Low temperatures limit the denitrification wastewater in activated sludge systems, but this can be mitigated by addition of redox mediators (RMs). Here, the effects of chlorophyll (Chl), 1,2-naphthoquinone-4-sulfonic acid (NQS), humic acid (HA), and riboflavin (RF), each tested at three concentrations, were compared for denitrification performance at low temperature, by monitoring the produced extracellular polymeric substances (EPS), and characterizing microbial communities and their metabolic potential. Chl increased the denitrification rate most, namely 4.12-fold compared to the control, followed by NQS (2.62-fold increase) and HA (1.35-fold increase), but RF had an inhibitory effect. Chl promoted the secretion of tryptophan-like and tyrosine-like proteins in the EPS and aided the conversion of protein from tightly bound EPS into loosely bound EPS, which improved the material transfer efficiency. NQS, HA, and RF also altered the EPS components. The four RMs affected the microbial community structure, whereby both conditionally abundant taxa (CAT) and conditionally rare or abundant taxa (CRAT) were key taxa. Among them, CRAT members interacted most with the other taxa. Chl promoted Flavobacterium enrichment in low-temperature activated sludge systems. In addition, Chl promoted the abundance of nitrate reduction genes narGHI and napAB and of nitrite reduction genes nirKS, norBC, and nosZ. Moreover, Chl increased abundance of genes involved in acetate metabolism and in the TCA cycle, thereby improving carbon source utilization. This study increases our understanding of the enhancement of low-temperature activated sludge by RMs, and demonstrates positive effects, in particular by Chl.

The non-pathogenic β-proteobacterium Cupriavidus necator has the ability to switch between chemoorganotrophic, chemolithoautotrophic and electrotrophic growth modes, making this microorganism a widely used host for cellular bioprocesses. Oxygen usually acts as the terminal electron acceptor in all growth modes. However, several challenges are associated with aeration, such as foam formation, oxygen supply costs, and the formation of an explosive gas mixture in chemolithoautotrophic cultivation with H2, CO2 and O2. Bioelectrochemical systems in which O2 is replaced by an electrode as a terminal electron acceptor offer a promising solution to these problems. The aim of this study was to establish a mediated electron transfer between the anode and the metabolism of living cells, i.e. anodic respiration, using fructose as electron and carbon source. Since C. necator is not able to transfer electrons directly to an electrode, redox mediators are required for this process. Based on previous observations on the extracellular electron transfer enabled by a polymeric mediator, we tested 11 common biological and non-biological redox mediators for their functionality and inhibitory effect for anodic electron transfer in a C. necator-based bioelectrochemical system. The use of ferricyanide at a concentration of 15 mM resulted in the highest current density of 260.75µAcm-2 and a coulombic efficiency of 64.1 %.

Gaseous pollutants like sulfur dioxide and nitrogen oxide(s) (SO2, NOx) have been increasing exponentially for the last two decades, which have had adverse effects on human health, aquatic life, and the environment. Recently, for air pollution taming, manganese/oxide (Mn/MnO) has become a very promising heterogeneous catalyst due to its environment-friendly, low-price, and remarkable catalytic abilities for toxic gases. In this work, cube-shaped Mn nanoparticles (cMn NPs) were decorated on the surface of reduced graphene oxide (rGO) by the solvothermal method. The resulting cMn@rGO composite was employed for electrochemical NOx reduction. However, the microscopic (TEM/HRTEM) and structural analysis were utilised to investigate the morphology and characteristics of the cMn@rGO composite. This electrochemical-based treatment for NOx reduction is employed by using electron shuttle or redox mediators. Here, four distinct redox mediators are used to address electrochemical obstacles, which effectively facilitate electron transportation and promoted NOx reduction on the electrode surface. These mediators not only significantly enhanced the NOx conversion into valuable products, i.e., N2 and N2O, but also made the process smooth with high performance. Among these mediators, neutral red (N.R) exhibited extraordinary potential in enhancing NOx reduction. The obtained results indicated that the remarkable catalytic performance (∼93%) of the cMn@rGO can be attributed to several factors, including the catalyst\'s three-dimensional architecture structure and abundant active sites. The designed catalyst (cMn@rGO) is not only cost-effective and sustainable but also exhibits excellent potential in effectively reducing NOx, which could be beneficial for large-scale NOx abatement.

Nonaqueous Li-O2 battery (LOB) represents one of the promising next-gen energy storage solutions owing to its ultrahigh energy density but suffers from problems such as high charging overpotential, slow redox kinetics, Li anode corrosion, etc., calling for a systemic optimization of the battery configuration and structural components. Herein, an ingenious \"trinity\" design of LOB is initiated by implementing a hollowed cobalt metal organic framework (MOF) impregnating iodized polypyrrole simultaneously as the cathode catalyst, anode protection layer, and slow-release capsule of redox mediators, so as to systemically address issues of impeded mass transport and redox kinetics on the cathode, dendrite growth, and surface corrosion on the anode, as well as limited intermediate solubility in the low donor-number (DN) solvent. As a result of the systemic effort, the LOB constructed demonstrates an ultralow discharge/charge polarization of 0.2 V, prolonged cycle life of 1244 h and total discharge capacity of 28.41 mAh cm-2 . Mechanistic investigations attribute the superb LOB performance to the redox-mediated solution growth mechanism of crystalline Li2 O2 with both enhanced reaction kinetics and reversibility. This study offers a paradigm in designing smart materials to raise the performance bar of Li-O2 battery toward realistic applications.

Lithium-sulfur (Li-S) batteries stand out for their high theoretical specific capacity and cost-effectiveness. However, the practical implementation of Li-S batteries is hindered by issues such as the shuttle effect, tardy redox kinetics, and dendrite growth. Herein, an appealingly designed covalent organic framework (COF) with bi-functional active sites of cyanide groups and polysulfide chains (COF-CN-S) is developed as cooperative functional promoters to simultaneously address dendrites and shuttle effect issues. Combining in situ techniques and theoretical calculations, it can be demonstrated that the unique chemical architecture of COF-CN-S is capable of performing the following functions: 1) The COF-CN-S delivers significantly enhanced Li+ transport capability due to abundant ion-hopping sites (cyano-groups); 2) it functions as a selective ion sieve by regulating the dynamic behavior of polysulfide anions and Li+ , thus inhibiting shuttle effect and dendrite growth; 3) by acting as a redox mediator, the COF-CN-S can effectively control the electrochemical behavior of polysulfides and enhance their conversion kinetics. Based on the above advantages, the COF-CN-S endows Li-S batteries with excellent performance. This study highlights the significance of interface modification and offers novel insights into the rational design of organic materials in the Li-S realm.

Indirect electrocatalytic conversion of cheap organic raw materials via the activation of S─H and N─H bonds into the value-added S─N/S─S bonds chemicals for industrial rubber production is a promising strategy to realize the atomic economic reaction, during which the kinetic inhibition that is associated with the electron transfer at the electrode/electrolyte interface in traditional direct electrocatalysis can be eliminated to achieve higher performance. In this work, a series of di-copper-substituted phosphotungstatebased foams (PW10 Cu2 @CMC) are fabricated with tunable loadings (17 to 44 wt%), which can be successfully applied in indirect electrocatalytic syntheses of sulfenamides and disulfides. Specifically, the optimal PW10 Cu2 @CMC (44 wt%) exhibits excellent electrocatalytic performance for the construction of S─N/S─S bonds (yields up to 99%) coupling with the efficient production of H2 (≈50 µmol g-1  h-1 ). Remarkably, it enables the scale-up production (≈14.4 g in a batch experiment) and the obtained products can serve as rubber vulcanization accelerators with superior properties to traditional industrial rubber additives in real industrial processes. This powerful catalysis system that can simultaneously produce rubber vulcanization accelerator and H2 may inaugurate a new electrocatalytic avenue to explore polyoxometalate-based foam catalysts in electrocatalysis field.

The storage time of Zn-air batteries (ZABs) for practical implementation have been neglected long-lastingly. ZABs based on organic solvents promise long shelf lives but suffer from sluggish kinetics. Here, we report a longly storable ZAB with accelerated kinetics mediated by I3 - /I- redox. In the charge process, the electrooxidation of Zn5 (OH)8 Cl2 ⋅H2 O is accelerated by I3 - chemical oxidation. In the discharge process, I- adsorbed on the electrocatalyst changes the energy level of oxygen reduction reaction (ORR). Benefitting from these advantages, the prepared ZAB shows remarkably improved round-trip efficiency (56.03 % vs. 30.97 % without the mediator), and long-term cycling time (>2600 h) in ambient air without replacing any components or applying any protective treatment to Zn anode and electrocatalyst. After resting for 30 days without any protection, it can still directly discharge continuously for 32.5 h and charge/discharge very stably for 2200 h (440 cycles), which is evidently superior to aqueous ZABs (only 0/0.25 h, and 50/25 h (10/5 cycles) by mild/alkaline electrolyte replenishment). This study provides a strategy to solve both storage and sluggish kinetics issues that have been plaguing ZABs for centuries, opening up a new avenue to the industrial application of ZABs.

Vibrio natriegens promises to be a new standard biotechnological working organism since it grows extraordinarily fast, its productivity surpasses E. coli by far, and genomic tools are getting readily available. Recent studies provided insights into its extracellular electron transfer pathway, revealing it to be similar to other well-known electroactive organisms. Therefore, we aimed to show for the first time that V. natriegens donates electrons from its metabolism to an electrode by direct contact as well as via an artificial redox mediator. Our results demonstrate current densities up to 196 μA cm-2 using an artificial mediator. Via direct electron transfer, 6.6 μA cm-2 were achieved within the first 24 h of cultivation. In the mediated system, mainly formate, acetate, and succinate were produced from glucose. These findings favor V. natriegens over established electroactive organisms due to its superior electron-transfer capabilities combined with an outstanding metabolism.

Azo dyes are significant organic pollutants known for their adverse effects on humans and aquatic life. In this study, anthraquinone-2-sulfonate (AQS) immobilized on biochar (BC) was employed as a novel carrier in up-flow anaerobic fixed-bed reactors to induce specific biofilm formation and promote the biotransformation efficiency of azo dyes. Novel carrier-packed reactor 1 (R1) and BC-packed reactor 2 (R2) were used to treat red reactive 2 (RR2) under continuous operation for 175 days. The decolorization rates of R1 and R2 were 96-83% and 91-73%, respectively. The physicochemical characteristics and extracellular polymeric substances (EPS) of the biofilm revealed a more stable structure in R1. Furthermore, the microbial community in R1 interacted more closely with each other and contained more keystone genera. Overall, this study provides a feasible method for improving the biotransformation of azo dyes, thus providing support for practical applications in wastewater treatment projects.

Thermophilic fungi are known to develop different metabolic and catabolic activities that enable them to function at elevated temperatures. Screening heat-resistant fungi, as promising resources for enzymatic activities, are still recommended. A total of eleven wood-decay thermophilic fungal strains were isolated from decaying organic materials (DOM) collected from arid areas of Khulais (Saudi Arabia). Six of these isolates are laccase-producing thermophilic strains growing at 50 °C. Among Laccase positive (Lac+) isolates, Chaetomium brasiliense (G3), Canariomyces notabilis (KW1), and Paecilomyces formosus (KW3) were exploited to treat single selected endocrine-disrupting chemicals (EDCs) that belonged to different classes (synthetic steroid hormone: 17α-ethinyl estradiol (EE2), and alkylphenols:4-tert-butylphenol (4-t-BP)). Chaetomium sp. was selected due to its potentialities against target EDCs, and then, their laccases were extracted and exploited for the biocatalytic degradation of treated municipal sewage wastewaters (TMWW) mixed with 4-t-BP and EE2. The results show that within 2 h of catalyzing at 50 °C, laccase could degrade 60 ± 4.8% of 4-t-BP; however, it oxidized EE2 less efficiently, reaching 35 ± 4.1%. The influence of some redox mediators on the laccase oxidation system was investigated. The 1-hydroxybenzotriazole (HBT) and syringaldehyde led to the highest transformation rates of EE2 (approximately 80 ± 2.4%). Near-total removal (90 ± 7.2%) of 4-t-BP was achieved with TEMPO in 2 h. With the metabolites identified through gas chromatography-tandem mass spectrometry (GC-MS), metabolic pathways of degradation were suggested. The results highlight the potential of Chaetomium sp. strains in the conversion of micropollutants.
UNASSIGNED: The online version contains supplementary material available at 10.1007/s13205-022-03439-1.