Protonation and microwave-assisted heating induced excitation of lone-pair electrons in graphitic carbon nitride for increased photocatalytic hydrogen generation

Abstract

Graphitic carbon nitride (g-C₃N₄) with pronounced excitation of lone pairs benefits from extended visible light absorption, which thus enhances its photocatalytic hydrogen (H₂) generation activity. However, achieving such lone pair excitation in g-C₃N₄ remains a grand challenge. Here we report on the synthesis of g-C₃N₄ with remarkable lone pair excitation through thermolysis of protonated melamine via a facile microwave-assisted heating. The g-C₃N₄ photocatalyst after optimizing the proton concentration offers a highest H₂ generation rate of 21.4 μmol h⁻¹, which is nearly 7 times higher than that of g-C₃N₄ created from unprotonated melamine under identical conditions (3.2 μmol h⁻¹). Furthermore, active H₂ generation at 490 nm light irradiation (2.3 μmol h⁻¹) is realized owing to the lone pair excitation. This work shows the great potential of protonation combined with microwave-assisted heating for activating the lone pair excitation in g-C₃N₄ for increased photocatalytic performance.