| There are various kinds of semiconductors, which exhibit excellent optical, electronic and magnetism properties, leading to extensive use. Among them, metal oxide semiconductor shows special importance. For they are not only semiconductors, the metal ions in them also bring a wealth of physicochemical properties such as catalysis, sensing, energy reservation. With the rapid development of nanotechnology, various physical as well as chemical routes were applied to control the composition and the structure of the material. Thus people get a better understanding of the nanostructure of the material and its close relationship with the properties.In order to get an ideal material with desired properties, many basic methods can be adopted, including doping foreign atoms, making porosity, fabricating hierarchical structure and exposing active facets. Herein, we try to synthesize some metal oxides containing In, Zn, Co or Ti by hydrothermal, solvothermal and electrospinning, respectively. These materials exhibit porous structure, hollow structure, assembly structure, and layered structure. The relationship between the structure and properties on gas sensing or methane conversion was investigated systematically. We attempted to improve their performance by optimizing their structure.Main contents of this thesis:1. Indium organic precursor was synthesized via solvothermal reaction in the mixture of isopropanol and glycerol. The In2O3 materials with porous structure and ultrathin nanosheet assembled hollow structure were obtained by calcining the precursors in the air atmosphere. Isopropanol is used as solvent during the synthesis of the precursor. And glycerol plays a triple role, acting as solvent, reactant as well as structure directing agent. With the help of glycerol, sphere structure and hollow structure assembled by ultrathin nanosheet were formed along different reaction time.Porous In2O3 microspheres were obtained by solvothermal treatment under 180℃ for 1 h followed by calcination process, the organic component is pyrolysed and the morphology is maintained during calcination. The porous microsphere has a large surface area and shows excellent sensing responses towards C1～C3 aliphatic hydrocarbons, including methane (CH4), ethane (C2H6), propane (C3H8), ethylene (C2H4) and acetylene (C2H2). And we find that porous In2O3 calcinated at 350℃ shows both highest surface area and best sensing performance towards alkanes.Hollow structure In2O3 assembled by ultrathin nanosheet were obtained by solvothermal treatment under 180℃ for 6 h followed by calcination process. After examined the structure of the material, we find that the thickness of the nanosheet is around 2 nm. The resulting In2O3 nanosheet show excellent amine sensing performance at room temperature because ultrathin nanosheet offer a large amount of active sites on the surface and the 3D structure adds an additional advantage to avoid aggregation and facilitate the diffusion of the target gas. However, the sensor shows no response towards other gas vapors at room temperature. Besides, we find that the In2O3 with porous structure also show response towards amine, but the response is much lower. The results reveal that the sensing performance is closely related to the structure of the material. The sensing mechanism was studied by us with the help of FT-IR.2. Porous ZnO nanofibers with hollow structure were prepared by the electrospinning method. And the sensing performance towards nitrocompound was studied in detail. The ZnO sensor shows excellent sensing performance, and the sensing limits towards DNT and nitromethane are 3 ppb and 0.1 ppm, respectively. The sensing response represents interaction on different sensing sites in the molecule, and will exhibit different results. The acidity of the material’s surface and the concentration of oxygen species have close relationship towards sensing response. Theoretical calculations were conducted to explain the sensing mechanism. All in all, we find that through investigation on the structure and activity of target molecules as well as that of sensing materials, further understanding of the nature of sensing will be learned.3. Cobalt precursor was synthesized by solvothermal process in the mixture of isopropanol and glycerol. Then Co3O4 with hollow structure were obtained by calcining the precursor in the air atmosphere. The Co3O4 sensor shows good response towards aldehyde and the sensing concentration limitation is 1 ppm. Then we studied the sensing performance of Co3O4 with different structures and correlated the structure and the sensing response. We attribute the sensing mechanism to the adsorption process. What’s more, the good sensing performance towards aldehyde means potential application.4. We studied methane conversion reaction in the confinement structure, porous structure, bimetal structure. (1). Synthesizing the ETS-10 molecular sieve and modified it with rare earth. (2). We synthesized porous TiO2 by stirring under certain temperature. BET test shows that the pore size is ～5 nm and the surface area is ～230 m2/g. Then Au, Ag, Pt, Pd were loaded on the surface of porous TiO2 by UV irradiation. And methane conversion ratio, product distribution and cycle stability under these noble metal modified porous TiO2 were studied. (3). Zn-Ti, Zn-Al, Zn-Ga, Ni-Ti, Ni-Al, Cu-Ti layered double hydroxides were synthesized.To get the accurate results, an online methane conversion and detection system was also developed. |
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