A DFT study of the electronic structures and optical properties of (Cr, C) co-doped rutile TiO2

[Display omitted] •We calculate (Cr,C) co-doped rutile TiO2 using density functional theory.•The (Cr,C) co-doping situation is more energetically favorable under oxidation condition.•The impurity states modify the electronic structures, resulting in band gap narrowing.•The electron transfer between Cr and C atoms reflects a stronger ionic bond than Ti–O bond in pure TiO2.•The optimal band gap is found to be about 2.3 eV after (Cr,C) co-doping. To get an effective doping model of rutile TiO2, we systematically study geometrical parameters, density of states, electron densities, dielectric functions, optical absorption spectra for the pure, C mono-doping, Cr mono-doping and (Cr,C) co-doping rutile TiO2, using density functional calculations. We find that a C doped system presents higher stability under Ti-rich condition, while Cr doped and (Cr,C) co-doped systems are more stable under O-rich condition. For (Cr,C) co-doping situation, the imaginary part of the dielectric function reflects the higher energy absorption efficiency for incident photons. Moreover, co-doping system exhibits much bigger red-shift of optical absorption edge compared with Cr/C single doping systems, because of the great reduction of the direct band gap. The calculated optical absorption spectra show that the (Cr,C) co-doping rutile TiO2 has higher photocatalytic activity in the visible light region.