Insights into a newly discovered mechanism for 1O2 formation in a chlorine ion-mediated sulfate radical-advanced oxidation process system for levofloxacin degradation in an aqueous solution

The dual effect of chloride anions (Cl−) on sulfate radical-advanced oxidation process (SR-AOP) systems has recently garnered increasing attention, particularly the inhibitory effects of Cl− on the degradation of organic pollutants. However, few studies have characterized the promoting effect of Cl− on SR-AOPs. Our study investigated the effect of Cl− on the degradation of levofloxacin (LVF) in peroxymonosulfate (PMS) with ZIF-67/VTM (Z-VTM) as an activator. With the addition of Cl−, singlet oxygen (1O2) was the dominant driver of LVF degradation in the Cl−/Z-VTM/PMS system, which differed from the dominant role of HOCl (generated from Cl−) in the degradation of organic pollutants in previous studies. To the best of our knowledge, our study is the first to describe the conversion of HOCl to 1O2 in a Cl−/Z-VTM/PMS system. 1O2 was effectively generated in Cl− containing water at a 3.0–9.0 pH range. This work provides novel insights into the formation of ROS from HOCl during the degradation of organic pollutants in SR-AOPs, which is of great significance for the removal of organic pollutants in wastewater with high salt concentrations.