Y. Wang, L. Feng, K. Zhang, K.‐Y. Wang, W. Fan, X. Wang, B. Guo, F. Dai, L. Zhang, D. Sun, H.‐C. Zhou, Uncovering Structural Opportunities for Zirconium Metal--Organic Frameworks via Linker Desymmetrization. Adv. Sci. 2019, 6, 1901855 10.1002/advs.201901855

Metal−organic frameworks (MOFs), or porous coordination polymers, are a well‐developed class of porous crystalline materials constructed from inorganic metal clusters and organic linkers.[1](#advs1384-bib-0001){ref-type="ref"}, [2](#advs1384-bib-0002){ref-type="ref"}, [3](#advs1384-bib-0003){ref-type="ref"}, [4](#advs1384-bib-0004){ref-type="ref"}, [5](#advs1384-bib-0005){ref-type="ref"}, [6](#advs1384-bib-0006){ref-type="ref"}, [7](#advs1384-bib-0007){ref-type="ref"}, [8](#advs1384-bib-0008){ref-type="ref"}, [9](#advs1384-bib-0009){ref-type="ref"} As highly tunable structures through judicious linker design, MOFs attracted considerable interests in fields, such as gas storage, separation, heterogeneous catalysis, sensing, light harvesting, and drug delivery.[4](#advs1384-bib-0004){ref-type="ref"}, [10](#advs1384-bib-0010){ref-type="ref"}, [11](#advs1384-bib-0011){ref-type="ref"} Among the numerous MOFs, zirconium MOFs have received increasing attention in recent years due to their highly stable feature originated from the robust Zr---O cooridnation bonds.[1](#advs1384-bib-0001){ref-type="ref"}, [12](#advs1384-bib-0012){ref-type="ref"} The high chemical stability of Zr‐MOF ensures its economical large‐scale production in water solution and also permits its structural intactness when exposed to harsh conditions.

The combination of Zr clusters and different organic linkers has contributed to the structural diversity and functional complexity of the MOF materials. Various synthetic approaches have been developed to synthesize Zr‐MOFs with structural complexicity, including linker design strategies, pillar strategies, postsynthetic methods, and preformed clusters.[1](#advs1384-bib-0001){ref-type="ref"} For example, Zhou group reported the steric control over ditopic linker based Zr‐PCN‐700, where bulky substituents on the 2‐ and 2′‐positions of BPDC (biphenyl‐4,4′‐dicarboxylate) were introduced to constrain the two carboxylates and phenyl rings into a perpendicular conformation.[13](#advs1384-bib-0013){ref-type="ref"} Later Guillerm and co‐workers descibed the topoligical influence of zigzag ligands during the assembly of **bcu** net.[14](#advs1384-bib-0014){ref-type="ref"} Speaking of 4‐connected linkers, the structural diversity based on Zr~6~ clusters can also be expanded by tuning linker conformation. For example, various topologies including **ftw**, **csq**, **shp**, **scu**, **she**, and **sqc** can be accessed when square or rectangle tetratopic linkers are chosen.[15](#advs1384-bib-0015){ref-type="ref"}, [16](#advs1384-bib-0016){ref-type="ref"}, [17](#advs1384-bib-0017){ref-type="ref"}, [18](#advs1384-bib-0018){ref-type="ref"}, [19](#advs1384-bib-0019){ref-type="ref"}, [20](#advs1384-bib-0020){ref-type="ref"} The effects of linker geometry and flexibility influenced by the bulkiness of substituents can also be utilized to enhance the diversity of Zr‐tetratopic carboxylate MOFs.[21](#advs1384-bib-0021){ref-type="ref"} However, how to continue enhancing the structural and compositional compilation of Zr‐tetratopic carboxylate MOFs poses a synthetic challenge.

Herein, we initiate a systematic study on Zr‐tetracarboxylate frameworks constructed from a series of bent tetratopic linkers with various substituents. The utilization of a bent ligand with lower symmetry overcomes the traditional topology problems limited by the rigid ligand backbones. The tunable linker geometries and conformations here by altering the composition of substituents generate a series of Zr‐MOFs with varying topologies including **scu**, **flu,** and **cor**. This work provides fresh insights into the discovery of Zr‐tetracarboxylate frameworks with unprecedented topologies and conformations of building blocks, and highlights the importance of linker desymmetrization for dictating MOF architectures.

As shown in **Figure** [**1**](#advs1384-fig-0001){ref-type="fig"}a, four bent tetratopic ligands with various substituents (R~1~ = ---H, ---CH~3~; R~2~ = ---NH~2~, ---CH~3~; R~3~ = ---SO~2~, ---CH~2~, ---O) were selected to construct Zr‐based MOFs. Due to the bulkiness differences of R~1~ substituents, the distances and angles between two central rings can be tuned. The presence of R~2~ substituents can effectively influence the rotation angles between two peripheral phenyl rings near the central ring, while R~3~ substituents are utilized to tune rotation degrees around the linker center.

![Illustration of various topologies in Zr‐tetracarboxylate frameworks based on bent linkers. a) The combination of bent tetratopic linkers and Zr~6~ clusters with varying connectivities (from 4‐c to 12‐c) leads to various topologies. b) The linking of 8‐connected Zr~6~ clusters with *C* ~2v~ linkers (L‐SO~2~) leads to the formation of a **scu** net. c) Employment of a *C* ~1~ 4‐c ligand (L‐O) prompted the formation of a novel 8‐c Zr~6~ cluster and its reticulation into a (4, 8)‐c **flu** net. d) Use of a *C* ~1~ 4‐c ligand L‐CH~2~ resulted in the discovery of the same (4, 8)‐c **flu** net. e) The combination of 6‐c Zr~6~ clusters and 4‐c ligands with multiple bulky methyl groups (*C* ~1~) generates a hierarchically assembled (4, 6)‐c **cor** net. Optical images of these Zr‐MOF single crystals were presented, showing varying morphologies of the corresponding structures.](ADVS-6-1901855-g001){#advs1384-fig-0001}

Large colorless crystals, PCN‐901‐SO~2~ (also named UPC‐901‐SO~2~), were obtained with cuboid morphology after the solvothermal reactions between L‐SO~2~ and ZrCl~4~ in the presence of trifluoroacetic acid as a modulator for 24 h (Figure [1](#advs1384-fig-0001){ref-type="fig"}b). The structure of PCN‐901‐SO~2~ was determined by single‐crystal X‐ray diffraction. Powder X‐ray diffraction (PXRD) patterns indicate the phase purity of the obtained product (**Figure** [**2**](#advs1384-fig-0002){ref-type="fig"}d). PCN‐901‐SO~2~ crystallized in the tetragonal space group P4/mmm (Table S1, Supporting Information). Crystallographically, it contains an 8‐connected Zr~6~ cluster \[Zr~6~(µ~3~‐O)~4~(µ~3~‐OH)~4~(OH)~4~(H~2~O)~4~(COO)~8~\] and a bent tetratopic linker with *C* ~2v~ symmetry. The 8‐connected Zr~6~ clusters can be simplified as cuboid nodes, while the bent tetratopic linker can be viewed as 4‐connected joint triangular nodes (Figure [2](#advs1384-fig-0002){ref-type="fig"}a). The overall structure was analyzed to be a 4,8‐connected **scu** net with a point symbol of {4^16^.6^12^}{4^4^.6^2^}~2~ as determined by TOPOS 4.0 (Figure [2](#advs1384-fig-0002){ref-type="fig"}a).[22](#advs1384-bib-0022){ref-type="ref"} Note that this topology has been reported previously in NU‐901 and PCN‐606, which are constructed from rectangular planar nodes and cuboid nodes.[21](#advs1384-bib-0021){ref-type="ref"}, [23](#advs1384-bib-0023){ref-type="ref"} In the structure of PCN‐901‐SO~2~, the arrangement of Zr~6~ clusters leads to two types of pores (Figure [2](#advs1384-fig-0002){ref-type="fig"}a). Remarkably, the linkers are restricted into a conformation with 113.6° dihedral angle between the two central phenyl rings, and 82.9° dihedral angle between the two peripheral phenyl rings and the central ones. The chemical stability of PCN‐901‐SO~2~ was further examined by immersing MOFs in various aquesous solutions for 24 h. PXRD patterns indicated that the PCN‐901‐SO~2~ has excellent chemical stability in solution with pH ranging from 0 to 12 as evidenced by the well‐maintained crystallinity (Figure S14, Supporting Information).

![Structural illustration of PCN‐901‐SO~2~ with (4, 8)‐c scu topology and PCN‐902‐O with (4, 8)‐c flu topology. a) The assembly of 8‐c Zr~6~ clusters and 4‐c ligands with a SO~2~ substituent (*C* ~2v~) into PCN‐901‐SO~2~ with a (4, 8)‐c **scu** net. b) The assembly of 8‐c Zr~6~ clusters and 4‐c ligands with an O substituent (*C* ~1~) into PCN‐902‐O with a (4, 8)‐c **flu** net. c) N~2~ isotherms of PCN‐901(Zr)‐SO~2~, PCN‐902(Zr)‐O, PCN‐902(Zr)‐CH~2~, PCN‐903(Zr)‐(CH~3~)~6~, and PCN‐903(Zr)‐(CH~3~)~6~ after Se adsorption. d) Simulated and experimental Powder X‐ray diffraction (PXRD) patterns of PCN‐901(Zr)‐SO~2~, PCN‐902(Zr)‐O, PCN‐902(Zr)‐CH~2~, and PCN‐903(Zr)‐(CH~3~)~6~.](ADVS-6-1901855-g002){#advs1384-fig-0002}

Interestingly, we observed large crystals of PCN‐902‐O with a different morphology formed after the reaction between ZrCl~4~ and L‐O under the same condition (Figure [1](#advs1384-fig-0001){ref-type="fig"}c). As indicated by single‐crystal X‐ray diffraction, L‐O possessed a *C* ~1~ symmetry due to the bulkiness influence of the substituents (Figure [2](#advs1384-fig-0002){ref-type="fig"}b). Notably, the dihedral angle between the two central phenyl rings in L‐O is 113.9° and the dihedral angles between the central phenyl ring and the two peripheral ones are around 60°. The corresponding phase purity of the products was supported by PXRD analysis (Figure [2](#advs1384-fig-0002){ref-type="fig"}d). PCN‐902‐O crystallized in the triclinic space group *P*‐1 (Table S1, Supporting Information). Crystallographically, it contains an 8‐connected Zr~6~ cluster \[Zr~6~(µ~3~‐O)~4~(µ~3~‐OH)~4~(OH)~4~(H~2~O)~4~(COO)~8~\] and a 4‐connected bent tetratopic linker with *C* ~1~ symmetry. The overall structure was determined to be a 4, 8‐connected **flu** net with a point symbol of {4^12^.6^12^.8^4^}{4^6^}~2~ by TOPOS 4.0 (Figure [2](#advs1384-fig-0002){ref-type="fig"}b). Replacing L‐O with a similar bent linker L‐CH~2~ generated the isostrucural PCN‐902‐CH~2~, as indicated by the PXRD pattern. The **flu** (fluorite) topology can be viewed as a cubic close packing (**ccp**) of the Ca^2+^ cations where the F^−^ anions occupy all tetrahedral interstitial cavities (Figure [2](#advs1384-fig-0002){ref-type="fig"}a), leaving all the octahedral interstitial cavities vacant. MOFs with **flu** topology can be assembled through 4‐connected linkers and 8‐connected metal clusters.

Additionally, introducing bulky methyl groups onto the phenyl rings of bent L‐CH~2~ can necessitate the two peripheral phenyl rings to exhibit a larger dihedral angle, leading to a different conformation for MOF construction. In order to obtain large single crystals, benzoic acid was used as the modulator to control the growth kinetics of PCN‐903‐(CH~3~)~6~, in which a truncated octahedron crystal with **cor** topology was built based upon an unprecedent 6‐c Zr~6~ cluster. Single‐crystal X‐ray analysis revealed that PCN‐903‐(CH~3~)~6~ crystallized in the trigonal space group *R‐3c* (**Figure** [**3**](#advs1384-fig-0003){ref-type="fig"}). It contains a novel 6‐connected Zr~6~ cluster \[Zr~6~(µ~3~‐O)~4~(µ~3~‐OH)~4~(OH)~6~(H~2~O)~6~(COO)~6~\] and a tetratopic linker with *C* ~1~ symmetry. Crystallographically, six bent tetratopic linkers bridged four neighboring Zr~6~ clusters, which can be simplified into a fascinating (4, 6)‐connected net with **cor** topology (Figure [3](#advs1384-fig-0003){ref-type="fig"}b).

![Structural illustration of PCN‐903‐(CH~3~)~6~ with (4, 6)‐c cor topology. a) Structural illustration of corundum (Al~2~O~3~) constructed from four‐connected O atoms and six‐connected Al atoms. b) The assembly of 6‐c Zr~6~ clusters and 4‐c ligands with bulky methyl substituents (*C* ~1~) into a (4, 6)‐c **cor** net. c) The top and side views of PCN‐903‐(CH~3~)~6~, showing the connectivity modes of the building units and pore arrangement. d) PCN‐903‐(CH~3~)~6~ contains three types of pores with 6.4, 10.1, and 17.2 Å size. e) Illustration of the cluster and linker conformations in PCN‐903‐(CH~3~)~6~.](ADVS-6-1901855-g003){#advs1384-fig-0003}

Different from the traditional 6‐connected Zr~6~ cluster observed in MOF‐808 and other 6‐c Zr‐MOFs, the Zr~6~ cluster in PCN‐903‐(CH~3~)~6~ displays two types of dihedral angles, 64.7° and 22.1°, between the O--Zr--Zr--O plane and the equatorial plane (Figure [3](#advs1384-fig-0003){ref-type="fig"}e). This unusual asymmetric feature of Zr~6~ clusters brings new opportuities to explore topology diversity within highly connected MOFs. The overall structure was analyzed to be a (4, 6)‐connected net with a point symbol of {4^3^.6^3^}~3~{4^6^.6^9^}~2~ as determined by TOPOS 4.0 (Figure [3](#advs1384-fig-0003){ref-type="fig"}b).

The intriguing **cor** topology originates from the lattice of corundum, a crystalline phase of aluminium oxide (Al~2~O~3~), where each Al atom is surrounded by six O atoms.[24](#advs1384-bib-0024){ref-type="ref"} In the corundum lattice, the O atoms never locate at the corners of a regular octahedron, instead, they form a slightly distorted hexagonal close packing, where two‐thirds of octahedral interstitial cavities are occupied by Al atoms. By replacing Al atoms with distorted 6‐connected Zr clusters and O atoms with bent tetratopic ligands, the extension from an inorganic material to a porous inorganic--organic hybrid compound is achieved (Figure [3](#advs1384-fig-0003){ref-type="fig"}a). The assembly of 6‐c Zr~6~ clusters and *C* ~1~ ligands initially generates a supramolecular triangular bipyramid building unit, where all equatorial vertices are occupied by the ligand building units while both polar vertices are placed by the inorganic clusters (Figure [3](#advs1384-fig-0003){ref-type="fig"}d). As a result, a microporous cage with 6.4 Å size is formed. Further hierarchical assembly of these triangular bipyramid building units into 3D network can be visualized in Figure [3](#advs1384-fig-0003){ref-type="fig"}. Each triangular bipyramid unit is connected to neighboring six units, resulting in a second type of pore with 10.1 Å size between each two triangular bipyramid units. Further assembly of these units also generates a larger cage with 17.2 Å size (Figure [3](#advs1384-fig-0003){ref-type="fig"}c). The discovery of PCN‐903‐(CH~3~)~6~ presents a very rare case, and a new level of sophisticated assembly of Zr‐cluster based MOFs involving multiple levels of structural hierarchy. It should be noted that there is a β‐UH~3~‐like topology based Zr‐MOF constructed from 4‐connected elongated linkers reported by Zhang and co‐workers.[25](#advs1384-bib-0025){ref-type="ref"} Our work here presents a powerful strategy to ascertain new structural mysteries of MOFs which mimic complicated inorganic structures. In addition, there is also a Zn‐MOF, Zn~4~O(BenzTB)~3/2~ (DUT‐13) with very high pore volume, exhibiting **cor** topology.[26](#advs1384-bib-0026){ref-type="ref"}

The permanent porosity of the PCN‐90X(Zr) series was confirmed by N~2~ sorption isotherms measured at 77 K (Figure [2](#advs1384-fig-0002){ref-type="fig"}c). PCN‐90X samples were washed thoroughly using *N*,*N*‐dimethylformamide (DMF), CH~2~Cl~2~ and hexane for several times before gas sorption measurements. PCN‐90X(Zr) series exhibit a typical type I isotherm, suggesting microporosity. Due to the densely packed building blocks, PCN‐902 and PCN‐903 showed relatively low N~2~ uptake and surface areas.

The effects of center functional groups on linker conformation have been explored through density functional theory calculations. The relative energies of selected linkers in PCN‐901, PCN‐902, and PCN‐903 were calculated and listed in **Figure** [**4**](#advs1384-fig-0004){ref-type="fig"} and Table S2 (Supporting Information). For clarify, the energies of a given linker fragment in different conformations were normalized by subtracting the energy of its unconstrained structure. Due to the constraints from Zr~6~ clusters in the frameworks, two lateral phenyl rings in the individual ligand will exhibit distinct torsion angles in the corresponding structures with different topologies. For linker L‐SO~2~, the linker is too rigid to distort, making the formation of conformations observed in PCN‐902 and PCN‐903 unfavorable. The energy difference of L‐O in PCN‐901 and PCN‐902 is ≈20.6 kJ mol^−1^, while the difference is ≈14.4 kJ mol^−1^ for L‐O in PCN‐902 and PCN‐903. This result indicates that the bent conformation of L‐O in PCN‐902 allows for the gyration of two lateral phenyl rings, which is beneficial for the formation of PCN‐902 with **flu** topology. For L‐CH~2~ with a similar conformation, the formation of **flu** topology is also favorable as indicated by the relative energies in PCN‐90X with varying topologies. Considering the linker L‐(CH~3~)~6~, its conformation is latched by bulky methyl groups. By comparing the relative energies of linkers in PCN‐90X, we observed that ligands with bulky groups such as ---CH~3~ tend to be obtained with a larger torsion angle, so only PCN‐903 with **cor** topology will be adapted in this case.

![Relative energies of ligands with various conformations in PCN‐90X series possessing different topologies. The relative energy for a given ligand is normalized through subtracting the energy of its unconstrained structure.](ADVS-6-1901855-g004){#advs1384-fig-0004}

Due to the existing large amount of coordinately unsaturated sites on Zr~6~ clusters, the highly defective PCN‐903‐(CH~3~)~6~ was tested for its ability to adsorb and remove selenite anions from aqueous solutions. Although trace amounts of selenium are vital for nutritional needs of animals, it becomes extremely toxic at high concentrations (\>400 µg d^−1^).[27](#advs1384-bib-0027){ref-type="ref"}, [28](#advs1384-bib-0028){ref-type="ref"}, [29](#advs1384-bib-0029){ref-type="ref"} The maximum acceptable concentrations were set as 40 and 50 ppb, respectively, by the World Health Organization (WHO) and the United States Environmental Protection Agency (USEPA).[30](#advs1384-bib-0030){ref-type="ref"} The uptake ability of PCN‐903‐(CH~3~)~6~ toward toxic SeO~3~ ^2−^ was first tested via a series of SeO~3~ ^2−^ aqueous solution from 10 to 500 ppm. To reach adsorption equilibrium, 10 mg PCN‐903‐(CH~3~)~6~ was immersed in the aqueous solutions for 24 h, which was followed by inductively coupled plasma mass spectrometry (ICP‐MS) analysis of supernatant fraction to determine the remaining SeO~3~ ^2−^ concentration. As indicated by **Figure** [**5**](#advs1384-fig-0005){ref-type="fig"}a, the adsorb amounts of SeO~3~ ^2−^ in the MOF absorbent increase as the initial concentrations of SeO~3~ ^2−^ increase. The maximum Se capacity of PCN‐903‐(CH~3~)~6~ was calculated as 75.5 mg g^−1^, which exhibits one of the highest adsorption capacities among MOF absorbents (Figure [5](#advs1384-fig-0005){ref-type="fig"}a and Table S4, Supporting Information).[30](#advs1384-bib-0030){ref-type="ref"}, [31](#advs1384-bib-0031){ref-type="ref"} The kinetic behavior for SeO~3~ ^2−^ was subsequently investigated (Figure [5](#advs1384-fig-0005){ref-type="fig"}b and Table S5, Supporting Information). Remarkably, PCN‐903‐(CH~3~)~6~ exhibits rapid removal, \>90% of SeO~3~ ^2−^ within 7 min, \>99% removal within 1 h and complete removal, \>99.9%, of SeO~3~ ^2−^ within 3 h. The excellent selenite removal efficiency places PCN‐903‐(CH~3~)~6~ as a promising porous absorbent for detoxification.

![Efficient removal of toxic selenite ions by PCN‐903‐(CH~3~)~6~. a) Sorption isotherms for selenite (SeO~3~ ^2−^) by PCN‐903‐(CH~3~)~6~. b) Sorption kinetics curves for selenite (SeO~3~ ^2−^) by PCN‐903‐(CH~3~)~6~.](ADVS-6-1901855-g005){#advs1384-fig-0005}

In conclusion, we have synthesized four new Zr‐MOFs based on desymmetrized tetratopic linkers with various substituents. For example, PCN‐901‐SO~2~ is constructed from the assembly between a bent linker L‐SO~2~ with *C* ~2v~ symmetry and an 8‐connected Zr~6~ cluster; PCN‐902‐O/CH~2~ contains a novel 8‐connected Zr~6~ cluster and a bent linker L‐O/‐CH~2~ with *C* ~1~ symmetry, exhibiting a CaF~2~‐like **flu** topology; further utilization of restricted bent linker \[(L‐(CH~3~)~6~)\] gives rise to PCN‐903‐(CH~3~)~6~ with a fascinating Al~2~O~3~‐like (4, 6)‐c **cor** net. Additionally, the highly defective PCN‐903‐(CH~3~)~6~ showed efficient removal of toxic selenite ions in aqueous solutions, achieving \>90% of SeO~3~ ^2−^ within 7 min, and complete removal, \>99.9%, of SeO~3~ ^2−^ within 3 h. This work points out a fresh direction for developing functional and stable Zr‐MOFs with unprecedented topologies by linker design.

Experimental Section {#advs1384-sec-0020}
====================

*Linker Synthesis*: The detailed synthetic approaches of organic linkers including L‐SO~2~, L‐CH~2~, L‐SO~2~, and L‐(CH~3~)~6~, are provided in the Supporting Information.

*Synthesis of PCN‐901(Zr)‐SO~2~*: ZrCl~4~ (20 mg), L‐SO~2~ (10 mg), and DMF (3 mL) were charged into a 10 mL vial, followed by the addition of 0.15 mL trifluoroacetic acid. The mixture was heated in 115 °C oven for 2 d. After cooling down to room temperature, the colorless crystals of PCN‐901(Zr)‐SO~2~ were harvested (yield: 75%).

*Synthesis of PCN‐902(Zr)‐O*: ZrCl~4~ (20 mg), L‐O (10 mg), and DMF (3 mL) were charged into a 10 mL vial, followed by the addition of 0.10 mL trifluoroacetic acid. The mixture was heated in 120 °C oven for 2 d. After cooling down to room temperature, the colorless crystals of PCN‐902(Zr)‐O were harvested (yield: 70%).

*Synthesis of PCN‐902(Zr)‐CH~2~*: ZrCl~4~ (20 mg), L‐CH~2~ (10 mg), and DMF (3 mL) were charged into a 10 mL vial, followed by the addition of 0.10 mL trifluoroacetic acid. The mixture was heated in 120 °C oven for 2 d. After cooling down to room temperature, the colorless crystals of PCN‐902(Zr)‐CH~2~ were harvested (yield: 71%).

*Synthesis of PCN‐903(Zr‐CH~3~)~6~*: ZrCl~4~ (20 mg), L‐(CH~3~)~6~ (10 mg), benzoic acid (500 mg), and DMF (3 mL) were charged into a 10 mL vial. The mixture was heated in 120 °C oven for 2 d. After cooling down to room temperature, the colorless crystals of PCN‐903(Zr‐CH~3~)~6~ were harvested (yield: 62%).

*Adsorption Isotherm Measurement*: PCN‐903‐(CH~3~)~6~ (10 mg) was mixed with a 10 mL stock solution of selenite (SeO~3~ ^2−^) with various concentrations. The mixture was kept at room temperature for 24 h to ensure complete adsorption. The ion concentration in the supernatant solutions was determined by ICP‐MS.

*Adsorption Kinetics Measurement*: PCN‐903‐(CH~3~)~6~ (10 mg) was mixed with a 10 mL stock solution of selenite (SeO~3~ ^2−^) at a concentration of 10 ppm. The mixture was kept at room temperature for various periods. During the adsorption process, the ion concentration in the supernatant solutions was analyzed by ICP‐MS.

Conflict of Interest {#advs1384-sec-0040}
====================

The authors declare no conflict of interest.

Supporting information
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Supplementary

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Click here for additional data file.

Y.W. and L.F. contributed equally to this work. This work was financially supported by the National Natural Science Foundation of China (NSFC Grant Nos. 21875285 and 21571187), Taishan Scholar Foundation (No. ts201511019). The gas adsorption--desorption studies of this research were supported as part of the Center for Gas Separations, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award No. DE‐SC0001015. The PXRD characterization and analysis were funded by the Robert A. Welch Foundation through a Welch Endowed Chair to H.‐C.Z. (A‐0030).
