Ni-N共掺杂锐钛矿型TiO_2的第一性原理

First-principles study of Ni-N codoped anatase TiO_2

采用基于密度泛函理论(DFT)的平面波超软赝势(PWPP)方法,对Ni-N共掺杂前后锐钛矿型TiO_2的超晶胞体系进行了几何结构优化,从理论上给出了掺杂体系的晶格参数。讨论了Ni掺杂、N掺杂、Ni-N共掺杂对锐钛矿型TiO_2的晶体结构、能带结构、态密度等的影响。结果表明:Ni-N共掺杂对锐钛矿型TiO_2的晶格参数和晶体结构的影响不大,从能带结构和态密度看,Ni掺杂后TiO_2价带和导带之间出现了主要由O-2p和Ni-3d共同作用而产生的杂质能级,N的掺入使得TiO_2导带下移。Ni、N的共同作用导致禁带宽度变窄,吸收带红移,拓宽了光响应范围。这些计算结果很好地解释了Ni-N共掺杂锐钛矿型TiO_2在可见光下具有良好的光催化性能的内在原因。本文从理论上对纯TiO_2,以及Ni掺杂、N掺杂、Ni-N共掺杂进行了较系统的研究,其中纯TiO_2和N掺杂TiO_2的结果与前人的一致;Ni掺杂和Ni-N共掺杂是这个系列的新内容。从理论上对这个系列的TiO_2光催化材料进行了比较,得出Ni掺杂和Ni-N共掺杂可以使TiO_2的禁带宽度变窄,有助于光催化活性提高这一结论,与我们的紫外可见吸收实验结果一致,与前人实验中发现Ni-N共掺杂TiO_2在可见光区的活性比纯TiO_2高1倍的实验事实相符。

Based on density function theory （DFT）, the electronic structure ofNi-N codoped anatase TiO2 （Ni-N/TiO2） has been studied using plane wave ultra-soft pseudo-potential （PWPP） in the present paper. Cell parameters, density of states and band structures of pure, Ni/TiO2, N/TiO2 and Ni-N/TiO2 have been calculated. There are some new bands appeared between the value band edge and the conduction band edge in Ni-N/TiO2, and the conduction bands shift downwards. These changes lead to the narrowing of band gap and then enhance the optical absorption in visible-light. There is a systemic discussion about the pure, Ni/TiO2, N/TiO2 and Ni-N/TiO2. The theoretical results may lead to the conclusion that there is little change about the cell parameters and electronic structures, whereas the dopings can make the band gap narrower and enhance the catalytic ability especially for Ni/TiO2 and Ni-N/TiO2. The calculations and results of pure and N/TiO2 agree with previous studies, and the calculations and results of Ni/TiO2（will be published in 2010） and Ni-N/TiO2 may provide some new information for this system. The experiments about the pure, Ni/TiO2, N/TiO2 and Ni-N/TiO2 also have been carried out and these materials have been prepared with sol-gel method. The higher photocatalytic property of Ni-N/TiO2 can be seen from the spectrogram of ultraviolet-visible. The theoretical results can fit well with the experimental results. In addition, our result can fit well the previous experimental results that Ni-N/TiO2 can double the photocatalytic ability of pure TiO2 when they tried to dissociation formaldehyde.