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  • 8/7/2019 Exfoliation of Graphite Oxide in Propylene Carbonate and Thermal Reduction of the Resulting Graphene Oxide Plat

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    Supporting Information

    Exfoliation of graphite oxide in propylene carbonate and thermal reduction

    of the resulting graphene oxide plateletsBy Yanwu Zhu, Meryl D. Stoller, Weiwei Cai, Aruna Velamakanni, Richard D. Piner,

    David Chen, and Rodney S. Ruoff*

    1. Effect of pH values on the dispersion of GO in PC

    It was found that the pH of the graphite oxide (GO) has a significant effect on its

    dispersion extent in propylene carbonate (PC). During the preparation of GO powder,

    10% HCl solution in water (200 ml) was used to wash the GO slurry before drying in

    vacuum. Thus the as-made GO dispersed in water or PC has a pH of about 3 (for 1

    mg/ml) (hereafter we shall label it as pH3 GO). To tune the pH of GO, pH3 GO was re-

    dispersed in water by magnetic stirring (no sonication) and diluted ammonium hydroxide

    (15% concentration) was added with a drop step till the pH reached 5, 7 or 10,

    respectively.

    Then, the GO suspensions with pH 5, pH 7 and pH 10 were filtered and dried in air; thus

    we obtained pH5 GO, pH7 GO and pH10 GO plate-like samples on filter membranes.

    The pH5 GO, pH7 GO and pH10 GO samples were subject to further drying in vacuum

    for two days. Following the same process described in the experimental section, 20 mg of

    dry pH5 GO, pH7 GO and pH10 GO were dispersed in 20 ml PC each and sonicated for

    2 hours in the bath sonicator (VWR B2500A-MT). As can be seen from Fig. S1, pH10

    GO has almost no dispersion in PC while pH7 GO has a small degree of dispersion

    degree in PC as observed by changing the color of PC to light brown. The pH5 GO

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    showed a similar dispersion with pH3 GO at this concentration (1 mg/ml). The highest

    concentrations of dispersed/exfoliated pH3 GO, pH7 GO and pH10 GO in PC were

    estimated as 1.3, 0.05 mg/ml and 0.01 mg/ml, respectively. As a comparison, pH3 GO

    dispersion has a highest concentration of about 3 mg/ml.

    Fig. S1 Optical images of GO with variable pH values in PC, after 2 hours of bath

    sonication.

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    2. High-resolution transmission electron microscopy of the reduced graphene oxide

    Fig. S2 Typical HRTEM image of the RG-O platelets from the 150oC treatment. From

    the fringes of the folded regions, we can see that this region of the sample is composed of

    a stack of RG-O platelets.

    3. FT-IR of pure PC, GO and RG-O paper

    FT-IR was done to investigate the functional groups and to detect any residual PC in the

    RG-O paper obtained by heating graphene oxide suspension in PC at 150 oC followed by

    drying in vacuum at 80oC for 2 days. Fig. S3 shows the spectra of pure PC, as-made GO

    and RG-O paper. All samples were made by mixing (for PC) or grounding (for GO and

    RG-O) with KBr. Those features at around 1044, 1610, 1708 and 3400 cm-1

    were

    observed for the GO sample, corresponding to the C-O (v(epoxy or alkoxy)), C=C

    (possibly due to skeletal vibrations of unoxidized graphitic domains), C=O in carboxylic

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    acid and carbonyl moieties (v(carbonyl)), and O-H stretching mode of intercalated water,

    respectively.1, 2 Clearly, after thermal treatment in PC followed by drying, most of these

    transmission features were nearly eliminated in the spectrum of RG-O sample. Moreover,

    no significant PC trace was observed in the RG-O spectrum.

    Fig. S3 FT-IR spectra of PC, GO and RG-O.

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    4. Comparison of the conductivity of paper-like samples composed of RG-O from

    different fabrication/reduction methods

    Table S1

    Materials/reduction Method Electrical properties Reference

    Heating GO (50-90oC) in alkaline conditions Unknown

    3

    Hydrothermal treatment of GO in supercritical

    water (120-180oC)

    Conductive (powder resistance of ~40

    )

    4

    Reduction of GO by sodium borohydride Highest conductivity of 45 S/m

    5

    Flash reduction of GO Conductivity of ~ 1000 S/m2

    Hydrazine reduction of GO Powder conductivity of 200 S/m6

    Hydrazine reduction of KOH-modified

    graphene oxide

    Conductivity of 690 S/m7

    Hydrazine reduction of GO in DMF/water

    mixture (HRG)

    Air drying 1700 S/m

    Annealing at 150oC 16000 S/m

    8

    Hydrazine reduction of GO in ammoniasolution

    Conductivity of ~ 7200 S/m 9

    Pre-reduction of GO by NaBH4 ---

    sulphonation --- Post reduction with hydrazine

    Conductivity of 1250 S/m10

    Pre-redcution of GO by NaBH4 --- Heating in

    H2SO4 --- Post annealing at 1100oC in Ar/H2

    Conductivity of 20200 S/m11

    Rapid heating of GO up to 1050oC Powder conductivity of 1000-2300 S/m

    12

    Reduced graphene oxide in PC at 200oC ~ 1800 S/m

    Annealing at 250oC ~2640 S/m

    Present work

    Reduced graphene oxide in PC at 150oC ~ 2100 S/m

    Annealing at 250oC ~ 5230 S/m

    Present work

    5. Calculation of capacitance from CV and galvanostatic curves

    Capacitance values were calculated from the CV curves by dividing the current by the

    voltage scan rate, C = I/(dV/dt). Specific capacitance reported is the capacitance for the

    mass of RG-O in one electrode (specific capacitance = capacitance of single electrode /

    weight RG-O material of a single electrode), as per the normal convention. Capacitance

    as determined from galvanostatic charge/discharge was measured using C = I/(dV/dt)

    with dV/dt calculated from the slope of the discharge curve.

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    6. References:

    1. Guo, H.-L.; Wang, X.-F.; Qian, Q.-Y.; Wang, F.-B.; Xia, X.-H. A Green

    Approach to the Synthesis of Graphene Nanosheets. Acs Nano 2009,3, 26532659.

    2. Cote, L. J.; Cruz-Silva, R.; Huang, J. Flash Reduction and Patterning of GraphiteOxide and Its Polymer Composite. J. Am. Chem. Soc. 2009,131, 11027-11032.

    3. Fan, X. B.; Peng, W. C.; Li, Y.; Li, X. Y.; Wang, S. L.; Zhang, G. L.; Zhang, F.

    B. Deoxygenation of Exfoliated Graphite Oxide under Alkaline Conditions: A Green

    Route to Graphene Preparation. Adv. Mater. 2008,20, 4490-4493.

    4. Zhou, Y.; Bao, Q.; Tang, L. A. L.; Zhong, Y.; Loh, K. P. Hydrothermal

    Dehydration for the Green Reduction of Exfoliated Graphene Oxide to Graphene and

    Demonstration of Tunable Optical Limiting Properties. Chem. Mater. 2009,21, 2950-

    2956.

    5. Shin, H.-J.; Kim, K. K.; Benayad, A.; Yoon, S.-M.; Park, H. K.; Jung, I.-S.; Jin,

    M. H.; Jeong, H.-K.; Kim, J. M.; Choi, J.-Y.; Lee, Y. H. Efficient Reduction of Graphite

    Oxide by Sodium Borohydride and Its Effect on Electrical Conductance. Adv. Func.

    Mater. 2009,19, 1987-1992.

    6. Stankovich, S.; Dikin, D. A.; Piner, R. D.; Kohlhaas, K. A.; Kleinhammes, A.;

    Jia, Y.; Wu, Y.; Nguyen, S. T.; Ruoff, R. S. Synthesis of Graphene-based Nanosheets via

    Chemical Reduction of Exfoliated Graphite Oxide. Carbon 2007,45, 1558-1565.

    7. Park, S.; An, J. H.; Piner, R. D.; Jung, I.; Yang, D. X.; Velamakanni, A.; Nguyen,

    S. T.; Ruoff, R. S. Aqueous Suspension and Characterization of Chemically Modified

    Graphene Sheets. Chem. Mater. 2008,20, 6592-6594.

    8. Park, S.; An, J. H.; Jung, I. W.; Piner, R. D.; An, S. J.; Li, X. S.; Velamakanni, A.;

    Ruoff, R. S. Colloidal Suspensions of Highly Reduced Graphene Oxide in a Wide

    Variety of Organic Solvents. Nano Lett. 2009,9, 1593-1597.

    9. Li, D.; Muller, M. B.; Gilje, S.; Kaner, R. B.; Wallace, G. G. Processable

    Aqueous Dispersions of Graphene Nanosheets. Nat. Nanotech. 2008,3, 101-105.

    10. Si, Y.; Samulski, E. T. Synthesis of Water Soluble Graphene. Nano Lett. 2008,8,

    1679-1682.

    11. Gao, W.; Alemany, L. B.; Ci, L.; Ajayan, P. M. New Insights into the Structure

    and Reduction of Graphite Oxide. Nat. Chem. 2009,1, 403-408.

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    12. Schniepp, H. C.; Li, J. L.; McAllister, M. J.; Sai, H.; Herrera-Alonso, M.;

    Adamson, D. H.; Prud'homme, R. K.; Car, R.; Saville, D. A.; Aksay, I. A. Functionalized

    Single Graphene Sheets Derived from Splitting Graphite Oxide. J. Phys. Chem. B 2006,

    110, 8535-8539.