Wen‐Wei Li

Microbial fuel cells (MFCs) have been conceived and intensively studied as a promising technology to achieve sustainable wastewater treatment. However, doubts and debates arose in recent years regarding the technical and economic viability of this technology on a larger scale and in a real-world applications. Hence, it is time to think about and examine how to recalibrate this technology's role in a future paradigm of sustainable wastewater treatment. In the past years, many good ideas/approaches have been proposed and investigated for MFC application, but information is scattered. Various review papers were published on MFC configuration, substrates, electrode materials, separators and microbiology but there is lack of critical thinking and systematic analysis of MFC application niche in wastewater treatment. To systematically formulate a strategy of (potentially) practical MFC application and provide information to guide MFC development, this perspective has critically examined and discussed the problems and challenges for developing MFC technology, and identified a possible application niche whereby MFCs can be rationally incorporated into the treatment process. We propose integration of MFCs with other treatment technologies to form an MFC-centered treatment scheme based on thoroughly analyzing the challenges and opportunities, and discuss future efforts to be made for realizing sustainable wastewater treatment.

Bimetallic spinel oxides are efficient catalysts for peroxymonosulfate (PMS) activation but the catalytic mechanism is unclear. The critical role of Mn−O covalency in determining the intrinsic activity of Co3−xMnxO4 and a new mechanism of Co–Mn synergy are revealed by Wen-Wei Li and co-workers in their Research Article on page 274. Co strengthens Mn−O covalency in the octahedral configuration of Co3−xMnxO4, which lowers the charge transfer energy of the MnOh–PMS interaction and drastically accelerates MnVI/MnIII redox cycling.

Biomass is increasingly perceived as a renewable resource rather than as an organic solid waste today, as it can be converted to various chemicals, biofuels, and solid biochar using modern processes. In the past few years, pyrolysis has attracted growing interest as a promising versatile platform to convert biomass into valuable resources. However, an efficient and selective conversion process is still difficult to be realized due to the complex nature of biomass, which usually makes the products complicated. Furthermore, various contaminants and inorganic elements (e.g., heavy metals, nitrogen, phosphorus, sulfur, and chlorine) embodied in biomass may be transferred into pyrolysis products or released into the environment, arousing environmental pollution concerns. Understanding their behaviors in biomass pyrolysis is essential to optimizing the pyrolysis process for efficient resource recovery and less environmental pollution. However, there is no comprehensive review so far about the fates of chemical elements in biomass during its pyrolysis. Here, we provide a critical review about the fates of main chemical elements (C, H, O, N, P, Cl, S, and metals) in biomass during its pyrolysis. We overview the research advances about the emission, transformation, and distribution of elements in biomass pyrolysis, discuss the present challenges for resource-oriented conversion and pollution abatement, highlight the importance and significance of understanding the fate of elements during pyrolysis, and outlook the future development directions for process control. The review provides useful information for developing sustainable biomass pyrolysis processes with an improved efficiency and selectivity as well as minimized environmental impacts, and encourages more research efforts from the scientific communities of chemistry, the environment, and energy.

Abstract Transition metal (TM)‐based bimetallic spinel oxides can efficiently activate peroxymonosulfate (PMS) presumably attributed to enhanced electron transfer between TMs, but the existing model cannot fully explain the efficient TM redox cycling. Here, we discover a critical role of TM−O covalency in governing the intrinsic catalytic activity of Co 3− x Mn x O 4 spinel oxides. Experimental and theoretical analysis reveals that the Co sites significantly raises the Mn valence and enlarges Mn−O covalency in octahedral configuration, thereby lowering the charge transfer energy to favor Mn Oh –PMS interaction. With appropriate Mn IV /Mn III ratio to balance PMS adsorption and Mn IV reduction, the Co 1.1 Mn 1.9 O 4 exhibits remarkable catalytic activities for PMS activation and pollutant degradation, outperforming all the reported TM spinel oxides. The improved understandings on the origins of spinel oxides activity for PMS activation may inspire the development of more active and robust metal oxide catalysts.