Investigations On The Preparation And Properties Of Micro/Nanostructure ZnO Synthesized Via Wet Chemical Approach

Zinc oxide ( ZnO ), with a wide band gap ( 3.37 eV ) and large exciton binding energy (～60 meV ), has attracted much more extensive interest owing to its significant and fascinating applications in many fields, and has potential for fundamental studies on nanoscale chemistry and physics. It has a wide range of applications in gas sensors, optoelectronic devices, light-emitting diodes ( LEDs ), electron field emitters, solar cells,micro electromechanical systems (MEMS), biomedicine and catalysis, and so on. So in recent years, the preparation and applications of micro/nano-structural ZnO have attracted more and more attention. In this dissertation, the various conformations of ZnO nanostructures were systematically synthesized and investigated. The main results are as follows:1. Polymorphic ZnO products were synthesized without using any surfactants in the reaction of aqueous solution of zinc chloride and NaOH at low temperature ( 40-90°C ). And the products were characterized by scanning electron microscope ( SEM ), X-ray diffraction ( XRD ), transmission electron microscopy ( TEM ), UV-Vis absorption and photoluminescence spectroscopy ( PL ). The results indicate that the nanorods were straight and smooth with the diameters ranging from 60-120 nm. The morphology and microstructure of ZnO can be tuned by varying the growth temperature and crystallization condition. The as-sythesized product exhibits weak blue luminescence and strong orange luminescence, which may arise from the specific defects ( e.g., O i?,O v et al ).2. Zn-ZnO core-shell nanomaterials, which consist of a Zn sphere core and ZnO nanorods shell, were synthesized by low-temperature water-bath process in the presence of oleic acid-ethanol. The sizes of the products depend on the diameter of Zn spheres and the ZnO nanorods which form the shell with the diameters ranging from 80-150nm. By changing the reaction conditions, different core-shell structures can be attained. The result indicates that oleic acid and ethanol mixture plays an important role in forming gap space of the core-shell structures, while the size of ZnO nanorods of the shell can be controlled by magnetic stirring.3. Novel hierarchically structured ZnO rods with polycrystalline nanostructures grown on the surface in large density were fabricated by cetyltrimethyl ammonium bromide ( CTAB ) assisted hydrothermal process. The microrods are approximately 1.5μm in diameter and the nanosheets which grown on the surface are ca. 5 nm in thickness. The morphology of hierarchical structures can be easily controlled by adjusting the reaction temperature and adding CTAB. The growth mechanism is suggested from two aspects: the development of crystal defects and the minimization of surface energy. The as-prepared hierarchical products are desirable for photodegradation of phenol in waste water treatment because of their hierarchical morphology, confirming the feasibility for the design of multifunctional ZnO by the development of hierarchical structures.