Insight into the Enhanced Hydrogen Evolution Activity of 2,4-Diaminopyrimidine-Doped Graphitic Carbon Nitride Photocatalysts

Molecular doping has been proven as an effective way for graphitic carbon nitride (GCN) to extend its light harvesting and improve its charge separation and transport, while little attention has been paid on its effect on the charge transfer at the interfaces between GCN and the cocatalyst. Herein, a pyrimidine-based molecule, 2,4-diaminopyrimidine (DAP), was first used to combine with urea for preparing doped GCN. It is found that the optimal doped GCN sample, CN-DAP(36), has a narrowed band gap, reduced photoluminescent emission, and longer carrier lifetime, as compared with the undoped GCN. The hydrogen evolution rate of the doped GCN is found to be 2.80 mmol/(h.g), 6.09 times that of the undoped GCN [0.46 mmol/(h.g)] under visible light irradiation. Furthermore, according to theoretical calculations, the pyrimidine groups in DAP possess a stronger adsorption capacity for Pt particles than the tri-s-triazine of GCN does, thus leading to more Pt particles deposited near the pyrimidine rings. The extension in optical absorption, the reduction in charge recombination, and the enhancement in charge transport, along with the facilitation in the interfacial charge transfer from the doped GCN sample to Pt, contribute to the enhanced photocatalytic performance of the doped GCN.