Paper-based photocured composite cation exchange membrane, preparation method and application thereof

Abstract

The application discloses a paper-based photocured composite cation exchange membrane and a preparation method thereof. The preparation method comprises the following steps: dissolving acrylic acid and sodium styrene sulfonate in a mixed solvent of deionized water and 1,4-dioxane, adding a hydrophobic monomer, a crosslinking agent and a composite initiator to obtain a prepolymer solution; immersing a quantitative filter paper in the prepolymer solution, and then taking out the filter paper to be subjected to photocuring, heat treatment, washing and drying to obtain a cation exchange membrane. The membrane has a bifunctional structure composed of sulfonic acid groups and carboxylic acid groups, and the introduction of the hydrophobic monomer effectively inhibits excessive swelling of the membrane. The application adopts a common photocuring lamp to initiate polymerization, and the process is simple and safe. In addition, biodegradable filter paper is used as a supporting material, and the application is green and environment-friendly. The obtained cation exchange membrane can be used in the fields of electrodialysis of brackish water desalination, industrial wastewater treatment and resource recovery.

Description

Technical Field

[0001] This invention belongs to the field of polymer ion exchange membrane technology, specifically relating to paper-based photocurable composite cation exchange membranes, methods for preparing paper-based photocurable composite cation exchange membranes, and applications of paper-based photocurable composite cation exchange membranes. Background Technology

[0002] As a core component of separation technologies such as electrodialysis and diffusion dialysis, the performance of ion exchange membranes directly determines separation efficiency and operating costs. Currently, most commercially available ion exchange membranes rely on a single sulfonic acid group (-SO3H) as their functional group. Their ionization degree and ion transport number are significantly affected by the solution pH, and their performance is prone to degradation in strongly acidic or alkaline environments, making it difficult to maintain efficient and stable operation over a wide pH range or under complex and variable actual water quality conditions. Traditional sulfonation processes often involve highly corrosive reagents such as concentrated sulfuric acid and chlorosulfonic acid, as well as toxic organic solvents, posing safety risks and environmental burdens. Furthermore, commonly used support materials such as nonwoven fabrics and polyolefins are difficult to biodegrade, potentially leading to a persistent environmental burden after membrane module disposal.

[0003] In the field of bifunctional cation exchange membranes, studies have used high-energy radiation grafting technology (such as electron beams or gamma rays) to graft acrylic acid and sodium styrene sulfonate onto polyolefin substrates to prepare bifunctional cation exchange membranes containing both sulfonic acid and carboxylic acid groups. However, this technology has the following obvious drawbacks: (1) It requires large-scale radiation devices, resulting in huge equipment investment and high operating and maintenance costs; (2) The radiation process carries the risk of leakage, and the requirements for the operating environment and personnel safety protection are extremely strict; (3) It is usually carried out in a strictly deoxygenated inert atmosphere, making the operation complex and difficult to achieve continuous production; (4) The grafting rate is affected by many factors, resulting in a narrow process window and poor reproducibility; (5) The polyolefin substrate used is difficult to biodegrade, and its disposal will cause a long-term burden on the environment.

[0004] In the field of paper-based photocurable separation membranes, existing research has used filter paper as the support material and thermosensitive monomers (such as N-isopropylacrylamide) as the solute to prepare paper-based functional membranes via photoinitiated graft polymerization for the separation and purification of biomacromolecules such as proteins. However, the thermosensitive monomers in the above systems are quite different from the ion exchange monomers (acrylic acid, sodium styrene sulfonate) described in this invention in terms of polarity, hydrophilicity / hydrophobicity, and interaction with cellulose fibers. Applying the ion exchange monomer system to paper-based photocurable systems faces unique technical obstacles: the size of cellulose fibers in the paper-based carrier (micrometers to hundreds of nanometers) is close to the wavelength of visible light (approximately several hundred nanometers), making them prone to scattering and affecting the penetration depth of light in the prepolymer solution, resulting in poor polymer loading uniformity; at the same time, the cellulose surface is rich in hydroxyl groups, which presents interfacial compatibility problems with the hydrophobic monomer system, potentially leading to insufficient adhesion between the polymer and the paper-based carrier. These technical difficulties result in existing paper-based photocurable technologies facing practical problems such as uneven polymer loading and insufficient adhesion when used to prepare ion exchange membranes, leading to a lack of reasonable expectations for success among those skilled in the art.

[0005] Furthermore, existing literature discloses methods for preparing ion exchange membranes by curing photocurable materials under a 405nm light source, or by coating a slurry of polymerizable monomers and photoinitiators onto a substrate to prepare cation exchange membranes. However, none of these methods use paper as a support material, nor do they involve technical solutions that combine bifunctional ion exchange systems with paper-based photocuring processes.

[0006] In summary, the existing technology lacks a method for preparing cation exchange membranes that can simultaneously meet the following requirements: (1) possessing the synergistic effect of sulfonic acid and carboxylic acid bifunctional groups, maintaining stable performance over a wide pH range; (2) using paper-based biodegradable support materials, making it green and environmentally friendly; (3) achieving it through a simple and safe photocuring process, avoiding large-scale radiation equipment and high-risk operations; and (4) overcoming technical obstacles such as light scattering and interfacial compatibility during paper-based photocuring, ensuring uniform polymer loading and strong bonding. Therefore, developing a paper-based photocurable bifunctional cation exchange membrane that is simple to process, environmentally friendly, and has excellent comprehensive performance is of great significance. Summary of the Invention

[0007] The primary objective of this invention is to provide a method for preparing a paper-based photocurable composite cation exchange membrane, which solves the technical problems of expensive equipment, complex processes, and difficulty in achieving green production in the preparation of existing bifunctional cation exchange membranes.

[0008] The second objective of this invention is to provide a paper-based photocurable composite cation exchange membrane, which has a bifunctional structure of sulfonic acid groups and carboxylic acid groups, solving the problem of performance degradation of traditional monofunctional membranes over a wide pH range. At the same time, the paper substrate solves the problem of environmental burden after disposal.

[0009] The third objective of this invention is to provide applications of the aforementioned paper-based photocurable composite cation exchange membrane, specifically in the fields of electrodialysis brackish water desalination, industrial wastewater treatment, or resource recycling.

[0010] The first technical solution adopted in this invention is a method for preparing a paper-based photocurable composite cation exchange membrane, comprising the following steps: Step 1: Dissolve acrylic acid and sodium styrene sulfonate in a mixed solvent of deionized water and 1,4-dioxane, and add hydrophobic modifying monomers; Step 2: Add divinylbenzene as a crosslinking agent and azobisisobutyronitrile and diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide as a composite initiator system to the functional monomer solution, and stir to obtain a prepolymer solution; Step 3: Immerse the quantitative filter paper in the prepolymer solution, remove it and drain off the excess solution, lay it flat on a polytetrafluoroethylene plate, and place it under a 405nm light lamp for photocuring; Step 4: After heat treatment of the photocured membrane, immerse it in deionized water and dry it to obtain a cation exchange membrane.

[0011] The first technical solution of this invention is further characterized by: In step 1, the hydrophobic modifying monomer is selected from methyl methacrylate, butyl acrylate or a mixture thereof, and the functional monomer solution is obtained by stirring. The molar ratio of sodium styrene sulfonate to acrylic acid is 8.5:100 to 34:100; The ratio of the total mass of acrylic acid and sodium styrene sulfonate to the total mass of the mixed solvent is 1:1; The mass ratio of deionized water to 1,4-dioxane is 2:1, and the amount of hydrophobic modified monomer added is 5% to 15% of the total molar amount of acrylic acid and sodium styrene sulfonate. The hydrophobic modifying monomer is a mixture of methyl methacrylate and butyl acrylate in a mass ratio of 1:1.

[0012] In step 2, the amount of divinylbenzene added is 3% of the total mass of the monomers, and the amounts of azobisisobutyronitrile and diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide added are each 0.5% of the total mass of the monomers.

[0013] The process of soaking, draining, spreading, and light curing in step 3 is repeated at least once to increase the number of polymer loading layers; The power of the light curing lamp is 6W, the wavelength is 405nm, and the curing time is 2 hours. During the curing process, the film is flipped over every 30 minutes. The area of ​​the quantitative filter paper is 5cm×5cm, and the soaking time is 10min~15min.

[0014] In step 4, the heat treatment conditions are to heat-treat the photocured film at 60°C for 2 hours; The deionized water soaking period is 24 hours, and the deionized water is changed every 4 hours during the soaking period. During the heat treatment, the membrane is turned over every 1 hour.

[0015] The second technical solution adopted in this invention is a paper-based photocurable composite cation exchange membrane, which is prepared by the above-mentioned preparation method of the paper-based photocurable composite cation exchange membrane.

[0016] The second technical solution of the present invention is further characterized by: The cation exchange membrane has a bifunctional structure composed of sulfonic acid groups and carboxylic acid groups.

[0017] The third technical solution adopted in this invention is the application of the above-mentioned paper-based photocurable composite cation exchange membrane in the fields of electrodialysis brackish water desalination, industrial wastewater treatment, or resource recycling.

[0018] Compared with the prior art, the beneficial effects of the present invention are: This invention is the first to combine an acrylic acid and sodium styrene sulfonate bifunctional system with a paper-based photocuring process. Utilizing the complementary ionization properties of sulfonic acid and carboxylic acid groups, the membrane maintains stable ion exchange capacity and selective permeability across a wide pH range, overcoming the limitation of traditional monofunctional membranes' performance degradation. By introducing hydrophobic modified monomers such as butyl acrylate, excessive membrane swelling is effectively suppressed, resulting in a desalination rate decrease of only 10 percentage points after ten electrodialysis cycles, more than half that of unmodified membranes. Polymerization is initiated using a common photochemical lamp (6W, 405nm), eliminating the need for large-scale radiation equipment and strict protection, making the process simple, safe, and easily scalable for industrial application. The use of biodegradable filter paper instead of traditional synthetic substrates eliminates environmental burden after disposal. This invention achieves significant progress in overall performance, process safety, and environmental friendliness, possessing outstanding substantive features and remarkable advancements. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the preparation method of the paper-based photocurable composite cation exchange membrane of the present invention. Detailed Implementation

[0020] The present invention will be further described in detail below with reference to specific embodiments and comparative examples. The embodiments and comparative examples are all in accordance with the present invention as follows: Figure 1The preparation method shown was carried out by only changing the composition of functional monomers, the type and amount of hydrophobic monomers, the type of substrate, or the initiation method, so as to systematically compare the technical effects of different technical solutions. All examples and comparative examples used the same test methods: the electrodialysis desalination rate (r), unit energy consumption (EC), current efficiency (η), and salt flux per unit area (J) were determined according to conventional electrodialysis desalination test methods; long-term stability was evaluated by ten cycles of electrodialysis test, and the change in desalination rate after each cycle was recorded; the adhesion between the membrane and the substrate was qualitatively evaluated by tape peel test; the biodegradability of the substrate was evaluated according to GB / T19276.1-2003 standard.

[0021] I. Preparation of the Comparative Example Comparative Example 1 (unmodified membrane, without hydrophobic monomers) This comparative example does not contain any hydrophobic modifying monomers and serves as a performance benchmark for evaluating the hydrophobic modification effect.

[0022] Step 1: Disperse 4.04g of acrylic acid (AA) and 1.96g of sodium styrene sulfonate (SSS) in a mixed solvent of 4g of deionized water and 2g of 1,4-dioxane. Add 0.18g of divinylbenzene (DVB) crosslinking agent, 0.03g of TPO photoinitiator, and 0.03g of AIBN thermal initiator (each initiator is 0.5% of the total mass of the monomers, and the total mass of the monomers is the sum of AA and SSS, which is 6g). Stir at 600rpm for 10-15min at room temperature until the solution is clear and transparent to obtain the prepolymer solution.

[0023] Step 2: Pour the prepolymer solution into a petri dish and soak a 5cm × 5cm quantitative filter paper for 10 minutes. Remove the filter paper, drain off excess solution, and lay it flat on a PTFE plate, ensuring no air bubbles remain. Place it under a 6W, 405nm light-curing lamp for 2 hours, turning it over every 30 minutes. Repeat the above soaking-curing process twice to increase the number of polymer loading layers.

[0024] Step 3: Transfer the photocured membrane to a 60℃ oven for heat treatment for 2 hours (turning it over every 1 hour during the process), then soak it in deionized water for 24 hours (changing the deionized water every 4 hours), and finally dry it in a 60℃ oven to constant weight to obtain an unmodified cation exchange membrane, denoted as P(AA-SSS).

[0025] Comparative Example 2 (monosulcite-based membrane, SSS only, containing 15% BA) This comparative example uses only sodium styrene sulfonate (SSS) as the functional monomer, without adding acrylic acid (AA), to verify the contribution of the carboxylic acid group in the bifunctional group.

[0026] Step 1: Disperse 1.96g of sodium styrene sulfonate (SSS) in a mixed solvent of 4g deionized water and 2g 1,4-dioxane, and add butyl acrylate (BA, 0.0328mol molar, 0.42g mass) at 15% of the molar weight of SSS, and stir until clear and transparent. Add 0.0714g of divinylbenzene (DVB) (calculated as 3% of the total monomer mass SSS+BA=1.96+0.42=2.38g), 0.0119g of azobisisobutyronitrile (AIBN), and 0.0119g of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO) (each 0.5% of the total monomer mass), and stir to obtain a prepolymer solution.

[0027] Steps 2-3: Same as Comparative Example 1, obtain a monosulfonic acid cation exchange membrane, denoted as P(SSS-15%BA).

[0028] Comparative Example 3 (monocarboxylic acid membrane, AA only, containing 15% BA) This comparative example uses only acrylic acid (AA) as the functional monomer and does not add sodium styrene sulfonate (SSS) to verify the contribution of the sulfonic acid group in the bifunctional group.

[0029] Step 1: Disperse 4.04 g of acrylic acid (AA) in a mixed solvent of 4 g of deionized water and 2 g of 1,4-dioxane (AA molar amount is 0.0561 mol, slightly less than the total molar amount in Comparative Example 1, but for comparability, the same AA mass is used here), and add butyl acrylate (BA, BA molar amount 0.00841 mol, mass 1.078 g) accounting for 15% of the AA molar amount, and stir until clear and transparent. Add 0.154 g of divinylbenzene (DVB) (calculated as 3% of the total monomer mass AA+BA=4.04+1.078=5.118 g), 0.0256 g of AIBN, and 0.0256 g of TPO (each 0.5%), and stir to obtain a prepolymer solution.

[0030] Steps 2-3: Same as Comparative Example 1, obtain a monocarboxylic acid cation exchange membrane, denoted as P(AA-15%BA).

[0031] Comparative Example 4 (non-paper-based control film, PP non-woven fabric, containing 15% BA) In this comparative example, the filter paper substrate was replaced with polypropylene (PP) nonwoven fabric to verify the advantages of the paper-based carrier in terms of load uniformity and adhesion.

[0032] Step 1: Prepare the prepolymer solution according to the formulation of Example 4 (15% BA modified membrane): Disperse 4.04g AA and 1.96g SSS in 4g water and 2g 1,4-dioxane, add BA (1.261g) accounting for 15% of the total molar amount of AA+SSS, then add 0.218g DVB (3% of the total monomer mass = 4.04+1.96+1.261=7.261g), 0.0363g AIBN, and 0.0363g TPO, and stir to obtain the prepolymer solution.

[0033] Step 2: Pour the prepolymer solution into a petri dish, and immerse a 5cm × 5cm polypropylene (PP) nonwoven fabric (0.2mm thickness, 80g / m² surface density) in it for 10 minutes. After removing it, drain off the excess solution on the surface, spread it evenly on a polytetrafluoroethylene plate, and repeat the remaining steps as in Comparative Example 1 to obtain a PP nonwoven fabric-based cation exchange membrane, denoted as P(AA-SSS-15%BA) / PP.

[0034] II. Preparation of the Embodiments of the Invention The following examples all use quantitative filter paper as the substrate, and the preparation steps are the same as those in Comparative Example 1, except that the monomer composition in step 1 is different. The specific formulations and membrane numbers of each example are as follows. In all examples, the amounts of acrylic acid (AA) and sodium styrene sulfonate (SSS) are fixed at 4.04 g and 1.96 g (molar ratio 100:16.9), the mass ratio of deionized water to 1,4-dioxane is 2:1, the ratio of the total mass of AA and SSS to the total mass of the mixed solvent is 1:1, the amount of crosslinking agent DVB is 3% of the total mass of monomers (AA+SSS+hydrophobic monomer), and the amounts of composite initiators AIBN and TPO are each 0.5% of the total mass of monomers. Note: By adjusting the molar ratio of sodium styrene sulfonate to acrylic acid within the range of 8.5:100 to 34:100, cation exchange membranes with bifunctional synergistic effects can be obtained; when the molar ratio changes within the above range, the sulfonic acid group content and hydrophilic / hydrophobic balance of the membrane are adjusted accordingly to adapt to different separation requirements.

[0035] Example 1 (5% MMA modified membrane) Step 1: Disperse 4.04g of acrylic acid (AA) and 1.96g of sodium styrene sulfonate (SSS) in a mixed solvent of 4g of deionized water and 2g of 1,4-dioxane. Add methyl methacrylate (MMA) at 5% of the total molar amount of AA and SSS (total molar amount of AA and SSS is 0.0656mol, 5% is 0.00328mol, MMA molecular weight is 100.12, mass is 0.328g), and stir until clear and transparent. Add 0.190g of divinylbenzene (DVB) (3% of the total monomer mass = 4.04 + 1.96 + 0.328 = 6.328g), 0.0316g of azobisisobutyronitrile (AIBN), and 0.0316g of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO) (each 0.5%), and stir to obtain a prepolymer solution.

[0036] Steps 2-3: Same as Comparative Example 1, to obtain a cation exchange membrane, denoted as P(AA-SSS-5%MMA).

[0037] Example 2 (15% MMA modified membrane) Step 1: The difference from Example 1 is the addition of MMA (0.00984 mol, 0.985 g) at 15% of the total molar amount of AA and SSS. Total monomer mass = 4.04 + 1.96 + 0.985 = 6.985 g, DVB added 0.210 g, and AIBN and TPO each added 0.0349 g. Everything else is the same, and the resulting membrane is denoted as P(AA-SSS-15%MMA).

[0038] Example 3 (5% BA modified membrane) Step 1: The difference from Example 1 is the addition of butyl acrylate (BA, 0.00328 mol, BA molecular weight 128.17, mass 0.420 g), accounting for 5% of the total molar amount of AA and SSS. Total monomer mass = 4.04 + 1.96 + 0.420 = 6.420 g, DVB added 0.193 g, and AIBN and TPO each added 0.0321 g. Everything else is the same, and the resulting membrane is denoted as P(AA-SSS-5%BA).

[0039] Example 4 (15% BA modified membrane) Step 1: The difference from Example 1 is the addition of BA (0.00984 mol, mass 1.261 g), which accounts for 15% of the total molar amount of AA and SSS. Total monomer mass = 4.04 + 1.96 + 1.261 = 7.261 g, DVB added 0.218 g, and AIBN and TPO each added 0.0363 g. Everything else is the same, and the resulting membrane is denoted as P(AA-SSS-15%BA).

[0040] Example 5 (5% BA + 5% MMA mixed modified membrane) Step 1: The difference from Example 1 is that BA (0.420g) and MMA (0.328g), accounting for 5% of the total molar amount of AA and SSS, are added simultaneously, with a mass ratio of approximately 1:1. Total monomer mass = 4.04 + 1.96 + 0.420 + 0.328 = 6.748g, DVB added 0.202g, and AIBN and TPO each added 0.0337g. Everything else is the same, and the resulting membrane is denoted as P(AA-SSS-5%BA-5%MMA).

[0041] Example 6 (15% BA + 15% MMA mixed modified membrane) Step 1: The difference from Example 1 is that BA (1.261g) and MMA (0.985g), accounting for 15% of the total molar amount of AA and SSS, are added simultaneously, with a mass ratio of approximately 1:1. Total monomer mass = 4.04 + 1.96 + 1.261 + 0.985 = 8.246g, DVB added 0.247g, and AIBN and TPO each added 0.0412g. Everything else is the same, and the resulting membrane is denoted as P(AA-SSS-15%BA-15%MMA).

[0042] III. Summary of Performance Test Results The cation exchange membranes prepared in Comparative Examples 1-4 and Examples 1-6 were subjected to electrodialysis desalination performance tests and long-term cycling stability tests. All tests were conducted under the same conditions, and the results are summarized in Table 1.

[0043] Table 1

[0044] IV. Comparative Analysis First round of comparison: The necessity of hydrophobic modification (Comparative Example 1 vs. Example 4) Comparative Example 1, without any added hydrophobic monomers, had an initial desalination rate of 86%, a unit energy consumption of 0.85 kWh / kg, and a current efficiency of 68%. After ten electrodialysis cycles, the desalination rate decreased from 86% to 64%, a drop of 22 percentage points, indicating that the unmodified membrane suffered from poor dimensional stability due to excessive water absorption and swelling, resulting in rapid long-term performance degradation. Example 4, with the addition of 15% BA, maintained a desalination rate of 84% (essentially equivalent), significantly reduced unit energy consumption to 0.63 kWh / kg (a 26% decrease), and increased current efficiency to 78%. Furthermore, after ten cycles, the desalination rate decreased by only 10 percentage points, more than half that of the unmodified membrane. In existing technology, adding hydrophobic comonomers typically sacrifices some ion exchange capacity for dimensional stability. However, the introduction of 15% BA in this application significantly reduced energy consumption and substantially improved current efficiency and long-term stability without almost reducing the desalination rate. This comprehensive improvement is something that those skilled in the art could not have anticipated based on existing knowledge.

[0045] Second round of comparison: Synergistic effect of dual functional groups (Comparative Examples 2 and 3 vs. Example 4) Comparative Example 2, containing only sulfonic acid groups (SSS), achieved a desalination rate of 72%, a current efficiency of only 61%, and a unit energy consumption of 0.92 kWh / kg. Comparative Example 3, containing only carboxylic acid groups (AA), achieved a desalination rate of only 58%, a current efficiency of 52%, and a unit energy consumption as high as 1.21 kWh / kg. Single-functional-group membranes cannot simultaneously achieve low resistance (sulfonic acid groups) and high current efficiency (carboxylic acid groups), exhibiting significant performance deficiencies. Example 4, containing both sulfonic acid and carboxylic acid groups, achieved a desalination rate of 84%, a current efficiency of 78%, and a unit energy consumption of only 0.63 kWh / kg, demonstrating significantly superior overall performance compared to any single-functional-group membrane. Conclusion: A synergistic effect exists between sulfonic acid and carboxylic acid groups. Sulfonic acid groups provide low-resistance ion transport channels, while carboxylic acid groups enhance hydrophilicity and wide pH adaptability. Their complementarity allows the membrane to achieve higher desalination and current efficiencies while maintaining low energy consumption, something that single-functional-group membranes cannot achieve.

[0046] Third round of comparison: The superiority of paper-based carriers (Comparative Example 4 vs. Example 4) Comparative Example 4 used polypropylene (PP) nonwoven fabric as the substrate, compared with Example 4 which used quantitative filter paper as the substrate. The desalination rate of the PP nonwoven fabric-based membrane was 79%, and the current efficiency was 71%, both lower than the 84% and 78% of the paper-based membrane, respectively. Furthermore, the tape peel test showed that after repeated application and removal of tape, the paper-based membrane of Example 4 showed no significant polymer detachment, while the PP nonwoven fabric-based membrane of Comparative Example 4 showed significant polymer layer peeling under the same conditions, indicating a superior bond between the paper substrate and the polymer. In contrast, the cellulose filter paper surface is rich in hydroxyl groups, forming strong hydrogen bonds with polar prepolymers containing carboxylic acid and sulfonic acid groups, resulting in uniform polymer loading and a strong bond. Moreover, according to standard tests, the filter paper-based membrane achieved a biodegradability rate of over 90% within 90 days under controlled composting conditions, while the PP nonwoven fabric-based membrane's degradation rate was less than 5%, fully demonstrating the excellent environmental friendliness of the paper-based membrane. Conclusion: Paper-based materials are not simply a substitute for substrates. Their surface chemical properties and environmental advantages bring about non-obvious performance improvements, while overcoming the technical bias of those skilled in the art who are concerned about the insufficient durability of paper-based materials in the humid environment of electrodialysis.

[0047] Fourth round of comparison: Optimization of hydrophobic monomer types and amounts (internal comparison of Examples 1-6) The test data from Examples 1 to 6 show that: MMA series (Example 1 → Example 2): As the MMA addition amount increased from 5% to 15%, the desalination rate decreased slightly (85% → 82%), but the unit energy consumption decreased (0.80 → 0.76 kWh / kg), and the attenuation rate improved (18 → 15 percentage points). MMA is a rigid hydrophobic monomer, and moderate addition is beneficial to improve dimensional stability, but excessive addition will reduce the ion exchange capacity.

[0048] BA series (Examples 3 to 4): As the BA addition increased from 5% to 15%, the desalination rate remained basically unchanged (85% → 84%), the unit energy consumption decreased significantly (0.78 → 0.63 kWh / kg), and the attenuation rate was greatly improved (16 → 10 percentage points). BA contains flexible long alkyl chains, which can enhance the flexibility of the membrane while inhibiting swelling, and its overall effect is better than MMA.

[0049] Hybrid system (Example 5 → Example 6): The use of BA and MMA can balance flexibility and rigidity, but the overall performance (desalination rate 83% → 80%, energy consumption 0.72 → 0.70, attenuation 13 → 12) is between that of BA alone and MMA alone, and does not exceed the best effect of 15% BA.

[0050] Conclusion: BA has unique advantages in comprehensive performance optimization as a hydrophobic modified monomer. The 15% BA addition (Example 4) is the preferred solution, which achieves the best balance between energy consumption and stability and produces unexpected technical effects.

[0051] V. Final Conclusion Based on the above four rounds of comparative analysis, it can be clearly concluded that: This invention is the first to combine the AA-SSS bifunctional system with paper-based UV curing technology and successfully solves technical problems such as light scattering and interface compatibility. This combination has not been disclosed or inspired in the prior art.

[0052] The 15% BA modified paper-based bifunctional membrane (Example 4) achieved excellent performance in terms of desalination rate (84%), unit energy consumption (0.63 kWh / kg), current efficiency (78%), and long-term stability (only 10 percentage points of decay after ten cycles). Its overall performance is significantly better than that of unmodified membrane, monofunctional membrane, non-paper-based membrane, and radiation-grafted membrane.

[0053] Paper-based materials are biodegradable, solving the environmental burden problem of traditional synthetic substrates (PP, HDPE, etc.), conforming to the principles of green chemistry, and at the same time, they utilize the surface chemical properties of cellulose to obtain better load-bearing bonding force.

Claims

1. A method for preparing a paper-based photocurable composite cation exchange membrane, characterized in that, Includes the following steps: Step 1: Dissolve acrylic acid and sodium styrene sulfonate in a mixed solvent of deionized water and 1,4-dioxane, and add hydrophobic modifying monomers; Step 2: Add divinylbenzene as a crosslinking agent and azobisisobutyronitrile and diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide as a composite initiator system to the functional monomer solution, and stir to obtain a prepolymer solution; Step 3: Immerse the quantitative filter paper in the prepolymer solution, remove it and drain off the excess solution, lay it flat on a polytetrafluoroethylene plate, and place it under a lamp with a wavelength of 405nm for photocuring; Step 4: After heat treatment of the photocured membrane, immerse it in deionized water and dry it to obtain a cation exchange membrane.

2. The method for preparing the paper-based photocurable composite cation exchange membrane according to claim 1, characterized in that, In step 1, the hydrophobic modifying monomer is selected from methyl methacrylate, butyl acrylate or a mixture thereof, and the functional monomer solution is obtained by stirring. The molar ratio of sodium styrene sulfonate to acrylic acid is 8.5:100 to 34:100; The ratio of the total mass of acrylic acid and sodium styrene sulfonate to the total mass of the mixed solvent is 1:1; The mass ratio of deionized water to 1,4-dioxane is 2:1, and the amount of hydrophobic modified monomer added is 5% to 15% of the total molar amount of acrylic acid and sodium styrene sulfonate. The hydrophobic modifying monomer is a mixture of methyl methacrylate and butyl acrylate in a mass ratio of 1:

1.

3. The method for preparing the paper-based photocurable composite cation exchange membrane according to claim 1, characterized in that, In step 2, the amount of divinylbenzene added is 3% of the total mass of the monomers, and the amounts of azobisisobutyronitrile and diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide added are each 0.5% of the total mass of the monomers.

4. The method for preparing the paper-based photocurable composite cation exchange membrane according to claim 1, characterized in that, The process of soaking, draining, spreading, and light curing in step 3 is repeated at least once to increase the number of polymer loading layers; The power of the light curing lamp is 6W, the wavelength is 405nm, and the curing time is 2 hours. During the curing process, the film is flipped over every 30 minutes. The area of ​​the quantitative filter paper is 5cm×5cm, and the soaking time is 10min~15min.

5. The method for preparing the paper-based photocurable composite cation exchange membrane according to claim 1, characterized in that, In step 4, the heat treatment conditions are to heat-treat the photocured film at 60°C for 2 hours; The deionized water soaking period is 24 hours, and the deionized water is changed every 4 hours during the soaking period. During the heat treatment, the membrane is flipped over every 1 hour.

6. A paper-based photocurable composite cation exchange membrane, characterized in that, The paper-based photocurable composite cation exchange membrane is prepared using the preparation method described in any one of claims 1 to 5.

7. The paper-based photocurable composite cation exchange membrane according to claim 6, characterized in that, The cation exchange membrane has a bifunctional structure composed of sulfonic acid groups and carboxylic acid groups.

8. The application of the paper-based photocurable composite cation exchange membrane according to claim 6 or 7 in the fields of electrodialysis brackish water desalination, industrial wastewater treatment or resource recycling.

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