Interfacial electron transfer and hydroxyl radical pathways in sulfate-enhanced perfluorobutanoic acid degradation on...

Electrochemical oxidation on boron-doped diamond (BDD) anodes is effective for per- and polyfluoroalkyl substances (PFAS) removal, yet the role of supporting electrolytes in regulating PFAS transformation at the anodic interface remains unclear. Here, perfluorobutanoic acid (PFBA) was used as a representative short-chain PFAS to evaluate electrochemical degradation in BDD systems with five common electrolytes. Na₂SO₄ exhibited the highest PFBA removal and defluorination efficiencies, with an apparent rate constant 1.6 and 2.6 times those of the Na₂S₂O₈ and NaNO₃ systems, respectively. The Na₂SO₄ system also maintained degradation efficiencies above 96% across initial PFBA concentrations from 4.67 × 10^-4 to 4.67 × 10^-1 mM. Evidence indicates that sulfate enhancement is not primarily governed by sulfate-radical or persulfate-mediated pathways, but arises from interfacial regulation at the BDD anode. Specifically, sulfate regulates the electrode-solution interface, suppresses oxygen evolution, facilitates anodic direct electron transfer to initiate PFBA oxidation, and sustains effective •OH participation in the subsequent chain defluorination process. Non-target screening, targeted quantification, and in situ analysis support a decarboxylation-initiated pathway involving CF₂O formation and stepwise defluorination. These findings provide mechanistic insight for electrolyte selection and interfacial design in electrochemical PFAS treatment systems.