Carbon nitride nanosheets for photocatalytic hydrogen evolution: Remarkably enhanced activity by dye sensitization

Carbon nitride (CN) nanosheets with a thickness of around 3 nm were prepared by pyrolysis of urea. Well-dispersed Pt nanoparticles of about 3 nm were pre-loaded on CN nanosheets as the co-catalyst by chemical reduction in ethylene glycol. The Pt/CN sample showed a H₂ evolution rate of 45.1 μmol h^-1 from an aqueous solution of triethanolamine (TEOA) under visible light irradiation (λ > 420 nm). By simply adding a low-cost dye Erythrosin B (ErB) in the photoreaction suspension, a remarkably enhanced H₂ evolution rate of 652.5 μmol h^-1 was observed. Efficient electron transfer from excited ErB to the conduction band of CN is expected due to the energy difference between the LUMO level of excited ErB (-3.59 eV vs. vacuum level) and the conduction band potential of CN (-3.71 eV vs. vacuum level). A dye sensitization mechanism between ErB and CN is proposed. Upon irradiation with light of long wavelength (λ > 550 nm), the Pt/CN-ErB photocatalyst system still exhibited a high H₂ evolution rate of 162.5 μmol h^-1. The highest quantum efficiency of 33.4% was obtained at 460 nm. Moreover, the Pt/CN photocatalyst could be easily recycled by simple filtration and 90% of the activity was still kept after five consecutive runs.