Photocatalytic Degradation of PFOA using Pt/La2Ti2O7 Catalyst: Roles of Electron Donors in Reductive Defluorination

Per- and polyfluoroalkyl substances (PFAS) have emerged as a major concern in aquatic systems worldwide due to their widespread applications and health concerns. Perfluorooctanoic acid (PFOA) is one of the most-detected PFAS. Yet, an effectively and economically technology has been lacking for effective degradation of PFAS due to their resistance to conventional treatment processes and advanced oxidation processes (AOPs). To address this challenge, we prepared a novel reductive photocatalyst, Pt/La₂Ti₂O₇, based on the La-Ti oxide material that has a unique 2D perovskite layered structure and high photo-reductive activity under UV irradiation. The composite material exhibited a synergistic effect of electrocatalytic and photocatalytic activity that resulted in effective degradation of PFOA in water. Pt/La₂Ti₂O₇ was able to adsorb PFOA, thereby effectively concentrating the target contaminant on the photoactive sites. Subsequently, Pt/La₂Ti₂O₇ with methanol as the electron donors degraded >40% of PFOA in 3 h under UV irradiation (254 nm, 1000 μW cm⁻², initial PFOA: 50 ppb). Different external electron donors (e.g., methanol, oxalic acid and formic acid ) were comparatively studied to aid the trapping of photo-generated h⁺ and the separation of charge carriers and production of hydrated electrons (e_aq⁻) for the reductive degradation of PFOA. The density functional theory (DFT) revealed that Pt as a co-catalyst on La₂Ti₂O₇ narrowed the band gap from 2.75 to 2.25 eV and accelerated interfacial electron transfer, which may partially explain the enhanced photocatalytic reductive degradation of PFOA. Compared to the traditional photocatalytic oxidation, this UV/Pt/La₂Ti₂O₇/CH₃OH system offered another efficient solution for the removal of PFOA and potentially other PFAS in water using the photocatalytic formation of hydrated electrons (e_aq⁻), which elicit superior photocatalytic reduction of polyhalogenated or perhalogenated organic compounds owing to its negative standard reduction potential of -2.9 V.