Synthesis of amidoxime-functionalized Fe3O4@SiO2 core-shell magnetic microspheres for highly efficient sorption of U(VI)

Amidoxime-functionalized silica coated Fe3O4 (Fe3O4@SiO2-AO) was synthesized and carefully characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transformed infrared spectroscopy, and magnetic measurements. The prepared Fe3O4@SiO2-AO was applied to adsorb U(VI) from aqueous solutions and exhibited enhanced sorption capacity for U(VI) in comparison with raw silica coated Fe3O4 due to the strong chelation of amidoxime to U(VI). Effects of contact time, pH, ionic strength, interfering ions, U(VI) concentration, and temperature on the sorption of U(VI) on Fe3O4@SiO2-AO were investigated. The kinetic process of U(VI) sorption on Fe3O4@SiO2-AO reached equilibrium within 2 h. The sorption was strongly dependent on pH and independent of ionic strength, indicating that the sorption was mainly dominated by inner-sphere surface complexation. The sorption isotherm agreed well with the Langmuir model, having a maximum sorption capacity of 0.441 mmol g(-1) at pH = 5.0 +/- 0.1 and T = 298 K. The U(VI)-loaded Fe3O4@SiO2-AO could be readily separated from aqueous solutions by an external magnetic field and efficiently regenerated by 1 mol L-1 HCl with only slight decrease in U(VI) sorption capability. Findings of the present work suggest that Fe3O4@SiO2-AO is a potential and suitable candidate for the preconcentration and separation of U(VI) from seawater and contaminated wastewater. (C) 2013 Elsevier B.V. All rights reserved.