Unexpected chloride-triggered organics removal in the zirconium oxide activated peroxymonosulfate system

Chloride ion (Cl-) is ubiquitous in diverse water bodies, yet poses a longstanding challenge in water pollution control by hindering the efficiency of pollutant degradation. Herein, we proposed a novel concept involving the direct utilization of endogenous Cl- ions in water for rapid water purification within a non-redox zirconium oxide (ZrO2)-activated peroxymonosulfate (PMS) system. In this process, PMS was complexed on the ZrO2 surface through inner-sphere coordination, and effectively activated by the partial electron cloud deviation from Zr(IV) sites to PMS, thereby forming a metastable surface complex with an elevated redox potential. Afterwards, the coexistence of Cl- could trigger the transformation of the reactive complex into free chlorine species, thus leading to a 255.0-fold enhancement in the elimination rate of micropollutants compared with the ZrO2/PMS system. Quantitative structure-activity relationship analysis revealed that the ZrO2/PMS/Cl system displayed strong target-dependence towards electron-rich compounds, showcasing a faster oxidation rate for pollutants with higher E-HOMO energy levels. Significantly, the novel system performed robust resistance to complex water matrices, achieved low oxidant consumption for pollutant removal, and demonstrated adaptation across a broad range of Cl- concentrations (1.0-100.0 mM). Overall, our findings provide new mechanistic insights into the influence of Cl- ions on PMS activation, which refresh the understanding of the role of Cl ions on pollutant degradation, and help to guide the treatment design for chloride-containing wastewater.