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

在弱激发条件下，飞秒时间分辨漫反射测量成功地检测了氮掺杂氧化钛（N-TiO_2）粉末中没有二阶电子-空穴复合过程的本征电荷分离和俘获动力学。在360 nm光激发后，随着N原子浓度的增加，表面捕获电子居数的衰减率呈非线性下降，这可以解释为电子捕获过程受到扩散限制。在450nm光激发后，电子在1ps内的深度捕获很明显，这可能是由于相邻的氧空位在N原子附近诱导电子在Ti3d能级上的快速和深度捕获。对于负载金属的N-TiO_2体系，在紫外光激发下，N-TiO_2向负载Cu或Fe发生了光致电子转移，而在可见光激发下，负载Cu或Fe没有减少。

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.