共掺杂TiO2可见光光催化活性协同效应的理论研究

Two key scientific problems including narrow range of light response and low quantum efficiency in TiO2 semiconductor photocatalytic material have severely obstructed its industrialization development and applications. To explore theoretically the method and physical mechanism on improving visible-light photocatalytic efficiency has very important practical significance and wide application merits. This project will make an exhaustive theory study on transition metal element Mo or rare earth metal element Nd and non-metal N or C codoped TiO2 system. The effects of different metal element and non-metal element doping on the electronic structures and optical properties of TiO2 will be investigated by first-principles calculations based on density functional theory. The similarities and differences on the doping modification mechanism and synergy mechanism between different metal element and non-metal element and on regulation mechanism of the visible-light photocatalytic properties of TiO2 resulted from codoping are also studied further. The project will lay special stress on analyzing chemical bond change of non-metal, different electronic configuration and the influence of specific 4f electron of rare earth metal element and their interaction on photocatalytic activity of codoped TiO2 system. It will also explain clearly the existing form of defects including impurities and oxygen vacancy and the effects of their interaction characteristics on photocatalytic properties of TiO2 and realize the scientific regulation of ultraviolet and visible-light photocatalytic performance. This project provides an important theoretical guidance for designing and developing new-type high-efficiency visible light responsible TiO2 photocatalytic material and its applications in energy and environmental photocatalysis including hydrogen production from water splitting and degradation of organic dyes.

TiO2半导体光催化材料光响应范围窄和量子效率低这两个关键科学问题严重阻碍了其工业化发展和应用。从理论上探索提高可见光光催化效率的方法和机理，具有重要的现实意义和广泛的应用价值。本项目拟以过渡金属元素Mo或稀土金属元素Nd与非金属（N或C）共掺杂TiO2体系为对象进行理论研究，利用基于密度泛函理论的第一性原理探讨不同金属元素与不同非金属元素掺杂对TiO2电子结构和光学性质的影响，研究不同金属元素与非金属元素之间的掺杂改性机理和协同作用机制及共掺杂对TiO2可见光光催化性能的调控机制的异同，分析非金属的化学键变化和Mo的不同电子组态以及稀土4f电子及相互作用对共掺杂TiO2体系光催化活性的影响，阐明杂质和氧空位等缺陷的存在形式及其对TiO2光催化性能的作用规律，实现可见光光催化性能的科学调控，为设计和开发高效的可见光响应的TiO2材料在分解水制氢及降解有机染料等方面的应用提供重要的理论指导。

利用基于密度泛函理论的第一性原理计算了未掺杂TiO2、C-TiO2、Mo-TiO2和C-Mo-TiO2体系的电子和光学性质，深入研究了非金属元素与金属元素共掺杂对TiO2电子结构和可见光光催化活性的影响，重点分析共掺杂改性机理和协同增强效应。研究结果表明C-TiO2和Mo-TiO2体系在带隙中均存在未被占据的杂质态，这些杂质态容易充当载流子的复合中心，因而不利于提高光催化效率；而C-Mo共掺杂TiO2体系的杂质能级全部被占据，这能使光生电子和空穴得到有效分离，同时C-Mo共掺杂TiO2体系的光学吸收边由于共掺杂引起的协同效应而呈现明显的红移，禁带宽度（2.35 eV）比纯TiO2（3.10 eV）明显减小，能有效提高可见光波段的利用率，从而提高光催化性能。电荷密度分析可以清楚地看出共掺杂后体系的电荷呈现重新分布，Mo原子和邻近的C原子形成了新的化学健。同时，我们也利用第一性原理研究了MoS2/TiO2(001)杂化复合体系的电子和光学性质。通过系统地研究了层状结构MoS2杂化对MoS2/TiO2(001)复合体系能带、界面电荷转移效应和可见光响应的影响。结果表明MoS2/TiO2(001)杂化复合体系的价带顶主要由O 2p和 S 2p态组成，而导带底主要是由Mo 4d 和Ti 3d的杂化态组成，同时Mo 4d态使导带向低能方向移动，导致了复合体系带隙变窄以及光学吸收边红移。差分电荷密度进一步的分析表明MoS2/TiO2(001)杂化复合体系的界面存在明显的电荷转移。MoS2有效的光敏化和稳定的界面是提高MoS2/TiO2(001) 复合体系可见光响应和增强光催化性能的主要原因。此外，利用第一性原理初步探讨了N-Cd共掺杂对TiO2体系电子结构和光学性质的影响。