Single oxidizable moiety enables complete defluorination of per- and polyfluoroalkyl substances in heat-activated...

Despite decades of research on the degradation of polyfluoroalkyl substances (PFAS) by heat-activated peroxydisulfate (PDS), a generalizable, structure-based predictive framework has remained elusive. Herein, we propose that the susceptibility of PFAS to complete defluorination by activated PDS is mechanistically determined by the presence of a single oxidizable moiety, including carboxylate (-CO₂^-), alkyl (-CH or -CH₂-), alkenyl (C=C), and (sulfon)amides (-CON- or -SO₂N-) groups. This principle was validated using 26 PFAS representative of the dominant structures encountered in contaminated environments, with near complete defluorination within 8 h at 85 °C. The defluorination efficiency was independent of oxidizable moiety position, perfluoroalkyl chain length, or the presence of non-oxidizable substituents. Mechanistic analyses reveal moiety-specific initiation pathways and distinct roles for reactive oxidants. Notably, SO₄^•- is not the primary oxidant but a precursor to ^•OH (via reaction with H₂O) and HSO₄^• (via protonation). Alkyl, alkenyl, and (sulfon)amide PFAS are first transformed by ^•OH into perfluoro(di)carboxylates before further defluorination by HSO₄^•, whereas HSO₄^• attack on -CO₂^- in parent PFAS and carboxylate intermediates is the rate-limiting defluorination step. This process was effective across wide concentration ranges and exhibited favorable energy consumption relative to established destructive technologies. Although ineffective for perfluoroalkyl sulfonic acids and their Cl/O derivatives, these findings establish an oxidizable-moiety framework that provides actionable guidance for broad PFAS remediation and the rational design of inherently degradable structures.