Computational insights into crystal plane dependence of thermal activity of anion (C and N)-substituted titania

Abstract

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 TiO_2−2xC_x and TiO_2−3xN_2x. 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%.