High selectivity and efficient utilization of H2O2 in a metal-free Electro-Fenton system with nitrogen doped cathode for the degradation of sulfamethazine

In this study, we constructed a metal-free Electro-Fenton system mediated by nitrogen-doped activated carbon modified graphite felt (NACs/GF) for degrading sulfamethazine (SMZ) through self-generation and utilization of H2O2. With the increase of activation temperature (700 similar to 1100 degrees C), graphitic N occupied the dominant position and whose nearest pyridinic N were released to form N vacancies. NAC-1100/GF E-F system had a high H2O2 selectivity (94.3 %) and an excellent H2O2 yield (44.6 mg center dot L-1). The OOH* as the main barrier of 2e(-)-ORR process was formed and desorbed at graphitic N sites, while the N vacancies could enhance electron transfer with O-2* and OOH* for accelerating generation of H2O2. The 50 mg center dot L-1 of SMZ as pollutant could be completely degraded within 60 min in NAC-1100/GF E-F system, during which the graphitic N and pyrrolic N adsorbed SMZ through van der Waals forces, and pyridinic N adsorbed H2O2 by hydrogen bonding interactions, thus establishing a controlled reaction zone near the cathode. The highly electronegativity pyridinic N could provide electrons for catalyzing the generation of center dot OH from H2O2, while N vacancies could form more unpaired electrons to facilitate the formation of O-1(2). Finally, the degradation pathway of SMZ and toxicity analysis of degradation products were further clarified. This study provided valuable information for constructing metal-free ElectroFenton systems and their application in environmental purification.