Ion exclusion by sub-2-nm carbon nanotube pores.

Biological pores regulate the cellular traffic of a large variety of solutes, often with high selectivity and fast flow rates. These pores share several common structural features: the inner surface of the pore is frequently lined with hydrophobic residues, and the selectivity filter regions often contain charged functional groups. Hydrophobic, narrow-diameter carbon nanotubes can provide a simplified model of membrane channels by reproducing these critical features in a simpler and more robust platform.

Identification of endohedral water in single-walled carbon nanotubes by (1)H NMR.

Water confinement within single-walled carbon nanotubes (SWCNTs) has been a topic of current interest, due in part to their potential nanofiltration applications. Experiments have recently validated molecular dynamics predictions of flow enhancement within these channels, although few studies have probed the detailed structure and dynamics of water in these systems. Proton nuclear magnetic resonance ( (1)H NMR) is a technique capable of providing some of these details, although care must be exercised in separating the confined water of interest from exterior water.

Fast mass transport through sub-2-nanometer carbon nanotubes.

We report gas and water flow measurements through microfabricated membranes in which aligned carbon nanotubes with diameters of less than 2 nanometers serve as pores. The measured gas flow exceeds predictions of the Knudsen diffusion model by more than an order of magnitude. The measured water flow exceeds values calculated from continuum hydrodynamics models by more than three orders of magnitude and is comparable to flow rates extrapolated from molecular dynamics simulations.