Cyano group-enriched crystalline graphitic carbon nitride photocatalyst: Ethyl acetate-induced improved ordered...

The molten salt-assisted route is one of the most important methods to improve the crystallinity of conventionally disordered bulk graphitic carbon nitride (g-C₃N₄). However, the residual potassium ions from potassium chloride/lithium chloride molten salt can greatly impact the ordered structure of g-C₃N₄ and serve as the recombination centers of photoinduced carriers, causing limited photocatalytic hydrogen-evolution performance. In this article, the ethyl acetate-mediated method is first developed to not only further improve the ordered structure of traditional crystalline g-C₃N₄, but also produce more cyano groups for preparing highly efficient g-C₃N₄ photocatalysts. Herein, the ethyl acetate can gradually hydrolyze to produce hydrogen ions, which can promote the more ordered sheet-like structure and more cyano groups by effective removal of residual potassium ions in the traditional crystalline g-C₃N₄, leading to the formation of cyano group-enriched crystalline g-C₃N₄ photocatalysts (CC-CN). As a result, the resultant CC-CN displays the remarkably enhanced photocatalytic hydrogen-evolution performance (295.30 µmol h^-1 with an apparent quantum efficiency about 12.61%), in comparison to the bulk g-C₃N₄ (14.97 µmol h^-1) and traditional crystalline g-C₃N₄ (24.60 µmol h^-1). The great improvement of photocatalytic performance can mainly be ascribed to the synergism of improved ordered structure and abundant cyano groups, namely, the efficient transfer and separation of photoinduced charges as well as excellent interfacial hydrogen-generation reaction, respectively. The present work may deliver new strategies to prepare other high-crystalline photocatalysts with great efficiency.