Preparation of CaCO3 and CaO nanoparticles via solid-state conversion of calcium oleate precursor

Article abstract of DOI:10.1166/jnn.2018.14208

Calcium carbonate (CaCO₃) and monodisperse calcium oxide nanoparticles (CaO NPs) are prepared by the calcination of solid-state calcium oleate precursor in air condition. The effect of calcination temperature on the synthesis of CaCO₃ and CaO NPs is examined. The polymorphism is confirmed by X-ray diffraction spectroscopy (XRD), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). The sample morphologies including their size and size distribution are investigated by field emission scanning electron microscopy (FESEM). Calcination of calcium oleate between 400 and 550 °C results in CaCO₃ NPs with mean sizes from 82 to 98 nm, whereas monodisperse spherical CaO NPs are obtained at 650 °C and an average size is estimated to be 40 nm. Beyond 650 °C, the size of CaO NPs increases with broad size distribution. The results of this study provide a novel approach to monodisperse CaCO₃ and CaO NPs that can be applied in a variety of fundamental and industrial fields.

Full text of DOI:10.1166/jnn.2018.14208

Article
Journal of
Nanoscience and Nanotechnology
Vol. 18, 1958–1964, 2018
Copyright © 2018 American Scientific Publishers
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www.aspbs.com/jnn
Printed in the United States of America
Preparation of CaCO3 and CaO Nanoparticles via
Solid-State Conversion of Calcium Oleate Precursor
Raji Atchudan†ꢀ‡, Nasreena Lone‡, and Jin Joo∗
School of Applied Chemical Engineering, Kyungpook National University, Daegu 41566, Republic of Korea
Calcium carbonate (CaCO3ꢀ and monodisperse calcium oxide nanoparticles (CaO NPs) are pre-
pared by the calcination of solid-state calcium oleate precursor in air condition. The effect of cal-
cination temperature on the synthesis of CaCO3 and CaO NPs is examined. The polymorphism is
confirmed by X-ray diffraction spectroscopy (XRD), Fourier transform infrared spectroscopy (FTIR),
and thermogravimetric analysis (TGA). The sample morphologies including their size and size dis-
tribution are investigated by field emission scanning electron microscopy (FESEM). Calcination of
ꢀ
calcium oleate between 400 and 550 C results in CaCO3 NPs with mean sizes from 82 to 98 nm,
whereas monodisperse spherical CaO NPs are obtained at 650 ꢀC and an average size is esti-
ꢀ
mated to be 40 nm. Beyond 650 C, the size of CaO NPs increases with broad size distribution.
The results of this study provide a novel approach to monodisperse CaCO3 and CaO NPs that can
be applied in a variety of fundamental and industrial fields.
Keywords: Calcium Carbonate, Calcium Oxide, Calcium Oleate, Monodisperse Nanoparticles.
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1. INTRODUCTION
the past few decades, a substantial progress has been made
in this field. However, many interesting phenomena still
remain unrevealed, especially the formation mechanism of
CaCO3 with intriguing shapes and properties.25–32
In recent years, various nanoparticles and nanoporous
materials, including inorganic metal oxides and organic
polymers have been intensively studied. Such nano-
structures are of significant importance because of their
unique chemical and physical properties, and find exten-
sive applications related to energy, catalysis, sensors,
adsorption, separation, storage, optics, photochemistry, and
biomedicine.1–12
Calcium carbonate (CaCO3ꢀ is one of the most abun-
dant minerals on earth and is an important substance
for industrial and environmental perspectives.13–19 Control
over morphology and particle size of calcium carbonate
nanoparticles (CaCO3 NPs) are prerequisites for determin-
ing their technical applications.20 Crystallinity of CaCO3
is highly interesting with three polymorphs being docu-
mented; calcite, aragonite, and vaterite.21ꢁ22 Among these
three crystal structures, calcite is the only stable form of
CaCO3 from the thermodynamic viewpoint.23ꢁ24 However,
tuning of desired crystallographic and morphological prop-
erties of CaCO3 particles is still under investigation. Over
In general, two methods have been widely employed
to synthesize CaCO3 NPs. The first method is slow CO2
diffusion method as first reported by Addadi and co-
workers.33 In this method, a solution of calcium salt in an
open vessel is placed near a CO2 source, such as ammo-
nium carbonate, in a closed system. Precipitation occurs
as CO2 diffuses into the solution of Ca2+ ions. Although
this method has often been employed for the polymorph
and morphology control, and the associated fundamental
studies, the production rate of CaCO3 particles from such
a process is usually very slow. In another method, fast pre-
cipitation occurs through the reaction between dissolved
Ca2+ cations and CO32− anions in solution.34ꢁ35 CaCO3
is produced instantaneously; therefore, this method could
be more appropriate for large-scale industrial productions.
In both methods, the use of organic additives has been
found important for controlled nucleation and crystalliza-
tion process.36–41 However, understanding the effect of
those additives and the crystallographic and morphologi-
cal properties of the resulting nanoparticles still remains
challenging.
∗Author to whom correspondence should be addressed.
†Present address: School of Chemical Engineering, Yeungnam
University, Gyeongsan 38541, Republic of Korea.
‡These two authors contributed equally to this work.
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J. Nanosci. Nanotechnol. 2018, Vol. 18, No. 3
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doi:10.1166/jnn.2018.14208

Atchudan et al.
Preparation of CaCO3 and CaO Nanoparticles via Solid-State Conversion of Calcium Oleate Precursor
CaO, both in bulk and nano-form is environmentally
benign and finds potential applications in numerous indus-
trial fields.42ꢁ43 It is extensively applied as a heteroge-
neous catalyst in numerous synthetic reactions. Catalytic
transesterification of triglycerides makes CaO remark-
ably important for the preparation of renewable and bio-
degradable alternate diesel fuel (biodiesel).44–46 CaO based
sorbents provide a cost-effective alternative to capture and
sequestrate CO2 emissions.47ꢁ48 It is noteworthy that the
ever increasing CO2 emission has a major contribution
in the increasing global climatic changes and oceanic
acidification.49 CaO also has an established niche in toxic
warfare chemical remediation,42 refractory additives,43
doping of electrical and optical (dielectric) materials,50
flue gas desulfurization,51 biomimetic oxidizing catalysts
for artificial photosynthesis,52 fluoride adsorbent for water
treatment,53 paper and art conservation,54 and pollutant
emission control, etc.44ꢁ51 Recently CaO NPs have found
superiority over bulk CaO because of the larger number
of extra surface active sites due to increased surface area.
Therefore, controlled morphology of CaO NPs becomes
important for efficient applications to improve their prop-
erties associated with nanomaterial morphology. CaO NPs
are often synthesized by thermal decomposition method.
Thermal decomposition method is favored for being sim-
ple, low cost, and achieving high purity nanoparticles. For
example, calcination of hydroxides, nitrates, and carbon-
(10 mmol) were placed in a round bottom flask. The tem-
perature of the mixture was kept at 100 C with constant
ꢀ
stirring for 1 h under vacuum condition to remove oxygen
and trace amount of moisture. After that, the temperature
ꢀ
was raised to 350 C and maintained at this temperature
for 5 h under vigorous stirring in an argon atmosphere.
After the reaction mixture was allowed to cool down
to room temperature, an excess amount of ethanol was
added, yielding a brownish precipitate. The product of cal-
cium oleate was collected by centrifugation, and ethanol-
washing and centrifugation step was repeated several times
to remove the excess unreacted oleic acid. The resulting
product was kept in a hot oven at 70 ꢀC to remove ethanol.
The obtained calcium oleate was calcined at different tem-
ꢀ
peratures (450–800 C) in a muffle furnace under static
condition. After completion of the calcination, the final
product was collected and subjected to characterization.
2.3. Characterization Methods
The synthesized CaCO3 and CaO NPs were character-
ized by various physico-chemical techniques such as X-ray
diffraction (XRD), Fourier transform infrared (FTIR) spec-
troscopy, thermogravimetric analysis (TGA), and field
emission scanning electron microscopy (FESEM). The
XRD patterns were obtained on a Rigaku D/MAX-2500
diffractometer using Cu-Kꢂ as the radiation source (ꢃ =
1ꢄ54 Å) and a liquid nitrogen cooled germanium-based
solid-state device as the detector. The diffraction patterns
were measured for the 2ꢅ angle range of 5–80ꢀ at a step
interval of 0.02ꢀ and an integration time of 5 s at each step.
The FTIR spectra were recorded in transmittance mode
on a Shimadzu IRPrestige-21 FTIR spectrometer in the
wavenumber range of 400–4000 cm−1 by the co-addition
of 50 scans at a resolution of 8 cm−1. The FTIR analy-
sis was carried out at room temperature using potassium
bromide (KBr) pellets containing around 1% of the solid
nanoparticle samples, which were compacted in a uniaxial
press under a nominal pressure of 60 kN. The spectrum of
dry KBr was recorded for background subtraction before
recording the sample spectra. The thermal stability of the
samples was measured by means of TGA with a Differ-
ence thermal analysis (DTA) instruments SDT Q600 setup.
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ates of calcium are conventional precursors for the prepa-
ration of CaO NPs.42ꢁ55ꢁ56
Copyright: American Scientific Publishers
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Recently, we have reported the morphology-controlled
syntheses of calcite by the reaction of calcium nitrate
with either sodium carbonate or citric acid in the pres-
ence of CTAB by the method of sonication or carboniza-
tion, respectively.57 In the present study, the synthesis of
monodisperse CaCO3 and CaO NPs using calcium oleate
as a precursor is reported. Calcium oleate is prepared by
ligand exchange of calcium stearate, and calcination under
air atmospheric condition results in CaCO3 and monodis-
perse CaO NPs.
2. EXPERIMENTAL DETAILS
2.1. Materials
Calcium stearate and oleic acid (90%) were purchased
from Aldrich. Oleic acid was purified by vacuum dis-
tillation before use. Ethanol was obtained from Duksan
Pure Chemicals and used as received without any further
purification.
ꢀ
Each sample was heated from 25 to 1000 C at the heat-
ꢀ
ing rate of 10 C/min under air atmosphere. SEM analysis
was performed on a Hitachi S-4800 with the acceleration
voltage of 4 kV by placing samples on conductive carbon
tape.
3. RESULTS AND DISCUSSION
2.2. Synthesis of CaCO3 NPs and CaO NPs
3.1. Formation Mechanism of CaCO3 NPs and
The CaCO3 and CaO NPs were synthesized by direct
calcination of calcium oleate at different temperatures
(400–900 ꢀC). Calcium oleate precursor was prepared
by exchanging stearate-ligand of calcium stearate with
an excess amount of oleic acid at an elevated tempera-
ture. Typically, calcium stearate (1 mmol) and oleic acid
CaO NPs
The synthesis procedure and formation mechanism are
illustrated in Figure 1. The molecular structure of ligand
on Ca2+ cations plays an important role in controlling the
morphology of the CaCO3 and CaO NPs. The calcination
J. Nanosci. Nanotechnol. 18, 1958–1964, 2018
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Preparation of CaCO3 and CaO Nanoparticles via Solid-State Conversion of Calcium Oleate Precursor
Atchudan et al.
the CaCO3 and CaO NPs synthesized from calcium oleate
with respect to their calcination temperature. Calcite crys-
tal structures of CaCO3 were obtained below 600 ꢀC for the
samples prepared at 450, 500, and 550 ꢀC (JCPDS Card no.
86-0174).58 The other diffraction peaks are much weaker
than the characteristic peak (104) plane. These patterns
exhibit only sharp calcite reflections, confirming that there
are no other crystal phases of CaCO3, such as aragonite and
vaterite. The peak intensities of the CaCO3 NPs become
stronꢀger with anꢀincrease in calcination temperature from
450 C to 550 C. Much greater number of diffraction
plane due to larger crystallite size produces more intense
X-ray diffraction peaks. This is because crystallization into
calcite structure and the growth of crystallite is favored
at an elevated temperature.ꢀThe thermal decomposition of
CaCO3 started above 580 C which will be discussed in
Figure 1. Schematic diagram of the formation of CaCO3 and CaO NPs.
of calcium oleate tends to produce more uniform and
smaller nanoparticles of CaCO3 and CaO than that of cal-
cium stearate. To complete ligand exchange, we reacted
calcium stearate with an excess amount of oleic acid at
high temperature as shown in Figure 1. The morphology
of nanoparticles was changed with calcination tempera-
ture. Calcium oleate produces CaCO3 with calcite crystal
ꢀ
structure until the calcination temperature reaches 550 C.
ꢀ
Section 3.4. Calcination above 600 C leads to the disap-
The phase transition of CaCO3 into CaO occurs at the
pearance of CaCO3 and it transforms into CaO (Fig. 2). The
XRD patterns for samples obtained at 600 and 625 ꢀC show
the mixed phases of CaO and a small amount of CaCO3.
The XRD patterns for samples obtained from 650–800 ꢀC
are in good agreement with rock-salt structure of CaO
(JCPDS Card number 43-1001). The peak intensities of the
CaO NPs increase with a higher calcination temperature
ꢀ
calcination temperatures between 575 and 625 C where
a small amount of CaCO3 remained unconverted. Finally,
pure CaO waꢀs obtained when the calcination temperature
reached 650 C. The carboxylate ligands start to decom-
ꢀ
pose from 400 C under air atmospheric condition, leav-
ing CO2 and H2O. In between the reaction (calcination)
temperature of 400–550 ꢀC, the produced CO2 reacts with
Ca2+ to form CaCO3 (Eq. (1)). At the calcination temper-
ꢀ
from 650 to 800 C, indicating larger crystallite size. The
average crystallite size of the nanoparticles was calculated
using the Debye–Scherrer Eq. (3):
ꢀ
ature beyond 650 C, the CaCO3 starts to decompose to
form CaO with releasing CO (Eq. (2)).
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2
Copyright: American Scientific Publishers
Kꢃ
O2
Crystallite size ꢆLꢀ =
(3)
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Ca2+ +CO2 −→ CaCO3
CaCO3 → CaO+CO2
(1)
ꢇcosꢅ
(2)
where K is a constant (ca. 0.94), ꢃ is the X-ray wavelength
used in XRD (1.54 Å), ꢅ is the angle between the incident
ray and the scattering planes, and ꢇ is the full width at half
maximum (FWHM) of the diffraction peak. The average
crystallite sizes of the CaCO3 NPs obtained at 450, 500
3.2. XRD Analysis of CaCO3 NPs and CaO NPs
The evolvement of the crystal structure was determined
by XRD analysis. Figure 2 shows the XRD patterns of
800 °C
650 °C
800 °C
700 °C
650 °C
625 °C
600 °C
600 °C
3640 cm–1
550 °C
JCPDS 43-1001 CaO
450 °C
550 °C
1797 cm–1
1442 cm–1
2518 cm–1
500 °C
450 °C
710 cm–1
875 cm–1
1000 500
JCPDS 86-0174 CaCO3
20
30
40
50
60
4000
3500
3000
2500
2000
1500
Wavenumber (cm–1
)
2θ (degree)
Figure 2. XRD patterns of CaCO3 and CaO NPs prepared from calcium
Figure 3. FTIR spectra of CaCO3 and CaO NPs prepared from calcium
oleate at different temperatures.
oleate at different temperatures.
1960
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Atchudan et al.
Preparation of CaCO3 and CaO Nanoparticles via Solid-State Conversion of Calcium Oleate Precursor
100
90
Hydroxyl group (–OH) can be produced by the reaction
of CaO surface and H2O as represented by the following
equation:
500°C
600°C
650°C
700°C
CaO+H2O → CaꢆOHꢀ2
(4)
80
800°C
The strong broad band around 1442 cm−1, as well as
a weak band around 875 cm−1 indicates the C–O bond
related to carbonation of CaO NPs.
70
80
DTG
70
60
60
50
50
3.4. Thermogravimetric Analysis of CaCO3
500°C
600°C
650°C
700°C
800°C
40
40
NPs and CaO NPs
30
The TGA and DTA curves of CaCO3 NPs and CaO NPs
synthesised from calcium oleate are shown in Figure 4.
For a sample calcined at 500ꢀꢀC, a trace amount of weight
loss is observed up to 150 C, which is due to removal
of the physisorbed water molecules from the host mate-
rial. The significant weight loss observed between 590 and
30
Air atmosphere
Heating rate: 10 °C/ min
20
100 200 300 400 500 600 700 800 900
Temperature (°C)
20
100 200 300 400 500 600 700 800 900
Temperature (°C)
Figure 4. TG/DTG curves of CaCO3 and CaO NPs prepared from cal-
cium oleate at different temperatures.
ꢀ
710 C which can be attributed to the thermal decom-
position of CaCO3 NPs obtained from calcium oleate at
500 ꢀC.61 The CaCO3 transforms into CaO (s) and CO2 (g)
during thermal decomposition (Eq. (2)). The loss of ∼40%
of the initial mass in this temperature range is due to the
escape of CO2 from the system. The highest temperature
at which CaCO3 phase is observed during TGA is found
ꢀ
and 550 C are around 82, 93, and 98 nm, respectively
(Fig. 2). When the calcination temperature is increased
above 600 ꢀC, CaCO3 NPs are converted to CaO NPs. The
ꢀ
calculated crystallite size of the CaO NPs at 650 C from
XRD peak is around 45 nm.
ꢀ
to be 690 C.62 In contrast to the initialꢀweight loss, no
3.3. FTIR Spectroscopic Analysis of CaCO3
NPs and CaO NPs
The FTIR spectra of the synthesized CaCO3 NPs and
decomposition was observed up to 1000 C. The thermo-
gram of nanoparticles synthesized above 600 ꢀC show two
distinct weight losses. The weight loss from 350 to 500 ꢀC
is due to the elimination of surface –OH groups on CaO
NPs, (Eq. (5)).61 This hydroxide group can be produced
from the reaction of CaO with the moisture in air.63
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Copyright: American Scientific Publishers
CaO NPs from calcium oleate is shown in Figure 3. As
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shown in Figure 3 (450 and 550 ꢀC), a single calcite
phase can be confirmed by the appearance of characteristic
band of ∼875 cm−1 and ∼710 cm−1 23ꢁ59
.
The strong broad
band around 1442 cm−1 corresponds to the asymmetric
stretching vibration, and the strong sharp bands around
710 and 875 cm−1 can be assigned to the bending out
of plane vibration and in plane vibration, respectively.60
The weak sharp bands around 1797 and 2518 cm−1 are
attributed to the characteristic bands of CaCO3. The weak
broad band around 3450 cm−1 can be attributed to the
hydroxyl groups (–OH), physically adsorbed water (ꢀlat-
tice water) molecules. Figure 3 (600, 650, and, 800 C)
shows the sharp bands around 3640 cm−1 corresponds to
the asymmetric stretching vibrations of –OH bonds from
the hydroxide on the external surface of the CaO sample.
CaꢆOHꢀ2 → CaO+H2O
(5)
Considering the XRDꢀdiffraction patterns, CaO NPs pro-
duced at above 600 C exhibit no Ca(OH)2 peaks that
exclude the possibility of Ca(OH)2 phase; causing weight
ꢀ
loss at the temperature ranging from 350 to 500 C. The
final ꢀweight loss occurs above the temperature of 500–
700 C, which arises from an incomplete conversion of
CaCO3 into CaO during calcination at the temperature
ꢀ
ꢀ
above 600 C. XRD patterns of the samples synthesized
above 600 C in Figure 2 reveal that small quantity of
(104) CaCO3 reflection peak is present in all the samples
Figure 5. FESEM images of CaCO3 NPs prepared at (a) 450, (b) 500, and (c) 550 ꢀC from calcium oleate.
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1961

Preparation of CaCO3 and CaO Nanoparticles via Solid-State Conversion of Calcium Oleate Precursor
Atchudan et al.
Figure 6. FESEM images of CaO NPs prepared at (a) 600, (b) 625, (c) 650 and (d) 700 ꢀC from calcium oleate.
ꢀ
calcined above the temperature of 600 C. The weight
loss resulting from CaCO3 conversion into CaO and CO2
Strong calcite CaCO3 peaks ofꢀ 710 and 875 cm−1 gradu-
ally decrease from 550 to 800 C.
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decreases with a higher calcination temperature of each
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3.5. Morphology Analysis of CaCO3 NPs and
sample. The weight losses in this temperature range for
the samples calcined at 600, 650, 700, and 800 ꢀC are 25,
15, 9.3, and 6.7%, respectively. This strongly suggests that
less CaCO3 phase remains with calcination procedure at
higher temperature, which is consistent with FTIR spectra.
CaO NPs
FESEM images of CaCO3 NPs synthesized from calcium
oleate at different temperatures (450–550 ꢀC) are shown in
Figure 5. It is clearly seen that the average size of prepared
Figure 7. FESEM images of CaCO3 NPs prepared at (a) 400 and (b) 500 ꢀC; CaO NPs prepared at (c) 600, (d) 700, (e) 800, and (f) 900 ꢀC from
calcium stearate.
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Atchudan et al.
Preparation of CaCO3 and CaO Nanoparticles via Solid-State Conversion of Calcium Oleate Precursor
Figure 8. FESEM images of CaO NPs with different magnifications prepared from calcium stearate at 650 ꢀC.
CaCO3 NPs increases from 82 nm to 98 nm as their calci-
nation temperature was raised from 450 to 550 ꢀC. Such a
dependence of size on the calcination temperature results
from an acceleration in agglomeration between small par-
ticles of CaCO3 at a higher temperature. Figures 6(a–c)
shows the FESEM images of CaO NPs prepared at a tem-
perature ranging from 600 to 650 ꢀC. Most of the nanopar-
ticles are spherical and become more monodisperse to
some degree compared to the CaCO3 NPs representedꢀin
Figure 5. For example, the sample synthesized at 650 C
shows <5% of standard size distribution (ꢈ), which can
be regarded as a monodisperse nanoparticles ensemble
(Fig. 6(c)). As far as our knowledge is concerned, the
CaO NPs were produced as a predominant phase with a
trace amount of unconverted CaCO3. The conversion of
calcium stearate precursor into CaCO3 and further CaO
with respect to calcination temperature follows exactly the
same trend as that of calcium oleate; CaCO3 is obtained
ꢀ
from 400 C and mixture of CaO and a small amount of
ꢀ
CaCO3 is observed at above 600 C in XRD and FTIR
spectra. However, there is a large difference in terms of
average size and size distribution. The morphologies of
CaCO3 and CaO NPs obtained from the calcination of cal-
cium stearate are very similar to the samples from cal-
cium oleate as shown in Figure 7. However, their size
distribution appears to become much broader and larger
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average sizes are produced. For instance, 120 nm of CaO
size distribution of our CaO NPs sample is the narrow-
Copyright: American Scientific Publishers
ꢀ
NPs were obtained at 650 C (Fig. 8). We speculate that
est one ever reported. The average nanoparticle sDizeelsivaerreed by Ingenta
differences in the average size and size distribution are
96 nm, 65 nmꢀ, and 40 nm for samples synthesized at 600,
625, and 650 C, respectively. The trend that smaller par-
ticles are produced at a higher temperature, opposite to
CaCO3 synthesis, implies that CaO forms by a direct con-
version of CaCO3 nanoparticles, not by agglomeration of
small particles or through a conventional nucleation and
growth of monomer species. The molar density of CaCO3
and CaO are 36.9 mL/mol and 16.5 mL/mol, respectively,
and decomposition of CaCO3 nanoparticles at an elevated
temperature leaves smaller CaO particles. The crystallite
size of the CaO NPs estimated from XRD peaks by Dye–
Scherrer equation is 45 nm, which is in good agreement
with the size of 40 nm obtained from FESEM analysis.
In other words, prepared CaO NPs have the single crys-
talline nature. The particle growth mechanism completely
changes from 700 ꢀC, where CaO NPs grow via agglomer-
ation between particles, whereas volume contraction takes
place below this temperature resulting in smaller particles
with a higher temperature (Fig. 6(d)).
associated with the cis-configuration of oleate ligand. The
introduction of double bond with cis-configuration in the
middle of hydrocarbon chain dramatically lowers the melt-
ing point of its metal carboxylate derivatives and thus
increases the solubility of monomers in solvent medium.64
Even though the synthesis of nanoparticles was carried
out in solid-state in our current experiment, it is obvious
that calcium carboxylate precursors melt into liquid phase
before thermal decomposition under air condition. At some
temperature, nuclei formation, followed by their growth
in melt-phase, associated with hydrocarbon configuration
of carboxylate ligand could become crucial in governing
particle growth dynamics. The relationship between the
kind of carboxylate ligand and nanoparticles morphology
is under investigation.
4. CONCLUSIONS
An efficient synthesis route for the preparation of CaCO3
and monodisperse CaO NPs from calcium oleate is
reported. The simple calcination of solid-state calcium
oleate precursor under air condition leads to CaCO3 and
We tried to synthesize CaCO3 and CaO NPs by using
calcium stearate also to figure out the effect of the lig-
and nature on morphologies of final products. FESEM
images of CaCO3 NPs synthesized from calcium stearate
at different temperatures (400–500 ꢀC) are shown in
Figures 7(a and b). When calcination was carried out
ꢀ
CaO NPs. The CaCO3 NPs are obtained below 600 C.
CaO NPs formation starts from 600 ꢀC and highly
monodisperseꢀCaO NPs with the size of 40 nm are pro-
duced at 650 C, which is the narrowest average size with
ꢀ
at/above 600 C, it was found out in XRD analysis that
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Preparation of CaCO3 and CaO Nanoparticles via Solid-State Conversion of Calcium Oleate Precursor
Atchudan et al.
the narrow size distribution ever reported. We believe that
monodisperse CaO NPs in our study will find a new appli-
cation, especially as an efficient catalyst.
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Acknowledgments: This work was supported by
the National Research Foundation of Korea (NRF)
grant funded by the Korea government (MSIP)
(2014R1A2A1A11054122), Basic Science Research
Program through the National Research Foundation
of Korea (NRF) funded by the Ministry of Education
(2012R1A1A2044157), and the Korea Ministry of Envi-
ronment (MOE) as Public Technology Program based on
Environmental Policy (2014000160001).
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Received: 11 October 2016. Accepted: 15 November 2016.
1964
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