Tungsten Trioxide Photocatalysts:

Hexagonal (h-) and monoclinic (m-) tungsten trioxide (WO₃₎ nano particles with controlled composition  were prepared through annealing (NH₄)_xWO_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, 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.

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Nanostructure -- WO3

Nanostructured WO₃ has been developed as a promising water-splitting material due to its ability of capturing parts of the visible light and high stability in aqueous solutions under acidic conditions. In this review, the fabrication, photocatalytic performance and operating principles of photoelectrically cells (PECs) for water splitting based on WO₃ photoanodes, with an emphasis on the last decade, are discussed. The morphology, dimension, crystallinity, grain boundaries, defect and separation, transport of photo generated charges will also be mentioned as the impact factors on photocatalytic performance.

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