Oxygen Functionalities Evolution in Thermally Treated Graphene Oxide Featured by EELS and DFT Calculations

The local atomic configuration of graphene oxide (GO) was investigated by identifying the different oxygen functionalities and following their evolution induced by thermal treatments in various environments (vacuum, nitrogen or argon flow). X-ray photoelectron spectroscopy and scanning transmission electron microscopy analyses were performed, and electron energy-loss (EEL) spectra were a) acquired in different regions of GO and thermally reduced GO flakes. Experimental results show a series of characteristic peaks related to C and O K-edge shells and different features of GO thermally annealed at the same temperature but in different environments. In order to understand the experimental results, density functional theory calculations of core-loss EEL spectra of GO (C and O K-edges) in the presence of oxygen functional groups have been performed for different combinations and/or concentrations. Such calculations have allowed for the association of the observed experimental peaks to the presence of specific oxygen functional groups, giving the opportunity to establish the atomic configurations that prevail in different ranges of annealing temperatures and environments.