Effects of Hydrothermal Temperature on the Microstructures of BiVO4 and Its Photocatalytic O2 Evolution Activity under Visible Light

Abstract

Microspheric and lamellar BiVO₄ powders were selectively prepared through a hydrothermal process by using cetyltrimethylammonium bromide (CTAB) as a template-directing reagent. The as-prepared BiVO₄ powders were characterized by X-ray diffraction, electron microscopy, nitrogen adsorption−desorption experimentation, Fourier transform infrared spectrometry, and UV−vis diffuse reflectance spectroscopy. Experimental results indicate that microspheric BiVO₄ with particle sizes in the range of 7∼12 μm can be derived from a relatively low hydrothermal temperature (≤160 °C) and possess a mixed crystal consisting of tetragonal and monoclinic phases, whereas lamellar BiVO₄ with a pure monoclinic phase can be obtained at a higher hydrothermal temperature (200 °C). Their photocatalytic activities for O₂ evolution were investigated by using Fe(NO₃)₃ as a sacrificial reagent under visible-light irradiation, and the lamellar BiVO₄ shows a better photoactivity than the microspheric product due to its pure monoclinic crystal phase. Moreover, the effects of CTAB content on the morphologies and crystal phases of the obtained products were also discussed. It was found that the addition of CTAB can adjust the morphologies of BiVO₄ and obstruct the crystal phase transformation from the mixed crystal to pure monoclinic BiVO₄ during the hydrothermal process.