Features of the surface layer structure of the magnetosensitive materials functionalized by silica with thiourea groups and their applying for selective Cu(II) and Au(III) ions removal

Abstract

One-step sol–gel synthesis for covering magnetic particles with polysiloxane layers with ≡Si(CH2)3NHC(S)NHC2H5 groups has been proposed. Unique properties of this functional group, containing sulfur and nitrogen, and the developed approach open wide (and novel) opportunities for the controlled surface design. A number of factors affecting the characteristics of such materials and their sorption properties towards heavy metal ions were analyzed. Results of scanning and transmission electron microscopy studies, Fourier-transform infrared spectroscopy, nitrogen adsorption–desorption measurements, elemental analysis, thermogravimetric analysis, and X-ray powder diffraction analysis indicated that, depending on the ratio of core/shell components, the resulting spherical moieties with size of 35.1–43.1 nm, can form agglomerates of larger sizes. Packing of these aggregates offers porosity to such materials, having a dense or loose polysiloxane shell, with thiourea groups load of 0.67–1.05 mmol/g. The synthesized materials proved to be effective in extraction of Cu(II), Pb(II), Cd(II), Hg(II), Ag(I), Au(III), Zn(II) ions from aqueous solutions, as well as in selectively adsorption of Au(III) ions at pH = 3 and Cu(II) ions at pH = 5.5. X-ray photoelectron spectroscopy demonstrated different types of interactions between metal ions and the thiourea groups, depending on pH.