Carbon aerogel / cofe alloy / co3o4 / carbon nanotube composite material and preparation method and application thereof

Abstract

This invention relates to the field of electromagnetic wave absorption technology, specifically to a carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite material, its preparation method, and its application. In this invention, an intermediate formed by cross-linking CoFe2O4, aramid nanofiber colloid, and chitosan is reduced in a hydrogen atmosphere. This reduces the CoFe2O4 inside the aerogel to Co3O4 and CoFe alloy. Subsequently, C2H2 and hydrogen are introduced, and the CoFe alloy catalyzes the reaction of C2H2 with CoFe2O4 in the aerogel to form carbon nanotubes, ultimately forming a carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite material. This composite material uses a carbon aerogel formed by the carbonization of a three-dimensional aerogel (formed by cross-linking chitosan and aramid nanofibers) as its matrix, internally loaded with CoFe alloy and Co3O4, and surface-modified with carbon nanotubes. The carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite material provided by this invention exhibits both excellent thermal insulation and wave absorption properties.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic wave absorption technology, specifically to a carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite material, its preparation method, and its application. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Currently, the development of thermal insulation / electromagnetic protection materials mostly involves selecting thermal insulation materials (organic polymer foam, aerogel, metal oxide ceramics) and wave-absorbing materials (magnetic coatings, carbon fiber plates, inert metamaterials, resin wave-absorbing plates) and then performing multi-layer composites through high-temperature welding, pressing, and curing to achieve a material with good thermal insulation and electromagnetic wave absorption properties. Related reports indicate that materials prepared using this method possess both thermal insulation and wave-absorbing functions and have been applied in scenarios such as low-altitude missiles and supersonic aircraft. However, this method merely involves the simple stacking and composite of two mature single-function materials, rather than achieving dual-function superposition through a single material. It only balances the thermal insulation and wave-absorbing performance indicators by adjusting the thickness ratio of the two substrates, failing to simultaneously improve the material's thermal insulation and wave-absorbing performance. Furthermore, most current thermal insulation / wave-absorbing materials are used in high-precision equipment, resulting in high manufacturing costs, complex processing techniques, and low production efficiency, hindering widespread adoption. Summary of the Invention

[0004] To overcome the above problems, this invention provides a carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite material, its preparation method, and its applications. The composite material provided by this invention possesses both excellent thermal insulation and wave absorption properties. Adding carbon nanotubes, magnetic CoFe2O4, and CoFe alloy to the composite aerogel effectively constructs a magnetic-dielectric synergistic effect, improves impedance matching, and enhances the absorption of incident electromagnetic waves. Simultaneously, the porous framework of the carbon aerogel effectively suppresses heat conduction and convection. The added carbon nanotubes and CoFe alloy Co3O4 nanoparticles increase interfacial thermal resistance, enhance phonon scattering, and reflect infrared radiation, synergistically improving thermal insulation performance.

[0005] To achieve the above technical objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite material, which has carbon aerogel as the matrix, CoFe alloy and Co3O4 loaded inside, and carbon nanotubes modified on the surface. Among them, carbon aerogel is obtained by carbonization of three-dimensional aerogel formed by cross-linking chitosan and aramid nanofibers.

[0006] A second aspect of the present invention provides a method for preparing the carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite material described in the first aspect, comprising the following steps: CoFe2O4, aramid nanofiber colloid and chitosan were dispersed in water, mixed evenly, and then a catalyst was added for cross-linking. The mixture was then freeze-dried to obtain an intermediate. The intermediate was subjected to a first heat treatment in a reducing gas atmosphere to obtain the precursor; The precursor was subjected to a second heat treatment in an atmosphere of gaseous carbon source and reducing gas to obtain the carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite material.

[0007] In one or more embodiments, the preparation method of CoFe2O4 includes the following steps: Cobalt source, iron source and urea are dispersed in water, mixed evenly and then subjected to hydrothermal reaction to obtain CoFe2O4.

[0008] Preferably, the cobalt source is cobalt nitrate; the iron source is ferric nitrate. More preferably, the molar ratio of cobalt source, iron source and urea is (1~2):(2~4):(4~8); More preferably, the concentration of the cobalt source in water is 0.01~0.04 mol / L, more preferably 0.02 mol / L.

[0009] Preferably, the hydrothermal reaction temperature is 160~200℃, more preferably 170~190℃, and the hydrothermal reaction time is 10~14 h, more preferably 12 h.

[0010] In one or more embodiments, the method for preparing aramid nanofiber colloids includes: Aramid nanofibers were dispersed in a dimethyl sulfoxide solution of potassium hydroxide and mixed evenly to obtain an aramid nanofiber / dimethyl sulfoxide mixed solution. A aramid nanofiber / dimethyl sulfoxide mixed solution was dispersed in water to obtain aramid nanofiber colloid.

[0011] Preferably, in the potassium hydroxide dimethyl sulfoxide solution, the concentration of potassium hydroxide is 20~25 g / L.

[0012] Preferably, the mass ratio of aramid nanofibers to potassium hydroxide is (2.8~3.2):4, more preferably 3:4.

[0013] Preferably, the aramid nanofibers are dispersed in a dimethyl sulfoxide solution of potassium hydroxide and mixed evenly by stirring at a speed of 700-900 rpm for 5-7 days.

[0014] Preferably, the volume ratio of the aramid nanofiber / dimethyl sulfoxide mixed solution to water is (0.8~1.2):2, more preferably 1:2.

[0015] In one or more embodiments, the mass ratio of aramid nanofiber colloid, chitosan and CoFe2O4 is 2:0.5:(0.05~0.2).

[0016] In one or more embodiments, the mass ratio of aramid nanofiber colloid to water is 1:(9~12).

[0017] In one or more embodiments, the reducing gas includes hydrogen.

[0018] In one or more embodiments, the temperature of the first heat treatment is 500-700°C.

[0019] In one or more embodiments, the gaseous carbon source includes C2H2; Preferably, the flow rate ratio of C2H2 to hydrogen is (0.8~1.2):1, and more preferably 1:1.

[0020] In one or more embodiments, the temperature of the second heat treatment is 550-750°C, preferably 570-730°C, and more preferably 600-700°C; the time of the second heat treatment is 20-40 min, preferably 25-35 min, and more preferably 30 min.

[0021] A third aspect of the present invention provides the application of the carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite material described in the first aspect or the carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite material prepared by the preparation method described in the second aspect in the preparation of electromagnetic wave absorbers.

[0022] A fourth aspect of the present invention provides an electromagnetic wave absorber comprising the carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite material described in the first aspect or the carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite material prepared by the preparation method described in the second aspect, and paraffin wax.

[0023] In one or more embodiments, the mass fraction of the carbon aerogel / CoFe alloy / CoFe2O4 / carbon nanotube composite material in the electromagnetic wave absorber is 16~22 wt.%, preferably 19 wt.%.

[0024] The beneficial effects of this invention are as follows: In this invention, an intermediate formed by cross-linking CoFe2O4, aramid nanofiber colloid, and chitosan is reduced under a hydrogen atmosphere. This reduces the CoFe2O4 inside the aerogel to Co3O4 and a CoFe alloy. Subsequently, C2H2 and hydrogen are introduced, and the CoFe alloy catalyzes the reaction of C2H2 with CoFe2O4 in the aerogel to form carbon nanotubes. This ultimately forms a carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite material. The matrix is ​​a carbon aerogel formed by the carbonization of a three-dimensional aerogel formed by the cross-linking of chitosan and aramid nanofibers, internally loaded with CoFe alloy and Co3O4, and surface-modified with carbon nanotubes. The carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite material provided by this invention exhibits excellent thermal insulation and wave absorption properties. Adding carbon nanotubes and magnetic CoFe2O4 and CoFe alloy to the composite aerogel effectively constructs a magnetic-dielectric synergistic effect, improves impedance matching, and enhances the absorption of incident electromagnetic waves. Meanwhile, the porous framework of carbon aerogel effectively inhibits heat conduction and convection; the added carbon nanotubes and CoFe alloy / Co3O4 nanoparticles increase interfacial thermal resistance, enhance phonon scattering, and reflect infrared radiation, thus synergistically improving thermal insulation performance. Attached Figure Description

[0025] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0026] Figure 1 Scanning electron microscope image of the carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite material obtained in Example 1; Figure 2 Scanning electron microscope image of the carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite material obtained in Example 2; Figure 3 Scanning electron microscope image of the carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite material obtained in Example 3; Figure 4 The images show the Raman spectra of the carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite materials prepared in Examples 1-3. Figure 5 X-ray diffraction patterns of the carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite materials prepared in Examples 1-3; Figure 6The images show TEM images of the carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite material prepared in Example 2, where (a) is the heterogeneous interface formed by graphite carbon encapsulating metal, (b) and (c) are the grown bamboo-like carbon nanotubes, and (d) and (e) are the heterogeneous interfaces formed by graphite carbon encapsulating metal. Figure 7 The electromagnetic wave absorption performance diagrams of the carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite materials prepared in Examples 1, 2 and 3 are shown. Among them, (a), (d) and (g) are the three-dimensional reflection loss diagrams of the carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite materials prepared in Examples 1, 2 and 3, respectively; (b), (e) and (h) are the two-dimensional effective absorption bandwidth diagrams of the carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite materials prepared in Examples 1, 2 and 3, respectively; and (c), (f) and (i) are the impedance matching diagrams of the carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite materials prepared in Examples 1, 2 and 3, respectively. Figure 8 The images show the thermal insulation performance and infrared stealth images of the carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite materials prepared in Examples 1, 2, and 3. (a) shows infrared images of the carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite materials prepared in Examples 1, 2, and 3 placed on a 150°C heating stage at 0, 15, and 30 min. (b) shows the temperature-time curves of the carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite materials prepared in Examples 1, 2, and 3 placed on a 150°C heating stage. (c) shows the temperature-time curve of the carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite material prepared in Example 2 placed on a 100°C heating stage. (d) shows the temperature-time curve of the carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite material prepared in Example 2 placed on a 50°C heating stage. (e) shows the thermal insulation mechanism of the aerogel. (f) shows the infrared stealth image of the aerogel. Detailed Implementation

[0027] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration 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.

[0028] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0029] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0030] Example 1 Preparation of carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite materials: (1) 1 mmol nickel nitrate, 2 mmol cobalt nitrate and 8 mmol urea were placed in 70 mL of deionized water and mixed evenly to obtain a mixed solution; the mixed solution was transferred to polytetrafluoroethylene for hydrothermal reaction and kept at 180 °C for 12 h to obtain CoFe2O4.

[0031] (2) 2000 mg of potassium hydroxide was placed in 90 mL of dimethyl sulfoxide solution and mixed evenly to obtain a dimethyl sulfoxide solution of potassium hydroxide; then 1500 mg of Kevlar fiber was added and magnetically stirred at a speed of 800 rpm for 6 days to obtain a mixed solution of aramid nanofiber / dimethyl sulfoxide. Mix 500 mL of aramid nanofiber / dimethyl sulfoxide mixed solution with 1000 mL of deionized water to form aramid nanofiber colloid.

[0032] (3) Mix 2 g of aramid nanofiber colloid, 0.5 g of chitosan and 0.05 g of CoFe2O4 in 25 mL of deionized water until homogeneous; add 0.05 mL of acetic acid to carry out the gelation reaction; The gel copper template was then directionally frozen at -70°C for 12 h, followed by vacuum drying for 48 h to obtain the intermediate. (4) The intermediate was placed in a quartz boat and pushed into a tube furnace. N2 was introduced to maintain an inert atmosphere inside the tube. The temperature was increased to 550°C at a heating rate of 5°C / min. Then, H2 was introduced at a rate of 0.3 L / min for reduction. When the temperature rose to 650°C, C2H2 and H2 were introduced at a flow rate ratio of 1:1 and kept at the temperature for 30 min for reduction and chemical vapor deposition growth of carbon nanotubes. Then, the mixture was cooled to room temperature under N2 atmosphere to obtain carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite material.

[0033] Figure 1 This is a scanning electron microscope image of the carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite material obtained in this embodiment.

[0034] Example 2 Preparation of carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite materials: (1) 1 mmol nickel nitrate, 2 mmol cobalt nitrate and 8 mmol urea were placed in 70 mL of deionized water and mixed evenly to obtain a mixed solution; the mixed solution was transferred to polytetrafluoroethylene for hydrothermal reaction and kept at 180 °C for 12 h to obtain CoFe2O4.

[0035] (2) 2000 mg of potassium hydroxide was placed in 90 mL of dimethyl sulfoxide solution and mixed evenly to obtain a dimethyl sulfoxide solution of potassium hydroxide; then 1500 mg of Kevlar fiber was added and magnetically stirred at a speed of 800 rpm for 6 days to obtain a mixed solution of aramid nanofiber / dimethyl sulfoxide. Mix 500 mL of aramid nanofiber / dimethyl sulfoxide mixed solution with 1000 mL of deionized water to form aramid nanofiber colloid.

[0036] (3) Mix 2 g of aramid nanofiber colloid, 0.5 g of chitosan and 0.1 g of CoFe2O4 in 25 mL of deionized water until homogeneous; add 0.05 mL of acetic acid to carry out the gelation reaction; The gel copper template was then directionally frozen at -70°C for 12 h, followed by vacuum drying for 48 h to obtain the intermediate. (4) The intermediate was placed in a quartz boat and pushed into a tube furnace. N2 was introduced to maintain an inert atmosphere inside the tube. The temperature was increased to 550°C at a rate of 5°C / min. Then, H2 was introduced at a rate of 0.3L / min for reduction. When the temperature was increased to 650°C, C2H2 and H2 were introduced at a flow rate ratio of 1:1 and kept at the temperature for 30min for reduction and chemical vapor deposition growth of carbon nanotubes. Then, the carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite material was obtained under N2 atmosphere.

[0037] Figure 2 This is a scanning electron microscope image of the carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite material obtained in this embodiment.

[0038] Example 3 Preparation of carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite materials: (1) 1 mmol nickel nitrate, 2 mmol cobalt nitrate and 8 mmol urea were placed in 70 mL of deionized water and mixed evenly to obtain a mixed solution; the mixed solution was transferred to polytetrafluoroethylene for hydrothermal reaction and kept at 180 °C for 12 h to obtain CoFe2O4.

[0039] (2) 2000 mg of potassium hydroxide was placed in 90 mL of dimethyl sulfoxide solution and mixed evenly to obtain a dimethyl sulfoxide solution of potassium hydroxide; then 1500 mg of Kevlar fiber was added and magnetically stirred at a speed of 800 rpm for 6 days to obtain a mixed solution of aramid nanofiber / dimethyl sulfoxide. Mix 500 mL of aramid nanofiber / dimethyl sulfoxide mixed solution with 1000 mL of deionized water to form aramid nanofiber colloid.

[0040] (3) Mix 2 g of aramid nanofiber colloid, 0.5 g of chitosan and 0.15 g of CoFe2O4 in 25 mL of deionized water until homogeneous; add 0.05 mL of acetic acid to carry out the gelation reaction; The gel copper template was then directionally frozen at -70°C for 12 h, followed by vacuum drying for 48 h to obtain the intermediate. (4) The intermediate was placed in a quartz boat and pushed into a tube furnace. N2 was introduced to maintain an inert atmosphere inside the tube. The temperature was increased to 550°C at a rate of 5°C / min. Then, H2 was introduced at a rate of 0.3L / min for reduction. When the temperature was increased to 650°C, C2H2 and H2 were introduced at a flow rate ratio of 1:1 and kept at the temperature for 30min for reduction and chemical vapor deposition growth of carbon nanotubes. Then, the carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite material was obtained under N2 atmosphere.

[0041] Figure 3 This is a scanning electron microscope image of the carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite material obtained in this embodiment.

[0042] Figure 4 Raman spectra of the carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite materials prepared in Examples 1-3. Figure 1 As can be seen from the data, the carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite material at 1350 cm⁻¹... -1 Nearby and 1580 cm -1 Two distinct peaks are observed nearby, corresponding to the D peak representing graphite defects / lattice distortion and the graphite sp peak. 2The G peak of carbon. A higher intensity ratio (R = ID / IG) of the D peak to the G peak in the Raman curve indicates a greater content of defects and amorphous carbon in the sample. The R value of pure aramid nanofiber carbon aerogel is 0.91. The R values ​​of the carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite materials are all lower than those of the pure aramid nanofiber carbon aerogel, with Example 2 < Example 3 < Example 1. This is because when the CoFe2O4 loading is low, the content of the metallic FeCo catalyst generated during hydrogen reduction is less. During chemical vapor deposition, the acetylene cracking rate exceeds the CoFe catalytic rate, leading to C atoms encapsulating the metal and causing catalyst poisoning, ultimately resulting in a large accumulation of amorphous carbon. Therefore, Example 1 has the highest R value. As the CoFe2O4 loading increases, the corresponding CoFe metal content increases, and the acetylene cracking rate and the CoFe catalytic rate reach a dynamic equilibrium. A large number of C atoms are deposited to form CNTs and CNFs, while the content of amorphous carbon decreases to a minimum. Therefore, the R value of Example 2 is even lower. As the CoFe₂O₄ loading continued to increase, the excess CoFe₂O₄ decomposed at high temperatures, leading to the aggregation of CoFe metal nanoparticles and reducing the catalytic active area. Large-particle catalysts could not effectively promote the ordered arrangement of C atoms; instead, they caused disordered stacking of the carbon layer, resulting in an increase in the R value in Example 3.

[0043] Figure 5 The images show X-ray diffraction patterns of the carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite materials prepared in Examples 1-3. Figure 5 As can be seen, the carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite material exhibits obvious broad diffraction peaks around 2θ≈25.3°, corresponding to the (002) crystal plane of graphitic carbon, which confirms the presence of graphite structure in the sample. Furthermore, the diffraction peaks at 30.0°, 35.5°, 37.3°, 43.3°, and 62.8° correspond to the (220), (311), (222), (400), and (440) crystal planes of CoFe2O4, respectively. The diffraction peaks at 44.6°, 65.0°, and 82.3° correspond to the (110), (200), and (211) crystal planes of CoFe. The diffraction peak at 31.2° belongs to the (220) crystal plane of Co3O4. The presence of CoFe and Co3O4 proves that during the CCVD process, under the action of hydrogen, some CoFe2O4 is reduced to Co3O4 and iron-rich phase. As the reaction proceeds, Fe reacts with the reduced Co to form CoFe alloy.

[0044] Figure 6 This is a TEM image of the carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite material prepared in Example 2. Figure 6Image (a) shows metal particles encapsulated by layers of graphite carbon, forming rich heterogeneous interfaces. (Magnified) Figure 6 The interplanar spacings of 0.177 nm and 0.199 nm in (a1) and (a2) correspond to the (220) crystal plane of Co3O4 and the (311) crystal plane of CoFe2O4, respectively. After inverse fast Fourier transform (IFFT), obvious lattice dislocations can be seen. Figure 6 Image (b) shows the microstructure of the grown BCNTs, revealing graphite sheets forming bamboo-like nodes at locations perpendicular to the tube diameter. Measurements showed that the outer diameter of the CNTs was approximately 45.28 nm, and the inner diameter was approximately 21.19 nm. Figure 6 Image (c) more clearly shows the bamboo-like structure and graphite sheet structure of CNTs. The graphite layer of BCNTs is not completely parallel to the tube diameter direction, exposing a large number of polarization sites, which is conducive to the formation of polarization loss. The interplanar spacing of graphitic carbon (002) is 0.362 nm, which is slightly larger than the standard 0.340 nm, indicating that there are some defects in the structure. Figure 6 In (d), the 0.198 nm interplanar spacing corresponds to the (311) crystal plane of CoFe2O4. A rich heterogeneous interface is formed between CoFe2O4 and the graphite carbon layer, which is conducive to generating a large amount of interfacial polarization loss. Figure 6 The (400) crystal plane of Co3O4 shown in (e) has a plane spacing of 0.241 nm. The corresponding IFFT of the lattice is magnified. Figure 6 As shown in (e1) and (e2), obvious lattice dislocations can be found, and GPA results indicate that there is significant stress concentration in the dislocation region. The 0.250 nm interplanar spacing corresponds to the (110) crystal plane of CoFe, and obvious dislocations are also present in its inverse fast Fourier transform image.

[0045] The hysteresis loop and coercivity data of the carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite materials prepared in Examples 1-3 are shown in Table 1. As can be seen from Table 1, the presence of metals and metal oxides enables the composite materials to exhibit good ferromagnetism under external magnetic field excitation. Meanwhile, Example 3 exhibits the highest saturation magnetization value, corresponding to the highest total magnetic material content, indicating the greatest magnetic loss, which is beneficial for improving the dissipation capability of electromagnetic waves.

[0046] Table 1. Hysteresis loop and coercivity data of carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite materials

[0047] Example 4 The carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite materials prepared in Examples 1-3 were mixed with paraffin to obtain electromagnetic wave absorbers, which were named Example 1, Example 2 and Example 3, respectively; wherein the concentration of the carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite material was 19 wt.% in each case.

[0048] The electromagnetic wave absorption performance of Examples 1, 2, and 3 is shown in Table 2. A comparative analysis was conducted by calculating their minimum reflection loss (RLmin), effective absorption bandwidth (EAB), corresponding thickness (t), specific minimum reflection loss (SRL = |RLmin|÷ (Filling amounts × t)), and specific effective absorption bandwidth (SEAB = EAB ÷ (Filling amounts × t)). The minimum reflection loss of the pure aramid nanofiber carbon aerogel was -1.33 dB (3 mm), with no effective absorption bandwidth. All examples maintained an effective absorption bandwidth consistently above 5.30 GHz under thin thickness and low filler content, and Example 2 also exhibited excellent absorption capability, verifying its broad application value. This is inseparable from the establishment of the three-dimensional network structure and the dual loss capability brought about by the magnetic-dielectric synergistic effect.

[0049] Table 2 Electromagnetic wave absorption performance of Examples 1, 2 and 3

[0050] Figure 7 The figures show the electromagnetic wave absorption performance of Examples 1, 2, and 3. Example 2 exhibits significantly stronger absorption intensity than Examples 1 and 3. Specifically: Example 1 shows an RLmin value of -16.31 dB at 2.00 mm, with its EAB value increasing to 5.30 GHz. Example 2 demonstrates superior electromagnetic wave absorption performance, achieving an RLmin value of -67.76 dB and an EAB value of 5.50 GHz at a matching thickness of only 1.85 mm. Example 3 shows an RLmin value of -24.36 dB at 5.00 mm, while its EAB value reaches 6.20 GHz at 2.42 mm. The appearance of a double absorption peak in Example 2 indicates that heteroatom doping and the presence of defects can achieve multi-band electromagnetic wave absorption. All embodiments exhibit typical strip-shaped matching regions, but the matching characteristics differ significantly: the matching strips in Embodiments 1 and 3 are significantly shrunken and their width increases, showing improved matching effects. Notably, Embodiment 2 forms a continuous and wide impedance matching region throughout the entire test frequency band, exhibiting optimal impedance matching characteristics.

[0051] The minimum reflection loss of pure aramid nanofiber carbon aerogel is -1.33dB, and there is no effective absorption bandwidth when the thickness is 3 mm.

[0052] Example 5 The thermal insulation properties of the aerogel were systematically evaluated. Samples from Examples 1, 2, and 3 were placed on a heating stage at 150°C. Figure 8 (a) and the temperature of the central region of the sample was measured using an infrared thermal imager at 0, 15 and 30 minutes. Figure 8 Figure (b) shows the time-temperature curves of the samples, in which Example 2 exhibits the best thermal insulation performance, with its aerogel surface temperature stabilizing at approximately 58°C. Figure 8 Tables (c) and (d) further illustrate the time-temperature profiles of the aerogel of Example 2 on heating platforms set at 100°C and 50°C, respectively. The abundant porous structure within the aerogel is key to its superior thermal insulation performance. This structure effectively hinders heat conduction and reduces the material's thermal conductivity, providing a material basis for achieving infrared stealth capabilities. Figure 8 (e)). For example Figure 8 As shown in (f), the arm appears light yellow, and its infrared radiation intensity is significantly higher than that of the environment (purple). After the aerogel is placed on the arm, the area covered by the aerogel blends well with the environment.

[0053] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite material, characterized in that, It uses carbon aerogel as the matrix, with CoFe alloy and Co3O4 loaded inside, and carbon nanotubes modified on the surface. Among them, carbon aerogel is obtained by carbonization of three-dimensional aerogel formed by cross-linking chitosan and aramid nanofibers.

2. The preparation method of the carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite material according to claim 1, characterized in that, Includes the following steps: CoFe2O4, aramid nanofiber colloid and chitosan were dispersed in water, mixed evenly, and then a catalyst was added for cross-linking. The mixture was then freeze-dried to obtain an intermediate. The intermediate was subjected to a first heat treatment in a reducing gas atmosphere to obtain the precursor; The precursor was subjected to a second heat treatment in an atmosphere of gaseous carbon source and reducing gas to obtain the carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite material.

3. The preparation method according to claim 2, characterized in that, The preparation method of CoFe2O4 includes the following steps: Cobalt source, iron source and urea are dispersed in water, mixed evenly and then subjected to hydrothermal reaction to obtain CoFe2O4.

4. The preparation method according to claim 3, characterized in that, The cobalt source is cobalt nitrate; the iron source is ferric nitrate; preferably, the molar ratio of cobalt source, iron source and urea is (1~2):(2~4):(4~8); Preferably, the concentration of the cobalt source in water is 0.01~0.04 mol / L, more preferably 0.02 mol / L; Alternatively, the hydrothermal reaction temperature is 160~200℃, preferably 170~190℃, and the hydrothermal reaction time is 10~14 h, preferably 12 h.

5. The preparation method according to claim 2, characterized in that, Methods for preparing aramid nanofiber colloids include: Aramid nanofibers were dispersed in a dimethyl sulfoxide solution of potassium hydroxide and mixed evenly to obtain an aramid nanofiber / dimethyl sulfoxide mixed solution. A aramid nanofiber / dimethyl sulfoxide mixed solution was dispersed in water to obtain aramid nanofiber colloid.

6. The preparation method according to claim 5, characterized in that, Preferably, in the potassium hydroxide dimethyl sulfoxide solution, the concentration of potassium hydroxide is 20-25 g / L; Alternatively, the mass ratio of aramid nanofibers to potassium hydroxide is (2.8~3.2):4, preferably 3:4; Alternatively, aramid nanofibers can be dispersed in a potassium hydroxide dimethyl sulfoxide solution and mixed evenly by stirring at a speed of 700-900 rpm for 5-7 days. The volume ratio of the aramid nanofiber / dimethyl sulfoxide mixed solution to water is (0.8~1.2):2, preferably 1:

2.

7. The preparation method according to claim 2, characterized in that, The mass ratio of aramid nanofiber colloid, chitosan, and CoFe2O4 is 2:0.5:(0.05~0.2). Alternatively, the mass ratio of aramid nanofiber colloid to water is 1:(9~12). Alternatively, reducing gases include hydrogen; Alternatively, the temperature for the first heat treatment is 500-700℃; Alternatively, the gaseous carbon source includes C2H2; preferably, the flow rate ratio of C2H2 to hydrogen is (0.8~1.2):1; Alternatively, the temperature of the second heat treatment is 550-750℃, preferably 570-730℃, and more preferably 600-700℃; the time of the second heat treatment is 20-40 min, preferably 25-35 min, and more preferably 30 min.

8. The application of the carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite material according to claim 1 or the carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite material prepared by the preparation method according to any one of claims 2 to 7 in the preparation of electromagnetic wave absorbers.

9. An electromagnetic wave absorber, characterized in that, The composite material includes the carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite material as described in claim 1 or the carbon aerogel / CoFe alloy / Co3O4 / carbon nanotube composite material prepared by the preparation method described in any one of claims 2 to 7 and paraffin wax.

10. The electromagnetic wave absorber as described in claim 9, characterized in that, In the electromagnetic wave absorber, the mass fraction of the carbon aerogel / CoFe alloy / CoFe2O4 / carbon nanotube composite material is 16~22 wt.%, preferably 19 wt.%.

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