Controllable synthesis and modification of carbon micro-spheres from deoiled asphalt

Article abstract of DOI:10.1016/j.jpcs.2009.11.012

A series of size-controllable carbon micro-spheres (CMSs) were synthesized from deoiled asphalt by chemical vapour deposition, with the emphasis on the effect of reaction temperature, Ar flow rate and collection zone. Graphitized carbon micro-spheres (GCMSs) were obtained from as-prepared CMSs by vacuum heat treatment at 2000 °C for 1 h. Air oxidation was performed to realize functionalization of CMSs. Morphologies and structures of CMSs and GCMSs were characterized by field emission scanning electron microscopy, high-resolution transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction and Raman spectroscopy, and the functional groups on the surface of GCMSs and CMSs were characterized by Fourier transformation infra-red spectrometry. Results show that effective mass production of size-controllable CMSs, with diameters ranging from 100 nm to 1 μm, was achieved. As-obtained high purity CMSs were spherical with uniform size and low graphitization degree, but the graphitization degree of GCMSs was enhanced obviously. By air oxidation, some oxygen-containing functional groups were introduced onto the surface of CMSs, while no functional groups were introduced onto the surface of GCMSs.

Full text of DOI:10.1016/j.jpcs.2009.11.012

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Journal of Physics and Chemistry of Solids 71 (2010) 235–241
Contents lists available at ScienceDirect
Journal of Physics and Chemistry of Solids
journal homepage: www.elsevier.com/locate/jpcs
Controllable synthesis and modification of carbon micro-spheres from
deoiled asphalt
Yongzhen Yang a,b, Xuguang Liu a,c,n, Chun Yi Zhang a,b, Mingcong Guo a,c, Bingshe Xu a,b
a Key Laboratory of Interface Science and Engineering in Advanced Materials, Taiyuan University of Technology, Ministry of Education, Taiyuan 030024, China
b College of Materials Science and Engineering, Taiyuan University of Technology, Taiyuan 030024, China
c College of Chemistry and Chemical Engineering, Taiyuan University of Technology, Taiyuan 030024, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of size-controllable carbon micro-spheres (CMSs) were synthesized from deoiled asphalt by
chemical vapour deposition, with the emphasis on the effect of reaction temperature, Ar flow rate and
collection zone. Graphitized carbon micro-spheres (GCMSs) were obtained from as-prepared CMSs by
vacuum heat treatment at 2000 1C for 1 h. Air oxidation was performed to realize functionalization of
CMSs. Morphologies and structures of CMSs and GCMSs were characterized by field emission scanning
electron microscopy, high-resolution transmission electron microscopy, energy dispersive X-ray
spectroscopy, X-ray diffraction and Raman spectroscopy, and the functional groups on the surface of
GCMSs and CMSs were characterized by Fourier transformation infra-red spectrometry. Results show
Received 10 February 2009
Received in revised form
25 November 2009
Accepted 26 November 2009
Keywords:
A. Amorphous materials
B. Vapour deposition
D. Microstructure
D. Surface properties
that effective mass production of size-controllable CMSs, with diameters ranging from 100 nm to 1 mm,
was achieved. As-obtained high purity CMSs were spherical with uniform size and low graphitization
degree, but the graphitization degree of GCMSs was enhanced obviously. By air oxidation, some oxygen-
containing functional groups were introduced onto the surface of CMSs, while no functional groups
were introduced onto the surface of GCMSs.
& 2009 Elsevier Ltd. All rights reserved.
1. Introduction
either in common organic solvents or in aqueous solution. Deoiled
asphalt (DOA) is a kind of carbon-rich by-product of petroleum
processing. Converting DOA into carbon materials with high
added value is an economically competent route [14–19]. The
purpose of this work is to synthesize a series of size-controllable
CMSs from DOA by CVD, and obtain graphitized carbon micro-
spheres (GCMSs) from as-prepared CMSs by vacuum heat
treatment, and then modify their surface by air oxidation.
In 1990s, some scientists, such as Ugarte [1] and Iijima [2],
brought the research of carbon materials to a new stage. Among
various forms of carbon, carbon micro-spheres (CMSs) as a kind of
advanced material are becoming increasingly important because
of their special properties. Many potential applications for CMSs
have been proposed, including anode material of secondary
lithium ion batteries, catalyst supporter, fillers in composite and
porous conductive material [3–6]. Up to now, various methods
have been demonstrated for the synthesis of CMSs, such as
emulsion, suspension, arc discharge, pressurized carbonization,
chemical vapour deposition (CVD), etc. [7–13]. CVD is considered
to be a suitable route for the synthesis of CMSs due to its simple
technological operation and low cost. But the graphitization
degree of CMSs synthesized by CVD is low. However, to expand
and optimize the use of CMSs in research field, it is necessary to
modify and functionalize their surface. The modification of CMSs
is an essential step to graft a wide variety of functional groups or
active molecules to their surface, or to improve their solubility
2. Experimental
2.1. Synthesis of CMSs
DOA used in this experiment was supplied by China University
of Petroleum-Beijing. Table 1 shows some analytical data of DOA,
and Table 2 shows the main compositions of its pyrolytic gases.
Fig. 1 shows the schematic of experimental apparatus and the
corresponding temperature profile along quartz tube reactor with
the central temperature of 1100 1C. CMSs were synthesized in the
quartz tube (32 mm i.d. and 1000 mm long), which was mounted
in a horizontal tubular furnace. At the beginning of synthesis
experiment, 2.0 g of DOA was placed in a small quartz boat
located at the inlet cool zone of the quartz tube, as shown in Fig. 1.
While the temperature of central reaction zone reached
n Corresponding author at: College of Chemistry and Chemical Engineering,
Taiyuan University of Technology, 79, West Yingze Street, Taiyuan 030024, China.
Tel./fax: +86 351 6014138.
E-mail address: liuxuguang@tyut.edu.cn (X. Liu).
0022-3697/$ - see front matter & 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jpcs.2009.11.012

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Y. Yang et al. / Journal of Physics and Chemistry of Solids 71 (2010) 235–241
predetermined temperature in Ar atmosphere, reaction was
allowed to proceed for 30 min by moving the quartz boat into
low temperature zone (500–600 1C) near the inlet of the quartz
tube, where the pyrolytic gases of DOA were carried into reaction
zone by Ar flow. Then the quartz tube was cooled to room
temperature under the protection of flowing Ar. Finally, the black
powder was collected from high temperature zone (denoted as
Zone A in Fig. 1) and low temperature zone near the outlet of the
quartz tube (denoted as Zone B in Fig. 1).
2.2. Preparation of GCMSs
The CMSs obtained in Section 2.1 were further treated by
vacuum heat treatment. Experimental parameters were as
follows: vacuum was between 2 Â 10À2 and 2 Â 10À3 Pa, the
vacuum furnace was heated to 2000 1C at the rate of 30 1C/min,
kept for 1 h and then cooled to room temperature.
2.3. Modification of CMSs and GCMSs
Air oxidation was performed to modify as-synthesized CMSs.
The process parameters and procedures were as follows: 50 mg of
CMSs was placed in a small quartz boat and then heated in open
air in a horizontal tubular furnace at 500 1C for 1, 2, 3, 5, 7 or 10 h.
GCMSs were also oxidized in air at 500 1C for 5 h.
Table 1
Analytical data of DOA.
Elemental analysis
(wt%)
H/C
(mol molÀ1
Softening point
Carbon residue
(wt%)
)
(1C)
2.4. Characterization
C
H
N
S
The products were characterized using field emission scanning
electron microscope (FESEM, JSM-6700F, operated at 10 kV)
equipped with an energy dispersive X-ray spectroscope (EDS),
high-resolution transmission electron microscope (HRTEM,
JEM-2010, working at an accelerating voltage of 200 kV),
87.84 9.39 1.28 0.42 1.28
193
41.08
Table 2
Main compositions of pyrolytic gases of DOA.
Raman spectrometer (JY-HR800, 532 nm), X-ray powder diffract-
˚
l=1.54018 A). Func-
tional groups were characterized using Fourier transformation
Composition
Vol%
H2
N2
CH4
CO
CO2
CnHm
17.32
ometer (XRD, D/Max-3C, Cu-K radiation,
a
4.92
37.58
30.43
3.52
2.43
infra-red spectrometer (FTIR, FTS-165).
Fig. 1. Schematic of experimental apparatus and the temperature profile along the quartz tube with the central temperature of 1100 1C.
Fig. 2. FESEM images of CMSs obtained at (a) 900, (b) 1000 and (c) 1100 1C.

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237
3. Results and discussion
the range of 650–750 nm, were basically invariable with
increasing reaction temperature from 900 to 1100 1C. This was
consistent with the results of Jin et al. [12]. On the other hand, the
yield increased obviously with increasing temperature, as shown
in Table 3. The corresponding size distribution and yield data are
also listed in Table 3.
Ar flow rate determined the retention time of pyrolytic gases
in reaction zone. Therefore, the effect of Ar flow rate on yield and
diameters of CMSs was investigated by fixing reaction tempera-
ture at 1100 1C and reaction time at 30 min (shown in Table 4). A
group of FESEM images are shown in Fig. 3, and the relationship
between Ar flow rate and CMSs yield can be found in Table 4. The
CMSs obtained at different Ar flow rates were uniform in size.
With increasing Ar flow rate from 60 to 300 ml/min, the size of
3.1. Controllable synthesis of CMSs
Fig. 2 shows typical FESEM images of CMSs obtained at
different reaction temperatures with Ar flow rate of 180 ml/min
and reaction time of 30 min. The diameters of CMSs, distributed in
Table 3
Effects of the reaction temperatures on the size and yield of CMSs.
a
No. Temperature Ar flow rate
Reaction time Size
Yield
(%)
(1C)
(ml/min)
(min)
distribution
(nm)
CMSs decreased from 1 mm to 220 nm (shown in Fig. 3) and the
1
2
3
900
180
180
180
30
30
30
650–750
650–750
650–750
21
yield of CMSs decreased from 44.7% to 30.7% (shown in Table 4).
In addition, CMSs obtained at Ar flow rate of 300 ml/min was
analyzed by EDS. In the as-prepared samples of CMSs, only carbon
was observed (see inset in Fig. 3(c)). It is clear that Ar flow rate
played an important role for the formation of CMSs. At lower Ar
flow rate, the higher concentration of carbon species formed by
decomposition of pyrolytic gases and longer retention time
favored the rapid growth of CMSs with subsequent higher yield
and larger size. On the other hand, as Ar flow rate got higher, the
lower concentration and shorter retention time of carbon species
in reaction zone resulted in lower yield and smaller size.
The products above-discussed were collected in high tem-
perature zone (Zone A in Fig. 1). The effect of collection zone was
also noticed in this paper. Fig. 4 shows the FESEM images of CMSs
obtained in different collection zones with the experimental
temperature of 1100 1C, reaction time of 30 min and Ar flow rate
of 180 ml/min. As can be seen from Fig. 4, the products obtained
in low temperature zone (200–900 1C, Zone B in Fig. 1) were CMSs
1000
1100
33.6
35.6
a
Yield=total mass of CMSs/mass of (raw materialsÀresidue in boat) Â 100%.
Table 4
Effects of Ar flow rate on the size and yield of CMSs.
a
No. Temperature Ar flow rate
Reaction time Size
Yield
(%)
(1C)
(ml/min)
(min)
distribution
(nm)
1
2
3
4
1100
1100
1100
1100
60
120
180
300
30
30
30
30
900–1000
800–900
650–750
200–300
44.7
41.7
35.6
30.7
a
Yield=total mass of CMSs/mass of (raw materialsÀresidue in boat) Â 100%.
Fig. 3. FESEM images of CMSs obtained at different Ar flow rates: (a) 60, (b) 120, and (c) 300 ml/min (inset in (c) shows EDS patterns of CMSs).
Fig. 4. FESEM images of CMSs collected in (a) high and (b) low temperature zones. Reaction temperature: 1100 1C, time: 30 min, Ar flow rate: 180 ml/min.

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with size ranging from 250 to 400 nm, which were smaller than
those obtained in high temperature zone (900–1100 1C, Zone A)
with size ranging from 650 to 750 nm. During deposition process,
some pyrolytic carbon species were carried into Zone B by Ar flow,
depositing on the tube wall and resulting in the formation of
CMSs with small diameters.
Table 5 and Fig. 5, and the histograms of size distribution of CMSs
were shown in the upper-right-hand corner of the corresponding
FESEM images in Fig. 5. By selection of preparation parameters,
CMSs with size ranging from 100 nm to 1
with good size controllability.
mm were synthesized
CMSs with different sizes have potential applications because
of their excellent properties. A large number of experiments were
conducted to synthesize a series of size-controllable and high-
quality CMSs from DOA. The experimental results were shown in
3.2. Microstructure analysis of CMSs and GCMSs
Fig. 6(a) and (b) show TEM images of CMSs obtained in 300 ml/
min Ar atmosphere at 1100 1C for 30 min, and Fig. 6(c) and (d)
show TEM images of GCMSs. Perfect spherical shapes with
uniform size and smooth surface can be seen in Fig. 5a, which is
consistent with FESEM observation. As shown in Fig. 6(b), CMSs
were of low graphitization degree, with discernible graphite
layers. The graphitization degree of GCMSs was enhanced, and the
graphite layers with space of 0.343 nm was clear (as shown in
Fig. 6(d)).
The graphitization degrees of CMSs and GCMSs were also
examined by XRD and Raman spectroscopy. Typical XRD patterns
of CMSs and GCMSs are shown in Fig. 7. The broad peak at 25.451
(Fig. 7(a)) and the sharp one at 25.91 (Fig. 7(b)) were attributed to
the (0 0 2) plane of graphite, and the corresponding d values were
Table 5
A series of size-controllable and high quality CMSs.
No. Experimental parameters
Collection zone Diameter (nm) Fig.
1
2
3
4
5
6
7
8
1100 1C, 30 min, Ar 60 ml/min
1000 1C, 30 min, Ar 150 ml/min Zone A
1100 1C, 30 min, Ar 180ml/min Zone A
Zone A
900–1000
750–900
650–750
450–600
400–550
300–400
200–300
100–200
5(a)
5(b)
5(c)
5(d)
5(e)
5(f)
1100 1C, 20 min, Ar 60 ml/min
Zone B
1000 1C, 10 min, Ar 120 ml/min Zone B
1000 1C, 20 min, Ar 180 ml/min Zone B
1100 1C, 30 min, Ar 300 ml/min Zone A
1000 1C, 30 min, Ar 300 ml/min Zone B
5(g)
5(h)
Fig. 5. FESEM images and size distribution histograms (insets) of size-controllable CMSs. Preparation parameters are listed in Table 5.

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239
Fig. 6. TEM images of (a) CMSs and (c) GCMSs. (b) and (d) are HRTEM images of the square areas in (a) and (c), respectively.
1594.73
25.9°
1348.62
1579.97
1584.89
1350.26
1356.82
b
a
25.45°
c
b
a
400 600 800 1000 1200 1400 1600 1800 2000
Raman shift (cm-1)
20
30
40
50
2θ (°)
60
70
80
Fig. 7. XRD patterns of (a) CMSs and (b) GCMSs. Preparation parameters for CMSs:
temperature: 1100 1C, time: 30 min, Ar flow rate: 300 ml/min. Preparation
parameters for GCMSs: vacuum heat treatment at 2000 1C for 1 h.
Fig. 8. Raman spectra of (a) graphite, (b) GCMSs and (c) CMSs. Preparation
parameters for CMSs and GCMS (see Fig. 7).
0.349 and 0.343 nm, respectively. This suggests that the
graphitization degree of GCMSs was largely enhanced after
vacuum heat treatment. Fig. 8 shows Raman spectra of graphite,
GCMSs and CMSs. In the Raman spectra, G band was attributed to
the stretching modes of C–C bonds of typical graphite, while D
band was related to the defects and disordered carbonaceous
solid. The D bands of graphite, GCMSs and CMSs were observed at
1356.82, 1350.26 and 1348.62 cmÀ1, respectively, as shown in
Fig. 8. The IG/ID values of graphite, GCMSs and CMSs were 5.172,
1.853 and 1.074, respectively, implying that the graphitization
degree of CMSs was improved by vacuum heat treatment, in good
agreement with HRTEM and XRD results.
3.3. Modification of CMSs and GCMSs
FTIR spectra were used to investigate the residual functional
groups on the surface of GCMSs and CMSs after oxidation in air for
different times, as shown in Figs. 9 and 10. The assignments of
absorption bands are listed in Table 6.

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Table 6
240
Observed FTIR bands for CMSs and their assignments.
Band (cmÀ1
)
Assignment
(g) 10h
(f) 7h
ꢀ1620
ꢀ1738
Carboxylate asymmetric stretching
C–O stretching
ꢀ2362
O–C–O stretching
2854, 2924
ꢀ3400
C–H stretching
(e) 5h
O–H stretching
(d) 3h
(c) 2h
of functional groups were grafted on the highly graphitized
surface of GCMSs.
(b) 1h
(a) 0h
This experiment reveals that there were some functional
groups such as carboxylate, carboxylic groups and hydroxyl group
presented on the surface of CMSs, which would facilitate the
grafting of biomolecules or catalytic species onto the surface.
500
1000 1500 2000 2500 3000 3500 4000 4500
Wavenumber (cm -1
)
4. Conclusion
Fig. 9. FTIR spectra of the CMSs oxidized in air for different times.
In brief, size-controllable CMSs were synthesized from DOA by
CVD, with emphasis on the effects of reaction temperature, Ar
flow rate and collection zone. GCMSs were obtained from as-
prepared CMSs by vacuum heat treatment at 2000 1C for 1 h.
Results show that an effective mass production of size-control-
lable CMSs, with diameters ranging from 100 nm to 1 mm, was
proposed. With the reaction temperature being increased from
900 to 1100 1C, the diameters of CMSs distributed in the range of
650–750 nm and the yield increased obviously. With increasing
Ar flow rate from 60 to 300 ml/min, the sizes of CMSs decreased
from 1 mm to 220 nm, and the yield of CMSs also decreased. The
products collected in low temperature zone were CMSs with
smaller size and broader size distribution than that obtained in
high temperature zone. The graphitization degree of GCMSs was
enhanced obviously after vacuum heat treatment. In addition, air
oxidation was performed to realize the surface modification of
CMSs. FTIR spectra indicated the existence of some oxygen-
containing functional groups, including anion carboxylate, car-
boxylic group and hydroxyl group, on the surface of CMSs
oxidized in the air for different times. On the other hand, no
functional groups were introduced onto the surface of GCMSs by
air oxidization.
b
a
500
1000
1500
2000
2500
3000
3500
4000
Wavenumber (cm-1
)
Fig. 10. FTIR spectra of (a) as-prepared GCMSs and (b) GCMSs oxidized in air
for 5 h.
Acknowledgements
The FTIR spectra of CMSs oxidized in air for 1 h (Fig. 9(b))
was similar to original sample (Fig. 9(a)), indicating that no
new functional groups were introduced onto the surface of CMSs
when oxidation time was less than 1 h. With the oxidation
time being increased to 2 h, two relatively weak peaks were
observed at 1593 and 1701 cmÀ1 (Fig. 9(c)), corresponding to
anion carboxylate and carboxylic group, respectively. When the
oxidation went on for 3 h, the intensity of anion carboxylate
(1613 cmÀ1) and carboxylic group (1738 cmÀ1) became stronger
and a new peak attributed to hydroxyl group was observed
at 3465 cmÀ1 (Fig. 9(d)). When the CMSs were oxidized for 5, 7
and 10 h (Fig. 9(e–g)), the peaks of carboxylate and carboxylic
groups were all observed at 1620 and 1738 cmÀ1, respectively;
however, red shift was observed for hydroxyl group at 3464, 3450
and 3450 cmÀ1. It seems that free hydroxyl groups became
associated among different molecules with increasing oxidation
time.
The authors acknowledge financial support from National
Nature Science Foundation of China (20676086), Natural Science
Foundation of Shanxi Province (2009011012-4), Program for New
Century Excellent Talent in University (NCET-06-0262), Interna-
tional S&T Co-operation Program (2007DFA50940), Shanxi Re-
search Fund for Returned Scholars (2008-31) and Taiyuan S&T
Program (08121024).
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