N掺杂TiO2纳米粉体的表面特性及可见光活性

旨在探究N掺杂纳米TiO2具有可见光活性的本质,采用XPS、ESR、XRD、SEM、DRS、SPS和PL分析技术对sol-gel法制备的未掺杂和N掺杂TiO2纳米粉体进行了对比研究,并以亚甲基蓝(MB)溶液在可见光下的光催化脱色评价其可见光活性。结果表明,N掺杂TiO2纳米粉体具有良好的可见光活性,未掺杂样品几乎没有可见光活性。N取代TiO2晶格中O形成了N─Ti─O和O─N─Ti键合结构产生杂质能级,N掺杂导致TiO2表面形成了大量束缚单电子的氧空位产生缺陷能级,二者协同作用致使带隙窄化,光吸收带边红移,产生可见光活性。N掺杂导致TiO2晶格中p-n结的形成及表面氧空位和表面羟基的增加均能促进光生e-/h+分离,有效抑制光生e-/h+复合,提高量子效率,进而提高其光活性。

Surface Properties and Visible-light Photoactivity of N-doped TiO2 Nano-powders

A comparative study on un-doped and N-doped TiO₂ nano-particles prepared by a sol-gel method was carried out by the analytic techniques such as X-ray photoelectron spectroscopy（XPS）,electron spin resonance（ESR）,X-ray diffraction（XRD）,scanning electron microscope（SEM）,UV-Vis diffuse reflection spectra（DRS）,surface photovoltage spectra（SPS） and photoluminescence spectra（PL）,in order to explore the origin of visible-light photoactivity for N-doped nano-TiO₂.Their visible-light photoactivities were evaluated by the photocatalytic decoloring of methylene blue（MB） in aqueous solution under visible-light irradiation.The results show that the N-doped sample exhibits a good visible-light photoactivity,whereas the un-doped sample has little visible-light photoactivity.The visible-light response of the N-doped TiO₂ nano-particles is ascribed to a synergetic effect of impurity energy levels due to the substitutional N-doping forming the N─Ti─O and O─N─Ti bonding structures and defect energy levels resulted from the formation of oxygen vacancies,which result in the band-gap narrowing and red-shift of optical absorption band.The separation of the photo-generated e^-/h⁺ can be accelerated by the formation of p-n junctions in crystal lattice of TiO₂ and the increase in both oxygen vacancies and surface hydroxyl groups resulted from N-doping.As a result,they can inhibit the recombination of the photo-generated e^-/h⁺ effectively and enhance the quantum efficiency,then increasing the photoactivity.