A flexible MOF microfiltration membrane, its preparation method and application

Abstract

The application provides a flexible MOF microfiltration membrane and a preparation method and application thereof, and belongs to the technical field of polymer composite membranes. The polymer nanofiber membrane formed by polymer nanofibers has a large specific surface area, so that the flexible MOF microfiltration membrane has a larger contact area with pollutants. Meanwhile, the defective MOF particles are uniformly distributed on the surface of the polymer nanofibers of the polymer nanofiber membrane, and the defective MOF nanoparticles provide abundant active sites, which can improve the adsorption capacity for pollutants. The results of the examples show that the flexible MOF microfiltration membrane provided by the application has an adsorption capacity for phosphate which is about 50% higher than that of MOF particles, and the terephthalic acid leaching rate in the adsorption process is reduced from 12.0% to 0.3%.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer composite membranes, and in particular to a flexible MOF microfiltration membrane and a preparation method and application thereof. Background Art

[0002] A microfiltration membrane is a filter membrane with a pore size of 0.1-1 μm. It can retain particulate matter through the membrane's physical structure and is primarily used in separation, filtration, and impurity removal. Microfiltration membranes are often made from organic polymers or inorganic materials, primarily through methods such as phase inversion, melt stretching, etching, radiation curing, and sintering. In recent years, surface modification of microfiltration membranes has become a method for constructing multifunctional microfiltration membranes. In particular, porous spun fiber membranes achieve extremely high filtration specific surface areas and modified sites, which can be used to improve the adsorption and removal efficiency of pollutants and enhance the treatment of wastewater or waste gases.

[0003] Metal-organic frameworks (MOFs) are crystalline porous materials with a hierarchical pore structure composed of inorganic metal centers and organic functional groups linked by covalent or ionic-covalent bonds. Due to their uniform pore structure and metal active sites, MOFs play a vital role in the energy, separation, and catalysis sectors, offering a potential for surface modification of microfiltration membranes and improving wastewater or gas treatment capacity. However, most MOFs are nanocrystalline. The incompatibility between the MOF and the polymer phase of the microfiltration membrane leads to non-ideal effects, such as interfacial voids and particle clogging of pores. Furthermore, MOF aggregation, caused by strong surface tension and high surface energy, results in uneven dispersion of the MOF within the polymer matrix. These phenomena limit the adsorption capacity of the resulting microfiltration membranes modified with MOFs, making them unsatisfactory.

[0004] Therefore, a flexible MOF microfiltration membrane with high adsorption capacity for pollutants is needed. Summary of the Invention

[0005] The purpose of the present invention is to provide a flexible MOF microfiltration membrane and a preparation method and application thereof. The flexible MOF microfiltration membrane provided by the present invention has excellent adsorption capacity for pollutants.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a flexible MOF microfiltration membrane, comprising a polymer nanofiber membrane and defective metal organic framework particles, wherein the defective metal organic framework particles are distributed on the surface of polymer nanofibers of the polymer nanofiber membrane; the diameter of the polymer nanofibers is 5-800 nm; and the particle size of the defective metal organic framework particles is 0.1-200 nm.

[0008] Preferably, the material of the polymer nanofiber includes one or more of polypropylene, polysulfone, polyethersulfone, polyvinylidene fluoride, polyvinyl pyrrolidone, polyvinyl alcohol, polyacrylonitrile and sulfonated polyethersulfone.

[0009] Preferably, the metal ions of the defective metal-organic framework particles include one or more of Zr ions, Ce ions, Fe ions, Zn ions, Cu ions, Ni ions, Pt ions and Co ions; the organic ligands of the defective metal-organic framework particles include one or more of terephthalic acid, aminoterephthalic acid, dimethylimidazole, succinic acid, dimethylbenzimidazole, succinic acid, imidazole, pyridine and piperidine.

[0010] Preferably, the mass content of the metal organic framework particles in the flexible MOF microfiltration membrane is 5-35%.

[0011] The present invention also provides a method for preparing the flexible MOF microfiltration membrane described in the above technical solution, comprising the following steps:

[0012] (1) mixing any one of MOF raw materials with a polymer solution to obtain a spinning solution, and electrospinning the spinning solution to obtain a polymer nanofiber membrane loaded with metal ions or organic ligands; the MOF raw materials include metal salts and organic ligands;

[0013] (2) Mixing another solution of the MOF raw material in step (1) with the polymer nanofiber membrane loaded with metal ions or organic ligands obtained in step (1) to carry out a self-assembly reaction to obtain a flexible MOF microfiltration membrane.

[0014] Preferably, the mass percentage of the polymer in the spinning solution in step (1) is 5-20%.

[0015] Preferably, the spinning solution contains a metal salt, and the mass percentage of the metal salt in the spinning solution is 0.1-30%.

[0016] Preferably, the spinning solution contains an organic ligand, and the mass percentage of the organic ligand in the spinning solution is 0.1-30%.

[0017] Preferably, the electrospinning parameters in step (1) include: spinning voltage of 5 to 30 kV; collector speed of 0 to 800 rpm; injection rate of 0.5 to 2 mL / h; and receiving distance of 5 to 20 cm.

[0018] The present invention also provides the use of the flexible MOF microfiltration membrane described in the above technical solution or the flexible MOF microfiltration membrane prepared by the preparation method described in the above technical solution in water treatment and / or waste gas treatment.

[0019] The present invention provides a flexible MOF microfiltration membrane comprising a polymer nanofiber membrane and defective metal-organic framework particles, wherein the defective metal-organic framework particles are distributed on the surface of the polymer nanofibers of the polymer nanofiber membrane; the polymer nanofibers have a diameter of 5 to 800 nm; and the defective metal-organic framework particles have a particle size of 0.1 to 200 nm. In the flexible MOF microfiltration membrane provided by the present invention, the polymer nanofibers comprise a large specific surface area, providing a larger contact area between the flexible MOF microfiltration membrane and pollutants. Furthermore, the defective MOF particles are distributed on the surface of the nanofibers of the polymer nanofiber membrane, forming more adsorption sites within the polymer nanofiber membrane, further improving its adsorption capacity for pollutants. Experimental results show that the flexible MOF microfiltration membrane provided by the present invention enhances phosphate adsorption by approximately 50% compared to MOF particles, and reduces the leaching rate of terephthalic acid from 12.0% to 0.3% during the adsorption process. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a SEM image of the flexible MOF microfiltration membrane prepared in Example 1 of the present invention;

[0021] Figure 2 The photoluminescence spectra of the flexible MOF microfiltration membrane prepared in Example 1 of the present invention and the UiO-66 prepared in Comparative Example 1 are shown;

[0022] Figure 3 Phosphorus adsorption diagrams for water treatment of the flexible MOF microfiltration membrane prepared in Example 1 of the present invention, the UiO-66 microfiltration membrane prepared in Comparative Example 1, and the microfiltration membrane prepared in Comparative Example 2;

[0023] Figure 4 This is a ligand leaching diagram of the flexible MOF microfiltration membrane prepared in Example 1 of the present invention and the UiO-66 prepared in Comparative Example 1;

[0024] Figure 5 The pH value of the solution after adsorption of phosphorus solution by the flexible MOF microfiltration membrane prepared in Example 1 of the present invention and the UiO-66 prepared in Comparative Example 1 at different material dosages;

[0025] Figure 6Graph showing the adsorption capacity of heavy metals and organic dyes for water treatment using the flexible MOF microfiltration membrane prepared in Example 1 of the present invention, the UiO-66 prepared in Comparative Example 1, and commercial ion exchange resin. DETAILED DESCRIPTION

[0026] The present invention provides a flexible MOF microfiltration membrane, comprising a polymer nanofiber membrane and defective metal organic framework particles, wherein the defective metal organic framework particles are distributed on the surface of polymer nanofibers of the polymer nanofiber membrane; the diameter of the polymer nanofibers is 5-800 nm; and the particle size of the defective metal organic framework particles is 0.1-200 nm.

[0027] In the present invention, the pore size of the flexible MOF microfiltration membrane is preferably 0.1-10 μm, more preferably 0.2-1.0 μm. The pore size of the flexible MOF microfiltration membrane provided by the present invention is within the above range, which is more conducive to the entry of pollutants into the microfiltration membrane and improves the adsorption capacity of pollutants.

[0028] The flexible MOF microfiltration membrane provided by the present invention comprises a polymer nanofiber membrane. The nanofiber membrane in the flexible MOF microfiltration membrane provided by the present invention is a fiber membrane formed by randomly and irregularly arranged polymer nanofibers.

[0029] In the present invention, the polymer nanofibers have a diameter of 5 to 800 nm, preferably 50 to 500 nm. The polymer nanofibers in the flexible MOF microfiltration membrane provided by the present invention have a diameter within this range and are nanoscale fibers with a large specific surface area. This increases the contact area between the flexible MOF microfiltration membrane and pollutants, providing a greater specific surface area for filtration.

[0030] In the present invention, the nanofiber structure is preferably strip, cylindrical, beaded, ribbon-like, porous, core-shell, hollow, micro-protruding, pleated, or spiral, and more preferably strip, cylindrical, beaded, ribbon-like, porous, core-shell, or hollow. The flexible MOF microfiltration membrane provided by the present invention has the above-mentioned nanofiber structure, which can provide a larger filtration specific surface area.

[0031] In the present invention, the polymer nanofibers are preferably made of one or more of polypropylene, polysulfone, polyethersulfone, polyvinylidene fluoride, polyvinyl pyrrolidone, polyvinyl alcohol, polyacrylonitrile, and sulfonated polyethersulfone, and more preferably one or more of polyacrylonitrile, polyvinyl pyrrolidone, and polyvinyl alcohol. The use of these polymers in the present invention facilitates the formation of continuous nanofibers with uniform diameters.

[0032] The flexible MOF microfiltration membrane provided by the present invention comprises defective metal organic framework particles. In the present invention, the defective metal organic framework particles have abundant lattice defects, and this lattice defect structure can improve the adsorption capacity of pollutants.

[0033] In the present invention, the defective metal-organic framework particles are distributed on the surface of the polymer nanofibers of the polymer nanofiber membrane. In the present invention, the distribution of the metal-organic framework particles on the surface of the polymer nanofibers can provide continuous molecular channels, which is more conducive to improving the adsorption capacity of the flexible MOF microfiltration membrane for pollutants.

[0034] In the present invention, the defective MOF particles are preferably continuously distributed on the surface of the polymer nanofibers of the polymer nanofiber membrane. By continuously distributing the defective MOF particles on the surface of the polymer nanofibers of the polymer nanofiber membrane, the continuously distributed defective MOF particles come into contact with each other, enabling the pores in the defective MOF particles to form continuous channels within the polymer nanofibers, further facilitating the adsorption and storage of pollutants and enhancing the adsorption effect.

[0035] In the present invention, the defective metal-organic framework particles have a particle size of 0.1 to 200 nm, more preferably 5 to 100 nm. By controlling the particle size of the metal-organic framework particles within this range, the present invention achieves nanoscale MOFs, which are more conducive to forming continuous particles on polymer nanofibers.

[0036] In the present invention, the metal ions of the defective metal-organic framework particles preferably include one or more of Zr, Ce, Fe, Zn, Cu, Ni, Pt, and Co, more preferably Zr, Ce, or Fe. The organic ligands of the defective metal-organic framework particles preferably include one or more of terephthalic acid, aminoterephthalic acid, dimethylimidazole, styrene-3-benzoic acid, dimethylbenzimidazole, succinic acid, imidazole, pyridine, and piperidine, more preferably terephthalic acid, aminoterephthalic acid, dimethylimidazole, styrene-3-benzoic acid, or dimethylbenzimidazole. The present invention utilizes the above-mentioned metal ions and organic ligands to produce a metal-organic framework.

[0037] In the present invention, the defective metal-organic framework particles preferably include UiO-66, ZIF-7, ZIF-8, MIL-53, MIL-101, HKUST-1, or MOF-5, with UiO-66, ZIF-7, or ZIF-8 being more preferred. These metal-organic framework particles, which possess a rich porous structure and a large specific surface area, are more conducive to improving the adsorption capacity of pollutants.

[0038] In the present invention, the mass content of the metal-organic framework particles in the flexible MOF microfiltration membrane is preferably 5-35%, more preferably 10-30%. In the present invention, when the mass content of the defective metal-organic framework particles is within the above range, it is more conducive to improving the adsorption capacity of the flexible MOF microfiltration membrane.

[0039] In the present invention, the structure of the flexible MOF microfiltration membrane is preferably a flat membrane, a spiral membrane or a hollow fiber membrane, more preferably a flat membrane. The flexible MOF microfiltration membrane provided by the present invention has the above structure and can be applied to different application environments.

[0040] In the flexible MOF microfiltration membrane provided by the present invention, the polymer nanofiber membrane composed of polymer nanofibers has a large specific surface area and a larger contact area with pollutants; the metal organic framework particles are distributed on the polymer nanofiber surface of the polymer nanofiber membrane, which can provide continuous molecular channels and is more conducive to the adsorption of pollutants; the defective MOF nanoparticles provide abundant active sites, which can improve the adsorption capacity of pollutants.

[0041] The present invention also provides a method for preparing the flexible MOF microfiltration membrane described in the above technical solution, comprising the following steps:

[0042] (1) mixing any one of MOF raw materials with a polymer solution to obtain a spinning solution, and electrospinning the spinning solution to obtain a polymer nanofiber membrane loaded with metal ions or organic ligands; the MOF raw materials include metal salts and organic ligands;

[0043] (2) Mixing another solution of the MOF raw material in step (1) with the polymer nanofiber membrane loaded with metal ions or organic ligands obtained in step (1) to carry out a self-assembly reaction to obtain a flexible MOF microfiltration membrane.

[0044] In the present invention, any one of MOF raw materials is mixed with a polymer solution to obtain a spinning solution, and the spinning solution is subjected to electrostatic spinning to obtain a polymer nanofiber membrane loaded with metal ions or organic ligands.

[0045] In the present invention, the MOF raw materials include metal salts and organic ligands.

[0046] In the present invention, the metal salt preferably includes one or more of a Zr salt, a Ce salt, an Fe salt, a Zn salt, a Cu salt, a Ni salt, a Pt salt, and a Co salt, and more preferably one or more of a Zr salt, a Ce salt, an Fe salt, and a Zn salt. In an embodiment of the present invention, the Zr salt may be zirconium tetrachloride; the Ce salt may be cerium nitrate hexahydrate; the Fe salt may be ferric chloride; the Zn salt may be zinc nitrate hexahydrate; and the Cu salt may be copper nitrate hexahydrate. The present invention utilizes metal salts to provide metals for the metal-organic framework particles.

[0047] In the present invention, the organic ligand preferably includes one or more of terephthalic acid, aminoterephthalic acid, dimethylimidazole, succinic acid, dimethylbenzimidazole, succinic acid, imidazole, pyridine and piperidine, more preferably one or more of terephthalic acid, aminoterephthalic acid and dimethylimidazole.

[0048] In the present invention, different types of metal salts and organic ligands correspond to different metal-organic framework particles. In an embodiment of the present invention, the metal salt is a Zr salt, the organic ligand is terephthalic acid, and the corresponding metal-organic framework particles may be UiO-66; the metal salt is a Zn salt, the organic ligand is benzimidazole C7H6N2, and the corresponding metal-organic framework particles may be ZIF-7; the metal salt is a Zn salt, the organic ligand is 2-methylimidazole, and the corresponding metal-organic framework particles may be ZIF-8; the metal salt is an Fe salt or an Al salt, the organic ligand is terephthalic acid, and the corresponding metal-organic framework particles may be MIL-53; the metal salt is an Fe salt or a Cr salt, the organic ligand is terephthalic acid, and the corresponding metal-organic framework particles may be MIL-101; the metal salt is a Cu salt, the organic ligand is 1,3,5-benzenetricarboxylic acid, and the corresponding metal-organic framework particles may be HKUST-1; the metal salt is a Zn salt, the organic ligand is terephthalic acid, and the corresponding metal-organic framework particles may be MOF-5.

[0049] In the present invention, the polymer in the polymer solution preferably includes one or more of polypropylene, polysulfone, polyethersulfone, polyvinylidene fluoride, polyvinyl pyrrolidone, polyvinyl alcohol, polyacrylonitrile, and sulfonated polyethersulfone, and more preferably one or more of polyacrylonitrile, polyvinyl pyrrolidone, and polyvinyl alcohol. The use of the above polymers in the present invention is more conducive to the formation of continuous polymer nanofibers.

[0050] In the present invention, the solvent in the polymer solution is preferably one or more of water, N,N-dimethylformamide, dimethylacetamide, methanol, acetone, ethanol, and dimethyl sulfoxide, and more preferably one or more of N,N-dimethylformamide, dimethylacetamide, methanol, and acetone. The above solvents used in the present invention have good solubility for the metal salt, organic ligand, and polymer, and are capable of dissolving these components to form a spinning solution.

[0051] In the present invention, the mass percentage of the polymer in the spinning solution is preferably 5-20%, more preferably 10-20%. The present invention controls the mass percentage of the polymer within the above range, which is more conducive to obtaining a nanoscale polymer nanofiber membrane with excellent mechanical properties.

[0052] In the present application, the metal salt is contained in the spinning solution, and the mass percentage of the metal salt in the spinning solution is preferably 0.1-30%, more preferably 1-20%, and further preferably 2-15%. Controlling the mass percentage of the metal salt in the spinning solution within the above range is more conducive to distributing the metal organic framework particles on the surface of the polymer nanofiber.

[0053] In the present application, the organic ligand is contained in the spinning solution, and the mass percentage of the organic ligand in the spinning solution is preferably 0.1-30%, more preferably 1-20%, and further preferably 10-15%. Controlling the mass percentage of the organic ligand in the spinning solution within the above range is more conducive to distributing the metal organic framework particles on the surface of the polymer nanofiber.

[0054] The present application does not have special limitations on the method of mixing the metal salt or the organic ligand with the polymer solution, and the metal salt or the organic ligand can be fully dissolved with the polymer to form a spinning solution.

[0055] In the present application, both the metal salt and the organic ligand are not used at the same time in the spinning solution. The present application uses the metal salt or the organic ligand alternatively in the spinning solution, which can uniformly distribute the metal salt or the organic ligand in the polymer nanofiber membrane.

[0056] In the present application, the electrospinning method is preferably coaxial spinning, super orientation spinning, melt spinning or wet spinning. The present application can obtain polymer nanofiber membranes with different structures by using different electrospinning methods.

[0057] In the present application, the spinning voltage of the electrospinning is preferably 5-30 kV, and more preferably 20-30 kV; the collector rotation speed of the electrospinning is preferably 0-800 rpm, and more preferably 300-500 rpm; the push injection rate of the electrospinning is preferably 0.5-2 mL / h, and more preferably 0.8-1 mL / h; and the receiving distance of the electrospinning is preferably 5-20 cm, and more preferably 10-20 cm. Controlling the parameters of the electrospinning within the above range is more conducive to forming continuous polymer nanofibers.

[0058] The present application preferably dries the membrane obtained by electrospinning after electrospinning to obtain a polymer nanofiber membrane loaded with metal ions or organic ligands. The present application does not have special limitations on the drying method, and the polymer nanofiber membrane can be fully dried by using a conventional drying method.

[0059] After obtaining the polymer nanofiber membrane loaded with metal ions or organic ligands, the solution of another kind of MOF raw material is mixed with the polymer nanofiber membrane loaded with metal ions or organic ligands to perform a self-assembly reaction to obtain a flexible MOF microfiltration membrane.

[0060] In the present invention, the other solution of the MOF raw material is preferably a metal salt solution or an organic ligand solution.

[0061] In the present invention, the metal salt in the metal salt solution preferably includes one or more of a Zr salt, a Ce salt, a Fe salt, a Zn salt, a Cu salt, a Ni salt, a Pt salt, and a Co salt, more preferably one or more of a Zr salt, a Ce salt, a Fe salt, and a Zn salt. In an embodiment of the present invention, the Zr salt may be zirconium tetrachloride.

[0062] In the present invention, the concentration of the metal salt solution is preferably 0.002-0.05 g / mL, more preferably 0.007 g / mL. Controlling the concentration of the metal salt solution within the above range is more conducive to the full progress of the self-assembly reaction.

[0063] In the present invention, the organic ligand in the organic ligand solution preferably includes one or more of terephthalic acid, aminoterephthalic acid, dimethylimidazole, succinic acid, dimethylbenzimidazole, succinic acid, imidazole, pyridine and piperidine, and more preferably one or more of terephthalic acid, aminoterephthalic acid and dimethylimidazole.

[0064] In the present invention, the concentration of the organic ligand solution is preferably 0.002-0.03 g / mL, more preferably 0.005 g / mL. Controlling the concentration of the organic ligand solution within the above range is more conducive to the full progress of the self-assembly reaction.

[0065] The present invention has no particular limitation on the volume of the metal salt solution or the organic ligand solution, as long as the polymer nanofiber membrane can be completely immersed in the metal salt solution or the organic ligand solution.

[0066] In the present invention, the metal salt solution and the organic ligand solution are not used simultaneously. In the present invention, when a metal salt is added to the spinning solution, the organic ligand solution is mixed with the polymer nanofiber membrane; in the present invention, when an organic ligand is added to the spinning solution, the metal salt solution is mixed with the polymer nanofiber membrane. In the present invention, by selecting either a metal salt solution or an organic ligand solution, the metal salt or organic ligand formed in the polymer nanofiber membrane undergoes a self-assembly reaction with the organic ligand solution or metal salt. The confined diffusion of the polymer or monomer in the nanofiber during the self-assembly reaction is utilized to form a stable metal-organic framework nucleation interface on the nanofiber surface, thereby forming stable and defective metal-organic framework particles.

[0067] In the present invention, the self-assembly reaction is preferably a hydrothermal method or a room temperature synthesis method.

[0068] In the present invention, the temperature of the hydrothermal method is preferably 100-150°C, more preferably 120°C; the hydrothermal reaction time is preferably 24-96 hours, more preferably 24 hours. The present invention uses a hydrothermal reaction to complete a self-assembly reaction to prepare UiO-66, ZIF-7, MIL-53, MIL-101, HKUST-1, or MOF-5.

[0069] In the present invention, the preparation method of ZIF-8 or ZIF-67 is preferably a room temperature method. The present invention has no particular limitation on the operation method of the room temperature method. A conventional room temperature method can be used to obtain ZIF-8 or ZIF-67 with a particle size of 0.1 to 200 nm.

[0070] In the present invention, the self-assembly reaction is preferably performed in one or more growth steps, and the number of such growth steps is preferably 1 to 10, and more preferably 1 to 5. The present invention can control the mass content of the metal-organic framework particles in the flexible MOF microfiltration membrane to 5 to 35% by performing the self-assembly reaction in one or more steps.

[0071] In the present invention, after the self-assembly reaction, cleaning, exchange and drying are preferably performed in sequence to obtain a flexible MOF microfiltration membrane.

[0072] In the present invention, the cleaning agent preferably includes one or more of water, N,N-dimethylformamide, dimethylacetamide, methanol, acetone, ethanol, and dimethyl sulfoxide, and more preferably one or more of water, N,N-dimethylformamide, dimethylacetamide, methanol, and acetone. The present invention can remove impurities from the surface of the flexible MOF microfiltration membrane through cleaning. The present invention is not particularly limited to the cleaning method, as long as it can fully remove impurities from the flexible MOF microfiltration membrane.

[0073] In the present invention, the exchange reagent preferably includes one or more of water, N,N-dimethylformamide, dimethylacetamide, methanol, acetone, ethanol, and dimethyl sulfoxide, and more preferably one or more of water, N,N-dimethylformamide, dimethylacetamide, methanol, and acetone. The present invention can remove impurities from the pores of a flexible MOF microfiltration membrane through exchange. In the present invention, the exchange method preferably involves immersing the cleaned microfiltration membrane in the exchange reagent. In the present invention, the immersion is preferably repeated twice, with each immersion lasting 6 to 24 hours, more preferably 12 hours.

[0074] The present invention preferably dries the microfiltration membrane obtained after the exchange to obtain a flexible MOF microfiltration membrane. The present invention does not particularly limit the temperature and time of the drying, and conventional drying temperature and time can be used to fully dry the flexible MOF microfiltration membrane.

[0075] The method provided by the application has simple operation, metal salt or organic ligand is added in the spinning solution first, so that the metal salt or organic ligand is uniformly distributed in the polymer nanofiber of the polymer nanofiber membrane; then, the limited diffusion in self-assembly of the polymer nanofiber membrane is utilized, so that a stable MOF nucleation interface is formed on the fiber surface, thereby forming a stable and defect metal organic framework particle.

[0076] The technical solutions in the application will be clearly and completely described below with reference to the embodiments in the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the application.

[0077] Embodiment 1

[0078] A flexible MOF microfiltration membrane, which is composed of a polymer nanofiber membrane and a defect metal organic framework particle, wherein the defect metal organic framework particle is distributed on the surface of the polymer nanofiber of the polymer nanofiber membrane; the average diameter of the polymer nanofiber is 360 nm; the average particle size of the defect metal organic framework particle is 15.2 nm; and the mass content of the metal organic framework particle in the flexible MOF microfiltration membrane is 25.6%.

[0079] The preparation method of the flexible MOF microfiltration membrane is as follows:

[0080] (1) 0.5 g of terephthalic acid, 0.25 g of polyacrylonitrile and 30 mL of N,N-dimethylformamide are mixed and dissolved to obtain a spinning solution, the spinning solution is loaded into an electrospinning push injector, a voltage of 20 kV is applied, the collector rotates at a speed of 300 rpm, and the push injection rate is 0.8 mL / h, and after drying, a polymer nanofiber membrane loaded with an organic ligand is obtained;

[0081] (2) 0.7 g of zirconium tetrachloride, 10 mL of N,N-dimethylformamide, 30 mL of acetone and 10 mL of glacial acetic acid are mixed and dissolved to obtain a mixed solution, the polymer nanofiber membrane is soaked in the mixed solution, placed in a hydrothermal kettle, and subjected to self-assembly by hydrothermal reaction at 120℃ for 24 h, then the obtained microfiltration membrane is cleaned with an acetone solution for 3 times, and soaked in methanol for 2 times, each time for 12 h, and after drying, a flexible MOF microfiltration membrane is obtained;

[0082] Test results show that the specific surface area of the flexible MOF microfiltration membrane prepared in this embodiment is 217.21 m 2 / g.

[0083] Comparative Example 1

[0084] A preparation method of UiO-66:

[0085] (1) Add 0.7 g of zirconium tetrachloride into 30 mL of N,N-dimethylformamide solution and dissolve to obtain solution A;

[0086] (2) Add 0.5 g of terephthalic acid into 30 mL of N,N-dimethylformamide solution and dissolve to obtain solution B;

[0087] (3) Solution A was added dropwise to solution B, and 10 mL of glacial acetic acid was added and stirred to obtain solution C;

[0088] (4) Add solution C to the hydrothermal reactor and react at 120°C for 24 hours;

[0089] (5) The obtained particles were washed with N,N-dimethylformamide solution for 3-5 times and immersed in methanol twice for 12 h each time to obtain UiO-66.

[0090] Comparative Example 2

[0091] A method for preparing a flexible MOF microfiltration membrane is as follows:

[0092] 0.1 g of UiO-66 prepared in Comparative Example 1 was mixed with 30 mL of N,N-dimethylformamide and 0.25 g of polyacrylonitrile to obtain a mixed solution, and the spinning solution was charged into an electrospinning injector, the applied voltage was 20 kV, the collector speed was 300 rpm, the injection rate was 0.8 mL / h, and the polymer nanofiber membrane was obtained after drying; the obtained microfiltration membrane was washed three times with an acetone solution and immersed in methanol twice, each time for 12 hours, and dried to obtain a flexible MOF microfiltration membrane;

[0093] The specific surface area of ​​the flexible MOF microfiltration membrane prepared in this comparative example is 49.73 m 2 / g.

[0094] Application Example 1

[0095] The adsorption performance of the flexible MOF microfiltration membrane prepared in Example 1 on the phosphorus-containing solution was tested as follows:

[0096] Ten milligrams of the flexible MOF microfiltration membrane prepared in Example 1 were added to a serum bottle containing 100 mL of potassium dihydrogen phosphate solution (phosphorus content: 1 mg / L, pH: 6.5). The solution was shaken at 200 rpm for 24 hours at 25°C to achieve adsorption equilibrium. The supernatant was collected at specific times (0, 1, 2.5, 4, 6, 8, and 10 hours) to determine the residual phosphate concentration. The adsorption kinetics were characterized using a pseudo-first-order model.

[0097] Comparative Application Example 1

[0098] The adsorption performance of UiO-66 prepared in Comparative Example 1 on phosphorus-containing solution was tested using the same testing method as that in Application Example 1.

[0099] Comparative Application Example 2

[0100] The adsorption performance of the microfiltration membrane prepared in Comparative Example 2 on the phosphorus-containing solution was tested using the same testing method as in Application Example 1.

[0101] Application Example 2

[0102] The flexible MOF microfiltration membrane prepared in Example 1 was tested for the adsorption of heavy metals and organic dyes. The method was as follows: a heavy metal salt solution with a concentration of 5 mg / L (the heavy metal ion was Cr 3+ 、As 5+ 、Sb 5+ 、Cd 2+ and Pb 2+ ) and organic dye (MB) solution, and then 10 mg of the flexible MOF microfiltration membrane prepared in Example 1 was added to a serum bottle containing 100 mL of the above heavy metal salt solution or organic dye solution, and shaken at 200 r / min at 25 ° C for 24 h to reach adsorption equilibrium. The pseudo-first-order model was used to characterize the adsorption kinetics.

[0103] Comparative Application Example 3

[0104] The adsorption performance of the flexible MOF microfiltration membrane prepared in Comparative Example 1 on heavy metals and organic dyes was tested using the same testing method as in Application Example 2.

[0105] Comparative Application Example 4

[0106] The adsorption performance of commercial ion exchange resin (D201 polystyrene anion exchange resin) for heavy metals and organic dyes was tested using the same test method as in Application Example 2.

[0107] Test Case

[0108] (1) The photoluminescence spectra of the flexible MOF microfiltration membrane prepared in Example 1 and the UiO-66 prepared in Comparative Example 1 are shown in Figure 2. Figure 2 As shown. Figure 2 It can be seen that at an excitation wavelength of 280 nm, the intensity of the fluorescence signal λex / λem=280 nm / 395 nm is mediated by the coordination number of Zr-O clusters and BDC in the UiO-66 matrix, and is negatively correlated with the content of defect sites. Among them, the defects in Example 1 are the most abundant, indicating that this method has a significant impact on defect formation.

[0109] (2) According to the adsorption performance test method of the flexible MOF microfiltration membrane prepared in Example 1, the UiO-66 prepared in Application Example 1 and the microfiltration membrane prepared in Comparative Example 2, the water treatment phosphorus adsorption graph of the flexible MOF microfiltration membrane prepared in Example 1, the UiO-66 prepared in Comparative Example 1 and the microfiltration membrane prepared in Comparative Example 2 is shown in Figure 3 Figure 3 It can be seen that the adsorption amount of the flexible MOF microfiltration membrane prepared in Example 1 can reach 66 mg / g, while the adsorption amount of the UiO-66 prepared in Comparative Example 1 is 42 mg / g, and the adsorption amount of the flexible MOF microfiltration membrane prepared in Example 1 is enhanced by about 50% for phosphorus adsorption. This is because the flexible MOF microfiltration membrane prepared by the method of the application is adsorbed by the active sites of the defect-rich MOF on the surface of the nanofiber, which improves the adsorption capacity of the pollutants and further improves the treatment effect of the wastewater.

[0110] (3) Stability test of the flexible MOF microfiltration membrane prepared in Example 1 and the UiO-66 prepared in Comparative Example 1, the method is: the samples are respectively added into a serum bottle containing 100 mL of potassium dihydrogen phosphate solution (phosphorus content is 0.5-50 mg / L, pH=6.5), and oscillated at 25°C and 200 r / min for 24 h to reach adsorption equilibrium, while the adsorption experiment is carried out, the ligand concentration is measured by extracting the solution to judge the ligand leaching of the UiO-66.

[0111] The ligand leaching graph of the flexible MOF microfiltration membrane prepared in Example 1, the UiO-66 prepared in Comparative Example 1 and the microfiltration membrane prepared in Comparative Example 2 is shown in Figure 4 The corresponding data is shown in Table 1.

[0112] Table 1 Ligand leaching results of different adsorption materials (%)

[0113]

[0114] From Figure 4 and Table 1, it can be seen that the mass percentage of ligand leaching of the UiO-66 prepared in Comparative Example 1 is much higher than that of the flexible MOF microfiltration membrane prepared in Example 1. This is because the method provided by the application can stably grow metal organic framework particles on the surface of the nanofiber, effectively reduce the ligand leaching of the UiO-66, and improve the stability of the flexible MOF microfiltration membrane.

[0115] (4) After the flexible MOF microfiltration membrane prepared in Example 1 and the UiO-66 prepared in Comparative Example 1 are respectively placed in a potassium dihydrogen phosphate solution with an initial phosphorus concentration of 1 mg / L and reach adsorption equilibrium, the pH value of the solution is observed, as shown in Figure 5 and Table 2.

[0116] Table 2 pH value of water after soaking of different adsorption materials in water ​

[0117]

[0118] From Figure 5 As can be seen from Table 2, under different material dosing conditions, the initial phosphorus concentration is 1 mg / L, and after adsorption equilibrium, the pH is measured. The comparative example 1 is extremely unstable during the adsorption process, and the leaching of BDC causes the solution to gradually become acidic, while the example 1 exhibits extremely high stability, and the pH of the solution does not change.

[0119] (5) The water treatment heavy metal and organic dye adsorption capacity diagram of the flexible MOF microfiltration membrane prepared by example 1 and the UiO-66 prepared by comparative example 1 and the commercial ion exchange resin (D201 polystyrene anion exchange resin) is as shown in Figure 3 and Table 3. Figure 6

[0120] Table 3 Water treatment heavy metal and organic dye adsorption capacity results (mg / g) of different adsorption materials

[0121]

[0122] From Figure 6 As can be seen from Table 3, the flexible MOF microfiltration membrane prepared by the present application exhibits excellent adsorption capacity for heavy metal ions and organic dyes.

[0123] As can be seen from the above results, the flexible MOF microfiltration membrane provided by the present application has excellent adsorption capacity for heavy metal ions and organic dyes, which is due to the fact that the polymer nanofiber membrane composed of polymer nanofibers in the flexible MOF microfiltration membrane provided by the present application has a large specific surface area and a larger contact area with pollutants. At the same time, the metal organic framework particles are distributed on the surface of the polymer nanofiber membrane, which can provide a continuous molecular channel and is more conducive to the adsorption of pollutants. The present application adjusts the unit structure of MOF through confinement strategy to obtain defective MOF nanoparticles, which provides more active sites and can improve the adsorption capacity for pollutants. This method has wide application prospects in the adsorption and separation of conventional pollutants (such as heavy metals, etc.), new pollutants (such as perfluorinated compounds, etc.), conventional gases (such as carbon dioxide, methane, etc.), and toxic gases (such as sulfur dioxide, dimethyl methylphosphonate, etc.).

[0124] The above only describes the preferred embodiments of the present application, and it should be noted that those skilled in the art can make some improvements and refinements without departing from the principles of the present application, and these improvements and refinements should also be considered as the protection scope of the present application.​

Claims

1. A flexible MOF microfiltration membrane, comprising a polymer nanofiber membrane and defective metal-organic framework particles, wherein the defective metal-organic framework particles are distributed on the surface of the polymer nanofibers of the polymer nanofiber membrane; the polymer nanofibers have an average diameter of 360 nm; the defective metal-organic framework particles have an average particle size of 15.2 nm; and the metal-organic framework particles have a mass content of 25.6% in the flexible MOF microfiltration membrane; The preparation method of the flexible MOF microfiltration membrane is as follows: (1) 0.5 g of terephthalic acid, 0.25 g of polyacrylonitrile and 30 mL of N,N-dimethylformamide were mixed and dissolved to obtain a spinning solution, and the spinning solution was loaded into an electrospinning injector with an applied voltage of 20 kV, a collector speed of 300 rpm, and an injection rate of 0.8 mL / h. After drying, a polymer nanofiber membrane loaded with an organic ligand was obtained; (2) 0.7 g zirconium tetrachloride, 10 mL N,N-dimethylformamide, 30 mL acetone and 10 mL glacial acetic acid were mixed and dissolved to obtain a mixed solution. The polymer nanofiber membrane was immersed in the mixed solution, placed in a hydrothermal reactor, and hydrothermally reacted at 120 ° C for 24 h for self-assembly. The obtained microfiltration membrane was then washed three times with acetone solution and immersed in methanol twice for 12 h each time. After drying, a flexible MOF microfiltration membrane was obtained.

2. Use of the flexible MOF microfiltration membrane according to claim 1 in water treatment and / or waste gas treatment.

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