Introduction of crystalline hexagonal-C3N4 into g-C3N4 with enhanced charge separation efficiency

Highlights: • A novel crystalline hexagonal-C₃N₄/g-C₃N₄ heterophase junction photocatalyst is firstly designed. • The obtained heterophase junction exhibits perfect interfacial contact and high hydrophilicity. • The proposed mechanism of photocatalytic hydrogen evolution was studied in-depth. Polymeric carbon nitride is a promising candidate for photocatalytic hydrogen evolution but mostly just shows moderate activity because of its inefficient charge separation and sluggish surface reaction kinetics. Phase-based heterostructures, especially crystal-phase heterostructures that are composed of identical compositions with different crystal phases, can endow nanomaterials with promising properties and efficient photocatalysis applications. In this study, a novel crystalline hexagonal-C₃N₄/g-C₃N₄ hetero-phase junction was synthesized using a direct in situ alkali salt template coupled with organic solvents strategy. High hydrophilicity was obtained because of the synergistic effect between alkali salt and organic solvents in the polycondensation process. The greatly increased separation and transfer efficiency of charge carriers and the improved proton absorption in the surface reaction of the photocatalyst were achieved by the constructed phase junctions between the crystalline hexagonal-C₃N₄ and amorphous g-C₃N₄ decorated with numerous hydrophilic groups. Thus, the carbon nitride hetero-phase junction exhibited dramatically enhanced photocatalytic performance in hydrogen evolution and excellent cycling stability under visible light irradiation. This work presents a novel insight into phase engineering based on carbon nitride materials with surface functional modification for an efficient photocatalytic activity.