Complete degradation of ciprofloxacin over g-C3N4-iron oxide composite via heterogeneous dark Fenton reaction.

Graphitic carbon nitride (g-C3N4) supported iron oxide (CN@IO) composite was first fabricated via synthesizing g-C3N4 in-situ onto iron oxide. The fabricated CN@IO composite was characterized by several techniques including XRD, XPS, TEM and nitrogen adsorption-desorption analysis. This composite was then used as a catalyst for the dark Fenton oxidative degradation of ciprofloxacin (CIP). Results demonstrated that the incorporation of g-C3N4 profoundly changed the structure and chemical properties of iron oxide, endowing CN@IO composites with high-efficient catalytic activity in dark Fenton system. In the synthesis process of CN@IO composites, iron oxide nanoparticles were successfully intercalated into the layers of g-C3N4, enlarging the surface area and thus providing more active sites for the reactions. Meanwhile, the existence of g-C3N4 can accelerate the Fe3+/Fe2+ redox cycle during the Fenton reaction, which further facilitated CIP degradation. In addition, the effects of reaction parameters, including pH, catalyst dosage, initial concentration of CIP and H2O2, on CIP degradation were investigated. Without any assistance of light irradiation, complete degradation and 48.5% mineralization of CIP were achieved under the best conditions of pH 3.0, 1 g/L CN@IO-2, 20 mg/L CIP and 0.0056 M H2O2. The trapping of iron oxide between g-C3N4 layers helped to stabilize iron oxide so the metal leaching problem that usually occurred in acidic media (pH = 3) can be effectively overcome. This work provides a new thought to develop environmental-friendly and high-efficient catalysts for the degradation of refractory pollutants in dark Fenton system, which is much easier to scale up for industrial application comparing with the photo-Fenton reaction.