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

Abstract To strategically overcome the shortcomings of conventional photocatalysts, particularly inadequate redox potentials, a series of precisely engineered TiO-BiWO heterojunction photocatalysts, coded as TB-x (x presents the molar ratio% of Bi:Ti), has been designed through deliberate bandgap adjustment. An optimal interfacial electronic structure, formed by coupling wide-bandgap TiO (3.0–3.2 eV) with narrower-bandgap BiWO (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) within 600 seconds, achieving a clean air delivery rate of 10.37 L min 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 demonstrates remarkable robustness, achieving an 81.6% conversion of FA to CO in 2 hours even at a FA concentration of 100 ppm. 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