PRODUCTION AND APPLICATIONS OF GRAPHENE AND ITS COMPOSITES

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PRODUCTION AND APPLICATIONS OF GRAPHENE AND ITS COMPOSITES ( production-and-applications-graphene-and-its-composites )

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2.3.3.1. Anodic exfoliation In anodic exfoliation, application of positive potentials to the graphite working electrode results in intercalation of anions such as: sulphate-based ions, nitrate ions, etc., and subsequent exfoliation to produce graphene flakes. Parvez et al. have reported exfoliation in different aqueous inorganic salts, including sodium sulphate, ammonium sulphate (showed highest exfoliation efficiency at 0.1 M concentration in water, +10 V for 3-5 min) and potassium sulphate, producing graphene sheets with low defect density (C/O ~ 17.2).119 The produced graphene sheets contained ~80 % > 5 μm lateral dimensions and ~85 % flakes between 1-3 layers. Lu et al. have reported IL containing nitrate ions (ethylammonium nitrate) can be used for electrochemical exfoliation of graphite in aqueous media.120 Unlike the failure of exfoliation in pure IL, addition of water showed successful exfoliation. Under applied potential (+2.2 V), the water oxidises generating oxygen-reactive species which opens the edges and grain boundaries of graphite sheets, that are utilised by the nitrate ions to intercalate and exfoliate, producing nitrogen doped graphene sheets.120 Figure 2.8: a,b) Schematic representation of electrochemical approaches using anions or cations for intercalation and exfoliation of graphene flakes117. c-g) Electrochemical exfoliation of HOPG using cations121: (c) Picture of HOPG. d) HOPG expansion after 1000 sec tetraethylammonium cation intercalation, e, f) HOPG expansion after 1000 sec and 10000 sec tetrabutylammonium cation (TBA+) intercalation, respectively. g) SEM image of HOPG expansion of 6000 sec TBA+ intercalation. Chapter 2 – Graphene: Properties and Production 52

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