Graphene oxide–MnFe₂O₄ nanohybrid material as an adsorbent of Congo red dye

The aim of this work is the synthesis and characterization of graphene oxide (GO)–MnFe₂O₄ nanohybrid material, as well as the study of its performance in the removal of Congo red (CR) dye from aqueous solutions. The GO–MnFe₂O₄ was prepared via a three-step method. Firstly, GO was produced via a modified Hummers' method, using graphite powder as starting material. Subsequently, GO was functionalized with ionic surfactants, cetyltrimethylammonium bromide and poly(sodium-4-styrenesulfonate). Following this, the functionalized GO was decorated with magnetic MnFe₂O₄ nanoparticles via an electrostatic self-assembly process using a solvothermal treatment at 200 °C for 12 h. The as-prepared GO–MnFe₂O₄ nanohybrid material was characterized by several techniques: X-ray diffraction analysis, Fourier-transform infrared spectroscopy, micro-Raman spectroscopy, thermogravimetric analysis, field emission scanning electron microscopy, and high-resolution transition electron microscopy with energy-dispersive spectroscopy mapping. The adsorption performance of GO–MnFe₂O₄ in the removal of CR dye was evaluated at different initial CR concentrations and contact times using an ultraviolet–visible spectrophotometer. In addition, its recyclability performance was investigated for 10 cycles. It is noteworthy that even after the last cycle, the removal efficiency of GO–MnFe₂O₄ exceeded 65%, indicating that the adsorbent had very good reusability. Finally, the Freundlich isotherm model yielded a better fit for the adsorption data, compared to Langmuir, while adsorption of CR by GO–MnFe₂O₄ showed pseudo-second-order kinetics.