A seawater desalination hydrogel evaporator and a preparation method thereof

Abstract

This invention provides a seawater desalination hydrogel evaporator and its preparation method. The evaporator includes an upper photothermal layer and a lower evaporation layer. The upper photothermal layer is composed of a polyvinyl alcohol, polyethyleneimine, and dopamine system, while the lower evaporation layer is formed by cross-linking polyvinyl alcohol with glutaraldehyde. The upper photothermal layer and the lower evaporation layer are integrated through interfacial chemical cross-linking and freeze-thaw induced physical interpenetration, forming a gradient pore structure at the interface between the two layers, transitioning from micron-scale water transport channels to nanoscale photothermal channels. The preparation method includes preparing solutions of polyvinyl alcohol, polyethyleneimine, dopamine, and glutaraldehyde to form the upper photothermal layer and the lower evaporation layer, followed by static settling and freeze-thaw treatment to achieve bilayer integration. This invention combines good photothermal conversion capability, continuous water transport capability, and interfacial bonding stability, which is beneficial for improving the evaporation performance of seawater desalination.

Description

Technical Field

[0001] This invention relates to the field of seawater desalination evaporation materials and preparation technology, and particularly to a seawater desalination hydrogel evaporator and its preparation method. Background Technology

[0002] With the increasing scarcity of freshwater resources, seawater desalination using solar-driven interfacial evaporation has attracted widespread attention due to its clean energy source, flexible device configuration, and low operating costs. This type of technology typically improves evaporation efficiency by concentrating the photothermal conversion process at the gas-liquid interface region, reducing heat loss caused by bulk heating. Therefore, the light absorption capacity, water transport capacity, thermal management capabilities, and overall structural configuration of the evaporation material directly affect the actual performance of the interfacial evaporation system.

[0003] Typical solar interface evaporation materials often employ a double-layer or multi-layer structure. The upper layer absorbs sunlight and performs photothermal conversion, while the lower layer provides continuous water supply and supports the evaporation process. Although this type of structure can balance photothermal conversion and water transport to some extent, it still suffers from the following shortcomings in practical applications: Firstly, the photothermal layer and the water transport layer are often combined using simple stacking, coating, or bonding methods, resulting in insufficient interfacial bonding and potential interruptions in heat and water transport paths at the interface. Secondly, the pore size and wetting characteristics between different layers often lack coordinated design, making it difficult to simultaneously meet the needs of localized photothermal utilization in the upper layer and continuous water supply in the lower layer. This limits further improvement in evaporation efficiency and affects long-term operational stability.

[0004] Meanwhile, in traditional evaporators, the photothermal layer material and the water-transporting layer material are often constructed separately, resulting in a fragmented preparation process and insufficient interfacial compatibility. This hinders the formation of an integrated evaporation structure that combines broadband light absorption, rapid water transport, and continuous heat transfer capabilities. Especially in bilayer hydrogel evaporation systems, if only the light absorption performance of the photothermal material or the water retention and supply capacity of the lower layer is considered, without addressing the integrated integration of the bilayer interface, it will still be difficult to fully leverage the comprehensive advantages of hydrogel materials in enthalpy control, pore water transport, and flexible construction.

[0005] To this end, a seawater desalination hydrogel evaporator and its preparation method are proposed. Summary of the Invention

[0006] In view of this, the present invention provides a seawater desalination hydrogel evaporator and its preparation method to solve or alleviate the technical problems existing in the prior art, and at least provide a beneficial alternative.

[0007] The technical solution of the present invention is implemented as follows: The first aspect of the present invention provides a seawater desalination hydrogel evaporator, comprising an upper photothermal layer and a lower evaporation layer; the upper photothermal layer is composed of a polydopamine system formed by the oxidative polymerization of polyvinyl alcohol, polyethyleneimine and dopamine, and the lower evaporation layer is composed of a hydrogel network formed by crosslinking polyvinyl alcohol and glutaraldehyde; the upper photothermal layer and the lower evaporation layer are integrated through interfacial chemical crosslinking and physical interpenetration; a gradient pore structure is formed between the upper photothermal layer and the lower evaporation layer, transitioning from micron-level water transport channels to nano-level photothermal channels.

[0008] Further, the polyvinyl alcohol has a molecular weight of 170,000, the polyethyleneimine has a molecular weight of 60,000, and the dopamine is derived from dopamine hydrochloride with a purity of 98%. The mass ratio of polyvinyl alcohol, polyethyleneimine, and dopamine solution in the upper photothermal layer is 20:1:20 to 10:1:10. The lower evaporation layer is formed by crosslinking polyvinyl alcohol solution and glutaraldehyde solution, with a volume ratio of polyvinyl alcohol solution to glutaraldehyde solution of 4:1, 3:1, 2:1, or 1:1.

[0009] Furthermore, the interfacial chemical crosslinking includes the crosslinking between residual glutaraldehyde and polyvinyl alcohol, and the hydrogen bonding between the catechol groups on the surface of polydopamine formed by dopamine oxidative polymerization and polyvinyl alcohol; the physical interpenetration is the interfacial entanglement formed by the crystallization and hydrogen bond rearrangement of polyvinyl alcohol molecular chains during freeze-thaw cycles. Through the above interfacial integration methods, the upper photothermal layer and the lower evaporation layer can form a continuously transitioning bilayer structure, thereby establishing a continuous bottom-up moisture transport path and heat transfer path within the material.

[0010] A second aspect of the present invention provides a method for preparing the above-mentioned seawater desalination hydrogel evaporator, comprising the following steps: S1. Polyvinyl alcohol is dissolved in deionized water to prepare a polyvinyl alcohol solution, polyethyleneimine is dissolved in deionized water to prepare a polyethyleneimine solution, dopamine hydrochloride is dissolved in deionized water to prepare a dopamine solution, and glutaraldehyde is dissolved in deionized water to prepare a glutaraldehyde solution. S2. Mix the polyvinyl alcohol solution, the polyethyleneimine solution and the dopamine solution and let them stand, so that the dopamine is oxidized and polymerized and forms an upper photothermal layer with polyvinyl alcohol and polyethyleneimine; S3. The glutaraldehyde solution is added dropwise to the polyvinyl alcohol solution and allowed to stand for crosslinking. Then, a freeze-thaw treatment and a freeze-drying treatment are performed to form a lower evaporation layer. S4. Place the lower evaporation layer on the upper photothermal layer and let it stand. Then perform a freeze-thaw process to integrate the upper photothermal layer and the lower evaporation layer through interfacial chemical cross-linking and physical interpenetration, thereby obtaining a seawater desalination hydrogel evaporator.

[0011] Further, the polyvinyl alcohol solution has a mass concentration of 4%–5%, the polyethyleneimine solution has a mass concentration of 40%–50%, the dopamine solution has a mass concentration of 15%–25%, and the glutaraldehyde solution has a mass concentration of 15%–25%. The polyvinyl alcohol solution is prepared by stirring at 4000–6000 rpm for 24 h at 90°C, and the polyethyleneimine solution is prepared by stirring at 4000–6000 rpm for 3 h at 25°C. In step S2, the mass ratio of the polyvinyl alcohol solution, the polyethyleneimine solution, and the dopamine solution is 20:1:20 to 10:1:10, and the standing time is 24 h. In step S3, the glutaraldehyde solution is added dropwise to the polyvinyl alcohol solution at a rate of 1–3 mL / min. The pH of the polyvinyl alcohol solution is adjusted to 2 before mixing with the glutaraldehyde solution, and the solution is allowed to stand for 1 h after the addition of the glutaraldehyde solution.

[0012] Furthermore, the freeze-thaw process in step S3 is repeated twice, with a freezing temperature of -8°C, a thawing temperature of 25°C, and a freeze-drying time of 8 h; the settling time in step S4 is 24 h, the freeze-thaw process is repeated twice, with a freezing temperature of -8°C and a thawing temperature of 25°C.

[0013] The embodiments of the present invention have the following advantages due to the adoption of the above technical solutions: I. This invention employs an upper PVA / PEI / dopamine system to form a photothermal layer and a lower PVA / glutaraldehyde system to form an evaporation layer. By integrating the two layers through interfacial chemical cross-linking and freeze-thaw induced physical interpenetration, a continuous bottom-up moisture transport path and heat transfer path are established within the material. This reduces the problem of interfacial transfer interruption in traditional layered stacked structures and is beneficial to improving the overall evaporation efficiency and operational stability of the evaporator.

[0014] Second, this invention uses the lower polyvinyl alcohol crosslinked network as the evaporation layer skeleton, utilizes the strong interaction between the hydroxyl groups on the polyvinyl alcohol molecular chain and water molecules, and combines the macroporous water transport channels formed by glutaraldehyde crosslinking, freeze-thaw and freeze-drying, so that the evaporation layer has both good water holding and supply capacity and continuous water transport capacity, which is beneficial to reduce energy consumption in the evaporation process and improve the transport efficiency of water to the evaporation interface.

[0015] Third, the present invention constructs a photothermal layer by synergistically using polyvinyl alcohol, polyethyleneimine and dopamine in the upper layer. Polydopamine formed by the oxidative polymerization of dopamine is used to achieve broad-spectrum light absorption and photothermal conversion. Combined with its interfacial adhesion properties, the bonding strength of the double layer interface is improved. At the same time, the gradient pore structure formed by the upper nanopores and the lower macropores is conducive to achieving the synergistic unity of light absorption, heat conversion, interfacial bonding and water transport.

[0016] IV. The preparation method of the present invention mainly consists of aqueous solution preparation, static crosslinking, dropwise crosslinking, freeze-thaw and freeze-drying. The process conditions are relatively mild and the parameters are highly adjustable, which makes it easy to control the photothermal layer, evaporation layer and interface structure. It has good repeatability and scale-up preparation potential. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 Fourier transform infrared spectra of samples S0, S1, S2, and S3; Wherein, PVA / GA represents pure PVA crosslinked hydrogel (corresponding to sample S0). PVA / PDA / PEI represents the photothermal layer hydrogel (corresponding to sample S1); PVA / PDA / PEI / GA represents a bilayer cross-linked integrated hydrogel (corresponding to sample S3). Figure 2 A scanning electron microscope image of the integrated hydrogel evaporator for sample S3; Figure 3 The graph shows the mass changes of samples S0, S1, S2, and S3 under one solar irradiation condition. Figure 4 The graph shows the temperature changes of samples S0, S1, S2, and S3 under one solar irradiation condition. Detailed Implementation

[0019] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0020] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0021] This invention provides a seawater desalination hydrogel evaporator and its preparation method. The seawater desalination hydrogel evaporator includes an upper photothermal layer and a lower evaporation layer. The upper photothermal layer is composed of a polyvinyl alcohol, polyethyleneimine and dopamine system, and the lower evaporation layer is formed by crosslinking polyvinyl alcohol and glutaraldehyde. The upper photothermal layer and the lower evaporation layer are integrated through interfacial chemical crosslinking and freeze-thaw induced physical interpenetration, and a gradient pore structure transitioning from micron-level water transport channels to nano-level photothermal channels is formed at the interface between the two layers. The main raw materials used in this invention are as follows: Polymer A is polyvinyl alcohol (PVA) with a molecular weight of 170,000, polymer B is polyethyleneimine (PEI) with a molecular weight of 60,000, small molecule C is dopamine hydrochloride with a purity of 98%, and small molecule D is a 50% glutaraldehyde aqueous solution. Polymer A, polymer B, small molecule C, and small molecule D are each prepared into corresponding solutions for later use. Specifically, polymer A is dissolved in deionized water and stirred continuously at 4000–6000 rpm for 24 h at 90°C to obtain a homogeneous PVA solution with a mass concentration of 4%–5%; polymer B is dissolved by stirring continuously at 4000–6000 rpm for 3 h at 25°C to obtain a PEI solution with a mass concentration of 40%–50%; and small molecule C and small molecule D are each prepared into stock solutions with a mass concentration of 15%–25% for later use.

[0022] Table 1. Preparation conditions of raw materials and stock solutions

[0023] Sample S0 1. Polyvinyl alcohol (PVA) with a molecular weight of 170,000, polyethyleneimine (PEI) with a molecular weight of 60,000, dopamine hydrochloride with a purity of 98%, and 50% glutaraldehyde aqueous solution were selected as raw materials.

[0024] 2. Dissolve PVA in deionized water and stir continuously at 4000–6000 rpm for 24 h at 90℃ to obtain a homogeneous PVA solution with a mass concentration of 4%–5%; stir PEI continuously at 4000–6000 rpm for 3 h at 25℃ to obtain a PEI solution with a mass concentration of 40%–50%; prepare stock solutions of dopamine hydrochloride and glutaraldehyde aqueous solution with a mass concentration of 15%–25% for later use.

[0025] 3. A 25% glutaraldehyde solution and a 5% PVA solution were titrated at a volume ratio of 1:1 at a rate of 2 mL / min, with the PVA solution adjusted to pH 2. After standing for 24 h, three freeze-thaw cycles were performed: freezing at -8℃ and thawing at 25℃. The resulting gel was then freeze-dried for 8 h to obtain a pure PVA hydrogel, denoted as sample S0. This sample contains only the evaporation layer structure and does not contain the photothermal layer structure.

[0026] Sample S1 1. The preparation methods for raw materials and stock solutions are the same as those for sample S0.

[0027] 2. A 5% PVA solution, a 25% dopamine solution, and a 50% PEI solution were blended at a mass ratio of 20:20:1 to 10:10:1, with a preferred ratio of 10:10:1. After blending, the mixture was allowed to stand for 24 hours, followed by three freeze-thaw cycles at -8°C and 25°C. The mixture was then freeze-dried for 8 hours to obtain a PVA / PDA / PEI hydrogel monolayer evaporator, denoted as sample S1. This sample contains only the photothermal layer system and does not include the lower evaporation layer.

[0028] Sample S2 1. The preparation methods for raw materials and stock solutions are the same as those for sample S0.

[0029] 2. Following the method in sample S1, 5% PVA solution, 25% dopamine solution and 50% PEI solution are mixed in a mass ratio of 20:20:1 to 10:10:1. After mixing, the mixture is allowed to stand for 24 hours to obtain a black and uniform solar energy absorption layer, i.e., a photothermal layer, for later use.

[0030] 3. Following the method in sample S0, 25% glutaraldehyde solution and 5% PVA solution were titrated at a volume ratio of 1:1 at pH=2 and at a rate of 2 mL / min. After standing for 24 h, three freeze-thaw cycles were performed, followed by freeze-drying for 8 h to obtain a pure PVA hydrogel evaporation layer.

[0031] 4. The obtained evaporation layer was placed directly on the photothermal layer to obtain a simple stacked double-layer hydrogel evaporator, denoted as sample S2. No interfacial cross-linking treatment was performed between the upper and lower layers in this sample.

[0032] Sample S3 1. The preparation methods for raw materials and stock solutions are the same as those for sample S0.

[0033] 2. Mix 5% PVA solution, 25% dopamine solution and 50% PEI solution in a mass ratio of 20:20:1 to 10:10:1, with a preferred ratio of 10:10:1; let stand for 24 h after mixing to obtain a black and uniform solar energy absorption layer, i.e., a photothermal layer for later use.

[0034] 3. 15% glutaraldehyde solution and 5% PVA solution were titrated at a volume ratio of 1:1 and a rate of 2 mL / min under the condition that the pH of the PVA solution was adjusted to 2. After titration, the mixture was allowed to stand for 1 h to form a cross-linked hydrogel. Subsequently, two freeze-thaw cycles were performed, with a freezing temperature of -8℃ and a thawing temperature of 25℃. After freeze-drying for 8 h, an evaporation layer matrix with a porous microstructure was obtained.

[0035] 4. The above-mentioned evaporation layer substrate is placed on the obtained photothermal layer system. After standing for 24 hours, two freeze-thaw cycles are performed. Through interfacial reaction, the double-layer cross-linking and structural integration are achieved, resulting in a seawater desalination hydrogel evaporator with gradient channels and strong interfacial bonding, denoted as sample S3. This sample is the sample of this invention.

[0036] For subsequent comparative experiments, samples S0, S1, S2 and S3 were used for structural characterization and evaporation performance testing, respectively; among them, Comparative Example 1 used sample S0, Comparative Example 2 used sample S1, Comparative Example 3 used sample S2 and Example 1 used sample S3.

[0037] Table 2 Comparison of structural characterization results

[0038] Depend on Figure 1 and Figure 2 It can be seen that sample S3 is not simply a combination of photothermal layer and evaporation layer, but rather a more stable integrated structure is formed at the interface; the upper layer has finer-scale channels, the lower layer has larger-scale channels, and a continuous transition is formed between the two layers.

[0039] Comparative Example 1 Hydrogel samples were prepared using a pure PVA crosslinking system without a photothermal layer.

[0040] After adjusting the pH of the polyvinyl alcohol solution to 2, a 25% glutaraldehyde solution was slowly added dropwise to the 5% polyvinyl alcohol solution at a volume ratio of 1:1 at a rate of 2 mL / min. The solution was then allowed to stand for 24 h after the addition to allow for sufficient cross-linking. The resulting system was then subjected to three freeze-thaw cycles: freezing at -8℃ for 12 h and thawing at 25℃ for 6 h. After the freeze-thaw cycles, the sample was placed in a freeze-drying apparatus and freeze-dried at a cold trap temperature of -50℃ for 8 h to obtain pure PVA hydrogel, denoted as sample S0.

[0041] Comparative Example 2 Monolayer hydrogel samples were prepared using a PVA / PDA / PEI system without a lower evaporation layer.

[0042] A mixture of 5% PVA solution, 25% dopamine solution, and 50% PEI solution at a mass ratio of 10:10:1 was prepared. The pH of the system was adjusted to 8.5 at room temperature, and the mixture was allowed to stand in air for 24 h to allow dopamine to undergo an oxidative self-polymerization reaction to form polydopamine, which then synergistically interacts with PVA and PEI to obtain a homogeneous photothermal layer precursor system. The system was then subjected to three freeze-thaw cycles: freezing at -8℃ for 12 h, thawing at 25℃ for 6 h, and finally freeze-drying (cold trap temperature -50℃) for 8 h to obtain a PVA / PDA / PEI hydrogel monolayer evaporator, denoted as sample S1.

[0043] Comparative Example 3 Samples were prepared using a simple two-layer physical stacking method.

[0044] First, a photothermal layer was prepared according to the method of sample S1, and then a pure PVA evaporation layer was prepared according to the method of sample S0. The evaporation layer was then placed directly on the photothermal layer to obtain a physical stacked bilayer hydrogel evaporator without interface crosslinking. This comparative example was used to characterize the structure and evaporation performance of the upper and lower layers without interface integration treatment, and sample S2 was used.

[0045] Example 1 Example 1 uses sample S3, and its specific preparation method is as follows: Raw material preparation: Polyvinyl alcohol (PVA) with a molecular weight of 170,000, polyethyleneimine (PEI) with a molecular weight of 60,000, dopamine hydrochloride with a purity of 98%, and 50% glutaraldehyde aqueous solution were selected as raw materials. Solution preparation: PVA was dissolved in deionized water and stirred at 4000–6000 rpm for 24 h at 90℃ to obtain a 5% PVA solution; PEI was dissolved in deionized water and stirred at 4000–6000 rpm for 3 h at 25℃ to obtain a 50% PEI solution; dopamine hydrochloride and glutaraldehyde were each prepared into 25% solutions for later use. Photothermal layer construction: The above PVA solution, dopamine solution and PEI solution were mixed in a mass ratio of 10:10:1, the pH of the system was adjusted to 8.5, and the mixture was left to stand in the air for 24 h to allow dopamine to undergo oxidative polymerization and form polydopamine, thereby obtaining the photothermal layer system. Evaporation layer construction: After adjusting the PVA solution to pH=2, glutaraldehyde solution was added dropwise to the PVA solution at a rate of 2 mL / min, with a volume ratio of glutaraldehyde solution to PVA solution of 1:1. After the addition was completed, the mixture was allowed to stand for 1 h to carry out the cross-linking reaction. Subsequently, two freeze-thaw cycles were performed (freezing temperature: -8℃, freezing time: 12 h; thawing temperature: 25℃, thawing time: 6 h), and then freeze-dried (cold trap temperature: -50℃) for 8 h to obtain the evaporation layer matrix. Interface integration: The obtained evaporation layer substrate is placed on the photothermal layer system and left to stand for 24 h. Two freeze-thaw cycles are then performed (freezing temperature is -8℃, thawing temperature is 25℃). The bilayer structure is integrated through interfacial chemical cross-linking and physical interpenetration to obtain a seawater desalination hydrogel evaporator.

[0046] Experimental Example 1: Structural Characterization Experiment Fourier transform infrared spectroscopy was performed on samples S0, S1, and S3 respectively, and the results are shown in the figure. Figure 1 Sample S3 was observed using a scanning electron microscope, and the results are shown below. Figure 2 .

[0047] Depend on Figure 1 It can be seen that sample S0 mainly exhibits the absorption characteristics related to the pure PVA cross-linked network, sample S1 exhibits the characteristics of a PVA / PDA / PEI monolayer photothermal system, sample S2 has the characteristics of both upper and lower layer components but the interface is in a simple superposition state, while sample S3 exhibits the characteristics of a composite cross-linked system of upper and lower layers. Figure 2 It can be seen that sample S3 exhibits a bilayer structure with fine pores in the upper layer and large pores in the lower layer, and the interface is continuously transitioned, indicating that sample S3 has formed an integrated bilayer cross-linked structure and a gradient pore structure.

[0048] Experiment Example 2: Light-induced temperature rise test Temperature changes of samples S0, S1, S2, and S3 were tested under one solar irradiation condition, and the results are shown in [Figure number missing]. Figure 3.

[0049] Depend on Figure 3 It can be seen that the temperature rise of sample S0 is relatively small, indicating that the photothermal conversion capacity is limited due to the lack of a photothermal layer; the temperature rise of sample S1 is more obvious, indicating that the single-layer photothermal system can achieve a certain amount of light absorption and photothermal conversion; the temperature rise of sample S2 is better than that of samples S0 and S1, indicating that the double-layer structure can improve photothermal utilization; the temperature rise of sample S3 is the best, indicating that the synergistic effect of the photothermal layer, evaporation layer and interface integration is more conducive to the overall heat utilization.

[0050] Table 3 Comparison of Temperature Change Results

[0051] Test Example 3: Evaporation Performance Test Mass changes of samples S0, S1, S2, and S3 were tested under one solar irradiation condition, and the results are shown in [Figure number missing]. Figure 4 ; Depend on Figure 4 It can be seen that the mass decrease of sample S0 is relatively small, indicating that the evaporation performance is limited when there is only an evaporation layer without a high-efficiency photothermal conversion structure; the mass decrease of sample S1 is more obvious, indicating that the single-layer photothermal system has a certain evaporation capacity, but the overall evaporation capacity is still limited due to the lack of a continuous water supply structure in the lower layer; the mass decrease of sample S2 is better than that of samples S0 and S1, indicating that simple superposition of two layers can improve evaporation to a certain extent; the mass decrease of sample S3 is the most obvious, indicating that the integrated double-layer cross-linked structure is more conducive to improving the overall evaporation efficiency.

[0052] Table 4 Comparison of mass changes and evaporation performance

[0053] Results Analysis Based on the above embodiments, comparative examples, and experimental examples, it can be seen that sample S0 mainly exhibits a pure PVA evaporation layer structure, sample S1 mainly exhibits a PVA / PDA / PEI single-layer photothermal structure, sample S2 exhibits a simple double-layer physical stacking structure, while sample S3, based on a specific material system, achieves integrated integration of the upper and lower layers through interfacial chemical cross-linking and freeze-thaw induced physical interpenetration.

[0054] Sample S3 exhibits more pronounced interface continuity and gradient pore characteristics in structural characterization; superior temperature change in light-induced heating tests; more pronounced weight loss characteristics in mass change tests; and superior evaporation performance compared with other literature samples.

[0055] This indicates that the present invention is not a simple layering or material replacement of a traditional double-layer evaporator, but rather a continuous heat and mass transfer path constructed within the material through the synergistic effect of a specific upper photothermal system, a specific lower evaporation system, and a specific interface integration process. This balances photothermal conversion capability, continuous water delivery capability, and interface transfer capability, ultimately achieving superior evaporation performance and operational stability.

[0056] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various variations or substitutions within the technical scope disclosed in the present invention, and these should all be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A seawater desalination hydrogel evaporator, characterized in that, It includes an upper photothermal layer and a lower evaporation layer; the upper photothermal layer is composed of polydopamine formed by the oxidative polymerization of polyvinyl alcohol, polyethyleneimine and dopamine; the lower evaporation layer is composed of a hydrogel network formed by crosslinking polyvinyl alcohol and glutaraldehyde; the upper photothermal layer and the lower evaporation layer are integrated and bonded together through interfacial chemical crosslinking and physical interpenetration. A gradient channel structure, transitioning from micron-level water transport channels to nanon-level photothermal channels, is formed between the upper photothermal layer and the lower evaporation layer. The mass ratio of polyvinyl alcohol, polyethyleneimine and dopamine solution in the upper photothermal layer is 20:1:20 to 10:1:

10. The interfacial chemical crosslinking includes the crosslinking between residual glutaraldehyde and polyvinyl alcohol, as well as the hydrogen bonding between polydopamine surface groups and polyvinyl alcohol.

2. The seawater desalination hydrogel evaporator according to claim 1, characterized in that, The polyvinyl alcohol has a molecular weight of 170,000, the polyethyleneimine has a molecular weight of 60,000, and the dopamine raw material is dopamine hydrochloride with a purity of 98%.

3. The seawater desalination hydrogel evaporator according to claim 1, characterized in that, The lower evaporation layer is formed by crosslinking a polyvinyl alcohol solution and a glutaraldehyde solution, wherein the volume ratio of the polyvinyl alcohol solution to the glutaraldehyde solution is 4:1, 3:1, 2:1 or 1:

1.

4. The seawater desalination hydrogel evaporator according to claim 1, characterized in that, The physical interpenetration refers to the interfacial entanglement formed by the crystallization of polyvinyl alcohol molecular chains and the rearrangement of hydrogen bonds during the freeze-thaw process.

5. A method for preparing a seawater desalination hydrogel evaporator, characterized in that, Includes the following steps: S1. Polyvinyl alcohol is dissolved in deionized water to prepare a polyvinyl alcohol solution, polyethyleneimine is dissolved in deionized water to prepare a polyethyleneimine solution, dopamine hydrochloride is dissolved in deionized water to prepare a dopamine solution, and glutaraldehyde is dissolved in deionized water to prepare a glutaraldehyde solution. S2. Mix the polyvinyl alcohol solution, the polyethyleneimine solution and the dopamine solution and let them stand, so that the dopamine is oxidized and polymerized and forms an upper photothermal layer with polyvinyl alcohol and polyethyleneimine; S3. The glutaraldehyde solution is added dropwise to the polyvinyl alcohol solution and allowed to stand for crosslinking. Then, a freeze-thaw treatment and a freeze-drying treatment are performed to form a lower evaporation layer. S4. Place the lower evaporation layer on the upper photothermal layer and let it stand. Then perform a freeze-thaw process to integrate the upper photothermal layer and the lower evaporation layer through interfacial chemical cross-linking and physical interpenetration, thereby obtaining a seawater desalination hydrogel evaporator.

6. The preparation method according to claim 5, characterized in that, The polyvinyl alcohol solution has a mass concentration of 4%–5%, the polyethyleneimine solution has a mass concentration of 40%–50%, the dopamine solution has a mass concentration of 15%–25%, and the glutaraldehyde solution has a mass concentration of 15%–25%. The polyvinyl alcohol solution is prepared by stirring at 4000–6000 rpm for 24 hours at 90°C, and the polyethyleneimine solution is prepared by stirring at 4000–6000 rpm for 3 hours at 25°C.

7. The preparation method according to claim 5, characterized in that, In step S3, the glutaraldehyde solution is added dropwise to the polyvinyl alcohol solution at a rate of 1-3 mL / min. The pH of the polyvinyl alcohol solution is adjusted to 2 before being mixed with the glutaraldehyde solution, and the solution is allowed to stand for 1 hour after the glutaraldehyde solution is added.

8. The preparation method according to claim 5, characterized in that, In step S3, the freeze-thaw process is repeated twice, with a freezing temperature of -8°C, a thawing temperature of 25°C, and a freeze-drying time of 8 hours. In step S4, the settling time is 24 hours, the freeze-thaw process is repeated twice, with a freezing temperature of -8°C and a thawing temperature of 25°C.

Images