Oxygen vacancies-dominated reactive species generation from peroxymonosulfate activated by MoO3−x for pollutant degradation

Interface oxygen vacancies (OVs) are commonly used to improve the catalytic performance of activators in persulfate-based advanced oxidation processes, but the underlying mechanism was not fully explored. This work reports a facile heat treatment method to regulate OVs in MoO3−x to elucidate the mechanism of peroxymonosulfate (PMS) activated by OVs to degrade 2,4,4-Trichlorobiphenyl (PCB28). Electron spin resonance, free radical quenching, X-ray photoelectron spectroscopy, and Raman spectroscopy confirmed that both reducing Mo species and OVs of MoO3−x surface were responsible for PMS activation. Further experiments and Density Function Theory (DFT) calculation suggest that OVs in MoO3−x induced the formation of superoxide radical (O2•−), and then O2•− was transformed into singlet oxygen (1O2) or mediated PMS activation to generate radicals, which contritbued to 70.2% of PCB28 degradation. The steady-state concentrations of free radical calculated with the kinetics model show that OVs were more favorable to mediate PMS to generate hydroxyl radicals (•OH) under oxic conditions, while reducing Mo species would like to induce PMS to produce sulfate radicals (SO4•−). Overall, this study is dedicated to a new insight into the in-depth mechanism of PMS activation by OVs-rich catalysts and provides a novel strategy for reactive species regulation in PMS based oxidation process.