Preparation method of polyester nanofiltration membrane based on hexahydro-1, 3, 5-tris (hydroxyethyl)-s-triazine

Abstract

The invention discloses a preparation method of a polyester nanofiltration membrane based on hexahydro-1, 3, 4-tris (hydroxyethyl)-s-triazine. The preparation method mainly comprises the following steps: dissolving hexahydro-1, 3, 4-tris (hydroxyethyl)-s-triazine (HET) in ultrapure water to form a water-phase solution; the preparation method comprises the following steps: dissolving 1, 3, 5-trimesoyl chloride in n-heptane to form an organic phase solution; the preparation method comprises the following steps: sequentially soaking a polyacrylonitrile-based membrane by using the aqueous phase solution and the organic phase solution, and reacting hydroxyl in HET with acyl chloride groups of 1, 3, 5-trimesoyl chloride at a phase interface to prepare the polyester nanofiltration membrane. Wherein the introduction of HET brings abundant hydroxyl groups and realizes high water flux, and at the same time, incompletely reacted acyl chloride groups are hydrolyzed to generate carboxyl groups, and then deprotonated to generate negatively charged carboxylate radicals, so that the membrane has electronegativity and can effectively intercept anionic dyes. The anion dye retention rate of the membrane is more than 99.5%, the dye / salt selectivity can reach up to 371.25, and the nanofiltration membrane prepared by the method can be applied to salt-containing wastewater resourceful treatment in pharmacy, printing and dyeing, food industry and the like, and has a wide application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of nanofiltration membrane separation, and particularly to a preparation method of a polyester nanofiltration membrane of hydroxyethyl hexahydro - s - triazine. Background Art

[0002] Industrial wastewater generated by the pharmaceutical, printing and dyeing, and food industries often contains high concentrations of dyes and salts. Due to its high chromaticity, strong toxicity, and difficult biodegradability, this dye wastewater poses a serious threat to the ecological system, biological health, and human life, and requires high treatment costs. Therefore, efficiently separating dyes and salts in wastewater and recycling the recovered resources to reduce wastewater treatment costs is the key to the resource utilization of wastewater and achieving sustainable development.

[0003] A variety of membrane materials such as polyamide (PA), polyester (PE), polyester amide (PEA), and covalent organic framework (COF) have been applied to the preparation of dye / salt separation nanofiltration membranes. Compared with traditional polyamide nanofiltration membranes, polyester membranes exhibit excellent chlorine resistance because their molecular chains do not contain amide bonds that are easily attacked by chlorine. The flux and selectivity of nanofiltration membranes are significantly restricted. Current research mainly focuses on increasing the water flux, while the separation performance of small - molecular - weight dyes is often overlooked. This research bias limits the comprehensive application of membrane technology in efficient dye separation and wastewater treatment. Starting from the separation mechanism of nanofiltration membranes, steric hindrance and Donnan effect are the most fundamental factors affecting the rejection rate. Polyester nanofiltration membranes can not only enhance the hydrophilicity of the membrane surface by introducing more abundant hydroxyl groups to increase the water flux, but also enhance the retention ability for dye molecules through the combined action of the Donnan effect and steric hindrance effect.

[0004] [References]

[0005] [1]Fini M N,Montesantos N,Maschietti M,et al.Performance evaluationof membrane filtration for treatment of H2S scavenging wastewater fromoffshore oil and gas production[J].Separation and Purification Technology,2021,277:119641.

[0006] [2] Ding L, Huang Y, Shi L, et al. Tris-phenol phosphine oxide-based polyester loose nanofiltration membranes with a three-dimensional structure for efficient dye / salt separation[J]. Separation and Purification Technology, 2025, 354: 128962.

[0007] [3] Zhao R, Jin P, Zhu J, et al. Amino acid-based loose polyamide nanofiltration membrane with ultrahigh water permeance for efficient dye / salt separation[J]. Journal of Membrane Science, 2023, 673: 121477.

[0008] [4] Li Q, Liao Z, Fang X, et al. Tannic acid assisted interfacial polymerization based loose thin-film composite NF membrane for dye / salt separation[J]. Desalination, 2020, 479: 114343.

[0009] [5] Fang YX, Lin YF, Xu ZL, et al. A novel clover-like COFs membrane fabricated via one-step interfacial polymerization for dye / salt separation[J]. Journal of Membrane Science, 2023, 673: 121470. Summary of the Invention

[0010] In view of the above-mentioned prior art, the present invention provides a method for preparing a polyester nanofiltration membrane based on 1,3,5-tris(2-hydroxy-ethyl)hexahydro-s-triazine (HET). [1] By interfacial polymerization of 1,3,5-tris(2-hydroxy-ethyl)hexahydro-s-triazine (HET) and 1,3,5-benzenetricarbonyl chloride (TMC), a polyester nanofiltration membrane is prepared to improve the separation performance of dyes / salts.

[0011] To solve the above technical problems, a method for preparing a polyester nanofiltration membrane based on 1,3,5-tris(2-hydroxy-ethyl)hexahydro-s-triazine provided by the present invention mainly includes: dissolving 1,3,5-tris(2-hydroxy-ethyl)hexahydro-s-triazine in ultrapure water to form an aqueous solution; dissolving 1,3,5-benzenetricarbonyl chloride in n-heptane to form an organic solution; soaking a polyacrylonitrile-based membrane successively with the above-mentioned aqueous solution and organic solution, and reacting the hydroxyl group in 1,3,5-tris(2-hydroxy-ethyl)hexahydro-s-triazine with the acyl chloride group of 1,3,5-benzenetricarbonyl chloride at the phase interface to obtain a polyester nanofiltration membrane. The specific steps are as follows:

[0012] Step 1, pretreatment of the polyacrylonitrile-based membrane: Wash the polyacrylonitrile-based membrane three times with ultrapure water, dry it at room temperature, and then fix it in a plastic mold;

[0013] Step 2, soaking the aqueous solution: Dissolve 1,3,5-tris(2-hydroxy-ethyl)hexahydro-s-triazine in ultrapure water to prepare an aqueous solution of 1,3,5-tris(2-hydroxy-ethyl)hexahydro-s-triazine with a mass percentage of 0.2-0.5%, and adjust the pH to 13 with a sodium hydroxide solution to obtain an aqueous solution. Add the aqueous solution to the mold in Step 1. The dosage of the aqueous solution is calculated according to 10 mL / 25 cm 2 of the area of the polyacrylonitrile-based membrane; After soaking and reacting for 10 min, take it out and remove the surface liquid, and then fix the soaked and reacted polyacrylonitrile-based membrane back into the mold again;

[0014] Step 3, reaction synthesis of polyester: Dissolve 1,3,5-benzenetricarbonyl chloride in n-heptane to prepare an organic solution with a mass percentage of 0.1%, and add the organic solution to the mold fixed with the polyacrylonitrile-based membrane treated in Step 2. The dosage of the organic solution is calculated according to 5-10 mL / 25 cm 2 of the area of the polyacrylonitrile-based membrane; After soaking and reacting for 3-10 min, take it out and air-dry it at room temperature, and then wash it three times with ethanol and ultrapure water respectively to obtain the polyester nanofiltration membrane.

[0015] Furthermore, in the preparation method of the present invention:

[0016] In Step 1, the molecular weight cut-off of the polyacrylonitrile-based membrane is 10 kDa, and the plastic mold has a bare area of the base membrane of 5×5 cm.

[0017] In Step 2, the mass percentage of the hydroxyethyl hexahydro - s - triazine solution is 0.3%. The molar concentration of the sodium hydroxide solution is 3M.

[0018] In Step 3, the ratio of the dosage of the organic - phase solution to the area of the polyacrylonitrile - based membrane is 5 mL / 25 cm 2 , and the soaking reaction time is 5 min.

[0019] Store the polyester nanofiltration membrane prepared by the present invention in ultrapure water.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] (1) Hydroxyethyl hexahydro - s - triazine (HET) is selected as the aqueous - phase monomer, which can react with 1,3,5 - benzene - tricarbonyl chloride (TMC) at normal temperature and pressure. As a hydroxyl monomer, HET has a lower reaction activity with the acyl chloride group in TMC than traditional amines, thus effectively reducing the reaction rate, promoting the uniform growth of the membrane layer, and being conducive to the formation of a looser active layer to increase the water - transmission path.

[0022] (2) The water flux of the membrane prepared by the present invention reaches 43.97 - 76.02 Lm -2 h -1 bar -1 . The rejection rate of the membrane for anionic dyes is greater than 99.5%, the rejection rate of NaCl reaches 13.68 - 29.54%, and the dye / salt selectivity is as high as 178.57 - 371.25. The polyester nanofiltration membrane prepared by the present invention can be used in the pharmaceutical, printing and dyeing, and food industries and their wastewater treatment, etc., with good separation effects and water fluxes, and high resource - utilization efficiency.

[0023] (3) The materials used are easily available, the preparation process is simple, the preparation process is short, and the operation is relatively convenient, which is conducive to large - scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a schematic diagram of the preparation and reaction mechanism of the polyester nanofiltration membrane based on hydroxyethyl hexahydro - s - triazine proposed by the present invention;

[0025] Figure 2 is a scanning electron microscope photograph of the surface of the NPE - 2 membrane prepared in Example 2;

[0026] Figure 3 is a scanning electron microscope photograph of the surface of the comparative membrane 1 prepared in Comparative Example 1;

[0027] Figure 4 is the water - contact - angle diagram of the membranes prepared in Examples 1 - 4 and Comparative Examples 1 - 2;

[0028] Figure 5 Dye rejection performance and water flux diagrams of the membranes prepared in Examples 1-4 and Comparative Membrane 1-2. Detailed implementation

[0029] The design concept of the preparation method of the polyester nanofiltration membrane based on hydroxyethyl hexahydro-s-triazine is that HET is used as the monomer in the aqueous solution, and TMC is used as the monomer in the organic solution. Through interfacial polymerization, it polymerizes on the polyacrylonitrile-based membrane to form a polyester nanofiltration membrane. Among them, the introduction of HET brings rich hydroxyl groups, achieving high flux. At the same time, since the unreacted acyl chloride groups are hydrolyzed to form carboxyl groups, and the carboxyl groups are further deprotonated to form negatively charged carboxylate ions, the polyester membrane has a negative charge and can effectively retain anionic dyes. As Figure 1 shown, the preparation of this polyester nanofiltration membrane mainly includes: dissolving HET in ultrapure water and adjusting the pH value with sodium hydroxide solution to obtain an aqueous solution; dissolving TMC in n-heptane to form an organic solution; soaking the polyacrylonitrile-based membrane with the above aqueous solution and organic solution in sequence, and reacting the hydroxyl groups in HET with the acyl chloride groups of TMC at the phase interface to obtain the polyester nanofiltration membrane. Due to the different diffusion coefficients of HET in water and TMC in the organic phase, it is more inclined to form a thin film near the organic phase. This method realizes the preparation of the polyester nanofiltration membrane based on HET, and at the same time improves the hydrophilicity of the membrane. The water flux of this polyester nanofiltration membrane reaches 43.97-76.02 Lm -2 h -1 bar -1 , the rejection rate of the membrane for anionic dyes is greater than 99.5%, the NaCl rejection rate reaches 13.68-29.54%, the separation factor reaches 178.57-371.25. Applying the nanofiltration membrane prepared by the present invention to the resource treatment of saline wastewater in the pharmaceutical, printing and dyeing, and food industries, etc., has high water flux and dye / salt resource utilization efficiency.

[0030] The evaluation of the separation performance of the prepared polyester nanofiltration membrane is mainly characterized by the salt rejection rate, dye rejection rate, salt-dye separation factor and water flux of the membrane.

[0031] Rejection rate calculation formula: R = (1 - C p / C f ) × 100%, where R represents the rejection rate, C p and C f are the concentrations (ppm) of dyes or salts in the permeate and feed liquid respectively. If not otherwise specified, the feed liquid is a 1000 ppm NaCl aqueous solution and a 100 ppm Congo red aqueous solution respectively.

[0032] Separation factor calculation formula: S = (1 - R salt ) / (1 - R dye ) × 100%, where Rsalt Represents the salt rejection rate, R dye Represents the dye rejection rate. Unless otherwise specified, the ratio of salt / dye in the feed solution is 10:1 (i.e., a 1000 ppm salt solution is mixed with a 100 ppm dye solution).

[0033] Water flux L m -2 h -1 bar -1 Is defined as: Under certain operating pressure conditions, the volume of water passing through the effective membrane area per unit pressure and per unit time. Unless otherwise specified, the test pressure of the membrane is 4 bar.

[0034] Specific embodiments of the present invention are given below. The specific embodiments are only used to further illustrate the present invention in detail and do not limit the protection scope of the claims of this application.

[0035] Example 1

[0036] Preparation of a polyester nanofiltration membrane based on hydroxyethyl hexahydro - s - triazine, the steps are as follows:

[0037] Step 1, Pretreatment of the polyacrylonitrile - based membrane: Wash the polyacrylonitrile - based membrane with a molecular weight cut - off of 10 kDa three times with ultrapure water, dry it at room temperature, and then fix it in a plastic mold with a 5×5 cm bare area of the base membrane.

[0038] Step 2, Immerse in the aqueous solution: Dissolve HET in ultrapure water to prepare an aqueous solution of hydroxyethyl hexahydro - s - triazine with a mass percentage of 0.2%, and adjust the pH to 13 with a sodium hydroxide solution with a molar concentration of 3M to obtain an aqueous solution; Take 10 mL of this aqueous solution and add it to the mold in Step 1 to immerse the polyacrylonitrile - based membrane therein. After 10 minutes, take out the polyacrylonitrile - based membrane, and use a rubber roller to remove the water droplets on the surface. Then fix the membrane back into the mold again.

[0039] Step 3, React to synthesize polyester: Dissolve TMC in n - heptane to prepare an organic solution with a mass percentage of 0.1%. Take 5 ml of this organic solution and quickly add it to the mold fixed with the polyacrylonitrile - based membrane treated in Step 2. After soaking and reacting for 5 minutes, take it out and air - dry it at room temperature. Wash it three times with ethanol and ultrapure water respectively to obtain a polyester nanofiltration membrane, simply referred to as the NPE - 1 membrane.

[0040] After testing, the NaCl rejection rate of the NPE - 1 membrane prepared in Example 1 is 13.68%, the Congo red rejection rate is 99.68%, the separation factor is 267.86, and the water flux is 76.02 L m -2 h -1 bar -1 .

[0041] Example 2

[0042] Preparation of a polyester nanofiltration membrane based on hydroxyethyl hexahydro-s-triazine. The preparation process is basically the same as that of Example 1, except that: in Step 2, the mass concentration of the HET is changed from 0.2% to 0.3%. The finally obtained polyester nanofiltration membrane is simply referred to as the NPE-2 membrane. Figure 2 It is a scanning electron microscope photograph of the surface of the NPE-2 membrane prepared in Example 2.

[0043] After testing, the NaCl rejection rate of the NPE-2 membrane prepared in Example 2 is 14.93%, the Congo red rejection rate is 99.78%, the separation factor is 371.25, and the water flux is 68.18 L m -2 h -1 bar -1 。

[0044] Example 3

[0045] Preparation of a polyester nanofiltration membrane based on hydroxyethyl hexahydro-s-triazine. The preparation process is basically the same as that of Example 1, except that: in Step 2, the mass concentration of the HET is changed from 0.2% to 0.4%. The finally obtained polyester nanofiltration membrane is simply referred to as the NPE-3 membrane.

[0046] After testing, the NaCl rejection rate of the NPE-3 membrane prepared in Example 3 is 25.44%, the Congo red rejection rate is 99.63%, the separation factor is 243.38, and the water flux is 51.94 L m -2 h -1 bar -1 。

[0047] Example 4

[0048] Preparation of a polyester nanofiltration membrane based on hydroxyethyl hexahydro-s-triazine. The preparation process is basically the same as that of Example 1, except that: in Step 2, the mass concentration of the HET is changed from 0.2% to 0.5%. The finally obtained polyester nanofiltration membrane is simply referred to as the NPE-4 membrane.

[0049] After testing, the NaCl rejection rate of the NPE-4 membrane prepared in Example 3 is 29.54%, the Congo red rejection rate is 99.51%, the separation factor is 178.57, and the water flux is 43.97 L m -2 h -1 bar -1 。

[0050] Comparative Example 1

[0051] Preparation of a polyester nanofiltration membrane based on hydroxyethyl hexahydro-s-triazine. The preparation process is basically the same as that of Example 1, except that: in Step 2, the mass concentration of the HET is changed from 0.2% to 0.1%. The finally obtained polyester nanofiltration membrane is simply referred to as Comparative Membrane 1. Figure 3It is a scanning electron microscope photograph of the membrane surface of Comparative Membrane 1 prepared in Comparative Example 1.

[0052] After testing, the NaCl rejection rate of Comparative Membrane 1 was 12.93%, the Congo red rejection rate was 99.15%, the separation factor was 93.75, and the water flux was 90.27 L m -2 h -1 bar -1 。

[0053] Comparative Example 2

[0054] Preparation of a polyester nanofiltration membrane based on hydroxyethyl hexahydro-s-triazine. The preparation process was basically the same as that of Example 1, except that: in Step 2, the mass concentration of HET was changed from 0.2% to 1.0%, and the finally obtained polyester nanofiltration membrane was abbreviated as Comparative Membrane 2.

[0055] After testing, the NaCl rejection rate of Comparative Membrane 3 was 30.67%, the Congo red rejection rate was 99.20%, the separation factor was 142.86, and the water flux was 22.37 L m -2 h -1 bar -1 。

[0056] Figure 4 It is the water contact angle diagram of NPE1 membrane, NPE2 membrane, NPE3 membrane, NPE4 membrane, Comparative Membrane 1 and Comparative Membrane 2. It can be seen that HET introduced hydroxyl groups, improving the hydrophilicity of the active layer of the membrane. This is because the increased concentration of the aqueous monomer HET provided more abundant hydroxyl groups, improving the hydrophilicity of the membrane and reducing the water contact angle.

[0057] Figure 5 Shows the Congo red rejection rate and water flux of NPE1 membrane, NPE2 membrane, NPE3 membrane, NPE4 membrane, Comparative Membrane 1 and Comparative Membrane 2. Table 1 lists the water flux, Congo red rejection rate, NaCl rejection rate and separation factor of NPE1 membrane, NPE2 membrane, NPE3 membrane, NPE4 membrane, Comparative Membrane 1, Comparative Membrane 2, polyacrylonitrile-based membrane, polyester (THPPO / TMC) [2] 、polyamide (Arg / TMC) [3] 、polyester amide (TAIP / TMC) [4] and covalent organic framework (MPD-TFB / Nylon) [5] 。From Figure 5 and Table 1, it can be seen that: under the condition of a lower aqueous monomer concentration, the water flux is larger, but the membrane rejection rate is low, resulting in poor membrane dye / salt selectivity. As the concentration of HET increases continuously, the formed membrane has a higher crosslinking degree, with high membrane rejection rate and excellent separation factor, and at the same time has a relatively high water flux; as the concentration of HET further increases, the membrane rejection rate is lower, the selectivity is poor and the water flux is too small.

[0058] Table 1

[0059]

[0060]

[0061] The present invention provides a preparation method of a polyester nanofiltration membrane based on hydroxyethyl hexahydro-s-triazine. The materials used are easy to obtain, the preparation process is simple, the preparation process is short, and the operation is relatively convenient. The membrane separation performance is mainly evaluated by the salt rejection rate, dye rejection rate, salt-dye separation factor and water flux of the membrane. Among them, the separation factor is the core index for evaluating the membrane separation performance. Compared with the individual salt rejection rate and dye rejection rate, it can more comprehensively reflect the actual separation ability of the membrane in a complex system. The current mainstream membrane materials all have significant limitations in performance balance. Although the polyacrylonitrile-based membrane exhibits ultra-high water flux, its separation factor is very small, and the Congo red rejection rate only reaches 98.05%. Although the polyester (THPPO / TMC) achieves a dye rejection rate of 99.3%, its disadvantages of low water flux and separation factor seriously restrict its wastewater treatment efficiency. Although the polyamide (Arg / TMC) and covalent organic framework (MPD-TFB / Nylon) have relatively large water fluxes, there is still room for optimization in the Congo red rejection rate and separation factor, and the comprehensive performance still needs to be further improved.

[0062] In the preparation method of the present invention, by introducing HET as an aqueous phase monomer to participate in interfacial polymerization, the preparation of a polyester nanofiltration membrane with high Congo red dye rejection rate, high separation factor and relatively high flux and excellent comprehensive performance is realized. The Congo red dye rejection rate of the prepared polyester nanofiltration membrane is greater than 99.5%, and can be as high as 99.78%. Since the unreacted acyl chloride groups are hydrolyzed to form carboxyl groups, and the carboxyl groups are further deprotonated to form negatively charged carboxylate ions, the polyester membrane has a negative charge. At the same time, the introduction of hydroxyl groups improves the hydrophilicity of the membrane, realizing the simultaneous improvement of the rejection rate and flux of the composite nanofiltration membrane.

[0063] In the present invention, through the comparison of Examples 1-4 and Comparative Examples 1-2, it can be obtained that the performance of the membrane will change with the change of the concentration of the aqueous phase monomer HET. Under the condition of a low HET concentration, due to the insufficient supply of hydroxyl functional groups in the reaction system, the crosslinking degree of the polyester separation layer decreases, and it is difficult to form a continuous and dense network structure. As Figure 3 shown, this structural defect results in a large water flux of the membrane material, but the membrane has a low rejection rate and poor selectivity, as Figure 5 and Table 1 show. As the concentration of HET continuously increases, the diffusion rate of the monomer to the interface increases, and the reaction rate at the interface also further increases, resulting in a thicker and denser separation layer. The membrane has good dye rejection rate and separation factor, but at the same time, due to the large hindrance to water transfer, the water flux decreases, asFigure 5 As shown in Table 1. However, in the presence of too high a concentration of the aqueous monomer HET, the diffusion of the monomer in the aqueous phase affects the efficiency of the monomer migrating to the interface, reducing the quality and formation efficiency of the membrane, resulting in a low membrane rejection rate, poor selectivity, and further reducing the water flux of the membrane, as Figure 5 shown in Table 1. Therefore, in the preparation method of the present invention, the concentration of the aqueous monomer HET was optimized, and the mass percentage of the HET aqueous solution was limited to 0.2-0.5%, so as to obtain a polyester nanofiltration membrane with high dye rejection rate, excellent separation factor, and high water flux at the same time. It can be used for the resource treatment of saline wastewater in applications such as the pharmaceutical, printing and dyeing, and food industries.

[0064] Although the present invention has been described above in conjunction with the accompanying drawings, the present invention is not limited to the above specific embodiments. The above specific embodiments are merely illustrative rather than restrictive. Under the inspiration of the present invention, those of ordinary skill in the art can also make many changes without departing from the purpose of the present invention, and all of these fall within the protection scope of the present invention.

Claims

1. A method for preparing a polyester nanofiltration membrane based on hydroxyethyl hexahydro-s-triazine, characterized in that: Hydroxyethyl hexahydro-s-triazine is dissolved in ultrapure water to form an aqueous solution; 1,3,5-trimethylbenzenecarboxylic acid chloride is dissolved in n-heptane to form an organic solution; a polyacrylonitrile-based membrane is soaked in the aqueous solution and the organic solution in sequence, and a polyester nanofiltration membrane is prepared by reacting the hydroxyl group in the hydroxyethyl hexahydro-s-triazine with the acyl chloride group in the 1,3,5-trimethylbenzenecarboxylic acid chloride at the phase interface.

2. The preparation method according to claim 1, characterized in that: The specific steps of this method are as follows: Step 1, pretreatment of the polyacrylonitrile-based membrane: washing the polyacrylonitrile-based membrane with ultrapure water three times, drying it at room temperature, and then fixing it in a plastic mold; Step 2, soaking in aqueous solution: dissolving hydroxyethyl hexahydro-s-triazine in ultrapure water to prepare a 0.2-0.5% by mass hydroxyethyl hexahydro-s-triazine aqueous solution, and adjusting the pH to 13 with sodium hydroxide solution to obtain an aqueous solution, and adding the aqueous solution to the mold in step 1. The amount of the aqueous solution and the area of ​​the polyacrylonitrile-based film are 10 mL / 25 cm 2 After soaking for 10 minutes, the reaction was removed and the surface liquid was removed, and the polyacrylonitrile-based film after the soaking reaction was fixed to the mold again; Step 3, reaction synthesis of polyester: dissolving 1,3,5-benzene trimesoyl chloride in n-heptane to prepare an organic phase solution with a mass percentage of 0.1%, and adding the organic phase solution to the mold fixed with the polyacrylonitrile base film treated in step 2. The amount of the organic phase solution and the area of ​​the polyacrylonitrile base film are 5-10mL / 25cm 2 After soaking for 3 to 10 minutes, the mixture was taken out and air-dried at room temperature. The polyester nanofiltration membrane was washed three times with ethanol and ultrapure water respectively.

3. The preparation method according to claim 2, characterized in that: In step 1, the molecular weight cutoff of the polyacrylonitrile base membrane is 10 kDa, and the plastic mold has a base membrane exposed area of ​​5×5 cm.

4. The preparation method according to claim 2, characterized in that: In step 2, the mass percentage of the hydroxyethyl hexahydro-s-triazine solution is 0.3%.

5. The preparation method according to claim 2, characterized in that: In step 2, the molar concentration of the sodium hydroxide solution is 3M.

6. The preparation method according to claim 2, characterized in that: In step 3, the ratio of the amount of the organic phase solution to the area of ​​the polyacrylonitrile-based membrane is 5 mL / 25 cm 2 , the immersion reaction time is 5 minutes.

7. The preparation method according to claim 2, characterized in that: The prepared polyester nanofiltration membrane was stored in ultrapure water.

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