A theoretical study of graphene oxide chemical structure

Abstract

Graphene is a 2D material that has many unique and excellent physical and electrical properties.Since its discovery, people have spent much time and money on the research of graphene. A film of graphene is transparent, conductive, flexible, light in weight but very strong. Unfortunately, research in the last decade has proved that it is nearly impossible to fabricate stable, defect-free, large scale graphene sheets which have extensive application, yet without any commercial success.However, compared with the high cost of graphene film, graphene oxide (GO) is an easy-to-make material which has a similar structure. The obstacle for GO's application is its low reproducibility sincea number of oxidized side chains are difficult to remove. Even today, the GO structure model is still controversial.This study introduces a new structural model of graphene oxide and its theoretical electronic properties. A number of different models for graphene oxide have been proposed and tested using ab initio calculations. The main simulation and computation theories to establish these structure models in this study are molecular mechanics (MM) and density functional theory (DFT). In the proposed GO structure, the para-substituted epoxide groups stay in close proximity to, but on the opposite sides of the carbon plane, to the hydroxyl molecule. On the edge of GO sheet, the carboxyl prefers attachment in the armchair orientation, while the carbonyl prefers the zigzag orientation.The carbon backbone has a moderate wrinkling located around hydroxyl and epoxide molecules but still maintains a hexagonal graphene-like structure. This configuration repeats along the carbon network with subtle variations so that the chemical composition of GO is variable from 1.5 to 2.5 . And the electronic model also suggests that the band gap of GO can be theoretically tuned both by chemical reduction and controlled oxidation process.3