Defect engineering-mediated Co₉S₈ with unexpected catalytic selectivity for heterogeneous Fenton-like reaction: Unveiling the generation route of ¹O₂ in V_S active site

Singlet oxygen (¹O₂) plays a crucial role in Fenton-like reactions due to its high efficiency and selectivity in removing trace organic pollutants from complex water matrices. Defect engineering, which allows the efficient exposure of active sites and optimization of electronic structures, has rapidly emerged as a fundamental strategy for enhancing ¹O₂ yield. Herein, we introduce tunable sulfur vacancy (V_S) density into Co₉S₈ catalysts for peroxymonosulfate (PMS) activation. The modulation of the octahedral Co (CoS₆) and tetrahedral Co (CoS₄) electronic structures by V_S triggers the unexpected selective generation of ¹O₂. The V_S/PMS system exhibits excellent resistance to interference and highly selective degradation of electron-donating organic pollutants. Experimental and theoretical calculations revealed a new evolutionary route for ¹O₂ involving two phases (Phase I: HSO₅⁻ → *O, Phase II: *O + HSO₅⁻ →*OO → ¹O₂). This study provides a molecular-level understanding of V_S-mediated catalytic selectivity for high-efficient decontamination applications.