Synthesis And Photocatalytic Properties Research Of ZnO Nanomaterials And Core-shell Structure

Searching the clean energy and settling the environment pollution are the urgent problems that we currently face. Especially, environmental pollution has surpassed the threshold of natural purification. In recent years, semiconductor based photocatalysis seems to be the most effective methods in wastewater treatment. Semiconductor based photocatalysis is a ‘green chemistry approach’ with many advantages, such as high efficiency, low cost, non-selectivity, low temperature and non-energy intensive approach for complete mineralization of pollutants. Among the various semiconductor photocatalyst, zinc oxide has attracted extensive attention for its photocatalytic applications owing to its easy preparation, low cost, various morphologies, good photocatalytic performance and perfect biocompatibility. But there are still many technical bottlenecks before the using of ZnO photocatalysts in large-scale application, such as simplifying of the synthesis process, reducing the cost, improving the photocatalytic efficiency and simplifying of the seperation of photocatalyst. In this thesis, we will focus on settling these problems.(1) The synthesis process is simple and the cost is low for ZnO production at present. But the environmental pollution is so seriously that the demand of ZnO photocatalyst will exceed the current production in future. Under the circumstances, we should simplify the process and reduce cost further to accelerate the marketization of ZnO photocatalyst. Four ZnO films with different surface morphologies have been synthesized via a hydrothermal method after different reaction times. It is worth mentioning that this is a completely green method which does not require any other chemicals except that Zn foil served as Zn source in the experiment. This method is also very simple and cost less. After the preparation, some analysis instruments were used to characterize the crystallinity, morphology and optical property of ZnO structures. Growth mechanisms of ZnO were proposed based on these results. Furthermore, ZnO films with different morphologies and crystal growth habits exhibited different photocatalytic activities. Optical properties and morphology did great influence on the photocatalytic activities of ZnO films.(2) To find ZnO materials with higher photocatalytic activity and make ready for commercial application of ZnO, the relationship between the morphologies and its photocatalytic activities should be clarified. Five kinds of ZnO nanopowders with different morphologies were successfully synthesized via hydrothermal method. By using different surfactants and controlling the concentration of surfactant in the reaction mixture, ZnO nanoparticles and nanoplates were obtained. Researches on structures and optical properties have been carried out by using some analysis instruments. Among all samples, ZnO particles with small sizes and rough surface have high concentration of Oxygen. These factors result in better photocatalytic activities.(3) To facilitate the separation process and reduce the usage cost of photocatalysts in practical application, Fe3O4@ZnO nanocomposites were synthesized by a simple two-step chemical method. Photocatalytic investigation of Fe3O4@ZnO core/shell nanoparticles was carried out using rhodamine B(RhB) solution under UV light. Fe3O4@ZnO core/shell nanoparticles showed enhanced photocatalytic performance in photodegradation of RhB in solution. The core/shell photocatalyst can also be separated from waste water easily. In addition, recycle property of the core/shell photocatalyst is pretty good and almost no decrease in photocatalytic efficiency was observed even after recycling many times.(4) In order to improve the activity of the core/shell photocatalytic further and inhibit the magnetic core from chemical corrosion, novel Fe3O4@SiO2@ZnO/Ag core-shell microstructures were synthesized through template synthesis and layer-by-layer deposition. The obtained samples were characterized in terms of morphology, composition, optical and magnetic property by various analytical techniques and subsequently tested for the photocatalytic activities. The enhanced photocatalytic activities of the core-shell photocatalyst are primarily ascribed to the loading of Ag nanoparticles, which can reduce recombination probability of photogenerated electrons-holes in the surface of hierarchical microspheres. Moreover, the hierarchical microstructured Fe3O4@SiO2@ZnO/Ag photocatalysts could be easily collected and separated by using a magnetic field and reused without any appreciable decrease on photocatalytic efficiency after running several times.(5) In order to using visible light in photocatalytic reaction, we developed the design and synthesis of urchin-like Fe3O4@SiO2@ZnO/CdS core shell microspheres, in which the multiple functional components were integrated successful into a single microcomposite. Photocatalytic preformances were evaluated by photocatalytic elimination of rhodamine B(RhB) under visible light irradiation. Compared with the Fe3O4@SiO2@ZnO microspheres, Fe3O4@SiO2@ZnO/CdS microspheres show remarkable enhanced visible light photocatalytic activity beneficial form the sensitization of CdS, which can extend visible light absorption and facilitate the separation of photoinduced carriers. Effect of CdS loading amount on photocatalytic activity was also investigated and the optimal CdS loading amount was founded. Furthermore, it is worth noting that these multifunctional microspheres exhibit excellent magnetic response and high stability. The core shell photocatalysts can also maintain high photocatalytic activity even after running five cycles.