过渡金属(Fe,Co,Ni,Zn)掺杂金红石TiO2的电子结构和光学性质

采用基于密度泛函理论的第一性原理方法对未掺杂以及不同浓度过渡金属Fe,Co,Ni,Zn掺杂金红石TiO₂的超晶胞体系进行了几何优化,并讨论了其晶格常数,电子能带结构和光学性质.研究结果表明:掺杂前后的晶格参数与实验值偏差在3.6%以下;适量的过渡金属掺杂不但影响体系能带结构,拓宽光吸收范围,而且扮演着俘获电子的重要角色,有利于光生电子-空穴对的有效分离以及增强光吸收能力;Fe,Co,Ni,Zn最佳理论掺杂体系分别为Ti_0.75Fe_0.25O₂,Ti_0.75Co_0.25O₂,Ti_0.75Ni_0.25O₂,Ti_0.83Zn_0.17O₂;Fe,Co,Ni3d态分裂为t_2g和e_g态,分别贡献于价带高能级和导带低能级部分,促进了电子-空穴对的生成,从而可提高TiO₂的光催化性能;Zn3d态电子成对填满轨道,不易被激发,故光催化活性无明显提高.

Electronic structures and optical properties of transition metals (Fe, Co, Ni, Zn) doped rutile TiO2

The geometric structures of transition metals (Fe, Co, Ni and Zn) doped rutile TiO₂ are studied using the first-principles method based on the density functional theory. The lattice parameters, the electronic energy band structure, and the optical properties are calculated and discussed. The results show that the errors between calculated and experimental values of lattice parameters are less than 3.6%. Appropriate dopants of transition metal ions not only influence the band structure of rutile TiO₂ system and broaden the scope of light absorption, but also play an important role in trapping electrons, improving the effective separation of electronic-hole pair and enhancing light absorption ability. The optimum Fe, Co, Ni, Zn doped rutile TiO₂ systems in theory are Ti_0.75Fe_0.25O₂, Ti_0.75Co_0.25O₂, Ti_0.75Ni_0.25O₂, Ti_0.17Zn_0.17O₂, respectively. The 3d orbits of Fe, Co, Ni split into two groups of energy bands, t_2g and e_g states contribute to the higher level of valence band and the lower level of conduction band, respectively, which is conducive to the generation of electronic-hole pair and the enhancement of photocatalytic performance of rutile TiO₂. Zn 3d orbit is completely filled with electrons, and the electrons are hardly excited, so the photocatalytic activity of rutile TiO₂ is not obviously improved.