Band gap engineering of (N, Si)-codoped TiO2 from hybrid density functional theory calculations

Abstract

We have investigated systematically the influence on electronic properties of anatase-TiO2 of codoping by N and Si at different concentrations using Heyd–Scuseria–Ernzerhof (HSE06) hybrid density functional theory calculations. The optimized total energy shows that TiO2 codoping by N and Si favours a configuration of two substitutional N atoms located at two adjacent O sites, with one substitutional Si atom at their neighbouring Ti site. We show that N–Si codoping can harvest longer-wavelength visible-light than either those of N and Si monodoping, owing to the contribution from N 2p in the ‘forbidden gap’ and Si 3s–3p at the tail of the conduction band. Increasing the N doping concentration leads to a larger extent of gap narrowing, which is directly related to coupling between N atoms. Our results suggest that double-hole coupling plays a key role in similar systems to obtain high visible-light photoactivity in TiO2-based photocatalysts.