Polyvinyl alcohol-based aerogel with radiation cooling and fireproof characteristics as well as preparation method and application of polyvinyl alcohol-based aerogel

Abstract

The invention relates to the technical field of functional materials, and particularly discloses polyvinyl alcohol-based aerogel with radiation cooling and fireproof characteristics as well as a preparation method and application of the polyvinyl alcohol-based aerogel. The preparation method comprises the following steps: compounding polyvinyl alcohol with radiation cooling hybrid particles containing elements such as P, N and Si, and preparing high-whiteness polyvinyl alcohol-based aerogel with a micro-nano dual-scale porous structure through a freeze-drying method; the double-scale porous structure of the aerogel enhances diffuse reflection of light; molecular bonds such as C-C, C-H, Si-O, N-H, P-O and the like are efficiently emitted in an atmospheric window area. The phonon polarization-phonon resonance characteristic of the hybrid particles is beneficial to radiation emission of heat and reduction of absorption of sunlight, and meanwhile, elements such as P, N and Si effectively improve the flame retardant property of polyvinyl alcohol. The preparation method disclosed by the invention is simple and low in cost, and the prepared polyvinyl alcohol-based aerogel shows excellent refrigeration effect and fireproof safety and can be applied to the fields of building energy conservation and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of functional materials, and particularly relates to a polyvinyl alcohol-based aerogel with both radiative cooling and fireproof properties, a preparation method thereof, and an application thereof. Background Art

[0002] With the acceleration of the urbanization process, the global surface temperature has been rising year by year, and the greenhouse effect and the heat island effect have become increasingly severe. The use of traditional temperature control systems (such as air conditioners, electric fans, etc.) supported by electricity not only exacerbates the global energy shortage problem, but also causes the global temperature to rise again due to the release of greenhouse gases. Obviously, there is an inevitable contradiction between reducing cooling energy consumption and maintaining human comfort. As an efficient and energy-saving refrigeration method that can achieve temperature regulation without additional energy input, radiative cooling technology can effectively solve the dual problems of the environment and energy consumption.

[0003] Polymer materials are considered to be ideal radiative cooling materials because of their significant emissivity in the atmospheric transparent window. Patent CN202411133776.0 relates to a passive radiative cooling coating textile and a preparation method and application thereof. The inventor coated a mixed coating composed of polylactic acid and a pore-forming agent on the surface of the textile, and prepared a radiative cooling fabric with high solar reflectivity and long-wave infrared emissivity by optimizing the coating structure through the phase separation method. Patent CN202410539609.X designs a nanofiber membrane with both waterproof, breathable and refrigeration properties, a preparation method thereof, and an application thereof. The inventor configured a spinning solution containing thermoplastic polyurethane, polydimethylsiloxane and inorganic nanoparticles, and prepared a nanofiber membrane with radiative cooling, high elasticity, waterproof and breathable properties through the electrospinning process. Li et al. prepared a refrigeration wood by complete delignification and hot pressing, and this material showed excellent refrigeration effect (Science, 2019, 364, 760). However, these polymer materials contain rich C, H, and O elements, which determines that they are highly flammable. When they are used as radiative cooling materials on the surfaces of buildings and the like, once a fire occurs, a large amount of heat and toxic smoke will be released, seriously endangering the safety of personnel. Therefore, developing a polymer-based composite material with both fireproof performance and radiative cooling performance can significantly improve the building energy-saving effect and safety, and is one of the development directions of future building energy-saving technologies. Summary of the Invention

[0004] The object of the present invention is to provide a polyvinyl alcohol-based aerogel with both radiative cooling and fireproof properties, its preparation method and application, aiming at the above-mentioned deficiencies of the prior art. Using polymer polyvinyl alcohol as the main matrix, a micro-nano dual-scale porous structure is created through structural design to increase the reflectivity. At the same time, hybrid particles with high whiteness and carrying P, N, and Si flame retardant elements are embedded inside, so as to prepare a polyvinyl alcohol aerogel with both radiative cooling and fireproof properties. This material can not only meet the requirements of building cooling and fire safety at the same time, but also reduce the dependence on petrochemical resources and reduce environmental pollution, meeting the requirements of modern green buildings and sustainable development.

[0005] To achieve the above object, the present invention adopts the following technical solutions: The first aspect of the present invention is to provide a polyvinyl alcohol-based aerogel with both radiative cooling and fireproof properties, its preparation method and application. The method includes the following steps: S1. Take an appropriate amount of inorganic particles containing Si elements and disperse them evenly in water; the particle size of the inorganic particles is 0.1~30 μm; S2. Take an appropriate amount of organic compound containing N and dissolve it in water, then drop it into the solution of S1, and adjust the pH of the solution to 8~10, and then continue to stir and react; S3. Drop a certain amount of phytic acid into S2, and stir and react at a reaction temperature of 80~95 °C. After the reaction is completed, the product is obtained by centrifugation, washed with a solvent, and then dried in an oven at 50~80 °C for 5~10 h to obtain hybrid particles; S4. Prepare a polyvinyl alcohol solution with a certain concentration, add the hybrid particles obtained in S3 to the polyvinyl alcohol solution and stir and react to obtain a mixed solution; S5. Add a chemical cross-linking agent to the mixed solution obtained in S4, stir evenly and pour it into a mold for freezing, and then perform freeze-drying treatment to obtain the polyvinyl alcohol-based aerogel.

[0006] Further, in step S1, the inorganic particles containing Si elements are any one of diatomite, silica, halloysite, montmorillonite, and kaolin; the organic compound containing N is melamine or chitosan.

[0007] Further, the mass ratio of the inorganic particles, the organic compound containing N, and phytic acid is (1~2):(1~3):3.

[0008] Further, in step S4, the mass ratio of the hybrid particles to polyvinyl alcohol is (1~5):10; the reaction temperature is 80 °C~95 °C; the reaction time is 1 h~5 h.

[0009] Further, in step S4, the type of the polyvinyl alcohol is polyvinyl alcohol 1790±50, and the mass fraction of the polyvinyl alcohol solution is 1% to 10%.

[0010] Further, in step S5, the chemical crosslinking agent is any one of boric acid, sodium borate, and borax.

[0011] Further, the mass ratio of the chemical crosslinking agent to the polyvinyl alcohol is 1:(5 - 100); the freeze-drying temperature is -50°C to -60°C; the freeze-drying time is 48h to 72 h.

[0012] The second aspect of the present invention is to provide a polyvinyl alcohol-based aerogel prepared by the above method.

[0013] Further, the polyvinyl alcohol-based aerogel has a micro-nano dual-scale structure, wherein the micron-scale pore size range of the aerogel is 1 - 7 μm, and the nano-scale pore size range of the aerogel is 10 - 500 nm The third aspect of the present invention is to provide the application of the above-prepared polyvinyl alcohol-based aerogel in the preparation of building radiative cooling materials and building flame-retardant materials.

[0014] Compared with the prior art, the beneficial effects brought by the technical solution provided by the present invention are: (1) A polyvinyl alcohol-based aerogel with both radiative cooling and fireproof characteristics provided by the present invention utilizes the correlation between the molecular bonding mode and the emissivity of the atmospheric window, selects "green" polyvinyl alcohol as the skeleton of the aerogel, and at the same time uses the synthesized hybrid particles with high whiteness and carrying P, N, and Si flame-retardant elements as fillers; the polyvinyl alcohol and the hybrid particles continuously emit heat to outer space, significantly enhancing the radiative cooling performance.

[0015] (2) Through the hydrogen bond action between the polyvinyl alcohol and the hybrid particles and the chemical action of the crosslinking agent, the present invention embeds the hybrid particles into the polyvinyl alcohol aerogel skeleton, combines the advantages of the polyvinyl alcohol and the hybrid particles, and prepares a polyvinyl alcohol-based aerogel with both radiative cooling and fireproof characteristics.

[0016] (3) By combining the freezing strategy and the intermolecular interaction, the present invention enables the polyvinyl alcohol aerogel to construct a micron-scale gradient pore structure while maintaining the nano-porous structure. This micro-nano dual-scale porous structure with coexisting micropores and nano-pores significantly enhances the optical properties of the polyvinyl alcohol aerogel through multiple scattering and optical resonance effects.

[0017] (4) The method adopted by the present invention has simple process steps, strong operability, and low preparation cost. The developed polyvinyl alcohol-based aerogel can not only meet the requirements of building refrigeration and fire safety simultaneously, but also meet the requirements of modern green buildings and environmentally friendly sustainable development, providing an efficient, environmentally friendly and safe solution for building energy conservation. Description of the Drawings

[0018] Figure 1 It is a schematic structural diagram of the polyvinyl alcohol-based aerogel with both radiative cooling and fireproof properties of the present invention; Figure 2 It is the X-ray electron diffraction pattern of the PVA aerogel and PVA / DIA@MPA aerogel prepared in Example 1 of the present invention; Figure 3 It is the Fourier transform infrared spectrum of the PVA aerogel and PVA / DIA@MPA aerogel prepared in Example 1 of the present invention; Figure 4a It is the scanning electron microscope image of the PVA aerogel prepared in Example 1 of the present invention; Figure 4b It is the scanning electron microscope image of the PVA / DIA@MPA aerogel prepared in Example 1 of the present invention; Figure 5 It is the reflectance of the PVA aerogel and PVA / DIA@MPA aerogel prepared in Example 1 of the present invention under the solar spectrum and the emissivity curve in the atmospheric window wavelength range; Figure 6 It is the curve of the surface temperature and ambient temperature of the PVA aerogel and PVA / DIA@MPA aerogel prepared in Example 1 of the present invention changing with time; Figure 7a It is the PVA / DIA@MPA aerogel prepared in Example 1 of the present invention with different non-radiative heat transfer coefficients ( h c ) under the theoretical net radiative cooling power and temperature change curve; Figure 7b It is the PVA / DIA@MPA aerogel prepared in Example 1 of the present invention with different non-radiative heat transfer coefficients ( h c ) under the theoretical net radiative cooling power and temperature change curve at night; Figure 8a It is the curve of the heat release rate changing with time of the PVA aerogel and PVA / DIA@MPA aerogel prepared in Example 1 of the present invention tested by a cone calorimeter; Figure 8bCurves showing the variation of carbon monoxide generation rate with time for the PVA aerogel and PVA / DIA@MPA aerogel prepared in Example 1 of the present invention, as measured by a cone calorimeter.

[0019] Figure 9 Digital photos of the PVA aerogel and PVA / DIA@MPA aerogel prepared in Example 1 of the present invention during the alcohol lamp combustion test. Detailed implementation manners

[0020] To make the objectives, technical solutions, and advantages of the present invention clearer, the following further describes the detailed implementation manners of the present invention in combination with specific examples and drawings. For those not specified in the examples regarding specific test methods, instrument equipment, or conditions, they shall be carried out according to the techniques or conditions described in the literature in this field or according to the product specifications. For reagents or instruments without indicating the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0021] The preparation method of the polyvinyl alcohol-based aerogel with both radiative cooling and fireproof properties provided by the present invention specifically includes the following steps: (1) Take an appropriate amount of inorganic particles containing Si element and disperse them in an appropriate amount of deionized water, and stir evenly; the inorganic particles are selected from one of diatomite, silica, halloysite, montmorillonite, and kaolin; the particle size is 0.1 - 30 μm, and the whiteness > 90%; diatomite (disc structure), silica (spherical structure), halloysite (tubular structure), montmorillonite (lamellar structure, single layer thickness ~ 1 nm, lamellar diameter 50 - 200 nm), kaolin (lamellar structure, single layer thickness ~ 0.5 nm, lamellar diameter 0.5 - 5 μm) (2) Take an appropriate amount of organic compound containing a single N element and dissolve it in deionized water at a temperature of 80 - 95 °C, then drop it into the solution in step (1), and adjust the pH of the solution, and then continue to stir and react; the organic compound containing a single N element is one of melamine and chitosan; (3) Drop a certain amount of phytic acid into step (2) and stir and react at a reaction temperature of 80 - 95 °C. After the reaction is completed, the product is obtained by centrifugation, washed 2 - 5 times with a solvent, and then dried in an oven at 50 - 80 °C for 5 - 10 h to obtain hybrid particles for radiative cooling with high whiteness and containing P, N, and Si flame retardant elements; (4) Prepare a polyvinyl alcohol solution with a certain concentration, drop an appropriate amount of the hybrid particle dispersion liquid into this solution, stir and react. After the reaction is completed, add an appropriate amount of cross-linking agent and continue to stir for a moment to form a homogeneous mixture; (5) Pour the mixed system into a mold and freeze it, and then perform freeze-drying to obtain the polyvinyl alcohol-based aerogel with both radiative cooling and fireproof properties.

[0022] All of the above methods can be used to prepare polyvinyl alcohol-based aerogels with micro-nano dual-scale porous structures. As Figure 1 shown, the microporous structure of the polyvinyl alcohol-based aerogel is loaded with hybrid particles with high whiteness, and pore structures at both the microscale and nanoscale exist simultaneously in its microscopic morphology. Among them, the micron-sized pore diameter range of the aerogel is 1-7 μm, and the nanometer-sized pore diameter range of the aerogel is 10-500 nm. Specific examples are described below.

[0023] Example 1 (1) Disperse 2.5 g of diatomite (DIA, disc-shaped structure, with a diameter of 10-30 μm and a pore size of 0.1-1 μm) in 250 mL of deionized water, heat it to 90 °C and stir for 1 h; (2) Dissolve 3.84 g of melamine in 125 mL of deionized water at 80 °C, then drop it into the diatomite dispersion, and at the same time adjust the solution pH = 9, and continuously stir at 90 °C for 1 h; (3) Add 6.0 g of 70 wt% phytic acid (PA) to the above solution, and continue to stir and react at 90 °C for 30 min. After the reaction is completed, centrifuge and wash 3 times, and then dry in an oven at 80 °C for 10 h to obtain the final product DIA@MPA; (4) Take 12.5 g of polyvinyl alcohol and dissolve it in 140 mL of deionized water at 95 °C. At the same time, disperse 1.05 g of DIA@MPA in 50 mL of deionized water; then drop the DIA@MPA dispersion into the polyvinyl alcohol solution and stir and react at 95 °C for 1 h; then drop 20 mL of an aqueous solution containing 0.21 g of boric acid and stir for 10 min to form a homogeneous mixed system; (5) Pour the mixed system into a mold, freeze it in liquid nitrogen for 12 h, and then dry it in a freeze dryer at -60 °C for 48 h to obtain the polyvinyl alcohol-based aerogel.

[0024] Example 2 (1) Disperse 2.5 g of DIA in 250 mL of deionized water, heat it to 90 °C and stir for 1 h; (2) Dissolve 5.0 g of melamine in 150 mL of deionized water at 80 °C, then drop it into the diatomite dispersion, and at the same time adjust the solution pH = 9, and continuously stir at 90 °C for 1 h; (3) Add 7.1 g of 70 wt% PA to the above solution, and continue to stir and react at 90 °C for 30 min. After the reaction is completed, centrifuge and wash 3 times, and then dry in an oven at 80 °C for 10 h to obtain the final product DIA@MPA; (4) Take 12.5 g of polyvinyl alcohol and dissolve it in 140 mL of deionized water at 95 °C. At the same time, disperse 2.1 g of DIA@MPA in 50 mL of deionized water. Then, drop the DIA@MPA dispersion into the polyvinyl alcohol solution and stir and react at 95 °C for 1 h. Subsequently, drop in 20 mL of an aqueous solution containing 0.21 g of boric acid and stir for 10 min to form a homogeneous mixed system. (5) Pour the mixed system into a mold, freeze it in liquid nitrogen for 12 h, and then place it in a freeze dryer at -60 °C to dry for 48 h to obtain the polyvinyl alcohol-based aerogel.

[0025] Example 3 (1) Disperse 1.0 g of silica (SiO 2 , with a particle size of 0.1 - 1 μm) in 250 mL of deionized water, heat it to 90 °C and stir for 1 h. (2) Dissolve 2.8 g of melamine in 100 mL of deionized water at 80 °C, and then drop it into the diatomite dispersion while adjusting the solution pH = 9, and continuously stir at 90 °C for 1 h. (3) Add 4.0 g of 70 wt% PA to the above solution and continue to stir and react at 90 °C for 30 min. After the reaction, centrifuge and wash 3 times, and then dry in an oven at 80 °C for 10 h to obtain the final product SiO 2 @MPA; (4) Take 12.5 g of polyvinyl alcohol and dissolve it in 140 mL of deionized water at 95 °C. At the same time, disperse 3.15 g of SiO 2 @MPA in 50 mL of deionized water. Then, drop the SiO 2 @MPA dispersion into the polyvinyl alcohol solution and stir and react at 95 °C for 1 h. Subsequently, drop in 20 mL of an aqueous solution containing 0.21 g of boric acid and stir for 10 min to form a homogeneous mixed system. (5) Pour the mixed system into a mold, freeze it in liquid nitrogen for 12 h, and then place it in a freeze dryer at -60 °C to dry for 48 h to obtain the polyvinyl alcohol-based aerogel.

[0026] Example 4 (1) Disperse 1.5 g of halloysite (HNT, outer diameter 30 - 150 nm, inner diameter 10 - 30 nm, length 0.5 - 2 μm) in 250 mL of deionized water, heat it to 90 °C and stir for 1 h. (2) Dissolve 2.0 g of chitosan (CS) in 100 mL of deionized water at 80 °C, and then drop it into the diatomite dispersion while adjusting the solution pH = 9, and continuously stir at 90 °C for 1 h. (3) Add 4.29 g of 70 wt% PA to the above solution, and continue stirring and reacting at 90 °C for 30 min. After the reaction is completed, centrifuge and wash 3 times, and then dry in an oven at 80 °C for 10 h to obtain the final product HNT@CSPA; (4) Take 12.5 g of polyvinyl alcohol and dissolve it in 140 mL of deionized water at 95 °C. At the same time, disperse 3.15 g of HNT@CSPA in 50 mL of deionized water; then drop the HNT@CSPA dispersion into the polyvinyl alcohol solution and stir and react at 95 °C for 1 h; subsequently, drop 20 mL of aqueous solution containing 0.21 g of borax and stir for 10 min to form a homogeneous mixed system; (5) Pour the mixed system into a mold, freeze it in liquid nitrogen for 12 h, and then place it in a freeze dryer at -60 °C for 48 h to obtain the polyvinyl alcohol-based aerogel.

[0027] The polyvinyl alcohol-based aerogels prepared in Examples 1-4 all have similar microscopic morphological structures. Here, Example 1 is taken as an example for detailed description. The polyvinyl alcohol-based aerogel prepared in Example 1 is respectively subjected to X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) analysis.

[0028] Figure 2 are the XRD patterns of the PVA aerogel and PVA / DIA@MPA aerogel prepared in Example 1. From Figure 2 It can be seen that the pure PVA aerogel has an obvious strong characteristic peak at 19.7°. After incorporating DIA@MPA into PVA, two new characteristic peaks appear on the curve, at 22.2° and 36.3° respectively, indicating the successful synthesis of the PVA / DIA@MPA aerogel.

[0029] Figure 3 are the FTIR patterns of the PVA aerogel and PVA / DIA@MPA aerogel prepared in Example 1. From Figure 3 It can be seen that for the PVA aerogel, the absorption signals at 3409, 2946, 1657, 1138, and 839 cm -1 are attributed to the vibrations of O-H, -CH 2 , C=O, C-O, and C-C bonds; compared with the pure PVA aerogel, the stretching vibration peaks of P-O and SiO-H in the PVA / DIA@MPA aerogel are located near 1062 and 788 cm -1 , originating from phytic acid and DIA of DIA@MPA; at the same time, the C=N characteristic peak (1505 cm -1 ) belonging to MPA is also observed.

[0030] Figure 4a - Figure 4b SEM images of the PVA aerogel and PVA / DIA@MPA aerogel prepared in Example 1. From Figure 4a it can be seen that the pure PVA aerogel has a continuous and dense pore structure with extremely small pore diameters. In contrast, Figure 4b as shown in, the pore diameter of the PVA / DIA@MPA aerogel increases, the uniformity of the pore structure distribution improves, and there are many small pores in the large pore structure.

[0031] Furthermore, the radiative cooling performance and fire resistance of the polyvinyl alcohol-based aerogel prepared in Example 1 were studied.

[0032] Figure 5 Curves of the reflectance of the PVA aerogel and PVA / DIA@MPA aerogel prepared in Example 1 under the solar spectrum and the emissivity within the atmospheric window wavelength range. From Figure 5 it can be seen that the reflectances of the pure PVA aerogel and PVA / DIA@MPA aerogel within the solar spectrum are 88.93% and 92.98% respectively, and the emissivities within the atmospheric window wavelength range are 90.61% and 92.98% respectively, indicating that the incorporation of DIA@MPA effectively improves the spectral performance of the PVA-based aerogel as a radiative cooling material.

[0033] Figure 6 Curves of the surface temperature and ambient temperature of the PVA aerogel and PVA / DIA@MPA aerogel prepared in Example 1 changing with time. From Figure 6 it can be seen that the maximum temperature differences that the pure PVA aerogel and PVA / DIA@MPA aerogel can generate relative to the environment are 6.6 °C and 15.3 °C respectively.

[0034] Figure 7a - Figure 7b Curves of the theoretical net radiative cooling power and temperature change of the PVA / DIA@MPA aerogel prepared in Example 1 under different non-radiative heat transfer coefficients ( h c ) during the day and at night. T a , T s and T a -T s are defined as the ambient temperature, the surface temperature of the aerogel, and the cooling temperature respectively. When the theoretical net radiative cooling power is 0 W / m 2 , the maximum cooling temperatures that the PVA / DIA@MPA aerogel can reach during the day and at night are 19.7 °C and 24.3 °C respectively; when the cooling temperature is 0 °C, the theoretical net radiative cooling powers at night and during the day are 82.3 and 99.9 W / m 2 respectively. At the same time, as the non-radiative heat transfer coefficient increases, the maximum cooling temperature shows a downward trend.

[0035] Figure 8a - Figure 8b Curves showing the variation of heat release rate and carbon monoxide generation rate over time for the PVA aerogel and PVA / DIA@MPA aerogel prepared in Example 1, tested using a cone calorimeter. From Figure 7a it can be seen that the peak heat release rate (pHRR) of the pure PVA aerogel is 177.9 kW / m 2 , while the pHRR value of PVA / DIA@MPA is 129.6 kW / m 2 , a decrease of 27.2%, indicating a significant improvement in flame retardancy. Observation Figure 7b shows that the pure PVA exhibits a relatively high peak carbon monoxide generation rate (pCOP), which is 3.99×10 -3 g / s, while the pCOP of PVA / DIA@MPA is reduced by 32.1%, which confirms that the addition of DIA@MPA can endow PVA with excellent smoke suppression and toxicity reduction properties.

[0036] Figure 9 Digital photos of the PVA aerogel and PVA / DIA@MPA aerogel prepared in Example 1 during the alcohol lamp combustion test. Once the pure PVA aerogel comes into contact with the flame, it is immediately ignited, accompanied by an obvious shrinking phenomenon. After removing the ignition source, the flame continues to burn for up to 35 s and is completely burned out; it cannot be ignited again during the second ignition. In contrast, although the PVA / DIA@MPA aerogel also shows a slight shrinking phenomenon, it can self-extinguish within 2 s after the flame is removed; after the second ignition, due to the protection of the carbon layer on the surface, the fire is immediately blocked, and finally the aerogel still shows most of its original white surface.

[0037] Without conflict, the above embodiments and the features in the embodiments in this article can be combined with each other.

[0038] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a polyvinyl alcohol-based aerogel having both radiation cooling and fireproof properties, characterized in that: The following steps are involved: S1. Take an appropriate amount of inorganic particles containing Si element and disperse them in water and stir them evenly; the particle size of the inorganic particles is 0.1-30 μm; S2, dissolving an appropriate amount of an organic compound containing N in water, then adding it dropwise to the solution obtained in S1, adjusting the pH of the solution to 8-10, and then continuing to stir the reaction; S3, adding a certain amount of phytic acid to S2, and stirring the mixture at a temperature of 80-95°C for reaction. After the reaction is completed, the mixture is centrifuged to obtain the product, which is then washed with a solvent and dried to obtain hybrid particles; S4, preparing a polyvinyl alcohol solution of a certain concentration, adding the hybrid particles obtained in S3 to the polyvinyl alcohol solution and stirring to react, to obtain a mixed solution; S5, adding a chemical crosslinking agent to the mixed solution obtained in S4, stirring the mixed solution evenly, pouring the mixture into a mold and freezing it, and then freeze-drying it to obtain the polyvinyl alcohol-based aerogel.

2. The preparation method according to claim 1, characterized in that In step S1, the inorganic particles containing Si element are any one of diatomaceous earth, silicon dioxide, halloysite, montmorillonite and kaolin; and the organic compound containing N is melamine or chitosan.

3. The preparation method according to claim 1, characterized in that: The mass ratio of the inorganic particles, the organic compound containing N and the phytic acid is (1-2):(1-3):

3.

4. The preparation method according to claim 1, characterized in that In step S4, the mass ratio of the hybrid particles to polyvinyl alcohol is (1-5):10; the reaction temperature is 80°C-95°C; and the reaction time is 1 h-5 h.

5. The preparation method according to claim 1, characterized in that: In step S4, the type of the polyvinyl alcohol is polyvinyl alcohol 1790±50, and the mass fraction of the polyvinyl alcohol solution is 1%~10%.

6. The preparation method according to claim 1, characterized in that: In step S5, the chemical cross-linking agent is any one of boric acid, sodium borate and borax.

7. The preparation method according to claim 6, characterized in that The mass ratio of the chemical cross-linking agent to polyvinyl alcohol is 1:(5-100); the freeze-drying temperature is -50°C to -60°C; and the freeze-drying time is 48h-72h.

8. A polyvinyl alcohol-based aerogel prepared by the preparation method according to any one of claims 1 to 9.

9. The polyvinyl alcohol-based aerogel according to claim 8, characterized in that The polyvinyl alcohol-based aerogel has a micro-nano dual-scale structure, wherein the micron-scale pore size range of the aerogel is 1-7 μm, and the nano-scale pore size range of the aerogel is 10-500 nm.

10. Use of the polyvinyl alcohol-based aerogel according to claim 8 in preparing building radiation cooling materials and building flame retardant materials.

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