Star-shaped polyelectrolyte composite membrane as well as preparation method and application thereof

Abstract

The invention discloses a star-shaped polyelectrolyte composite membrane as well as a preparation method and application thereof, and belongs to the technical field of high-salinity wastewater treatment. The star-shaped polyelectrolyte composite membrane provided by the invention comprises a base material and a polyelectrolyte compound compounded on the surface of the base material, the polyelectrolyte compound comprises a modified star-shaped polycation electrolyte and a modified star-shaped polyanion electrolyte; the modified star-shaped polycation electrolyte comprises acyl halide modified cyclodextrin and a polycation electrolyte chemically bonded with the acyl halide modified cyclodextrin, the modified star-shaped polyanion electrolyte comprises acyl halide modified cyclodextrin and a polyanion electrolyte chemically bonded with the acyl halide modified cyclodextrin. The star-shaped polyelectrolyte composite membrane prepared by the invention can realize continuous purification of high-salinity wastewater, realizes simultaneous improvement of water treatment flux and salt resistance, and has a wide application prospect in high-salinity wastewater treatment.

Description

Technical Field

[0001] This application belongs to the field of high-salt wastewater treatment technology, and particularly relates to a star-shaped polyelectrolyte composite membrane, its preparation method and application. Background Technology

[0002] In China, over 300 million cubic meters of high-salinity wastewater (with a salt content greater than 3.5 wt%) are generated annually. Using a combined treatment strategy of reverse osmosis and thermal desalination, over ten million tons of high-salinity hazardous waste are generated as a byproduct, most of which requires subsequent landfill or discharge into the sea, causing irreversible damage to the ecological environment. Zero-liquid-discharge (ZLD) technology has emerged and quickly become a focus of the industry, aiming to completely convert wastewater into solid salts and recyclable purified water, fundamentally eliminating wastewater discharge and achieving efficient water resource recycling and zero pollutant discharge. Current methods typically employ multi-stage membrane separation / thermal desalination coupling processes to achieve ZLD; however, during treatment, the pressure and operating costs of multi-stage membrane separation increase exponentially with increasing salt concentration. Therefore, improving the salt resistance of water purification substrates has become crucial to overcoming this technological bottleneck.

[0003] Currently, the main strategies for improving salt resistance efficiency are: (1) Vertical nanopore design: increasing the difference in mass transfer rates between water molecules and salt ions through capillary action. Water molecules are restricted by the pore walls within the pores, and the interface effect causes water molecules to diffuse directionally along the pores, thereby significantly improving the diffusion coefficient. (2) Marangoni convection design: initiating Marangoni convection by designing micron- or millimeter-scale macrostructures (such as micro-protrusions, grooves, or ordered textures) on the material surface. Salt ions do not accumulate on the surface but are carried away by convection, thus avoiding salt precipitation. (3) Polyelectrolyte surface modification: modifying the substrate surface with polyelectrolyte materials and adjusting the surface potential of the material using the charge repulsion effect. When water molecules evaporate, salt ions in the solution are effectively blocked due to the charge repulsion effect, thereby inhibiting salt crystallization and avoiding salt precipitation.

[0004] However, existing polyelectrolyte materials are usually linear chain structures in practical applications, making it difficult to achieve high-density modification on the material surface. This directly leads to unsatisfactory salt resistance and poor stability. Summary of the Invention

[0005] This application discloses a star-shaped polyelectrolyte composite membrane, its preparation method and application, aiming to solve the technical problems of poor salt resistance and poor stability of existing polyelectrolyte materials.

[0006] To achieve the above objectives, the technical solution of this application is:

[0007] The first aspect of this application provides a star-shaped polyelectrolyte composite membrane, comprising: a substrate and a polyelectrolyte composite compound laminated on the surface of the substrate;

[0008] The polyelectrolyte complex includes a modified star-shaped polycationic electrolyte and a modified star-shaped polyanionic electrolyte;

[0009] The modified star-shaped polycationic electrolyte comprises: acyl halide-modified cyclodextrin and a polycationic electrolyte chemically bonded to the acyl halide-modified cyclodextrin;

[0010] The modified star-shaped polyanionic electrolyte comprises: acyl halide-modified cyclodextrin and a polyanionic electrolyte chemically bonded to the acyl halide-modified cyclodextrin.

[0011] Preferably, in conjunction with the first aspect, the substrate is a substrate with a positive surface potential or a substrate with a negative surface potential;

[0012] The surface positive potential substrate includes one or a combination of polyvinyl alcohol / titanium pentoxide composite hydrogel and polyacrylamide / carbon black composite hydrogel.

[0013] The negative surface potential substrate includes one or a combination of cellulose acetate filter membrane, nylon filter membrane, etc.

[0014] Preferably, in conjunction with the first aspect, if the substrate is a surface positive potential substrate,

[0015] The polyelectrolyte complex includes: a modified star-shaped polyanionic electrolyte and a modified star-shaped polycationic electrolyte compounded on the surface of the modified star-shaped polyanionic electrolyte.

[0016] Preferably, in conjunction with the first aspect, if the substrate is a substrate with a negative surface potential,

[0017] The polyelectrolyte complex includes: a modified star-shaped polycationic electrolyte and a modified star-shaped polyanionic electrolyte compounded on the surface of the modified star-shaped polycationic electrolyte.

[0018] Preferably, in conjunction with the first aspect, the polyanionic electrolyte is one or a combination of sodium polystyrene sulfonate and polyacrylic acid.

[0019] Preferably, in conjunction with the first aspect, the polycationic electrolyte is one or a combination of poly(4-vinylpyridine) quaternary ammonium salt, poly(dimethylaminoethyl methacrylate) quaternary ammonium salt, and poly(4-vinylpyridine) quaternary ammonium salt.

[0020] The second aspect of this application provides a method for preparing the star-shaped polyelectrolyte composite membrane described in the first aspect, the method comprising:

[0021] Provides acyl halide-modified cyclodextrins;

[0022] Polycationic electrolytes and polyanionic electrolytes were reacted onto the surface of acyl halide-modified cyclodextrin via atom transfer radical polymerization to obtain modified star-shaped polycationic electrolytes and modified star-shaped polyanionic electrolytes, respectively.

[0023] The substrate is immersed in the modified star-shaped polycationic electrolyte aqueous solution and the modified star-shaped polyanionic electrolyte aqueous solution for reaction, and then removed and dried to obtain the star-shaped polyelectrolyte composite membrane.

[0024] In conjunction with the second aspect, preferably, if the substrate is a surface positive potential substrate:

[0025] The surface positive potential substrate is immersed in a modified star-shaped polyanionic electrolyte aqueous solution, removed and dried to obtain the modified positive potential substrate;

[0026] The modified positive potential substrate is immersed in a modified star-shaped polycationic electrolyte aqueous solution, then removed and dried to obtain the star-shaped polyelectrolyte composite membrane.

[0027] Alternatively, if the substrate is a substrate with a negative surface potential:

[0028] The surface negative potential substrate is immersed in a modified star-shaped polycationic electrolyte aqueous solution, removed and dried to obtain the modified negative potential substrate;

[0029] The modified negative potential substrate is immersed in a modified star-shaped polyanionic electrolyte aqueous solution, then removed and dried to obtain the star-shaped polyelectrolyte composite membrane.

[0030] Preferably, in conjunction with the second aspect, the concentration of the modified star-shaped polycationic electrolyte aqueous solution is 5-20 g / L;

[0031] The concentration of the modified star-shaped polyanionic electrolyte aqueous solution is 5-20 g / L;

[0032] The immersion time in the modified star-shaped polycationic electrolyte aqueous solution is 5-15 min;

[0033] The immersion time in the modified star-shaped polyanionic electrolyte aqueous solution is 5-15 min.

[0034] The third aspect of this application provides the application of the star-shaped polyelectrolyte composite membrane described in the first aspect or the star-shaped polyelectrolyte composite membrane prepared by the preparation method described in the second aspect in the treatment of high-salt wastewater.

[0035] Compared with the prior art, the advantages or beneficial effects of the embodiments of this application include at least the following:

[0036] The star-shaped polyelectrolyte composite membrane provided in this application is constructed by chemically bonding modified star-shaped polyanionic electrolytes and modified star-shaped polycationic electrolytes to an acyl halide-modified cyclodextrin structure, and then composited onto a substrate surface. Firstly, the polyanionic or polycationic electrolytes can chemically bond with the hydroxyl groups on the acyl halide-modified cyclodextrin, forming a star-shaped structure with cyclodextrin as the core and multiple polyelectrolyte chains as arms. This multi-arm structure endows it with excellent structural stability, making it less prone to dissociation of the polyelectrolyte composite, thereby improving the overall durability and interfacial stability of the composite. Secondly, due to its multi-arm structure, it can provide a higher charge density per unit volume, and its charge distribution is more concentrated and stereosymmetrical, making it easier to form stable, size-controllable nanoscale composites when combined with counter-charged polyelectrolytes. It not only reaches adsorption equilibrium in a short time, but also, due to the presence of hydrophobic microregions inside, helps to disrupt the hydrogen bond network between water molecules, significantly improving water flux performance. In high-salt environments, the star-shaped polyelectrolyte composite membrane exhibits excellent salt resistance. Furthermore, its structure retains a large amount of unneutralized excess charge, which can effectively hinder the entry and deposition of salt ions through the Donnan repulsion effect and electrostatic repulsion mechanism, thereby suppressing scaling problems on the membrane surface. It has significant advantages in structural stability, charge density distribution, and salt resistance, not only ensuring the long-term operational stability of the membrane material in high-salt wastewater treatment, but also achieving a synergistic improvement in water treatment flux and salt resistance, showing broad application prospects. Attached Figure Description

[0037] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 This is a schematic diagram of the structure of the A1-star-shaped polyelectrolyte composite membrane in the embodiments of this application;

[0039] Figure 2 The images show the Raman spectra of the A1-star polyelectrolyte composite membrane in different concentrations of saline solution in the embodiments of this application.

[0040] Figure 3 The images show the Raman spectra of the A1-star polyelectrolyte composite membrane in pure salt systems of different concentrations in the embodiments of this application.

[0041] Figure 4 The results of long-cycle performance tests of the A1-star polyelectrolyte composite membrane in the embodiments of this application are shown. Detailed Implementation

[0042] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0043] In the following description of this embodiment, the term "and / or" is used to describe the association relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, B existing alone, and A and B existing simultaneously. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0044] In the following description of this embodiment, the term "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0045] Those skilled in the art should understand that, in the following description of the embodiments of this application, the sequence of numbers does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0046] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms "a" and "the" as used in the embodiments of this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0047] It should be noted that all raw materials and reagents in the embodiments of this application were purchased from the market or prepared according to conventional methods known to those skilled in the art.

[0048] In a first aspect, embodiments of this application provide a star-shaped polyelectrolyte composite membrane, comprising: a substrate and a polyelectrolyte composite compound laminated on the surface of the substrate;

[0049] The polyelectrolyte complex includes a modified star-shaped polycationic electrolyte and a modified star-shaped polyanionic electrolyte;

[0050] The modified star-shaped polycationic electrolyte comprises: acyl halide-modified cyclodextrin and a polycationic electrolyte chemically bonded to the acyl halide-modified cyclodextrin;

[0051] The modified star-shaped polyanionic electrolyte comprises: acyl halide-modified cyclodextrin and a polyanionic electrolyte chemically bonded to the acyl halide-modified cyclodextrin.

[0052] Firstly, polyanionic or polycationic electrolytes can chemically bond with the hydroxyl groups on acyl halide-modified cyclodextrins to form a star-shaped structure with cyclodextrin as the core and multiple polyelectrolyte chains as arms. This multi-arm structure endows it with excellent structural stability, making it less prone to dissociation of the polyelectrolyte complex, thereby improving the overall durability and interfacial stability of the complex. Secondly, due to its multi-arm structure, it can provide a higher charge density per unit volume, and its charge distribution is more concentrated and stereosymmetrical, making it easier to form stable, size-controllable nanoscale complexes when combined with counter-charged polyelectrolytes. It can not only reach adsorption equilibrium in a short time, but also, due to the presence of hydrophobic microregions, helps to disrupt the hydrogen bond network between water molecules, significantly improving water flux performance. More importantly, in high-salt environments, the star-shaped polyelectrolyte composite membrane exhibits excellent salt resistance. Its structure retains a large amount of unneutralized excess charge, which can effectively hinder the entry and deposition of salt ions through the Donnan repulsion effect and electrostatic repulsion mechanism, thereby inhibiting scaling problems on the membrane surface. It not only ensures the long-term operational stability of membrane materials in the treatment of high-salt wastewater, but also achieves a synergistic improvement in water treatment flux and salt tolerance, and has broad application prospects.

[0053] It should be noted that polyanionic or polycationic electrolytes can be chemically bonded to the hydroxyl sites on modified cyclodextrin molecules to construct a star-shaped polyelectrolyte structure with cyclodextrin as the core. Compared with traditional linear polyelectrolytes, the star structure has high symmetry and a multi-arm configuration, which not only improves the stability of the molecular configuration but also significantly enhances its solubility and compatibility in the aqueous environment. The modified polycationic and polyanionic electrolytes can undergo electrostatic recombination in a short time and quickly reach adsorption equilibrium, forming a composite structure with a nanoscale size. This composite structure contains hydrophobic microregions, which help break the hydrogen bond network of water molecules, thereby improving the mobility and flux of water molecules at the interface. At the same time, due to its high specific surface area, it further enhances the water transport efficiency. On the other hand, when treating high-salinity wastewater, the molecular structure of the star-shaped polyelectrolyte retains abundant unneutralized charges, which can continuously generate electrostatic repulsion at the molecular scale. Through the Donnan effect, it effectively repels salt ions in seawater, inhibits their enrichment and scaling on the membrane surface, and thus significantly improves the salt resistance of the material. Thanks to this structural design, this type of composite membrane can achieve continuous and stable purification of high-salinity wastewater, while ensuring high water flux and excellent salt resistance, demonstrating its broad application potential and engineering promotion value in the field of high-salinity wastewater treatment.

[0054] It should be noted that the cyclodextrin used in this application can be one of α-cyclodextrin, β-cyclodextrin, or γ-cyclodextrin, all of which are relatively hydrophobic internally, while all hydroxyl groups are external. The number of hydroxyl groups in a cyclodextrin depends on the number of its glucose units. Taking β-cyclodextrin as an example, it consists of 7 glucose units, each with 3 hydroxyl groups (one primary hydroxyl and two secondary hydroxyl groups), thus β-cyclodextrin has a total of 21 hydroxyl groups. α-cyclodextrin (6 glucose units): 18 hydroxyl groups; γ-cyclodextrin (8 to 12 glucose units): 24 to 36 hydroxyl groups. The structure of β-cyclodextrin is shown in Formula 1.

[0055]

[0056] It should be noted that the acyl halide-modified cyclodextrin used in this application is preferably acyl chloride cyclodextrin or acyl chloride cyclodextrin. In this application, the synthesis of the star-shaped polyelectrolyte uses acyl halide-modified cyclodextrin as a multifunctional initiator, preferably acyl bromide cyclodextrin or acyl chloride cyclodextrin. Cyclodextrin molecules have multiple reactive hydroxyl sites. By introducing acyl halide functional groups, multi-point grafting on a single molecule can be achieved, thereby precisely controlling the grafting density of the star-shaped polymer. This structural design not only ensures the high branching and water solubility of the polymer but also enhances its conformational stability and interfacial activity during assembly.

[0057] In practical applications, acyl brominated cyclodextrins are suitable for initiating the polymerization of conventional monomers such as PSS, PAA, and PDEAEMA, exhibiting good initiation efficiency and controllability. However, it should be noted that bromine may inhibit the polymerization of P4VP in high-temperature or highly polar systems, reducing polymerization activity. Therefore, to ensure the efficient polymerization of P4VP and the smooth progress of subsequent quaternization reactions, this application preferably uses acyl chloride cyclodextrin as a multifunctional initiator for Star-QP4VP. Acyl chloride cyclodextrins have milder reactivity and better compatibility, effectively avoiding side reactions of halogens on the polymerization system and ensuring the degree of polymerization and structural uniformity. In summary, using acyl halide-modified cyclodextrins as star initiators not only endows the material with high structural controllability but also allows for flexible selection of different acyl halide types according to the type of target polyelectrolyte, achieving broad compatibility and functional tunability of the material system. This significantly improves the synthesis efficiency and final performance of star polyelectrolytes, providing a solid molecular basis for constructing high-performance polyelectrolyte composite membranes.

[0058] The structure of acylbromocyclodextrin is shown in Formula 2:

[0059]

[0060] The structure of acyl cyclodextrin is shown in Formula 3:

[0061]

[0062] It should be noted that the modified star-shaped polycationic electrolyte used in the embodiments of this application is preferably quaternized star-shaped poly(4-vinylpyridine) (star-QP4VP), where Star represents a star structure and QP4VP represents a poly(4-vinylpyridine) quaternary ammonium salt, the structure of which is shown in Formula 4:

[0063]

[0064] It should be noted that the modified star-shaped polycationic electrolyte used in the embodiments of this application is preferably quaternized star-shaped N,N-dimethylaminoethyl methacrylate (star-QPDEAEMA), where Star represents a star structure and QPDEAEMA represents the quaternary ammonium salt of N,N-dimethylaminoethyl methacrylate, and its structure is shown in Formula 5:

[0065]

[0066] It should be noted that the modified star-shaped polyanionic electrolyte used in the embodiments of this application is preferably star-shaped sodium polyphenylene sulfonate (star-PSS), where star represents star structure and PSS represents sodium polyphenylene sulfonate, and its structure is as follows.

[0067] As shown in Equation 6:

[0068]

[0069] It should be noted that the modified star-shaped polyanionic electrolyte used in the embodiments of this application is preferably star-shaped polyacrylic acid (star-PAA), where star represents star structure and PAA represents polyacrylic acid, and its structure is shown in Formula 7:

[0070]

[0071] In this embodiment, the substrate includes a positively charged surface substrate or a negatively charged surface substrate. The positively charged surface substrate includes one or a combination of polyvinyl alcohol / titanium pentoxide composite hydrogel and polyacrylamide / carbon black composite hydrogel. The negatively charged surface substrate includes one or a combination of cellulose acetate filter membrane and nylon filter membrane. In terms of performance, different surface potentials help form a stable composite structure with the counter-charged polyelectrolyte, improving interfacial adhesion and membrane stability. Simultaneously, these substrates all possess good hydrophilicity, porous structure, and photothermal synergy, which helps enhance water flux and evaporation efficiency. In terms of commercialization, the selected substrates have widely available and low-cost raw materials, mature processing technologies, good process compatibility, and a solid industrial foundation, facilitating large-scale continuous preparation and possessing broad application and promotion potential.

[0072] In this application, the polyanionic electrolyte is preferably one or more of sodium polystyrene sulfonate (PSS) and polyacrylic acid (PAA). The modified star-shaped polycationic PSS and PAA prepared in this application combine strong and weak acidity characteristics with polyelectrolyte functionality. PSS is a typical strong acid polyelectrolyte; its sodium sulfonate groups can be completely ionized in various aqueous environments, exhibiting good charge retention and excellent salt resistance, making it an ideal component for constructing high-performance composite membranes. PAA is a weak acid polyelectrolyte; its carboxyl groups gradually ionize under neutral or alkaline conditions, exhibiting good pH responsiveness and interfacial flexibility, which can improve the adjustability and interfacial compatibility of the composite membrane. Both can be synthesized into star structures via atom transfer radical polymerization (ATRP), making it easy to control the molecular weight and number of arms, providing an excellent material basis for constructing high-performance polyelectrolyte composite systems.

[0073] In this embodiment, the polycationic electrolyte is preferably one or a combination of poly(4-vinylpyridine) quaternary ammonium salt (QPDEAEMA) and poly(4-vinylpyridine) quaternary ammonium salt (QP4VP). Both the star-shaped polycationic QPDEAEMA and QP4VP selected in this application have been fully quaternized with methyl iodide, transforming them into structurally stable strong cationic polyelectrolytes. Quaternization significantly improves their charge density and salt resistance, enabling them to maintain a positive charge state even under high salt or extreme pH conditions, making them suitable for interfacial stability construction and long-term operation in complex aqueous systems. The QPDEAEMA backbone is flexible and readily soluble in water; the modified star structure can rapidly form a composite in the aqueous phase. The quaternized QP4VP possesses a rigid framework, which helps enhance the mechanical stability and durability of the composite membrane. Both can be prepared into star structures using polymerization methods such as ATRP, with mild reaction conditions and mature processes, providing excellent cationic component selection for constructing high-performance, salt-resistant composite membrane materials.

[0074] Secondly, embodiments of this application also provide a method for preparing the star-shaped polyelectrolyte composite membrane described in the first aspect, the method comprising:

[0075] Provides acyl halide-modified cyclodextrins;

[0076] Polycationic electrolytes and polyanionic electrolytes were reacted onto the surface of acyl halide-modified cyclodextrin via atom transfer radical polymerization to obtain modified star-shaped polycationic electrolytes and modified star-shaped polyanionic electrolytes, respectively.

[0077] The substrate is immersed in the modified star-shaped polycationic electrolyte aqueous solution and the modified star-shaped polyanionic electrolyte aqueous solution for reaction, and then removed and dried to obtain the star-shaped polyelectrolyte composite membrane.

[0078] It should be noted that this application can also combine modified star-shaped polycationic electrolyte and modified star-shaped polyanionic electrolyte onto the substrate by electric field grafting, which can improve the bonding strength with the substrate.

[0079] In this embodiment, if the substrate is a surface-positive potential substrate: the surface-positive potential substrate is immersed in a modified star-shaped polyanionic electrolyte aqueous solution, removed and dried to obtain a modified positive potential substrate; the modified positive potential substrate is immersed in a modified star-shaped polycationic electrolyte aqueous solution, removed and dried to obtain the star-shaped polyelectrolyte composite membrane. If the substrate is a surface-negative potential substrate: the surface-negative potential substrate is immersed in a modified star-shaped polycationic electrolyte aqueous solution, removed and dried to obtain a modified negative potential substrate; the modified negative potential substrate is immersed in a modified star-shaped polyanionic electrolyte aqueous solution, removed and dried to obtain the star-shaped polyelectrolyte composite membrane. The construction sequence of the polyelectrolyte composite used in this application is designed based on the surface potential of the substrate, primarily grounded in the principle of electrostatic adsorption: when the substrate surface is positively charged, a negatively charged modified star-shaped polyanionic electrolyte is preferentially introduced to form a stable electrostatic bond with the substrate, followed by the composite formation of a modified star-shaped polycationic electrolyte on its surface; conversely, when the substrate surface is negatively charged, a modified star-shaped polycationic electrolyte is introduced first, followed by the composite formation of a polyanionic electrolyte. This strategy achieves stable layered assembly through charge complementarity, significantly enhancing the interfacial bonding and structural stability of the composite membrane, and improving its salt resistance and long-term operational performance in high-salt environments.

[0080] In this embodiment, the concentration of the modified star-shaped polycationic electrolyte aqueous solution is preferably 5-20 g / L; the concentration of the modified star-shaped polyanionic electrolyte aqueous solution is preferably 5-20 g / L; the immersion time in the modified star-shaped polycationic electrolyte aqueous solution is preferably 5-15 min; and the immersion time in the modified star-shaped polyanionic electrolyte aqueous solution is preferably 5-15 min.

[0081] It should be noted that this application prepares an evaporation material with a surface containing a multilayer polyelectrolyte composite. The polyelectrolyte composite can induce water molecule orientation and disrupt hydrogen bonds, thereby drastically reducing the energy required for water molecule evaporation. The polyelectrolyte composite contains a large amount of excess charge, which can prevent the diffusion of salt ions to the evaporator surface through the Donnan effect and repulsion effect, thus effectively preventing scaling on the evaporator surface. Furthermore, due to the continuous counter-current movement of water molecules and salt ions, this evaporator can achieve zero liquid discharge. Moreover, because the hydrogen bond network on the surface of the star-shaped polyelectrolyte composite membrane is disrupted by the polyelectrolyte composite, this evaporator exhibits excellent performance under both light and dark conditions at high temperatures (40 to 50°C), making it highly suitable for hot and dry regions and emergency water purification scenarios.

[0082] It should be noted that this is the first time that zero liquid discharge for wastewater treatment has been achieved through pure solar energy; the salt resistance of existing substrates has been increased from 90% to 99.9%, increasing water flux (8 liters per square meter per hour LMH) while avoiding salt precipitation; during 150 hours of continuous operation, the salt resistance and flux decreased by no more than 5%; it can still operate stably even when the water temperature reaches 50°C, making it suitable for water purification in hot and dry regions such as Dubai or Xinjiang; since the core mechanism of the star-shaped polyelectrolyte composite membrane lies in disrupting the hydrogen bond network between water molecules, thereby reducing the enthalpy of vaporization of water, an evaporation rate of about 1.2 LMH can still be achieved even under no-light conditions, which is about 3 times the natural evaporation rate of pure water under the same conditions, demonstrating a significant non-photothermal driven evaporation enhancement effect.

[0083] Thirdly, this application also provides the application of the star-shaped polyelectrolyte composite membrane described in the first aspect or the star-shaped polyelectrolyte composite membrane prepared by the preparation method described in the second aspect in the treatment of high-salinity wastewater. Based on the excellent water treatment flux and salt tolerance of the aforementioned star-shaped polyelectrolyte composite membrane, it has broad application prospects in the treatment of high-salinity wastewater.

[0084] The technical solution of this application will be further described below with reference to specific embodiments.

[0085] Example 1

[0086] This embodiment provides a method for preparing an A1-star-shaped polyelectrolyte composite membrane, specifically including:

[0087] S101: Preparation of modified cyclodextrin as a multi-arm initiator for atom transfer radical polymerization (ATRP): 1 mmol of β-cyclodextrin (β-CD) was added to a 50 mL dry Schlenk flask and dried in a vacuum oven at 60 °C for 48 hours. The flask was evacuated three times, purged with argon, and 16 mL of N-methyl-2-pyrrolidone was added. The mixture was stirred until β-CD was completely dissolved, and then 37.8 mmol of triethylamine was added. The mixture was stirred continuously in an ice-water bath. A 31.5 mmol solution of 2-bromoisobutyryl bromide diluted with 5 mL of chloroform was added dropwise over 30 minutes. After the addition was complete, the mixture was kept in an ice-water bath for 2 hours, then brought to room temperature and stirred for 1 day. Stirring was stopped, 25 mL of chloroform was added, and the mixture was extracted three times with saturated NaCl solution. The organic phase was dried over anhydrous sodium sulfate. The mixture was filtered, the filtrate was collected and concentrated, and then precipitated in n-hexane. After centrifugation, a yellow precipitate was obtained. The precipitate was then diluted with chloroform three times. Finally, the precipitate was vacuum dried to obtain the product acyl β-cyclodextrin (Br-β-CD), which was a white powder. Similarly, 2-bromoisobutyryl bromide was replaced with 2-bromoisobutyryl chloride, the reaction time was extended to 60 hours, and the reaction temperature was increased to 60℃ to obtain the product acyl chloride β-cyclodextrin (Cl-β-CD).

[0088] S102: Preparation of star-shaped polycationic electrolyte: ATRP polymerization was initiated using β-cyclodextrin chloride (Cl-β-CD) as the initiator, cuprous chloride / tris(2-dimethylaminoethyl)amine as the catalyst, and isopropanol as the solvent at 45°C. Specifically, 0.1 mmol of the macromolecular initiator β-cyclodextrin chloride, 2.1 mmol of tris(2-dimethylaminoethyl)amine, 105 mmol of 4-vinylpyridine, and 8 mL of isopropanol were added sequentially to a 50 mL Schlenk flask, and the reactants were dissolved at 45°C. After the sample was fully dissolved, the reaction flask was connected to a double-row tube and subjected to three freeze-thaw cycles using liquid nitrogen. In the last freeze-thaw cycle, 2.1 mmol of cuprous chloride was added. After the reaction returned to room temperature, argon gas was introduced, and the flask was sealed with vacuum grease. The system was placed in a 45°C oil bath and reacted for 4 hours, with a conversion rate of approximately 40%. The vacuum valve was opened to quench the reaction solution by connecting it to atmospheric pressure. After returning to room temperature, the reaction solution was diluted and passed through a neutral alumina column to remove the copper catalyst. The solution was collected and concentrated, then precipitated in ice-cold diethyl ether. The precipitate was centrifuged and vacuum dried to obtain a dark red star-shaped poly(4-vinylpyridine) powder with a degree of polymerization of 20. The star-shaped poly(4-vinylpyridine) (star-P4VP) was then quaternized by adding 20 times the molar amount of iodomethane (monomer) to an ethanol solution of the star-shaped poly(4-vinylpyridine) and stirring for 24 hours. The solution was transferred to a dialysis belt and dialyzed against methanol and water for 24 hours each. The solution was then freeze-dried into a powder to obtain quaternized star-shaped poly(4-vinylpyridine) (star-QP4VP).

[0089] S103: Preparation of star-shaped polyanionic electrolyte: ATRP polymerization was initiated using acyl-β-cyclodextrin bromide (Br-β-CD) as the initiator, cuprous bromide / bipyridine as the catalyst, and methanol / water as the solvent at room temperature. Specifically, 0.1 mmol of the macromolecular initiator acyl-β-cyclodextrin bromide (Br-β-CD), 4.2 mmol of bipyridine, 105 mmol of sodium 4-styrene sulfonate, and 20 mL of a methanol / water mixture (volume ratio 1:1) were added sequentially to a 50 mL Schlenk flask to dissolve the reactants at room temperature. After the sample was fully dissolved, the reaction flask was connected to a double-row tube and subjected to three freeze-thaw cycles using liquid nitrogen. In the final freeze-thaw cycle, 2.1 mmol of CuBr was added. After the reaction returned to room temperature, argon gas was introduced, and the flask was sealed with vacuum grease. The system was allowed to react at room temperature for 4 hours, with a conversion rate of approximately 40%. The vacuum valve was opened to quench the reaction solution by connecting it to atmospheric pressure. After returning to room temperature, the reaction solution was diluted and passed through a neutral alumina column to remove the copper catalyst. The solution was collected and concentrated, then precipitated in ice-cold ether. After centrifugation, the precipitate was dried under vacuum to obtain a white powder solid with a degree of polymerization of 20.

[0090] S104: Preparation of Star-Shaped Polyelectrolyte Composite Membrane: Using titanium pentoxide / polyvinyl alcohol composite hydrogel as the substrate, a layer-by-layer self-assembly (LBL) method was employed to prepare the polyelectrolyte composite membrane. The specific steps were as follows: The substrate was sequentially dipped into a positively charged star-shaped polycationic solution (star-QP4VP) and a negatively charged star-shaped polyanionic solution (star-PSS). The membrane was then alternately assembled via electrostatic adsorption to form a stable composite membrane structure. This process was repeated to construct five bilayer (10-layer) polyelectrolyte membranes. Each layer was rinsed to remove unbound polymers, ensuring uniform membrane layers and tight bonding, thus obtaining the star-shaped polyelectrolyte composite membrane described in A1.

[0091] A schematic diagram of the structure of the A1-star-shaped polyelectrolyte composite membrane prepared in Example 1 of this application is shown below. Figure 1 As shown.

[0092] according to Figure 1 As can be seen, a modified polycationic electrolyte layer is first formed on the substrate surface, followed by a modified polyanionic electrolyte layer through electrostatic adsorption, constructing a layered, ordered star-shaped polyelectrolyte composite structure. These star-shaped polyelectrolytes possess multi-arm branched chains, which not only significantly increase the specific surface area of ​​the membrane but also form a stable charge distribution and composite-induced hydrophobic microregions at the interface. These hydrophobic microregions mainly originate from the charge neutralization process during the composite of cationic and anionic polyelectrolytes, which reduces the overall hydrophilicity of the chain segments, promoting the local aggregation of neutral polymer segments or hydrophobic side chains, forming nanoscale hydrophobic regions. These hydrophobic microregions effectively disrupt the hydrogen bond network between water molecules, reduce the local enthalpy of vaporization, and promote the rapid desorption and migration of water molecules at the interface, thereby significantly improving the water flux and salt resistance of the composite membrane. Simultaneously, since some unneutralized charges remain in the composite structure, forming charge-rich regions, these regions effectively repel salt ions from entering the membrane interior or depositing on the surface through the Donnan effect and electrostatic repulsion, inhibiting crystallization and scaling, and significantly enhancing the membrane's salt resistance and operational stability in high-salt environments.

[0093] Example 2

[0094] This embodiment provides a method for preparing an A2-star-shaped polyelectrolyte composite membrane, specifically including:

[0095] S201: Preparation of modified cyclodextrin as a multi-arm initiator for ATRP: 1 mmol of α-cyclodextrin (α-CD) was added to a 50 mL dry Schlenk flask and dried in a 60 °C vacuum oven for 48 hours. The flask was evacuated three times, purged with argon, and 16 mL of N-methyl-2-pyrrolidone was added. The mixture was stirred until α-CD was completely dissolved, and then 32.4 mmol of triethylamine was added. The mixture was stirred continuously in an ice-water bath. A 27 mmol solution of 2-bromoisobutyryl bromide diluted with 5 mL of chloroform was added dropwise over 30 minutes. After the addition was complete, the mixture was kept in an ice-water bath for 2 hours, then brought to room temperature and stirred for 1 day. Stirring was stopped, 25 mL of chloroform was added, and the mixture was extracted three times with saturated NaCl solution. The organic phase was dried over anhydrous sodium sulfate. The mixture was filtered, the filtrate was collected and concentrated, and then precipitated in n-hexane. After centrifugation, a yellow precipitate was obtained. The precipitate was then diluted with chloroform three times. Finally, the precipitate was dried under vacuum to obtain the product acylbromo-α-cyclodextrin (Br-α-CD), which was a white powder.

[0096] S202: Preparation of star-shaped polycationic electrolyte: ATRP polymerization was initiated using acyl-α-cyclodextrin bromide (Br-α-CD) as the initiator, cuprous bromide / tris(2-dimethylaminoethyl)amine as the catalyst, and N,N-dimethylformamide as the solvent at 45°C. Specifically, 0.1 mmol of the macromolecular initiator acyl-α-cyclodextrin bromide (Br-α-CD), 4.2 mmol of bipyridine, 180 mmol of N,N-dimethylaminoethyl methacrylate, and 20 mL of N,N-dimethylformamide solvent were added sequentially to a 50 mL Schlenk flask, and the reactants were dissolved at room temperature. After the sample was fully dissolved, the reaction flask was connected to a double-row tube, and three freeze-thaw cycles were performed using liquid nitrogen. In the last freeze-thaw cycle, 1.8 mmol of CuBr was added. After the reaction returned to room temperature, argon gas was introduced, and the flask was sealed with vacuum grease. The system was allowed to react at room temperature for 12 hours, with a conversion rate of approximately 20%. The reaction solution was quenched by connecting it to atmospheric pressure after opening the vacuum valve. After returning to room temperature, the reaction solution was diluted and passed through a neutral alumina column to remove the copper catalyst. The solution was collected, concentrated, and then precipitated in ice-cold ether. The precipitate was centrifuged and vacuum-dried to obtain a white powder solid with a degree of polymerization of 20. The above-mentioned star-shaped N,N-dimethylaminoethyl methacrylate (star-PDEAEMA) was quaternized by adding 20 times the molar amount of iodomethane (monomer) to an ethanol solution of star-shaped N,N-dimethylaminoethyl methacrylate and stirring for 24 hours. The solution was transferred to a dialysis belt and dialyzed against methanol and water for 24 hours each. The solution was then freeze-dried into a powder to obtain quaternized star-shaped N,N-dimethylaminoethyl methacrylate (star-QPDEAEMA).

[0097] S203: Preparation of star-shaped polyanionic electrolyte: ATRP polymerization was initiated at room temperature using acyl-α-cyclodextrin bromide (Br-α-CD) as the initiator, cuprous bromide / pentamethyldiethylenetriamine as the catalyst, and N,N-dimethylformamide as the solvent. Specifically, 0.1 mmol of the macromolecular initiator acyl-α-cyclodextrin bromide (Br-α-CD), 4.2 mmol of pentamethyldiethylenetriamine, 180 mmol of tert-butyl acrylate, and 20 mL of N,N-dimethylformamide solvent were added sequentially to a 50 mL Schlenk flask to dissolve the reactants at room temperature. After the sample was fully dissolved, the reaction flask was connected to a double-row tube and subjected to three freeze-thaw cycles using liquid nitrogen. In the final freeze-thaw cycle, 1.8 mmol of CuBr was added. After the reaction returned to room temperature, argon gas was introduced, and the flask was sealed with vacuum grease. The system was placed in a 60°C oil bath and reacted for 4 hours, with a conversion rate of approximately 40%. The reaction solution was quenched by connecting it to atmospheric pressure after the vacuum valve was opened. After returning to room temperature, the reaction solution was diluted and passed through a neutral alumina column to remove the copper catalyst. The solution was collected, concentrated, and then precipitated in ice-cold diethyl ether. The precipitate was centrifuged and vacuum-dried to obtain a white powder solid with a degree of polymerization of 20. To deprotect the above-mentioned star-shaped polytert-butyl acrylate (star-PtBA), 0.1 mmol of PtBA polymer was dissolved in 20 mL of trifluoroacetic acid, and the mixture was magnetically stirred at room temperature for 24 hours to completely remove the tert-butyl groups. After the reaction, the mixture was slowly poured into excess ice-cold diethyl ether to precipitate, and the supernatant was separated by centrifugation. The resulting precipitate was washed three times with ice-cold diethyl ether and then vacuum-dried to obtain a white powdery star-shaped polyacrylic acid (star-PAA).

[0098] S204: Preparation of Star-Shaped Polyelectrolyte Composite Membrane: Using titanium pentoxide / polyimide composite hydrogel as the substrate, a layer-by-layer self-assembly (LBL) method was employed to prepare the polyelectrolyte composite membrane. The specific steps were as follows: The substrate was sequentially dipped into a positively charged star-shaped cationic solution (star-QPDEAEMA) and a negatively charged star-shaped anionic solution (star-PAA). The membranes were then alternately assembled via electrostatic adsorption to form a stable composite membrane structure. This process was repeated to construct five bilayer (10-layer) polyelectrolyte membranes. Each layer was rinsed to remove unbound polymers, ensuring uniform membrane layers and tight bonding, thus obtaining the A2-star-shaped polyelectrolyte composite membrane.

[0099] The resulting A1-star polyelectrolyte composite membrane and A2-star polyelectrolyte composite membrane have both excellent interfacial stability and salt resistance, making them suitable for high-efficiency water treatment and evaporation applications.

[0100] Meanwhile, to verify the comprehensive performance of the composite membranes prepared in the above embodiments, this application provides the following comparative examples for detailed illustration.

[0101] Comparative Example 1

[0102] The comparative example provides a method for preparing a B1-linear polyelectrolyte composite membrane, which specifically includes:

[0103] D101: Preparation of linear polyanionic electrolyte: Sodium styrene sulfonate (SSNa) was used as the monomer and potassium persulfate (KPS) as the initiator, and free radical polymerization was carried out in deionized water. Specifically, 40 mmol of sodium styrene sulfonate and 100 mL of deionized water were added to a 250 mL three-necked flask, and the mixture was magnetically stirred in a 70 °C water bath until completely dissolved. After bubbling with argon gas for 30 minutes to remove dissolved oxygen, 0.4 mmol of potassium persulfate was added as the initiator. The reaction was continued at 70 °C for 6 hours under an argon atmosphere. After the reaction was completed, the mixture was naturally cooled to room temperature, and the resulting solution was dialyzed in deionized water for 1 day using a dialysis bag to remove residual small molecules. The final product was freeze-dried to obtain powdered linear sodium styrene sulfonate.

[0104] D102: Preparation of linear polycationic electrolyte: 4-vinylpyridine (4VP) was used as the monomer and azobisisobutyronitrile (AIBN) as the initiator, followed by free radical polymerization in ethanol and quaternization. Specifically, 20 mmol of 4-vinylpyridine, 1 mmol of AIBN, and 20 mL of anhydrous ethanol were added to a 100 mL Schlenk flask, stirred and dissolved under an argon atmosphere, and reacted in an oil bath at 70 °C for 12 hours. After cooling, 80 mmol of iodomethane was added, and the reaction was carried out at room temperature in the dark for 48 hours to complete the quaternization. The resulting mixture was collected by centrifugation after being added dropwise to a large amount of ice-cold diethyl ether. The precipitate was washed three times with anhydrous diethyl ether and then vacuum dried to obtain a pale yellow powder of quaternized poly(4-vinylpyridine).

[0105] D103: Preparation of linear polyelectrolyte composite membranes: Using titanium pentoxide / polyvinyl alcohol composite hydrogel as the substrate, polyelectrolyte composite membranes were prepared by layer-by-layer self-assembly (LBL) method. The specific steps were as follows: The substrate was sequentially dipped into a positively charged linear cationic QP4VP solution and a negatively charged linear anionic PSSNa solution, and then assembled alternately through electrostatic adsorption to form a stable composite membrane structure. This process was repeated to construct 5 bilayer (10-layer) polyelectrolyte membranes. Each layer was rinsed to remove unbound polymers, ensuring uniform membrane layers and tight bonding, resulting in the B1-linear polyelectrolyte composite membrane.

[0106] This application evaluates the evaporation performance and salt resistance of the star-shaped polyelectrolyte composite membrane prepared in the embodiments using a simulated solar interface evaporation system. The test apparatus includes an evaporation tank capable of solid-liquid separation, used to hold the liquid to be treated (such as a NaCl solution) and collect NaCl crystals precipitated at the bottom of the tank during evaporation, thus achieving liquid-solid separation. The polyelectrolyte composite membrane sample floats on the liquid surface via a support frame, ensuring full contact between the bottom and the water, while the top is exposed to air to form an evaporation interface.

[0107] A solar simulator (AM 1.5G, light intensity 1000W / m²) is installed above the device. 2 As a stable light source, the experimental environment temperature was maintained at 25±2℃, and the relative humidity was controlled at 40-60%. Before the test, the initial mass of the membrane sample and the system water level were recorded, and the water mass change during evaporation was monitored in real time using a high-precision electronic balance or a differential level gauge. The evaporation experiment was conducted for 60 minutes under light or dark conditions, and the evaporation rate (unit: L·m) was calculated per unit time and per unit membrane area. -2 ·h -1 (abbreviated as LMH).

[0108] To evaluate the salt resistance of the polyelectrolyte composite membrane, membrane samples were placed in a 24% NaCl solution for prolonged continuous evaporation. The occurrence of salt crystallization on the membrane surface was observed, and changes in the evaporation flux were recorded simultaneously to assess the membrane's stability and fouling resistance in a high-salt environment. The condensate collected during evaporation was analyzed using inductively coupled plasma optical emission spectrometry (ICP-OES) to determine ion concentration, and the anti-ion rate was calculated to quantitatively evaluate the composite membrane's ability to retain salt ions. The test results for the A1-star-shaped polyelectrolyte composite membrane are shown in Table 1.

[0109] Table 1 shows the results of treatment with 24% sodium chloride solution.

[0110]

[0111] Furthermore, according to Figure 2 Raman spectroscopy analysis of the A1-star-shaped polyelectrolyte composite membrane and the brine system showed that with increasing salt concentration (0%, 10%, 17%, and 24% respectively), H2O at 3200-3800 cm⁻¹... -1 The characteristic peaks in the region show a significant blue shift, indicating that the hydrogen bond structure between water molecules is weakened, intermolecular forces are reduced, and the evaporation energy barrier is lowered. Simultaneously, the relative proportion of strongly hydrogen-bonded water (low wavenumber region) is significantly reduced, indicating that the polyelectrolyte composite membrane can still effectively suppress the formation of strong hydrogen bond networks in high-salt environments, maintaining the perturbation effect of hydrophobic microregions on the water structure. In contrast, according to... Figure 3 It is known that in a pure salt water system, as the salt concentration increases, water molecules rearrange themselves under the influence of salt ions, and the hydrogen bond network tends to become more regular, forming a more stable structure. This structural rearrangement increases the energy required to break hydrogen bonds, making it difficult for water molecules to escape and significantly reducing the evaporation rate. Further comparison demonstrates that the star-shaped polyelectrolyte composite membrane can effectively break the salt-induced stability trend of water structure, maintaining high evaporation efficiency in high-salt environments and exhibiting excellent salt-resistant evaporation performance. Figure 4It can be seen that during 150 hours of continuous operation, the salt tolerance and flux decline does not exceed 5%, demonstrating excellent cycle stability.

[0112] Therefore, the star-shaped polyelectrolyte composite membrane provided in this application is constructed by chemically bonding a modified star-shaped polyanionic electrolyte or a modified star-shaped polycationic electrolyte to an acyl halide-modified cyclodextrin structure, and then composited onto the surface of a substrate. It exhibits significant advantages in structural stability, charge density distribution, and salt resistance. The star-shaped polyelectrolyte composite membrane prepared in this application can achieve continuous purification of high-salinity wastewater, simultaneously improving water treatment flux and salt resistance, and has broad application prospects in high-salinity wastewater treatment.

[0113] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0114] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit this application. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of this application.

Claims

1. A star-shaped polyelectrolyte composite membrane, characterized in that, include: The substrate and the polyelectrolyte composite bonded to the surface of the substrate; The polyelectrolyte complex includes a modified star-shaped polycationic electrolyte and a modified star-shaped polyanionic electrolyte; The modified star-shaped polycationic electrolyte comprises: acyl halide-modified cyclodextrin and a polycationic electrolyte chemically bonded to the acyl halide-modified cyclodextrin; The modified star-shaped polyanionic electrolyte comprises: acyl halide-modified cyclodextrin and a polyanionic electrolyte chemically bonded to the acyl halide-modified cyclodextrin.

2. The star-shaped polyelectrolyte composite membrane according to claim 1, characterized in that, The substrate is a substrate with a positive surface potential or a substrate with a negative surface potential; The surface positive potential substrate includes one or a combination of polyvinyl alcohol / titanium pentoxide composite hydrogel and polyacrylamide / carbon black composite hydrogel. The negative surface potential substrate includes one or a combination of cellulose acetate filter membrane, nylon filter membrane, etc.

3. The star-shaped polyelectrolyte composite membrane according to claim 2, characterized in that, If the substrate is a surface positive potential substrate The polyelectrolyte complex includes: a modified star-shaped polyanionic electrolyte and a modified star-shaped polycationic electrolyte compounded on the surface of the modified star-shaped polyanionic electrolyte.

4. The star-shaped polyelectrolyte composite membrane according to claim 2, characterized in that, If the substrate is a substrate with a negative surface potential The polyelectrolyte complex includes: a modified star-shaped polycationic electrolyte and a modified star-shaped polyanionic electrolyte compounded on the surface of the modified star-shaped polycationic electrolyte.

5. The star-shaped polyelectrolyte composite membrane according to claim 1, characterized in that, The polyanionic electrolyte is one or a combination of sodium polystyrene sulfonate and polyacrylic acid.

6. The star-shaped polyelectrolyte composite membrane according to claim 1, characterized in that, The polycationic electrolyte is one or a combination of poly(dimethylaminoethyl methacrylate) quaternary ammonium salt, poly(4-vinylpyridine) quaternary ammonium salt, or a combination thereof.

7. A method for preparing a star-shaped polyelectrolyte composite membrane according to any one of claims 1-6, characterized in that, The preparation method includes: Provides acyl halide-modified cyclodextrins; Polycationic electrolytes and polyanionic electrolytes were reacted onto the surface of acyl halide-modified cyclodextrin via atom transfer radical polymerization to obtain modified star-shaped polycationic electrolytes and modified star-shaped polyanionic electrolytes, respectively. The substrate is immersed in the modified star-shaped polycationic electrolyte aqueous solution and the modified star-shaped polyanionic electrolyte aqueous solution for reaction, and then removed and dried to obtain the star-shaped polyelectrolyte composite membrane.

8. The method for preparing the star-shaped polyelectrolyte composite membrane according to claim 7, characterized in that, If the substrate is a surface positive potential substrate: The surface positive potential substrate is immersed in a modified star-shaped polyanionic electrolyte aqueous solution, removed and dried to obtain the modified positive potential substrate; The modified positive potential substrate is immersed in a modified star-shaped polycationic electrolyte aqueous solution, then removed and dried to obtain the star-shaped polyelectrolyte composite membrane. Alternatively, if the substrate is a substrate with a negative surface potential: The surface negative potential substrate is immersed in a modified star-shaped polycationic electrolyte aqueous solution, removed and dried to obtain the modified negative potential substrate; The modified negative potential substrate is immersed in a modified star-shaped polyanionic electrolyte aqueous solution, then removed and dried to obtain the star-shaped polyelectrolyte composite membrane.

9. The method for preparing the star-shaped polyelectrolyte composite membrane according to claim 7, characterized in that, The concentration of the modified star-shaped polycationic electrolyte aqueous solution is 5-20 g / L; The concentration of the modified star-shaped polyanionic electrolyte aqueous solution is 5-20 g / L; The immersion time in the modified star-shaped polycationic electrolyte aqueous solution is 5-15 min; The immersion time in the modified star-shaped polyanionic electrolyte aqueous solution is 5-15 min.

10. The application of a star-shaped polyelectrolyte composite membrane prepared according to any one of claims 1-6 or the preparation method according to any one of claims 7-9 in the treatment of high-salt wastewater.

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