Oxidized Platinum Cocatalyst and Self-Assembled Graphene over Graphitic Carbon Nitride for Photocatalytic Hydrogen Evolution

Abstract

The nanostructural design of graphitic carbon nitride (g-C3N4) plays a primary role in addressing the drawbacks posed by low surface area, which results in poor dispersion of accessible active sites in the reaction media of bare g-C3N4. Here, we report the solid-state structure transformation through solvothermal treatment of bulk g-C3N4 in an environmentally sustainable organic solvent. The grid-like structure of the monolayered g-C3N4 nanosheets was achieved using a facile solvothermal process. The formation of self-assembled graphene on g-C3N4 during the process facilitated charge transfer and separation on the photocatalyst, as confirmed by density functional theory calculations. The grid-like structure of the g-C3N4 contributed to the formation of a platinum oxide cocatalyst, while the formation of metallic platinum was observed in the bulk g-C3N4 sample. The platinum oxide cocatalyst enhanced the hydrogen evolution rate (HER) by inhibiting the reversible reaction pathway of hydrogen gas to protons. As a result, the platinum support on the grid-like structure of g-C3N4 and self-assembled graphene hybrid (hCN-G) achieve a photocatalytic H2 evolution rate 7.5 times that of bulk g-C3N4 (CN-b). The hCN-G contained 2.04 wt % graphene, which contributed significantly to the improvement in photocatalytic activity. The HER of hCN-G at the stationary point reached 16 832.9 μmol g–1 h–1 under 1 sun of simulated sunlight irradiation.