Efficient charge separation and transfer in a CdS/BiOBr/Bi2S3 heterojunction via a dual S-scheme mechanism and photothermal effect for enhanced Cr(vi) photoreduction

Abstract

The construction of S-scheme heterojunctions has emerged as a promising strategy to enhance the photocatalytic performance of semiconductor materials. Nevertheless, single S-scheme heterojunctions typically face limitations owing to their constrained charge transfer channels, hindering the effective migration of charge carriers. To remedy this drawback, a CdS/BiOBr/Bi₂S₃ dual S-scheme heterojunction photocatalyst was constructed using ion exchange and the in situ growth method, enabling rapid charge transfer through multiple channels. The novel CdS/BiOBr/Bi₂S₃ photocatalyst demonstrated a remarkable 100% photocatalytic reduction rate of Cr(VI) within 8 min, significantly outperforming BiOBr and binary Bi₂S₃/BiOBr photocatalysts. The high photocatalytic activity was attributed to the dual S-scheme heterojunction, which promotes efficient charge separation and transfer by facilitating multicarrier migration paths. Furthermore, the introduction of Bi₂S₃ and oxygen vacancies enhanced near-infrared absorption, induced a robust photothermal effect and near-field temperature rise, thereby accelerating reaction kinetics and further boosting photocatalytic efficiency. The charge transfer mechanism of the dual S-scheme heterojunction was corroborated through spectroscopy, electrochemical analysis, and density functional theory calculations. This study offers valuable insights into designing high-performance S-scheme photocatalysts with multichannel charge transfer capabilities.