An approach to produce single and double layer graphene from re-exfoliation of expanded graphite

We report the production of high quality single and double layer graphene from sonication and centrifugation of re-exfoliated expanded graphite (EG) in an organic solvent. The prepared graphene-sheets are identified by Ultraviolet-visible spectroscopy and characterized using different techniques. Transmission and scanning electron microscopy observations show that the graphene-sheets have an area of similar to(12 x 10) mu m(2). The selected area electron diffraction analysis and Raman spectroscopy have confirmed the presence of single layer graphene-sheet. The I(2D)/I(G) ratio from the Raman spectrum of graphene is found to be similar to 1.7 which suggests the presence of single and double layer graphene. Scanning probe microscopy studies reveals that on re-exfoliation of EG, thickness of graphene layer decreases from 6-7 nm to 0.75-1.075 nm. This suggests that re-exfoliation overcomes the problem of insufficient oxidation or inadequate pressure that builds-up during first thermal exfoliation of graphite intercalated compound. The photoluminescence spectrum of graphene shows the emission of blue light at similar to 390 nm which indicates the presence of some functional groups. These graphene-sheets should facilitate the manipulation and processing of graphene based material for various applications. (C) 2011 Elsevier Ltd. All rights reserved.