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Chapter 6 – Production of Few Layer Graphene in Aqueous Media for Biological Studies Figure 6.3: UV-Visible absorbance spectra of control and dialysed dispersions along with solvent cut-off wavelengths. a) G/DMF and b) G/NMP. Cut-off wavelength was measured at A=1 (reference cell-water). The concentration of the dispersions were caluclated from absorbance at 660 nm using Beer-Lambert law (𝛼 - 4632 mL mg-1 m-1). All the dispersions were diluted 50 fold with water. UV-Visible absorbance spectra of the dispersions were recorded along with control samples without graphene (Figure 6.3). The control samples were carefully prepared by diluting the organic solvents in water at the specified concentrations. The absorbance spectra of the starting (100 v/v%) and the dialysed (10 v/v%, 1 v/v% and 0.1 v/v%) dispersions show flat and featureless absorption. The graphene absorption was observed around ~269 nm (attributed to 𝜋 → 𝜋∗ transition of the aromatic 𝐶 − 𝐶 bonds), indicating that the electronic conjugation within graphene was retained.167 The level of dialysis was confirmed by comparing the cut-off wavelengths of the organic solvents in the control and the dialysed samples, which are in excellent agreement with each other (Table 6-1) indicating successful dialysis. The organic solvent levels in the dialysed samples were further confirmed by NMR spectroscopy in section 6.2.3.2. Table 6-1: UV cut-off wavelength and concentrations of control and dialysed graphene dispersions Sample 100 v/v% 242 ± 3 - 238 ± 3 241 ± 3 221 ± 3 UV cut-off wavelength* at A=1 a.u. (nm) Concentration after dialysis (mg/ml) 0.78 ± 0.02 0.51 ± 0.01 0.41 ± 0.02 0.19 ± 0.01 DMF Control G/DMF NMP (dialysed) Control (dialysed) G/DMF G/NMP G/NMP 10 v/v% 234 ± 2 237 ± 2 230 ± 3 231 ± 3 0.46 ± 0.02 0.21 ± 0.02 1 v/v% 225 ± 3 228 ± 3 221 ± 2 *Samples were 50 fold diluted in water 0.1 v/v% 213 ± 3 214 ± 3 207 ± 3 204 ± 3 0.33 ± 0.02 0.16 ± 0.01 166PDF Image | PRODUCTION AND APPLICATIONS OF GRAPHENE AND ITS COMPOSITES
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