Mn3O4 and Mn3O4-based composites as efficient catalysts for peroxymonosulfate activation: A critical review

Manganese oxide (Mn3O4) has emerged as a highly promising catalyst for peroxymonosulfate (PMS) activation in advanced oxidation processes (AOPs), owing to its unique spinel structure, mixed-valence Mn2+ /Mn3+ chemistry, environmental benignity, and tunable surface properties. This review systematically explores recent progress in the synthesis strategies of Mn3O4, including chemical precipitation, hydro/solvothermal methods, and thermal decomposition, emphasizing their influence on crystallinity, morphology, surface area, and defect engineering. The critical structure-property-performance relationships are highlighted, focusing on the roles of Mn valence states, surface hydroxyl groups, oxygen vacancies, and lattice oxygen in modulating PMS activation pathways. Both radical (SO4--OH) and non-radical (1O2, direct electron transfer, PMS∗) mechanisms are elucidated, with mechanistic insights into the dominance of specific pathways under varying structural and environmental conditions. Mn3O4-based composites by combining with MnxOy or other materials are discussed in enhancing catalytic performance and stability. Despite significant advances, challenges such as long-term stability, efficiency under strong alkaline conditions, and mechanistic ambiguities remain. Future research directions are proposed to guide the rational design of Mn3O4-based catalysts for efficient, robust, and selective environmental applications. © 2025 Elsevier B.V., All rights reserved.