Anti-pollution composite nanofiltration membrane, preparation method and application thereof

Abstract

The application belongs to the technical field of water treatment membrane materials, and particularly relates to an anti-pollution composite nanofiltration membrane and a preparation method and application thereof. The nanofiltration membrane comprises a porous base film and a polyamide separation layer formed on the upper surface of the porous base film; the polyamide separation layer is formed by interfacial polymerization of water-phase monomer 8-amino-1-naphthol-3,6-disulfonic acid monosodium salt and organic-phase monomer, so that the polyamide separation layer has a screening effect and a Donnan exclusion effect; and the chemical bonding and physical embedding effect formed by interfacial polymerization between the porous base film and the polyamide separation layer are combined. The porous base film is used as a substrate, the chemical bonding and physical embedding effect formed by interfacial polymerization form a polyamide separation layer with high hydrophilicity, strong negative charge and loose structure on the porous base film, and based on the accurate screening effect and Donnan exclusion effect of the polyamide separation layer, efficient selective separation of natural organic matter and mineral salt is realized.

Description

Technical Field

[0001] This invention belongs to the field of water treatment membrane material technology, specifically relating to an antifouling composite nanofiltration membrane, its preparation method, and its application. Background Technology

[0002] In recent years, the public's demand for high-quality drinking water has been increasing. This water not only needs to meet safety standards but also needs to retain beneficial mineral ions. In the field of drinking water treatment, conventional processes commonly use chlorination disinfection to effectively remove pathogenic microorganisms and natural organic pollutants (NOMs). However, when NOMs react with commonly used disinfectants such as chlorine, ozone, or chlorine dioxide, more than 700 different disinfection byproducts (DBPs) are generated. Epidemiological studies have confirmed that human exposure to DBPs may pose serious health risks due to their toxicity, mutagenicity, and carcinogenicity. Furthermore, NOMs can form complexes with heavy metals and metals such as aluminum and iron, thereby increasing the concentration and migration of these metals in water. Therefore, efficient NOM removal is crucial for controlling DBP formation and ensuring the safety and health of drinking water. Nanofiltration technology, due to its low energy consumption and simple operation, is considered a key technology for producing high-quality drinking water. However, traditional polyamide nanofiltration membranes suffer from an inherent contradiction of "selectivity-permeability" conflict. More notably, these membranes exhibit high rejection rates for both NOM and beneficial mineral ions, which helps ensure water quality safety but also makes efficient separation of natural organic matter and minerals difficult. Furthermore, existing nanofiltration membranes generally suffer from low permeability, poor selectivity, and weak antifouling performance, severely limiting their practical application in water treatment. Therefore, developing nanofiltration membranes capable of simultaneously achieving high NOM rejection, low mineral rejection, and high water flux has become an important research direction and technological challenge in this field.

[0003] Currently, the industrial preparation of nanofiltration membranes mainly relies on the interfacial polymerization process of piperazine and trimesoyl chloride. While this technology is relatively mature, it has certain drawbacks: the high reactivity of piperazine monomers and their rapid diffusion rate in the aqueous phase lead to a violent and difficult-to-precise interfacial polymerization process, ultimately resulting in a polyamide separation layer with high crosslinking density, a dense structure, and considerable thickness, and generally high surface roughness. Although this type of traditional nanofiltration membrane has good retention capacity for natural organic matter, it also results in extremely low water permeability and the rejection of beneficial mineral ions such as sodium. + Mg 2+ Ca 2+ The excessive retention of certain substances not only leads to high system energy consumption but also results in severe mineral loss in the effluent, resulting in unsatisfactory taste and health benefits. This fails to meet the requirements for high-quality drinking water treatment and severely limits its practical application in the field of high-quality drinking water.

[0004] In existing technologies, the preparation of nanofiltration membranes with low salt rejection rates often involves interfacial polymerization of aqueous amine monomers containing sulfonic acid groups with trimesoyl chloride (TMC). For example, amine sulfonates with flexible aliphatic chains, such as N-aminoethylpiperazine propanesulfonate, are used, and their molecules contain multiple highly reactive amine groups. However, an inherent drawback of such monomers is that these highly reactive amine groups tend to undergo vigorous cross-linking reactions with TMC, easily forming an overly dense polyamide network. To achieve the low salt rejection target, extremely stringent control of reaction conditions is necessary to "suppress" this excessive cross-linking. The resulting membrane structure is porous and unstable, often making it difficult to achieve a good balance between permeability, selectivity, and antifouling properties. Summary of the Invention

[0005] The purpose of this invention is to provide an antifouling composite nanofiltration membrane, its preparation method, and its application. Using a porous membrane as a substrate, a polyamide separation layer with high hydrophilicity, strong negative charge, and a loose structure is formed in the porous membrane through interfacial polymerization, chemical bonding, and physical embedding. Based on the precise sieving effect and Dornan repulsion effect of the polyamide separation layer, highly efficient selective separation of NOM and mineral salts is achieved.

[0006] The present invention solves the above-mentioned technical problems through the following technical solutions.

[0007] The first objective of this invention is to provide an antifouling composite nanofiltration membrane, the nanofiltration membrane comprising a porous base membrane and a polyamide separation layer formed on the upper surface of the porous base membrane; the polyamide separation layer is formed by interfacial polymerization of an aqueous monomer 8-amino-1-naphthol-3,6-disulfonic acid monosodium salt and an organic monomer, thereby giving the polyamide separation layer a sieving effect and a Donnan repulsion effect; the porous base membrane and the polyamide separation layer are combined by chemical bonding and physical intercalation formed by interfacial polymerization.

[0008] In this invention, the 8-amino-1-naphthol-3,6-disulfonic acid monosodium salt monomer used, abbreviated as ANDSA, has the following structural formula:

[0009] .

[0010] ANDSA is an aromatic monomer containing one amino group, one phenolic hydroxyl group, and two sulfonic acid groups. The sulfonic acid groups possess several advantages, such as high hydrophilicity, strong acidity, and a low tendency to complex with divalent cations. These properties work together to enhance the surface hydrophilicity of the membrane while imparting a strong negative charge. By using ANDSA monomers instead of traditional piperazine monomers for interfacial polymerization, the inherent low reactivity and strong hydrophilicity of ANDSA molecules significantly regulate and optimize the film formation process and separation layer properties. The slow diffusion rate of its monomers in the aqueous phase makes the interfacial polymerization reaction more mild and controllable, ultimately producing an ultrathin polyamide functional layer with a smooth surface and loose structure. Simultaneously, the hydrophilic and ionizing groups, such as the sulfonic acid groups, carried by ANDSA introduce a persistent strong negative charge into the separation layer. This property generates a strong electrostatic repulsion against naturally negatively charged NOMs in water, achieving efficient retention; while the loose membrane structure and suitable pore size allow small molecule mineral ions to permeate freely.

[0011] This invention, based on a rigid planar naphthalene ring structure, creatively selects ANDSA molecules as the sole or key aqueous functional monomer. This rigid aromatic ring, as an incompressible and non-foldable structural unit, is directly introduced into the polyamide network backbone during interfacial polymerization, fundamentally preventing the close packing of polymer chains and providing a skeletal basis for the formation of open and stable channels. Through interfacial polymerization of ANDSA molecules and organic phase monomers, this invention designs a unique "high-activity, complementary-activity" reaction site system: containing only one highly active primary amine group to initiate and dominate the film-forming reaction; simultaneously introducing a phenolic hydroxyl group as a complementary and regulatory nucleophilic site. This design "self-limits" the chemical reaction from its source: it ensures the effective formation of continuous films, and due to the combination of the number and activity of its reaction sites, it actively and naturally guides the formation of a polymer network with moderate cross-linking and intrinsically loose structure, without relying on external conditions to strongly inhibit excessive reactions.

[0012] This invention is based on the formation of a polyamide separation layer through interfacial polymerization of the aqueous monomer ANDSA and the organic monomer. The two sulfonic acid groups and one phenolic hydroxyl group of the ANDSA molecule are directly and firmly bonded to a rigid naphthalene ring backbone. This "rigid anchoring" method ensures the efficient and stable exposure of hydrophilic groups, providing a guarantee for durable and strong surface hydrophilicity and antifouling properties. This gives the polyamide separation layer a sieving effect, a Donnan repulsion effect, and both hydrophilicity and antifouling properties. Sieving effect: Through the mild interfacial polymerization reaction between the ANDSA monomer and the organic monomer, a polyamide separation layer with a relatively loose cross-linked network structure and relatively large inherent pores is formed. This structure allows mineral salt ions such as Ca²⁺ to pass through. 2+ Mg 2+Beneficial ions can pass through while NOM molecules with larger hydration radii are effectively retained. The Dornan repulsion effect: The sulfonic acid groups introduced into the ANDSA monomer molecule endow the polyamide separation layer with a permanently strong negatively charged surface. Since most NOM molecules are also negatively charged in the aquatic environment (e.g., humic acid, fulvic acid), a strong electrostatic repulsion occurs between the membrane surface and NOM, further preventing NOM from passing through the membrane pores, thus significantly enhancing the NOM rejection rate and achieving selective separation of NOM / mineral ions. Hydrophilicity and antifouling properties: The sulfonic acid and hydroxyl groups in the ANDSA monomer significantly improve the hydrophilicity of the separation layer. This allows water molecules to pass through the membrane pores quickly with lower resistance, achieving high water flux. The strong hydrophilicity and the strong negative charge of the membrane surface work together to effectively reduce the adsorption and deposition of hydrophobic organic matter and negatively charged pollutants on the membrane surface, thus giving the membrane excellent antifouling properties.

[0013] In some embodiments, the base membrane is made of a porous hydrophilic material. In a preferred embodiment, the base membrane is made of polyethersulfone, polysulfone, etc., with a molecular weight cutoff of 100 kDa to 150 kDa.

[0014] A second objective of this invention is to provide a method for preparing the aforementioned antifouling composite nanofiltration membrane, comprising the following steps:

[0015] S1. Cover the surface of the porous base membrane with an aqueous monomer solution and allow it to stand for immersion so that the 8-amino-1-naphthol-3,6-disulfonic acid monosodium salt is adsorbed into the pores and surface of the porous base membrane.

[0016] In this invention, the concentration of 8-amino-1-naphthol-3,6-disulfonic acid monosodium salt in the aqueous monomer solution is 0.1 wt.% to 2.5 wt.%, wherein the solvent used in the aqueous monomer solution is water, and the pH of the aqueous monomer solution is adjusted to 11.0 by a strong base to enhance the solubility and reactivity of the monomer.

[0017] In this invention, the porous base membrane needs to be soaked in ultrapure water before use to remove oxides, stains, etc. from the membrane surface.

[0018] In this invention, the covering method is as follows: the aqueous monomer solution is evenly poured onto the surface of the PES base membrane, ensuring that the solution completely covers the membrane surface, and allowed to stand for 2 to 5 minutes to allow ANDSA molecules to be fully adsorbed into the pores and surface of the base membrane. After the standing and impregnation is completed, excess aqueous solution remaining on the membrane surface is removed until there are no obvious water stains or droplets on the membrane surface.

[0019] S2. Then cover with the organic phase monomer solution, and allow the 8-amino-1-naphthol-3,6-disulfonic acid monosodium salt and the organic phase monomer to undergo interfacial polymerization at room temperature to form a polyamide separation layer, thus obtaining the antifouling composite nanofiltration membrane.

[0020] In this invention, the organic phase is a monomer solution containing acyl chloride groups. In a preferred embodiment, the organic phase is a trimesoyl chloride / hexane solution or an isophthaloyl chloride / hexane solution. The covering method is as follows: the trimesoyl chloride / hexane solution is rapidly and uniformly poured onto the surface of the base film treated with ANDSA solution, so that it completely covers the substrate and undergoes an interfacial polymerization reaction with the ANDSA monomer in the aqueous phase. The reaction lasts for 2 min to 5 min, forming a polyamide separation layer. The concentration of the organic phase monomer in the organic phase monomer solution is 0.3 wt.% to 0.5 wt.% to increase the separation selectivity for NOM and mineral ions.

[0021] In this invention, the volume ratio of the organic phase monomer solution to the aqueous phase monomer solution is 1 to 5:1. After the interfacial polymerization reaction is completed, the membrane is removed and rinsed three times with sufficient n-hexane solvent to completely terminate the reaction and remove unreacted TMC monomers and byproducts. Then, it is heat-treated at 60°C to 80°C for 5 to 10 minutes to completely dry it and stabilize its structure, thus obtaining an antifouling composite nanofiltration membrane.

[0022] This invention, by precisely controlling the concentration of aqueous monomers and reaction conditions, can form a polyamide separation layer with high hydrophilicity, strong negative charge, and loose structure. The thickness of the polyamide separation layer is determined by the concentration of 8-amino-1-naphthol-3,6-disulfonic acid monosodium salt and organic monomers, as well as the reaction time, thereby achieving efficient selective separation of NOM from mineral salts.

[0023] The third objective of this invention is to provide the application of the above-mentioned antifouling composite nanofiltration membrane in the purification of drinking water.

[0024] This invention successfully overcomes the "selectivity-permeability" trade-off effect. The ANDSA membrane, while achieving NOM retention, boasts a water flux approximately six times that of traditional PIP membranes, and also effectively retains beneficial mineral ions such as Ca. 2+ Mg 2+ With an extremely low rejection rate (<15%), the membrane achieves a balance between high throughput, high selectivity, and healthy drinking water. The sulfonic acid groups introduced into the ANDSA monomer endow the membrane with permanent superhydrophilicity and strong negative charge. This not only enhances NOM rejection through electrostatic repulsion but also endows the membrane with inherent antifouling capabilities, resulting in an FRR of 84.06% after cleaning, significantly reducing maintenance costs. The sterically hindered naphthalene ring structure and mild reactivity of ANDSA facilitate the formation of a loose, smooth, and ultra-thin separation layer, which is the structural basis for its high throughput and high selectivity.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] This invention provides an antifouling composite nanofiltration membrane, comprising a porous base membrane and a polyamide separation layer formed on the surface of the porous base membrane. The polyamide separation layer is formed by interfacial polymerization of an aqueous monomer, 8-amino-1-naphthol-3,6-disulfonic acid monosodium salt, and an organic monomer, giving the polyamide separation layer a sieving effect and a Donnan repulsion effect. The porous base membrane and the polyamide separation layer are combined through chemical bonding and physical intercalation formed during the interfacial polymerization process. This invention uses ANDSA monomer instead of traditional piperazine monomer for interfacial polymerization. Leveraging the inherent low reactivity and strong hydrophilicity of ANDSA molecules, the film formation process and separation layer properties are significantly controlled and optimized. The monomer diffuses slowly in the aqueous phase, making the interfacial polymerization reaction more mild and controllable. This ultimately produces an ultrathin polyamide functional layer with a smooth surface and loose structure, giving the polyamide separation layer a sieving effect, a Donnan repulsion effect, and hydrophilicity and antifouling properties. It also exhibits a strong electrostatic repulsion effect on naturally negatively charged NOM in water, achieving efficient retention.

[0027] This invention achieves highly efficient selective separation of NOM and mineral salts by precisely controlling the concentration of monomers in the aqueous phase and the reaction conditions, thus forming a polyamide separation layer with high hydrophilicity, strong negative charge, and a loose structure. It successfully overcomes the "selectivity-permeability" trade-off effect; the ANDSA membrane achieves NOM retention of >90% while maintaining a water flux approximately six times that of traditional PIP membranes, and also effectively separates beneficial mineral ions such as Ca. 2+ Mg 2+ With an extremely low retention rate of less than 15%, it achieves a balance between high throughput, high selectivity, and healthy drinking water. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the antifouling composite nanofiltration membrane of the present invention.

[0029] Figure 2 The images show the water contact angles of the composite nanofiltration membranes prepared in Examples 1 to 5 and Comparative Example 1 of this invention.

[0030] Figure 3 The diagram shows the electrokinetic potential of the composite nanofiltration membranes prepared in Example 2 and Comparative Example 1 of this invention.

[0031] Figure 4 The images show the microstructure of the composite nanofiltration membranes prepared in Examples 1 to 3 and Comparative Example 1 of this invention.

[0032] Figure 5 The graph shows the rejection rates of the composite nanofiltration membranes prepared in Examples 1 to 5 and Comparative Example 1 of this invention.

[0033] Figure 6 The diagram shows the permeability of the composite nanofiltration membranes prepared in Examples 1 to 5 and Comparative Example 1 of this invention.

[0034] Figure 7 The diagram shows the permeability of the composite nanofiltration membranes prepared in Examples 1 to 5 and Comparative Example 2 of this invention.

[0035] Figure 8 The graph shows the rejection rate of the composite nanofiltration membranes prepared in Example 2 and Comparative Example 2 of this invention.

[0036] Figure 9 This is a diagram showing the separation of mineral ions and HA mixed solution by the composite nanofiltration membrane prepared in Example 2 of the present invention.

[0037] Figure 10 The diagram shows the antifouling properties of the composite nanofiltration membranes prepared in Example 2 and Comparative Examples 1 to 2 of this invention. Figure 10 In Figure a, there is a comparison diagram between Example 2 and Comparative Example 1, and in Figure b, there is a comparison diagram between Example 2 and Comparative Example 2. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0039] The following specific examples will provide further explanation.

[0040] Example 1

[0041] A method for preparing an antifouling composite nanofiltration membrane includes the following steps:

[0042] S1. Provide a porous base membrane made of polyethersulfone with a molecular weight cutoff of 150 kDa. Immerse the porous base membrane in ultrapure water to remove oxides, stains and other contaminants from the membrane surface.

[0043] S2. Dissolve 8-amino-1-naphthol-3,6-disulfonic acid monosodium salt, i.e., ANDSA monomer, in deionized water to prepare an aqueous solution with a mass concentration of 0.1 wt.%. Adjust the pH of the aqueous solution to 11.0 using NaOH solution to enhance the solubility and reactivity of the aqueous monomer. Weigh 50 mL of the aqueous solution and pour it evenly onto the surface of the porous membrane, ensuring that the solution completely covers the membrane surface. Let it stand for 3 minutes to allow ANDSA molecules to fully adsorb onto the membrane pores and surface. After standing and soaking, remove any excess aqueous solution remaining on the membrane surface until there are no obvious water stains or droplets on the membrane surface.

[0044] S3. Weigh 50 mL of 0.3 wt.% trimesoyl chloride n-hexane solvent, i.e., TMC / n-hexane solution, and pour it quickly and evenly onto the surface of the base film treated with the aqueous solution at room temperature, so that it completely covers the base film and reacts with the ANDSA monomer in the aqueous phase for 2 min to form a polyamide separation layer.

[0045] S4. After the interfacial polymerization reaction is complete, remove the membrane and rinse the membrane surface three times with sufficient n-hexane solvent to completely terminate the reaction and remove unreacted TMC monomers and byproducts. Then, heat-treat at 60°C for 10 minutes to completely dry and stabilize the structure, obtaining the antifouling composite nanofiltration membrane. The structure of the antifouling composite nanofiltration membrane is as follows: Figure 1 As shown, Figure 1 In the diagram, 1 represents the porous base membrane, and 2 represents the polyamide separation layer.

[0046] Example 2

[0047] A method for preparing an antifouling composite nanofiltration membrane includes the following steps:

[0048] S1. Provide a porous base membrane made of polyethersulfone with a molecular weight cutoff of 150 kDa. Immerse the porous base membrane in ultrapure water to remove oxides, stains and other contaminants from the membrane surface.

[0049] S2. Dissolve ANDSA monomer in deionized water to prepare an aqueous solution with a mass concentration of 0.5 wt.%. Adjust the pH of the aqueous solution to 11.0 using NaOH solution to enhance the solubility and reactivity of the monomer. Weigh 50 mL of the aqueous solution and pour it evenly onto the surface of the porous membrane, ensuring that the solution completely covers the membrane surface. Let it stand for 3 minutes to allow ANDSA molecules to fully adsorb onto the membrane pores and surface. After standing and soaking, remove any excess aqueous solution remaining on the membrane surface until there are no obvious water stains or droplets on the membrane surface.

[0050] S3. Weigh 50 mL of a 0.3 wt.% TMC / n-hexane solution and pour it quickly and evenly onto the surface of the base film treated with the aqueous solution at room temperature, so that it completely covers the base film and reacts with the ANDSA monomer in the aqueous phase for 2 min to form a polyamide separation layer.

[0051] S4. After the interfacial polymerization reaction is complete, remove the membrane and rinse the membrane surface three times with sufficient n-hexane solvent to completely terminate the reaction and remove unreacted TMC monomers and byproducts. Then, heat-treat at 60°C for 10 minutes to completely dry and stabilize the structure, obtaining the antifouling composite nanofiltration membrane. The structure of the antifouling composite nanofiltration membrane is as follows: Figure 1 As shown, Figure 1 In the diagram, 1 represents the porous base membrane, and 2 represents the polyamide separation layer.

[0052] Example 3

[0053] A method for preparing an antifouling composite nanofiltration membrane includes the following steps:

[0054] S1. Provide a porous base membrane made of polyethersulfone with a molecular weight cutoff of 150 kDa. Immerse the porous base membrane in ultrapure water to remove oxides, stains and other contaminants from the membrane surface.

[0055] S2. Dissolve ANDSA monomer in deionized water to prepare an aqueous solution with a mass concentration of 1.0 wt.%. Adjust the pH of the aqueous solution to 11.0 using NaOH solution to enhance the solubility and reactivity of the monomer. Weigh 50 mL of the aqueous solution and pour it evenly onto the surface of the porous membrane, ensuring that the solution completely covers the membrane surface. Let it stand for 3 minutes to allow ANDSA molecules to fully adsorb onto the membrane pores and surface. After standing and soaking, remove any excess aqueous solution remaining on the membrane surface until there are no obvious water stains or droplets on the membrane surface.

[0056] S3. Weigh 50 mL of a 0.3 wt.% TMC / n-hexane solution and pour it quickly and evenly onto the surface of the base film treated with the aqueous solution at room temperature, so that it completely covers the base film and reacts with the ANDSA monomer in the aqueous phase for 2 min to form a polyamide separation layer.

[0057] S4. After the interfacial polymerization reaction is complete, remove the membrane and rinse the membrane surface three times with sufficient n-hexane solvent to completely terminate the reaction and remove unreacted TMC monomers and byproducts. Then, heat-treat at 60°C for 10 minutes to completely dry and stabilize the structure, obtaining the antifouling composite nanofiltration membrane. The structure of the antifouling composite nanofiltration membrane is as follows: Figure 1 As shown, Figure 1 In the diagram, 1 represents the porous base membrane, and 2 represents the polyamide separation layer.

[0058] Example 4

[0059] A method for preparing an antifouling composite nanofiltration membrane includes the following steps:

[0060] S1. Provide a porous base membrane made of polyethersulfone with a molecular weight cutoff of 150 kDa. Immerse the porous base membrane in ultrapure water to remove oxides, stains and other contaminants from the membrane surface.

[0061] S2. Dissolve ANDSA monomer in deionized water to prepare an aqueous solution with a mass concentration of 1.5 wt.%. Adjust the pH of the aqueous solution to 11.0 using NaOH solution to enhance the solubility and reactivity of the monomer. Weigh 50 mL of the aqueous solution and pour it evenly onto the surface of the porous membrane, ensuring that the solution completely covers the membrane surface. Let it stand for 3 minutes to allow ANDSA molecules to fully adsorb onto the membrane pores and surface. After standing and soaking, remove any excess aqueous solution remaining on the membrane surface until there are no obvious water stains or droplets on the membrane surface.

[0062] S3. Weigh 50 mL of a 0.3 wt.% TMC / n-hexane solution and pour it quickly and evenly onto the surface of the base film treated with the aqueous solution at room temperature, so that it completely covers the base film and reacts with the ANDSA monomer in the aqueous phase for 2 min to form a polyamide separation layer.

[0063] S4. After the interfacial polymerization reaction is complete, remove the membrane and rinse the membrane surface three times with sufficient n-hexane solvent to completely terminate the reaction and remove unreacted TMC monomers and byproducts. Then, heat-treat at 60°C for 10 minutes to completely dry and stabilize the structure, obtaining the antifouling composite nanofiltration membrane. The structure of the antifouling composite nanofiltration membrane is as follows: Figure 1 As shown, Figure 1 In the diagram, 1 represents the porous base membrane, and 2 represents the polyamide separation layer.

[0064] Example 5

[0065] A method for preparing an antifouling composite nanofiltration membrane includes the following steps:

[0066] S1. Provide a porous base membrane made of polyethersulfone with a molecular weight cutoff of 150 kDa. Immerse the porous base membrane in ultrapure water to remove oxides, stains and other contaminants from the membrane surface.

[0067] S2. Dissolve ANDSA monomer in deionized water to prepare an aqueous solution with a mass concentration of 2.5 wt.%. Adjust the pH of the aqueous solution to 11.0 using NaOH solution to enhance the solubility and reactivity of the monomer. Weigh 50 mL of the aqueous solution and pour it evenly onto the surface of the porous membrane, ensuring that the solution completely covers the membrane surface. Let it stand for 3 minutes to allow ANDSA molecules to fully adsorb onto the membrane pores and surface. After standing and soaking, remove any excess aqueous solution remaining on the membrane surface until there are no obvious water stains or droplets on the membrane surface.

[0068] S3. Weigh 50 mL of a 0.3 wt.% TMC / n-hexane solution and pour it quickly and evenly onto the surface of the base film treated with the aqueous solution at room temperature, so that it completely covers the base film and reacts with the ANDSA monomer in the aqueous phase for 2 min to form a polyamide separation layer.

[0069] S4. After the interfacial polymerization reaction is complete, remove the membrane and rinse the membrane surface three times with sufficient n-hexane solvent to completely terminate the reaction and remove unreacted TMC monomers and byproducts. Then, heat-treat at 60°C for 10 minutes to completely dry and stabilize the structure, obtaining the antifouling composite nanofiltration membrane. The structure of the antifouling composite nanofiltration membrane is as follows: Figure 1 As shown, Figure 1 In the diagram, 1 represents the porous base membrane, and 2 represents the polyamide separation layer.

[0070] Comparative Example 1

[0071] A method for preparing a composite nanofiltration membrane, differing from Example 2 in that the aqueous phase monomer is piperazine, abbreviated as PIP, and includes the following steps:

[0072] S1. Provide a porous base membrane made of polyethersulfone with a molecular weight cutoff of 150 kDa. Immerse the porous base membrane in ultrapure water to remove oxides, stains and other contaminants from the membrane surface.

[0073] S2. Dissolve the PIP monomer in deionized water to prepare an aqueous solution with a mass concentration of 0.3 wt.%. Adjust the pH of the aqueous solution to 11.0 using NaOH solution to enhance the solubility and reactivity of the aqueous monomer. Weigh 50 mL of the aqueous solution and pour it evenly onto the surface of the porous membrane, ensuring that the solution completely covers the membrane surface. Let it stand for 3 minutes to soak. After the soaking period, remove any excess aqueous solution remaining on the membrane surface until there are no obvious water stains or droplets on the membrane surface.

[0074] S3. Weigh 50 mL of a 0.3 wt.% TMC / n-hexane solution and pour it quickly and evenly onto the surface of the base film treated with the aqueous solution at room temperature, so that it completely covers the film and reacts with the PIP monomer in the aqueous phase for 2 min to form a polyamide separation layer.

[0075] S4. After the interfacial polymerization reaction is completed, remove the membrane and rinse the membrane surface three times with sufficient n-hexane solvent to completely terminate the reaction and remove unreacted TMC monomers and byproducts. Then, heat treat it at 60°C for 10 minutes to obtain the composite nanofiltration membrane.

[0076] Comparative Example 2

[0077] A method for preparing a composite nanofiltration membrane includes the following steps:

[0078] S1. Provide a porous base membrane made of polyethersulfone with a molecular weight cutoff of 150 kDa. Immerse the porous base membrane in ultrapure water to remove oxides, stains and other contaminants from the membrane surface.

[0079] S2. Dissolve N-aminoethylpiperazine propanesulfonate monomer in deionized water to prepare an aqueous solution with a mass concentration of 0.5 wt.%. Adjust the pH of the aqueous solution to 11.0 using NaOH solution to enhance the solubility and reactivity of the aqueous monomer. Weigh 50 mL of the aqueous solution and pour it evenly onto the surface of the porous membrane, ensuring that the solution completely covers the membrane surface. Let it stand for 3 minutes to allow N-aminoethylpiperazine propanesulfonate to be fully adsorbed into the pores and surface of the membrane. After standing and soaking, remove any excess aqueous solution remaining on the membrane surface until there are no obvious water stains or droplets on the membrane surface.

[0080] S3. Weigh 50 mL of 0.3 wt.% TMC / n-hexane solution and pour it quickly and evenly onto the surface of the base film treated with the aqueous solution at room temperature, so that it completely covers the base film and reacts with N-aminoethylpiperazine propanesulfonate in the aqueous phase for 2 min to form a polyamide separation layer.

[0081] S4. After the interfacial polymerization reaction is completed, remove the membrane and rinse the membrane surface three times with sufficient n-hexane solvent to completely terminate the reaction and remove unreacted TMC monomers and byproducts. Then, heat-treat it at 60°C for 10 minutes to completely dry it and stabilize its structure to obtain a composite nanofiltration membrane.

[0082] The performance of the composite nanofiltration membranes prepared in Examples 1 to 5 and Comparative Examples 1 to 2 was tested, and the results are shown below.

[0083] Among the tests, mineral ion and NOM rejection rates were tested using a cross-flow nanofiltration device. Single solutions of CaCl2 and MgSO4 were selected as representative mineral salts, each with a concentration of 2000 mg / L; humic acid solution was selected as a representative NOM, with a concentration of 10 mg / L. The operating pressure was 4 bar, conducted at room temperature, and with humidity <50%.

[0084] Permeability test: A cross-flow nanofiltration device was used, with deionized water as the influent, and the operating pressure was 4 bar, conducted at room temperature.

[0085] NOM and mineral ion separation test: A cross-flow nanofiltration device was used. The operating pressure was 4 bar and the humidity was <50%. The rejection rate of the nanofiltration membrane for a mixed solution of 2.0 g / L MgSO4 and 10 mg / L HA was tested to analyze the separation selectivity.

[0086] Antifouling test: A cross-flow nanofiltration unit was used. The operating pressure was 4 bar, and the humidity was <50%. The water flux of the nanofiltration membrane to a mixed solution of 1.0 g / L CaCl2 and 50 mg / L HA after three cycles of fouling-washing was tested to analyze its antifouling properties.

[0087] Figure 2 The images show the water contact angles of the composite nanofiltration membranes prepared in Examples 1 to 5 and Comparative Example 1 of this invention. Figure 2 As shown, compared to Comparative Example 1, the composite nanofiltration membranes prepared in Examples 1 to 5 have smaller water contact angles and stronger hydrophilicity.

[0088] Figure 3 This is a potentiodynamic diagram of the composite nanofiltration membranes prepared in Example 2 and Comparative Example 1 of the present invention. Figure 3 As shown, compared to Comparative Example 1, the composite nanofiltration membrane prepared in Example 2 has a lower negative charge value and a stronger Donnan effect repulsion.

[0089] Figure 4 These are microstructure diagrams of the composite nanofiltration membranes prepared in Examples 1 to 3 and Comparative Example 1 of the present invention. Figure 4 As shown, compared to Comparative Example 1, the composite nanofiltration membranes prepared in Examples 1 to 3 have smoother surfaces.

[0090] Figure 5 This is a graph showing the rejection rates of the composite nanofiltration membranes prepared in Examples 1 to 5 and Comparative Example 1 of the present invention. Figure 5 As shown, compared to Comparative Example 1, the composite nanofiltration membranes prepared in Examples 1 to 5 showed a slight decrease in HA retention at low concentrations, but a significant decrease at high concentrations. The HA retention rates of the composite nanofiltration membranes prepared in Examples 1 to 5 were all above 92%. Furthermore, the retention rates of CaCl2 and MgSO4 decreased with increasing amounts of the regulator, but remained below 15%, while Comparative Example 1 showed excessively high retention rates of CaCl2 and MgSO4, at 68.57% and 89.79%, respectively.

[0091] Figure 6 The images show the permeability of the composite nanofiltration membranes prepared in Examples 1 to 5 and Comparative Example 1 of this invention. Figure 6 As shown, using ANDSA as a new monomer significantly improves the permeability of nanofiltration membranes, increasing the water flux from 36.48 L / m³. 2 • h • bar increased to 117.34 L / m 2 • h·bar, water flux of Example 2: 62.40 L / m 2 The h·bar is 10.25 L / m² for Comparative Example 1. 2 6.08 times that of h bar.

[0092] Figure 7 The images show the permeability of the composite nanofiltration membranes prepared in Examples 1 to 5 and Comparative Example 2 of this invention. Figure 7As shown, because the separation layer is an intrinsically loose network constructed from a rigid framework, its water permeation channels are more unobstructed. The water flux of the composite nanofiltration membrane in Example 2 of this invention is 62.40 L / m³. 2 The h·bar is 6.0 L / m² for Comparative Example 2. 2 6.24 times that of h·bar.

[0093] Figure 8 This is a graph showing the rejection rate of the composite nanofiltration membranes prepared in Example 2 and Comparative Example 2 of the present invention. Figure 2 As shown, the composite nanofiltration membrane of Comparative Example 2 has a CaCl2 rejection rate of 55.4%, while the composite nanofiltration membrane of Example 2 has a rejection rate of only 8.2%.

[0094] Figure 9 This is a separation diagram of a mixed solution of mineral ions and HA prepared by the composite nanofiltration membrane in Example 2 of the present invention. Figure 9 As shown, using ANDSA as a new monomer, the retention rate of HA was 82.81%, while the retention rate of CaCl2 was 10.85%, perfectly achieving the efficient separation of NOM and beneficial minerals.

[0095] Figure 10 The diagram shows the antifouling properties of the composite nanofiltration membranes prepared in Example 2 and Comparative Examples 1 to 2 of this invention. Figure 10 Figure a is a comparison diagram of Example 2 and Comparative Example 1, and figure b is a comparison diagram of Example 2 and Comparative Example 2. Figure 10 As shown, after three contamination-cleaning cycles, the flux recovery rate (FRR) remained above 84.06%, while the FRR of Comparative Example 1 was only 73.52% and the FRR of Comparative Example 2 was only 72%, proving that its surface hydrophilicity and strong negative charge effectively inhibited the formation of irreversible contamination.

[0096] In summary, this invention uses a porous membrane as a substrate and forms a polyamide separation layer with high hydrophilicity, strong negative charge, and a loose structure based on the chemical bonding and physical embedding effect of interfacial polymerization. By introducing ANDSA, a novel functional monomer with the triple characteristics of a "rigid planar framework," "one high- and one complementary reaction site," and "multiple rigidly anchored hydrophilic groups," this invention pioneers a new path for constructing high-performance nanofiltration membranes from the fundamental design of materials chemistry. The composite nanofiltration membrane exhibits a triple synergistic enhancement effect of "high permeability, high selectivity, and high antifouling." Based on the precise sieving effect and Donald's repulsion effect of the polyamide separation layer, highly efficient selective separation of NOM and mineral salts is achieved. Although the cost of ANDSA monomer is slightly higher than that of conventional piperazine monomers (market price: piperazine monomer is 616 yuan / kg, ANDSA monomer is 952 yuan / kg), this invention achieves a significant improvement. However, it offers greater economic benefits, such as energy saving: high flux reduces system operating energy consumption and saves electricity costs; reduced energy consumption: excellent antifouling properties extend cleaning cycles, saving on chemical and labor costs; and high added value: producing healthy, high-quality drinking water with "retained minerals and low organic matter content," significantly enhancing product value. These performance advantages and reduced life-cycle costs give it significant commercial value and market competitiveness. It not only significantly improves the membrane's antifouling performance and operating flux but also achieves efficient separation of NOM and beneficial minerals, making it particularly suitable for the energy-efficient and healthy production of high-quality drinking water.

[0097] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described here to avoid redundancy. Although preferred embodiments of the invention have been described, those skilled in the art, once they understand the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this invention.

[0098] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A fouling-resistant composite nanofiltration membrane, characterized in that, The nanofiltration membrane includes a porous base membrane and a polyamide separation layer formed on the upper surface of the porous base membrane; The polyamide separation layer is formed by interfacial polymerization of aqueous monomer 8-amino-1-naphthol-3,6-disulfonic acid monosodium salt and organic monomer, giving the polyamide separation layer a sieving function and a repulsive effect. The porous base membrane and the polyamide separation layer are combined through chemical bonding and physical embedding formed by interfacial polymerization.

2. The antifouling composite nanofiltration membrane according to claim 1, characterized in that, The porous base membrane is made of polyethersulfone or polysulfone, with a molecular weight cutoff of 100 kDa to 150 kDa.

3. A method for preparing the antifouling composite nanofiltration membrane according to claim 1 or claim 2, characterized in that, Includes the following steps: An aqueous monomer solution was applied to the surface of a porous membrane, and the membrane was allowed to stand and soak to allow the sodium 8-amino-1-naphthol-3,6-disulfonic acid monosodium salt to be adsorbed onto the pores and surface of the porous membrane. Then, an organic phase monomer solution is covered, and 8-amino-1-naphthol-3,6-disulfonic acid monosodium salt and organic phase monomer are subjected to interfacial polymerization at room temperature to form a polyamide separation layer, thus obtaining an antifouling composite nanofiltration membrane.

4. The method for preparing the antifouling composite nanofiltration membrane according to claim 3, characterized in that, The concentration of 8-amino-1-naphthol-3,6-disulfonic acid monosodium salt in the aqueous monomer solution was 0.1 wt.% to 2.5 wt.%.

5. The method for preparing the antifouling composite nanofiltration membrane according to claim 3, characterized in that, The concentration of organic monomers in the organic monomer solution is 0.3 wt.% to 0.5 wt.%.

6. The method for preparing the antifouling composite nanofiltration membrane according to claim 5, characterized in that, The organic phase monomer is pyromellitic acid chloride or isophthaloyl chloride, and the solvent for the organic phase monomer solution is n-hexane.

7. The method for preparing the antifouling composite nanofiltration membrane according to claim 3, characterized in that, The pH of the aqueous monomer solution is 11.0, and the soaking time is 2 min to 5 min.

8. The method for preparing the antifouling composite nanofiltration membrane according to claim 3, characterized in that, The interfacial polymerization reaction takes 2 to 5 minutes. After the reaction is completed, the mixture is heat-treated at 60°C to 80°C for 5 to 10 minutes.

9. The application of the antifouling composite nanofiltration membrane according to claim 1 or claim 2 in the purification of drinking water.

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