more effective use of the iron. An aspect of iron nanoparticle reactivity that has not been explored is the impact of anions present during iron metal nanoparticle synthesis. Solutions containing chloride, phosphate, sulfate, and nitrate anions and ferric ions were used to generate iron oxide nanoparticles. The resulting materials were dialyzed to remove dissolved by-products and then dried and reduced by hydrogen gas at high temperature. The reactivity of the resulting zero-valent iron nanoparticles was quantified by monitoring the kinetics as well as products of carbon tetrachloride reduction, and significant differences in reactivity and chloroform yield were observed. The reactivity of nanoparticles prepared in the presence of sulfate and phosphate demonstrated the highest reactivity and chloroform yield. Furthermore, substantial variations in the solid-state products of oxidation (magnetite, iron sulfide, goethite, etc.) were also observed.

Photocatalytic reduction of carbon tetrachloride by natural sphalerite under visible light irradiation

The photoreductive degradation of carbon tetrachloride (CT) in natural sphalerite ((Zn, Fe)S mineral) suspensions irradiated by visible light (VL) is studied in this paper. 92% of CT is degraded in N,N-dimethylformamide (DMF) organic solvent system after 8 h of VL irradiation. The effects of light source, sphalerite dosage, electron donors, dissolved oxygen and CT initial concentration on CT photocatalytic degradation efficiency are discussed. The degradation products are analyzed by gas chromatography–mass spectrometry (GC–MS), and the photocatalytic degradation mechanism is then proposed.

Simple menaquinones reduce carbon tetrachloride and iron (III)

Cell-free supernatant from Shewanella oneidensis MR-1 reduced carbon tetrachloride to chloroform, a suspension of Fe(III) and solid Fe(III) to iron (II). The putative reducing agent was tentatively identified as menaquinone-1 (MQ-1)-a water-soluble menaquinone with a single isoprenoid residue in the side chain. Synthetic MQ-1 reduced carbon tetrachloride to chloroform and amorphous iron (III) hydroxide to iron (II). To test the generality of this result among menaquinones, the reductive activities of vitamin K(2) (MQ-7)-a lipid-associated menaquinone with 7 or 8 isoprenoid residues-was evaluated. This molecule also reduced carbon tetrachloride to chloroform and iron (III) to iron (II). The results indicate that molecules within the menaquinone family may contribute to both the extracellular and cell-associated reduction of carbon tetrachloride and iron (III).

Aging of Iron Nanoparticles in Aqueous Solution: Effects on Structure and Reactivity

Aging (or longevity) is one of the most important and potentially limiting factors in the use of nano-Fe0 to reduce groundwater contaminants. We investigated the aging of FeH2 (Toda RNIP-10DS) in water with a focus on changes in (i) the composition and structure of the particles (by XRD, TEM, XPS, and bulk Fe0 content) and (ii) the reactivity of the particles (by carbon tetrachloride reaction kinetics, electrochemical corrosion potentials, and H2 production rates). Our results show that FeH2 becomes more reactive between 0 and ∼2 days exposure to water and then gradually loses reactivity over the next few hundred days. These changes in reactivity correlate with evidence for rapid destruction of the original Fe(III) oxide film on FeH2 during immersion and the subsequent formation of a new passivating mixed-valence Fe(II)−Fe(III) oxide shell. The effect of aging on the rate of carbon tetrachloride reduction was best described by the corrosion potential of FeH2, whereas the yield of chloroform from this reaction correlated best with the rate of H2 production. The behavior of unaged nano-Fe0 in the laboratory may be similar to that in field-scale applications for source-zone treatment due to the short reaction times involved. Long-term aged FeH2 acquires properties that are relatively stable over weeks or even months.

Effect of biogenic iron species and copper ions on the reduction of carbon tetrachloride under iron-reducing conditions

In this study, the cell-mediated and abiotic reduction of carbon tetrachloride (CCl 4) by biogenic iron species produced from the reductive dissolution of ferrihydrite in the presence of Geobacter sulfurreducens and copper ions (Cu(II)) were investigated. 9,10-Anthraquinone-2,6-disulfonate (AQDS), serving as a surrogate of natural organic matters and an electron shuttling compound, was added to enhance the efficiency of biological reduction of the solid Fe(III) minerals. G. sulfurreducens drove the reduction of CCl 4, primarily through the formation of biogenic surface-bound iron species produced from the reductive dissolution of ferrihydrite, in the presence of 10 μM AQDS. The pseudo-first-order rate constant ( k obsCT) for CCl 4 transformation in the presence of ferrihydrite was 3.0 times higher than that resulting from the use of G. sulfurreducens alone. Addition of 0.5 mM Cu(II) slightly inhibited both the growth of G. sulfurreducens and the production of biogenic Fe(II). However, the k obsCT values for CCl 4 transformation in ferrihydrite suspensions containing G. sulfurreducens and 0.3–0.5 mM Cu(II) were 2.1–4.2 times higher than that observed in the absence of Cu(II). X-Ray powder diffraction analysis indicated that the added Cu(II) reacted with the biogenic Fe(II) ions to produce catalytic cuprous ions (Cu(I)) and secondary iron oxide minerals such as magnetite and goethite, resulting in accelerating the chemical transformation efficiency and rate of CCl 4 under iron-reducing conditions.

On Assembling Polychlorinated Aromatic Hydrocarbons from Carbon Tetrachloride via Dichlorocarbene Intermediary by a Solvothermal Reaction: A Reaction Pattern from Carbene−Ylide Interconversion

[reaction: see text] The forced one-electron reduction of carbon tetrachloride with sodium in a sealed steel vessel is shown to have a narrow window of conditions to arrest the reaction at the polychlorinated aromatic hydrocarbons (PCAHs), as well as to prevent the reaction from proceeding all the way to the final stage of graphite and other carbon solids. The intermediates are quenched with toluene or benzene to give electrophilic substitution products and with water to give a quinomethine as the major product. The product pattern leads us to propose the carbene, perchlorobenzo[c,d]pyren-6-ylidene, or its reversible dimer as the major intermediate among others, that survives the severe conditions until coming into contact with these nucleophiles. Mainly from aromatic resonance stabilization, the carbene is proposed to have a delocalized singlet state analogous to a ylide electronic structure and, thus, undergoes observed ionic reactions instead of typical carbene reactions. This work serves as a mechanistic link on the structural evolution of carbon networks between molecular chemistry and nanomaterial chemistry.