New Insight into Singlet Oxygen Generation in the Mixed-Mode Activation Route of Peroxymonosulfate on an Oxygen-Vacant Zno/Co3o4 Interface

Abstract

While inert elements consistently enhance the catalysis of Co3O4 in peroxymonosulfate (PMS) activation, the precise mechanism behind this improvement remains unclear despite the understanding of their role in the formation of oxygen vacancies (OVs). Herein, we designed a simple pyrolysis process to synthesize OV-ZnO/Co3O4 heterojunctions featuring Zn−Co tetrahedral coordination near OVs at their interface. This heterojunction served as a model catalyst for studying the relationship between the generation of singlet oxygen (1O2) and the incorporation of Zn. Quenching experiments indicated that the generation of 1O2 was not solely dependent on free radical interactions. Theoretical calculations showed that the hydroxyl groups at the Zn site (Zn−OH) were reactivated following catalytic cleavage of the peroxo bond in PMS through extension of the hydroxy bond and increased polarization. This reactivation enabled Zn−OH to participate in the nonradical generation of 1O2. Consequently, the OV-ZnO/Co3O4 heterojunctions demonstrated superior catalysis in PMS-advanced oxidation processes (AOPs) compared to the corresponding mixture, particularly in the mineralization of organic wastewater. The system also showed acceptable stability, robust anti-interference capabilities, and potential for scale-up. This study provides new insights into the effects of inert element incorporation on PMS activation and informs the design of more effective catalysts for PMS-AOPs.

Keywords: Cobalt oxide, Inert species, advanced oxidation processes, Singlet oxygen, wastewater treatment