High-valent cobalt-oxo species triggers hydroxyl radical for collaborative environmental decontamination

The overlooked role of high-valent cobalt-oxo species (Co(IV)) in the Co(II)/peroxymonosulfate (PMS) process was uncovered recently using methyl phenyl sulfoxide (PMSO) as the probe. Herein, we further interestingly found that Co(IV) could trigger hydroxyl radical (•OH) formation, resulting in the oxidized products distribution of PMSO heavily relied on the relative concentration of PMSO. More significantly, the generation of a series of 18O-labeled hydroxylated products (i.e., hydroxylated methyl phenyl sulfone, nitrobenzene and 4-nitrobenzoic acid) in H218O conclusively verified that •OH was triggered by Co(IV) species. Density functional theory calculation demonstrated that Co(IV) initiated •OH formation via oxo ligand protonation-induced valence tautomerization. Moreover, the oxidative contribution of Co(IV) and •OH on organic degradation was specifically dependent on the type and concentration of the substrate. This study provided deeper insights into the evolution pathway of •OH mediated by Co(IV) species and enriched the understandings on the collaborative oxidation mechanism in Co(IV)-involved processes.