Construction of rGO-coupled C3N4/C3N5 2D/2D Z-scheme heterojunction to accelerate charge separation for efficient visible light H2 evolution

As a fascinating two-dimensional (2D) conjugated polymer, graphitic carbon nitride (C3N4) has drawn broad attention as metal-free photocatalyst, but it’s further utilization is confined by the limited visible light harvesting and severe charge recombination. Herein, N-rich carbon nitride (C3N5) with an azo-linked two s-heptazine units, different from C3N4 with a tertiary N-atom linked three s-heptazines, is prepared for constructing a novel sandwich heterojunction composed of reduced graphene oxide (rGO)-coupled C3N5 and C3N4. The introduced rGO in C3N4/rGO/C3N5 heterojunction can accelerate the interfacial charge separation and promote a rGO-mediated solid-state Z-scheme mechanism with an obvious synergistic effect, whereby C3N4 and C3N5 serve as electron-rich and hole-rich reservoirs, respectively. The resultant 2D/2D heterojunction delivers efficient visible-light-responsive activity with H2 evolution rate of 319 μmol h−1, 5.6 and 2.7 times higher than that of C3N4 and C3N5 alone, respectively. This work presents a new concept to design highly efficient carbon nitride-based artificial photosynthetic system.