Kinetics and thermodynamics of diquat removal from water using magnetic graphene oxide nanocomposite

A graphene oxide nanocomposite ( GO- Fe3O4) was synthesized with a simple and low-cost method. This nanocomposite was characterized by XRD, TEM, FT- IR, TGA, and VSM. Spherical Fe3O4 nanoparticles with an average size of 10nm were uniformly applied to the surface of graphene oxide sheets. GO- Fe3O4 nanocomposite showed a superparamagnetic characteristic at room temperature and its saturation magnetization was 8.5 A. M2/ kg. The adsorption behaviour of diquat at the surface of GO- Fe3O4 was investigated, including effects of pH, temperature, and water matrix. The adsorption kinetics, thermodynamics, and adsorption isotherm were also examined. The adsorption was strongly dependent on pH. The adsorption process obeyed the pseudo- second order kinetic model, and the rate- determining step might be chemical sorption. The Langmuir adsorption isotherm model was applicable for describing the adsorption of diquat onto GO- Fe3O4, and the adsorption capacity was 74.85 mg/ g at room temperature. Thermodynamic parameters indicated that the adsorption process was spontaneous and exothermic. Most importantly, the GOFe3O4 could remove 96.6% of diquat from a real water sample when the concentration of diquat is 20 mg/ L.