Direct Electron Transfer Reaction Research Articles

Intra/extracellular transmembrane electron transfer for bioelectric enhancement mediated by in-situ bio-FeS and polypyrrole coating

This study involves the construction of an “inside-out” electronic network channel with in-situ formation of biogenic FeS (bio-FeS) nanoparticles in cells of Shewanella oneidensis MR-1 (S. oneidensis MR-1) and a coating of conductive polypyrrole (PPy) on the outer surface of entire cells. The microbial fuel cell driven by bio-FeS and PPy co-modified S. oneidensis MR-1 (FeS/PPy@MR-1) has a maximum power density 3.6 times higher than that of the native strain. Electrochemical analysis demonstrates that the modifications of bio-FeS and PPy markedly enhance the direct electron transfer and c-type cytochrome-bound flavin-mediated single-electron reaction pathways and expand the electron output flux. The electron-donating ability of FeS/PPy@MR-1 is 7 times greater than that of the native strain. Bio-FeS and PPy can mediate novel intra/extracellular transmembrane electron transport pathways independent of the traditional respiratory chain, bridge spatially discrete redox environments, and optimize electron transfer pathways to intracellular to extracellular transfer electrons rapidly and maximally. These findings provide insights into conductive nanomaterial-mediated intra/extracellular transmembrane electron transfer, which is critical for the environment and bioenergy fields.

Cobalt-modified digestate-derived biochar enhances kitchen waste anaerobic dry digestion: Performance, microbial mechanisms, and metabolic pathways

To achieve simultaneous in-situ high-value utilization of digestate and efficient resource recovery of kitchen waste (KW). In this work, Co-modified digestate-derived biochar (DDB-Co) was prepared for the first time, the effects of DDB-Co on KW mesophilic dry anaerobic digestion were investigated, and the underlying mechanisms were elucidated. The results showed that the specific surface area of DDB-Co increased to 98.7 m2/g, which was 37.4 % higher than that of the unmodified group (DDB). DDB-Co exhibited a dose-dependent effect on biogas production from the KW dry digestion, with the optimal dose of 4.0 g/L (calculated on a solid content) DDB-Co yielding 205.3 mL/(g·VS) of biogas, representing an 80.9 % increase compared to the CK group. However, higher doses, such as 8.0 g/L DDB-Co, reduced the cumulative biogas production. Mechanistic analysis indicated that 4.0 g/L DDB-Co facilitated the dissolution of particulate organic matter and accelerates the conversion process of volatile fatty acids (VFA) in KW, thereby preventing excessive acidification. Microbial community structure analysis revealed that DDB-Co reduced microbial richness and diversity but selectively enriched microorganisms such as Lactobacillus and Methanothrix, accelerating the direct interspecific electron transfer (DIET) reaction rate and increasing biogas production. Metagenomic analysis demonstrated that DDB-Co primarily upregulated the relative abundances of key enzymes in the acetate decarboxylation methanogenesis pathway, such as acetate kinase (ackA), phosphate acetyltransferase (pta), and acetyl-CoA synthetase (acs), enhancing biogas yield and maintaining system stability. The findings of this work expand the high-value utilization pathways for digestate and provide an alternative solution for the efficient resource recovery of KW.

Enhanced Electron Transfer Efficiency of Fructose Dehydrogenase onto Roll-to-Roll Thermal Stamped Laser-Patterned Reduced Graphene Oxide Films.

Herein, a strategy to stamp laser-produced reduced graphene oxide (rGO) onto flexible polymers using only office-grade tools, namely, roll-to-roll thermal stamping, is proposed, proving for the first time its effectiveness for direct bioelectrocatalysis. This straightforward, scalable, and low-cost approach allows us to overcome the limits of the integration of laser-induced rGO-films in bioanalytical devices. Laser-produced rGO has been thermally stamped (TS) onto different polymeric substrates (PET, PVC, and EVA) using a simple roll-laminator; the obtained TS-rGO films have been compared with the native rGO (untransferred) via morphochemical and electrochemical characterization. Particularly, the direct electron transfer (DET) reaction between fructose dehydrogenase (FDH) and TS-rGO transducers has been investigated, with respect to the influence of the amount of enzyme on the catalytic process. Remarkable differences have been observed among TS-rGO transducers; PET proved to be the elective substrate to support the transfer of the laser-induced rGO, allowing the preservation of the morphochemical features of the native material and returning a reduced capacitive current. Noteworthily, TS-rGOs ensure superior electrocatalysis using a very low amount of FDH units (15 mU). Eventually, TS-rGO-based third-generation complete enzymatic biosensors were fabricated via low-cost benchtop technologies. TS-rGOPET exhibited bioanalytical performances superior to the native rGO, allowing a sensitive (0.0289 μA cm-2 μM-1) and reproducible (RSD = 3%, n = 3) d-fructose determination at the nanomolar level (LOD = 0.2 μM). TS-rGO exploitability as a point-of-need device was proved via the monitoring of d-fructose during banana (Musa acuminata) postharvest ripening, returning accurate (recoveries 110-90%; relative error -13/+1%) and reproducible (RSD ≤ 7%; n = 3) data.

Transient Short Circuit-Based Degradation of Lithium and Sodium Anode-Free Batteries

The demand for an extended range of electric vehicles has created a renaissance of interest in replacing the common lithium-ion with a higher energy-density metal anode (e.g., Li or Na). However, alkali metal cells suffer from capacity fading and potential safety issues. The uneven metal electrodeposition often results in dendrite formation and potentially hazardous situations such as cell short-circuiting and thermal runaway.Though lithium plating has been studied widely, a better understanding of the short-circuiting mechanisms and metal battery failure is required. Moreover, a considerable performance gap exists between symmetric metal cells and realistic metal batteries."Soft shorts" are small localised electrical connections between two electrodes that allow the co-existence of direct electron transfer and interfacial reaction. Although soft shorts were identified as a major safety issue in the early nineties, their detection and prevention were not widely studied. Therefore, a fundamental understanding of passivated metals' plating and a reliable testing method for soft short circuits is critical for realising metal batteries, such as Li-Air, Li-S, and anode-free batteries.Here we compared short circuit formation mechanisms and degradation in symmetric cells and anode-free lithium and sodium batteries using coupled galvanostatic impedance spectroscopy (GEIS) and in-situ nuclear magnetic resonance spectroscopy (NMR) for the first time.The coupling of in-situ NMR and EIS allows the observation of metal batteries' electrochemical and chemical dynamics and degradation in real time without affecting the cells' operation.We demonstrated that lithium and sodium short circuit formation mechanisms fundamentally differ and strongly depend on electrolyte composition and SEI stability. This new understanding of the metal plating mechanism is crucial to develop the next generation of rechargeable batteries with high energy density, prolonged cycling life and improved sustainability.

Promotion of Direct Electron Transfer to Cytochrome c by Functionalized Thiophene‐based Conducting Polymers

AbstractControlling direct electron transfer (DET) to redox proteins is of great interest for fundamental studies on biochemical processes and the development of biotechnological devices, such as biosensors or enzymatic fuel cells. Cytochrome c is a classical model protein for studying DET reactions that plays a key role in the onset of cellular apoptosis and the mitochondrial respiratory chain. In this contribution, we explored DET between cyt c and conducting polymers bearing the chemical structure of thiophene, specifically PEDOT, and its OH‐containing derivative, PHMeEDOT. The combination of electrochemistry and in situ FTIR spectroscopy allowed us to gain more insight into the inner mechanism of DET at physiological pH. Hydrophilic interactions favour the correct orientation of the heme crevice of cytochrome c towards the polymer surface. When a positive charge is injected into the conducting polymer, the increasing electrostatic repulsion between protein and surface induces the desorption of lysine residues near the heme group and stimulates protein flipping. This effect was more pronounced at PEDOT‐ than PHMeEDOT‐modified electrodes since the latter shows stronger interactions with lysine residues, partially hindering protein rotation at moderate potential. The potential‐induced reorientation process was similar on both polymer surfaces, only at high positive potentials.

Electrooxidation of chlorophene and dichlorophen by reactive electrochemical membrane: Key determining factors of removal efficiency

This study systematically investigated the variable main electrooxidation mechanism of chlorophene (CP) and dichlorophen (DCP) with the change of reaction conditions at Ti4O7 anode operated in batch and reactive electrochemical membrane (REM) modes. Significant degradation of CP and DCP was observed, that is, CP exhibited greater removal efficiency in batch mode at 0.5–3.5 mA cm−2 and REM operation (0.5 mA cm−2) with a permeate flow rate of 0.85 cm min−1 under the same reaction conditions, while DCP exhibited a faster degradation rate with the increase of current density in REM operation. Density functional theory (DFT) simulation and electrochemical performance tests indicated that the electrooxidation efficiency of CP and DCP in batch mode was primarily affected by the mass transfer rates. And the removal efficiency when anodic potentials were less than 1.7 V vs SHE in REM operation was determined by the activation energy for direct electron transfer (DET) reaction, however, the adsorption function of CP and DCP on the Ti4O7 anode became a dominant factor in determining the degradation efficiency with the further increase of anodic potential due to the disappeared activation barrier. In addition, the degradation pathways of CP and DCP were proposed according to intermediate products identification and frontier electron densities (FEDs) calculation, the acute toxicity of CP and DCP were also effectively decreased during both batch and REM operations.

Degradation of 17β-estradiol and antifouling properties of magnéli phase Ti4O7 reactive electrochemical membrane in the presence of fulvic acid

This study systematically investigated the electrooxidation of 17β-estradiol (E2) and inhibition of formation of fulvic acid (FA) aggregation in reactive electrochemical membrane (REM) made of Ti4O7. Our results indicate that aggregated FA in the membrane could retard the breakthrough rate of E2, while the interception for E2 was significantly alleviated for treated FA due to its structural change during REM electrooxidation. The electrooxidation removal efficiency of E2 during REM operation increased with the decrease of permeate flow rates due to the longer residence time within REM, and 95.90 ± 0.92% removal was reached at 20 mA cm−2 with the permeate flow rate of 7.5 mL min−1. FA inhibited the electrooxidation of E2 accompanied by the generation of specific intermediate products. Our results involving designed experiments and molecular simulation calculation indicated that direct electron transfer (DET) reaction induced polymer generation, and the generation of hydroxylation and ring-opening products was initiated by the reaction with hydroxyl radicals (•OH). Permeate flux analysis and excitation-emission matrix characterization indicated that significant antifouling performance of REM was mainly attributed to the structural change of FA during REM treatment. These results revealed the potential roles of natural organic matter in Ti4O7 REM treatment of organic contaminants that greatly promoted the development of REM operation application.

An economic, self-supporting, robust and durable LiFe5O8 anode for sulfamethoxazole degradation

Electrochemically activating peroxydisulfate (PDS) to degrade organic pollutants is one of the most attractive advanced oxidation processes (AOPs) to address environmental issues, but the high cost, poor stability, and low degradation efficiency of the anode materials hinder their application. Herein, an economic, self-supporting, robust, and durable LiFe5O8 on Fe substrate (Fe@LFO) anode is reported to degrade sulfamethoxazole (SMX). When PDS is electrochemically activated by the Fe@LFO anode, the degradation rate of SMX is significantly improved. It is found that hydroxyl radicals (•OH), superoxide radical (O2•–), singlet oxygen (1O2), Fe(Ⅳ), activated PDS (PDS*), and direct electron transfer (DET) reactions synergistically contribute to the degradation of SMX, which can realize the degradation of SMX in four possible routes: cleavage of the isoxazole ring, hydroxylation of the benzene ring, oxidation of the aniline group, and cleavage of the S–N bond, as evidenced by a series of tests of radicals quenching, electron paramagnetic resonance (EPR), linear sweep voltammetry (LSV) and liquid chromatograph mass spectrometer (LC-MS). Furthermore, Fe@LFO has good structural stability, excellent cyclability and low degradation cost, demonstrating its great potential for practical applications. This work contributes to a stable and effective anode material in the field of AOPs.

Mechanistic study of electrooxidation of coexisting chloramphenicol and natural organic matter: Performance, DFT calculation and removal route

The electrooxidation performance of coexisting chloramphenicol (CAP) and natural organic matter (NOM) by Ti4O7 anode was systematically investigated in this study. Intrinsic reaction kinetics showed that the removal of CAP followed pseudo-first-order kinetics, 72.42 ± 0.20 % removal with 40.79 ± 0.41 % mineralization rate of CAP was achieved in 60 min using 5 mA cm−2. The oxidation mechanisms of CAP were elucidated by density functional theory (DFT) simulations and experiments involving hydroxyl free radical (•OH) scavenger, which indicated that the efficient degradation of CAP was attributed to the combined action of •OH attack and direct electron transfer (DET) reaction. The degradation pathway of CAP was proposed based on frontier electron densities (FEDs) calculation and intermediate products identification, and less ecological risks of CAP degradation solution were also proved by acute toxicity test. Humic acid (HA), selected as the typical NOM, could inhibit the degradation of CAP to a certain extent by competitive action for electrooxidation with effective removal and mineralization of HA, which was further confirmed based on real wastewater treatment experiments. Specifically, the degree of humification and aromaticity of HA was weakened, and some complex small molecular organic matters such as aromatic proteins were generated. These findings proved the feasibility of Ti4O7 anode electrooxidation to remove CAP antibiotics and organic matter from water, in consideration of the potential negative role of CAP and organic matter for ecological environment and human health.

Extending semiconductor-based photo-fenton reaction to circumneutral pH using chelating agents: The overlooked role of pH on the reduction mechanism of Fe3+

In this work, we conceived a novel vis/H2O2/Fe3+/nitrilotriacetic acid (NTA)/g-C3N4 system to address the bottlenecks of traditional homogeneous photo-Fenton reactions, i.e., the narrow pH application range and unsustainable electron supply by the ligand to metal charge transfer (LMCT) process. A strong synergistic effect was observed with efficient organic contaminant degradation in a broad pH range (3–8), and hydroxyl radical (HO•) was proved to be the primary active species. Intriguingly, we found that the mechanism of rate-limiting Fe3+ reduction process was highly pH-dependent. At acidic condition (pH 3.0), the reduction of Fe3+ was dominated by direct photogenerated electron (e−) transfer and LMCT reaction. However, as the pH increased to 7.0, it gradually converted into a superoxide radical (O2•−) mediated reduction process, which was mainly attributed to the enhanced electrostatic repulsion between g-C3N4 and iron species, and the species transformation from protonated HO2• to more active deprotonated O2•−. Notably, H2O2 played a triple role in this system including (1) serving as the precursor of O2•−(2) scavenging photogenerated holes (h+) to complete the closed-loop of photocatalytic reaction and (3) boosting the generation of HO•. Finally, the vis/H2O2/Fe3+/NTA/g-C3N4 system also featured with a strong water matrix resistance capacity (e.g., chloride, bicarbonate, Ca2+/Mg2+ and humic acid), which enables it a promising platform for practical wastewater purification.

Electrocatalytic degradation of pesticide micropollutants in water by high energy pulse magnetron sputtered Pt/Ti anode

The increasing occurrence of pesticide micropollutants highlights the need for innovative water treatment technologies, particularly for small-community and household applications. Electro-oxidation is being widely studied in this area, unfortunately, safe, stable and efficient electrocatalytic anodes without released heavy metal ions are still highly required. In this study, we fabricated a Pt/Ti anode by high energy pulse magnetron sputtering (HiPIMS-PtTi) which was used to decompose dichlorvos (DDVP) and azoxystrobin (AZX) in water. The results show that the reaction rate constant (kENR) on HIPIMS was 35.7 min–1 (DDVP) and 41.3 min–1 (AZX), respectively, superior to electroplating Pt/Ti anode (EP-PtTi). The identification of radicals (•OH, 1O2, •O2−) and micro-area analyses evidenced that Pt atoms were embedded into the TiO2 lattice on the surface of Ti plate by high-energy ions, which resulted in more adsorbed hydroxyls, and higher production of •OH under polarization conditions. Besides, the electro-oxidation intermediates of DDVP and AZX were identified and the degradation pathways were speculated: (1) indirect oxidation dominated by •OH attack, and (2) direct electron transfer reaction of pesticides on the anode surface. The cooperated reactions achieve the complete degradation and highly efficient mineralization of DDVP and AZX.

Unveiling the Role of Sulfur in Rapid Defluorination of Florfenicol by Sulfidized Nanoscale Zero-Valent Iron in Water under Ambient Conditions.

Groundwater contamination by halogenated organic compounds, especially fluorinated ones, threatens freshwater sources globally. Sulfidized nanoscale zero-valent iron (SNZVI), which is demonstrably effective for dechlorination of groundwater contaminants, has not been well explored for defluorination. Here, we show that SNZVI nanoparticles synthesized via a modified post-sulfidation method provide rapid dechlorination (∼1100 μmol m-2 day-1) and relatively fast defluorination (∼6 μmol m-2 day-1) of a halogenated emerging contaminant (florfenicol) under ambient conditions, the fastest rates that have ever been reported for Fe0-based technologies. Batch reactivity experiments, material characterizations, and theoretical calculations indicate that coating S onto the metallic Fe surface provides a highly chemically reactive surface and changes the primary dechlorination pathway from atomic H for nanoscale zero-valent iron (NZVI) to electron transfer for SNZVI. S and Fe sites are responsible for the direct electron transfer and atomic H-mediated reaction, respectively, and β-elimination is the primary defluorination pathway. Notably, the Cl atoms in florfenicol make the surface more chemically reactive for defluorination, either by increasing florfenicol adsorption or by electronic effects. The defluorination rate by SNZVI is ∼132-222 times higher with chlorine attached compared to the absence of chlorine in the molecule. These mechanistic insights could lead to new SNZVI materials for in situ groundwater remediation of fluorinated contaminants.

Direct Electron Transfer Reaction of Cytochrome c Immobilized on a Bare ITO Electrode

Abstract To measure the direct electron transfer (DET) reaction of cytochrome c (Cytc) immobilized on a bare ITO electrode after removing the adsorbed molecules, automated solution exchange (ASE) processes were performed to induce their desorption. By fitting the absorbance decay curve observed at the Soret band peak position of Cytc at around 408 nm during the ASE processes with a double exponential equation, the final immobilized fraction was estimated to be 58.6% of the Cytc adsorbed on bare ITO electrodes under the experimental conditions. Cyclic voltammograms (CVs) of Cytc adsorbed on the bare ITO electrodes were measured for 60 min to elucidate the DET activity of immobilized Cytc. After repeated CV measurements, approximately 90% of immobilized Cytc was found to remain from the evaluation based on the coulombic amount of reduction and oxidation peaks. The scan rate dependent peak separation data from the immobilized Cytc between reduction and oxidation peaks in CVs produced 2.7 times larger DET reaction rate constant than that previously reported for the Cytc adsorbed on the bare ITO electrode.

Direct Electron Transfer Between Single-Walled Carbon Nanotube and Fructose Dehydrogenase

In this paper, we report the direct electron transfer (DET) reaction between debundled single-walled carbon nanotubes (SWCNTs) and the enzyme flavin adenine dinucleotide (FAD)-dependent fructose dehydrogenase (FDH). An anionic surfactant, sodium cholate (SC), was used to debundle the SWCNTs and disperse them in an aqueous solution, and the experimental conditions were optimized. The DET electrode, FDH/SWCNT-SC, was fabricated by the layer-by-layer drop-casting technique. Cyclic voltammetry experiments were conducted, and the experimental results revealed the presence of a high level of fructose concentration-dependent current (FDC). In the control experiment, FDC was not observed with either multi-walled carbon nanotubes (MWCNTs) or graphene flakes. The reported dimension of the FDH molecule is ~7 nm, which is larger than the diameter of an individual SWCNT (1 nm) but smaller than the diameter of an individual MWCNT (10 nm) and the dimensions of a graphene flake (~100 nm square). Only individual SWCNTs can reside in close proximity (within the distance for DET) of the cofactors FAD and heme c, both of which remain deeply embedded within the protein shell. The FDH/SWCNT-SC electrode had a sensitivity of 27 μA mM <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> , a linear dynamic range of 1.4-18.5 mM, and a detection limit of 2.1 μM. The electrode, combined with the enzyme invertase (IVT), can detect the total concentration of fructose and sucrose in samples (using the IVT/FDH/SWCNT-SC electrode). Therefore, fructose and sucrose can be separately quantified when both FDH/SWCNT-SC and IVT/FDH/SWCNT-SC electrodes are used. The amounts of fructose and sucrose in real food samples (100% fruit juice in the present case) determined using these electrodes agreed well with the amounts obtained from high-performance liquid chromatography (HPLC) experiments.

Bioelectrochemical detection of histamine release from basophilic leukemia cell line based on histamine dehydrogenase-modified cup-stacked carbon nanofibers

Histamine released from mast cells plays an important role as not only a physiological active substance for the trigger of allergic reactions but also a neurotransmitter in a nervous system. To detect histamine directly, we immobilized oxygen-independent histamine dehydrogenase (HmDH) onto the surface of cup-stacked carbon nanofibers (CSCNFs), which work both as an electrical nanowire and an enzyme support, and investigated the direct electron transfer reaction from HmDH reduced by histamine to CSCNF. Current responses of histamine oxidation at the HmDH-modified CSCNF electrode showed a linear relationship between 0.3 µM and 300 µM with detection limit of 0.1 µM in a Briton Robinson buffer (pH 9.4) and was about 25 times larger than those at a flat glassy carbon electrode modified with HmDH because of its three-dimensional network. Using the HmDH-modified CSCNF electrode, we successfully observed histamine release from rat basophilic leukemia cell line RBL-2H3 after stimulation with degranulation agents, such as antigen 2,4-dinitrophenylated bovine serum albumin and calcium ionophore A23187. The present sensing system might be applied to at least advanced in vitro allergic diagnostic methods.

The Glucose Effect on Direct Electrochemistry and Electron Transfer Reaction of Glucose Oxidase Entrapped in a Carbon Nanotube‐Polymer Matrix

AbstractIn this work, glucose oxidase (GOx) cross‐linking to a single‐wall carbon nanotubes (SWCNTs)‐poly(ethylenimine) (PEI) matrix is investigated using cyclic voltammetry (CV) for its direct electrochemistry and kinetics with presence of glucose. The electrochemistry of the bound flavin cofactor, flavin adenine dinucleotide (FAD) of the GOx, is impeded by glucose and recovered at absence of glucose, whereas a non‐specific sugar (e. g. sucrose) has no such effect. The Faradaic current of the GOx in CV decreases when the concentration of glucose increases, while the calculated electron transfer (ET) rate constant (k0) of the GOx presents a monotonic increment manner up to 144 % at 70 mM glucose concentration vs. absence of glucose in a deaerated electrolyte solution. The k0 and Faradaic current changes demonstrate a strong linear relationship to logarithmic value of glucose concentration up to 20 mM. These results suggest that the entrapped GOx, when exposing to glucose, becomes deactivated in the direct electrochemistry. Further mechanistic analysis suggests the ET reaction of GOx shows a responsive correlation to the non‐ergodicity of those active GOx sites. A control experiment using pure FAD immobilized in the matrix doesn't show responses to glucose addition.

Electron Spin Resonance Evidence for Electro-generated Hydroxyl Radicals

Electro-generated hydroxyl radicals (•OH) are of fundamental importance to the electrochemical advanced oxidation process (EAOP). Radical-specific electron spin resonance (ESR) evidence is still lacking in association with the direct electron transfer (DET) reaction of spin trap (e.g., 5,5-dimethyl-1-pyrroline-N-oxide; DMPO) and side reactions of the DMPO-OH adduct in the strongly oxidative environment offered by anodic polarization. Herein, we showed ESR identification of electro-generated •OH in EAOP based on the principle of kinetic selection. Excessive addition of a DMPO agent and fast spin trapping allowed suitable kinetic conditions to be set for effective spin trapping of electro-generated •OH and subsequent ESR identification. Otherwise, interferential triplet signals would emerge due to formation of paramagnetic dimer via dehydrogenation, DET oxidation, and dimerization reactions of the DMPO-OH adduct. The results demonstrate that •OH formation during spin-trapping on the titanium suboxide (TiSO) anode could be quantified as 47.84 ± 0.44 μM at current density of 10 mA cm-2. This value revealed a positive dependence on electrolysis time, current density, and anode potential. The effectiveness of ESR measurements was verified by the results obtained with the terephthalic acid probe. The ESR identification not only provides direct evidence for electro-generated •OH from a fundamental point of view, but also suggests a strategy to screen effective anode materials.

Bioelectrosynthesis technology for enhancing methane production using a thermophilic methanogenic consortium

This work investigated the electrocatalytic activity of a thermophilic methanogenic consortia (TMC) for developing a bioelectrosynthesis process to convert food and paper wastes to methane. Electroanalytical techniques were used to analyze the electrocatalytic activity of the TMC biofilm formed onto the electrodes. The developed electromethanogenesis process enhanced the yield of methane by 54.7% than control experiments. Scanning electron micrographs of the TMC bioelectrodes showed that the electrosynthesis process accelerates biofilm formation onto the electrodes leading to enhanced direct electron transfer reactions at electrode–electrolyte interface. This study will help in developing a novel approach for valorization of food and paper waste to biofuels.

Electric Field (EF) in the Core of the Electrochemical (EC) Disinfection

Killing pathogens by different electrochemical (EC) disinfection means has been largely reported in the literature, even if the influence of process variables and reactor conception on kill performance has not been well comprehended. This review concentrates on EC microbial killing mechanisms especially the free radicals’ contribution and the effect of the electric field (EF), which are by their nature poisonous to microbes. Some mechanisms have been suggested to interpret the deadliness of EC application. Such pathways comprise: 1) oxidative stress and cell loss of life because of electrochemically produced oxidants, 2) irreversible permeabilization of cell membranes by the placed EF, 3) electrooxidation of vital cellular constituents during exposure to electric current or induced EFs, and 4) electrosorption of negatively charged E. coli cells to the anode surface followed by direct electron transfer reaction. Future investigations have to be more dedicated to the EF influence in the EC disinfection, as it is the main part of the involved mechanisms. Employing granular activated carbon post-treatment could greatly reduce the concentrations and poisonous effects of disinfection by-products. Moreover, secure multi-barrier techniques, like distillation, plasma discharge, nanotechnologies, and membrane processes remain to be suggested, tested, and industrially encouraged. Despite their limitations, both adsorptive techniques and membrane processes persist to be an encouraging domain of research thanks to their relatively low costs and ease of applications.

Mechanistic Investigation of Haloacetic Acid Reduction Using Carbon-Ti4O7 Composite Reactive Electrochemical Membranes.

Carbon-Ti4O7 composite reactive electrochemical membranes (REMs) were studied for adsorption and electrochemical reduction of haloacetic acids (HAAs). Powder activated carbon (PAC) or multiwalled carbon nanotubes (MWCNTs) were used in these composites. Results from flow-through adsorption experiments with dibromoacetic acid (DBAA) as a model HAA were interpreted with a transport model. It was estimated that ∼46% of C in the MWCNT-REM and ∼10% of C in the PAC-REM participated in adsorption reactions. Electrochemical reduction of 1 mg L-1 DBAA in 10 mM KH2PO4/K2HPO4 at -1.5 V/SHE (hydraulic residence time, ∼11 s) resulted in 73, 94, and 96% DBAA reduction for Ti4O7, PAC-Ti4O7, and MWCNT-Ti4O7 REMs, respectively. The reactive-transport model yielded kobs values between 9.16 and 33.3 min-1, which were 2 to 4 orders of magnitude higher than previously reported. PAC-Ti4O7 REM was tested with tap water spiked with 0.11 mg L-1 of nine different HAAs in a similar reduction experiment. The results indicated that all HAAs were reduced to <20 μg L-1. Moreover, the total combined concentration of five regulated HAAs was lower than the regulatory limit (60 μg L-1). Density functional theory simulations suggest that a direct electron transfer reaction was the probable rate-determining step for HAA reduction.