Functional Group Effects on the HOMO–LUMO Gap of g-C(3)N(4)

Graphitic carbon nitride (g-C(3)N(4)) is a promising semiconductor material which has been widely studied in nanoscience. However, the effect of modifying the performance of g-C(3)N(4) is still under debate. In this communication, we show the size and functional group effects on the g-C(3)N(4) using density functional theory (DFT) calculations. It was found that a molecule with six repeated g-C(3)N(4) units (g-C(3)N(4)-6) could be the smallest unit that converges to the limit of its HOMO–LUMO gap. Calculations of g-C(3)N(4)-6 with varying numbers of substituted C≡N, C=O, and O−H functional groups show that C≡N and C=O could narrow down the HOMO–LUMO gap, while O−H could slightly raise the gap. This study shows that the change of substituents could tune the band gap of g-C(3)N(4), suggesting that rationally modifying the substituent at the edge of g-C(3)N(4)-based materials could help to significantly increase the photocatalytic properties of a metal-free g-C(3)N(4).