Graphene nanostructures functionalization: Hydrogen bonds and oxide coverage effect

Abstract

Density functional theory is the most used tool to predict the fundamental properties of crystalline and molecular systems. Here we present a study on the passivated oxidized graphene structures with hydrogen atoms at the edges (GO). A stability analysis was performed using the ground-state energies and first-principles thermodynamics. Initially, two stability pseudo-mappings were made on the GO structures, the first varying the position of an epoxide functional group and the second varying the position of a hydroxyl functional group. It was found that the adsorption of a hydroxyl group could occur at any position on the GO structure. The epoxy group has greater stability towards the nanostructure edges. Oxygen adsorption strengthens in Stone-Wales and C vacancy defects. Vacancies dominate the adsorption process. The O/C ratios were increased to 5%, 9%, 13%, and 16% with 27, 20, 19, and 4 oxidation configurations, respectively. All constructed GO structures are thermodynamically stable. For each selected coverage, the calculated bandgap follows the experimental trend. In addition, hydrogen bonds were observed at all coverages. At 13% and 16% O/C ratios, H2O formation happens without energy barriers, leaving epoxy and carbonyl groups as by-products. Our calculations suggest that hydroxyl groups can spontaneously promote the generation of water molecules together with epoxy and/or carbonyl groups. Hydrogen bridge interactions between the ligands in the hydroxyl group induce such an effect. The mechanism described here helps to understand the reactivity observed in experimental studies of GO nanostructures obtained from the bamboo Guadua Angustifolia ‘Kunth’.