Functional groups to modify g-C_3N_4 for improved photocatalytic activity of hydrogen evolution from water splitting

Rational modification by functional groups was regarded as one of efficient methods to improve the photocatalytic performance of graphitic carbon nitride (g-C₃N₄). Herein, g-C₃N₄ with yellow (Y-GCN) and brown (C-GCN) were prepared by using the fresh urea and the urea kept for five years, respectively, for the first time. Experimental results show that the H₂ production rate of the C-GCN is 39.06 μmol/h, which is about 5 times of the Y-GCN. Meantime, in terms of apparent quantum efficiency (AQE) at 420 nm, C-GCN has a value of 6.3% and nearly 7.3 times higher than that of Y-GCN (0.86%). The results of XRD, IR, DRS, and NMR show, different from Y-GCN, a new kind of functional group of NCH was firstly in-situ introduced into the C-GCN, resulting in good visible light absorption, and then markedly improving the photocatalytic performance. DFT calculation also confirms the effect of the NCH group band structure of g-C₃N₄. Furthermore, XPS results demonstrate that the existence of NCH groups in C-GCN results in tight interaction between C-GCN and Pt nanoparticles, and then improves the charge separation and photocatalytic performance. The present work demonstrates a good example of “defect engineering” to modify the intrinsic molecular structure of g-C₃N₄ and provides a new avenue to enhance the photocatalytic activity of g-C₃N₄ via facile and environmental-friendly method.