Research Institute of Photocatalysis, State Key Laboratory Breeding Base of Photocatalysis Fuzhou University, Fuzhou, China.
Chemphyschem. 2012 Apr 23;13(6):1542-50. doi: 10.1002/cphc.201100991. Epub 2012 Mar 7.
The electronic structure and photoactivation process in N-doped TiO(2) is investigated. Diffuse reflectance spectroscopy (DRS), photoluminescence (PL), and electron paramagnetic resonance (EPR) are employed to monitor the change of optical absorption ability and the formation of N species and defects in the heat- and photoinduced N-doped TiO(2) catalyst. Under thermal treatment below 573 K in vacuum, no nitrogen dopant is removed from the doped samples but oxygen vacancies and Ti(3+) states are formed to enhance the optical absorption in the visible-light region, especially at wavelengths above 500 nm with increasing temperature. In the photoactivation processes of N-doped TiO(2), the DRS absorption and PL emission in the visible spectral region of 450-700 nm increase with prolonged irradiation time. The EPR results reveal that paramagnetic nitrogen species (N(s)·, oxygen vacancies with one electron (V(o)·), and Ti(3+) ions are produced with light irradiation and the intensity of N(s)· species is dependent on the excitation light wavelength and power. The combined characterization results confirm that the energy level of doped N species is localized above the valence band of TiO(2) corresponding to the main absorption band at 410 nm of N-doped TiO(2), but oxygen vacancies and Ti(3+) states as defects contribute to the visible-light absorption above 500 nm in the overall absorption of the doped samples. Thus, a detailed picture of the electronic structure of N-doped TiO(2) is proposed and discussed. On the other hand, the transfer of charge carriers between nitrogen species and defects is reversible on the catalyst surface. The presence of oxygen-vacancy-related defects leads to quenching of paramagnetic N(s)· species but they stabilize the active nitrogen species N(s)(-).
研究了掺氮 TiO(2) 的电子结构和光致激活过程。采用漫反射光谱（DRS）、光致发光（PL）和电子顺磁共振（EPR）来监测热诱导和光诱导掺氮 TiO(2) 催化剂中光学吸收能力的变化以及氮物种和缺陷的形成。在低于 573 K 的真空热处理下，掺杂样品中没有氮掺杂剂被去除，但形成了氧空位和 Ti(3+) 态，以增强可见光区域（尤其是波长大于 500nm 的区域）的光学吸收，且随温度升高而增强。在掺氮 TiO(2)的光致激活过程中，DRS 吸收和在 450-700nm 可见光区域的 PL 发射随辐照时间的延长而增加。EPR 结果表明，在光照下产生了顺磁氮物种（N(s)·、带一个电子的氧空位（V(o)·）和 Ti(3+)离子，且 N(s)·物种的强度取决于激发光的波长和功率。综合表征结果证实，掺杂氮物种的能级定位于 TiO(2)的价带上方，对应于掺氮 TiO(2)在 410nm 的主要吸收带，而氧空位和 Ti(3+)态作为缺陷则有助于掺杂样品整体吸收中 500nm 以上的可见光吸收。因此，提出并讨论了掺氮 TiO(2)的电子结构的详细情况。另一方面，氮物种和缺陷之间的载流子转移在催化剂表面是可逆的。氧空位相关缺陷的存在会导致顺磁 N(s)·物种的猝灭，但它们会稳定活性氮物种 N(s)(-)。
