School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100, China.
Phys Chem Chem Phys. 2018 May 9;20(18):12785-12790. doi: 10.1039/c8cp00895g.
Doping is an effective way to extend the optical absorption of TiO2 to the visible range. Doping of TiO2 by carbon has been found to enhance the water splitting efficiency significantly in experiment. However, the mechanism behind this is elusive. Using the ab initio many-body Green's function theory, we find that the C2 dimer formed on the TiO2 surface produces a shallow delocalized occupied Ti 3d state just below the bottom of the conduction bands. Therefore, band-gap narrowing in carbon-doped TiO2 is caused by the opposite shifts of both valence and conduction bands simultaneously, which is in contrast to the generally accepted idea that anionic dopants can only affect the valence band of TiO2. Optical absorption in the infrared region is also increased compared to reduced TiO2. The spatially well-separated photogenerated electrons and holes might help to reduce the recombination rate of carriers, in favor of improvement in photocatalysis efficiency. This novel behavior of anionic dopants is distinct from previous understandings and may guide the engineering of TiO2.
掺杂是将 TiO2 的光学吸收扩展到可见光范围的有效方法。实验发现，通过碳掺杂 TiO2 可以显著提高水分解效率。然而，其背后的机制尚不清楚。我们使用从头算多体格林函数理论发现，在 TiO2 表面形成的 C2 二聚体在导带底部下方产生一个浅的离域占据 Ti 3d 态。因此，碳掺杂 TiO2 中的带隙变窄是由于价带和导带同时发生相反的移动，这与通常认为的阴离子掺杂剂只能影响 TiO2 的价带的观点相反。与还原 TiO2 相比，在红外区域的光吸收也增加了。空间上分离良好的光生电子和空穴可能有助于降低载流子的复合率，有利于提高光催化效率。这种阴离子掺杂剂的新行为与以前的理解不同，可能指导 TiO2 的工程设计。
