Syngthesis And Gas-sensing Properties Of Low-dimensional Tungsten Oxide Nanostructured Materials

WO3 nanocrystals have superior properties, and are widely used as functional materials in gas sensors, electrochromic devices and chemical catalysts. WO3 nanostructured materials, including nanowires, nanoslice, nanoarray and nanotubes, show excellent gas-sensing performance due to their very large specific surface areas and unique morphologies. This thesis mainly investigated the synthesis and gas-sensing performance of the WO3 nanoplates and nanosized tetragonal prisms, compared with the gas-sensing performance of WO3 nanoparticle from tungstic acid. The related mechanism and the influencing factors of morphologies on gas-sensing performance were also analyzed.First of all, H2W2O7-xH2O powders, prepared using the WO3 and Bi2O3 as the raw materials, were used as the starting materials to synthesize H2WO4 and WO3 nanoplates, via highly ordered tungstate-based inorganic-organic hybrids, which were derived from a reaction of H2W2O7·XH2O and n-octylamine in heptane. Ultra-thin WO3 nanoplates were used to fabricate gas sensors. WO3 nanoplate sensors had high sensitivity and short response/recovery times to the alcohol, acetone, NO, CO, and H2. The response and recovery times of the WO3 nanoplate sensors were less than 15 s for alcohols and acetone at an operating temperature of 300℃, and the sensitivity to 50-ppm-NO gas was up to 578 operating at 200℃. A good linear relationship between the sensitivity and alcohol vapor concentrations was observed in the range of 2-300 ppm in an operating temperature range of 260-360℃.Secondly, WO3 nanocolumns were prepared by a hydrothermal method. For the synthesis of WO3 nanocolumns, ammonium paratungstate, polyethylene glycol (PEG), dodecylbenzenesulfonic acid sodium (SDBS), and cetyltrimethyl ammonium bromide (CTAB) were used as the starting materials, and the hydrothermal treating temperatures were 160-200℃using a 1mol/L HNO3 aqueous solution as the solvents. The morphology and structures were investigated using scanning electron microscopy, and powder X-ray diffraction. The gas-sensing performance of WO3 nanocrystal sensors to alcohol, acetone and NO gas was investigated. The results showed that the gas-sensing properties were improved with an increase in hydrothermal temperature, and that the sensors showed high sensitive to NO,acetone at low operation temperature. Finally, commercial H2WO4 nanoparticles were calcined directly in 550℃to synthesize WO3 nanoparticles. The gas-sensing performance of the as-obtained WO3 nanoparticles was measured, and the results showed that the gas-sensing properties of WO3 nanoparticle sensors were worse than those of WO3 nanoplate and WO3 nanocolumn sensors.The effects of the size and shape of WO3 nanocrystals on the gas-sensing properties were compared on the basis of the three types of WO3 nanocrystals (i.e., nanoplates, nanocolumns and nanoparticles). WO3 nanoplate sensors were of more excellent gas-sensitive performance than WO3 nanocolumn and nanoparticles. The possible reason was that the WO3 nanoplate had a large specific surface area, ultrathin plate-like shape, high crystallinity and loose self-assembly structure.