A method of magnetically induced tuning of a metal organic framework film

Abstract

The application discloses a method for preparing a metal organic framework film by magnetic field induction regulation control. The method comprises the following steps: vertically immersing a sheet carrier into a film forming solution of the metal organic framework film; placing a container provided with the film forming solution and the carrier into a uniform magnetic field; and standing for 4-24 hours to obtain the metal organic framework film prepared by the magnetic field induction regulation control. The metal organic framework film is a cobalt-based, nickel-based or iron-based metal organic framework film. The carrier material comprises alumina, porous carbon and porous organic material. The magnetic field direction is perpendicular to or parallel to the surface of the carrier. The metal organic framework film prepared by the application has excellent gas separation performance, and the film forming process is simple, convenient, easy to enlarge and popularize.

Description

Technical Field

[0001] The technical solution of this invention relates to a method for preparing metal-organic framework (MOF) membranes by magnetic field-induced regulation, which belongs to the field of MOF membrane preparation. Background Technology

[0002] Compared with traditional separation technologies, membrane separation technology has advantages such as high efficiency, low energy consumption, simple equipment, and easy scale-up, making it highly promising for applications in gas separation, water treatment, and petrochemicals. Membrane materials are the core of membrane separation technology and have a decisive impact on separation performance. Metal-organic frameworks (MOFs) are a new type of porous material formed by coordination bonds between metal centers or metal clusters and carboxylic acid or nitrogen-containing organic polydentate ligands. MOFs are highly diverse, and their pore size and shape can be controlled and designed. Another unique advantage is that various functional groups can be modified into their structure, giving MOFs special chemical properties. Based on these excellent properties, MOFs have become a research hotspot in the field of porous materials. MOF membrane materials, combining the advantages of both MOFs and membrane materials, are currently the focus of attention in the membrane field.

[0003] Currently, the focus of MOF membrane research is on membrane preparation. Reported MOF membrane preparation methods mainly include in-situ growth, secondary seed growth, metal precursor induction, and electrochemical deposition. Although some progress has been made, certain problems still exist in MOF membrane research. On the one hand, MOF membrane synthesis generally requires high temperature and high pressure, which will not only lead to increased energy consumption in future practical applications but also increase the risk of the preparation process. On the other hand, to achieve successful membrane preparation and microstructure control, it is often necessary to introduce a high-quality seed layer or metal precursor on the carrier surface. For example, the invention patent "A Preparation Method of UiO-66 Series Gasoline Desulfurization Membrane for Pervaporation Metal-Organic Framework" (Publication No. CN 108031303 B) introduces a zirconium oxide particle layer on the surface of a porous carrier using a sol-gel method, and then places it in a synthesis solution to convert it into a UiO-66 series membrane. The thickness of the prepared MOF membrane can be controlled by adjusting the thickness of the zirconium oxide particle layer introduced on the carrier surface. However, this method is complex, has poor membrane reproducibility, and is not conducive to scale-up and promotion. Electrochemical deposition can achieve rapid synthesis of MOF membranes at room temperature, and the microstructure of the membrane can be controlled by parameters such as voltage and current. For example, Professor Wang Haihui's research group at South China University of Technology can prepare continuous and defect-free ZIF-8 membranes in a short time using a current-driven method. Due to the poor conductivity of ZIF-8 material, the generated ZIF-8 membrane can block the contact between the substrate current and the solution, thereby inhibiting further growth of the membrane layer, which is beneficial for preparing ultrathin membranes [Zhou Z, Wei YY, Li LB, et al. Paralyzed membrane: Current-driven synthesis of a metal-organic framework with sharpened propene / propane separation[J]. Science Advances, 2018, 4(10): eaau1393]. However, the process of preparing MOF membranes by electrochemical deposition is relatively complicated, and it is often necessary to avoid the separation of the membrane from the substrate and extend the storage time of the electrolytic cell during the preparation process. In addition, when using a sealed electrolytic cell, hydrogen gas is generated by water electrolysis, and how to dissipate the hydrogen gas and reduce safety hazards is also a problem that needs to be considered. Based on the above discussion, it is clear that how to achieve a simple synthesis of MOF membranes at room temperature remains a problem that urgently needs to be solved by researchers. Summary of the Invention

[0004] This invention addresses the shortcomings of existing technologies by proposing a method for magnetically induced and controlled preparation of MOF membranes. The method first prepares a film-forming solution, then vertically immerses a sheet-like support into the solution. The container containing the solution and support is placed in a uniform magnetic field. Under the influence of the magnetic field, metal center ions migrate at an accelerated rate in a specific direction, thereby inducing the formation of a continuous MOF membrane on the support surface. During the preparation process, the formation and microstructure of the MOF membrane can be easily controlled by adjusting the direction and intensity of the magnetic field. The MOF membrane prepared by this invention exhibits excellent gas separation performance, and the membrane preparation process is simple, facilitating scale-up and widespread application.

[0005] The technical solution of this invention is as follows:

[0006] A method for magnetic field-induced modulation to prepare MOF films, the method comprising the following steps:

[0007] The sheet-like support is vertically immersed into the film-forming solution of the MOF membrane, and then the container containing the film-forming solution and the support is placed in a uniform magnetic field and allowed to stand for 4 to 24 hours to obtain the MOF membrane prepared by magnetic field induction.

[0008] The strength of the magnetic field is 0.1–10 T;

[0009] The MOF film is a cobalt (Co), nickel (Ni), or iron (Fe) based MOF film, preferably a Co-MOF film, specifically a ZIF-67 film, a Co-ZIF-L film, or a Co-MOF-74 film.

[0010] The film-forming solution of the ZIF-67 membrane consists of cobalt nitrate hexahydrate, dimethylimidazole and methanol, with a molar ratio of 1:(4.5-5.5):(1100-1300).

[0011] The film-forming solution of the Co-ZIF-L membrane consists of cobalt nitrate hexahydrate, dimethylimidazole and water, with a molar ratio of 1:(1.5-1.7):(400-500);

[0012] The film-forming solution of the Co-MOF-74 membrane consists of cobalt nitrate hexahydrate, 2,5-dihydroxyterephthalic acid, N,N-dimethylformamide, and water; the molar ratio of cobalt nitrate hexahydrate, 2,5-dihydroxyterephthalic acid, and solvent is 1:(0.9-1.1):(900-1000), wherein the molar amount of solvent is calculated as the sum of the molar amounts of N,N-dimethylformamide and water, and the molar ratio of N,N-dimethylformamide to water in the solvent is 2:1.

[0013] The magnetic field comes from a device or apparatus capable of generating a magnetic field, preferably a magnet or a superconducting magnetic field meter.

[0014] The magnetic field strength is preferably 0.2 to 2 T.

[0015] The magnetic field is directed either perpendicularly to or parallel to the surface of the carrier.

[0016] The carrier material includes alumina, porous carbon, and porous organic materials.

[0017] The above-described method for preparing MOF membranes using magnetic field-induced modulation involves commercially available raw materials, and the equipment and processes used are well-known to those skilled in the art.

[0018] The essential features of this invention are:

[0019] In the MOF membrane preparation process of the present invention, Co, Ni and Fe ions in the film-forming solution will move directionally under the regulation of a magnetic field, causing them to be rapidly and orderly deposited or rapidly and orderly migrated on the surface of the support in a specific direction, thereby changing their coordination process with ligands, and finally realizing the formation and growth of MOF membrane on the support surface.

[0020] The beneficial effects of this invention are as follows:

[0021] This invention introduces a magnetic field into the MOF membrane preparation process for the first time. By utilizing the rapid and orderly migration of metal ions under the control of the magnetic field, MOF membranes can be prepared at room temperature. Furthermore, the microstructure of the MOF membrane can be easily controlled by adjusting the direction and intensity of the magnetic field during the membrane synthesis process. The prepared MOF membrane exhibits excellent gas separation performance and good membrane preparation reproducibility. The MOF membrane preparation method recommended in this invention is simple to operate, has low energy consumption, and is suitable for industrial scale-up and production, providing a new technical route for MOF membrane synthesis. Attached Figure Description

[0022] Figure 1 This is a scanning electron microscope (SEM) image of the ZIF-67 film prepared in Example 1.

[0023] Figure 2 The image shows a cross-sectional SEM image of the ZIF-67 membrane prepared in Example 1.

[0024] Figure 3 The image shows the X-ray diffraction (XRD) pattern of the ZIF-67 film prepared in Example 1.

[0025] Figure 4 The image shows a surface SEM image of the Co-ZIF-L membrane prepared in Example 2.

[0026] Figure 5 The image shows a surface SEM image of the ZIF-67 film prepared in Example 3.

[0027] Figure 6This is a surface SEM image of the ZIF-67 film prepared in Example 4.

[0028] Figure 7 This is a surface SEM image of the Co-MOF-74 membrane prepared in Example 5.

[0029] Figure 8 The image shows the surface SEM image of the sample prepared in Comparative Example 1.

[0030] Figure 9 The image shows the surface SEM image of the sample prepared in Comparative Example 2.

[0031] Figure 10 The image shows the surface SEM image of the sample prepared in Comparative Example 3.

[0032] Figure 11 The image shows the surface SEM image of the sample prepared in Comparative Example 4. Detailed Implementation

[0033] The present invention will now be described in detail through specific embodiments, but this does not limit the scope of protection of the present invention.

[0034] In the MOF membrane material described in this invention, ZIF stands for Zeolitic imidazolate framework, which refers to a type of MOF material with a molecular sieve-like structure. 67, L, and 74 are industry-standard serial numbers.

[0035] The neodymium iron boron strong magnets involved in this invention are commercially available products, with the following elemental mass fractions: neodymium 29%-32.5%, iron 63.95-68.65%, boron 1.1-1.2%, dysprosium 0.6-1.2%, niobium 0.3-0.5%, aluminum 0.3-0.5%, and copper 0.05-0.15%.

[0036] Example 1:

[0037] Magnetic field controlled preparation of ZIF-67 films on alumina supports:

[0038] 0.291 g (1 mmol) of cobalt nitrate hexahydrate and 0.410 g (5 mmol) of 2-methylimidazole were dissolved in 50 mL (1.2 mol) of methanol and magnetically stirred for 30 minutes until homogeneous to obtain a film-forming solution. An alumina sheet support (2.5 cm in diameter and 1 mm in thickness) was vertically immersed in the above solution. A neodymium iron boron magnet was placed directly above and below the alumina support, with the upper magnet being the positive pole and the lower magnet being the negative pole. This generated a uniform magnetic field parallel to the alumina sheet, and the strength of the magnetic field could be controlled by adjusting the distance between the magnet and the support or by the number of magnets. In this experiment, the magnetic field strength was controlled at 0.2 T (the distance between the magnet and the support was 4 cm). The reaction was allowed to stand at room temperature for 24 h. After the reaction was completed, the prepared sample was washed with methanol and dried under vacuum at 60 °C to obtain the ZIF-67 membrane.

[0039] Figure 1 The image shows the surface SEM image of the ZIF-67 membrane prepared in this embodiment. It can be seen that the surface of the alumina support is covered by the MOF film layer. The film layer is continuous and dense, without obvious defects such as cracks or voids.

[0040] Figure 2 The image shows a cross-sectional SEM image of the ZIF-67 membrane prepared in this embodiment. It can be clearly seen that the MOF membrane is tightly bonded to the carrier, the membrane layer is dense and continuous, and the thickness is about 1 μm.

[0041] Figure 3 The image shows the XRD pattern of the ZIF-67 film prepared in this embodiment. The image clearly shows the characteristic peaks of ZIF-67.

[0042] The ZIF-67 membrane prepared in this embodiment was subjected to single-component ideal gas separation performance tests to examine the compactness and sieving performance of the prepared membrane layer. To evaluate the membrane's separation performance, four gas molecules—H2 (molecular dynamic diameter 0.29 nm), CO2 (molecular dynamic diameter 0.33 nm), N2 (molecular dynamic diameter 0.36 nm), and CH4 (molecular dynamic diameter 0.38 nm)—were used to separate the MOF membrane. All tests were conducted at room temperature (25°C). The separation test apparatus was built by the research group. The prepared membrane sample was fixed in a membrane module sealed with an O-ring, and then the membrane module was placed in a membrane cell, connecting the various gas paths. During the experiment, the membrane-side pressure was controlled at 0.1 MPa using a back pressure valve, and the gas flow rate was controlled at 50 mL / min using a mass flow meter. The permeate side was connected to the atmosphere, and the gas flow rate was measured using a soap flow meter. The separation test results show that the ideal separation coefficients of H2 / CO2, H2 / N2, and H2 / CH4 are 13.2, 38.6, and 56.5, respectively, which are all much higher than their corresponding Norsen diffusion coefficients (4.7, 3.7, and 2.8, respectively), indicating that the MOF membrane has excellent gas separation performance.

[0043] Example 2:

[0044] Magnetic field controlled preparation of Co-ZIF-L films on alumina supports:

[0045] 2.624 g of cobalt nitrate hexahydrate (9 mmol) and 1.164 g (14 mmol) of 2-methylimidazole were dissolved in 80 mL (4.4 mol) of deionized water and stirred for 30 minutes until homogeneous. The alumina support was vertically immersed in the above solution, and then a neodymium iron boron magnet was placed on each of the left and right sides of the alumina support. The magnetic field generated was perpendicular to the film growth surface of the alumina support and the magnetic field strength was 1 T. The reaction was allowed to stand at room temperature for 4 h. After the reaction was completed, the prepared sample was washed with deionized water and ethanol and dried under vacuum at 60 °C to obtain the Co-ZIF-L membrane.

[0046] Figure 4 The image shows a SEM image of the Co-ZIF-L membrane prepared in this embodiment. The membrane layer is continuous and dense with no obvious defects.

[0047] The Co-ZIF-L membrane prepared in this embodiment was subjected to single-component ideal gas separation test at 25℃ and 0.1MPa. The test method was the same as in Example 1. The ideal separation coefficients of H2 / CO2, H2 / N2, and H2 / CH4 were 17.2, 5.7, and 7.0, respectively, all of which were higher than their corresponding Norsen diffusion coefficients, indicating that the MOF membrane has excellent gas separation performance.

[0048] Example 3:

[0049] Magnetic field controlled preparation of Co-MOF-74 films on alumina supports:

[0050] 0.21 g (0.72 mmol) of cobalt nitrate hexahydrate and 0.14 g (0.71 mmol) of 2,5-dihydroxyterephthalic acid were dissolved in a mixed solvent consisting of 34 mL (0.44 mol) of N,N-dimethylformamide and 4 mL (0.22 mol) of deionized water. The mixture was magnetically stirred for 30 minutes until homogeneous. The alumina support was vertically immersed in the above solution, and then the alumina support was placed in a magnetic field generated by a superconducting magnetic field instrument. The magnetic field direction was perpendicular to the alumina sheet and the strength was 2T. The reaction was allowed to stand at room temperature for 2 hours. After the reaction was completed, the prepared sample was washed with deionized water and ethanol, and then vacuum dried at 60 °C to obtain the Co-MOF-74 membrane.

[0051] Figure 5 The image shows a SEM image of the Co-MOF-74 membrane prepared in this embodiment. The membrane layer is continuous and dense with no obvious defects.

[0052] Under conditions of 25℃ and 0.1MPa, the Co-MOF-74 membrane prepared in this embodiment was subjected to single-component ideal gas separation test. The test method was the same as in Example 1. The ideal separation coefficients of H2 / CO2, H2 / N2, and H2 / CH4 were 12.5, 5.7, and 6.9, respectively, all of which were higher than the Norsen diffusion coefficient, indicating that the MOF membrane has excellent gas separation performance.

[0053] Example 4:

[0054] Magnetic field controlled preparation of ZIF-67 membranes on porous carbon supports:

[0055] The preparation process differs from that in Example 1 in that the carrier is a carbon nanotube film (from Chengdu Jiacai Technology Co., Ltd., with a diameter of 2.5 cm and a thickness of 10 μm), while the other parameters and processes are the same as in Example 1.

[0056] Figure 6 This is a SEM image of the ZIF-67 membrane prepared in this embodiment. As can be seen from the image, the membrane layer is continuous and dense, with no obvious defects.

[0057] Under conditions of 25℃ and 0.1MPa, the ZIF-67 membrane prepared in this embodiment was subjected to single-component ideal gas separation test. The test method was the same as in Example 1. The ideal separation coefficients of H2 / CO2, H2 / N2, and H2 / CH4 were 12.8, 37.1, and 49.8, respectively, which were all much higher than the Norsen diffusion coefficient, indicating that the MOF membrane has excellent gas separation performance.

[0058] Example 5:

[0059] Magnetic field controlled preparation of ZIF-67 membranes on porous organic supports:

[0060] The preparation process differs from that in Example 1 in that the carrier is an organic polyvinylidene fluoride filter membrane (diameter 2.5 cm, thickness 200 μm, pore size 0.45 μm), while other parameters and processes are the same as in Example 1.

[0061] Figure 7 The image shows a SEM image of the ZIF-67 membrane prepared in this embodiment. It can be seen from the image that the membrane layer is continuous and there are no obvious defects.

[0062] Under conditions of 25℃ and 0.1MPa, the ZIF-67 membrane prepared in this embodiment was subjected to single-component ideal gas separation test. The test method was the same as in Example 1. The ideal separation coefficients of H2 / CO2, H2 / N2, and H2 / CH4 were 11.5, 39.6, and 50.5, respectively, which were all much higher than the Norsen diffusion coefficient, indicating that the MOF membrane has excellent gas separation performance.

[0063] Example 6:

[0064] Magnetic field controlled preparation of Ni-MOF-74 films on alumina supports:

[0065] 0.21 g of nickel nitrate hexahydrate (0.72 mmol) and 0.14 g of 2,5-dihydroxyterephthalic acid (0.71 mmol) were dissolved in 34 mL (0.44 mol) of N,N-dimethylformamide and 4 mL (0.22 mol) of deionized water, and the mixture was magnetically stirred for 30 minutes until homogeneous. The alumina support was vertically immersed in the above solution and then placed in a magnetic field generated by a superconducting magnetic field instrument, with the magnetic field direction perpendicular to the alumina sheet and an intensity of 2T. The reaction was allowed to proceed at room temperature for 2 hours. After the reaction was completed, the prepared sample was washed with deionized water and ethanol and dried under vacuum at 60 °C to obtain the Ni-MOF-74 film.

[0066] Under conditions of 25℃ and 0.1MPa, the Ni-MOF-74 membrane prepared in this embodiment was subjected to single-component ideal gas separation test. The test method was the same as in Example 1. The ideal separation coefficients of H2 / CO2, H2 / N2, and H2 / CH4 were 11.2, 5.1, and 6.5, respectively, all of which were higher than their Norsen diffusion coefficient, indicating that the MOF membrane has excellent gas separation performance.

[0067] Example 7:

[0068] Magnetic field controlled preparation of Fe-MOF-74 films on alumina supports:

[0069] 0.17 g of ferric nitrate hexahydrate (0.70 mmol) and 0.14 g of 2,5-dihydroxyterephthalic acid (0.71 mmol) were dissolved in 34 mL (0.44 mol) of N,N-dimethylformamide and 4 mL (0.22 mol) of deionized water. The alumina support was vertically immersed in the above solution, and then the alumina support was placed in a magnetic field generated by a superconducting magnetic field instrument, with the magnetic field direction perpendicular to the alumina sheet and the strength of 2T. The reaction was allowed to stand at room temperature for 2 h. After the reaction was completed, the prepared sample was washed with deionized water and ethanol, and then vacuum dried at 60 °C to obtain the Fe-MOF-74 membrane.

[0070] Under conditions of 25℃ and 0.1MPa, the Fe-MOF-74 membrane prepared in this embodiment was subjected to single-component ideal gas separation test. The test method was the same as in Example 1. The ideal separation coefficients of H2 / CO2, H2 / N2, and H2 / CH4 were 10.6, 4.9, and 6.3, respectively, all of which were higher than the Norsen diffusion coefficient, indicating that the MOF membrane has excellent gas separation performance.

[0071] Comparative Example 1:

[0072] The synthesis steps are the same as in Example 1, except that no external magnetic field is applied during the synthesis process.

[0073] Figure 8 The surface SEM image of the ZIF-67 membrane obtained in Comparative Example 1 shows that no continuous film layer was formed.

[0074] Comparative Example 2:

[0075] The synthesis steps are the same as in Example 1, except that the magnetic field direction is perpendicular to the alumina sheet during the synthesis process.

[0076] Figure 9 The image shows the surface SEM image of the ZIF-67 film prepared in this embodiment. It can be seen that no continuous film layer was obtained.

[0077] Comparative Example 3:

[0078] The synthesis steps are the same as in Example 1, except that the magnetic field strength is 0.1T during the synthesis process.

[0079] Figure 10 The image shows the surface SEM image of the ZIF-67 film prepared in this embodiment. It can be seen that no continuous film layer was obtained.

[0080] Comparative Example 4:

[0081] The synthesis steps are the same as in Example 1, except that the magnetic field strength is 10T during the synthesis process.

[0082] Figure 11 The image shows a surface SEM image of the ZIF-67 film prepared in this embodiment. It can be seen that no continuous MOF film layer was obtained.

[0083] In Comparative Example 1, there was no inductive effect of the magnetic field; in Comparative Example 2, the direction of the magnetic field was different, resulting in different migration directions of Co ions; in Comparative Example 3, the magnetic field strength was relatively small, resulting in slow migration of Co ions; in Comparative Example 4, the magnetic field strength was too large, resulting in excessively fast migration of Co ions. Therefore, none of the above four comparative examples could obtain a continuous MOF film, thus demonstrating the advantages of the present invention.

[0084] The steps in the examples are all preferred steps for magnetic field-induced preparation of MOF membranes. As can be seen from the SEM images and the excellent gas separation performance, continuous and complete MOF membranes can be obtained in Examples 1 to 7.

[0085] Matters not covered in this invention are common knowledge.

Claims

1. A method for preparing metal-organic framework membranes by magnetic field-induced modulation, characterized in that the method includes the following steps: The sheet-like support is vertically immersed into the film-forming solution of the metal-organic framework (MOF) membrane, and then the container containing the film-forming solution and the support is placed in a uniform magnetic field. After standing for 4 to 24 hours, the MOF membrane prepared by magnetic field induction can be obtained. The strength of the magnetic field is 0.1~10 T; The MOF film is a cobalt-based, nickel-based, or iron-based MOF film; The magnetic field direction is perpendicular or parallel to the carrier surface; The carrier is made of alumina, porous carbon, or porous organic materials.

2. The method for preparing metal-organic framework membranes by magnetic field induction and control as described in claim 1, characterized in that, The MOF membrane is a cobalt-based MOF membrane.

3. The method for preparing metal-organic framework membranes by magnetic field induction and control as described in claim 1, characterized in that, The MOF membrane is a ZIF-67 membrane, a Co-ZIF-L membrane, or a Co-MOF-74 membrane.

4. The method for preparing metal-organic framework membranes by magnetic field induction and control as described in claim 3, characterized in that: The film-forming solution of the ZIF-67 membrane consists of cobalt nitrate hexahydrate, dimethylimidazole and methanol, with a molar ratio of 1:(4.5~5.5):(1100~1300); The film-forming solution of the Co-ZIF-L membrane consists of cobalt nitrate hexahydrate, dimethylimidazole and water, with a molar ratio of 1: (1.5~1.7):(400~500); The film-forming solution of the Co-MOF-74 membrane consists of cobalt nitrate hexahydrate, 2,5-dihydroxyterephthalic acid, N,N-dimethylformamide, and water; the molar ratio of cobalt nitrate hexahydrate, 2,5-dihydroxyterephthalic acid, and solvent is 1:(0.9~1.1):(900~1000), wherein the molar amount of solvent is calculated as the sum of the molar amounts of N,N-dimethylformamide and water, and the molar ratio of N,N-dimethylformamide to water in the solvent is 2:

1.

5. The method for preparing metal-organic framework membranes by magnetic field induction and control as described in claim 1, characterized in that: The magnetic field comes from a device or apparatus capable of generating a magnetic field.

6. The method for preparing metal-organic framework membranes by magnetic field induction and control as described in claim 1, characterized in that the magnetic field comes from a magnet or a superconducting magnetic field meter.

7. The method for preparing metal-organic framework membranes by magnetic field induction and control as described in claim 1, characterized in that the magnetic field strength is 0.2~2 T.

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