A method for preparing a defect-free MOFs membrane by COF in-situ interfacial polymerization

Abstract

The present application belongs to the field of gas membrane separation technology, and provides a method for preparing a defect-free MOFs membrane by in-situ interface polymerization of COF. In the membrane, acrylic cage polysilsesquioxane is grafted on MOFs by addition with amino groups in MOFs, and excess COF amino monomers are grafted with acrylic cage polysilsesquioxane, so that the subsequently synthesized COF is crosslinked with MOF, the interfacial compatibility of the two is improved, the selectivity of CO2 is increased, the intercrystalline defects generated in the repair preparation process of COF are repaired at the same time, the mechanical properties of the MOFs membrane are improved, the preparation difficulty of the MOFs membrane is greatly reduced, and in addition, the COF itself has many active groups and has high adsorption capacity for CO2. The MOFs membrane prepared by the present application realizes efficient H2 / CO2 separation by the simultaneous action of adsorption and screening effect in the gas separation process, and has higher practical value compared with the traditional MOFs membrane.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of gas separation, and particularly relates to a method for preparing a defect-free MOFs membrane through COF in-situ interface polymerization. BACKGROUND

[0002] New energy development is imminent in today's world because the currently used energy such as oil and natural gas is non-renewable energy, so new energy must be found. Hydrogen energy is a recognized clean energy and is emerging as a low-carbon and zero-carbon energy. It is abundant in sources, has a huge output, is safe, economical and efficient, and is pollution-free. In addition, hydrogen energy has great prospects in fuel cells and new energy vehicles. Membrane separation method is widely used in gas separation due to its low energy consumption and environmental friendliness.

[0003] Composite membranes are membranes composed of a selective layer for separation and a supporting layer for support. The materials of the selective layer and the supporting layer can be designed separately to optimize selectivity, permeability and mechanical properties. At the same time, the presence of the supporting layer is conducive to the realization of an ultra-thin selective layer, thereby improving the separation performance of the membrane. The performance of gas separation membranes is often affected by the trade-off relationship between permeability (P) and selectivity (S). The preparation of new membranes using porous materials with customizable pores may have an important impact on improving performance. Metal-organic frameworks (MOFs) as a representative porous material have the advantages of high porosity, high specific surface area, regular pores and adjustable pore size, and have great potential in gas separation. The known MOFs membranes all have excellent performance, however, there are some difficulties in the synthesis of MOFs membranes, such as the difficulty in synthesizing dense and defect-free MOFs membranes, the poor mechanical properties of the membranes, and the intergranular defects in the synthesis process of MOFs membranes, which can greatly reduce the selectivity of the MOFs membranes. Based on these problems, some researchers have proposed a defect repair strategy for MOFs membranes, that is, the MOFs membranes are modified by coating with polymers to repair the intergranular defects between MOF particles. This strategy can greatly improve the mechanical properties of the MOFs membranes while repairing the defects. Zhang Guoliang et al. of Zhejiang University of Technology invented a metal-organic framework composite membrane and its preparation method and application (201811148962.6), in which a modification strategy of a composite hydrogel of sodium alginate and polyvinyl alcohol was used to coat and modify various organic base membranes to realize the preparation of dense metal-organic framework selective separation membranes. The obtained functional membranes can be applied to gas separation. However, most of the known polymers such as PDMS, PVDF and PES have poor gas separation performance, which will affect the gas separation performance of the MOFs membranes.

[0004] Covalent organic frameworks (COFs) are a class of periodic, crystalline porous materials connected by covalent bonds. The periodic or ordered channels facilitate gas transport. In addition, the presence of covalent bonds makes it more stable than metal-organic frameworks, so covalent organic frameworks are excellent materials for gas separation. With extensive research in recent years, more and more COFs have been discovered, and the types of covalent bonds in COFs are also increasing, such as imine bonds, boron-oxygen bonds, etc. Most of the known COFs are connected by imine bonds. Imine bonds are formed by the condensation reaction of amino and aldehyde groups, and have higher stability than other covalent bonds. COFs with moderate crystallinity have high flexibility similar to polymers while achieving rapid molecular sieving, and by adjusting the crystallinity of COFs, the molecular sieving rate can be adjusted.

[0005] Therefore, a method for repairing defects of MOFs membranes by using COFs with moderate crystallinity is designed, which can repair the intercrystalline defects of MOFs and improve the mechanical properties of MOFs membranes. In addition, due to the rich groups of COFs, MOFs can simultaneously have gas sieving and adsorption capacity, thereby realizing efficient gas separation. SUMMARY

[0006] In view of the above-mentioned disadvantages of the prior art, the present application aims to design a defect repair strategy for MOFs membranes by in-situ polymerization of COFs, thereby preparing dense and defect-free MOFs membranes, which can repair the intercrystalline defects of MOFs and improve the mechanical properties of MOFs membranes.

[0007] The present application designs a method for preparing defect-free MOFs membranes by in-situ polymerization of COFs. First, MOFs membranes are prepared by anti-diffusion method. Certain concentrations of metal ions and ligand solutions are added to both sides of the base membrane. The ligand passes through the base membrane to the other side to meet the metal ions for coordination, generating MOFs particles on the surface of the base membrane. Under further reaction, a large amount of MOFs covers the base membrane, thereby generating MOFs membranes. The addition of inhibitors during preparation helps to prepare MOFs membranes with thinner thickness (<1 μm), because the inhibitors inhibit austenite aging, resulting in MOFs membranes with thinner thickness (<1 μm). Due to various influencing factors (such as temperature, coordination competition, etc.) during the preparation of MOFs membranes, intercrystalline defects are generally present in the prepared MOFs membranes, and the mechanical properties of MOFs membranes are poor, which makes them unable to be applied to gas separation. By in-situ polymerization of COFs with moderate crystallinity on the basis of MOFs membranes, the intercrystalline defects of MOFs membranes are repaired, thereby preparing defect-free MOFs membranes. Due to the high flexibility and high permeability of COFs with moderate crystallinity, the intercrystalline defects of MOFs are repaired without affecting the permeability of MOFs membranes, and the mechanical properties of the membranes are improved.

[0008] In order to achieve the above-mentioned purposes, the technical scheme of the present application is:

[0009] A method for preparing a defect-free MOFs membrane by COF in-situ interfacial polymerization, the steps are as follows:

[0010] (1) Preparation of modified MOFs membrane

[0011] The MOFs membrane is prepared by a back diffusion method, 1.322-13.218 parts of acrylic cage polysilsesquioxane (CAS No.: 1620202-27-8) is dissolved in 10-100 parts of ethanol to form solution A, the MOFs membrane is soaked in solution A for 0.5-5 hours, and finally dried at room temperature after ethanol washing to obtain the modified MOFs membrane.

[0012] (2) Preparation of defect-free MOFs membrane by COF in-situ interfacial polymerization

[0013] According to the mass fraction, 0.1-2 parts of scandium triflate is dissolved in 10-80 parts of mixed solvent (volume ratio of mesitylene to 1, 4-dioxane is 1:4) to obtain solution B; 0.025-0.5 parts of 1, 3, 5-triformylphloroglucinol and 0.02-0.4 parts of p-phenylenediamine are dissolved in 1-6 parts of mixed solvent (volume ratio of mesitylene to 1, 4-dioxane is 1:4) to obtain solution E; finally, solution B and solution C are added to the electrolytic cell respectively, located on both sides of the modified MOFs membrane, solution B is added to the electrolytic cell on the front side of the modified MOFs membrane, the osmotic pressure of the two sides of the membrane is different, COF is polymerized on the front side of the modified MOFs membrane and gradually crystallized, and the reaction is carried out at room temperature for 1-3 days, at the same time, the prepared MOFs membrane is washed by acetone for more than three times, and finally dried at room temperature.

[0014] Preferably, the MOFs membrane in step (1) is one of amino ZIF-8 and amino UIO-66, and the metal salt and the ligand are determined according to the corresponding MOFs;

[0015] Preferably, the COF in step (2) is one of TpPa-1, TpHz and TpBD, and the monomer ratio is determined according to the corresponding COF.

[0016] The reaction mechanism of the method of the application is as follows:

[0017] 1. Zinc nitrate and 2-aminobenzimidazole are coordinated on the surface of PAN to synthesize amino ZIF-7, and the addition of polyethylene glycol can inhibit the austenitic ripening of amino ZIF-7, so as to generate an ultra-thin MOFs membrane;

[0018] 2. Acrylic cage polysilsesquioxane is grafted on the MOFs by addition with the amino groups in the MOFs.

[0019] 3. Excess COF amine monomers can also graft with the acrylic-caged polysilsesquioxane, crosslinking the subsequent synthesized COF with the MOF, and improving the interfacial compatibility of the two.

[0020]

[0021]

[0022] Advantages of the present application:

[0023] Zinc nitrate and 2-aminobenzimidazole are coordinated on the surface of PAN to synthesize amino ZIF-7, and the addition of polyethylene glycol can inhibit the austenitic ripening of the amino ZIF-7, thereby generating an ultra-thin MOFs film. The acrylic-caged polysilsesquioxane is grafted on the MOFs by addition with the amino in the MOFs. Excess COF amine monomers can also graft with the acrylic-caged polysilsesquioxane, crosslinking the subsequent synthesized COF with the MOF, and improving the interfacial compatibility of the two. Since COF has high adsorption capacity for CO2, the defect-free MOFs film prepared by in-situ interfacial polymerization of COF can simultaneously function in adsorption and sieving effect in the gas separation process, thereby helping to achieve efficient H2 / CO2 separation.

[0024] The MOFs film prepared by the present application can repair the intergranular defects generated in the preparation process while improving the mechanical properties of the MOFs film, greatly reducing the difficulty of preparing the MOFs film. Compared with traditional polymers (PDMS, PVDF, etc.), the moderately crystallized COF has high flexibility similar to polymers, and the porous structure helps to realize efficient molecular sieving, thereby minimizing the influence on the permeability of the MOFs film while repairing the intergranular defects of the MOFs. Since COF itself has many active groups (imine bond, etc.), it has high adsorption capacity for CO2, so the defect-free MOFs film prepared by in-situ interfacial polymerization of COF can simultaneously function in adsorption and sieving effect in the gas separation process, thereby helping to achieve efficient H2 / CO2 separation. In addition, the crystallinity of the COF in the MOFs film can be adjusted by adjusting the reaction time according to actual needs, and these characteristics make it have higher practical value compared with traditional MOFs films. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 SEM image of the amino ZIF-7 film in the example.

[0026] Figure 2 SEM image of the amino ZIF-7 / TpPa-1 film in the example.

[0027] Figure 3A comparison chart of gas separation performance of the amino ZIF-7 membrane and the amino ZIF-7 / TpPa-1 membrane in the examples.

[0028] Figure 4 A comparison chart of gas separation performance of the amino ZIF-7 / TpPa-1 membranes under different reaction times in the examples. DETAILED DESCRIPTION

[0029] In order to better explain the present application, the technical solutions of the present application will be further described in combination with examples below, and it should be understood that the examples cannot be understood as limitations of the present application only.

[0030] Example 1

[0031] (1) Preparation of MOFs membrane

[0032] A certain area of polyacrylonitrile-based membrane was immersed in a mixed solution (ethanol and water in a volume ratio of 1:1) and soaked at 40°C overnight for cleaning; the cleaned and dried polyacrylonitrile-based membrane was clamped between two electrolytic cells with a volume of 20 mL and fixed.

[0033] According to mass parts, 0.297 g of zinc nitrate hexahydrate and 0.1 g of polyethylene glycol (MW = 6000) were added to 10 g of deionized water to obtain solution A; 1.133 g of 2-aminobenzimidazole was dissolved in 10 g of deionized water to obtain solution B; solutions A and B were added to the two sides of the base membrane in the electrolytic cell (solution A was added to the electrolytic cell on the positive side of the base membrane), and after reaction at room temperature for 6 h, the prepared MOFs membrane was cleaned with methanol for more than three times; 1.322 g of acrylic cage polysilsesquioxane (CAS No.: 1620202-27-8) was dissolved in 10 g of ethanol to obtain solution C, the MOFs membrane was immersed in solution C for 0.5 h, and finally washed with ethanol and dried at room temperature.

[0034] (2) In-situ interface polymerization of COF to prepare defect-free MOFs membrane

[0035] 0.1 g of scandium triflate was dissolved in 10 g of mixed solvent (mesitylene and 1,4-dioxane in a volume ratio of 1:4) to obtain solution A; 0.025 g of 1,3,5-triformylphloroglucinol and 0.02 g of p-phenylenediamine were dissolved in 1 g of mixed solvent (mesitylene and 1,4-dioxane in a volume ratio of 1:4) to obtain solution B; finally, solutions A and B were added to the two sides of the MOFs membrane in the electrolytic cell (solution A was added to the electrolytic cell on the positive side of the MOFs membrane), and the COF was polymerized and gradually crystallized on the positive side of the MOFs membrane by using the different osmotic pressures on the two sides of the membrane, after reaction for 24 h, the prepared MOFs membrane was cleaned with acetone for more than three times, and finally dried at room temperature.

[0036] Example 2

[0037] (1) Preparation of MOFs membrane

[0038] A certain area of polyacrylonitrile-based membrane was immersed in a mixed solution (ethanol and water in a volume ratio of 1:1) and soaked at 60°C overnight for cleaning; the cleaned and dried polyacrylonitrile-based membrane was clamped between two electrolytic cells with a volume of 80 mL and fixed.

[0039] By mass fraction, 1.485 g of zinc nitrate hexahydrate and 0.5 g of polyethylene glycol (MW = 6000) were added to 40 g of deionized water to obtain solution A; 5.665 g of 2-aminobenzimidazole was dissolved in 40 g of deionized water to obtain solution B; solutions A and B were added to the two sides of the base membrane in the electrolytic cell (solution A was added to the electrolytic cell on the positive side of the base membrane), and after reaction at room temperature for 6 h, the prepared MOFs membrane was cleaned with methanol for more than three times; 6.61 g of acrylic cage polysilsesquioxane (CAS No.: 1620202-27-8) was dissolved in 50 g of ethanol to obtain solution C, and the MOFs membrane was immersed in solution C for 2 h, and finally washed with ethanol and dried at room temperature.

[0040] (2) In-situ interface polymerization of COF to prepare defect-free MOFs membrane

[0041] 0.5 g of scandium triflate was dissolved in 50 g of mixed solvent (mestilene and 1,4-dioxane in a volume ratio of 1:4) to obtain solution A; 0.125 g of 1,3,5-triformylphloroglucinol and 0.25 g of p-phenylenediamine were dissolved in 3 g of mixed solvent (mestilene and 1,4-dioxane in a volume ratio of 1:4) to obtain solution B; finally, solutions A and B were added to the two sides of the MOFs membrane in the electrolytic cell (solution A was added to the electrolytic cell on the positive side of the MOFs membrane), and COF was polymerized and gradually crystallized on the positive side of the MOFs membrane by using the different osmotic pressures on the two sides of the membrane; after reaction for 24 h, the prepared MOFs membrane was cleaned with acetone for more than three times, and finally dried at room temperature.

[0042] Example 3

[0043] (1) Preparation of MOFs membrane

[0044] A certain area of polyacrylonitrile-based membrane was immersed in a mixed solution (ethanol and water in a volume ratio of 1:1) and soaked at 80°C overnight for cleaning; the cleaned and dried polyacrylonitrile-based membrane was clamped between two electrolytic cells with a volume of 100 mL and fixed.

[0045] By mass parts, 2.97 g of zinc nitrate hexahydrate and 1 g of polyethylene glycol (MW = 6000) are added to 50 g of deionized water to obtain solution A; 13.315 g of 2-aminobenzimidazole is dissolved in 50 g of deionized water to obtain solution B; solutions A and B are added to the electrolytic cell on both sides of the base film (solution A is added to the electrolytic cell on the positive side of the base film), and after reaction at room temperature for 6 h, the prepared MOFs film is washed with methanol for more than three times; 13.218 g of acrylic cage polysilsesquioxane (CAS No.: 1620202-27-8) is dissolved in 100 g of ethanol to obtain solution C, and the MOFs film is soaked in the C solution for 5 h, and finally dried at room temperature after ethanol washing.

[0046] (2) In-situ interface polymerization of COF to prepare defect-free MOFs film

[0047] 2 g of scandium triflate is dissolved in 80 g of mixed solvent (mestilene: 1,4-dioxane = 1:4) to obtain solution A; 0.5 g of 1,3,5-triformylphloroglucinol and 0.4 g of p-phenylenediamine are dissolved in 6 g of mixed solvent (mestilene: 1,4-dioxane = 1:4) to obtain solution B; finally, solutions A and B are added to the electrolytic cell on both sides of the MOFs film (solution A is added to the electrolytic cell on the positive side of the MOFs film), and the COF is polymerized and gradually crystallized on the positive side of the MOFs film by using the different osmotic pressures on both sides of the film, and after reaction for 24 h, the prepared MOFs film is washed with acetone for more than three times, and finally dried at room temperature.

[0048] Comparative Example 1

[0049] A certain area of polyacrylonitrile-based film is soaked in a mixed solution (ethanol and water in a volume ratio of 1:1) and soaked at 40°C overnight for cleaning; the cleaned and dried polyacrylonitrile-based film is clamped between two electrolytic cells with a volume of 20 mL and fixed.

[0050] By mass parts, 0.297 g of zinc nitrate hexahydrate and 0.1 g of polyethylene glycol (MW = 6000) are added to 10 g of deionized water to obtain solution A; 1.133 g of 2-aminobenzimidazole is dissolved in 10 g of deionized water to obtain solution B; solutions A and B are added to the electrolytic cell on both sides of the base film (solution A is added to the electrolytic cell on the positive side of the base film), and after reaction at room temperature for 6 h, the prepared MOFs film is washed with methanol for more than three times; 1.322 g of acrylic cage polysilsesquioxane (CAS No.: 1620202-27-8) is dissolved in 10 g of ethanol to obtain solution C, and the MOFs film is soaked in the C solution for 0.5 h, and finally dried at room temperature after ethanol washing.

[0051] Comparative Example 2

[0052] (1) Preparation of MOFs membrane

[0053] A certain area of polyacrylonitrile-based membrane was immersed in a mixed solution (ethanol and water in a volume ratio of 1:1) and soaked at 40°C overnight for cleaning; the cleaned and dried polyacrylonitrile-based membrane was clamped between two electrolytic cells with a volume of 20 mL and fixed.

[0054] According to parts by mass, 0.297 g of zinc nitrate hexahydrate and 0.1 g of polyethylene glycol (MW = 6000) were added to 10 g of deionized water to obtain solution A; 1.133 g of 2-aminobenzimidazole was dissolved in 10 g of deionized water to obtain solution B; solutions A and B were added to the two sides of the base membrane in the electrolytic cell (solution A was added to the electrolytic cell on the positive side of the base membrane), and after reaction at room temperature for 6 h, the prepared MOFs membrane was cleaned with methanol three times or more; 1.322 g of acrylic cage polysilsesquioxane (CAS No.: 1620202-27-8) was dissolved in 10 g of ethanol to obtain solution C, and the MOFs membrane was immersed in solution C for 0.5 h, and finally washed with ethanol and dried at room temperature.

[0055] (2) In-situ interface polymerization of COF to prepare defect-free MOFs membrane

[0056] 0.1 g of scandium triflate was dissolved in 10 g of mixed solvent (mesitylene and 1,4-dioxane in a volume ratio of 1:4) to obtain solution A; 0.025 g of 1,3,5-triformylphloroglucinol and 0.02 g of p-phenylenediamine were dissolved in 1 g of mixed solvent (mesitylene and 1,4-dioxane in a volume ratio of 1:4) to obtain solution B; finally, solutions A and B were added to the two sides of the MOFs membrane in the electrolytic cell (solution A was added to the electrolytic cell on the positive side of the MOFs membrane), and the COF was polymerized and gradually crystallized on the positive side of the MOFs membrane by using the different osmotic pressures on the two sides of the membrane, and after reaction for 72 h, the prepared composite membrane was cleaned with acetone three times or more, and finally dried at room temperature.

[0057] From Figure 3 The gas separation performance comparison chart of the amino ZIF-7 membrane and the amino ZIF-7 / TpPa-1 membrane shows that the gas separation performance of the amino ZIF-7 / TpPa-1 membrane is obviously higher than that of the amino ZIF-7 membrane, which indicates that the defect-free MOFs membrane prepared by in-situ interface polymerization of COF simultaneously acts on adsorption and sieving effect in the gas separation process, thereby helping to achieve efficient H2 / CO2 separation.

[0058] From Figure 4The gas separation performance comparison chart of amino ZIF-7 / TpPa-1 membrane under different reaction times can be clearly seen that, compared with Comparative Example 2, the gas permeation performance of amino ZIF-7 / TpPa-1 membrane gradually increases with the increase of reaction time, which is due to the increase of reaction time, which will lead to the increase of TpPa-1 crystallinity, the structure gradually ordered, thus leading to the increase of gas permeation performance and the decrease of selectivity. According to the actual demand, amino ZIF-7 / TpPa-1 membrane with different reaction times is prepared for H2 / CO2 separation.

[0059] The above examples are only as the conception and description of the technical scheme of the present application, and the purpose is to explain the content of the present application more clearly and to implement it, which cannot be understood as the limitation of the present application. Any further change or variation made according to the spirit and essence of the present application shall belong to the protection scope of the present application.

Claims

1. A method for preparing defect-free MOF membranes via in-situ interfacial polymerization of COF, characterized in that, The steps are as follows: (1) Preparation of modified MOF membranes MOFs membranes were prepared by reverse diffusion method according to mass. 1.322-13.218 parts of acrylic-cage polysilsesquioxane were dissolved in 10-100 parts of ethanol to form solution A. The MOFs membrane was immersed in solution A for 0.5-5 h. Finally, it was washed with ethanol and dried at room temperature to obtain the modified MOFs membrane. (2) Preparation of defect-free MOF membranes by in-situ interfacial polymerization of COF By mass: Dissolve 0.1-2 parts of scandium trifluoromethanesulfonate in 10-80 parts of mixed solvent to obtain solution B; dissolve 0.025-0.5 parts of 1,3,5-trialdehyde phloroglucinol and 0.02-0.4 parts of p-phenylenediamine in 1-6 parts of mixed solvent to obtain solution C; finally, add solutions B and C to the electrolytic cell on both sides of the modified MOF membrane, with solution B added to the electrolytic cell on the front side of the MOF membrane. Utilizing the difference in osmotic pressure on both sides of the membrane, COF polymerizes and gradually crystallizes on the front side of the modified MOF membrane. The reaction is carried out at room temperature for 1-3 days, while the prepared modified MOF membrane is washed with acetone more than three times. Finally, it is dried at room temperature.

2. The method according to claim 1, characterized in that, In step (1), the MOFs membrane is one of amino ZIF-8 or amino UIO-66, and the metal salt and ligand are determined according to the corresponding MOFs.

3. The method according to claim 1, characterized in that, In step (2), the COF is one of TpPa-1, TpHz, and TpBD, and the monomer ratio depends on the corresponding COF.

4. The method according to claim 1, characterized in that, In step (2), the mixed solvent is trimethylbenzene and 1,4-dioxane in a volume ratio of 1:4.

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