Reduction mechanism of hydroxyl group from graphene oxide with and without -NH2 agent

First-principles calculations have been performed to investigate the reduction mechanism of hydroxyl group from graphene oxide (GO). We find that when the system is negatively charged the hydroxy group can be directly desorbed from GO due to the Coulomb repulsion derived from the extra charge accumulation between hydroxyl group and GO. And then we choose ammonia as the reducing agent for the hydroxyl group of GO. The results of substitution energy indicates that the -NH2 group can easily substitute the -OH. Such substitution maybe a viable reduction process because -NH2 group can also be easily reduced when the system is negatively charged. Both reduction mechanisms proposed in our present work involve negatively charged state which provide hint to understand the GO reduction in experiment.