Synthesis of Oxygen Functional Group-Controlled Monolayer Graphene Oxide

Graphene oxide (GO) contains various types of oxygen functional groups (e.g., C-OH, C-O-C, C=O, and O=C-OH groups), which provide superior functions such as proton conductivity, catalytic activity, and selective absorption. In contrast, the complex structure of GO complicates control over its function; therefore, GO with a simple and/or uniform structure is desired. In this study, we demonstrated that monolayer GO, in which surface oxygen functional groups are controlled as epoxy groups, was successfully prepared by exfoliating graphite oxide prepared using Brodie's method. The monolayer ratio of GO reached 99.2%, and the nanosheets were stable in water for I month. Fourier transform infrared, X-ray photoelectron spectroscopy, and temperature-programmed desorption analyses indicated that most oxygen functional groups on GO were epoxy groups. Further, it was determined that GO had structural regularity over a wide range and small amounts of lattice defects despite being oxidized. This means that the developed GO can potentially advance considerably GO studies by replacing previous GO.