Mixed matrix membrane material for directly capturing CO2 from air as well as preparation method and application of mixed matrix membrane material

Abstract

The invention relates to the technical field of gas separation membranes, and provides a mixed matrix membrane material for directly capturing CO2 from air as well as a preparation method and application of the mixed matrix membrane material. An MOC metal organic cage is used as a filler, 6FDA-DAM is used as a polymer matrix, and a dense MOC-based mixed matrix membrane material is formed through a nanocage induced polymer chain shrinkage strategy. Under the condition of keeping a certain gas transmission flux, the defect of low selectivity of a traditional membrane material for separating CO2 from air is overcome, and the gas transmission permeability difference of the membrane material to CO2 and N2 is improved. Under the condition of keeping the structure of the metal organic cage unchanged, the fluorine element sites of the metal organic cage are added, and the CO2 transmission performance of the membrane material is enhanced by using the strong affinity of the fluorine element sites to CO2, so that the membrane material can directly capture CO2 in air.

Description

Technical Field

[0001] The present invention belongs to the technical field of gas separation membranes, and in particular relates to a mixed matrix membrane material for direct air capture of CO2, and a preparation method and application thereof. Background Art

[0002] The combustion of fossil fuels has accelerated carbon dioxide (CO2) emissions, posing a major challenge to human well-being and global ecosystems. Reducing atmospheric CO2 concentrations is crucial, and CO2 capture is one of the most viable technologies. Direct air capture (DAC) has attracted widespread attention as a carbon capture technology with the potential to achieve negative CO2 emissions. A key challenge in utilizing this technology is capturing CO2 at a concentration of just 400 ppm from nitrogen in the air (the main gas, which accounts for approximately 78%). Traditional polymer membrane materials, due to their large molecular chain spacing and insufficient CO2 affinity, generally suffer from poor CO2 / N2 selectivity and low permeation flux at low concentrations, making them difficult to meet practical application requirements.

[0003] Metal-organic cages (MOCs) are a specialized subset of supramolecular cages, formed by the coordinated self-assembly of metal ions or metal clusters with multidentate organic bridging linkers. As an emerging class of porous materials, MOCs boast a rich array of modifiable functional groups and excellent solvent processability. However, their application in membrane materials still faces several challenges: limited compatibility with polymer matrices and the tendency for conventional MOCs to aggregate when mixed with polymers, leading to increased defects within the membrane and decreased gas selectivity. Furthermore, conventional MOCs lack specific CO adsorption sites, and their lack of strong affinity groups for CO makes it difficult to efficiently capture target molecules at low concentrations, thus compromising CO separation and capture efficiency. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the present invention provides a mixed matrix membrane material for direct air capture of CO2 and a preparation method and application thereof, which aims to solve the problems mentioned in the background technology.

[0005] This paper uses zirconium (Zr)-based metal-organic cages (MOCs), known for their excellent solvent processability and chemical stability, as a mixed matrix membrane filler, and a 6FDA-DAM polymer as the matrix. A dense MOC-based mixed matrix membrane is formed by nanocage-induced polymer chain contraction. By adjusting the MOC doping level, a direct air capture CO2 mixed matrix membrane material is prepared.

[0006] The present invention provides a method for preparing a mixed matrix membrane material for direct air capture of CO2, comprising the following steps: Step S1: 4,4'-(hexafluoroisopropylene) diphthalic anhydride, 2,4,6-trimethyl-1,3-phenylenediamine, N,N-dimethylformamide, acetic anhydride and triethylamine were cooled and stirred under an inert atmosphere, and then purified in methanol and heated at 80 o C under vacuum drying for 10-12 hours to obtain 6FDA-DAM polymer; Step S2: reacting 2,3,5,6-tetrafluoroterephthalic acid and zirconocene dichloride with N,N-dimethylformamide solvent or N,N-dimethylacetamide solvent. After the reaction is completed, the reaction product is washed, dried, and baked to obtain a MOC metal organic cage; Step S3: 6FDA-DAM polymer, MOC metal organic cage and N,N-dimethylformamide are mixed and dissolved, and then stirred for 1-2 days to obtain a casting liquid, and the casting liquid is dropped into a circular mold made of polytetrafluoroethylene, and then subjected to a constant temperature drying treatment to obtain a molded mixed matrix membrane material, and then the molded mixed matrix membrane material is peeled off and vacuum activated.

[0007] Furthermore, in step S1, 4,4'-(hexafluoroisopropylene) diphthalic anhydride, 2,4,6-trimethyl-1,3-phenylenediamine, and N,N-dimethylformamide are sequentially added to a three-necked flask and mixed evenly, and argon or nitrogen is introduced for protection. o C under magnetic stirring for 24 hours to obtain a preliminary reaction solution.

[0008] Furthermore, in step S1, the molar ratio of 4,4'-(hexafluoroisopropylene) diphthalic anhydride, 2,4,6-trimethyl-1,3-phenylenediamine, acetic anhydride and triethylamine is 1:1:1:1; acetic anhydride and triethylamine are respectively mixed with N,N-dimethylformamide to prepare solutions with the same concentration ratio, and then added to the preliminary reaction solution. After reacting for 24 hours, a crude product is obtained. Finally, the crude product is immersed in methanol for purification, and then 80 o C for 10-12 hours to obtain 6FDA-DAM polymer.

[0009] Furthermore, in step S2, 2,3,5,6-tetrafluoroterephthalic acid and dichlorozirconocene are added to N,N-dimethylformamide solvent or N,N-dimethylacetamide solvent at a molar mass ratio of 2:1, and a certain amount of water is added, and a synthesis reaction is carried out using a microwave synthesis method or a solvent thermal synthesis method, and the synthesis reaction temperature is 60-70 o C, a white zirconium-based metal organic cage was obtained.

[0010] Furthermore, the white zirconium-based metal organic cage is washed and dried, and then added to small bottles containing N,N-dimethylformamide and iodomethane respectively, sealed, and stirred at room temperature until clarified to obtain a clear light yellow solution, which is then subjected to reduced pressure distillation to obtain a light yellow powder, and then washed and dried to obtain a light yellow zirconium-based metal organic cage powder.

[0011] Furthermore, in step S3, a certain amount of light yellow zirconium-based metal organic cage powder is weighed and added to a vial containing N,N-dimethylformamide solvent. After ultrasonic treatment for 0.5-1 hour, a uniformly mixed light yellow clear solution is obtained. Then, a certain amount of 6FDA-DAM polymer is added and stirred for 1-2 days to obtain a casting solution.

[0012] Furthermore, the casting solution is ultrasonically treated for ≥30 min, then dripped into a circular mold made of polytetrafluoroethylene, and then heated for 60-100 min. o C constant temperature drying process, after obtaining the formed mixed matrix membrane material, the formed mixed matrix membrane material was peeled off and o C was vacuum activated for 10-12 hours.

[0013] In a second aspect, the present invention provides a method for preparing a mixed matrix membrane material for direct air capture of CO2 and a direct air capture of CO2 mixed matrix membrane material prepared therefrom.

[0014] In a third aspect, the present invention provides an application of a mixed matrix membrane material for direct air capture of CO2, which is used for direct air capture of 400 ppm CO2.

[0015] Furthermore, 10 wt% 4F-Zr-I / 6FDA-DAM mixed matrix membrane material was applied to direct air capture of 400 ppm concentration of CO2.

[0016] The present invention has the following beneficial effects: (1) By using a nanocage-induced polymer chain contraction strategy, the spacing between polymer molecular chains is reduced, thereby increasing the permeability difference between CO2 and N2, which enables the polymer matrix of the membrane material to have the ability to directly capture CO2 from air. (2) By introducing zirconium (Zr)-based metal organic cages (iodine ions), more metal organic cages can be incorporated into the casting solution and membrane material, thereby increasing the density of the nanocage framework in the membrane material. (3) By introducing perfluorinated element sites on the zirconium (Zr)-based metal organic cages (iodine ions), the strong affinity of the fluorinated element sites for CO2 is utilized to enhance the transmission flux of the membrane material for CO2 and improve the selectivity of the membrane material for CO2. (4) The prepared perfluorinated MOC-based mixed matrix membrane material was applied to direct air capture of CO2 for the first time, showing strong gas capture and separation performance. The pale yellow zirconium (Zr)-based metal organic cage (iodide ion) has the characteristics of inducing polymer molecular chain contraction, strong solvent processability, and stable chemical properties. These characteristics create a foundation for direct air capture of CO2; the perfluorinated metal organic cage (4F-Zr-I) not only causes the polymer chain to contract, but the fluorine element sites on its nanocage structure have a strong affinity for CO2, thereby allowing the membrane material to maintain a high permeability for CO2 gas transmission while enhancing the permeability difference of the membrane material to CO2 / N2. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] A more complete understanding of exemplary embodiments of the present invention may be obtained by referring to the following drawings: Figure 1 Schematic diagram of gas separation test of mixed matrix membrane material according to an embodiment of the present invention.

[0018] Figure 2 1 is a gas separation test performance curve of the mixed matrix membrane material in an embodiment of the present invention. DETAILED DESCRIPTION

[0019] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs; the terms used herein are only for the purpose of describing specific embodiments rather than limiting the present invention.

[0021] An embodiment of the present invention provides a method for preparing a mixed matrix membrane material for capturing CO2 from air, comprising the following steps: Step S1: 4,4'-(hexafluoroisopropylene) diphthalic anhydride, 2,4,6-trimethyl-1,3-phenylenediamine, N,N-dimethylformamide, acetic anhydride and triethylamine were cooled and stirred under an inert atmosphere, and then purified in methanol and heated at 80 o C under vacuum drying for 10-12 hours to obtain 6FDA-DAM polymer; Step S2: reacting 2,3,5,6-tetrafluoroterephthalic acid and zirconocene dichloride with N,N-dimethylformamide solvent or N,N-dimethylacetamide solvent. After the reaction is completed, the reaction product is washed, dried, and baked to obtain a MOC metal organic cage; Step S3: 6FDA-DAM polymer, MOC metal organic cage and N,N-dimethylformamide are mixed and dissolved, and then stirred for 1-2 days to obtain a casting liquid, and the casting liquid is dropped into a circular mold made of polytetrafluoroethylene, and then subjected to a constant temperature drying treatment to obtain a molded mixed matrix membrane material, and then the molded mixed matrix membrane material is peeled off and vacuum activated.

[0022] In some embodiments, in step S1, 4,4'-(hexafluoroisopropylene) diphthalic anhydride, 2,4,6-trimethyl-1,3-phenylenediamine, and N,N-dimethylformamide are sequentially added to a three-necked flask and mixed evenly, and argon or nitrogen is introduced for protection. o C under magnetic stirring for 24 hours to obtain a preliminary reaction solution.

[0023] In some embodiments, in step S1, the molar ratio of 4,4'-(hexafluoroisopropylene) diphthalic anhydride, 2,4,6-trimethyl-1,3-phenylenediamine, acetic anhydride and triethylamine is 1:1:1:1; acetic anhydride and triethylamine are respectively mixed with N,N-dimethylformamide to prepare solutions with the same concentration ratio, and then added to the preliminary reaction solution. After reacting for 24 hours, a crude product is obtained, and finally the crude product is immersed in methanol for purification, and then 80 o C for 10-12 hours to obtain 6FDA-DAM polymer.

[0024] In some embodiments, in step S2, 2,3,5,6-tetrafluoroterephthalic acid and dichlorozirconocene are added to N,N-dimethylformamide solvent or N,N-dimethylacetamide solvent at a molar mass ratio of 2:1, and a certain amount of water is added, and a synthesis reaction is carried out using a microwave synthesis method or a solvent thermal synthesis method, and the synthesis reaction temperature is 60-70 o C, a white zirconium-based metal organic cage was obtained.

[0025] In some embodiments, the white zirconium-based metal organic cage is washed and dried, and then added to small bottles containing N,N-dimethylformamide and iodomethane, respectively, and sealed. The solution is stirred at room temperature until it becomes clear to obtain a clear light yellow solution, which is then subjected to reduced pressure distillation to obtain a light yellow powder. The solution is then washed and dried to obtain a light yellow zirconium-based metal organic cage powder.

[0026] In some embodiments, in step S3, a certain amount of light yellow zirconium-based metal organic cage powder is weighed and added to a vial containing N,N-dimethylformamide solvent. After ultrasonic treatment for 0.5-1 hour, a uniformly mixed light yellow clear solution is obtained. Then, a certain amount of 6FDA-DAM polymer is added and stirred for 1-2 days to obtain a casting solution.

[0027] In some embodiments, the casting solution is ultrasonically treated for ≥30 min, then dripped into a circular mold made of polytetrafluoroethylene, and then subjected to 60-100 o C constant temperature drying treatment to obtain a formed mixed matrix membrane material, the formed mixed matrix membrane material is peeled off and vacuum activation treatment is performed at 60° C. for 10-12 hours.

[0028] In some embodiments, the present invention provides a method for preparing a mixed matrix membrane material for direct air capture of CO2 and a direct air capture of CO2 mixed matrix membrane material prepared therefrom.

[0029] In some embodiments, the present invention provides an application of a direct air capture CO2 mixed matrix membrane material for direct air capture of 400 ppm CO2.

[0030] In some embodiments, 10 wt % 4F-Zr-I / 6FDA-DAM mixed matrix membrane material is applied to direct air capture of 400 ppm concentration of CO2.

[0031] Example 1: (1) Preparation of 6FDA-DAM polymer: 4,4'-(hexafluoroisopropylene) diphthalic anhydride, 2,4,6-trimethyl-1,3-phenylenediamine, and N,N-dimethylformamide were added to a three-necked flask in sequence and mixed evenly. Argon or nitrogen was introduced for protection. o C for 24 hours to obtain a preliminary reaction solution; acetic anhydride and triethylamine were respectively mixed with N,N-dimethylformamide to prepare a solution with a concentration ratio of 1:1, and then added to the preliminary reaction solution, wherein the molar ratio of 4,4'-(hexafluoroisopropylene) diphthalic anhydride, 2,4,6-trimethyl-1,3-phenylenediamine, acetic anhydride and triethylamine was 1:1:1:1; after reacting for 24 hours, a crude product was obtained, and finally the crude product was immersed in methanol for purification, and then 80 oC for 12 hours to obtain 6FDA-DAM polymer.

[0032] (2) Preparation of MOC metal organic cage: In step S2, 2,3,5,6-tetrafluoroterephthalic acid and dichlorozirconocene were added to 5 mL of N,N-dimethylformamide solvent or N,N-dimethylacetamide solvent at a molar mass ratio of 2:1, and a certain amount of water was added. The synthesis reaction was carried out using a microwave synthesis method at a reaction temperature of 70 o C, to obtain a white zirconium-based metal organic cage 4F-Zr-Cl; 4F-Zr-Cl was washed and dried, and then 100 mg was weighed and added to a vial containing 1 mL of N,N-dimethylformamide and 20 μL of iodomethane, sealed, and stirred at room temperature until clear to obtain a clear light yellow solution, which was then distilled under reduced pressure to obtain a light yellow powder, which was then washed and dried to obtain a light yellow zirconium-based metal organic cage powder 4F-Zr-I.

[0033] (3) Preparation of mixed matrix membrane material: Weigh a certain amount of light yellow zirconium-based metal organic cage powder 4F-Zr-I and add it to a vial containing 3 mL of N,N-dimethylformamide solvent. After ultrasonic treatment for 1 hour, a uniform light yellow clear solution is obtained. Then, 118 mg of 6FDA-DAM polymer is added and stirred for 2 days to obtain a casting solution. The casting solution is ultrasonically treated for 30 minutes and then dropped into a round mold made of polytetrafluoroethylene. Then, the solution is ultrasonically treated for 100 minutes. o After a constant temperature drying treatment at C to obtain a formed mixed matrix membrane material, the formed mixed matrix membrane material is peeled off and subjected to a vacuum activation treatment at 60° C. for 12 hours.

[0034] The calculation formula for the doping amount of metal organic cage filler is as follows: .

[0035] Comparative Example 1: (1) Preparation of 6FDA-DAM polymer: 4,4'-(hexafluoroisopropylene) diphthalic anhydride, 2,4,6-trimethyl-1,3-phenylenediamine, and N,N-dimethylformamide were added to a three-necked flask in sequence and mixed evenly. Argon or nitrogen was introduced for protection. o C for 24 hours to obtain a preliminary reaction solution; acetic anhydride and triethylamine were respectively mixed with N,N-dimethylformamide to prepare a solution with a concentration ratio of 1:1, and then added to the preliminary reaction solution, wherein the molar ratio of 4,4'-(hexafluoroisopropylene) diphthalic anhydride, 2,4,6-trimethyl-1,3-phenylenediamine, acetic anhydride and triethylamine was 1:1:1:1; after reacting for 24 hours, a crude product was obtained, and finally the crude product was immersed in methanol for purification, and then 80 oC for 12 hours to obtain 6FDA-DAM polymer.

[0036] (2) Preparation of MOC metal organic cage: In step S2, terephthalic acid and zirconocene dichloride were added to 5 mL of N, N-dimethylformamide solvent or N, N-dimethylacetamide solvent at a molar mass ratio of 2:1, and a certain amount of water was added. The synthesis reaction was carried out using a microwave synthesis method at a reaction temperature of 70 o C, to obtain 4H-Zr-Cl; 4H-Zr-Cl was washed and dried, and then 100 mg was weighed and added to a vial containing 1 mL of N,N-dimethylformamide and 20 μL of iodomethane, sealed, and stirred at room temperature until clear to obtain a clear light yellow solution, which was then distilled under reduced pressure to obtain a light yellow powder. After further washing and drying, four light yellow zirconium-based metal organic cage powders were obtained, namely 4H-Zr-I.

[0037] (3) Preparation of mixed matrix membrane material: Weigh a certain amount of 4H-Zr-I and add it to a vial containing 3 mL of N,N-dimethylformamide solvent. After ultrasonic treatment for 1 hour, a uniform light yellow clear solution is obtained. Then, 118 mg of 6FDA-DAM polymer is added and stirred for 2 days to obtain a casting solution. The casting solution is ultrasonically treated for 30 minutes and then dropped into a circular mold made of polytetrafluoroethylene. Then, the solution is ultrasonically treated for 100 minutes. o After a constant temperature drying treatment at C to obtain a formed mixed matrix membrane material, the formed mixed matrix membrane material is peeled off and subjected to a vacuum activation treatment at 60° C. for 12 hours.

[0038] Comparative Example 2: (1) Preparation of 6FDA-DAM polymer: 4,4'-(hexafluoroisopropylene) diphthalic anhydride, 2,4,6-trimethyl-1,3-phenylenediamine, and N,N-dimethylformamide were added to a three-necked flask in sequence and mixed evenly. Argon or nitrogen was introduced for protection. o C for 24 hours to obtain a preliminary reaction solution; acetic anhydride and triethylamine were respectively mixed with N,N-dimethylformamide to prepare a solution with a concentration ratio of 1:1, and then added to the preliminary reaction solution, wherein the molar ratio of 4,4'-(hexafluoroisopropylene) diphthalic anhydride, 2,4,6-trimethyl-1,3-phenylenediamine, acetic anhydride and triethylamine was 1:1:1:1; after reacting for 24 hours, a crude product was obtained, and finally the crude product was immersed in methanol for purification, and then 80 o C for 12 hours to obtain 6FDA-DAM polymer.

[0039] (2) Preparation of MOC metal organic cage: In step S2, dicarboxyfluorobenzene and dichlorozirconocene were added to 5 mL of N,N-dimethylformamide solvent or N,N-dimethylacetamide solvent at a molar mass ratio of 2:1, and a certain amount of water was added. The synthesis reaction was carried out using a microwave synthesis method at a reaction temperature of 70 o C to obtain F-Zr-Cl; F-Zr-Cl was washed and dried, and 100 mg was weighed and added to a vial containing 1 mL of N,N-dimethylformamide and 20 μL of iodomethane, sealed, and stirred at room temperature until clear to obtain a clear light yellow solution, which was then distilled under reduced pressure to obtain a light yellow powder, which was then washed and dried to obtain F-Zr-I.

[0040] (3) Preparation of mixed matrix membrane material: Weigh a certain amount of F-Zr-I and add it to a vial containing 3 mL of N,N-dimethylformamide solvent. After ultrasonic treatment for 1 hour, a uniform light yellow clear solution is obtained. Then, 118 mg of 6FDA-DAM polymer is added and stirred for 2 days to obtain a casting solution. The casting solution is ultrasonically treated for 30 minutes and then dropped into a circular mold made of polytetrafluoroethylene. Then, the solution is ultrasonically treated for 100 minutes. o After a constant temperature drying treatment at C to obtain a formed mixed matrix membrane material, the formed mixed matrix membrane material is peeled off and subjected to a vacuum activation treatment at 60° C. for 12 hours.

[0041] Comparative Example 3: (1) Preparation of 6FDA-DAM polymer: 4,4'-(hexafluoroisopropylene) diphthalic anhydride, 2,4,6-trimethyl-1,3-phenylenediamine, and N,N-dimethylformamide were added to a three-necked flask in sequence and mixed evenly. Argon or nitrogen was introduced for protection. o C for 24 hours to obtain a preliminary reaction solution; acetic anhydride and triethylamine were respectively mixed with N,N-dimethylformamide to prepare a solution with a concentration ratio of 1:1, and then added to the preliminary reaction solution, wherein the molar ratio of 4,4'-(hexafluoroisopropylene) diphthalic anhydride, 2,4,6-trimethyl-1,3-phenylenediamine, acetic anhydride and triethylamine was 1:1:1:1; after reacting for 24 hours, a crude product was obtained, and finally the crude product was immersed in methanol for purification, and then 80 o C for 12 hours to obtain 6FDA-DAM polymer.

[0042] (2) Preparation of MOC metal organic cage: In step S2, 2,5-difluoroterephthalic acid and dichlorozirconocene were added to 5 mL of N,N-dimethylformamide solvent or N,N-dimethylacetamide solvent at a molar mass ratio of 2:1, and a certain amount of water was added. The synthesis reaction was carried out using a microwave synthesis method at a reaction temperature of 70o C to obtain 2F-Zr-Cl; 2F-Zr-Cl was washed and dried, and 100 mg was weighed and added to a vial containing 1 mL of N,N-dimethylformamide and 20 μL of iodomethane, sealed, and stirred at room temperature until clear to obtain a clear light yellow solution, which was then distilled under reduced pressure to obtain a light yellow powder, which was then washed and dried to obtain 2F-Zr-I.

[0043] (3) Preparation of mixed matrix membrane material: Weigh a certain amount of 2F-Zr-I and add it to a vial containing 3 mL of N,N-dimethylformamide solvent. After ultrasonic treatment for 1 hour, a uniform light yellow clear solution is obtained. Then, 118 mg of 6FDA-DAM polymer is added and stirred for 2 days to obtain a casting solution. The casting solution is ultrasonically treated for 30 minutes and then dropped into a circular mold made of polytetrafluoroethylene. Then, the solution is ultrasonically treated for 100 minutes. o After a constant temperature drying treatment at C to obtain a formed mixed matrix membrane material, the formed mixed matrix membrane material is peeled off and subjected to a vacuum activation treatment at 60° C. for 12 hours.

[0044] Direct air capture CO2 gas separation performance test: (1) Test equipment and test conditions In the test, compressed air (CO2 concentration is 400ppm), He gas, gas mass flow meter, self-made metal membrane cell, gas chromatograph and connected computer are used. The gas separation test diagram is shown in the figure. Figure 1 shown.

[0045] In the test, mixed matrix membrane materials with different metal-organic cage filler concentrations and different metal-organic cage types were tested at 1 bar and 400 ppm CO2 concentration.

[0046] In the tests, the best performing mixed matrix membrane material, 10wt% 4F-Zr-I / 6FDA-DAM, was tested at different pressures.

[0047] The 0~15wt% 4F-Zr-I / 6FDA-DAM (mixed matrix membrane material) obtained in Example 1 was tested for 400ppm CO2, 1bar gas separation performance. The test results are as follows: Figure 2 The specific results are shown in Table 1: Table 1 Gas separation performance test of 4F-Zr-I / 6FDA-DAM

[0048] It can be seen that at a CO2 concentration of 400ppm, as the 4F-Zr-I doping level increases, the CO2 / N2 selectivity shows an upward trend, the CO2 permeability maintains a high gas transmission performance, and the N2 permeability gradually decreases. This shows that the nanocage induces polymer chain contraction, reducing the average free volume inside the membrane material, thereby enhancing the CO2 / N2 selectivity at a CO2 concentration of 400ppm. When the 4F-Zr-I doping level is 15wt%, its N2 permeability increases and the gas separation selectivity decreases. This is because the filler agglomerates inside the membrane material and produces non-selective defects, which reduces the CO2 / N2 gas separation performance.

[0049] Gas separation tests were performed on Example 1 and Comparative Examples 1-3 (10 wt%) at a CO2 concentration of 400 ppm. The specific results are shown in Table 2: Table 2 Gas separation test of membrane materials of Example 1 and Comparative Examples 1-3

[0050] It can be seen that at a CO2 concentration of 400 ppm, the introduction of the metal-organic cage structure reduces the gas permeability, and with the increase of fluorine elements, the CO2 permeability of the membrane material increases, which makes the membrane material have high CO2 / N2 selectivity and maintains a stable CO2 permeability.

[0051] The 10 wt% 4F-Zr-I / 6FDA-DAM mixed matrix membrane material obtained in Example 1 was subjected to gas separation tests at different pressures and a CO2 concentration of 400 ppm. The specific results are shown in Table 3: Table 3 Gas separation test of the mixed matrix membrane material of Example 1

[0052] It can be seen that at a CO2 concentration of 400 ppm, the 10 wt% 4F-Zr-I / 6FDA-DAM mixed matrix membrane material can have stable gas separation performance within a certain pressure range, which provides new ideas for the actual needs of different application scenarios in industry.

[0053] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a mixed matrix membrane material for direct air capture of CO2, characterized by: The following steps are involved: Step S1: 4,4'-(hexafluoroisopropylene) diphthalic anhydride, 2,4,6-trimethyl-1,3-phenylenediamine, N,N-dimethylformamide, acetic anhydride and triethylamine were cooled and stirred under an inert atmosphere, and then purified in methanol and heated at 80 o C under vacuum drying for 10-12 hours to obtain 6FDA-DAM polymer; Step S2: reacting 2,3,5,6-tetrafluoroterephthalic acid and zirconocene dichloride with N,N-dimethylformamide solvent or N,N-dimethylacetamide solvent. After the reaction is completed, the reaction product is washed, dried, and baked to obtain a MOC metal organic cage; Step S3: 6FDA-DAM polymer, MOC metal organic cage and N,N-dimethylformamide are mixed and dissolved, and then stirred for 1-2 days to obtain a casting liquid, and the casting liquid is dropped into a circular mold made of polytetrafluoroethylene, and then subjected to a constant temperature drying treatment to obtain a molded mixed matrix membrane material, and then the molded mixed matrix membrane material is peeled off and vacuum activated.

2. The preparation method according to claim 1, wherein: In step S1, 4,4'-(hexafluoroisopropylene) diphthalic anhydride, 2,4,6-trimethyl-1,3-phenylenediamine, and N,N-dimethylformamide are sequentially added to a three-necked flask and mixed evenly, and argon or nitrogen is introduced for protection. o C under magnetic stirring for 24 hours to obtain a preliminary reaction solution.

3. The preparation method according to claim 1, wherein: In step S1, the molar ratio of 4,4'-(hexafluoroisopropylene) diphthalic anhydride, 2,4,6-trimethyl-1,3-phenylenediamine, acetic anhydride and triethylamine is 1:1:1:1; acetic anhydride and triethylamine are respectively mixed with N,N-dimethylformamide to prepare solutions with the same concentration ratio, and then added to the preliminary reaction solution. After reacting for 24 hours, a crude product is obtained. Finally, the crude product is immersed in methanol for purification, and then 80 o C for 10-12 hours to obtain 6FDA-DAM polymer.

4. The preparation method according to claim 1, wherein: In step S2, 2,3,5,6-tetrafluoroterephthalic acid and dichlorozirconocene are added to N,N-dimethylformamide solvent or N,N-dimethylacetamide solvent at a molar mass ratio of 2:1, and a certain amount of water is added, and a synthesis reaction is carried out using a microwave synthesis method or a solvent thermal synthesis method. The synthesis reaction temperature is 60-70 o C, a white zirconium-based metal organic cage was obtained.

5. The preparation method according to claim 4, wherein: The white zirconium-based metal organic cage was washed and dried, and then added to small bottles containing N,N-dimethylformamide and iodomethane respectively, sealed, and stirred at room temperature until clarified to obtain a clear light yellow solution, which was then subjected to reduced pressure distillation to obtain a light yellow powder. After further washing and drying, a light yellow zirconium-based metal organic cage powder was obtained.

6. The preparation method according to claim 1, wherein: In step S3, a certain amount of light yellow zirconium-based metal organic cage powder is weighed and added to a vial containing N,N-dimethylformamide solvent. After ultrasonic treatment for 0.5-1 hour, a uniformly mixed light yellow clear solution is obtained. Then, a certain amount of 6FDA-DAM polymer is added and stirred for 1-2 days to obtain a casting solution.

7. The preparation method according to claim 6, wherein: The casting solution was ultrasonically treated for ≥30 min, then dropped into a circular mold made of polytetrafluoroethylene, and then o C constant temperature drying process, after obtaining the formed mixed matrix membrane material, the formed mixed matrix membrane material was peeled off and o C was vacuum activated for 10-12 hours.

8. A mixed matrix membrane material for direct air capture of CO2 obtained by the preparation method according to any one of claims 1 to 7.

9. Application of mixed matrix membrane materials for direct air capture of CO2, characterized by: Direct air capture of 400ppm CO2.

10. The use according to claim 6, characterized in that: 10wt% 4F-Zr-I / 6FDA-DAM mixed matrix membrane material was applied to direct air capture of 400ppm concentration CO2.

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