High-crystalline polymeric carbon nitride flake composed porous nanotubes with significantly improved photocatalytic water splitting activity: The optimal balance between crystallinity and surface area

Enlarging surface area by fabricating special architectures is a common way to enhance photocatalytic activity of polymeric carbon nitride (PCN), but generally accompanied with decreased crystallinity that deteriorates the photoactivity. Herein, high-crystalline PCN flake composed porous nanotubes (cPCNt) were simply synthesized, using the melamine/cyanuric acid supramolecular complex as a precursor under assistance of silicane oil, and the cPCNt with the optimal balance between crystallinity and surface area exhibits prominently enhanced visible light absorption, charge separation and transport, and photocatalytic water splitting activity. The visible-light photocatalytic H-2 evolution rate of cPCNt in the presence of triethanolamine is -69.7-fold higher than that of PCN, with apparent quantum yields of 13.0% at 420 nm and 5.5% at 480 nm, and its overall water splitting activity is -6.9-fold higher under simulated solar light irradiation. This work clarifies the significance of balancing influences of crystallinity and surface area for photoactivity improvement.