Front. Mater. Sci. 2014, 8(2): 193–198 DOI 10.1007/s11706-014-0249-5
COMMUNICATION
Facile synthesis of magnetic iron oxide nanoparticles and their characterization Sushilkumar A. JADHAV (✉)1 and Suresh V. PATIL2 1 Department of Chemistry and NIS Center, University of Torino, 10125 Torino, Italy 2 Department of Chemistry, K.B.P. College Pandharpur affiliated to Solapur University, Solapur (MH), India
© Higher Education Press and Springer-Verlag Berlin Heidelberg 2014
ABSTRACT: Magnetic iron oxide nanoparticles are synthesized by suitable modification of the standard synthetic procedure without use of inert atmosphere and at room temperature. The facile synthesis procedure can be easily scaled up and is of important from industrial point of view for the commercial large scale production of magnetic iron oxide nanoparticles. The synthesized nanoparticles were characterized by thermal, dynamic light scattering, scanning electron microscopy and transmission electron microscopy analyses. KEYWORDS:
iron oxide; iron oxide nanoparticle; co-precipitation
Iron oxides have shown tremendous applications in different technological fields [1]. Especially magnetic iron oxide nanoparticles have shown potential applications in the fields of magnetic separation, magnetic resonance, as pigments and in biomedical fields [2–4]. Various methods are used for the synthesis of magnetic iron oxide nanoparticles they are microemulsion, co-precipitation, sol–gel syntheses, sonochemical reactions, hydrothermal reactions, hydrolysis and thermolysis of precursors, flow injection syntheses and electrospray syntheses. Each method has its advantages and disadvantages and it is difficult to generalize one of them as simple or industrially feasible method [5–6]. Although several simple or modified methods for the synthesis of such nanoparticles do appear in literature each of these method is adopted or modified to prepare magnetic iron oxide nanoparticles for the application of them under study. Use of magnetic iron oxide nanoparticles for biomedical or drug delivery applications require nanoparticles of highest purity and Received April 2, 2014; accepted May 10, 2014 E-mail:
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very narrow particle size distribution (monodispersed). Instead other technological applications such as use of magnetic iron oxide as pigments, coloring agents, traps for magnetic waste removal or as a substitute for carbon black in inks which is recently categorized as toxic material etc. requires black (magnetic) iron oxide nanoparticles of size in the range of 100–500 nm [7–8]. The amount of such iron oxide nanoparticles required in real use is very large and the quantity produced at industrial scale is in several tons. Hence the sophisticated synthetic techniques used for the synthesis of extra high purity and monodisperse iron oxide nanoparticles for biological or biomedical applications cannot be easily scaled up in real production plants. Another issue is the costs associated with the synthesis and the complexity of the apparatus or set-up used. Thus there is a constant need for efforts to simplify the existing synthesis techniques for magnetic iron oxide nanoparticles. In the present letter we describe the synthesis of magnetic iron oxide (magnetite) nanoparticles by a method which can be easily scaled up for large scale production. The synthesized magnetic iron oxide nanoparticles are characterized by dynamic light scattering (DLS) technique to
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determine their average particle size and magnitude of the overall charge on the nanoparticles. The particles are further characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses to study their morphology. Co-precipitation synthesis technique of magnetic iron oxide nanoparticles uses mixture of solutions of Fe2+ and Fe3+ salts and a precipitating agent which is strong base such as sodium hydroxide or ammonium hydroxide solution which guarantees high pH (app. 10–12). Ammonium hydroxide as such or diluted according the requirement is preferred base over other bases such as sodium hydroxide. In the present attempt for the synthesis of magnetites the solution of weighed quantities of ferric chloride and ferrous chloride in 2:1 mole ratio was prepared in deionized water in a round bottom flask equipped with mechanical stirrer. Concentrated ammonia solution (40 mL) was then added to this solution with vigorous stirring which was continued for further 60 min. The black magnetite precipitate obtained was separated with a strong magnet and re-dispersed in fresh deionized water. The precipitate washed four times with deionized water. The supernatant water is tested with litmus paper. The magnetite nanoparticles obtained were dried at 40°C– 45°C in ventilated oven for 24 h. Care must be taken while drying because phase change of iron oxide by heating at elevated temperatures or drying rapidly can occur. Generally this precipitation is carried out under inert atmo-
Fig. 1 Outline of set-up used for magnetite nanoparticle synthesis, pictures showing suspension of synthesized nanoparticles and their attraction towards strong magnetic field.
sphere to avoid the oxidation of iron [9–11]. However in the modified synthesis method it is found that use of high quality iron salts free of oxidized material ensures high purity of the nanoparticles obtained. Hence use of nitrogen or argon gas to make inert atmosphere can be completely excluded. Also the post-synthesis heating of the product at elevated temperatures is found to be not necessary. Post synthesis surface modification of iron oxides with different organic compounds or polymers used as stabilizers may require treatment of the nanoparticles with such compounds at elevated temperatures but for synthesis of bare magnetite nanoparticles heating is not required. Although such attempts of simplification of the synthesis of magnetite nanoparticles were carried out the characterization presented on the product especially the phase purity of synthesized magnetic iron oxide is doubtful [12]. Figure 1 shows the outline of apparatus used for the synthesis of nanoparticles. Following equation shows the overall chemical reaction taking place in hydrolysis precipitation of iron salts to form magnetic iron oxide Fe3O4: Fe2þ þ 2Fe3þ þ 8OH – – 4H2 O ! FeðOHÞ2 þ 2FeðOHÞ3 ! Fe3 O4
Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) spectrum of the synthesized nanoparticles is shown in Fig. 2. It shows the typical absorption bands of magnetite nanoparticles at 559 cm–1 due to Fe–O-vibration and band at 1400 cm–1 is assigned to Fe–O stretching and the band at app. 4000 cm–1 is due to the stretching vibrations of surface –OH groups [13–14]. The X-ray diffraction (XRD) pattern of synthesized magnetic iron oxide is shown in Fig. 3, which represents the XRD pattern of Fe3O4 nanoparticles. Under the synthesis conditions mentioned the formation of magnetite nanoparticles as the predominant phase is evident from the XRD pattern [15–16]. The synthesized nanoparticles were strongly attracted towards magnetic field applied with the help of a strong magnet which proves that other nonmagnetic iron oxide phases were not formed. The supernatant liquid (water) obtained was free of any iron oxide particles further confirming the purity and phase homogeneity of the synthesized magnetite nanoparticles. Thermogravimetric analysis (TGA) curve of the magnetite nanoparticles is shown in Fig. 4. It mainly shows 2.3% of weight loss upon heating which is due to the physisorbed water on the iron oxide. Apart from the loss of water due to heating no other thermal degradation was observed
Sushilkumar A. JADHAV et al. Facile synthesis of magnetic iron oxide nanoparticles and their characterization
Fig. 2
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ATR-FTIR spectrum of magnetic iron oxide nanoparticles.
confirming phase and chemical purity of the obtained nanoparticles.
Fig. 4 TGA curve of magnetic iron oxide nanoparticles.
Fig. 3 XRD pattern of the synthesized magnetic iron oxide nanoparticles and comparison with the standard diffraction pattern of magnetite nanoparticles.
DLS analysis was carried out on very dilute suspensions prepared from the synthesized nanoparticles. Approximately 0.01% w/v suspensions of synthesized magnetite nanoparticles were prepared in deionized water for measurement of hydrodynamic diameter by DLS instrument. Instead for the measurement of zeta potential the suspensions of 0.1% w/v were used. The suspensions were sonicated at room temperature for 15 min before starting
the measurements. All types of iron oxide nanoparticles contain large number of hydroxyl groups and the nanoparticles tend to aggregate immediately when they are put in water, sonication helps to break the bigger aggregates and provide a reasonably stable suspension to carry out the DLS measurements. Figure 5 shows the particle size distribution (PSD) histograms obtained. The average particle sizes as calculated by intensity, volume and number distribution are (1985), (2125) and (1905) nm, respectively. It indicates similar average particle size obtained by taking into consideration all three variables. It is important to stress that the average hydrodynamic diameter obtained by DLS is of the most stable cluster formed by the very small primary nanoparticles and hence cannot be considered as the diameter of the
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Fig. 6 Zeta potential of synthesized nanoparticles.
Fig. 5 Histograms showing PSD of synthesized magnetite nanoparticles by intensity, volume and number distribution.
primary particles. The zeta potential of the synthesized magnetite nanoparticles was + 8.7(0.5) mV (Fig. 6), which is in accordance with the reported value for bare magnetite nanoparticles [17]. The positive charge on the nanoparticles comes from the –OH groups present on the surface of magnetic iron oxide nanoparticles. Figure 7 shows the high field SEM images of the nanoparticles which are similar to the commercial magnetite powder synthesized by other techniques and presently marketed by different commercial producers. It can be seen that the surface of the nanoparticles is relatively rough. Figure 8 shows the TEM image of the nanoparticles. Spherical or quasi-spherical morphology of the particles can be seen
Fig. 7 SEM images of synthesized magnetite nanoparticles.
Sushilkumar A. JADHAV et al. Facile synthesis of magnetic iron oxide nanoparticles and their characterization
which indicates efficiency of the synthetic procedure adapted. The average particle size obtained is 25–30 nm.
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Fig. 8
TEM image of synthesized magnetite nanoparticles.
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In summary facile synthesis method for the synthesis of magnetite nanoparticles by co-precipitation at room temperature without use of inert atmosphere is reported. This observation clearly shows the possibility to exclude the use of nitrogen or argon atmosphere during the synthesis of such nanoparticles. The post synthesis heating of the magnetite suspension obtained can also be avoided. These two modifications will greatly reduce the cost of production of such nanoparticles. The method gives nanoparticles of reasonably narrow PSD as observed by the DLS and TEM characterization. The synthesis method can be easily scaled up for large scale synthesis of magnetic or simply black iron oxide nanoparticles for various applications.
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Abbreviations
2014, 5(2): 524–534 [12] Abdalla M A, Jaafar M H, Al-Othman Z A, et al. New route for preparation and characterization of magnetite nanoparticles.
ATR-FTIR DLS PSD SEM TEM TGA XRD
attenuated total reflection Fourier transform infrared spectroscopy dynamic light scattering particle size distribution scanning electron microscopy transmission electron microscopy thermogravimetric analysis X-ray diffraction
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