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Keywords:

  • graphene;
  • graphene oxide paper;
  • carbon plane unzipping;
  • X-ray absorption near-edge structure spectroscopy;
  • X-ray emission spectroscopy

Abstract

The electronic structure and chemical bonding of three differently prepared samples of graphene oxide paper-like sheets are studied. Two are created by water filtration of fully oxidized graphene sheets, although one is later intercalated with dodecylamine. The third is created by reducing graphene oxide with hydrazine hydrate. The spectroscopic fingerprints of the aligned epoxide functional groups that unzip the carbon basal plane are found. This unzipping appears to be a result of aging, and the extent to which the basal plane is unzipped can be controlled via the preparation method. In particular, reduction with hydrazine enhances line defect formation, whereas intercalation inhibits the process.The hydroxyl functional group also has a tendency to gather in zones of dense oxidation on the carbon basal plane, a predilection that is not shared by the other prominent functional group species. Finally, the non-functionalized carbon sites exhibit very similar bonding despite the increase in the sp2/sp3 ratio, confirming that reduction alone is insufficient for producing pristine graphene from graphene oxide. These results are obtained by directly probing the electronic structure of the graphene oxide samples via X-ray absorption near-edge structure spectroscopy (XANES) and resonant X-ray emission spectroscopy (RXES). This work has important significance for the development of graphene oxide as a band gap-engineered electronic material, as preparation methodology strongly affects not only the initial condition of the sample, but how the electronic structure evolves over time.