Probing Prismatic/Basal Surfaces of Carbon Materials upon Graphitization by Gas Adsorption, TPD, and XPS
Résumé
The prismatic and basal plane surfaces of carbon materials dictate most of their anisotropic physicochemical properties. For many applications where interfacial interactions are key, high-temperature treatments are performed to achieve their graphitization. Such treatment changes edge and basal plane configuration, impacting the energetical behavior of the carbon surfaces, particularly for carbon nanomaterials, with consequences for their properties. Therefore, efforts should be devoted to probing the prismatic and basal plane surfaces of such materials to understand their surface properties for the development of high-performance carbon materials. Herein, we investigate the effect of high-temperature graphitization (3073 K) on the structural, textural, chemical, and magnetic properties of graphitic carbon nanomaterials presenting different prismatic/basal surfaces. The evolution of the prismatic/basal surfaces has been probed by nitrogen adsorption, temperature-programmed desorption, and X-ray photoelectron spectroscopy (XPS). Although these three techniques are in agreement for the starting materials, they diverge in the case of materials that have undergone thermal annealing. This is linked in particular to the formation of loops following the heat treatment, which are identified as belonging to the prismatic surface by XPS and modified the N2 adsorptive potentials. Formed small vacancies on closed loops and nonperfect closure of certain loops can contribute to the accumulation of very reactive defects at the loop level. The thermal annealing also has a pronounced influence on the magnetic properties of these materials. Interestingly, we show that a positive correlation exists between the spin density of the annealed graphitic carbons and their prismatic and basal surfaces.