The Structure Adjustment Of Zn-based Photocatalyst And The Synergy Effect In Photocatalytic Applications

Solving the pollution problem and searching for abundant and renewable energies is one of the most important challenges of the 21st century. Semiconductor photocatalytic technology can achieve the advantage of degradation pollutants, producing hydrogen energy and photovoltaic conversion by the rich solar energy. So the synthesis, optimization and application of semiconductor photocatalyst are the quick and efficient way of utilization, transformation and storage of solar energy. In the process of finding, synthesising and applying the catalysts, there are many factors that can affect the performance, such as the electronic structure of materials, morphology, crystallinity, defects and particle size etc. All the factors work together to influence the ability of the catalysts. Based on the structural control and optimization of the performance of zinc-base nanomaterials, this thesis took the catalytic synergetic effect on the catalytic performance as the guiding ideology to design and synthesize. Starting with the research of the electronic structure of nanomaterials, morphology and charge transfer. And explore the role of different influence factors in the formation and optimization process of nanometer materials. It reveals the cooperation of the various factors in the material system optimization, which realizes the controlled synthesis of nanomaterials and their functionalization. The main research contents are listed as follow:The first chapter introduced the research background of this thesis, including the research status and development of semiconductor photocatalytic technology, the background of the Zn-based photocatalysts; then we pointed the importance of the nanomaterials systemic design and optimization and demonstrated the influence of the catalytic synergetic effect on catalytic performance in the process of synthesizing the effective photocatalysts. Finally, we briefly introduced the research ideas and content.In the second chapter, with BiOI/ZnO 2D/2D heterojunction as a model system, we report a new strategy that utilizing synergistic effect of inner built-in field, internal polar field and porous nanostructure of polar semiconductors to improve photocatalytic activity. The construction of a semiconductor/semiconductor heterojunction demonstrates its superiority when properly designed, because the band level differences and inner built-in field in the heterojunction could provide the driving force for the separation of photogenerated electrons and holes. Besides the BiOI/ZnO 2D/2D system may possess a strong electronic and physical coupling effect, which is believed to increase the contact area between the components, thus facilitating fast electron transfer across the heterojunction interface and resulting in the enhancement of photoactivity. And the transfer direction and distance of the separated carriers is controlled by the inter electric field and porous structure. Our study should facilitate a deeper understanding of both enhancing the separation and ingeniously controlling the spatial charge transfer of the separated carries in heterojunction photocatalysts, and provide a reference for the design of higher efficiency heterojunction photocatalysts based on polar semiconducors.In the third chapter, we chose the zinc gallate as the effective catalyst and synthesized the hollow spheres by the hydrothermal method in one step. In the process, the thermodynamics (reaction temperature) and the dynamics (surface active agent, reaction temperature/time) work together to control the morphology. The spheres had better ability than the particles and there was also difference ability between the spheres with different degree of crystallinity and particle size. By characterized the structure, components and photoelectric property of the nanomaterials, we demonstrated the influence of the synergetic effect on catalytic performance. And we proved the fact that the ability of the catalysts was influenced by many factors and the final ability was up to the cross-multiplication, as η=ηcrystallinity×ηdects×ηcharge transfer resistance×η...The research provides a theoretical guidance and reference to the design, synthesis and optimization the performance of other nanomaterials.In the last chapter, we summarized the conclusions, demonstrated the innovative points of this dissertation and made the prospects of the further studies.