The synthesis of silica-coated magnetic nanoparticles and using as adsorbent

In this work, the silica-coated magnetic field-sensitive iron nanoparticles (Si-γFe2O3) were successfully prepared by sol–gel method and used as the adsorbent in the adsorption of methylene blue. The adsorption capacity was evaluated. Batch adsorption experiments were performed as a function of contact time, initial dye concentration (5–20 mg/L), solution pH (4.0–9.6) and temperature (298–328 K). The structure and the morphology of this material were characterized by the Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The adsorption kinetic studies were achieved using pseudo-first order, and pseudo-second order kinetic models. The adsorption kinetic of methylene blue on Si-γFe2O3 is consistent with the pseudo-second order kinetic model. Thermodynamic parameters such as Gibbs free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) changes were evaluated and the results indicated that adsorption process was endothermic and spontaneous. The equilibrium isotherms for the adsorption of methylene blue on the adsorbent were described by the Freundlich and Langmuir isotherm models.