Radiation refrigeration film and ceramic based on nano SiO2 and preparation method of radiation refrigeration film and ceramic

Abstract

The invention discloses a transparent radiation refrigeration film and radiation refrigeration ceramic for building heat management and a preparation method of the transparent radiation refrigeration film and the radiation refrigeration ceramic. According to the film and the ceramic, SiO2 nano-particles are selected as base materials for achieving radiation refrigeration, dendritic silicon oxide nano-particles are adopted as inorganic particle emission materials of the film, PDMS is adopted as a polymer matrix, ITO coating PET is adopted as a flexible substrate, DMSNs are dispersed in PDMS, and the film is formed on the ITO-PET substrate through a blade coating technology. The white or colored ceramic takes spherical SiO2 nano-particles as a radiation refrigeration material and is sintered into white SiO2 porous ceramic, namely white radiation refrigeration ceramic, through phase inversion, and then the white radiation refrigeration ceramic is colored through chemical dye to form the colored ceramic. The radiation refrigeration film is good in transparency and bright in ceramic color, both the radiation refrigeration film and the ceramic have excellent radiation refrigeration performance, the transparent film can achieve the indoor cooling effect of about 12 DEG C on sunny days, and the colored ceramic can achieve the cooling effect of about 5 DEG C on sunny days.

Description

Technical Field

[0001] The present invention relates to the field of daytime radiative cooling, and particularly to a transparent film and a radiative cooling ceramic for building thermal management, and a preparation method and application thereof. Background Art

[0002] The global energy shortage and rising temperatures pose significant challenges to sustainable development, among which heat management has become increasingly important in maintaining human comfort and social well-being. Statistical data shows that building energy consumption accounts for 40% of the global energy use. Windows are an important factor, accounting for 60% of building energy consumption. In summer, sunlight shines through the windows into the narrow indoor space, raising the room temperature to 35 - 60 °C, which can cause significant discomfort to the human body. In addition, the absorption of solar heat by the roof also increases the building's heat load. Traditional cooling devices, such as air conditioners and fans, although effective, consume a large amount of energy, and the greenhouse gases such as carbon dioxide generated by energy consumption also exacerbate the greenhouse effect, further driving up the temperature. Therefore, there is an urgent need for new environmentally friendly heat management technologies to reduce building energy consumption and meet the needs of sustainable development.

[0003] Daytime radiative cooling, as an emerging cooling technology, has been widely studied. Among them, transparent radiative cooling materials provide a promising solution for building energy consumption caused by windows, because they radiate heat through the atmospheric window to achieve passive cooling without additional energy consumption. In addition, colored radiative cooling materials can meet people's aesthetic needs while providing a cooling effect.

[0004] However, despite its great potential, there are still huge challenges in achieving effective radiative cooling while maintaining a transparent and colored appearance. High visible transmittance and visible absorptance usually exacerbate the heating effect of solar radiation, thus weakening the radiative cooling effect. This limits the practical applications of transparent and colored radiative cooling materials. In addition, the complex and expensive manufacturing process also restricts the current transparent and colored radiative cooling materials in applications. Summary of the Invention

[0005] Based on the above background, the present invention proposes a transparent radiative cooling thin film, a white or colored radiative cooling ceramic. The thin film has both transparency and cooling characteristics, and the ceramic has both a white or colored appearance and cooling characteristics. Both the thin film and the ceramic select inorganic SiO2 nanoparticles as the basic material for realizing radiative cooling. The thin film selects the form of dendritic mesoporous SiO2 nanoparticles randomly dispersed in a polymer matrix, and adopts a low-cost blade coating process, using silicon oxide as the inorganic particle emission material, polydimethylsiloxane as the polymer matrix, and ITO-coated PET film (ITO-PET) as the flexible substrate. The white or colored porous ceramic is sintered from spherical SiO2 nanoparticles, and the colored ceramic is colored with chemical dyes.

[0006] Silicon oxide is an ideal infrared emission material, which has a very strong infrared emissivity in the atmospheric window band range. Dendritic mesoporous silica nanoparticles have a large specific surface area, and their three-dimensional network dendritic structure enables DMSNs to be well dispersed in the polymer matrix and tightly combined with the polymer, and it is not easy to fall off, agglomerate and crack, which promotes the passage of light and is suitable for preparing transparent thin films. In addition, the polymer used for film formation selects polydimethylsiloxane which also has high emission performance in the atmospheric window; and the refractive index of PDMS is close to that of SiO2, which makes no strong reflection occur at the interface between the two, further improving the transparency of the thin film. The ITO-PET material as the substrate has many advantages. First, as a flexible substrate, it has a high visible light transmittance, which ensures the transparency of the transparent radiative cooling (TRC) thin film. Second, the melting point of PET is relatively high, about 250 °C, and this characteristic ensures that the substrate will not soften or deform due to high temperature during the subsequent preparation process of the TRC thin film (100 °C curing temperature). For the radiative cooling ceramic, spherical silicon oxide nanoparticles have a strong scattering effect on light, and using this characteristic, silicon oxide porous ceramics are prepared. The porous structure in the ceramic further enhances the reflection of the material to visible light, thereby reducing the temperature rise caused by coloring.

[0007] The present invention designs a DMSNs / PDMS / ITO-PET composite transparent radiative cooling thin film and a white or colored SiO2 porous ceramic with radiative cooling effect according to the actual application requirements. DMSNs are synthesized by the template method, and the process parameters are controlled to make its surface and interior have dendritic channels, effectively improving the light transmittance. The designed composite transparent radiative cooling thin film has good cooling performance and becomes a potential energy-saving and environmental-friendly material. Through the phase transformation method, the sintered SiO2 porous ceramic has a porous structure, enhancing the scattering of sunlight, and at the same time has excellent cooling performance.

[0008] Based on the above invention object, the present invention firstly provides a transparent radiative cooling film, which is a composite structure composed of DMSNs (dendritic mesoporous silica nanoparticles), a film-forming polymer PDMS (polydimethylsiloxane), and ITO-PET (ITO-coated PET film); wherein ITO-PET is used as the substrate, DMSNs are randomly dispersed in the PDMS matrix to form a DMSNs / PDMS composite material, and this composite material forms a DMSNs / PDMS composite film on the ITO-PET substrate, thus obtaining the DMSNs / PDMS / ITO-PET transparent radiative cooling film.

[0009] Furthermore, the diameter of the DMSNs nanospheres is about 200 nm, and there are a large number of dendritic pores and channels on the surface and inside; this three-dimensional network porous dendritic structure helps the DMSNs to be uniformly dispersed in the polymer, tightly combined with the polymer, avoiding agglomeration, cracks, etc., and ensuring the uniformity and stability of the material. The thickness of the DMSNs / PDMS composite film is about 20 μm, and the mass fraction of DMSNs is 3 wt.% - 10 wt.%.

[0010] The present invention also provides a preparation method of the above-mentioned DMSNs / PDMS / ITO-PET transparent radiative cooling film, and the preparation method is to stir and mix DMSNs and PDMS to form a uniform mixture; form the mixture into a film on the ITO-PET substrate, and form the DMSNs / PDMS / ITO-PET transparent radiative cooling film by drying and curing. The mass fraction of DMSNs is 3 wt.% - 10 wt.% of the mixture. In the embodiments of the present invention, a more specific preparation process includes the following steps:

[0011] (1) Add TEA (triethylamine) to deionized water, stir in a water bath to make it uniformly dispersed, and obtain a pretreated TEA base solution;

[0012] (2) Gradually add sodium salicylate and CTAB to the TEA base solution obtained in step (1), and stir to form a transparent and uniform mixed solution;

[0013] (3) Dropwise add TEOS to the mixed solution obtained in step (2), carry out a hydrothermal reaction, and after the reaction is completed, cool to room temperature to obtain a precipitate product;

[0014] (4) Centrifuge the precipitate product obtained in step (3), collect the solid, wash it, and dry it to obtain a powder;

[0015] (5) Transfer the powder obtained in step (4) to a muffle furnace, calcine to remove the template, and collect the final product DMSNs;

[0016] (6) Mix the DMSNs obtained in step (5) with PDMS and stir evenly to form a mixture; the mass fraction of DMSNs is 3 wt.% - 10 wt.% of the mixture.

[0017] (7) Coating the mixture in step (6) onto the ITO-PET substrate by a doctor blade process, and transferring it to an oven for curing to obtain the DMSNs / PDMS / ITO-PET transparent radiative cooling film.

[0018] In the above process steps, the ratio of each raw material, the control of the temperature and time of the hydrothermal reaction are the key to forming the final specific microscopic morphology and chemical composition of the materials of the present invention.

[0019] In step (1), the water bath stirring temperature is 80 °C and the time is 30 min.

[0020] In step (2), the stirring time is 1 h.

[0021] In step (3), the reaction temperature is 80 °C and the time is 3 h.

[0022] In step (4), the drying temperature is 60 °C and the time is 12 h.

[0023] In step (5), the calcination temperature is 400 °C and the time is 8 h.

[0024] In step (7), the curing temperature is 100 °C.

[0025] The present invention also provides a white radiative cooling ceramic and a colored radiative cooling ceramic. The white radiative cooling ceramic is a SiO2 porous ceramic composed of nano-SiO2 particles, and there are a large number of pores on the surface and inside of the ceramic; the average particle size of the nano-SiO2 particles is about 50 nm, the average size of the pores is about 40 nm, and the thickness of the ceramic is about 400 μm. The colored radiative cooling ceramic is formed by chemically coloring the white radiative ceramic.

[0026] The present invention also provides a preparation method of the above white radiative cooling ceramic, and its preparation method forms a porous ceramic precursor through a phase inversion process and then is sintered. More specifically, the steps are as follows:

[0027] (1) Add spherical SiO2 nanoparticles and PES into NMP, heat and stir to form a suspension with uniformly dispersed particles.

[0028] (2) Coat the prepared suspension on a glass substrate and immerse it in ethanol to complete the phase inversion process to form a ceramic precursor.

[0029] (3) Dry the ceramic precursor at room temperature and cut it into the required shape.

[0030] (4) Transfer the ceramic precursor obtained in step (3) to a muffle furnace for sintering to obtain the porous white radiative cooling ceramic.

[0031] Furthermore, the present invention also provides the colored radiative cooling ceramic, which is obtained by coloring the white radiative cooling ceramic. The coloring step is as follows: Immerse the white radiative cooling ceramic prepared by the present invention into a dye for coloring, and obtain the colored porous ceramic after drying. In the above process steps, the ratio of each raw material, the phase transition time, and the sintering temperature control are the keys to forming the final specific microstructure and chemical composition of the materials of the present invention.

[0032] The heating and stirring temperature in step (1) is 40 °C and the time is 1 h.

[0033] The mass ratio of nano-SiO2, PES, and NMP in the suspension in step (1) is 1-3:5:20.

[0034] The phase transition time in step (2) is 24 h.

[0035] The sintering temperature in step (4) is 1000 °C and the time is 3 h.

[0036] The drying time after coloring is 12 h.

[0037] The beneficial effects of the present invention are as follows:

[0038] The DMSNs / PDMS / ITO-PET transparent radiative cooling film prepared by the present invention has good visible light transmittance and ultraviolet and near-infrared blocking ability. The average transmittance in the visible light band (0.38-0.76 μm) is about 70%, and the blocking rate in the ultraviolet band (<0.38 μm) is as high as 71%. The prepared white and colored radiative cooling ceramics have extremely high reflectivity in the solar spectrum range (0-2.5 μm), and the average reflectivity is 92%, which can prevent buildings from absorbing excessive solar energy and causing temperature rise.

[0039] The DMSNs / PDMS / ITO-PET transparent radiative cooling film prepared by the present invention has excellent mid-infrared emission ability, and the average emissivity in the atmospheric window (8-13 μm) is as high as 0.95. The prepared white and colored radiative cooling ceramics also have excellent mid-infrared emission ability, and the average emissivity in the atmospheric window (8-13 μm) is as high as 0.96.

[0040] In the outdoor temperature test, the transparent radiative cooling film and radiative cooling ceramics prepared by the present invention both have good actual cooling effects. On sunny days, the transparent radiative cooling film can achieve a maximum cooling of about 12 °C, and the white and colored radiative cooling ceramics can achieve maximum coolings of about 7 °C and 5 °C respectively. Moreover, the prepared colored ceramics have bright colors and good appearance, and are suitable for use in buildings. Description of the Drawings

[0041] Figure 1 Scanning electron microscope (SEM) image of the dendritic mesoporous SiO2 nanoparticles DMSNs prepared in Example 1.

[0042] Figure 2 Transmission electron microscope (TEM) image of the dendritic mesoporous SiO2 nanoparticles DMSNs prepared in Example 1.

[0043] Figure 3 X-ray diffraction (XRD) pattern of the dendritic mesoporous SiO2 nanoparticles DMSNs prepared in Example 1.

[0044] Figure 4 Ultraviolet-visible-near-infrared (UV-Vis-NIR) spectrum of the DMSNs / PDMS / ITO-PET transparent radiative cooling film prepared in Example 1.

[0045] Figure 5 Fourier transform infrared (FTIR) spectrum of the DMSNs / PDMS / ITO-PET transparent radiative cooling film prepared in Example 1.

[0046] Figure 6 Scanning electron microscope (SEM) image of the colored SiO2 porous ceramics prepared in Example 7.

[0047] Figure 7 Ultraviolet-visible-near-infrared (UV-Vis-NIR) spectrum of the colored SiO2 porous ceramics prepared in Example 7.

[0048] Figure 8 Fourier transform infrared (FTIR) spectrum of the colored SiO2 porous ceramics prepared in Example 7. Detailed Description of the Invention

[0049] The present invention will be further described below in conjunction with specific embodiments.

[0050] Example 1

[0051] In this example, a DMSNs / PDMS / ITO-PET transparent radiative cooling film was prepared. The specific preparation process of this example is as follows:

[0052] (1) Weigh 340 mg of triethylamine, add it to 125 ml of deionized water, stir in a water bath at 80 °C for 30 min to completely disperse it, and obtain a pretreated triethylamine base solution;

[0053] (2) Add 840 mg of sodium salicylate and 1900 mg of CTAB to the triethylamine base solution obtained in step (1), stir for 1 h, and obtain a transparent and uniform mixed solution;

[0054] (3) Slowly add 20 ml of tetraethyl orthosilicate dropwise to the mixed solution obtained in step (2), react in a water bath at 80 °C for 3 h, and cool to room temperature;

[0055] (4) Centrifuge the precipitate obtained in (3), collect the solid, wash it with ethanol 3 - 5 times, transfer it to an oven, and dry it at 60 °C for 12 h to obtain a powder;

[0056] (5) Transfer the powder obtained in step (4) to a muffle furnace, under an air atmosphere, heat it to 400 °C at a rate of 5 °C / min, and keep it for 8 h to calcine and remove the template, and collect the final product, dendritic mesoporous SiO2 nanoparticles (DMSNs);

[0057] (6) Weigh 950 mg of polydimethylsiloxane colloid and 50 mg of the DMSNs obtained in step (5) and mix them, stir for 30 min;

[0058] (7) Use the doctor - blade coating process to form a film of the mixture obtained in step (6) on an ITO - PET substrate, scrape a 10 - μm - thick film, and transfer it to an oven at 100 °C for curing to obtain the DMSNs / PDMS / ITO - PET transparent radiative cooling film.

[0059] Example 2

[0060] In this example, a DMSNs / PDMS / ITO - PET transparent radiative cooling film was prepared. The specific preparation process of this example is as follows:

[0061] (1) Weigh 340 mg of triethylamine, add it to 125 ml of deionized water, stir in a water bath at 80 °C for 30 min to completely disperse it, and obtain a pretreated triethylamine base solution;

[0062] (2) Add 840 mg of sodium salicylate and 1900 mg of CTAB to the triethylamine base solution obtained in step (1), stir for 1 h, and obtain a transparent and uniform mixed solution;

[0063] (3) Slowly add 20 ml of tetraethyl orthosilicate dropwise to the mixed solution obtained in step (2), react in a water bath at 80 °C for 3 h, and cool to room temperature;

[0064] (4) Centrifuge the precipitate obtained in (3), collect the solid, wash it with ethanol 3 - 5 times, transfer it to an oven, and dry it at 60 °C for 12 h;

[0065] (5) Transfer the powder obtained in step (4) to a muffle furnace, under an air atmosphere, heat it at a rate of 5 °C / min to 400 °C, hold for 8 h, calcine to remove the template, and collect the final product, dendritic mesoporous SiO₂ nanoparticles;

[0066] (6) Weigh 930 mg of polydimethylsiloxane colloid and 70 mg of the DMSNs obtained in step (5) and mix them, stir for 30 min;

[0067] (7) Use the doctor - blade coating process to form a film of the mixture obtained in step (6) on an ITO - PET substrate, scrape a 10 - μm - thick film, and transfer it to an oven at 100 °C for curing.

[0068] Example 3

[0069] In this example, a DMSNs / PDMS / ITO - PET transparent radiative cooling film was prepared. The specific preparation process of this example is as follows:

[0070] (1) Weigh 340 mg of triethylamine, add it to 125 ml of deionized water, stir in a water bath at 80 °C for 30 min to make it completely dispersed, and obtain a pretreated triethylamine base solution;

[0071] (2) Add 840 mg of sodium salicylate and 1900 mg of CTAB to the triethylamine base solution obtained in step (1), stir for 1 h, and obtain a transparent and homogeneous mixed solution;

[0072] (3) Slowly add 20 ml of tetraethyl orthosilicate dropwise to the mixed solution obtained in step (2), react in a water bath at 80 °C for 3 h, and cool to room temperature;

[0073] (4) Centrifuge the precipitate obtained in (3), collect the solid, wash it with ethanol 3 - 5 times, transfer it to an oven, and dry it at 60 °C for 12 h;

[0074] (5) Transfer the powder obtained in step (4) to a muffle furnace, under an air atmosphere, heat it at a rate of 5 °C / min to 400 °C, hold for 8 h, calcine to remove the template, and collect the final product, dendritic mesoporous SiO₂ nanoparticles;

[0075] (6) Weigh 900 mg of polydimethylsiloxane colloid and 100 mg of the DMSNs obtained in step (5) and mix them, stir for 30 min;

[0076] (7) The mixture obtained in step (6) was formed into a film on an ITO-PET substrate by a doctor blade process, and a 10-μm-thick film was doctor-bladed and transferred to an oven at 100 °C for curing.

[0077] Example 4

[0078] In this example, a DMSNs / PDMS / ITO-PET transparent radiative cooling film was prepared. The difference from Example 1 was that 970 mg of polydimethylsiloxane colloid and 30 mg of DMSNs were added in step (6), and the two were mixed and stirred; other steps and process parameters were the same as those in Example 1.

[0079] Example 5

[0080] In this example, a white radiative cooling ceramic, i.e., SiO2 porous ceramic, was prepared, and through dyeing, the colored radiative cooling ceramic of the present invention was also obtained. The specific steps are as follows.

[0081] (1) Weigh 0.5 g of nano-SiO2 and add it to 10 ml of N-methylpyrrolidone (NMP), stir and ultrasonically disperse until homogeneous. Add 2.5 g of polyethersulfone (PES), heat and stir at 40 °C for 2 h until the particles are uniformly dispersed and there is no obvious agglomeration;

[0082] (2) The prepared suspension was doctor-bladed to a thickness of 400 μm on a 10 * 10 cm glass substrate, and then immersed in ethanol for 24 h to complete the phase inversion process to form a ceramic precursor;

[0083] (3) The ceramic precursor obtained in step (2) was dried at room temperature for 24 h and cut into the required shape before sintering;

[0084] (4) The ceramic precursor obtained in step (3) was transferred to a muffle furnace for sintering. The temperature was gradually increased from room temperature to over 1000 °C at a rate of 5 °C / min, then held at a high temperature for 3 h, and finally cooled to room temperature to obtain the white radiative cooling ceramic described in the present invention.

[0085] (5) The white radiative cooling ceramic obtained in step (4) was immersed in a commercial pigment and dried for 12 h to obtain a colored SiO2 porous ceramic, i.e., the colored radiative cooling ceramic described in the present invention.

[0086] Example 6

[0087] (1) Weigh 1 g of nano-SiO2 and add it to 10 ml of N-methylpyrrolidone (NMP), stir and ultrasonically disperse until homogeneous. Add 2.5 g of PES, heat and stir at 40 °C for 2 h until the particles are uniformly dispersed and there is no obvious agglomeration;

[0088] (2) The prepared suspension was doctor-bladed to a thickness of 400 μm on a 10*10 cm glass substrate, and then immersed in ethanol for 24 h to complete the phase inversion process;

[0089] (3) The ceramic precursor obtained in step (2) was dried at room temperature for 24 h and cut into the desired shape before sintering;

[0090] (4) The ceramic precursor obtained in step (3) was transferred to a muffle furnace for sintering. The temperature was gradually increased from room temperature to over 1000 °C at a rate of 5 °C / min, then held at a high temperature for 3 h, and finally cooled to room temperature to obtain the white radiative cooling ceramic of the present invention.

[0091] (5) The white ceramic obtained in step (4) was immersed in commercial pigments and dried for 12 h to obtain the colored SiO2 porous ceramic, i.e., the colored radiative cooling ceramic of the present invention.

[0092] Example 7

[0093] (1) Weigh 1.5 g of nano-SiO2 and add it to 10 ml of N-methylpyrrolidone (NMP). Stir and sonicate until evenly dispersed. Add 2.5 g of PES and heat and stir at 40 °C for 2 h until the particles are evenly dispersed and there is no obvious agglomeration;

[0094] (2) The prepared suspension was doctor-bladed to a thickness of 400 μm on a 10*10 cm glass substrate, and then immersed in ethanol for 24 h to complete the phase inversion process;

[0095] (3) The ceramic precursor obtained in step (2) was dried at room temperature for 24 h and cut into the desired shape before sintering;

[0096] (4) The ceramic precursor obtained in step (3) was transferred to a muffle furnace for sintering. The temperature was gradually increased from room temperature to over 1000 °C at a rate of 5 °C / min, then held at a high temperature for 3 h, and finally cooled to room temperature to obtain the white radiative cooling ceramic of the present invention.

[0097] (5) The white ceramic obtained in step (4) was immersed in commercial pigments and dried for 12 h to obtain the colored SiO2 porous ceramic, i.e., the colored radiative cooling ceramic of the present invention.

[0098] Performance Test:

[0099] 1) SEM Test: The samples prepared in the above examples were observed under a scanning electron microscope. The dendritic mesoporous SiO2 nanoparticles DMSNs prepared in each example had a nano-mesoporous sphere morphology, and the surface of the nano-spheres was a dendritic pore structure. For example, Figure 1SEM image of the dendritic mesoporous SiO2 nanoparticles prepared in Example 1 under a scanning electron microscope. It can be seen that the microscopic morphology of the sample is nanospheres with a diameter of about 200 nm, and the surface of the nanospheres is dendritic and porous. The obtained dendritic mesoporous SiO2 nanoparticles (DMSNs) have the characteristics of good dispersibility and uniform morphology. The porous structure on the surface of the nanospheres is beneficial to increasing the specific surface area, enhancing the contact between the nanoparticles and the polymer substrate PDMS, and achieving more uniform dispersion. Such a morphology, as well as its pore size and size distribution, is very conducive to promoting the passage of light and weakening scattering.

[0100] 2) The white or colored radiative cooling ceramics prepared in each example are SiO2 porous ceramics with porous structures on both the surface and inside, and have excellent appearance. The prepared colored ceramics have bright colors and are suitable for buildings. For example, Figure 6 SEM image of the colored radiative cooling ceramic prepared in Example 7 under a scanning electron microscope. It can be observed that there are a large number of pores on the surface and inside of the ceramic, and the pore size is about 40 nm; the average size of the SiO2 particles is about 50 nm.

[0101] 2) TEM test: The samples prepared in each of the above examples were observed under a transmission electron microscope. For example, Figure 2 TEM image of the dendritic mesoporous SiO2 nanoparticles (DMSNs) prepared in Example 1. There are also many dendritic channels and pores inside the dendritic mesoporous SiO2 nanoparticles. These three-dimensional network dendritic structures enable DMSNs to be better dispersed in the polymer matrix and tightly combined with the polymer, and it is not easy to appear shedding, agglomeration and cracks, creating conditions for the passage of light.

[0102] 3) XRD test: The samples prepared in each of the above examples were tested under an X-ray diffractometer. For example, Figure 3 XRD pattern of the dendritic mesoporous SiO2 nanoparticles prepared in Example 1. It shows a typical broad diffraction peak of amorphous silica, and no sharp diffraction peaks of other crystal phases are detected, indicating that DMSNs are amorphous.

[0103] 4) UV-Vis-NIR Test: The samples prepared in the above-mentioned examples were subjected to UV-Vis-NIR test, indicating that the DMSNs / PDMS / ITO-PET transparent radiative cooling films prepared in each example (Examples 1-4) have good visible light transmittance and ultraviolet-near infrared blocking ability. The average transmittance in the visible light band (0.38 - 0.76 μm) is about 70%, and the blocking rate in the ultraviolet band (<0.38 μm) is as high as 71%. The white and colored SiO2 porous ceramics prepared in each example (Examples 5-7) have extremely high reflectivity in the solar spectrum range (0 - 2.5 μm). The average reflectivity of the white radiative cooling ceramic in the solar spectrum range (0 - 2.5 μm) is 97%, and the average reflectivity of the colored radiative cooling ceramic in the solar spectrum range (0 - 2.5 μm) is 92%; this avoids excessive absorption of solar energy and causing temperature rise. As Figure 4 Figure Figure 4 shows the UV-Vis-NIR spectrogram of the DMSNs / PDMS / ITO-PET transparent radiative cooling film prepared in Example 1 under ultraviolet-visible-near infrared spectrophotometer test. It can be seen that the DMSNs / PDMS / ITO-PET transparent radiative cooling film has good spectral selectivity. This film selectively transmits visible light and blocks the energy of ultraviolet and near infrared. Figure 7 Figure Figure 7 shows the UV-Vis-NIR spectrogram of the colored SiO2 porous ceramic prepared in Example 7 under ultraviolet-visible-near infrared spectrophotometer test, indicating its excellent solar spectrum reflection performance.

[0104] 5) FTIR Test: The samples finally prepared in the above-mentioned examples were subjected to FTIR test. The DMSNs / PDMS / ITO-PET transparent radiative cooling films prepared in each example have excellent mid-infrared emission ability, and the average emissivity in the atmospheric window (8 - 13 μm) is as high as 0.95. The white and colored SiO2 porous ceramics prepared in each example also have excellent mid-infrared emission ability, and the average emissivity in the atmospheric window (8 - 13 μm) is as high as 0.96. As Figure 5 Figure Figure 5 shows the FTIR diagram of the DMSNs / PDMS / ITO-PET transparent radiative cooling film prepared in Example 1 under Fourier transform infrared test, showing that the uniform dispersion of DMSNs in PDMS enables the composite film to obtain excellent optical properties and has more excellent mid-infrared emission performance. Figure 8 Figure Figure 8 shows the FTIR diagram of the colored SiO2 porous ceramic prepared in Example 7 under Fourier transform infrared test, showing its high emission in a wide range in the mid-infrared.

[0105] 6) Outdoor temperature test: The finally prepared transparent radiative cooling films, white radiative cooling ceramics, and colored radiative cooling ceramics in the above embodiments were respectively installed in a self-made outdoor test device for all-day temperature monitoring. Table 1 records the actual cooling effects of the transparent radiative cooling films and radiative cooling ceramics. Among them, on sunny days, the DMSNs / PDMS / ITO-PET transparent radiative cooling film can achieve a maximum temperature reduction of about 12 °C, and the white and colored SiO2 porous ceramics can achieve maximum temperature reductions of about 7 °C and 5 °C, respectively.

[0106] Table 1 Cooling performance of DMSNs / PDMS / ITO-PET transparent radiative cooling film and colored SiO2 porous ceramics

[0107]

Claims

1. A transparent radiation cooling film, characterized in that: The transparent radiation cooling film is a composite structure composed of DMSNs and film-forming polymers PDMS and ITO-PET; wherein ITO-PET is a substrate, DMSNs are randomly dispersed in the PDMS matrix to form a DMSNs / PDMS composite film, and the DMSNs / PDMS composite film is formed on the ITO-PET substrate.

2. The transparent radiation cooling film according to claim 1, characterized in that: The diameter of the DMSNs nanosphere is about 200nm, and a large number of dendrite holes and channels are provided on the surface and inside of the DMSNs nanosphere; the mass fraction of DMSNs in the DMSNs / PDMS composite film is 3wt.%-10wt.%.

3. The transparent radiation cooling film according to claim 1, characterized in that: The transparent radiation cooling film has an average transmittance of 70% in the visible light band (0.38-0.76 μm) and a blocking rate of 71% in the ultraviolet band (<0.38 μm); the mid-infrared emission capability of the transparent radiation cooling film has an average emissivity of 0.95 in the atmospheric window (8-13 μm); in outdoor temperature tests, the transparent radiation cooling film can achieve a maximum cooling of 12°C on a sunny day.

4. A radiation cooling ceramic, characterized in that: The radiation cooling ceramic is white radiation cooling ceramic or colored radiation cooling ceramic. The white radiation cooling ceramic is a SiO2 porous ceramic composed of nano-SiO2 particles, and contains a large number of pores on the surface and inside of the ceramic. The average particle size of the nano-SiO2 particles is 50nm, and the average size of the pores is 40nm. The colored radiation cooling ceramic is formed by coloring the white radiation ceramic in a dye.

5. The radiation cooling ceramic according to claim 4, characterized in that: The average reflectivity of the white radiation cooling ceramic in the solar spectrum range (0-2.5μm) is 97%; the average reflectivity of the colored radiation cooling ceramic in the solar spectrum range (0-2.5μm) is 92%; the infrared emission capability of the radiation cooling ceramic has an average emissivity of 0.96 within the atmospheric window (8-13μm); in outdoor temperature tests, the white radiation cooling ceramic can achieve a maximum cooling of 7°C on a sunny day, and the colored radiation cooling ceramic can achieve a maximum cooling of 5°C on a sunny day.

6. A method for preparing a transparent radiation cooling film according to any one of claims 1 to 3, characterized in that: The preparation method comprises the following steps: stirring and mixing DMSNs and PDMS to form a uniform mixture; forming a film of the mixture on an ITO-PET substrate, and drying and curing the film to form the transparent radiation cooling film.

7. The method for preparing a transparent radiation cooling film according to claim 6, characterized in that: The mass fraction of DMSNs is 3wt.%-10wt.% of the mixture.

8. The method for preparing a transparent radiation cooling film according to claim 6, characterized in that: The drying and curing temperature is 100°C.

9. A method for preparing a radiation cooling ceramic as claimed in claim 4 or 5, characterized in that: The steps include: 1) adding spherical SiO2 nanoparticles and PES into NMP, heating and stirring to form a suspension in which the particles are evenly dispersed; 2) applying the prepared suspension onto a glass substrate by blade coating and immersing it in ethanol to complete the phase inversion process to form a ceramic precursor; 3) The ceramic precursor is dried at room temperature and cut into a desired shape; 4) transferring the ceramic precursor obtained in step 3) to a muffle furnace for sintering to obtain the porous white radiation cooling ceramic; 5) The white radiation cooling ceramic is immersed in a dye for coloring and dried to obtain the colored radiation cooling ceramic.

10. The method for preparing a radiation cooling ceramic according to claim 9, characterized in that: The mass ratio of nano-SiO2, PES and NMP in the suspension in step 1) is 1-3:5:20; the heating and stirring temperature in step 1) is 40°C and the time is 1 hour; the phase inversion time in step 2) is 24 hours; and the drying time after coloring in step 5) is 12 hours.

11. The method for preparing a radiation cooling ceramic according to claim 9, characterized in that: In the step 4), the sintering temperature is 1000° C. and the sintering time is 3 hours.

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