Band structure modulation and carrier transport process of g-C3N4 doped with alkali metals

Abstract

The effects of Li, Na, and K alkali metal ions on the band structures and carrier transfer of graphitic carbon nitride (g-C3N4) are investigated using the plane-wave ultrasoft pseudopotential method. The generalized gradient approximation and local density approximation are used to calculate total energies of six adsorption configurations. The three alkali ions all tend to adsorb on the large central cavity (F position) in g-C3N4 layers. The calculated band structures and work function values indicate that the interface charge balance of the n-type Schottky junctions formed between the alkali metal ions and g-C3N4 induces the total band edge potential of g- C3N4 to shift down by 1.52 V (Li), 1.07 V (Na), and 0.86 V (K). The incorporation of K ion adjusts the valence and conduction bands to more appropriate redox potentials than those of pure g-C3N4, and increases the distribution of the HOMO and LOMO of g-C3N4, which helps to improve the mobility of carriers. Meanwhile, the non-coplanar HOMO and LOMO favor the separation of electrons and holes.