Preparation of hollow carbon nanospheres at low temperature via new reaction route

Article abstract of DOI:10.1016/j.jssc.2004.12.008

Hollow carbon nanospheres were obtained at 200°C via a new reaction route, by using magnesium, hexachloroethane and aluminum trichloride as starting materials and benzene as solvent. The products were characterized with X-ray diffraction pattern, transmission electron microscope, high-resolution transmission electron microscope images and Raman spectrum. The reaction conditions are easy to be maintained and controlled. They may provide a new method to produce other carbonaceous materials. A possible mechanism of reaction was proposed.

Full text of DOI:10.1016/j.jssc.2004.12.008

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Journal of Solid State Chemistry 178 (2005) 908–911
www.elsevier.com/locate/jssc
Preparation of hollow carbon nanospheres at low temperature via
new reaction route
Ã
Youbao Ni, Mingwang Shao , Yanhua Tong, Guixiang Qian, Xianwen Wei
Auhui Key Laboratory of Functional Molecular Solids, College of Chemistry and Materials Science, Anhui Normal University, Number 1, Beijing East
Road, Wuhu City, Anhui province 241000, P.R. China
Received 23 October 2004; received in revised form 2 December 2004; accepted 7 December 2004
Abstract
Hollow carbon nanospheres were obtained at 200 1C via a new reaction route, by using magnesium, hexachloroethane and
aluminum trichloride as starting materials and benzene as solvent. The products were characterized with X-ray diffraction pattern,
transmission electron microscope, high-resolution transmission electron microscope images and Raman spectrum. The reaction
conditions are easy to be maintained and controlled. They may provide a new method to produce other carbonaceous materials. A
possible mechanism of reaction was proposed.
r 2004 Elsevier Inc. All rights reserved.
Keywords: Nanostructure; Chemical synthesis; Grignard reagent; Hollow carbon nanospheres
1. Introduction
tion process [9], chemical vapor deposition method by
using mesoporous silica [10], pyrolysis hydrocarbon via
high temperature with certain catalyzers [11,12], shock
compression from C60 fullerene [13], media-reduction
route [14,15], self-assembly approach [16], etc. These
methods are very useful and are of widespread
importance. However, there are some limitations to
their utilities, such as the need of elevated temperature
resulting from the high melting temperature of carbon
materials (E4000 K), and the use of alkali metals K and
Na as reductants for their excellent active property
[14,16]; but on account of their violence, it is incon-
venient to employ the alkali metals as initial reagents.
Therefore, it is a challenge to synthesize the production
with other materials at mild conditions.
In this paper, we described how HCSs were prepared
via a new reaction route at 200 1C. Alkaline-earth Mg,
C2Cl6, AlCl3 were employed as starting materials and
benzene as solvent. The reactions were under easy
control and operated at mild conditions. Based on the
experimental results, we proposed a possible mechanism
to illustrate the formation of HCSs.
The discovery of carbon nanotubes by Iijima in 1991 [1]
has stimulated intense interest in carbon structures. What
makes carbon nanotubes and other carbon structures so
attractive is their unique structures, special chemical and
physical properties, including the capability for the storage
of a large amount of hydrogen [2], conductive and high-
strength composites [3], nanotweezers [4], gas storage
media [5], semiconductor devices [6] and field emission
displays [7]. Among the various forms of carbon, hollow
carbon nanospheres (HCSs) are of increasing interest due
to their low density, large surface area, stability, and
surface permeability, and in the medical field, they are
expected to act as effective oral sorbents for the removal of
uremicwaste metabolities from the intestine [8].
Because of carbon’s flexible structure, various meth-
ods have been demonstrated for the synthesis of HCSs
[9–16], such as mixed-valent oxide-catalytic carboniza-
Ã
Corresponding author. Fax: +86 553 386 9303.
E-mail address: zhengcui@mail.ahnu.edu.cn (M. Shao).
0022-4596/$ - see front matter r 2004 Elsevier Inc. All rights reserved.
doi:10.1016/j.jssc.2004.12.008

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Y. Ni et al. / Journal of Solid State Chemistry 178 (2005) 908–911
909
2. Experimental procedure
All reagents were commercially available and used
without further purification. In a typical experiment,
metallicMg powder (0.206 g, 99%), AlCl (0.210 g) and
3
C2Cl6 (0.980 g) were added into a vitreous conical flask
[17]; 10 mL C6H6 was filled in and the mixture was
stirred uniformly. Then the flask was put in an autoclave
of about 50 mL capacity. The reactor was sealed and
maintained at 200 1C for 12 h and then allowed to cool
down to room temperature naturally. The dark resultant
was collected, washed with absolute ethanol, HCl
solution (about 2 mol Lꢀ1), and distilled water. Finally,
it was dried in a vacuum at 60 1C for 6 h and about
0.08 g samples were obtained.
10
20
30
40
50
60
70
2θ(degree)
The phase and crystallography of the products were
characterized by X-ray diffraction (XRD) pattern,
which was recorded by using a Shimadzu XRD-6000
X-ray diffractometer equipped with CuKa radiation
(l ¼ 0:15406 nm), and the scanning rate of 0.05 1 sꢀ1 was
applied to record the pattern in the 2y range of 10–701.
The transmission electron microscope (TEM) image
was taken with a Hitachi Model H-800 TEM, using an
accelerating voltage of 200 kV to determine the mor-
phological features. The high-resolution transmission
electron microscope (HRTEM) image was investigated
with a JEOL-2010 TEM, using an accelerating voltage
of 200 kV.
Fig. 1. The XRD pattern of as-prepared products, which indicates a
hexagonal phase of carbon.
about 3.8 nm. The exact graphitic sheet number could
not be counted for most of them were entangled
together.
Further evidence for the purity of products was
obtained through the Raman spectrometer. Fig. 3 shows
that there exist two strong peaks at 1596 and 1360 cmꢀ1
.
The peak at 1596 cmꢀ1 corresponds to an E2g mode of
graphite, related to the vibration of sp2-bonded carbon
atoms in a two-dimensional hexagonal lattice, such as in
a graphite layer. The peak at 1360 cmꢀ1 is associated
with vibrations of carbon atoms with dangling bonds in
plane terminations of disordered graphite [19]. This
peak is quite broadened, which means that in the basal
plane there exists two-dimensional disorder, which is to
be expected, as the reaction temperature is low.
Raman spectrum was measured on a Spex 1403
Raman spectrometer at ambient temperature, employ-
ing an argon ion laser at an excitation wavelength of
514.5 nm.
3. Results and discussion
A possible mechanism of reaction was proposed.
Magnesium, as an active metal, easily forms Grignard
reagent with the organic-chloride as RCl+Mg-
RMgCl. Grignard reagent will react with the chlorides
of all elements below magnesium in the electromotive
series, usually by replacing the chlorine with alkyl
group, similar to the reaction RMgCl+AlCl3-
R3Al+MgCl2. Here, Grignard reagent, functioning as
a strong base, is attracted to electron-deficient centers
AlCl3, and obtains intermediate products R3Al [20].
In this method, AlCl3 also plays another role of
importance. It can polarize the chlorine atom to aid
the attraction on the highly stabilized material
C2Cl6 according to the route RCl+AlCl3-
[AlCl3 Á Clꢀ]+[R+]. Although the intermediated cation
The XRD pattern of the products (Fig. 1) shows the
presence of reflections characteristic of carbon hexago-
nal phase. Reflections in the figure can be indexed to
(002) and (101). The (002) peak is strong while (101) is
weak and wide. Compared with the reported data of
graphite (JCPDS Card Files, No. 41-1487), the position
of the (002) peak shifts a little angle from 2y ¼ 26.41 to
26.21, probably owing to the increase in the spacing
between sp2 carbon layers from 0.337 nm for graphite to
0.341 nm for HCSs [18].
The typical morphology of the samples is presented in
Fig. 2 via TEM observations. From Figs. 2a and b, it
can be seen that most of them are hollow nanospheres
with diameter of 30–60 nm. The strong contrast between
the dark edge and pale center is the evidence of its
hollow nature. The inset in Fig. 2a is the selected area
electron diffraction (SAED) pattern of the HCSs, which
can be indexed as (002) reflection of the graphite.
Fig. 2c shows the wall structure of typical HCSs
observed by HRTRM. The whole sheets thickness is
R
+ is stabilized to a degree, it is a higher-energy species
than the fully conjugated structure of the unsubstitued
chloride carbon. So, the R3Al is easily attacked by an
electrophile R+, to give an intermediate, and obviously,
an electrophile eventually must be released from the
intermediate to produce a neutral molecule R–R as the

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Y. Ni et al. / Journal of Solid State Chemistry 178 (2005) 908–911
910
Fig. 2. (a) TEM images of HCSs and SAED pattern (inset); (b) with large magnification of (a); (c) HRTEM images of the wall of HCSs; (d) some
short nanotubes could be observed at 300 1C and (e) many sheets of graphite could be seen under 150 1C.
reaction [R+]+R3Al-R-R+Al3+ [20]. As R–R still
contains chlorine atoms, it will act with metal Mg to
form Grignard reagent continuously until R–R loses all
the chlorine atoms and becomes carbon at last. The
fresh carbon atoms assemble into graphite layers, which
curl up to produce hollow nanospheres. Al3+ can also
combine with [AlCl3 Á Clꢀ] to provide the initial materi-
als AlCl3. The total reaction can be represented as
C2Cl6 þ Mg Aꢀl!Cl3 C þ MgCl2.
500
1000
1500
2000
In order to confirm this mechanism, we conducted a
control experiment without the use of AlCl3 and kept
other experimental invariables; no carbon was obtained.
It is supposed that the Lewis acid AlCl3 plays a vital role
wavenumber
Fig. 3. Raman spectrum of products which shows two graphite peaks
at 1350 and 1585 cmꢀ1
.

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Y. Ni et al. / Journal of Solid State Chemistry 178 (2005) 908–911
911
in the formation of carbonaceous materials. In addition,
References
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surface of Mg powder. The newly produced carbon
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lattice of sp2-bonded graphite sheets, which cover the
magnesium particles. After magnesium is consumed,
HCS is formed.
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The project was supported by the National Natural
Science Foundation of China (20271002) and the Special
Project Grants of Anhui Normal University.