Facile one-step synthesis of porous graphene-like g-C3N4 rich in nitrogen vacancies for enhanced H2 production from photocatalytic aqueous-phase reforming of methanol

Exfoliation of bulk graphitic carbon nitride (g-C3N4) to single- or few-layered structures is an effective way to improve the photocatalytic performance. However, the synthesis methods for few-layer g-C3N4 are relatively complicated and time-consuming, with the bandgap of g-C3N4 increasing through quantum size effects, thus hampering effective utilization of visible light. To effectively exfoliate the bulk g-C3N4 to single or few-layered structures in a facile way without losing its visible light absorption ability is still a challenge. Herein, porous graphene-like g-C3N4 nanosheets with abundant nitrogen vacancies were prepared by facile thermal polymerization of melamine using graphene oxide (GO) as a sacrificial template. The two-dimensional (2D) layer morphology and nitrogen defect structure were proved using AFM, SEM, TEM, EA, XPS and EPR techniques. Compared with the bulk g-C3N4, the as-prepared g-C3N4 nanosheet possesses a high specific surface area, enhanced absorption ability of visible light, and elevated charge carrier generation and separation efficiency because of the unique structural features. The in situ DRIFT spectrum indicates that the surface nitrogen vacancies also serve as excellent locations for methanol adsorption and activation. Consequently, an excellent photocatalytic activity of hydrogen production from methanol aqueous-phase reforming is obtained, which is about 14 times more productive than the bulk g-C3N4.