A high-flexibility MOF composite film and a preparation method and application thereof

Abstract

The present application relates to a kind of high flexibility MOF composite film and its preparation method and application, the high flexibility MOF composite film includes flexible polymer substrate layer and MOF film layer above the flexible polymer substrate layer;The flexible polymer substrate layer and the MOF film layer are connected between AgNWs@MOF seed layer deposited on the flexible polymer substrate layer;The AgNWs@MOF is the core-shell structure of MOF wrapping one-dimensional silver nanowire, and the AgNWs@MOF seed layer is the fiber mesh structure formed by the core-shell structure.This application uses one-dimensional silver nanowire as MOF seed carrier, and by vacuum assisted self-assembly, secondary growth is assisted with functional polymer spin-coating strategy, and high flexibility MOF composite film is prepared, effectively improves the interface bonding force of MOF film and polymer substrate, and enhances the stability of membrane structure.Meanwhile, secondary growth method improves the crystallinity of MOF film, reduces intercrystalline defect, so as to improve the selectivity of film.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of gas separation, in particular to a high-flexibility MOF composite membrane and a preparation method and application thereof. BACKGROUND

[0002] Carbon capture, utilization and storage (CCUS) technology is one of the key technologies for reducing carbon dioxide emissions, and efficient carbon capture technology is the premise and foundation for reducing carbon emissions and further conversion and utilization of CO2. The current mature CO2 capture technology in industrial application mainly includes physical adsorption, chemical absorption and membrane separation technology. However, the physical adsorption technology needs to regenerate the adsorbent, and the adsorption capacity and selectivity are low; and the chemical absorption technology has problems such as high energy consumption and large equipment corrosion. Compared with the above traditional technologies, the new type of membrane separation technology has the advantages of low energy consumption, small occupation area, and being suitable for various processing scales, etc., and has great application potential in the field of CO2 separation. However, the existing membrane materials generally have the trade-off effect that permeability and selectivity cannot be compatible, which limits their industrial application. Therefore, it is urgent to develop high-performance CO2 separation membrane materials to improve the market competitiveness of membrane carbon capture.

[0003] Metal-organic framework (MOF) materials have the characteristics of high porosity, adjustable pore size, and functionalized topological structure, and are considered to be one of the most promising materials for preparing high-performance CO2 separation membranes. Hou et al. prepared ZIF-7-8 membranes on an anodic aluminum oxide-based membrane by a fast current-driven synthesis method (FCDS), which has excellent separation performance for CO2 / N2 binary mixture (Angew. Chem. Int. Ed. 2019, 58, 327-331). Zhang et al. prepared highly oriented ZIF-8 membranes on an anodic aluminum oxide-based membrane by a secondary growth method, which has good CO2 / N2 separation performance (J. Membr. Sci. 2022, 641, 119915). Patent CN202110544809.0 discloses a method for preparing MOF membranes on an inorganic substrate by crystal-assisted supercritical fluid technology and its application in gas separation.

[0004] The above researches have made positive contributions to the preparation and application development of MOF membranes for CO2 / N2 separation. However, most of these MOF membranes are prepared on rigid inorganic substrates, which have technical bottlenecks such as difficulty in large-scale preparation of membranes and poor flexibility in processing and manufacturing of membrane modules. Polymeric microporous membranes have the advantages of high mechanical strength and easy expansion, and have been widely used as substrates for pervaporation, nanofiltration and reverse osmosis membrane materials. However, due to the significant differences in physical and chemical properties between the two, it is still a great challenge to prepare ultra-thin and defect-free MOF membranes with continuous transmission channels (high permeability) and high symbiosis (high selectivity) on flexible polymer substrates. Therefore, it is of great research significance and application value to develop a simple and effective method for preparing high-flexibility MOF membranes. SUMMARY

[0005] In order to solve the defects and deficiencies of the prior art, the present application develops a high-flexibility MOF composite membrane and a preparation method thereof for efficient separation of CO2 / N2.

[0006] The present application is realized by the following solutions:

[0007] A high-flexibility MOF composite membrane comprises:

[0008] a flexible polymer substrate layer and a MOF membrane layer located above the flexible polymer substrate layer;

[0009] The flexible polymer substrate layer and the MOF membrane layer are connected through a AgNWs@MOF seed layer deposited on the flexible polymer substrate layer; the AgNWs@MOF is a core-shell structure formed by wrapping one-dimensional silver nanowires with MOF, and the AgNWs@MOF seed layer is a fiber mesh structure formed by the core-shell structure.

[0010] Further, the relationship between the deposition amount of the AgNWs@MOF seed layer and the area of the flexible polymer substrate layer is 0.1-0.6 g / m 2 .

[0011] Specifically, the above-mentioned area should be understood as the surface area where the deposition behavior occurs.

[0012] Further, the flexible polymer substrate layer is a polymer microporous base membrane, specifically comprising one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), polyethylene (PE) or polypropylene (PP).

[0013] Preferably, the polymer microporous base membrane is in the shape of a flat plate, a tube or a hollow fiber.

[0014] Further, the MOF comprises ZIF-8, ZIF-67, ZIF-71, ZIF-7 or ZIF-62.

[0015] Further, the MOF membrane layer further comprises a functional polymer layer above it, and the functional polymer is one or more of Pebax1657, Pebax 2533, Pebax 4033, Pebax 5533.

[0016] The present application also provides a preparation method of a high-flexibility MOF composite membrane, comprising the following steps:

[0017] S1) mixing the one-dimensional silver nanowires, the metal ion solution of the MOF and the organic ligand solution of the MOF to prepare AgNWs@MOF;

[0018] S2) depositing the AgNWs@MOF on the flexible polymer substrate layer by a vacuum-assisted self-assembly method to form an AgNWs@MOF seed layer, to obtain a first composite film;

[0019] S3) placing the first composite film in a mixed solution of metal ions and organic ligands of the MOF, growing a MOF film layer on the AgNWs@MOF seed layer, to obtain the high-flexibility MOF composite film.

[0020] The application also provides another method for preparing a high-flexibility MOF composite film, characterized by comprising the following steps:

[0021] S1) mixing the one-dimensional silver nanowires, a metal ion solution of the MOF, and an organic ligand solution of the MOF to obtain AgNWs@MOF;

[0022] S2) depositing the AgNWs@MOF on the flexible polymer substrate layer by a vacuum-assisted self-assembly method to form an AgNWs@MOF seed layer, to obtain a first composite film;

[0023] S3) placing the first composite film in a mixed solution of metal ions and organic ligands of the MOF, growing a MOF film layer on the AgNWs@MOF seed layer, to obtain a second composite film;

[0024] S4) spin-coating a functional polymer on the MOF film layer of the second composite film, to obtain the high-flexibility MOF composite film.

[0025] Further, in step S1), the one-dimensional silver nanowires, the metal ion solution of the MOF, and the organic ligand solution of the MOF are mixed, and after the reaction is completed, the mixture is subjected to centrifugation, washing, and drying treatment to obtain AgNWs@MOF.

[0026] Further, the one-dimensional silver nanowires in step S1) are obtained by the following method:

[0027] The silver salt, polyvinylpyrrolidone, and halide are dissolved in a liquid polyhydroxy alcohol, and after being uniformly mixed, a suspension is obtained through a microwave solvent thermal synthesis reaction, and the suspension is subjected to centrifugation, washing, and drying to obtain the one-dimensional silver nanowires.

[0028] Specifically, the silver salt is selected from one or more of silver nitrate, silver sulfate, and silver chloride. The liquid polyhydroxy alcohol is selected from one or more of ethylene glycol, propylene glycol, glycerol, and polyethylene glycol, and is preferably ethylene glycol. The halide is selected from one or more of sodium chloride, potassium chloride, ammonium chloride, magnesium chloride, zinc chloride, iron chloride, copper chloride, sodium bromide, potassium bromide, copper bromide, sodium iodide, and potassium iodide.

[0029] Specifically, the molar ratio of the polyvinylpyrrolidone and the silver ions in the silver salt is 1:3-10; the molar ratio of the halogen ions in the halide and the silver ions in the silver salt is 1:1-200.

[0030] Specifically, the microwave solvent synthesis reaction time is 0.5-3h, the reaction temperature is 150-250℃, and the power is 800-1500W.

[0031] Further, the molar ratio of the metal ions and the organic ligand in step S1) is 1:1-10; the molar ratio of the metal ions and the organic ligand in the mixed solution in step S3) is 1:20-100.

[0032] Specifically, in step S1), the metal ion solution of the MOF and the organic ligand solution of the MOF are both methanol solvents; in step S3), the mixed solution is a water solvent.

[0033] Further, the metal ions and the organic ligand of the MOF in step S1) are the same as in step S3).

[0034] Specifically, in steps S1) and S3), the metal ion of the MOF uses a metal salt as a raw material, including any one or more of a nitrate salt of zinc, a chloride salt of zinc, an acetate salt of zinc, a nitrate salt of cobalt, a chloride salt of cobalt, and an acetate salt of cobalt.

[0035] Specifically, in steps S1) and S3), the organic ligand of the MOF includes one or more of imidazole, 2-methylimidazole, 2-vinylimidazole, benzimidazole, 4,5-dichloroimidazole, and imidazole-2-carboxaldehyde.

[0036] Preferably, in some embodiments, in step S1), the organic ligand of the MOF is dissolved in methanol, and then the AgNWs are added and ultrasonically dispersed to obtain a first mixed solution; a metal salt is dissolved in methanol to obtain a second mixed solution; the first mixed solution and the second mixed solution are quickly mixed and stirred to react for 0.1-2h at a reaction temperature of 20-60℃, and then centrifuged, washed, and dried to obtain AgNWs@MOF seed crystals.

[0037] Preferably, in step S3), a water solution of a metal salt and a water solution of an organic ligand are respectively prepared, and after being mixed uniformly, a mixed solution of the metal ions of the MOF and the organic ligand is obtained; the first composite film is placed in the mixed solution to grow a MOF film layer for a second time, and the reaction is carried out for 2-10h at a reaction temperature of 20-60℃. After the reaction is completed, the first composite film is fully immersed and washed with deionized water and methanol, and then dried to obtain the high-flexibility MOF composite film or the second composite film.

[0038] Preferably, the first composite film is vertically placed in the metal ion and organic ligand mixed solution of the MOF to grow the MOF film layer, which can prevent the MOF crystals generated in the solution from adhering to the first composite film, so as to avoid difficult cleaning in the later stage.

[0039] Preferably, the non-deposited surface of the first composite film away from the AgNWs@MOF seed layer is subjected to wall sticking or other treatment, so that the non-deposited surface will not grow the MOF film layer, preventing the MOF film layer grown on both sides from blocking the polymer microporous substrate channels and increasing the gas mass transfer resistance.

[0040] Preferably, in step S2), the AgNWs@MOF is dispersed in a methanol solution, and one-dimensional AgNWs@MOF is deposited on the flexible polymer substrate layer by vacuum-assisted self-assembly, and the first composite film is obtained after room temperature standing and drying.

[0041] Preferably, in step S4), the functional polymer is dissolved in ethanol to obtain a casting solution; preferably, the dissolution is carried out at 70-90℃; preferably, the mass fraction of the functional polymer is 3-10wt%.

[0042] Preferably, in step S4), the casting solution is spin-coated onto the MOF film layer of the second composite film. Preferably, the spin-coating rate is 200-2000rpm, and the spin-coating times are 1-5 times; preferably, after spin-coating, drying is carried out at 50-80℃ for 12-24h to obtain a high-flexibility MOF composite film.

[0043] The application also provides a use of the high-flexibility MOF composite film in CO2 / N2 gas separation.

[0044] Beneficial effects:

[0045] 1. The one-dimensional silver nanowire (AgNWs) is used as a MOF seed carrier, and a high-flexibility MOF composite film is prepared by vacuum-assisted self-assembly, secondary growth, and spin-coating of a functional polymer, which effectively improves the interfacial bonding force between the MOF film and the polymer substrate and enhances the stability of the film structure. At the same time, the secondary growth method improves the crystallinity of the MOF film and reduces the intercrystalline defects, thereby improving the selectivity of the film.

[0046] 2. The AgNWs@MOF in a fiber network arrangement is used as a seed, and a continuous transfer channel for the molecules to be separated is constructed in the MOF film by in-situ secondary growth to induce high symbiosis of the MOF, which reduces the diffusion resistance of the target molecules, strengthens the mass transfer process of the molecules in the film, and improves the selectivity and permeability of the film.

[0047] 3. By polymer spin-coating strategy, the intercrystalline defects of MOF are effectively repaired, the stability and mechanical strength of the MOF film are improved, the gas separation performance is further improved, and the difficulty of film amplification preparation is reduced.

[0048] 4. The application first uses one-dimensional silver nanowires as seed carriers to prepare a high-flexibility MOF composite film through secondary growth assisted by a polymer spin-coating strategy, thereby providing a high-performance film material for the field of gas separation. BRIEF DESCRIPTION OF DRAWINGS

[0049] Figure 1 SEM image of AgNWs obtained in step 1) in Example 3;

[0050] Figure 2 SEM image of AgNWs@ZIF-8 obtained in step 2) in Example 3;

[0051] Figure 3 SEM image of the surface of the ZIF-8 film in the second composite film obtained in step 4) in Example 3;

[0052] Figure 4 SEM image of the film cross section of the second composite film obtained in step 4) in Example 3;

[0053] Figure 5 SEM image of the surface of the Pebax-ZIF-8-AgNWs@ZIF-8-PAN composite film obtained in step 5) in Example 3;

[0054] Figure 6 CO2 / N2 separation performance comparison result graph of the Pebax-ZIF-8-AgNWs@ZIF-8-PAN composite film obtained in Examples 1-4;

[0055] Figure 7 CO2 / N2 separation performance comparison result graph of the Pebax-ZIF-8-AgNWs@ZIF-8-PAN composite film obtained in Example 3 and the film materials prepared in Comparative Examples 1-3;

[0056] Figure 8 Stress-strain curve graph of the PAN film and the Pebax-ZIF-8-AgNWs@ZIF-8-PAN composite film obtained in Examples 1-4;

[0057] Figure 9 Bending test and surface SEM image after bending of the Pebax-ZIF-8-AgNWs@ZIF-8-PAN composite film obtained in Example 3. DETAILED DESCRIPTION

[0058] The application will be further described in conjunction with the accompanying drawings and examples and comparative examples, but the scope of the application claimed is not limited to the following examples.

[0059] Example 1:

[0060] 1) A PVP ethylene glycol solution with a concentration of 0.47 g / mL was prepared in an amount of 30 mL, and then 0.06 mmol of sodium chloride was added to the solution, and after being fully dissolved, a solution 1 was obtained. Silver nitrate was dissolved in ethylene glycol to obtain a solution 2 with a concentration of 0.06 mol / L in an amount of 50 mL. The solution 1 was added dropwise to the solution 2, and after being stirred uniformly, the obtained mixture was transferred to a microwave reactor, and reacted at 160°C and a power of 1000 W for 1 h. The obtained suspension was centrifuged, washed with methanol, and dried to obtain the AgNWs.

[0061] 2) A dimethylimidazole methanol solution with a concentration of 0.5 mol / L was prepared in an amount of 20 mL, and then 20 mg of the AgNWs were added and ultrasonically dispersed to obtain a solution 3; a zinc nitrate hexahydrate methanol solution with a concentration of 0.1 mol / L was prepared in an amount of 12 mL to obtain a solution 4. The solution 3 and the solution 4 were mixed and stirred to react for 1 h, and then washed with methanol and dried to obtain the AgNWs@ZIF-8.

[0062] 3) The AgNWs@ZIF-8 was dispersed in a methanol solution, and a flat-plate type polyacrylonitrile polymer film (PAN film) was used as a substrate, and one-dimensional AgNWs@ZIF-8 was deposited on one face of the PAN film by a vacuum-assisted self-assembly method, and the deposition amount was 0.1 g / m 2 , and the first composite film was obtained after being placed at room temperature and dried.

[0063] 4) A zinc nitrate hexahydrate aqueous solution with a concentration of 0.018 mol / L was prepared in an amount of 200 mL, and a dimethylimidazole aqueous solution with a concentration of 1.28 mol / L was prepared in an amount of 200 mL, and then mixed uniformly. The non-deposited face of the first composite film, which was away from the AgNWs@MOF seed layer, was attached to the wall, and was vertically placed in the mixed solution, and reacted at 25°C for 6 h to prepare a ZIF-8 layer by secondary growth, and then the composite film was fully immersed and washed with deionized water and methanol, and then placed at room temperature and dried to obtain a second composite film.

[0064] 5) A Pebax 1657 ethanol solution with a mass fraction of 5 wt% was prepared in an amount of 50 g, and was spin-coated on the surface of the second composite film at a rotation speed of 600 rpm for 3 times, and the prepared film was dried at 60°C for 12 h to obtain a high-flexibility Pebax-ZIF-8-AgNWs@ZIF-8-PAN composite film.

[0065] Example 2:

[0066] The difference between Example 1 and Example 2 is only that in step 3), the deposition amount of AgNWs@ZIF-8 is 0.2 g / m 2 .

[0067] Example 3:

[0068] The difference between Example 1 and Example 2 is only that in step 3), the deposition amount of AgNWs@ZIF-8 is 0.4 g / m 2 .

[0069] Example 4:

[0070] The difference between Example 1 and Example 2 is only that in step 3), the deposition amount of AgNWs@ZIF-8 is 0.6 g / m 2 .

[0071] Comparative Example 1:

[0072] The difference between Example 1 and Example 2 is only that in step 3), the deposition amount of AgNWs@ZIF-8 is 0.6 g / m

[0073] Comparative Example 2:

[0074] The difference between Example 1 and Example 2 is only that in step 3), the deposition amount of AgNWs@ZIF-8 is 0.6 g / m

[0075] Comparative Example 3:

[0076] The difference between Example 1 and Example 2 is only that in step 3), the deposition amount of AgNWs@ZIF-8 is 0.6 g / m

[0077] Performance Test:

[0078] The film materials prepared in Examples 1-4 and Comparative Examples 1-3 were tested for CO2 / N2 separation performance by a gas separation device, and the results are shown in Table 1, and the specific test standards are as follows: Figure 6

[0079] The test area is 25 cm 2 , the temperature is 25℃, the test gas is a mixed gas of CO2 / N2 (15:85), the pressure is kept at 0.1 MPa, Ar is the carrier gas, and the permeability (P) and separation factor (a) are calculated by the following formula:

[0080]

[0081] wherein, N​i is the permeation rate of component i (mol / s), ΔP i is the transmembrane partial pressure (Pa). A is the effective area of ​​the membrane (m 2 ). X and Y are the mole fractions of components i and j in the feed and permeate, respectively.

[0082] Depend on Figure 6 It can be seen that in Examples 1-4, high-performance flexible MOF composite membranes were obtained by secondary growth using one-dimensional AgNWs@ZIF-8 as seeds, and the addition of one-dimensional AgNWs@ZIF-8 seeds in step 3) greatly contributed to the improvement of the separation performance of the membrane. By changing the deposition amount of one-dimensional AgNWs@ZIF-8 seeds in step 3), the CO2 permeation rate was 995~1264 Barrer, and the CO2 / N2 selectivity was 37~45, of which the deposition amount of one-dimensional AgNWs@ZIF-8 was 0.4g / m 2 When , the CO2 / N2 separation performance reaches the highest, the permeation rate reaches 1264 Barrer and the selectivity is 45. Figure 7 It shows that a high-performance flexible MOF composite membrane was prepared by secondary growth using one-dimensional AgNWs@ZIF-8 as the seed, and its separation factor and permeation flux were much higher than those of the membrane materials prepared in Comparative Examples 1-3.

[0083] The mechanical properties of the PAN base film and the film materials of Examples 1-4 were tested. The film materials were mounted on the fixture of a universal tensile testing machine and the tensile rate was set to 10 mm / min. The results are as follows: Figure 8 The stress-strain curves show that the presence of silver nanowires increases the maximum tensile stress and tensile strength of the prepared flexible ZIF-8 film, and the maximum tensile stress increases and the tensile strength decreases with the increase of the amount of seed crystal deposition.

[0084] like Figure 9 As shown, the highly flexible Pebax-ZIF-8-AgNWs@ZIF-8-PAN composite membrane obtained in Example 3 was subjected to 90° and 180° bending tests, and was repeatedly bent 20 times at 90° and 180°, respectively. The electron microscope image of the composite membrane finally obtained showed that there was no obvious change on the membrane surface, further proving that the composite membrane obtained in this application has high flexibility.

[0085] The above-described embodiments merely illustrate several implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, and all such variations and improvements fall within the scope of protection of the present invention.

Claims

1. A flexible MOF composite membrane, characterized in that: include: A flexible polymer substrate layer and a MOF film layer located above the flexible polymer substrate layer; The flexible polymer base layer and the MOF membrane layer are connected by an AgNWs@MOF seed layer deposited on the flexible polymer base layer; the AgNWs@MOF is a core-shell structure formed by MOF wrapping one-dimensional silver nanowires, and the AgNWs@MOF seed layer is a fibrous mesh structure formed by the core-shell structure.

2. The flexible MOF composite membrane according to claim 1, characterized in that The relationship between the deposition amount of the AgNWs@MOF seed layer and the area of ​​the flexible polymer substrate layer is 0.1-0.6 g / m 2 .

3. The flexible MOF composite membrane according to claim 1, characterized in that The flexible polymer substrate layer includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyacrylonitrile, polyethylene and polypropylene.

4. The flexible MOF composite membrane according to claim 1, characterized in that The MOF includes ZIF-8, ZIF-67, ZIF-71, ZIF-7 or ZIF-62.

5. The flexible MOF composite membrane according to claim 1, characterized in that A functional polymer layer is further provided above the MOF membrane layer, and the functional polymer is one or more of Pebax 1657, Pebax 2533, Pebax 4033, and Pebax 5533.

6. A method for preparing a flexible MOF composite membrane according to any one of claims 1 to 4, characterized in that: The steps include: S1) mixing the one-dimensional silver nanowires, the metal ion solution of the MOF and the organic ligand solution of the MOF to prepare AgNWs@MOF; S2) depositing the AgNWs@MOF on the flexible polymer substrate layer by a vacuum-assisted self-assembly method to form an AgNWs@MOF seed layer to obtain a first composite film; S3) placing the first composite membrane in a mixed solution of metal ions and organic ligands of the MOF, growing a MOF membrane layer on the AgNWs@MOF seed layer, and obtaining the flexible MOF composite membrane.

7. A method for preparing a flexible MOF composite membrane according to claim 5, characterized in that: The steps include: S1) mixing the one-dimensional silver nanowires, the metal ion solution of the MOF and the organic ligand solution of the MOF to prepare AgNWs@MOF; S2) depositing the AgNWs@MOF on the flexible polymer substrate layer by a vacuum-assisted self-assembly method to form an AgNWs@MOF seed layer to obtain a first composite film; S3) placing the first composite film in a mixed solution of metal ions and organic ligands of the MOF, and growing a MOF film layer on the AgNWs@MOF seed layer to obtain a second composite film; S4) spin-coating the functional polymer on the MOF film layer of the second composite film to obtain the flexible MOF composite film.

8. The preparation method according to claim 6 or 7, characterized in that The one-dimensional silver nanowires in step S1) are obtained by the following method: Silver salt, polyvinyl pyrrolidone and halide are dissolved in liquid polyhydroxy alcohol, mixed evenly, and then subjected to microwave solvent thermal synthesis reaction to obtain a suspension, which is then centrifuged, washed and dried to obtain the one-dimensional silver nanowires.

9. The preparation method according to claim 6 or 7, characterized in that: The molar ratio of the metal ion to the organic ligand in step S1) is 1:1-10; the molar ratio of the metal ion to the organic ligand in the mixed solution in step S3) is 1:20-100.

10. Use of the flexible MOF composite membrane according to any one of claims 1 to 5 in CO2 / N2 gas separation.

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