EPJ B Colloquium - Origin of optical bandgap fluctuations in graphene oxide

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Published on 11 June 2020

Graphene Oxide (GO) is a carbon-based nanomaterial prepared through the chemical oxidation of natural graphite in the presence of strong oxidants. It was identified long before pristine graphene, first reported in the 17th century by Brodie et al. Among many potential applications, GO can be used to produce reduced GO (rGO) for transparent conducting electrodes (TCEs), which has been, for instance, employed in the preparation of organic-light emitting diodes and organic photovoltaic devices. Other works also report the successful use of GO for the preparation of membranes for desalination and water purification, as well as active layers in biosensors, among many other applications. To address the needs of theses versatile applications several modifications in the synthesis of GO have been developed.

In a new colloquium paper published in EPJ B, authors from the departments of chemistry and physics at UFJF, Juiz de Fora/MG Brazil explore the electrical, optical and spectroscopic properties of different Graphene Oxide (GO) samples focusing on new oxidative strategies to tune their physicochemical properties. Three types of GO samples were prepared by changing the oxidative conditions resulting in carbonyl-, epoxy- or hydroxyl-rich GO. These materials were characterized by UV-VIS absorption, Raman spectroscopy and X-ray diffraction. The experimental results indicate that all samples exhibit oxidation and exfoliation degrees typical of graphene oxides obtained by using the modified Hummers’ method. The optical bandgap values were measured using the Tauc’s plot from UV-VIS data and showed that the stoichiometry of GO impacts the width of the bandgap. The carbonyl-rich sample presented the lowest gap around 3.20±0.02 eV, while epoxy- and hydroxyl-rich GOs showed out gaps of about 3.48±0.07 and 3.72±0.05 eV, respectively. These experimental results are consistent with theoretical calculations of bandgaps obtained with coronene and circumcoronene GO models. The calculations were obtained using different theoretical approaches, such as: Huckel, PM3, AM1 and DFT.

The present work suggests that a precise tuning of the optical bandgap of GOs can be achieved by only changing their stoichiometry thus allowing their use in a large range of electronic applications.