Iodine self-doping and oxygen vacancies doubly surface-modified BiOIO3: Facile in situ synthesis, band gap modulation, and excellent visible-light photocatalytic activity

A novel BiOIO3 photocatalyst surface-modified with both iodine ions and oxygen vacancies, was successfully synthesized via a microwave route followed by heat treatment and can be used for the efficient degradation of various environmental pollutants under visible-light irradiation. Pure BiOIO3, with a band gap of 3.2 eV, was first prepared by a rapid microwave method. Then, during a mild heat-treatment process, BiOIO3 served as a self-sacrificial template and oxidant, while surface-adsorbed ethylene glycol derived from the microwave reaction acted as a reducing agent to in situ generate iodine ions and oxygen vacancies, resulting in a doubly modified BiOIO3 product. By controlling the treatment temperature, the band gaps of the modified BiOIO3 samples can be reversibly tuned by introducing defect energy levels below the conduction band and new impurity energy levels above the valence band, which is supported by the theoretical calculations and experimental analysis. The doubly surface-modified BiOIO3 exhibits excellent visible-light photocatalytic performance for the degradation of several model pollutants, including parabens, rhodamine B, bisphenol A, and 4-hydroxybenzoic acid. Among the synthesized materials, the BiOIO3 sample heat-treated at 125 °C shows a band gap of 2.18 eV and a photocatalytic activity approximately 229 times higher than that of pure BiOIO3. The h+ and O2− radicals are verified to be the key reactive species in the photodegradation process through radical-trapping experiments and electron paramagnetic resonance spectroscopy. This work presents an effective strategy for developing superior visible-light photocatalysts through a mild in situ surface-modification technique.