Preparation And Gas Sensing Properties Of Hierarchical Nanostructures Of Oxide Semiconductor/TiO₂

Since twentieth Century, the rapid development of the economy to create a huge economic benefits for people, but also to the sustainable development of the natural environment has brought many problems. The toxic and harmful gases in the atmosphere is most closely related to human life, Therefore, it is an urgent task for researchers to prepare the sensors which can detect these toxic and harmful gases rapidly. The TiO2 is a wide band gap semiconductor material, the band gap is 3.2 eV（anatase） or 3 eV（rutile）, because of its unique structure and chemical properties,has been widely used in the field of photocatalysis, gas sensors and so on. The gas sensing materials of TiO2 has the disadvantages of high operating temperature, poor selectivity and so on, doping, surface modification and composite formation with other gas sensing materials are commonly used to improve the gas sensing properties of TiO2.In this paper, TiO2 was selected as the basic material, and TiO2 nanofibers were prepared by electrospinning technique, and the active sites of TiO2 nanofibers were adjusted by doping or surface modification. At the same time, ZnO/TiO2 and Fe₂O₃/TiO2 hierarchical nanostructures of gas sensing materials were prepared by two-step hydrothermal method, systematic study of the different hydrothermal time and concentration to get hierarchical nanostructures on the gas sensing properties of impact, due to the larger specific surface area and more active sites, which will improve the gas sensing properties of providing a hierarchical nanostructures.Specific research work is as follows:1. The principle of electrospinning technology was introduced in this paper,and preparation of TiO2 nanofibers by electrospinning technology, effect of the working temperature of TiO2 nanofibers on the gas sensing properties were studied, the results showed that the working temperature is 375 C, TiO2 nanofibers has higher sensitivity to acetone gas.2. Studied the effect on the gas sensing properties of the ZnO nanoparticles surface modified TiO2 nanofiber. The results show that the surface modification ofZnO nanoparticles can improve the gas sensing properties of TiO2 nanofibers, ZnO nanoparticles modified TiO2 nanofibers improves the sensitivity to acetone gas, and its operating temperature is 375 ℃, the sensitivity of ZnO nanoparticles modified TiO2 nanofibers reached 4.90 to 100 ppm acetone gas. At the same time, the Zn doped TiO2 nanofibers were prepared by electrospinning, and the effect of gas sensing properties of the Zn doped TiO2 nanofibers was studied. The results showed that Zn doping could significantly improve the sensitivity of TiO2 nanofibers to acetone gas, When the working temperature of the sensor is 375℃,the sensitivity of Zn doped TiO2 nanofibers reached 6.36 to 100 ppm acetone gas.Moreover, ZnO/TiO2 hierarchically nanostructured materials were prepared by electrospinning method and hydrothermal method. First of all, TiO2 nanofibers were prepared by electrospinning; then TiO2 nanofibers as template substrate, ZnO/TiO2 hierarchical nanostructures were prepared by hydrothermal method, the hierarchical nanostructures were analyzed by SEM and TEM, we also study the different hydrothermal reaction time of growth on different TiO2 nanofibers on the influence of the morphology of ZnO nanocone column. The results showed that the gas sensing properties of ZnO/TiO2 hierarchically nanostructured materials is better than by the gas sensing properties of TiO2 nanofibers and ZnO nanocone column,the optimum reaction time of ZnO nanocone column for 2h, the hierarchical nanostructures optimal sensor operating temperature to 350 ℃,and the sensitivity of ZnO/TiO2 hierarchical nanostructures reached 21.70 to 100 ppm acetone gas.3. We prepared α-Fe₂O₃/TiO2 hierarchical nanostructures by electrospinning method and hydrothermal method successfully. First of all, we prepared TiO2 nanofibers via electrospinning, and TiO2 nanofiber as the substrate for the two step hydrothermal, then was annealed at 500 ℃ for 2h in air atmosphere, andα-Fe₂O₃/TiO2 hierarchical nanostructures were prepared, the hierarchical nanostructures were analyzed by SEM and TEM, the results showed that α-Fe₂O₃ nanorods uniformly distributed on the outer surface of the TiO2 nanofibers andα-Fe₂O₃ nanorods is about 20 nm in diameter. The gas sensing properties of the hierarchical nanostructures, TiO2 nanofibers and α-Fe₂O₃ nanostructures were tested by instrument, the gas sensing properties of the α-Fe₂O₃/TiO2 nanostructuredmaterials were significantly better than that of the TiO2 nanofibers and the α-Fe₂O₃ nanostructures, sensitivity of α-Fe₂O₃/TiO2 hierarchical nanostructures reached 40.1to 100 ppm acetone gas at 275℃.