In situ reduction and exfoliation of g-C3N4 nanosheets with copious active sites via a thermal approach for effective water splitting

Abstract

Poor optical absorbance and charge recombination are the major drawbacks of polymeric graphitic carbon nitride (g-C₃N₄)-based photocatalysts. In this paper, we show for the first time a single-step in situ technique to control the porosity of two-dimensional g-C₃N₄ sheets and exfoliate them by introducing ascorbic acid (AA) molecules. The AA simultaneously acts as the carbon (C) source and deposits amorphous C onto g-C₃N₄ sheets. Nanosized pores are also introduced into the g-C₃N₄ sheets, leading to a large number of active sites. The as-prepared C-doped porous g-C₃N₄ nanosheets demonstrate a high visible light-photocatalytic H₂ production activity of 793 μmol g⁻¹ with the optimum structure, which is almost 25 times higher than the value obtained with bulk g-C₃N₄ (31 μmol g⁻¹). This exceptional photocatalytic performance arises from the C-doped conjugated system and porous nanosheets. The enhanced photocatalytic H₂ evolution was attributed to the effective separation and transport of charge carriers by the deposition of C onto the nanosheets and an increased number of active sites resulting from the nanopores created inside the g-C₃N₄ sheets. Moreover, molecular dynamics (MD) simulations confirm that the interaction between AA and melamine molecules at elevated temperatures results in the formation of C-doped porous and exfoliated g-C₃N₄ structures. Therefore, the present approach is very promising for application to the design of new and efficient photocatalysts for photocatalytic H₂ evolution under visible irradiation.