Graphene, 2013, 2, 42-48 Published Online January 2013 (
One Pot Synthesis of Graphene by Exfoliation of
Graphite in ODCB
Sumanta Sahoo, Goutam Hatui, Pallab Bhattacharya, Saptarshi Dhibar, Chapal Kumar Das*
Materials Science Centre, Indian Institute of Technology, Kharagpur, India
Email: *
Received November 14, 2012; revised December 18, 2012; accepted January 15, 2013
Graphene, an extraordinary allotropy of carbon, the 2D nanosheet, have been synthesized through exfoliation of graph-
ite in ortho-dichloro benzene by sonication. The morphological changes in different interval of sonication have been
investigated by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). Raman Spectra
confirmed the formation of defect free Graphene sheets. As prepared Graphene showed high thermal stability under N2
atmosphere. It has been observed that sonication for 4 hours, effectively exfoliates graphite to form Graphene sheets.
However, further sonication leads to restacking of Graphene sheets. The formation of Graphene is supposed to be due to
the Sonopolymerization of the solvent (ortho-dichloro benzene) and graphite-solvent interaction.
Keywords: Graphene; Graphite; Ortho-Dichloro Benzene; Sonication; Raman Spectra
1. Introduction
The discovery of Graphene stimulates the scientists to
unlock a new aspect in the field of nanoscience and
nanotechnology. Graphene has become the “miracle ma-
terial” of the 21st Century. It is considered as the thinnest
material of today’s world. It has no band gap, which al-
lows it to be a wonderful candidate for use in photo-vol-
taic (PV) cells. Beside this, it has attracted great deal of
research due to its excellent electrical conductivity, ex-
traordinary mechanical properties, large surface area,
high aspect ratio, low coefficient of thermal expansion
[1-5]. Graphene is the flat layer of carbon atoms, com-
pactly packed into a two-dimensional honeycomb lattice.
It is expected that, with its outstanding properties, Gra-
phene can replace Silicone in near future. However, great
deal of researches has been done to synthesize single
layer as well as multi-layer Graphene. Earlier, Graphene
were synthesized by different procedures like mechanical
exfoliation of graphite [6], Chemical vapor deposition
method [7] etc. But these are not efficient method to
synthesize Graphene in commercial scale. Chemical route
is the most realistic as well as most promising method for
Graphene synthesis from graphite. The simplest and most
common method of graphite exfoliation is the oxidation
of graphite to graphite oxide by strong oxidizing agent
[8]. Further exfoliation and reduction of Graphene oxide
forms chemically converted Graphene [9-11]. Though
some other methods like thermal expansion [12], ball
mixing, liquid phase exfoliation [13] etc. were tried to
synthesize Graphene, but this oxidation-reduction meth-
od is the most widely used method for large scale syn-
thesis of Graphene. Though this method is most practical
method, it also has some disadvantages like presence of
defects, low yield, presence of harsh oxidation chemistry
and long term reaction.
The homogeneous Graphene dispersion in some com-
mon organic solvents like benzene, toluene, nitrobenzene
etc was reported [14]. Polar solvents like N, N-dimethyl-
formamide (DMF), N-methylpyrrolidone (NMP) can also
exfoliate graphite to form homogeneous Graphene dis-
persion [15,16]. But, among the nonpolar solvents, ortho-
dichloro benzene (ODCB) was reported to produce ho-
mogeneous Graphene dispersion [17].
Here we have demonstrated one pot synthesis of Gra-
phene through exfoliation of graphite in ODCB. The syn-
thesis based only on sonication. We have studied the ef-
fect of chlorinated organic molecules on the electronic
structure of Graphene upon sonication. Further, we have
tried to find the mechanism of the formation of Graphene
through exfoliation of graphite. Sonication for a particu-
lar time interval leads complete dispersion of graphite
molecules in ODCB to form homogeneous dispersion of
Graphene. Further, the electronic structure of Graphene
has been characterized by FTIR, SEM, TEM and Raman
spectra. The advantages of this synthesis method are its
simplicity, absence of long term synthetic route and high
ODCB is a versatile, high boiling solvent. It is a pre-
*Corresponding author.
opyright © 2013 SciRes. Graphene
ferred solvent for dissolving fullerenes and also it can
form stable Single Wall Carbon Nano tube (SWCNT)
dispersion. However the reasons behind the choice of this
solvent for graphiteexfoliation were well described by
Hamilton et al. [16]. Additionally one of the major ad-
vantages of ODCB is, like other organic halides, it is also
known to decompose during sonication to liberate chlo-
rine and polymerize [17,18].
2. Experimental
2.1. Materials Used
Graphite Fine Powder (Extra Pure) was obtained from
Loba Chemie Pvt. Ltd. Mumbai (India). 1,2-dichloro
benzene was supplied by MERCK Limited. Mumbai
(India). Both the chemicals used as received, without any
further distillation or purification.
2.2. Synthesis of ODCB Suspension of Graphene
Stable homogeneous dispersion of Graphene was ob-
tained through a simple chemical approach [16]. In a
typical process, Graphite (1 gm) was mixed with ODCB
(300 ml) in a beaker. The black colored solution was
homogenized for different time interval in an ultrasonic
bath (Freq. 40 KHz and Power 100 W). All the solutions
were heated at 185˚C for solvent evaporation. The sam-
ple codes with sonication time are shown in the Table 1.
After each time interval (1 hr) some solution were taken
out from the beaker and kept in sample vial for charac-
All the sample vials were kept for one month in room
temperature in order to verify stable dispersion of Gra-
phene. The corresponding vial pictures are shown in
Figure 1. As observed from the Figure 1, it is clear that
in Gr1, the graphite molecules were settled down in the
bottom part of the vial. Partial settle down was observed
for Gr2. So, it can be concluded that 2 hrs sonication is
not sufficient to get colloidal dispersion of Graphene.
However for rest of the samples black colored colloidal
solution was observed. As prepared colloids were homo-
geneous and they remained stable for more than 6
months without any sediment. Stable uniform dispersion
of Graphene can be achieved after 4 hrs sonication.
Table 1. Sample details.
Sample Codes Sonication Time (mins)
Gr1 60
Gr2 120
Gr3 180
Gr4 240
Gr5 300
Figure 1. Vial images (before and after one month).
3. Characterization Techniques
3.1. Fourier Transform Infrared Spectroscopy
FTIR analysis of Graphene samples was characterized
using a NEXUS 870 FTIR (Thermo Nicolet). For the IR
spectrum a small amount of material was mixed with
KBr in adequate level to make a disk and the disk was
analyzed for getting the spectrum.
3.2. Scanning Electron Microscopy (SEM)
The surface morphologies of the samples were analyzed
by using Tescan VEGA LSU SEM.
3.3. Transmission Electron Microscopy (TEM)
All the samples were analyzed by TEM, JEOL 2100 in
order to understand exact morphological change of Gra-
phene dispersion in ODCB with sonication time. A small
amount of the sample was dispersed in acetone and de-
posited on copper grid.
3.4. Raman Spectra
Raman spectra were recorded between 500 to 3500 cm1
in a Raman Imaging System WITEC alpha 300 R with
532 nm wavelength.
3.5. Thermogravimetric Analysis (TGA)
Thermogravimetric analysis curve was recorded with a
Dupont 2100. Thermogravimetric analyzer. The TGA
measurement was conducted with a heating rate of
10˚C/min under N2 atmosphere from room temperature
to 800˚C.
4. Results and Discussion
4.1. FTIR Analysis
The chemical environment of all Graphene samples has
Copyright © 2013 SciRes. Graphene
been analyzed by FTIR and spectrums of are shown in
Figure 2. All the characteristic peaks of graphite are
present in all the samples. The peak at 1634 cm1 arises
due to the C=O stretching vibration of carbonyl func-
tional group. Broad peak at 3434 cm1 corresponds to the
O-H stretching vibration. Further, peaks at 2854 and
2924 cm1 attributes to the symmetric and asymmetric
stretching vibrations of C-H bonds respectively. Addi-
tionally, several peaks arises in the range of 400 - 800
cm1 due to several vibration modes of C-H like outer
bending vibration, C-H in plane bending, C-H out of
plane wagging [19,20]. However, there are no drastic
changes in the spectrums of the prepared samples. These
indicate the absence of any functional group in as pre-
pared samples.
4.2. Morphological Study
The morphological changes upon sonication for different
time interval are analyzed by SEM and TEM analysis
and the images are presented in Figures 3 and 4. Figure
3 shows the SEM image of graphite fine powder which
clearly demonstrated the stacked Graphene sheet struc-
ture. Sonication for 1 hr, exfoliated the Graphene sheets
and the intergalary distance increased tremendously (Gr1).
Further increase in the sonication time (2 hrs), resulted in
the delamination of the Graphene sheets (Gr2). Sonica-
tion for 3 hrs showed reduction in the Graphene layers,
as compared to two hour sonication (Gr3). However, 4
hour sonication showed complete delamination of Gra-
phene layers (Gr4). Increase in sonication time to 5 hrs
(Gr5) showed restacking of the Graphene sheets. The
delamination process was further confirmed by TEM.
The characteristic TEM images of as prepared samples
are shown in the Figure 4. In Gr1 graphite particles are
present in agglomerated form. On the other hand, in Gr2,
some portions of the graphite particles are remained in
agglomerated form as well as in some portion, Gra-
Figure 2. FTIR spectra of Gr1, Gr2, Gr3, Gr4, Gr5.
phene nanosheets are formed. However, homogeneous
dispersion of Graphene nanosheets is observed only for
Gr4. The TEM image of Gr4 shows the multilayered
Graphene nanosheets and the thicknesses of the Gra-
phene nanosheets are 10 - 15 nm. This indicates that a
particular sonication time is required for the exfoliation
of Graphene in ODCB. 4 hrs sonication is sufficient for
the homogeneous dispersion of Graphene. Further soni-
cation leads to the agglomeration of graphite.
Based on the morphological study and other relevant
characterizations, we have demonstrated a diagram (Fig-
ure 5) for better understanding of the changes during
sonication for different time interval. As shown in the
diagram, 1 hr sonication has not able to separate the
graphite particles. 2 hrs sonication can only separate
some portion of the graphite particles. However, better
exfoliation of Graphene sheets is observed for Gr4. Fur-
ther re stacking of Graphene sheets is found for Gr5.
The characteristic SAED (Selected Area Electron Dif-
fraction) images of the samples are shown in Figure 6.
For Gr1, no ring patterns are observed, which is due to
the amorphous nature of graphite. A perfect six mem-
bered ring pattern is observed for Gr4 among all the
samples. This is due to the crystalline nature of Graphene.
These results indicate the formation of Graphene sheets
in Gr4.
4.3. Raman Spectra
Raman spectroscopy is mainly used to understand the
structural properties of Graphene materials. It is also an
important tool for identification of disorder and defect in
molecular structure as well as to calculate defect density,
doping level etc. The major Raman features of the Gra-
phene samples are so called G band (~1575 cm1) and D
band (~1350 cm1). However G band initiates from in-
plane vibration of sp2 carbon atoms of Graphene samples
[21], whereas the D mode arising from a breathing mode
of a K-point photons of A1g symmetry [22]. Besides these
two, one additional peak arises from a two phonon dou-
ble resonance Raman process, known as 2D band (~2670
cm1). The Raman spectra of all the samples and Graph-
ite (inset) are shown in Figure 7. Among all the samples,
Gr4 shows G band at 1353 cm1 and D band at 1584 cm1,
which are comparable with the characteristic peaks of
Graphene. The peak intensity ratio (ID/IG) is found to be
0.015 for Gr4 (Figure 8). Similar value was reported by
W. Yang et al. [13]. However, the peak intensity ratio
decreases from Gr1 to Gr4 and then increases for Gr5.
The decrease in D band intensity with increasing sonica-
tion time indicates that sonication induces defect-free
Graphene sheets. It is also found that among all the sam-
ples, Gr4 shows lowest D band intensity, after that D
band intensity increases with further sonication. This
proves that sonication for a particular time interval
Copyright © 2013 SciRes. Graphene
Copyright © 2013 SciRes. Graphene
Figure 3. SEM images of Graphite, Gr1, Gr2, Gr3, Gr4, Gr5.
Figure 4. TEM images of Gr1, Gr2, Gr3, Gr4, Gr5.
Figure 5. Schematic Diagram indicating the physical changes
of graphite particles during sonication for different time
Figure 6. SAED images of Gr1, Gr2, Gr3, Gr4, Gr5.
efficiently exfoliates graphite without initiating defects.
4.4. Mechanism of Stable Dispersion of
The mechanism of formation of stable homogeneous
dispersion of Graphene in ODCB can be explained
through solvent-graphite interaction concept. Sonication
leads to the Sonopolymerization of ODCB [23], which is
responsible for the stabilization of Graphene dispersion.
However, there occurs no chemical interaction between
graphite layers and ODCB, which is confirmed by FTIR
analysis. The dispersion of graphite in ODCB leads to
the formation of Sonopolymer [24-26], which adheres to
the graphite layers. Sonication leads to the separation of
graphite layers. Once the graphite layers are separated,
solvent molecules penetrates inside the inter gallery of
graphite. Further sonication induces the formation of
Sonopolymer between the graphite layers. With increas-
ing sonication time the formation of polymer bounded
graphite sheets increases as well as distance between the
graphite layers increases. This leads to the formation of
Figure 7. Raman spectra of Gr1, Gr2, Gr3, Gr4, Gr5. Inset
shows the Raman Spectr a of Gr aphite.
Figure 8. Peak intensity ratio vs. sonication time curve.
Graphene sheets as in Gr4. On the other hand, it is al-
ready confirmed that the key factor for graphite disper-
sion is the enthalpy of mixing [15]. The enthalpy of mix-
ing for graphite dispersion in solvents should be close to
zero. That can only be achieved if the surface energy of
graphite matches with the surface tension of the solvent.
It is also predicted that good solvents for graphite disper-
sions should have surface tensions in the region of 40 -
50 mJ/m2. The surface tension of ODCB is very close to
this region (36.01 mJ/m2). Thus minimum energy cost is
required for the exfoliation of graphite in this solvent.
However, further sonication directs to the decomposition
of ODCB, which induces re agglomeration of graphite
layers as observed in Gr5.
The preparation of composites based on this synthe-
sized Graphene for different applications like superca-
pacitors, polymer blends, formation of radar absorbing
substances are in progress and will be reported elsewhere
in future.
Copyright © 2013 SciRes. Graphene
Figure 9. TGA curve of Gr4.
4.5. Thermogravimetric Analysis
In order to analyze the thermal behavior of as prepared
Graphene sample (Gr4), we have carried out the TGA
analysis and the curve is shown in Figure 9. As shown in
the Figure, a slight mass loss is observed at below 100˚C,
which can be attributed to the removal of adsorbed water
molecules. However, in spite of this minor weight loss,
no significant mass loss is detected upto 650˚C. The ma-
jor mass loss occurred at around 650˚C. The 5% weight
loss is observed at 682˚C and 10% weight loss is ob-
served at 714˚C. Hence, the TGA analysis confirms the
enhanced thermal stability of this Graphene sample.
5. Conclusions
In Summary, a simple method has been developed for the
synthesis of multilayered Graphene through sonication
via exfoliation of graphite in ODCB. Graphite powder
provides Graphene sheets through graphite-solvent in
teraction. The major advantage of this method is the ab-
sence of harsh chemicals like strong acids, reducing
agents etc. The formation of Graphenenanosheets upon
exfoliation of graphite is expected due to several factors:
1) Sonopolymerization of the solvent;
2) Graphite-solvent interaction;
3) Matching of the surface energy of graphite with the
surface tension of solvent;
4) The enthalpy of mixing for the graphite dispersion
is close to zero.
As prepared Graphene sheets could be useful for both
scientific studies and various commercial applications.
6. Acknowledgements
The authors are thankful to CSIR, New Delhi, India for
their financial support.The authors would like to thank
Prof. Dieter Fischar and Prof. Jurgan Pionteck of Leib-
nitz Institute of Polymer Research, Dresden, Germany
for the characterization and interpretation of Raman
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