Introduction of nitrogen defects into a graphitic carbon nitride framework by selenium vapor treatment for enhanced photocatalytic hydrogen production

Graphitic carbon nitride (g-C3N4) is a metal-free semiconductor photocatalyst that has attracted significant attention due to its promising application in photocatalytic hydrogen production. However, pristine g-C3N4 suffers from a high recombination rate of photo-generated charge carriers and also has a limited visible-light absorption range, resulting in low photocatalytic activity. Herein, we report on the preparation and testing of a g-C3N4 photocatalyst with tunable nitrogen defects that delivered improved photocatalytic activity. The nitrogen defects were gradually introduced into the g-C3N4 framework by a selenium vapor treatment of pure g-C3N4, which resulted in improved, stable catalytic activity for photocatalytic hydrogen production. Based on the experimental results and DFT calculations, we proposed that the enhanced photoactivity is attributed to the defect state (DS) formed by the nitrogen vacancy (VN) in the unit cell of g-C3N4 and a small widening of visible light absorption. This nitrogen-based photocatalyst with nitrogen deficiencies was found to deliver an average hydrogen generation rate of 1.16 mmol g(-1) h(-1) at room temperature (25 degrees C), which was 3.4 times greater than pristine g-C3N4. This process of introducing nitrogen defects into the graphitic carbon provides a promising way for enhancing the photocatalytic activity of g-C3N4-based materials for hydrogen production.