Bandgap-adjusted bismuth tungstate-titanium dioxide S-scheme heterojunctions: Optimizing interfacial electronic structure for rapid VOC mineralization

To strategically overcome the shortcomings of conventional photocatalysts, particularly inadequate redox potentials, a series of precisely engineered TiO 2 -Bi 2 WO 6 heterojunction photocatalysts, coded as TB-x (x represents the molar ratio% of Bi: Ti), has been designed and synthesized through deliberate bandgap adjustment. An optimal interfacial electronic structure, formed by coupling wide-bandgap TiO 2 (3.0–3.2 eV) with narrower-bandgap Bi 2 WO 6 (2.6–2.9 eV), enables efficient charge dynamics under low-intensity UV irradiation (~ 1 W). The optimized TB-5 demonstrates complete removal of 5 ppm formaldehyde (FA: 100% X FA ) within 600 s, achieving a clean air delivery rate of 10.37 L min -1 and apparent quantum yield of 2.68E-01%. The exceptional activity is supported by the formation of a robust S-scheme heterojunction, as confirmed both experimentally and theoretically via density functional theory calculations. This charge preservation mechanism is remarkably robust, converting 81.6% of FA (initial concentration: 100 ppm) into CO 2 within 2 h. In-situ DRIFTS analysis further suggests that FA oxidation proceeds sequentially through dioxymethylene and formate intermediates. This work thus establishes a foundational strategy for practical indoor air purification by integrating advanced S-scheme design with atomic-level mechanistic insight, charting a clear path from lab-scale discovery to real-world application.