Gas-Solid Phase Reaction Derived Silver Bismuth Iodide Rudorffite: Structural Insight and Exploring Photocatalytic Potential of CO₂ Reduction

Photocatalytic reduction of CO₂ is a promising strategy to mitigate the effects of global warming by converting CO₂ into valuable energy-dense products. Silver bismuth iodide (SBI) is an attractive material owing to its tunable bandgap and favorable band-edge positions for efficient CO₂ photoreduction. In this study, SBI materials, including AgBi₂I₇, AgBiI₄, Ag₂BiI₅, and Ag₃BiI₆ are first synthesized, through gas-solid reaction by controlling the stoichiometric ratio of reactants. The X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) results revealed that the distance between Ag-I is proportional to the degree of Ag ions delocalization, which occupies the vacant sites. That greatly retards the charge recombination at vacant sites. In addition, the surface potential via photo-assisted Kelvin probe force measurements of various SBI catalysts shows that Ag₃BiI₆ exhibits the highest surface potential change due to the rich delocalized Ag ions. This results in effective charge carrier transport and prevention of charge recombination at vacant sites. Taking the above advantages, the averaged CO and CH₄ production rates for Ag₃BiI₆ achieved 0.23 and 0.10 µmol g^-1 h^-1, respectively. The findings suggest that Ag₃BiI₆ has a high potential as a novel photocatalyst for CO₂ reduction and sheds light on the possibility of solving environmental contamination and sustainable energy crises.