Discerning\nthe Relevance\nof Singlet Oxygen in Pollutant\nDegradation in Peroxymonosulfate Activation Processes

Abstract

Significant efforts have recently\nbeen exerted toward\nconstruction\nof singlet oxygen (¹O₂)-dominated catalytic\noxidation systems for selective removal of organic contaminants from\nwastewater, with peroxides serving as the chemical source. However,\nthe relevance of ¹O₂ in the removal of pollutants\nremains ambiguous and requires elucidation. In this study, we scrupulously\nexclude the significant role of ¹O₂ in contaminant\ndegradation in various peroxymonosulfate (PMS) activation systems.\nMultiple experimental results indicate that the activation of PMS\ncatalyzed by CuO, MnO₂, Fe-doped g-C₃N₄ (Fe–CN), or N-doped graphite does not predominantly follow\nthe ¹O₂ pathway. More importantly, the reactivity\nof ¹O₂ is remarkably overestimated in the literature,\ngiven its inferior capacity in degradation of a range of heterocyclic\ncontaminants and aromatic compounds possessing electron-withdrawing\ngroups. In addition, the strong physical quenching effect of water,\ncoupled with the low oxidizing ability of ¹O₂, would notably reduce the utilization efficiency of peroxide, which\nis particularly apparent in the degradation of micropollutants. We\nreckon that this study is expected to end the long-running dispute\nassociated with the relevance of ¹O₂ in pollutant\nremoval.