Synthesis of chitosan functionalized magnetic graphene oxide composite and adsorption on methyl orange

The chitosan/magnetic graphene oxide (CS/MGO) composites were synthesized by the modified Hummers and hydrothermal methods and applied as an adsorbent for the removal of methyl orange (MO). CS/MGO composite was characterized by SEM, XRD, BET, FTIR and a vibrating sample magnetometer (VSM). Results show that Fe₃O₄ nanoparticles mainly exist on the surface of graphene oxide and chitosan (CS) composite with less aggregation and a good magnetic response. In addition, the thermal stability is good, and the specific surface area of CS/MGO is 36.873 m²·g⁻¹. CS/MGO composite could be easily separated by magnetic separation and demonstrates good stability and reusability. The effects of pH, initial concentration of MO, CS/MGO composite amount and regeneration on the removal of MO were systematically investigated. The results reveal that the initial MO concentration of 20 mg·L⁻¹, CS/MGO composite amount of 0.12 g·L⁻¹, and pH=3 lead to the adsorption equilibrium after 210 min. CS/MGO composite maintains 83.7% of its maximum MO adsorption capacity after five consecutive cycles. The adsorption process conforms to the pseudo-second-order kinetic model, and the adsorption isotherms conform to the Langmuir model. The maximum adsorption amounts at 298.15, 303.15 and 308.15 K are 129.96, 138.94 and 145.03 mg·g⁻¹, respectively. The adsorption thermodynamics indicate that the adsorption process is endothermic; entropy increases the spontaneous adsorption process.