Bidirectional rod-shaped metal organic framework material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of synthesis of metal organic framework materials, and particularly discloses a bidirectional rod-like metal organic framework material and a preparation method and application thereof, and the preparation method comprises the following steps: proportionally dispersing zinc nitrate hexahydrate and 2-hydroxyterephthalic acid in N, N-dimethylformamide, sealing, and reacting at the constant temperature of 90-100 DEG C for 5-7 days to obtain the bidirectional rod-like metal organic framework material. An octahedral crystal is obtained, and the octahedral crystal is single crystal CCNUF-74; washing with N, N-dimethylformamide, exchanging with an acetonitrile solvent, carrying out step-by-step vacuumizing treatment at 20-40 DEG C, and heating for 10-15 hours at 110-130 DEG C under a vacuum condition, so as to obtain the activated CCNUF-74. By adopting the bidirectional rod-like metal organic framework material as well as the preparation method and the application thereof, directional reconstruction of rod-like SBUs from one direction to two directions is realized, and the MOF material with smaller pore openings, higher porosity and excellent low-pressure benzene adsorption performance is obtained.

Description

Technical Field

[0001] This invention relates to the field of metal-organic framework material synthesis technology, and in particular to a bidirectional rod-shaped metal-organic framework material, its preparation method, and its application. Background Technology

[0002] Metal-organic frameworks (MOFs), a class of porous crystalline materials assembled from organic ligands and metal ions or metal secondary building units (SBUs), have shown broad application prospects in gas adsorption and separation, energy conversion, and photocatalysis due to their high specific surface area, tunable pore structure, and abundant functional sites. Among them, rod-shaped MOFs constructed from infinitely extended rod-shaped SBUs have become a research hotspot in the field of gas adsorption and separation due to their unique interlocking and breathing effects.

[0003] In existing technologies, during the synthesis of most rod-shaped MOFs, the SBUs of the rod-shaped MOFs are arranged in a single parallel direction, forming unidirectional one-dimensional (1D) channels, which limits the diversity of their pore structure and the optimization of their adsorption performance. Furthermore, MOFs with multi-oriented rod-shaped SBUs lack rational design and synthesis strategies because the configuration of the rod-shaped SBUs is difficult to precisely control and predict.

[0004] Furthermore, benzene, as a highly volatile, carcinogenic, and teratogenic volatile organic compound (VOC), poses a serious threat to human health and the ecological environment, necessitating the development of porous materials with efficient trace benzene capture capabilities. Existing rod-shaped MOFs (such as MOF-74 and BUT-66) have limited benzene adsorption capacity under low-pressure conditions, making it difficult to meet practical application requirements.

[0005] Therefore, developing a method to rationally control the orientation of rod-shaped SBUs, construct MOFs materials with novel pore structures, and achieve their efficient capture of low-pressure benzene has significant academic value and practical application implications. Summary of the Invention

[0006] The purpose of this invention is to provide a bidirectional rod-shaped metal-organic framework material, its preparation method and application, to achieve the directional reconstruction of rod-shaped SBUs from unidirectional to bidirectional, and to obtain MOF materials with smaller pore openings, higher porosity and excellent low-pressure benzene adsorption performance.

[0007] To achieve the above objectives, the present invention provides a method for preparing a bidirectional rod-shaped metal-organic framework material, comprising the following steps: Zinc nitrate hexahydrate and 2-hydroxyterephthalic acid were dispersed in N,N-dimethylformamide in a certain proportion, sealed, and reacted at a constant temperature of 90-100℃ for 5-7 days to obtain octahedral crystals, namely single crystal CCNUF-74. Washed with N,N-dimethylformamide, exchanged with acetonitrile solvent, and gradually activated under vacuum at 20-40℃. Then heated at 110-130℃ under vacuum for 10-15h to obtain activated CCNUF-74.

[0008] Preferably, zinc nitrate hexahydrate and 2-hydroxyterephthalic acid are dispersed in N,N-dimethylformamide in a certain proportion, sealed, and reacted at 95°C for 6 days to obtain octahedral crystals, namely single crystal CCNUF-74. Washed with N,N-dimethylformamide, exchanged with acetonitrile solvent, subjected to gradual vacuum treatment at 30°C, and heated at 120°C under vacuum for 12 hours to obtain activated CCNUF-74.

[0009] Preferably, the ratio of zinc nitrate hexahydrate, 2-hydroxyterephthalic acid, and N,N-dimethylformamide is 0.227 mmol: 0.111 mmol: 1.0 mL.

[0010] Preferably, the N,N-dimethylformamide washing is performed at least three times.

[0011] Preferably, the acetonitrile solvent exchange is performed three times a day for at least 6 days.

[0012] Preferably, the gradual vacuuming process specifically includes: The solid products were kept under pressures of 30, 25, 20, 15, 10, 5, 3 and 1 kPa for 30 min each.

[0013] The present invention also provides a single-crystal CCNUF-74 material.

[0014] Preferably, the single-crystal CCNUF-74 material is crystallized in the tetragonal crystal system space group P41212, and bidirectional isomorphic Zn-O based rod-shaped SBUs are arranged along the crystal axes a and b. The single-crystal CCNUF-74 material has pore opening sizes of 8.9 Å × 10.7 Å and 8.0 Å × 5.1 Å, a porosity of 69.5%, and a BET specific surface area of ​​980 m². 2 / g.

[0015] This invention also provides an application of single-crystal CCNUF-74 material in benzene capture.

[0016] Preferably, in 298K, P / P Under the condition of 0=0.005, the adsorption capacity of single-crystal CCNUF-74 material for benzene is 2.46 mmol / g. -1 ; in 298K, P / P Under the condition of 0=0.01, the adsorption capacity of single-crystal CCNUF-74 material for benzene is 3.09 mmol g.-1 .

[0017] Therefore, the present invention employs the above-mentioned bidirectional rod-shaped metal-organic framework material, its preparation method, and its application, with the following beneficial effects: This invention proposes a solvent-modified rod-shaped SBUs orientation control strategy. By removing water from the reaction system, the in-situ introduction of formic acid anions and precise control of ligand torsion angle are achieved, successfully reconstructing a unidirectional rod-shaped MOF (CPM-74) into a bidirectional rod-shaped MOF (CCNUF-74). This marks the first time that the rational design and synthesis of multi-oriented rod-shaped MOFs has been realized.

[0018] The single-crystal CCNUF-74 prepared by this invention has a unique bidirectional orthogonal bar-shaped SBU structure, forming a three-dimensional interconnected channel network. Compared with CPM-74, it has smaller pore openings and higher porosity, providing a structural basis for the efficient adsorption of low-pressure benzene. It can be widely used in trace benzene capture scenarios such as indoor air purification and industrial waste gas treatment.

[0019] The present invention has a simple process, mild conditions, and high repeatability. It does not require complex equipment and is conducive to large-scale production and practical application.

[0020] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the synthesis route of the bidirectional rod-shaped metal-organic framework material of the present invention, its preparation method and application example 1 and comparative example 1; Figure 2 This is an SXRD result diagram of a bidirectional rod-shaped metal-organic framework material of the present invention, its preparation method and application example 1 and comparative example 1, where (a) shows the structure of rod-shaped SBUs in CPM-74 and CCNUF-74, with color coding: gray for carbon (C), red for oxygen (O), blue, cyan and purple for zinc (Zn), and yellow for hydrogen (H); (b) shows a comparison of the ligand torsion angles in CPM-74 and CCNUF-74. The torsion angle of the carboxylic acid group in OBDC is defined as the dihedral angle between the plane formed by the two carboxyl carbon atoms and the hydroxyl oxygen atom (green triangle) and the plane of the carboxylic acid group (yellow and orange triangles); Figure 3 These are optical microscope images of Example 1 and Comparative Examples 1 to 5 of the present invention, which describe a bidirectional rod-shaped metal-organic framework material, its preparation method, and its application. (a) is Comparative Example 1, (b) is Comparative Example 3, (c) is Comparative Example 4, (d) is Comparative Example 5, (e) is Comparative Example 2, and (f) is Example 1. Figure 4The images are PXRD patterns of Example 1 and Comparative Examples 1 to 5 of the present invention, which describe a bidirectional rod-shaped metal-organic framework material, its preparation method and application. (a) is Comparative Examples 1 to 5, and (b) is Example 1. Figure 5 The results are the benzene adsorption test results of the bidirectional rod-shaped metal-organic framework material, its preparation method and application example 1 of the present invention, wherein (a) is the N2 adsorption isotherm at 77K and (b) is the benzene vapor adsorption isotherm at 298K. Figure 6 The figures are giant canonical Monte Carlo (GCMC) simulation results of Example 1 and Comparative Example 1 of the present invention, which describes a bidirectional rod-shaped metal-organic framework material, its preparation method and application. (a) shows the simulated benzene adsorption isotherm and the experimental benzene adsorption isotherm of Example 1, and (b) shows the simulated benzene adsorption isotherm of Example 1 and Comparative Example 1. Figure 7 This is an SXRD diagram of the benzene molecule adsorption sites of a bidirectional rod-shaped metal-organic framework material, its preparation method, and an application example of the present invention. Detailed Implementation

[0022] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0023] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0024] Example 1 A single-crystal CCNUF-74 material is prepared by the following method: Zinc nitrate hexahydrate (Zn(NO3)2·6H2O, 67.5 mg, 0.227 mmol) and 2-hydroxyterephthalic acid (H3OBDC, 20.25 mg, 0.111 mmol) were dissolved in 1.0 mL of N,N-dimethylformamide (DMF). The solution was placed in a 4 mL reaction flask, sealed, and placed in a 95 °C oven for 6 days to obtain octahedral crystals. The product was washed three times with DMF to collect the solid product, which was then solvent-exchanged with acetonitrile (three times a day for 6 days). Next, it was subjected to gradual vacuum treatment at 30°C (maintained for 30 min at pressures of 30, 25, 20, 15, 10, 5, 3 and 1 kPa respectively). Finally, the sample was heated at 120°C under vacuum for 12 hours to obtain the activated product.

[0025] Comparative Example 1 A CPM-74 material ([Zn4(OH)2(OBDC)2], H3OBDC = 2-hydroxyterephthalic acid) is prepared as follows: Zn(NO3)2·6H2O (7.75 mg, 0.026 mmol), H3OBDC (2.35 mg, 0.013 mmol), DMF (543 μL), N,N-dibutylformamide (DBF, 150 μL), water (129 μL), isopropanol (iPrOH, 165 μL), and tetrapropylammonium hydroxide (TPAOH, 13 μL) were stirred and mixed in a 4 mL reaction flask. The reaction flask was then sealed and placed in an oven at 120 °C for 24 h to obtain rod-shaped crystals.

[0026] like Figure 1 As shown, in CPM-74, the dihedral angle (collectively referred to as the carboxyl torsion angle) between the carboxyl group on the OBDC ligand and the central plane COC exhibits slight distortion. Due to the inherent flexibility of the OBDC ligand, these torsion angles can be further increased, thereby achieving the directional reconstruction of rod-shaped SBUs from unidirectional to bidirectional. The strategy of increasing the torsion angle of the ligand to achieve orientation regulation of rod-shaped SBUs and obtain a bidirectional rod-shaped structure was employed. The introduction of formic acid significantly altered the torsion angle of the ligand, ultimately forming a novel three-dimensional channel structure with orthogonally arranged rod-shaped SBUs. In CCNUF-74, rod-shaped SBUs labeled with different colors have the same structure but different orientations, while the different colors of the ligands represent differences in their torsion angles. Color coding: gray represents carbon atoms, red represents oxygen atoms, blue or green polyhedra represent zinc atoms, and yellow and orange rods represent ligands.

[0027] Comparative Example 2 A polycrystalline CCNUF-74 material is prepared by the following method: Zn(NO3)2·6H2O (7.75 mg, 0.026 mmol), H3OBDC (2.35 mg, 0.013 mmol), DMF (543 μL), DBF (150 μL), iPrOH (165 μL) and TPAOH (13 μL) were mixed in a 4 mL reaction flask and then sealed and placed in an oven at 120 °C for 24 h to obtain a colorless powder.

[0028] Comparative Example 3 The difference from Comparative Example 1 is that the amount of water added was reduced to 90 μL.

[0029] Comparative Example 4 The difference from Comparative Example 1 is that the amount of water added was reduced to 60 μL.

[0030] Comparative Example 5 The difference from Comparative Example 1 is that the amount of water added was reduced to 30 μL.

[0031] Test 1. Single-crystal X-ray diffraction (SXRD) analysis was performed on the materials obtained in Example 1 and Comparative Example 1. The results are as follows: Figure 2 As shown.

[0032] Depend on Figure 2 It is known that CCNUF-74 crystallizes in the tetragonal crystal system, space group P41212, and its bidirectional isomorphic Zn-O rod-shaped SBUs are arranged along the crystal axes a and b. The asymmetric unit of this structure contains four crystallographically independent Zn atoms. 2+ The structure consists of ions, two fully deprotonated OBDC ligands, a formate anion, a bridging μ-OH group, and an N,N-dimethylformamide (DMF) molecule or water molecule present due to disorder. Zn1 adopts a tetrahedral coordination configuration, coordinating with three carboxylic acid oxygens and one μ-OH; Zn2 forms an octahedral configuration through coordination with three carboxylic acid oxygens, one phenolic oxygen, one μ-OH, and one formate; Zn3 has a five-coordinate tetrapyramidal configuration, combining two carboxylic acid oxygens, two μ-OH, and one formate; and Zn4 forms a tetrahedral coordination through one carboxylic acid oxygen, one phenolic oxygen, one μ-OH, and one DMF or water molecule. Compared to CPM-74, the distance between adjacent Zn2 and Zn3 ions within the rod-shaped SBU in CCNUF-74 is increased to approximately 3.123 Å, providing space for bridging the formate, while the smaller μ-OH cannot bridge these sites. Adjacent ZnO... n (n=4, 5 or 6) units form zigzag Zn-O chains by sharing vertices or edges. The molecular formula of CPM-74 is [Zn4(OH)2(OBDC)2], while that of CCNUF-74 is [Zn4(OH)(OBDC)2(HCOO)], the difference being that the latter replaces μ-OH with formate.

[0033] In CCNUF-74, the torsion angle of the carboxylic acid groups in half of the OBDC ligands increased significantly (from 5.15° and 27.57° in CPM-74 to 23.83° and 39.92°, respectively), resulting in the formation of two sets of rod-shaped SBUs with identical chemical compositions but orthogonal to each other. Some of the OBDC ligands that were originally aligned along the pore wall turned towards the pore center, reducing the pore window size. Since the ligand length is fixed, the angle between the Zn-O chain and the ligand decreased from 63.8° in CPM-74 to 49.4° and 46.6° in CCNUF-74, shortening the vertical distance between adjacent chains. This reduction in interchain spacing, combined with the structural feature that the ligands are more exposed to the pore environment, leads to a significant contraction of the pore opening. At the same time, the bidirectional orientation of the rod-shaped SBUs promotes the formation of a three-dimensional interconnected channel network in CCNUF-74. Therefore, the pore openings of CCNUF-74 (8.9 Å × 10.7 Å and 8.0 Å × 5.1 Å) are smaller than those of CPM-74 (13.3 Å × 13.3 Å), yet it still maintains a high porosity of 69.5% (compared to 56.3% for CPM-74). Furthermore, the difference in torsion angles between the rod-shaped SBUs and OBDC ligands results in a distinctly different topological network between CCNUF-74 and CPM-74. These results validate the feasibility and effectiveness of the orientation modulation strategy—constructing multidirectional rod-shaped MOF structures by controlling the ligand torsion angle.

[0034] 2. Powder X-ray diffraction (PXRD) analysis was performed on the materials obtained in Example 1 and Comparative Examples 1 to 5. The results are as follows: Figure 3 and Figure 4 As shown.

[0035] Depend on Figure 3 and Figure 4 It was found that when 129 μL of water was added, light gray rod-shaped crystals were obtained, which were confirmed as the CPM-74 phase by powder X-ray diffraction (PXRD) analysis. When the water content was reduced to 90 μL, the product was a mixture of rod-shaped crystals and polycrystalline powder, and the PXRD spectrum still corresponded to the CPM-74 phase. When the water content was further reduced to 60 μL and 30 μL, only polycrystalline powder was obtained, and the PXRD peak intensity further decreased, indicating that the crystal quality continued to deteriorate. When no water was added at all, although the product was still polycrystalline powder, the characteristic diffraction peaks of CPM-74 completely disappeared, and only the diffraction peaks corresponding to CCNUF-74 were observed, indicating that a complete phase transition had occurred. These results indicate that small changes in water content can significantly affect the phase transition process: higher water content is conducive to the formation of CPM-74, while a completely anhydrous environment promotes the assembly of the CCNUF-74 phase. To obtain high-quality CCNUF-74 single crystals, a colorless octahedral crystal was finally obtained. The good agreement between the experimental and simulated PXRD spectra confirmed the bulk purity of the CCNUF-74 crystal.

[0036] 3. The permanent porosity analysis and benzene vapor adsorption test were performed on the material obtained in Example 1. The results are as follows: Figure 5 As shown.

[0037] Depend on Figure 5 As shown in (a), CCNUF-74 exhibits a value of 980m. 2 The BET specific surface area per g is approximately equal to the theoretical value of 1690 m². 2 There is a certain deviation in / g. This difference may be related to the significant increase in the ligand torsion angle, which leads to a decrease in the stability of the framework structure.

[0038] Depend on Figure 5 As shown in (b), CCNUF-74 operates in the low-pressure region ( P / P (0 < 0.01) The benzene vapor adsorption capacity shows a steep upward trend, which is typical micropore filling behavior and suitable for trace benzene capture. Specifically, in P / P When α = 0.005, the adsorption capacity reaches 2.46 mmol g. -1 , P / P When 0 = 0.01, it further increased to 3.09 mmol g. -1 It exhibits excellent low-pressure adsorption capacity. As pressure increases, the adsorption capacity gradually approaches saturation, with a maximum adsorption capacity of approximately 4.04 mmol g. -1 Although the measured BET specific surface area of ​​CCNUF-74 is significantly lower than the theoretical value, it still exhibits a high low-pressure benzene adsorption capacity, indicating a strong affinity and good size matching between the pore structure and benzene molecules.

[0039] 4. Giant canonical Monte Carlo (GCMC) simulations were performed on the materials obtained in Example 1 and Comparative Example 1. The results are as follows: Figure 6 As shown.

[0040] Depend on Figure 6 It is evident that the simulated benzene saturation adsorption capacity of CCNUF-74 is significantly higher than its experimental value, consistent with the trend that the theoretical BET surface area is greater than the experimental value. More importantly, under both low-pressure and saturated conditions, the calculated adsorption capacity of CCNUF-74 is superior to that of CPM-74. This performance difference mainly stems from two factors: First, unlike the one-dimensional through-hole macropores of CPM-74, CCNUF-74 has smaller pore openings and a serrated channel structure, enhancing host-guest interactions through strong multi-site binding between benzene molecules (especially under low-pressure conditions); second, the three-dimensional pore network of CCNUF-74 endows it with higher overall porosity and more accessible pore space, thereby improving the total adsorption capacity.

[0041] 5. The material obtained in Example 1 was immersed in benzene for one week, and its structure was determined by single-crystal X-ray diffraction (SXRD). The structure is as follows: Figure 7 As shown.

[0042] Benzene molecules are anchored in the network structure via C–H···O (3.43–4.6 Å) interactions and further stabilized via C–H···π (2.28 Å) interactions. This synergistic effect enhances the host-guest affinity. This specific interaction is the key mechanism by which the material exhibits significant benzene adsorption capacity in the low-pressure region.

[0043] Therefore, this invention utilizes the aforementioned bidirectional rod-shaped metal-organic framework material, its preparation method, and its application to achieve directional reconstruction of rod-shaped SBUs from unidirectional to bidirectional, thereby obtaining MOF materials with smaller pore openings, higher porosity, and excellent low-pressure benzene adsorption performance.

[0044] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a bidirectional rod-shaped metal-organic framework material, characterized in that, Includes the following steps: Zinc nitrate hexahydrate and 2-hydroxyterephthalic acid were dispersed in N,N-dimethylformamide in a certain proportion, sealed, and reacted at a constant temperature of 90-100℃ for 5-7 days to obtain octahedral crystals, namely single crystal CCNUF-74. Washed with N,N-dimethylformamide, exchanged with acetonitrile solvent, subjected to gradual vacuum treatment at 20-40℃, and heated at 110-130℃ under vacuum for 10-15h to obtain activated CCNUF-74.

2. The method for preparing a bidirectional rod-shaped metal-organic framework material according to claim 1, characterized in that, The ratio of zinc nitrate hexahydrate, 2-hydroxyterephthalic acid, and N,N-dimethylformamide is 0.227 mmol: 0.111 mmol: 1.0 mL.

3. The method for preparing a bidirectional rod-shaped metal-organic framework material according to claim 1, characterized in that: The N,N-dimethylformamide washing is performed at least three times.

4. The method for preparing a bidirectional rod-shaped metal-organic framework material according to claim 1, characterized in that: The acetonitrile solvent exchange is performed three times a day for at least 6 days.

5. The method for preparing a bidirectional rod-shaped metal-organic framework material according to claim 1, characterized in that, The gradual vacuuming process specifically involves: The solid products were kept under pressures of 30, 25, 20, 15, 10, 5, 3 and 1 kPa for 30 min each.

6. A single-crystal CCNUF-74 material prepared by the method for preparing a bidirectional rod-shaped metal-organic framework material as described in any one of claims 1-5.

7. The single-crystal CCNUF-74 material according to claim 6, characterized in that: The single-crystal CCNUF-74 material is crystallized in the tetragonal space group P41212 and has bidirectional isomorphic Zn-O rod-shaped SBUs arranged along crystal axes a and b. The single-crystal CCNUF-74 material has pore opening sizes of 8.9 Å × 10.7 Å and 8.0 Å × 5.1 Å, a porosity of 69.5%, and a BET specific surface area of ​​980 m². 2 / g.

8. The application of a single-crystal CCNUF-74 material prepared by the preparation method of the bidirectional rod-shaped metal-organic framework material according to any one of claims 1-5 in benzene capture.

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