Controlled synthesis of spherical α-Ni(OH)2 hierarchical nanostructures via a simple hydrothermal process and their conversion to NiO

Article abstract of DOI:10.1016/j.poly.2011.11.054

Hierarchical pure α-nickel hydroxide (α-Ni(OH)₂) nanostructures have been successfully synthesized through a one-step hydrothermal synthesis with nickel nitrate hexahydrate, ethylene-1,2-diamine (en) and hydrazine (N₂H₄) as morphology-directing agents. Optimum conditions to obtain high yield and phase pure α-Ni(OH) ₂ were identified by varying experimental parameters, such as the en and N₂H₄ concentration, and the reaction temperature. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and photoluminescence (PL) spectroscopy. For determination of the structural formula of such α-nickel hydroxides, Fourier transform infrared (FT-IR) spectra and thermogravimetric analysis (TGA) were carried out on the as-prepared products. These results indicated that the α-nickel hydroxide contains water molecules and anions. The hierarchical NiO nanostructures are obtained on annealing the α-Ni(OH)₂ nanostructures at 300 °C for 4 h. The magnetic properties of the as-prepared NiO nanostructures show a superparamagnetic behavior for the as-synthesized NiO nanostructures.

Full text of DOI:10.1016/j.poly.2011.11.054

Polyhedron 33 (2012) 302–309
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Controlled synthesis of spherical
a-Ni(OH) hierarchical nanostructures via a
2
simple hydrothermal process and their conversion to NiO
a,b,
⇑
, Maryam Entesari b
Masoud Salavati-Niasari
a
Institute of Nano Science and Nano Technology, University of Kashan, Kashan, P.O. Box 87317-51167, Islamic Republic of Iran
Department of Inorganic Chemistry, Faculty of Science, University of Kashan, Kashan, P.O. Box 87317-51167, Islamic Republic of Iran
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 25 July 2011
Accepted 22 November 2011
Available online 6 December 2011
Hierarchical pure
through a one-step hydrothermal synthesis with nickel nitrate hexahydrate, ethylene-1,2-diamine (en)
and hydrazine (N ) as morphology-directing agents. Optimum conditions to obtain high yield and
phase pure -Ni(OH) were identified by varying experimental parameters, such as the en and N con-
2
a-nickel hydroxide (a-Ni(OH) ) nanostructures have been successfully synthesized
2 4
H
a
2
2 4
H
centration, and the reaction temperature. The products were characterized by X-ray diffraction (XRD),
scanning electron microscopy (SEM), transmission electron microscopy (TEM), and photoluminescence
Keywords:
Nickel hydroxide
Nickel oxide
Chemical synthesis
Hierarchical structure
Hydrothermal
(
PL) spectroscopy. For determination of the structural formula of such
form infrared (FT-IR) spectra and thermogravimetric analysis (TGA) were carried out on the as-prepared
products. These results indicated that the -nickel hydroxide contains water molecules and anions. The
hierarchical NiO nanostructures are obtained on annealing the -Ni(OH) nanostructures at 300 °C for
h. The magnetic properties of the as-prepared NiO nanostructures show a superparamagnetic behavior
for the as-synthesized NiO nanostructures.
a-nickel hydroxides, Fourier trans-
a
a
2
4
Ó 2011 Elsevier Ltd. All rights reserved.
1
. Introduction
In view of these advantages, the synthesis of phase pure
-Ni(OH) and its stabilization in alkali solutions have attracted
a
2
Hierarchical nano/micro-structures with specific morphologies
many researchers and mixed results have been reported. The
have fascinated scientists all over the world because of their
sophisticated architectures, which are expected to provide some
unique and exciting properties [1–3].
Nickel hydroxide is widely used in many applications, from
power tools to portable electronics and electric vehicles. There
are two polymorphs of nickel hydroxide, which are designated as
formation of mixed phases by homogeneous precipitation of nickel
salts in the presence of (NH
haye-Vidal and Figiarz [11] precipitated the
nickel nitrate solutions with NH [12]. Al-substituted
2
)
2
CO has been reported [10]. Dela-
-phase from aqueous
-Ni(OH)
a
3
a
2
was prepared by Zhao et al. [13] in the presence of surfactants such
as Tween-20 and polyvinyl alcohol at 90 °C; the particles were
a
-Ni(OH)
2
and b-Ni(OH)
2
, respectively. The
a
-Ni(OH)
2
phase dis-
58–283 nm in size. Electrochemical impregnation of the
into sintered nickel plates was shown to be temperature depen-
dent [14]; -Ni(OH) forms below 60 °C, but a mixed phase with
nickel oxyhydroxy nitrate forms above 60 °C. The most significant
work has been reported by Akine et al. [15], who hydrothermally
a-phase
plays a more disordered and larger interlayer spacing (47.5 Å) as
À
2À
2À
the interlamellar space contains anions, e.g., NO
and water molecules. The hexagonal b-Ni(OH) phase is composed
of brucite-like and well-oriented Ni(OH) layers which are per-
fectly stacked along the c-axis with an interlamellar distance of
.60 Å [4–6]. As an active material of the positive electrode of alka-
line rechargeable batteries, the performance of such batteries
highly depends on the size, morphology and phase of Ni(OH) . Con-
siderable work has been focused on the morphology-controllable
preparation of Ni(OH) and related composite materials [7–9].
3
, CO
3
, SO
4
a
2
2
2
synthesized
2 2 2
a-Ni(OH) at 90 °C with a concentration of (NH ) CO
4
that was 30 times higher than that of nickel nitrate and in the pres-
ence of the dispersant HPMC (hydroxyl propyl methyl cellulose).
The surface area of the particles was good with a submicrometre
range size and the yield was nominal.
Nickel oxide (NiO) is an antiferromagnetic oxide semiconductor
of the NaCl-type structure and is one of the most exhaustively inves-
tigated transition metal oxides. It is a promising candidate for many
applications, such as battery cathodes [16], catalysis [17], gas sen-
sors [18] and magnetic materials [19]. NiO is another material
which, being a wide bandgap p-type semiconductor (direct gap
2
2
⇑
Corresponding author at: Institute of Nano Science and Nano Technology,
University of Kashan, Kashan, P.O. Box 87317-51167, Islamic Republic of Iran. Tel.:
+98 361 591 2383; fax: +98 361 555 29 30.
3
.9 eV), can be employed for the fabrication of p–n heterojunctions
E-mail address: salavati@kashanu.ac.ir (M. Salavati-Niasari).
0
277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.11.054

M. Salavati-Niasari, M. Entesari / Polyhedron 33 (2012) 302–309
303
Table 1
Experimental conditions for the preparation of Ni(OH)
2
and NiO nanostructures.
Sample No.
Ni:en
N
H
2 4
(mL)
Time (h)
Temperature (°C)
1
2
3
4
5
6
7
8
9
0
1
2
3
4
1:4
1:3
1:2
1:4
1:4
1:4
1:4
1:4
1:4
1:4
1:4
1:4
1:4
1
1
1
2
3
12
12
12
12
12
12
12
12
12
12
12
6
180
180
180
180
180
180
180
180
200
160
120
180
0.5
0.25
0.125
1
1
1
1
1
1
1
1
1
1
18
180
Calcination sample No.1 at 300 °C for 4 h
with ZnO [20,21]. Although NiO nanostructures have been synthe-
sized by the hydrothermal method and the decomposition of
2. Experimental
Ni(OH)
2
[22], little research has been done on the optical and field
2.1. Materials and physical measurements
emission properties of NiO nanostructures.
In our group, for a few years, has been interested in the synthesis
of metal, metal oxide and metal sulfide nanoparticles, using new
inorganic precursors and taking benefit of the tools of organometal-
lic chemistry [23–28]. At present, the development of organometal-
lic or inorganic compounds for the preparation of nanoparticles is of
major interest [29–31]. Use of a novel compound can be helpful in
opening a new way for preparing nanomaterials and in controlling
the nanocrystal size, shape and distribution size.
All reagents used were commercial products of analytical pure
grade, and they were used without further purification. XRD pat-
terns were recorded by a Rigaku D-max C III, X-ray diffractometer
using Ni-filtered Cu
Ka radiation. Elemental analyses were
obtained from a Carlo ERBA Model EA 1108 analyzer. The composi-
tional analysis was done by energy dispersive X-ray (EDX, Kevex,
Delta ClassI). Fourier transform infrared (FT-IR) spectra were
recorded on a Shimadzu Varian 4300 spectrophotometer in KBr
pellets. Room temperature photoluminescence (PL) was studied on
an F-4500 fluorescence spectrophotometer. Thermogravimetric dif-
ferential thermal analysis (TG-DTA) was carried out using a thermal
gravimetric analysis instrument (Shimadzu TGA-50H) with a flow
Herein, we first report an easy method to synthesis hierarchi-
cally
synthesis with ethylene-1,2-diamine (en) and hydrazine (N
as morphology-directing agents. Furthermore, NiO nanostructures
were obtained by calcining the -Ni(OH) at 300 °C under
2
a-Ni(OH) nanostructures through a one-step hydrothermal
H )
2 4
À1
a
2
rate of 20.0 ml/min and a heating rate of 10 °C min . Scanning
ambient pressure. The optical properties of the as-prepared sam-
ples were also investigated with the help of photoluminescence
spectra.
electron microscopy (SEM) images were obtained on a Philips XL-
30ESEM equipped with an energy dispersive X-ray spectroscope.
Transmission electron microscopy (TEM) images were obtained on
2
Scheme 1. The proposed evolution process for the preparation of Ni(OH) and NiO nanostructures.

3
04
M. Salavati-Niasari, M. Entesari / Polyhedron 33 (2012) 302–309
a
Philips EM208 transmission electron microscope with an
b-Ni(OH)
indexed to a pure hexagonal
No diffraction peaks due to b-Ni(OH)
observed. The phases are indexed to the (003), (006), (009),
101) and (110) planes of -Ni(OH) with well-defined peaks at
2
and (c) NiO. All the diffraction peaks in Fig. 1a are well
-Ni(OH) phase (JCPDS 03-0177).
(JCPDS 14-0117) could be
accelerating voltage of 200 kV. The magnetic measurements were
carried out on a vibrating sample magnetometer (VSM) (BHV-55, Ri-
ken, Japan) at 300 K.
a
2
2
(
a
2
2
2.2. Preparation of spherical a-Ni(OH) hierarchical nanostructures
3 2 2
In a typical procedure, Ni(NO ) .6H O (1 mmol), ethylene-1,
2
-diamine (en) (4 mmol) and hydrazine hydrate (1 mL) were first
dissolved in distilled water (40 mL), and the solution was constantly
stirred for 15 min at room temperature. Then the solution was
transferred into a 50 mL Teflon-lined stainless steel autoclave. The
autoclave was sealed and maintained at 180 °C for 12 h and then
cooled to room temperature naturally. The product was filtered
off, washed with distilled water and ethanol for three times, and
finally dried in a vacuum oven at 60 °C for 4 h. Control experiments
were carried out by adjusting the reaction temperature (120–
1
(
80 °C), time of reaction (12–20 h) and the amount of N
0.25–3 mL), while keeping the other reaction parameters
unchanged (Table 1 and Scheme 1).
2 4 2
H .H O
2.3. Thermal conversion to NiO nanostructures
The obtained products were then calcined at 300 °C for 4 h in a
furnace under air to synthesize NiO. The black powder was col-
lected for characterization.
2
Fig. 2. Thermal gravimetric curve of b-Ni(OH) (sample No. 13).
3
. Results and discussion
3.1. XRD analysis of the products
Fig. 1 presents the typical XRD patterns of the (a) spherical
nickel hydroxide hierarchical nanostructures (sample No. 1), (b)
Fig. 1. XRD patterns of samples prepared under different conditions: (a) sample No.
Fig. 3. FTIR spectra of samples prepared under different conditions: (a) sample No.
1
, (b) sample No. 13 and (c) sample No. 14.
12 (b) sample No. 1, (c) sample No. 13 and (d) sample No. 14.

M. Salavati-Niasari, M. Entesari / Polyhedron 33 (2012) 302–309
305
9
.42, 4.73, 3.17, 2.70 and 1.55 Å. When the hydrothermal time was
3.3. FT-IR spectra of products
prolonged to 18 h (sample No. 13), a predominant well-crystalline
brucite-like phase of b-Ni(OH)
formed (Fig. 1b). However, when the reaction time was prolonged
to 18 h, the single phase of b-Ni(OH) was obtained from the trans-
formation of the metastable -Ni(OH) . All of the reflection peaks
of the XRD pattern of sample No. 13 (Fig 1b) can be indexed to
the pure hexagonal phase of b-Ni(OH) , with lattice constants
2
with a hexagonal structure was
IR spectroscopy is a useful tool to investigate the functional
groups of any organic molecule. Fig. 3a shows mixed characteris-
tics of Ni(en) and Ni(OH) , (sample No. 12). According to Fig. 3a,
2 2
2
a
2
we can conclude that 6 h are not long enough to prepare nickel
hydroxide. So, for the synthesis of the pure product we must pro-
long the reaction time to 12 h. Fig. 3b shows the IR spectrum of the
spherical nickel hydroxide hierarchical nanostructures (sample No.
2
a = 3. 128 Å, c = 4. 610 Å (JCPDS 14-0117). The typical peaks at
about d = 4.53, 2.68, 2.32, 1.75 and 1.56 Å can be assigned to the
À1
1). The narrow band at 3749 cm was attributed to the free hydro-
À1
(
001), (100), (101), (102) and (110) planes, respectively, and also
to the (111), (200), (103), (201) and (202) planes, indicating the
formation of pure -Ni(OH) [31,32]. Fig. 1c is the typical XRD pat-
tern of NiO obtained by calcining an -Ni(OH) sample at 400 °C
xyl groups, and the broad band at 3600–3400 cm represented
the hydroxyl groups and water molecules, which were extensively
À1
a
2
hydrogen bonded. The band at 1630 cm
corresponds to the
a
2
bending vibration of water molecules [37]. It can be seen from
À1
for 4 h under ambient pressure. The reflection peaks in Fig. 1c
can be indexed as cubic NiO phase (JCPDS 02-1216); the main dif-
fraction peaks were observed at 37.80°, 43.44°, 62.80°, 75.21° and
the strength of these two bands (1630 cm and the broad bands
À1
at 3600–3400 cm ) that the hierarchical nanostructures of nickel
hydroxide contain water molecules. The absorption around
À1
7
9.90°. The XRD pattern of sample No. 14 confirms that the formed
1485 cm is attributed to carbonate ions [38–40] due to the open
À1
material is nickel oxide. All the diffraction peaks can be indexed to
the pure NiO crystalline phase (space group: Fm3m). No obvious
reflection peaks assignable to impurities can be detected in
Fig. 1c, indicating the pure phase and good crystallinity of the pres-
ent samples.
system used in the synthesis. The bands around 648 and 480 cm
are due to the dOH and mNi–OH vibrations, individually [41]. Fig. 3c
shows a typical IR spectrum of b-Ni(OH)
and sharp peak at 3646 cm is because of the
2
, sample No. 13. A narrow
À1
mO–H stretching
vibration, which confirms the brucite structure of the b-Ni(OH)
2
À1
phase. Peaks at 3446 and 1632 cm are assigned to the
m(H
2
O)
3.2. Thermal gravimetric analysis
2
stretching vibration and d(H O) bending vibration of water mole-
cules adsorbed in the sample. The strong band at 515 cm corre-
À1
The b-Ni(OH)
ric analysis (TGA). The TG curve (Fig. 2) shows a weight loss of
8.9% at around 300 °C, which is equivalent to the calculated
weight loss (19.4%) of one H O molecule from b-Ni(OH) to NiO.
The XRD pattern of the calcined product, sample No. 14, (Fig. 1c)
can be indexed to NiO (JCPDS 02-1216) [33–36].
2
phase was also confirmed by thermal gravimet-
sponds to dO–H of hydroxyl groups. A small weak peak centered on
460 cm is assigned to the Ni–O stretching mode [42]. Fig. 3d
À1
1
shows an IR spectrum of NiO, sample No. 14. Metal oxides gener-
À1
ally give absorption bands below 1000 cm , arising from inter-
2
2
À1
atomic vibrations. The peak at 442 cm in the spectrum, showing
the Ni–O bond, gives clear evidence about the presence of the
Fig. 4. SEM images of samples prepared under different conditions: (a) sample No. 3, (b) sample No. 2 and (c and d) sample No. 1.

3
06
M. Salavati-Niasari, M. Entesari / Polyhedron 33 (2012) 302–309
À1
crystalline NiO. The broad peak at 3430 cm
in spectrum is
180 °C for 12 h. With 0.125 mL, (Fig. 5a), Ni(OH)
shape was formed. By increasing the amount of hydrazine to
0.25 mL, Ni(OH) nanorods were obtained (see Fig. 5b). To prepare
a spherical shape, the amount of hydrazine was increased to
.5 mL, with this amount of hydrazine, microspheres were formed
and already assembled into nanorods (Fig. 5c). Clearly, the Ni(OH)
spheres were made up of a few layers of nanorods. On increasing
the concentration of hydrazine, hierarchical Ni(OH) microspheres
2
without a clear
representative of H
2
O. Also, the H–OH bending vibration appears
À1
at 1631 cm
.
2
0
3
3
.4. SEM studies
2
.4.1. Effect of Ni:en molar ratio
2
Fig. 4 shows SEM images of samples prepared with different
will be finally formed from the assembly of the nanorods, as shown
in Fig. 4c and d. By increasing the hydrazine concentration to 2 and
molar ratios of Ni:en. By increasing the molar ratio of Ni:en from
:2 to 1:4, spherical nickel hydroxide hierarchical nanostructures
were obtained. At a Ni:en ratio of 1:2 (see Fig. 4a) some plates with
sizes bigger than 1 m were obtained. By increasing the concentra-
tion of ethylene diamine, microsphere nanostructures were pre-
pared (see Fig. 4b). Ethylene diamine can play a key role in
preparing spherical nanostructures. With increasing concentra-
tions of en, to a Ni:en ratio of 1:4, larva shape nanorods were ob-
tained (see Fig. 4c and d). The spheres are composed of a
massive larva shape (or nanowall) nearly vertical to the spherical
surface, which shows a high specific surface area.
1
3
mL, microspheres were formed (Fig. 5d and e). This great differ-
ence in the hierarchical morphology is just because of the concentra-
tion of hydrazine, which may be ascribed to the different nuclei and
growth ratio of Ni(OH) at the different concentrations of hydrazine.
2
At lower concentrations (0.125, 0.25 and 0.5 mL), the nanorods can
slowly be assembled into spheres with the assistance of en as a sur-
factant, which will further congregate into microspheres. However,
under these conditions, the initial nuclei and growth ratio will be
quite fast, which may destroy the assembly of the surfactant.
l
3.4.2. Effect of concentration of hydrazine
The formation process of hierarchical Ni(OH)
2
spheres was ob-
3.4.3. Effect of reaction temperature
served via different concentrations of hydrazine, by monitoring
the SEM characteristics. Fig. 5 shows the SEM images of Ni(OH)
samples prepared with 0.125, 0.25, 0.5, 2 and 3 mL of hydrazine at
The hydrothermal reaction was carried out at 120 °C (Ni:en
(1:4) and with hydrazine (1 mL) for 12 h, sample No. 11, but at this
temperature no precipitate was observed. Fig. 6 shows the SEM
2
Fig. 5. SEM images of samples prepared under different conditions: (a) sample No. 8, (b) sample No. 7, (c) sample No. 6, (d) sample No. 4 and (e) sample No. 5.

M. Salavati-Niasari, M. Entesari / Polyhedron 33 (2012) 302–309
307
nanosheets on their surfaces were obtained with a size of about
m and length of about 0.5 m. When the reaction time was in-
1
l
l
creased to 8 h, the blocks gradually diminished, while nanorods
gradually appeared (not shown here). Then, on prolonging the
reaction time to 12 h, all the sheets disappeared and larva shape
nanorods appeared in the solution, which were about 50 nm in
diameter and 1 lm in length (Fig. 4d). Looking carefully at
Fig. 4d, we found that the surfaces of some nanorods were
smooth. When the reaction time was 12 h, the hierarchical nano-
rods derived from the former smooth nanorods take shape and
become the main morphology of products, as shown in Fig. 4d
[
7
2]. After prolonging the reaction time to 18 h, as shown in Fig
b, the hierarchical nanorods become more uniform and perfect,
there being no obvious variation in the diameter and length of
the rods, which further demonstrates that the obtained products
are not formed by the growth of additional nanorods.
Fig. 6. SEM image of sample No. 10.
3.5. TEM studies
image of sample made at 160 °C which shows that the morphology
is similar to sample No. 7 (see Fig. 5b).
Fig. 8 demonstrates representative TEM images of the as-ob-
tained (a)
In Fig. 8a, it can be seen that the sample consists of a number of
-Ni(OH) spheres with high hierarchical structures, having an
average diameter of 400 nm. These -Ni(OH) spheres are actually
2
a-Ni(OH) , sample No. 1, and (b) NiO, sample No. 14.
3.4.4. Effect of reaction time
a
2
In order to investigate the formation mechanism of the hierar-
a
2
chical Ni(OH)
2
, detailed time-dependent experiments were car-
constructed from a large number of nanorods. The present TEM re-
ried out at 180 °C. From the SEM images of these products,
shown in Fig. 7, the morphology evolution of the hierarchical
nickel hydroxide nanostructures is observed. In the middle, when
the reaction time was 6 h (Fig. 7a), some blocks with some
sults, to some extent, contribute to the previous reports on the syn-
thesis of a-Ni(OH) [43]. Fig. 8b shows the TEM image of the NiO
2
nanostructures without spherical shape, but hierarchical nanorods
can be seen in Fig. 8b.
Fig. 7. SEM images of samples prepared with different reaction times: (a) sample No. 12 and (b) sample No. 13.
2
Fig. 8. TEM images of samples prepared under different conditions: (a) a-Ni(OH) , sample No. 1 and (b) NiO, sample No. 14.

3
08
M. Salavati-Niasari, M. Entesari / Polyhedron 33 (2012) 302–309
can be assigned to the 1 1g(G) ? A2g and 1
T T2g(D) ? A2g transi-
3
3
3.6. Photoluminescence studies
tions, respectively [45]. Compared to the bulk, the photolumines-
cence from the NiO nanostructures is red shifted. This may be
due to the wide particle size distribution and the native defects
in the NiO nanostructures. No remarkable emission peak was ob-
Fig. 9 shows the PL spectrum of nickel oxide nanostructures,
sample No. 14, excited at a wavelength of 270 nm. An emission
band centered at 395.0 nm (3.17 eV) and a weak emission peak
at 470 nm (2.64 eV) can be observed. As a typical transition metal
element, the optical properties and carrier related phenomena in
Ni compounds are governed by d M d transitions present within
served in the PL spectra of
a
-Ni(OH)
2
nanostructures [46].
3.7. Magnetic properties
2
6
8
the band gap. The nickel(II) ion has the configuration 3s 3p 3d .
This transition metal ion has six O2 surrounding ions to form an
elementary octahedron with octahedral symmetry. The oxygen
À
The magnetic properties of Ni(OH)
2
, sample No. 1, and NiO, sam-
ple No. 14, nanostructures have been measured at 300 K (Fig. 10). It
can be seen that Fig. 10a exhibits typical antiferromagnetism, while
in Fig. 10b the NiO nanostructures present superparamagnetic
behavior, although NiO bulk material is antiferromagnetic [47].
ions crystal field splits the d electron states into e
g
and t2g states.
[
44]. According to ligand field theory, the two emission transitions
4
. Conclusions
In summary, we have demonstrated that
2
a-Ni(OH) and
b-Ni(OH)
synthesized through the reaction of Ni(NO
as morphology-directing agents via an easy hydrothermal method.
The formation of hierarchically Ni(OH) nanostructures followed a
self-aggregation mechanism. The key factors influencing the forma-
tion of hierarchical Ni(OH) were monitored using SEM character-
izations. The effect of the amount of hydrazine on the Ni(OH)
2
hierarchical structures aggregated by nanorods can be
3
)
2
Á6H O, en and N
2
2 4
H
2
2
2
morphology was also investigated. NiO nanostructures assembled
from nanorods were also obtained by calcination of the as-prepared
a
2
-Ni(OH) at 300 °C for 4 h in the air. Two photoluminescence emis-
1
3
1
3
sion peaks assigned to the T1g(G) ? A2g and T2g(D) ? A2g transi-
tions of nickel(II) in oxygen coordinated octahedral sites were
detected. The investigated physical properties of the
a-Ni(OH)
2
nanostructures and NiO nanostructures is very important for the
their applications in the future. The magnetic investigation has
Fig. 9. PL spectrum of NiO nanostructures, sample No. 14, excited at a wavelength
of 270 nm.
shown
a superparamagnetic behavior for the obtained NiO
nanostructures.
Acknowledgement
The authors are grateful to the council of the University of Ka-
shan for their unending effort to provide financial support to
undertake this work.
References
[
[
[
[
[
1] C. Xu, L. Wang, D. Zou, T. Ying, Mater. Lett. 62 (2008) 3181.
2] Y. Shao, J. Sun, L. Gao, J. Phys. Chem. C 113 (2009) 6566.
3] K. Xu, W. Ding, Mater. Lett. 62 (2008) 4437.
4] C. Coudun, J.F. Hochepied, J. Phys. Chem. B 109 (2005) 6069.
5] X. Wang, H. Luo, P.V. Parkhutik, A.C. Millan, E. Matveeva, J. Power Sources 115
(
2003) 153.
[
[
6] J.J. Braconniera, C. Delmas, P. Hagenmuller, Mater. Res. Bull. 17 (1982) 993.
7] B. Liu, X.Y. Wang, H.T. Yuan, Y.S. Zhang, D.Y. Song, Z.X. Zhou, J. Appl.
Electrochem. 29 (1999) 855.
[
[
8] I. Zhitomirsky, J. Appl. Electrochem. 34 (2004) 235.
9] W.Y. Li, S.Y. Zhang, J. Chen, J. Phys. Chem. B 109 (2005) 14025.
[
[
[
[
10] R. Acharya, T. Subbaiah, S. Anand, R.P. Das, Mater. Chem. Phys. 81 (2003) 45.
11] A. Delahaye-Vidal, M. Figiarz, J. Appl. Electrochem. 17 (1987) 589.
12] M. Dixit, G.N. Subbanna, P.V. Kamath, J. Mater. Chem. 6 (1996) 1429.
13] Y.L. Zhao, J.M. Wang, H. Chen, T. Pan, J.Q. Zhang, C.N. Cao, Int. J. Hydrogen
Energy 29 (2004) 889.
[
[
14] F. Portemer, A. Delahaye-Vidal, M. Figiarz, J. Electrochem. Soc. 139 (1992) 671.
15] M. Akine, N. Jongen, J. Lemaitre, H. Hofmann, J. Eur. Ceram. Soc. 18 (1998)
1559.
[
16] M. Yoshio, Y. Todorov, K. Yamato, H. Noguchi, J. Itoh, M. Okada, T. Mouri, J.
Power Sources 74 (1998) 46.
[
[
[
17] B. Sheela, H. Gomathi, G.P. Rao, J. Electroanal. Chem. 394 (1995) 267.
18] C.B. Alcock, B.Z. Li, J.W. Fergus, L. Wang, Solid State Ionics 53 (1992) 39.
19] A.C. Felici, F. Lama, M. Piacentini, T. Papa, D. Debowska, A. Kisiel, A. J. Appl.
Phys. 80 (1996) 6925.
Fig. 10. The hysteresis loops of (a) Ni(OH)
4) nanostructures at 300 K.
2
(sample No. 1) and (b) NiO (sample No.
1
[20] D. Adler, J. Feinleib, Phys. Rev. B 2 (1970) 3112.

M. Salavati-Niasari, M. Entesari / Polyhedron 33 (2012) 302–309
309
[
[
21] A. Chrissanthopoulos, S. Baskoutas, N. Bouropoulos, V. Dracopoulos, P.
Poulopoulos, S.N. Yannopoulos, Photon. Nanostruct. Fundament. Appl.
2011) 132.
22] X. Wang, J.M. Song, L.S. Gao, J.Y. Jin, H.G. Zheng, Z.D. Zhang, Nanotechnology 16
2005) 37.
23] F. Davar, M. Salavati-Niasari, Z. Fereshteh, J. Alloys Compd. 496 (2010) 638.
24] M. Salavati-Niasari, F. Davar, Mater. Lett. 63 (2009) 441.
25] M. Salavati-Niasari, M.R. Loghman-Estarki, F. Davar, J. Alloy. Compd. 145
[34] Z.H. Liang, Y.J. Zhu, X.L. Hu, J. Phys. Chem. B 108 (2004) 3488.
[35] W.K. Hu, X.P. Gao, D. Noreus, T. Burchardt, N. Nakstad, J. Power Source 160
(2006) 704.
[36] H. Zhang, H. Liu, X. Cao, S. Li, C. Sun, Mater. Chem. Phys. 79 (2003) 37.
[37] P. Jeevanandam, Y. Koltypin, A. Gedanken, Nano. Lett. 1 (2001) 263.
[38] M. Salavati-Niasari, F. Davar, Z. Fereshteh, J. Alloys Compd. 494 (2010) 410.
[39] M. Salavati-Niasari, N. Mir, F. Davar, J. Alloys Compd. 493 (2010) 163.
[40] N.V. Kosova, E.T. Devyatkina, V.V. Kaichev, J. Power Source 174 (2007) 735.
[41] L. Xu, Y.-S. Ding, C.-H. Chen, L. Zhao, C. Rimkus, R. Joesten, S.L. Suib, Chem.
Mater. 20 (2008) 308.
[42] L.-X. Yang, Y.J. Zhu, H. Tong, Z.H. Liang, L. Li, L. Zhang, J. Solid State Chem. 180
(2007) 2095.
[43] X. Chen, Z. Zhang, C. Shi, X. Li, Mater. Lett. 62 (2008) 346.
[44] C. Dıáz-Guerra, A. Remo n´ E, J.A. Garcıá, J. Piqueras, Phys. Status Solid A: Appl.
Res. 163 (1991) 497.
9
(
(
[
[
[
(
2009) 346.
[
[
[
26] M. Salavati-Niasari, N. Mir, F. Davar, J. Alloys Compd. 476 (2009) 908.
27] F. Davar, Z. Fereshteh, M. Salavati-Niasari, J. Alloys Compd. 476 (2009) 797.
28] N. Bouropoulos, G.C. Psarras, N. Moustakas, A. Chrissanthopoulos, S. Baskoutas,
Phys. Status Solidi A 205 (2008) 2033.
29] F. Mohandes, F. Davar, M. Salavati-Niasari, J. Magn. Magn. Mater. 322 (2010) 872.
30] M. Salavati-Niasari, F. Mohandes, F. Davar, K. Saberyan, Appl. Sur. Sci. 256
[
[
(
2009) 1476.
[45] T. Tsuboi, W. Kleeman, J. Phys. Condens. Mater. 6 (1994) 8625.
[46] Y. Qi, H. Qi, C. Lu, Y. Yang, Y. Zhao, J. Matter. Sci.: Mater. Electron. 20 (2009)
479.
[
31] S. Baskoutas, P. Giabouranis, S.N. Yannopoulos, V. Dracopoulos, L. Toth, A.
Chrissanthopoulos, N. Bouropoulos, Thin Solid Films 515 (2007) 8461.
[
[
32] D. Yang, R. Wang, M. He, J. Zhang, Z. Liu, J. Phys. Chem. B 109 (2005) 7654.
33] M. Jayalakshmi, N. Venugopal, B.R. Reddy, M.M. Rao, J. Power Source 150
[47] H. Bia, S. Li, Y. Zhang, Y. Du, J. Magn. Magn. Mater. 277 (2004) 363.
(
2005) 272.