Upgrading Type-II Heterojunction to S-Scheme Heterojunction for Enhanced Photocatalytic Toluene Oxidation Performance

Construction of heterojunctions has been extensively applied to enhance the catalytic performance of TiO₂-based semiconductor photocatalysts in the oxidation of volatile organic compounds (VOCs). However, improper charge transfer directions in type-II heterojunctions often result in inadequate redox reactions for O₂/·O₂ ^- and OH^-/·OH at lower potentials. In this study, a three-component heterojunction with multi-stage S-Scheme charge transfer was constructed by a self-assembled growth strategy, where CeO₂ and WO₃ were strategically deposited onto TiO₂ nanosheets and applied to the photocatalytic oxidation of toluene. Catalytic performance evaluation revealed that the Ce-W/TiO₂ heterojunction significantly enhanced the photocatalytic oxidation activity of toluene. Notably, Ce-W/TiO₂ reached a mineralization rate of 98.4%, surpassing most other catalysts. Further systematic characterizations and theoretical calculations demonstrated that the incorporation of CeO₂ and WO₃ not only broadened the photoresponse range but also optimized the charge transfer and surface reaction kinetics, thereby enabling the highest photocatalytic toluene oxidation activity on Ce-W/TiO₂. This work highlighted the critical role of charge transfer pathways in TiO₂-based semiconductor photocatalysts for toluene oxidation and provided valuable insights for the rational design of highly efficient photocatalysts for VOCs mineralization through heterojunction engineering.