supporting information highly permeable and selective ... · s1 supporting information highly...

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Supporting Information

Highly permeable and selective zeolitic imidazolate framework ZIF-95

membrane for hydrogen separation

Aisheng Huang*a, Yifei Chen b, Nanyi Wang c, Zhongqiao Hu b, Jianwen Jiang b and Jürgen Caro *c

a Institute of New Energy Technology, Ningbo Institute of Material Technology and Engineering, CAS,

519 Zhuangshi Road, 315201 Ningbo, P. R. China. b Department of Chemical and Biomolecular Engineering, National University of Singapore, 117576,

Singapore c Institute of Physical Chemistry and Electrochemistry, Leibniz University Hannover, Callinstraße 3-3A,

D-30167 Hannover, Germany

Electronic Supplementary Material (ESI) for Chemical CommunicationsThis journal is © The Royal Society of Chemistry 2012

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Experimental details:

Materials: Chemicals were used as received: zinc nitrate tetrahydrate (>99%, Merck), 5-

chlorobenzimidazole (cbIM, >96%, ABCR), 3-aminopropyltriethoxysilane (APTES, 98%, Abcr), toluene

(Acros), N, N-Dimethylformamide (DMF, water<50 ppm, Acros). Porous α-Al2O3 disks (Fraunhofer

Institute IKTS, former HITK/Inocermic, Hermsdorf, Germany: 18 mm in diameter, 1.0 mm in thickness,

70 nm particles in the top layer) were used as supports.

APTES modificaton of the support surface: Porous α-Al2O3 disks were treated with APTES (0.2 mM

in 10 mL toluene) at 110 °C for 2 h under argon, leading to APTES monolayer deposited on the α-Al2O3

support surface. 1

Synthesis of ZIF-95 membrane: The ZIF-95 membrane was prepared by a solvothermal reaction of

zinc nitrate tetrahydrate and cbIMI in DMF according to the previous report. 2 The APTES-treated or

APTES-free α-Al2O3 supports were placed horizontally in a Teflon-lined stainless steel autoclave which

was filled with synthesis solution, and heated at 120 °C in air oven for 3 days. After solvothermal reaction,

the ZIF-95 membranes were washed with DMF several times, and then dried in air at 100 °C over night.

Characterization of ZIF-95 membrane: Scanning electron microscopy (SEM) micrographs were

taken on a JEOL JSM-6700F with a cold field emission gun operating at 2 kV and 10 µA. using the same

SEM microscope at 20 kV and 20 µA. The X-ray diffraction (XRD) patterns were recorded at room

temperature under ambient conditions with Bruker D8 ADVANCE X-ray diffractometer with CuKa

radiation at 40 kV and 40 mA.

Permeation of single gas and separation of mixed gases: For the single gas and mixture gas

permeation, the supported ZIF-95 membrane was sealed in a permeation module with silicone O-rings.


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The feed gases were fed to the top side of the membrane, and sweep gas was fed on the permeate side to

keep the concentration of permeating gas low providing a driving force for permeation. Before gas

permeation, the as-synthesized ZIF-95 membrane was on-stream activated to remove guest DMF at 325

ºC with a heating rate of 0.2 °C min-1 by using an equimolar H2-CO2 mixture in the Wicke-Kallenbach

permeation apparatus (Figure S2). The activation is completed at 325 ºC for 24 h. and then before

measurements of every single gas permeation and mixture separation, the membrane was in-situ heated at

325°C for 24 h under sweep gas to remove the adsorbed CO2. The sweep gas N2 (except for the N2

permeation measurement where CH4 was used as sweep gas) was fed on the permeate side to keep the

concentration of permeating gas as low as possible thus providing a driving force for permeation. On both

sides of the membranes was atmospheric pressure. The fluxes of feed and sweep gases were determined

with mass flow controllers, and a calibrated gas chromatograph (HP6890) was used to measure the gas

concentrations, as shown in Figure S2. The separation factor αi,j of a binary mixture permeation is defined

as the quotient of the molar ratios of the components (i,j) in the permeate, divided by the quotient of the

molar ratio of the components (i, j) in the retentate, as show in Eq. 1.

(1)

Simulation Models and Methods: The adsorption of H2/CO2 mixture in ZIF-95 was examined by

molecular simulation. The model structure of ZIF-95 was adopted from experimentally determined X-ray

crystallographic data. 2 To estimate the charges of ZIF-95 framework atoms, a fragmental cluster (Figure

S1E) was cleaved and saturated by lithium. The electrostatic potentials around the cluster were calculated

by density-functional theory (DFT). It has been widely recognized that first-principles derived charges

fluctuate appreciably when a small basis set is used; however, they tend to converge beyond 6-31G(d)

basis set. 3 Consequently, 6-31G(d) basis set was used in the DFT calculation for all the atoms except Zn

metals, for which LANL2DZ basis set was used with effective pseudopotentials. The DFT calculation

used the Lee-Yang-Parr correlation functional (B3LYP) and was carried out with Gaussian 03.4 The

tjti

PermjPermiji yy

yy

Re,Re,

,,/ /

/=α


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concept of atomic charges is solely an approximation and no unique straightforward method is currently

available to rigorously determine atomic charges. In this study, the atomic charges were estimated by

fitting to the electrostatic potential using the CHelpG scheme. 5

Figure S1E. A fragmental cluster of ZIF-95 used to calculate atomic charges. The dangling bonds

connected to N were saturated by Li. Color code: Zn, pink; N, blue; C, grey; H, white; Cl, green.

The adsorption isotherms of CO2, CH4 and N2 in ZIF-95 were predicted and compared with available

experimental data. CO2 was represented as a three-site molecule and its intrinsic quadrupole moment was

described by a partial-charge model. 6 A united-atom model was used for CH4 with the Lennard-Jones (LJ)

potential parameters from the TraPPE force field. 7 N2 was mimicked by two-site models with a bond

length of 1.10 Å. 8 The dispersion interactions of the framework atoms in ZIF-95 were represented by the

universal force field (UFF).9 Similar to recent studies,10,11 the well depths of the framework atoms were

scaled by a factor (0.6). The cross LJ interaction parameters between ZIF-95 and adsorbates were

evaluated by the Lorentz-Berthelot combining rules. As shown in Figure S5, the predicted isotherms of

CO2, CH4 and N2 match well with experimental data.

H1 (0.008)

H2 (0.128)

H3 (0.090)

C1 (0.318)

C2 (0.152)

C3 (-0.233) C4 (-0.052) C5 (0.250)

Cl (-0.267)

Zn (0.939)

N (-0.456)


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References

(1) A. Huang, F. Liang, F. Steinbach, J. Caro, J. Membr. Sci. 2010, 350, 5.

(2) B. Wang, A. P. Côté, H. Furukawa, M. O’Keeffe, O. M. Yaghi, Nature, 2008, 453, 207.

(3) P. C. Hariharan, J. A. Pople, Chem. Phys. Lett. 1972, 16, 217.

(4) M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, V. G.

Zakrzewski, J. A. Montgomery, R. E. Stratmann, J. C. Burant, S. Dapprich, J. M. Millam, A. D.

Daniels, K. N. Kudin, M. C. Strain, O. Farkas, J. Tomasi, V. Barone, M. Cossi, R. Cammi, B.

Mennucci, C. Pomelli, C. Adamo, S. Clifford, J. Ochterski, G. A. Petersson, P. Y. Ayala, Q. Cui, K.

Morokuma, D. K. Malick, A. D. Rabuck, K. Raghavachari, J. B. Foresman, J. Cioslowski, J. V. Ortiz,

B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. Gomperts, R. L. Martin, D. J. Fox,

T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara, C. Gonzalez, M. Challacombe, P. M. W. Gill,

B. G. Johnson, W. Chen, M. W. Wong, J. L. Andres, M. Head-Gordon, E. S. Replogle, J. A. Pople,

Gaussian 03, Revision D.01 ed.; Gaussian, Inc.: Wallingford CT, 2004.

(5) C. M. Breneman, K. B. Wiberg, J. Comp. Chem 1990, 11, 361.

(6) A. Hirotani, K. Mizukami, R. Miura,H. Takaba, T. Miya, A. Fahmi, A. Stirling, M. Kubo, A.

Miyamoto, Appl. Surf. Sci. 1997, 120, 81.

(7) M. G. Martin, J. I. Siepmann, J. Phys. Chem. B. 1998, 102, 2569.

(8) C. S. Murthy, K. Singer, M. L. Klein, I. R. McDonald, Mol. Phys. 1980, 41, 1387.

(9) A. K. Rappe, C. J. Casewit, K. S. Colwell, W. A. Goddard, W. M. Skiff, J. Am. Chem. Soc. 1992, 114,

10024.

(10) J. Perez-Pellitero, H. Amrouche, F. R. Siperstein, G. Pirngruber, C. Nieto-Draghi, G. Chaplais, A.

Simon-Masseron, D. Bazer-Bachi, D. Perala, N. Bats, Chem. Eur. J. 2010, 16, 1560.

(11) A. Battisti, S. Taioli, G. Garberoglio, Microporous and Mesoporous Mater. 2011, 143, 46.


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Figure S1

ZIF-95 layer Al2O3 support

H2

CO2

Fig. S1. Scheme of the fabrication of ZIF-95 molecular sieve membrane

as carbon dioxide captor for H2/CO2 separation.


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Figure S2

10 µm

ZIF-95 layer

Al2O3 support

(c) (d)

100 µm

(a)

25 µm

10 µm

(b)

Figure S2. SEM images of the ZIF-95 membrane prepared on the APTES-

modified asymmetric macroporous α-Al2O3 disk: (a-c) top views, (d) cross-

section. The circle in (c) indicates the “folded filters” structure.


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Figure S3

Fig. S3. SEM image of the ZIF-95 layer prepared on the non-

APTES-modified Al2O3 support.


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Figure S4

GC MFC

MFC

MFC

fsweep, psweep

ffeed, pfeed

fpermeate, ppermeate

fretentate, pretentate

PC

Fig. S4. Measurement equipment for both single and mixed gas permeation.

Legend:

MFC: mass flow controller

PC: permeation cell with mounted membrane

GC: gas chromatograph

f: volumetric flow rate

p: pressure


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Figure S5

-100 0 100 200 300 400 500 600 700 800

0.0

0.2

0.4

0.6

0.8

1.0

Upt

ake

(m m

ol /g

)

Pressure (Torr)

Simulated CO2

Experimental CO2

Simulated CH4

Experimental CH4

Simulated N2

Experimental N2

Simulated H2

Fig. S5. The comparison of the experimental and simulated

adsorption isotherms of CO2, CH4 and N2 in ZIF-95 at 25 °C.


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Figure S6

-100 0 100 200 300 400 500 600 700 800

0.0

0.2

0.4

0.6

Upt

ake

(m m

ol /g

)

Pressure (Torr)

CO2

H2

Fig. S6. The simulated adsorption isotherms of equimolar

H2/CO2 mixture in ZIF-95 at 25 °C.


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Figure S7

Fig. S7. Mixed gas permeances and H2/CO2 selectivity of the ZIF-95

membrane as function of the operating temperatures at 1 bar.

0 50 100 150 200 250 300 3500.0

2.0x10-7

4.0x10-7

6.0x10-7

8.0x10-7

1.0x10-6

1.2x10-6

1.4x10-6

1.6x10-6

1.8x10-6

2.0x10-6

Temperature / οC

Per

mea

nce

/ mol

m-2s-1

Pa

-1

8

12

16

20

24

28

32

H2 permeance

CO2 permeance

Separation factor Mixtu

re se

pa

ratio

n fa

ctor


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Figure S8

Fig. S8. The adsorption isotherms of CO2 in ZIF-95 as function of the operating temperature.

-100 0 100 200 300 400 500 600 700 800

0.0

0.2

0.4

0.6

0.8

1.0

Up

take

(m

mo

l /g

)

Pressure (Torr)

25 οC

125 οC

225 οC

325 οC


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Figure S9

Fig. S9. Mixed gas permeances and H2/CO2 selectivity of the ZIF-95

membrane as function of the operating time at 325 °C and 1 bar.

0 4 8 12 16 20 24

0.0

4.0x10-7

8.0x10-7

1.2x10-6

1.6x10-6

2.0x10-6

2.4x10-6

H2 permeance

CO2 permeance

Separation factor

Time / h

Per

me

ance

/ m

ol m

-2s-1

Pa

-1

20

22

24

26

28

30

Mixture

separation facto

r


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Figure S10

Fig. S10. XRD patterns of the as-prepared ZIF-95 membrane prepared on

the APTES-modified α-Al2O3 support (a), and the spent ZIF-95

membrane after the measurement of gas separation at 325 °C. (●): Al2O3

support, (not marked): ZIF-95.

0 5 10 15 20 25 30 35 40 45

Inte

nsi

ty

2θ/degrees

(b)

(a)


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Figure S11

0 4 8 12 16 20 24 28

0.0

2.0x10-7

4.0x10-7

6.0x10-7

8.0x10-7

1.0x10-6

1.2x10-6

1.4x10-6

1.6x10-6

1.8x10-6

2.0x10-6

H2 permeance

CO2 permeance

Separation factor

Time / h

Pe

rmea

nce

/ mol

m-2s-1

Pa-1

16

18

20

22

24

26

28

30

Mixture se

paration factor

Fig. S11. Hydrothermal stability measurement of the ZIF-95

membrane for the separation of an equimolar H2/CO2 mixture with

adding of 3 mol% steam at 325 °C.


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Table S1 Single and mixed gases permeances (mol/m2s1Pa1) and separation factors for the ZIF-95 membrane at

325 ºC and 1 bar with 1:1 binary mixtures of H2 with CO2, N2, CH4 and C3H8.

Gasi/j Knudsen constant

Separation performances of the ZIF-95 membrane

Single gas Mixed gases

Permeances(i) (mol/m2·S1·Pa1)

Permeances(j) (mol/m2·S1·Pa1)

Ideal Separation factor

Permeances(i) (mol/m2·S1·Pa1)

Permeances(j) (mol/m2·S1·Pa1)

Separation factor

H2/CO2 4.7 2.46 x 10-6 7.04 x 10-8 34.9 1.95 x 10-6 7.59 x 10-8 25.7

H2/N2 3.7 2.46 x 10-6 2.27 x 10-7 10.8 2.18 x 10-6 2.16 x 10-7 10.1

H2/CH4 2.8 2.46 x 10-6 1.61x 10-7 15.3 2.04 x 10-6 1.85x 10-7 11.0

H2/C3H8 4.7 2.46 x 10-6 3.69 x 10-8 66.8 1.93 x 10-6 3.23 x 10-8 59.7


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Reference

(1) Y. Li, F. Liang, H. Bux, A. Feldhoff, W. Yang, J. Caro, Angew. Chem. Int. Ed. 2010, 49, 548.

(2) H. Bux, F. Liang, Y. Li, J. Cravillon, M. Wiebcke, J. Caro, J. Am. Chem. Soc. 2009, 131, 16000.

(3) A. Huang, H. Bux, F. Steinbach, J. Caro, Angew. Chem. Int. Ed. 2010, 49, 4958.

(4) Y. Liu, E. Hu, E. A. Khan, Z. Lai, J. Membr. Sci. 2010, 353, 36.

(5) A. Huang, W. Dou, J. Caro, J. Am. Chem. Soc. 2010, 132, 15562.

(6) Y. Hu, X. Dong,J. Nan, W. Jin, X. Ren, N. Xu, Y. M. Lee, Chem. Commun. 2011, 47, 737.

(7) H. Guo, G. Zhu, I. J. Hewitt, S. Qiu, J. Am. Chem. Soc. 2009, 131, 1646.

ZIF membranes Pore size

(nm) Thickness

(µm) H2 permeances (mol/m2·S1·Pa1)

H2 permeability*

(Barrers) H2/CO2

selectivity References

ZIF-7 0.30 1.5 7.71 x 10-8 345 6.48 1

ZIF-8 0.34 30 6.04 x 10-8 5412 4.54 2

ZIF-22 0.30 40 1.66 x 10-7 19832 7.2 3

ZIF-69 0.44 50 6.50 x 10-8 9707 2.7 4

ZIF-90 0.35 20 2.37 x 10-7 14158 7.3 5

MIL-53 0.73X0.77 8 5.01x 10-7 11971 6.8 6

KUUST-1 0.9 60 1.00x 10-6 179211 2.7 7

ZIF-95 0.37 30 1.95 x 10-6 174732 25.7 This study

* Permeability is calculated as the membrane permeance multiplied by the membrane thickness. 1 Barrer = 3.348 × 10-16 mol m / (m2 s Pa).

Table S2. Comparation of H2/CO2 selectivity versus H2 permeability for ZIF-95

membrane with the previously reported MOF membranes.


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Membrane H2 permeance

(mol·m-2·s-1·Pa-1) CO2 permeance

(mol·m-2·s-1·Pa-1) H2/CO2

selectivity Average

selectivity standard deviation

of selectivity

M1 5.05 x 10-7 5.96 x 10-8 8.48

8.49 0.065 M2 4.96 x 10-7 5.81x 10-8 8.54

M3 5.11 x 10-7 6.05 x 10-8 8.45

Table S3. Separation performances of ZIF-95 membranes for the separation of

H2/CO2 mixtures at 25 ºC and 1 bar.


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