Preparation of NiO nanoparticles from metal-organic frameworks via a solid-state decomposition route

Article abstract of DOI:10.1016/j.ica.2009.04.025

This study focuses on the preparation and characterization of single phase NiO nanoparticles. At first, nickel-o-phthalate complexes as precursor were synthesized through semisolid phase reaction method and then NiO nanoparticles were obtained via a solid

Full text of DOI:10.1016/j.ica.2009.04.025

Inorganica Chimica Acta 362 (2009) 3691–3697
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Preparation of NiO nanoparticles from metal-organic frameworks via a
solid-state decomposition route
a,b,*
, Fatemeh Mohandes , Fatemeh Davar a,b, Mehdi Mazaheri c,
b
Masoud Salavati-Niasari
d
e
Majid Monemzadeh , Nooshin Yavarinia
Institute of Nano Science and Nano Technology, University of Kashan, P.O. Box 87317-51167, Kashan, Islamic Republic of Iran
Department of Chemistry, University of Kashan, P.O. Box 87317-51167, Kashan, Islamic Republic of Iran
Materials and Energy Research Center, P.O. Box 14155-4777, Tehran, Islamic Republic of Iran
Department of Physics, University of Kashan, P.O. Box 87317-51167, Kashan, Islamic Republic of Iran
Department of Materials Science, Science and Research Branch, Islamic Azad University, Tehran, Islamic Republic of Iran
a
b
c
d
e
a r t i c l e i n f o
a b s t r a c t
Article history:
This study focuses on the preparation and characterization of single phase NiO nanoparticles. At first,
nickel-o-phthalate complexes as precursor were synthesized through semisolid phase reaction method
and then NiO nanoparticles were obtained via a solid-state decomposition procedure of layered coordi-
Received 1 March 2009
Received in revised form 4 April 2009
Accepted 17 April 2009
Available online 3 May 2009
2 2 2
nation nickle-o-phthalate complexes formulated as [Ni(pht)(H O) ] and [Ni(pht) ]. In addition, the effects
of calcination temperature and metal-to-ligand ratio on the particle size and morphology of NiO were
investigated. Thermogravimetric analysis (TGA) was applied to determine the thermal behavior of com-
plexes. The crystalline structure of products by X-ray diffractometer (XRD), morphology of particles by
scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were studied. The
composition of as-prepared sample was studied by X-ray photoelectron spectroscopy (XPS) spectra.
Analysis of FT-IR spectra confirmed the composition of products. The magnetic property was studied with
vibrating sample magnetometer (VSM).
Keywords:
Nanoparticles
Nickel oxide
Solid-state synthesis
Chelating ligand
Phthalate
Ó 2009 Elsevier B.V. All rights reserved.
1
. Introduction
There is considerable scientific and technological interest in
viewed [8,9]. Dry thermal decomposition, precipitation and
combustion routes from aqueous solutions, for the synthesis of
high surface area metal oxides have been investigated by Hage-
meyer and co-workers [10]. In their work, common and readily
available metal precursors such as carbonate, acetate, oxalate, cit-
rate, etc. were used without making use of expensive templates,
surfactants or alcoholic solvents or supercritical drying or high
pressure equipment. Also, the Pechini or citrate method [11–13]
has already been reported which involves combining a metal pre-
cursor with water, citric acid and a poly hydroxyl alcohol such as
ethylene glycol. Sol–gel [14] and sonochemical [15] techniques
are considered as advancing method for preparation of nano metal
oxides. Present work reports the synthesis of NiO nanoparticles
using solid-state decomposition method. Solid-state decomposi-
tion is introduced as one type of the thermal decomposition pro-
cesses in dry condition under air atmosphere. Hydrothermal,
solvothermal and thermal decomposition using organic solvent
or surfactant [4,16] carry out under vigorous controlled conditions
but the choice of suitable metal precursor and calcination temper-
ature are known as key factors in solid-state decomposition.
The preparation of metal oxide nanostructures through thermal
decomposition of complexes opens a new view for chemists since
there are many advantages in it such as: control of process condi-
tions, particle size, particle crystal structure, and purity. Recently,
the synthesis of various metal and metal oxide nanoparticles by
developing nanostructure metal oxides. High surface area metal
oxides with the size of 1–100 nm are desirable absorbents, carriers
and catalysts. One of the most commonly used metal oxides for a
wide range of applications is NiO. Nano-structured NiO is intro-
duced as p-type semiconductor with stable wide band gap (3.6–
4
.0 eV) [1], although, bulk NiO is an antiferromagnetic insulator
with a Néel temperature (T ) of 523 K [2]. Important applications
N
of nano-sized NiO include preparation of cathode materials of alka-
line batteries [3], electrochemical capacitors [4], smart windows
[
5] and active layer for gas sensors [6]. Yan and co-workers have
studied the catalytic activity of NiO nanoparticles in pyrolyzing
biomass components and they found due to the different effects
in terms of volume, quantum size, surface and macroscopic quan-
tum tunnel, NiO nanoparticles contain many important properties
over those of bulk and micro-NiO particles [7]. The various tradi-
tional synthetic methods of inorganic nanoparticles have been re-
*
Corresponding author. Address: Institute of Nano Science and Nano Technology,
University of Kashan, P.O. Box 87317-51167, Kashan, Islamic Republic of Iran. Tel.:
+98 361 5555 333; fax: +98 361 5552935.
E-mail address: salavati@kashanu.ac.ir (M. Salavati-Niasari).
0
020-1693/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2009.04.025

3
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M. Salavati-Niasari et al. / Inorganica Chimica Acta 362 (2009) 3691–3697
thermal decomposition process successfully has been reported
17–23].
Recently, metal-benzenedicarboxylate complexes are used as
potential O-banded precursors for the synthesis of metal oxides.
It has been found that some complexes which have chain-like or
tube-like metal-organic framework architecture such as metal-
X-ray diffractometer using Ni-filtered Cu K
a radiation. Elemental
[
analysis were obtained from Carlo ERBA Model EA 1108 ana-
lyzer. Scanning electron microscopy (SEM) images were obtained
on Philips XL-30ESEM equipped with an energy dispersive X-ray
spectroscopy. Transmission electron microscopy (TEM) images
were obtained on a Philips EM208 transmission electron micro-
scope with an accelerating voltage of 100 kV. Fourier transform
infrared (FT-IR) spectra were recorded on Shimadzu Varian
4300 spectrophotometer in KBr pellets. X-ray photoelectron
spectroscopy (XPS) of the as-prepared products were measured
on an ESCA-3000 electron spectrometer with monochromatized
1
,4-benzenedicarboxylate (p-BDC or terphthalate) can be used as
precursor to grow 1D nano-sized structure material [24]. Duffy
and co-workers have reported the synthesis of nano-sized ZnO from
Zn-1,3-benzenedicarboxylate (m-BDC or isophthalate) [25]. Among
o-phthalate, isophthalate and terphthalate complexes, o-phthal-
ate(1,2-benzenedicarboxylate) ones have lower thermal stability
Mg Ka X-ray as the excitation source. Thermogravimetric-differ-
[
26]. The lower thermal stability of the o-phthalate complexes
ential thermal analysis (TG-DTA) was carried out using a ther-
mal gravimetric analysis instrument (Shimadzu TGA-50H) with
a flow rate of 20.0 ml/min and a heating rate of 10 °C/min.
The magnetic measurement was carried out in a vibrating sam-
ple magnetometer (VSM) (BHV-55, Riken, Japan) at room
temperature.
can be justified by considering that the two carboxylate groups of
the o-phthalate both interact with the same metal ion giving a che-
late seven membered ring that stabilizes the complex, increasing
the intramolecular and decreasing the intermolecular bonds with
a consequent decrease in the thermal stability. Therefore, this dis-
tinct character is considered as a wonderful parameter for selecting
the o-phthalate complexes because decomposition process is oc-
curred in lower temperature compared to terphthalate and iso-
phthalate ones. Here, Ni-o-phthalate complexes were synthesized
by semisolid phase reaction method. There are many advantages
in it such as: saving time and energy, free organic solvent, using
cheap available chemicals, the surface area of solid particle can be
efficiently utilized, heat exchange is very good, local overheating
can be avoided and the reaction temperature is easy to control.
2 2 2
2.2. Synthesis of [Ni(pht)(H O) ] and [Ni(pht) ]
Nickel(II) acetate tetrahydrate and o-phthalic acid (C
8
8 4
H O )
were fully mixed by grinding in 1:1 and 1:2 molar ratio and about
2 ml distilled water was added. Above mixture was ground for
15 min. The resultant semisolid-state mixture was heated and
dried at 80, 90 and 100 °C for 4 h. The results of XRD pattern and
FT-IR spectroscopy showed that the optimum reaction tempera-
ture for the forming of Ni-o-phthalate had been at 100 °C. There-
fore, green pure crystalline [Ni(pht)(H
obtained in Ni/pht = 1:1 and 1:2 at 100 °C, respectively. (Anal. Calc.
for [Ni(pht)(H O) ]; NiC : C, 37.12; H, 3.12; Ni, 22.68. Found:
C, 37.09; H, 3.10; Ni, 22.65% and Anal. Calc. for [Ni(pht) ]; Ni-
: C, 49.67; H, 2.08; Ni, 15.17. Found: C, 49.64; H, 2.05;
Ni, 15.13%).
2 2 2
O) ] and [Ni(pht) ] were
2
. Experimental
2
2
8 8 6
H O
2.1. Materials and physical measurements
2
16 8 8
C H O
All chemicals were of reagent grade and were used as re-
ceived. XRD patterns were recorded by a Rigaku D-max C III,
Scheme 1. Schematic diagram illustrating the formation of NiO nanoparticles.

M. Salavati-Niasari et al. / Inorganica Chimica Acta 362 (2009) 3691–3697
3693
2.3. Synthesis of NiO nanoparticles
in Fig. 1a thermal decomposition of [Ni(pht)(H
2 2
O) ] takes place
in two steps. In the first step, at 110–210 °C, it loses the two coor-
The as-prepared Ni-o-phthalate complexes were loaded in to a
dination water molecules and next, the anhydrous salt decomposes
platinum crucible and then it was placed in oven and heated at a
2
to NiO at 320–420 °C. According to Fig. 1b anhydrous [Ni(pht) ]
rate of 5 °C/min in air. NiO nanoparticles were synthesized at
salt decomposes at 260–440 °C. These findings suggest the solid-
state decomposition takes place in the range of 400–450 °C. There-
fore, the choice of suitable calcination temperature is highly
dependent on the results of TG analysis.
5
00 and 700 °C (Scheme 1).
3
. Results and discussion
Fig. 2a shows the FT-IR spectrum of the o-phthalic acid with
2
point group C . Ring vibrations have been divided into: tangential,
2 2
Fig. 1a and b show the TGA curves of [Ni(pht)(H O) ] and
Ni(pht) ] heated at a heating rate of 5 ° min in air. As shown
2
ꢀ1
radial and out-of-plane vibrations. All distinct absorption peaks
were illustrated in Table 1 and every absorption peak was assigned
to corresponding vibration [25]. Fig. 2b shows the FT-IR spectrum
[
2 2
of [Ni(pht)(H O) ] obtained at 100 °C. The broad absorption band
Table 1
FT-IR absorption peaks of o-phthalic acid.
3
2
2
009 (wb)
650 (w)
525 (w)
20b;
v
(CH) A
1068 (s)
1005 (w)
975 (w)
907 (sb)
830 (w)
797 (s)
738 (s)
672 (s)
555 (m)
421 (m)
9b;d(CH) B
5; (CH) A
10a; (CH) B
(OH) B
12;d(CC) B
(OCO) A
11; (CH)
4; (CC) A
6a;d(CC) A
r(OCO) B
v
v
v
v
(C–O)a
(C–O)a
g
+ d(OH)b
u
;B
;B
;A
u
c
g
+
v
(C–O)b
u
u
c
(C@O)a
(C@O) B
(C–C) A
19b; (C–C) A
d(OH) B
(C–O) B
15;d(CH) A
g
+
c
(OH)a
u
u
c
g
1698 (sb)
1585 (s)
1495 (m)
1402 (s)
1277 (s)
1147 (m)
u
8a;
v
c
u
v
c
2 2 2
Fig. 1. TG curves of (a) [Ni(pht)(H O) ] and (b) [Ni(pht) ] in air.
u
c
v
u
u
Fig. 2. FT-IR spectra of (a) o-phthalic acid, (b) [Ni(pht)(H
Ni(pht) ] obtained at 100 °C and (d) NiO nanoparticles.
2
O)
2
] obtained at 100 °C, (c)
Fig. 3. XRD patterns of [Ni(pht)(H
2 2
O) ] obtained at(a) 80, (b) 90, (c)100 °C and (d)
[
2
[Ni(pht) ] obtained at 100 °C.
2

3
694
M. Salavati-Niasari et al. / Inorganica Chimica Acta 362 (2009) 3691–3697
ꢀ
1
centered at 3423 cm is attributable to the
v
(OH) stretching vibra-
fraction peaks in the XRD pattern. Ni-o-phthalate structure may be
regarded as an amorphous cross-linked polymer contained of
bidentate ligand in which some interchange of bonding or spatial
rearrangement of ligands, can probably occur at this reaction tem-
tions which indicates the presence of physisorbed and coordinated
water linked to precursor [27–29]. This spectrum has no broad
absorption bands at 3260–3200 cm and a sharp band at 1630–
ꢀ1
ꢀ1
1
600 cm . Therefore, there are not crystallization water mole-
2 2
perature [33]. Fig. 3b introduces the XRD pattern of [Ni(pht)(H O) ]
ꢀ
1
cules in the outer sphere [30]. The C@O band at 1698 cm in
the FT-IR spectrum of the o-phthalic acid does not appear in the
precursor one which indicates the absence of uncoordinated o-
phthalic acid in precursor. Two very strong peaks at 1556 and
414 cm can be attributed to the asymmetric and symmetric
stretching vibrations of coordinated carboxylate groups. The sepa-
ration between the asymmetric and symmetric stretching frequen-
obtained at 90 °C. In this case, an amorphous phase was changed
into a crystalline phase with increasing temperature but some
impurities are still available. When this pattern was compared to
the XRD pattern of o-phthalic acid (JCDPS No. 02–0468) and
ꢀ1
1
[Ni(CH
3
COO)
2
]ꢁ4H
2
O (JCDPS No. 26–1282), it was found impurity
peaks are due to residual starting materials which have not reacted
together completely. By increasing temperature from 90 to 100 °C,
ꢀ1
cies (
D
v =
v
asym
ꢀ vsym) is 142 cm which indicates the o-phthalic
acid ligand is bidentate coordinating through both carboxylic
ꢀ
1
groups [31]. The weak peaks at 1486 and 1359 cm correspond
ꢀ1
to
(CH) and the weak peak at 1143 cm is attributable to d(CH) of
benzene ring and all of remaining weak peaks are due to benzene
ring vibrations. The FT-IR spectrum of [Ni(pht) ] obtained at 100 °C
is similar to [Ni(pht)(H O) ] one that is shown in Fig. 2c. The FT-IR
spectrum of NiO nanoparticles is shown in Fig. 2d. The intense
v(CC) and medium peaks at 734 and 695 cm is assigned to
ꢀ1
c
2
2
2
ꢀ1
peak at 430 cm is assigned to stretching mode of NiO [32]. This
spectrum has no characteristic peaks of impurities or other precur-
sor compounds.
Fig. 3 shows XRD pattern of [Ni(pht)(H
and 100 °C, respectively in the range 0 < 2h < 50. As shown in
Fig. 3a, when the semisolid mixture of [Ni(CH COO) O and
2 2
O) ] obtained at 80, 90
3
2
]ꢁ4H
2
o-phthalic acid as starting materials were heated at 80 °C, an amor-
phous solid was formed as illustrated by the disappearance of dif-
Fig. 4. XRD patterns of NiO nanoparticles.
Fig. 5. SEM images of NiO nanoparticles.

M. Salavati-Niasari et al. / Inorganica Chimica Acta 362 (2009) 3691–3697
3695
all impurities disappeared and
a
pure crystalline phase
of NiO (JCDPS No. 71–1179) without detectable impurities. XRD
peaks are markedly broad at relatively lower temperature
(T = 500 °C) which suggests that the particle size of as-calcined
NiO increases with increasing the calcination temperature .It can
be seen that all particles are grown slowly with the increase of
[
Ni(pht)(H O) ] was obtained. Fig. 3c was also compared to the
2
2
XRD pattern of magnesium phthalate dihydrate which have al-
ready been reported [34]. According to the reported results, it is
considered the [Ni(pht)(H O) ] complex crystallizes in a layered
2 2
structure. In Fig. 3c, it can be seen that the intensity of first strong
2
temperature. All these results are observed about [Ni(pht) ] with
diffraction peak (h = 6.5) is very more than the second one
Ni/pht = 1:2 (see Fig. 4c and d). In order to further investigation,
the crystallite size of NiO was calculated from the major diffraction
peak of the corresponding NiO (2 0 0) using the Debye–Scherrer
formula [35].
(
h = 30.85). The layered structure contains the plans of Ni ions
which are surrounded by benzene rings on two sides of Ni ion
planes. After all results about [Ni(pht)(H O) ], we synthesized
] using starting materials at 100 °C. The XRD pattern of
] is shown in Fig. 3d. On the basis of above results, the
] confirms that the structure of [Ni(pht)
2
2
[
[
Ni(pht)
Ni(pht)
2
D ¼ 0:89k=bcosh
2
0
XRD pattern of [Ni(pht)
2
2
]
where k is the wavelength of X-ray (1.5418 ÅA ) for Cu ka radiation,
is layered because the intensity of first strong diffraction peak is
very more than the second one.
The effects of calcination temperature and nickel(II) acetate tet-
rahydrate to o-phthalic acid (Ni/pht) ratio on the structure proper-
ties and particle size of NiO powders were investigated by using
XRD in the range 10 < 2h < 80. Fig. 4 shows the XRD pattern of
b full width at half maximum, FWHM of prominent intensity peak
(using the 100% relative intensity peak will be used), h peak posi-
tion. The estimated grain sizes using Debye–Scherrer formula were
2 2
NiO obtained from [Ni(pht)(H O) ] with Ni/pht = 1:1. All peaks
can be well indexed to the cubic lattice with a Fm–3m space group
Fig. 7. XPS spectra of Ni 2p and O 1s of NiO nanoparticles.
Fig. 6. TEM images of NiO nanoparticles.
Fig. 8. Magnetization vs. applied at 300 K for NiO nanoparticles.

3
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M. Salavati-Niasari et al. / Inorganica Chimica Acta 362 (2009) 3691–3697
Table 2
Comparison of particle size of NiO in several works.
Precursor
Method
Calcination temperature
°C)
Calcination
time (h)
Particle size (nm)
(according to XRD results)
(
Nickel citrate [15]
ultrasonic spray pyrolysis
thermal decomposition
solid-state decomposition
500
00
500
00
500
00
2
2
2
2
2
2
22.0
54.0
35.3
70.0
15.0
29.0
7
Nickel dimethylglyoximate [38]
7
2
Nickel phthalate [Ni(pht) ]
7
found to be about 24, 36, 15, 29 nm for Fig. 4a–d XRD patterns
respectively. According to the results of XRD, it is found that the
NiO prepared from Ni/pht = 1:2 precursor has lower grain size
especially at calcination temperature 500 °C (15 nm). We have al-
ready explained the effect of calcination temperature on grain size
of NiO but here, we investigate the effect of metal-to-ligand ratio
on the grain size of NiO. O-phthalic acid as a chelating ligand coor-
dinate to Ni ions, making the nucleation complete at the early
stage of the thermal decomposition process and inhibiting the
crystal growth. When metal-to-ligand ratio is 1:2, Ni ions are
capped completely with phthalate ligands. So that, the Ni ions
are protected against agglomeration, on the other hand, by
increasing the phthalate molecules around the metal, we can ob-
tain nanoparticles with the smallest size specially at lower calcina-
tion temperature.
was selected to form coordination compounds which is more suit-
able than m,p-phthalic acid for thermal decomposition processes.
The kinetic of thermal decomposition of phthalate complexes
was studied completely [26,30–34]. So far 26 different coordina-
tion types have been observed in crystal structures containing this
ligand [37] while this ligand is bidentate coordinating through
both carboxylic groups about [Ni(pht)(H O) ]and [Ni(pht) ] com-
plexes. The all complexes were synthesized according to a facile
semisolid phase reaction method. We compared our obtained re-
sults to several reports and the results are shown in Table 2.
According to these results, by solid-state decomposition of
2
2
2
[Ni(pht) ] complex, NiO nanoparticles were synthesized success-
2
fully with the smallest size.
4
. Conclusions
2 2 2
SEM images of the NiO obtained [Ni(pht)(H O) ] and [Ni(pht) ]
with Ni/pht = 1:1 and 1:2 at 500 and 700 °C also show morpholog-
ical changes. As shown in Fig. 5, the effects of calcination temper-
ature and Ni/pht ratio on the morphology of NiO are clearly
In summary, a simple and economical method to synthesize
NiO nanoparticles by solid-state decomposition of layered coordi-
nation nickle-o-phthalate precursors is developed. The all precur-
sor were synthesized via a semisolid phase reaction method.
With increasing the ligand to metal ratio and decreasing calcina-
tion temperature, the particle size becomes smaller without
agglomeration. We hope that the procedure mentioned in experi-
mental section can be a suitable route for large-scale synthesis of
nickle oxide nanomaterials.
2 2
observed. The micrograph of NiO obtained of [Ni(pht)(H O) ] with
Ni/pht = 1:1 at 500 °C shows that these particles are composed of
submicron-sized (ꢂ300 nm) primary particles which form second-
2
ary agglomerates. SEM image of NiO obtained of [Ni(pht) ] with Ni/
pht = 1:2 at 500 °C indicates that the nano-sized primary particles
are dispersed satisfactorily. On increasing the calcination tempera-
ture to 700 °C, the growth and agglomeration of particles occur.
In order to observe the detailed morphological differences of
the NiO that exhibit drastic changes at specific calcination temper-
ature, TEM images of nanoparticles were taken. On the other hand,
the particle size of NiO is estimated by TEM images. The NiO nano-
Acknowledgement
Authors are grateful to Council of University of Kashan for pro-
viding financial support to undertake this work.
2 2 2
particles obtained of [Ni(pht)(H O) ] and [Ni(pht) ] at 500 °C were
chosen for TEM analysis, which is presented in Fig. 6a. It can be ob-
served from Fig. 6a that NiO is made up of primary spherical par-
ticles which contain secondary ones with a diameter of ꢂ25 nm.
This diameter is close to the estimated crystallite size by XRD anal-
ysis (24 nm). Fig. 6b indicates that uniform spherical NiO nanopar-
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