Preparation of high-efficient donor-π-acceptor system with crystalline g-C3N4 as charge transfer module for enhanced photocatalytic hydrogen evolution

Donor-π-acceptor (D-π-A) type photocatalysts with g-C₃N₄ as π-module have attracted much attention due to their optimized conjugate structure and enhanced electron directed driving. However, the inefficient charge migration of g-C₃N₄ due to its amorphous or semi-crystalline structure and limitation of available functional groups are present challenges. In this work, the D-π-A type high crystalline carbon nitride (HCCN) has been obtained by in-situ introducing amide and cyanide groups into the high-crystallinity melon framework. The synergistic effect of functional group modification and crystallinity regulation greatly enhances the electron induction driving and charge carrier density. Moreover, the density functional theory (DFT) calculations demonstrate that the D-π-A structure could induce the local charge distribution of melon units to provide a unique and stable pathway for photoinduced charge migration. The as-prepared HCCN sample shows a superior visible-light photocatalytic performance for hydrogen evolution with an apparent quantum efficiency (AQE) of 12.2% at 420 ± 15 nm, which is 23.7 times higher than that of original g-C₃N₄. Finally, the charge separation and transfer processes as well as the possible photocatalytic reaction mechanisms of HCCN sample are also investigated.