Strengthened H₂O adsorption and photogenerated carrier separation: surface C-coupled hydroxylation of g-C₃N₄ photocatalysts for efficient H₂ production

A photocatalysis based g-C3N4 system is a green and eco-friendly method for hydrogen production, but limited activity of g-C3N4 is undesirable. Presently, most of the modification strategies for the g-C3N4-based photocatalytic system are centered on doping and heterojunction engineering outside the bulk phase, and little consideration is given to functional group modification within the bulk phase. Herein, surface C-coupled hydroxylated g-C3N4 photocatalysts for efficient H-2 evolution are presented. A C-coupled hydroxylation process is proposed through the reaction of formaldehyde with the unsaturated carbon in the g-C3N4 framework. Compared to pristine g-C3N4 photocatalysts, the surface C-coupled hydroxylated g-C3N4 photocatalyst exhibited over 11.18 times more photocatalytic efficiency for H-2 production, and impressive apparent quantum yield. The experimental findings and theoretical calculations reveal that the morphology, photo-response features, and crystal structure are maintained after the introduction of C-coupled hydroxylation on the g-C3N4 surface, but the H2O adsorption and H-2 production efficiency of g-C3N4 are significantly increased due to excellent photoinduced carrier migration efficiency. Therefore, the functional modification of g-C3N4 photocatalysts with C-coupled hydroxylation is highly favorable. This work could offer a new and useful protocol for designing highly efficient functional photocatalysts from a structural modification perspective.