Preparation method and application of hydrophilic breathable gel-based photo-thermal fiber membrane

Abstract

The invention belongs to the technical field of seawater desalination, and relates to a preparation method and application of a hydrophilic breathable gel-based photo-thermal fiber membrane, and the preparation method comprises the following steps: preparing a precursor solution containing polyvinyl alcohol, polyacrylic acid and a photo-thermal material, and sequentially carrying out electrostatic spinning, thermal crosslinking and water absorption swelling to obtain the hydrophilic breathable gel-based photo-thermal fiber membrane. Compared with the prior art, the fiber membrane and the hydrogel have the advantages of the fiber membrane and the hydrogel, not only have the characteristic of activating water of the hydrogel and effectively reduce evaporation enthalpy, but also retain the advantages of flexibility, high specific surface area, high porosity, low curvature and the like of the fiber membrane, and promote steam overflow, water transportation and light absorption. Therefore, the hydrophilic air-permeable gel-based photo-thermal fiber membrane provides a new thought for developing high-performance photo-thermal materials and application of the high-performance photo-thermal materials in the field of solar seawater desalination.

Description

Technical Field

[0001] The present invention belongs to the technical field of seawater desalination, and relates to a preparation method of a hydrophilic and breathable gel-based photothermal fiber membrane and its application in solar seawater desalination. Background Art

[0002] Solar-driven interfacial evaporation is considered an effective strategy to alleviate the freshwater crisis due to its advantages such as greenness, high efficiency, and sustainability. The key to solar seawater desalination is to prepare high-performance photothermal conversion materials. Currently, a variety of photothermal materials (hydrogels, aerogels, fiber membranes, etc.) have been developed. Among them, hydrogels are a class of polymers rich in hydrophilic groups and three-dimensional network structures, which can effectively activate the state of water molecules, weaken the hydrogen bond interaction, reduce the evaporation enthalpy, and promote the evaporation of water molecules at the material interface, and are widely used in the field of seawater desalination. However, traditional hydrogels have a high-curvature pore structure, resulting in the detour of steam and water, restricting water transportation and steam overflow, and thus reducing the evaporation performance; in addition, hydrogels have poor flexibility and mechanical properties, and generally require a freeze dryer for preparation, resulting in limited preparation area and difficulty in large-scale production, which limits their practical application.

[0003] The prior art CN109206553B provides a solar photothermal conversion material and a preparation method thereof. The method includes the steps of mixing and dispersing a light-absorbing material, a water-soluble monomer, an initiator, and a crosslinking agent in water to obtain a reaction solution; or mixing and dispersing a light-absorbing material, a water-soluble polymer, and a crosslinking agent in water to obtain a reaction solution; adsorbing the above reaction solution with a sponge, subjecting it to gelation to obtain a hydrogel, then performing multiple cycles of freeze-thawing, freeze-drying, and dissolving it in water until saturated swelling to obtain the solar photothermal conversion material. The porous properties of the sponge material improve the water absorption of this solar photothermal conversion material and can solve the salt crystallization problem, that is, self-cleaning property. At the same time, in the solar photothermal conversion material prepared by this method, the light-absorbing material ensures the light absorption of this solar photothermal conversion material, and the hydrogel material can reduce the latent heat required for water evaporation, which ensures the high efficiency of photothermal conversion and a high evaporation rate. However, from the perspective of the preparation method, this technical solution uses a chemical crosslinking method combined with a freeze-thaw method to prepare a hydrogel, which is complex in operation and energy-consuming. At the same time, the small-scale freeze-dryer in the laboratory limits the large-scale production of hydrogels. At the same time, the mixed hydrogel prepared by the chemical crosslinking method on the sponge has poor flexibility and mechanical properties, affecting the long-term stability of the evaporator; in terms of the device, this technical solution selects a floating device to directly contact the sponge with water, resulting in large heat loss; most importantly, although the water transmission is relatively fast with the addition of a hydrogel outside the sponge, the path of steam in the pores with a high curvature is very tortuous, resulting in steam detours and affecting steam overflow. At the same time, the porous structure is easily blocked by the outer composite hydrogel, making it difficult to control. Generally speaking, the hydrogel prepared by this technical solution has problems such as difficulty in large-scale production, difficulty in steam overflow, poor mechanical properties, and large heat loss in the floating mode, and further improvement is still needed.

[0004] Currently, hydrogels generally have the advantage of low evaporation enthalpy, which promotes evaporation. However, there is less exploration of the large-scale preparation method of hydrogels. At the same time, the pores of hydrogels have a high curvature, which limits steam overflow, and the water conductivity of hydrogels is poor, affecting evaporation performance. Therefore, the preparation and development of high-performance, green, and large-scale photothermal conversion materials are of great significance for the development of solar seawater desalination. Summary of the Invention

[0005] The object of the present invention is to provide a preparation method of a hydrophilic and breathable gel-based photothermal fiber membrane and its application in solar seawater desalination, aiming at the defects that the existing hydrogels cannot simultaneously meet the requirements of low evaporation enthalpy, high water absorption, and high evaporation rate. The method has the advantages of high air permeability, high water transmission, and large-scale production, and has great application prospects in the field of solar seawater desalination.

[0006] The object of the present invention can be achieved by the following technical solutions:

[0007] The first aspect of the present invention provides a method for preparing a hydrophilic and breathable gel-based photothermal fiber membrane, comprising: preparing a precursor solution containing polyvinyl alcohol, polyacrylic acid, and a photothermal material, and then successively undergoing electrospinning, thermal crosslinking, and water absorption and swelling to obtain it.

[0008] The present invention combines the advantages of fiber membranes and hydrogels. The fiber membrane is prepared by electrospinning. Utilizing the characteristics of the fiber membrane such as high specific surface area and high porosity helps to improve breathability, light absorption, water transportation, and steam overflow. At the same time, a hydrogel is prepared by thermal crosslinking using polyvinyl alcohol and polyacrylic acid as the base materials. Utilizing its activated water performance, it reduces the enthalpy of evaporation, while retaining the interconnected porous structure of the fiber membrane, promoting steam overflow and water transmission.

[0009] That is, the present invention not only has the characteristics of hydrogel-activated water, effectively reducing the enthalpy of evaporation, but also retains the advantages of the fiber membrane such as flexibility, high specific surface area, high porosity, and low-curvature pores, promoting steam overflow, water transportation, and light absorption. Therefore, this hydrophilic and breathable gel-based photothermal fiber membrane provides new ideas for the development of high-performance photothermal materials and their applications in the field of solar desalination.

[0010] In some specific embodiments, the mass ratio of polyvinyl alcohol (PVA) to polyacrylic acid (PAA) is 0.1:10 to 10:0.1. If the content of polyacrylic acid is too large, the swelling is excessive, which easily blocks the pores and affects steam overflow. If it is too small, it will affect the enthalpy of evaporation, thus affecting the evaporation performance.

[0011] In some specific embodiments, the molecular weight of polyvinyl alcohol is 25,000 to 300,000, and the degree of alcoholysis is 78% to 98%. The molecular weight of polyacrylic acid is 2,000 to 150,000.

[0012] In some specific embodiments, the photothermal material is composed of one or more of metal nanoparticles, carbon materials, organic materials, or semiconductor photothermal materials.

[0013] In some specific embodiments, the metal nanoparticles are selected from at least one of gold, silver, copper, platinum, palladium, ruthenium, rhodium, or aluminum.

[0014] In some specific embodiments, the carbon materials are selected from at least one of carbon fibers, carbon cloths, carbon felts, carbon blacks, porous carbons, carbon nanotubes, graphene, or fullerenes.

[0015] In some specific embodiments, the organic materials are selected from at least one of polypyrrole, polythiophene, polyaniline, polydopamine, indocyanine green, or Prussian blue.

[0016] In some specific embodiments, the semiconductor photothermal material is at least one of copper sulfide, copper selenide, bismuth sulfide, bismuth selenide, tungsten sulfide, tungsten oxide, titanium oxide, aluminum oxide, iron sulfide or molybdenum sulfide.

[0017] In some specific embodiments, the mass ratio of the polyvinyl alcohol to the photothermal material is 4:1 to 100:1.

[0018] In some specific embodiments, the electrospinning is performed by needle-free electrospinning.

[0019] In some specific embodiments, in the electrospinning, the spinning voltage is 30-90 kV, the spiral speed is 1-15 r / min, the winding speed is set to 0.1-0.8 m / min, the fiber membrane is collected by aluminum foil or non-woven fabric, the spinning temperature is 40-80°C, and the humidity is 10-80%.

[0020] In some specific embodiments, the crosslinking temperature is 30-300°C and the crosslinking time is 0.1-0.8h. If the crosslinking heat treatment temperature is too low, the fiber membrane has poor water resistance and is easily soluble in water. If the heat treatment temperature is too high, it has little effect on the hydrophilicity and morphology of the fiber membrane, but the operation is more dangerous and difficult.

[0021] In some specific embodiments, during the water absorption and swelling, the swelling time is 0.5 to 5 hours.

[0022] In some specific embodiments, the method for preparing the hydrophilic air-permeable gel-based photothermal fiber membrane comprises the following steps:

[0023] S1, preparing an electrospinning precursor solution; adding polyvinyl alcohol to a solvent to prepare a polyvinyl alcohol solution of a predetermined concentration, and mixing it with a polyacrylic acid solution of a predetermined concentration in a certain proportion, and then adding a photothermal material, stirring sufficiently to obtain a mixed solution, wherein the total mixture concentration is 0.1 to 50 wt%;

[0024] S2. Preparation of nanofiber membrane by needle-free electrospinning: injecting the precursor solution obtained in step S1 into a syringe and performing electrospinning to obtain a large-area hydrophilic fiber membrane;

[0025] S3, post-treatment of the fiber membrane: put the fiber membrane obtained in step S2 into an oven for heat treatment at a temperature of 30 to 1000° C. for 0.1 to 12 hours. Finally, take out the sample and soak it in water for 0.5 to 50 hours to swell and obtain a gel-based fiber membrane.

[0026] In some specific embodiments, in step S1, the solvent of the polyvinyl alcohol solution is water, and the dissolution temperature is 40-200°C.

[0027] In some specific embodiments, in step S1, the concentration of the polyvinyl alcohol solution is 0.1-20 wt%, and the concentration of the polyacrylic acid solution is 0.1-100 wt%.

[0028] The second aspect of the present invention provides an application of the hydrophilic and breathable gel-based photothermal fiber membrane prepared by the above method, including using the hydrophilic and breathable gel-based photothermal fiber membrane for solar desalination.

[0029] The present invention prepares a hydrophilic and breathable gel-based photothermal fiber membrane by electrostatic spinning, thermal crosslinking, and swelling of polyvinyl alcohol, polyacrylic acid, and a photothermal material. Among them, due to the esterification reaction between the hydroxyl groups in polyvinyl alcohol and the carboxyl groups in polyacrylic acid at high temperatures, the water resistance of the gel-based fiber membrane is improved. At the same time, some carboxyl groups ionize in water to generate negative charges, and more water enters the fiber through the electrostatic repulsion effect, forming hydrogen bonds with the unreacted hydroxyl and carboxyl groups, breaking the hydrogen bonds of water molecules. The electrostatic effect and the active groups act in coordination to increase the proportion of intermediate water to a greater extent and reduce the evaporation enthalpy. In addition, the crosslinked superabsorbent polymer fiber membrane, due to its own swelling effect, will retain the advantages of low curvature and high porosity of the fiber membrane, forming a low-curvature porous gel-based fiber membrane, integrating the advantages of hydrogels and fiber membranes. The two work together to promote steam overflow and water transport.

[0030] Compared with the prior art, the present invention has the following characteristics:

[0031] 1) The present invention provides a hydrophilic and breathable gel-based photothermal fiber membrane, which is composed of a superabsorbent polymer polyglycolic acid, polyacrylic acid, and a photothermal material carbon black. The electrostatic spinning technology and thermal crosslinking are used to prepare a large-area fiber membrane, and the large-scale production of hydrogels is quickly realized by the method of swelling of the polymer with water absorption. Experiments show that the width of the gel-based fiber membrane that can be prepared by the present invention is 1-100 cm, the length ≥ 1 cm, and it is proportional to the spinning time, and can be extended as needed, and the longest can reach more than 100 m.

[0032] 2) The hydrophilic and breathable gel-based photothermal fiber membrane prepared by the present invention still maintains the three-dimensional network structure of the fiber membrane with high porosity, high specific surface area, and low curvature. The micro-nano structure has a wider spectral absorption, making it have high-efficiency light absorption performance. At the same time, the low-curvature pore structure promotes steam overflow and water transportation.

[0033] 3) The hydrophilic and breathable gel-based photothermal fiber membrane prepared by the present invention still maintains the water absorption and swelling characteristics of the hydrogel. More water molecules enter through the surface active groups of the fiber and the polyelectrolyte effect to form activated water, reducing the energy required for water molecule evaporation (the evaporation enthalpy is reduced from ~2500 J / g of pure water to ~1000 J / g), promoting evaporation, and the evaporation rate can reach up to 3.15 kg·m -2 ·h -1 .

[0034] 4) In the existing hydrogel preparation process, cross-linking preparation is usually achieved by the freeze-thaw method of a freeze dryer. This method is limited by the limited working space, high price, and high power consumption of the freeze dryer, making it difficult to achieve large-scale production. At the same time, the preparation of hydrogels by the freeze-thaw method requires many times and complex operations. In contrast, the present invention can easily and quickly achieve large-scale production through needleless electrospinning and simple self-swelling, effectively reducing production costs and improving production efficiency, and having good application prospects. Description of the Drawings

[0035] Figure 1 It is a physical picture of a hydrophilic and breathable gel-based photothermal fiber membrane prepared in Example 1 before swelling, with a length of 70 cm and a width of 35 cm.

[0036] Figure 2 It is a physical picture of a hydrophilic and breathable gel-based photothermal fiber membrane prepared in Example 1.

[0037] Figure 3 It is a comparison diagram of a nanofiber membrane prepared by needleless electrospinning (left) and an electron microscope of a hydrophilic and breathable gel-based photothermal fiber membrane after swelling (right) prepared in Example 1.

[0038] Figure 4 It is a physical picture (a) and an electron microscope picture (b) of a traditional hydrogel prepared in Comparative Example 1.

[0039] Figure 5 It is a pore size distribution diagram of a hydrophilic and breathable gel-based photothermal fiber membrane prepared in Example 1.

[0040] Figure 6 It is a comparison diagram of the air permeability test of a hydrophilic and breathable gel-based photothermal fiber membrane prepared in Example 1 and a traditional CB@PVA / PAA hydrogel prepared in Comparative Example 1.

[0041] Figure 7 It is a comparison diagram of the water transmission test of a hydrophilic and breathable gel-based photothermal fiber membrane prepared in Example 1 and a traditional CB@PVA / PAA hydrogel prepared in Comparative Example 1.

[0042] Figure 8 It is an evaporation enthalpy performance test diagram of hydrophilic and breathable gel-based photothermal fiber membranes with different ratios prepared in Examples 1-4.

[0043] Figure 9 It is a comparison diagram of the evaporation rates of hydrophilic and breathable gel-based photothermal fiber membranes with different ratios prepared in Examples 1-4. Detailed Description of the Invention

[0044] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented on the premise of the technical solution of the present invention, and the detailed implementation manners and specific operation processes are given, but the protection scope of the present invention is not limited to the following embodiments.

[0045] The following are more detailed implementation cases to further illustrate the technical solution of the present invention and the technical effects that can be obtained.

[0046] In the following embodiments, unless otherwise specified for raw material reagents or treatment techniques, it means that they are all conventional commercially available products or conventional treatment techniques in the art.

[0047] In the following embodiments, polyvinyl alcohol is purchased from the 1788 type product of Shanghai Bide Pharmaceutical Technology Co., Ltd., and the degree of alcoholysis is 88%-98%; polyacrylic acid is purchased from Shanghai Titan Technology Co., Ltd., and the molecular weight is 2000-5000.

[0048] Example 1:

[0049] This embodiment provides a preparation method of a hydrophilic and breathable gel-based photothermal fiber membrane, including the following steps:

[0050] S1: Prepare an electrospinning precursor solution: Weigh 10 g of polyvinyl alcohol PVA and add it to 90 mL of water, stir magnetically at 98 °C for 2 hours to prepare a PVA solution with a concentration of 10 wt%. Subsequently, add 20 mL of a polyacrylic acid PAA solution with a concentration of 50 wt% to the above solution, stir at room temperature for 30 min, then add 0.2 g of carbon black to 80 mL of water, sonicate for 60 min, and finally mix the above mixed polymer solution with the carbon black solution and stir overnight at room temperature to obtain an electrospinning precursor solution with a PVA:PAA ratio of 5:5;

[0051] S2: Prepare a nanofiber membrane by needleless electrospinning: Take 10 mL of the spinning precursor solution and inject it into a syringe for electrospinning. The spinning temperature is 60 °C, the relative humidity is about 25%, the voltage is 65 kV, the spiral speed is 9 rpm, and the winding speed is set to 0.3 m / min. Use aluminum foil to collect the nanofibers to obtain a hydrophilic fiber membrane containing active groups, as Figure 1 shown. A large-area fiber membrane with an area of 70×35 cm 2 can be prepared in 4 hours. As can be seen from Figure 2 the left figure, the diameter distribution of these nanofibers is relatively uniform, and the average diameter is between 200-350 nm;

[0052] S3: Post-treatment of the fiber membrane: Put the fiber membrane obtained in step S2 into an oven and heat-treat the fiber membrane at 145 °C for 30 min. Finally, take out the sample and soak it in water for 2 h to obtain a hydrophilic and breathable gel-based photothermal fiber membrane by swelling. From Figure 2 As can be seen from the right figure, the diameter of the swollen fiber membrane increases, about 300 - 700 nm, but it still maintains the porous structure of the fiber membrane with cross-interconnected pores, which is beneficial to promoting the overflow of steam and water transportation during evaporation.

[0053] Example 2:

[0054] This example provides a method for preparing a hydrophilic and breathable gel-based photothermal fiber membrane, which includes the following steps:

[0055] S1: Preparation of electrospinning precursor solution: Weigh 10 g of polyvinyl alcohol (PVA) and add it to 90 mL of water. Stir magnetically at 98 °C for 2 hours to prepare a PVA solution with a concentration of 10 wt%. Subsequently, take 80 mL of the above solution and add 24 mL of a polyacrylic acid (PAA) solution with a concentration of 50 wt%. Stir at room temperature for 30 min. Then, add 0.2 g of carbon black to 96 mL of water and ultrasonicate for 60 min. Finally, mix the above mixed polymer solution with the carbon black solution and stir overnight at room temperature to obtain an electrospinning precursor solution with a PVA:PAA ratio of 4:6.

[0056] S2: Preparation of nanofiber membrane by needleless electrospinning: Take 10 mL of the spinning precursor solution and inject it into a syringe for electrospinning. The spinning temperature is 60 °C, the relative humidity is about 25%, the voltage is 70 kV, the spiral speed is 9 rpm, and the winding speed is set to 0.3 m / min. Use aluminum foil to collect the nanofibers to obtain a large-area hydrophilic fiber membrane containing active groups.

[0057] S3: Post-treatment of the fiber membrane: Put the fiber membrane obtained in step S2 into an oven and heat-treat the fiber membrane at 145 °C for 30 min. Finally, take out the sample and soak it in water for 2 h to obtain a hydrophilic and breathable gel-based photothermal fiber membrane by swelling.

[0058] Example 3:

[0059] This example provides a method for preparing a hydrophilic and breathable gel-based photothermal fiber membrane, which includes the following steps:

[0060] S1: Preparation of electrospinning precursor solution: Weigh 14 g of polyvinyl alcohol (PVA) and add it to 126 mL of water. Stir magnetically at 98 °C for 2 hours to prepare a PVA solution with a concentration of 10 wt%. Subsequently, add 12 mL of a 50 wt% polyacrylic acid (PAA) solution to the above solution and stir at room temperature for 30 min. Then, add 0.2 g of carbon black to 48 mL of water and ultrasonicate for 60 min. Finally, mix the above mixed polymer solution and carbon black solution and stir overnight at room temperature to obtain an electrospinning precursor solution with a PVA:PAA ratio of 7:3.

[0061] S2: Preparation of nanofiber membrane by needleless electrospinning: Take 10 mL of the spinning precursor solution and inject it into a syringe for electrospinning. The spinning temperature is 60 °C, the relative humidity is about 25%, the voltage is 60 kV, the spiral speed is 9 rpm, and the winding speed is set to 0.3 m / min. Use aluminum foil to collect the nanofibers to obtain a large-area hydrophilic fiber membrane containing active groups.

[0062] S3: Post-treatment of fiber membrane: Put the fiber membrane obtained in step S2 into an oven and heat-treat the fiber membrane at 145 °C for 30 min. Finally, take out the sample and soak it in water for 2 h to swell and obtain a hydrophilic and breathable gel-based photothermal fiber membrane.

[0063] Example 4:

[0064] This example provides a method for preparing a hydrophilic and breathable gel-based photothermal fiber membrane, which includes the following steps:

[0065] S1: Preparation of electrospinning precursor solution: Weigh 18 g of polyvinyl alcohol (PVA) and add it to 162 mL of water. Stir magnetically at 98 °C for 2 hours to prepare a PVA solution with a concentration of 10 wt%. Subsequently, add 4 mL of a 50 wt% polyacrylic acid (PAA) solution to the above solution and stir at room temperature for 30 min. Then, add 0.2 g of carbon black to 16 mL of water and ultrasonicate for 60 min. Finally, mix the above mixed polymer solution and carbon black solution and stir overnight at room temperature to obtain an electrospinning precursor solution with a PVA:PAA ratio of 9:1.

[0066] S2: Preparation of nanofiber membrane by needleless electrospinning: Take 10 mL of the spinning precursor solution and inject it into a syringe for electrospinning. The spinning temperature is 60 °C, the relative humidity is about 25%, the voltage is 50 kV, the spiral speed is 9 rpm, and the winding speed is set to 0.3 m / min. Use aluminum foil to collect the nanofibers to obtain a large-area hydrophilic fiber membrane containing active groups;

[0067] S3: Post-treatment of the fiber membrane: Put the fiber membrane obtained in step S2 into an oven and heat-treat the fiber membrane at 145 °C for 30 min. Finally, take out the sample and soak it in water for 2 h to obtain a hydrophilic and breathable gel-based photothermal fiber membrane by swelling.

[0068] Comparative Example 1:

[0069] This example provides a preparation method of traditional CB@PVA / PAA hydrogel, including the following steps:

[0070] S1: Weigh 10 g of polyvinyl alcohol PVA and add it to 90 mL of water. Stir magnetically at 98 °C for 2 hours to prepare a PVA solution with a concentration of 10 wt%. Subsequently, add 20 mL of polyacrylic acid PAA solution with a concentration of 50 wt% to the above solution and stir at room temperature for 30 min. Then, add 0.2 g of carbon black to 80 mL of water and ultrasonicate for 60 min. Finally, mix the above mixed polymer solution with the carbon black solution and stir overnight at room temperature to obtain an electrospinning precursor solution with PVA:PAA of 5:5.

[0071] S2: Add a cross-linking agent of glutaraldehyde with a concentration of 1 wt% to the prepared electrospinning precursor solution and stir evenly. Then pour it into a silicone mold and cross-link at 40 °C for 2 h to obtain a traditional CB@PVA / PAA bulk hydrogel.

[0072] Comparative Example 2:

[0073] This example provides a preparation method of CB@PVA fiber membrane, which is only different from Example 1 in that:

[0074] In step S1, keeping the carbon black content unchanged, use an equal amount of PVA to replace PAA.

[0075] The rest is the same as in Example 1. The obtained CB@PVA fiber membrane is soluble in water and has poor solar water evaporation performance, so it cannot be applied to seawater desalination.

[0076] Comparative Example 3:

[0077] This example provides a preparation method of CB@PAA, which is only different from Example 1 in that:

[0078] In step S1, keeping the carbon black content unchanged, use an equal amount of PAA to replace PVA.

[0079] The rest is the same as in Example 1. The obtained CB@PAA fiber membrane is soluble in water and has poor solar water evaporation performance, so it cannot be applied to seawater desalination.

[0080] Comparative Example 4:

[0081] This embodiment provides a method for preparing a CB@PVA / PAA fiber membrane, which is only different from Embodiment 1 in that:

[0082] In step S3, no swelling treatment is performed.

[0083] The rest is the same as in Embodiment 1. The obtained fiber membrane is extremely soluble in water and is prone to moisture absorption and dissolution after being placed in the air for a long time, and cannot be applied to seawater desalination.

[0084] Test Example 1: Morphology performance test

[0085] The morphology test of the sample was measured by Scanning Electron Microscope (SEM) S-4800 The specific operation steps are as follows:

[0086] Take the superabsorbent fiber membrane prepared in Comparative Example 4 and the hydrophilic and breathable gel-based photothermal fiber membrane sample prepared in Embodiment 1, and cut them into 1×1 cm 2 small pieces. Stick the freeze-dried sample on the electron microscope stage with conductive glue. After drying, perform sputtering on it. Subsequently, place the sample stage in the vacuum chamber of the electron microscope instrument. Under high voltage, by adjusting different magnifications, characterize the morphology of the sample. As Figure 3 shown, the left figure is the superabsorbent fiber membrane, and the right figure is the gel-based fiber membrane obtained after swelling. It can be seen that the diameter of the gel-based fiber membrane becomes thicker, but it still retains the high-porosity pore structure. At the same time, the pores formed by the fiber membrane have a low curvature. Compared with the traditional gel with high-curvature pores ( Figure 4 ), it improves the tortuosity of water and gas, and can better promote water transport and steam overflow.

[0087] Test Example 2: Pore size distribution performance test

[0088] The pore size distribution test of the sample was measured by a gas-liquid pore size distribution tester. The specific operation steps are as follows:

[0089] Take the hydrophilic and breathable gel-based photothermal fiber membrane sample prepared in Embodiment 1, and cut it into 2×2 cm 2 small pieces. Put the sample into the GQ-16 wetting liquid and soak it in a vacuum wetting instrument (Kemite Technology (Shanghai) Co., Ltd.) for 4-5 minutes. Take out the sample and assemble it in the order of washer - support net - sample - washer, and put it into a PSDA-30 type microfiltration membrane pore size analyzer for pore size test. The test results are as Figure 5As shown, it can be seen that the pore size distribution of the hydrophilic and breathable gel-based photothermal fiber membrane is between 125.4 nm and 20.99 μm. The nanopores promote the activation of water molecules and the formation of water clusters, while the micropores provide channels for water transport and steam overflow. At the same time, the pore structure with low curvature promotes water transport and steam overflow. In addition, it can be known from the test that this gel-based fiber membrane still has 59% air holes in the swollen state, further proving that while it transports water, it retains a certain number of air holes, providing conditions for gas diffusion.

[0090] Test Example 3: Air Permeability Test

[0091] Take the sample of the hydrophilic and breathable gel-based photothermal fiber membrane prepared in Example 1, with an area of 10×10 cm 2 , and place it at the air inlet of a fully automatic air permeability tester (Wenzhou Fangyuan Instrument Co., Ltd., YG461E). The test pressure is 200 Pa, and the test area is 20 cm 2 . Under the same test conditions, place the traditional CB@PVA / PAA hydrogel prepared in Comparative Example 1 at the air inlet for testing and comparison. The test results are as Figure 6 shown. The hydrophilic and breathable gel-based photothermal fiber membrane promotes steam overflow due to its high-porosity structure that maintains the low-curvature pore structure of the fiber membrane. In contrast, the traditional hydrogel has a high-curvature pore structure, causing steam to meander and be trapped in it, making it difficult to overflow and diffuse. Therefore, the air permeability of the hydrophilic and breathable gel-based photothermal fiber membrane is much greater than that of the traditional hydrogel.

[0092] Test Example 4: Water Transport Performance Test

[0093] Take the sample of the hydrophilic and breathable gel-based photothermal fiber membrane prepared in Example 1 (size: 2×10 cm), fix it on the inner wall of the water tank with a magnet, hang it between two water tanks, and flatten it in the middle; the two water tanks are at different heights (the distance is 2 cm, and the height difference is 1 cm). The higher water tank is filled with seawater, submerging the upper end of the photothermal conversion cloth, and the lower water tank remains empty. Use infrared thermal imaging to record the water transport process. To more clearly observe the water transport phenomenon, the water in the water tank is selected as an ice-water mixture, and the sample is irradiated under simulated sunlight (power: 1 kW / m 2 ) for ten minutes. Under the same conditions as above, conduct a comparative test on the water transport of the same-sized traditional hydrogel sample prepared in Comparative Example 1. The test results are as Figure 7 shown in a. The upper figure is the hydrophilic and breathable gel-based photothermal fiber membrane prepared in Example 1, which can be transported from the high tank to the low tank in 70 s. The lower figure is the traditional hydrogel in Comparative Example 1, whose surface is still dry after 70 s, proving that the water transport performance of the hydrophilic and breathable gel-based photothermal fiber membrane has been further improved. To further prove this conclusion, the water transport volume per unit area per unit time of the two was also statistically analyzed, as shown in Figure 7As shown in Figure b, the water transport volume of the hydrophilic and breathable gel-based photothermal fiber membrane is significantly higher than that of the traditional hydrogel, and the result is corresponding to Figure 7 Figure a.

[0094] Test Example 5: Evaporation Enthalpy Performance Test

[0095] Take two identical molds, weigh the same volume of pure water into the molds respectively, and weigh the initial mass M of one of the molds according to the thermogravimetric method 1-Pure water ; Cut the dry fiber membrane into the same evaporation area as the pure water in the mold (area: 6 cm 2 ), and place the cut fiber membrane in another mold and float it on the surface of the pure water, and weigh its initial mass M1.

[0096] Put the above two molds containing pure water and the placed fiber membrane into the constant temperature and humidity chamber at the same time, place them under dark conditions for 13 h, and take them out and weigh the masses M 2-Pure water and M2 at this time.

[0097] The evaporation enthalpy (ΔH ev ) of pure water can be calculated by formula (1):

[0098] ΔH ev = C1 + C2T + C3T 1.5 + C4T 2.5 + C5T 3 (1)

[0099] where, C1 = 2500.304, C2 = -2.2421025, C3 = -0.021465847, C4 = 3.1750136×10 -4 , C5 = 2.8607959×10 -5 are all constants, and T is the temperature (°C).

[0100] Assume that the input energy is the same (U in ) during the evaporation process of water, then the evaporation enthalpy of the water on the membrane can be calculated by formula (2):

[0101] U in = ΔH ev ·(M 1-Pure water - M 2-Pure water ) = ΔH ev * ·(M1 - M2) (2)

[0102] where, ΔH ev and ΔH ev* represent the enthalpy of evaporation of pure water and water on the membrane, respectively. M 1-Pure water and M 2-Pure water represent the initial mass and the mass after testing of pure water, respectively. M1 and M2 represent the initial mass and the mass after testing of the sample, respectively. Substituting the above-obtained data into formulas (1) to (2) can obtain the enthalpy of evaporation of the sample. The results are as Figure 8 shown. The enthalpy of evaporation of the hydrophilic and breathable gel-based photothermal fiber membranes prepared by the present invention with different ratios is significantly less than that of pure water. This is because the hydrophilic and breathable gel-based photothermal fiber membrane provided by the present invention contains polyelectrolyte PAA, which makes it negatively charged in water. Due to the electrostatic effect, more water molecules are promoted to enter the fiber and form hydrogen bonds with active groups such as hydroxyl and carboxyl groups on the fiber surface, thereby breaking the hydrogen bonds of water molecules to reduce the enthalpy of evaporation. Different ratios change the state of water molecules. As the content of PAA increases, the swelling performance of the hydrophilic and breathable gel-based photothermal fiber membrane is higher, allowing more water molecules to enter the fiber and form hydrogen bonds with the surface active groups. However, when the content of PAA is too large, excessive swelling occurs and the pore size decreases, inhibiting the overflow of steam. Therefore, the order of decreasing enthalpy of evaporation is CB@PVA / PAA-5:5 < CB@PVA / PAA-7:3 < CB@PVA / PAA-4:6 < CB@PVA / PAA-9:1.

[0103] Test Example 6: Test on solar water evaporation performance

[0104] The indoor seawater evaporation experiment was carried out through a small evaporation device, which consisted of a small-sized hydrophilic and breathable gel-based photothermal fiber membrane (2 cm × 10 cm), a bench scale (YP-20002, accuracy: 0.01 g), and two PMMA water tanks (3 cm × 8 cm × 10 cm). The device was constructed as follows: The photothermal material was fixed on the inner wall of the water tank by a magnet, suspended between the two water tanks, and flattened in the middle; the two water tanks were at different heights (the distance was 2 cm and the height difference was 1 cm). The higher water tank was filled with seawater, submerging the upper end of the photothermal conversion cloth, and the lower water tank was kept empty; the openings of the two water tanks were covered with plastic sheets to avoid natural evaporation; a bench scale was placed below the water tank to record the weight change of the device at different times. The light source was a solar simulator (model: OrielNewport 69911, light intensity: 1.0 kW m -2 ) or a xenon lamp (model: PLS-SXE300, power: 300 W, Beijing Perfect Light Technology Co., Ltd.). The test conditions were: room temperature 24 - 26 °C, humidity 28% - 30%. The natural evaporation rate was tested in the dark, and other conditions remained the same. The test results are as Figure 9 shown. The highest evaporation rate is CB@PVA / PAA-5:5, reaching 3.15 kg·m -2 ·h-1 。The evaporation rate of CB@PVA / PAA-7:3 can reach 2.64 kg·m -2 ·h -1 , that of CB@PVA / PAA-4:6 is 2.55 kg·m -2 ·h -1 , that of CB@PVA / PAA-9:1 is 2.13 kg·m -2 ·h -1 (The evaporation rate of pure water is about 0.45 kg·m -2 ·h -1 ). As the content of PAA increases, the swelling performance of the hydrophilic and breathable hydrogel-based photothermal fiber membrane becomes higher. Therefore, more water molecules enter the fiber and form hydrogen bonds with the surface active groups, thereby breaking the hydrogen bonds between water molecules, reducing the enthalpy change of evaporation, lowering the energy required for water molecules to evaporate, and promoting evaporation. However, when the content of PAA is too large, excessive swelling occurs and the pore size decreases, inhibiting the steam from overflowing. Therefore, the evaporation rate of CB@PVA / PAA-4:6 is lower than that of CB@PVA / PAA-5:5 and CB@PVA / PAA-7:3.

[0105] The above description of the embodiments is to enable those of ordinary skill in the art to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative efforts. Therefore, the present invention is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art without departing from the scope of the present invention according to the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A preparation method of a hydrophilic and breathable gel-based photothermal fiber membrane, characterized in that Including: Prepare a precursor solution containing polyvinyl alcohol, polyacrylic acid, and a photothermal material, and then successively carry out electrospinning, thermal crosslinking, and water absorption swelling to obtain it.

2. The preparation method of the hydrophilic and breathable gel-based photothermal fiber membrane according to claim 1, characterized in that, The mass ratio of the polyvinyl alcohol to the polyacrylic acid is 0.1:10 to 10:0.

1.

3. The preparation method of the hydrophilic and breathable gel-based photothermal fiber membrane according to claim 1, characterized in that, The molecular weight of the polyvinyl alcohol is 25,000 to 300,000, and the degree of alcoholysis is 78% to 98%. The molecular weight of the polyacrylic acid is 2,000 to 150,000.

4. The preparation method of the hydrophilic and breathable gel-based photothermal fiber membrane according to claim 1, characterized in that, The photothermal material is composed of one or more of metal nanoparticles, carbon materials, organic materials, or semiconductor photothermal materials.

5. The preparation method of the hydrophilic and breathable gel-based photothermal fiber membrane according to claim 4, wherein The metal nanoparticles are selected from at least one of gold, silver, copper, platinum, palladium, ruthenium, rhodium, or aluminum. The carbon materials are selected from at least one of carbon fiber, carbon cloth, carbon felt, carbon black, porous carbon, carbon nanotube, graphene, or fullerene. The organic materials are selected from at least one of polypyrrole, polythiophene, polyaniline, polydopamine, indocyanine green, or Prussian blue. The semiconductor photothermal materials are at least one of copper sulfide, copper selenide, bismuth sulfide, bismuth selenide, tungsten sulfide, tungsten oxide, titanium oxide, aluminum oxide, iron sulfide, or molybdenum sulfide.

6. The preparation method of the hydrophilic and breathable gel-based photothermal fiber membrane according to claim 1, characterized in that, The mass ratio of the polyvinyl alcohol to the photothermal material is 4:1 to 100:

1.

7. The preparation method of the hydrophilic and breathable gel-based photothermal fiber membrane according to claim 1, wherein In the electrospinning, the spinning voltage is 40 to 90 kV.

8. The preparation method of the hydrophilic and breathable gel-based photothermal fiber membrane according to claim 1, characterized in that, In the thermal crosslinking, the crosslinking temperature is 30 to 300 °C, and the crosslinking time is 0.1 to 3 h.

9. The preparation method of the hydrophilic and breathable gel-based photothermal fiber membrane according to claim 1, characterized in that, In the water absorption swelling, the swelling time is 0.5 to 5 h.

10. Use of a hydrophilic and breathable gel-based photothermal fiber membrane prepared by the method according to any one of claims 1 to 9, characterized in that, The hydrophilic and breathable gel-based photothermal fiber membrane is used for solar seawater desalination.

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