Electron Transfer Mediator Research Articles

Carbonised Typha tassel-modified enzymatic electrodes for ferrocene-mediated glucose biosensor and glucose/air biofuel cell applications

This study demonstrates the application of carbonised Typha tassel (CTT) in ferrocene-mediated enzymatic glucose biosensing and enzymatic biofuel cell (EnBFC) applications. Typha tassel was carbonised under an inert atmosphere to obtain conductive CTT which was then mixed with an effective electron transfer mediator, ferrocene (Fc) obtaining a redox-active electrode material. The successful immobilisation of the glucose oxidase (GOx) enzyme was performed on a CTT-Fc modified screen-printed electrode followed by a chitosan protective coating. The resulting enzymatic electrode was electrochemically characterised as a glucose biosensor with a working range of 0–10 mM and LOD and LOQ values of 0.19 mM and 0.56 mM, respectively. The developed glucose biosensor also showed good reproducibility and reusability with RSD% values of 6.68 % and 8.75 %, respectively. Furthermore, a real sample demonstration was performed using commercial jam samples with good recovery values. Finally, an EnBFC demonstration was performed using the enzymatic biosensor as an anode and a non-enzymatic cathode prepared using platinum black on gas diffusion carbon electrodes reaching a maximum power density of 3.6 µW cm−2. This study shows the promise of CTT as an alternative to conventional materials in enzymatic biosensor and bioelectronic applications as a suitable, cheap, and sustainable material.

Peroxidase-like Nanoparticles of Noble Metals Stimulate Increasing Sensitivity of Flavocytochrome b2-Based L-Lactate Biosensors.

We report the development of amperometric biosensors (ABSs) employing flavocytochrome b2 (Fcb2) coupled with nanoparticles (NPs) of noble metals on graphite electrode (GE) surfaces. Each NPs/GE configuration was evaluated for its ability to decompose hydrogen peroxide (H2O2), mimicking peroxidase (PO) activity. The most effective nanoPO (nPO) was selected for developing ABSs targeting L-lactate. Consequently, several Fcb2/nPO-based ABSs with enhanced sensitivity to L-lactate were developed, demonstrating mediated ET between Fcb2 and the GE surface. The positive effect of noble metal NPs on Fcb2-based sensor sensitivity may be explained by the synergy between their dual roles as both PO mimetics and electron transfer mediators. Furthermore, our findings provide preliminary data that may prompt a re-evaluation of the mechanism of L-lactate oxidation in Fcb2-mediated catalysis. Previously, it was believed that L-lactate oxidation via Fcb2 catalysis did not produce H2O2, unlike catalysis via L-lactate oxidase. Our initial research revealed that the inclusion of nPO in Fcb2-based ABSs significantly increased their sensitivity. Employing other PO mimetics in ABSs for L-lactate yielded similar results, reinforcing our hypothesis that trace amounts of H2O2 may be generated as a transient intermediate in this reaction. The presence of nPO enhances the L-lactate oxidation rate through H2O2 utilization, leading to signal amplification and heightened bioelectrode sensitivity. The proposed ABSs have been successfully tested on blood serum and fermented food samples, showing their promise for L-lactate monitoring in medicine and the food industry.

Electron Transfer Mediator Modulates Type II Porphyrin-Based Metal-Organic Framework Photosensitizers for Type I Photodynamic Therapy.

Photodynamic therapy (PDT), a minimally invasive and effective local treatment, heavily depends on photosensitizer (PS) performance and oxygen availability. Despite the use of PS-based metal-organic frameworks (MOFs) to address the solubility and aggregation issues of PSs, the inherent hypoxic intolerance of mainstream Type II PDT remains challenging. Herein, we report an electron transfer strategy for the fabrication of hypoxia-tolerant Type I MOFs by encapsulating thymoquinone (TQ) into existing Type II MOFs. With TQ serving as an effective electron transfer mediator, it facilitates the electron transfer process from the MOF ligand PS to oxygen, establishing the Type I pathway and attenuating the original Type II pathway. Four representative porphyrin-based MOFs are synthesized to demonstrate the proposed strategy. Our findings reveal that TQ@MOF-1 nanoparticles (NPs) exhibit enhanced anticancer activity under hypoxic conditions and superior in vivo antitumor efficacy compared to parent MOF-1 NPs. This work offers an effective and universal strategy to modulate ROS generation in PS-based MOFs, endowing hypoxic tolerance with improved PDT performance against solid tumors.

Electron Transfer Mediator Modulates Type II Porphyrin‐Based Metal‐Organic Framework Photosensitizers for Type I Photodynamic Therapy

Photodynamic therapy (PDT), a minimally invasive and effective local treatment, heavily depends on photosensitizer (PS) performance and oxygen availability. Despite the use of PS‐based metal‐organic frameworks (MOFs) to address the solubility and aggregation issues of PSs, the inherent hypoxic intolerance of mainstream Type II PDT remains challenging. Herein, we report an electron transfer strategy for the fabrication of hypoxia‐tolerant Type I MOFs by encapsulating thymoquinone (TQ) into existing Type II MOFs. With TQ serving as an effective electron transfer mediator, it facilitates the electron transfer process from the MOF ligand PS to oxygen, establishing the Type I pathway and attenuating the original Type II pathway. Four representative porphyrin‐based MOFs are synthesized to demonstrate the proposed strategy. Our findings reveal that TQ@MOF‐1 nanoparticles (NPs) exhibit enhanced anticancer activity under hypoxic conditions and superior in vivo antitumor efficacy compared to parent MOF‐1 NPs. This work offers an effective and universal strategy to modulate ROS generation in PS‐based MOFs, endowing hypoxic tolerance with improved PDT performance against solid tumors.

Microbial Reduction of Solid-Phase Humin by Shewanella oneidensis MR-1 and its Potential Effect on Contaminant Transformation

Insoluble humic substances-humin (HM) are ubiquitous in the environment and often coexist with iron reducers. Previous research has focused on the electron-donating process from HM to iron reducers; however, the reduction process of HM by iron reducers and its impact on the fate of typical contaminants are still poorly understood. In this study, Shewanella oneidensis MR-1 was selected as a model iron reducer, and its ability to reduce HM and the potential environmental impact of bioreduced HM were investigated. The results showed that S. oneidensis MR-1 reduced HMs extracted from different sources to different extents. This process is highly dependent on lactate concentration, salinity, pH, and dissolved oxygen concentration. Alginate bead experiments indicated that the indirect pathway accounted for 40% of the total electrons transferred from S. oneidensis MR-1 to HM. Electrochemical and spectrochemical analyses further revealed that in addition to flavin, c-type cytochrome may mediate electron transfer. The quinone and iron components may be the main functional groups of HM that accept electrons. Finally, we showed that after being reduced by S. oneidensis MR-1, HM can act as an electron donor for microbial nitrate reduction and the chemical reduction of Cr(VI), with electron-mediation efficiencies of 93% and 56%, respectively.

Efficient activation of peracetic acid by defect-engineered MoO2−x: Oxygen vacancies and surface Mo(Ⅴ)-mediated electron transfer processes

The role of defect regulation of transition metal catalysts in peracetic acid (PAA) activation is equivocal. To reveal the corresponding mechanism, this work provides a high-efficiency and eco-friendly catalyst (MoO2−x) for PAA activation by introducing various degrees of oxygen vacancies on the MoO2 surface. Interestingly, 95.83 % of tetracycline (TC) is rapidly degraded by MoO2−x with rich oxygen vacancies within 20 min via PAA activation, which is superior over that of MoO2−x with poor oxygen vacancies and other typical oxidants (H2O2, SO32−, S2O82−, HSO5−, IO4−). In addition, the defect-regulated MoO2−x exhibits good de-biotoxicity towards TC. Moreover, MoO2−x shows satisfactory purification of various contaminants and actual pharma wastewater. Active species identification suggests that the electron transfer process triggered by the active complex (MoO2−x −PAA*) of PAA bonded on the MoO2−x surface plays the dominant role in TC degradation, while •OH plays a minor role. Mechanism analysis reveals that oxygen vacancies play an indispensable role in accelerating the adsorption and complexation of PAA as well as improving electrical conductivity. Active site analysis demonstrates that Mo(Ⅴ) on the MoO2−x surface acts as an electron shuttle and is the main PAA activation site. This work provides a new approach into the application of MoO2 in hospital wastewater purification via defect engineering.

Modifying functional groups of straw-based hydrogel provide soil N2O mitigation potential by complete denitrification

Farmed soil is considered to contribute more than 60% anthropogenic N2O emission which plays critical role in global warming potential. Straw-based hydrogels with abundant functional groups are commonly used in environmental and agronomic applications primarily as adsorbents. Those functional groups could mediate electron transfer in the process of adsorbates and might also regulate N2O emission. However, it was still unclear whether and how these functional groups affect the process. To address this knowledge gap, we employed spectral analysis and a robotized incubation system to determine mechanisms of different functional groups in influencing soil N2O. The results indicated that the straw-based hydrogel was capable of significantly reducing the emission of N2O in denitrification, and the electrochemical properties of the hydrogel had promoting effect of the microbial genetic potential for N2O reduction. Specifically, carboxymethyl (R-COO) and primary amine groups (R-NH2) promoted complete denitrification through electron supply. Furthermore, R-NH2 had a significant negative correlation with N2O emissions. To further verify the role of specific structures and functional groups in denitrification, we conducted an experiment using pure lignin as a template. This experiment resulted in an increase in R-NH2 content to 13.2% and a decrease in N2O emissions by 49.1% compared with straw hydrogel. These results prove the feasibility of straw-based hydrogel as a redox system to accelerate complete denitrification, and the electron-donating functional groups were significantly related to the reduction rate of N2O. Finally, based on these mechanisms, functional group targeted grafting technology was proposed to improve its ability to mitigate N2O emission reduction.

Efficient degradation of Enrofloxacin with novel magnetic MnFe2O4/NiS2 composite as an activator of peroxymonosulfate

The development of highly active and recoverable heterogeneous catalysts for peroxymonosulfate (PMS) activation to remove the persistent presence of antibiotics in aquatic environments, such as Enrofloxacin (ENR), remains a significant challenge. Here, we introduce a pioneering magnetic nanocomposite catalyst, MnFe2O4-NiS2, synthesized via a two-step hydrothermal process, which activates PMS to efficiently degrade ENR. The optimized 0.25MnFe2O4-NiS2/PMS system reached an ENR removal efficiency of 89.9 % within 90 min, outperforming both NiS2/PMS and MnFe2O4/PMS by 5.6 and 2.5 times, respectively. Quenching experiments and electron spin response analysis confirmed SO4•- and •O2– as the primary reactive oxygen species. The enhanced mediated electron transfer capability of the 0.25MnFe2O4-NiS2 nanocomposite improved the redox cycling of Ni (Ⅱ), Mn (Ⅱ) and Fe (Ⅲ) on its surface, as verified by Density Functional Theory calculations. Furthermore, the activation of surface PMS complexes (PMS*) played a crucial role in ENR degradation. The proposed degradation pathways of ENR were confirmed, and toxicity analysis indicated a decrease in intermediate toxicity with the 0.25MnFe2O4-NiS2/PMS system. This study presents an innovative magnetically recoverable, multifunctional catalyst with easy reusability for potential applications in the degradation of organic pollutants.

Enhancing sulfamerazine degradation via peroxymonosulfate with Fe-doped Mo2C materials: Catalytic performance and mechanistic insights

Sulfonamide antibiotics are a common group of drugs that have the potential to induce the generation of resistance genes even at low concentrations. Herein, a novel Fe3Mo3C/Mo2C/Mo composite (Fe-Mo2C-1.0) was prepared by modifying the synthesis process of Fe-doped Mo2C and used to activate peroxymonosulfate (PMS) to degrade sulfamerazine (SMR). The optimal performance catalyst was obtained at Fe/Mo = 1.0 and a calcination temperature of 900 ℃. Fe-Mo2C-1.0 achieved 98.8 % SMR removal in 20 min, which was 4.5 and 44.3 times higher than that of Fe-Mo2C-0.5/PMS and Mo2C/PMS systems, respectively. In Fe-Mo2C-1.0, multiple low-valent forms of the element Mo, including Mo, Mo(II) and Mo(IV), which are highly reductive, participated in and contributed to the regeneration of Fe(II). The proportion of Fe(II) on the surface of Fe-Mo2C-1.0 before and after the reaction was maintained at a stable level. In addition, the high Fe content and sp2 hybridized carbon in Fe-Mo2C-1.0 promoted the role of mediated electron transfer during catalysis process. Electrochemical characterization indicated that Fe-Mo2C-1.0 had better redox properties, smaller electron transfer resistance and a faster corrosion rate than Fe-Mo2C-0.5 and Mo2C. Other SMR oxidation mechanisms included SO4∙-, O2∙- and 1O2, with 1O2 contributing the most. Finally, three possible degradation pathways of SMR were proposed. This work provided thoughts on the synthesis of Fe/Mo bimetallic carbide catalysts as well as reference for the removal of SMR by PMS activation.

Reductive dehalogenase of Dehalococcoides mccartyi strain CBDB1 reduces cobalt- containing metal complexes enabling anodic respiration.

Microorganisms capable of direct or mediated extracellular electron transfer (EET) have garnered significant attention for their various biotechnological applications, such as bioremediation, metal recovery, wastewater treatment, energy generation in microbial fuel cells, and microbial or enzymatic electrosynthesis. One microorganism of particular interest is the organohalide-respiring bacterium Dehalococcoides mccartyi strain CBDB1, known for its ability to reductively dehalogenate toxic and persistent halogenated organic compounds through organohalide respiration (OHR), using halogenated organics as terminal electron acceptors. A membrane-bound OHR protein complex couples electron transfer to proton translocation across the membrane, generating a proton motive force, which enables metabolism and proliferation. In this study we show that the halogenated compounds can be replaced with redox mediators that can putatively shuttle electrons between the OHR complex and the anode, coupling D. mccartyi cells to an electrode via mediated EET. We identified cobalt-containing metal complexes, referred to as cobalt chelates, as promising mediators using a photometric high throughput methyl viologen-based enzyme activity assay. Through various biochemical approaches, we show that cobalt chelates are specifically reduced by CBDB1 cells, putatively by the reductive dehalogenase subunit (RdhA) of the OHR complex. Using cyclic voltammetry, we also demonstrate that cobalt chelates exchange electrons with a gold electrode, making them promising candidates for bioelectrochemical cultivation. Furthermore, using the AlphaFold 2-calculated RdhA structure and molecular docking, we found that one of the identified cobalt chelates exhibits favorable binding to RdhA, with a binding energy of approximately -28 kJ mol-1. Taken together, our results indicate that bioelectrochemical cultivation of D. mccartyi with cobalt chelates as anode mediators, instead of toxic halogenated compounds, is feasible, which opens new perspectives for bioremediation and other biotechnological applications of strain CBDB1.

Sunlight-Driven Direct/Mediated Electron Transfer for Cr(VI) Reductive Sequestration on Dissolved Black Carbon-Ferrihydrite Coprecipitates.

Surface runoff horizontally distributed chromium (Cr) pollution into various surface environments. Sunlight is a vital factor for the Cr cycle in the surface environment, which may be affected by photoactive substances such as ferrihydrite (Fh) and dissolved black carbon (DBC). Herein, sunlight-driven transformation dynamics of Cr species on DBC-Fh coprecipitates were studied. Under sunlight, the removal of aqueous Cr(VI) by DBC-Fh coprecipitates occurred through sunlight-driven reductive sequestration including adsorption, followed by surface reduction (pathway 1) and aqueous reduction, followed by precipitation (pathway 2). Additionally, coprecipitates with a higher DBC content exhibited a more effective reduction of both adsorbed (kapp,S_red) and aqueous Cr(VI) (kapp,A_red). Photoelectrons facilitated Cr(VI) reduction through direct electron transfer; notably, electron donating DBC promoted the production of photoelectrons by consuming photogenerated holes. Photogenerated Fe(II) species (mineral-phase and aqueous Fe(II)) mediated electron transfer for Cr(VI) reduction, which was reinforced via a ligand-to-metal charge transfer (LMCT) process between DBC-organic ligands and mineral Fe(III). Furthermore, ·O2- also mediated Cr(VI) reduction, although this impact was limited. Overall, this study demonstrates that photoelectrons and photogenerated electron mediators play a crucial role in Cr(VI) reductive sequestration on DBC-Fh coprecipitates, providing new insights into the geochemical cycle of Cr pollution in sunlight-influenced surface environments.

Bioreceptors’ immobilization by hydrogen bonding interactions and differential pulse voltammetry for completely label-free electrochemical biosensors

Label-free electrochemical biosensors show great potential for the development of point-of-care devices (POCDs) for environmental and clinical applications. These sensors operate with shorter analysis times and are more economic than the labelled ones. Here, four completely label-free biosensors without electron transfer mediators were developed for hepatitis B virus (HBV) detection. The approach consisted in (i) the modification of gold surfaces with cysteamine (CT) or cysteine (CS) linkers, (ii) the subsequent antibody (Ab) immobilization, either directly by hydrogen bonding (HB) interactions or by covalent bonds (CB) using additional reagents, and (iii) measuring the biosensor response by electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV). The electrode surfaces at each stage of the modification process were characterised by X-ray photo-electron spectroscopy (XPS) and atomic force microscopy (AFM). The combination of Ab immobilization by HB with the DPV analysis displayed improved repeatability, lower interference to serum matrix and similar limits of detection and quantification than the traditional biosensors that immobilize the Ab via CB and use EIS as readout technique. The Ab immobilization by HB is shown as a simple, efficient and low-cost alternative to CB ones, while DPV was faster and showed better performance than EIS. The CT-HB biosensor displayed the lowest limits of detection and quantification of 0.14 and 0.46 ng/mL, respectively, a 0.46–12.5 ng/mL linear analytical range, and 100% of recovery for 1/10 human serum media during HBV surface antigen detection by DPV. Even, it preserved the initial sensing capability after 7 days of its fabrication.Graphical abstract

Edge-Hosted Graphitic Nitrogen Sites Carbocatalysts Mediated Electron Transfer Process for Powerful Fenton-Like Reactions

Edge-Hosted Graphitic Nitrogen Sites Carbocatalysts Mediated Electron Transfer Process for Powerful Fenton-Like Reactions

Cysteine-Facilitated Cr(VI) reduction by Fe(II/III)-bearing phyllosilicates: Enhancement from In-Situ Fe(II) generation

Structural Fe in phyllosilicates represents a crucial and potentially renewable reservoir of electron equivalents for contaminants reduction in aquatic and soil systems. However, it remains unclear how in-situ modification of Fe redox states within Fe-bearing phyllosilicates, induced by electron shuttles such as naturally occurring organics, influences the fate of contaminants. Herein, this study investigated the processes and mechanism of Cr(VI) reduction on two typical Fe(II/III)-bearing phyllosilicates, biotite and chlorite, in the presence of cysteine (Cys) at circumneutral pH. The experimental results demonstrated that Cys markedly enhanced the rate and extent of Cr(VI) reduction by biotite/chlorite, likely because of the formation of Cr(V)-organic complexes and consequent electron transfer from Cys to Cr(V). The concomitant production of non-structural Fe(II) (including aqueous Fe(II), surface bound Fe(II), and Cys-Fe(II) complex) cascaded transferring electrons from Cys to surface Fe(III), which further contributed to Cr(VI) reduction. Notably, structural Fe(II) in phyllosilicates also facilitated Cr(VI) reduction by mediating electron transfer from Cys to structural Fe(III) and then to edge-sorbed Cr(VI). 57Fe Mössbauer analysis revealed that cis-coordinated Fe(II) in biotite and chlorite exhibits higher reductivity compared to trans-coordinated Fe(II). The Cr end-products were insoluble Cr(III)-organic complex and sub-nanometer Cr2O3/Cr(OH)3, associated with residual minerals as micro-aggregates. These findings highlight the significance of in-situ produced Fe(II) from Fe(II/III)-bearing phyllosilicates in the cycling of redox-sensitive contaminants in the environment.

Periodate activation with polyaniline-derived carbon for bisphenol A degradation: Insight into the roles of nitrogen dopants and non-radical species formation

Periodate-based advanced oxidation processes (PI-AOPs) activated by carbon catalysts have shown promising application prospects in the removal of emerging contaminants. Herein, a series of N-doped carbon catalysts (NC) were prepared by in-situ pyrolysis of N-containing polymers (polyaniline) to unveil the potential mechanism of N dopants on PI activation. The optimized sample NC700 showed a satisfying degradation performance, achieving 100 % removal of bisphenol A (BPA) at a concentration of 10 mg/L within 90 min in the presence of 0.1 mM PI. The impacts of various N types on PI activation were systematically investigated by dynamic fitting and density functional theory computations. These analyses highlighted the crucial role of graphitic N configuration on carbon surface, which exhibited the highest adsorption energy and a positive correlation with the normalized degradation efficiency. The chemical quenching experiments and electrochemical experiments confirmed that the BPA oxidation mechanism was primarily mediated electron transfer by [NC-PI]* complex, with singlet oxygen (1O2) /superoxide radicals (O2•–) playing a supplementary role. In situ ATR-SERAS measurement strengthened the understanding of PI activation by carbon catalyst based on electron transfer pathway. Owing to the non-radical oxidation mechanism, the NC/PI system had a broad pH adaptability and great anti-interference ability against typical wastewater components. This study provides mechanistic insights into the carbon-driven PI activation process for wastewater treatment, advancing the practical application of PI-AOPs.

Determination of surface acidity of mixed oxide of silicon and titanium by calorimetric titration

Silica-titania mixed oxide with catalytic and adsorption properties has been of great academic and industrial interest. Metal oxides supported on silica have been used as a matrix for immobilizing electron transfer mediators, generating materials with diverse properties. The characterization of the surface acidity of these materials is essential and has been carried out using various techniques, including IR spectroscopy and calorimetry. However, no single technique completely analyses the present acidic sites. This study used calorimetric titration to investigate a mixed oxide containing titanium and silica, prepared by the sol-gel method, and its interaction with pyridine. The results showed that thermal treatment increased the enthalpy values (ΔH), indicating water removal from the matrix surface. The presence of pyridine resulted in a decrease in ΔH values, suggesting a preferential occupation of the stronger acidic sites. After thermal treatments between 473 and 573 K, the solids exhibited similar ΔH values, indicating a homogenization of the surface acidic sites. Calorimetric analysis revealed that the acidic sites were occupied in descending order of strength, with the strongest sites being filled initially. The increase in temperature did not result in new acidic sites but rather in greater occupation of the existing ones. Correlation between calorimetric and infrared data is suggested as the next investigation step. Thus, the results of this study contribute to a deeper understanding of the physicochemical properties, especially regarding their surface acidity, with the potential for more effective and controlled practical applications of this silica-titania mixed oxide in catalysis and adsorption.

Preparation of La-doped NiAl-LDH with boosted electron transfer for the enhanced photocatalytic activity of tetracycline: Performance evaluation, degradation pathway, and mechanism insight

Developing a photocatalysis-based system is an effective strategy for removing antibiotics. Herein, La-doped NiAl-layered double hydroxides (LaNiAl-LDH) photocatalyst was synthesized using a chemical co-precipitation-hydrothermal method. The prepared samples were characterized by various advanced analyses and investigated for the photocatalytic degradation of tetracycline (TC). The crystalline phase and functional groups of the synthesized samples were successfully confirmed by XRD and FTIR analyses. By doping La into NiAl-LDH structure, the band gap was reduced from 3.01 eV to 2.57 eV, indicating higher photocatalytic activity of 1% LaNiAl-LDH. The surface morphology of the synthesized samples shows the formation of nanosheets in the structure of LDH. Under the optimum status ([TC]0 = 10 mg/L, [1% LaNiAl-LDH] = 0.2 g/L, and pH = 6), the photocatalytic activity of 1% LaNiAl-LDH (84.85%) was higher than NiAl-LDH (71.52%) within 90 min reaction. This difference can be attributed to the presence of La sites in 1% LaNiAl-LDH which act as electron-transfer mediators, leading to a significant improvement in the separation of photogenerated charge carriers. The effect of the addition of various scavengers was evaluated. Moreover, using the o-phenylenediamine (OPD), and photoluminescence (PL) analysis, the formation of •OH radicals was supported. The higher charge-transfer efficiency of 1% LaNiAl-LDH was confirmed by photoelectrochemical analysis. Furthermore, the reusability, stability, and degradation pathway of the as-synthesized nanocomposite were systematically examined. This work presents guidance for applying doped LDH-based materials in photocatalysis and promising applications in wastewater remediation.

Dependence of Protein Immobilization and Photocurrent Generation in PSI-FTO Electrodes on the Electrodeposition Parameters.

This study investigates the immobilization of cyanobacterial photosystem I (PSI) from Synechocystis sp. PCC 6803 onto fluorine-doped tin oxide (FTO) conducting glass plates to create photoelectrodes for biohybrid solar cells. The fabrication of these PSI-FTO photoelectrodes is based on two immobilization processes: rapid electrodeposition driven by an external electric field and slower adsorption during solvent evaporation, both influenced by gravitational sedimentation. Deposition and performance of photoelectrodes was investigated by UV-Vis absorption spectroscopy and photocurrent measurements. We investigated the efficiency of PSI immobilization under varying conditions, including solution pH, applied electric field intensity and duration, and electrode polarization, with the goals to control (1) the direction of migration and (2) the orientation of the PSI particles on the substrate surface. Variation in the pH value of the PSI solution alters the surface charge distribution, affecting the net charge and the electric dipole moment of these proteins. Results showed PSI migration to the positively charged electrode at pH 6, 7, and 8, and to the negatively charged electrode at pH 4.4 and 5, suggesting an isoelectric point of PSI between 5 and 6. At acidic pH, the electrophoretic migration was largely hindered by protein aggregation. Notably, photocurrent generation was consistently cathodic and correlated with PSI layer thickness, and no conclusions can be drawn on the orientation of the immobilized proteins. Overall, these findings suggest mediated electron transfer from FTO to PSI by the used electrolyte containing 10 mM sodium ascorbate and 200 μM dichlorophenolindophenol.

Activation of peroxydisulfate by endogenous nitrogen-doped carbon for efficient degradation of sulfamethoxazole

An endogenous nitrogen-doped carbon (ENC) was synthesized to activate peroxydisulfate (PDS) for Sulfamethoxazole (SMX) removal using graphitic carbon nitride as the raw material. The characterization of the surface properties of ENC demonstrated that ENC is rich in functional groups and mesoporous structure, coupled with a very large specific surface area (1034.6 m²·g−1). The ENC/PDS system demonstrated up to 98.5% degradation capability of SMX within 30 min and maintained over 80% in a complex aqueous environment. Further investigation of the intrinsic mechanism of SMX decomposition by ENC/PDS confirmed the dominant roles of surface-bound radicals and mediated electron transfer, with surface-bound SO₄·⁻ and a transient active complex (PDS/ENC*) identified as the key reactive species. This study significantly broadens the scope of nitrogen-doped carbon materials in environmental treatment by conducting an extensive investigation of the ENC/PDS/SMX system.

Riboflavin derivatives as a novel electron transfer mediator for enhancing Cr(VI) removal by Shewanella oneidensis MR-1

Bioremediation has garnered considerable interest due to its advantages of economy and no secondary pollution. However, the direct electron transfer rate between microorganisms and Cr(VI) is low. The bioreduction of Cr(VI) by Shewanella oneidensis MR-1 (S. oneidensis) in the presence of formylmethylflavin (FMF) was conducted to understand how FMF mediated the extracellular electron transfer process to improve Cr(VI) removal. In this study, FMF was firstly synthesized by modifing RF to increase its solubility and redox activity. The findings indicate that S. oneidensis/FMF exhibited better Cr(VI) removal performance compared to that of S. oneidensis. Under optimum conditions, 40 mg/L Cr(VI) could be completely removed by S. oneidensis/FMF within 120 h, while only 48.6% of Cr(VI) was removed by S. oneidensis, and the first order rate constant (k) for the Cr(VI) elimination by S. oneidensis/FMF (0.033 h−1) was about 4.1-fold greater than that of S. oneidensis (0.008 h−1). Moreover, the removal of Cr(VI) by S. oneidensis/FMF were dominated by reduction, and supplemented by adsorption and complexation. FMF enhance the extracellular electron transfer rate (EETR) was confirmed by electrochemical cyclic voltammetry (CV) and linear scanning voltammetry (LSV) experiments. This study emphasizes the potential important role of FMF in environmental bioremediation.