介孔单晶TiO2的形貌调控对光催化全分解水增效机制研究

Photocatalytic overall water splitting using solar energy is one of the most desired methods to solve the energy and environmental problems. Semiconductor mesoporous single crystals have attracted considerable attention due to the merits of excellent light absorption ability, large surface area for catalysis and superior charge-transport capability. However, most of the materials have a relative large size and do not afford the low recombination rates of the photogenerated electrons and holes. Besides, the diameters of the internal mesopore are usually larger than 40 nm and each pore act as a separate reaction center. Furthermore, the catalytic reaction on the surface need enhancement. This project aims to desire and synthesize mesoporous TiO2 single crystals with relative small sizes and small mesopores to promote the efficiency of photogenerated charge separation, light absorption and increase the active sites on the surface. In addition, in order to increase the sluggish overall water splitting kinetics, the project emphasis on loading spatial separation dual cocatalysts to promote the H2/O2-evolution efficiency. Various techniques will be introduced to investigate the dynamics of excited state deactivation, confirm the influence condition and control mechanism of photogenerated electron/hole separation, transfer and recombination processes. On the basis of experimental data and theory calculation, we will construct the dynamic model of charge transfer and consequently reveal the catalytic mechanism in the present overall water splitting system.

利用太阳能全分解水制氢是解决全球性能源危机与环境污染的理想途径之一。介孔单晶半导体材料因具有优异的吸光能力，丰富的反应活性位点和优异的导电性、电子迁移率等优势得到了广泛关注。目前，制约介孔单晶半导体效率提高的主要原因有：（1）材料粒径和孔径较大，导致光生电子/空穴的分离只限于局部的孔结构，不能充分发挥其促进电荷分离方面的优势；（2）表面催化反应效率还有待进一步提高。基于此，本项目旨在设计和制备相对小尺寸、小孔径、有效促进光生电荷分离的一维介孔单晶TiO2，从结构层次提高光生电荷分离效率、吸光效率和反应活性位点。通过改进合成方法，负载空间分离的双助催化剂，促进表面反应的动力学过程，从而达到提高全分解水效率的目的。探究材料中电子-空穴的光激发生成、分离、迁移、复合影响因素。利用实验与理论计算相结合的方式建立电子传递动力学模型，确定活性中间体和反应位点，揭示体系光催化全分解水反应机理。

光生电荷复合严重和表面反应速率慢是制约光催化分解水制氢效率提高的关键因素。为解决上述关键科学问题，本课题主要围绕构建纳米级一维介孔单晶TiO2和助催化剂构效调控等方面，深入研究了光生载流子的迁移和表面反应动力学过程。项目执行期间制备了一系列一维介孔TiO2和新型助催化剂并对其催化机理进行了详细研究。这些研究结果对于构建高效太阳能转化制氢体系具有重要的科学研究意义。具体研究成果分为以下两个方面：1)系统研究了纳米级一维介孔TiO2可控合成，深入研究TiO2晶型和表面性质对光催化分解纯水过程的影响规律；2）在半导体纳米材料上选择性修饰助催化剂，进一步促进表面反应速率，从而大幅度提高体系催化性能。项目执行期间在Angew. Chem. Int. Ed.; Joule; Nano Energy; Nano Today期刊发表13篇研究论文，其研究结果为提高光催化制氢研究提供了相应实验依据和理论指导。总之，本研究项目基本完成了计划书上规定的任务及预期研究目标。