Molecular engineering of supramolecular precursor to modulate g-C3N4 for boosting photocatalytic hydrogen evolution

Herein, a novel strategy was explored to enhance the photocatalytic activity of graphitic carbon nitride (g-C3N4, GCN) by modulating its molecular structure, which involved modifying supramolecular precursor by molecular engineering, followed by pyrolysis. Specifically, 1-amino-2-propanol (monoisopropanolamine, MIPA), a substance that carries both –NH2 and –OH, was introduced into the system of hydrothermally treating dicyandiamide (DCDA). The precursors obtained at the MIPA volume concentration of more than 0.5% display hexagonal prisms, and then transform into the ethyl grafted GCN with a tubular-like morphology, abundant pores and enlarged specific surface area. Besides the intrinsic band absorption, the obtained GCN exhibit an enhanced visible light absorption in the region between 450 and 560 nm, owing to the existence of a midgap state related to the ethyl grafting. A much reduction in charge recombination is observed for the ethyl-grafted GCN, originated from its spatial separation between LUMO and HOMO. Consequently, the hydrogen evolution rate of the GCN sample, obtained at the optimal concentration of MIPA, is 13.84 mmol/h/g (AQE = 18.25% at 420 nm), about 30.1 times higher than that of the bulk C3N4 (BCN) under visible light (λ > 420) irradiation. This work sheds light on modulating GCN by molecular engineering of supramolecular precursors.