Shape controlled synthesis of Cu2O and its catalytic application to synthesize amorphous carbon nanofibers

Article abstract of DOI:10.1016/j.materresbull.2008.04.011

Octahedral Cu₂O particles and Cu₂O nanowires were synthesized by a simple solution-phase route using N₂H₄·H₂O as reducing agent at room temperature. Amorphous carbon nanofibers were synthesized using

Full text of DOI:10.1016/j.materresbull.2008.04.011

Materials Research Bulletin 44 (2009) 25–29
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Materials Research Bulletin
journal homepage: www.elsevier.com/locate/matresbu
Shape controlled synthesis of Cu2O and its catalytic application to synthesize
amorphous carbon nanofibers
b
a
Fanglin Du a, , Jungang Liu , Zhiyan Guo
*
a Key Laboratory for Nanostructured Materials, Qingdao University of Science and Technology, Qingdao 266042, China
b Technical development center, Laiwu Steel Corp. Ltd., Laiwu 271104, China
A R T I C L E I N F O
A B S T R A C T
Article history:
Octahedral Cu2O particles and Cu2O nanowires were synthesized by a simple solution-phase route using
N2H4ꢀH2O as reducing agent at room temperature. Amorphous carbon nanofibers were synthesized using
octahedral Cu2O particles and an acetylene gas source at atmospheric pressure. The samples were
characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron
microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy and thermogravimetric (TG) analysis.
SEM and TEM images indicated that most of the obtained octahedral Cu2O particles had an edge length of
400–700 nm. The obtained nanowires had uniform diameters of about 15 nm, and the length of the
Received 30 September 2006
Received in revised form 6 April 2008
Accepted 17 April 2008
Available online 24 April 2008
Keywords:
A. Nanostructures
B. Crystal growth
B. Chemical synthesis
D. Catalytic properties
D. Crystal structure
nanowires ranged from 5 to 10
mm. The XRD result revealed the amorphous feature of the nanofibers. IR
spectrum revealed that the nanofibers consist of –CH, –CH2, –C C– and –CH3 groups. The concentrations
of N2H4ꢀH2O and NaOH played important roles in controlling the geometric shape of the Cu2O.
ß 2008 Elsevier Ltd. All rights reserved.
1. Introduction
amorphous carbon nanofibers using cuprous oxide particles as
catalyst.
It is important to control the size, shape and structure of
particles because of the tight correlation between these para-
meters and optical, electrical and catalytic properties [1]. Metal
and semiconductor nanoparticles have been widely studied in
various fields such as electronics devices [2] and catalysis [3,4].
Over the past several decades, cuprous oxide (Cu2O) has attracted
much interest because of its potential applications in catalysis,
biosensors, and micro/nanoelectronics [5–7]. Nanostructured
Cu2O with different morphologies has been synthesized using
solution routes [8–13] and electrodeposition method [14].
Carbon nanofibers and nanotubes can be synthesized by metal
powders such as nickel, cobalt and iron [15–17]. Qin et al. [18]
reported the growth of helical nanofibers on copper nanoparticles
by using acetylene as a gas source. Helically shaped multiwalled
carbon nanotubes were obtained as main products in large
quantities by using co-pyrolysis of Fe(CO)5 as floating catalyst
precursor and pyridine or toluene as carbon source [19]. Carbon
nanofibers were synthesized by using alumina-supported Ni
catalyst [20]. However, there are few reports on the synthesis of
Herein we reported a simple solution-phase route to control the
morphology of cuprous oxide at room temperature and its catalytic
applications to synthesize amorphous carbon nanofibers.
2. Experimental
All of the chemical reagents used in this experiment were
analytical grade. In a typical synthesis, 0.250 g Cu(NO3)2ꢀ3H2O and
0.250 g polyethylene glycol (PEG; Mw 20000) were dissolved in
200 ml H2O, which was stirred with a magnetic stirrer for 10 min.
Then, 1.2 ml of 4 M NaOH solution was slowly dropped into the
Cu(NO3)2 solution. After stirring for 10 min, 2.4 ml of 1.5 M
N2H4ꢀH2O solution was slowly dropped into the mixed suspension.
The solution was kept for 10 min under constant stirring. The
resulting products were collected, washed several times using
absolute ethanol and distilled water and dried in a vacuum oven at
80 8C for 2 h.
Acetylene was used as the only carbon source and the as-
synthesized octahedral Cu2O particles were used as catalyst in our
experiment. The reaction tube of quartz was used as a reactor,
which was heated by an electric furnace. After the reactor was
pumped to vacuum, the acetylene gas was introduced into the
reaction room. The reaction began at 265 8C and this temperature
was kept constantly until the reaction finished.
* Corresponding author. Tel.: +86 532 84022870; fax: +86 532 84022870.
E-mail address: dufanglin@qust.edu.cn (F. Du).
0025-5408/$ – see front matter ß 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.materresbull.2008.04.011

26
F. Du et al. / Materials Research Bulletin 44 (2009) 25–29
3. Characterization
X-ray powder diffraction (XRD) patterns of the samples were
obtained on a XB-3A instrument using monochromatic Cu K
radiation ( = 0.15418 nm). The experimental conditions corre-
a
l
spond to step width of 0.028 and scan speed of 78/min.
Transmission electron microscopy (TEM) was carried out on a
JEM-1200EX operating at an accelerating voltage of 60 kV. The
overview morphology of the samples was measured by field
emission scanning electron microscopy (FESEM), performed on a
JSM-6700F. The samples for characterization were prepared by
dripping the precipitate onto a silicon wafer. FT-IR spectrum was
performed on a Nicolet Fourier transform infrared (FT-IR) spectro-
scopy. The nanofibers were characterized by a thermogravimetric
analysis (TG) at a heating rate of 10 8C/min.
Fig. 1. XRD pattern of the as-synthesized octahedral Cu2O.
4. Results and discussion
Fig. 1 shows the XRD pattern of the as-prepared octahedral
Cu2O particles. The diffraction peaks in this pattern can be indexed
to cubic structure of octahedral Cu2O with lattice constants of
length of 1 mm. All of the particles had a mean edge length of 400–
700 nm and smooth surface. To investigate the effects of
concentration of NaOH, 1.2 ml of 24 M NaOH solution was slowly
dropped into the suspension with other conditions unchanged. As
shown in Fig. 2(c), only octahedral Cu2O particles were observed.
Different concentrations of PEG were also investigated in this
experiment. As shown in Fig. 2(d), when 0.500 g PEG was added
into the suspension, octahedral Cu2O particles and Cu2O nanowires
were observed. We can conform that the concentration of PEG is
not the crucial factor to control the morphology of Cu2O. All the
results above suggested that it was possible to tune the
morphology of Cu2O by controlling the experimental conditions.
Fig. 3(a) shows the typical transmission electron microscopy
(TEM) image of octahedral Cu2O particles prepared with 2.4 ml of
1.5 M N2H4ꢀH2O, 1.2 ml of 24 M NaOH and 0.250 g PEG. Bulk
quantities of octahedral particles were formed with symmetrical
˚
a = 4.26 A. This is in good agreement with the literature values
(JCPDS05-0667). The peaks with 2 values of 29.598, 36.528, 42.368,
u
61.568, 73.708 and 77.608 correspond to the crystal planes of 1 1 0,
1 1 1, 2 0 0, 2 2 0, 3 1 1 and 2 2 2 of crystalline Cu2O, respectively.
Fig. 2 shows the overall morphology of Cu2O prepared under
different conditions. As shown in Fig. 2(a), when 2.4 ml of 1.5 M
N2H4ꢀH2O solution was added into the suspension, the major
products were nanowires. Few octahedral Cu2O particles were
observed. Most nanowires had uniform diameters of about 15 nm
and length from 5 to 10
m
m. When 2.4 ml of 5 M N2H4ꢀH2O
solution was added into the suspension with other conditions
unchanged, only octahedral Cu2O particles were obtained, which is
shown in Fig. 2(b). Most of the octahedral particles had an edge
Fig. 2. SEM images of products prepared under different conditions.

F. Du et al. / Materials Research Bulletin 44 (2009) 25–29
27
Fig. 3. (a) TEM image of octahedral Cu2O particles, (b) single octahedral Cu2O particle, (c) the corresponding SAED pattern, (d) and (e) schematic illustrations of octahedral
Cu2O particle.
morphology. Fig. 3(b) shows a typical octahedral particle. The size
and morphology were in good agreement with the results of SEM
images. Fig. 3(c) shows the selected area electron diffraction
(SAED) pattern of the particle. This pattern indicates the single
crystal nature of the octahedral Cu2O particles.
we can formulate the main reaction process as follows:
C2H2ðaÞ ! C2ðaÞ þ 2H
(3)
(4)
ðaÞ
2HðaÞ þ Cu2O ! 2Cu þ H2O
Fig. 5 shows typical SEM and TEM images of the fibers catalyzed
by octahedral Cu2O particles. Fig. 5(a) shows that all of the fibers
had a ribbon-like shape. It can be seen that most fibers have
In the experiment, hydrazine hydrate was used as the reducing
agent. Cu2O with different morphologies was obtained by
following reactions:
diameters of 400–500 nm and length from 10 to 20
mm. Fig. 5(b)
CuðNO3Þ2 þ 2NaOH ! CuðOHÞ2 þ 2NaNO3
4CuðOHÞ2 þ N2H4 ! 2Cu2O þ 6H2O þ N2
(1)
(2)
shows that the catalyst particles seemed to have a regular
projected faceted shape, such as rhombic and triangular after
the fibers grew. The changes of the catalyst particles’ shape were
found in Fig. 5(b). Fig. 5(c) shows that the fiber diameter was
approximately equal to the size of the single catalyst particles.
From Fig. 5(b) and Fig. 5(c), we can conclude that the fiber diameter
was determined on the size of the single catalyst particles and the
shape of catalyst particles was not a crucial factor to control the
morphology of the fibers. Helical carbon nanofibers were
synthesized with a copper catalyst [21] as a catalyst. It can be
noted that the size of copper catalyst in their experiment was
about 50 nm, which was much smaller than the Cu2O particles in
our experiment. We can conclude that the size of the catalyst was a
crucial factor to control the morphology of the fibers.
Bulk Cu2O was a cubic structure. Choi [14] reported that it was
possible to modify the growth ratio, R, which was defined as the
growth rate along the h1 0 0i direction to that along h1 1 1i
direction. In our experiment, we hypothesized that copper(II)
coordinated to the oxygens of the PEG initially in water. The
observed Cu2O nanowires suggested that the capping groups of
PEG on the Cu2O surface led to anisotropic shapes. Since there was
a small quantity of N2H4ꢀH2O and NaOH, the reaction rate was also
slow. Cu2O crystals grew to nanowires because of the surfactant. As
the concentration of N2H4ꢀH2O and NaOH was increased, the
growth ratio R was also increased above 1.73. As a result, relatively
faster growing {1 0 0} facets were eliminated in the final
morphology forming octahedral Cu2O. This hypothesis was in
good agreement with our experiment.
The XRD pattern of nanofibers is shown in Fig. 4. The broad
diffraction peaks of amorphous nanofibers can be observed. No
diffraction peak of graphitic carbon appears, revealing an
amorphous feature of the nanofibers. The other diffraction peaks
at higher diffraction angles can be indexed to cubic structure of Cu
˚
with lattice constants of a = 3.615 A. This is in good agreement
with the literature values (JCPDS04-0836). No peaks due to
impurities were found. Jiang [18] synthesized amorphous carbon
nanofibers and reported that about 6% hydrogen was released from
the acetylene precursor. In our reaction, the heat treatment led to
the cleavage of acetylene. The C–H cleavage process produces
atomic hydrogen which was in an adsorbed state. After Cu2O was
reduced by the atomic hydrogen, the deposition reaction of
acetylene occurs on the surfaces of copper obtained. In our study,
Fig. 4. XRD pattern of the carbon fibers.

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F. Du et al. / Materials Research Bulletin 44 (2009) 25–29
Fig. 5. (a and b) SEM images of carbon nanofibers. (c) TEM image of the fibers catalyzed by Cu2O.
The peaks ascribed to the –C–H vibration in –CH2 or –CH were
observed at 2926 cmꢁ1, 2871 cmꢁ1 and 1451 cmꢁ1, respectively.
The peak at 1601 cmꢁ1 was ascribed to the –C C– stretching
vibration. The peak at 1376 cmꢁ1 could be assigned to –C–H
deformation in –CH3 induces. The IR spectrum indicated the high
hydrogen content in the nanofibers.
The thermal stability of the nanofibers was determined by
thermogravimetric (TG) analysis. As shown in Fig. 7, with the
increase of the temperature, obvious weight loss was observed.
The weight loss of nanofibers indicated that the products released
small hydrocarbon molecules because of the C–H cleavage and
structural reconfiguration of the nanofibers.
5. Conclusions
In conclusion, Cu2O with different morphologies had been
synthesized by controlling the experimental conditions. With low
concentration of N2H4ꢀH2O and NaOH, Cu2O nanowires were major
products. When the concentration of N2H4ꢀH2O and NaOH was
increased, only octahedral Cu2O particles were obtained. The
concentration of PEG was not the crucial factor to control the
morphology of Cu2O. In addition, octahedral Cu2O particles were
successfully used to synthesize amorphous carbon nanofibers. The
size of the catalyst was the crucial factor to control the diameter
and morphology of the fibers.
Fig. 6. IR spectrum of nanofibers.
Fig. 6 shows the infrared (IR) spectrum of the nanofibers. The
peaks at 3449 cmꢁ1 and 1705 cmꢁ1 are ascribed to the stretching
vibrations of –O–H and –C O, indicating the slight oxidation of
the product when the nanofibers were took out from the reactor.
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