ZnO Nanorod-Induced Heteroepitaxial Growth of SOD Type Co-Based

Jan 11, 2018 - (48) Our experimental results indicated that a layer of (Zn,Co) HDS was easily produced after the ZnO nanorods grown on the glass suppo...
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Research Article Cite This: ACS Appl. Mater. Interfaces 2018, 10, 4151−4160

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ZnO Nanorod-Induced Heteroepitaxial Growth of SOD Type CoBased Zeolitic Imidazolate Framework Membranes for H2 Separation Pei Nian, Yujia Li, Xiang Zhang, Yi Cao, Haiou Liu, and Xiongfu Zhang* State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology, Dalian 116024, China S Supporting Information *

ABSTRACT: Up to now, the fabrication of well-intergrown Co-based zeolitic imidazolate framework (ZIF) membranes on porous tubular supports is still a major challenge. We report here a heteroepitaxial growth for preparing well-intergrown Co-based ZIFs (ZIF-67 and ZIF-9) tubular membranes with high performance and excellent thermal stability by employing a thin layer of ZnO nanorods acting as both nucleation centers and anchor sites for the growth of metal−organic framework membranes. The results show that well-intergrown Co-ZIF-67 and Co-ZIF-9 membranes are successfully achieved on the ZnO nanorod-modified porous ceramic tubes. This highly active heteroepitaxial growth may be attributed to the fact that the (Zn,Co) hydroxy double salt intermediate produced in situ from ZnO nanorods acts as heteroseeds and enables the uniform growth of Co-based membranes. The H2/CO2 selectivity of the as-prepared Co-ZIF-9 tubular membrane could reach about 23.8 and the H2/CH4 selectivity of Co-ZIF-67 tubular membrane is as high as 45.4. Moreover, the membranes demonstrate excellent stability because of the ZnO nanorods as linkers between the membrane and substrate. KEYWORDS: metal−organic framework membrane, ZnO nanorods, Co-based membrane, heteroepitaxial growth, gas separation

1. INTRODUCTION Metal−organic frameworks (MOFs) are superb candidates for membranes and have great potential in many separation processes because of their well-defined pore structures, diverse chemistry, and attractive adsorption properties.1−3 In particular, zeolitic imidazolate frameworks (ZIFs) with zeolite topologies, consisting of transition metals (Zn or Co) and imidazolate ligands, a relatively new subfamily of MOFs, are of more attractive interest for membrane-based gas separation because of their exceptional thermal/chemical stabilities and ultramicropores (less than 0.5 nm).4−6 In fact, some ZIF membranes have exhibited impressive capacities for separating important gas mixtures, including hydrogen purification, CO2 capture, and olefin/paraffin separation.7−10 Co-based ZIF membranes can not only separate some small-molecular gas mixtures but also be applied in catalytic reactions as membrane reactors because of their small pore size and the presence of the redox catalytic cobalt centers.11−14 Therefore, it is extremely expected that well-intergrown continuous Co-based ZIF membranes, especially tubular membrane, could be achieved. The reason for choosing a tubular substrate is mainly due to their prominent advantages over planar geometry for facile scaling of separation units in industrial production.15,16 Nowadays, there are two important Co-based ZIFs including ZIF-67 and ZIF-9, which are paid to intense attention. ZIF-67, constructed by cobalt ions and 2-methylimidazole, is of isostructural sodalite (SOD) zeolite topology and the effective aperture size is ∼4.0 Å,10,17 while ZIF-9 consisting of cobalt ions and benzimidazole has a SOD zeolite topology with a pore size of 3.0 Å.11,18 They as membranes are rather appropriate to © 2018 American Chemical Society

separate propylene (4.0 Å) from propylene/propane (4.2 Å) mixtures17 and H2 (2.9 Å) from H2/CO2 (3.3 Å) mixtures,11 respectively. There have already been some attempts and progress made in preparing ZIF-67 and ZIF-9 membranes for gas separation,10,19−21 but all the Co-ZIF membranes achieved are still grown on porous discs as substrates, which greatly limits their industrial applications. For example, Jeong et al. achieved well-intergrown ZIF-67/ZIF-8 polycrystalline membranes on α-Al2O3 discs for the separation of propylene/ propane mixtures through the heteroepitaxial growth of ZIF-67 membranes on ZIF-8 seeds.10 Pan et al. also fabricated a zincsubstituted ZIF-67 membrane for the separation of propylene/ propane mixtures on α-alumina discs by incorporation of zinc ions into the ZIF-67 framework.19 In addition, Zhou et al. prepared a ZIF-67 membrane on the Co(OH)2 nanosheetmodified stainless-steel nets via an electrodeposition method.20 As for the synthesis of ZIF-9 membrane, Zhong et al. grew a CNT@IL/ZIF-9 hybrid membrane on α-Al2O3 discs that exhibited high selectivity for H2/CO2.21 Compared to the synthesis of Zn-based ZIF membranes, it is more difficult to prepare Co-based ZIF membranes. The reason is mainly ascribed to the fact that the formation of Co-based ZIF crystals is very fast in the synthesis solution rather than growing their corresponding membranes on the substrates, thereby leading to poor-quality Co-based ZIF membranes. Received: November 17, 2017 Accepted: January 11, 2018 Published: January 11, 2018 4151

DOI: 10.1021/acsami.7b17568 ACS Appl. Mater. Interfaces 2018, 10, 4151−4160

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ACS Applied Materials & Interfaces In fact, for the preparation of crystalline MOF membranes, the core issue is to select a feasible synthesis method for obtaining a continuous and well-intergrown membrane. So far, numerous approaches have been employed for fabricating wellintergrown MOF membranes, such as in situ synthesis,22 secondary growth,23−25 organic functional surface modification,26−29 inorganic microstructure surface modification,20,30−38 along with other techniques.39−41 Among them, recently, significant attention has been devoted to inorganic surface modifiers, which possess unique advantages, such as high affinity with the substrate, high activity for the MOF membrane growth, high thermal stability, eco-friendly, and easy fabrication.42 For instance, Qiu et al. successfully fabricated Ni-based and Cu-based MOF membranes on Ni30 and Cu nets31 by a twin metal source technique. Zhang et al.32 fabricated ZIF-8 membranes on ZnO nanorod-modified tubular substrates, where the ZnO layer served as an intermediate layer to facilitate the nucleation and growth of ZIF-8 membranes. Wang et al.36 directly synthesized ZIF-8 membranes on the ZnO−Al2O3 composite hollow fiber, which show excellent hydrogen permeance and good reproducibility. In addition, Liu et al.37 prepared a ZnAl−CO3 layered double hydroxide (LDH) layer on the α-Al2O3 substrate to promote the heterogeneous nucleation of ZIF-8 crystals and result in uniform ZIF-8 membranes. These homologous metals or metal oxides acted as the nucleation centers for the preparation of continuous MOF membranes. Besides, very recently, a heteroepitaxial growth strategy was also used to grow MOF membranes with improved microstructures, thereby leading to excellent separation performances. Jeong et al.10 and co-workers first reported a well-intergrown ZIF-67/ZIF-8 polycrystalline membrane by heteroepitaxially growing ZIF-67 on ZIF-8 seeds layer, which exhibited unprecedentedly high propylene/propane separation. Similarly, Peng et al.43 grew MIL-110 nanorods on porous substrates as heteroseeds to grow a continuous HKUST-1 membrane. Although such progress has been made based on the above methods in preparing MOF membranes on porous disc supports, there are few reports on growing Co-based ZIF membranes on porous tubular substrates. Thus, it is essential to develop an available and universal surface modifier with excellent reactivity and stability for preparing Co-based ZIF membranes. Herein, inspired by the heteroepitaxially grown MOF membranes, we present an efficient methodology for preparing well-intergrown and stable Co-based ZIF tubular membranes by introducing ZnO nanorod layers on porous tubular substrates as induction sites for membrane growth. Up to now, there has been no report on the successful growth of CoZIF membranes on porous tubular substrates by ZnO-induced heteroepitaxial growth. This protocol employs the readily available and malleable ZnO as heterogeneous nucleation bars for the growth of the Co-ZIF-67 or Co-ZIF-9 membrane. As shown in the preparation scheme of Figure 1, a thin layer of ZnO nanorod arrays was first grown on the porous α-Al2O3 tube by a hydrothermal process, and then the ZnO nanorods acting as both seeds and linkers induced the formation of a continuous Co-ZIF-67 or Co-ZIF-9 membrane in its corresponding precursor solution by a solvothermal growth.

Figure 1. Schematic illustration of the synthesis of Co-ZIFs (ZIF-67 and ZIF-9) membranes via ZnO nanorod-induced heteroepitaxial growth. (Zn(Ac)2·2H2O, 98.0%), ethylene glycol monomethyl ether (C3H8O2, EGME, 99.0%), monoethanolamine (C2H7NO, MEA, 99.0%), hexamethylenetetramine (C6H12N4, ≥ 99.0%), anhydrous methanol (≥99.5%), and N,N′-dimethylformamide (DMF, ≥99.5%), which were provided by Sinopharm Chemical Reagent Co. Ltd. Benzimidazole (Bim, ≥99.0%) and 2-methylimidazole (Hmim, 99.0%) were purchased from Sigma-Aldrich Chemical. Zinc oxide nanoparticles (cal. 50 ± 10 nm) were supplied by Beijing Nachen S&T Ltd. Porous α-Al2O3 tubes (o.d. 4 mm, i.d. 3 mm, with average 100 nm pore diameter) were provided by Hyflux Co. Ltd. The tubes were cut into 55 mm in lengths, ultrasonically washed with deionized water, and then dried at 150 °C for 6 h. 2.2. Preparation of ZnO Nanorods. The ZnO nanorods on the porous α-Al2O3 tube were prepared by a hydrothermal synthesis according to our previous reports.32,33 In a typical procedure, first, a thin Zn-based sol layer was dip-coated on the inner surface of the tube. For synthesis of the Zn-based sol, 5 g Zn(Ac)2·2H2O was first dispersed in 30 mL of EGME and stirred at 70 °C for 1 h. Then, 1.3 mL of MEA was dropwise added to the above solution and stirred at 25 °C for 12 h to get a stable Zn-based sol. After that, the α-Al2O3 tube was coated with the sol and dried at 100 °C for 1 h. This coating process was repeated two times and followed by calcining at 400 °C for 2 h to get a thin ZnO nanoparticle layer supported on the tube. Second, the ZnO nanorods were grown on the seeded α-Al2O3 tube as follows: 1.1 g hexamethylenetetramine and 2.3 g Zn(NO3)2·6H2O were dissolved in 80 mL water and stirred for 0.5 h to achieve a synthesis solution. Then, the seeded tube was vertically placed in the synthetic solution for crystallization at 100 °C for 6 h. Finally, the tube was washed with deionized water and dried at 80 °C for 24 h. 2.3. Preparation of the ZIF-67 Membrane. The ZIF-67 membrane was grown heteroepitaxially on the ZnO nanorod layer under solvothermal conditions. The synthesis solution was prepared according to the following procedure as reported elsewhere, with minor modifications.10 Briefly, 0.22 g of Co(NO3)2·6H2O and 4.54 g of Hmim were dissolved in a mixture of 5 mL of methanol and 35 mL of deionized water, respectively. Two solutions were blended for 2 min and poured into a 100 mL autoclave containing a ZnO nanorodmodified tube. The autoclave was kept in an oven at 120 °C for 24 h. Afterward, the ZIF-67 membrane (purple) was rinsed with fresh methanol. Then, the as-synthesized ZIF-67 membrane was placed in 30 mL methanol and kept for 2 days for solvent exchange, and the sample was replenished with fresh methanol every 12 h. Finally, the membrane was dried in a vacuum oven at 60 °C for 12 h before characterization and testing. 2.4. Preparation of the ZIF-9 Membrane. First, the ZnO nanorod-grown tube was immersed in a solution with 0.5 M Bim and DMF at 60 °C for 1 h for activation. The purpose is the implantation of the ligand (Bim) into the ZnO nanorods for favoring the nucleation and growth of ZIF-9 membranes. Subsequently, the ZIF-9 membrane was grown heteroepitaxially on the activated ZnO nanorod layer under solvothermal conditions. In a typical synthesis solution,21 Co(NO3)2· 6H2O (0.3 g) was dissolved in 60 mL of DMF and a solid of Bim (0.52 g) was added after constant stirring. The activated ZnO nanorodmodified tube was placed vertically into the mother solution and kept

2. MATERIALS AND METHODS 2.1. Materials. The chemicals used in the membrane synthesis include the cobalt nitrate hexahydrate (Co(NO3)2·6H2O, ≥99.0%), zinc nitrate hexahydrate (Zn(NO3)2·6H2O, ≥ 99.0%), zinc acetate 4152

DOI: 10.1021/acsami.7b17568 ACS Appl. Mater. Interfaces 2018, 10, 4151−4160

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ACS Applied Materials & Interfaces at 120 °C for 24 h. After the solvothermal synthesis, the ZIF-9 membrane (dark purple) was taken out and washed with fresh methanol. Then, the solvent exchange process for the as-prepared ZIF9 membrane was similar to that for the ZIF-67 membrane mentioned above. 2.5. Characterization. Powder X-ray diffraction (PXRD) patterns were recorded in the 2θ range of 3−60° using a D/max-2400 X-ray diffractometer with Cu Kα radiation. The membrane morphology was checked by scanning electron microscopy (SEM, FEI Nova NanoSEM 450 and Quanta 450 operating at 3 and 20 keV, respectively). Energydispersive X-ray spectrometry (EDX) line scanning analyses were operated with 20 keV of acceleration and 10 mm of working distance. Infrared spectra were collected using a Bruker EQUINOX55 FT-IR spectrometer. 2.6. Evaluation of Membrane Separating Performance. Gas permeation of the prepared membranes was carried out with different kinetic diameters of gases H2 (0.29 nm), CO2 (0.33 nm), N2 (0.36 nm), and CH4 (0.38 nm) using a home-made gas permeation apparatus.32−34 The membrane was sealed in a permeation module with silicone O-rings. For the permeation test for single gases, the feed stream was pressurized and controlled with the exactitude manometer, while maintaining the permeate pressure at 1 bar. The gas flux was measured by a soap bubble flow meter. The data were recorded until a constant permeance lasted at least 2 h. The ideal selectivity was the value of the ratio for different gas permeances. The binary gas mixture permeation measurements were performed with the Wicke− Kallenbach technique. A 50:50 mixture of gas was applied to the feed side, and the pressure at both feed side and permeate side was 1 bar. An online gas chromatograph (GC7890T) was used to measure the gas composition. The separation factor of H2 over other gases αH2/j was defined as the molar fractions of the components (H2, j) in the permeate side, divided by the molar fractions of the components (H2, j) in the feed side, as shown in the following equation

αH2 / j =

yH ,Perm /yj ,Perm 2

x H2,Feed /xj ,Feed Figure 2. SEM images of ZnO nanorods grown on the α-Al2O3 tube (a,b); ZIF-67 membrane on the ZnO nanorod-modified tube at 120 °C for 1 h (c,d) and 24 h (e,f); XRD patterns of the samples (g); EDX elemental profiles of the cross section of the ZIF-67 membrane grown for 24 h (h).

3. RESULTS AND DISCUSSION 3.1. Formation and Characterization of Co-Based ZIF Membranes on ZnO Nanorods. As reported in our previous work,32 ZnO nanorods acting as seeds and linkers could successfully induce forming a high-performance Zn-ZIF (ZIF8) membrane because the metal oxide, which is the same metal source as the MOF to be grown, greatly favors the formation of its corresponding MOF membrane. Thus, it is important to pre-introduce a thin layer of ZnO nanorods on the surface of the porous ceramic tube. In this work, based on the heteroepitaxial growth of the Co-ZIF-67 membrane on ZnO nanorods, a layer of ZnO nanorods was first grown on the substrate to act as heteroseeds and anchoring sites for subsequent growth of the Co-ZIF-67 membrane. Figure 2a,b shows that the ZnO nanorods were aligned vertically with hexagonal cross sections of 200−250 nm in diameter and 2−2.5 μm in length. It can be observed that the ZnO nanorods uniformly covered the entire surface of the tube to serve as an intermediate layer for the formation of ZIF-67 membrane. Meanwhile, the ZnO nanorod layer can also modify some large defects of the substrate and favor growing a dense membrane. From the cross-sectional image, it can be seen obviously that the ZnO nanorods grew seamlessly on the substrate, revealing a strong adhesion with the porous tube. Then, the ZnO nanorodmodified tube was immersed into the ZIF-67 precursor solution for crystallization and membrane growth. Initially, after the short reaction for 1 h, as shown in Figure 2c, a layer of unknown phase with flocculent species was uniformly formed

over the ZnO nanorods. The flocculent species might be the metastable phase produced at the initial stage, as the degree of crystallization was very low and no peak was detected in XRD. The cross-sectional image indicates that the ZnO nanorods partly dissolved and intergrew together (Figure 2d). The flocculent species were subsequently incubated into bulk crystals after 2 h (Figure S1). When the reaction time was prolonged to 24 h, a well-intergrown and defect-free polycrystalline ZIF-67 membrane consisting of well-formed prismatic crystals with a thickness of around 3 μm was produced by heteroepitaxially growth on the ZnO nanorods (Figure 2e,f). It was found that the ZIF-67 polycrystalline crystals grew with the interseptal space between the ZnO nanorods, and even packed the ZnO nanorods, forming a uniform and continuous ZIF-67 layer. The XRD analysis detected the ZIF-67 layer grown on the ZnO nanorods. The peaks of both ZIF-67 structure phase and ZnO structure phase existed in the XRD pattern, indicating that the ZnO nanorods have not completely dissolved during the heteroepitaxial growth (Figure 2g). Simultaneously, the EDX line scanning analysis was conducted along the cross section of the ZIF-67 membrane marked with a red solid line (Figure 2h). As expected, a cobalt-rich region of ca. 2 μm in thickness was 4153

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ACS Applied Materials & Interfaces clearly seen from the top membrane to the ZnO region, demonstrating that the uniform membrane was, indeed, CoZIF-67 rather than the Zn-ZIF-8 structure. The zinc-rich region with ca. 3 μm in depth was located under the Co-ZIF-67 layer, demonstrating that the ZnO nanorods only slightly dissolved and most of them are still embedded in the support at one end and connected the continuous ZIF-67 layer at another end, thus acting as excellent linkers. The EDX result revealed that the ZnO nanorods partly penetrated into the ZIF-67 layer, and thus, the ZnO nanostructure could allow the expansion of the membrane, preventing the cracks possibly produced during heating/cooling processes. Thus, this approach makes it feasible to achieve a reproducible and stable ZIF-67 membrane. In this work, it was found that both the induced activity of ZnO nanorods for the heteroepitaxial growth of Co-ZIF-67 membrane and strong attachment of the ZnO nanorod layer on ceramic tubes were extremely critical for achieving a wellintergrown ZIF-67 membrane. Without the ZnO nanorod layer, it is impossible to form high-quality ZIF-67 membranes under the current synthesis conditions, with only a few flake-like particles attached on the substrate (Figure S2a). However, the powders precipitated simultaneously in the solution were determined to be pure ZIF-67 phase with the polyhedral shape of about 1 μm (Figure S3), which was in good agreement with the regular morphology of ZIF-67 crystals (Figure S2b). This may be attributed to the fact that for the formation of ZIF-67, homogeneous nucleation and growth in the solution is much faster than heterogeneous one on the substrate,10 resulting in only producing ZIF-67 powders in solution rather than ZIF-67 layers on a naked alumina substrate. Once Co2+ solution was added and mixed with Hmim solution, ZIF-67 crystals were immediately formed as shown in Figure S4. Therefore, it is difficult to achieve continuous and dense ZIF-67 membranes on porous tubular substrates without the aid of a layer of ZnO nanorods. To check the universality and superiority of our proposed heteroepitaxial synthesis strategy in fabricating Co-MOF membranes, we also choose ZIF-9 as the candidate to prepare the ZIF-9 membrane by using this heteroepitaxial growth. Similarly, without the ZnO nanorod layer, the surface of the substrate was covered with a layer of loose ZIF-9 crystals which are poor-intergrown as shown in Figure 3a. The ZIF-9 layer of about 10 μm in thickness has visible gaps between the layer and the substrate, showing the weak interaction between the membrane and the substrate. In comparison, the membrane crystallized better and more continuous on a layer of ZnO nanorod-modified alumina support as shown in Figure 3c. The ZIF-9 crystals were uniform and well-intergrown, demonstrating that ZnO nanorods could be used as efficient nucleation sites for the heteroepitaxial growth of the ZIF-9 membrane. It is worth noting that different from the preparation of the above ZIF-67 membrane, here, the activation of ZnO nanorods in a DMF solution containing Bim ligands plays a key role in forming a dense ZIF-9 membrane as shown in Figure 4. After the activation of the ZnO nanorods with the Bim solution, there were many spherical particles (∼500 nm) produced (Figure 4a,b), standing on top of each of the ZnO nanorods. As we reported previously,32 these small particles were similar to “ZIF-like” nuclei and can act as the heteroseeds for ZIF-9 growth, leading to the formation of a well-intergrown and defect-free ZIF-9 membrane with 12 μm as shown in Figure 4c,d. The composition change with the reaction time was shown by EDX scan line analysis (Figures 4e, and S5). It

Figure 3. SEM images of the ZIF-9 membrane synthesized on the naked α-Al2O3 tube using in situ growth (a,b); ZIF-9 membrane synthesized on the ZnO nanorod-modified α-Al2O3 tube (c,d).

Figure 4. SEM images of ZnO nanorods after activation by the Bim solution (a,b); ZIF-9 membrane grown on the ZnO nanorods activated with Bim (c,d); change in the Zn/Co molar ratio of the ZIF-9 membrane during the reaction for 48 h based on EDX results (e); EDX elemental profiles of the cross section of the ZIF-9 membrane grown on the ZnO nanorod-modified tube (f).

showed that the molar ratio of Co to Zn increased with the time and then reached an equilibrium after 24 h, demonstrating that the growth of ZIF-9 membrane had ceased because of the absence of enough nutrients. Figure 4f shows an EDX line along the cross section of the ZIF-9 membrane marked with a red solid line. Indeed, a cobalt-rich region of ca. 12 μm was clearly seen from the top membrane to the ZnO region. This cobalt-rich thickness was right similar to that of the wellintergrown ZIF-9 membrane, demonstrating that the uniform 4154

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Figure 5. XRD patterns of the ZIF-9 membrane on the ZnO nanorod-modified ceramic tube (a,b) and ZIF-9 membrane on the naked tube (c,d); magnified XRD patterns for ZIF-9 membranes with 2θ angle between 6° and 18° (b,d).

Figure 6. Schematic illustration of the proposed mechanism for the heteroepitaxial growth of the Co-ZIF (ZIF-67 and ZIF-9) membrane on the ZnO nanorod layer.

deemed preferentially oriented parallel to the support.44 In this work, the ZIF-9 membrane grown on the ZnO nanorodmodified substrate had an OI (122) value of 2.65 which is much larger than 1, indicating that the crystals are oriented with their (122) planes parallel to the substrate. The similar orientation growth was also observed in ZIF-67 membranes grown on ZnO nanorod-modified substrates (Figure S7). Similarly, the peak intensity of the (011) planes decreased obviously, whereas the (112) peak increased when the ZIF-67 crystals grew on the ZnO nanorod-modified substrates, indicating that the ZIF-67 membrane preferentially grows along the (112) plane on the ZnO nanorod-modified substrate. The orientation change may be attributed to the preferentially c-oriented ZnO nanorods which have the highest relative intensity for the (002) diffraction peak (Figure S8). Therefore, addition of highly c-oriented ZnO nanorod layers in preparing MOF membranes could alter the crystal orientation from the random orientation to a preferred one. The preferentially oriented growth manner favors the intergrowth of the MOF crystals and thus reduces the defects produced during the membrane formation. Moreover, the directional growth of MOF crystals is significant for their corresponding membrane for gas permeation performance.38 Therefore, the c-oriented ZnO nanorod-assisted strategy might be meaningful for

membrane was Co-ZIF-9 rather than the Zn-ZIF-7 structure phase. The structure of the achieved ZIF-9 membrane was further characterized by PXRD as shown in Figure 5. Interestingly, we found that the orientation of the ZIF-9 membrane on the ZnO nanorod-modified substrate was obviously different from those of random ZIF-9 powder crystals simulated and the ZIF-9 membrane grown on the bare substrate. From the XRD pattern of the membrane on the ZnO nanorods as shown in Figure 5a,b, the three main peaks at 7.1, 7.7, and 16.3°, corresponding to (01−1), (−120), and (122) crystal planes, respectively, matched well with the simulated ones from ZIF-9 single-crystal data, indicating that the membrane is ZIF-9 phase. However, the peak of (−120) planes for the membrane decreased to almost invisible, while the (122) peak increased obviously, compared with those of simulated ZIF-9 crystals and the membrane grown on the bare substrate as shown in Figure 5b,d, suggesting that the ZIF-9 membrane preferentially grew along the (122) plane on the ZnO-modified substrate. The propagation of the (122) plane through the ZIF-9 structure is shown in Figure S6. For further analysis of the orientation of the ZIF-9 membrane, orientation indices (OIs) were calculated for the three main diffractions (Table S1). It is believed that if the OI value for any crystal plane surpasses 1, which was 4155

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and S9c). When the ZnO nanorods were treated with ZIF-9 precursor solution (denoted as ZIF-9-M) without containing any ligand (Bim) at 120 °C for 24 h as shown in Figure 7b, there were no nanoflakes and only some substances formed and unevenly attached on the ZnO nanorods, in which both Zn and Co were also detected on the ZIF-9-M sample by the EDX analysis (Figures 7d, and S9d). The morphology discrepancy between ZIF-67-M and ZIF-9-M might be due to the reason that ZnO nanorods have different solubility in the two kinds of different precursor solutions, which was in accordance with previous results.49 The XRD patterns of the two samples derived ZIF-67-M and ZIF-9-M matched well with the (Zn,Co) hydroxy nitrate as shown in Figure 8a,b. Furthermore, Figure 8c,d shows the Fourier-transform infrared spectroscopy (FTIR) spectra collected from ZnO nanorods and after sequential exposure to Co(NO3)2 and ligand solutions. After the ZnO nanorod layer was treated with ZIF-67-M solution and ZIF-9-M solution, the negative-going modes confirmed the appearance of NO3− (1360 and 1420 cm−1) and distinct O−H group modes (∼3300−3620 cm−1), indicating the formation of hydroxy nitrate.50,51 But the sample treated with ZIF-9 precursor solution gave weak absorption peaks of O−H, which was consistent with the SEM results (Figure 7b). After the ZIF-67-M sample was subsequently exposed to the Hmim solution, it can be seen from Figure 8c that the peaks for NO3− and O−H diminished, while both the C−H stretching vibration from the imidazole ring (∼3136 cm−1) and C−H stretching vibration of the methyl (∼2927 cm−1) from the Hmim ligand appeared. In addition, the Co−N vibration (∼425 cm−1) appeared, revealing the incorporation of Co into the structure of ZIF-67. For the sample of ZIF-9-M, after the exposure to Bim, the CC stretching vibration of the benzene ring (∼1456 cm−1), C−H bending vibration of ortho-disubstituted benzene (∼745 cm−1), which is contributed from the Bim ligand, and Co−N vibration (∼425 cm −1 ) appeared (Figure 8d), demonstrating the formation of ZIF-9 after the exposure of ZIF-9-M to Bim solution.52 These changes clearly reveal that the anion exchange process easily occurs in the (Zn,Co) HDS and thus favors the formation of Co-based ZIFs, which further supports our proposed reaction process, that is, ZnO nanorods first react with Co2+ in the synthesis solution to form (Zn,Co) hydroxy nitrate salt (HDS), followed by anion exchange between NO3− and OH− in the HDSs and ligands. Then, the exchanged HDSs drive the growth of Co-based ZIFs, thus leading to the formation of continuous and dense Co-based ZIF membranes. From the above discussion, it can be confirmed that a (Zn,Co) HDS intermediate formed in situ from the ZnO layer, indeed, enables the heteroepitaxial growth of Co-based MOF membranes because this intermediate can not only act as heterogeneous nucleation sites by introducing Co2+ to the substrate but also has excellent anion exchangeability, which greatly favors the formation of uniform Co-based MOF membranes. To further demonstrate the universality of the ZnO layer-assisted heteroepitaxial growth of MOF membranes, we synthesized other three types of MOF membranes including Cu-based CuBDC53 and HKUST-131 membranes and Ni-based USO-2-Ni54,55 on the ZnO nanorod-modified substrates (Figures S10−S12). It is clearly seen that all the three kinds of MOF membranes derived from ZnO nanorod-modified substrates were more continuous and denser than those obtained by the in situ method. Therefore, it is no doubt

fabricating the MOFs with 1D channels to achieve a membrane with highly efficient molecular permeation properties. 3.2. Mechanism of the Heteroepitaxial Growth of CoBased ZIF Membranes. According to the principle that the metal oxide which has the same metal source as the MOF to be grown favors the growth of its corresponding membrane, ZnO in the form of nanorods or ultrathin layers introduced onto the surface of a porous substrate can successfully induce the formation of a continuous Zn-based ZIF membranes.32−34 However, up to date, there is no report on ZnO-induced heteroepitaxial growth of Co-based ZIF membranes. Here, we for the first time achieved continuous Co-ZIF-67 and Co-ZIF-9 membranes by using this ZnO nanorod-induced heteroepitaxial growth strategy. To further understand this heteroepitaxial strategy, a membrane growth mechanism was proposed and discussed as shown schematically in Figure 6. We hypothesized that during the membrane growth, the ZnO nanorods first react with Co2+ in the synthesis solution to form (Zn,Co) hydroxy nitrate salts (hydroxy double salts, HDSs), which then drives the Co-MOF formation. This was also confirmed by Parsons et al.’s work in which (Zn,Cu) HDSs formed in situ from ZnO particles enabled rapid growth of HKUST-1.45,46 The HDSs are layered compounds consisting of cationic sheets connected by inorganic/organic interlamellar anions47 and easily formed by reaction of one divalent metal oxide with another different divalent cation. These materials possess high reaction activity and excellent anion exchangeability.48 Our experimental results indicated that a layer of (Zn,Co) HDS was easily produced after the ZnO nanorods grown on the glass support were treated with the ZIF-67 precursor solution (denoted as ZIF-67M) without containing any ligand (Hmim) at 120 °C for 24 h as shown in Figure 7a. The nanosheets consisted of regular

Figure 7. SEM images of ZnO nanorods grown on glass substrates treated with ZIF-67 (a) and ZIF-9 (b) precursor solutions without containing ligands Hmim and Bim, respectively; and (c,d) EDX mapping images of the corresponding red square marked in parts (a and b).

nanoflakes, typically 3−4 μm in length and 50−80 nm in thickness, were cross-linked and grew vertically on the glass substrate (Figures 7a, and S9a). This morphology was similar to that observed at the initial stage of growing the ZIF-67 membrane on ZnO nanorods (Figure 2c). Elemental mapping showed that Zn and Co elements were homogeneously distributed throughout the whole nanosheet layer (Figures 7c, 4156

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Figure 8. (a) XRD patterns of ZnO nanorods grown on glass substrates treated with ZIF-67 and ZIF-9 precursor solutions without containing ligands Hmim and Bim, respectively; (b) XRD patterns of (Zn,Co) HDS (red) derived from ZnO powder (black); (c) FTIR spectra for ZnO nanorods (black), after sequential exposure to Co(NO3)3 (red) and Hmim (blue) solution, and the ZIF-67 membrane (purple); (d) FTIR spectra for ZnO nanorods (black), after sequential exposure to Co(NO3)3 (red) and Bim (dark blue) solution, and the ZIF-9 membrane (violet).

Figure 9. (a) Single gas transport behaviors through the ZIF-67 membrane at 25 °C and 0.1 MPa as a function of the kinetic diameter. The inset shows the ideal selectivity of H2 over CO2, N2, and CH4. (b) H2/CH4 binary gases selectivity of the ZIF-67 membrane vs test time at different temperatures. (c) H2/CO2 binary gases selectivity of the ZIF-9 membrane vs test time at different temperatures. (d) Comparison of the H2/CO2 separation performances of the prepared ZIF-9 (red) and ZIF-67 (blue) membranes with the 2008 Robeson upper bound of polymeric membranes (blue line) and other membranes reported in the previous studies (black), such as MOF nanosheets,8 CuBTC/MIL-100,58 ZIF-8/rGO,59 zeolite,60 ZIF-7,61 NiAl−CO3LDH,62 ZIF-8/GO,63 ZnO/ZIF-8,32 ZIF-22,26 ZIF-9@P84,11 ZIF-9@IL@CNTs,21 Co(OH)2/ZIF-67,20 CuBTC,31 and NH2MIL-53.64

superior reactivity for crystallization of continuous MOF membranes. It is believed that the ZnO-assisted growth strategy developed here could be employed to prepare various MOFs and their membranes because the conversion is wellmanipulated. 3.3. Gas Permeation Performance of the Co-ZIF Membranes. The gas permeation properties of the asprepared Co-ZIFs (ZIF-67 and ZIF-9) tubular membranes

that the ZnO layer enables the assisted fabrication of the nonZn based MOF membranes because of the formation of (Zn,M2+) HDSs, such as (Zn,Co) HDS, (Zn,Cu) HDS, and (Zn,Ni) HDS, which could provide heterogeneous nucleation sites and anchoring bars. As demonstrated above, ZnO nanorods are an excellent modification layer for a porous tubular substrate and enable the heteroepitaxial growth of MOF membranes because of their high affinity with substrate and 4157

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permeance, showing that the membranes have high quality and have the advantages for H2 purification. Moreover, the membranes prepared by our strategy own excellent thermal stability.

were evaluated by using a home-made gas permeation setup. The single gas permeation properties of ZIF-67 and ZIF-9 membranes, respectively, at 25 °C and 0.1 MPa as a function of the kinetic diameters of molecule are shown in Figures 9a and S13. The H2 permeances of the both the membranes are much higher than those of the other gases, and there is an obvious cut-off between H2 and other larger gases. In the case of the ZIF-67 membrane, the H2 permeance is 22.75 × 10−8 mol m−2 s−1 Pa−1 and the ideal selectivity of H2/CO2, H2/N2, and H2/ CH4 are 8.6, 21.8, and 45.4, respectively, which are superior to Knudsen diffusion coefficients (4.7, 3.7, and 2.8 for H2/CO2, H2/N2, and H2/CH4, respectively). For the ZIF-9 membrane, the H2 permeance is 18.48 × 10−8 mol m−2 s−1 Pa−1, while the ideal selectivity of H2/CO2 is as high as 23.8, indicating that the ZIF-9 membrane has an efficient separation performance for H2/CO2. The high reproducibility of membrane preparation and performance is an effective method to reduce the cost of membrane preparation in industrial production. Tables S2 and S3 list the single gas permeances of the membranes obtained in separate batches. Among them, 9 of 10 membranes had comparable H2 permeances with a mean value of 22 × 10−8 mol m−2 s−1 Pa−1 for ZIF-67 and 18 × 10−8 mol m−2 s−1 Pa−1 for ZIF-9 membranes. Moreover, the ideal selectivities of the prepared membranes are also similar, showing the good reproducibility of the ZnO nanorod-induced heteroepitaxial growth of Co-ZIF membranes. The separation performance of some binary mixtures for the prepared membranes was also measured as shown in Tables S4 and S5. The gas permeances and mixture selectivities have a slight decrease compared to those of corresponding single gases because of the competitive adsorption of gases. These results above show that the Cobased ZIF membranes prepared by ZnO-induced heteroepitaxial growth are dense without any pinholes and cracks. The stability of the membrane is another crucial factor for its successful commercial application. Figure 9b,c shows the longtime separation performances of the Co-based membranes for binary mixtures of H2/CH4 and H2/CO2 with the temperature change from 30 to 150 °C, respectively. It is clearly indicated that the ZIF-67 membrane gives a slight decrease for H2 permeance from 15.65 × 10−8 to 12.71 × 10−8 mol m−2 s−1 Pa−1 and a little increase for H2/CH4 separation selectivity from 41.8 to 48.2. This trend can be explained by different behaviors of H2 and CH4 in the relative values of adsorption and diffusion toward the ZIF-67 membrane with increasing temperature.56,57 Similar results are also obtained in the ZIF-9 membrane for binary mixtures of H2/CO2 with the temperature change, and the Co-based ZIF membranes achieved in this work could exhibit exceeding stability during the long-term operation, even after a series of temperature changes. This excellent thermal stability of the membranes formed by ZnO-induced heteroepitaxial growth results from the special microstructure of the membrane, that is, the ZnO nanorod arrays could provide some freedom for the different expansion coefficients between the MOF membrane and substrate during heating/cooling processes, avoiding the defects from propagating cracks. To demonstrate the comprehensive separation performance of ZnO-induced Co-based ZIF membranes (ZIF-67 and ZIF-9) in this work, the plots of H2/CO2 selectivity versus H2 performance are summarized in Figure 9d. It can be seen that the H2/CO2 separation results of both our achieved Cobased ZIF membranes exceed the trade-off line of polymeric membranes. Our Co-ZIF membranes formed by ZnO nanorodinduced growth possess a good balance between selectivity and

4. CONCLUSIONS In summary, we successfully prepared well-intergrown Cobased ZIF (ZIF-67 and ZIF-9) membranes by the heteroepitaxial growth on ZnO nanorod-modified ceramic tubes, displaying high H2 separation performance and excellent stability. The strong attachment of the ZnO nanorod layer on the substrate was found to be essential to heteroepitaxially grown ZIF-67 and ZIF-9 membranes, as the (Zn,Co) HDS intermediate formed in situ from ZnO layer acted as heteroseeds and anchors enabling the heteroepitaxial growth of Co-based membranes. In addition, a similar synthetic strategy had been applied to the preparation of CuBDC, CuBTC, and USO-2-Ni membranes, demonstrating the excellent universality of this synthesis strategy. The resulting ZIF-9 membrane exhibited a high ideal selectivity of 23.8 for H2/CO2. The ZIF-67 membrane also showed excellent hydrogen separation performance with H2 permeance of 22.75 × 10−8 mol m−2 s−1 Pa−1 and H2/CH4 ideal selectivity up to 45.4. Moreover, both of the membranes demonstrated excellent stability because the ZnO nanorods acted as linkers between the membrane and substrate, which can prevent defects from propagating cracks. Therefore, the proposed heteroepitaxial growth of Co-based MOF membranes by the ZnO nanorod-induced strategy is simple and efficient and also can be employed to prepare various MOF membranes, as long as the metal source of the MOF membrane could react with ZnO to form the corresponding (Zn,M2+) hydroxy nitrate salt (HDS).

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.7b17568. Additional XRD, SEM, and EDS analyses on the ZIF powders and membranes; Intensities of diffraction peaks, intensity factors, and OIs; and gas separation performance of the ZIF membranes (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Phone/Fax: +86-411-84986155. ORCID

Xiongfu Zhang: 0000-0002-1850-8801 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Financial support from the National Natural Science Foundation of China (nos. 21476039 and 21076030) is gratefully acknowledged.

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REFERENCES

(1) Furukawa, H.; Cordova, K. E.; O’Keeffe, M.; Yaghi, O. M. The Chemistry and Applications of Metal-Organic Frameworks. Science 2013, 341, 1230444.

4158

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Research Article

ACS Applied Materials & Interfaces (2) Li, B.; Wen, H.-M.; Cui, Y.; Zhou, W.; Qian, G.; Chen, B. Emerging Multifunctional Metal-Organic Framework Materials. Adv. Mater. 2016, 28, 8819−8860. (3) Li, J.-R.; Sculley, J.; Zhou, H.-C. Metal−Organic Frameworks for Separations. Chem. Rev. 2011, 112, 869−932. (4) Park, K. S.; Ni, Z.; Côté, A. P.; Choi, J. Y.; Huang, R.; UribeRomo, 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. (5) Morris, W.; He, N.; Ray, K. G.; Klonowski, P.; Furukawa, H.; Daniels, I. N.; Houndonougbo, Y. A.; Asta, M.; Yaghi, O. M.; Laird, B. B. A Combined Experimental-Computational Study on the Effect of Topology on Carbon Dioxide Adsorption in Zeolitic Imidazolate Frameworks. J. Phys. Chem. C 2012, 116, 24084−24090. (6) Yao, J.; Wang, H. Zeolitic Imidazolate Framework Composite Membranes and Thin Films: Synthesis and Applications. Chem. Soc. Rev. 2014, 43, 4470−4493. (7) Hu, Y.; Wu, Y.; Devendran, C.; Wei, J.; Liang, Y.; Matsukata, M.; Shen, W.; Neild, A.; Huang, H.; Wang, H. Preparation of Nanoporous Graphene Oxide by Nanocrystal-Masked Etching: Toward a NacreMimetic Metal−Organic Framework Molecular Sieving Membrane. J. Mater. Chem. A 2017, 5, 16255−16262. (8) Peng, Y.; Li, Y.; Ban, Y.; Jin, H.; Jiao, W.; Liu, X.; Yang, W. MetalOrganic Framework Nanosheets as Building Blocks for Molecular Sieving Membranes. Science 2014, 346, 1356−1359. (9) Kwon, H. T.; Jeong, H.-K. In Situ Synthesis of Thin Zeolitic− Imidazolate Framework ZIF-8 Membranes Exhibiting Exceptionally High Propylene/Propane Separation. J. Am. Chem. Soc. 2013, 135, 10763−10768. (10) Kwon, H. T.; Jeong, H.-K.; Lee, A. S.; An, H. S.; Lee, J. S. Heteroepitaxially Grown Zeolitic Imidazolate Framework Membranes with Unprecedented Propylene/Propane Separation Performances. J. Am. Chem. Soc. 2015, 137, 12304−12311. (11) Cacho-Bailo, F.; Matito-Martos, I.; Perez-Carbajo, J.; EtxeberríaBenavides, M.; Karvan, O.; Sebastián, V.; Calero, S.; Téllez, C.; Coronas, J. On the Molecular Mechanisms for the H2/CO2 Separation Performance of Zeolite Imidazolate Framework Two-Layered Membranes. Chem. Sci. 2017, 8, 325−333. (12) Chaikittisilp, W.; Torad, N. L.; Li, C.; Imura, M.; Suzuki, N.; Ishihara, S.; Ariga, K.; Yamauchi, Y. Synthesis of Nanoporous CarbonCobalt-Oxide Hybrid Electrocatalysts by Thermal Conversion of Metal-Organic Frameworks. Chem.Eur. J. 2014, 20, 4217−4221. (13) Tonigold, M.; Lu, Y.; Bredenkötter, B.; Rieger, B.; Bahnmüller, S.; Hitzbleck, J.; Langstein, G.; Volkmer, D. Heterogeneous Catalytic Oxidation by MFU-1: A Cobalt (II)-Containing Metal-Organic Framework. Angew. Chem., Int. Ed. 2009, 48, 7546−7550. (14) Beier, M. J.; Kleist, W.; Wharmby, M. T.; Kissner, R.; Kimmerle, B.; Wright, P. A.; Grunwaldt, J.-D.; Baiker, A. Aerobic Epoxidation of Olefins Catalyzed by the Cobalt-Based Metal-Organic Framework STA-12(Co). Chem.Eur. J. 2012, 18, 887−898. (15) Xie, Z.; Yang, J.; Wang, J.; Bai, J.; Yin, H.; Yuan, B.; Lu, J.; Zhang, Y.; Zhou, L.; Duan, C. Deposition of Chemically Modified αAl2O3 Particles for High Performance ZIF-8 Membrane on a Macroporous Tube. Chem. Commun. 2012, 48, 5977−5979. (16) Kong, C.; Du, H.; Chen, L.; Chen, B. Nanoscale MOF/ Organosilica Membranes on Tubular Ceramic Substrates for Highly Selective Gas Separation. Energy Environ. Sci. 2017, 10, 1812−1819. (17) Zhang, C.; Koros, W. J. Zeolitic Imidazolate FrameworkEnabled Membranes: Challenges and Opportunities. J. Phys. Chem. Lett. 2015, 6, 3841−3849. (18) He, M.; Yao, J.; Liu, Q.; Zhong, Z.; Wang, H. Toluene-Assisted Synthesis of RHO-Type Zeolitic Imidazolate Frameworks: Synthesis and Formation Mechanism of ZIF-11 and ZIF-12. Dalton Trans. 2013, 42, 16608−16613. (19) Wang, C.; Yang, F.; Sheng, L.; Yu, J.; Yao, K.; Zhang, L.; Pan, Y. Zinc-Substituted ZIF-67 Nanocrystals and Polycrystalline Membranes for Propylene/Propane Separation. Chem. Commun. 2016, 52, 12578− 12581.

(20) Zhou, S.; Wei, Y.; Zhuang, L.; Ding, L.-X.; Wang, H. Introduction of Metal Precursors by Electrodeposition for the In Situ Growth of Metal−Organic Framework Membranes on Porous Metal Substrates. J. Mater. Chem. A 2017, 5, 1948−1951. (21) Huang, Y.; Xiao, Y.; Huang, H.; Liu, Z.; Liu, D.; Yang, Q.; Zhong, C. Ionic Liquid Functionalized Multi-Walled Carbon Nanotubes/Zeolitic Imidazolate Framework Hybrid Membranes for Efficient H2/CO2 Separation. Chem. Commun. 2015, 51, 17281− 17284. (22) Friebe, S.; Geppert, B.; Steinbach, F.; Caro, J. Metal−Organic Framework UiO-66 Layer: A Highly Oriented Membrane with Good Selectivity and Hydrogen Permeance. ACS Appl. Mater. Interfaces 2017, 9, 12878−12885. (23) Li, Y.-S.; Liang, F.-Y.; Bux, H.; Feldhoff, A.; Yang, W.-S.; Caro, J. Molecular Sieve Membrane: Supported Metal-Organic Framework with High Hydrogen Selectivity. Angew. Chem. 2010, 122, 558−561. (24) Bux, H.; Feldhoff, A.; Cravillon, J.; Wiebcke, M.; Li, Y.-S.; Caro, J. Oriented Zeolitic Imidazolate Framework-8 Membrane with Sharp H2/C3H8 Molecular Sieve Separation. Chem. Mater. 2011, 23, 2262− 2269. (25) Yin, H.; Wang, J.; Xie, Z.; Yang, J.; Bai, J.; Lu, J.; Zhang, Y.; Yin, D.; Lin, J. Y. S. A Highly Permeable and Selective AminoFunctionalized MOF CAU-1 membrane for CO2−N2 Separation. Chem. Commun. 2014, 50, 3699−3701. (26) Huang, A.; Bux, H.; Steinbach, F.; Caro, J. Molecular-Sieve Membrane with Hydrogen Permselectivity: ZIF-22 in LTA Topology Prepared with 3-Aminopropyltriethoxysilane as Covalent Linker. Angew. Chem. 2010, 122, 5078−5081. (27) 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. (28) Huang, A.; Chen, Y.; Wang, N.; Hu, Z.; Jiang, J.; Caro, J. A Highly Permeable and Selective Zeolitic Imidazolate Framework ZIF95 membrane for H2/CO2 Separation. Chem. Commun. 2012, 48, 10981−10983. (29) Huang, A.; Liu, Q.; Wang, N.; Caro, J. Highly Hydrogen Permselective ZIF-8 Membranes Supported on Polydopamine Functionalized Macroporous Stainless-Steel-Nets. J. Mater. Chem. A 2014, 2, 8246−8251. (30) 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. (31) Guo, H.; Zhu, G.; Hewitt, I. J.; Qiu, S. “Twin Copper Source” Growth of Metal−Organic Framework Membrane: Cu3(BTC)2 with High Permeability and Selectivity for Recycling H2. J. Am. Chem. Soc. 2009, 131, 1646−1647. (32) Zhang, X.; Liu, Y.; Li, S.; Kong, L.; Liu, H.; Li, Y.; Han, W.; Yeung, K. L.; Zhu, W.; Yang, W.; Qiu, J. New Membrane Architecture with High Performance: ZIF-8 Membrane Supported on Vertically Aligned ZnO Nanorods for Gas Permeation and Separation. Chem. Mater. 2014, 26, 1975−1981. (33) Zhang, X.; Liu, Y.; Kong, L.; Liu, H.; Qiu, J.; Han, W.; Weng, L.T.; Yeung, K. L.; Zhu, W. A Simple and Scalable Method for Preparing Low-Defect ZIF-8 Tubular Membranes. J. Mater. Chem. A 2013, 1, 10635−10638. (34) Kong, L.; Zhang, X.; Liu, H.; Qiu, J. Synthesis of a Highly Stable ZIF-8 Membrane on a Macroporous Ceramic Tube by ManualRubbing ZnO deposition as a multifunctional layer. J. Membr. Sci. 2015, 490, 354−363. (35) Meckler, S. M.; Li, C.; Queen, W. L.; Williams, T. E.; Long, J. R.; Buonsanti, R.; Milliron, D. J.; Helms, B. A. Sub-micron polymer− zeolitic imidazolate framework layered hybrids via controlled chemical transformation of naked ZnO nanocrystal films. Chem. Mater. 2015, 27, 7673−7679. (36) Wang, X.; Sun, M.; Meng, B.; Tan, X.; Liu, J.; Wang, S.; Liu, S. Formation of continuous and highly permeable ZIF-8 membranes on 4159

DOI: 10.1021/acsami.7b17568 ACS Appl. Mater. Interfaces 2018, 10, 4151−4160

Research Article

ACS Applied Materials & Interfaces porous alumina and zinc oxide hollow fibers. Chem. Commun. 2016, 52, 13448−13451. (37) Liu, Y.; Pan, J. H.; Wang, N.; Steinbach, F.; Liu, X.; Caro, J. Remarkably Enhanced Gas Separation by Partial Self-Conversion of a Laminated Membrane to Metal-Organic Frameworks. Angew. Chem., Int. Ed. 2015, 54, 3028−3032. (38) Sun, Y.; Yang, F.; Wei, Q.; Wang, N.; Qin, X.; Zhang, S.; Wang, B.; Nie, Z.; Ji, S.; Yan, H.; Li, J.-R. Oriented Nano-MicrostructureAssisted Controllable Fabrication of Metal-Organic Framework Membranes on Nickel Foam. Adv. Mater. 2016, 28, 2374−2381. (39) Yao, J.; Dong, D.; Li, D.; He, L.; Xu, G.; Wang, H. ContraDiffusion Synthesis of ZIF-8 Films on a Polymer Substrate. Chem. Commun. 2011, 47, 2559−2561. (40) Zhang, S.; Wang, Z.; Ren, H.; Zhang, F.; Jin, J. Nanoporous Film-Mediated Growth of Ultrathin and Continuous Metal−Organic Framework Membranes for High-Performance Hydrogen Separation. J. Mater. Chem. A 2017, 5, 1962−1966. (41) Brown, A. J.; Brunelli, N. A.; Eum, K.; Rashidi, F.; Johnson, J. R.; Koros, W. J.; Jones, C. W.; Nair, S. Interfacial Microfluidic Processing of Metal-Organic Framework Hollow Fiber Membranes. Science 2014, 345, 72−75. (42) Liu, Y.; Ban, Y.; Yang, W. Microstructural Engineering and Architectural Design of Metal-Organic Framework Membranes. Adv. Mater. 2017, 29, 1606949. (43) Mao, Y.; Cao, W.; Li, J.; Sun, L.; Peng, X. HKUST-1 Membranes Anchored on Porous Substrate by Hetero MIL-110 Nanorod Array Seeds. Chem.Eur. J. 2013, 19, 11883−11886. (44) Yoshida, T.; Tochimoto, M.; Schlettwein, D.; Wöhrle, D.; Sugiura, T.; Minoura, H. Self-Assembly of Zinc Oxide Thin Films Modified with Tetrasulfonated Metallophthalocyanines by One-Step Electrodeposition. Chem. Mater. 1999, 11, 2657−2667. (45) Zhao, J.; Nunn, W. T.; Lemaire, P. C.; Lin, Y.; Dickey, M. D.; Oldham, C. J.; Walls, H. J.; Peterson, G. W.; Losego, M. D.; Parsons, G. N. Facile Conversion of Hydroxy Double Salts to Metal−Organic Frameworks Using Metal Oxide Particles and Atomic Layer Deposition Thin-Film Templates. J. Am. Chem. Soc. 2015, 137, 13756−13759. (46) Lemaire, P. C.; Zhao, J.; Williams, P. S.; Walls, H. J.; Shepherd, S. D.; Losego, M. D.; Peterson, G. W.; Parsons, G. N. Copper Benzenetricarboxylate Metal−Organic Framework Nucleation Mechanisms on Metal Oxide Powders and Thin Films formed by Atomic Layer Deposition. ACS Appl. Mater. Interfaces 2016, 8, 9514−9522. (47) Meyn, M.; Beneke, K.; Lagaly, G. Anion-Exchange Reactions of Hydroxy Double Salts. Inorg. Chem. 1993, 32, 1209−1215. (48) Hara, T.; Ishikawa, M.; Sawada, J.; Ichikuni, N.; Shimazu, S. Creation of Highly Stable Monomeric Pd (II) Species in an AnionExchangeable Hydroxy Double Salt Interlayer: Application to Aerobic Alcohol Oxidation under an Air Atmosphere. Green Chem. 2009, 11, 2034−2040. (49) Zhan, W.-w.; Kuang, Q.; Zhou, J.-z.; Kong, X.-j.; Xie, Z.-x.; Zheng, L.-s. Semiconductor@Metal−Organic Framework Core−Shell Heterostructures: A Case of ZnO@ZIF-8 Nanorods with Selective Photoelectrochemical Response. J. Am. Chem. Soc. 2013, 135, 1926− 1933. (50) Newman, S. P.; Jones, W. Comparative Study of Some Layered Hydroxide Salts Containing Exchangeable Interlayer Anions. J. Solid State Chem. 1999, 148, 26−40. (51) Biswick, T.; Jones, W.; Pacuła, A.; Serwicka, E. Synthesis, Characterisation and Anion Exchange Properties of Copper, Magnesium, Zinc and Nickel Hydroxy Nitrates. J. Solid State Chem. 2006, 179, 49−55. (52) Hillman, F.; Zimmerman, J. M.; Paek, S.-M.; Hamid, M. R. A.; Lim, W. T.; Jeong, H.-K. Rapid microwave-assisted synthesis of hybrid zeolitic−imidazolate frameworks with mixed metals and mixed linkers. J. Mater. Chem. A 2017, 5, 6090−6099. (53) Carson, C. G.; Hardcastle, K.; Schwartz, J.; Liu, X.; Hoffmann, C.; Gerhardt, R. A.; Tannenbaum, R. Synthesis and Structure Characterization of Copper Terephthalate Metal-Organic Frameworks. Eur. J. Inorg. Chem. 2009, 2338−2343.

(54) Dybtsev, D. N.; Chun, H.; Kim, K. Rigid and Flexible: A Highly Porous Metal−Organic Framework with Unusual Guest-Dependent Dynamic Behavior. Angew. Chem. 2004, 116, 5143−5146. (55) Arstad, B.; Fjellvåg, H.; Kongshaug, K. O.; Swang, O.; Blom, R. Amine Functionalised Metal Organic Frameworks (MOFs) as Adsorbents for Carbon Dioxide. Adsorption 2008, 14, 755−762. (56) Ania, C. O.; García-Pérez, E.; Haro, M.; Gutiérrez-Sevillano, J. J.; Valdés-Solís, T.; Parra, J. B.; Calero, S. Understanding Gas-Induced Structural Deformation of ZIF-8. J. Phys. Chem. Lett. 2012, 3, 1159− 1164. (57) Kumari, G.; Jayaramulu, K.; Maji, T. K.; Narayana, C. Temperature Induced Structural Transformations and Gas Adsorption in the Zeolitic Imidazolate Framework ZIF-8: A Raman Study. J. Phys. Chem. C 2013, 117, 11006−11012. (58) Li, W.; Zhang, Y.; Zhang, C.; Meng, Q.; Xu, Z.; Su, P.; Li, Q.; Shen, C.; Fan, Z.; Qin, L.; Zhang, G. Transformation of Metal-Organic Frameworks for Molecular Sieving Membranes. Nat. Commun. 2016, 7, 11315. (59) Li, W.; Zhang, Y.; Su, P.; Xu, Z.; Zhang, G.; Shen, C.; Meng, Q. Metal−Organic Framework Channelled Graphene Composite Membranes for H2/CO2 Separation. J. Mater. Chem. A 2016, 4, 18747− 18752. (60) Wang, H.; Lin, Y. S. Synthesis and Modification of ZSM-5/ Silicalite Bilayer Membrane with Improved Hydrogen Separation Performance. J. Membr. Sci. 2012, 396, 128−137. (61) Li, Y.; Liang, F.; Bux, H.; Yang, W.; Caro, J. Zeolitic Imidazolate Framework ZIF-7 Based Molecular Sieve Membrane for Hydrogen Separation. J. Membr. Sci. 2010, 354, 48−54. (62) Liu, Y.; Wang, N.; Caro, J. In Situ Formation of LDH Membranes of Different Microstructures with Molecular Sieve Gas Selectivity. J. Mater. Chem. A 2014, 2, 5716−5723. (63) Hu, Y.; Wei, J.; Liang, Y.; Zhang, H.; Zhang, X.; Shen, W.; Wang, H. Zeolitic Imidazolate Framework/Graphene Oxide Hybrid Nanosheets as Seeds for the Growth of Ultrathin Molecular Sieving Membranes. Angew. Chem., Int. Ed. 2016, 55, 2048−2052. (64) Zhang, F.; Zou, X.; Gao, X.; Fan, S.; Sun, F.; Ren, H.; Zhu, G. Hydrogen Selective NH2-MIL-53 (Al) MOF Membranes with High Permeability. Adv. Funct. Mater. 2012, 22, 3583−3590.

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DOI: 10.1021/acsami.7b17568 ACS Appl. Mater. Interfaces 2018, 10, 4151−4160