Metal-free carbonaceous composite membranes have been proven to effectively drive novel in situ catalytic oxidation for the degradation of organic pollutants via persulfates activation. In this study, nitrogen-doped graphene (NG) was employed as a modifier to enhance the catalytic activity of the carbon mats by assembly with reduced graphene oxide (rGO) and carbon nanotubes (CNTs) on the top of a nylon supporter. The morphology and performance of the NG/rGO/CNTs composite membrane were compared to those obtained without the addition of NG (rGO/CNTs). Owing to the larger nanochannels for water delivery and stronger hydrophobicity on the surface, the NG/rGO/CNTs composite membrane shows a superior low-pressure filtration performance in favor of energy-saving operation. For the in situ catalytic oxidation of the NG/rGO/CNTs composite membrane through the activation of peroxydisufate (PDS), the average removal rate of sulfamethoxazole (SMX), one of frequently detected sulfonamide antibiotics in water, can reach 21.7 mg·m-2·h-1 under continuous filtration mode, which was 17% more rapid than that of the rGO/CNTs, resulting in significant detoxifying of the oxidation intermediates. Owing to the addition of NG into the carbon mats, the reactive nitrogen-doped sites identified by X-Ray photoelectron spectroscopy (XPS), such as pyridinic and graphitic N, played important roles in PDS activation, while both the radical and non-radical pathways were involved in in situ catalytic oxidation. According to the experimental evidence of the effects that solution environment has on the SMX removal and transmembrane pressure, the NG/rGO/CNTs composite membrane shows a relatively high resistance to changes in the solution pH, chloride ion inhibition, and background organics fouling. These results suggest a new approach to the application of activated persulfate oxidation in water treatment, such that improvements to the reaction stability warrant further investigation.
Keywords: Composite membrane; In situ catalytic oxidation; Nitrogen-doped graphene; Peroxydisufate activation; Solution environment; Sulfamethoxazole.