Degradation of organic contaminants in the CoFe2O4/peroxymonosulfate process: The overlooked role of Co(II)-PMS complex

Cobalt ferrite (CoFe 2 O 4 ) has been widely employed as a catalyst for the activation of peroxymonosulfate (PMS), in which hydroxyl radicals ( • OH) and sulfate radicals (SO 4 •− ) are generally recognized as the main reactive species responsible for the degradation of pollutants. In this study, we find that both one-electron transfer and oxygen-atom transfer reactions are involved in the CoFe 2 O 4 /PMS process, by using methyl phenyl sulfoxide (MPSO) as a chemical probe. Results from radical quenching and electron paramagnetic resonance (EPR) experiments indicate that the free radicals (i.e., • OH and SO 4 •− ) play only a minor role in the degradation of sulfamethoxazole (SMX). A mechanism involving Co(II)-PMS complex both on the surface of CoFe 2 O 4 and in solution as the dominant reactive species is proposed. Furthermore, the degradation performance of SMX under different conditions were investigated to further cognize the Co(II)-PMS complex-mediated oxidation process. This study broadens our understanding of the role of transition metal-based catalysts in the activation of PMS for the degradation of organic pollutants.