RESUMO
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%.
RESUMO
Two adsorbents with covalently bound aminomethylenephosphonic acid functions (and referred to as MNPs/AMPA and MNPs/SiO2-AMPA) were synthesized from two types of amino-functionalized magnetic nanoparticles (MNPs) via Moedritzer-Irani reaction. The sorbents with anchored dopamine ligand (MNPs/dopa) or aminopropyl groups (MNPs/SiO2-NH2), and the MNPs/AMPA were characterized by X-ray diffraction, FTIR, transmission electron microscopy and vibrating sample magnetometry. Surface modification does not adversely impact the physical properties of the starting magnetite. Compared to the size of the unmodified Fe3O4 (magnetite) nanoparticles (7-12 nm), the average size of functionalized nanoparticles is increased to 10-16 nm. Similarly, the magnetic saturation decreased from 67.5 emu g-1 to 42.0 emu g-1, and the surface area is increased up to 205 m2 g-1 for MNPs/SiO2-AMPA. The kinetics of the adsorption of Eu(III) on the sorbent is ultra-fast, and equilibria are attained within 5-10 min at room temperature. The adsorption kinetics can be described by a pseudo-second-order model. Adsorption and desorption conditions were tested with respect to the removal of Eu(III) ions from water solution. The adsorption capacities for Eu(III) at pH 7.0 are 77 mg g-1 and 69 mg g-1 for MNPs/AMPA and MNPs/SiO2-AMPA nanoparticles, respectively. Eu(III) was quantified by ICP-MS. The limit of detection (LOD) for Eu(III) is 0.05 ng L-1 (based on the 3σ criterion), with an enrichment factor of 150. The selectivity over ions such as Tb(III), Fe(III), Zn(II), Cu(II), and Ca(II) ions was studied. Under optimal condition the distribution coefficient for Eu(III) relative to these ions is near 105 mL g-1. The sorbents can be easily retrieved from even large volumes of aqueous solutions by magnetic separations. The method was tested for spiked water samples (with recoveries from 96.6-102.5%) and for rock minerals. Graphical abstract A schematic showing the regeneration of magnetite nanoparticles (MNPs), core-shell (MNPs/SiO2), and the structures with covalently bonded aminomethylenephosphonic acid (AMPA) after preconcentration of Eu(III) from largewater sample volumes onto a small specimen.
