Preparation method of flexible material with double functions of radiation refrigeration and photothermal conversion storage

Abstract

The invention discloses a preparation method of a flexible material with double functions of radiation refrigeration and photothermal conversion storage, and relates to the field of composite phase change materials. The preparation method comprises the following steps: 1) preparing the flexible phase change material matrix by utilizing n-octadecane, SEBS and POE through hot pressing; 2) preparing a BaSO4 solution by using absolute ethyl alcohol, deionized water, a water-based defoaming agent, a water-based dispersing agent and an acrylic resin emulsion; (3) preparing an MXene solution; and 4) spraying the BaSO4 solution on the surface of one side of the flexible composite phase change material matrix by using a spray gun, and spraying the MXene solution on the surface of the other side of the flexible composite phase change material matrix to obtain the flexible composite phase change material. The radiation refrigeration layer can strongly reflect visible light and near-infrared light, has high emissivity in an infrared light area, especially in an atmospheric window wave band, reduces absorbed atmospheric heat radiation, reduces urban heat island effect caused by dense building groups in cities, and can effectively solve the problems of large day and night temperature difference and heat supply and demand in summer and winter.

Description

Technical Field

[0001] The present application relates to the field of composite phase change materials, and in particular to a method for preparing a flexible composite phase change material having dual functions of selective light-heat conversion and daytime radiation cooling and storage. Background Art

[0002] Phase change material is a functional material that can store and release heat by changing its phase at a specific temperature, and can achieve reversible temperature control operation with the ambient temperature. That is, when the external temperature is higher than the phase change temperature of the phase change material, the phase change material undergoes a phase change, absorbs and stores a large amount of heat energy; when the external temperature drops below the phase change temperature, the phase change material undergoes a reverse phase change, accompanied by the release of heat. Phase change materials have many significant advantages over other types of energy storage materials: such as low preparation cost, high energy storage density, and small temperature change range during phase change. Phase change materials have high energy storage density, low manufacturing cost, and can complete the storage and release of heat energy at a constant temperature. They have become the best carrier for energy conservation and environmental protection, and have been widely used in energy storage, electronic devices, intelligent control, and building components.

[0003] When phase change materials are actually applied in the field of building thermal management, they can effectively reduce the energy consumption of building heating and cooling by virtue of their high thermal energy storage density. However, they also face challenges such as seasonal adaptability, which limits their development in the field of building phase change energy storage. To address this problem, the main solution is to adjust the structure of the phase change material to change its spectral properties in order to prepare various new composite phase change materials. Chinese patent CN118580839A discloses a MXene-based composite phase change material with photothermal conversion and storage functions and a preparation method thereof, in order to achieve efficient and rapid photothermal energy conversion and storage; however, the method requires a large amount of MXene, which is costly, and the material is not flexible and cannot fit the complex geometric surface and contact thermal resistance of the building. In addition, the material does not have the characteristics of selective photothermal conversion, and the efficiency of photothermal conversion and storage is low in practical applications.

[0004] Radiative cooling technology is a process in which objects on the earth's surface emit infrared radiation into the universe through the "atmospheric window" (band 8-13 μm) to achieve self-cooling. The radiator has a high emissivity in the "atmospheric window" (8-13 μm). This technology can reduce the demand for fossil energy and has no pollution to the environment. It is a clean technology that does not require any external energy input. The currently reported radiative cooling materials can only radiate cooling at night and do not meet the conditions for daytime radiative cooling. Generally speaking, daytime radiative cooling materials need to meet the following requirements: high reflectivity in the 0.3-4 μm band and high emissivity in the 8-13 μm band. A Chinese patent with publication number CN118562453A discloses a method for preparing a biochar-based photothermal composite phase change material, which can realize the conversion of sunlight and the storage and release of heat to solve the problems of large temperature difference between day and night and heat supply and demand. However, the material does not have a radiation cooling function, which makes it unable to reduce building energy consumption in summer, and its photothermal coating cannot reduce the emitted thermal radiation, so it cannot maximize the photothermal conversion efficiency, and also cannot effectively solve the dual function problems of selective photothermal conversion and daytime radiation cooling and storage. Summary of the invention

[0005] In view of the above problems, the present invention provides a method for preparing a flexible material with the dual functions of radiation cooling and photothermal conversion and storage, which solves the functional limitations of composite phase change materials in the prior art and the problem of lack of selective photothermal conversion, realizes the dual-functional characteristics of phase change materials, and overcomes the problem that composite phase change materials can only effectively solve the large temperature difference between day and night and the supply and demand of heat in winter; at the same time, the composite phase change material is a flexible material, which is more suitable for fitting to the geometric outer surface of a building.

[0006] Specifically, the above invention object is achieved by the following method: First, the present application provides a method for preparing a flexible material having dual functions of radiation cooling and photothermal conversion storage, and the specific steps are as follows: S1. 130g C 18 H 38 (n-octadecane) and 17.5g SEBS (thermoplastic elastomer) were slowly poured into a beaker and mixed, and stirred in an oil bath at 160°C (300rpm) for 40min to obtain a mixture; then 52.5g POE (polyolefin elastomer) was slowly added to the mixture within 10min; then stirred in an oil bath at 160°C (300rpm) to obtain a mixture, and the mixture was hot-pressed at 160°C, and then cooled at room temperature to obtain a 2mm thick flexible phase change material matrix for standby use; The preferred hot pressing pressure is 5 MPa and the hot pressing time is 30 min to ensure uniform mixing of the materials); In this step, considering the building cooling application, C 18 H 38 The phase change point of (n-octadecane) is about 26-28°C (similar to the comfortable temperature range of the human body), so n-octadecane is selected as the phase change material, and SEBS and POE are selected as polymers to respectively play the role of encapsulation (leakage prevention) and improvement of mechanical properties. If the addition amount of SEBS and POE is too high, the phase change enthalpy value will drop significantly, reducing the energy storage effect of the material; if the addition amount of SEBS and POE is too high, the encapsulation performance and mechanical properties of the phase change material will drop significantly. Therefore, the phase change material finally prepared has good flexibility, high phase change enthalpy and thermal conductivity, and good shape stability. In addition, as the intermediate layer material, the flexible phase change material matrix must have good energy storage performance. Subsequent DSC tests also verified that within the ratio range of this application, the obtained material has good energy storage performance.

[0007] S2. Mix anhydrous ethanol, deionized water, aqueous defoamer, aqueous dispersant and acrylic resin emulsion, add BaSO 4 Particles (particle size about 2 μm), shake well to make BaSO 4 The particles were completely dissolved, and then ultrasonicated (200W) for 15 min to obtain a uniform milky white solution, which is BaSO 4 Solution, set aside; In this step, anhydrous ethanol, deionized water, aqueous defoamer, aqueous dispersant, acrylic resin emulsion and BaSO 4 The mass ratio of the particles is preferably 20:20:0.3:0.3:15:40.

[0008] In this step, the aqueous defoamer and aqueous dispersant are used as functional additives to respectively inhibit foam generation and improve the uniform distribution of solid particles in the liquid phase to prevent particle agglomeration, while the acrylic resin emulsion has excellent film-forming properties.

[0009] S3. Weigh 1.6 g of lithium fluoride and add it to 20 ml of 9 mol / L hydrochloric acid solution. Stir magnetically to dissolve the lithium fluoride completely to obtain an etching reagent. Then, add 1 g of Ti 3 AlC 2 Add to the etching reagent, stir and react for 12 hours at a water bath temperature of 35°C to obtain a suspension; centrifuge the suspension obtained by the reaction (centrifuge at 3500rpm for 5 minutes), then wash the precipitate obtained by centrifugation with 1mol / L hydrochloric acid for 3 times (washing-centrifugation, repeat 3 times), and then wash the precipitate with deionized water until the pH of the washing solution is ≥6; then add the precipitate and deionized water into a centrifuge tube, mix well and shake the centrifuge tube to make the Ti that has not been completely separated 3 AlC 2The layers were peeled off and centrifuged again at 1000 rpm for 40 min. The obtained suspension (the solution was not stratified after centrifugation) was freeze-dried to obtain a MXene solution for later use.

[0010] In this step, the added lithium fluoride and Ti 3 AlC 2 The mass ratio of the added lithium fluoride to the 9 mol / L hydrochloric acid solution is preferably 1.6:20, and the unit of mass volume ratio is g / mL.

[0011] As the core component of the solar thermal conversion system, the photothermal coating can achieve efficient absorption of solar energy, but the high emissivity will reduce the photothermal conversion efficiency of the coating. In order to maximize the photothermal conversion efficiency, the photothermal coating should absorb as much solar radiation as possible and emit as little thermal radiation as possible. Therefore, a solar spectrum selective absorption coating with both high solar absorptivity and low infrared emissivity can significantly improve the photothermal conversion efficiency. The photothermal coating prepared in this application is a MXene coating, that is, a solar spectrum selective absorption coating, which has both high solar absorptivity and low infrared emissivity. At the same time, it can also store heat in combination with phase change materials, further improving the photothermal conversion efficiency.

[0012] S4. Use a spray gun to spray BaSO 4 The solution was evenly sprayed on the surface of one side of the flexible composite phase change material substrate: the spray gun was vertically aimed at the flexible composite phase change material substrate, the height was maintained at 15-20 cm, then the solution was loaded into the spray gun, the spray gun was turned on, and spraying began from left to right and from top to bottom (room temperature, spraying rate of about 15 cm / min). After the substrate surface was sprayed, it was placed at room temperature for 30 minutes. After the coating was dry, the spraying was continued. The method steps were repeated and kept consistent. After repeating three times, the desired radiation cooling coating (white BaSO 4 Coating), the coating thickness is about 100μm; Then use a spray gun to evenly spray the MXene solution on the other side of the flexible composite phase change material substrate: vertically aim the spray gun at the flexible composite phase change material substrate, keep the height at 15-20cm, then load the solution into the spray gun, turn on the spray gun, and start spraying from left to right and from top to bottom (the spraying rate is about 15cm / min). After the substrate surface is sprayed, place it at room temperature for 30 minutes. After the coating is dry, continue spraying. Repeat the method steps and keep it consistent. After repeating three times, the desired selective absorption coating (black MXene coating) is obtained, and the coating thickness is about 1.5-2μm; finally, a dual-functional flexible composite phase change material is prepared.

[0013] Secondly, the present application provides a flexible material having the dual functions of radiation cooling and photothermal conversion storage prepared according to the above method.

[0014] In practical applications of this flexible material, the different sides of the material can be switched by simply flipping (such as flipping in the form of a "blind"), so that the functions of radiative cooling and selective photothermal conversion can be freely switched. 4 When coated, the composite phase change material has the function of radiation cooling, which reduces the surface temperature of the building through the radiation cooling coating; at the same time, the phase change material undergoes phase change to store cold; when flipped to the black MXene coating on the surface, the composite phase change material has the function of selective light-heat conversion, which can efficiently absorb sunlight during the day, and at the same time, the composite phase change material undergoes phase change to store heat. In addition, at night, because the black MXene coating has a low emissivity in the infrared band, it can reduce energy loss.

[0015] Compared with the prior art, the composite material provided by this application has the following advantages: The flexible material with dual functions of radiation cooling and photothermal conversion storage prepared in this application can effectively solve the problems of large temperature difference between day and night and heat supply and demand in summer and winter; compared with existing materials (such as CN118978743A), the phase change material prepared in this application is not only flexible, but also has a higher phase change enthalpy value and better heat storage performance.

[0016] The flexible material BaSO 4 The radiation cooling layer can strongly reflect visible light and near-infrared light, and has a high emissivity in the infrared region, especially in the atmospheric window band, while reducing the absorbed atmospheric thermal radiation. In addition, the present application can also bring greater advantages by combining the radiation cooling coating with the phase change material (compared to CN118978743A). The phase change material can store heat during the phase change process, further improving the cooling performance. For example, the average sunlight reflectivity (94%) of the radiation cooling coating prepared in the embodiment of the present application is higher than the average sunlight reflectivity of the radiation cooling coating reported in the prior art (such as patent CN118978743), and the cooling performance is better.

[0017] This application uses barium sulfate (BaSO 4 ) The microparticles can increase the reflectivity of the coating in the near-ultraviolet part, the addition of aqueous defoaming agent and aqueous dispersant can accelerate the uniform dispersion in the solution, and the added acrylic resin emulsion can not only combine with barium sulfate to accelerate film formation, but also help to increase the emissivity of the radiation cooling coating in the atmospheric window band, reduce the urban heat island effect caused by densely packed buildings in the city (the temperature in the center of the city is higher than the surrounding areas), prevent the surface temperature of buildings from being too high due to strong sunlight, and the surface of the building is aged due to heat, so it cannot maintain its original performance, and there will be discoloration, blistering, cracking and falling off, etc., which will reduce its service life and pose a safety hazard.

[0018] The dual-function flexible composite phase change material prepared by the present invention is a flexible material, which can better fit complex geometric surfaces and contact thermal resistance in the field of building thermal management.

[0019] This application uses barium sulfate as raw material, which is low in cost, rich in sources, and easy to apply on a large scale. The heat-insulating coating prepared in this application is applied on the surface of the building, and the radiation cooling coating formed after curing can reduce the absorption of sunlight by the surface, effectively improve the heat insulation performance of the house, and protect the building at the same time. Therefore, the radiation cooling coating has broad prospects in the application of building thermal management, and can significantly reduce the energy consumption of buildings in summer. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a real photo of the flexible phase change material matrix prepared in Example 1.

[0021] Figure 2 The white BaSO4 is a flexible material with dual functions of radiation cooling and photothermal conversion storage prepared in Example 1. 4 SEM images of the coating.

[0022] Figure 3 This is an SEM image of the black MXene coating of the flexible material with dual functions of radiation cooling and photothermal conversion storage prepared in Example 1.

[0023] Figure 4 This is a differential scanning calorimetry image of the flexible material with dual functions of radiation cooling and photothermal conversion storage prepared in Example 1.

[0024] Figure 5 The white BaSO4 is a flexible material with dual functions of radiation cooling and photothermal conversion storage prepared in Example 1. 4 UV-visible-near-infrared spectra of the coatings.

[0025] Figure 6 The white BaSO4 is a flexible material with dual functions of radiation cooling and photothermal conversion storage prepared in Example 1. 4 Fourier transform infrared spectrum analysis of the coating.

[0026] Figure 7 This is the UV-visible-near-infrared spectrum of the black MXene coating of the flexible material with dual functions of radiation cooling and photothermal conversion storage prepared in Example 1.

[0027] Figure 8 This is a Fourier infrared spectrum analysis diagram of the black MXene coating of the flexible material with dual functions of radiation cooling and photothermal conversion storage prepared in Example 1. DETAILED DESCRIPTION

[0028] The examples involve sources of reagents and raw materials: C 18 H 38 Sigma-Aldrich (Shanghai) Trading Co., Ltd.; SEBS G1650 was purchased from Kraton Performance Polymers Ltd.; POE 8180 was purchased from Dow Chemical Co.; Aqueous defoamer (J0401), aqueous dispersant (SN-5040), and acrylic resin emulsion were purchased from Shenzhen Yoshida Chemical Co., Ltd.; BaSO 4 The particles (particle size of about 2 μm) were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; Lithium fluoride was purchased from Shanghai MacLean Biochemical Co., Ltd. Ti 3 AlC 2 Purchased from Beijing DK Nanotechnology Co., Ltd.; Preparation method of hydrochloric acid solution: Take 9 ml of hydrochloric acid (Luoyang Chemical Reagent Factory) and dilute it with water to a concentration of 9 mol / L or 1 mol / L; The spray gun was purchased from Weichuan Hardware Store, model ED-AS18-2. Example 1

[0029] This embodiment prepares a flexible composite phase change material with dual functions of selective light-heat conversion and daytime radiation cooling and storage, and the specific method steps are as follows: S1. 130g C 18 H 38 17.5g SEBS G1650 was slowly poured into a beaker and mixed. After stirring at 160°C in an oil bath at 300rpm for 40min, a uniform mixture was obtained. 52.5g POE 8180 was slowly added to the mixture within 10min. Then, the mixture was stirred at 160°C in an oil bath at 300rpm for 2h. Then, the mixture was hot-pressed at 160°C with a pressure of 5Mpa for 30min. Then, it was cooled at room temperature to obtain a 2mm thick flexible phase change material matrix for use. The actual photo (product after hot pressing) is shown in the figure. Figure 1 shown.

[0030] S2. Slowly pour 20g of anhydrous ethanol, 20g of deionized water, 0.3g of aqueous defoamer, 0.3g of aqueous dispersant and 15g of acrylic resin emulsion into a beaker and mix them. Then slowly add 40g of BaSO 4 Pellet, shake to make BaSO 4 After the particles were completely dissolved, the solution was treated with ultrasound (200W) for 15 min to obtain a uniform milky white solution, which was BaSO4 Solution, set aside; S3. Weigh 1.6 g of lithium fluoride and add it to 20 ml of 9 mol / L hydrochloric acid solution. Stir magnetically to dissolve the lithium fluoride completely to obtain the etching reagent. 3 AlC 2 Add to the etching reagent, stir at 600rpm for 12h under the condition of 35℃ water bath temperature to obtain a suspension. Centrifuge the suspension obtained by the reaction (centrifuge at 3500rpm for 5min), then wash the precipitate obtained by centrifugation with 1mol / L hydrochloric acid for 3 times (wash-centrifuge, repeat 3 times), then take the precipitate and wash it with deionized water until the pH of the washing liquid is ≥6. Add the washed precipitate and deionized water to a centrifuge tube and shake it by hand for 5min to make the Ti that has not been completely separated 3 AlC 2 The layers were peeled off and centrifuged again (1000 rpm) for 40 min. Finally, the suspension obtained by centrifugation was freeze-dried at -10 °C for 24 h to obtain the MXene solution for later use.

[0031] S4. Use a spray gun to spray BaSO 4 The solution is evenly sprayed on the surface of the flexible composite phase change material substrate: the spray gun is vertically aimed at the flexible composite phase change material substrate, and the height is maintained at 15-20cm. Then the solution is loaded into the spray gun, the spray gun is turned on, and spraying is started from left to right and from top to bottom (the spraying rate is about 15cm / min). After the substrate surface is sprayed, it is placed at room temperature for 30min (drying), and then the spraying is continued. The method steps are repeated to keep the same. After repeating three times, the desired radiation cooling coating (BaSO 4 Layer), the coating thickness is about 100μm; Then use a spray gun to evenly spray the MXene solution on the other surface of the flexible composite phase change material matrix: vertically aim the spray gun at the flexible composite phase change material matrix, keep the height at 15-20cm, then load the solution into the spray gun, turn on the spray gun, and start spraying from left to right and from top to bottom (the spraying rate is about 15cm / min). After the surface of the substrate is sprayed, it is placed at room temperature for 30 minutes (drying), and then continue to spray. The method steps are repeated and kept consistent. After repeating three times, the desired selective absorption coating (MXene layer) is obtained, and the coating thickness is about 1.5-2μm; finally, the dual-functional flexible composite phase change material in this application can be prepared.

[0032] In this example, white BaSO4 is prepared as a flexible material. 4 The SEM images of the coating and the black MXene coating are shown in Figure 2 , Figure 3 shown.

[0033] Figure 4 The differential scanning calorimetry diagram of the flexible material with dual functions of radiation cooling and photothermal conversion storage prepared in this embodiment shows that the phase change exothermic peak corresponding to the temperature of the dual-functional flexible composite phase change material obtained in Example 1 is 35.2°C, the temperature corresponding to the endothermic peak is 51.1°C, and the phase change enthalpy value is 160~162J / g. This enthalpy value is higher than that of existing materials (such as CN118978743A). The higher the enthalpy value means that the phase change material can absorb or release more heat during the phase change process, and can store more thermal energy under the same mass or volume. This makes it superior to low enthalpy materials in terms of energy storage density and efficiency; in addition, high enthalpy phase change materials can maintain temperature stability for a long time when absorbing or releasing a large amount of heat; it can be used for building energy conservation to further reduce energy consumption.

[0034] The white BaSO was measured by UV-Vis-NIR spectrophotometer. 4 The reflectance spectrum of the coating in the 0.25-2.5μm band is measured, and the test results are as follows Figure 5 As shown in the figure, white BaSO 4 The coating has a high reflectivity of up to 94%.

[0035] The white BaSO 4 The emissivity of the coating in the 2.5~16μm band is measured, and the test results are as follows Figure 6 As shown in the figure, white BaSO 4 The coating has an emissivity of up to 96%. The coating can radiate energy to outer space through the atmospheric window in the form of thermal radiation through spectral regulation, thereby reducing the temperature of the building without energy input. 4 The coating can effectively reduce the building temperature in summer and achieve a cooling effect.

[0036] The reflectance spectrum of the black MXene coating in the 0.25-2.5 μm band was measured by UV-Vis-NIR spectrophotometer. Figure 7 As shown in the figure, it can be seen that the black MXene coating has a high absorption rate, up to 81.8%.

[0037] The emissivity of the black MXene coating in the 2.5-16 μm band was measured by Fourier transform infrared spectrometer. Figure 8As shown. It can be seen from the figure that the emissivity of the black MXene coating is as low as 16.1%. The coating can radiate energy to outer space through the atmospheric window in the form of thermal radiation through spectral regulation, thereby reducing the temperature of the building without energy input. Therefore, the black MXene coating can effectively reduce the temperature of the building in summer and achieve a cooling effect. The coating can efficiently absorb sunlight during the day with its high absorptivity, and can minimize energy loss at night with its low emissivity; in addition, the black MXene coating can also effectively increase the building temperature in winter and reduce energy loss, which can effectively increase the building temperature in winter and achieve a thermal insulation effect.

[0038] In summary, the flexible material with dual functions of radiation cooling and light-heat conversion storage prepared in this embodiment switches the function of the surface coating by flipping the surface, and the phase change material matrix has a high heat storage density and can store energy efficiently. When the material is applied on the roof of a building, it can greatly reduce the energy consumption required for the building and achieve energy-saving effects.

Claims

1. A method for preparing a flexible material with dual functions of radiation cooling and photothermal conversion storage, characterized in that: The specific steps are as follows: 1) Mix n-octadecane and SEBS evenly, then add POE, mix evenly and hot press to form, and obtain a flexible phase change material matrix after cooling, which is ready for use; The mass ratio of n-octadecane, SEBS and POE is 130:17.5:52.5; 2) After mixing anhydrous ethanol, deionized water, aqueous defoamer, aqueous dispersant and acrylic resin emulsion, BaSO4 particles are added, and after ultrasonic dispersion, a BaSO4 solution is obtained for later use; The mass ratio of anhydrous ethanol, deionized water, aqueous defoamer, aqueous dispersant, acrylic resin emulsion and BaSO4 particles added is 20:20:0.3:0.3:15:40; 3) Dissolve lithium fluoride in hydrochloric acid solution, then add Ti3AlC2 to react to obtain suspension I; after centrifugation, take the precipitate and wash it, add the precipitate and deionized water into a centrifuge tube, mix them evenly, and centrifuge again to obtain suspension II; after freeze-drying suspension II, obtain MXene solution for later use; The mass ratio of added lithium fluoride to Ti3AlC2 is 1.6:1; 4) Use a spray gun to evenly spray the BaSO4 solution obtained in step 2) on the surface of one side of the flexible composite phase change material substrate in step 1), and form a BaSO4 coating after drying; then spray the MXene solution obtained in step 3) on the surface of the other side of the flexible composite phase change material substrate in step 1), and form a MXene coating after drying; finally, the flexible material with the dual functions of radiation cooling and photothermal conversion storage is obtained.

2. The method for preparing a flexible material having dual functions of radiation cooling and light-heat conversion storage according to claim 1, characterized in that: Step 1) The thickness of the flexible phase change material matrix is ​​2 mm.

3. The method for preparing a flexible material having dual functions of radiation cooling and light-heat conversion storage according to claim 1, characterized in that: Step 1) The hot pressing is performed at a temperature of 160°C and a pressure of 5 MPa.

4. The method for preparing a flexible material having dual functions of radiation cooling and light-heat conversion storage according to claim 1 is characterized in that: Step 2) The BaSO4 particles are 2 μm.

5. The method for preparing a flexible material having dual functions of radiation cooling and light-heat conversion storage according to claim 1, characterized in that: In step 3), the molar concentration of the hydrochloric acid solution is 9 mol / L, the mass volume ratio of the added lithium fluoride to the hydrochloric acid solution is 1.6:20, and the unit of mass volume ratio is g / mL.

6. The method for preparing a flexible material having dual functions of radiation cooling and light-heat conversion storage according to claim 1, characterized in that: In step 3), the washing means washing the precipitate obtained by centrifuging the suspension I with 1 mol / L hydrochloric acid, and then centrifuging and washing again, and repeating this process until the pH of the washing solution is ≥6.

7. The method for preparing a flexible material having dual functions of radiation cooling and light-heat conversion storage according to claim 1, characterized in that: In step 4), the BaSO4 coating has a thickness of 100 μm and the MXene coating has a thickness of 1.5-2 μm.

8. The method for preparing a flexible material having dual functions of radiation cooling and light-heat conversion storage according to claim 1, characterized in that: In step 4), the spraying means that the spray gun is vertically aimed at the flexible composite phase change material substrate at a height of 15-20 cm and a spraying rate of 15 cm / min. After the coating is dry, spray again.

9. A flexible material having dual functions of radiation cooling and photothermal conversion storage obtained by any method of claims 1-8.

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