Controlled hydrothermal synthesis of bismuth oxychloride/bismuth oxybromide/bismuth oxyiodide composites exhibiting visible-light photocatalytic degradation of 2-hydroxybenzoic acid and crystal violet

Abstract This paper presents an unprecedented systematic synthetic study of a controlled hydrothermal method for the preparation of bismuth oxychloride/bismuth oxybromide/bismuth oxyiodide ternary composites (BiO x Cl y /BiO m Br n /BiO p I q ). The pH, temperature, and KCl:KBr:KI molar ratio for the reactions were adjusted to control the compositions and morphologies of BiO x Cl y /BiO m Br n /BiO p I q composites. Scanning electron microscopy-energy dispersive X-ray spectroscopy, transmission electron microscopy, X-ray diffraction, ultraviolet–visible diffuse reflectance spectroscopy, Brunauer–Emmett–Teller specific surface areas, photoluminescence spectroscopy, and X-ray photoelectron spectroscopy, and electron paramagnetic resonance spectroscopy were applied to the products. The photocatalytic activities of dispersions were examined by monitoring the 2-hydroxybenzoic acid (HBA) and crystal violet concentrations. Various scavengers demonstrated quenching effects. O 2 − was crucial to HBA degradation, whereas h + and OH played minor roles in HBA degradation. This text hypothesizes possible photodegradation mechanisms.