Acid and alkali resistant nanofiltration membrane and preparation method thereof

Abstract

The invention discloses an acid and alkali resistant nanofiltration membrane and a preparation method thereof, and relates to the technical field of nanofiltration membranes. The nanofiltration membrane with better acid resistance and alkali resistance is prepared by combining a surfactant, click chemistry reaction and a metal organic framework; zirconium chloride is used as a metal node, 2-amino p-benzoic acid is used as an organic ligand, a Zr-MOF metal organic framework is constructed by adopting a solvothermal method, sulfydryl is introduced, pentaerythritol triacrylate and octyldithiol in a grafting solution are combined, free radical polymerization is carried out under UV illumination, and a high-crosslinking-degree network is formed; the charge repulsive effect of the sulphobetaine monomer realizes efficient screening of ions or molecules; a gradient ultraviolet polymerization process is adopted, and the ultraviolet intensity and density are dynamically adjusted, so that the surface flatness of the nanofiltration membrane and the uniformity of pore size distribution are improved; through chemical component design and process optimization, the mechanical property and chemical property stability of the nanofiltration membrane are synergistically improved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of nanofiltration membranes, in particular to an acid-alkali-resistant nanofiltration membrane and a preparation method thereof. BACKGROUND

[0002] As an important membrane separation technology, the nanofiltration membrane plays an irreplaceable role in the fields of drinking water purification, wastewater treatment, food and pharmaceutical industry concentration separation, chemical product refining, biological engineering and the like due to its separation characteristics between ultrafiltration and reverse osmosis. The core advantage lies in that small-molecule organic matters, multivalent salt ions, part of monovalent salt ions, heavy metal ions and part of viruses and bacteria in water can be effectively removed while relatively low operating pressure and high water flux are maintained.

[0003] At present, the nanofiltration membrane widely used is mainly based on polyamide material, and an active separation layer is formed on the surface of a porous support base membrane through interfacial polymerization. However, the amide bond in the main chain of the polyamide material is easily attacked by strong acid and strong base, and is irreversibly chemically degraded, thereby damaging the membrane structure.

[0004] In the prior art, more acid-alkali-resistant monomers or crosslinking agents are tried to be used for interfacial polymerization, but the improvement range is limited, and it is difficult to simultaneously consider strong acid and strong base resistance, high rejection rate and high flux; a layer of acid-alkali-resistant protective layer is coated on the surface of the nanofiltration membrane or hydrophilic groups or inert groups are grafted, but the long-term stability of the coating layer and the bonding force with the base membrane are challenges. Therefore, the application provides an acid-alkali-resistant nanofiltration membrane and a preparation method thereof to solve the above technical problems. SUMMARY

[0005] The application aims to provide an acid-alkali-resistant nanofiltration membrane and a preparation method thereof to solve the problems in the prior art.

[0006] To achieve the above-mentioned purpose, the application provides the following technical scheme: A preparation method of an acid-alkali-resistant nanofiltration membrane comprises the following steps: (1) A base membrane is immersed in sodium dodecyl sulfate and ultrasonically treated to obtain a pretreated base membrane; (2) Pentaerythritol triacrylate, octanedithiol and a photoinitiator are mixed, a solvent is added, and then sulfobetaine monomers and MOFs are added and dispersed to obtain a grafting solution; (3) The base membrane is immersed in the grafting solution, and then subjected to UV irradiation under nitrogen protection, reaction, post-treatment and vacuum drying to obtain an acid-alkali-resistant nanofiltration membrane.

[0007] In the above technical solution, the base membrane is pretreated with sodium dodecyl sulfate, which increases the surface energy of the base membrane. The trifunctional acrylic monomer of pentaerythritol triacrylate undergoes free radical polymerization under UV light to form a highly cross-linked network. The dithiol monomer of octanedithiol cross-links with acrylate through thiol-ene click chemistry, increasing the network density and improving mechanical strength and chemical stability, thereby enhancing the acid and alkali resistance of the nanofiltration membrane. The flexible long chain of octanedithiol buffers stress and prevents membrane embrittlement. Sulfobetaine is introduced into the grafting solution to form a zwitterionic hydrophilic layer, which inhibits the adsorption of organic matter or inorganic salts through electrostatic repulsion, thereby improving the antifouling properties of the nanofiltration membrane. The porous crystalline structure of metal-organic frameworks (MOFs) provides molecular sieving channels, the nanopores control the molecular weight cutoff, and the rigid structure enhances the membrane's resistance to swelling.

[0008] More preferably, the grafting solution comprises the following components by weight: 10-20 parts of pentaerythritol triacrylate, 5-10 parts of octanedithiol, 3-6 parts of sulfobetaine monomer, 0.5-1 part of photoinitiator, 50-60 parts of solvent, and 1.5-3 parts of MOFs.

[0009] More preferably, the photoinitiator is 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone.

[0010] More preferably, the solvent is a 50-55 wt% ethanol solution.

[0011] More preferably, the dispersion process conditions are: high-speed dispersion at a rotation speed of 2400~3000 r / min for 10~20 min.

[0012] More preferably, in step (3), the UV irradiation process conditions are as follows: using a gradient UV polymerization process, the UV density is 50-60 mW / cm² during the 0-5 min period. 2 At 5–8 min, the UV density is 100–120 mW / cm³. 2 At 8–12 min, the UV density was 50–60 mW / cm³. 2 .

[0013] In the above technical solution, a gradient UV polymerization process is adopted. In the initial stage (0~5min, low intensity): the polymerization is gently initiated to avoid rapid cross-linking of monomers that could lead to membrane surface collapse; in the middle stage (5~8min, high intensity): the deep cross-linking reaction is accelerated to form a high-density network structure and improve the retention rate; in the later stage (8~12min, low intensity): the surface is smoothed to reduce membrane defects; the gradient energy controls the monomer diffusion rate to ensure that sulfobetaine monomers and MOFs are evenly distributed in the membrane; and the surface smoothness and pore size distribution uniformity are improved by dynamically adjusting the UV intensity density.

[0014] More preferably, the ultrasonic treatment process conditions are: a temperature of 30~40℃, a frequency of 40~50kHz, and a pressure of 0.3~0.5W / cm. 3 At a power density of 30-40 min, ultrasonic treatment was performed.

[0015] More preferably, in step (3), the post-treatment process conditions are: rinsing with deionized water at a temperature of 60~80℃ for 30~40 minutes.

[0016] More preferably, in step (3), the vacuum drying process conditions are: drying at a temperature of 60~70℃ for 1~1.5h.

[0017] More preferably, the base film is prepared by the following process: Step 1: Add methyl 4-azidobenzoate, ethyl perfluorooctanoate, and ethyl α-bromophenylacetate to a reaction vessel, add triethylamine dropwise, and irradiate with UV light to obtain a perfluoroazido copolymer; Step 2: Dissolve the perfluoroazide copolymer in dichloromethane, immerse the polysulfone membrane in the perfluoroazide copolymer solution for 4-6 hours, remove it, and dry it at 60-70°C for 2-4 hours to obtain the base film.

[0018] In the aforementioned technical effects, the polysulfone-based membrane, as a support layer, provides excellent mechanical strength and high-temperature resistance. Surface treatment with a perfluoroazide copolymer allows the azide groups (-N3) to generate highly reactive nitrogen ions under UV irradiation, which then covalently graft with the carbon-hydrogen bonds (CH) on the polysulfone membrane surface, forming stable carbon-nitrogen bonds (CN). This enables the perfluoroazide copolymer to exist on the polysulfone membrane surface for a long period. The chemical inertness of fluorine itself endows the membrane with excellent hydrophobicity and acid / alkali resistance. Fluorinated monomers adhere to the polysulfone membrane surface; due to the high bond energy and stability of the carbon-fluorine bonds, the base membrane is less prone to chemical bond breakage in acidic and alkaline environments, maintaining excellent performance even in extreme chemical environments. The bromoaryl group of α-bromopropyl ethyl acetate serves as the active reaction site, introduced into the molecular chain through copolymerization to form a fluorinated functionalized polymer. Triethylamine acts as a catalyst, promoting reaction uniformity. Dichloromethane, a polar aprotic solvent, facilitates rapid solvent penetration into the polysulfone membrane pores, ensuring the bonding strength between the functional layer and the support layer.

[0019] More preferably, the mass ratio of methyl 4-azidobenzoate, ethyl perfluorooctanoate, ethyl α-bromophenylacetate, and triethylamine is (8~9):(8~8.5):0.01:0.005.

[0020] More preferably, the mass ratio of the perfluoroazide copolymer to dichloromethane is 0.1:(5~8).

[0021] More preferably, in step 1, the UV irradiation process conditions are: at a power of 5~6W, using a wavelength of 250~300nm, at a distance of 3~5cm from the polysulfone film, irradiation for 4~6h.

[0022] More preferably, the MOFs are prepared by the following process: Step ①: Dissolve zirconium chloride and 2-aminobenzoic acid in N,N-dimethylformamide, heat to react, filter, wash, and dry to obtain aminated Zr-MOF; Step 2: Disperse the aminated Zr-MOF in anhydrous toluene, add a dispersant, sonicate, add 3-mercaptopropionic acid, filter, wash, and dry to obtain MOFs.

[0023] In the above technical solution, this invention uses zirconium chloride as the metal node and 2-aminobenzoic acid as the organic ligand to construct a Zr-MOF metal-organic framework via a solvothermal method. The carboxylate group in the ligand coordinates with zirconium ions to form a stable metal-organic framework structure. At the same time, the ligand retains amino functional groups, directly imparting amination to the metal. The introduction of amino groups provides active sites for subsequent grafting of thiol groups. Its regular channels can provide uniform nanoscale pore size. Combined with the charge repulsion effect of sulfobetaine monomer, it achieves efficient sieving of ions or molecules. The introduction of thiol groups causes a click chemical reaction between the base film and the thiol in the grafting solution, which enhances the interfacial bonding between MOFs and the polymer layer and prevents inorganic particles from falling off. The rigid skeleton of the perfluoroazide copolymer complements the elastic network of the grafted layer, balancing the flexibility and rigidity of the film. The addition of a dispersant and ultrasonic dispersion effectively prevents the metal-organic framework from agglomerating during the reaction, increases the contact area with 3-thiopropionic acid, improves the modification rate, and ensures the integrity of the MOF structure during the modification process.

[0024] More preferably, the mass ratio of zirconium chloride, 2-aminobenzoic acid, and N,N-dimethylformamide is (0.1~10):1:20.

[0025] More preferably, the mass ratio of amino-modified Zr-MOF, anhydrous toluene, dispersant, and 3-mercaptopropionic acid is (0.5~1):20:0.01:2.

[0026] More preferably, the dispersant is polyvinylpyrrolidone.

[0027] More preferably, in step ①, the process conditions for the heating reaction are: at a temperature of 70~85℃, the reaction is carried out for 6~8 hours.

[0028] More preferably, in step ①, the drying process conditions are: drying at a temperature of 60~70℃ for 1~2 hours.

[0029] More preferably, in step ②, the ultrasonic dispersion process conditions are: dispersion for 5-8 minutes at a frequency of 5-8 MHz.

[0030] More preferably, in step ②, the drying process conditions are: drying at a temperature of 55~60℃ for 1~2 hours.

[0031] Compared with the prior art, the beneficial effects of the present invention are: 1. The acid and alkali resistant nanofiltration membrane of the present invention, through the thiol-ene click reaction, crosslinks the dithiol monomer of octanedithiol with acrylate, increases the network density, improves the mechanical strength and chemical stability of the nanofiltration membrane, thereby enhancing the acid and alkali resistance of the nanofiltration membrane.

[0032] 2. The acid and alkali resistant nanofiltration membrane of the present invention, by introducing sulfobetaine to form a zwitterionic hydrophilic layer, inhibits the adsorption of organic matter or inorganic salts through electrostatic repulsion, thereby improving the antifouling properties of the nanofiltration membrane.

[0033] 3. The acid and alkali resistant nanofiltration membrane of the present invention, by adding a metal-organic framework to the base membrane solution, provides molecular sieving channels with its porous crystalline structure, and the nanopores control the molecular weight cutoff. The rigid structure enhances the membrane's anti-swelling properties. Functionalized thiol groups are introduced on the surface of the metal-organic framework, causing a click chemical reaction between the base membrane and the thiols in the grafting solution. This enhances the interfacial bonding between the thiol-azide covalent bonds and the polymer layer, preventing the detachment of inorganic particles. The rigid skeleton of the perfluoroazide copolymer complements the elastic network of the grafted layer, balancing the membrane's flexibility and rigidity.

[0034] 4. The acid and alkali resistant nanofiltration membrane of the present invention avoids membrane surface collapse caused by rapid cross-linking of monomers by adopting a gradient ultraviolet polymerization process, thereby reducing membrane defects. The gradient energy controls the monomer diffusion rate, so that sulfobetaine monomers and MOFs are evenly distributed in the membrane. By dynamically adjusting the ultraviolet intensity density, the smoothness of the membrane surface and the uniformity of pore size distribution are improved. Detailed Implementation

[0035] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] In the following specific implementation: Polysulfone membrane, model P-3700HC; The photoinitiator is 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone; The solvent is a 50-55% vol% ethanol solution; The dispersant is polyvinylpyrrolidone with an average molecular weight of 40,000; Example 1:

[0037] A method for preparing an acid and alkali resistant nanofiltration membrane includes the following steps: (1) The base membrane was immersed in sodium dodecyl sulfate and ultrasonically treated to obtain a pretreated base membrane; (2) Mix pentaerythritol triacrylate, octanedithiol, and photoinitiator, add solvent, then add sulfobetaine monomer and MOFs, and disperse at high speed for 10 min at a speed of 2400 r / min to obtain grafting solution; the grafting solution includes the following components by mass: 10 parts pentaerythritol triacrylate, 5 parts octanedithiol, 3 parts sulfobetaine monomer, 0.5 parts photoinitiator, 50 parts solvent, and 1.5 parts MOFs; (3) The base film was immersed in the grafting solution and subjected to a gradient UV polymerization process under nitrogen protection. The UV density was 50 mW / cm³ during the 0-5 min period. 2 The UV density was 100 mW / cm³ at 5–8 min. 2 The UV density was 50 mW / cm³ at 8–12 min. 2 The membrane was subjected to UV irradiation for 12 minutes to allow the reaction to proceed. After the reaction, it was rinsed with deionized water at 60°C for 30 minutes. After rinsing, it was vacuum dried at 60°C for 1 hour to obtain an acid and alkali resistant nanofiltration membrane.

[0038] The base film is prepared by the following process: Step 1: Methyl 4-azidobenzoate, ethyl perfluorooctanoate, and ethyl α-bromophenylacetate were added to a reaction vessel. Triethylamine was added dropwise at a power of 5W and a wavelength of 250nm, 3cm away from the polysulfone film. The mixture was irradiated with UV for 4h to obtain a perfluoroazido copolymer. The mass ratio of methyl 4-azidobenzoate, ethyl perfluorooctanoate, ethyl α-bromophenylacetate, and triethylamine was 8:8:0.01:0.005. Step 2: Dissolve the perfluoroazide copolymer in dichloromethane, immerse the polysulfone membrane in the perfluoroazide copolymer solution for 4-6 hours, remove it, and dry it at 60-70℃ for 2-4 hours to obtain the base film; the mass ratio of perfluoroazide copolymer to dichloromethane is 0.1:5.

[0039] MOFs are prepared by the following processes: Step ①: Zirconium chloride and 2-amino-terebenzoic acid were dissolved in N,N-dimethylformamide and reacted at 70°C for 6 hours. After filtration and washing, the mixture was dried at 60°C for 1 hour to obtain aminated Zr-MOF. The mass ratio of zirconium chloride, 2-amino-terebenzoic acid, and N,N-dimethylformamide was 0.2:1:20. Step 2: Disperse the aminated Zr-MOF in anhydrous toluene, add a dispersant, and sonicate at a frequency of 5 MHz for 5 min. Add 3-mercaptopropionic acid. After the reaction is complete, filter and wash, and dry at 55 ℃ for 1 h to obtain MOFs. The mass ratio of aminated Zr-MOF, anhydrous toluene, dispersant, and 3-mercaptopropionic acid is 0.5:20:0.01:2.

[0040] Example 2:

[0041] A method for preparing an acid and alkali resistant nanofiltration membrane includes the following steps: (1) The base membrane was immersed in sodium dodecyl sulfate and ultrasonically treated to obtain a pretreated base membrane; (2) Mix pentaerythritol triacrylate, octanedithiol, and photoinitiator, add solvent, then add sulfobetaine monomer and MOFs, and disperse at high speed for 15 min at a speed of 2800 r / min to obtain grafting solution; the grafting solution includes the following components by mass: 15 parts pentaerythritol triacrylate, 8 parts octanedithiol, 5 parts sulfobetaine monomer, 0.8 parts photoinitiator, 55 parts solvent, and 2 parts MOFs; (3) The base film was immersed in the grafting solution and subjected to a gradient UV polymerization process under nitrogen protection. The UV density was 55 mW / cm³ during the 0-5 min period. 2 The UV density was 110 mW / cm³ at 5–8 min. 2 The UV density was 55 mW / cm³ at 8–12 min. 2 The membrane was subjected to UV irradiation for 12 minutes to allow the reaction to proceed. After the reaction, it was rinsed with deionized water at 70°C for 35 minutes. After rinsing, it was vacuum dried at 65°C for 1.2 hours to obtain an acid and alkali resistant nanofiltration membrane.

[0042] The base film is prepared by the following process: Step 1: Methyl 4-azidobenzoate, ethyl perfluorooctanoate, and ethyl α-bromophenylacetate were added to a reaction vessel. Triethylamine was added dropwise at a power of 5.5W and a wavelength of 280nm, 4cm away from the polysulfone film. The mixture was irradiated with UV for 4h to obtain a perfluoroazido copolymer. The mass ratio of methyl 4-azidobenzoate, ethyl perfluorooctanoate, ethyl α-bromophenylacetate, and triethylamine was 8:8:0.01:0.005. Step 2: Dissolve the perfluoroazide copolymer in dichloromethane, immerse the polysulfone membrane in the perfluoroazide copolymer solution for 4 hours, remove it, and dry it at 60°C for 2 hours to obtain the base film; the mass ratio of perfluoroazide copolymer to dichloromethane is 0.1:5.

[0043] MOFs are prepared by the following processes: Step ①: Zirconium chloride and 2-amino-terebenzoic acid were dissolved in N,N-dimethylformamide and reacted at 70°C for 6 hours. After filtration and washing, the mixture was dried at 60°C for 1 hour to obtain amination-modified Zr-MOF. The mass ratio of zirconium chloride, 2-amino-terebenzoic acid, and N,N-dimethylformamide was 5:1:20. Step ②: Disperse the aminated Zr-MOF in anhydrous toluene, add a dispersant, and sonicate at a frequency of 5 MHz for 5 min. Add 3-mercaptopropionic acid. After the reaction is complete, filter and wash, and dry at 55 ℃ for 1 h to obtain MOFs. The mass ratio of aminated Zr-MOF, anhydrous toluene, dispersant, and 3-mercaptopropionic acid is 0.8:20:0.01:2.

[0044] Example 3:

[0045] A method for preparing an acid and alkali resistant nanofiltration membrane includes the following steps: (1) The base membrane was immersed in sodium dodecyl sulfate and ultrasonically treated to obtain a pretreated base membrane; (2) Mix pentaerythritol triacrylate, octanedithiol, and photoinitiator, add solvent, then add sulfobetaine monomer and MOFs, and disperse at high speed for 20 min at 3000 r / min to obtain grafting solution; the grafting solution includes the following components by mass: 20 parts pentaerythritol triacrylate, 10 parts octanedithiol, 6 parts sulfobetaine monomer, 1 part photoinitiator, 60 parts solvent, and 3 parts MOFs; (3) The base film was immersed in the grafting solution and subjected to a gradient UV polymerization process under nitrogen protection. The UV density was 60 mW / cm³ during the 0-5 min period. 2 The UV density was 120 mW / cm³ at 5–8 min. 2 The UV density was 60 mW / cm³ at 8–12 min. 2 The membrane was subjected to UV irradiation for 12 minutes to allow the reaction to proceed. After the reaction, it was rinsed with deionized water at 80°C for 40 minutes. After rinsing, it was vacuum dried at 70°C for 1.5 hours to obtain an acid and alkali resistant nanofiltration membrane.

[0046] The base film is prepared by the following process: Step 1: Methyl 4-azidobenzoate, ethyl perfluorooctanoate, and ethyl α-bromophenylacetate were added to a reaction vessel. Triethylamine was added dropwise at a power of 6W and a wavelength of 300nm, 5cm away from the polysulfone film. The mixture was irradiated with UV for 6h to obtain a perfluoroazido copolymer. The mass ratio of methyl 4-azidobenzoate, ethyl perfluorooctanoate, ethyl α-bromophenylacetate, and triethylamine was 9:8.5:0.01:0.005. Step 2: Dissolve the perfluoroazide copolymer in dichloromethane, immerse the polysulfone membrane in the perfluoroazide copolymer solution for 6 hours, remove it, and dry it at 70°C for 4 hours to obtain the base film; the mass ratio of perfluoroazide copolymer to dichloromethane is 0.1:8.

[0047] MOFs are prepared by the following processes: Step ①: Zirconium chloride and 2-amino-terebenzoic acid were dissolved in N,N-dimethylformamide and reacted at 85°C for 8 hours. After filtration and washing, the mixture was dried at 70°C for 2 hours to obtain aminated Zr-MOF. The mass ratio of zirconium chloride, 2-amino-terebenzoic acid, and N,N-dimethylformamide was 9:1:20. Step ②: Disperse the aminated Zr-MOF in anhydrous toluene, add a dispersant, and sonicate at 8 MHz for 8 min. Add 3-mercaptopropionic acid. After the reaction is complete, filter and wash, and dry at 60 ℃ for 2 h to obtain MOFs. The mass ratio of aminated Zr-MOF, anhydrous toluene, dispersant, and 3-mercaptopropionic acid is 1:20:0.01:2.

[0048] Comparative Example 1: This comparative example provides a method for preparing a nanofiltration membrane, wherein the base membrane is a polysulfone membrane, and the remaining methods are the same as in Example 1.

[0049] Comparative Example 2: This comparative example provides a method for preparing a nanofiltration membrane. The grafting solution includes the following components by mass: 6 parts of sulfobetaine monomer, 1 part of photoinitiator, 90 parts of solvent, and 3 parts of MOFs; the remaining methods are the same as in Example 1.

[0050] Comparative Example 3: This comparative example provides a method for preparing a nanofiltration membrane. The grafting solution includes the following components by mass: 10 parts of pentaerythritol triacrylate, 5 parts of octanedithiol, 3 parts of sulfobetaine monomer, 0.5 parts of photoinitiator, and 55 parts of solvent; the remaining methods are the same as in Example 1.

[0051] Comparative Example 4: This comparative example provides a method for preparing a nanofiltration membrane. In step (3), the UV irradiation process conditions are: 100 mW / cm 2 The ultraviolet density was determined, and the irradiation was carried out for 12 minutes. The remaining methods were the same as in Example 1.

[0052] experiment: Samples were prepared from the samples obtained in Examples 1-3 and Comparative Examples 1-4, and their performance was tested and the test results were recorded.

[0053] Solution preparation: Prepare a 2 g / L sodium sulfate solution; a 2 mol / L concentrated sulfuric acid solution; and a 3 mol / L sodium hydroxide solution. Acid resistance test: Using GB / T 34242-2017 as the reference standard, the sample was immersed in 2 mol / L concentrated sulfuric acid solution for 24 hours, then removed and rinsed with deionized water 3 times before testing the sodium sulfate rejection rate. Alkali resistance test: Using GB / T 34242-2017 as the reference standard, the sample was immersed in a 3 mol / L sodium hydroxide solution for 24 hours, then removed and rinsed three times with deionized water before testing the sodium sulfate rejection rate. Flux test: Using GB / T 32373-2015 as the reference standard, the nanofiltration membrane was placed in the filtration system at a temperature of 30℃. Before the test, a stable pure water flux was obtained by pre-pressurizing with a pressure of 0.8MPa for 20 minutes, and then the flux was tested. Tensile strength test: Using GB / T 1040.2-2006 as the reference standard, the tensile strength is tested at 25℃ using a universal testing machine at a speed of 25mm / min.

[0054] Cost-performance ratio comparison table

[0055] Based on the data in the table above, the following conclusions can be clearly drawn: The results of the tests conducted in Examples 1-3 and Comparative Examples 1-4 show that: Compared with the comparative examples, the nanofiltration membranes obtained in Examples 1-3 have higher sodium sulfate rejection rates after acidification and after alkali treatment, higher flux, and higher tensile strength.

[0056] Compared with Example 1, the nanofiltration membrane obtained in Comparative Example 1 uses a polysulfone membrane as the base membrane. After being treated with acid and alkali, the sodium sulfide rejection rate is low, the flux is small, and the tensile strength is low. This indicates that the base membrane was not prepared by a zirconia perfluoropolymer, which significantly reduced the acid and alkali resistance of the nanofiltration membrane.

[0057] Compared with Example 1, the nanofiltration membrane obtained in Comparative Example 2 did not contain pentaerythritol triacrylate or octanedithiol in the grafting solution. The sodium sulfide rejection rate was low and the flux was high after the acid and alkali treatment. The tensile strength was low. The number of thiol-ene click chemical reaction sites in the surface reaction system was reduced. The cross-linking network on the surface of the nanofiltration membrane was sparse. The flux was increased but the selectivity was reduced. The metal-organic framework was weakly bonded to the nanofiltration membrane, which reduced the acid and alkali resistance and rejection rate of the nanofiltration membrane.

[0058] Compared with Example 1, the nanofiltration membrane obtained in Comparative Example 3, without the addition of metal-organic frameworks in the grafting solution, exhibited low sodium sulfide rejection rate, low flux, and low tensile strength after acid and alkali treatment. This indicates that the lack of nano-sieving channels in MOFs leads to a decrease in molecular sieving efficiency. The reduction in tensile strength confirms the enhancing effect of the rigid structure of MOFs on the membrane's anti-swelling properties.

[0059] Compared with Example 1, the nanofiltration membrane obtained in Comparative Example 4, without the gradient UV polymerization process, had a low sodium sulfide rejection rate, low flux, and low tensile strength after being treated with excessive acid and alkali. This indicates that constant high-intensity light irradiation caused rapid cross-linking and collapse of the surface, forming defects. This verifies that the gradient UV polymerization irradiation process can achieve pore size uniformity and surface smoothing, ensuring the acid and alkali resistance of the nanofiltration membrane.

[0060] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method for preparing an acid and alkali resistant nanofiltration membrane, characterized in that: Includes the following steps: (1) The base membrane was immersed in sodium dodecyl sulfate and ultrasonically treated to obtain a pretreated base membrane; (2) Mix pentaerythritol triacrylate, octanedithiol and photoinitiator, add solvent, then add sulfobetaine monomer and MOFs, disperse to obtain grafting solution; (3) Immerse the base membrane in the grafting solution, irradiate with UV light under nitrogen protection, react, post-process, and vacuum dry to obtain an acid and alkali resistant nanofiltration membrane.

2. The method for preparing an acid and alkali resistant nanofiltration membrane according to claim 1, characterized in that: The grafting solution comprises the following components by weight: 10-20 parts of pentaerythritol triacrylate, 5-10 parts of octanedithiol, 3-6 parts of sulfobetaine monomer, 0.5-1 part of photoinitiator, 50-60 parts of solvent, and 1.5-3 parts of MOFs.

3. The method for preparing an acid and alkali resistant nanofiltration membrane according to claim 2, characterized in that: The photoinitiator is 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone; the solvent is a 50-55 vol% ethanol solution.

4. The method for preparing an acid and alkali resistant nanofiltration membrane according to claim 1, characterized in that: In step (3), the UV irradiation process conditions are as follows: a gradient UV polymerization process is used, and the UV density is 50-60 mW / cm² during the 0-5 min period. 2 The UV density was 100-120 mW / cm² at 5-8 min and 50-60 mW / cm² at 8-12 min. 2 .

5. The method for preparing an acid and alkali resistant nanofiltration membrane according to claim 1, characterized in that: The base film is prepared by the following process: Step 1: Add methyl 4-azidobenzoate, ethyl perfluorooctanoate, and ethyl α-bromophenylacetate to a reaction vessel, add triethylamine dropwise, and irradiate with UV light to obtain a perfluoroazido copolymer; Step 2: Dissolve the perfluoroazide copolymer in dichloromethane, immerse the polysulfone membrane in the perfluoroazide copolymer solution for 4-6 hours, remove it, and dry it at 60-70°C for 2-4 hours to obtain the base film.

6. The method for preparing an acid and alkali resistant nanofiltration membrane according to claim 5, characterized in that: The mass ratio of methyl 4-azidobenzoate, ethyl perfluorooctanoate, ethyl α-bromophenylacetate, and triethylamine is (8~9):(8~8.5):0.01:0.005; the mass ratio of perfluoroazido copolymer to dichloromethane is 0.1:(5~8).

7. The method for preparing an acid and alkali resistant nanofiltration membrane according to claim 5, characterized in that: In step 1, the UV irradiation process conditions are as follows: at a power of 5~6W, using a wavelength of 250~300nm, at a distance of 3~5cm from the polysulfone film, irradiate for 4~6h.

8. The method for preparing an acid and alkali resistant nanofiltration membrane according to claim 1, characterized in that: The MOFs are prepared by the following process: Step ①: Dissolve zirconium chloride and 2-aminobenzoic acid in N,N-dimethylformamide, heat to react, filter, wash, and dry to obtain aminated Zr-MOF; Step 2: Disperse the obtained amino-modified Zr-MOF in anhydrous toluene, add a dispersant, sonicate, add 3-mercaptopropionic acid, filter, wash, and dry to obtain MOFs.

9. The method for preparing an acid and alkali resistant nanofiltration membrane according to claim 8, characterized in that: The mass ratio of zirconium chloride, 2-aminobenzoic acid, and N,N-dimethylformamide is (0.1~10):1:20; the mass ratio of aminated Zr-MOF, anhydrous toluene, dispersant, and 3-mercaptopropionic acid is (0.5~1):20:0.01:2; the dispersant is polyvinylpyrrolidone.

10. An acid and alkali resistant nanofiltration membrane, characterized in that: Prepared by the preparation method according to any one of claims 1-9.

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