MOF / Polyamide Composite Membrane and Its Preparation Method and Application

Abstract

The present invention relates to the technical field of reverse osmosis membranes, and specifically discloses a MOF / polyamide composite membrane, a preparation method thereof and an application. The preparation method comprises the following steps: coating / immersing the surface of a flexible porous polymer-based membrane in an aqueous polymer-metal complex solution to uniformly attach metal ions to its surface, obtaining a polymer membrane rich in metal ions; immersing the polymer membrane rich in metal ions in an aqueous solution of a metal-ligand mixture to obtain a continuous and complete MOF layer attached to the surface of the polymer membrane rich in metal ions; contacting the MOF layer with an aqueous solution of a polyamine, and after washing, contacting the MOF layer with an organic phase solution of an acyl chloride monomer to complete an interfacial polymerization reaction of polyamide in a confined space, obtaining a composite membrane; and performing heat treatment on the composite membrane to obtain a MOF / polyamide composite membrane. The MOF / polyamide composite membrane of the present invention has no selective defects eliminated in the membrane and the structure of the composite separation layer is regulated, has good desalination performance, and has a good application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of reverse osmosis membranes, and particularly to a MOF / polyamide composite membrane, a preparation method thereof, and an application thereof. Background Art

[0002] As the current mainstream reverse osmosis (RO) membrane, polyamide membranes occupy most of the market share due to their good stable structure and excellent desalination performance. However, commercial membranes generally have the problem of low water permeation rate. In practical applications, it is often necessary to increase the operating pressure of the separation process, which will inevitably bring additional high energy consumption problems. Therefore, the permeation performance has always been an important factor to be considered first in the design and development of high-performance polyamide RO membranes.

[0003] Regulating the microstructure of separation membranes is the core technology and key common technology for the research and development of high-flux membrane materials. It is very difficult to simultaneously improve the water permeation flux and desalination rate of membranes only by regulating the cross-linked structure of the dense polyamide separation layer. The emergence and rapid development of metal-organic framework materials (MOF), and the thin-film nanocomposite membranes compounded with them have shown unique charm in constructing water molecule channels in the membrane and improving water flux. Currently, most of its research focuses on doping in the polyamide layer through a simple interfacial polymerization process. The selection and introduction method of MOF are relatively single, and the introduction amount of MOF is relatively low, so it is impossible to truly maximize the leading role of MOF separation. In addition, problems such as the requirements of green and mild membrane preparation processes, the problem of interfacial compatibility in the membrane, the easy shedding and leakage of MOF caused by high operating pressure, and the crystal defects of MOF caused by the excessive pursuit of ultrathin separation layers still limit its expansion in water treatment applications. Summary of the Invention

[0004] Based on this, the present invention provides a MOF / polyamide composite membrane and a preparation method thereof. The prepared composite membrane has good desalination performance and shows good application prospects.

[0005] According to the first aspect of the present invention, a preparation method of a MOF / polyamide composite membrane is provided, including the following steps:

[0006] Coat / submerge the surface of a flexible porous polymer substrate membrane in an aqueous solution of a polymer-metal complex to uniformly attach metal ions to its surface, obtaining a polymer membrane rich in metal ions;

[0007] Submerge the polymer membrane rich in metal ions in an aqueous solution of a metal-ligand mixture to obtain a continuous and complete MOF layer attached to the polymer membrane rich in metal ions;

[0008] Contact the MOF layer with an aqueous solution of polyamine, and after cleaning, contact the MOF layer with an organic phase solution of an acyl chloride monomer to complete the polyamide interfacial polymerization reaction in a confined space, obtaining a composite membrane;

[0009] The composite film is heat-treated to obtain the MOF / polyamide composite film.

[0010] According to an embodiment of the present invention, the material of the flexible porous polymer-based film includes one of polysulfone, polyethersulfone, polyacrylonitrile, polyimide, polyvinylidene fluoride, and polypropylene;

[0011] and / or, the average pore size of the flexible porous polymer-based film is 10-100 nm.

[0012] According to an embodiment of the present invention, the ligand in the metal-ligand mixed aqueous solution is 2-methylimidazole;

[0013] and / or, the ratio of metal ions, ligand to deionized water in the metal-ligand mixed aqueous solution is 0.00-2.00 g: 1.00-5.00 g: 100-500 mL.

[0014] According to an embodiment of the present invention, the aqueous solution of polyamine includes polyamine and an additive;

[0015] and / or, the aqueous solution of polyamine is in a neutral or alkaline environment;

[0016] and / or, the contact time between the MOF layer and the aqueous solution of polyamine is 5 min - 30 min.

[0017] According to an embodiment of the present invention, the organic phase solution of acyl chloride monomer includes a solvent and an acyl chloride monomer;

[0018] and / or, the solvent is one or more of Iaopar-G and n-hexane;

[0019] and / or, the acyl chloride monomer is one or more of trimesoyl chloride, isophthaloyl chloride, phthaloyl chloride, and terephthaloyl chloride, and the acyl chloride monomer is 0.05% - 0.3% of the mass fraction of the organic phase solution.

[0020] According to an embodiment of the present invention, the polyamine includes one or more of piperazine, m-phenylenediamine, and p-phenylenediamine, and the polyamine is 1% - 5% of the mass fraction of the aqueous solution;

[0021] and / or, the additive includes triethylamine and camphorsulfonic acid; wherein, the mass fraction of triethylamine is 0% - 3%; the mass fraction of camphorsulfonic acid is 0 - 5%.

[0022] According to an embodiment of the present invention, the cleaning includes: using a good solvent and deionized water to clean the residual amine monomers on the film surface;

[0023] And / or, the good solvent is one or more of absolute ethanol, absolute methanol, Iaopar-G, and n-hexane.

[0024] According to an embodiment of the present invention, the interfacial polymerization time of the polyamide interfacial polymerization is 1 - 10 min;

[0025] And / or, the temperature of the heat treatment is 50 - 90 °C;

[0026] And / or, the time of the heat treatment is 5 min - 30 min.

[0027] According to a second aspect of the present invention, there is provided a MOF / polyamide composite membrane prepared by the above preparation method.

[0028] According to a third aspect of the present invention, there is provided an application of the MOF / polyamide composite membrane in the separation process of high-concentration sodium chloride in an aqueous solution system.

[0029] It can be seen from the above technical solutions that the MOF / polyamide composite membrane, its preparation method and application provided by the present invention have the following beneficial effects:

[0030] The present invention provides a MOF / polyamide composite membrane for seawater desalination, its preparation method and application. A continuous and complete MOF / polyamide composite separation layer is formed on the surface of the flexible porous polymer-based membrane. The prepared membrane surface fully exposes the continuous structure of MOF, giving play to its functional porous sieving ability. At the same time, the highly cross-linked polyamide thin layer network formed in the confined space covers and eliminates the non-selective defects between MOFs and between MOF and the base membrane, firmly attaching the MOF particles on the surface of the base membrane. In addition, the film preparation process of this method is mild, and the morphology and scale of the composite separation layer can be controllably designed, expanding the further application of the MOF / polyamide composite membrane in the field of seawater desalination.

[0031] The present invention focuses on the preparation of a water-stable MOF / polyamide composite separation layer, the elimination of non-selective defects in the membrane, and the regulation of the structure of the composite separation layer. This composite membrane has good desalination performance and shows good application prospects. Description of the Drawings

[0032] Figure 1 It is a schematic diagram of the water molecule transfer path inside the MOF / polyamide composite membrane according to an embodiment of the present invention.

[0033] Figure 2 It is a scanning electron microscope photograph of the ZIF-L / polyamide composite membrane in Example 1 of the present invention.

[0034] Figure 3 It is a scanning electron microscope photograph of the 2D ZIF-L layer with different ligand concentrations and different growth times in Examples 1 - 5 of the present invention.

[0035] Figure 4 This is the scanning electron microscope photograph of the ZIF-8 polyamide composite membrane in Comparative Example 1 of the present invention.

[0036] Figure 5 This is the separation performance diagram of the ZIF-L / polyamide composite membrane in Example 1 of the present invention.

[0037] Figure 6 This is the separation performance diagram of the ZIF-8 / polyamide composite membrane in Comparative Example 1 of the present invention. Detailed implementation manners

[0038] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the following further describes the present invention in detail with reference to specific embodiments and the accompanying drawings.

[0039] According to a first aspect of the present invention, there is provided a method for preparing a MOF / polyamide composite membrane, comprising the following steps:

[0040] S1: Coating / submerging the surface of a flexible porous polymer matrix membrane in an aqueous solution of a polymer-metal complex to uniformly attach metal ions to its surface, obtaining a polymer membrane rich in metal ions;

[0041] S2: Submerging the polymer membrane rich in metal ions in an aqueous solution of a metal-ligand mixture to obtain a MOF layer attached to the polymer membrane rich in metal ions;

[0042] S3: Contacting the MOF layer with an aqueous solution of a polyamine, and after washing, contacting the MOF layer with an organic phase solution of an acyl chloride monomer to complete an interfacial polymerization reaction of polyamide in a confined space, obtaining a composite membrane;

[0043] S4: Heat-treating the composite membrane to obtain a MOF / polyamide composite membrane.

[0044] According to an embodiment of the present invention, the polymer membrane rich in metal ions obtained in S1 is to anchor metal ions on the surface of the flexible porous polymer matrix membrane. The introduction of the polymer is to stably place the metal ions on the surface, reduce their large amount of penetration into the membrane pores, and at the same time make the distribution of the surface metal ions more uniform.

[0045] According to an embodiment of the present invention, in S3, the heat treatment of the composite membrane is to cause more cross-linking reactions of the low-cross-linked polyamide in the layer of the composite membrane, so that the MOF layer is more firmly fixed and the performance of the MOF / polyamide composite membrane is better.

[0046] In the film-making process, a continuous and complete MOF layer is formed in-situ under room-temperature aqueous conditions, maximizing the retention of the unique morphological features of MOF. The reaction conditions are relatively mild, avoiding damage to the base film under conditions such as high temperature, high pressure, and organic solvents, and the synthesis route is easy to implement. In addition, due to the flexible designability and functionalization characteristics of MOF, this method can achieve controllable design of the morphology and scale of the composite separation layer, expanding the further application of MOF / polyamide composite membranes in the field of seawater desalination.

[0047] According to an embodiment of the present invention, in S1, the material of the flexible porous polymer base film includes one of polysulfone, polyethersulfone, polyacrylonitrile, polyimide, polyvinylidene fluoride, and polypropylene, preferably one of polysulfone, polyethersulfone, and polyacrylonitrile.

[0048] According to an embodiment of the present invention, in S1, the average pore diameter of the flexible porous polymer base film is 10 - 100 nm.

[0049] According to an embodiment of the present invention, in S1, the polymer in the polymer-metal complex aqueous solution can be polyvinyl alcohol, polyethyleneimine, polyacrylamide, etc., preferably polyvinyl alcohol.

[0050] According to an embodiment of the present invention, in S1, the polymer does not participate in the interfacial polymerization, but relies on the complexation of the polymer-metal to attach the metal to the film surface. Preferably, the degree of alcoholysis of polyvinyl alcohol is above 90.

[0051] According to an embodiment of the present invention, in S1, the number of coating / infiltration times is 1 - 2 times.

[0052] According to an embodiment of the present invention, in S1, the mass fraction of the polymer in the complex aqueous solution is 0% - 0.01%.

[0053] According to an embodiment of the present invention, in S1, the mass fraction of metal ions is 1% - 5%.

[0054] According to an embodiment of the present invention, in S1, the metal ions are one or two of zinc ions and cobalt ions.

[0055] According to an embodiment of the present invention, S1 is specifically as follows: Immerse the flexible porous polymer base film in deionized water for soaking and cleaning to remove the impurities remaining on the surface and inside of the flexible porous polymer base film. Subsequently, fix the flexible porous polymer base film in a customized polytetrafluoroethylene frame. At room temperature, repeatedly coat / submerge it in the polymer-metal complex aqueous solution on its surface for 4 - 12 h to uniformly attach metal ions to its surface, obtaining a polymer film rich in metal ions. Finally, dry the film at room temperature for 12 h for use.

[0056] According to an embodiment of the present invention, in S2, the ligand in the metal-ligand mixed aqueous solution is 2-methylimidazole;

[0057] According to an embodiment of the present invention, in S2, the ratio of metal ions, ligands to deionized water in the metal-ligand mixed aqueous solution is 0.00 - 2.00 g: 1.00 - 5.00 g: 100 - 500 mL.

[0058] According to an embodiment of the present invention, S2 is specifically that at room temperature, the polymer membrane rich in metal ions is immersed in the metal-ligand mixed aqueous solution for 1 - 12 h to prepare a continuous and complete MOF layer, and finally dried at room temperature for 12 h for use.

[0059] According to an embodiment of the present invention, in S3, the aqueous solution of polyamine includes polyamine and additives;

[0060] According to an embodiment of the present invention, in S3, the aqueous solution of polyamine is in a neutral or alkaline environment.

[0061] According to an embodiment of the present invention, in S3, the contact time between the MOF layer and the aqueous solution of polyamine is 5 min - 30 min.

[0062] According to an embodiment of the present invention, in S3, the polyamine includes one or more of piperazine, m-phenylenediamine, and p-phenylenediamine, and the polyamine is 1% - 5% of the mass fraction of the aqueous solution;

[0063] According to an embodiment of the present invention, in S3, the additives include triethylamine and camphorsulfonic acid; wherein, the mass fraction of triethylamine is 0% - 3%; the mass fraction of camphorsulfonic acid is 0 - 5%.

[0064] According to an embodiment of the present invention, in S3, the organic phase solution of acyl chloride monomer includes a solvent and an acyl chloride monomer;

[0065] According to an embodiment of the present invention, in S3, the solvent is one or more of Iaopar-G and n-hexane;

[0066] According to an embodiment of the present invention, in S3, the acyl chloride monomer is one or more of trimesoyl chloride, isophthaloyl chloride, phthaloyl chloride, and terephthaloyl chloride, and the acyl chloride monomer is 0.05% - 0.3% of the mass fraction of the organic phase solution.

[0067] According to an embodiment of the present invention, in S3, the cleaning includes: using a good solvent and deionized water to clean the residual amine monomers on the membrane surface;

[0068] According to an embodiment of the present invention, in S3, the good solvent is one or more of absolute ethanol, absolute methanol, Iaopar-G, and n-hexane.

[0069] According to an embodiment of the present invention, in S3, the interfacial polymerization time of the polyamide interfacial polymerization reaction is 1 - 10 min;

[0070] According to an embodiment of the present invention, in S4, the temperature of the heat treatment is 50-90° C.;

[0071] According to an embodiment of the present invention, in S4, the heat treatment time is 5 min-30 min.

[0072] According to a second aspect of the present invention, there is provided a MOF / polyamide composite membrane prepared by the above-mentioned preparation method.

[0073] Structurally, the membrane prepared by the present invention has abundant water molecule transfer channels. The MOF porous structure, MOF intercrystalline sub-nano channels, and polyamide cross-linked layers all create more and shorter flow paths for water molecules. The composite layer structure fully exposes the MOF continuous structure, ensuring that the pores are fully open, and can better exert its functional porous screening ability; the highly cross-linked polyamide thin layer network bridges the MOFs and between the MOF and the base membrane, eliminating the non-selective defects caused by the multi-dimensional morphology and interface compatibility of MOF; at the same time, polyamide stabilizes the MOF layer structure, improving the flexibility of the composite separation layer and the cross-flow high-pressure resistance.

[0074] According to a third aspect of the present invention, Figure 1 As shown, an application of a MOF / polyamide composite membrane in a high-concentration sodium chloride separation process in an aqueous solution system is provided.

[0075] According to an embodiment of the present invention, the application of the MOF / polyamide composite membrane in the high concentration sodium chloride separation process in an aqueous solution system can be a brackish water reverse osmosis membrane with a sodium chloride concentration of 2 g / L or a seawater desalination reverse osmosis membrane with a sodium chloride concentration of 32 g / L.

[0076] According to an embodiment of the present invention, compared with the traditional polyamide membrane, the composite separation layer combining polyamide in the confined space and continuous MOF particles contains abundant water transmission channels; Figure 1 As shown, the porous structure of the water-stable MOF itself has a size between the sizes of water and hydrated salt ions, providing a more precise selective screening channel for water-salt molecules. The intercrystalline and interlayer gaps formed between MOFs due to growth can serve as another sub-nano channel for the transmission of water molecules. The polyamide cross-linked layer in the confined space itself has certain water-salt separation properties and water permeability. In short, more flow paths are created for water molecules in the membrane, achieving a significant increase in the permeation flux.

[0077] According to the embodiments of the present invention, the MOF / polyamide composite membrane can be applied to the field of seawater desalination.

[0078] The MOF / polyamide composite membrane prepared by the method of the present invention has good seawater desalination ability. For the separation system of sodium chloride (32 g / L) in high-concentration seawater, the water flux can reach 66.26 L / m 2 *h or more, and the desalination rate remains at 95%.

[0079] Example 1

[0080] 0.075 g of polyvinyl alcohol, 3 g of zinc nitrate hexahydrate and 96.975 g of deionized water were stirred evenly to form a polymer-metal complex aqueous solution. At room temperature, a polysulfone ultrafiltration membrane with an average pore size of 30 nm was placed in deionized water and washed three times, and then infiltrated into the above polymer-metal complex aqueous solution at room temperature for 6 h and then dried at room temperature for 12 h;

[0081] At room temperature, an aqueous solution of zinc nitrate hexahydrate at 14.5 g / L and an aqueous solution of 2-methylimidazole (2-mIm) at 24.63 g / L were respectively prepared. After the two were mixed evenly, the above-prepared organic-metal ion interface layer was immersed for 3 h, and the membrane after the reaction was dried at room temperature for 12 h to obtain a continuous and complete ZIF-L layer, and the thickness of the ZIF-L layer was 3.0 μm.

[0082] At room temperature, an aqueous solution of m-phenylenediamine was prepared, in which m-phenylenediamine was 2.4 wt%, camphorsulfonic acid was 3.15%, and triethylamine was 1.37 wt%; an organic phase solution of trimesoyl chloride was prepared, in which trimesoyl chloride was 0.15 wt%. At room temperature, the membrane prepared in the previous step was immersed in the aqueous solution for 20 min, and then the surface was quickly washed with deionized water and absolute ethanol and dried with nitrogen, and then immersed in the organic phase solution for 5 min to complete interfacial polymerization, and heat-treated at 80 °C for 5 min. The finally obtained ZIF-L / polyamide composite membrane was dried at room temperature for 12 h for use, denoted as PSF-ZIF-L / PA membrane.

[0083] Structural characterization:

[0084] Figure 2 This is the scanning electron microscope photograph of the ZIF-L / polyamide composite membrane in Example 1 of the present invention. Among them, (a) is the structural diagram of the ZIF-L / polyamide composite membrane at a scale of 5 μm, (b) is the structural diagram of a certain part of the ZIF-L / polyamide composite membrane at a scale of 3 μm, (c) is the structural diagram of another part of the ZIF-L / polyamide composite membrane at a scale of 3 μm, and (d) is the structural diagram of the ZIF-L / polyamide composite membrane at a scale of 1 μm, as Figure 2As shown, the ZIF-L / polyamide composite membrane material fully exposes the ZIF-L flake structure on its surface, which presents a multi-level stacked orientation structure, ensuring that the two-dimensional through-pore channels between crystal layers are fully open. The polyamide network tightly bridges the ZIF-L nanosheets and fixes the ZIF-L nanosheets. At the same time, it covers the unreacted porous surface of the base membrane formed by the arrangement of ZIF-L nanosheets, achieving full coverage of non-selective defects in the membrane.

[0085] Example 2

[0086] Same as Example 1, except that the immersion time of the organic-metal ion interface layer is 6 h.

[0087] Example 3

[0088] Same as Example 1, except that the content of 2-methylimidazole is 41.05 g / L;

[0089] The immersion time of the organic-metal ion interface layer is 6 h;

[0090] The thickness of the ZIF-L layer is 5.0 μm.

[0091] Example 4

[0092] Same as Example 1, except that the content of 2-methylimidazole is 8.21 g / L;

[0093] The immersion time of the organic-metal ion interface layer is 6 h;

[0094] The thickness of the ZIF-L layer is 0.1 μm.

[0095] Example 5

[0096] Same as Example 1, except that the content of 2-methylimidazole is 24.63 g / L;

[0097] The immersion time of the organic-metal ion interface layer is 1 h;

[0098] The thickness of the ZIF-L layer is 0.0 μm.

[0099] Structural characterization:

[0100] Figure 3 These are scanning electron microscope photos of ZIF-L layers with different ligand concentrations and different growth times. Compared with the dense polyamide cross-linked structure, the MOF regulation method is more flexible and precise. The ligand concentration and growth time affect the arrangement and density of the ZIF-L layer. The interactive growth mode of ultrathin ZIF-L nanosheets and leaf-shaped ZIF-L sheets enables small-sized nanosheets to fill the large spaces between the leaf-shaped ZIF-L sheets, forming a multi-level stacked orientation structure.

[0101] Comparative Example 1

[0102] Same as Example 1, except that the polysulfone ultrafiltration membrane was immersed in the above polymer-metal complex aqueous solution and metal aqueous solution at room temperature, specifically: the polysulfone ultrafiltration membrane was first immersed in the polymer-metal complex aqueous solution in Example 1 for 6 h, and then immersed in an aqueous solution of zinc nitrate with a mass fraction of 3 wt% for 4 h to ensure an adequate metal source;

[0103] At room temperature, the prepared composite interfacial layer was immersed in an aqueous solution of 2-methylimidazole with a mass fraction of 3.2 wt% for 4 h, and the membrane after reaction was dried at room temperature for 12 h to obtain a continuous and complete ZIF-8 layer.

[0104] Structural characterization:

[0105] Figure 4 This is the scanning electron microscope photograph of the ZIF-8 / polyamide composite membrane in Example 1 of the present invention, showing the microstructure of the ZIF-8 / polyamide composite membrane after confined space interfacial polymerization. Among them, (a) is the top-view structure diagram of the ZIF-8 / polyamide composite membrane at a scale of 2 μm, (b) is the top-view structure diagram of the ZIF-8 / polyamide composite membrane at a scale of 1 μm, (c) is the side-view structure diagram of the ZIF-8 / polyamide composite membrane at a scale of 2 μm, and (d) is the side-view structure diagram of the ZIF-8 / polyamide composite membrane at a scale of 1 μm. As Figure 4 shown, the morphology of ZIF-8 particles in the ZIF-8 / PA composite membrane did not change significantly, and a thin layer of PA could be seen between the particles and between the particles and the PSF substrate membrane. In particular, the interfacial gap was covered by the polyamide layer; it should be noted that the surface of a single ZIF-8 particle was not completely coated with polyamide, and most of its original structural framework was still exposed to ensure the smoothness of the ZIF-8 transport channels. In addition, the ZIF-8 particles were more firmly fixed by the polyamide, achieving a similar interlocking effect.

[0106] Experimental Example:

[0107] Test the separation performance of the samples in Example 1 and Comparative Example 1 of the present invention at room temperature, working pressure of 5.6 MPa, and 32 g / L sodium chloride aqueous solution. The results are as Figure 5 - Figure 6 shown,

[0108] Figure 5 is the separation performance diagram of the sodium chloride aqueous solution of the sample in Example 1. The solution of the defect problem of this sample has greatly improved the desalination rate of the ZIF-L / polyamide composite membrane (PSF-ZIF-L / PA membrane) (from 3.26% to 95.57%). Compared with the pure polyamide membrane (PSF-PA membrane), its permeation flux has increased to 66.21 L / m 2*h, which benefits from the fact that the two-dimensional sheet structure of ZIF-L, the sub-nanometer channels between the sheets, and the polyamide cross-linked layer jointly create a more regular and orderly orientation flow path for water molecules.

[0109] Figure 6 It is the separation performance diagram of the sodium chloride aqueous solution of the sample in Comparative Example 1; although the large-sized dense and continuous ZIF-8 layer minimizes the defects of the PSF-ZIF-8 membrane, the water flux of the membrane reaches as high as 312.67 L / m 2 *h. However, its desalination rate is only 2.11%, which is mainly due to the large-scale interfacial gaps in the unevenly arranged loose ZIF-8 layer, showing obvious non-selective separation performance. After interfacial polymerization in the confined space, the cross-linked polyamide layer eliminates the non-selective defects in the membrane, and the desalination rate of the ZIF-8 / polyamide composite membrane (PSF-ZIF-8 / PA membrane) has been greatly improved (from 2.11% to 86.52%); compared with the pure polyamide membrane (PSF-PA membrane), its permeation flux is 72.36 L / m 2 *h, which is nearly doubled, thanks to the developed multiple water transport channels in the composite layer. The three-dimensional porous structure of ZIF-8, the intercrystalline sub-nanometer channels of ZIF-8, and the polyamide cross-linked layer all create shorter flow paths for water molecules, thereby achieving a substantial increase in the permeation flux of membrane water while meeting relatively good selectivity.

[0110] The specific embodiments described above further elaborate on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a MOF / polyamide composite membrane, characterized in that: The following steps are involved: The surface of the flexible porous polymer base membrane is coated / immersed in a polymer-metal complex aqueous solution so that metal ions are uniformly attached to the surface to obtain a polymer membrane rich in metal ions; Immersing the metal ion-rich polymer membrane in a metal-ligand mixed aqueous solution to obtain a MOF layer attached to the metal ion-rich polymer membrane; The MOF layer is contacted with an aqueous solution of a polyamine, and after washing, the MOF layer is contacted with an organic solution of an acyl chloride monomer to complete a polyamide interfacial polymerization reaction in a confined space to obtain a composite membrane; heat-treating the composite membrane to obtain the MOF / polyamide composite membrane; The polymer-metal complex aqueous solution includes polyvinyl alcohol, zinc nitrate hexahydrate and deionized water; The metal-ligand mixed aqueous solution includes an aqueous solution of zinc nitrate hexahydrate and an aqueous solution of 2-methylimidazole.

2. The preparation method according to claim 1, characterized in that: The material of the flexible porous polymer base membrane includes one of polysulfone, polyethersulfone, polyacrylonitrile, polyimide, polyvinylidene fluoride and polypropylene; And / or, the average pore size of the flexible porous polymer-based membrane is 10-100 nm.

3. The preparation method according to claim 1, characterized in that: The ratio of the zinc nitrate hexahydrate aqueous solution, 2-methylimidazole and deionized water in the metal-ligand mixed aqueous solution is 0.00-2.00 g: 1.00-5.00 g: 100-500 mL.

4. The preparation method according to claim 1, characterized in that: The aqueous phase solution of the polyamine comprises the polyamine and an additive; And / or, the aqueous solution of the polyamine is in a neutral or alkaline environment; And / or, the contact time between the MOF layer and the aqueous solution of polyamine is 5 min-30 min.

5. The preparation method according to claim 1, characterized in that: The organic phase solution of the acyl chloride monomer comprises a solvent and the acyl chloride monomer; And / or, the solvent is one or more of Iaopar-G and n-hexane; And / or, the acyl chloride monomer is one or more of trimesoyl chloride, isophthaloyl chloride, phthaloyl chloride, and terephthaloyl chloride, and the acyl chloride monomer accounts for 0.05%-0.3% of the mass fraction of the organic phase solution.

6. The preparation method according to claim 4, characterized in that: The polyamine includes one or more of piperazine, m-phenylenediamine, and p-phenylenediamine, and the polyamine accounts for 1% to 5% of the mass fraction of the aqueous phase solution; And / or, the additives include triethylamine and camphorsulfonic acid; wherein the mass fraction of the triethylamine is 0%-3%; and the mass fraction of the camphorsulfonic acid is 0-5%.

7. The preparation method according to claim 1, characterized in that: The cleaning comprises: using a good solvent and deionized water to clean the residual amine monomers on the membrane surface; And / or, the good solvent is one or more of anhydrous ethanol, anhydrous methanol, Iaopar-G, and n-hexane.

8. The preparation method according to claim 1, characterized in that: The interfacial polymerization time of the polyamide interfacial polymerization reaction is 1-10min; And / or, the temperature of the heat treatment is 50-90°C; And / or, the heat treatment time is 5 min-30 min.

9. A MOF / polyamide composite membrane prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the MOF / polyamide composite membrane according to claim 9 in a high-concentration sodium chloride separation process in an aqueous solution system.

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