Preparation method for optical scatterer, preparation method for coating, use, and prepared optical scatterer and coating

Abstract

Provided in the present invention are an optical scatterer, a preparation method, and a coating prepared from the optical scatterer. The optical scatterer is light magnesium carbonate having a specific microstructure and obtained by means of modification, and same has a controllable particle size and efficient scattering efficiency. The coating prepared by using the optical scatterer as a filler has a sunlight reflectivity of no less than 95% and an atmospheric transparent window emissivity of no less than 0.95. Moreover, the preparation process of the optical scatterer has a significant carbon-negative effect.

Description

Preparation method of optical scatterer, preparation method of coating, use thereof, and optical scatterer and coating obtained

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 202410151276.3 filed on February 2, 2024, entitled “A method for preparing an optical scatterer, a method for preparing a coating, uses, and the optical scatterer and coating obtained”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The invention relates to a preparation method of a light magnesium carbonate optical scatterer, a preparation method of a coating, uses thereof, and the prepared optical scatterer and coating, belonging to the field of optical materials. Background Art

[0004] Global warming and the energy crisis are two major challenges facing humanity in the 21st century. The continued extreme heatwave has significantly increased demand for space cooling. The International Energy Agency's latest forecast indicates that global cooling capacity is expected to increase from 1.17 GW in 2016 to 3.70 GW by 2050, with a compound annual growth rate of 4%. However, traditional active cooling systems based on vapor compression (such as air conditioners and electric fans) consume significant amounts of energy. Globally, the International Energy Agency's 2021 annual report shows that energy consumption for building cooling has more than tripled over the past three decades, accounting for nearly 20% of total building electricity consumption, and this figure continues to rise annually. From a Chinese perspective, according to the "China High-Efficiency Air Conditioning and Refrigeration Room Development Research Report (2021)," my country's current building stock is as high as 6.96 million square meters, with electricity used for building cooling accounting for over 15% of total electricity consumption, and this figure continues to soar at a rate of 20% annually. Fluorocarbons and hydrofluorocarbons (HFCs) emitted by air conditioners and other refrigeration equipment are major contributors to global warming. Furthermore, electricity for these refrigeration systems is primarily generated by burning traditional fossil fuels such as coal, oil, and natural gas, further exacerbating the greenhouse effect and energy crisis, creating a vicious cycle. Therefore, identifying and developing new passive cooling technologies that are safe, efficient, energy-efficient, environmentally friendly, and have low carbon emissions is key to the implementation and long-term development of future "green buildings."

[0005] Compared with traditional vapor compression cooling technology, all-weather radiant cooling is a green, environmentally friendly, energy-saving and carbon-reducing passive cooling strategy that meets the requirements of sustainable development and the "3060" dual-carbon strategy. The cooling load required for conventional buildings is about 100W m –2 The maximum cooling power that existing radiation cooling materials can provide at room temperature is about 150W m –2Therefore, radiative cooling technology can achieve passive cooling of buildings, effectively mitigating the greenhouse effect and urban heat island effect. To achieve this, radiative cooling materials must have a high reflectivity (>94%) in the sunlight band (0.3-2.5μm) and a high emissivity (>0.9) in the atmospheric transparent window band (8-13μm).

[0006] Among the many reported radiative cooling materials, radiative cooling coatings have the advantages of being suitable for large-scale preparation, simple and effective, and easy to modify, showing broad application prospects in the field of building energy conservation. Radiative cooling coatings are generally obtained by doping optical scatterers (such as titanium dioxide, barium sulfate, and hexagonal boron nitride) into polymer resins. Among them, the polymer resin matrix components (such as fluorocarbon resins, polyvinylidene fluoride, and polydimethylsiloxane) are usually in the range of 770 to 1250 cm –1 The wavenumber band has strong intrinsic absorption, which makes the coating show high emissivity in the atmospheric window band; the optical scatterer determines the reflectivity of the coating in the sunlight band by interacting with the incident light.

[0007] However, conventional optical scatterers have a relatively simple structure (particle size and morphology) and low scattering efficiency, making it difficult to achieve efficient Mie scattering and total internal reflection. Even at high loadings (>60%), they struggle to effectively enhance the solar reflectivity and subambient cooling performance of radiative cooling coatings. Furthermore, the expensive raw materials and high carbon emissions associated with their preparation offset the carbon reduction benefits of radiative cooling. These challenges significantly limit its further development and application.

[0008] Summary of the Invention

[0009] In order to solve the above technical problems, the present invention provides an optical scatterer and a coating made using the optical scatterer. The optical scatterer is light magnesium carbonate obtained by modifying magnesium carbonate. The particle size of the scatterer is controllable to achieve wide-spectrum scattering. The coating made using the optical scatterer has a solar reflectivity of not less than 95% and an atmospheric transparent window emissivity of not less than 0.95. In addition, the preparation process of the optical scatterer has a significant negative carbon effect.

[0010] The technical solutions adopted by the present invention are as follows:

[0011] Option 1 provides an optical scatterer, and the preparation method of the optical scatterer is: modifying magnesium carbonate to enhance the optical scattering performance of the particles, specifically by changing its microstructure to form two-dimensional sheets that assemble into three-dimensional spherical particles. During the modification process, the particle size of light magnesium carbonate can be controlled by regulating the modifier, so that the light scatterer can achieve a wide spectral response.

[0012] In some embodiments, magnesium carbonate is produced by capturing carbon dioxide using magnesium chloride and ammonia as raw materials.

[0013] In some embodiments of the present invention, magnesium carbonate is prepared by utilizing waste. The specific preparation method is as follows: magnesium-rich tailings and liquid ammonia are used as raw materials, carbon dioxide in the tail gas is captured, and a reaction occurs to obtain magnesium carbonate:

[0014] Reaction 1 is carried out at room temperature and pressure. Stirring is required during the reaction process. The stirring speed is 100 to 600 r / min, preferably in the range of 200 to 500 r / min. The reaction time is 2 to 6 hours, preferably in the range of 3 to 5 hours. In the process of preparing magnesium carbonate, solid waste magnesium-rich tailings (i.e., MgCl2·6H2O), CO2 in industrial flue gas, and liquid ammonia NH3 are used as raw materials. While producing magnesium carbonate optical scatterers, ammonium chloride and water are also co-produced. The by-product ammonium chloride can be directly put into the market, and the water can be recycled into the reaction system. The preparation process of magnesium carbonate has a negative carbon effect and can achieve an emission reduction of 0.2 to 1 tCO2-eq / t.

[0015] As a preferred embodiment, the molar ratio of the magnesium-rich tailings, CO2 in the industrial tail gas and liquid ammonia is 5:4:10.

[0016] As a preferred method, the obtained magnesium carbonate (MgCO3·3H2O) is modified using a modifier to obtain modified light magnesium carbonate, wherein the modifier is a combination of one or more of pentaerythritol, glucose, soluble starch, sucrose, polyethylene glycol or sodium lauryl sulfate. The modified light magnesium carbonate particles are three-dimensional spheres formed by self-assembly of two-dimensional lamellar microunits, specifically a three-dimensional hydrangea-like structure, with a large number of nanovoids on the particle surface. The average particle size of the particles is 1 to 5 μm. The magnesium carbonate particles with this morphology have a large number of nanovoids. The combination of two-dimensional units and three-dimensional units enhances the light scattering performance of the optical scatterer, and the combination of multi-level structure and multiple sizes enables the scatterer to achieve a wide spectrum response.

[0017] As a preferred embodiment, the modifier is an aqueous solution of a combination of one or more of pentaerythritol, glucose, soluble starch, sucrose, polyvinyl pyrrolidone, polyacrylic acid, polyethylene glycol or sodium lauryl sulfate, more preferably one or more of polyvinyl pyrrolidone (PVP), polyacrylic acid (PAA), polyethylene glycol and sodium lauryl sulfate (SDS). By adding the above modifiers, the microstructure (including micromorphology and particle size distribution) of the light magnesium carbonate optical scatterer can be regulated. PVP has high intrinsic covalent bond energy, which will enable tight connection between particle units during the induced modification process; low concentrations of PAA can completely dissociate in water and release protons into the bulk solution: Under the resulting acidic conditions, the solubility of MgCl2 increases, producing more Mg 2+ , thus producing Mg 2+ -Multiple electrolyte complexes, the reaction is: PAA(COO)Mg + The formation of the complex can inhibit the Mg 2+ With CO3 2- OH - The combination of polyethylene glycol and hydroxyl groups can effectively reduce the solubility of carbonates, thereby regulating the nucleation rate of light magnesium carbonate particles. The modifier is preferably SDS, which is an anionic surfactant. Both ends of the molecule have hydrophilic and hydrophobic functions. The hydrophilic sulfate group can react with Mg 2+ The combination makes the hydrophobic end face the water molecules, thereby inhibiting the aggregation and growth of the light magnesium carbonate crystal nucleus, and then obtaining small-sized light magnesium carbonate particles. The particles prepared by this method are flower-like structures formed by self-assembly of sheet units. The particle size matches the wavelength of sunlight and can exert an efficient light scattering effect. During the modification process, the temperature of the modification system is 60-100℃ and the solution concentration is 0.2-5mmol·L –1 , the preferred range is 1 to 2 mmol·L – 1 .

[0018] The aqueous solution of SDS is preferably used as the modifier, and the modification process undergoes two reactions:

[0019] Magnesium carbonate is placed in a modified solution, stirred and dispersed continuously at a speed of 100-300 r / min for 1-2 hours, and the solid obtained after filtration and drying is the modified light magnesium carbonate. The CO2 generated in this reaction process can be put into reaction one to achieve a closed CO2 loop and avoid direct CO2 emissions. After modification, modified light magnesium carbonate is obtained. The modified light magnesium carbonate particles are in the shape of flower balls (self-assembled from flaky particles), with an average particle size of about 1-5 μm and a large number of nanovoids on the particle surface.

[0020] The solution generated in reaction 1 is subjected to salt precipitation reaction to obtain ammonium chloride precipitate, which can be put into the market after simple treatment.

[0021] The salting-out process is carried out at room temperature and pressure, with a reaction time of 2 to 6 hours, preferably in the range of 3 to 5 hours. Stirring is required during the reaction process, with a stirring speed of 100 to 600 r / min, preferably in the range of 200 to 500 r / min.

[0022] The preparation process of the modified light magnesium carbonate scatterer is the overall reaction: 5MgCl2·6H2O+4CO2+10NH3→4MgCO3·Mg(OH)2·4H2O (main product)+10NH4Cl(by-product)+20H2O overall reaction.

[0023] In this process, an emission reduction of (0.2 to 1) tCO2-eq / t can be achieved.

[0024] Solution 2: A coating is provided, produced using the optical diffuser obtained above. Specifically, the optical diffuser is dispersed in a polymer resin emulsion, and high-speed stirring is performed to achieve uniform dispersion of the optical diffuser powder in the resin emulsion, thereby producing a radiant cooling coating emulsion. During this high-speed dispersion process, a strong chemical bond is formed between the polymer resin matrix and the modified light magnesium carbonate filler, allowing the modified light magnesium carbonate to be fully coated by the polymer matrix, thereby ensuring the coating's film-forming effect.

[0025] As a preferred solution, the matrix resin in the polymer resin emulsion is one or more of polyurethane, acrylate, polydimethylsiloxane and polyvinylidene fluoride (PVDF), preferably PVDF. The PVDF molecular chain contains a large number of fluorine atoms, which makes it have good chemical corrosion resistance and high temperature resistance, as well as high tensile strength and toughness, so that the PVDF binder can maintain good bonding performance and weather resistance under various environmental conditions; the organic solvent is one or more of toluene, ethylene glycol, acetone and N,N-dimethylformamide (DMF), preferably a mixed solvent of acetone and DMF. The polymer resin has high solubility in acetone and DMF solvents, and the blending ratio of acetone and DMF in the mixed solvent is (1:5) to (5:1). At this ratio, a sufficient amount of polymer resin can be completely dissolved and can fully coat the added modified light magnesium carbonate particles after high-speed stirring.

[0026] As a preferred solution, PVDF is selected as the matrix resin, acetone and DMF are selected as the solvent, and the ratio of the modified light magnesium carbonate optical scatterer to the polymer resin PVDF is (2:3) to (4:1). Within this range, the polymer resin PVDF can fully coat the modified light magnesium carbonate optical scatterer. The stirring speed during the dispersion process is preferably (500 to 2000) r / min. Taking into account the equipment performance, the dispersion effect of the scatterer and the time benefit, the final preferred range is (800 to 1500) r / min, and the dispersion time is (0.2 to 5) h, preferably (0.5 to 2) h. Under this dispersion setting, a strong chemical bond can be formed between the resin and the modified light magnesium carbonate, thereby allowing the modified light magnesium carbonate to be wrapped by the polymer matrix.

[0027] As a preferred solution, a hydrophobic modifier is added to the coating. The hydrophobic modifier is preferably 1H,1H,2H,2H-perfluorodecyltriethoxysilane. The concentration of the modifier in the coating is (0.1-4.0) wt%, which helps the coating achieve the best hydrophobic effect at the minimum dosage.

[0028] Option 3: The above-mentioned coating can be applied by brushing, rolling, or spraying onto a substrate to achieve a radiative cooling effect. The substrate can be energy-saving buildings, space probes, outdoor power and electronic equipment, personal thermal management, etc. The coating thickness is (50-500) μm. Taking into account the coating's reflective and emissive properties, the preferred range is (100-400) μm. The radiative cooling coating must have a solar reflectivity of no less than 95%, and an atmospheric transparent window emissivity of no less than 0.95.

[0029] Option 4, an optical scatterer, including magnesium carbonate particles, the microscopic morphology of a single magnesium carbonate particle is a three-dimensional structure formed by two-dimensional flakes, preferably the three-dimensional structure is a spherical structure, the average particle size of the particles is preferably 1 to 5 μm, and the particle size range of the particles forming the scatterer is preferably 1 to 5 μm, and preferably there are a large number of nanovoids on the surface of the magnesium carbonate particles.

[0030] The beneficial effects of the present invention include: the modified magnesium carbonate has a hierarchical particle size distribution with a wide particle size distribution, a biomimetic multi-level structure characterized by two-dimensional nanosheets assembled into three-dimensional spheres, exhibits efficient optical scattering performance, and exhibits high reflection in the sunlight band and high emission in the infrared band;

[0031] The present invention creatively prepares magnesium carbonate from magnesium-rich tailings solid waste. This preparation process not only realizes waste utilization but also has negative carbon performance, achieving a negative carbon amount of (0.2-1) tCO2-eq / t, reducing carbon emissions and effectively addressing global climate change issues from the two dimensions of "carbon sequestration and energy saving and cooling" simultaneously.

[0032] The coating prepared by the present invention has radiative cooling performance. When coated on a substrate, the solar reflectivity is as high as 96.24%, and the mid- and far-infrared emissivity is as high as 0.978.

[0033] The coating of the present invention can be used in a wide range of fields requiring thermal control, including energy-saving buildings, space probes, outdoor power and electronic equipment, and personal thermal management. Furthermore, the present invention meets current market demands, features a scientific and rational preparation method, simple procedures, and strong operability, thereby increasing the added value of solid waste products and expanding the application scope of CCUS technology, presenting broad market prospects and significant social benefits.

[0034] This invention innovatively uses magnesium-rich tailings, obtained from the sun-drying of potassium salt in salt lakes, as a raw material for sequestering CO2 from flue gas. This method, while simultaneously treating waste with waste, produces a light magnesium carbonate optical scatterer in a controllable and carbon-reducing manner. By controlling the type and content of modifiers during the reaction, the microstructure (micromorphology and particle size distribution) of the optical scatterer is regulated. The resulting multi-level optical scatterer is constructed from two-dimensional nanosheets and nano-microscale three-dimensional hydrangea-like flowers self-assembled from the two-dimensional nanosheets. This scatterer also exhibits a graded particle size distribution that matches the wavelength of sunlight. This highly efficient light magnesium carbonate optical scatterer with a specific structure is dispersed in PVDF resin to form a composite coating. When the coating is exposed to sunlight, the optical scatterer's unique graded particle size distribution forms a strong Mie resonance with the incident light. Furthermore, the two-dimensional nanosheets and the three-dimensional nano-microscale hydrangea-like flowers facilitate thin-film interference and total internal reflection. The synergistic effect of these three effects results in highly efficient sunlight reflection (>95%), laying a solid foundation for the coating's excellent all-weather radiative cooling performance.

[0035] More specific effects have been introduced in detail in the implementation plan part of the invention content. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The above and other features, advantages, and aspects of the various embodiments of the present disclosure will become more apparent with reference to the following detailed description in conjunction with the accompanying drawings. Throughout the drawings, the same or similar reference numerals represent the same or similar elements. It should be understood that the drawings are schematic and that components and elements are not necessarily drawn to scale.

[0037] Figure 1 (a) SEM image of modified light magnesium carbonate in Example 1;

[0038] Figure 1(b) is an SEM image of unmodified magnesium carbonate of Comparative Example 1;

[0039] FIG2 is a particle size distribution diagram of light magnesium carbonate of Example 1 and magnesium carbonate of Comparative Example 1;

[0040] Figure 3 explores the effect of magnesium carbonate optical scatterers on the reflectivity of radiative cooling coatings before and after modification, with the filler volume ratio controlled at 70% and the coating film thickness at 200 μm.

[0041] Figure 4 explores the reflectivity of the radiative cooling coating at different volume ratios of modified light basic magnesium carbonate, with the coating film thickness controlled at 200 μm.

[0042] Figure 5: Under the premise of controlling the volume ratio of modified light basic magnesium carbonate to 70%, the reflectivity of the radiative cooling coating at different coating film thicknesses is explored;

[0043] Figure 6 shows the spectral performance of the radiative cooling coating in the sunlight band and the atmospheric window band when the volume ratio of the modified light basic magnesium carbonate filler is 70% and the coating thickness is 300 μm;

[0044] FIG7 shows the contact angle of the best radiative cooling coating obtained in the present invention. DETAILED DESCRIPTION

[0045] The present invention will be further explained in detail below with reference to the accompanying drawings and specific embodiments. However, it should be understood that the protection scope of the present invention is not limited to the specific embodiments.

[0046] Example 1

[0047] Preparation method of optical scatterers:

[0048] dissolving the magnesium-rich tailings in water to obtain a magnesium chloride solution;

[0049] Ammonia is passed into the magnesium chloride solution to adjust the pH, and then industrial flue gas is passed through to capture the carbon dioxide in it, resulting in the following reaction:

[0050] The raw materials and their masses are 4.487kg MgCl2·6H2O and 0.388kg liquid ammonia, and the CO2 content in the exhaust gas introduced is at least 0.42kg;

[0051] The reaction was carried out at room temperature and pressure, and the reaction solution was continuously stirred during the reaction at a stirring speed of 300 r / min to ensure sufficient reaction.

[0052] (3) After sufficient reaction, the reaction solution was filtered to obtain MgCO3·3H2O, which was then placed in an aqueous solution of SDS for modification. The concentration of the modified solution was 1.387 mmol L –1 , stirring continuously at 80℃ and 300r / min, the following reaction occurs:

[0053] After modification, modified light magnesium carbonate, i.e., an optical scatterer, is obtained. After testing, the average particle size of the obtained modified light magnesium carbonate particles is 3.93 μm;

[0054] (4) The solution after the sufficient reaction in step (2) is evaporated and salt is precipitated to obtain ammonium chloride, which is then put into the market or used for other purposes.

[0055] Example 2

[0056] The only difference from Example 1 is that the concentration of the modified solution is 0.347 mmol L –1 The average particle size of the modified light magnesium carbonate particles obtained is 6 μm.

[0057] Example 3

[0058] The only difference from Example 1 is that the concentration of the modified solution is 0.694 mmol L –1 The average particle size of the modified light magnesium carbonate particles obtained is 5.5 μm.

[0059] Example 4

[0060] The only difference from Example 1 is that the concentration of the modified solution is 1.040 mmol L –1 The average particle size of the obtained light magnesium carbonate particles is 5.2 μm.

[0061] Example 5

[0062] The only difference from Example 1 is that the concentration of the modified solution is 1.733 mmol L –1 The average particle size of the light magnesium carbonate particles obtained is 3.96 μm.

[0063] Example 6

[0064] The only difference from Example 1 is that the concentration of the modified solution is 3.468 mmol L –1 The average particle size of the obtained light magnesium carbonate particles is 3.88 μm.

[0065] Example 7

[0066] The only difference from Example 1 is that the concentration of the modified solution is 10.402 mmol L –1 The average particle size of the light magnesium carbonate particles obtained is 3.92 μm.

[0067] It can be seen from Examples 1-7 that the particle size distribution of the magnesium carbonate particles can be regulated by adjusting the concentration of the modified solution.

[0068] Example 8

[0069] The only difference from Example 1 is the modified solution. In this example, the modified solution is an aqueous solution of pentaerythritol with a concentration of 3 g / L. The particle size of the obtained light magnesium carbonate is shown in Table 1.

[0070] Example 9

[0071] The only difference from Example 1 is the modified solution. In this example, the modified solution is an aqueous solution of glucose with a concentration of 3 g / L. The particle size of the obtained light magnesium carbonate is shown in Table 1.

[0072] Example 10

[0073] The only difference from Example 1 is the modified solution. In this example, the modified solution is an aqueous solution of soluble starch with a concentration of 3 g / L. The particle size of the obtained light magnesium carbonate is shown in Table 1.

[0074] Example 11

[0075] The only difference from Example 1 is the modified solution. In this example, the modified solution is an aqueous solution of sucrose with a concentration of 3 g / L. The particle size of the obtained light magnesium carbonate is shown in Table 1.

[0076] Example 12

[0077] The only difference from Example 1 is the modified solution. In this example, the modified solution is an aqueous solution of polyethylene glycol with a concentration of 3 g / L. The particle size of the obtained light magnesium carbonate is shown in Table 1.

[0078] Table 1 Effect of different modifiers on particle size of light magnesium carbonate

[0079] It can be seen from Table 1 that each improver has a particle size regulating effect on light magnesium carbonate, making the particle size of light magnesium carbonate closer to the sunlight band. According to the principle of Mie scattering, the scattering rate is strongly enhanced, which is beneficial to enhance the reflectivity of light magnesium carbonate in the sunlight band, thereby enhancing the radiation cooling performance.

[0080] Comparative Example 1

[0081] No modification reaction is performed on magnesium carbonate, that is, the preparation method is:

[0082] (1) Add 4.487kg MgCl2·6H2O and 0.388kg liquid ammonia into the reaction system, and introduce flue gas (CO2 content is 0.42kg) into the reaction solution to react.

[0083] (2) filtering the reaction solution to obtain MgCO3·3H2O;

[0084] (3) The reaction solution precipitates salt to obtain ammonium chloride and magnesium chloride, and the second reaction occurs:

[0085] The microscopic morphologies of the magnesium carbonate obtained in Example 1 and Comparative Example 1 were observed, as shown in Figures 1(a) and 1(b). The particle size distributions of the magnesium carbonate obtained in Example 1 and Comparative Example 1 were tested. It can be seen that the introduction of a trace amount of SDS can significantly regulate the microstructure of light magnesium carbonate. The light magnesium carbonate obtained in the reaction system without the addition of an SDS modification agent has a long rod-like structure and a particle size between 3.35 and 48.90 μm, which cannot effectively respond to sunlight. The light magnesium carbonate obtained by SDS-induced modification has a spherical structure and a particle size between 1.21 and 7.15 μm, which can effectively respond to sunlight, thereby significantly improving the sunlight reflection performance of the radiant cooling coating.

[0086] In addition, it has been calculated that the light magnesium carbonate high-efficiency optical scatterer with graded particle size distribution and biomimetic multi-level structure characteristics prepared in accordance with Example 1 has a relatively significant negative carbon effect during the preparation process, and its production of 1 ton can seal 0.817 tCO2-eq.

[0087] Example 13

[0088] The optical scatterer obtained in Example 1 was used to prepare a coating, and the preparation method was as follows: (1) 0.102 kg of PVDF was dissolved in a mixed solvent of acetone (0.462 kg) and DMF (0.114 kg) to obtain a polymer resin emulsion;

[0089] (2) adding an optical scatterer (modified light magnesium carbonate powder) to the polymer resin emulsion, and controlling the volume ratio of the multi-level structure light magnesium carbonate optical scatterer to the polymer resin PVDF in the formula system to be 2:3;

[0090] (3) adding 2 wt% of 1H,1H,2H,2H-perfluorodecyltriethoxysilane to the polymer resin emulsion to form a mixed system;

[0091] (4) After continuous stirring at a stirring speed of 1200 r / min for 1.5 hours, a radiative cooling coating is obtained, in which the volume ratio of the optical scatterer in the coating is 40%.

[0092] An aluminum plate was used as the substrate, and a 200μm thick radiation cooling film layer was applied on it, and its reflectivity in the solar band was tested and analyzed.

[0093] Example 14

[0094] The remaining parameters remained the same as in Example 13, except for the 1:1 volume ratio of the optical diffuser to the PVDF polymer. This resulted in a radiative cooling coating emulsion with a 50% volume ratio of the optical diffuser. Subsequently, a 200 μm thick radiative cooling film layer was applied to an aluminum substrate, and its reflectivity in the solar wavelength range was tested and analyzed.

[0095] Example 15

[0096] The remaining parameters remained the same as in Example 13, with the volume ratio of the optical diffuser to the PVDF polymer changed to 3:2. This resulted in a radiative cooling coating emulsion with a 60% volume ratio of the optical diffuser. Subsequently, a 200 μm thick radiative cooling film layer was applied to an aluminum substrate, and its reflectivity in the solar wavelength range was tested and analyzed.

[0097] Example 16

[0098] The volume ratio of the hierarchical light magnesium carbonate optical diffuser to the PVDF polymer resin was changed to 7:3 in Example 13, while all other parameters remained the same. This resulted in a radiative cooling coating emulsion with a 70% optical diffuser volume ratio. Subsequently, a 200 μm thick radiative cooling film layer was applied to an aluminum substrate, and its reflectivity in the solar wavelength range was tested and analyzed.

[0099] Example 17

[0100] The volume ratio of the hierarchical light magnesium carbonate optical diffuser to the PVDF polymer resin was changed to 4:1 in Example 13, while all other parameters remained the same. This resulted in a radiative cooling coating emulsion with an 80% optical diffuser volume ratio. Subsequently, a 200 μm thick radiative cooling film layer was applied to an aluminum substrate, and its reflectivity in the solar wavelength range was tested and analyzed.

[0101] Example 18

[0102] Only the thickness of the radiative cooling film layer in Example 16 was changed to 100 μm, and other parameters were the same as those in Example 16. The reflectivity in the solar light band was tested and analyzed.

[0103] Example 19

[0104] Only the thickness of the radiative cooling film layer in Example 16 was changed to 300 μm, and other parameters were the same as those in Example 16. The reflectivity in the solar wavelength band was tested and analyzed.

[0105] Example 20

[0106] Only the thickness of the radiative cooling film layer in Example 16 was changed to 400 μm, and other parameters were the same as those in Example 16. The reflectivity in the solar wavelength band was tested and analyzed.

[0107] Comparative Example 2

[0108] The magnesium carbonate obtained in Comparative Example 1 was used as an optical scatterer to prepare a coating, and the coating preparation method was the same as that in Example 16.

[0109] The coatings obtained in Example 16 and Comparative Example 2 were respectively coated on aluminum plates with a coating thickness of 200 μm. The radiative cooling performance of the two coatings was observed. As shown in FIG3 , the reflectivity of the coating before modification was 84.92%, and the reflectivity of the coating after modification was 93.32%.

[0110] The coatings prepared in Examples 13-17 were respectively coated on aluminum plates with a coating thickness of 200 μm. The radiative cooling performance of the four coatings was observed. As shown in FIG4 , the reflectivities of Examples 13-17 were 78.75%, 84.6%, 89.14%, 93.32%, and 93.9%, respectively.

[0111] The coating obtained in Example 16 was coated on an aluminum plate with a coating thickness of 100 μm, 200 μm, 300 μm and 400 μm, respectively, and the effect of coatings of different thicknesses on the radiative cooling performance was observed. As shown in Figure 5, the reflectivities corresponding to the coatings of 100 μm, 200 μm, 300 μm and 400 μm were 91.58%, 93.32%, 96.24% and 96.8%, respectively.

[0112] The spectral performance of the coating obtained in Example 19 in the sunlight band and the atmospheric window band is observed, as shown in Figure 6. It can be seen that the emissivity in the sunlight band reaches 96.24%, the emissivity in the atmospheric window is 0.978, and the contact angle of Example 19 is 151.10°, with good hydrophobic performance.

[0113] Example 21

[0114] An optical scatterer is formed by a large number of light magnesium carbonate particles. The microscopic morphology of a single light magnesium carbonate particle is shown in Figure 1(a). A three-dimensional spherical structure is formed by a large number of two-dimensional flakes, and a large number of gaps are formed between the two-dimensional flakes. The particle size distribution of the particles is shown in Figure 2, and the particle size distribution is between 1.21 and 7.15 μm. The optical scatterer having this structure can be prepared by the preparation method in Example 1.

[0115] This invention pioneers the use of magnesium-rich tailings solid waste, derived from the widespread use of potassium salt in salt lakes, as a raw material. It innovatively combines carbon capture, utilization, and storage (CCUS) technology to produce a highly efficient magnesium-calcium carbonate optical scatterer in a controllable and carbon-reducing manner. The resulting biomimetic multi-layered structure, constructed from two-dimensional nanosheets and nano- and micro-scale three-dimensional hydrangeas formed by self-assembly of two-dimensional nanosheets, exhibits a graded particle size distribution that matches the wavelength of sunlight, potentially significantly improving the coating's solar reflectivity. Furthermore, the preparation process is carbon-negative. This invention can provide a theoretical foundation and practical support for the development and application of high-performance, long-life radiative cooling materials for green buildings, thereby contributing to addressing the global triple crisis of solid waste, climate change, and energy.

[0116] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing an optical scatterer, characterized in that: Magnesium carbonate is produced by capturing carbon dioxide using magnesium chloride and ammonia as raw materials; Magnesium carbonate is modified with a modifier to obtain an optical scatterer.

2. The preparation method according to claim 1, wherein: The magnesium chloride is derived from magnesium-rich tailings, and the carbon dioxide is preferably derived from industrial flue gas.

3. The preparation method according to claim 1 or 2, characterized in that: The magnesium carbonate is placed in a modifier for modification. The modifier is an aqueous solution of pentaerythritol, glucose, soluble starch, sucrose, polyethylene glycol or sodium lauryl sulfate. Preferably, the modifier is an aqueous solution of sodium lauryl sulfate.

4. The preparation method according to claim 1 or 2, characterized in that: Magnesium carbonate is placed in a modifier for modification. The modifier is an aqueous solution of sodium dodecyl sulfate. The concentration of sodium dodecyl sulfate in the aqueous solution is 0.2 to 5 mmol·L-1.

5. The preparation method according to claim 1 or 2, characterized in that: The temperature of the modification system is 60-100°C during the modification process.

6. The preparation method according to claim 1 or 2, characterized in that: The modification reaction was continued with stirring at a speed of 100 to 300 r / min.

7. The preparation method according to claim 1 or 2, characterized in that: When the modifier is SDS solution, the reaction formula of the modification process is:

8. The preparation method according to claim 2, wherein: The molar ratio of magnesium-rich tailings, CO2 in industrial tail gas, and ammonia is (3-7):(3-5):(8-12), and preferably the molar ratio of magnesium-rich tailings, CO2 in industrial tail gas, and ammonia is 5:4:

10.

9. The preparation method according to claim 1 or 2, characterized in that: The modified magnesium carbonate optical scatterer structure satisfies one or more of the following combinations: —Particle size ranges from 1.21 to 7.15 μm; - Average particle size of 1 to 5 μm; —Nanovoids exist on the particle surface; - After modification, the magnesium carbonate optical scatterer is a three-dimensional structure formed by assembling two-dimensional sheets under a microscope.

10. The preparation method according to claim 1 or 2, characterized in that: The particle size and micromorphology of the modified magnesium carbonate can be regulated by adjusting the type and / or content of the modifier.

11. A method for preparing an optical scatterer, characterized in that: The magnesium carbonate is modified to enhance the optical scattering performance of the magnesium carbonate particles.

12. The preparation method according to claim 11, characterized in that: The modified magnesium carbonate particles meet one or more of the following requirements: —The microscopic morphology is a three-dimensional spherical structure formed by self-assembly of two-dimensional flakes; —Particle size is 1 to 14 μm; —After modification, it becomes light magnesium carbonate particles.

13. The preparation method according to claim 11 or 12, characterized in that: The magnesium carbonate is prepared from magnesium chloride, ammonia and carbon dioxide.

14. The preparation method according to claim 11, characterized in that: The magnesium carbonate is modified by using pentaerythritol, glucose, soluble starch, sucrose, polyethylene glycol or sodium lauryl sulfate.

15. An optical scatterer, characterized in that: The invention comprises light magnesium carbonate particles, wherein the light magnesium carbonate particles meet one or a combination of the following: The microstructure of the light magnesium carbonate particles is a three-dimensional structure formed by the assembly of two-dimensional sheets; - The particle size of the magnesium carbonate particles is distributed in the range of 1 to 14 μm.

16. An optical scatterer produced by the method according to any one of claims 1 to 14.

17. A coating, characterized in that: The optical scatterer comprises an optical scatterer and a fluid, wherein the optical scatterer is the optical scatterer according to claim 15 or 16.

18. The coating according to claim 17, characterized in that: The fluid is a polymer resin emulsion, which includes a resin matrix and an organic solvent. The resin matrix is preferably one or more of polyurethane, acrylate, polydimethylsiloxane and polyvinylidene fluoride; the organic solvent is preferably one or more of toluene, ethylene glycol, acetone and N,N-dimethylformamide.

19. The coating according to claim 18, characterized in that: The polymer resin emulsion satisfies one or a combination of the following: - The organic solvent is a mixed solvent of acetone and DMF, and the blending mass ratio of acetone to DMF is (1:5) to (5:1); The resin matrix is polyvinylidene fluoride, and the mixing mass ratio of the optical scatterer to the polyvinylidene fluoride is (2:3) to (4:1).

20. The coating according to any one of claims 17 to 19, characterized in that: A hydrophobic modifier is added to the coating, wherein the hydrophobic modifier is preferably 1H,1H,2H,2H-perfluorodecyltriethoxysilane; preferably, the amount of the hydrophobic modifier added to the coating is (0.1-4.0) wt%.

21. A method for preparing the coating according to any one of claims 17 to 20, characterized in that: The optical scatterer according to claim 15 or 16 is dispersed in a fluid.

22. Use of the coating material according to any one of claims 17 to 20.

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