Facile Fabrication of Multifunctional Metal–Organic Framework Hollow

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Facile Fabrication of Multifunctional Metal-Organic Framework Hollow Tubes to Trap Pollutants Yifa Chen, Fan Chen, Shenghan Zhang, Ya Cai, Sijia Cao, Siqing Li, Wenqi Zhao, Shuai Yuan, Xiao Feng, Anyuan Cao, Xiaojie Ma, and Bo Wang J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.7b10265 • Publication Date (Web): 30 Oct 2017 Downloaded from http://pubs.acs.org on October 30, 2017

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Facile Fabrication of Multifunctional Metal-Organic Framework Hollow Tubes to Trap Pollutants Yifa Chen†, Fan Chen†, Shenghan Zhang†, Ya Cai†, Sijia Cao†, Siqing Li†, Wenqi Zhao‡, Shuai Yuan†, Xiao Feng†, Anyuan Cao‡, Xiaojie Ma†* and Bo Wang†* †

Key Laboratory of Cluster Science, Ministry of Education of China, School of Chemistry, Beijing Institute of Technology, 5 South Zhongguancun Street, Beijing, 100081, P.R. China

‡

Department of Materials Science and Engineering, College of Engineering, Peking University, Beijing 100871, P. R. China Supporting Information Placeholder

ABSTRACT: Pollutant treatment is critical in modern society and often requires tedious workup and expensive facilities. By virtue of structural diversity and tunability, metal-organic frameworks (MOFs) have shown promise in pollutant control. We herein report a powerful templated freeze-drying protocol for the fabrication of multifunctional MOF hollow tubular structures for both air and liquid contaminants filtration. Various hollow tube systems (e.g., “Janus”, “coaxial” and “cellular”) are produced. Specially, a multilayer coaxial MOF hollow tube is prepared for highly efficient capture of mixed inorganic-organic liquid contaminants with > 94% filtration efficiency. Further, a “cellular” hollow tube with low pressure-drop (12 Pa, 10 cm s-1) is applied in particulate matter filtration with high efficiency (> 92%). Given the rich structural and functional diversities, this protocol might bring MOFs into industrial applications to remediate environmental problems.

Pollutant treatment has been a worldwide issue, which needs to be carefully addressed from both biological and environmental standpoint.1 Reducing deaths caused by contaminants in air or water is a major public health goal in many developing countries.2 Liquid contaminant treatment is still a challenge especially in conditions where inorganic (e.g., fertilizers containing nutrients, heavy metals, etc.) and organic components (e.g., petroleum hydrocarbons, dyes, etc.) are highly mixed.3 Organic contaminants in solution are usually treated with techniques like granular activated carbon adsorption while inorganic parts are often treated with ion exchange or reverse osmosis filtration.4 Nevertheless, activated carbon faces the problems of pulverization and limited absorbable species while ion exchange or reverse osmosis often require complex prefiltration treatments and their regeneration can also be costly. Due to the highly complicated inorganic/organic components, liquid purification often requires many steps and huge set-ups. Efficient methods that can simultaneously treat various kinds of organic and inorganic impurities are highly desirable yet largely unmet. With regard to the atmospheric pollution, air contaminants like particulate matter (PM) (especially PM2.5 and

PM10, PM with aerodynamic diameter less than 2.5 and 10 µm) emitting from sources such as power plants and refinery factories can be toxic to people and also detrimental to processing facilities (e.g., gas turbine and combustion engine).5 For instance, fine PM, accumulated in valves and joints, can easily cause clogging and even explosion.6 Specially designed devices that can be easily retrofitted into piping systems and exhaust pipes for efficient capture of PM particles are also longsought-after for industrial applications.

Figure 1. (a) Photo image of the ZIF-8@SA-HT (50 wt%). (b) SEM image of ZIF-8@SA-HT (50 wt%). (c) SEM image of enlarged place in b. (d) Pressing test conducted with an autoclave (0.7 kg), insert picture is the state before pressing. (e) Side-direction pressing test conducted with an autoclave (0.7 kg). (f) Stretching test conducted with an autoclave (0.7 kg) holding downside. (g) PXRD patterns of ZIF-8@SA-HT (50 wt%). (h) Outer-diameter and wallthickness of ZIF-8@SA-HT (50 wt%) along the hollow tube (about 6 cm in length).

Metal-organic frameworks (MOFs), a class of highly porous crystalline materials constructed from metal ions and organic linkers, have attracted broad interests in scientific society.7 By virtue of their structural periodicity and tunability, high porosity and rich functionality, MOFs or MOF composites with different metal centers, tunable functional groups and charges have been used for pollutant treatments in various systems and are

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promising alternatives for contaminants filtration.8 However, the crystalline nature of MOFs hampers their further applications. Besides, works reported to date usually use one MOF to treat one kind of pollutant.8f It is still hard and challenging in exploring novel methods to construct MOFs or MOF-based devices with multifunctionalities to efficiently treat mixed-pollutant systems (especially for pollutants contain both inorganic and organic species). Thus methods that can integrate various MOFs in a system for mixed-pollutant filtration and conquer the brittle nature of MOFs to process into required shapes are particularly urgent and necessary before they can be widely adopted in practical application situations.9 Herein, we report a versatile templated freeze-drying protocol for the fabrication of MOF-based hollow tubes. Five typical MOFs are picked to produce robust hollow tubes with tunable loadings and hole-diameters by employing sodium alginate (SA) as the polymer. Besides, various kinds of hollow tube systems are produced. Thus-obtained multifunctional hollow tubes show great potential in efficient filtration of single or mixed contaminants in both air and liquid phase. The fabrication of MOF based hollow tube through templated freeze-drying is achieved as follows. Highfrequency sonication is applied in this work to promote the uniform dispersion of MOF nanoparticles in the SA solution. The obtained MOF@SA solution is then filled in a mold with a template in the middle. After freezing in liquid nitrogen, an ice solid with the shape of the mold is achieved. Then the template is peeled off and the hollow ice solid is treated with freeze-drying to produce the hollow tube (Figure S1). To prove the versatility, five representative MOFs (i.e. ZIF-8,8a UIO-66,10 NH2-UIO66,10 Zn-MOF-7411 and NH2-MIL-1018d) with distinct topologies and functionalities are synthesized and successfully fabricated into hollow tubes under the same procedures (Figure S2). These MOF based hollow tubes all possess porous textures with remained underlying topology and uniformly dispersed morphology of MOF nanocrystals (Figure 1, Figure S3, S10, S13, S14, S17 and S19). Taking UIO-66@SA based hollow tube with 50 wt% loading (denoted as UIO-66@SA-HT (50 wt%)) for example, UIO-66 shows unchanged structure integrity and uniformly dispersed morphology as evidenced by powder X-ray diffraction (PXRD), scanning electron microscope (SEM) and elemental mapping analyses (Figure S3-5). Additionally, the loadings (from 30 to 70 wt%) and hole diameters (from 4.5 to 8.0 mm) of UIO66@SA-HT can be easily tuned (Figure S3 and S6). It is noteworthy that these hollow tubes all present low density (< 0.1 g cm-3) even the MOF loadings increase to 70 wt% (Table S1).

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Figure 2. (a) Photo image of conjugated hollow tube. (b) “Janus” hollow tube. (c) Double-layer hollow tube. (d-f) UIO-66@SA-HT (50 wt%) with “cellular” structure. Average hole-diameter: d, 6.5 mm, e, 4.5 mm and f, 1.0 mm. (g) Conjugated hollow tube with one side sealed. (h) Doublelayer hollow tube. (i) Three-layer hollow tube. (j) Threelayer membrane.

Combining MOF nanoparticles with SA (a kind of polymer rich in functional groups (e.g., -COOH, -OH)), thus-obtained hollow tubes present high robustness and uniform shape-regularity. For example, ZIF-8@SA-HT (50 wt%) has regular shape (wall-thickness and outerdiameter retain intact) and can withstand pressing and stretching compared with SA-HT (Figure 1d-h and Figure S7). The high mechanical stability of the hollow tube is supported by the compressive tests. The compressive stress-strain (σ-ε) curve of ZIF-8@SA-HT (50 wt%) shows a viscoelastic behavior with a hysteresis loop between the loading and unloading (Figure S8). During loading, initially the hollow tube is compressed to a small strain with the stress rapidly increasing (ε = 10%, σ = 0.1 MPa), dominated by the flexible hollow tube deformation. Then the stress at about 40% strain is reached smoothly, and afterwards the stress tends to fast approach a high value of 0.38 MPa at 60% strain. Other hollow tubes present similar curves with high stress (> 0.27 MPa) at ε = 60% compared with SA-HT (0.088 MPa) (Table S2). Besides, higher stresses of the hollow tubes are achieved with the increase of MOF loadings (e.g., 0.24, 0.37 and 0.44 MPa for UIO-66@SA-HT with 30, 50 and 70 wt% loadings, respectively) (Figure S9). The porosities of these hollow tubes are also investigated. Taking ZIF-8@SA-HT (50 wt%) and NH2-MIL101@SA-HT (50 wt%) for example, they both show remained surface areas and pore volumes (ZIF-8@SAHT (50 wt%), 579 m2 g-1, 0.462 cm3 g-1 and NH2-MIL101@SA-HT (50 wt%), 924 m2 g-1, 0.615 cm3 g-1) compared with ZIF-8 (1320 m2 g-1 and 1.080 cm3 g-1) and NH2-MIL-101 (2026 m2 g-1 and 1.422 cm3 g-1) based on the N2 sorption tests at 77 K (Figure S12 and S16).8a,d

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Figure 3. (a) Device for pollutants filtration. The filtration speed is controlled with a propulsion unit. (b) Photo image of ZIF-8@SA-HT (50%). The thickness of the sealed part is the same as the wall thickness. (c) Recycle performances of ZIF-8@SA-HT (50 wt%) in AsO43- (20 mg L-1, DMF) filtration experiments. (d) Photo image of the double-layer hollow tube. (e) SEM image of the circled place (green) in d. (f) SEM image of the circled place (red) in e. (g) SEM image of the circled place (blue) in e. (h, i) Photo images of the mixed solution (AsO43-, 20 mg L-1 and MO, 5 mg L-1, DMF) before and after filtration. (j) Filtration efficiency of the double-layer hollow tube and relative comparisons (in the image, ZIF-8 + NH2-MIL-101 represents for (ZIF-8 + NH2-MIL-101)@SA-HT).

Templated freeze-drying method, utilizing ice as the desired platform, confers excellent processibility for these MOF based composites.12 As a proof-of-concept, we apply five MOF@SA composites as basic units to assemble various hollow tubes (Figure 2). For instance, hollow tubes with conjugated structures are attained when connecting two parts of MOF@SA composites (Figure 2a,b). And when utilizing different sizes of templates, “cellular” hollow tubes with various holediameters (from 6.5 mm to 1.0 mm) are produced (Figure 2d-f). Moreover, a piece of NH2-MIL-101@SA based ice solid can be connected to one side of UIO66@SA hollow ice tube with trace amount of water. After freeze-drying, a hollow tube with one side sealed is manufactured (Figure 2g). Beside, various double/threelayer hollow tube or membrane systems can be produced in a layer-by-layer fashion (Figure 2c,h,i,j). Taking (ZIF8 + NH2-MIL-101)@SA-HT double-layer hollow tube for example, SEM images show the interface is tightly connected without any gap or crack (Figure 3d-g). This indicates the method is efficient to seamlessly combine different MOF systems together. The robustness and diversity of these hollow tubes set fundamental basis for further applications. To study the feasibility of trapping certain analytes, we further fabricate ZIF-8@SA into a hollow tube with one side sealed and utilize it in AsO43- treatment (Figure 3a,b). This hollow tube exhibits 96.8% efficiency for AsO43- (20 mg L-1, N,N-dimethylformamide (DMF)) extraction and can be

recycled for three times with remained structure integrity and porosity (Figure 3c, Figure S11 and S12). Additionally, a double-layer (ZIF-8 + NH2-MIL-101)@SAHT with seamless integration of two MOF parts is produced for mixed-pollutants extraction (Figure 3d-g). As reported, ZIF-8 and NH2-MIL-101 have strong interactions with AsO43- and methyl orange (MO).8a-d As a result, these two pollutants are successfully extracted from the mixed solution and high efficiency (AsO43-, 95.3% and MO, 97.1%) are obtained compared with relative comparisons (Figure 3h-j, S21-22). Despite the excellent properties in robustness and contaminant treatment, hollow tubes prepared through this protocol have poor water stability. SA, a water-soluble polymer composed of carboxylic sodium can be crossedlinked with metal ions like Ca2+ (Figure S26a).13 After treating with CaCl2·2H2O solution, water stable ZIF8@SA-HT (50 wt%) with remained robustness, morphology and AsO43- filtration efficiency is produced (Figure S26b,c, S27 and S28). Conducted under the same conditions, water stable (ZIF-8 + NH2-MIL101)@SA-HT shows high efficiency (94.3% and 96.8%) for mixed-pollutants (aqueous solution, AsO43-, 20 mg L1 and MO, 5 mg L-1) filtration compared with SA-HT (28.2% and 36.4%). In addition, the saturated capacity values of ZIF-8@SA-HT (50 wt%) and NH2-MIL101@SA-HT (50 wt%) for AsO43- and MO are calculated to be 51.9 and 152.7 mg g-1 respectively (based on the Langmuir adsorption isotherms), which are comparable to most of materials reported (Figure S23-25, Table S3-6). Considering the practical situations, we further set out to explore the filtration properties of the hollow tube for low-concentration mixed pollutants (AsO43-, 200 µg L-1 and MO, 200 µg L-1) and it shows high filtration efficiency (> 96%) even after seven cycles (Figure S29).

Figure 4. (a) The schematic representation of “cellular” PM filter. (b) Photo image of the “cellular” ZIF-8@SA-HT (30 wt%). (c) PM filtration efficiency of “cellular” ZIF8@SA-HT (30 wt%). (d) Pressure drop under various air velocities. (e) SEM image of “cellular” ZIF-8@SA-HT after tests. (f) The enlarged place in e. PM particles are pointed out with dark arrows.

Furthermore, a “cellular” ZIF-8@SA-HT (30 wt%) is produced for PM filtration (Figure 4b). PM is highly polar due to the existence of ions, water and other com-

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pounds. MOFs with positive charges (attributed to the unbalanced metal ions or defects) can polarize the surface of PM to improve the electrostatic interactions between MOFs and PM.14a ZIF-8 with high positive charge has been proved to be promising candidate for PM filtration.14 Specially, ZIF-8 is fabricated into “cellular” hollow tube which can provide functional pathways for the interaction between exposed MOF surface and PM within the scaffold (Figure 4a). It shows superior efficiency (PM2.5, 92 ± 2.2%; PM10, 95 ± 2.6 %) compared with the SA based “cellular” hollow tube (PM2.5, 31 ± 1.2%; PM10, 33 ± 1.4%). The outstanding efficiency here is comparable to previously reported materials (e.g., PAN/ZIF-8 (PM2.5, 88.33 ± 1.52%; PM10, 89.67 ± 1.33%)14a and ZIF-8@Melamine foam (PM2.5, 99.5 ± 1.7%; PM10, 99.3 ± 1.2%)14b). After tests, SEM images show that the PM particles are attached onto the surface of the hollow tube (Figure 4e,f). Additionally, it presents low pressure-drop (e.g., 12 Pa, 10 cm s-1; 47 Pa, 20 cm s1 ) in a pressure resistance test (Figure 4d). With low pressure-drop and high efficiency, this “cellular” structure holds great promise as the pre-filter for devices like gas turbine and internal combustion engine, and may prove valuable in a diesel particulate filter (DPF) attached to all exhaust pipes in diesel vehicles. In summary, we report a versatile templated freezedrying protocol for the fabrication of multifunctional hollow tubes for pollutants treatment. Various hollow tubes are successfully prepared and can be used for one or mixed-pollutant filtration. Specially, a multilayer coaxial hollow tubes is prepared for highly efficient capture (> 94%) of mixed inorganic-organic contaminants. Besides, a “cellular” hollow tube with low pressure-drop is produced and shows high PM filtration efficiency (> 92%). Given the rich MOF chemistry learned, this unique method of MOF fabrication offers a robust protocol to shape porous framework crystals into functional devices to address the growing global environmental issues. ASSOCIATED CONTENT Supporting Information Experimental details and additional characterizations. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author [email protected]; [email protected] Notes The authors declare no competing financial interests.

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of China (Grant No. 21625102, 21471018, 21404010, 21490570, 21674012); 1000 Plan (Youth). REFERENCES (1) (a) Forgacs, E.; Cserháti, T.; Oros, G. Environ. Int. 2004, 30, 953. (b) Ng, J. C.; Wang, J. P.; Shraim, A. Chemosphere 2003, 52, 1353. (2) Duker, A. A.; Carranza, E. J. M.; Hale, M. Environ. Int. 2005, 31, 631. (3) Petrie, B.; Barden, R.; Kasprzyk-Hordern, B. Water Res. 2015, 72, 3. (4) (a) Aygün, A.; Yenisoy-Karakaş, S.; Duman, I. Micropor. Mesopor. Mat. 2003, 66, 189. (b) Rengaraj, S.; Yeon, K. H.; Moon, S. H. J. Hazard. Mater. 2001, 87, 273. (c) Lee, S.; Lueptow, R. M. J. Membrane Sci. 2001, 182, 77. (5) (a) Lelieveld, J.; Evans, J. S.; Fnais, M.; Giannadaki, D.; Pozzer, A. Nature 2015, 525, 367. (b) Nel, A. Science 2005, 308, 804. (6) (a) Bojdo, N.; Filippone, A. J. Am. Helicopter Soc. 2012, 57, 1. (b) Liu, C.; Hsu, P. C.; Lee, H. W.; Ye, M.; Zheng, G. Y.; Liu, N. A.; Li, W. Y.; Cui, Y. Nat. Commun. 2015, 6, 1. (7) (a) Li, H.; Eddaoudi, M.; O'Keeffe, M.; Yaghi, O. M. Nature 1999, 402, 276. (b) Kitaura, R.; Kitagawa, S.; Kubota, Y.; Kobayashi, T. C.; Kindo, K.; Mita, Y.; Matsuo, A.; Kobayashi, M.; Chang, H. C.; Ozawa, T. C.; Suzuki, M.; Sakata, M.; Takata, M. Science 2002, 298, 2358. (c) Férey, G.; Mellot-Draznieks, C.; Serre, C.; Millange, F.; Dutour, J.; Surble, S.; Margiolaki, I. Science 2005, 309, 2040. (d) Shekhah, O.; Belmabkhout, Y.; Chen, Z. J.; Guillerm, V.; Cairns, A.; Adil, K.; Eddaoudi, M. Nat. Commun. 2014, 5, 1. (e) Liao, P. Q.; Zhang, W. X.; Zhang, J. P.; Chen, X. M. Nat. Commun. 2015, 6, 1. (8) (a) Jian, M. P.; Liu, B.; Zhang, G. S.; Liu, R. P.; Zhang, X. W. Colloid Surf., A. 2015, 465, 67. (b) Wu, Y. N.; Zhou, M. M.; Zhang, B. R.; Wu, B. Z.; Li, J.; Qiao, J. L.; Guan, X. H.; Li, F. T. Nanoscale 2014, 6, 1105. (c) Haque, E.; Lee, J. E.; Jang, I. T.; Hwang, Y. K.; Chang, J. S.; Jegal, J.; Jhung, S. H. J. Hazard. Mater. 2010, 181, 535. (d) Seoane, B.; Téllez, C.; Coronas, J.; Staudt, C. Sep. Purif. Technol. 2013, 111, 72. (e) Ke, F.; Qiu, L. G.; Yuan, Y. P.; Peng, F. M.; Jiang, X.; Xie, A. J.; Shen, Y. H.; Zhu, J. F. J. Hazard. Mater. 2011, 196, 36. (f) Li, S. Q.; Chen, Y. F.; Pei, X. K.; Zhang, S. H.; Feng, X.; Zhou, J. W.; Wang, B. Chin. J. Chem. 2016, 34, 175. (9) (a) Chen, Y. F.; Huang, X. Q.; Zhang, S. H.; Li, S. Q.; Cao, S. J.; Pei, X. K.; Zhou, J. W.; Feng, X.; Wang, B. J. Am. Chem. Soc. 2016, 138, 10810. (b) Falcaro, P.; Buso, D.; Hill, A. J.; Doherty, C. M. Adv. Mater. 2012, 24, 3153. (c) Falcaro, P.; Ricco, R.; Doherty, C. M.; Liang, K.; Hill, A. J.; Stylesb, M. J. Chem. Soc. Rev. 2014, 43, 5513. (d) Wu, Y.; Li, F.; Xu, Y.; Zhu, W.; Tao, C.; Cui. J.; Li, G. Chem. Commun. 2011, 47, 10094. (e) Aguado, S.; Canivet, J.; Farrusseng, D. J. Mater. Chem. 2011, 21, 7582. (f) Liu. B. J. Mater. Chem. 2012, 22, 10094. (10) Schaate, A.; Roy, P.; Godt, A.; Lippke, J.; Waltz, F.; Wiebcke, M.; Behrens, P. Chem. Eur. J. 2011, 17, 6643. (11) Glover, T. G.; Peterson, G. W.; Schindler, B. J.; Britt, D.; Yaghi, O. Chem. Eng. Sci. 2011, 66, 163. (12) (a) Gutiérrez, M. C.; Ferrer, M. L.; del Monte, F. Chem. Mater. 2008, 20, 634. (b) Seub, J.; Leloup, J.; Richaud, S.; Deville, S.; Guizard, C.; Stevenson, A. J. J. Eur. Ceram. Soc. 2017, 37, 2423. (c) Soon, Y. M.; Shin, K. H.; Koh, Y. H.; Choi, W. Y.; Kim, H. E. J. Eur. Ceram. Soc. 2011, 31, 415. (13) (a) Sun, J. Y.; Zhao, X. H.; Illeperuma, W. R. K.; Chaudhuri, O.; Oh, K. H.; Mooney, D. J.; Vlassak, J. J.; Suo, Z. G. Nature 2012, 489, 133. (b) Nokhodchi, A.; Tailor, A. Il Farmaco 2004, 59, 999. (14) (a) Zhang, Y. Y.; Yuan, S.; Feng, X.; Li, H. W.; Zhou, J. W.; Wang, B. J. Am. Chem. Soc. 2016, 138, 5785. (b) Chen, Y. F.; Zhang, S. H.; Cao, S. J.; Li, S. Q.; Chen, F.; Yuan, S.; Xu, C.; Zhou, J. W.; Feng, X.; Ma, X. J.; Wang, B. Adv. Mater. 2017, 29, 1606221.

ACKNOWLEDGMENT This work was financially supported by the 973 Program 2013CB834702; the National Natural Science Foundation

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