Cement-based coating for daytime radiative cooling and method of making the same

Abstract

This invention discloses a cement-based coating for daytime radiative cooling and its preparation method. The preparation method includes the following steps: Step 1, ball milling white cement to obtain a white cement suspension; Step 2, sieving the white cement suspension, drying it, and grinding it until there are no lumps to obtain finely ground white cement; Step 3, mixing the finely ground white cement, functional filler, organic solvent, and water evenly. This invention discloses a cement-based coating that, when applied to a building substrate and sealed and cured, yields a cement-based coating for daytime radiative cooling; the coating has a submicron-level porous structure. The daytime radiative cooling cement-based coating prepared by this invention has excellent radiative cooling performance, significantly reducing the temperature rise of building surfaces caused by sunlight while effectively solving the building heat dissipation problem, thus contributing to building energy conservation; it can be exposed to the outdoor environment for a long time, has good durability, can be applied to building surfaces, and has good adhesion performance.

Description

Technical Field

[0001] This invention pertains to coatings and their preparation methods, specifically a cement-based coating for daytime radiative cooling and its preparation method. Background Technology

[0002] Against the backdrop of the escalating greenhouse effect and global warming, the demand for cooling in buildings due to excessive solar radiation in hot climates is increasing. Currently, the main cooling method is the traditional compression-based cooling system, such as air conditioning. This method not only consumes a large amount of energy but also increases the concentration of greenhouse gases in the atmosphere, such as carbon dioxide and ozone. Due to the impact of extreme weather, air conditioning accounts for 20% of global building energy consumption, and the increased carbon dioxide emissions from cooling demand account for one-eighth of the annual increase in global emissions. Therefore, developing energy-efficient and environmentally friendly cooling technologies is of great significance.

[0003] Passive daytime radiative cooling technology can radiate the heat of an object into the sky through atmospheric windows (wavelength 8–13 μm) without consuming energy, while minimizing the absorption of daytime sunlight (wavelength 0.3–2.5 μm) to achieve a cooling effect on the object's surface. Currently, radiative cooling materials can be mainly divided into organic and inorganic types based on their material composition. For long-term use on building exteriors, organic radiative cooling materials may experience UV aging and yellowing due to prolonged exposure to the outdoor environment, leading to a decline in the material's radiative cooling performance and durability. Chinese patent CN110317521A discloses a selective radiative cooling coating, its composite material, and its application. To ensure the adhesion of the resin-based radiative cooling functional layer to the substrate and its own weather resistance, an additional primer resin layer and a weather-resistant resin layer are required in some cases. The construction process is relatively cumbersome, and the coating itself may suffer reduced adhesion or weather resistance due to damage to the additional resin layer. Inorganic micron- or nano-sized ceramic particles suitable for radiative cooling, such as silicon dioxide, titanium dioxide, alumina, and barium sulfate, while stable in nature, exhibit poor mechanical strength when coated without additional binders, making them unsuitable for application on building surfaces. Some radiative cooling ceramic coating materials undergo high-temperature sintering to improve strength and adhesion. Chinese patent CN118344177A discloses a self-cleaning daytime passive radiative cooling ceramic and its preparation method, which requires sintering at 800-1200℃ for 3-6 hours, resulting in a high energy consumption process. Summary of the Invention

[0004] Purpose of the invention: In order to overcome the shortcomings of the existing technology, the purpose of this invention is to provide a method for preparing a cement-based coating for daytime radiative cooling that is low in cost, easy to produce and apply, and has good heat dissipation and energy efficiency. Another purpose of this invention is to provide a cement-based coating for daytime radiative cooling that has good heat dissipation and energy efficiency.

[0005] Technical solution: The present invention provides a method for preparing a cement-based coating for daytime radiative cooling, comprising the following steps:

[0006] Step 1: Ball mill the white cement to finer the particle size and obtain a white cement suspension.

[0007] Step 2: Sieve the white cement suspension, dry it, and grind it until there are no lumps to obtain finely ground white cement;

[0008] Step 3: Mix finely ground white cement, functional filler, organic solvent, and water evenly to obtain a cement-based coating for daytime radiative cooling.

[0009] Furthermore, in step one, the ball milling is a wet ball milling process, with a ball-to-material ratio of 12 to 20:1, a milling time of 0.5 to 6 hours, and a milling speed of 300 to 600 r / min. An organic solvent is added during the ball milling process.

[0010] Furthermore, the mass ratio of organic solvent to white cement is 4 to 16:1.

[0011] Furthermore, in step two, the drying temperature is set to 40–60°C, and the drying time is 6–24 hours.

[0012] Furthermore, in step two, the sieving is performed through an 800-1500 mesh sieve.

[0013] Furthermore, the organic solvent is ethanol or isopropanol; the functional filler is the main filler and / or auxiliary filler, the main filler is any one of alumina, barium sulfate, and titanium dioxide, and the auxiliary filler is modified glass fiber.

[0014] Furthermore, the main filler has a spherical morphology with an average particle size of 100–1200 nm, and the modified glass fiber has an average length of 2–5 mm and a dosage of 0–3 wt%.

[0015] Furthermore, the modified glass fiber is prepared by adding hexyltrimethoxysilane to anhydrous ethanol to form a homogeneous solution, then adding glass fiber and mixing it evenly. After standing for 6-8 hours, the mixture is filtered and washed to remove excess substances, and then dried and stored.

[0016] Furthermore, in step three, the mass ratio of finely ground white cement, functional filler, organic solvent, and water is 8–20:15–30:10–15:45–55.

[0017] The present invention discloses a cement-based coating for daytime radiative cooling, which is applied to a building substrate and sealed and cured to obtain a cement-based coating for daytime radiative cooling; the coating has a submicron-level pore structure, which can improve the solar spectral reflectivity.

[0018] Preparation Principle: Using readily available and inexpensive white cement with high whiteness and atmospheric window emissivity as the binder matrix, and adjusting the proportions and curing methods, a coating material with a submicron-scale porous structure was obtained under conventional conditions. This effectively scatters sunlight, achieving high solar spectral reflectivity. Simultaneously, submicron-sized functional fillers were introduced to enhance Mie scattering and atmospheric window infrared emissivity, while modified glass fibers improved the coating's strength and toughness. Furthermore, the silica component in the glass fibers also enhances the coating's infrared emissivity at the atmospheric window. This coating material can be easily and quickly applied to the surfaces of various building materials, showing great promise for future applications.

[0019] Beneficial effects: Compared with the prior art, the present invention has the following significant features:

[0020] 1. The prepared daytime radiation cooling cement-based coating can effectively solve the building heat dissipation problem while greatly reducing the building surface temperature rise caused by sunlight, which is conducive to building energy conservation.

[0021] 2. The main components of the prepared daytime radiation cooling cement-based coating are all inorganic materials, which is beneficial for long-term service in outdoor environments. It can be exposed to the outdoor environment for a long time, has good durability, can be applied to building surfaces, and has good bonding performance.

[0022] 3. The preparation method and process are convenient, the raw material cost is low, and it is easy to carry out, which is conducive to large-scale production and application. Attached Figure Description

[0023] Figure 1 This is a photograph of the daytime radiation cooling cement-based coating prepared in Example 1 of this invention applied to ceramic tiles;

[0024] Figure 2 This is a magnified micrograph of the surface of the daytime radiation cooling cement-based coating prepared in Example 1 of the present invention, magnified 10,000 times.

[0025] Figure 3 This is a 40,000x magnified micrograph of the surface of the daytime radiation cooling cement-based coating prepared in Example 1 of this invention;

[0026] Figure 4 This is a schematic diagram of the internal pore size distribution of the daytime radiation cooling cement-based coating prepared in Example 1 of the present invention, obtained by mercury porosimetry, showing the staged mercury impregnation amount (pore volume) - pore size.

[0027] Figure 5 This is a schematic diagram of the reflectance of the daytime radiation-cooled cement-based coating prepared in Example 1 of the present invention in the 0.3–2.5 μm wavelength band;

[0028] Figure 6 This is a schematic diagram of the emissivity of the daytime radiation-cooled cement-based coating prepared in Example 1 of the present invention in the 8-13 μm band;

[0029] Figure 7 This is a schematic diagram of the reflectance of the white cement coating prepared in Comparative Example 1 of the present invention in the 0.3-2.5 μm wavelength band;

[0030] Figure 8 This is a schematic diagram showing the surface temperature and light intensity of the cement-based coating obtained in Embodiment 2 and Comparative Example 1 at different times during a sunny midday.

[0031] Figure 9 This is a schematic diagram of the reflectance of the daytime radiation-cooled cement-based coating prepared in Example 3 of the present invention in the 0.3-2.5 μm band;

[0032] Figure 10 This is a schematic diagram of the reflectance of the daytime radiation-cooled cement-based coating prepared in Example 4 of the present invention in the 0.3–2.5 μm wavelength band;

[0033] Figure 11 This is a schematic diagram showing the surface temperature of the daytime radiation cooling cement-based coating prepared in Embodiment 5, Comparative Example 1, and Comparative Example 2 of the present invention at different times during sunny noon. Detailed Implementation

[0034] In the following examples, all materials and reagents used, unless otherwise specified, are commercially available. Experimental methods not specifically described in the examples are generally performed under standard conditions or as recommended by the manufacturer. The filler was obtained by laboratory modification of commercially available silica glass fiber. Specifically, the modification method involved adding 3% by mass of hexyltrimethoxysilane to anhydrous ethanol to form a homogeneous solution, then adding SiO2 glass fiber and mixing thoroughly. After standing for 6 hours, the mixture was filtered, washed with anhydrous ethanol to remove excess substances, and dried in a 40°C oven for 4 hours.

[0035] The prepared daytime radiation cooling cement-based coating was applied to a 3cm×7cm acrylic plate. The solar spectral reflectance and atmospheric window infrared emissivity of the coating were measured using a UV / Vis / Near-Infrared spectrophotometer (UV-3600i Plus) and a Fourier transform infrared spectrometer (Nicolet iS50), respectively.

[0036] The term "average solar reflectivity" refers to the ability of an object's surface to reflect light within the solar spectrum of 0.3–2.5 μm, and its calculation formula is as follows:

[0037]

[0038] Where λ is the incident light wavelength in the 0.3–2.5 μm band, and I AM1.5 R(λ) is the standardized ASTM G173 global solar intensity spectrum, and R(λ) is the reflectance of the object's surface.

[0039] The term "mean atmospheric window emissivity" refers to the thermal emissivity of a surface object in the mid-infrared band of 8–13 μm, and its calculation formula is as follows:

[0040]

[0041] Where λ is the incident light wavelength in the 8–13 μm band, I BB (λ,T) is the spectral radiation intensity of a blackbody at temperature T, and ε(λ) is the thermal emissivity of the object's surface.

[0042] The prepared daytime radiation-cooled cement-based coating was applied to the surface of ceramic tiles measuring 15cm×15cm×1.2cm or 7.5cm×7.5cm×1.2cm. These tiles were then placed inside a polystyrene foam sample chamber wrapped with aluminum foil and covered with a layer of transparent PE film. The surface temperature beneath the coating was measured using a thermal resistor at the bottom of the ceramic tile, and the data was transmitted via wired connection to a thermometer. Wind speed, relative humidity, and ambient temperature were recorded during the outdoor measurements using a meteorological instrument, while solar irradiance was recorded using a solar irradiance meter.

[0043] Example 1

[0044] A cement-based coating for daytime radiative cooling and its preparation method, comprising the following steps:

[0045] (1) White cement was wet-milled in a 50ml ball mill jar, and anhydrous ethanol was added. The volume-to-mass ratio of anhydrous ethanol to white cement was 10:1ml / g. Zirconia grinding beads were added, with a ball-to-material ratio of 12:1. The ball milling time was 4h and the ball milling speed was 500r / min to obtain a white cement suspension.

[0046] (2) The ball-milled white cement suspension is passed through a 1000-mesh sieve, placed in an oven at 40°C and dried for 12 hours, and then ground until there are no lumps to obtain finely ground white cement.

[0047] (3) Weigh 18 parts of finely ground white cement and 28 parts of alumina into a 50ml ball mill grinding jar, add 12 parts of anhydrous ethanol and 53 parts of water and disperse evenly, then add 10mm zirconia grinding beads. The mass ratio of ball to material (solid material) is 3:1. The morphology of the main filler alumina is spherical, α phase, with an average particle size of 400nm.

[0048] (4) The components are mixed and dispersed by using a ball mill for 3 minutes and the ball mill speed is 300 r / min to obtain a cement-based coating for daytime radiative cooling.

[0049] (5) The cement-based coating for daytime radiative cooling obtained in step (4) is applied to ceramic tiles and acrylic sheets using a coater. The coating thickness is controlled to be 600 μm. The coating is cured at 20°C for 3 days under sealed conditions to obtain the cement-based coating for daytime radiative cooling.

[0050] like Figure 1 The extremely high whiteness of the coating obtained in this embodiment has a strong diffuse reflection effect on solar radiation.

[0051] like Figures 2-3 The functional filler is relatively uniformly dispersed and bonded in the cement matrix, and the coating has a micron and submicron pore structure.

[0052] like Figure 4 The stage of mercury immersion (pore volume) is also known as log differential intrusion. In this embodiment, the internal pore size of the cement-based coating for daytime radiative cooling is generally distributed at around 500 nm, which can effectively scatter high-intensity light in the ultraviolet band of the solar spectrum.

[0053] like Figure 5 The cement-based coating for daytime radiative cooling prepared in this embodiment has an average solar reflectance of 94.3% in the 0.3–2.5 μm band.

[0054] like Figure 6 The cement-based coating for daytime radiative cooling prepared in this embodiment has an average atmospheric window emissivity of 98.6% in the 8–13 μm band.

[0055] Comparative Example 1

[0056] (1) Weigh 40 parts of uncrushed white cement and 100 parts of water and place them in a mixer.

[0057] (2) Stir at low speed for 60 seconds, then stir at high speed for 3 minutes.

[0058] (3) The white cement coating obtained in step (2) was applied to ceramic tiles and acrylic sheets using a coater to control the coating thickness to 600 μm, and cured in a standard curing room at 20°C for 28 days.

[0059] like Figure 7 The white cement coating prepared in this comparative example has an average solar reflectance of 79.1% in the 0.3–2.5 μm wavelength range.

[0060] Example 2

[0061] A cement-based coating for daytime radiative cooling and its preparation method, comprising the following steps:

[0062] (1) White cement was wet-milled in a 50ml ball mill jar, and anhydrous ethanol was added. The volume-to-mass ratio of anhydrous ethanol to white cement was 15:1ml / g. Zirconia grinding beads were added, with a ball-to-material ratio of 12:1. The ball milling time was 6h and the ball milling speed was 400r / min to obtain a white cement suspension.

[0063] (2) The ball-milled white cement suspension is passed through a 1000-mesh sieve, placed in an oven at 40°C and dried for 12 hours, and then ground until there are no lumps to obtain finely ground white cement.

[0064] (3) Weigh 10 parts finely ground white cement, 24 parts alumina, and 1 part modified glass fiber into a 50ml ball mill jar. Add 12 parts isopropanol and 53 parts water, and disperse evenly. Add 10mm zirconia grinding beads, with a ball-to-material (solid) mass ratio of 3:1. The main filler, alumina, has a spherical morphology with an average particle size of 400nm. The modified glass fiber has an average length of 3mm and a dosage of 3wt%.

[0065] (4) The components are mixed and dispersed by using a ball mill for 5 minutes and the ball mill speed is 300 r / min to obtain a cement-based coating for daytime radiative cooling.

[0066] (5) The cement-based coating for daytime radiative cooling obtained in step (4) is applied to ceramic tiles and acrylic sheets using a coater. The coating thickness is controlled to be 600 μm. The coating is cured at 20°C for 3 days under sealed conditions to obtain the cement-based coating for daytime radiative cooling.

[0067] like Figure 8 When the average light intensity exceeds 800W / m 2 During the midday period, the surface temperature of the cement-based coating with radiative cooling was consistently lower than that of the ambient temperature and the surface temperature of the white cement coating prepared in Comparative Example 1. The surface temperature was 5.8°C lower than the average ambient temperature and 17.1°C lower than the average surface temperature of the white cement coating, indicating excellent radiative cooling performance.

[0068] Example 3

[0069] A cement-based coating for daytime radiative cooling and its preparation method, comprising the following steps:

[0070] (1) White cement was wet-milled in a 50ml ball mill jar, and anhydrous ethanol was added. The volume-to-mass ratio of anhydrous ethanol to white cement was 15:1ml / g. Zirconia grinding beads were added, with a ball-to-material ratio of 12:1. The ball milling time was 6h and the ball milling speed was 400r / min to obtain a white cement suspension.

[0071] (2) The ball-milled white cement suspension is passed through a 1000-mesh sieve, placed in an oven at 40°C and dried for 12 hours, and then ground until there are no lumps to obtain finely ground white cement.

[0072] (3) Weigh 10 parts of finely ground white cement and 25 parts of barium sulfate into a 50ml ball mill grinding jar, add 12 parts of isopropanol and 53 parts of water and disperse evenly, then add 10mm zirconia grinding beads. The mass ratio of ball to material (solid material) is 3:1. The morphology of the main filler, barium sulfate, is spherical with an average particle size of 1000nm.

[0073] (4) The components are mixed and dispersed by using a ball mill for 3 minutes and the ball mill speed is 300 r / min to obtain a cement-based coating for daytime radiative cooling.

[0074] (5) The cement-based coating for daytime radiative cooling obtained in step (4) is applied to ceramic tiles and acrylic sheets using a coater. The coating thickness is controlled to be 600 μm. The coating is cured at 20°C for 3 days under sealed conditions to obtain the cement-based coating for daytime radiative cooling.

[0075] like Figure 9 The cement-based coating for daytime radiative cooling prepared in this embodiment has an average solar reflectance of 88.6% in the 0.3–2.5 μm band.

[0076] Example 4

[0077] A cement-based coating for daytime radiative cooling and its preparation method, comprising the following steps:

[0078] (1) White cement was wet-milled in a 50ml ball mill jar, and anhydrous ethanol was added. The volume-to-mass ratio of anhydrous ethanol to white cement was 15:1ml / g. Zirconia grinding beads were added, with a ball-to-material ratio of 12:1. The ball milling time was 6h and the ball milling speed was 400r / min to obtain a white cement suspension.

[0079] (2) The ball-milled white cement suspension is passed through a 1000-mesh sieve, placed in an oven at 40°C and dried for 12 hours, and then ground until there are no lumps to obtain finely ground white cement.

[0080] (3) Weigh 10 parts of finely ground white cement and 25 parts of titanium dioxide into a 50ml ball mill grinding jar, add 12 parts of anhydrous ethanol and 53 parts of water and disperse evenly, then add 10mm zirconia grinding balls. The mass ratio of ball to material (solid material) is 3:1. The morphology of the main filler, titanium dioxide, is spherical with an average particle size of 800nm.

[0081] (4) The components are mixed and dispersed by using a ball mill for 3 minutes and the ball mill speed is 300 r / min to obtain a cement-based coating for daytime radiative cooling.

[0082] (5) The cement-based coating for daytime radiative cooling obtained in step (4) is applied to ceramic tiles and acrylic sheets using a coater. The coating thickness is controlled to be 600 μm. The coating is cured at 20°C for 3 days under sealed conditions to obtain the cement-based coating for daytime radiative cooling.

[0083] like Figure 10 The cement-based coating for daytime radiative cooling prepared in this embodiment has an average solar reflectance of 89.7% in the 0.3–2.5 μm band.

[0084] Example 5

[0085] A cement-based coating for daytime radiative cooling and its preparation method, comprising the following steps:

[0086] (1) White cement was wet-milled in a 50ml ball mill jar, and anhydrous ethanol was added. The volume-to-mass ratio of anhydrous ethanol to white cement was 12:1 ml / g. Zirconia grinding beads were added, with a ball-to-material ratio of 12:1. The ball milling time was 5h and the ball milling speed was 500r / min to obtain a white cement suspension.

[0087] (2) The ball-milled white cement suspension is passed through a 1000-mesh sieve, placed in an oven at 40°C and dried for 12 hours, and then ground until there are no lumps to obtain finely ground white cement.

[0088] (3) Weigh 10 parts of finely ground white cement and 25 parts of alumina into a 50ml ball mill grinding jar, add 12 parts of anhydrous ethanol and 48 parts of water respectively, disperse evenly, and put in 10mm zirconia grinding beads. The mass ratio of ball to material (solid material) is 3:1. The morphology of the main filler alumina is spherical with an average particle size of 400nm.

[0089] (4) The components are mixed and dispersed by using a ball mill for 3 minutes and the ball mill speed is 300 r / min to obtain a cement-based coating for daytime radiative cooling.

[0090] (5) The cement-based coating for daytime radiative cooling obtained in step (4) is applied to ceramic tiles and acrylic sheets using a coater. The coating thickness is controlled to be 600 μm. The coating is cured at 20°C for 3 days under sealed conditions to obtain the cement-based coating for daytime radiative cooling.

[0091] Comparative Example 2

[0092] The remaining steps of this comparative example are the same as those of Example 5, except that step (3) is replaced with 20 parts of anhydrous ethanol and 40 parts of water.

[0093] Comparative Example 3

[0094] The remaining steps of this comparative example are the same as those of Example 5, except that step (3) is replaced with 40 parts of anhydrous ethanol and 20 parts of water.

[0095] like Figure 11 It can be seen that the daytime radiation cooling cement-based coating with a volume ratio of ethanol to water of 1:4 (Example 5) has the best radiation cooling performance.

[0096] Example 6

[0097] A cement-based coating for daytime radiative cooling and its preparation method, comprising the following steps:

[0098] (1) White cement was wet-milled in a 50ml ball mill jar, and anhydrous ethanol was added. The volume-to-mass ratio of anhydrous ethanol to white cement was 5:1ml / g. 10mm zirconia grinding beads were added, the ball-to-material ratio was 16:1, the ball milling time was 0.5h, and the ball milling speed was 600r / min to obtain a white cement suspension.

[0099] (2) The ball-milled white cement suspension is passed through an 800-mesh sieve, dried in an oven at 60°C for 6 hours, and then ground until there are no lumps to obtain finely ground white cement.

[0100] (3) Weigh 8 parts of finely ground white cement and 15 parts of alumina into a 50ml ball mill grinding jar, add 10 parts of anhydrous ethanol and 45 parts of water and disperse evenly, then add 10mm zirconia grinding beads. The mass ratio of ball to material (solid material) is 3:1. The morphology of the main filler alumina is spherical with an average particle size of 100nm.

[0101] (4) The components are mixed and dispersed by using a ball mill for 4 minutes and the ball mill speed is 300 r / min to obtain a cement-based coating for daytime radiative cooling.

[0102] (5) The cement-based coating for daytime radiative cooling obtained in step (4) is applied to ceramic tiles and acrylic sheets using a coater. The coating thickness is controlled to be 600 μm. The coating is cured at 20°C for 3 days under sealed conditions to obtain the cement-based coating for daytime radiative cooling.

[0103] Example 7

[0104] A cement-based coating for daytime radiative cooling and its preparation method, comprising the following steps:

[0105] (1) White cement was wet-milled in a 50ml ball mill jar, and anhydrous ethanol was added. The volume-to-mass ratio of anhydrous ethanol to white cement was 20:1ml / g. 10mm zirconia grinding beads were added, the ball-to-material ratio was 20:1, the ball milling time was 3h, and the ball milling speed was 300r / min to obtain a white cement suspension.

[0106] (2) After ball milling, the white cement suspension is passed through a 1500-mesh sieve, placed in an oven at 50°C and dried for 24 hours. Then it is ground until there are no lumps to obtain finely ground white cement.

[0107] (3) Weigh 20 parts of finely ground white cement and 30 parts of barium sulfate into a 50ml ball mill grinding jar, add 15 parts of anhydrous ethanol and 55 parts of water and disperse evenly, then add 10mm zirconia grinding beads. The mass ratio of ball to material (solid material) is 3:1. The morphology of the main filler, barium sulfate, is spherical with an average particle size of 1200nm.

[0108] (4) The components are mixed and dispersed by using a ball mill for 5 minutes and the ball mill speed is 300 r / min to obtain a cement-based coating for daytime radiative cooling.

[0109] (5) The cement-based coating for daytime radiative cooling obtained in step (4) is applied to ceramic tiles and acrylic sheets using a coater. The coating thickness is controlled to be 600 μm. The coating is cured at 20°C for 3 days under sealed conditions to obtain the cement-based coating for daytime radiative cooling.

Claims

1. A method for preparing a cement-based coating for daytime radiative cooling, characterized in that, Includes the following steps: Step 1: Ball mill the white cement to obtain a white cement suspension; Step 2: Sieve the white cement suspension, dry it, and grind it until there are no lumps to obtain finely ground white cement; Step 3: Mix finely ground white cement, functional filler, organic solvent, and water evenly to obtain a cement-based coating for daytime radiative cooling.

2. The method for preparing a cement-based coating for daytime radiative cooling according to claim 1, characterized in that: In step one, the ball milling is a wet ball milling process, with a ball-to-material ratio of 12 to 20:1, a milling time of 0.5 to 6 hours, and a milling speed of 300 to 600 r / min. An organic solvent is added during the ball milling process.

3. The method for preparing a cement-based coating for daytime radiative cooling according to claim 2, characterized in that: The mass ratio of the organic solvent to white cement is 4 to 16:

1.

4. The method for preparing a cement-based coating for daytime radiative cooling according to claim 1, characterized in that: In step two, the drying temperature is set to 40–60°C, and the drying time is 6–24 hours.

5. The method for preparing a cement-based coating for daytime radiative cooling according to claim 1, characterized in that: In step two, the sieving is performed through an 800-1500 mesh sieve.

6. A method for preparing a cement-based coating for daytime radiative cooling according to claim 1 or 2, characterized in that: The organic solvent is ethanol or isopropanol; the functional filler is the main filler and / or auxiliary filler, the main filler is any one of alumina, barium sulfate, and titanium dioxide, and the auxiliary filler is modified glass fiber.

7. The method for preparing a cement-based coating for daytime radiative cooling according to claim 6, characterized in that: The main filler has a spherical morphology with an average particle size of 100–1200 nm, and the modified glass fiber has an average length of 2–5 mm and a dosage of 0–3 wt%.

8. A method for preparing a cement-based coating for daytime radiative cooling according to claim 6, characterized in that: The modified glass fiber is prepared by adding hexyltrimethoxysilane to anhydrous ethanol to form a uniform solution, then adding glass fiber and mixing it evenly. After standing for 6-8 hours, the mixture is filtered and washed to remove excess substances, and then dried and stored.

9. The method for preparing a cement-based coating for daytime radiative cooling according to claim 1, characterized in that: In step three, the mass ratio of finely ground white cement, functional filler, organic solvent, and water is 8-20:15-30:10-15:45-55.

10. A cement-based coating for daytime radiative cooling obtained by the preparation method of a cement-based coating for daytime radiative cooling according to any one of claims 1 to 9, characterized in that: After being coated onto a building substrate and sealed and cured, a cement-based coating for daytime radiative cooling is obtained; the coating has a submicron-level pore structure inside.

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