Journal of Industrial and Engineering Chemistry 20 (2014) 113–117

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Journal of Industrial and Engineering Chemistry

journal homepage: www.elsevier.com/locate/jiec

Preparation and characterization of CaO nanoparticles from Ca(OH)2

by direct thermal decomposition method
Zahra Mirghiasi a,b, Fereshteh Bakhtiari a,c,*, Esmaeel Darezereshki c,d,
Esmat Esmaeilzadeh e
a
Faculty of Engineering, Department of Chemical Engineering, Shahid Bahonar University of Kerman, P.O. Box 76169-133, Kerman, Iran
b
Young Researchers Society, Shahid Bahonar University of Kerman, Kerman, Iran
c
Mineral Industries Research Centre, Shahid Bahonar University of Kerman, Kerman, Iran
d
Energy & Environmental Engineering Research Center, Shahid Bahonar University of Kerman, Kerman, Iran
e
Research & Development Division, Sarcheshmeh Copper Complex, Rafsanjan, Iran

A R T I C L E I N F O A B S T R A C T

Article history: CaO is an important material because of its application as catalyst and effective chemisorbents for toxic
Received 30 October 2012 gases. In this research CaO nanoparticles were prepared via direct thermal decomposition method using
Accepted 18 April 2013 Ca(OH)2 as a wet chemically synthesized precursor. Nanocrystalline particles of Ca(OH)2 have been
Available online 24 April 2013
obtained by adding 1 and 2 M NaOH aqueous solutions to 0.5 M CaCl22H2O aqueous solutions at 80 8C.
The precursor [Ca(OH)2] was calcined in N2 atmosphere at 650 8C for 1 h. Samples were characterized by
Keywords: X-ray diffraction (XRD), thermogravimetric analysis (TGA), infrared spectrum (IR), scanning electron
Calcium hydroxide
microscopy (SEM), transmission electron microscopy (TEM) and Brunaure–Emett–Teller (BET). SEM
Calcium oxide
Nanoparticles
images showed that CaO nano-particles were nearly spherical in morphology. TEM images illustrated
Synthesis that produced CaO nano-particles had the mean particle size of 91 and 94 nm for 1 and 2 M NaOH
Thermal decomposition concentration, respectively. As a result, this method could be used for production of CaO nano-particles
on large-scale as a cheap and convenient way, without using any surfactant, organic medium or
complicated equipment.
ß 2013 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights
reserved.

1. Introduction Properties and applications of inorganic nano-materials depend

on their morphology [5,12]. So controlled production of metal
Metal oxide nanoparticles are important materials due to the oxide nanoparticles is important for effective and successful
widespread applications in various aspects including catalysis, applications [1,5,12]. It is reported that solution-phase methods
sensors, optoelectronic materials, and environmental remediation provide a large degree of control over the synthesis products [12].
[1]. Calcium oxide as an alkaline earth metal oxide have many Furthermore organic solvents and high temperature have signifi-
applications such as catalyst [2], toxic-waste remediation agent, cant effects on the shape, size, uniformity and other properties of
additive in refractory [3,4], doped material to modify electrical and produced particles [13–16]. Although the increasing temperature
optical (dielectric) properties [5], crucial factor for CO2 capture [6– led to smaller particles and higher symmetry of nanoparticles, but
8], flue gas desulfurization and pollutant emission control [9]. In using of organic solvent as a medium of reaction involves several
general, nanocrystalline alkaline earth metal oxides can be used as peptizations because of agglomeration of the synthesized particles
effective chemisorbents for toxic gases, HCl, and chlorinated and [16].
phosphorus-containing compounds [10,11]. Alkaline-earth oxides, Ca(OH)2 nanoparticles are synthesized by several methods such
mostly calcium and barium-based oxides are useful for the as sonochemical [5], hydrogen plasma-metal reaction [9], sol–gel
purification of hot gases [11]. method [11], precipitation [15] and water-in-oil (W/O) micro-
emulsions [17]. Most of the methods suffer from limitations like
the use of organic solvents [3,5,14], high temperature [9], long
times [11] and complicated equipment [9]. CaO nanoparticles are
often produced via thermal treatment of Ca(OH)2 [5,18] or CaCO3
* Corresponding author at: Faculty of Engineering, Department of Chemical
[6,19] as precursors. In this study, CaO nanoparticles were
Engineering, Shahid Bahonar University of Kerman, P.O. Box 76169-133, Kerman,
Iran. Tel.: +98 913 1405795; fax: +98 341 2118918. prepared by calcination of Ca(OH)2 which was synthesized by
E-mail addresses: fereshteh@uk.ac.ir, fereshteb@yahoo.com (F. Bakhtiari). adding NaOH solution to CaCl22H2O solution without using any

1226-086X/$ – see front matter ß 2013 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jiec.2013.04.018
114 Z. Mirghiasi et al. / Journal of Industrial and Engineering Chemistry 20 (2014) 113–117

surfactant, organic medium and complicated tools. The reactions

that occurred in this work are shown at Eqs. (1) and (2).

CaCl2 þ 2NaOH ! CaðOHÞ2 þ 2NaCl (1)

Calcination
CaðOHÞ2 ! CaO þ H2 O (2)

So this method can be used as a simple, cheap and convenient

way for producing calcium oxide and hydroxide nanoparticles at
an industrial large scale.

2. Materials and methods

CaCl22H2O (Scharlua), NaOH (Shiminab, Iran, 98%), distilled

water and argon with purity of 99% were used in the experiments.
All of the chemicals were of analytical grade. Precursor [Ca(OH)2]
was prepared by addition of 1 and 2 M NaOH aqueous solution to a
0.5 M calcium chloride aqueous solution drop wise with vigorous Fig. 1. X-ray patterns of Ca(OH)2 as precursor (a) precursor #1 and (b) precursor #2.
stirring (1300 rpm) at 80 8C, while the inert gas (argon) was
flowing on the solution surface. Over time, the white precipitate of
calcium hydroxide was produced and the reaction stopped at particle size of nano-particles were further investigated by a
pH = 11.2. The precipitate was then collected by filtration and scanning electron microscope (SEM, Tescan Vega-II) and transmis-
rinsed five times with warm distilled water and dried at desiccator sion electron microscopy (TEM, PHILIPS CM20).
for several hours. A small fraction of the produced powder was
used for analysis and the rest was calcined in a muffle furnace at
650 8C for 1 h under N2 atmosphere at a heating rate of 5 8C/min. 3. Results and discussion
The obtained precursor which was produced by 0.5 M CaCl2 and
1 M NaOH, will be referred hereinafter as ‘‘precursor #1’’, and that X-ray diffraction patterns of Ca(OH)2 samples are presented in
was 0.5 M CaCl2 and 2 M NaOH will be named as ‘‘precursor #2’’. Fig. 1. All the diffraction peaks in Fig. 1a and b are consistent with
And, the obtained CaO powders after calcinations will be referred the standard structure of Ca(OH)2 (Portlandite, JCPDS card No. 00-
hereinafter as ‘‘powder #1’’ (from precursor #1) and ‘‘powder #2’’ 004-0733) with hexagonal crystal system and lattice parameters
(from precursor #2). The crystalline structure of Ca(OH)2 and CaO (a = 3.5956 Å, b = 3.5956 Å, c = 4.9280 Å).
nanoparticles were characterized by X-ray diffraction (XRD, According to thermogravimetric (TG) analysis (Fig. 2), there
PHILIPS, X’pert-MPD system, l = 1.54 Å). Thermal behavior for were three weight losses from 43 to 375 8C, 375 to 480 8C and 480
the precursor was studied through thermogravimetric analysis to 650 8C. These three weight losses were correspond to the
(TGA–DSC), which was performed with a STA409PG under vaporization of physically adsorbed water, the decomposition of
nitrogen flow. IR spectra were recorded in the 400–4000 cm1 Ca(OH)2 to CaO, and the decomposition of CaCO3 to CaO,
range with a resolution of 4 cm1, using Bruker tensor 27 FTIR respectively. The main weight loss of 25% related to transformation
spectrometer with RT-DLATGS detector and KBr pellet technique. of Ca(OH)2 precursor to CaO phase was well corresponded with the
The specific surface area, pore volume and pore diameter of calculated weight loss from Eq. (2) (24.3 wt.%). Differential
samples were conducted by nitrogen physisorption using the scanning calorimeter (DSC) analysis (Fig. 2) also showed three
Brunaure–Emett–Teller (BET). The morphology and average endothermic peaks. The larger peak at 463.8 8C was due to

Fig. 2. TGA–DSC curves of the Ca(OH)2 nano-particles from 25 to 1000 8C.

 Z. Mirghiasi et al. / Journal of Industrial and Engineering Chemistry 20 (2014) 113–117 115

Transmiance (%)
(b)
(a)

4000 3500 3000 2500 2000 1500 1000 500 0

wave number (cm-1)

Fig. 4. FT-infrared spectra of Ca(OH)2 for (a) precursor #1 and (b) precursor #2.

Fig. 3. X-ray patterns of CaO nanoparticles (a) powder #1 and (b) powder #2.

(a)
transformation of Ca(OH)2 to CaO phase (Eq. (2)) and two tiny

Transmiance (%)
peaks at about 100 8C and 650 8C were related to the vaporization
of physically adsorbed water and the decomposition of CaCO3 to (b)
CaO, respectively which is in agreement with TG results. According
to DSC results, decomposition temperature of CaCO3 (650 8C) is
higher than Ca(OH)2 (463.8 8C), so calcination temperature for the
precursor was considered 650 8C. Also very low height of the third
peak confirms minor amounts of CaCO3 at Ca(OH)2 phase.
From Fig. 3a and b was observed that when the precursors
[Ca(OH)2] were heated at 650 8C for 1 h, they decomposed easily
into CaO (lime, syn, JCPDS card No. 00-004-0777) with cubic crystal
4000 3500 3000 2500 2000 1500 1000 500 0
system and lattice parameters (a = 4.8105 Å). Some calcite peaks
[CaCO3] presented in the XRD pattern of Figs. 1 and 3, illustrated wave number (cm-1)
rapid carbonation of Ca(OH)2 and CaO by atmospheric CO2.
Fig. 5. FT-infrared spectra of CaO nano-particles for (a) powder #1 and (b) powder
Literature reported that carbonation reaction occurs very fast for #2.
Ca(OH)2 and CaO [20] and carbonation rate increases with
increasing specific surface area [20,21]. This shows the high
potential of these nanoparticles for capturing greenhouse gas CO2
from air [6]. to reduce some related peaks of carbonate group compared to
The mean crystallite size of CaO nano-particles was calculated previous studies [9,14,15,17]. It indicate more purity of produced
using Scherrer’s equation (Eq. (3)) to be about 40 and 41 nm for Ca(OH)2 phase at this work.
powder #1 and powder #2 respectively. Fig. 5a and b shows the FT-infrared (FTIR) spectrum of the CaO
for powder #1 and powder #2, respectively. At Fig. 5a and b the
0:9l
D¼ (3) strong band at 3647 cm1 corresponds to the O–H bonds from the
bcosu remaining hydroxide [4,9,14] or from water molecules on the
where D is the mean crystalline size (nm), l is the wavelength of Cu external surface of the samples during handling to record the
Ka (0.154 nm), b is the full width at half maximum intensity spectra [19]. The broad band around 1400–1500 cm1, as well as a
(FWHM) in radian and u is the Bragg angle (). weak band at 873 cm1 indicates the C–O bond related to
Fig. 4a and b shows the FT-infrared (FTIR) spectrum of the carbonation of CaO nanoparticles [4,9,14]. The strong band at
Ca(OH)2 for precursor #1 and precursor #2, respectively. Fig. 4a, 557 cm1 identified vibration of the Ca–O bond [4]. There is a tiny
shows a sharp absorption peak at 3645 cm1 related to hydroxyl dip in the spectra at 2359 cm1 due to the presence of atmospheric
group (OH–) stretching mode [9,15,19,22], and the peak at CO2 [24].
1473 cm1 correspond to the out of plane bending of CO32 in The specific surface areas (aBET), mean pore diameter and pore
CaCO3 [9,14,23]. These peaks are also observed in Fig. 4b. Synthesis volume of samples are presented in Table 1. Since the mean pore
of Ca(OH)2 were carried out under atmospheric air and more diameters of synthesized materials are between 2 and 50 nm, so
carbonate peaks were observed at the FTIR spectrum (no shown). the nanoparticles are in the mesopores range and can be used as
Then the experiments were done under inert gas (argon) which led catalyst, energy storage, adsorption, gas sensing, etc [25].

Table 1
BET surface area, mean pore diameter and pore volume of Ca(OH)2 and CaO.

Sample Surface area (m2 g1) Mean pore diameter (nm) Pore volume (cm3 g1)

Precursor #1 14.05 18.932 0.066

Precursor #2 19.30 18.594 0.089
Powder #1 13.86 11.999 0.041
Powder #2 21.08 14.100 0.074
116 Z. Mirghiasi et al. / Journal of Industrial and Engineering Chemistry 20 (2014) 113–117

Fig. 6. SEM images of (a) precursor #1, (b) precursor #2, (c) powder #1 and (d) powder #2.

Fig. 7. TEM image and the particle size distribution of powder #1 (a, c) and powder #2 (b, d).
 Z. Mirghiasi et al. / Journal of Industrial and Engineering Chemistry 20 (2014) 113–117 117

The SEM images of nanoparticles are illustrated in Fig. 6. Fig. 6a Acknowledgments

and b shows that the morphology of the Ca(OH)2 nano-particles are
hexagonal platelets with the average surface diameter of 135 and We would like to acknowledge the Research and Development
143 nm and thickness of 35 and 40 nm for precursor #1 and Division Center of Sarcheshmeh Copper Complex for financial
precursor #2, respectively. Fig. 6c and d shows that after support and also Mr. Ali Behrad Vakylabad for his great assistance.
calcination, hexagonal plates of Ca(OH)2 are converted to smaller
nano-particles CaO with approximately spherical morphology. References
However, some of the Ca(OH)2 nano-structures have not been able
[1] G. Oskam, Sol–Gel Science and Technology 37 (2006) 161.
to be completely converted which may be because of insufficient
[2] C. Ngamcharussrivichai, W. Meechan, A. Ketcong, K. Kangwansaichon, S. Butnark,
heating time. Also some CaO particles are sintered during Journal of Industrial and Engineering Chemistry 17 (2011) 587.
calcination as indicated in the SEM images (Fig. 6c and d). [3] Z. Tang, D. Claveau, R. Corcuff, K. Belkacemi, J. Arul, Materials Letters 62 (2008)
Fig. 7a and b shows TEM images of CaO nanoparticles with 2096.
[4] A. Roy, J. Bhattacharya, International Journal of Nanoscience 10 (2011) 413.
spherical shape. Particle size distributions of CaO nanoparticles are [5] M.A. Alavi, A. Morsali, Journal of Experimental Nanoscience 5 (2010) 93.
given in Fig. 7c and d by counting about 50 particles from TEM [6] Y. Zhu, S. Wu, X. Wang, Chemical Engineering Journal 175 (2011) 512.
images. Both particle size distributions are wide and the average [7] H.K. Park, M.W. Bae, I.H. Nam, S.G. Kim, Journal of Industrial and Engineering
Chemistry 19 (2013) 633.
particle sizes were obtained about 90 and 94 nm for powder #1 [8] S. Assabumrungrat, P. Sonthisanga, W. Kiatkittipong, N. Laosiripojana, A. Arporn-
and powder #2, respectively. The difference between XRD and TEM wichanop, A. Soottitantawat, W. Wiyaratn, P. Praserthdam, Journal of Industrial
results are because of XRD shows crystalline size of particles while and Engineering Chemistry 16 (2010) 785.
[9] T. Liu, Y. Zhu, X. Zhang, T. Zhang, T. Zhang, X. Li, Materials Letters 64 (2010) 2575.
TEM shows grain size of particles. [10] G. Patel, U. Pal, S. Menon, Separation Science and Technology 44 (2009) 2806.
[11] N.A. Oladoja, I.A. Ololade, S.E. Olaseni, V.O. Olatujoye, O.S. Jegede, A.O. Agunloye,
Industrial and Engineering Chemistry Research 51 (2012) 639.
4. Conclusion [12] M.A. Alavi, A. Morsali, Chapter 9, in: Y. Masuda (Ed.), Nanocrystal, InTech under CC
BY-NC-SA 3.0 license, 2011, pp. 237–262. , http://dx.doi.org/10.5772/16431.
[13] L.A. Pe’rez-Maqueda, L. Wang, E. Matijevic, Langmuir 14 (1998) 4397.
This study showed that CaO nano-particles can be produced by [14] B. Salvadori, L. Dei, Langmuir 17 (2001) 2371.
direct thermal-decomposition of Ca(OH)2 as precursor, at 650 8C [15] A. Roy, J. Bhattacharya, Micro & Nano Letters 5 (2010) 131.
for 1 h. The SEM images of CaO nano-particles showed that the [16] M. Ambrosi, L. Dei, R. Giorgi, C. Neto, P. Baglioni, Langmuir 17 (2001) 4251.
[17] A. Nanni, L. Dei, Langmuir 19 (2003) 933.
particles were nearly spherical in morphology. The mean particle [18] T. Sato, J.J. Beaudoin, V.S. Ramachandran, L.D. Mitchell, P.J. Tumidajski, Advances
sizes of CaO nano-particles determined by TEM analysis were 90 in Cement Research 19 (2007) 1.
and 94 nm for 1 and 2 M NaOH, respectively. The BET results [19] M. Ghiasi, A. Malekzadeh, Crystal Research and Technology 47 (2012) 471.
[20] K.V. Balen, Cement and Concrete Research 35 (2005) 647.
indicated that the porosity of prepared nano-particles was in the
[21] V. Nikulshina, M.E. G’alvez, A. Steinfeld, Chemical Engineering Journal 129 (2007)
mesopore range and the particles could be used as catalysis and gas 75.
sorbent. The proposed method does not require organic solvents, [22] P. Lagarde, M.A.H. Nerenberg, Y. Farge Lagarde, Physical Review B 8 (1973) 1731.
long time, expensive raw materials, and complicated equipment. [23] M.A. Lejodi, D. Waal, J.H. Potgieter, S.S. Potgieter, Minerals Engineering 14 (2001)
1107.
So, this method could be used as a simple and convenient route in [24] E. Darezereshki, Materials Letters 64 (2010) 1471.
production of CaO nano-particles at the large scale. [25] Y. Ren, Z. Ma, P.G. Bruce, Chemical Society Reviews 41 (2012) 4909.