Graphene is an outstanding material both thanks to its properties, such as excellent electrical conductivity and optical transparency, and because of its ability to give rise to a variety of new materials through chemical modification, e.g. forming graphene oxide or graphane. Various synthetic routes give rise to graphene-based materials, such as reduced graphene oxide, graphene flakes and graphene aerogels. It is important to understand the relationship between the structures and electronic and optical properties of these various graphene-based materials. In this work, we used computational modelling to predict electronic and optical properties of graphene oxide (oxygenated graphene) and graphene aerogels (curved graphene).<br/>Density-functional theory calculations were carried out on graphene sheets containing epoxide and hydroxyl groups in various arrangements and at different concentrations (1-12% oxygen), as realistic models for graphene oxide and reduced graphene oxide. To model graphene aerogels, graphene sheets curved in the armchair or zigzag direction were modelled. Oxygen functional groups were also added to these graphene aerogel structures. It was found that curvature did not have a significant effect on the electronic properties of graphene: curved graphene structures remained semimetallic and displayed graphene-like density of electronic states, and simulated optical absorption spectra were broadly similar to the spectrum of graphene. On the other hand, oxygenation had significant effect on the optical and electronic properties: although the materials remained semimetallic, their densities of states were no longer graphene-like, and the impact extended far beyond the carbon atoms immediately bonded to the oxygen functional groups. Moreover, additional peaks appeared in the simulated optical absorption spectra, even at oxygen concentrations as low as 1%.<br/>These results suggest that morphologically disordered graphene aerogels, thanks to their electronic properties similar to graphene, can be used in similar types of applications where pure graphene is used, while oxygenation significantly changes these materials’ optical and electronic properties, potentially opening new applications in sensing and catalysis.

Beyond graphene: Theoretical modelling of structure-property relationships of graphene oxide and graphene aerogels

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