流化床原子层沉积可控制备超细半导体纳米簇改性TiO2光催化剂及其催化机理研究

Surface modification of titanium dioxide nanoparticles using semiconductor nanoclusters is one of the popular techniques for photocatalytic activity enhancement. However, traditional wet-chemistry methods have several shortcomings, especially the ability to precisely control the cluster size at ultrasmall scale (i.e., a few nanometers or smaller). Therefore, photocatalysis research at this scale is still limited.. In this proposal, we will employ atomic layer deposition (ALD) in a fluidized bed reactor to deposit metal oxide semiconductor (MOS) nanoclusters onto TiO2 nanopowders for surface modification. Owing to its self-saturating chemical reactions, ALD provides the ability to precisely control the amount of depositing materials and the cluster size at the atomic level. This allows us to study the photocatalytic activity of modified TiO2 nanomaterials at ultrasmall scale. The main research of this project includes (1) the investigation of fluidization behavior of the nanoparticles in a fluidized bed reactor and its influence on the ALD products, and (2) the photocatalytic properties of the MOS/TiO2 nanomaterials with the focus on the influence of cluster size and density at ultrasmall scale, the charge transfer at the interface between the TiO2 and the MOS nanoclusters, and the effects of the surface acidity and other surface properties to the photocatalytic activity. This project aims not only to explore a novel synthesis method for advanced photocatalysts, but also to bring new insights into the photocatalytic properties of the MOS/TiO2 materials.

半导体纳米簇复合是提高TiO2光催化活性的有效手段。传统制备方法很难精确控制纳米簇尺寸，超细尺寸纳米簇半导体复合所引起的特殊表界面效应难以彰显，对其电荷转移路径及其光催化机理还缺乏认识。本申请拟采用原子层沉积（ALD）技术，精确控制界面薄膜厚度、粒子尺寸，在TiO2纳米颗粒表面沉积超细且均匀的纳米簇粒子，充分发挥表界面效应，提升光催化剂的制备水平。通过研究颗粒在流化床中的流化性能、界面传质机理，建立以流化床反应器为基础的制备均匀、可控纳米团簇的ALD反应技术，研究气相沉积条件对超细纳米簇尺寸和结构的影响规律，探明团簇尺寸对光催化性能的影响机制，探究纳米簇存在时的界面电荷传输效应与电子转移催化氧化还原反应特性，探索表面酸性等表面性质对光催化过程的影响，为TiO2基纳米复合光催化剂制备提供理论支撑。

半导体纳米簇复合与离子掺杂是提高TiO2光催化活性的有效手段。传统制备方法很难精确控制物质的沉积量，亚纳米尺度的特殊表界面效应难以彰显，对其电荷转移路径及其光催化机理还缺乏认识。本项目采用常压流化床原子层沉积（ALD）技术，精确控制界面层厚度，以SiCl4和H2O为前驱体在TiO2纳米颗粒表面沉积超薄SiO2膜，调控TiO2的光催化活性，充分发挥表界面效应，提升光催化剂的制备水平。通过ALD SiO2改性TiO2探明了膜层厚度与其光催化活性之间的关系，证实了ALD在探究材料表界面效应方面的突出优势。成功将高温ALD SiO2拓展到室温下进行，且膜层中无Cl元素残留，采用密度泛函理论模拟探究了常温ALD SiO2和高温ALD SiO2的反应机理，有望将该成果应用到温度敏感型材料的沉积改性。利用超重力技术强化化学沉淀过程中的微观混合，制备了系列Fe、Co掺杂纳米TiO2光催化剂，其高效的微观混合使Fe、Co均匀分散进入TiO2的晶格内部，有效提高了TiO2的量子效率和光能利用率。该设备成功将纳米TiO2的制备与掺杂改性同步实现，有望为高效纳米光催化剂的连续制备提供借鉴。