Ce-N共掺杂锐钛矿型二氧化钛的理论研究

Theoretical study on Ce-N codoped anatase titanium dioxide

[目的]研究Ce-N共掺杂对锐钛矿TiO_2晶体可见光区催化活性的影响。[方法]采用基于密度泛函理论(DFT)框架下的第一性原理平面波赝势(PWPP)方法,研究掺杂对锐钛矿TiO_2晶体的晶体结构、能带、态密度的改变,推断Ce-N共掺杂对锐钛矿TiO_2晶体可见光区催化活性的影响。[结果]Ce-N共掺杂TiO_2后,晶体的对称性和点群没有改变。通过对比纯TiO_2,N掺杂TiO_2,Ce掺杂TiO_2和Ce-N共掺杂TiO_2的能带和态密度可以得出:纯TiO_2的能隙较宽,价带顶主要为O-2p轨道的贡献,导带底主要为Ti-3d轨道的贡献;N掺杂后,由于N-2p轨道的作用会使导带底向低能端移动,价带顶向高能端移动;Ce掺杂后,由于Ce-4f轨道进入导带,会使导带底向低能端移动;Ce-N共掺杂后,由于N和Ce的共同作用,使导带底向低能端移动,价带顶向高能端移动,同时Ce-4f轨道进入导带底,从而使禁带宽度进一步变小,会拓展该晶体的可见光响应范围。这一结果与我们在实验中获得的紫外-可见光谱相一致。[结论]通过我们的计算和实验,说明Ce-N共掺杂可以改善和提高TiO_2在可见光区的活性,这种材料具有很好的应用前景,值得做进一步的实验研究。

[objective]To investigate the optical catalytic property of Ce-N codoped TiO_2 crystal.[method]Using density function theory（DFT）,the geometry,the band structure and the electronic density of states of pure TiO_2,N doped TiO_2,Ce doped TiO_2 and Ce-N codeped TiO_2 were calculated at plane wave ultra-soft pseudo-Potential level（PWPP）.Based on the calculated results,the optical catalytic properties of them can be predicted and compared.[result]It shows that the symmetry of Ce-N codoped anatase TiO_2 maintains the same as pure TiO_2＇s,while the lattice parameters a and c become larger.For pure TiO_2,the top of the value bands mainly involves O-2p electrons and the bottom of conduction bands contains Ti-3d electrons. For N doped TiO_2,the N-2p electrons make the band gap narrower by shift the value bands and the conduction bands near to each other.For Ce doped TiO_2,the 4f orbitals of Ce insert into the bottom of the conduction bands,therefore the band gap becomes narrower.For Ce-N codoped TiO_2,the band gap is narrowed by both N-2p electrons and Ce-4f electrons,so it should have better optical catalytic property at visible-light range.At the same time, the experiments about the pure,N doped TiO_2,Ce doped TiO_2 and Ce-N codeped TiO_2 were carried out,and the Ce-N codeped TiO_2 crystal possesses better visible absorbency in the ultraviolet-visible spectrogram.The theory results can fit well with the experimental results.[conclusion]Ce-N codoped TiO_2 crystal has narrower band gap than the pure TiO_2 crystal,and its optical catalytic property is remarkably improved during visible-light range.These results have important implications for the understanding and further development of photocatalytic materials that are active under visible- light irradiation.