A flexible metal-organic framework material and its preparation method and application

Abstract

This invention belongs to the technical field of metal-organic framework materials and discloses a flexible metal-organic framework material, its preparation method, and its application. The material is self-assembled from an organic ligand, H2TNCA, and a transition metal zinc through the formation of coordination bonds, with the molecular formula being [Zn(TNCA)]·NMF; the organic ligand, H2TNCA, is (1,4-bis(2-methylimidazol-1-yl)terephthalic acid). The imidazole ligand and the transition metal zinc are used to construct a three-dimensional flexible structure with flexible diamond-shaped channels, exhibiting "gated" adsorption properties and capable of effectively separating C3H6 and C3H8. The preparation process is simple and easy, and the stability and recyclability are excellent.

Description

Technical Field

[0001] The present invention belongs to the technical field of porous metal organic framework materials, and more particularly relates to a flexible metal organic framework material and a preparation method and application thereof. Background Art

[0002] Propylene (C3H6) is the main olefin feedstock for petrochemical production, second only to ethylene in importance, and is an important component in the manufacture of various chemicals, including polypropylene. The purity of propylene mainly depends on the removal of propane impurities, but due to the similarity between propylene and propane, the separation of the two remains a difficult task. Traditional distillation methods consume a lot of energy due to the similar boiling points of the two, which has prompted people to become interested in adsorptive separation with lower energy consumption. In the exploration of porous materials for adsorptive separation, metal-organic frameworks (MOFs) stand out in providing precise control of structure and function at the molecular level. As a class of crystalline porous materials with a designable and tailorable framework and rich and diverse pore structures, MOFs have shown great application prospects in the field of gas storage and separation in recent years.

[0003] MOFs, with their rigid, narrow pores, can act as size-based molecular sieving, absorbing small molecules while excluding large molecules. However, since molecules of matching size must pass through many pores, the adsorption-desorption kinetics are slow, resulting in reduced energy efficiency and making it difficult to achieve equilibrium. In contrast, using flexible MOFs for adsorption separation can not only reduce energy consumption but also improve separation efficiency. For example, the MOF CPL-1 reported by Xia's group can achieve the separation of C3H6 / C3H8 mixtures at low pressure by utilizing the open-door adsorption of C3H6 rather than C3H8. Although this flexible MOF shows good performance in separation, it still has some disadvantages: there is almost no difference in affinity for C3H6 and C3H8, resulting in a small difference in opening pressure, and therefore low adsorption selectivity for effective separation.

[0004] Therefore, exploring suitable flexible MOF materials with obvious gate opening pressure differences, as well as their preparation methods and applications, is of great significance for practical C3H6 / C3H8 separation. Summary of the Invention

[0005] To overcome the instability and incomplete gas separation shortcomings of existing gas separation materials, the present invention provides a flexible metal-organic framework (MOF) material, its preparation method, and its application. This novel MOF material is constructed by self-assembly of flexible imidazole carboxylic acid ligands and transition metal zinc through coordination bonds. The methyl groups in this material can modulate the flexibility of the MOF structure, inducing gated opening under varying pressures, making it an ideal material for complete C3H6 / C3H8 separation.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A flexible metal-organic framework material, self-assembled by forming coordination bonds between the organic ligand H2TNCA and the transition metal zinc, with the molecular formula [Zn(TNCA)]·NMF;

[0008] The organic ligand H2TNCA=(1,4-bis(2-methylimidazol-1-yl)terephthalic acid).

[0009] The structural formula of the organic ligand H2TNCA is as follows:

[0010]

[0011] Preferably, the metal organic framework material is a monoclinic system with a space group of P21 / c and a unit cell parameter of α=β=γ=90°.

[0012] Preferably, the flexible metal organic framework material is composed of Zn 2+ and deprotonated flexible imidazole carboxylic acid ligand TNCA 2- Self-assembled through coordination bonds; each ligand TNCA 2- Attached to four independent mononuclear metal centers; ligand TNCA 2- It exhibits a coordination mode, in which the two carboxyl groups and two nitrogen atoms of each ligand coordinate with four zinc ions in a monodentate chelate manner; each zinc ion coordinates with two carboxylic acid oxygen atoms and two nitrogen atoms from four different ligands, which can be simplified to a tetrahedral geometric configuration; the carboxyl groups and 2-methylimidazole exist in a monodentate coordination mode, giving the inner wall of the pore a rich active site oxygen atom, and 2-methylimidazole and carboxylic acid have different torsion angles under different pressures; the three-dimensional framework has a rhombus channel with pore sizes of The stated pore sizes do not include van der Waals radii.

[0013] The present invention also provides a method for preparing the above-mentioned flexible metal-organic framework material, comprising the following steps:

[0014] (1) Weigh Zn(NO3)2·6H2O and H2TNCA and add them to the reaction vessel;

[0015] (2) adding NMF to the reaction vessel, and then adding nitric acid;

[0016] (3) The reaction vessel is sealed and ultrasonicated to obtain a mixed solution, which is then placed in an oven and allowed to stand at normal pressure to obtain colorless crystals under solvent thermal reaction conditions.

[0017] Preferably, the molar ratio of Zn(NO3)2·6H2O to H2TNCA is 1:3 to 1:5, and the mass volume ratio of Zn(NO3)2·6H2O to NMF is 8 mg:1 mL.

[0018] Preferably, the volume ratio of NMF to nitric acid is 2:1 to 3:1.

[0019] Preferably, the ultrasonic treatment time is 5 to 15 minutes, and the ultrasonic frequency is 40 KHz.

[0020] Preferably, the temperature of the oven is 90-105° C., and the standing time is 8-16 hours.

[0021] Beneficial effects of adopting the above technical solution: Synthesis conditions such as molar ratio, polarity, temperature, time, etc. will affect the formation of secondary structural units, thereby realizing the assembly of the framework structure.

[0022] The present invention also provides application of the above-mentioned flexible metal organic framework material in the adsorption and separation of propylene and propane.

[0023] It can be seen from the above technical solutions that, compared with the prior art, the present invention provides a flexible metal-organic framework material and its preparation method and application, which have the following beneficial effects:

[0024] (1) Based on coordination chemistry and crystal engineering, the present invention selects transition metal zinc and flexible imidazole carboxylic acid ligands to form diamond-shaped channels. This diamond-shaped channel exhibits unique structural flexibility and can induce "gating" opening under different pressures.

[0025] (2) The flexible metal-organic framework material ZJNU-403 prepared in the present invention has a pore environment modified with active site oxygen atoms and methyl functional groups, showing excellent stability and flexible adsorption properties, enabling it to exhibit the effect of complete separation of C3H6 / C3H8, achieving the purpose of one-step purification of propylene.

[0026] (3) The flexible metal-organic framework material prepared by the present invention can completely separate propylene and propane, the preparation process is simple and easy, and the stability and recyclability are good. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0028] Figure 1Figures 2 and 3 are PXRD spectra of different samples and after adsorption of different gases, where (a) is the PXRD spectrum of ZJNU-403 prepared in Example 1 in different solvents, and (b) is the PXRD spectrum of single crystal simulation data, samples synthesized in Example 1, Example 2, and Example 3.

[0029] Figure 2 This is the nitrogen cycle adsorption-desorption test isotherm of ZJNU-403 in Example 1 at 77K and 1 atm.

[0030] Figure 3 Schematic diagram of the structure of ZJNU-403 of Example 1, wherein (ab) are coordination mode diagrams of organic ligands and metals, and (cd) are three-dimensional network perspective diagrams and network topology diagrams of ZJNU-403 of Example 1 presented in CPK mode.

[0031] Figure 4 These are the single-component gas adsorption and desorption curves of ZJNU-403 of Example 1 for C3H6 and C3H8 at different temperatures.

[0032] Figure 5 These are the breakthrough curve and cyclic breakthrough curve of ZJNU-403 in Example 1 at 303K with a 1:1 C3H6 / C3H8 ratio. DETAILED DESCRIPTION

[0033] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0034] Example 1

[0035] The reactants Zn(NO3)2·6H2O (8 mg, 0.027 mmol) and H2TNCA (3 mg, 0.009 mmol) were weighed into a 20 mL glass bottle, and N-methylformamide (NMF) (1 mL) and nitric acid (2.7 M in NMF, 0.35 mL) were added. The glass bottle was sealed and ultrasonicated at 40 kHz for 5 min in a KQ-200KDB ultrasonic instrument to mix evenly. The mixture was then placed in a 90°C oven and allowed to react for 12 h. The resulting mixture was washed three times with NMF to obtain colorless, transparent octahedral crystals, named ZJNU-403.

[0036] Example 2

[0037] Weigh Zn(NO3)2·6H2O (80 mg, 0.27 mmol) and H2TNCA (30 mg, 0.09 mmol) into a 20 mL glass bottle, add NMF (7 mL) and nitric acid (2.7 M in NMF, 3 mL), and stir in an oil bath at 90 °C for 12 h to obtain white powder crystals, named ZJNU-403-power.

[0038] Example 3

[0039] Zn(NO₃)₂·6H₂O (4g, 0.162mmol) and H₂TNCA (18mg, 0.054mmol) were weighed into a 20mL glass vial. NMF (6mL) and nitric acid (2.7M in NMF, 3mL) were added. The vial was sealed and mixed thoroughly using a KQ-200KDB ultrasonic instrument at 40kHz for 5 minutes. The mixture was then placed in a 90°C oven and allowed to react for 12 hours, yielding colorless, transparent octahedral crystals. Changing the metal-to-ligand molar ratio affected the formation of secondary structural units, while varying the reaction time yielded single crystals of varying sizes. Ultimately, optimal conditions were determined to obtain single crystals suitable for crystallographic data collection.

[0040] Comparative Example 1

[0041] The reactants Zn(NO3)2·6H2O (8 mg, 0.027 mmol) and H2TNCA (3 mg, 0.009 mmol) were weighed into a 20 mL glass bottle, NMF (1 mL) was added and the glass bottle was sealed. After ultrasonication for 5 min to mix evenly, the mixture was placed in a 90°C oven and allowed to react for 12 h. No colorless, transparent octahedral crystals were obtained.

[0042] Comparative Example 2

[0043] The reactants Zn(NO3)2·6H2O (8 mg, 0.027 mmol) and H2TNCA (3 mg, 0.009 mmol) were weighed into a 20 mL glass bottle, and NMF (1 mL), DMF (0.5 mL) and nitric acid (2.7 Min NMF, 0.35 mL) were added. The glass bottle was sealed and ultrasonicated in an ultrasonic instrument for 5 min to mix evenly. Then, it was placed in a 90°C oven and allowed to react for 12 h. No colorless, transparent octahedral crystals were obtained.

[0044] Comparative Example 3

[0045] The reactants Zn(NO3)2·6H2O (8 mg, 0.027 mmol) and H2TNCA (3 mg, 0.009 mmol) were weighed into a 20 mL glass bottle, and NMF (1 mL), DMA (0.5 mL) and nitric acid (2.7 Min NMF, 0.35 mL) were added. The glass bottle was sealed and ultrasonicated in an ultrasonic instrument for 5 min to mix evenly. Then, it was placed in a 90°C oven and allowed to react for 12 h. No colorless, transparent octahedral crystals were obtained.

[0046] Comparative Example 4

[0047] The reactants Zn(NO3)2·6H2O (8 mg, 0.027 mmol) and H2TNCA (3 mg, 0.009 mmol) were weighed into a 20 mL glass bottle, and NMF (1 mL), H2O (0.5 mL) and nitric acid (2.7 Min NMF, 0.5 mL) were added. The glass bottle was sealed and ultrasonicated in an ultrasonic instrument for 5 min to mix evenly. Then, it was placed in a 90°C oven and allowed to react for 12 h. No colorless, transparent octahedral crystals were obtained.

[0048] Comparative Example 5

[0049] The reactants Zn(NO3)2·6H2O (8 mg, 0.027 mmol) and H2TNCA (3 mg, 0.009 mmol) were weighed into a 20 mL glass bottle, and NMF (1 mL), CH3CN (0.5 mL) and nitric acid (2.7 M in NMF, 0.5 mL) were added. The glass bottle was sealed and ultrasonicated in an ultrasonic instrument for 5 min to mix evenly. Then, it was placed in a 90°C oven and allowed to react for 12 h. No colorless, transparent octahedral crystals were obtained.

[0050] Changing the pH value of the system can control the number of nucleations and the crystal growth rate. Changing the second solvent can adjust the polarity of the solvent, affecting the morphology and crystallinity of the crystal. It is necessary to find the optimal synthesis conditions to obtain single crystals for crystallographic data collection.

[0051] The single crystal of ZJNU-403 with a crystal size of more than 100 microns prepared in Example 1 was subjected to single crystal X-ray diffraction test, and the crystallographic parameters obtained through crystal analysis are shown in Table 1. 2+ and deprotonated flexible imidazole carboxylic acid ligand TNCA 2- Self-assembled through coordination bonds; each ligand TNCA 2-Connected to four independent mononuclear metal centers; two carboxyl groups and two nitrogen atoms of each ligand are coordinated with four zinc ions in a monodentate manner; each zinc ion is coordinated with two carboxylic acid oxygen atoms and two nitrogen atoms from four different ligands, which can be simplified to a tetrahedral geometric configuration; the presence of carboxyl groups and 2-methylimidazole in a monodentate coordination mode gives the inner wall of the pore rich active site oxygen atoms, and 2-methylimidazole and carboxylic acid have different torsion angles under different pressures; the three-dimensional framework has a rhombus channel with pore sizes of Van der Waals radii are not included.

[0052] Table 1 Crystallographic parameters of ZJNU-403

[0053]

[0054] Stability test:

[0055] (1) Adsorption stability

[0056] 100 mg of the crystal sample of Example 1-3 was weighed, and the material was activated using an Autosrob iQ surface adsorption instrument (50° C. / 3 h, then 90° C. / 4 h, then 110° C. / 3 h), and then subjected to single-component gas adsorption and desorption tests of propylene and propane.

[0057] Gas adsorption performance test:

[0058] The ZJNU-403 material from Example 1 was tested for nitrogen gas adsorption and desorption using a Quantachrome Autosrob iQ gas adsorption and desorption instrument. 100 mg of ZJNU-403 from Example 1 was soaked in dehydrated acetone for seven days, with the solvent exchanged every six hours. The activated sample was then activated on an Autosrob iQ surface adsorption instrument (50°C / 3h, 90°C / 4h, and 110°C / 3h). Nitrogen adsorption was measured using liquid nitrogen at 77K to obtain pore surface area and pore size distribution data. Single-component gas adsorption of propylene and propane was measured using a circulating water bath at temperatures of 273, 283, 293, 298, 303, and 308K.

[0059] The results of the above test:

[0060] Powder X-ray diffraction was used to characterize the purity of the prepared materials and the crystallinity of the crystals, such as Figure 1 As shown in a, the main characteristic diffraction peaks are 9.18967; 10.42454; 11.93553; 15.57877; 18.21725; 18.65443; 19.91231; and 20.66397. The diffraction peak positions of ZJNU-403 prepared in Example 1 in different solvents are consistent with those of the single crystal sample, indicating that ZJNU-403 has good crystallinity and phase purity. Figure 1 The diffraction peaks of the powder sample, the single crystal sample of Example 1, and the single crystal sample of Example 3 in b are consistent with the diffraction peaks of the single crystal diffraction simulation data, indicating that the powder sample and the single crystal sample are the same substance.

[0061] In order to characterize the pore characteristics of ZJNU-403 in Example 1, a nitrogen adsorption test was performed at 77K. Figure 2 As shown, the adsorption curve belongs to the adsorption-desorption curve of flexible materials.

[0062] The ZJNU-403 of Example 1 was subjected to a systematic single-component adsorption and desorption test of propylene and propane (273 / 283 / 293 / 298 / 303 / 308K). Figure 4 As shown in (a), the adsorption capacities of C3H6 are 149 / 143 / 138 / 134 / 130 / 119 cm 3 ·g -1 ,like Figure 4 As shown in (b), the adsorption capacities of C3H8 are 142 / 136 / 112 / 85 / 10 / 10cm 3 ·g -1 At the same time, dynamic adsorption and penetration experiments were conducted on ZJNU-403. Figure 5 As shown in (a), at 303K, the separation effect of C3H6 / C3H8 (1; 1) mixture is good. C3H6 stays in the column longer than C3H8, and the retention time of C3H6 is 48min·g -1 The retention time of C3H8 is 32 min·g -1 ;like Figure 5 As shown in (b), the cyclic breakthrough experiment also shows that ZJNU-403's capture ability and separation performance for C3H6 remain stable after several cycles.

[0063] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Reference can be made to the common and similar parts between the various embodiments. For the solutions disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the method section.

[0064] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A flexible metal-organic framework material, characterized in that: It is self-assembled by the organic ligand H2TNCA and transition metal zinc through the formation of coordination bonds, and its molecular formula is [Zn(TNCA)]·NMF; The organic ligand H2TNCA=(1,4-bis(2-methylimidazol-1-yl)terephthalic acid).

2. A flexible metal organic framework material according to claim 1, characterized in that: The metal organic framework material crystallizes in the monoclinic system with a space group of P21 / c and a unit cell parameter of α=β=γ=90°.

3. The flexible metal-organic framework material according to claim 1, characterized in that: Each ligand TNCA in the metal organic framework material 2- The two carboxyl groups and two nitrogen atoms of the ligand are coordinated with the four zinc ions in a monodentate chelate manner. Each zinc ion is coordinated with two carboxylic acid oxygen atoms and two nitrogen atoms from the four ligands, forming a tetrahedral geometry. The carboxyl group and 2-methylimidazole exist in a monodentate coordination mode. Under different pressures, 2-methylimidazole and carboxylic acid have different torsion angles. The metal and ligand are interconnected to form a three-dimensional framework network with diamond-shaped channels and pore sizes of The stated pore sizes do not include van der Waals radii.

4. The method for preparing a flexible metal organic framework material according to any one of claims 1 to 3, characterized in that: The following steps are involved: (1) Weigh Zn(NO3)2·6H2O and H2TNCA and add them to the reaction vessel; (2) adding NMF to the reaction vessel, and then adding nitric acid; (3) The reaction vessel is sealed and ultrasonicated to obtain a mixed solution, which is then placed in an oven and allowed to stand at normal pressure to obtain colorless crystals under solvent thermal reaction conditions.

5. The method for preparing a flexible metal organic framework material according to claim 4, characterized in that: The molar ratio of Zn(NO3)2·6H2O and H2TNCA is 1:3 to 1:

5.

6. The method for preparing a flexible metal organic framework material according to claim 4, characterized in that: The volume ratio of the NMF to nitric acid is 2:1 to 3:1, and the mass volume ratio of the Zn(NO3)2·6H2O to NMF is 8 mg:1 mL.

7. The method for preparing a flexible metal organic framework material according to claim 4, characterized in that: The ultrasonic time is 5 to 15 minutes, and the ultrasonic frequency is 40 KHz.

8. The method for preparing a flexible metal organic framework material according to claim 4, characterized in that: The temperature of the oven is 90-105° C., and the standing time is 8-16 hours.

9. Use of the flexible metal-organic framework material according to any one of claims 1 to 3 or the flexible metal-organic framework material prepared by the preparation method according to any one of claims 4 to 8 in the adsorption and separation of propylene and propane.

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