Green Synthesis of Fe3O4 Nanoparticles and Survey their Magnetic

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characterized with X-ray diffraction (XRD), vibrating sample magnetometer (VSM), FT-IR .... FeCl2-4H2O and 2.35 g of FeCl3-6H2O were dissolved in.
Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry

ISSN: 1553-3174 (Print) 1553-3182 (Online) Journal homepage: http://www.tandfonline.com/loi/lsrt20

Green Synthesis of Fe3O4 Nanoparticles and Survey their Magnetic Properties Javad Safari, Zohre Zarnegar & Hoda Hekmatara To cite this article: Javad Safari, Zohre Zarnegar & Hoda Hekmatara (2016) Green Synthesis of Fe3O4 Nanoparticles and Survey their Magnetic Properties, Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 46:7, 1047-1052, DOI: 10.1080/15533174.2013.776597 To link to this article: http://dx.doi.org/10.1080/15533174.2013.776597

Accepted author version posted online: 23 Nov 2015.

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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry (2016) 46, 1047–1052 Copyright © Taylor and Francis Group, LLC ISSN: 1553-3174 print / 1553-3182 online DOI: 10.1080/15533174.2013.776597

Green Synthesis of Fe3O4 Nanoparticles and Survey their Magnetic Properties JAVAD SAFARI1, ZOHRE ZARNEGAR1, AND HODA HEKMATARA2 1

Laboratory of Organic Compound Research, Department of Organic Chemistry, College of Chemistry, University of Kashan, Kashan, I. R. Iran. 2 Department of Physics, Guilan University, Rasht, I. R. Iran

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Received 17 December 2012; accepted 10 February 2013

Fe3O4 nanoparticles were synthesized via a modified coprecipitation green method under ultrasound irradiations, and were characterized with X-ray diffraction (XRD), vibrating sample magnetometer (VSM), FT-IR spectroscopy, scanning electron microscope (SEM), and transmission electron microscopy. The influences of temperatures, effect of alkali and ultrasound irradiations on the grain size and properties of Fe3O4 nanoparticles were investigated. Keywords: magnetite, Fe3O4 nanoparticles, ultrasound irradiation, magnetic properties

Introduction Nanotechnology is now expanding very rapidly, as result of the unique physical and or chemical properties that nanoparticles (NPs) exhibit compared to bulk materials. Magnetic iron oxide nanoparticles (MNPs) have attracted much research interest over the recent years because of their inherent properties such as large surface area and fast response under applied external magnetic field, their superparamagnety, high coercivity, and low curie temperature.[1–3] In addition to these characters, magnetite nanoparticle because of its low toxicity can be used in biomedical applications. Therefore, Fe3O4 MNPs have brought out some new kinds of biomedical applications. In several pioneering works MNPs were claimed as an effective tool for magnetically assisted biomolecule separation,[4] biochemical sensing,[5] NMR imaging,[6,7] targeted drug delivery,[8,9] and magnetic hyperthermia.[10,11] Furthermore, a novel application of MNPs for tissue engineering, termed magnetic force-based tissue engineering (Mag-TE) has been proposed recently.[12] Superparamagnetic iron oxide nanoparticles are a kind of important magnetic materials. In contrast to bulk iron oxide, which is a multi-domain ferromagnetic material (exhibits a permanent magnetization in the absence of a magnetic field), iron oxide MNPs smaller than approximately 20–30 nm in size contain a single magnetic domain with a single magnetic moment

Address correspondence to Javad Safari, Laboratory of Organic Compound Research, Department of Organic Chemistry, College of Chemistry, University of Kashan, P.O. Box: 8731751167, Kashan, I. R. Iran. E-mail: [email protected] Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/lsrt.

and exhibit superparamagnetism.[13] There for it is very important to ensure the narrow size distribution, good dispersion and high magnetic response of Fe3O4 MNPs in tissue fluid for applications. Therefore, investigations on preparation and application of nano-Fe3O4 crystals are receiving particular attention. Among the numerous preparation methods, chemical coprecipitation process had the advantages of simple operation, low cost and mass production. However, it also shared some flaws and deficiencies such as impurity of production, poor dispersity, and nonuniform particle size, and so on.[14] During the last three decades, ultrasound-accelerated organic chemical reactions have been increasingly developed by researchers across the globe for the synthesis of organic molecules. Ultrasound irradiation offers an alternative energy source for organic reactions which are ordinarily accomplished by heating. Ultrasound-assisted reactions proceed by the formation, growth, and collapse of acoustic bubbles in the reaction medium.[15–19] The extremely high temperature about 5000 K, pressure (»20 MPa), and very high cooling rates (»1010 K/S) that come from the collapse of the bubbles can mean extreme reaction conditions, which lead to many unique properties for the synthesized particles; the macrosteam which that form the collapse of the bubbles can obtain a microscopic mixing in the synthesis procedure, which creates a relatively uniform reaction condition.[15] Ultrasonic irradiation has proven to be an effective method to synthesize magnetic nanoparticles.[17–19] In this work, we developed an efficient modification method using ultrasound irradiation for the synthesis of Fe3O4 at different temperatures. The effect of temperature, effect of alkali and ultrasound irradiation on the crystal structure, morphology, grain size, and magnetic properties and superparamagnetic performance of Fe3O4 MNPs were investigated.

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Experimental

Results and Discussion

Chemical and Apparatus

The Fe3O4 MNPs were prepared by the well-known Massart’s method,[24] which consists of Fe(III) and Fe(II) coprecipitation in alkaline solutions. The alkali as precipitator plays an important role in the reaction system. In this work, NaOH and NH4OH were compared and evaluated, and pH value saltated and jumped intensely as NaOH was being added, so the final pH value was uncontrollable. When NH4OH was used, the terminal pH value could be controlled exactly due to the smooth increase of the pH value. Therefore, NH4OH was more stable and controllable than NaOH.

Chemical reagents in high purity were purchased from the Merck Chemical Company. All materials were of commercial reagent grade. FT-IR spectra were obtained with potassium bromide pellets in the range 400–4000 cm–1 with a Perkin Elmer 550 spectrometer. The magnetic properties were characterized by a vibrating sample magnetometer (VSM; Lakeshore7407) at room temperature. Nanostructures were characterized using a Holland Philips Xpert X-ray powder diffraction (XRD) diffractometer (CuK, radiation, λ D 0.154056 nm), at a scanning speed of 2 /min from 10 to 100 (2u). Scanning electron microscope (SEM) was performed on a FEI Quanta 200 SEM operated at a 20 kV accelerating voltage. The samples for SEM were prepared by spreading a small drop containing nanoparticles onto a silicon wafer and being dried almost completely in air at room temperature for 2 h, and then were transferred onto SEM conductive tapes. The transferred sample was coated with a thin layer of gold before measurement. The particle size and morphology were investigated by a JEOL JEM-2010 transmission electron microscope (TEM) on an accelerating voltage of 200 kV. Sonication was performed in a UP 400S ultrasonic processor equipped with a 3 mm wide and 140 mm long probe, which was immersed directly into the reaction mixture. The operating frequency was 40 kHz and the output power was 0– 400 W through manual adjustment. A circulating water bath (DC2006, Shanghai Hengping Apparatus Factory) with an accuracy of 0.1 K was adopted to keep the reaction temperature at a constant. Synthesis of Magnetic Nanoparticles Nanosized magnetic particles were synthesized by chemical coprecipitation method[20] under alkaline condition and molar ratio between Fe2C salt and Fe3C salt was maintained at 1:2. In order to synthesize 1 g of Fe3O4 particle, 0.86 g of FeCl2-4H2O and 2.35 g of FeCl3-6H2O were dissolved in 40 ml ultrapure water under Ar atmosphere with vigorous stirring at speed of 600 rpm for 1 h. Thereafter, 5 mL of NH4OH solution was dropped slowly into the mixture solution until the pH value was titrated to 11.0.[21–23] It can be observed that the solution became black due to the formation of Fe3O4 particles. The reaction was continued at different temperature for another 1 h. The resulting suspension was cooled down to room temperature and washed with ultrapure water. The product of magnetic nanoparticles were isolated from the solvent by magnetic decantation. The washing– decantation procedure was repeated five times to eliminate any unreacted chemicals. Then dried in a vacuum oven at 70 C and stored in a desiccator for the next investigations.

2FeðIIIÞ C FeðIIÞ C 8OH ! Fe3 O4 C 8H2 O Figure 1 shows XRD patterns of MNPs in alkaline solutions. The position and relative intensities of all peaks confirm well with standard XRD pattern of Fe3O4 (JCPDS card No. 79–0417) indicating retention of the crystalline cubic spinel structure of MNPs.25 The crystal size of MNPs with NaOH (Figure 1a) and NH4OH (Figure 2b) can be determined from the XRD pattern by using Debye–Scherrer’s equation. D.hkl/ D

0:94λ bcosu

where D (h k l) is the average crystalline diameter, 0.94 is the Scherrer’s constant, λ is the X-ray wavelength, b is the half width of XRD diffraction line, and u is the Bragg’s angle in degrees. Here, the (3 1 1) peak of the highest intensity was picked out to evaluate the particle diameter of the nanoparticles. MNPs with NaOH and NH4OH were calculated to be 47 and 18 nm, respectively. Compared to NaOH, the particle average diameter is obviously smaller with NH4OH, because NaOH has a higher concentration of OH¡ and a higher pH value with the same concentration of alkali, which will accelerate the reaction and lead to large particle size. On the

Ultrasonic-Assisted Synthesis of Magnetic Nanoparticles Fe3O4-MNPs were prepared in this section at the same conditions except during all the time, the reaction was under ultrasonic condition (40 KHz, 200 W) at 50 C temperature.

Fig. 1. XRD patterns of MNPs in (a) NaOH and (b) NH4OH solution.

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Fig. 3. Magnetization curves for the prepared MNPs at various temperatures.

Fig. 2. XRD patterns of MNPs at (a) 30 C, (b) 50 C, (c) 70 C, and (d) 90 C.

contrary, NH4OH releases OH¡ gradually to make the particle size controllable. As the stability and the particle size are involved, NH4OH is selected as alkali source. Influence of temperature on Fe3O4 nanoparticles were tested at 30 C, 50 C, 70 C, and 90 C. Figure 2 shows the XRD patterns of Fe3O4 nanoparticles at various temperatures when the pH value was 11 using NH4OH. The phase could be determined as magnetite Fe3O4 (JCPDS no. 79– 0417) according to the XRD patterns. The mean grain size of sample is 12, 14, 18, and 35 nm according to preparation temperature of 30 C, 50 C, 70 C, and 90 C, respectively. It could be seen that the grain size of Fe3O4 nanoparticles increases with temperature rising. Magnetic properties of MNPs were recorded in a Quantum Design VSM. Figure 3 shows hysteresis curves collected at 30 C, 50 C, and 70 C. It indicates that all the prepared nanoparticles possess superparamagnetic behavior.[26] It can be seen that the saturation magnetization of sample a, b c and d are 61.63, 61.79, and 62.76 emm¢g–1, respectively, which are obviously lower than that of the bulk Fe3O4 (90 emm¢g–1).[27] The saturation magnetization is increased with the increase of temperature. Considering the relationship between crystalline grain size and Ms, it seems that Ms of

nanoparticles would increase with the increase of grain size.[26,28] There is hysteresis in the hysteresis loop and remanence and coercivity are no zero, with the increase of temperature at 70 C, it shows that nanoparticles are no uniform in size. Thus, 50 C is selected as a proper reaction temperature when particle size is uniform. In a typical procedure, Fe3O4 nanoparticles were prepared at the same conditions, the only difference in our method was the application of ultrasonic irradiation at 40 kHz instead of mechanical agitation during the synthesis at 50 C temperature. Ultrasonic waves were generated from a titanium horn which was directly immersed into solution. To avoid rapid increase of temperature in the reaction medium, the generated ultrasonic is triggered following a cycled periodic pulse. The width of the pulse in a period was 22 s. The duration of ultrasound was 20 s, and the resting time was 2 s. In this study, the reaction time was usually no more than 30 min at 50 C. Figure 4 displays the XRD patterns of the Fe3O4 nanoparticles under ultrasonic irradiation (sample a) and conventional

Fig. 4. XRD patterns of MNPs in at 50 C under (a) ultrasonic irradiation and (b) mechanical stirring.

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Fig. 5. Magnetization curves for the prepared MNPs in at 50 C under (a) ultrasonic irradiation and (b) mechanical stirring

mechanical stirring (sample b) at 50 C. From the XRD results, it can be concluded that the particle sizes of the samples synthesized under ultrasonic irradiation are larger than those synthesized under mechanical stirring, and the crystallinity of the magnetite phase could be greatly improved by ultrasonic irradiation.29 The magnetization properties of Fe3O4-MNPs, are investigated at 50 C by VSM under ultrasonic irradiation (sample

Fig. 6. FT-IR spectra of Fe3O4-MNPs.

Safari et al. a) and conventional mechanical stirring (sample b) in Figure 5. The saturation magnetization of sample a is larger than that of sample b, which may be ascribed to the increase of particle size of Fe3O4 MNPs. It shows that there is no hysteresis in the hysteresis loop and remanence and coercivity are zero, illustrating that MNPs are superparamagnetic. Superparamagnetism is the responsiveness to an applied magnetic field without retaining any magnetism after removal of the applied magnetic field.[30] The as-prepared nanoparticles under ultrasonic irradiation at 50 C, were characterized by Figure 6 shows the Fourier transform infrared (FTIR) spectra of magnetic nanoparticles. The Fe–O stretching vibration near 580 cm–1, O-H stretching vibration near 3432 cm–1, and O–H deformed vibration near 1629 cm–1were observed.[26] SEM was used to observe the morphologies of the products synthesized with ultrasound and without it in Figures 7a and 7b. Aggregated morphology is illustrated in Figure 7a, which shows Fe3O4 nanoparticles were synthesized under mechanical stirring. Figure 7b shows the formation of uniform and wellshaped nanosized particles with an increase of crystallite size. The size and shape of synthesized nanoparticles are deduced from the TEM images in Figure 7c. The mean diameter of Fe3O4 nanoparticles is about 18 nm, which is consistent with SEM and XRD. Both images show the nanoparticles are well dispersed and uniform in shape and size.

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Fig. 7. SEM images (a) Fe3O4-MNPs prepared by mechanical stirring, (b) Fe3O4-MNPs prepared by ultrasound irradiation and TEM, and (c) images of MNPs by ultrasound irradiation

When the pH of the reaction system increases, Fe(OH)3 generated in the first step, which was owing to the hydrolysis of Fe3C. Then, Fe(OH)2 generated as pH of the reaction system increased, which was owing to the hydrolysis of Fe2C. Finally Fe3O4 just can be synthesized as more increase of the solution pH.[31] Fe3 C C 3OH ¡ ! Fe.OH/3 Fe.OH/3 ! FeOOH C H2 O Fe2 C C 2OH ¡ ! Fe.OH/2 2FeOOH C Fe.OH/2 ! Fe3 O4 C 2H2 O Recently it was assumed that three effects of sonication contribute to the phenomenon of sonocrystallization (a) the local transient heating of a liquid phase after bubble collapse, (b) the shock waves generated during bubbles implosion hinder agglomeration, and (c) the excellent mixing conditions created by acoustic cavitation. All these phenomena allow a reduction of particle size and increase particle size homogeneity owing to control of the local nucleus population.[1] On the other hand, to observe the effect of ultrasound waves on magnetite precipitation and the hydrolysis of iron ions and magnetite particles,

nucleation should occur in the acoustic cavitation to avoid interference with coprecipitation in the bulk solution in the absence of cavitation. But in the coprecipitation method under mechanical stirring, it is difficult to separate the short burst of nucleation from the period of nuclei growth. Therefore ultrasonic assisted process leads to more uniform Fe3O4 nanoplates. Moreover, as the reaction proceeded, the amounts of initial particles decreased while plate-shaped crystals appeared and grew larger continuously and the particle size of the sample synthesized under ultrasonic was larger than those under mechanical stirring is caused by Ostwald ripening processes. In this process, small nanoparticles dissolved and grew into large crystals. The dissolution and crystal growth on the surface are the parallel processes. At the end of the reaction, the formation of uniform and well-shaped nanosized particles can be considered as a result of the balance between dissolution and crystal growth in the solvent.[1,29,32]

Conclusions Fe3O4 nanoparticles were prepared by chemical coprecipitation method under ultrasonic irradiation and conventional

1052 mechanical stirring. The transmission of high-frequency ultrasound in liquid could cause the formation, growth, and collapse of bubbles, and the rapid collapse of bubbles creates high temperature (about 5000 K), high pressure (about 20 MPa), and high cooling rate (about 1010 K/S), which lead to many unique properties for the synthesized nanoparticles. Thus create uniform nanoparticles with excellent properties.

Funding The authors gratefully acknowledge the financial support from the Research Council of the University of Kashan for supporting this work by Grant NO. (159198/V).

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