Mn-Co bimetallic spinel catalyst towards activation of peroxymonosulfate for deep mineralization of toluene: The key roles of SO4 center dot- and O2 center dot- in the ring-opening and mineralization of toluene

Developing novel method that can deeply mineralize low concentration volatile organic compounds (VOCs) under ambient temperature is still a challenge. This study fabricates a nonstoichiometric Mn-Co bimetallic spinel catalyst, MnCo2O4.5, which exhibits excellent activity towards peroxymonosulfate (PMS) activation and superior to other similar advanced oxidation processes (AOPs) in mineralization of toluene. The crystalline phase, microstructure and composition of the catalyst were revealed by a series of characterization methods. The MnCo2O4.5/PMS system can stably remove 97.3 % of toluene over 25 h with less PMS dosage, and the CO2 selectivity reaches 85.3 %, its CO2 yield is 2.8 and 6.4 times as many as those of Co3O4 and MnO. MnCo2O4.5 also exhibits a good pH adaptivity (pH = 3-7) and highly chemical stable in acidic conditions, with low metals leaching rate and excellent reusability. Electron paramagnetic resonance (EPR) and radical quenching tests reveal the radicals' contributions to the conversion and mineralization of toluene, i.e. SO4 center dot- > O2 center dot- > HO center dot >1O2 and O2 center dot- > 1O2 > HO center dot > SO4 center dot-, respectively. Combined the gas chromatography-mass spectrometry (GC-MS) analyses and quantum chemical calculation, the toluene degradation routes induced by HO center dot and SO4 center dot- were detailedly summarized. This novel mild method provides a new thought on the development of low-temperature VOCs control technologies.