A graphitic carbon nitride metal-free visible light photocatalyst with controllable carbon self-doping towards efficient hydrogen evolution

Abstract

Controlling molecular defects via element doping is an effective strategy for tailoring electronic structures and charge separation in photocatalysts. However, the rational design of self-doped catalysts is generally confronted with the need for expensive reagents, high dopant ratios and environmentally unfriendly materials. Herein, carbon self-doped graphitic carbon nitride (DCN-x) is obtained via one-pot thermal polymerization of urea and D-mannitol. The sp²-hybridized nitrogen atoms are partially substituted by carbon atoms from dopants. The corresponding defects provide the photocatalyst with extended light harvesting up to 600 nm, a tunable optical bandgap, and the formation of more delocalized electrons with a uniform distribution at the defect scope of a C–C bond. In addition, increased band-tail states are found in DCN-3, which greatly enhance charge separation. A high photocatalytic hydrogen evolution rate of 3180 μmol g⁻¹ h⁻¹ is achieved under visible light irradiation (λ > 420 nm), which is about 5.3 fold higher than that of pristine g-C₃N₄. This work provides a green and economical method to synthesize g-C₃N₄ with controllable carbon self-doping sites for efficient energy conversion related applications.