Nitrogen doping in coexposed (001)-(101) anatase TiO2 surfaces: a DFT study.

In this work we study the effect of nitrogen (N)-doping on the structural and electronic properties of coexposed anatase (001)-(101) surfaces by means of Density Functional Theory (DFT). This work is motivated by recent experiments, showing that these materials are highly active for photocatalysis. The introduction of doping species such as N further improves their activity under visible light. Our results indicate a tendency toward dopant segregation at the interface at low N concentrations, while at larger concentrations also doping sites in the bulk regions are populated. N-Doping does not affect the reciprocal band alignment of TiO2(101) and (001), where the former stabilizes photogenerated electrons and the latter hosts the holes. However, N-doping enhances the visible light absorption of the composite material, due to the introduction of gap states. Moreover, N-doping strongly stabilizes oxygen vacancies, which in turn enhance the light absorption properties.