Activating Peroxymonosulfate via Sulfur-Vacancy-Rich Co8FeS8: Unveiling the Pivotal Role of Singlet Oxygen in Glyphosate Degradation

Abstract

Developing advanced catalysts for the selective degradation of refractory organic pollutants is of great significance for environmental remediation. Herein, we report a sulfur-deficient Co8FeS8 catalyst derived from bimetallic zeolitic imidazolate frameworks (ZIFs) via a combined sulfurization and hydrogen–argon thermal etching strategy. Systematic characterizations reveal that the introduction of sulfur vacancies modulates the electronic structure of Co8FeS8, creating abundant unsaturated active sites. The optimized sulfur-deficient Co8FeS8 exhibits exceptional performance in activating peroxymonosulfate (PMS) for the degradation of glyphosate, a representative organophosphorus pollutant. Mechanistic investigations, including quenching experiments and electron paramagnetic resonance (EPR) spectroscopy, demonstrate that singlet oxygen (1O2) is the dominant reactive oxygen species responsible for glyphosate oxidation. Notably, a strong positive correlation is established between the 1O2 concentration and the glyphosate degradation efficiency, highlighting the pivotal role of 1O2 in the catalytic process. Density functional theory (DFT) calculations further reveal that the phosphonate group (−PO(OH)2) of glyphosate exhibits the highest Fukui index, rendering it the preferential attack site for electrophilic 1O2, which is consistent with the degradation intermediates identified by LC–MS analysis. The nonphytotoxic nature of the treated water was further validated by pea germination assays: the germination rate increased from 55% in the pristine glyphosate solution to 87%, approaching the 90% observed for ultrapure water. Moreover, efficient phosphorus removal from the degraded water was implemented, thereby completely eliminating the risk of secondary pollution from phosphorus enrichment in aquatic systems. This work not only provides a defect engineering strategy for designing efficient PMS activators but also offers mechanistic insights into the selective oxidation of organophosphorus pollutants via nonradical pathways.