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

Abstract

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.