Nitrogen Self-Doped Graphitic Carbon Nitride with Optimized Band Gap as a Visible-Light-Driven Photocatalyst for Hydrogen Production and Pollutant Degradation

Abstract

The photocatalytic activity of graphitic carbon nitride (g-C₃N₄) is always constrained by rapid carrier recombination, a low specific surface area, and narrowed light response. In this study, nitrogen self-doped g-C₃N₄ (NCN) with optimized band structure was successfully fabricated by the copolymerization of a mixture including melamine and ethylenediamine. The resultant samples were perfectly applied to the photocatalytic hydrogen production and photodegradation of tetracycline. Characterizations and density functional theory (DFT) calculations identified the introduction of a nitrogen doping site within the g-C₃N₄ framework. The narrowed band gap, limited photoinduced carrier recombination, and rapid charge transfer were attributed to the DFT, optical properties, and photoelectrochemical analysis, which improved the visible light absorption and optimized the carrier migration channel. Specifically, NCN6 exhibited a 13.47 times higher hydrogen evolution rate (3.07 mmol g^–1 h^–1) with an apparent quantum yield of 12.65% at 420 nm and 1.78-fold (82.49%) better photodegradation efficiencies than pristine g-C₃N₄ (0.23 mmol g^–1 h^–1 and 58.79%), respectively. This study offers a straightforward approach to the synthesis of functionalized g-C₃N₄, with the objective of enhancing the photocatalytic activity and elucidating the doping mechanism. Furthermore, it provides guidance for the development of nonmetal-doped organic semiconductor photocatalysts.