Ultra-Fast Proton Transport in Sub-1-nm Diameter Carbon Nanotube Porins

Abstract

Proton transport plays a key role in many biological processes due to the proton's ability to rapidly translocate along the chains of hydrogen-bonded water molecules. Molecular dynamics simulations have predicted that confinement in hydrophobic nanochannels should enhance the rate of proton transport. We demonstrate that 0.8 nm diameter carbon nanotube porins, which promote formation of true one- dimensional water wires, support proton transport with rates exceeding those in bulk water by an order of magnitude. Proton transport rates in these narrow CNT pores also exceed those of biological channels and Nafion. Surprisingly, the larger 1.5 nm diameter nanotube porins still showed proton transport rates comparable to bulk water. This work establishes small diameter CNT porins as a promising membrane proton conductor material and points to strong spatial confinement as a key factor in enabling efficient proton transport.