The large loss of catalysts and secondary pollution problems are bottlenecks for the utilization of persulfate advanced oxidation processes. Thus, a modified Hummers method combined with a hydrothermal method was used to prepare N-doped graphene as a catalyst for peroxymonosulfate (PMS) activation. The produced sulfate radical (SO4-·) and hydroxyl radical (·OH) were able to degrade RBk5. N-doped graphene was characterized by Fourier transform infrared, X-ray photoelectron spectroscopy, Raman spectroscopy, and transmission electron microscopy. The influences of vital parameters (i. e., initial pH, catalyst dosage, and PMS dosage) on RBk5 removal were investigated systematically to examine the catalytic performance. The results showed that the N element doping can effectively improve the catalytic activity of graphene, and the activity is greatly affected by the N doping ratio. The initial pH of the wastewater had no significant effect on the degradation efficiency. Under the condition of 1.5 g·L-1 catalyst dosage and 0.3 g·L-1 PMS dosage, the removal rate of RBk5 dye reached 99% after 25 min of reaction. The reaction process accorded with first-order reaction kinetics. Radical quenching experiments were done and indicated that the degradation of RBk5 in N-doped graphene/PMS systems was a surface reaction, and SO4-· and ·OH were identified as the main radical species. The catalyst exhibited excellent stability over five successive degradation cycles.
Keywords: N-doped graphene; RBk5; advanced oxidation processes; catalysis; peroxymonosulfate.