F-Doped Porous Ti/SnO ₂ –Sb Electrode for Electrochemical Oxidation of Fluorinated and Nonfluorinated Surfactants: Impact on Direct and Indirect Oxidation

Electrochemical advanced oxidation is a promising green solution for waterborne organic contaminant control, and its degradation performance is closely related to the characteristics of the anode material. In this study, we fabricated a novel F-doped Ti/SnO2–Sb electrode with tailored surface properties to investigate how pollutant-anode interactions influence the overall degradation performance. Compared with the pristine Ti/SnO2–Sb electrode, the F-doped Ti/SnO2–Sb electrode exhibited a highly porous structure, enhanced hydrophobicity, and an increased oxygen evolution reaction overpotential. The type of cation in the fluoride salt used for doping, as well as the calcination temperature and duration in the electrode preparation, was found to influence the formation of the porous structure. Two representative surfactants, perfluorooctanoic acid (PFOA) and sodium dodecyl sulfate (SDS), with widespread occurrence and well-documented electrochemical degradation mechanisms, were selected as the model pollutants to evaluate the performance of both F-doped and pristine Ti/SnO2–Sb electrodes. Interestingly, the porous, hydrophobic F-doped electrode exhibited opposite effects on the degradation of PFOA and SDS. While its higher surface area and enhanced hydrophobicity greatly promoted hydroxyl free radical generation and hence SDS degradation via the indirect oxidation pathway, the F-doped electrode exhibited a lower degradation rate of PFOA compared to the pristine electrode, presumably due to the higher surface hydrophobicity, which hindered direct electron transfer from the carboxyl group of PFOA to the anode. The distinct degradation behaviors observed with SDS and PFOA highlight the important role of the interactions between the anode and the target organic contaminants in electrochemical advanced oxidation.