A Robust Zeolitic Imidazolate Framework Membrane with High H2

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Functional Inorganic Materials and Devices

A Robust Zeolitic Imidazolate Framework Membrane with High H2/CO2 Separation Performance under Hydrothermal Conditions Zhan Li, Pingping Yang, Shichen Yan, Qianrong Fang, Ming Xue, and Shilun Qiu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b01051 • Publication Date (Web): 09 Apr 2019 Downloaded from http://pubs.acs.org on April 11, 2019

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ACS Applied Materials & Interfaces

A

Robust

Membrane

Zeolitic with

Imidazolate

High

H2/CO2

Framework Separation

Performance under Hydrothermal Conditions Zhan Li, PingPing Yang, Shichen Yan, Qianrong Fang, Ming Xue,* and Shilun Qiu* State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Jilin University, Changchun 130012, P. R. China. KEYWORDS: zeolitic imidazolate framework, membrane, molecular sieving, gas separation, hydrothermal stability

ABSTRACT

An upsurge in searching membranes with high selectivity, permeability and stability, which have been considered to be promising in membrane-based gas separation process, has received huge attentions in academia and industry. In this work, we demonstrated a new molecular sieving ZIF membrane, which has a unique mixed-ligand ZIF structure constructed by two bulk imidazolate linkers within the zeolite GIS topology, resulting in appropriate aperture size, strong affinity to CO2, exceptional thermal and chemical stabilities, and superhydrophobic properties.

ACS Paragon Plus Environment

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Benefited from these features, the resulting JUC-160 membrane indeed exhibited remarkable separation efficiency and stability, with excellent H2/CO2 selectivity of 26.3 and considerable H2 permeance of 9.75×10-7 mol m-2 s-1 Pa-1 under temperature high up to 200°C. Furthermore, owing to its superhydrophobicity, JUC-160 membrane could remain its prominent separation performance even with the presence of steam.

INTRODUCTION Membrane-based separation technology is more feasible for gas separation in comparison to conventional technologies such as pressure-swing adsorption (PSA) and cryogenic distillation, owing to lower energy consumption and ease of operation.1-4 Currently, the commercially available polymeric membranes cannot achieve both high permeability and selectivity, known as Robeson upper bound limitation, which hindered the research and application of gas separation process. 5-6 As emerging microporous materials, Metal–Organic Framework (MOF) materials are very appealing for assembly into MOF membranes,7-12 which present a new promise and opportunity to overcome the limitations for gas separation, due to their uniform pore size, diverse structures, controllable pore characteristics and special chemical selectivity, thus have undergone rapid development over the past decade.13-20 Particularly, Zeolitic Imidazolate Frameworks (ZIFs), a cage-type microporous MOFs with zeolite topologies, which combine the unparalleled properties of both MOFs and zeolites, exhibiting preferential adsorption of gases as well as thermally and chemically stable properties.21 Taking advantage of its uniform pore structure and excellent stability, ZIF materials have been used to manufacture advanced membranes with exceptional


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separation performance.22-25 For example, 10% ZIF-71 has been incorporated into 6FDA-Durene matrix to produce the Mixed-Matrix Membrane, and the resulting membrane showed excellent performance in H2/CO2 separation.26 In a recent report, a thin and compact ZIF-8 membrane was successfully made by ligand-induced permselectivation method on porous Al2O3 supports for the gas separation, which is a notable step toward realizing scalable molecular sieving ZIF membranes.27 Nowadays the global carbon dioxide levels have approached a worrisome milestone, which caused many environmental problems such as greenhouse effect and climate changes. The precombustion carbon capture involves the water-gas shift (WGS) reaction yielding H2 and CO2 mixtures. Membrane separation is an effective separation technology to capture carbon dioxide while obtain high-purity hydrogen as a clean fuel.28-30 Considering the relatively harsh condition of the scenario, feasible membrane materials should possess high permeability, high selectivity and hydrothermal stability performances. Membranes work by forming a barrier between two phases that restricts the movement of some molecules while letting others through.31 For H2/CO2 gas mixture separation, the difference in kinetic diameters (2.89 Å for H2 and 3.30 Å for CO2) can be utilized to generate different diffusion rates in microporous MOF membranes. The aperture size is critical factor influencing diffusion rates of components in molecular sieving process.20, 32-34 Pores with aperture size dramatically larger than CO2 kinetic diameter will allow both H2 and CO2 molecules to permeate readily, leading to high gas permeance but low selectivity. For example, our reported HKUST-1 membrane presented very high H2 permeance but unsatisfying selectivity for H2/CO2 mixture (separation factor = 6.84) based on its larger aperture size (9 Å).35 On the contrary, pores with aperture diameter smaller than CO2 generally favor high selectivity for H2/CO2, while sacrificing gas


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permeances due to strong impulsive interaction between gas molecules and microporous walls. Both ZIF-736 and JUC-15037 membranes had ultra-microporous aperture smaller than CO2, exhibiting superior selectivity but low permeance of H2 (4.55 × 10-8 mol m-2 s-1 Pa-1 for ZIF-7 membrane and 1.83 × 10-7 mol m-2 s-1 Pa-1 for JUC-150 membrane, respectively). It is worth noting that both permeance and selectivity are long-sought-after parameters to assess the performance of a membrane in gas separation. Through theoretical calculations and experimental results, it has been demonstrated the diffusion rate of CO2 faced a steep fall when the aperture size is diminished to approximately the kinetic diameter of CO2, because considerable activation energy was required to overcome tremendous energy barrier to diffusion generated by repulsive interactions between windows and gas molecules.32, 38 In this case, CO2 molecules are really hard to permeate through this confined aperture, whilst H2 molecules diffusion rate still run at a satisfying level, resulting in high selectivity over CO2 along with high permeance of H2. Therefore, to achieve highly effective separation, the optimized effective aperture should be slightly larger than the kinetic diameter of CO2. On the other hand, gas permeation experiments and hybrid molecular simulation studies indicated that strong affinity towards CO2 result in the further decrease of CO2 permeability and the remarkable enhancement of H2/CO2 selectivity.39-40 Huang and Caro creatively improved the H2/CO2 separation performance of ZIF-90 membrane by post-synthesis modification (PSM), due to the presence of the imine functionality in ZIF-90 cages can constrict the pore size and enhance the affinity for CO2.41 It is worth of mention that, among all ZIF materials, the mixed-ligand ZIFs comprising two different imidazolate linkers, possess narrow pore aperture and especially stronger affinity for CO2, probably due to enhanced electrostatic interactions towards CO2 caused by


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asymmetric of the framework.42-43 However, mixed-ligand ZIF membranes have been barely explored yet.22 In light of these studies, the strategy to maximize H2/CO2 separation efficiency of ZIF membranes can be concluded as designing proper aperture size and enhancing interactions between CO2 and ZIF structures. Herein, we fabricated a new mixed-ligand ZIF membrane (JUC160 membrane) for gas separation. Different to other mixed-ligand ZIFs, JUC-160 [Zn4(2mBIm)3(BIm)5] has a unique ZIF structure constructed by two bulk imidazolate linkers (2methylbenzimidazole and benzimidazole).44 Methyl group and bulk phenyl rings on imidazolate linkers fill in the void space inside the framework, resulting in the optimized aperture size to block CO2, strong affinity towards CO2, and excellent thermal and chemical stabilities. As expected, the resulting ZIF membranes are stable under 200°C with the presence of steam and exhibit excellent gas separation efficiency, achieving high selectivity, high permeability and hydrothermal stability simultaneously.

EXPERIMENTAL SECTION Reagents and chemicals. Benzimidazole (named bIM, 98%, Sigma-Aldrich), 2methylbenzimidazole (named 2-mbIM, 98%, Sigma-Aldrich), zinc nitrate hexahydrate (Zn(NO3)2·6H2O, 98%, Sigma-Aldrich), zinc acetate dihydrate (Zn(Ac)2·2H2O, Sinopharm Chemical Reagent Co., Ltd, AR), and N,N’-dimethylformamide (DMF, West Long Chemical Co., Ltd, AR). All reagents and chemicals were obtained from commercial sources and used without further purification. Synthesis of JUC-160 nanoseeds. 0.4 mmol bIM and 0.5 mmol 2-mbIM were dissolved in 8 ml DMF, then 8 ml DMF containing 0.45 mmol Zn(Ac)2·2H2O was added drop-wise into the


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ligand solution. The mixture was kept stirring at room temperature for 10 hours. The JUC-160 nanoseeds were collected by centrifuging and washed with ethanol for 3 times. Particle size of obtained JUC-160 nanoseeds was approximately 200 nm. Preparation of porous Alumina Discs as Membrane Support. Alumina discs (25mm of diameter and 1.5mm of thickness) were home-made. Commercially available high purity αalumina powders (Aladdin Corp.) with particle size about 200nm were used as received. The powders were compressed under 12 Mpa for 1 min and sintered at 1000°C for 12 h. After cooling down, one side of the α-alumina disc was polished by sand papers (grit #800, #1200), then cleaned in deionized water under sonication for 10 min and dried over night at 60°C. Preparation of JUC-160 Membranes. JUC-160 membranes supported on porous alumina supports were prepared through secondary growth method. Well-dispersed seeding solution containing 1wt% JUC-160 nanoseeds were dip-coated onto alumina support for 3 times to guarantee full coverage of the support surface. After drying, the seeded support was held vertically in a Teflon autoclave. A mixture of 0.3 mmol 2-mbIM, 0.375 mmol of bIM and 0.4 mmol of Zinc nitrate hexahydrate in 20 ml DMF was poured into the autoclave. Then the autoclave was sealed and placed in a pre-heated oven under 180°C for 36h. After cooling down, the membrane was washed with ethanol for 3 times and dried at room temperature overnight. Characterization. X-Ray Diffraction (PANalytical B.V. Empyreanpowderdiffractometer) was used to determine the crystalline structure of JUC-160 powders and JUC-160 membranes. Diffraction intensities were collected using CuKα radiation (wavelengths λ=1.5418Å) under a range of 2θ from 5° to 40°. Thermal stability test was conducted on Rigaku D/max 2200 vpc diffractometer. Samples were placed inside a chamber and heated in nitrogen with heating rate of 5°C /min. Each temperature step was maintained 30 min for PXRD measurement. Morphology of


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the prepared JUC-160 nanoseeds and membranes were examined through Scanning Electron Microscope (JSM-6510A, JEOL). Gas adsorption measurement of JUC-160 was performed on an Autosorb iQ2 adsorptometer. Membrane separation performance evaluation. Gas permeation of JUC-160 membrane was conducted in a Wicke–Kallenbach system (Scheme S1). High purity H2 (>99.995%), CH4 (>99.95), N2 (>99.995) and CO2 (>99.995) were used as feed gases. Gas chromatography (GC2014C, SHIMAZU) was employed as a real-time monitor, analysing the composition of permeated gas. High purity Argon (>99.995%) was used as carrier with flow rate set at 35 ml/min. To avoid any interference on gas permeation caused by solvent guest molecules, the membrane was degassed under 180°C for 12h before permeation test. This approach is important to guarantee high permeances of gases. The degassed JUC-160 membrane was then placed into a stainless-steel membrane cell. At membrane upstream, flow rate was set to 50 ml/min for single gas component and 100 ml/min in total for binary gas mixture permeation test. High purity Argon (>99.995%) was used as sweep gas to carry permeate gas from downstream of the membrane into gas chromatography. The flux of gas was measured by an electronic soap-film flow meter. Membrane permeance, Pi (mol m-2s-1Pa-1), can be calculated by: 𝑁𝑖

𝑃𝑖 = ∆𝑝𝑖 × 𝐴 (1) Where Ni (mol s-1) is the permeate rate of component i, ∆pi (Pa) is the trans-membrane pressure difference of component i, and A (m2) is the effective area of membrane. Ideal selectivity (also called permselectivity) is defined as ratio of single component permeances. Separation factor for component i and j is evaluated according to following equation: 𝑋𝑖/𝑋𝑗

𝛼𝑖,𝑗 = 𝑌𝑖/𝑌𝑗 (2)


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RESULTS AND DISCUSSION JUC-160 was obtained by using two bulk imidazolate linkers (2-mbIM and bIM) with a zeolite GIS topology. The unique structure feature of JUC-160 was that it possessed micro cages connected each other through small apertures. The existence of methyl side chains and phenyl rings on the imidazolate linkers projected into the pore regions and felicitously modulated the aperture size for gas molecular sieving (Figure 1 and S1). The TGA trace and the in-situ PXRD patterns of JUC-160 indicated its remarkable thermal stability up to 450°C (Figure S2). In addition, JUC-160 had excellent chemical stability in various solvents including water, benzene and aqueous alkaline solution under high temperature for seven days (Figure S3). Another important feature of JUC-160 was its exceptional superhydrophobic properties with a water contact angle of > 150° (Figure S4), which endowed JUC-160 membranes certain advantages over polymer membranes and sol–gel-derived silica membranes in the presence of steam at high temperature. The PXRD patterns of JUC-160 nanoseeds and membranes were in good agreement with corresponding ones in the simulated pattern (Figure S5), indicating that pure JUC-160 phase was

Figure 1. (A) 3D structure of JUC-160 and yellow balls are placed to indicate the space in the cages (Color code: Zn, blue; N, black; C, gray; Hydrogen atoms have been omitted for clarity); (B) the GIS net is shown as a stick and tiling diagram (red: four-membered rings; cyan: eight-membered rings).


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obtained. Sharp peaks and strong intensities suggested highly crystallinity of the prepared membranes. Morphologies of JUC-160 nanoseeds and as-prepared membranes were observed under SEM. The particle size of cubic nanoseeds was about 200nm (Figure 2a). A continuous and defect-free membrane was compactly prepared on the α-alumina disc as shown in Figure 2b and 2c. Grains of JUC-160 were well intergrown and fully covered porous alumina support without any visible cracks. The thickness of the as-synthesized membrane was approximate 2.5μm measured from cross-sectional view (Figure 2d), which is one of the thinnest ZIF membranes reported to date. This ultra-thin membrane guarantees high permeance, which is of vital concern in gas separation. Due to the flexibility of ZIF structures, aperture size measured from crystalline data may not be able to precisely interpret accessibility of ZIF pore structure during kinetic separation process45-47. Therefore, to verify the effective aperture size of JUC-160, gas adsorption measurements of the activated JUC-160 sample were performed (Figure S6a).48-49 Adsorption isotherms of N2 (3.64 Å)

Figure 2. (a) SEM images of JUC-160 nanoseeds. (b) top view of as-prepared JUC-160 membrane under lower magnification. (c) top view of as-prepared JUC-160 under higher magnification. (d) cross-sectional view of as-prepared JUC-160 membrane.


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and Ar (3.4 Å) revealed that JUC-160 basically takes up a negligible number of Ar and N2 even at 87K and 77K, respectively. Whereas using CO2 (3.3 Å) as the probing molecule, a significant increase was observed in the amount of CO2 adsorbed by JUC-160 with a typical Type-I sorption behavior. These clear results intuitively suggest that the effective aperture size of JUC-160 is between 3.3 Å and 3.4 Å, which is just slightly larger than CO2. It is worth of mention that this appropriate aperture would increase the energy barrier for CO2 diffusion, conversely, facilitate H2 transport through the JUC-160 membrane. Furthermore, to quantify the strength of interaction between CO2 and JUC-160 structure, the adsorption isotherms of CO2 at 273K and 298K were investigated (Figure S6b) to calculate the Henry’s constant (KH) and the isosteric heat of adsorption (Qst).50 Henry’s constant, a measure of the partitioning of a gas between the gas phase and gas adsorbed onto the surface of an adsorbent material under a constant temperature at very low pressure, is a common indicator to demonstrate interaction between the adsorbate and the adsorbent. A higher value of KH means a stronger adsorbate/adsorbent interaction because at the initial stage there is very little interaction between adsorbate molecules. In the limit of very low pressure, the sorption capacity exhibits a linear dependency on pressure, which can be expressed as equation 3. 𝐾H = lim

𝑃𝑖→0

𝑀𝑖 𝑃𝑖

(3)

Where KH is the Henry’s constant, and Mi and Pi are the pressure and the amount of adsorbed species i, respectively. KH of JUC-160 for CO2 at 298K is calculated to be 35.3 mol m-3 kPa-1.


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Isosteric heat of adsorption is another parameter to evaluate interactions between CO2 and JUC160 framework from the view of enthalpy changes inside the system. For a certain amount of adsorption, Qst can be calculated by Clausius–Clapeyron equation (4): 𝑄𝑠𝑡 =

𝑅𝑇1𝑇2ln(𝑝2/𝑝1) 𝑇2 ― 𝑇1

(4)

Where Qst is isosteric heat of adsorption, R is gas constant, T and p represent the temperature and pressure corresponding to the given amount, respectively. Initial Qst value for CO2 was calculated to be 24.9kJ/mol (Figure S6c). KH and Qst of JUC-160 are of the highest among MOF materials (Table 1), indicating strong interaction between CO2 and JUC-160 framework, which favored low CO2 diffusion rate during Table 1. Comparison of Henry’s constants and initial Qst value of CO2 molecules adsorbed on various MOF materials. KH

Qst

(103 kmol·m-3·kPa-1)

(kJ·mol-1)

UiO-66

10.76

16.1

52

MIL-53(Al)

38.41

12.5

52

MOF-177

3.44

12.0

52

MOF-5

6.91

10.0

52

ZIF-68

27.51

NA

53

ZIF-69

30.87

NA

53

ZIF-70

27.14

NA

53

ZIF-76

18.6

25.1

54

ZIF-8

5.1

15.93

54

JUC-160

35.3

24.9

this work

MOFs

Ref.


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membrane separation process. Based on the above studies, JUC-160 material showed a great promise for applications in H2/CO2 membrane separation with a satisfying H2 permeance and an extremely low CO2 permeance. Encouraged by the optimized aperture size and specific adsorption affinity towards CO2 of JUC160 structure, the permeances of four small-molecule gases with different diameters (H2: 2.89 Å, CO2: 3.3 Å, N2: 3.64 Å, CH4: 3.8 Å) were evaluated through the Wicke–Kallenbach permeation apparatus.51 As shown in Figure 3a, the single gas permeances of H2, CO2, N2 and CH4 decreased with the increasing kinetic diameters, indicating the JUC-160 membrane was a molecular sieving (size-selective) membrane. Among all tested gased, H2 presented a very high permeance of 6.68 × 10-7mol m-2 s-1 Pa-1, whereas not only N2 and CH4 but also CO2 exhibited lower permeances below 1.0 × 10-7 mol m-2 s-1 Pa-1. This result clearly revealed that JUC-160 membrane allowed H2 to pass through with a satisfying permeance, but CO2, N2 and CH4 gas molecules had to overcome a considerable energy barrier to diffuse in JUC-160 membrane, due to the effective aperture size of JUC-160. It was worth mentioning that CO2 exhibited the extremely low permeance, due to the extra strong interaction between CO2 and JUC-160 framework further slowed down permeation of CO2, which resulted in the remarkable enhancement of H2/CO2 selectivity. To evaluate the performance of the JUC-160 membranes in the purification and recycling of hydrogen from gas mixtures, gas separation studies of binary gases (H2/CH4, H2/N2 and H2/CO2) were carried out. As shown in Table 2, the separation factor of the gas mixtures dramatically exceeded Knudsen diffusion ratio, further proving the high quality of JUC-160 membranes. In particular, JUC-160 membrane showed excellent separation efficiency towards H2/CO2 mixture (Figure 3b). It was worth noting that H2 permeance of JUC-160 membrane was fairly high


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Table 2. Binary gas mixture separation performance of 3 parallel JUC-160 membranes.* H2 Permeance (10-7 mol m-2 s-1Pa-1)

Separation factor

H2/CO2

2.54/2.61/2.58

15.27/15.15/15.22

H2/N2

2.63/2.70/2.61

7.23/7.48/7.31

H2/CH4

2.73/2.65/2.68

8.42/8.51/8.44

* Separation test was conducted at 25°C with feed pressure at 1 bar. JUC-160 membrane exhibited strong size-selective effect. Particularly, due to appropriate pore structure and strong affinity towards CO2, JUC-160 membrane showed very high separation efficiency for H2/CO2 mixture. Also, reproducibility of JUC-160 was also good since all 3 parallel JUC-160 membrane showed similar separation efficiency. comparing to other ZIF and MOF membranes, which was attributed to the ultra-thin JUC-160 layer and the appropriate aperture size. As illustrated above, the narrow aperture of JUC-160 offered relatively spacious pathway for rapid passage of H2 molecules but rather confined space for larger CO2 molecules to permeate, showing strong molecular sieving effect. Moreover, strong affinity to CO2 rendered a reduced diffusivity of CO2, benefiting high H2/CO2 selectivity. 41, 44, 55 Therefore, high permeance of H2 and high selectivity for H2/CO2 was simultaneously achieved in the unique pore structure of JUC-160 membrane. This separation process is further quantified by the calculation of solubility and diffusivity (see supplementary information). Considering the relatively harsh conditions for practical steam reforming of natural gas, the H2/CO2 separation performance of JUC-160 membrane were further evaluated under thermal and hydrothermal conditions. The membrane cell was placed in a heatable chamber with a programmable temperature controller. Separation test was conducted under temperature ranging from 30°C to 200°C with heating rate of 5°C/min. Permeance of H2 and CO2 along with selectivity during heating stage were shown in Figure 4a. Permeance of H2 climbed higher under elevated


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Figure 3. (a) Single gas (H2, CO2, N2 and CH4) permeances through the prepared JUC-160 membrane at normal temperature and pressure versus molecular kinetic diameters. (b) Permeances of H2, CO2 and corresponding H2/CO2 separation factor over time. temperature while only a subtle increase in CO2 permeance was found, resulting in improved selectivity at the higher temperature. As for H2 molecule, which is much smaller than the effective aperture size of JUC-160, acquired extra initial energy from heating, boosted its thermal motion, leading to higher permeance at higher temperature. However, the effective pore aperture was only slightly larger than the kinetic diameter of CO2, hence CO2 molecules had to overcome extremely high energy barrier at the entrance of the constricted pores. Although heating of the gas mixture endowed CO2 some energy to penetrate, strong interaction between CO2 and JUC-160 framework dramatically faded this effect. As a consequence of these effects, CO2 permeance did not show


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apparent improve under high temperature but H2 did, thus selectivity for H2/CO2 reached remarkably high up to 26.3 at 200°C. Concurrent increase in gas permeance and selectivity resulted in the superior separation efficiency of JUC-160 membrane. To the best of our knowledge, this separation efficiency of JUC-160 under high temperature is extremely competitive among MOF membranes reported to date (Figure 5).36, 41, 56-63 The limited hydrothermal stability of membranes will exclude their use for H2 removal with the presence of steam. Furthermore, in order to explore the hydrothermal stability of JUC-160 membrane, the gas separation studies were proceeded with equimolar H2/CO2 gas mixtures containing 3vol% or 12vol% steam at 200°C, respectively. The result clearly showed that adding

Figure 4. H2/CO2 separation performance during heating (a) and under hydrothermal condition (b). Red symbols and blue symbols are permeance of hydrogen and separation factor for H2/CO2, respectively.


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steam into feed gas caused a slight decrease of both H2 and CO2 permeances compared with the dry feed, but no substantial difference on selectivity for H2/CO2 (Figure 4b). It can be explained by superhydrophobicity of JUC-160 structure. When the permeation test was conducted with the presence of steam, hydrophobic pores within JUC-160 structure were either empty or occupied by water molecule, making no influence on gas selectivity.63 The subtle loss in permeance can be attributed to parallel permeation of H2O molecules and gas molecules. Since H2O molecules may block the way for the passage of gas molecules, increasing H2O content from 3 vol% to 12 vol% leaded to more loss in gas permeance. It was worth-noting that the H2 and CO2 permeances can be restored after switching off the steam, showing excellent recyclability of JUC-160 membrane. This complete reversibility indicated a mutual mixture permeation effect rather than the JUC-160 structural damage. Moreover, the membrane showed steady separation performance under 200°C with the presence of steam for 24 hours (Figure S7), SEM images and PXRD patterns revealed that the crystal structure and morphology of the JUC-160 membrane remained essentially unchanged after gas separation under harsh conditions (Figures S8 and S9). These properties indicated that the JUC-160 membrane possessed excellent thermal and hydrothermal durability.

Figure 5. Comparison of reported MOF membranes for H2/CO2 separation under high temperature.


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CONCLUSION In summary, to achieve high efficiency membrane-based gas separation, a new and robust ZIF membrane was successfully synthesized and systematically investigated the separation performances under different operational environments. JUC-160 has the unique ZIF structure constructed by two bulk imidazolate ligands, which enables high H2/CO2 separation performance of JUC-160 membrane. The as-prepared JUC-160 membrane showed high H2 permeance of 9.75 × 10-7mol m-2s-1Pa-1 under 200°C and high H2/CO2 selectivity of 26.3. This excellent separation performance can be attributed to the strong molecular sieving effect generated by narrow aperture. Moreover, the strong affinity to CO2 also benefited high H2/CO2 selectivity of JUC-160 membrane, since it rendered a reduced diffusivity of CO2. Furthermore, excellent thermal and chemical stabilities and superhydrophobicity rendered excellent durability of JUC-160 membrane, thus outstanding separation performance can be achieved even under hydrothermal conditions. These characteristics of the JUC-160 membrane offer great potential for application in the separation of H2/CO2 released from steam reforming of natural gas. Given the very versatile structures and special features of ZIFs, ZIF membranes will continue to emerge and revolutionize gas separation in the future.

ASSOCIATED CONTENT Supporting Information. Schematic illustration of separation performance evaluation system; In-situ PXRD pattern TGA curve of JUC-160; PXRD pattern of JUC-160 after being treated in different solvents; water contact angle of bulk JUC-160 powder; PXRD of nanoseeds, as-prepared membrane and membrane after separation test under harsh condition; gas adsorption isotherm and calculation of


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heat of adsorption; durability test of JUC-160 membrane under hydrothermal condition; PXRD of JUC-160 after tested for 120min under hydrothermal conditions; SEM image of JUC-160 after tested for 120min under hydrothermal conditions; Binary gas mixture separation performance and reproducibility of JUC-160 membrane (PDF). AUTHOR INFORMATION Corresponding Author * E-mail: [email protected] (M.X). * E-mail: [email protected] (S.Q.). Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This work was financially supported by National Natural Science Foundation of China (21571076, 21390394, 21571079), and “111” project (B07016). REFERENCES 1. Ge, Q.; Wang, Z.; Yan, Y., High-Performance Zeolite NaA Membranes on PolymerZeolite Composite Hollow Fiber Supports. J. Am. Chem. Soc. 2009, 131, 17056-17057. 2. Pham, T. C.; Kim, H. S.; Yoon, K. B., Growth of Uniformly Oriented Silica Mfi and Bea Zeolite Films on Substrates. Science 2011, 334, 1533-1538. 3. Koros, W. J.; Zhang, C., Materials for Next-Generation Molecularly Selective Synthetic Membranes. Nat. Mater. 2017, 16, 289-297. 4. Ockwig, N. W.; Nenoff, T. M., Membranes for Hydrogen Separation. Chem. Rev. 2007, 107, 4078-4110. 5. Robeson, L. M., The Upper Bound Revisited. J. Membr. Sci. 2008, 320, 390-400. 6. Shao, L.; Low, B. T.; Chung, T.-S.; Greenberg, A. R., Polymeric Membranes for the Hydrogen Economy: Contemporary Approaches and Prospects for the Future. J. Membr. Sci. 2009, 327, 18-31.


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Page 19 of 23 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


7. Hod, I.; Bury, W.; Karlin, D. M.; Deria, P.; Kung, C.-W.; Katz, M. J.; So, M.; Klahr, B.; Jin, D.; Chung, Y.-W.; Odom, T. W.; Farha, O. K.; Hupp, J. T., Directed Growth of Electroactive Metal-Organic Framework Thin Films Using Electrophoretic Deposition. Adv. Mater. 2014, 26, 6295-6300. 8. So, M. C.; Jin, S.; Son, H. J.; Wiederrecht, G. P.; Farha, O. K.; Hupp, J. T., Layer-by-Layer Fabrication of Oriented Porous Thin Films Based on Porphyrin-Containing Metal-Organic Frameworks. J. Am. Chem. Soc. 2013, 135, 15698-15701. 9. Ye, Y.; Guo, W.; Wang, L.; Li, Z.; Song, Z.; Chen, J.; Zhang, Z.; Xiang, S.; Chen, B., Straightforward Loading of Imidazole Molecules into Metal-Organic Framework for High Proton Conduction. J. Am. Chem. Soc. 2017, 139, 15604-15607. 10. Huang, X. C.; Lin, Y. Y.; Zhang, J. P.; Chen, X. M., Ligand-Directed Strategy for ZeoliteType Metal-Organic Frameworks: Zinc(Ii) Imidazolates with Unusual Zeolitic Topologies. Angew. Chem. Int. Ed. Engl. 2006, 45, 1557-1559. 11. Pang, J.; Jiang, F.; Wu, M.; Liu, C.; Su, K.; Lu, W.; Yuan, D.; Hong, M., A Porous MetalOrganic Framework with Ultrahigh Acetylene Uptake Capacity under Ambient Conditions. Nat. Commun. 2015, 6, 7575. 12. Zhu, C.; Perman, J. A.; Gerald Ii, R. E.; Ma, S.; Huang, J., Chemical Detection Using a Metal-Organic Framework Single Crystal Coupled to an Optical Fiber. ACS Appl. Mater. Interfaces 2019, 11, 4393-4398. 13. Qiu, S.; Xue, M.; Zhu, G., Metal-Organic Framework Membranes: From Synthesis to Separation Application. Chem. Soc. Rev. 2014, 43, 6116-6140. 14. Zhang, X.; Zhao, Y.; Mu, S.; Jiang, C.; Song, M.; Fang, Q.; Xue, M.; Qiu, S.; Chen, B., Uio-66-Coated Mesh Membrane with Underwater Superoleophobicity for High-Efficiency OilWater Separation. ACS Appl. Mater. Interfaces 2018, 10, 17301-17308. 15. Chen, Y.; Zhang, S.; Cao, S.; Li, S.; Chen, F.; Yuan, S.; Xu, C.; Zhou, J.; Feng, X.; Ma, X.; Wang, B., Roll-to-Roll Production of Metal-Organic Framework Coatings for Particulate Matter Removal. Adv. Mater. 2017, 29, 1606221. 16. Peng, Y.; Li, Y.; Ban, Y.; Jin, H.; Jiao, W.; Liu, X.; Yang, W., Membranes. Metal-Organic Framework Nanosheets as Building Blocks for Molecular Sieving Membranes. Science 2014, 346, 1356-1359. 17. Brown, A. J.; Brunelli, N. A.; Eum, K.; Rashidi, F.; Johnson, J. R.; Koros, W. J.; Jones, C. W.; Nair, S., Separation Membranes. Interfacial Microfluidic Processing of Metal-Organic Framework Hollow Fiber Membranes. Science 2014, 345, 72-75. 18. Wang, X.; Chi, C.; Zhang, K.; Qian, Y.; Gupta, K. M.; Kang, Z.; Jiang, J.; Zhao, D., Reversed Thermo-Switchable Molecular Sieving Membranes Composed of Two-Dimensional Metal-Organic Nanosheets for Gas Separation. Nat. Commun. 2017, 8, 14460. 19. Lin, Y. S., Metal Organic Framework Membranes for Separation Applications. Curr. Opin. Chem. Eng. 2015, 8, 21-28. 20. Li, H.; Haas-Santo, K.; Schygulla, U.; Dittmeyer, R., Inorganic Microporous Membranes for H2 and Co2 Separation—Review of Experimental and Modeling Progress. Chem. Eng. Sci. 2015, 127, 401-417. 21. Park, K. S.; Ni, Z.; Cote, A. P.; Choi, J. Y.; Huang, R.; Uribe-Romo, F. J.; Chae, H. K.; O'Keeffe, M.; Yaghi, O. M., Exceptional Chemical and Thermal Stability of Zeolitic Imidazolate Frameworks. Proc. Natl. Acad. Sci. U. S. A. 2006, 103, 10186-10191. 22. Yao, J.; Wang, H., Zeolitic Imidazolate Framework Composite Membranes and Thin Films: Synthesis and Applications. Chem. Soc. Rev. 2014, 43, 4470-4493.


19


Page 20 of 23

23. Kwon, H. T.; Jeong, H.-K., In Situ Synthesis of Thin Zeolitic–Imidazolate Framework Zif8 Membranes Exhibiting Exceptionally High Propylene/Propane Separation. J. Am. Chem. Soc. 2013, 135, 10763-10768. 24. Huang, K.; Dong, Z.; Li, Q.; Jin, W., Growth of a Zif-8 Membrane on the Inner-Surface of a Ceramic Hollow Fiber Via Cycling Precursors. Chem. Commun. (Camb) 2013, 49, 10326-10328. 25. Shekhah, O.; Swaidan, R.; Belmabkhout, Y.; du Plessis, M.; Jacobs, T.; Barbour, L. J.; Pinnau, I.; Eddaoudi, M., The Liquid Phase Epitaxy Approach for the Successful Construction of Ultra-Thin and Defect-Free Zif-8 Membranes: Pure and Mixed Gas Transport Study. Chem. Commun. (Camb) 2014, 50, 2089-2092. 26. Japip, S.; Liao, K. S.; Chung, T. S., Molecularly Tuned Free Volume of Vapor CrossLinked 6fda-Durene/Zif-71 Mmms for H2 /Co2 Separation at 150° C. Adv. Mater. 2017, 29, 1603833. 27. Ma, X.; Kumar, P.; Mittal, N.; Khlyustova, A.; Daoutidis, P.; Mkhoyan, K. A.; Tsapatsis, M., Zeolitic Imidazolate Framework Membranes Made by Ligand-Induced Permselectivation. Science 2018, 361, 1008-1011. 28. D'Alessandro, D. M.; Smit, B.; Long, J. R., Carbon Dioxide Capture: Prospects for New Materials. Angew. Chem. Int. Ed. Engl. 2010, 49, 6058-6082. 29. Bae, Y. S.; Snurr, R. Q., Development and Evaluation of Porous Materials for Carbon Dioxide Separation and Capture. Angew. Chem. Int. Ed. Engl. 2011, 50, 11586-11596. 30. Gallucci, F.; Fernandez, E.; Corengia, P.; Annaland, M. V., Recent Advances on Membranes and Membrane Reactors for Hydrogen Production. Chem. Eng. Sci. 2013, 92, 40-66. 31. Gin, D. L.; Noble, R. D., Chemistry. Designing the Next Generation of Chemical Separation Membranes. Science 2011, 332, 674-676. 32. Thornton, A. W.; Hilder, T.; Hill, A. J.; Hill, J. M., Predicting Gas Diffusion Regime within Pores of Different Size, Shape and Composition. J. Membr. Sci. 2009, 336, 101-108. 33. Haldoupis, E.; Nair, S.; Sholl, D. S., Efficient Calculation of Diffusion Limitations in Metal Organic Framework Materials: A Tool for Identifying Materials for Kinetic Separations. J. Am. Chem. Soc. 2010, 132, 7528-7539. 34. Wilmer, C. E.; Farha, O. K.; Bae, Y.-S.; Hupp, J. T.; Snurr, R. Q., Structure–Property Relationships of Porous Materials for Carbon Dioxide Separation and Capture. Energy Environ. Sci. 2012, 5, 9849-9856. 35. Guo, H.; Zhu, G.; Hewitt, I. J.; Qiu, S., "Twin Copper Source" Growth of Metal-Organic Framework Membrane: Cu(3)(Btc)(2) with High Permeability and Selectivity for Recycling H(2). J. Am. Chem. Soc. 2009, 131, 1646-1647. 36. Li, Y. S.; Liang, F. Y.; Bux, H. G.; Yang, W. S.; Caro, J., Zeolitic Imidazolate Framework Zif-7 Based Molecular Sieve Membrane for Hydrogen Separation. J. Membr. Sci. 2010, 354, 4854. 37. Kang, Z.; Xue, M.; Fan, L.; Huang, L.; Guo, L.; Wei, G.; Chen, B.; Qiu, S., Highly Selective Sieving of Small Gas Molecules by Using an Ultra-Microporous Metal–Organic Framework Membrane. Energy Environ. Sci. 2014, 7, 4053-4060. 38. Ruthven, D. M., Molecular Sieve Separations. Chemie Ingenieur Technik 2011, 83, 44-52. 39. Zhang, L.; Hu, Z.; Jiang, J., Sorption-Induced Structural Transition of Zeolitic Imidazolate Framework-8: A Hybrid Molecular Simulation Study. J Am Chem Soc 2013, 135, 3722-3728. 40. Krishna, R.; van Baten, J. M., In Silico Screening of Zeolite Membranes for Co2 Capture. J. Membr. Sci. 2010, 360, 323-333.


20

Page 21 of 23 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


41. Huang, A.; Wang, N.; Kong, C.; Caro, J., Organosilica-Functionalized Zeolitic Imidazolate Framework ZIF-90 Membrane with High Gas-Separation Performance. Angew. Chem. Int. Ed. Engl. 2012, 51, 10551-10555. 42. Morris, W.; Leung, B.; Furukawa, H.; Yaghi, O. K.; He, N.; Hayashi, H.; Houndonougbo, Y.; Asta, M.; Laird, B. B.; Yaghi, O. M., A Combined Experimental-Computational Investigation of Carbon Dioxide Capture in a Series of Isoreticular Zeolitic Imidazolate Frameworks. J. Am. Chem. Soc. 2010, 132, 11006-11008. 43. Li, J.-R.; Ma, Y.; McCarthy, M. C.; Sculley, J.; Yu, J.; Jeong, H.-K.; Balbuena, P. B.; Zhou, H.-C., Carbon Dioxide Capture-Related Gas Adsorption and Separation in Metal-Organic Frameworks. Coord. Chem. Rev. 2011, 255, 1791-1823. 44. Huang, L.; Xue, M.; Song, Q.; Chen, S.; Pan, Y.; Qiu, S., Carbon Dioxide Selective Adsorption within a Highly Stable Mixed-Ligand Zeolitic Imidazolate Framework. Inorg. Chem. Commun. 2014, 46, 9-12. 45. Phan, A.; Doonan, C. J.; Uribe-Romo, F. J.; Knobler, C. B.; O'Keeffe, M.; Yaghi, O. M., Synthesis, Structure, and Carbon Dioxide Capture Properties of Zeolitic Imidazolate Frameworks. Acc. Chem. Res. 2010, 43, 58-67. 46. Cuadrado-Collados, C.; Fernández-Català, J.; Fauth, F.; Cheng, Y. Q.; Daemen, L. L.; Ramirez-Cuesta, A. J.; Silvestre-Albero, J., Understanding the Breathing Phenomena in Nano-Zif7 Upon Gas Adsorption. J. Mater. Chem. A 2017, 5, 20938-20946. 47. Fairen-Jimenez, D.; Moggach, S. A.; Wharmby, M. T.; Wright, P. A.; Parsons, S.; Duren, T., Opening the Gate: Framework Flexibility in Zif-8 Explored by Experiments and Simulations. J. Am. Chem. Soc. 2011, 133, 8900-8902. 48. Sing, K. S. W.; Williams, R. T., The Use of Molecular Probes for the Characterization of Nanoporous Adsorbents. Part. Part. Syst. Charact. 2004, 21, 71-79. 49. Thommes, M.; Cychosz, K. A., Physical Adsorption Characterization of Nanoporous Materials: Progress and Challenges. Adsorption 2014, 20, 233-250. 50. Wu, X.; Niknam Shahrak, M.; Yuan, B.; Deng, S., Synthesis and Characterization of Zeolitic Imidazolate Framework Zif-7 for Co2 and Ch4 Separation. Microporous Mesoporous Mater. 2014, 190, 189-196. 51. Koros, W. J.; Ma, Y. H.; Shimidzu, T., Terminology for Membranes and Membrane Processes (Iupac Recommendations 1996). Pure Appl. Chem. 1996, 68, 1479-1489. 52. Bahamon, D.; Vega, L. F., Systematic Evaluation of Materials for Post-Combustion Co2 Capture in a Temperature Swing Adsorption Process. Chem. Eng. J. 2016, 284, 438-447. 53. Banerjee, R.; Furukawa, H.; Britt, D.; Knobler, C.; O'Keeffe, M.; Yaghi, O. M., Control of Pore Size and Functionality in Isoreticular Zeolitic Imidazolate Frameworks and Their Carbon Dioxide Selective Capture Properties. J. Am. Chem. Soc. 2009, 131, 3875-3877. 54. Perez-Pellitero, J.; Amrouche, H.; Siperstein, F. R.; Pirngruber, G.; Nieto-Draghi, C.; Chaplais, G.; Simon-Masseron, A.; Bazer-Bachi, D.; Peralta, D.; Bats, N., Adsorption of Co(2), Ch(4), and N(2) on Zeolitic Imidazolate Frameworks: Experiments and Simulations. Chemistry 2010, 16, 1560-1571. 55. Ray, K. G.; Olmsted, D.; He, N.; Houndonougbo, Y.; Laird, B. B.; Asta, M., Van Der Waals Density Functional Study of Co 2 binding in Zeolitic Imidazolate Frameworks. Phys. Rev. B 2012, 85, 085410. 56. Ranjan, R.; Tsapatsis, M., Microporous Metal Organic Framework Membrane on Porous Support Using the Seeded Growth Method. Chem. Mater. 2009, 21, 4920–4924.


21


Page 22 of 23

57. Guerrero, V. V.; Yoo, Y.; McCarthy, M. C.; Jeong, H. K., HKUST-1 Membranes on Porous Supports Using Secondary Growth. J. Mater. Chem. 2010, 20, 3938-3943. 58. Huang, A.;Chen, Y.; Liu, Q.; Wang, N.; Jiang, J.; Caro, J., Synthesis of Highly Hydrophobic and Permselective Metal–Organic Framework Zn (BDC)(TED) 0.5 Membranes for H2/CO2 Separation. J. Membr. Sci. 2014, 454, 126-132. 59. Jin, H.; Wollbrink, A.; Yao, R.; Li, Y.; Caro, J.; Yang, W., A Novel CAU-10-H MOF Membrane for Hydrogen Separation under Hydrothermal Conditions. J. Membr. Sci. 2016, 513, 40-46. 60. Liu, Q.; Wang, N.; Caro, J.; Huang, A., Bio-inspired Polydopamine: A Versatile and Powerful Platform for Covalent Synthesis of Molecular Sieve Membranes. J. Am. Chem. Soc. 2013, 135, 17679-17682. 61. Huang, A.; Dou, W.; Caro, J., Steam-stable Zeolitic Imidazolate Framework ZIF-90 Membrane with Hydrogen Selectivity Through Covalent Functionalization. J. Am. Chem. Soc. 2010, 132, 15562-15564. 62. Huang, A.; Chen, Y.; Wang, N.; Hu, Z.; Jiang, J.; Caro, J., A highly Permeable and Selective Zeolitic Imidazolate Framework ZIF-95 Membrane for H2/CO2 Separation. Chem. Commun. 2012, 48, 10981-10983. 63. Wang, N.; Liu, Y.; Qiao, Z.; Diestel, L.; Zhou, J.; Huang, A.; Caro, J., Polydopamine-based Synthesis of A Zeolite Imidazolate Framework ZIF-100 Membrane with High H2/CO2 Selectivity. J. Mater. Chem. A 2015, 3, 4722-4728.


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A Robust Zeolitic Imidazolate Framework Membrane with High H2

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