A post-grafting strategy to modify g-C₃N₄ with aromatic heterocycles for enhanced photocatalytic activity

A novel and facile post-grafting strategy, instead of conventional copolymerization, via a Schiff base chemical reaction between aldehyde and -NH₂ groups has been developed to construct aromatic heterocycle-grafted graphitic carbon nitride (g-C₃N₄) photocatalysts for the first time. The high-resolution N 1s XPS spectrum and the CO₂ TPD analysis confirmed the successful introduction of heterocycles and the reduced structural defects (unreacted -NH₂ groups during the copolymerization modification of g-C₃N₄). The post-grafting of aromatic rings into the g-C₃N₄ network did not disrupt the original framework of g-C₃N₄, but effectively expanded its π-delocalized system, enlarged its surface area and promoted the separation and transfer of photo-excited charge carriers. As a result, the obtained copolymer composites exhibit significantly enhanced visible-light photocatalytic activity for H₂ evolution over pristine g-C₃N₄. This strategy is general and can be used to graft large numbers of aromatic rings of different molecular structures onto g-C₃N₄.