Electronic Structure and Optical Absorption Spectra of C-Cr Co-Doped Anatase TiO2 Based on First Principles

The geometrical structure, defect formation energies, electrical and optical properties of C and/or Cr doped anatase TiO2 are calculated by GGA+U method under the framework of density functional theory. The relationship between band structure and light absorption is revealed. The results show that the lattice is obviously distorted after doping, and the stability of C and Cr co-doping is higher than just Cr doping, second only to Cr doped TiO2. The contribution of C is forming impurity energy levels, and the contribution of Cr is to reduce the band gap in the single doped system. In the co-doped system, Cr atoms are used as donor impurities and C atoms act as acceptor impurities. The impurity energy is composed of C 2p and Cr 3d orbital hybridization, which reduces the band gap and promotes the separation of the impurity levels. C and Cr co-doping expands the light absorption of TiO2 to the entire visible region, thereby increasing the absorption coefficient and effectively enhancing the photocatalytic efficiency.