Lignosulfonate-assisted in situ synthesis of Co9S8-Ni3S2 heterojunctions encapsulated by S/N co-doped biochar for efficient water oxidation.

The development of highly active and stable earth-rich electrocatalysts remains a major challenge to release the reliance on noble metal catalysts in sustainable (electro)chemical processes. In this work, metal sulfides encapsulated with S/N co-doped carbon were synthesized with a one-step pyrolysis strategy, where S was introduced during the self-assembly process of sodium lignosulfonate. Due to the precise coordination of Ni and Co ions with lignosulfonate, an intense-interacted Co9S8-Ni3S2 heterojunction was formed inside the carbon shell, causing the redistribution of electrons. An overpotential as low as 200 mV was obtained over Co9S8-Ni3S2@SNC to reach a current density of 10 mA cm-2. Only a slight increase of 14.4 mV was observed in a 50 h chronoamperometric stability test. Density functional theory (DFT) calculations showed that Co9S8-Ni3S2 heterojunctions encapsulated with S/N co-doped carbon can optimize the electronic structure, lower the reaction energy barrier, and improve the OER reaction activity. This work provides a novel strategy for constructing highly efficient and sustainable metal sulfide heterojunction catalysts with the assistance of lignosulfonate biomass.

Rice husk-intensified cathode driving bioelectrochemical reactor for remediating nitrate-contaminated groundwater.

To achieve economical and eco-friendly denitrification, rice husk-intensified cathode driving bioelectrochemical reactor (RCBER) was constructed with rice husk as solid-phase carbon source and microbial carrier. Results demonstrated that the application of current improved the utilization of rice husk and enhanced the denitrification, and the quenching of anodic hydroxyl radicals by rice husk also improved the microbial resistance to current. The highest nitrate removal rate as 0.34 mg-N/(L∙d), higher economic benefits, i.e., current efficiency as 31.6% and energy consumption as 2.43 kWh/g NO3--N, and the highest environmental benefit, i.e., hydrogenotrophic denitrification contribution as 37.9%, were obtained at 200 mA/m2. The best performance at 200 mA/m2 was related to its better microenvironment, such as lower accumulation of anodic by-products and higher bioavailability of rice husks, as well as higher microbial metabolic activity, such as stable extracellular polymeric substance, the maximum electron transport system activity as 11.63 ± 0.14 µg O2·g-1·min-1·mg protein-1 and the highest activity of nitrate reductase (3.15-fold that of control check). The application of current realized the coexistence of heterotrophic and hydrogenotrophic denitrifiers, and multiple functional bacteria such as anaerobic denitrifiers Flavobacterium, aerobic denitrifiers Comamonas, hydrogenotrophic denitrifiers Thermomonas and electron transfer-related Enterobacter coexisted at 200 mA/m2, thereby improving RCBER's adaptability to the complex microenvironment. This study provides the theoretical basis for realizing a win-win situation of environmental pollution remediation and agricultural waste disposal.

Performance and mechanism of a novel woodchip embedded biofilm electrochemical reactor (WBER) for nitrate-contaminated wastewater treatment.

In this study, a woodchip biofilm electrode reactor (WBER) with woodchips embedded anode and cathode was developed, and its denitrification mechanism was analyzed by investigating the denitrification performance, organic matter change, redox environment and microbial community. The results show that the WBER with a carbon rod as anode (C-WBER) had a higher denitrification efficiency (2.58 mg NO- 3-N/(L·h)) and lower energy consumption (0.012 kWh/g NO- 3-N) at 350 mA/m2. By reducing the hydroxyl radical and dissolved oxygen concentrations, anode embedding technology effectively decreased the inhibition on microorganisms. Lignin decomposition, nitrification and aerobic denitrification were carried out in anode. Additionally, hydrogen autotrophic denitrification and heterotrophic denitrification were occurred in cathode. The WBER effectively removed nitrate and reduced the cost, providing a theoretical basis and direction for further develop BERs.