Preparation of bismuth oxyiodides and oxides and their photooxidation characteristic under visible/UV light irradiation

Bismuth oxyiodides and oxides were prepared by a solution combination with thermal treatment method. The prepared samples were characterized by X-ray diffraction, thermogravimetry, scanning electron microscopy, transmission electron microscopy, and UV–vis diffuse reflectance spectra, and Brunauer–Emmett–Teller surface areas. The photooxidation activity of the samples was evaluated by photocatalytic decolorization of acid orange II under both visible light (λ > 420 nm) and UV light (λ = 365 nm) irradiation. Results show that a series of changes in the compounds take place during the course of calcination, described as: BiOI → Bi5O7I → α-Bi2O3. Under visible light irradiation, the photocatalytic activities follow the order: BiOI > Bi5O7I > Bi5O7I/Bi2O3 mixture > Bi2O3, which is mainly attributed to the different absorption ability to visible light due to the different band gap energy; the activities are in the order: BiOI < Bi2O3 < Bi5O7I/Bi2O3 mixture < Bi5O7I under UV light irradiation, which is mainly caused by the different oxidability.