Tio <sub> 2 </ Sub> Based Nanomaterials Preparation And Oxygen Sensor Research

TiO₂ is an n-type semiconductor and has been widely studied as gas sensor material for detecting CO, ethonal, H₂. Rutile TiO₂ has been an important material for oxygen sensor after ZrO₂ oxygen gas sensor. In order to improve oxygen sensitive characteristics, noble metals such as Pt ,Pd were doped for TiO₂ based sensor and these can be considered to improve the properties for TiO₂ oxygen sensor. As reported, the Pt/TiO₂ oxygen sensor was applied, and the other kinds of oxygen sensors were in research step. Nanomaterial applied as oxygen sensor was undoubtedly as a novel materials synthesized by new methods. This dissertation shows that a new synthesis method for nanometerials as oxygen sensor. The structure characteristics and gas properties were analyzed thoroughly. The relationship between synthesis process, structure and gas properties was studied. The mechanism for the oxygen, CO, H₂ and NH₃ characteristics was discussed synthetically. And the results are listed below: 1.The nanopowder was synthesized by oxidation sol-gel process. The microstructure and crystal structure were detected XRD, IR, ESEM measurements. Rutile phase of pure TiO2 (phase of oxygen sensitivity) is obtained under low dried temperature (80℃). The oxygen and reduce gas sensitivity are not affected by sintering temperature. 2. The Mo⁶⁺,W⁶⁺,Ce⁴⁺ ions were doped in the TiO₂ based nanomaterials by same process. The crystal phase, microstructure, oxygen and reduce gas properties of doped TiO₂ were studied. The doping by Mo⁶⁺ into TiO₂ is favor to the phase transformation of rutile. The crystal and particle size is decreased by Mo⁶⁺ doping. Ti-O vibration peaks of Mo⁶⁺ doped TiO₂ samples are largely blue-shifted compared with pure TiO₂. The particle size is small and uniform from ESEM image as 35mol% Mo⁶⁺ doping. Pure rutile phase and large crystal size is both in 1mol% and 5mol% W⁶⁺ doped TiO₂ powder. As W⁶⁺ doped content up to 10mol%, anatase phase is separated out. IR characteristics of W⁶⁺ doped TiO₂ is not affected by the doped content. The particle size is large and porosity showed on the surface morphology of 5mol%W⁶⁺ doping sensor. The crystal size decreases with Ce⁴⁺ doped content, and particle size increases due to crystals reuniting strongly. The Ti-O vibration peak of Ce⁴⁺ doped TiO₂ is a little blue-shifted. The particle size is large and in poor uniform from ESEM image. The sensitivity of sensors made by Ce⁴⁺ doped TiO₂ is almost unchanged with the Ce⁴⁺ doped content. 3.The sensitivity of Mo6+ doped TiO₂ (21mol% and 35mol%) for oxygen, CO, H₂ and NH3 are all enhanced. However, the gas properties of sensor made by 7mol% Mo6+ are invariable. The gas sensitivity (O2, CO, NH3 and H2) are increased as 5mol% W6+ doped sensor. And gas sensitivity of sensor is not influenced by 1mol% and 10mol%W6+ doped TiO2. The sensitivity of oxygen sensor made by 5mol% W6+doped TiO2 is increased. The O2, CO, NH3 and H2 sensitivity of sensor made by 35mol%Mo6+ doped TiO2 are all lower due to higher sintering temperature up to 600℃. 4. With the different ions for doping, the mechanism for gas sensitivity is based on the adsorbed ability of oxygen molecules on the surface of doped TiO2.