Large impact of heating time on physical properties and photocatalytic H2 production of g-C3N4 nanosheets synthesized through urea polymerization in Ar atmosphere

•G-C3N4 nanosheets were synthesized via the urea polymerization in Ar atmosphere.•The g-C3N4 nanosheets are very active for visible-light-driven H2 production.•The highest H2 rate was up to 1.4 mmol h−1 g−1 (2.6% quantum efficiency at 420 nm).

The effect of heating time on the polymerization processes of urea into g-C3N4 nanosheets was studied in Ar atmosphere. It was found that heating time had a great influence on the crystalline quality, specific surface area (SBET) and photocatalytic H2 production of the obtained g-C3N4 nanosheets. G-C3N4 nanosheets with some degree of disorders in crystal structure were formed within 1 h at 550 °C, and these structural disorders maintained after 4 h, however disorders disappeared after extended heating of 6 h. G-C3N4 nanosheets with similar disorders in the crystal structure hold similar SBET and exhibit comparable H2 production rates. The highest H2 production rate of 1.4 mmol h−1 g−1 occurs after 8 h heating, corresponding to 2.6% quantum efficiency at 420 nm.