A bp membrane loaded with a metal organic framework and a method for preparing the same

Abstract

This invention provides a metal-organic framework (MOF)-loaded BP membrane and its preparation method. The raw materials for preparing the MOF-loaded BP membrane include a MOF material and a matrix solution. The raw materials for preparing the MOF material include nitrates, imidazoles, and graphene oxide. The raw materials for preparing the matrix solution include polyethylene glycol monomethyl ether acrylate, polyethylene glycol diacrylate, and a crosslinking agent. The MOF-loaded BP membrane prepared by this invention exhibits high permeability and selectivity for carbon dioxide gas, and the process is simple. It improves the compatibility between the MOF and the matrix membrane, thereby enabling the production of monolayer membrane materials, avoiding membrane separation and bubbling problems, and improving the stability and durability of the BP membrane.

Description

Technical Field

[0001] This invention belongs to the field of separation membrane technology, specifically relating to a BP membrane carrying a metal-organic framework and its preparation method. Background Technology

[0002] Effective control and reduction of CO2 emissions, as well as the efficient capture and separation of CO2 from industrial waste gases, are of great significance for mitigating the greenhouse effect and achieving sustainable development. Against this backdrop, membrane separation technology, due to its energy-saving, high-efficiency, clean, and environmentally friendly characteristics, has become a research hotspot in the field of CO2 separation. Bipolar membranes (BP membranes) are ion exchange membranes with a special structure that can simultaneously generate hydrogen ions (H+) and hydroxide ions (OH-) under the influence of an electric field, thus achieving the simultaneous generation of acids and bases during electrodialysis. Metal-organic frameworks (MOFs) are porous crystalline materials with a periodic network structure formed by the self-assembly of metal ions or metal clusters with organic ligands through coordination bonds. MOFs possess significant characteristics such as high specific surface area, high porosity, tunable pore size, and strong structural designability, which make them exhibit great application potential in gas separation, storage, catalysis, and other fields. Especially in gas separation, MOFs, due to their unique pore structure and chemical properties, exhibit highly selective adsorption of specific gas molecules (such as CO2), making them one of the ideal materials for achieving efficient gas separation. Although traditional bipolar membranes are mainly used in fields such as water electrolysis for hydrogen production or acid and alkali recovery, the composite membrane formed by introducing MOFs into BP membranes can be used for CO2 separation.

[0003] However, in the existing technology, the prepared composite membranes not only have low selectivity and permeability for carbon dioxide gas, affecting the separation effect, but also have poor compatibility between the metal-organic framework and the matrix membrane material, further affecting the lifespan and stability of the BP membrane. Summary of the Invention

[0004] The purpose of this invention is to provide a BP membrane with a metal-organic framework and its preparation method. The BP membrane with the metal-organic framework has high permeability and selectivity for carbon dioxide gas, and the process is simple. It improves the compatibility between the metal-organic framework and the matrix membrane, thereby improving the stability and durability of the BP membrane.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A BP membrane carrying a metal-organic framework, the raw materials for which are prepared include metal-organic framework materials and matrix solutions.

[0007] Preferably, the raw materials for preparing the metal-organic framework material include nitrates, imidazoles, and graphene oxide.

[0008] Preferably, the raw materials for preparing the matrix solution include polyethylene glycol monomethyl ether acrylate, polyethylene glycol diacrylate, and a crosslinking agent.

[0009] Preferably, the metal-organic framework material accounts for 2% to 10% of the mass of the BP membrane.

[0010] Preferably, the average thickness of the BP film is 130–170 μm.

[0011] Preferably, the nitrate includes zinc nitrate and cobalt nitrate.

[0012] Preferably, the molar ratio of zinc nitrate to cobalt nitrate is 1:(0.5-2).

[0013] Preferably, the imidazole is 2-methylimidazole.

[0014] Preferably, the molar ratio of the nitrate to the imidazole is 1:(6-12).

[0015] The inventors selected zinc nitrate as one of the raw materials to prepare a zinc-based metal-organic framework (MOF) material, which, when applied to a BP membrane, can improve the selectivity and permeability of the BP membrane for carbon dioxide. This is because the zinc-based MOF material has a high specific surface area, allowing it to expand into a larger free volume within the organic matrix prepared in this application, thus enhancing the gas permeability of the prepared BP membrane. Simultaneously, the pore size of the zinc-based MOF material matches the kinetic diameter of carbon dioxide molecules, thereby improving gas selectivity. However, the selectivity of the zinc-based MOF for carbon dioxide is limited, and BP membranes prepared solely with the zinc-based MOF exhibit poor separation performance for carbon dioxide.

[0016] The inventors discovered that introducing appropriate cobalt ions in addition to zinc ions can improve both the permeability and selectivity of the BP membrane for carbon dioxide. This is likely due to a synergistic effect between the two ions. Firstly, the different coordination modes and spatial arrangements of cobalt and zinc can form channels of specific sizes and shapes, selectively allowing carbon dioxide molecules to pass through while repelling other gas molecules. Secondly, certain oxidation states of cobalt may form active sites on the surface of the metal-organic framework (MOF). These sites can interact with carbon dioxide molecules, enhancing the MOF's adsorption capacity for carbon dioxide. Simultaneously, the coordination environment of zinc can regulate the number and distribution of these active sites, further optimizing its adsorption performance. Furthermore, the co-introduction of cobalt and zinc may lead to the formation of different energy barriers and diffusion channels within the MOF, affecting the diffusion and adsorption rates of gas molecules within the MOF, thus achieving efficient separation of carbon dioxide. However, the poor compatibility between the framework material and the polymer matrix affects the stability of the BP membrane and its carbon dioxide separation efficiency.

[0017] Preferably, the graphene oxide includes single-layer graphene oxide and multi-layer graphene oxide.

[0018] Preferably, the weight ratio of the single-layer graphene oxide to the multilayer graphene oxide is (2-5):1; more preferably, it is 4:1.

[0019] Preferably, the average thickness of the monolayer graphene oxide is 0.5–1.2 nm, and the diameter is 4–7 μm.

[0020] Preferably, the average thickness of the multilayer graphene oxide is 1-3 nm, the diameter is 4-7 μm, and the number of layers is 2-5.

[0021] In some preferred embodiments, both the single-layer graphene oxide and the multilayer graphene oxide are purchased from Zhejiang Zhitai Nanomaterials Co., Ltd.

[0022] Preferably, the mass ratio of graphene oxide to nitrate is 1:(10-20).

[0023] To improve the separation efficiency and stability of the BP membrane, two specific types of graphene oxide were selected. This is likely because, on the one hand, the use of specific single-layer and multi-layer graphene oxides, with similar diameters and thicknesses, creates a synergistic effect. This achieves complementarity in terms of layer count, retaining the high activity of single-layer graphene oxide while improving the mechanical properties of the BP membrane. On the other hand, the interweaving and stacking of similarly sized single-layer and multi-layer graphene oxides forms a stable three-dimensional network structure, which enhances the structural stability of the metal-organic framework material, thereby further improving its separation efficiency. However, considering the aggregation effect of graphene oxide, its addition should not be excessive; excessive graphene oxide may clog the membrane pores and affect the separation effect.

[0024] Preferably, the average molecular weight of the polyethylene glycol monomethyl ether acrylate is 600 to 1400 Da; more preferably, it is 1000 Da.

[0025] Preferably, the average molecular weight of the polyethylene glycol diacrylate is 300-800 Da; more preferably, it is 600 Da.

[0026] In some preferred embodiments, both the polyethylene glycol monomethyl ether acrylate and the polyethylene glycol diacrylate are purchased from Shanghai Yuanye Biotechnology Co., Ltd.

[0027] Preferably, the mass ratio of polyethylene glycol monomethyl ether acrylate to polyethylene glycol diacrylate is (1-3):1.

[0028] The inventors discovered that crosslinking two specific polymer matrices can improve the selectivity and permeability of BP membranes for carbon dioxide, while also enhancing their mechanical properties, making them more stable and durable. This is likely because the ether-oxygen bonds in these two specific substances can generate strong dipole-quadrupole interactions with carbon dioxide molecules, thus endowing the BP membrane with excellent affinity for carbon dioxide molecules, facilitating their dissolution and diffusion within the membrane, and increasing the carbon dioxide permeation flux. Meanwhile, the hydrophilic nature of the polyethylene glycol segments allows them to form hydrogen bonds with water-soluble carbon dioxide molecules, promoting their permeation and diffusion within the membrane. Furthermore, the selection of specific molecular weights gives the BP membrane obtained from the crosslinking reaction of the two organic compounds good flexibility and mechanical properties, helping to reduce stress concentration and the risk of rupture during the separation process, improving the membrane's durability and stability. By adjusting parameters such as the ratio of the two organic compounds, the type of crosslinking agent, and the crosslinking temperature, the structure and performance of the membrane can be flexibly controlled when introducing metal-organic framework materials, selectively allowing carbon dioxide molecules to pass through while repelling other gas molecules, thereby improving the selectivity for carbon dioxide. This controllability helps optimize the carbon dioxide separation performance of BP membranes.

[0029] Preferably, the crosslinking agent is one or more of azobisisobutyronitrile and benzoyl peroxide; more preferably, it is azobisisobutyronitrile.

[0030] Preferably, the amount of crosslinking agent added is 0.5% to 1.5% of the total mass of polyethylene glycol monomethyl ether acrylate and polyethylene glycol diacrylate.

[0031] A method for preparing a BP membrane carrying a metal-organic framework includes the following steps:

[0032] S1. Preparation of metal-organic framework materials: Graphene oxide powder is mixed and ultrasonically dispersed in methanol aqueous solution. Nitrate is added and ultrasonic treatment is continued for 4-7 hours. Then imidazole is added and ultrasonic treatment is carried out for 10-15 hours to obtain a suspension. The solid is collected by centrifugation and dried to obtain the final product.

[0033] S2. Preparation of matrix solution: Mix the raw materials and ultrasonically stir for 4-6 hours to homogenize the solution.

[0034] S3. Preparation of BP membrane: Add metal-organic framework material to matrix solution, ultrasonically stir for 4-6 hours to homogenize the solution, remove air bubbles, fill the solution into two glass plates, control the thickness of BP membrane by controlling the distance between the glass plates, let stand at 65-75℃ for 2-3 hours, remove and cool to room temperature, separate the BP membrane from the glass plates to obtain the final product.

[0035] The inventors discovered that introducing graphene oxide through a specific method can improve the permeability and selectivity of BP membranes for carbon dioxide gas. This is likely because the oxygen-containing functional groups abundant in graphene oxide not only endow it with a high affinity for carbon dioxide gas molecules, enhancing the selectivity of the BP membrane for carbon dioxide, but also provide growth sites for the metal-organic framework, greatly increasing its dispersibility in the organic matrix solution and improving its compatibility with the polymer matrix solution, thereby enhancing the selectivity and permeability of the BP membrane. Furthermore, the unique layered structure of graphene oxide promotes the efficient penetration of gas molecules through the separation membrane matrix, achieving high flux and further improving the gas permeation efficiency of the BP membrane.

[0036] In some preferred embodiments, the preparation of the metal-organic framework material in step S1 can be further optimized as follows:

[0037] A1. Mix graphene oxide powder and ultrasonically disperse it in methanol aqueous solution. Add zinc nitrate and continue ultrasonic treatment for 4-7 hours. Then add imidazole and ultrasonically treat for 10-15 hours to obtain a suspension. Centrifuge to collect the solid, wash with anhydrous methanol and dry in a vacuum oven at 50-60°C for 24-48 hours to obtain substance one.

[0038] A2. Imidazole, Substance 1, and cobalt nitrate were dissolved in deionized water to obtain imidazole solution, Substance 1 solution, and cobalt nitrate solution, respectively. Substance 1 solution and cobalt nitrate solution were mixed evenly and then poured into imidazole solution. After stirring for 10-20 min, the solid was collected by centrifugation, washed with deionized water, and dried in a vacuum oven at 50-60℃ for 24-48 h to obtain metal-organic framework material.

[0039] The inventors discovered that while simultaneously growing cobalt and zinc ions on graphene oxide improves carbon dioxide selectivity to some extent during the preparation of metal-organic frameworks (MOFs), the improvement in permeability is limited. This may be because the simultaneous introduction of cobalt and zinc results in a wider distribution of active sites, making the diffusion path of gas molecules within the membrane more complex and affecting carbon dioxide permeability to some extent. Through extensive experiments, the inventors found that by first growing a zinc-based MOF on graphene oxide and then coating the zinc-based MOF with a cobalt-based MOF, it is possible to further improve permeability while improving carbon dioxide selectivity. This may be because cobalt, as a coating layer covering the zinc surface, makes the cobalt sites on the membrane surface more concentrated, while the zinc sites inside are relatively fewer. This structure not only helps to form a specific surface chemical environment with stronger affinity and selectivity for carbon dioxide molecules, but also optimizes the pore structure, reducing the diffusion resistance of carbon dioxide molecules within the membrane, thereby improving permeability.

[0040] Preferably, the solid-liquid ratio of the graphene oxide and the methanol aqueous solution is 1 g: (60-100) mL.

[0041] Preferably, the molar ratio of zinc nitrate to imidazole in step A1 is 1:(2-6).

[0042] Preferably, the molar ratio of cobalt nitrate to imidazole in step A2 is 1:(10-15).

[0043] Preferably, the solid-liquid ratio of substance one, cobalt nitrate, and deionized water is 1 g:(30-50) mL.

[0044] Preferably, in step A2, the solid-liquid ratio of imidazole to deionized water is 1 g: (60-100) mL.

[0045] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0046] 1. This invention provides a BP membrane with a metal-organic framework (MOF) that exhibits high permeability and selectivity for carbon dioxide gas. The process is simple, improving the compatibility between the MOF and the matrix membrane. This allows for the fabrication of a monolithic bipolar membrane material, avoiding membrane separation and bubbling problems, and enhancing the stability and durability of the BP membrane. It is suitable for large-scale industrial use. Furthermore, by capturing and separating carbon dioxide through membrane separation technology, it reduces environmental pollution, which is of great significance for achieving carbon neutrality and addressing climate change.

[0047] 2. In this invention, zinc nitrate is selected as one of the raw materials. The zinc-based metal-organic framework material prepared and applied to BP membrane can improve the selectivity and permeability of BP membrane for carbon dioxide.

[0048] 3. Based on the introduction of zinc ions, this invention further introduces appropriate cobalt ions, which can improve the permeability of the BP membrane to carbon dioxide gas while also improving its selectivity.

[0049] 4. This invention introduces graphene oxide through a specific method, which can improve the permeability and selectivity of the BP membrane for carbon dioxide gas. At the same time, in order to improve the separation effect and stability of the BP membrane, two specific types of graphene oxide are selected.

[0050] 5. This invention uses two specific polymer matrix crosslinking methods, which can improve the selectivity and permeability of the BP membrane for carbon dioxide, and at the same time improve the mechanical properties of the BP membrane, making it more stable and durable.

[0051] 6. This invention improves carbon dioxide selectivity and further enhances its permeability by first growing a zinc-based metal-organic framework on graphene oxide and then coating the surface of the zinc-based metal-organic framework with a cobalt-based metal-organic framework. Detailed Implementation

[0052] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0053] All raw materials used in this invention are commercially available, specifically:

[0054] The average thickness of single-layer graphene oxide is 0.5–1.2 nm, and the diameter is 4–7 μm; the average thickness of multilayer graphene oxide is 1–3 nm, the diameter is 4–7 μm, and the number of layers is 2–5; all were purchased from Zhejiang Zhitai Nano-Micro New Materials Co., Ltd.

[0055] The average molecular weight of polyethylene glycol monomethyl ether acrylate is 1000 Da; the average molecular weight of polyethylene glycol diacrylate is 600 Da; both were purchased from Shanghai Yuanye Biotechnology Co., Ltd.

[0056] Example 1

[0057] This embodiment provides a BP membrane carrying a metal-organic framework, the raw materials for which are metal-organic framework materials and matrix solutions.

[0058] The raw materials for preparing the metal-organic framework material are nitrates, imidazoles, graphene oxide, methanol aqueous solution, and deionized water.

[0059] The raw materials for preparing the matrix solution are polyethylene glycol monomethyl ether acrylate, polyethylene glycol diacrylate, and a crosslinking agent.

[0060] The metal-organic framework material accounts for 5% of the mass of the BP membrane.

[0061] The average thickness of the BP film is 150 μm.

[0062] The nitrates are zinc nitrate and cobalt nitrate.

[0063] The molar ratio of zinc nitrate to cobalt nitrate is 1:1.

[0064] The imidazole is 2-methylimidazole.

[0065] The molar ratio of nitrate to imidazole is 1:8.

[0066] The graphene oxide is either single-layer graphene oxide or multi-layer graphene oxide.

[0067] The weight ratio of the single-layer graphene oxide to the multi-layer graphene oxide is 4:1.

[0068] The mass ratio of graphene oxide to nitrate is 1:15.

[0069] The mass ratio of polyethylene glycol monomethyl ether acrylate to polyethylene glycol diacrylate is 2:1.

[0070] The crosslinking agent is azobisisobutyronitrile.

[0071] The amount of crosslinking agent added is 1% of the total mass of polyethylene glycol monomethyl ether acrylate and polyethylene glycol diacrylate.

[0072] The preparation method of the BP membrane includes the following steps:

[0073] S1. Preparation of metal-organic framework materials;

[0074] S2. Preparation of matrix solution: Mix the raw materials and ultrasonically stir for 5 hours to homogenize the solution.

[0075] S3. Preparation of BP membrane: The metal-organic framework material is added to the matrix solution and ultrasonically stirred for 5 hours to homogenize the solution. After removing the air bubbles, the solution is filled into two glass plates. The thickness of the BP membrane is controlled by controlling the distance between the glass plates. After standing at 70°C for 2.5 hours, it is taken out and cooled to room temperature. The BP membrane is then separated from the glass plates to obtain the final product.

[0076] The preparation of the metal-organic framework material in step S1 is as follows:

[0077] A1. Mix graphene oxide powder and ultrasonically disperse it in methanol aqueous solution. Add zinc nitrate and continue ultrasonic treatment for 5 hours. Then add imidazole and ultrasonically treat for 12 hours to obtain a suspension. Centrifuge to collect the solid, wash with anhydrous methanol and dry in a vacuum oven at 55°C for 36 hours to obtain substance one.

[0078] A2. Imidazole, Substance 1 and cobalt nitrate were dissolved in deionized water to obtain imidazole solution, Substance 1 solution and cobalt nitrate solution respectively. Substance 1 solution and cobalt nitrate solution were mixed evenly and poured into imidazole solution. After stirring for 15 min, the solid was collected by centrifugation, washed with deionized water and dried in a vacuum oven at 55℃ for 36 h to obtain metal-organic framework material.

[0079] The volume fraction of the methanol-water solution is 30%.

[0080] The solid-liquid ratio of the graphene oxide and the methanol aqueous solution is 1g:80mL.

[0081] In step A1, the molar ratio of zinc nitrate to imidazole is 1:4.

[0082] In step A2, the molar ratio of cobalt nitrate to imidazole is 1:12.

[0083] The solid-liquid ratio of substance one, cobalt nitrate, and deionized water is 1 g: 40 mL.

[0084] In step A2, the solid-liquid ratio of imidazole to deionized water is 1g:80mL.

[0085] Example 2

[0086] The difference between this embodiment and Embodiment 1 is that the weight ratio of the single-layer graphene oxide to the multi-layer graphene oxide is 2:1.

[0087] Example 3

[0088] The difference between this embodiment and Embodiment 1 is that the molar ratio of nitrate to imidazole is 1:6; the molar ratio of zinc nitrate to imidazole in step A1 is 1:3; and the molar ratio of cobalt nitrate to imidazole in step A2 is 1:9.

[0089] Comparative Example 1

[0090] The difference between this comparative example and Example 1 is that the nitrate is zinc nitrate; S1, preparation of metal-organic framework material: graphene oxide powder is mixed and ultrasonically dispersed in methanol aqueous solution, nitrate is added and ultrasonic treatment is continued for 5 hours, then imidazole is added and ultrasonic treatment is carried out for 12 hours to obtain a suspension, the solid is collected by centrifugation, washed with anhydrous methanol and dried in a vacuum oven at 55°C for 36 hours to obtain the final product.

[0091] Comparative Example 2

[0092] The difference between this comparative example and Example 1 is that the molar ratio of zinc nitrate to cobalt nitrate is 1:4; the molar ratio of nitrate to imidazole is 1:8; the molar ratio of zinc nitrate to imidazole in step A1 is 1:4; and the molar ratio of cobalt nitrate to imidazole in step A2 is 1:9.

[0093] Comparative Example 3

[0094] The difference between this comparative example and Example 1 is that the weight ratio of the single-layer graphene oxide to the multi-layer graphene oxide is 1:1.

[0095] Comparative Example 4

[0096] The difference between this comparative example and Example 1 is that the mass ratio of graphene oxide to nitrate is 1:5.

[0097] Comparative Example 5 – Uncovered

[0098] The difference between this comparative example and Example 1 is as follows: the preparation of the metal-organic framework material in step S1 is as follows: graphene oxide powder is mixed and ultrasonically dispersed in methanol aqueous solution, nitrate is added, and ultrasonic treatment is continued for 5 hours. Then, imidazole is added and ultrasonic treatment is carried out for 12 hours to obtain a suspension. The solid is collected by centrifugation, washed with anhydrous methanol, and dried in a vacuum oven at 55°C for 36 hours to obtain the metal-organic framework material.

[0099] Comparative Example 6 – No growth on graphene oxide

[0100] The difference between this comparative example and Example 1 is that the preparation of the metal-organic framework material in step S1 is as follows:

[0101] A1. Imidazole and zinc nitrate were dissolved in deionized water to obtain imidazole solution and zinc nitrate solution, respectively. The two solutions were mixed and stirred for 5 hours, and the solid was collected by centrifugation and dried in a vacuum oven at 55°C for 12 hours to obtain substance one.

[0102] A2. Imidazole, Substance 1 and cobalt nitrate were dissolved in deionized water to obtain imidazole solution, Substance 1 solution and cobalt nitrate solution respectively. Substance 1 solution and cobalt nitrate solution were mixed evenly and poured into imidazole solution. After stirring for 15 min, the solid was collected by centrifugation, washed with deionized water and dried in a vacuum oven at 55℃ for 36 h to obtain Substance 2.

[0103] A3. Mix graphene oxide powder and ultrasonically disperse it in methanol aqueous solution. Add substance II and ultrasonically treat for 15 hours to obtain a suspension. Collect the solid by centrifugation, wash with anhydrous methanol, and dry in a vacuum oven at 55°C for 36 hours to obtain the final product.

[0104] The volume fraction of the methanol-water solution is 30%.

[0105] The solid-liquid ratio of the graphene oxide and the methanol aqueous solution is 1g:80mL.

[0106] In step A1, the molar ratio of zinc nitrate to imidazole is 1:4.

[0107] In step A1, the solid-liquid ratio of zinc nitrate, imidazole, and deionized water is 1g:40mL.

[0108] In step A2, the solid-liquid ratio of imidazole to deionized water is 1g:80mL, and the solid-liquid ratio of substance one and cobalt nitrate to deionized water is 1g:40mL.

[0109] In step A2, the molar ratio of cobalt nitrate to imidazole is 1:12.

[0110] Comparative Example 7

[0111] The difference between this comparative example and Example 1 is that the average molecular weight of the polyethylene glycol diacrylate is 2000, and it was purchased from Hubei Shineng Chemical Technology Co., Ltd.

[0112] Comparative Example 8 – No Graphene Oxide Added

[0113] The difference between this comparative example and Example 1 is that the preparation of the metal-organic framework material in step S1 is as follows:

[0114] A1. Imidazole and zinc nitrate were dissolved in deionized water to obtain imidazole solution and zinc nitrate solution, respectively. The two solutions were mixed and stirred for 5 hours, and the solid was collected by centrifugation and dried in a vacuum oven at 55°C for 12 hours to obtain substance one.

[0115] A2. Imidazole, Substance 1 and cobalt nitrate were dissolved in deionized water to obtain imidazole solution, Substance 1 solution and cobalt nitrate solution respectively. Substance 1 solution and cobalt nitrate solution were mixed evenly and poured into imidazole solution. After stirring for 15 min, the solid was collected by centrifugation, washed with deionized water and dried in a vacuum oven at 55℃ for 36 h to obtain the final product.

[0116] Performance testing

[0117] The selectivity and permeation capacity of the BP membrane for carbon dioxide were tested according to the method described in the article "Performance Study of CO2 / CH4 Separation Based on Two-Dimensional Vermiculite Nanosheet Hybrid Matrix Membrane" published by Hou Jinpeng et al. Simultaneously, to measure the operational stability of the BP membrane, its selectivity for carbon dioxide was tested after 120 hours of operation, and the rate of change was calculated. The results are shown in Table 1.

[0118] Table 1 Measurement Results

[0119]

[0120] According to statistics, the metal-organic framework-loaded BP membranes prepared in Examples 1-3 of this invention exhibit high selectivity and permeation capacity for carbon dioxide molecules, and still maintain high selectivity after 120 hours of operation. Comparative Example 1 did not add cobalt nitrate; Comparative Example 2 had excessively high cobalt nitrate content; Comparative Example 3 had relatively low monolayer graphene oxide content; Comparative Example 4 had excessively high graphene oxide content; Comparative Example 5 did not undergo coating treatment; Comparative Example 6 did not grow MOF on graphene oxide; Comparative Example 7 had excessively high average molecular weight of polyethylene glycol diacrylate; and Comparative Example 8 did not add graphene oxide. The BP membranes prepared using these methods all showed poor selectivity, permeation capacity, and stability for carbon dioxide gas. Therefore, the metal-organic framework-loaded BP membranes prepared using the raw materials and methods described in this application exhibit high permeation and selectivity for carbon dioxide gas, and the process is simple. The compatibility between the metal-organic framework and the matrix membrane is good, allowing for the preparation of monolayer membrane materials, avoiding membrane layer separation and bubbling problems, and improving the stability and durability of the BP membrane.

[0121] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A BP membrane carrying a metal-organic framework, characterized in that, The raw materials for preparing the BP membrane carrying the metal-organic framework include metal-organic framework materials and matrix solutions. The raw materials for preparing the metal-organic framework material include nitrates, imidazoles, and graphene oxide; The raw materials for preparing the matrix solution include polyethylene glycol monomethyl ether acrylate, polyethylene glycol diacrylate, and a crosslinking agent; The nitrates include zinc nitrate and cobalt nitrate; The molar ratio of zinc nitrate to cobalt nitrate is 1:(0.5-2); The imidazole is 2-methylimidazol; The molar ratio of the nitrate to the imidazole is 1:(6-12); The graphene oxide includes single-layer graphene oxide and multi-layer graphene oxide. The weight ratio of the single-layer graphene oxide to the multi-layer graphene oxide is (2-5):1; The average thickness of the monolayer graphene oxide is 0.5–1.2 nm, and the diameter is 4–7 μm. The average thickness of the multilayer graphene oxide is 1–3 nm, the diameter is 4–7 μm, and the number of layers is 2–5. The mass ratio of graphene oxide to nitrate is 1:(10-20).

2. The BP membrane carrying a metal-organic framework according to claim 1, characterized in that, The metal-organic framework material accounts for 2% to 10% of the mass of the BP membrane.

3. The BP membrane carrying a metal-organic framework according to claim 1, characterized in that, The average thickness of the BP film is 130–170 μm.

4. The BP membrane carrying a metal-organic framework according to claim 1, characterized in that, The average molecular weight of the polyethylene glycol monomethyl ether acrylate is 600–1400 Da.

5. The BP membrane carrying a metal-organic framework according to claim 4, characterized in that, The average molecular weight of the polyethylene glycol diacrylate is 300–800 Da.

6. The BP membrane carrying a metal-organic framework according to claim 5, characterized in that, The mass ratio of polyethylene glycol monomethyl ether acrylate to polyethylene glycol diacrylate is (1-3):

1.

7. A method for preparing a BP membrane carrying a metal-organic framework according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1. Preparation of metal-organic framework materials: Graphene oxide powder is mixed and ultrasonically dispersed in methanol aqueous solution. Nitrate is added and ultrasonic treatment is continued for 4-7 hours. Then imidazole is added and ultrasonic treatment is carried out for 10-15 hours to obtain a suspension. The solid is collected by centrifugation and dried to obtain the final product. S2. Preparation of matrix solution: Mix the raw materials and ultrasonically stir for 4-6 hours to homogenize the solution. S3. Preparation of BP membrane: Add metal-organic framework material to matrix solution, ultrasonically stir for 4-6 hours to homogenize the solution, remove air bubbles, fill the solution into two glass plates, control the thickness of BP membrane by controlling the distance between the glass plates, let stand at 65-75℃ for 2-3 hours, remove and cool to room temperature, separate the BP membrane from the glass plates to obtain the final product.

8. The method for preparing a BP membrane carrying a metal-organic framework according to claim 7, characterized in that, The preparation method in step S1 includes the following steps: A1. Mix graphene oxide powder and ultrasonically disperse it in methanol aqueous solution. Add zinc nitrate and continue ultrasonic treatment for 4-7 hours. Then add imidazole and ultrasonically treat for 10-15 hours to obtain a suspension. Centrifuge to collect the solid, wash with anhydrous methanol and dry in a vacuum oven at 50-60°C for 24-48 hours to obtain substance one. A2. Imidazole, Substance 1, and cobalt nitrate were dissolved in deionized water to obtain imidazole solution, Substance 1 solution, and cobalt nitrate solution, respectively. Substance 1 solution and cobalt nitrate solution were mixed evenly and then poured into imidazole solution. After stirring for 10-20 min, the solid was collected by centrifugation, washed with deionized water, and dried in a vacuum oven at 50-60℃ for 24-48 h to obtain metal-organic framework material.

9. The method for preparing a BP membrane carrying a metal-organic framework according to claim 8, characterized in that, In step A1, the molar ratio of zinc nitrate to imidazole is 1:(2-6).

10. The method for preparing a BP membrane carrying a metal-organic framework according to claim 8, characterized in that, In step A2, the molar ratio of cobalt nitrate to imidazole is 1:(10-15).

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