Carbonyl-Grafted g-C₃ N₄ Porous Nanosheets for Efficient Photocatalytic Hydrogen Evolution

Carbonyl-grafted g-C₃ N₄ porous nanosheets (COCNPNS) were fabricated by means of a two-step thermal process using melamine and oxalic acid as starting reagents. The combination of melamine with oxalic acid to form a melamine-oxalic acid supramolecule as a precursor is key to synthesizing carbonyl-grafted g-C₃ N₄ . The bulk carbonyl-grafted g-C₃ N₄ (COCN) was further thermally etched onto porous nanosheets by O₂ under air. In such a process, the carbonyl groups were partly removed and the obtained sample showed remarkably enhanced visible-light harvesting and promoted the separation and transfer of photogenerated electrons and holes. With its unique porous structure and enhanced light-harvesting capability, under visible-light illumination (λ>420 nm) the prepared COCNPNS exhibited a superior photocatalytic hydrogen evolution rate of 83.6 μmol h^-1 , which is 26 times that of the p-CN obtained directly from thermal polycondensation of melamine.