Achieving a balance between catalytic activity and stability of MnCo₂O₄ for sustainable flow-through wastewater treatment in peroxymonosulfate-advanced oxidation process

Catalytic fixed-bed/membrane systems using the peroxymonosulfate-advanced oxidation process (PMS-AOP) are promising for organic wastewater treatment due to their high efficiency and operational convenience. In this study, a modulating strategy based on calcination temperature was developed to balance the catalytic activity and stability of MnCo₂O₄ during its pyrolysis synthesis, meeting the requirements for both high flux and durability in catalytic fixed-bed/membrane systems. As the calcination temperature increased, the average crystal size of MnCo₂O₄ grew from 100 to over 200 nm, resulting in a 57 % reduction in catalytic activity for PMS activation and methyl orange (MO) degradation but an improvement in catalytic stability. A balance point at the calcination temperature of 800 °C was identified in the activity-structure relationship. The PMS-AOP system with MnCo₂O₄ calcined at 800 °C exhibited a degradation rate constant of 0.614 (mg·L⁻¹)⁻¹·min⁻¹ for MO and achieved a mineralization degree of 64 %, maintaining effectiveness after 20 catalytic cycles. Mechanistic analysis revealed that Co and Mn sites, along with oxygen vacancies on the MnCo₂O₄ surface, acted as catalytic centers for PMS activation, generating reactive oxygen species. A catalytic fixed-bed assembling by MnCo₂O₄ achieved over 95 % MO degradation and a 35 % mineralization degree during a continuous 150-hour filtration process, which was one of the most stable catalytic reactors in flow-through organic wastewater treatment. This study presents a practical approach to balancing the catalytic activity and stability of MnCo₂O₄, contributing to the development of high-efficiency and sustainable catalytic fixed-bed/membrane systems for organic wastewater treatment.