Phase-Engineered Bismuth-Rich Oxybromides (BixOyBrz) for Visible-Light Photocatalytic Degradation of Emerging Pollutants and Harmful Algal Blooms

Abstract

Non-stoichiometric bismuth-rich bismuth oxybromides (Bi_xO_yBr_z) have earned momentous attention due to their excellent stability, tunable band structure, visible light responsiveness, and unique 2D layered morphology. In this study, a modified hydrolysis method was adopted to synthesize BiOBr precursor using elevated concentration of Bi³⁺ precursor. Subsequent calcination of the as-prepared BiOBr precursor at varying temperatures induced phase transformation into Bi₂₄O₃₁Br₁₀, Bi₄O₅Br₂, Bi₅O₇Br, and Bi₁₂O₁₇Br₂, as confirmed by XRD analysis. Morphological characterization via FESEM and TEM revealed the retention of layered 2D plate-like structures, while XPS analysis further corroborated the phase transitions by identifying changes in surface composition and chemical states. The photocatalytic activities of these phase-engineered Bi_xO_yBr_z materials were evaluated through the degradation of methylene blue dye and acetaminophen under visible-light irradiation. Notably, Bi₁₂O₁₇Br₂ demonstrated superior photocatalytic performance and was further investigated for its efficacy in degrading Microcystis aeruginosa algal cells. The enhanced activity of Bi₁₂O₁₇Br₂ is attributed to improved generation of reactive oxygen species and reduced electron-hole pair recombination, facilitated by its inherent ability to generate internal static electric field. This work highlights a cost-effective strategy for designing Bi_xO_yBr_z photocatalysts with phase-dependent activity toward both chemical and biological pollutants of emerging concern.