N-doped low-rank coal based carbon catalysts for heterogeneous activation of peroxymonosulfate for ofloxacin oxidation via electron transfer and non-radical pathway

Background: Advanced oxidation processes based on sulfate radicals were promising technologies for deep wastewater treatment. There was an urgent need of low-cost and green catalytic materials. Methods: In this study, N-doped low-rank coal based carbon catalysts (NLCs) were prepared under different urea and low-order coal ratios and pyrolysis temperatures, which showed excellent catalytic performance for peroxymonosulfate (PMS) activation. 
Significant findings: The NLCs had a high degree of graphitization and electrical conductivity, which leading to a high removal rates as 100% in 45 min. The N-doped structure lead to the formation of electron-rich regions, which favored the adsorption of PMS. Mechanistic studies revealed that the main reactive oxygen species in the NLC/PMS system was singlet oxygen (¹O₂), and that electron transfer pathways and surface-bound reactive complexes also played an important role in this system. The NLC/PMS system had a wide pH adaptation and good environment adaptation because of the electron transfer mechanism. It could remove 100% OFL in the pH range of 3-9. Therefore, the prepared N-doped coal based carbon catalytic materials had good prospects for application in advanced oxidation processes for wastewater treatment.