Comparison and Characterization of Nitrogen/Sulfur-Doped Activated Carbon for Activating Peroxydisulfate to Degrade Acid Orange 7: an Experimental and Theoretical Study

Nitrogen-doped (NAC), sulfur-doped (SAC), and nitrogen/sulfurco-dopedactivated carbon (NSAC) were prepared to activate peroxydisulfate(PDS) for degrading acid orange 7 (AO7) in water, where urea, sulfurelement, and thiourea were used as N/S sources. Greater degradationof AO7 was achieved by all modified samples with PDS compared withthat of pristine AC, where the NSAC/PDS system achieved the highestdegradation performance. Quenching tests, electrochemical analysis,and theoretical calculations suggested that the degradation of AO7led by modified carbon catalysts and PDS was mainly attributed tothe non-radical pathway (e.g., singlet oxygen formation and electron-transfermechanism). The doping of N or S resulted in the generation of pyridinicN and thiophenic S. These groups significantly changed the chargedistribution, creating more abundant edge defects and active sites,which enhanced the catalytic degradation of AO7. Co-doping of AC withN and S produced a higher abundance of graphitic N groups and edgedefect, which likely promoted AO7 degradation compared with the othercatalysts. The results of this study can provide theoretical supportfor the application of N/S-modified carbon materials for activatingpersulfates to effectively treat dyeing wastewater.