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

The local atomic con fi guration of graphene oxide (GO) was investigated by identifying the di ff erent oxygen functionalities and following their evolution induced by thermal treatments in various environments (vacuum, nitrogen or argon fl ow). X-ray photoelectron spectroscopy and scanning transmission electron microscopy analyses were performed, and electron energy-loss (EEL) spectra were acquired in di ff erent regions of GO and thermally reduced GO fl akes. Experimental results show a series of characteristic peaks related to C and O K-edge shells and di ff erent features of GO thermally annealed at the same temperature but in di ff erent 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 di ff erent combinations and/or concentrations. Such calculations have allowed for the association of the observed experimental peaks to the presence of speci fi c oxygen functional groups, giving the opportunity to establish the atomic con fi gurations that prevail in di ff erent ranges of annealing temperatures and environments.