A Core-shell nanostructure of carbon

Article abstract of DOI:10.1246/cl.2005.168

Core-shell structured carbon nanospheres with 300-500 nm in diameter have been synthesized at 600°C by reducing ethyl ether with metallic magnesium. Copyright

Full text of DOI:10.1246/cl.2005.168

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Chemistry Letters Vol.34, No.2 (2005)
A Core-shell Nanostructure of Carbon
ꢀ
Tao Luo, Xiaogang Yang, Jianwei Liu, Weichao Yu, and Yitai Qian
Structure Research Laboratory and Department of Chemistry, University of Science and Technology of China,
Hefei 230026, P. R. China
(Received August 27, 2004; CL-041013)
Core-shell structured carbon nanospheres with 300–500 nm
ꢁ
in diameter have been synthesized at 600 C by reducing ethyl
ether with metallic magnesium.
M
C: amorphous carbon
M: face-centered cubic
magnesium oxide
In 1991, the carbon nanotubes were observed and stimulated
1
M
intense interest in the structures accessible to carbon. In recent
years, considerable efforts have been made to fabricate different
M
a
b
C
C
M
M
2
–9
carbon nanostructures and explore their applications.
Jiang
and co-workers developed a catalytic-assembly benzene-thermal
route to multiwall carbon nanotubes using reduction of hexa-
chorobenzene by metallic potassium in the presence of Co/Ni
catalyst at 350 C. Lately, Liu et al. has successfully synthe-
sized bamboo-shaped carbon nanotubes on a large scale through
an ethanol thermal reduction process, in which ethanol was used
2
0
40
60
θ /Degree
80
2
ꢁ
10
Figure 1. XRD patterns of the products with different treat-
ments: (a) not washed: (b) washed with dilute HCl aq solution
and distilled water.
as the carbon source and metallic magnesium was used as the
reductant.11 In 1997, A. Krishnan and his co-workers have
successfully synthesized graphitic cones by the pyrolysis of
reaction.
The products were observed on a Hitachi 800 transmission
electron microscopy (TEM) performed at 200 kV. From the
TEM images in Figure 2, it can be seen that the sample consists
of the core-shell structured nanospheres with 300–500 nm in
diameter. There is a clear shell-like space between core and
shell, which is essential to distinguish core and shell of the same
component. The thickness of the shell is about 20 nm and the
core is 200–400 nm in diameter. The gap between core and shell
is about 30 nm. The electron diffraction (ED) pattern can be
attributed to amorphous carbon, which confirms the XRD
result.
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hydrocarbon in a carbon arc. The hollow carbon cones have
been synthesized by reduction of butyl alcohol with metallic
ꢁ
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magnesium at 500 C. Hu and his co-workers have synthesized
hollow carbon spheres by a self-assembly approach using
1
4
hexachorobenzene and Na. In the previous work, hollow car-
bon spheres had been synthesized by the medial-reduction route
using metallic magnesium powder, and the inorganic salts
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Na2CO3 and CCl4 as reactants in benzene solvent. To the best
of our knowledge, there has been no report about the synthesis of
the core-shell structured carbon yet.
Here we used a chemical approach to synthesize core-shell
structured carbon nanospheres. Such a process involved ethyl
ether as carbon source and magnesium as reducing agent. The re-
dox reaction could be expressed as:
C2H5OC2H5 þ Mg ¼ 4C þ MgO þ 5H2
In a typical experiment, 0.997 g of metallic magnesium
powder (99%) and 15 mL of ethyl ether were put into a 20-mL
stainless steel autoclave. After being sealed, the autoclave was
ꢁ
maintained at 600 C for 12 h and then cooled to room tempera-
ture naturally. The product was collected and washed with pure
ethanol, dilute hydrochloric acid and distilled water several
ꢁ
times. After that, the product was dried in vacuum at 60 C
for 6 h.
The phase of as-obtained products and the reaction were de-
termined by XRD on a Philips X’Pert PROSUPER X-ray powder
ꢀ
diffractometer (Cu Kꢀ radiation ꢁ ¼ 1:541874 A). Figure 1a
shows the XRD pattern of the product before washing. All the
reflection peaks can be indexed to the face-centered cubic
MgO (JCPDS Card File, No. 78-0430) and amorphous carbon.
Figure 1b is the XRD pattern of the products after being washed
by dilute HCl aq solution and distilled water, which can be
indexed to amorphous carbon. The results confirm the redox
Figure 2. (a) and (b) TEM images of the washed sample by
HCl. (c) The electron diffraction pattern, which was taken from
one sphere in Figure 2b.
Copyright Ó 2005 The Chemical Society of Japan

Chemistry Letters Vol.34, No.2 (2005)
169
Figure 4. Schematic growth model for core-shell structure
carbon nanospheres.
the edge. The magnesium oxide was removed by washing the
products with the dilute HCl aqueous solution. So the core-shell
structured carbon nanospheres were left.
In summary, the core-shell structured carbon nanospheres
300–500 nm in diameter have been successfully prepared by
an ethyl ether thermal reduction process with magnesium as re-
ductant. The model of the core-shell structured carbon nano-
spheres growth can be summarized to enclosure- diffusion proc-
ess. It provides a new pathway to interpret the core-shell struc-
tured carbon growth. It is also a promising approach to design
and fabricate semiconductor, noble metal and transition metal/
carbon core-shell nanostructure.
Figure 3. (a) and (b) TEM micrograph of the products without
washing. (c) The electron diffraction pattern, which was taken
from one of the spheres in Figure 3b.
To investigate the growth process of the core-shell struc-
tured carbon nanospheres, the products with various treatments
have been studied. The XRD pattern of Figure 1a proves that
the products includes MgO and C before being washed by dilute
HCl aq solution, meanwhile, it can be seen from the TEM im-
ages in Figure 3 that the nanospheres are solid and include many
darker and smaller particulates. And two sets of electron diffrac-
tion pattern are identified in Figure 3c. One is attributed to amor-
phous carbon. The other matches well to the diffraction pattern
of the face-centered cubic MgO: R1 to 111, R2 to 200, and R3
to 220. These prove that the nanospheres include MgO. After be-
ing washed with dilute HCl aqueous solution, MgO is removed,
which can be confirmed by XRD pattern of Figure 1b. And the
core-shell structured carbon nanospheres can be seen in TEM
images of Figure 2. So, we suggest that the enclosure-diffusion
process could be used to explain the formation of the core-shell
structure (in Figure 4): The reaction of this experiment is highly
Financial support from the National Natural Science Funds
and the 973 Projects of China is gratefully acknowledged.
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Published on the web (Advance View) December 25, 2004; DOI 10.1246/cl.2005.168