Driving S-scheme charge transfer via Fermi level disparity: efficient toluene mineralization over oxygen vacancy engineered Bi2WO6 coupled with TiO2

Photocatalytic degradation is a sustainable strategy for the remediation of stable aromatic volatile organic compounds such as toluene. Yet, the energy-efficient mineralization of these pollutants under ambient conditions remains a critical bottleneck. Herein, an n–n S-scheme heterojunction photocatalyst is constructed via in situ hydrothermal coupling of TiO 2 with oxygen-vacancy-engineered Bi 2 WO 6 (TB-x: x represents the TiO 2 /Bi 2 WO 6 molar ratio). A work function difference of 0.39 eV induces band bending and an internal electric field from Bi 2 WO 6 to TiO 2 , enabling an efficient S-scheme charge transfer pathway. Consequently, the optimized TB-2 exhibits a longer charge carrier lifetime (21.1 ps) than the pristine components. In a fixed-bed flow system, TB-2 achieves 97.2% degradation of 5 ppm toluene within 60 min under UV irradiation, delivering a high dynamic clean air delivery rate (1940 L h −1 g −1 ) and an apparent quantum yield of 0.1%, with high stability across reuse cycles and under varying humidity conditions. In situ DRIFTS, EPR, and DFT analyses reveal a stepwise oxidation pathway via benzyl alcohol and benzaldehyde intermediates, ultimately forming CO 2 and H 2 O. This work highlights the critical role of interfacial band engineering in constructing an efficient air purification system based on direct mechanistic evidence for oxygen-vacancy-assisted S-scheme charge transfer in TiO 2 /Bi 2 WO 6 heterojunctions.