Vesicles-shaped MOF-based mixed matrix membranes with intensified interfacial affinity and CO2 transport freewayVesicles-shaped MOF-based mixed matrix membranes with intensified inter facial affinity and CO2 transport freeway
Rui Ding, Yan Dai, Wenji Zheng, Xiangcun Li, Xiaoming Yan, Yi Liu, Xuehua Ruan, Shaojie Li, Xiaochen Yang, Kai Yang, Gaohong He
PII: S1385-8947(21)00404-6 DOI: https://doi.org/10.1016/j.cej.2021.128807 Reference: CEJ 128807
To appear in: Chemical Engineering Journal
Received Date: 30 October 2020 Revised Date: 18 January 2021 Accepted Date: 31 January 2021
Please cite this article as: R. Ding, Y. Dai, W. Zheng, X. Li, X. Yan, Y. Liu, X. Ruan, S. Li, X. Yang, K. Yang, G. He, Vesicles-shaped MOF-based mixed matrix membranes with intensified interfacial affinity and CO2
transport freeway, Chemical Engineering Journal (2021), doi: https://doi.org/10.1016/j.cej.2021.128807
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© 2021 Published by Elsevier B.V.
interfacial affinity and CO2 transport freeway
Rui Dinga, Yan Daia,c, Wenji Zhenga,b*, Xiangcun Lia, Xiaoming Yanb, Yi Liua,
Xuehua Ruanb, Shaojie Lib, Xiaochen Yangb, Kai Yanga, Gaohong Hea,b*
a State Key Laboratory of Fine Chemicals, R&D Center of Membrane Science and
Technology, School of Chemical Engineering, Dalian University of Technology,
Dalian, 116023, P. R. China
b State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian
University of Technology, Panjin, 124221, P. R. China
c Liaoning Key Laboratory of Chemical Additive Synthesis and Separation, Panjin
Institute of Industrial Technology, Dalian University of Technology, Panjin 124221,
Liaoning, China
Corresponding author:
2
Abstract
The trade-off between gas permeability and selectivity represents a huge
challenge for membrane separation. In this work, we design unique polystyrene-
acrylate (PSA) modified hollow ZIF-8 (PHZ) nanospheres via a facile hard template-
incomplete etching strategy as fillers for mixed matrix membranes (MMMs). In the
vesicles shaped PHZ, the hollow core builds a low-resistance CO2 transport freeway,
leading to improved CO2 permeability. Meanwhile, the outside PSA layer intensifies
the interface affinity between ZIF-8 and Pebax through molecular chains
entanglements and hydrogen bonding, enhancing membrane selectivity. Through
controlling the PSA etching process, both the hollow core with tunable size and the
outside PSA layer with adjustable thickness are achieved. The 10 wt. % PHZ-2/Pebax
MMMs present the best performance with a CO2 permeability of 172.4 Barrer and
CO2/N2 selectivity of 87.9. The higher CO2/N2 selectivity proves that the PSA layer
on the PHZ has better compatibility with Pebax. The higher CO2 permeability is
attributed to the low-resistance hollow core. The gas separation performance of PHZ-
based MMMs not only well exceeded the 2008 Robeson upper-bond line but also was
superior to those of other published MOF-based MMMs. The concept of vesicle-
shaped PHZ paves a way to concurrently enhance both the gas permeability and
selectivity of MMMs.
3
1. Introduction
The capture and storage of CO2, a major greenhouse gas as well as an important
carbon resource, has been urgently required for environmental protection and
sustainable development. As a new technology combining the advantages of polymer
membrane and inorganic membrane, mixed matrix membranes (MMMs) have been
widely developed for the CO2 capture and much more appealing results have been
acquired over the past years. [1-3] Particularly, metal-organic framework (MOF)-
based mixed matrix membranes have been demonstrated as a prospective way to
capture CO2, and been expected to overcome Robeson’s upper bound due to the
abundant micropores and organic linkers in MOFs. [4, 5] However, poor interfacial
compatibility between MOFs and polymer matrix remains a critical issue resulting in
CO2 separation performance far from the ideal situation. [6, 7]
Recently great efforts have been devoted to effective interface engineering
between MOFs and polymer, such as filler geometry, [8, 9] in-situ synthesis [10] and
surface modification. [11-13] Benefiting from operability and universality, surface
modification strategy, including functional group modification, hydrocarbyl chain
modification, and polymer modification, has been extensively studied. In general,
functional groups, such as amino, carboxyl or hydroxyl, etc. are used to modify MOFs
to improve the affinity between MOFs and polymer [14] or to cross-link with the
matrix to eliminate interfacial defects. [15] Moreover, hydrocarbyl chains including
alkyl and aromatic on MOFs could form hydrogen bonds or π-π stacking with
polymer to improve interfacial compatibility. So far various polymers, such as PI and
4
PEI, have been used to decorate MOFs to modify the interface. Besides the
electrostatic and hydrogen bonding interaction between MOFs and membrane matrix,
[16] unique segment interactions between the modified polymer and membrane
matrix also enable to enhance the interface compatibility. [17] However, in most
cases, the gas selectivity in most reported MMMs is greatly improved at the expense
of reducing gas permeability. For further improving the permeability, MOFs with
core-shell [18] and hollow structure [19] were introduced into MMMs to provide low-
resistance transport pathway for gas molecules. Nevertheless, as mentioned above, the
increase in permeability usually sacrifices some selectivity.
Aiming at concurrently improving the gas permeability and selectivity, based on
the goal of one-bullet-two-objects, herein we present a facile hard template-
incomplete etching strategy to synthesize a special polystyrene-acrylate (PSA)
modified hollow ZIF-8 (PHZ) in one step. This unique structure not only intensifies
the interface affinity, but also provides a low-resistance CO2 transport channel. As
illustrated in Scheme S1, PSA is first used as a hard template to allow ZIF-8 to grow
on its outer surface. Through controlling the PSA etching process, hollow core with a
tunable size is obtained. Meanwhile, residual PSA molecules penetrate through the
interval space among ZIF-8 nanoparticles and adhere to hollow ZIF-8 nanospheres to
form an outer PSA coating layer. With this method the thickness of the coating layer
can be easily controlled by adjusting the PSA etching time. The gas separation
mechanism of PHZ/MMM is shown in Scheme 1. With the help of functional PSA
layer, the PHZ can be readily dispersed into polymer matrix (shown in Scheme 1 left).
5
Different from the ZIF-8/Pebax MMM with interfacial defects (white parts), PSA
molecular chains outside PHZ entangle with Pebax (red parts and enlarged view) and
the hydrogen bonding between Pebax and PHZ is formed (imine groups and carboxyl
groups, carbonyl groups and carboxyl groups, enlarged view). The hydrogen bonding
can reinforce the interfacial compatibility between PHZ and Pebax, resulting in less
interface defects and thus considerable improvements in selectivity. In addition,
benefiting from the hollow structure, the effective gas mass transfer distance (DE=a +
b + c) of PHZ based MMMs is shorter than the normal mass transfer distance (DN) of
ZIF-8 based MMMs, resulting in higher gas permeability of PHZ-based MMM. As a
result, the synergistic effect of PSA modification and hollow structure leads to
simultaneous improvements in gas selectivity and permeability.
DE: Effective gas mass transfer distance (DE =a + b + c) DN: Normal gas mass transfer distance
Scheme 1 Schematic diagram of gas separation mechanism of PHZ-based MMM (left) and
ZIF-8-based MMM (right).
2. Experimental
2.1 Materials
Commercial Pebax MH 1657 was used as the polymer for preparation of
MMMs. Sodium dodecyl sulfate (SDS, C12H25SO4Na, 99%), potassium persulfate
(KPS, K2S2O8, 99%), styrene (C8H8, 99.5%), acrylic acid (C3H4O2, 99.5%), methanol
(CH3OH, 99%), sodium bicarbonate (NaHCO3, 98%) and N,N-dimethylformamide
(DMF, C3H7NO, 99%) were purchased from Sinopharm Chemical Reagent Co., Ltd.
Zinc nitrate hexahydrate (Zn(NO3)2•6H2O, 98%), 2-methylimidazole (Hmim, C4H6N2,
98%) were purchased from Aladdin. All solvents and chemicals were used without
further purification.
Nanosized PSA particles were synthesized via an emulsion polymerization
method as published with some modification. [20] Typically, 100 mL deionized water
was added into a three-necked flask and followed by addition of 24.8 mg sodium
dodecyl sulfate, 240 mg sodium bicarbonate and 100 mg potassium persulfate. Then,
8 mL styrene and 2 mL acrylic acid were poured into the aqueous solution. The
sample were kept stirring for 4 h at 80 °C under N2 atmosphere. The obtained samples
were centrifuged and washed with ethanol and deionized water for several times.
2.3 Synthesis of PSA modified hollow ZIF-8 nanospheres
Generally, 120 mg of zinc nitrate hexahydrate and 66.4 mg of 2-methylimidazole
were dissolved in 64 mL of methanol. Then, 176 mg PSA were added into the
precursor solution with ultra-sonication for 5 min. The samples were kept in an oil
7
bath at 70 °C for 30 min and subsequently centrifuged to collect the PSA@ZIF-8
particles. Then the PSA@ZIF-8 samples were dissolved in 200 ml DMF at 25 °C for a
controlled time to remove the PSA core incompletely, and the final PHZ nanospheres
were collected by centrifugation at 9000 rpm for 10 min. Then the obtained PHZ
nanoparticles were washed with ethanol and water several times and dispersed in
ethanol. In this work, we prepared three kind of PHZ with different PSA modification
by controlling the etching time (PHZ-1: 2 days, PHZ-2: 8 days and PHZ-3: 16 days).
Meanwhile, unmodified ZIF-8 without the addition of PSA was synthesized in the
same way for comparison.
2.4 Fabrication of MMMs
The MMMs were fabricated by solution casting. [21, 22] Firstly, the Pebax MH
1657 solution (3.0 wt. %) was prepared as the common method. Then, a certain
amount of PHZ were dispersed in the Pebax solution and sonicated to remove the
bubbles of the casting solution. Then the PHZ/Pebax solution was poured into petri
dishes and the membrane was obtained after drying the solution at 40 °C for 24 h. The
membranes were putted at the vacuum oven for 24 h to remove residual solvents.
The PHZ loading is defined as subsequent equation:
PHZ loading (wt. %) = ×100%
+
In this work, the loading of PHZ in MMMs ranged from 0 to 15 wt. %.
2.5 Characterization
The size and the morphology of PHZ and the dispersion of the filler in MMMs
were characterized with Nova Nano SEM 450 scanning electron microscopy (SEM) at
8
20 kV. The cross sections of MMMs were prepared under liquid N2. Transmission
electron microscopy (TEM) was used to characterize the hollow structure of ZIF-8.
X-ray diffraction (XRD) data of all materials and films were obtained from 5 to 40 °
at a scanning rate of 5 ° from an XRD-7000S X-ray diffractometer (60 kV and 80
mA). Nitrogen adsorption-desorption isotherms were used to characterize the surface
area of PHZ and measured at -196 °C using a porosity analyzer (Autosorb-iQ-C,
Quantachrome Instruments). Thermo gravimetric analyses (TGA) were performed
using a Mettler Toledo TGA/DSC1 system. Samples were heated in N2 flow from
30 °C to 600 °C at a heating rate of 10 °C/min.
3. Results and discussion
3.1 Characterizations of PHZ nanospheres
XRD patterns of PSA@ZIF-8 and PHZ are shown in Fig. 1a and Fig. S1. It can
be seen that all samples exhibit a diffraction peak at 19.4°, which originates from the
PSA polymer. [23] This result indicates the presence of residual PSA in all PHZ
samples. It is obvious that PHZ-2 shows the same diffraction peaks with ZIF-8,
confirming that ZIF-8 is synthesized successfully in PHZ-2 and retains the
crystallinity. [24-26] The same conclusion can be drawn from PHZ-3 (Fig. S1).
However, no diffraction peak for ZIF-8 is observed in PHZ-1 (Fig. S1), which can be
attributed to the fact that specific diffraction peaks of ZIF-8 are masked by PSA
residuals with slight etching of PHZ-1.
FTIR spectra of ZIF-8, PSA, PSA@ZIF-8 and PHZ-2 are recorded in Fig. 1b. It
is noted that PSA, PSA@ZIF-8 and PHZ-2 show different FTIR spectra with ZIF-8
9
due to the existence of PSA. Particularly, -CH stretching vibration peaks on the
benzene ring appear in 3025, 3059 and 3082 cm-1; the new peak at 3400 cm-1 is
derived from the -OH; the other peak at 1720 cm-1 represents the stretching vibration
peak of C=O. Besides, there is no peak in 1639 cm-1, revealing that acrylic acid is
polymerized with styrene and -COOH is introduced into PSA successfully. [22, 27] It
is worth noting that the vibration peak of Zn-N at 420 cm-1 appears in PHZ-2 and
PHZ-3, but not in PHZ-1 and PSA@ZIF-8 (Fig. 1b and Fig. S2), which is similar to
the XRD result. It is probably that the Zn-N peak in PHZ-1 and PSA@ZIF-8 is
masked by the PSA.
Fig. 1. XRD patterns (a), and FTIR (b) of PSA, PSA@ZIF-8 and PHZ-2 nanospheres.
The thermal analysis curve of PHZ conducted under N2 atmosphere is shown in
Fig. S3. Obviously, the small mass remaining (related to ZnO) of all PHZ samples
reveals a lot of PSA existing in all PHZ samples. And all samples exhibit quite similar
TGA curves with only one major weight loss. In contrast, the decomposition
temperature of PHZ is higher than that of PSA, benefiting from the higher
decomposition temperature of ZIF-8 (500-600 °C) [28, 29] on the surface of PSA.
10
Meanwhile, the decomposition temperature of PHZ slightly increases from 420 °C
(PHZ-1) to 430 °C (PHZ-3) accompanying with concurrent increase of residual
weight which is attributed to the decrease of PSA and increase of ZIF-8 in PHZ with
increasing the etching time. Anyway, the above results prove that the PSA content in
PHZ can be controlled through the etching time.
The size, morphology and hollow structure of PSA and PHZ-2 are characterized
by SEM and TEM (shown in Fig. 2). To confirm the PSA etching process and the
formed PHZ structure further, SEM, TEM images and EDS mappings of all PHZ
samples are shown in Fig. S4. Fig. 2a implies that spherical PSA nanospheres have
uniform sizes of about 100 nm with smooth surface. After ZIF-8 growth, the PSA
surface becomes rough and the size increases to 110 nm (shown in Fig. 2b), indicating
the successful coating of ZIF-8 shell on the surface of PSA. As shown in Fig. 2c and
Fig. S4a-c, compared with PSA@ZIF-8, all PHZ samples exhibit smooth surface, and
ZIF-8 nanoparticles on PSA nanospheres surface disappear due to the etching in
DMF. Meanwhile, the size of all PHZ samples becomes larger than that of PSA@ZIF-
8. Increasing the etching time leads to increase of the size of PHZ from 114 nm to 132
nm (Fig. S4a-c). Therefore, it is reasonable to conjecture the PSA dissolution process
as following. DMF transports through both the intervals among ZIF-8 nanoparticles
and the micropores of ZIF-8 into the PSA core, resulting in the PSA core swell and
dissolved in DMF, then the dissolved PSA molecules penetrate through the intervals
among ZIF-8 nanoparticles into the DMF solvent. The gradually increased hollow
size of PHZ with etching time from the TEM results in Fig. S4 also verified this.
11
During the PSA molecules transport back into the DMF solvent, due to the interaction
between the -COOH of PSA and the Zn2+ of ZIF-8, PSA molecules are adsorbed on
the ZIF-8 surface, and they are more difficult to swell and dissolve again into DMF
solvent. Consequently, hollow ZIF-8 nanosphere with PSA coating layer is formed.
Fig. 2. SEM, TEM and EDS images of PSA (a, d), PSA@ZIF-8 (b, e) and PHZ-2 (c, f).
As shown in Fig. 2f and Fig. S4d-f, the hollow structure of PHZ is well
presented. The PHZ size is enlarged in comparison with PSA@ZIF-8, and the size
shows an increase with increasing the etching time, which is consistent with SEM
results. It is clearly seen that all PHZ samples show the same morphology and vesicle
shape and the hollow size can be adjusted from 42 nm (PHZ-1) to 91 nm (PHZ-3) by
controlling the etching time (Fig. S4d-f and Table S1). Specially, the hollow size of
PHZ-3 is close to that of PSA, revealing that PHZ-3 is almost completely etched.
Insets in Fig. 2d-f and Fig. S4d-f are EDS elemental mappings (Zn and O) of
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PSA@ZIF-8 and PHZ. The Zn element (green) confirms the existence of ZIF-8, and
the O element (red) belongs to the PSA (-COOH). The inset in Fig. 2d shows the large
amount of O elements existing in PSA, while lots of Zn elements (green) are observed
in the inset in Fig. 2e, indicating the coating of ZIF-8 on PSA. Meanwhile, scattered
O element (red) also appears through the whole sphere, which may be caused by the
certain depth of EDX irradiation. On the contrary, it is observed that one distinct layer
of red O element spreads the outside surface for the three kinds of PHZ samples (the
inset in Fig. S4d-f), indicating that PSA template molecules begin to dissolve from the
core center, penetrate outside through the interval space among ZIF-8 nanoparticles,
and finally adhere on the surface of ZIF-8 to form a PSA coating layer. [30, 31]
The etching process is further confirmed by etching photographs (Fig. S5). It
illustrates that pure PSA dissolves rapidly in DMF (<1 s) and the solution becomes
clear. However, for PSA@ZIF-8 nanospheres, the etching becomes slower and the
solution becomes cloudy, indicating that the coating ZIF-8 blocks and slows PSA
molecules dissolving in DMF. The PSA substrate retained by the incomplete etching
provides an anchoring effect on the dissolved PSA segments, meanwhile, Zn2+ in ZIF-
8 also interacts with the carboxyl group in the PSA segments, inducing adherents of
some dissolved PSA segments on the surface of ZIF-8. Besides, thickness of the
coating PSA layer (Table S1) increases from 3.1 nm (PHZ-1) to 11.9 nm (PHZ-3)
with the increase of the etching time, demonstrating that more PSA molecules are
adsorbed on ZIF-8 surface.
The pore structure of PHZ and ZIF-8 are characterized by nitrogen adsorption-
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desorption isotherms (shown in Fig. S6). ZIF-8 shows type I isotherm curve,
indicating the microporous nature of ZIF-8. [32] For the PHZ-1 and PHZ-2, there are
no obvious adsorption in low relative pressure (< 0.1), which is due to ZIF-8 channel
blocking by residual PSA. With the increase of the etching time, PHZ-3 shows a
higher adsorption than PHZ-1 and PHZ-2 at the low relative pressure, owing to the
reduced PSA content and regenerated pores in PHZ-3 caused by long-time etching.
3.2 PHZ/Pebax MMMs
To explore the potential of PHZ nanospheres in CO2 separation, PHZ/Pebax-
based MMMs are further prepared. Two peaks of Zn (2p) in XPS spectrum (Fig. S7)
confirm the successful incorporation of PHZ into the Pebax matrix. Moreover, from
the surface (Fig. S8) and cross-section SEM images (Fig. 3) and the inserted EDS
pattern of PHZ-2/Pebax MMMs, the PHZ-2 nanospheres distribute uniformly in the
Pebax matrix, and no obvious interface defects are observed, confirming that defect-
free MMMs have been successfully prepared. The cross-section image in Fig. 3d
illustrates that significant particle agglomeration appears in MMMs with 15 wt. %
PHZ-2 loading. However, there is still no visible interface defect in the PHZ-2/Pebax
MMMs, revealing excellent compatibility between the PHZ and polymer.
14
Fig. 3. Cross-section SEM images and EDS results of different concentrations PHZ-2-based
MMMs: (a): 0%; (b): 5%; (c): 10%; (d): 15%.
2.3 Gas permeability properties
Fig. 4 represents the CO2 permeability and CO2/N2 selectivity of MMMs with
different fillers at 10 wt. % loading (Fig. 4a) and PHZ-2/Pebax MMMs with different
PHZ-2 loading (Fig. 4b). As shown in Fig. 4a, it is observed that PHZ-2/Pebax
MMMs exhibit both higher CO2 permeability and CO2/N2 selectivity. The CO2
permeability of all kinds of MMMs are higher than that of pure Pebax membrane,
which is attributed to the fact that incorporated fillers destroy the packing of polymer
segments and therefore, improve the free volume. The CO2/N2 selectivity of PHZ-
based MMMs are higher than that of ZIF-8 and PSA@ZIF-8 (without PSA
modification)-based MMMs, confirming that the PSA segment outside PHZ provides
a better compatibility with Pebax due to entanglements and hydrogen bonding
between PSA and Pebax molecular chains. [17, 33, 34] Meanwhile, PHZ-2/Pebax
MMMs also show higher CO2 permeability than ZIF-8 and PSA@ZIF-8 based
15
MMMs. The increased permeability mainly originates from the hollow structure,
which effectively reduces the gas transfer resistance. [35] As shown in Fig. S9, the
CO2 permeability of PHZ-based MMMs increases from 123.5 Barrer (PHZ-1) to
188.4 Barrer (PHZ-3), further demonstrating that the increase of hollow size leads to
further reduction in the gas transportation resistance. PHZ-3/Pebax MMMs show a
drop in CO2/N2 selectivity compared with PHZ-2 and PHZ-1. The reason is probably
that the thicker PSA layer on ZIF-8 surface makes PHZ-3 similar with PSA, thus
PHZ-3 based MMM shows the similar separation performance with that of
PSA/Pebax MMMs (Fig. 4a). Obviously, the gas separation performance of PHZ-
based MMMs can be effectively tuned via controlling PSA layer and hollow size.
As shown in Fig. 4b, it is obvious that the CO2 permeability and CO2/N2
selectivity of PHZ-2/Pebax MMMs are higher than those of pure Pebax membrane.
The CO2 permeability of PHZ-2/Pebax MMMs increases with the increase of PHZ-2
loading, owing to improved free volume and low gas transfer resistance caused by the
hollow structure of PHZ-2. As for the CO2/N2 selectivity, in the case that the PHZ-2
loading is 10 wt. %, the selectivity reaches the highest value of 87.9, which is 80%
higher than that of pure Pebax membrane. Further increasing the PHZ-2 loading to 15
wt. %, however, leads to easy formation of non-selective defects between the
interface and agglomeration of the fillers, resulting in decreased CO2/N2 selectivity.
Meanwhile, Table S2 presents gas diffusion and solubility coefficients of PHZ-
2/Pebax MMMs obtained by time delay method. It is observed that diffusion
coefficients of CO2 and N2 increase with the increase of PHZ-2 loading due to the
16
hollow structure of PHZ. Moreover, the DCO2/DN2 increases while the loading of PHZ-
2 reaches to 10 wt. %; simultaneously, compared with the DCO2/DN2, the SCO2/SN2
shows a slower increase, revealing that the increased selectivity mainly depends on
the diffusion selectivity, which should originate from the superior compatibility
between PHZ-2 and Pebax as well as the retarded non-selective diffusion. The long-
time stability of the obtained MMMs for CO2/N2 separation is shown in Fig. S10,
both the CO2 permeability and CO2/N2 selectivity keep almost unchanged, indicating
the fine long-term stability of the PHZ based MMMs.
Fig. 4. CO2 permeability and CO2/N2 selectivity of MMMs with different fillers at 10 wt. %
loading (a) and PHZ-2/Pebax MMMs with different filler loadings (b).
The comparison of CO2/N2 separation performances of PHZ-2/Pebax MMMs
under different pressures (1bar, 5bar and 9bar) with other reported MOF-based and
Pebax-based MMMs are presented in Robeson upper bond in 2008 (shown in Fig. 5)
and listed in Table S3. [36] It is observed that, compared with the MOF-based and
Pebax-based MMMs, the 10 wt. % PHZ-2/Pebax-based MMMs at 1 bar possess both
acceptable CO2 permeability (172.4 Barrer) and CO2/N2 selectivity (87.9) and well
17
exceeds the 2008 Robeson upper bound. Meanwhile, with the increase of the feed
pressure, the CO2 separation performance of PHZ-2/Pebax MMMs steadily increases.
[9, 17, 37-70]
Fig. 5. CO2/N2 separation performances of 10 wt. % PHZ-2/Pebax MMMs under different
pressure in Robeson upper bound.
4. Conclusion
In our study, PSA modified hollow ZIF-8 nanospheres are synthesized via a hard
template-incomplete etching strategy. The hollow structure can reduce the gas mass
transfer resistance so that the gas permeability is improved. In addition, there exist
residual PSA segments on the surface of PHZ during formation of the hollow
structure, which combines PHZ with Pebax tightly and therefore, enhances the
compatibility between PHZ and Pebax. At 10 wt. % PHZ-2 loading, the permeability
of MMMs reaches 172.4 Barrer, which is 118.5% and 16% higher than that of pure
18
Pebax membrane and ZIF-8/Pebax MMMs, respectively. Meanwhile, the selectivity
of 10 wt. % PHZ-2/Pebax MMMs increases to 87.9, which is 80% and 118.7% higher
than that of pure Pebax membrane and ZIF-8/Pebax MMMs, respectively. The
superior gas separation performance of PHZ based MMMs not only well exceeds
other published MOF-based MMMs but also is far beyond the 2008 Robeson upper
bond. The present study presents a new strategy to synthesize hollow MOF
nanoparticles with surface modified PSA in one step and therefore, to concurrently
improve the gas permeability and selectivity.
Declaration of Competing Interest
Acknowledgements
We are grateful for the National Natural Science Foundation of China (21978035,
21506028, 21706023, 21978033), the Fundamental Research Funds for the Central
Universities (DUT18RC(3)071) and the China Postdoctoral Science Foundation
(2018M631167).
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Characterization and molecular simulation of Pebax-1657-based mixed matrix membranes
incorporating MoS2 nanosheets for carbon dioxide capture enhancement, J. Membr. Sci. 582 (2019)
358-366.
1. PSA modified hollow ZIF-8 were designed by a hard template-incomplete etching strategy.