Tuning Water Sorption in Highly Stable Zr(IV)-MOFs through Local

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Functional Inorganic Materials and Devices

Tuning Water Sorption in Highly Stable Zr(IV)-MOFs through Local Functionalization of Metal-Clusters Yong-Zheng Zhang, Tao He, Xiang-Jing Kong, Xiu-Liang Lv, Xue-Qian Wu, and Jian-Rong Li ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b09333 • Publication Date (Web): 25 Jul 2018 Downloaded from http://pubs.acs.org on July 25, 2018

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ACS Applied Materials & Interfaces

Tuning Water Sorption in Highly Stable Zr(IV)-MOFs through Local Functionalization of Metal-Clusters Yong-Zheng Zhang, Tao He, Xiang-Jing Kong, Xiu-Liang Lv, Xue-Qian Wu, and Jian-Rong Li* Beijing Key Laboratory for Green Catalysis and Separation, Department of Chemistry and Chemical Engineering, College of Environmental and Energy Engineering, Beijing University of Technology, Beijing 100124, P. R. China.

KEYWORDS: Zr(IV)-MOF, (6,9)-connected network, post-modification, stability, water sorption

ABSTRACT: Water adsorption of MOFs is attracting intense interest due to their potential applications in atmospheric water harvesting, dehumidification, and adsorption-based heating and cooling. In this work, through using a hexacarboxylate ligand, four new isostructural Zr(IV)MOFs (BUT-46F, -46A, -46W, and -46B) with rare low-symmetric 9-connected Zr6 clusters were synthesized and structurally characterized. These MOFs are highly stable in water, HCl aqueous solution (pH = 1), and NaOH aqueous solution (pH = 10) at room temperature, as well as in boiling water. Interestingly, the rational modification of the metal clusters in these MOFs with different functional groups (HCOO–, CH3COO–, H2O/OH, and PhCOO–) enables the precise tuning of their water adsorption properties, which is quite important for given application. Furthermore, all four MOFs show excellent regenerability under mild conditions and good cyclic performance in water adsorption.

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Introduction The adsorption of water by porous solids has been applied in a lot of crucial processes that require efficient and “smart” capture and release of water, such as in dehumidification, atmospheric water harvesting, as well as adsorption heating and cooling pumps.1-3 As the wellknown inorganic porous materials silica gels and zeolites have been widely used in these aspects on a large scale. However, silica gels are not very energy-efficient since a large part of the water sorption occurs outside their operating pressure windows,4,5 and zeolites always require high temperature for regeneration.6,7 Extensive research on the development of new porous materials with excellent water adsorption properties that can be rationally designed and expediently regulated, are still high necessary. As a class of newly emerged porous materials, metal-organic frameworks (MOFs) are offering great potentials in addressing many challenges, including the water adsorption related ones.8-17 Extraordinary porosity and high degree of structural tunability are always regarded as the most prominent features of MOFs, and now the advance in MOF chemistry has allowed the rational construction and precise tuning of target functionalized MOFs for specific applications to some extent.18-30 Zr(IV)-MOFs with excellent water stability and rich structural diversity are among representatives.31 However, their application in water adsorption was scarcely explored,32-35 notwithstanding some other MOFs15-17 have shown great potentials and even extraordinary superiority, such as ISE-1,36 MIL-101,37 Y-shp-MOF-5,38 Cr-soc-MOF-1,39 and M2Cl2(BTDD) (M = Mn, Co, Ni).40 With regard to a desired MOF for water adsorption application, a steep adsorption isotherm at a specific relative pressure (relative humidity, RH), a high water uptake capacity, an energy-


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efficient desorption, an excellent water stability, and a good reproducible cycling performance of the materials are all expected.32,39 Accordingly, to rationally tune the water adsorption properties of MOFs, two approaches can usually be considered: (1) designing or decorating organic linkers with suitable sized/shaped and specific hydrophilic or hydrophobic groups and (2) modifying the hydrophilicity of pre-reserved metal-containing cluster nodes with different functional groups. A synergistic effect of functionalizing organic linkers and metal clusters is usually responsible to the optimized water adsorption. The former is comparatively common and easy, and has been adopted in several pioneering works.15,33 Whereas the latter seems more difficult to access and has been rarely explored,41,42 since modifying metal clusters requires the coordination of coming entities, which can damage the structure integrity of MOFs. Herein, we report the first example of water adsorption tuning in a stable Zr(IV)-MOF via rational modification of the Zr6 cluster with different functional groups. Owing to the presence of coordinately unsaturated Zr6 cluster (9 vs. full 12-connection) in BUT-46F (BUT = Beijing University of Technology), decorating such cluster with other terminal functional groups of different sizes and hydrophilicities (CH3COO–, H2O/OH, and PhCOO–) resulted in three isostructural MOFs (BUT-46A, -46W and -46B), and achieved the precise control of the water uptake step over a range of 24% RH.

Results and Discussion Synthesis and general characterizations Initially, BUT-46F (Zr6O8(TPHB)1.5(HCOO)3(H2O)3) was synthesized as single crystals (suitable for single-crystal X-ray diffraction (SXRD) structure determination) through the reaction of H6TPHB (4,4',4'',4''',4'''',4'''''-(triphenylene-2,3,6,7,10,11-hexayl)hexabenzoic acid) and


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ZrOCl2·8H2O in N,N-dimethylformamide (DMF) at 120 oC in presence of formic acid (F). Given the unsaturated connectivity of the Zr6 cluster (9 vs. full 12-connection) in this MOF, several functional groups (CH3COO–, H2O/OH, and PhCOO–) with different sizes and hydrophilicities were expected to be attached on the cluster by substituting the terminal HCOO– or H2O in BUT46F. The direct syntheses of MOFs with CH3COOH, HCl, and PhCOOH instead of HCOOH as competing reagents through solvo-thermal methods were conducted, respectively. Only the trial with CH3COOH as modulator has successfully afforded a MOF (BUT-46A) with CH3COO– replacing the coordinated HCOO– on the Zr6 cluster in BUT-46F, however, all attempts using HCl aqueous solution and PhCOOH as modulating reagents under various conditions have failed to give MOFs. Then, the post-modification functionalization protocol was adopted to locally modify the Zr6 cluster in BUT-46F.30,43-46 When the BUT-46F samples were separately immersed into 1 M HCl aqueous solution and 0.08 M benzoic acid solution in DMF under appropriate temperatures, good crystals of other two target MOFs were finally obtained. SXRD structure analyses revealed that these three MOFs, Zr6O8(TPHB)1.5(CH3COO)3(H2O)3 (BUT46A), Zr6O8(TPHB)1.5(OH)3(H2O)6 (BUT-46W) and Zr6O8(TPHB)1.5(PhCOO)3(HCOO)3 (BUT46B), were isostructural with BUT-46F. All MOFsʹ structures were further characterized by powder X-ray diffraction (PXRD), and the degrees of functionalization in BUT-46W and 46B were quantified by 1H NMR after decomposing the samples in a D2SO4/DMSO-d6 mixture. Structural description Taking BUT-46F as the example for detailed structure description, SXRD analysis revealed that it crystallizes in the cubic P4332 space group (Table S1) and has a novel three-dimensional (3D) porous framework structure. In the structure, there exist two crystallographically independent Zr atoms (Zr1 and Zr2). Zr1 is coordinated by three O atoms from carboxylates of three different


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TPHB6– ligands, four µ3-O/OH entities, and one O from a terminal H2O, while Zr2 is coordinated by two O atoms from carboxylates of two different TPHB6–, two O atoms from carboxylates of two different HCOO–, and four µ3-O/OH entities. The Zr6O8(HCOO)3(H2O)3 building unit is formed by eight µ3-O/OH groups connecting three Zr1 and three Zr2 atoms, in which three Zr1 and three Zr2 atoms respectively form a triangle and occupy a plane (Figure 1a). This Zr6 cluster possesses a lower symmetry (C3) compared with those observed in commonly reported Zr6-based MOFs (Oh and D4h).31 Each Zr(IV)-based cluster links to nine ligand linkers with three carboxylate groups being of monodentate coordination, and each ligand contacts to six Zr6 clusters. Three H2O and three HCOO– groups terminate the remaining coordination sites of the 9-connected node and account for the charge balance.

Figure 1. Combination of the Zr6 cluster (a) with the TPHB6– ligand (b) leads to the spindle cage in BUT-46F (c). Four kinds of windows on a spindle cage (d).


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Interestingly, in the structure of BUT-46F, unique spindle-shaped supramolecular cage unit was formed, with six TPHB6– ligands covering the faces and sixteen Zr6 clusters occupying the vertices (Figure 1c). Its internal pore size is 1.6 × 3.4 nm. Due to a bulky triphenylene ring linking six benzoates in TPHB6– ligand (Figure 1b), the length of the peripheral benzoate arms is relatively short and the corresponding windows on the cage is accordingly narrow with the distance between neighboring Zr6 clusters less than 4.8 Å (Figure 1d). All terminal HCOO− locate in window 1 (W1), and terminal H2O decorate windows 2, 3, and 4 (W2, W3, and W4). Such cages are connected with each other through sharing the faces and vertices of the cage to form a 3D framework with small open channels (Figure S1 in SI). The total solvent-accessible volume in BUT-46F was estimated to be 62.5% by using PLATON.47 Pore volume calculated based on PLATON is about 0.70 cm3 g−1, suggesting BUT-46F may have a high water uptake capacity. Topologically, the TPHB6– ligand and the Zr6 cluster in BUT-46F can be regarded as a 6-connected linker and a 9-connected node, respectively. Its overall framework can thus be simplified as a novel (6,9)-connected network with the point symbol of (410.65)3(430.66)2 (Figure S2 in SI), being the first example in MOFs to the best of our knowledge. In the structure of BUT-46A, just three CH3COO– ligands replace three HCOO– initially coordinated to the Zr6 cluster of BUT-46F (Figure 2), leading to W1 much smaller and more hydrophobic. While in BUT-46W three terminal HCOO– are replaced by six H2O/OH entities (1H NMR data of the decomposed sample indicated that there is almost no residual HCOO– in BUT-46W (Figure S5a and 5b in SI), allowing the widows more hydrophilic. For BUT-46B, the three HCOO– are still attached on the cluster, but three terminal H2O molecules are exchanged by three PhCOO–, possibly owning to the weaker acidity of PhCOOH compared with HCOOH, as well as the spatial effect. 1H NMR spectra of the decomposed BUT-46B sample revealed that


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besides the H6THPB ligand, both PhCOOH and HCOOH are also integrated into this framework, showing that ∼1.9 PhCOO– are incorporated onto each Zr6 node within BUT-46B, with 3 terminal HCOO– on each node remained (Figure S5a and 5c in SI). Introducing so many PhCOO– definitely makes BUT-46B have narrower and more hydrophobic pores. Clearly, the change of functional groups would affect the pore surface property of the resulting MOFs, thereby their adsorption property. The total solvent-accessible volumes in these frameworks are 61.4, 62.2, and 53.5% for BUT-46A, -46W, and -46B, respectively.

Figure 2. The Zr6 clusters in four BUT-46 MOFs with different terminal functional groups.


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Porosity and stability The porosities of four new Zr(IV)-MOFs were then examined by N2 adsorption at 77 K (Figure 3). Saturated uptakes of 460, 458, 445, and 420 cm3 g−1 (STP) are achieved, and evaluated BET surface areas are 1565, 1563, 1550, and 1403 m2 g−1 for BUT-46W, -46F, -46A, and -46B, respectively. The experimental total pore volumes are in the range from 0.71 to 0.65 cm3 g–1, close to the calculated values by PLATON. Based on the N2 adsorption data, the pore size distributions of four MOFs are in the range of 1.6−3.5 nm (Figure S7 in SI), being consistent with the results from crystal structural analysis.

Figure 3. N2 adsorption/desorption isotherms at 77 K of the pristine MOF and samples treated under different conditions for (a) BUT-46W, (b) BUT-46F, (c) BUT-46A and (d) BUT-46B.


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The hydrothermal stability of MOFs is the primary property to be must considered for their application in most cases. In order to examine the chemical stability of BUT-46W, -46F, -46A, and -46B, their samples were treated in HCl aqueous solution (pH = 1), NaOH aqueous solution (pH = 10) at room temperature, as well as in boiling water. After treatments for 24 h, checked PXRD patterns show good crystallinity and unchanged diffraction peaks, demonstrating their excellent water/acid/base stability (Figure 4). Besides, the N2 adsorption isotherms at 77 K of the treated samples were found to be almost the same as those of the respective pristine samples as well, which further confirms the robustness of these MOFs (Figure 3). Experimentally, we also carefully checked whether there is pendant ligand and/or framework ligand leaching after four

Figure. 4 PXRD patterns of the pristine MOF and samples treated under different conditions for (a) BUT-46W, (b) BUT-46F, (c) BUT-46A and (d) BUT-46B.


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MOFs were treated by pH 1 HCl and pH 10 NaOH aqueous solution at room temperature by UV-vis spectrum measurements. As shown in Figure S12 and S13, no corresponding peaks of these ligands were observed in UV-vis adsorption spectra, suggesting there is no ligands leaching during the treatment of samples. These results, as well as the almost the same mass of MOF samples before and after treatments (Table S3) further attest the chemical stability of BUT-46. The thermal stability of the four MOFs was also checked. Thermogravimetric analysis (TGA) curves show that they can be stable up to ca. 430 °C (Figure S4 in SI), being comparable to most of Zr(IV)-MOFs.28,31 Water vapor adsorption In terms of their high porosity and excellent stability, water adsorptions were subsequently explored for four BUT-46 MOFs. All the adsorption/desorption isotherms measured at 298 K (equilibration time of 10 s) show S-shaped (sigmoidal) curves without an obvious hysteresis loop (Figure 5a). To check whether the equilibration time affects the hysteresis in these measurements, water sorption with different equilibration time was performed. The isotherms measured with equilibration time of 30 s also show no hysteresis (Figure S8 in SI), suggesting almost no influence of equilibration time on the hysteresis in water sorption isotherms of these MOFs. Very limited water uptakes at lower pressure before the inflection point indicate that the affinity of water molecules with the surfaces of the MOFs is weak.32 This could be attributed to the high hydrophobicity of their framework surfaces derived from the large aromatic ligands and hydrophobic functional groups on Zr6 clusters. Therefore, higher water vapor pressure is required to induce the pore filling. For BUT-46A, in which CH3COO− and H2O act as the terminal entries of the clusters, the condensation of water into the pores started at P/P0 = 0.44, followed by an abrupt uptake before the relative pressure reaching to P/P0 = 0.49 (575 cm3 g−1). Then, water in


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pores underwent capillary condensation and the maximum uptake was up to 645 cm3 g−1 at P/P0 = 0.87 (corresponding to a water accessible pore volume (PVW) of 0.52 cm3 g−1, with the N2 accessible pore volume (PVN) of 0.69 cm3 g−1). With terminal HCOO− and H2O on the clusters, BUT-46F showed a water isotherm with the inflection point shifted to a lower pressure compared

Figure 5. (a) Water vapor adsorption/desorption isotherms of four BUT-46 MOFs at 298 K. (b) The comparison of water uptakes of four BUT-46 MOFs in the first and fifth runs. In the histograms, green, blue, and yellow bar respectively represent the uptakes of three steps in their S-shaped adsorption curves.


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to that of BUT-46A. The steep adsorption commenced at P/P0 = 0.39 and rapidly reached to 605 cm3 g−1 at P/P0 = 0.43, then the maximum uptake of 735 cm3 g−1 (PVW = 0.59 cm3 g−1, PVN = 0.70 cm3 g−1) at P/P0 = 0.87. Furthermore, when HCOO− was replaced by more hydrophilic H2O/OH to afford BUT-46W, it showed further enhanced hydrophilicity and water adsorption capacity. The relative pressure of water condensation into the pores of BUT-46W decreased to P/P0 = 0.27, and the maximum uptake increased to 785 cm3 g−1 (PVW = 0.63 cm3 g−1, PVN = 0.71 cm3 g−1) at P/P0 = 0.87 (630 cm3 g−1, at P/P0 = 0.37). The uptake of water before P/P0 = 0.27 in BUT-46W was up to 150 cm3 g−1, almost twice higher than that in BUT-46A and -46F, both of which can only capture less than 80 cm3 g−1 of water at their first inflection of adsorption branches. However, when the terminal H2O on Zr6 clusters in BUT-46F was replaced by more hydrophobic PhCOO−, the resulting BUT-46B showed the strongest hydrophobicity among four MOFs. For it, the steep adsorption just started at P/P0 = 0.51 and reached to 560 cm3 g−1 at P/P0 = 0.55, and then the maximum of 614 cm3 g−1 (PVW = 0.49 cm3 g−1, PVN = 0.65 cm3 g−1) at P/P0 = 0.87. Clearly, compared with BUT-46F, BUT-46B exhibits a lower maximum uptake and higher step pressure, due to the larger size and stronger hydrophobicity of PhCOO− relative to H2O, which lead to a decrease in the pore volume and an increase of the open pressure. These results show that the slight modification of the Zr6 clusters can lead to distinct changes of water adsorption property in these Zr(IV)-MOFs. In addition, to evaluate the regeneration and cycle performance of the four MOFs in the water adsorption, three continuous adsorption/desorption cycles were first performed. As shown in Figure S9, the maximum uptakes of water vapor for BUT-46W and 46F have a visible decrease and uptakes in the first step of S-shaped isotherm have a minor increase. By contrast, only slight changes were observed in BUT-46A and 46B due to their weaker hydrophilicity


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compared with BUT-46W and 46F. These results suggest that the activation of MOFs samples between water sorption cycles is essential for good recycling performance. Then, we investigated the optimal activation conditions of BUT-46 samples between cycles by degassing under high vacuum at 298 K for 2 h and by exchanging with acetone, respectively. N2 adsorptions at 77 K were measured with samples after different treatments. Two kinds of samples exhibited almost the same N2 adsorption isotherms (Figure S10 in SI). Therefore, to evaluate the regeneration and cycle performance of the four MOFs in the water adsorption, all of the samples were reevacuated under vacuum at 298 K for 2 h by degassing after initial measurements. Water adsorption isotherms of five cycles were successively recorded (Figure S11 in SI). The results demonstrated that all four MOFs show easy regeneration by simple degassing, and good cyclic performance as indicated by the high similarity of their water adsorption isotherms in all five cycles (Figure 5b). In order to explore the process of the water adsorption and identify preferential adsorption sites in these MOFs, as the example, diffraction data of BUT-46F single crystals saturated under different RH were collected. For the crystals treated under 15% RH at 298 K, the structural refinement showed that the residual electron densities were just located near the W2, W3 and W4 (Figure S6a in SI) while none near W1 and inside the cage, indicating the absence of guest molecules in the pore. Subsequently, the crystals were exposed in 40% RH, and then a new data set was collected. High residual electron densities were found in all windows and cavities of the cage (Figure S6b in SI). These results suggest that water molecules prefer to firstly occupy the adsorption sites in larger windows first and then, with the pressure increasing, largely enter into cages to give an abrupt uptake.


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As discussed above, the water uptake capacities and the PVW / PVN of four MOFs are in the order of BUT-46W > BUT-46F > BUT-46A > BUT-46B, and the condensation pressures of water into their pores vary from P/P0 = 2.7 to 5.1 (Table 1). It is clearly that the simple modifications on the Zr6 clusters are quite effective to obviously tune the water adsorption properties of their frameworks. With different functional groups attached on the Zr6 clusters, a synergistic effect of the change in both the hydrophobicity and pore size of MOFs might be responsible for their varied water adsorption performances. Compared with other reported MOFs, the four Zr(IV)-MOFs show excellent performances in both the water adsorption and the material regeneration (Table S4 in SI), making them promising candidates for various wateradsorption related applications such as water harvesting and dehumidification.

Table 1. BET surface areas, pore volumes, and relative pressure of the steep adsorption for BUT-46 samples MOF

BET

PVN

PVW

PVW / PVN

surface area

(cm3 g–1)

(cm3 g–1)

(%)

(m2 g–1)

(P/P0 = 0.995)

(P/P0 = 0.87)

Relative pressure of the steep adsorption (P/P0)

BUT-46W

1565

0.71

0.63

88.7

0.27-0.37

BUT-46F

1563

0.71

0.59

83.1

0.39-0.43

BUT-46A

1550

0.69

0.52

75.4

0.44-0.49

BUT-46B

1403

0.65

0.49

75.4

0.51-0.55

Conclusions


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In summary, four new highly stable Zr(IV)-MOFs containing rare 9-connected Zr6 clusters have been designed and synthesized, and their water adsorption performances were explored. These MOFs showed steep adsorption isotherms at a specific pressure, high water uptakes at ambient conditions, and good cyclic reproducibility, being promising for the water adsorption application. Particularly, through decorating the Zr(IV)-based clusters with different functional groups, the water adsorption properties of them were precisely tuned. This work demonstrates that modifying the metal-containing clusters of MOFs could be a valid and feasible approach to rationally adjust their water adsorption performances, as well as of course other adsorption related properties for given applications.

Experimental procedures Materials and Instruments: The ligand acid 4,4',4'',4''',4'''',4'''''-(triphenylene-2,3,6,7,10,11hexayl) hexabenzoate acid (H6TPHB) was synthesized according to the literature method.48 All reagents (AR grade) were commercially purchased. 1H NMR data were collected on a BRUKER AVANCE III HD 400M NMR spectrometer. FT-IR spectra were recorded on an IRAffinity-1 instrument. TGA data were obtained on a TGA-50 (SHIMADZU) thermogravimetric analyzer with a heating rate of 10 °C min–1 under air atmosphere. The powder X-ray diffraction (PXRD) patterns were recorded on a BRUKER D8-Focus Bragg-Brentano X-ray Powder Diffractometer at room temperature. Simulation of the PXRD patterns was carried out by the single-crystal data and diffraction-crystal module of the Mercury available free of charge via internet at https://www.ccdc.cam.ac.uk/. The UV-vis absorption spectra were collected on a Shimadzu UV2600 spectrophotometer. A Micrometrics ASAP 2020 Surface Characterization Analyzer was


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used to measure N2 adsorption/desorption isotherms. Water vapor adsorption isotherms were measured by a volumetric method using a Micromeritics ASAP 2020 HD88 analyzer. Single-crystal X-ray diffraction: The diffraction data for BUT-46F, BUT-46F-15%RH, BUT46F-40%RH,-46A, -46W, and -46B were collected in a Rigaku Supernova CCD (charge-coupled device) diffractometer equipped with mirror-monochromatic-enhanced Cu-Kα radiation (λ = 1.54184 Å). The data set were corrected by empirical absorption correction using spherical harmonics. The structure were solved by direct methods and refined by full-matrix least squares on F2 with anisotropic displacement by using the SHELXTL software package.49 Hydrogen atoms of ligands (except those in the coordination OH and H2O) were calculated in ideal positions with isotropic displacement parameters. Those in the coordinated OH and H2O groups were not added but were taken account into molecular formula of their crystal data. Some O and C atoms of ligand in BUT-46B were disordered and treated by split or occupancies refinement. For all these MOFs, there exist large solvent accessible pore volumes in their structure, which are occupied by disordered solvent molecules. No satisfactory models for these entities could be achieved due to their severe crystallographic disorder, and therefore the electron densities of these disordered species were removed by using the MASK routine in the Olex2 software package.50 Crystal parameters and structure refinement are summarized in Table S1 and S2 (for details, see CCDC: BUT-46A, 1821894; BUT-46F, 1821896; BUT-46W, 1821895; BUT-46B, 1821990; BUT-46F-15%RH, 1822653; and BUT-46F-40%RH, 1822652.

Synthesis of BUT-46F: H6TPHB (0.03 mmol, 24.4 mg) and ZrOCl2·8H2O (0.12 mmol, 39.0 mg) were ultrasonically dissolved in 8 mL of DMF in a 20 mL pyrex vial, then 3.2 mL formic


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acid was added and sealed. The reaction system was heated at 120 oC for 48 h in an oven. After cooling to RT, the resulting colorless block polyhedral crystals were harvested by filtration and washed with fresh DMF and ethanol, and then dried under vacuum at RT (yield 30 mg). Synthesis of BUT-46A: H6TPHB (0.03 mmol, 24.4 mg) and ZrOCl2·8H2O (0.12 mmol, 39.0 mg) were ultrasonically dissolved in 8 mL of DMF in a 20 mL pyrex vial, then 5.6 mL acetic acid was added and sealed. The reaction system was heated at 120 oC for 96 h in an oven. After cooling to RT, the resulting colorless block polyhedral crystals were harvested by filtration and washed with fresh DMF and ethanol, and then dried under vacuum at RT (yield 32 mg). Synthesis of BUT-46W: BUT-46W was obtained by immersing the as-synthesized BUT-46F (100 mg) in 15 mL of 1 M HCl solution at 60 oC for 12 h (exchanging the supernatant with fresh 1 M HCl solution every 4 h). After cooling to RT, the colorless block polyhedral crystals were collected by filtration and washed with fresh water, DMF, and ethanol, and then dried under vacuum at RT (yield 90 mg). Synthesis of BUT-46B: Crystals of BUT-46B were incubated by soaking BUT-46F (100 mg) in the solution of benzoic acid (200 mg) in DMF (20 ml) at 75 oC for 15 h (exchanging the supernatant with fresh benzoic acid solution every 5 h). After cooling to RT, the colorless block polyhedral crystals were collected by filtration and washed with fresh DMF and ethanol, and then dried under vacuum at RT (yield 93 mg). Sample Activation: The as-synthesized samples were soaked in 10 mL of acetone for 3 days to exchange the involved guest molecules, during which the solvent was removed and freshly replenished three times. The resulting samples were collected by decanting and dried under vacuum at RT. Before the gas adsorption tests, the dry samples were loaded in a sample tube and


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further activated under high vacuum at an optimized temperature of 60 °C for 4 h. Finally, about 80 mg of degassed sample was used for the gas sorption measurement in each case. The N2 adsorption measurements were carried out at 77 K in a liquid nitrogen bath, and water vapor adsorption experiments were carried out at 298 K in a water bath. Sample for 1H NMR Test: Before 1H NMR test, the activated samples of the four MOFs (about 20 mg for each) were immersed into a mixture of 0.5 mL DMSO-d6 and ten drops of D2SO4-d6 (98%) and ultrasonically dissolved, respectively. Then the uniform samples were used for 1H NMR test. Stability Test: The activated samples of the four MOFs (about 100 mg for each) were immersed in 20 mL pH 1 HCl aqueous solution, pH 10 NaOH aqueous solution at RT, and in boiling water for 24 h, respectively. Then, they were collected and washed with fresh water (20 mL × 3) and ethanol (20 mL × 3) subsequently, and dried in air for PXRD and N2 adsorption characterizations. Before N2 adsorption tests, the samples were further soaked in 20 mL of acetone for 24 h and then degassed on an ASAP 2020 adsorption system at 60 °C for 4 h.

ASSOCIATED CONTENT Supporting Information. The Supporting Information (SI) is available free of charge on the ACS Publications website at DOI: Additional figures of crystal structure and adsorption/desorption isotherms, FT-IR, TGA, 1

HNMR and tables of crystal data and structure refinements (PDF).


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Crystallographic data (CIF) AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]. Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation (No. 51621003, 21576006, 21771012).

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Tuning Water Sorption in Highly Stable Zr(IV)-MOFs through Local

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