The adsorption of ions on a graphene surface is very important to control relevant graphene-based processes. In this work, a multiscale simulation was carried out to study the adsorption of Na /Cl ions on graphene by combining quantum mechanics calculations and molecular dynamics (MD) simulations. The interaction energies of the ions with graphene were computed using density functional theory (DFT). It was found that the ions show strong interaction with a graphene cluster and the overwhelming portion of the interaction energy is the ion-π orbital interaction. The large orbital interaction can be ascribed to the two contributions arising from the ion-induced polarization of graphene and the charge transfer between ion and graphene. Their different contribution degrees reveal that the polarization effect plays a main role on the orbital interaction for ion adsorption. Comparatively, for Na/Cl atom adsorption, the charge transfer shows large part to the orbital interaction with weak atom-induced polarization. The obtained interaction energies were applied to develop new interaction potentials between ion and graphene, and then MD simulations were used to study the interfacial adsorption behavior of Na /Cl aqueous solution onto the graphene surface. Due to enhanced ion-π interactions, Na /Cl cooperatively demonstrates a strong ion adsorption layer through direct contact with the hydrophobic graphene surface. Our simulation result presents a new understanding of ion-graphene interactions.

Density functional theory simulations were carried out to study the binding interaction between hydrated Na+/Cl– and graphene oxide (GO) under electric fields. External electric fields can modify the binding interactions of the hydrated ions with GO. The field-dependent binding energy is mainly controlled by the orbital interaction driven by the field-dependent electron transfer, in which miscellaneous electron-transfer routes in the interfaces between hydrated ions and GO surface were disclosed. The electric field is able to influence the electron-transfer degree for each route, thereby creating various electron acceptor–donor coupling interactions. Furthermore, we preliminarily explored the effect of the electric field on the interlayer structure of bilayer GO with NaCl and water confined inside. Electric fields can enlarge the interlayer spacing through tuning of the hydrated ion–GO interactions. Our simulations present a new understanding of hydrated ion–GO interactions in the presence of an electric field, which is expected to be valuable in the electrical modulation of GO nanomaterials.