New insight into the activation mechanism of peroxymonosulfate by N, O-doped carbonaceous materials: Active sites, intermediates, and pathways

Persulfates activation by N,O-doped carbonaceous materials is an emerging advanced oxidation process for removing organic pollutants from water. However, the specific activation mechanisms including active sites, intermediates, and pathways are unknown. We prepared a N,O-doped carbocatalyst (NOGM) as model material to unveil the activation mechanism. Reaction occurred on the surface. After ruling out oxyl radicals, singlet oxygen, persistent free radicals, and through-surface direct electron transfer, a two-electron (nucleophilic-electrophilic) reaction involving short-lived bound PMS species or PMS-transformed surface groups was found to be the most likely pathway. Pre-contact of NOGM with PMS generates bound -OO- groups and causes major transformations of surface functionality identified in unprecedented detail. Results indicate that imine-type edge-N (A-1 and A '-1) would be the possible active sites and oxaziridine (neutral and charged) is possible active intermediates. Activation pathways are proposed. This study goes far in providing a strategy for designing new carbonaceous materials with high efficiency for activation peroxides.