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Chapter 6 – Production of Few Layer Graphene in Aqueous Media for Biological Studies Figure 6.1: Photographs showing the stability and concentration of G/DMF and G/NMP on different dilution with water. G/DMF and G/NMP dispersions were produced at 24 hr sonication and 6000 rpm centrifuge speed. One way of achieving this low level of organic solvents is just by simple dilution. It can be seen clearly from Figure 6.1 that graphene dispersions upon dilution with water, the organic solvent content in the dispersion can certainly be reduced while leading to a stable dispersion even after 12 hr. However, the concentration of graphene also reduces upon dilution (as observed even by the naked eye), making it unsuitable for biological studies, where higher concentrations may be required, certainly for the toxicity studies here. Solvent exchange techniques such as dialysis could potentially be employed to reduce the organic solvent content in these graphene dispersions when dialysed against water. 6.2.2. Dialysis of graphene dispersions against aqueous media Dialysis works on the principle of the diffusion of molecules across a semipermeable membrane separating regions of high and low concentration. The working principle and experimental details are given in section 4.1.6. The initial graphene dispersions were produced by the direct exfoliation of graphite in DMF and NMP using a sonication time of 60 hr (see 5.2.1). The resultant dispersions were then centrifuged at 6000 rpm for 20 min, the supernatant was collected and centrifuged at 10000 rpm. The sediment from this step was then collected and redispersed in 10-15 ml of fresh solvent to achieve a high concentration of graphene. The concentrations obtained for graphene in DMF (G/DMF) and graphene in NMP (G/NMP) were ~0.78 mg/ml and ~0.51 mg/ml, respectively. 164PDF Image | PRODUCTION AND APPLICATIONS OF GRAPHENE AND ITS COMPOSITES
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