The complete restoration of a perfect carbon lattice has been a central issue in the research on graphene derived from graphite oxide since this preparation route was first proposed several years ago, but such a goal has so far remained elusive. Here, we demonstrate that the highly defective structure of reduced graphene oxide sheets assembled into free-standing, paper-like films can be fully repaired by means of high temperature annealing (graphitization). Characterization of the films by X-ray photoelectron and Raman spectroscopy, X-ray diffraction and scanning tunneling microscopy indicated that the main stages in the transformation of the films were (i) complete removal of oxygen functional groups and generation of atomic vacancies (up to 1500 °C), and (ii) vacancy annihilation and coalescence of adjacent overlapping sheets to yield continuous polycrystalline layers (1800-2700 °C) similar to those of highly oriented graphites. The prevailing type of defect in the polycrystalline layers were the grain boundaries separating neighboring domains, which were typically a few hundred nanometers in lateral size, exhibited long-range graphitic order and were virtually free of even atomic-sized defects. The electrical conductivity of the annealed films was as high as 577,000 S m-1 , which is by far the largest value reported to date for any material derived from graphene oxide, and strategies for further improvement without the need to resort to higher annealing temperatures are suggested. Overall, the present work opens the prospect of truly achieving a complete restoration of the carbon lattice in graphene oxide materials.

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The production of stable aqueous suspensions of several inorganic graphene analogues was performed by exfoliation of the corresponding bulk layered materials via sonication using non-ionic surfactants as dispersing agents.

High temperature annealing is the only method known to date that allows the complete repair of a defective lattice of graphenes derived from graphite oxide, but most of the relevant aspects of such restoration processes are poorly understood. Here, we investigate both experimentally (scanning probe microscopy) and theoretically (molecular dynamics simulations) the thermal evolution of individual graphene oxide sheets, which is rationalized on the basis of the generation and the dynamics of atomic vacancies in the carbon lattice. For unreduced and mildly reduced graphene oxide sheets, the amount of generated vacancies was so large that they disintegrated at 1773-2073 K. By contrast, highly reduced sheets survived annealing and their structure could be completely restored at 2073 K. For the latter, a minor atomic-sized defect with six-fold symmetry was observed and ascribed to a stable cluster of nitrogen dopants. The thermal behavior of the sheets was significantly altered when they were supported on a vacancy-decorated graphite substrate, as well as for the overlapped/stacked sheets. In these cases, a net transfer of carbon atoms between neighboring sheets via atomic vacancies takes place, affording an additional healing process. Direct evidence of sheet coalescence with the step edge of the graphite substrate was also gathered from experiments and theory.

Detailed knowledge of the dispersion behavior of reduced graphene oxide (RGO) in solvents is important for its practical applications. Such behavior is expected to be different to that observed for pristine graphene, as a result of the chemically heterogeneous structure of RGO (patchwork of pristine and highly oxidized graphene domains). We have investigated the dispersibility of RGO in a wide range of solvents and analyzed the results on the basis of solvent surface energies and Hansen solubility parameters. Although RGO exhibited some features that are characteristic of pristine graphene, its dispersion behavior was dominated by its oxidized graphene domains, with alcohols being commonly the most successful solvents. Estimates of the effective Hansen parameters for RGO derived from the experimental data ( D ≈ 16.9 MPa 1/2 ,  P ≈ 10.7 MPa 1/2 and  H ≈ 14.1 MPa 1/2) were consistent with this view and afforded the rational design of solvent mixtures that surpassed the best single-component solvents in terms of dispersed amount of RGO. RGO-polymer composites could then be readily prepared in the best performing solvents. Overall, the present results provide a guide to the processing of RGO in the liquid phase with practical utility in the preparation of different graphene-based materials.

Chemical reduction of exfoliated graphite oxide (graphene oxide) has become one of the most promising routes for the mass production of graphene sheets. Nonetheless, the material obtained by this method exhibits considerable structural disorder and residual oxygen groups, and reports on their microscopic structure are quite scarce. We have investigated the structure and chemistry of graphene oxide samples reduced to different degrees using atomic force and scanning tunneling microscopy (AFM/STM) as well as X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD), respectively. TPD and XPS results indicate that reduction proceeds mainly by eliminating the most labile oxygen groups, which are ascribed to epoxides and hydroxyls on basal positions of the graphene plane. AFM/STM shows that the sheets are composed of buckled oxidized regions intermingled with flatter, non-oxidized ones, with the relative area of the latter increasing with the reduction degree.

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