Improving PMS oxidation of organic pollutants by single cobalt atom catalyst through hybrid radical and non-radical pathways

Highly efficient single-atom catalysts attracted much research interest recently. Here we investigated the mechanism and application potential of a single cobalt atom catalyst (Co-N-C) in improving peroxymonosulfate (PMS) oxidation of several organic pollutants. With low cobalt content (0.45 at%), the Co-N-C was more active than Co₃O₄ for catalytic oxidation, and the PMS/Co-N-C oxidation achieved high pollutant removal rates over 60 h’ continuous flow reaction. Degradation of the selected pollutants followed distinct radical and non-radical pathways. Radical reaction dominated for the degradation of benzotriazole and diatrizoate ; in comparision, non-radical oxidation was also significant during the degradation of 5-benzoyl-4-hydroxy-2-ethoxybenzenesulfonic acid and 2,4-dichlorophenol (2,4-DCP). The PMS/Co-N-C utilized more PMS oxidation capacity than PMS/Co²⁺ (100% vs. 86%) for the degradation of 2,4-DCP. The non-radical oxidation cannot be ascribed to singlet oxygen which has been frequently reported. The hybrid reaction pathways will make this PMS/Co-N-C oxidation process promising in removing complex water pollutants.