An efficient interfacial solar evaporation film integrating photothermal conversion and thermal localization and its preparation method

Abstract

The present invention discloses a high-efficiency interfacial solar evaporation film integrating photothermal conversion and thermal localization and a preparation method thereof, which belongs to the field of water treatment. First, a porous fiber substrate containing seed crystals is placed in a hydrothermal reaction solution for a hydrothermal growth reaction to obtain a photothermal layer A with a micro-nano structure on the surface. Then, a hydrophobic polymer B and an organic solvent C are fully stirred and dissolved to obtain a spinning solution. Finally, the photothermal layer A is used as a receiving substrate, and the spinning solution is electrostatically spun to obtain a thermal insulation layer B, thereby obtaining an interfacial solar evaporation film integrating the photothermal layer A and the thermal insulation layer B. The upper layer of the interfacial solar evaporation film is a hydrophilic photothermal layer, and the lower layer is a hydrophobic thermal insulation layer with a low thermal conductivity coefficient. It can spontaneously drive water to transfer from the hydrophobic layer to the hydrophilic layer from bottom to top. The photothermal layer evaporates the transferred water through photothermal conversion, while the thermal insulation layer prevents heat from being transferred downward. The method of the present invention is simple, recyclable, and has broad application prospects.

Description

Technical Field

[0001] The present invention belongs to the field of water treatment, and in particular relates to a high-efficiency interface solar evaporation film integrating light-heat conversion and heat localization and a preparation method thereof. Background Art

[0002] With the development of human society and the acceleration of industrialization, the scarcity of freshwater resources and water pollution have become one of the global problems that need to be solved urgently. As an emerging concept in solar energy conversion, the use of interfacial solar thermal-steam conversion to produce clean water is considered to be an effective new water treatment technology due to its green, efficient and sustainable advantages. Compared with traditional methods based on large-scale water heating, interfacial solar evaporation technology places the light absorber at the steam-water interface. It only needs to heat a thin layer of water at the interface to produce steam without heating a large amount of water, thus achieving higher solar-steam conversion efficiency. However, current interfacial evaporation materials face problems such as low photothermal conversion efficiency, insufficient utilization of sunlight, and large heat conduction and heat radiation losses to the water and the environment due to direct contact between the photothermal material and the water. In addition, the top-down preparation method used in current reports affects the practical applicability and long-term stability of the material. Summary of the Invention

[0003] To address the current challenges of insufficient light utilization, high heat loss, and low steam conversion efficiency in interfacial solar materials, this paper proposes a high-efficiency interfacial solar evaporation film that integrates light-to-heat conversion and heat localization, as well as a method for its preparation. This interfacial solar evaporation film exhibits excellent light absorption and heat localization characteristics, significantly enhancing the solar-to-steam conversion efficiency of the material system.

[0004] The interfacial solar evaporation film is a composite double-layer film structure, with the upper layer being a photothermal layer with a micro-nano structure and the lower layer being a thermal insulation layer with a low thermal conductivity coefficient; the thermal insulation layer is hydrophobic and the photothermal layer is hydrophilic, so that the interfacial solar evaporation film has a wettability gradient in the direction perpendicular to the material interface, and can spontaneously drive water to transfer from the hydrophobic layer to the hydrophilic layer from bottom to top. At the same time, the hydrophobicity of the thermal insulation layer is utilized to make the solar evaporation film float on the liquid surface.

[0005] The working principle of the interfacial solar evaporation film is as follows: the photothermal layer absorbs light to generate heat, which heats the interfacial water pumped to the hydrophilic layer to generate steam; the thermal insulation layer blocks direct contact between the photothermal layer and the water body, avoiding heat loss due to transfer to the large amount of water below.

[0006] The diameter of the nanostructure of the photothermal layer is in the range of 10nm-100μm; the fiber diameter of the thermal insulation layer is in the range of 50nm-3μm, and the pore size of the fiber membrane is in the range of 1-100μm.

[0007] The method for preparing the interface solar evaporation film comprises the following steps:

[0008] Step 1, preparing a hydrothermal reaction substrate containing seed crystals;

[0009] There are two methods for preparing a porous fiber substrate containing crystal seeds:

[0010] (1) soaking a porous fiber fabric in a solution containing one or both of copper ions and tungsten particles to obtain a porous fiber fabric containing seed crystals, and placing the porous fiber fabric in an oven for heat treatment to expose the seed crystals, thereby obtaining a hydrothermal reaction substrate containing the seed crystals;

[0011] (2) A solution containing one or both of tungsten particles or copper ions is mixed with polyvinylidene fluoride to form a spinning precursor solution, a porous fiber membrane containing seed crystals is prepared by electrospinning, and the membrane is placed in an oven for heat treatment to expose the seed crystals, thereby obtaining a hydrothermal reaction substrate containing the seed crystals.

[0012] Step 2: placing the hydrothermal reaction substrate containing the seed crystals in the hydrothermal reaction solution A to perform a hydrothermal growth reaction to obtain a photothermal layer A;

[0013] The specific conditions of the hydrothermal growth reaction are:

[0014] The hydrothermal reaction device is transferred to a 40-200° C. oven and reacted for 4-18 hours to obtain a photothermal layer A having a nanosheet / nanoneedle microstructure on the surface through hydrothermal synthesis.

[0015] The diameter of the nanosheets / nanoneedles ranges from 10 nm to 100 μm.

[0016] The hydrothermal reaction solution A is a mixed hydrothermal growth solution composed of one or more of copper sulfate, copper acetate, copper chloride, ammonium tungstate and ammonium metatungstate and one of ammonia water, ammonium sulfide or sodium thiosulfate solution, wherein the concentration of metal ions is between 0.02-0.80M.

[0017] According to the different metal ions in the hydrothermal reaction solution A, the obtained nanosheet / nanoneedle microstructure is one or more of copper oxide, copper sulfide, tungsten oxide and tungsten sulfide.

[0018] Step 3: placing the hydrophobic polymer B in the organic solvent C and stirring thoroughly until it is completely dissolved, thereby obtaining a spinning solution containing 5% to 30% by weight of the hydrophobic polymer B;

[0019] The hydrophobic polymer B is a polymer material with low thermal conductivity, including one or more of polystyrene, polyvinylidene fluoride, polyvinylidene fluoride hexafluoropropylene or polyacrylonitrile;

[0020] The organic solvent C is a mixed solvent formed by one or more solvents selected from tetrahydrofuran, acetone, dimethyl sulfoxide, N,N-dimethylformamide, or N,N-dimethylacetamide;

[0021] Step 4: Place the spinning solution containing the hydrophobic polymer B in a syringe, and use the photothermal layer A as a receiving substrate to perform electrostatic spinning to obtain a hydrophobic insulation layer with low thermal conductivity, thereby obtaining an interface solar evaporation film integrating the photothermal layer and the insulation layer.

[0022] The specific parameters of the electrospinning are: the spinneret of the syringe is 0.2-1.5 mm, the spinning receiving distance is 10-30 cm, the high voltage static electricity applied between the receiving substrate and the spinning nozzle is 8-30 kV, and the spinning time is 30.0 s-30.0 min.

[0023] Furthermore, when the material of the thermal insulation layer B is intrinsically hydrophilic, such as cellulose acetate, polylactic acid and chitosan, a low surface energy chemical substance D can be introduced to hydrophobically modify the surface of the electrospun fiber membrane.

[0024] The low surface energy chemical substance D is one or more of methoxysilane, ethoxysilane, phenylsilane, alkylsilane, aminosilane, epoxysilane, acyloxysilane, vinylsilane, isocyanatepropyltriethoxysilane or fluoric acid.

[0025] The advantages of the present invention are:

[0026] The disclosed hydrophilic photothermal layer / hydrophobic thermal insulation layer composite interfacial evaporation system is prepared using hydrothermal synthesis and electrospinning techniques, respectively. The resulting self-floating interfacial evaporation material can be used for rapid interfacial solar-to-steam conversion. This invention features a rational design, simple method, and multiple recycling capabilities, potentially alleviating water resource crises and finding widespread application in areas such as seawater desalination, steam disinfection, and steam power generation.

[0027] 2. The disclosed micro- / nanostructured photothermal layer / thermal insulation layer composite interfacial evaporation system integrates excellent photothermal conversion performance and thermal localization, achieving enhanced interfacial solar-to-steam conversion efficiency. The micro- / nanostructured photothermal layer enhances light absorption and utilization efficiency by inducing light scattering and multiple reflections, resulting in excellent photothermal performance. The thermal insulation layer also prevents heat loss to the water and environment, ensuring thermal localization.

[0028] 3. The hydrophilic photothermal layer / hydrophobic thermal insulation layer composite interface evaporation system disclosed in the present invention has a wettability gradient that provides a driving force for water transmission from bottom to top, enabling autonomous water supply. At the same time, the thermal insulation layer prevents heat loss downward. By regulating the interfacial wettability gradient force and the thickness of the thermal insulation layer, the water supply / thermal insulation performance can be regulated and optimized, resulting in excellent evaporation performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of the double-layer composite structure of the interfacial solar evaporation film prepared by the method of the present invention;

[0030] Figure 2 This is an electron microscope image of the copper oxide photothermal layer with nanosheet structures grown on the surface obtained in Example 1;

[0031] Figure 3 This is an electron microscope image of the nanofiber thermal insulation layer obtained by electrospinning in Example 1;

[0032] Figure 4 This is a photo of the photothermal layer and the thermal insulation layer prepared in Example 1; wherein, Figure 4 a is the actual image of the copper oxide photothermal layer, Figure 4 b is a physical image of the polyvinylidene fluoride-hexafluoropropylene thermal insulation layer;

[0033] Figure 5 This is an infrared thermal image of the interface solar evaporation film prepared in Example 1 under irradiation of simulated sunlight;

[0034] Figure 6 This is the process in which water in the interfacial solar evaporation film prepared in Example 1 is rapidly vaporized and evaporated under simulated sunlight. DETAILED DESCRIPTION

[0035] The present invention will be described in detail below with reference to the accompanying drawings and embodiments, but the present invention is not limited thereto.

[0036] The present invention comprehensively considers the two aspects of efficient light capture and utilization and reduction of heat loss, and discloses a double-layer self-floating interface solar evaporation film composed of a "multi-level structure hydrophilic light absorption layer" and a "hydrophobic heat insulation water supply layer" by introducing a heat insulation layer to achieve efficient steam generation. Figure 1 As shown, the upper layer is a photothermal layer A made of a high-efficiency photothermal conversion material with a micro-nanoscale structure, and the bottom layer is a porous fiber membrane insulation layer B with a low thermal conductivity coefficient; the photothermal layer A can achieve efficient absorption of sunlight, and the insulation layer B with a low thermal conductivity coefficient can effectively prevent the conversion heat from being transferred to a large amount of water below, avoiding heat loss and enhancing heat utilization efficiency.

[0037] The interfacial solar evaporation film of the present invention has a hydrophilic photothermal layer and a hydrophobic thermal insulation layer, resulting in a wettability gradient at the vertical interface of the interfacial solar evaporation film. This allows water to be autonomously transferred from the thermal insulation layer to the photothermal layer, but not downwardly. This design helps achieve an excellent water supply-evaporation balance.

[0038] The photothermal layer is a semiconductor high-efficiency photothermal material with a rough structure, such as copper oxide, copper sulfide, tungsten oxide and tungsten sulfide, and the micro-nano rough structure is prepared by hydrothermal synthesis. The composition, concentration, reaction temperature and time of the hydrothermal solution can produce photothermal materials with different products and morphologies. The electrospinning method is a technology that prepares porous nanofiber membranes by applying an electric field to a polymer solution precursor, allowing the electrostatic field force to compete and overcome the surface tension. The composition and morphology of the fiber material can be controlled by adjusting the composition of the spinning solution precursor and the voltage and spinneret aperture during the electrospinning process.

[0039] This invention, based on the interfacial properties of materials, proposes a feasible research approach for designing high-performance interfacial evaporation materials. By integrating efficient photothermal conversion with thermal insulation, it expands new approaches to the design of novel, high-efficiency solar evaporators, possessing significant theoretical and practical significance. This integrated, double-layer heterogeneous interfacial evaporator achieves efficient steam generation by integrating photothermal conversion, thermal localization, and water supply. It has broad application prospects and significant practical significance in areas such as seawater desalination, wastewater purification, salinity-based power generation, steam sterilization, and steam power generation.

[0040] Example 1

[0041] Step 1: soak a commercially available fiber fabric in a 0.15M copper sulfate solution to obtain a hydrothermal base fabric containing seed crystals, and place the fabric in an oven at 130°C for heat treatment to expose the seed crystals, thereby obtaining a hydrothermal reaction base fabric containing seed crystals.

[0042] The pore size of the commercially available fiber fabrics selected ranges from 100 nm to 1 mm.

[0043] Step 2: Place the hydrothermal reaction substrate containing the seed crystals in a 0.15M copper ammonia reaction solution consisting of copper sulfate and ammonia water, and transfer the hydrothermal reaction device to an 80°C oven for 12 hours to obtain a copper oxide photothermal layer with a nanosheet microstructure on the surface. Figure 2 As shown in Figure 2, the photothermal layer exhibits super-hydrophilic properties.

[0044] Step 3: Using N,N-dimethylformamide as solvent, a polyvinylidene fluoride-hexafluoropropylene spinning solution with a mass concentration of 15% is prepared, a magnet is added and stirred on a magnetic stirrer for 6 hours to obtain a uniform and transparent polyvinylidene fluoride-hexafluoropropylene spinning solution.

[0045] Polyvinylidene fluoride-hexafluoropropylene is a polymer material with low thermal conductivity.

[0046] Step 4: Using the photothermal layer as a receiving substrate, electrospinning the polyvinylidene fluoride-hexafluoropropylene spinning solution prepared in step 3 to obtain a hydrophobic insulation layer with low thermal conductivity, thereby obtaining an interface solar evaporation film integrating the photothermal layer and the insulation layer.

[0047] The electrospinning process involves placing the spinning solution into a 0.5mm diameter syringe nozzle and slowly applying a voltage of 16kV at a working distance of 15cm. Under the influence of the electrostatic field, the polymer is stretched, resulting in a polymer fiber membrane that acts as a thermal insulation layer with superhydrophobic properties.

[0048] The electron microscope image of the heat insulation fiber membrane prepared by electrospinning in this embodiment is as follows: Figure 3 As shown, the fiber diameter ranges from 100 nm to 1 μm, and the fiber membrane pore size ranges from 20 nm to 50 μm.

[0049] The prepared double-layer composite interface solar evaporation film was placed under 1 sun of simulated sunlight for evaporation testing. The mass change caused by water evaporation was automatically measured and recorded by an electronic balance. The double-layer composite interface solar evaporation film can float on the surface of water. The micro / nano structure of its photothermal layer helps to enhance light absorption, and the thermal insulation layer prevents heat loss to the water body and the environment to form a thermal localization, which helps to enhance the interface solar energy-steam conversion efficiency. The actual picture of the double-layer composite interface solar evaporation film is as follows Figure 4 As shown, Figure 4 a is the actual image of the copper oxide photothermal layer, Figure 4 b is a real image of the polyvinylidene fluoride-hexafluoropropylene thermal insulation layer. Figure 5 As shown in the figure, under the irradiation of simulated sunlight, the copper oxide photothermal layer of the interface solar evaporation film undergoes photothermal conversion, and the optical image of the surface rapidly heats up, with the surface temperature reaching 80.6°C.

[0050] In the interfacial solar evaporation film, the photothermal layer is hydrophilic and the thermal insulation layer is hydrophobic. There is a wettability gradient force at the vertical interface of the material, which can realize autonomous water supply from the thermal insulation layer to the photothermal layer, ensuring the water supply-evaporation process. Figure 6 The water-soaked evaporation material is exposed to simulated sunlight and the water is rapidly vaporized and evaporated, demonstrating the excellent photothermal conversion properties of the material.

[0051] Through the integrated design of the photothermal layer and the thermal insulation layer, the interfacial solar evaporation film achieved a heat release rate of 1.9 kg m -2 h -1 The evaporation capacity is higher than the water vapor yield of the existing reported membrane interface evaporator.

[0052] Example 2

[0053] Step 1: prepare a blend solution of copper acetate and polyvinylidene fluoride as a spinning precursor solution, and use electrospinning to spin the blend solution to prepare an electrospun polyvinylidene fluoride fiber membrane containing copper acetate. The obtained fiber membrane is placed in a 120°C oven for heat treatment to expose the doped copper acetate seeds to the outside, thereby obtaining a hydrothermal reaction substrate containing the seeds.

[0054] Step 2: Place the hydrothermal reaction substrate containing the seed crystals in a 0.10M copper ammonia reaction solution consisting of copper acetate and ammonia water, transfer the hydrothermal reaction device to a 60°C oven, and react for 15 hours to obtain a copper oxide photothermal layer with a nanosheet microstructure on the surface.

[0055] Step 3: using a mixed solvent of N,N-dimethylformamide and tetrahydrofuran in a volume ratio of 1:1 as a solvent, preparing a polyurethane spinning solution with a mass concentration of 7%, adding a magnet and stirring on a magnetic stirrer for 6 hours to obtain a uniform and transparent polyurethane spinning solution.

[0056] Polyurethane is a polymer material with low thermal conductivity.

[0057] In step 4, the polyurethane spinning solution prepared in step 3 is electrospun using the photothermal layer as the receiving substrate. The spinning solution is placed in a syringe nozzle with a diameter of 0.7 mm. A voltage of 14 kV is slowly adjusted and applied, and electrospinning is performed at a working distance of 18 cm. Under the action of the electrostatic field, the polymer is stretched by the electric field, forming a polymer fiber film that serves as the thermal insulation layer, thereby forming an interfacial solar evaporation film integrating the photothermal layer and the thermal insulation layer.

[0058] In this embodiment, the fiber diameter of the thermal insulation layer fiber membrane prepared by electrospinning is in the range of 100 nm-2 μm, the pore size of the thermal insulation layer fiber membrane is in the range of 20 nm-80 μm, and the thermal insulation layer has superhydrophobic properties.

[0059] The prepared double-layer composite interfacial solar evaporation film was exposed to simulated sunlight of one sun for evaporation testing. The mass change caused by water evaporation was automatically measured and recorded by an electronic balance. The double-layer composite interfacial solar evaporation film can float on the water surface. The micro / nanostructure of the copper oxide photothermal layer enhances light absorption, while the thermal insulation layer prevents heat loss to the water and environment, forming thermal localization, which helps enhance the interfacial solar-to-steam conversion efficiency.

[0060] The photothermal layer of this composite evaporation system is hydrophilic, and the thermal insulation layer is hydrophobic. There is a wettability gradient force at the vertical interface of the materials, which can realize autonomous water supply from the thermal insulation layer to the photothermal layer, ensuring the water supply-evaporation process.

[0061] Example 3

[0062] Step 1: soak a commercially available fiber fabric in a 0.1M copper acetate solution to obtain a hydrothermal base fabric containing seed crystals, and place the fabric in an oven at 135°C for heat treatment to expose the seed crystals, thereby obtaining a hydrothermal reaction base fabric containing seed crystals.

[0063] Step 2: placing the hydrothermal reaction substrate containing the seed crystals in a hydrothermal reaction solution to perform a hydrothermal growth reaction to obtain a copper oxide photothermal layer with a nanosheet microstructure on the surface.

[0064] Hydrothermal reaction solution: 2.5 M sodium hydroxide solution was added dropwise to 0.10 M copper sulfate solution, and concentrated ammonia was added to dissolve the solution, so that the copper ion concentration in the hydrothermal reaction solution was 0.02 M.

[0065] The conditions for the hydrothermal growth reaction are: transferring the hydrothermal reaction device to a 200°C oven and reacting for 4 hours to obtain a copper oxide photothermal layer with a nanosheet microstructure on the surface.

[0066] Step 3: using N,N-dimethylformamide as a solvent, preparing a polystyrene spinning solution with a mass concentration of 5%, adding a magnet and stirring on a magnetic stirrer for 10 hours to obtain a uniform and transparent polystyrene spinning solution.

[0067] In step 4, the polystyrene spinning solution prepared in step 3 is electrospun using the hydrothermally prepared photothermal layer from step 2 as the receiving substrate. The spinning solution is placed in a syringe nozzle with a diameter of 0.2 mm. A voltage of 30 kV is slowly adjusted and applied. Electrospinning is performed at a working distance of 10 cm for 30 minutes. Under the action of the electrostatic field, the polymer is stretched by the electric field, forming a polymer fiber membrane that serves as the thermal insulation layer, thereby forming an interfacial solar evaporation film integrating the photothermal layer and the thermal insulation layer.

[0068] The fiber diameter of the heat-insulating layer fiber membrane prepared by electrospinning is in the range of 200nm-3μm, the pore size of the heat-insulating layer fiber membrane is in the range of 40nm-100μm, and the heat-insulating layer has superhydrophobic properties.

[0069] The prepared interfacial solar evaporation film was exposed to simulated sunlight of one sun for evaporation testing. The mass change caused by water evaporation was automatically measured and recorded by an electronic balance. The double-layer composite interfacial solar evaporation film can float on the water surface. The micro / nanostructure of the copper oxide photothermal layer enhances light absorption, while the thermal insulation layer prevents heat loss to the water and environment, forming thermal localization, which helps enhance the interfacial solar-to-steam conversion efficiency.

[0070] The photothermal layer of the solar evaporation film on this interface is hydrophilic, and the thermal insulation layer is hydrophobic. There is a wettability gradient force at the vertical interface of the material, which can realize autonomous water supply from the thermal insulation layer to the photothermal layer, ensuring the water supply-evaporation process.

[0071] Due to the good photothermal and thermal barrier properties of the evaporation material, a 1.8 kg m -2 h -1 The evaporation yield is better than the currently reported evaporation yield based on membrane materials.

[0072] Example 4

[0073] Step 1: Using electrospun polyvinylidene fluoride-co-hexafluoropropylene containing copper acetate as a hydrothermal reaction substrate, heat-treating in an oven at 120° C. to expose the seed crystals, thereby obtaining a hydrothermal reaction substrate containing the seed crystals.

[0074] Step 2: placing the hydrothermal reaction substrate containing the seed crystals in a hydrothermal reaction solution to perform a hydrothermal growth reaction to obtain a photothermal layer.

[0075] The hydrothermal reaction solution is: ammonium sulfide solution is added to 0.20M copper sulfate solution to obtain a hydrothermal reaction solution with a copper ion concentration of 0.8M.

[0076] The conditions for the hydrothermal growth reaction are: transferring the hydrothermal reaction device to a 40°C oven and reacting for 18 hours to obtain a copper sulfide photothermal layer with a nanoneedle microstructure on the surface.

[0077] Step 3: Using N,N-dimethylformamide as a solvent, a polyvinylidene fluoride-hexafluoropropylene spinning solution with a mass concentration of 30% is prepared, a magnet is added and stirred on a magnetic stirrer for 6 hours to obtain a uniform and transparent polyvinylidene fluoride-hexafluoropropylene spinning solution.

[0078] In step 4, the polyvinylidene fluoride-hexafluoropropylene spinning solution prepared in step 3 is electrospun using the photothermal layer prepared by the hydrothermal reaction in step 2 as the receiving substrate. The spinning solution is placed in a syringe nozzle with a diameter of 1.5 mm, and a voltage of 8 kV is slowly adjusted and applied. Electrospinning is performed at a working distance of 30 cm. Under the action of the electrostatic field, the polymer is stretched by the electric field, forming a polymer fiber film that serves as the thermal insulation layer, resulting in an interfacial solar evaporation film integrating the photothermal layer and the thermal insulation layer.

[0079] The fiber diameter of the heat-insulating layer fiber membrane prepared by electrospinning is in the range of 50nm-2μm, the pore size of the heat-insulating layer fiber membrane is in the range of 1nm-80μm, and the heat-insulating layer has superhydrophobic properties.

[0080] The resulting double-layer composite interfacial solar evaporation film was exposed to simulated sunlight at one sun for evaporation testing. The mass change caused by water evaporation was automatically measured and recorded by an electronic balance. The double-layer composite interfacial solar evaporation film can float on the water surface. The micro / nanostructure of the copper sulfide photothermal layer enhances light absorption, while the thermal insulation layer prevents heat loss to the water and environment, forming thermal localization, which helps enhance the interfacial solar-to-steam conversion efficiency.

[0081] The photothermal layer of this composite evaporation system is hydrophilic, and the thermal insulation layer is hydrophobic. There is a wettability gradient force at the vertical interface of the materials, which can realize autonomous water supply from the thermal insulation layer to the photothermal layer, ensuring the water supply-evaporation process.

[0082] Under simulated sunlight, the interface solar evaporation film composed of a double layer of "photothermal layer" and "insulation layer" achieved a heat release rate of 1.9 kg m -2 h -1 The evaporation yield is greatly improved compared with the evaporation system without thermal insulation layer.

Claims

1. A method for preparing an interfacial solar evaporation film, characterized in that: The following steps are involved: Step 1, preparing a hydrothermal reaction substrate containing seed crystals; There are two preparation methods: (1) soaking a porous fiber fabric in a solution containing one or both of copper ions and tungsten particles to obtain a porous fiber fabric containing seed crystals, and placing the porous fiber fabric in an oven for heat treatment to expose the seed crystals, thereby obtaining a hydrothermal reaction substrate containing the seed crystals; (2) A solution containing one or both of tungsten particles or copper ions is mixed with polyvinylidene fluoride to form a spinning precursor solution, a porous fiber membrane containing seed crystals is prepared by electrospinning, and the membrane is placed in an oven for heat treatment to expose the seed crystals, thereby obtaining a hydrothermal reaction substrate containing the seed crystals; Step 2: placing the hydrothermal reaction substrate containing the seed crystals in the hydrothermal reaction solution A to perform a hydrothermal growth reaction to obtain a photothermal layer A; The hydrothermal reaction solution A is a mixed hydrothermal growth solution composed of one or more of copper sulfate, copper acetate, copper chloride, ammonium tungstate and ammonium metatungstate and one of ammonia water, ammonium sulfide or sodium thiosulfate solution, wherein the concentration of the metal ions is between 0.02-0.8 M; Depending on the metal ions in the hydrothermal reaction solution A, the obtained nanosheet / nanoneedle microstructure is one or more of copper oxide, copper sulfide, tungsten oxide and tungsten sulfide; The specific conditions of the hydrothermal growth reaction are: The hydrothermal reaction device is transferred to an oven at 40-200°C and reacted for 4-18 hours to obtain a photothermal layer A having a nanosheet / nanoneedle microstructure on the surface through hydrothermal synthesis; Step 3: placing the hydrophobic polymer B in the organic solvent C and stirring thoroughly until it is completely dissolved, thereby obtaining a spinning solution containing 5% to 30% by weight of the hydrophobic polymer B; The hydrophobic polymer B is a polymer material with low thermal conductivity; Step 4: Place the spinning solution containing the hydrophobic polymer B in a syringe, and use the photothermal layer A as a receiving substrate to perform electrostatic spinning to obtain a hydrophobic insulation layer with low thermal conductivity, thereby obtaining an interface solar evaporation film integrating the photothermal layer and the insulation layer.

2. The method for preparing an interfacial solar evaporation film according to claim 1, wherein: The diameter of the nanosheets / nanoneedles ranges from 10 nm to 100 μm.

3. The method for preparing an interfacial solar evaporation film according to claim 1, characterized in that: The hydrophobic polymer B includes one or more of polystyrene, polyvinylidene fluoride, polyvinylidene fluoride hexafluoropropylene or polyacrylonitrile; the organic solvent C is a solvent formed by one or more of tetrahydrofuran, acetone, dimethyl sulfoxide or N,N-dimethylformamide or N,N-dimethylacetamide.

4. The method for preparing an interfacial solar evaporation film according to claim 1, wherein: The specific conditions of the electrospinning are: the diameter of the spinneret of the syringe is 0.2-1.5 mm, the spinning receiving distance is 10-30 cm, the high voltage static electricity applied between the receiving substrate and the spinning nozzle is 8-30 kV, and the spinning time is 30.0 s-30.0 min.

5. The method for preparing an interfacial solar evaporation film according to claim 1, wherein: When the polymer B is intrinsically hydrophilic, a low surface energy chemical substance D is introduced to hydrophobically modify the surface of the electrospun fiber membrane; The chemical substance D with low surface energy is one or more of methoxysilane, ethoxysilane, phenylsilane, alkylsilane, aminosilane, epoxysilane, acyloxysilane, vinylsilane or fluoric acid.

6. An interfacial solar evaporation film, prepared by the preparation method according to any one of claims 1 to 5, characterized in that: The interfacial solar evaporation film is a composite double-layer film structure, with an upper layer being a photothermal layer with a micro-nanostructure and a lower layer being a thermal insulation layer with a low thermal conductivity coefficient. The thermal insulation layer is hydrophobic, and the photothermal layer is hydrophilic, so that the interfacial solar evaporation film has a wettability gradient in a direction perpendicular to the material interface, and can spontaneously drive water from the hydrophobic layer to the hydrophilic layer from bottom to top. At the same time, the hydrophobicity of the thermal insulation layer is used to make the solar evaporation film float on the liquid surface. The photothermal layer with micro-nano structure is a nanosheet / nanoneedle microstructure grown on a hydrothermal reaction substrate containing seed crystals through hydrothermal synthesis; The working principle of the interfacial solar evaporation film is as follows: the photothermal layer absorbs light to generate heat, which heats the interfacial water pumped to the hydrophilic layer to generate steam; the thermal insulation layer blocks direct contact between the photothermal layer and the water body, avoiding heat loss due to transfer to the large amount of water below.

7. The interface solar evaporation film according to claim 6, characterized in that: The diameter of the micro-nano structure of the photothermal layer is in the range of 10 nm-100 μm; the fiber diameter of the thermal insulation layer is in the range of 50 nm-3 μm, and the pore size of the fiber membrane of the thermal insulation layer is in the range of 1 nm-100 μm.

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