Abstract
Fe3O4 nanoparticles were synthesized by hydrothermal technique and then modified with tetraethyl orthosilicate to form Fe3O4@SiO2 nanospheres through Stober method. The characterization results of X-ray diffraction, Fourier transformed infrared spectroscopy, transmission electron microscopy, scanning electron microscopy and magnetic measurements evidenced the successful synthesis of Fe3O4@SiO2 nanospheres. The as-prepared Fe3O4@SiO2 was applied as adsorbent to remove congo red (CR) from aqueous solutions at different experimental conditions, and the results indicated that CR adsorption on Fe3O4@SiO2 was strongly pH-dependent and weakly ionic strength-dependent at relative low pH values, indicating that the adsorption was mainly dominated by electrostatic interactions. The maximum adsorption capacities of CR on Fe3O4@SiO2 were calculated to be 54.64 mg/g from Sips model and 50.54 mg/g from Langmuir model at T = 308 K and pH = 5.3. The thermodynamic parameters calculated from temperature-dependent isotherms indicated that the adsorption of CR on Fe3O4@SiO2 was an spontaneous and endothermic process. The CR-adsorbed Fe3O4@SiO2 nanospheres could be easily separated from aqueous solutions using magnetic separation technique within 40 s. These results suggested that the Fe3O4@SiO2 nanospheres might be suitable materials for the efficient separation of dye pollutants from aqueous solutions in possible real applications. (C) 2016 Elsevier B.V. All rights reserved.