Synthesis, Characterization, And Properties Of ZnO Micro/nano Materials By Hydrothermal Process

ZnO is a direct and wide band gap semiconductor of II-VI group with an energy gap of3.37eV at roomtemperature. Nanostructured ZnO materials have the promising applications in LCD displays, solar cells,protecting coatings, gas sensors, solid illuminations and UV optical devices. Due to the novel properties ofsemiconductors depend on their size, shape, and crystalline structure, it is of significant importance tocontrol the shape and size of semiconductors in a controllable way. The method for preparation of Zn0nanomaterials can be divided into physical methods and chemical methods among which, the hydrothermalsynthesis method is favorable because it is simple, cheaper and need no expensive apparatus. In this thesis,we synthesized several nanostructures using hydrothermal synthesis method. The as-obtained product wasinvestigated by X-ray diffractometer, high-resolution transmission electron microscopy, scanning electronmicroscopy and ultaviolet (UV)-visible spectrum. The main contents of our work are as follows:1. Mannite supported hydrothermal synthesis of hollow flower-like ZnO structures for photocatalyticapplicationsWith the introduction of mannite, hollow flower-like complex superstructures assembled by ZnOnanorods have been successfully constructed via a simple hydrothermal method. The results reveal that themannite-directed hydrothermal process is essential for the final products. The morphologies of the ZnOpowers could be easily tuned by changing the molar ratios of mannite to zinc ion, the amount of ammonia,the reaction time and temperature. A possible formation mechanism of the hollow superstructures has beenproposed, the optical and electrical properties of these ZnO multilevel structures were investigated in somedetail, which showed high photocatalytic activity towards Congo Red (CR) under ultraviolet (UV)irradiation.2. Apple pectin-mediated green synthesis of hollow double-caged peanut-like ZnO hierarchicalsuperstructures and photocatalytic applicationsHollow ZnO superstructures have potential technological applications. With this motivation, a simpleapproach is developed to prepare hollow double-caged peanut-like ZnO hierarchical superstructures withthe assistance of apple pectin. The biotemplate-assisted approach concurs with ‘‘green’’ chemistry as it is simple and environmentally friendly. The products are characterized by SEM and XRD. The results revealthat the pectin-directed hydrothermal process is essential to obtain the final products. The morphologiesand dimensions of the ZnO structures could be easily tuned by varying the molar ratios of the pectin to zincion, the amount of ammonia, the reaction time and the temperature. A possible formation mechanism forthe hollow superstructures is described. In addition, the optical properties of the ZnO multilevel structureswere investigated in some detail. The as-prepared samples showed high photocatalytic activity towardsmethyl orange (MO) under ultraviolet (UV) irradiation.3. In situ synthesis of polydopamine-Ag hollow microspheres for hydrogen peroxide sensingIn this paper, monodisperse polydopamine PDA-Ag hybrid hollow microspheres were synthesized byself-polymerization of dopamine on ZnO microspheres as sacrificial templates. The templates weredissolved in basic media and in situ reduced the incorporated Ag+ion with ascorbic acid. The as-preparedPDA–Ag composites modified glassy carbon electrode exhibited a broad linear range of0.092–20mM forH2O2determination, with a remarkable sensitivity of6.79μA mM1, a detection limit of1.97μM (S/N=3),and rapid response (within5s). Moreover, the electrode showed good reproducibility, anti-interferantability and long-term stability.