Reassessing structural models of graphitic carbon nitride for reliable photocatalytic predictions

Abstract

Among emerging photocatalysts, graphitic carbon nitride (g-C3N4) has attracted considerable attention as a metal-free, visible-light-active semiconductor for sustainable hydrogen production and environmental remediations. Here we demonstrate that many of the obvious models for the layer structure and preferred stacking arrangements of g-C3N4 lead to incorrect predictions of photocatalytic properties. We present a systematic structural exploration of monolayer and bulk geometries of heptazine-based g-C3N4 using first principles density functional theory (DFT) to assess their stability and elucidate how these configurations influence their electronic properties. Across all systems investigated, we show that buckled heptazine structure—rather than the conventional planar geometry—represents the true energetic ground-state structure. Further analysis of buckling and different stacking registries in g-C3N4 layered structures reveals newly identified low-energy corrugated stackings (with P1 symmetry) that give rise to a broad range of electronic band gaps, several of which closely match experimentally reported values of ∼ 2.7 eV. Moreover, introducing non-metal P and metal Ni dopants at identical lattice sites across 2D-planar/buckled and 3D-corrugated hosts shows distinct electronic responses. Our findings demonstrate that accurate structural modelling, including buckling and stacking registry, is crucial for reliably capturing the stability and tunable electronic properties of g-C3N4.