S1

SUPPLEMENTARY INFORMATION

In situ synthesis of thin zeolitic-imidazolate framework ZIF-8 membranes exhibiting

exceptionally high propylene/propane separation

Hyuk Taek Kwon1 and Hae-Kwon Jeong

1,2*

1Artie McFerrin Department of Chemical Engineering and

2Materials Science and

Engineering Program, Texas A&M University, 3122 TAMU, College Station, TX, USA.

*Author to whom correspondence should be addressed. Email: hjeong7@mail.che.tamu.edu.

Tel: +1 979 862 4850 Fax: +1 979 845 6446.

S2

Figure S1. SEM images of ZIF-8 membranes grown for 2 min (a, b), 10 min (c, d), 30 min (e, f), 1 h (g,

h), 2 h (i, j), 3 h (k, l), and 4 h (m, n)

(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

(i)

(j)

(k)

(l)

(m) (n)

S3

Figure S2. SEM images of ZIF-8 films synthesized by solvothermally treating a support soaked with a

ligand solution containing sodium formate in a metal solution (a) and by solvothermally treating a support

soaked with a metal solution in a ligand solution without sodium formate (b). Both films were prepared at

at 120ºC.

(b)

(a)

S4

Figure S3. SEM images of ZIF-8 films synthesized when a ligand solution is saturated inside of a support

and solvothermally treated in a metal solution; the addition of extra sodium formate of 0.35g in a metal

solution (a), and the addition of extra sodium formate of 0.35g and 0.5g in both of a metal solution and a

ligand solution, respectively (b). In a original recipe, a support saturated with a metal solution (0.98g of

ZnCl2 in 40 ml of methanol) is solvothermally treated in a ligand solution (5.19 g of 2-methylimidazole +

0.5g of sodium formate in 40 ml of methanol).

(a)

(b)

S5

Figure S4. XRD patterns of of ZIF-8 films synthesized when a ligand solution is saturated inside of a

support and solvothermally treated in a metal solution; the addition of extra sodium formate of 0.35g in a

metal solution (a), and the addition of extra sodium formate of 0.35g and 0.5g in both of a metal solution

and a ligand solution, respectively (b). In an original recipe, a support saturated with a metal solution

(0.98g of ZnCl2 in 40 ml of methanol) is solvothermally treated in a ligand solution (5.19 g of 2-

methylimidazole + 0.5g of sodium formate in 40 ml of methanol).

6 9 12 15 18 21 24

Simulated pattern

(b)

Intensity (a.u.)

2 theta (degree)

(a)

S6

Figure S5. Schematic diagram of gas permeation set-up (Wicke-Kallenbach technique).

Propylene

MFC

MFC

Ar

Propane

MFC

Vent

GC

Bubble flow

meter

S7

Figure. S6 SEM images of ZIF-8 membranes synthesized by conventional in-situ method1; top view (a)

and cross-section (b)

(a)

(b)

S8

Figure S7. Propylene/propane separation performance of ZIF-8 membranes grown for 4 h as a function of

temperature; binary (a) and single gas (b)

20 40 60 80 100 120 140 160

0

40

80

120

160

200

Perm

eance (x 10

-10 m

ol m

-2s-1 Pa

-1)

Temperature (oC)

0

25

50

75

100

Separation factor

Propane

C3H

6/C

3H

8 separation factor

Propylene

20 40 60 80 100 120 140 160

0

40

80

120

160

200

Propylene

Perm

eance (x 10

-10 m

ol m

-2s-1 Pa

-1)

Temperature (oC)

0

20

40

60

80

100

C3H

6/C

3H

8 id

eal selectivity

Ideal selectivity

Propane

(a)

(b)

S9

Figure S8. Schematic illustration of the defect healing process via the CD-based in situ method. The self-

limiting nature of the counter-diffusion concept enables the defective membranes to be identified since

crystals grow preferentially from defects or cracks where the separated metal ions and ligand molecules

are in contact.

S10

Figure S9. Digital photograph of a home-made counter diffusion cell. Note that the picture was taken

after the healing process was completed.

Membrane side Support side

S11

Figure S10. XRD patterns of ZIF-8 membranes; synthesized with a ligand solution recycled four times

(a), healed by a counter-diffusion-based in situ growth (b), and healed by a secondary growth (c)

5 10 15 20

(b)

(c)

Intensity (a.u.)

2 theta

(a)

S12

Table S1 Room-temperature propylene/propane separation performance of the ZIF-8 membranes after

being healed in a diffusion cell. The defective membranes showed no separation performance.

Membrane

Permeance of propylene

(10-10

mol/m2· s· pa)

Selectivity

(After healing)

Before healing After healing

M1 2496.94 406.35 8.77

M2 2139.47 392.02 9.43

M3 2385.11 407.75 9.78

S13

Figure S11. XRD patterns of ZIF-8 membranes synthesized in recycled solutions obtained after;

counter-diffusion-based in situ growth (a) and conventional in-situ method1 (b). R0 and R1 denote the

membranes prepared in a fresh precursor solution and in a solution recycled once, respectively.

6 9 12 15 18 21 24

R5

R4

R3

R2

R1

Intensity (a.u.)

2 theta (degree)

R0

6 9 12 15 18 21 24

X 1/5

R1

Intensity (a.u.)

2 theta (degree)

R0

(a)

(b)

S14

Table S2 Room-temperature propylene/propane separation performance of the ZIF-8 membranes

synthesized with recycled ligand solutions

# of recycling Permeance of propylene

Separation factor (10

-10 mol m

-2 s

-1 Pa

-1)

1st 231.87 ± 39.55 34.48 ± 5.25

2nd

200.40 ± 18.98 26.99 ± 4.70

3rd

285.50 ± 23.12 31.06 ± 4.87

4th Defective -

5th Defective -

S15

Figure S12. Binding strength of ZIF-8 membranes on a support measured by normalized (110)

peak intensity as a function of sonication time (a) and a SEM image of the ZIF-8 membrane after

sonication for 2 h (b)

0.0 0.5 1.0 1.5 2.00

20

40

60

80

100

I (110)/Io

(110) (%

)

Sonication time (h)

(a)

(b)

S16

Table S3 Propylene/propane separation performance of ZIF-8 membranes before and after 2 h of

sonication

Sonication time

(h)

Permeance

(x 10-10 mol m-2

s-1 Pa-1

) Separation factor

(C3H6/C3H8) C3H6 C3H8

0 192.88 ± 2.32 4.61 ± 0.63 43.25 ± 5.82

2 277.99 ± 12.19 7.67 ± 0.41 37.09 ± 2.66

S17

Synthesis of SIM-1 membranes

In a typical synthesis, 5 g of zinc nitrate hexahydrate (Zn(NO3)2·6H2O, 98%, Sigma-Aldrich)

was dissolved in 40 mL of ethanol (99.88%, Sigma-Aldrish), and 1 g of 4-methyl-5-

imidazolecarboxaldehyde (C5H6N2O, 95%, Santa Cruz Biotechnology) and 0.05 g of sodium

formate (HCOONa, 99%, Sigma-Aldrich) was dissolved in 40 mL of ethanol (solution B). A

home-made α-Al2O3 disk was soaked in the solution A for 1 hr. The disk saturated with the zinc

salt solution was positioned vertically in a Teflon-lined autoclave containing the solution B.

Then, the autoclave was subjected to solvothermal synthesis for 4 h at 85⁰C. After synthesis, the

membrane sample was rinsed with ethanol several times and immersed in ethanol for washing

under stirring for 1 day. Afterward, one side of the supported membranes was polished with sand

paper manually since films are formed on both sides of supports. Additional washing of 4 days

was conducted before drying at room temperature for 48 h.

S18

Synthesis of ZIF-7 membranes

In a typical synthesis, 3.06 g of zinc nitrate hexahydrate (Zn(NO3)2·6H2O, 98%, Sigma-

Aldrich) was dissolved in 40 mL of dimethylformamide (99.88%, Alfa Aesar, hereafter DMF),

and 1.62 g of benzimidazole (C7H6N2, 98%, Sigma-Aldrich, hereafter b-Im) and 0.01 g of

sodium formate (HCOONa, 99%, Sigma-Aldrich) was dissolved in 40 mL of DMF (solution B).

A home-made α-Al2O3 disk was soaked in the solution A for 1 hr. The disk saturated with the

zinc salt solution was positioned vertically in a Teflon-lined autoclave containing the solution B.

Then, the autoclave was subjected to solvothermal synthesis for 4 h at 85⁰C. After synthesis, the

membrane sample was rinsed with DMF and ethanol several times and immersed in ethanol for

solvent exchange under stirring for 1 day. Afterward, one side of the supported membranes was

polished with sand paper manually since films are formed on both sides of supports. Additional

solvent exchange of 4 days was conducted before drying at room temperature for 48 h.

S19

Figure S13. SEM images of a SIM-1 membrane (a, b) and a ZIF-7 membrane (c, d)

(a) (b)

(c) (d)

S20

Figure S14. XRD patterns of a SIM-1 membrane (a) and a ZIF-7 membrane (b)

* Due to the lack of the crystallographic information of SIM-1, SIM-1 powders were synthesized by

following the previous report2 and its XRD pattern is compared to confirm the SIM-1 phase.

5 10 15 20 25 30

Powders*

Intensity (a.u.)

2 theta (degree)

A SIM-1 membrane

α −Al2O

3

5 10 15 20 25 30

α −Al2O

3

Simulated pattern

A ZIF-7 membrane

Intensity (a.u.)

2 theta (degree)

(a)

(b)

S21

References

(1) Shah, M.; Kwon, H. T.; Tran, V.; Sachdeva, S.; Jeong, H.-K. Microporous Mesoporous Mater. 2013, 165,

63.

(2) Aguado, S.; Canivet, J.; Farrusseng, D. Chem. Commun. 2010, 46, 7999.