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

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 BiOxIy/BiOpIq 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 BiOxIy/BiOpIq composites as promising visible- light- responsive photocatalysts. The quenching effects of various scavengers and EPR indicate that the reactive O-2(center dot-) plays a major role and (OH)-O-center dot 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.