CHINESE JOURNAL OF PHYSICS
VOL. 53, NO. 4
August 2015
Polymer-Mediated Synthesis of Iron Oxide (Fe2 O3 ) Nanorods
Farzaneh Soflaee, Majid Farahmandjou,∗ and Tahereh Pormirjaafari Firoozabadi
Department of Physics, Varamin Pishva Branch,
Islamis Azad University, Varamin, Iran
(Received July 8, 2014; Revised April 7, 2015)
Ferric oxide (Fe2 O3 ) nanoparticles were synthesized by using iron chloride hexahydrate
(FeCl3 · 6H2 O) as the precursor and polyvinylpyrrolydon (PVP) as the surfactant and polymer agent. The samples were characterized by high resolution transmission electron microscopy (HRTEM), field effect scanning electron microscopy (FESEM), X-ray diffraction
(XRD), Fourier transform infrared spectroscopy (FTIR), a UV-Vis spectrophotometer, and
a vibration sampling magnetometer (VSM). The XRD pattern showed that the iron oxide
nanoparticles exhibited a gamma-Fe2 O3 (maghemite) to alpha-Fe2 O3 (hematite) structural
phase transition in the nanocrystals. The particle size of the as-prepared sample was around
20 nm and the annealed sample was around 48 nm in diameter, as estimated by the XRD
technique and direct HRTEM observation. The surface morphological studies from SEM
depicted sphere-like shaped to rod-like shaped particles with the formation of clusters by
increasing the annealing temperature. The sharp peaks in the FTIR spectrum determined
the purity of the Fe2 O3 nanoparticles, and the absorbance peak of the UV-Vis spectrum
showed a bandgap energy of 2.58 eV. The result of the magnetic measurements showed a
good coercive field and saturation magnetism around 85 G and 9.83 emu/g, respectively.
DOI: 10.6122/CJP.20150413
PACS numbers: 78.67.-n, 78.67.Bf, 75.75.-c, 61.46.-w
I. INTRODUCTION
Magnetic nanoparticles have many unique magnetic properties, such as superparamagnetic, high coercivity, low Curie temperature, high magnetic susceptibility, etc. Magnetic
nanoparticles are of great interest for researchers from a broad range of disciplines, including magnetic fluids, data storage, catalysis, and bioapplications [1–5]. Especially, magnetic
ferrofluids and data storage are the applied researches that have led to the integration of
magnetic nanoparticles in a myriad of commercial applications. Iron oxide is widely used
as a catalyst, pigment, and gas sensitive material [6]. In many cases nanocrystalline iron
oxide can enhance a materials performance or improve industrial processing. There are two
well-known crystalline types of Fe2 O3 : maghemite (the γ-phase) with cubic structure and
hematite (the α-phase) with rhombohedral structure. For instance, synthesis of the ferric
oxide can be achieved at a much lower temperature by using nano-sized iron oxide as a raw
material [7]. Additionally, the gas sensitivity of α-Fe2 O3 also can be improved remarkably
by using ultrafine α-Fe2 O3 powders [8]. Therefore it is of importance to control the particle
∗
Electronic address: [email protected]
http://PSROC.phys.ntu.edu.tw/cjp
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c 2015 THE PHYSICAL SOCIETY
⃝
OF THE REPUBLIC OF CHINA
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POLYMER-MEDIATED SYNTHESIS OF IRON . . .
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size, morphology, and texture of the iron oxide system. Recently, many different methods
have been used in preparing nanosized α-Fe2 O3 . The phase transition of γ → α-Fe2 O3
takes place during calcination at about 400 ◦ C [9]. The phase transformation which occurs
during calcination gives rise to transforming α-Fe2 O3 powder which has undergone considerable aggregation and grain growth [10]. Over the past decades, synthesis techniques
of magnetite and iron oxide nanoparticles have always been of scientific and technological
interest. These methods include oxidation precipitation [11], chemical co-precipitation [12],
thermal decomposition [13], microemulsion [14], Sol-Gel [15], and the method of oxidation of precipitation [16]. However, uniform physical and chemical properties of magnetite
nanoparticles greatly depend upon the synthesis route, and how to develop a simple and
effective way to synthesize magnetite particles with high dispersion and narrow size distribution remains a challenge. In this paper, ferric oxide nanorods were synthesized using
iron chloride precursor and PVP surfactant. Structural, optical, and surface morphological
properties are discussed by XRD, HRTEM, FESEM, FTIR, UV-visible, and VSM analyses.
II. EXPERIMENTAL DETAIL
Iron oxide nanoparticles were synthesized by a new polymer-mediated synthesis according to the following manner. Firstly, 6 g PVP was completely dissolved in 100 mL
pure water with stirring at room temperature. Then 15 g of FeCl3 ·6H2 O was added to the
solution and the synthesis temperature was increased to 90 ◦ C. The color of the solution
changed from orange color to dark brown color. The pH=1 was maintained during the synthesis. The product were evaporated for 3 hours, cooled to room temperature, and finally
calcined at 500 ◦ C for 4 hours. All analyses were done for samples without any washing
and purification.
The specification of the size, structure and optical properties of the as-synthesised and
annealed Fe2 O3 nanoparticles were carried out. An X-ray diffractometer (XRD) was used to
identify the crystalline phase and to estimate the crystalline size. The XRD patterns were
recorded with 2θ in the range of 4–85◦ with a type X-Pert Pro MPD, Cu-Kα : λ = 1.54 Å.
The morphology was characterized by field emission scanning electron microscopy (SEM)
with a type KYKY-EM3200, 25 kV and transmission electron microscopy (TEM) with
a type Zeiss EM-900, 80 kV. The optical properties of absorption were measured by an
ultraviolet–visible spectrophotometer (UV–Vis) with an optima SP-300 plus, and Fourier
transform infrared spectroscopy (FTIR) with a WQF 510. All the measurements were
carried out at room temperature. Magnetic measurements were carried out using a vibration
sampling magnetometer with type VSM 7400 Lake Shore.
III. RESULT AND DISCUSSION
The X-ray diffractometer (XRD) with CuKα radiation, operated at 40 kV, 250 mA
was used to identify the crystalline phases and to estimate the crystalline sizes. Figure 1
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F. SOFLAEE, M. FARAHMANDJOU, AND T. P. FIROOZABADI
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shows the X-ray diffraction patterns of the powder before and after heat treatment. Figure 1(a) shows the XRD pattern of the iron oxide before annealing. A γ → α-Fe2 O3 phase
transformation took place during calcination between 300 and 400 ◦ C. Figure 1(b) shows
the XRD pattern of the iron oxide after annealing. An abrupt increase in the amount of
a phase occurred when the calcinations temperature rose above 400 ◦ C. α-Fe2 O3 was the
only phase present for the powder calcined above 500 ◦ C. The exhibited peaks correspond
to the (012), (104), (110), (113), (024), (116), (018), (214), and (300) of a rhombohedral
structure of α-Fe2 O3 as identified using the standard data. The mean size of the ordered
Fe2 O3 nanoparticles has been estimated from the full width at half maximum (FWHM)
and the Debye-Sherrer formula according to the following equation:
0.89λ
,
(1)
B cos θ
where 0.89 is the shape factor, λ is the X-ray wavelength, B is the line broadening at half
the maximum intensity (FWHM) in radians, and θ is the Bragg angle. The mean size of the
as-prepared α-Fe2 O3 nanoparticles was around 28 nm from this Debye-Sherrer equation.
D=
FIG. 1: XRD patterns of as-prepared and annealed iron oxide nanoparticles.
SEM analysis was used for the morphological study of nanoparticles of the Fe2 O3
samples. These analyses show that high crystallinity emerged in the samples surface by
increasing annealing temperature. With increasing temperature the morphology of the
particles changes to the rod-like shaped and nanopowders were less agglomerate. Figure 2(a)
shows the SEM image of the as-prepared Fe2 O3 nanoparticles prepared by the polymermediated method. In this figure, the particles were prepared with the formation of clusters.
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Figure 2(b) shows the SEM image of the annealed Fe2 O3 nanoparticles at 500 ◦ C for 4
hours. The Fe2 O3 nanocrystals formed were agglomerated. The rod-like shaped particles
with clumped distributions are visible through the SEM analysis. The particle size of the
as-prepared Fe2 O3 nanoparticles were measured at about 20 nm and the crystallite size of
the annealed nanocrystals were about 48 nm in diameter.
FIG. 2: TEM images of the (a) as-prepared (b) annealed Fe2 O3 nanoparticles at 500 ◦ C.
The transmission electron microscopic (TEM) analysis was carried out to confirm
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the actual size of the particles, their growth pattern and the distribution of the crystallites.
Figure 3 shows the as-synthesized TEM image of the spherical Fe2 O3 nanoparticles prepared
by the chemical reduction route. It can be seen that the particles were prepared with less
aggregation.
FIG. 3: TEM images of the as-prepared Fe2 O3 nanoparticles.
Figure 4 shows the size measurement of 100 randomly selected particles. By fitting
it with a log normal curve leads to a measured mean diameter of 20 nm with standard
deviation of about 9%.
In Figure 5, the infrared spectrum (FTIR) of the synthesized Fe2 O3 nanoparticles
was in the range of 400–4000 cm−1 wavenumber which identifies the chemical bonds as well
as functional groups in the compound. The large broad band at 3398 cm−1 is ascribed
to the O-H stretching vibration in the OH− groups. The absorption peaks around 1604
cm−1 , 1487 cm−1 are due to the asymmetric and symmetric bending vibration of C=O,
and the absorption peaks around 1293 cm−1 are ascribed to the PVP group. The strong
band below 700 cm−1 is assigned the Fe-O stretching mode. The band corresponding to
the Fe-O stretching mode of Fe2 O3 is seen at 576 cm−1 .
The UV-visible absorption spectral study may be of assistance in understanding electronic structure of the optical band gap of the material. Absorption in the near ultraviolet
region arises from electronic transitions associated within the sample. UV–Vis absorption
spectra of as-prepared and annealed Fe2 O3 nanoparticles are shown in Figure 6. For assynthesized Fe2 O3 nanoparticles, the strong absorption band at wavelengths near 480 nm
corresponds to the direct band-gap energy at around Eg = 2.58 eV and for the annealed one
the strong absorption band at wavelengths near 450 nm corresponds to the direct band-gap
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FIG. 4: Particle diameter histogram of as-prepared Fe2 O3 nanoparticles.
FIG. 5: FTIR spectrum of Fe2 O3 sample.
energy at around Eg = 2.76 eV.
Magnetizations M versus applied magnetic field H for powders of the samples are
measured at room temperature by cycling the magnetic field between −20k to 20k G. The
magnetization curve in Figure 7 shows hysteresis behavior in the low field region. Fig-
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FIG. 6: UV–Vis absorption spectra of Fe2 O3 nanoparticles.
ure 7(a) shows the coercive field and saturation magnetism around 85 G and 9.83 emu/g,
respectively, for the as-prepared sample and Figure 7(b) shows the coercive field and saturation magnetism around 441 G and 17.20 emu/g, respectively, for the annealed one.
As can be seen, the coercive field and saturation magnetism are increased with annealing
temperature because of the increasing size of the particles with temperature.
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FIG. 7: Magnetic hysteresis loop at 300 K for representative iron oxide nanoparticles: (a) asprepared, (b) annealed particles.
IV. CONCLUSION
The polymer-mediated α-Fe2 O3 nanoparticles have been successfully synthesized using iron chloride hexa hydrate and PVP. The XRD spectrum shows the rhombohedral
(hexagonal) structure of α-Fe2 O3 . From the SEM images, it is clear that with increasing
temperature the morphology of the particles changes from sphere-like shaped to rod-like
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shaped, and the nanopowders were less agglomerated. The TEM image exhibits that the
as-synthesized Fe2 O3 nanorods prepared by the polymer agent route with an average diameter about 20 nm with less aggregation. The FTIR data shows the presence of the Fe-O
stretching mode of Fe2 O3 . The Fe2 O3 nanoparticles show a strong UV–vis absorption below 500 nm with a well-defined absorption peak at 480 nm, the direct band gap is found
to be 2.58 eV. Magnetic measurements studies showed a good coercive field and saturation
magnetism around 85 G and 9.83 emu/g, respectively
Acknowledgements
The authors are thankful for the financial support of the Varamin Pishva branch at
Islamic Azad University for analysis and the discussions on the results.
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