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 pi-pi 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 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 mu mol 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.