The liquid phase epitaxy approach for the …S1 The liquid phase epitaxy approach for the successful...

S1

The liquid phase epitaxy approach for the successful construction of ultra-

thin and defect-free ZIF-8 Membranes: Pure and mixed gas transport study.

Osama Shekhah,1 Raja Swaidan,

2 Youssef Belmabkhout,

1 Marike du Plessis,

3 Tia Jacobs,

3

Leonard J. Barbour,3 Ingo Pinnau,

2 Mohammed Eddaoudi

1*

Table of content:

1. Experimental:

- Synthesis of ZIF-8 crystals S3

- ZIF-8 membrane fabrication S3

- Characterization of ZIF-8 crystals and ZIF-8 membranes S3

- Pure gas permeation measurements S4

- Mixed gas permeation measurements S4

- Adsorption and kinetics S4

- Measurement of gas adsorption equilibrium and kinetics using Rubotherm Magnetic

balance

S4

- Figure S1. Structure of ZIF-8 with the growth along the (100) direction, the 2-

methylimidazol (mIm) organic ligand bridge, cavity and window size are also shown.

S6

- Figure S2. Schematic representation of the permeation setup used for the pure- and

mixed-gas permeation measurements.

S7

- Figure S3. PXRD diffractograms of ZIF-8 thin film membranes grown on alumina

substrate using the LPE method, (a) after 150 growth cycles (b) after 300 growth cycles.

All diffractograms were background-subtracted.

S8

- Figure S4: Cross-section SEM image of the ZIF-8 thin film fabricated (150 cycles) using

the LPE method with a thickness of ~0.5µm.

S9

- Figure S5. Permeability of single gases measured for the ZIF-8 membrane fabricated

using the LPE method at (T = 308 K and P= 18 psig) versus the Lennard-Jones diameter

of the gases.

S10

- Figure S6. Permeate pressure of CO2, measured versus time using the constant

volume/variable pressure technique on ZIF-8 membrane fabricated using the LPE

method at 308 K and 18 psig, where is the calculated time-lag.

S11

-Figure S7. Sorption coefficient of single gases measured for the ZIF-8 membrane at

(T = 308 K) versus the boiling point of the gases.

S12

Electronic Supplementary Material (ESI) for Chemical CommunicationsThis journal is © The Royal Society of Chemistry 2014

S2

-Figure S8: Qualitative adsorption kinetics of CO2, CH4, C3H6, C3H8 and n-C4H10 on the

ZIF-8 crystals at various pressures and 308 K.

S13

-Figure S9. Single component adsorption isotherms of H2, CO2, N2 and CH4 on ZIF-8

powder at 308 K. Filled symbols represent adsorption, open symbols represent

desorption.

S14

-Figure S10. (a) Single component adsorption isotherms of CH4, C2H6, C2H4, C3H8, C3H6

and n-C4H10 on ZIF-8 powder at 308 K. Filled symbols represent adsorption, open

symbols represent desorption. (b) Kinetics of adsorption (in fractional uptake) of CO2,

CH4, C3H6, C3H8 and n-C4H10 collected at various pressures and 308 K

S15

-Figure S11. N2 sorption isotherm on ZIF-8 crystals measured at 77 K. S16

-Figure S12. Permeability and selectivity of the 50/50 C3H6/C3H8 mixture (2.7 bar/40

psig) with time, measured using the constant-volume/variable-pressure technique on

ZIF-8 membrane at 308 K.

S17

-Figure S13. Permeability and selectivity of the 25/75 CH4/n-C4H10 mixture (2.7 bar/40

psig) with time, measured using the constant-volume/variable-pressure technique on

ZIF-8 membrane at 328 K.

S18

-Table S1: Comparison of the single gas permeance values measured on ZIF-8

membranes found in literature.

S19

2. Crystal structure data. S20

-Table S2. Crystal data and structure refinement for ZIF-8 under vacuum. S21

-Table S3. Crystal data and structure refinement for ZIF-8 at 50 bar Methane. S22

-Table S4. Crystal data and structure refinement for ZIF-8 at 35 bar Ethane. S23

-Table S5. Crystal data and structure refinement for ZIF-8 at 2 bar Propane. S24

-Table S6. Crystal data and structure refinement for ZIF-8 at 4 bar Propane. S25


S3

1. Experimental:

Synthesis of ZIF-8 crystals:

The ZIF-8 crystals were synthesized according to the procedure reported by Park et al., where zinc nitrate

tetrahydrate Zn(NO3)2.4H2O (0.210 g) and 2-methylimidazole (H-mIm) (0.060 g) were dissolved in 18 ml

of DMF in a 20-ml vial. The vial was capped and heated at a rate of 5°C/min to 140°C in a programmable

oven and held at this temperature for 24 h, then cooled at a rate of 0.4°C/min to room temperature. After

removal of mother liquor from the mixture, chloroform (20 ml) was added to the vial. Colorless

polyhedral crystals were collected from the upper layer, washed with DMF, and then exchanged with

methanol for 24 hours.1

ZIF-8 membrane fabrication:

ZIF-8 membrane was grown on porous supports by the stepwise deposition method. The alumina

substrates (Cobra Technologies BV) were first washed with water and dried at 140°C, to remove any

water or organic contaminants from the surface. The alumina substrate was then vertically mounted on the

teflon sample holder in the robot using teflon screws. The growth was performed briefly using the

following steps: (1) The substrate was immersed in the metal ions methanolic solution for 90 seconds, (2)

washed with fresh solvent, (3) immersed in the organic ligand methanolic solution for 120 seconds, and

(4) washed with fresh solvent t. This process was considered as one cycle and then repeated many times,

in order to grow more layers (see Fig. 1). After 150 cycles, the supports seemed to be homogeneously

deposited by visual inspection. The resulting membrane was immediately covered with a watch glass, and

allowed to dry slowly in ambient air overnight.2

Characterization of ZIF-8 crystals and ZIF-8 membranes:

X-ray powder diffraction (PXRD) patterns were recorded on a Panalytical X’pert PRO MPD X-ray

Diffractometer with Cu Kα radiation (λ = 0.15418 nm, 45 kV, 40 mA). Low pressure gas sorption

measurements were performed on a fully automated micropore gas analyzer Autosorb-1C (Quantachrome

Instruments) at relative pressures up to 1 atm. The cryogenic temperatures were controlled using a liquid

nitrogen bath at 77 K. The apparent surface area of ZIF-8 crystals was determined from the nitrogen

adsorption isotherm by applying the Brunauer-Emmett-Teller (BET) model using adsorption points in the

relative pressure (P/P0) range of 0.015 to 0.046. SEM was performed using an FEI Quanta 600 field

emission scanning electron microscope (accelerating voltage: 30 kV)

Permeability analysis

Pure Gas Permeation Measurements:

A constant-volume/variable-pressure (CV/VP) apparatus (see Fig. S2 in the supporting information (SI)),

was used to determine the pure gas permeability, diffusion and sorption coefficients of the thin films via

the time-lag analysis. A custom cell was used to mount the film and sealed with O-rings on both surfaces.

Modified with feed-inlet and retentate outlet lines, the cell enabled both pure and mixed gas testing

without relocation of the membrane. In pure gas experiments with the CV/VP technique, the retentate line

was closed. Before each run, the entire system was evacuated under high vacuum at 35oC until any

downstream pressure rise – “virtual leak rate” - was less than 1% of the rate of steady-state pressure rise

for any penetrant gas. All pure gas experiments were run at 2 bar feed pressure. The downstream pressure

rise during permeation was monitored with a 10 Torr MKS Baratron transducer and the experiment was

stopped after seven to ten time-lags elapsed to ensure steady-state. The permeability of the pure gas is

given by

where P is the permeability coefficient in Barrer (10-10 cm3(STP) cm/(cm2 s cmHg)), dpd/dtSS is the

steady-state rate of permeate pressure rise (cmHg/s) , dpd/dtLR is the downstream “leak rate” (cmHg/s)

(negligible here), Vd is the downstream volume (cm3), l is the active layer thickness (cm), pup is the

P DS 1010dpd

dt

SS

dpd

dt

LR

Vd l

(pup pd )ART


S4

upstream pressure (cmHg), A is the membrane area (cm2), R is the gas constant (0.278 cm3

cmHg/(cm3(STP) K)), and T is the temperature at measurement (K). The apparent diffusion coefficient D

(cm2/s) is calculated from the time-lag (s), derived from the transient regime of pressure rise, as D=l2/6

via solution to the differential equations governing mass transport across the film.3 Assuming permeation

occurs via the solution-diffusion mechanism, a reasonable assumption for microporous materials with

nominal pore diameter less than 10 A,3 the solubility coefficient S (cm3(STP)/(cm3 cmHg)), is given from

the relation P=DS by S=P/D.

Mixed Gas Permeation Measurements:

The mixed gas permeation properties of the ZIF-8 thin-film composites were measured at 35 oC. Feed gas

mixtures of 50/50 C3H6/C3H8 and 75/25 CH4/n-C4H10 were run at 2.7 bar (40 psi) feed pressure such that

the penetrant partial pressures were comparable to those in the pure gas experiments. The stage-cut, that

is, the ratio of permeate flow rate to feed flow rate, was kept less than 1% such that the residue

composition was essentially equal to that of the feed mixture. An Agilent 3000A Micro GC equipped with

four columns and thermal conductivity detectors was calibrated for each gas pair over the composition

range of interest using several calibration mixtures. Steady state was assumed to be achieved once the

permeability and permeates composition ceased to vary with time. The mixed gas permeability coefficient

of gas i was determined by

where y and x are the molar fractions in the permeate and feed, respectively, and the rate of pressure rise

is the total rate measured for the permeate gas mixture. When the downstream pressure is negligible as

compared to the upstream pressure, the separation factor for a gas pair (i/j) is calculated by

Adsorption and kinetics:

The procedure for adsorption and kinetics is described in detail in the supporting Information. Preliminary

investigation of gas adsorption properties (thermodynamics and kinetics) on the MOF microcrystals is an

important step towards the evaluation and characterization of MOF-based membranes. Study of

adsorption thermodynamics and kinetics allows quantitative information about the affinity of the given

gas to the MOF framework as well as the extent of the accessibility of different probe molecules, with

different dimensions, into the porosity. For this purpose, a serie of adsorption experiments were carried

out using probe molecules such as of H2, N2, O2, CH4, CO2 as well as larger probe molecules such as

C2H4, C2H6, C3H6, C3H8 and n-C4H10 at 308 K.

Measurement of gas adsorption equilibrium and kinetics using Rubotherm Magnetic balance Adsorption equilibrium measurements of all gases were performed using a Rubotherm gravimetric-

densimetric apparatus (Bochum, Germany), composed mainly of a magnetic suspension balance (MSB)

and a network of valves, mass flowmeters and temperature and pressure sensors. The MSB overcomes the

disadvantages of other commercially available gravimetric instruments by separating the sensitive

microbalance from the sample and the measuring atmosphere and is able to perform adsorption

measurements across a wide pressure range, i.e. from 0 to 20 MPa. The adsorption temperature may also

be controlled within the range of 77 K to 423 K. In a typical adsorption experiment, the adsorbent is

precisely weighed and placed in a basket suspended by a permanent magnet through an electromagnet.

Pi 1010 dpd

dt

SS

dpd

dt

LR

yiVd l

(x ipup yipd )ART

j

i Pi

Pj

y ix i

y jx j


S5

The cell in which the basket is housed is then closed and vacuum or high pressure is applied. The

evacuated adsorbent is then exposed to a continuous gas flow (typically 50 ml/min) at a constant

temperature. The gravimetric method allows the direct measurement of the reduced gas adsorbed amount

. Correction for the buoyancy effect is required to determine the excess adsorbed amount using equation

1, where Vadsorbent and Vss refer to the volume of the adsorbent and the volume of the suspension system,

respectively. These volumes are determined using the helium isotherm method by assuming that helium

penetrates in all open pores of the materials without being adsorbed. The density of the gas is determined

experimentally using a volume-calibrated titanium cylinder. By weighing this calibrated volume in the

gas atmosphere, the local density of the gas is also determined. Simultaneous measurement of adsorption

capacity and gas phase density as a function of pressure and temperature is therefore possible. The excess

uptake is the only experimentally accessible quantity and there is no reliable experimental method to

determine the absolute uptake. For this reason, only the excess amounts are considered in this work.

)( ssadsorbentgasexcess VVm

(1)

The pressure is measured using two Drucks high-pressure transmitters ranging from 0.5 to 34 bar and 1 to

200 bar, respectively, and one low pressure transmitter ranging from 0 to 1 bar. Prior to each adsorption

experiment, about 100 mg to 300 mg sample is outgassed at 423 K at a residual pressure 10-6 mbar. The

temperature during adsorption measurements is held constant by using a thermostated circulating fluid.

The kinetics measurementswere carried out by monitoring the change in the weight of the sample after its

contact with the gas in study (CO2, C3H8, C3H6 and n-C4H10) at various pressures.

[1] K. S. Park, Z. Ni, A. P. Cote, J. Y. Choi, R. Huang, F. J. Uribe-Romo, H. K. Chae, M. O'Keeffe, O.

M. Yaghi, PNAS, 2006, 103, 10186-10191.

[2] O. Shekhah, H. Wang, S. Kowarik, F. Schreiber, M. Paulus, M. Tolan, C. Sternemann, F. Evers, D.

Zacher, R. A. Fischer, C. Wöll, J. Am. Chem. Soc. 2007, 129, 15118-15119.

[3] S. W. Rutherford, D. D. Do, Adsorption, 1997, 3, 283-312.


S6

Figure S1. Structure of ZIF-8 with the growth along the (100) direction, the 2-methylimidazol (mIm)

organic ligand bridge, cavity and window size are also shown.


S7

Figure S2. Schematic representation of the permeation setup used for the pure- and mixed-gas

permeation measurements.


S8

Figure S3. PXRD diffractograms of ZIF-8 thin film membranes grown on alumina substrate using the

LPE method, (a) after 150 growth cycles (b) after 300 growth cycles. All diffractograms were

background-subtracted.

5 10 15 20 25 30 35 400

5

10

15

20

*

*

*

Inte

ns

ity x

10

3

2 theta (degree)

ZIF-8 thin film 300 cycles

ZIF-8 thin film 150 cycles

Al2O

3

*


S9

Figure S4: Cross-section SEM image of the ZIF-8 thin film fabricated (150 cycles) using the LPE

method with a thickness of ~0.5µm.


S10

Figure S5. Permeability of single gases measured for the ZIF-8 membrane fabricated using the LPE

method at (T = 308 K and P= 18 psig) versus the Lennard-Jones diameter of the gases.

2.5 3.0 3.5 4.0 4.5 5.0 5.5

0

5

10

15

20

25

30

C

4H

10

C3H

8

C3H

6

C2H

6

C2H

4

CO

2

CH

4

N2

O2

H2

Lennard-Jones Diameter []

Perm

eab

ilit

y [

Barr

er]

Single gas permeabilityH

e

o


S11

Figure S6. Permeate pressure of CO2, measured versus time using the constant volume/variable pressure

technique on ZIF-8 membrane fabricated using the LPE method at 308 K and 18 psig, where is the

calculated time-lag.

10 20 30 40 500

1

2

3

4

5

6

10 x

Perm

ea

te [

To

rr]

Time [min]

CO2 permeation in ZIF-8

membrane

Linear fit


S12

Figure S7. Sorption coefficient of single gases measured for the ZIF-8 membrane at (T = 308 K) versus

the boiling point of the gases.

0 50 100 150 200 250 300

0.01

0.1

1

n-C4H

10

C3H

8

C3H

6

C2H

6

C2H

4

CO2

CH4

O2

N2

S [

cm

3 (

ga

s)/

(cm

3 (

MO

F)

cm

Hg

)]

Normal boiling point [K]

H2


S13

Figure S8: Qualitative adsorption kinetics of CO2, CH4, C3H6, C3H8 and n-C4H10 on the ZIF-8 crystals at

various pressures and 308 K.


S14

Figure S9. Single component adsorption isotherms of H2, CO2, N2 and CH4 on ZIF-8 powder at 308 K.

Filled symbols represent adsorption, open symbols represent desorption.

0 5 10 15 20 25 30

0

1

2

3

4

5

6

7

8

CO2

CH4

H2O2

Ad

so

rpti

on

up

tak

e m

mo

l/g

Pressure (bar)

N2


S15

Figure S10. (a) Single component adsorption isotherms of CH4, C2H6, C2H4, C3H8, C3H6 and n-C4H10 on

ZIF-8 powder at 308 K. Filled symbols represent adsorption, open symbols represent desorption. (b)

Kinetics of adsorption (in fractional uptake) of CO2, CH4, C3H6, C3H8 and n-C4H10 collected at various

pressures and 308 K.

0 1 2 3 4 5 6 7 80

1

2

3

4

5a

n-C4H

10

C3H

6

C3H

8

C2H

4

C2H

6

CH4

Ad

so

rpti

on

up

tak

e m

mo

l/g

Pressure (bar)

0 5 10 15 20 25 300.0

0.2

0.4

0.6

0.8

1.0

CO2-adsorption kinetics at 0.2 bar

C3H

8-adsorption kinetics at 0.2 bar

C3H


CH4-adsorption kinetics at 0.2 bar

n-C4H


Fra

cti

on

al

up

tak

e

time (min)

b


S16

Figure S11. N2 sorption isotherm on ZIF-8 crystals measured at 77 K.

0 700 710 720 730 740 750 7600

50

100

150

200

250

300

350

400

450

Q

ua

nti

ty A

ds

orb

ed

(c

m3

/g S

TP

)

Absolute Pressure (mmHg)

ZIF-8 N2 sorption at 77 K


S17

Figure S12. Permeability and selectivity of the 50/50 C3H6/C3H8 mixture (2.7 bar/40 psig) with time,

measured using the constant-volume/variable-pressure technique on ZIF-8 membrane at 308 K.


S18

Figure S13. Permeability and selectivity of the 25/75 CH4/n-C4H10 mixture (2.7 bar/40 psig) with time,

measured using the constant-volume/variable-pressure technique on ZIF-8 membrane at 328 K.


S19

Table S1: Comparison of the single gas permeance values measured on ZIF-8 membranes found in

literature.

Gas Permeance x 10-8

[mol/s m2 Pa]

Ref. 1 Ref. 1 Ref. 2 Ref. 3 Ref. 4 Ref. 5 Ref. 6 Ref. 7 Ref. 8 this

work

He - - - - - - - - - 0.89

H2 - - 17.3 - 36 6.0 5730 10000 35.0 1.9

N2 - - 1.49 - 9.0 0.52 336 - 8.0 0.19

O2 - - 5.22 - - 1.04 - - - 0.49

CO2 2430 1690 4.45 - 14.0 1.33 371 1500 13.0 0.20

CH4 472 242 1.33 - 7.8 0.48 - 500 7.2 0.41

C2H4 - - - 1.8 14.0 - - - 14.0 0.41

C2H6 - - - 0.65 6.9 - - - 7.0 0.19

C3H6 - - - - - - - - 1.0 0.06

C3H8 - - - - - - - 20 0.04 0.017

n-C4H10 - - - - - - - - 0.03 0.023

References:

1. Venna, S. R.; Carreon, M. A. J. Am. Chem. Soc. 2010, 132, 76.

2. McCarthy, M. C.; Guerrero, V. V.; Barnett, G.; Jeong, H. K. Langmuir 2010, 26, 14636.

3. Bux, H.; Chmelik, C.; Krishna, R.; Caro, J. J. Membr. Sci. 2011, 369, 284–289.

4. Pan, Y.; Lai, Z. Chem. Commun. 2011, 47, 10275.

5. Bux, H.; Liang, F. Y.; Li, Y. S.; Cravillon, J.; Wiebcke, M.; Caro, J. J. Am. Chem. Soc. 2009,

131, 16000-16001.

6. Zhong Xie , Jianhua Yang , Jinqu Wang , Ju Bai , Huimin Yin , Bing Yuan , Jinming Lu ,

Yan Zhang , Liang Zhou and Chunying Duan, , Chem. Comm., 2012,48, 5977.

7. Helge Bux , Armin Feldhoff , Janosch Cravillon , Michael Wiebcke , Yan-Shuo Li , and Juergen

Caro, Chem. Mater., 2011, 23, 2262.

8. Pan Y.C., Li T., Lestari G., Lai Z.P., J. Membr. Sci., 2012, 390, 93.


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http://pubs.acs.org/action/doSearch?action=search&author=Caro%2C+Juergen&qsSearchArea=author

S20

2. Crystal structure data.

The program PLATON-SQUEEZE was used to estimate the number of guest molecules (adsorbed gas

molecules at equilibrium under a given gas pressure).

Details of the SQUEEZE results are presented below.

ZIF8

vacuum

ZIF8

50 bar

Methane

ZIF8

35 bar

Ethane

ZIF8

2 bar

Propane

ZIF8

4 bar

Propane

SQUEEZE electron

count per cell 0 231 55 105 179

The structures were refined with the updated chemical formula and CIF files were created. The associated

structure parameters (e.g. formula unit, crystal density, ...) are listed between brackets in the crystal data

tables.


S21

Table S2. Crystal data and structure refinement for ZIF-8 under vacuum.

Empirical formula C8H10N4Zn

Formula weight 227.57

Temperature (K) 298(2)

Wavelength (Å) 0.71073

Crystal system cubic

Space group I-43m

Unit cell dimensions (Å, °) a = 17.033(2) = 90.00

b = 17.033(2) = 90.00

c = 17.033(2) = 90.00

Volume (Å3) 4941.2(10)

Z 12

Calculated density (g cm-3) 0.918

Absorption coefficient (mm-1) 1.466

F000 1392

Crystal size (mm3) 0.20 0.19 0.18

range for data collection () 1.69 to 28.29

Miller index ranges -21 h 22, -22 k 14, -22 l 22

Reflections collected 17433

Independent reflections 1173 [Rint = 0.0346]

Completeness to max (%) 100.0

Max. and min. transmission 0.7783 and 0.7581

Refinement method Full-matrix least-squares on F2

Data / restraints / parameters 1173 / 0 / 33

Goodness-of-fit on F2 1.241

Final R indices [I2(I)] R1 = 0.0325, wR2 = 0.0950

R indices (all data) R1 = 0.0385, wR2 = 0.1030

Largest diff. peak and hole (e Å-3) 0.790 and -0.376


S22

Table S3. Crystal data and structure refinement for ZIF-8 at 50 bar Methane.

Empirical formula C8H10N4Zn [C11.90H25.60N4Zn]

Formula weight 227.57 [290.13]




Space group I-43m


b = 17.001(6) = 90.00

c = 17.001(6) = 90.00

Volume (Å3) 4914(3)

Z 12

Calculated density (g cm-3) 0.923 [1.176]

Absorption coefficient (mm-1) 1.474 [1.487]

F000 1392 [1860]

Crystal size (mm3) 0.20 0.19 0.18






Max. and min. transmission 0.7773 and 0.7570 [0.7756 and 0.7552]








S23

Table S4. Crystal data and structure refinement for ZIF-8 at 35 bar Ethane.

Empirical formula C8H10N4Zn [C9H13N4Zn]





Space group I-43m


b = 16.986(14) = 90.00

c = 16.986(14) = 90.00

Volume (Å3) 4901(7)

Z 12



F000 1392 [1500]

Crystal size (mm3) 0.20 0.19 0.18














S24

Table S5. Crystal data and structure refinement for ZIF-8 at 2 bar Propane.






Space group I-43m


b = 16.987(3) = 90.00

c = 16.987(3) = 90.00

Volume (Å3) 4901.4(13)

Z 12



F000 1392 [1610]

Crystal size (mm3) 0.20 0.19 0.18














S25

Table S6. Crystal data and structure refinement for ZIF-8 at 4 bar Propane.






Space group I-43m


b = 16.9956(12) = 90.00

c = 16.9956(12) = 90.00

Volume (Å3) 4909.2(6)

Z 12



F000 1392 [1735]

Crystal size (mm3) 0.20 0.19 0.18














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