Structural tuning of BiOI toward Bi\(_{2}\)O\(_{3}\)/AgI heterostructures via room-temperature ion exchange for improved photocatalytic activity

In this work, a bismuth oxide/silver iodide (Bi2O3/AgI) heterojunction photocatalyst was successfully fabricated via a room-temperature ion exchange process using bismuth oxyiodide (BiOI) as a morphology-directing precursor. Building upon our previous work on solvent-modulated BiOI nanostructures, this study employs a chemical transformation route to develop interfacially connected heterostructures while preserving key morphological features. Structural, morphological, and optical characterizations, including X-ray diffraction, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, Fourier-transform infrared spectroscopy, and ultraviolet–visible diffuse reflectance spectroscopy, provided supporting evidence for the successful formation of Bi2O3/AgI heterojunctions with likely close interfacial contact. The optimized Bi2O3/AgI composite with a 50:50 mass ratio demonstrated the highest photocatalytic activity, enabling nearly complete degradation of indigo carmine within 30 minutes under visible-light irradiation, clearly outperforming both pristine Bi2O3 and AgI. The enhanced performance is attributed to efficient charge carrier separation and improved visible-light absorption enabled by favorable band alignment. These findings highlight the potential of BiOI-based ion-exchange strategies for designing efficient and scalable photocatalysts for environmental remediation.