Abstract
A traditional semiconductor (WO3) was synthesized from different precursors via hydrothermal crystallization targeting the achievement of three different crystal shapes (nanoplates, nanorods and nanostars). The obtained WO3 microcrystals were analyzed by the means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and diffuse reflectance spectroscopy (DRS). These methods contributed to the detailed analysis of the crystal morphology and structural features. The synthesized bare WO3 photocatalysts were totally inactive, while the P25/WO3 composites were efficient under UV light radiation. Furthermore, the maximum achieved activity was even higher than the bare P25’s photocatalytic performance. A correlation was established between the shape of the WO3 crystallites and the observed photocatalytic activity registered during the degradation of different substrates by using P25/WO3 composites.
Highlights
WO3 is a well-known semiconductor with a large applicability spectrum
The visible light activity can be attributed to the presence of a small fraction of rutile crystal phase in P25 [22,23]
The obtained microcrystals have hierarchical structure, their secondary morphology was in the micrometer range. It is already known in the case of titania that, over a certain particle size, the overall photocatalytic activity decreases
Summary
WO3 is a well-known semiconductor with a large applicability spectrum. Its color can vary from yellow, green, bluish and grayish depending on the oxidation state of the tungsten atoms in the crystal structure. It is a widely studied transition metal oxide with a light absorption maximum « 480 nm (the band gap of WO3 is «2.6 eV [1], yellowish color), stable under acidic and oxidative conditions and most importantly, it is considered harmless. WO3 nanocrystallites can be synthesized using various methods, the most common being the ones using hydrothermal crystallization. Tungsten trioxide shows four well-known crystal phases: Materials 2016, 9, 258; doi:10.3390/ma9040258 www.mdpi.com/journal/materials
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