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

Abstract

Microspheric and lamellar BiVO(4) powders were selectively prepared through a hydrothermal process by using cetyltrimethylammonium bromide (CTAB) as a template-directing reagent. The as-prepared BiVO(4) 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 BiVO(4) with particle sizes in the range of 7-12 microm can be derived from a relatively low hydrothermal temperature (<or=160 degrees C) and possess a mixed crystal consisting of tetragonal and monoclinic phases, whereas lamellar BiVO(4) with a pure monoclinic phase can be obtained at a higher hydrothermal temperature (200 degrees C). Their photocatalytic activities for O(2) evolution were investigated by using Fe(NO(3))(3) as a sacrificial reagent under visible-light irradiation, and the lamellar BiVO(4) 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 BiVO(4) and obstruct the crystal phase transformation from the mixed crystal to pure monoclinic BiVO(4) during the hydrothermal process.