| Zinc oxide (ZnO) is an important Ⅱ-Ⅵ direct band gap semiconductor material, with a wide band gap (3.37eV) and high exciton binding energy (60meV). Zinc oxide nanomaterials possess excellent properties of both nano material and semiconductor material. Zinc oxide nanomaterials have much more superior characteristics than general zinc oxide in photoelectric,piezoelectric and thermoelectric properties. In recent years, nano ZnO have attracted great ateention at home and abroad.It has been demonstrated that the catalytic properties of nanometer-sized ZnO were related to its microstructure morphology closely and then more and more researches focus on morphology of nano ZnO. Zinc oxide of hexagonal wurtzite structure is polar crystal along the c-axis and for this reason, rod-like nano zinc oxide with high aspect ratio can be easily achieved. However, by altering external factors, the growth rate of specific crystal plane can be inhibited or promoted, so as to change the relative rates of growth of its various faces, finally ZnO nanocrystals of different morphology are synthesized. So it is popular for scholars to study the influence of external reaction conditions on morphology of nano zinc oxide.In this thesis, hydro thermal/solvothermal method、liquid paraffin high (atmospheric) pressure heat treatment and solvothermal-inverse microemulsion method were used to synthesize nano ZnO. The crystal structures and morphologies of synthesized ZnO were characterized by XRD、SEM、TEM、 FTIR and other analytical techniques respectively.The influence of preparation methods and reaction conditions on the morphology of ZnO were discussed, the main results are summarized as follows:In hydrothermal/solvothermal method, micron-sized spherical-like、multi-dimensioal granular-like、nano rod-like and a series of different morphology of ZnO crystal were synthesized through organic amine auxiliary route. Meanwhile the effects of the variety of temperature, precipitation agents, reaction solvent, zinc sources, reaction time and precipitant concentration on the nanometer ZnO morphology were investigated systematically. Results show that it is easier to generate multi-dimensional grains with the increasing of reaction temperrature. The stronger the polarity of the solvent is, the smaller the length to diameter ratio of nano ZnOparticles is. Different sources of zinc salt, different the morphology of ZnO synthesized.In the liquid paraffin high (atmospheric) pressure heat treatment, liquid paraffin and Span80were used as reaction solvent and surfactant respectively. The zinc acetate (zinc nitrate)-isopropanol pretreatment mixture was dispersed amo ong them aiming to yield ZnO directly without calcination under atmospheric pressure or high pressure. Results showed that the heat treatment environment in the liquid paraffin changed ZnO crystal growth process, but still followed the preferred orientation growth habit along the crystal C axis.In solvothermal-inverse microemulsion method, liquid paraffin is used as the oil phase and the pretreatment mixture of zinc salt, diethanolamine and isopropanol is used as the water phase. Firstly, using Span80and Tween80as complex matching surfactants and n-butyl alcohol as the assistant surfactant, the inverse microemulsion was prepared. Then the nano zinc oxide is obtained after solvothermal reaction. Results showed that the solvothermal-inverse microemulsion method can make nano-ZnO morphology more unified and the size more uniform. It is also observed that when zinc nitrate is used, hexagonal layered nano ZnO is achieved, while zinc acetate is employed, micro spherical-Ike ZnO is abtained.Compared with other two methods, size distribution of nanometer ZnO particles synthesized by solvothermal-inverse microemulsion method is more uniform. The agglomeration of ZnO particles is also reduced. |
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