Metal Nanotubule Membranes with Electrochemically Switchable Ion-Transport Selectivity

TLDR

Membranes with cylindrical metal nanotubules spanning the full thickness are described. Permselectivity arises from excess charge on the inner walls, which can be reversibly switched potentiostatically to make the membrane cation or anion selective. The membranes exhibit tunable nanotube radii down to 0.8 nm and selectively reject ions of the same sign while transporting opposite‑sign ions, mimicking ion‑exchange polymers.

Abstract

Membranes containing cylindrical metal nanotubules that span the complete thickness of the membrane are described. The inside radius of the nanotubules can be varied at will; nanotubule radii as small as 0.8 nanometer are reported. These membranes show selective ion transport analogous to that observed in ion-exchange polymers. Ion permselectivity occurs because excess charge density can be present on the inner walls of the metal tubules. The membranes reject ions with the same sign as the excess charge and transport ions of the opposite sign. Because the sign of the excess charge on the tubule can be changed potentiostatically, a metal nanotubule membrane can be either cation selective or anion selective, depending on the potential applied to the membrane.