Exploring the mechanism of graphene-oxide reduction by hydrazine in a multi-epoxide environment with DFT calculations

Reduction mechanisms between hydrazine and a multi-epoxide arrangement were investigated on a finite-sized graphene-oxide model with density functional theory. Three multistep reaction pathways were explored to examine different graphene-oxide (GO) deoxygenation scenarios. Epoxides sharing the same hexagonal ring show the typical one-by-one elimination of the oxygen functional groups through two protonation steps and the formation of cis-diazine and water. Nevertheless, the migration of one of the epoxy groups to an out-of-ring position has to precede the reduction. When a hexagonal ring separates two epoxy groups, forming a partially reduced surface with two hydroxyl groups is energetically favoured. This reduction product is so stable that it may remain on the surface after the termination of the reduction process. If further deoxygenation occurs, it can lead to surface fragmentation due to the ring opening of the remaining epoxides. The formation of nitrogen-containing functional groups at the edge of the graphene-oxide flake is also considered, and their surface presence is evaluated based on their thermodynamic stabilities.