The Construction of S-Scheme AgI/Bi₇O₉I₃ Heterojunction via Interfacial Engineering for Enhanced Photocatalytic Oxygen Evolution

The rational design of heterojunction photocatalysts is essential for overcoming the persistent challenge of charge recombination in solar water-splitting systems. Herein, a step-scheme (S-scheme) AgI/Bi₇O₉I₃ heterojunction was fabricated using a facile one-pot hydrothermal method, where deliberate interfacial engineering enables efficient charge separation and transfer. The optimized heterojunction demonstrated remarkable photocatalytic oxygen (O₂) evolution activity, achieving a rate of 2046.22 μmol·g⁻¹·h⁻¹ under visible-light irradiation (λ ≥ 420   nm)—3.1 and 1.97 times higher than those of pristine AgI and Bi₇O₉I₃, respectively. Ultraviolet photoelectron spectroscopy (UPS) and electron spin resonance (ESR) analyses collectively revealed that a built-in electric field formed at the interface drives the directional migration of electrons from AgI to Bi₇O₉I₃, following an S-scheme charge transfer pathway. This mechanism not only enhances the separation of photogenerated carriers but also preserves strong redox capabilities for the water oxidation reaction. This study presents an effective interfacial engineering strategy for developing high-performance heterojunction photocatalysts and provides fundamental insights into charge behavior in S-scheme photocatalytic systems.