Augmented photocatalytic NO removal by the S-scheme BiOI/BiS heterojunctions with surface oxygen vacancies: Experimental analyses and theoretical calculations.

The establishment of S-scheme heterojunctions represents an effective strategy for enhancing the transfer and separation of charge carriers, thereby bolstering redox capacities and consequently benefiting subsequent photocatalytic reactions. In this study, the pristine BiOI underwent a facile vulcanization process to in-situ produce various composites. Systematical characterizations confirmed the simultaneous generation of BiOI/BiS (BI-BS) heterojunctions with surface oxygen vacancies (OVs). Under visible light, these BI-BS composites exhibited improved NO removal efficiencies with reduced NO generation compared to bare BiOI. Particularly, the best candidate BI-BS2 possesses the highest NO removal (43.02%) and lowest NO generation (5.44%) among all tested samples. The improvement was primarily attributed to synergetic effects of heterojunction and surface OVs, including enhanced charge separation, heightened light responsiveness, and improved generation of reactive oxygen-containing species through an S-scheme mode. Furthermore, the Density Functional Theory (DFT) calculations had demonstrated that the establishment of BI-BS heterojunctions with surface OVs not only optimized the electronic structure to facilitate the transfer and separation of charge carriers, but also significantly enhanced the adsorption of NO, HO, and O molecules, ultimately favoring the generation of NO species. These as-synthesized composites indicated sufficient structural stability and hold potential for the photocatalytic removal of NO at ppb levels.