Enhanced degradation of triclosan by cobalt manganese spinel-type oxide activated peroxymonosulfate oxidation process via sulfate radicals and singlet oxygen: Mechanisms and intermediates identification

Abstract

Spinel is a kind of desirable catalyst to activate peroxymonosulfate (PMS) for chemical oxidation of organic contaminants in wastewater treatment. However, apart from classic sulfate radical based AOPs (SR-AOPs), the generation and oxidative pathways of singlet oxygen (1O2) by Co/Mn spinels have been little explored in PMS catalysis. In this study, spinel-type oxide Co2Mn1O4 was successfully synthesized, and used as highly effective catalyst in PMS activation for heterogeneous degradation of TCS (up to 96.4% within 30 min) at initial pH of 6.8, which was also slightly impacted by coexisting ions. Based on radical scavengers and electron paramagnetic resonance (EPR) experiments, sulfate radicals and singlet oxygen (1O2) were unveiled to be the dominant reactive oxygen species (ROS) in Co2Mn1O4/PMS system. Co2Mn1O4 catalyst exhibited reversible redox properties based on the results of cyclic voltammetry (CV). More importantly, the generation of 1O2 might not only promote the TCS removal rate directly, but also facilitate the metal redox cycle in spinel structure in Co2Mn1O4/PMS system. Finally, degradation pathways of TCS in Co2Mn1O4/PMS system were proposed, which involved the breakage of ether bond and cycloaddition reaction.