Layered porous radiation refrigeration film and preparation method thereof

Abstract

The invention discloses a layered porous radiation refrigeration film and a preparation method thereof. The preparation method comprises the following steps: growing metal oxide nanorods on the surface of mica in situ; the preparation method comprises the following steps: modifying mica with metal oxide nanorods growing on the surface by adopting a silane coupling agent, adding the modified mica into an organic dispersing agent, mixing with a fiber material to form sol, and carrying out vacuum filtration to prepare the layered porous radiation refrigeration film. The layered porous radiation refrigeration film has high reflectivity, high atmospheric window emissivity and excellent radiation refrigeration performance, can be applied to radiation refrigeration of electronic products such as mobile phones and the like, and can obtain an excellent radiation refrigeration effect.

Description

Technical Field

[0001] The invention belongs to the technical field of passive daytime radiation cooling, and in particular relates to a layered porous radiation cooling film and a preparation method thereof. Background Art

[0002] Passive daytime radiative cooling (PDRC) is a cooling technology that can be achieved without external energy input. It achieves a cooling effect below ambient temperature by reflecting sunlight (wavelength 0.3-2.5μm) and radiating heat to the cold outer space through the long-wave infrared (LWIR) transmission window of the atmosphere (wavelength 8-13μm). PDRC technology has the characteristics of zero energy consumption and zero environmental pollution. Compared with traditional cooling systems, it provides a revolutionary cooling strategy that helps alleviate major problems such as global warming. This technology shows great application potential in many fields such as building energy conservation, personal thermal management, and solar cell cooling.

[0003] At present, the research on passive radiation cooling materials mainly focuses on porous structures and polymer-dielectric scatterer composites. Solar reflectivity is usually achieved by using light scattering materials with different refractive indices to form a porous structure and multiple scattering of sunlight. Since the refractive index inside the porous structure of the material does not match the emissivity of the air, this will cause sunlight to be reflected or scattered. Therefore, porous structure materials play a vital role in high-performance daytime radiation cooling. In addition, in order to improve the mid-infrared emissivity, it is usually achieved by introducing dielectric particles with significant refractive index contrast into the polymer matrix. It uses dielectric nanoparticles or microspheres, such as SiO2, TiO2 or Al2O3, randomly distributed in the polymer. The optical impedance matching of dielectric microspheres with air and the dipole resonance effect in the mid-infrared region can be used to improve the emissivity.

[0004] However, the scattering ability of randomly distributed nanospheres is limited, making it difficult to obtain high reflectivity, and the easy agglomeration of dielectric scatterers will lead to a serious decline in the optical and mechanical properties of the material. Therefore, it is of great significance to research and develop radiative cooling materials with superior optical properties and strong outdoor practicality. Summary of the invention

[0005] In view of this, the primary purpose of the present invention is to provide a method for preparing a layered porous radiative cooling film, in which metal oxide nanorods are in situ grown on a smooth mica sheet, and fiber materials are introduced to combine with the mica sheet to form a layered porous structure, thereby forming a layered porous radiative cooling film with high reflectivity and high atmospheric window emissivity and excellent performance.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] One aspect of the present invention first provides a method for preparing a layered porous radiative cooling film, comprising the following steps:

[0008] In situ growth of metal oxide nanorods on mica surface;

[0009] After the mica with metal oxide nanorods grown on the surface is modified by a silane coupling agent, the mica is added into an organic dispersant and mixed with a fiber material to form a sol, which is then vacuum filtered to obtain a layered porous radiation refrigeration film.

[0010] By growing vertical, dense and non-agglomerated metal oxide nanorods on the surface of mica, an optical structure composed of media with different optical properties is formed, which effectively reflects and absorbs radiation in a specific band. In addition, these nanorods enhance the backscattering ability of sunlight due to their surface area and volume, thereby improving the reflection of sunlight. At the same time, the fiber material forms a layered porous structure, and the micropores in the layered structure also enhance the reflection ability of sunlight through interface scattering, so that the prepared layered porous radiation cooling film has a good radiation cooling effect.

[0011] Another aspect of the present invention provides a layered porous radiation cooling film, which is prepared by the preparation method described above and has a good radiation cooling effect due to its special structure.

[0012] Beneficial effects of the present invention:

[0013] 1. The method for preparing a layered porous radiative cooling film provided by the present invention grows a metal oxide nanorod array on the surface of mica, and obtains a radiative cooling film with a layered porous structure by vacuum filtration. The method is simple to operate, the raw materials are readily available, and the film can be prepared in a general chemical laboratory, and is easy to promote.

[0014] 2. The layered porous radiation cooling film prepared in the present invention forms a vertical, dense, non-agglomerated metal oxide nanorod array in situ grown on the surface of mica, forming an optical structure composed of three media with different optical properties, namely, a matrix, a nanorod array and air, thereby effectively reflecting and absorbing radiation in a specific band. At the same time, these nanorod arrays enhance the backscattering ability of sunlight due to their surface area and volume, thereby improving the reflection of sunlight. In addition, the layered porous structure is formed after vacuum filtration of the fiber material, and the micropores in the layered structure further enhance the reflection ability of sunlight through interface scattering, thereby achieving a good radiation cooling effect.

[0015] 3. The layered porous radiation cooling film prepared in the present invention has extremely high reflectivity in the ultraviolet-visible-near infrared band and high emissivity in the infrared band, and has excellent sub-environment cooling effect in outdoor tests.

[0016] 4. The layered porous radiation cooling film prepared in the present invention can be applied to the radiation cooling field of electronic products such as mobile phones, and has excellent effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The SEM images of the titanium dioxide nano-seed layer particles grown on the mica surface prepared in Example 1 at different magnifications are shown, wherein: Figure 1 The scale bar of a is 5 μm, Figure 1 The scale bar in b is 500 nm.

[0018] Figure 2 The SEM images of titanium dioxide nanorod arrays grown on the mica surface prepared in Example 1 at different magnifications are shown, wherein: Figure 2 The scale bar of a is 2 μm, Figure 2 The scale bar in b is 500 nm.

[0019] Figure 3 This is an optical photograph of the layered porous radiative cooling film prepared in Example 1 ( Figure 3 a) and SEM images ( Figure 3 b).

[0020] Figure 4 The UV-visible-near infrared reflection spectra of the layered porous radiative cooling films prepared in Examples 1 and 2.

[0021] Figure 5 1 is the infrared emission spectrum of the layered porous radiation cooling film prepared in Examples 1 and 2.

[0022] Figure 6 It is the tensile strength of the layered porous radiation cooling film prepared in Example 1, Example 3, and Example 4.

[0023] Figure 7 Schematic diagram of the test device used in the outdoor cooling effect test of the layered porous radiant cooling film prepared in Example 1 ( Figure 7 a) and temperature variation curve ( Figure 7 b).

[0024] Figure 8 This is a photo of the layered porous structure radiation cooling film prepared in Example 1 applied to a mobile phone model ( Figure 8 a) and infrared photos ( Figure 8 b). DETAILED DESCRIPTION

[0025] Embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0027] The first aspect of the present invention provides a method for preparing a layered porous radiative cooling film, the main steps of the preparation method are as follows:

[0028] In situ growth of metal oxide nanorods on mica surface;

[0029] After the mica with metal oxide nanorods grown on the surface is modified by a silane coupling agent, the mica is added into an organic dispersant and mixed with a fiber material to form a sol, which is then vacuum filtered to obtain a layered porous radiation refrigeration film.

[0030] The present invention firstly grows vertical, dense and non-agglomerated metal oxide nanorods in situ on the mica surface, then modifies the surface with a silane coupling agent, mixes with a fiber material to form a sol, and then vacuum filters to obtain a layered porous radiation cooling film. The film has high reflectivity and a high atmospheric window, thus having an excellent radiation cooling effect, and can be applied to the radiation cooling of electronic products such as mobile phones.

[0031] S1. In situ growth of metal oxide nanorods on mica surface

[0032] The metal oxide described in the present invention is preferably a metal oxide having dielectric properties, and specific examples include but are not limited to at least one of titanium dioxide, iron oxide, and cobalt oxide.

[0033] The preferred method for growing metal oxide nanorods is to first prepare a metal oxide nanoseed layer on the mica surface and then grow the metal oxide nanorods in situ. However, it is understandable that other growth methods are also possible, as long as the method can grow metal oxide nanorods on the mica surface.

[0034] In some specific embodiments of the present invention, the metal oxide is titanium dioxide, and the step of in-situ growing metal oxide nanorods on the mica surface comprises:

[0035] (1) Preparing a titanium dioxide nano seed layer on a mica surface;

[0036] (2) adding a titanium sheet to a reaction solution composed of melamine, nitric acid and hydrogen peroxide and stirring to form a reddish brown solution, pouring the reddish brown solution onto mica having a titanium dioxide nano seed layer on the surface, and performing a hydrothermal reaction at 60 to 100° C. for 2 to 6 hours;

[0037] (3) After step (2) is repeated 6 times, the product is calcined at 500-800° C. for 4-6 hours in an air atmosphere to obtain mica with titanium dioxide nanorods in situ grown on the surface.

[0038] In the present invention, the growth principle of titanium dioxide nanorods is as follows:

[0039] Ti+H2O2→[TiO(H2O2)] 2+ →Ti 4+ (OH) x →H2Ti5O 11 3H2O→TiO2;

[0040] Among them, melamine is hydrolyzed to generate NH 4+ The TiO2 seed layer selectively adsorbs NH 4+ , adding H2Ti5O 11 · The "directional attachment" of 3H2O occurs, and finally the monoclinic H2Ti5O 11 ·3H2O is converted into TiO2 at high temperature (500-800℃).

[0041] The titanium dioxide nano seed layer is prepared by adding mica powder to a titanium dioxide precursor solution, subjecting the solution to a hydrothermal reaction at 100 to 140° C. for 14 to 18 hours, and then drying the reactant and calcining it at 400 to 500° C. for 4 to 8 hours in an air atmosphere.

[0042] In the present invention, the titanium dioxide precursor solution is well known in the art, and is usually composed of a titanium dioxide precursor and a catalyst, etc. In a specific embodiment of the present invention, the titanium dioxide precursor is tetrabutyl titanate, and the acid catalyst used is hydrochloric acid, but it is understandable that it is not limited to this. Common titanium dioxide precursors in the art, such as isopropyl titanate, titanyl sulfate, TiCl4, etc., and common acid catalysts such as nitric acid, etc. can be used in the present invention, and those skilled in the art can specifically select as needed. In addition, in the titanium dioxide precursor solution, the ratio of the titanium dioxide precursor, the acid catalyst and water can be selected or designed by those skilled in the art as needed, for example, according to the density and number of nanorods to be grown, etc., and the technicians in the field have such ability, so there is no special limitation. In some specific embodiments of the present invention, in the titanium dioxide precursor solution, the volumes of the titanium dioxide precursor, the acid catalyst and the water are 1 to 3 mL: 6 to 10 mL, 20 to 25 mL, respectively; the amount of mica powder added is 1 to 3 g.

[0043] Furthermore, in some specific embodiments of the present invention, the mass of the titanium sheet is 4-6 g; the amounts of melamine, nitric acid and hydrogen peroxide in the reaction solution are 0.2-0.8 g, 0.5-3.5 mL and 50-200 mL respectively.

[0044] It is understandable that when the grown metal oxide is an iron oxide or cobalt oxide nanorod, it can also be prepared by a method similar to that of titanium oxide nanorod, that is, firstly, mica powder is added to the metal oxide precursor solution, a metal oxide seed layer is formed by hydrothermal treatment, and then an iron oxide or cobalt oxide nanorod array is grown in situ by directional attachment. Among them, the iron oxide precursor can be FeCl3·6H2O, and the cobalt oxide precursor can be cobalt oxalate, but it is not limited thereto. Those skilled in the art can perform corresponding operations and parameter settings as needed to prepare a metal oxide nanorod array that meets the requirements.

[0045] S2. Preparation of layered porous radiative cooling films

[0046] The steps mainly include: firstly, modifying the mica with metal oxide nanorods grown on the surface with a silane coupling agent; then adding the mica into an organic dispersant and fully mixing it with the fiber material to form a sol; and finally, vacuum filtering the sol to obtain a layered porous radiation refrigeration film.

[0047] Among them, the mica with metal oxide nanorods grown on the surface is modified by using a silane coupling agent, which has the property of chemically bonding (coupling) with organic and inorganic materials to increase the adhesion between the subsequent mica and the fiber material. The modification treatment in the present invention can be performed by dispersing in a specific solvent and refluxing as is familiar in the art. In some specific embodiments of the present invention, the preferred silane coupling agent is (3-aminopropyl) triethoxysilane, and the specific treatment steps are: dispersing the mica with metal oxide nanorods grown on the surface in a mixture of ethanol and deionized water, adding a silane coupling agent, and refluxing at 60-80°C for 3-5 hours.

[0048] Preferably, the mass of the mica on which the metal oxide nanorods are grown is 3-5 g, and the amount of the silane coupling agent added is 2-4 mL.

[0049] Furthermore, the modified mica is added into an organic dispersant and fully mixed with the fiber material to form a sol, and finally vacuum filtered.

[0050] By adding fiber materials, the film can be improved or endowed with excellent mechanical properties, stability and flame retardant properties, etc. Specific examples include aramid fiber or carbon fiber, but not limited thereto, and aramid fiber is preferred.

[0051] The organic dispersant used is dimethyl sulfoxide, N,N-dimethylacetamide or glycerol.

[0052] The amounts of the fiber material and the organic dispersant can be adjusted according to specific circumstances or needs. In some specific embodiments of the present invention, the amount of the fiber material added is 1 to 3 g, and the volume of the organic dispersant is 50 to 200 mL.

[0053] The present invention is described below by means of specific examples. It should be noted that the following specific examples are only for illustrative purposes and do not limit the scope of the present invention in any way. In addition, unless otherwise specified, methods without specific conditions or steps are conventional methods, and the reagents and materials used can be obtained from commercial channels.

[0054] Among them, mica powder was purchased from Henan Borun Casting Materials Co., Ltd., model 1000 mesh;

[0055] Aramid fiber was purchased from Dongguan Shengxin Special Rope Factory, an American DuPont brand, model K29.

[0056] Example 1

[0057] This embodiment provides a method for preparing a layered porous radiative cooling film, and the specific steps are as follows:

[0058] S1. Preparation of titanium dioxide nano seed layer

[0059] (1) adding tetrabutyl titanate dropwise into a hydrochloric acid aqueous solution at room temperature and stirring for 2 hours to obtain a precursor solution, wherein tetrabutyl titanate: hydrochloric acid: water = 1:8:22 (volume ratio);

[0060] (2) pouring the precursor solution into a stainless steel autoclave lined with polytetrafluoroethylene to fill the autoclave to 60% volume, then immersing mica in the precursor solution, and then placing the autoclave in an environment of 120° C. for 16 hours;

[0061] (3) washing the solution after the reaction in step (2) with water twice and drying it at 100° C.;

[0062] (4) The dried product is placed in an air atmosphere and calcined at 450°C for 6 hours to obtain a TiO2 nanoseed layer uniformly grown on the surface of the mica sheet.

[0063] S2. In situ growth of titanium dioxide nanorods

[0064] (1) After 5 g of titanium sheet was thoroughly cleaned in ethanol by ultrasonic cleaning for 20 min, the cleaned titanium sheet was immersed in a mixed solution consisting of 0.4 g of melamine, 2.0 mL of nitric acid and 100 mL of hydrogen peroxide, and stirred continuously at 25 ° C for 48 h to obtain a reddish brown precursor solution;

[0065] (2) Then, the precursor solution is poured onto the product of step S1 until it is completely immersed; after a hydrothermal reaction at 80° C. for 4 h, the solution is filtered and dried using a centrifuge;

[0066] (3) adding fresh precursor solution to the reactants in step (2), and repeating the operation in step (2) 6 times;

[0067] (4) The final reactant was thoroughly washed twice with water and then dried at 70°C;

[0068] (5) The dried product was placed in an air atmosphere and calcined at 600° C. for 5 h to obtain vertically aligned titanium dioxide nanorods grown in situ on the mica surface.

[0069] S3. Preparation of layered porous radiative cooling film

[0070] (1) 4.5 g of the product in step S2 was dispersed in a mixture of ethanol and deionized water, 3 mL of (3-aminopropyl)triethoxysilane was added, and the mixture was refluxed at 70° C. for 4 h;

[0071] (2) filtering the reactant in step (2) and washing it with deionized water 5 times;

[0072] (3) dispersing the mica with titanium dioxide nanorods on the surface treated with (3-aminopropyl)triethoxysilane into dimethyl sulfoxide and treating it with ultrasound for 20 min;

[0073] (4) Add 2 g of aramid fiber to the dispersion of step (3), stir mechanically to mix evenly, form a uniform flax-colored sol, and then vacuum filter to obtain a layered porous radiant refrigeration film.

[0074] Example 2

[0075] This embodiment provides another method for preparing a layered porous radiative cooling film, which is implemented in the same manner as in Example 1, except that in step S2, the mixed solution in which the 4 g titanium sheet is immersed in step (2) is composed of 0.2 g melamine, 0.5 mL nitric acid and 50 mL hydrogen peroxide. The other process steps and condition parameters are the same as in Example 1.

[0076] Example 3

[0077] This embodiment provides another method for preparing a layered porous radiation cooling film, which adopts the same implementation as that of Embodiment 1, except that in step S3, the amount of aramid fiber added is different, which is 1 g in this embodiment.

[0078] Example 4

[0079] This embodiment provides another method for preparing a layered porous radiation cooling film, which adopts the same implementation as that of Embodiment 1, except that in step S3, the amount of aramid fiber added is different, which is 3 g in this embodiment.

[0080] Performance Testing

[0081] 1. Characterize the layered porous radiative cooling film prepared in Example 1.

[0082] Figure 1 This is a SEM image of the titanium dioxide nano seed layer grown on the mica surface prepared in step S1 of Example 1. It can be observed that the mica surface is evenly coated with titanium dioxide particles, indicating that the titanium dioxide nano seed layer in the present invention is composed of a large number of disorderly and closely arranged nanoparticles.

[0083] Figure 2 This is a SEM image of the titanium dioxide nanorod array grown on the mica surface prepared in step S2 of Example 1. It can be observed that all the titanium dioxide nanorods grow freely on the mica surface without aggregation or fusion. It is composed of a large number of disorderly arranged dense needle-like nanorod arrays, and the scattered disordered needle-like nanorod array structures are intertwined to form secondary pores. This structure can effectively enhance the scattering of sunlight.

[0084] Figure 3 This is an optical photograph of the layered porous radiative cooling film prepared in step S3 of Example 1 ( Figure 3 a) and SEM images ( Figure 3 b), it can be observed that the film has a silvery white appearance and obvious skin-like wrinkles on the surface, which can enhance the infrared emission performance of the film. And through the SEM photos, it can be observed that the film has an obvious layered porous structure, which can effectively enhance the backscattering of sunlight and thus improve the reflectivity.

[0085] 2. The layered porous radiative cooling films prepared in Examples 1 and 2 were subjected to UV-visible-near infrared reflection and infrared emission tests.

[0086] Figure 4 The UV-Vis-NIR reflectance spectra of the layered porous radiative cooling films prepared in Examples 1 and 2 show that they both have excellent reflectivity, wherein the layered porous radiative cooling film in Example 1 has the best reflectivity of 97.5%.

[0087] Figure 5 3 is the infrared emission spectra of the layered porous radiative cooling films prepared in Examples 1 and 2. It can be seen that they both have excellent infrared emissivity, among which the layered porous radiative cooling film in Example 1 has the best emissivity, which is 96.3%.

[0088] 3. Perform a tensile test on the layered porous radiative cooling films prepared in Examples 1, 3, and 4.

[0089] Figure 6 It is the tensile strength of the layered porous radiative cooling film prepared in Examples 1, 3, and 4. It can be seen that they all have excellent mechanical properties. Among them, the layered porous radiative cooling film in Example 1 has the best mechanical properties, with a tensile strength of 98 MPa and a Young's modulus of 1.49 GPa.

[0090] 4. Use outdoor radiation cooling temperature measuring device (structure such as Figure 7 a) The layered porous radiative cooling film prepared in Example 1 was tested for radiative cooling effect.

[0091] Use polystyrene foam as the base to eliminate ground heat conduction and place a transparent polyethylene film on top of the radiant cooling film to resist heat convection in the air; then cover the film on an aluminum plate and place it in the sun. The outdoor temperature ranges from 26℃ to 37℃ throughout the day, and the temperature is monitored throughout the day by a thermocouple to obtain a temperature change curve. The results are as follows: Figure 7 As shown in b.

[0092] The results show that the layered porous radiative cooling film prepared in Example 1 can achieve a sub-ambient cooling of up to 8.62°C during the day and 4.84°C at night.

[0093] 5. Cover the layered porous radiation cooling film with surface-grown nanorod arrays prepared in Example 1 on the mobile phone model ( Figure 8 a), placed in an open, unobstructed outdoor environment, with an outdoor temperature of 28℃~33℃, exposed to sunlight for 4 hours, and took photos with an infrared camera to obtain infrared photos that can reflect the radiation cooling effect. The results are as follows Figure 8 As shown in b.

[0094] The results show that after the surface of the mobile phone is covered with the layered porous radiation cooling film in Example 1, the temperature can be reduced by up to 8.8°C.

[0095] It should be noted that the purpose of the present invention can be achieved when the experimental process meets the following conditions:

[0096] As for the metal oxide grown on the surface of mica, it can also be iron oxide or cobalt oxide;

[0097] For the preparation of the titanium dioxide nanoseed layer, the hydrothermal reaction conditions are preferably 100-140°C for 14-18h, for example, 100°C for 18h, 120°C for 16h or 140°C for 14h. The amount of mica powder added is preferably 1-3g, for example, 1g, 2g or 3g. The amount of titanium dioxide precursor, acid catalyst and water added to the titanium dioxide precursor solution is preferably 1-3mL, 6-10mL, 20-25mL, for example, 1mL, 6mL, 20mL respectively; 2mL, 8mL, 22mL respectively; 3mL, 10mL, 25mL respectively. The high temperature heating conditions are preferably 400-500°C for 4-8h, for example, 400°C for 8h, 450°C for 6h or 500°C for 4h.

[0098] For the in-situ growth of titanium dioxide nanorods, the mass of the titanium sheet is preferably 4-6 g; the addition amounts of melamine, nitric acid and hydrogen peroxide in the reaction solution are preferably 0.2-0.8 g, 0.5-3.5 mL and 50-200 mL, respectively. The hydrothermal conditions are preferably 60-100°C hydrothermal for 2-6 h, for example, 60°C hydrothermal for 6 h, 80°C hydrothermal for 4 h or 100°C hydrothermal for 2 h. The calcination conditions are preferably 500-800°C calcination for 4-6 h, for example, 500°C calcination for 6 h, 600°C calcination for 5 h or 800°C calcination for 4 h.

[0099] For the silane coupling agent modification treatment, the reflux condition is preferably 60-80°C for 3-5h, for example, 60°C for 5h, 70°C for 4h or 80°C for 3h. The mass of the mica on which the metal oxide nanorods are grown is preferably 3-5g, and the amount of the silane coupling agent added is preferably 2-4mL.

[0100] Those skilled in the art can select or adjust the above conditions as needed, and can prepare a layered porous radiative cooling film with high reflectivity, high atmospheric window emissivity and excellent radiative cooling effect, which will not be described in detail here.

[0101] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0102] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing a layered porous radiation cooling film, characterized in that: The following steps are involved: In situ growth of metal oxide nanorods on mica surface; After the mica with metal oxide nanorods grown on the surface is modified by a silane coupling agent, the mica is added into an organic dispersant and mixed with a fiber material to form a sol, which is then vacuum filtered to obtain a layered porous radiation refrigeration film.

2. The method for preparing a layered porous radiative cooling film according to claim 1, characterized in that: The metal oxide is at least one of titanium dioxide, iron oxide and cobalt oxide.

3. The method for preparing a layered porous radiative cooling film according to claim 2, characterized in that: The metal oxide is titanium dioxide, and the step of in-situ growing metal oxide nanorods on the mica surface comprises: (1) Preparing a titanium dioxide nano seed layer on a mica surface; (2) adding a titanium sheet to a reaction solution composed of melamine, nitric acid and hydrogen peroxide and stirring to form a reddish brown solution, pouring the reddish brown solution onto mica having a titanium dioxide nano seed layer on the surface, and performing a hydrothermal reaction at 60 to 100° C. for 2 to 6 hours; (3) After step (2) is repeated 4 to 6 times, the product is calcined at 500 to 800° C. for 4 to 6 hours in an air atmosphere to obtain mica with titanium dioxide nanorods in situ grown on the surface.

4. The method for preparing a layered porous radiative cooling film according to claim 3, characterized in that: The titanium dioxide seed layer is prepared by adding mica powder to a titanium dioxide precursor solution, hydrothermally reacting at 100-140° C. for 14-18 hours, drying the reactant, and calcining it at 400-500° C. for 4-8 hours in an air atmosphere.

5. The method for preparing a layered porous radiative cooling film according to claim 4, characterized in that: The titanium dioxide precursor solution includes a titanium dioxide precursor and an acid catalyst; In the titanium dioxide precursor solution, the volumes of the titanium dioxide precursor, the acid catalyst and the water are 1-3 mL, 6-10 mL and 20-25 mL respectively; and the added amount of the mica powder is 1-3 g.

6. The method for preparing a layered porous radiative cooling film according to claim 3, characterized in that: In step (2), the mass of the titanium sheet is 4-6 g; the amounts of melamine, nitric acid and hydrogen peroxide added to the reaction solution are 0.2-0.8 g, 0.5-3.5 mL and 50-200 mL respectively.

7. The method for preparing a layered porous radiative cooling film according to claim 1, characterized in that: The steps of the modification process are as follows: The mica with metal oxide nanorods grown on the surface is dispersed in a mixture of ethanol and deionized water, and a silane coupling agent is added, and refluxed at 60 to 80° C. for 3 to 5 hours, wherein the silane coupling agent is (3-aminopropyl) triethoxysilane; Preferably, the mass of the mica on which the metal oxide nanorods are grown is 3 to 5 g, and the amount of the silane coupling agent added is 2 to 4 mL.

8. The method for preparing a layered porous radiative cooling film according to claim 1, characterized in that: The fiber material is aramid fiber or carbon fiber, and the added amount of the fiber material is 1 to 3 g.

9. The method for preparing a layered porous radiative cooling film according to claim 1, characterized in that: The organic dispersant is dimethyl sulfoxide, N,N-dimethylacetamide or glycerol, and the volume of the organic dispersant is 50 to 200 mL.

10. A layered porous radiation cooling film, characterized in that: The method is prepared by the method according to any one of claims 1 to 9.

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