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.