Nanofiber aerogel composite for seawater desalination and method of making the same

Abstract

This invention provides a nanofiber aerogel composite material for seawater desalination and its preparation method. The composite material includes an aerogel matrix with a vertical pore structure and a photothermal conversion layer, the photothermal conversion layer being composed of magnetic microneedles arranged in an array. This invention prepares a nanofiber aerogel with a vertical pore structure using nanofiber / polymer materials, and directionally grows magnetic microneedles with strong photothermal properties on the aerogel surface, resulting in a nanofiber aerogel composite material with high water absorption rate, evaporation rate, and photothermal conversion rate, suitable for seawater purification. When this nanofiber aerogel composite material is used for seawater desalination, the aerogel matrix with the vertical pore structure contacts the seawater surface, and the magnetic microneedles of the photothermal conversion layer absorb solar energy, converting it into heat. This allows water to be transported along the vertical pores and converted into steam, achieving the purpose of seawater desalination, which is of great significance for solving the problem of water scarcity.

Description

Technical Field

[0001] This invention relates to the field of seawater desalination technology, and in particular to a nanofiber aerogel composite material for seawater desalination and its preparation method. Background Technology

[0002] With the rapid development of the global economy, freshwater scarcity has become a serious threat to the sustainable development of human society. Two-thirds of the world's population experiences severe water shortages for at least one month each year, and 500 million people face water scarcity year-round. Therefore, seawater desalination has become an important way to solve water shortages. Seawater desalination, which uses seawater to produce freshwater, is an incremental technology for water resource utilization, increasing the total amount of freshwater and is unaffected by time, space, or climate. Currently, seawater desalination methods include seawater freezing, electrodialysis, distillation, reverse osmosis, and ammonium carbonate ion exchange, among others; reverse osmosis and distillation are the mainstream methods in the seawater desalination market. Due to the abundance, renewability, and environmental friendliness of solar energy, solar-driven interfacial evaporation technology has stood out among many freshwater production technologies and is considered the most promising and environmentally friendly method for alleviating global water shortages.

[0003] In the prior art, scholars in related fields have designed and developed many solar evaporators with porous structures. For example, invention patent (application number CN 202210933461.9) discloses a method for preparing a sandwich-type long-lasting salt-barrier gel photothermal evaporator. This gel photothermal evaporator consists of an inorganic metal salt-nano carbon composite aerogel as the upper light absorption layer, an inorganic metal salt water gel as the lower water supply layer, and an intermediate hydrophobic layer. Simultaneously, fabric fibers are added during the gel preparation process to enhance mechanical strength to meet application requirements. However, the evaporator in this invention patent uses a combination of aerogel and hydrogel, resulting in an irregular and limited number of pores. Since the pore structure is crucial for steam diffusion and water transport within the evaporator, the seawater purification effect of this evaporator is not ideal and cannot meet the efficiency requirements of industrial seawater purification.

[0004] In view of this, it is necessary to design an improved nanofiber aerogel composite material for seawater desalination and its preparation method to solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to provide a nanofiber aerogel composite material for seawater desalination and its preparation method. The method involves preparing a nanofiber aerogel with a vertical pore structure using nanofiber / polymer materials, and directionally growing magnetic microneedles with strong photothermal properties on the surface of the aerogel to obtain a nanofiber aerogel composite material with high water absorption rate, evaporation rate, and photothermal conversion rate that can be used for seawater desalination.

[0006] To achieve the above-mentioned objectives, the present invention provides a nanofiber aerogel composite material for seawater desalination. The nanofiber aerogel composite material includes an aerogel matrix and a photothermal conversion layer loaded on the aerogel matrix. The photothermal conversion layer is composed of a plurality of magnetic microneedles loaded on the surface of the aerogel matrix. The magnetic microneedles are arranged in an array structure. The aerogel matrix contains a vertical channel structure.

[0007] As a further improvement of the present invention, the height of the magnetic microneedle is 500-2000 μm; the magnetic microneedle is composed of magnetic particles and resin, and the size of the magnetic particles is 50-1000 nm.

[0008] As a further improvement of the present invention, the aerogel matrix is ​​a nanofiber aerogel, and the nanofibers in the nanofiber aerogel are one or more of PVA-co-PE nanofibers, polyester fibers, and nylon nanofibers; the diameter of the nanofibers is 100-400 nm.

[0009] As a further improvement of the present invention, the magnetic particles are one or more of iron(II,III) oxide and carbonyl iron powder; the resin is one or more of polydimethylsiloxane and epoxy resin.

[0010] The present invention also provides a method for preparing the nanofiber aerogel composite material for seawater desalination as described in any one of the above-mentioned methods, comprising the following steps:

[0011] S1. Mix polymer A, crosslinking agent and nanofiber suspension evenly to obtain a mixture, and place the mixture in a mold for freezing and shaping;

[0012] S2. Freeze-dry the mixture after freezing and shaping in step S1 to obtain nanofiber aerogel with vertical pore structure.

[0013] S3. A resin solution containing magnetic particles is sprayed onto the surface I of the nanofiber aerogel obtained in step S2. The surface I is a surface perpendicular to the vertical channel structure. During the spraying process, a magnetic field perpendicular to the surface I is applied. After drying, a nanofiber aerogel composite material with a surface-loaded magnetic microneedle array structure is obtained.

[0014] As a further improvement of the present invention, in step S3, the mass percentage concentration of magnetic particles in the resin solution is 10wt% to 30wt%, and the size is 50 to 1000 nm; the resin solution also includes one or more of polydimethylsiloxane and epoxy resin, and the solvent of the resin solution is toluene.

[0015] As a further improvement of the present invention, in step S1, the polymer A includes one of polyacrylamide, chitosan, polyethyleneimine, polylysine, and polydopamine; in the mixture, the mass percentage concentration of the polymer A is 1 wt% to 10 wt%.

[0016] As a further improvement of the present invention, in step S2, the freeze-drying time is 24 to 72 hours and the temperature is -80 to -60°C.

[0017] As a further improvement of the present invention, in step S1, the mass percentage concentration of nanofibers in the nanofiber suspension is 1wt% to 5wt%; the freezing and setting time is 6 to 48 hours, and the temperature is -80 to -60°C.

[0018] As a further improvement of the present invention, in step S1, the crosslinking agent is one of glutaraldehyde, dialdehyde, and polyvinylpyrrolidone; the method for uniformly mixing the polymer A, the crosslinking agent, and the nanofiber suspension is magnetic stirring or ultrasonic treatment; in the mixture, the mass percentage concentration of the crosslinking agent is 0.5wt% to 3wt%.

[0019] The beneficial effects of this invention are:

[0020] 1. This invention provides a nanofiber aerogel composite material for seawater desalination, comprising an aerogel matrix and a photothermal conversion layer loaded on the aerogel matrix. The photothermal conversion layer is composed of a plurality of magnetic microneedles loaded on the surface of the aerogel matrix, the magnetic microneedles being in an array structure, and the aerogel matrix containing a vertical pore structure. This invention prepares a nanofiber aerogel with a vertical pore structure using nanofiber / polymer materials, and directionally grows magnetic microneedles with strong photothermal properties on the aerogel surface to obtain a nanofiber aerogel composite material with high water absorption rate, evaporation rate, and photothermal conversion rate, suitable for seawater purification. When this nanofiber aerogel composite material is used for seawater desalination, the aerogel matrix with the vertical pore structure contacts the seawater surface, and the magnetic microneedles of the photothermal conversion layer absorb solar energy, converting it into heat, causing water to be transported along the vertical pores and converted into steam to escape, thus achieving the purpose of seawater desalination.

[0021] 2. The matrix of the composite material of this invention is an aerogel with a vertical pore structure. Its pore structure is uniform and continuous, which can utilize capillary action to promote water transport, increase the energy of water molecules, and thus lower the evaporation barrier, facilitating water evaporation. Furthermore, the photothermal conversion layer is made by mixing magnetic particles with a resin solution and spraying it onto the surface of the aerogel matrix. Under the induction of a magnetic field, the magnetic particles drive the resin to grow in a regular and orderly arranged needle-like microneedle structure. This microneedle structure has a large specific surface area, absorbs solar energy strongly, and the black magnetic particles absorb heat more quickly, which is conducive to the generation of local high temperatures, promoting water evaporation. The magnetic microneedle structure also has strong hydrophobicity, resulting in high water vapor generation efficiency. This invention also uses a mixture of resin solution and magnetic particles as the photothermal conversion layer. The resin also acts as a connector between the photothermal conversion layer and the aerogel matrix, resulting in a nanofiber aerogel composite material with good integrity and strong practicality.

[0022] 3. In preparing the aerogel matrix, this invention adds specific polymers to adjust the pore structure of the aerogel, causing the disordered pore structure to become vertically oriented. By controlling the type and content of polymers, a three-dimensional network structure of vertically oriented pores similar to lignin is obtained, which is beneficial for the rapid transport of water molecules. Furthermore, nanofiber suspension is used as the main material of the aerogel. The nanofibers play a skeletal role in the aerogel, improving the mechanical properties of the composite material and making it more suitable for industrial production of seawater desalination. This is of great significance for solving the problem of water shortage. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the preparation method of a nanofiber aerogel composite material for seawater desalination according to the present invention.

[0024] Figure 2 Macroscopic and microscopic photographs of the composite material prepared in Example 1 of this invention, surface affinity and temperature distribution of the material surface under xenon lamp irradiation.

[0025] Figure 3 The diagram shows the seawater desalination process of the composite material prepared in Example 1 of this invention under simulated sunlight irradiation by a xenon lamp, and the seawater evaporation rate curves tested at different times.

[0026] Figure 4 The images show the electron microscope images of the nanofiber aerogel composite materials prepared in Example 1 and Comparative Example 1.

[0027] Figure 5 Photographs showing an experiment comparing the water absorption rates of the nanofiber aerogel composite materials prepared in Example 1 and Comparative Example 1.

[0028] Figure 6Microscopic electron microscope images of the nanofiber aerogel composite materials prepared in Examples 1-3 and Comparative Examples 1-3. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0030] It should also be noted that, in order to avoid obscuring the present invention with unnecessary details, only the structures and / or processing steps closely related to the present invention are shown in the accompanying drawings, while other details that are not closely related to the present invention are omitted.

[0031] Additionally, it should be noted that the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0032] A nanofiber aerogel composite material for seawater desalination includes an aerogel matrix and a photothermal conversion layer loaded on the aerogel matrix. The photothermal conversion layer consists of a plurality of magnetic microneedles arrayed on the surface of the aerogel matrix. The aerogel matrix contains a vertical pore structure. The matrix of this nanofiber aerogel composite material is an aerogel with a vertical pore structure. Its pore structure is uniform and continuous, which can promote water transport through capillary action, increasing the energy of water molecules and thus lowering the evaporation barrier, which is beneficial for water evaporation. When the composite material is used for seawater desalination, the aerogel matrix with the vertical pore structure contacts the seawater surface. The magnetic microneedles of the photothermal conversion layer absorb solar energy and convert it into heat, causing water to be transported along the vertical pores and converted into steam for escape, thus achieving the purpose of seawater desalination.

[0033] Specifically, the height of the magnetic microneedles is 500–2000 μm; the magnetic microneedles are composed of magnetic particles and resin, and the size of the magnetic particles is 50–1000 nm. The height of the magnetic microneedles determines the strength of the photothermal conversion performance of the nanofiber aerogel composite material. However, the height of the magnetic microneedles cannot be too high. Excessively high magnetic microneedles will not only affect heat transfer but also be detrimental to the mechanical properties of the composite material, thus reducing its practicality.

[0034] In some specific embodiments, the magnetic particles are one or more of iron(II,III) oxide and carbonyl iron powder; the resin is one or more of polydimethylsiloxane and epoxy resin.

[0035] Specifically, the aerogel matrix is ​​a nanofiber aerogel, and the nanofibers are one or more of PVA-co-PE nanofibers, polyester fibers, and nylon nanofibers; the diameter of the nanofibers is 100-400 nm. The nanofibers can act as a skeleton in the aerogel, improving the mechanical properties of the aerogel composite material and making it more suitable for industrial production in seawater desalination, which is of great significance for solving the problem of water shortage.

[0036] Please see Figure 1 As shown, the present invention also provides a method for preparing a nanofiber aerogel composite material for seawater desalination, comprising the following steps:

[0037] S1. Mix polymer A, crosslinking agent and nanofiber suspension evenly to obtain a mixture, and place the mixture in a mold for freezing and shaping;

[0038] S2. Freeze-dry the mixture after freezing and shaping in step S1 to obtain nanofiber aerogel with vertical pore structure.

[0039] S3. A resin solution containing magnetic particles is sprayed onto the surface I of the nanofiber aerogel obtained in step S2. Surface I is a surface perpendicular to the vertical channel structure. A magnetic field perpendicular to surface I is applied during the spraying process. After drying, a nanofiber aerogel composite material with a magnetic microneedle array structure loaded on the surface is obtained. The direction of the magnetic field is perpendicular to surface I and points from the nanofiber aerogel to the sprayed resin solution. In this way, the magnetic field can induce the resin solution to grow away from the growth of the nanofiber aerogel, so that it grows into a magnetic microneedle array structure.

[0040] Specifically, this invention prepares nanofiber aerogels with vertical pore structures using nanofiber / polymer materials, and directionally grows magnetic microneedles with strong photothermal properties on the aerogel surface to obtain a nanofiber aerogel composite material with high water absorption rate, evaporation rate, and photothermal conversion rate, suitable for seawater purification. The photothermal conversion layer is made by mixing magnetic particles with a resin solution, spraying it onto the aerogel matrix surface, and under the induction of a magnetic field, the magnetic particles drive the resin to grow in a regular and orderly arranged needle-like microneedle structure. This microneedle structure has a large specific surface area, absorbs solar energy strongly, and the black magnetic particles absorb heat more quickly, which is conducive to the generation of local high temperatures and promotes water evaporation. Furthermore, the magnetic microneedle structure has strong hydrophobicity, resulting in high water vapor generation efficiency. This invention also uses a mixture of resin solution and magnetic particles as the photothermal conversion layer, where the resin also acts as a connector between the photothermal conversion layer and the aerogel matrix, resulting in a nanofiber aerogel composite material with good integrity and strong practicality.

[0041] Specifically, in step S3, the mass percentage concentration of magnetic particles in the resin solution is 10wt%–30wt%, and the size is 50–1000 nm. By adjusting the concentration of magnetic particles, the growth height of the magnetic microneedle array structure is controlled, thereby obtaining a nanofiber aerogel composite material with excellent photothermal conversion efficiency. The resin solution also includes one or more of polydimethylsiloxane and epoxy resin, and the solvent of the resin solution is toluene.

[0042] In step S1, polymer A includes one of polyacrylamide, chitosan, polyethyleneimine, polylysine, and polydopamine; the mass percentage concentration of polymer A in the mixture is 1 wt% to 10 wt%. When preparing the aerogel matrix, specific polymers are added to adjust the pore structure of the aerogel, causing the disordered pore structure to become vertically oriented. By controlling the type and content of the polymer, a three-dimensional network structure of vertically oriented pores, similar to lignin, is obtained, which is beneficial for the rapid transport of water molecules. Polymer A is preferably polyacrylamide, and its content is preferably 1.5 wt%.

[0043] Specifically, in step S2, the freeze-drying time is 24–72 h, and the temperature is -80 to -60 °C. In step S1, the mass percentage concentration of nanofibers in the nanofiber suspension is 1 wt%–5 wt%; the freeze-setting time is 6–48 h, and the temperature is -80 to -60 °C. The freeze-drying parameters and the concentration of nanofibers both affect the pore structure of the aerogel. Controlling the freeze-drying parameters and the concentration of nanofibers is beneficial for forming a pore structure with a distinct vertical orientation.

[0044] As a further improvement of the present invention, in step S1, the crosslinking agent is one of glutaraldehyde, dialdehyde, and polyvinylpyrrolidone; the method for uniformly mixing polymer A, crosslinking agent and nanofiber suspension is magnetic stirring or ultrasonic treatment; in the mixture, the mass percentage concentration of crosslinking agent is 0.5wt% to 3wt%.

[0045] In some specific implementations, the magnetic stirring time is 30 to 60 minutes.

[0046] Example 1

[0047] This embodiment provides a method for preparing a nanofiber aerogel composite material for seawater desalination, including the following steps:

[0048] S1. Polyacrylamide (PAM), glutaraldehyde, and PVA-co-PE nanofiber suspension are mixed and magnetically stirred for 40 minutes to obtain a homogeneous mixture. The mixture is then placed in a mold and frozen to set. The mixture contains 1.5 wt% polyacrylamide, 3 wt% PVA-co-PE nanofibers, and 1 wt% glutaraldehyde. The freezing temperature is -80℃, and the freezing time is 6 hours. The average diameter of the PVA-co-PE nanofibers is 200 nm.

[0049] S2. Freeze-dry the mixture after freeze-setting in step S1 for 48 hours at a temperature of -60°C to obtain nanofiber aerogel with vertical pore structure.

[0050] S3. A polydimethylsiloxane and toluene resin solution containing magnetite particles is sprayed onto surface I of the nanofiber aerogel obtained in step S2. Surface I is a surface perpendicular to the vertical channel structure. During the spraying process, a magnetic field perpendicular to surface I is applied. After drying, a nanofiber aerogel composite material with a magnetic microneedle array structure loaded on the surface is obtained. The height of the magnetic microneedles is 1000 μm. The concentration of magnetic particles in the resin solution is 20 wt%, and the average size is 1000 nm.

[0051] A schematic diagram of the preparation of the nanofiber aerogel composite material with seawater desalination capability in this embodiment is shown below. Figure 1 As shown, firstly, nanofibers are subjected to high-speed shearing to obtain a nanofiber suspension. After adding a crosslinking agent and polyacrylamide and mixing, the crosslinked fiber suspension is placed in a freeze dryer. By controlling the amount of polyacrylamide added and the freeze-drying time, a lignin-like nanofiber aerogel is prepared. Then, a resin solution containing magnetic particles is sprayed onto the surface of the aerogel to form a nanofiber aerogel composite material with a magnetic microneedle array structure on the surface.

[0052] Please see Figure 2 Figure 1 shows macroscopic and microscopic photographs, surface affinity / repulsion images, and temperature distribution diagrams of the composite material prepared in Example 1 under xenon lamp irradiation. (a) shows the macroscopic and microscopic photographs, and the surface affinity / repulsion image, respectively. (b) shows the temperature distribution diagram of the material surface under xenon lamp irradiation. Figure (a) shows that the upper layer of the composite material is a hydrophobic black magnetic microneedle array structure, and the lower layer is a superhydrophilic aerogel with a lignin-like structure that is easily processed into various shapes. Figure (b) shows that the initial temperature of the composite material is 24℃. After 10 minutes of xenon lamp irradiation, the surface temperature reaches 114.2℃, and after 60 minutes of xenon lamp irradiation, the surface temperature is still around 110℃. This result demonstrates that the magnetic microneedle array structure has excellent photothermal conversion properties.

[0053] Please see Figure 3 Figure 1 shows the desalination process of the composite material prepared in Example 1 under simulated sunlight irradiation with a xenon lamp, and the seawater evaporation rate curves tested at different times. Figure (a) shows the desalination process, and Figure (b) shows the seawater evaporation rate curve. Figure (a) shows that the composite material can float on the water surface with obvious steam escaping from the surface. Figure (b) shows that under one simulated solar irradiation, the evaporation rate of the composite material can reach a maximum of 3.5 kgm³. -2 h -1 .

[0054] Comparative Example 1

[0055] Comparative Example 1 provides a method for preparing a nanofiber aerogel composite material for seawater desalination. The difference from Example 1 is that polyacrylamide was not added in step S1. The rest is roughly the same as Example 1 and will not be repeated here.

[0056] Please see Figure 4 The figures show electron micrographs of the nanofiber aerogel composite materials prepared in Example 1 and Comparative Example 1, where (a) is Comparative Example 1 and (b) is Example 1. As can be seen from the figures, without the addition of polyacrylamide, the PVA-co-PE nanofibers intertwine to form a typical disordered three-dimensional network structure under the action of the crosslinking agent glutaraldehyde. When polyacrylamide is added to the nanofiber suspension in Example 1, the PVA-co-PE nanofibers form a vertically oriented three-dimensional network structure similar to lignin.

[0057] Figure 5 These are photographs comparing the water absorption rates of the nanofiber aerogel composite materials prepared in Example 1 and Comparative Example 1, where (a) is Comparative Example 1 and (b) is Example 1. Figure 5 It can be seen that after 120s of water absorption time, the water absorption height of PVA-co-PE nanofiber aerogel with oriented channels is significantly higher than that of PVA-co-PE nanofiber aerogel with disordered channels. This result confirms that the vertically oriented channel structure is beneficial to water transport.

[0058] Comparative Examples 2-3

[0059] Comparative Examples 2 and 3 provide a method for preparing a nanofiber aerogel composite material for seawater desalination. The difference from Example 1 is that in step S1, the mass percentage concentration of polyacrylamide is 0.1 wt% and 0.5 wt%, respectively. The rest is roughly the same as in Example 1 and will not be repeated here.

[0060] Examples 2-3

[0061] Examples 2 and 3 provide a method for preparing a nanofiber aerogel composite material for seawater desalination. The difference from Example 1 is that in step S1, the mass percentage concentration of polyacrylamide is 1.0 wt% and 2.0 wt%, respectively. The rest is roughly the same as in Example 1 and will not be repeated here.

[0062] Please see Figure 6 The figures show electron micrographs of the nanofiber aerogel composites prepared in Examples 1-3 and Comparative Examples 1-3, where (a) and (a1) are Comparative Example 1, (b) and (b1) are Comparative Example 2, (c) and (c1) are Comparative Example 3, (d) and (d1) are Example 2, (e) and (e1) are Example 1, and (f) and (f1) are Example 3. As can be seen from the figures, with the increase of polyacrylamide content, the PVA-co-PE nanofibers gradually transform from an initially intertwined, disordered three-dimensional network structure to a vertically oriented three-dimensional network structure similar to lignin. The higher the polyacrylamide content, the more pronounced the vertical orientation. It should be noted that the polyacrylamide content should not be excessive, as too much will result in a larger pore size, making the composite material more porous and adversely affecting its mechanical properties.

[0063] Comparative Example 4

[0064] Comparative Example 4 provides a nanofiber aerogel composite material for seawater desalination and its preparation method. Compared with Example 1, the difference is that in step S3, after spraying a polydimethylsiloxane and toluene resin solution containing ferric oxide magnetic particles onto the surface I of the nanofiber aerogel, it is directly dried to obtain a photothermal coating. The rest is roughly the same as in Example 1, and will not be described again here.

[0065] Comparative Example 5

[0066] Comparative Example 5 provides a nanofiber aerogel composite material for seawater desalination and its preparation method. Compared with Example 1, the difference is that in step S3, the concentration of magnetic particles in the resin solution is 5 wt%, so that the height of the magnetic microneedles in the obtained composite material is 200 μm. The rest is roughly the same as in Example 1, and will not be repeated here.

[0067] Comparative Example 6

[0068] Comparative Example 6 provides a nanofiber aerogel composite material for seawater desalination and its preparation method. Compared with Example 1, the difference is that in step S3, the concentration of magnetic particles in the resin solution is 35%, so that the height of the magnetic microneedles in the obtained composite material is 2500 μm. The rest is roughly the same as Example 1, and will not be repeated here.

[0069] Comparative Example 7

[0070] Comparative Example 7 provides a nanofiber aerogel composite material for seawater desalination and its preparation method. The difference from Example 1 is that in step S3, only the magnetic particles are mixed with toluene for spraying. The rest is roughly the same as Example 1 and will not be repeated here.

[0071] The nanofiber aerogel composite materials prepared in Examples 1 and Comparative Examples 4-7 were tested for seawater evaporation rate and evaporation efficiency. The results are shown in the table below.

[0072] Table 1. Properties of nanofiber aerogel composite materials in Examples 1 and Comparative Examples 4–7

[0073] Example 1 3.5 93.5 Comparative Example 4 2.1 81.6 Comparative Example 5 2.7 84.5 Comparative Example 6 2.3 78.3 Comparative Example 7 1.8 73.9

[0074] As shown in Table 1, the evaporation rate and efficiency of the nanofiber aerogel composite material prepared in Example 1 are superior to those prepared in Comparative Examples 4-7, demonstrating excellent performance in seawater desalination and effectively alleviating water shortages. In Comparative Example 4, no magnetic field was applied, and the photothermal coating was directly obtained. The photothermal performance of the resulting composite material was inferior to that of the composite material in Example 1, which was loaded with arrayed magnetic microneedles. Comparative Examples 5-6 show that the concentration of magnetic particles affects the growth height of the magnetic microneedles; excessively high or low heights are detrimental to the maximum evaporation rate and efficiency of the aerogel composite material. Comparative Example 7 lacked resin, making it difficult to grow a magnetic microneedle structure, resulting in a poor photothermal performance of the aerogel composite material.

[0075] In summary, this invention provides a nanofiber aerogel composite material for seawater desalination and its preparation method. The nanofiber aerogel composite material includes an aerogel matrix and a photothermal conversion layer loaded on the aerogel matrix. The photothermal conversion layer is composed of a plurality of magnetic microneedles loaded on the surface of the aerogel matrix, and the magnetic microneedles are arranged in an array structure. The aerogel matrix contains a vertical channel structure. This invention prepares nanofiber aerogel with a vertical channel structure through nanofiber / polymer materials, and directionally grows magnetic microneedles with strong photothermal properties on the surface of the aerogel to obtain a nanofiber aerogel composite material with high water absorption rate, evaporation rate, and photothermal conversion rate, which can be used for seawater purification. When this nanofiber aerogel composite material is used for seawater desalination, the aerogel matrix with the vertical channel structure contacts the seawater surface, and the magnetic microneedles of the photothermal conversion layer absorb solar energy and convert it into heat, causing water to be transported along the vertical channels and converted into steam to escape, thus achieving the purpose of seawater desalination. This is of great significance for solving the problem of water shortage.

[0076] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for the preparation of nanofibrous aerogel composites for seawater desalination, characterized by, The nanofiber aerogel composite material includes an aerogel matrix and a photothermal conversion layer loaded on the aerogel matrix. The photothermal conversion layer is composed of a plurality of magnetic microneedles loaded on the surface of the aerogel matrix. The magnetic microneedles are in an array structure. The aerogel matrix contains a vertical channel structure. The height of the magnetic microneedles is 500~2000μm. The magnetic microneedles are composed of magnetic particles and resin. The size of the magnetic particles is 50~1000nm. The preparation method includes the following steps: S1. Polymer A, crosslinking agent and nanofiber suspension are mixed evenly to obtain a mixture, and the mixture is placed in a mold for freezing and shaping; in the mixture, the mass percentage concentration of polymer A is 1wt%~10wt%, and polymer A is polyacrylamide; S2. Freeze-dry the mixture after freezing and shaping in step S1 to obtain nanofiber aerogel with vertical pore structure. S3. A resin solution containing magnetic particles is sprayed onto surface I of the nanofiber aerogel obtained in step S2. Surface I is a surface perpendicular to the vertical channel structure. A magnetic field perpendicular to surface I is applied during the spraying process. After drying, a nanofiber aerogel composite material with a surface-loaded magnetic microneedle array structure is obtained. The mass percentage concentration of magnetic particles in the resin solution is 10wt%~30wt%, and the size is 50~1000nm. The resin solution also includes one or more of polydimethylsiloxane and epoxy resin. The solvent of the resin solution is toluene.

2. The method for the preparation of nanofibrous aerogel composite for seawater desalination as claimed in claim 1, wherein, The aerogel matrix is ​​a nanofiber aerogel, wherein the nanofibers are one or more of PVA-co-PE nanofibers, polyester fibers, and nylon nanofibers; the diameter of the nanofibers is 100~400nm.

3. The method for the preparation of nanofibrous aerogel composite for seawater desalination as claimed in claim 1, wherein, The magnetic particles are one or more of iron(II,III) oxide and carbonyl iron powder.

4. The method for the preparation of nanofibrous aerogel composite for seawater desalination as claimed in claim 1, wherein, In step S2, the freeze-drying time is 24~72h and the temperature is -80~-60℃.

5. The method for the preparation of nanofibrous aerogel composite for seawater desalination as claimed in claim 1, wherein, In step S1, the mass percentage concentration of nanofibers in the nanofiber suspension is 1wt%~5wt%; the freeze-setting time is 6~48h, and the temperature is -80~-60℃.

6. The method for the preparation of nanofibrous aerogel composite for seawater desalination as claimed in claim 1, wherein, In step S1, the crosslinking agent is glutaraldehyde; the method for uniformly mixing the polymer A, the crosslinking agent, and the nanofiber suspension is magnetic stirring or ultrasonic treatment; in the mixture, the mass percentage concentration of the crosslinking agent is 0.5wt%~3wt%.

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