In situ reduction and exfoliation of g-C ₃ N ₄ nanosheets with copious active sites via a thermal approach for effective water splitting

Poor optical absorbance and charge recombination are the major drawbacks of polymeric graphitic carbon nitride (g-C ₃ N ₄ )-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-C ₃ N ₄ 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-C ₃ N ₄ sheets. Nanosized pores are also introduced into the g-C ₃ N ₄ sheets, leading to a large number of active sites. The as-prepared C-doped porous g-C ₃ N ₄ nanosheets demonstrate a high visible light-photocatalytic H ₂ production activity of 793 μmol g ^-1 with the optimum structure, which is almost 25 times higher than the value obtained with bulk g-C ₃ N ₄ (31 μmol g ^-1 ). This exceptional photocatalytic performance arises from the C-doped conjugated system and porous nanosheets. The enhanced photocatalytic H ₂ 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-C ₃ N ₄ 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-C ₃ N ₄ structures. Therefore, the present approach is very promising for application to the design of new and efficient photocatalysts for photocatalytic H ₂ evolution under visible irradiation.