Sangil Kim 1,2, Francesco Fornasiero 1, Michael Stadermann 1, Alexander Chernov 1, Hyung Gyu Park 1, Jung Bin In 3, Ji Zang 5, David Sholl 5, Michael Colvin 4, Aleksandr Noy 1,4, Olgica Bakajin, 1,2 and Costas P. Grigoropoulos 3 1 Physical and Life Sciences, LLNL; 2 NSF Center for Biophotonics, UC Davis; 3 Mechanical Engineering, UC Berkeley; 4 School of Natural Sciences, UC Merced, 5 Chemical and Biochemical Engineering, Georgia Tech Gated Transport through Carbon Nanotube Membranes NIRT CBET CARBON NANOTUBE MEMBRANE: A NANOFLUIDIC PLATFORM  Unique surface properties of carbon nanotubes enable very rapid and very efficient transport of gases and liquids  We need to understand:  Fundamental physics of transport through these nanoscale channels  Membrane selectivity and rejection properties  Fabrication issues associated with making CNT membranes with desired geometry and properties  Control of transport through CNT membranes: Are artificial ion channels possible? ION EXCLUSION Si DWCNT / Si 3 N 4  Free standing membrane  Highly aligned DWCNTs  Inner diameter ~ 1.6 nm  LPCVD Si 3 N 4 pinhole- free matrix MULTI-COMPONENT GAS PERMEATION SYSTEM BINARY GAS PERMEATION CH 4 /N 2 and CO 2 /N 2  At 263 K, the separation factor increased because of increased gas solubility at lower temperature. Comparison with atomistic simulations (CH 4 /N 2 ) CONCLUSIONS Part of the work at LLNL was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA PUBLICATIONS Holt et. al., Science, 312, 1034 (2006) Noy et. al., Nano Today, 2, 22 (2007) Fornasiero et. al. Proc. Natl. Acad. Sci USA, 105, (2008) Stadermann et. al., Nano Letters, in revision (2008) GROWTH OF ALIGNED NANOTUBE ARRAYS Selectivity ≡  A/B = [ y A /(y B ) ]/[ x A /(x B ) ]=[ y A /(1-y A ) ]/[ x A /(1-x A ) ] where x : the mole fractions of gas species at the feed side y : the mole fractions of gas species at the permeate side  Smaller tube has higher separation factor for CH 4 /N 2.  Polydisperse of tube size in CNT membrane affects the separation factor. SINGLE GAS PERMEATION  Strongly absorbing gas species (CO 2, CH 4, and C 2 H 4 ) deviated from the scaled Knudsen permeance  Weakly absorbing gas species (He, N 2, Ar, and SF 6 ) did not show the deviation.  Electrostatic interactions dominate the ion rejection mechanism  The largest ion in this series, Ru(bipy) 3 Cl 2, permeates freely through the membrane suggesting that size effects are less important Rejection declines at larger salt solution concentrations  Rejection ~ constant when the Debye length is >> CNT diameter K 3 Fe(CN) 6 KCl K 3 Fe(CN) 6 KCl CNT membrane Pressure Feed (salt solution) Permeate 6.7 A 8.1 A Ion rejection coefficient: CNT growth rates exhibit a non-monotonic dependence on total pressure and humidity. Optimal process pressure and water concentration produce growth rate of ~30  m/min. Nanotube growth rate remains essentially constant until growth reaches an abrupt and irreversible termination. We developed a model that predicts termination kinetics Iijima’s model Poisoning model VA-CNT arrays grow from catalytic decomposition of carbon precursor, C 2 H 4, over nanoscale Fe catalyst KINETICS OF CARBON NANOTUBE ARRAY GROWTH K+K+ CNT Aquaporin K + channel Gas transport in CNTs and other nanoporous materials CNT MEMBRANE Carbon nanotube membranes support high flux transport of liquids and gases Nanotube growth kinetics studies allowed high-yield, high-quality growth of aligned nanotube arrays CNT membranes show good ion rejection characteristics Ion rejection mechanism is based on electrostatic repulsion and follows Donnan model predictions Strongly absorbing gas species deviated from Knudsen permeance due to preferential interactions with CNTs side walls. At low temperature gas separation factor increased because of increased gas solubility; overall gas separation factors are still lower than necessary for practical gas separation