Changing the sp2 Carbon Clusters in Graphene Oxide During Exfoliation

The change of the chemical structure of graphene oxide (GO) was investigated by periodical sampling of GO during exfoliation by using a sonicator. A significant amount of GO was exfoliated during up to 10 hr of sonication. Raman and Fourier transform infrared spectroscopy revealed a continuous increase of the G/D or C=C/C=O peak ratio of GO, as the sonication time increases. The photoluminescence (PL) intensity of each GO sample also decreased as a function of the sonication time. PL excitation spectra with three major peaks indicate that the sizes of sp(2) carbon clusters were enlarged by longer sonication. In addition, new excitation at around 300 nm proves the existence of newly developed small clusters of sp(2) carbons as the sonication time increased.