S-scheme mediated charge transfer in titania-tungsten trioxide heterojunctions for photocatalytic mineralization of gaseous formaldehyde

Abstract

The prevalence of extended indoor activities has raised concerns about health risks associated with exposure to volatile organic compounds (VOCs). In response, WO3-coupled TiO2 S-scheme heterojunction photocatalysts are synthesized with varying nominal WO3 molar contents (1, 3, or 5 mol%). To clarify charge transfer mechanisms in TW-x heterojunctions during the photocatalytic degradation of VOCs like formaldehyde (FA), the interfacial electronic structure and charge-separation behavior of TiO2/WO3 composites are comprehensively assessed. To map these electronic properties, a suite of complementary techniques is employed, including ultraviolet photoelectron spectroscopy, Kelvin probe force microscopy, and Mott-Schottky analysis. The combined results provide converging evidence consistent with an S-scheme charge-transfer pathway. Among the composites, TW-3 exhibits optimal performance, achieving complete removal of 100 ppm FA (50% RH and a flow rate of 100 mL min−1) with a dynamic-clean air delivery rate of 600 L g−1 h−1 and an apparent quantum yield of 3.08%. In-situ DRIFTS analysis reveals a reaction pathway consistent with FA mineralization through key formate intermediates. This process ultimately leads to oxidation into CO2 and H2O, driven by highly reactive oxygen species generated during photocatalysis. Overall, this study not only presents a strategy for building advanced heterojunction materials but also provides a strengthened mechanistic framework for interpreting their charge-transfer behavior in indoor air purification.