Unveiling the structural, electronic, and optical effects of carbon-doping on multi-layer anatase TiO₂ (1 0 1) and the impact on photocatalysis

Carbon-doped (C-doped) TiO₂ has demonstrated effective photocatalytic activity in the visible-light region. Here, we make use of density functional theory (DFT) methods to understand the photocatalytic activity of C-doped anatase-TiO₂ (1 0 1) surfaces as a function of layer thickness. The formation energy results show that C-doped O sites (C_O) are more stable in the bulk than in the subsurface or on the surface, while C-doped Ti sites (C_Ti) are more stable on the surface than in the bulk or subsurface. C_O defects introduce impurity states in the band gap, do not affect the band gap energy, and induce an electron trap close to the conduction band edge and enhances light absorption in the visible and IR spectrum. C_Ti defects induce structural distortions caused by a C–O covalent bond with no impurity states formed in the band gap although there is a reduction in the band gap energy, which leads to a red-shifted absorption. These results shed insight on how carbon doping influences the electronic and optical properties of anatase that can be implemented in the design of semiconductor materials with high photocatalytic activity.