Efficient degradation of PFOA by peroxymonosulfate activated with sulfurized nanoscale zero-valent iron: Synergistic radical and non-radical pathways

Perfluorooctanoic acid (PFOA) resists conventional oxidation due to its strong C-F bonds. We hypothesized that sulfurization might improve zero-valent iron’s ability to activate peroxymonosulfate (PMS) for PFOA degradation. Here we show that a hydrothermally synthesized sulfurized nanoscale zero-valent iron (S-nZVI, S: Fe = 1: 10) coupled with PMS degraded PFOA (1 mg/L) and released fluoride during a 360 min reaction. The S-nZVI/PMS system substantially outperformed PMS or S-nZVI alone. After 360 min, the residual PFOA fraction fell to ~ 0.15, and fluoride release reached 47.33% (17.1 µM F − , 0.326 mg/L) - evidence of C-F bond cleavage. Higher PMS dosage improved degradation; the optimal S-nZVI loading was near 0.5 g/L. Acidic conditions favored the reaction. Mechanistic experiments (quenching, oxygen-control, ROS analysis, PMS consumption and EPR) indicated a radical/non-radical hybrid process involving •OH/SO 4 •− -type radical reactions, O 2 •− -related chemistry and a 1 O 2 -mediated non-radical pathway. Shorter-chain intermediates (PFHpA, PFHxA, PFPeA and PFBA) confirmed stepwise chain shortening, while fluorine mass balance showed that fluoride, residual PFOA and detected intermediates accounted for most of the initial fluorine. Real waters (tap and surface water) inhibited the reaction due to dissolved organic matter and inorganic ions, yet the system still removed about half of the PFOA. S-nZVI remained active over multiple cycles and also degraded GenX, albeit more slowly than PFOA. These results identify sulfurized nZVI as a promising PMS activator for PFAS treatment under environmentally relevant conditions.