Multi-scale structure composite carbon aerogel wave-absorbing material and preparation method thereof

Abstract

The invention relates to the technical field of aerogel wave-absorbing materials, in particular to a multi-scale structure composite carbon aerogel wave-absorbing material and a preparation method thereof. The aerogel wave-absorbing material comprises a three-dimensional skeleton, a functional component and a conductive network. The three-dimensional skeleton is of a hierarchical porous structure formed by crosslinking two-dimensional graphene oxide and one-dimensional aramid nanofibers through hydrogen bonds, the functional component is zero-dimensional CoFe2O4 nanoparticles which are uniformly dispersed on the three-dimensional skeleton through in-situ growth, and the conductive network is an sp / sphybrid carbon matrix formed by carbonizing the three-dimensional skeleton and the functional component at high temperature. Through multi-dimensional cooperative construction of the zero-dimensional CoFe2O4 nanoparticles, the one-dimensional aramid nanofibers and the two-dimensional graphene, a rich heterogeneous interface and a polarization center are formed in the material, the electromagnetic wave loss capacity is remarkably enhanced, the broadband efficient wave absorbing requirement can be met, and the electromagnetic compatibility of aerospace electronic equipment is remarkably optimized.

Description

Technical Field

[0001] The present invention relates to the technical field of aerogel absorbing materials, and more specifically, to a multi-scale structured composite carbon aerogel absorbing material and a preparation method thereof. Background Art

[0002] With the continuous development of deep space exploration missions, the electromagnetic environment faced by spacecraft is becoming increasingly complex, placing higher demands on electromagnetic protection materials. While traditional resin-based electromagnetic protection materials (such as absorbing patches, shielding films, and carbon fiber composites) perform well under conventional conditions, they are susceptible to problems such as resin matrix aging and microstructural damage in the extreme environments of deep space (such as high and low temperature fluctuations, cosmic ray radiation, and atomic oxygen corrosion). This leads to degradation of electromagnetic protection performance, making it difficult to meet the requirements of long-duration, high-reliability exploration missions. Therefore, there is an urgent need to develop a new material that combines broadband electromagnetic protection capabilities, excellent environmental stability, and lightweight properties.

[0003] Graphene is an ideal candidate for deep space electromagnetic shielding due to its unique two-dimensional structure, excellent chemical stability (stable in the range of -300°C to 200°C), and resistance to ionized oxygen corrosion (it can form a dense protective layer). Furthermore, graphene's adjustable electromagnetic parameters and designable assembly structure give it significant advantages in the field of electromagnetic shielding and wave absorption. However, conventional homogeneous graphene aerogels, due to their simple composition and structure, are difficult to construct optimized impedance matching interfaces, limiting their efficient absorption of electromagnetic waves. Therefore, how to develop resin-free, lightweight, and high-strength graphene-based aerogel materials through precise assembly and large-scale preparation techniques, and how to achieve multi-scale control of their composition and structure, has become a key scientific issue in improving deep space electromagnetic shielding performance. Summary of the Invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, one aspect of the present invention is to provide a multi-scale structured composite carbon aerogel absorbing material, wherein the aerogel absorbing material includes a three-dimensional skeleton, functional components and a conductive network.

[0005] Preferably, the three-dimensional skeleton is a hierarchical porous structure formed by cross-linking two-dimensional graphene oxide and one-dimensional aramid nanofibers through hydrogen bonds.

[0006] Preferably, the two-dimensional graphene oxide has a thickness of 0.8-1.2 nm and a specific surface area of ​​≥800 m 2 / g, the one-dimensional aramid nanofiber has a diameter of 8-15 nm and a length of 20-50 μm, and the pore size of the porous structure is 50 nm-5 μm.

[0007] Preferably, the functional component is zero-dimensional CoFe2O4 nanoparticles uniformly dispersed on the three-dimensional skeleton through in-situ growth.

[0008] Preferably, the particle size of the zero-dimensional CoFe2O4 nanoparticles is 20-50 nm, and the mass fraction is 15-30%.

[0009] Preferably, the conductive network is a sp² / sp³ hybrid carbon matrix formed by high-temperature carbonization of a three-dimensional skeleton and functional components, with an electrical conductivity of 10 -2 ~10 2 S / m.

[0010] Another aspect of the present invention is to provide a method for preparing a multi-scale structured composite carbon aerogel absorbing material, wherein the preparation method comprises the following steps: S1. Preparation of precursor solution: Graphene oxide (GO) and aramid nanofibers (ANF) were dissolved in a DMF / NMP mixture according to the appropriate ratio. Ultrasonic dispersion was performed for 2 h to form a uniform dispersion. A mixed solution of CoCl2·6H2O and FeCl3·6H2O was added to the dispersion and magnetic stirring was performed for 60 min to allow the metal ions to fully adsorb onto the surfaces of GO and ANF. S2. Sol-gel process: The pH of the precursor solution was adjusted to 9.5±0.2, and then the solution was transferred to a polytetrafluoroethylene reactor. The heating rate was set to 2°C / min, the holding temperature was 80°C, and the hydrothermal reaction was carried out for 12 hours. During the hydrothermal process, Co 2+ with Fe 3+ Nanoparticles were formed by in situ co-precipitation and modified on the surfaces of GO and ANF. The chemical reaction equation is as follows: After the reaction, ANF / GO@CoFe2O4 hydrogel was prepared; S3. Replacement and aging: A gradient replacement process was used to prevent the collapse of the aerogel pore structure. The first replacement was performed with an ethanol / water mixture for 4 hours, repeated three times. The second replacement was performed with anhydrous ethanol for 6 hours, repeated four times. The third replacement was performed with tert-butyl alcohol for 8 hours, repeated two times. The replaced ANF / GO@CoFe2O4 hydrogel was immersed in a 0.5 wt% epichlorohydrin / acetone solution and aged at 60°C for 24 hours to enhance hydrogen bonding between the ANF and GO. S4. Supercritical drying: The aged ANF / GO@CoFe2O4 hydrogel was placed in an autoclave. Liquid CO2 was first injected at a rate of 0.5 MPa / min to a pressure of 7.5 MPa, and the pressure was allowed to stand for 12 h to complete solvent replacement. Subsequently, supercritical conversion was initiated, and the temperature was maintained at 40°C for 2 h. The temperature was then raised to 45°C at a rate of 0.5°C / min, maintaining the pressure at 7.5 MPa ± 0.05 for 4 h. Finally, the pressure was linearly reduced at 0.3 MPa / h to ambient pressure to obtain the ANF / GO@CoFe2O4 aerogel precursor. S5. Carbonization treatment: The ANF / GO@CoFe2O4 aerogel precursor was treated by programmed temperature carbonization. In the first stage, the temperature was increased from room temperature to 200°C at a rate of 2°C / min under an Ar atmosphere. In the second stage, the temperature was increased from 200°C to 400°C at a rate of 1°C / min under an Ar atmosphere. In the third stage, the temperature was increased from 400°C to 600°C at a rate of 3°C / min under an Ar atmosphere. In the fourth stage, the temperature was kept constant at 600°C for 2 hours. In the fifth stage, the temperature was naturally cooled to room temperature to prepare a multi-scale structured composite carbon aerogel absorbing material.

[0011] Preferably, the graphene oxide and the aramid nanofibers in S1 are dissolved in a DMF / NMP mixed solution at a mass ratio of 3:1 to 1:1, the volume ratio of the DMF / NMP mixed solution is 1:1, the ultrasonic power is 500W, the frequency is 40kHz, and a uniform dispersion is formed, the solid content of the dispersion is 2wt% to 8wt%, and a mixed solution of CoCl2·6H2O and FeCl3·6H2O is added to the dispersion. 2+ with Fe 3+ The molar ratio is 1:2.

[0012] Preferably, in S2, 25% ammonia water is added dropwise to the precursor solution to adjust the pH to 9.5±0.2.

[0013] Preferably, in the first replacement in S3, the solvent is an ethanol / water mixed solution, and the volume ratio of ethanol to water is 1:1.

[0014] The beneficial effects of the present invention are as follows: Excellent electromagnetic wave absorption performance: Through the multi-dimensional synergistic construction of zero-dimensional CoFe2O4 nanoparticles (20-50nm), one-dimensional aramid nanofibers (8-15nm), and two-dimensional graphene (0.8-1.2nm), the material forms a rich heterogeneous interface and polarization centers within it, significantly enhancing its electromagnetic wave absorption capacity. At a thickness of 2.2mm, the reflection loss reaches -56.8dB, and the effective absorption bandwidth reaches 5.3GHz, a 220% improvement over single-component materials. This meets the requirements for broadband and high-efficiency wave absorption and significantly improves the electromagnetic compatibility of aerospace electronic equipment.

[0015] Excellent mechanical properties and structural stability: The introduction of aramid nanofibers enhances the aerogel's mechanical strength, achieving a compressive strength of 7.2 MPa (at 50% strain) and an elastic recovery of 88%, representing increases of 260% and over 50%, respectively, compared to pure carbon aerogels. This overcomes the brittleness and easy collapse issues of traditional carbon aerogels. Furthermore, the material remains stable in extreme temperatures (-300°C to 200°C) and radiation environments, making it suitable for demanding applications such as deep space exploration.

[0016] Ultra-light, low-density, and low-shrinkage preparation process: Utilizing gradient solvent replacement and supercritical gradient decompression technology, the material density is reduced to 9.8 mg / cm³, while the drying shrinkage is controlled within 5%. This overcomes the industry challenge of lightweight materials being prone to shrinkage and deformation, achieving the coordinated optimization of ultra-lightness, high strength, and low deformation, and providing a reliable solution for spacecraft weight reduction and structural stability.

[0017] Multi-scale structural design and environmental adaptability: Through the "zero-dimensional-one-dimensional-two-dimensional" multi-dimensional composite strategy, combined with heteroatom doping and heterogeneous interface regulation, the material has excellent impedance matching characteristics and loss mechanism. At the same time, it has the ability to resist atomic oxygen corrosion, high and low temperature alternation and radiation. It is suitable for long-term deep space exploration missions and greatly improves the reliability and life of spacecraft electronic systems.

[0018] Additional aspects and advantages of the invention will become apparent from the description which follows, or may be learned by practice of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments with reference to the accompanying drawings, in which: Figure 1 This is an SEM image of a multi-scale structured composite carbon aerogel absorbing material according to an embodiment of the present invention; Figure 2 3 is a graph comparing the wave absorbing properties of different carbon aerogels according to the embodiments of the present invention. DETAILED DESCRIPTION

[0020] In order to more clearly understand the above-mentioned objects, features and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that, in the absence of conflict, the embodiments of the present application and the features therein can be combined with each other.

[0021] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from the description. Therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below.

[0022] Example 1 S1. Precursor solution preparation: Accurately weigh 60.0 mg of graphene oxide (GO, thickness 0.8-1.2 nm) and 30.0 mg of aramid nanofibers (ANF, diameter 8-15 nm). Disperse the mixture in 20 mL of a 1:1 v / v DMF / NMP solvent using an ultrasonicator (500 W, 40 kHz) for 120 min. Pipette 15 mL of a pre-prepared mixture of 0.1 M CoCl₂·6H₂O and 0.2 M FeCl₃·6H₂O and magnetically stir at 600 rpm for 60 min. S2. Sol-gel process: The pH was adjusted dropwise to 9.50 ± 0.02 using 25% aqueous ammonia (analytical grade). The mixture was transferred to a 50 mL polytetrafluoroethylene-lined reactor and programmed to 80.0 ± 0.5°C (2°C / min) for 12 h. After the reaction, the mixture was cooled to 25°C to obtain a black block of ANF / GO@CoFe2O4 hydrogel, which was then washed with deionized water until neutral. S3. Replacement and aging: First replacement: immersion in ethanol / water (1:1 v / v), changing the solution every 4 hours, repeated three times; second replacement: immersion in anhydrous ethanol, changing the solution every 6 hours, repeated four times; third replacement: immersion in tert-butyl alcohol, changing the solution every 8 hours, repeated two times; the gel was immersed in a 0.5 wt% epichlorohydrin / acetone solution and aged at 60°C for 24 hours to enhance hydrogen bonding between ANF and GO. S4. Supercritical drying: The wet gel was placed in a 300 mL supercritical drying reactor and liquid CO2 was injected at 0.5 MPa / min to 7.50 MPa. After maintaining the temperature at 40°C for 2 h, the temperature was raised to 45°C at a rate of 0.5°C / min and maintained for 4 h. The pressure was then linearly reduced at 0.3 MPa / h to ambient pressure to obtain the ANF / GO@CoFe2O4 aerogel precursor. S5. Carbonization treatment: Place in a tubular furnace with an Ar flow rate of 50 sccm; first stage: 2°C / min → 200°C (holding for 30 minutes); second stage: 1°C / min → 400°C (holding for 60 minutes); third stage: 3°C / min → 600°C (holding for 120 minutes); cool naturally to room temperature to obtain the final product, a multi-scale structured composite carbon aerogel absorber, as shown in the SEM image. Figure 1 shown.

[0023] Example 2 S1. Preparation of precursor solution: Accurately weigh 45.0 mg of graphene oxide (GO, 0.8-1.2 nm) and 45.0 mg of aramid nanofibers (ANF, 8-15 nm) in a 1:1 mass ratio. Disperse the mixture in 20 mL of a 1:1 v / v DMF / NMP solvent using an ultrasonicator (500 W, 40 kHz) for 120 min. Pipette 15 mL of a pre-prepared mixture of 0.075 M CoCl₂·6H₂O and 0.15 M FeCl₃·6H₂O and magnetically stir at 600 rpm for 60 min. S2. Sol-gel process: The pH was adjusted dropwise to 9.50 ± 0.02 using 25% aqueous ammonia (analytical grade). The mixture was transferred to a 50 mL polytetrafluoroethylene-lined reactor and programmed to 80.0 ± 0.5°C (2°C / min) for 12 h. After the reaction, the mixture was cooled to 25°C to obtain a black block of ANF / GO@CoFe2O4 hydrogel, which was then washed with deionized water until neutral. S3. Replacement and aging: First replacement: Soak in ethanol / water (1:1 v / v), changing the solution every 4 hours, repeated three times; Second replacement: Soak in anhydrous ethanol, changing the solution every 6 hours, repeated four times; Third replacement: Soak in tert-butyl alcohol, changing the solution every 8 hours, repeated two times; The gel was immersed in a 1.0 wt% epichlorohydrin / acetone solution and aged at 60°C for 36 hours to increase the hydrogen bond crosslinking density by 30%; S4. Supercritical drying: The wet gel was placed in a 300 mL supercritical drying reactor and liquid CO2 was injected at 0.5 MPa / min to 7.50 MPa. After maintaining the temperature at 40°C for 2 h, the temperature was raised to 45°C at a rate of 0.5°C / min and maintained for 4 h. The pressure was then linearly reduced at 0.3 MPa / h to ambient pressure to obtain the ANF / GO@CoFe2O4 aerogel precursor. S5. Carbonization treatment: Place in a tubular furnace with an Ar flow rate of 50 sccm; first stage: 2°C / min to 200°C (hold for 30 minutes); second stage: 1°C / min to 400°C (hold for 60 minutes); third stage: 3°C / min to 600°C (hold for 120 minutes); naturally cool to room temperature to obtain the final product, a multi-scale structured composite carbon aerogel absorber.

[0024] Example 3 S1. Precursor solution preparation: Accurately weigh 75.0 mg of graphene oxide (GO, thickness 0.8-1.2 nm) and 25.0 mg of aramid nanofibers (ANF, diameter 8-15 nm) in a mass ratio of 3:1. Prepare a mixed solution of 0.2 M CoCl₂·6H₂O and 0.4 M FeCl₃·6H₂O, increasing the metal salt loading to 30 wt %. Use 20 mL of a DMF / NMP (1:1 v / v) solvent system and ultrasonically disperse (500 W, 40 kHz) for 150 min until uniformly suspended. Sol-gel reaction: The pH was adjusted dropwise to 9.50 ± 0.02 using 25% aqueous ammonia (analytical grade). The mixture was transferred to a 50 mL polytetrafluoroethylene-lined reactor and programmed to 80.0 ± 0.5°C (2°C / min) for 12 h. After the reaction, the mixture was cooled to 25°C to obtain a black block of ANF / GO@CoFe2O4 hydrogel, which was then washed with deionized water until neutral. S3. Replacement and aging: First replacement: immersion in ethanol / water (1:1 v / v), changing the solution every 4 hours, repeated 6 times; second replacement: immersion in anhydrous ethanol, changing the solution every 6 hours, repeated 8 times; third replacement: immersion in tert-butyl alcohol, changing the solution every 8 hours, repeated 4 times; the gel was immersed in 0.5 wt% epichlorohydrin / acetone solution and aged at 60°C for 24 hours to enhance hydrogen bonding between ANF and GO. S4. Supercritical drying: The wet gel was placed in a 300 mL supercritical drying reactor and liquid CO2 was injected at 0.5 MPa / min to 7.50 MPa. After maintaining the temperature at 40°C for 2 h, the temperature was raised to 45°C at a rate of 0.5°C / min and maintained for 4 h. The pressure was then linearly reduced at 0.3 MPa / h to ambient pressure to obtain the ANF / GO@CoFe2O4 aerogel precursor. S5. Carbonization treatment: Place in a tubular furnace with an Ar flow rate of 50 sccm; first stage: 2°C / min to 200°C (hold for 30 minutes); second stage: 1°C / min to 400°C (hold for 60 minutes); third stage: 3°C / min to 800°C (hold for 120 minutes); naturally cool to room temperature to obtain the final product, a multi-scale structured composite carbon aerogel absorber.

[0025] Comparative Example 1 (Pure Carbon Aerogel) S1. Precursor solution preparation: Accurately weigh 90.0 mg of graphene oxide (GO, thickness 0.8–1.2 nm) and add 20 mL of DMF / NMP (1:1 v / v) solvent. Disperse the mixture using an ultrasonicator (500 W, 40 kHz) for 120 min and magnetically stir at 600 rpm for 60 min. S2. Sol-Gel Process: Adjust the pH to 9.50 ± 0.02 dropwise with 25% aqueous ammonia (analytical grade). Transfer the solution to a 50 mL polytetrafluoroethylene-lined reactor and program the temperature (2°C / min) to 80.0°C ± 0.5°C for 12 h. After the reaction, cool the solution to 25°C to obtain a black block of hydrogel, which is then washed with deionized water until neutral. S3. Gradient solvent replacement and aging: First replacement: immersion in ethanol / water (1:1 v / v), changing the solution every 4 hours, repeated three times; second replacement: immersion in anhydrous ethanol, changing the solution every 6 hours, repeated four times; third replacement: immersion in tert-butyl alcohol, changing the solution every 8 hours, repeated two times; the gel was immersed in a 0.5 wt% epichlorohydrin / acetone solution and aged at 60°C for 24 hours to enhance hydrogen bonding between ANF and GO. S4. Supercritical drying: The wet gel was placed in a 300 mL supercritical drying reactor and liquid CO2 was injected at 0.5 MPa / min to 7.50 MPa. After maintaining the temperature at 40°C for 2 h, the temperature was raised to 45°C at 0.5°C / min and maintained for 4 h. The pressure was then linearly reduced at 0.3 MPa / h to atmospheric pressure to obtain an aerogel precursor. S5. Carbonization treatment: Place in a tubular furnace with an Ar flow rate of 50 sccm; first stage: 2°C / min to 200°C (hold for 30 min); second stage: 1°C / min to 400°C (hold for 60 min); third stage: 3°C / min to 600°C (hold for 120 min); naturally cool to room temperature to obtain the final product.

[0026] Comparative Example 2 (Traditional Magnetic Composite Material) S1. Precursor solution preparation: Accurately weigh 90.0 mg of graphene oxide (GO, thickness 0.8-1.2 nm) and 27.0 mg of micron-sized Fe₃O₄ particles (1-3 μm). Disperse the mixture in 20 mL of a 1:1 v / v DMF / NMP solvent using an ultrasonicator (500 W, 40 kHz) for 120 min and magnetically stir at 600 rpm for 60 min. S2. Sol-Gel Process: Adjust the pH to 9.50 ± 0.02 dropwise with 25% aqueous ammonia (analytical grade). Transfer the solution to a 50 mL polytetrafluoroethylene-lined reactor and program the temperature (2°C / min) to 80.0°C ± 0.5°C for 12 h. After the reaction, cool the solution to 25°C to obtain a black block of hydrogel, which is then washed with deionized water until neutral. S3. Gradient solvent replacement and aging: First replacement: immersion in ethanol / water (1:1 v / v), changing the solution every 4 hours, repeated three times; second replacement: immersion in anhydrous ethanol, changing the solution every 6 hours, repeated four times; third replacement: immersion in tert-butyl alcohol, changing the solution every 8 hours, repeated two times; then immerse the gel in a 0.5 wt% epichlorohydrin / acetone solution and age at 60°C for 24 hours; S4. Vacuum drying: vacuum drying at 60°C for 24 h (pressure -0.1 MPa) to obtain an aerogel precursor;

[0027] S5. Carbonization treatment: Place in a tubular furnace with an Ar flow rate of 50 sccm; first stage: 2°C / min to 200°C (hold for 30 min); second stage: 1°C / min to 400°C (hold for 60 min); third stage: 3°C / min to 500°C (hold for 120 min); naturally cool to room temperature to obtain the final product.

[0028] Comparative Example 3 (No Gradient Process) S1. Precursor solution preparation: Accurately weigh 75.0 mg of graphene oxide (GO, thickness 0.8-1.2 nm) and 25.0 mg of aramid nanofibers (ANF, diameter 8-15 nm) at a mass ratio of 3:1. Prepare a mixed solution of 0.2 M CoCl₂·6H₂O and 0.4 M FeCl₃·6H₂O. Use 20 mL of a DMF / NMP (1:1 v / v) solvent system and ultrasonically disperse (500 W, 40 kHz) for 150 min until uniformly suspended. S2. Sol-Gel Reaction: Adjust the pH to 9.50 ± 0.02 dropwise with 25% aqueous ammonia (analytical grade). Transfer the solution to a 50 mL polytetrafluoroethylene-lined reactor and program the temperature (2°C / min) to 80.0°C ± 0.5°C for 12 h. After the reaction, cool the solution to 25°C to obtain a black block of hydrogel, which is then washed with deionized water until neutral. S3. Solvent replacement and aging: The hydrogel was transferred to tert-butyl alcohol and soaked for 12 h. The gel was then immersed in a 0.5 wt% epichlorohydrin / acetone solution and aged at 60°C for 24 h to enhance hydrogen bonding between the ANF and GO. S4. Vacuum drying: vacuum drying at 60°C for 24 h (pressure -0.1 MPa) to obtain an aerogel precursor. S5. Carbonization treatment: Place in a tubular furnace with an Ar flow rate of 50 sccm; first stage: 2°C / min to 200°C (hold for 30 min); second stage: 1°C / min to 400°C (hold for 60 min); third stage: 3°C / min to 800°C (hold for 120 min); naturally cool to room temperature to obtain the final product.

[0029] Comparative Example 4 (no magnetic component) S1. Precursor solution preparation: Accurately weigh 60.0 mg of graphene oxide (GO, thickness 0.8-1.2 nm) and 30.0 mg of aramid nanofibers (ANF, diameter 8-15 nm). Disperse the mixture in 20 mL of a 1:1 v / v DMF / NMP solvent using an ultrasonicator (500 W, 40 kHz) for 120 min. S2. Sol-gel process: The pH was adjusted dropwise to 9.50 ± 0.02 using 25% ammonia (analytical grade). The mixture was transferred to a 50 mL polytetrafluoroethylene-lined reactor and programmed to rise to 80.0 ± 0.5°C (2°C / min) for 12 h. After the reaction, the mixture was cooled to 25°C to obtain a black block of ANF / GO hydrogel, which was then washed with deionized water until neutral. S3. Replacement and aging: First replacement: immersion in ethanol / water (1:1 v / v), changing the solution every 4 hours, repeated three times; second replacement: immersion in anhydrous ethanol, changing the solution every 6 hours, repeated four times; third replacement: immersion in tert-butyl alcohol, changing the solution every 8 hours, repeated two times; the gel was immersed in a 0.5 wt% epichlorohydrin / acetone solution and aged at 60°C for 24 hours to enhance hydrogen bonding between ANF and GO. S4. Supercritical drying: The wet gel was placed in a 300 mL supercritical drying reactor and liquid CO2 was injected at 0.5 MPa / min to 7.50 MPa. After maintaining the temperature at 40°C for 2 h, the temperature was raised to 45°C at a rate of 0.5°C / min and maintained for 4 h. The pressure was then linearly reduced at 0.3 MPa / h to ambient pressure to obtain the ANF / GO aerogel precursor. S5. Carbonization treatment: Place in a tubular furnace with an Ar flow rate of 50 sccm; first stage: 2°C / min to 200°C (hold for 30 minutes); second stage: 1°C / min to 400°C (hold for 60 minutes); third stage: 3°C / min to 600°C (hold for 120 minutes); naturally cool to room temperature to obtain the final product, a multi-scale structured composite carbon aerogel absorber.

[0030] The above examples and comparative examples were tested, and the results are shown in Table 1 below. Table 1. Performance test results The microwave absorption performance of different carbon aerogels in Example 1, Comparative Example 1 and Comparative Example 4 was tested, and the results are as follows: Figure 2 As shown, the black curve is Comparative Example 1; the red curve is Comparative Example 4; and the blue curve is Example 1. Comparative Example 1 is a pure carbon aerogel without aramid nanofibers or CoFe2O4. It exhibits essentially no absorbing performance, with a minimum reflection loss of only -11 dB and a negligible absorption bandwidth (RL ≤ -10 dB). In Comparative Example 4, the pure carbon aerogel is modified with only aramid nanofibers. Both the minimum reflection loss and absorption bandwidth are significantly improved, reaching -23.8 dB and 3.7 GHz (12.7-9.0 GHz), respectively, demonstrating the positive effect of aramid nanofiber incorporation on absorption performance. In Example 1, the simultaneous introduction of aramid nanofibers and CoFe2O4 further significantly enhances absorption performance, with a minimum reflection loss of -56.8 dB and an absorption bandwidth of 5.3 GHz.

[0031] The results of the performance test comparison between the embodiment and the comparative example are as follows: 1. Density: The density of Example 1 is 9.8 mg / cm³, which is significantly lower than that of Comparative Example 2 (22.8 mg / cm³) and Comparative Example 3 (18.9 mg / cm³), indicating that the supercritical drying process of the present invention plays a vital role in maintaining the porous structure and lightweight of the material.

[0032] 2. Porosity: The porosity of the embodiment is as high as over 95% and has excellent electromagnetic wave absorption capacity, indicating that high porosity helps to improve the material's absorption performance, and the use of multi-scale structural design and supercritical drying process has a significant effect on improving and maintaining the high porosity of the material.

[0033] 3. Compressive Strength: The compressive strength of Example 2 was higher than that of Example 1, and the high-pressure strength of the Example was significantly higher than that of the Comparative Example, demonstrating that the introduction of aramid nanofibers significantly enhances the mechanical strength of the carbon aerogel. Furthermore, the supercritical drying and gradient carbonization processes are also important factors in achieving the aerogel's excellent mechanical properties. Combined with the Examples and Comparative Examples, the material of the present invention exhibits excellent mechanical properties while maintaining a high porosity.

[0034] 4. Elastic Recovery: The elastic recovery of the Example exceeds 85%, a significant improvement compared to Comparative Example 1 (52.1%), demonstrating that the introduction of aramid nanofibers significantly improves the toughness of the carbon aerogel. The resilience of Comparative Examples 2 and 3 is lower than that of Comparative Example 1, indicating that the supercritical drying process is also a key factor in achieving the high resilience of the aerogel. Combined, the Examples and Comparative Examples demonstrate that the material of the present invention can quickly recover to its original shape after being subjected to external forces, maintaining long-term stability.

[0035] 5. Absorption bandwidth and minimum reflection loss: The absorption bandwidth of Example 3 is higher than that of Examples 1 and 2, and the minimum reflection loss is lower than that of Examples 1 and 2, indicating that increasing the content of the magnetic component CoFe2O4 helps to expand the absorption bandwidth of the material and reduce the reflection loss; while the absorption bandwidths of Comparative Examples 1, 2, and 3 are much smaller than those of the Examples, indicating that the high porosity and the integrity of the aerogel skeleton structure have a significant impact on the absorption bandwidth. It can be further seen that the supercritical drying process, gradient solvent replacement process, and gradient carbonization process have a significant impact on the aerogel skeleton structure and porosity, and none of them can be dispensable. The material prepared by the optimized process can achieve good impedance matching and broadband electromagnetic absorption.

[0036] In summary, the three-dimensional composite carbon aerogel absorber of the present invention, as demonstrated in Example 2, exhibits extremely low density, excellent porosity, compressive strength, and elastic recovery, as well as an ideal absorption bandwidth and minimal reflection loss, demonstrating its superior performance in the field of electromagnetic protection. These improvements are attributed to the synergistic effects of zero-dimensional, one-dimensional, and two-dimensional nanomaterials, a multi-scale structural optimization strategy, a gradient solvent exchange process, a supercritical drying process, and a gradient carbonization process.

[0037] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A multi-scale structured composite carbon aerogel absorbing material, characterized by: The aerogel absorbing material comprises a three-dimensional skeleton, functional components and a conductive network.

2. The multi-scale structured composite carbon aerogel absorbing material according to claim 1, characterized in that: The three-dimensional skeleton is a hierarchical porous structure formed by cross-linking two-dimensional graphene oxide and one-dimensional aramid nanofibers through hydrogen bonds.

3. The multi-scale structured composite carbon aerogel absorbing material according to claim 2, characterized in that: The two-dimensional graphene oxide has a thickness of 0.8-1.2 nm and a specific surface area of ​​≥800 m 2 / g, the one-dimensional aramid nanofiber has a diameter of 8-15 nm and a length of 20-50 μm, and the pore size of the porous structure is 50 nm-5 μm.

4. The multi-scale structured composite carbon aerogel absorbing material according to claim 1, characterized in that: The functional component is zero-dimensional CoFe2O4 nanoparticles uniformly dispersed on the three-dimensional skeleton through in-situ growth.

5. The multi-scale structured composite carbon aerogel absorbing material according to claim 4, characterized in that: The particle size of the zero-dimensional CoFe2O4 nanoparticles is 20-50 nm, and the mass fraction is 15-30%.

6. The multi-scale structured composite carbon aerogel absorbing material according to claim 1, characterized in that: The conductive network is a sp² / sp³ hybrid carbon matrix formed by high-temperature carbonization of the three-dimensional skeleton and functional components, with an electrical conductivity of 10 -2 ~10 2 S / m.

7. The method for preparing a multi-scale structured composite carbon aerogel absorbing material according to claim 1, characterized in that: The specific steps of the preparation method are as follows: S1. Preparation of precursor solution: Graphene oxide and aramid nanofibers were dissolved in a DMF / NMP mixture according to the appropriate ratio and ultrasonically dispersed for 2 h to form a uniform dispersion. A mixed solution of CoCl2·6H2O and FeCl3·6H2O was added to the dispersion and magnetically stirred for 60 min to allow the metal ions to fully adsorb onto the surfaces of the graphene oxide and aramid nanofibers. S2. Sol-gel process: The pH of the precursor solution was adjusted to 9.5 ± 0.

2. The solution was then transferred to a polytetrafluoroethylene reactor and heated at a rate of 2°C / min, holding at 80°C, for 12 h. After the reaction, the ANF / GO@CoFe2O4 hydrogel was prepared. S3. Replacement and aging: A gradient replacement process was used. The first replacement was performed with an ethanol / water mixture for 4 hours, repeated three times. The second replacement was performed with anhydrous ethanol for 6 hours, repeated four times. The third replacement was performed with tert-butyl alcohol for 8 hours, repeated two times. The replaced ANF / GO@CoFe2O4 hydrogel was immersed in a 0.5 wt% epichlorohydrin / acetone solution and aged at 60°C for 24 hours to enhance hydrogen bonding between the ANF and GO. S4. Supercritical drying: The aged ANF / GO@CoFe2O4 hydrogel was placed in an autoclave. Liquid CO2 was first injected at a rate of 0.5 MPa / min to a pressure of 7.5 MPa, and the pressure was allowed to stand for 12 h to complete solvent replacement. Subsequently, supercritical conversion was initiated, and the temperature was maintained at 40°C for 2 h. The temperature was then raised to 45°C at a rate of 0.5°C / min, maintaining the pressure at 7.5 MPa ± 0.05 for 4 h. Finally, the pressure was linearly reduced at 0.3 MPa / h to ambient pressure to obtain the ANF / GO@CoFe2O4 aerogel precursor. S5. Carbonization: The ANF / GO@CoFe2O4 aerogel precursor was treated by temperature-programmed carbonization. In the first stage, the temperature was increased from room temperature to 200°C at a rate of 2°C / min under an Ar atmosphere. In the second stage, the temperature was increased from 200°C to 400°C at a rate of 1°C / min under an Ar atmosphere. In the third stage, the temperature was increased from 400°C to 600°C at a rate of 3°C / min under an Ar atmosphere. In the fourth stage, the temperature was maintained at 600°C for 2 h. In the fifth stage, the temperature is naturally cooled to room temperature to prepare a multi-scale structure composite carbon aerogel absorbing material.

8. The multi-scale structured composite carbon aerogel absorbing material according to claim 7, characterized in that: The graphene oxide and aramid nanofibers in S1 are dissolved in a DMF / NMP mixed solution at a mass ratio of 3:1 to 1:1, the volume ratio of the DMF / NMP mixed solution is 1:1, the ultrasonic power is 500W, the frequency is 40kHz, and a uniform dispersion is formed. The solid content of the dispersion is 2wt% to 8wt%. A mixed solution of CoCl2·6H2O and FeCl3·6H2O is added to the dispersion. Co 2+ with Fe 3+ The molar ratio is 1:

2.

9. The multi-scale structured composite carbon aerogel absorbing material according to claim 7, characterized in that: In S2, 25% ammonia water is added dropwise to the precursor solution to adjust the pH to 9.5±0.

2.

10. The multi-scale structured composite carbon aerogel absorbing material according to claim 7, characterized in that: In the first replacement in S3, the solvent is an ethanol / water mixed solution, and the volume ratio of ethanol to water is 1:1.

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