Underestimated Role of Surface-Bound Peroxymonosulfate and Overestimated Role of SO ₄ ^•– and ¹ O ₂ in Peroxymonosulfate Activation with Metal Oxides

Peroxymonosulfate (PMS) activation with metal oxides is promising for removing organic pollutants, but the key reactive species remains ambiguous. Herein, Co, Ni, and Mn oxides and their composite oxides were investigated as PMS catalysts for phenol degradation. The generated reactive species were identified by various methods, and the effects of scavengers on phenol degradation and PMS consumption were examined. The results indicated that the degradation efficiencies of phenol were independent of the amount of SO4•– and 1O2. Ethanol and furan methanol showed a strong inhibitory effect on Co-based oxides but had a slight effect on Ni-based oxides. This can be ascribed to the higher oxidation potential of Co-PMS (surface-bound PMS) than that of Ni-PMS. Co-PMS can react readily with ethanol and furan methanol, resulting in the false assignment of an important role of SO4•– and 1O2. Me-PMS was significantly underestimated and should be the crucial reactive species for these oxides. Both Co-PMS and Ni-PMS were efficient in the removal of various organic pollutants. Investigating Me-PMS and PMS consumption is necessary for the identification of reactive species. We reckon that this study is useful for avoiding the misapplication of the quenching method and the misunderstanding of the PMS activation mechanism.