A nanofiltration membrane, a preparation method and application thereof

Abstract

The application relates to a preparation method of a nanofiltration membrane, which comprises the following steps: carrying out interfacial polymerization reaction of a water-phase monomer solution and an organic-phase solution on a porous support layer to form a nanofiltration membrane separation layer containing both amide bonds and ester bonds; and carrying out hydrolysis reaction on the nanofiltration membrane separation layer by using an acidic solution or an alkaline solution to prepare the nanofiltration membrane. The nanofiltration membrane separation layer can be simply and quickly regulated by the method, and the method has the characteristics of high efficiency, low cost and industrial promotion.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, and in particular to a nanofiltration membrane, its preparation method, and its application. Background Technology

[0002] Nanofiltration membranes, as the core component of nanofiltration technology, have attracted much attention in water treatment, chemical, food, and pharmaceutical fields. Currently, nanofiltration membranes synthesized by interfacial polymerization of piperazine (PIP) and trimesoyl chloride to form a polyamide separation layer on a porous support layer dominate the commercial market.

[0003] However, the rapid, nonlinear polymerization reactions between monomers and the strong "self-limiting effect" lead to the uncontrollability of interfacial polymerization reactions, resulting in a polyamide separation layer that typically possesses a non-uniform pore structure. The pore size distribution of a typical polyamide nanofiltration membrane exhibits a normal distribution, with both excessively large and excessively small pores existing near the average pore size. Theoretically, given the same average pore size, a wider pore size distribution leads to a sharp decrease in solute selectivity.

[0004] Therefore, to address the problem of insufficient selectivity in nanofiltration membranes, it is necessary to regulate the interfacial polymerization process to narrow the pore size distribution of the nanofiltration membrane, ensure the uniformity of the pore structure, and thus improve the separation performance of the nanofiltration membrane. Summary of the Invention

[0005] To address at least one of the aforementioned technical problems, the present invention provides a nanofiltration membrane, its preparation method, and its application.

[0006] In one aspect, the present invention provides a method for preparing a nanofiltration membrane, comprising: on a porous support layer, a composite aqueous monomer solution and an organic phase solution undergo an interfacial polymerization reaction to form a nanofiltration membrane separation layer containing both amide bonds and ester bonds; and the nanofiltration membrane separation layer is subjected to a hydrolysis reaction using an acidic solution or an alkaline solution to prepare a nanofiltration membrane.

[0007] In some embodiments of the present invention, the monomer in the composite aqueous monomer solution includes one or more of 1,3-diamino-2-propanol and piperazine; and / or, the solute in the organic phase solution is a polyacrylamide chloride monomer; and / or, the solvent used in the organic phase solution is selected from one or more of isoalkanes, n-hexane, cyclohexane, n-heptane, and n-octane.

[0008] In some embodiments of the present invention, the concentration of piperazine monomer in the composite aqueous monomer solution is 0.1-1.0% (w / v), the concentration of 1,3-diamino-2-propanol monomer is 0.01-0.1% (w / v); and / or, the concentration of polyacrylamide chloride monomer in the organic phase solution is 0.03-0.3% (w / v); and / or, the polyacrylamide chloride monomer includes one or more of trimesoyl chloride, terephthaloyl chloride, and isophthaloyl chloride.

[0009] In some embodiments of the present invention, the pH of the acidic solution is 1 to 3; and / or the pH of the alkaline solution is 12 to 14.

[0010] In some embodiments of the present invention, the solute in the acidic solution includes any one of hydrochloric acid, sulfuric acid, or nitric acid.

[0011] In some embodiments of the present invention, the solute in the alkaline solution includes sodium hydroxide or potassium hydroxide.

[0012] In some embodiments of the present invention, the hydrolysis reaction is carried out at a temperature of 25–60°C, and preferably for a time of 5–30 min.

[0013] In another aspect, the present invention provides a nanofiltration membrane obtained according to the preparation method described above.

[0014] In some embodiments of the present invention, the average pore size of the nanofiltration membrane is 0.2 nm to 0.7 nm; and / or, the thickness of the separation layer of the nanofiltration membrane is 15 nm to 95 nm.

[0015] In another aspect, the present invention provides a nanofiltration membrane obtained according to the above preparation method or the application of the above nanofiltration membrane in water treatment.

[0016] The technical solution provided by the embodiments of the present invention has the following advantages:

[0017] The preparation method provided in this invention involves co-mixing 1,3-diamino-2-propanol (DAP) monomers in an aqueous piperazine (PIP) solution and then sequentially immersing the aqueous and organic phase solutions to undergo interfacial polymerization reactions, thereby obtaining a nanofiltration membrane sample. The DAP molecule contains two amino groups and one hydroxyl group, exhibiting stronger polarity and reactivity than PIP. The addition of DAP can regulate the interfacial polymerization reaction, thereby controlling the structure and properties of the separation layer. After co-mixing DAP in the PIP aqueous solution, the stronger polarity of DAP facilitates its slower diffusion rate in the organic phase. Simultaneously, the hydrogen bonding interaction between DAP and PIP further reduces the diffusion rate of PIP, promoting a more balanced interfacial polymerization reaction. The stronger reactivity of DAP helps to fill the macroporous defects left by the PIP monomer reaction. These two effects jointly regulate the structure and properties of the nanofiltration membrane separation layer, resulting in a thicker, more hydrophilic separation layer with a narrower pore size distribution, thus improving the separation capacity of the nanofiltration membrane. This achieves the first-ever regulation of the structure and properties of the nanofiltration membrane separation layer.

[0018] The hydroxyl groups in DAP can also participate in the reaction to form a small number of ester bonds. However, since the strength of ester bonds is lower than that of amide bonds, when the nanofiltration membrane separation layer has been formed for a short time with a strong acid or strong base solution, the ester bonds can be selectively hydrolyzed and destroyed while retaining the amide bonds. Simultaneously, the amide bonds that support the dominant framework structure in the nanofiltration membrane are preserved. This hydrolysis of ester bonds can improve the water flux and ion selectivity of the nanofiltration membrane. This achieves a second regulation of the structure and properties of the nanofiltration membrane separation layer.

[0019] Therefore, the preparation method provided in this embodiment of the invention regulates the subsequent interfacial polymerization process by co-mixing a small amount of 1,3-diamino-2-propanol (DAP) monomer in an aqueous piperazine (PIP) solution, thereby controlling the structure and properties of the nanofiltration membrane separation layer. The separation layer becomes thicker, more hydrophilic, and exhibits a narrower pore size distribution. In addition, the hydrolysis reaction carried out by soaking in acid and alkali treatment achieves selective hydrolysis and destruction of ester bonds while retaining amide bonds, thereby generating hydroxyl and carboxyl groups. This can further regulate the structure and properties of the nanofiltration membrane separation layer, improving its water flux and ion selectivity. Attached Figure Description

[0020] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 A comparison of the surface morphology of the conventional nanofiltration membrane prepared in Comparative Example 1 and the regulated nanofiltration membrane prepared in Example 1 of the present invention;

[0023] Figure 2 A comparison diagram of the pore size distribution of the conventional nanofiltration membrane prepared in Comparative Example 1 and the regulated nanofiltration membrane prepared in Example 1 of the present invention;

[0024] Figure 3 A comparison diagram of the separation layer thickness between the conventional nanofiltration membrane prepared in Comparative Example 1 and the regulated nanofiltration membrane prepared in Example 1 of the present invention;

[0025] Figure 4 A comparison diagram of the aqueous properties (water contact angle) of the conventional nanofiltration membrane prepared in Comparative Example 1 and the regulated nanofiltration membrane prepared in Example 1 of the present invention.

[0026] Figure 5 The images shown are SEM characterization images of the regulated nanofiltration membranes prepared in Examples 2-8 of this invention. Detailed Implementation

[0027] To better understand the above-mentioned objectives, features, and advantages of the present invention, the solutions of the present invention will be further described below. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

[0028] Many specific details are set forth in the following description in order to provide a full understanding of the invention, but the invention may also be practiced in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of the invention, and not all embodiments.

[0029] According to an embodiment of the present invention, a method for preparing a nanofiltration membrane is provided, comprising: performing an interfacial polymerization reaction between a composite aqueous monomer solution and an organic phase solution on a porous support layer to form a nanofiltration membrane separation layer containing both amide bonds and ester bonds; and performing a hydrolysis reaction on the nanofiltration membrane separation layer using an acidic solution or an alkaline solution to prepare a nanofiltration membrane.

[0030] The nanofiltration membrane preparation method provided in this invention involves co-mixing a small amount of 1,3-diamino-2-propanol (DAP) monomer into an aqueous piperazine (PIP) solution. This allows DAP to be used to control the interfacial polymerization process, thereby regulating the structure and properties of the nanofiltration membrane separation layer, narrowing the pore size distribution, and improving the selectivity of the nanofiltration membrane. While the hydroxyl groups in DAP can form a small number of ester bonds during the reaction, the strength of ester bonds is lower than that of amide bonds, and they are easily hydrolyzed under strong acid or strong base conditions. Therefore, acid-base post-treatment can be used to selectively hydrolyze and destroy ester bonds while preserving amide bonds, further improving the water flux and ion selectivity of the nanofiltration membrane.

[0031] In some embodiments of the present invention, a method for preparing a nanofiltration membrane includes the following steps: (1) introducing a small amount of 1,3-diamino-2-propanol (DAP) as a comonomer into a piperazine (PIP) aqueous monomer solution, and the resulting composite aqueous monomer solution undergoes interfacial polymerization reaction with polyacrylamide chloride in the organic phase solution on a porous support layer to form a nanofiltration membrane separation layer containing both amide bonds and ester bonds; thereby achieving the first regulation of the structure and properties of the nanofiltration membrane separation layer; (2) using an acidic solution or an alkaline solution to perform a post-treatment hydrolysis reaction on the nanofiltration membrane separation layer formed above, while retaining the amide bonds, selectively hydrolyzing and destroying the ester bonds, thereby generating hydroxyl and carboxyl groups, thereby achieving the second regulation of the structure and properties of the nanofiltration membrane separation layer, and preparing a nanofiltration membrane.

[0032] In some embodiments of the present invention, in step (1), the concentration of piperazine monomer in the composite aqueous monomer solution is 0.1-1.0% (w / v), and the concentration of 1,3-diamino-2-propanol monomer is 0.01-0.1% (w / v). For example, the concentration of piperazine monomer is selected from any value including 0.13% (w / v), 0.29% (w / v), 0.33% (w / v), 0.46% (w / v), 0.68% (w / v), 0.79% (w / v), and 0.93% (w / v); the concentration of 1,3-diamino-2-propanol monomer is selected from any value including 0.013% (w / v), 0.019% (w / v), 0.023% (w / v), 0.036% (w / v), 0.058% (w / v), 0.069% (w / v), 0.083% (w / v), and 0.098% (w / v).

[0033] In some embodiments of the present invention, in step (1), the polyacryl chloride is one or more of trimesoyl chloride, terephthaloyl chloride, or isophthaloyl chloride, and the polyacryl chloride is soluble in one or more of isoalkyl, n-hexane, cyclohexane, n-heptane, and n-octane, and the concentration of the polyacryl chloride monomer after dissolution is 0.03-0.3% (w / v). For example, the concentration of the polyacryl chloride monomer is selected from any value including 0.033% (w / v), 0.098% (w / v), 0.13% (w / v), 0.19% (w / v), 0.21% (w / v), 0.24% (w / v), 0.26% (w / v), and 0.29% (w / v).

[0034] In some embodiments of the present invention, in step (2), the acidic solution or alkaline solution is obtained by dissolving an inorganic acid or an inorganic base in ultrapure water. The inorganic acid used is one of hydrochloric acid, sulfuric acid and nitric acid, and the inorganic base used is one of sodium hydroxide and potassium hydroxide.

[0035] In some embodiments of the present invention, in step (2), the amount of solute inorganic acid or solute inorganic base added to the acidic or alkaline solution is determined according to the pH of the solution. The pH of the acidic solution is controlled to be 1 to 3, for example, the pH of the acidic solution is selected from any value including 1.4, 1.9, 2.3, 2.6, and 2.9; the pH of the alkaline solution is controlled to be 12 to 14, for example, the pH of the alkaline solution is selected from any value including 12.4, 12.9, 13.3, 13.6, and 13.9; the temperature of the acidic or alkaline solution is controlled to be 25 to 60°C, for example, the temperature is selected from any temperature value including 28°C, 36°C, 48°C, 51°C, and 59°C; the time of the post-treatment hydrolysis reaction is 5 to 30 minutes, for example, the time of the hydrolysis reaction is selected from any value including 9 minutes, 16 minutes, 19 minutes, 23 minutes, and 29 minutes.

[0036] In some embodiments of this disclosure, the average pore size of the nanofiltration membrane is 0.2 nm to 0.7 nm; for example, the average pore size of the nanofiltration membrane is selected from any value including 0.23 nm, 0.29 nm, 0.35 nm, 0.41 nm, 0.49 nm, 0.53 nm, and 0.59 nm; and / or, the thickness of the separation layer of the nanofiltration membrane is 15 nm to 95 nm; for example, the thickness of the separation layer of the nanofiltration membrane is selected from any value including 23 nm, 39 nm, 45 nm, 51 nm, 69 nm, 73 nm, and 89 nm.

[0037] In order to make the above-mentioned and other objects, features and advantages of the present invention readily apparent, the following detailed description is provided through specific embodiments.

[0038] Example 1

[0039] (1) Prepare an aqueous solution A containing 0.1% (w / v) piperazine and 0.03% (w / v) 1,3-diamino-2-propanol (DAP) using ultrapure water as the aqueous solvent, and prepare an organic solution B containing 0.1% (w / v) trimesoyl chloride using n-hexane as the organic solvent;

[0040] (2) Immerse the surface of the porous support layer completely with aqueous solution A, then pour out the solution and scrape off the excess liquid droplets on the surface with a flexible rubber plate;

[0041] (3) Pour the organic phase solution B from step (1) onto the surface of the membrane material obtained in step (2) and let it stand for 60 seconds. Then pour off the organic phase solution B on the surface.

[0042] (4) Rinse the membrane surface thoroughly with n-hexane solvent to remove unreacted monomers;

[0043] (5) Place the membrane obtained in step (4) into an oven for heat treatment at 50°C for 3 minutes;

[0044] (6) Use ultrapure water to thoroughly clean the nanofiltration membrane obtained in step (5) to obtain a nanofiltration membrane sample after the first regulation of the separation layer structure and characteristics of the nanofiltration membrane.

[0045] (7) Prepare a solution with pH=12 by dissolving sodium hydroxide in ultrapure water, soak the nanofiltration membrane sample after the first adjustment for 30 minutes for hydrolysis reaction, and then thoroughly wash the nanofiltration membrane sample with ultrapure water to obtain the final nanofiltration membrane sample after the second adjustment.

[0046] Example 2

[0047] The difference between this embodiment and Example 1 is that the concentration of piperazine in aqueous solution A is 0.8% (w / v).

[0048] Example 3

[0049] The difference between this embodiment and Example 1 is that the concentration of 1,3-diamino-2-propanol in aqueous solution A is 0.06% (w / v).

[0050] Example 4

[0051] The difference between this embodiment and Example 1 is that the concentration of pyromellitic chloroformyl chloride in organic phase solution B is 0.2% (w / v).

[0052] Example 5

[0053] The difference between this embodiment and Embodiment 1 is that pyromellitic chloride is replaced with terephthaloyl chloride.

[0054] Example 6

[0055] The difference between this embodiment and Example 1 is that n-hexane is replaced with isoparaffin G solvent (ExxonMobil, ISOPAR G).

[0056] Example 7

[0057] The difference between this embodiment and Embodiment 1 is that sodium hydroxide is replaced with potassium hydroxide.

[0058] Example 8

[0059] The difference between this embodiment and Embodiment 1 is that sodium hydroxide is replaced with sulfuric acid and the pH is adjusted to 2.

[0060] Comparative Example 1

[0061] Conventional nanofiltration membranes were prepared on the same porous support layer using the traditional interfacial polymerization method.

[0062] (1) Prepare an aqueous solution A containing 0.1% (w / v) piperazine using ultrapure water as the aqueous solvent, and prepare an organic solution B containing 0.1% (w / v) trimesoyl chloride using n-hexane as the organic solvent;

[0063] (2) Immerse the surface of the porous support layer completely with aqueous solution A, then pour out the solution and scrape off the excess liquid droplets on the surface with a flexible rubber plate;

[0064] (3) Pour the organic phase solution B described in step (1) onto the surface of the membrane material obtained in step (2) and let it stand for 60 seconds. Then pour off the organic phase solution B on the surface.

[0065] (4) Rinse the membrane surface thoroughly with n-hexane solvent to remove unreacted monomers;

[0066] (5) Place the film obtained in step (4) together with the plate and frame mold into an oven for heat treatment at 50°C for 3 minutes.

[0067] (6) Use ultrapure water to thoroughly clean the conventional nanofiltration membrane obtained in step (5) to obtain a conventional nanofiltration membrane sample.

[0068] The surface morphology of the nanofiltration membrane controlled by the method described in Example 1 of this invention and a conventional nanofiltration membrane are compared. The surface morphology is as follows: Figure 1 As shown.

[0069] from Figure 1 The data shown leads to the following conclusion: the nanofiltration membrane surface regulated by this invention is covered with a dense and complete nanofiltration membrane separation layer, while exhibiting a distinct granular nodular structure. Traditional nanofiltration membranes, on the other hand, have a smooth and dense surface structure.

[0070] Related tests of nanofiltration membranes

[0071] I. Detection of Pore Size Distribution in Nanofiltration Membranes

[0072] 1. Testing Method

[0073] Pore ​​size distribution of the test samples was tested using diethylene glycol (106 Da), triethylene glycol (150 Da), and polyethylene glycol (200 Da, 300 Da, 400 Da, 600 Da, 800 Da) solutions of different molecular weights at a concentration of 200 ppm.

[0074] 2. Aperture distribution test results

[0075] The test samples included the nanofiltration membrane from Example 1 and the conventional nanofiltration membrane from Comparative Example 1.

[0076] Test results are as follows Figure 2 As shown, from Figure 2 The data shown leads to the following conclusion: Unlike the conventional nanofiltration membrane of Comparative Example 1, the nanofiltration membrane prepared in Example 1 has a significantly narrower pore size distribution, and the average pore size has also been reduced from 0.742 nm to 0.513 nm.

[0077] II. Separation Layer Thickness Measurement of Nanofiltration Membranes

[0078] 1. Test method for the thickness of the separation layer

[0079] The nonwoven fabric and ultrafiltration base membrane were removed using tweezers and dimethylformamide solvent. Then, the nanofiltration membrane separation layer was transferred to the silicon wafer. Scratches were made on the surface of the separation layer using a scalpel. The height difference between the separation layer and the silicon wafer was measured using an atomic force microscope, which is the thickness of the separation layer.

[0080] 2. Test results of the thickness of the separation layer

[0081] The test samples included the nanofiltration membrane from Example 1 and the conventional nanofiltration membrane from Comparative Example 1.

[0082] Test results are as follows Figure 3 As shown, from Figure 3 The results shown lead to the following conclusions: the thickness of the separation layer of the conventional nanofiltration membrane in Comparative Example 1 is 8.5 nm. After the adjustment of the present invention, the thickness of the separation layer of the nanofiltration membrane in Example 1 is increased to 55 nm. The significant increase in the thickness of the separation layer can not only enhance its solute retention capacity, but also is expected to increase the stability and service life of the nanofiltration membrane.

[0083] III. Hydrophilicity Testing of Nanofiltration Membranes

[0084] 1. Test methods for hydrophilicity detection

[0085] The hydrophilicity or hydrophobicity of a nanofiltration membrane can be indicated by measuring its water contact angle using a droplet shape analyzer after the nanofiltration membrane sample has been dried.

[0086] 2. Test results of hydrophilicity test

[0087] The test samples included the nanofiltration membrane from Example 1 and the conventional nanofiltration membrane from Comparative Example 1.

[0088] Test results are as follows Figure 4 As shown, from Figure 4 The results shown lead to the following conclusion: the water contact angle of the nanofiltration membrane in Example 1 is significantly smaller than that of the conventional nanofiltration membrane in Comparative Example 1, indicating that the hydrophilicity of the nanofiltration membrane is enhanced after regulation, which will help to significantly improve its antifouling ability.

[0089] IV. Performance Testing of Nanofiltration Membranes

[0090] 1. Performance testing methods

[0091] The performance of pure water flux and salt rejection rate was tested on the test sample using pure water and 2000ppm aqueous solutions of magnesium sulfate, magnesium chloride, and sodium chloride through a cross-flow filtration device at 5 bar.

[0092] The test samples included the nanofiltration membrane after the first conditioning in Example 1, the nanofiltration membrane after the second conditioning, and the conventional nanofiltration membrane in Comparative Example 1.

[0093] 2. Performance test results

[0094] The test results are shown in Table 1.

[0095] Table 1. Comparison of pure water flux and salt rejection rate of nanofiltration membranes prepared in Example 1 and Comparative Example 1.

[0096]

[0097] The following conclusions can be drawn from the data in Table 1:

[0098] The water flux of the conventional nanofiltration membrane prepared in Comparative Example 1 was 45.8 L / (m²). 2 (·h·bar), but the magnesium sulfate retention rate was only 69.9%.

[0099] The water flux of the nanofiltration membrane prepared in Example 1 after the first conditioning was 20.7 L / (m²). 2 The magnesium sulfate rejection rate was 97.4% (·h·bar). After the second adjustment, the water flux could be increased to 23.6 L / (m²). 2Despite maintaining a relatively stable desalination rate (·h·bar), the magnesium sulfate rejection rate remained at 97.1%, achieving a significant increase in permeate flux while keeping the desalination rate relatively stable. This effectively overcame the trade-off effect between permeability and selectivity, demonstrating the significance of secondary regulation. The specific explanation is as follows: Compared to traditional PIP monomers, 1,3-diamino-2-propanol (DAP) monomers, composed of two amino groups and one hydroxyl group, possess stronger polarity and higher reactivity. Theoretically, DAP's stronger polarity can be used to regulate monomer diffusion, while its stronger reactivity can fill macroporous defects in the separation layer. Therefore, DAP can be used to regulate the interfacial polymerization process, thereby controlling the structure and properties of the nanofiltration membrane separation layer, narrowing the pore size distribution, and improving the selectivity of the nanofiltration membrane. When the hydroxyl groups in DAP participate in the reaction, they can form a small number of ester bonds. However, since the strength of ester bonds is lower than that of amide bonds and they are easily hydrolyzed and destroyed under strong acid or strong base conditions, acid-base post-treatment can be used to selectively hydrolyze and destroy ester bonds while retaining amide bonds, so as to further improve the water flux and ion selectivity of nanofiltration membranes.

[0100] Therefore, it can be seen that the nanofiltration membrane prepared in the embodiments of the present invention improves the solute selectivity on the basis of traditional nanofiltration membranes.

[0101] Figure 5 Table 2 shows the SEM characterization images of the regulated nanofiltration membranes prepared in Examples 2-8, and Table 2 shows the performance characterization data of the nanofiltration membranes prepared in Examples 2-8. (See Table 2 and...) Figure 5 As shown, the nanofiltration membranes prepared in Examples 2-8 exhibited similar performance to those in Example 1, as verified by experiments. Therefore, the aqueous monomer, organic monomer, and organic solvent can be freely substituted within the scope defined by this invention.

[0102] Table 2 Performance of nanofiltration membranes prepared in Examples 2-8

[0103]

[0104] Note: Examples 2-6 represent the performance under the first regulation, and Examples 7-8 represent the performance under the second regulation. The water contact angle is the data at 10 seconds after the water droplet has fallen.

[0105] In summary, the nanofiltration membrane preparation method provided in this invention involves first adding a small amount of 1,3-diamino-2-propanol (DAP) to an aqueous monomer solution of piperazine (PIP). DAP contains two amino groups and one hydroxyl group, exhibiting higher reactivity and stronger polarity compared to PIP. Therefore, in the subsequent interfacial polymerization process, DAP not only influences the reaction between PIP and polyacrylamide chlorides but also participates in the polymerization reaction itself, generating amide and ester bonds. This achieves the first regulation of the nanofiltration membrane separation layer structure and properties. After completing the interfacial polymerization reaction and heat treatment, the formed nanofiltration membrane separation layer is post-treated again with a strong acid or strong alkali aqueous solution. During this process, the ester bonds formed between DAP and polyacrylamide chlorides hydrolyze under the action of strong acid or strong alkali, regenerating hydrophilic hydroxyl and carboxyl groups, while the amide bonds are retained. This achieves "directional bursting" of the ester bonds, thereby completing the second regulation of the nanofiltration membrane separation layer structure and properties and improving its permeation selectivity. The process involves two control procedures. The first control makes the separation layer of the nanofiltration membrane thicker, more hydrophilic, and exhibits a narrower pore size distribution, thereby improving the separation capacity of the nanofiltration membrane. The second control further enhances the water flux and ion selectivity of the nanofiltration membrane. Furthermore, the preparation method of this invention eliminates the need for time-consuming and complex base membrane modification processes or the construction of intermediate layers, enabling the simple and rapid construction of a separation layer with a narrower pore size distribution on an ultrafiltration membrane with a mesoporous structure. The method involves only interfacial polymerization, making it easily adaptable to upgrade existing production processes.

[0106] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0107] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments described herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a nanofiltration membrane, characterized in that, include: On the porous support layer, the composite aqueous monomer solution and the organic phase solution undergo interfacial polymerization reaction to form a nanofiltration membrane separation layer containing both amide and ester bonds. The monomers in the composite aqueous monomer solution include 1,3-diamino-2-propanol and piperazine. In the composite aqueous monomer solution, the concentration of piperazine monomer is 0.1~1.0%, and the concentration of 1,3-diamino-2-propanol monomer is 0.01~0.1%. The nanofiltration membrane separation layer was hydrolyzed using an acidic solution with a pH of 1-3 to prepare the nanofiltration membrane. The hydrolysis reaction takes 5 to 30 minutes.

2. The preparation method according to claim 1, characterized in that, The solute in the organic phase solution is a polyacryl chloride monomer; And / or, the solvent used in the organic phase solution is selected from one or more of isoalkanes, n-hexane, cyclohexane, n-heptane, and n-octane.

3. The preparation method according to claim 2, characterized in that, In the organic phase solution, the concentration of polyacrylamide chloride monomer is 0.03~0.3%; And / or, the polyacrylamide chloride monomer includes one or more of pyromellitic trimethylolpropionate chloride, terephthaloyl chloride, and isophthaloyl chloride.

4. The preparation method according to claim 1, characterized in that, The solute in the acidic solution includes any one of hydrochloric acid, sulfuric acid, or nitric acid.

5. The preparation method according to claim 1, characterized in that, The hydrolysis reaction is carried out at a temperature of 25~60℃.

6. A nanofiltration membrane obtained by the preparation method according to any one of claims 1 to 5.

7. The nanofiltration membrane according to claim 6, characterized in that, The nanofiltration membrane has an average pore size of 0.2 nm to 0.7 nm; And / or, the thickness of the separation layer of the nanofiltration membrane is 15nm~95nm.

8. The application of a nanofiltration membrane obtained by the preparation method according to any one of claims 1 to 5 or the nanofiltration membrane according to claim 6 or 7 in water treatment.

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