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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: [email protected].
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.
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)