2 Mediated Reduction of Graphene Oxide at Room Temperature
Supporting Information
Rate and Mechanistic Investigation of Eu(OTf)2 Mediated Reduction of Graphene Oxide at Room Temperature Tufan Ghosh, Sandeepan Maity and Edamana Prasad* Department of Chemistry, Indian Institute of Technology Madras, Chennai-600036, India Email: [email protected]
Table of Contents Synthesis of graphene oxide
S4
UV-visible absorption spectrum of graphene oxide
S4
Powder XRD study of GO and pristine graphite
S5
TGA of GO and pristine graphite
S5
Scanning and transmission electronic microscopic characterization of GO
S6
Atomic force microscopic characterization of GO
S6
Zeta potential characterization of GO
S7
Characterization of Eu(OTf)2 by UV-visible absorption and steady state fluorescence
S8
spectroscopy
S1
Photograph of the solution during reduction of GO
S8
FT-IR spectra of graphene oxide and reduced graphene oxide
S8
Powder XRD pattern of pristine graphite, graphene oxide and reduced graphene oxide
S9
Raman spectrum of reduced graphene oxide
S10
Determination of bimolecular rate constant for the reduction of GO in acetonitrile-
S10
water mixture (12:1) Determination of bimolecular rate constant for the reduction of GO by hydrazine
S11
hydrate-ammonia mixture in water Determination of bimolecular rate constant for the reduction of GO by sodium
S11
borohydride in water Determination of bimolecular rate constant for the reduction of GO by glucose-
S12
ammonia mixture in water Cyclic voltammogram of of Eu(OTf)2 in THF in absence and presence of water
S12
Plot of growth data for run 2
S13
Condition for different excess experiment for rate order of Eu(OTf)2 in ACN
S13
Plot of growth data for run 4
S13
Plot of rate vs. [4] for rate order of Eu(OTf)2 in ACN
S14
Plot of normalized rate vs. [4] for rate order of Eu(OTf)2 in ACN
S14
Condition for different excess experiment for rate order of GO in THF
S14
Plot of growth data for run 6
S15
Plot of rate vs. [4] for rate order of GO in THF
S15
Plot of normalized rate vs. [4] for rate order of GO in THF
S16
Condition for different excess experiment for rate order of GO in ACN
S16
S2
Plot of growth data for run 8
S16
Plot of rate vs. [4] for rate order of GO in ACN
S17
Plot of normalized rate vs. [4] for rate order of GO in ACN
S17
Condition for different excess experiments for rate order of H2O in THF
S17
Plot of growth data for run 9
S18
Plot of rate vs. for rate order of H2O in THF
S18
Plot of normalized rate vs. [4] for rate order of H2O in THF
S19
Condition of different excess experiments for rate order of H2O in ACN
S19
Plot of growth data for run 12
S19
Plot of rate vs. [4] for rate order of H2O in ACN
S20
Plot of rate vs. [4] for rate order of H2O in ACN
S20
Effect of water as proton donor towards the reduction of GO
S21
Concentration dependent UV-visible absorption spectra of Eu(II) in THF
S21
S3
Synthesis of graphene oxide Graphene oxide has been synthesized according to Hummers’ method. In briefly, 0.5 g of NaNO3 and 23 ml of 98% H2SO4 were taken in a 500 ml beaker. The mixture was stirred for 5 min. in an ice bath. To the stirred mixture, 1 g of natural graphite powder was added slowly and the mixture was further stirred for 30 min. in the ice bath. Next, 3 g of KMnO4 was added very slowly to the mixture at 20 oC and the mixture was stirred for 2 h. The temperature of the reaction was increased to 35±3 oC and stirred for 30 minutes. Then 46 ml of double distilled water has been added to the reaction mixture. The temperature of the mixture was increased to 98 oC and stirred for 15 minutes. The reaction mixture was further diluted by adding 140 ml of double distilled water. To complete the oxidation, 30% H2O2 solution was added slowly till the color of the solution turns to yellow. The brownish yellow precipitate was filtered and washed with 5% HCl followed by 300 ml of double distilled water. Then dialysis was carried out for 7 days for the further purification of the graphite oxide.
Characterization of graphene oxide UV-visible absorption spectrum of GO
Absorbance
1.2 0.9 0.6 0.3 0.0 200
300
400
500
600
700
Wavelength, nm Figure S1: The UV-visible absorption spectrum of aqueous dispersion of graphene oxide. The absorption peak centered at 231 nm is assigned to the π-π* transition of C=C bonds whereas the broad band around 300 nm arises due to the n-π* transition of C=O bonds in graphene oxide.
S4
Powder XRD of GO and pristine graphite
5000
Counts, a.u.
4000 3000 2000 1000 0
5
10
15
20
25
30
35
40
2-Theta (2 Figure S2: Powder XRD pattern of exfoliated graphene oxide (black line) and pristine graphite (red line). The layer-to-layer distance (d-spacing) for the exfoliated graphene oxide has been calculated to be 0.841 nm (with a 2θ value of 10.5o; for 002 planes), whereas the d-spacing for the pristine graphite has been calculated to be 0.336 nm (with a 2θ value of 26.3 o; for 002 planes). The increase in the d-spacing in graphene oxide is presumably due to the presence of oxygen containing functional groups at the basal plane of graphene oxide and also intercalation of the water molecules in between the of graphene oxide planes. TGA of GO and pristine graphite 100
Weight %
80 60 40 20 0
0
200
400
600
0
800
Temperature, C Figure S3: TGA plot of graphite (black line) and graphite oxide (red line). Small weight loss (~20%) bellow 150 oC is presumably due to the losses of adsorbed water molecules and the major weight loss (~51%) in the temperature range of 200–400 oC is could be due to the removal of most labile oxygen functional groups present in GO (e.g., CO, CO2 etc.). And a slow weight loss in the range of 500–900 oC is due to the removal of more stable oxygen functionalities.
S5
Scanning and transmission electron microscopic characterization of GO
a)
b)
Figure S4: (a) A SEM image of GO, prepared by drop casting an aqueous solution of graphene oxide on an ITO glass plate. (b) A TEM image of graphene oxide prepared by drop casting an aqueous dispersion of graphene oxide on a carbon coated copper grid shows the sheet of graphene oxide. Atomic force microscopic (AFM) characterization of GO
a)
b)
Figure S5: (a) Tapping mode AFM image of graphene oxide. (b) The height profile shows the layer thickness in the range of 2.4–3.8 nm which corresponds to 2–3 layers of graphene oxide sheets.
S6
Zeta potential characterization of GO
Total Counts x10
4
18
12
6
0 -100
-50
0
50
Zeta Potential, mV Figure S6: Zeta potential histogram of an aqueous solution of graphene oxide at neutral pH. The measured zeta potential of the dispersion is −38 mV (
Rate and Mechanistic Investigation of Eu(OTf)2 Mediated Reduction of Graphene Oxide at Room Temperature Tufan Ghosh, Sandeepan Maity and Edamana Prasad* Department of Chemistry, Indian Institute of Technology Madras, Chennai-600036, India Email: [email protected]
Table of Contents Synthesis of graphene oxide
S4
UV-visible absorption spectrum of graphene oxide
S4
Powder XRD study of GO and pristine graphite
S5
TGA of GO and pristine graphite
S5
Scanning and transmission electronic microscopic characterization of GO
S6
Atomic force microscopic characterization of GO
S6
Zeta potential characterization of GO
S7
Characterization of Eu(OTf)2 by UV-visible absorption and steady state fluorescence
S8
spectroscopy
S1
Photograph of the solution during reduction of GO
S8
FT-IR spectra of graphene oxide and reduced graphene oxide
S8
Powder XRD pattern of pristine graphite, graphene oxide and reduced graphene oxide
S9
Raman spectrum of reduced graphene oxide
S10
Determination of bimolecular rate constant for the reduction of GO in acetonitrile-
S10
water mixture (12:1) Determination of bimolecular rate constant for the reduction of GO by hydrazine
S11
hydrate-ammonia mixture in water Determination of bimolecular rate constant for the reduction of GO by sodium
S11
borohydride in water Determination of bimolecular rate constant for the reduction of GO by glucose-
S12
ammonia mixture in water Cyclic voltammogram of of Eu(OTf)2 in THF in absence and presence of water
S12
Plot of growth data for run 2
S13
Condition for different excess experiment for rate order of Eu(OTf)2 in ACN
S13
Plot of growth data for run 4
S13
Plot of rate vs. [4] for rate order of Eu(OTf)2 in ACN
S14
Plot of normalized rate vs. [4] for rate order of Eu(OTf)2 in ACN
S14
Condition for different excess experiment for rate order of GO in THF
S14
Plot of growth data for run 6
S15
Plot of rate vs. [4] for rate order of GO in THF
S15
Plot of normalized rate vs. [4] for rate order of GO in THF
S16
Condition for different excess experiment for rate order of GO in ACN
S16
S2
Plot of growth data for run 8
S16
Plot of rate vs. [4] for rate order of GO in ACN
S17
Plot of normalized rate vs. [4] for rate order of GO in ACN
S17
Condition for different excess experiments for rate order of H2O in THF
S17
Plot of growth data for run 9
S18
Plot of rate vs. for rate order of H2O in THF
S18
Plot of normalized rate vs. [4] for rate order of H2O in THF
S19
Condition of different excess experiments for rate order of H2O in ACN
S19
Plot of growth data for run 12
S19
Plot of rate vs. [4] for rate order of H2O in ACN
S20
Plot of rate vs. [4] for rate order of H2O in ACN
S20
Effect of water as proton donor towards the reduction of GO
S21
Concentration dependent UV-visible absorption spectra of Eu(II) in THF
S21
S3
Synthesis of graphene oxide Graphene oxide has been synthesized according to Hummers’ method. In briefly, 0.5 g of NaNO3 and 23 ml of 98% H2SO4 were taken in a 500 ml beaker. The mixture was stirred for 5 min. in an ice bath. To the stirred mixture, 1 g of natural graphite powder was added slowly and the mixture was further stirred for 30 min. in the ice bath. Next, 3 g of KMnO4 was added very slowly to the mixture at 20 oC and the mixture was stirred for 2 h. The temperature of the reaction was increased to 35±3 oC and stirred for 30 minutes. Then 46 ml of double distilled water has been added to the reaction mixture. The temperature of the mixture was increased to 98 oC and stirred for 15 minutes. The reaction mixture was further diluted by adding 140 ml of double distilled water. To complete the oxidation, 30% H2O2 solution was added slowly till the color of the solution turns to yellow. The brownish yellow precipitate was filtered and washed with 5% HCl followed by 300 ml of double distilled water. Then dialysis was carried out for 7 days for the further purification of the graphite oxide.
Characterization of graphene oxide UV-visible absorption spectrum of GO
Absorbance
1.2 0.9 0.6 0.3 0.0 200
300
400
500
600
700
Wavelength, nm Figure S1: The UV-visible absorption spectrum of aqueous dispersion of graphene oxide. The absorption peak centered at 231 nm is assigned to the π-π* transition of C=C bonds whereas the broad band around 300 nm arises due to the n-π* transition of C=O bonds in graphene oxide.
S4
Powder XRD of GO and pristine graphite
5000
Counts, a.u.
4000 3000 2000 1000 0
5
10
15
20
25
30
35
40
2-Theta (2 Figure S2: Powder XRD pattern of exfoliated graphene oxide (black line) and pristine graphite (red line). The layer-to-layer distance (d-spacing) for the exfoliated graphene oxide has been calculated to be 0.841 nm (with a 2θ value of 10.5o; for 002 planes), whereas the d-spacing for the pristine graphite has been calculated to be 0.336 nm (with a 2θ value of 26.3 o; for 002 planes). The increase in the d-spacing in graphene oxide is presumably due to the presence of oxygen containing functional groups at the basal plane of graphene oxide and also intercalation of the water molecules in between the of graphene oxide planes. TGA of GO and pristine graphite 100
Weight %
80 60 40 20 0
0
200
400
600
0
800
Temperature, C Figure S3: TGA plot of graphite (black line) and graphite oxide (red line). Small weight loss (~20%) bellow 150 oC is presumably due to the losses of adsorbed water molecules and the major weight loss (~51%) in the temperature range of 200–400 oC is could be due to the removal of most labile oxygen functional groups present in GO (e.g., CO, CO2 etc.). And a slow weight loss in the range of 500–900 oC is due to the removal of more stable oxygen functionalities.
S5
Scanning and transmission electron microscopic characterization of GO
a)
b)
Figure S4: (a) A SEM image of GO, prepared by drop casting an aqueous solution of graphene oxide on an ITO glass plate. (b) A TEM image of graphene oxide prepared by drop casting an aqueous dispersion of graphene oxide on a carbon coated copper grid shows the sheet of graphene oxide. Atomic force microscopic (AFM) characterization of GO
a)
b)
Figure S5: (a) Tapping mode AFM image of graphene oxide. (b) The height profile shows the layer thickness in the range of 2.4–3.8 nm which corresponds to 2–3 layers of graphene oxide sheets.
S6
Zeta potential characterization of GO
Total Counts x10
4
18
12
6
0 -100
-50
0
50
Zeta Potential, mV Figure S6: Zeta potential histogram of an aqueous solution of graphene oxide at neutral pH. The measured zeta potential of the dispersion is −38 mV (
