Electronic structure and band-edge engineering of Sc-doped g-C₃N₄: a first-principles study

Abstract In this study, graphitic carbon nitride, often known as g-C₃N₄, has also been shown to be a highly attractive photocatalyst that works well with visible light. However, its performance has been adversely affected by its relatively large bandgap, sluggish charge transfer, and rapid recombination of electrons and holes. Here, we apply density functional theory (DFT) to compare pure-state g-C₃N₄ and g-C₃N₄ doped with scandium (Sc) and investigate their structural, electronic, optical, and vibrational characteristics. After optimizing the structure, this led to a slight expansion of the lattice, where Sc fills the heptazine pore locations, resulting in an increase in overall stability. We observe that the hybridization between Sc 3d and N 2p decreases the bandgap from around 2.1 eV to around 1.9 eV. This also shifts the conduction band edge to more negative potentials and increases visible light absorption. The difference in charge density and Bader charge calculation suggests a large transfer from Sc to N, which leads to a local polarization field, allowing us to separate electrons from the holes. No imaginary modes are present in the phonon dispersion spectra, which indicates dynamic stability. Furthermore, mode hardening indicates more rigidity of lattices. The effect of these factors and combined energy generation with photocatalytic activity allows an efficient synthesis of solar hydrogen and a low emission of CO₂, and a degradation of pollutants and utilization of it in an energy storage system. Thus, Sc-doped g-C₃N₄ is a strong, stable, and productive platform for photocatalysis enhancement.