A method for the directed preparation of large-area MOF films from two polymers and a large-area MOF film

Abstract

The application discloses a method for preparing a large-area MOF film by using a double polymer and the large-area MOF film, and the MOF film comprises a polymer support body, a ultrafiltration membrane and a polydimethylsiloxane coating layer, the coating layer completely or incompletely covers one side surface of the ultrafiltration membrane; a MOF metal-organic framework is assembled on the polymer support body; the method comprises the following operations: soaking one side of the polydimethylsiloxane coating layer of the polymer support body in a dispersion liquid to deposit a cross-linked polymer network layer; soaking one side of the ultrafiltration membrane in a ligand solution to perform ligand back diffusion and assemble a MOF metal-organic framework on the cross-linked polymer network layer; and the dispersion liquid comprises polyvinyl alcohol, polyvinylamine, a metal salt and a solvent. The preparation method can realize the preparation of a large-area ultra-thin continuous MOF film with an area greater than 100 cm 2 , and the MOF film has good C3H6 / C3H8 separation performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of MOF films, in particular to a method for directional preparation of large-area MOF films by double polymers and large-area MOF films. BACKGROUND

[0002] Metal-organic frameworks (MOFs) have uniform and adjustable pore size, high porosity, strong structural versatility, and other advantages, and can be applied to the field of membrane gas separation. In particular, membranes with ultra-thin MOF layers can achieve high gas permeation rate and good selectivity, and have broad application prospects. Existing ultra-thin MOF membranes are mainly deposited on inorganic support layers or metal surfaces by metal salts, ligands or two-dimensional MOF nanosheets, while ultra-thin MOF membranes prepared in situ on polymer support layers with higher processing performance and lower cost are less.

[0003] In the prior art, ZIF-8 membranes have been prepared on organic polymer substrates by reverse diffusion method, and the membranes exhibit good gas separation performance. Unfortunately, there is no ultra-thin MOF membrane with an area greater than 50cm 2 at present, and the preparation of large-area ultra-thin membranes, especially high-permeation membranes, on polymer support layers is a prerequisite for realizing industrial practical applications, thus greatly limiting the practical application of MOF membranes.

[0004] Referring to Chinese patent application No. CN112246111A, the inventor prepared an ultra-thin low-crystalline MOF membrane on a polymer support layer by interfacial layer polarization induction, and the membrane exhibits excellent C3H6 / C3H8 separation performance. However, the preparation of large-area continuous MOF membranes is still a challenge. SUMMARY

[0005] The present application provides a method for directional preparation of large-area MOF membranes by double polymers and large-area MOF membranes, which can realize the preparation of large-area continuous MOF membranes, and the MOF membranes have good C3H6 / C3H8 separation performance.

[0006] In a first aspect, the present application provides a method for directional preparation of large-area MOF membranes by double polymers, wherein the MOF membrane comprises:

[0007] A polymer support body having an ultrafiltration membrane and a polydimethylsiloxane coating layer, which completely or incompletely covers the single-sided surface of the ultrafiltration membrane;

[0008] A MOF metal-organic framework assembled on the polymer support body;

[0009] The method comprises the following operations:

[0010] The one side of the polymeric support polydimethylsiloxane coating is infiltrated in the dispersion liquid, a cross-linked polymer network layer is deposited; the one side of the ultrafiltration membrane is infiltrated in the ligand solution, ligand back diffusion is carried out, and a MOF metal-organic framework is assembled on the cross-linked polymer network layer; the dispersion liquid comprises polyvinyl alcohol, polyvinylamine, metal salt and solvent.

[0011] Preferably, the use amount of the polyvinyl alcohol and the polyvinylamine is 0.025% to 0.01% of the mass of the dispersion liquid respectively.

[0012] Preferably, the mass concentration of the metal salt in the dispersion liquid is 1% to 4%, more preferably 1% to 3%.

[0013] The selection of the raw materials such as polyvinyl alcohol and polyvinylamine has no special requirements in the application, and the commercially available products can be used.

[0014] Preferably, the molar ratio of the polyvinyl alcohol and the polyvinylamine is 1:2 to 6.

[0015] Preferably, the polymerization degree of the polyvinyl alcohol is 1500 to 3000.

[0016] Preferably, the alcoholysis degree of the polyvinyl alcohol is 85% to 99%.

[0017] Preferably, the molecular weight of the polyvinylamine is 300000 to 500000 Da.

[0018] Preferably, the mass concentration of the ligand solution is 2% to 4%, more preferably 2.5% to 3.5%.

[0019] Preferably, the ultrafiltration membrane is a polysulfone, polypropylene or polyacrylonitrile ultrafiltration membrane.

[0020] Preferably, the average pore size of the ultrafiltration membrane is 10nm to 100nm, more preferably 20nm to 60nm.

[0021] Preferably, the area of the MOF metal-organic framework is greater than 50cm 2 , more preferably greater than 100cm 2 .

[0022] Preferably, the thickness of the MOF metal-organic framework is 30nm to 300nm, more preferably 30nm to 150nm.

[0023] Preferably, the thickness of the polydimethylsiloxane coating is 15nm to 50nm.

[0024] In the above preparation method, the ligand solution and the metal ion solution are separated by the polymer support to perform ligand back diffusion, and then a large-area continuous defect-free MOF film (MOF metal-organic framework) is formed. Specifically, first, a PDMS coating (polydimethylsiloxane coating) is contacted with a dispersion liquid. The polyvinyl alcohol (PVA) and polyvinylamine (PVAm) in the dispersion liquid have good affinity with the PDMS, and under the hydrogen bonding action between the active hydroxyl groups in the PVA and the active amino groups in the PVAm, a two-dimensional (2D) cross-linked double polymer network layer can be formed on the PDMS coating. The cross-linked polymer network layer can adsorb metal ligand ions through its complexation and polarization induction, thereby forming uniform ion nucleation sites on the surface thereof. Then, the surface of the ultrafiltration membrane is contacted with the ligand solution to perform ligand back diffusion. In this process, the cross-linked double polymer network allows the ligand to diffuse to the surface of the PDMS under the effect of the ligand solvent swelling effect, and assemble into a large-area ultra-thin MOF film with the ion nucleation sites, but does not allow the Zn 2+ to diffuse to the surface of the other side of the ultrafiltration membrane.

[0025] Experiments show that when the ligand is added to the dispersion liquid by a conventional process, and the membrane growth is performed on the same side, the cross-linked polymer network-Zn 2+ composite layer cannot form a large-area MOF film. The reason may be that the heterogeneous nucleation process of the MOF is difficult to control at this time, the reaction rate of the metal ions in the dispersion liquid with the ligand is relatively fast, and the reaction on the PDMS is very little, and defects are easily generated on the MOF film, resulting in poor compactness.

[0026] It should be noted that the ultrafiltration membrane of the present application can be selected from commercially available ultrafiltration membranes containing a polydimethylsiloxane coating, or a polydimethylsiloxane coating can be prepared on the ultrafiltration membrane by a solution method, a sol-gel method, chemical vapor deposition, etc.

[0027] Preferably, the MOF metal-organic framework is selected from any one of ZIF-8, ZIF-L, ZIF-61, ZIF-67 or MIL-68.

[0028] When the MOF metal-organic framework is ZIF-8, ZIF-L, ZIF-61 or ZIF-67, the metal ion is selected from zinc salt or cobalt salt, and the ligand solution is an imidazole ligand solution.

[0029] Preferably, the imidazole ligand is selected from at least one of 2-methyl imidazole and imidazole, and more preferably is 2-methyl imidazole.

[0030] Preferably, the solvent of the ligand solution is selected from a polar small organic solvent such as methanol, ethanol, water or alcohol-water mixture.

[0031] When the MOF metal-organic framework is MIL-68, the metal salt is a soluble salt containing transition metal ions, for example, Fe2+ In 3+ Al 3+ The ligand solution is preferably a solution of a dicarboxylic acid ligand, such as terephthalic acid, trimesic acid.

[0032] In a second aspect, the application provides a large-area MOF film prepared by any of the above preparation methods.

[0033] Using the preparation method of the application, a continuous defect-free MOF film with an area greater than 100 cm 2 A continuous defect-free MOF film with a thickness of less than 150 nm has a broad application prospect in the field of membrane gas separation industry.

[0034] In summary, the application has the following beneficial effects:

[0035] 1. The application proposes a ligand anti-diffusion assisted double polymer network directional preparation method, which uses polyvinyl alcohol and polyvinylamine as raw materials to form a cross-linked polymer network layer on an ultrafiltration membrane, and then uses the polarization induction effect to adsorb metal ligand ions to form uniform nucleation sites; then using the ligand anti-diffusion method, organic ligands are assembled at each nucleation site to form a continuous defect-free large-area MOF film. It overcomes the problem that the current membrane layer has many defects in the preparation process of the MOF film, and cannot form a large-area continuous MOF film. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 is a low-magnification SEM surface image of the MOF film in Example 1.

[0037] Figure 2 is a high-magnification SEM surface image of the MOF film in Example 1.

[0038] Figure 3 is a SEM cross-sectional image of the MOF film in Example 1.

[0039] Figure 4 is a thickness distribution graph of the ZIF-8 film in Example 1.

[0040] Figure 5 is a gas separation performance graph of the ZIF-8 film in Example 1.

[0041] Figure 6 is a low-magnification SEM surface image of the MOF film in Example 2.

[0042] Figure 7 is a high-magnification SEM surface image of the MOF film in Example 2.

[0043] Figure 8 is a SEM cross-sectional image of the MOF film in Example 2.

[0044] Figure 9 is a thickness profile plot of the ZIF-8 membrane in Example 2.

[0045] Figure 10 is an AFM plot of the ZIF-8 membrane in Example 2.

[0046] Figure 11 is a low magnification SEM surface image of the MOF membrane in Example 3.

[0047] Figure 12 is a high magnification SEM surface image of the MOF membrane in Example 3.

[0048] Figure 13 is a SEM cross-section image of the MOF membrane in Example 3.

[0049] Figure 14 is a thickness profile plot of the ZIF-L membrane in Example 3.

[0050] Figure 15 is an AFM plot of the ZIF-L membrane in Example 3.

[0051] Figure 16 is a low magnification SEM surface image of the MOF membrane in Example 4.

[0052] Figure 17 is a high magnification SEM surface image of the MOF membrane in Example 4.

[0053] Figure 18 is a SEM cross-section image of the MOF membrane in Example 4.

[0054] Figure 19 is a thickness profile plot of the ZIF-61 membrane in Example 4.

[0055] Figure 20 is an AFM plot of the ZIF-61 membrane in Example 4.

[0056] Figure 21 is a low magnification SEM surface image of the MOF membrane in Example 5.

[0057] Figure 22 is a high magnification SEM surface image of the MOF membrane in Example 5.

[0058] Figure 23 is a SEM cross-section image of the MOF membrane in Example 5.

[0059] Figure 24 is a thickness profile plot of the MIL-68 membrane in Example 5.

[0060] Figure 25is an AFM image of the MIL-68 membrane in Example 5.

[0061] Figure 26 is a SEM surface image and elemental mapping image of the MOF membrane in Comparative Example 1.

[0062] Figure 27 is a SEM surface image of the MOF membrane in Comparative Example 2. DETAILED DESCRIPTION

[0063] Preparation Example

[0064] Preparation Example 1

[0065] The polymer support comprises a polysulfone ultrafiltration membrane (average pore size of 50 nm) and a polydimethylsiloxane coating. The coating completely covers one side of the surface of the polysulfone ultrafiltration membrane, and the specific preparation method is as follows:

[0066] First, 0.4 g of polydimethylsiloxane (PDMS), 0.8 g of tetraethyl silicate, and 0.8 g of dibutyltin dilaurate are mixed with 98 g of n-heptane to obtain a 0.4 wt% PDMS solution. After stirring for 30 min, a doctor blade with a gap accuracy of ±5 μm is used to coat the obtained PDMS solution on the surface of the polysulfone ultrafiltration membrane with an average pore size of 50 nm at a temperature of 25-35 °C. The wet coating thickness is 200 μm (the gap between the substrate and the doctor blade). Then, it is dried in a constant temperature and humidity box at 30 °C and 40% relative humidity (RH) for 24 h to obtain the coating.

[0067] Preparation Example 2

[0068] The polymer support is different from that of Preparation Example 1 in that the average pore size of the polysulfone ultrafiltration membrane is 50 nm.

[0069] Preparation Example a

[0070] The polyvinylamine is prepared by dissolving 9.83 mL of N-vinyl formamide (0.14 mol) and 60 mg of AIBA (initiator azobisdimethylaminoformate hydrochloride) in 40 mL of deionized water in a flask equipped with a stirrer, and polymerizing at 50±2 °C under a nitrogen atmosphere for 2 h. After polymerization, concentrated HCl (40 ml, 36 wt%) is added, and acid hydrolysis is induced at 70±2 °C for 5 h, and HCl in the polymer solution is removed by a quaternary ammonium anion exchange resin. The treated solution is poured into excess ethanol to precipitate the polymer, which is recovered and dried in a vacuum oven at 40 °C for 48 h to obtain PVAm (300000-500000 Da). Example

[0071] Example 1

[0072] A large-area MOF film, comprising a polymer support and a MOF metal-organic framework assembled on the polymer support, the polymer support is prepared in Preparation Example 1, and the MOF metal-organic framework is a ZIF-8 film, the ZIF-8 film is assembled on the surface of the polydimethylsiloxane coating layer of the polymer support.

[0073] The MOF film preparation method is as follows:

[0074] Dispersion liquid preparation: 0.025 g of PVA-1799 was dissolved in 99.975 g of deionized water to obtain a 0.025 wt% PVA solution. 0.4874 g of PVAm was dissolved in 99.5126 g of deionized water to obtain a 0.4874 wt% PVAm aqueous solution. 5.1 g of the PVAm aqueous solution (0.4874 wt%) and 0.55 g of Zn(NO3)2·6H2O were mixed with 50 g of the PVA aqueous solution (0.025 wt%) to obtain a dispersion liquid.

[0075] Ligand solution: 6.48 g of 2-methylimidazole was dissolved in 200 mL of anhydrous methanol to obtain the ligand solution.

[0076] MOF film preparation: at room temperature (23±2℃), the PDMS coating layer was placed in 50 mL of the dispersion liquid to form a cross-linked polymer network layer for 2 h. Then, the side of the ultrafiltration membrane without the PDMS coating layer was contacted with 200 mL of the ligand solution for 2 min to obtain a white ZIF-8 film with an area of 2400 cm 2 . After washing with deionized water for three times, the ZIF-8 film was dried in a constant temperature and humidity box at 30℃ and 40% RH for 12 h to obtain the large-area MOF film. The morphology of the MOF film is shown in Figure 1 、 2 , 3. As can be seen from the figure, the MOF film has high compactness and no obvious defects.

[0077] As can be seen from Figure 3 , the thickness of the obtained ZIF-8 film is 107 nm.

[0078] As can be seen from Figure 4 , a 100 cm 2 sample was cut from the large-area MOF film. The sample was divided into 10 parts, and 5 positions were randomly selected in each part to calculate the standard deviation (σ) of 5.21 nm. It can be seen that the thickness of the obtained MOF film is uniform. The reason may be that the cross-linked polymer network layer can uniformly adsorb metal ligand ions through polarization induction, and then coordinate to obtain a uniform ZIF-8 film in the subsequent ligand counter-diffusion process.

[0079] As can be seen from Figure 5 , the separation selectivity of the selective layer (ZIF-8 film) of the obtained MOF film to C3H6 and C3H8 can reach 28.5.

[0080] Example 2

[0081] Large-area MOF membrane, which is different from Example 1 in that the polymer support prepared in Preparation Example 2 is used instead of the polymer support prepared in Preparation Example 1; at the same time, in the MOF membrane preparation step, the reaction time after the side of the ultrafiltration membrane without the PDMS coating is contacted with 200 mL of the ligand solution is 3 min. A ZIF-8 membrane with an area of 2400 cm 2 is finally prepared. The morphology of the MOF membrane is shown in FIG. 8, and it can be seen from the figure that the MOF membrane has high compactness and no obvious defects. Figure 6 、 7

[0082] Referring to FIG. 7, it can be seen that the thickness of the MOF membrane is 50 nm. Figure 8

[0083] Referring to FIG. 7, it can be seen that the thickness of the MOF membrane is 50 nm. Figure 9 A 100 cm 2 sample is cut on the large-area MOF membrane. The sample is divided into 10 parts, and 5 positions are randomly selected in each part to calculate the standard deviation (σ) of 2.12 nm; referring to FIG. 7, it can be seen that the surface roughness of the MOF membrane is 35.4 nm. It can be seen that the surface morphology of the MOF membrane of the present embodiment is compact and uniform. Figure 10

[0084] Example 3

[0085] Large-area MOF membrane, which includes a polymer support and a MOF metal-organic framework assembled on the polymer support, the polymer support is prepared in Preparation Example 1, and the MOF metal-organic framework is a ZIF-L membrane, the ZIF-L membrane is assembled on the surface of the polydimethylsiloxane coating of the polymer support.

[0086] The preparation method of the MOF membrane is as follows:

[0087] Dispersion liquid preparation: 0.025 g of PVA-2099 is dissolved in 99.975 g of deionized water to obtain a 0.025 wt% PVA solution. 0.4874 g of PVAm is dissolved in 99.5126 g of deionized water to obtain a 0.4874 wt% PVAm aqueous solution. 5.1 g of the PVAm aqueous solution (0.4874 wt%) and 2 g of ZnCl2 are mixed with 50 g of the PVA aqueous solution (0.025 wt%) to obtain a dispersion liquid.

[0088] Ligand solution: 6.48 g of 2-methylimidazole is dissolved in 200 mL of anhydrous methanol to obtain the ligand solution.

[0089] ​​​MOF film preparation: the PDMS coating was placed in 50 mL dispersion solution for 1.5 h at room temperature (23±2℃) to form a cross-linked polymer network layer. Then the side of the ultrafiltration membrane without PDMS coating was contacted with 200 mL ligand solution for 0.5 min. A white ZIF-8 film with an area of 100 cm 2 The white ZIF-8 film was washed with deionized water for three times and dried in a constant temperature and humidity chamber at 30℃ and 40% RH for 12 h to obtain a large-area MOF film. The morphology of the MOF film is shown in Figure 11 、 12 , 13. As can be seen from the figure, the MOF film has high compactness and no obvious defects.

[0090] As can be seen from Figure 13 , the thickness of the obtained ZIF-L film is 53 nm.

[0091] As can be seen from Figure 14 , a sample with an area of 100 cm 2 was cut on the large-area MOF film. The sample was divided into 10 parts, and 5 positions were randomly selected in each part to calculate the standard deviation (σ) of 2.35 nm; as can be seen from Figure 15 , the surface roughness of the MOF film is 35.3 nm. It can be seen that the surface morphology of the MOF film of the present embodiment is compact and uniform.

[0092] Example 4

[0093] The large-area MOF film comprises a polymer support and a MOF metal-organic framework assembled on the polymer support, the polymer support is prepared in Preparation Example 1, and the MOF metal-organic framework is a ZIF-61 film, which is assembled on the surface of the polydimethylsiloxane coating of the polymer support.

[0094] The MOF film is prepared as follows:

[0095] Dispersion solution preparation: 0.025 g of PVA-1788 was dissolved in 99.975 g of deionized water to obtain a 0.025 wt% PVA solution. 0.4874 g of PVAm was dissolved in 99.5126 g of deionized water to obtain a 0.4874 wt% PVAm aqueous solution. 5.1 g of the PVAm aqueous solution (0.4874 wt%) and 0.55 g of Zn(NO3)2·6H2O were mixed with 50 g of the PVA aqueous solution (0.025 wt%) to obtain a dispersion solution.

[0096] Ligand solution: 2.8 g of 2-methylimidazole and 2.8 g of imidazole were dissolved in 200 mL of anhydrous methanol to obtain the ligand solution.

[0097] MOF film preparation: the PDMS coating was contacted with 50 mL of the dispersion solution for 2 h at room temperature (23±2℃) to form a cross-linked polymer network layer. Then the side of the ultrafiltration membrane without the PDMS coating was contacted with 200 mL of the ligand solution for 0.5 min. A white ZIF-61 film with an area of 100 cm 2 was obtained. After being washed with deionized water for three times, the large-area MOF film was dried in a constant temperature and humidity chamber at 30℃ and 40% RH for 12 h. The morphology of the MOF film is shown in Figure 16 、 17 , 18. As can be seen from the figure, the MOF film has high compactness and no obvious defects.

[0098] As can be seen from Figure 18 , the thickness of the obtained ZIF-61 film is 53 nm.

[0099] As can be seen from Figure 19 , a sample with an area of 100 cm 2 was cut from the large-area MOF film. The sample was divided into 10 parts, and 5 positions were randomly selected in each part to calculate the standard deviation (σ) of 2.65 nm. As can be seen from Figure 20 , the surface roughness of the MOF film is 11.1 nm. It can be seen that the surface morphology of the MOF film of the present embodiment is compact and uniform.

[0100] Example 5

[0101] The large-area MOF film comprises a polymer support and a MOF metal-organic framework assembled on the polymer support, the polymer support is prepared in Preparation Example 1, and the MOF metal-organic framework is a MIL-68 film, which is assembled on the surface of the polydimethylsiloxane coating of the polymer support.

[0102] The preparation method of the MOF film is as follows:

[0103] Dispersion solution preparation: 0.025 g of PVA-1799 was dissolved in 99.975 g of deionized water to obtain a 0.025 wt% PVA solution. 0.4874 g of PVAm was dissolved in 99.5126 g of deionized water to obtain a 0.4874 wt% PVAm aqueous solution. 5.1 g of the PVAm aqueous solution (0.4874 wt%) and 0.5 g of In(NO3)3·H2O were mixed with 50 g of the PVA aqueous solution (0.025 wt%) to obtain a dispersion solution.

[0104] Ligand solution: 2.8 g of trimesic acid was dissolved in 200 mL of anhydrous methanol to obtain the ligand solution.

[0105] MOF film preparation: at room temperature (23±2℃), the PDMS coating was placed in 50 mL dispersion solution for 2 h to form a cross-linked polymer network layer. Then the side of the ultrafiltration membrane without PDMS coating was contacted with 200 mL ligand solution for 0.5 min. A white MIL-68 film with an area of 100 cm 2 was obtained. After washing with deionized water for three times, the large-area MOF film was dried in a constant temperature and humidity box at 30℃ and 40% RH for 12 h. The morphology of the MOF film is shown in Figure 21 、 22 , 23. As can be seen from the figure, the MOF film has high compactness and no obvious defects.

[0106] As can be seen from Figure 23 , the thickness of the obtained MIL-68 film is 130 nm.

[0107] As can be seen from Figure 24 , a sample of 100 cm 2 was cut on the large-area MOF film. The sample was divided into 10 parts, and 5 positions were randomly selected in each part to calculate the standard deviation (σ) of 4.75 nm; as can be seen from Figure 25 , the surface roughness of the MOF film is 7.02 nm. It can be seen that the surface morphology of the MOF film in this embodiment is compact and uniform.

[0108] Comparative example

[0109] Comparative example 1 differs from example 1 in that the MOF film preparation method is different, specifically as follows:

[0110] Dispersion solution preparation: 0.4874 g of PVAm was dissolved in 99.5126 g of deionized water to obtain a 0.4874 wt% PVAm aqueous solution. 55 g of the PVAm aqueous solution (0.4874 wt%) and 0.5 g of Zn(NO3)2·6H2O were mixed to obtain a dispersion solution.

[0111] Ligand solution: 6.48 g of 2-methylimidazole was dissolved in 200 mL of anhydrous methanol to obtain the ligand solution.

[0112] MOF film preparation: at room temperature (23±2℃), the PDMS coating was placed in 50 mL dispersion solution for 2 h to form a cross-linked polymer network layer. Then the side of the ultrafiltration membrane without PDMS coating was contacted with 200 mL ligand solution for 2 min. As can be seen from Figure 26 , the preparation process did not form a ZIF-8 film, and the MOF film could not be prepared.

[0113] Comparative example 2 differs from example 1 in that the MOF film preparation method is different, specifically as follows:

[0114] Polymer solution preparation: 0.025 g PVA-1799 was dissolved in 99.975 g deionized water to obtain a 0.025 wt% PVA solution. 0.4874 g PVAm was dissolved in 99.5126 g deionized water to obtain a 0.4874 wt% PVAm aqueous solution.

[0115] Ligand solution: 6.48 g 2-methylimidazole was dissolved in 200 mL anhydrous methanol to obtain the ligand solution.

[0116] Dispersion preparation: 5.1 g PVAm aqueous solution (0.4874 wt%) and 0.5 g Zn(NO3)2·6H2O were mixed with 50 g PVA aqueous solution (0.025 wt%) and 3.2 g ligand solution to obtain the dispersion.

[0117] MOF film preparation: PDMS coating was placed in 50 mL dispersion at room temperature (23±2℃) for 2 h to obtain a white ZIF-8 film. After washing with deionized water for three times, the film was dried in a constant temperature and humidity box at 30℃ and 40% RH for 12 h to obtain a MOF film with an area of 100 cm 2 The morphology of the MOF film is shown in Figure 27 It can be seen from the figure that the MOF film has obvious defects and is not applicable.

[0118] It can be seen from Examples 1-5 and Comparative Example 1 that the present application can prepare a continuous and defect-free large-area MOF film by using the ligand anti-diffusion assisted double polymer network directional preparation method, in the presence of PVA and PVAm. When PVA is involved in the preparation raw material, ZIF-8 film cannot be formed on the PDMS coating. Further, in combination with Examples 1-5 and Comparative Example 2, it can be seen that when the dispersion contains both organic ligand and metal ion ligand, ZIF-8 film can be formed on the PDMS coating, but a large-area ZIF-8 film cannot be formed.

[0119] The specific embodiments are only an explanation of the present application, and are not a limitation of the present application. Those skilled in the art can make modifications to the embodiments without creative contribution after reading the specification, and the modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A method for the directed preparation of large area MOF films from two polymers, characterized in that, The MOF film comprises: a polymer support with an ultrafiltration membrane and a polydimethylsiloxane coating layer, which is fully or not fully covered on one side surface of the ultrafiltration membrane; a MOF metal-organic framework assembled on the polymer support; The method comprises the following operations: immersing one side of the polydimethylsiloxane coating layer of the polymer support in a dispersion liquid to deposit a cross-linked polymer network layer; immersing one side of the ultrafiltration membrane in a ligand solution to perform ligand back diffusion and assemble a MOF metal-organic framework on the cross-linked polymer network layer; the dispersion liquid comprises polyvinyl alcohol, polyvinylamine, a metal salt and a solvent.

2. The method of claim 1, wherein, The MOF metal-organic framework is selected from any one of ZIF-8, ZIF-L, ZIF-61, ZIF-67 or MIL-68.

3. The method of claim 1, wherein, The use amount of the polyvinyl alcohol and the polyvinylamine is 0.025% to 0.01% of the mass of the dispersion liquid respectively.

4. The method of claim 1, wherein, The mass concentration of the metal salt in the dispersion liquid is 1% to 4%.

5. The method of claim 3, wherein, The molar ratio of the polyvinyl alcohol and the polyvinylamine is 1:2 to 6.

6. The method of claim 1, wherein, The mass concentration of the ligand solution is 2% to 4%.

7. The method of claim 1, wherein the MOF film has a large area. The ultrafiltration membrane is a polysulfone, polypropylene or polyacrylonitrile ultrafiltration membrane.

8. The method of claim 7, wherein, The average pore size of the ultrafiltration membrane is 20nm to 60nm.

9. The method of claim 1, wherein, The MOF metal-organic framework has an area greater than 50 cm 2 ; the MOF metal-organic framework has a thickness of 30-300 nm.

10. A large area MOF film characterized in that, The MOF film is prepared according to any one of the methods of claims 1 to 9.

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