Thermal oxidative etching method derived graphitic C3N4: highly efficient metal-free catalyst in the selective epoxidation of styrene

A series of g-C3N4 nanosheets were synthesized by thermal oxidation with long time heating and etching. With an increase in heating time from 1.0 to 3.0 h, the g-C3N4 nanosheet was obtained with a thinner layer thickness, larger BET surface area and higher graphic nitrogen ratio. As a metal-free heterogeneous catalyst, the g-C3N4 NS-3 h nanosheets show a superior catalytic performance for the epoxidation of styrene to styrene oxide than that of the bulk g-C3N4 and other recently reported metal-free materials. The higher activity of the g-C3N4 NS-3 h synthesized by long time thermal oxidative etching might be ascribed to the enlarged specific surface, pore volume and higher graphic nitrogen ratio with the loose and soft laminar morphology. The graphitic nitrogen species play a key role in the catalytic reaction based on a good linear correlation between the content of these species and the activity results. The g-C3N4 nanosheets are very stable and can be reused 5 times without obvious loss of catalytic activity.