Delocalization of pi-Electron in Graphitic Carbon Nitride to Promote its Photocatalytic Activity for Hydrogen Evolution

摘要

Polymers with a large pi-electron conjugated system have aroused extensive concern in photocatalysis due to their appropriate bandgap and high stability. In order to overcome such drawbacks as its inadequate visible light absorption and rapid recombination of the photogenerated electron-hole pairs of graphic carbon nitride (g-C3N4), a facile strategy is proposed to tune its electronic structure by grafting small molecules. The conjugated photocatalysts were prepared by attaching 3-Aminobenzoic acid (AB) and 6-Aminopyridine-2-carboxylic acid (APy) to the framework of g-C3N4 via low-temperature condensation. The obtained catalysts UCN-AB and UCN-APy possess higher visible light absorption that results from the modified band structure by extending pi-electron delocalization. Additionally, AB and APy worked as the electron acceptors which further enhance transport of the photogenerated electrons. The optimal UCN-AB and UCN-APy accomplished remarkable photocatalytic hydrogen evolution rates of 104.0 and 133.2 mu mol/h, respectively, which are nearly four or five times of that over g-C3N4. This work provides a simple and feasible modification approach to extend pi-electron delocalization in g-C3N4 with a stronger visible light response and accelerated charge transfer for high photocatalytic hydrogen evolution.