Hexagonal (h-) and monoclinic (m-) tungsten trioxide (WO3) nano particles with controlled composition were prepared through annealing (NH4)xWO3−y. The formation, structure, composition, morphology, and optical properties of the samples were analyzed by powder X-ray diffraction, scanning and transmission electron microscopy combined with electron diffraction, and Raman, X-ray photoelectron, H magic angle spinning nuclear magnetic resonance, diffuse reluctance ultraviolet–visual, and photoluminescence spectroscopy. Oxidized m-WO3 (m-WO3 ox) was the most active photocatalyst both in the aqueous and in the gas phase, followed by the oxidized h-WO3 (h-WO3 ox) sample. Reduced h-WO3 (h-WO3 red) and m-WO3 (m-WO3 red) exhibited much lower activity. Thus, in contrast to TiO2, where crystalline structure (rutile or anatase) plays a key effect in photocatalysis, for WO3, it is the composition that is of greatest importance: the more oxidized the WO3 sample, the better a photocatalyst it is. The crystal structure of WO3 has only an indirect effect, in that it influences the composition of WO3 samples. Consequently, an oxidized monoclinic WO3 material will always provide better photocatalytic activity than an oxidized hexagonal one.
Please visit our website www.tungsten-powder.com to get more information about tungsten trioxide.
没有评论:
发表评论