Direct Electron Transfer Process Research Articles

Iron(III)-(1,10-Phenanthroline) Complex Can Enhance Ferrate(VI) and Ferrate(V) Oxidation of Organic Contaminants via Mediating Electron Transfer.

Recent research has primarily focused on the utilization of reductants as activators for Fe(VI) to generate high-valent iron species (Fe(IV)/Fe(V)) for the degradation of emerging organic contaminants (EOCs). However, a significant drawback of this approach arises from the reaction between reductants and ferrates, leading to a decrease in oxidation capacity. This study introduces a novel discovery that highlights the potential of the iron(III)-(1,10-phenanthroline) (Fe(III)-Phen) complex as an activator, effectively enhancing the degradation of EOCs by Fe(VI) and augmenting the overall oxidation capacity of Fe(VI). The degradation of EOCs in the Fe(VI)/Fe(III)-Phen system is facilitated through two mechanisms: a direct electron transfer (DET) process and electron shuttle action. The DET process involves the formation of a Phen-Fe(III)-Fe(VI)* complex, which exhibits a stronger oxidation ability than Fe(VI) alone and can accept electrons directly from EOCs. On the other hand, the electron shuttle process utilizes Fe(III)-Phen as a redox mediator to transfer electrons from EOCs to Fe(VI) through the Fe(IV)/Fe(III) or Fe(IV)/Fe(II)/Fe(III) cycle. Moreover, the Fe(III)-Phen complex can improve the utilization efficiency of Fe(V) by preventing its self-decay. This study's findings may present a viable option for utilizing an effective catalyst to enhance the oxidation of EOCs by Fe(VI) and Fe(V).

Unveiling the spatially confined oxidation processes in reactive electrochemical membranes

Electrocatalytic oxidation offers opportunities for sustainable environmental remediation, but it is often hampered by the slow mass transfer and short lives of electro-generated radicals. Here, we achieve a four times higher kinetic constant (18.9 min−1) for the oxidation of 4-chlorophenol on the reactive electrochemical membrane by reducing the pore size from 105 to 7 μm, with the predominate mechanism shifting from hydroxyl radical oxidation to direct electron transfer. More interestingly, such an enhancement effect is largely dependent on the molecular structure and its sensitivity to the direct electron transfer process. The spatial distributions of reactant and hydroxyl radicals are visualized via multiphysics simulation, revealing the compressed diffusion layer and restricted hydroxyl radical generation in the microchannels. This study demonstrates that both the reaction kinetics and the electron transfer pathway can be effectively regulated by the spatial confinement effect, which sheds light on the design of cost-effective electrochemical platforms for water purification and chemical synthesis.

Electron transfer route tuning caused by photo-irradiation: Stability enhancement of N-doped carbon materials in Fenton-like reactions

Improving the stability of N-doped carbon materials is still a great challenge in Fenton-like reactions. Herein, a hollow structure with TiO2 nanoparticles supported on the inner surface of N-doped carbon spheres (H-TiO2 @NC) is designed for peroxydisulfate (PDS)-based Fenton-like reactions with photo-irradiation. Impressively, the stability of H-TiO2 @NC is greatly enhanced with photo-irradiation. The degradation rate constant of bisphenol A (BPA) with photo-irradiation is ∼61 times larger than dark condition after four runs. The photovoltage enables more electrons to be transferred from BPA to PDS via active carbons. Less electrons from the carbon framework are expended, thus inhibiting the oxidation and deactivation of H-TiO2 @NC effectively. Additionally, the direct electron transfer (DET) process is improved due to conductivity enhancement, which also weakens the oxidation of carbon skeleton. This work provides a reliable method to enhance the stability of N-doped carbon materials. And giving some new insights into the mechanism of stability enhancement.

Tunable peroxymonosulfate activation by ( −1 1 1) crystal plane exposed δ-MnO2: Oxidant concentration induced intrinsic mechanisms transformation

The dual role of manganese oxides in peroxymonosulfate (PMS) activation for the degradation of organic contaminants makes the mechanism investigation complicated. Herein, a (−111) crystal plane exposed δ-MnO2 (SN-KMO) was synthesized to decipher the debate between direct oxidation process (DOP) and electron transfer process (ETP) mechanisms. Generally, 5 mg/L bisphenol A (BPA) could be efficiently removed in 15 min regardless of in the presence of high (0.5 mM) or low (0.05 mM) PMS concentration. Mechanisms analysis showed that nonradical pathways of DOP and ETP simultaneously contributed to the BPA degradation without the participation of radicals oxidation. Yet, contributions of DOP and ETP at certain PMS dosages differed significantly. Specifically, at high PMS concentration of 0.5 mM, DOP played the dominant role, and the overly protonated manganese active sites could bond with O-O bridged species derived from two PMS molecules to form outer-sphere complexes. Comparatively, at low PMS concentration of 0.05 mM, BPA oxidization was primarily dominated by ETP. The specific ETP was highly dependent on solution pH, and it only existed in the presence of high PMS concentration. The significance of this work lies in synthesizing a (−111) crystal plane exposed δ-MnO2 for efficient BPA degradation with low PMS dosage (0.05 mM) and discovering the unreported outer-sphere complexes for understanding the PMS activation mechanisms by manganese oxides.

Enhancement of anaerobic digestion of ciprofloxacin wastewater by nano zero-valent iron immobilized onto biochar

The commonly used antibiotic ciprofloxacin (CIP) can significantly inhibit and interfere with the anaerobic digestion (AD) performance. This work was developed to explore the effectiveness and feasibility of nano iron-carbon composites to simultaneously enhance methane production and CIP removal during AD under CIP stress. The results demonstrated that when the nano-zero-valent iron (nZVI) content immobilized on biochar (BC) was 33% (nZVI/BC-33), the CIP degradation efficiency reached 87% and the methanogenesis reached 143 mL/g COD, both higher than Control. Reactive oxygen species analysis demonstrated that nZVI/BC-33 could effectively mitigate microorganisms subjected to the dual redox pressure from CIP and nZVI, and reduce a series of oxidative stress reactions. The microbial community depicted that nZVI/BC-33 enriched functional microorganisms related to CIP degradation and methane production and facilitated direct electron transfer processes. Nano iron-carbon composites can effectively alleviate the stress of CIP on AD and enhance methanogenesis.

Electrocatalytic dechlorination of florfenicol using a Pd-loaded on blue TiO2 nanotube arrays cathode

Electrocatalytic hydrodechlorination technology provides an attractive strategy to effectively eliminate the biotoxicity of halogenated organic pollutants (HOPs). Herein, we demonstrated a highly dispersed Pd loaded on blue TiO2 nanotube arrays (Pdx-BTNA) cathode that can achieve efficient dechlorination and detoxification toward florfenicol (FLO). Characterization results indicated that strong interaction between Pd and BTNA was achieved through Pd-O bonds, which facilitated the electron transfer rate. Pdx-BTNA significantly outperformed other cathodes (i.e., BTNA, Pdx-TNA and Pdx-Ti) in the electrocatalytic dechlorination of FLO due to enhanced utilization of active H*. The dechlorination performances of FLO well followed the pseudo-first-order kinetic, and the reaction constant rate on Pdx-BTNA cathode (0.035 min−1) was 17.5, 1.94, 7.0 times higher than that on BTNA, Pdx-TNA and Pdx-Ti cathodes, respectively. Quenching experiments and electrochemical characterization indicated that both direct electron transfer and indirect reduction process mediated by H* were involved in the dechlorination of FLO. The optimal dechlorination efficiency of 98.79% was obtained by Pdx-BTNA cathode within 120 min at 1 mM PdCl2, applied cathode potential of −1.2 V. In addition, Pdx-BTNA exhibited superior stability and durability with almost no Pd leaching (0.0011 mg/L) during five dechlorination cycles. Our research proposed a novel strategy to design low noble Pd-loaded cathode material for efficient dechlorination and detoxification of HOPs.

A double-chamber microbial electrolysis cell improved the anaerobic digestion efficiency and elucidated the underlying bio-electrochemical mechanism

Bioelectrochemical regulation has been proven to enhance the traditional anaerobic digestion (AD) of biowastes. However, most of the research has been conducted using a single-chamber reactor that could not explain the underlying mechanism and/or role of electrodes in CH4 production. Herein, a double-chamber microbial electrolysis cell integrated anaerobic digestion system (MEC-AD) was fed with corn stover (CS) and was exposed to 0.0 V to 1.5 V to elucidate the possible effects of cathode and anode on the AD performance. It was shown that CH4 yield was enhanced by 80.41% at 0.6 V, however, there was a sharp decline in methanogens at 0.9 V, which finally resulted in acidification. Interestingly, electroactive bacteria of Enterococcus were enriched on the electrode at 0.6 V which accelerated the degradation of CS, and thus, enhanced the subsequent mixotrophic methanogenesis dominated by Methanosarcina in the bulk solution of the anode chamber. While, Enterococcus and Methanobacterium were shown to be the dominating microbes in the cathode chamber, which were found syntrophically associated to enhance hydrogenotrophic methanogenesis via the direct interspecies electron transfer process. The synergistic stabilization of both anode and cathode chambers resulted in the final performance improvement in the MEC-AD system. This MEC-AD system provided a deeper understanding for methane enhancement, which will facilitate the scale-up application of the double-chamber systems.

Degradation pathways of atrazine by electrochemical oxidation at different current densities: Identifications from compound-specific isotope analysis and DFT calculation

Current density was the key factor that impacted pollutant degradation by electrochemical oxidation, and reaction contributions at various current densities were non-negligible for the cost-effective treatments of organic pollutants. This research introduced compound specific isotope analysis (CSIA) into atrazine (ATZ) degradation by boron doped diamond (BDD) with current density of 2.5–20 mA/cm2, in order to provide “in-situ” and “fingerprint” analysis of reaction contributions with changed current densities. As results, the increased current density displayed a positive impact on ATZ removal. The ɅC/H values (correlations of Δδ13C and Δδ2H) were 24.58, 9.18 and 8.74 when current densities were 20, 4, and 2.5 mA/cm2, with ·OH contribution of 93.5%, 77.2% and 80.35%, respectively. While DET process favored lower current density with contribution rates up to ∼20%. What's more interesting, though the carbon and hydrogen isotope enrichment factors (εC and εH) were fluctuate, the ɅC/H linearly increased accompanied with applied current densities. Therefore, increasing current density was effective due to the larger ·OH contribution even though side reactions may occur. DFT calculations proved the increase of C–Cl bond length and the delocalization of Cl atom, confirming dechlorination reaction mainly occurred in the direct electron transfer process. While ·OH radical mainly attack the C–N bond on the side chain, which was more benefit to the fast decomposition of ATZ molecule and intermediates. It was forceful to discuss pollutant degradation mechanism by combining CSIA and DFT calculations. Target bond cleavage (i.e., dehalogenation reaction) can be conducted by changing reaction conditions like current density due to the significantly different isotope fractionation and bond cleavage.

Selective Removal of Emerging Organic Contaminants from Water Using Electrogenerated Fe(IV) and Fe(V) under Near-Neutral Conditions.

Fe(IV) and Fe(V) are promising oxidants for the selective removal of emerging organic contaminants (EOCs) from water under near-neutral conditions. The Fe(III)-assisted electrochemical oxidation system with a BDD anode (Fe(III)-EOS-BDD system) has been employed to generate Fe(VI), while the generation and contributions of Fe(IV) and Fe(V) have been largely ignored. Thus, we examined the feasibility and involved mechanisms of the selective degradation of EOCs in the Fe(III)-EOS-BDD system under near-neutral conditions. It was found that Fe(III) application selectively accelerated the electro-oxidation of phenolic and sulfonamide organics and made the oxidation system be resistant to interference from Cl-, HCO3-, and humic acid. Several lines of evidence indicated that EOCs were decomposed via direct electron-transfer process on the BDD anode and by Fe(IV) and Fe(V) but not Fe(VI), besides HO•. Fe(VI) was not generated until the exhaustion of EOCs. Furthermore, the overall contributions of Fe(IV) and Fe(V) to the oxidation of phenolic and sulfonamide organics were over 45%. Our results also revealed that Fe(III) was oxidized primarily by HO• to Fe(IV) and Fe(V) in the Fe(III)-EOS-BDD system. This study advances the understanding of the roles of Fe(IV) and Fe(V) in the Fe(III)-EOS-BDD system and provides an alternative for utilizing Fe(IV) and Fe(V) under near-neutral conditions.

Insights into the well-dispersed nano-Fe3O4 catalyst supported by N-doped biochar prepared from steel pickling waste liquor for activating peroxydisulfate to degrade tetracycline

The harmless and high-value added utilization of steel pickling waste liquor (SPWL) is a major challenge in the metallurgical advancement. Herein, well-dispersed nano-Fe3O4 (NF) composite with N-doped biochar as a spatial support (NF/0.5N3BC) is synthesized from SPWL and corncob, which has a large specific surface area (159.12 m2/g) and mesoporous structure. Besides, it exhibits excellent degradation efficiency (91.56%) and rate constant (0.042 min−1) of tetracycline (TC, 50 mg/L) by activating peroxydisulfate (PDS). Both free radicals and non-free radicals contribute to the TC degradation, among which the Fe species, defective edges, C = O, graphitic-N, and pyridinic-N are identified as the possible active sites. Particularly, N3BC cooperates with NF to form an internal electronic field to accelerate the Fe(III)/Fe(II) redox cycle and direct electron transfer process. Further, the possible degradation pathways are proposed based on DFT and HPLC-MS analysis, and the toxicity prediction results verify that NF/0.5N3BC + PDS system has an excellent TC degradation/detoxification ability. This study provided a novel strategy for high-value added utilization of SPWL and economically feasible treatment of TC-contaminated wastewater, so as to realizing the goal of “treating waste with waste”.

Electrochemical oxidation of phenol in chloride containing electrolyte using a carbon-coated Ti4O7 anode

Magnéli-phase Ti4O7 is an excellent anode material for electrochemical advanced oxidation process (EAOP). However, the development of Ti4O7 electrodes is always limited by the high cost and high energy consumption in their preparation process. In this study, the carbon-coated Ti4O7 electrode was successfully synthesized by an in-situ pyrolysis method, which exhibited high specific surface area (143.8 m2 g−1) and efficient electron transfer (47.3 Ω). The accelerated service life was measured to be 102.5 h, demonstrating its excellent stability. EAOP performance of the C-coated Ti4O7 electrode was evaluated under various operating conditions. The result showed that a complete degradation of phenol (100 mg L−1) was obtained in 60 min, under the condition of 0.1 M NaCl electrolyte and 20 mA cm−2 current density. Owing to the high oxygen evolution potential (OEP, 2.25 V vs. RHE) of the C-coated Ti4O7 electrode, high TOC removal ratio (68.9%) and low energy consumption (113.8 kWh kg−1TOC) were achieved under the optimal condition. Moreover, the mechanism of phenol degradation was investigated by linear sweep voltammetry (LSV) and free radical scavenging experiments. The results indicated that the degradation of phenol can be mainly attributed to the synergistic effects between adsorbed ·OH (M(·OH)) and Cl−, rather than the direct electron transfer process (DET) on the surface of the C-coated Ti4O7 electrode. This study provides an efficient strategy for the mineralization of phenolic wastewater by the C-coated Ti4O7 electrode.

Regulating Interlayer Confinement FeOCl for Accelerating Polymerization of Pollutants to Reduce Carbon Emission in Water Purification

The spatial structure regulation of catalysts could optimize the reaction pathway and enhance the mass transfer kinetics, which might realize the efficient and low-consumption removal of pollutants in Fenton-like technology. In this study, N,N-dimethylformamide (DMF) intercalation was used to adjust the interlayer spacing of FeOCl from 7.90 to 11.84 Å by a simple and rapid intercalation method, thereby enhancing the mass transfer kinetics and altering the catalytic pathway. The removal rate of BPA in the DMF-FeOCl/PS system increased by 8.78 times, showing good resistance to complex water environments (such as pH, humic acid, and anions), especially in 5 g/L high-salt wastewater. The direct electron transfer processes between Fe(IV) and pollutants mediated by interlayer Fe sites generate phenoxy radicals, and the polymerization processes occur, achieving efficient removal of pollutants and low CO2 emissions. This study provides new insight into the efficient and low-carbon treatment of high-salt wastewater.

Rational regulation of peroxymonosulfate activation over porous Co3O4 with carbon coating to boost utilization efficiency of peroxymonosulfate and achieve rapid removal of pollutants

It is of great significance to regulate rationally the activation mechanism of persulfate for promoting the development of sulfate radical-based advanced oxidation processes in wastewater treatment. Herein, carbon coated porous Co3O4 with hollow structure was synthesized. Notably, the formation of porous hollow structure improved specific surface area of Co3O4 and offered more redox couples of Co2+/Co3+, thereby reducing electron transfer resistance. Thus, the generation of reactive oxygen species and the role of high-valent transition metal complexes (namely Co3O4Co4+) were improved. The formation of carbon layer on the Co3O4 surface can avoid the release of Co ion during reaction process. Benefiting from the role of carbon layer in electron transport, catalyst-mediated the direct electron transfer from pollutant to PMS was boosted. Radical and nonradical pathways worked in coordination each other and realized the rapid removal of various organic pollutants in the presence of a little PMS. In short, current work revealed that modulating rationally the microstructure of catalyst was an efficient strategy for achieving controllable regulation of PMS activation process. More significantly, whether the direct electron transfer process can occur or not depended on both catalyst structure and electronic density of pollutants.

Carbon ink modified α-MnO2 as a peroxymonosulfate activator for enhanced degradation of organic pollutants via a direct electron transfer process

Transition metal oxides and carbon can activate peroxymonosulfate (PMS) to decompose organic contaminants. The combination of two materials can facilitate the adsorption of oxidants and pollutants on the catalyst and improve electron transfer efficiency. In this study, carbon nanoparticles-MnO2 composites (IC-MnO2) were synthesized by coating carbon ink on α-MnO2 and applied in PMS activation for acid orange 7 (AO7) degradation. The results showed that carbon nanoparticles were uniformly loaded on the α-MnO2 surface. Complete degradation of AO7 (20 mg/L) can be achieved in 15 min in the IC-MnO2/PMS system with a first-order kinetic rate constant of 0.22 min−1. Electrochemical analysis, quenching experiments, electron paramagnetic resonance, PMS decomposition, and removal of various contaminants demonstrated that AO7 could be efficiently degraded via a direct electron transfer pathway. A galvanic oxidation system containing the salt bridge and two separate cells was further established to confirm the electron transfer mechanism of the catalytic system. The study expands MnO2 applications by compositing nanocarbon materials in advanced oxidation processes and sheds light on the direct electron transfer mechanism.

Iron cobalt-doped carbon nanofibers anode to simultaneously boost bioelectrocatalysis and direct electron transfer in microbial fuel cells: Characterization, performance, and mechanism

A self-supporting electrode (FeCo-MOF/CNFs) combining iron cobalt bimetallic metal–organic frameworks (FeCo-MOFs) with carbon nanofibers (CNFs) was applied as the anode of a microbial fuel cell (MFC). The introduction of FeCo-MOFs enhanced graphitization degree and electrical conductivity, which endowed FeCo-MOF/CNFs with excellent electrocatalytic performance and good biocompatibility. The hierarchical porous structure of FeCo-MOF/CNFs provided abundant attachment sites for electroactive bacteria (EAB) and facilitated rapid electron transfer. The MFC equipped with FeCo-MOF/CNFs anode (FeCo/CNFs-MFC) exhibited considerable power generation output (maximum power density: 5.3 ± 0.2 W/m2, coulombic efficiency: 54 ± 4 %). In addition, FeCo/CNFs-MFC achieved a direct electron transfer (DET) catalytic current density of 0.63 A/m2. FeCo-MOF/CNFs could simultaneously enhance the bioelectrocatalysis activity and promote the DET process of EAB, which provided an effective way to improve the sluggish extracellular electron transport process of the MFC anode.

Energy-efficient removal of trace antibiotics from low-conductivity water using a Ti4O7 reactive electrochemical ceramic membrane: Matrix effects and implications for byproduct formation

The inevitably high energy consumption of traditional electrochemical processes to treat low-conductivity water has limited their wider application. Herein, we present an energy-efficient alternative, i.e., a Ti4O7 reactive electrochemical ceramic membrane (Ti4O7-REM) system with a superior mass transfer ability. For the removal of 10−200 μM norfloxacin (NOR) from low-conductivity (178−832 μS cm−1) water, the Ti4O7-REM system increased the kinetics rate constant by 4.3−34.0 times, thus decreasing the energy cost by 80.5−97.3% compared with a flow-by system. The rapid NOR removal was related to the enhanced direct electron transfer process in the Ti4O7-REM system, which allowed for higher resistance to HCO3− scavenging and a favorable reaction between NOR and the active sites. Meanwhile, this mechanism likely contributed to the less formation of inorganic chlorinated product, ClO3−, in the presence of Cl−. Although organic chlorinated byproducts were not detected during NOR degradation in the Ti4O7-REM system, Cl– influenced the speciation of the intermediates. A single-pass Ti4O7-REM system demonstrated 94−97% removal of trace antibiotics from real water samples in 30 s. The additional energy consumption (<0.02 kWh m−3) using a Ti4O7-REM system only contributed to 5.0−6.4% of the total in a typical tertiary wastewater treatment plant. Based on the above results, we can conclude that the convection-enhanced REM technique is viable for the purification of low-conductivity natural waters.

Structures of methanogenic Fdh-Hdr-Fmd complexes give insight into direct electron transfer and electron bifurcation processes

Structures of methanogenic Fdh-Hdr-Fmd complexes give insight into direct electron transfer and electron bifurcation processes

Efficient tetracycline degradation via peroxymonosulfate activation by magnetic Co/N co-doped biochar: Emphasizing the important role of biochar graphitization

The accumulation of tetracycline (TC) in aquatic environments raised the risk to ecosystems and human health due to its potential biological toxicity. The development of carbon-based materials with features of low cost, easy isolation and excellent performance for activating peroxymonosulfate (PMS) to generate reactive oxygen species toward TC degradation is essential but remains a grand challenge. Herein, sustainable biomass kelp-derived self-nitrogen doped biochar (KC)-stabilized Co nanoparticles were developed for PMS activation toward TC degradation. The influences of calcination temperature on the microstructure were studied to further optimize the degradation performance for TC. The Co-N/KC-900 exhibited an optimal performance for activating PMS to degrade TC with a removal efficiency of 99 % within 15 min. Additionally, the magnetic Co-N/KC-900 had robust recycling stability because of the enhanced interaction between the Co nanoparticles and graphitized biochar. Characterization results indicated that Co nanoparticles, graphite nitrogen, and direct electron transfer process participate in the PMS activation. Quenching experiments and electron paramagnetic resonance analyses revealed the combined radical and non-radical pathways for TC degradation, and the non-radical pathway plays a dominant role. The possible degradation pathways of tetracycline were proposed, and the toxicity of intermediates in the degradation process was evaluated. This study offers a facile and low-cost strategy to prepare an efficient PMS activator for antibiotic wastewater remediation.

Direct Electrochemical Detection of Glucose on PEDOT Functionalized Screen-Printed Electrodes

This study reports a novel strategy to fabricate a third-generation glucose sensor on screen-printed carbon electrode (SPCE). The direct electron transfer (DET) between glucose oxidase (GOx) and SPCE was accomplished by immobilization of GOx in poly (3, 4-ethylenedioxythiophene) (PEDOT) functionalized electrodes. The use of PEDOT relaxed the requirement for the distance between the redox site of GOx, flavin adenine dinucleotide (FAD) cofactors, and the electrodes in the DET process due to its low ionization potential and good hole-injection ability. This strategy has not required the introduction of an additional mediated agent, and the response current of glucose consisted of DET current. The developed sensor demonstrated high electrochemical responses of glucose in human blood plasma with a wide linear range of 1–14 mM l−1. The reproducibility of the sensor (electrodes) was also studied by sequential determinations of glucose under analogous parameters over time, showing no significant decrease in the faradic response. The construction of DET process with facile methods (3 steps of drop-coating), and simultaneously, the fundamental SPCE does not need any activation process, which makes large mass production of third-generation biosensing systems possible.

Natural Magnetite Minerals Enhance 1,2-Dichloroethane Reductive Dechlorination

Contamination of soil and groundwater by chlorinated solvents is an environmental issue of primary concern. Recently, electrically conductive iron particles have been proposed as a novel approach to accelerate anaerobic bioremediation processes. In fact, it was demonstrated that conductive particles facilitate the exchange of electrons between microorganisms via Direct Interspecies Electron Transfer (DIET) processes, thus enhancing the pollutant-degrading potential of the microbial community. However, the use of natural minerals in this context has not been reported so far. In this study, we applied, for the first time, natural magnetite and hematite to accelerate the reductive dechlorination of 1,2-dichloroethane by an enrichment culture in lab-scale anaerobic microcosms. After four feeding cycles, low magnetite-amended microcosms (13 mg/L) yielded the highest rate of 1,2-DCA reductive dechlorination and reduced methanogenic activity. By contrast, hematite did not display any apparent stimulatory effect. Surprisingly, in the presence of higher amounts of iron oxides, a weaker effect was obtained, probably because iron(III) present in the minerals competed for the electrons necessary for reductive dechlorination. For all microcosms, the concentration of the toxic byproduct vinyl chloride was negligible throughout the whole study. The SEM/EDS analysis confirmed the close interaction between the conductive iron oxide particles and the dechlorinating bacteria. This work opens the possibility of using natural conductive minerals for bioremediation applications as well as shedding light on the previously unrecognized role of such minerals in contaminated ecosystems.