Oxidative Tearing of Graphene Sheets: Insights into the Probable Situations by Computational and Experimental Studies

Abstract

Nanometer size graphene sheet has become a subject of interest both for technological as well as medical applications. In this work, we have focused on the oxidative tearing of nanoscale graphene sheets using ab initio density functional theory. We have geometry optimized several model systems depicting all possible graphene oxide sheets containing either a single or multiple oxygen atoms. We have found that a single oxygen atom prefers to bind to two carbon atoms of the cis-edge by forming an epoxy linkage. Such epoxidation also induces a large curvature into the graphene sheet by breaking the involved C−C bond. This initial epoxidation also favors formation of similar epoxy-linkages at nearby sites in a cooperative manner during the oxidation of a nascent graphene sheet. Such bond breaking, however, is not observed when we try similar epoxidation at the trans-edge. A series of epoxidation starting from the cis-edge thus can cause tearing of the graphene oxide sheet leading to formation of smaller size graphene sheets containing exposed functionalized trans-edges. Because of symmetry in a graphene sheet, we can expect to obtain a smaller functionalized graphene sheet of triangular shape having predominantly trans-edges (cis edges may appear at the corners) during the oxidation process. Our subsequent experiment of magnetic hysteresis compliments the theoretical finding of the tearing pattern.