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Chapter 6 – Production of Few Layer Graphene in Aqueous Media for Biological Studies The final concentration obtained for the G/DMF and G/NMP dispersions at 0.1 v/v% organic solvent content (99.9 v/v% water) was 0.33 ± 0.02 mg/ml and 0.16 ± 0.01 mg/ml, respectively. The stability of the dialysed dispersions was measured over a period of a month by using UV-Vis spectroscopy. The sedimentation curves of the G/DMF and G/NMP dialysed dispersions are shown in Figure 6.4a,b. The dispersions were relatively stable over a month. The 0.1 v/v% G/DMF and 0.1 v/v% showed < 25 % sedimentation over 10 days, however, 55-60 % sedimentation was observed over a month. Khan et al. reported that a graphene dispersion in NMP (0.7 mg/ml) showed faster sedimentation (25 % over 160 hr) upon lesser, 100 fold dilution in water (1 v/v% NMP, 0.007 mg/ml).59 6.2.3.2. Organic solvent content by 1H NMR spectroscopy The amount of organic solvent content present in the dialysed dispersions was determined by estimating the 1H present using 1H NMR spectroscopy. In order to avoid the signal interference from H2O to organic molecules, the graphene dispersions were dialysed against heavy water (D2O) using a similar procedure to that for water dialysis. This allows the quantification of residual organic solvent content by integration of the 1H signals. Figure 6.5: 1H NMR spectra of 10, 1 and 0.1 v/v% D2O-dialysed G/DMF (a) and G/NMP (b) dispersions. Note: black trace – graphene dispersions, red trace – control (without graphene). 168PDF Image | PRODUCTION AND APPLICATIONS OF GRAPHENE AND ITS COMPOSITES
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