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Chapter 6 – Production of Few Layer Graphene in Aqueous Media for Biological Studies 59-62, sonication does not introduce any new basal plane defects in the graphene. Additionally, for the dialysed and starting graphene dispersions, the 𝐼𝐷⁄𝐼𝐷′ was ~4, suggested that the defects are mainly boundary type defects (edges).57, 127 Moreover, the absence of obvious FWHM(G) and FWHM(D) broadening (Table 6-3) of the dialysed dispersions suggested negligible structural disorder in the basal plane.259 Table 6-3: 2D band position, FWHM(G), FWHM(D), 𝐼2𝐷⁄𝐼𝐺, 𝐼𝐷⁄𝐼𝐺, 𝐼𝐷⁄𝐼𝐷′of starting (100 v/v%) and dialysed (0.1 v/v%) graphene dispersions Sample 0.1 v/v% G/DMF 0.1 v/v% G/NMP Raman 2D position (cm-1) 2668.5 ± 0.4 2667.1 ± 0.6 FWHM(G) (cm-1) 23.1 ± 0.5 22.9 ± 0.7 FWHM(D) (cm-1) 42.7 ± 0.5 43.3 ± 0.2 𝑰𝟐𝑫 𝑰𝑮 0.45 ± 0.04 0.42 ± 0.06 𝑰𝑫 𝑰𝑮 0.74 ± 0.02 0.86 ± 0.03 𝑰𝑫 𝑰𝑫′ 3.98 ± 0.31 4.24 ± 0.08 Starting G/DMF 2669.7 ± 0.6 22.5 ± 0.6 42.1 ± 0.4 0.02 0.51 ± 0.63 ± 0.06 0.25 3.92 ± Starting G/NMP 2667.2 ± 0.5 21.5 ± 0.5 43.4 ± 0.3 0.47 ± 0.03 0.81 ± 4.05 ± 0.05 0.17 The XRD analysis (Figure 6.7b) of the starting graphite showed a sharp diffraction peak around 26.5o due to diffraction from the (002) crystalline planes of graphite corresponding to an interlayer distance of ~3.34 Å. Whereas the diffraction peak was slightly broader for the starting and dialysed dispersions with an interlayer distance ranging between ~ 3.35 – 3.36 Å. This implies that during filtration, graphene restacks to form turbostratic graphene rather than graphite.245, 383, 384 These observations, along with the Raman results, confirm that the basal plane of the dialysed graphene had not suffered any severe in-plane disruptions, as in the case of GO.173 6.2.4.1. Discussion on stability mechanism The colloidal stability of dispersions can be indicated by measuring their 𝜁 values. The 𝜁 values of as-prepared 0.1 v/v% dialysed dispersions were ~ -48.87 mV (pH ~7.6) and ~ -47.7 mV (pH ~7.7) for G/DMF and G/NMP, respectively. Colloidal solutions with 𝜁 > ± 30 are normally considered to be stable systems, 385, 386 thus these high values indicate that the dialysed dispersions were stabilised through electrostatic repulsion between the graphene particles. 173PDF Image | PRODUCTION AND APPLICATIONS OF GRAPHENE AND ITS COMPOSITES
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