Supplementary Material
Preparation of graphene nanosheets from microcrystalline graphite exfoliated at
low-temperature and atmospheric pressure and their supercapacitive behavior
Haiyang Xiana, Tongjiang Penga, b*, Hongjuan Suna, Jiande Wang
a
Institute of Mineral Materials & Application, Southwest University of Science and Technology, Mianyang 621010, P.R. China.
b
School of Material Science and Engineering, Southwest University of Science and Technology, Mianyang 621010, P.R. China.
ABSTRACT
Supplementary information is provided for (i) the Experimental phenomena difference between
flake and microcrystalline graphite in the oxidation process, (ii) the basis for the the exfoliation
temperature spots selection, (iii) the detail evidence for oxygen groups change in the oxidation and
exfoliation processes, (iv) the evidence for the present of graphitic layers in MGS after the
exfoliation process, and (v) the detail CV and GCD data for the MGS samples.
1. Experimental
1.1 Preparation of microcrystalline graphite oxide
Firstly, natural microcrystalline graphite powder (2 g, 99%, from the concentrating mill of Panshi,
Jilin province, China, designated as NMG) was added to concentrated H2SO4 (95%-98%, 46 mL),
and the mixture was cooled down to 0 ˚C by using an ice bath, then KMnO4 (10 g) was added
slowly to keep the reaction temperature below 15 ˚C for 0.5 h. Secondly, the reaction mixture was
heated to 35 ˚C and stirred for 2 h, at which ultrapure water was added slowly, giving rise to a
pronounced exothermal effect up to 70˚C±. The reaction mixture was stirred for 30 min, then 5%
of H2O2 was added until no gas produced and, finally, the mixture was deposited for 12h, until the
supernatant being decanted away. The remaining solid material was then washed with ultrapure
water and deposited again, this process being repeated until the pH was neutral. The reaction
product (MGO) was dried at 60 ˚C for 24 h.
To investigate the experimental phenomena difference between flake and microcrystalline
graphite in the oxidation process, a comparison experiment was implemented. Nature flake
graphite (-200 mesh, from the concentrating mill of Huangtuyao graphite deposit in the Nei
Monggol Autonomous Region, China) was used to prepare graphite oxide. The experimental
procedure was same to the microcrystalline graphite.
1.2 Characterization
The TG-DSC curves were measured using a TA SDT Q600 analyzer. The temperature was
increased to 1000 ˚C at a heating rate of 10 ˚C min-1 under a nitrogen flow of 100 mL min-1. FT-IR
spectra of MGO, MGS-100 and MGS-400 were recorded at room temperature using a
transmission mode with KBr tableting and a Fourier transform infrared spectrometer (FT-IR,
Nicolet 5700).
2. Results and discussion
*
Corresponding author: Fax: +86-816-6089509.
E-mail address: tjpeng@swust.edu.cn (T. Peng).
1
Fig. S1 shows the experimental phenomena difference between flake and
microcrystalline graphite in the oxidation process. On one hand, it can be seen that the
graphite oxide from flake graphite displays golden yellow, after 12h sedimentation,
the supernate is clear while the bottom displays gradual change from golden yellow to
dark black, indicating that the graphite is colloidal. In this case, graphite oxide film
can be obtained after drying. On the other hand, the experimental phenomena of the
microcrystalline graphite is obvious different from the former, the graphite oxide from
microcrystalline graphite displays dark olivine, after 12h sedimentation, all the
graphite oxide become the sediment in the bottom of the beaker. In this case, it cannot
form graphite oxide file, but a heap of graphite powder.
Fig. S1–Experimental phenomena difference between flake and microcrystalline
graphite in the oxidation process.
Fig. S2 shows the TG-DSC curves of MGO. A sharp endothermic peak at 213 ˚C
can be found easily in this figure. The exfoliation temperature spots in this work were
chosen according to the endothermic peak.
2
28
213 C
26
100
24
22
20
Weight / %
16
14
12
10
60
8
6
4
Heat flow / (mW/mg)
18
80
2
40
0
-2
-4
20
200
400
600
800
-6
1000
Temperature / C
Fig. S2–TG-DSC curves of MGO.
Fig. S3 shows the TEM images of MGS-100 with graphitic layers. The lattice
fringe can be seen in the figure clearly, indicating that there still graphitic layers
inMGS-100.
Fig. S3–TEM images of MGS-100 with graphitic layers, the insert is the SAED
pattern of the corresponding area.
3
C1s
O(KLL)
O1s
MGS-400
MGS-100
MGO
1000
800
600
400
200
0
Binding Energy (eV)
Fig. S4–XPS survey spectra of MGO, MGS-100 and MGS-400.
Fig. S5 shows the FT-IR spectra of MGO, MGS-100 and MGS-400. The
relatively broad peak at 3415 cm-1 and relatively sharp peak at 1627 cm-1 indicate that
the samples contain adsorbed water. The peaks at 1739 cm-1, 1400 cm-1 and 1220 cm-1
can be assigned to the carbonyl, hydroxyl and epoxy groups in the structure of MGO.
Compared with the pristine MGO, the intensities of the peaks at 1400 cm-1 and1220
cm-1 for MGS-100, which indicates that the functional groups on the surface of the
MGO layers decomposes partially. The disappearance of the peaks at 1739 cm−1, 1400
cm−1, and 1220cm−1 for MGS-400 indicates that the functional groups have been
almost removed.
LTEG-400
LTEG-100
AGO
4000
3500
3000
2500
2000
1500
Wavenumbers / cm
1000
500
-1
Fig. S5–FT-IR spectra of MGO, MGS-100 and MGS-400.
4
6
4
MGS-100
(a)
5
-1
0
Current / A g
-1
2
Current / A g
MGS-400
(b)
10
-1
-2
5 mV s
-1
10 mV s
-1
20 mV s
-1
30 mV s
-1
50 mV s
-4
-6
-8
-0.8
-0.6
-0.4
-0.2
0.0
0
-1
-5
5 mV s
-1
10 mV s
-1
20 mV s
-1
30 mV s
-1
50 mV s
-10
-15
-20
-0.8
0.2
-0.6
-0.4
-0.2
0.0
0.2
Potential / V (vs Hg/HgO)
Potential / V (vs Hg/HgO)
Fig. S6–Cyclic voltammograms for MGS-100 (a) and MGS-400 (b) at different
scan rates from 5 to 50mV s−1.
0.2
(a)
(b)
MGS-100
MGS-400
0.0
Potential(V vs Hg/HgO)
Potential(V vs Hg/HgO)
0.2
-1
0.5 A g
-1
1.0 A g
-1
2.0 A g
-1
3.0 A g
-1
5.0 A g
-0.2
-0.4
-0.6
0.0
-1
0.5 A g
-1
1.0 A g
-1
2.0 A g
-1
3.0 A g
-1
5.0 A g
-0.2
-0.4
-0.6
-0.8
-0.8
0
50
100
150
200
250
300
350
0
400
100
200
300
400
500
600
t (s)
t (s)
Fig. S7–GCD curves for MGS-100 (a) and MGS-400 (b) at different current
density from 0.5 to 5.0 A g−1.
5
700