Probing the photocatalytic CO₂ reduction potential of non-stoichiometric bismuth oxyhalides: A case study on Bi₂₄O₃₁Br_xI_10-x nanosheets

Photocatalysts offer a promising approach for utilizing light energy to drive chemical reactions that traditionally require high energy inputs. Among the extensively researched compounds for photocatalysis, non-stoichiometric bismuth oxyhalides stand out due to the capacity of manipulating their bandgap and band structure, enhancing efficiency. This study presents the synthesis of Bi₂₄O₃₁Br_xI_10-x through a single-step solid-state reaction. Field-emission scanning electron microscopy (FESEM) unveiled the sheet-like morphology, while X-ray photoelectron spectroscopy (XPS) confirmed their chemical purity. X-ray diffraction (XRD) validated the phase-pure monoclinic structure, and transmission electron microscopy (TEM) affirmed their good crystallinity. UV–Vis diffuse reflectance spectroscopy (DRS) demonstrated a decreasing bandgap in Bi₂₄O₃₁Br_xI_10-x with increased iodine concentration. Efficiency of Bi₂₄O₃₁Br_8.5I_1.5 towards the degradation of methylene blue dye molecules was more than twice in comparison to Bi₂₄O₃₁Br₁₀. For gas phase photocatalytic carbon dioxide (CO₂) reduction, Bi₂₄O₃₁Br₁₀ exhibited the best performance, producing 161 μmol g⁻¹ of CO and 15 μmol g⁻¹ of CH₄, which were more than twice the amounts produced with Bi₂₄O₃₁Br_8.5I_1.5. These findings not only contribute to the understanding of solid-solution photocatalysts but also propose a scalable and easy production method, offering promising solutions for practical photocatalytic applications across environmental and industrial realms.