Amz A CnzC
Gated Transport through Carbon Nanotube Membranes
NIRT CBET-0709090
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 and Costas 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
ION EXCLUSION
Pressure
-1
40
Cation
Anion
20
0
2
Feed (salt solution)
60
pH=7.2
Ion rejection coefficient:
80
Rejection [%]
cpermeate
R  1  feed
c
60
40
20
Permeate
K+ channel
 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?
Concentration dependence
GROWTH OF ALIGNED NANOTUBE ARRAYS
•VA-CNT arrays grow from catalytic
decomposition of carbon precursor, C2H4,
over nanoscale Fe catalyst
2
N2
SF6
Ar
1
Cation
60
XY (Scatter)
K3Fe(CN)
3
6
XY (Scatter)
4
0.1
0.2
-1/2
M
0.4
1/2
-1/2
(mol g
0.5
0.6
)
BINARY GAS PERMEATION
CH4/N2 and CO2/N2
60
KCl
40
1.6
1.3
1.5
1.2
Ideal selectivity
1.4
20
20
Donnan 1:3
Donnan 1:1
0
0
10
0.3
80
40
1
P263K
P293K
0
K3Fe(CN)6
80
KCl
CH4
CO2
3
0.0
Anion
0
100
2
4
6
8 10 12 14 16 18 20
1.3
Knudsen Separation
298 K
1.1
1.0
80%
60%
40
50
60
70
0%
0.7
20
30
Ru(bipy)3Cl2
2.0
1.0
1.0
-
0.5
0.5
+
Z /Z
 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
50
60
70
80
Comparison with atomistic simulations (CH4/N2)
4.2
4.0
Pf=1.5 Bar, Pp=1 Bar
3.8
5
(10,10), 298K
4
(20,20), 263K
3
(20,20), 298K
(40,40), 263K
2
298K
263K
3.6
Nanotube membrane made of
(10,10) and (40,40) SWNT
3.4
3.2
3.0
2.8
2.6
2.4
(40,40), 298K
Pf=1.5 Bar, Pp=1 Bar
2.2
3.0
40
CO2 in Feed (%)
1
-20%
Knudsen Separation
 At 263 K, the separation factor increased because of
increased gas solubility at lower temperature.
6
CaCl2
0.8
CH4 in Feed (%)
KCl
20%
298 K
80
(10,10), 263K
CaSO4
0.9
0.5
30
7
40%
Ideal Selectivity
1.0
0.6
0.8
Cation
Anion
Donnan
K2SO4
263 K
1.2
 Rejection ~ constant when the Debye length is >> CNT diameter
K3Fe(CN)6
100%
263 K
1.1
0.9
l D [nm]
concentration [mM]
% Rejection
Si
C2H4
4
100
CNT MEMBRANE
DWCNT / Si3N4
5
Debye length dependence
100
0.1
 Free standing membrane
 Highly aligned DWCNTs
 Inner diameter
~ 1.6 nm
 LPCVD Si3N4 pinholefree matrix
He
Selectivity (CH4/N2)
Aquaporin
6.7 A
pH=3.8
(b)
6
Selectivity (CH4/N2)
CNT
0
Rejection declines at larger salt solution concentrations
% Rejection coefficient
Gas transport in CNTs and
other nanoporous materials
Cation
Anion
Selectivity (CH4/N2)
K+
-5
100
8.1 A
CNT
membrane
 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.
7
-1
80
Permeance (x10 , mol.m .sec .Pa )
100
Rejection [%]
 Unique surface properties of carbon nanotubes enable very
rapid and very efficient transport of gases and liquids
SINGLE GAS PERMEATION
Selectivity (CO2/N2)
CARBON NANOTUBE MEMBRANE:
A NANOFLUIDIC PLATFORM
0.3
0.4
0.5
0.6
CH4 In Feed (%)
0.7
0.8
2.0
0.0
0.2
0.4
0.6
0.8
1.0
# ratio of (10,10) SWNT
 Smaller tube has higher separation factor for CH4/N2.
 Polydisperse of tube size in CNT membrane affects the
separation factor.
CONCLUSIONS
MULTI-COMPONENT GAS PERMEATION SYSTEM
KINETICS OF CARBON NANOTUBE ARRAY GROWTH
Iijima’s
model
Poisoning
model
• 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
PUBLICATIONS
• 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
• Selectivity ≡ A/B= [ yA/(yB) ]/[ xA/(xB) ]=[ yA/(1-yA) ]/[ xA/(1-xA) ]
where x : the mole fractions of gas species at the feed side
y : the mole fractions of gas species at the permeate side
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.
• 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)