Copolymerized composite cation exchange membrane containing amino functionalized inorganic phase as well as preparation method and application of copolymerized composite cation exchange membrane

Abstract

The invention discloses a copolymerized composite cation exchange membrane containing an amino-functionalized inorganic phase as well as a preparation method and application of the copolymerized composite cation exchange membrane. The preparation method of the cation exchange membrane comprises the following steps: (1) preparing the amino-functionalized inorganic phase; (2) preparing rigid-flexible copolymerization-inorganic phase composite membrane liquid; (3) defoaming and coating forming of the composite membrane liquid; and (4) carrying out protonation activation on the composite membrane. A rigid polymer containing reactive hydrogen is used as a structural support phase, a flexible polymer containing high-density amido is used as a functional site carrier, an amino-functionalized inorganic phase is used as a synergistic reinforcement phase, and a cross-linking agent is added, so that the composite material is prepared. The composite cation exchange membrane is prepared through a three-step core process of amino functional modification, rigid-flexible polymer copolymerization crosslinking and protonation activation, and the obtained composite cation exchange membrane has high ion exchange capacity, low surface resistance and low swelling ratio and also has excellent cycle performance.

Description

Technical Field

[0001] This invention belongs to the field of ion exchange membrane material technology. Specifically, this invention relates to a copolymer composite cation exchange membrane containing an amino-functionalized inorganic phase, its preparation method, and its application. Background Technology

[0002] Cation exchange membranes (CEMs) are core functional materials in technologies such as electrodialysis, capacitive membrane deionization (MCDI), and electrolytic refining. Their performance directly determines the desalination efficiency, energy consumption, and long-term stability of the system, playing an irreplaceable role in seawater desalination, industrial wastewater treatment, pure water production, and chemical separation. An ideal cation exchange membrane must simultaneously possess high ion exchange capacity (IEC), low surface resistivity, low swelling ratio, excellent mechanical strength, and chemical stability. However, current technologies still face bottlenecks in optimizing the synergy of these multiple properties, making it difficult to meet the demands of industrial applications for high efficiency, long-term effectiveness, and environmental friendliness.

[0003] Traditional cation exchange membrane preparation mainly relies on two technical routes: "single polymer modification" or "simple inorganic-organic blending," both of which have significant drawbacks. In the polymer modification route, existing technologies often introduce ion exchange groups (such as -SO3H, -PO3H2) onto the polymer chain through chemical modification methods such as sulfonation and phosphorylation. Typical examples include sulfonated polyether ether ketone (SPEEK) and sulfonated polysulfone (SPSF) membranes. While these membranes can provide a certain ion exchange capacity, they suffer from two major problems: first, the functional groups lack stability; sulfonic acid and phosphoric acid groups are easily hydrolyzed and detached in aqueous solutions, leading to rapid performance degradation over time; second, the modification process is demanding, requiring sulfonation / phosphorylation reactions to be carried out at high temperatures (80-120℃) and under strong acid conditions, resulting in high energy consumption, easy polymer chain degradation, and the generation of large amounts of acidic wastewater, posing a high risk of environmental pollution. Furthermore, there is an inherent contradiction between "ion conduction and structural stability" in single polymer membranes. To increase ion capacity, the content of hydrophilic groups needs to be increased. However, excessive hydrophilic groups can cause the membrane to swell excessively in aqueous solution, which can disrupt the regularity of ion transport channels, thereby increasing the surface resistivity and even causing mechanical rupture of the membrane.

[0004] To improve structural stability, existing technologies attempt to modify the membrane through chemical crosslinking or blending with inorganic phases. Chemical crosslinking modification often uses crosslinking agents such as epichlorohydrin to suppress polymer chain swelling by constructing a covalent network. However, the crosslinking reaction requires precise control of temperature and time, is sensitive to reaction conditions, and excessive crosslinking can block ion channels, leading to a decrease in ion exchange capacity. In addition, some crosslinking agents pose a risk of toxic residues, limiting the application of membranes in fields such as drinking water treatment. Simple inorganic-organic blend membranes, on the other hand, physically mix inorganic particles such as silica and montmorillonite with polymers, utilizing the physical support of the inorganic phase to suppress swelling. However, inorganic particles have poor interfacial compatibility with the polymer matrix and are prone to aggregation, leading to defects and pores within the membrane. This not only fails to improve ion conduction efficiency but also increases ion transport resistance. Furthermore, physical blends lack stable chemical bonding, and after long-term immersion or repeated use, inorganic particles easily detach from the membrane matrix, causing a sharp decline in membrane performance. For example, the ion exchange capacity of existing SPEEK / inorganic particle blend membranes is typically below 1.6 mmol / g, and the sheet resistance exceeds 5.5 Ω·cm. 2 With a swelling rate exceeding 18% and a performance retention rate of less than 80% after 100 cycles, it is difficult to meet the high-efficiency and long-lasting requirements of scenarios such as electrodialysis.

[0005] Furthermore, existing cation exchange membrane preparation processes suffer from insufficient economic and environmental benefits: some processes rely on expensive functional monomers, scarce inorganic fillers, or difficult-to-recover toxic solvents (such as fluorinated solvents), resulting in high production costs; and the high-temperature, high-pressure reaction conditions and the use of large amounts of chemical reagents further exacerbate energy consumption and environmental pollution, which is inconsistent with the development trend of green chemistry. Therefore, developing a cation exchange membrane preparation technology that does not rely on sulfonation / phosphorylation modification, has a mild and environmentally friendly process, and can achieve synergistic optimization of multiple performance characteristics such as "high ion capacity, low surface resistivity, low swelling, and long lifespan" has become the key to breaking through the existing technological bottlenecks. It is of great practical significance for promoting the industrial upgrading of desalination and separation technologies and practicing the concept of energy conservation and environmental protection. Summary of the Invention

[0006] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, embodiments of this invention propose a copolymeric composite cation exchange membrane containing an amino-functionalized inorganic phase, its preparation method, and its application.

[0007] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: In a first aspect, embodiments of the present invention provide a method for preparing a copolymeric composite cation exchange membrane containing an amino-functionalized inorganic phase, comprising the following steps: (1) Add inorganic materials to an alcohol solvent and disperse them by ultrasonication to form a first suspension; then add an aminosilane coupling agent dropwise to the first suspension, heat the reaction, and centrifuge, wash and dry the resulting reaction product to obtain an amino-functionalized inorganic phase; (2) The amino-functionalized inorganic phase is mixed and stirred with a rigid polymer, an amine-containing flexible polymer and a polar organic solvent to form a second suspension; then a crosslinking agent is added to the second suspension and the temperature is raised to react; then an antifoaming agent is added to the obtained copolymer system, the temperature is lowered and stirred to obtain a copolymer-inorganic phase composite membrane liquid. (3) After the copolymer-inorganic phase composite film liquid is degassed, it is coated onto the pretreated substrate. After coating, it is allowed to stand and then dried in a gradient to obtain the composite film. (4) The composite membrane is immersed in a protonating reagent, and then washed and dried to obtain the copolymer composite cation exchange membrane containing amino-functionalized inorganic phase.

[0008] In some embodiments, in step (1), the mass ratio of the inorganic material, the alcohol solvent and the aminosilane coupling agent is (3-4):(60-80):(5-8); Optionally, the inorganic material includes at least one of hydroxyapatite, titanium dioxide, and hydroxyapatite-silica composite powder, and the particle size of the inorganic material is 50-100 nm. Optionally, the alcohol solvent includes at least one of anhydrous ethanol, isopropanol, and ethylene glycol; Optionally, the aminosilane coupling agent includes at least one of 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, and N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane.

[0009] In some embodiments, in step (1), the power of ultrasonic dispersion is 200-300W and the dispersion time is 40-50min; And / or, the heating reaction is carried out at a temperature of 75-85°C for 8-10 hours. And / or, the centrifugation speed is 4000-4500 r / min, and the centrifugation time is 20-25 min each time; And / or, the drying pressure is 0.06-0.1 MPa, the drying temperature is 70-90℃, and the drying time is 16-20 h.

[0010] In some embodiments, in step (2), the mass ratio of the amino-functionalized inorganic phase, the rigid polymer, the amine-containing flexible polymer, the polar organic solvent, and the crosslinking agent is (4-9):(55-65):(25-35):(150-180):(3-5); Optionally, the rigid polymer includes at least one of polyetheretherketone, polysulfone, and polyethersulfone, and the number average molecular weight of the rigid polymer is 30,000-50,000. Optionally, the amine-containing flexible polymer includes at least one of polyallylamine, polyethyleneimine, and polylysine, and the number-average molecular weight of the amine-containing flexible polymer is 10,000-20,000. Optionally, the polar organic solvent includes at least one of N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide; Optionally, the crosslinking agent includes at least one of formaldehyde, glutaraldehyde, and melamine-formaldehyde resin; And / or, the amount of the defoamer added is 0.4-0.7 wt% of the copolymer system; Optionally, the defoamer includes at least one of polyether-modified silicone oil, organosilicon defoamer, and polyoxyethylene polyoxypropylene ether.

[0011] In some embodiments, in step (2), the mixing speed is 400-450 r / min, the mixing temperature is 60-70℃, and the mixing time is 24-30 h; And / or, the reaction temperature of the heating reaction is 80-90℃, and the reaction time is 10-12h; And / or, the temperature of the cooling and stirring is 30-35℃, and the stirring time is 25-35min.

[0012] In some embodiments, in step (3), the degassing process is carried out in a vacuum degassing machine, and the vacuum degree of the vacuum degassing machine is set to -0.08~-0.1MPa, the temperature is 30-35℃, and the degassing time is 2-3h.

[0013] In some embodiments, in step (3), the substrate is selected from any one of glass plate, polytetrafluoroethylene plate, and stainless steel plate; the pretreatment process of the substrate is: wiping the surface of the substrate with anhydrous ethanol or acetone, and then fixing it on a horizontal coating table after drying with nitrogen. And / or, the coating is applied using a coater with a thickness of 200-280 μm, the coater being selected from a stainless steel coater or a polytetrafluoroethylene coater; and the coating speed is 5-8 cm / s. And / or, the settling time is 8-12 minutes; And / or, the gradient drying process is as follows: first, dry at 55-65℃ for 2.5-3.5h, then dry at 80-90℃ for 2.5-3.5h, and finally dry at 100-110℃ and 0.06-0.1MPa vacuum for 2-3h.

[0014] In some embodiments, in step (4), the protonating agent includes at least one of hydrochloric acid solution, sulfuric acid solution, and phosphoric acid solution, and the concentration of the protonating agent is 0.5-0.7 mol / L; And / or, the soaking temperature is 25-35℃, and the soaking time is 10-14h; And / or, the drying is carried out at 55-65°C and 0.06-0.1 MPa for 8-12 hours.

[0015] Secondly, embodiments of the present invention also propose a copolymeric composite cation exchange membrane containing an amino-functionalized inorganic phase, wherein the copolymeric composite cation exchange membrane containing an amino-functionalized inorganic phase is prepared by the preparation method described in the first aspect.

[0016] Thirdly, embodiments of the present invention further propose the application of a copolymer composite cation exchange membrane containing an amino-functionalized inorganic phase as described in the second aspect in electrodialysis desalination.

[0017] The advantages and beneficial effects of the embodiments of the present invention are as follows: (1) Traditional cation exchange membranes often rely on sulfonation (-SO3H) or phosphorylation (-PO3H2) to provide ion sites. However, these groups are easily hydrolyzed and detached, leading to long-term degradation of membrane performance. Furthermore, the sulfonation / phosphorylation reaction requires high-temperature and strong acid conditions, making the process demanding. In contrast, the embodiments of this invention innovatively employ a synergistic protonation activation pathway of "amino-functionalized inorganic phase + rigid-flexible polymer copolymer crosslinking activation". Through protonation reagent treatment, the amino group (-NH2) is converted into a stable cation exchange site (-NH3). + The hydrolytic stability of this site is significantly better than that of traditional sulfonic acid / phosphate groups. At the same time, the rigid polymer and the amine-containing flexible polymer form a covalent copolymer network through a crosslinking agent, which can not only ensure the mechanical strength of the membrane, but also limit the excessive swelling of the flexible chain segments through the rigid skeleton. This achieves a synergistic effect of "high ion capacity + low swelling rate + long stability" from a mechanistic perspective, solving the pain points of traditional cation exchange membranes such as "rapid performance degradation and environmentally unfriendly process".

[0018] (2) Existing inorganic-organic composite ion exchange membranes are mostly physical blend systems. The inorganic phase and polymer interface have poor compatibility and are prone to aggregation and shedding, resulting in ion channel defects. Moreover, single polymer membranes cannot meet the requirements of ion conduction and anti-swelling due to their simple structure. In contrast, the embodiments of the present invention construct a ternary system of "amino-functionalized inorganic phase-rigid polymer-amine-containing flexible polymer": the rigid polymer provides a rigid framework, which can suppress membrane swelling and ensure the mechanical strength of the membrane; the amine-containing flexible polymer can provide a high density of protonable amine groups, laying the foundation for ion exchange; the amino groups on the surface of the amino-functionalized inorganic phase can form hydrogen bonds and electrostatic interactions with the amine groups of the flexible polymer, which not only solves the problem of inorganic phase aggregation, but also forms "dual amine ion sites" to improve ion exchange capacity; at the same time, the physical filling effect of the inorganic phase further regulates the ion transport channels, reduces the surface resistance, and improves the ion conduction efficiency and structural stability of the membrane simultaneously.

[0019] (3) Existing methods for preparing some ion exchange membranes rely on high-temperature and high-pressure copolymerization reactions, toxic crosslinking agents, or solvents that are difficult to recover, resulting in problems such as high energy consumption, significant pollution, and high costs. In contrast, the inorganic materials, rigid polymers, and amine-containing flexible polymers used in the embodiments of this invention are all conventional chemical raw materials with wide availability. Furthermore, the organic solvents used can be recovered and recycled through vacuum distillation. At the same time, the amount of crosslinking agents and protonating reagents used is small, and the reaction conditions are mild, avoiding environmental pollution caused by high-temperature and strong acids. The entire preparation process generates no harmful byproducts, and the inorganic phase functionalization and protonation activation processes only require simple washing for purification. The operation process is simple and controllable, simplifying the preparation process from a mechanistic perspective and reducing energy consumption and raw material costs. At the same time, it ensures the stability and consistency of product performance, which is more in line with the development trend of green chemistry and the requirements of large-scale industrial production. Attached Figure Description

[0020] Figure 1 The graph shows the conductivity changes of the cation exchange membranes prepared in Example 1 and Comparative Example 1 of this invention in the desalination chamber solution.

[0021] Figure 2 The TGA thermogravimetric curves of the cation exchange membranes prepared in Example 6 and Comparative Example 2 of this invention in the desalination chamber solution are shown.

[0022] Figure 3 This is a desalination cycle performance curve of the copolymer composite cation exchange membrane containing amino-functionalized inorganic phase prepared in Example 6 of the present invention. Detailed Implementation

[0023] The embodiments of the present invention are described in detail below. These embodiments are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0024] In this invention, when a value is described as a range, it should be understood that such disclosure includes disclosure of all possible subranges within that range, as well as specific numerical values ​​falling within that range, regardless of whether specific numerical values ​​or specific subranges are explicitly specified.

[0025] In this invention, the terms “comprising” and “including” and their various variations mean that other elements or wholes may be included but are not specifically described.

[0026] In this invention, the term "and / or" is merely a description of the relationship between related objects, indicating that there can be three relationships. For example, A and / or B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone.

[0027] In a first aspect, embodiments of the present invention provide a method for preparing a copolymeric composite cation exchange membrane containing an amino-functionalized inorganic phase, comprising the following steps: (1) Preparation of amino-functionalized inorganic phase: Inorganic materials are added to alcohol solvent and ultrasonically dispersed to form a first suspension; aminosilane coupling agent is then added dropwise to the first suspension and heated to react. The resulting reaction product is centrifuged, washed and dried to obtain amino-functionalized inorganic phase. (2) Preparation of rigid-flexible copolymer-inorganic phase composite membrane liquid: The amino-functionalized inorganic phase is mixed and stirred with a rigid polymer, an amine-containing flexible polymer and a polar organic solvent to form a second suspension; then a crosslinking agent is added to the second suspension and the temperature is raised to react; then, an antifoaming agent is added to the obtained copolymer system, the temperature is lowered and stirred to obtain copolymer-inorganic phase composite membrane liquid; (3) Degassing and coating of composite membrane liquid: After degassing the copolymer-inorganic phase composite membrane liquid, it is coated onto the pretreated substrate. After coating, it is allowed to stand and then dried in a gradient to obtain the composite membrane. (4) Protonation activation of the composite membrane: The composite membrane is immersed in a protonation reagent, and then washed and dried to obtain the copolymer composite cation exchange membrane containing amino-functionalized inorganic phase.

[0028] This invention utilizes a rigid polymer containing active hydrogen as the structural support phase, a flexible polymer containing high-density amine groups as the functional site carrier, and an amino-functionalized inorganic phase as the synergistic reinforcing phase, with the addition of a crosslinking agent. A composite cation exchange membrane is prepared through a three-step core process: "amino-functionalization modification - rigid-flexible polymer copolymerization and crosslinking - protonation activation." By strictly controlling the amount of reactants and reaction conditions, the synergistic structure of "covalent copolymer network - dual amine ion sites - regular transport channels" within the membrane is optimized. The resulting composite cation exchange membrane possesses high ion exchange capacity, low surface resistivity, low swelling ratio, and excellent cycling performance, providing a new approach for preparing high-performance, long-life cation exchange membranes for electrodialysis desalination systems.

[0029] In some embodiments, in step (1), the mass ratio of the inorganic material, the alcohol solvent, and the aminosilane coupling agent is (3-4):(60-80):(5-8). The inventors discovered that if too much inorganic material is added, the concentration of inorganic particles in the first suspension will be too high, making it difficult for ultrasonic dispersion to completely break up agglomerates. This leads to easy stacking between particles, resulting in the aminosilane coupling agent failing to uniformly cover the surface of the inorganic particles, significantly reducing the efficiency of functionalization modification. Furthermore, excessive inorganic material increases the viscosity of the system, making it prone to precipitation and clumping during centrifugal washing, making it difficult to obtain a well-dispersed amino-functionalized inorganic phase. However, if the amount of inorganic material added is too low, the proportion of inorganic particles in the first suspension per unit volume will be insufficient, resulting in a relative excess of the aminosilane coupling agent. The coupling agent molecules are prone to self-polymerization to form siloxane oligomers, which cannot be effectively grafted onto the surface of the inorganic material, leading to insufficient amino grafting density in the amino-functionalized inorganic phase. This weakens the subsequent interfacial interaction with the polymer matrix, preventing the synergistic effect from being fully realized. The same enhancement effect; however, if the amount of aminosilane coupling agent added is too much, in addition to initiating the self-polymerization of the coupling agent, the excess coupling agent will also remain in the product, increasing the difficulty of washing and purification, and the residual coupling agent is prone to causing side reactions in the subsequent copolymerization process, destroying the polymer network structure; but if its addition amount is too low, it cannot completely cover the active hydroxyl groups on the surface of the inorganic material, the amino grafting density is low, and the functionalized inorganic phase cannot provide enough hydrogen bond binding sites, resulting in a decrease in the ion exchange capacity and structural stability of the composite membrane; in addition, if the amount of alcohol solvent added is too much, it will dilute the concentration of inorganic material and coupling agent, reduce the probability of contact between the two, prolong the reaction time, and the excessive solvent will increase the subsequent recovery cost; but if the amount of alcohol solvent added is too low, it will lead to a large viscosity of the first suspension, uneven dispersion of inorganic material, and hindered diffusion of coupling agent, which will also lead to a decrease in modification efficiency. Therefore, in the embodiments of the present invention, it is advantageous to control the mass ratio of inorganic material, alcohol solvent and aminosilane coupling agent in the range of (3-4):(60-80):(5-8). Optionally, the inorganic material includes at least one of hydroxyapatite (HAP), titanium dioxide (TiO2), and hydroxyapatite-silica composite powder (HAP-SiO2), wherein the particle size of the inorganic material is 50-100 nm; by selecting natural biocompatible or industrially commonly used inorganic materials, the surface of which contains a large number of -OH and / or -PO4. 3- It can provide active sites for the functional modification of materials; Optionally, the alcohol solvent includes at least one of anhydrous ethanol, isopropanol, and ethylene glycol; Optionally, the aminosilane coupling agent includes at least one of 3-aminopropyltriethoxysilane (KH-550), 3-aminopropyltrimethoxysilane (KH-540), and N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane (KH-792).

[0030] In some embodiments, in step (1), the power of ultrasonic dispersion is 200-300W and the dispersion time is 40-50min; And / or, the heating reaction is carried out in a constant temperature water bath at a temperature of 75-85°C for a time of 8-10 hours; and the heating reaction is accompanied by magnetic stirring at a speed of 300-350 r / min. And / or, the centrifugation speed is 4000-4500 r / min, and the centrifugation time is 20-25 min each time; And / or, the washing is first performed by washing with an alcohol solvent multiple times, followed by centrifugation after each wash to remove unreacted aminosilane coupling agent and byproducts, and finally by washing with deionized water multiple times to remove residual alcohol solvent. And / or, the drying pressure is 0.06-0.1 MPa, the drying temperature is 70-90℃, and the drying time is 16-20 h.

[0031] In step (1) of this embodiment, the alkoxy group in the aminosilane coupling agent molecule undergoes a hydrolysis-condensation reaction with the -OH group on the surface of the inorganic material, thereby covalently grafting the amino group (-NH2) onto the surface of the inorganic material to obtain an amino-functionalized inorganic phase (denoted as NH2-inorganic phase). The amino group on the surface of this amino-functionalized inorganic phase can be protonated in concert with the amino group of the subsequent amino-containing polymer, providing a high density of cation exchange sites for the composite membrane.

[0032] In some embodiments, in step (2), the mass ratio of the amino-functionalized inorganic phase, the rigid polymer, the amine-containing flexible polymer, the polar organic solvent, and the crosslinking agent is (4-9):(55-65):(25-35):(150-180):(3-5). The inventors have found that if the amount of amino-functionalized inorganic phase is too high, the inorganic particles will be difficult to disperse uniformly in the polymer matrix, and excessive particles are prone to agglomeration, forming defects within the membrane. Simultaneously, the rigid structure of excessive inorganic phase will damage the flexibility of the polymer network, increasing the brittleness of the composite membrane, decreasing its tensile strength, and agglomerated particles will block ion transport channels, leading to increased sheet resistance. However, if its... If the dosage is too low, the synergistic enhancement effect of the inorganic phase cannot be fully utilized. It cannot provide enough additional amino ion sites, leading to a decrease in ion exchange capacity (IEC). Simultaneously, due to the lack of physical filling by the inorganic phase, the polymer segments are prone to excessive swelling in aqueous solution, with a swelling rate exceeding 15%, which distorts the ion channels and affects the long-term cycling stability of the membrane. Conversely, if too much rigid polymer is used, the polymer network becomes overly rigid, with insufficient proportion of flexible segments, significantly reducing the membrane's elongation at break and decreasing its flexibility, making it prone to brittleness during the assembly and operation of the electrodialysis device. Furthermore, excessive rigid polymer will crowd out the distribution space of the amine-containing flexible polymer, leading to a decrease in protonation site density and a decline in IEC. However, if the dosage is too low, a stable rigid framework cannot be formed, and the hydrophilic swelling of the flexible polymer segments cannot be effectively limited. The swelling rate of the membrane will increase sharply, and even swelling and rupture may occur. Insufficient rigid support will lead to insufficient mechanical strength of the membrane, making it difficult to withstand the water flow pressure and electric field forces during electrodialysis. On the other hand, if the dosage of amine-containing flexible polymers is too high, the polymer network will become too flexible, the inter-segment forces will weaken, and the membrane's anti-swelling performance will decrease significantly. At the same time, excessive flexible segments will encapsulate some inorganic phase particles, hindering the contact between the inorganic phase amino groups and protonating reagents, reducing the utilization rate of ion sites, and easily causing the membrane to shrink and deform during drying. However, if the dosage is too low, it will not provide enough amine groups. The lack of cation exchange sites after protonation of the crosslinking agent results in a low IEC (intercalation efficiency), significantly reducing ion conduction efficiency and failing to meet the application requirements of electrodialysis desalination. Excessive crosslinking agent can lead to over-crosslinking of the polymer, making the network structure too dense, hindering the penetration and diffusion of water molecules and ions, resulting in decreased ion conduction rate and increased sheet resistance. Furthermore, excessive crosslinking reduces membrane flexibility, increases brittleness, and decreases bending resistance. Conversely, insufficient crosslinking density leads to weak covalent bonds between polymer segments, resulting in poor membrane structural stability, easy segment dissociation in aqueous solution, and increased swelling rate. Additionally, the polymer network is prone to loosening during cycling, causing inorganic phase particles to detach and rapidly degrading membrane performance.Furthermore, excessive use of polar organic solvents will dilute the concentration of each reaction component, reduce the contact probability between the rigid polymer, flexible polymer, and crosslinking agent, prolong the copolymerization reaction time, and increase the energy consumption of subsequent degassing and drying, thus increasing production costs. Simultaneously, excessive solvents will lead to low membrane viscosity, making it prone to sagging during coating and difficult to control the uniformity of membrane thickness. However, if the amount is too low, the membrane viscosity will be too high, making it difficult for the components to mix uniformly, especially the amino-functionalized inorganic phase, which is prone to sedimentation and aggregation. High-viscosity membrane solutions also increase coating difficulty, increase the coating resistance of the coater, and easily form unevenly thick liquid films, ultimately resulting in poor performance consistency of the finished membrane. Therefore, controlling the mass ratio of the amino-functionalized inorganic phase, rigid polymer, amine-containing flexible polymer, polar organic solvent, and crosslinking agent within the above-mentioned range is advantageous in this embodiment of the invention. Optionally, the rigid polymer includes at least one of polyether ether ketone (PEEK), polysulfone (PSF), and polyether sulfone (PES), with a number average molecular weight of 30,000-50,000. The selected rigid polymer contains a benzene ring or heterocyclic rigid backbone in its molecular structure, which can ensure the mechanical strength and thermal stability of the membrane. Furthermore, the active hydrogen contained in the backbone can undergo nucleophilic substitution reaction with the amine group. Optionally, the amine-containing flexible polymer includes at least one of polyallylamine (PAH), polyethyleneimine (PEI), and polylysine (PLL), with a number-average molecular weight of 10,000-20,000. The molecular chain of the selected amine-containing flexible polymer contains a large number of primary, secondary, or tertiary amine groups, which are both monomers participating in copolymerization and functional group carriers providing cation exchange sites. Optionally, the polar organic solvent includes at least one of N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMAc); Optionally, the crosslinking agent includes at least one of formaldehyde, glutaraldehyde, and melamine-formaldehyde resin; And / or, the amount of the defoamer added is 0.4-0.7 wt% of the copolymer system; Optionally, the defoamer includes at least one of polyether-modified silicone oil, organosilicon defoamer (e.g., methyl silicone oil), and polyoxyethylene polyoxypropylene ether.

[0033] In some embodiments, in step (2), the mixing speed is 400-450 r / min, the mixing temperature is 60-70℃, and the mixing time is 24-30 h; And / or, the reaction temperature of the heating reaction is 80-90℃, and the reaction time is 10-12h; And / or, the temperature of the cooling and stirring is 30-35℃, and the stirring time is 25-35min.

[0034] In step (2) of this embodiment, by mixing and stirring the amino-functionalized inorganic phase with the rigid polymer, the amine-containing flexible polymer, and the polar organic solvent, the rigid polymer and the amine-containing flexible polymer can be fully dissolved, while the amino-functionalized inorganic phase is uniformly dispersed in the system to form a second suspension. Then, a crosslinking agent is added to the second suspension. The crosslinking agent molecules first form imine or amide intermediates with the amine groups of the amine-containing flexible polymer, and then undergo nucleophilic substitution or addition reactions with the active hydrogens on the rigid polymer backbone, ultimately forming a covalently crosslinked interpenetrating network of "rigid polymer-crosslinking agent-flexible polymer," which can significantly enhance the structural stability of the base membrane. Afterwards, an antifoaming agent is used to remove the bubbles and dissolved gases generated during the above reaction process, thereby obtaining a homogeneous, transparent, stable, and precipitate-free copolymer-inorganic phase composite membrane liquid. In this composite membrane liquid system, the rigidity of the rigid polymer and the flexibility of the amine-containing flexible polymer form a synergistic structure, and the amine groups in the amine-containing flexible polymer and the amino groups in the amino-functionalized inorganic phase form a complementary function, laying the foundation for subsequent improvement of ion exchange performance.

[0035] In some embodiments, in step (3), the degassing process is performed in a vacuum degassing machine, with the vacuum level set to -0.08 to -0.1 MPa, the temperature to 30-35°C, and the degassing time to 2-3 hours. It should be noted that during the degassing process, gas needs to be released every 30 minutes to thoroughly remove dissolved air and residual micro-bubbles from the copolymerization reaction in the composite film solution, thus preventing defects such as pinholes and cracks after subsequent film formation.

[0036] In some embodiments, in step (3), the substrate is selected from any one of glass plate, polytetrafluoroethylene plate, and stainless steel plate; the pretreatment process of the substrate is: wiping the surface of the substrate with anhydrous ethanol or acetone to remove oil and impurities from the substrate surface, and then fixing it on a horizontal coating table after drying with nitrogen to ensure that the substrate surface is flat and without tilt. And / or, the coating is applied using a coater with a thickness of 200-280 μm, the coater being selected from a stainless steel coater or a polytetrafluoroethylene coater; and the coating speed is 5-8 cm / s. And / or, the settling time is 8-12 minutes; by settling, the liquid film on the substrate is allowed to level naturally, eliminating scratches, while the solvent is allowed to diffuse slowly, ensuring a uniform internal structure of the film. Since the viscosity of this copolymer system is moderate (5000-8000 mPa·s at 25°C), its leveling properties are significantly better than those of traditional single polymer-based systems, which can effectively improve the film quality. And / or, the gradient drying process is as follows: first, drying at 55-65℃ for 2.5-3.5h to slowly evaporate most of the polar organic solvent in the liquid film, avoiding uneven film shrinkage due to rapid solvent evaporation; then drying at 80-90℃ for 2.5-3.5h to further remove residual solvent, while strengthening the interfacial bonding force between the copolymer crosslinking network and the amino-functionalized inorganic phase, so that the amine groups on the amine-containing flexible polymer molecular chain and the amines on the surface of the amino-functionalized inorganic phase form a stable bond through hydrogen bonding and electrostatic interaction, improving the structural compactness of the film; finally, drying at 100-110℃ and 0.06-0.1MPa vacuum for 2-3h to completely remove the residual polar organic solvent in the film, avoiding the impact of solvent residue on ion transport performance.

[0037] In some embodiments, in step (4), the protonating agent includes at least one of hydrochloric acid solution, sulfuric acid solution, and phosphoric acid solution, and the concentration of the protonating agent is 0.5-0.7 mol / L; by immersing the preliminarily formed composite membrane in the protonating agent, the amine groups on the amine-containing flexible polymer molecular chain can fully undergo a protonation reaction with the amino groups on the surface of the amino-functionalized inorganic phase (-NH2+ H + → -NH3 + This process creates stable cation exchange sites; at the same time, the protonating agent can slightly etch the membrane surface to form a micron-scale rough structure, increasing the contact area between ions and the membrane surface, thereby improving ion transport efficiency. And / or, the soaking temperature is 25-35°C, and the soaking time is 10-14 hours; and the inventors have found through research that if the protonation time is too long (more than 14 hours), it will lead to excessive protonation reaction: on the one hand, excessive H... + This can disrupt the hydrogen bond and covalent cross-linking network of the "rigid polymer-flexible polymer-amino-functionalized inorganic phase" within the membrane, causing the polymer chains to swell and relax, reducing the interfacial bonding between the inorganic phase particles and the polymer matrix, and consequently leading to a decrease in the membrane's mechanical strength and an increase in its swelling rate. On the other hand, excessive protonation can cause the amino groups on the membrane surface to be completely protonated (-NH2→-NH3). + This creates a high-density positively charged region, triggering a charge repulsion effect that hinders the migration and transport of cations within the membrane, leading to a "saturation decrease" in ion exchange capacity (IEC). Simultaneously, the membrane's surface resistivity increases. However, if the protonation time is too short (less than 10 hours), the protonation reaction is insufficient: the amine-containing flexible polymer molecular chains and the amine groups on the surface of the amino-functionalized inorganic phase cannot be fully activated and converted into cation exchange sites (-NH3). +Insufficient cation exchange sites result in a low ion exchange capacity of the membrane, failing to meet the ion conduction requirements of electrodialysis desalination. Simultaneously, unprotonated amine groups remain within the membrane, reducing its hydrophilicity and the continuity of ion transport channels, ultimately leading to a significant decrease in desalination efficiency in the electrodialysis system. Therefore, in this embodiment of the invention, the protonation time is controlled within 10-14 hours to achieve efficient and appropriate protonation of amine groups, ensuring the formation of sufficient cation exchange sites while maintaining the structural stability of the intramembrane cross-linked network, thereby achieving synergistic optimization of the membrane's ion conduction and mechanical properties. And / or, the washing involves washing the composite membrane multiple times with deionized water, and the pH value of the washing solution is tested after each washing until the pH value of the washing solution reaches 6.5-7.5, so as to completely remove the protonating reagents remaining on the membrane surface. And / or, the drying is carried out at 55-65°C and 0.06-0.1 MPa for 8-12 hours.

[0038] Secondly, embodiments of the present invention also propose a copolymeric composite cation exchange membrane containing an amino-functionalized inorganic phase, wherein the copolymeric composite cation exchange membrane containing an amino-functionalized inorganic phase is prepared by the preparation method described in the first aspect.

[0039] Thirdly, embodiments of the present invention further propose the application of a copolymer composite cation exchange membrane containing an amino-functionalized inorganic phase as described in the second aspect in electrodialysis desalination.

[0040] The following are non-limiting embodiments and comparative examples of the present invention. It should be noted that the schemes in the comparative examples are not prior art, but are only set up for comparison with the schemes in the embodiments, and are not intended to limit the present invention. Unless otherwise stated, all raw materials used in the embodiments and comparative examples are conventional commercially available products, or can be prepared by known methods.

[0041] Example 1 This embodiment provides a method for preparing a copolymeric cation exchange membrane containing an amino-functionalized inorganic phase, comprising the following steps: (1) Preparation of amino-functionalized hydroxyapatite (NH2-HAP) By mass fraction, 3.5 parts of hydroxyapatite (HAP, particle size 80 nm) were added to 80 parts of anhydrous ethanol and ultrasonically dispersed for 45 min at a power of 250 W to form a uniform and stable first suspension. Then, 6 parts of 3-aminopropyltriethoxysilane (KH-550) were added dropwise to the first suspension and placed in an 80°C constant temperature water bath. The mixture was magnetically stirred at 320 r / min for 9 h. After the reaction was completed, the mixture was cooled to room temperature and then transferred to a centrifuge tube. The mixture was centrifuged at 4200 r / min for 22 min, and the bottom solid precipitate was collected. The precipitate was washed three times with anhydrous ethanol and twice with deionized water. The precipitate was then placed in a vacuum drying oven and dried at 80°C and 0.08 MPa for 18 h. The precipitate was then ground into a fine powder to obtain amino-functionalized hydroxyapatite (denoted as NH2-HAP), which was sealed, dried, and stored for later use.

[0042] (2) Preparation of rigid-flexible copolymer-inorganic phase composite film liquid (functional group synergistic copolymerization system) By mass, 6 parts of amino-functionalized hydroxyapatite (NH2-HAP), 60 parts of polyether ether ketone (PEEK), and 30 parts of polyallylamine (PAH) were weighed and placed together in a three-necked flask. 160 parts of N-methylpyrrolidone (NMP) were added to the flask, and the mixture was magnetically stirred at 420 r / min for 26 h at 65 °C to form a second suspension. Then, 4 parts of formaldehyde were added to the second suspension, the temperature was raised to 85 °C, and the mixture was stirred for 11 h. After that, 0.5% of the total mass of polyether-modified silicone oil was added to the obtained copolymer system, the temperature was lowered to 32 °C, and the mixture was stirred for another 30 min to obtain a homogeneous, transparent, stable, and precipitate-free copolymer-inorganic phase composite film solution.

[0043] (3) Degassing and coating of membrane solution The copolymer-inorganic phase composite membrane liquid prepared in step (2) was transferred to a vacuum degassing machine for degassing treatment. The vacuum degree of the vacuum degassing machine was set to -0.09MPa, the temperature to 32℃, and the degassing time to 2.5h. During this period, the gas was released once every 30min to completely remove the dissolved air and trace bubbles remaining in the copolymerization reaction from the membrane liquid. Then, take a 15cm×15cm glass plate with a smooth, clean, and dry surface. Wipe the surface with anhydrous ethanol to remove oil and impurities. After drying with nitrogen, fix it on a horizontal coating table, ensuring that the glass plate surface is flat and without tilt. Then, use a graduated cylinder to transfer 14 portions of the degassed copolymer-inorganic phase composite film liquid, and pour it evenly onto one end of the glass plate. Then, use a 220μm thick stainless steel coater to coat the film at a uniform speed in the same direction, so that the film liquid forms a continuous and uniform liquid film on the surface of the glass plate. The coating speed is controlled at 6cm / s to ensure the consistency of film thickness. After coating, let the glass plate stand for 10 minutes to allow the liquid film to level naturally. Then, place the leveled liquid film together with the glass plate in a vacuum drying oven. First, dry at 60℃ for 3 hours, then at 85℃ for 3 hours, and finally at 105℃ and 0.08MPa vacuum for 2.5 hours. After drying, let it cool naturally to room temperature. Use a blade to gently scratch along the edge of the substrate and slowly peel off the preliminarily formed composite film.

[0044] (4) Protonation activation Prepare 0.6 mol / L hydrochloric acid and immerse the preliminarily formed composite membrane obtained in step (3) completely in it. Static soak in a constant temperature water bath at 30℃ for 12 hours. After soaking, wash the membrane repeatedly with deionized water. Detect the pH value of the washing solution after each wash until the pH value of the washing solution reaches 6.5-7.5. Finally, place the washed membrane in a vacuum drying oven and dry it at 60℃ and 0.08 MPa for 10 hours. With constant membrane quality, a copolymer composite cation exchange membrane containing amino-functionalized inorganic phase can be obtained.

[0045] Example 2 The preparation method of this embodiment is basically the same as that of Example 1, except that in step (1) of this embodiment, titanium dioxide (TiO2 with a particle size of 80nm) is used instead of hydroxyapatite (HAP).

[0046] Example 3 The preparation method of this embodiment is basically the same as that of Example 1, except that in step (1) of this embodiment, N-(β-aminoethyl)-γ-aminopropyltriethoxysilane (KH-792) is used instead of 3-aminopropyltriethoxysilane (KH-550).

[0047] Example 4 The preparation method of this embodiment is basically the same as that of Example 1, except that in step (2) of this embodiment, the amount of amino-functionalized hydroxyapatite (NH2-HAP) is 4 parts.

[0048] Example 5 The preparation method of this embodiment is basically the same as that of Example 1, except that in step (2) of this embodiment, the amount of amino-functionalized hydroxyapatite (NH2-HAP) is 8 parts.

[0049] Example 6 The preparation method of this embodiment is basically the same as that of Example 1, except that in step (2) of this embodiment, the amount of amino-functionalized hydroxyapatite (NH2-HAP) is 9 parts.

[0050] Example 7 The preparation method of this embodiment is basically the same as that of Example 1, except that in step (2) of this embodiment, the amount of polyether ether ketone (PEEK) is 55 parts and the amount of polyallylamine (PAH) is 35 parts.

[0051] Example 8 The preparation method of this embodiment is basically the same as that of embodiment 1, except that in step (2) of this embodiment, the amount of formaldehyde used is 3 parts.

[0052] Example 9 The preparation method of this embodiment is basically the same as that of embodiment 1, except that in step (2) of this embodiment, the amount of formaldehyde used is 5 parts.

[0053] Example 10 The preparation method of this embodiment is basically the same as that of Example 1, except that in step (2) of this embodiment, polysulfone (PSF) is used instead of polyether ether ketone (PEEK).

[0054] Example 11 The preparation method of this embodiment is basically the same as that of Example 1, except that in step (2) of this embodiment, polylysine (PLL) is used instead of polyallylamine (PAH).

[0055] Example 12 The preparation method of this embodiment is basically the same as that of embodiment 1, except that in step (2) of this embodiment, melamine-formaldehyde resin is used instead of formaldehyde.

[0056] Example 13 The preparation method of this embodiment is basically the same as that of embodiment 1, except that the soaking time of the protonating reagent in step (4) of this embodiment is 10h.

[0057] Example 14 The preparation method of this embodiment is basically the same as that of embodiment 1, except that the soaking time of the protonating reagent in step (4) of this embodiment is 14h.

[0058] Comparative Example 1 The preparation method of this comparative example is basically the same as that of Example 1. The difference is that this comparative example does not include step (1), and amino-functionalized hydroxyapatite (NH2-HAP) is not added in step (2). At the same time, the amount of polyether ether ketone (PEEK) is adjusted to 66 parts and the amount of polyallylamine (PAH) is adjusted to 34 parts. The final product is a pure copolymer cation exchange membrane.

[0059] Comparative Example 2 The preparation method of this comparative example is basically the same as that of Example 1. The difference is that in step (2) of this comparative example, no crosslinking agent methanol is added. That is, the rigid polymer PEEK and the amine-containing flexible polymer PAH are only physically mixed, and the final product is also a polymer-inorganic phase physical blend film.

[0060] Comparative Example 3 The preparation method of this comparative example is basically the same as that of Example 1. The difference is that in step (2) of this comparative example, polyallylamine (PAH) is not added, and the amount of polyether ether ketone (PEEK) is adjusted to 96 parts. The final product is a rigid polymer-inorganic phase composite cation exchange membrane.

[0061] Comparative Example 4 The preparation method of this comparative example is basically the same as that of Example 1. The difference is that polyether ether ketone (PEEK) is not added in step (2) of this comparative example. The final product is an amine-containing flexible polymer-inorganic phase composite cation exchange membrane.

[0062] Comparative Example 5 The preparation method of this comparative example is basically the same as that of Example 1. The difference is that in step (3) of this comparative example, the drying process of the coated liquid film is as follows: the leveled liquid film together with the glass plate is placed in a vacuum drying oven and dried at 105°C and 0.06-0.1MPa vacuum for 3 hours.

[0063] Comparative Example 6 The preparation method of this comparative example is basically the same as that of Example 1, except that step (4) is not included in this comparative example.

[0064] The performance of the cation exchange membranes prepared in the above embodiments and comparative examples was tested: 1) Membrane thickness test The cation exchange membrane was cut into flat samples, and the thickness was measured in different areas of the membrane (at least 5 evenly distributed test points) using a digital thickness gauge (accuracy 0.01 μm). The average value of the data at each point was recorded as the final thickness of the membrane.

[0065] 2) Ion exchange capacity (IEC) test The cation exchange membrane was cut into 2cm × 2cm square samples and dried in a vacuum drying oven at 60℃ and 0.08MPa until the mass was constant. The mass of the dried membrane (m0) was recorded. Then, the dried membrane was completely immersed in a 0.5mol / L NaCl solution and soaked at 25℃ for 24h to allow the cation exchange sites inside the membrane to interact with the NaCl in the solution. + Complete exchange; after removing the membrane, rinse the surface with deionized water, then immerse the membrane in a 0.1 mol / L NaOH solution and stir at 25°C for 2 hours to allow the bound Na to be fully exchanged. + by OH - Displacement; finally, titrate the above NaOH solution with 0.1 mol / L HCl standard solution and record the volume of HCl consumed (V). The ion exchange capacity is calculated using the formula: IEC retention rate = (C × V) / m0, where C is the concentration of the HCl standard solution (mol / L).

[0066] 3) Surface resistivity (MR) test The AC impedance method was used for testing: the cation exchange membrane was cut into 2cm×2cm samples and completely immersed in 0.5mol / L NaCl solution for equilibration for 24h; then the membrane was fixed between two platinum electrodes (electrode area 2cm×2cm) to form a two-electrode system, and the impedance value of the system was tested at a frequency of 1kHz using an electrochemical workstation; at the same time, the impedance value of the blank system without the membrane was tested, and the difference between the two was the sheet resistance of the membrane.

[0067] 4) Swelling rate test The cation exchange membrane was cut into 2cm × 2cm square samples and dried in a vacuum drying oven at 60℃ and 0.08MPa until the mass was constant. The mass of the dry membrane (m1) was recorded. The dry membrane was then completely immersed in deionized water and soaked at 25℃ for 24 hours. After removal, the surface moisture was blotted dry with filter paper, and the mass of the wet membrane (m2) was immediately recorded. The swelling rate was calculated using the formula: Swelling rate = (m2 - m1) / m1 × 100%.

[0068] 5) Performance retention rate test after 100 cycles A cation exchange membrane was assembled into an electrodialysis desalination single cell (membrane area 2cm × 2cm, both desalination and concentration chambers are 0.5mol / L NaCl solution). Operating parameters were set as follows: 30 min of desalination at 1.5V + 30 min of short-circuit regeneration constitutes one cycle. The final conductivity (σ1) of the desalination chamber was measured after the first cycle. After 100 consecutive cycles, the final conductivity (σ1) of the 100th cycle was measured. 100 Cyclic performance retention rate is calculated using the formula: Cyclic performance retention rate after 100 cycles = (σ1 - σ) 100 ) / σ1×100%.

[0069] The test results are shown in Table 1.

[0070] Table 1

[0071] Table 1 clearly presents the control mechanism of the core raw material characteristics and dosage on the cation exchange membrane performance. Regarding the selection of inorganic materials and coupling agents, Example 2 used titanium dioxide instead of hydroxyapatite. Because titanium dioxide has a lower hydroxyl density on its surface and insufficient amino grafting efficiency, this resulted in lower IEC (1.82 mmol / g) and lower sheet resistivity (4.2 Ω·cm). 2 Example 3 was slightly inferior to Example 1; however, Example 3 used a diamino coupling agent KH-792 instead of KH-550. The diamino structure provided a higher density of active sites and stronger hydrogen bonding with the polymer, increasing the IEC to 1.91 mmol / g and reducing the sheet resistivity to 3.8 Ω·cm. 2 This study verified the enhancing effect of coupling agent type on functionalization efficiency. Regarding the amount of inorganic phase used for amino-functionalization, as the amount of NH2-HAP increased from 4 parts to 9 parts, the IEC increased from 1.72 mmol / g to 1.98 mmol / g, and the sheet resistivity increased from 4.7 Ω·cm. 2 Reduced to 3.4Ω·cm 2 The swelling ratio decreased from 16.8% to 12.8%. This is because the appropriate addition of inorganic phase can both supplement amino sites to achieve synergistic protonation and physically fill the regular ion channels. In contrast, Comparative Example 1, which did not add inorganic phase, lacked physical enhancement and additional ion sites, and its IEC was only 1.56 mmol / g, while its swelling ratio soared to 19.7%, highlighting the core synergistic effect of inorganic phase.

[0072] The polymer system formulation and process parameters have a crucial impact on membrane performance. Regarding the polymer-to-crosslinker ratio, Example 7 adjusted the ratio of rigid polymer PEEK to flexible polymer PAH to 55:35. Although the swelling rate slightly increased to 14.8% due to the increased proportion of flexible segments, the IEC remained at 1.83 mmol / g, demonstrating the flexibility of the formulation range. In Example 8, due to only 3 parts of formaldehyde as the crosslinker, the crosslinking density was insufficient, resulting in a loose membrane structure, a swelling rate of 17.3%, and a cycle retention rate of 87.8%. In contrast, Example 9 used 5 parts of crosslinker to achieve sufficient crosslinking, improving the membrane structure density, achieving an IEC of 1.89 mmol / g, and a sheet resistivity of 3.7 Ω·cm. 2In Comparative Example 2, due to the absence of a crosslinking agent, the polymers were only physically mixed, resulting in a cation exchange membrane with a swelling ratio as high as 23.5% and a cycle retention rate of only 65.7%, fully verifying the crucial role of the crosslinking agent in membrane structure stability. Furthermore, Comparative Example 3, lacking the flexible polymer PAH and relying solely on a small amount of amino groups in the inorganic phase, resulted in a final cation exchange membrane with an IEC of only 1.51 mmol / g, indicating insufficient ion conduction. In contrast, Comparative Example 4, lacking the rigid polymer PEEK and lacking skeletal support, exhibited a swelling ratio as high as 21.3% and a cycle retention rate of only 72.8%, indicating a membrane structure prone to relaxation. This further corroborates the synergistic innovation of the "rigid-flexible-inorganic phase" ternary system, which overcomes the limitations of traditional pathways through an amine matrix protonation mechanism, achieving synergistic optimization of multiple performance characteristics.

[0073] Furthermore, key process steps and system integrity directly determine the upper limit of membrane performance. Regarding protonation time, Example 13 (10h) showed insufficient protonation, resulting in an IEC of 1.81 mmol / g and a sheet resistivity of 4.3 Ω·cm. 2 In contrast, Example 14 (14h) showed adequate protonation, with the IEC increasing to 1.90 mmol / g; while Comparative Example 6, lacking protonation, had only trace amino sites remaining, resulting in an IEC of only 0.42 mmol / g and a surface resistivity as high as 15.3 Ω·cm. 2 This clearly demonstrates that protonation is a necessary step for the formation of effective cation exchange sites. However, in the drying process, Comparative Example 5 used a one-step drying method, leading to rapid solvent evaporation, the formation of intramembrane defects, and a sheet resistivity as high as 5.0 Ω·cm. 2 The swelling rate was 18.5%, which was significantly worse than the gradient drying process in Example 1, verifying the role of gradient drying in ensuring the compactness of the membrane structure.

[0074] Figure 1The graph shows the conductivity changes of the cation exchange membranes prepared in Example 1 and Comparative Example 1 in the desalination chamber solution (the test method was as follows: the membranes were assembled into an electrodialysis desalination single cell, and a NaCl solution with an initial conductivity of 14 mS / cm was used as the desalination chamber solution. The desalination process was run at 1.5V, and the ionic conductivity of the desalination chamber solution was tested every 10 minutes for 180 minutes. The changes in ionic conductivity over time were recorded to obtain the ionic conductivity change graph). As can be seen from the graph, the copolymeric cation exchange membrane containing amino-functionalized inorganic phase prepared in Example 1 showed a rapid and continuous decrease in ionic conductivity from 14 mS / cm within 180 minutes, with a final value of only about 1.7 mS / cm. In contrast, the pure copolymeric cation exchange membrane prepared in Comparative Example 1 showed a slower rate of conductivity decrease, with a final value of about 1.2 mS / cm after 180 minutes, indicating a significantly weaker desalination depth than that of Example 1. This is mainly because the "PEEK+PAH+NH2-HAP" ternary system in Example 1 constructs a synergistic structure of "high-capacity ion sites + low-resistance transport channels": the rigid framework of PEEK ensures the mechanical strength of the membrane, and the amino groups of PAH and NH2-HAP are protonated in synergistic manner, resulting in sufficient ion exchange capacity, with an IEC as high as 1.86 mmol / g; at the same time, the uniform pores formed by the copolymer network can reduce ion transport resistance, so the sheet resistivity of the cation exchange membrane prepared in Example 1 is only 4.0 Ω·cm. 2 This can accelerate the migration efficiency of cations. However, in Comparative Example 1, due to the absence of NH2-HAP and reliance solely on the amino groups of PAH to provide ion sites, the ion exchange capacity is insufficient, with an IEC of only 1.56 mmol / g; furthermore, the single PAH segment is prone to swelling, leading to ion channel distortion and an increase in surface resistivity to 5.8 Ω·cm. 2 The cation migration rate is limited, resulting in a more gradual decrease in the conductivity of the desalination chamber and a significant reduction in desalination efficiency.

[0075] Figure 2The thermogravimetric analysis (TGA) curves of the cation exchange membranes prepared in Example 6 and Comparative Example 2 in the desalination chamber solution are shown below. (The test method was as follows: the membrane sample was ground into a fine powder, placed in an alumina crucible, and heated from room temperature to 1000℃ at a rate of 10℃ / min under a nitrogen atmosphere (flow rate 50 mL / min). The change in sample mass with temperature was recorded in real time to obtain the thermogravimetric curves.) As can be seen from the figure, the copolymeric cation exchange membrane containing amino-functionalized inorganic phase prepared in Example 6 exhibits a "low-temperature micro-weight loss - high-temperature slow decrease" characteristic: only about 5% of the mass is lost before 200℃, corresponding to the residual NMP solvent and adsorbed water; the mass decreases slowly after 400℃, with a residual amount of about 35% at 800℃. In contrast, the polymer-inorganic phase physical blend membrane prepared in Comparative Example 2 shows rapid mass decay after 200℃, with a loss of over 40% at 400℃, and a residual amount of less than 20% at 800℃. This is because the "PEEK-PAH covalent copolymer network + NH2-HAP inorganic reinforcing phase" in Example 6 forms a dual thermally stable structure: on the one hand, the rigid benzene ring skeleton of PEEK and PAH form a dense interpenetrating network through formaldehyde crosslinking, which restricts the thermal movement of polymer chain segments and avoids weight loss caused by chain segment untangling at low temperatures; on the other hand, the hydroxyapatite inorganic skeleton of NH2-HAP has high heat resistance, and the hydrogen bonding between its surface amino groups and polymer amine groups further enhances the thermal stability of the system and slows down the decomposition rate of the polymer at high temperatures. In contrast, Comparative Example 2 is a physical blend system, where PEEK and PAH do not form covalent bonds, and the chain segments are only bound by van der Waals forces. After heating, the chain segments are easily loosened and small molecules are easily released; moreover, the interfacial bonding force between NH2-HAP and the polymer is weak, and it cannot play a thermal barrier role. Therefore, the thermal stability of the resulting cation exchange membrane is significantly deteriorated.

[0076] Figure 3 The figure shows the desalination cycle performance curve of the copolymer composite cation exchange membrane containing amino-functionalized inorganic phase prepared in Example 6 of this invention (the test method was as follows: the membrane was assembled into an electrodialysis desalination single cell, using 0.5 mol / L NaCl solution as the treatment solution, and desalination at 1.5V for 100 min was set as one cycle, and 6 cycles were run continuously; the ionic conductivity of the desalination chamber solution was monitored in real time during each cycle, and the ionic conductivity-time curve of each cycle was recorded to obtain the desalination cycle performance curve). As can be seen from the figure, all 6 curves show a "rapid decrease" pattern, and the final conductivity value of each cycle is basically consistent with the rate of decrease, without significant fluctuations. This is because the amount of NH2-HAP in Example 6 was as high as 89 parts, and its surface amino groups formed a high-density protonation sites (-NH3) with the amino groups of PAH. +With an IEC as high as 1.95 mmol / g, it ensures continuous cation exchange capacity. Simultaneously, the copolymer crosslinking network of PEEK and PAH controls the membrane swelling rate at 13.2%, maintaining the regularity of ion transport channels and avoiding the channel distortion problem caused by swelling in traditional membranes. Furthermore, the interfacial hydrogen bonding between NH2-HAP and the polymer inhibits the shedding of the inorganic phase, ensuring stable ion site density in each cycle. Therefore, in six consecutive desalination cycles, cations from the desalination chamber can stably migrate to the concentration chamber through the regular channels of the membrane, with highly consistent conductivity changes, demonstrating the long-term desalination stability of the membrane.

[0077] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0078] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a copolymeric composite cation exchange membrane containing an amino-functionalized inorganic phase, characterized in that, Includes the following steps: (1) Add inorganic materials to an alcohol solvent and disperse them by ultrasonication to form a first suspension; then add an aminosilane coupling agent dropwise to the first suspension, heat the reaction, and centrifuge, wash and dry the resulting reaction product to obtain an amino-functionalized inorganic phase; (2) The amino-functionalized inorganic phase is mixed and stirred with a rigid polymer, an amine-containing flexible polymer and a polar organic solvent to form a second suspension; then a crosslinking agent is added to the second suspension and the temperature is raised to react; then an antifoaming agent is added to the obtained copolymer system, the temperature is lowered and stirred to obtain a copolymer-inorganic phase composite membrane liquid. (3) After the copolymer-inorganic phase composite film liquid is degassed, it is coated onto the pretreated substrate. After coating, it is allowed to stand and then dried in a gradient to obtain the composite film. (4) The composite membrane is immersed in a protonating reagent, and then washed and dried to obtain the copolymer composite cation exchange membrane containing amino-functionalized inorganic phase.

2. The method for preparing the copolymer composite cation exchange membrane containing an amino-functionalized inorganic phase according to claim 1, characterized in that, In step (1), the mass ratio of the inorganic material, the alcohol solvent and the aminosilane coupling agent is (3-4):(60-80):(5-8); Optionally, the inorganic material includes at least one of hydroxyapatite, titanium dioxide, and hydroxyapatite-silica composite powder, and the particle size of the inorganic material is 50-100 nm. Optionally, the alcohol solvent includes at least one of anhydrous ethanol, isopropanol, and ethylene glycol; Optionally, the aminosilane coupling agent includes at least one of 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, and N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane.

3. The method for preparing the copolymer composite cation exchange membrane containing an amino-functionalized inorganic phase according to claim 1, characterized in that, In step (1), the power of ultrasonic dispersion is 200-300W, and the dispersion time is 40-50min; And / or, the heating reaction is carried out at a temperature of 75-85°C for 8-10 hours. And / or, the centrifugation speed is 4000-4500 r / min, and the centrifugation time is 20-25 min each time; And / or, the drying pressure is 0.06-0.1 MPa, the drying temperature is 70-90℃, and the drying time is 16-20 h.

4. The method for preparing the copolymer composite cation exchange membrane containing an amino-functionalized inorganic phase according to claim 1, characterized in that, In step (2), the mass ratio of the amino-functionalized inorganic phase, the rigid polymer, the amine-containing flexible polymer, the polar organic solvent, and the crosslinking agent is (4-9):(55-65):(25-35):(150-180):(3-5). Optionally, the rigid polymer includes at least one of polyetheretherketone, polysulfone, and polyethersulfone; Optionally, the amine-containing flexible polymer includes at least one of polyallylamine, polyethyleneimine, and polylysine; Optionally, the polar organic solvent includes at least one of N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide; Optionally, the crosslinking agent includes at least one of formaldehyde, glutaraldehyde, and melamine-formaldehyde resin; And / or, the amount of the defoamer added is 0.4-0.7 wt% of the copolymer system; Optionally, the defoamer includes at least one of polyether-modified silicone oil, organosilicon defoamer, and polyoxyethylene polyoxypropylene ether.

5. The method for preparing the copolymer composite cation exchange membrane containing an amino-functionalized inorganic phase according to claim 1, characterized in that, In step (2), the mixing speed is 400-450 r / min, the mixing temperature is 60-70℃, and the mixing time is 24-30 h. And / or, the reaction temperature of the heating reaction is 80-90℃, and the reaction time is 10-12h; And / or, the temperature of the cooling and stirring is 30-35℃, and the stirring time is 25-35min.

6. The method for preparing the copolymer composite cation exchange membrane containing an amino-functionalized inorganic phase according to claim 1, characterized in that, In step (3), the degassing process is carried out in a vacuum degassing machine, and the vacuum degree of the vacuum degassing machine is set to -0.08~-0.1MPa, the temperature is 30-35℃, and the degassing time is 2-3h.

7. The method for preparing the copolymer composite cation exchange membrane containing an amino-functionalized inorganic phase according to claim 1, characterized in that, In step (3), the substrate is selected from any one of glass plate, polytetrafluoroethylene plate, and stainless steel plate; And / or, the coating is applied using a coater with a thickness of 200-280 μm and a coating speed of 5-8 cm / s; And / or, the settling time is 8-12 minutes; And / or, the gradient drying process is as follows: first, dry at 55-65℃ for 2.5-3.5h, then dry at 80-90℃ for 2.5-3.5h, and finally dry at 100-110℃ and 0.06-0.1MPa vacuum for 2-3h.

8. The method for preparing the copolymer composite cation exchange membrane containing an amino-functionalized inorganic phase according to claim 1, characterized in that, In step (4), the protonating agent includes at least one of hydrochloric acid solution, sulfuric acid solution, and phosphoric acid solution, and the concentration of the protonating agent is 0.5-0.7 mol / L; And / or, the soaking temperature is 25-35℃, and the soaking time is 10-14h; And / or, the drying is carried out at 55-65°C and 0.06-0.1 MPa for 8-12 hours.

9. A copolymer composite cation exchange membrane containing an amino-functionalized inorganic phase, characterized in that, The copolymer composite cation exchange membrane containing amino-functionalized inorganic phase is prepared by the preparation method according to any one of claims 1-8.

10. The application of a copolymer composite cation exchange membrane containing an amino-functionalized inorganic phase as described in claim 9 in electrodialysis desalination.

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