Defects Engineering Leads to Enhanced Photocatalytic H₂ Evolution on Graphitic Carbon Nitride–Covalent Organic Framework Nanosheet Composite

Abstract Graphitic carbon nitride nanosheet (CNS) represents an attractive candidate for solar fuel production. However, the abundant defects in CNS lead to serious charge recombination and limit the photocatalytic performance. Herein, the synthesis of a CNS–covalent organic framework (CNS–COF) nanosheet composite is presented for the first time. CNS with significantly reduced defects is first obtained by rationally tuning the thermal exfoliation conditions of bulk carbon nitride. Subsequent modification of the CNS with trace COF nanosheet through chemical imine bonding can not only passivate the surface termination of carbon nitride in the boundary region, but also establish strong electronic coupling between these two components. As a consequence, enhanced charge separation and photocatalytic activity are realized on the resulting CNS–COF nanosheet composite. Under optimum conditions, hydrogen is evolved at a rate of 46.4 mmol g⁻¹ h⁻¹. This corresponds to an apparent quantum efficiency of 31.8% at 425 nm, which is among the best values ever reported for carbon nitride‐based materials.