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 ∼ 1100 ℃), 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·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 O2* and OOH* for accelerating generation of H2O2. The 50 mg·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 ·OH from H2O2, while N vacancies could form more unpaired electrons to facilitate the formation of 1O2. Finally, the degradation pathway of SMZ and toxicity analysis of degradation products were further clarified. This study provided valuable information for constructing metal-free Electro-Fenton systems and their application in environmental purification.