Investigation of Structural Regularity of Graphene Oxide by Experimental and Computational Methods

Graphene oxide (GO) is a well-known multifunctional 2D material. Owing to its highly useful properties, GO and reduced GO (rGO) are applied to a wide range of applications such as batteries, catalysts, and functional membranes. Furthermore, GO is easily produced via a liquid process from inexpensive natural graphite, and normally obtained as monolayer nanosheet well-dispersed in many kinds of solvents; thus, it is recognized that GO is a 2D material that is closest to practical use. However, the complex structure, which contains many types of functional groups and defects (nano-pores), has become a major impediment to studying GO. For example, its complex structure has prevented the elucidation of GO’s useful properties and research using theoretical calculations. In addition, lack of repeatability, accuracy, and controllability is induced by its complex structure, which causes differences in results and discussions between papers. Moreover, rGO with the same characteristics as graphene has not been achieved because graphene structure cannot be restored perfectly using any reduction process. Recently, we developed an monolayer GO with low defect density and one type of oxygen functional group prepared by effective exfoliation of graphite oxide oxidized using Brodie’s method. The high structural regularity of developed GO allows for detailed discussions in theoretical calculations and other methods that were not possible in the past. Herein, combining experimental results from FT-IR and UV-vis absorption measurements with DFT calculations, the structure of the developed GO is discussed in more depth. The experimental FT-IR and UV-vis absorption spectra were best explained by modelling a graphene backbone with regularly arranged epoxy groups. When slight structural defects were introduced in the model structure, inconsistencies arise in the experimentally obtained spectra. The high structural regularity of the developed GO was also discussed from the experimental results of carrier mobility and electrical properties.