An Amino-Coordinated Metal–Organic Framework for Selective Gas

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An Amino-Coordinated Metal−Organic Framework for Selective Gas Adsorption Nian Zhao,† Fuxing Sun,*,† Ping Li,† Xin Mu,† and Guangshan Zhu*,‡,§,∥ †

State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun, People’s Republic of China 130012 ‡ Key Laboratory of Polyoxometalate Science of the Ministry of Education, Faculty of Chemistry, Northeast Normal University, Changchun, People’s Republic of China 130024 § Key Laboratory for Micro-Nano Energy Storage and Conversion Materials of Henan Province,Institute of Surface Micro and Nano Materials, Xuchang University, Henan, People’s Republic of China 461000 S Supporting Information *

ABSTRACT: A novel 3D porous metal organic framework, JUC-141, constructed by 5-aminoisophthalic acid and Cu(NO3)2, has been synthesized successfully. The carboxyl groups in the ligand coordinate to Cu2+ to form the classic Cu2(COO)4 paddle wheel SBU, and the assembly of the SBUs with the isophthalic acid moieties leads to a kagome lattice. Interestingly, the amino groups in the ligand also take part in the coordination and link to the dipole of the paddle wheel as pillars, thus forming a 3D porous framework with eea topology. The sizes of the channels are 5.2 Å in the direction of [111] and 10.9 Å in the direction of [001]. Gas sorption tests show that the CO2 adsorption capacities of JUC-141 are 79.94 and 51.39 cm3 g−1 at 273 and 298 K under 1 atm pressure, respectively. However, the N2 adsorption capacities of JUC-141 are 13.90 and 6.76 cm3 g−1 at 273 and 298 K under 1 atm pressure, respectively. IAST calculations indicate that the selectivity values of CO2/N2 are 21.62 at 273 K and 27.60 at 298 K under 101 kPa, respectively. Good selective adsorption of CO2 over N2 makes JUC-141 possible for CO2 storage and separation.

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INTRODUCTION Nowadays, energy crises and environmental pollution have been worldwide issues and have attracted a great deal of attention from scientists all over the world. One of the most serious issues is the excessive emissions of CO2 from the combustion of fossil fuels, which is the chief culprit leading to the greenhouse effect. The achievement of efficient storage and separation of CO2 from N2 is still urgent and challenging. Among all the current separation technologies, adsorption separation is one of the most low-cost and most efficient approaches. Many materials have been investigated for CO2 storage and separation, such as polymer membranes,1 inorganic porous materials,2 alkylamine-containing liquids3 and so on. However, low CO2 adsorption capacity and high expense greatly restrict their industrial applications. Metal−organic frameworks (MOFs) constitute a new class of porous inorganic−organic hybrid crystalline materials that have attracted tremendous interest from scientists and material researchers all over the world due to their varieties of topologies,4 tunable pore sizes,5 functional structures,6 and great potential applications in many fields such as gas storage and separation,7 catalysis,8 molecular sensing,9 drug delivery,10 and so on. The variety of topologies may guarantee higher BET surface and larger adsorption capacity. Tunable pore sizes can increase the selectivity as a molecular screening effect. Functional structures can enhance the host−guest interaction © 2017 American Chemical Society

force. All three of these factors are in favor of increasing gas adsorption capacity and selectivity. Therefore, designing and synthesizing functional MOF materials with specific functional groups and satisfactory channel sizes should be the most feasible and practical approach. Herein, we report a novel 3D porous metal organic framework, JUC-141, constructed by 5-aminoisophthalic acid and Cu(NO3)2. JUC-141 possesses a 2D channel structure, and the sizes of the channels are 5.2 Å in the direction of [111] and 10.9 Å in the direction of [001]. In addition, CO2 adsorption capacities of JUC-141 are 79.94 and 51.39 cm3 g−1 at 273 and 298 K under 1 atm pressure, respectively. However, the N2 adsorption capacities of JUC-141 are 13.90 and 6.76 cm3 g−1 at 273 and 298 K under 1 atm pressure, respectively. IAST calculations indicate that the selectivity values of CO2/N2 are 21.61 at 273 K and 27.6 at 298 K under 101 kPa, respectively. Good selective adsorption of CO2 over N2 makes JUC-141 possible for CO2 storage and separation.

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EXPERIMENTAL SECTION

Materials and Methods. All reagents and solvents were purchased from commercial sources and were used as received without any purification. Powder X-ray diffraction (PXRD) data were Received: February 17, 2017 Published: May 31, 2017 6938

DOI: 10.1021/acs.inorgchem.7b00436 Inorg. Chem. 2017, 56, 6938−6942

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Inorganic Chemistry collected by a Rigaku DMAX 2550 diffractometer (50 kV/20 mA, λ(Cu Kα) = 1.5418 Å). Thermogravimetric analysis (TGA) data were obtained on a Perkin-Elmer thermogravimetric analyzer. Gas sorption isotherms were measured using a Micromeritics ASAP2020 gas adsorption instrument at up to 1 atm of gas pressure. The highly pure N2 (99.999%), CO2 (99.999%), and CH4 (99.999%) were used in sorption experiments. Synthesis of JUC-141. 5-Aminoisophthlic acid (H2L, 18.1 mg, 0.1 mmol), pyrazole (13.6 mg, 0.2 mmol), Cu(NO3)2 (18.7 mg, 0.1 mmol), 1 mL of DMF, 1 mL of H2O, and 3 mL of EtOH were combined in a 20 mL glass vial. After the mixture dissolved completely with stirring, the vial was sealed and heated to 85 °C for about 2 days and then cooled to room temperature. Blue block crystals were collected, washed three times with DMF, and then air-dried (yield: 60%). Elemental and ICP analysis calcd for [CuL] = C8H5O4NCu (%): C, 39.59; H, 2.06; N, 5.77. Found: C, 40.01; H, 2.51; N, 5.31. Single-Crystal X-ray Crystallography. Single-crystal X-ray diffraction data were obtained with a Bruker SMART APEX2 CCD diffractometer (Mo Kα, λ = 0.71073 Å). Data indexing, integration, and absorption correction were carried out with the APEX 2 software package. Structure solvation and refinement were done by using SHELXL-2014 software. Hydrogen atoms were calculated by a theoretical method. The disordered guest molecules in the channels were removed by using the SQUEEZE routine of PLATON. The squeezed guest molecules were not contained in the formula. Crystallographic data and structural refinements for JUC-141 are summarized in Table S1 in the Supporting Information.

the isophthlic acid moieties in the ligand led to a 2D kagome lattice (Figure 1b). Interestingly, the amino groups in the ligand also took part in the coordination and linked to the dipole of the paddle wheel SBUs as pillars, thus forming a 3D porous framework with 2D interconnected channels, which are the hexagonal channels in the [001] direction (Figure 1c and Figure S2a in the Supporting Information) and the square channels in the [111] direction (Figure 1d and Figure S2b). The sizes of the channels were about 12.3 and 6.9 Å as measured by Materials Studio, respectively. The solventaccessible volume of JUC-141 was calculated to be about 52.4% by the PLATON software package.11 The topology analysis was conducted with the TOPOS 4.0 software package.12 Each ligand was connected to two paddle wheel SBUs, and the amino group was coordinated to the dipole of another paddle wheel SBU; thus, the ligand could be simplified as a 3-connected node. Each paddle wheel was connected to four ligands by the carboxyl groups and two amino groups from other two ligands; thus, each paddle wheel SBU could be simplified as a 6-connected node. Therefore, the whole framework of JUC-141 could be simplified as a (3,6)-connected eea net (Figure 1e). The point symbol for the net was {42· 6}2{44·62·86·103}. The phase purity was confirmed by the similarity between the simulated and experimental X-ray diffraction patterns (Figure S3 in the Supporting Information). Thermogravimetric analysis (TGA) showed that JUC-141 started to decompose around 130 °C and the weight loss before 130 °C could be mainly attributed to the isolated guest molecules in the channels (Figure S4 in the Supporting Information). In order to assess the permanent porosity of JUC-141, the assynthesized samples were soaked in dry methanol for 2 days and then in CH2Cl2 for another 2 days and finally activated under vacuum for 8 h at 80 °C. The N2 sorption isotherms of the activated sample at 77 K revealed a typical type I adsorption curve according to the definition of the IUPAC classfication, a characteristic of microporous materials. The fast increase in N2 adsorption amounts under low relative pressure (P/P0 < 0.01) and the following plateau at about 270 cm3 g−1 (STP) indicated a uniform microporous structure. On the basis of the N2 adsorption data, the Brunauer−Emmett−Teller (BET) surface area was calculated to be 1057 m2 g−1. Using the t-plot method model, the pore volume was calculated to be 0.406 cm3 g−1. According to nonlocal density functional theory (NLDFT), there were two narrow pore width distributions located at 5.2 and 10.9 Å (Figure 2), which agreed well with that measured by Materials Studio, as mentioned above. The PXRD pattern of the activated samples indicated that JUC-141 still maintained its crystallinity after activation (Figure S3 in the Supporting Information). We further investigated the sorption behaviors of JUC-141 for other gases. The adsorption enthalpy (Qst) was calculated from the adsorption isotherms at 273 and 298 K using the virial method. The CO2 adsorption capacities of JUC-141 were observed to be 79.94 cm3 g−1 (3.57 mmol g−1) (Figure 3a) and 51.39 cm3 g−1 (2.29 mmol g−1) (Figure 3b) at 273 and 298 K under 1 atm pressure, respectively. The Qst value of CO2 was 27.85 kJ mol−1 (Figure S6 in the Supporting Information), which was higher than those of other reported MOF materials, such as UMCM-1 (12 kJ mol−1),14 MAF-2 (27 kJ mol−1),16 MOF-5 (17 kJ mol−1),13 and NOTT-140 (25 kJ mol−1).15 This higher adsorption enthalpy could be mainly attributed to the strong interactions of CO2 with the amino groups and the

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RESULTS AND DISCUSSION The reaction of 5-aminoisophthlic acid (H2L) with Cu(NO3)2 in a DMF/H2O/EtOH (1/1/3 v/v/v) mixture at 85 °C for 72 h gave blue block crystals of JUC-141 formulated as [CuL](Guest) (yield: 60% based on H2L). Single-crystal Xray diffraction showed that JUC-141 crystallized in the trigonal space group R3̅m with the lattice parameters a = 19.119 Å and c = 20.303 Å. There were half a ligand and half a Cu atom in the asymmetric unit (Figure 1a). The carboxyl groups in the ligands coordinated to Cu atoms to form the classic Cu2(COO)4 paddle wheel SBUs. The assembly of paddle wheel SBUs with

Figure 1. (a) Asymmetric unit of JUC-141. (b) Kagome lattice constructed by isophthlic acid moieties in the ligand and paddle wheel SBUs. (c) Hexagonal channel structures in the [001] direction of JUC141. (d) Square channel structures in the [111] direction of JUC-141. (e) eea topology of JUC-141. The green sheets are the kagome lattices, and the blue lines are simplified by amino groups as pillars. 6939

DOI: 10.1021/acs.inorgchem.7b00436 Inorg. Chem. 2017, 56, 6938−6942

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Inorganic Chemistry

Supporting Information). The estimated selectivity data were obtained from a function of pressure at a general feed composition of landfill gas (50/50, m/m) at 273 and 298 K under 101 kPa, respectively. At 273 K and 101 kPa, the selectivity values for CO2/N2 and CO2/CH4 were 21.62 and 4.20 (Figure 3c), respectively; at 298 K and 101 kPa, the selectivity values were 27.60 and 8.72 (Figure 3d), respectively, which were significantly higher than those of many reported MOFs under the same conditions.18

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CONCLUSIONS

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ASSOCIATED CONTENT

A novel 3D porous amino-coordinated metal organic framework, JUC-141, has been synthesized successfully. The assembly of the paddle wheel SBUs with the isophthalic acid moieties leads to a kagome lattice, and the amino groups link to the dipole of the paddle wheel as pillars, thus forming a 3D porous framework with eea topology. Gas sorption studies reveal that JUC-141 possesses a relatively high CO2 adsorption capacity and good separation performance toward CO2 over N2 and CH4, which make JUC-141 possible for CO2 storage and separation.

Figure 2. N2 adsorption isotherms of JUC-141 at 77 K.

confined channel structures.17 In addition, the sorption isotherms of N2 and CH4 were also measured at 273 and 298 K under 1 atm pressure. The adsorption capacities for N2 were 13.90 cm3 g−1 (Figure 3a) and 6.76 cm3 g−1 (Figure 3b) at 273 and 298 K under 1 atm pressure, respectively, and the values for CH4 were 37.89 cm3 g−1 (Figure 3a) and 21.85 cm3 g−1 (Figure 3b) at 273 and 298 K under 1 atm pressure, respectively. The Qst values of N2 and CH4 were 27.24 kJ mol−1 (Figure S5 in the Supporting Information) and 22.73 kJ mol−1 (Figure S7 in the Supporting Information), respectively. In order to estimate the practical separation ability of CO2, CO2/N2 and CO2/CH4 theoretical gas mixtures were evaluated by the IAST model, a method used to determine binary mixture adsorption from experimental single-component isotherms. The dual-site Langmuir−Frendlich equation was employed to fit the data with excellent correlation coefficients (Figures S8 and S9 in the

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.7b00436. IAST selectivity and Qst calculation details, PXRD, TGA, and a supplementary crystal structure representation of JUC-141 (PDF)

Figure 3. (a) 273 K adsorption isotherms of JUC-141. (b) 298 K adsorption isotherms of JUC-141. (c) IAST CO2/N2 and CO2/CH4 adsorption selectivity at 273 K. (d) IAST CO2/N2 and CO2/CH4 adsorption selectivity at 298 K. 6940

DOI: 10.1021/acs.inorgchem.7b00436 Inorg. Chem. 2017, 56, 6938−6942

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Inorganic Chemistry Accession Codes

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CCDC 1531941 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

*F.S.: e-mail, [email protected]. *G.Z.: e-mail, [email protected]. ORCID

Guangshan Zhu: 0000-0001-6841-737X Present Address ∥

G.Z.: State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun, People’s Republic of China 130012. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors acknowledge financial support from the National Basic Research Program of China (973 Program, grant no. 2014CB931804) and the NSFC (grant nos. 21501064 and 21531003).

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DOI: 10.1021/acs.inorgchem.7b00436 Inorg. Chem. 2017, 56, 6938−6942