N掺杂TiO_2光催化剂的微结构与吸光特性研究

以紫外可见漫反射光谱(UV-VIS-DRS)和X射线光电子能谱(XPS)分析和研究了四种方法制备的N掺杂TiO2光催化剂的结构,即水解法(N/TiO2-H)、氨热还原法(N/TiO2-A)、机械化学法(N/TiO2-M)和尿素热处理法(N/TiO2-T)等.结果表明,N/TiO2-H和N/TiO2-T两种催化剂在490 nm处有吸收带边,可见光激发途径是掺杂的N以填隙方式形成的杂质能级吸收电子发生的跃迁引起的;而N/TiO2-A和N/TiO2-M两种催化剂在整个可见光区域内具有可见光吸收,其对可见光的激发途径是掺杂N和氧空缺共同作用的结果.理论计算的N杂质能级位于价带上0.75 eV,与实验观察到的吸收带边结果十分吻合.XPS结果表明,几种催化剂的N1 s结合能位置都在399 eV附近,显示为填隙掺杂的N原子.填隙掺杂的N/TiO2,其Ti原子的2p结合能与未掺杂的TiO2相比增加了+0.3-+0.6 eV,而O1s电子的结合能增加了+0.2-+0.5eV,这是因为填隙的N原子夺取Ti和O的电子,Ti和O原子周围的电子密度降低了.电子能谱和吸光特性的研究都表明,掺杂的机理是在TiO2晶格内形成N原子的填隙.

Studies on the structures and light absorbance of nitrogen-doped titanium dioxides photocatalyst

Nitrogen doped dioxide titanium photocatalysts (N/TiO2) had been prepared by various methods: hydrolysis of tetrabutyl titanate (N/TiO2-H), ammonia thermal treatment of titanium dioxide (N/TiO2-A), mechanochemica1 treatment of titanium dioxide (N/TiO2-M) and urea thermal treatment of Ti(OH)4 (N/TiO2-T). Results of UV-Vis-DRS indicated there had obvious onset of visible light absorption at 490nm of catalysts N/TiO2-H and N/TiO2-T, which initiated by impurity energy level located at above valance band formed by doped nitrogen. Excitations from localized states to the conduction band account for the absorption edge shift toward lower energies (visible region) observed in the case of N/TiO2 with respect to pure TiO2. Mixture of visible light absorption of nitrogen doping and oxygen defect gave no obvious onset in the whole range between 400 and 800nm were observed of the samples N/TiO2-A and N/TiO2-M. Impurity energy level located at 0.75eV above valance band of TiO2 calculated by theoretical method, which was well corresponding to experimental UV-Vis-DRS results. Binding energy of N 1s at about 399eV for all N/TiO2 catalysts were observed and there corresponding to interstitial nitrogen. Binding energy of Ti 2p and O 1s were increased about 0.3-0.6eV and 0.2-0.5eV respectively of various nitrogen doped TiO2 with respect to pure TiO2. These results indicated the doped mechanism of nitrogen in the TiO2 was interstitial nitrogen.