Geometric confinement-driven oxygen vacancy enrichment regulates interfacial charge utilization in ultrathin BiOI

Ultrathin flower-like BiOI was constructed with confinement-enriched oxygen vacancies. • Geometric confinement lowered the oxygen vacancy formation energy from 3.96 to 3.73 eV. • Oxygen vacancy enrichment reduced the work function and promoted interfacial charge transfer. • The optimized BiOI showed 137-fold faster TC-HCl oxidation under visible light. Geometric confinement, defect thermodynamics, and interfacial charge utilization are closely coupled in layered semiconductors, yet their relationship remains insufficiently understood. Here, we show that reducing the thickness of BiOI lowers the oxygen-vacancy formation energy and is associated with enhanced vacancy enrichment, thereby reconstructing the surface electronic structure and improving visible-light oxidation. The optimized BOI-F consists of hierarchical flower-like assemblies built from ultrathin nanosheets with an average thickness of about 2.4 nm, whereas BOI-S shows a compact bulk-like morphology. Relative to BOI-S, BOI-F exhibits a wider band gap, a longer carrier lifetime, a stronger photocurrent response, and a lower charge-transfer resistance. As a result, its apparent oxidation rate for tetracycline hydrochloride (100 mg L −1 ) reaches 0.0434 ± 0.0004 min −1 , which is about 145 times that of BOI-S (0.0003 min −1 ). DFT calculations show that the oxygen-vacancy formation energy decreases from 2.63 eV for the monolayer to 3.73 eV for the bilayer, 3.77 eV for the four-layer, and 3.95 eV for the bulk, indicating that geometric confinement thermodynamically favors vacancy formation in the ultrathin limit. The enriched oxygen vacancies lower the work function, facilitate O 2 adsorption and activation, and strengthen the adsorption and interfacial charge coupling of organic pollutants. Reactive-species trapping experiments identify photogenerated holes as the dominant oxidative species, with singlet oxygen serving as a secondary pathway. This work links thickness confinement to defect thermodynamics and interfacial charge utilization in layered BiOI, and provides a practical strategy for designing efficient layered photocatalysts. Download: Download high-res image (492KB) Download: Download full-size image