Superior sponge-like carbon self-doping graphitic carbon nitride nanosheets derived from supramolecular pre-assembly of a melamine–cyanuric acid complex for photocatalytic H2 evolution

The photocatalytic evolution of hydrogen (H2) from water splitting is considered a promising route to overcome the energy crisis, and the key lies in the preparation of efficient photocatalysts. Herein, superior ordered sponge-like carbon self-doped graphitic carbon nitride (g-C3N4) nanosheets (SCCNS) were prepared via a combined strategy of melamine-cyanuric acid complex supramolecular pre-assembly and solvothermal pre-treatment using ethylene glycol (EG) aqueous solutions (EG:water = 50:50 vol.%) as a solvent and carbon doping source. The following pyrolysis converts the naturally arranged melamine-EG-cyanuric acid supramolecular intermediates to highly crystalline SCCNS with large specific surface areas. The optimal SCCNS-180 exhibits superior photocatalytic H2 evolution activities (∼4393 and 11 320 μmol h-1 g-1) when irradiated with visible light and simulated sunlight; these values are up to ∼17- and ∼18-fold higher than that of bulk g-C3N4. The quantum efficiency of SCCNS-180 at λ = 420 nm can reach 6.0%. The excellent photocatalytic performance of SCCNS-180 derives from its distinct ordered sponge-like nanosheet structure with highly crystallinity and the carbon doping, leading to its improved optical absorption, accelerated photoinduced electron-hole pair transfer and separation rate and enlarged specific surface area (134.4 m2 g-1).