GROWTH OF ALIGNED NANOTUBE ARRAYS
MULTI-COMPONENT GAS PERMEATION SYSTEM
BINARY GAS PERMEATION
SINGLE GAS PERMEATION
Ion rejection coefficient:
Feed (salt solution)
DWCNT / Si3N4
Sangil Kim1,2, Francesco Fornasiero1, Michael Stadermann1, Alexander Chernov1, Hyung Gyu Park1, Jung Bin In3, Ji Zang5, David Sholl5, Michael Colvin4, Aleksandr Noy1,4, Olgica Bakajin,1,2 andCostas P. Grigoropoulos3
1 Physical and Life Sciences, LLNL; 2 NSF Center for Biophotonics, UC Davis; 3Mechanical Engineering, UC Berkeley; 4School of Natural Sciences, UC Merced, 5Chemical and Biochemical Engineering, Georgia Tech
CARBON NANOTUBE MEMBRANE:A NANOFLUIDIC PLATFORM
- Strongly absorbing gas species (CO2, CH4, and C2H4) deviated from the scaled Knudsen permeance
- Weakly absorbing gas species (He, N2, Ar, and SF6) did not show the deviation.
- 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?
Rejection declines at larger salt solution concentrations
Gas transport in CNTs and other nanoporous materials
CH4/N2 and CO2/N2
Gated Transport through Carbon Nanotube MembranesNIRT CBET-0709090
- Free standing membrane
- Highly aligned DWCNTs
- Inner diameter ~ 1.6 nm
- LPCVD Si3N4 pinhole-free matrix
- Rejection ~ constant when the Debye length is >> CNT diameter
- At 263 K, the separation factor increased because of increased gas solubility at lower temperature.
Comparison with atomistic simulations (CH4/N2)
- VA-CNT arrays grow from catalytic decomposition of carbon precursor, C2H4, over nanoscale Fe catalyst
- Smaller tube has higher separation factor for CH4/N2.
- Polydisperse of tube size in CNT membrane affects the separation factor.
- Electrostatic interactions dominate the ion rejection mechanism
- The largest ion in this series, Ru(bipy)3Cl2, permeates freely through the membrane suggesting that size effects are less important
- 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
KINETICS OF CARBON NANOTUBE ARRAY GROWTH
- CNT growth rates exhibit a non-monotonic dependence on total pressure and humidity. Optimal process pressure and water concentration produce growth rate of ~30m/min.
- Nanotube growth rate remains essentially constant until growth reaches an abrupt and irreversible termination.
- We developed a model that predicts termination kinetics
- Holt et. al., Science, 312, 1034 (2006)
- Noy et. al., Nano Today, 2, 22 (2007)
- Fornasiero et. al. Proc. Natl. Acad. Sci USA, 105, 17217 (2008)
- Stadermann et. al., Nano Letters, in revision (2008)
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-AC52-07NA27344.