Excellent Catalytic Performances of S-Doped g-C3N4 through Electrical Redistribution and Internal Electric Field Formation for Photo-Fenton-Like Reaction

Carbon nitride (g-C₃N₄, CN) is always used as a metal-free catalyst to activate peroxymonosulfate (PMS) without toxic metal ion leaching in solutions. However, it is still a challenge to enhance the catalytic activity for CN. Herein, sulfur (S)-doped g-C₃N₄ is synthesized by a facile method as named CNS_x, where x represents the mass ratio of ammonium sulfate to melamine during the CNS_x synthesis. Partial N atoms such as pyridinic N in CN were replaced by S atoms. CNS_1.75 exhibited an excellent catalytic activity to degrade Rhodamine B (RhB) via PMS activation under the assistance of the visible light (Vis). The rate constant (k) increased about 9 and 7 times for CNS_1.75/Vis/PMS than that of CNS_1.75/PMS and CNS/Vis/PMS systems. Moreover, the k value is higher than that of some metal-doped CN as reported. The toxicity of RhB was effectively reduced after the degradation process with the total organic carbon (TOC) removal ratio 48% after 40 min. The RhB removal efficiency kept 95% after continuous operation for 12 h. The catalytic mechanism was proposed in which ¹O₂ was the dominant reactive oxygen species (ROS).