The excellent electrical, optical and mechanical properties of graphene have driven the search to find methods for its large-scale production, but established procedures (such as mechanical exfoliation or chemical vapour deposition) are not ideal for the manufacture of processable graphene sheets. An alternative method is the reduction of graphene oxide, a material that shares the same atomically thin structural framework as graphene, but bears oxygen-containing functional groups. Here we use molecular dynamics simulations to study the atomistic structure of progressively reduced graphene oxide. The chemical changes of oxygen-containing functional groups on the annealing of graphene oxide are elucidated and the simulations reveal the formation of highly stable carbonyl and ether groups that hinder its complete reduction to graphene. The calculations are supported by infrared and X-ray photoelectron spectroscopy measurements. Finally, more effective reduction treatments to improve the reduction of graphene oxide are proposed.

We have studied the thermal conductance of tilt grain boundaries in graphene using nonequilibrium molecular dynamics simulations. When a constant heat flux is allowed to flow, we observe sharp jumps in temperature at the boundaries, characteristic of interfaces between materials of differing thermal properties. On the basis of the magnitude of these jumps, we have computed the boundary conductance of twin grain boundaries as a function of their misorientation angles. We find the boundary conductance to be in the range 1.5 × 10(10) to 4.5 × 10(10) W/(m(2) K), which is significantly higher than that of any other thermoelectric interfaces reported in the literature. Using the computed values of boundary conductances, we have identified a critical grain size of 0.1 μm below which the contribution of the tilt boundaries to the conductivity becomes comparable to that of the contribution from the grains themselves. Experiments to test the predictions of our simulations are proposed.

By use of molecular dynamics simulations, we have studied the evolution of epoxy and hydroxyl functional groups on graphene oxide (GO) during high-temperature thermal reduction. We find that the reduced GO sheets are characterized by a large number of stable holelike defects formed by breaking of C−C bonds in the basal plane. These defects are always decorated by the carbonyl (CO) groups and are formed due to the strain in the basal plane created by epoxy and hydroxyl functional groups that are located close to each other. With very few exceptions, the carbonyl groups that are observed in Raman spectroscopy and other experimental studies are generally attributed to the CO terminations of the edges. However, our study using first-principles calculations and a reactive force field approach clearly shows that the formation of carbonyl groups within the graphene basal plane is energetically favorable compared to other well-known functional groups such as epoxies and ethers. We have identified the specific reaction mechanisms that lead to the formation of these holes starting from particular initial configurations of epoxy and hydroxyl functional groups. These configurations can be readily found on GO sheets with random distribution of epoxy and hydroxyl groups and do not require an ordered arrangement of any particular functional groups.