Template-Free Synthesis of Monoclinic BiVO₄ with Porous Structure and Its High Photocatalytic Activity.

Monoclinic BiVO₄ photocatalysts with porous structures were synthesized by a two-step approach without assistance of any templates. The as-prepared samples were characterized by X-ray diffraction pattern (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET), ultraviolet-visible (UV-vis) diffuse reflectance spectroscopy (DRS), photocurrent responses, and electrochemical impedance spectra (EIS). It is found that the as-prepared BiVO₄ samples had a porous structure with aperture diameter of 50-300 nm. Moreover, the BET specific surface area of the porous BiVO₄-200 °C sample reaches up to 5.69 m²/g, which is much higher than that of the sample of BiVO₄ particles without porous structure. Furthermore, a possible formation mechanism of BiVO₄ with porous structure was proposed. With methylene blue (MB) as a model compound, the photocatalytic oxidation of organic contaminants in aqueous solution was investigated under visible light irradiation. It is found that the porous BiVO₄-200 °C sample exhibits the best photocatalytic activity, and the photocatalytic rate constant is about three times of that of the sample of BiVO₄ particles without porous structure. In addition, the photocurrent responses and electrochemical impedance spectra strongly support this conclusion.