Metal ion binding with carbon nanotubes and graphene: Effect of chirality and curvature

► Contrasting binding preferences observed for alkali and alkaline earth metal ions. ► Alkali metal ions prefer armchair and alkaline earth metal ions prefer zigzag CNTs. ► Graphene exhibits stronger binding affinity for metal ions. ► HOMO-LUMO energy gap of the CNTs can be fine tuned through metal ion binding.