Room-temperature intercalation and ~1000-fold chemical expansion ...
Supporting Information Room-temperature intercalation and ~1000-fold chemical expansion for scalable preparation of high quality graphene Shan Lin‡, Lei Dong‡, Jiajia Zhang and Hongbin Lu* State Key Laboratory of Molecular Engineering of Polymers, Collaborative Innovation Center of Polymers and Polymer Composite Materials and Department of Macromolecular Science, Fudan University, 220 Handan Road, Shanghai 200433, China. Email: [email protected]. ‡
These authors contributed equally.
1. The change in thickness of graphite before and after the CrO3 intercalation
(a)
(b)
Figure S1. The field emission scanning electron microscopic (FESEM) images of the starting graphite (a) and the GICs (b). Only a small thickness change was observed from 30 μm to 50 μm. 2. X-ray diffraction patterns of starting graphite, GICs and chemically expanded graphite (CEG). As shown in Figure S2(a), the starting graphite reveals only one characteristic peak at 26.3, with a relatively high diffraction intensity due to the good order along c-axis direction. After the intercalant molecules enter the interlayer galleries, such order structures in GICs are significantly reduced, which can result in the disappearance of this graphite peak and the appearance of other intercalation peaks. If the intercalation is incomplete and part of graphite structure is still retained, an intensity-reduced graphite peak can be observed. However, if no graphite
structure is retained in GICs, there will be only intercalation peaks able to be observed. As shown in Figure S2(b), four adjacent diffraction peaks (18.3, 24.5, 26.8and 30.4) rather than the graphite peak (26.3) are visible, from which a stage-3 intercalation structure is able to be determined definitely. In addition, it is seen that the intensity of these diffraction peaks decreased by over 2 orders of magnitude relative to the graphite diffraction peak, due to increased interlayer distance. After expansion, CEG shows a further lowered diffraction intensity, as shown in Figure S2(c), where one very weak graphite diffraction peak (26.3) can be discernible due to further decreased degree of interlayer order. Sometimes, such a weak is probably invisible if the sample for examination is in a highly loose state.
Figure S2. XRD patterns of the starting graphite, 3-stage CrO3-GICs and CEG.
C
3. Morphological observation of wet CEG with optical microscope.
Breakdown Figure S3. Optical microscopic images of CEG in which the broken strips are visible, as denoted by red arrows (a), and the local morphology of CEG in liquid phase (b).
4. Observation of chemical expansion process of GICs with optical microscope.
0 min
0.5 min
1 min
3 min
Bar: 100 μm Figure S4. Optical images of the surface expansion process of CrO3-GICs in 30% H2O2 solution at different times.
5. Preparation method of TEG and methylene blue (MB) absorption experiments of CEGW, CEGD and TEG. Natural graphite flake (1 g) and concentrated sulfuric acid (30 mL) were stirred rigorously for 24 h to which fuming nitric acid (10 mL) was added and then the mixture continued to be stirred for 24 h at room temperature. Deionized water (DI water, 40 mL) was added slowly to the above mixture, standing for 1 h. After washing the mixture with DI water for three times, the product was centrifuged at 4,000 rpm for 20 min, and the resulting sediment was then dried at 60 C for 2 days to obtain the graphite intercalation compounds (GICs). The obtained GICs were placed in a ceramic boat and subsequently inserted into a quartz tube. The quartz tube was sealed using a rubber stopper, and then filled with argon. The sealed quartz tube was inserted into a furnace pre-set at 1000 C for 30 second to give the TEG.1
The adsorption amounts of MB in CEGW, CEGD and TEG were calculated according to the following equation,2
where Qe (mg g-1) is the amount of MB adsorbed at equilibrium, C0 (mg l-1) is the initial solute concentration, Ce (mg l-1) the equilibrium solute concentration, V the volumn of MB solution, and m is the amount of adsorbate.
The adsorption isotherms were fitted (correlation coefficients, R2＞0.99) using the Langmuir adsorption model:3
where Qe (mg g-1) is the amount of MB adsorbed at equilibrium, Ce (mg l-1) the equilibrium solute concentration, Qm the maximum adsorption capacity corresponding to complete monolayer coverage, and b the equilibrium constant (l mg-1).
6. FESEM images of CEGW, TEG and CEGD
Figure S5. FESEM images of wet CEGW (a-c), TEG(d-f) and CEGD (g-i). 7. The representative FESEM, AFM and HRTEM images for the exfoliated graphene sheets obtained in this work.
(a)
(b)
Figure S6. FESEM images of graphene (a) and the maximum graphene sheet with 15 μm width (b).
1.0 nm 1.1 nm
1.6 nm
1.7 nm
1.2 nm
1.2 nm 1.1 nm 0.8 nm
1.2 nm
1.1 nm
1.1 nm
1.0 nm
2.5 nm
0.9 nm
1.1 nm
2μm 1.2 nm
Figure S7. The representative AFM images of the exfoliated graphene sheets for thickness measurement.
Figure S8. HRTEM images of few-layer graphene sheets
8. Representative 2D Raman images of the exfoliated graphene sheet
(a)
(b)
Figure S9. The 2-dimensional mapping of 2D band (a), and ID/IG ration images (b) of an exfoliated grahene sheet deposited on a Si substrate.
Figure S10. The Raman spectra of other locations (spots 2-11) denoted in Figure 5a.
Table S1 Raman parameters from the dots 1-11. Location
ID
IG
I2D
ID/IG
I2D/IG
FWHM
1
56.1
607
180
0.09
0.30
53.8
2
23.54
1292
354
0.02
0.27
63.1
3
42.8
1043
283
0.04
0.27
61.5
4
70.1
1325
451
0.05
0.34
58.8
5
87.8
1148
368
0.08
0.32
63.1
6
35.8
961
311
0.04
0.32
62.7
7
56.2
1541
480
0.03
0.31
58.7
8
59.6
1418
447
0.04
0.31
58.5
9
23.9
918
251
0.02
0.27
57.5
10
64
880
246
0.07
0.28
62.9
11
48.5
901
252
0.05
0.28
55.7
9. A comparison between the present method and other published methods on the yield, intrinsic properties of graphene sheets.
Table S2. Comparison of non-oxidization/reduction exfoliation methods for preparation of few-layer and single-layer graphene sheets. Graphene
Method and comments
Yield
Lateral size
Thickness
ID/IG
Electrical resistence
C/O
Oxygen content
Ref
Few-layer
Electrochemical expansion and sonication exfoliation in organic solvents. Possible limitation of electrode size for large-scale production.
>70%
-
50% 2-3 layers, 70% < 5 layers
10 μm
52% 1-3 layers,
10 μm
These authors contributed equally.
1. The change in thickness of graphite before and after the CrO3 intercalation
(a)
(b)
Figure S1. The field emission scanning electron microscopic (FESEM) images of the starting graphite (a) and the GICs (b). Only a small thickness change was observed from 30 μm to 50 μm. 2. X-ray diffraction patterns of starting graphite, GICs and chemically expanded graphite (CEG). As shown in Figure S2(a), the starting graphite reveals only one characteristic peak at 26.3, with a relatively high diffraction intensity due to the good order along c-axis direction. After the intercalant molecules enter the interlayer galleries, such order structures in GICs are significantly reduced, which can result in the disappearance of this graphite peak and the appearance of other intercalation peaks. If the intercalation is incomplete and part of graphite structure is still retained, an intensity-reduced graphite peak can be observed. However, if no graphite
structure is retained in GICs, there will be only intercalation peaks able to be observed. As shown in Figure S2(b), four adjacent diffraction peaks (18.3, 24.5, 26.8and 30.4) rather than the graphite peak (26.3) are visible, from which a stage-3 intercalation structure is able to be determined definitely. In addition, it is seen that the intensity of these diffraction peaks decreased by over 2 orders of magnitude relative to the graphite diffraction peak, due to increased interlayer distance. After expansion, CEG shows a further lowered diffraction intensity, as shown in Figure S2(c), where one very weak graphite diffraction peak (26.3) can be discernible due to further decreased degree of interlayer order. Sometimes, such a weak is probably invisible if the sample for examination is in a highly loose state.
Figure S2. XRD patterns of the starting graphite, 3-stage CrO3-GICs and CEG.
C
3. Morphological observation of wet CEG with optical microscope.
Breakdown Figure S3. Optical microscopic images of CEG in which the broken strips are visible, as denoted by red arrows (a), and the local morphology of CEG in liquid phase (b).
4. Observation of chemical expansion process of GICs with optical microscope.
0 min
0.5 min
1 min
3 min
Bar: 100 μm Figure S4. Optical images of the surface expansion process of CrO3-GICs in 30% H2O2 solution at different times.
5. Preparation method of TEG and methylene blue (MB) absorption experiments of CEGW, CEGD and TEG. Natural graphite flake (1 g) and concentrated sulfuric acid (30 mL) were stirred rigorously for 24 h to which fuming nitric acid (10 mL) was added and then the mixture continued to be stirred for 24 h at room temperature. Deionized water (DI water, 40 mL) was added slowly to the above mixture, standing for 1 h. After washing the mixture with DI water for three times, the product was centrifuged at 4,000 rpm for 20 min, and the resulting sediment was then dried at 60 C for 2 days to obtain the graphite intercalation compounds (GICs). The obtained GICs were placed in a ceramic boat and subsequently inserted into a quartz tube. The quartz tube was sealed using a rubber stopper, and then filled with argon. The sealed quartz tube was inserted into a furnace pre-set at 1000 C for 30 second to give the TEG.1
The adsorption amounts of MB in CEGW, CEGD and TEG were calculated according to the following equation,2
where Qe (mg g-1) is the amount of MB adsorbed at equilibrium, C0 (mg l-1) is the initial solute concentration, Ce (mg l-1) the equilibrium solute concentration, V the volumn of MB solution, and m is the amount of adsorbate.
The adsorption isotherms were fitted (correlation coefficients, R2＞0.99) using the Langmuir adsorption model:3
where Qe (mg g-1) is the amount of MB adsorbed at equilibrium, Ce (mg l-1) the equilibrium solute concentration, Qm the maximum adsorption capacity corresponding to complete monolayer coverage, and b the equilibrium constant (l mg-1).
6. FESEM images of CEGW, TEG and CEGD
Figure S5. FESEM images of wet CEGW (a-c), TEG(d-f) and CEGD (g-i). 7. The representative FESEM, AFM and HRTEM images for the exfoliated graphene sheets obtained in this work.
(a)
(b)
Figure S6. FESEM images of graphene (a) and the maximum graphene sheet with 15 μm width (b).
1.0 nm 1.1 nm
1.6 nm
1.7 nm
1.2 nm
1.2 nm 1.1 nm 0.8 nm
1.2 nm
1.1 nm
1.1 nm
1.0 nm
2.5 nm
0.9 nm
1.1 nm
2μm 1.2 nm
Figure S7. The representative AFM images of the exfoliated graphene sheets for thickness measurement.
Figure S8. HRTEM images of few-layer graphene sheets
8. Representative 2D Raman images of the exfoliated graphene sheet
(a)
(b)
Figure S9. The 2-dimensional mapping of 2D band (a), and ID/IG ration images (b) of an exfoliated grahene sheet deposited on a Si substrate.
Figure S10. The Raman spectra of other locations (spots 2-11) denoted in Figure 5a.
Table S1 Raman parameters from the dots 1-11. Location
ID
IG
I2D
ID/IG
I2D/IG
FWHM
1
56.1
607
180
0.09
0.30
53.8
2
23.54
1292
354
0.02
0.27
63.1
3
42.8
1043
283
0.04
0.27
61.5
4
70.1
1325
451
0.05
0.34
58.8
5
87.8
1148
368
0.08
0.32
63.1
6
35.8
961
311
0.04
0.32
62.7
7
56.2
1541
480
0.03
0.31
58.7
8
59.6
1418
447
0.04
0.31
58.5
9
23.9
918
251
0.02
0.27
57.5
10
64
880
246
0.07
0.28
62.9
11
48.5
901
252
0.05
0.28
55.7
9. A comparison between the present method and other published methods on the yield, intrinsic properties of graphene sheets.
Table S2. Comparison of non-oxidization/reduction exfoliation methods for preparation of few-layer and single-layer graphene sheets. Graphene
Method and comments
Yield
Lateral size
Thickness
ID/IG
Electrical resistence
C/O
Oxygen content
Ref
Few-layer
Electrochemical expansion and sonication exfoliation in organic solvents. Possible limitation of electrode size for large-scale production.
>70%
-
50% 2-3 layers, 70% < 5 layers
10 μm
52% 1-3 layers,
10 μm
