When studying the ubiquitous and practically significant phenomena of annealing or aging of carbon materials, it is instructive to distinguish the reduction of site (re)activity from a decrease in the concentration of (re)active sites. While the latter has been analyzed extensively for different carbon precursors and heating rates, the former - being more complex even though it can occur at constant temperature - has not received sufficient attention. Here we use computational quantum chemistry to define more precisely and quantify the phenomenon of nascent site deactivation (NSD). The NSD process, which determines the fate of so-called "dangling bonds" in graphene, takes place within a relatively short time (e.g., seconds) and is a consequence of radical stabilization during formation or reactions of sp2- hybridized carbon materials, both flat and curved. Stabilization of reactive zigzag sites results in the formation of carbene-like edges. Free armchair sites can also rehybridize, to form carbyne-like edges. Adjacent zigzag edges can reconstruct to form pentagon-heptagon pairs that preserve planarity but convert the reactive sites from zigzag to armchair. We report the thermodynamic driving forces for these fundamental processes by determining the optimized geometries of ground states, as well as charge and spin density distributions, in prototypical graphene molecules.
All Science Journal Classification (ASJC) codes
- Materials Science(all)