Unveiling product selectivity in S-scheme heterojunctions: Harnessing charge separation for tailored photocatalytic oxidation

ABSTRACT The utilization of semiconductor-based photocatalytic technology holds immense promise for harnessing solar energy. However, the inherent issue of strong Coulombic attraction between photo-generated electrons and holes within a single photocatalyst often leads to rapid recombination, limiting efficiency. Addressing this challenge, the development of S-scheme heterojunction photocatalysts has emerged as an effective strategy. Nevertheless, the impact of this spatial separation on the photocatalytic reaction has remained largely unexplored. This study reveals that the recombination of useless charge carriers significantly influences the oxidation product. In the pristine ZnIn2S4 system, the spatially unseparated holes interact with the H2O2 generated on the surface of ZnIn2S4, all of which are converted to •OH with higher oxidation ability, causing excessive oxidation of 5-hydroxymethylfurfural (HMF). Conversely, the BiOBr/ZnIn2S4 system, effective separation of electrons and holes in space, selectively oxidizes HMF into valuable 2,5-dimethylfuran (DFF) while efficiently generating H2O2 (1.15 mmol∙L–1, 5 h). This outcome, elucidated through in-situ Fourier-transform infrared spectroscopy, density functional theory calculation, and femtosecond transient absorption spectroscopy, underscores the role of spatially separated charge carriers in influencing product selectivity within S-scheme heterojunctions. This work sheds new light on selective oxidation phenomena and underscores the significance of charge separation in S-scheme heterojunctions.