Silicon-based cellulose composite aerogel material for passive thermal management and preparation method and application thereof

Abstract

The application discloses a kind of silicon-based cellulose composite aerogel materials for passive thermal management and preparation method and application thereof, belong to radiation cooling and passive thermal management technical field.The silicon-based aerogel material includes cellulose nanofiber skeleton and silica network in situ crosslinked on the cellulose nanofiber skeleton, material inside has directional arrangement vertical honeycomb pore structure;In preferred embodiment, the aerogel material also includes silica nanosphere distributed in composite network.The application improves the structural stability and heat insulation performance of silicon-based aerogel material by the synergistic effect of cellulose nanofiber skeleton, silica network and directional pore structure, and gives it higher solar reflectance and infrared radiation heat dissipation capacity, and can be used in building envelope, cold chain packaging, outdoor equipment and passive thermal management and other fields.

Description

Technical Field

[0001] This invention belongs to the field of radiation cooling and passive thermal management technology, specifically relating to a silicon-based cellulose composite aerogel material for passive thermal management, its preparation method, and its application. Background Technology

[0002] Global warming has led to more frequent extreme heat events, placing higher demands on energy conservation and emission reduction in fields such as buildings, transportation, outdoor equipment, and personal thermal management. Passive thermal control technologies have therefore received widespread attention. Radiative cooling, a typical passive cooling method, releases heat into outer space through atmospheric windows in the form of infrared radiation, achieving cooling without consuming additional energy. Ideal daytime radiative cooling materials typically need to possess both high solar reflectivity and high atmospheric window infrared emissivity to reduce solar radiation absorption and enhance infrared heat dissipation.

[0003] However, existing radiative cooling materials typically function primarily for continuous heat dissipation. At night, during cold seasons, or in low-temperature environments, they may still radiate heat, causing the protected object to become overcooled, thus increasing heating energy consumption or reducing human thermal comfort. Therefore, materials with only a single cooling function are insufficient to meet the dynamic thermal management needs under conditions of large diurnal temperature variations, seasonal changes, or complex climates.

[0004] Aerogel materials possess high porosity, low thermal conductivity, and tunable optical properties, making them promising for applications in thermal insulation and radiative cooling. Among them, silica aerogels exhibit excellent infrared radiation characteristics and thermal insulation performance. However, traditional silica aerogels typically suffer from high brittleness, easy pulverization, insufficient structural stability, and complex preparation processes, limiting their long-term use in building envelopes, outdoor equipment, and cold chain packaging.

[0005] To improve the mechanical properties of silica aerogels, existing technologies attempt to introduce polymer or fiber-reinforcing phases, such as polyvinyl alcohol, polyimide, or cellulose nanomaterials. Cellulose nanofibers, in particular, possess characteristics such as renewability, high aspect ratio, and good interfacial compatibility, making them suitable for constructing organic-inorganic composite aerogels. However, existing cellulose / silica composite aerogels primarily focus on improving compression resilience, reducing thermal conductivity, or enhancing hydrophobicity, with insufficient attention paid to the synergistic control of material structure, mechanical stability, thermal insulation performance, and radiative cooling properties.

[0006] Therefore, it is necessary to provide a silicon-based aerogel material that is structurally stable, has a relatively simple preparation process, and combines thermal insulation and radiative cooling properties to meet the application requirements of building energy conservation, cold chain packaging, and passive thermal management of outdoor equipment. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a silicon-based cellulose composite aerogel material for passive thermal management, its preparation method, and its application, in order to solve the problems of insufficient mechanical stability, difficulty in controlling pore structure, and insufficient adaptability of single radiation cooling materials to thermal management in complex environments.

[0008] The objective of this invention can be achieved through the following technical solutions: A silicon-based cellulose composite aerogel material for passive thermal management comprises a cellulose nanofiber framework and a silica network in situ crosslinked on the cellulose nanofiber framework; the aerogel material has an internal structure of oriented vertical honeycomb pores.

[0009] Furthermore, the aerogel material also includes silica nanospheres, which are distributed in the composite structure formed by the cellulose nanofiber skeleton and the silica network.

[0010] Furthermore, the silica nanospheres are solid silica nanospheres synthesized by the Stober method.

[0011] The above-mentioned method for preparing a silicon-based cellulose composite aerogel material for passive thermal management includes the following steps: S1, Disperse cellulose nanofibers in a solution to obtain a cellulose gel solution; S2, methyltrimethoxysilane is added to an acetic acid solution for hydrolysis to obtain a silicon precursor solution; S3, the silicon precursor solution and silicon nanospheres are added to the cellulose gel solution and mixed evenly to obtain a composite gel solution; S4. The composite gel solution is subjected to unidirectional directional freezing and then freeze-dried to obtain the silicon-based aerogel material.

[0012] Further, in S3, the solid-liquid ratio of the cellulose nanofibers to the composite gel solution is 0.01 g / mL to 0.02 g / mL.

[0013] Furthermore, in step S3, after adding the silicon precursor solution to the cellulose gel solution, the step further includes: adding silica nanospheres to the mixture and stirring until homogeneous to obtain a composite gel solution.

[0014] Furthermore, in step S3, after obtaining the composite gel solution and before performing unidirectional freezing, the method further includes: removing air bubbles from the composite gel solution.

[0015] Furthermore, in S2, the acetic acid solution has a pH of 2-6, and the molar ratio of MTMS to the acetic acid solution is (1-2):1.

[0016] Further, in step S4, the unidirectional directional freezing includes: injecting the composite gel solution into a thermally conductive mold, and placing the thermally conductive mold on a cold source pre-cooled to -196°C, so that the composite gel solution freezes along the temperature gradient direction.

[0017] The above-mentioned application of silicon-based cellulose composite aerogel materials for passive thermal management in radiative cooling.

[0018] The beneficial effects of this invention are: 1. This invention forms an organic-inorganic composite support structure by in-situ crosslinking a cellulose nanofiber skeleton with a silica network, which can alleviate the problems of high brittleness and easy pulverization of pure inorganic silica aerogel, and improve the structural integrity and compressive stability of the material.

[0019] 2. This invention controls the solid-liquid ratio of cellulose nanofibers to composite gel solution to 0.01-0.02 g / mL, which is beneficial to forming a stable composite gel system. Combined with a unidirectional directional freezing process, a vertically honeycomb-like pore structure with directional arrangement is obtained, thereby improving the thermal insulation performance and structural stability of the material.

[0020] 3. The porous structure formed by the present invention can reduce the contribution of solid heat transfer and gas heat transfer, while the silica component is beneficial to improving the material's reflectivity in the solar spectrum and its radiative heat dissipation capability in the mid-infrared band, so that the resulting material has the potential for both heat insulation and radiative cooling applications.

[0021] 4. In a preferred embodiment of the present invention, silica nanospheres are distributed in a composite structure composed of a cellulose nanofiber skeleton and a silica network, which can further enhance light scattering and improve the support stability of the composite skeleton, thereby improving the overall thermal management performance of the material.

[0022] 5. The present invention adopts a preparation process that combines sol-gel, unidirectional directional freezing and freeze drying. It does not rely on supercritical drying equipment, the process flow is relatively simple, it is suitable for further scale-up preparation, and it can be applied to building envelope, outdoor equipment, cold chain packaging and passive thermal management materials. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 Here is a scanning electron microscope image of CNSi from Example 1; Figure 2 EDS plot of CNSi in Example 1; Figure 3 Scanning electron microscope image of CNSi-R for Comparative Example 1 Figure 4 This is a transmission electron microscope (TEM) image of the silicon precursor from Example 1. Figure 5 This is a transmission electron microscope (TEM) image of the silica nanospheres from Example 2. Figure 6 This is a photograph of the silicon-based cellulose composite aerogel material from Example 3. Figure 7 Comparison of the thermal insulation results of the silicon-based cellulose composite aerogel materials prepared in Examples 1, 3 and Comparative Example 1; Figure 8 Solar spectral reflectance diagrams of CNF aerogel, Example 3, Comparative Example 1, and Example 1 silicon-based cellulose composite aerogel materials; Figure 9 The cooling power calculation diagram is shown in Example 3; Figure 10 Figure showing the results of the radiation cooling potential test for cellulose silica-based aerogels. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] A silicon-based cellulose composite aerogel material for passive thermal management comprises a cellulose nanofiber framework and a silica network in situ crosslinked on the cellulose nanofiber framework; the aerogel material has an internal structure of oriented vertical honeycomb pores.

[0027] In some embodiments, the aerogel material further comprises silica nanospheres, which are distributed in the interlayer of the composite structure formed by the cellulose nanofiber skeleton and the silica network; the silica nanospheres are solid silica nanospheres synthesized by the Stober template method.

[0028] A method for preparing a silicon-based cellulose composite aerogel material for passive thermal management includes the following steps: (1) Preparation of cellulose gel solution: cellulose nanofibers (CNF) are dispersed in a solution to obtain a cellulose gel solution; (2) Preparation of silicon precursor solution: Methyltrimethoxysilane (MTMS) is added to acidic acetic acid solution for hydrolysis to obtain silicon precursor solution; (3) Preparation of composite gel solution: The silicon precursor solution is added to the cellulose gel solution and mixed evenly to obtain a composite gel solution; wherein the solid-liquid ratio of the cellulose nanofibers to the composite gel solution is between 0.01 g / mL and 0.02 g / mL (inclusive of endpoint values). (4) Directional freezing and drying: The composite gel solution is injected into a copper mold, and the copper mold is placed on a pre-cooled copper block for unidirectional directional freezing. After complete freezing, freeze drying is performed to obtain the adaptive silicon-based cellulose composite aerogel material.

[0029] In step (1), the solution is water or a solution containing water, the ultrasonic dispersion time is more than 10 minutes, and the stirring is carried out at 200~1000 rpm (preferably 400 rpm) for more than 2 hours.

[0030] In step (2), the acetic acid solution has a pH of 2-6, and the molar ratio of MTMS to acetic acid solution is 1:(1-2).

[0031] In step (2), the mixture is stirred at 800~1200 rpm for 2 h.

[0032] In some embodiments, after adding the silicon precursor solution to the cellulose gel solution, step (3) further includes adding silica nanospheres to the mixture and stirring until homogeneous to obtain a composite gel solution.

[0033] In step (3), after obtaining the composite gel solution and before injecting it into the copper mold, the composite gel solution is further subjected to ultrasonic centrifugation to remove air bubbles.

[0034] In step (4), the copper block is pre-cooled at a temperature of -196℃, the freeze-drying temperature is -30~-50℃, and the freeze-drying time is 6~12h.

[0035] The technical solution of the present invention will be described below through the following embodiments; in the embodiments, the sources of the relevant raw materials are as follows: Cellulose nanofibers: McLean, diameter: 4-10 nm, length: 1-3 μm; TEOS (Tetraethoxysilane): A Chinese medicine company; MTMS (methyltrimethoxysilane): sigma; Hexadecyltrimethylammonium bromide (CTAB): Maclean; Acetic acid solution: Prepare an acetic acid solution with the appropriate pH value by adding deionized water to acetic acid using a pH meter; Anhydrous ethanol: McLean.

[0036] Example 1 This embodiment provides a method for preparing a silicon-based cellulose composite aerogel material, including the following steps: (1) Preparation of cellulose gel solution: Weigh 1 g of cellulose nanofibers and add them to a 100 mL beaker. Add 70 g of deionized water, sonicate for 10 min, and then stir at 400 rpm for 2 h to obtain a uniform cellulose gel solution.

[0037] (2) Preparation of silicon precursor solution: Methyltrimethoxysilane was added to an acetic acid solution with pH 4 and hydrolyzed for 30 min under stirring to obtain silicon precursor solution.

[0038] (3) Preparation of composite gel solution: The silicon precursor solution is added to the cellulose gel solution and stirred for 2 h to obtain a uniform milky white composite gel solution; then the composite gel solution is defoamed and injected into a 2 cm × 2 cm × 2 cm copper mold.

[0039] (4) Unidirectional freezing and freeze-drying: The copper mold containing the composite gel solution is placed on a copper block pre-cooled to -196℃ for 30 min, so that the composite gel solution freezes along the temperature gradient direction; after it is completely frozen, it is placed in a freeze dryer and freeze-dried at -40℃ for 12 h to obtain the silicon-based cellulose composite aerogel material, denoted as CNSi.

[0040] Example 2 This embodiment describes the preparation process of silica nanospheres.

[0041] SiO2 nanospheres can be synthesized by hydrolysis-condensation reaction of tetraethoxysilane under alkaline conditions. Subsequent steps include washing, centrifugation, and drying. The entire process includes the following steps: i) Add 0.64 g of hexadecyltrimethylammonium bromide and 4 mL of ammonia solution to a deionized water and ethanol solution prepared in a specific ratio. Stir the mixture in a 35°C water bath at 800 rpm for 30 minutes, then add 4 mL of tetraethoxysilane and continue stirring for 24 hours. Solid SiO2 nanospheres can be obtained by adjusting the ratio of ionized water to ethanol to 1:1.

[0042] ii) The nanospheres were centrifuged and washed twice each with anhydrous ethanol and deionized water. The silica nanospheres prepared in this example were analyzed by transmission electron microscopy, and the results are as follows: Figure 4 As shown in the image. Figure 4 TEM images show that its silica is nanoscale and uniformly distributed.

[0043] Example 3 This embodiment provides a method for preparing biomimetic silica nanosphere composite cellulose aerogel. The experimental procedure is the same as in Example 1, except that the silicon-based material is not limited to silicon precursors. The specific steps include: (1) Preparation of cellulose gel solution: 1 g of cellulose was placed in a 100 mL beaker, 70 g of deionized water was poured into the beaker, sonicated for 10 min, and stirred at 400 rpm for 2 h until CNF was completely dissolved and homogeneous to obtain cellulose gel solution. (2) Preparation of silicon precursor solution: MTMS in an equimolar ratio was placed in a 25 mL beaker, poured into an acetic acid solution with pH=4, and stirred vigorously for 30 min to obtain the silicon precursor solution. Figure 4 ); (3) Preparation of silicon-based cellulose composite gel solution: Add silicon precursor solution to cellulose gel solution, stir vigorously and then add 10% by mass of silica nanospheres (solid). Stir at 400 rpm for 2 hours until the solution is uniformly white to obtain silicon-based cellulose composite gel solution. After the solution is ultrasonically centrifuged to remove bubbles, pour it into a 2×2×2 cm copper mold. (4) Preparation of directional ice template aerogel: Place a copper mold containing a silicon-based cellulose composite gel solution on a pre-cooled copper block for 30 min. After it is completely frozen, place it in a freeze-drying oven, set the freeze-drying temperature to -40℃, and the drying time to 12 h. After freeze-drying, a silicon-based cellulose composite material with adaptive properties can be obtained.

[0044] In this example, a biomimetic silica nanosphere composite cellulose aerogel CNSi-S was prepared, wherein the CNF in the total solvent system has a mass percentage of 0.014 g / mL, and the silica nanospheres have a mass percentage of 10% in the CNF. Therefore, the biomimetic silica nanosphere composite cellulose aerogel CNSi-S is prepared. Figure 6 This is a physical image of a silicon-based cellulose composite aerogel material.

[0045] Example 4 The experimental procedure was the same as in Example 1, except that the ratio of CNF to the total volume system was changed to 0.02, 0.014, and 0.01 to prepare 3 groups of silicon-based cellulose composite aerogel materials, named CNSi-50, CNSi, and CNSi-100 respectively.

[0046] Scanning electron microscopy analysis was performed on the cryogenic materials in the above three groups of aerogel composites, and the results are as follows: Figure 1 As shown. By Figure 1 , 2 As can be seen, the uniform pore structure formed by CNF dosage of 0.014 g / mL is vertically arranged, with a certain cavity structure forming a skeleton support and silicon-based material uniformly distributed in the whole material.

[0047] Comparative Example 1 The experimental procedure for this comparative example is the same as in step 1, except that a directional ice template is not used for freezing to prepare a porous aerogel material, denoted as CNSi-R. Figure 3 This is a scanning electron microscope (SEM) image of CNSi-R. The schematic diagram shows the random pore structure due to the chaotic ice crystal growth in this structure. The SEM image verifies this principle. It is compared with the different pore structures formed in Experiment 3 using the directional template method, which will facilitate further research and discussion on its thermal management applications in subsequent performance comparisons.

[0048] Comparative Example 2 The only difference between this comparative example and Example 1 is that the ratio of CNF to the total volume system is 0.02, denoted as CNSi-50. Everything else is the same as Example 1.

[0049] Comparative Example 3 The only difference between this comparative example and Example 1 is that the ratio of CNF to the total volume system is 0.01, denoted as CNSi-100. Everything else is the same as Example 1.

[0050] Experimental Test The thermal insulation properties of the aerogel materials prepared in Examples 1, 3, and Comparative Example 1 were tested. During the test, a block aerogel sample with dimensions of 2 cm × 2 cm × 2 cm was placed on the surface of a heating stage and tested continuously for 450 min under heating conditions of 50–250 °C. The temperature change of the upper surface of the sample was recorded, and the results are shown in Figure 7.

[0051] As shown in Figure 7, compared with the blank control sample, the aerogel materials prepared in Examples 1, 3, and Comparative Example 1 all exhibited better thermal insulation effects. Specifically, the non-directional porous aerogel CNSi-R obtained in Comparative Example 1 had an upper surface temperature of 47°C after being heated to 250°C for 450 min; the directional porous aerogel CNSi obtained in Example 1 had an upper surface temperature of 32°C; and the composite aerogel CNSi-S containing silica nanospheres obtained in Example 3 had an upper surface temperature of 25°C. These results indicate that the directional porous structure formed by unidirectional directional freezing is beneficial for reducing heat transfer, and the introduction of silica nanospheres can further improve the thermal insulation performance of the material.

[0052] The solar spectral reflectance of the obtained material was tested, and the results are shown in Figure 8. The CNSi-S sample exhibits high reflectance within the solar spectral range, with a solar spectral reflectance of 90.73%. Further calculations show that the cooling power of this material can reach 50.71 W / m². 2 This indicates its potential application in passive radiation cooling scenarios.

[0053] In addition, the compressive properties of CNF aerogel, CNSi, CNSi-50, CNSi-100, and CNSi-S samples were tested. Since radiative cooling materials are typically used for extended periods on rooftops, building facades, cold chain packaging, or outdoor equipment surfaces, they are inevitably subjected to external loads and environmental disturbances. The silicon-based composite aerogel obtained in this invention combines a lightweight porous structure with a high compressive modulus, which can improve the material's mechanical durability while maintaining good thermal insulation performance, making it more suitable for practical engineering applications. The results are shown in Figure 9. The compressive modulus of the CNSi-S sample reached 0.2791 MPa, higher than other comparative samples, indicating that it has good compressive stiffness and structural stability. A higher compressive modulus helps the material maintain the integrity of its pore structure during transportation, installation, and outdoor use, thereby improving its long-term service stability.

[0054] This invention alters the nanostructure of cellulose by controlling the overall direction of heat transfer in the aerogel, while simultaneously selecting a high cellulose content in a 75 mL solvent system. This changes the nanostructure and thus affects its spatial arrangement within an equal amount of cellulose. Notably, the chosen synthesis system exhibits higher adaptability than commercially available radiative cooling films, achieving both heat preservation in low-temperature indoor environments and radiative cooling in high-temperature environments.

[0055] Figure 10 This indicates that the cellulose silica-based aerogel has stable radiation cooling potential: On the one hand, the material exhibits a positive net cooling power under isothermal conditions, indicating its ability to radiate heat into outer space. On the other hand, the net cooling power significantly increases as the material's temperature rises, suggesting its suitability for outdoor thermal management, building cooling, packaging insulation, and equipment heat dissipation. However... Figure 10 The study also indicates that the actual cooling effect of a material depends not only on its infrared radiation performance but also is strongly influenced by environmental heat transfer conditions. For applications seeking greater sub-environmental cooling, the focus should be on optimizing the thermal insulation, low thermal conductivity, and surface structure of the aerogel to reduce non-radiative heat loss.

[0056] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0057] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A silicon-based cellulose composite aerogel material for passive thermal management, characterized in that, The silicon-based aerogel material includes a cellulose nanofiber framework and a silica network in situ crosslinked on the cellulose nanofiber framework. The interior of the aerogel material has a vertical honeycomb-like pore structure oriented in at least one direction.

2. The silicon-based cellulose composite aerogel material for passive thermal management according to claim 1, characterized in that, The aerogel material further comprises silica nanospheres, which are distributed in the composite structure formed by the cellulose nanofiber skeleton and the silica network.

3. The silicon-based cellulose composite aerogel material for passive thermal management according to claim 2, characterized in that, The silica nanospheres are solid silica nanospheres synthesized by the Stober method.

4. The method for preparing the silicon-based cellulose composite aerogel material for passive thermal management according to any one of claims 1 to 3, characterized in that, Includes the following steps: S1, Disperse cellulose nanofibers in water or an aqueous solution to obtain a cellulose gel solution; S2, methyltrimethoxysilane is added to an acidic acetic acid solution for hydrolysis to obtain a silicon precursor solution; S3, the silicon precursor solution is added to the cellulose gel solution and mixed evenly to obtain a composite gel solution; S4, the composite gel solution is subjected to unidirectional directional freezing, followed by freeze drying, to obtain the silicon-based cellulose composite aerogel material for passive thermal management.

5. The method for preparing a silicon-based cellulose composite aerogel material for passive thermal management according to claim 4, characterized in that, In step S3, the solid-liquid ratio of the cellulose nanofibers to the composite gel solution is 0.01 g / mL to 0.02 g / mL.

6. The preparation method according to claim 4, characterized in that, In step S3, after adding the silicon precursor solution to the cellulose gel solution, the step further includes adding silica nanospheres to the resulting mixture and stirring until homogeneous.

7. The method for preparing a silicon-based cellulose composite aerogel material for passive thermal management according to claim 4, characterized in that, In step S3, after obtaining the composite gel solution and before performing unidirectional freezing, the method further includes: removing air bubbles from the composite gel solution.

8. The preparation method according to claim 4, characterized in that, In step S2, the pH of the acetic acid solution is 2-6, and the molar ratio of the methyltrimethoxysilane to the acetic acid solution is (1-2):

1.

9. The preparation method according to claim 4, characterized in that, In step S4, the unidirectional freezing includes: injecting the composite gel solution into a thermally conductive mold and placing the thermally conductive mold on a cold source pre-cooled to -196°C, so that the composite gel solution freezes along the temperature gradient direction.

10. The application of the silicon-based cellulose composite aerogel material for passive thermal management as described in any one of claims 1 to 3 in radiative cooling.

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