Preparation method of salt-tolerant polyelectrolyte porous material and its application in photothermal seawater desalination

Abstract

The present invention relates to a method for preparing a salt-tolerant polyelectrolyte porous material and its application in photothermal seawater desalination, comprising: (1) dissolving a polyelectrolyte in water to obtain a uniform solution, pouring the solution into a prefabricated mold and freezing it; (2) demolding the frozen sample and immersing it in a low-temperature organic solvent to obtain a polyelectrolyte porous material; and (3) rinsing the polyelectrolyte porous material with an organic solvent and then immersing it in an organic solvent containing a crosslinking agent to obtain the salt-tolerant polyelectrolyte porous material. The present invention removes ice crystals by ice dissolution instead of ice sublimation, resulting in a simple operation process, low energy consumption, and no complex operation process involved. The material preparation rate is greatly improved. The polyelectrolyte porous composite material prepared by this method remains structurally stable after being immersed in 3.5% salt water for 7 days, and no salt particle precipitation is observed after continuous 10 hours of photothermal seawater desalination, demonstrating excellent salt tolerance.

Description

Technical Field

[0001] The present invention belongs to the field of porous polymer materials, and in particular relates to a method for preparing a salt-resistant polyelectrolyte porous material and application thereof in photothermal seawater desalination. Background Art

[0002] With economic development and population growth, the problem of water shortage is becoming increasingly serious. The uncontrolled discharge of industrial wastewater, domestic wastewater and agricultural pollutants has caused serious water pollution problems and exacerbated water shortages. Solar-based photothermal desalination technology has the advantages of being green, pollution-free, economical, efficient and sustainable. It is one of the important methods to alleviate water shortages (M. Sheng, et al., Nano Energy, 2021, 89, 106468.). Porous membranes are key materials for photothermal desalination technology. However, in actual use, salt crystallization causes clogging of the membrane pores, seriously affecting its evaporation efficiency and service life (F. Zhu, et al, Materials Horizons, 2020, 7, 3187.). Therefore, it is very necessary to design a porous membrane that is structurally stable in salt solution and has resistance to salting out.

[0003] Polyelectrolytes are polymers with ionizable groups (such as amino, carboxyl, and sulfonic acid groups) on their structural units. Their abundant hydrophilic and ionizable functional groups impart excellent hydrophilicity, while their porous structure possesses strong capillary water transport, making them suitable for the preparation of high-performance photothermal desalination membranes (J. Zeng et al., Advanced Energy Materials, 2019, 1900552). Currently, commonly used methods for preparing porous polyelectrolytes include template methods, freeze-drying, and layer-by-layer assembly. The template method creates pores by embedding and removing nanoparticle templates (such as silica microspheres and polystyrene microspheres) within the polyelectrolyte. However, template removal requires the use of highly hazardous reagents such as hydrofluoric acid (Chinese Patent: CN108434122 B). The freeze-drying method first freezes the polyelectrolyte solution into a solid at low temperatures, followed by ice crystal sublimation under a high vacuum environment to produce a porous structure. However, the slow sublimation rate results in low material preparation efficiency and high energy consumption (Chinese Patent: CN109157982B). The layer-by-layer assembly method, which utilizes the alternating deposition of oppositely charged polyelectrolytes on a substrate surface, is a commonly used method for preparing polyelectrolyte coatings (Chinese patent: CN113262963 A). However, this method involves many steps and must be combined with other methods to obtain a stable pore structure.

[0004] The pore structure and cross-linking degree of polyelectrolyte porous membranes have a significant impact on their resistance to salting-out and structural stability. The ice template method, also known as the directional freezing method or freeze casting method, is simple to operate, environmentally friendly, and easy to control the pore structure and morphology, and has attracted great attention from researchers (Chinese Patent: CN 109157982B). The ice template method is suitable for the processing and casting of hydrophilic polyelectrolyte materials and mainly includes two steps: ice crystal formation and ice crystal removal. Currently, ice crystal formation is the focus of research, while ice crystal removal methods are less studied. Vacuum drying is usually used (Chinese Patent: CN109157982 B), that is, the ice template is removed by ice crystal sublimation under high vacuum. However, the rate of ice sublimation is relatively slow, and the material preparation is time-consuming. In addition, the pore structure produced by freeze drying is easy to swell or even dissolve in water, especially in salt solutions, and its stability needs to be further improved. So far, there is no method for preparing salt-resistant polyelectrolyte porous materials by simple means. Summary of the Invention

[0005] In view of this, the present invention aims at the above defects and improvement needs of the prior art, and provides a simple and efficient method for preparing salt-resistant polyelectrolyte porous materials.

[0006] It should be noted that the present invention.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A method for preparing a salt-resistant polyelectrolyte porous material comprises the following steps:

[0009] (1) dissolving a polyelectrolyte in water to obtain a uniform polyelectrolyte solution, and pouring the polyelectrolyte solution into a prefabricated mold for freezing;

[0010] The polyelectrolyte is one or more combinations of sodium alginate, sodium carboxymethyl cellulose, polyacrylic acid, sodium polystyrene sulfonate, chitosan, polyethyleneimine, polyallylamine hydrochloride, and polydiallyldimethylammonium chloride; the mass concentration of the polyelectrolyte aqueous solution is 0.5 wt% to 5 wt%; the pH of the polyelectrolyte solution is 3 to 10; and the freezing temperature is -70°C;

[0011] (2) demolding the frozen sample and immersing it in a low-temperature organic solvent to obtain a polyelectrolyte porous material;

[0012] The organic solvent is one or more combinations of methanol, ethanol, isopropanol, acetone, tetrahydrofuran, dimethylformamide, and acetonitrile; the low temperature is -20°C; and the soaking time is 1 hour to 3 hours;

[0013] (3) The polyelectrolyte porous material is immersed in an organic solvent containing a cross-linking agent to perform chemical cross-linking to obtain a salt-resistant polyelectrolyte porous material.

[0014] The organic solvent is one or more combinations of acetone, tetrahydrofuran, dimethylformamide, and acetonitrile; the cross-linking agent is an acyl chloride molecule, specifically one or more combinations of terephthaloyl chloride, phthaloyl chloride, 1,3,5-trimesoyl chloride, and 1,2,4,5-pyromellitotetracoyl chloride; the mass concentration of the cross-linking agent is 0.5wt% to 2wt%, the immersion temperature is room temperature, and the immersion time is 1h to 10h.

[0015] The principle of preparing the salt-tolerant polyelectrolyte porous material in the present invention is as follows:

[0016] On the one hand, the present invention uses ice dissolution instead of ice sublimation to react with acyl chloride molecules, so that the prepared porous polyelectrolyte material has a better cross-linking density and improves its structural stability in salt solution; on the other hand, the porous polyelectrolyte material prepared by ice template technology has a vertical through-pore structure to ensure that high-concentration salt solution is transmitted to the lower layer of water along the shortest path, preventing salt crystallization during evaporation.

[0017] It should be noted that in step (1), at least one polyelectrolyte contains an amino or hydroxyl functional group for reacting with a cross-linking agent to stabilize the pore structure; and in step (2), the frozen sample is immersed in an organic solvent and rapidly stirred to remove water produced by melting ice crystals to prevent the sample from dissolving again; and the polyelectrolyte porous material obtained in step (3) is first washed with an organic solvent to remove trace water, and then a cross-linking agent is added for cross-linking.

[0018] The present invention also provides an application of the salt-resistant polyelectrolyte porous material prepared by the method in photothermal seawater desalination.

[0019] Specifically provided is a photothermal seawater desalination membrane based on the salt-tolerant polyelectrolyte porous material.

[0020] It should be noted that the preparation of the photothermal seawater desalination membrane is similar to the preparation of the salt-resistant polyelectrolyte porous material, except that 6% to 10% multi-walled carbon nanotubes are added as photothermal conversion materials in step (1), and the multi-walled carbon nanotubes have a diameter of 30 to 80 nm and a length of 30 to 80 μm.

[0021] It can be seen from the above technical solutions that, compared with the prior art, the preparation method of a salt-tolerant polyelectrolyte porous material provided by the present invention and its application in photothermal seawater desalination have the following excellent effects:

[0022] (1) The present invention prepares salt-resistant polyelectrolyte porous membranes through an ice template method, which utilizes ice crystals to dissolve in organic solvents to form pores instead of vacuum sublimation. It does not rely on equipment such as freeze dryers, and has the advantages of high preparation efficiency and low energy consumption. At the same time, the cross-linking degree of the polyelectrolyte porous membrane is higher than that of the cross-linked sample after freeze-drying, and both water resistance and salt resistance are excellent.

[0023] (2) The salt-resistant polyelectrolyte porous membrane prepared by the present invention utilizes the hydroxyl or amine groups contained in the polyelectrolyte to chemically crosslink with the acyl chloride functional groups of the crosslinking agent, so the porous structure of the polyelectrolyte porous membrane remains stable after being immersed in a salt solution for 7 days.

[0024] (3) The photothermal seawater desalination membrane prepared by the present invention can absorb about 97% of sunlight. –2 Under simulated light intensity, the evaporation rate of seawater is 2.02 kg m –2 h –1 , showing structural stability and salt precipitation resistance during continuous 10h seawater desalination. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0026] Figure 1 This is a preparation route for the salt-tolerant polyelectrolyte porous material in the embodiments of the present invention.

[0027] Figure 2 This is the morphology of the porous material prepared in Example 1 of the present invention and the freeze-dried cross-linked material after being soaked in water for 24 hours.

[0028] Figure 3 These are the optical images and morphologies of the porous material prepared in Example 1 of the present invention after being immersed in 3.5 wt % saline for 7 days.

[0029] Figure 4 This is a UV-visible-near-infrared absorption spectrum of the salt-resistant porous composite material prepared in Example 1 of the present invention.

[0030] Figure 5 The salt-resistant porous composite material prepared in Example 1 of the present invention is subjected to a –2 Surface temperature variation under irradiation.

[0031] Figure 6 The salt-resistant porous composite material prepared in Example 1 of the present invention is subjected to a–2 Graph of the evaporation rates of pure water and seawater under illumination.

[0032] Figure 7 The salt-resistant porous composite material prepared in Example 1 of the present invention is subjected to a –2 Graph of seawater evaporation rate under illumination for 10 hours. DETAILED DESCRIPTION

[0033] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the embodiments of the present invention and the accompanying drawings. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0034] The embodiment of the invention discloses a method for preparing a salt-resistant polyelectrolyte porous material.

[0035] For a better understanding of the present invention, the present invention is further specifically described below through the following examples, but it should not be understood as limiting the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above invention content are also considered to fall within the scope of protection of the present invention.

[0036] The technical solution of the present invention will be further described below in conjunction with specific embodiments.

[0037] Example 1

[0038] A method for preparing a salt-resistant polyelectrolyte porous material comprises the following steps:

[0039] (1) Dissolve sodium carboxymethyl cellulose in deionized water to obtain a uniform solution, take an appropriate amount of sodium carboxymethyl cellulose solution into a prefabricated mold, and freeze it at -70°C;

[0040] (2) Demolding the frozen sample, and then transferring it to -20 °C ethanol, stirring it during the soaking process, and obtaining the sodium carboxymethyl cellulose porous material after 1 h to 3 h;

[0041] (3) The porous material in step (2) is rinsed with an organic solvent, and then immersed in tetrahydrofuran containing acyl chloride molecules for chemical crosslinking. The immersion temperature is room temperature and the immersion time is 1 hour to 10 hours. A salt-resistant sodium carboxymethyl cellulose porous material is obtained, which is named CMC-TMC.

[0042] Example 2

[0043] (1) Dissolve sodium alginate in deionized water to obtain a uniform solution, take an appropriate amount of sodium alginate solution into a prefabricated mold, and freeze it at -70°C;

[0044] (2) Demolding the frozen sample, then transferring it to -20°C ethanol, stirring it during the soaking process, and obtaining a porous sodium alginate material after 1 to 3 hours;

[0045] (3) The porous material in step (2) is rinsed with tetrahydrofuran, and then immersed in tetrahydrofuran containing acyl chloride separation for chemical crosslinking. The immersion temperature is room temperature and the immersion time is 1 hour to 10 hours, thereby obtaining a salt-resistant sodium alginate porous material.

[0046] Example 3

[0047] (1) Dissolve chitosan in dilute acetic acid to obtain a uniform solution, take an appropriate amount of chitosan solution into a prefabricated mold, and freeze it at -70°C;

[0048] (2) Demolding the frozen sample, and then transferring it to -20 °C ammonia / ethanol, stirring it during the soaking process, and obtaining the chitosan porous material after 1 h to 3 h;

[0049] (3) The porous material in step (2) is rinsed with tetrahydrofuran, and then immersed in tetrahydrofuran containing acyl chloride separation for chemical crosslinking. The immersion temperature is room temperature and the immersion time is 1 hour to 10 hours, thereby obtaining a salt-resistant chitosan porous material.

[0050] Example 4

[0051] (1) Dissolve polyethyleneimine in deionized water to obtain a uniform solution, take an appropriate amount of polyethyleneimine solution into a prefabricated mold, and freeze it at -70°C;

[0052] (2) Demolding the frozen sample, then transferring it to -20°C ethanol, stirring it during the soaking process, and obtaining the polyethyleneimine porous material after 1 to 3 hours;

[0053] (3) The porous material in step (2) is rinsed with tetrahydrofuran, and then immersed in tetrahydrofuran containing acyl chloride separation for chemical crosslinking. The immersion temperature is room temperature and the immersion time is 1 hour to 10 hours to obtain a salt-resistant polyethyleneimine porous material.

[0054] Example 5

[0055] (1) Dissolve polyallylamine salt in deionized water to obtain a uniform solution, take an appropriate amount of the polyallylamine solution into a prefabricated mold, and freeze it at -70°C;

[0056] (2) Demolding the frozen sample, then transferring it to -20°C ethanol, stirring it during the soaking process, and obtaining the polyallylamine porous material after 1 to 3 hours;

[0057] (3) The porous material in step (2) is rinsed with tetrahydrofuran, and then immersed in tetrahydrofuran containing acyl chloride separation for chemical crosslinking. The immersion temperature is room temperature and the immersion time is 1 hour to 10 hours to obtain a salt-resistant polyallylamine porous material.

[0058] Comparative Example 1

[0059] The difference between this comparative example and Example 1 is that in Comparative Example 1, ice crystals are removed by vacuum sublimation, and then chemical cross-linking is performed. The specific steps are as follows:

[0060] (1) Dissolve sodium carboxymethyl cellulose in water to obtain a uniform solution, take an appropriate amount of sodium carboxymethyl cellulose solution into a prefabricated mold, and freeze it at -70°C;

[0061] (2) demolding the frozen sample and then transferring it to a freeze dryer to obtain a porous material of sodium carboxymethyl cellulose after the ice crystals are completely sublimated;

[0062] (3) Soak the porous material in step (2) in tetrahydrofuran containing acyl chloride molecules at room temperature for 1 to 10 hours to obtain the target material, named CMC-TMC fd The subscript fd represents freeze drying, which is distinguished from the method provided by the present invention.

[0063] Comparative Example 2

[0064] This comparative example differs from Example 1 in that physical crosslinking is performed between copper ions and the carboxyl groups of sodium carboxymethyl cellulose in Comparative Example 2, rather than chemical crosslinking between acyl chloride and hydroxyl groups in Example 1. The specific steps are as follows:

[0065] (1) Dissolve sodium carboxymethyl cellulose in water to obtain a uniform solution, take an appropriate amount of sodium carboxymethyl cellulose solution into a prefabricated mold, and freeze it at -70°C;

[0066] (2) Demolding the frozen sample, and then transferring it to -20 °C ethanol, stirring it during the soaking process, and obtaining the sodium carboxymethyl cellulose porous material after 1 h to 3 h;

[0067] (3) Soak the porous material in step (2) in ethanol containing copper ions at room temperature for 1 to 10 hours to obtain the target material, named CMC-Cu 2+ , to distinguish it from the method provided by the present invention.

[0068] The present invention also provides a photothermal seawater desalination membrane based on a salt-tolerant polyelectrolyte porous material prepared in Example 1. The specific steps are as follows:

[0069] (1) Sodium carboxymethyl cellulose was dissolved in deionized water to obtain a uniform solution, and then 6% to 10% multi-walled carbon nanotubes were added as a photothermal conversion material, stirred evenly, and an appropriate amount of the solution was placed in a prefabricated mold and frozen at -70°C;

[0070] (2) Demolding the frozen sample and then transferring it to -20°C ethanol. Stirring the sample during immersion is important. After 1 to 3 hours, a porous composite material based on sodium carboxymethyl cellulose is obtained.

[0071] (3) The porous composite material in step (2) is rinsed with tetrahydrofuran, and then immersed in an organic solvent containing acyl chloride molecules for chemical cross-linking to obtain a photothermal seawater desalination membrane based on a salt-tolerant polyelectrolyte porous material, which is named CMC-TMC-CNT.

[0072] Test Experiment

[0073] The salt resistance of the polyelectrolyte porous materials prepared in Example 1, Comparative Example 1, and Comparative Example 2 was characterized below, and the photothermal seawater desalination membrane prepared based on Example 1 was subjected to absorbance testing, photothermal conversion experiments, and photothermal water evaporation experiments.

[0074] Salt tolerance test

[0075] The salt resistance of the salt-resistant polyelectrolyte porous material prepared by the method provided by the present invention is illustrated by comparing the morphological changes of the polyelectrolyte material before and after immersion in water for 24 hours and in a 3.5 wt% sodium chloride solution for 7 days.

[0076] Absorbance test

[0077] The absorbance of the porous polyelectrolyte composite CMC-TMC-CNT was evaluated using a Lambda-750S UV-Vis-Infrared spectrophotometer. The measurement range was 400–2500 nm with a 5 nm interval. The sample was 3.0 mm thick and sandwiched between clean glass slides.

[0078] Photothermal conversion test

[0079] CMC-TMC-CNT was placed in a 1kW m -2 Under simulated sunlight, an infrared thermal imager (DM-I220) was used to monitor the surface temperature of CMC-TMC-CNT over time.

[0080] Photothermal water evaporation test

[0081] Add water or seawater to a beaker and float CMC-TMC-CNT on the water surface. -2 Data collection began after stabilization under the radiation intensity for 30 minutes. The balance was mainly used to record the mass loss of water during the test. Water evaporation rate (v, kgm -2 h -1 ) is obtained by the following formula:

[0082]

[0083] Where Δm is the change in water mass within 1 hour (kg), S is the area of ​​the membrane (m -2 ), t is the irradiation time (1h).

[0084] Example test result analysis

[0085] like Figure 1 Shown is a roadmap for preparing salt-tolerant porous polyelectrolyte materials. During the freezing process of a polyelectrolyte solution, growing ice crystals repel the polyelectrolyte molecular chains, resulting in phase separation between the molecular chains and the ice crystals. When the frozen sample is immersed in an organic solvent at -20°C, the ice crystals gradually dissolve, yielding a porous polyelectrolyte material whose microscopic morphology is consistent with that of the ice crystal template. The polyelectrolytes selected in this invention contain hydroxyl or amine functional groups. When immersed in an organic solvent containing a crosslinker, the hydroxyl or amine groups react with acyl chlorides to crosslink, resulting in a salt-tolerant porous polyelectrolyte material that is stable in both water and salt solutions.

[0086] like Figure 2 As shown in a, the growth of ice crystals was controlled by a directional freezing device to obtain a salt-tolerant polyelectrolyte porous material CMC-TMC with a parallel lamellar morphology. After immersing CMC-TMC in water for 24 hours, it was found that it still maintained its original morphology ( Figure 2 b) As a comparison, CMC-TMC was prepared by vacuum sublimation. fd The original morphology is almost unobservable, indicating that its porous structure is unstable in water ( Figure 2 c) The above results indicate that the method provided by the present invention can produce a polyelectrolyte porous material with a stable structure in aqueous solution.

[0087] like Figure 3 As shown in a, after CMC-TMC was immersed in 3.5wt% saline for 7 days, the optical image shows that ( Figure 3 a), the salt solution always remains clear, and the sample maintains its initial shape both in the solution and after drying. The microscopic morphology is suppressed from the initial morphology, showing a parallel lamellar morphology ( Figure 3 a), indicating that CMC-TMC is stable in salt solution. 2+On the second day of immersion, the blue color of the sample was observed to weaken. On the fourth day, the CMC-Cu 2+ The macroscopic morphology of the sample was difficult to maintain. After immersion for seven days, the sample collapsed and the morphology of the material was severely damaged ( Figure 3 b), its parallel lamellar morphology is destroyed, showing a random porous microstructure ( Figure 3 b). The above results indicate that the method provided by the present invention can obtain a polyelectrolyte porous material with a stable structure in a salt solution.

[0088] like Figure 4 As shown, based on Example 1 of the present invention, a salt-resistant polyelectrolyte porous composite material CMC-TMC-CNT was prepared by adding multi-walled carbon nanotubes. The gray area represents the irradiation intensity distribution of sunlight. About 50% of the energy is distributed in the visible light region (400-760nm), and 43% of the energy is distributed in the near-infrared light region (760-2500nm). CMC-TMC-CNT has a strong light absorption capacity (97%) in the range of 400-2500nm.

[0089] like Figure 5 As shown in the figure, the surface temperature of CMC-TMC was 33.4°C after 10 seconds of illumination and 38.2°C after 240 seconds, with a slow heating rate. After adding multi-walled carbon nanotubes, the surface temperature of CMC-TMC-CNT rapidly increased to 70°C after 10 seconds of illumination and reached a steady-state temperature of 87.8°C after 60 seconds, demonstrating that CMC-TMC-CNT has excellent light-to-heat conversion capabilities and has application prospects in the field of photothermal desalination.

[0090] like Figure 6 As shown, at 1kW m –2 Under simulated sunlight, the evaporation rate of pure water without CMC-TMC-CNT is 0.52 kg / m –2 h –1 The water evaporation rate of CMC-TMC-CNT is 2.21 kg m –2 h –1 , which is about 4.2 times the evaporation rate of pure water. Since the boiling point of seawater is higher than that of pure water, the evaporation rate of CMC-TMC-CNT on Bohai Seawater is 2.02 kg m –2 h –1 , slightly lower than the evaporation rate of pure water. The above results show that CMC-TMC-CNT is beneficial to the evaporation of photothermal water.

[0091] like Figure 7 As shown, 1kW m –2 When continuously exposed to simulated sunlight for 10 h, the evaporation rate of seawater from CMC-TMC-CNT was 1.99 kg m –2 h –1, similar to the initial evaporation rate, and no salt particles were observed on the sample surface. This is attributed to the directional freezing structure that directly connects the evaporation interface layer and seawater, ensuring that the high-concentration salt solution at the interface is transferred to the lower-concentration seawater layer below along the shortest path, preventing salt crystals from clogging the pores. These results indicate that CMC-TMC-CNT is resistant to salt precipitation and is suitable for continuous seawater desalination.

[0092] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a salt-tolerant polyelectrolyte porous material, characterized in that: The steps include: (1) dissolving a polyelectrolyte in water to obtain a uniform polyelectrolyte solution, and then pouring the polyelectrolyte solution into a prefabricated mold and freezing it for later use; The polyelectrolyte in step (1) is one or more combinations of sodium alginate, sodium carboxymethyl cellulose, polyacrylic acid, sodium polystyrene sulfonate, chitosan, polyethyleneimine, polyallylamine hydrochloride, and polydiallyldimethylammonium chloride, the mass concentration of the polyelectrolyte solution is 0.5wt% to 5wt%, the pH of the polyelectrolyte solution is 3 to 10, and the freezing temperature is -70°C; (2) demolding the polyelectrolyte sample frozen in step (1) and immersing it in a low-temperature organic solvent to obtain a polyelectrolyte porous material; The low temperature is -20°C and the soaking time is 1h~3h; The organic solvent in step (2) is one or more combinations of methanol, ethanol, isopropanol, acetone, tetrahydrofuran, dimethylformamide, and acetonitrile; (3) immersing the polyelectrolyte porous material in an organic solvent containing a cross-linking agent to perform chemical cross-linking, so as to finally obtain the salt-resistant polyelectrolyte porous material; The organic solvent in step (3) is one or more combinations of acetone, tetrahydrofuran, dimethylformamide, and acetonitrile; the cross-linking agent is an acyl chloride molecule; the mass concentration of the cross-linking agent is 0.5 wt% to 2 wt%; the immersion temperature is room temperature; and the immersion time is 1 h to 10 h.

2. The method for preparing the salt-resistant polyelectrolyte porous material according to claim 1, wherein: The cross-linking agent is one or a combination of terephthaloyl chloride, phthaloyl chloride, 1,3,5-trimesoyl chloride, and 1,2,4,5-pyromellitotetracoyl chloride.

3. A salt-tolerant polyelectrolyte porous material prepared by the method according to any one of claims 1 to 2.

4. Use of a salt-tolerant polyelectrolyte porous material prepared by the method according to any one of claims 1 to 2 or the salt-tolerant polyelectrolyte porous material according to claim 3 in photothermal seawater desalination.

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