| Up to now, nano- and microcrystalline ZnO with various size and morphologies have been reported, including nanorods, hexagonal plates, nanotubes, nanotube bundles, nanobelts, ring-like, flowerlike, nutlike, and hierarchical structures. The investigation of synthesis of ZnO nanomaterials with various structures and morphologies is the basis of the exploration of characteristics and applications of ZnO. On the other hand, for the ternary semiconducting metal oxide ZnSnO3, there are little reports about its fabrications and applications. How to synthesize ZnO and ZnSnO3 with uniform structure, size and low cost is considered as a hot subject of research. It is of great importance to investigate the gas-sensing properties of ZnO and ZnSnO3 nanostructures and explore the relationship between the component, morphology and gas-sensing properties, which are also the research topic of the modification of the gas-sensing properties of sensitive materials. This dissertation is to study the synthesis, characterization, growth mechanism, and gas-sensing properties of ZnO and ZnSnO3. The main results and significance are as follows.Cu-Zn alloy nanoparticles have been prepared by wire electrical explosion method, and Cu-Zn/ZnO core-shell nanocomposites have been prepared by wet-chemical method. The mechanism for the formation of Cu-Zn/ZnO core-shell nanocomposite is also explained. The gas-sensing devices have been fabricated based on the core-shell Cu-Zn/ZnO nanocomposites annealed at different temperatures. The maximal response is obtained for the sensor based on the Cu-Zn/ZnO film annealed at 350°C at the operating temperature of 240°C. The responses of the sensor are about 2.6, 3.3, 6.3, and 9.6 to 20, 50, 100, and 200 ppm CO, respectively. The response and recovery time of the sensor are 20 and 35 s, respectively.The aggregated flowerlike ZnO nanostructures have been synthesized by hydrothermal method. The flowerlike ZnO nanostructures have been prepared by Poly (ethylene glycol) (PEG)-assisted hydrothermal process, which are composed of many ZnO nanorods with ZnO nanoparticles as the building blocks. The ZnO nanorods share the same center, which distribute ununiformly. The nanorods gather into bundles from the active sites in several directions. The ZnO nanorods are single-crystal structures composed of many ZnO nanoparticles serving as the building blocks. The diameter and length of the ZnO nanorods are in the range of 50-280 nm and 1-1.5μm, respectively. There are lots of structural faults between the nanoparticles in the surface of the ZnO nanorods, including stacking faults, crystal plane distortions and dislocations. The possible growth mechanism is also discussed, which reveals that PEG plays an important role of template in obtaining the novel flowerlike nanostructures. The gas sensors have been fabricated based on the above sensitive ZnO materials, and the responses of the sensor are about 3.5, 15.6, 87.8, and 154.3 to 1, 10, 50, and 100 ppm ethanol.Novel aggregative flowerlike ZnO nanorods have been synthesized through a low temperature hydrothermal route without any surfactants and templates. The effect of the reaction time on the size and morphology of the ZnO products is investigated, and the possible formation mechanism is also discussed. The gas sensors have been fabricated based on the above sensitive ZnO materials, and the responses of the sensor are about 6.4, 10.8, 18.1, and 35.7 to 10, 20, 50, and 100 ppm ethanol. The response and recovery time of the sensor are 4.7 and 15 s, respectively.Ti-doped flowerlike ZnO nanorods have been synthesized by a hydrothermal method and the consequent beam evaporation method. The gas sensing properties of the pristine and Ti-doped flowerlike ZnO have also been investigated. It is found that the Ti-doped ZnO sensor exhibits remarkably enhanced selectivity and response to toluene. The Ti-doped ZnO sensor exhibits rapid response and excellent repeatability to toluene. The responses of the sensor are about 1.9, 2.7, 4.3, 5.8, 10.9, and 17.1 to 1, 5, 10, 20, 50, and 100 ppm toluene. The response and recovery time of the sensor are 8 and 20 s, respectively.The nutlike ZnO microcrystals with special morphology and structures have been successfully synthesized via a facile triethanolamine(TEA)-assisted hydrothermal process. The average diameter of ZnO microcrystals is 1.8μm, and the average length is about 2.2μm. The structural characterization reveals that the nutlike ZnO microcrystals are composed of two asymmetrical wurtzite single crystal ZnO twinned-cones. The bottom of the relatively large cone is hexagonal and rough, and the surface of the cone is very smooth. The relatively small cone is composed of lots of ZnO nanoparticles with very rough surface. The reaction time plays a crucial role in determining the final size and morphology of the ZnO samples. With increasing the hydrothermal reaction time, the relatively small cone grows rapidly. Extending the reaction time to 12 h causes the formation of symmetric spindlelike ZnO microcrystals. The investigation of the growth mechanism reveals that during the hydrothermal process TEA plays an important dual role. As a surfactant, TEA not only can affect the growth rate of different planes, but also can hydrolyze and release OH- to affect the alkaline of the solution. The nutlike ZnO sensor exhibits rapid response and recovery to ethanol. The response and recovery time of the sensor are 2 and 7 s, respectively. The responses of the nutlike sensor are about 1.8, 2.2, 4.0, 6.9, 14.1, and 27.2 to 1, 5, 10, 20, 50, and 100 ppm ethanol.The hollow ZnSnO3 nanocubes with peculiar cage- and skeleton-like architectures have been successfully synthesized for the first time. The side length of the cubic structures is in the range of 200-400 nm. The possible formation process and formation mechanism is proposed. The gas sensors have been fabricated based on the above peculiar ZnSnO3 materials, which exhibits rapid response to ethanol and toluene. The optimal operating temperatures to ethanol and toluene are 270 and 210°C, respectively. The response and recovery time of the sensor are about within 2 and 6 s, respectively. At the optimal operating temperature of 270°C, the responses of the sensor are about 2.8, 4.7, 7.2, 13.1 and 22.5 to 10, 20, 50, 100 and 200 ppm ethanol. At the optimal operating temperature of 210°C, the responses of the sensor are about 1.96, 2.85, 3.14, 3.9 and 4.91 to 10, 20, 30, 40 and 50 ppm toluene.Furthermore, the hierarchical ZnSnO3 hollow nanocages have been prepared for the first time. The structural characterizations reveal that the ZnSnO3 nanocages are composed of lots of ZnSnO3 nanoparticles. The reaction time plays a crucial role in determining the final morphology of the ZnSnO3 samples. With the reaction time increasing to 4 h, the hierarchical ZnSnO3 cubes begin to form. With the reaction time prolonged to 8 h, the morphologies and structures of the hierarchical ZnSnO3 cubes are similar to those of the samples with the reaction time of 12 h. When the reaction time is further up to 24 h, the hierarchical ZnSnO3 nanostructures are gradually etched into ZnSnO3 nanoparticles and fragments. There are two key factors in determining the formation of the hierarchical nanostructures: one is the numerous ZnSnO3 nucleus formed in the early stage of the reaction, and the other is the change of the growth rate of {100} and {111} planes by the addition of (CH2)6N4 (HMT). At the corresponding optimal operating temperature, the responses of the sensor are about 3.1, 4.0, 9.2, 13.3 and 30.9 to 10, 20, 50, 100 and 200 ppm ethanol. At the optimal operating temperature of 210°C, the responses of the sensor are about 3.0, 3.7, 4.3 and 5.0 to 10, 20, 30, and 50 ppm toluene.
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