Photo-thermal hydrogel sponge with excellent salt resistance as well as preparation method and application of photo-thermal hydrogel sponge

Abstract

The invention discloses a photo-thermal hydrogel sponge with excellent salt resistance and a preparation method and application thereof, and belongs to the technical field of solar evaporators. The preparation method comprises the following steps: firstly, preparing melamine sponge (MS) with an asymmetric structure, filling a prepared polyacrylamide / graphene oxide (PAM / GO) hydrogel precursor solution and a prepared polyacrylamide / polyquaternium-7 (PAM / PQ7) hydrogel precursor solution into the melamine sponge by adopting a method of combining entering and injection, and preparing the polyacrylamide / polyquaternium-7 / PAM / PQ7 hydrogel composite material. The Janus structure photo-thermal hydrogel sponge with excellent salt resistance is obtained. The evaporator adopting the photo-thermal hydrogel sponge has an automatic salt resistance characteristic and an efficient salt resistance performance.

Description

Technical Field

[0001] This invention belongs to the field of solar evaporator technology, specifically relating to a photothermal gel sponge with excellent salt-barrier capabilities, its preparation method, and its application. Background Technology

[0002] To address the shortage of freshwater resources, technologies such as membrane distillation, low-temperature multi-effect distillation, and forward and reverse osmosis membranes have been proposed. However, traditional seawater desalination typically faces significant energy consumption and environmental pollution. Solar energy, as a distributed renewable energy source, utilizes abundant and harmless solar energy for the clean reuse of seawater resources, providing an effective solution to the freshwater shortage problem. The basic principle of solar-driven seawater desalination technology is to convert sunlight into heat through photothermal materials, heating and evaporating seawater, which is then condensed into freshwater. Currently, researchers have developed a solar-driven interfacial evaporation (SDIE) system to alleviate the global freshwater shortage problem. This system primarily confines heat conversion to the evaporator surface, thereby minimizing energy loss.

[0003] Solar-driven interfacial water evaporation is a promising technology with advantages such as high evaporation efficiency, simple structure, and low cost. It can produce clean water from seawater or wastewater entirely using solar energy. It achieves this by separating the evaporation interface from the water column using a solar evaporator. This device confines the converted heat to a limited area, effectively suppressing energy loss and thus promoting rapid water evaporation and high energy utilization. This technology provides a sustainable solution to effectively alleviate water scarcity by utilizing solar energy to convert seawater or polluted water into safe freshwater. The technology efficiently collects and converts solar energy into heat energy, thereby promoting water evaporation, leaving behind impurities and salts, which are ultimately condensed to produce usable freshwater. Developing efficient solar interfacial evaporation systems not only has a profound impact on improving the availability of global water resources but also provides an innovative path for the sustainable management and utilization of water resources. Therefore, researching and promoting solar interfacial evaporation technology is of significant practical importance for solving the global water crisis.

[0004] However, in actual seawater evaporation processes, salt deposits accumulate at the evaporation interface over time, especially in high-concentration brine. This accumulation weakens light absorption and hinders steam escape, leading to a continuous decrease in the evaporation rate until the evaporator fails. Therefore, reducing salt deposition is crucial for achieving efficient and stable operation of SDIE (Self-Drying Evaporator). To address these issues, various effective anti-salt strategies have been designed, including physical cleaning, edge salt deposition, promoting salt diffusion, and ion repulsion. Despite the variety of anti-salt methods, they still cannot fully meet the evaporator's requirements for efficient and convenient anti-salt operation.

[0005] Therefore, the development of an evaporator with independent salt-blocking characteristics and high-efficiency salt-blocking performance is of practical significance for solar-driven interfacial evaporation technology. Summary of the Invention

[0006] In order to overcome the shortcomings of the prior art, the present invention aims to provide a photothermal hydrogel sponge with excellent salt barrier capability, its preparation method and application, and an evaporator using the photothermal hydrogel sponge has autonomous salt barrier characteristics and high-efficiency salt barrier performance.

[0007] To achieve the above objectives, the present invention employs the following technical solution: This invention provides a method for preparing a photothermal hydrogel sponge with excellent salt-barrier ability, comprising the following steps: A melamine sponge with an asymmetrical structure was prepared, wherein the melamine sponge was divided into an upper part and a lower part; AM powder and GO aqueous solution were added to pure water and stirred to prepare PAM / GO solution. Then, crosslinking agent, initiator and gel accelerator were added to prepare PAM / GO hydrogel precursor solution. AM powder and polyquaternium-7 were added to pure water and stirred to prepare PAM / PQ7 solution. Then, crosslinking agent, initiator and gel accelerator were added to prepare PAM / PQ7 hydrogel precursor solution. The upper half of the melamine sponge was immersed in a PAM / GO hydrogel precursor solution and then removed. The PAM / GO hydrogel precursor solution was then injected with a syringe to accelerate polymerization at a set temperature. The lower half was then immersed in a PAM / PQ7 hydrogel precursor solution and removed. The PAM / PQ7 hydrogel precursor solution was then injected with a syringe to accelerate polymerization at a set temperature. Finally, freeze-drying and immersion in pure water were performed sequentially to obtain a Janus-structured photothermal hydrogel sponge with excellent salt-barrier properties.

[0008] In one embodiment, the volume of the upper half of the melamine sponge is smaller than the volume of the lower half of the melamine sponge.

[0009] In one embodiment, the ratio of AM powder, GO aqueous solution, and pure water is 1~3 g: 4~5 mL: 15 mL; the concentration of the GO aqueous solution is 3~5 mg / mL.

[0010] In one embodiment, the ratio of AM powder, polyquaternium-7 and pure water is 1~3 g: 1~3 g: 15 mL.

[0011] In one embodiment, the crosslinking agent is N,N'-methylenebisacrylamide; the initiator is ammonium persulfate; and the gel accelerator is tetramethylethylenediamine.

[0012] In one embodiment, the ratio of PAM / GO solution, crosslinking agent, initiator, and gel accelerator in the PAM / GO hydrogel precursor solution is 20 mL: 0.05 g: 20 mg: 10 µL.

[0013] In one embodiment, the ratio of PAM / PQ7 solution, crosslinking agent, initiator, and gel accelerator in the PAM / PQ7 hydrogel precursor solution is 17 mL: 0.03 g: 20 mg: 10 µL.

[0014] In one embodiment, the set temperature is 40°C; the freeze-drying temperature is -20°C and the time is 48 hours; the pure water soaking time is 24 hours.

[0015] The present invention also provides a method for preparing a photothermal hydrogel sponge with excellent salt barrier properties.

[0016] The present invention also provides a method for preparing a photothermal hydrogel sponge with excellent salt barrier ability, and the application of the photothermal hydrogel sponge with excellent salt barrier ability in a solar evaporator. The solar evaporator includes a photothermal hydrogel sponge, a clean cloth, and polystyrene foam. The photothermal hydrogel sponge is placed on the polystyrene foam wrapped in the clean cloth, and the upper part of the photothermal hydrogel sponge faces the light source.

[0017] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a method for preparing a photothermal hydrogel sponge with excellent salt-barrier capabilities. It employs a combination of injection and immersion methods to rapidly and stably prepare Janus-structured hydrogel sponges. Furthermore, it allows for the rapid fabrication of hydrogel sponge evaporators with asymmetric structures without the need for molds. In the preparation process, neutral PAM hydrogel is mixed with anionic GO and fixed cation-containing PQ7, and then filled into the upper and lower parts of a microstructure (MS). By using a combination of immersion and injection methods, Janus-structured hydrogel sponges with different functional layers are prepared on the MS. Since the upper and lower parts of the MS sponge are filled with hydrogels carrying opposite charges, during evaporation, when brine flows through the hydrogels, the fixed positive charge of the lower hydrogel effectively repels cations in the brine, forming the first salt-barrier barrier. The fixed negative charge of the upper hydrogel effectively repels anions in the brine, forming the second salt-barrier barrier. Under the combined action of these two barriers, the anions and cations in the brine exist separately in the upper and lower parts of the hydrogel sponge, further forming an internal electric field generated by ion migration, thereby achieving the purpose of salt barrier. This salt-barrier mechanism enables the hydrogel sponge evaporator to operate stably for 8 hours in a 20 wt% high-salinity brine solution without salt crystallization on the surface, achieving an evaporation rate of 4.05 kg m³ / h. 2 h -1 .

[0018] While single-layer hydrogel sponges exhibit some salt-blocking properties at low concentrations, these properties diminish as salinity increases due to the concentration gradient breaking down electrostatic repulsion. This leads to the loss of salt-blocking characteristics, resulting in water evaporation on the surface, salt accumulation, and salt crystal formation. In contrast, double-layer Janus hydrogel sponge evaporators possess a dual ion-repulsion effect, effectively repelling salt ions in brine. Even in high-salinity brine, ion repulsion creates an internal electric field within the hydrogel, synergistically blocking salt and achieving highly efficient salt barrier properties. Attached Figure Description

[0019] Figure 1 These are actual images of the hydrogel sponges prepared in Comparative Examples 1, 2, and 1 of the present invention. Figure 2 This is a diagram of a solar evaporator with a photothermal gel sponge having excellent salt-barrier capabilities, according to one application of the present invention. Figure 3 This is a SEM image of the PG-MS-PP hydrogel sponge prepared in Example 1 of the present invention; Figure 4 The graph shows the evaporation rate test results of the PG-MS-PP hydrogel sponge prepared in Example 1 of this invention in NaCl solutions of different concentrations. Figure 5The graph shows the mass loss of the hydrogel sponge prepared in Example 1 after 8 hours of long-term evaporation in different NaCl solution environments. Figure 6 The images show the PG-MS, PP-MS, and PG-MS-PP hydrogel sponges prepared in Comparative Example 1, Comparative Example 2, and Example 1 after evaporation in 20 wt% NaCl solution for 8 h. Detailed Implementation

[0020] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0021] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0022] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0023] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0024] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0025] This invention provides a photothermal gel sponge with excellent salt-barrier capabilities, its preparation method, and its application in evaporators.

[0026] This invention provides a photothermal hydrogel sponge with excellent salt barrier properties, comprising the following steps: first, a melamine sponge (MS) with an asymmetric structure is prepared; then, a prepared polyacrylamide / graphene oxide (PAM / GO) hydrogel precursor solution and a polyacrylamide / polyquaternium-7 (PAM / PQ7) hydrogel precursor solution are filled into the melamine sponge using a combination of insertion and injection methods to obtain a Janus structure photothermal hydrogel sponge with excellent salt barrier properties.

[0027] A method for preparing a photothermal hydrogel sponge with excellent salt barrier properties includes the following steps: A melamine sponge with an asymmetrical structure is prepared, wherein the melamine sponge is divided into an upper part and a lower part; the volume of the upper part of the melamine sponge is smaller than the volume of the lower part of the melamine sponge. AM powder and GO aqueous solution are added to pure water and stirred to prepare PAM / GO solution. Then, N,N'-methylenebisacrylamide, ammonium persulfate, and tetramethylethylenediamine are added to prepare PAM / GO hydrogel precursor solution. The ratio of AM powder, GO aqueous solution and pure water is 1~3 g: 4~5 mL: 15 mL; the concentration of GO aqueous solution is 3~5 mg / mL. Preferably, the ratio of AM powder, GO aqueous solution and pure water is 2 g: 5 mL: 15 mL; the concentration of GO aqueous solution is 4 mg / mL; the ratio of PAM / GO solution, crosslinking agent, initiator and gel accelerator in PAM / GO hydrogel precursor solution is 20 mL: 0.05 g: 20 mg: 10 µL. AM powder and polyquaternium-7 were added to pure water and stirred to prepare a PAM / PQ7 solution. Then, N,N'-methylenebisacrylamide, ammonium persulfate, and tetramethylethylenediamine were added to prepare a PAM / PQ7 hydrogel precursor solution. The ratio of AM powder, polyquaternium-7 and pure water was 1~3 g: 1~3 g: 15 mL. Preferably, the ratio of AM powder, polyquaternium-7 and pure water was 2 g: 2 g: 15 mL. The ratio of PAM / PQ7 solution, crosslinking agent, initiator and gel accelerator in the PAM / PQ7 hydrogel precursor solution was 17 mL: 0.03 g: 20 mg: 10 µL. The upper half of the melamine sponge was immersed in a PAM / GO hydrogel precursor solution and then removed. The PAM / GO hydrogel precursor solution was then injected with a syringe, and polymerization was accelerated at a set temperature of 40°C. The lower half was then immersed in a PAM / PQ7 hydrogel precursor solution and removed. The PAM / PQ7 hydrogel precursor solution was then injected with a syringe, and polymerization was accelerated at a set temperature of 40°C. Subsequently, the sponge was freeze-dried at -20°C for 48 h and then soaked in pure water for 24 h to obtain a Janus-structured photothermal hydrogel sponge with excellent salt-barrier properties.

[0028] The specific steps of the above-mentioned method for preparing a photothermal hydrogel sponge with excellent salt barrier ability are as follows: S1: The melamine sponge was repeatedly washed in pure water and ethanol and then ultrasonically treated for 30 minutes. The ultrasonically treated MS was then dried in an oven at 50℃. The lower half of the sponge was cut into 2.5×2.5×0.8 cm pieces, and the upper half was cut into asymmetrical structures of 1.6×1.6×0.7 cm pieces, which were reserved for later use. The volume of the upper half of the melamine sponge was smaller than that of the lower half.

[0029] S2: Add 2 g of acrylamide powder (AM) and 5 mL of graphene oxide (GO) aqueous solution with a concentration of 4 mg / mL to 15 mL of pure water, and sonicate for 30 min to obtain PAM / GO solution. Add 0.05 g of crosslinking agent N,N'-methylenebisacrylamide (MBA), 20 mg of initiator ammonium persulfate (APS), and 10 µL of gel accelerator tetramethylethylenediamine (TMEDA) to finally obtain PAM / GO hydrogel precursor solution.

[0030] S3: The upper half of the asymmetric MS sponge was quickly immersed in the PAM / GO hydrogel precursor solution and then removed. Utilizing the self-absorption properties of MS, the PAM / GO hydrogel precursor solution was absorbed into the sponge. The solution was then drawn into the sponge using a syringe and injected onto the partially immersed MS sponge. The resulting hydrogel sponge was placed in a 40°C oven to accelerate the polymerization reaction.

[0031] S4: Add 2 g of acrylamide powder (AM) and 2 g of polyquaternium-7 (PQ7) to 15 mL of pure water and stir to obtain a PAM / PQ7 solution. Add 0.03 g of crosslinking agent N,N'-methylenebisacrylamide (MBA), 20 mg of initiator ammonium persulfate (APS) and 10 µL of accelerator TMEDA to obtain a PAM / PQ7 hydrogel precursor solution.

[0032] S5: Immerse the other side of the hydrogel sponge obtained in step 3 into the PAM / PQ7 hydrogel precursor solution, and use a syringe to draw in the PAM / PQ7 hydrogel precursor solution and inject it into the lower half of the incompletely reacted MS sponge to obtain the PG-MS-PP sample, which is then placed in a 40℃ oven to accelerate the reaction.

[0033] S6: The reacted PG-MS-PP hydrogel sponge was left overnight at -20℃ and then freeze-dried for 48 h. The freeze-dried sample was then soaked in pure water for one day to remove unreacted polymer monomers, thus obtaining a porous PG-MS-PP hydrogel sponge.

[0034] This invention also provides an application of PG-MS-PP hydrogel sponge in a solar evaporator, specifically a photothermal hydrogel sponge evaporator with excellent salt-barrier capabilities. The evaporator comprises a photothermal hydrogel sponge, a lint-free cloth, and polystyrene foam. The photothermal hydrogel sponge is placed on the polystyrene foam wrapped in the lint-free cloth, with the upper half of the sponge facing the light source. An evaporation test was conducted under one day of sunlight after placing the PG-MS-PP hydrogel sponge on the polystyrene foam wrapped in the lint-free cloth. The polystyrene foam wrapped in the lint-free cloth not only provides insulation to prevent heat loss but also effectively utilizes the hydrophilic properties of the lint-free cloth for water management in the hydrogel evaporator.

[0035] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0036] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0037] Comparative Example 1: This comparative example provides a PG-MS hydrogel sponge, including the following steps: 1. The melamine sponge was repeatedly washed in pure water and ethanol and then ultrasonically treated for 30 minutes. The ultrasonically treated MS was then dried in an oven at 50°C. The lower half of the sponge was cut into 2.5×2.5×0.8 cm pieces, and the upper half was cut into 1.6×1.6×0.7 cm asymmetrical structures, which were reserved for later use.

[0038] 2. Add 2 g of acrylamide powder (AM) and 5 mL of 4 mg / mL graphene oxide (GO) aqueous solution to 15 mL of pure water, and sonicate for 30 min to obtain a PAM / GO solution. Add 0.05 g of N,N'-methylenebisacrylamide (MBA) as a crosslinking agent, 20 mg of ammonium persulfate (APS) as an initiator, and 10 µL of tetramethylethylenediamine (TMEDA) as a gel accelerator to finally obtain the PAM / GO hydrogel precursor solution. 3. Quickly immerse the upper half of the asymmetric MS sponge into the PAM / GO hydrogel solution and remove it. Utilize the self-absorption properties of MS to absorb the PAM / GO hydrogel precursor solution into the sponge. Then, use a syringe to draw the solution and inject it onto the partially immersed MS sponge. Place the resulting hydrogel sponge in a 40°C oven for heat treatment to accelerate the polymerization reaction.

[0039] 4. The reacted PG-MS hydrogel sponge was incubated overnight at -20℃, followed by freeze-drying for 48 h. The freeze-dried sample was then thoroughly soaked in pure water for one day to remove unreacted polymer monomers, resulting in a porous PG-MS hydrogel sponge.

[0040] Comparative Example 2: This comparative example provides a PP-MS hydrogel sponge, including the following steps: 1. The melamine sponge was repeatedly washed in pure water and ethanol and then ultrasonically treated for 30 minutes. The ultrasonically treated MS was then dried in an oven at 50°C. The lower half of the sponge was cut into 2.5×2.5×0.8 cm pieces, and the upper half was cut into 1.6×1.6×0.7 cm asymmetrical structures, which were reserved for later use.

[0041] 2. Add 2 g of AM powder and 2 g of PQ7 to 15 mL of pure water and stir to obtain a PAM / PQ7 solution. Add 0.03 g of crosslinking agent MBA, 20 mg of initiator APS and 10 µL of accelerator TMEDA to obtain a PAM / PQ7 hydrogel precursor solution.

[0042] 3. Immerse the cut MS sponge in the PAM / PQ7 hydrogel precursor solution, and use a syringe to draw up the PAM / PQ7 mixed solution and inject it into the remaining unreacted MS sponge to obtain PP-MS sample. Place it in a 40℃ oven for heat treatment to accelerate the polymerization reaction.

[0043] 4. The reacted PP-MS hydrogel sponge was incubated overnight at -20℃, followed by freeze-drying for 48 h. The freeze-dried sample was then thoroughly soaked in pure water for one day to remove unreacted polymer monomers, resulting in a porous PP-MS hydrogel sponge.

[0044] Example 1: This embodiment provides a photothermal hydrogel sponge with excellent salt barrier properties, including the following steps: 1. The melamine sponge was repeatedly washed in pure water and ethanol and then ultrasonically treated for 30 minutes. The ultrasonically treated MS was then dried in an oven at 50°C. The lower half of the sponge was cut into 2.5×2.5×0.8 cm pieces, and the upper half was cut into 1.6×1.6×0.7 cm asymmetrical structures, which were reserved for later use.

[0045] 2. Add 2 g of acrylamide powder (AM) and 5 mL of 4 mg / mL graphene oxide (GO) aqueous solution to 15 mL of pure water, and sonicate for 30 min to obtain a PAM / GO solution. Add 0.05 g of N,N'-methylenebisacrylamide (MBA) as a crosslinking agent, 20 mg of ammonium persulfate (APS) as an initiator, and 10 µL of tetramethylethylenediamine (TMEDA) as a gel accelerator to finally obtain the PAM / GO hydrogel precursor solution. 3. Quickly immerse the upper half of the asymmetric MS sponge into the PAM / GO hydrogel solution and remove it. Utilize the self-absorption property of MS to absorb the PAM / GO hydrogel precursor solution into the sponge. Use a syringe to draw the solution and inject it onto the partially immersed MS sponge. Place the resulting hydrogel sponge in a 40°C oven to accelerate the polymerization reaction.

[0046] 4. Add 2 g of AM powder and 2 g of PQ7 to 15 mL of pure water and stir to obtain a PAM / PQ7 solution. Add 0.03 g of crosslinking agent MBA, 20 mg of initiator APS and 10 µL of accelerator TMEDA to obtain a PAM / PQ7 hydrogel precursor solution. Immerse the other side of the hydrogel sponge obtained in step 3 into the PAM / PQ7 hydrogel precursor solution, and use a syringe to draw up the PAM / PQ7 mixture and inject it into the lower half of the incompletely reacted MS sponge to obtain a PG-MS-PP sample. Place it in a 40℃ oven to accelerate the reaction.

[0047] 5. The reacted PG-MS-PP hydrogel sponge was incubated overnight at -20℃, followed by freeze-drying for 48 h. The freeze-dried sample was then thoroughly soaked in pure water for one day to remove unreacted polymer monomers, resulting in a porous PG-MS-PP hydrogel sponge.

[0048] Example 2: This embodiment provides a photothermal hydrogel sponge with excellent salt barrier properties, including the following steps: 1. The melamine sponge was repeatedly washed in pure water and ethanol and then ultrasonically treated for 30 minutes. The ultrasonically treated MS was then dried in an oven at 50°C. The lower half of the sponge was cut into 2.5×2.5×0.8 cm pieces, and the upper half was cut into 1.6×1.6×0.7 cm asymmetrical structures, which were reserved for later use.

[0049] 2. Add 1 g of acrylamide powder (AM) and 5 mL of 3 mg / mL graphene oxide (GO) aqueous solution to 15 mL of pure water, and sonicate for 30 min to obtain a PAM / GO solution. Add 0.05 g of N,N'-methylenebisacrylamide (MBA) as a crosslinking agent, 20 mg of ammonium persulfate (APS) as an initiator, and 10 µL of tetramethylethylenediamine (TMEDA) as a gel accelerator to finally obtain the PAM / GO hydrogel precursor solution. 3. Quickly immerse the upper half of the asymmetric MS sponge into the PAM / GO hydrogel solution and remove it. Utilize the self-absorption property of MS to absorb the PAM / GO hydrogel precursor solution into the sponge. Then, use a syringe to draw the solution and inject it onto the partially immersed MS sponge. Place the resulting hydrogel sponge in a 40°C oven to accelerate the polymerization reaction.

[0050] 4. Add 1 g of AM powder and 1 g of PQ7 to 15 mL of pure water and stir to obtain a PAM / PQ7 solution. Add 0.03 g of crosslinking agent MBA, 20 mg of initiator APS and 10 µL of accelerator TMEDA to obtain a PAM / PQ7 hydrogel precursor solution. Immerse the other side of the hydrogel sponge obtained in step 3 into the PAM / PQ7 hydrogel precursor solution, and use a syringe to draw up the PAM / PQ7 mixture and inject it into the lower half of the incompletely reacted MS sponge to obtain a PG-MS-PP sample. Place the sample in a 40℃ oven to accelerate the reaction.

[0051] 5. The reacted PG-MS-PP hydrogel sponge was incubated overnight at -20℃, followed by freeze-drying for 48 h. The freeze-dried sample was then thoroughly soaked in pure water for one day to remove unreacted polymer monomers, resulting in a porous PG-MS-PP hydrogel sponge.

[0052] Example 3: This embodiment provides a photothermal hydrogel sponge with excellent salt barrier properties, including the following steps: 1. The melamine sponge was repeatedly washed in pure water and ethanol and then ultrasonically treated for 30 minutes. The ultrasonically treated MS was then dried in an oven at 50°C. The lower half of the sponge was cut into 2.5×2.5×0.8 cm pieces, and the upper half was cut into 1.6×1.6×0.7 cm asymmetrical structures, which were reserved for later use.

[0053] 2. Add 3 g of acrylamide powder (AM) and 4 mL of 5 mg / mL graphene oxide (GO) aqueous solution to 15 mL of pure water, and sonicate for 30 min to obtain a PAM / GO solution. Add 0.05 g of N,N'-methylenebisacrylamide (MBA) as a crosslinking agent, 20 mg of ammonium persulfate (APS) as an initiator, and 10 µL of tetramethylethylenediamine (TMEDA) as a gel accelerator to finally obtain the PAM / GO hydrogel precursor solution. 3. Quickly immerse the upper half of the asymmetric MS sponge into the PAM / GO hydrogel solution and remove it. Utilize the self-absorption property of MS to absorb the PAM / GO hydrogel precursor solution into the sponge. Then, use a syringe to draw the solution and inject it onto the partially immersed MS sponge. Place the resulting hydrogel sponge in a 40°C oven to accelerate the polymerization reaction.

[0054] 4. Add 3 g of AM powder and 3 g of PQ7 to 15 mL of pure water and stir to obtain a PAM / PQ7 solution. Add 0.03 g of crosslinking agent MBA, 20 mg of initiator APS and 10 µL of accelerator TMEDA to obtain a PAM / PQ7 hydrogel precursor solution. Immerse the other side of the hydrogel sponge obtained in step 3 into the PAM / PQ7 hydrogel precursor solution, and use a syringe to draw up the PAM / PQ7 mixture and inject it into the lower half of the incompletely reacted MS sponge to obtain a PG-MS-PP sample. Place the sample in a 40℃ oven to accelerate the reaction.

[0055] 5. The reacted PG-MS-PP hydrogel sponge was incubated overnight at -20℃, followed by freeze-drying for 48 h. The freeze-dried sample was then thoroughly soaked in pure water for one day to remove unreacted polymer monomers, resulting in a porous PG-MS-PP hydrogel sponge.

[0056] Figure 1The images show physical images of the hydrogel sponges prepared in Comparative Example 1, Comparative Example 2, and Example 1. MS represents the unfilled original sponge matrix, PG-MS represents a hydrogel sponge filled with a fixed negative charge, PP-MS represents a hydrogel sponge filled with a fixed positive charge, and PG-MS-PP represents a hydrogel sponge filled with a fixed negative charge on the top and a fixed positive charge on the bottom. As can be seen from the images, PG-MS-PP exhibits a distinct Janus structure.

[0057] Figure 2 This shows a schematic diagram of an evaporation device with excellent thermal insulation management and water supply characteristics. Figure 2 Image 'a' shows the actual evaporator, with a layer of polyethylene foam wrapped around the beaker to prevent heat loss. Figure 2 b is a schematic diagram of the evaporation process. When water evaporates on the upper surface, the cleanroom cloth continuously supplies water to the PG-MS-PP on the lower surface, so as to promote the balance between water evaporation and water supply.

[0058] Figure 3 This is a SEM image of the PG-MS-PP hydrogel sponge prepared in Example 1. Figure 3 'a' represents the internal structure of the unfilled MS, while Figure 3 b and c are internal structural diagrams of the upper and lower parts of PG-MS-PP, respectively. It can be clearly seen that PAM / GO and PAM / PQ7 hydrogels are filled between the MS backbone. Figure 3 (b2, c2). It is precisely because these filled hydrogels each carry fixed positive and negative charges that the evaporator can utilize its own properties to repel ions in high-concentration salt water, causing cations and anions to separate into layers in the hydrogel, thereby achieving the purpose of salt barrier.

[0059] Figure 4 The figure shows the evaporation rate test results of the PG-MS-PP hydrogel sponge prepared in Example 1 in NaCl solutions of different concentrations. As can be seen from the figure, the prepared PG-MS-PP hydrogel sponge, used as an evaporator, achieved an evaporation rate of 4.80 kg·m⁻¹ for a 3.5 wt% NaCl solution under sunlight irradiation. -2 ·h -1 This evaporation rate is greater than most interfacial evaporators reported to date, reaching 4.17 kg·m³ when the salinity gradually increases to 20 wt%. -2 ·h -1 The evaporation rate decreased by only 13%, indicating that the evaporator still has an excellent evaporation rate in a high-salinity environment.

[0060] Figure 5The graph shows the mass loss of the hydrogel sponge prepared in Example 1 after 8 hours of long-term evaporation in different NaCl solution environments. As can be seen from the graph, even when the salt concentration increases from 3.5 wt% to a saturation concentration of 26.47 wt%, the mass loss remains relatively similar, indicating that the hydrogel sponge evaporator exhibits long-term stability during the 8-hour evaporation process.

[0061] Figure 6 The images show the PG-MS, PP-MS, and PG-MS-PP hydrogel sponges prepared in Comparative Examples 1, 2, and 1 after evaporation in 20 wt% NaCl solution for 8 h. As can be seen from the images, with increasing evaporation time, salt gradually precipitates on the surface of the PG-MS and PP-MS hydrogel sponges, while no salt precipitates on the surface of the PG-M-PP sponge. This indicates that during the 8-h evaporation process, the long-term stability and salt barrier capacity of PG-M-PP are far superior to those of PG-MS and PP-MS hydrogel sponges using only a single filler. This also demonstrates that the PG-MS-PP hydrogel sponge evaporator prepared in this invention possesses excellent salt barrier performance and long-term stability.

[0062] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for preparing a photothermal hydrogel sponge with excellent salt-barrier ability, characterized in that, Includes the following steps: A melamine sponge with an asymmetrical structure was prepared, wherein the melamine sponge was divided into an upper part and a lower part; AM powder and GO aqueous solution were added to pure water and stirred to prepare PAM / GO solution. Then, crosslinking agent, initiator and gel accelerator were added to prepare PAM / GO hydrogel precursor solution. AM powder and polyquaternium-7 were added to pure water and stirred to prepare PAM / PQ7 solution. Then, crosslinking agent, initiator and gel accelerator were added to prepare PAM / PQ7 hydrogel precursor solution. The upper half of the melamine sponge was immersed in a PAM / GO hydrogel precursor solution and then removed. The PAM / GO hydrogel precursor solution was then injected with a syringe to accelerate polymerization at a set temperature. The lower half was then immersed in a PAM / PQ7 hydrogel precursor solution and removed. The PAM / PQ7 hydrogel precursor solution was then injected with a syringe to accelerate polymerization at a set temperature. Finally, freeze-drying and immersion in pure water were performed sequentially to obtain a Janus-structured photothermal hydrogel sponge with excellent salt-barrier properties.

2. The method for preparing a photothermal hydrogel sponge with excellent salt-barrier ability according to claim 1, characterized in that, The volume of the upper half of the melamine sponge is smaller than the volume of the lower half of the melamine sponge.

3. The method for preparing the photothermal hydrogel sponge with excellent salt-barrier ability according to claim 1, characterized in that, The ratio of AM powder, GO aqueous solution and pure water is 1~3 g: 4~5 mL: 15 mL; the concentration of the GO aqueous solution is 3~5 mg / mL.

4. The method for preparing the photothermal hydrogel sponge with excellent salt-barrier ability according to claim 1, characterized in that, The ratio of AM powder, polyquaternium-7 and pure water is 1~3 g: 1~3 g: 15 mL.

5. The method for preparing a photothermal hydrogel sponge with excellent salt-barrier ability according to claim 1, characterized in that, The crosslinking agent is N,N'-methylenebisacrylamide; the initiator is ammonium persulfate; and the gel accelerator is tetramethylethylenediamine.

6. The method for preparing the photothermal hydrogel sponge with excellent salt-barrier ability according to claim 1, characterized in that, The ratio of PAM / GO solution, crosslinking agent, initiator, and gel accelerator in the PAM / GO hydrogel precursor solution is 20 mL: 0.05 g: 20 mg: 10 µL.

7. The method for preparing the photothermal hydrogel sponge with excellent salt-barrier ability according to claim 1, characterized in that, The ratio of PAM / PQ7 solution, crosslinking agent, initiator, and gel accelerator in the PAM / PQ7 hydrogel precursor solution is 17 mL: 0.03 g: 20 mg: 10 µL.

8. The method for preparing the photothermal hydrogel sponge with excellent salt-barrier ability according to claim 1, characterized in that, The set temperature is 40℃; the freeze-drying temperature is -20℃ and the time is 48 h; the pure water soaking time is 24 h.

9. A photothermal hydrogel sponge with excellent salt barrier properties prepared by the method for preparing photothermal hydrogel sponge with excellent salt barrier properties as described in any one of claims 1 to 8.

10. The application of the photothermal hydrothermal gel sponge with excellent salt barrier capability prepared by the method for preparing the photothermal hydrothermal gel sponge with excellent salt barrier capability according to any one of claims 1 to 8 in a solar evaporator, characterized in that, The solar evaporator includes a photothermal gel sponge, a lint-free cloth, and polystyrene foam. The photothermal gel sponge is placed on the polystyrene foam wrapped in the lint-free cloth, with the upper part of the photothermal gel sponge facing the light source.

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