Preparation, Characterization And Properties Study Of WO₃Nanomaterials

As an n-type metal oxide semiconductor, tungsten trioxide (WO3) nanomaterials havebeen extensively studied due to their excellent properties in chemical catalysis, gas detection,storage and photoelectric conversion. Generally, the preparation methods of thenanostructured WO3include hydrothermal method, liquid phase deposition method, sol-gelmethod, gas phase precipitation method, magnetron sputtering method and microemulsionmethod etc. Among all kinds of synthesis routes, one-step template-free hydrothermal routecan offer significant advantages, such as high homogeneity, shape-and size-controllable, lowprocessing temperature, easy manipulation, cost effective and large-scale production.Meanwhile the amount of impurities in the final product can be kept in a low level and abateenvironmental pollution. Scientific researches indicate that the performance of the WO3nanomaterials are determined by their crystal phases, morphologies and particle sizes.Therefore, the design and synthesis of WO3nanomaterials with tailored phases andmorphologies are of crucial importance. This thesis includes the following aspects:1. Monoclinic WO3nanoplates were synthesized by a one-step template-free hydrothermalroute, using Na2WO4·2H2O and HCl as starting materials and H2O as solvent, and theformation mechanism was proposed. The visible-light-driven photocatalytic activity of theas-prepared WO3nanoplates was evaluated and the photodegradation mechanism wasdiscussed. Compared to the commercial WO3powder, the as-prepared m-WO3nanoplateexhibited a superior photocatalytic activity, which may be ascribed to not only its largerBET surface area but also the higher crystallinity. Moreover, we also investigated theinfluence of calcination temperature on photocatalytic activity of the monoclinic WO3nanoplates. The results show that the calcination at600℃significantly increased thephotocatalytic activity of the WO3nanoplates. The fluorescence (FL) technique confirmedthat the OH was the active species responsible for the photocatalytic oxidation reaction ofrhodamine B over the WO3photocatalysts rather than the photogenerated holes.2. Series of tungsten oxide nanostructures with different crystal phases and morphologieswere synthesized at two temperatures by a facile hydrothermal method, using HNO3andNa2WO4·2H2O as raw materials and were characterized systemically. The effects of HNO3quantity, hydrothermal temperature and time on the crystal phases and morphologies ofthe WO3nanostructures were investigated in detail and the formation mechanism of theWO3nanoplates was explored. After calcination at450℃for2h, the gas-sensingproperties of chosen WO3samples were measured at an operating temperature of300℃and the acetone-sensing mechanism was discussed. The WO3nanoplate showed a highsensitivity, fast response and distinct selectivity to acetone gas. Therefore, the WO3 nanoplate is a promising material for fabrication of an acetone gas sensor.