Catalytic degradation of antibiotics by metal-free catalysis over nitrogen-doped graphene

Emerging pharmaceutical contaminants, for example antibiotics, have raised severe challenges to remediation technologies due to their resistance to biodegradation and the ineffectiveness in adsorptive removal or membrane separation. In this study, we observed the direct degradation of antibiotic sulfachlorpyridazine (SCP), one of sulfonamides, by peroxymonosulfate (PMS) with high efficiency. Nevertheless, SCP could be rapidly decomposed, but the overall mineralization efficiency was rather low. Then, nitrogen-doped reduced graphene oxide (N-rGO), synthesized by a facile hydrothermal route, was employed as a metal-free catalyst to improve the degradation and mineralization of SCP. A comprehensive investigation of in situ electron paramagnetic resonance (EPR), selective radical quenching, and PMS decomposition was performed, revealing the direct and nonradical reactions between PMS and SCP in PMS-based and non-catalytic system without producing free radicals such as [rad]OH and SO4[rad]-. Upon the introduction of N-rGO, the SCP removal rate was similar to the PMS-only reaction, however, an enhanced total organic removal was achieved. This suggests that N-doped nanocarbon materials would achieve a greater extent of mineralization of SCP into inorganic salts, carbon dioxide and water. The findings show that the direct oxidation of SCP with PMS can be used to selectively convert the toxic antibiotics to less or non-toxic organic substances whereas the robust carbocatalysis would contribute to the practical wastewater remediation by metal-free advanced oxidation processes (AOPs)