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interlayer spacing, thereby reducing the van der Waals forces between the layers and forming GICs which are then dispersed in a liquid medium through sonica- tion to form single-layer graphene [45]. Alkali metals are the only choice of ma- terials as they easily form GICs on reaction with graphite due to the difference in ionization potential between graphite and alkali metals. Chemical exfoliation methodology was used by Viculis et al. to obtain graphene nanoplatelets (GNP) using potassium alkali metal [46]. Potassium graphite (KC8) intercalated com- pound was formed when potassium reacted with graphite at 200 ̊C under inert atmosphere. Dispersion of the GIC in aqueous ethanol (CH3CH2OH) resulted in an exothermic reaction as shown in (1) and produced GNP. KC8 + CH3CH2OH → 8C + KOCH2CH3 + 1 H2 (1) 2 Potassium ions dissolve into the ethanol solution forming potassium ethoxide (KOCH2CH3) and hydrogen gas is formed to aid the separation of the layers of graphene. Precaution must be taken during this reaction as alkali metals vigo- rously react with water and alcohol, as such there is a need for an ice bath to dis- sipate heat during reaction. The main advantage of alkali metals, such as potas- sium, is their relatively small atomic radius which is smaller than the interlayer spacing in graphite and hence fits the interlayer spacing easily as shown in Fig- ure 5(a). Figure 4. (a) Mechanical exfoliation process by using AFM; (b) SEM micrograph of mechanically exfoliated thin graphite layers from HOPG using AFM; (c) Optical micro-graph of few graphene flakes produced by the scotch tape method (scale bar 50 μm); (d) Graphene layer of various thickness on SiO2/Si substrate. A. Adetayo, D. Runsewe DOI: 10.4236/ojcm.2019.92012 211 Open Journal of Composite MaterialsPDF Image | Synthesis and Fabrication of Graphene and Graphene Oxide
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