Nanofiber-based aerogels and methods of making and using the same

Abstract

The application provides a nanofiber-based aerogel and a preparation method and application thereof, relates to the technical field of aerogels, and the preparation method of the nanofiber-based aerogel comprises the following steps: electrospinning a polymer-containing spinning solution to obtain a nanofiber membrane; performing mechanical dispersion treatment on the nanofiber membrane to obtain a nanofiber suspension; and after mixing the nanofiber suspension with a functional nanomaterial, performing solidification to obtain the nanofiber-based aerogel. The electrospun nanofiber is peeled off, cut and then reassembled into a three-dimensional porous block (i.e. an aerogel), which not only retains the advantages of a high specific surface area and connected pores of the nanofiber membrane, but also significantly reduces water flow resistance by constructing a three-dimensional network, and meanwhile, the heat insulation performance is enhanced. The structure can more effectively realize fast water supply and low heat loss, reduce the accumulation of salt on the surface of the material, and thus improve the stability and efficiency of interfacial water evaporation.

Description

Technical Field

[0001] This invention relates to the field of aerogel technology, and in particular to a nanofiber-based aerogel, its preparation method, and its applications. Background Technology

[0002] Interfacial water evaporation technology, as a highly efficient and low-energy solution for seawater desalination and wastewater purification, hinges on the development of photothermal conversion materials capable of rapid water supply, efficient light absorption, adequate heat insulation, and low salinity accumulation. Early and current research has largely utilized natural wood, sponges, or porous carbon materials obtained through carbonized commercial sponges as interfacial water evaporation materials. These materials offer advantages such as abundant raw materials, low cost, and a certain degree of pore structure. However, their structure is often difficult to precisely control, resulting in uneven pore distribution, leading to tortuous and inefficient water transport channels. Furthermore, their photothermal conversion performance relies on overall heating, resulting in significant heat loss, and they are prone to structural collapse or salt blockage during use, leading to performance degradation.

[0003] With the development of nanotechnology, electrospun nanofiber membranes have been applied in the field of interfacial water evaporation. Nanofiber membranes prepared by electrospinning technology possess a high specific surface area and interconnected pores, which are beneficial for water transport. Current technologies typically use these nanofiber membranes directly as a substrate or after coating with photothermal materials as a light-absorbing surface and evaporation interface. However, this dense two-dimensional membrane structure often presents significant resistance to water flow and has limited thermal insulation properties. Summary of the Invention

[0004] One of the objectives of this invention is to provide a method for preparing nanofiber-based aerogels, so as to at least solve one of the technical problems existing in the prior art.

[0005] The second objective of this invention is to provide a nanofiber-based aerogel.

[0006] The third objective of this invention is to provide an application of nanofiber-based aerogel in the preparation of seawater desalination products for interfacial water evaporation.

[0007] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0008] In a first aspect, the present invention provides a method for preparing nanofiber-based aerogels, comprising the following steps:

[0009] (a) Electrospinning a polymer-containing spinning solution to obtain a nanofiber membrane; wherein the spinning solution is obtained by dissolving the polymer in a solvent; the polymer includes one or more of polyvinylidene fluoride, polysulfone, and thermoplastic polyurethane;

[0010] (b) The nanofiber membrane is mechanically dispersed to obtain a short nanofiber suspension;

[0011] (c) After mixing the nanofiber suspension with functional nanomaterials, the mixture is solidified to obtain the nanofiber-based aerogel;

[0012] The functional nanomaterials include one or more of multi-walled carbon nanotubes, carbon black, activated carbon, and graphite.

[0013] Furthermore, the solvent includes one or both of N,N-dimethylformamide and N,N-dimethylacetamide;

[0014] In the spinning solution, the polymer has a mass fraction of 15%-25%;

[0015] During the electrospinning process, the flow rate of the injection pump used is 25-30 μL·min. -1 The spinneret voltage is 18-21kV.

[0016] Specifically, electrospinning is a technique that uses high-voltage electrostatic force to prepare ultrafine fibers. Its core lies in overcoming the surface tension of polymer solutions or melts through an electric field, forming and stretching a jet, which is then solidified to obtain nano- to micron-sized fibers. For example... Figure 1 As shown, in the electrospinning process, an injection pump pushes a syringe loaded with polymer solution at a constant rate, causing the spinning solution to be smoothly extruded from the needle tip. Simultaneously, a high-voltage power supply connected to the needle tip applies a DC voltage of tens of thousands of volts, charging the droplet at the needle tip. When the electric field force exceeds the surface tension of the liquid, a charged jet is ejected from the apex of the cone. This jet, en route to the grounded receiving plate, undergoes violent stretching and thinning due to the electric field and its own instability, accompanied by solvent evaporation, ultimately solidifying and depositing on the receiving plate to form a nanofiber membrane. The entire process is driven by a high-voltage electric field, enabling continuous preparation from solution to ultrafine fibers.

[0017] Furthermore, the process includes a pretreatment of the nanofiber membrane prior to the mechanical dispersion process.

[0018] The pretreatment includes solvent wetting, wherein the solvent used in the solvent wetting process includes at least one of ethanol, propylene glycol, butanediol, and tert-butanol.

[0019] Furthermore, the mechanical dispersion process includes: mechanical shearing and ultrasonic disruption.

[0020] The power of the mechanical shearing process is 180-250 W;

[0021] The power of the ultrasonic fragmentation process is 600-700 W;

[0022] The mechanical dispersion process takes 3-10 minutes;

[0023] The ultrasonic disruption process is carried out in a dispersion medium; the dispersion medium includes deionized water or an aqueous ethanol solution; the volume fraction of the aqueous ethanol solution is 10%-20%.

[0024] Furthermore, the fiber content of the nanofiber suspension is 8-20 mg / ml.

[0025] Furthermore, the nanofiber suspension is mixed with the functional nanomaterial to obtain a functional electrospun short fiber suspension;

[0026] In the functional electrospun short fiber suspension, the mass fraction of the functional nanomaterial is 0.15%-3%.

[0027] Furthermore, the curing includes freeze curing; the freeze curing is performed using a low-temperature medium.

[0028] The cryogenic medium includes at least one of dry ice-ethanol mixture and liquid nitrogen.

[0029] Furthermore, after the functional electrospun short fiber suspension is solidified, it is dried.

[0030] The drying process includes freeze drying; the freeze drying process takes 24-72 hours.

[0031] Secondly, the present invention provides a nanofiber-based aerogel, which is prepared by the aforementioned preparation method.

[0032] Thirdly, the present invention provides the application of nanofiber-based aerogel in the preparation of seawater desalination products for interfacial water evaporation.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] The present invention provides a method for preparing nanofiber-based aerogels. This method involves mechanically dispersing a nanofiber membrane obtained from electrospinning to obtain a short nanofiber suspension, then combining it with functional nanomaterials and curing it to construct a three-dimensional network structure. The resulting aerogel material possesses high specific surface area, interconnected pore structure, and excellent photothermal properties. This preparation method involves peeling and cutting the electrospun nanofibers, then reassembling them into a three-dimensional porous mass (i.e., aerogel). The aerogel not only retains the advantages of the high specific surface area and interconnected pores of the nanofiber membrane, but also significantly reduces water flow resistance and enhances thermal insulation performance by constructing a three-dimensional network. This structure enables more effective rapid water supply and low heat loss, reduces salt accumulation on the material surface, and thus improves the stability and efficiency of interfacial water evaporation. Attached Figure Description

[0035] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0036] Figure 1 This is a flowchart illustrating the preparation process of electrospun short fiber-based aerogels according to an embodiment of the present invention.

[0037] Figure 2 This is a photograph of the actual solar-powered seawater desalination testing device.

[0038] Figure 3 A graph showing the water evaporation rate of aerogels (AGs) with different contents of multi-walled carbon nanotubes;

[0039] Figure 4 The images show the actual nanofiber-based aerogels prepared in Examples 1-7: where (a)-(g) in the images are the nanofiber-based aerogels of Examples 2, 3, 4, 1, 5, 6 and 7, respectively.

[0040] Figure 5 The images show the actual nanofiber-based aerogels prepared in Comparative Examples 1-2: (a) is the nanofiber-based aerogel prepared in Comparative Example 1, and (b) is the nanofiber-based aerogel prepared in Comparative Example 2.

[0041] Figure 6 SEM images of electrospun nanofiber membranes and nanofiber-based aerogels are shown below: (a1) and (a2) are TPU nanofiber membranes prepared in Comparative Example 3, (b1) and (b2) are TPU aerogels prepared in Comparative Example 4, and (c1) and (c2) are CNTs / TPU aerogels prepared in Example 1. (a1), (b1), and (c1) were observed at 1 kx magnification; (a2), (b2), and (c2) were observed at 20 kx magnification.

[0042] Figure 7 The following diagrams are provided for the water evaporation rate, average pore size, porosity, and permeability of aerogels (AGs) with different short fiber densities: (a) is the water evaporation rate diagram, (b) is the average pore size diagram, (c) is the porosity diagram, and (d) is the permeability diagram.

[0043] Figure 8 Absorbance diagram of electrospun short fiber-based photothermal aerogel;

[0044] Figure 9 This is a surface temperature distribution diagram of the aerogel material. Detailed Implementation

[0045] Unless otherwise defined herein, the scientific and technical terms used in conjunction with this invention shall have the meanings commonly understood by one of ordinary skill in the art. The meaning and scope of terms shall be clear; however, in any case of potential ambiguity, the definitions provided herein shall prevail over any dictionary or foreign definitions. In this application, unless otherwise stated, the use of "or" means "and / or". Furthermore, the use of the term "comprising" and other forms is non-limiting.

[0046] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0047] The first aspect of this invention provides a method for preparing nanofiber-based aerogels, comprising the following steps:

[0048] (a) Electrospinning of a polymer-containing spinning solution yields nanofiber membranes;

[0049] (b) The nanofiber membrane is mechanically dispersed to obtain a short nanofiber suspension;

[0050] (c) After mixing the nanofiber suspension with the functional nanomaterial, the mixture is solidified to obtain the nanofiber-based aerogel.

[0051] This invention successfully prepared a high-performance interfacial water evaporation material integrating rapid water transport, efficient thermal localization, and excellent salt resistance through a technical path of "electrospinning to prepare high-strength nanofibers - short-cut dispersion to form a homogeneous matrix - composite with functional nanomaterials (CNTs) - ultra-low temperature freeze-drying to construct a stable three-dimensional network". The method of this invention is simple and convenient to operate, highly practical, and the obtained aerogel material exhibits excellent photothermal conversion performance and interfacial water evaporation performance.

[0052] The nanofiber-based aerogel provided by this invention is an aerogel material based on the reassembly of electrospun short nanofibers, also known as electrospun short fiber-based aerogel. This aerogel material uses polyurethane as the substrate, with carbon nanotubes deposited on the surface of the polyurethane fibers. As a photothermal conversion material, this aerogel material exhibits an absorbance of no less than 95% in the 200-2500 nm wavelength range and a thermal conductivity of 0.0240 W / (m·K). This aerogel material possesses excellent light absorption performance and thermal management capabilities, while also exhibiting self-floating properties and superior interfacial water evaporation performance.

[0053] In some preferred embodiments, the spinning solution is obtained by dissolving the polymer in a solvent; the polymer includes one or more of polyvinylidene fluoride (PVDF) and thermoplastic polyurethane (TPU); the solvent includes one or two of N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAC); the mass fraction of the polymer in the spinning solution is 15%-25%, for example, 15%, 20%, 25%, etc.; during the electrospinning process, the flow rate of the injection pump used is 25-30 μL·min. -1 For example, it could be 25 μL·min -1 26 μL·min -1 27 μL·min -1 28 μL·min -1 29 μL·min -1 30 μL·min -1 The spinneret voltage is 18-21kV, for example, it can be 18 kV, 19 kV, 20 kV, 21 kV, etc.

[0054] Specifically, this invention selects PVDF or TPU as the polymer substrate due to their excellent fiber-forming properties, mechanical strength, and chemical stability, especially TPU, which has a low thermal conductivity. Using highly polar aprotic solvents such as DMF or DMAC effectively dissolves the polymers and forms a uniform spinning solution, avoiding gelation or precipitation. The polymer concentration is controlled within the range of 15%-25%, ensuring sufficient solution viscosity for continuous fiber formation while preventing difficulties in spinning or excessively large fiber diameters due to excessive concentration. Optimized electrospinning parameters balance the electric field force and solution surface tension, contributing to the acquisition of nanofiber membranes with uniform diameter and no bead-like defects, providing a high-quality precursor for subsequent chopped and reconstituted fibers.

[0055] In some preferred embodiments, prior to the mechanical dispersion process, a pretreatment of the nanofiber membrane is further included; the pretreatment includes a solvent wetting process, wherein the solvent used in the solvent wetting process includes at least one of ethanol, propylene glycol, butanediol and tert-butanol.

[0056] Specifically, the present invention uses reagents such as ethanol for wetting pretreatment, which can effectively penetrate the fiber gaps, reduce the van der Waals forces and capillary forces between fibers, thereby improving the efficiency of subsequent mechanical dispersion and promoting the uniform dissociation of fibers into short fiber units.

[0057] In some preferred embodiments, the mechanical dispersion process includes: mechanical shearing and ultrasonic disruption.

[0058] The power of the mechanical shearing process is 180-250 W, for example, it can be 180 W, 200 W, 250 W, etc., preferably 200 W;

[0059] The power of the ultrasonic crushing process is 600-700 W, for example, it can be 600 W, 650 W, 700 W, etc.;

[0060] The mechanical dispersion process takes 3-10 minutes, for example, 3 minutes, 4 minutes, 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, etc.

[0061] The ultrasonic disruption process is carried out in a dispersion medium; the dispersion medium includes deionized water or an aqueous ethanol solution; the volume fraction of the aqueous ethanol solution is 10%-20%, for example, it can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, etc.

[0062] Specifically, the present invention uses deionized water or low-concentration ethanol aqueous solution as dispersion medium, which helps to maintain the stability of suspension and reduce agglomeration. Especially for polymer fibers with certain hydrophobicity, an appropriate amount of ethanol can improve wettability and enhance dispersion effect.

[0063] In some preferred embodiments, the fiber content of the nanofiber suspension is 8-20 mg / ml, for example, it can be 8 mg / ml, 10 mg / ml, 12 mg / ml, 14 mg / ml, 16 mg / ml, 18 mg / ml, 20 mg / ml, etc., and it needs to be stored in an environment of 1-4℃.

[0064] Specifically, fiber concentration directly affects the density and pore structure of the three-dimensional network during subsequent molding. Too low a concentration may lead to insufficient skeletal support and structural collapse after freeze-drying; too high a concentration can easily cause fiber aggregation and pore blockage. Controlling the fiber content within the range of 8-20 mg / mL ensures that the final aerogel has a sufficiently high solids content to form a continuous network while maintaining good flowability.

[0065] In some preferred embodiments, the nanofiber suspension is mixed with the functional nanomaterial to obtain a functional electrospun short fiber suspension; the functional nanomaterial includes one or more of multi-walled carbon nanotubes (MWCNTs), carbon black, activated carbon, and graphite.

[0066] Specifically, the present invention employs functional nanomaterials, which can be selectively deposited or encapsulated on the fiber surface during subsequent molding processes to construct continuous light absorption and heat generation channels and water transport networks. At the same time, the deposition of nanomaterials at fiber intersections enhances the interfacial bonding force between fibers and improves the overall mechanical strength of the aerogel.

[0067] Preferably, the amount of functional nanomaterials (preferably multi-walled carbon nanotubes) added to the functional electrospun short fiber suspension is 0.15%-3%, for example, it can be 0.15%, 0.5%, 1%, 1.5%, 3%, etc.

[0068] In some preferred embodiments, the curing includes freeze curing; the freeze curing is performed using a cryogenic medium; the cryogenic medium includes at least one of dry ice-ethanol mixture and liquid nitrogen.

[0069] Specifically, in this invention, freeze-curing is the core step in constructing the porous structure of the aerogel. Rapid freezing using a cryogenic medium such as liquid nitrogen allows water in the suspension to crystallize rapidly, forming fine and uniformly distributed ice crystal templates. This leaves a highly interconnected macroporous structure after subsequent drying. This structure not only facilitates the rapid transport of water molecules to the evaporation interface but also significantly reduces the solid-phase heat transfer path, promoting heat localization. Compared to slow freezing, rapid freezing better inhibits ice crystal growth, prevents large-sized ice cracks from damaging the network structure, and improves material uniformity and mechanical integrity.

[0070] In some preferred embodiments, after the functional electrospun staple fiber suspension is solidified, it is dried; the drying process includes freeze drying; the freeze drying time is 24-72 hours, for example, 24 hours, 36 hours, 48 ​​hours, 60 hours, 72 hours, etc.

[0071] A second aspect of the present invention provides a nanofiber-based aerogel, which is prepared using the preparation method described above.

[0072] A third aspect of the present invention provides the application of nanofiber-based aerogels in the preparation of seawater desalination products for interfacial water evaporation.

[0073] The present invention will be further illustrated by the following examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly from the market.

[0074] Example 1

[0075] This embodiment provides a nanofiber-based aerogel, such as Figure 1 As shown, its preparation process is as follows:

[0076] (1) Dissolve thermoplastic polyurethane (molecular weight around 100 kDa) in solvent N,N-dimethylformamide to prepare a spinning solution; wherein the mass fraction of thermoplastic polyurethane is 20%.

[0077] (2) The spinning solution obtained in step (1) is subjected to electrospinning to prepare an electrospinned nanofiber membrane; wherein, during the electrospinning process, the flow rate of the injection pump is 28 μL·min. -1 The spinneret voltage is 20 kV.

[0078] (3) After the nanofiber membrane obtained in step (2) is pretreated by immersion in ethanol (analytical grade), it is then sheared (i.e. mechanical shearing) and then subjected to ultrasonic homogenization (i.e. ultrasonic crushing) in a dispersion medium (15% ethanol aqueous solution by volume) to obtain a uniform electrospun nanofiber suspension.

[0079] The ultrasonic shearing treatment had a power of 200 W, the ultrasonic homogenization treatment had a power of 650 W, and a pulse mode was used. The total duration of the mechanical shearing and ultrasonic homogenization treatments was 8 minutes. The fiber content of the electrospun nanofiber suspension was 16 mg / ml.

[0080] (4) The electrospun nanofiber suspension prepared in step (3) is mixed with multi-walled carbon nanotubes in a predetermined ratio and fully dispersed to obtain a functional electrospun nanofiber suspension; the multi-walled carbon nanotubes added in the functional electrospun nanofiber suspension account for 0.5% of the total mass of the functional electrospun nanofiber suspension.

[0081] (5) The functional electrospun short fiber suspension prepared in step (4) is subjected to deep freeze-curing, followed by freeze-drying treatment to finally obtain electrospun nano short fiber-based photothermal aerogel.

[0082] Among them, deep freezing is carried out by rapid freezing with liquid nitrogen, and the freeze drying (temperature -40℃) process takes 48 hours.

[0083] Example 2

[0084] This embodiment provides a nanofiber-based aerogel, which differs from Embodiment 1 in that the mass fraction of multi-walled carbon nanotubes is 0.15%.

[0085] Example 3

[0086] This embodiment provides a nanofiber-based aerogel, which differs from Embodiment 1 in that the mass fraction of multi-walled carbon nanotubes is 0.3%.

[0087] Example 4

[0088] This embodiment provides a nanofiber-based aerogel, which differs from Embodiment 1 in that the mass fraction of multi-walled carbon nanotubes is 0.375%.

[0089] Example 5

[0090] This embodiment provides a nanofiber-based aerogel, which differs from Embodiment 1 in that the mass fraction of multi-walled carbon nanotubes is 0.75%.

[0091] Example 6

[0092] This embodiment provides a nanofiber-based aerogel, which differs from Embodiment 1 in that the mass fraction of multi-walled carbon nanotubes is 1.5%.

[0093] Example 7

[0094] This embodiment provides a nanofiber-based aerogel, which differs from Embodiment 1 in that the mass fraction of multi-walled carbon nanotubes is 3%.

[0095] Example 8

[0096] This embodiment provides a nanofiber-based aerogel, which differs from Embodiment 1 in that: in step (3), the fiber content of the electrospun nanofiber suspension is 20 mg / ml.

[0097] Example 9

[0098] This embodiment provides a nanofiber-based aerogel, which differs from Embodiment 1 in that: in step (3), the fiber content of the electrospun nanofiber suspension is 18 mg / ml.

[0099] Example 10

[0100] This embodiment provides a nanofiber-based aerogel, which differs from Embodiment 1 in that: in step (3), the fiber content of the electrospun nanofiber suspension is 14 mg / ml.

[0101] Example 11

[0102] This embodiment provides a nanofiber-based aerogel, which differs from Embodiment 1 in that: in step (3), the fiber content of the electrospun nanofiber suspension is 12 mg / ml.

[0103] Example 12

[0104] This embodiment provides a nanofiber-based aerogel, which differs from Embodiment 1 in that: in step (3), the fiber content of the electrospun nanofiber suspension is 10 mg / ml.

[0105] Example 13

[0106] This embodiment provides a nanofiber-based aerogel, which differs from Embodiment 1 in that: in step (3), the fiber content of the electrospun nanofiber suspension is 8 mg / ml.

[0107] Example 14

[0108] This embodiment provides a nanofiber-based aerogel, which differs from Embodiment 1 in that polyvinylidene fluoride (PVDF) is used instead of thermoplastic polyurethane (TPU).

[0109] Comparative Example 1

[0110] This embodiment provides a nanofiber-based aerogel, which differs from Embodiment 1 in that the mass fraction of multi-walled carbon nanotubes is 15%.

[0111] Comparative Example 2

[0112] This embodiment provides a nanofiber-based aerogel, which differs from Embodiment 1 in that the mass fraction of multi-walled carbon nanotubes is 30%.

[0113] Comparative Example 3

[0114] This comparative example provides an electrospun nanofiber membrane, which differs from Example 1 in that steps (3), (4), and (5) are not performed.

[0115] Comparative Example 4

[0116] This comparative example provides a nanofiber-based aerogel, which differs from Example 1 in that step (4) is not performed, i.e., multi-walled carbon nanotubes are not added.

[0117] Test Example 1

[0118] The nanofiber-based aerogels prepared in Examples 1-7 were used as samples for testing.

[0119] Test method: Relying on a solar-powered seawater desalination test system (such as...) Figure 2 As shown in the figure, the water evaporation performance of nanofiber-based aerogel materials was evaluated. A xenon lamp was used as a simulated light source, and an AM1.5G spectral filter was used to create simulated solar radiation with a spectral distribution similar to that of sunlight. The nanofiber-based aerogel sample to be tested was placed in a beaker containing 5 mL of deionized water, ensuring that the sample was in close contact with the water surface and that there were no residual air bubbles. Under an irradiation intensity of 1 sun, the test environment temperature was controlled at 25±1℃. An electronic balance with an accuracy of 0.1 mg was connected to the system to record the total mass change of the beaker and the solution inside (i.e., the mass of water evaporated) in real time under different irradiation times, and then the water evaporation rate of nanofiber-based aerogel materials prepared with different amounts of carbon nanotubes was calculated.

[0120] The test results are shown in Table 1 and Figure 3 As shown.

[0121] Table 1. Water evaporation rates of aerogels (AGs) with different multi-walled carbon nanotube contents

[0122]

[0123] like Figure 4 As shown, the electrospun nanofiber-based photothermal aerogels with a multi-walled carbon nanotube mass fraction of 0.15% to 3% are illustrated in Examples 1-7. Figure 4 The mass fractions of carbon nanotubes in products (a)-(g) were 0.15%, 0.3%, 0.375%, 0.5%, 0.75%, 1.5%, and 3%, respectively. Figure 5 The carbon nanotube mass fractions of products (a) and (b) were 15% and 30%, respectively, which are the nanofiber-based aerogels prepared in Comparative Example 1 and Comparative Example 2, respectively. In Comparative Example 1 and Comparative Example 2, the excessive addition of carbon nanotubes led to increased material brittleness and loss of structural integrity (see...). Figure 5 The sample was broken, therefore it was not feasible to conduct evaporation performance testing.

[0124] like Figure 6 As shown, Figure 6 In the figures, (a1), (b1), and (c1) represent the TPU nanofiber membrane (i.e., the TPU nanofiber membrane prepared in Comparative Example 3), TPU aerogel (i.e., the TPU nanofiber membrane prepared in Comparative Example 4), and CNTs / TPU aerogel (i.e., the TPU nanofiber membrane prepared in Example 1) observed at 1k magnification, respectively. (a2), (b2), and (c2) represent the TPU nanofiber membrane (i.e., the TPU nanofiber membrane prepared in Comparative Example 3), TPU aerogel (i.e., the TPU nanofiber membrane prepared in Comparative Example 4), and CNTs / TPU aerogel (the TPU nanofiber membrane prepared in Example 1) observed at 20k magnification, respectively. Figure 6 It is known that the internal structure of the nanofiber-based composite aerogel is a 3D network of stacked short fibers, forming highly ordered and more interconnected channels with pore sizes ranging from a few micrometers to tens of micrometers. These regularly sized channels can transport water molecules and vapor more efficiently while maintaining good mechanical support. The surface of the fiber network is covered with a large number of carbon nanotubes, which endow the composite aerogel material with excellent photothermal conversion properties.

[0125] It is evident that the deposition of carbon nanotubes on the fiber surface effectively enhances the mechanical interlocking between fibers, thereby improving the strength of the aerogel. However, excessive addition of carbon nanotubes can lead to increased brittleness of the aerogel, which is detrimental to subsequent applications. Based on the water evaporation performance test results, the optimal mass fraction of added carbon nanotubes was ultimately determined to be 0.5%.

[0126] Test Example 2

[0127] The nanofiber-based aerogels prepared in Examples 1 and 8-13 were used as samples for testing.

[0128] Test methods: Referring to the water evaporation rate test method described in Test Example 1, the water evaporation rate of aerogel materials with different short fiber contents was tested. The pore structure parameters of aerogel materials with different short fiber contents were determined by mercury porosimetry. By exploring the relationship between the average pore size, porosity, and permeability of the material and the water evaporation performance, the structure-property relationship between pore structure and water evaporation performance was established. The light absorption performance of aerogel materials was evaluated by ultraviolet / visible / near-infrared diffuse reflectance. The diffuse reflected light of the material was collected by an integrating sphere to calculate the absorptivity of the aerogel material.

[0129] The test results are shown in Table 2 and Figure 7 As shown.

[0130] Table 2. Average pore size, porosity, and permeability of nanofiber membranes (NFM) and aerogels (AGs) with different short fiber densities.

[0131]

[0132] Test results are as follows Figure 7 As shown, Figure 7 (a) shows the water evaporation rate of aerogels (AGs) with different short fiber densities. Figure 7 (b) in the figure shows the average pore size of aerogels (AGs) with different short fiber densities. Figure 7 (c) in the figure shows the porosity of aerogels (AGs) with different short fiber densities. Figure 7 (d) in the figure represents the permeability of aerogels (AGs) with different short fiber densities.

[0133] The light absorption properties of photothermal aerogels prepared with different short fiber suspension concentrations were tested. The UV / Vis / Near-infrared diffuse reflectance test results are as follows: Figure 8 As shown in Table 2, the photothermal aerogel with added CNTs (carbon nanotubes) exhibits high light absorption in the 200-2500 nm wavelength range, with an absorbance of no less than 95%. The pore structure of the interfacial evaporation material directly determines the water transport capacity (permeability), the number of evaporation sites (specific surface area), and the material's thermal management performance, and is a key factor affecting the evaporation rate and efficiency. Pore structure analysis was performed on photothermal aerogels of different densities, and the test results are shown in Table 2 and... Figure 7As shown in the figure, all samples exhibit high porosity (>84%), indicating that aerogel materials effectively limit convective heat transfer and solid-phase heat conduction, localizing heat at the evaporation interface and demonstrating excellent thermal management performance. Among them, the aerogel with a short fiber concentration of 20 mg / ml may have slightly higher heat loss due to its lowest porosity. The high-speed water transport network formed by high permeability and large pore size ensures sufficient water supply, thereby achieving high water evaporation performance. The aerogel with a short fiber concentration of 16 mg / ml has the best pore connectivity, allowing water to be smoothly supplied to the evaporation interface and avoiding local water shortages, which is key to stable high-speed evaporation. In addition, the large pore size provides a smooth escape channel for the generated water vapor, reducing the resistance to vapor escape and helping to maintain a high evaporation rate. The perfect combination of high porosity, large pore volume, ultra-large pore size, and ultra-high permeability ensures water supply capacity and vapor escape efficiency, which are the decisive factors in maintaining a high evaporation rate.

[0134] like Figure 7 As shown, the water evaporation rate exhibits a trend of first increasing and then decreasing. Combined with the aforementioned pore structure characteristics, when the fiber density is too low, the structure partially collapses during freeze-drying, causing the pores to be flattened. This results in a decrease in pore size and porosity, affecting the water supply at the interface and leading to a lower water evaporation rate. When the concentration of the short fiber suspension is reduced to a suitable range (14-16 mg / ml), the fibers have sufficient space to disperse, the inter-fiber connection points are not too dense, and there are sufficient support points to ensure structural stability. Simultaneously, a large number of open, interconnected macropores are left, forming an ideal hierarchical porous structure, which is beneficial for interfacial water evaporation. When the short fiber suspension concentration is 16 mg / ml, the water evaporation rate can reach 1.9 kg·m³ under 1 sun irradiation. -2 ·h -1 If the fiber density is too high, the fibers become tightly entangled, resulting in smaller pores, which severely affects vapor diffusion and thermal management performance, leading to a decrease in the water evaporation rate.

[0135] Test Example 3

[0136] Test Methods: The thermal conductivity of the wetted nanofiber-based aerogel was tested using a thermal conductivity meter. The sample was completely immersed in deionized water until saturated, then removed and excess water was gently wiped off. It was then placed on the test platform of the thermal conductivity meter, with appropriate test modes and parameters selected to ensure full contact between the sample and the probe without air gaps. Each sample was tested at least three times, and the average value was taken as the final thermal conductivity result. Infrared thermal imagers were used to monitor the temperature distribution changes on the material surface. The saturated wetted aerogel sample was placed horizontally in a beaker of a suitable size. Under 1 Sun illumination, the temperature distribution image of the sample surface was captured at regular intervals from the start of illumination, recording the highest surface temperature at different times. By analyzing the changes in the thermal conductivity and surface temperature over time, the photothermal conversion performance and thermal localization ability of the aerogel material were evaluated.

[0137] Test samples: Nanofiber-based aerogels prepared in Examples 1 and 14.

[0138] The test results are shown in Table 3.

[0139] Table 3. Thermal conductivity coefficients of PVDF and TPU aerogels

[0140]

[0141] Under critical wet conditions, the thermal conductivity of TPU / CNTs aerogel (0.1513 W / m·K) is significantly lower than that of PVDF / CNTs aerogel (0.2934 W / m·K), indicating that TPU-based materials can more efficiently confine heat to the interface and reduce heat loss during actual evaporation.

[0142] The thermal conductivity of a material is closely related to its microstructure. As an elastomer, TPU maintains good flexibility in a wet state, and the three-dimensional network structure formed with CNTs is more stable, with uniform pore distribution and moderate connectivity, effectively suppressing the formation of heat conduction paths. Furthermore, the strong interfacial bonding between TPU and CNTs better restricts phonon transfer between CNTs, further reducing the overall thermal conductivity. This provides important theoretical support for the superior thermal localization properties of TPU / CNTs aerogels in the field of photothermal evaporation, giving them the potential to achieve higher evaporation efficiency.

[0143] like Figure 9As shown, the longitudinal temperature distribution on the surface of the aerogel material, as tested by infrared thermal imaging, visually demonstrates the difference in heat accumulation between PVDF and TPU-based aerogel materials. Under the same illumination conditions, TPU-based aerogel exhibits a higher surface temperature compared to PVDF-based aerogel. However, regarding the surface temperature of the material side and the water temperature, TPU-based aerogel is lower than PVDF-based aerogel, indicating that PVDF-based aerogel transfers and dissipates more heat axially (longitudinally). TPU-based aerogel can more effectively confine heat to the upper surface (evaporation interface), possessing superior "photothermal conversion-heat localization" synergistic ability, making it a more ideal platform material for efficient interfacial water evaporation.

[0144] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a nanofiber-based aerogel, characterized in that, Includes the following steps: (a) Electrospinning a polymer-containing spinning solution to obtain a nanofiber membrane; wherein the spinning solution is obtained by dissolving the polymer in a solvent; the polymer includes polyvinylidene fluoride and / or thermoplastic polyurethane; (b) The nanofiber membrane is mechanically dispersed to obtain a nanofiber suspension, wherein the fiber content of the nanofiber suspension is 8-20 mg / ml; (c) The nanofiber suspension is mixed with functional nanomaterials to obtain a functional electrospun short fiber suspension, which is then solidified to obtain the nanofiber-based aerogel. The functional nanomaterials include one or more of multi-walled carbon nanotubes, carbon black, activated carbon, and graphite. In the functional electrospun short fiber suspension, the mass fraction of the functional nanomaterial is 0.15%-3%.

2. The preparation method according to claim 1, characterized in that, The solvent includes one or both of N,N-dimethylformamide and N,N-dimethylacetamide; In the spinning solution, the polymer has a mass fraction of 15%-25%; During the electrospinning process, the flow rate of the injection pump used is 25-30 μL·min. -1 The spinneret voltage is 18-21kV.

3. The preparation method according to claim 1, characterized in that, Prior to the mechanical dispersion process, a pretreatment of the nanofiber membrane is also included. The pretreatment includes solvent wetting, wherein the solvent used in the solvent wetting process includes at least one of ethanol, propylene glycol, butanediol, and tert-butanol.

4. The preparation method according to claim 1, characterized in that, The mechanical dispersion process includes: mechanical shearing and ultrasonic fragmentation. The power of the mechanical shearing process is 180-250 W; The power of the ultrasonic fragmentation process is 600-700 W; The mechanical dispersion process takes 3-10 minutes; The ultrasonic disruption process is carried out in a dispersion medium; the dispersion medium includes deionized water or an aqueous ethanol solution; the volume fraction of the aqueous ethanol solution is 10%-20%.

5. The preparation method according to claim 1, characterized in that, The curing includes freeze curing; the freeze curing is performed using a low-temperature medium. The cryogenic medium includes at least one of dry ice-ethanol mixture and liquid nitrogen.

6. The preparation method according to claim 1, characterized in that, After the functional electrospun short fiber suspension is solidified, it is dried. The drying process includes freeze drying; the freeze drying process takes 24-72 hours.

7. A nanofiber-based aerogel, characterized in that, It is prepared by the preparation method according to any one of claims 1-6.

8. The application of the nanofiber-based aerogel as described in claim 7 in the preparation of seawater desalination products for interfacial water evaporation.

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