High-flux anti-fouling loose nanofiltration membrane, preparation method and application thereof

Abstract

The application relates to the technical field of membrane separation and water treatment, in particular to a high-flux anti-pollution loose nanofiltration membrane and a preparation method and application thereof. The high-flux anti-pollution loose nanofiltration membrane is constructed by using pyridine compounds and aromatic polyacyl chloride monomers to construct a loose polyamide selective layer containing a pyridine ring; the electron-withdrawing effect of the pyridine ring is used to realize charge regulation, and the hydrophilic end groups on the polyamide chain are combined to cooperatively regulate the membrane layer structure and surface properties. The rejection rate of the nanofiltration membrane to anionic dyes with a molecular weight not less than 500 Da can reach more than 98%, and the rejection rate of sodium chloride is less than 6%, so that the nanofiltration membrane can realize efficient grading separation of dyes and monovalent salts, has high water permeability and excellent anti-pollution capacity, and is suitable for resource treatment of printing and dyeing high-salt wastewater. The preparation process is simple and easy to scale up, the obtained nanofiltration membrane has stable separation performance, and has a good industrial application prospect.

Description

Technical Field

[0001] This invention relates to the field of membrane separation and water treatment technology, specifically to a high-flux, fouling-resistant, loose nanofiltration membrane, its preparation method, and its application. In particular, it relates to the application of this loose nanofiltration membrane in achieving high dye retention, low inorganic salt retention, and efficient dye / salt separation in high-salt wastewater from textile printing and dyeing. Background Technology

[0002] Textile printing and dyeing, as well as dye synthesis processes, generate large amounts of organic wastewater. This wastewater is characterized by high color, high salt content, complex composition, and poor biodegradability. Dye molecules in the wastewater typically possess aromatic conjugated skeletons and ionized groups such as sulfonic acid and carboxyl groups; the concentration of inorganic salts like sodium chloride and sodium sulfate can reach grams per liter. Direct discharge causes severe environmental pollution and wastes dye and salt resources. Efficiently separating large-molecule dyes from small-molecule inorganic salts to achieve dye concentration and recovery, and reusing brine production, is a crucial technological approach for reducing and recycling printing and dyeing wastewater.

[0003] Existing treatment processes include reverse osmosis, dense nanofiltration, electrodialysis, and evaporation crystallization. Reverse osmosis and dense nanofiltration have high rejection rates for monovalent salts, resulting in co-concentration of dyes and salts, making it impossible to achieve dye-salt fractional separation. Electrodialysis is easily fouled by organic dyes and causes membrane scaling. Evaporation crystallization has high energy consumption and large equipment investment. Loose nanofiltration membranes have a pore size between ultrafiltration and conventional nanofiltration, and can achieve "retention of large molecular dyes and permeation of small molecular inorganic salts" through size sieving and electrostatic repulsion, making it the preferred technology for dye-salt separation.

[0004] The current mainstream loose nanofiltration membranes are prepared by interfacial polymerization of aliphatic amines (piperazine, polyethyleneimine PEI) and aromatic polyacrylamide chlorides. However, the reaction rate of aliphatic amines is too fast, making it difficult to match monomer diffusion and film formation reactions, which easily leads to localized over-crosslinking, uneven membrane thickness, and surface defects. Excessive crosslinking reduces water flux and salt permeability, while insufficient crosslinking results in dye retention failure. At the same time, the hydrophobic regions and rough structure of the membrane surface easily adsorb dyes and colloidal organic matter, resulting in rapid flux decay and frequent chemical cleaning. How to simultaneously achieve high flux, high dye retention, low salt retention, excellent antifouling properties, and long-term stability under high salt conditions is a technical challenge that loose nanofiltration membranes urgently need to solve.

[0005] Pyridine compounds possess both an outer-ring amino group capable of participating in amidation reactions and a pyridine ring nitrogen with lone pairs of electrons. Compared to conventional aliphatic amines, their heterocyclic aromatic ring structure exhibits a certain degree of rigidity, allowing for the regulation of the diffusion and reaction rate of aqueous monomers at the organic phase interface. The pyridine ring nitrogen, along with the residual carboxyl, amino, hydroxyl, and amide groups after polymerization, endow the material with polarity and hydrophilicity, while also enabling pH-responsive charge tunability. Utilizing pyridine monomers to regulate the monomer diffusion rate during interfacial polymerization holds promise for constructing continuous, moderately porous polyamide selective layers. However, current technologies lack porous nanofiltration membrane schemes that utilize pyridine compounds as the core reactive monomer, have clearly defined process conditions, and balance high salt stability and cyclic antifouling performance. Inconsistent performance testing conditions across different literature sources make it difficult to reproduce and compare technical solutions. Summary of the Invention

[0006] To overcome the shortcomings of the prior art, the first objective of this invention is to provide a high-flux, anti-fouling, loose nanofiltration membrane that, under conditions of high-salt dye wastewater, balances high water permeability, high dye rejection rate, and low inorganic salt rejection rate, and also possesses excellent circulating anti-fouling performance.

[0007] To overcome the shortcomings of the prior art, the second objective of this invention is to provide a method for preparing a high-flux, anti-fouling, loose nanofiltration membrane. This method uses pyridine compounds and aromatic polyacrylamide chlorides to construct an interfacial polymerization system. Through the synergistic control of aqueous phase loading, interfacial polymerization, and post-hydration treatment, a loose polyamide selective layer containing a pyridine structure is formed. The preparation method is simple, the process conditions are mild, and it does not require nanofillers or complex chemical grafting, making it easy for large-scale industrial production.

[0008] The third objective of this invention is to provide an application of a high-flux, anti-fouling, loose nanofiltration membrane.

[0009] To achieve the first objective of the invention, the technical solution adopted by the present invention is as follows:

[0010] The present invention provides a high-flux, anti-fouling, loose nanofiltration membrane, comprising a porous support layer and a polyamide selective layer formed on at least one side surface of the porous support layer; the polyamide backbone of the polyamide selective layer contains a pyridine ring and the ends of the polyamide chains have hydrophilic end groups.

[0011] This invention discloses a high-flux, antifouling, loose nanofiltration membrane. Its polyamide selective layer is a cross-linked or branched polymer network continuously covering the surface of a porous support layer, undertaking solute recognition and selective separation functions. The nitrogen atoms within the pyridine rings of the polymer network enhance the interfacial polarity, hydrophilicity, and charge tunability of the polyamide selective layer. The porous support layer primarily provides mechanical support strength to the composite membrane while exhibiting low mass transfer resistance. This invention's high-flux, antifouling, loose nanofiltration membrane achieves synergistic optimization of water permeability, dye rejection rate, and salt permeability; wherein the water permeability can reach 90~135 μm. -2 h -1 bar -1 The anionic dye rejection rate can reach over 98%, while the sodium chloride rejection rate is less than 6%. Furthermore, the electron-withdrawing effect of the pyridine ring can regulate the degree of polymer crosslinking during interfacial polymerization, constructing moderately loose sieve channels while ensuring the integrity of the polyamide selective layer without through-hole defects. This ensures high rejection of macromolecular anionic dyes while allowing the smooth passage of inorganic salt ions. Simultaneously, the highly hydrophilic surface facilitates the formation of a stable hydration layer, weakening the direct contact between dye contaminants and the membrane surface, thus improving cyclic antifouling performance.

[0012] The polyamide selective layer of this invention is a functional polymer thin layer that can achieve high retention of anionic dyes with a molecular weight of not less than 500 Da, while allowing a large amount of monovalent inorganic salts to permeate. This polyamide selective layer does not have through-hole macroporous defects and does not rely on obvious pore structure sieving. Instead, it forms a nanoscale mass transfer space by controlling the degree of crosslinking, free volume, hydrophilic channels, and charge state of the polymer network, allowing water molecules and small inorganic ions to pass through smoothly while blocking large molecular weight anionic dyes.

[0013] Furthermore, the polyamide selective layer is formed by polymerizing pyridine compounds with aromatic polyacrylamide monomers; wherein, the pyridine heterocycle is embedded in the polyamide crosslinking network backbone; the pyridine ring has a strong electron-withdrawing effect, which can regulate the polymerization rate and inhibit excessive crosslinking of the polymer; the nitrogen atom in the pyridine ring carries a lone pair of electrons, enhancing the overall polarity of the polymer and improving the hydrophilicity of the membrane layer. Simultaneously, the pyridine ring possesses acid-base responsiveness, which can regulate the interfacial charge of the membrane, generating electrostatic repulsion with anionic dyes, and synergistically improving dye separation performance through sieving. The polymerization system readily undergoes chain termination, thus retaining hydrophilic end groups on the polymer network; the pyridine ring and the hydrophilic end groups work synergistically to endow the membrane with high flux, excellent dye retention performance, and good antifouling properties, making it suitable for separating dyes and salts in dyeing and printing wastewater.

[0014] The hydrophilic end groups include at least one of terminal carboxyl, terminal amino, terminal hydroxyl, or terminal amide groups. In this invention, during the interfacial polymerization of pyridine compounds and aromatic polyacrylamide monomers, some acrylamide groups cannot continue to undergo cross-linking reactions. After hydrolysis and chain termination, hydrophilic end groups, including at least one of terminal carboxyl, terminal amino, terminal hydroxyl, or terminal amide groups, are retained on the polyamide network. On the one hand, these polar groups can form hydrogen bonds with water molecules, improving the overall hydrophilicity of the polyamide selective layer and reducing the resistance of water molecules across the membrane. On the other hand, terminal amino and terminal carboxyl groups can regulate the surface charge of the membrane, generating electrostatic repulsion with anionic dyes, and synergistically achieving efficient dye retention through the size sieving effect of the polymer network. These polar hydrophilic end groups can bind water molecules to form a stable hydration membrane on the membrane surface, weakening the interaction between organic dyes and the membrane, and reducing irreversible fouling. At the same time, the hydrophilic end groups limit the excessive development of cross-linking, preventing the formation of a dense polyamide layer, and forming nano-mass transfer channels within the network that allow monovalent inorganic salt ions to pass through, ultimately achieving efficient separation of anionic dyes and monovalent salts.

[0015] The polymerization method is water-organic phase interfacial polymerization.

[0016] To achieve the second objective of the invention, the technical solution adopted by the present invention is as follows:

[0017] This invention provides a method for preparing a high-flux, anti-fouling, loose nanofiltration membrane, comprising the following steps:

[0018] S1. Pre-treat the porous support membrane by immersing it in deionized water.

[0019] S2. The porous support membrane after soaking and pretreatment is brought into contact with an aqueous solution containing pyridine compounds to form an aqueous layer on the surface of the porous support membrane.

[0020] S3. The aqueous phase layer is brought into contact with an organic phase solution containing aromatic polyacrylamide monomers to carry out an interfacial polymerization reaction, forming a polyamide selective layer.

[0021] S4. Remove the residual organic phase solution from step S3, then wash and dry it, and then soak it in deionized water for post-treatment to obtain the high-flux anti-fouling loose nanofiltration membrane.

[0022] Furthermore, in step S1, the porous support membrane is one of a flat sheet microfiltration membrane, a flat sheet ultrafiltration membrane, a hollow fiber microfiltration membrane, or a hollow fiber ultrafiltration membrane; the porous support membrane has sufficient mechanical strength, good water wettability, and a surface pore structure suitable for loading ultrathin selective layers.

[0023] The porous support membrane is made of polyethersulfone, polysulfone, polyacrylonitrile, polyvinylidene fluoride, or polyimide.

[0024] Furthermore, in step S1, the soaking pretreatment time is 2-24 hours. The soaking pretreatment serves two purposes: firstly, it removes water-soluble additives from the porous support membrane and impurities from the membrane surface; secondly, it ensures the porous support membrane is fully wetted, displacing any trapped air within the membrane pores, facilitating the uniform entry of the subsequent aqueous solution into the surface channels of the support membrane. Additionally, after the soaking pretreatment, the membrane can be rinsed 1-3 times with fresh deionized water.

[0025] Furthermore, in step S2, the pyridine ring of the pyridine compound is substituted with at least one group selected from primary or secondary amino groups; wherein, the amino group can react with the acyl chloride group to form an amide bond. The pyridine ring is completely retained inside the polymer network, and the nitrogen atom in the ring acts as a polar site, which can form hydrogen bonds with water molecules; in an acidic aqueous environment, the nitrogen atom of the pyridine ring can be protonated, giving the polymer network a positive charge. For pyridine monomers with two or more amino groups, they can directly participate in the construction of crosslinked or branched networks; for monoamino pyridines, they can be used as reactants or comonomers to regulate the growth process of the polymer network and the distribution of hydrophilic end groups. The monoamino structure easily induces chain termination, which is beneficial for retaining hydrophilic end groups in the polymer network.

[0026] The pyridine compound is selected from at least one of 2-aminopyridine, 3-aminopyridine, 4-aminopyridine, 2,3-diaminopyridine, 2,4-diaminopyridine, 3,5-diaminopyridine or 2-(methylamino)pyridine.

[0027] Furthermore, in step S2, the mass concentration of pyridine compounds in the aqueous solution is 0.5wt%~1.0wt%; wherein, if the concentration of pyridine compounds in the aqueous solution is too low, it will easily cause incomplete coverage of the polyamide selective layer; if the concentration is too high, it will accelerate the interfacial polymerization reaction rate, which will easily lead to an excessively thick polyamide selective layer or a rough film surface.

[0028] The contact time is 0.5 min to 10 min. This contact time allows for sufficient adsorption of pyridine compounds on the surface of the porous support membrane, providing ample reaction sites for subsequent interfacial polymerization.

[0029] The contact method of the present invention can be single-sided dip coating, double-sided dip coating, or slot spraying.

[0030] The aqueous solution may be prepared solely from pyridine compounds and deionized water, or a small amount of pH adjuster, acid absorbent, or surfactant may be added as needed; however, the added additives shall not significantly reduce the reactivity of the pyridine compounds, nor shall they cause swelling of the porous support membrane.

[0031] After the contact, excess aqueous solution on the surface is removed; the method of removing excess aqueous solution on the surface includes at least one of pouring, rolling, scraping, air knife blowing or natural drying.

[0032] Furthermore, in step S3, the aromatic polyacryl chloride monomer has at least two acryl chloride groups on its molecule; wherein, the use of diacryl chloride is beneficial for generating extended linear polymer chain segments, which is easy to construct a relatively loose network structure; the use of triacryl chloride can provide three-dimensional crosslinking nodes, improving the continuity and mechanical stability of the polymer network; by using diacryl chloride and triacryl chloride in combination, the overall degree of crosslinking can be flexibly controlled.

[0033] The aromatic polyacrylic chloride monomer is selected from at least one of isophthaloyl chloride, terephthaloyl chloride, trimesoyl chloride, or biphenyl chloride; and / or

[0034] The organic phase solution contains aromatic polyacrylamide chloride monomers at a mass concentration of 0.02 wt% to 0.20 wt%; and / or

[0035] The interfacial polymerization reaction time is 10~120s; if the interfacial polymerization reaction time is too short, the polyamide selective layer will not be fully covered and separation defects will exist; if the interfacial polymerization reaction time is too long, the cross-linking reaction will continue to advance, resulting in an increase in the thickness of the polyamide selective layer and an increase in the cross-linking density, thereby reducing the water permeability.

[0036] The organic solvent in the organic phase solution is selected from at least one of petroleum ether, n-hexane, cyclohexane, n-heptane, n-decane, n-dodecane, toluene, or xylene.

[0037] Furthermore, in step S4, the method for removing the residual organic phase solution from step S3 includes at least one of leaching, pouring, rolling, or scraping; wherein leaching involves vertically draining the membrane; rolling involves using a rubber roller to remove the surface organic phase. Removing the residual organic phase solution from the membrane surface reduces unreacted acyl chloride monomer residue, avoids subsequent continuous side reactions, and ensures the stability of the polyamide selective layer structure.

[0038] The cleaning is performed by rinsing with an organic solvent that is the same as or compatible with the organic phase solution in step S3 for 5-30 seconds; and / or

[0039] The drying process is performed at 25-35°C for 1-30 minutes; and / or

[0040] The soaking and post-treatment time is 12-24 hours. This soaking and post-treatment ensures thorough wetting of the polyamide selective layer, dissolves small molecule byproducts generated during interfacial polymerization, and stabilizes the water transport channels within the polymer. The prepared nanofiltration membrane can be stored short-term in deionized water at 4°C and restored to the test temperature before formal use.

[0041] The high-flux, antifouling, porous nanofiltration membrane prepared by this invention exhibits high dye rejection performance primarily due to the synergistic effect of size sieving and electrostatic repulsion. Anionic dyes possess large hydration sizes and high negative charge densities, making it difficult for them to enter the effective mass transfer channels within the polyamide network. Under neutral or weakly alkaline conditions, the hydrophilic terminal carboxyl groups in the polyamide selective layer of this invention undergo deprotonation, further enhancing the electrostatic repulsion against anionic dyes. Sodium and chloride ions generated from the dissociation of sodium chloride have small hydration sizes, allowing monovalent cations and anions to jointly penetrate the porous polyamide selective layer while maintaining electroneutrality. Therefore, the nanofiltration membrane of this invention has a low sodium chloride rejection rate. The pyridine ring nitrogen atom, amide group, and hydrophilic end group are all polar sites, capable of forming hydrogen bonds with water molecules to construct a hydration interface, reducing water transmembrane transport resistance, and simultaneously weakening the hydrophobic interaction between dye molecules and the membrane surface, thereby enhancing the membrane's antifouling capability.

[0042] To achieve the third objective of the invention, the technical solution adopted by the present invention is as follows:

[0043] This invention provides an application of a high-flux, anti-fouling, loose nanofiltration membrane. The high-flux, anti-fouling, loose nanofiltration membrane prepared by the above-described method can be used in the treatment of high-salt wastewater from textile printing and dyeing, dye concentration and recovery, brine reuse, wastewater decolorization and desalination, organic / inorganic salt separation, or industrial water resource treatment.

[0044] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0045] (1) A high-flux, anti-fouling, loose nanofiltration membrane of the present invention is formed by interfacial polymerization of pyridine compounds and aromatic polyacrylamide monomers to form a loose polyamide selective layer containing a pyridine ring structure. The pyridine ring changes the reactivity of the pyridine monomers through the electron-withdrawing effect, thereby regulating the degree of crosslinking of the polyamide network and constructing a nanoscale mass transfer channel. At the same time, the nitrogen atoms in the ring can increase the polarity of the membrane layer and endow the membrane surface with tunable charge characteristics. The hydrophilic end groups left during the polymerization process further enhance the hydrophilicity of the membrane surface, form a hydration barrier, reduce irreversible dye adsorption, and assist in regulating the interfacial charge, inhibiting the accumulation of irreversible fouling. After multiple cycles of cleaning, the membrane can exhibit a high flux recovery rate and better long-term operational stability. This membrane breaks through the contradiction between the flux and separation selectivity of traditional nanofiltration membranes, achieving synergistic optimization of performance. Under the test conditions, the water permeability can reach 90~135 L m. -2 h -1 bar -1It achieves a rejection rate of over 98% for anionic dyes with a molecular weight of not less than 500 Da, and a sodium chloride rejection rate of <6%, efficiently separating anionic dyes from monovalent inorganic salts. It also exhibits excellent antifouling capabilities and a gradual decrease in operating flux. Within a sodium chloride concentration range of 1–20 g / L, the membrane maintains a high rejection rate for anionic dyes and a low rejection rate for sodium chloride, meeting the treatment requirements for high-salinity textile dyeing wastewater. It is suitable for applications such as high-salinity wastewater treatment in textile dyeing, dye concentration and recovery, brine reuse, and organic / inorganic salt separation, demonstrating promising prospects for industrial application.

[0046] (2) A high-flux, antifouling, loose nanofiltration membrane of the present invention has polyamide selective layer with incompletely reacted hydrophilic end groups at the ends of the polyamide chains. These hydrophilic end groups include at least one of terminal carboxyl, terminal amino, terminal hydroxyl, or terminal amide groups. These polar hydrophilic end groups can enhance the hydrophilicity of the polyamide selective layer, construct continuous hydration channels, reduce water mass transfer resistance, and obtain high flux. At the same time, they can adjust the surface charge of the membrane and improve the anionic dye rejection performance by relying on electrostatic repulsion and synergistic size sieving. The hydration membrane formed on the membrane surface can inhibit dye adsorption and improve the membrane's antifouling ability. In addition, the hydrophilic end groups, as chain termination sites in the interfacial polymerization process, can regulate the degree of crosslinking of the polyamide network, construct a loose structure with both nanoscale mass transfer space and no through defects, and achieve synergistic optimization of high flux, high dye rejection, and low monovalent salt rejection.

[0047] (3) A method for preparing a high-flux, anti-fouling, loose nanofiltration membrane according to the present invention utilizes the interfacial polymerization of pyridine compounds and aromatic polyacrylamide monomers to form a continuous, uniform, and moderately loose polyamide selective layer on the surface of a porous support membrane. The aromatic polyacrylamide monomers contain multiple acrylamide functional groups, which can undergo polymerization reactions with the active amino groups of pyridine compounds to construct a continuous polyamide crosslinking network. The rigid heterocyclic structure of the pyridine ring can regulate the degree of crosslinking during the interfacial polymerization process, avoiding the formation of a highly dense polymer film, and constructing nano-mass transfer channels within the network that allow water molecules and monovalent inorganic salts to pass through. The nitrogen atoms within the pyridine ring enhance the polarity and hydrophilicity of the polymer network, reducing water mass transfer resistance. At the same time, the pyridine ring has charge-tunable characteristics, which can achieve efficient retention of anionic dyes by means of electrostatic repulsion and size sieving. In addition, this polymerization system easily retains hydrophilic end groups in the polyamide network, further enhancing the hydrophilicity and antifouling ability of the membrane layer, and achieving a synergistic balance of high flux, high dye retention, and low monovalent salt retention.

[0048] (4) A method for preparing a high-flux, anti-fouling, loose nanofiltration membrane according to the present invention. The high-flux, anti-fouling, loose nanofiltration membrane of the present invention uses pyridine compounds and aromatic polyacrylamide monomers to construct a loose polyamide selective layer containing pyridine rings. Charge regulation is achieved by relying on the electron-withdrawing effect of the pyridine rings. Combined with hydrophilic end groups on the polymer network, the membrane structure and surface properties are synergistically optimized. It can ensure the smooth passage of monovalent salts while maintaining a high rejection rate of anionic dyes with a molecular weight of not less than 500 Da, thereby obtaining high water permeability and excellent antifouling performance. It can effectively achieve efficient separation of dyes and salts and is suitable for the resource-based treatment of high-salt wastewater from printing and dyeing. In addition, the preparation process does not require complex surface grafting modification or doping with nanoparticles. The process steps are simple, the interfacial polymerization reaction can be carried out at room temperature, the raw materials and conventional equipment used are easy to obtain, the process has excellent reproducibility, and it is easy to promote on a large scale.

[0049] (5) An application of a high-flux, anti-fouling, loose nanofiltration membrane of the present invention. This high-flux, anti-fouling, loose nanofiltration membrane can achieve efficient separation of anionic dyes and monovalent inorganic salts. Within a wide salt concentration range of 1~20 g / L sodium chloride, it maintains a high rejection rate of anionic dyes and a low rejection rate of sodium chloride, making it suitable for high-salt dyeing and printing wastewater treatment. The membrane layer achieves stable separation performance through the synergistic effect of size sieving and electrostatic repulsion. The abundant polar sites of the polyamide selective layer endow the membrane with excellent hydrophilicity, effectively inhibiting irreversible dye adsorption. After multiple cycles of cleaning, the flux recovery rate is high, and the long-term operation shows a gradual decline. The nanofiltration membrane has a simple preparation process, requiring no nanofiller doping or complex post-grafting modification, and is easy to scale up for production. It can not only be used for decolorization of high-salt textile dyeing and printing wastewater, dye recovery, and wastewater resource reuse, but also for dye chemical mother liquor separation, organic small molecule and monovalent salt separation, and surface water trace organic pollutant removal, etc., and has broad industrial application prospects. Attached Figure Description

[0050] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0051] Figure 1 The images show surface SEM images of the high-flux antifouling loose nanofiltration membrane (LNF-1) of Example 1, the substrate membrane (PES@1) of Comparative Example 1, and the commercial support membrane (PES@2) of Comparative Example 2 of the present invention.

[0052] Figure 2 The X-ray photoelectron spectroscopy (XPS) spectra of the high-throughput antifouling loose nanofiltration membrane (LNF-1) of Example 1 and the base membrane (PES@1) of Comparative Example 1 are shown.

[0053] Figure 3 The graph shows the water contact angle and zeta potential test results of the membranes prepared in Example 1, Comparative Example 1, and Comparative Example 2.

[0054] Figure 4 The graphs show the molecular weight cutoff curves and pore size distribution test results of the membranes prepared in Example 1, Comparative Example 1, and Comparative Example 2.

[0055] Figure 5 The results are the water permeability, Congo red rejection rate, and sodium chloride rejection rate of the membranes prepared in Examples 1 to 7.

[0056] Figure 6 The results show the separation performance of the membranes prepared in Example 1, Comparative Example 1, and Comparative Example 2 in a high-salt system for different anionic dye / sodium chloride mixed solutions.

[0057] Figure 7 The results show the changes in water permeability and dye rejection rate of the LNF-1 membrane prepared in Example 1 during long-term operation.

[0058] Figure 8 The results are the normalized flux change test results of the membranes prepared in Example 1, Comparative Example 1 and Comparative Example 2 during three fouling-cleaning cycles. Detailed Implementation

[0059] To make the technical problem to be solved, the technical solution, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0060] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. In this invention, the singular forms “a,” “the,” and “the” as used in the embodiments and appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0061] The aromatic polyacryl chloride monomers described in this invention refer to aromatic acryl chlorides with at least two acryl chloride (-COCl) functional groups on their monomer molecular structure, including difunctional aromatic diacryl chlorides and trifunctional aromatic triacryl chlorides.

[0062] In this embodiment of the invention, a high-flux, anti-fouling, loose nanofiltration membrane includes a porous support layer and a polyamide selective layer formed on at least one side surface of the porous support layer; the polyamide backbone of the polyamide selective layer contains a pyridine ring, and the ends of the polyamide chains have hydrophilic end groups.

[0063] As one embodiment, the polyamide selective layer is formed by polymerization of pyridine compounds and aromatic polyacrylamide monomers;

[0064] The hydrophilic end group includes at least one of terminal carboxyl, terminal amino, terminal hydroxyl, or terminal amide groups; and / or

[0065] The polymerization method is water-organic phase interfacial polymerization.

[0066] In this embodiment of the invention, a method for preparing a high-flux, anti-fouling, loose nanofiltration membrane includes the following steps:

[0067] S1. Pre-treat the porous support membrane by immersing it in deionized water.

[0068] S2. The porous support membrane after soaking and pretreatment is brought into contact with an aqueous solution containing pyridine compounds to form an aqueous layer on the surface of the porous support membrane.

[0069] S3. The aqueous phase layer is brought into contact with an organic phase solution containing aromatic polyacrylamide monomers to carry out an interfacial polymerization reaction, forming a polyamide selective layer.

[0070] S4. Remove the residual organic phase solution from step S3, then wash and dry it, and then soak it in deionized water for post-treatment to obtain the high-flux anti-fouling loose nanofiltration membrane.

[0071] In one embodiment, in step S1, the porous support membrane is one of a flat sheet microfiltration membrane, a flat sheet ultrafiltration membrane, a hollow fiber microfiltration membrane, or a hollow fiber ultrafiltration membrane.

[0072] The porous support membrane is made of polyethersulfone, polysulfone, polyacrylonitrile, polyvinylidene fluoride, or polyimide.

[0073] In one embodiment, the soaking pretreatment time in step S1 is 2 to 24 hours.

[0074] In one embodiment, in step S2, the pyridine ring of the pyridine compound is substituted with at least one group selected from primary or secondary amino groups; and / or

[0075] The pyridine compound is selected from at least one of 2-aminopyridine, 3-aminopyridine, 4-aminopyridine, 2,3-diaminopyridine, 2,4-diaminopyridine, 3,5-diaminopyridine or 2-(methylamino)pyridine.

[0076] In one embodiment, in step S2, the mass concentration of the pyridine compound in the aqueous solution is 0.5 wt% to 1.0 wt%; and / or

[0077] The contact time is 0.5 min to 10 min; and / or

[0078] After the contact, excess aqueous solution on the surface is removed; the method of removing excess aqueous solution on the surface includes at least one of pouring, rolling, scraping, air knife blowing or natural drying.

[0079] In one embodiment, in step S3, the aromatic polyacrylamide monomer has at least two acrylamide groups on its molecule; and / or

[0080] The aromatic polyacrylic chloride monomer is selected from at least one of isophthaloyl chloride, terephthaloyl chloride, trimesoyl chloride, or biphenyl chloride; and / or

[0081] The organic phase solution contains aromatic polyacrylamide chloride monomers at a mass concentration of 0.02 wt% to 0.20 wt%; and / or

[0082] The interfacial polymerization reaction takes 10-120 seconds; and / or

[0083] The organic solvent in the organic phase solution is selected from at least one of petroleum ether, n-hexane, cyclohexane, n-heptane, n-decane, n-dodecane, toluene, or xylene.

[0084] In one embodiment, in step S4, the method for removing the residual organic phase solution from step S3 includes at least one of leaching, pouring, rolling, or scraping; and / or

[0085] The cleaning is performed by rinsing with an organic solvent that is the same as or compatible with the organic phase solution in step S3 for 5-30 seconds; and / or

[0086] The drying process is performed at 25-35°C for 1-30 minutes; and / or

[0087] The soaking and post-treatment time is 12-24 hours.

[0088] In this embodiment of the invention, an application of a high-flux anti-fouling loose nanofiltration membrane is described. The high-flux anti-fouling loose nanofiltration membrane prepared by the above-described method is used in the treatment of high-salt wastewater in textile printing and dyeing, dye concentration and recovery, brine reuse, wastewater decolorization and desalination, organic / inorganic salt separation, or industrial water resource treatment.

[0089] The following description is based on specific embodiments.

[0090] Example 1

[0091] A method for preparing a high-flux, anti-fouling, porous nanofiltration membrane includes the following steps:

[0092] S1. The polyethersulfone porous support membrane is immersed in deionized water for 24 hours for pretreatment; in this embodiment, the porous support membrane is a flat sheet microfiltration membrane.

[0093] S2. The pretreated polyethersulfone porous support membrane is contacted with an aqueous solution containing 1.0 wt% 2-aminopyridine for 5 minutes. The aqueous solution is poured out, and the visible liquid on the surface is removed by rolling with a rubber roller to form an aqueous layer on the surface of the polyethersulfone porous support membrane.

[0094] S3. The aqueous phase layer is brought into contact with a hexane solution containing 0.10 wt% isophthaloyl chloride to carry out an interfacial polymerization reaction for 60 s to form a polyamide selective layer.

[0095] S4. Pour out the organic phase solution, use a rubber roller to roll and remove the visible residual liquid on the surface, then rinse with n-hexane for 15s, dry at 30℃ for 15min, and then soak in deionized water for 12h to obtain a high-flux antifouling loose nanofiltration membrane (denoted as LNF-1), and store it in deionized water at 4℃ for later use.

[0096] Example 2

[0097] A method for preparing a high-flux, anti-fouling, loose nanofiltration membrane. The difference between this embodiment and Example 1 is that, in this embodiment, the pyridine compound in step S2 is 3,5-diaminopyridine with a mass concentration of 0.5 wt%; the organic phase solution in step S3 is a hexane solution containing 0.10 wt% trimesoyl chloride; the remaining preparation methods in this embodiment are the same as in Example 1, and a high-flux, anti-fouling, loose nanofiltration membrane (denoted as LNF-2) is obtained.

[0098] Example 3

[0099] A method for preparing a high-flux, anti-fouling, loose nanofiltration membrane is disclosed. The difference between this embodiment and Example 1 is that in this embodiment, step S1 uses a polysulfone porous support membrane; the pyridine compound in step S2 is 1.0 wt% 2,3-diaminopyridine; and the organic phase solution in step S3 is a petroleum ether solution containing 0.10 wt% terephthaloyl chloride. The remaining preparation methods in this embodiment are the same as in Example 1, resulting in a high-flux, anti-fouling, loose nanofiltration membrane (denoted as LNF-3).

[0100] Example 4

[0101] A method for preparing a high-flux, anti-fouling, loose nanofiltration membrane. The difference between this embodiment and Example 1 is that in this embodiment, step S1 uses a polyacrylonitrile porous support membrane; the pyridine compound in step S2 is 0.75 wt% 2-(methylamino)pyridine; the organic phase solution in step S3 is a cyclohexane solution containing 0.10 wt% biphenyl dicarboxylate chloride; the remaining preparation methods in this embodiment are the same as in Example 1, and a high-flux, anti-fouling, loose nanofiltration membrane (denoted as LNF-4) is obtained.

[0102] Example 5

[0103] A method for preparing a high-flux, anti-fouling, loose nanofiltration membrane is disclosed. The difference between this embodiment and Example 1 is that in this embodiment, step S1 uses a polyvinylidene fluoride porous support membrane; the pyridine compound in step S2 is 0.5 wt% 2,4-diaminopyridine; and the organic phase solution in step S3 is a toluene solution containing 0.10 wt% trimesoyl chloride. The remaining preparation methods in this embodiment are the same as in Example 1, resulting in a high-flux, anti-fouling, loose nanofiltration membrane (denoted as LNF-5).

[0104] Example 6

[0105] A method for preparing a high-flux, anti-fouling, loose nanofiltration membrane. The difference between this embodiment and Example 1 is that in this embodiment, step S1 uses a polysulfone porous support membrane; the pyridine compound in step S2 is 1.0 wt% 3,5-diaminopyridine; the organic phase solution in step S3 is a heptane solution containing 0.15 wt% trimesoyl chloride; the remaining preparation methods in this embodiment are the same as in Example 1, and a high-flux, anti-fouling, loose nanofiltration membrane (denoted as LNF-6) is obtained.

[0106] Example 7

[0107] A method for preparing a high-flux, anti-fouling, loose nanofiltration membrane. The difference between this embodiment and Example 1 is that in this embodiment, the pyridine compound in step S2 is 1.0 wt% 2,4-diaminopyridine; the organic phase solution in step S3 is a xylene solution containing 0.20 wt% trimesoyl chloride; the remaining preparation methods in this embodiment are the same as in Example 1, and a high-flux, anti-fouling, loose nanofiltration membrane (denoted as LNF-7) is obtained.

[0108] Example 8

[0109] A method for preparing a high-flux, anti-fouling, porous nanofiltration membrane includes the following steps:

[0110] S1. The polysulfone porous support membrane is immersed in deionized water for 12 hours for pretreatment; in this embodiment, the porous support membrane is a flat sheet ultrafiltration membrane.

[0111] S2. The pretreated polysulfone porous support membrane is contacted with an aqueous solution containing 0.6 wt% 3-aminopyridine for 10 min. Excess aqueous solution on the surface is removed by scraping to form an aqueous layer on the surface of the polysulfone porous support membrane.

[0112] S3. The aqueous phase layer is brought into contact with a solution of n-decane containing 0.02 wt% isophthaloyl chloride to carry out an interfacial polymerization reaction for 120 s to form a polyamide selective layer.

[0113] S4. Remove the residual organic phase solution from step S3 by scraping, then rinse with n-hexane for 5 seconds, dry at 25°C for 30 minutes, and then soak in deionized water for 24 hours to obtain a high-flux, anti-fouling, loose nanofiltration membrane.

[0114] Example 9

[0115] A method for preparing a high-flux, anti-fouling, porous nanofiltration membrane includes the following steps:

[0116] S1. The polyacrylonitrile porous support membrane is immersed in deionized water for 2 hours for pretreatment; in this embodiment, the porous support membrane is a hollow fiber microfiltration membrane.

[0117] S2. The pretreated polyacrylonitrile porous support membrane is contacted with an aqueous solution containing 0.9wt% 4-aminopyridine for 0.5 min. Excess aqueous solution on the surface is removed by air knife purging to form an aqueous layer on the surface of the polyacrylonitrile porous support membrane.

[0118] S3. The aqueous phase layer is brought into contact with a solution of n-dodecane containing 0.08 wt% isophthaloyl chloride to carry out an interfacial polymerization reaction for 80 s to form a polyamide selective layer.

[0119] S4. Remove the residual organic phase solution from step S3 by leaching, then rinse with n-hexane for 30 seconds, dry at 35°C for 1 minute, and then soak in deionized water for 15 hours to obtain a high-flux, anti-fouling, loose nanofiltration membrane.

[0120] Example 10

[0121] A method for preparing a high-flux, anti-fouling, porous nanofiltration membrane includes the following steps:

[0122] S1. The polyvinylidene fluoride porous support membrane is immersed in deionized water for 18 hours for pretreatment; in this embodiment, the porous support membrane is a hollow fiber ultrafiltration membrane.

[0123] S2. The pretreated polyvinylidene fluoride porous support membrane is contacted with an aqueous solution containing 0.7wt% 2-aminopyridine for 3 minutes. Excess aqueous solution on the surface is removed by air knife blowing to form an aqueous layer on the surface of the polyvinylidene fluoride porous support membrane.

[0124] S3. The aqueous phase layer is brought into contact with a hexane solution containing 0.18 wt% isophthaloyl chloride to carry out an interfacial polymerization reaction for 10 seconds to form a polyamide selective layer.

[0125] S4. Remove the residual organic phase solution from step S3 by scraping, then rinse with n-hexane for 10 seconds, dry at 28°C for 20 minutes, and then soak in deionized water for 20 hours to obtain a high-flux, anti-fouling, loose nanofiltration membrane.

[0126] Example 11

[0127] A method for preparing a high-flux, anti-fouling, porous nanofiltration membrane includes the following steps:

[0128] S1. The polyimide porous support membrane is immersed in deionized water for 8 hours for pretreatment; in this embodiment, the porous support membrane is a flat sheet microfiltration membrane.

[0129] S2. The pretreated polyimide porous support membrane is contacted with an aqueous solution containing a mixture of 0.8wt% 2-aminopyridine and 2,3-diaminopyridine for 7 minutes. Excess aqueous solution on the surface is removed by natural air drying to form an aqueous layer on the surface of the polyimide porous support membrane.

[0130] S3. The aqueous phase layer is brought into contact with a hexane solution containing a mixture of isophthaloyl chloride and terephthaloyl chloride at a mass concentration of 0.13 wt% to undergo an interfacial polymerization reaction for 100 s to form a polyamide selective layer; in this embodiment,

[0131] S4. The residual organic phase solution in step S3 is removed by rolling, then washed with n-hexane for 20 minutes, dried at 32°C for 6 minutes, and then soaked in deionized water for 16 hours to obtain a high-flux, anti-fouling, loose nanofiltration membrane.

[0132] Example 12

[0133] Application of a high-flux, anti-fouling, loose nanofiltration membrane: The high-flux, anti-fouling, loose nanofiltration membranes prepared in Examples 1-11 are used in the treatment of high-salt wastewater from textile printing and dyeing, dye concentration and recovery, brine reuse, wastewater decolorization and desalination, organic / inorganic salt separation, or industrial water resource treatment.

[0134] Comparative Example 1

[0135] A method for preparing a membrane, the difference between this comparative example and Example 1 is that only the soaking pretreatment step S1 is performed, and the subsequent interfacial polymerization to prepare the polyamide selective layer is no longer carried out; the obtained membrane is stored in deionized water at 4°C for later use, and the obtained base membrane is denoted as PES@1.

[0136] Comparative Example 2

[0137] A method for preparing a membrane, the difference between this comparative example and Example 1 is that: a commercial polyethersulfone porous support membrane with a pure water flux of 60 LMH (test conditions: 25℃, 0.6 MPa) is used instead of the polyethersulfone porous support membrane in step S1 of Example 1; this comparative example only performs the soaking pretreatment step S1, and does not carry out the relevant operations of subsequent interfacial polymerization to prepare the polyamide selective layer; the obtained membrane is stored in deionized water at 4℃ for later use, and the obtained commercial support membrane is denoted as PES@2.

[0138] Structural morphology characterization

[0139] (I) Morphological characterization by scanning electron microscopy

[0140] The surfaces of the high-flux antifouling loose nanofiltration membrane (LNF-1) of Example 1, the substrate membrane (PES@1) of Comparative Example 1, and the commercial support membrane (PES@2) of Comparative Example 2 were characterized by scanning electron microscopy (SEM). Figure 1 As shown.

[0141] Depend on Figure 1 As can be seen, the surfaces of PES@1 and PES@2 exhibit the original pore morphology of a porous support substrate. After interfacial polymerization, a continuous polyamide selective layer forms on the surface of the LNF-1 membrane. The membrane surface structure is uniform, dense, and smooth, with no obvious through cracks or large-scale defects observed. These results demonstrate that pyridine compounds and aromatic polyacrylamide chloride monomers can construct a polyamide selective layer on the surface of a porous support membrane. This polyamide selective layer possesses a suitable pore structure, which can trap large-sized dye molecules while allowing water molecules and small inorganic salt molecules to permeate.

[0142] (II) X-ray photoelectron spectroscopy characterization

[0143] The high-flux, antifouling, loose nanofiltration membrane (LNF-1) of Example 1 and the substrate membrane (PES@1) of Comparative Example 1 were characterized by X-ray photoelectron spectroscopy (XPS) to determine their surface chemical structure and elemental composition. The test results are as follows: Figure 2 As shown. Among them, Figure 2 a is the XPS plot for PES@1. Figure 2 b is the XPS plot of LNF-1.

[0144] Depend on Figure 2As can be seen, a low binding energy component with a binding energy of approximately 398.5~399.0 eV appears in the N 1s spectrum of LNF-1 in Example 1. This signal can be attributed to the C=N–C structure within the pyridine ring. This characteristic component did not appear in the PES@1 base film, proving that the pyridine ring structure was successfully introduced into the polyamide selective layer.

[0145] Performance testing

[0146] (a) Water contact angle and zeta potential test

[0147] The high-flux, antifouling, loose nanofiltration membrane (LNF-1) of Example 1, the substrate membrane (PES@1) of Comparative Example 1, and the commercial support membrane (PES@2) of Comparative Example 2 were selected. The zeta potential and water contact angle of the membrane surface were measured using a SurPAss surface potential analyzer and a contact angle meter, respectively, to evaluate the membrane surface charge characteristics and hydrophilicity. The test results are as follows: Figure 3 As shown. Among them, Figure 3 'a' represents the water contact angle test result. Figure 3 b represents the result of the Zeta potential test.

[0148] Depend on Figure 3 As can be seen, the water contact angle of the substrate membrane (PES@1) in Comparative Example 1 was 66.0°, the water contact angle of the commercial support membrane (PES@2) in Comparative Example 2 was 60.1°, and the water contact angle of the LNF-1 membrane prepared in Example 1 was reduced to 45.6°. The lower water contact angle indicates that the polyamide selective layer significantly improved the hydrophilicity of the membrane surface. This phenomenon is attributed to the pyridine ring nitrogen atoms and polar groups such as the terminal carboxyl groups generated by interfacial polymerization. Excellent hydrophilicity facilitates the construction of a stable hydration layer on the membrane surface, reducing water transmembrane transport resistance on the one hand, and reducing hydrophobic interactions between dye molecules and the membrane surface on the other.

[0149] Depend on Figure 3 As can be seen from b, the LNF-1 membrane prepared in Example 1 exhibits overall negative charge within the tested pH range; compared to the PES@1 substrate membrane and the commercially available PES@2 support membrane, LNF-1 displays a more significant surface negative charge characteristic. The negative charge on the membrane surface originates from the carboxylate groups generated by the hydrolysis of trimesoyl chloride and the nitrogen- and oxygen-containing polar structures within the polyamide selective layer. The negatively charged membrane surface can generate an electrostatic repulsion effect on anionic dyes; while the loose polyamide pore structure combined with the charge shielding effect allows the membrane to maintain a low rejection level for monovalent salts. In summary, the LNF-1 membrane obtained in Example 1 possesses both excellent permeability and separation selectivity, thanks to the synergistic effect of its loose pore structure, hydrophilic surface, and uniform and smooth membrane morphology.

[0150] (II) Molecular weight cutoff curve and pore size distribution test

[0151] The high-flux, antifouling, loose nanofiltration membrane (LNF-1) of Example 1, the substrate membrane (PES@1) of Comparative Example 1, and the commercial support membrane (PES@2) of Comparative Example 2 were selected, and molecular weight cutoff curves and pore size distribution tests were conducted respectively. The test results are as follows: Figure 4 As shown. Among them, Figure 4 a is the molecular weight cutoff curve. Figure 4 b is the aperture probability density distribution curve.

[0152] Depend on Figure 4 The molecular weight cutoff test results show that the PES@1 membrane has a molecular weight cutoff of 44 kDa, the PES@2 membrane has a molecular weight cutoff of 31 kDa, and the LNF-1 membrane in Example 1 of this invention has a molecular weight cutoff of 27 kDa. Combined with the pore size distribution curves, it can be seen that the most probable pore size of the LNF-1 membrane is smaller than that of the two comparison membranes, the pore size distribution range is narrower, and the pore size uniformity is better.

[0153] This invention uses amino monomers containing pyridine rings to construct a polyamide selective layer; the pyridine ring is a rigid aromatic heterocyclic structure. During the interfacial polymerization reaction, the unique electron-withdrawing effect of the pyridine ring can regulate the electron cloud distribution of the polyamide molecular chain, reduce the cross-linking reactivity of the amide bond, effectively limit the tight twisting and stacking of the polyamide molecular chain, inhibit excessive chain entanglement and tight cross-linking, and avoid the formation of a highly dense cross-linking network. This results in the construction of a continuous, uniform polyamide selective layer with moderately loose pores on the surface of the porous support membrane. Traditional polyamide nanofiltration membranes often use flexible aliphatic monomers or ordinary benzene ring monomers, which tend to bring the molecular chains close together and stack tightly during polymerization, easily forming a dense, non-porous skin after cross-linking. In contrast, the rigid pyridine heterocycle acts as a skeletal unit embedded in the cross-linking network, serving as a "molecular spacer scaffold," maintaining stable molecular gaps between cross-linking sites, and controllably constructing loose, porous sieving channels.

[0154] Figure 4 The pore size distribution test results of b confirm the above mechanism. Compared with PES@1 and PES@2 membranes, the LNF-1 membrane, by controlling the stacking degree of the cross-linked network through rigid pyridine rings, forms a narrow pore size structure while obtaining a molecular weight cutoff range suitable for dye / salt separation requirements, enabling the retention of large molecular weight anionic dyes and the permeation of small molecular weight inorganic salts. The electron-withdrawing effect of the pyridine rings can precisely control the interfacial polymerization cross-linking density. Under the premise of ensuring sufficient cross-linking reaction and no through defects in the polyamide selective layer, it inhibits excessive aggregation and dense cross-linking of polyamide segments, constructing a loose cross-linked network that is different from the traditional dense polyamide skin, and achieving controllable preparation of a loose nanofiltration sieving structure.

[0155] (III) Separation performance test

[0156] To investigate the effects of preparation parameters on the separation performance of nanofiltration membranes, a single-factor control experiment was conducted, and the test results are shown in Table 1.

[0157] The experiment systematically investigated the effects of the aqueous phase concentration of pyridine compounds, the organic phase concentration of aromatic polyacrylamide chlorides, and the interfacial polymerization (IP) time on the membrane's pure water permeability and dye / salt selectivity. Only when all preparation parameters fall within a suitable range can a continuous and uniform loose polyamide selective layer be formed; if the parameters deviate from this range, the polyamide selective layer is prone to through-hole defects or excessive cross-linking and densification, which respectively cause dye leakage and a significant reduction in permeate flux, causing the membrane to lose its ability to selectively separate dyes and salts.

[0158] Table 1. Test data on the optimized separation performance of nanofiltration membranes

[0159]

[0160] As shown in Table 1, with a fixed aromatic polyacrylamide chloride concentration of 0.1 wt% and an interfacial polymerization time of 60 s, the mass concentration of pyridine compounds in the aqueous phase was adjusted to be 0.05–4.0 wt%. When the mass concentration of pyridine compounds in the aqueous phase was in the range of 0.5–1.0 wt%, the monomer supply at the interface was balanced, the polymerization reaction proceeded smoothly, and a continuous and uniform loose polyamide network could be constructed. When the aqueous concentration of pyridine compounds is reduced to 0.05 wt%, the system lacks sufficient reactive functional groups, resulting in incomplete polymerization. The polyamide selective layer exhibits numerous through-pore defects, allowing dye molecules to permeate along with the inorganic salt. The dye / salt selectivity factor is only 108.43±1.5, indicating significant dye leakage. When the aqueous concentration of pyridine compounds is increased to 3.0 wt% and 4.0 wt%, the excess monomer accelerates the interfacial polymerization rate, forming a highly cross-linked dense skin. This significantly reduces mass transfer channels, reduces water permeability, and causes the sieving structure to fail. The selectivity factors decrease to 112.58±3.70 and 74.32±2.40, respectively.

[0161] With a fixed aqueous concentration of pyridine compounds at 1.0 wt% and an interfacial polymerization time of 60 s, the concentration of the aromatic polyacrylamide organic phase was adjusted to 0.02–1.0 wt%. When the concentration of the aromatic polyacrylamide organic phase was in the range of 0.02–0.20 wt%, the functional group ratio of the two phases was suitable, resulting in a loose and continuous polyamide selective layer. However, when the concentration of the aromatic polyacrylamide organic phase was as low as 0.02 wt%, crosslinking sites were scarce, and continuous pore defects existed within the polyamide selective layer, resulting in a water permeability as high as 163.75 ± 6.42 L / m². -2 h -1 bar -1However, the dye retention performance is insufficient, with a selectivity factor of only 136.21±7.10. When the mass concentration of the aromatic polyacrylamide organic phase increases to 0.6 wt% or above, the excess acrylamide induces violent and rapid cross-linking, resulting in membrane densification, a significant decrease in water permeability, and deterioration of sieving performance. The selectivity factor is below 100, making it impossible to achieve effective separation of dye and salt.

[0162] With a fixed concentration of pyridine compounds in the aqueous phase (1.0 wt%) and aromatic polyacrylamide organic phase (0.1 wt%), the interfacial polymerization time was controlled between 10 and 300 s. When the interfacial polymerization time was within the range of 10–120 s, a loosely structured polyamide selective layer with controllable structure could be prepared. When the polymerization time was shortened to 10 s, the two-phase reaction time was insufficient, the film could not completely cover the pores of the supporting membrane, there were many primary defects, and dye leakage was significant, with a selectivity factor of 372.54 ± 7.80. When the polymerization time was extended to 300 s, the cross-linking reaction continued, the skin layer thickened continuously, many pores closed, water permeability decreased significantly, the sieve window failed, and the selectivity factor was only 83.64 ± 2.80.

[0163] In summary, the suitable preparation parameters for this system are: an aqueous phase concentration of pyridine compounds of 0.5–1.0 wt%, an organic phase concentration of aromatic polyacrylamide chlorides of 0.02–0.20 wt%, and an interfacial polymerization time of 10–120 s. Within these parameter ranges, a continuous, uniform, and porous polyamide selective layer can be formed. Any deviation from these parameters can lead to porosity defects or excessive cross-linking and densification of the selective layer, resulting in dye leakage or a significant decrease in permeation flux, making it difficult to achieve selective separation of dyes and inorganic salts.

[0164] In addition, the separation performance of LNF-1, LNF-2, LNF-3, LNF-4, LNF-5, LNF-6 and LNF-7 membranes prepared in Examples 1 to 7 were compared and tested. The results are as follows: Figure 5 As shown in the figure. The separation performance test was conducted using a cross-flow filtration mode. The feed solution was a mixed aqueous solution containing 100 mg / L Congo red and 2 g / L sodium chloride. The cross-flow rate was 0.5 L / min, the test temperature was 25℃, and the operating transmembrane pressure was 6 bar.

[0165] Depend on Figure 5 As can be seen, the water permeability of the samples in each embodiment is approximately 90~135 L m. -2 h -1 bar -1Within the specified range, the Congo red rejection rate was no less than 98%, and the sodium chloride rejection rate was less than 6%. These results indicate that, within a suitable process window, by adjusting the type of pyridine compound, the porous support membrane material, the type of aromatic polyacrylamide chloride, and the organic solvent system, the prepared membranes can maintain a combination of high water permeability, high dye rejection rate, and low salt rejection rate.

[0166] (iv) Membrane separation performance test for different anionic dye / sodium chloride mixed solutions

[0167] Four anionic dyes—Congo Red (CR), Direct Red 80 (DR80), Evans Blue (EB), and Direct Blue 38 (DB38)—were prepared in mixed solutions with sodium chloride. The molecular weight of each anionic dye was not less than 500 Da. Separation performance was tested using cross-flow filtration. The concentration of each anionic dye in the feed solution was 100 mg / L, and the concentration of sodium chloride was 2 g / L. The cross-flow rate was 0.5 L / min, the test temperature was 25 °C, and the operating transmembrane pressure was 6 bar. The separation performance of PES@1 (Comparative Example 1), PES@2 (Comparative Example 2), and LNF-1 (Example 1) in various dye / salt mixtures was tested. The results are as follows: Figure 6 As shown. Figure 6 In the graph, the bar chart represents the dye rejection rate (right vertical axis), and the line chart represents the sodium chloride rejection rate (left vertical axis).

[0168] Depend on Figure 6 As can be seen, the LNF-1 membrane of this invention achieves high-efficiency retention of all four types of anionic dyes, with the dye rejection rate consistently maintained above 96%; simultaneously, the sodium chloride rejection rate is below 6%, achieving the dye-salt fractionation separation target of high dye rejection and low salt rejection. Furthermore, the PES@1 membrane exhibits a significant decrease in sodium chloride rejection rate in the EB dye system, indicating poor stability of the membrane sieving window; the PES@2 membrane shows significant fluctuations in sodium chloride rejection rate with changes in dye type. Compared to the two comparative samples, the LNF-1 membrane demonstrates stable sodium chloride rejection levels and smaller fluctuations under the four anionic dye conditions, indicating that the porous polyamide selective layer constructed in this invention has a more uniform pore size distribution, and the membrane pore sieving structure is less affected by differences in dye molecular structure.

[0169] In addition, the performance of the four anionic dyes varied slightly under different operating conditions: the molecular weight, molecular size, and charge quantity of the four anionic dyes were different. EB had a larger molecular size, which created a stronger steric hindrance at the membrane pore inlet, crowding out the salt ion permeation channels. Therefore, the sodium chloride rejection rate of the LNF-1 membrane reached its peak in the EB mixed system. The molecular sizes of CR, DR80, and DB38 showed a gradient, and the degree to which the salt ion permeation channels inside the membrane were affected by the dye molecules changed accordingly, resulting in slight fluctuations in the sodium chloride rejection rate.

[0170] In summary, the LNF-1 membrane maintained a dye rejection rate of over 96% and a sodium chloride rejection rate of less than 6% in all test systems. This demonstrates that the loose nanofiltration membrane of this invention possesses universal dye / salt separation capabilities for various anionic dyes with diverse structures, and its separation performance is not easily affected by differences in the molecular configuration of anionic dyes, exhibiting a wide range of applicability to dye wastewater.

[0171] (v) Long-term operational stability test

[0172] The LNF-1 membrane prepared in Example 1 was selected for a 72-hour long-term stability test of the continuous dye / salt mixed system. The test employed cross-flow filtration mode, with a feed solution consisting of a mixed aqueous solution containing 100 mg / L Congo red and 2 g / L sodium chloride; the cross-flow rate was 0.5 L / min, the test temperature was 25 °C, and the operating transmembrane pressure was 6 bar. The test results are as follows: Figure 7 As shown.

[0173] Depend on Figure 7 It can be seen that in the initial stage of operation, the membrane water permeability is The Congo red rejection rate was 99.00%; after 72 hours of continuous operation, the membrane water permeability was... The overall decrease in water permeability was only 6.1%, and the Congo red rejection rate remained at 98.15%.

[0174] Throughout the entire 72-hour continuous operation cycle, the membrane's water permeability and Congo red rejection rate only decreased slightly and gradually, without any precipitous performance decline. These results indicate that the loose polyamide selective layer structure constructed in this invention is stable, and no problems such as separation layer damage or pore collapse occurred during long-term operation. The slight decrease in water permeability only stemmed from the weak adsorption of a small amount of dye on the membrane surface, forming a thin filter cake layer. This filter cake layer did not significantly block the sieving channels within the membrane, and the membrane's sieving and separation capabilities were effectively maintained. This demonstrates that the loose nanofiltration membrane of this invention possesses excellent continuous operational stability under dye / salt separation conditions.

[0175] (vi) Cyclic antifouling performance test

[0176] A three-stage fouling-cleaning cycle cross-flow filtration experiment was conducted on LNF-1, PES@1, and PES@2 membranes using a mixed aqueous solution containing 100 mg / L Congo red and 2 g / L sodium chloride. The cross-flow rate was 0.5 L / min, the test temperature was 25 °C, and the operating transmembrane pressure was 6 bar. The normalized flux change over time is shown in the figure. Figure 8 As shown.

[0177] Depend on Figure 8 As can be seen, during the fouling stage, the normalized flux of all three membranes decreased. After rinsing with deionized water, the flux recovery of the LNF-1 membrane was significantly better than that of PES@1 and PES@2. Test results showed that the flux recovery rate of the LNF-1 membrane reached 94.6%, with an irreversible fouling rate of no more than 8%; the flux recovery rate of the PES@1 substrate membrane was only about 70%, with an irreversible fouling rate of about 32%. These results indicate that the polyamide selective layer with a pyridine ring structure can prevent pollutants from directly contacting the supporting membrane pores, while its high surface hydration capacity weakens the irreversible adsorption of dye molecules, allowing the membrane to maintain excellent flux recovery performance even after multiple fouling and pure water physical cleanings.

[0178] Based on the above test results regarding surface morphology, separation performance, long-term operational stability, and cyclic antifouling performance, it is evident that this invention utilizes interfacial polymerization of pyridine compounds and aromatic polyacrylamide chlorides to construct a high-flux, loose polyamide selective layer on the surface of various porous support membranes. The resulting nanofiltration membrane exhibits high rejection rates for macromolecular anionic dyes and low rejection rates for monovalent inorganic salts. It also possesses excellent antifouling properties and flux cleaning recovery capabilities, making it suitable for the concentration and recovery of dyes from high-salt dye wastewater and the resource reuse of brine. This enables the fractional separation of dyes and salts, providing technical support for the resource-based treatment of high-salt dyeing wastewater.

[0179] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A high-flux, anti-fouling, loose nanofiltration membrane, characterized in that, It includes a porous support layer and a polyamide selective layer formed on at least one side surface of the porous support layer; the polyamide backbone of the polyamide selective layer contains a pyridine ring and the ends of the polyamide chain have hydrophilic end groups.

2. The high-flux, anti-fouling, loose nanofiltration membrane as described in claim 1, characterized in that, The polyamide selective layer is formed by polymerization of pyridine compounds and aromatic polyacryl chloride monomers; The hydrophilic end group includes at least one of terminal carboxyl, terminal amino, terminal hydroxyl, or terminal amide groups; and / or The polymerization method is water-organic phase interfacial polymerization.

3. A method for preparing a high-flux, anti-fouling, porous nanofiltration membrane according to any one of claims 1 to 2, characterized in that, Includes the following steps: S1. Pre-treat the porous support membrane by immersing it in deionized water. S2. The porous support membrane after soaking and pretreatment is brought into contact with an aqueous solution containing pyridine compounds to form an aqueous layer on the surface of the porous support membrane. S3. The aqueous phase layer is brought into contact with an organic phase solution containing aromatic polyacrylamide monomers to carry out an interfacial polymerization reaction, forming a polyamide selective layer. S4. Remove the residual organic phase solution from step S3, then wash and dry it, and then soak it in deionized water for post-treatment to obtain the high-flux anti-fouling loose nanofiltration membrane.

4. The method for preparing a high-flux, anti-fouling, loose nanofiltration membrane as described in claim 3, characterized in that, In step S1, the porous support membrane is one of a flat sheet microfiltration membrane, a flat sheet ultrafiltration membrane, a hollow fiber microfiltration membrane, or a hollow fiber ultrafiltration membrane. The porous support membrane is made of polyethersulfone, polysulfone, polyacrylonitrile, polyvinylidene fluoride, or polyimide.

5. The method for preparing a high-flux, anti-fouling, loose nanofiltration membrane as described in claim 3, characterized in that, In step S1, the soaking pretreatment time is 2~24h.

6. The method for preparing a high-flux, anti-fouling, loose nanofiltration membrane as described in claim 3, characterized in that, In step S2, the pyridine ring of the pyridine compound is substituted with at least one group selected from primary or secondary amino groups; and / or The pyridine compound is selected from at least one of 2-aminopyridine, 3-aminopyridine, 4-aminopyridine, 2,3-diaminopyridine, 2,4-diaminopyridine, 3,5-diaminopyridine or 2-(methylamino)pyridine.

7. The method for preparing a high-flux, anti-fouling, loose nanofiltration membrane as described in claim 3, characterized in that, In step S2, the mass concentration of pyridine compounds in the aqueous solution is 0.5 wt% to 1.0 wt%; and / or The contact time is 0.5 min to 10 min; and / or After the contact, excess aqueous solution on the surface is removed; the method of removing excess aqueous solution on the surface includes at least one of pouring, rolling, scraping, air knife blowing or natural drying.

8. The method for preparing a high-flux, anti-fouling, loose nanofiltration membrane as described in claim 3, characterized in that, In step S3, the aromatic polyacrylamide chloride monomer has at least two acrylamide chloride groups on its molecule; and / or The aromatic polyacrylic chloride monomer is selected from at least one of isophthaloyl chloride, terephthaloyl chloride, trimesoyl chloride, or biphenyl chloride; and / or The organic phase solution contains aromatic polyacrylamide chloride monomers at a mass concentration of 0.02 wt% to 0.20 wt%; and / or The interfacial polymerization reaction takes 10-120 seconds; and / or The organic solvent in the organic phase solution is selected from at least one of petroleum ether, n-hexane, cyclohexane, n-heptane, n-decane, n-dodecane, toluene, or xylene.

9. The method for preparing a high-flux, anti-fouling, loose nanofiltration membrane as described in claim 3, characterized in that, In step S4, the method for removing the residual organic phase solution from step S3 includes at least one of leaching, pouring, rolling, or scraping; and / or The cleaning is performed by rinsing with an organic solvent that is the same as or compatible with the organic phase solution in step S3 for 5-30 seconds; and / or The drying process is performed at 25-35°C for 1-30 minutes; and / or The soaking and post-treatment time is 12-24 hours.

10. An application of a high-flux, fouling-resistant, porous nanofiltration membrane, characterized in that, The high-flux anti-fouling loose nanofiltration membrane prepared by the preparation method of the high-flux anti-fouling loose nanofiltration membrane according to any one of claims 1 to 2 or any one of claims 3 to 9 can be used in the treatment of high-salt wastewater in textile printing and dyeing, dye concentration and recovery, brine reuse, wastewater decolorization and desalination, organic / inorganic salt separation or industrial water resource treatment.

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