The overestimated role of singlet oxygen for pollutants degradation in some non-photochemical systems

Singlet oxygen (¹O₂) is considered as the dominant reactive oxygen species (ROS) responsible for micropollutants degradation in many non-photochemical systems. However, the role of ¹O₂ in non-photochemical systems is overrated due to overlooking the fast quenching of ¹O₂ in water and the false positive results of electron paramagnetic resonance (EPR) experiments for ¹O₂ identification. Herein, we systematically compared the classical ¹O₂-generation H₂O₂/OCl⁻ system and some non-photochemical systems in pollutants oxidation, electron paramagnetic resonance (EPR) experiments and dimol emission of singlet oxygen in different solvents for the first time. The results showed that almost all ¹O₂ were deactivated by water and hardly consumed by micropollutants in non-photochemical systems considering the high deactivation rate constant of ¹O₂ in water. Moreover, the EPR signals of TEMPO free radical detected in non-photochemical systems may not precisely represent the existence of ¹O₂. These results indicated that some others ROS rather than ¹O₂, for example, dioxiranes in the ketone-catalysed decomposition of peroxomonosulfate (PMS), were responsible for the degradation of micropollutants in some non-photochemical systems, and further investigation about the real ROS are needed.