High-Pressure Methane Adsorption in Two Isoreticular Zr-Based Metal

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High-Pressure Methane Adsorption in Two Isoreticular Zr-Based MetalOrganic Frameworks Constructed from C3-Symmetrical Tricarboxylates Huimin Liu, Fengli Chen, Dongjie Bai, Jingjing Jiao, Wei Zhou, Taner Yildirim, and Yabing He Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.6b01507 • Publication Date (Web): 06 Dec 2016 Downloaded from http://pubs.acs.org on December 8, 2016

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Crystal Growth & Design

High-Pressure

Methane

Adsorption

in

Two

Isoreticular Zr-Based Metal-Organic Frameworks Constructed from C3-Symmetrical Tricarboxylates Huimin Liu,a Fengli Chen,a Dongjie Bai,a Jingjing Jiao,a Wei Zhou,b Taner Yildirimb,c and Yabing Hea* a

College of Chemistry and Life Sciences, Zhejiang Normal University, Jinhua 321004, China.

E-mail: [email protected] b

NIST Center for Neutron Research, Gaithersburg, Maryland 20899-6102, USA.

c

Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia,

Pennsylvania 19104-6272, USA. KEYWORDS. Metal-organic frameworks, Methane storage, Zirconium, Tricarboxylate

Abstract: Development of porous metal-organic frameworks (MOFs) with enhanced stability and high methane working capacity is of paramount importance to facilitate the use of natural gas as a transportation fuel. In this work, we used C3-symmetrical tricarboxylates to construct two isoreticular Zr-based MOFs (ZJNU-30 and ZJNU-31) featuring the coexistence of onedimensional channel and two different types of cages in the overall structures. High-pressure

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methane adsorption studies show that the two compounds have good methane adsorption capacities. In particular, the methane working capacity of ZJNU-30a is among the highest reported for Zr-based MOFs. More importantly, the two compounds display exceptional hydrostability, making them attractive for the use as methane adsorbent.

1. INTRODUCTION Natural gas, whose principle component is methane, has recently received renewed attention as an alternative bridging fuel source that replaces the current petroleum-derived fuels for the transportation applications because of the dramatic increase in the accessibility and the low CO2 emission of natural gas. However, the critical challenge related to widespread use of natural gas as a transportation fuel is its low volumetric energy density at ambient conditions (0.04 MJ L-1 for natural gas vs 34.2 MJ L-1 for gasoline). To overcome this problem, many densification methods have been investigated to increase the energy density of natural gas, including compressed natural gas (CNG), liquefied natural gas (LNG) and adsorbed natural gas (ANG). It has been widely recognized that the last one approach involving the use of porous materials to adsorb natural gas would be desirable because ANG makes it possible to store methane under relatively mild conditions, thus avoiding hyperbaric pressure (above 200 bar) and cryogenic temperature (111 K) involved in CNG and LNG methods. However, the success of methane adsorption storage relies on the development of efficient methane adsorbent materials. The earlier studies regarding methane adsorbents mainly focused on the improvement of the adsorption properties of activated carbons and zeolites materials, but no significant breakthrough has been achieved.1 In the past few decades, metal-organic frameworks (MOFs), also known as porous coordination polymers (PCPs), have been rapidly emerging as a new type of crystalline


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porous materials that are composed of metal ions or metal clusters coordinated to polytopic organic bridged ligands to form multidimensional networks. Compared with the traditional activated carbons and zeolites, MOFs have prominent characteristics such as large internal specific surface area, high porosity, adjustable pore size, and functionalized pore surface. Because of these attractive characteristics, MOFs have increasingly become a hot topic of the research for methane adsorbent.2 Indeed, a wide variety of MOFs have already been reported to show high capacities for methane storage that exceed those of traditional activated carbons and zeolites materials.3 For example, HKUST-1 exhibits the methane storage and working capacities (assuming the desorption at 5 bar) of 264~267 and 188~190 cm3 (STP) cm-3 at 298 K and 65 bar.2b,3l An ideal MOF material for methane storage should not only have high methane storage capacity, but more importantly have good hydrolytic stability. Of porous MOFs reported for methane storage, such as copper-multicarboxylate frameworks,3a,3c,3g,3h,3l,3m,3q,3s-u,4 MOF-74 series,5 and Zn4O-based MOFs,3d,3f,3p,3x,6 some of them have high methane storage capacity, but suffer from relatively low stability under humidity, thus hindering their practical applications. Consequently, there is a clear growing need to develop porous MOFs with enhanced stabilities for methane storage. In this regard, zirconium (Zr)-based MOFs based on multicarboxylate ligands are very attractive. This is mainly due to the following several reasons: (1) firstly, compared to traditional transition metal counterparts, Zr-based MOFs often exhibit exceptional thermal, chemical and mechanical stability due to strong ionic bonding between Zr4+ and carboxylate oxygen atoms. For instance, UiO-66 built up from Zr6O4(OH)4 inorganic metal nodes and dianions of terephthalic acid is shown to be thermally stable up to 773 K, and unaltered upon water adsorption and mechanical pressure;7 (2) secondly, Zr-based MOFs usually


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contain hierarchal molecular cages, which have been shown to be favorable for high-pressure gas storage and release; (3) thirdly, recent studies have demonstrated that in addition to the typical 12-connected Zr6O4(OH)4(COO)12 secondary building unit (SBU), other types of SBUs with different connectivities were also observed between Zr4+ and carboxylate groups,8 which affords Zr-based MOFs with diverse topological structures when combined with organic carboxylic acid ligands of different symmetry. As a result, the methane adsorption properties of Zr-based MOFs can be finely tailored towards high performance by appropriate design of Zr clusters and organic linkers; (4) last but not least, there exist some missing-linker defects in Zr-based MOFs. The defect concentration can be tuned by controlling the reaction temperature and time, reactant concentration, different solvents and modulators, thus gas adsorption properties of Zr-MOFs can be further optimized.9 Despite these aforementioned advantages, the research on Zr-based MOFs for methane storage is relatively limited so far.3i,10 Based on the above considerations, we turned our attention to develop stable Zr-based MOFs for methane storage. In this work, we presented the methane adsorption properties of two isoreticular Zr-based MOFs, ZJNU-30 and ZJNU-31, which were constructed form C3-symmetrical aromatic tricarboxylates, 4,4’,4’’-benzene-1,3,5-triyl-1,1’,1’’-trinaphthoic acid (H3L1) and 5,5’,5’’benzene-1,3,5-triyl-1,1’,1’’-trinaphthoic acid (H3L2),

respectively (Scheme 1). It should be

mentioned that ZJNU-30 has been reported by us in a recent work which mainly focused on selective adsorption separation of C4 hydrocarbons.11 Aside from methane adsorption properties, we also investigated their hydrolytic stabilities. The results show that the two compounds not only exhibit good methane adsorption capacities, but also display exceptional hydrolytic stabilities, which make them more attractive for practical methane storage application. To the best of our knowledge, there are only a few examples of Zr-based MOFs fabricated from C3-


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symmetrical ligands in the open literature so far,12 and their methane adsorption properties were not studied so far. HOOC HOOC

COOH COOH

COOH H3L1

COOH H3L2

Scheme 1. The chemical structure of the two organic ligands used to construct ZJNU-30 and ZJNU-31. 2. EXPERIMENTAL 2.1 Martials and methods All starting materials and reagents employed in this study are commercially available and used as supplied without further purification. The organic ligands were prepared according to the previously reported procedure.11,13 Zirconium (IV) chloride (purity ≥ 98%) was purchased from Alfa Aesar. Benzoic acid (purity ≥ 99.5%) was procured from SINOPHARM. 1H NMR and 13C NMR spectra were measured at room temperature in CDCl3 or DMSO-d6 with a Bruker AV400 or AV600 spectrometer, and referenced to the residual solvent peaks. Fourier transform infrared (FTIR) spectra were acquired via a Nicolet 5DX FT-IR spectrometer with KBr discs in 4000-400 cm-1 range. Elemental analyses (C, H, and N) were performed using a Perkin–Elmer 240 CHN analyzer. Thermogravimetric analyses (TGA) data were collected using a Netzsch STA 449C thermal analyzer. The sample was heated at a ramp rate of 5 K min-1 from room temperature to 1073 K under a flowing nitrogen atmosphere (10 mL min-1). Powder X-ray diffraction (PXRD) patterns were recorded using a Philips PW3040/60 automated powder diffractometer with Cu-Kα radiation (λ = 1.542 Å). Simulated PXRD patterns were generated from the single-crystal data


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using Mercury 1.4.1. The N2 adsorption-desorption isotherms at 77 K were obtained using a micromeritics ASAP 2020 HD88 surface-area-and-porosity analyzer. The temperature of 77 K was maintained by a liquid nitrogen bath. High-pressure methane sorption measurements were performed at the Centre for Neutron Research, National Institute of Standards and Technology (NIST) using a computer-controlled Sieverts apparatus, detail of which can be found in a previous publication.14 Research-grade methane was used for high-pressure measurements with a purity of 99.999%. 2.2 Single crystal X-ray diffraction The crystal data were collected on a Bruker Apex II CCD diffractometer equipped with a graphite-monochromatized Mo-Kα radiation (λ = 0.71073 Å). The structures were solved by direct methods and refined with full-matrix least squares technique using the SHELXTL-97 package. There are large solvent accessible void volumes in the crystals which are occupied by highly disordered solvent molecules. No satisfactory disorder model could be achieved, and therefore the SQUEEZE program implemented in PLATON15 was used to remove these electron densities. Structures were then refined again using the data generated. CCDC 1446516 and 1504294 contain the supplementary crystallographic data for ZJNU-30 and ZJNU-31. The data can be obtained free of charge at www.ccdc.cam.ac.uk/conts/retrieving.html 2.3 Synthesis and characterization of ZJNU-31 A mixture of H3L2 (5.0 mg, 8.5 µmol), ZrCl4 (5.0 mg, 21.4 µmol) and benzoic acid (250.0 mg, 2.0 mmol) was dissolved in N,N-dimethylformamide (DMF, 1.5 mL) under ultrasonication, and transferred to a 20-mL Teflon-lined autoclave. The autoclave was tightly sealed and placed in an oven preheated to 403 K. After 86 h of reaction time, the autoclave was removed from the oven and allowed to cool to room temperature. The resulting colorless crystals were collected by


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vacuum filtration, and washed repeatedly with dry DMF. The yield is 31% based on the organic ligands. Selected FTIR (KBr, cm-1): 1655, 1599, 1560, 1508, 1417, 1383, 1255, 1099, 796, 721, 648, 459; For C240H304N28O76Zr9, calcd: C 51.31%, H, 5.45%, N 6.98%; found: C 51.18%, H 5.52%, N 6.86%. 3. RESULTS AND DISCUSSION Solvothermal reactions between the organic linkers and ZrCl4 in the presence of benzoic acid as a modulator under carefully optimized reaction conditions afforded micrometer-sized single crystals. The detailed synthesis procedures were provided in the experimental sections. It should be mentioned that a high concentration of benzoic acid is necessary to produce the single crystals of sufficient size for single crystal X-ray diffraction. Their structures were analyzed by means of single–crystal X-ray diffraction studies, and the phase purity of the bulk materials was verified by powder X-ray diffraction (Figure S1). Based on the single-crystal X-ray diffraction studies, TGA (Figure S2) and microanalysis, ZJNU-30 and ZJNU-31 can be best formulated to be [Zr9O6(OH)6(PhCOO)6(L1)4]·24DMA and [Zr9(µ3-OH)12(OH)12(L2)4]·28DMF, respectively. The single-crystal X-ray studies showed the two compounds are isostructural although the organic ligands employed are positional isomers, so the crystal structure of ZJNU-31 was representatively described in detail. ZJNU-31 is a three-dimensional framework that crystallizes in a cubic space group Pm-3m with a = 28.850 Å. Besides the guest molecules, the asymmetric unit contains three eighths of Zr4+ ions, one sixth of deprotonated ligands, and a half of µ3-OH and a half of hydroxyl groups. Both Zr1 and Zr2 ions are octa-coordinated displaying squareantiprism geometry but their coordination environments are distinctly different. Each Zr1 ion is coordinated by four carboxylate oxygen atoms from four independent L23- organic ligands and four µ3-OH oxygen atoms, while each Zr2 ion is surrounded by two carboxylate oxygen atoms


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from two different L23- organic ligands, four µ3-OH oxygen atoms and two oxygen atoms coming from the terminal hydroxyl groups. The Zr-Ocarboxylate distances are in the range of 2.207-2.274 Å, which are comparable to the values in the reported Zr-carboxylate frameworks. The distance of Zr-O(µ3-OH) ranges from 2.146 to 2.158 Å, and the distance of Zr-OHterminal is 2.182 Å. The assembly of two Zr1, four Zr2 with eight µ3-OH provides an octahedral Zr6 cluster Zr6(µ3OH)8(OH)8(COO)8 acting as inorganic SBU in which the vertexes of an octahedron are occupied by Zr4+ ions and the triangular faces are capped by µ3-OH groups. Only eight edges of the Zr6 octahedron are bridged by carboxylates from L23- ligands. This type of SBU was also observed in the reported Zr-based MOFs.16 The octahedral cores are interconnected by the organic linkers to give rise to an extended three-dimensional periodic structure. There exist two different types of polyhedral cages in the framework. If the Zr clusters are taken as the vertices of polyhedra, one is the octahedral cage that is formed by six Zr6 clusters occupying the vertices and eight organic ligands covering the faces, as shown in Figure 1c, while the other is the cuboctahedral cage that consists of twelve Zr6 clusters occupying the vertices and eight organic ligands covering the triangular faces, as shown in Figure 1d. Each cuboctahedral cage is surrounded by eight octahedral cages via the sharing of the triangular faces and vice versa. Viewed along each crystallographical axis direction, one-dimensional infinite channels can be observed (Figure 1e), which were formed by packing cuboctahedral cages via sharing four-membered windows. The total solvent-accessible volume is 76.4% of the volume of the unit cell when the disordered solvent molecules are removed (18335.8 Å3 out of the 24012.5 Å3 per unit cell volume) as calculated using the PLATON routine. Topologically, the overall network can be simplified to a (3,8)-connected net with Schläfli symbol of {48·64·812·104} if the Zr6 core and the organic ligand are regarded as 8-connected and 3-connected nodes (Figure 1a and 1b), respectively.


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Figure 1. Single-crystal X-ray structure of ZJNU-31: (a) each Zr6 cluster links to 8 organic ligands; (b) each organic ligand links to three Zr6 clusters; (c, d) two different types of cages in the framework: octahedral cage (c) and cuboctahedral cage (d); (e) one-dimensional channel running along each crystallographical axis. Hydrogen atoms are omitted for clarity The textural properties of two compounds were studied by means of nitrogen adsorption desorption isotherms acquired at 77 K using a micromeritics ASAP 2020 HD88 surface-areaand-porosity analyzer. Prior to gas adsorption measurement, the as-synthesized samples were guest-exchanged with low-boiling-point acetone followed by evacuation at dynamic vacuum at


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373 K until the degassed rate reached 2 µmHg min-1. The nitrogen adsorption-desorption isotherms at 77 K of these two compounds were shown in Figure 2. It can be appreciated that the two compounds display reversible pseudo-type-I adsorption isotherms. The change of slopes at relatively low pressures might be ascribed to the presence of different pore geometries within the structures. Based on the nitrogen adsorption isotherms, the Brunauer–Emmett–Teller (BET) surface areas were calculated to be 3116 m2 g-1 for ZJNU-30a and 3739 m2 g-1 for ZJNU-31a, respectively, using established consistency criteria (Figure S4).17 The BET surface area of ZJNU-31a is higher than those of NU-800 (~3150 m2 g-1)3i, UiO(bpdc) (2646 m2 g-1)3j, pbzMOF-1 (2415 m2 g-1)18 and DUT-51(Zr) (2335 m2 g-1)19. The pore volumes estimated from the maximum amount of N2 adsorbed are 1.152 cm3 g-1 for ZJNU-30a and 1.236 cm3 g-1 for ZJNU31a, which are in fairly good agreement with the theoretical values calculated using PLATON, indicating that the samples are fully activated. By comparison, ZJNU-31a has larger specific surface area and pore volume than ZJNU-30a, which is consistent with the above single-crystal X-ray structure analyses.


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Figure 2. N2 adsorption-desorption isotherms of ZJNU-30a and ZJNU-31a at 77 K. The solid and open symbols represent adsorption and desorption, respectively. The inset shows the DFT pore size distribution of ZJNU-30a and ZJNU-31a. In light of such favorable porosities, high-pressure methane sorption measurements were performed at the Centre for Neutron Research, National Institute of Standards and Technology (NIST) using a computer-controlled Sieverts apparatus. Figure 3 shows the excess and total methane adsorption isotherms of ZJNU-30a and ZJNU-31a at 273 K and 298 K for pressures up to 65 bar on a gravimetric basis. In this point, it should be mentioned that the total uptakes were evaluated from the measured excess uptakes and the N2-derieved pore volumes. For these two samples, the excess methane uptakes show a continuous increase with pressure with no maximum or decline observed in the pressure range evaluated. At 298 K and 35 bar, ZJNU-30a and ZJNU-31a exhibit the excess gravimetric methane uptakes of 162.3 and 137.8 cm3 (STP) g−1, corresponding to the total gravimetric methane uptakes of 201.5 and 178.5 cm3 (STP) g−1. When the pressure is further increased to 65 bar, the total gravimetric methane uptake capacities reach 300.8 cm3 (STP) g-1 for ZJNU-30a and 274.8 cm3 (STP) g-1 for ZJNU-31a. Because the volumetric uptake is more appropriate to qualify the adsorption capacity of the adsorbents for ANG vehicular application, we also calculated the volumetric uptakes according to the equation: volumetric uptake (cm3 (STP) cm-3) = gravimetric uptake (cm3 (STP) g-1) × ideal crystal density (g cm-3). Herein, the framework densities of ZJNU-30a and ZJNU-31a are 0.596 and 0.494 g cm-3, respectively. At 298 K and 35 bar, the total volumetric methane uptakes reach 120.1 cm3 (STP) cm−3 for ZJNU-30a and 88.2 cm3 (STP) cm-3 for ZJNU-31a. The volumetric methane storage capacity of ZJNU-30a are comparable to those of UiO-66(Zr) (127 cm3 (STP) cm-3 at 303 K and 35 bar)10d, and UiO-67-BN (124 cm3 (STP) cm-3 at 298 K and 35 bar)10a under the


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similar condition. When the pressure is further increased to 65 bar, the total volumetric methane uptake reaches 179.3 cm3 (STP) cm-3) for ZJNU-30a and 135.7 cm3 (STP) cm-3 for ZJNU-31a. It can be seen that despite the lower surface area and pore volume, ZJNU-30a exhibits much better methane adsorption properties than ZJNU-31a in terms of gravimetric and volumetric adsorption amounts, which indicates that in our cases the pore size distribution might play a more important role in methane adsorption because the narrower pore size can enhance the affinity towards methane molecules due to overlapping attractive potentials from pore walls and thus methane adsorption capacity (Figure 1 inset). Apart from methane storage capacities, we also assessed the methane deliverable/working capacities of the two compounds, which are more important than the total methane uptake capacities for ANG application because the driving range of natural gas vehicles is determined by the methane deliverable capacity. The methane deliverable capacity is defined as the difference between the amount of methane stored at the maximum fill service pressure and the amount stored at the depletion pressure. Assuming the isothermal conditions and a 5-35 bar operating pressure range, ZJNU-30a and ZJNU-31a exhibit deliverable capacities of 155.6 cm3 (STP) g-1 (92.7 cm3 (STP) cm-3) and 137.3 cm3 (STP) g-1 (67.8 cm3 (STP) cm-3) at 298 K, which increases to 254.9 cm3 (STP) g-1 (151.9 cm3 (STP) cm-3) and 233.6 cm3 (STP) g-1 (115.4 cm3 (STP) cm-3) if the upper pressure limits are set to 65 bar. Under 65 to 5 bar operating pressure, a tank filled with ZJNU-30a can deliver 70.4% as much fuel as the CNG tank operating at 200-5 bar pressure, indicating ZJNU-30a as a potential material for methane delivery. We note that the volumetric methane delivery capacity of ZJNU-30a is comparable to that of PCN-14 (157 cm3 (STP) cm-3)3l, PCN-66 (152 cm3 (STP) cm-3)3u, PCN-68 (157 cm3 (STP) cm-3)3u, DUT-8(Cu) (153 cm3 (STP) cm-3 )20, and DUT-49 (156 cm3 (STP) cm-3)3q, and even better than Ni-MOF-74


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(129 cm3 (STP) cm-3)3l. Table 1 summarizes the methane storage and working capacities for the reported Zr-based MOFs. It can be seen that among Zr-based MOFs reported for methane storage, ZJNU-30a has methane delivery capacity comparable to that of NU-1100 (156 cm3 (STP) cm-3)10c, and close to that of NU-800 (167 cm3 (STP) cm-3)3i under the same conditions. Note that NU-800 is currently the best performing Zr-based MOF that was discovered by Snurr et al. through screening over 200 hypothetical MOFs based on Zirconium inorganic nodes on the basis of the results of Grand Canonical Monte Carlo (GCMC) simulation.3i Interestingly, the volumetric methane working capacities increase with decreasing temperatures, which is in contrast with the behavior observed in other top-performing MOFs.3l Specifically, when the temperature decreases from 298 K to 273 K, the methane working capacity increases from 151.9 to 170.3 cm3 (STP) cm-3 for ZJNU-30a, and from 115.4 to 137.3 cm3 (STP) cm-3 for ZJNU-31a. Although the real reason is not unclear at the moment, we speculate that the positive effect of the decreased storage temperature on the methane working capacity might be attributed to the large pore dimension and moderate methane binding interaction. When the temperature is lowered, the extent to which the methane uptake increases at high pressure of 65 bar is larger than the one at low pressure of 5 bar, thus leading to the higher working capacities.


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Figure 3. High-pressure methane adsorption isotherms of ZJNU-30a and ZJNU-31a at 273 K (a) and 298 K (b). Solid and open symbols represent adsorption and desorption, respectively. STP = standard temperature and pressure, 273.15 K and 1 bar. Table 1 Methane adsorption in the reported Zr-based MOFsa BET MOFs

Methane uptakeb

methane deliveryc

(m2 g-1) [cm3 (STP) cm-3 (g g-1)] [cm3 (STP) cm-3 (g g-1)]

Ref.

NU-800

3150

198 (0.256)

167 (0.216)

3i

pbz-MOF-1

2415

192 (0.208)

162 (0.176)

18

NU-1100

4060

180 (0.27)

156 (0.24)

21

ZJNU-30a

3116

179.3 (0.215)

151.9 (0.182)

This work

ZJNU-31a

3739

135.7 (0.196)

115.4 (0.167)

This work


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UiO-67

2583

127

104

10a

UiO-67-Me

1978

135

104

10a

UiO-67-BN

1416

147

104

10a

a

The Zr-based MOFs are listed in the order of decreasing working capacities; b at 298 K and 65 bar; c at 298 K and 5-65 bar pressure range As demonstrated in our recent work, ZJNU-30a exhibited relatively good stability against water.11 Herein, hydrolytical stability of ZJNU-31a was evaluated using the similar method. The activated ZJNU-31a was exposed to air for one month, or immersed in water as well as 2 M HCl aqueous solution for one week at ambient temperature. The treated samples were collected for PXRD measurement. As shown in Figure 4a, no appreciable loss of crystallinity was observed for these treated samples. Because PXRD did not detect a small degradation of the framework, N2 adsorption isotherms of these treated samples at 77 K were further measured. Prior to N2 adsorption measurements, the treated samples were exchanged with dry acetone followed by evacuation at 373 K. It was found that when the activated sample was exposed in air for one month or in water for one week, no significant loss of the amount of N2 adsorbed was observed, whereas exposure of the activated sample to 2 M HCl for one week led to a certain reduction of the adsorption amount of N2 (Figure 4b). The similar situation has also been observed in the other Zr-based MOFs such as PCN-222.16c These above results indicate that the compounds have exceptional hydrostabilities, compared to most of the traditional transitional metal counterparts. Furthermore, the variable-temperature PXRD studies showed that ZJNU-31 can be thermally stable up to 773 K (Figure S5), which is consistent with the results of TGA.


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Figure 4. PXRD patterns (a) and N2 adsorption isotherms (b) of ZJNU-31a before and after exposure to air for one month, water for one week, and 2 M HCl for one week in room temperature.

3. CONCLUSION In summary, we have successfully synthesized and characterized two highly porous and stable Zr-based MOF materials constructed from C3-symmetrical organic tricarboxylate ligands, exhibiting very promising gas uptakes with respect to methane. The volumetric methane deliverable capacity of ZJNU-30a between 65 and 5 bar reaches 151.9 cm3 (STP) cm-3, which is among the highest reported for Zr-based MOFs, and comparable to those of the most promising


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methane storage materials. Furthermore, the two MOFs show the exceptional stability towards water compared to most of the transitional metal counterparts. The good methane uptake capacity and exceptional hydrostability make them very attractive materials for methane storage applications. ASSOCIATED CONTENT Supporting Information. PXRD (Figure S1); TGA (Figure S2); FTIR (Figure S3); BET plots (Figure S4); Variable-temperature PXRD (Figure S5), Additional high-pressure CO2 isotherms (Figure S6); NMR (Figure S7); crystal data and structure refinement parameters (Table S1); CCDC 1446516 and 1504294. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]. Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes The authors declare no competing financial interest. ACKNOWLEDGMENT We acknowledge the Natural Science Foundation of Zhejiang province, China (LR16B010001), the Natural Science Foundation of China (no. 21301156), and the Qianjiang talents project in


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For Table of Contents Use Only

High-Pressure

Methane

Adsorption

in

Two

Isoreticular Zr-Based Metal-Organic Frameworks Constructed from C3-Symmetrical Tricarboxylates Huimin Liu,a Fengli Chen,a Dongjie Bai,a Jingjing Jiao,a Wei Zhou,b Taner Yildirimb,c and Yabing Hea*

Two Zr-based MOFs based on C3-symmetrical tricarboxylates exhibit good methane adsorption capacities as well excellent hydro-stabilities, making them attractive as methane adsorbents.


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High-Pressure Methane Adsorption in Two Isoreticular Zr-Based Metal

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