Synthesis of bismuth oxyiodides and their composites: characterization, photocatalytic activity, and degradation mechanisms

Abstract

Bismuth oxyiodides have been prepared using controlled hydrothermal methods. The products are characterized by SEM-EDS, XRD, XPS, FTIR, PL, EPR, and DRS. It is illustrated that BiOI, Bi₄O₅I₂, Bi₇O₉I₃, Bi₅O₇I, and BiO_xI_y/BiO_pI_q composites can be selectively synthesized through a facile solution-based hydrothermal method. UV-Vis spectra display the bismuth oxyiodide materials as indirect semiconductors with an optical bandgap of 1.86–3.316 eV. The photocatalytic efficiency of the powder suspension is evaluated by measuring the Crystal Violet (CV) concentration. This is the first study to demonstrate the superior activities of BiOI, Bi₄O₅I₂, Bi₇O₉I₃, Bi₅O₇I, and BiO_xI_y/BiO_pI_q composites as promising visible-light-responsive photocatalysts. The quenching effects of various scavengers and EPR indicate that the reactive O₂˙⁻ plays a major role and ˙OH and h⁺ play a minor role. The Bi₇O₉I₃/Bi₅O₇I composite shows the highest photocatalytic activity reaching a maximum rate constant of 0.2225 h⁻¹, which is 6 times higher than that of BiOI and Bi₇O₉I₃ and 4 times higher than that of Bi₅O₇I.