Oxidation of graphite by different modified Hummers methods

Graphite oxides with different oxygen contents and specifications were prepared from a commercial graphite by different versions of the Hummers method and by oxidation with sodium dichromate. The chemical and structural characteristics of the graphite oxides were studied by elemental analysis, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD). Dichromate oxidation provided a low oxygen fixation, mainly in the form of hydroxyl and epoxy groups. A much more efficient oxidation was achieved by using the Hummers method. The use of NaNO3 and a reaction time of 2 h led to the highest oxygen content in the graphite oxide, over 40 wt%, and oxygen was found to be single- and double-bonded to carbon. SEM and XRD observations showed a high spacing of the graphitic layers under these conditions. These results prove that, even using the same oxidizing method, the chemical structure of graphite oxides can be tailored by changing reaction conditions.