Experiment No: 5. Polymer-Coated Iron Oxide Magnetic Nanoparticles Preparation and Characterization

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1 Experiment No: 5 Polymer-Coated Iron Oxide Magnetic Nanoparticles Preparation and Characterization Purpose The aim is to synthesize and characterize polymer-coated iron oxide magnetic nanoparticles carrying functional groups on their surface. Introduction Transition metal oxides have been of scientific and technological interest for many decades due to their interesting optical, magnetic, electrical and catalytic properties. Among these, magnetite (Fe 3 O 4 ) is a common magnetic iron oxide that has a cubic inverse spinel structure with fcc close packed oxygen anions and Fe cations occupying interstitial tetrahedral and octahedral sites [1]. Due to its strong magnetic and semiconducting properties, magnetite (Fe 3 O 4 ) is one of the preferred well known filler materials, which is combined with polymers to be used as magnetic recording media, and in medical applications. In general, polymer coating can reduce the aggregation and improve the colloidal stability of the magnetic nanoparticles for biomedical applications [2]. A great variety of polymers with hydroxyl, carboxylate, carboxyl, styrene or vinyl alcohol groups have been used in magnetic nanoparticles production. Coating or encapsulation of particles with polymers is the oldest and simplest method of magnetic particles preparation. Other methods include e. g. suspension, dispersion or emulsion polymerization [3]. The schematic illustration of polymer coated iron oxide nanoparticle is shown in Figure 1. This experiment is focused on the preliminary results of the two-step preparation process of polymer-coated iron oxide magnetic nanoparticles carrying carboxyl groups on their surface and their brief characterization [4]. 1

2 Figure 1: Schematic illustration of polymer coated iron oxide nanoparticle. Materials 1. Ferrous chloride tetrahydrate (FeCl 2.4H 2 O, 99%), 2. Ferric chloride hexahydrate (FeCl 3.6H 2 O, 99%) 3. Tetramethylammonium hydroxide, (CH 3 ) 4 NOH (TMAOH), 4. Sodium dodecyl sulfate (SDS) 5. Acrylic acid (AAc) 6. Sodium hydroxide (NaOH) 7. Sulfuric acid (98%) 8. Methanol 9. Potassium persulfate (KPS) 10. The main monomer methyl methacrylate (MMA). Purify it by distillation before use. 11. Distilled water deoxygenated with bubbling N 2 for 10 min to be used for particles preparation. 2

3 Experimental Procedure 1. Preparation of iron oxide magnetic nanoparticles: The reaction apparatus is shown in Fig. 2. It consists of a flat bottom flask, an overhead stirrer, a heating circulator and a peristaltic pump. Two silicone tubes are used for transport and mixing of reagents. Prepare two samples of magnetite nanoparticles with different molar ratio of Fe 2+ :Fe 3+. First Fe 2+ :Fe 3+ =1:1 and mark it as sample 1 and second Fe 2+ :Fe 3+ = 1:2 as sample 2. In the both cases, mix 25 ml of aqueous solution containing Fe 2+ and Fe 3+ salts in a total concentration of 1.25 M with 25 ml of 5 M NaOH solution. Add the precipitate dropwise into 35 ml of water at 80 C and stir the resulting mixture continuously for 2 hours. Stabilize prepared magnetic nanoparticles by the slow addition of 1.7 ml of 25 % TMAOH. Note that the nanoparticles obtained from previous experiment can also be used for the task. Figure 2: Reaction apparatus used for the iron oxide nanoparticles preparation. 1 Heating circulator, 2 Reactor, 3 Stirrer, 4 Ferrous and ferric solution, 5 NaOH solution, 6 Peristaltic pump 3

4 2. Preparation of polymer coated magnetic nanoparticles: Previously produced iron oxide nanoparticles will be coated with polymer. The emulsion polymerization will be conducted at a high surfactant to monomer ratio. Prepare a mixture of MMA and AAc as comonomers with a weight ratio of 9/1. The surfactant and monomer concentrations must be 9.33 and 6.34% by weight, respectively. Add surfactant to 50 ml of previously 10 min ultrasonically dispersed iron oxide nanoparticles suspension (2% wt) and wait 10 min for dispersion. Then, add the comonomer mixture to the dispersion and mix the system in an ultrasonic bath for 40 min in order to ensure dispersion of the Fe 3 O 4 nanoparticles and the monomers. Prior to polymerization, transfer mixture to the 250 ml reactor, add initiator KPS and shake the system at constant temperature of 65 C for 24 h. After this time period, wash the coated magnetic nanoparticles three times with mixture of methanol and water to remove the surfactant and the unreacted monomers and then three times with pure water with the help of a magnet. Then immerse these particles in 0.1 M of H 2 SO 4 solution for 48 h to separate the nanoparticles, which are not coated with the polymer. After 48 h, further wash polymer-coated nanoparticles with deoxygenated water. Mark the samples of polymer-coated magnetite nanoparticles as sample 1PC and sample 2PC. The color change of iron oxide nanoparticles before and after the coating is shown in Figure 3. Figure 3: The color of (a) magnetite nanoparticles alone-black and of (b) polymer coated magnetite nanoparticles- brownish-black 4

5 3. Characterization of the Films: Determine an approximate particle size of prepared nanoparticles by transmission electron microscopy (TEM) or Perform X-ray powder diffraction (XRD). Take the FTIR spectra of Fe3O4 nanoparticles and their composites to study the molecular structure. Perform VSM measurements in order to study the magnetic properties of polymer coated nanoparticles. Results and Calculations 1. Find out the particle size of Fe3O4 and polymer coated Fe3O4 either using TEM or XRD. Discuss the results. 2. Measure the magnetic properties of polymer coated Fe3O4 by drawing VSM curve. Problems/Questions: 1. Discuss the advantage of coating Fe3O4 nanoparticles with polymers carrying carboxyl groups on their surface. 2. Discuss the influence of Fe 2+ :Fe 3+ ratio in the initial mixture on the nanoparticle size and success of polymer coating. 3. Discuss the color change of magnetite nanoparticles after coating with polymer. 4. Discuss the FTIR spectra by assigning the peaks to the corresponding bong stretching. References [1] R.M. Cornell, U. Schwertmann, The Iron Oxides: Structure Properties Reactions Occurrence and Uses, VCH, New York, [2] M.R. Phadatare, V.M. Khot, A.B. Salunkhe, N.D. Thorat, S.H. Pawar, J. Magn. Magn. Mater. 324 (2012) [3] G. Utkan et al., Journal of Colloid and Interface Science, 353, 2 (2011) [4] P. Businova et al. NANOCON 2011, , Brno, Czech Republic 5