Carbon Doping of the TiO2 (110) Rutile Surface. A Theoretical Study Based on DFT

A detailed analysis of the structural and electronic properties of the C-doped rutile TiO2(110) surface has been performed by means of periodic density-functional calculations. C atoms adsorb exothermically on the surface, although they are unstable with respect to the CO escape and formation of an oxygen vacancy. C implantation at lattice positions is an endothermic process, in contrast with what was observed in the case of N implantation. These C implanted atoms are also unstable in the presence of molecular oxygen. A strong cooperative interaction between implanted C atoms and surface oxygen vacancies is observed: (i) the presence of vacancies significantly lowers the implantation energy and stabilizes the C atoms, although not enough to avoid their escape in the presence of O2; (ii) the presence of implanted C atoms noticeably lowers the energy of formation of oxygen vacancy in the surface. Finally, an analysis of the electronic structure confirms the presence of in-gap states that could improve the photocatalytic activity of rutile upon being doped with C.