Discerning the Relevance of Singlet Oxygen in Pollutant Degradation in Peroxymonosulfate Activation Processes

Significant efforts have recently been exerted toward construction of singlet oxygen (¹O₂)-dominated catalytic oxidation systems for selective removal of organic contaminants from wastewater, with peroxides serving as the chemical source. However, the relevance of ¹O₂ in the removal of pollutants remains ambiguous and requires elucidation. In this study, we scrupulously exclude the significant role of ¹O₂ in contaminant degradation in various peroxymonosulfate (PMS) activation systems. Multiple experimental results indicate that the activation of PMS catalyzed by CuO, MnO₂, Fe-doped g-C₃N₄ (Fe-CN), or N-doped graphite does not predominantly follow the ¹O₂ pathway. More importantly, the reactivity of ¹O₂ is remarkably overestimated in the literature, given its inferior capacity in degradation of a range of heterocyclic contaminants and aromatic compounds possessing electron-withdrawing groups. In addition, the strong physical quenching effect of water, coupled with the low oxidizing ability of ¹O₂, would notably reduce the utilization efficiency of peroxide, which is particularly apparent in the degradation of micropollutants. We reckon that this study is expected to end the long-running dispute associated with the relevance of ¹O₂ in pollutant removal.