An aerogel interfacial evaporator, its preparation method and application

Abstract

This application discloses an aerogel interfacial evaporator, its preparation method, and its applications. The preparation method includes: taking chitosan and preparing a chitosan solution; mixing anionic polyelectrolytes and a structural stabilizer to prepare a mixed solution; slowly adding the mixed solution dropwise to the chitosan solution to form a composite solution; adding a photothermal conversion material to the composite solution to form a suspension; injecting the suspension into a pre-cooled mold and freezing the mold to solidify the suspension; subsequently, vacuum drying the solidified suspension to obtain an aerogel with a porous structure; immersing the aerogel with the porous structure in a solution containing a crosslinking agent for reaction; after crosslinking is completed, cleaning and drying the aerogel to obtain the aerogel interfacial evaporator. The aerogel interfacial evaporator disclosed in this application has multiple effects, such as improving evaporation efficiency, inhibiting salt crystallization, and enhancing evaporator stability, and has broad application prospects in seawater desalination, wastewater treatment, and other fields.

Description

Technical Field

[0001] This application relates to the field of seawater desalination technology, and in particular to an aerogel interface evaporator, its preparation method and application. Background Technology

[0002] Freshwater scarcity and the energy crisis are major challenges hindering the sustainable development of human society. Developing green and low-carbon seawater desalination technologies to promote the efficient utilization of seawater resources is of great significance. Solar-driven interfacial evaporation (SDIE) technology converts solar energy into heat energy to heat the water surface through photothermal materials, achieving efficient freshwater production and providing a sustainable solution to the freshwater scarcity and energy crisis. Among these technologies, aerogel materials, due to their three-dimensional porous structure, rapid water transport capacity, and excellent thermal insulation properties, have become ideal matrix materials for constructing solar interfacial evaporators. Therefore, constructing high-performance aerogel-based solar interfacial evaporators is currently a key research focus.

[0003] Interfacial evaporators can be classified into two-dimensional and three-dimensional evaporators based on their spatial dimension. Two-dimensional evaporators often use paper, cotton fabrics, and polymer membranes as carriers, and their evaporation rate is limited due to the limited evaporation area and energy loss. In contrast, three-dimensional evaporators, through geometric design, can capture light at different incident angles and increase the evaporation area, thus breaking through the theoretical evaporation rate limitations of two-dimensional evaporators. The core structure of an interfacial evaporator consists of three parts: a support layer with low thermal conductivity, a photothermal layer with broad-spectrum light absorption and high photothermal conversion efficiency, and a transmission channel for efficient continuous water supply. Aerogel materials, due to their unique three-dimensional porous structure, ultra-low density, and excellent thermal insulation properties, have become ideal matrix materials for constructing three-dimensional interfacial evaporators. However, in practical applications, when the salt ion concentration reaches a certain level, the formation of salt crystals can hinder the absorption of sunlight and the transport of water to the photothermal surface, thus affecting the long-term stability of the evaporator. Summary of the Invention

[0004] In view of this, this application provides an aerogel interface evaporator, its preparation method and application. By constructing a microchannel structure with a fixed negative charge inside the evaporator, the ion distribution is regulated based on the Donnan effect, thereby suppressing salt accumulation at the evaporation interface. The aim is to improve the water transport efficiency, salt repulsion performance and long-term stability of the evaporator.

[0005] This application provides a method for preparing an aerogel interface evaporator, comprising the following steps: Prepare a chitosan solution by dissolving chitosan in a weakly acidic aqueous solution; Mix the anionic polyelectrolyte and the structure stabilizer to prepare a mixed solution; The mixed solution is slowly added dropwise to the chitosan solution to form a composite solution; Photothermal conversion material is added to the composite solution to form a suspension; The suspension is injected into a pre-cooled mold and the mold is frozen to solidify the suspension. The solidified suspension is then vacuum dried to obtain an aerogel with a porous structure. An aerogel with a porous structure is immersed in a solution containing a crosslinking agent for reaction. After crosslinking is completed, the aerogel is washed and dried to obtain an aerogel interface evaporator. The anionic polyelectrolyte can regulate the migration behavior of ions in the solution during the treatment of salt-containing aqueous solutions in the aerogel interface evaporator, thereby reducing the enrichment and crystallization of salt on the surface of the aerogel interface evaporator.

[0006] In some embodiments, the mass ratio of the chitosan, the anionic polyelectrolyte, and the structural stabilizer is 1~3:1:0.5~3; In the composite solution, the mass fraction of chitosan, the anionic polyelectrolyte, and the structural stabilizer is 2-5 wt%.

[0007] In some embodiments, the concentration of the photothermal conversion material in the composite solution is 1~10 mg / mL.

[0008] In some embodiments, the anionic polyelectrolyte is selected from at least one of sodium polyacrylate, sodium polystyrene sulfonate, and sodium polyaspartate; the structural stabilizer is selected from at least one of polyvinyl alcohol and nanocellulose. Wherein, the sodium polyacrylate has a weight-average molecular weight of 1,000,000 to 5,000,000 Da; the sodium polystyrene sulfonate has a weight-average molecular weight of 50,000 to 100,000 Da; and the sodium polyaspartate has a weight-average molecular weight of 10,000 to 50,000 Da. The weight-average molecular weight of the chitosan is 100,000 to 500,000 Da.

[0009] In some embodiments, the photothermal conversion material is selected from at least one of reduced graphene oxide, carbon nanotubes, and carbon black; wherein the average particle size of the photothermal conversion material is 10~200 nm.

[0010] In some embodiments, the crosslinking agent is selected from at least one of sodium tripolyphosphate and sodium hexametaphosphate, and the mass fraction of the crosslinking agent in the solution is 1 to 5 wt%.

[0011] In some embodiments, the porosity of the aerogel is 70-85%, and the pore size contained in the aerogel is 10-250 μm; The ions in the saline aqueous solution are selected from chloride ions or sulfate ions; The salt in the saline solution is selected from at least one of sodium chloride, magnesium chloride, sodium sulfate, and magnesium sulfate; The mold is either frustum-shaped or cylindrical.

[0012] In some embodiments, the freezing temperature of the mold is -100 to -200 ℃, and after freezing, it is vacuum dried. The vacuum degree of the vacuum drying is 1 to 10 Pa, and the drying time is 20 to 30 h.

[0013] The cross-linking reaction temperature is 20~40 ℃, and the cross-linking reaction time is 2~12 h.

[0014] In some embodiments, this application also provides an aerogel interface evaporator prepared by the method.

[0015] In some embodiments, this application also provides the application of aerogel interface evaporators in seawater desalination or wastewater purification.

[0016] The beneficial effects of this application are as follows: This application uses chitosan to construct an aerogel. Because the chitosan molecular chain contains a large number of amino and hydroxyl groups, these groups can form abundant hydrogen bonds during the aerogel formation process, thereby constructing a more uniform and stable three-dimensional structure. This structure gives the aerogel higher porosity, providing more channels for water transport and evaporation. Simultaneously, anionic polyelectrolytes are introduced during the preparation process. On the one hand, their fixed negative charge can generate electrostatic repulsion against anions in the solution, regulating ion distribution; on the other hand, they can form a polyelectrolyte composite structure with chitosan, constructing a functional layer on the surface of the aerogel pores. Through the synergistic effect of charge repulsion and ion transport regulation, the evaporator's resistance to salt contamination in saline aqueous solutions is improved, and the accumulation of salt at the evaporation interface is reduced, thus helping to extend the evaporator's service life and maintain stable evaporation performance. Therefore, the aerogel interface evaporator disclosed in this application has multiple effects, including improving evaporation efficiency, inhibiting salt crystallization, and enhancing evaporator stability, and has broad application prospects in seawater desalination, wastewater treatment, and other fields. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of a biomimetic frustum-shaped aerogel interface evaporator based on the Donnan effect.

[0018] Figure 2 The images show SEM images of the surface (a) and cross-section (b) of the aerogel interface evaporator in Example 1.

[0019] Figure 3 The relationship between the evaporation performance of the aerogel interface evaporator in Example 1 under outdoor conditions and changes in environmental parameters.

[0020] Figure 4Example 1 illustrates the effect of the aerogel interface evaporator on the removal of major ions from seawater. Detailed Implementation

[0021] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. In addition, it should be understood that the specific embodiments described herein are only for illustration and explanation of this application and are not intended to limit this application. In this application, unless otherwise stated, directional terms such as "upper" and "lower" specifically refer to the drawing directions in the accompanying drawings. In addition, in the description of this application, the term "including" means "including but not limited to". Various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and conciseness and should not be construed as a hard limitation on the scope of the present invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single values ​​within that range. For example, it should be assumed that the description of a range from 1 to 6 specifically discloses subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the range referred to.

[0022] Studies have shown that solar interfacial evaporation (SDIE) technology has broad application prospects and has received widespread attention in recent years due to its high efficiency and zero-carbon emission characteristics in seawater desalination, wastewater purification, and other fields. However, in practical applications, this technology still faces the following key scientific challenges: first, limited water transport leads to a low evaporation rate; second, salt crystallization at the evaporation interface affects light absorption and its lifespan; third, significant heat loss during evaporation results in low evaporation efficiency; and fourth, most existing studies have failed to fully utilize the multiple energy forms generated during solar energy conversion. Therefore, constructing an interfacial evaporator with high evaporation performance, stable operation in seawater and high-concentration brine, and multi-efficiency energy utilization is of great significance for promoting the development of SDIE technology.

[0023] Aerogel materials, due to their porous structure, ultra-low density, and excellent thermal insulation properties, have become ideal matrix materials for constructing efficient interfacial evaporators. Therefore, addressing key issues in solar interfacial evaporation technology such as slow water transport efficiency, salt crystallization, heat loss, and low energy utilization, this application systematically explores the structure-property relationship between the construction and performance of aerogel-based interfacial evaporators through strategies including material design, three-dimensional structure control, optimization of water transport channels, enhancement of environmental energy input, water activation to reduce evaporation energy requirements, and salt discharge channel design. This provides a new solution for achieving efficient, stable, and multifunctional solar seawater desalination.

[0024] To address the aforementioned problems, this application provides a method for preparing an aerogel interface evaporator, comprising the following steps: taking chitosan and preparing a chitosan solution; mixing anionic polyelectrolyte and a structural stabilizer and preparing a mixed solution; slowly adding the mixed solution dropwise to the chitosan solution to form a composite solution; adding a photothermal conversion material to the composite solution to form a suspension; injecting the suspension into a pre-cooled mold and freezing the mold to solidify the suspension, followed by vacuum drying of the solidified suspension to obtain an aerogel with a porous structure; immersing the aerogel with the porous structure in a solution containing a crosslinking agent for reaction, and after crosslinking is completed, cleaning and drying the aerogel to obtain the aerogel interface evaporator; wherein, the anionic polyelectrolyte can regulate the migration behavior of ions in the solution during the treatment of salt-containing aqueous solutions by the aerogel interface evaporator, thereby reducing the enrichment and crystallization of salt on the surface of the aerogel interface evaporator.

[0025] It is understandable that chitosan, when formulated into a solution, possesses active groups such as amino groups, exhibiting excellent film-forming properties and biocompatibility. Anionic polyelectrolytes, such as sodium polyacrylate and sodium polystyrene sulfonate, carry a large number of negative charges. When solutions containing both are mixed, the amino groups of chitosan can, under appropriate conditions, form stable complexes with the anions of the anionic polyelectrolytes through electrostatic interactions. This complex provides a more stable network structure basis for the subsequent aerogel formation process. Adding photothermal conversion materials to the solution to form a suspension endows the aerogel with highly efficient photothermal conversion capabilities. These materials absorb energy from sunlight and convert it into heat, providing a local heat source for the interfacial evaporation process and thus enhancing the evaporation driving force. During the subsequent aerogel formation process, these photothermal conversion materials are encapsulated within the porous structure of the aerogel, forming a highly efficient photothermal conversion network. A freeze-drying process creates a high-quality porous structure. The suspension is injected into a pre-cooled mold for freeze-curing, followed by vacuum drying to obtain an aerogel with a porous structure. During freezing, water in the solution forms ice crystals, which sublimate during subsequent vacuum drying, leaving a porous structure. This porous structure has a large specific surface area, increasing the contact area between the aerogel and water and improving water evaporation efficiency. Simultaneously, the porous structure provides channels for water transport, allowing water to be rapidly transported from the aerogel's interior to the surface for evaporation. Furthermore, the fixed negative charge on the anionic polyelectrolyte surface electrostatically repels anions in the solution when the aerogel contacts the salt-containing aqueous solution, regulating their distribution at the evaporation interface and reducing salt accumulation on the surface, thus slowing down salt crystal formation and growth. Meanwhile, the structural stabilizer inhibits aerogel shrinkage during freeze-drying. Excessive shrinkage collapses the aerogel pores, reducing connectivity and hindering water transport, vapor diffusion, and the actual evaporation area, significantly reducing the evaporation rate. The structural stabilizer enhances the rigidity of the gel skeleton by forming a hydrogen bond network, resisting pore collapse caused by capillary forces. These steps and components synergistically improve the performance of the aerogel interface evaporator. The stable network structure formed by chitosan and anionic polyelectrolytes provides an excellent carrier for photothermal conversion materials, enabling them to function more effectively. The porous structure increases the contact area between the aerogel and water, improving evaporation efficiency. The constructed microchannel structure with fixed negative charges mimics the electrical characteristics of mangrove roots, regulating ion transport behavior based on the Donnan effect and reducing anion enrichment at the evaporation interface, thereby inhibiting salt migration and accumulation. Combined with the role of anionic polyelectrolytes, the evaporator's resistance to salt contamination in saline solutions can be further improved, reducing the impact of salt crystallization on evaporation performance and thus contributing to enhanced operational stability.

[0026] In some embodiments, the preparation method of this application, by separately preparing chitosan solution and anionic polyelectrolyte solution and then slowly mixing the two, can avoid the precipitation phenomenon caused by directly mixing chitosan and anionic polyelectrolyte. Furthermore, slow mixing can effectively avoid local high concentrations and prevent instantaneous compound precipitation.

[0027] In some embodiments, this application uses chitosan as the matrix material for the aerogel. Chitosan molecular chains possess a certain degree of flexibility, and the amino groups in its molecules can be protonated under acidic conditions, enabling them to form a dynamic ionic cross-linked network with anionic polyelectrolytes through electrostatic interactions. This is fundamentally different from traditional materials such as sodium alginate, which relies on the cross-linking of divalent cations (such as calcium ions), resulting in low overall mechanical strength. This dynamic ionic cross-linked network of chitosan exhibits unique advantages during freezing. When the suspension freezes in the mold, ice crystal growth generates stress on the polymer network. The dynamic cross-linked network of chitosan can dynamically reorganize to adapt to this stress, thereby forming a vertical gradient pore structure. This vertical gradient pore structure facilitates rapid water transport, providing a good structural basis for subsequent evaporation, while the pore structure formed by sodium alginate is relatively disordered. Furthermore, chitosan molecules can self-assemble through hydrogen bonds, electrostatic interactions, etc. In solutions mixed with anionic polyelectrolytes, chitosan can spontaneously form ordered aggregates with the anionic polyelectrolytes. Sodium alginate exhibits relatively weak self-assembly capabilities, relying primarily on external ions for cross-linking and assembly. Therefore, chitosan-based aerogels possess better mechanical strength and flexibility. Their dynamic ionic cross-linking network endows the aerogel with a certain degree of elasticity, allowing it to deform to some extent without breaking under external force. Sodium alginate-based aerogels, due to their rigid cross-linked structure, are prone to brittle fracture under external force, exhibiting relatively poor flexibility. In practical applications, chitosan-based aerogels better resist water flow impact and salt crystallization stress during the treatment of saline solutions, maintaining structural integrity. During photothermal conversion, chitosan maintains structural and performance stability within a certain temperature range; sodium alginate is prone to thermal degradation at high temperatures, leading to gel structure destruction. The protonated amino groups in chitosan molecules carry a positive charge, enabling them to synergistically interact with anionic polyelectrolytes to repel anions in the solution. This repulsion effectively inhibits salt crystallization on the aerogel interface evaporator surface during saline solution treatment. Sodium alginate primarily reduces salt crystallization through physical barrier, but its effect is relatively limited, and its salt-repellent ability is weak. Therefore, the amino properties, dynamic cross-linking ability, and self-assembly behavior of chitosan bring about entirely new changes to the structure and properties of aerogels.

[0028] In some embodiments, the mass ratio of chitosan, anionic polyelectrolyte, and structural stabilizer is 1~3:1:0.5~3. For example, the preferred mass ratio of chitosan, anionic polyelectrolyte, and structural stabilizer is 2:1:1.

[0029] In some embodiments, the mass fraction of chitosan, anionic polyelectrolyte, and structural stabilizer in the composite solution is 2-5 wt%. For example, the preferred mass fraction is any one or any two of 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, and 5 wt%.

[0030] In some embodiments, the concentration of the photothermal conversion material in the composite solution is 1 to 10 mg / mL. For example, the concentration of the photothermal conversion material in the solution can be any one or a range between any two of the following values: 1 mg / mL, 2 mg / mL, 3 mg / mL, 4 mg / mL, 5 mg / mL, 6 mg / mL, 7 mg / mL, 8 mg / mL, 9 mg / mL, and 10 mg / mL.

[0031] In some embodiments, the anionic polyelectrolyte is selected from at least one of sodium polyacrylate, sodium polystyrene sulfonate, and sodium polyaspartate. It is understood that sodium polyacrylate molecules are rich in carboxylic acid groups, which ionize in water to generate a high density of negative charges. This allows for the regulation of ion distribution based on the Donnan effect, thus affecting the concentration of anions (such as...) in the solution. The hydrophilic backbone of the polystyrene sulfonate generates electrostatic repulsion and forms a hydration layer, physically blocking the migration of salt ions. Sodium polystyrene sulfonate contains sulfonic acid groups, which have a high degree of ionization and can provide a strong fixed negative charge, thereby enhancing the electrostatic repulsion of anions and regulating ion migration behavior. Furthermore, its sulfonic acid groups interact with some cations, helping to regulate the ion transport process. The carboxyl groups on the sodium polyaspartate molecular chain ionize in water to generate a negative charge, which can electrostatically repel anions. Simultaneously, it has a certain complexing ability, forming complexes with some metal ions, thereby reducing their deposition and improving the system's resistance to salt contamination. In this embodiment, chitosan and anionic polyelectrolytes form a dense composite network through electrostatic attraction. The negative charge of the anionic polyelectrolyte neutralizes the positive charge of chitosan, also reducing ion adsorption; the composite forms an electric double layer structure, enhancing the overall electrostatic repulsion ability. The amino and hydroxyl groups of chitosan form hydrogen bonds with the functional groups of the polyelectrolyte (such as carboxyl and sulfonic acid groups), further improving the gel's mechanical strength.

[0032] In some embodiments, the weight-average molecular weight of chitosan is 100,000 to 500,000 Da.

[0033] In some embodiments, the weight-average molecular weight of sodium polyacrylate is 1,000,000 to 5,000,000 Da; the weight-average molecular weight of sodium polystyrene sulfonate is 50,000 to 100,000 Da; and the weight-average molecular weight of sodium polyaspartate is 10,000 to 50,000 Da.

[0034] In some embodiments, the structural stabilizer is selected from at least one of polyvinyl alcohol (PVA) and nanocellulose. It is understood that PVA molecular chains are rich in hydroxyl groups, enabling the formation of dense intramolecular and intermolecular hydrogen bonds, maintaining the rigidity of the gel skeleton during freeze-drying and resisting pore collapse caused by capillary forces. Simultaneously, the hydroxyl groups of PVA can form additional hydrogen bonds with the amino groups of chitosan, enhancing the stability of the three-dimensional network. The negative charge of the anionic polyelectrolyte can also interact with the polar hydroxyl groups of PVA, regulating the swelling behavior of the gel and preventing excessive shrinkage. Nanocellulose is a class of cellulose-based materials with a diameter less than 100 nanometers. Its molecular chains form a rigid rod-like or fibrous structure through a hydrogen bond network, exhibiting high aspect ratio and high strength. It can form a reinforcing skeleton in hydrogels, supporting the hydrogel structure and preventing shrinkage during freezing. Nanocellulose and chitosan can form a composite structure through hydrogen bonding and electrostatic interactions, which enhances the mechanical properties and anti-shrinkage ability of the hydrogel.

[0035] In some embodiments, the photothermal conversion material is selected from at least one of reduced graphene oxide, carbon nanotubes, and carbon black. After absorbing sunlight, the photothermal conversion material converts light energy into heat energy. When combined with chitosan, the abundant amino and hydroxyl groups on the chitosan molecular chain help form a dynamic hydrogen bond network, connecting hydrophilic channels, reducing the enthalpy of evaporation, and accelerating water transport. During the photothermal conversion process, water can be transported to the evaporation interface more efficiently, improving evaporation efficiency.

[0036] In some embodiments, the average particle size of the photothermal conversion material is 10~200 nm.

[0037] In some embodiments, the crosslinking agent is selected from at least one of sodium tripolyphosphate and sodium hexametaphosphate, and the mass fraction of the crosslinking agent in the solution is 1 to 5 wt%.

[0038] In some embodiments, the porosity of the aerogel is 70-85%, and the pore size contained in the aerogel is 10-250 μm.

[0039] In some embodiments, the anion in the saline aqueous solution is selected from chloride ions or sulfate ions. It is understood that a saline aqueous solution is defined as an aqueous solution containing salt or other electrolytes, such as seawater or wastewater.

[0040] In some embodiments, the salt in the saline aqueous solution is selected from at least one of sodium chloride, magnesium chloride, sodium sulfate, and magnesium sulfate.

[0041] In some embodiments, the mold is shaped like a frustum or a cylinder. A frustum shape is preferred because, inspired by the water transport and salt repulsion mechanisms of mangrove roots, a frustum-shaped aerogel three-dimensional interface evaporator was constructed. The frustum-shaped structure increases the contact area between the bottom and the water, ensuring sufficient water supply to the evaporation interface. The Donnan effect, induced by negatively charged microchannels inside the evaporator, effectively suppresses salt accumulation at the evaporation interface.

[0042] In some embodiments, the freezing temperature of the mold is -100 to -200 °C. Specifically, the mold can be frozen in liquid nitrogen.

[0043] In some embodiments, the vacuum degree of vacuum drying is 1~10 Pa, and the drying time is 20~30 h.

[0044] In some embodiments, the crosslinking reaction temperature is 20~40 °C, and the crosslinking reaction time is 2~12 h.

[0045] In some embodiments, an aerogel interface evaporator prepared by the method of this embodiment is provided. See also Figure 1 Mangroves can grow in high-salt environments, which is related to the high zeta potential (-91.4±0.93 mV) of their roots, thus regulating salt ion distribution to a certain extent. Simultaneously, their well-developed root structure provides a continuous water supply for growth. Inspired by this, this embodiment provides a frustum-shaped aerogel interfacial evaporator based on the Donnan effect. By constructing a microchannel structure with a fixed negative charge inside the material, the electrical characteristics of mangrove roots are simulated to regulate ion transport behavior and reduce anion (such as...) The salt is enriched at the evaporation interface, thus inhibiting the migration and accumulation of salt to the evaporation interface. In addition, the frustum-shaped structure design mimics the water transport path of mangrove roots, increasing the water transport area to provide sufficient moisture to the evaporation surface.

[0046] In some embodiments, the aerogel interface evaporator provided in this embodiment can be used in seawater desalination or wastewater purification.

[0047] The present disclosure will be described in detail below with reference to specific embodiments. However, the present disclosure may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments of the present disclosure are provided so that this specification will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0048] Experimental methods not specifying specific conditions in the embodiments of this disclosure are generally performed under conventional conditions or as recommended by the raw material or product manufacturer. Reagents not specifying their source are commercially available, conventional reagents.

[0049] The known starting materials disclosed herein can be synthesized using or in accordance with methods known in the art, or can be purchased from companies such as McLean and Aladdin.

[0050] In the following embodiments: Chitosan, with a weight-average molecular weight of 100,000 Da, was purchased from Shanghai Maclean Biochemical Technology Co., Ltd. Sodium polyacrylate, sodium polystyrene sulfonate, and sodium polyaspartate have weight-average molecular weights of 3,000,000 Da, 70,000 Da, and 10,000 Da, respectively, and were all purchased from Shanghai Maclean Biochemical Technology Co., Ltd. The weight-average molecular weight of polyvinyl alcohol was 89,000 Da, and the aspect ratio of nanocellulose was 500. Both were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. The average particle sizes of the reduced graphene oxide, carbon nanotubes, and carbon black were 20–200 nm, and they were purchased from the Shanxi Coal Chemistry Institute of the Chinese Academy of Sciences and Shanghai Maclean Biochemical Technology Co., Ltd., respectively. The seawater used in the experiment was taken from Nan'ao Beach in Fuzhou City. In this embodiment, room temperature refers to the range of 25±5℃.

[0051] Example 1 Chitosan was dissolved in a weakly acidic aqueous solution with pH=4 to obtain a chitosan solution. Sodium polyacrylate and polyvinyl alcohol were dissolved in deionized water to obtain an anionic polyelectrolyte / stabilizer solution. The anionic polyelectrolyte / stabilizer solution was slowly added to the chitosan solution and mixed evenly to form a composite solution system. The mass ratio of chitosan, sodium polyacrylate, and polyvinyl alcohol in the composite system was 2:1:2, and the total mass fraction of the three in the composite system was 3.5 wt%. Subsequently, reduced graphene oxide was added to achieve a concentration of 5 mg / mL in the composite system, resulting in a uniformly dispersed suspension. This suspension was injected into a pre-cooled polytetrafluoroethylene frustum mold and rapidly placed in liquid nitrogen (-196 ℃) for rapid freezing to achieve complete solidification. The frozen-formed sample was then placed in a freeze dryer and dried for 24 h at a cold trap temperature of -55 ℃ and a vacuum degree of 5 Pa to remove moisture, resulting in a porous aerogel. The obtained aerogel was immersed in a 3 wt% sodium tripolyphosphate aqueous solution and crosslinked at 30 °C for 7 h. After the reaction was completed, it was repeatedly rinsed with deionized water and dried to obtain an aerogel interface evaporator.

[0052] See Figure 2Figure 1 shows a SEM image of the aerogel interface evaporator prepared in Example 1, where a and b represent the surface and cross-sectional morphology of the evaporator, respectively. Figure 2 As can be seen, the evaporator surface exhibits a three-dimensional porous structure. Image analysis and statistics show that its pore size distribution ranges from 20 to 200 μm, and no significant structural collapse occurred during the drying process. Cross-sectional observation results show that a continuous vertical channel structure is formed inside the material, which is conducive to the rapid vertical transport of moisture. The porosity of this porous structure is approximately 78% as determined by the density method, which is beneficial for enhancing light absorption capacity and improving mass transfer performance.

[0053] Example 2 Chitosan was dissolved in a weakly acidic aqueous solution with pH=4 to obtain a chitosan solution. Sodium polystyrene sulfonate and polyvinyl alcohol were dissolved in deionized water to obtain an anionic polyelectrolyte / stabilizer solution. The anionic polyelectrolyte / stabilizer solution was slowly added to the chitosan solution and mixed evenly to form a composite solution system. The mass ratio of chitosan, sodium polystyrene sulfonate, and polyvinyl alcohol in the composite system was 3:1:2, and the total mass fraction of the three in the composite system was 4 wt%. Subsequently, carbon nanotubes were added to achieve a concentration of 8 mg / mL in the composite system, resulting in a uniformly dispersed suspension. This suspension was injected into a pre-cooled polytetrafluoroethylene frustum mold and rapidly placed in liquid nitrogen (-196 ℃) for rapid freezing to achieve complete solidification. The frozen-formed sample was then placed in a freeze dryer and dried for 24 h at a cold trap temperature of -55 ℃ and a vacuum degree of 5 Pa to remove moisture, resulting in a porous aerogel. The obtained aerogel was immersed in a 2 wt% sodium hexametaphosphate aqueous solution and crosslinked at 30 °C for 8 h. After the reaction was completed, it was repeatedly rinsed with deionized water and dried to obtain an aerogel interface evaporator.

[0054] Example 3 Chitosan was dissolved in a weakly acidic aqueous solution with pH=4 to obtain a chitosan solution. Sodium polyaspartate and nanocellulose were dissolved in deionized water to obtain an anionic polyelectrolyte / stabilizer solution. The anionic polyelectrolyte / stabilizer solution was slowly added to the chitosan solution and mixed evenly to form a composite solution system. The mass ratio of chitosan, sodium polyaspartate, and nanocellulose was 2:1:1, and the total mass fraction of the three in the composite system was 3 wt%. Carbon black was then added to achieve a concentration of 5 mg / mL in the composite system, resulting in a uniformly dispersed suspension. This suspension was injected into a pre-cooled polytetrafluoroethylene frustum mold and rapidly placed in liquid nitrogen (-196 ℃) for rapid freezing to ensure complete solidification. The frozen-formed sample was then placed in a freeze dryer and dried for 20 h at a cold trap temperature of -55 ℃ and a vacuum degree of 2 Pa to remove moisture, resulting in a porous aerogel. The obtained aerogel was immersed in a 3 wt% sodium tripolyphosphate aqueous solution and crosslinked at 35 °C for 5 h. After the reaction was completed, it was repeatedly rinsed with deionized water and dried to obtain an aerogel interface evaporator.

[0055] Example 4 Chitosan was dissolved in a weakly acidic aqueous solution with pH=4 to obtain a chitosan solution. Sodium polyacrylate and polyvinyl alcohol were dissolved in deionized water to obtain an anionic polyelectrolyte / stabilizer solution. The anionic polyelectrolyte / stabilizer solution was slowly added to the chitosan solution and mixed evenly to form a composite solution system. The mass ratio of chitosan, sodium polyacrylate, and polyvinyl alcohol in the composite system was 3:1:3, and the total mass fraction of the three in the composite system was 5 wt%. Subsequently, reduced graphene oxide was added to achieve a concentration of 10 mg / mL in the composite system, resulting in a uniformly dispersed suspension. This suspension was injected into a pre-cooled polytetrafluoroethylene frustum mold and rapidly placed in liquid nitrogen (-196 ℃) for rapid freezing to achieve complete solidification. The frozen-formed sample was then placed in a freeze dryer and dried for 30 h at a cold trap temperature of -55 ℃ and a vacuum degree of 10 Pa to remove moisture, resulting in a porous aerogel. The obtained aerogel was immersed in a 5 wt% sodium tripolyphosphate aqueous solution and crosslinked at 40 °C for 2 h. After the reaction was completed, it was repeatedly rinsed with deionized water and dried to obtain an aerogel interface evaporator.

[0056] Example 5 Chitosan was dissolved in a weakly acidic aqueous solution with pH=4 to obtain a chitosan solution. Sodium polyacrylate and polyvinyl alcohol were dissolved in deionized water to obtain an anionic polyelectrolyte / stabilizer solution. The anionic polyelectrolyte / stabilizer solution was slowly added to the chitosan solution and mixed evenly to form a composite solution system, wherein the mass ratio of chitosan, sodium polyacrylate, and polyvinyl alcohol was 1:1:0.5, and the total mass fraction of the three in the composite system was 2 wt%. Subsequently, reduced graphene oxide was added to achieve a concentration of 1 mg / mL in the composite system, resulting in a uniformly dispersed suspension. This suspension was injected into a pre-cooled polytetrafluoroethylene frustum mold and rapidly placed in liquid nitrogen (-196 ℃) for rapid freezing to achieve complete solidification. The frozen-formed sample was then placed in a freeze dryer and dried for 20 h at a cold trap temperature of -55 ℃ and a vacuum degree of 1 Pa to remove moisture, resulting in a porous aerogel. The obtained aerogel was immersed in a 1 wt% sodium tripolyphosphate aqueous solution and crosslinked at 20 °C for 12 h. After the reaction was completed, it was repeatedly rinsed with deionized water and dried to obtain an aerogel interface evaporator.

[0057] Comparative Example 1 An interfacial evaporator is provided, and the specific preparation process is the same as that of Example 1, except that the anionic polyelectrolyte sodium polyacrylate is not used in the preparation of Comparative Example 1.

[0058] Comparative Example 2 An interfacial evaporator is provided, and the specific preparation process is the same as that of Example 1, except that no structural stabilizer is used in the preparation of Comparative Example 2.

[0059] Comparative Example 3 An interfacial evaporator is provided, and the specific preparation process is the same as that of Example 1. The difference is that sodium alginate is used instead of chitosan in the preparation of Comparative Example 3, and calcium chloride is used as the crosslinking agent in Comparative Example 3.

[0060] The aerogel interface evaporators prepared in Examples 1-5 and Comparative Examples 1-3 were subjected to performance tests. The specific test results are shown in Tables 1 and 2.

[0061] Mechanical property testing: Compressive strength and compressive modulus were used as indicators to evaluate the mechanical properties of the aerogel interface evaporator. The sample was processed into a cylinder (15 mm in diameter and 10 mm in height) and subjected to uniaxial compression testing at room temperature using a universal testing machine. The compression rate was [value missing]. The load is compressed axially to 70% of its original height or fails. Load-displacement data are recorded and stress-strain curves are obtained. The compressive strength is taken as the maximum stress value (MPa), and the compressive modulus is calculated from the slope of the 10%–30% linear strain interval, using the following formula (a): (a) in, E It is the compressive modulus (MPa). This represents the stress difference (MPa) corresponding to the linear segment. The strain difference (dimensionless) corresponds to the linear segment.

[0062] Structural stability test: Shrinkage rate was used as an indicator to evaluate the structural stability of the aerogel interface evaporator. The drying shrinkage performance was characterized by the height change between the freeze-cured sample in the mold and the vacuum-dried aerogel. The height dimensions of the sample in the freeze-cured state in the mold and the vacuum-dried aerogel state were measured using vernier calipers. The shrinkage rate was calculated according to formula (b): (b) in, S Shrinkage rate (%) The height of the sample after freeze-curing in the mold. The height of the aerogel after vacuum drying.

[0063] Evaporation performance testing: Evaporation rate was used as the indicator to evaluate the evaporation performance of the aerogel interface evaporator. A xenon lamp source was used to simulate sunlight irradiation, and the light intensity was calibrated using a light flux meter. (Equivalent to 1 standard solar radiation intensity). The evaporator was placed on a high-precision electronic balance (accuracy 0.0001 g) and the evaporation experiment was conducted under ambient conditions of 25 ℃ and 60% relative humidity. The evaporation rate was calculated using the following formula (c): (c) in, v Evaporation rate ( ), Δ m This represents the change in water mass (kg) per unit time. A The evaporation area is (m²). t Evaporation time (h).

[0064] Salt rejection performance test: The stability of the evaporation rate during long-term continuous evaporation was used as an indicator to evaluate the salt rejection performance of the aerogel interface evaporator. The evaporator was placed in a 10 wt% NaCl solution, and an evaporation experiment was conducted continuously for 10 hours under continuous light irradiation. The changes in the evaporation rate of the brine were recorded at different time points to assess the impact of salt accumulation at the evaporation interface on the evaporation performance. The evaporation rate test method was the same as the evaporation rate test method described in the evaporation performance test above.

[0065] Table 1 Mechanical properties, structural stability, and evaporation performance of aerogel interfacial evaporators

[0066] As shown in Table 1, in terms of mechanical properties, the compressive strength of the aerogel interfacial evaporators in each embodiment ranges from 0.103 to 0.185 MPa, and the compressive modulus ranges from 1.53 to 2.95 MPa, which are significantly higher than those of the comparative system. Superior mechanical properties help ensure the structural integrity and long-term reliability of the interfacial evaporator during seawater desalination, thereby maintaining a stable water transport channel and continuous evaporation performance. Comparative Example 2, lacking a structural stabilizer, is prone to pore shrinkage and local collapse under capillary forces, resulting in a significant decrease in both compressive strength and compressive modulus. Comparative Example 3 uses sodium alginate as the matrix polymer and... Ionic crosslinking forms an "egg-box" structured gel network. While this type of ionic crosslinking system has a certain structure-forming ability, its network regulation and stress adaptation capabilities are relatively limited, resulting in slightly lower continuity of the load-bearing network compared to the system in the example, thus exhibiting a certain degree of difference in mechanical properties. In contrast, the chitosan-based dynamic ionic crosslinking network in the example can be synergistically enhanced through electrostatic interactions and hydrogen bonding, and can achieve stress adaptive adjustment, thereby obtaining superior structural integrity and load-bearing capacity.

[0067] Regarding structural stability, the shrinkage rates of all embodiments ranged from 6.8% to 9.7%, significantly lower than Comparative Example 2 (22.5%). Comparative Example 2, lacking a structural stabilizer, struggled to effectively resist capillary stress during freeze-drying, resulting in significant pore wall shrinkage and volume changes. Comparative Example 3 used sodium alginate. The cross-linked system exhibits relatively stable structure formation, but its ability to mitigate structural stress during ice crystal template-induced pore formation and drying is limited, causing the porous framework to exhibit a certain degree of compression behavior. In this embodiment, the structural stabilizer enhances the rigidity of the framework and provides continuous support through a hydrogen bond network, effectively suppressing volume shrinkage.

[0068] Regarding evaporation performance, the evaporation rates of the various embodiments ranged from 4.623 to 4.725. The overall efficiency was higher than that of the comparative system. Specifically, in comparative example 2, the effective evaporation interface decreased due to structural collapse, resulting in an evaporation rate of 3.209. Comparative Examples 1 and 3 still possess some evaporation capacity, but due to the relatively limited integrity of their porous structure and the degree of construction of continuous water transport channels, their water transport and interfacial supply capabilities are affected, thus their overall performance is lower than that of the Example System. Comparative Example 3, in particular, suffers from lower evaporation capacity due to sodium alginate. The network differs from the chitosan-based composite system in pore formation regulation and structural evolution, resulting in relatively weaker continuity of mass transfer channels and photothermal-water transport synergy, thus exhibiting slightly lower evaporation performance.

[0069] In summary, the introduction of structural stabilizers plays a crucial role in maintaining the integrity of the porous structure of aerogels. Compared to sodium alginate, the chitosan-based dynamic ionic crosslinking system demonstrates superior performance. The system exhibits superior structural adaptability and continuity, with the multi-scale porous structure and photothermal materials working synergistically to enhance overall evaporation performance.

[0070] Table 2 Salt rejection performance of aerogel interfacial evaporators

[0071] As shown in Table 2, after continuous evaporation in 10 wt% NaCl solution for 10 h, the evaporation rate decay rate of the aerogel interface evaporators in each embodiment was only 1.7%~2.9%, significantly lower than that of the comparative system (3.2%~18.6%). Among them, Examples 1-5 maintained a high and stable evaporation rate (approximately 3.865~4.015) during the evaporation process. The slow decay within a certain range indicates that there is no significant salt crystallization accumulation or blockage of mass transfer channels at its interface, demonstrating excellent resistance to salt contamination and long-term operation capability.

[0072] Comparative Example 1 did not introduce anionic polyelectrolytes, and the material lacked fixed negative charge sites, making it difficult to suppress electrostatic repulsion. Anions accumulate at the evaporation interface, easily leading to salt crystallization and deposition, which gradually blocks the evaporation channels, resulting in the most significant performance degradation (18.6%). In Comparative Example 2, no structural stabilizer was introduced; during long-term evaporation, the aerogel's pores were prone to shrinkage or even partial collapse due to capillary forces, obstructing water transport channels and reducing interfacial water supply capacity, thus causing a continuous decrease in the evaporation rate (8.7%). Although Comparative Example 3 possessed a certain porous structure, sodium alginate... The cross-linked network is relatively rigid and has limited structural regulation capabilities. Under long-term exposure to salt solution, it is insufficient to inhibit salt migration and local enrichment, and therefore still exhibits a certain degree of performance degradation (3.2%).

[0073] In contrast, the dynamic ionic cross-linking network constructed from chitosan and anionic polyelectrolytes in the example system introduces stable, fixed negatively charged sites, which can continuously generate electrostatic repulsion against anions based on the Donnan effect, effectively reducing the accumulation of salt ions at the evaporation interface. Simultaneously, the structural stabilizer maintains the stability and pore connectivity of the porous structure by enhancing the hydrogen bond network and framework rigidity, avoiding mass transfer blockage caused by structural collapse. Furthermore, the continuous three-dimensional porous channels promote continuous water replenishment and salt ion diffusion into the bulk phase, further reducing the risk of local supersaturation and crystallization. Therefore, the synergistic effect of multiple structural and interfacial ion regulation enables the example system to maintain stable water transport channels and low salt deposition during long-term brine evaporation, thus exhibiting excellent salt rejection performance and operational stability.

[0074] To verify the performance of the aerogel interface evaporator of this application in a real environment, an outdoor seawater desalination experiment was conducted using the aerogel interface evaporator prepared in Example 1. The experimental water was taken from Nan'ao Beach in Fuzhou City and used as the actual seawater sample. The aerogel interface evaporator was placed in a container filled with the seawater, ensuring its bottom was in full contact with the water and maintaining stable floating. The experiment was conducted in an open-air environment on the rooftop of Jingcheng Building at Minjiang University, with the evaporator operating under natural sunlight. During the experiment, a photometer was used to monitor changes in solar irradiance in real time, a thermometer was used to record the ambient temperature, and a high-precision electronic balance was used to measure changes in the system's mass at regular intervals to calculate the evaporation rate at each time point. Simultaneously, data on solar irradiance, ambient temperature, and evaporation rate were recorded at 1-hour intervals to evaluate its outdoor evaporation performance and environmental adaptability. The salt ion concentration before and after seawater desalination was determined using ion chromatography to evaluate the desalination effect.

[0075] Depend on Figure 3 It is evident that under outdoor natural light conditions, solar irradiance exhibits a typical unimodal variation trend, with ambient temperature fluctuating synchronously, indicating that the experimental process occurred within a stable natural photothermal driven environment. Under these conditions, the evaporation rate of the aerogel interface evaporator gradually increased with increasing light intensity, reaching a maximum of 4.697 at 12:00. It then gradually decreased to 2.441 at 17:00 as the light intensity decreased. The changing trend is consistent with the photothermal environment, indicating that it has good photothermal response characteristics.

[0076] Throughout the entire experimental period, the cumulative evaporation rate of the evaporator reached 31.01. This indicates that it possesses a high actual seawater evaporation capacity. This performance is mainly attributed to the efficient water transport and interfacial supply achieved by the three-dimensional interconnected porous structure, the efficient absorption and localized thermal conversion of solar energy by the photothermal conversion material, the inhibition of Cl⁻ enrichment and salt crystallization by the anionic polyelectrolyte based on the Donnan effect, and the maintenance of the porous framework stability by the structural stabilizer, thereby ensuring a continuous and stable interfacial evaporation process.

[0077] Depend on Figure 4 It can be seen that in the original seawater and The concentrations of the main salt ions were 11158.3 mg / L, 438.9 mg / L, 490.7 mg / L, and 1254.5 mg / L, respectively, which were reduced to 4.712 mg / L, 2.929 mg / L, 1.365 mg / L, and 0.973 mg / L after treatment. The results show that the concentrations of all major salt ions were significantly reduced, with an overall desalination rate of 99.9% and high purity in the produced water. This desalination performance is mainly attributed to the directional transport of water and selective escape of steam during interfacial evaporation. Simultaneously, the presence of a negatively charged microenvironment constructed by the anionic polyelectrolyte effectively inhibits the enrichment and retention of salt ions at the interface, thereby reducing salt entrainment and achieving efficient salt-water separation. In summary, the aerogel interfacial evaporator of this application can stably achieve efficient seawater evaporation and simultaneous desalination in a real outdoor environment, demonstrating good potential for practical application.

[0078] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0079] The products and preparation methods provided in the embodiments of this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are only for the purpose of helping to understand the methods and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method for preparing an aerogel interfacial evaporator, characterized in that, Includes the following steps: Take chitosan and prepare a chitosan solution; Mix the anionic polyelectrolyte and the structure stabilizer to prepare a mixed solution; The mixed solution is slowly added dropwise to the chitosan solution to form a composite solution; Photothermal conversion material is added to the composite solution to form a suspension; The suspension is injected into a pre-cooled mold and the mold is frozen to solidify the suspension. The solidified suspension is then vacuum dried to obtain an aerogel with a porous structure. An aerogel with a porous structure is immersed in a solution containing a crosslinking agent for reaction. After crosslinking is completed, the aerogel is washed and dried to obtain an aerogel interface evaporator. The anionic polyelectrolyte can regulate the migration behavior of ions in the solution during the treatment of salt-containing aqueous solutions in the aerogel interface evaporator, thereby reducing the enrichment and crystallization of salt on the surface of the aerogel interface evaporator.

2. The method for preparing an aerogel interface evaporator according to claim 1, characterized in that, The mass ratio of the chitosan, the anionic polyelectrolyte, and the structural stabilizer is 1~3:1:0.5~3; In the composite solution, the mass fraction of chitosan, the anionic polyelectrolyte, and the structural stabilizer is 2-5 wt%.

3. The method for preparing an aerogel interface evaporator according to claim 2, characterized in that, The concentration of the photothermal conversion material in the composite solution is 1~10 mg / mL.

4. The method for preparing an aerogel interface evaporator according to claim 1, characterized in that, The anionic polyelectrolyte is selected from at least one of sodium polyacrylate, sodium polystyrene sulfonate, and sodium polyaspartate; the structural stabilizer is selected from at least one of polyvinyl alcohol and nanocellulose. Wherein, the sodium polyacrylate has a weight-average molecular weight of 1,000,000 to 5,000,000 Da; the sodium polystyrene sulfonate has a weight-average molecular weight of 50,000 to 100,000 Da; and the sodium polyaspartate has a weight-average molecular weight of 10,000 to 50,000 Da. The weight-average molecular weight of the chitosan is 100,000 to 500,000 Da.

5. The method for preparing an aerogel interfacial evaporator according to claim 1, characterized in that, The photothermal conversion material is selected from at least one of reduced graphene oxide, carbon nanotubes, and carbon black; wherein the average particle size of the photothermal conversion material is 10~200 nm.

6. A method for preparing an aerogel interfacial evaporator according to claim 1, characterized in that, The crosslinking agent is selected from at least one of sodium tripolyphosphate and sodium hexametaphosphate, and the mass fraction of the crosslinking agent in the solution is 1~5wt%.

7. A method for preparing an aerogel interfacial evaporator according to claim 1, characterized in that, The aerogel has a porosity of 70-85% and the pore size of the pores in the aerogel is 10-250 μm. The ions in the saline aqueous solution are selected from chloride ions or sulfate ions; The salt in the saline solution is selected from at least one of sodium chloride, magnesium chloride, sodium sulfate, and magnesium sulfate; The mold is either frustum-shaped or cylindrical.

8. A method for preparing an aerogel interfacial evaporator according to claim 1, characterized in that, The freezing temperature of the mold is -100~-200 ℃, the vacuum degree of the vacuum drying is 1~10 Pa, and the drying time is 20~30 h; The cross-linking reaction temperature is 20~40 ℃, and the cross-linking reaction time is 2~12 h.

9. An aerogel interface evaporator prepared by the method of any one of claims 1-8.

10. The application of the aerogel interface evaporator according to claim 9 in seawater desalination or wastewater purification.

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