Metal sulfides as emerging materials for advanced oxidation of wastewater: Recent developments, challenges, and prospects

Catalytic advanced oxidation processes (CAOPs) have received considerable attention for wastewater treatment. However, the insufficient stability of catalysts, coupled with the sluggish regeneration of active sites, poses a limitation to the sustained performance of CAOPs in practical applications over prolonged periods. To overcome these challenges, accelerating the M(n+1)+/Mn+ redox cycle (where M denotes transition metals and n denotes oxidation state) of catalysts during the treatment process emerges as a highly promising approach. This approach not only holds the potential to enhance efficiency but also offers a comprehensive solution for bolstering the stability of CAOPs. This comprehensive review summarizes the advancements in metal sulfide research, specifically emphasizing the evolving trend from homogeneous to heterogeneous reductants, with the objective of expediting the redox cycles of catalysts. The catalytic and co-catalytic roles of various metal sulfides, including MoS2, WS2, transition metals doped MoS2/WS2, iron sulfides, S-modified zero valent-iron, S-doped iron oxides, non-iron metals sulfides, S-modified layered double hydroxides, and S-based single-atom catalysts, in CAOPs, have been systematically summarized. These studies specifically concentrate on accelerating the M(n+1)+/Mn+ redox cycles of catalysts, thereby enhancing the overall efficiency, stability, and catalytic performance of both homogeneous and heterogeneous systems. Finally, the current challenges and future perspectives related to the applications of metal sulfide-based CAOPs for wastewater treatment were proposed to assist researchers in making efficient and stable heterogeneous Fenton/Fenton-like systems for industrial applications.