A double-network hydrogel evaporator for interfacial water evaporation, preparation method and application

Abstract

The present application relates to the technical field of seawater desalination material preparation, and particularly relates to a double-network hydrogel evaporator for interfacial water evaporation, a preparation method and application, comprising a polyvinyl alcohol first network and a 2-acrylamide-2-methylpropanesulfonic acid second network which penetrate each other, and Ti4O7 photo-thermal absorption material is dispersed in the first network; the evaporator has a macroporous skeleton formed by the first network and a multistage pore composed of nanoscale fibrous and membranous secondary structures derived from the second network on the macroporous skeleton, the mechanical stability is improved through a double-network synergistic enhancement mechanism, the multistage pore structure is used to accelerate water transmission and increase the evaporation interface, so that the evaporator has a high evaporation rate, excellent salt resistance and long-term operation stability, and is more suitable for solar-driven seawater desalination, and solves the problems of weak mechanical strength, poor structural stability and poor environmental adaptability of the hydrogel-based evaporator in the prior art.

Description

Technical Field

[0001] This invention relates to the field of seawater desalination material preparation technology, specifically to a dual-network hydrogel evaporator for interfacial water evaporation, its preparation method, and its application. Background Technology

[0002] With the continuous development of the global economy and the ongoing expansion of the population, human society's demand for freshwater resources is showing a sustained and accelerating growth trend. As a fundamental strategic resource supporting human survival and social operation, the contradiction between water supply capacity and increasing demand is becoming increasingly prominent. Looking at the global distribution of water resources, the vast majority of the water bodies covering the Earth's surface are seawater containing high concentrations of salt and various minerals, leaving a very limited proportion of freshwater resources truly available for direct human use. Against this backdrop, efficiently extracting freshwater resources from the extremely abundant seawater has become one of the most feasible technological pathways to alleviate the global water shortage problem.

[0003] In the development of seawater desalination technology, traditional methods such as low-temperature multi-effect distillation, reverse osmosis, and ion exchange have achieved large-scale application to a certain extent after decades of technological accumulation and engineering practice, making significant contributions to the global supply of freshwater resources. However, from the perspective of energy consumption and environmental impact, these seawater desalination methods are generally costly and energy-intensive, failing to meet the requirements of low-carbon and environmentally friendly development. Therefore, how to combine improving energy efficiency with green environmental protection has become a major challenge in seawater desalination technology research.

[0004] Solar energy, as the most abundant and widely distributed renewable energy source in nature, has become a crucial pillar of global energy transition and green development strategies due to its four core advantages: zero environmental impact, strong economic sustainability, high technological universality, and good social inclusion. Deeply integrating solar energy with seawater desalination technology to achieve efficient, low-cost, and environmentally friendly freshwater acquisition has become a cutting-edge research direction attracting common attention from the international academic and industrial communities. Among the many research branches of solar-driven seawater desalination technology, solar-driven interfacial evaporation technology has attracted much attention due to its unique working mechanism and outstanding energy utilization efficiency. The core principle of this technology lies in utilizing photothermal conversion materials to efficiently absorb solar energy and convert it into heat energy, concentrating the heat at the interface between the evaporator and water, thereby achieving rapid evaporation of water molecules. In the design of various interfacial evaporators, hydrogel-based evaporators have become one of the research hotspots in recent years due to their unique material properties. Hydrogel materials possess excellent hydrophilicity and a rich three-dimensional network structure, enabling them to continuously transport seawater from the bottom layer to the evaporation interface through capillary forces, ensuring the continuity and stability of the evaporation process. However, in practical engineering applications, their structural stability and long-term operational reliability under high evaporation rates still face severe challenges. Especially under the combined effects of high solar radiation intensity and high salt concentration environments, hydrogel materials with a single network structure are prone to a series of degradation problems due to continuous water evaporation and salt crystallization, such as network structure relaxation, pore collapse, and a decrease in overall mechanical strength. These problems directly lead to the blockage or failure of water transport channels, resulting in a sharp decline in evaporation rate and irreversible loss of water production capacity. Therefore, how to systematically enhance the mechanical strength, structural stability, and environmental adaptability of hydrogel evaporators under complex operating conditions while maintaining or even improving high evaporation efficiency has become a key challenge that urgently needs to be overcome in promoting the transformation of solar interface evaporation technology from laboratory research to practical engineering applications. Summary of the Invention

[0005] To address the problems of weak mechanical strength, poor structural stability, and poor environmental adaptability in existing hydrogel-based evaporators, this invention provides a dual-network hydrogel evaporator for interfacial water evaporation, its preparation method, and its application.

[0006] To achieve the above objectives, the present invention employs the following technical solution: The present invention provides a dual-network hydrogel evaporator for interfacial water evaporation, the dual-network hydrogel evaporator comprising a first network and a second network that penetrate each other, the first network being a polyvinyl alcohol (PVA) network and containing a photothermal absorbing material dispersed therein; the second network being a 2-acrylamide-2-methylpropanesulfonic acid (AMPS) network.

[0007] Optionally, the dual-network hydrogel evaporator has a multi-level pore structure, which includes a macroporous framework formed by the first network and nanoscale fibrous and membrane-like secondary structures derived from the macroporous framework by the second network.

[0008] Optionally, the photothermal absorbing material is Ti4O7.

[0009] The present invention also provides a method for preparing a dual-network hydrogel evaporator for interfacial water evaporation as described above, characterized in that it includes: The photothermal absorbing material was uniformly dispersed in a PVA aqueous solution to obtain the first precursor solution; Glutaraldehyde aqueous solution and HCl solution were added to the first precursor solution, and then directional freezing and freeze-drying were performed to obtain the shaped precursor. The preform was placed in water and allowed to expand fully to obtain a Ti4O7-based PVA hydrogel evaporator. The BIS crosslinking agent and APS initiator were uniformly dispersed in an AMPS aqueous solution to obtain a second precursor solution. The Ti4O7-based PVA hydrogel evaporator was placed in a second precursor solution and heated to polymerize, thus obtaining a prefabricated double-network hydrogel evaporator. The prefabricated dual-network hydrogel evaporator was immersed in water to obtain the dual-network hydrogel evaporator.

[0010] Optionally, the PVA concentration in the PVA aqueous solution is 5%-15% by mass.

[0011] Optionally, the mass concentration of the photothermal absorbing material in the first precursor solution is 0.5%-25%.

[0012] Optionally, the glutaraldehyde aqueous solution has a glutaraldehyde mass concentration of 40%-60% and the HCl solution has a concentration of 1-1.4M.

[0013] Optionally, the mass concentration of the AMPS aqueous solution is 10%-20%; the amount of BIS crosslinking agent added is 0.25%-1% of the mass of AMPS, the amount of APS initiator added is 0.5%-2% of the mass of AMPS, the BIS crosslinking agent is N,N′-methylenebisacrylamide, and the APS initiator is ammonium persulfate.

[0014] Optionally, the temperature for the heating polymerization is 85-95°C.

[0015] The above-mentioned dual-network hydrogel evaporator for interfacial water evaporation is applied in seawater desalination.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a dual-network hydrogel evaporator for interfacial water evaporation. This dual-network hydrogel evaporator employs a dual-network design, utilizing a synergistic mechanism of sacrificial bond breaking and continuous network support. The dual-network hydrogel maintains high strength while effectively avoiding the brittle fracture problem of single-network hydrogels under large deformation conditions. This dual-network hydrogel evaporator is a hydrogel-based evaporator with polyvinyl alcohol (PVA) as the first network and 2-acrylamide-2-methylpropanesulfonic acid (AMPS) as the second network. The PVA network forms a stable three-dimensional structure through crystalline regions and hydrogen bonding, providing necessary mechanical support for the evaporator. The AMPS network imparts higher hydrophilicity and swelling capacity to the material, helping to maintain a continuous water supply under high evaporation rates. Simultaneously, this dual-network structure significantly improves the mechanical stability of the hydrogel during large-area preparation and long-term operation, providing structural assurance for the reliable operation of the evaporator in complex environments. In terms of evaporation performance, the interpenetrating network and hierarchical pore structure formed by the dual-network hydrogel effectively shorten the transport path of water molecules from the bulk phase to the evaporation surface and enhance the effective area of ​​the evaporation interface. Simultaneously, the stable structure helps maintain good thermal localization characteristics, allowing absorbed solar energy to be more concentrated for the interfacial evaporation process rather than being ineffectively dissipated into the bulk water. Furthermore, under high-salinity seawater conditions, the continuous and stable water channels in the dual-network hydrogel help dilute the concentration of salt ions at the interface and alleviate salt accumulation, thereby improving the salt resistance of the evaporator to a certain extent. Testing showed that the dual-network hydrogel of this invention maintains structural integrity without macroscopic cracks even under 80% compressive strain, exhibiting significantly better compressive stability than single-network hydrogels, avoiding the brittle fracture problem of single-network materials under large deformation.

[0017] This dual-network hydrogel evaporator features a multi-level porous structure. Its macroporous framework combined with nanoscale secondary structures effectively shortens the water transport path, increases the evaporation interface area, and improves thermal localization effects. At a solar intensity of 1 kW m³ / s... -2 Under these conditions, the evaporation rate of this dual-network hydrogel can reach 4.45 kg / m³. -2 h -1 Compared to a single-network hydrogel, it exhibits better evaporation efficiency. The continuous and stable water channels formed within the dual-network hydrogel help dilute the salt ion concentration at the evaporation interface, mitigating salt accumulation. Even under high salinity (7.0 wt%) conditions, its evaporation rate remains at 2.08 kg m³. -2 h -1 It exhibits good salt resistance and operational stability.

[0018] This invention also provides a method for preparing a dual-network hydrogel evaporator for interfacial water evaporation as described above. The method first prepares a PVA first network and performs directional freeze-drying to form an ordered oriented pore structure. Then, the first network is immersed in an AMPS precursor solution for in-situ free radical polymerization, allowing the PAMPS network to uniformly penetrate the PVA framework, ensuring the independence and interpenetration of the two networks. Glutaraldehyde, as a crosslinking agent, undergoes an acetalization reaction with PVA to form chemical crosslinking points, enhancing the structural stability of the PVA network in water and preventing it from dissolving or deforming during the polymerization of the second network. This achieves a unified combination of mechanical enhancement, high hydrophilicity, excellent evaporation performance, and salt resistance in the dual-network hydrogel evaporator, with controllable material costs, and has the potential to be transformed from laboratory research to practical engineering applications.

[0019] The application of the aforementioned dual-network hydrogel evaporator for interfacial water evaporation in seawater desalination is advantageous because it possesses excellent photothermal conversion performance and a multi-level pore structure, while also exhibiting superior structural stability and evaporation rate. Under complex operating conditions such as high salinity and high radiation, it is less prone to pore collapse or structural damage, ensuring reliable long-term continuous operation. Compared to single-network hydrogels, it can better meet the needs of efficient seawater desalination. Attached Figure Description

[0020] Figure 1 This is a schematic flowchart of a method for preparing a dual-network hydrogel evaporator for interfacial water evaporation according to the present invention.

[0021] Figure 2 The images shown are SEM images of the evaporators prepared in Examples 1-4 and Comparative Examples 1-2 of this invention. Specifically, a1-a3 are SEM images of the evaporator prepared in Comparative Example 1 at different magnifications, b1-b3 are SEM images of the evaporator prepared in Example 1 at different magnifications, c1-c3 are SEM images of the evaporator prepared in Example 2 at different magnifications, d1-d3 are SEM images of the evaporator prepared in Example 3 at different magnifications, e1-e3 are SEM images of the evaporator prepared in Example 4 at different magnifications, and f1-f3 are SEM images of the evaporator prepared in Comparative Example 2 at different magnifications.

[0022] Figure 3 These are photographs of the evaporators prepared in Examples 1-4 and Comparative Examples 1-2 of the present invention under 80% compressive stress in the vertical direction.

[0023] Figure 4 The diagram shows the compression stress-strain curves of the evaporators prepared in Examples 1-4 and Comparative Examples 1-2 of this invention.

[0024] Figure 5This is a comparison chart of the evaporation rates of the evaporators prepared in Examples 1-4 and Comparative Examples 1-2 of the present invention.

[0025] Figure 6 The above is a comparison chart of the evaporation rates of the evaporators prepared in Examples 1-4 and Comparative Examples 1-2 of the present invention under one solar intensity. Detailed Implementation

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.”

[0030] 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.

[0031] 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.

[0032] 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.

[0033] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0034] This invention provides a dual-network hydrogel evaporator for interfacial water evaporation. The dual-network hydrogel evaporator includes a first network and a second network that interpenetrate with each other. The first network is a polyvinyl alcohol network, and a photothermal absorbing material is dispersed within the first network. The second network is a 2-acrylamide-2-methylpropanesulfonic acid network. The dual-network hydrogel evaporator has a hierarchical porous structure, which includes a macroporous framework formed by the first network, and nanoscale fibrous and membrane-like secondary structures derived from the macroporous framework by the second network. The photothermal absorbing material is Ti4O7.

[0035] This dual-network hydrogel evaporator utilizes a PVA network to form a stable macroporous framework through crystalline regions and hydrogen bonds, providing compressive strength. A PAMPS network forms nanoscale fiber / film-like secondary structures on this macroporous framework, capable of reversible deformation and energy dissipation under stress. This significantly improves the structural stability of the evaporator under long-term operation and high-salt or high-irradiation conditions, avoiding the channel collapse and brittle fracture problems common with single-network evaporators. Simultaneously, the macroporous framework structure provides vertically oriented macroscopic channels, serving as pathways for rapid water transport and effectively shortening the path of water molecules from the bulk phase to the evaporation surface. The high specific surface area nanostructures derived from the macroporous framework greatly increase the effective area of ​​the evaporation interface, while also facilitating the formation of a continuous water film and reducing the enthalpy of evaporation. Ti4O7, as a photothermal absorbing material, has high solar light absorption rate and good photothermal stability. When uniformly dispersed in the PVA network and combined with the PVA framework, heat can be generated in situ and quickly transferred to water molecules in the channels, reducing heat diffusion loss to the bulk water phase. This allows the absorbed solar energy to be used more concentratedly for interfacial evaporation, improving energy utilization efficiency. It can also continuously flush salt ions from the evaporation surface back to the bulk solution, preventing interfacial salt crystallization.

[0036] See Figure 1 The present invention also provides a method for preparing a dual-network hydrogel evaporator for interfacial water evaporation as described above, comprising: S1: The photothermal absorbing material is uniformly dispersed in a PVA aqueous solution to obtain the first precursor solution, specifically: PVA powder is dissolved in deionized water and stirred at 85-95℃ to form a PVA aqueous solution with a mass concentration of 8%-12%. Photothermal absorbing material is added to PVA aqueous solution and stirred evenly to form a first precursor solution with a photothermal absorbing material mass concentration of 0.5%-25%.

[0037] S2: Glutaraldehyde aqueous solution and HCl solution are added to the first precursor solution, followed by directional freezing and freeze-drying to obtain the stabilized precursor, specifically: Under stirring conditions, glutaraldehyde aqueous solution and HCl solution are added to the first precursor solution, and the solution is placed in a mold and then placed in a container filled with liquid nitrogen for directional freezing until the solution is completely frozen. Subsequently, the solution is placed in a freeze dryer and dried for more than 18 hours at a pressure of 0.08-0.12 Pa and a condensation temperature of -75 to -65 °C to obtain a shaped precursor. The glutaraldehyde aqueous solution contains 40%-60% glutaraldehyde by mass, and the HCl solution contains 1-1.4 M.

[0038] S3: The preform was placed in water and allowed to fully expand to obtain a Ti4O7-based PVA hydrogel evaporator, specifically: The preform was placed in deionized water and allowed to expand fully to obtain a Ti4O7-based PVA hydrogel evaporator.

[0039] S4: The BIS crosslinking agent and APS initiator are uniformly dispersed in an AMPS aqueous solution to obtain the second precursor solution, specifically as follows: AMPS monomer was added to deionized water to prepare an AMPS aqueous solution with a mass concentration of 10%-20%; BIS crosslinking agent and APS initiator were added to the AMPS aqueous solution to obtain a second precursor solution. After ultrasonic treatment at room temperature, dissolved oxygen in the solution was removed by purging with nitrogen for more than 8 minutes, and centrifuged at 6500-7500 rpm for 3-7 minutes to remove air bubbles in the solution, resulting in a homogeneous second precursor solution. The amount of BIS crosslinking agent added is 0.25%-1% of the mass of AMPS, and the amount of APS initiator added is 0.5%-2% of the mass of AMPS. The BIS crosslinking agent is N,N′-methylenebisacrylamide, and the APS initiator is ammonium persulfate.

[0040] S5: The Ti4O7-based PVA hydrogel evaporator was placed in the second precursor solution and heated to polymerize, resulting in a prefabricated dual-network hydrogel evaporator, specifically: The Ti4O7-based PVA hydrogel evaporator was placed in the second precursor solution and a free radical polymerization reaction was carried out at 85-95℃. This temperature can ensure a moderate polymerization rate, which is conducive to the formation of a uniform cross-linked network structure.

[0041] S6: Immerse the prefabricated double-network hydrogel evaporator in water to obtain the double-network hydrogel evaporator.

[0042] The application of the aforementioned dual-network hydrogel evaporator for interfacial water evaporation in seawater desalination is advantageous because it possesses excellent photothermal conversion performance and a multi-level pore structure, while also exhibiting superior structural stability and evaporation rate. Under complex operating conditions such as high salinity and high radiation, it is less prone to pore collapse or structural damage, ensuring reliable long-term continuous operation. Compared to single-network hydrogels, it can better meet the needs of efficient seawater desalination.

[0043] Example 1 2g of PVA powder and 18ml of deionized water were continuously stirred at 90℃ to form a 10% PVA aqueous solution; Ti4O7 photothermal absorbing material was added to the PVA aqueous solution and stirred evenly to form a first precursor solution with a Ti4O7 concentration of 10%. During stirring, 125 μL of glutaraldehyde aqueous solution (mass concentration of 50%) and 250 μL of 1.2 M HCl solution were added to the first precursor solution. The resulting solution was poured into a waffle mold, and the mold was then placed in a liquid nitrogen container for directional freezing until the solution was completely frozen. The frozen sample was then placed in a freeze dryer and dried at -70 °C under 0.1 Pa conditions for 24 h to obtain the shaped precursor. The pre-formed precursor was placed in deionized water and fully expanded to obtain a Ti4O7-based PVA hydrogel evaporator. Add 1g of AMPS monomer (by mass ratio, PVA:AMPS = 1:0.5) to deionized water and stir continuously until completely dissolved to form an AMPS aqueous solution with a mass concentration of 15%. Then add 0.01g of N,N′-methylenebisacrylamide and 0.02g of ammonium persulfate. After sonication at room temperature, purge with nitrogen for 10 min to remove dissolved oxygen from the solution. Centrifuge at 7000 rpm for 5 min to remove air bubbles from the solution to obtain a homogeneous second precursor solution. The Ti4O7-based PVA hydrogel evaporator was immersed in the second precursor solution and placed in a furnace at 90°C for free radical polymerization to obtain the prefabricated double-network hydrogel evaporator. The prefabricated dual-network hydrogel evaporator was immersed in deionized water for 12 hours to obtain the dual-network hydrogel evaporator, denoted as DNWH1.

[0044] Example 2 2g of PVA powder and 18ml of deionized water were continuously stirred at 90℃ to form a 10% PVA aqueous solution; Ti4O7 photothermal absorbing material was added to the PVA aqueous solution and stirred evenly to form a first precursor solution with a Ti4O7 concentration of 10%. During stirring, 125 μL of glutaraldehyde aqueous solution (mass concentration of 50%) and 250 μL of 1.2 M HCl solution were added to the first precursor solution. The resulting solution was poured into a waffle mold, and the mold was then placed in a liquid nitrogen container for directional freezing until the solution was completely frozen. The frozen sample was then placed in a freeze dryer and dried at -70 °C under 0.1 Pa conditions for 24 h to obtain the shaped precursor. The pre-formed precursor was placed in deionized water and fully expanded to obtain a Ti4O7-based PVA hydrogel evaporator. Add 2 g of AMPS monomer (corresponding to PVA:AMPS=1:1) to deionized water and stir continuously until completely dissolved to form an AMPS aqueous solution with a mass concentration of 15%. Then add 0.01 g of N,N′-methylenebisacrylamide and 0.02 g of ammonium persulfate. After sonication at room temperature, purge with nitrogen for 10 min to remove dissolved oxygen from the solution. Centrifuge at 7000 rpm for 5 min to remove air bubbles from the solution to obtain a homogeneous second precursor solution. The Ti4O7-based PVA hydrogel evaporator was immersed in the second precursor solution and placed in a furnace at 90°C for free radical polymerization to obtain the prefabricated double-network hydrogel evaporator. The prefabricated dual-network hydrogel evaporator was immersed in deionized water for 12 hours to obtain the dual-network hydrogel evaporator, denoted as DNWH2.

[0045] Example 3 2g of PVA powder and 18ml of deionized water were continuously stirred at 90℃ to form a 10% PVA aqueous solution; Ti4O7 photothermal absorbing material was added to the PVA aqueous solution and stirred evenly to form a first precursor solution with a Ti4O7 concentration of 10%. During stirring, 125 μL of glutaraldehyde aqueous solution (mass concentration of 50%) and 250 μL of 1.2 M HCl solution were added to the first precursor solution. The resulting solution was poured into a waffle mold, and the mold was then placed in a liquid nitrogen container for directional freezing until the solution was completely frozen. The frozen sample was then placed in a freeze dryer and dried at -70 °C under 0.1 Pa conditions for 24 h to obtain the shaped precursor. The pre-formed precursor was placed in deionized water and fully expanded to obtain a Ti4O7-based PVA hydrogel evaporator. Add 3 g of AMPS monomer (corresponding to PVA:AMPS=1:1.5) to deionized water and stir continuously until completely dissolved to form an AMPS aqueous solution with a mass concentration of 15%. Then add 0.01 g of N,N′-methylenebisacrylamide and 0.02 g of ammonium persulfate. After sonication at room temperature, purge with nitrogen for 10 min to remove dissolved oxygen from the solution. Centrifuge at 7000 rpm for 5 min to remove air bubbles from the solution to obtain a homogeneous second precursor solution. The Ti4O7-based PVA hydrogel evaporator was immersed in the second precursor solution and placed in a furnace at 90°C for free radical polymerization to obtain the prefabricated double-network hydrogel evaporator. The prefabricated dual-network hydrogel evaporator was immersed in deionized water for 12 hours to obtain the dual-network hydrogel evaporator, denoted as DNWH3.

[0046] Example 4 2g of PVA powder and 18ml of deionized water were continuously stirred at 90℃ to form a 10% PVA aqueous solution; Ti4O7 photothermal absorbing material was added to the PVA aqueous solution and stirred evenly to form a first precursor solution with a Ti4O7 concentration of 10%. During stirring, 125 μL of glutaraldehyde aqueous solution (mass concentration of 50%) and 250 μL of 1.2 M HCl solution were added to the first precursor solution. The resulting solution was poured into a waffle mold, and the mold was then placed in a liquid nitrogen container for directional freezing until the solution was completely frozen. The frozen sample was then placed in a freeze dryer and dried at -70 °C under 0.1 Pa conditions for 24 h to obtain the shaped precursor. The pre-formed precursor was placed in deionized water and fully expanded to obtain a Ti4O7-based PVA hydrogel evaporator. Add 4 g of AMPS monomer (corresponding to PVA:AMPS=1:2) to deionized water and stir continuously until completely dissolved to form an AMPS aqueous solution with a mass concentration of 15%. Then add 0.01 g of N,N′-methylenebisacrylamide and 0.02 g of ammonium persulfate. After sonication at room temperature, purge with nitrogen for 10 min to remove dissolved oxygen from the solution. Centrifuge at 7000 rpm for 5 min to remove air bubbles from the solution to obtain a homogeneous second precursor solution. The Ti4O7-based PVA hydrogel evaporator was immersed in the second precursor solution and placed in a furnace at 90°C for free radical polymerization to obtain the prefabricated double-network hydrogel evaporator. The prefabricated dual-network hydrogel evaporator was immersed in deionized water for 12 hours to obtain the dual-network hydrogel evaporator, denoted as DNWH4.

[0047] Comparative Example 1 2g of PVA powder and 18ml of deionized water were continuously stirred at 90℃ to form a 10% PVA aqueous solution; Ti4O7 photothermal absorbing material was added to the PVA aqueous solution and stirred evenly to form a first precursor solution with a Ti4O7 concentration of 10%. During stirring, 125 μL of glutaraldehyde aqueous solution (mass concentration of 50%) and 250 μL of 1.2 M HCl solution were added to the first precursor solution. The resulting solution was poured into a waffle mold, and the mold was then placed in a liquid nitrogen container for directional freezing until the solution was completely frozen. The frozen sample was then placed in a freeze dryer and dried at -70 °C under 0.1 Pa conditions for 24 h to obtain the shaped precursor. The preform was placed in deionized water and allowed to expand fully to obtain a Ti4O7-based PVA hydrogel evaporator, denoted as the pure PVA evaporator (TPWH).

[0048] Comparative Example 2 Add 2 g of AMPS monomer to deionized water and stir continuously until completely dissolved to form an AMPS aqueous solution with a mass concentration of 15%. Then add 0.01 g of N,N′-methylenebisacrylamide and 0.02 g of ammonium persulfate. Continue sonicating until the system is homogeneous. Then purge the solution with nitrogen for 10 min to remove dissolved oxygen. Finally, centrifuge at 7000 r / min for 5 min to remove air bubbles to obtain a homogeneous precursor solution.

[0049] The precursor solution was poured into a mold and placed in a furnace at 90°C for free radical polymerization for 24 hours to obtain pure AMPS hydrogel. The obtained hydrogel was soaked in deionized water for 12 hours to remove unreacted monomers and residual reagents; then it underwent repeated freeze-thaw cycles (10 cycles), and after freeze-drying, it was fully swollen and ready for use, and was designated as a pure AMPS evaporator.

[0050] See Figure 2 SEM analysis was performed on the evaporators prepared in Examples 1-4 and Comparative Examples 1-2. The results showed that the mass ratio of PVA to AMPS significantly affected the microstructure and pore structure of the hydrogel. Even after introducing a small amount of AMPS into the system, the proportion of PVA remained high (2:1), as indicated by the SEM images. Figure 2(b1-b3) shows that the overall sample still maintains a relatively obvious oriented structure, mainly inheriting the pore structure of pure PVA hydrogel. However, the structural arrangement begins to show some disturbance, and the cross-sectional roughness increases. This indicates that the introduction of AMPS has disrupted the crystalline structure of PVA to some extent, promoting the initial formation of an interpenetrating polymer network. However, at this stage, due to the relatively low AMPS content, the second network is relatively sparse, mainly playing the role of filling and partially reinforcing the PVA skeleton, and has not formed a significantly independent continuous network. Therefore, the structure is closer to a porous hydrogel dominated by PVA. As the AMPS content further increases ( Figure 2 (c1-c3) The microstructure of the sample underwent significant changes. The original regular orientation structure gradually became blurred, and was replaced by a wrinkled and serrated cross-sectional morphology, accompanied by the appearance of interconnected pores.

[0051] When AMPS levels continue to increase ( Figure 2 When the mass ratio of PVA to AMPS reaches 1:1.5 (d1-d3), the pore structure formed by PVA still exists, but abundant, uniform, and dense nanoscale fibrous and membrane-like secondary structures are derived on its pore walls, corresponding to a fully developed AMPS chemical cross-linking network. When the proportion of AMPS is further increased (1:2), the morphology further evolves, such as... Figure 2 As shown in e1-e3, the macroporous framework of PVA becomes blurred, and the overall structure tends to be homogeneous, with nanofibers and membrane structures becoming more prominent. This is because during polymerization, the strong hydrophilicity of the high-content AMPS monomer and the electrostatic repulsion between its sulfonic acid groups promote the formation of a dense chemical network with extremely high self-crosslinking. At this point, PVA can no longer form a continuous crystalline framework, and the AMPS-dominated ionic network structure becomes the main supporting framework of the system. For pure AMPS evaporators ( Figure 2 f), its SEM image shows a typical sponge-like porous structure with large, interconnected pores and smooth walls. This material relies solely on chemical cross-linking to maintain its structure, lacking the skeletal support of a PVA semi-crystalline network. During evaporation testing, it is prone to severe volume shrinkage and structural collapse, failing to maintain a stable evaporation interface and water transport channels. Therefore, its evaporation rate data lacks effective comparability, and it was not used as the primary comparison object in this study. In summary, the SEM results clearly show that with increasing AMPS content, the microstructure of the PVA / AMPS system gradually transforms from a dense, ordered semi-crystalline structure dominated by PVA to a loose, porous, amorphous network structure dominated by AMPS. Among them, the DNWH3 sample exhibits the most typical interpenetrating polymer network morphology, a structure that promises a good balance between mechanical properties, flexibility, and energy dissipation capacity.

[0052] See Figure 3 and Figure 4The evaporators prepared in Examples 1-4 and Comparative Examples 1-2 were subjected to 80% compressive stress in the vertical direction. The results showed that the pure PVA samples exhibited significant lateral bulging and uneven deformation earlier during the compression process, indicating that their network structure mainly relies on PVA crystalline regions and hydrogen bonding, which limits their load-bearing capacity and energy dissipation. In contrast, the DNWH series samples all exhibited more regular and stable columnar deformation under the same compressive strain, with no obvious macroscopic cracks or structural collapse observed. This indicates that the dual-network structure can effectively disperse the external load and maintain the overall structural integrity. However, when the AMPS content was too high, the DNWH4 sample experienced significant rupture under 80% compressive deformation. In summary, DNWH is significantly superior to pure PVA in terms of mechanical properties, with DNWH3 exhibiting the best overall mechanical performance. This superior performance mainly comes from the synergistic enhancement mechanism of "sacrificial bond fracture - continuous network load bearing" in the dual-network structure: the first network is preferentially destroyed during the stress process to dissipate energy, while the second network maintains the overall structural stability and prevents crack propagation, thereby significantly improving the material's load bearing capacity and compressive stability.

[0053] See Figure 5 The evaporators prepared in Examples 1-4 and Comparative Example 1 were tested at 1 kW / m². 2 Evaporation rate tests were conducted on a 3.5% simulated seawater solution under conditions of solar radiation intensity, temperature of 20-30℃, humidity of 30%-50%, and near-static air. The results showed that all dual-network hydrogel samples exhibited higher evaporation rates compared to TPWH (Comparative Example 1), indicating that the introduction of the dual-network structure effectively improves evaporation performance. Specifically, the evaporation rate of TPWH was 3.91 kg m³ / s. -2 h -1 The evaporation rates of DNWH1, DNWH2, DNWH3, and DNWH4 increased to 4.22, 4.31, 4.45, and 4.23 kg m³, respectively. -2 h -1 As the ratio of the two-network mixture gradually increases, the evaporation rate shows a trend of first increasing and then decreasing. Among them, DNWH3 exhibits the highest evaporation rate (4.45 kg m³). -2 h -1The evaporation rate increased by approximately 13.8% compared to TPWH, indicating that the dual-network structure at this ratio achieved a superior synergistic state in terms of water transport and thermal management. An appropriate dual-network ratio helps to construct more continuous and efficient water transport channels, increasing the available free water content on the hydrogel surface, thus ensuring continuous water supply to the evaporation interface. Simultaneously, this structure also enhances the effective area of ​​the evaporation interface and improves the thermal localization effect, allowing the input heat to be used more effectively for the phase change process of water. However, when the dual-network ratio is further increased to DNWH4, the evaporation rate decreases to some extent. This may be because excessively high second-network content or cross-linking density leads to a denser internal structure of the gel, increasing the diffusion resistance of water molecules in the network and decreasing the free water content, thereby limiting the water replenishment rate at the evaporation interface. Simultaneously, structural densification may also alter the heat conduction path, causing some heat to be transferred to the bulk phase or substrate, weakening the effective heat input required for evaporation. These results indicate that the evaporation performance of the dual-network hydrogel does not increase linearly with increasing ratio, but rather has an optimal structural range, corresponding to the DNWH3 sample under the conditions of this study.

[0054] See Figure 6 At 1 solar intensity (1 kg m -2 The evaporators prepared in Examples 1-4 and Comparative Example 1 were tested at 1 kW / m³. 2 Evaporation rate tests were conducted under various conditions, including solar radiation intensity, temperature (20-30℃), humidity (30%-50%), near-static air, and different salinities. The results showed that the evaporation rate of DNWH3 under pure water conditions was 2.14 kg / m³. -2 h -1 When the salinity was 3.5 wt% and 7.0 wt%, the evaporation rates were 2.15 and 2.08 kg m³, respectively. -2 h -1 The overall variation was relatively small, indicating that the introduction of salt has a limited impact on the evaporation performance of DNWH3 within the low to medium salinity range. This phenomenon can mainly be attributed to the structure and interfacial transport characteristics of the DNWH3 dual-network hydrogel. Furthermore, the dual-network structure maintains good mechanical stability and pore structure integrity even in high-salinity environments, making the evaporator less prone to structural collapse or blockage of mass transfer channels during long-term operation, thus ensuring the continuity and stability of the evaporation process.

[0055] Example 5 2g of PVA powder and 18ml of deionized water were continuously stirred at 90℃ to form a 10% PVA aqueous solution; Ti4O7 photothermal absorbing material was added to the PVA aqueous solution and stirred evenly to form a first precursor solution with a Ti4O7 concentration of 0.5%. During stirring, 125 μL of glutaraldehyde aqueous solution (mass concentration of 50%) and 250 μL of 1.2 M HCl solution were added to the first precursor solution. The resulting solution was poured into a waffle mold, and the mold was then placed in a liquid nitrogen container for directional freezing until the solution was completely frozen. The frozen sample was then placed in a freeze dryer and dried at -72 °C under 0.1 Pa conditions for 24 h to obtain the shaped precursor. The pre-formed precursor was placed in deionized water and fully expanded to obtain a Ti4O7-based PVA hydrogel evaporator. 1 g of AMPS monomer was added to deionized water and stirred until completely dissolved to form a 10% (w / w) AMPS aqueous solution. 0.01 g of N,N′-methylenebisacrylamide and 0.02 g of ammonium persulfate were then added. After sonication at room temperature, the solution was purged with nitrogen for 10 min to remove dissolved oxygen. The solution was then centrifuged at 7500 rpm for 3 min to remove air bubbles, resulting in a homogeneous second precursor solution. The Ti4O7-based PVA hydrogel evaporator was immersed in the second precursor solution and placed in a furnace at 95°C for free radical polymerization to obtain the prefabricated double-network hydrogel evaporator. The prefabricated dual-network hydrogel evaporator was immersed in deionized water for 12 hours to obtain the dual-network hydrogel evaporator.

[0056] Example 6 2g of PVA powder and 18ml of deionized water were continuously stirred at 90℃ to form a 10% PVA aqueous solution; Ti4O7 photothermal absorbing material was added to the PVA aqueous solution and stirred evenly to form a first precursor solution with a Ti4O7 concentration of 15%. During stirring, 125 μL of glutaraldehyde aqueous solution (mass concentration of 50%) and 250 μL of 1.2 M HCl solution were added to the first precursor solution. The resulting solution was poured into a waffle mold, and the mold was then placed in a liquid nitrogen container for directional freezing until the solution was completely frozen. The frozen sample was then placed in a freeze dryer and dried at -65 °C and 0.12 Pa for 24 h to obtain the shaped precursor. The pre-formed precursor was placed in deionized water and fully expanded to obtain a Ti4O7-based PVA hydrogel evaporator. 1 g of AMPS monomer was added to deionized water and stirred until completely dissolved to form an AMPS aqueous solution with a mass concentration of 20%. 0.01 g of N,N′-methylenebisacrylamide and 0.02 g of ammonium persulfate were then added. After sonication at room temperature, the solution was purged with nitrogen for 10 min to remove dissolved oxygen. The solution was then centrifuged at 6500 rpm for 8 min to remove air bubbles, resulting in a homogeneous second precursor solution. The Ti4O7-based PVA hydrogel evaporator was immersed in the second precursor solution and placed in a furnace at 90°C for free radical polymerization to obtain the prefabricated double-network hydrogel evaporator. The prefabricated dual-network hydrogel evaporator was immersed in deionized water for 12 hours to obtain the dual-network hydrogel evaporator.

[0057] Example 7 2g of PVA powder and 18ml of deionized water were continuously stirred at 85℃ to form a 10% PVA aqueous solution; Ti4O7 photothermal absorbing material was added to the PVA aqueous solution and stirred evenly to form a first precursor solution with a Ti4O7 concentration of 20%. During stirring, 125 μL of glutaraldehyde aqueous solution (mass concentration of 50%) and 250 μL of 1.2 M HCl solution were added to the first precursor solution. The resulting solution was poured into a waffle mold, and the mold was then placed in a liquid nitrogen container for directional freezing until the solution was completely frozen. The frozen sample was then placed in a freeze dryer and dried at -70 °C under 0.1 Pa conditions for 24 h to obtain the shaped precursor. The pre-formed precursor was placed in deionized water and fully expanded to obtain a Ti4O7-based PVA hydrogel evaporator. 1 g of AMPS monomer was added to deionized water and stirred until completely dissolved to form an AMPS aqueous solution with a mass concentration of 18%. 0.01 g of N,N′-methylenebisacrylamide and 0.02 g of ammonium persulfate were then added. After sonication at room temperature, the solution was purged with nitrogen for 10 min to remove dissolved oxygen. The solution was then centrifuged at 7000 rpm for 5 min to remove air bubbles, resulting in a homogeneous second precursor solution. The Ti4O7-based PVA hydrogel evaporator was immersed in the second precursor solution and placed in a furnace at 90°C for free radical polymerization to obtain the prefabricated double-network hydrogel evaporator. The prefabricated dual-network hydrogel evaporator was immersed in deionized water for 12 hours to obtain the dual-network hydrogel evaporator.

[0058] Example 8 2g of PVA powder and 18ml of deionized water were continuously stirred at 90℃ to form a 10% PVA aqueous solution; Ti4O7 photothermal absorbing material was added to the PVA aqueous solution and stirred evenly to form a first precursor solution with a Ti4O7 concentration of 25%. During stirring, 125 μL of glutaraldehyde aqueous solution (mass concentration of 50%) and 250 μL of 1.2 M HCl solution were added to the first precursor solution. The resulting solution was poured into a waffle mold, and the mold was then placed in a liquid nitrogen container for directional freezing until the solution was completely frozen. The frozen sample was then placed in a freeze dryer and dried at -70 °C under 0.1 Pa conditions for 24 h to obtain the shaped precursor. The pre-formed precursor was placed in deionized water and fully expanded to obtain a Ti4O7-based PVA hydrogel evaporator. 1 g of AMPS monomer was added to deionized water to form an AMPS aqueous solution with a mass concentration of 14%. 0.01 g of N,N′-methylenebisacrylamide and 0.02 g of ammonium persulfate were then added. After sonication at room temperature, the solution was purged with nitrogen for 10 min to remove dissolved oxygen. The solution was then centrifuged at 7000 rpm for 5 min to remove air bubbles, resulting in a homogeneous second precursor solution. The Ti4O7-based PVA hydrogel evaporator was immersed in the second precursor solution and placed in a furnace at 90°C for free radical polymerization to obtain the prefabricated double-network hydrogel evaporator. The prefabricated dual-network hydrogel evaporator was immersed in deionized water for 12 hours to obtain the dual-network hydrogel evaporator.

[0059] The above description is merely a preferred embodiment of the present invention and is not intended to limit the technical solution of the present invention in any way. Those skilled in the art should understand that, without departing from the spirit and principles of the present invention, the technical solution can be modified and replaced in several simple ways, and these modifications and replacements are all within the scope of protection covered by the claims.

Claims

1. A dual-network hydrogel evaporator for interfacial water evaporation, characterized in that, The dual-network hydrogel evaporator includes a first network and a second network that penetrate each other. The first network is a polyvinyl alcohol network, and photothermal absorbing material is dispersed in the first network. The second network is a 2-acrylamide-2-methylpropanesulfonic acid network.

2. The dual-network hydrogel evaporator for interfacial water evaporation according to claim 1, characterized in that, The dual-network hydrogel evaporator has a multi-level pore structure, which includes a macroporous framework formed by the first network and nanoscale fibrous and membrane-like secondary structures derived from the macroporous framework by the second network.

3. The dual-network hydrogel evaporator for interfacial water evaporation according to claim 1, characterized in that, The photothermal absorbing material is Ti4O7.

4. A method for preparing a dual-network hydrogel evaporator for interfacial water evaporation as described in any one of claims 1-3, characterized in that, include: The photothermal absorbing material was uniformly dispersed in a PVA aqueous solution to obtain the first precursor solution; Glutaraldehyde aqueous solution and HCl solution were added to the first precursor solution, and then directional freezing and freeze-drying were performed to obtain the shaped precursor. The preform was placed in water and allowed to expand fully to obtain a Ti4O7-based PVA hydrogel evaporator. The BIS crosslinking agent and APS initiator were uniformly dispersed in an AMPS aqueous solution to obtain a second precursor solution. The Ti4O7-based PVA hydrogel evaporator was placed in a second precursor solution and heated to polymerize, thus obtaining a prefabricated double-network hydrogel evaporator. The prefabricated dual-network hydrogel evaporator was immersed in water to obtain the dual-network hydrogel evaporator.

5. The method for preparing a dual-network hydrogel evaporator for interfacial water evaporation according to claim 4, characterized in that, The PVA aqueous solution contains 5%-15% PVA by mass.

6. The method for preparing a dual-network hydrogel evaporator for interfacial water evaporation according to claim 4, characterized in that, The mass concentration of the photothermal absorbing material in the first precursor solution is 0.5%-25%.

7. The method for preparing a dual-network hydrogel evaporator for interfacial water evaporation according to claim 4, characterized in that, The glutaraldehyde aqueous solution has a glutaraldehyde mass concentration of 40%-60%, and the HCl solution has a concentration of 1-1.4M.

8. The method for preparing a dual-network hydrogel evaporator for interfacial water evaporation according to claim 4, characterized in that, The mass concentration of the AMPS aqueous solution is 10%-20%; the amount of BIS crosslinking agent added is 0.25%-1% of the mass of AMPS, and the amount of APS initiator added is 0.5%-2% of the mass of AMPS. The BIS crosslinking agent is N,N′-methylenebisacrylamide, and the APS initiator is ammonium persulfate.

9. The method for preparing a dual-network hydrogel evaporator for interfacial water evaporation according to claim 4, characterized in that, The heating polymerization temperature is 85-95℃.

10. The application of the dual-network hydrogel evaporator for interfacial water evaporation according to any one of claims 1-3 in seawater desalination.

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