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Synthesis of Cerium Oxide (CeO2) nanoparticles using simple CO-precipitation method

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Synthesis of cerium oxide (CeO2) nanoparticles was studied by new and simple co-precipitation method. The cerium oxide nanoparticles were synthesized using cerium nitrate and potassium carbonate precursors. Their physicochemical properties were characterized by high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR) and UV-Vis spectrophotometer. XRD pattern showed the cubic structure of the cerium oxide nanoparticles. The average particle size of CeO2 was around 20 nm as estimated by XRD technique and direct HRTEM observations. The surface morphological studies from SEM and TEM depicted spherical particles with formation of clusters. The sharp peaks in FTIR. spectrum determined the existence of Ce-O stretching mode and the absorbance peak of UV-Vis spectrum showed the bandgap energy of 3.26 eV.
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RESEARCH Revista Mexicana de F´
ısica 62 (2016) 496–499 SEPTEMBER-OCTOBER 2016
Synthesis of Cerium Oxide (CeO2) nanoparticles using
simple CO-precipitation method
M. Farahmandjou, M. Zarinkamar and T.P. Firoozabadi
Department of Physics, Varamin Pishva Branch,
Islamis Azad University, Varamin, Iran
e-mail: farahamndjou@iauvaramin.ac.ir
Received 6 May 2015; accepted 8 June 2016
Synthesis of cerium oxide (CeO2) nanoparticles was studied by new and simple co-precipitation method. The cerium oxide nanoparticles
were synthesized using cerium nitrate and potassium carbonate precursors. Their physicochemical properties were characterized by high
resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive
spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR) and UV-Vis spectrophotometer. XRD pattern showed the cubic structure
of the cerium oxide nanoparticles. The average particle size of CeO2was around 20 nm as estimated by XRD technique and direct HRTEM
observations. The surface morphological studies from SEM and TEM depicted spherical particles with formation of clusters. The sharp peaks
in FTIR spectrum determined the existence of Ce-O stretching mode and the absorbance peak of UV-Vis spectrum showed the bandgap energy
of 3.26 eV.
Keywords: CeO2nanoparticles; Co-precipitation; synthesis; optical properties.
PACS: 75.75.-c; 75.75.Cd; 61.46.-w; 61.46.Df; 61.46.Hk
1. Introduction
Cerium oxide with different valence states and various crys-
talline structures have been explored for various applica-
tions such as electrical, electronic, catalytic, adsorption, op-
tical, electrochemical, batteries, functional materials, energy
storage, magnetic data storage and sensing properties [1-5].
However, to enhance various properties of nanomaterials
to meet the increasing needs for different applications, it
is needed to reduce the particle size and increase the ac-
tive surface area of nanomaterials. Decrease in the particle
size enhancing conductivity, electrical, sensing and catalytic
properties of nonomaterial [6-8]. Ceria (CeO2) is a cubic
fluorite-type structured ceramic material that does not show
any known crystallographic change from room temperature
up to its melting point (2700C) [9]. Most of the applications
require the use of nonagglomerated nanoparticles, as aggre-
gated nanoparticles lead to inhomogeneous mixing and poor
sinter ability. In the recent years, due to the excellent phys-
ical and chemical properties of nano-sized particles, which
are significantly different from those of bulk particles, there
is considerable interest in enhancing catalytic activity, sinter-
ability, and other properties by decreasing the grain size into
a nanometer range [10,11]. A remarkable property of CeO2
is the number of effective redox Ce4+/Ce3+ sites and their
ability to exchange oxygen [12,13]. CeO2nanopowders have
been reported to be synthesized by different techniques, such
as hydrothermal [14], mechanochemical [15], sonochemi-
cal [16], combustion synthesis [17], sol-gel [18], semi-batch
reactor [19], microemulsion [20] and spray-pyrolysis [21].
Among the chemical processes, precipitation method is sim-
ple in process, low in cost and saving in time in comparison to
the another techniques. In the present work, we focused on
synthesis of CeO2nanoparticles system by co-precipitation
route. The aim of this study was to synthesize cerium oxide
of low dimension and investigation of morphological proper-
ties. This method has novel features which are of consider-
able interest due to its low cost, easy preparation and indus-
trial viability. In this work, synthesis of the CeO2nanopar-
ticles is reported by Ce(NO3)3.6H2O precursor by precipi-
tation technique and samples then calcined at 600C. The
structural and optical properties of CeO2have been studied
by XRD, EDS, HRTEM, SEM, FTIR and UV-visible analy-
ses.
2. Experimental details
CeO2nanoparticles were synthesized by a new approach
according to the following manner. In separate burettes,
0.02 M solution of Ce(III) nitrate was prepared by dissolving
2.17 gr, Ce(NO3)3.6H2O in 250 mL distilled water. Simi-
larly, 0.03 M of K2CO3solution was prepared by dissolving
1.036 gr, K2CO3in 250 mL distilled water. Aqueous solution
of Ce(III) nitrate (50 mL) and potassium carbonate (20 mL)
were added drop by drop to a well stirred water (100 mL) to
precipitate a white precursor, namely cerium (III) carbonate.
The constant Ph=6 was maintained during the precipitation
method. Resulting CeO2were dried at 65C for 2 hours,
cooled to room temperature. Then, the product was aged at
220C for 2.5 hours without any washing and purification
and finally calcined at 600C for 3 hours. The specifica-
tion of the size, structure and optical properties of the as-
synthesis and annealed CeO2nanoparticles were carried out.
X-ray diffractometer (XRD) was used to identify the crys-
talline phase and to estimate the crystalline size. The XRD
pattern were recorded with 2θin the range of 4-85with type
SYNTHESIS OF CERIUM OXIDE (CeO2) NANOPARTICLES USING SIMPLE CO-PRECIPITATION METHOD 497
FIGURE 1. XRD pattern of the annealed CeO2nanoparticles at
600C.
FIGURE 2. EDS spectrums of the CeO2samples (a) as-synthesized
and (b) annealed one.
X-Pert Pro MPD, Cu-Kα:λ= 1.54 ˚
A. The morphology
was characterized by field emission scanning electron mi-
croscopy (SEM) with type KYKY-EM3200, 25 kV and trans-
mission electron microscopy (TEM) with type Zeiss EM-900,
80 kV. The optical properties of absorption were measured by
ultraviolet-visible spectrophotometer (UV-Vis) with optima
SP-300 plus, and Fourier transform infrared spectroscopy
(FTIR) with WQF 510. The Ce and O elemental analysis
of the samples was performed by energy dispersive spec-
troscopy (EDS) type VEGA, 15 kV. All the measurements
were carried out at room temperature.
FIGURE 3. SEM images of the (a) as-prepared (b) annealed CeO2
samples at 600C
3. Results and discussion
X-ray diffraction (XRD) at 40 kV was used to identify crys-
talline phases and to estimate the crystalline sizes. Figure 1
shows the XRD morphology of CeO2nanoparticles annealed
at 600C for 3 hours. The exhibited is peak correspond to
the (111), (200), (220), (311), (222), (400), (331) and (420)
of a cubic fluorite structure of CeO2 and identified using
the standard data [22,23]. The mean size of the ordered
CeO2nanoparticles has been estimated from full width at half
maximum (FWHM) and Debye-Sherrer formula according to
equation the following:
D=0.98λ
Bcos θ(1)
where, 0.89 is the shape factor, λis the X-ray wavelength,
B is the line broadening at half the maximum intensity
(FWHM) in radians, and θis the Bragg angle. The mean
Rev. Mex. Fis. 62 (2016) 496–499
498 M. FARAHMANDJOU, M. ZARINKAMAR AND T.P. FIROOZABADI
FIGURE 4. TEM image of the as-prepared CeO2nanoparticles.
FIGURE 5. FTIR spectrum of the as-synthesized CeO2sample.
size of annealed CeO2nanoparticles was determined around
20 nm.
Energy dispersive spectroscopy (EDS) of CeO2prepared
by wet synthesis is shown in Fig. 2 which confirms the ex-
istence of Ce and O with weight percent. EDS was used to
analyze the chemical composition of a material under SEM.
EDS shows peaks of cerium and oxygen of as-prepared sam-
ple with less impurity such as K, Cl and N (Fig. 2a). Further-
more, the EDS spectrum of annealed CeO2samples was done
(Fig. 2b) it can be seen that the atomic fraction of the nitrogen
and oxygen was decreased because of annealing process.
SEM analysis was used for the morphological study of
nanoparticles of CeO2. These analyses show that high ho-
mogeneity emerged in the samples surface by increasing an-
nealing temperature. The results show that the morphology
of the particles changes to the spherical shape with less ag-
glomeration by increasing temperature. Figure 3(a) shows
the SEM image of the as-prepared CeO2nanoparticles pre-
pared by co-precipitation method. In this figure, the particles
prepared with formation of clusters. Figure 3(b) shows the
SEM image of the annealed CeO2nanoparticles at 600C for
3 hours. It can be seen that the CeO2nanoparticles were not
agglomerated. The sphere-like shaped of the particles with
clumped distributions are visible through the SEM analysis.
The average crystallite size of annealed nanocrystals is about
20 nm.
The transmission electron microscopic (TEM) analysis
was carried out to confirm the actual size of the particles,
their growth pattern and the distribution of the crystallites.
Figure 4 shows the as-synthesized TEM image of spherical
CeO2nanoparticles prepared by co-precipitation route with a
diameter in the range of 40-80 nm.
According to Fig. 5, the infrared spectrum (FTIR) of
the synthesized CeO2nanoparticles was in the range of
400-4000 cm1wavenumber which identify the chemical
bonds as well as functional groups in the compound. The
large broad band at 3415 cm1is ascribed to the O-H stretch-
ing vibration in OHgroups. The absorption is peak around
1464 cm1is assigned to the bending vibration of C-H
stretching. The intense band at 500 cm1corresponds to
the Ce-O stretching vibration [24,25]. The bands located at
around 741, 750, and 1036 cm1have been attributed to the
CO2asymmetric stretching vibration, CO2
3bending vibra-
tion, andC-O stretching vibration, respectively. The bands
FIGURE 6. Optical analysis of the CeO2samples, (a) UV-Vis ab-
sorption spectra, (b) plotting (αhν)mof the microcrystalline mate-
rials against the photon energy ().
Rev. Mex. Fis. 62 (2016) 496–499
SYNTHESIS OF CERIUM OXIDE (CeO2) NANOPARTICLES USING SIMPLE CO-PRECIPITATION METHOD 499
located at 1298 cm1are attributed to carbonate species vi-
brations [26] and are clearly attenuated after calcination, in-
dicating that the carbonate species have been decomposed by
heat treatment.
UV-visible absorption spectral study may be assisted 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-V is absorption spectra of as-prepared and annealed
CeO2nanoparticles are shown in Fig. 6(a). For as-
synthesized CeO2nanoparticles, the strong absorption band
at low wavelength near 380 nm correspond to bandgap en-
ergy of 3.26 eV (black line) and for annealed one the strong
absorption band at low wavelength near 385 nm correspond
to 3.22 eV (red line). In comparison with UV visible ab-
sorption spectrum of CeO2nanoparticles reported in the lit-
erature [27], band/peak in the spectrum located at around
400-700 nm are observed to be shifted towards lower wave-
length side, which clearly shows the blue shift. It indicates
the absorption positions depend on the morphologies and
sizes of CeO2. The UV absorption ability of CeO2is related
with band gap energy. The UV-absorption edge provides a
reliable estimate of the band gap of any system. The band
gap energy was estimated by plotting (αhν)mof the micro-
crystalline materials against the photon energy (). Where
αis the absorption coefficient, is the photon energy, Eg
is the band gap energy. The band gap energy fallowed direct
transitions of as-prepared CeO2nanoparticles is 3.22 eV as
estimated from the Tauc plot in Fig. 6(b).
4. Conclusion
CeO2nanoparticles have been successfully synthesized us-
ing Chemical precipitation of cerium nitrate hexahydrate and
potassium carbonate. XRD spectra showed cubic fluorite
structure of CeO2identified using the standard data. SEM
images indicated that with increasing temperature the mor-
phology of the particles changes to the sphere-like shaped
with less agglomeration. TEM results exhibited the spheri-
cal CeO2nanoparticles with a diameter in the range size of
40-80 nm. FTIR data exhibited the presence of Ce-O stretch-
ing mode of CeO2. The Ceria nanoparticles showed a strong
UV-vis absorption at 500 nm with a well-defined absorption
peak at 380 nm and finally the direct band gap was deter-
mined about 3.26 eV.
Acknowledgments
The authors are thankful for the financial support of varamin
pishva branch at Islamic Azad University for analysis and the
discussions on the results.
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