N掺杂TiO_2的催化活性与电子结构关系探究

The study of relation of photocatalytic activity and electronic structure of Ndoped TiO_2

以钛酸四丁酯和三乙醇胺为主要原料,采用钛溶胶水热合成方法,制备氮掺杂锐钛矿型纳米TiO_2。利用XRD、DRS对其进行表征,以甲基橙为目标物,研究产物的光降解活性。实验结果表明,N掺杂造成了TiO_2的晶格缺陷,禁带宽度减小,光响应范围红移,光催化活性增强。从第一性原理出发,结合密度泛函理论计算,探讨N掺杂TiO_2的电子结构,发现其能带结构中出现了杂质能级,这可以很好地解释N掺杂TiO_2光响应波长范围红移和光降解效果优于P25的实验观测结果。

Anatase N-doped TiO2 photocatalysts were prepared by the hydrothermal method with tetra-n-butyl titanate （TTNB） and triethanolamine as precursors. The obtained samples were characterized by X-ray diffraction （XRD） and UV-visible diffuse reflectance spectra （DRS）, respectively. Photocatalytic activities of the anatase products were investigated on the degradation of methyl orange （MO）. Nitrogen doping resulted in crystal defects, with the band gap （Eg） decreasing and the absorption shoulder having been extended into the visible light region. The incorporation of nitrogen impurity in anatase TiO2 was studied by the first-principles calculations based on density functional theory （DFT）. The calculated electronic band structures for N-doped TiO2 indicated the formation of localized states in the band gap, which lied above the valence band. Excitation from the impurity states to the conduction band could account for the optical absorption edge shift toward the lower energies （longer-wavelength light） and the excellent photocatalytic activity observed in the case of N-doped TiO2 better than the experimental and observed results of P25.