Nature of Interactions between Epoxides in Graphene Oxide

Abstract

Graphene oxide exhibits extensive disorder with a multitude of functional groups and holes making its structure an abstract concept. Multiple structural models make it a dark horse and hamper its utility despite its synthetic ease, maneuverability, and promising applications. Here we probe the impact of the epoxidation process, which is arguably the first kinetic step in graphene oxidation, to identify the induced vulnerabilities of its backbone and to cognize possible pathways for further oxidation. Probing the topological and geometrical variations in the distribution of epoxide on the graphene lattice, we find that the conformational entropy, driven by the combinatorial growth of isomers, aids and abets disorder. Graph theoretical enumeration gives 16 distinct epoxide environments within symmetrically equivalent epoxides. Their stability is primarily influenced by the steric repulsion between the oxygen lone pairs and overlap compatibility of the interepoxy C–C bond. Avoiding steric repulsion either by topology or by equatorial splaying of oxygens leads to stability, without which the network is weakened either by elongation of C–C bonds or by axial splaying of oxygens leading to uneven C–O bonds. The proposed unzipping of the underlying epoxy C–C bond through the cooperativity of strain from three-membered rings and conjugative stabilization from residual sp2 character are found to be incongruous. With an improved bonding model of epoxide, we account for the observed variations in C–C bond lengths and energetics of epoxides in different environments that facilitate strategic mechanistic control for further oxidation.