(604b) Fast Fluid Flow and Electrolyte Transport in Carbon Nanotube Pores

Through advancing our understanding of novel fluid behavior at nanoscale, nanofluidic research is expected to significantly advance many technological areas such as chemical and biological sensing, drug delivery, lab-on-chip, and fluid separations. Robust nanofluidic platforms will allow us to develop a basic understanding of fluid flow under nanoscale confinement.

In our laboratory, we have developed a nanofluidic membrane with well-aligned, sub 2-nm carbon nanotubes as pores. We have used these membranes to study mass transport and selectivity through carbon nanotubes for both pure fluids and mixtures. Our measured gas and water transport rates confirm the molecular dynamic predictions of an exceptionally fast fluid flow in carbon nanotube pores. For example, the measured water flow exceeds values calculated from continuum hydrodynamics models by more than three orders of magnitude [1]. Our work on the mass-transport selectivity for single [2] and binary electrolyte solutions through carbon nanotubes suggest that, for dilute solutions, small ions can be selectively excluded by carbon nanotube pores when their open rim is enriched by charged groups. In some cases, ion exclusion can be as high as 98%. The selectivity mechanism for salt rejection/permeation through 1-2 nm carbon-nanotube pores appears to be dominated by electrostatic interactions between the ions and the charged carbon nanotube rims. The observed ion selectivity rules agree with the Donnan membrane equilibrium theory. Steric and hydrodynamic effects are less important [2]. For binary electrolyte solutions with common cation, we observed a negative rejection of the monovalent anion at the smallest mole fractions. The measured rejection of binary salt solutions as a function of the salt mole fraction is also consistent with a charge-based exclusion mechanism. Demonstrated ion selectivity, high multivalent ion rejection, and simultaneous ultrafast fluid transport make our carbon nanotube membranes promising platforms for future low-cost water purification processes.

This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

[1] J. Holt, H.G. Park, Y. Wang, M. Stadermann, A.B. Artyukhin, C.P. Grigoropoulos, A. Noy and O. Bakajin, ?Fast Mass Transport Through Sub-2-Nanometer Carbon Nanotubes,? Science, 312, 1034 (2006)

[2] F. Fornasiero, H.G. Park, J. Holt, M. Stadermann, C.P. Grigoropoulos, A. Noy and O. Bakajin, ?Ion exclusion by sub-2-nm carbon nanotube pores,? Proc. Natl. Acad. Sci. USA, 10.1073/pnas.0710437105 (2008)