Synergistic hydroxyl and chlorine radicals in contact-electro-catalysis for sustainable PFAS remediation

Contact-electro-catalysis (CEC) provides a promising route for per- and polyfluoroalkyl substances (PFAS) remediation, yet the mechanistic role of chloride ions (Cl^-) in real water matrices remains unclear. Here, we demonstrate that Cl^- markedly enhances removal of perfluorooctanoic acid, perfluorooctanesulfonic acid, hexafluoropropylene oxide dimer acid, perfluorononyloxybenzene sulfonate, and 6:2 fluorotelomer sulfonate, achieving 97.04 -99.99% degradation and 96.90 -99.98% defluorination within 120 min at 200 mM Cl^-. These rates were 1.43-2.29-fold higher than Cl^--free systems. Mechanistic analyses reveal that hydroxyl radicals (^•OH) oxidizes Cl^- to generate chlorine radicals (Cl^•), which selectively attack the carboxylate group of PFAS, enabling thermodynamically favorable decarboxylation followed by mineralization. Unlike conventional electrochemical methods, the Cl^•-mediated pathway avoids oxychlorine and chlorinated byproducts. Zebrafish embryo assays further confirmed negligible toxicity of treated solutions. These results establish a sustainable paradigm that achieves high defluorination efficiency and operational safety, offering strong potential for PFAS remediation in saline and industrial waters.