Aerogel for radiation refrigeration and preparation method thereof

Abstract

The invention belongs to the technical field of polymer composite materials, and relates to aerogel for radiation refrigeration, which takes biomass cellulose as a framework and is loaded with a functional layer formed by SiO2 sol derived from wollastonite and calcium phytate. Wherein the SiO2 microspheres form a radiation refrigeration layer, so that the material is endowed with high solar reflectivity (greater than or equal to 95.1%) and high infrared emissivity (greater than or equal to 91.2%); calcium phytate formed by coordination of phytic acid and calcium ions in wollastonite forms a flame-retardant layer, so that the material has rapid self-extinguishing capability. The preparation method comprises the following steps: carrying out acid treatment on wollastonite, and preparing silica sol by a sol-gel method; the radiation refrigeration layer is constructed by loading the radiation refrigeration layer on the cellulose aerogel; and then treatment is carried out through a phytic acid solution, so that calcium resource fixation and flame-retardant layer construction are synchronously realized. All-element high-value utilization of silicon and calcium components of wollastonite is achieved, the problem of waste liquid in a traditional process is solved, and the obtained aerogel integrates efficient radiation refrigeration, active flame retardance, greenness and low cost and has wide application prospects in the field of building energy conservation.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of polymer composites, and relates to aerogels, in particular to an aerogel for radiative cooling and a preparation method thereof. BACKGROUND

[0002] The acceleration of global urbanization has led to a continuous increase in energy consumption in the field of construction. According to statistics, air conditioning and refrigeration has become one of the main driving forces for the growth of building energy consumption. Traditional refrigeration methods generally rely on active systems, which not only increase the energy consumption burden of buildings, but also cause significant carbon emissions. Therefore, developing a building refrigeration method without additional energy consumption has become a key path to reduce building energy consumption. Radiative cooling is a refrigeration method using radiative heat regulation. Radiative cooling materials use outer space as a cold source and radiate their own heat through the atmospheric window (8-13 μm). At the same time, radiative cooling materials efficiently reflect sunlight to reduce heat input, thereby achieving passive refrigeration without external energy input. Radiative cooling materials with high refrigeration power usually have high mid-infrared emissivity and high solar reflectivity. Cellulose molecules contain a large number of C-C, C-H and C-O-C functional groups, which have high infrared radiation in the atmospheric window, making cellulose materials have high emissivity; cellulose aerogels have the advantages of lightweight design, composite, and scalability, making them have broad application space in building scenarios such as roof insulation layers, wall envelope structures and energy-saving coatings, and their adjustable pore structure causes high-frequency Mie scattering when sunlight is incident, making them have high solar reflectivity. Although cellulose aerogels have a wide range of sources and good optical properties, they still face key technical bottlenecks such as unstable performance, poor thermal stability and insufficient flame retardant performance in building radiative cooling applications, which seriously limit their practical application potential in the field of building energy saving.

[0003] Wollastonite is a natural silicon-containing mineral with considerable reserves and mature ore-forming conditions, and its production in China has long been among the world's top ranks, with a wide distribution and extremely sufficient resource base. Wollastonite has excellent optical properties, with high refractive index and wide band gap characteristics, as well as significant Si-O-Si bond vibration response, making it exhibit high infrared emissivity in the atmospheric window (8-13 μm). However, the use of wollastonite in traditional industrial systems is relatively limited, and it is mostly consumed as a filler or additive, making resource utilization difficult, and the conversion path of high-quality and high-value is still insufficient. Its crystal nature is chain silicate, which is rich in active SiO xThe wollastonite can be efficiently converted into high-purity silicon dioxide under mild acid treatment or hydrothermal conditions, providing a feasible approach for resource upgrading. The silicon dioxide prepared based on wollastonite has advantages of easy construction of hierarchical pore structure, realization of strong light scattering and high infrared emission, and the like, and is very suitable for construction of high-performance radiative cooling materials. Therefore, conversion of wollastonite resources into high-value green optical materials not only helps to promote efficient resource utilization, but also opens up a new way for low-cost and sustainable radiative cooling materials.

[0004] At present, the application of wollastonite in radiative cooling materials still has certain limitations. In existing research, Deng et al. prepared a radiative cooling coating by using wollastonite as raw material, and Wang et al. constructed a radiative cooling aerogel with high thermal insulation performance by using silicon dioxide. However, the existing research on the utilization of wollastonite mainly focuses on the extraction of silicon elements therein, and a large amount of waste (or waste liquid) containing calcium chloride is generated in the process, causing resource waste and environmental burden. Notably, the calcium content in wollastonite is more than 30%, and the rich calcium resources have not been effectively developed and utilized. Therefore, research on the full-component utilization of wollastonite resources to construct long-acting and sustainable radiative cooling building materials has significant research value and engineering application prospect, which can not only improve the resource utilization efficiency, but also provide a new technical path for building energy saving and green low-carbon development. SUMMARY

[0005] In view of the problems of insufficient utilization of wollastonite resources, insufficient performance of radiative cooling materials and lack of flame retardant performance in the prior art, the purpose of the present application is to disclose an aerogel for radiative cooling, which skillfully realizes the full-component high-value utilization of wollastonite, and integrates efficient radiative cooling function and active flame retardant capacity.

[0006] TECHNICAL SOLUTION

[0007] An aerogel for radiative cooling is composed of a biomass cellulose skeleton and a wollastonite derivative loaded thereon, the wollastonite derivative being SiO2 sol and calcium phytate, wherein the silicon sol forms a radiative cooling layer composed of SiO2 microspheres on the surface and in the pores of the biomass cellulose skeleton; the calcium phytate forms a flame retardant layer on or in the radiative cooling layer through coordination reaction of phytic acid with calcium ions in the silicon sol layer.

[0008] In a preferred embodiment of the present application, the radiative cooling layer is composed of SiO2 microspheres with a particle size of 0.5-1.5 μm, the thickness is 0.5-1.5 μm, and the radiative cooling layer accounts for 1-10% of the total mass of the aerogel.

[0009] In a preferred embodiment of the present application, the flame retardant layer is composed of calcium phytate with a particle size of 0.5-1.5 μm, and accounts for 1-10% of the total mass of the aerogel.

[0010] In a preferred embodiment of the present application, the biomass cellulose aerogel is a lignocellulose aerogel or a nanocellulose / lignocellulose composite aerogel.

[0011] A second object of the present application is to disclose a method for preparing the aerogel for radiative cooling, comprising the following steps:

[0012] a) according to the mass / volume ratio of wollastonite and hydrochloric acid of 3-10 g / 100 mL, the wollastonite powder is added to the hydrochloric acid solution, stirred at 50-70℃ for 1-2 h, and the unreacted solid is removed by filtration to obtain a silicic acid solution; under stirring, 5-25% ammonia water is added dropwise to the silicic acid solution, the pH is adjusted to 8-10, and after continuous stirring for 4-6 h, it is placed at 5-35℃ for aging for 12-48 h to form a stable silica sol solution;

[0013] b) according to the mass / volume ratio of biomass cellulose aerogel and silica sol solution of 0.01-0.1 g / mL, the biomass cellulose aerogel is immersed in the silica sol solution, after water bath immersion at 50-70℃ for 5-15 h, it is uniformly frozen and freeze-dried for 24-72 h to obtain a silica sol loaded aerogel;

[0014] c) according to the mass / volume ratio of silica sol loaded aerogel and phytic acid solution of 0.01-0.1 g / mL, the silica sol loaded aerogel is immersed in a phytic acid solution with a concentration of 1-2.8 mol / L, after water bath immersion at 40-90℃ for 2-4 h, it is uniformly frozen and freeze-dried for 24-72 h.

[0015] In a preferred embodiment of the present application, the concentration of hydrochloric acid is 10-15 wt %.

[0016] In a preferred embodiment of the present application, the biomass cellulose aerogel is a lignocellulose aerogel or a nanocellulose / lignocellulose composite aerogel.

[0017] The aerogel of the present application can be widely used in radiative cooling of building roofs, walls and other parts, and is a kind of efficient low-carbon building energy-saving material.

[0018] Advantages

[0019] The radiation-cooling aerogel provided by this invention possesses excellent optical properties, with a solar reflectivity of up to 95.1% and an infrared emissivity of 91.2%. It can achieve a passive cooling effect of 5-7°C lower than the ambient temperature, effectively reducing building energy consumption by approximately 51.5%. This aerogel requires no external energy consumption or refrigerant emissions, offering advantages such as being green, low-carbon, environmentally friendly, and sustainable. It is of great significance for promoting energy conservation and emission reduction in buildings, contributing to the achievement of "dual-carbon" goals, and fostering the development of new functional building materials. The radiation-cooling aerogel provided by this invention can rapidly form a dense carbon layer upon contact with a flame, achieving a self-extinguishing effect within ≤2.5 seconds, effectively inhibiting combustion, delaying flame propagation, and significantly improving the fire safety performance of buildings. The radiation-cooling aerogel provided by this invention cleverly utilizes wollastonite derivatives (nano-silica and calcium phytate) to significantly enhance the material's radiation-cooling performance and flame-retardant effect, while avoiding the generation of calcium chloride waste (or waste liquid), achieving high-value utilization of all components of wollastonite resources, with good environmental benefits and application prospects. This invention uses biomass cellulose and natural minerals as raw materials to prepare aerogels, which has the advantage of low cost compared to chemically synthesized aerogel materials. Cellulose resources are abundant, renewable, and biodegradable, giving the material excellent environmental friendliness and sustainability, which aligns with the requirements of green and low-carbon development. Attached Figure Description

[0020] Figure 1 Scanning electron microscopy image of the balsa wood aerogel prepared in Example 3;

[0021] Figure 2 Scanning electron microscope image of the radiation-cooled aerogel prepared in Example 5. Detailed Implementation

[0022] The present invention will be described in detail below with reference to embodiments, so that those skilled in the art can better understand the present invention, but the present invention is not limited to the following embodiments.

[0023] Example 1

[0024] Preparation of silica sol solution (Part 1)

[0025] Wollastonite powder was sieved, washed with ethanol and water, and dried at 80℃ for 24 h to obtain pretreated wollastonite powder. 6 g of the pretreated wollastonite powder was weighed and slowly added to 100 mL of 10 wt.% hydrochloric acid. The solution was then transferred to a water bath at 65℃ and mechanically stirred for 1.5 h. After stirring, the unreacted product was filtered to obtain a silicic acid solution. Under vigorous stirring, 10% ammonia solution was added dropwise to the silicic acid solution until the pH reached 9. Mechanical stirring was continued for 2 h, and the solution was then sealed and allowed to stand for 12 h at 25℃ to obtain a stable silica sol solution.

[0026] Example 2

[0027] Preparation of silica sol solution (two)

[0028] The wollastonite powder was sieved, washed with ethanol and water, and then dried at 80 °C for 24 h to obtain pretreated wollastonite powder. 10 g of the pretreated wollastonite powder was slowly added to 100 mL of 10 wt.% hydrochloric acid, and then transferred to a 70 °C water bath for mechanical stirring for 2 h. After the stirring was completed, the unreacted product was filtered to obtain a silicic acid solution. Under the condition of vigorous stirring, 12% ammonia water was added dropwise to the silicic acid solution until the pH of the solution was 9.5, and mechanical stirring was continued for 2 h. After being sealed and static at 25 °C for 12 h, a stable silica sol solution was obtained.

[0029] Example 3

[0030] Preparation of basswood cellulose aerogel

[0031] An aqueous NaClO2 solution was prepared by dispersing 5 g of NaClO2 in 100 mL of deionized water. Glacial acetic acid was added dropwise to the aqueous NaClO2 solution until the pH of the solution was 4 to obtain a NaClO2 mixture. Three basswood flakes with a length, width and height of 2 cm, 1 cm and 0.5 cm, respectively, were added to the above-mentioned NaClO2 mixture and placed in a water bath at 80 °C for magnetic stirring for 4 h, then taken out and cooled to room temperature, and washed with distilled water until neutral. The NaClO2 treated basswood was transferred to 100 mL of anhydrous ethanol and soaked for 12 h at room temperature, and then transferred to 100 mL of deionized water and soaked for 12 h to further remove impurity ions in the wood, to obtain delignified basswood cellulose. The delignified basswood cellulose was placed in a freezer for 24 h, and then transferred to a vacuum chamber (-53 °C and 0.113 mbar) of a freeze dryer for treatment for 48 h to obtain a basswood cellulose aerogel.

[0032] Figure 1 The horizontal cross-sectional morphology of the basswood cellulose aerogel is shown, and the porous structure of the cross-section indicates the successful preparation of the basswood cellulose aerogel, and the unique vertical porous structure of the basswood cellulose aerogel is successfully preserved.

[0033] The average reflectivity of the prepared basswood cellulose aerogel is not less than 86.4%, and the average emissivity is not less than 87.5%.

[0034] Example 4

[0035] Preparation of basswood cellulose aerogel

[0036] A NaCIO2 aqueous solution was prepared by dispersing 5 g of NaCIO2 into 100 mL of deionized water. Glacial acetic acid was added dropwise into the NaCIO2 aqueous solution until the pH of the solution reached 4 to obtain a NaCIO2 mixture. Four poplar wood flakes with dimensions of 1 cm, 1 cm, and 0.5 cm were obtained, and the poplar wood flakes were added to the NaCIO2 mixture and placed in an 80 °C water bath environment for magnetic stirring for 4 h. After being taken out and cooled to room temperature, the poplar wood flakes were washed with distilled water until neutral. The poplar wood treated with NaCIO2 was transferred to 100 mL of anhydrous ethanol for immersion for 12 h and then transferred to 100 mL of deionized water for immersion for 12 h to further remove impurity ions in the wood, thereby obtaining delignified poplar cellulose. The delignified poplar cellulose was placed in a freezer freezing layer, frozen for 24 h, and then transferred to a vacuum chamber (-53 °C and 0.113 mbar) of a freeze dryer for treatment for 48 h to obtain poplar cellulose aerogel.

[0037] The average reflectivity of the prepared poplar cellulose aerogel was not less than 86.6%, and the average emissivity was not less than 87.3%.

[0038] Example 5

[0039] Preparation of a radiation cooling aerogel (based on basswood)

[0040] a) 3 g of the basswood cellulose aerogel obtained in Example 3 was taken and immersed in 100 mL of the silica sol solution obtained in Example 1. After immersion for 10 h under the condition of water bath heating at 60 °C, the basswood cellulose aerogel was uniformly frozen. A silica sol-loaded basswood aerogel precursor was obtained, and then transferred to a vacuum chamber (-53 °C and 0.113 mbar) of a freeze dryer for treatment for 48 h to obtain a silica sol-loaded basswood aerogel.

[0041] b) A 100 mL phytic acid solution with a concentration of 2 mol / L was prepared, and the above-mentioned silica sol-loaded poplar aerogel was immersed in the phytic acid solution. After immersion for 3 h in an 80 °C water bath environment, the silica sol-loaded poplar aerogel was uniformly frozen in a freezer freezing layer. Then, the silica sol-loaded poplar aerogel was transferred to a vacuum chamber (-53 °C and 0.113 mbar) of a freeze dryer for treatment for 72 h to obtain an aerogel for radiation cooling.

[0042] Figure 2 The vertical cross-sectional morphology of the aerogel for radiation cooling was shown. After loading and in-situ growth of the calcium phytate layer through the radiation cooling layer, it can be clearly seen that the surface of the basswood cellulose aerogel presents a multi-layer covered structure, which indicates the successful preparation of the aerogel for radiation cooling.

[0043] The prepared aerogel for radiation cooling has flame-retardant properties and can achieve self-extinguishing effect within 2.1s; the prepared aerogel for radiation cooling has an average reflectivity of not less than 95.1% and an average emissivity of not less than 91.2%.

[0044] The aerogel used for radiative cooling was placed in a radiative cooling test device and tested for 4 hours in a real outdoor environment from 10:00 to 14:00. The average cooling effect was 6.87 ℃.

[0045] Example 6

[0046] Preparation of radiation-cooled aerogels (based on poplar wood)

[0047] a) Take 3g of poplar cellulose aerogel obtained in Example 3 and 100mL of silica sol solution obtained in Example 1. Immerse the poplar cellulose aerogel in the obtained silica sol and soak it for 10 h under water bath heating at 60°C. Then freeze it uniformly to obtain a silica sol-loaded poplar aerogel precursor. Subsequently, transfer it to the vacuum chamber of a freeze dryer (-53°C and 0.113mbar) for 48 h to obtain silica sol-loaded poplar aerogel.

[0048] b) Prepare 100 mL of 2 mol / L phytic acid solution, immerse the poplar aerogel loaded with silica sol in the phytic acid solution, soak in an 80°C water bath for 3 h, and then freeze evenly in the freezer compartment of a refrigerator. Subsequently, transfer it to the vacuum chamber of a freeze dryer (-53°C and 0.113 mbar) for 72 h to obtain the aerogel for radiation cooling.

[0049] The prepared aerogel for radiation cooling has flame-retardant properties and can achieve self-extinguishing effect within 2.5s; the prepared aerogel for radiation cooling has an average reflectivity of not less than 94.8% and an average emissivity of not less than 91.0%.

[0050] The aerogel used for radiative cooling was placed in a radiative cooling test device and tested for 4 hours in a real outdoor environment from 10:00 to 14:00. The average cooling effect was 6.73℃.

[0051] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. An aerogel for radiation cooling, comprising a biomass cellulose framework and a wollastonite derivative supported thereon, wherein the wollastonite derivative is SiO2 sol and calcium phytate, characterized in that: The silica sol forms a radiation-cooling layer composed of SiO2 microspheres on the surface and within the pores of the biomass cellulose skeleton; the calcium phytate forms a flame-retardant layer on or within the radiation-cooling layer through the coordination reaction of phytic acid with calcium ions in the silica sol layer.

2. The aerogel for radiative cooling according to claim 1, characterized in that: The radiation cooling layer is composed of SiO2 microspheres with a particle size of 0.5-1.5 μm and a thickness of 0.5-1.5 μm, accounting for 1-10% of the total mass of the aerogel.

3. The aerogel for radiative cooling according to claim 1, characterized in that: The flame-retardant layer is composed of calcium phytate with a particle size of 0.5-1.5 μm, accounting for 1-10% of the total mass of the aerogel.

4. The aerogel for radiative cooling according to claim 1, characterized in that: The biomass cellulose aerogel is a lignocellulose aerogel or a nanocellulose / lignocellulose composite aerogel.

5. A method for preparing an aerogel for radiation cooling as described in any one of claims 1-4, characterized in that, Includes the following steps: a) Add wollastonite powder to hydrochloric acid solution, stir at 50-70℃ for 1-2 hours, filter to remove unreacted solids, and obtain silicic acid solution; while stirring, add 5-25% ammonia water dropwise to silicic acid solution to adjust pH to 8-10, continue stirring for 4-6 hours, and then let it stand at 5-35℃ for 12-48 hours to form a stable silica sol solution. b) Immerse the biomass cellulose aerogel in a silica sol solution, soak it in a water bath at 50-70℃ for 5-15 hours, then freeze it uniformly and freeze-dry it for 24-72 hours to obtain silica sol-loaded aerogel. c) The silica sol-loaded aerogel is immersed in a phytic acid solution with a concentration of 1-2.8 mol / L, immersed in a water bath at 40-90℃ for 2-4 hours, then uniformly frozen and freeze-dried for 24-72 hours to obtain the aerogel.

6. The method for preparing aerogel for radiation cooling according to claim 5, characterized in that: The mass-to-volume ratio of wollastonite to hydrochloric acid in step a) is 3-10 g / 100 mL.

7. The method for preparing aerogel for radiation cooling according to claim 5, characterized in that: The concentration of hydrochloric acid mentioned in step a) is 10-15 wt%.

8. The method for preparing aerogel for radiation cooling according to claim 5, characterized in that: The mass-to-volume ratio of the biomass cellulose aerogel to the silica sol solution in step b) is 0.01-0.1 g / mL.

9. The method for preparing aerogel for radiation cooling according to claim 5, characterized in that: The mass-to-volume ratio of the silica sol-loaded aerogel to the phytic acid solution in step b) is 0.01-0.1 g / mL.

10. An application of the aerogel for radiation cooling as described in any one of claims 1-4, characterized in that: It can be applied to building radiant cooling or energy-saving materials.

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