One-step template-free solution route for Cu(OH)2 nanowires

Article abstract of DOI:10.1134/S0036023608010063

Cu(OH)₂ nanowires with a diameter of 8-10 nm and lengths of tens of micrometers were fabricated in the basic solution by dropping simply NaOH solution into CuCl₂ solution at ambient temperature. The formation mechanism of nanowires was discussed. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD) were used to characterize the samples.

Full text of DOI:10.1134/S0036023608010063

ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2008, Vol. 53, No. 1, pp. 36–39. © Pleiades Publishing, Ltd., 2008.
SYNTHESIS AND PROPERTIES
OF INORGANIC COMPOUNDS
One-step Template-free Solution Route for Cu(OH)2 Nanowires1
Jinhe Suna,b, Yongzhong Jiaa,c, Yan Jinga, Ying Yaoa, and Wu Lia
a Institute of Salt Lakes, Chinese Academy of Sciences, Qinghai, 810008, P. R. China
b Graduate School of the Chinese Academy of Sciences, Beijing, 100008, P. R. China
c Taizhou University, Zhejiang, 317000, P. R. China
Abstract—Cu(OH)2 nanowires with a diameter of 8-10 nm and lengths of tens of micrometers were fabricated
in the basic solution by dropping simply NaOH solution into CuCl2 solution at ambient temperature. The for-
mation mechanism of nanowires was discussed. Scanning electron microscopy (SEM), transmission electron
microscopy (TEM), and X-ray diffraction (XRD) were used to characterize the samples.
DOI: 10.1134/S0036023608010063
1
For their novel and fascinating properties, and their
potential applications in nanodevices, the considerable
interest has been attracted to fabrication of one-dimen-
sional (1D) nanomaterials, such as nanorods, nanow-
ires, nanoribbons, and nanotubes [1]. Many methods
have been developed for the fabrication of ID materials,
including solvothermal methods [2], template-based
methods [3, 4], VLS methods [5, 6], and so on. Among
these methods, solution phase synthesis attracted
increasing attention for its low cost, controllable syn-
thesis [7, 8]. As a well-known layered material with
orthorhombic structure, Cu(OH)2 has received much
attention in recent years. The magnetic properties of
Cu(OH)2 are remarkably sensitive to the intercalation of
molecular anions, making the material a candidate for
sensor applications [9–11]. Using Cu(OH)2 nanowires
as precursors, it is easy to prepare CuO, Cu2O and Cu
nanowires [12–14]. In previous works, copper (II)
hydrous oxide solutions of various particle shapes and
uniformity were obtained by aging copper salt solu-
tions at different temperatures under controlled pH con-
ditions [15, 16]. Cu(OH)2 nanowires were synthesized
mainly by two routes: precipitating cupric salt by the
mixture of ammonia and NaOH solution [17–20] and
oxidizing copper foil in the basic solution of ammonia
[12, 21, 22]. Luo synthesized Cu(OH)2 nanostrands by
adding ammonia solution to Cu(NO3)2 solution [23].
Cu(OH)2 nanofibers and nanotubes arrays were synthe-
sized by oxidization of a copper foil in a basic solution
electrically or chemically [24–26].
EXPERIMENTAL
1 mol/L NaOH (96.0%, Xi’an Chemicals Plant)
solution was dropped into 150 mL 0.05 mol/L CuCl2
solution under agitation at room temperature. The pH
value of CuCl2 solution was controlled by a pH meter
of the PHS-3C type (2nd analytical instruments plant,
Shanghai). When the pH value of solution reached
12.5, the pH value was maintained for 30 min by care-
fully dropping 1 mol/L NaOH solution or 1 mol/L HCl
solution. After 1.5 h, agitation was stopped and the pre-
cipitate was aged for 1–3 days. The precipitate was
washed with distilled water and absolute ethanol sev-
eral times.
The products were characterized by JSM-5600LV
scanning electron microscopy (SEM) (JEOL Ltd,
Japan), X’Pert PRO X-ray diffractometer (XRD)
(PANalytical, Holland), and Hitachi H-6000 transmis-
sion electron microscopy (TEM) (Hitachi, Japan). The
X-ray diffraction analysis was performed at 40.0 KV
and 30.0 mA with CuKα radiation (λ = 0.15406 nm).
RESULTS AND DISCUSSION
Fig. 1 shows the XRD pattern of the as-synthesized
Cu(OH)2 a nanowires. All the peaks in Fig. 1 can be
well indexed into the orthorhombic ëu(éç)2 structure
with lattice constants a = 2.951Å, b = 10.59 Å, and n =
5.273 Å (JCPDS 13-420). In the XRD pattern, the
broadening peaks indicated the tiny size of crystals of
as-synthesized products.
Fig. 2 are the scanning electron microscopy (SEM)
images of Cu(OH)2 nanowires. Two existing manners,
bundle and nest in the Cu(OH)2 nanowires, were
observed from Fig. 2a,b. The bundle-like structure,
which consisted of several or tens of single nanowires,
was the dominant component. Fig. 2c shows the diam-
eter of bundles was up to several hundred nanometers
In this work, a simple and facile method was devel-
oped to synthesize ëu(OH)2 nanowires by dropping
NaOH solution into CuCl2 solution at ambient temper-
ature under controlled pH conditions. The formation
mechanism of nanowires was discussed.
1
This article was submitted by the authors in English.
36

ONE-STEP TEMPLATE-FREE SOLUTION ROUTE
37
TEM images of as-synthesized Cu(OH)2 nanowires
are shown in Fig. 3. Though Cu(OH)2 nanowires existed
in two congregating manners, the diameter of single nanow-
ires was relatively uniform. It ranged from 8 to l0 nm. The
single nanowire was straight and its aspect ratio was up
to several thousands. The bundle-like structures in
Fig. 3a were composed of tens of single Cu(OH)2
nanowires connecting closely side-by-side. The surface
of bundles was full of holes, the diameters of which
were about several nanometers. Fig. 3b are TEM
images of nest-like structures in which well-dispersed
thicker nanowires were composed of single or several
Cu(OH)2 nanowires. Among nest-like structures, holes
were not found on the surface of single nanowires. It
could be inferred that the holes were formed at the
boundary between single nanowires during single
nanowires connecting side-by-side.
10
20
30
40
50
60
70
2θ, deg
Fig. 1. The XRD pattern of the as-synthesized Cu(OH)
nanowires.
2
In previous works, ammonia solution were used to
prepare Cu(OH)2 nanowires, in which NH3 was consid-
and length was about tens of micrometers. Fig. 2d
shows the nest-like structures scattered among the bun-
dles. They were constituted by short well-dispersed
Cu(OH)2 nanowires which interconnected to form a
clew. The length of single ëu(OH)2 nanowires in the
nest-like structures was about 500–2 µm, which was
much shorter than that of bundles. The bundle-like
structures of Cu(OH)2 nanowires were similar to that of
Cu(OH)2 nanowires synthesized by the KOH/NH3
route, but in which nest-like structures were not be
observed [17].
ered to formed complex [Cu(NH3)4]2+ with Cu2+ ion,
played a transporter role of Cu2+ ion, and NH3 adsorbed
on the (010) surface of Cu(OH)2 to prevent the forma-
tion of hydrogen bridges. Consequently, the packing of
the (010) slices resulted in forming elongated particles
and the preferential growth of planes [17, 18, 23]. In
this work, we proposed that OH– ions played an impor-
tant role during the formation of Cu(OH)2 nanowires,
which replaced NH3 of previous works to coordinate
with Cu2+ ions to form [Cu(OH)4]2– complexes which
transported Cu2+ to the nanowires growing tips with
5 µm
1 µm
(‡)
(b)
1 µm
1 µm
(c)
(d)
Fig. 2. SEM images of the as-synthesized Cu(OH) nanowires.
2
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 53 No. 1 2008

38
JINHE SUN et al.
100 nm
(b)
100 nm
(‡)
Fig. 3. TEM images of the as-synthesized Cu(OH) nanowires.
2
OH– ligands attached. Cu(OH)2 strongly absorbed OH–
room temperature. Cu(OH)2 nanowires existed in two
ions in the strong basic solution for its positively charg- manners: bundle and nest. OH– ions played an impor-
tant role in transporting Cu2+ by forming the complex
[Cu(OH)4]2– and resulting in varying growth rates of
crystal planes by absorption on the surfaces of Cu(OH)2
crystals. This paper presented a facile and simple
method to synthesize Cu(OH)2 nanowires at ambient
conditions without any surfactant. It may be extended
to the synthesis of other hydroxides nanowires, such as
Ni(OH)2 and Co(OH)2, which we are investigating.
ing. It was well-known that the surface energy density
of different crystal planes was varied drastically, which
suggested that the different crystal planes of Cu(OH)2
absorbed different amounts of OH– ions. The crystal
planes that absorbed more OH– ions would repel the
approach of [Cu(OH)4]2– and growth of the crystal
planes would be hindered. On the contrary, proper
absorption would favor the growth of crystal planes. As
a result, Cu(OH)2 nanowires were fabricated. When the
pH of solution was about 10, the precursor atacamite
Cu2Cl(OH)3 was obtained, which was about 5–8 nm.
The diameter of the atacamite nanoparticle was paral-
leled to the diameter of Cu(OH)2 nanowires. It sug-
gested that the atacamite nanoparticles played a tem-
plate role at the beginning of the formation of Cu(OH)2
nanowires. With the increasing of pH and the prolong-
ing of aging time, the templates were dissolved by
forming [Cu(OH)4]2– ions, which reprecipitated by self-
assembly to the growing tips of Cu(OH)2 crystals. For
the slow growth of side crystal planes of Cu(OH)2
nanowires, the diameter of nanowires was increased to
8–10 nm.As for the single Cu(OH)2 nanowires connect-
ing side-by-side, the marginal hydrogen bonds in the
nanowires reacted with OH– ions in the strong basic
solution to form hydrogen bond bridges between adja-
cent nanowires with aging. The driving dynamics was
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