The Evolution Rule of Three-Dimensional Structures of Graphite During Oxidation

Abstract

The graphite oxidation samples with different degrees of oxidation were prepared from natural flake graphite via a modified Hummers method with controlled addition of KMnO 4. The evolution of oxygen-containing functional groups was analyzed by Fourier transform infrared spectrometry (FT-IR) and X-ray photoelectron spectroscopy (XPS). The evolution rule of three-dimensional (3D) graphite structures during oxidation has been verified via X-ray diffraction (XRD). Experimental results show that the evolution of the interplanar spacing of samples during oxidation can be approximately divided into four stages. When the dosage of KMnO 4 is 0.5 g per 1 g of graphite (g/g), a graphite intercalation compound (GIC) is formed through intercalating reactions, and a slight increase is observed in the values of d100 and d110, suggesting that the π–π interactions which decrease the length of carbon–carbon bonds were partially disrupted. Adding additional KMnO 4 initiates the second stage, in which GIC begins to oxidize. The insertion of oxygen-containing functional groups in the graphene basal plane leads to dramatic changes in the values of d100 and d110. The d100 is greatly reduced while d110 increases slightly. These trends are attributed to the fact that the basal plane is stretched during the oxidation process. Further addition of KMnO 4 in the third stage leads to relatively small increases in the values of d100 and d110. This result is consistent with the evolution rule of hydroxyl groups. In this research, the evolution rule of the value of d001 is also clearly demonstrated. When the concentration of KMnO 4 is not more than 3.0 g/g, the value of products d001 keeps gradually increasing, indicating that oxygen-containing groups continue to form bonds with carbons in the basal plane, and that additional water molecules are adsorbed between the layers of the samples. All the interplanar spacing values (d001, d100 and d110) are reduced significantly in the fourth stage, when the amount of KMnO 4 added up to 4.0 g/g. FT-IR and XPS analyses demonstrate that the decrease in the values of d100 and d110 is due to a reduction in the content of external hydroxyl groups. The change in d001 is attributed to the partial release of water molecules confined in the interlayer spaces between adjacent sheets are partly released.