Tungsten Oxide Hydrates Crystallites

The past couple of decades have witnessed an exponential growth of activities in this field worldwide, driven both by the excitement of understanding new science and by the potential hope for applications and economic impacts. The largest activity in this field at this time has been in the synthesis of new nanoparticles of different sizes and new shapes. Besides giving us new properties, creating novel nanostructures requires new understanding of the properties of their surfaces, which has been in the center of attentions from many scientific researchers. As one kind of well-known semiconductor materials, tungsten oxide and its hydrates (WO3•nH2O, n=0~2) have been extensively researched and employed in various application fields. Because many of their nanostructures and morphologies are inextricably bound to properties in several fields, scientists have been concentrating on the research of the preparation of micro/nanostructures of these materials. However, there still remains further investigations on the exploration of developing facile, green and economical techniques when controlling these interesting promising structures, which are believed to be very necessary for expanding the application fields of tungsten oxide hydrates materials. In this dissertation, a facile hydrothermal technique has been developed to prepare micro/nanostructured tungsten oxide hydrates materials (particles and films) with/without the assistant of templates and microwave heating. The following are the main results and conclusions:

Tungsten oxide hydrates crystallites with a diversity of phases and morphologies were successfully controlled by using tungsten powders as starting materials via a facile and additive-free hydrothermal process. Various micro/nanostructures of products, including cubic blocks, “snowflakes”, round angular blocks, hexagonal “gears”, cuboid rods, hexagonal plates and nanoflakes,were obtained by simply changing the reaction conditions. Results show that the nucleation, crystallization and diffusion of the growth units were found to play key roles in different conditions to vary the products phases and morphologies.

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