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.