Removing phenol contaminants from wastewater using graphene nanobuds: DFT and reactive MD simulation investigations

Abstract

Phenol and phenolic compounds are extensively found in effluents and are toxic even at low concentrations hence their elimination from aqueous solutions is necessary. In the present work, the interaction of phenol and water molecules with graphene and graphene nanobud (GNB) was investigated using DFT-D3 calculations with revPBE/def2-TZVP model of theory. Various binding sites and ways of approach for phenol/water molecule approaching the selected adsorbents were evaluated. We found that water molecule tends to interact weakly with both graphene and GNB compared with the phenol molecule. The strength of adsorption for GNB at the top of the fullerene cage as well as near the neck site and onto the graphene surface was found to be stronger for phenol rather than water molecule. This can be attributed to the existence of simultaneous π-π stacking and electrostatic attractions for phenol/adsorbent system. Our first-principles calculations showed that binding nature of interacting molecules depends strongly on the long-range non-local dispersion forces but slightly to the solvent entity. The obtained binding energies compared with the experimental and highly accurate quantum-mechanical values available in literature for water/benzene adsorbed onto the graphene surface. Moreover, the adsorption ability and capacity of GNB was verified by reactive MD simulation carrying out at ambient condition. The desirable binding strength obtained accompanied with high specific surface area of GNB (due to fastened buckyballs) compared with the graphene lead to practically arrest these novel hybrid nano-materials as superior adsorbents for phenol adsorption and remediation from water-contaminated environment.