Composite ultrafiltration membrane based on blending modification and surface modification as well as preparation method and application of composite ultrafiltration membrane

Abstract

The invention relates to the technical field of membrane separation, in particular to a composite ultrafiltration membrane based on blending modification and surface modification and a preparation method and application thereof. The method comprises the following steps: firstly, preparing a polydopamine functionalized multi-walled carbon nanotube through oxidation cross-linking auto-polymerization and adhesion of a dopamine compound in an aqueous solution; dissolving a film-forming polymer, a pore-foaming agent and the prepared polydopamine functionalized multi-walled carbon nanotube in an organic solvent, degassing, and preparing a blend film by adopting a non-solvent induced phase separation method; the prepared blended membrane is sequentially and alternately immersed in a tannic acid solution and an aluminum salt solution, a tannic acid-aluminum ion metal phenolic aldehyde network layer is formed on the surface of the blended membrane through a coordination-driven layer-by-layer self-assembly method, and the composite ultrafiltration membrane is obtained. The composite ultrafiltration membrane prepared by the invention has high flux, high selectivity and excellent anti-pollution performance, and is especially suitable for treating and recycling wastewater containing organic macromolecules such as protein, colloid and the like.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, specifically to a composite ultrafiltration membrane based on blending modification and surface modification, its preparation method, and its application. Background Technology

[0002] With global population growth and industrial development, the increasing discharge of industrial wastewater seriously endangers water environment health, exacerbates the water shortage crisis, and jeopardizes the healthy development of human society. Therefore, separation and purification technologies for wastewater treatment have gradually received widespread attention. Electroplating wastewater treatment and recycling are important ways to solve the shortage of industrial water and are also a major requirement for the green development of my country's electroplating industry. Electroplating effluent is characterized by diverse sources, large volume, complex composition, large fluctuations in water quality, and high pollution levels. Single wastewater treatment methods are ineffective, energy-intensive, costly, and have low removal rates. Therefore, finding an economical, efficient, and environmentally friendly sustainable water production technology for electroplating effluent is a pressing problem to be solved in my country's electroplating industry.

[0003] Membrane separation technology, with its advantages of simple operation and stable water quality, has received increasing attention and research in wastewater treatment applications. Ultrafiltration, as a pressure-driven physical separation process, demonstrates great application potential in water treatment due to its simple operation, low energy consumption, and lack of phase change requirement. Polyethersulfone (PES) is widely used as an ultrafiltration membrane material due to its excellent mechanical strength, thermal stability, and membrane-forming properties. However, the inherent hydrophobicity of PES leads to two key challenges in practical applications: first, the membrane surface is easily fouled by organic matter such as proteins, causing a sharp and difficult-to-recover decrease in flux, shortening membrane life; second, the prevalent "flux-selectivity trade-off" means that a high rejection rate often comes at the cost of reduced water permeate flux.

[0004] Studies have shown that hydrophilic modification of separation membranes is key to improving their antifouling ability. Currently, the main hydrophilic modification methods include blending modification and surface modification. Blending modification involves uniformly dispersing hydrophilic fillers in a dissolved or dispersed form into a casting solution, followed by coating and phase inversion methods to prepare the blended membrane. Blending modification has advantages such as a wide availability of fillers, low cost, and ease of scale-up; however, introducing new modifying materials into the existing casting solution system requires consideration of the compatibility between different polymers, which can affect phase separation and membrane pore structure during membrane formation, thus impacting the relevant performance of the ultrafiltration membrane. CN108771978 A discloses a method for preparing ultrafiltration membranes using nanocellulose crystals for blending modification. By introducing nanocellulose crystals, a modified ultrafiltration membrane is prepared, significantly improving antifouling performance and pure water flux. However, if the process control is not properly managed, the nanocellulose crystals may still agglomerate, affecting membrane uniformity. Surface modification involves altering the membrane surface after film formation to improve its properties, thereby enhancing antifouling performance and separation efficiency. However, a drawback is that modification may clog surface pores, leading to a decrease in membrane flux. CN120079271A discloses an amino acid derivative polymeric membrane material and its preparation method. This method involves copolymerizing amino acid derivatives with polyethers, spin-coating, surface modification, and crosslinking to prepare a functionalized membrane material with high selectivity, good biocompatibility, and stability. However, the surface modification strategy employed in this method carries risks such as weak adhesion between the modified layer and the base membrane, and the potential for group detachment or functional degradation during long-term use. Furthermore, this surface modification process may result in uneven modification, affecting the stability of membrane separation performance.

[0005] Therefore, current technologies have the problem that it is difficult to synergistically improve the flux, selectivity and antifouling properties of PES ultrafiltration membranes. Summary of the Invention

[0006] To address the technical problems existing in the prior art, the present invention aims to provide a composite ultrafiltration membrane based on blending modification and surface modification, its preparation method, and its application to solve the aforementioned technical problems. To address the difficulty in synergistically improving flux, selectivity, and antifouling properties of PES ultrafiltration membranes, the present invention proposes a composite ultrafiltration membrane based on blending modification and surface modification, and its preparation method. This method integrates a synergistic strategy of blending and surface modification. It constructs efficient water channels by blending polydopamine-functionalized multi-walled carbon nanotubes, and performs surface modification by combining the layer-by-layer self-assembly of tannic acid-aluminum ion metal phenolic network. This results in a composite ultrafiltration membrane with high water flux, high rejection rate, and excellent antifouling performance.

[0007] According to a first aspect of the present invention, the present invention provides a method for preparing a composite ultrafiltration membrane based on blend modification and surface modification. The method first prepares polydopamine-functionalized multi-walled carbon nanotubes by oxidative crosslinking self-polymerization of dopamine compounds in aqueous solution and their adhesion. Then, the film-forming polymer, pore-forming agent and the prepared polydopamine-functionalized multi-walled carbon nanotubes are dissolved in an organic solvent, and after degassing, a blend membrane is prepared by a non-solvent-induced phase separation method. The prepared blend membrane is sequentially and alternately immersed in tannic acid solution and aluminum salt solution, and a tannic acid-aluminum ion metal phenolic network layer is formed on the surface of the blend membrane by a coordination-driven layer-by-layer self-assembly method to obtain a composite ultrafiltration membrane.

[0008] The present invention provides a method for preparing a composite ultrafiltration membrane based on blending modification and surface modification, which specifically includes the following steps: (1) Preparation of modified nanomaterials: Carbon nanotubes are dispersed in water and dispersed evenly to obtain a dispersion (suspension). Dopamine compounds are added and polymerization reaction is carried out at room temperature. The residue is filtered, washed and dried to obtain polydopamine-functionalized multi-walled carbon nanotubes. (2) Preparation of blended membrane: The film-forming polymer, pore-forming agent and polydopamine-functionalized multi-walled carbon nanotubes described in step (1) are added to an organic solvent, dispersed evenly, and a casting solution is prepared to prepare a blended membrane; (3) Surface functional layer construction: The blend membrane described in step (2) is immersed in tannic acid solution and aluminum salt solution in turn (tannic acid-aluminum ion metal phenolic network is assembled onto the surface of blend membrane by layer-by-layer self-assembly method) to obtain a composite ultrafiltration membrane based on blend modification and surface modification.

[0009] In some embodiments, the dopamine compound in step (1) is at least one of dopamine hydrochloride, dopamine methyl ester hydrochloride, and 6-hydroxydopamine hydrochloride; the carbon nanotube is at least one of multi-walled carbon nanotube, single-walled carbon nanotube, and double-walled carbon nanotube; and the mass ratio of the carbon nanotube to the dopamine compound is 1:1 to 1:3.

[0010] In some embodiments, the mass ratio of the carbon nanotubes to the dopamine compound is 1:1 to 1:3.

[0011] In some embodiments, the mass-to-volume ratio of the carbon nanotubes to water in step (1) is 0.25-1:1 g / L.

[0012] In some embodiments, in step (1), the carbon nanotubes are dispersed in water by ultrasonic dispersion.

[0013] In some embodiments, in step (1), the pH of the dispersion is adjusted to alkaline before adding the dopamine compound, so that the polymerization reaction is carried out under alkaline conditions.

[0014] In some embodiments, in step (1), the pH of the dispersion is adjusted to 8.5 before adding the dopamine compound.

[0015] In some embodiments, the polymerization reaction in step (1) is carried out under stirring, with a stirring rate of 500-800 r / min and a polymerization time of 6-24 h.

[0016] In some embodiments, the film-forming polymer in step (2) is at least one of polyethersulfone, polysulfone, polyvinylidene fluoride and polyacrylonitrile; and the pore-forming agent is at least one of polyvinylpyrrolidone, polyethylene glycol and polyethylene oxide.

[0017] In some embodiments, the organic solvent in step (2) is at least one of N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, and N,N-dimethylformamide; in the casting solution, the concentration of the film-forming polymer is 10-20 wt%, the concentration of the pore-forming agent is 0.5-5 wt%, and the concentration of polydopamine-functionalized multi-walled carbon nanotubes is 0.1-1 wt%.

[0018] In some embodiments, step (2), the preparation of the casting solution, includes the following steps: The pore-forming agent and the polydopamine-functionalized multi-walled carbon nanotubes described in step (1) are added to an organic solvent and ultrasonically dispersed evenly. Then, the film-forming polymer is added and stirred for 4-8 h at a temperature of 40-80 ℃ to obtain a casting solution.

[0019] In some embodiments, step (2) of preparing the blend membrane includes the following steps: The casting solution was allowed to stand for 12-48 hours to defoam, and the defoamed casting solution was obtained. The blended membrane was then prepared by the immersion precipitation phase inversion method (prepared by a non-solvent induced phase separation method).

[0020] In some embodiments, step (2) of preparing the blend membrane includes the following steps: The casting solution was allowed to stand for 12 hours to defoam, resulting in a defoamed casting solution. The defoamed casting solution was then scraped flat onto a clean glass plate and allowed to stand for 30 seconds. It was then immersed in a deionized coagulation bath and detached from the glass plate to form a film after 1 minute.

[0021] In some embodiments, the concentration of the tannic acid solution in step (3) is 0.1-1 g / L, and the time for which the blended membrane is immersed in the tannic acid solution is 10-300 s; the aluminum salt solution is a solution obtained by mixing aluminum salt and water; the aluminum salt is at least one of aluminum trichloride hexahydrate, aluminum sulfate, aluminum nitrate and alum; the mass-volume ratio of the aluminum salt to water is 0.01-0.1:1 g / L; and the time for which the blended membrane is immersed in the aluminum salt solution is 10-300 s.

[0022] In some embodiments, in step (3), the blended membrane is first soaked in a tannic acid solution, taken out, rinsed, and then soaked in an aluminum salt solution and rinsed to obtain a composite ultrafiltration membrane based on blending modification and surface modification.

[0023] According to a second aspect of the present invention, a composite ultrafiltration membrane based on blending modification and surface modification, prepared by the above-described method, is provided. The composite ultrafiltration membrane obtained by this method is a high-flux, antifouling polyethersulfone ultrafiltration membrane.

[0024] According to a third aspect of the present invention, the present invention provides the application of composite ultrafiltration membranes based on blending modification and surface modification in wastewater treatment and reuse.

[0025] This invention selects polyethersulfone (PES) as the film-forming substrate, which possesses excellent chemical stability, mechanical strength, and processability. By introducing polydopamine-functionalized multi-walled carbon nanotubes (labeled PDA@MWCNTs) as a blending modifier, their unique tubular structure is utilized to construct preferential water channels within the membrane matrix, thereby enhancing the membrane's water flux and mechanical strength. The dopamine compound (PDA), rich in catechol and amino groups, not only imparts high hydrophilicity to the multi-walled carbon nanotubes (MWCNTs) but also improves their compatibility with the polymer matrix, inhibits nanoparticle aggregation, and avoids the formation of non-selective interfacial defects.

[0026] This invention utilizes the reaction of tannic acid (TA) and aluminum ions (Al) 3+ Coordination-driven layer-by-layer (LBL) self-assembly (LBL) of tannins is used to construct a metal-phenolic network (MPN) functional layer on the membrane surface. Tannins contain abundant hydrophilic groups and can act as polydentate ligands to coordinate with metal ions, forming stable and adhesive complexes on the substrate. Aluminum ions have low biotoxicity and excellent environmental compatibility, and their high charge density is conducive to the formation of stable coordination complexes, which further coordinate with water molecules to construct a robust MPN highly hydrophilic interface layer.

[0027] In terms of process, this invention employs a solvent-inducing phase separation method to prepare the base membrane. N,N-dimethylacetamide (DMAc) is used as the organic solvent; its high boiling point and solubility facilitate the formation of a homogeneous casting solution. Polyvinylpyrrolidone (PVP) is used as a pore-forming agent to regulate the properties of the casting solution and promote the formation of finger-like pore structures during phase separation. Sufficient immersion time in the coagulation bath ensures complete phase inversion, forming a base membrane with an asymmetric structure. Subsequent LBL assembly process parameters can precisely control the thickness, density, and surface structure of the metal-phenolic network layer (MPN layer), thereby balancing the membrane's permeability and selectivity.

[0028] In summary, the method provided by this invention is a novel strategy that synergistically integrates the advantages of blending and surface modification. This strategy aims to combine the enhancing effect of blending modification on membrane structure and permeability with the precise control of interfacial hydrophilicity, selectivity and stability by surface modification. This is expected to simultaneously solve problems such as filler dispersibility, modification layer robustness and flux-selectivity, providing a new and effective approach for preparing high-performance ultrafiltration membranes.

[0029] The preparation method provided by this invention employs a blending-surface synergistic modification strategy. The PDA@MWCNTs inside the prepared ultrafiltration membrane construct highly efficient water channels, significantly improving water flux; the surface TA-Al... 3+ The MPN layer provides a dense, hydrophilic barrier, simultaneously enhancing retention and antifouling properties. This is achieved by regulating Al... 3+ Concentration (0.01-0.1:1 g / L) and assembly time (30-300 s) can achieve an optimized balance between membrane permeability, selectivity, and fouling recovery performance. Furthermore, experiments show that in Al... 3+ At a concentration of 0.06 g / L and an assembly time of 30 s, the membrane pure water flux reached 178.71 L·m⁻¹. -2 ·h -1 The BSA rejection rate is >95%, and the flux recovery rate is good.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows: The preparation method provided by this invention involves the internal blending of polydopamine-functionalized multi-walled carbon nanotubes (labeled PDA@MWCNTs) with TA-Al 3+ The synergistic effect of surface modification in MPN effectively overcomes the flux-selectivity trade-off effect of traditional ultrafiltration membranes; its internally embedded PDA@MWCNTs construct efficient water channels to enhance permeability, while the surface-coated TA-Al 3+The MPN layer provides a dense, hydrophilic barrier while optimizing the membrane surface structure, thereby achieving excellent selectivity, permeability, and antifouling properties. The method provided by this invention offers a novel and effective approach to preparing high-performance PES ultrafiltration membranes through a synergistic modification strategy. These membranes are suitable for the treatment and reuse of wastewater containing organic macromolecules such as proteins and colloids. Attached Figure Description

[0031] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments 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.

[0032] Figure 1 Scanning electron microscope images of the surface of the modified film prepared as experimental examples and comparative examples of the present invention; Figure 2 Scanning electron microscope (SEM) images of cross-sections of modified membranes prepared as experimental examples and comparative examples of this invention; Figure 3 The graph shows the hydrophilic properties of the modified membranes prepared in the experimental and comparative examples of this invention. Detailed Implementation

[0033] To better understand the technical solution of the present invention, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Experimental Example 1 A method for preparing a composite ultrafiltration membrane based on blending modification and surface modification includes the following steps: (1) Preparation of modified nanomaterials: 250 mg of multi-walled carbon nanotubes (MWCNTs) were weighed and dispersed in 500 mL of deionized water. After sonication for 20 min to ensure uniform dispersion of the MWCNTs, the pH was adjusted to 8.5 using Tris-HCl buffer. Then, 500 mg of dopamine hydrochloride was added and the polymerization reaction was carried out by magnetic stirring (12 h). After washing and drying, polydopamine-functionalized multi-walled carbon nanotubes (labeled as PDA@MWCNTs) were obtained. (2) Preparation of uniform dispersion: Weigh 0.025 g of polydopamine-functionalized multi-walled carbon nanotubes (PDA@MWCNTs) and 0.1 g of polyvinylpyrrolidone (PVP) and disperse them in 8.275 g of N,N-dimethylacetamide (DMAc). Sonicate for 2 h to form a uniform dispersion. (3) Preparation of casting solution: Stir the above uniformly dispersed liquid with magnetic force, and after stirring evenly, add 1.6 g of polyethersulfone (PES), and then place it in an oil bath at a temperature of 60 ℃ and stir magnetically for 6 h to form a uniform and transparent casting solution.

[0035] (4) Defoaming of casting solution: The casting solution was allowed to stand at room temperature for 12 hours to defoam, and the defoamed casting solution was obtained.

[0036] (5) Preparation of blended membrane by immersion precipitation phase inversion method: The above deaerated casting solution is scraped onto a clean glass plate, left to stand in the air for 30 s, and then immersed in deionized water at 25 ℃. After 1 min, it is detached from the glass plate to form a membrane, thus obtaining a blended membrane.

[0037] (6) Construction of surface functional layer: A tannic acid (TA) solution with a concentration of 0.4 g / L and an aluminum trichloride hexahydrate (AlCl3·6H2O) with a concentration of 0.02 g / L were prepared as Al 3+ The prepared blend membrane was first immersed in a TA solution (tannic acid solution) for 30 seconds, then rinsed with deionized water; subsequently immersed in Al... 3+ Immerse the membrane in a solution (aluminum trichloride solution) for 30 seconds, then rinse again with deionized water to construct a TA-Al layer on the surface of the blended membrane. 3+ The metal-phenolic network functional layer (MPN layer) is used to finally obtain the composite ultrafiltration membrane based on blending modification and surface modification.

[0038] Experiment Example 2 A method for preparing a composite ultrafiltration membrane based on blending modification and surface modification includes the following steps: (1) Preparation of modified nanomaterials: 250 mg of multi-walled carbon nanotubes (MWCNTs) were weighed and dispersed in 500 mL of deionized water. After sonication for 20 min to ensure uniform dispersion of the MWCNTs, the pH was adjusted to 8.5 using Tris-HCl buffer. Then, 500 mg of dopamine hydrochloride was added and the polymerization reaction was carried out by magnetic stirring (12 h). After washing and drying, polydopamine-functionalized multi-walled carbon nanotubes (labeled as PDA@MWCNTs) were obtained.

[0039] (2) Preparation of uniform dispersion: Weigh 0.025 g of polydopamine-functionalized multi-walled carbon nanotubes (PDA@MWCNTs) and 0.1 g of polyvinylpyrrolidone (PVP) and disperse them in 8.275 g of N,N-dimethylacetamide (DMAc). Sonicate for 2 h to form a uniform dispersion.

[0040] (3) Preparation of casting solution: Stir the above uniformly dispersed liquid with magnetic force, and after stirring evenly, add 1.6 g of polyethersulfone (PES), and then place it in an oil bath at a temperature of 60 ℃ and stir magnetically for 6 h to form a uniform and transparent casting solution.

[0041] (4) Defoaming of casting solution: The casting solution was allowed to stand at room temperature for 12 hours to defoam, and the defoamed casting solution was obtained.

[0042] (5) Preparation of blended membrane by immersion precipitation phase inversion method: The above deaerated casting solution is scraped onto a clean glass plate, left to stand in the air for 30 s, and then immersed in deionized water at 25 ℃. After 1 min, it is detached from the glass plate to form a membrane, thus obtaining a blended membrane.

[0043] (6) Construction of surface functional layer: A tannic acid (TA) solution with a concentration of 0.4 g / L and an aluminum trichloride hexahydrate (AlCl3·6H2O) with a concentration of 0.04 g / L were prepared as Al 3+ The prepared blend membrane was first immersed in a TA solution (tannic acid solution) for 30 seconds, then rinsed with deionized water; subsequently immersed in Al... 3+ Immerse the membrane in a solution (aluminum trichloride solution) for 30 seconds, then rinse again with deionized water to construct a TA-Al layer on the surface of the blended membrane. 3+ The metal-phenolic network functional layer (MPN layer) is used to finally obtain the composite ultrafiltration membrane based on blending modification and surface modification.

[0044] Experimental Example 3 A method for preparing a composite ultrafiltration membrane based on blending modification and surface modification includes the following steps: (1) Preparation of modified nanomaterials: 250 mg of multi-walled carbon nanotubes (MWCNTs) were weighed and dispersed in 500 mL of deionized water. After sonication for 20 min to ensure uniform dispersion of the MWCNTs, the pH was adjusted to 8.5 using Tris-HCl buffer. Then, 500 mg of dopamine hydrochloride was added and the polymerization reaction was carried out by magnetic stirring (12 h). After washing and drying, polydopamine-functionalized multi-walled carbon nanotubes (labeled as PDA@MWCNTs) were obtained.

[0045] (2) Preparation of uniform dispersion: Weigh 0.025 g of polydopamine-functionalized multi-walled carbon nanotubes (PDA@MWCNTs) and 0.1 g of polyvinylpyrrolidone (PVP) and disperse them in 8.275 g of N,N-dimethylacetamide (DMAc). Disperse the mixture by ultrasonication for 2 h to form a uniform dispersion.

[0046] (3) Preparation of casting solution: Stir the above uniformly dispersed liquid with magnetic force, and after stirring evenly, add 1.6 g of polyethersulfone (PES), and then place it in an oil bath at a temperature of 60 ℃ and stir magnetically for 6 h to form a uniform and transparent casting solution.

[0047] (4) Defoaming of casting solution: The casting solution was allowed to stand at room temperature for 12 hours to defoam, and the defoamed casting solution was obtained.

[0048] (5) Preparation of blended membrane by immersion precipitation phase inversion method: The above deaerated casting solution is scraped onto a clean glass plate, left to stand in the air for 30 s, and then immersed in deionized water at 25 ℃. After 1 min, it is detached from the glass plate to form a membrane, thus obtaining a blended membrane.

[0049] (6) Construction of surface functional layer: A tannic acid (TA) solution with a concentration of 0.4 g / L and an aluminum trichloride hexahydrate (AlCl3·6H2O) solution with a concentration of 0.06 g / L were prepared as Al 3+ The prepared blend membrane was first immersed in a TA solution (tannic acid solution) for 30 seconds, then rinsed with deionized water; subsequently immersed in Al... 3+ Immerse the membrane in a solution (aluminum trichloride solution) for 30 seconds, then rinse again with deionized water to construct a TA-Al layer on the surface of the blended membrane. 3+ The metal-phenolic network functional layer (MPN layer) is used to finally obtain the composite ultrafiltration membrane based on blending modification and surface modification.

[0050] Experiment Example 4 A method for preparing a composite ultrafiltration membrane based on blending modification and surface modification includes the following steps: (1) Preparation of modified nanomaterials: 250 mg of multi-walled carbon nanotubes (MWCNTs) were weighed and dispersed in 500 mL of deionized water. After sonication for 20 min to ensure uniform dispersion of the MWCNTs, the pH was adjusted to 8.5 using Tris-HCl buffer. Then, 500 mg of dopamine hydrochloride was added and the polymerization reaction was carried out by magnetic stirring (12 h). After washing and drying, polydopamine-functionalized multi-walled carbon nanotubes (labeled as PDA@MWCNTs) were obtained.

[0051] (2) Preparation of uniform dispersion: Weigh 0.025 g of polydopamine-functionalized multi-walled carbon nanotubes (PDA@MWCNTs) and 0.1 g of polyvinylpyrrolidone (PVP) and disperse them in 8.275 g of N,N-dimethylacetamide (DMAc). Sonicate for 2 h to form a uniform dispersion.

[0052] (3) Preparation of casting solution: Stir the above uniformly dispersed liquid with magnetic force, and after stirring evenly, add 1.6 g of polyethersulfone (PES), and then place it in an oil bath at a temperature of 60 ℃ and stir magnetically for 6 h to form a uniform and transparent casting solution.

[0053] (4) Defoaming of casting solution: The casting solution was allowed to stand at room temperature for 12 hours to defoam, and the defoamed casting solution was obtained.

[0054] (5) Preparation of blended membrane by immersion precipitation phase inversion method: The above deaerated casting solution is scraped onto a clean glass plate, left to stand in the air for 30 s, and then immersed in deionized water at 25 ℃. After 1 min, it is detached from the glass plate to form a membrane, thus obtaining a blended membrane.

[0055] (6) Construction of surface functional layer: A tannic acid (TA) solution with a concentration of 0.4 g / L and an aluminum trichloride hexahydrate (AlCl3·6H2O) with a concentration of 0.08 g / L were prepared as Al 3+ The prepared blend membrane was first immersed in a TA solution (tannic acid solution) for 30 seconds, then rinsed with deionized water; subsequently immersed in Al... 3+ Immerse the membrane in a solution (aluminum chloride solution) for 30 seconds, then rinse again with deionized water to construct TA-Al on the membrane surface. 3+ The metal-phenolic network functional layer (MPN layer) is used to finally obtain the composite ultrafiltration membrane based on blending modification and surface modification.

[0056] Experimental Example 5 A method for preparing a composite ultrafiltration membrane based on blending modification and surface modification includes the following steps: (1) Preparation of modified nanomaterials: 250 mg of multi-walled carbon nanotubes (MWCNTs) were weighed and dispersed in 500 mL of deionized water. After sonication for 20 min to ensure uniform dispersion of the MWCNTs, the pH was adjusted to 8.5 using Tris-HCl buffer. Then, 500 mg of dopamine hydrochloride was added and the polymerization reaction was carried out by magnetic stirring (12 h). After washing and drying, polydopamine-functionalized multi-walled carbon nanotubes (labeled as PDA@MWCNTs) were obtained.

[0057] (2) Preparation of uniform dispersion: Weigh 0.025 g of polydopamine-functionalized multi-walled carbon nanotubes (PDA@MWCNTs) and 0.1 g of polyvinylpyrrolidone (PVP) and disperse them in 8.275 g of N,N-dimethylacetamide (DMAc). Sonicate for 2 h to form a uniform dispersion.

[0058] (3) Preparation of casting solution: Stir the above uniformly dispersed liquid with magnetic force, and after stirring evenly, add 1.6 g of polyethersulfone (PES), and then place it in an oil bath at a temperature of 60 ℃ and stir magnetically for 6 h to form a uniform and transparent casting solution.

[0059] (4) Defoaming of casting solution: The casting solution was allowed to stand at room temperature for 12 hours to defoam, and the defoamed casting solution was obtained.

[0060] (5) Preparation of blended membrane by immersion precipitation phase inversion method: The above deaerated casting solution is scraped onto a clean glass plate, left to stand in the air for 30 s, and then immersed in deionized water at 25 ℃. After 1 min, it is detached from the glass plate to form a membrane, thus obtaining a blended membrane.

[0061] (6) Construction of surface functional layer: A tannic acid (TA) solution with a concentration of 0.4 g / L and an aluminum trichloride hexahydrate (AlCl3·6H2O) solution with a concentration of 0.06 g / L were prepared as Al 3+ The prepared blend membrane was first immersed in a TA solution (tannic acid solution) for 30 seconds, then rinsed with deionized water; subsequently immersed in Al... 3+ Immerse the membrane in a solution (aluminum chloride solution) for 60 seconds, then rinse again with deionized water to construct TA-Al on the membrane surface. 3+ The metal-phenolic network functional layer (MPN layer) is used to finally obtain the composite ultrafiltration membrane based on blending modification and surface modification.

[0062] Experimental Example 6 A method for preparing a composite ultrafiltration membrane based on blending modification and surface modification includes the following steps: (1) Preparation of modified nanomaterials: 250 mg of multi-walled carbon nanotubes (MWCNTs) were weighed and dispersed in 500 mL of deionized water. After sonication for 20 min to ensure uniform dispersion of the MWCNTs, the pH was adjusted to 8.5 using Tris-HCl buffer. Then, 500 mg of dopamine hydrochloride was added and the polymerization reaction was carried out by magnetic stirring (12 h). After washing and drying, polydopamine-functionalized multi-walled carbon nanotubes (labeled as PDA@MWCNTs) were obtained.

[0063] (2) Preparation of uniform dispersion: Weigh 0.025 g of polydopamine-functionalized multi-walled carbon nanotubes (PDA@MWCNTs) and 0.1 g of polyvinylpyrrolidone (PVP) and disperse them in 8.275 g of N,N-dimethylacetamide (DMAc). Sonicate for 2 h to form a uniform dispersion.

[0064] (3) Preparation of casting solution: Stir the above uniformly dispersed liquid with magnetic force, and after stirring evenly, add 1.6 g of polyethersulfone (PES), and then place it in an oil bath at a temperature of 60 ℃ and stir magnetically for 6 h to form a uniform and transparent casting solution.

[0065] (4) Defoaming of casting solution: The casting solution was allowed to stand at room temperature for 12 hours to defoam, and the defoamed casting solution was obtained.

[0066] (5) Preparation of blended membrane by immersion precipitation phase inversion method: The above deaerated casting solution is scraped onto a clean glass plate, left to stand in the air for 30 s, and then immersed in deionized water at 25 ℃. After 1 min, it is detached from the glass plate to form a membrane, thus obtaining a blended membrane.

[0067] (6) Construction of surface functional layer: A tannic acid (TA) solution with a concentration of 0.4 g / L and an aluminum trichloride hexahydrate (AlCl3·6H2O) solution with a concentration of 0.06 g / L were prepared as Al 3+ The prepared blend membrane was first immersed in a TA solution (tannic acid solution) for 30 seconds, then rinsed with deionized water; subsequently immersed in Al... 3+ Immerse the membrane in a solution (aluminum chloride solution) for 300 s, then rinse again with deionized water to construct TA-Al on the membrane surface. 3+ The metal-phenolic network functional layer (MPN layer) is used to finally obtain the composite ultrafiltration membrane based on blending modification and surface modification.

[0068] Comparative Example 1 A method for preparing a PES ultrafiltration membrane includes the following steps: (1) Preparation of uniform dispersion: Weigh 0.1 g of polyvinylpyrrolidone (PVP) and disperse it in 8.3 g of N,N-dimethylacetamide (DMAc). Disperse it by ultrasonication for 2 h to form a uniform dispersion.

[0069] (2) Preparation of casting solution: Stir the above uniformly dispersed liquid with magnetic force, and after stirring evenly, add 1.6 g of polyethersulfone (PES), and then place it in an oil bath at a temperature of 60 ℃ and stir magnetically for 6 h to form a uniform and transparent casting solution.

[0070] (3) Defoaming of casting solution: The casting solution was allowed to stand at room temperature for 12 hours to defoam, and the defoamed casting solution was obtained.

[0071] (4) Preparation of PES ultrafiltration membrane by immersion precipitation phase inversion method: The above deaerated casting solution is scraped onto a clean glass plate, left to stand in the air for 30 s, and then immersed in deionized water at 25 ℃. After 1 min, it is detached from the glass plate to form a membrane, thus obtaining the PES ultrafiltration membrane.

[0072] Comparative Example 2 A method for preparing a blended membrane includes the following steps: (1) Preparation of modified nanomaterials: 250 mg of multi-walled carbon nanotubes (MWCNTs) were weighed and dispersed in 500 mL of deionized water. After sonication for 20 min to ensure uniform dispersion of the MWCNTs, the pH was adjusted to 8.5 using Tris-HCl buffer. Then, 500 mg of dopamine hydrochloride was added, and the polymerization reaction was carried out by magnetic stirring (12 h). After washing and drying, polydopamine-functionalized multi-walled carbon nanotubes (labeled as PDA@MWCNTs) were obtained.

[0073] (2) Preparation of uniform dispersion: Weigh 0.025 g of polydopamine-functionalized multi-walled carbon nanotubes (PDA@MWCNTs) and 0.1 g of polyvinylpyrrolidone (PVP) and disperse them in 8.275 g of N,N-dimethylacetamide (DMAc). Sonicate for 2 h to form a uniform dispersion.

[0074] (3) Preparation of casting solution: Stir the above uniformly dispersed liquid with magnetic force, and after stirring evenly, add 1.6 g of polyethersulfone (PES), and then place it in an oil bath at a temperature of 60 ℃ and stir magnetically for 6 h to form a uniform and transparent casting solution.

[0075] (4) Defoaming of casting solution: The casting solution was allowed to stand at room temperature for 12 hours to defoam, and the defoamed casting solution was obtained.

[0076] (5) Preparation of blended membrane by immersion precipitation phase inversion method: The above deaerated casting solution is scraped onto a clean glass plate, left to stand in the air for 30 s, and then immersed in deionized water at 25 ℃. After 1 min, it is detached from the glass plate to form a membrane, thus obtaining a blended membrane.

[0077] The composite ultrafiltration membrane based on blend modification and surface modification prepared in the experimental example, and the PES ultrafiltration membrane / blend membrane prepared in the comparative example were observed under a scanning electron microscope (the composite ultrafiltration membrane based on blend modification and surface modification, the PES ultrafiltration membrane, and the blend membrane are collectively referred to as modified membranes below). The results are as follows: Figure 1 and Figure 2 As shown; Figure 1 Scanning electron microscope images of the surface of the modified film prepared as experimental examples and comparative examples of the present invention; Figure 2 Scanning electron microscope (SEM) images of cross-sections of modified membranes prepared as experimental examples and comparative examples of this invention; Figure 1 and Figure 2 The image shows the morphological structure of different ultrafiltration membrane cross-sections and surfaces. This can be seen from... Figure 1 and Figure 2It was observed that, similar to the pure PES ultrafiltration membrane (prepared in Comparative Example 1), the modified ultrafiltration membrane (the composite ultrafiltration membrane based on blend modification and surface modification prepared in the experimental example) also exhibited a typical asymmetric structure, including a thin and dense surface layer and a sublayer containing finger-like macropores. Scanning electron microscopy (SEM) analysis showed that TA-Al... 3+ Surface modification significantly alters the microstructure of the film through coordination-driven layer-by-layer self-assembly: In the preparation methods of Experimental Examples 1 to 4, with the addition of aluminum ions (Al) in step (6) of the preparation method... 3+ The concentration was increased from 0.02 g / L to 0.06 g / L, and in Experiments 3, 5, and 6, the Al concentration was optimized. 3+ Prolonging the assembly time under concentration (0.06 g / L) conditions, TA and Al 3+ The continuous deposition and densification of the metal-phenolic network (MPN) layer on the membrane surface leads to a gradual reduction in the membrane pore size; simultaneously, a dense MPN separation layer forms and gradually thickens above the finger-like pore structure of the membrane cross-section. This structural evolution is mainly due to Al 3+ As the coordination reaction is dominated by the coordination center, its concentration and time directly determine the density and thickness of the coordination network, thereby achieving precise control over the porosity of the membrane surface and the structure of the separation layer.

[0078] Performance testing Experiments were conducted on composite ultrafiltration membranes based on blending modification and surface modification, PES ultrafiltration membranes, and ultrafiltration membranes / blended membranes prepared according to the methods of Comparative Examples 1 to 6 (composite ultrafiltration membranes based on blending modification and surface modification, PES ultrafiltration membranes, and blended membranes are collectively referred to as modified membranes below), including: Hydrophilicity evaluation: After the modified membranes prepared in each experimental example and comparative example were dried at room temperature, the ultrafiltration membranes / blended membranes prepared by the methods of Experimental Examples 1 to 6 and Comparative Examples 1 to 2 were respectively set as Experimental Example 1, Experimental Example 2, Experimental Example 3, Experimental Example 4, Experimental Example 5, Experimental Example 6, Comparative Example 1, and Comparative Example 2. Three samples were selected from each group of membranes for testing. The water contact angle of each group of modified membranes was measured using a contact angle meter (OCA 25, Dataphysics, Germany) to obtain the hydrophilicity of the surface of each group of modified membranes (results are shown in Figure 1). Figure 3 (As shown).

[0079] Compared to the PES-based film of Comparative Example 1 (water contact angle of 78.85°), the water contact angle of Comparative Example 2 decreased to 76.5° after the introduction of polydopamine-functionalized multi-walled carbon nanotubes (PDA@MWCNTs) in the blend, due to the introduction of hydrophilic groups. And after TA-Al... 3+ After surface modification by layer-by-layer self-assembly of the metal phenolic network, the water contact angle of the film surface further decreased significantly. Specifically, with the addition of aluminum ions (Al) in step (6) of the preparation method...3+ As the concentration of Al increased from 0.02 g / L to 0.08 g / L (Experiments 1 to 4), the water contact angle of the membrane remained stable between 52.9° and 46.6°. At the optimal Al concentration... 3+ At a concentration of 0.06 g / L, the assembly time was extended (immersion in Al). 3+ The solution time further reduced the water contact angle to 44.05° and 40.5° (Examples 5 and 6). These data indicate that blending modification and subsequent surface layer-by-layer self-assembly effectively improved the hydrophilicity of the membrane surface.

[0080] Filtration performance evaluation: Three samples were randomly selected from each group of modified membranes, with an effective area of ​​38.465 cm². 2 Filtration experiments were conducted using a dead-end filtration device (XFUF04701, Merck, Germany). Before each filtration experiment, the membrane was pre-pressurized at 0.15 MPa for 0.5 h to stabilize before proceeding with subsequent experiments. All filtration experiments were conducted at 0.1 MPa, sequentially passing the membrane through pure water for 1 h, followed by passing it through a 0.3 g / L BSA solution (crystallized bovine serum albumin solution, used as the contaminant) for 1 h, then washing with pure water for 0.5 h, and finally passing it through pure water for 1 h (the 1-h pass through pure water was to investigate the flux recovery rate). The filtration performance of each modified membrane was evaluated using pure water flux, contaminant flux, rejection rate, and flux recovery rate. The experimental results are shown in Table 1 below.

[0081] Table 1 As can be seen from the experimental results in Table 1: From Experiment 1 to 4, with the increase of aluminum ions (Al) in step (6) of the preparation method... 3+ When the concentration was increased from 0.02 g / L to 0.06 g / L, the pure water flux of the prepared membrane increased from 103.68 L·m⁻¹. -2 ·h -1 It gradually increased to 178.71 L·m -2 ·h -1 This indicates that the TA-Al formed at a moderate pace 3+ Metal-phenolic network (MPN) layers can effectively enhance the hydrophilicity of the membrane surface and reduce water transfer resistance; however, when Al... 3+ When the concentration was further increased to 0.08 g / L, the pure water flux dropped back to 142.44 L·m -2 ·h -1 This indicates that excessive cross-linking may lead to densification of the surface layer structure or even blockage of micropores, which is not conducive to improving water flux.

[0082] As can be seen from the experimental results in Table 1: Experiments 3, 5, and 6, under optimized Al... 3+Under concentration (0.06 g / L) conditions, the assembly time (immersion in Al) was extended. 3+ The solution time (in terms of solution time) showed a trend of first decreasing and then partially recovering in terms of water flux. After immersion for 60 seconds, the pure water flux significantly decreased to 61.61 L·m⁻¹. -2 ·h -1 However, after immersion for 300 seconds, it recovered to 98.61 L·m. -2 ·h -1 This indicates that while extending the assembly time can introduce more hydrophilic groups, it also leads to thickening of the MPN layer and densification of the structure. Under the competitive effect of these two factors, a net effect of partial flux recovery is ultimately achieved.

[0083] Table 1 shows that all MPN-modified films exhibited excellent BSA retention rates (>92.01%), especially in Al... 3+ The membrane prepared at a concentration of 0.06 g / L and an immersion time of 30 seconds (Example 3) achieved the highest rejection rate of 95.07%, which is significantly improved compared to the unmodified PES membrane (Comparative Example 1). This indicates that the surface MPN layer of the modified membrane prepared in the experimental examples of this invention can effectively enhance the selective separation performance of the membrane without significantly sacrificing the pure water flux.

[0084] The experimental results in Table 1 also show that the polydopamine-functionalized carbon nanotubes (PDA@MWCNTs) introduced through blending in the experimental examples of this invention constructed efficient water channels inside the membrane, interacting with the surface TA-Al. 3+ The hydrophilic and antifouling functions of the MPN layer work synergistically, enabling the membrane to maintain good flux recovery capability after fouling (76.14% recovery rate in Experimental Example 6).

[0085] In summary, this invention successfully prepared a composite ultrafiltration membrane with high water flux, high rejection rate, and good antifouling properties through a synergistic strategy of blending modification and surface modification. Experiments show that when the aluminum ion concentration is 0.06 g / L and the immersion time is 30 s (Example 3), the membrane exhibits the best overall performance, with a pure water flux of 178.71 L·m³. -2 ·h -1 A retention rate higher than 95% indicates that TA-Al under these conditions... 3+ The MPN layer effectively maintained high flux while improving hydrophilicity and selectivity; extending the impregnation time to 300 s (Experimental Example 6) further improved the flux recovery rate to 76.14%, enhancing the membrane's fouling resistance and easy cleaning properties. This synergistic modification method, by controlling the Al³⁺ concentration and assembly time, achieved controllable optimization of membrane permeability, selectivity, and antifouling properties, providing an effective approach for the preparation of high-performance ultrafiltration membranes.

[0086] The above descriptions are merely some embodiments of the present invention. Those skilled in the art can make various modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a composite ultrafiltration membrane based on blending modification and surface modification, characterized in that, Includes the following steps: (1) Disperse carbon nanotubes in water to obtain a dispersion, add dopamine compounds, carry out a polymerization reaction, filter and take the filter residue to obtain polydopamine-functionalized multi-walled carbon nanotubes. (2) The film-forming polymer, pore-forming agent and the polydopamine-functionalized multi-walled carbon nanotubes described in step (1) are added to an organic solvent, dispersed evenly, and a casting solution is prepared to prepare a blended film; (3) The blended membrane described in step (2) is immersed in tannic acid solution and aluminum salt solution in turn to obtain a composite ultrafiltration membrane based on blending modification and surface modification.

2. The preparation method according to claim 1, characterized in that, The dopamine compound in step (1) is at least one of dopamine hydrochloride, dopamine methyl ester hydrochloride, and 6-hydroxydopamine hydrochloride; the carbon nanotube is at least one of multi-walled carbon nanotube, single-walled carbon nanotube, and double-walled carbon nanotube; the mass ratio of the carbon nanotube to the dopamine compound is 1:1 to 1:3; the mass-volume ratio of the carbon nanotube to water in step (1) is 0.25 to 1:1 g / L.

3. The preparation method according to claim 1, characterized in that, In step (1), the pH of the dispersion is adjusted to alkaline before adding dopamine compounds; the polymerization reaction in step (1) is carried out under stirring, with a stirring rate of 500-800 r / min and a polymerization reaction time of 6-24 h.

4. The preparation method according to claim 1, characterized in that, The film-forming polymer in step (2) is at least one of polyethersulfone, polysulfone, polyvinylidene fluoride and polyacrylonitrile; the pore-forming agent is at least one of polyvinylpyrrolidone, polyethylene glycol and polyethylene oxide.

5. The preparation method according to claim 1, characterized in that, The organic solvent in step (2) is at least one of N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide and N,N-dimethylformamide; in the casting solution, the concentration of the film-forming polymer is 10-20 wt%, the concentration of the pore-forming agent is 0.5-5 wt%, and the concentration of polydopamine-functionalized multi-walled carbon nanotubes is 0.1-1 wt%.

6. The preparation method according to claim 1, characterized in that, In step (2), the preparation of the casting solution includes the following steps: The pore-forming agent and the polydopamine-functionalized multi-walled carbon nanotubes described in step (1) are added to an organic solvent and ultrasonically dispersed evenly. Then, the film-forming polymer is added and stirred for 4-8 h at a temperature of 40-80 ℃ to obtain a casting solution.

7. The preparation method according to claim 1, characterized in that, Step (2) in preparing the blended membrane includes the following steps: The casting solution was allowed to stand for 12-48 hours to defoam, and the defoamed casting solution was then used to prepare a blended membrane by immersion precipitation phase inversion method.

8. The preparation method according to claim 1, characterized in that, In step (3), the concentration of the tannic acid solution is 0.1-1 g / L, and the time for immersing the blended membrane in the tannic acid solution is 10-300 s; the aluminum salt solution is a solution obtained by mixing aluminum salt and water; the aluminum salt is at least one of aluminum trichloride hexahydrate, aluminum sulfate, aluminum nitrate and alum; the mass-volume ratio of the aluminum salt to water is 0.01-0.1:1 g / L; and the time for immersing the blended membrane in the aluminum salt solution is 10-300 s.

9. A composite ultrafiltration membrane based on blending modification and surface modification, prepared by the preparation method according to any one of claims 1-8.

10. The application of the composite ultrafiltration membrane based on blending modification and surface modification as described in claim 9 in wastewater treatment and reuse.

Images