| The unique properties of multivalent and oxygen vacancies in tin oxide decide their potential applications in gas sensing, photocatalysis, lithium-ion batteries, super capacitors, semiconductors and so on. Sn3O4 with mixed tin valences is a narrow band gap semiconductor material, electrons in the valence band could transfer to the conduction band under visible light excitation, showing the advantage in utilization of solar energy. However, the photocatalytic hydrogen evolution of Sn3O4 suffers inefficient and relies on noble metal as co-catalys, thus increasing the cost of applications. In addition, tin oxide is an excellent gas sensing material, while their gas sensing performance is difficult to be improved because of the stable exposed facets by hydrothermal method, which have poor electron transport properties.To find effective ways to solve the above problems, the thesis choices a visible light active photocatalyst Sn3O4 nanosheets as basis, constructing heterostructures with UV active photocatalyst TiO2 nanobelts and exploring their photocatlysis and gas sensing activity. The main contents of this thesis are as follows:1. Snl2·2H2O is adopted as the source of tin and partial oxided into scaly Sn3O4 nanosheets via hydrothermal nucleation-growth process, the size of the nanosheets are 100 to 400nm, and thickness is about 10nm, forming intertwined petal-like structure. Analysising the structural characterization, element content, valence composition, optical properties, UV-Visible diffuse reflectance (DRS), photofluorescence (PL) spectraof the synthesized Sn3O4. Also, a standard three-electrode cell in the dark and light atmosphere was used to trace the change of photoelectricalchemical (PEC). On this basis, Sn3O4 sample was excitated in the UV and visible light to simulate photocatalytic degradation, hydrogen production, and cycle experiments.2. The obtained Sn2O4 nanosheets intermediate were further heated to complete oxidized into SnO2. The nanosheet morphology was substantially maintained, and the exposed planet of the SnO2 was found to be high energy (001) facet, which in turn exhibited strong absorption to oxygen and contributed in lowing working temperature. The influence of different heating temperature on the formation of SnO2 was also explored. Furthermore, the gas sensing activity, optical properties and resistance change of the gas sensors that based on active SnO2 nanosheets when exposed to alcohol, methanol and acetone at different operating temperatures were traced.3. Construction of a novel scaly Sn3O4/TiO2 nanobelts heterostructure photocatalyst via a simple hydrothermal method. TiO2 nanobelts were pre-synthesized by alkaline hydrothermal process, and roughened by sulfuric acid at at a high temperature. Similarly, scaly Sn3O4 nanosheets can assembled on TiO2 nanobelts in situ by the co-hydrothermal methold. The morphology and distribution of Sn3O4 can be easily controlled by adjusting the Sn/Ti atomic ratio. The effect of Sn/Ti ratio on photoelectrochemical and photocatalytic activity were conducted to find the optimum Sn/Ti ratio, and explored the possible mechanism.4. Imspired by the combination of Sn3O4 and TiO2, and conversion process of Sn3O4 to SnO2, SnO2/TiO2 nanobelts heterostructures were synthesized by two-step process, in which the TiO2 nanobelts acted as a support material on the surface of the epitaxial growth of Sn3O4, then Sn3O4/TiO2 heterostructure were heated at a high temperature to obtain SnO2/TiO2 heterostructure. The improvement in gas sensing activity of the SnO2/TiO2 were compared with single material TiO2 and SnO2, and the impact of different amounts of TiO2 were explored.It was found the prepared Sn3O4 is yellow powder, tests show it is an n-type semiconductor, with the band gap of 2.61 eV. Sn3O4 could efficiently degrade pollutant organic dyes under visible light excitation, and shows good recycliblity. SnO2 nanosheets that oxided from Sn3O4 is black powder. Compared with SnO2 prepared by traditional method, the prepared SnO2 gas sensor exhibits selectivity to ethanol, low temperature sensitivity to 43℃, and good repeatability. Sn3O4/TiO2 nanobelts heterostructure that modified from Sn3O4 shows enhanced UV-visible light photocatalysis, which could be related to the band match between Sn3O4 and TiO2, and the efficient transport and separation of photo-excited electrons and holes of the heterostructure.Thanks to the high active exposed facets of the SnO2 nanosheets, dispersion effect of TiO2 nanobelts in gas detection and electronic conduction, the modified SnO2/TiO2 nanbelts heterostructure exhibts nearly twice that of SnO2 in response to ethanol within working temperature 43 to 276℃.To sum up, this thesis assembled Sn3O4 on TiO2 nanobelts and formed scaly Sn3O4/TiO2 nanobelts heterostructures for the first time, this material has outstanding visible light photocatalytic degradation of organic dyes and photocatlytic hydrogen evolution, which should have promising application in environmental protection and new energy; SnO2 with high energy facets were successfully prepared by conversion of Sn3O4 to SnO2 by heat treatment. The prepared SnO2/TiO2 nanbelts heterostructure show impressive near room temperature gas sensing performance, will win its applications in sensing area. |
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