Evaluation of size of graphene sheet in anthracite by a temperature-programmed oxidation method

To evaluate the average layer size of carbonaceous material, it is essential to have its accurate elemental composition data. However, accurate determination of the hydrogen content is not easy. In the previous paper, we reported that a temperature-programmed oxidation (TPO) technique is suitable to accurately determine the amounts of carbon and hydrogen of the organic portion of carbonaceous material, using three Chinese anthracites as examples. In the present study, we attempt to determine the structure of the same set of anthracites on the basis of the elemental analysis data obtained by a TPO method. The contents of other components, such as oxygen, sulfur, nitrogen, and free radicals, were estimated by referring to the literature. The average layer sizes of the three anthracites range from 2.1 to 3.7 nm, and these values were compared with those estimated from XRD and HRTEM analysis. The size estimated from the TPO technique was larger than those from other techniques, and this discrepancy was attributed to the fact that these techniques are based on different theoretical and mathematical assumptions. The combination of these three techniques provided a more comprehensive understanding about the structure of these materials. In addition to the average structure, an attempt was made to obtain more detailed information through the deconvolution of TPO peaks of H2O, CO, and CO2 in the temperature region between 500 and 800 degreesC. The peaks could be reasonably resolved into at least two peaks. The H/C atomic ratio determined from the lower temperature peaks was smaller than that for the higher temperature peaks. This is likely because the oxidation of smaller size molecules takes place at lower temperatures.