Thermal removal of partial nitrogen atoms in N-doped graphene for enhanced catalytic oxidation

Carbon materials are effective catalysts to activate peroxymonosulfate (PMS) for organic pollutant degradation. Both nitrogen doping and structural defects could enhance their catalytic performance for PMS activation. In this study, nitrogen-doped graphene (NG) is first synthesized by the calcination of graphene oxide (GO) with ammonium nitrate (NH₄NO₃). The obtained NG is then annealed further at a higher temperature under a N₂ atmosphere to remove partially doped N atoms and create new structural defects. The obtained defective nitrogen-doped graphene (D-NG) can activate PMS for bisphenol A (BPA) degradation more effectively. Different annealing temperatures from 850 to 1150 °C are investigated, and D-NG synthesized at 1050 °C exhibits the highest activity. The enhanced catalytic performance is proposed to originate from the synergistic effect between doped N atoms and created structural defects. According to radical quenching, electron paramagnetic resonance (EPR), and electrochemical results, both radical and nonradical pathways are present during PMS activation, and the nonradical pathway plays the dominant role. This study provides a facile method for metal-free catalyst synthesis, which also enriches the synergistic mechanism between doped N and structural defects and thus should have great potential in wastewater remediation.