Preparation method and application of PVDF / MOFs / GO composite membrane

Abstract

The invention mainly relates to the technical field of composite material preparation, in particular to a preparation method and application of a PVDF / MOFs / GO composite membrane, and the preparation method comprises the following steps: cleaning and drying a PVDF membrane for carboxylation treatment; then immersing the PVDF membrane into a sodium hydroxide solution to obtain a carboxylated PVDF membrane; adding GO into deionized water to obtain a solution A; co (NO3) 2.6 H2O is dissolved, and a solution B is obtained; adding the solution A into the solution B, and stirring to obtain a Co < 2 + > / GO mixed solution; and filtering to the surface of the carboxylated PVDF membrane in vacuum, and immersing into a 2-methylimidazole solution to obtain the PVDF / MOFs / GO composite membrane. The compact and uniform MOFs composite material layer rapidly grows on the surface of the polyvinylidene fluoride membrane to prepare the MOFs composite membrane, and the MOFs composite membrane is used as an adsorption membrane to adsorb and separate organic matters or natural products in water, so that wastewater purification and organic matter extraction are realized.

Description

TECHNICAL FIELD

[0001] The present application mainly relates to the technical field of composite material preparation, and particularly relates to a preparation method and application of a PVDF / MOFs / GO composite membrane. BACKGROUND

[0002] In the field of separation membrane technology, metal organic frameworks (MOFs) have shown great potential in the field of adsorption separation due to their unique advantages of porosity and adjustable pore size. By selecting different metal ions and organic ligands, a three-dimensional framework structure of ligand-metal ion-ligand can be constructed to achieve selective adsorption of specific substances. In order to expand the application direction of MOFs, MOFs are often loaded on a suitable carrier to form a composite membrane. Polyvinylidene fluoride (PVDF) is an ideal choice for a composite membrane carrier due to its excellent chemical corrosion resistance, heat resistance and mechanical properties, and has a broad application prospect in the fields of wastewater treatment and electrolyte separation. At the same time, graphene oxide (GO) is an excellent carbon functional material with a two-dimensional network structure and a large number of functional groups such as hydroxyl and carboxyl groups on the surface, which provides effective support for the loading of MOFs.

[0003] However, in the prior art, the PVDF / MOFs / GO composite membrane still has certain limitations. For example, in the water phase adsorption scene, MOFs are still prone to hydrophobic aggregation, which limits the contact area with pollutants in water, and the adsorption efficiency is difficult to meet the application requirements of wastewater purification and extraction of organic matter in water. At the same time, the three are usually put into a 100℃ sealed reaction kettle, the reaction conditions are harsh, the energy consumption is high, and the final application only focuses on the gas adsorption of volatile organic compounds, which cannot meet the requirements of high efficiency, stability and low cost of composite membranes in water phase adsorption scenes.

[0004] Therefore, there is an urgent need for a preparation method of a PVDF / MOFs / GO composite membrane to solve the above problems. SUMMARY

[0005] To achieve the above purpose, the following technical scheme is adopted: The preparation method of the PVDF / MOFs / GO composite membrane comprises the following steps: Step 100, pretreatment, the polyvinylidene fluoride membrane (PVDF membrane) is cleaned with deionized water, and dried for standby use; Step 200, surface treatment, the surface modification of the PVDF membrane is treated by carboxylation. First, the PVDF membrane is immersed in a sodium hydroxide solution at room temperature, then the PVDF membrane is immersed in an aqueous solution containing acrylic acid and an initiator, and soaked in a vacuum drying box for 2-4h, and finally the PVDF membrane is immersed in deionized water; Step 300, carboxyl grafting treatment, the PVDF membrane after step 200 operation is immersed into sodium hydroxide solution for 1h, then washed with deionized water to neutral, to obtain carboxylated PVDF membrane, drying for standby; Step 400, configuration A solution, 19-21 mg of graphene oxide (GO) is added to 10 mL of deionized water, ultrasonic cleaning machine for 15 min, to obtain GO water dispersion, namely A solution; Step 500, configuration B solution, 200 mg of Co (NO3) 2·6H20 is dissolved in 20 ml of deionized water, stirring for 30 min, finally to obtain B solution; Step 600, configuration Co 2+ / GO mixed solution, then the A solution is added to the B solution and stirred for 2 h to obtain Co 2+ / GO mixed solution; Step 700, vacuum filtration, the Co 2+ / GO mixed solution is filtered by vacuum filtration to the surface of the carboxylated PVDF membrane, to obtain PVDF / Co 2+ / GO composite membrane; Step 800, the PVDF / Co 2+ / GO composite membrane is immersed in 2-methyl imidazole solution, constant temperature reaction at 50 DEG C for 2-3h, to obtain PVDF / ZIF-67 / GO composite membrane by in situ growth method, wherein ZIF-67 is MOFs material, namely PVDF / MOFs / GO composite membrane.

[0006] Further, in step 200, the concentration of the sodium hydroxide solution is 1-3 mol•L -1 , and the immersion time is 4-6h.

[0007] Further, in step 200, the mass fraction of acrylic acid and initiator in the aqueous solution is 9-11% and 0.5-1.5% respectively, and the initiator is K2S2O4.

[0008] Further, in step 300, the concentration of the sodium hydroxide solution is 1.5-2.5 mol•L -1 .

[0009] Further, in step 400, 0.01-0.03g of polyethylene glycol is added.

[0010] Further, in step 500, 0.01-0.03g of glucosamine is added.

[0011] The application of a PVDF / MOFs / GO composite membrane prepared according to the preparation method of the PVDF / MOFs / GO composite membrane.

[0012] Compared with the prior art, the application has the following beneficial effects: 1. The application uses polyvinylidene fluoride (PVDF) as a membrane carrier, and makes MOFs grow on the membrane, and uses graphene oxide (GO) to form a stable mesh with PVDF, thereby making up for the shortcomings of insufficient hydrophilicity of the PVDF membrane; 2. In the application, polyvinylidene fluoride (PVDF) is surface-modified to endow it with abundant carboxyl groups, so that MOFs grow on the surface of the thin film, and the finally generated PVDF / MOFs / GO composite membrane not only solves the defects of traditional membrane materials, but also has adjustable morphology and can be reused, and can fully exert the excellent adsorption performance of MOFs. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 is a process flow chart of the preparation method in the application; Figure 1 Figure 2 is an XRD spectrum of the PVDF / MOFs / GO composite membrane in the application; Figure 3 is an FTIR spectrum of the PVDF / MOFs / GO composite membrane in the application; Figure 2 Figure 4 is a SEM image of the PVDF / MOFs / GO composite membrane in the application. Figure 5 is a SEM image of the PVDF / MOFs / GO composite membrane in the application. Figure 3 Figure 6 is a SEM image of the PVDF / MOFs / GO composite membrane in the application. Figure 7 is a SEM image of the PVDF / MOFs / GO composite membrane in the application. Figure 4 Figure 8 is a SEM image of the PVDF / MOFs / GO composite membrane in the application. DETAILED DESCRIPTION

[0014] The application will be further described in combination with the drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the application and are not used to limit the scope of the application. In addition, it should be understood that after reading the content taught by the application, those skilled in the art can make various modifications or modifications to the application, and these equivalent forms also fall within the scope defined by the application.

[0015] In combination with the drawings and specific embodiments, Figure 1 A preparation method of a PVDF / MOFs / GO composite membrane, comprising the following steps: Step 100, pretreatment, the polyvinylidene fluoride membrane (PVDF membrane) is ultrasonically cleaned with deionized water for 3 times, 10 min each time, after removing the surface impurities, drying for standby; Step 200, surface treatment, the surface modification of the PVDF membrane is treated by carboxylation, first immerse it in 1-3 mol•L -1PVDF membrane is immersed in 1.5-2.5 mol•L-1 sodium hydroxide solution for 1 h, so that the grafted acrylic acid ester is hydrolyzed into carboxyl and the carboxyl is grafted to the surface of the PVDF membrane, and then the PVDF membrane is washed with deionized water to neutral, to obtain a carboxylated PVDF membrane, which is dried for use; Step 300, carboxyl grafting treatment, the PVDF membrane after step 200 is immersed in 1.5-2.5 mol•L-1 sodium hydroxide solution for 1 h, so that the grafted acrylic acid ester is hydrolyzed into carboxyl and the carboxyl is grafted to the surface of the PVDF membrane, and then the PVDF membrane is washed with deionized water to neutral, to obtain a carboxylated PVDF membrane, which is dried for use; -1 Step 300, carboxyl grafting treatment, the PVDF membrane after step 200 is immersed in 1.5-2.5 mol•L-1 sodium hydroxide solution for 1 h, so that the grafted acrylic acid ester is hydrolyzed into carboxyl and the carboxyl is grafted to the surface of the PVDF membrane, and then the PVDF membrane is washed with deionized water to neutral, to obtain a carboxylated PVDF membrane, which is dried for use; Step 400, preparation of solution A, 19-21 mg of graphene oxide (GO) is added to 10 mL of deionized water, the high hydrophilicity of GO in aqueous solution can improve the hydrophobicity of MOFs, and ultrasonic cleaning machine is used for ultrasonic treatment for 15 min to obtain a GO water dispersion, namely solution A. In some preferred embodiments of the present application, 0.01-0.03 g of polyethylene glycol is also added, which can further improve the hydrophilicity of GO and provide auxiliary dispersion sites for the growth of MOFs later; Step 500, preparation of solution B, 200 mg of Co(NO3)2·6H2O is dissolved in 20 mL of deionized water, and stirred for 30 min to obtain solution B. In some preferred embodiments of the present application, 0.01-0.03 g of glucosamine is also added, so that the hydroxyl and amino groups in the glucosamine can be combined with the organic ligand of MOFs later, to improve the hydrophilicity of MOFs; 2+ In some preferred embodiments of the present application, polyethylene glycol and glucosamine are introduced into solution A and solution B respectively, on the one hand, the glucosamine can be combined with the organic ligand of MOFs later, to increase the number of surface hydroxyl and amino groups and improve the hydrophilicity; on the other hand, the polyethylene glycol can synergize with GO to inhibit the agglomeration of MOFs during the growth process. In some preferred embodiments of the present application, polyethylene glycol and glucosamine are introduced into solution A and solution B respectively, on the one hand, the glucosamine can be combined with the organic ligand of MOFs later, to increase the number of surface hydroxyl and amino groups and improve the hydrophilicity; on the other hand, the polyethylene glycol can synergize with GO to inhibit the agglomeration of MOFs during the growth process.

[0016] Step 600, preparation of Co 2+ / GO mixed solution, and then solution A is added to solution B and stirred for 2 h to obtain a Co 2+ / GO mixed solution; Step 700, vacuum filtration, the Co 2+ / GO mixed solution is filtered onto the surface of the carboxylated PVDF membrane by vacuum filtration to obtain a PVDF / Co 2+ / GO composite membrane; Step 800, PVDF / Co 2+ The / GO composite membrane was immersed in a 2-methylimidazole solution and reacted at 50°C for 2-3 hours to allow Co to react. 2+ A PVDF / ZIF-67 / GO composite membrane was obtained by in-situ growth after undergoing a complexation reaction with 2-methylimidazole. ZIF-67 is a MOF material, which is the PVDF / MOFs / GO composite membrane.

[0017] In some preferred embodiments of this application, the 2-methylimidazole solution contains glucosamine to assist in the complexation reaction. Furthermore, the in-situ growth method in this application operates at a temperature of only 50°C, significantly reducing energy consumption compared to reactor reactions in the prior art.

[0018] In the PVDF / MOFs / GO composite membrane system of this application, graphene oxide (GO) forms a stable sieve structure with PVDF through a triple mechanism, significantly enhancing its hydrophilicity: First, the oxygen-containing functional groups such as hydroxyl (-OH) and carboxyl (-COOH) groups abundant on the GO surface, from Figure 3 3400 cm⁻¹ in FTIR spectrum -1 and 1710 cm -1 Characteristic peaks show that the -CF2 groups of carboxylated PVDF bind to each other through hydrogen bonds and electrostatic interactions, forming a tight GO-PVDF interfacial anchoring layer that inhibits GO exfoliation. Secondly, the two-dimensional layered structure of GO forms a multi-level sieve channel with PVDF micropores, with a pore size of 0.5 nm-0.1 μm, enhancing mechanical stability through physical interlocking. Simultaneously, the hydrophilic functional groups of GO form a hydration layer on the membrane surface, neutralizing the inherent hydrophobicity of PVDF and accelerating water molecule mass transfer. Finally, GO serves as a platform for in-situ MOF growth, and its oxygen-containing groups interact with Co... 2+ Coordination promotes the uniform distribution of MOF crystal nuclei, while the added glucosamine further forms a hydrogen bond network with GO through —NH2 / —OH, constructing a synergistic pathway of "hydrophilic-adsorption-sieving", ultimately achieving efficient adsorption and separation of organic matter in water by the composite membrane.

[0019] The appendix to this application Figure 2 , 3 Figures 4 and 5 show the XRD pattern, FTIR pattern, and SEM image of the PVDF / MOFs / GO composite film, respectively. The XRD pattern was used to verify the crystal structure and successful loading of the MOF material, ZIF-67. The characteristic peaks of ZIF-67, such as 2θ = 7.3°, 10.4°, and 12.7°, are clearly visible in the spectrum, consistent with the standard ZIF-67 spectrum. Figure 1 To, indicating Co 2+The complexation reaction with 2-methyl imidazole forms an ordered crystal structure in the composite membrane. In addition, the diffraction peaks of PVDF and GO in the figure, such as 2θ = 20.3° and 26.5°, are not significantly shifted, indicating that the composite process does not destroy the intrinsic structure of the carrier material, that is, it indicates that the MOFs grow densely and uniformly on the surface of the membrane, avoiding the problem of MOFs aggregation. Through XRD analysis, the porosity and pore size adjustability of the PVDF / MOFs / GO composite membrane are confirmed, providing a structural basis for its high efficiency in organic adsorption separation.

[0020] In addition, FTIR spectrograms are used to analyze the changes in surface functional groups and the formation of chemical bonds. In the spectrum, the characteristic peak of the carboxyl group (1710 cm -1 ) and the hydroxyl absorption band (3400 cm -1 ) are significantly enhanced, proving that the PVDF membrane successfully introduced hydrophilic groups after carboxylation treatment. At the same time, the characteristic peaks of ZIF-67, such as the imidazole ring at 1570 cm -1 and the Co-N bond at 420 cm -1 are clearly visible, verifying the formation of the MOFs layer in the in-situ growth method. After FTIR analysis, it is shown that the introduction of glucosamine and polyethylene glycol further enhances the number of hydrophilic functional groups, improving the stability of the composite membrane in water adsorption.

[0021] Finally, SEM images visually demonstrate the surface morphology and MOFs distribution of the PVDF / MOFs / GO composite membrane. The images show that the ZIF-67 crystals uniformly cover the surface of the PVDF membrane, forming a dense and porous MOFs layer with uniform pore size distribution and no aggregation phenomenon, confirming the effectiveness of the vacuum filtration step and the in-situ growth method, achieving the rapid growth of a dense and uniform MOFs layer. The network structure of GO is clearly visible, serving as a scaffold for MOFs growth, improving the mechanical strength and adsorption area of the composite membrane. The PVDF membrane surface is free of cracks or defects, reflecting the success of the surface modification. SEM analysis shows that the microstructure of the PVDF / MOFs / GO composite membrane optimizes the sieve performance, enabling it to have high contact area and reusability in water organic adsorption.

[0022] The PVDF / MOFs / GO composite membrane finally generated in this application is applied as an adsorption membrane for adsorption and separation of organic matter or natural products in water, thereby realizing wastewater purification and extraction of organic matter.

[0023] Example 1 A method for preparing a PVDF / MOFs / GO composite membrane, comprising the following steps: Step 100, pretreatment, ultrasonic cleaning the polyvinylidene fluoride membrane (PVDF membrane) with deionized water for 3 times, 10 min each time, after removing the surface impurities, dry for standby; Step 200, surface treatment, the surface modification of the PVDF film is treated by carboxylation, first immerse it in a 2 mol•L -1 solution of sodium hydroxide, immerse at room temperature for 5 h, then immerse the PVDF film in an aqueous solution containing 10% by mass of acrylic acid and 1% by mass of K2S2O4, soak in a vacuum drying box for 3 h, and finally immerse it in deionized water; Step 300, carboxyl grafting treatment, immerse the PVDF film after step 200 operation in a 2 mol•L -1 solution of sodium hydroxide for 1 h, then wash with deionized water to neutral, obtain carboxylated PVDF film, dry for standby; Step 400, prepare solution A, add 20 mg of graphene oxide (GO) to 10 mL of deionized water, ultrasonic in an ultrasonic cleaner for 15 min, obtain GO aqueous dispersion, namely solution A.

[0024] Step 500, prepare solution B, dissolve 200 mg of Co(NO3)2·6H20 in 20 ml of deionized water, stir for 30 min, finally obtain solution B.

[0025] Step 600, prepare Co 2+ / GO mixed solution, then add solution A to solution B and stir for 2 h to obtain Co 2+ / GO mixed solution; Step 700, vacuum filtration, vacuum filter the Co 2+ / GO mixed solution to the surface of the carboxylated PVDF film to obtain a PVDF / Co 2+ / GO composite film; Step 800, immerse the PVDF / Co2+ / GO composite film in a 2-methylimidazole solution, react at 50℃ for 2-3 h, obtain a PVDF / ZIF-67 / GO composite film by in-situ growth method, ZIF-67 is a MOFs material, namely a PVDF / MOFs / GO composite film.

[0026] Example 2 A method for preparing a PVDF / MOFs / GO composite film, comprising the following steps: Step 100, pretreatment, ultrasonic clean the polyvinylidene fluoride film (PVDF film) with deionized water for 3 times, 10 min each time, remove surface impurities, and dry for standby; Step 200, surface treatment, the surface modification of the PVDF film is treated by carboxylation, first immerse it in a 1 mol•L -1hydroxide solution for 6h at room temperature, then the PVDF membrane was immersed in an aqueous solution containing 9% acrylic acid and 1.5% K2S2O4 by mass fraction for 4h in a vacuum drying box, and finally immersed in deionized water; Step 300, carboxyl grafting treatment, the PVDF membrane after step 200 was immersed in a 1.5 mol•L -1 hydroxide solution for 1h, then washed with deionized water to neutral, to obtain a carboxylated PVDF membrane, dried for use; Step 400, preparation of solution A, 19 mg of graphene oxide (GO) was added to 10 mL of deionized water, and 0.02 g of polyethylene glycol was added, and ultrasonic cleaning was performed for 15 min in an ultrasonic cleaner to obtain a GO aqueous dispersion, namely solution A; Step 500, preparation of solution B, 200 mg of Co(NO3)2·6H2O was dissolved in 20 mL of deionized water, and 0.02 g of glucosamine was added, and stirred for 30 min, to obtain solution B; Step 600, preparation of Co 2+ / GO mixed solution, then solution A was added to solution B and stirred for 2h to obtain a Co 2+ / GO mixed solution; Step 700, vacuum filtration, the Co 2+ / GO mixed solution was filtered onto the surface of the carboxylated PVDF membrane by vacuum filtration to obtain a PVDF / Co 2+ / GO composite membrane; Step 800, the PVDF / Co 2+ / GO composite membrane was immersed in a 2-methylimidazole solution containing glucosamine, and reacted at 50℃ for 2h to allow the Co 2+ to complex with 2-methylimidazole, and a PVDF / ZIF-67 / GO composite membrane was obtained by in-situ growth, and ZIF-67 is a MOFs material, namely a PVDF / MOFs / GO composite membrane.

[0027] Example 3 A method for preparing a PVDF / MOFs / GO composite membrane, comprising the following steps: Step 100, pretreatment, a polyvinylidene fluoride membrane (PVDF membrane) was ultrasonically cleaned with deionized water for 3 times, 10 min each time, after removing surface impurities, dried for use; Step 200, surface treatment, the surface of the PVDF membrane was modified by carboxyl group treatment, first immersed in a 3 mol•L -1PVDF membrane was immersed in 2.5 mol•L-1 sodium hydroxide solution for 1 h, then washed with deionized water to neutral, to obtain carboxylated PVDF membrane, dried for use; Step 300, carboxyl grafting treatment, PVDF membrane after step 200 operation was immersed in 2.5 mol•L-1 sodium hydroxide solution for 1 h, then washed with deionized water to neutral, to obtain carboxylated PVDF membrane, dried for use; -1 Step 300, carboxyl grafting treatment, PVDF membrane after step 200 operation was immersed in 2.5 mol•L-1 sodium hydroxide solution for 1 h, then washed with deionized water to neutral, to obtain carboxylated PVDF membrane, dried for use; Step 400, configuration of A solution, 21 mg of graphene oxide (GO) was added to 10 mL of deionized water, while 0.03 g of polyethylene glycol was added, and ultrasonic cleaning machine was used for ultrasonic for 15 min, to obtain GO water dispersion, namely A solution; Step 500, configuration of B solution, 200 mg of Co(NO3)2·6H2O was dissolved in 20 mL of deionized water, and 0.03 g of glucosamine was added, and stirred for 30 min, to obtain B solution; Step 600, configuration of Co 2+ / GO mixed solution, then A solution was added to B solution and stirred for 2 h to obtain Co 2+ / GO mixed solution; Step 700, vacuum filtration, Co 2+ / GO mixed solution was filtered by vacuum filtration to the surface of carboxylated PVDF membrane, to obtain PVDF / Co 2+ / GO composite membrane; Step 800, PVDF / Co 2+ / GO composite membrane was immersed in 2-methyl imidazole solution containing glucosamine, and reacted at 50℃ for 3 h, to make Co 2+ complexation reaction with 2-methyl imidazole, and PVDF / ZIF-67 / GO composite membrane was obtained by in-situ growth method, ZIF-67 was MOFs material, namely PVDF / MOFs / GO composite membrane.

[0028] Finally, it should be pointed out that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing a PVDF / MOFs / GO composite membrane, characterized in that it comprises the following steps: Step 100, pretreatment, ultrasonic cleaning of a polyvinylidene fluoride membrane (PVDF membrane) with deionized water, drying for standby; Step 200, surface treatment, carboxylation treatment of the surface modification of the PVDF membrane, first immerse it in a sodium hydroxide solution, immerse at room temperature, then immerse the PVDF membrane in an aqueous solution containing acrylic acid and initiator, soak in a vacuum drying oven for 2-4 h, and finally immerse it in deionized water; Step 300, carboxyl grafting treatment, immerse the PVDF membrane after step 200 operation in a sodium hydroxide solution for 1 h, then wash it with deionized water to neutral, obtain carboxylated PVDF membrane, dry for standby; Step 400, preparation of A solution, 19-21 mg of graphene oxide (GO) is added to 10 mL of deionized water, ultrasonic cleaning machine for 15 min, to obtain GO water dispersion, namely A solution; Step 500, preparation of B solution, 200 mg of Co(NO3)2·6H20 is dissolved in 20 ml of deionized water, stirring for 30 min, finally to obtain B solution; 2. The method for preparing a PVDF / MOFs / GO composite membrane according to claim 1, characterized in that: Step 600, Co 2+ / GO mixture solution, and then the A solution was added to the B solution and stirred for 2 h to obtain Co 2+ / GO mixture solution; Step 700, vacuum filtration, Co 2+ / GO mixed solution is filtered by vacuum filtration to the surface of the carboxylated PVDF membrane to obtain a PVDF / Co 2+ / GO composite film; Step 800, the PVDF / Co 2+ / GO composite film is immersed into a 2-methylimidazole solution, and is reacted at 50°C for 2-3h, to obtain a PVDF / ZIF-67 / GO composite film by in-situ growth, wherein ZIF-67 is a MOFs material, i.e. a PVDF / MOFs / GO composite film.

3. The method for preparing a PVDF / MOFs / GO composite membrane according to claim 1, characterized in that: In step 200, the concentration of the sodium hydroxide solution is 1-3 mol•L. -1 The soaking time is 4-6 hours. In step 200, the mass fraction of acrylic acid and initiator in the aqueous solution is 9-11% and 0.5-1.5% respectively, and the initiator is K2S2O4.

4. The method for preparing a PVDF / MOFs / GO composite membrane according to claim 1, characterized in that:

5. The method for preparing a PVDF / MOFs / GO composite membrane according to claim 1, characterized in that: The concentration of the sodium hydroxide solution in step 300 is 1.5-2.5 mol•L -1 . In step 400, 0.01-0.03 g of polyethylene glycol is added.

6. The method for preparing a PVDF / MOFs / GO composite membrane according to claim 1, characterized in that: In step 500, 0.01-0.03 g of glucosamine is added.

7. The application of a PVDF / MOFs / GO composite membrane prepared by the method according to any one of claims 1-6. ​

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