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.