Highly stable Cu doped SnO2/TiO2 photocatalyst enables selective 3e− ORR-driven •OH generation for robust GenX removal

Abstract

In this study, the photocatalytic degradation efficiencies of GenX using SnO<inf>2</inf>/TiO<inf>2</inf> composites and their Cu-doped counterparts were investigated. Although SnO<inf>2</inf> and TiO<inf>2</inf> separately exhibited limited GenX removal, the SnO<inf>2</inf>/TiO<inf>2</inf> composite demonstrated significantly enhanced activity, which was further boosted by aeration. Cu doping at 2 wt% [Cu(2 %)-SnO<inf>2</inf>/TiO<inf>2</inf>] magnified the GenX (Hexafluoropropylene oxide dimer acid; HFPO-DA) removal efficiency (96.4 %) with superior kinetics (0.399 min−1) and stability. Various characterization results revealed that Cu doping induced a type II heterojunction, facilitating electron transfer from TiO<inf>2</inf> to SnO<inf>2</inf> and ultimately to Cu<inf>2</inf>O. Cu(2 %)-SnO<inf>2</inf>/TiO<inf>2</inf> exhibited a unique band structure with a lower conduction band minimum and higher valence band maximum, which suppressed photocorrosion while promoting reactive oxygen species generation, particularly •OH. This was evidenced by the enhanced H<inf>2</inf>O<inf>2</inf> production, increased photocurrent density, and decreased charge recombination, as confirmed by time-resolved photoluminescence analysis. Notably, Cu doping altered the electron transfer pathway, favoring a 3-electron oxygen reduction reaction for efficient •OH production. In situ surface-enhanced Raman spectroscopy analysis revealed dynamic changes in the electronic structure of Cu(2 %)-SnO<inf>2</inf>/TiO<inf>2</inf> upon O<inf>2</inf>, UV-LED (400 nm), and H<inf>2</inf>O<inf>2</inf> exposure, further supporting the proposed mechanism. These findings demonstrate that Cu doping at optimal levels significantly enhances the photocatalytic activity and stability of SnO<inf>2</inf>/TiO<inf>2</inf> composites for efficient GenX degradation. © 2025 Elsevier B.V.