Preparation of graphene oxide and characterisation using electron spectroscopy

•Graphene oxide by ozonation and cold glow air plasma from 8nm graphene platelets.•XPS, REELS for characterising the surface chemical composition and the structure.•C sp3 and carbon–oxygen groups content smaller contrary to wet chemical methods.•REELS shows decreasing number of graphene layers: platelets>ozone>plasma.•Oxidation separates graphene layers via incorporating interlayer oxygen-H2O groups. Graphene oxide was prepared from commercial graphene powder (G) platelets of 8nm thickness by oxidation in ozone (G-O3) and low-energy (cold) glow air plasma in a pink region (G-PP). X-ray photoelectron spectroscopy (XPS) was applied for chemical characterisation of the atomic content and for obtaining quantitative information on C hybridisation. Reflection electron energy loss spectroscopy (REELS) was used for characterising the surface structure including the content of surface and bulk carbon atoms of sp2 and sp3 hybridisation. The G-O3 and G-PP graphene oxide samples contain a low amount of C sp3 bonds and carbon–oxygen groups in comparison to graphene oxide prepared by the “wet” chemical methods. Oxidation of commercial graphene platelets powder, especially in air plasma, leads to increasing surface C sp3 and significantly bulk C sp3 contributions, indicating intercalation by oxygen groups. The intensity ratio of the REELS π+σ C sp2 bulk to the C sp2 surface energy loss peaks, decreasing in the order G>G-O3>G-PP, indicates exfoliation of layers in G-O3 and G-PP by oxygen functional groups and water with decreasing average number of layers in graphene oxide nanostructures due to oxidation. Although, the “wet” chemical methods are more effective for oxidation leading to a larger amount of C sp3 and oxygen groups, the proposed methods of oxidation by ozonation and in air plasma are inexpensive, safe, effective, environmentally friendly and do not result in toxic chemical waste products.