Sulfur-doped g-C3N4/TiO2 anatase (101) composites for photocatalytic applications: a DFT-based computational investigation

Abstract

With the aim of improving the visible-light photocatalytic activity of TiO₂, the structural, electronic and optical properties of bare and sulfur-doped g-C₃N₄/TiO₂ composites have been investigated as potential candidate materials. Both periodic DFT calculations for all structural and electronic properties and TD-DFT calculations which are carried out on finite clusters extracted from the periodic structures and embedded in an array of point charges devised to reproduce the periodic electrostatic environment have been performed. Two dopant positions were considered, and a systematic comparison of key properties of the composites and their isolated components was carried out to clarify the effect of S dopant and TiO₂ substrate. Overall, we find that both g-C₃N₄ and S-g-C₃N₄ can significantly modify TiO₂ properties. In particular, compared to TiO₂, the composites present an overall improved generation of electron–hole pairs and a decrease of their recombination rates, as well as an enhanced absorption in the visible region, but with distinct photocatalytic mechanisms for non-doped and doped composites. Although this suggests that all investigated composites appear in principle as good candidates to enhance solar light-driven photocatalytic activity of TiO₂, the dependence of the results on the doping position that we observed, which is difficult to control experimentally, indicates that S doping of g-C₃N₄ could be a delicate approach to producing g-C₃N₄/TiO₂-based composites with improved properties in an experimentally controlled and systematic way.