High-yield lactic acid-mediated route for a g-C₃N₄ nanosheet photocatalyst with enhanced H₂-evolution performance

Facile and novel strategies to prepare g-C3N4 nanosheets are required to greatly improve their photocatalytic H2-production activity. In this study, a lactic acid-mediated synthesis route has been developed to prepare g-C3N4 nanosheets, which includes the preassembled formation of lactic acid-melamine co-monomers, followed by direct high-temperature calcination. In this case, it is found that during high-temperature calcination, the lactic acid molecules can greatly prevent the serious polymerization of melamine molecules, resulting in the formation of g-C3N4 nanosheets. Moreover, owing to the strong coupling with melamine molecules, lactic acid can also significantly increase the production rate (ca. 35.16 wt%) of g-C3N4 nanosheets from the melamine precursor via preventing the rapid sublimation of melamine and its intermediates during the calcination progress compared with the well-known two-step calcination method. Photocatalytic experimental data reveal that the resultant g-C3N4 nanosheet photocatalysts show a greatly improved H2-production rate, and the g-C3N4 (500 μL) sample exhibits the best photocatalytic performance, which is obviously two times higher than that of the conventional bulk g-C3N4. In addition to lactic acid, it is very interesting to find that acetic acid can also be used to prepare g-C3N4 nanosheets via a similar formation mechanism, strongly suggesting the universality and versatility of the present lactic acid-mediated synthesis route. The present synthesis strategy may broaden the horizons for the synthesis of high-efficiency photocatalysts.