Preparation of Congo red functionalized Fe3O4@SiO2 nanoparticle and its application for the removal of methylene blue

A novel core-shell structure congo red composite nanoparticle (Fe3O4@SiO2-CR) was synthesized under mild conditions, aiming to remove methylene blue (MB) from aqueous solution. The structure, morphology and magnetic characteristics of the adsorbent Fe3O4@SiO2-CR were investigated by X-ray diffraction (XRD), fourier transformed infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and vibrating sample magnetometer (VSM). Fe3O4@SiO2-CR exhibited a typical super-paramagnetic with a saturation magnetization value of 55.8 emu/g, which can be rapidly separated from aqueous solution under external magnetic field. The influencing factors such as contact time, initial pH, and MB concentration on final removal efficiency were evaluated. When the initial concentration of MB was 27 mg/L, the maximum adsorption capacity of methylene blue at room temperature was 31.44 mg/g within 30 s at pH 11. In addition, the adsorption behavior of this new adsorbent follows the Freundlich isotherm and the pseudo-second-order kinetic model. The regeneration study proved that the Fe3O4@SiO2-CR can be repeatedly utilized. The adsorption mechanism studies indicate that the adsorption of MB onto Fe3O4@SiO2-CR may be related to electrostatic attraction, aromatic-aromatic attraction, and hydrogen bonding attraction. All the results suggest that Fe3O4@SiO2-CR composites can be a promising material for the removal of MB from wastewater.