Micro-controlled Synthesis Of Nano-zinc Oxide And Photocatalytic Properties

Nanometer zinc oxide (ZnO) is a versatile and technologically interesting semiconductor material with a wide direct band gap (3.37eV) and a large exciton binding energy of 60 meV at room temperature. It has great potential in applications such as optoelectronics, sensors, antibiosis, ultraviolet ray shield and solar cells. Nowadays nano ZnO has a variety of nanostructures; this makes it a promising material. The properties and application of ZnO nanostructures are strongly dependent on its structures, including the morphology, aspect ratio, size, and orientation. These structural characteristics have an important role in many applications. Consequently, several different synthesis approaches also come into effect to tune the size, shape, and hence the properties of such materials. Among the various synthesis approaches, surfactants can be used in aqueous solutions to tune the size and morphology of ZnO nanostructures which can reduce the surface tension and surface energy, alter the relative stability of the crystal faces and hence result in the formation of various structures of particles. The size and shape of ZnO nanostructures have critically affected its photocatalytic activity.In this article, ZnO nanostructures of different shapes have been synthesized in the presence of different surfactants by a microwave homogeneous precipitation method. The photocatalytic activities of the ZnO samples were also described by photocatalytic decolorization of three dyes aqueous solution at ambient temperature. The experiments showed that the catalytic activity of ZnO is strongly dependent on its size, morphologies and specific surface area, even crystal orientations.Primary contents of the thesis are as follows:Firstly, nanomaterials and nano-zinc oxide have been introduced, providing an overview of preparation, characterization and application. At the same time, the classification and application of surfactants have been described.Secondly, ZnO nanoparticle has been prepared by a microwave homogeneous precipitation method using Zinc nitrate hexahydrate [Zn(NO3)2-6H2O] and hexamethylenetetramine (HMT) [C6H12N4] as raw materials. They have been characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffractometer (XRD), scanning electron microscopy (SEM), and high resolution transmission electron microscopy (HRTEM), respectively. The results demonstrated that the crystallite sizes of the prepared samples are mostly uniform with narrow size distributions.Thirdly, nano-ZnO have been prepared using Zinc nitrate hexahydrate [Zn(NO3)2·6H2O] and hexamethylenetetramine (HMT) [C6H12N4] as raw materials in the presence of various amount of cationic, anionic and non-ionic surfactant. The ZnO powders have been characterized by FT-IR, XRD, SEM, and HRTEM, respectively. The results demonstrated that the type and concentration of surfactant and deposition time have important influence on the morphology and size of ZnO nanostructures. The cationic surfactant and anionic surfactant were better than non-ionic surfactant. Club-shaped hollow ZnO nanostructures have been synthesized in the presence of surfactants SDS. The average crystallite size of the sample prepared in the presence of 0.002M SDS reaches a minimum value (12.9nm).Fourthly, the photocatalytic activity of the as-synthesized ZnO nanostructures was tested with three dyes as the objective decomposition matter, such as Fuchsin acid, Methylene Violet and Malachite Green. The results show that the ZnO nanoparticles present higher photocatalytic activity used as catalysts, and the sample prepared in the presence of 0.002M SDS exhibits the highest photocatalytic activity than other samples. The photocatalytic activity of ZnO is greatly dependent on the combined effects of several factors such as surface composition, the crystallite size and morphology.