A multi-layer composite radiation cooling-hygroscopic functional layered material and its preparation method

Abstract

The present invention belongs to the field of ecological restoration technology and specifically discloses a multi-layer composite radiative cooling-hygroscopic functional layered material and a preparation method thereof. The multi-layer composite radiative cooling-hygroscopic functional layered material comprises four layers from top to bottom: an emissive layer, a reflective film, a glass substrate, and a water collection layer. The emissive layer serves as the upper surface of the material and spontaneously dissipates heat to outer space through an atmospheric window, thereby lowering the temperature of the entire material below the ambient temperature. The water collection layer serves as the lower surface of the material and is loaded with hygroscopic salts to spontaneously collect atmospheric moisture. The present invention innovatively constructs a double-sided sheet structure. The upper surface has a radiative cooling function, enabling all-weather cooling and providing a surface for atmospheric water condensation. The lower surface is loaded with hygroscopic salts to collect atmospheric moisture. At the same time, the radiative cooling structure on the upper surface lowers the overall temperature of the material, increasing the relative humidity of the water surrounding the material and promoting the atmospheric water collection process on the lower surface.

Description

Technical Field

[0001] The present invention relates to the technical field of ecological restoration, and in particular to a multi-layer composite radiation cooling-hygroscopic functional layered material and a preparation method thereof. Background Art

[0002] Atmospheric water harvesting, that is, extracting water from the air, is considered to be a very promising technology that can produce fresh water without centralized facilities and without regional restrictions. At present, many materials with atmospheric water harvesting functions have been prepared. For example, CN117582934A discloses "Preparation method and application of atmospheric water adsorption polymeric materials and atmospheric water harvesting method", which realizes atmospheric water harvesting function by loading hygroscopic salts such as calcium chloride and lithium chloride on carriers such as sodium carboxymethyl cellulose and maltodextrin. However, this type of atmospheric water harvesting material is limited by the relative humidity of the surrounding environment, and its water harvesting ability is poor under low relative humidity conditions.

[0003] Radiative cooling utilizes the thermal radiation of a material within the atmospheric window (wavelength 8–13 μm) to dissipate heat into the cold outer space, thereby lowering the temperature of the material and its surroundings and promoting the condensation of atmospheric water. For example, in the "Silicon-Based Radiative Cooling Emitter for Atmospheric Water Collection and Its Preparation Method" disclosed in CN118670023A, the material has excellent radiative cooling effects and promotes the condensation of atmospheric water on the material surface, thereby achieving atmospheric water collection. However, collecting atmospheric water through radiative cooling also has limitations. Clouds and water vapor can greatly reduce the radiation efficiency.

[0004] To overcome the limitations of current technologies, this invention leverages the advantages of hygroscopic salt-based atmospheric water-collecting materials and radiative cooling materials, respectively imparting radiative cooling and atmospheric water-collecting capabilities to the upper and lower surfaces of a layered material. Radiative cooling lowers the temperature of the material surface and the surrounding environment, increasing relative humidity and thereby enhancing atmospheric water collection on the lower surface. Furthermore, the hygroscopic salt-based atmospheric water-collecting material mitigates the low condensation efficiency of radiative cooling materials in thick cloud cover or high ambient humidity. Summary of the Invention

[0005] In order to solve the problems existing in the prior art, the present invention provides a multi-layer composite radiation cooling-hygroscopic functional layered material and a preparation method thereof, which solves the problems mentioned in the above background technology.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: a multi-layer composite radiation cooling-hygroscopic functional layered material, wherein the multi-layer composite radiation cooling-hygroscopic functional layered material comprises four layers from top to bottom: an emission layer, a reflective film, a glass substrate and a water collection layer; wherein the emission layer serves as the upper surface of the material, spontaneously dissipates heat to outer space through the atmospheric window 8–13 μm, and has a radiation cooling function, thereby making the temperature of the entire material lower than the ambient temperature; the water collection layer serves as the lower surface of the material, loads hygroscopic salt, and spontaneously collects atmospheric moisture.

[0007] Preferably, the emission layer is composed of polyvinyl alcohol and nanoparticles and has a radiation cooling function; the water collection layer is composed of polyvinyl alcohol, polyethylene oxide, silica nanoparticles and calcium chloride; the emission layer can achieve all-weather cooling to increase the humidity around the material, providing a surface for condensation of atmospheric water; the emission layer and the water collection layer synergize to promote the water collection layer to collect more moisture in the atmosphere and accelerate the atmospheric water collection process.

[0008] On the other hand, to achieve the above-mentioned purpose, the present invention also provides the following technical solution: a method for preparing a multi-layer composite radiation cooling-hygroscopic functional layered material, comprising the following steps:

[0009] S1. Pasting the reflective film: Select a reflective film with a reflectivity greater than 95%, and then paste it on the glass substrate; then prepare a 1% concentration of silane coupling agent aqueous solution, apply it on the upper surface of the reflective film and the lower surface of the glass substrate, and dry it at room temperature to complete the surface pretreatment;

[0010] S2. preparing a polyvinyl alcohol solution: soaking polyvinyl alcohol in pure water for 1 hour, and then heating to 90° C. to dissolve the polyvinyl alcohol solution;

[0011] S3. Preparation of the emission layer: Place the nanoparticles in a polyvinyl alcohol solution and ultrasonicate for 10 minutes to ensure complete dispersion. Then, apply the nanoparticles evenly on the surface of the pretreated reflective film and dry at 50°C.

[0012] S4. Preparing a water collection layer: adding polyethylene oxide to the polyvinyl alcohol solution prepared in step S2 to form a mixed solution, then adding calcium chloride and silica nanoparticles to the mixed solution, ultrasonicating for 10 minutes to ensure complete dispersion, and then evenly applying the mixture to the lower surface of the glass substrate after surface pretreatment. After drying in a 50°C oven, a multilayer composite radiative cooling-hygroscopic functional layered material is obtained.

[0013] Preferably, in step S2, the degree of polymerization of the polyvinyl alcohol is in the range of 1700 to 2500, the degree of alcoholysis is in the range of 88% to 99%, and the mass concentration of the prepared polyvinyl alcohol solution is 1% to 10%.

[0014] Preferably, in step S3, the mass ratio of the nanoparticles to polyvinyl alcohol is 1-10:1.

[0015] Preferably, in step S3, the mass ratio of the nanoparticles to polyvinyl alcohol is 10:1.

[0016] Preferably, in step S3, the size of the nanoparticles is between 100 nanometers and 10 micrometers.

[0017] Preferably, the nanoparticles are barium sulfate or aluminum oxide nanoparticles.

[0018] Preferably, in step S4, the molecular weight of the polyethylene oxide is between 1 million and 5 million, and the mass concentration of the polyethylene oxide is not higher than 0.1%.

[0019] Preferably, in step S4, the mass ratio of the calcium chloride to the polyvinyl alcohol is 1-2:1-2; the mass ratio of the silicon dioxide nanoparticles to the polyvinyl alcohol is 1-2:1-2.

[0020] The present invention has the following beneficial effects: The method innovatively constructs a double-sided layered structure with atmospheric water collection capabilities. The reflective layer reflects sunlight or light originating from above the material back into the environment, reducing the amount of light entering the water collection layer and thereby minimizing the temperature rise in the water collection layer caused by light absorption. In addition to providing support for the other layers, the glass substrate's high light transmittance reduces light absorption (primarily scattered light from the environment), thereby reducing the risk of temperature rise in the material. The combination of the reflective layer and the glass substrate ensures that the overall material temperature does not exceed the ambient temperature, even during the day. The emissive layer on the upper surface achieves radiative cooling, driving the overall material temperature down. The water collection layer on the lower surface spontaneously absorbs moisture from the air using hygroscopic salts. Simultaneously, a synergistic effect exists between the emissive and water collection layers. The radiative cooling function of the emissive layer lowers the material temperature, increasing the relative humidity of the surrounding air and enhancing the water collection layer's hygroscopic properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the structure of a multi-layer composite radiation cooling-moisture absorption functional layered material in an embodiment of the present invention;

[0022] Figure 2 This is a schematic diagram of the emissivity information of the emissive layer in Example 1 of the present invention;

[0023] Figure 3 This is a schematic diagram of the emissivity information of the emission layer in Example 2 of the present invention;

[0024] Figure 4 This is a schematic diagram of the emissivity information of the emission layer in Example 3 of the present invention;

[0025] Figure 5 This is a schematic diagram of the emissivity information of the emission layer in Example 4 of the present invention;

[0026] Figure 6 This is a schematic diagram of the emissivity information of the emissive layer of Comparative Example 1 of the present invention;

[0027] Figure 7 Schematic diagram of the contact angle of the glass substrate corresponding to Example 1 of the present invention;

[0028] Figure 8 Schematic diagram of the contact angle of the emission layer corresponding to Example 1 of the present invention;

[0029] Figure 9 Schematic diagram of the contact angle of the water collecting layer corresponding to Example 1 of the present invention;

[0030] In the figure, 1-emission layer; 2-reflection film; 3-glass substrate; 4-water collection layer. DETAILED DESCRIPTION

[0031] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0032] It should be noted that, unless there is a conflict, the embodiments and features of the embodiments of the present invention may be combined with each other. It should be noted that similar reference numerals and letters represent similar items in the following figures. Therefore, once an item is defined in one figure, it does not need to be further defined or explained in subsequent figures.

[0033] In the description of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, or are the orientations or positional relationships in which the inventive product is typically placed when in use, or are the orientations or positional relationships commonly understood by those skilled in the art. These terms are intended only to facilitate the description of the present invention and to simplify the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limiting the present invention. Furthermore, the terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0034] In the description of the present invention, it should also be noted that, unless otherwise expressly specified or limited, the terms "disposed," "installed," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; they may refer to mechanical connections or electrical connections; they may refer to direct connections or indirect connections through an intermediate medium; and they may refer to internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0035] See also Figure 1 The present invention provides a technical solution: a multi-layer composite radiation cooling-hygroscopic functional layered material, such as Figure 1 As shown, the structure consists of four layers, from top to bottom: an emitting layer 1, a reflective film 2, a glass substrate 3, and a water-collecting layer 4. The emitting layer 1, as the upper surface of the material, spontaneously dissipates heat to outer space through an atmospheric window (8–13 μm), providing radiative cooling, thereby keeping the entire material temperature below the ambient temperature. The water-collecting layer 4, as the lower surface of the material, carries hygroscopic salts and spontaneously collects atmospheric moisture. The glass substrate 3 provides support, while the reflective film 2 reflects sunlight during the day, preventing it from entering the glass substrate 3 and water-collecting layer 4 and causing a temperature increase.

[0036] The emission layer 1 is composed of polyvinyl alcohol and nanoparticles and has a radiation cooling function; the water collection layer 4 is composed of polyvinyl alcohol, polyethylene oxide, silicon dioxide nanoparticles and calcium chloride; the emission layer 1 can achieve all-weather cooling to increase the humidity around the material, providing a surface for condensation of atmospheric water; the emission layer 1 and the water collection layer 4 synergistically enhance the efficiency, prompting the water collection layer 4 to collect more moisture in the atmosphere and accelerate the atmospheric water collection process.

[0037] The atmospheric water collection principle of the multi-layer composite radiative cooling and hygroscopic layered material of this invention is as follows: Because emissive layer 1 enables radiative cooling, atmospheric water vapor condenses on the cooler emissive layer 1, thereby collecting moisture. Water collection layer 4, containing calcium chloride (a hygroscopic salt), also absorbs atmospheric moisture. Furthermore, thanks to the lowering of the overall material temperature by emissive layer 1, the relative humidity surrounding the material increases. Compared to a standalone water collection layer 4, the water collection layer 4 of this invention is able to absorb more atmospheric water.

[0038] The preparation method of the multi-layer composite radiation cooling-hygroscopic functional layered material of the present invention is as follows:

[0039] 1) Select a reflective film with a reflectivity greater than 95% (3M's ESR reflective film is used in this example) and adhere it to the glass substrate using an acrylic adhesive. Then, prepare a 1% aqueous solution of silane coupling agent and apply it to the upper surface of the reflective film and the lower surface of the glass substrate with a knife. Dry at room temperature to complete the surface pretreatment. The glass substrate should be no thicker than 500 microns, and the reflective film no thicker than 200 microns.

[0040] 2) Soak the polyvinyl alcohol in pure water for 1 hour, then heat to 90°C to dissolve it, forming a polyvinyl alcohol solution. The polyvinyl alcohol must have a degree of polymerization (DP) of at least 1700 and a degree of alcoholysis (OD) of at least 88%, with a concentration of at least 1%.

[0041] 3) Select barium sulfate or aluminum oxide nanoparticles, place them in a polyvinyl alcohol solution, and ultrasonicate for 10 minutes to ensure complete dispersion. Then, apply the solution evenly to the pretreated reflective film surface with a doctor blade and dry at 50°C. To ensure excellent radiation within the atmospheric window, the nanoparticle size must match the wavelength of radiation within the atmospheric window, thus maintaining a size between 100 nanometers and 10 microns. The mass ratio of nanoparticles to polyvinyl alcohol should be between 1:1 and 10:1. The thickness of the emissive layer should be between 200 and 500 microns.

[0042] 4) Soak the polyvinyl alcohol in pure water for 1 hour, then heat to 90°C to dissolve it. Then, add polyethylene oxide to form a mixed solution. The polyethylene oxide must have a molecular weight of at least 1,000,000 and a concentration of no more than 0.1%. Then, add calcium chloride and silica nanoparticles. The mass ratio of calcium chloride to polyvinyl alcohol is between 1:2 and 2:1, and the mass ratio of silica nanoparticles to polyvinyl alcohol is between 1:2 and 2:1. The mixed solution, containing calcium chloride and silica nanoparticles, is sonicated for 10 minutes to ensure complete dispersion. The solution is then evenly applied by scraper to the lower surface of a pre-treated glass substrate and dried in an oven at 50°C to obtain the finished product.

[0043] Example 1

[0044] Soak polyvinyl alcohol in pure water for 1 hour, then heat to 90°C to dissolve it, forming a 2% polyvinyl alcohol solution. Select alumina particles (200 nm) and place them in the polyvinyl alcohol solution. Ultrasonicate for 10 minutes to ensure complete dispersion. Then, apply the mixture evenly to the surface of the pre-treated reflective film and air-dry at room temperature. The mass ratio of alumina particles to polyvinyl alcohol is 1:1.

[0045] After soaking the polyvinyl alcohol in pure water for one hour, the mixture was heated to 90°C to dissolve, forming a 2% polyvinyl alcohol solution. Polyethylene oxide was then added to a concentration of 0.1%. Calcium chloride and silica nanoparticles were then added. The mass ratio of calcium chloride to polyvinyl alcohol was 1:2, and the mass ratio of silica nanoparticles to polyvinyl alcohol was 1:1. The mixed solution was then sonicated for 10 minutes to ensure complete dispersion. The mixture was then evenly applied to the glass backplane and dried in a 50°C oven for 6 hours to obtain the finished product.

[0046] The emissivity of the emissive layer 1 film was determined using Fourier transform infrared spectroscopy, as Figure 2 The emissivity information of the emissive layer in Example 1 shows that the average emissivity is 86.56% in the wavelength range of 2.5 μm to 25 μm.

[0047] The addition of calcium chloride gives the water-collecting layer the ability to absorb moisture. The silica nanoparticles in the water-collecting layer optimize the surface roughness of the water-collecting layer, increase the specific surface area of ​​the water-collecting layer, and also reduce the water contact angle of the water-collecting layer. The contact angles of the emitting layer 1, the water-collecting layer 4 film, and the glass substrate 3 were measured using a contact angle meter. Figures 7 to 9 As shown. Figure 7 As shown, the corresponding contact angle of the glass substrate is 17.76°, and the water contact angle is reduced, making the surface of the water collection layer more hydrophilic and more conducive to collecting atmospheric water; Figure 8 As shown, the corresponding contact angle of the emission layer is 55.51°, which is more conducive to the formation of condensed dew droplets than the glass substrate. Figure 9 As shown in Figure 1, the contact angle of the water-collecting layer corresponding to Example 1 is 7.56°, which is due to the addition of polyethylene oxide and nano-silicon dioxide during the preparation process. Compared with the emissive layer, the water-collecting layer is more hydrophilic, which is conducive to the atmospheric water collection process.

[0048] The 180° peel strength of the reflective layer, the emitting layer, and the water collection layer of the material was measured using a peel strength tester at an ambient temperature of 23°C and a relative humidity of 50%. The results are shown in Table 1.

[0049] Table 1 Peel strength test results of each layer of material

[0050]

[0051] Example 2

[0052] Soak polyvinyl alcohol in pure water for 1 hour, then heat to 90°C to dissolve it, forming a 2% polyvinyl alcohol solution. Select alumina particles (200 nm) and place them in the polyvinyl alcohol solution. Ultrasonicate for 10 minutes to ensure complete dispersion. Then, apply the mixture evenly to the surface of the pre-treated reflective film and air-dry at room temperature. The mass ratio of alumina particles to polyvinyl alcohol is 10:1.

[0053] After soaking the polyvinyl alcohol in pure water for one hour, the mixture was heated to 90°C to dissolve, forming a 2% polyvinyl alcohol solution. Polyethylene oxide was then added to a concentration of 0.1%. Calcium chloride and silica nanoparticles were then added. The mass ratio of calcium chloride to polyvinyl alcohol was 2:1, and the mass ratio of silica nanoparticles to polyvinyl alcohol was 1:1. The mixed solution was then sonicated for 10 minutes to ensure complete dispersion. The mixture was then evenly applied to the glass backplane and dried in a 50°C oven for 6 hours to obtain the finished product.

[0054] The emissivity of the emissive layer 1 film was determined using Fourier transform infrared spectroscopy, as Figure 3 The emissivity information of the emissive layer in Example 2 shows that the average emissivity is 94.22% in the wavelength range of 2.5 μm to 25 μm.

[0055] Example 3

[0056] Soak polyvinyl alcohol in pure water for 1 hour, then heat to 90°C to dissolve it, forming a 2% polyvinyl alcohol solution. Select barium sulfate particles (1 micron) and place them in the polyvinyl alcohol solution. Ultrasonicate for 10 minutes to ensure complete dispersion. Then, apply the particles evenly to the surface of the pre-treated reflective film and air-dry at room temperature. The mass ratio of aluminum oxide particles to polyvinyl alcohol is 1:1.

[0057] After that, the polyvinyl alcohol was soaked in pure water for 1 hour and then heated to 90°C to dissolve, forming a polyvinyl alcohol solution with a mass concentration of 2%. Polyethylene oxide was added to a mass concentration of 0.1%. Calcium chloride and silica nanoparticles were then added. The mass ratio of calcium chloride to polyvinyl alcohol was 1:2, and the mass ratio of silica nanoparticles to polyvinyl alcohol was 1:1. The mixed solution was then ultrasonicated for 10 minutes to ensure complete dispersion, and evenly applied to the glass backplane. The finished product was then dried in a 50°C oven for 6 hours.

[0058] The emissivity of the emissive layer 1 film was determined using Fourier transform infrared spectroscopy, as Figure 4 As shown in Figure 3, the emissivity of the emissive layer in Example 3 shows an average emissivity of 86.74% within the wavelength range of 2.5 μm to 25 μm.

[0059] Example 4

[0060] Soak polyvinyl alcohol in pure water for 1 hour, then heat to 90°C to dissolve it, forming a 2% polyvinyl alcohol solution. Select barium sulfate particles (1 micron) and place them in the polyvinyl alcohol solution. Ultrasonicate for 10 minutes to ensure complete dispersion. Apply the particles evenly to the pre-treated reflective film and air-dry at room temperature. The mass ratio of aluminum oxide particles to polyvinyl alcohol is 10:1.

[0061] After that, the polyvinyl alcohol was soaked in pure water for 1 hour and then heated to 90°C to dissolve, forming a polyvinyl alcohol solution with a mass concentration of 2%. Polyethylene oxide was added to a mass concentration of 0.1%. Calcium chloride and silica nanoparticles were then added. The mass ratio of calcium chloride to polyvinyl alcohol was 2:1, and the mass ratio of silica nanoparticles to polyvinyl alcohol was 1:1. The mixed solution was then ultrasonicated for 10 minutes to ensure complete dispersion, and evenly applied to the glass backplane. The finished product was then dried in a 50°C oven for 6 hours.

[0062] The emissivity of the emissive layer 1 film was determined using Fourier transform infrared spectroscopy, as Figure 5 The emissivity information of the emissive layer in Example 4 shows that the average emissivity is 96.16% in the wavelength range of 2.5 μm to 25 μm.

[0063] Comparative Example 1

[0064] Soak polyvinyl alcohol in pure water for 1 hour, then heat to 90°C to dissolve it, forming a 2% polyvinyl alcohol solution. Select alumina particles (200 nm) and place them in the polyvinyl alcohol solution. Ultrasonicate for 10 minutes to ensure complete dispersion. Then, apply the mixture evenly to the surface of the pre-treated reflective film and air-dry at room temperature. The mass ratio of alumina particles to polyvinyl alcohol is 1:10.

[0065] After soaking the polyvinyl alcohol in pure water for one hour, the mixture was heated to 90°C to dissolve, forming a 2% polyvinyl alcohol solution. Polyethylene oxide was then added to a concentration of 0.1%. Calcium chloride and silica nanoparticles were then added. The mass ratio of calcium chloride to polyvinyl alcohol was 1:2, and the mass ratio of silica nanoparticles to polyvinyl alcohol was 1:1. The mixed solution was then sonicated for 10 minutes to ensure complete dispersion. The mixture was then evenly applied to the glass backplane and dried in a 50°C oven for 6 hours to obtain the finished product.

[0066] In comparative example 1, when preparing the emission layer 1, the amount of nanoparticles added was too small (not reaching the mass ratio required by the present invention), resulting in poor radiation cooling effect and atmospheric water collection effect. Figure 6 As shown, the emissivity information of the emissive layer in Comparative Example 1 has an average emissivity of 53.14% in the wavelength range of 2.5 μm to 25 μm, which is relatively low.

[0067] Comparative Example 2

[0068] Soak polyvinyl alcohol in pure water for 1 hour, then heat to 90°C to dissolve it, forming a 2% polyvinyl alcohol solution. Select alumina particles (200 nm) and place them in the polyvinyl alcohol solution. Ultrasonicate for 10 minutes to ensure complete dispersion. Then, apply the mixture evenly to the surface of the pre-treated reflective film and air-dry at room temperature. The mass ratio of alumina particles to polyvinyl alcohol is 1:1.

[0069] After soaking the polyvinyl alcohol in pure water for one hour, the mixture was heated to 90°C to dissolve, forming a 2% polyvinyl alcohol solution. Polyethylene oxide was then added to a concentration of 0.1%. Silica nanoparticles were then added at a 1:1 mass ratio of silica nanoparticles to polyvinyl alcohol. The mixed solution was then ultrasonically applied for 10 minutes to ensure complete dispersion, then evenly applied to the glass backplane and dried in a 50°C oven for 6 hours to obtain the finished product.

[0070] In Comparative Example 2, when preparing the water collection layer 4, no hygroscopic salt such as calcium chloride was added. Although the radiation cooling effect was acceptable, the atmospheric water collection effect was not good.

[0071] Under clear, partly cloudy weather conditions, the materials in the above examples and comparative examples were placed in polystyrene foam with the upper surface (emissive layer) facing the sky. After 12 hours, the ambient temperature, material temperature, and the amount of water collected on the upper and lower surfaces of the materials were measured. The results are shown in Table 2.

[0072] Table 2 Comparison of water collection capacity between the embodiment and the comparative example

[0073]

[0074] It can be seen that both the emissive layer and the water-collecting layer have water-collecting functions. The water-collecting function of the emissive layer is related to its emissivity; higher emissivity leads to stronger water-collecting effects. The water-collecting function of the water-collecting layer is also related to its calcium chloride content; higher calcium chloride content increases water collection. Furthermore, the radiative cooling effect of the emissive layer can also enhance the atmospheric water-collecting effect of the water-collecting layer (see Comparative Example 1 and Example 1).

[0075] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A multi-layer composite radiation cooling-hygroscopic functional layered material, characterized in that: The multi-layer composite radiation cooling-hygroscopic functional layered material comprises four layers from top to bottom: an emission layer (1), a reflection film (2), a glass substrate (3) and a water collection layer (4); wherein the emission layer (1) serves as the upper surface of the material and spontaneously dissipates heat to outer space through an atmospheric window of 8–13 μm, thus having a radiation cooling function, thereby making the temperature of the entire material lower than the ambient temperature; the water collection layer (4) serves as the lower surface of the material and carries hygroscopic salts to spontaneously collect atmospheric moisture; The emission layer (1) is composed of polyvinyl alcohol and nanoparticles and has a radiation cooling function; the water collection layer (4) is composed of polyvinyl alcohol, polyethylene oxide, silicon dioxide nanoparticles and calcium chloride; the emission layer (1) can achieve all-weather cooling to increase the humidity around the material, providing a surface for condensation of atmospheric water; the emission layer (1) and the water collection layer (4) synergistically enhance the efficiency, prompting the water collection layer (4) to collect more moisture in the atmosphere and accelerate the atmospheric water collection process; The polymerization degree of the polyvinyl alcohol is in the range of 1700 to 2500, the alcoholysis degree is in the range of 88% to 99%, and the mass concentration of the prepared polyvinyl alcohol solution is 1% to 10%.

2. A method for preparing the multi-layer composite radiative cooling-hygroscopic functional layered material according to claim 1, characterized in that: The steps include: S1. Pasting the reflective film: Select a reflective film (2) with a reflectivity greater than 95%, and then paste it on the glass substrate (3); then prepare a 1% concentration of silane coupling agent aqueous solution, scrape it on the upper surface of the reflective film and the lower surface of the glass substrate, and dry it at room temperature to complete the surface pretreatment; S2. preparing a polyvinyl alcohol solution: soaking polyvinyl alcohol in pure water for 1 hour, and then heating to 90° C. to dissolve the polyvinyl alcohol solution; S3. Preparation of the emission layer: Place the nanoparticles in a polyvinyl alcohol solution and ultrasonicate for 10 minutes to ensure complete dispersion. Then, apply the nanoparticles evenly on the surface of the pretreated reflective film and dry at 50°C. S4. Preparing a water collection layer: adding polyethylene oxide to the polyvinyl alcohol solution prepared in step S2 to form a mixed solution, then adding calcium chloride and silica nanoparticles to the mixed solution, ultrasonicating for 10 minutes to ensure complete dispersion, and then evenly applying the mixture to the lower surface of the glass substrate after surface pretreatment. After drying in a 50°C oven, a multilayer composite radiative cooling-hygroscopic functional layered material is obtained.

3. The method for preparing the multi-layer composite radiation cooling and moisture absorption functional layered material according to claim 2, characterized in that: In step S3, the mass ratio of the nanoparticles to polyvinyl alcohol is 1 to 10:

1.

4. The method for preparing the multi-layer composite radiation cooling and moisture absorption functional layered material according to claim 2, characterized in that: In step S3 , the size of the nanoparticles is between 100 nanometers and 10 micrometers.

5. The method for preparing the multi-layer composite radiation cooling-hygroscopic functional layered material according to claim 2 or 3, characterized in that: The nanoparticles are barium sulfate or aluminum oxide nanoparticles.

6. The method for preparing the multi-layer composite radiation cooling and moisture absorption functional layered material according to claim 2, characterized in that: In step S4, the molecular weight of the polyethylene oxide is between 1 million and 5 million, and the mass concentration of the polyethylene oxide is not higher than 0.1%.

7. The method for preparing the multi-layer composite radiation cooling and moisture absorption functional layered material according to claim 2, characterized in that: In step S4, the mass ratio of the calcium chloride to the polyvinyl alcohol is 1-2:1-2; the mass ratio of the silicon dioxide nanoparticles to the polyvinyl alcohol is 1-2:1-2.

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