Preparation and adsorption properties of nano magnetite silica gel for methylene blue from aqueous solution

A novel magnetic silica gel (Fe 3 O 4 -Si-COOH) adsorbent was successfully prepared and used to removal methylene blue (MB) from aqueous solution by adsorption method. Several techniques, including scanning electron microscope (SEM), transmission electron microscope (TEM), thermo-gravimetric analyzer (TGA), fourier transform infrared (FTIR), nitrogen physisorption and vibrating sample magnetometer (VSM), were used to characterize the adsorbent. Batch experiments were conducted to investigate the MB adsorption performance of Fe 3 O 4 -Si-COOH. The maximum adsorption efficiency of MB appeared at pH 11.0. The adsorption equilibrium was reached within 60 min and commendably described by pseudo-second-order model, and Langmuir model fitted the adsorption isotherm better. The maximum adsorption capacity can reach to 246.31 mg/g. Moreover, thermodynamic parameters including enthalpy (ΔH), free energy (ΔG) and entropy (ΔS) were also investigated and revealed that the adsorption process was spontaneous and endothermic in nature. Desorption and repeatability studies showed that Fe 3 O 4 -Si-COOH could still maintain about 76% in the fifth consecutive adsorption-regeneration cycle. Above the results showed that Fe 3 O 4 -Si-COOH was a promising adsorbent in environment pollution cleanup.