Electrooxidation of perfluorooctanesulfonic acid on porous Magnéli phase titanium suboxide Anodes: Impact of porous structure and composition

Destruction of per- and polyfluoroalkyl substances (PFASs) in water is of great interest for water and wastewater treatment purposes. This study examined the electro-oxidative degradation of a representative PFAS, perfluorooctanesulfonic acid (PFOS), on different porous Magnéli phase titanium suboxide (TSO) anodes, with energy efficiency compared in both batch and reactive electrochemical membrane (REM) systems at different operation conditions. The anode materials are of different primary compositions (Ti4O7 or Ti9O17) and have different porous structures. The experiment results along with electrochemical characterization and density functional theory (DFT) computation reveal that the greater fraction of Ti3+ ion in Ti4O7 than that in Ti9O17 enhances the anodic reactivity by increasing the affinity of PFOS and reducing the energy barrier of direct electron transfer, leading to greater PFOS degradation efficiency. The data also suggest that the pores in the TSO anodes with sizes smaller than 1.03 μm do not contribute to their effective electroactive surface because of restrictive electrolyte transport, and thus may not contribute to PFOS degradation. The results of this study provide a basis for design and optimization of TSO-based electro-oxidative treatment of PFAS-contaminated waters.