Mediated Electron Transfer Processes Research Articles

Dual single atomic Fe-Ni sites in N‑doped nanoporous carbon for high-efficiency potassium periodate activation toward pollutant abatement

Diatomic catalysts (DACs) with atomically isolated metal pairs hold the potential for activating potassium periodate (PI) in sustainable pollution control, yet their synthesis poses a significant challenge. In this study, Fe/Ni species anchored to a nitrogen-doped carbon as diatomic catalysts (FeNi-NC DAC) were precisely synthesized by direct carbonization of metal–organic frameworks (MOFs) assembled by Fe/Ni-doped ZnO nanoparticles and used for the effective decomposition of organic pollutants through PI activation. As anticipated, FeNi-NC exhibited superior catalytic properties due to the abundance of adjacent bimetallic active sites (Fe/Ni-Nx), rich doped nitrogen, high specific surface area, and electron transport conductivity, surpassing single-atom Fe-NC and Ni-NC, as well as nonmetallic NC catalysts. Free radical quenching, electron paramagnetic resonance, and electrochemical experiments have shown that the FeNi-NC/PI system can oxidize organic compounds through non-free radical oxidation pathways, including singlet oxygen (1O2) oxidation and mediated electron transfer processes. Electron transfer mediated by FeNi-NC/PI* complexes is the primary mechanism for organic oxidation. Additionally, the FeNi-NC catalyst demonstrated remarkable stability in both inorganic-containing and real water samples, as well as in continuous-flow microreactors. This study introduces a novel approach for designing highly efficient DACs and offers fundamental insights into the mechanism of PI-activated oxidation of organic pollutants.

Nonlinear Reaction-Diffusion and Mediated Electron Transfer Process at Conducting Polymer Modified Ultramicroelectrodes

The primary goal of this article is to present novel analytical solutions for the coupled nonlinear equation found in the mediated electron transfer process at polymer-modified conducting ultramicroelectrodes. Taylor’s series method is utilized to obtain approximate analytical solutions for the reaction-diffusion equations, allowing for the determination of the substrate and mediator concentrations and the current response concerning the substrate concentration at the electrode’s surface. The impact of different factors on concentration and current is also explored. The derived analytical results are in strong agreement with numerical results and with other analytical outcomes from the literature.

Hierarchical modulation of extracellular electron transfer processes in microbial fuel cell anodes for enhanced power output through improved Geobacter adhesion

Although microbial fuel cell (MFC) technology is nearing practical realization, the challenge of attaining higher power output continues to impede its widespread implementation. In this study, we successfully developed free-standing three-dimensional high-performance anode materials for MFCs using a straightforward "one-step" process based on garlic. The resulting anode not only promotes the accumulation of biomass and the enrichment of exoelectrogen Geobacter but also facilitates interfacial extracellular electron transfer. This led to rapid start-up within just three days, a robust power density of 12.37 W/m3, and an impressive 24.04 % coulombic efficiency in mixed-culture MFC reactors. Our investigation into the underlying mechanisms of exocellular electron transfer revealed improvements in both direct electron transfer and mediated electron transfer processes. Notably, the fabrication of carbonized garlic MFC anodes proves to be technically competitive and economically relevant. It not only paves the way for the development of high-performance MFCs but also provides valuable insights for the rational design of materials related to microbial electrochemical technologies.

Mediated electron transfer process in α-MnO2 catalyzed Fenton-like reaction for oxytetracycline degradation

In Fenton-like oxidation, the catalyst directly influences the reaction mechanism for the degradation of pollutants from water. Here, a α-MnO2 catalyst (OAm-1) was synthesized via a self-assembly method with the assistance of a surfactant. OAm-1 possessed a large specific surface area of 221 m2/g, abundant mesoporous structures and a large proportion of Mn(III). Further characterization exhibited that OAm-1 had abundant oxygen vacancies and excellent reducibility and conductivity. The adsorption and catalytic ability of OAm-1 were studied in the degradation of oxytetracycline (OTC) via the activation of hydrogen peroxide (H2O2). Through the radical quenching experiments, electron resonance spectroscopy (EPR), X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FT-IR) analysis, Mn(III) of OAm-1 was proved to be the active sites for the chemisorption of OTC. Systematic electrochemical experiments and analysis have shown that a process of electron transfer mediated by OAm-1 occurred between the pollutant and H2O2 during a Fenton-like reaction. This work experimentally verifies the electron transfer process dominated nonradical mechanism over α-MnO2, which is helpful for understanding the catalytic mechanism of the Fenton-like oxidation.

Piezoelectrically Mediated Reactions: From Catalytic Reactions to Organic Transformations

Comprehensive SummaryRecently, piezocatalysis has attracted considerable attention as a new type of renewable mechanical energy conversion technology, which relies on the strain induced polarization of the piezoelectric material. This new technology has been extensively applied in the applications of water splitting, water remediation, gas purification and tumor therapy. Despite the rapid development in the piezocatalysis, the utilization of piezoelectric materials for synthetic purpose is still under exploration. Piezoelectric means to promote organic reactions expand the scope of piezoelectrically mediated reactions and show successes in both organic and polymer synthesis. Herein, we provide a comprehensive review on recent progress of piezoelectrically mediated reactions, catalytic mechanisms and applications in the last few years. The limitations and future directions of this area are also discussed. We believe this review will provide new insights into the underlying mechanism of piezoelectric mediated electron transfer process and guide the design of new chemistry.

Utilization of methylene blue-adsorbed halloysite after carbonization to activate peroxymonosulfate degrading phenol: Performance and mechanism

In this study, a new low-cost carbon-based material was prepared via the carbonization of methylene blue adsorbed halloysite (CMH) at different temperatures in a nitrogen atmosphere, which was named CMH-T (T-Temperature). The performance of CMH-T was explored and the effects of initial pH values, catalyst dosage, phenol (PE) concentrations, peroxymonosulfate (PMS) concentrations, and water background compounds on PE degradation were investigated systematically. The results indicated that CMH800 exhibited the best performance to activate PMS for degrading PE. Specifically, 92% PE was degraded within 30 min with a constant rate (kobs) of 0.1186 min−1 in the CMH800/PMS system. Furthermore, CMH800 was efficient over a wide pH range (pH 3–9) and showed a slight inhibition to inorganic anions. Quenching experiments, electron spin resonance (ESR) analysis, and electrochemical analysis confirmed that PE was degraded through non-radical pathways dominated by single oxygen (1O2) and mediated electron transfer processes in the CMH800/PMS system. In addition, the predicted toxicity of intermediates through ECOSAR software based on QSAR (Quantitative Structure - Activity Relationship) model indicated that most of the intermediates had a low risk to water environment. Therefore, the CMH800 has a good potential for wastewater treatment applications.

Response of electron transfer capacity of humic substances to soil microenvironment

The humic substances (HS) - mediated electron transfer process is of great significance to the reduction and degradation of pollutants and the improvement of soil quality. Different soil conditions lead to different characteristics of HS, resulting in differences in the electron transfer capacity (ETC) of HS. It is unclear how the environmental conditions in soil affect the ETC by affecting on HS. In this study, the response relationship of soil microenvironment, HS and ETC has been studied. The results show that the ETC follows the descending order of: Langshan > Nanchang > Anqing > Beijing > Guilin. There were significant differences in ETC in soil HS in different regions. There were significant differences in electron-donating capacity (EDC) in soil HS in different regions and depths. EDC in soil was higher than electron-accepting capacity (EAC), and on average, are 22.4 times higher than the EAC. The HS components of soils in different regions are different. The most significant differences were in tyrosine-like substances and soluble microbial by-products (SMPs). The five components of the soil HS from Langshan were the most different from those in other regions. There were differences in SMPs and humic-like substances in soils of different depths in Anqing and Guilin. ETC can be affected by the composition of HS components in different regions. The composition of HS at different soil depths in the same regions had little effect on ETC. SMPs can promote ETC and EDC, and tyrosine-like substance can promote EDC. Moisture content, pH and TOC are the main factors affecting the composition of HS components. This results can provide a research basis for the sustainable and safe utilization of agricultural soil.

Effects of foreign metal doping on the step-by-step oxidation process in M-OMS-2 catalyzed activation of PMS

Various metal cations M (M = Mg2+, Ca2+, Zn2+, Cu2+, Fe3+) were doped into the tunnel of manganese octahedral molecular sieve (OMS-2). Redox-inactive metal (Ca, Mg and Zn) doped OMS-2 exhibited better peroxymonosulfate (PMS) catalytic activity than redox metal-doped Cu-OMS-2 and Fe-OMS-2. Redox-inactive metals doping improves the conductivity and reducibility of the catalyst, while transition metal doping reduces the dispersion of manganese. More importantly, the degradation of ACE can be divided into two stages. In the first stage, ACE was oxidized dominantly through mediated electron transfer process. Subsequently, singlet oxygen (1O2) gradually dominated oxidative degradation in the second stage, which was derived from the reaction between superoxide radical (O2•-) and metastable manganese intermediates. The long half-life of O2•- on the surface of OMS-2 ensured the delay generation of 1O2. This study not only provides a new idea for improving the efficiency of heterogeneous catalysts activation of PMS, but also meaningful for the in-depth study of multiple reaction mechanisms in PMS activation processes.

Photoactive Manganese Ferrite-Modified Bacterial Anode to Simultaneously Boost Both Mediated and Direct Electron Transfer Processes in Microbial Fuel Cells

Photoactive Manganese Ferrite-Modified Bacterial Anode to Simultaneously Boost Both Mediated and Direct Electron Transfer Processes in Microbial Fuel Cells

Controlling surface nanoarchitectures of DNA modified electrodes for improved label-free electrochemical detection of p53 gene

Combined superb electron transfer ability of gold nanoparticles with target recycling amplification strategy for label-free electrochemical detection of p53 gene. • An efficient p53 gene biosensor was developed by controlling surface nanoarchitectures of DNA modified electrodes. • Nicking endonuclease combined with gold nanoparticles was employed for improved sensing behavior. • How the different status of DNA strands on electrode surfaces affect GNPs mediated ET process was studied. • The proposed biosensor showed high performance with a detection limit of 0.0835 fM and a linear calibration range of 0.1 fM ~ 1 fM. P53 gene plays a vital role in regulating cellular processes and its accurate quantification is of great significance for the early cancer screening. Herein, by controlling surface nanoarchitectures of DNA modified electrode, we designed a new biosensing interface for the detection of p53 gene. In this method, gold nanoparticles (GNPs) were used to mediate electron transfer (ET) across different DNA monolayers modified electrode surfaces, and NESA was incorporated into the bio-sensing system. The proposed simple and label-free biosensor exhibited high performance with a detection limit of 0.0835 fM and a linear calibration range of 0.1 fM ~ 1 fM for p53 DNA sensing. Moreover, the method shows good sequence selectivity and reproducibility, demonstrating this strategy has potential applications in clinical diagnosis and biomedical research.

Response of exoelectrogens centered consortium to nitrate on collaborative metabolism, microbial community, and spatial structure

Exoelectrogens are widespread and participate in building up interspecies electron-sharing network between anaerobic microbes. However, the exoelectrogens-centered electron-sharing networks might be affected by over-released nitrate, which competes with solid minerals or electrodes as the electron acceptor. The knowledge on the mechanism on the response of exoelectrogens-centered community to nitrate disturbance is still limited. This study applied the microbial electrochemical system as a platform and provided insights into the response of electroactive biofilm to nitrate under a constant potential of + 0.2 V. Under a fixed carbon–nitrogen ratio of 6, the biofilm partially processed dissimilatory nitrate reduction to ammonium (DNRA) transitorily and gradually loses electron-output capability. After sufficient succession, the biofilm achieved complete denitrification without ammonia accumulation and started to acquire electrons from the electrode. With nitrate disturbance, the exoelectrogens-centered biofilm dominated by Geobacter sp. preferred to cooperate with highly enriched hydrogenotrophic denitrifiers for mutualistic growth with hydrogen as the electron mediator. Different scan rates of CVs also suggested the mediated electron transfer process. The extracellular polymer substrate (EPS) serving as a network contributed to aggregates formation. The enhanced humic acid and protein secretion in the EPS of nitrate-affected biofilm suggested frequent interactions between cells. Therefore, a mutualistic interaction was established between exoelectrogens and denitrifiers under nitrate stress.

Artificial, Photoinduced Activation of Nitrogenase Using Directed and Mediated Electron Transfer Processes

Nitrogenase, a bacteria-based enzyme, is the sole enzyme that is able to generate ammonia by atmospheric nitrogen fixation. Thus, improved understanding of its utilization and developing methods to artificially activate it may contribute to basic research, as well as to the design of future artificial systems. Here, we present methods to artificially activate nitrogenase using photoinduced reactions. Two nitrogenase variants originating from Azotobacter vinelandii were examined using photoactivated CdS nanoparticles (NPs) capped with thioglycolic acid (TGA) or 2-mercaptoethanol (ME) ligands. The effect of methyl viologen (MV) as a redox mediator of hydrogen and ammonia generation was tested and analyzed. We further determined the NPs conductive band edges and their effect on the nitrogenase photoactivation. The nano-biohybrid systems comprising CdS NPs and nitrogenase were further imaged by transmission electron microscopy, visualizing their formation for the first time. Our results show that the ME-capped CdS NPs–nitrogenase enzyme biohybrid system with added MV as a redox mediator leads to a five-fold increase in the production of ammonia compared with the non-mediated biohybrid system; nevertheless, it stills lag behind the natural process rate. On the contrary, a maximal hydrogen generation amount was achieved by the αL158C MoFe-P and the ME-capped CdS NPs.

Active N dopant states of electrodes regulate extracellular electron transfer of Shewanella oneidensis MR-1 for bioelectricity generation: Experimental and theoretical investigations

Anodic N doping is an effective way to improve power generation of bioelectrochemical systems (BESs), but the role of various active N dopant states of the anode on BES performance is still unclear. Herein, the effect of anodic active N dopant states on bioelectricity generation of Shewanella oneidensis MR-1 inoculated BESs particularly including microbial extracellular electron transfer (EET) was explored using experiments and theoretical simulations. It was found a positive linear correlation between the peak current density of BESs and pyrrolic N content of the anode, which would mainly ascribe to the enhancement of both direct electron transfer (DET) and mediated electron transfer (MET) of S. oneidensis MR-1. Morever, the molecule dynamic simulation revealed that such EET improvements of S. oneidensis MR-1 could be due to more remarkable reduction in the thermodynamic and kinetic resistances of the DET and MET processes with anodic doping of pyrrolic N compared to pyridinic N and graphitic N. This work provides a valuable guideline to design of high-performance anodes for potential BES applications.

Electrochemical Charge Transfer Through the Supramolecular Discogen‐DNA Hybrid Multi‐layered Assembly

AbstractIn the present work, charge transfer phenomenon through the films of an ionic discotic liquid crystal (discogen) that is pyridinium tethered with hexaalkoxytriphenylene (PyTp) and its complex with DNA (PyTp‐DNA) was studied by using electrochemical methods. The PyTp and PyTp‐DNA hybrid films were first formed at the air‐water interface and then transferred onto the gold substrates by Langmuir‐Blodgett (LB) technique. Electrochemical measurements carried out on these films in three different redox systems, namely, ferrocene, hexaammineruthenium (III), and ferrocyanide, revealed that the ferrocene and the hexaammineruthenium (III) systems allow the electron transfer reaction between redox probes and metal, whereas the ferrocyanide system completely blocks it. The electrochemical response of the films, in the former two systems, has been attributed to the bridge mediated electron transfer process, whereas, in the ferrocyanide system, the impermeability of redox ions through these LB films is responsible for the complete blocking of electron transfer. Based on the observed results, this work highlights the possibility of novel charge transfer properties of discogen‐DNA type hybrid films for applications in molecular electronics.

How the Intricate Interactions between Carbon Nanotubes and Two Bilirubin Oxidases Control Direct and Mediated O2 Reduction.

Due to the lack of a valid approach in the design of electrochemical interfaces modified with enzymes for efficient catalysis, many oxidoreductases are still not addressed by electrochemistry. We report in this work an in-depth study of the interactions between two different bilirubin oxidases, (from the fungus Myrothecium verrucaria and from the bacterium Bacillus pumilus), catalysts of oxygen reduction, and carbon nanotubes bearing various surface charges (pristine, carboxylic-, and pyrene-methylamine-functionalized). The surface charges and dipole moment of the enzymes as well as the surface state of the nanomaterials are characterized as a function of pH. An original electrochemical approach allows determination of the best interface for direct or mediated electron transfer processes as a function of enzyme, nanomaterial type, and adsorption conditions. We correlate these experimental results to theoric voltammetric curves. Such an integrative study suggests strategies for designing efficient bioelectrochemical interfaces toward the elaboration of biodevices such as enzymatic fuel cells for sustainable electricity production.

Nickel hydroxide nanopetals: One-pot green synthesis, characterization and application for the electrocatalytic oxidation and sensitive detection of montelukast

Nickel hydroxide nanopetals were synthesized by a simple hydrothermal method in one step in the presence of arginine as shape directing and pH adjusting agent. The nanopetals were then employed as the modifier of a carbon paste electrode. The kinetics of the charge transfer across the modified electrode/solution interface was studied and the modified electrode was employed to fabricate an amperometric sensor of montelukast. The mechanism and kinetics of the electrocatalytic oxidation of montelukast on the modified electrode surface, as a mediated electron transfer process by the high valence nickel species, were studied by cyclic voltammetry and chronoamperometry. An amperometric method was developed for determination of montelukast with a sensitivity of 36.54mAmol−1Lcm−2 and a limit of detection of 8.9μmolL−1. The method was used for the direct assay of montelukast in human serum samples and montelukast tablets. The sensor had the advantages of high electrocatalytic activity and sensitivity, and long-term stability toward montelukast.

A friendly detergent for H2 oxidation by Aquifex aeolicus membrane-bound hydrogenase immobilized on graphite and Self-Assembled-Monolayer-modified gold electrodes

Immobilization of membrane bound enzymes onto electrodes is of great interest for studying physiological electron transfer processes and for biotechnological devices. Hydrogenases are the key enzymes for hydrogen metabolism in many microorganisms. Due to the high efficiency and specificity they develop for H2 oxidation, research in the last 5 years has aimed towards their use as biocatalysts for H2/O2 biofuel cells to replace platinum-based bioanodes. We demonstrate in this work that the O2-, CO- and T°-resistant membrane-bound [NiFe] hydrogenase purified from the hyperthermophilic bacterium Aquifex aeolicus can be efficiently immobilized onto electrodes. Both pyrolytic graphite (PG) and hydrophobic Self-Assembled-Monolayers (SAMs) on gold electrodes are used for hydrogenase immobilization. According to the chemistry and structure of the electrochemical interface, a different process for H2 oxidation is observed, from direct to mediated electron transfer process. To gain new insight in the catalytic process, a quantification of the remaining detergent surrounding the membrane protein is performed. Adsorption isotherms of hydrogenase are determined as a function of the electrode material and the amount of detergent. Competitive adsorption of free detergent and hydrogenase is demonstrated coupling electrochemistry and Polarization Modulation Infrared Reflexion Adsorption Spectroscopy (PM-IRRAS). The efficiency of the enzymatic process is then analyzed according to the tiny interaction between the lipophilic redox mediator (methylene blue), the detergent, the enzyme and the electrochemical interface.

Orientational ordering of the second layer of C60 molecules on Au(111)

We have studied the orientational ordering of the second layer of C(60) molecules on Au(111) using scanning tunnelling microscopy (STM) at 77 K. The orientation of individual molecules within the second layer follows a regular pattern, giving rise to a 2 × 2 superlattice. The long-range order of the 2 × 2 lattice depends on the structure of the first molecular layer with the best ordering found inside the R14° domain. The second layer formed on top of the contrast-disordered R30° domain consists of patches of bright and dim molecules. The contrast between bright and dim patches shows a clear dependence on the sample bias. This bias-dependent contrast is explained by considering the contributions to tunnel current from HOMO and LUMO mediated electron transfer processes. Scanning tunnelling spectroscopic measurement reveals the narrowing of the HOMO-LUMO gap for the layer of molecules in direct contact with the Au(111) substrate.

Electrochemistry, AFM, and PM‐IRRA Spectroscopy of Immobilized Hydrogenase: Role of a Hydrophobic Helix in Enzyme Orientation for Efficient H2 Oxidation

A transmembrane helix surrounded by detergent molecules close to the surface electron relay is shown, by electrochemical, AFM, and PM-IRRAS studies, to control the orientation of a membrane-bound [NiFe] hydrogenase on electrochemical interfaces. Hence, H2 oxidation proceeds as a mixture of direct (DET) and mediated electron transfer (MET) on hydrophilic interfaces, but by a MET process on hydrophobic interfaces (see picture).

How far can hydroxyl radicals travel? An electrochemical study based on a DNA mediated electron transfer process

Using photocatalytic reactive nanoparticles and DNA composite modified gold electrodes, exploiting the sensitivity of DNA-mediated electron transfer to base pair stacking, we examined the effects of DNA oxidation damage by photocatalytically generated hydroxyl radicals (˙OH) on charge transfer efficiency and proposed an electrochemical technique to read the effective diffusing distance of ˙OH.