Structural Evolution during the Oxidation Process of Graphite

The structural evolution during the oxidation process of graphite by a modified Hummers method is investigated. The graphite oxide (GO) composition, disorder parameter, and structures are confirmed by means of x-ray diffraction, Fourier transform infrared spectroscopy, Raman, and scanning electron microscope techniques. Results show that: Hydroxyl, carboxyl and ether groups are present in the low-temperature oxide (at 0 degrees C); and the degree of oxidation is increased with a longer oxidation time. The middle-temperature oxidation (35 degrees C) is a transitory stage with a slight change to the GO structures. While for the high-temperature oxidation (95 degrees C), the hydroxyl, carboxyl and epoxide functional groups are largely originated on the GO flakes. Hydroxyl groups are transformed into more epoxide groups with longer oxidation time, and at the same time, ether groups are eliminated, leading to defects (such as holes) on the GO flakes.