Thiol-ene photopolymerization of vinyl-functionalized metal-organic frameworks towards mixed-matrix membranes

Article abstract of DOI:10.1039/C8TA03803A

We developed a facile methodology for fabricating a free-standing mixed-matrix membrane (MMM) containing covalently incorporated metal-organic framework (MOF) particles up to 60 wt% by utilizing thiol-ene photopolymerization with the MOF consisting of vinyl functionality. Vinyl-functionalized UiO-66 (UiO-66-CH═CH₂) was synthesized from 2-vinyl-1,4-dicarboxylic acid with ZrCl₄, and a free-standing MMM was readily produced by irradiation of a polymerization mixture containing UiO-66-CH═CH₂, poly(ethylene glycol) divinyl ether (PEO-250), pentaerythritol tetra(3-mercaptopropionate) (PETM), 2,2′-(ethylenedioxy)diethanethiol (EDDT), and 2,2-dimethoxy-2-phenylacetophenone (DMPA) as a photoradical initiator. Assorted analyses combining FTIR, thermogravimetric analysis, scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction strongly supported the fact that the desired MMM containing well-dispersed UiO-66-CH═CH₂ particles was successfully produced by C-S bond formation, which provided strong union of the MOF with the polymer matrix without interfacial voids. The produced MMM was highly flexible and showed improved mechanical properties as compared to the pristine polymeric membrane, indicating that the covalently immobilized UiO-66-CH═CH₂ particles were homogeneously distributed in the polymer matrix. Gas permeability across the MMM was significantly enhanced compared with the pristine polymeric membrane as diffusion of the gas molecules was facilitated in the porous space in the MOF.

Full text of DOI:10.1039/C8TA03803A

View Article Online
View Journal
Journal of
Materials Chemistry A
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: C.
Satheeshkumar, H. J. Yu, H. Park, M. Kim, J. S. Lee and M. Seo, J. Mater. Chem. A, 2018, DOI:
10.1039/C8TA03803A.
This is an Accepted Manuscript, which has been through the
Volume
4 Number 1 7 January 2016 Pages 1–330
Royal Society of Chemistry peer review process and has been
accepted for publication.
Journal of
Materials Chemistry A
Accepted Manuscripts are published online shortly after
Materials for energy and sustainability
www.rsc.org/MaterialsA
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 2050-7488
PAPER
Kun Chang, Zhaorong Chang et al.
Bubble-template-assisted synthesis of hollow fullerene-like
MoS2 nanocages as a lithium ion battery anode material
rsc.li/materials-a

Please do not adjust margins
Journal of Materials Chemistry A
Page 1 of 9
View Article Online
DOI: 10.1039/C8TA03803A
Journal Name
ARTICLE
Thiol-Ene Photopolymerization of Vinyl-Functionalized Metal-
Organic Framework towards Mixed-Matrix Membranes
Chinnadurai Satheeshkumar,a,† Hyun Jung Yu,b,† Hyojin Park,c,† Min Kim,*c Jong Suk Lee,*b
Myungeun Seo*a,d
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
We developed a facile methodology for fabricating a free-standing mixed-matrix membrane (MMM) containing covalently
incorporated metal-organic framework (MOF) particles up to 60 wt% by utilizing thiol-ene photopolymerization with MOF
consisting of vinyl functionality. Vinyl-functionalized UiO-66 (UiO-66-CH=CH2) was synthesized from 2-vinyl-1,4-dicarboxylic
acid with ZrCl4, and a free-standing MMM was readily produced by irradiation of a polymerization mixture containing UiO-
66-CH=CH2, poly(ethylene glycol) divinyl ether (PEO-250), pentaerythritol tetra(3-mercaptopropionate) (PETM), 2,2’-
(ethylenedioxy)diethanethiol (EDDT), and 2,2-dimethoxy-2-phenylacetophenone (DMPA) as a photoradical initiator.
Assorted analyses combining FTIR, thermogravimetric analysis, scanning electron microscopy, energy dispersive X-ray
spectroscopy, and X-ray diffraction strongly supported that the desired MMM containing well-dispersed UiO-66-CH=CH2
particles was successfully produced by C-S bond formation between the MOF surface and the polymer matrix, which
provided strong union without interfacial voids. The produced MMM was highly flexbile and showed improved mechanical
properties as compared to the pristine polymeric membrane, indicating that the covalently immobilized UiO-66-CH=CH2
particles were homogeneously distributed in the polymer matrix. Gas permeability across MMM was significantly
enhanced when it compared with the pristine polymeric membrane as diffusion of the gas molecules was facilitated in the
porous space in MOF.
www.rsc.org/
targeted at large industrial scale applications.5
Introduction
Significant attention has been paid on dispersing MOF into
polymer matrix to fabricate mixed-matrix membranes
The Metal-organic frameworks (MOFs) are an emerging class
of porous crystalline materials promising for molecular
storage, separation, and catalysis. In addition to their diverse
and controllable micropore structures, facile and versatile
modification of the chemical properties can be realized by
molecular engineering of the constituting ligands.1-4
Especially, their excellent molecular sieving behavior has
promoted extensive research on developing polycrystalline
membranes for gas separations. As a crystalline material,
however, MOFs are typically obtained in the form of large
crystals or micro-crystalline powders and inherently fragile,
brittle, and not malleable. Such inferior mechanical properties
and low processability have been serious issues in utilization of
MOF to developing defect-free polycrystalline membranes for
(MMMs) as a composite material to combine the adventurous
pore characteristics of MOF with superior mechanical
performances provided by the polymer.6-9 The well-defined
micropores in MOFs can sieve out relatively large penetrants
while accelerating the permeation of smaller components due
to free diffusion through the pores.5 In general, MOFs exhibit
better adhesion with polymer chains than conventional
molecular sieves including zeolites and carbon molecular
sieves due to the presence of organic ligands. However, initial
attempts to produce MMMs by using polymer binders to
compatibilize MOF particles with the polymer matrix has been
challenging due to the low compatibility between MOF and the
host polymer, often resulting in undesirable gas selectivity.10, 11
Agglomeration and void formation at the MOF/polymer
interface is indicative of a heterogeneous distribution of MOF
particles, preventing the fabrication of MMMs with high MOF
loading.12-16
To circumvent the compatibility and interfacial adhesion
issue, interfacial engineering of the MOF/polymer interface is
crucial.17 Integration of MOF in MMMs by covalent bonding
appears to be a particularly promising method for the
construction of defect-free interfaces with strong adhesion.
This requires chemical modification of MOF to introduce
polymerizable functional groups to the ligand exposed to the
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2018, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry A
Page 2 of 9
View Article Online
DOI: 10.1039/C8TA03803A
ARTICLE
MOF surface. Then the modified MOF can be added in the conditions.29,
Journal Name
30
Moreover, UiO-66 can be rather easily
polymerization mixture to produce a chemically cross-linked functionalized by simply incorporating BDC ligands carrying
MMM where MOF particles are covalently joined to the functional groups such as double bond in the MOF synthesis.18,
28
polymer matrix. In this case, high loading of MOF (> 30 wt%) is
Thus we synthesized vinyl-functionalized UiO-66 (UiO-66-
possible without aggregation or void formation. For instance, CH=CH2) and directly introduced into a polymerization mixture
Zhang et al. reported post-modification of UiO-66-NH2 (UiO = containing multivalent thiols and PEG-containing diene, and
University of Oslo) containing amine groups with methacrylic copolymerized in the presence of photoradical initiator under
anhydride to introduce methacrylate moieties on the MOF UV irradiation. The double bond in the ligand of UiO-66-
surface.18 MMM with 60% MOF loading could be prepared by CH=CH2 allowed us to covalently incorporate the MOF particles
copolymerization with methacrylate monomers via via the thiol-ene reaction. PEG was chosen as the main
photoinduced free radical polymerization and was shown component of the polymer matrix because of its affinity to CO2
useful for Cr6+ removal from water using n-butylmethacrylate via strong dipole-quadrupole interaction. We demonstrate the
as a comonomer. In another example by Jiang et al., UiO-66- fabrication of defect-free and free-standing MMMs exhibiting
NH2 was again reacted with methacrylic anhydride and uniform particle distribution while containing up to 60 wt% in
subjected to thiol-ene polymerization with thiol-functionalized MOF content. The MMM exhibited improved mechanical
polysiloxanes under UV irradiation to produce MMM.19 When properties compared with the neat polymer film by the
Au nanoparticles were further incorporated, the MMM incorporation of UiO-66 as a covalent filler. We further
exhibited catalytic reactivity to Knovenagel condensation. UiO- analyzed transport properties of different gases including CH4,
66-NH2 has been also introduced to the polymerization CO2, N2, and O2 to explore utility of the MMM as a CO2
mixture for a polymer of intrinsic microporosity (PIM-1) to separation membrane. The 60 wt% UiO-66(Zr) containing
produce chemically cross-linked MMM.20 A recent paper by MMM exhibited high CO2 permeability of 429 barrer probably
Yao et al. describes synthesis of UiO-66 from a new MOF ligand due to free diffusion through the pores of UiO-66(Zr) with
containing 2-hydroylethylimidazolium bromide and reaction of moderate CO2/N2 and CO2/CH4 selectivity of 13.1 and 8.5,
the functional MOF with isocyanate-terminated polyurethane respectively. We believe our finding nicely demonstrates how
oligomers to produce the chemically cross-linked MMM useful chemical modification of MOF can open up new possibilities in
for CO2 conversion.21 Nonetheless, more efforts are needed to generating composite materials with improved performances.
further develop a process enabling direct introduction of
polymerizable moieties on the MOF ligand and fabrication of
2. Experimental Section
free-standing MMMs via simple and straightforward
polymerization methods.
Materials. Unless otherwise noted, chemicals purchased from
Here we report utilization of thiol-ene chemistry in the
chemical vendors were used as received. Pentaerythritol
fabrication of MMMs containing a functional MOF, which
tetra(3-mercaptopropionate)
(PETM)
(>90.0%),
2,2’-
carries a polymerizable double bond on the aromatic ligand.
Thiol-ene reaction in the presence of a radical initiator has
been well-known as one of click reactions that efficiently forms
a C-S bond between a double bond and a thiol in mild
condition.22 Because of its excellent reaction efficiency, high
functional group tolerance, and versatile combination of
reaction components, thiol-ene reaction has been well suited
for the synthesis of dendrimers23 and high molar mass
polymers24 as well as fabrication of cross-linked free-standing
polymer membranes.25 Particularly for the cross-linked
polymer membranes, thiol-ene polymerization offers uniform
network formation with controllable cross-linking density.26
For example, Kwisnek et al. has shown that poly(ethylene
glycol) (PEG)-based membranes can by readily synthesized by
thiol-ene photopolymerization and applied as a free-standing
membrane for CO2 separation.27
(ethylenedioxy)diethanethiol (EDDT)
(
≥97%), and 2,2-
dimethoxy-2-phenylacetophenone (DMPA) (>98.0%) were
received from TCI (Tokyo, Japan). Poly(ethylene glycol) divinyl
ether (average Mn = 250 g mol-1) (PEO-250), Lindlar catalyst (5
wt% palladium) and bis(triphenylphosphine)palladium chloride
(>98.0%), and quinoline (>98.0%) were purchased from Sigma-
Aldrich (St. Louis, MO, USA). 2-Bromoterephthalic acid
(>97.0%),
(trimethylsilyl)acetylene
(>98.0%),
tetra-n-
butylammonium fluoride (1 M solution in THF), zirconium
chloride (>99.5%) were received from Alfa Aesar (Thermal
Fischer Scientific, Waltham, MA, USA). Concentrated HCl
aqueous solution (approx. 35%) was purchased from Samchun
(Pyeongteck, Korea). Triethylamine (>98.0%) was obtained
from Junsei chemical (Tokyo, Japan). HPLC grade solvent N,N-
dimethylformamide (DMF) was purchased from J. T. Baker
(Center Valley, PA, USA) and purified using
a solvent
To directly adopt this methodology for MMM synthesis
without laborious MOF post-functionalization steps,10 we
synthesized UiO-66(Zr) containing a vinyl group per ligand by
utilizing 2-ethenyl-1,4-benzenedicarboxylic acid (BDC-vinyl) as
a ligand.28 As a highly oxo-philic Zr(IV)-based MOF consisting
of Zr6O4(OH)4(CO2)12 secondary building unit (SBU) nodes and
benzene-1,4-dicarboxylate (BDC) ligands, UiO-66 is known to
be relatively stable in aqueous and acidic media and
synthesized under simple solvothermal or hydrothermal
purification system (C&T International, Suwon, Korea).
Instrumentation. Powder X-ray diffraction (PXRD) for MOF was
obtained on a Bruker D8 Discover at 40 kV, 40 mA for CuKa (1
= 1.5406 Å), with a scan speed of 1 sec/step, a step size of
0.02° in 2θ, and a 2θ range of 5-55°. XRD data for MMM were
measured using a strong synchrotron X-ray source (0.9000 Å)
in Pohang Accelerator Laboratory (2D SMC beamline)
equipped with 2D area CCD detector. The MMM sample was
2 | J. Name., 2018, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry A
Page 3 of 9
View Article Online
DOI: 10.1039/C8TA03803A
Journal Name
ARTICLE
prepared in a 0.5 mm borosilicate capillary and mounted on a chromatography (n-hexane/ethyl acetate 20/1) gave BDCE-
goniometer head. The diffraction data was collected using a TMS-ethylnyl as a pale yellow solid (2.79 g, 96%).
Debye-Scherrer mode with a detector distance of 180 mm. The BDCE-ethynyl: To a solution of BDCE-TMS-ethynyl (2.50 g, 8.6
collected 2D diffraction image was merged and processed mmol) in THF 40 mL was added tetra-n-butylammonium
using a fit2d program. 1H and 13C NMR of ligand and MOFs fluoride (TBAF, 10 mL, 1M THF solution). The mixture was
were obtained on Bruker FT AM 400 or 500 (400 MHz or 500 stirred at room temperature for an hour. H2O was added and
MHz). Chemical shifts were quoted in parts per million (ppm) the mixture was extracted with DCM (2×50 mL). The combined
referenced to the appropriate solvent peak or 0 ppm for TMS. organic phases were dried over MgSO4. Removal of the solvent
13C NMR was fully decoupled by broad band decoupling. For under reduced pressure and purification by flash column
MOF digestion NMR sample, approximately 10 mg of MOF chromatography (n-hexane/ethyl acetate 10/1) gave BDCE-
material was dried under vacuum and digested with sonication ethynyl as a pale red solid (1.53 g, 70%).
in 590 μL of DMSO-d6 and 10 μL of HF aqueous solution.
BDCE-vinyl: To a solution of BDCE-ethylnyl (327 mg, 1.5 mmol)
Fourier transform infrared (FTIR) spectra were obtained on in CH2Cl2 (6 mL), n-hexane (6 mL) and EtOH(6 mL) was added
a Bruker Alpha FTIR spectrometer using a Platinum attenuation quinoline (1.1 mL, 1.5 mmol) and Lindlar catalyst (60 mg, 0.03
total reflection (ATR) single reflection module. Scanning mmol). After stirring the solultion for 20 min, the flask was
electron microscope (SEM) images were obtained on Hitachi fitted with rubber septum and the gas volume was repeatedly
SU8230 instrument with a 3.0 kV accelerating voltage and an evacuated and flushed with H2. The mixture was stirred for 2 h
upper secondary electron detector. Energy dispersive X-ray at room temperature under an H2 atmosphere. The mixture
spectroscopy (EDS) was performed on the Hitachi SU8230 SEM was filtered over a celite plug and the solvent was removed
with 10 kV condition. Samples were sputter coated with ∼3 nm under reduced pressure. Purified to by column
of Os prior to imaging. Photoirradiation was conducted with a chromatography (n-hexane/ethyl acetate 20/1) gave BDCE-
200-W Super Pressure Hg lamp (Lumatec Superlite SUV-DC-P) vinyl as a colorless solid (228 mg, 69%).
through a lightguide and an UV color filter (315 < λ < 390 nm). BDC-vinyl: BDCE-vinyl (220 mg, 1.0mmol) was dissolved in THF
UV intensity at the tip of the lightguide was ca. 6500 mW cm-2. (10 mL) and aqueous 4% KOH solution (10 mL). The solution
For fabrication of large-area films (20 cm × 20 cm), JHCI-102S- was stirred at room temperature overnight. The THF was
R3 UV tape curing system (JECO, Anyang, Korea) equipped removed under reduced pressure and remaining aqueous
with 1kW UV lamp (320 < λ < 420 nm) was used. Nitrogen phase was acidified with 1.0 M HCl aqueous solution. The
sorption isotherms were acquired on
a
Mirae SI precipitate was collected by filtration, and washed with water.
nanoPOROSITY-XQ analyzer at the temperature of liquid The desired compound was obtained by air drying. (165 mg,
nitrogen (77.3 K). Samples were loaded in 6 mm stems and 86%).
degassed at room temperature for
∼
20
h
before Preparation of UiO-66-CH=CH2. BDC-vinyl (73 mg, 0.38 mmol),
measurement. Pore size distribution data were calculated from ZrCl4 (63 mg, 0.27 mmol), DMF (7.5 mL), and HCl (0.5 mL) were
N2 adsorption isotherm based on non-local density function placed in a vial, which was then capped with vial cap and
theory (NLDFT)31, 32 model using 3Flex program (Micromeritics sonicated until all reagents had dissolved. Then the solution
Instrument Corp.). The pore size distribution was regularized was heated at 80 °C for 12 h. The microcrystalline powders
by choosing λ = 0.032 as a user-adjustable parameter. Specific were isolated by centrifugation. Residual DMF and ligand
surface area was estimated by multipoint Brunauer-Emmett- precursors were removed from the material by washing with
Teller (BET) analysis (between 0.05 < P/P0 < 0.35).33
20 mL DMF three times. Then the solids were washed with
3×20 mL of MeOH, after which the solids were left to soak in
20 mL MeOH for one day. The solids were centrifuged and
dried under vacuum.
Synthesis of MOF-Ligand (BDC-vinyl).
BDCE-Br: 2-Bromoterephthalic acid (4.9 g, 20 mmol) was
dissolved in 200 mL of methanol and conc. H2SO4 (10 mL) was
added by dropwise. The mixture was heated to reflux
overnight. After cooling to room temperature, MeOH was
removed by evaporation and then 200 mL of ethyl acetate was
added. The solution was washed with 1.0 M K2CO3. Then the
organic solution was dried with MgSO4, the desired compound
was obtained after removal of solvent in 66% yield.
Preparation of MMMs via thiol-ene photopolymerization. A
polymerization mixture of UiO-66-CH=CH2, PEO-250, PETM,
EDDT, and DMPA as a photoradical initiator was prepared
using DMF as a solvent. In the polymerization mixture, the
weight fraction of UiO-66-CH=CH2 was varied from 0 to 60%
while the weight ratio of PEO-250:PETM:EDDT was fixed as
54:26:20. For instance, the polymerization mixture for
MMM(35%) was composed of UiO-66-CH=CH2 (105 mg, 0.058
mmol), PEO-250 (105 mg , 0.42 mmol), PETM (50 mg, 0.102
mmol), EDDT (40 g, 0.22 mmol), and DMPA (9 mg, 0.035
mmol) dispersed in DMF (33% (w/v) relative to the UiO-66-
CH=CH2). The mixture was well mixed using a vortex machine,
and then sandwiched between two glass plates followed by
irradiation with UV (365 nm) for 30 min to produce a free-
standing membrane, which was completely dried under
vacuum for overnight.
BDCE-TMS-ethynyl
:
Under
N2,
a
solution
of
tremethylsilylacetylene (1.52 mL, 11 mmol) was added to a
solution of 2-bromoterephthalate (2.73 g, 10 mmol), PPh3 (52
mg, 0.20 mmol), CuI (19 mg, 0.10 mmol), Pd(PPh3)2Cl2 (140 mg,
0.20 mmol) and Et3N (15 mL). The mixture was heated at 85 °C
for hours. The mixture was cooled down to room
8
temperature and filtered. Then the solvent were removed
under reduced pressure. Purified to by column
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry A
Page 4 of 9
View Article Online
DOI: 10.1039/C8TA03803A
ARTICLE
As a reference, a MMM containing 20 wt% of pristine UiO-
Journal Name
66 (i.e., without the vinyl groups) was also synthesized
following the procedure described above.
Transport Characterization
. Gas permeation tests were
performed with single component gases including carbon
dioxide (CO2, 99.999%), nitrogen (N2, 99.999%), and methane
(CH4, 99.995%) by using a standard isochoric technique at
different feed pressures and 35 °
C.34 The detailed procedure
was described in our previous work.35 The gas permeability
was obtained by using the Equation (1):
Scheme 1. Synthetic route to BDC-vinyl and UiO-66-CH=CH2.
22,414Vl dp
(1)
P=
×
RTꢀpA dt
suggested a bimodal pore size distribution with two mode
where
(STP) cm cm-2 s-1 cmHg-1),
thickness of the membrane,
P
is the gas permeability in barrer (barrer = 10-10 cm3 diameters of 0.8 and 1.2 nm, which is similar with the data of
V
is the downstream volume,
is the gas constant,
l
is the pristine UiO-66 containing defects.36 The Brunauer-Emmett-
T is the Teller (BET) surface area of UiO-66-CH=CH2 was determined as
R
temperature, Δp is the pressure difference across the 930 m2/g.
membranes, is the effective area of the membranes, and
dp/dt is the change in downstream pressure at steady state. photopolymerization
A
With UiO-66-CH=CH2 in hand, we pursued thiol-ene
of
multifunctional
thiols
and
The average diffusivity,
time-lag method:
D
in cm2 s-1 was obtained by using the multifunctional enes including UiO-66-CH=CH2 as shown in
l2
D =
(2)
6θ
where
l
is the thickness of the membrane and
θ
is the time
lag of permeation. Since the permeability is a product of
diffusivity and solubility, the average solubility in cm3 (STP) cm-
3
cmHg-1 can be obtained from Equation (3).
S = P / D
(3)
Scheme 2. Synthetic route to MMMs with controlled UiO-66-CH=CH2 content via thiol-
ene photopolymerization.
3. Results and Discussion
Scheme 2. For the polymer matrix, we utilized a mixture of
pentaerythritol tetrakis(3-mercaptopropionate) (PETM) and
2,2′-(ethylenedioxy)diethanethiol (EDDT) as multivalent thiols,
and poly(ethylene glycol) divinyl ether (Mn = 250 g mol-1)
(PEO-250) as a PEG-containing diene. Guided by Kwisnek et
al.,27 we set the weight ratio of PEO-250:PETM:EDDT as
54:26:20 to produce highly elastic membranes. Because UiO-
66-CH=CH2 was well dispersed in DMF, we prepared the
polymerization mixture using DMF as a solvent and 2,2-
dimethoxy-2-phenylacetophenone (DMPA) as a photoradical
initiator. Sandwiching the polymerization mixture and
irradiating with UV for 30 min was sufficient to produce MMM
as a well cross-linked and free-standing film.
A synthetic route to 2-ethenyl-1,4-benzenedicarboxylic
acid (BDC-vinyl) and the corresponding vinyl-functionalized
UiO-66 (UiO-66-CH=CH2) is depicted in Scheme
1 (see
Appendix for 1H and 13C NMR spectra of the intermediates and
BDC-vinyl). We pursued an alkynylation-reduction pathway to
install the vinyl group on the aromatic ring since the starting
material 2-bromo-1,4-benzenedicarboxylic acid (BDC-Br) is
commercially available, and BDC-vinyl can be readily obtained
via two reaction steps including Sonogashira cross-coupling
and reduction with Lindlar catalyst followed by relatively
simple separation. Then BDC-vinyl was combined with Zr(IV)Cl4
and HCl (aq) in solvothermal condition using
N,N-
The MMMs were designated based on the weight fraction
of UiO-66-CH=CH2 in the polymerization in the parenthesis,
such as MMM(50%). As a reference, a neat polymer film
without UiO-66-CH=CH2 was also synthesized and denoted
MMM(0). We were able to increase the MOF loading up to
60% while maintaining the integrity of the resulting free-
standing film (Figure S4). It appears that UiO-66-CH=CH2
particles in white color dominate appearance of the MMM
when the MOF content is more than 50%. As the weight
fraction of UiO-66-CH=CH2 increased, FTIR spectra of MMMs
showed a gradual decrease in intensity of the vibrational
dimethylformamide (DMF) as a solvent at 80 °C to produce
UiO-66-CH=CH2 as colorless, microcrystalline powder. UiO-66-
CH=CH2 was found to be a structural analogue of the pristine
UiO-66 evidenced by power X-ray diffraction (PXRD), and the
PXRD pattern was also identical with previously reported UiO-
66-CH=CH2 by Li et al. (Figure S1).28 1H NMR analysis of UiO-66-
CH=CH2 after acid digestion showed that the vinyl functionality
was totally retained in the MOF pore (Figure S2). A nitrogen
sorption isotherm obtained at 77 K indicated that UiO-66-
CH=CH2 was discernable as a type I curve, indicating UiO-66-
CH=CH2 is microporous (Figure S3). Non-local density function
theory (NLDFT) analysis of the nitrogen sorption isotherm
frequency at
∼
1100 cm-1 correponding to C-O linkages in the
4 | J. Name., 2018, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry A
Page 5 of 9
View Article Online
DOI: 10.1039/C8TA03803A
Journal Name
ARTICLE
polymer, which was consistent with the relative decrease in dispersed UiO-66-CH=CH2 particles in the polymer matrix
the polymer fraction (Figure S5). Thermogravimetric analysis without agglomeration (Figure 2a) (see Figure S7 for other
(TGA) data of MMMs indicated that the polymer matrix was MMMs synthesized in this study). The rough texture of the
completely decomposed at the temperature range of 300 – cross-section was attributed to plastic deformation during
400
°C (Figure S6). Based on the weight loss corresponding to sample preparation (See Figure S8 for cross-section SEM
the polymer matrix and filler around 455
°C, estimated the images). Nevertheless, the UiO-66-CH=CH2 particles were
MOF fraction in the MMM. The values were well consistent completely surrounded by the polymer indicating that the
with the fraction of UiO-66-CH=CH2 in the polymerization formation of the thioether linkage was effective in enhancing
mixture, indicating complete conversion of all the monomers the adhesion between the UiO-66-CH=CH2 surface and the
in the polymerization mixture and quantitative incorporation polymer matrix and eliminated interfacial defects. We
of UiO-66-CH=CH2 into MMM. Detailed information on observed that MMMs with up to 60 wt% loading of UiO-66-
composition of the MMMs synthesized in this study is CH=CH2 could be successfully produced without macrophase
summarized in Table S1.
separation thanks to covalent attachment of the MOF particles
to the polymer matrix. In contrast, incorporating 20 and 30
wt% of pristine UiO-66 without vinyl groups in the MMM
synthesis resulted in a highly heterogeneous film accompanied
with severe aggregation of the UiO-66 particles separated
from the polymer matrix, emphasizing the importance of
interfacial engineering via covalent bond formation (Figure S9
and S10).
When immersed in DMF for 1 h at room temperature,
weight loss of MMM(50%) was only 3% and the membrane
totally retained the shape without losing the structural
integrity, indicating that the thiol-ene cross-linked network
reinforced by the covalently bound UiO-66-CH=CH2 was robust
agaist the solvent (Figure S11). Surface morphology of
MMM(50%) after immersing in DMF was virtually
indistinguishable to the pristine film, consistent with stable
adhesion of the MOF particles to the polymer matrix via
Fig. 1. Representative photos of MMM(50%).
1
covalent bond formation (Figure S12). A H NMR spectrum of
Fig. 2. (a) SEM images of MMM(50%). (b) Zr element mapping of MMM (50%).
the sol fraction suggested that incompletely cross-linked
clusters of small molecular weight may be extracted (Figure
S13). Presence of aromatic protons in low intensity suggests
Fig. 3. XRD data of MMM(0), MMM(35%), MMM(50%) and MMM(60%) in comparison
with a physical mixture of UiO-66-CH=CH2 and MMM(0).
Figure 1 shows representative photos of obtained MMM(50%)
after drying. A homogeneous free-standing film could be
readily obtained by irradiation. The dried film was highly
flexible, withstanding significant deformation without
mechanical failure (Figure 1b). Scanning electron microscopy
Fig. 4. A representative strain-stress curve of MMM(50%) (solid line) obtained by
tensile test in comparison with MMM(0) (dashed line).
(SEM) imaging of the MMM
revealed homogeneously
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry A
Page 6 of 9
View Article Online
DOI: 10.1039/C8TA03803A
Journal Name
ARTICLE
Table 1. Single gas transport properties of MMM(0), MMM(35%), and MMM(60%) at 35 °C.
Feed
Pressurea
Sample
PO2b
PCO2
PN2
PCH4
αO2/N2
αCO2/N2
αCO2/CH4
1
3
5
1
3
5
1
3
5
4.5
4.6
76.7
78.4
1.6
1.6
5.1
5.1
2.8
2.9
2.9
2.8
2.7
2.7
1.7
1.9
1.9
47.7
49.0
50.5
38.1
38.9
39.9
13.1
13.4
14.1
15.0
15.3
15.6
17.3
17.5
17.9
8.5
MMM(0)
4.7
80.7
1.6
5.2
5.9
82.0
2.2
4.8
MMM(35%)
5.8
82.4
2.1
4.7
5.7
83.4
2.1
4.7
56.5
62.4
62.8
429.0
444.2
467.7
32.8
33.1
33.1
50.7
54.9
58.7
MMM(60%)
8.1
8.0
aFeed pressure in atm
bPermeability in Barrer, where 1 Barrer = 10-10 cm3 (STP) cm/cm2 s cmHg
small number of UiO-66-CH=CH2 may be bound to the clusters, MMM(0) seem to be dominated by gas condensability (i.e.
but absence of protons corresponding to the double bond in critical temperature, Tc) rather than by gas size (i.e. kinetic
UiO-66-CH=CH2 again supports formation of the thioether diameter) since the CH4 permeability (Tc of 190.6 K and size of
bond by covalently linking UiO-66-CH=CH2 to the polymer.
3.8 Å) was much higher than the N2 permeability (Tc of 126.2 K
Energy dispersive X-ray spectroscopy (EDS) analysis of the and size of 3.64 Å).37 Also, a much higher CO2 permeability
SEM images also indicated homogeneous distribution of Zr was observed compared to other penetrants, which was
element and supported successful formation of thiol-ene attributed to dipole-quadrupole interactions between the
cross-linked MMM (Figure 2b). Synchrotron X-ray diffraction ethylene oxide group of PEO (or EDDT) and CO2.35 MMM(35%)
(XRD) data of MMMs was virtually identical to a physical exhibited CO2 permeability of 82 Barrers with moderate
mixture of UiO-66-CH=CH2 and MMM(0) (i.e., the polymer CO2/N2 and CO2/CH4 selectivity of 38.1 and 17.3, respectively.
matrix), indicating that the micropore structure in UiO-66- The increase in CO2 permeability despite the decrease in PEO
CH=CH2 was totally intact during thiol-ene polymerization content in the MMM by incorporation of UiO-66-CH=CH2 can
(Figure 3).
be explained by the strong interaction between CO2 and the
Figure
4
shows the tensile strain-stress curves of UiO-66 framework combined with free diffusion through the
MMM(50%) in comparison with MMM(0). MMM(50%) pores.38, 39 A slight and continuous increase in both CO2/N2
exhibited significantly improved mechanical properties and CO2/CH4 selectivities with increasing feed pressure
including an ultimate tensile strength of > 3 MPa, an ultimate indicates that polymeric chains in MMM(35%) were well
elongation of 20%, and a Young’s modulus of 59 MPa. 800% adhered to UiO-66-CH=CH2 particles without undesirable
increase in Young’s modulus as well as 130% increase in the interfacial voids due to thiol-ene based crosslinking.
ultimage elongation suggests that UiO-66-CH=CH2 particles MMM(60%) showed siginificantly enhanced permeability for
containing a number of vinyl groups on the surface was all the gas penetrants used in this work. Also, permeation
homogeneously incorporated in the MMM as a covalent filler isotherms of different gas penetrants for MMM(60%)
and improved overall mechanical performances of the exhibited continuous increases in permeabilities with
composite material.
increasing feed pressure. A careful inspection, however,
We examined the single gas transport properties of revealed that the O2/N2 and CO2/N2 selectivity for MMM(60%)
MMMs in comparison with MMM(0) to investigate the effect slightly increased with increasing feed pressure. This tendency
of covalently incorporated UiO-66-CH=CH2 on gas transport. is opposite of that seen in MMMs that exhibit a with “sieve-in-
For MMM(60%), MMM(35%), and MMM(0), transport a-cage” morphology, causes significant reduction in gas
properties of O2, CO2, N2, and CH4 were determined at varying selectivity with increasing feed pressure.40 Thus we interpret
feed pressures as summarized in Table 1. MMM(0), a pristine that no agglomeration-induced interfacial voids exist due to
polymeric membrane, exhibited transport characteristics covalent attachment of UiO-66-CH=CH2 to the polymer matrix
typical for rubbery polymers. Gas transport properties in which is consistent with the SEM analysis. The decrease in
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2018, 00, 1-3 | 6
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry A
Page 7 of 9
View Article Online
DOI: 10.1039/C8TA03803A
Journal Name
ARTICLE
selectivity seen in MMM (60%) can be assumed to be due to largely unchanged at moderate UiO-66-CH=CH2 loadings.44,45
the formation of percolative networks consisting of significant Figure 5 provides a comparison of O2/N2, CO2/N2 and CO2/CH4
amounts of UiO-66-CH=CH2 crystals.41
separation performances with the respective Robeson upper
We are aware that the effective aperture size of UiO-66- bound.46 Noteworthy was that such a high concentration (i.e.,
CH=CH2 may differ from that of the pristine UiO-66, but it is 60 wt%) of MOF nanoparticles were homogeneously blended
beyond the scope of the current work. Nevertheless, in light of with polymeric chains, resulting in moderate CO2/N2 and
the apparent pore size of 6.0 Å for conventional UiO-66 based CO2/CH4 selectivities.
on crystallographic analysis, such a substantial increase in
permeability of all the gas penetrants for MMM(60%) is
associated with free diffusion through the pores of UiO-66.42,43
Conclusions
Thus, the O2/N2, CO2/N2, and CO2/CH4 ideal selectivities remain
We have demonstrated that mixed-matrix membranes
consisting of covalently bound MOF particles can be readily
prepared by thiol-ene photopolymerization of vinyl-
functionalized MOF particles with monomer mixtures. While
retaining the pristine crystalline structure of MOF, up to 60
wt% of the MOF particles were homogeneously dispersed in
the MMM without defects due to C-S bond formation at the
MOF/polymer interface. By including highly flexible and CO2-
philic PEG moieties in the polymer matrix, the produced
MMMs showed improved mechanical properties and higher
gas permeability compared with the pristine polymeric
membrane. Considering the vast tunability of pore
characteristics and chemical properties of MOFs, we believe
our current proof-of-concept work suggests promise of this
methodology for further development of gas separation
membranes with high MOF loading.
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
This research was supported by the Science Research Center
(2016R1A5A1009405; M. K.) through the National Research
Foundation of Korea (NRF) funded by the Ministry of Science
and ICT. The XRD experiment for MMM sample at the PLS-II,
2DSMC beamline was supported in part by MSIP and POSTECH.
C. S. and M. S. thank financial support from BK21 plus program
through NRF funded by the Ministry of Education of Korea.
Notes and references
1
2
H. Li, M. Eddaoudi, M. O’Keeffe and O. M. Yaghi, Nature
1999, 402, 276-279.
G. Ferey, C. Serre, C. Mellot-Draznieks, F. Millange, S. Surble,
J. Dutour and I. Margiolaki, Angew. Chem. 2004, 116, 6456-
6461.
3
H. Furukawa, K. E. Cordova, M. O'Keeffe and O. M. Yaghi,
Science, 2013, 341, 1230444.
4
5
C. Janiak and J. K. Vieth, New J. Chem. 2010, 34, 2366-2388.
M. S. Denny Jr., J. C. Moreton, L. Benz and S. M. Cohen, Nat.
Rev. Mater. 2016, 1, 16078.
6
M. S. Denny Jr. and S. M. Cohen, Angew. Chem. Int. Ed. 2015,
54, 9029-9032.
Fig. 5. Single gas separation performance of (a) O2/N2, (b) CO2/N2 and (c) CO2/CH4
in MMM compared with the respective Robeson upper bound (2008).
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
Please do not adjust margins

Please do not adjust margins
Journal of Materials Chemistry A
Page 8 of 9
View Article Online
DOI: 10.1039/C8TA03803A
ARTICLE
Journal Name
7
G. W. Peterson, A. X. Lu, M. G. Hall, M. A. Browe, T. Tovar 37 Y. Yampolskii, I. Pinnau and B. Freeman, Materials science of
and T. H. Epps III, ACS Appl. Mater. Interfaces 2018, 10, 6820-
6824.
membranes for gas and vapor separation, John Wiley &
Sons, New Jersey, 2006.
8
9
H. Gong, T. H. Nguyen, R. Wang and T. –H. Bae, J. Membr. 38 Q. Huang, J. Ding, X. Huang, X. Wei and W. Wang, Energy
Sci. 2015, 495, 169-175. Procedia 2017, 105, 4395-4401.
B. Zornoza, A. Martinez-Joaristi, P. Serra-Crespo, C. Tellez, J. 39 S. Biswas and P. V. D. Voort, Eur. J. Inorg. Chem. 2013, 12
,
Coronas, J. Gascon and F. Kapteijn, Chem. Commun. 2011,
47, 9522-9524.
10 J. Shen, G. Liu, K. Huang, Q. Li, K. Guan, Y. Li and W. Jin, J.
Membr. Sci. 2016, 513, 155-165.
11 B. Zornoza, C. Tellez, J. Coronas, J. Gascon and F. Kapteijn,
Microporous Mesoporous Mater. 2013, 166, 67-78.
2154-2160.
40 P. Kumar, S. Kim, J. Ida, V. V. Guliants, Ind. Eng. Chem. Res.
2008, 47, 201-208.
41 N. C. Su, D. T. Sun, C. M. Beavers, D. K. Britt, W. L. Queen, J. J.
Urban, Energy Environ. Sci. 2016, 9, 922-931.
42 H. R. Abid, J. Shang, H. –M. Ang and S. Wang, Int. J. Smart.
12 H. Ren, J. Jin, J. Hu and H. Liu, Ind. Eng. Chem. Res. 2012, 51
10156-10164.
13 Y. Dai, J. R. Johnson, O. Karvan, D. S. Sholl and W. J. Koros, J.
Membr. Sci. 2012, 401-402, 76-82.
14 M. Liu, L. Wang, X. Zheng and Z. Xie, ACS Appl. Mater.
,
Nano Mater. 2013, 4, 72-82.
43 G. E. Cmarik, M. Kim, S. M. Cohen and K. S. Walton, Langmuir
2012, 28, 15606-15613.
44 S. J. D. Smith, B. P. Ladewig, A. J. Hill, C. H. Lau, M. R. Hill, Sci.
Rep. 2015, 5, 7823.
Interfaces 2017,
9
, 41512-41520.
45 O. G. Nik, X. Y. Chen, S. Kaliaguine, J. Membr. Sci. 2012, 413-
414, 48-61.
Guigner, N. B. McKeown, K. J. Msayib, M. Carta, R. Malpass- 46 L. M. Robeson, J. Membr. Sci. 2008, 320, 390-400.
15 M. Benzaqui, R. Semino, N. Menguy, F. Carn, T. Kundu, J. –M.
Evans, C. L. Guillouzer, G. Clet, N. A. Ramsahye, C. Serre, G.
Maurin and N. Steunou, ACS Appl. Mater. Interfaces 2016, 8,
27311-27321.
16 R. Lin, L. Ge, L. Hou, E. Strounina, V. Rudolph and Z. Zhu, ACS
Appl. Mater. Interfaces 2014, , 5609-5618.
17 R. Lin, B. V. Hernandez, L. Ge and Z. Zhu, J. Mater. Chem. A
2018, , 293-312.
6
6
18 Y. Zhang, X. Feng, H. Li, Y. Chen, J. Zhao, S. Wang, L. Wang
and B. Wang, Angew. Chem. 2015, 127, 4333-4337.
19 W. –L. Jiang, L. –G. Ding, B. –J. Yao, J. –C. Wang, G. –J. Chen,
Y. –A. Li, J. –P. Ma, J. Ji, Y. Dong, and Y. –B. Dong, Chem.
Commun. 2016, 52, 13564-13567.
20 N. Tien-Binh, D. Rodrigue and S. Kaliaguine, J. Membr. Sci.
2018, 548, 429-438.
21 B.-J. Yao, L. –G. Ding, F. Li, J.-T. Li, Q.-J. Fu, Y. Ban, A. Guo and
Y. –B. Dong, ACS Appl. Mater. Interfaces 2017,
38930.
9, 38919-
22 C. E. Hoyle and C. N. Bowman, Angew. Chem. Int. Ed. 2010,
49, 1540-1573.
23 K. L. Killops, L. M. Campos and C. J. Hawker, J. Am. Chem.
Soc. 2008, 130, 5062-5064.
24 A. B. Lowe, Polym. Chem. 2014, 5, 4820-4870.
25 L. Kwisnek, M. Kaushik, C. E. Hoyle and S. Nazarenko,
Macromolecules 2010, 43, 3859-3867.
26 J. J. Cash, T. Kubo, A. P. Bapat and B. S. Sumerlin,
Macromolecules 2015, 48, 2098-2106.
27 L. Kwisnek, J. Goetz, K. P. Meyers, S. R. Heinz, J. S. Wiggins
and S. Nazarenko, Macromolecules 2014, 47, 3243−3253.
28 Y. Li, X. Zhang, L. Zhang, K. Jiang, Y. Cui, Y. Yang and G. Qian,
J. Solid State Chem. 2017, 255, 97-101.
29 M. Kim and S. M. Cohen, CrystEngComm. 2012, 14, 4096-
4104.
30 X. Liu, N. K. Demir, Z. Wu and K. Li, J. Am. Chem. Soc. 2015,
137, 6999-7002.
31 P. I. Ravikovitch, A. V. Neimark, J. Phys. Chem. B., 2001, 105
,
6817-6823.
32 A. A. Barkhordarian, C. J. Kepert, J. Mater. Chem. A, 2017, 5,
5612-5618.
33 S. Brunauer, P. H. Emmett and E. Teller, J. Am. Chem. Soc.
1938, 60, 309-319.
34 H. An, S. Park, H. T. Kwon, H. –K. Jeong and J. S. Lee, J.
Membr. Sci. 2017, 526, 367-376.
35 S. Park, A. S. Lee, Y. S. Do, S. S. Hwang, Y. M. Lee, J. –H. Lee
and J. S. Lee, Chem. Commun. 2015, 51, 15308-15311.
36 S.-J. Lee, S. Kim, E.-J. Kim, M. Kim, Y.-S. Bae, Chem. Eng. J.
2018, 335, 345-351.
8 | J. Name., 2018, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 9 of 9
Journal of Materials Chemistry A
View Article Online
DOI: 10.1039/C8TA03803A
Table of Contents
Thiol-ene ‘click’ photopolymerization methodology for the ‘covalent’ connection between vinyl-
functionalized metal-organic framework (MOF) and the polymer matrix