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

Abstract

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.