Degradation of an Emerging PFAS Compound-Sodium <i>p</i> -Perfluorous Nonenoxybenzenesulfonate via Phosphate-Enhanced Activation of Peroxymonosulfate by Trace Co(II)

Sodium p-perfluorous nonenoxybenzenesulfonate (OBS), an emerging per- and polyfluoroalkyl substance (PFAS), exhibits high environmental persistence and biological toxicity, highlighting the urgent need for effective removal strategies. In this study, we developed an efficient homogeneous system in which trace Co(II) activates peroxymonosulfate (PMS) with phosphate assistance for the rapid degradation of OBS. The HPO42– ligand modulated the electronic structure of the cobalt center, thereby enhancing PMS bonding and activation. 99.2% of OBS was degraded within 60 min, with an observed rate constant of 0.109 min–1, which was 15.6 times higher than that of the Co(II)/PMS system without phosphate (0.007 min–1). Hydroxyl radicals and sulfate radicals were identified as the dominant reactive species, with steady-state concentrations of 4.1 × 10–13 M and 1.5 × 10–11 M, respectively. Four possible degradation pathways of OBS were proposed based on quantum chemical calculations and ultrahigh-resolution mass spectrometry analysis. This study not only provides a feasible strategy for the removal of emerging PFAS but also offers mechanistic insights into phosphate-promoted trace Co(II) activation of PMS.