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Chapter 6 β Production of Few Layer Graphene in Aqueous Media for Biological Studies G band appears around ~1580 cm-1 and the presence of an intense D band (~1330 cm-1) and Dβ band (~1617 cm-1) indicates the presence of defects. These defects could be due to the edges as the flakes produced are smaller as determined by DLS and AFM. The G/TDOC dispersions were spray deposited on mica followed by rinsing with DI water (to remove excess free surfactant molecules) followed by annealing (400 oC in argon) before AFM measurements. The πΏπ΄πΉπ obtained was ~90 nm and is comparable with the πΏπ·πΏπ (~100 nm) as seen in Figure 6.8d,e. AFM statistical measurements over 100 flakes indicate that the dispersion contained π1βππ ~17 % and π1β5βππ > 92 % with γπγ as 3.2 Β± 1.8. As mentioned earlier, the observed πΌπ·βπΌπΊ ratio ~1.25 could be attributed to the flake edges rather than basal plane defects based on the following considerations: ο· Since the πΏπ΄πΉπ~ 90nm and the laser spot was ~2 ΞΌm, a considerable amount of edges contributed to the D band intensity. ο· No obvious broadening of FWHM(G) ~21.5 Β± 1.1 or FWHM(D) ~40.1 Β± 1.2 was observed, suggesting the absence of high structural disorder (For highly disordered graphene the G band merges with the Dβ band, and G and D band exhibit large FWHM 173, 259). ο· The observed πΌπ·βπΌπ·β² ~4.15 suggests boundary-type defects rather than basal plane defects.57, 127 Finally, the as-produced G/TDOC dispersion had a pH value of ~7.6 with π ~ -63 mV, similar to that reported in the literature.80 This π value suggests that the colloidal stability against aggregation was mainly due to electrostatic repulsion of TDOC-coated graphene sheets.79, 80 6.4. EXFOLIATION OF FEW LAYER GRAPHENE USING LIPIDS The hydrophobic nature of pristine graphene has led to the assumption that its stability in aqueous media is possible only with the addition of surfactants60, 77, 79 facilitating biological studies.218 Whereas, due to its hydrophilic functional groups, GO remains stable in water, making it by far the most studied (among GBMs) candidate for biological applications and toxicity studies.5 However, in an electrolyte environment 177PDF Image | PRODUCTION AND APPLICATIONS OF GRAPHENE AND ITS COMPOSITES
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