C2H2 Mixtures

36 mins ago - A CuI-MOF was found to be a highly selective visual sensor for recognizing C2H2. Gas chromatography studies indicated that it can be use...
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Visual Recognition and Removal of C2H2 from C2H4/C2H2 Mixtures by a CuI‑MOF Guo-Xia Jin,† Jia Wang,† Jing-Yi Liu, Jian-Ping Ma,* and Yu-Bin Dong* College of Chemistry, Chemical Engineering and Materials Science, Collaborative Innovation Centre of Functionalized Probes for Chemical Imaging, Key Laboratory of Molecular and Nano Probes, Ministry of Education, Shandong Normal University, Jinan 250014, P. R. China S Supporting Information *

Upon exposure to C2H2 gas at ambient conditions, the activated (under high vacuum, 333 K, 2h) crystals of 1 undergo a rapid naked-eye-detectable color change. As shown in Figure 1,

ABSTRACT: A CuI-MOF was found to be a highly selective visual sensor for recognizing C2H 2 . Gas chromatography studies indicated that it can be used to effectively remove minor amounts of C2H2 from C2H4/ C2H2 mixtures (98:2) and produce highly pure C2H4 (nearly 100%).

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thylene (C2H4), as the most produced petrochemicals in the world (over 140 million tons per year), is widely used for the synthesis of polyethylene. Acetylene (C2H2), a byproduct in the process to form ethylene by pyrolysis of hydrocarbons, acts as a catalyst poison during ethylene polymerization. Thus, it is essential to remove the small amount of C2H2 from C2H4/C2H2 mixtures to gain polymer-grade ethylene (the maximum acetylene concentration is 5 ppm).1 The commonly used techniques in the petrochemical industry include selective catalytic hydrogenation of C2H2 into C2H4 and the recovery of C2H2 by solvent extraction.2 Both methods have their drawbacks in the aspect of either commercial or energy efficiency. Therefore, the development of a convenient and low-cost C2H2 recognition system for the separation of C2H4/C2H2 mixtures is in high demand. Recent studies indicate that a number of porous metal−organic frameworks (MOFs) with functionalized interior surface areas possess a bright potential for this purpose based on selective adsorptive separation.3−5 For instance, mixed-metal M′MOFs,6 MOF-74 series,7 UTSA-100a,8 “SIFSIX” materials,9 NOTT-300,10 UTSA-67,11 and UTSA-7412 exhibit interesting C2H2 recognition and absorption properties, and their separation efficiency for mixed gas was studied in detail. However, MOFs that exhibit a C 2H 2 -responsive visual colorimetric property after the incorporation of a C2H2 guest have never been reported to date, to the best of our knowledge. In this contribution, we report a single-crystal system of a microporous CuI-MOF [H2O⊂Cu2(L)2I2 (1); L = 1-benzimidazolyl-3,5-bis(4-pyridyl)benzene]13 that exhibits a specific color response to C2H2: the red-brown crystals turn yellow green even in a 98:2 C2H4/C2H2 gas mixture under ambient conditions. A gas chromatography (GC) study indicates that MOF 1 can efficiently remove a small amount of C2H2 from a 98:2 C2H4/C2H2 mixture. The significance of this observation lies in the naked-eye colorimetric recognition of C2H2 and the practical issue of ethylene purification by functionalized porous solid-state materials. © XXXX American Chemical Society

Figure 1. Photographs showing the color change of the bulk crystal samples of 1 in different atmospheres with different C2H2/C2H4 concentrations. 2 showing the crystal color after encapsulation of C2H2.

the color of 1 turns from red brown (1) to yellow green [C2H2⊂Cu2(L)2I2 (2)] in 0.5 h. When the C2H2 concentration is lowered, 1 shows the same yellow-green color response to 1:1 and 98:2 C2H4/C2H2 gas mixtures, respectively, except in a longer time. In contrast, after immersion in a C2H4 atmosphere even for 12 h under the same conditions, the crystals of 1 show no apparent color change. The color response to C2H2 of 1 herein is also distinguished from its yellow or orange color response to volatile organic compounds (methanol, acetone, dichloromethane, etc.) by our previous report.13b The difference in the color response demonstrates that porous MOF 1 can selectively recognize C2H2 molecules, and the new guest molecules are encapsulated in the pores instead of the external surface. Thanks to the unusual stability of the MOF crystals, such a speculation can be well demonstrated by single-crystal X-ray analysis. As shown in Figure 2, the C2H2 molecules are encapsulated in the cavities. Further insight into the structure shows that the guest molecules are fixed inside pores by weak inter-host−guest C−H···Nimidazolyl hydrogen bonds [dN···H = 2.38(2) Å; ∠CHN = 175.45(9)°] and C−H···πacetylene (dH··π = 2.32(1) Å; ∠CHπ = 163.58(6)°]. Here, the uncoordinated benzoimidazolyl groups and the coordinated pyridyl groups on Received: April 11, 2018

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DOI: 10.1021/acs.inorgchem.8b00971 Inorg. Chem. XXXX, XXX, XXX−XXX

Communication

Inorganic Chemistry

Figure 3. Molar percentage of C2H4 and C2H2 in the 98:2 C2H4/C2H2 binary mixtures at different adsorption times over 1 based on the HS-GC peak area.

C2H4 separation efficiency for C2H2/C2H4 mixtures containing a small amount of C2H2 (for example, 1.90%). For exploration of the overall gas adsorption and selectivity of 1, single-component adsorption isotherms for C2H2 and C2H4 were examined on the activated samples based on a virial-type equation, respectively.14 At 298 K and 1 atm, the C2H2 and C2H4 uptake amounts of 1 are 28.0 and 23.0 cm3 g−1, respectively (Figure 4). The corresponding C2H2/C2H4 uptake ratio is 1.22, Figure 2. (top) Single-crystal X-ray host−guest structures of 2 (the guest C2H2 molecules are shown in orange and green as space-filling models, and the host frameworks are shown as stick models). (bottom) Strong C−H···N [H···N = 2.376(2) Å] and C−H···π [H···π = 2.317(1) Å] hydrogen bonds are displayed as green and yellow dotted lines, respectively.

the framework synergistically provide specific recognition sites for the incorporated C2H2 molecules. According to the crystal structure, each unit cell is filled with five C2H2 molecules, namely, 1.25 C2H2 molecules per Cu2(L)2I2 unit. The adsorption of C2H2 by 1 was further confirmed by 1H NMR spectroscopy and thermogravimetric analysis (Figure S1). The proton chemical shift at 1.95 ppm in the 1H NMR spectrum recorded for CDCl3 extracts clearly evidences that a C2H2 guest exists in 1. The powder X-ray diffraction patterns indicate that the solid structure of 1 is maintained upon guest sorption (Figure S1). The UV−vis diffuse-reflectance spectrum of C2H2⊂CuIL (2) displays absorption bands in both the blue-violet (380−540 nm) and red (620−780 nm) regions (Figure S1), which is well consistent with the color change. The color change herein could be attributed to an intermolecular electron-transfer transition between the host framework and encapsulated guests. The removal of 1% acetylene from C2H2/C2H4 mixtures is a very important but challenging industrial separation task to secure polymer-grade ethylene. To evaluate CuI-MOF 1 for acetylene removal capability from binary C2H2/C2H4 mixtures, a 10 mL headspace vial containing 400 mg of activated single crystals of 1 was filled with a C2H4/C2H2 mixture containing 1.90% acetylene (molar percentage determined by GC), and then static headspace gas chromatograpy (HS-GC) for the gas mixtures was carried out at 0, 1, 2, 3, 4, and 5 h (Figures 3 and S2 and Table S2). The concentration of C2H2 in the gas mixture decreased rapidly to 0.79% in 1 h and then gradually to 0.07% in 4 h. Finally, the GC experiment showed no detectable C2H2 gas after 5 h. This experimental result demonstrates that CuI-MOF 1 possesses high acetylene selectivity and extraordinary C2H2/

Figure 4. (a) C2H2 (red) and C2H4 (blue) sorption isotherms on the activated 1 at 298 K. (b) C2H2 (red) and C2H4 (blue) sorption isotherms on the activated 1 at 273 K. Adsorption and desorption branches are shown with closed and open symbols, respectively.

which is comparable to those of the MOF-74 series (1.11−1.16)7 and NOTT-300 (1.48),10 (Table S3). 1 exhibits higher C2H2 and C2H4 uptake capacity (39.0 and 29.2 cm3 g−1) and higher C2H2/ C2H4 uptake ratio (1.33) at lower temperature (273 K) and 1 atm. Applying the ideal adsorbed solution theory (IAST)15 model on pure component isotherms, we have determined the adsorption selectivity of the binary gas mixture of C2H2/C2H4 (1:99, v/v) and C2H2/C2H4 (50:50, v/v) (Figure S4). The IASTpredicted binary gas mixture selectivity of C2H2 over C2H4 is 1.4 (298 K) and 1.5 (273 K), respectively, at 100 kPa. These selectivity values are lower than those of headspace adsorption experiments, which might be caused by the different measuring conditions. The isosteric heat of adsorption for C2H2 was calculated by employing a virial equation, which results in a value of 21.4 kJ mol−1 at the low surface coverage, which was increased to 26.4 kJ mol−1 with increasing C2H2 loading (Figure S5). This implies a cooperative binding mechanism; probably interguest interactions simultaneously exist besides host−guest interactions. In contrast, the Qst value for C2H4 adsorption in 1 is nearly constant with increasing loading. The Qst values of 1 for C2H2 are B

DOI: 10.1021/acs.inorgchem.8b00971 Inorg. Chem. XXXX, XXX, XXX−XXX

Communication

Inorganic Chemistry

Y.; Mita, Y. Highly controlled acetylene accommodation in a metal− organic microporous material. Nature 2005, 436, 238−241. (b) Wu, H.; Gong, Q.; Olson, D. H.; Li, J. Commensurate Adsorption of Hydrocarbons and Alcohols in Microporous Metal Organic Frameworks. Chem. Rev. 2012, 112, 836−868. (c) Pang, J.; Jiang, F.; Wu, M.; Liu, C.; Su, K.; Lu, W.; Yuan, D.; Hong, M. A porous metal-organic framework with ultrahigh acetylene uptake capacity under ambient conditions. Nat. Commun. 2015, 6, 7575. (4) (a) Samsonenko, D. G.; Kim, H.; Sun, Y.; Kim, G.-H.; Lee, H.-S.; Kim, K. Microporous Magnesium and Manganese Formates for Acetylene Storage and Separation. Chem. - Asian J. 2007, 2, 484−488. (b) Zhang, M.; Li, B.; Li, Y.; Wang, Q.; Zhang, W.; Chen, B.; Li, S.; Pan, Y.; You, X.; Bai, J. Finely tuning MOFs towards high performance in C2H2 storage: synthesis and properties of a new MOF-505 analogue with an inserted amide functional group. Chem. Commun. 2016, 52, 7241−7244. (c) Plonka, A. M.; Chen, X.; Wang, H.; Krishna, R.; Dong, X.; Banerjee, D.; Woerner, W. R.; Han, Y.; Li, J.; Parise, J. B. Light Hydrocarbon Adsorption Mechanisms in Two Calcium-Based Microporous Metal Organic Frameworks. Chem. Mater. 2016, 28, 1636−1646. (5) (a) Cui, Y.; Li, B.; He, H.; Zhou, W.; Chen, B.; Qian, G. Metal− Organic Frameworks as Platforms for Functional Materials. Acc. Chem. Res. 2016, 49, 483−493. (b) Hazra, A.; Jana, S.; Bonakala, S.; Balasubramanian, S.; Maji, T. K. Separation/Purification of Ethylene from Acetylene/Ethylene Mixture in a Pillared-layer Porous MetalOrganic Framework. Chem. Commun. 2017, 53, 4907−4910. (6) Xiang, S.-C.; Zhang, Z.; Zhao, C.-G.; Hong, K.; Zhao, X.; Ding, D.R.; Xie, M.-H.; Wu, C.-D.; Das, M. C.; Gill, R.; Thomas, K. M.; Chen, B. Rationally tuned micropores within enantiopure metal-organic frameworks for highly selective separation of acetylene and ethylene. Nat. Commun. 2011, 2, 204. (7) Bloch, E. D.; Queen, W. L.; Krishna, R.; Zadrozny, J. M.; Brown, C. M.; Long, J. R. Hydrocarbon Separations in a Metal-Organic Framework with Open Iron(II) Coordination Sites. Science 2012, 335, 1606−1610. (8) Hu, T. L.; Wang, H.; Li, B.; Krishna, R.; Wu, H.; Zhou, W.; Zhao, Y.; Han, Y.; Wang, X.; Zhu, W.; Yao, Z.; Xiang, S.; Chen, B. Microporous metal-organic framework with dual functionalities for highly efficient removal of acetylene from ethylene/acetylene mixtures. Nat. Commun. 2015, 6, 7328−7336. (9) Cui, X.; Chen, K.; Xing, H.; Yang, Q.; Krishna, R.; Bao, Z.; Wu, H.; Zhou, W.; Dong, X.; Han, Y.; Li, B.; Ren, Q.; Zaworotko, M. J.; Chen, B. Pore chemistry and size control in hybrid porous materials for acetylene capture from ethylene. Science 2016, 353, 141−144. (10) Yang, S.; Ramirez-Cuesta, A. J.; Newby, R.; Garcia-Sakai, V.; Manuel, P.; Callear, S. K.; Campbell, S. I.; Tang, C. C.; Schröder, M. Supramolecular binding and separation of hydrocarbons within a functionalized porous metal−organic framework. Nat. Chem. 2015, 7, 121−129. (11) Wen, H.-M.; Li, B.; Wang, H.; Krishna, R.; Chen, B. High acetylene/ethylene separation in a microporous zinc(II) metal-organic framework with low binding energy. Chem. Commun. 2016, 52, 1166− 1169. (12) Luo, F.; Yan, C.; Dang, L.; Krishna, R.; Zhou, W.; Wu, H.; Dong, X.; Han, Y.; Hu, T.-L.; O’Keeffe, M.; Wang, L.; Luo, M.; Lin, R.-B.; Chen, B. UTSA-74: A MOF-74 Isomer with Two Accessible Binding Sites per Metal Center for Highly Selective Gas Separation. J. Am. Chem. Soc. 2016, 138, 5678−5684. (13) (a) Yu, Y.; Zhang, X.-M.; Ma, J.-P.; Liu, Q.-K.; Wang, P.; Dong, Y.B. Cu(I)-MOF: naked-eye colorimetric sensor for humidity and formaldehyde in single-crystalto-single-crystal fashion. Chem. Commun. 2014, 50, 1444−1446. (b) Yu, Y.; Ma, J.-P.; Zhao, C.-W.; Yang, J.; Zhang, X.-M.; Liu, Q.-K.; Dong, Y.-B. Copper(I) Metal − Organic Framework: Visual Sensor for Detecting Small Polar Aliphatic Volatile Organic Compounds. Inorg. Chem. 2015, 54, 11590−11592. (14) (a) Park, J.; Wang, Z. U.; Sun, L.-B.; Chen, Y.-P.; Zhou, H.-C. Introduction of Functionalized Mesopores to Metal−Organic Frameworks via Metal−Ligand−Fragment Coassembly. J. Am. Chem. Soc. 2012, 134, 20110−20116. (b) Abrahams, B. F.; Grannas, M. J.; Hudson, T. A.; Robson, R. A Simple Lithium(I) Salt with a Microporous Structure and Its Gas Sorption Properties. Angew. Chem., Int. Ed. 2010,

comparable to those in MOFs without open metal sites, like M′MOF-3a,6 UTSA-100a,8 and UTSA-67a,11 and lower than those for the MOF-74 series7 and NOTT-30010 with open metal sites. In summary, we report a single-crystal system of a porous CuIMOF (1) that exhibits specific naked-eye colorimetric recognition for C2H2. The specific binding sites for acetylene in CuIL hosts are determined by single-crystal X-ray diffraction studies. HS-GC experiments demonstrate that the selective recognition of 1 for C2H2 molecules enables high ethylene/ acetylene separation efficiency (nearly 100%). This study provides direct information on molecular binding modes of C2H2 within the space of MOF hosts. We expect that it will provide some hints on the screening and design of MOF materials for gas uptake and separation.

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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/acs.inorgchem.8b00971. Experimental details, Figures S1−S5, and Tables S1−S3 (PDF) Accession Codes

CCDC 1830667 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing data_ [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (J.-P.M.). *E-mail: [email protected] (Y.-B.D.). ORCID

Guo-Xia Jin: 0000-0001-5554-6412 Jian-Ping Ma: 0000-0002-5300-3307 Yu-Bin Dong: 0000-0002-9698-8863 Author Contributions †

The authors contributed equally to this work.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We are grateful for financial support from the NSFC (Grant 21771120). REFERENCES

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DOI: 10.1021/acs.inorgchem.8b00971 Inorg. Chem. XXXX, XXX, XXX−XXX

Communication

Inorganic Chemistry 49, 1087−1089. (c) Noro, S.-I.; Mizutani, J.; Hijikata, Y.; Matsuda, R.; Sato, H.; Kitagawa, S.; Sugimoto, K.; Inubushi, Y.; Kubo, K.; Nakamura, T. Porous coordination polymers with ubiquitous and biocompatible metals and a neutral bridging ligand. Nat. Commun. 2015, 6, 5851. (15) Myers, A. L.; Prausnitz, J. M. Thermodynamics of mixed-gas adsorption. AIChE J. 1965, 11, 121−127.

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DOI: 10.1021/acs.inorgchem.8b00971 Inorg. Chem. XXXX, XXX, XXX−XXX