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

First principles calculations have been used to comprehensively study the binding of a series alkali (Li+, Na+, K+) and alkaline earth (Be2+, Mg2+, Ca2+) metal ions with carbon nanotubes (CNTs) and graphene. It is interesting to note that the mono-cationic systems prefer binding to armchair CNTs over zigzag CNTs, while the preference for the di-cationic systems is exactly opposite. We have also observed significant changes in the HOMO–LUMO energy gap of the CNTs on metal ion binding and these results indicate that the fine tuning of energy gap of the CNTs can be effected through metal ion binding