RESUMO
Geometry optimizations of anion (C and N) doped anatase TiO2 were carried out by using DFT+U calculations. Various anion vacancy sites were examined to study the synergistic effects of anion doping accompanied with anion vacancy formation on lattice oxygen activation. Two non-identical crystal planes (0 0 1) and (1 0 0) were chosen for C and N substitutions. Energetically favoured N-vacancy pairs were identified on TiO2 surfaces. Substitution of N along with anion vacancies at various sites was energetically more favoured than that of C-doping in bulk TiO2 while the energies were comparable for surface substitutions. Bond length distributions due to the formation of differential bonds were determined. Net oxygen activation and accompanying reversible oxygen exchange capacities were compared for TiO2-2xCx and TiO2-3xN2x. Substitution of C in the surface exposed (1 0 0) plane of TiO2 resulted in 47.6% and 23.8% of bond elongation and compression, respectively, resulting in 23.8% of net oxygen activation which was higher when compared to N substitution in the (1 0 0) plane of TiO2 resulting in a net oxygen activation of 17%.
