Catalysis of nonstoichiometric Mn–Co spinel oxides in effective peroxymonosulfate activation: Structure–activity relationship and flow-through organic wastewater treatment

An effective catalytic membrane requires heterogeneous catalysts that combine high activity and stability in peroxymonosulfate (PMS) activation to ensure efficient and durable organic wastewater treatment. Herein, the crystallographic evolution of Mn–Co spinel oxides was manipulated by adjusting the calcination temperature of the precursor, yielding nonstoichiometric MnCo₂O_4.5 with markedly superior catalytic activity in the PMS-based advanced oxidation process (PMS-AOP). Among the parameters involving in this evolution, the formation of Mn(IV) species and the accompanying lattice contraction were identified as dominant factors driving catalytic enhancement. Theoretical calculations revealed charge separation and an upward shift of the d-band centers of Co and Mn sites in MnCo₂O_4.5, which favored PMS chemisorption and contributed to the activation of Co sites. In particular, Mn(IV) sites with empty e_g orbitals enhanced PMS adsorption and promoted the redox conversion of adjacent Co sites through internal electron transfer. Therefore, the MnCo₂O_4.5-based catalytic membrane achieved sustainable mineralization efficiency (40–63%) for organic effluent during 100 h of continuous flow-through operation, demonstrating both high stability and strong potential for industrial wastewater treatment applications.