Femtosecond Diffuse Reflectance Spectroscopic Study on Nitrogen-Doped Titanium Oxide Photocatalysts

利用飞秒时间分辨漫反射光谱技术，在弱激发条件下成功地研究了氮掺杂氧化钛（N-TiO_2）粉末中的本征电荷分离和俘获动力学过程。在360 nm光激发后，表面俘获电子数的衰减速率随N原子浓度的增加呈非线性下降，这可以用电子俘获过程受扩散限制来解释。在450 nm光激发后，在1 ps内的电子的深捕获是明显的，这可能可以解释为通过邻近的N原子附近诱导的氧空位在Ti 3d能级中的电子的快速和深捕获。对于负载金属的N-TiO_2体系，在紫外光激发下发生了光诱导电子转移，而在可见光激发下没有检测到负载Cu或Fe物种的还原。

Femtosecond time-resolved diffuse reflectance measurements under weak excitation conditions successfully detected the intrinsic charge separation and trapping dynamics in nitrogen-doped titanium oxide(N-TiO_2) powders without second-order electron-hole recombination processes. The decay rate of the population of the surface-trapped electrons decreased nonlinearly with increasing N atom concentration after 360 nm light excitation, which can be explained by the electron trapping process being diffusion-limited. The deep trapping of electrons within 1 ps was evident after 450 nm light excitation, which can probably be explained by quick and deep trapping of the electron in the Ti3d level by an adjacent oxygen vacancy induced near N atoms. For metal loaded N-TiO_2 system, it has been revealed that the photoinduced electron transfer occurred from N-TiO_2 to the loaded Cu or Fe species under UV light excitation whereas no reduction of the loaded Cu or Fe species was detected under visible light excitation.