Synthesis of graphite oxide from milled graphite studied by solid-state 13C nuclear magnetic resonance

In the present work we investigate the influence of the degree of crystallinity of graphite on the production of graphite oxide (GO). Graphite precursors with varying degrees of crystallinity were produced by milling a high-purity synthetic graphite powder during different times and the milled materials were used for the synthesis of GO, using a modified Hummers method. The products were characterized by X-ray diffraction (XRD), thermogravimetry, solid-state 13C nuclear magnetic resonance (NMR), elemental and textural analysis. 13C NMR spectra revealed the presence of epoxy, hydroxyl, carbonyl and lactol groups in the oxides. However, the oxidation degree was found to be largely dependent on the milling time, with the best GO samples being produced from graphites with intermediate milling times. These results were rationalized in terms of the structural changes brought about by the milling process, as revealed by the solid-state 13C NMR spectra and the XRD patterns obtained for the milled graphites.