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Chapter 6 β Production of Few Layer Graphene in Aqueous Media for Biological Studies study, leading to a very stable dispersion without any visible aggregation over 8 months.) Sun et al. have achieved very high concentration of G/TDOC up to 7.1 mg/ml (24 hr, 500 rpm) using more intense, probe tip sonication.79 Lotya et al. observed smaller graphene flakes were produced at higher centrifugation rates (longer sonication time, up to 400 hr), which had basal plane defects.60 The surfactant used in their study was SC rather than TDOC and hence may not be directly comparable to this study. Nevertheless, as explained below, Raman spectra of G/TDOC did not show the presence of basal plane defects in these TDOC preparations. Figure 6.8: a) UV-Vis absorbance spectra of G/TDOC (36 hr, 10 fold diluted). Inset showing a stable G/TDOC dispersion. b) Graphene concentration obtained against sonication time (all samples centrifuged at 10000 rpm for 20 min). c) Raman spectra of thin film prepared G/TDOC (36 hr) dispersions. Spectrum of starting graphite is shown for reference. d) Intensity particle size distribution of G/TDOC (36 hr) by DLS. e) AFM height image of spray coated G/TDOC (36 hr) dispersion. f) Corresponding amplitude image of (e). Note: after spray deposition, the mica substrate was rinsed with DI water to remove the surfactant. Representative Raman spectra obtained on a thin film prepared by vacuum filtration of G/TDOC (36 hr, 10000 rpm) are shown in Figure 6.8c. Typical Raman bands (G band, 2D band and D band) of graphene are clearly seen and are similar to that of LPE graphene.54, 60, 77, 94, 390 The 2D band is broad (but still a single Lorentzian) and down shifted (2652 Β± 2.1 cm-1) by ~20 cm-1 compared to the starting graphite, and the πΌ2π·βπΌπΊ ~0.75 suggesting G/TDOC as few-layer (< 5 layers) in nature.48, 60, 79, 390 The characteristic 176PDF Image | PRODUCTION AND APPLICATIONS OF GRAPHENE AND ITS COMPOSITES
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