REV. CHIM. (Bucharest) ♦ 62♦ No. 6 ♦ 2011 http://www.revistadechimie.ro 622 Fe 3 O 4 /SiO 2 /APTMS Nanoparticles with Core-Shell Structure as Potential Materials for Cooper Removal DENISA FICAI 1 , ANTON FICAI* 1 , MIHAELA ALEXIE 1 , MARIA MAGANU 2 , CORNELIA GURAN 1 , ECATERINA ANDRONESCU 1 1 Politehnica University of Bucharest, 1-7 Polizu Str., 011061, Bucharest, Romania 2 Romanian Academy, Organic Chemistry Center,“Costin D. Nenitzescu”, 202B Spalaiul Independentei, 050461, Bucharest, Romania In this paper the preparation and characterization of 3-aminotrimethoxysilane functionalized silica-coated magnetite nanoparticles with core-shell structure (Fe 3 O 4 /SiO 2 -APTMS) are presented as well as the ability of these nanoparticles to remove Cu 2+ ions from aqueous solutions. Magnetite nanoparticles (Fe 3 O 4 ) were synthesized by the co-precipitation of FeCl 2 and FeCl 3 (1:2 molar ratio) with sodium hydroxide. To improve the chemical stability of Fe 3 O 4 nanoparticles, a silica layer was coated onto the surface of magnetic nanoparticles. The SiO 2 network was obtained by the hydrolysis of a mixture of tetraethoxysilane (TEOS) and 3-aminopropyltrimethoxysilane (APTMS) at room temperature and pH = 7. The resulting nanoparticles with core-shell structure were characterized by infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), X-ray diffraction (XRD) while the ability to remove the Cu(II) ions from aqueous solution was proved by UV-Vis spectroscopy. Keywords: magnetite nanoparticles, the silica-coated core-shell, adsorbents cooper(II) ion removal In the last years a considerable attention has been paid to the preparation and characterization of the Fe 3 O 4 nanoparticles or Fe 3 O 4 based particles with core-shell structure [1]. The synthesis of these nanoparticles is justified owing to their potential to act as remarkable adsorbents for heavy metals (Cu, Pd, Co, Ni, Hg), due to their high surface area as well as the possibility to be easily and quickly removed from solution when external magnetic fields are imposed [2-5]. Although the Fe 3 O 4 nanoparticles are non-toxic and could be easily synthesized by co-precipitation methods they have limited chemical and thermal stability [6]. This is why, the formation of a passive coating (inert materials such as organic or inorganic compounds, metals [7,8], including silica [9], carbon [10] and biopolymers [11–14]) on the surfaces of Fe 3 O 4 nanoparticles could prevent their dissolution or aggregation in solution [15]. The purpose of this study is to obtain amino functionalized silica-coated magnetite nanoparticles with core-shell structure (Fe 3 O 4 /SiO 2 /NH 2 ) in order to be used for heavy metals removal from aqueous solutions. The synthesis of amino functionalized silica-coated magnetite nanoparticles starts from Fe 3 O 4 nanoparticles and hydrolyzed tetraethoxysilane (TEOS) and 3-amino- trimethoxysilane (3-APTMS) mixture. The SiO 2 network formation is promoted by increasing the pH increase from acidic pH up to slightly basic pH. The resulted nanoparticles with core-shell structure (Fe 3 O 4 /SiO 2 /APTMS) were characterized by infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and transmission electron microscopy (TEM). Also, the adsorption capacity of silica-coated core- shell magnetite nanoparticles toward Cu(II) ions from an aqueous solution was studied. Experimental part Materials Anhidrous iron (III) chloride (FeCl 3 ), iron (II) chloride heptahydrate (FeCl 2 . 7H 2 O), sodium hydroxide (NaOH, used for preparation of 5M NaOH solution), TEOS (tetra- etoxysilan) were analytical grade and were used without further purification. Distilled water was used throughout the experiments. Equipment Vibrational spectra were recorded using a Shimadzu 8400 spectrometer in the wavenumbers range of 400 – 4000 cm -1 . X-ray diffraction analysis was performed using a Shimadzu XRD 6000 diffractometer at room temperature. In all the cases, Cu K α radiation from a Cu X-ray tube (run at 15mA and 30 kV) was used. The samples were scanned in the Bragg angle, 2θ range of 10 – 80 0 , with a sampling interval of 0.02. TEM measurements were performed on a Tecnai G2 F30 S-TWIN high resolution transmission electron microscope (HR-TEM) equipped with selected area electron diffraction detector (SAED). The microscope was operated in transmission mode at 300 kV while TEM point resolution was 2Å and line resolution was 1Å. UV-Vis measurements were made using a Thermo Evolution 300 spectrometer operated in transmission or diffuse reflectance over the range of 190-1100nm. Synthesis of Fe 3 O 4 /SiO 2 -APTMS Samples of 10 mL tetraethoxysilane (TEOS) were hydrolyzed under magnetic stirring with 15.5 mL deionized water, at room temperature and pH = 3. To this gel, 1g Fe 3 O 4 (Fe 3 O 4 prepared by the co-precipitation of FeCl 2 and FeCl 3 (1:2 molar ratio) with sodium hydroxide [16] (fig. 1)) and 5mL 3-aminotrimethoxysilane (APTMS) were added under vigorous stirring until a homogeneous sol is obtained. Copper (II) removal experiments The ability of Fe 3 O 4 /SiO 2 -APTMS to be used for Cu(II) ions removal from aqueous solutions was tested by UV- Vis spectroscopy. With this purpose in view, an amount of 0.3g Fe 3 O 4 /SiO 2 -APTMS was immersed in 5 mL 0.5mM CuSO 4 solution at pH=5.5 (realized with phosphate buffer) and let 1, 3, 6, 25h to interact. Then, the Fe 3 O 4 /SiO 2 -APTMS * email: anton_ficai81@yahoo.com