Generation mechanism of singlet oxygen from the interaction of peroxymonosulfate and chloride in aqueous systems.

Peroxymonosulfate (PMS, HSO) is a widely-used disinfectant and oxidant in environmental remediation. It was deemed that PMS reacted with chloride (Cl) to form free chlorine during water purification. Here, we demonstrated that singlet oxygen (O) was efficiently generated from PMS and Cl interaction. Mechanism of O formation was uniquely verified by the reaction of HSO and chlorine molecule (Cl) and the oxygen atoms in O deriving from the peroxide group of HSO were revealed. Density functional theory calculations determined that the reaction of HSO and Cl was thermodynamically favorable and exergonic at 37.8 kcal/mol. Quite intriguingly, O was generated at a higher yield (1.5 × 10 M   s  ) than in the well-known reaction of HO with Cl (35 M   s  ). Besides chlorine, O formed in PMS-Cl interaction dominated the degradation of micropollutants, also it substantially enhanced the damage of deoxynucleoside in DNA, which were beneficial to micropollutant oxidation and pathogen disinfection. The contribution of O for carbamazepine degradation was enhanced at higher Cl level and lower pH, and reached 96.3% at pH 4.1 and 5 min. Natural organic matter (NOM) was a sink for chlorine, thereby impeding O formation to retard carbamazepine degradation. O also played important roles (48.3 - 63.5%) on the abatement of deoxyguanosine and deoxythymidine at pH 4.1 and 10 min in PMS/Cl. On the other hand, this discovery also alerted the harm of O for human health as it can be formed during the interaction of residual PMS in drinking water/swimming pools and the high-level Cl in human bodies.