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

Abstract

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 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.

Evolution of oxygen functionalities in graphene oxide and its impact on structure and exfoliation: An oxidation time based study

“…Further it has been reported based on molecular dynamic simulations that desorption of C-OH groups during thermal treatment introduce minimal disorder to the basal plane structure, whereas the destruction is much larger with C-O-C reduction [56]. It is also important to note that the TGA analysis was carried out under identical conditions for all samples, thus eliminating the environmental effect for the observed changes in the thermographs [66]. Therefore, the observed change in the thermal behavior of GO4 to that of GO1, GO2, and GO3 can be related to the special distribution of the oxygen functionalities, especially that of C-OH and C-O-C on the above samples.…”

EPR Study of Porous Si:C and SiO2:C Layers

“…After oxidation, we observed the obvious development of additional peak at 288.6 eV that can be attributed to COC oxygen epoxy bonds or COH carboxylic groups . Taking into account that several studies show that the epoxides disappear after thermal treatments at temperatures between 150 and 450 °C, while hydroxyl and carboxylic groups survive and are stable up to 1000 °C it can be suggested that additional peak comes from carboxylic groups.…”

“…Such shift can be attributed to the highly disordered structure with mixing sp 2 and sp 3 CC bonds as well as to the presence of O chemically bonded to C in the form of hydroxyl groups. It is well known that incorporation of O in carbon structures results in appearing of specific spectral features in the range of 285–290 eV caused by excitation of π* states of CO bonds in form of epoxy bridges, hydroxyl, carboxyl, and carboxylate groups …”

Theoretical X-ray absorption spectroscopy database analysis for oxidised 2D carbon nanomaterials

“…It shall be mentioned, though, that especially these two signals allow for a lot of different interpretations and are heavily discussed in literature. In other reports, the signal around 288.9 eV was assigned to CQO transitions related to COOH groups, 59,60 interlayer states, 61 as well as contaminant effects on the GO surface. 6 Although our theoretical study cannot rule out the possibility of interlayer effects or contaminants, we can confirm that the signal at 288.9 eV is, in principle, describable as p*(CQO) related transition from both carbonylic as well as carboxylic group XA spectra.…”