N-F共掺杂锐钛矿二氧化钛（101）面纳米管的第一性原理研究∗

摘要

共掺杂是提高二氧化钛纳米管可见光催化性能的一种有效方式.采用基于密度泛函理论的第一性原理方法,研究了N单掺杂、F单掺杂及N-F共掺杂二氧化钛纳米管的原子结构、电子性质和光学性质.计算结果表明,相比N单掺杂和F单掺杂,N-F共掺杂二氧化钛纳米管的形成能更低,掺杂后的体系热力学稳定性更好.此外,相比未掺杂时的带隙, N-F共掺杂后体系的带隙变化最多,减少了0.557 eV,而这主要源于价带顶附近的杂质能级的贡献.此外,通过分析掺杂后的光催化活性发现,N-F 共掺杂时纳米管的还原性和氧化性都有所降低,但并没有丧失活性,并且光吸收谱表明,共掺杂体系的红移现象最为明显.因此,N-F共掺杂可有效提高二氧化钛纳米管可见光的光催化性能.%The method of co-doping is very useful to improve the photocatalytic performances of titanium dioxide nanotubes. The absorption capacity to the visible light of the titanium dioxide nanotubes can be improved significantly in experiment by doping both N and F in titanium dioxide nanotubes, but the theoretical explanations are still not clear. Doping the atom N alone, the atom F alone, and both N and F in titanium dioxide nanotubes respectively, their atomic structures, electronic properties and optical performance are studied by the first principles method based on the density functional theory. It is found that formation energies are lower in titanium-rich environment than that in oxygen-rich environment. In titanium-rich environment, the N-F co-doped TiO2 nanotube has the low formation energy and stable thermodynamic system compared with the N alone and the F alone doped TiO2 nanotube. Besides, the O3C can be replaced more easily than the O2C when doping N alone, F alone and co-doping N-F in TiO2 nanotube. By analyzing the energy band, we can find that the band gap changes little with doping N and the change of the band gap for the co-doping N-F case is the most prominent, which reduces by 0.557 eV compared with that for the un-doped TiO2 nanotube case, and this is mainly from the contributions of the impurity level near the top of the valence band. Besides, the different charges are calculated and it is indicated that the ability to gain electrons of N is stronger than that of F, and through analyzing the photocatalytic performance, it is found that though the gap of the nanotube is larger than that of the body, the reducibility of nanotube is better than that of the body. Both the reducibility and the oxidability of the nanotube are reduced but its activity is not lost when co-coping the atoms of N and F in titanium dioxide nanotubes. Moreover, the optical absorption spectrum shows that the red shift phenomenon is obvious for doped system and also for the co-doped system. Therefore, co-doping both N and F in titanium dioxide nanotubes is the most useful method to improve the photocatalytic performances of the TiO2 nanotubes.