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International Journal of Nanoelectronics and Materials
Volume 12, No. 1, Jan 2019 [37-46]
Preparation and Characterization of Magnetite (Fe3O4) nanoparticles
By Sol-Gel Method
Zakiyyu I. Takai1,2, Mohd K. Mustafa1,2*, Saliza Asman2 and Khairunnadim A. Sekak3*
1Microelectronic and Nanotechnology-Shemsuddin Research Centre (Mint-SRC) Uvniversiti Tun Hussein Onn
Malaysia (UTHM).
2Department of Physics and Chemistry, Faculty of Applied Sciences and Technology, Universiti Tun Hussein
Onn Malaysia, Educational Hub Pagoh, 84000, Muar, Johor, Malaysia.
3 Faculty of Applied Sciences, Universiti Teknologi Mara. 40450 Shah Alam, Salangor, Malaysia.
Received 18 March 2018; Revised 12 July 2018; Accepted 29 July 2018
ABSTRACT
The magnetite (Fe3O4) nanoparticles were successfully synthesized and annealed under
vacuum at different temperature. The Fe3O4 nanoparticles prepared via sol-gel assisted
method and annealed at 200-400ºC were characterized by Fourier Transformation
Infrared Spectroscopy (FTIR), X-ray Diffraction spectra (XRD), Field Emission Scanning
Electron Microscope (FESEM) and Atomic Force Microscopy (AFM). The XRD result
indicate the presence of Fe3O4 nanoparticles, and the Scherer`s Formula calculated the
mean particles size in range of 2-25 nm. The FESEM result shows that the morphologies of
the particles annealed at 400ºC are more spherical and partially agglomerated, while the
EDS result indicates the presence of Fe3O4 by showing Fe-O group of elements. AFM
analyzed the 3D and roughness of the sample; the Fe3O4 nanoparticles have a minimum
diameter of 79.04 nm, which is in agreement with FESEM result. In many cases, the
synthesis of Fe3O4 nanoparticles using FeCl3 and FeCl2 has not been achieved, according to
some literatures, but this research was able to obtained Fe3O4 nanoparticles base on the
characterization results.
Keyword: Sol-Gel Method, Magnetite Nanoparticles, Particles Size, Morphologies, XRD.
1. INTRODUCTION
Recently, the magnetite (Fe3O4) nanoparticles have been explored extensively due to their
unlimited physical and chemical properties at the nanoscale [1]. In most of the application of
magnetite nanoparticles, uniform shape and size particles are required to be well dispersed in
the solvent. The major factors that influence the interest of many researchers are the particles
size. However, the shape and size of the Fe3O4 nanoparticles usually controlled by their
synthesis techniques. Therefore, synthesis technique is the most significant method for
preparation of certain materials, such as metal oxide powder and ceramic materials [2].
Magnetite nanoparticles synthesized with effective properties such as shape, size and suitable
morphologies, will help to achieve a wider range of application [3]. Up to now, the focus have
been made on the synthesis of iron oxide particles because it can be crystalline in different
polymorphic phases which include hematite (α-Fe2O3), maghemite (γ-Fe2O3), and magnetite
(Fe3O4) [4]. Among these inorganic nanoparticles, Fe3O4 nanoparticles has interesting electric
and magnetic properties as well as extensive potential applications in colour imaging, magnetic
recording media, soft magnetic materials, ferrofluid, spintronic and biomedical applications
such as drugs delivery, cell separation, imaging and therapeutic in vivo technology [3,4].
* Corresponding Author: zitakai21@gmail.com
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38
Numerous synthesis method like co-precipitation method [5], hydrothermal method [6],
microwave irradiation method [7], ultrasonic method [8] and sol-gel method [9] have been used
to synthesize magnetite nanoparticles.
Among all synthesis method, sol-gel techniques has been chosen compared to the remaining
traditional synthesis techniques due to its advantageous properties including low cost, high
purity, and suitable homogeneity [10]. However, in the quest to produce nanoparticles by sol-
gel techniques suitable for product, many parameter need to be optimized to control the
reaction condition [11,12]. It was gathered that, increasing the reactivity enhance wider surface
area of the nanoparticles obtained by sol-gel techniques [13]. In recent time, the attention have
been on the preparation of magnetite nanoparticles in order to overcome certain problem,
through different chemical synthesis method, although a lot of research have been published
demonstrating the preparation of magnetite (Fe3O4) nanoparticles using several method for
different applications such as drug delivery, magnetic recorder, ferrofluid and sensing
application [14, 15]. Furthermore, the Fe3O4 nanoparticles were prepared by [16, 17] through
sol-gel method using chepest materials of ferric nitrite as the precusor. The Fe3O4 nanoparticles
was observed at 250ºC. When the temperature rises to 350ºC, the himatate (Fe2O3) also appear
causing major deffiency that hinder its applications [18-20]. In the research reported by [21-
23], sol-gel method were used to synthesized iron oxide and its mixture using ethlylene glycol,
FeCl3 and FeCl2, but the magnetite nanoparticles has not been observed.
In this work, the Fe3O4 nanoparticles were prepared effectivitily through sol-gel techniques and
it was annealed under vacuum in different temperature. The major material used in the
synthesis of Fe3O4 nanoparticles are iron (III) chloride (FeCl3), iron (II) chloride (FeCl2) and
ethylene glycol (C2H6O). The Fe3O4 nanoparticles samples are prepared in the form of S1, S2 and
S3 with different annealed temperature of 200ºC, 300ºC and 400ºC respectively. The
morphologies of the Fe3O4 nanoparticles annealed at 400ºC were found to be more spherical
and partially agglomerated with continues size distribution.
2. EXPERIMENTAL METHOD
2.1 Materials
Iron (III) chloride FeCl3.6H2O, Iron (II) chloride FeCl2.4H2O and ethylene glycol (C2H6O) grade
were obtained from SIGMA ALDRICH chemical cooperation. The entire reagents were used
without any further purification.
2.2 Synthesis of Fe3O4 Nanoparticles
The synthesis of magnetite nanoparticles is described as follows: 2.35g of Fe (III) and 8.35g of
Fe (II) were firstly dissolved in 60 ml of ethylene glycol and vigorously stirred for a period of 3h
at 45ºC to form a sol. Subsequently, the sol was heated and maintained at a temperature of 80ºC
until dark colour gel was formed. This gel was aged for a period of 72h and later dried at 140ºC
for 5h. The obtained xerogel was annealed at a certain temperature ranging from 200-400ºC
under vacuum condition. Finally, different size magnetite nanoparticles were successfully
obtained. The synthesized Fe3O4 nanoparticles were washed with a certain amount of acetone
and ethanol several times to enhance its magnetic properties. Table 1 tabulates the effect of a
change in temperature towards the mean size of magnetic nanoparticles calculated from XRD
data using Scherer’s formula (see Figure 4). However, from Table 1, the Fe3O4 nanoparticles size
increases as the annealing temperature increases.
International Journal of Nanoelectronics and Materials
Volume 12, No. 1, Jan 2019 [37-46]
39
Table 1 Effect of change in temperature toward the mean size of magnetite nanoparticles
Sample
Annealing temperature
(ºC)
Mean particles size (nm)
S1
200
2.02
S2
300
5.58
S3
400
8.35
2.3 Characterization
A sample was characterized using the Fourier Transform Infrared Spectrum (FTIR) (Perkin
Elmer Spectrum 100 FTIR spectrometer). The absorption spectra of the magnetite nanoparticles
were determined using Ultraviolet (Uv-Vis) spectroscopy (SHIMDZU 1800 UV-visible series).
The X-ray diffraction spectroscopy (XRD) (Shimadzu XD-610) is used to determine the phase
structure of the magnetite nanoparticles; the rays were radiated at a wavelength of (= 0.15406
nm). However, the morphological analysis of the particles were obtained by Field Emission
Scanning Electron Microscope (FESEM JEOL model JDM-7600F) equipped with X-ray dispersive
spectrometer (EDS). To quantitatively examined the high and three dimension (3D) profiles of
the structure formed by Fe3O4, Atomic Force Microscopes (AFM) (Bruker 59 × 413) was used in
the tapping mode to image the topography of a two-layer grid formed by Fe3O4. The 3D image
showed the spatial profiles of the grids.
3. RESULT AND DISCUSSION
3.1 Fourier Transform Infrared Spectra (FTIR) Analysis
The analysis of the infrared (IR) spectra confirms the monomer fixation of Fe3O4 nanoparticles
(Figure 1), which resulted in the formation of Fe-O bands which is proven by the appearance of
the absorptions band at 476cm-1, 519cm-1, 688cm-1, 743cm-1 and 875cm-1 [7-10]. Moreover, the
existence of peaks at 1069cm-1 to 1600cm-1 and 2606cm-1 to 2941cm-1 are assigned to O-H
stretching, C-H stretching, C=C stretching, C=O stretching and C-O stretching bands respectively,
indicating acidic medium condition of Fe3O4 nanoparticles preparation [19, 23]. The bonds
appear at 3226cm-1, 3293cm-1 and 3325cm-1 may be attributed to the H2O molecules or O-H
vibrating stretching which are probably existed due to ethylene glycol (CH2OH)2 [24].
4000 3500 3000 2500 2000 1500 1000 500
50
100
150
200
Trasmittance (a.u)
wavenumber(cm-1)
S1
S2
S3
Figure 1. FTIR spectra of the magnetite nanoparticles.
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40
3.2 UV-Visible Spectroscopy Study
The UV-visible spectroscopy was used to characterize the structure of Fe3O4 nanoparticles.
Figure 2 reveals that the absorption peaks of the prepared Fe3O4 nanoparticles was found
within the average UV-vis absorption region [5, 17], the average lower absorption wavelength
of 262.13nm and 230 nm is observed in all the samples. This can easily be assigned to the
intrinsic band gap absorption of the magnetite nanoparticles. The mobility of electrons from
valence band to conduction band can be determined by the equation of the energy gap (Eg) of
the Fe3O4 nanoparticles, was calculated using the relation
(1)
Where c is the velocity of light, h is the Planck constant, is the wavelength of light the
estimated band gap energy result is 4.7.eV
200 300 400 500
-5
0
5
10
15
20
Absorbance(a.u)
wavelength (nm)
S3
S2
S1
(262nm)
(230nm)
Figure 2. UV-visible spectra of the magnetite nanoparticles.
3.2 The Analysis Pattern of XRD in Magnetite (Fe3O4) Nanoparticles
The X-ray diffraction (XRD) pattern of the Fe3O4 nanoparticles was obtained at different
annealing temperatures as shown at diffraction peak of 2 = 26.75º, 32.67º, 35.44º, 55.88º, and
62.55º. This can be assigned to (310), (110), (311), (440), and (330) crystal planes of pure Fe3O4
nanoparticles with spinal structure of (JCPDS98-3969) [7, 21], respectively in 200ºC and 300ºC.
At 400ºC some peaks are also observed at 46.54º and 55.98º which can be easily be assigned to
(331), and (240). This indicates that these peaks are related to Fe2O3 of (JCPDS98-0625) and
-Fe2O3 of (JCPDS98-2012) [22, 23] respectively, these data are in agreement with what was
reported by [16, 18]. This reveals that the resultants nanoparticles in the first sample (S1) is
purely Fe3O4 nanoparticles [25], while the remaining second (S2) and third (S3) samples are
probablyFe2O3 and -Fe2O3 nanoparticles, respectively [26]. The peak of the sample S1 in
Figure 3 matched very well with Fe3O4 of (JCPDS98-3969) nanoparticles, same peaks are shifted
slightly to the higher angle in the S2, which is possibly due to oxidation of Fe3O4 in air at 300ºC
resulted toFe2O3 same result of this transformation of Fe3O4 toFe2O3 have been reported in
the literature by [13, 25] . The XRD pattern of the S3 indicates the oxidation of Fe3O4 at 400ºC in
air. The diffraction peaks matched well with -Fe2O3 (JCPDS98-2012), showing the
transformation of Fe3O4 to -Fe2O3 at 400ºC in air [8, 11].
International Journal of Nanoelectronics and Materials
Volume 12, No. 1, Jan 2019 [37-46]
41
20 30 40 50 60 70 80 90
500
600
700
800
900
1000
1100
1200
1300
Intensity (a.u)
2(deg)
S3
S2
S1
(310)
(110)
(311)
(331)
(240)(440)
(330)
Figure 3. XRD analysis of Fe3O4 nanoparticles obtained at different temperature.
The following is the Scherer’s formula used to calculated the crystalline particles size:
Cos
D
(2)
Where K (0.94) is a dimensionless quantity, is the X-ray wavelength,
is the line broadening
at half-maximum intensity (FWHM) and
is the Bragg angle. Therefore, the obtained particles
size result is plotted as the function of temperature in (Figure 5). As observed in the plot, the
magnetite nanoparticles size increase as the temperature increases from 200ºC to 400ºC.
Therefore, the average particles size as calculated by Scherer`s formula is 2.02nm, 5.58nm and
8.35nm for S1, S2, and S3 respectively. This shows that, with rising annealing temperatures, the
size of the Fe3O4 nanoparticles is gradually increasing as shown.
200 250 300 350 400
0
5
10
15
20
25
Size(nm)
Temperature(oC)
Figure 4. Size of Fe3O4 nanoparticles calculated using Scherer’s formula as a function of annealing
temperature.
Zakiyyu I. Takai, et al. / Preparation and Characterization of Magnetite…
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3.3 Field Emission Scanning Electron Microscope (FESEM) and Energy Dispersive
Spectrometer (EDS) Image of Magnetite (Fe3O4) Nanoparticles
FESEM observed the morphologies of the (Fe3O4) nanoparticles; the obtained images are shown
in (Figure 5). The Fe3O4 nanoparticles sample (S3) annealed at 400ºC appeared in a spherical
structure and nearly agglomerated. However, the spherical nanoparticles exhibit magnificent
internationalisation rate and highest cellular take up instead of another shape such as nanorods,
nanocubes or nanodisk [25]. Moreover, due to strong inter-particles Van der Waals force and
magnetic attraction among the Fe3O4 nanoparticles, some agglomeration is detected in the
samples (S3). The irregular shapes are observed at elevated changes in temperature (see S1 and
S2) due to agglomeration process [22, 23]. The image obtained through EDS analysis shown in
(Figure 5) confirmed the appearance of Fe3O4 nanoparticles by indicating Fe-O group of the
element.
Figure 5. FESEM image of mag netite nanoparticles annealed under vacuum at 200 for S1, 300 for S2 and
400 0C for S3 and the EDS image of magnetite (Fe3O4) nanoparticles.
3.4 Atomic Force Microscope (AFM) Characterization
The magnetite nanoparticles were deposited and dried on the glass for AFM characterization.
The results were obtained to determine the three dimensions (3D) and roughness of the
samples. Figure 5 shows the resulting 3D images of the sample, the maximum high of the
particles is about 10.4nm and the diameter of 79.09nm for the scanned area of 1 × 1
according to histogram in Figure 6. This results is in agreement with particles size obtained by
FESEM. The knobs spots (yellow spots) indicate the present of small agglomeration of Fe3O4
International Journal of Nanoelectronics and Materials
Volume 12, No. 1, Jan 2019 [37-46]
43
nanoparticles, which is also seen as a yellow area at phase contrast of the 3D image as reported
by [23]. The light yellow area is obtained due to the high moisture content in the ethylene
glycol; the sample was melted down because of heat absorption from the laser light [26-28].
Figure 5. AFM 3D image of the magnetite nanoparticles annealed at 400ºC.
Figure 6. Histogram obtained from AFM Analysis.
4. CONCLUSION
This research has demonstrated the preparation of Fe3O4 nanoparticles by sol-gel assisted
method and annealed under vacuum at different temperature 200-400ºC. The phase and
molecular structure, functional group, morphologies and roughness analysis of the Fe3O4
nanoparticles were successfully characterized; the results indicated that the different sized
Fe3O4 nanoparticles were obtained, simply by varying annealing temperature. The
morphologies observed by FESEM shows that the sample S3 annealed at 400ºC is more
spherical and different size Fe3O4 nanoparticles were observed in S1, and S2 annealed at 200
and 300ºC respectively. This method offers several significant properties for the preparation of
Fe3O4 nanoparticles. Firstly, the synthetic method is economically important and
environmentally friendly, because it includes cheaper and toxic free iron salts. Secondly, the size
of the obtained Fe3O4 nanoparticles can be easily controlled by varying the annealing
temperature.
Zakiyyu I. Takai, et al. / Preparation and Characterization of Magnetite…
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ACKNOWLEDGEMENT
The authors gratefully acknowledge the Centre for Graduate Studies (CGS) Universiti Tun
Hussein Onn Malaysia (UTHM) and Universiti Teknologi Mara (UiTM) for their kind support and
encouragement through this research.
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