Advanced core-shell EDTA-functionalized magnetite nanoparticles for rapid and efficient magnetic solid phase extraction of heavy metals from water samples prior to the multi-element determination by ICP-OES.

A method for preconcentration and simultaneous determination of trace heavy metals in water media by core-shell superparamagnetic nanoparticles with the immobilized derivative of ethylenediaminetriacetic acid (referred to as MNPs/SiO2-EDTA) is proposed. The specific layer-by-layer covering of magnetite endowed the new material with essentially increased chemical stability of MNPs including acidic media and improved the affinity toward traces of toxic metal ions. The initial and modified materials were characterized by X-ray powder diffraction, Fourier transform infrared spectroscopy, transmission and scanning electron microscopies, elemental analysis, and vibrating sample magnetometry. The obtained particles were nanodimensional with a 7-12-nm magnetic core and a 4-6-nm silica shell. The MNPs/SiO2-EDTA quantitatively removes heavy metals from contaminated media at pH ≥ 3.5 within 15 min. The adsorption data were successfully fitted to the pseudo-second-order kinetic model. The preconcentration factor was 150 and maximum adsorption capacity was 36.9 mg g-1 for Cu(II), 108.8 mg g-1 for Pb(II), 30.9 mg g-1 for Zn(II), 34.32 mg g-1 for Cr(III), and 59.5 mg g-1 for Cd(II). Due to high stability in the wide range of pH, the magnetic adsorbent can be regenerated at least six times using 0.1 M HNO3. Following adsorption/desorption, determination of metal ions is provided by inductively coupled plasma optical emission spectrometry (ICP-OES) . The linear range of the proposed method is 0.1 - 200 μg L-1. The limits of detection (LOD) are 0.12 μg L-1 for Zn(II); 0.06 μg L-1 for Cd(II); 0.39 for Cu(II); 0.15 μg L-1 for Cr(III); and 0.76 μg L-1 for Pb(II). The method performance was evaluated in the analysis of environmental, tap, and wastewater samples with recoveries in the range of 94.0-104.0%.