WOˇˇ3ˇˇˇ photocatalysts: Influence of structure and composition

Szilágyi, Imre Miklós and Fórizs, Balázs and Rosseler, O. and Szegedi, Ágnes and Németh, Péter and Király, Péter and Tárkányi, Gábor and Vajna, Balázs and Vargáné Josepovits, Katalin and Nagyné László, Krisztina and Tóth, Attila Lajos and Baranyai, Péter (2012) WOˇˇ3ˇˇˇ photocatalysts: Influence of structure and composition. JOURNAL OF CATALYSIS, 294. pp. 119-127. ISSN 0021-9517

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Abstract

Hexagonal (h-) and monoclinic (m-) WO 3 nanoparticles with controlled composition (oxidized/yellow color or partially reduced/blue color) were prepared through annealing (NH 4) x WO 3- 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, 1H magic angle spinning nuclear magnetic resonance, diffuse reflectance ultraviolet-visual, and photoluminescence spectroscopy. Their photocatalytic properties were tested by decomposing methyl orange in the aqueous phase and acetone in the gas phase. Oxidized m-WO 3 (m-WO 3 ox) was the most active photocatalyst both in the aqueous and in the gas phase, followed by the oxidized h-WO 3 (h-WO 3 ox) sample. Reduced h-WO 3 (h-WO 3 red) and m-WO 3 (m-WO 3 red) exhibited much lower activity. Thus, in contrast to TiO 2, where crystalline structure (rutile or anatase) plays a key effect in photocatalysis, for WO 3, it is the composition that is of greatest importance: the more oxidized the WO 3 sample, the better a photocatalyst it is. The crystal structure of WO 3 has only an indirect effect, in that it influences the composition of WO 3 samples. While oxidized m-WO 3 is completely oxidized, oxidized h-WO 3 is always in a partially reduced state due to the presence of stabilizing positive ions in its hexagonal channels. Consequently, an oxidized monoclinic WO 3 material will always provide better photocatalytic activity than an oxidized hexagonal one. © 2012 Elsevier Inc. All rights reserved.

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