Research On The Controlled Syntheses Of Different Morphologies Of Tungsten Oxides Under Mild Condition And Their Gas Sensing Properties

Effectively control of the structure, size and morphology of inorganic compounds is a very important prerequisite for manufacturing various nanodevices. Semiconductor sensor has the advantages of sensitive reaction, long life. But how to further improve the sensitivity degree of semiconductor sensor, a lot of research works have been done by scientific research workers on the structure of the semiconductor oxides through the way of chemical means to control size and morphology. As to WO3, which has special crystal structure and physical and chemical properties, the preparation of this kind of powder materials with special dimension structure through different preparation methods is also extensive. But there are also faults such as low controllability, low production efficiency, complex process. Therefore, through a method that is simple operation, low cost, and has the industrialization prospect, to get WO3 nanomaterials with controllable morphology and uniform size is still very difficult. In addition, by analyzing the growth mechanism, to further optimize structure, improve the stability of the preparation technology of nanomaterials, improve the performance of gas sensitive applications, is a very meaningful research.This main works of this project is the preparation of different dimensions and different shape of tungsten oxide nanomaterials by hydrothermal method, water bath method with the adding of a template or adjuvant, the characterization of microstructure and micro morphology of the material by characterization testing means such as XRD, SEM and TEM, the discussion of growth mechanism with the assist of crystal structure analysis software Diamond, the gas sensing testing of different powders to different gases such as ethanol at different concentration, temperature and other conditions to get their gas response performance parameters such as sensitivity, optimum temperature, selectivity, detection limit and stability. This project aims to find the controllable simple preparation method of low dimension of tungsten oxide nanometer material, and to discusses its growth mechanism and provide guidance for gas sensitive performance improvements. Further optimize and improve the preparation technology to controllable synthesis tungsten oxide with hierarchical structure and discuss their growth mechanism. Test its gas sensitive properties and discuss the influence of hierarchical nanostructures on the gas sensitive performance, providing reference for further modification research of tungsten oxides. The main conclusions are as follows:① One-dimensional(1D) nanostructured tungsten oxide. Monodisperse h-WO3 nanowires can be controlled synthesized under hydrothermal conditions by adding appropriate amount of Na2SO4 and K2SO4 as capping agent. The one dimensional directional growth is due to the anisotropy of growth caused by the deposit of Na+ and K+ ions, and as a result of adsorption of SO42- ion. It showed good gas response and selectivity to toxic gas such as ethanol and formaldehyde. The gas response to 10 ppm of two gases under the condition of 300 oC can reach more than 10.② Two-dimensional(2D) nanostructured tungsten oxide. Monodisperse WO3·H2O nanoplates can be controlled synthesized by hydrothermal method with the adding malic acid. Its main exposed surface is(010) facet and its thickness can be controlled by adjusting the reaction time. Selective adsorption of malic acid on the(010) crystal plane and different reaction time could lead to the different thickness of WO3·H2O. The sensor based on two kinds of powder has good gas sensitive properties because that its gas response sensitivity to 100 ppm of ethanol at 300 oC ban be 29.8 and 26.1, respectively. Additionally, the thinner WO3·H2O nanoplates based sensor can show better gas sensitive, due to the more exposure of(010) crystal planes, the higher reactivity.③ Three dimensional(3D) hierarchical nanostructured tungsten oxide. A variety of three-dimensional hierarchical structures of WO3 nanomaterials have be controlled synthesized. The growth mechanism was discussed and their superior gas sensing performance was proved. C/WO3 microsphere can be hydrothermally prepared with carbon microsphere(C) as template. Mesoporous WO3 microsphere can be synthesized by further sintering. This kind of microsphere has a larger specific surface area(22.2 m2/g) and significant response to 50 ppm ethanol, which can reach to as large as 17.7. Urchin-like h-WO3 microsphere can be successfully prepared by hydrothermal method with the auxiliary of K2SO4. Through check experiment, it can be found that K2SO4 play a major role in the formation of urchin structure. Gas sensitive test showed that the sensitivity to 400 ppm ethanol at 300 oC can reach to 17. Assembled WO·H2O nanoflowers also can be prepared by water bath method with the assistance of oxalic acid. It is found that in W/C ratio of 1:1. 6, the obtained WO3·H2O has the best crystallization performance and perfect assembled three-dimensional hierarchical structure. This kind of structure showed enhanced gas-sensing performance due to the specific surface area, less accumulation of the nanoparticles.