Studies On Preparation And Mechanism Of Porous ZnO Nanostructures

Zinc oxide (ZnO) is an important member in the II—VI group semiconductors with wide direct bandgap energy of 3.37 eV. The large exciton binding energy (60 meV) of ZnO crystal can ensure efficient excitonic emission of ultraviolet (UV) luminescence at and above room temperature. ZnO is a unique material that exhibits semiconducting and piezoelectric dual properties. Because of the richest nanostructures and unique properties, ZnO could have great potential applications in optoelectronics, sensors, transducers and biomedical sciences such as light-emitting diodes, photodiodes, nanolasers, dye-sensitized solar cells, varistors, photocatalysis, and gas sensors. So far, ZnO nanorods, nanotubes, nanorings and urchin-like, bone-like, feather-like patterns and structures have been synthesize by physical or chemical methods, sunch as sol-gel process, chemical vapor deposition (CVD), and electro-deposition and so on. Now, searching new structures, properties and applications of ZnO has become one of the most important fields in materials science.In this thesis, at first, we retrospect the wurtzite structure model of ZnO crystal. Then, the electrical, optical properties of ZnO are discussed. And the applications of ZnO in preparation of photocatalysis, sensors and ceramic are presented. Then we introduce the synthetic methods, such as sol-gel process, chemical vapor deposition, and electro-deposition and so on.In Chapter 2, surface nanonized ZnO ceramic have been obtained using ZnO ceramic made from commercial ZnO powders and chloroform (CHCl₃) during autoclave tests and pyrolysis process. The SEM and XRD observation are used to characterize the morphologies and crystalline structures, and then the possible growth process is discussed: at first, CHCl₃ decompose into HCl, and HCl react with ZnO and synthesize Zn₅(OH)₈Cl₂-H₂O on the surface of ZnO ceramic; secondly, Zn₅(OH)₈Cl₂-H₂O decompose into porous ZnO plates. The surface nanonized ZnO ceramic is obtained.In Chapter 3, we use ZnCl₂ and (CH₂NH₂)₂ as starting materials to prepare porous ZnO micro-flakes through Solution-based Method and pyrolysis process. The morphologies and crystalline structures of ZnO are also obtained by SEM and XRD observation. The results show the precursor and final product has the similitude structure. The effect of (CH₂NH₂)₂ is discussed in this article. Thereby, the possible growth process is explained. Furthermore, the relationship between the specific surface area of the sample and the reaction condition is discussed in the thesis.