Chemically Cross-Linked MOF Membrane Generated from

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Chemically Cross-Linked MOF Membrane Generated from Imidazolium-Based Ionic Liquid Decorated UiO-66 Type NMOF and its Application toward CO2 Separation and Conversion Bing-Jian Yao, Luo-Gang Ding, Fei Li, Jiang-Tao Li, Qi-Juan Fu, Yujie Ban, Ang Guo, and Yu-Bin Dong ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b12697 • Publication Date (Web): 13 Oct 2017 Downloaded from http://pubs.acs.org on October 13, 2017

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ACS Applied Materials & Interfaces

Chemically Cross-Linked MOF Membrane Generated from Imidazolium-Based Ionic Liquid Decorated UiO-66 Type NMOF and its Application toward CO2 Separation and Conversion Bing-Jian Yao,a* Luo-Gang Ding, a Fei Li a Jiang-Tao Li,a Qi-Juan Fu,a Yujie Ban,b Ang Guo,b Yu-Bin Dong a* a

College of Chemistry, Chemical Engineering and Materials Science, Collaborative Innovation

Center of Functionalized Probes for Chemical Imaging in Universities of Shandong, Key Laboratory of Molecular and Nano Probes, Ministry of Education, Shandong Normal University, Jinan 250014, P. R. China. b

State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, CAS, 457 Zhongshan

Road, Dalian 116023, P. R. China.

1

ACS Paragon Plus Environment


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ABSTRACT. CO2 capture and transformation are of great importance to make cuts in greenhouse gas emissions. Nano metal-organic frameworks (NMOFs) could serve as the ideal fillers for polymer-membranes owing to their structural diversity and regulable microenvironment of the nanocage. Herein, a bifunctional robust and chemically cross-linked NMOFbased membrane was successfully constructed by the post-synthetic polymerization of imidazolium-based ionic liquid decorated UiO-66 type nanoparticles (NPs) and isocyanateterminated polyurethane oligomer under mild condition. The ionic liquid-modified MOFpolymer membranes exhibit a highly selective adsorption for CO2 over N2 and CH4. In addition, the obtained membrane can also be a highly active heterogeneous catalyst for CO2 transformation by cycloaddition with epoxide under ambient pressure.

KEYWORDS: MOFs, gas separation, cross-linked membrane, catalytic cycloaddition, Polyurethane, ionic liquid

INTRODUCTION Carbon dioxide is directly linked with the greenhouse effect.1-2 Thus, the need to capture CO2 emanating from the burning of fossil fuel has received lot of attention in recent years. In order to reduce the greenhouse effect, CO2 capture and storage/sequestration (CCS) and its chemical transformation are areas of intense current interest.3-5 Membrane-based gas separation technologies have attracted much attention because of their low energy consumption, continuous operation, and cost effectiveness.6-8 Polymeric membrane-based CO2 capture is superior to the current chemical adsorption techniques in terms of energy consumption, however, it subject to a trade-off between permeability and selectivity which is demonstrated by the Robeson’s upper

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bound.9 Recently, numerous microporous materials, such as carbon molecular sieves,10-11 activated

carbons,12-13

carbon

nanotubes,14-15

graphene

oxide,16

and

zeolite

nanoparticle/nanosheets,17-19 have been used as the superb building platform or just functional fillers for the new generation of separation membranes with high gas separation efficiency due to the extreme low mass-transfer barrier and the ideal molecular-unit thickness. Despite the many reports of improved separation and transport properties in the composite polymer membranes, there are still technical challenges to be met with because the fillers usually do not have a good interfacial compatibility with the polymers matrix, thus leaving lower selective pathways.20 On the other hand, catalytic CO2 conversion into value added C1 building block is of great significance.21-22 Recently, ionic liquid (IL) and poly (ionic liquid) have attracted much attention owing to their unique properties in the CO2 absorption and chemical fixation.23-24 Although recent progress on CCS and catalytic CO2 conversion is remarkable, bifunctional membranes with both selective CO2 adsorption and catalytic conversion functionality are still rarely reported. Metal-organic frameworks (MOFs), as an emerging class of porous materials, have a variety of attractive features.25 The organic-inorganic hybrid composition and porous structure endow the MOFs with interesting physical and chemical properties and promising applications such as gas storage and separation,26-27 chemical sensors,28 and catalysis.29-31 A distinct advantage of MOFs is their controllable synthesis and diverse pre-/post-modification options, which provide a number of possibility for altering their effective pore sizes and functional structures.31-33 For example, ionic liquid such as imidazolium moiety can be tethered and immobilized in MOFs via pre-ligand functionalization. In this way, the MOFs with ionic liquid functional groups would be generated and lead to the expected membrane fillers for CO2 selective adsorption and its catalytic chemical transformation.

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As we know, the inherently fragile and rigid nature of MOFs severely astricted their processability,

consequently,

their

practical

applications.34

Besides

the

MOF-based

polycrystalline membranes,35-37 a recent developed strategy for solving the such problem is the fabrication of MOF NPs containing mixed matrix membrane (MMM), which was demonstrated to be a useful approach to access practical materials. The preparation of MMM is highly promising and could endow MOFs with broad applications. However, the poor compatibility of the polymer binders with MOF particles is still a major barrier to the fabrication of high-quality membranes due to the agglomeration of MOF particles.38 When used as the gas separation materials, the membrane will suffer from poor selectivity due to the non-selective holes caused by the inhomogeneous physical blending. However, the covalent polymerization of polymerizable moieties decorated MOF NPs with functionalized organic oligomers might be an alternative and useful method to solve the above problem and to access MOF-based membranes with good dispersion, compact and homogeneous texture. Nevertheless, only a handful chemically cross-linked MOF-based membranes have been reported so far.39 We have recently initiated a synthetic program for the preparation of the NMOF-based homogeneous membranes via post-synthetic approach, in which MOF NPs with polymerizable precursor are covalently anchored by the functionalized oligomer linkages.40-41 In this way, the MOF NPs agglomeration in polymer binder could be effectively avoided, and the homogeneous NMOF involved membranes with good dispersion, processability and flexibility are generated. In this contribution, we report a new imidazolium-based IL unit-tethered UiO-66 type NMOF membrane filler (UiO-66-IL-X, X = halide ion) via direct ligand functionalization. Furthermore, the UiO-66-IL-X based membranes are fabricated by chemically cross-linking the hydroxyl group on UiO-66-IL-X NPs with the isocyanate-terminated polyurethane oligomer. Furthermore,

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the CO2 adsorption and separation over N2 and CH4 are evaluated on the UiO-66-IL-X fillers and also the membranes based on them. Besides selective CO2 membrane separation, the obtained membranes can also be a highly active heterogeneous catalyst for CO2 cycloaddition with epoxides under ambient pressure. EXPERIMENTAL SECTION Materials and Instrumentations. All the chemicals were obtained from commercial sources (Acros) and used without further purification. 1H NMR data were collected on a Bruker Avance400 spectrometer. Chemical shifts are reported in δ relative to TMS. Infrared spectra were obtained in the 400−4000 cm−1 range using a Bruker ALPHA FT-IR spectrometer. Thermogravimetric analysis was carried out with a TA Instruments Q5 simultaneous TGA under flowing nitrogen of 60 mL min-1 at a heating rate of 10 °C min-1. SEM micrographs were recorded on a Gemini Zeiss Supra TM scanning electron microscope equipped with energydispersive X-ray detector (EDS). To improve the electrical conductivity of the samples, they were sputtered with gold for 50 s before characterization. The XRD pattern was obtained on D8 ADVANCE X-ray powder diffractometer with Cuka radiation (λ = 1.5405 Å). Gel permeation chromatography (GPC) equipped with a Waters 515 system, a 2410 refractive index detector and three Styragel gel columns was calibrated with narrow-molecular-weight polystyrene (PS) standards for molecular weight characterization. Elemental analyses were performed on a PerkinElmer model 2400 analyzer. ICP measurement was performed on an IRIS Interpid (II) XSP and NU AttoM. HRMS analysis was carried out on a Bruker maXis UHR-TOF ultrahigh resolution quadrupole-time-of-flight mass spectrometer. The mechanical properties of the membrane were determined by fixing the sample (dimensions: length = 20 mm, width = 5 mm,

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thickness = 0.1 mm) between two stainless steel clamps with a strain rate of 1 mm min-1 in a mechanical strength microtest device (WDW-5 Changchun KeXin). Synthesis of Intermediate A. 2-Methylterephthalic acid (0.9 g, 5 mmol), methanol (50 mL), and concentrated sulfuric acid (5 mL) were added to a round-bottomed flask. The reaction was conducted with reflux for 12 h with magnetic stirring. After that, the pH value of the reactant solution was adjusted to 7.0 by saturated solution of sodium carbonate. The product was collected and dried in vacuum to generate A (0.99 g, 95 %). 1H NMR (400 MHz, CDCl3), δ (ppm): 2.65 (3H, s, −CH3), 3.94-3.96 (6H, d, −OCH3), 7.90−7.98 (3H, m, −Ar). FTIR (KBr, cm−1): 3100 (w), 2950 (s), 2844 (m), 1712 (s), 1602 (s), 1552 (m), 1461 (m), 1108 (m), 762 (m). ESI-MS: calcd for C11H12O4Na+, m/z 231.07, found, m/z 231.06. Synthesis of Intermediate B. A mixture of intermediate A (1.04 g, 5 mmol), Nbromosuccinimide (0.445 g, 2.5 mmol), AIBN (0.08 g, 0.5 mmol), and carbon tetrachloride (45 mL) was stirred at 76 °C for 1 h, then, additional N-bromosuccinimide (0.445 g, 2.5 mmol) was added to the reactant solution, and it was stirred at 76⁰C for additional 1 h. After removal of the solvent in vacuum, the crude product was purified by column chromatography on silica gel using petroleum ether-dichloromethane (1:1 v/v) as the eluent to generate B as a light-yellow semisolid (1.45 g, 45 %). 1H NMR (400 MHz, CDCl3), δ (ppm): 3.95-3.97 (6H, s, −OCH3), 4.96 (2H, s, −ArCH2Br), 8.02−8.13 (3H, m, −Ar). FTIR (KBr, cm−1): 3100 (w), 2956 (m), 2838 (m), 1720 (s), 1602 (m), 1552 (m), 1461 (m), 1116 (m), 763 (m), 627 (m). ESI-MS: calcd for C11H11O4BrNa+, m/z 308.98; found, m/z 308.97. Synthesis of Intermediate C. A mixture of intermediate B (0.572 g, 2 mmol), 1-(2hydroxyethyl)imidazole (0.27g, 2.4 mmol), and acetonitrile (45 mL) was stirred at 80 °C for 2 h. After removal of the solvent in vacuum, the residue was purified by column chromatography on

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silica gel using dichloromethane-methanol (10:1, v/v) as the eluent to generate C as brown oil (0.506 g, 79 %). 1H NMR (400 MHz, CDCl3), δ (ppm): 3.71-3.73(2H, t, CH2CH2OH), 3.89 (6H, s, −OCH3), 4.25-4.28 (2H, t, NCH2CH2), 5.79 (2H, s, −NCH2Ar), 7.31 (1H, s, NCHCHN), 7.40 (H, s, NCHCHN), 7.80-8.12 (3H, m, −Ar-H), 9.20 (1H, s, −NCHN). FTIR (KBr, cm−1): 3167 (m), 3054 (m), 2956 (m), 2896 (m), 2836 (m), 1712 (s), 1529 (w), 1604 (w), 1556(w), 1123 (m), 905 (m), 762 (m). ESI-MS: calcd for C23H23N2O4 M+, m/z 391.17; found, m/z 391.16. Synthesis of L. Intermediate C was hydrolyzed by LiOH (10 equiv) in a methanol/water (3:1, v/v) at room temperature (12 h). Then the pH value of the reaction solution was adjusted to 2−3 by hydrobromic acid. Then product was treated by freeze drying. The product precipitated from ethanol solution by acetone to generate 0.4 g imidazolium-attached ligand L as an orange-red semisolid in 87 % yield. 1H NMR (400 MHz, CH3DO), δ (ppm): 3.86 (2H, t, CH2CH2OH), 4.27 (2H, t, NCH2CH2), 5.71 (2H, s, −NCH2Ar), 7.58-7.68 (1H, d, NCHCHN), 7.76-7.78 (H, d, NCHCHN), 7.95-7.98 (3H, m, −Ar-H), 9.00 (1H, s, −NCHN). FTIR (KBr, cm−1): 3377 (s), 3160 (w), 3092 (m), 2859 (m), 2776 (m), 1717(s), 1529 (w), 1604 (m), 1556 (m), 1100 (m), 987 (m), 920 (m), 769 (m). ESI-MS: calcd for C14H15N2O5, M+, m/z 291.10; found, m/z 289.08. Synthesis and Characterization of UiO-66-IL-Br. ZrCl4 (28.8 mg, 0.12 mmol) and 50 equiv of acetic acid (0.34 mL) were dissolved in DMF (4.8 mL) by using ultrasound for about 10 min. L (34.93 mg, 0.12 mmol) was added to the clear solution in an equimolar ratio with regard to ZrCl4. The tightly capped flasks were kept in an oven at 120 °C under static conditions. After 24 h, the reaction system was cooled to room temperature and the precipitate was isolated by centrifugation. The solid were suspended in fresh DMF for 2 h, followed by decanting off the solvent. The obtained particles were then washed with ethanol several times in the same way as described for washing with DMF. Finally, the solids were dried under reduced pressure to

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generate the as-synthesized UiO-66-IL-Br NPs with a yield of 75 %. FTIR (KBr, cm−1): 3362 (m), 3147 (w), 2973 (m), 1587 (s), 1497 (w), 1413 (s), 1385 (s), 1207 (w), 1156 (m), 1084 (w), 1049 (w), 749 (w), 650(m). Elemental analysis (%) calcd for C14H15.7ZrN2O6.3Br (desolvated): C 34.78, H 3.24, N 5.80, Zr 18.84, Br 16.56. Found: C 34.65, H 3.22, N 5.82, Zr 18.85, Br 16.54. Synthesis of UiO-66-IL-PF6, UiO-66-IL-SO3CF3, and UiO-66-IL-ClO4. The imidazoliumbased MOFs particles with different anion were obtained by anion exchange. Activated UiO-66IL-Br (0.1 g) was dispersed in 10 mL saturated ethanol solution of the corresponding sodium salts. After the mixture was stirred for 24 h (with the infrared monitoring and tracking), the residue was filtered by centrifugalization. The precipitate was washed with ethanol (5 mL) for several times. After drying, the goal product was obtained. For easy of editing, the UiO-66-IL bearing PF6-, SO3CF3-, and ClO4- was termed as UiO-66-IL-PF6, UiO-66-IL-SO3CF3, and UiO66-IL-ClO4, respectively. The ICP analysis results are provided in Supporting Information. Preparation of UiO-66-IL-based Membranes. Isocyanate-terminated polyurethane oligomer was synthesized from polypropylene glycol (PPG, Mn = 2000 Da) and 4,4’-methylene diphenyl diisocyanate (MDI) by our previous reported method.40 For the membrane preparation, isocyanate-terminated polyurethane oligomer (0.035 g) was dissolved in anhydrous chloroform (5 mL) in a 25 mL three-necked round-bottom flask, and appropriate amount (30, or 50 wt % MOF) of the as-synthesized UiO-66-IL-X particles was added to the above solution. The mixture was dispersed by ultrasound for about 10 min, followed by stirring at room temperature for 10 h. Then, the reaction solution was poured into a clean PTFE dish (5 cm in diameter). The cast membranes were allowed to dry at room temperature, followed by programmed heating in an air-circulating oven at 60 °C for 2 h. After being peeled off from the substrate, the resulting cross-linked membranes were soaked in DMF and ethanol in sequence for purification and

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activation, and subsequently dried in drying chamber with temperature controlled at 80 °C (8 h) to remove any excess solvent. The membranes were stored at room temperature for further characterization. Adsorption Measurements. Gas adsorption isotherms were collected on a Micromeritics ASAP 2020/TriStar 3000 volumetric gas sorption instrument. About 200 mg of the dissolved sample was used for the entire adsorption measurement. Prior to the measurement, samples were pre-treated in a vacuum oven at 373 K for 24 h and further degassed at 393 K for 10 h to remove the residual solvent molecules before characterization. The nitrogen sorption isotherm was collected at 77 K in a liquid nitrogen bath, in order to study its permanent porosity and robustness. For selective adsorption evaluation, the gas sorption experiments of CO2, N2, and CH4 were carried out at 298 K in a temperature controlled circular bath. The ideal adsorption selectivity (Henry adsorption selectivity) toward CO2/N2 and CO2/CH4 of the membrane was based on the linear fitting of the low-pressure Henry region of gas adsorption isotherms. Evaluation of Membrane Separating Performance. For gas separation tests of the membrane, the as-synthesized membrane was sealed into a home-made stainless-steel permeation cell. The Wicke-Kallenbach cells with an on-line gas chromatography (Agilent 7890 B) were used to measure its separation performance for CO2/CH4, and CO2/N2 gas mixture and conduct the single gas permeation tests. Membranes were covered with silicone rubber pads and stainless-steel gaskets with a hole of 5 mm diameter in the center to prevent any scratches on the membrane from O-rings. An equimolar gas mixture (100 mL/min in total) was deployed as feed gas, with 100 mL/min Argon (Ar) as sweep gas for the permeate side. The flow rates were regulated by mass flow controllers (Alicat Scientific Inc.). There was no pressure drop between the two sides of the membrane to avoid any distortion of the distortion of the membrane. For the

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single gas permeation tests, the feed gas flow rates were kept at 100 mL/min with the same sweep gas flow rate. Gas permeance was calculated by the following equation:

Pi =

Ni F = i A∆Pi ∆Pi

Where Pi is the permeance of component i (mol/(m2. s. Pa)), Ni is the permeate rate of component i (mol/s), A is the effective membrane area (m2), and ∆Pi is the trans-membrane pressure difference of component i (Pa). Permeance can also be expressed as pressure normalized flux. Fi is the flue of componet i (mol/m2·s). Every permeance was calculated by the average of four data points after the establishment of permeation equilibrium. Binary gas separation factor ( α i / j )was calculated by the following equation:

αi / j =

yi / y j xi / x j

Where x and y are the molar fractions of component i, j in the feed side and permeate side, respectively. Catalytic Cycloaddition of CO2 with Epoxides. The solvent free cycloaddition reaction was carried out in a 10mL flask with magnetic stirrer with given amounts of epoxides, membrane catalyst, and co-catalyst (TBAB) charged into the reactor. The temperature was 90 °C, and the CO2 was provided through a balloon under 1 atm of pressure. The membrane catalyst was removed by filtration. After addition of methylene chloride, the reaction system was completely washed by water to remove the co-catalyst TBAB. The cycloaddition yields are up to 99 % (determined by the 1H NMR spectrum). RESULTS AND DISSCUSSION

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Scheme 1. Synthesis of L (a), UiO-66-IL-X NPs with different counter ions (b), and chemically crosslinked membrane based on UiO-66-IL-ClO4 NPs and polyurethane oligomer (c). Ligand Synthesis. As shown in Scheme 1, ligand L with imidazolium unit was synthesized as an orange-red semisolid. The intermediate A was obtained by the esterification of 2methylterephthalic acid with methanol under acidic condition at room temperature. After esterification, the bromination reaction was carried out with NBS in carbon tetrachloride in the presence of AIBN to generate B. The imidazolium group was introduced by the combination of B and 1-(2-hydroxyethyl)imidazole in CH3CN at 80 °C to provide C. Dicarboxylic ligand L was

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obtained via hydrolyzation of C by LiOH in a MeOH/H2O mixed solvent system in good yield. The 1H NMR, IR and MS spectra for intermediates A, B, C, and ligand L were provided in the Supporting Information. Synthesis and Characterization of Imidazolium-Based UiO-66-IL-X NPs. UiO-66-IL-Br was prepared according to the reported method. As indicated in Scheme 1, ZrCl4 and L reacted in DMF using acetic acid as the regulator under the solvothermal conditions (120 °C, 24 h) to yield a white crystalline powder of UiO-66-IL-Br. Scanning electronic microscopy (SEM) and dynamic light scattering (DLS) measurement shows that UiO-66-IL-Br was obtained as nanoscale particles (ca. 221 nm) with a regular octahedral shape (Figure 1a). The powder X-ray diffraction (PXRD) pattern obtained for the as-synthesized UiO-66-IL-Br sample is shown in Figure 1b and indicated that it is highly crystalline with a topological structure identical to that of pristine UiO-66. Therefore, the introduced imidazolium group did not affect the UiO-66 framework formation under the reaction conditions.

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Figure 1. a) SEM images and DLS results of UiO-66-IL-Br, UiO-66-IL-PF6, UiO-66-ILSO3CF3 and UiO-66-IL-ClO4. b) Their PXRD patterns. c) Their N2 sorption isotherms at 77 K. d) IR spectra monitoring of the anion-exchange processes of Br- by PF6-, SO3CF3- and ClO4anions in UiO-66-IL-Br, respectively. To examine the permanent porosity, N2 adsorption property of UiO-66-IL-Br was measured at 77 K (Figure 1c). The crystalline tagged MOF sample displays a typical type-I adsorption isotherm, featuring characteristics of the microporous materials. As indicated in Figure 1c, the N2 adsorption amount of UiO-66-IL-Br was 477.23 cm3/g, and its Brunauer-Emmett-Teller (BET) surface area was found to be 663.70 m2/g. The corresponding pore volume of UiO-66-IL-Br based on the maximal nitrogen adsorption was 0.379 cm3/g (SI). These values are smaller than

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those of UiO-66. Observed decreases in surface area are largely attributed to both reduced free space available and increased overall weight of the UiO-66-IL-Br MOF as a result of introducing large imidazolium groups and heavy Br atoms. UiO-66-IL-PF6 (light yellow powder), UiO-66-IL-SO3CF3 (light brown powder) and UiO66-IL-ClO4 (brown powder) were prepared based on UiO-66-IL-Br via solid-liquid anionexchange (Figure 1a). The anion exchange of UiO-66-IL-Br with different anion was carried out in the corresponding saturated ethanol solution of sodium salt at room temperature. As shown in Figure 1a, they are all obtained as crystalline NPs with the similar nanoparticle size to their pristine UiO-66-IL-Br MOF. FTIR spectrum was used to monitor the anion-exchange processes. As shown in Figure 1d, the intensities of characteristic peaks for PF6- (558 and 829 cm-1), SO3CF3- (1041, 1172 and 1251 cm-1) and ClO4- (1108 cm-1) gradually increased as time went on, indicating the target products formed. After 24 h, no more changes for the peak intensities were observed, indicating that the exchange reactions of Br- by other kinds of anions were finished. After washed with EtOH and dried at 80 °C, the obtained samples were characterized by the Ion Chromatography analysis. The results indicated that the Br- anions in UiO-66-IL-Br were basically replaced by the PF6-, SO3CF3- and ClO4- anions, respectively (SI). The energydispersive X-ray spectra (EDS) further confirmed this complete anion-exchange, and the elements of incursive anions are evenly distributed in the MOF NPs after the anion-exchange (SI). In addition, the PXRD patterns (Figure 1b) confirmed that the structural integrity of UiO66-IL was well maintained during the anion exchange processes. It is similar to UiO-66-IL-Br, UiO-66-IL-PF6, UiO-66-IL-SO3CF3 and UiO-66-IL-ClO4 also possess permanent porosity. However, because the larger sized and heavier anions were induced into MOF systems after anion exchange, so their BET surface areas for UiO-66-IL-PF6,

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UiO-66-IL-SO3CF3 and UiO-66-IL-ClO4 accordingly decreased to 608.21, 538.23 and 588.52 m2/g, and their pore volumes (based on their maximal nitrogen adsorption, Figure 1c) reduced to 0.379, 0.377 and 0.378 cm3/g, respectively. CO2 Selective Adsorption. Considering high porosity together with the high-density imidazolium groups in the UiO-66-IL-X frameworks, and the possible acidity originates from the Brønsted acid (Zr-OH/Zr-OH2) sites of defect Zr6 nodes, the adsorption isotherms on the evacuated UiO-66-IL-PF6, UiO-66-IL-CF3SO3, and UiO-66-IL-ClO4 for CO2, CH4 and N2 at 298 K were examined, respectively (Table 1, SI). Table 1. Gas Adsorption on UiO-66-IL-X MOFs with Different Anions CO2

CH4

N2

adsorption

adsorption

adsorption

(cm3/g)

(cm3/g)

(cm3/g)

CO2/N2

CO2/CH4

UiO-66-NH2

75.66

20.83

7.56

32.74

7.16

UiO-66-IL-Br

21.82

3.85

1.40

30.00

17.50

UiO-66-IL-PF6

28.98

3.05

1.17

41.37

12.55

UiO-66-IL-CF3SO3

21.10

2.58

1.23

21.61

18.68

UiO-66-IL-ClO4

31.04

2.59

1.01

55.65

18.95

Sample

a

Ideal adsorption selectivity a

Calculated using the initial slope in the Henry region of isotherms at 298 K based on Henry’s law.

As illustrated in Table 1, UiO-66-IL-X (X = Br-, PF6-, SO3CF3- and ClO4-) showed a moderate the CO2 adsorption amount (21.10-31.04 cm3/g) at 298 K under 1 atm. It is different from CO2 uptake, however, only a tiny amount of CH4 (2.58-3.85 cm3/g) and N2 (1.01-1.40 cm3/g) uptake was observed for UiO-66-IL-X (X = Br-, PF6-, SO3CF3- and ClO4-) under the same conditions. To predict the selective CO2 separation performance over N2 and CH4 under ambient conditions, the ideal adsorption selectivity toward 50:50 of CO2/CH4 and CO2/N2 binary mixtures was calculated from the ratio of the initial slopes in the low-pressure Henry region of the single-

15



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Page 16 of 39

component gas-adsorption isotherms. Due to the good solubility of CO2 in imidazolium groups, a significant improvement in CO2/CH4 and CO2/N2 adsorption selectivity was achieved for UiO66-IL-X (SI). It should be noted that the different counter ions have great effect on the adsorption and selectivity of CO2. As shown in Table 1, the UiO-66-IL-X exhibits a clear selectivity for CO2 and obeys the sequence UiO-66-IL-ClO4> UiO-66-IL-PF6> UiO-66-IL-Br> UiO-66-IL-SO3CF3. In order to further understand this phenomenon, the theoretical calculations of the interaction between imidazolium with different anions and CO2 were performed (SI). All calculations were performed at the BP86 level of the density functional theory using the Gaussian 09 program, and the 6-311++G (d, p) basis set account was adopted for all the atoms. The results of two-body dissociation channel of A-B → A + B (A = UiO-66-IL-X (X = ClO4-, Br-, PF6- and SO3CF3-), B = CO2), and corresponding dissociation energy ∆H indicated that UiO66-IL-ClO4 exhibited the maximum combining capacity with CO2 (∆H = -4.33 kJ·mol-1). Thus, the interaction between CO2 and UiO-66-IL-ClO4 is more energy favorable than those of between CO2 and UiO-66-IL with other three kinds of anions (∆H = -3.85 ~ -4.31 kJ·mol-1), which could be the reason for the highest CO2 selectivity of UiO-66-IL-ClO4. In particular, the CO2/N2 and CO2/CH4 selectivity of UiO-66-IL-ClO4 is up to 55.65 and 18.95, respectively, which is in a strong position among the UiO-66-MOFs based CO2-philic adsorbent competitors (Table 2). Obviously, the high density 1-ethoxyl-3-benzylimidazolium perchlorate groups anchored on the UiO-66 framework are the dominating factor for the CO2 selectivity. Thus, UiO66-IL-ClO4 was chosen and used for the fabrication of MOF-based CO2-selective adsorption membrane. Table 2. A Summary of CO2, N2 and CH4 Adsorption and Selectivity Based on the UiO-66 Type NMOFs

16


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Entry 1 2

MOF UiO-66-SO3K UiO-66-SO3H

CO2 (cm3/g) 20.38 7.16

N2 (cm3/g) 1.70 1.03

CH4 (cm3/g)

Selectivity a Ref

T (K)

－－

CO2/N2

CO2/CH4

298

43.3 b

－

42

298

18.7

b

－

42

b

－

42

3

UiO-66

40.1

3.23

－

298

19.4

4a

UiO-66-I

114.2

－

71.7

306

－

4.7

43

5

UiO-66-(CH3)2

82

2.0

－

293

58

－

44

6

UiO-66-CO2H

－

－

－

303

19.2

－

45

7

UiO-66-Br

－

－

－

303

9.8

－

45

8

UiO-66-(OH)2

－

－

－

303

13.8

－

45

9

UiO-66-AD6

58.9

－

10.8

298

10.0

－

46

10

UiO-66-AD10

12.8

－

2.91

298

9.26

－

46

11

UiO-66-EA

38

0.32

－

298

365 b

－

47

12

UiO-66-2,5-(OMe)2

44.8

4.5

13.4

298

62.2 b

18.0

48

13

opt-UiO-66(Zr)-(OH)2

126.1

11.4

26.4

298

105

44

49

14

UiO-66 (Zr)-(COOH)2

17.7

6.7

－

298

37.9 b

－

50

15

UiO-66 (Zr)-(COOLi)2

30.5

5.2

－

298

50.8 b

－

50

This work a selectivity is calculated based on single-component gas adsorption isotherms. The CO2 and CH4 uptake values as well as ideal CO2/CH4 adsorption selectivity was measured at 25 bar. b CO2/N2 ratio is 15:85, and 50:50 for the rest. 16

UiO-66-IL-ClO4

31.04

1.01

2.59

298

55.65

18.95

Fabrication and Characterization of UiO-66-IL-ClO4 based Membranes. For the potential practical applications in gas separation, the fabrication of chemically cross-linked UiO-66-ILClO4-based membrane was investigated by post-synthetic polymerization and subsequent solution casting. The isocyanate-terminated polyurethane oligomer was chosen as the bridge to link hydroxyl-decorated UiO-66-IL-ClO4 NPs via -OH and -NCO addition reaction. As shown in Scheme 1, the UiO-66-IL-ClO4 NPs were mixed with polyurethane oligomer in anhydrous chloroform and then fully dispersed by ultrasound. After the obtained mixture was stirred for 10 h at room temperature, the reaction solution was poured into a clean PTFE dish, and the cast membrane was allowed to washing and drying to afford elastic free-standing membranes. The

17



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Page 18 of 39

MOF loading can be easily controlled by adjusting the MOF/polymer precursor ratio. The membranes with MOF loading of 30 and 50 wt % were fabricated, and they were readily delaminated from the substrate without any additional treatment. The membranes are insoluble in common organic solvents, and the cross-linked matrix restricts the free volume of the polymer and prevents excessive solvent swelling. As shown in Figure 2a, the free-standing membrane was free of cracks or macroscopic defects, mechanically robust, and flexible, which is very important for further application in gas separation.

Figure 2. a) different views of UiO-66-IL-ClO4-based membranes. b) FTIR spectra of polyurethane oligomer, UiO-66-IL-ClO4 MOF, and the membranes with different MOF loading. c) PXRD patterns of polyurethane, UiO-66-IL-ClO4, and the membranes with different loading. FTIR spectra of the polyurethane oligomer and the UiO-66-IL-ClO4-based membranes with different MOF loading are shown in Figure 2b. In the membranes, the characteristic absorption band for the isocyanate group (2200 cm-1) on the isocyanate-terminated polyurethane oligomer completely disappeared for 50 wt % MOF loaded membrane and basically disappeared for 30 wt % MOF loaded membrane, meanwhile the new characteristic adsorption peaks of carbamic acid ester at 1018 cm-1 appeared. This unambiguously demonstrates that polymerization occurred and afforded cross-linked hybrid membranes. It is different from pure polyurethane membrane (SI), the PXRD patterns of the obtained MOF-loaded membranes are consistent with that of UiO-66-

18


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IL-ClO4 NPs, which indicated that the crystallinity and structural features of UiO-66-IL-ClO4 were maintained in the membrane (Figure 2c). Thermostability of the membrane was determined by thermogravimetric analysis (TGA). Compared to MOF NPs, the membranes exhibited a similar thermal decomposition behavior, and no weight loss was observed up to 200 °C, which showed that the membrane have good thermostability. Besides, the char yields of the membranes with different composition are correlated with the MOF loading (Figure 3).

Figure 3. Left: TGA traces of polyurethane, UiO-66-IL-ClO4, and the membranes with 30 and 50 wt % MOF loading. Right: SEM images of the UiO-66-IL-ClO4-based membranes. a) Surface morphology and b), c) cross-sectional view of the membrane with 30 wt % MOF loading. d) Surface morphology and e), f) cross-sectional view of the membrane with 50 wt % MOF loading. SEM images of the membranes are shown in Figure 3. After post-synthetic polymerization, the as-synthesized UiO-66-IL-ClO4 particles are closely connected with one another by oligomer linkages, which result in a high-quality hybrid membrane. The dense packing of the MOF particles is clearly observed in the cross-section image of the membrane (30 and 50 wt % MOF loading). The membrane is about 120 µm in thickness. The mechanical properties of the hybrid membranes were determined by stress-strain testing. The tensile strengths of the 30 and 50 wt % MOF-loaded membranes are 3.2 and 3.9 MPa, respectively, and the elongations at break are 21.5 19



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Page 20 of 39

and 15.5 %, respectively (SI). The tensile strength increases and the ultimate elongation decreases with increasing MOF content. The membranes are robust to withstand mechanical stress in practical application.

Figure 4. a) N2 adsorption isotherms of pure polyurethane membrane, and the membranes with different MOFs loading at 77 K. b) CO2, CH4, and N2 adsorption isotherms of the membrane with 30 wt % MOF loading at 298 K. c) CO2, CH4, and N2 adsorption isotherms of the membrane with 50 wt % MOF loading at 298 K. To determine the permanent porosity, the N2 adsorption properties of the UiO-66-IL-ClO4based membranes with different MOF NPs loading (30 and 50 wt %) and the pure polyurethane membrane were measured at 77 K (Figure 4). Compared to the pure UiO-66-IL-ClO4 NPs, the generated membranes possess smaller BET surface areas (10.491 m2/g, 30 wt % MOF; 34.264 m2/g, 50 wt % MOF) with smaller pore volumes (0.124 cm3/g for 30 wt % MOF-loaded membrane and 0.131 cm3/g for 50 wt % MOF loaded membrane), consequently, show lower N2 loading amounts (6.583 and 10.822 cm3/g for 30 and 50 wt % MOF loaded membranes, respectively). This is clearly due to the involved polyurethane matrix which showed almost no affinity for N2 (2.60 cm3/g, Figure 4a). As shown in Figures 4b and 4c, the membranes showed an increased CO2 uptake (12.499 and 17.122 cm3/g for 30 and 50 wt % MOF-loaded membranes, respectively) with the increased MOF NPs loading at 298 K under 1 atm, meanwhile no

20


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significant gas uptake increase for CH4 (1.286 and 2.208 cm3/g for 30 and 50 wt % MOF-loaded membranes, respectively) and N2 (0.574 and 0.887 cm3/g for 30 and 50 wt % MOF-loaded membranes, respectively) was observed under the same conditions. Remarkably, the 50 wt % UiO-66-IL-ClO4 loaded membrane exhibited the high selective values for CO2/N2 (37.60) and CO2/CH4 (24.61). For further demonstrating the functionality of the MOF NPs in the membranes, the similar ionic polyurethane membrane IPU-ClO4 (SI) was prepared and examined. The result showed that the IPU-ClO4 membrane exhibited a very low CO2 adsorption amount (3.808 cm3/g) at 298 K and 1 atm (SI), which was slightly better than the pristine polyurethane membrane, but much lower than those of MOF-based membranes. Its gas selectivity for CO2/N2 and CO2/CH4 under the given conditions was only 5.16 and 3.38, respectively. Table 3. Gas Permeation and Separation Performances toward CO2/CH4 and CO2/N2 of the Polyurethane Membrane, UiO-66-IL-ClO4-Based Membranes with Different MOF Loadinga Operation conditions Membrane

a

CO2

N2

CH4

permeance

permeance

permeance

CO2/CH4

T (K)

∆P (bar)

mol/(m2·s·Pa)

mol/(m2·s·Pa)

mol/(m2·s·Pa)

MOF-50 wt %b

298

6

9.94×10-10

3.08×10-11

5.42×10-11

32.3

18.3

MOF-30 wt %b

298

6

7.62×10-10

3.12×10-11

4.97×10-11

24.4

15.3

Polyurethaneb

298

6

1.69×10-10

2.51×10-11

2.46×10-11

6.7

6.9

MOF-50 wt %b

308

6

1.12×10-9

4.53×10-11

7.61×10-11

24.7

14.7

MOF-50 wt %b

323

6

1.93×10-9

9.24×10-11

1.32×10-10

20.9

14.6

MOF-50 wt %b

298

2

1.25×10-9

4.72×10-11

9.06×10-11

26.5

13.8

MOF-50 wt %b

298

10

7.55×10-10

1.93×10-11

3.01×10-11

39.1

25.1

MOF-50 wt %c

298

6

7.78×10-10

4.34×10-11

5.89×10-11

17.9

13.2

The reported data correspond to averages of the results; Mixed gas as feed: CO2/CH4 = 30/70; CO2/N2 = 10/90 vol %.

21

CO2/N2

b

Mixed gas as feed: CO2/CH4 = 50/50; CO2/N2 = 50/50 vol %


c


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

For evaluating the practical gas separation performance of the UiO-66-IL-ClO4 based membranes, the permeability and selectivity of CO2, N2, and CH4 for both binary mixed gases were examined using Wicke-Kallenbach cells (Table 3). Compared with pure polyurethane membrane, the incorporation of MOF NPs greatly increased the CO2 permeability, with a CO2 permeance increase of ~4.5 (30 wt % MOF loading) and ~5.9 times (50 wt % MOF loading). Meanwhile, the permeance for N2 and CH4 was enhanced by only ~1 and ~ 2 times at 50 wt % MOF loading. Thus, the ideal CO2/N2 or CO2/CH4 separation selectivity was largely enhanced, respectively (Table 3). The post-synthetic cross-linked UiO-66-IL-ClO4 membrane achieved preferential affinity for the target CO2 gas, improved homogeneity and compatibility MOFpolymer interface and optimized membrane structure and performance. Based on the analysis of different MOF loading, we found increase of MOF loading could optimize the CO2 separation performances of the membrane. As can been seen from Table 3, when the content of UiO-66-ILClO4 NPs increased from 30 to 50 wt %, the CO2 permeance increased by 1.3 times, while the CH4 permeance increased by 1.1 times. However, the N2 permeance of the membrane was basically unchanged after the increase of MOF NPs content. Thus, taking into account the gas permselectivity and mechanical property of the membranes, the 50 wt % MOF NPs loaded hybrid membrane present the optimal separation performance. As indicated in Table 3, the selectivity for CO2/N2 and CO2/CH4 on the membrane with 50 wt % loading of UiO-66-IL-ClO4 is up to 32.3 and 18.3 at 298 K, respectively. Furthermore, the relative reproducibility of accepted tests for typical gas separation performances was within 2 % (SI). Operating temperature is crucial determining the application of the membrane. As shown in Table 3, the gas permeability gradually increased with a rise of temperature, meanwhile the

22


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Page 23 of 39

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selectivity of CO2/N2 and CO2/CH4 decreased, which might be caused by the more rapid diffusion of CH4 and N2 molecules than that of CO2 with the temperature increasing. Gas permeability and selectivity of the membrane with 50 wt % loading of UiO-66-IL-ClO4 as a function of feed pressure toward equimolar CO2/CH4 and CO2/N2 are also shown in Table 3. The permeability of CO2, N2, and CH4 shows similar trends, that is, the values decrease with feed pressure. Interestingly, the gas selectivity of the MOF-based membrane increased with feed pressure increasing from 2 to 10 bar. The pores of MOF may be serve as CO2 transport channels and CO2 transport was remarkably enhanced in the membrane at higher pressure. While the transport of CH4 and N2 through the membrane followed the solution-diffusion mechanism which was independent on the feed gas pressure. Similar trends were found for some mixed matrix membranes using MOF particles as reported in the literature.51-52 The gas permeability and selectivity of the membrane as a function of CO2 concentration in the feed at fixed temperature and feed pressure were also examined. As indicated in Table 3, the CO2 permeability and selectivity was enhanced with an increase in the CO2 concentration in feed. This might be caused by the increase of the partial pressure of CO2 in the feed, which is consistent with the previous reports.53 Table 4. Comparison of Selectivity for CO2/N2 and CO2/CH4 of MOF NPs Based Polymer Supported Membranes

Entry

23

MOF

MOF loading (wt %)

Operation conditions

Selectivity

Polymer

Ref T (K)

∆P (bar)

CO2/N2

CO2/CH4

1

NH2-UiO-66

25

6FDA-ODA

308

10

---

44.7

54

2

UiO-67

25

6FDA-ODA

308

10

---

15.0

54



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 39

3

NH2-MIL-125(Ti)

0

PSF

303

3

---

22.0

55

4

NH2-MIL-125(Ti)

30

PSF

303

3

---

29.2

55

5

NH2-MIL-53(Al)

20

6FDA-DAM

298

1

---

26.3

56

6

NH2-MIL-53(Al)

25

PSF

308

3

---

27.5

57

7

NH2-MIL-101(Al)

25

PSF

308

3

---

29.0

57

8

NH2-UiO-66

30

PI

308

9

---

37.3

58

9

NH2-UiO-66

30

Matrimid 9725

308

9

---

37.3

58

10

Mg-MOF-74

20

PIM-1

298

2

---

19.1

59

11

MOF-5

24

Matrimid

298

3

---

61

60

12

NH2-MIL-53

36

PI

308

10

---

10.3

61

13

Cu3(BTC) 2

15

PI

298

6

35

72

62

14

MOF-5

5

PI

298

6

14.16

---

62

15

MIL-53

5

PI

298

6

27.53

----

62

16

NH2-UiO-66

40

PSF

308

3

26.0

24.0

63

17

ZIF-8

30

SEBS

308

3

12.0

5.4

64

18

ZIF-8

20

Matrimide 5218

333

4

11.1

18.6

65

19

ZIF-8

35

Pebax-2533

298

6

32.3

9.0

66

20

HKUST-1

10

PPO

303

3

24

28

67

21

MIL-53(Al)

10

Ulterm

298

5

41.1

---

68

22

Cu3(BTC)2

6

Matrimid

298

10

5.9

---

69

23

MIL-53

5

Ultem

298

5

24.1

---

70

24

ZIF-8

13

Ultem

308

7

36

---

71

25

ZIF-8

30

Matrimid

308

10

23

---

72

24


Page 25 of 39

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26

ZIF-8

30

6FDA-durene

298

2

17.0

17.1

73

27

UiO-66-IL-ClO4

30

Polyurethane

298

6

24.4

15.3

This work

28

UiO-66-IL-ClO4

50

Polyurethane

298

6

32.3

18.3

This work

To our knowledge, no polymer supported UiO-66 type MOFs based membranes for CO2/N2 selectivity are reported so far. Compared with reported polymer supported MMMs (Table 4), the ideal CO2/N2 selectivity of 32.3 exceeded most of reported values except Cu3(BTC)2-PI (35, Table 4, entry 13), MIL-53(Al)-Ultem (41.1, Table 4, entry 21), and ZiF-8-Ultem (36, Table 4, entry 24). On the other hand, the ideal CO2/CH4 selectivity of 18.3 is lower those of aminodecorated MOF-based MMMs, but higher than those of ZIF-8 based MMMs. Notably, all the reported MOFs-based polymer supported MMMs in Table 4 are generated from the inhomogeneous physical blending approach, and the UiO-66-IL-ClO4-polyurethane herein is the first homogeneous chemically cross-linked MMM for gas separation. The incorporation of the polymer support and MOF particles via covalent bonding is expected to improve the interfacial interaction between the polymer matrix and MOF fillers, consequently, enhancing NPs dispersion in the membrane and their compatibility with polymer support. CO2 Cycloaddition Catalyzed by MOF-based Membrane. We recently reported some imidazolium units containing MOFs which are demonstrated to be highly active class of heterogeneous catalysts for the organic transformations such as azidation, thiolation and CO2 cycloaddition.74-75 As shown above, IL moieties are fixed in the membrane via post chemical cross-linking approach. So we wondered if the UiO-66-IL-ClO4-polyurethane membrane could promote CO2 chemical transformation besides its selective adsorption. In a typical experiment, CO2 cycloaddition with epibromohydrin was chosen as a model reaction to evaluate the catalytic

25



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Page 26 of 39

performance of the obtained membranes. As shown in Table 5, with only UiO-66-IL-ClO4 membrane (0.7 mol % MOF NPs) or n-Bu4-NBr (TBAB, 1 mol %) as the catalyst, the CO2 cycloaddition yields are 29 (entry 1) and 86 % (entry 2), respectively. To our delight, when the reaction was performed in the presence of UiO-66-IL-ClO4 membrane (50 wt % loading, 0.7 mol % MOF) with the assistance of n-Bu4-NBr (TBAB, 1 mol %), the target product was obtained in 99 % yield under the same reaction conditions (entry 3), which is comparable to that exhibited by UiO-67-IL reported by us recently.75 The pure polyurethane (entry 4) and IPU-ClO4 (entry 5) membranes, however, cannot effectively promote CO2 cycloaddition. In addition, the present catalytic CO2 cycloaddition was extended to epichlorohydrin, and the expected chlorinated cyclic carbonate was also provided with excellent yield (99 %) under the optimized conditions (Table 5, entry 8). Table 5. CO2 Cycloaddition with Epoxides Catalyzed by MOF Membrane

Catalyst

Yield [%] a

1

UiO-67-IL-ClO4 membrane (0.7 mol % MOF)

29

2

TBAB (1 mol %)

86

3

UiO-67-IL-ClO4 membrane (0.7 mol % MOF)/TBAB (1 mol %)

99

4

polyurethane (0.7 mol %)

≤1

5

IPU-ClO4- (0.7 mol %)

˂3

7

UiO-67-IL-ClO4 membrane (0.7 mol % MOF)/TBAB (1 mol %)

99

Entry

a

Epoxide

Cyclic carbonate

The yields were determined by 1H NMR spectrum. The products characterization data were provided in SI.

We believe that the mechanism of the catalytic cycloaddition of CO2 with epoxides into cyclic carbonate over UiO-66-IL-X is similar to that of the reported works.76-78 Firstly, the epoxide ring

26


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is activated by the weak interaction between the epoxide O atom and the Brønsted acid (ZrOH/Zr-OH2) sites of defect Zr6 node in UiO-66-IL-X. Secondly, the less-hindered C atom of the weakly coordinating epoxide is attacked by X- from both MOF and TBAB to open the epoxy ring. Meanwhile, CO2 inserts into this anionic intermediate to form an alkylcarbonate anion. Thirdly, the alkylcarbonate anion is converted into the cyclic carbonate through the final ring-closing step, and the imidazolium and TBAB species are regenerated (SI). Thus, the synergistic effect of UiO66-IL-X and TBAB should be the dominating factor for this highly efficient CO2 cycloaddition under the given conditions.

CONCLUSION A novel chemical cross-linked membrane was fabricated by post-synthetic polymerization of imidazolium-decorated UiO-66-type MOF NPs and polyurethane oligomer. The covalent binding interaction driven polymer supported MMMs significantly improved NPs dispersion, NPspolymer interfacial interaction, consequently, the membrane processability and mechanical property. Compared to pure polymer support, the MMMs with 50 wt % MOF loading presented highly affinity for CO2, greatly enhanced CO2 permeance and ideal CO2 selectivity vs N2 and CH4. In addition, the obtained MMMs can be a highly active heterogeneous catalyst to promote CO2 transformation by cycloaddition with epihalohydrins under mild conditions. The results reported herein effectively expanded the application scope of MOFs, and could be a general approach to access many other kinds of MOF-based multifunctional chemically cross-linked membrane materials. ASSOCIATED CONTENT

27



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Supporting Information. The following files are available free of charge. 1

H NMR, IR, MS, ICP, SEM-EDX spectra, pore-sizes distribution, adsorption isotherms,

mechanical property (PDF). AUTHOR INFORMATION Corresponding Author *[email protected] *[email protected] Notes The authors declare no competing financial interest. ACKNOWLEDGMENT We are grateful for financial support from NSFC (Grant Nos. 21671122, 21604049 and 21475078), Shandong Provincial Natural Science Foundation (BS2015CL015), China and A Project of Shandong Province Higher Educational Science and Technology Program (J15LC05), and the Taishan Scholar’s Construction Project. We thank Prof. Zeng Chang (Nankai University) for very helpful discussion. REFERENCES (1) Yuan, Z. H.; Eden, M. R. Toward the Development and Deployment of Large-Scale Carbon Dioxide Capture and Conversion Processes. Ind. Eng. Chem. Res. 2016, 55, 3383–3419. (2) Darensbourg, D. J. Chemistry of Carbon Dioxide Relevant to Its Utilization: A Personal Perspective. Inorg. Chem. 2010, 49, 10765–10780.

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For Table Content

A bifunctional chemically cross-linked UiO-66-IL-X NMOF based membrane with both selective CO2 adsorption and catalytic conversion functionality is reported.

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Chemically Cross-Linked MOF Membrane Generated from

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