Insights into the pollutant electron property inducing the transformation of peroxymonosulfate activation mechanisms on manganese dioxide

Herein, using manganese dioxide octahedral molecular sieve (Mn-OMS) as the catalyst, we investigate how pollutant electron property affects the peroxymonosulfate (PMS) activation mechanism. More than 95% of electron-rich pollutants are degraded in the Mn-OMS/PMS system after 30 min reaction time, but oxidative decomposition of electron-poor pollutants takes at least 150 min. This difference in reaction rate is proved to be pollutant-dependent. We then combine multiple methods to cross-validate the PMS activation mechanism, including the quenching test, EPR characterization, solvent-exchange experiment, PMS decomposition rate test, and electrochemical analysis. Catalyst-mediated electron transfer is determined as the main activation mechanism for electron-rich pollutants degradation, while removal of electron-poor pollutants relies on singlet oxygen (1O2) and/or radicals. Additionally, the PMS activation mechanism depends on whether H2O or pollutants or low-valence Mn ions preferentially transfer electrons to the adsorbed PMS. This work provides mechanistic insights into the effect of pollutants type on PMS activation.