Effect of Cl- on activated peroxymonosulfate based advanced oxidation process: Transformation of radicals and mechanism of singlet oxygen generation

The introduction of chloride (Cl-) triggers a series of chain radical/non-radical reactions in the advanced oxidation process, including the formation of singlet oxygen (O-1(2)). However, the mechanism of O-1(2) generation remains unclear. This study investigated the transformation mechanisms of reactive species and the impact on pollutant abatement based on a Cl--mediated simulated solar/peroxymonosulfate process. Thermodynamic calculations confirmed that the reaction between HSO5- and ClO center dot was the principal pathway for O-1(2) generation, which involved a nucleophilic attack of the oxygen atom in the peroxide group on the chloride atom in ClO center dot. The reaction rate was calculated to be 8.5 x 1010 M-1 s(-1) based on the transition state theory. Major reactive species, including HO center dot, SO4 center dot-, Cl-center dot, Cl-2(center dot-), ClO center dot, and O-1(2) were confirmed and quantified by probes kinetics. Analysis of the products via Q-TOF-MS/MS suggested that HO center dot and SO4 center dot- interacted with acetaminophen through an addition, while reactive chlorine radicals would through electron transfer. Furthermore, the abatement ability of the reaction system for micropollutants was investigated based on real water and solar irradiation. Overall, this study enhances understanding of O-1(2) generation and contaminant transformation in the Cl--mediated solar/PMS process, both from theoretical and practical applications.