Facile Synthesis of Self-Assembled g-C3N4 with Abundant Nitrogen Defects for Photocatalytic Hydrogen Evolution

In this work, g-C3N4 with different morphologies is prepared using melamine as precursor via self-assembly and calcination. Compared with pristine g-C3N4, the resultant materials possess thinner lamellar structure and abundant nitrogen defects. Hydrolysis of partial melamine occurs in a hydrothermal process, and a consequent supramolecular intermediate is formed between melamine and its hydrolysates via hydrogen bonding. In addition to enlarging the π–π conjugated systems of the polymer, the formation of intermolecular hydrogen bonds is also interesting for increasing the lifetime of fluorescence as well as for decreasing the recombination rate of electron–hole pairs. Optical absorption characterization indicates that the samples formed by surface self-assembly show remarkably extended light absorption in the visible-light region in comparison with the original g-C3N4. Under visible-light irradiation, all modified materials have outstanding photocatalytic activity, especially the optimally modified catalyst; the hydrogen evolution activity is as high as 8910.7 μmol g–1, which is 9.9 times higher than that of g-C3N4. The improved photocatalytic performance benefits from the nitrogen defects and the structural advantages, more exposed active edges and higher surface area. This method opens a window for facile preparation of metal-free catalysts and inspires similar attempts for the modification of nanomaterials.