A simple wet chemical route for large-scale synthesis of Cu(OH)2 nanowires

Article abstract of DOI:10.1016/S0009-2614(02)01571-3

Polycrystalline Cu(OH)₂ nanowires with a ～ 8 nm avg dia and lengths of up to hundreds of micrometers were synthesized using a simple chemical route at ambient temperature. Several comparative experiments were performed to study the effects on the Cu(OH)₂ particle size and shape of PH, NH₃, and SO₄/^2- at different concentration. NH₃ and NaOH were required to obtain the Cu(OH)₂ nanowires. Cu²⁺ ion formed complex with anions and ligands present in the precipitating solutions, the bond strength of which follows the order OH^- > NH₃ > SO₄/^2-. The most stable species was the square-planar amino complex [Cu(NH₃)₄/²⁺. At pH > 8, a large number of nuclei was formed instantaneously that grow to reasonably uniform, but when the concentration of NaOH was above 4 M, only large particle formed because the formation of cuprate ions at high pH led to lower supersaturation and a smaller number of nuclei that grow to large Cu(OH)₂ particles.

Full text of DOI:10.1016/S0009-2614(02)01571-3

Chemical Physics Letters 366 (2002) 220–223
www.elsevier.com/locate/cplett
A simple wet chemical route for large-scale synthesis
of CuðOHÞ nanowires
2
c
d
a
Wenzhong Wang a,b,1, Chun Lan , Yuanzhi Li , Kunquan Hong ,
a,b,
*
Guanghou Wang
a
National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093, PR China
b
Structure Research Laboratory, University of Science and Technology of China, Hefei, Anhui 230026, PR China
c
Department of Physics, Nanjing University, Nanjing 210093, PR China
d
Department of Chemistry, Nanjing University, Nanjing 210093, PR China
Received5 September 2002; in final form 9 September 2002
Abstract
Polycrystalline CuðOHÞ nanowires with an average diameter of ca. 8 nm and lengths of up to hundreds of mi-
2
crometers were synthesizedby using a simple chemical route at ambient temperature. The crystallity, purity, mor-
phology, andstructure features of the as-preparedCu ðOHÞ nanowires were investigated by powder X-ray diffraction
2
(XRD), transmission electron microscopy (TEM), andhigh-resolution transmission electron microscopy (HRTEM).
The growth mechanism of the CuðOHÞ nanowires were studied in detail.
2
Ó 2002 Elsevier Science B.V. All rights reserved.
Developing a controlled-synthesis method of
nanostructures at the mesoscopic level is one of the
most challenging issues presently facedby mate-
rials scientists [1]. This is especially true of nano-
wires, which are one-dimensional (1D) objects, for
which the control of growth at the molecular level
seems particularly difficult [2–11]. Several methods
have been usedto grow nanowires, such as laser-
assistedcatalytic growth [2–5], solution–liqui–d
solid(SLS) method[6–8], templating method
[9–13]. To the best of our knowledge, there are a
few reports on the preparation of CuðOHÞ
2
nanoparticles. For example, McFadyen and
Matijevic [14] synthesizedCu ðOHÞ colloids par-
2
ticles by using a wet chemical method. There are
no report on the synthesis of CuðOHÞ nanowires.
2
Herein we demonstrate a new and simple wet
chemical route for large-scale synthesis of the
nestedCu ðOHÞ nanowires.
2
The synthesis of CuðOHÞ nanowires includes
2
the following steps: 0.998 g CuSO4 Á 5H2O was
dissolved in 100 ml distilled water, which was
stirredwith a magnetic stirrer. This solution was
stirredfor 15 min to ensure that the CuSO dis-
4
solvedcompletely. Then 30 ml of 0.15 M NH OH
4
* Corresponding author. Fax: +86-25-3595535.
E-mail address: wangqun@nju.edu.cn (G. Wang).
was fast added into CuSO4 solution, under con-
stant stirring. After stirring for 15 min, 6 ml of 1.2
1
Also Corresponding author.
0009-2614/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved.
PII: S0009-2614(02)01571-3

W. Wang et al. / Chemical Physics Letters 366 (2002) 220–223
221
M NaOH was added dropwise into the above so-
lution, under constant stirring. A blue precipitate
pattern. The following TEM images (Fig. 2) indi-
cate that the diameters of these nanowires are very
small, andthe lengths are long. The as-synthesized
nanowires aggregate together easily due to their
small dimension. Thus the pattern of XRD may be
the result of the same as bulk.
of CuðOHÞ was produced. After stirring for 15
2
min, the blue CuðOHÞ precipitate was washed
2
with distilled water several times, filtered, and
dried in an oven at 35 °C for 24 h.
The powder X-ray diffraction (XRD) analysis
was performedusing a Rigaku (Japan) D max X-ray
diffractometer with graphite monochromatized Cu
Ka radiation (k ¼ 0:154178 nm). Transmission
electron microscopy (TEM) images were obtained
on a JEM-200 CX transmission electron micro-
scope, using an accelerating voltage of 200 kV.
High-resolution transmission electron microscopy
(HRTEM) images were obtainedon a JEOL-2010
transmission electron microscope, using an accel-
erating voltage of 200 kV.
The morphology of the nanowires was observed
by TEM. TEM images of the as-synthesized
CuðOHÞ nanowires are shown in Fig. 2. Bulk
2
quantities of the nestedCu ðOHÞ nanowires were
2
fabricatedwith relatively uniform diameters. The
nanowires are relatively straight andlong, result-
ing in a large aspect ratio. The diameters of
nanowires range from 4 to 12 nm. It can be seen
that most nanowires have diameters of ca. 8 nm,
and the lengths of up to hundreds of micrometers;
but nanowires with diameters of less than 5 nm
were also found. The average diameter of nano-
wires is ca. 8 nm estimatedfrom the TEM images.
Due to the small diameters and aggregated to-
gether of nanowires, it is very difficult to accu-
rately give the size distribution of diameters.
Fig. 1 show powder XRD pattern of the as-
preparedCu ðOHÞ nanowires. All of the reflec-
2
tions of the XRD pattern of the as-synthesized
CuðOHÞ nanowires can be easily indexed to those
2
of orthorhombic crystalline CuðOHÞ (JCPDS 13-
2
420), indicating the formation of single-phase
CuðOHÞ . The CuðOHÞ lattice constants calcu-
A typical HRTEM image of a single nanowire
with a diameter of ca. 8 nm is shown in Fig. 3a.
The visible lattice fringes illustrate that the nano-
wire is a polycrystalline rather than a single crystal
within the lateral dimension, as shown. The in-
terplanar spacing is about 0.2625 nm, which cor-
responds to the {0 0 2} planes of orthorhombic
2
2
latedfrom the XRD adta are
ꢀ
a ¼ 2:954;
b ¼ 10:386 and c ¼ 5:270 A, consistent with those
of bulk CuðOHÞ (JCPDS 13-420).In the XRD
2
pattern, the peaks were not widened obviously due
to the facts that it is normal to the same as bulk
CuðOHÞ . This result reveals that the growth plane
2
of the nanowires is one of the {0 0 2} planes in the
area shown. The two-dimensional lattice image
Fig. 1. The XRD pattern of the as-synthesizedCu ðOHÞ
2
nanowires.
Fig. 2. TEM images of the as-preparedCu ðOHÞ nanowires.
2

222
W. Wang et al. / Chemical Physics Letters 366 (2002) 220–223
2CuSO4 þ 2NH3 Á H2O
! Cu2ðOHÞ SO4 þ ðNH4Þ SO4
ð1Þ
ð2Þ
2
2
Cu2ðOHÞ SO4 þ 8NH3
2
! 2½CuðNH3Þ Š2þ þ SO42À þ 2OHÀ
4
2þ
½CuðNH3Þ Š ! Cu2þ þ 4NH3
ð3Þ
ð4Þ
4
Cu2þ þ 2OHÀ ! CuðOHÞ
2
We can give a reasonable explanation for wire
formation of CuðOHÞ according to CuðOHÞ
2
2
structure feature andspecific interaction of con-
stituent Cu2þ ions with ligands forming solutes in
the mother solutions. Oswaldet al. [16] have de-
terminedthat the Cu ðOHÞ structure consists of
2
oblate chains
in the planes (0 0 1), orientedalong [1 0 0], with
characteristic of the square planar coordinated
Cu2þ ion and rx2Ày2 strong bonds. This strong
Fig. 3. (a) and(b) HRTEM images of a ca. 8 nm Cu ðOHÞ
2
nanowire.
olatedchain is parallel with the shortest lattice
parameter, andacts as a structure-making factor,
aroundwhich another set of stronger bound
chains is createdthrough olation/oxolation bridges
pointed by the arrowheads (Fig. 3b) also indicates
that the CuðOHÞ nanowires are polycrystalline.
2
This work has shown that both ammonia and
sodium hydroxide are needed in order to obtain
À
connectedwith the first one by the OH or O2À
anions. This bond structure leads to a two-di-
mensional or quasi-one-dimensional framework
packed together by hydrogen bridges, yielding the
the CuðOHÞ nanowires. In the present case, it is
2
well known that Cu2þ ion forms complex with
anions andligansd present in the precipitating
solutions, the bondstrength of which follows the
order OHÀ > NH3 > SO24À. At the pH of interest
(before the addition of NaOH), stability constants
formation of wire-like CuðOHÞ . On the other
2
hand, Matijevic and co-workers [15] applied the
periodic bond chains (PBC) theory, which is based
on the existence of strong bonds in the particle of a
[15] indicate the most stable species to be the
square-planar amino complex ½CuðNH3Þ Š. A rise
2þ
given morphology, to the CuðOHÞ structure.
2
4
They concluded that the {0 1 0} is very important
face of morphological significance. Basedon these
results, we can make another rational explanation
in the pH on addition of NaOH causes a decrease
in the stability of this complex, resulting in the
precipitation of CuðOHÞ . The chemical reactions
2
for the formation of CuðOHÞ wire particles. The
we employedfor the synthesis of Cu ðOHÞ nano-
2
2
formation of the CuðOHÞ nanowires couldbe due
wires can be formulatedas
2

W. Wang et al. / Chemical Physics Letters 366 (2002) 220–223
223
to the adsorption of solutes on the crystal faces.
In conclusion, a new andsimple synthetic ap-
proach has been successfully developed to synthe-
This process shouldbe relatedto the bondstrength
of such species to Cu2þ; thus, the strong bonds in
the planar coordination of copper will always be
occupiedby OH À. However, NH3 may adsorb on
(0 1 0) surface, thus preventing the formation of
hydrogen bridges and, consequently, the packing
of the (0 1 0) slices; as a result elongatedparticles
are formed. This explanation is corroborated by
size the nestedCu ðOHÞ crystalline nanowires with
2
an average diameter of ca. 8 nm and the lengths of
up to hundreds of micrometers. This method re-
quires neither complex apparatus andsophisticated
techniques nor metal catalysts andsurfactants. The
process is carriedout at ambient temperature and
the yieldof the final Cu ðOHÞ nanowires is bulk.
2
the presence of NH3 in the CuðOHÞ particles,
From these points of view, this methodhas po-
tential for industrial-scale application.
2
detected by infrared spectroscopy (not shown
here) of the CuðOHÞ .
2
In order to investigate the effects on the
Acknowledgements
CuðOHÞ particle size andshape of PH, NH and
3
2
SO24À at different concentration, several compara-
tive experiments were made. Keeping other con-
ditions the same, the concentration of NH3 Á H2O
This work was supportedby the National
Natural Science Foundation of P.R. China (No:
29890210, 10023001, 10074024).
is between 0.05 and0.15 M, Cu ðOHÞ nanowires
2
can be successfully synthesized. Because higher
concentration of NH3 Á H2O may cause a decrease
2þ
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