Ab initio Study of Direct Diffusion Pathway for H⁺, Li⁺, Na⁺, K⁺ Cations into the (3,3), (4,4), and (5,5) Open-Ended Single-Walled Carbon Nanotubes

Abstract

To probe the ability of ions to enter and leave a nanotube interior, we calculated the energetic of a direct diffusion pathway for H⁺, Li⁺, Na⁺, K⁺ cations to move through the (3,3), (4,4) and (5,5) open-ended single-walled carbon nanotubes (SWNTs) with ab initio techniques. For three nanotubes, there is no energy barrier for the Li⁺ ions to enter the open tubes. In fact, there is a net decrease in the energy of the system, showing that the nanotubes actually act as an attractor for the Li⁺ ions. Similar results also hold for the H⁺ and Na⁺ ions into (4,4) nanotube. These ions can easily diffuse and leave the nanotube from other side. H⁺ strongly attract with the (3,3) nanotube but cannot diffuse and is trapped. Our results show that the entry of K⁺ and Na⁺ ions into (3,3) nanotube is forbidden. In contrast, (4,4) and (5,5) nanotubes for H⁺ and K⁺ ions and (5,5) nanotubes for Na⁺ act as ion channels that conduct these ions. In all NT-H systems and (3,3) NT-Li system, the charge transferred between ion and nanotube and nanotube achieve the positive charge.

Keywords:

• Carbon nanotubes (SWNTs)
• cations
• ab initio
• potential energy