Co-MOF-74 composite membrane with simultaneous oil-water separation and catalytic degradation properties, its preparation method and application

Abstract

This invention discloses a Co-MOF-74 composite membrane with simultaneous oil-water separation and catalytic degradation performance, its preparation method, and its application. The invention involves introducing hydrophilic monomers into a cellulose acetate system and performing free radical polymerization, combined with a phase inversion method to construct continuous porous hydrophilic transport channels. Carboxyl functional sites are introduced onto the membrane surface and pore walls using a diazo reaction to achieve coordination anchoring of metal ions. Based on this, an in-situ growth strategy is used to directionally construct Co-MOF-74 along the membrane surface and pore walls, forming an interface confinement structure where catalytic active sites are distributed along the aqueous transport path. The Co-MOF-74 composite membrane of this invention can achieve simultaneous oil-water separation and organic pollutant removal, and has the advantages of high treatment efficiency, simplified process, and reduced energy consumption.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials and functional materials, specifically relating to a Co-MOF-74 composite membrane with simultaneous oil-water separation and catalytic degradation properties, its preparation method and application. Background Technology

[0002] With the continuous advancement of industrialization, industries such as petrochemicals, printing and dyeing, and food processing discharge large amounts of oily wastewater and wastewater containing organic pollutants during production, posing a serious threat to the ecological environment and water resource security. How to efficiently treat oily wastewater and degrade organic pollutants has become an urgent scientific challenge in the field of environmental governance.

[0003] Currently, the main methods for treating oily wastewater and organic pollutants include physical separation, biological treatment, and chemical oxidation. Among these, membrane separation technology has received widespread attention in the field of oil-water separation due to its advantages such as simple operation, high separation efficiency, and low energy consumption. However, traditional membrane materials generally suffer from problems such as rapid flux decline, susceptibility to fouling, and decreased separation efficiency when treating complex oily wastewater.

[0004] In recent years, metal-organic frameworks (MOFs), as a class of porous materials with high specific surface area and tunable pore structure, have been widely used to support metal active components or construct heterogeneous catalytic systems. With the deepening of related research, the composite structure of MOFs and membrane materials has gradually attracted attention. In oil-water separation, MOFs can participate in the regulation of oil-water systems through their pore structure characteristics or the surface properties of organic groups in their ligands; in the field of catalysis, they also show certain potential as carriers of active components.

[0005] However, existing technologies have some shortcomings, such as insufficient bonding stability between MOFs and the membrane substrate, uneven MOF loading, low utilization of active sites, and the fact that existing catalytic membrane structures are mostly single-function, making it difficult to achieve efficient oil-water separation and synergistic removal of water-soluble organic pollutants in the same treatment unit, which restricts their practical application in the treatment of complex oily wastewater.

[0006] Therefore, developing a MOF-based cellulose acetate membrane material with stable structure, excellent wettability, and both oil-water separation and organic pollutant catalytic degradation functions is of great significance for improving the treatment efficiency of oily wastewater and expanding the application range of membrane materials. Summary of the Invention

[0007] The purpose of this invention is to provide a Co-MOF-74 composite membrane and its preparation method, as well as its application in simultaneous oil-water separation and catalytic degradation of organic pollutants.

[0008] This invention constructs a hydrophilic crosslinked network on a cellulose acetate membrane substrate and introduces carboxyl functional sites, further growing Co-MOF-74 in situ. The resulting composite membrane possesses both a stable structure and excellent wettability and catalytic degradation performance, thereby achieving simultaneous and efficient oil-water separation and removal of organic pollutants.

[0009] The technical solution of the present invention is as follows:

[0010] A method for preparing a Co-MOF-74 composite membrane includes the following steps:

[0011] (1) Preparation of casting solution

[0012] A hydrophilic monomer and an initiator are added to a cellulose acetate solution, and a free radical polymerization reaction is carried out at 60–80 °C for 6–10 h under an inert atmosphere (nitrogen or argon) to obtain a casting solution.

[0013] The cellulose acetate solution is obtained by dissolving cellulose acetate in a solvent; the solvent is selected from one or more of N,N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, and N,N-dimethylacetamide; preferably, the concentration of the cellulose acetate solution is 0.02–0.2 g / mL.

[0014] The hydrophilic monomer is 2-hydroxyethyl methacrylate or acryloyloxyethyltrimethylammonium chloride; preferably, the mass ratio of the hydrophilic monomer to cellulose acetate is 1:1 to 2.

[0015] The initiator is selected from one or more of azobisisobutyronitrile, diisopropylbenzene peroxide, and benzoyl peroxide; preferably, the amount of initiator used is 1% to 5% of the mass of the hydrophilic monomer;

[0016] (2) Film formation

[0017] The casting solution obtained in step (1) was subjected to ultrasonic defoaming, scraped, and solidified in deionized water by phase inversion. After that, it was taken out and dried at room temperature to obtain a hydrophilic modified cellulose acetate membrane.

[0018] The preferred conditions for coating are: ambient temperature 20-30℃, humidity 30-50%, and coating thickness 200-400 μm.

[0019] (3) Diazo reaction introduces carboxyl groups

[0020] The hydrophilic modified cellulose acetate membrane obtained in step (2) was immersed in a diazonium salt hydrochloric acid solution, and vitamin C was added to carry out a diazonium reaction to obtain a membrane material with introduced carboxyl groups.

[0021] The diazonium salt hydrochloric acid solution is prepared by reacting sodium nitrite and 3-aminobenzoic acid in hydrochloric acid at 0 °C; preferably, the concentration of sodium nitrite in the reaction system is 0.001–0.005 g / mL; the mass ratio of sodium nitrite to 3-aminobenzoic acid is 1:2–5;

[0022] After adding vitamin C, a diazo reaction was carried out at room temperature for 12 h; under the action of vitamin C, carboxyl functional sites were introduced into the surface of the membrane pores; the preferred mass ratio of vitamin C to sodium nitrite was 1:1 to 20.

[0023] (4) In situ growth of Co-MOF-74

[0024] The membrane material with carboxyl groups introduced in step (3) was immersed in a methanol solution of cobalt acetate tetrahydrate, and then a methanol solution of ligand 2,5-dihydroxyterephthalic acid was added to grow Co-MOF-74 in situ. After washing and vacuum drying (40-65℃), a Co-MOF-74 composite membrane was obtained.

[0025] The preferred concentration of the methanol solution of cobalt acetate tetrahydrate is 0.005–0.03 g / mL;

[0026] The preferred mass ratio of 2,5-dihydroxyterephthalic acid to cobalt acetate tetrahydrate is 1:2 to 3;

[0027] Specifically, the carboxyl-introduced membrane material was immersed in a methanol solution of cobalt acetate tetrahydrate for 1 h to allow cobalt ions to be adsorbed onto the membrane surface. Subsequently, a methanol solution of ligand 2,5-dihydroxyterephthalic acid was added, and the reaction was stirred at room temperature for 2 h to allow Co-MOF-74 to grow in situ on the inner wall and surface of the membrane pores.

[0028] This invention relates to the Co-MOF-74 composite membrane prepared by the above-described method.

[0029] The Co-MOF-74 composite membrane of this invention can be used for simultaneous oil-water separation and catalytic degradation of organic pollutants.

[0030] The technical principles of this invention include:

[0031] By introducing hydrophilic monomers into the cellulose acetate system and carrying out free radical polymerization, a continuous porous hydrophilic transport channel was constructed using the phase inversion method. Carboxyl functional sites were introduced on the membrane surface and pore inner wall using the diazo reaction to achieve coordination anchoring of metal ions. Based on this, Co-MOF-74 was oriented along the membrane surface and pore inner wall using an in-situ growth strategy to form an interfacial confinement structure in which catalytic active sites are distributed along the aqueous transport path.

[0032] When the composite membrane of this invention treats an oil-water system containing organic pollutants, the aqueous phase preferentially passes through the membrane channels and carries the organic pollutants with it. At the same time, the organic pollutants continue to contact the catalytic sites and undergo degradation during the transport process, thereby achieving simultaneous oil-water separation and organic pollutant removal.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) The present invention constructs a hydrophilic crosslinking network on a cellulose acetate membrane substrate, and the resulting cellulose acetate composite membrane has super-amphiphilic surface properties, which is beneficial to improving the liquid phase permeation rate and oil-water separation efficiency.

[0035] (2) The carboxyl functional site can coordinate with subsequently introduced metal ions to form Co 2+ Stable anchoring on the membrane surface provides binding sites and acts as a nucleation induction center to promote the in-situ directional growth of Co-MOF-74 on the inner wall of the membrane pores, thereby avoiding the disordered deposition and aggregation of MOF particles and achieving a uniform distribution of catalytic active sites in the membrane pores.

[0036] (3) The catalytically active Co-MOF-74 is directionally and fixedly distributed along the inner wall of the membrane pores in the aqueous transport path, so that the cellulose acetate membrane can achieve oil-water separation while having the ability to catalytically degrade organic pollutants.

[0037] (4) The Co-MOF-74 composite membrane of the present invention can simultaneously achieve oil-water separation and organic pollutant degradation, which helps to simplify the treatment process and improve the treatment efficiency. Attached Figure Description

[0038] Figure 1 : Schematic diagram of the preparation process of the Co-MOF-74 composite membrane of the present invention.

[0039] Figure 2 The contact angles (a) of the Co-MOF-74 composite membrane prepared in Example 1 to water and (b) in air; the contact angles (c) of the membrane to water in oil and (d) of the membrane to oil in water.

[0040] Figure 3 Water contact angle of pure cellulose acetate membrane in Comparative Example 1 and hydrophilically modified cellulose acetate membrane in Comparative Example 2 after free radical polymerization.

[0041] Figure 4 The catalytic degradation effects of organic pollutants on the pure cellulose acetate membrane of Comparative Example 1, the hydrophilically modified cellulose acetate membrane after free radical polymerization of Comparative Example 2, and the Co-MOF-74 composite membrane prepared in Example 1 were compared.

[0042] Figure 5Example 1 describes the process of simultaneous oil-water separation and catalytic degradation of organic pollutants using a Co-MOF-74 composite membrane (the organic pollutant is methylene blue, and the oil phase is n-hexane). Detailed Implementation

[0043] The present invention is further described below through specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0044] Example 1:

[0045] A method for preparing a Co-MOF-74 composite membrane for simultaneous oil-water separation and catalytic degradation (the preparation process is shown in the figure below). Figure 1 (As shown), including the following process steps:

[0046] First, 1.2 g of cellulose acetate powder was added to 20 g of N,N-dimethylformamide solvent and dissolved under magnetic stirring. After dissolution, 1 g of the hydrophilic monomer 2-hydroxyethyl methacrylate and 0.02 g of the initiator azobisisobutyronitrile were added to the cellulose acetate solution. The polymerization reaction was carried out at a constant temperature of 70 °C for 6 h under nitrogen protection to obtain a homogeneous solution. Subsequently, the solution was ultrasonically defoamed, and a film was formed using a film scraping machine at an ambient temperature of 25 °C and a humidity of 40% to a film thickness of 300 μm. The film was then cured in deionized water at 25 °C for 15 min using a phase inversion method to obtain a hydrophilic modified cellulose acetate film. This film was then removed and dried at room temperature.

[0047] Diazo reaction: Dissolve 0.23 g of sodium nitrite in 60 mL of 1 mol·L⁻¹ solution. -1 A hydrochloric acid solution was prepared, followed by the addition of 0.42 g of 3-aminobenzoic acid. The solution was shaken in an ice-water bath at 0 °C for 1 hour to generate a diazonium hydrochloric acid solution. A hydrophilic modified cellulose acetate membrane was immersed in this solution, followed by the addition of 0.053 g of vitamin C, and the reaction was carried out at room temperature for 12 hours. After the diazo reaction, the membrane was thoroughly washed with water until all unreacted substances were removed, and then allowed to air dry at room temperature.

[0048] In-situ growth of Co-MOF-74: First, 1.5 g of cobalt acetate tetrahydrate was dissolved in 50 mL of methanol and sonicated for 5 minutes until completely dissolved. Similarly, 0.5 g of 2,5-dihydroxyterephthalic acid was dissolved in 25 mL of methanol. The hydrophilically modified cellulose acetate membrane with introduced carboxyl groups was immersed in the methanol solution containing cobalt acetate tetrahydrate for 1 hour to adsorb cobalt ions. Then, the methanol solution of 2,5-dihydroxyterephthalic acid was slowly added, and the reaction was carried out under magnetic stirring for about 2 hours. Subsequently, the membrane was washed repeatedly with methanol and deionized water alternately to remove unbound MOF particles and residual chemicals. Finally, it was dried in a vacuum oven at 60 °C for 6 hours to obtain the Co-MOF-74 composite membrane.

[0049] The contact angles (a) of the prepared Co-MOF-74 composite membrane for simultaneous oil-water separation and catalytic degradation of organic pollutants with water in air and with oil in water are shown in the figures (b); the contact angles (c) of the membrane with water in oil and with oil in water are shown in the figures (d). Figure 2 As shown.

[0050] The prepared Co-MOF-74 composite membrane for simultaneous oil-water separation and catalytic degradation of organic pollutants exhibits the following catalytic degradation effect: Figure 4 As shown.

[0051] The prepared Co-MOF-74 composite membrane for simultaneous oil-water separation and catalytic degradation of organic pollutants is as follows: Figure 5 As shown (the organic pollutant is methylene blue, and the oil phase is n-hexane).

[0052] Example 2:

[0053] First, 1.5 g of cellulose acetate powder was added to 20 g of N-methylpyrrolidone and dissolved under magnetic stirring. After dissolution, 0.8 g of the hydrophilic monomer 2-hydroxyethyl methacrylate and 0.02 g of the initiator azobisisobutyronitrile were added to the cellulose acetate solution. The polymerization reaction was carried out at a constant temperature of 75 ℃ for 6 h under nitrogen protection to obtain a homogeneous solution. Subsequently, the solution was ultrasonically defoamed, and a film was formed using a film scraping machine at an ambient temperature of 25 ℃ and humidity of 40% to a film thickness of 250 μm. The film was then cured in deionized water at 25 ℃ for 15 min using a phase inversion method to obtain a hydrophilic modified cellulose acetate film. This film was then removed and dried at room temperature.

[0054] Diazo reaction: Dissolve 0.23 g of sodium nitrite in 60 mL of 1 mol·L⁻¹ solution. -1 A hydrochloric acid solution was prepared, followed by the addition of 0.42 g of 3-aminobenzoic acid. The solution was shaken in an ice-water bath at 0 °C for 1 hour to generate a diazonium hydrochloric acid solution. A hydrophilic modified cellulose acetate membrane was immersed in this solution, followed by the addition of 0.053 g of vitamin C, and the reaction was carried out at room temperature for 12 hours. After the diazo reaction, the membrane was thoroughly washed with water until all unreacted substances were removed, and then allowed to air dry at room temperature.

[0055] In-situ growth of Co-MOF-74: First, 1.5 g of cobalt acetate tetrahydrate was dissolved in 50 mL of methanol and sonicated for 5 minutes until completely dissolved. Similarly, 0.5 g of 2,5-dihydroxyterephthalic acid was dissolved in 25 mL of methanol. The hydrophilically modified cellulose acetate membrane with introduced carboxyl groups was immersed in the methanol solution containing cobalt acetate tetrahydrate for 1 hour to adsorb cobalt ions. Then, the methanol solution of 2,5-dihydroxyterephthalic acid was slowly added, and the reaction was carried out under magnetic stirring for about 2 hours. Subsequently, the membrane was washed repeatedly with methanol and deionized water alternately to remove unbound MOF particles and residual chemicals. Finally, it was dried in a vacuum oven at 60 °C for 6 hours to obtain the Co-MOF-74 composite membrane.

[0056] Example 3:

[0057] First, 1.8 g of cellulose acetate powder was added to 20 g of N,N-dimethylformamide solvent and dissolved under magnetic stirring. After dissolution, 0.7 g of the hydrophilic monomer acryloyloxyethyltrimethylammonium chloride and 0.02 g of the initiator azobisisobutyronitrile were added to the cellulose acetate solution. The polymerization reaction was carried out at 80 °C for 6 h under nitrogen protection to obtain a homogeneous solution. Subsequently, the solution was ultrasonically defoamed, and a film was formed using a film scraper at an ambient temperature of 25 °C and humidity of 40% to a film thickness of 350 μm. The film was then cured in deionized water at 25 °C for 15 min using a phase inversion method to obtain a hydrophilic modified cellulose acetate film. This film was then removed and dried at room temperature.

[0058] Diazo reaction: Dissolve 0.23 g of sodium nitrite in 60 mL of 1 mol·L⁻¹ solution. -1 A hydrochloric acid solution was prepared, followed by the addition of 0.42 g of 3-aminobenzoic acid. The solution was shaken in an ice-water bath at 0 °C for 1 hour to generate a diazonium hydrochloric acid solution. A hydrophilic modified cellulose acetate membrane was immersed in this solution, followed by the addition of 0.053 g of vitamin C, and the reaction was carried out at room temperature for 12 hours. After the diazo reaction, the membrane was thoroughly washed with water until all unreacted substances were removed, and then allowed to air dry at room temperature.

[0059] In-situ growth of Co-MOF-74: First, 1.5 g of cobalt acetate tetrahydrate was dissolved in 50 mL of methanol and sonicated for 5 minutes until completely dissolved. Similarly, 0.5 g of 2,5-dihydroxyterephthalic acid was dissolved in 25 mL of methanol. The hydrophilically modified cellulose acetate membrane with introduced carboxyl groups was immersed in the methanol solution containing cobalt acetate tetrahydrate for 1 hour to adsorb cobalt ions. Then, the methanol solution of 2,5-dihydroxyterephthalic acid was slowly added, and the reaction was carried out under magnetic stirring for about 2 hours. Subsequently, the membrane was washed repeatedly with methanol and deionized water alternately to remove unbound MOF particles and residual chemicals. Finally, it was dried in a vacuum oven at 60 °C for 6 hours to obtain the Co-MOF-74 composite membrane.

[0060] Comparative Example 1:

[0061] 1.2 g of cellulose acetate powder was dissolved in 20 g of N,N-dimethylformamide solvent by magnetic stirring. After dissolution, the solution was defoamed by ultrasonication, and a film was scraped using a film scraper. The film was then cured and shaped using the phase inversion method to obtain a pure cellulose acetate membrane. The membrane was then removed and dried at room temperature to obtain a pure cellulose acetate membrane.

[0062] The water contact angle of the prepared pure cellulose acetate membrane in air is as follows: Figure 3 As shown.

[0063] The catalytic degradation effect of the prepared pure cellulose acetate membrane is as follows: Figure 4 As shown.

[0064] Comparative Example 2:

[0065] First, 1.2 g of cellulose acetate powder was dissolved in 20 g of N,N-dimethylformamide solvent using magnetic stirring. After dissolution, 1 g of the hydrophilic monomer 2-hydroxyethyl methacrylate and 0.02 g of the initiator azobisisobutyronitrile were added to the cellulose acetate solution. The polymerization reaction was carried out at a constant temperature of 70 °C for 6 h under nitrogen protection to obtain a homogeneous solution. Subsequently, the solution was ultrasonically defoamed, and a film was formed using a film scraper. The film was then cured using a phase inversion method to obtain the formed hydrophilic modified cellulose acetate. The film was then removed and dried at room temperature.

[0066] The water contact angle of the hydrophilically modified cellulose acetate membrane prepared after free radical polymerization in air is as follows: Figure 3 As shown.

[0067] The catalytic degradation effect of the hydrophilically modified cellulose acetate membrane prepared after free radical polymerization is as follows: Figure 4 As shown.

[0068] Simultaneous oil-water separation and catalytic degradation tests were conducted on the membrane materials prepared in Examples 1-3 and Comparative Examples 1-2. First, the membrane was horizontally fixed in a dead-end filtration device. 100 mL of dye wastewater containing 20 mg / L organic pollutants (methylene blue, Congo red, methyl orange) and 2 mg / L potassium persulfate was prepared in advance and mixed with 100 mL of oil phase (n-hexane, petroleum ether, n-heptane), then slowly poured onto the upper layer of the membrane. The device outlet was connected to a circulating water multi-purpose vacuum pump, and the transmembrane pressure was controlled to −0.04 MPa (gauge pressure) by adjusting the vacuum level. Under vacuum, the aqueous phase was forced to permeate through the membrane layer, while the oil phase (n-hexane) was retained on the upper layer of the membrane due to hydrophobic interactions and the selective permeability of the membrane. During permeation, the aqueous phase contacted the Co-MOF-74 loaded on the membrane and activated the potassium persulfate, generating reactive oxygen species that catalytically degraded the methylene blue. The permeate was collected in a receiving bottle for subsequent analysis. After simultaneous separation and degradation are completed, the oil-water separation efficiency and catalytic degradation efficiency are calculated.

[0069] The separation efficiency of the membrane for oil-water mixtures is calculated using the following formula:

[0070]

[0071] V0 is the initial aqueous phase volume on the feed side, and V1 is the actual aqueous phase volume permeating through the membrane.

[0072] The catalytic degradation efficiency of the membrane for organic pollutants is calculated using the following formula:

[0073]

[0074] C0 is the initial concentration of organic pollutants in the original solution, and C1 is the concentration of organic pollutants in the permeate.

[0075] Under the same operating conditions, the membrane materials prepared in Examples 1-3 and Comparative Examples 1-2 were used to conduct simultaneous oil-water separation and catalytic degradation tests on oil-water mixtures containing organic pollutants. The oil-water separation efficiency and organic pollutant catalytic degradation efficiency of each membrane material are shown in the table below:

[0076]

[0077] The above results show that the Co-MOF-74 composite membrane prepared by the method of the present invention exhibits high oil-water separation efficiency and excellent catalytic degradation ability of organic pollutants in the process of simultaneous oil-water separation and catalytic degradation.

[0078] In contrast, although the membrane materials prepared in Comparative Examples 1 and 2 have a certain oil-water separation capability, they lack effective active sites due to the absence of Co-MOF-74. Their removal of organic pollutants is mainly characterized by adsorption behavior, without showing a significant catalytic degradation effect, making it difficult to achieve efficient removal of organic pollutants.

[0079] Therefore, the Co-MOF-74 composite membrane prepared by this invention can achieve simultaneous oil-water separation and organic pollutant removal in a single operation, and both have high efficiency, indicating its application potential in the integrated treatment of oil-water systems containing organic pollutants.

Claims

1. A method for preparing a Co-MOF-74 composite membrane, characterized in that, Includes the following steps: (1) Preparation of casting solution A hydrophilic monomer and an initiator were added to a cellulose acetate solution, and a free radical polymerization reaction was carried out at 60–80 °C for 6–10 h under an inert atmosphere to obtain a casting solution. The hydrophilic monomer is 2-hydroxyethyl methacrylate or acryloyloxyethyltrimethylammonium chloride; The initiator is selected from one or more of azobisisobutyronitrile, dicumyl peroxide, and benzoyl peroxide; (2) Film formation The casting solution obtained in step (1) was subjected to ultrasonic defoaming, the film was scraped, and then solidified in deionized water by phase inversion. After that, it was taken out and dried at room temperature to obtain a hydrophilic modified cellulose acetate membrane. (3) Diazo reaction introduces carboxyl groups The hydrophilic modified cellulose acetate membrane obtained in step (2) was immersed in a diazonium salt hydrochloric acid solution, and vitamin C was added to carry out a diazonium reaction to obtain a membrane material with introduced carboxyl groups. The diazonium salt hydrochloric acid solution is prepared by reacting sodium nitrite and 3-aminobenzoic acid in hydrochloric acid at 0 °C. (4) In situ growth of Co-MOF-74 The membrane material with carboxyl groups introduced in step (3) was immersed in a methanol solution of cobalt acetate tetrahydrate, and then a methanol solution of ligand 2,5-dihydroxyterephthalic acid was added to grow Co-MOF-74 in situ. After washing and vacuum drying, Co-MOF-74 composite membrane was obtained.

2. The method of claim 1, wherein the Co-MOF-74 composite membrane is prepared by the steps of: In step (1), the cellulose acetate solution is obtained by dissolving cellulose acetate in a solvent; the solvent is selected from one or more of N,N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, and N,N-dimethylacetamide; the concentration of the cellulose acetate solution is 0.02 to 0.2 g / mL.

3. The method of claim 1, wherein the Co-MOF-74 composite membrane is prepared by the steps of: In step (1), the mass ratio of hydrophilic monomer to cellulose acetate is 1:1 to 2; the amount of initiator is 1% to 5% of the mass of hydrophilic monomer.

4. The method for preparing the Co-MOF-74 composite membrane as described in claim 1, characterized in that, In step (2), the conditions for film scraping are: ambient temperature 20-30℃, humidity 30-50%, and film thickness 200-400 μm.

5. The method for preparing the Co-MOF-74 composite membrane as described in claim 1, characterized in that, In step (3), the concentration of sodium nitrite in the diazonium salt hydrochloric acid solution reaction system is 0.001 to 0.005 g / mL; the mass ratio of sodium nitrite to 3-aminobenzoic acid is 1:2 to 5.

6. The method for preparing the Co-MOF-74 composite membrane as described in claim 1, characterized in that, In step (3), after adding vitamin C, a diazo reaction was carried out at room temperature for 12 h; the mass ratio of vitamin C to sodium nitrite was 1:1 to 20.

7. The method for preparing the Co-MOF-74 composite membrane as described in claim 1, characterized in that, In step (4), the concentration of the methanol solution of cobalt acetate tetrahydrate is 0.005-0.03 g / mL; the mass ratio of 2,5-dihydroxyterephthalic acid to cobalt acetate tetrahydrate is 1:2-3.

8. The method for preparing the Co-MOF-74 composite membrane as described in claim 1, characterized in that, In step (4), the membrane material with introduced carboxyl groups is immersed in a methanol solution of cobalt acetate tetrahydrate for 1 h to allow cobalt ions to be adsorbed onto the membrane surface. Then, a methanol solution of ligand 2,5-dihydroxyterephthalic acid is added, and the reaction is stirred at room temperature for 2 h to allow Co-MOF-74 to grow in situ on the inner wall and surface of the membrane pores.

9. The Co-MOF-74 composite membrane prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the Co-MOF-74 composite membrane as described in claim 9 in simultaneous oil-water separation and catalytic degradation of organic pollutants.

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