Preparation method and application of MOF-based composite membrane

Abstract

The present invention belongs to the technical field of composite membrane materials, and specifically relates to a method for preparing a MOF-based composite membrane and its application. The preparation method comprises uniformly dissolving a copper source, a polymer matrix, and a modifier, and reacting to produce Cu-BTC; preparing a homogeneous casting solution using a thermally induced phase separation method; and hot-pressing the homogeneous casting solution into a film to produce a MOF-based composite membrane. The MOF-based composite membrane is then used to treat printing and dyeing wastewater. The present invention modifies existing Cu-BTC to produce MOF, which is then further prepared into a MOF-based composite membrane, thereby resolving the compatibility issues between MOF and the polymer matrix that currently exist in MOF-based composite membranes.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite membrane materials, and in particular relates to a preparation method and application of a MOF-based composite membrane. Background Art

[0002] Printing and dyeing wastewater is a unique type of wastewater. Due to its complex composition, traditional precipitation, adsorption and degradation processes cannot completely remove dye impurities. Therefore, there is an urgent need to develop efficient water treatment technology to meet this challenge. Membrane separation technology has become the main means of treating printing and dyeing wastewater due to its simplicity of operation, low cost and low energy consumption.

[0003] Nanofiltration membranes are a new type of separation membrane between reverse osmosis membranes and ultrafiltration membranes. Composed of a support layer and a separation layer, they can be used to separate inorganic salts, alkaline compounds, and heavy metal impurities from printing and dyeing wastewater. Traditional nanofiltration membranes are primarily produced using interfacial polymerization. While they offer good separation performance, their service life is limited by the cumbersome preparation process, the difficulty in precisely controlling the interfacial polymerization process, and the easily detached active layer. Thermophase inversion (TIPI) membrane preparation offers a simpler and more efficient approach for nanofiltration membrane production. It can be prepared in a single step, reducing the complex preparation process. Furthermore, since no active layer is required, nanofiltration membranes produced using TPI exhibit more stable and durable performance, significantly extending their service life. In addition, to address the trade-off effect in polymer membranes, that is, the mutual constraint between the flux (permeability) and the retention rate (selectivity) of polymer membranes, porous fillers MOFs can be added to make composite membranes to introduce additional transmission channels. In this case, the compatibility between the filler particles and the polymer is the main factor affecting the separation performance of the composite membrane. How to achieve a defect-free structure with ideal filler distribution and filler-polymer interface in the composite membrane remains a huge challenge.

[0004] Chinese patent CN110449034A discloses a method for preparing a mixed matrix membrane containing MOF filler, wherein the mixed matrix membrane includes a metal organic framework material (MOF) and a polymer matrix. The preparation method comprises the following steps: dispersing the metal organic framework material in a solvent, heating, stirring and ultrasonically treating to obtain a solution A; adding the polymer matrix to the solvent, heating, stirring and ultrasonically treating to obtain a solution B; mixing the solution A and solution B, heating, stirring and ultrasonically treating to form a solution, filtering the filtrate to obtain a homogeneous casting liquid, and casting the homogeneous casting liquid on a glass plate to form a flat membrane; and vacuum treating the flat membrane to remove residual solvent to obtain a mixed matrix membrane.

[0005] Since this patent relies on the properties of the solvent itself to mix MOF and polymer, it is difficult to ensure the dispersion of MOF, and it does not solve the problem that MOF is still easy to agglomerate under high loading, resulting in interfacial stress concentration and damaging the life of the membrane. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for preparing a MOF-based composite membrane to solve the compatibility problem between MOF and polymer matrix in the current MOF-based composite membrane; the present invention also provides the application of MOF-based composite membrane in the field of printing and dyeing wastewater.

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] The method for preparing the MOF-based composite membrane of the present invention comprises the following steps: uniformly dissolving a copper source, a polymer matrix, and a modifier, and reacting to obtain Cu-BTC; preparing a homogeneous casting solution by a heat-induced phase separation method; and hot-pressing the homogeneous casting solution into a film to obtain the MOF-based composite membrane.

[0009] in:

[0010] The modifier is 5-acetovaleric acid, the copper source is copper nitrate trihydrate or copper acetate, and the polymer matrix is trimesic acid or terephthalic acid. The solvent used for dissolution is an ethanol-water solution, prepared from ethanol and water in a volume ratio of (0.5-4):1.

[0011] The mass ratio of the copper source to the polymer matrix is (0.5-5):1, and the mass ratio of the polymer matrix to the modifier is 10:(1-10).

[0012] The reaction temperature is 110-140° C., and the reaction time is 6-18 hours.

[0013] The heat-induced phase separation method comprises heating a thermoplastic resin and a diluent to dissolve each other, then adding Cu-BTC or a mixture of Cu-BTC and a film-forming aid to prepare a homogeneous casting solution; wherein the heating temperature is 60-90°C.

[0014] Based on the total mass of the thermoplastic resin and the diluent being 100 wt%, the thermoplastic resin is 15-50 wt% and the diluent is 50-85 wt%.

[0015] The film-forming aid is one or more of polyvinyl alcohol, polyethylene glycol or hexamethylenetetramine. Based on the total mass of the homogeneous casting solution as 100wt%, the amount of Cu-BTC added is 1-3wt%; the amount of the film-forming aid added is 3-6wt%.

[0016] The diluent is a mixture of soybean oil and dibutyl phthalate, N,N-dimethylformamide or N,N-dimethylacetamide; the mass ratio of soybean oil to dibutyl phthalate is (2-10):1.

[0017] The thermoplastic resin is one or two of thermoplastic phenolic resin, ultra-high molecular weight polypropylene or polysulfone.

[0018] Application of the MOF-based composite membrane prepared by the preparation method of the MOF-based composite membrane of the present invention: the MOF-based composite membrane is used to treat printing and dyeing wastewater.

[0019] The beneficial effects of the present invention are as follows:

[0020] (1) It is known that MOF (Cu-BTC) is prone to agglomeration due to electrostatic and van der Waals forces at high loading, forming large particles, which leads to the appearance of non-selective pores in the membrane. The difference in polarity between MOF and polymer matrix leads to insufficient compatibility, and micropores or cracks are easily formed at the contact interface, resulting in non-selective permeability of the membrane and affecting the service life of the composite membrane.

[0021] The above problems all stem from the lack of compatibility between the inorganic MOF (Cu-BTC) and the organic polymer matrix. The present invention, by adding the modifier 5-acetovaleric acid, can optimize the structure and performance of the MOF-based composite membrane through multi-dimensional synergistic effects with the copper source, polymer matrix, film-forming aid, and diluent:

[0022] Surface modification: the carboxylic acid group of 5-acetovaleric acid interacts with the Cu in Cu-BTC 2+ The ions coordinate to form a stable coordination bond, which covers the surface of MOF, namely Cu-BTC particles. After the surface of Cu-BTC is modified by carboxylic acid groups, it carries a negative charge (-COO － ), the particles are more evenly dispersed due to the increased electrostatic repulsion; at the same time, the long carbon chain acetyl group of 5-acetovaleric acid extends outward, forming a physical barrier through hydrogen bonding, and utilizing the steric effect to prevent direct contact between Cu-BTC particles and reduce agglomeration.

[0023] Hydrogen bond bridging: The carboxylic acid groups of 5-acetovaleric acid not only coordinate with the MOF but also form hydrogen bonds with the carboxylic acid groups in the polymer matrix, forming a three-dimensional MOF-modifier-polymer matrix network, effectively improving interfacial compatibility and avoiding pore defects caused by phase separation. The hydrophobic segments of the modifier and the thermoplastic resin improve interfacial compatibility based on the principle of like attracts like. The present invention can optionally add a film-forming aid, in which hydroxyl groups, amino groups, etc. in the film-forming aid are complexed with the three-dimensional network through hydrogen bonds, further improving interfacial compatibility.

[0024] (2) It is known that in traditional MOF synthesis, the crystal growth rate is fast and the size distribution is uneven, which affects the uniformity of the membrane structure; and the MOF pores are easily blocked by large molecular dyes (such as Congo red) in printing and dyeing wastewater, resulting in a rapid decrease in membrane flux.

[0025] The above problems belong to the inherent shortcomings of MOF materials. The present invention modifies the surface of MOF by adding 5-acetovaleric acid as a modifier to regulate the growth of MOF crystals and improve the anti-fouling performance of the membrane:

[0026] Dynamic coordination inhibits excessive nucleation: 5-acetovaleric acid and Cu 2+ The coordination effect of Cu forms a dynamic coordination equilibrium, slowing down the 2+ The coordination rate with the polymer matrix controls the crystal nucleation speed and size.

[0027] Crystal morphology guidance: The hydrophobic chain segments of the modifier are adsorbed on specific crystal planes, inhibiting crystal growth in that direction, and ultimately forming a more regular and anisotropic MOF morphology (such as cubic Cu-BTC) to retain specific channels as much as possible and reduce the trade-off effect in the polymer membrane.

[0028] Hydrophobic surface design: The long carbon chain hydrophobic segments of 5-acetovaleric acid cover the MOF surface, are electrically neutral, and form a low surface energy layer, which reduces the electrostatic adsorption of pollutants (such as negatively charged Congo red dye) on the membrane surface, thereby reducing the clogging of large molecular dyes and ensuring stable water flux. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is the infrared spectrum of Cu-BTC in Example 1;

[0030] Figure 2 is the X-ray photoelectron spectrum of Cu-BTC in Example 1;

[0031] Figure 3 is the ball-and-stick model of Cu-BTC in Example 1;

[0032] Figure 4 is the infrared spectrum of the MOF-based composite membrane in Example 1;

[0033] Figure 5 is the SEM image of the MOF-based composite membrane in Example 1; DETAILED DESCRIPTION

[0034] The present invention is described and illustrated in detail below with reference to the embodiments.

[0035] The raw materials used in the following examples and comparative examples are from the following manufacturers:

[0036] Thermoplastic phenolic resin, brand SBHPP 33426, was provided by Shandong Baofeng New Materials Co., Ltd.; ultra-high molecular weight polypropylene, brand UHMWPP-B, was provided by Shandong Jincheng Petrochemical Co., Ltd.; polysulfone, brand Ultrason® S 2010 NAT, was provided by BASF, Germany.

[0037] Example 1

[0038] Preparation of highly stable MOFs

[0039] An ethanol-water solution was prepared at a ratio of ethanol to pure water = 1:1 (v / v) and added to the reactor. 87.5g of copper nitrate trihydrate, 42.0g of trimesic acid, and 4.2g of 5-acetovaleric acid were then added. The mixture was reacted at 120°C for 18h to allow crystallization. The mixture was then washed with ethanol and dried to obtain Cu-BTC, a highly stable MOF. Infrared spectroscopy and X-ray photoelectron spectroscopy confirmed the formation of Cu-BTC. The infrared spectrum of Cu-BTC is shown in the figure below. Figure 1 As shown, the X-ray photoelectron spectrum of Cu-BTC is as follows Figure 2 The ball-and-stick model of Cu-BTC is shown as Figure 3 As shown, there are Cu, C, O and H atoms in the figure.

[0040] Preparation of MOF-based composite membranes

[0041] A diluent was prepared at a ratio of soybean oil to dibutyl phthalate of 4:1 (m / m), and the two were mixed at a ratio of ultra-high molecular weight polypropylene (UHMWPP) to diluent of 15:85 (wt%). The mixture was heated to 60°C until they were mutually soluble. 1.0 wt% of Cu-BTC (based on the total mass of the homogeneous casting solution being 100 wt%) was added, and the temperature was maintained while stirring evenly to obtain a homogeneous casting solution.

[0042] The homogeneous casting solution was poured into a stainless steel mold and hot pressed into a film using a hot press. The mold was placed in deionized water at 20°C to cool and form the film. The diluent was then removed with ethanol and the film was placed in deionized water for storage. A MOF-based composite membrane was obtained, which was labeled as Sample 1. Infrared spectroscopy and scanning electron microscopy tests confirmed that Sample 1 was the MOF-based composite membrane of the present invention. The infrared spectrum of the MOF-based composite membrane is shown in FIG. Figure 4 As shown in the SEM images of MOF-based composite membranes, Figure 5 shown.

[0043] Example 2

[0044] Preparation of highly stable MOFs

[0045] An ethanol-water solution was prepared in a ratio of ethanol to pure water = 1:1 (v / v) and added to the reactor. 210.0 g of copper nitrate trihydrate, 42.0 g of trimesic acid, and 21.0 g of 5-acetovaleric acid were then added. The mixture was reacted at 120°C for 12 hours to allow crystallization. The mixture was then washed with ethanol and dried to obtain Cu-BTC, a highly stable MOF.

[0046] Preparation of MOF-based composite membranes

[0047] A diluent was prepared at a ratio of soybean oil to dibutyl phthalate of 2:1 (m / m), and the two were mixed at a ratio of ultra-high molecular weight polypropylene (UHMWPP) to diluent of 30:70 (wt%). The mixture was heated to 80°C until they were mutually soluble. 2.0 wt% of Cu-BTC (based on the total mass of the homogeneous casting solution being 100 wt%) was added, and the temperature was maintained while stirring evenly to obtain a homogeneous casting solution.

[0048] The homogeneous casting liquid was poured into a stainless steel mold and hot pressed into a film using a hot press. The mold was placed in deionized water at 20°C to cool and form the film. The diluent was then removed with ethanol and the film was placed in deionized water for storage. A MOF-based composite membrane was obtained, which was marked as sample 2.

[0049] Example 3

[0050] Preparation of highly stable MOFs

[0051] An ethanol-water solution was prepared at a ratio of ethanol to pure water = 2:1 (v / v) and added to the reactor. 42 g of copper acetate, 42.0 g of trimesic acid, and 42 g of 5-acetovaleric acid were then added. The mixture was reacted at 120 °C for 6 h to allow crystallization. The mixture was then washed with ethanol and dried to obtain Cu-BTC, a highly stable MOF.

[0052] Preparation of MOF-based composite membranes

[0053] A diluent was prepared at a ratio of soybean oil to dibutyl phthalate of 10:1 (m / m), and the two were mixed at a ratio of thermoplastic phenolic resin (PFNR) to diluent of 50:50 (wt%). The mixture was heated to 90°C until they were mutually soluble. 3.0 wt% of Cu-BTC (based on the total mass of the homogeneous casting solution being 100 wt%) was added, and the temperature was maintained while stirring to obtain a homogeneous casting solution.

[0054] The homogeneous casting liquid was poured into a stainless steel mold and hot-pressed into a film using a hot press. The mold was placed in deionized water at 15°C to cool and form the film. The diluent was then removed with ethanol and the film was placed in deionized water for storage. A MOF-based composite membrane was obtained, which was marked as sample 3.

[0055] Example 4

[0056] Preparation of Cu-BTC

[0057] An ethanol-water solution was prepared at a ratio of ethanol to pure water = 4:1 (v / v) and added to the reactor. 210.0 g of copper nitrate trihydrate, 42.0 g of terephthalic acid, and 4.2 g of 5-acetovaleric acid were then added. The mixture was reacted at 110°C for 6 h to allow crystallization. The mixture was then washed with ethanol and dried to obtain Cu-BTC.

[0058] Preparation of MOF-based composite membranes

[0059] N,N-dimethylformamide was selected as the diluent, and the two were mixed in a ratio of polysulfone (PES): diluent = 15:85 (wt%), and heated to 60°C until they were mutually soluble; 2.0wt% Cu-BTC and 3.0wt% polyvinyl alcohol (PVP) were added (the total mass of the homogeneous casting liquid was 100wt%), and the temperature was maintained and stirred evenly to obtain a homogeneous casting liquid.

[0060] The homogeneous casting liquid was poured into a stainless steel mold and hot-pressed into a film using a hot press. The mold was placed in deionized water at 20°C to cool and form the film. The diluent was then removed with ethanol and the film was placed in deionized water for storage. A MOF-based composite membrane was obtained, which was marked as sample 4.

[0061] Example 5

[0062] Preparation of Cu-BTC

[0063] An ethanol-water solution was prepared at a ratio of ethanol to pure water = 0.5:1 (v / v) and added to the reactor. 126.0 g of copper nitrate trihydrate, 42.0 g of trimesic acid, and 30.0 g of 5-acetovaleric acid were then added. The mixture was reacted at 120°C for 6 h to allow crystallization. The solution was then washed with ethanol and dried to obtain Cu-BTC.

[0064] Preparation of MOF-based composite membranes

[0065] N,N-dimethylformamide was selected as the diluent, and the two were mixed in a ratio of thermoplastic phenolic resin (PFNR): diluent = 25:75 (wt%), and heated to 60°C until they were mutually soluble; 1.0 wt% of Cu-BTC, 3.0 wt% of hexamethylenetetramine and 3.0 wt% of polyethylene glycol (with the total mass of the homogeneous casting solution being 100 wt%) were added, and the temperature was maintained and stirred evenly to prepare a homogeneous casting solution.

[0066] The homogeneous casting liquid was poured into a stainless steel mold and hot-pressed into a film using a hot press. The mold was placed in deionized water at 20°C to cool and form the film. The diluent was then removed with ethanol and the film was placed in deionized water for storage. A MOF-based composite membrane was obtained, which was marked as sample 5.

[0067] Example 6

[0068] Preparation of Cu-BTC

[0069] An ethanol-water solution was prepared at a ratio of ethanol to pure water = 0.5:1 (v / v) and added to the reactor. 21.0 g of copper nitrate trihydrate, 42.0 g of trimesic acid, and 15.0 g of 5-acetovaleric acid were then added. The mixture was reacted at 140°C for 6 h to allow crystallization. The solution was then washed with ethanol and dried to obtain Cu-BTC.

[0070] Preparation of MOF-based composite membranes

[0071] N,N-dimethylacetamide was selected as the diluent, and the two were mixed in a ratio of thermoplastic phenolic resin (PFNR): diluent = 25:75 (wt%), and heated to 60°C until they were mutually soluble; 2.0wt% Cu-BTC, 3.0wt% hexamethylenetetramine (HMTA) and 2.0wt% polyethylene glycol (PEG) were added (the total mass of the homogeneous casting solution was 100wt%), and the temperature was maintained and stirred evenly to prepare a homogeneous casting solution.

[0072] The homogeneous casting liquid was poured into a stainless steel mold and hot-pressed into a film using a hot press. The mold was placed in deionized water at 20°C to cool and form the film. The diluent was then removed with ethanol and the film was placed in deionized water for storage. A MOF-based composite membrane was obtained, which was marked as sample 6.

[0073] Comparative Example 1

[0074] No modifier was used, and the remaining steps were the same as in Example 1 to obtain a membrane material, which was marked as Comparative 1.

[0075] Comparative Example 2

[0076] The modifier was replaced with talc powder, and the remaining steps were the same as in Example 1 to obtain a membrane material, which was marked as Comparative 2.

[0077] Comparative Example 3

[0078] The modifier was replaced with dibenzoyl peroxide, and the remaining steps were the same as in Example 1 to obtain a membrane material, which was marked as Comparative 3.

[0079] Comparative Example 4

[0080] The modifier was replaced by formic acid, and the remaining steps were the same as in Example 1 to obtain a membrane material, which was marked as Comparative 4.

[0081] Comparative Example 5

[0082] Without adding diluent, the remaining steps were the same as in Example 1 to obtain a membrane material, which was marked as Comparative 5.

[0083] Comparative Example 6

[0084] The Cu-BTC prepared in Example 1 was used to prepare a MOF-based composite membrane by interfacial polymerization: Cu-BTC and m-xylenediamine were dissolved in deionized water, and ultrasonic dispersion was performed to obtain an aqueous phase, wherein the mass fraction of Cu-BTC was 1.0 wt %, and the mass fraction of m-xylenediamine was 0.5 wt %.

[0085] A diluent was prepared at a ratio of 4:1 (m / m) soybean oil to dibutyl phthalate. Ultrahigh molecular weight polypropylene (UHMWPP) and diluent were mixed at a ratio of 15:85 (wt%). The mixture was heated to 60°C until they dissolved. Trimesoyl chloride was then added and ultrasonically dispersed to obtain an organic phase with a trimesoyl chloride concentration of 0.5 wt%. The aqueous and organic phases were then brought into contact at a 1:1 (v / v) volume ratio to allow polymerization of the monomers at the interface. The reaction lasted 30 minutes to obtain a membrane material, designated Comparative 6.

[0086] Test Example 1

[0087] Membrane performance test

[0088] Under room temperature conditions, the water flux of commercially available PAN membranes (purchased from Zhongke Ruiyang Membrane Technology (Beijing) Co., Ltd.), the MOF-based composite membranes prepared in the examples, and the membrane materials prepared in the comparative examples, as well as the rejection rates of organic impurities (taking Congo red as an example) and inorganic impurities (taking magnesium sulfate as an example) in printing and dyeing wastewater were tested. By calculating the rejection ratio, the removal capacity of inorganic salt impurities in printing and dyeing wastewater was determined. The test steps are as follows: The permeability and retention performance of the samples were tested using a membrane material evaluation device (produced by Hangzhou Kemo Water Treatment Engineering Co., Ltd., model KM1812-NF). The effective membrane area was 7 cm 2 The data were collected using a cross-flow filtration device with the following test conditions: pH 7.0, 25°C. At the beginning of the experiment, each sample was pre-pressed at 3 bar pressure for 1 hour, then tested at 3 bar pressure for 0.5 hours, and the data were recorded. The concentrations of Congo red and magnesium sulfate in the test solution were 200 ppm and 1000 ppm, respectively. For each sample, at least four different data were measured and the average value was obtained. The water flux (J) was determined by measuring the volume of filtrate (V) passing through the filter under pressure (P), time (T) and effective membrane area (S). The water flux was calculated as follows:

[0089] ;

[0090] Where V (unit L) is the volume of the filtrate, A (unit m 2 ) is the effective filter membrane area, T (unit: h) is the filtration time during the test, and P (bar) is the test pressure.

[0091] The test solution was filtered through a membrane to obtain a filtrate. The concentrations of Congo red and magnesium sulfate before and after membrane filtration were measured using a UV-visible spectrophotometer and a digital conductivity meter. The concentration (C f ) and the concentration of the filtrate (C p ), the retention rate (R) is calculated as follows:

[0092] ;

[0093] The calculation formula of desalination selectivity (S) is as follows:

[0094] ;

[0095] where R salt and R dye The specific membrane performance test data are shown in Table 1.

[0096]

[0097] It can be seen from Table 1 that compared with the nanofiltration membrane without MOF composite, the water flux of the MOF-based composite membrane prepared after the introduction of MOF has been significantly improved. The test of filtration of test liquid containing dye and inorganic salt also shows that the desalination selectivity of the MOF-based composite membrane is higher, showing excellent dye desalination performance.

[0098] Comparisons 1 to 4 show that when Cu-BTC that has not been modified with the modifier of the present invention is used to prepare membrane materials, although the water flux is enhanced compared to commercially available nanofiltration membranes, its ability to separate dyes and salts is insufficient and does not meet the performance requirements for dye desalination.

[0099] The present invention prepares a MOF-based composite membrane based on modified Cu-BTC, maintaining high selectivity (higher desalination selectivity) while improving the membrane's permeability (higher water flux), achieving rapid separation of dye molecules, and improving the problem that traditional polymer membranes are limited by the trade-off effect and cannot simultaneously improve their permeability and selectivity, thereby improving production efficiency. The MOF of the present invention has good interfacial compatibility with the polymer matrix, does not contain a large number of micropores and defects, does not produce non-selective permeability channels, and can effectively separate Congo red and magnesium sulfate.

[0100] The present invention only takes the separation of Congo red and magnesium sulfate as an example. The MOF-based composite membrane of the present invention is not limited to the separation of wastewater containing Congo red and magnesium sulfate. Other application scenarios of separating organic dyes from other inorganic salts or metal impurities are within the scope of protection of the present invention.

Claims

1. A method for preparing a MOF-based composite membrane, characterized in that: A copper source, a polymer matrix, and a modifier are uniformly dissolved and reacted to produce Cu-BTC; a homogeneous casting solution is prepared by a thermally induced phase separation method; and the homogeneous casting solution is hot-pressed into a film to produce a MOF-based composite membrane; the modifier is 5-acetovaleric acid, the copper source is copper nitrate trihydrate or copper acetate, and the polymer matrix is trimesic acid or terephthalic acid. The heat-induced phase separation method is to heat the thermoplastic resin and the diluent to dissolve each other, and then add Cu-BTC, or a mixture of Cu-BTC and a film-forming aid, to prepare a homogeneous casting solution; the heating temperature is 60~90℃.

2. The method for preparing a MOF-based composite membrane according to claim 1, wherein The mass ratio of the copper source to the polymer matrix is (0.5~5):1, and the mass ratio of the polymer matrix to the modifier is 10:(1~10).

3. The method for preparing a MOF-based composite membrane according to claim 1, wherein The reaction temperature is 110~140℃, and the reaction time is 6~18h.

4. The method for preparing a MOF-based composite membrane according to claim 1, wherein Based on the total mass of the thermoplastic resin and the diluent being 100 wt %, the thermoplastic resin is 15-50 wt % and the diluent is 50-85 wt %.

5. The method for preparing a MOF-based composite membrane according to claim 1, wherein: The film-forming aid is one or more of polyvinyl alcohol, polyethylene glycol or hexamethylenetetramine. Based on the total mass of the homogeneous casting solution being 100wt%, the added amount of Cu-BTC is 1-3wt%; the added amount of the film-forming aid is 3-6wt%.

6. The method for preparing a MOF-based composite membrane according to claim 1, wherein: The diluent is a mixture of soybean oil and dibutyl phthalate, N,N-dimethylformamide or N,N-dimethylacetamide; the mass ratio of soybean oil to dibutyl phthalate is (2~10):

1.

7. The method for preparing a MOF-based composite membrane according to claim 1, wherein: The thermoplastic resin is one or two of thermoplastic phenolic resin, ultra-high molecular weight polypropylene or polysulfone.

8. An application of a MOF-based composite membrane prepared by the method for preparing a MOF-based composite membrane according to any one of claims 1 to 7, characterized in that: MOF-based composite membranes are used to treat printing and dyeing wastewater.

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