Preparation and study of silica and APTES-silica-modified NiFe2O4 nanocomposites for removal of Cu2+ and Zn2+ ions from aqueous solutions

Silica and (3-aminopropyl)triethoxysilane (APTES)-silica-modified NiFe2O4 samples were successfully synthesized by a two-/three-step process, depending on the sample, including the preparation of nickel ferrite sample by hydrothermal synthesis, the coating of its surface with silica, and the subsequent functionalization with APTES. Samples were characterized by X-ray diffraction (XRD), Fourier transform-infrared (FTIR) analysis, transmission electron microscopy, and M-H curves. XRD data of the NiFe2O4 sample shows diffraction maxima that can be indexed in a cubic symmetry of space group Fd-3m with Z=8, compatible with an inverse spinel-type structure. The estimated average crystalline size is 22nm. All FTIR spectra show absorption bands between 600 and 400cm(-1), characteristic of spinel-type structure. Bands attributed to the vibration of O-Si-O and Si-O-Si bonds are found in the spectra of the silica-coated samples. APTES-silica-modified NiFe2O4 nanocomposites show an increase in coating thickness as the reaction time with tetraethoxysilane increases. A practically superparamagnetic behavior was found for the synthesized NiFe2O4 sample with a magnetization of 47emu/g. This value is slightly reduced with the thickness of the nonmagnetic coating. The ultraviolet-visible spectroscopy measurements and titration curves clearly demonstrated that the APTES-silica-modified NiFe2O4 nanocomposites could be efficient materials for the removal of Cu2+ and Zn2+ ions from aqueous solutions. The best adsorption is found in the NiFe2O4@SiO2(3)-APTES(6) sample, while the NiFe2O4@SiO2(6)-APTES(12) sample seems to be the most suitable for its application, considering its better adsorption capacity and its easy separation from the aqueous solution in the presence of an external magnetic field. [GRAPHICS] . HighlightsAmino-functionalized NiFe2O4@SiO2 core-shell nanocomposites are prepared.Magnetic cores are obtained by a urea-mediated hydrothermal synthesis.TEM confirms the formation of a uniform coating around magnetic nanoparticles.Cu2+ and Zn2+ adsorption evidence the reaction of the cations with amino groups.Nanocomposites reach an adsorption capacity higher than 10% of their own weight.