Synthesis And Characterization Of ZnO Nano Materials And Superstructures

In this dissertation, the conventional solid state reaction and the solvothermal-hydrothermal technique have been developed for the synthesis and assembly of ZnO nanomaterials. The suitable solid dispersant were used in the mechanochemical solid state reaction combining with a following thermal decomposition reaction to prepare well-dispersed ZnO nanocrystals with uniform diameter of < 5 nm. We also adopt a designed one-step, low-temperature, direct, and inexpensive solvothermal processing to prepare comet-like pattern of highly-oriented, standing ZnO nano/micro rod arrays. The main points are summarized as following:1: Promoted mechanochemical solid state reaction - thermal decomposition reaction. Hexagonal nanocrystalline ZnO with uniform average diameter of 3.8 nm were prepared by a former room-temperature mechanochemical grinding of the Zn(CH3COO)2 and H2C2O4(2H2O powder mixture for obtaining Zn(C2O4)2(2H2O nanoparticles and a subsequent thermal decomposition reaction of ZnC2O4(2H2O nanoparticles for obtaining nanocrystalline ZnO with uniform diameter of 3.8nm. the solid NaCl was added in the above processes. There are two key points in this experiment: (1) The reactant can directly decompose to ZnO, which avoids the impurity of production; (2) The solid inert salt NaCl plays as the dispersant to decrease the agglomeration and the secondary growth of generated nanoparticles in both the grinding and the thermal decomposition. These can be applied to prepare other nanomaterials. 2: Preparation of ZnO superstructures by solvothermal processing. Highly-oriented ZnO nanorod arrays were grown on the top surface of the Au particles to form comet-like ZnO superstructures by a one-step, low-temperature, direct, and inexpensive solvothermal processing, involving three reaction stages. 1.) The formation of Au particles by the solvothermal reduction of the Au(ethylenediamine)23+ complex in relatively short time. 2.) To pattern the top surface of the Au particles generated at stage 1 with the ZnO-Au coating formed by both the epitaxial growth of ZnO clusters and the continuous deposition of Au particles till the HAuCl4·4H2O was consumes. 3.) The continuously epitaxial growth of the ZnO clusters to create radial and standing ZnO nanorod arrays above the ZnO-Au coating till the Zn(CH3COO)2·2H2O was consumes. In experiment, we found that the formation of the Au particles is faster than the formation of ZnO clusters in the solvothermal reaction; There exists the lattice matching between the ZnO (001) plane and the Au(111) plane, as well as the natural growth of the ZnO atoms of the (001) plane on the Au (111) plane; The morphology and structure can be controlled by changing the concentration of reactants and the reaction time. This design may provide a new idea to directly grow patterned one-dimensional superstructures.