Molecular dynamics simulation study of ionic hydration in negatively charged single-walled carbon nanotubes

Molecular dynamics simulation is applied to study the surface charge effects on the hydration of Na+ and K+ confined in pristine and negatively charged carbon nanotubes (CNTs). The CNTs are modified through negative charges. The structural characteristics of the coordination shells of Na+ and K+ including the ion-oxygen radial distribution functions (RDFs), the coordination numbers and the orientation distributions of the water molecules are studied. The simulation results show that the orientation distributions of the water molecules in the first coordination shell of K+ are more sensitive to the wall charge than those of Na+. The electric field effects produced by the wall charge dominate in the CNTs with large diameter. On contrary, in the narrow CNTs, the confinement effects dominate.