Electron Mediator Research Articles

Direct transformation of rice straw to electricity and hydrogen by a single yeast strain: Performance and mechanism

Lignocellulosic waste is one of the most abundant renewable energy sources. However, pretreatment or complex microbial consortia are usually required for the biological transformation into energy products. This study demonstrates the direct transformation of raw rice straw biomass into electricity and hydrogen without any pretreatment by employing a single yeast strain, Cystobasidium slooffiae JSUX1, in microbial fuel cells (MFCs). The yeast-MFCs exhibit a maximum power density of 28.56 ± 2.54 mW/m2 with simultaneous production of hydrogen gas (4.9 ± 0.52 L/m3) from raw straw. Further analysis reveals that enzymes secreted by the yeast strain degraded rice straw into sugars or organic acids, serving as fuel for electricity and hydrogen production. In addition, humic acid (HA) and Fe-HA derived from biomass consumption serve as electron mediators for extracellular electron transfer (EET) in MFCs. This study demonstrates the power of the yeast strain for renewable energy recovery from straw, diversifying the toolbox for the lignocellulose industry.

Comparison of Fenton-like catalytic activity of biochar by in-situ and ex-situ nitrogen doping: Role of carbon quantum dots

Nitrogen-doped biochar as Fenton-like catalysts has been widely used to remove emerging pollutants in wastewater. However, the effect of in-situ and ex-situ nitrogen doping on the Fenton-like catalytic activity of biochar is unclear. In this study, the nitrogen-doped biochar was prepared by in-situ (NBC) and ex-situ (BC–N) nitrogen doping, and the Fenton-like catalytic activity of NBC and BC-N was compared for activating hydrogen peroxide (H2O2), peroxydisulfate (PDS) and peroxymonosulfate (PMS). The results showed that NBC had higher Fenton-like catalytic activity than BC-N, because the formation of carbon quantum dots (CQDs) significantly increased the adsorption capacity to H2O2, PDS and PMS. NBC could activate H2O2, PDS and PMS for degradation of sulfamethoxazole (SMX), but showed different catalytic activity and degradation mechanism. In the systems of NBC/H2O2 and NBC/PDS, CQDs played a key role in the activation of H2O2 and PDS, and surface-bound reactive species were mainly responsible for SMX degradation. In the system of NBC/PMS, NBC acted as both electron mediator and activator, direct electron transfer between PMS and SMX and surface-bound reactive species contributed to SMX degradation. This study provides an insight into the catalytic activity of NBC for H2O2, PDS and PMS.

Hydrogen-powered enzymatic valorization using multi-enzyme co-immobilization reactor with polypeptide-based cofactor swing-arm

The chemical valorization of organic matter into high-energy products through reduction using oxidoreductase is a pivotal aspect from an energy perspective. Enzymatic valorization, utilizing the reduction potential of hydrogen contained in inexpensive resources such as coke oven gas (COG) and certain gasified plastics, enables environmentally friendly processes. Here, a strategy was proposed utilizing hydrogenase (H2ase), particularly soluble hydrogenase (SH), for selective utilization of H2 from mixtures without the separation processes. The co-immobilization of SH, elastin-like polypeptide (ELP)-based cofactor swing arm, and mannitol dehydrogenase (MDH) in a microreactor system were demonstrated for enzymatic valorization. The swing arm length and in-resin concentration were optimized to enhance electron mediation efficiency, leading to an improvement in productivity of about 3 mM/hr. Comparable productivity was observed in simulated COG and plastic waste-derived gas, which are promising results for the utilization of such low-purity H2 sources. Furthermore, the system demonstrates robustness and recyclability across maintaining productivity over 6 repeated batch reactions, highlighting its potential for industrial applications. Overall, our study provides valuable insights into the development of sustainable enzymatic microreactors for chemical valorization processes, contributing to greener and more efficient industrial practices.

Rational design and construction of direct Z-scheme ternary heterojunction photocatalyst AgBr/CoWO4/Ag for efficient environmental remediation

The indiscriminate discharge of micropollutants (e.g., dyes, antibiotics, industrial additives, etc.) represents a significant risk to human health, and the removal of these substances from water bodies has become a prominent area of research within the field of environmental remediation. A simple hydrothermal-precipitation-photoreduction method was employed to synthesize novel Z-scheme heterojunction photocatalysts of AgBr/CoWO4/Ag. The catalysts demonstrated remarkable degradation capabilities with regard to a range of micropollutants present in wastewater. Of the catalysts tested, 5AgBr/CoWO4/Ag exhibited the highest degradation rates, reaching 98.58% for Rhodamine B, 86.82% for tetracycline hydrochloride, and 95.60% for 2-mercaptobenzothiazole within 60 min. In particular, the reaction kinetic rate of 5AgBr/CoWO4/Ag towards Rhodamine B degradation (k2 = 0.26278 L mg−1·min−1) is 9 times that of AgBr (k2 = 0.02953 L mg−1·min−1) and 113 times that of CoWO4 (k2 = 0.00233 L mg−1·min−1), which serves to highlight the exceptional photocatalytic activity of the material. The experimental data and subsequent analysis indicated that the enhanced photocatalytic performance can be attributed to two factors: firstly, the electron mediation by Ag nanoparticles leading to improved charge separation efficiency, and secondly, the formation of Z-scheme heterojunctions between AgBr and CoWO4. The cyclic tests provided confirmation of the excellent stability and recyclability of the AgBr/CoWO4/Ag photocatalysts. It is anticipated that this study will facilitate the development of novel methods for the degradation of refractory micropollutants and provide insights into environmental remediation, thereby contributing to the sustainable development of society.

Metal-free carbon nanotube boosted periodate oxidation towards organic pollutants: Identification of active sites and activation mechanism

Recent studies have indicated that metal-free carbon material-enhanced periodate (PI) oxidation is a promising strategy for mitigating organic pollution in water. However, the complicated physicochemical properties of carbon materials make it challenging to determine the activation mechanism and roles of the active sites. In this study, various metal-free carbon materials (GO, GP, ND, CNF, and MCNT) were used as catalysts for activating PI in the degradation of organic pollutants, with a focus on elucidating the underlying reaction mechanisms. All of these materials were found to be highly effective in PI activation, and MCNT showed the best catalytic performance. Quenching experiments and EPR results show that the MCNT/PI system primarily oxidizes organic contaminants via two non-radical oxidation routes as electron donors and electron mediators, respectively. Specifically, the oxygen-containing groups of MCNT (particularly carbonyl groups) play a crucial role in electron donation to enhance PI oxidation. Moreover, the structural defects of MCNT significantly accelerate electron transfer from the SIZ (target contaminant) to PI. These insights contribute to unveiling the activation of PI using metal-free carbon materials and hold substantial promise for advancing carbon-based catalysts in environmental cleanup efforts.

Exoelectrogenic behaviors of Shewanella oneidensis MR-1 and cytochrome knock-out mutants on smooth electrodes of different materials

The development of anodes supporting a high rate of current generation stands as a crucial and challenging aspect in microbial electrochemical systems. A well-defined electrode surface morphology is essential for comprehending the impact of material intrinsic properties on microbial current generation, offering molecular insights into the respiration of exoelectrogens with electrodes made of diverse materials. We fabricated smooth electrodes (root mean square roughness below 10 nm) using four materials, each representing a distinct class of materials commonly utilized to construct bioanodes. These electrodes were employed to investigate current generation, electrochemical characteristics, and biofilm formation by Shewanella oneidensis MR-1 and mutants lacking cytochromes MtrC (ΔmtrC), MtrA (ΔmtrA), or CymA (ΔcymA). In reactors inoculated with MR-1, the poly(3,4-ethylenedioxythiophene) polystyrene sulfonate electrodes demonstrated a current density of 12.5 ± 1.1 μA cm-2, surpassing the 3.57 ± 0.50 μA cm-2 observed with indium tin oxide electrodes, while current generation levels by gold and glassy carbon electrodes fell in between. This disparity was not attributed to distinct biofilm formations by MR-1, as it formed stable monolayer biofilms on all types of working electrodes. At least five electron transfer pathways were identified in the MR-1 Vammograms, with the activities of these pathways depending on the electrode materials. The effectiveness of both endogenous and exogenous electron mediators varied with the electrode materials involved. Additionally, a phenazine compound exhibited diverse formal potentials when interacting with the biofilm and different types of electrodes. The mutants displayed varying degrees of impaired current generation and biofilm formation capabilities, with ΔmtrA and ΔcymA being the most affected regardless of the electrode used. However, for a specific mutant, the overall current generation, relative contribution by individual pathways, and biofilm formations underwent significant changes based on the electrode materials employed.

Regulation of Microalgal Photosynthetic Electron Transfer.

The global ecosystem relies on the metabolism of photosynthetic organisms, featuring the ability to harness light as an energy source. The most successful type of photosynthesis utilizes a virtually inexhaustible electron pool from water, but the driver of this oxidation, sunlight, varies on time and intensity scales of several orders of magnitude. Such rapid and steep changes in energy availability are potentially devastating for biological systems. To enable a safe and efficient light-harnessing process, photosynthetic organisms tune their light capturing, the redox connections between core complexes and auxiliary electron mediators, ion passages across the membrane, and functional coupling of energy transducing organelles. Here, microalgal species are the most diverse group, featuring both unique environmental adjustment strategies and ubiquitous protective mechanisms. In this review, we explore a selection of regulatory processes of the microalgal photosynthetic apparatus supporting smooth electron flow in variable environments.

Preliminary investigations of microbiologically influenced corrosion of 304 stainless steel by anaerobic Clostridioides difficile biofilm

Clostridioides difficile is a pathogenic anaerobe that potentially causes microbiologically influenced corrosion (MIC). Coupons of 304 stainless steel (SS) were incubated with C. difficile in deoxygenated brain heart infusion supplement medium. After a 7-d incubation, C. difficile biofilms were observed on the 304 SS coupon surfaces. The sessile cell count on 304 SS coupons were (1.9 ± 0.5) × 107 cells/cm2. It was found that this high-grade SS did not suffer measurable corrosion weight loss and pitting. X65 carbon steel was used to verify C. difficile bio-corrosivity. A 7-d weight loss of 0.9 ± 0.2 mg/cm2 was found on X65 coupons with the same incubation condition, which manifested as uniform corrosion. 13%Cr steel, also known as 420 SS which is a low-grade SS that is prone to pitting, was used to verify pitting by C. difficile. A 15.2 μm pit was observed after 26 d of incubation. Electrochemical tests were conducted in a 10 mL biofilm/MIC test kit. The electrochemical analysis of electron mediator injection indicated that MIC of 304 SS by C. difficile belongs to extracellular electron transfer-MIC. A 100 ppm (w/w) tetrakis (hydroxymethyl)phosphonium sulfate (a green biocide) injection test proved that it is a suitable disinfectant for C. difficile.

Sulfur-driven microbial fuel cells denitrification system for targeted treatment of nitrate-containing groundwater: Performance and mechanism

Sulfur (S0)-driven autotrophic denitrification system has obvious advantages in economy and performance in treating the low carbon/nitrogen groundwater. However, the by-products produced from S0 oxidation will cause disturbance to the water quality. In this study, a dual-chamber microbial fuel cell was driven by S0 (S0-MFC) to separate the S0 and nitrate, the electrons generated by the oxidation of S0 in the anodic chamber transferred to the cathode for nitrate reduction. Under the action of the anode microorganisms, the S0 was directly oxidized to sulfate. The maximum nitrate removal rate (NRR) in the cathodic chamber was 2.31 ± 0.03 mg N/L/h, and the anode electron utilization rate could reached to 19.69 %. Electrochemical results showed that flavin and c-type cytochrome could acted as electron mediators promote the electron transfer processes. The presence of loop current contributed to the enhancement of microbial metabolic activity, thus improving the stability of sludge and NRR. The denitrifiers (Thiobacillus and Denitratisoma) and sulfur autotrophs (Desulfocapsa and Acidithiobacillus) played an important role in the high NRR. A low-cost and pollution-free method for removing nitrate from groundwater was realized in this study.

Refining metallic nano-copper by electron-rich black carbon for superior Fenton-like catalysis in water purification: The capacitive regulation of corrosive electron transfer

Transition metals are promising catalysts for environmental remediation. However, their low reactivity, poor stability and weak reusability largely limit practical applications. Herein, we report that the electron-rich dissolved black carbon (DBC) incorporated into the nanoscale zero-valent copper (nZVCu) can boost intrinsic reactivity, structural stability and cyclic reusability for superior peroxymonosulfate (PMS) activation and pollutant degradation. A series of refractory pollutants can be effectively removed on the DBC/nZVCu, in comparison with the nZVCu reference. Hydroxyl radical (‧OH) is identified as the dominant reactive oxygen species by electron spin resonance (ESR) and chemical quenching tests, mediated by the metastable Cu(III) as the key reactive intermediate. The electron-rich DBC protects nanoscale Cu from oxidative corrosion to slow down the surface formation of inert CuO layer, rendered by the thermodynamically and dynamically capacitive regulation of corrosive electron transfer from metallic core. By this refining way, the conducive DBC improves the neighboring utilization of reactive electron during metal corrosion, oxidant activation, radical generation and pollutant degradation in Fenton-like catalysis. Our findings suggest that the ubiquitous DBC can be an efficient chelating agent to refine transition metals by serving as the surface deactivator and electron mediator, and take new insights into their environmental and agricultural geochemistry.

Biomimetic Activation of N‐Nitrosamides with Red Light‐Triggered Nitric Oxide Release via Mediated Electron Transfer

Mediated electron transfer (MET) is fundamental to many biological functions, including cellular respiration, photosynthesis, and enzymatic catalysis. However, leveraging the MET process to enable the release of therapeutic gases has been largely unexplored. Herein, we report the bio‐inspired activation of a series of UV‐absorbing N‐nitrosamide derivatives (NOA) under red light exposure, enabling the quantitative release of nitric oxide (NO) gasotransmitter via an MET process. The cornerstone of our design is the covalent linkage of a 2,4‐dinitroaniline moiety, which acts as an electron mediator to the N‐nitrosamide groups. This facilitates efficient electron transfer from the excited palladium(II) meso‐tetraphenyltetrabenzoporphyrin (PdTPTBP) photocatalyst and the selective activation of NOA. Our approach has been validated with distinct photocatalysts and various N‐nitrosamides, including those derived from carbamates, amides, and ureas. Notably, the modulation of the linker length between the electron mediator and N‐nitrosamide groups serves as a regulatory mechanism for controlling NO release kinetics. Moreover, this biomimetic NO release platform demonstrates effective operation under both normoxic and hypoxic conditions, and it enables localized delivery of NO under physiological conditions, exhibiting significant anticancer efficacy within the phototherapeutic window and enhanced selectivity towards tumor cells.

Biomimetic Activation of N-Nitrosamides with Red Light-Triggered Nitric Oxide Release via Mediated Electron Transfer.

Mediated electron transfer (MET) is fundamental to many biological functions, including cellular respiration, photosynthesis, and enzymatic catalysis. However, leveraging the MET process to enable the release of therapeutic gases has been largely unexplored. Herein, we report the bio-inspired activation of a series of UV-absorbing N-nitrosamide derivatives (NOA) under red light exposure, enabling the quantitative release of nitric oxide (NO) gasotransmitter via an MET process. The cornerstone of our design is the covalent linkage of a 2,4-dinitroaniline moiety, which acts as an electron mediator to the N-nitrosamide groups. This facilitates efficient electron transfer from the excited palladium(II) meso-tetraphenyltetrabenzoporphyrin (PdTPTBP) photocatalyst and the selective activation of NOA. Our approach has been validated with distinct photocatalysts and various N-nitrosamides, including those derived from carbamates, amides, and ureas. Notably, the modulation of the linker length between the electron mediator and N-nitrosamide groups serves as a regulatory mechanism for controlling NO release kinetics. Moreover, this biomimetic NO release platform demonstrates effective operation under both normoxic and hypoxic conditions, and it enables localized delivery of NO under physiological conditions, exhibiting significant anticancer efficacy within the phototherapeutic window and enhanced selectivity towards tumor cells.

Bio-electrocatalytic Alkene Reduction Using Ene-Reductases with Methyl Viologen as Electron Mediator.

Asymmetric hydrogenation of alkene moieties is important for the synthesis of chiral molecules, but achieving high stereoselectivity remains a challenge. Biocatalysis using ene-reductases (EReds) offers a viable solution. However, the need for NAD(P)H cofactors limits large-scale applications. Here, we explored an electrochemical alternative for recycling flavin-containing EReds using methyl viologen as a mediator. For this, we built a bio-electrocatalytic setup with an H-type glass reactor cell, proton exchange membrane, and carbon cloth electrode. Experimental results confirm the mediator's electrochemical reduction and enzymatic consumption. Optimization showed increased product concentration at longer reaction times with better reproducibility within 4-6 h. We tested two enzymes, Pentaerythritol Tetranitrate Reductase (PETNR) and the Thermostable Old Yellow Enzyme (TOYE), using different alkene substrates. TOYE showed higher productivity for the reduction of 2-cyclohexen-1-one (1.20 mM h-1), 2-methyl-2-cyclohexen-1-one (1.40 mM h-1) and 2-methyl-2-pentanal (0.40 mM h-1), with enantiomeric excesses ranging from 11 % to 99 %. PETNR outperformed TOYE in terms of enantioselectivity for the reduction of 2-methyl-2-pentanal (ee 59 % ± 7 % (S)). Notably, TOYE achieved promising results also in reducing ketoisophorone, a challenging substrate, with similar enantiomeric excess compared to published values using NADH.

Photoredox Cascade Catalysts for Solar Hydrogen Production from Sustainable Hydrogen Sources.

Visible-light-driven photocatalytic hydrogen (H2) production has been extensively studied as a clean and sustainable energy resource. Although sacrificial electron donors (SEDs) are commonly used to evaluate photocatalytic activity, their irreversible decomposition forces charge separation, which disrupts the inherent dual productivity of photocatalysis, that is, the formation of both the reduction and oxidation products. To achieve highly efficient photoinduced charge separation without SED decomposition, the layer-by-layer assembly of redox-active photosensitizing dyes and electron mediators through Zr4+-phosphonate bonds has been extensively studied as an artificial mimic of the electron transport chain in natural photosynthesis. This concept paper presents an overview of photoredox cascade catalytic (PRCC) systems comprising multiple Ru(II)-trisbipyridine-type dyes and mediator layers on Pt-loaded TiO2 nanoparticles for H2 production from redox reversible electron donors (RREDs). The PRCC structure-activity relationship for photocatalytic H2 production is briefly discussed in terms of layer thickness, surface structure and modification, and cooperativity with molecular oxidation catalysts. Finally, new insights into the design of efficient dual-production photocatalysts based on the PRCC structure are presented.

Construction of dual Z-scheme ternary carbon nitride homojunction pectin microspheres as a multifunctional photocatalyst for tetracycline degradation, H2O2 production, and N2 fixation

Graphitic carbon nitride (GCN) has gathered phenomenal research interest as a metal-free, safe, and affordable photocatalyst. However, GCN suffers several problems, such as lower utilization of visible light, higher recombination ratio, slower electron immobility, poor reusability, and a tedious recovery process. Herein, a ternary homojunction (OPACN) was effectively constructed between oxidized GCN (OCN), amino-rich GCN (ACN), and phosphorylated GCN (PCN) and then formulated into 3D hydrogels (OPACN) using pectin as the catalyst support via a crosslinking strategy using FeCl3. The photocatalytic studies using OPACN hydrogel reported 88 % degradation of tetracycline in 30 min with a maximum reusability of 15 cycles. The ternary homojunction hydrogel photocatalyst produced 1204 µM of H2O2 and 404 µM of ammonia in 60 min of visible light irradiation. The phenomenal catalytic activity of the OPACN hydrogel is ascribed to the effective construction of homojunction between the OCN, PCN, and ACN, which facilitated the separation efficiency and boosted the visible light utilization. This study affirmed that the utilization of pectin as a catalytic support enhanced the visible light utilization, reusability, stability, and easiness in recoverability. In addition to this, pectin can act as an electron mediator, and the robust interactions between the GCN components via hydrogen bonding can also facilitate H2O2 production and nitrogen fixation. Overall, this study illuminates the usage of pectin as ideal photocatalytic support for environmental applications.

EFEKTIVITAS MEDIASI DALAM PENYELESAIAN PERKARA PERCERAIAN DI PENGADILAN AGAMA PURWODADI

<p>Initially, mediation was part of an alternative dispute resolution method in Law Number 30 of 1999 concerning Arbitration and Alternative Dispute Resolution. Mediation is considered an effective tool for resolving disputes quickly and cheaply and can provide parties with better access to finding satisfactory solutions. In this research, we examine the effectiveness of mediation in resolving divorce cases at the Purwodadi Religious Court. This research aims to determine the level of success of mediation at the Purwodadi Religious Court, the inhibiting factors and efforts to resolve it. This research uses a normative juridical type of research. The research used descriptive and qualitative research which took place at the Purwodadi Religious Court. Data taken in the field was collected using observation, interview and note-taking techniques. The collected data is then processed using data reduction analysis, data presentation and concluding. Based on the results of research regarding the effectiveness of mediation in divorce cases at the Purwodadi Religious Court, this is following Supreme Court Regulation (PERMA) Number 1 of 2016 concerning procedures for mediation in court. The mediator had difficulty reconciling the parties due to several factors and considered mediation to be ineffective. Inhibiting factors include the absence of one of the parties, the strong desire of the parties to divorce, family disputes that can no longer be maintained, psychological or mental factors of disappointment (psychiatric), lack of knowledge of mediation between the parties, community compliance, lack of intention. Good. Efforts to resolve these include: Providing guidance and counselling, the parties are active/open to resolving the case, providing counselling on the importance of mediation, the mediator's abilities, mediation facilities and electronic mediation.</p>

Construction of a bioelectrocatalytic system with bacterial surface displayed enzyme-nanomaterial hybrids

To take advantage of the high specificity of enzymatic catalysis along with the high efficiency of electrochemical cofactor regeneration, a bacterial surface displayed enzyme-nanomaterial hybrid bioelectrocatalytic system is herein developed. A cofactor-dependent xylose reductase, capable of reducing xylose to xylitol, is displayed on the surface of Bacillus subtilis, followed by the attachment of copper nanomaterials via the binding of His-tagged enzyme with the nickel ion. This hybrid system can regenerate NADPH with a highest efficiency of 71.6% in 4 h without the usage of extra electron mediators, and 2.35 mM of xylitol can be synthesized after a series of optimization processes. This work opens up new possibilities for the construction and application of bioelectrocatalytic systems with enzyme-nanomaterial hybrids.

A novel cobalt-iron bimetallic hydrochar for the degradation of triclosan in the aqueous solution: performance, reusability, and synergistic degradation mechanism

Low activation performance is a critical issue limiting the practical application of low-cost biochar in the advanced oxidation. Given the high potential of transition metals in the persulfate activation process and abundant oxygen-containing groups of hydrochar, hydrochar derived from cobalt (Co)-modified iron (Fe)-enriched sludge was synthesized and its performance and activation mechanism for the degradation of triclosan were investigated. Co modification significantly altered the morphology of hydrochar, and the increased Co–Fe mass ratios transformed hydrochar from granular to rose-shaped lamellar and then to helical sheet structures. Specific surface area, defect degree, and oxygen-containing groups of hydrochar increased with increasing cobalt-iron mass ratios. The highest removal of triclosan was up to 98% in the hydrochar/peroxymonosulfate (PMS) system under a wide range of pHs (3–10) and still remained higher than 90% after four cycles. Both Radical (mainly hydroxyl radical) and nonradical pathways (singlet oxygen and electron transfer) were evidenced to play roles in the triclosan removal. Fe3+ promoted the regeneration of Co2+ and realized the efficient circulation of Co3+/Co2+. A ternary system consisting of electron donor (triclosan)-electron mediator (hydrochar)-electron acceptor (PMS) provided channels for electron transfer. No measurable Co and Fe were released during the reaction, and the toxicity of degradation intermediates was lower than that of triclosan. Beside triclosan, rhodamine B, bisphenol A, sulfamethoxazole, and phenol were also almost degraded completely in this oxidation system. This study provides a promising way for the enhancement of catalytic activity of carbonaceous material.

Combined use of versatile peroxidase and aryl alcohol oxidase of Pleurotus eryngii to decolorize melanin on the skin

Melanin plays an important role in protecting skin cells from harmful UV radiation, but its uneven pigmentation in the skin sometimes demands cosmetic resolution. As a safe and effective way of evening the skin tone, enzymatic decolorization of melanin at the stratum corneum has been proposed. In this regard, the use of lignin peroxidase, in the presence of hydrogen peroxide and veratryl alcohol, an electron mediator, has been explored. Here, we first show that versatile peroxidase (VP) and aryl alcohol oxidase (AAO) purified from the Pleurotus eryngii liquid culture can be used to decolorize melanin without exogenous hydrogen peroxide. This resembles the oxidative degradation pathway of lignin in nature; AAO generates hydrogen peroxide from veratryl alcohol, and VP utilizes generated hydrogen peroxide while using veratryl alcohol as a mediator. We further explored the use of POX_Pe, the crude peroxidase preparation of the Pleurotus eryngii liquid culture, for melanin decolorization because of its better stability. Using POX_Pe and veratryl alcohol, over 60 % of melanin decolorization was obtained in 1 h in the absence of exogenous hydrogen peroxide addition. Furthermore, POX_Pe could decolorize melanin in a 3D human pigmented epidermis model, demonstrating its possible applications in cosmetics.

AQDS-functionalized biochar enhances the bioreduction of Cr(VI) by Shewanella putrefaciens CN32

The bioreduction of toxic chromium(VI) to sparingly soluble chromium(III) represents an environmentally friendly and cost-effective method for remediating Cr contamination. Usually, this bioreduction process is slow and requires the addition of quinone compounds as electron shuttles to enhance the reaction rate. However, the dissolved quinone compounds are susceptible to loss with water flow, thereby limiting their effectiveness. To address this challenge, this study loaded anthraquinone-2,6-disulfonate (AQDS), a typical quinone compound, onto biochar (BC) to create a novel solid-phase electron mediator (BC-AQDS) that can sustainably promote Cr(VI) bioreduction. The experimental results demonstrated that BC-AQDS significantly promoted the bioreduction of Cr(VI), where the reaction rate constant increased by 4.81 times, and the reduction extent increased by 38.31%. X-ray photoelectron spectroscopy and Fourier-Transform Infrared Spectroscopy analysis revealed that AQDS replaced the –OH functional groups on the BC surface to form BC-AQDS. Upon receiving electrons from Shewanella putrefaciens CN32, BC-AQDS was reduced to BC-AH2DS, which subsequently facilitated the reduction of Cr(VI) to Cr(III). This redox cycle between BC-AQDS and BC-AH2DS effectively enhanced the bioreduction rate of Cr(VI). Our study also found that a lower carbonization temperature of BC resulted in a higher surface –OH functional group content, enabling a greater load of AQDS and a more pronounced enhancement effect on the bioreduction of Cr(VI). Additionally, a smaller particle size of BC and a higher dosage of BC-AQDS further contributed to the enhancement of Cr(VI) bioreduction. The preparation of BC-AQDS in this study effectively improve the utilization of quinone compounds and offer a promising approach for enhancing the bioreduction of Cr(VI). It provides a more comprehensive reference for understanding and solving the problem of Cr pollution in groundwater.