Graphene and graphene oxide as adsorbents for cadmium and lead heavy metals: A theoretical investigation

[Display omitted] •DFT was used to study the adsorption of Cd and Pb on graphene and graphene oxide.•Dispersion has an essential role in the binding of these heavy metals with graphene.•The adsorption energies of Cd and Pb decrease as the coverage increases.•In all studied systems of graphene and graphene oxide, Pb binds more strongly than Cd.•Oxygen functional groups on GO stabilize more the binding compared to pure graphene. The geometrical and electronic parameters for the interaction of two toxic heavy metals, namely: cadmium (Cd) and lead (Pb), on graphene and graphene oxide (GO) surfaces are investigated by using local Gaussian type basis sets and the hybrid PBE0 functional as implemented in the CRYSTAL code. The role of including long-range dispersion (D3) contribution as well as the basis set superposition error (BSSE) on the adsorption process is found to be crucial in the description of such interactions. Generally, Cd and Pb adatoms are found to be adsorbed more strongly on GO rather than pristine graphene due to the incorporation of oxygen functional groups (epoxy and/or hydroxyl) on the surface. Moreover, Pb has interestingly been found to play as an electron donor and to form covalent bonding with the GO surface. Such findings could have an impact in water treatment applications using graphene-based nanomaterials.