Tailoring the architecture of BiOI microspheres for enhanced photocatalytic wastewater purification

Bismuth oxyiodide (BiOI) features alternating [Bi₂O₂]²⁺ layers and double I^- interlayers, which forms an intrinsic electric field that enhances charge carrier transfer and facilitates the efficient separation of photogenerated electron-hole pairs. Owing to its exceptional visible-light absorption capability and high photocatalytic activity, BiOI has emerged as a promising candidate for environmental remediation. Herein, BiOI microsphere photocatalysts were fabricated via a facile solvothermal method, and various morphologies were obtained through different synthesis conditions. Among all BiOI catalysts synthesized in this work, the flower-like BiOI hollow microspheres (BiOI-6) exhibited superior dark adsorption and extremely fast photocatalytic degradation rates, with ultra-rapid kinetics and excellent stability. The rate constant k of BiOI-6 reached 0.130 min^-1, which is 8.7 times higher than those of BiOI-5 and BiOI-7. This catalyst demonstrated a zeta potential of -34.20 mV, ensuring high dispersion stability, and possessed a bandgap energy of 2.07 eV as estimated using the Kubelka-Munk equation with a valence band position of 1.50 eV as determined by XPS. The high efficiency of the flower-like BiOI hollow microsphere catalyst was attributed to its large specific surface area, porous hollow structure, narrow bandgap energy, high hydrophilicity (water contact angle of ∼30°), and enhanced charge carrier separation efficiency. Based on these findings, BiOI shows significant potential in the development of efficient and stable photocatalysts for wastewater pollution control and purification.