Tuneable Phase, Morphology, and Performance of Bismuth Oxyhalide Photocatalysts via Microwave-Assisted Synthesis

In this study, a facile microwave-assisted synthesis approach was used to produce a series of bismuth oxyhalide photocatalysts, with systematic changes in synthesis pH between 1 and 14 allowing control over a broad range of material properties and characteristics. Detailed structural and morphological investigations with powder X-ray diffraction (PXRD), Rietveld refinements, pair distribution function (PDF) analysis, and scanning electron microscopy (SEM) show that thin particles of BiOCl, BiOBr, Bi₂₄O₃₁Cl₁₀, and Bi₂₄O₃₁Br₁₀ were selectively produced, with progressive changes in morphology, facet dominance, and phase as a function of pH. The impact of these changes on photocatalytic performance was evaluated by studying the aerobic oxidation of benzylamine to N-benzylidenebenzylamine, with all materials exhibiting photocatalytic abilities under UV or blue light. While a combination of material properties and characteristics influenced the photocatalytic performance, certain factors such as surface area, facet dominance, amorphous content, and band gap were found to have a larger impact on the photocatalytic yield. Overall, this study demonstrates the possibilities of phase, morphology, and performance of bismuth oxyhalide photocatalysts over the entire pH range, produced using a fast and facile microwave-assisted synthesis technique as an alternative to the more widely applied hydrothermal synthesis approach. Additionally, the detailed structural and morphological investigations of the materials contribute to a greater understanding of bismuth oxyhalide photocatalysts in general, while also highlighting some of the most desirable properties for improved photocatalytic performance of these materials.