Pyrolysis mechanisms of graphene oxide revealed by ReaxFF molecular dynamics simulation

Abstract

Pyrolysis dynamics of graphene oxide (GO) is critical for composite material design, and a few experimental evaluations were conducted so far since extremely high temperature condition is needed. In this work, with help of ReaxFF reactive molecular dynamics simulations, the pyrolysis mechanisms of GO were investigated from two aspects: (1) the structural evolutions of the carbon skeleton and (2) the desorption of the superficial functional groups. At low temperature, desorption of functional groups is dominant, and little point defects or vacancies are introduced to the carbon skeleton. Meanwhile, generation of a number of pyrolysis products was confirmed at higher temperatures. Accordingly, the carbon skeleton is significantly disordered, resulting in an amorphous transformation. Analysis of bonds breaking ratio, hybridization types of carbon atoms and pyrolytic fragments indicated that the restored sp2-hybridized carbons increase with the increasing annealing time, and structure of final products are controlled by hydroxyl and oxygen dangling bonds. Finally, annealing process of GO with different oxygenal group density (R) and OH/O ratio are quantitatively analyzed and found pyrolysis is R and OH/O ratio dependent. These results uncover the pivotal role of oxygen and hydrogen in pyrolysis, and provide a guidance for heat resistant composite designs.