Evaporative membrane material and method of making same

Abstract

This application provides an evaporation membrane material and its preparation method, belonging to the field of solar evaporator evaporation membrane materials. The preparation method of the evaporation membrane material includes a skin layer and a core layer, with the skin layer disposed on the side peripheral surface of the core layer. The skin layer has a radially extending first porous structure; the core layer has an axially connected second porous structure; the tortuosity factor of the first porous structure is smaller than that of the second porous structure. The evaporation membrane material of this application can form channels for water transport and resistance to high-concentration salt solutions through the synergistic cooperation of the first and second porous structures, resulting in an evaporation membrane material with high water transport rate, good photothermal performance, low heat loss, and good salt resistance.

Description

Technical Field

[0001] This application relates to the field of solar evaporator evaporation film materials technology, specifically to an evaporation film material and its preparation method. Background Technology

[0002] Currently, usable groundwater and freshwater from rivers and lakes account for only 0.77% of the Earth's total water resources. Industrial development generates large amounts of high-concentration wastewater, exacerbating water pollution and making the freshwater shortage even more severe. Therefore, the treatment of high-concentration brine has become a critical issue. Among various renewable resources, solar energy is an abundant and clean energy source. Solar-driven evaporation membrane materials have shown significant advantages in freshwater production technology and are one of the strategies for alleviating the water crisis in an environmentally friendly way. Due to the energy-saving and low-cost advantages of solar energy, it has become a research hotspot in the field of solar evaporator membrane materials.

[0003] In related technologies, there are various composite structure evaporation membrane materials. However, most evaporation membrane materials only have a single pore structure, resulting in poor salt resistance and difficulty in maintaining stable operation in practical applications. Salt crystallization is a key factor affecting the water production capacity of evaporation membrane materials in the treatment of high-concentration wastewater. Furthermore, existing composite structure evaporation membrane materials employ multi-step splicing processes, resulting in insufficient interlayer bonding strength, cumbersome preparation processes, and high costs, making it difficult to meet the needs of large-scale industrial production. In summary, existing evaporation membrane materials have poor salt resistance, cumbersome preparation processes, and cannot meet industrial requirements.

[0004] In view of this, it is necessary to design an evaporation membrane material and its preparation method to solve the above problems. Summary of the Invention

[0005] In view of the technical problems existing in the background art, this application provides an evaporation membrane material and its preparation method. The evaporation membrane material forms a channel for water transport and resistance to high concentration salt solutions through the synergistic cooperation of a first porous structure and a second porous structure, thereby obtaining an evaporation membrane material with high water transport rate, good photothermal performance, low heat loss and good salt resistance.

[0006] To achieve the above objectives, in a first aspect, this application provides an evaporation membrane material, including a substrate, a skin layer, and a core layer, wherein the skin layer is disposed on the side peripheral surface of the core layer; The cortex has a first porous structure, which has multiple channels extending radially along the matrix; The core layer has a second porous structure, which has multiple micropores that are interconnected along the matrix axis; The first porous structure is connected to the second porous structure; The tortuosity factor of the first porous structure is smaller than that of the second porous structure.

[0007] Furthermore, the tortuosity factor of the first porous structure is 2.1-2.5; and / or, The tortuosity factor of the second porous structure is 2.8-3.5.

[0008] Furthermore, the diameter ratio of the cortex to the core is 2.5:(1.5-2).

[0009] Furthermore, the porosity of the cortex is 60%-70%; and / or, The porosity of the core layer is 70%-80%.

[0010] Furthermore, the length of the channel is 0.1cm-1cm; and / or, The pore size of the micropores is 65μm-70μm.

[0011] Secondly, this application also provides a method for preparing an evaporation membrane material, including providing a mixed solution, the mixed solution comprising photothermal nanomaterials and polymer materials; The mixed solution was frozen at a first temperature for a first time to obtain the precursor; The precursor is frozen at a second temperature for a second time to obtain the intermediate. The intermediate is frozen at a third temperature for a third time and then dried to obtain an evaporation membrane material; wherein the first temperature is (-200℃) - (-180℃). The first time is 10s-60s; The second temperature is (-40℃) - (-25℃); The second time period is 12h-24h; The third temperature is (-60℃) - (-50℃); The third time period is 36h-72h.

[0012] Furthermore, in the mixed solution, the mass percentage of photothermal nanomaterials is 0.1%-5%.

[0013] Furthermore, in the mixed solution, the mass percentage of the polymer material is 0.1%-5%.

[0014] Furthermore, the photothermal nanomaterials include at least one of Mxene (two-dimensional transition metal carbon / nitride), graphene, graphene oxide, carbon nanotubes, iron(II,III) oxide, black phosphorus, and melanin particles; and / or, The polymeric material includes at least one of sodium alginate, polyvinyl alcohol, and chitosan.

[0015] Thirdly, embodiments of this application also provide a solar evaporator, including the aforementioned evaporation film material; or, Evaporation membrane materials prepared by the methods described above include those prepared by the above-mentioned methods.

[0016] The beneficial effects of this application are as follows: In the technical solution of this application, the skin layer is disposed on the peripheral surface of the core layer, and the first porous structure has multiple channels extending radially along the substrate, providing sufficient space and time for salt ions to precipitate, which can reduce the salt crystallization content in the core layer and extend the service life of the evaporation membrane material. The second porous structure has multiple micropores interconnected along the axial direction of the substrate. These interconnected micropores provide transport paths and storage space for water molecules, reducing the resistance to longitudinal transport of water molecules and providing moisture to the evaporation surface. This allows the water transport rate on the evaporation surface to be slightly greater than the evaporation rate, thereby maintaining the stability of the evaporation membrane material. Furthermore, the tortuosity factor of the first porous structure is smaller than that of the second porous structure. During transport, salt ions migrate along low-resistance channels and crystallize in the skin layer, reducing salt crystallization on the evaporation surface and maintaining the continuous stability of the evaporation membrane material. The second porous structure transports water to the evaporation surface through capillary action, providing transport channels for water molecules and controlling the water transport efficiency. Because the tortuosity factors of the porous structures in the skin and core layers are different, the thermal conductivity of the two layers is different. The first porous structure has weak longitudinal heat transfer capacity, while the second porous structure has strong longitudinal heat transfer. The first porous structure can reduce longitudinal heat loss, resulting in different heat transfer modes, forming a thermal gradient interface, and reducing the heat loss of the evaporation film material.

[0017] In summary, by working together with the first porous structure and the second porous structure, channels for water transport and resistance to high-concentration salt solutions are formed, resulting in an evaporation membrane material with high water transport rate, good photothermal performance, low heat loss, and good salt resistance.

[0018] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0020] Figure 1 This application provides a schematic diagram of a mold for preparing evaporation film materials; Figure 2 Images of the evaporation membrane material of this application; Figure 3 SEM image of the core layer of Embodiment 1 of this application; Figure 4 SEM image of the dermis in Example 1 of this application; Figure 5 Images of the evaporation membrane material of Embodiment 1 of this application; Figure 6 Images of the evaporation membrane material of Embodiment 2 of this application; Figure 7 This is an image of the evaporation membrane material of Comparative Example 1 of this application; Figure 8 Image of the evaporation membrane material of Comparative Example 2 of this application; Figure 9 Images showing the process of conducting salt resistance tests on the evaporation membrane material of Example 1 of this application; Figure 10 Images showing the process of conducting salt resistance tests on the evaporation membrane material of Example 2 of this application; Figure 11 Images showing the process of conducting salt resistance tests on the evaporation membrane material of Comparative Example 1 of this application; Figure 12 Images showing the process of conducting salt resistance tests on the evaporation membrane material of Comparative Example 2 of this application; Figure 13 This is a comparison graph showing the evaporation rates of the evaporation membrane materials in Examples 1 and 2 of this application and Comparative Examples 1 and 2. Detailed Implementation

[0021] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0023] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0024] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0025] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0026] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0027] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0028] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0029] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0030] Currently, usable groundwater and freshwater from rivers and lakes account for only 0.77% of the Earth's total water resources. Industrial development generates large amounts of high-concentration wastewater, exacerbating water pollution and making the freshwater shortage even more severe. Therefore, the treatment of high-concentration brine has become a critical issue. Among various renewable resources, solar energy is an abundant and clean energy source. Solar-driven evaporation membrane materials have shown significant advantages in freshwater production technology and are one of the strategies for alleviating the water crisis in an environmentally friendly way. Due to the energy-saving and low-cost advantages of solar energy, it has become a research hotspot in the field of solar evaporator membrane materials.

[0031] In related technologies, there are various composite structure evaporation membrane materials. However, most evaporation membrane materials only have a single pore structure, resulting in poor salt resistance and difficulty in maintaining stable operation in practical applications. Salt crystallization is a key factor affecting the water production capacity of evaporation membrane materials in the treatment of high-concentration wastewater. Furthermore, existing composite structure evaporation membrane materials employ multi-step splicing processes, resulting in insufficient interlayer bonding strength, cumbersome preparation processes, and high costs, making it difficult to meet the needs of large-scale industrial production. In summary, existing evaporation membrane materials have poor salt resistance, cumbersome preparation processes, and cannot meet industrial requirements.

[0032] In order to solve the above-mentioned technical problems, in a first aspect, this application provides an evaporation membrane material and a method for preparing the same, including a substrate, the substrate including a skin layer and a core layer, the skin layer being disposed on the side peripheral surface of the core layer; The cortex has a first porous structure, which has multiple channels extending radially along the matrix; The core layer has a second porous structure, which has multiple micropores that are interconnected along the matrix axis; The first porous structure is connected to the second porous structure; The tortuosity factor of the first porous structure is smaller than that of the second porous structure.

[0033] In the technical solution of this application, the skin layer is disposed on the peripheral surface of the core layer, and the first porous structure has multiple channels extending radially along the substrate, providing sufficient space and time for salt ions to precipitate, which can reduce the salt crystallization content in the core layer and extend the service life of the evaporation membrane material. The second porous structure has multiple micropores interconnected along the axial direction of the substrate. These interconnected micropores provide transport paths and storage space for water molecules, reducing the resistance to longitudinal transport of water molecules and providing moisture to the evaporation surface. This allows the water transport rate on the evaporation surface to be slightly greater than the evaporation rate, thereby maintaining the stability of the evaporation membrane material. Furthermore, the tortuosity factor of the first porous structure is smaller than that of the second porous structure. During transport, salt ions migrate along low-resistance channels and crystallize in the skin layer, reducing salt crystallization on the evaporation surface and maintaining the continuous stability of the evaporation membrane material. The second porous structure transports water to the evaporation surface through capillary action, providing transport channels for water molecules and controlling the water transport efficiency. Because the tortuosity factors of the porous structures in the skin and core layers are different, the thermal conductivity of the two layers is different. The first porous structure has weak longitudinal heat transfer capacity, while the second porous structure has strong longitudinal heat transfer. The first porous structure can reduce longitudinal heat loss, resulting in different heat transfer modes, forming a thermal gradient interface, and reducing the heat loss of the evaporation film material.

[0034] In summary, by working together with the first porous structure and the second porous structure, channels for water transport and resistance to high-concentration salt solutions are formed, resulting in an evaporation membrane material with high water transport rate, good photothermal performance, low heat loss, and good salt resistance.

[0035] It is understandable that the substrate here is the main body of the evaporation film material, the radial direction is perpendicular to the substrate axis, and the axial direction is consistent with the substrate axis.

[0036] It should be noted that the tortuosity factor here describes the degree of tortuosity of the actual path of fluid flowing through a porous material. The range of the tortuosity factor will have a certain resistance to water transport; the smaller the tortuosity factor, the smaller the resistance, and the larger the tortuosity factor, the greater the resistance.

[0037] In some embodiments, the tortuosity factor of the first porous structure is 2.1-2.5.

[0038] In this embodiment, the tortuosity factor of the first porous structure is set within the range of 2.1-2.5, allowing salt ions to move along the axial direction of the matrix and precipitate within the pores. This improves the salt resistance of the evaporation membrane material and extends its service life. Furthermore, setting the tortuosity factor of the first porous structure within the range of 2.1-2.5 results in greater resistance to longitudinal heat transfer, allowing heat to be fully applied to the evaporation surface, reducing longitudinal heat loss, and maintaining the evaporation rate of the evaporation surface.

[0039] In some embodiments, the tortuosity factor of the second porous structure is 2.8-3.5.

[0040] In this embodiment, setting the tortuosity factor of the second porous structure within the range of 2.8-3.5 provides ample storage space for moisture and sufficient moisture for the evaporation surface. Furthermore, setting the tortuosity factor of the second porous structure within this range dilutes the concentration of salt ions within the core layer, reduces the upward transport rate of salt ions, and limits the rate of salt ion precipitation on the evaporation surface of the evaporation membrane material. This improves the salt resistance of the evaporation membrane material and extends its service life.

[0041] In some embodiments, the diameter ratio of the skin layer to the core layer is 2.5:(1.5-2).

[0042] In this embodiment, by setting the diameter ratio of the skin layer to the core layer to 2.5:(1.5-2), the water delivery rate can be slightly higher than the evaporation rate, forming a dynamic adaptive effect and maintaining the stability of the evaporation membrane material. Furthermore, setting the diameter ratio of the skin layer to the core layer to 2.5:(1.5-2) ensures sufficient space for salt crystallization in the skin layer, keeping the surface of the evaporation membrane material clean, while sufficient space for diluting salt ions in the core layer reduces the salt crystallization load on the skin layer. The synergistic effect of these two factors maintains the long-term stable operation of the evaporation membrane material and improves its salt resistance. In addition, within this range, the longitudinal heat transfer resistance of the skin layer is high, and the lateral heat transfer resistance of the core layer is high. Their synergistic effect ensures that heat is fully utilized on the evaporation surface, reducing heat loss from the evaporation membrane material.

[0043] In some embodiments, the porosity of the skin layer is 60%-70%.

[0044] In this embodiment, by setting the porosity of the skin layer within the range of 60%-70%, the thickness of the skin layer can be controlled, thereby improving its mechanical strength and making it less prone to damage. Furthermore, setting the porosity of the skin layer within the range of 60%-70% provides sufficient branching paths and residence space for salt ions, enabling crystallization, reducing clogging of the porous structure, and improving the salt resistance of the evaporation membrane material.

[0045] In some embodiments, the porosity of the core layer is 70%-80%.

[0046] In this embodiment, by setting the porosity of the core layer within the range of 70%-80%, the water storage capacity of the core layer can be controlled, enabling the replenishment of moisture to the evaporation surface, providing movable water, controlling the water transport rate of the evaporation surface, limiting the drying of moisture on the evaporation surface, and maintaining the stability of the evaporation membrane material. Furthermore, setting the porosity of the core layer within the range of 70%-80% provides sufficient water storage space to dilute salt ions, reducing the salt crystallization load on the skin layer. This synergistic effect with the skin layer improves the salt resistance of the evaporation membrane material and extends its service life.

[0047] In some embodiments, the length of the channel is 0.1cm-1cm.

[0048] In this embodiment, the length of the channel is set in the range of 0.1cm-1cm, which can control the time of horizontal migration of salt ions in the skin channel, so that salt ions can migrate along the channel of the first porous structure to the interior or edge of the skin and precipitate, thereby reducing the deposition rate of salt crystals on the evaporation surface and maintaining the evaporation rate of the evaporation film material.

[0049] In some embodiments, the pore size of the micropores is 65μm-70μm.

[0050] In this embodiment, by setting the pore size of the micropores in the range of 65μm-70μm, sufficient storage space can be provided for water, sufficient water can be provided for the evaporation surface, the water transport rate of the evaporation surface can be controlled, and the stability of the evaporation membrane material can be maintained.

[0051] Secondly, this application also provides a method for preparing an evaporation membrane material, including providing a mixed solution, the mixed solution comprising photothermal nanomaterials and polymer materials; The mixed solution was frozen at a first temperature for a first time to obtain the precursor; The precursor is frozen at a second temperature for a second time to obtain the intermediate. The intermediate is freeze-dried at a third temperature for a third time and then dried to obtain an evaporation membrane material; wherein the first temperature is (-200℃) - (-180℃). The first time is 10s-60s; The second temperature is (-40℃) - (-25℃); The second time period is 12h-24h; The third temperature is (-60℃) - (-50℃); The third time period is 36h-72h.

[0052] In this embodiment, setting the first temperature to (-200℃)-(-180℃) allows the nucleation rate of the mixed solution to exceed the growth rate. Before the ice nuclei can fully grow, the mixed solution solidifies, resulting in a porous structure in the outer layer of the evaporation membrane material. Setting the first time to 10s-60s ensures insufficient heat transfer, preventing the inner layer of the mixed solution from receiving enough heat. This causes the outer layer to solidify while the inner layer remains unsolidified, thus forming the skin structure of the evaporation membrane material. Setting the second temperature to (-40℃)-(-25℃) controls the temperature difference and reduces the freezing rate, creating a temperature gradient within the mixed solution. This allows the ice nuclei to grow into ice crystals, forming the porous structure in the core layer of the evaporation membrane material. Setting the second time to 12h-24h provides sufficient time for heat transfer, allowing the ice nuclei in the mixed solution to grow into ice crystals, thus forming the core layer of the evaporation membrane material. Setting the third temperature to (-60℃)–(-50℃) keeps the intermediate in a solid state, allowing for the direct removal of ice nuclei and crystals through sublimation, thus forming an evaporation membrane material with a porous structure. Furthermore, maintaining the third temperature at (-60℃)–(-50℃) throughout the process protects the properties of the photothermal nanomaterials and polymers, improving the performance of the evaporation membrane material. Setting the third time to 36h–72h provides sufficient time for the ice nuclei and crystals to fully sublimate, resulting in a porous structure in the evaporation membrane material.

[0053] It can be explained that the first temperature can be achieved by freezing with liquid nitrogen. The mold is immersed in liquid nitrogen to freeze the solution. Liquid nitrogen is an inert gas that is colorless, non-toxic, odorless, and non-flammable, and it is safe enough during the operation.

[0054] It can be explained that the second temperature can be achieved in several ways. For example, freezing can be done using a cold storage facility. The mold is moved into a low-temperature cold storage room, where a forced air circulation system is provided by a cold air fan. The cold storage room uses a single-stage compression refrigeration system, where the compressor compresses the low-pressure gaseous refrigerant into a high-temperature, high-pressure gas. This gas then releases heat and liquefies in the condenser, and the expansion valve reduces the pressure, causing the evaporator to absorb heat and vaporize, completing the refrigeration cycle. This freezing method is relatively slow and energy-intensive, making it suitable for mass production. Alternatively, freezing can be done using a refrigerator. It is worth noting that this refrigerator needs to be a laboratory refrigerator capable of meeting the temperature requirements. The mold is moved into the refrigerator, where the unit is connected to a heat exchange device (such as a reactor jacket). This allows the refrigerant to be cooled to the target temperature in the evaporator. A circulating pump then delivers the low-temperature refrigerant to the equipment requiring cooling, allowing the refrigerant to return to the unit for recooling after absorbing heat, achieving the desired cooling effect. This freezing method is suitable for laboratory sample preparation, is simple to operate, and the freezing process is easy to observe.

[0055] It can be noted that the third temperature can be achieved in several ways. For example, a bell-shaped freeze dryer can be used, where the mold is placed inside to rapidly freeze and solidify the solution, maintaining its structure for freeze-drying. This method is simple and economical, with the drying chamber and cold trap being separate units. The solution needs to be manually transferred after freezing, making it suitable for laboratory use. Alternatively, an in-situ freeze dryer can be used, where the mold is placed inside to rapidly freeze and solidify the solution, maintaining its structure for freeze-drying. This method features an independent freezing chamber and cold trap, shelves with refrigeration capabilities, and requires no manual intervention throughout the freezing and drying process, resulting in good process repeatability.

[0056] In some embodiments, the mass percentage of photothermal nanomaterials in the mixed solution is 0.1%-5%.

[0057] In this embodiment, setting the mass percentage of photothermal nanomaterials to 0.1%-5% allows for control over light scattering loss and photothermal efficiency, converting light energy into heat energy and increasing the evaporation rate of the evaporation film material. Furthermore, the photothermal nanomaterials act as nucleating agents in the mixed solution, influencing ice crystal growth. The surface of the photothermal nanoparticles provides nucleation sites, lowering the nucleation energy barrier. Moreover, the photothermal nanoparticles can hinder polymer chain movement and solvent diffusion, refining the porous structure, increasing porosity, and enhancing the connectivity of the porous channels, thereby improving the performance of the evaporation film material. In addition, the interface between the photothermal nanomaterials and the matrix can transfer stress, hindering crack propagation and improving the mechanical strength and toughness of the evaporation film material. The distribution of the photothermal nanomaterials can influence the location of heat generation, increasing the thermal conductivity of the evaporation film material, regulating the heat concentration area, and improving the stability of the evaporation film material.

[0058] In some embodiments, the polymeric material has a mass percentage of 0.1%-5% in the mixed solution.

[0059] In this embodiment, when the mass percentage of polymer material is set to 0.1%-5%, the polymer material can form a porous structure of the evaporation membrane material through ice crystal growth during the mixing and freeze-drying process. The mass percentage of polymer material can affect the viscosity of the mixed solution, regulate the dispersion effect of photothermal nanomaterials, reduce the agglomeration of photothermal nanomaterials, and improve the photothermal conversion performance of the evaporation membrane material.

[0060] In some embodiments, the photothermal nanomaterials include at least one of Mxene (two-dimensional transition metal carbon / nitride), graphene, graphene oxide, carbon nanotubes, iron oxide, black phosphorus, and melanin particles.

[0061] In this embodiment, Mxene (a two-dimensional transition metal carbon / nitride) was selected as the photothermal nanomaterial. This material possesses high electrical conductivity similar to metals and a unique localized surface plasmon resonance effect, resulting in a light absorption rate exceeding 90% in the ultraviolet, visible, and near-infrared range, thus providing photothermal conversion capability for the evaporation membrane material. Furthermore, its surface contains hydroxyl and oxygen hydrophilic groups, allowing it to be processed in aqueous systems and providing water storage capacity for the evaporation membrane material. Graphene was selected as the photothermal nanomaterial. This material, composed of a two-dimensional honeycomb structure of carbon atoms, provides thermal conductivity and chemical stability, enabling heat transfer to the evaporation surface of the evaporation membrane material. Graphene oxide was selected as the photothermal nanomaterial. This material has a similar structure to graphene but higher hydrophilicity, enhancing the water storage capacity of the evaporation membrane material. Carbon nanotubes were selected as the photothermal nanomaterial. This material, a one-dimensional tubular structure formed by rolling up graphene, possesses unique blackbody properties, capturing most of the incident light. It can build a three-dimensional light absorption and heat conduction network within the matrix, improving the evaporation performance and salt resistance of the evaporation membrane material. Iron oxide (Fe3O4) was chosen as the photothermal nanomaterial because it generates heat through the photothermal effect, has a mature preparation process, and low cost, thus reducing the production cost of evaporation film materials. Black phosphorus was chosen as the photothermal nanomaterial because its electron valence band and conduction band can be tuned. By controlling the number of layers, its absorption range can cover the visible to near-infrared region, improving the light absorption capacity of the evaporation film material and increasing photothermal conversion efficiency. Melanin particles were chosen as the photothermal nanomaterial because they possess broadband light absorption and non-radiative relaxation efficiency. Broadband light absorption refers to the wide range of light that melanin particles can absorb, and non-radiative relaxation means that electrons do not emit photons but instead transfer energy to the material itself through lattice vibrations (i.e., generating phonons), leading to an increase in material temperature. This method improves heat conversion efficiency and enhances the photothermal conversion efficiency of the evaporation film material.

[0062] Understandably, the aforementioned photothermal nanomaterials can be used individually or in combination, allowing their properties and commonalities to complement each other to achieve the performance required for evaporation film materials. The electronic band structure or free electrons of these materials can interact with photons, fully utilizing the solar spectrum to provide efficient photothermal conversion capabilities for evaporation film materials. Furthermore, these materials are used in the form of nanoparticles, nanosheets, and nanotubes. The nanoscale increases the specific surface area, increases the light absorption cross-section, improves the density of the nano-polymer interface, enhances phonon scattering, and forms interfacial thermal resistance, concentrating heat on the evaporation surface. The atomic structural differences between these materials and the polymer matrix can cause phonon spectrum mismatch at the crystalline (photothermal nanomaterials) and amorphous (polymer materials) interfaces, resulting in thermal localization, reducing heat loss, and improving the performance of the evaporation film material. In addition, photothermal nanomaterials possess high intrinsic strength or high modulus, and the nanoscale allows for a large interfacial bonding area, forming a three-dimensional nanonetwork, improving the mechanical strength of the evaporation film material and extending its service life.

[0063] In some embodiments, the polymeric material includes at least one of sodium alginate, polyvinyl alcohol, and chitosan.

[0064] In this embodiment, the abundant carboxyl and hydroxyl hydrophilic groups in sodium alginate endow the evaporation membrane material with good saturated water absorption and strong capillary water supply capacity, thereby improving the water storage capacity of the evaporation membrane material and maintaining the water transport rate of the evaporation surface. The good flexibility and tear resistance of polyvinyl alcohol provide flexibility to the evaporation membrane material. The amino and hydroxyl groups of chitosan allow for chemical modification, providing other properties to the evaporation membrane material.

[0065] Understandably, the aforementioned polymeric materials can be used alone or in combination, allowing their properties and commonalities to complement each other to achieve the required performance of the evaporation membrane material. These polymeric materials all contain hydrophilic functional groups, which can form strong hydrogen bonds with water molecules, resulting in excellent wettability and providing good water storage capacity for the evaporation membrane material. Furthermore, these polymeric materials have linear chain structures, and hydrogen bond networks can form between the molecular chains, ensuring continuous water transport channels and enabling the delivery of water to the evaporation surface. Moreover, these polymeric material solutions exhibit adjustable viscosity and phase separation behavior, allowing for the control of porous structures through parameters such as concentration, temperature, and solvent composition. This enables the preparation of multi-scale structures ranging from nanopores to micropores, and allows for the adjustment of the structure and proportion of the skin and core layers, thereby improving the performance of the evaporation membrane material. In addition, these polymer materials all have polar functional groups and are compatible with photothermal nanomaterials. They can combine with photothermal nanomaterials through hydrogen bonding and electrostatic interactions to form uniform nanocomposite materials without phase separation. The two work synergistically to improve the hydrophilicity, photothermal conversion efficiency and salt resistance of the evaporation membrane material.

[0066] Thirdly, embodiments of this application also provide a solar evaporator, including the evaporation film material described above; or, including the evaporation film material prepared by the method described above.

[0067] It is understood that the solar evaporator has all the beneficial effects of the above-mentioned evaporation film material or the evaporation film material prepared by the above-mentioned preparation method, and will not be elaborated further here.

[0068] It can be explained that when the evaporation membrane material is used in conjunction with the condensation device, the photothermal layer can absorb solar energy and concentrate heat on the surface of the evaporation membrane material, heating the surface water film to evaporate the water. The water vapor then condenses into fresh water on the condensation device.

[0069] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0070] I. Preparation Method Example 1 A mixed solution is provided, comprising sodium alginate and melanin particles; the mass percentage of melanin particles in the mixed solution is 2.5%, and the mass percentage of sodium alginate is 2.5%.

[0071] The mixed solution was frozen under liquid nitrogen for 15 seconds to obtain the precursor. The precursor was frozen at -25°C for 24 hours to obtain the intermediate. The intermediate was frozen at -51.5°C for 48 hours and then dried to obtain the evaporation membrane material of Example 1.

[0072] Example 2 The difference from Example 1 is that the first time is 30 seconds. The remaining steps are roughly the same as in Example 1 and will not be repeated here. The evaporation membrane material of Example 2 is obtained.

[0073] Comparative Example 1 The difference from Example 1 is that there is no first step of freezing. The remaining steps are roughly the same as in Example 1, and will not be repeated here. The evaporation membrane material of Comparative Example 1 is obtained.

[0074] Comparative Example 2 The difference from Example 1 is that the first freezing time is 120s, and there is no second freezing step. The remaining steps are roughly the same as in Example 1, and will not be repeated here. The evaporation membrane material of Comparative Example 2 is obtained.

[0075] II. Testing Methods Test method for tortuosity factor: The test is conducted using a mercury porosimeter (instrument model: AUTOPORE9600).

[0076] Porosity testing method: The test is conducted using a mercury porosimeter (instrument model: AUTOPORE9600).

[0077] Salt resistance test: at a light intensity of 1kW / m 2 Under simulated fluorescent light, a 20% sodium chloride solution was desalinated. The mass change of the entire system (including the sodium chloride solution, evaporation membrane material, and reaction vessel) was recorded using an electronic balance. The result was calculated using the formula: V = Δm / A. The evaporation rate is calculated using t (Δm is the mass of water evaporated, A is the area of ​​the evaporation film material, and t is the evaporation time).

[0078] SEM: A Hitachi SU500 scanning electron microscope was used for testing at room temperature.

[0079] III. Analysis of Test Results for Each Embodiment and Comparative Example In Example 1, the tortuosity factor of the first porous structure of the cortex is 2.4, the tortuosity factor of the second porous structure of the core is 3, the porosity of the cortex is 66%, and the porosity of the core is 76%.

[0080] Figure 9 The images show the process of the salt resistance test in Example 1. Image a shows the state of the evaporation membrane material in Example 1 after working for 1 hour. Image b shows the state of the evaporation membrane material in Example 1 after working for 4 hours. Image c shows the state of the evaporation membrane material in Example 1 after working for 6 hours. Figure 10 Images showing the salt resistance test process of Example 2: a) is a picture of the state of the evaporation membrane material of Example 2 after working for 1 hour; b) is a picture of the state of the evaporation membrane material of Example 2 after working for 4 hours; and c) is a picture of the state of the evaporation membrane material of Example 2 after working for 6 hours. Figure 11 Images showing the salt resistance test process of Comparative Example 1: a) is a picture of the state of the evaporation membrane material of Comparative Example 1 after working for 1 hour; b) is a picture of the state of the evaporation membrane material of Comparative Example 1 after working for 4 hours; and c) is a picture of the state of the evaporation membrane material of Comparative Example 1 after working for 6 hours. Figure 12 Images show the salt resistance test process of Comparative Example 2. Image a shows the state of the evaporation membrane material of Comparative Example 2 after working for 1 hour, image b shows the state of the evaporation membrane material of Comparative Example 2 after working for 4 hours, and image c shows the state of the evaporation membrane material of Comparative Example 2 after working for 6 hours. Comparing the images of Examples 1 and 2 with those of Comparative Examples 1 and 2 after working, it can be seen that the salt resistance performance of Examples 1 and 2 is better than that of Comparative Examples 1 and 2, while the salt resistance performance of Example 1 is the best.

[0081] Figure 13 This represents a comparison of the evaporation rates of Examples 1 and 2 with those of Comparative Examples 1 and 2 under the same test conditions. Figure 13 In the figure, the horizontal axis represents the sample number, and the vertical axis represents the evaporation rate (unit: kg / m³). -2 h -1 ),like Figure 13 As shown, the evaporation rate of LN-15 in Example 1 reached 3.32 kg / m³. -2 h -1 The concentration was significantly higher than that of LN-30 in Example 2 (2.89 kg / m³). -2 h -1 Comparative Example 1LN-0 (1.47 kg m³) -2 h -1 ) and comparative example 2LN-120 (0.76 kgm -2 h -1 As can be seen, Examples 1 and 2 (LN-15, LN-30) treated with the method of the present invention exhibit higher evaporation rates than Comparative Examples 1 and 2 (LN-0), indicating that this application improves the evaporation performance of the evaporation film material. Among them, Example 1 (LN-15) shows the best effect.

[0082] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. An evaporation film material, characterized in that, include: The matrix includes a skin layer and a core layer, wherein the skin layer is disposed on the peripheral surface of the core layer; The skin layer has a first porous structure, the first porous structure having a plurality of channels extending radially along the matrix; The core layer has a second porous structure, which has a plurality of micropores that are connected along the axial direction of the substrate. The first porous structure is connected to the second porous structure; The tortuosity factor of the first porous structure is smaller than that of the second porous structure.

2. The evaporation film material according to claim 1, characterized in that, The tortuosity factor of the first porous structure is 2.1-2.5; and / or, The tortuosity factor of the second porous structure is 2.8-3.

5.

3. The evaporation film material according to claim 1, characterized in that, The diameter ratio of the skin layer to the core layer is 2.5:(1.5-2).

4. The evaporation film material according to claim 1, characterized in that, The porosity of the skin layer is 60%-70%; and / or, The porosity of the core layer is 70%-80%.

5. The evaporation film material according to claim 1, characterized in that, The length of the channel is 0.1cm-1cm; and / or, The pore size of the micropores is 65μm-70µm.

6. A method for preparing an evaporation membrane material, characterized in that, include: A mixed solution is provided, the mixed solution comprising photothermal nanomaterials and polymeric materials; The mixed solution is frozen at a first temperature for a first time to obtain the precursor; The precursor is frozen at a second temperature for a second time to obtain an intermediate. The intermediate is frozen at a third temperature for a third time and then dried to obtain an evaporation membrane material; wherein the first temperature is (-200℃) - (-180℃). The first time period is 10s-60s; The second temperature is (-40℃) - (-25℃); The second time period is 12h-24h; The third temperature is (-60℃) - (-50℃); The third time period is 36h-72h.

7. The method for preparing the evaporation film material according to claim 6, characterized in that, In the mixed solution, the mass percentage of the photothermal nanomaterial is 0.1%-5%.

8. The method for preparing the evaporation film material according to claim 6, characterized in that, In the mixed solution, the polymeric material has a mass percentage of 0.1%-5%.

9. The method for preparing the evaporation film material according to claim 6, characterized in that, The photothermal nanomaterials include at least one of Mxene (two-dimensional transition metal carbon / nitride), graphene, graphene oxide, carbon nanotubes, iron oxide, black phosphorus, and melanin particles; and / or, The polymeric material includes at least one of sodium alginate, polyvinyl alcohol, and chitosan.

10. A solar evaporator, characterized in that, Includes the evaporation film material as described in any one of claims 1-5; or, The evaporation membrane material prepared by the method for preparing the evaporation membrane material as described in any one of claims 6-9 includes the evaporation membrane material prepared according to any one of claims 6-9.

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