Oxygen-containing functional groups can be present in considerable amount intentionally or unintentionally on graphene, and a complete reduction of graphene oxide is difficult to achieve. To address the origin of this behavior, we have performed pseudopotential density functional theory calculations to investigate in particular the adsorption of hydroxyl (OH) on perfect and defected graphene, individually and in the presence of other coadsorbed functional groups. We found that hydroxyl groups weakly adsorb on perfect graphene, easily aggregate, also with coadsorbed epoxy groups, and can react with each other with a barrier of about 0.5 eV forming water. Defect sites are more reactive for OH adsorption but play different roles. At variance with single vacancy defects where the OH adsorption is highly dissociative, Stone−Wales defects could stabilize the hydroxyl groups on the graphene basal plane, with a much stronger binding and higher barriers for recombination and water formation than pristine.
