In situ near-edge x-ray absorption fine structure spectroscopy investigation of the thermal defunctionalization of graphene oxide

In situ near-edge x-ray absorption fine structure (NEXAFS) spectroscopy is used in conjunction with measurements of sheet resistance to examine the electronic structure recovery of graphene oxide upon thermal annealing. Several different defunctionalization regimes are identified with the initial removal of basal plane epoxide and hydroxyl functionalities and subsequent elimination of carboxylic acid moieties. The measured electrical conductivity is closely correlated to recovery of the conjugated π structure. A pronounced broadening of the C K-edge π* resonance is observed upon annealing and is ascribed to the superposition of the NEXAFS signatures of sp 2-hybridized domains of varying dimensionality. Such incipient conjugated domains generated upon thermal defunctionalization mediate variable range hopping transport and further lead to an increase in the electrical conductance. Finally, both C K-edge and O K-edge spectra suggest that ring ether functionalities such as pyrans or furans and/or 1,2- and 1,4-quinones are stabilized at higher temperatures.