It was now a widely accepted fact that oxidized graphene surfaces were populated, to a greater or lesser extent, with epoxide groups. And yet the origin of these groups has previously been mysterious. A computational (DFT) analysis of this was carried out by combining theoretical and experimental knowledge on three seemingly unrelated fundamental processes: (i) formation of pentagon-heptagon pairs (or Thrower-Stone-Wales defects); (ii) surface diffusion of oxygen atoms on the basal plane; and (iii) graphene unzipping by oxygen insertion. Thermodynamic and kinetic evidence was provided for the hypothesis that a key intermediate step in the stabilization of free adjacent zig-zag sites - before they reconstructed to form an armchair site or become quinone surface functionalities upon dissociative O2 chemisorption - was the formation of an epoxide group in the basal plane. The presence of epoxide groups on the graphene surface was therefore a result of spillover of edge oxygen (e.g., non-dissociatively adsorbed O2 on carbene-type sites), mechanistically reminiscent of the extensively investigated migration of carbon in the conversion of phenyl carbene to bicycloheptatriene.

Oxygen Migration on the Graphene Surface. 1. Origin of Epoxide Groups. Radovic, L.R., Silva-Tapia, A.B., Vallejos-Burgos, F.: Carbon, 2011, 49[13], 4218-25