Synthesis and characterization of flower-like β-Ni(OH)2 nanoarchitectures

Article abstract of DOI:10.1016/j.jssc.2007.05.025

Flower-like Ni(OH)₂ nanoarchitectures have been synthesized through a one-step mild hydrothermal reaction with the aid of ethylenediamine in NiCl₂ aqueous solution. The flower with the size of several micrometers in diameter is composed of the ultra-thin nanosheets of several nanometers in thickness. It was found the ethylenediamine is vital to the formation of the flower-like nanoarchitectures. The influence of the concentration of the ethylenediamine and the reaction temperature on the formation of the flowers was analyzed and the formation mechanism of the flowers was proposed. Such flower-like β-Ni(OH)₂ nanoarchitectures will find potential applications in the fields, such as electrode, or will be used as a starting material to produce NiO, which is widely used in the magnetic, catalysts, sensor and electrochromic devices.

Full text of DOI:10.1016/j.jssc.2007.05.025

ARTICLE IN PRESS
Journal of Solid State Chemistry 180 (2007) 2149–2153
www.elsevier.com/locate/jssc
Synthesis and characterization of flower-like b-Ni(OH)2
nanoarchitectures
Ã
Yuanyuan Luo, Guotao Duan, Guanghai Li
Key Laboratory of Materials Physics, Anhui Key Laboratory of Nanomaterials, Nanotechnology Institute of Solid State Physics,
Chinese Academy of Sciences, Hefei 230031, PR China
Received 9 February 2007; received in revised form 22 May 2007; accepted 28 May 2007
Available online 3 June 2007
Abstract
Flower-like Ni(OH)
ethylenediamine in NiCl aqueous solution. The flower with the size of several micrometers in diameter is composed of the ultra-thin
2
nanoarchitectures have been synthesized through a one-step mild hydrothermal reaction with the aid of
2
nanosheets of several nanometers in thickness. It was found the ethylenediamine is vital to the formation of the flower-like
nanoarchitectures. The influence of the concentration of the ethylenediamine and the reaction temperature on the formation of the
2
flowers was analyzed and the formation mechanism of the flowers was proposed. Such flower-like b-Ni(OH) nanoarchitectures will find
potential applications in the fields, such as electrode, or will be used as a starting material to produce NiO, which is widely used in the
magnetic, catalysts, sensor and electrochromic devices.
r 2007 Elsevier Inc. All rights reserved.
2
Keywords: Ni(OH) ; Nanoarchitectures; Hydrothermal synthesis; Nanosheet
1
. Introduction
Nickel-based secondary alkaline batteries have been
extensively used in industry and daily life [1,2]. The
hydrothermal hydrolysis of the nickel(II) complex solution
of macrocycle polyamine [13] or from a water-in-oil reverse
micelle/microemulsion system [14] also has been reported.
But one-step simple fabrication of flower-like b-Ni(OH)2
active material with high surface area remains a consider-
able challenge. To optimize the functional properties of the
nanostructures for electrochemical applications, self-as-
sembly method has been indispensable. At present,
considerable efforts, such as wet chemical routes, solid
liquid-phase arc-discharge, electrochemical method and
vapor-phase evaporation, have been dedicated to the
design of various nanoarchitectures [15–21], which undergo
the special dynamics processes with different formation
mechanisms, such as, Ostwald ripening [17,18], Kirkendall
effect [19], and self-assembly of nanoscale blocks through
hydrophobic interactions [20] or ‘‘oriented attachment’’
[21]. However, the full knowledge and precise control of
the self-assemble process are still difficult.
fabrication of b-Ni(OH) with high electric conductivity
2
and high proton diffusion ability is essential and a great
challenge in order to improve the performance of these
batteries. It has been reported that the nanostructured
nickel electrodes with high specific surface area will speed
proton diffusion, and thus have an improved electroche-
mical performance [3].
The b-Ni(OH) with different shapes has been fabri-
2
cated, such as tubes [4] and rods [5] by template synthesis,
nanoribbon by hydrothermal treating [6], stacks of
pancakes by a chemical method [7], hollow spheres by a
simple solution chemistry method [8], and sheet-like
geometry by the hydrothermal method [9–11]. The growth
of flower-like b-Ni(OH) nanostructures from the alkali
2
solution of nickel dimethylglyoximate [12], from the
In this paper, we report the one-step simple hydro-
thermal synthesis of flower-like b-Ni(OH) nanoarchitec-
ture with the aid of ethylenediamine in NiCl aqueous
2
2
Ã
Corresponding author. Fax: +86 551 5591434.
E-mail address: ghli@issp.ac.cn (G. Li).
solution.
0022-4596/$ - see front matter r 2007 Elsevier Inc. All rights reserved.
doi:10.1016/j.jssc.2007.05.025

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Y. Luo et al. / Journal of Solid State Chemistry 180 (2007) 2149–2153
2150
2
. Experimental
c-axis (L001) is evaluated at 0.465 nm and that along the
(1 1 0) direction (L110) equals 0.27 nm.
Fig. 2 shows the FESEM images of the products on Si
2
.1. Preparation of the sample
substrate. One can see that the as-prepared sample consists
of a large quantity of fairly uniform particles with the
average size of about 2 mm in diameter (Fig. 2a). The high-
magnification FESEM images (Fig. 2b–d) reveal that all
All chemicals were purchased and used without further
purification. In a typical preparation of the b-Ni(OH)2
nanoarchitectures, 0.5 g of NiCl ꢀ 2H O was dissolved in
2
2
3
0 mL of deionized water. Then 1.0 mL of ethylenediamine
en) was added drop by drop under constant stirring until
the b-Ni(OH) particles have flower-like morphology. The
2
(
flower is composed of many nanosheets with thickness of
several nanometers, and some small nanosheets random
situate in the center of the flower and some large
nanosheets surround these small ones. The nanosheets
grow perpendicularly to the surface of Si substrate and
intersect with each other.
Fig. 3 shows the TEM images of the flowers from Si
substrate. Si substrate was used only for easy morphology
observations. In fact, flower-like nanoarchitectures were
also formed on other substrates. One can see that the
thickness of the nanosheet gradually changes from edge to
center being thick in center (Fig. 3a). The lattice fringes can
be clearly seen in the HRTEM image of the tip zone of a
single nanosheet with the electron beam parallel to the
surface of the nanosheet (Fig. 3b). The spacing between
the neighboring fringes is about 0.46 nm, belonging to the
the solution became blue and homogeneous. For easy
morphology observations, the Si substrates were put
directly inside the reaction container. Then the mixture
was kept in oven in an ordinary glass jar at 90 1C for 12 h.
Finally, the products and substrates were washed with
deionized water several times to remove any residuals and
then dried at 75 1C for 1 h.
2
.2. Analyses of the sample
X-ray diffraction (XRD) was performed on the Philips
X’Pert using CuKa line. The morphology and microstruc-
ture were examined using field emission scanning electron
microscopy (FESEM, Sirion 200) and transmission elec-
tron microscopy (TEM H-800 and HRTEM JEOL-2010).
The nitrogen adsorption–desorption isotherm was mea-
sured on an Omnisorp 100CX.
(
0 0 0 1) crystal planes of b-Ni(OH) , which is in good
2
agreement with the XRD results. The average thickness of
a single nanosheet was found to be about 2.81 nm. The
brim of the nanosheet is of good transparency to the
electron beam (Fig. 3c), and the corresponding HRTEM
image (Fig. 3d) shows that the fringe spacing is
3
. Results and discussion
3.1. Characterization of flower-like b-Ni(OH)2
nanoarchitectures
¯
about 0.27 nm, corresponding to the ð0 1 1 0Þ crystal planes
of b-Ni(OH) , which is in accordance with XRD results.
2
Fig. 1 shows the XRD pattern of the products on Si
substrate. All the diffraction peaks can be indexed as b-
Ni(OH)2 phase with cell constants of a ¼ 3.125 and
c ¼ 4.660, which are consistent with the standard values
(
JCPDS card 74-2075). No diffraction peaks corresponding
to other phases are observed. According to Scherrer’s
formula, the length of the crystalline domain along the
Fig. 1. XRD pattern of nickel hydroxide prepared at 90 1C for 12 h and
that from the JCPDS card 74-2075.
2
Fig. 2. FESEM images of the Ni(OH) flowers prepared at 90 1C for 12 h
at different magnifications.

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Y. Luo et al. / Journal of Solid State Chemistry 180 (2007) 2149–2153
2151
Fig. 3. Morphologies of the Ni(OH)
(
2
flowers prepared at 90 1C for 12 h:
a) TEM image of an individual flower, (b) HRTEM image of the tip
Fig. 4. FESEM images of the Ni(OH) prepared at 120 1C with (a and b)
1.0 mL, (c) 0.5 mL and (d) 0.2 mL ethylenediamine in a Teflon-lined
autoclave for 6 h.
2
region of a nanosheet with the electron beam parallel to the surface of a
nanosheet, (c) a single nanosheet and corresponding SAED and (d)
corresponding HRTEM image of a nanosheet with the electron beam
perpendicular to the surface of the nanosheet.
The selected area electron diffraction (SAED) pattern
shown in the inset in Fig. 3c also reveals the hexagonal
structure of the b-Ni(OH) . The results indicate that the
2
nanosheet grows within the (0 0 0 1) plane and some of the
nanosheets observed in Fig. 2 are ultra-thin and easily
assemble up.
It was found that the concentration of the ethylenedia-
mine and reaction temperature both affect the formation of
the flower-like b-Ni(OH) . When the concentration of the
2
ethylenediamine is higher than 2 mL, no b-Ni(OH) was
2
formed except Ni film. It is worth noting that the Ni film
only formed on the silicon substrate, and nothing was
formed when used Cu, Ni, Au, stainless steel, glass and
ZrO substrates. The origin of these phenomena is not clear
2
2 2
Fig. 5. N adsorption–desorption isotherm of the Ni(OH) flowers. The
right now. It might be due to the activation of Si substrate
by ethylenediamine. When the reaction temperature
increased to 120 1C (in autoclave), the size of the b-
inset is a schematic illustration of the thickness calculation of the Ni(OH)
nanosheets.
2
that when ethylenediamine was replaced by ammonia and
CTAB, or water was replaced by alcohol and ethylene
Ni(OH) flower increases to about 5 mm in diameter, and
2
the number of nanosheet composed of the flower increases
(
glycol, no b-Ni(OH) flower was formed [9–11].
see Fig. 4a and b). When the concentration of ethylene-
diamine was reduced to 0.5 mL, no size change of the b-
2
Ni(OH) flower was observed, but the nanosheet composed
2
3.2. Specific surface area and thickness of nanosheet
of the flower decreased (Fig. 4c), and when the concentra-
tion of ethylenediamine was further decreased to 0.2 mL,
no flower except very large nanosheet was formed (see Fig.
4d). These results indicated that high reaction temperature
and high ethylenediamine concentration can speed the
The N2 adsorption–desorption isotherms of the b-
Ni(OH) flowers at different relative pressures are shown
in Fig. 5. It is found that the specific surface area of
2
2
Ni(OH)2 flowers is about 182 m /g calculated by the
Brunauer–Emmett–Teller (BET) method, which is higher
nucleation and growth of b-Ni(OH) flower. It was found
2

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Y. Luo et al. / Journal of Solid State Chemistry 180 (2007) 2149–2153
2152
2
than that of 114 m /g previously reported for nickel
hydroxide power [22]. Specific surface area is defined as
the accessible area of solid surface per unit mass of
materials. Assuming the contact area between the na-
nosheets and side area of the nanosheets are very small and
can be ignored comparing with the surface area of the
good complexing agent [23,24] and the amide is easy to
absorb on the surface of Si substrate [25,26]. At first,
NiCl ꢀ 2H O would combine with deionized water to get
2
2
intermediate products such as hydrated nickel cation
2
named [Ni(H O) ] in solution. The rate of replacement
+
2
6
of bound water in nickel complexes can be greatly affected
by ligands coordinated to the nickel. As the number of
nitrogen coordinated to the nickel increases, the rate of
exchange of water by amine increases, and the other
intermediate product such as the trisethylenediamine
nanosheets, in this case the specific surface area (S ) can be
0
described as S ¼ 2S/m, where S is the single surface area
0
of nanosheets and m is the mass of the nanosheets, as
shown in the inset in Fig. 5. From the relation
m ¼ rV ¼ rSd, here m is the mass of the sample, r the
mass density and d the thickness of the nanosheet, we have
S ¼ 2S/m ¼ 2S/rSd ¼ 2/rd, and thus we get d ¼ 2/(rS ).
2
+
complexes of nickel(II) named [Ni(en)3]
was formed
[27–29] and the whole mixed solution became blue. With
increasing temperature, the complexes reacted with water
to form nanosheets on Si substrate, and as the reaction
continued, the nanosheets assembled to Ni(OH) flowers,
2
as shown schematically in Fig. 7. The chemical reactions
can be described as follows:
0
0
2
3
Using the data S ¼ 182 m /g and r ¼ 3.97 g/cm , we
0
finally get the average thickness of the nanosheet
d ¼ 2.76 nm, which almost equals the results obtained
from TEM. This result also proved that this method can
effectively solve the average thickness of the flexible and
ultra-thin nanosheets, which is generally difficult to be
observed directly from FESEM and TEM. It is worth
2
þ þ 6H2O ! ½NiðH2OÞ6ꢁ2þ
,
Ni
(1)
(2)
2
þ þ 3en ! ½NiðenÞ3ꢁ2þ
½
NiðH2OÞ6ꢁ
þ 6H2O,
noting that the flower-like b-Ni(OH) has a tap density of
2
3
about 2.72 g/cm , which is higher than the minimum
3
requirement for commercial material (2.2 g/cm ), and thus
½NiðenÞ3ꢁ2þ þ 3H2O ! NiðOHÞ þ 2½H2NCH2CH2NH3ꢁ þ en.
2þ
2
the flower-like b-Ni(OH) will be expected to be used as
2
(3)
positive electrode material for rechargeable batteries.
As is known, in hydrotalcite-like compounds, the alkaline
layered hydroxide has a hexagonal close packing of
hydroxyl ions, where each divalent metal ion (e.g.,
3
.3. Formation mechanism of b-Ni(OH) flower
2
a
2+
2+
2+
M ¼ Mg , Ca , Ni ) is octahedron sharing their
edges to form 2D brucite-like sheets which then stack upon
one another to form a layered solid via various interlayer
chemical interactions [30,31]. In general, under normal
precipitation condition, such compounds easily present the
thin sheet-like crystallite morphology with the sheet surface
perpendicular to the c-axis of crystal. It is believed that the
formation of the flower composed of many nanosheets
depends not only on the type of the metal hydroxide but on
the existence of ethylenediamine as well. During the
reaction, the ethylenediamine not only acts as the complex
regent but also plays a key role in the formation of the
flower. Because of the ethylenediamine, the Ni(OH)2
nanosheet becomes very flexible [29], and can be wrinkled
and bent, which will help nanosheets connect with each
other and leads the formation of flower. In the initial
growth stage, the interfacial energy between the nuclei and
Si substrate is minimum when the lowest energy plane of
To study the formation mechanism of the flower-like b-
Ni(OH) nanoarchitectures, some of the Si substrates were
taken out at different reaction times. After reaction at
2
120 1C for 0.5 h, the nanosheets perpendicular to Si
substrate were formed (see Fig. 6a). The number and the
size of the nanosheets increase with time, and after reaction
for 1.5 h, the b-Ni(OH) flower was formed (see Fig. 6b).
2
The observation of the morphology below the flower after
reaction for 6 h, as shown in Fig. 4a, clearly indicates that
the flower is formed on the dispersive nanosheets.
From above results, a formation mechanism of the
flower-like nanoarchitectures can be proposed. It was
reported that the ethylenediamine is known to be a very
2
Fig. 6. FESEM images of the layer of Ni(OH) nanosheets hydrothermal
synthesis with solution 1 in a Teflon-lined autoclave at 120 1C for (a) 0.5 h,
and (b) 1.5 h.
Fig. 7. Schematic illustration of the formation mechanism of the Ni(OH)
flowers.
2

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Y. Luo et al. / Journal of Solid State Chemistry 180 (2007) 2149–2153
2153
the nuclei faces parallel to the substrate surface, the
Ni(OH) nuclei grow within their (0 0 1) plane parallel to
National Major Project of Fundamental Research for
Nanomaterials and Nanostructures (No.: 2005CB623603).
2
the substrate, and thus the nuclei are randomly packed
with an instantaneous process on the substrate. As the
reaction continues, the secondary nucleation is much more
References
[
1] P.A. Nelson, J.M. Elliott, G.S. Attard, J.R. Owen, Chem. Mater. 14
(
preferential on the Ni(OH) particle surface than on the
2
2002) 524.
2] N. Tzanetakis, K. Scott, J. Chem. Technol. Biotechnol. 79 (2004) 919.
3] D.E. Reisner, A.J. Salkind, P.R. Strutt, T.D. Xiao, J. Power Sources
substrate surface due to the fact that the nucleus/particle
interfacial energy has a minimum value. In this case, the
newly formed nucleus is attached onto the surface of the
[
[
6
5 (1997) 231.
Ni(OH) particles. Since the concentration of the nickel
2
[4] F.S. Cai, G.Y. Zhang, J. Chen, X.L. Gou, H.K. Liu, S.X. Dou,
Angew. Chem. 116 (2004) 4308.
complexes is kept lower around the growing crystals near
the substrate, the growth continues in the direction of the
bulk solution. The subsequent nucleation grows preferen-
tially on the surface of the already grown particles. In this
case, there is no preferential growth direction until the
growing crystals come into contact with each other. As a
[
[
5] K. Matsui, T. Kyotani, A. Tomita, Adv. Mater. 14 (2002) 1216.
6] D.N. Yang, R.M. Wang, J. Zhang, Z.F. Liu, J. Phys. Chem. B 108
(
7] C. Coudun, J.F. Hochepied, J. Phys. Chem. B 109 (2005) 6069.
2004) 7531.
[
[8] Y. Wang, Q.S. Zhu, H.G. Zhang, Chem. Commun. (2005) 5231.
9] Z.H. Liang, Y.J. Zhu, X.L. Hu, J. Phys. Chem. B 108 (2004) 3488.
10] D.L. Chen, L. Gao, Chem. Phys. Lett. 405 (2005) 159.
[
[
[
hydrotalcite-like compound, the Ni(OH) can easily form a
2
11] X.H. Liu, G.Z. Qiu, Z. Wang, X.G. Li, Nanotechnology 16 (2005)
1
sheet-like particle [30,31]. Then the Ni(OH)2 particles
assemble and form flowers [32]. Such flower-like nanoarch-
itectures with high specific surface area will find potential
applications in the fields, such as electrode, or can be used
as a starting material to produce NiO used in magnetic,
catalysts, sensor and electrochromic devices [33,34].
400.
[
[
12] X.M. Ni, Q.B. Zhao, J. Cheng, H.G. Zheng, B.B. Li, D.G. Zhang,
Chem. Lett. 34 (2005) 1408.
13] Z.C. Wu, X. Zhu, C. Pan, Z.Y. Yao, Y. Xie, Chin. J. Inorg. Chem. 22
(
2006) 1371.
[
[
14] M. Cao, X. He, J. Chen, C. Hu, Cryst. Growth Des. 7 (2007) 170.
15] G.T. Duan, W.P. Cai, Y.Y. Luo, Z.G. Li, Y. Lei, J. Phys. Chem. B
1
10 (2006) 15729.
[16] G.T. Duan, W.P. Cai, Y.Y. Luo, F.Q. Sun, Adv. Funct. Mater. 17
2007) 644.
4
. Conclusion
(
[
[
17] H.G. Yang, H.C. Zeng, J. Phys. Chem. B 108 (2004) 3492.
18] X.W. Lou, C. Yuan, E. Rhoades, Q. Zhang, L.A. Archer, Adv.
Funct. Mater. 16 (2006) 1679.
The flower-like b-Ni(OH) nanoarchitectures have been
2
synthesized by hydrothermal synthesis with the aid of
ethylenediamine in NiCl2 aqueous solution. The flower
with the size of several micrometers is composed of many
nanosheets. The nanosheet grows within the (0 0 0 1)
[19] Y. Yin, R.M. Rioux, C.K. Erdonmez, S. Hughes, G.A. Somorjai,
A.P. Alivisatos, Science 304 (2004) 711.
[
[
[
20] S. Park, J.H. Lim, S.W. Chung, C.A. Mirkin, Science 303 (2004) 348.
21] R.L. Penn, J.F. Banfield, Science 281 (1998) 969.
22] M.B.J.G. Freitas, J. Power Sources 93 (2001) 163.
planes. The flowers have a specific surface area of about
2
1
82 m /g, and the average thickness of a single b-Ni(OH)
2
[23] E.G.S. Michael, A.C. David, M. Philip, Chem. Commun. 13 (2000)
1167.
[24] S.K. Panda, S. Gorai, S. Chaudhuri, Mater. Sci. Eng. B 129 (2006) 265.
nanosheet is about 2.8 nm. It was found the ethylenedia-
mine plays an important role in the formation Ni(OH)2
nanoarchitecture, and no flower is formed when it is higher
than 2 mL. It was considered that the nuclei/Si substrate
and nucleus/b-Ni(OH)2 particle interfacial energies are
controlling factors in the formation of the nanosheets and
assembling of the flowers. The flowers with high specific
surface area are promising positive-electrode materials for
alkaline rechargeable batteries or can be used as a starting
material to produce NiO nanostructure that is widely used
in the catalysts, sensor and electrochromic devices.
[
[
25] X.P. Cao, R.J. Hamers, J. Am. Chem. Soc. 123 (2001) 10988.
26] J.B. Wu, Y.W. Yang, Y.F. Lin, H.T. Chiu, J. Phys. Chem. B 108
(
2004) 1677.
[27] A.Y. Ali-Mohamed, Trans. Metal Chem. 27 (2002) 861.
[28] N.V. Peganova, V.I. Kravtsov, R.K. Astakhova, Russ. J. Electro-
chem. 38 (2002) 644.
[
[
29] J.T. Sampanthar, H.C. Zeng, J. Am. Chem. Soc. 124 (2002) 6668.
30] I. Carpani, M. Giorgetti, M. Berrettoni, P.L. Buldini, M. Gazzano,
D. Tonelli, J. Solid State Chem. 179 (2006) 3981.
[
[
[
[
31] P. Benito, F.M. Labajos, V. Rives, J. Solid State Chem. 179 (2006)
3784.
32] E. Hosono, S. Fujihara, T. Kimura, H. Imai, J. Colloids Interface Sci.
2
72 (2004) 391.
Acknowledgments
33] A. Galtayries, E. Laksono, J.M. Siffre, C. Argile, P. Marcus, Surf.
Interface Anal. 30 (2000) 140.
This work was supported by the National Natural
Science Foundation of China (No.: 10674137) and the
34] Y.L. Cao, J.M. Cao, M.B. Zheng, J.S. Liu, G.B. Ji, J. Solid State
Chem. 180 (2007) 792.