Flexible metal-organic framework materials, methods of making the same, and applications in methane storage

Abstract

The application belongs to the technical field of gas storage, and particularly relates to a kind of flexible metal organic framework material and a preparation method and application in methane storage thereof. The metal organic framework material is formed by coordination of divalent metal ions and pyrazole ligands, wherein the divalent metal ions are Zn 2+ or Co 2+ In the metal organic framework material, the divalent metal cations are coordinated with pyrazole groups of the ligands in a tetrahedral manner to form rod-like secondary building units M(pz)2, and the rod-like secondary building units are connected by the ligands to form a three-dimensional network structure with one-dimensional channels. The M(dpt) in the flexible metal organic framework material can be applied in the field of methane storage.

Description

Technical Field

[0001] This invention belongs to the field of gas storage technology, and specifically relates to a class of flexible metal-organic framework materials, their preparation methods, and their applications in methane storage. Background Technology

[0002] As a relatively clean fossil fuel, the efficient and safe storage technology of natural gas has become a research hotspot. Ambient temperature adsorption (ANG) natural gas storage technology utilizes porous adsorbents to store gas at ambient temperature and low to medium pressure, offering advantages in safety and energy consumption compared to high-pressure compression and cryogenic liquefaction technologies. However, the practical application of this technology has long been limited by the overall performance of the adsorbents.

[0003] Currently, methane adsorbents mainly include activated carbon, zeolite, metal-organic frameworks (MOFs), and covalent organic frameworks (COFs). Among them, rigid porous materials, while exhibiting high adsorption capacity under high pressure, have limited working capacity within the operating pressure range (e.g., 5-65 bar). In recent years, flexible MOFs with a breathing effect have attracted attention due to their unique S-shaped adsorption isotherm. These materials can undergo a reversible transition from a narrow-pore phase to a macroporous phase under specific pressures, theoretically achieving higher working capacity. However, these representative materials still have significant drawbacks: First, they are extremely sensitive to water vapor and have poor water stability, while water vapor is an unavoidable impurity in natural gas, severely affecting the material's service life and cycle performance; second, these flexible crystalline materials often have poor mechanical strength, making them difficult to form using conventional tableting processes, hindering their filling and engineering applications in actual storage tanks.

[0004] Therefore, there is an urgent need to develop a new type of adsorbent material that simultaneously meets the following requirements: (1) excellent methane storage capacity within a range of ambient temperature and low to medium pressure; (2) good chemical stability, especially hydrophobicity and water stability; and (3) adaptability to industrial molding and processing (such as tableting) while maintaining structural integrity and high cycling performance. Currently, there is a lack of adsorbent materials that can comprehensively meet the above performance indicators, which has become a key bottleneck restricting the large-scale application of ANG technology. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a class of flexible metal-organic framework materials, their preparation methods, and their applications in methane storage.

[0006] The technical solution of this invention is as follows: A class of flexible metal-organic framework materials, wherein the metal-organic framework material is formed by coordination of a divalent metal ion with a pyrazole ligand, and the divalent metal ion is Zn. 2+ or Co 2+In the metal-organic framework material, divalent metal cations coordinate with the pyrazole groups of the ligands in a tetrahedral manner to form rod-shaped secondary building units M(pz)2. The rod-shaped secondary building units are connected by ligands to form a three-dimensional network structure with one-dimensional channels.

[0007] Furthermore, the pyrazole ligand is one of the following compounds: , , , .

[0008] Furthermore, when the ligand is H2dpt, the molecular formula of the metal-organic framework material is C 10 H6N4SM, space group is I 41 md Named M(dpt), the metal-organic framework material has a flexible single-walled structure, and during the adsorption of methane, the metal-organic framework material can undergo a reversible structural transformation between a narrow-pore phase and a macroporous phase.

[0009] Furthermore, when the ligand is H2dpi, the molecular formula of the metal-organic framework material is C 10 H5N4SM, space group is I4 1 / amd The ligand is named M(dpi); when the ligand is H2dpf, the molecular formula of the metal-organic framework material is C 10 H6N4OM, space group is I4 1 / amd The ligand is named M(dpf); when the ligand is H2dpn, the molecular formula of the metal-organic framework material is C 16 H 10 N4M, space group is P 43, named M(dpn); When the ligands are H2dpi and H2dpf, the metal-organic framework material has a double-walled network supported by π…π stacking, and when the ligand is H2dpn, the metal-organic framework material has a flexible single-walled structure.

[0010] The present invention also provides a method for preparing the metal-organic framework material, comprising the following steps: S1. Dissolve the pyrazole ligand and the divalent metal salt in a mixed solvent containing N,N-dimethylformamide and water, and add acetic acid; the mass ratio of metal salt to ligand is 1:2. S2. A solvothermal reaction is carried out at a temperature of 80-150℃ to generate the initial product of metal-organic framework material. S3. The initial product is washed and subjected to solvent exchange treatment; the product after solvent exchange treatment is activated by vacuum heating to obtain activated metal-organic framework material.

[0011] Furthermore, when the metal-organic framework material is Zn(dpt), the volume ratio of N,N-dimethylformamide, water, and acetic acid is 10:3:0.01, and the reaction conditions are 80 °C for 24 hours. When the metal-organic framework material is Co(dpt), the volume ratio of N,N-dimethylformamide, water and acetic acid is 5:0.8:0, and the reaction conditions are 150 °C for 24 hours.

[0012] Furthermore, when the metal-organic framework material is Co(dpn), the volume ratio of N,N-dimethylformamide, water, and acetic acid is 5:0.5:0.01, and the reaction conditions are 135 °C for 24 hours. When the metal-organic framework material is Zn(dpn), the volume ratio of N,N-dimethylformamide, water and acetic acid is 5:1:0.01, and the reaction conditions are 80 °C for 24 hours.

[0013] Furthermore, when the metal-organic framework material is M(dpf), the volume ratio of N,N-dimethylformamide, water and acetic acid is 5:1.5:0.01, and the reaction conditions are 80 °C for 24 hours.

[0014] Furthermore, when the metal-organic framework material is Zn(dpi), the volume ratio of N,N-dimethylformamide, water, and acetic acid is 5:1.5:0.01, and the reaction conditions are 80 °C for 24 hours; when the metal-organic framework material is Co(dpi), the volume ratio of N,N-dimethylformamide, water, and acetic acid is 5:0.5:0.01, and the reaction conditions are 135 °C for 24 hours.

[0015] The present invention also provides a method for large-scale synthesis of Zn(dpt), comprising the following steps: ultrasonically dissolving H2dpt ligand and Zn(NO3)2·6H2O in a mass ratio of 1:2 in a mixed solvent of DMF:H2O:acetic acid in a volume ratio of 5:1:0.04, sealing, ultrasonic treatment, and heating the resulting solution in an oven at 80 °C for 24 hours; after cooling to room temperature, washing and solvent exchange treatment of the initial product; and activating the product after solvent exchange treatment by vacuum heating to obtain activated Co(dpt).

[0016] The present invention also provides a method for large-scale synthesis of Co(dpt), comprising the following steps: dissolving H2dpt ligand and Co(OTf)2 in a mass ratio of 1:2.48 by ultrasonication in a mixed solvent of DEF:acetic acid in a volume ratio of 100:1, sealing, ultrasonic treatment, and heating the resulting solution in an oven at 150 °C for 24 hours; after cooling to room temperature, washing and solvent exchange treatment of the initial product; and activating the product after solvent exchange treatment by vacuum heating to obtain activated Co(dpt).

[0017] The present invention also provides the application of the M(dpt) in methane storage.

[0018] Beneficial technical effects of the present invention: (1) The present invention reports a new type of flexible metal-dipyrazole framework material, particularly Zn(dpt) and Co(dpt), which outperforms existing materials in the field of adsorbed natural gas (ANG) storage and achieves the highest known volumetric methane storage capacity.

[0019] Among them, Zn(dpt) achieved a working capacity of 173 cm⁻¹ under conditions of 298 K, 5-35 bar, and 5-65 bar. 3 (STP) cm -3 and 225 cm 3 (STP) cm -3 Co(dpt) also reached 227 cm at 5-65 bar. 3 (STP) cm -3 High capacity.

[0020] (2) This invention utilizes ligand engineering and a slightly angled dpt 2- Ligand substitution linear BDP 2- The ligands effectively weaken the π-π stacking effect in the narrow-pore (np) phase, resulting in a significant reduction in the opening pressure (transition from the np phase to the lp phase) of the material (e.g., Zn(dpt) at approximately 17.5 bar), making it more suitable for practical operating pressure ranges. This controllable, methane-induced reversible phase transition is key to achieving its high operating capacity.

[0021] (3) Zn(dpt) and Co(dpt) exhibit significant hydrophobicity and water stability. The water adsorption capacity is extremely low (<1 wt%) at room temperature and 95% relative humidity (RH), and they can still maintain the crystalline structure after one month at 40 °C and 75% RH or six months of exposure to air. This solves the long-standing problem of humidity stability faced by ANG adsorbents.

[0022] The materials exhibited stable performance during multiple pressure cycles. After 100 methane storage-desorption cycles at 5–65 bar, Zn(dpt) and Co(dpt) retained 95% and 96% of their working capacity, respectively. In 250 mL tank tests, Zn(dpt) loaded with the novel formulation (combination of adsorbent and elastic packing) demonstrated stable and high performance, validating its potential for practical applications.

[0023] To address the challenge of compressing flexible materials into tablets due to large volume changes during phase transitions, this invention proposes an alternative formulation using an elastic filler to support the flexible adsorbent. This formulation provides space for the material's phase transition, allowing it to be filled into a storage tank while maintaining structural properties, without significantly increasing system volume or cost. Furthermore, the synthesis of Zn(dpt) has been successfully scaled up to 5 grams per batch, maintaining the same crystallinity and adsorption performance as the laboratory samples. Attached Figure Description

[0024] Figure 1 Crystal photographs of (a) Co(dpn), (b) Zn(dpf), (c) Zn(dpi) and (d) Co(dpi).

[0025] Figure 2 Crystallographic images of synthesized Zn(dpt) at (a) 20 mg scale and (b) 5 g scale, and crystallographic images of Co(dpt) at (c) 20 mg scale and (d) 5 g scale.

[0026] Figure 3 (a,b) Crystal structure and (c,d) Channel structure of Zn(dpn) / Co(dpn) as observed along the (a,b)c-axis and (c,d)b-axis directions, respectively. (e) Arrangement of adjacent ligands in Zn(dpn) / Co(dpn) and (f) Internal channel structure shown on the blue Connolly surface.

[0027] Figure 4 Zn(dpf) crystal structure (a,b) and pore structure (c,d) as observed along the crystallographic (a,b) c-axis and (c,d) b-axis, respectively. (e) Intermolecular interactions (red: π-π interaction, pink: CH…π interaction, green: CH…N interaction) and (f) Internal pore structure of Zn(dpf) as shown on the blue Connolly surface.

[0028] Figure 5(a,b) crystal structure and (c,d) pore structure of Zn(dpi) / Co(dpi) as observed along the crystallographic (a,b) c-axis and (c,d) b-axis, respectively. (e) Intermolecular interactions (red: π-π interaction, pink: CH…π interaction, green: CH…N interaction) and (f) Internal pore structure of Zn(dpi) / Co(dpi) as shown on the blue Connolly surface.

[0029] Figure 6 Crystal structure of Zn(dpt) / Co(dpt) as observed along the crystallographic (a,b)c-axis and (c)b-axis. (d) Channels and open windows, (e) Ligand interactions (pink: CH…π interaction, green: CH…N interaction), and (f) Internal structure of Zn(dpt) / Co(dpt) channels as shown on the blue Connolly surface.

[0030] Figure 7 A novel family of metal-dipyrazole frameworks was constructed using crystal engineering methods. Structural diversification of the metal-dipyrazole frameworks (red box) was achieved based on the precursor materials BUT-53 and Co(bdp) (green box) through a ligand substitution strategy.

[0031] Figure 8 Experimental and calculated PXRD spectra of synthesized and activated (a)Zn(dpt) and (b)Co(dpt), as well as PXRD spectra recorded after gas adsorption tests.

[0032] Figure 9 Experimental and calculated PXRD spectra of synthesized and activated Zn(dpf), as well as PXRD spectra recorded after gas adsorption tests.

[0033] Figure 10 Experimental and calculated PXRD spectra of synthesized and activated (a) Zn (dpi) and (b) Co (dpi), as well as PXRD spectra recorded after gas adsorption tests.

[0034] Figure 11 Experimental and calculated PXRD spectra of synthesized and activated (a)Zn(dpt) and (b)Co(dpt), as well as PXRD spectra recorded after high-pressure CH4 cycling test.

[0035] Figure 12 Thermogravimetric analysis curves of activated Zn / Co(dpn), Zn(dpf), and Zn / Co(dpi).

[0036] Figure 13 Thermogravimetric analysis curves of (a) Zn(dpt) and (b) Co(dpt).

[0037] Figure 14 (a) CO2 adsorption isotherms of Zn / Co(dpn) and (b) Zn(dpf) and Zn / Co(dpi) at 195 K.

[0038] Figure 15 The N2 adsorption isotherms of Co(bdp) and Zn(dpt) at 77 K and the CO2 adsorption isotherms at 195 K are plotted on (a,c) linear pressure and (b,d) logarithmic pressure coordinates, respectively.

[0039] Figure 16 The N2 adsorption isotherm of Co(dpt) at 77 K and the CO2 adsorption isotherm at 195 K are plotted on (a) linear pressure and (b) logarithmic pressure coordinates, respectively.

[0040] Figure 17 High-pressure CH4 excess adsorption isotherms (molar units) of (a) Zn (dpt) and (b) Co (dpt) measured at 273 K and 298 K.

[0041] Figure 18 High-pressure CO2 excess adsorption isotherms of Zn(dpt) and Co(dpt) measured at (a) 273 K and (b) 298 K (molar units).

[0042] Figure 19 High-pressure adsorption isotherms (a) for CO2 and (b) for CH4 in Zn / Co(dpn) and Zn / Co(dpi) at 298 K. Since the low CO2 adsorption capacity of Zn(dpf) at 195 K indicates its low porosity, high-pressure experiments were not performed.

[0043] Figure 20 In-situ pressure swing PXRD pattern of Zn(dpt) adsorption / desorption process.

[0044] Figure 21High-pressure CH4 adsorption performance of Zn / Co(dpt) at 298 K. (a) High-pressure CH4 adsorption isotherm of Zn / Co(dpt), providing the release capacity of CH4 between 5-35 bar and 5-65 bar. (b) Comparison of release capacity of high-performance MOFs and COFs at 298 K, calculated from the adsorption isotherm, between 5-35 bar (x-axis) and 5-65 bar (y-axis) (the release capacity of CH4 for MFU-4l-Li and NU-1500-Al is calculated from the adsorption isotherm recorded at 296 K, while the data for UTSA-110, Co(bdp), and Fe(bdp) correspond to a pressure range of 5.8-35 / 65 bar). (c) Results of cyclic testing of Zn(dpt) and (d) Co(dpt) under 100 CH4 pressure swings between 5-65 bar.

[0045] Figure 22 Dynamic water vapor adsorption isotherms of Zn(dpt) and Co(dpt) at 298 K: (a) full-range isotherm; (b) magnified view highlighting adsorption capacity.

[0046] Figure 23 (a) PXRD patterns and (b) CO2 adsorption isotherms at 195 K for Zn(dpt) samples synthesized in different solvents.

[0047] Figure 24 PXRD patterns of Zn(dpt) samples synthesized under different conditions.

[0048] Figure 25 (a) CO2 adsorption isotherm at 195 K and (b) CH4 adsorption isotherm at 298 K for Zn(dpt) samples synthesized under different conditions.

[0049] Figure 26 Scale-up synthesis and methane storage performance of Zn(dpt). (a) Scale-up photographs of Zn(dpt) and HKUST-1 samples. (b) Tanks loaded with Zn(dpt) adsorbent and elastic packing in two ways (Zn(dpt)-1, Zn(dpt) in the middle, covered with elastic packing at both ends; Zn(dpt)-2, Zn(dpt) layer and thin elastic packing layer uniformly spaced; yellow: Zn(dpt), green: elastic packing); control tank loaded with HKUST-1. (c) Comparison of average volumetric release capacity of the three tanks after five cycles based on (top) crystal density and (bottom) actual packing density. Detailed Implementation

[0050] Example 1: Single Crystal Synthesis of Zn(dpt) H₂dpt ligand (20.0 mg, 0.0920 mmol) and Zn(NO₃)₂·6H₂O (40.0 mg, 0.135 mmol) were dissolved in a DMF:H₂O:AcOH mixture (10 mL:3 mL:0.01 mL) and placed in a 20 mL reactor. The mixture was then solvothermically reacted at 80 °C for 24 hours to obtain light yellow rod-shaped Zn(dpt) single crystals. The synthesized sample was washed three times with fresh DMF (10 mL each time) until the supernatant was colorless, and then exchanged six times with fresh acetone (10 mL each time) over two days. After the exchange was completed, the sample was loaded into an adsorption tube and activated at 60 °C under vacuum for 6 hours (22.7 mg of product was obtained, with a yield of 87.8% based on the H₂dpt ligand).

[0051] Example 2: Single-crystal synthesis of Co(dpt) H₂dpt ligand (20.0 mg, 0.0920 mmol) and Co(NO₃)₂·6H₂O (40.0 mg, 0.138 mmol) were dissolved in a DMF:H₂O (5 mL:0.8 mL) mixture and placed in a 20 mL reactor. The mixture was then solvothermically reacted at 150 °C for 24 hours to obtain purple rod-shaped Co(dpt) single crystals. The synthesized sample was washed three times with fresh DMF (10 mL each time) until the supernatant was colorless, and then exchanged six times with fresh acetone (10 mL each time) over two days. After the exchange was completed, the sample was loaded into an adsorption tube and activated at 60 °C under vacuum for 6 hours (yielding 21.6 mg of product, with a yield of 85.5% based on the H₂dpt ligand).

[0052] Example 3 Single crystal synthesis of Co(dpn) H₂dpn ligand (20.0 mg, 0.0770 mmol) and Co(NO₃)₂·6H₂O (40.0 mg, 0.138 mmol) were dissolved in a mixed solvent of DMF:H₂O:AcOH (5 mL: 0.5 mL: 0.01 mL) in a 20 mL reactor and reacted solvothermally at 135°C for 12 hours to obtain purple rod-shaped Co(dpn) crystals. The synthesized sample was washed three times with fresh DMF (10 mL each time) until the supernatant was colorless, and then exchanged six times with fresh acetone (10 mL each time) over two days. After the exchange was completed, the sample was loaded into an adsorption tube and activated at 60°C under vacuum for 6 hours (yielding 17.6 mg of product, with a yield of 72.2% based on H₂dpn ligand).

[0053] Example 4: Single-crystal synthesis of Zn(dpn) H₂dpn ligand (20.0 mg, 0.0770 mmol) and Zn(NO₃)₂·6H₂O (40.0 mg, 0.135 mmol) were dissolved in a DMF:H₂O:AcOH mixture (5 mL:1 mL:0.01 mL) and placed in a 20 mL reactor. The mixture was then solvothermically reacted at 80 °C for 24 hours to obtain colorless microcrystalline Zn(dpn) powder. The synthesized sample was washed three times with fresh DMF (10 mL each time) until the supernatant was colorless, and then exchanged six times with fresh acetone (10 mL each time) over two days. After the exchange was completed, the sample was loaded into an adsorption tube and activated at 60 °C under vacuum for 6 hours (20.4 mg of product was obtained, with a yield of 82.0% based on the H₂dpn ligand).

[0054] Example 5 Single-crystal synthesis of Zn(dpf) H₂dpf ligand (20.0 mg, 0.100 mmol) and Zn(NO₃)₂·6H₂O (40.0 mg, 0.135 mmol) were dissolved in a DMF:H₂O:AcOH mixture (5 mL:1.5 mL:0.01 mL) and placed in a 20 mL reactor. The mixture was then solvothermically reacted at 80 °C for 24 hours to obtain colorless rod-shaped Zn(dpf) single crystals. The synthesized sample was washed three times with fresh DMF (10 mL each time) until the supernatant was colorless, and then exchanged six times with fresh acetone (10 mL each time) over two days. After the exchange was completed, the sample was loaded into an adsorption tube and activated at 60 °C under vacuum for 6 hours (yielding 12.3 mg of product, with a yield of 46.7% based on the H₂dpf ligand).

[0055] Example 6: Single-crystal synthesis of Zn(dpi): H2dpi ligand (20.0 mg, 0.0920 mmol) and Zn(NO3)2·6H2O (40.0 mg, 0.135 mmol) were dissolved in a DMF:H2O:AcOH mixture (5 mL:1.5 mL:0.01 mL) and placed in a 20 mL reactor. The mixture was then solvothermically reacted at 80 °C for 24 hours to obtain light yellow rod-shaped Zn(dpi) single crystals. The synthesized sample was washed three times with fresh DMF (10 mL each time) until the supernatant was colorless, and then exchanged six times with fresh acetone (10 mL each time) over two days. After the exchange was completed, the sample was loaded into an adsorption tube and activated at 60 °C under vacuum for 6 hours (yielding 16.9 mg of product, with a yield of 65.4% based on H2dpi ligand).

[0056] Example 7 Single-crystal synthesis of Co(dpi) H2dpi ligand (20.0 mg, 0.0920 mmol) and Co(NO3)2·6H2O (40.0 mg, 0.138 mmol) were dissolved in a DMF:H2O:AcOH mixture (5 mL:0.5 mL:0.01 mL) and placed in a 20 mL reactor. The mixture was then solvothermal at 135 °C for 12 hours to obtain purple rod-shaped Co(dpi) single crystals. The synthesized sample was washed three times with fresh DMF (10 mL each time) until the supernatant was colorless, and then exchanged six times with fresh acetone (10 mL each time) over two days. After the exchange was completed, the sample was loaded into an adsorption tube and activated at 60 °C under vacuum for 6 hours (yielding 18.1 mg of product, with a yield of 71.6% based on H2dpi ligand).

[0057] Example 8: Scale-up synthesis of Zn(dpt) H₂dpt ligand (1.00 g, 4.62 mmol) and Zn(NO₃)₂·6H₂O (2.00 g, 6.75 mmol) were sonicated and dissolved in a DMF:H₂O (50 mL:10 mL) mixture (in an 80 mL reaction flask). 0.4 mL of acetic acid was added as a conditioning agent. The reaction flask was sealed, and the mixture was sonicated for 15 minutes. The resulting solution was heated in an 80°C oven for 24 hours. After cooling to room temperature, the synthesized sample was washed three times with fresh DMF (40 mL each time), followed by six exchanges with fresh acetone (40 mL each time) over two days. After the exchanges, the sample was loaded into an adsorption tube and activated at 60°C under vacuum for 6 hours (yielding 1.10 g of product, with a yield of 85.7% based on the H₂dpt ligand).

[0058] The synthesis was scaled up to the five-gram level, yielding a considerable Zn(dpt) yield (5.20 g, with a yield of 82.5% based on H2dpt).

[0059] Example 9: Scale-up synthesis of Co(dpt) H₂dpt ligand (1.00 g, 4.62 mmol) and Co(OTf)₂ (2.48 g, 6.94 mmol) were sonicated and dissolved in 40 mL of DEF (in an 80 mL reaction flask). 0.4 mL of acetic acid was added to the solution as a conditioning agent. The reaction flask was sealed, and the mixture was sonicated for 15 minutes. The resulting solution was heated in a 150 °C oven for 24 hours. After cooling to room temperature, the synthesized sample was washed three times with fresh DMF (40 mL each time), followed by six exchanges with fresh acetone (40 mL each time) over two days. After the exchanges, the sample was loaded into an adsorption tube and activated at 60 °C under vacuum for 6 hours (yielding 1.04 g of product, with a yield of 82.3% based on the H₂dpt ligand).

[0060] Material characterization: Crystal diagrams of the synthesized crystals in Examples 1-9 are shown below. Figure 1-2 As shown.

[0061] The crystal structure diagrams synthesized in Examples 1-9 are shown below. Figure 3-6 As shown in Table 1, single-crystal X-ray diffraction analysis indicates that Co(dpn) belongs to space group P43 (…). Figure 3 ), while Zn(dpf) ( Figure 4 ), Zn / Co(dpi) Figure 5 ) and Zn / Co(dpt) Figure 6 Zn(dpf) belongs to the I41 / amd or I41md space group; Zn(dpf) and Zn / Co(dpi) are isomorphic; while Zn / Co(dpt) has a novel network structure. Zn(dpt) is a three-dimensional (3D) framework composed of thiophene-centered angular ligands dpt. 2- It consists of zinc-based rod-shaped secondary building blocks. (Zn) 2+ The cation coordinates the pyrazole group in a tetrahedral manner to generate RBBs with the chemical formula Zn(pz)2. Similar RBBs have been reported in Co(bdp) and BUT-53, but the orientation / arrangement of the metal ions is different, resulting in different topologies and pore shapes / sizes. Figure 7 ).

[0062] In Co(bdp), linear bdp 2- This makes Co(pz)2RBBs approximately linear ( Figure 7Co(bdp) is a flexible framework with a single-layer bridging ligand and large square or rhomboid channels. In BUT-53, Co(pz)2RBBs are helical, while the helicity of Zn(pz)2RBBs in Zn(dpt) lies between that of the linear RBBs in Co(bdp) and the helical RBBs in BUT-53. Zn(pz)2RBBs are coupled with an angular ligand dpt with a bending angle of 150°. 2- The combination of these elements allows Zn(dpt) to exhibit flexibility similar to Co(bdp). 2- The orientation of the ligands enables them to generate multiple CH…π interactions with adjacent ligands in an edge-to-face manner, as well as multiple CH…N interactions with surrounding ligands. Co(dpt) is isomorphic to Zn(dpt).

[0063] from Figure 7 It can be seen that a bending angle of 120-138° is conducive to the formation of a double-walled network supported by π…π stacking, while ligands that are closer to linear (bending angle of 150-180°) generate a flexible single-walled structure. This series of adsorbents exhibits very different pore sizes: Zn / Co(dpn) is 14.0 Å; Zn(dpf) is 7.2 Å; Zn / Co(dpi) is 7.6 Å; and Zn / Co(dpt) is 12.1 Å (pore size 7.0 Å).

[0064] Table 1. Crystallographic Data Co(dpn) Zn(dpi) Co(dpi) Zn(dpf) Zn(dpt) Co(dpt) Molecular formula <![CDATA[C 16 A 10 N4Co]]> <![CDATA[C 10 H5N4SZn]]> <![CDATA[C 10 H5N4SCo]]> <![CDATA[C 10 H6N4OZn]]> <![CDATA[C 10 H6N4SZn]]> <![CDATA[C 10 H6N4SCo]]> 317.21 278.62 272.17 263.56 279.62 273.18 Crystal system Quartet Quartet Quartet Quartet Quartet Quartet Space Group <![CDATA[ P 43]]> <![CDATA[ I4 1 / amd ]]> <![CDATA[ I4 1 / amd ]]> <![CDATA[ I4 1 / amd ]]> <![CDATA[ I 41 md ]]> <![CDATA[ I 41 md ]]> ÅÅÅ 15.4110(3)15.4110(3)14.2175(6) 23.6212(13)23.6212(13)12.8923(10) 23.748(15)23.748(15)12.720(12) 22.1604(5)22.1604(5)12.1476(3) 24.9577(5)24.9577(5)14.1668(4) 25.015(4)25.015(4)14.023(3) <![CDATA[ α / o β / o γ / o ]]> 909090 909090 909090 909090 909090 909090 <![CDATA[ V / Oh 3 ]]> 3376.66(19) 7193.4(10) 7174(11) 5965.5(3) 8824.3(4) 8775(9) The powder X-ray diffraction of the newly synthesized material (denoted as α phase) is shown in Figures 8-11, verifying the bulk purity of the newly synthesized material; the thermogravimetric analysis of the activated sample (denoted as β phase) is shown in Figures 8-11. Figure 12-13 As shown, there is no weight loss before decomposition at 400-500°C.

[0065] The adsorption isotherms of CO2 and N2 of the above materials are as follows: Figure 14-17 As shown. By fitting the N2 adsorption isotherm with Langmuir, the specific surface area of ​​the Zn(dpt) phase with the largest pore size was determined to be 1900 m². 2 g -1 For Co(dpt), the specific surface area was measured to be 2115 m² by Langmuir fitting of its N₂ adsorption isotherm. 2 g -1 The adsorption isotherms of Zn(dpt) and Co(dpt) for N2 and CO2 show different inflection points. The relative pressure (P / P0) of Zn(dpt) for N2 is 5.3 × 10⁻⁶. -5And 0.011, for CO2 pressures are 0.016 and 0.32 bar; Co(dpt): for N2 relative pressure (P / P0) is 8.5 × 10 -4 And 0.023, for CO2 pressures of 0.020 and 0.32 bar.

[0066] To investigate the potential applications of these materials in ANG storage, the high-pressure CH4 adsorption isotherm was measured at 298 K. Figure 17-18 For Zn(dpt), low CH4 adsorption was observed at lower pressures, followed by a sharp, stepwise increase at 17.5 bar and 27.5 bar. Although a hysteresis loop was observed in the desorption isotherm, it ended at 6.5 bar, and the CH4 adsorption was less than 0.2 mmol g at pressures below 5 bar. -1 Similarly, for Co(dpt), lower CH4 adsorption was also observed at lower pressures (steps appearing before 22.5 bar and 42.5 bar), with the hysteresis loop of its desorption isotherm closing at 18 bar. While Zn(dpi) showed a step at 5 bar, no steps were observed in Zn / Co(dpn) and Co(dpi). Figure 19 ).

[0067] Excess CH4 adsorption capacity of Zn(dpt) and Co(dpt) at 65 bar (10.74 and 10.95 mmol g, respectively) -1 The concentrations were higher than those of Zn / Co(dpn) and Zn / Co(dpi) (1.92-5.66 mmol g). -1 BUT-53 (4.77 mmol g) -1 BUT-55 (4.70 mmol g) -1 ) and Co(bdp) (9.77 mmol g -1 ).

[0068] Structural transformation of Zn(dpt) To elucidate the structural changes corresponding to the Zn(dpt) stepwise CH4 / CO2 adsorption isotherm, simultaneous in-situ PXRD and high-pressure adsorption measurements were performed. The activated Zn(dpt)-β phase (Fddd space group) undergoes a reversible structural phase transition during gas adsorption.

[0069] The specific process is as follows: Under 10 bar CH4, the β phase transforms into the mesophase γ1 (adsorption capacity 1.00 mmol g). -1 When the pressure was increased to 20 bar, the γ1 phase pores filled and transformed into the more open γ2 phase (adsorption capacity 4.88 mmol g).-1 When the pressure reaches 30-40 bar, the system transforms into a highly porosity α' phase (space group I41 / amd, adsorption capacity 9.47 mmol g). -1 This process corresponds perfectly to the two adsorption steps on the isotherm. After desorption and reactivation, the structure reversibly reverts to the β phase. Figure 20 ).

[0070] Structural analysis shows that the transition from the β phase to the α' phase is accompanied by a significant increase in porosity, but Zn 2+ The quasi-tetrahedral coordination geometry and the connectivity of the Zn(pz)2 structural unit are both preserved; the main difference is only in dpt. 2- The orientation and conformational changes of the ligands. This series of structural transformations also reasonably explains the multi-step steps and hysteresis observed in its adsorption of N2 at 77 K and CO2 at 195 K.

[0071] Methane storage HKUST-1 exhibited the highest volumetric CH4 adsorption capacity reported to date, reaching 267 cm⁻¹ at 65 bar and 298 K. 3 (STP) cm -3 However, its high adsorption capacity for CH4 at 5 bar also leads to a decrease in the working capacity from 5 to 65 bar to 190 cm⁻¹. 3 (STP) cm -3 The CH4 working capacity of Zn(dpt) in the pressure range of 298 K and 5-65 bar is 225 cm³. 3 (STP)cm -3 ( Figure 21 a, 21b), and because its adsorption capacity at 5 bar is almost negligible, it outperforms other porous materials in terms of CH4 working capacity ( Figure 21 b). The cobalt analogue of Zn(dpt), Co(dpt), has a similar CH4 working capacity of 227 cm⁻¹. 3 (STP) cm -3 (5-65 bar).

[0072] The 5-35 bar pressure range is also significant, as 35 bar is the typical operating pressure for a single-stage compressor. Although Zn(dpt) has a smaller specific surface area than Co(bdp) and some rigid MOFs, its CH4 operating capacity (173 cm³) within the 5-35 bar range is still considerable. 3 (STP) cm -3 This exceeds the previous benchmark material Co(bdp) (155 cm⁻¹). 3 (STP) cm -3 () Figure 21b). The CH4 working capacity of Co(dpt) at 5-35 bar is 121 cm³. 3 (STP) cm -3 The volumetric capacity of Zn(dpt) is much lower than that of Zn(dpt), which is attributed to their different phase transition threshold pressures. Zn(dpt) has a volumetric capacity of 262 cm³ at 298 K and 80 bar. 3 (STP) cm -3 The reference material for rigid COF is 3D-TFB-COF-Et (264 cm at 100 bar). 3 (STP) cm -3 )quite.

[0073] Both Zn(dpt) and Co(dpt) exhibited excellent cycling stability, maintaining capacity retention of over 95% (95% and 96%, respectively) after 100 high-pressure (65 bar) adsorption-desorption (5 bar) cycles, with the crystal structure remaining intact. This demonstrates their potential for practical applications. Figure 21 cd).

[0074] Stability, Cyclicity and Practical Applications Good water stability: Tests showed that the β phases of Zn(dpt) and Co(dpt) maintained their intact crystal structure after being exposed to 40 °C and 75% relative humidity for one month, and exhibited low water adsorption at room temperature (<0.75 wt%), indicating their hydrophobicity. Figure 22 ).

[0075] Synthesis scale-up: The synthesis of Zn(dpt) and Co(dpt) has been successfully scaled up to 5 grams per batch. The scaled-up samples maintained the same crystal structure, porosity, and methane adsorption performance as the crystalline samples. Figure 23-25 ).

[0076] To investigate the performance of flexible materials as adsorbents, two types of storage tanks filled with MOF adsorbents were designed. The filling methods were as follows: (1) Elastic filler (quartz wool) was placed at the top and bottom of the storage tank, and block MOF adsorbent (Zn(dpt)-1) was filled in the middle; (2) The MOF adsorbent layer and the elastic filler layer were evenly spaced (Zn(dpt)-2). As a control, a microcrystalline HKUST-1 storage tank without elastic filler was prepared.

[0077] Each tank was filled with approximately 250 mL of MOF material (130 g) and 100 mL of elastic packing. For the control tank, approximately 250 mL of HKUST-1 sample (78 g) was filled.

[0078] The gas storage performance of the tank was evaluated by recording the weight change of the tank before and after methane adsorption / desorption cycles (5-65 bar) using a balance with an accuracy of 1 gram. In each cycle, the tank was connected to the gas cylinder, the pressure was increased to 65 bar, and maintained at this pressure for 30 minutes to ensure adsorption equilibrium. The tank was then weighed three times and the average value was taken. During desorption, the gas cylinder valve was carefully opened to release the pressure to 5 bar (maintained at this pressure for 30 minutes to ensure desorption equilibrium), and the tank was weighed three times again and the average value was taken. In both cases, Zn(dpt) performed better than HKUST-1 (actual working capacities were 219 vs 139 cm³). 3 (STP) cm -3 133 vs 49 cm 3 (STP) cm -3 ).

[0079] In summary, this invention synthesizes a novel family of framework materials based on metal rod-shaped secondary building blocks, exhibiting diverse structures and varying degrees of flexibility. In addition to excellent hydrolytic stability, ease of scale-up synthesis, mild regeneration conditions, and good recyclability, Zn(dpt) also demonstrates a two-step CH4 adsorption isotherm, thus making it suitable for application in ANG technology.

Claims

1. A class of flexible metal-organic framework materials, characterized in that: The metal-organic framework material is formed by coordination of a divalent metal ion with a pyrazole ligand, wherein the divalent metal ion is Zn. 2+ or Co 2+ In the metal-organic framework material, divalent metal cations coordinate with the pyrazole groups of the ligands in a tetrahedral manner to form rod-shaped secondary building units M(pz)2. The rod-shaped secondary building units are connected by ligands to form a three-dimensional network structure with one-dimensional channels. The pyrazole ligand is one of the following compounds: ， ， ， 。 2. The flexible metal-organic framework material according to claim 1, characterized in that: When the ligand is H2dpt, the molecular formula of the metal-organic framework material is C 10 H6N4SM, space group is I 41 md Named M(dpt), the metal-organic framework material has a flexible single-walled structure, and during the adsorption of methane, the metal-organic framework material can undergo a reversible structural transformation between a narrow-pore phase and a macroporous phase.

3. The flexible metal-organic framework material according to claim 1, characterized in that: When the ligand is H2dpi, the molecular formula of the metal-organic framework material is C 10 H5N4SM, space group is I4 1 / amd The ligand is named M(dpi); when the ligand is H2dpf, the molecular formula of the metal-organic framework material is C 10 H6N4OM, space group is I4 1 / amd The ligand is named M(dpf); when the ligand is H2dpn, the molecular formula of the metal-organic framework material is C 16 H 10 N4M, space group is P 43, named M(dpn); When the ligands are H2dpi and H2dpf, the metal-organic framework material has a double-walled network supported by π…π stacking, and when the ligand is H2dpn, the metal-organic framework material has a flexible single-walled structure.

4. A method for preparing a flexible metal-organic framework material as described in claim 2 or 3, characterized in that: Includes the following steps: S1. Dissolve the pyrazole ligand and the divalent metal salt in a mixed solvent containing N,N-dimethylformamide and water, and add acetic acid; the mass ratio of metal salt to ligand is 1:

2. S2. A solvothermal reaction is carried out at a temperature of 80-150℃ to generate the initial product of metal-organic framework material. S3. The initial product is washed and subjected to solvent exchange treatment; the product after solvent exchange treatment is activated by vacuum heating to obtain activated metal-organic framework material.

5. The method for preparing the flexible metal-organic framework material according to claim 4, characterized in that: When the metal-organic framework material is Zn(dpt), the volume ratio of N,N-dimethylformamide, water and acetic acid is 10:3:0.01, and the reaction conditions are 80 °C for 24 hours. When the metal-organic framework material is Co(dpt), the volume ratio of N,N-dimethylformamide, water and acetic acid is 5:0.8:0, and the reaction conditions are 150 °C for 24 hours.

6. The method for preparing the flexible metal-organic framework material according to claim 4, characterized in that: When the metal-organic framework material is Co(dpn), the volume ratio of N,N-dimethylformamide, water and acetic acid is 5:0.5:0.01, and the reaction conditions are 135 °C for 24 hours. When the metal-organic framework material is Zn(dpn), the volume ratio of N,N-dimethylformamide, water and acetic acid is 5:1:0.01, and the reaction conditions are 80 °C for 24 hours.

7. The method for preparing the flexible metal-organic framework material according to claim 4, characterized in that: When the metal-organic framework material is M(dpf), the volume ratio of N,N-dimethylformamide, water and acetic acid is 5:1.5:0.01, and the reaction conditions are 80 °C for 24 hours.

8. The method for preparing the flexible metal-organic framework material according to claim 4, characterized in that: When the metal-organic framework material is Zn(dpi), the volume ratio of N,N-dimethylformamide, water, and acetic acid is 5:1.5:0.01, and the reaction conditions are 80 °C for 24 hours; when the metal-organic framework material is Co(dpi), the volume ratio of N,N-dimethylformamide, water, and acetic acid is 5:0.5:0.01, and the reaction conditions are 135 °C for 24 hours.

9. A method for large-scale synthesis of the flexible metal-organic framework material as described in claim 2, characterized in that: The process includes the following steps: H2dpt ligand and Zn(NO3)2·6H2O are ultrasonically dissolved in a mixed solvent of DMF:H2O:acetic acid with a volume ratio of 5:1:0.04, sealed, and ultrasonically treated. The resulting solution is heated in an oven at 80°C for 24 hours. After cooling to room temperature, the initial product is washed and solvent exchanged. The product after solvent exchange is activated by vacuum heating to obtain activated Zn(dpt).

10. A method for large-scale synthesis of the flexible metal-organic framework material as described in claim 2, characterized in that: The process includes the following steps: H2dpt ligand and Co(OTf)2 at a mass ratio of 1:2.48 are ultrasonically dissolved in a DEF:acetic acid mixed solvent at a volume ratio of 100:1, sealed, and ultrasonically treated. The resulting solution is heated in an oven at 150°C for 24 hours. After cooling to room temperature, the initial product is washed and solvent exchanged. The product after solvent exchange is activated by vacuum heating to obtain activated Co(dpt).

11. The application of the flexible metal-organic framework material M(dpt) as described in claim 2 in methane storage.

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