A simple calcination process was used to create g-C3N4 (CN) from melamine, and the modified g-C3N4 (MCN) was synthesized with hydrochloric acid (HCl), sulfuric acid (H2SO4), and nitric acid (HNO3). After acid modification, CN successfully introduced oxygen-containing functional groups and obtained CN-HNO3 with multiple holes, which improved the photocatalytic efficiency. The bandgap of CN-HNO3 (2.46 eV) is 0.24 eV lower than that of CN (2.70 eV), resulting in more electron holes and improved light absorption of the catalyst. CN-HNO3 has a conduction band (CB) of -1.23 eV, while CN has a CB of -1.13 eV. CN-HNO3 is simpler to convert O2 to ·O2- than CN, which can boost photocatalytic efficiency. The degradation of rhodamine B(RhB) was used to investigate the photocatalytic properties of CN and MCN. The results show that the photocatalytic efficiency of MCN was higher than that of pure CN, and the photocatalytic efficiency and degradation rate constant of CN-HNO3 was 36.6% and 5.5 times higher than that of the CN, reaching 99.7% and 0.0341 min-1. The degradation efficiency remained more than 85% after five cycles, showing that MCN was more photo-catalytically stable than CN.

Hao Yang, Wenjie Cheng, Mengdi Xu, Guijun Yang, Huiyuan Chen, Caihong Xue, Guocai Ma and Heqi Li