Morphology-Dependent Photocatalytic Performance of Monoclinic BiVO4 for Methyl Orange Degradation under Visible-Light Irradiation

Monoclinic BiVO4 with multiple morphologies were fabricated using the alcoho-hydrothermal strategy with bismuth nitrate and ammonium metavanadate as inorganic sources, NaOH for pH adjustment, and the triblock copolymer P123 as a surfactant. The materials were characterized by X-ray diffraction, nitrogen adsorption-desorption, scanning electron microscopy, X-ray photoelectron spectroscopy, and ultraviolet-visible diffuse reflectance spectroscopy. The photocatalytic performance of the BiVO4 samples was evaluated for the degradation of methyl orange (MO) under visible-light irradiation condition. The results showed that the surfactant and pH had a significant influence on the particle morphology of the BiVO4 product. Porous spherical, flower-like, and sheet-like BiVO4 were fabricated at an alcoho-hydrothermal temperature of 180 °C and at a pH of 2, 7, or 10, respectively, whereas rod-like BiVO4 was obtained in the presence of P123 at an alcoho-hydrothermal temperature of 180 °C and at a pH of 2. The difference in BiVO4 particle morphology led to differences in surface area, surface oxygen vacancy density, and (040) crystal plane exposure. Among the four BiVO4 samples, the rod-like sample had the highest surface area, surface oxygen vacancy density, and (040) crystal plane exposure, and the lowest bandgap energy resulting in it having the best photocatalytic activity for MO photodegradation. It can be concluded that a morphological effect is responsible for the photocatalytic performance and the rod-like morphology seems to favor an enhancement in the photocatalytic performance of the BiVO4 material.