Clay mineral-based microporous radiation refrigeration material and preparation method thereof

Abstract

The invention relates to a clay mineral-based microporous radiation refrigeration material and a preparation method thereof. The preparation method comprises the following steps: firstly, mixing and uniformly dispersing ethyl cellulose and clay minerals in a solution state, then carrying out blade coating on a substrate by using the obtained mixed material to form a film, and finally, modifying a coating by using a polyethyleneimine solution and a trimesoyl chloride solution in sequence to obtain the water-resistant clay mineral-ethyl cellulose microporous radiation refrigeration coating material. A large number of micron holes and micron-sized clay mineral particles exist in the radiation refrigeration material, an ethyl cellulose / air hole interface, and Mie scattering of the ethyl cellulose / clay mineral interface and the clay mineral / air hole interface enables the material to have high sunlight reflectivity; rich silicon-oxygen bonds in the clay minerals enable the material to have high infrared emissivity in an 8-13 [mu] m infrared atmosphere window wave band, so that the material can spontaneously send heat to the universe in a heat radiation mode, and low-cost and zero-energy-consumption refrigeration is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of special functional materials, in particular to the technical field of radiation refrigeration and clay composite materials, and specifically to a clay mineral-based microporous radiation refrigeration material and a preparation method thereof. Background Art

[0002] The energy crisis and climate change are two major challenges facing the world. Statistics show that traditional cooling equipment, such as fans and air conditioners, accounts for 10% of global electricity consumption. While consuming energy, these devices also produce large amounts of carbon dioxide and other greenhouse gases, exacerbating global warming and extreme weather. For the sustainable development of human society, the development of new, low-carbon, and green cooling technologies with low or even zero energy consumption is imperative.

[0003] Radiative cooling (abbreviated as radiative cooling) is an emerging zero-energy, zero-pollution cooling technology. It is based on two objective laws: the blackbody radiation peak of an object at a temperature of 300K at an infrared wavelength of 10μm, and the high transmittance of the atmosphere to infrared radiation with a wavelength of 8-13μm (atmospheric window). This technology enables objects to spontaneously emit heat into the deep cold outer space (3K) in the form of infrared thermal radiation, thereby achieving a significant cooling effect.

[0004] To achieve efficient daytime radiative cooling under direct solar radiation, researchers have reduced the material's solar absorption rate in the 0.2-2.5μm band by introducing dielectric materials and periodic nanostructures. For example, Ziming Cheng's team, inspired by the wrinkles of human skin, incorporated barium sulfate (BaSO4) and silicon dioxide (SiO2) nanoparticles into a polytetrafluoroethylene (PTFE) coating. Leveraging the Mie scattering effect, they achieved a 93% reflectivity in the visible light band (0.38-0.78μm) while maintaining a high emissivity of 95% in the mid-infrared band (8-13μm). Under 800W / m² of solar radiation, the coating's surface temperature was reduced by 6.2°C compared to the ambient temperature (Ziming Cheng, Han Han, etc. Nano Energy. Efficient radiative cooling coating with biomimetic human skin wrinkle structure. November 2021. 106377). Tong Wang's team alternately arranged micropores (2-5μm) and nanopores (50-200nm) in a polymethyl methacrylate (PMMA) film. Through this periodic alternating structure of micropores and nanopores, they reduced the absorption of near-infrared and ultraviolet-visible light energy, increased the film's solar reflectivity to 95%, and achieved a daytime radiative cooling power of 85W / m² (Tong Wang, Yi Wu, etc. Nature communications. A structural polymer for highly efficient all-day passive radiative cooling. January 2021).

[0005] While existing radiative cooling materials offer excellent cooling performance, the complex preparation conditions for periodic microstructures make them difficult to manufacture in large quantities. They are also susceptible to environmental influences, which can easily lead to structural damage and reduce cooling efficiency, making them difficult to withstand the harsh environments encountered in practical applications. Furthermore, while composites of organic matter and dielectric materials also offer high radiative cooling effects, nanoscale materials like barium sulfate, silicon dioxide, and aluminum oxide are relatively expensive (approximately 200,000 to 600,000 yuan per ton), making them economically unfeasible.

[0006] Natural clay minerals, such as kaolin, talc, montmorillonite, and eletrosite, are typically composed of silicon-oxygen tetrahedra, aluminum-oxygen octahedra, and magnesium-oxygen octahedra. Because aluminum oxide, silicon oxide, and magnesium oxide all have high band gaps (>4.13 eV), sunlight is not absorbed by the layered structures of these phyllosilicate minerals, resulting in a solar reflectivity exceeding 85%. Furthermore, the abundance of silicon-oxygen bonds allows these minerals to exhibit a broad-spectrum emissivity of nearly 90% in the infrared atmospheric window (8-13 μm), resulting in a strong daytime radiant cooling effect. Therefore, we sought to utilize inexpensive and readily available natural clays to prepare radiant cooling materials, addressing the common challenges of these materials, such as complex preparation processes, high costs, and suboptimal performance. Summary of the Invention

[0007] One of the objectives of the present invention is to provide a clay mineral-based microporous radiation cooling material that can efficiently scatter and reflect solar radiation and efficiently emit medium-wave infrared radiation, thereby reducing the temperature of the material itself and achieving zero-energy daytime radiation cooling.

[0008] The clay mineral-based microporous radiative cooling material provided by the present invention mainly comprises clay mineral and ethyl cellulose. Specifically, the clay mineral-based microporous radiative cooling material is assembled by cross-linking clay mineral particles and ethyl cellulose.

[0009] Furthermore, the clay mineral-based microporous radiation cooling material has a porous structure, and its pores are micron-sized, with a size of 2-5 μm.

[0010] Furthermore, the clay mineral particles are in the micron range, and particles with a diameter less than 2 μm account for ≥90%.

[0011] Furthermore, the clay mineral is selected from at least one of kaolin, talc, bentonite, montmorillonite, and eidolite. Clay minerals are abundant in source and relatively low in cost, which helps to reduce the cost of radiant cooling materials.

[0012] Specifically, the clay mineral is a mixture of kaolin and montmorillonite in a mass ratio of 5:1, or a mixture of kaolin, montmorillonite and talc in a mass ratio of 2:1:1, or a mixture of montmorillonite and talc in a mass ratio of 1:1.

[0013] Furthermore, the mass ratio of ethyl cellulose to clay mineral in the microporous radiative cooling material is 1:19 to 4:1. The composite ratio of ethyl cellulose to clay mineral must be controlled within a reasonable range; excessive or insufficient amounts of either component can affect the product's mechanical and radiative cooling properties.

[0014] Furthermore, the microporous radiation cooling material is usually presented in the form of a coating with a multi-layer structure, including at least a clay mineral-ethyl cellulose composite layer at the bottom and a polyethyleneimine layer and a trimesoyl chloride layer located above the composite layer.

[0015] The present invention also provides a method for preparing the aforementioned clay mineral-based microporous radiative cooling material. This method simply involves uniformly mixing ethyl cellulose with a clay mineral in a solution, followed by forming a coating on the substrate surface. Compared to existing processes for preparing radiative cooling materials, the present method offers significant advantages, including simplicity, ease of implementation, and low cost.

[0016] In the present invention, ethyl cellulose and clay mineral are mixed in at least two ways: The first method is to prepare an ethyl cellulose solution with a mass percentage concentration of 1% to 8% and a clay mineral suspension with a mass percentage concentration of 5% to 20% and a pH of 3.0 to 11, and then mix the two evenly.

[0017] The second method: prepare an ethyl cellulose solution with a mass percentage concentration of 1% to 8%, then add clay minerals and disperse evenly.

[0018] Furthermore, the solvent used to prepare the ethyl cellulose solution and the clay mineral suspension is a mixture of ethanol and deionized water, wherein the mass proportion of ethanol is 60%-95%.

[0019] Furthermore, water bath heating, stirring, ultrasound and the like are used to uniformly disperse the ethyl cellulose and clay mineral in the solution, suspension or mixed solution.

[0020] Furthermore, the water bath heating temperature is controlled between 60-80°C, the stirring speed is controlled between 400-1200 rpm, and the ultrasonic power is controlled between 300-500w.

[0021] Furthermore, the substrate is selected from any one of polyethylene terephthalate (PET), polyethylene (PE), polystyrene (PS), and wood board.

[0022] Furthermore, at least one coating layer is formed on the substrate by scraping, and the amount of the mixed liquid used during scraping is controlled at 0.5~1.5L / m 2 .

[0023] As a preferred embodiment, the preparation method of the present invention further includes a subsequent modification treatment of the coating: coating the coating surface with a polyethyleneimine aqueous solution and a trimesoyl chloride solution in sequence, reacting for a period of time after each coating, then wiping off the coating liquid and drying at room temperature.

[0024] Furthermore, the mass percentage concentration of the polyethyleneimine aqueous solution is 0.2%-5%.

[0025] Furthermore, the mass percentage concentration of the trimesoyl chloride solution is 0.05%-1.5%, and the solvent used to prepare the trimesoyl chloride solution is selected from any one of pentane, n-hexane, and heptane.

[0026] The clay minerals used in the preparation of the clay mineral-based microporous radiation cooling coating material of the present invention are kaolin, talc, bentonite, elutite or montmorillonite, which appear as white, light yellow or light gray solid particles with a particle size of about 2 microns after treatment. Ethyl cellulose is selected as a matching cross-linking agent, which will produce a large number of 2-5 micron pores due to the uneven volatilization of the solvent, and ultimately a large number of micron pores and micron-sized clay mineral particles are distributed in the formed coating. When sunlight enters the coating material, Mie scattering occurs at the ethyl cellulose / air pore interface, the ethyl cellulose / clay mineral interface and the clay mineral / air pore interface, so that the material as a whole exhibits a high solar reflectivity. In addition, because the clay mineral contains rich silicon-oxygen bonds, the material has a high infrared emissivity in the 8-13μm infrared atmospheric window band, and can spontaneously send heat into the universe in the form of thermal radiation, ultimately significantly reducing the temperature of the coating surface.

[0027] Compared with existing similar technologies, the advantages of the present invention are mainly reflected in the following points: (1) Compared with the existing radiative cooling coatings that use expensive and difficult-to-disperse nanoparticles as raw materials, the present invention uses natural clay minerals to prepare radiative cooling materials, which not only greatly reduces production costs but also has a simpler process.

[0028] (2) The present invention combines the Mie scattering of three interfaces: organic matter-micron pores, organic matter-dielectric particles, and micron pores-dielectric materials, significantly enhancing the diffuse scattering effect of solar radiation of the material. Therefore, it can reflect and scatter most of the energy under direct sunlight, ultimately achieving excellent radiative cooling effect.

[0029] (3) Compared with the periodic nanostructured radiative cooling materials in the prior art, the present invention adopts a solution method to prepare a clay-based microporous radiative cooling coating, which has many advantages such as simple steps, mild reaction conditions, environmental friendliness, long service life, and suitability for large-scale production.

[0030] (4) The present invention also creatively improves the water resistance of the radiation refrigeration material through secondary modification and cross-linking of polyethyleneimine-trimethylenediamine chloride, thereby significantly extending the service life of the coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 These are SEM photos of the clay-based microporous radiation-cooled coatings prepared in Example 1 and Example 4.

[0032] Figure 2 The contact angle photos of the clay-based microporous radiation-cooled coatings prepared in Examples 1-4 are shown.

[0033] Figure 3 This is a comparison chart of outdoor temperature tests of the clay-based microporous radiant cooling coatings prepared in Examples 2-4 and Comparative Example 1. DETAILED DESCRIPTION

[0034] To enable those skilled in the art to fully understand the technical solutions and beneficial effects of the present invention, the following is a further detailed description with reference to specific embodiments and accompanying drawings. It should be emphasized that the embodiments listed in the present invention are merely preferred implementations and do not constitute any limitation. Simple modifications or substitutions made without departing from the spirit of the present invention will fall within the scope of protection of the present invention.

[0035] The methods for preparing clay-based microporous radiation-cooled coating materials in various embodiments of the present invention are as follows: 1) Disperse a certain amount of ethyl cellulose (viscosity 45-55 mPa•s) in an ethanol / deionized water mixture (ethanol content 60%-95% by mass). Place the resulting mixture in a 60-80°C water bath and stir (400-800 rpm) for 0.2-3 hours to completely dissolve it, yielding a clear, transparent ethyl cellulose solution with a concentration of 1%-8% by mass. 2) Disperse the selected clay mineral particles that meet the requirements in an ethanol / deionized water mixture (same as above), stir (speed 400-800 rpm) for 0.25-0.5 h, and then ultrasonicate (ultrasonic power 300-500 W) for 0.25-0.5 h to obtain a white clay mineral suspension with a mass percentage concentration of 5%-20%; 3) Mix the ethyl cellulose solution and clay mineral suspension in a specific ratio (ethyl cellulose to clay mineral dry weight ratio = 1:19 to 4:1). Stir (800-1200 rpm) for 0.25-0.5 h, then sonicate (300-500 W) for 1.5-2.5 h to obtain a white clay mineral-ethyl cellulose suspension for later use. Stir the suspension thoroughly before use to prevent sedimentation of the clay mineral particles.

[0036] As an alternative, clay mineral particles that meet the requirements can also be directly added to the ethyl cellulose solution and mixed and dispersed evenly by stirring, ultrasound, etc.

[0037] 4) Fix a suitable substrate (such as PET, PE, PS, wood, etc.) on the coating machine, set the appropriate coating height, pour the clay mineral-ethyl cellulose suspension solution prepared in 3) on the front side of the coating machine scraper, and then immediately apply the scraper (the amount of suspension solution is 0.5~1.5L / m2 ), and then dried at room temperature to obtain a clay mineral-ethyl cellulose microporous radiation cooling coating.

[0038] 5) Applying a polyethyleneimine aqueous solution (mass percent concentration of 0.2%-5%) on the coating surface, allowing it to react for 1-30 minutes, and then wiping off excess solution. Then, applying a trimesoyl chloride solution (mass percent concentration of 0.05%-1.5%) on the coating surface, allowing it to react for 1-30 minutes, and then wiping off excess solution. Finally, the coating surface is naturally dried at room temperature to obtain a water-resistant clay mineral-ethyl cellulose microporous radiative cooling coating.

[0039] In this process, the selection of raw clay mineral particles is very critical and must meet the following conditions at the same time: 1. Powder whiteness ≥ 80%, 2. Particles with a particle size of less than 2μm ≥ 90%, 3. The pH of the clay mineral suspension or mixture is controlled between 3.0 and 11 (if it exceeds this range, hydrochloric acid or ammonia water must be added to adjust the pH to meet the requirements).

[0040] The present invention prepares a radiative cooling material based on the characteristics of natural clay minerals such as high infrared emissivity in the wavelength range of 8-13 microns. It achieves zero-energy cooling while reducing costs, realizing high-value applications of mineral materials. The present invention also uses natural clay minerals to replace traditional nanomaterials, effectively solving the problems of high production costs, complex production processes, and difficulty in large-scale preparation that were common in the development of radiative cooling materials. Although the clay mineral material has a high whiteness after purification and its reflectivity to sunlight is around 85%, the reflectivity needs to be further improved when used alone as a daytime radiative cooling material. Combined with the Mie scattering of the clay mineral micropores, the coating's reflectivity to sunlight can be further increased to more than 90%, ultimately significantly improving its daytime radiative cooling power.

[0041] Example 1 Weigh 0.6 kg of ethyl cellulose powder with a viscosity of 45-55 mPa·s and mix it with 11.52 kg of anhydrous ethanol and 2.88 kg of water. Stir the resulting mixture at 500 rpm in a 60°C water bath for 2 hours to obtain a transparent ethyl cellulose solution with a concentration of 4%.

[0042] 2 kg of kaolin and 0.4 kg of montmorillonite were slowly added to the ethyl cellulose solution and mixed evenly to obtain a light yellow suspension. The mixture was then ultrasonically peeled at an ultrasonic intensity of 350 W for 0.5 h to obtain a white suspension. The mixture was then stirred at 800 rpm using a magnetic stirrer for 1 h to finally obtain a clay mineral-ethyl cellulose suspension.

[0043] According to the standard of water film thickness of 1mm, the clay mineral-ethyl cellulose suspension is evenly coated on the PET substrate using a coating machine, and the clay mineral-based microporous radiative cooling coating is obtained after natural drying.

[0044] Example 2 Weigh 0.6 kg of ethyl cellulose powder with a viscosity of 45-55 mPa·s and mix it with 10.8 kg of anhydrous ethanol and 3.6 kg of water. Stir the resulting mixture at 500 rpm in a 60°C water bath for 2 hours to obtain a transparent ethyl cellulose solution with a concentration of 4%.

[0045] 1.2 kg of kaolin, 0.6 kg of montmorillonite and 0.6 kg of talc were slowly added to the ethyl cellulose solution and mixed evenly to obtain a gray suspension. Then, the mixture was ultrasonically peeled at an ultrasonic intensity of 350 W for 0.5 h to obtain a white suspension. After that, the mixture was stirred at a speed of 800 rpm using a magnetic stirrer for 1 h to finally obtain a clay mineral-ethyl cellulose suspension.

[0046] According to the standard of water film thickness of 1mm, the clay mineral-ethyl cellulose suspension is evenly coated on the PET substrate using a coating machine, and the clay mineral-based microporous radiative cooling coating is obtained after natural drying.

[0047] A 1% by weight polyethyleneimine solution was prepared using water as the solvent and applied to the coating. The excess solution was removed after 5 minutes. A 0.3% by weight solution of trimesoyl chloride (in cyclohexane) was also applied to the coating. The solution reacted for 1 minute and then the excess solution was removed. Finally, the coating was allowed to air dry at room temperature to obtain a water-resistant clay mineral-based microporous radiative cooling coating.

[0048] Example 3 Weigh 0.6 kg of ethyl cellulose powder with a viscosity of 45-55 mPa·s and mix it with 10.1 kg of anhydrous ethanol and 4.3 kg of water. Stir the resulting mixture at 500 rpm in a 60°C water bath for 2 hours to obtain a transparent ethyl cellulose solution with a concentration of 4%.

[0049] 1.2 kg of montmorillonite and 1.2 kg of talc were slowly added to the ethyl cellulose solution and mixed evenly to obtain a light gray suspension. The mixture was then exfoliated by ultrasonication at an ultrasonic intensity of 350 W for 0.5 h to obtain a white suspension. The mixture was then stirred at 800 rpm using a magnetic stirrer for 1 h to finally obtain a clay mineral-ethyl cellulose suspension.

[0050] According to the standard of water film thickness of 1mm, the clay mineral-ethyl cellulose suspension was evenly coated on the PET substrate using a coating machine, and the clay mineral-based microporous radiative cooling coating was obtained after natural drying.

[0051] A 1% by mass polyethyleneimine aqueous solution was applied to the coating, and the excess solution was removed after 5 minutes. A 0.3% by mass solution of trimesoyl chloride (in cyclohexane) was applied to the coating, reacted for 1 minute, and the excess solution was removed. Finally, the coating was transferred to room temperature and naturally dried to obtain a water-resistant clay mineral-based microporous radiative cooling coating.

[0052] Example 4 Weigh 0.6 kg of ethyl cellulose powder with a viscosity of 45-55 mPa·s and mix it with 9.36 kg of anhydrous ethanol and 5.04 kg of water. Stir the resulting mixture at 500 rpm in a 60°C water bath for 2 hours to obtain a transparent ethyl cellulose solution with a concentration of 4%.

[0053] 2 kg of kaolin and 0.4 kg of montmorillonite were slowly added to the ethyl cellulose solution and mixed evenly to obtain a light gray suspension. The mixture was then ultrasonically peeled at an ultrasonic intensity of 350 W for 0.5 h to obtain a white suspension. The mixture was then stirred at 800 rpm using a magnetic stirrer for 1 h to obtain a clay mineral-ethyl cellulose suspension.

[0054] According to the standard of water film thickness of 1mm, the clay mineral-ethyl cellulose suspension was evenly coated on the PET substrate using a coating machine, and the clay mineral-based microporous radiative cooling coating was obtained after natural drying.

[0055] A 1% by mass polyethyleneimine aqueous solution was applied to the coating, and the excess solution was removed after 5 minutes. A 0.3% by mass solution of trimesoyl chloride (in cyclohexane) was applied to the coating, reacted for 1 minute, and the excess solution was removed. Finally, the coating was transferred to room temperature and naturally dried to obtain a water-resistant clay mineral-based microporous radiative cooling coating.

[0056] Comparative Example 1 According to the standard of wet film thickness of 1 mm, commercially available light gray Xuanleshi exterior wall paint was evenly coated on the PET substrate to obtain a conventional coating.

[0057] In order to fully understand the various properties of the different coatings prepared in various embodiments and comparative examples of the present invention, we took samples and conducted a series of tests.

[0058] (1) Scanning electron microscopy (SEM) The SEM images of the clay mineral-based microporous radiation-cooled coatings prepared in Example 1 and Example 4 are as follows: Figure 1As shown in the figure, the network structure is ethyl cellulose, which mainly assists the clay mineral in forming the coating. The particulate material in the figure is also clay mineral. The figure also shows that the coating has a large number of evenly distributed pores. These pores are caused by the uneven volatilization of ethanol and water in the solvent. Therefore, the pore size of the material can be controlled by adjusting the ratio of ethanol to water.

[0059] (2) Contact angle test The contact angle test results of the clay mineral-based microporous radiation-cooled coatings prepared in Examples 1-4 are as follows: Figure 2 As shown in the figure, the contact angle of Example 1 is less than 90°, showing hydrophilic characteristics, which is due to the lack of modification; while the contact angles of Examples 2-4 are all greater than 90°, showing hydrophobic characteristics, which is the result of modification with polyethyleneimine-trimethylenediamine chloride.

[0060] (3) Thermal performance test The coatings prepared in Examples 2-4 and Comparative Example 1 were used as test samples to test their thermal properties. Both solar reflectance and infrared emissivity were measured using an infrared reflectance / emissivity / diffuse reflectance test. The instrument used was a Nicolet is50, a Thermo Fisher Scientific instrument equipped with an integrating sphere. The solar reflectance test wavelength range was 2.5–25 μm at room temperature (25°C), while the infrared emissivity test wavelength range was 8–14 μm at room temperature (25°C). The thermal performance test results are shown in Table 1 below.

[0061] Table 1 Performance test results of Examples 2-4 and Comparative Example 1

[0062] It can be seen from the table that the coatings prepared in Examples 2-4 all have high solar radiation reflectivity and infrared emissivity, and as the values of these two parameters increase, the radiative cooling effect of the coating becomes more obvious.

[0063] (4) Coating surface temperature test The coatings prepared in Examples 2-4 and Comparative Example 1 were used as test samples, and the surface temperature of each sample was tested according to the following method: The sample size is 5cm×5cm, and the total coating thickness is 90μm. The sample to be tested is placed on a cavity of 10cm×10cm×10cm EPS polypropylene foam wrapped with smooth aluminum paper on all four sides and the top. The cavity volume is 5cm×5cm×5cm, and there is no aluminum paper on the cavity. The bottom of the sample to be tested is connected with a K-type thermocouple surface-adhesive probe patch to measure and record temperature changes. The reading recording interval is 10s. The thermocouple is connected to a four-channel K-type thermocouple thermometer. The top of the sample to be tested is covered with a 0.05mm transparent PE film to reduce the impact of air convection. The test location is a rooftop of a building in Hongshan District, Wuhan. The test time is a cloudless sunny day in October 2024. The test results are as follows Figure 3 shown.

[0064] from Figure 3 It can be seen that the radiative cooling effect of the coatings of Examples 2-4 is the best when the temperature is highest at noon, especially when the temperature difference between the coatings of Example 4 and Comparative Example 1 is as high as 10°C.

[0065] In summary, the clay mineral-based microporous radiation cooling coating provided by the present invention can efficiently scatter and reflect solar radiation, while efficiently emitting medium-wave infrared radiation. It has a significant cooling effect and achieves zero-consumption cooling, and has good application prospects.

Claims

1. A clay mineral-based microporous radiative cooling material, characterized by: The material has a porous structure and is mainly composed of clay mineral particles and ethyl cellulose cross-linked assembly.

2. The clay mineral-based microporous radiative cooling material according to claim 1, wherein: The pores and clay mineral particles in the material are all micron-sized, and ≥90% of the clay mineral particles have a particle size of less than 2μm.

3. The clay mineral-based microporous radiative cooling material according to claim 1, wherein: The clay mineral particles are selected from at least one of kaolin, talc, bentonite, montmorillonite and eidolite.

4. The clay mineral-based microporous radiative cooling material according to claim 1, wherein: The mass ratio of ethyl cellulose to clay mineral particles in the material is 1:19~4:

1.

5. The clay mineral-based microporous radiative cooling material according to claim 1, wherein: This material is a multi-layer composite coating, including a bottom layer, a middle layer, and a surface layer. The bottom layer is made of a composite of clay mineral particles and ethyl cellulose, the middle layer is made of polyethyleneimine, and the surface layer is made of trimesoyl chloride.

6. A method for preparing a clay mineral-based microporous radiation cooling material, characterized in that The method comprises: uniformly mixing ethyl cellulose and clay mineral particles in a solution state, and using the obtained mixed solution to prepare a coating on a substrate.

7. The method according to claim 6, wherein The mixing method of ethyl cellulose and clay mineral particles includes: preparing an ethyl cellulose solution and a clay mineral suspension separately, and then mixing the two evenly; or preparing an ethyl cellulose solution, and then adding clay mineral particles and dispersing them evenly; wherein the solvent used to prepare the ethyl cellulose solution or the clay mineral suspension is a mixture of ethanol and deionized water, and the mass proportion of ethanol in the mixture is 60%-95%.

8. The method according to claim 6, wherein: The substrate is selected from any one of PET, PE, PS, and wood, and at least one coating layer is formed on the substrate by scraping. The amount of the mixed liquid used during scraping is 0.5-1.5 L / m 2 .

9. The method according to claim 6, wherein The method also includes coating modification treatment: coating the coating surface with a polyethyleneimine aqueous solution and a trimesoyl chloride solution in sequence, wiping off the coating liquid after each coating is fully reacted and drying.

10. The method according to claim 9, wherein: The mass percentage concentration of the polyethyleneimine aqueous solution is 0.2%-5%, and the mass percentage concentration of the trimesoyl chloride solution is 0.05%-1.5%.

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