Lignin radiation cooling material as well as preparation method and application thereof

Abstract

The invention discloses a lignin radiation cooling material and a preparation method and application thereof. The material is prepared by using light-color lignin and polyvinyl alcohol as matrixes, constructing frozen gel with a layered porous structure through a directional freezing technology, and growing silicon dioxide nanoparticles in pores of the frozen gel in situ. The preparation method comprises the following steps: mixing the light-color lignin with a polyvinyl alcohol solution, performing directional freezing and freeze-drying to form a porous skeleton, performing crosslinking treatment to enhance the stability, and finally performing in-situ generation of the silicon dioxide nanoparticles in an ethanol system under the catalysis of ammonia by taking tetraethyl orthosilicate as a silicon source. According to the method, the intrinsic infrared emission characteristic of lignin, the light scattering capacity of a porous structure and the high reflection performance of silicon dioxide are ingeniously combined, so that the obtained material has high reflectivity in the solar spectrum band and has high emissivity in the atmosphere window band, passive radiation cooling without external energy is achieved, and the service life of the material is prolonged. And a remarkable cooling effect can be generated in a noon strong light environment. The material provides a new solution for the fields of high-valued utilization of biomass resources and energy-saving cooling.

Description

Technical Field

[0001] This invention belongs to the field of lignin functionalized materials, specifically involving a lignin-derived material for passive radiative cooling and its related preparation method and application. This material can effectively reflect sunlight and emit heat, thereby achieving cooling and energy saving. Background Technology

[0002] Rapid global industrial development has led to massive emissions of heat-absorbing greenhouse gases such as carbon dioxide, causing a continuous rise in global average temperatures. To cope with these high temperatures, air conditioning equipment is widely used, but its operation consumes a large amount of electricity, further exacerbating energy shortages and the greenhouse effect, creating a vicious cycle. Against this backdrop, passive radiative cooling technology has gained widespread attention as a zero-energy, sustainable thermal management strategy. This technology relies on the high reflectivity of materials in the solar spectrum (0.3–2.5 μm) and high infrared emissivity within the atmospheric transparency window (8–13 μm) to achieve cooling through radiative heat dissipation from the Earth without external energy input.

[0003] Lignin, the second most abundant biomass polymer in nature, is widely available and renewable, showing great potential as a substitute for petrochemical-based materials. Its molecular structure is rich in functional groups such as phenolic hydroxyl groups and ether bonds, endowing it with excellent ultraviolet absorption capabilities, making it suitable for long-term outdoor exposure scenarios. Simultaneously, the polar bond vibration modes such as C–O and C–O–C give it a high intrinsic emissivity in the mid-infrared region, meeting the basic requirements for thermal emission performance in radiative cooling materials. However, natural lignin contains a large number of chromophores (such as phenolic and quinone structures), resulting in strong absorption in the visible light band and a generally dark color, limiting its application in reflective cooling materials. Therefore, how to effectively reduce its visible light absorption without weakening its infrared emission capability has become a key issue in the development of lignin-based radiative cooling materials.

[0004] Several lignin-based functional materials have been reported in the prior art. For example, CN117903473A provides a lignin nanobottle / chitosan nanocrystal / polyvinyl alcohol nanocomposite membrane, which focuses on improving the material's mechanical properties, antibacterial properties, and photothermal conversion efficiency, and is used for seawater desalination. However, its design goal is photothermal conversion, which contradicts the high solar reflectance required for radiative cooling. CN113150364A discloses a photothermally responsive bio-based aerogel that introduces liquid metal to enhance photothermal performance, but its core focus remains on absorbing rather than reflecting sunlight. In addition, CN114920979A reports a modified lignin-based biomass gel that achieves 98% solar absorption by carbonizing lignin and constructing a bilayer structure, also focusing on photothermal evaporation applications. It is evident that existing lignin-based materials are mostly dedicated to the development of photothermal conversion, lacking systematic research on their application in radiative cooling, especially lacking an effective way to achieve high solar reflectance while maintaining high infrared emission.

[0005] Therefore, it is necessary to develop a new type of lignin-based material that can retain the inherent infrared emission advantage of lignin while significantly enhancing its ability to reflect the solar spectrum, thereby truly achieving a highly efficient passive radiative cooling effect and expanding the application prospects of lignin in energy-saving and cooling materials. Summary of the Invention

[0006] Technical problem to be solved: The present invention aims to overcome the shortcomings of existing technologies in which lignin is difficult to use for radiation cooling due to its dark color and strong visible light absorption. It provides a high-efficiency radiation cooling material based on light-colored lignin, its preparation method and application, and solves the technical problem that lignin is difficult to achieve high solar reflectivity while maintaining high infrared emissivity.

[0007] Technical solution: A method for preparing lignin radiation cooling material, comprising the following steps: (1) dissolving polyvinyl alcohol in deionized water to obtain a polyvinyl alcohol solution with a concentration of 0.06-0.1 g / mL; (2) cooling the polyvinyl alcohol solution to room temperature and ultrasonically treating it; (3) adding 1-2 M sodium hydroxide solution and light-colored lignin to the polyvinyl alcohol solution, and stirring and mixing at 60-70℃ to obtain a lignin / polyvinyl alcohol mixed solution; wherein, the volume ratio of sodium hydroxide solution to deionized water is 1:1, and the amount of light-colored lignin added is 12.5%-50% of the mass of polyvinyl alcohol; (4) pouring the lignin / polyvinyl alcohol mixed solution into a polytetrafluoroethylene mold, pouring liquid nitrogen into it for directional freezing, so that the mixture is frozen along the direction of cold gas conduction; (5) placing the frozen sample in a freeze dryer to dry it, to obtain a lignin / polyvinyl alcohol cryogel; (6) The lignin / polyvinyl alcohol cryogel was cross-linked in a mixed solution of epichlorohydrin and methanol with a volume ratio of 4:1. Then it was rinsed with methanol and deionized water and then freeze-dried. (7) The cross-linked cryogel was placed in anhydrous ethanol, and 25wt.%-28wt.% ammonium hydroxide solution and tetraethyl orthosilicate were added. The mixture was stirred at 40-60℃ to allow silica nanoparticles to grow in situ. The amount of ammonium hydroxide solution added was 5%-15% of the volume of anhydrous ethanol, and the amount of tetraethyl orthosilicate added was 1%-5% of the volume of anhydrous ethanol. (8) After the reaction was completed, the mixture was rinsed with ethanol and freeze-dried to obtain the lignin radiation cooling material.

[0008] The concentration of the polyvinyl alcohol solution in step (1) is 0.08 g / mL.

[0009] The concentration of the sodium hydroxide solution in step (3) is 2 M, and the volume ratio of the added sodium hydroxide solution to the volume of deionized water in step (1) is 1:1. The amount of light-colored lignin added is 25% of the mass of polyvinyl alcohol.

[0010] In step (7), the amount of ammonium hydroxide solution added is 15% of the volume of anhydrous ethanol. The amount of tetraethyl orthosilicate added is 2.5% of the volume of anhydrous ethanol. The stirring speed is 500 rpm and the reaction time is 6 h.

[0011] The lignin radiation cooling material prepared by the above method.

[0012] The above-mentioned lignin radiation cooling material is used in the preparation of passive radiation cooling materials.

[0013] Beneficial Effects: This invention selects light-colored lignin as the functional building block, whose absorption in the visible light region is significantly lower than that of conventional dark-colored lignin, laying the material foundation for achieving high solar reflectivity. By using directional freezing technology to freeze a mixed solution of lignin and polyvinyl alcohol along a specific direction, inducing the directional growth of ice crystals, a cryogel with an ordered layered porous structure was successfully constructed. This porous structure can effectively scatter sunlight, especially exhibiting a strong reflective effect on solar radiation in the 0.3 to 2.5 micrometer wavelength range, thus significantly reducing the material's absorption of solar energy. Based on this structure, this invention further grows silica nanoparticles on the surface of the cryogel framework through in-situ reaction. Silica not only has high reflectivity in the solar spectrum itself, but its coverage further enhances the light scattering ability of the porous structure, synergistically improving the material's solar reflectivity. Simultaneously, the inherent CO and COC chemical bonds in the lignin molecules, as well as the silicon-oxygen bonds in the introduced silica, all possess strong intrinsic vibrations in the atmospheric transparency window (8-13 μm) band, resulting in the composite material exhibiting high infrared emissivity across the entire atmospheric window band. This combination of high solar reflectivity and high infrared thermal emission, achieved through structural design and material composites, is key to achieving efficient passive radiative cooling. The properties of the aforementioned components are effectively integrated and synergistically amplified through the preparation process, enabling the resulting lignin-based radiative cooling material to achieve significant cooling effects without any external energy input. Figure 3 As shown, this material can achieve a temperature reduction of up to 18°C ​​compared to the ambient temperature at noon when solar irradiance is at its strongest, fully demonstrating the excellent radiative cooling performance of the material of this invention. Therefore, this invention not only opens up new avenues for the high-value utilization of lignin, but also provides a highly efficient, environmentally friendly, and energy-saving passive cooling material solution. Attached Figure Description

[0014] Figure 1 The lignin radiation cooling material prepared for this invention has good solar reflectivity.

[0015] Figure 2 The lignin radiation cooling material prepared for this invention has a high infrared emissivity.

[0016] Figure 3 The lignin radiation cooling material prepared for this invention has a good cooling effect. Detailed Implementation

[0017] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0018] Example 1

[0019] 0.4 g of polyvinyl alcohol (PVA) was dissolved in 5 mL of deionized water and stirred vigorously at 95 °C for 30 min. The resulting PVA solution was cooled to room temperature and sonicated for 10 min. 5 mL of 2 M sodium hydroxide solution and 0.05 g of light-colored lignin were added to the treated PVA solution, and the mixture was stirred at 65 °C for 12 h. The resulting lignin / PVA mixture was poured into a custom-made polytetrafluoroethylene (PTFE) mold, and liquid nitrogen was poured in. The lignin / PVA mixture was directionally frozen along the direction of cold gas conduction. After freezing, the sample was placed in a freeze dryer and dried for 48 h. A lignin / PVA cryogel was obtained after drying. This cryogel was placed in a mixture of epichlorohydrin and methanol (4:1 volume ratio) for 24 h, then rinsed with methanol and deionized water. After rinsing, the sample was placed in a freeze dryer for 48 h to obtain a lignin / PVA membrane. This membrane is designated as Sample 1.

[0020] Example 2

[0021] 0.4 g of polyvinyl alcohol (PVA) was dissolved in 5 mL of deionized water and stirred vigorously at 95 °C for 30 min. The resulting PVA solution was cooled to room temperature and sonicated for 10 min. 5 mL of 2 M sodium hydroxide solution and 0.1 g of light-colored lignin were added to the treated PVA solution, and the mixture was stirred at 65 °C for 12 h. The resulting lignin / PVA mixture was poured into a custom-made polytetrafluoroethylene (PTFE) mold, and liquid nitrogen was poured in. The lignin / PVA mixture was directionally frozen along the direction of cold gas conduction. After freezing, the sample was placed in a freeze dryer and dried for 48 h. A lignin / PVA cryogel was obtained after drying. This cryogel was placed in a mixture of epichlorohydrin and methanol (4:1 volume ratio) for 24 h, then rinsed with methanol and deionized water. After rinsing, the sample was placed in a freeze dryer for 48 h to obtain a lignin / PVA membrane. This membrane is designated as Sample 2.

[0022] Example 3

[0023] 0.4 g of polyvinyl alcohol (PVA) was dissolved in 5 mL of deionized water and stirred vigorously at 95 °C for 30 min. The resulting PVA solution was cooled to room temperature and sonicated for 10 min. 5 mL of 2 M sodium hydroxide solution and 0.2 g of light-colored lignin were added to the treated PVA solution, and the mixture was stirred at 65 °C for 12 h. The resulting lignin / PVA mixture was poured into a custom-made polytetrafluoroethylene (PTFE) mold, and liquid nitrogen was poured in. The lignin / PVA mixture was directionally frozen along the direction of cold gas conduction. After freezing, the sample was placed in a freeze dryer and dried for 48 h. A lignin / PVA cryogel was obtained after drying. This cryogel was placed in a mixture of epichlorohydrin and methanol (4:1 volume ratio) for 24 h. It was then rinsed with methanol and deionized water. After rinsing, the sample was placed in a freeze dryer for 48 h to obtain a lignin / PVA membrane. This membrane was designated as Sample 3.

[0024] Example 4

[0025] 0.4 g of polyvinyl alcohol (PVA) was dissolved in 5 mL of deionized water and stirred vigorously at 95 °C for 30 min. The resulting PVA solution was cooled to room temperature and sonicated for 10 min. 5 mL of 2 M sodium hydroxide solution and 0.05 g of light-colored lignin were added to the treated PVA solution, and the mixture was stirred at 65 °C for 12 h. The resulting lignin / PVA mixture was poured into a custom-made polytetrafluoroethylene (PTFE) mold, and liquid nitrogen was poured in, causing the lignin / PVA mixture to freeze directionally along the direction of cold gas conduction. After freezing, the sample was placed in a freeze dryer and dried for 48 h. A lignin / PVA cryogel was obtained after drying. This cryogel was placed in a mixture of epichlorohydrin and methanol (4:1 volume ratio) for 24 h, then rinsed with methanol and deionized water. After rinsing, the sample was placed in a freeze dryer for 48 h to obtain a lignin / PVA membrane. The mixture was placed in 100 mL of anhydrous ethanol, and 15 mL of ammonium hydroxide solution and 2.5 mL of tetraethyl orthosilicate solution were added. The mixture was stirred at 500 rpm for 6 hours at 40 °C. After stirring, it was rinsed with ethanol and then freeze-dried to obtain the lignin radiation-cooled material. This was designated as Sample 4.

[0026] Example 5

[0027] 0.4 g of polyvinyl alcohol (PVA) was dissolved in 5 mL of deionized water and stirred vigorously at 95 °C for 30 min. The resulting PVA solution was cooled to room temperature and sonicated for 10 min. 5 mL of 2 M sodium hydroxide solution and 0.1 g of light-colored lignin were added to the treated PVA solution, and the mixture was stirred at 65 °C for 12 h. The resulting lignin / PVA mixture was poured into a custom-made polytetrafluoroethylene (PTFE) mold, and liquid nitrogen was poured in, causing the lignin / PVA mixture to freeze directionally along the direction of cold gas conduction. After freezing, the sample was placed in a freeze dryer and dried for 48 h. A lignin / PVA cryogel was obtained after drying. This cryogel was placed in a mixture of epichlorohydrin and methanol (4:1 volume ratio) for 24 h, then rinsed with methanol and deionized water. After rinsing, the sample was placed in a freeze dryer for 48 h to obtain a lignin / PVA membrane. The mixture was placed in 100 mL of anhydrous ethanol, and 15 mL of ammonium hydroxide solution and 2.5 mL of tetraethyl orthosilicate solution were added. The mixture was stirred at 500 rpm for 6 hours at 40 °C. After stirring, it was rinsed with ethanol and then freeze-dried to obtain the lignin radiation-cooled material. This was designated as Sample 5.

[0028] The cooling effect of the material prepared by this invention is as follows: Figure 3 As shown, the cooling effect can reach up to 18°C ​​when the solar radiation intensity is highest at noon, indicating that this material has a good radiative cooling effect.

[0029] Table 1 Comparison of solar reflectance and infrared emissivity of each sample

[0030]

Claims

1. A method for preparing lignin radiation cooling materials, characterized in that, Includes the following steps: (1) Dissolve polyvinyl alcohol in deionized water to obtain a polyvinyl alcohol solution with a concentration of 0.06-0.1 g / mL; (2) Cool the polyvinyl alcohol solution to room temperature and sonicate it; (3) Add 1-2 M sodium hydroxide solution and light-colored lignin to the polyvinyl alcohol solution, and stir and mix at 60-70℃ to obtain a lignin / polyvinyl alcohol mixed solution; wherein, the volume ratio of sodium hydroxide solution to deionized water is 1:1, and the amount of light-colored lignin added is 12.5%-50% of the mass of polyvinyl alcohol; (4) Pour the lignin / polyvinyl alcohol mixed solution into a polytetrafluoroethylene mold, pour in liquid nitrogen for directional freezing, so that the mixture freezes along the direction of cold gas conduction; (5) Place the frozen sample in a freeze dryer to dry, and obtain a lignin / polyvinyl alcohol cryogel; (6) Place the lignin / polyvinyl alcohol cryogel in a mixed solution of epichlorohydrin and methanol for crosslinking treatment, the volume ratio of epichlorohydrin and methanol is 4:1, then rinse with methanol and deionized water, and then freeze dry; (7) The cross-linked cryogel was placed in anhydrous ethanol, and 25wt.%-28wt.% ammonium hydroxide solution and tetraethyl orthosilicate were added. The mixture was stirred at 40-60℃ to allow silica nanoparticles to grow in situ. The amount of ammonium hydroxide solution added was 5%-15% of the volume of the anhydrous ethanol, and the amount of tetraethyl orthosilicate added was 1%-5% of the volume of the anhydrous ethanol. (8) After the reaction was completed, the mixture was rinsed with ethanol and freeze-dried to obtain the lignin radiation cooling material.

2. The method according to claim 1, characterized in that, The concentration of the polyvinyl alcohol solution in step (1) is 0.08 g / mL.

3. The method according to claim 1, characterized in that, The concentration of the sodium hydroxide solution in step (3) is 2M, and the ratio of the volume added to the volume of deionized water in step (1) is 1:

1.

4. The method according to claim 1, characterized in that, The amount of light-colored lignin added in step (3) is 25% of the mass of polyvinyl alcohol.

5. The method according to claim 1, characterized in that, The amount of ammonium hydroxide solution added in step (7) is 15% of the volume of anhydrous ethanol.

6. The method according to claim 1, characterized in that, The amount of tetraethyl orthosilicate added in step (7) is 2.5% of the volume of anhydrous ethanol.

7. The method according to claim 1, characterized in that, The stirring speed in step (7) is 500 rpm and the reaction time is 6 h.

8. The lignin radiation cooling material prepared by any one of the methods described in claims 1-7.

9. The application of the lignin radiation cooling material according to claim 8 in the preparation of passive radiation cooling materials.

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