Generation of Electronically Unsaturated Carbon Sites on Carbon Materials and Study of Their Magnetic and Chemical Properties

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The presence of defects in carbon materials, such as electronically unsaturated carbon sites, can profoundly affect their magnetic ordering and chemical reactivity. The detailed analysis of these species (edge states, σ free radicals, or carbene), which are pivotal for many applications, remains a significant challenge for carbon bulk materials. Today, the engineering of defective carbon materials often relies on the use of hardly up-scalable physical methods not accessible to synthetic chemists. It is therefore important to develop simple and scalable methods to generate well-defined electronically unsaturated sites in carbon materials. Herein, we followed the transformation and evolution of surface oxygen functional groups of various oxidized carbon materials during thermal treatment under an inert atmosphere using various analytical techniques and ab initio molecular dynamics, with the aim of producing stabilized localized electronic states from condensation reactions. Synchrotron-based in situ XPS analyses show a decrease in the number of carboxylic surface groups with a concomitant increase in the number of defect sites upon defunctionalization, which is expected from condensation reactions. Echo-detected field-swept EPR spectra show the apparition of a signal only upon defunctionalization, particularly for samples showing a high proportion of prismatic surface. The contribution of these electronically unsaturated carbon sites to the catalytic activity for the catalytic oxidative dehydrogenation of indoline is moderate, and the surface oxygen functional groups are the main active sites.