2D/2D homojunction-mediated charge separation: Synergistic effect of crystalline C₃N₅ and g-C₃N₄ via electrostatic self-assembly for photocatalytic hydrogen and benzaldehyde production

Homojunction engineering is a promising modification strategy to improve charge carrier separation and photocatalytic performance of carbon nitrides. Leveraging intrinsic heptazine/triazine phase and face-to-face contact, crystalline C₃N₅ (CC3N5) was combined with protonated g-C₃N₄ (pgCN) through electrostatic self-assembly to achieve robust 2D/2D homojunction interfaces. The highest photocatalytic performance was obtained through crystallinity and homojunction engineering, by controlling the pgCN:CC3N5 ratio. The 25:100 pgCN:CC3N5 homojunction (25CgCN) had the highest hydrogen production (1409.51 µmol h^-1) and apparent quantum efficiency (25.04%, 420 nm), 8-fold and 180-fold higher than CC3N5 and pgCN, respectively. This photocatalytic homojunction improves benzaldehyde and hydrogen production activity, retaining 89% performance after 3 cycles (12 h ) on a 3D-printed substrate. Electron paramagnetic resonance demonstrated higher ·OH^-, ·O₂^- and hole production of irradiated 25CgCN, attributed to crystallinity and homojunction interaction. Thus, electrostatic self-assembly to couple CC3N5 and pgCN in a 2D/2D homojunction interface ameliorates the performance of multifunctional solar-driven applications.