Synthesis and Characterization of Ni(OH)2 Single-crystal Nanorods

Article abstract of DOI:10.1246/cl.2003.1126

A template-free hydrothermal method to Ni(OH)₂ single-crystal nanorods were successfully established based on the 2-D layered structures of Ni(OH)₂. The obtained Ni(OH)₂ nanorods were 40-90 nm in diameters and 1-3 μm in lengths. It is interesting that Ni(OH)₂ nanorods would be converted into NiO nanorings when they were annealed at 500°C for 6 h.

Full text of DOI:10.1246/cl.2003.1126

1126
Chemistry Letters Vol.32, No.12 (2003)
Synthesis and Characterization of Ni(OH)2 Single-crystal Nanorods
Jiahe Liang and Yadong LiÃ
Department of Chemistry and the Key Laboratory of Atomic & Molecular Nanoscience
(China Ministry of Education), Tsinghua University, Beijing 100084, P. R. China
(Received August 14, 2003; CL-030755)
A template-free hydrothermal method to Ni(OH)2 single-
crystal nanorods were successfully established based on the
2-D layered structures of Ni(OH)2. The obtained Ni(OH)2 nano-
rods were 40–90 nmin diameters and 1–3 mm in lengths. It is in-
teresting that Ni(OH)2 nanorods would be converted into NiO
nanorings when they were annealed at 500 ꢀC for 6 h.
a
b
Nickel hydroxide (Ni(OH)2) is widely used as a positive
electrode active material in rechargeable Ni-based alkaline bat-
teries (e.g. Ni/Fe, Ni/Zn, Ni/Cd, Ni/H2, and Ni/MH) on the ba-
sis of its chemical and thermal stability, low self-discharge rate,
and low toxicity.1 Several chemical and electrolytic methods
were attempted to synthesize nickel hydroxide, for example,
force precipitation of Ni(NO3)2, direct precipitaion with KOH,
electrolytic pricipitation, and sol-gel method and electrochemi-
cal method.2–5 It is well known that, nanoscale 1-D materials
have stimulated great interest on the basis of their importance
in basic scientific research and potential technology applica-
tions.6,7 However, there are few reports for the synthesis of 1-
D nanostructure of nickel hydroxide.8 In present work, we suc-
cessfully developed a template-free hydrothermal method to pre-
pare Ni(OH)2 single-crystal nanorods based on the understand-
ing of the mechanism from 2-D layered structure compounds
to 1-D nanostructures.9,10 It is the first time, to our knowledge,
to synthesize Ni(OH)2 nanorods by a controlled direct precipita-
tion method. It is expected that the current method may be devel-
oped to a general method to 1-D nanorods or nanotubes of hy-
droxides M(OH)2 (M = Co, Fe, Cd, Mg, Ca) with CdI2 type.
Nanorods of Ni(OH)2 were synthesized as follows: 1.6 g
NiCl2Á6H2O was dissolved in aqueous ammonia (NH3ÁH2O),
and the mixtures of solution were stirred for 15 min and then
transferred into a 50 mL autoclave up to 80% of the total volume,
sealed, and heated at 180 ꢀC for 6 and 12 h, respectively. The
systemwere then allowed to cool to roomtemperature and the
final products were collected by filtration, and washed with de-
ionized water and absolute ethanol, and then dried at 50 ꢀC in
air. The XRD pattern of the synthesized Ni(OH)2 nanorod is
shown in Figure 1a.
10
20
30
40
50
60
70
2θ (degree)
Figure 1. (a) XRD pattern of the samples of Ni(OH)2 nanorods;
(b) XRD pattern of the samples of NiO nanorings synthesized
when the Ni(OH)2 nanorods were annealed at 500 ꢀC for 6 h.
Figure 2. (a) A TEM image showing the morphology of
Ni(OH)2 nanorods. (b) A HRTEM photo, taken on an individual
nanorod, of Ni(OH)2 nanorods, the inset is a SAED pattern of
Ni(OH)2 nanorods.
ꢀ
form. The interplanar spacing is 0.46 nm (4.6 A), which is good
agreement with the d spacing of (001) plane of hexagonal
Ni(OH)2 and shows that the growth direction is [001]. The inset
of Figure 2b is the corresponding SAED pattern, taken on the
single Ni(OH)2 nanorod, It is observed that the SAED pattern
consists of many spots, which shows that the nanorod of nickel
hydroxide is single crystal. All spots are identified as the diffrac-
Nanorings of NiO were synthesized when as-obtained
Ni(OH)2 nanorods were directly annealed at 500 ꢀC for 6 h in
muffle furnace. The XRD pattern of NiO nanoring is shown in
Figure 1b.
tion fromhexagonal Ni(OH) .
2
The size and morphology of the as-synthesized products of
Ni(OH)2 were further examined by TEM. Figure 2a displays that
the sample is rod-like structure with diameters 40–90 nm and
lengths 1–3 mm, and aspect ratios ranging from20–50. The
structure of Ni(OH)2 is further examined by HRTEM (high-res-
olution transmission electron microscopy) in Figure 2b. It is
shown that the lattice fringes in the nanorods are clearly ob-
served, which confirms that the nanorods are structurally uni-
The factors on the formation of Ni(OH)2 nanorods have
been investigated. We find that moderately higher temperature
and relatively longer time and higher ammonia concentration
will facilitate the rod-like structure formation. On the basis of
previous work, many 1-D nanostructures (nanotubes or nano-
rods) have been successfully synthesized fromlayered struc-
tures, the so-called 2-D structures.9–13 It is well known that
Ni(OH)2 is a layered compound of CdI2 type, therefore, we
Copyright ꢀ 2003 The Chemical Society of Japan

Chemistry Letters Vol.32, No.12 (2003)
1127
may justly suppose that the formation of Ni(OH)2 nanorods
might be related to the nature of its lamellar 2-D structures.
The further research is on the way.
It is interesting that Ni(OH)2 nanorods would be converted
into NiO nanorings when Ni(OH)2 nanorods were annealed at
500 ꢀC for 6 h. Quantumring-like structures, with the capability
of trapping magnetic flux in their interiors, are regarded as the
ideal candidates for observing Aharonov–Bohm(AB) effects,
such as energy oscillation and persistent currents,14 which has
triggered a strong interest in recent years.15
Figures 3a and 3b shows the overviews of TEM images of
NiO nanorings with different magnifications. It is shown that
the NiO nanorings are uniformand the range is 42–87 nmin di-
ameter. The size and morphology of NiO nanorings are further
examined on a HRTEM and the images of single NiO nanorings
are shown in Figure 3c. The magnification of Figure 3c is
400000, and the shape of single NiO nanoring is clearly ob-
served. It is shown that the ring is a quasi-circle structure and
more like an irregular pentagon structure, of which the longer
outer diameter is about 68.5 nm and the shorter outer diameter
is about 57.5 nm, and of which the longer inner diameter is about
22.5 nm and the shorter inner diameter is about 12.5 nm. The in-
set of Figure 3d is the corresponding SAED pattern of NiO
nanorings, and it is shown that the SAED pattern consists of
many spots, which shows that the NiO nanoring is single crystal.
All spots were identified as the diffraction fromcubic NiO. The
lattice fringes in the nanorings are shown in Figure 3d, which
confirms that structurally uniform and the high crystallizability
of the NiO nanorings. The inset of bottomof Figure 3d corre-
sponds to the area covered by the block plan. It can be calculated
ꢀ
that the interplanar spacing is 0.24 nm(2.4 A), which is in good
agreement with the d spacing of (111) plane of cubic NiO.
This work was supported by NSFC (20025102, 50028201,
20151001), the Foundation for the Author of National Excellent
Doctoral Dissertation of P. R. China, and the state key project of
fundamental research for nanomaterials and nanostructures.
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Figure 3. The typical TEM (HRTEM) images of the NiO
nanorings (a), (b) the overview of TEM images of NiO nanorings
with different magnifications; (c) the amplified TEM images of
single NiO nanoring, the inset is the SAED pattern of single
NiO nanoring; (d) the HRTEM image corresponding to single
NiO nanoring of (c), the inset in the bottomis the HRTEM image
of lattice fringes corresponding to the area the block plan indi-
ꢀ
cated, and the interplanar spacing is 0.24 nm(2.4 A), (the bar
in (d) is equal to 50 nm).
Published on the web (Advance View) November 10, 2003; DOI 10.1246/cl.2003.1126