Preparation method of magnetic nitrogen-doped porous carbon aerogel wave-absorbing material

Abstract

The application relates to a preparation method of a magnetic nitrogen-doped porous carbon aerogel wave-absorbing material, which is prepared by the following steps: under the action of a scandium triflate catalyst, a COF hydrogel is obtained through an ultrasonic-assisted self-crosslinking reaction; a metal salt solution is in-situ immersed into the COF hydrogel; and the magnetic nitrogen-doped porous carbon aerogel wave-absorbing material is prepared through freeze drying and external heat driving. The preparation process is simple, the reliability is high, the material has excellent stability, uniform particles, light weight and strong absorption capacity. The optimal reflection loss value of the magnetic nitrogen-doped porous carbon aerogel wave-absorbing material of the application is up to -63.8 dB at 2.09 mm RL min The application can reach -63.8 dB, and 10 wt.% of the aerogel material in a paraffin matrix can obtain a super-wide wave-absorbing bandwidth of 6.56 GHz, and the matching thickness is only 2.28 mm, which meets the requirements of ideal wave-absorbing materials on "thin, light, wide and strong", and has multi-scene applicability.

Description

Technical Field

[0001] This invention relates to a method for preparing a magnetic nitrogen-doped porous carbon aerogel microwave absorbing material, specifically belonging to the field of electromagnetic wave absorbing material technology. Background Technology

[0002] The rapid development of wireless technology has improved our quality of life, but the widespread use of wireless electronic devices has inevitably led to serious electromagnetic pollution, which is considered the fourth largest source of pollution after air, water, and noise pollution. Therefore, it is urgent to find feasible methods to solve the problem of electromagnetic pollution. Currently, aerogel materials, mainly graphene and biomass, are considered promising candidates for electromagnetic wave absorption due to their lightweight and porous properties. However, the preparation conditions for graphene aerogels are stringent and the process is complex, while the absorption performance of biomass aerogels is unstable; both are difficult to meet the needs of practical production.

[0003] Patent "A novel method for preparing three-dimensional porous biomass-derived carbon aerogel" (CN 117756093A): Using tofu as raw material, a three-dimensional porous biomass-derived carbon aerogel is obtained after heat treatment. Although this method is relatively simple, its microwave absorption performance is poor; when the matching thickness is 3.38 mm, the minimum reflection loss value (…) RL min The RL (Rapid Reduction) is -57.23 dB, and biomass materials often have unclear compositions and contain impurities, resulting in poor performance reproducibility and making it difficult to apply them in more complex and variable environments. Patent "A Nitrogen-Doped Graphene Aerogel Absorbing Material and Its Preparation Method" (CN 118062833A) first adds a nitrogen source to an aqueous solution of graphene oxide to prepare a nitrogen-doped graphene hydrogel. The nitrogen-doped graphene hydrogel is then dialyzed and freeze-dried to obtain the nitrogen-doped graphene aerogel absorbing material. This method requires the addition of a nitrogen source as a gelling agent, making it difficult to spontaneously form a hydrogel in situ. Furthermore, due to the lack of magnetic loss, when the coating thickness is 1.62 mm, the RL... min The absorption rate can only reach -28.3 dB. The patent "A Preparation Method of a Cobalt-Nickel / Graphite-Phase Carbon Nitride / Reduced Graphene Oxide Composite Aerogel Absorbing Material" (CN 116456707A) describes a method for preparing cobalt-nickel magnetic nanoparticles and graphite-phase carbon nitride using solvothermal and thermal polymerization methods, respectively. Then, a one-pot hydrothermal method is used to mix and react the cobalt-nickel magnetic nanoparticles, graphite-phase carbon nitride, and graphene oxide to obtain a hydrogel of the composite material. Finally, freeze-drying and thermal annealing are performed to obtain the cobalt-nickel / graphite-phase carbon nitride / reduced graphene oxide composite aerogel. This method is cumbersome and requires stringent conditions, making it difficult to meet the needs of industrial production and practical applications. Furthermore, the added magnetic particles cannot achieve good electromagnetic wave absorption due to agglomeration and other issues. Currently, the preparation methods and the stability of the absorption performance of aerogel absorbing materials require further improvement.

[0004] Compared with other traditional porous materials such as molecular sieves, porous polymers, and metal-organic frameworks (MOFs), emerging porous covalent organic frameworks (COFs) have the following characteristics: 1. COFs are connected by strong covalent bonds in an orderly manner, thus exhibiting good thermal and chemical stability; 2. They possess ultra-large specific surface area and adjustable pore channels, allowing for the construction of different network structures through different building blocks and connection methods; 3. Their composition and pore size are designable. However, most COF absorbing materials still suffer from problems such as cumbersome synthesis processes, high preparation costs, and environmental pollution during production, hindering the further widespread application of advanced absorbing materials. To fully utilize their structural advantages, this invention designs a COF-derived porous carbon aerogel with high specific surface area and low density, providing a simple, practical, and innovative method for preparing nitrogen-doped porous carbon aerogels.

[0005] It is worth noting that achieving broadband absorption in a single carbon material remains challenging. Therefore, introducing magnetic components into carbon materials to optimize impedance and broaden bandwidth is a forward-looking strategy. However, directly adding magnetic particles to the gel can lead to particle aggregation or deposition at the bottom of the gel, resulting in poor dispersion and hindering the formation of magnetic aerogels. Therefore, developing a simple and sustainable preparation method to achieve uniform dispersion of magnetic particles in aerogels, thereby obtaining high-performance, multifunctional magnetic porous carbon aerogels, remains a highly challenging task. Summary of the Invention

[0006] This invention addresses the problems of current microwave absorbing materials, such as high density, narrow effective absorption bandwidth, large thickness, and poor absorption intensity, by providing a simple method for fabricating nitrogen-doped porous carbon aerogel microwave absorbing materials derived from magnetic COF.

[0007] This invention discloses a method for preparing a magnetic nitrogen-doped porous carbon aerogel microwave absorbing material. The method involves obtaining a COF hydrogel through an ultrasound-assisted self-crosslinking reaction under the catalysis of scandium trifluoromethanesulfonate. A metal salt solution is then in-situ immersed in the COF hydrogel, followed by freeze-drying and external thermal drive to obtain the magnetic nitrogen-doped porous carbon aerogel microwave absorbing material. The specific steps are as follows:

[0008] Step 1: Terephthalaldehyde, 1,3,5-tris(4-aminophenyl)benzene and scandium trifluoromethanesulfonate (Sc(OTf)3) were added to N,N-dimethylformamide. After ultrasonic-assisted self-crosslinking reaction, the mixture was allowed to crystallize to form a COF gel. Then, the solvent was exchanged sequentially with N,N-dimethylformamide, acetone, ethanol, methanol and water to obtain a COF hydrogel.

[0009] Step 2: Add solutions of nickel chloride (II) hexahydrate and ferric chloride (III) hexahydrate to the COF hydrogel to allow metal ions to be in situ immersed in the hydrogel. Then freeze-dry overnight to obtain FeNi. 10 @COF aerogel;

[0010] Step 3: Calcine and pyrolyze the COF aerogel under a protective atmosphere to obtain FeNi. 10 @NCA aerogel, namely magnetic nitrogen-doped porous carbon aerogel microwave absorbing material.

[0011] In step 1, the ratio of terephthalaldehyde, 1,3,5-tris(4-aminophenyl)benzene, scandium trifluoromethanesulfonate, and N,N-dimethylformamide is 0.0134–0.0268 g: 0.0234–0.0468 g: 0.05–0.1 g: 4 mL, and the ultrasonic-assisted self-crosslinking reaction takes 5–10 minutes.

[0012] In step 2, the ratio of nickel chloride hexahydrate (II) to ferric chloride hexahydrate (III) is 0.0862~0.3457g : 0.0098~0.0393g.

[0013] In step 3, the protective gas is nitrogen or argon, the calcination pyrolysis temperature is 600~900℃, the holding time is 2~3 h, and the heating rate is 2~3 ℃ / min.

[0014] The beneficial effects of this invention are:

[0015] 1. Unique preparation method: This invention employs an ultrasound-assisted COF self-crosslinking reaction and an in-situ metal salt impregnation method to successfully design FeNi 10 This invention relates to an electromagnetically functionalized composite material composed of alloy nanoparticles and nitrogen-doped porous carbon aerogel (NCA). Under the catalysis of scandium trifluoromethanesulfonate catalyst, COF gel can be directly obtained within five minutes through a self-crosslinking reaction. After metal salt impregnation, metal ions are uniformly adsorbed within the porous channels of the COF hydrogel. Further freeze-drying and calcination pyrolysis yield an ultralight magnetic porous carbon aerogel. This invention features a simple and reliable preparation process, and the material exhibits excellent stability, uniform particle size, light weight, and strong absorption capacity.

[0016] 2. Excellent electromagnetic wave absorption capability: The FeNi of this invention... 10 @NCA aerogel material has the optimal reflection loss value at 2.09 mm ( RL minIt can reach -63.8 dB. Moreover, only 10 wt.% of aerogel material in the paraffin matrix can achieve an ultra-wide absorption bandwidth of 6.56 GHz, and the matching thickness is only 2.28 mm, which meets the requirements of "thin, light, wide and strong" for ideal absorbing materials. This has great potential for industrial production and application.

[0017] 3. Versatile Applicability: The multifunctional properties of these materials compensate for the limitations of single-application scenarios, and the multifunctionality of materials is also a future trend in metamaterial development. Aerogels possess excellent thermal insulation properties, superior radar stealth capabilities, and a wide absorption bandwidth. Therefore, nitrogen-doped porous carbon aerogels derived from magnetic COFs are suitable for practical applications. Attached Figure Description

[0018] Figure 1 X-ray diffraction patterns of magnetic nitrogen-doped porous carbon aerogel microwave absorbing materials prepared in Examples 1, 2, 3 and 4 of this invention;

[0019] Figure 2 Scanning electron microscopy image of the magnetic nitrogen-doped porous carbon aerogel absorbing material prepared in Example 3 of this invention;

[0020] Figure 3 Transmission electron microscope image of the magnetic nitrogen-doped porous carbon aerogel microwave absorbing material prepared in Example 3 of this invention;

[0021] Figure 4a The nitrogen adsorption-desorption isotherms of the magnetic nitrogen-doped porous carbon aerogel microwave absorbing materials prepared in Examples 1, 2, 3 and 4 of this invention;

[0022] Figure 4b Pore ​​size distribution curves of magnetic nitrogen-doped porous carbon aerogel microwave absorbing materials prepared in Examples 1, 2, 3 and 4 of this invention;

[0023] Figure 5 Vibrational sample magnetometer (VSM) images of the magnetic nitrogen-doped porous carbon aerogel absorbing materials prepared in Examples 1, 2, 3 and 4 of this invention;

[0024] Figure 6a Electromagnetic wave absorption diagram of the magnetic nitrogen-doped porous carbon aerogel absorbing material prepared in Example 1 of this invention;

[0025] Figure 6b Electromagnetic wave absorption diagram of the magnetic nitrogen-doped porous carbon aerogel absorbing material prepared in Example 2 of this invention;

[0026] Figure 6c Electromagnetic wave absorption diagram of the magnetic nitrogen-doped porous carbon aerogel absorbing material prepared in Example 3 of this invention;

[0027] Figure 6d Electromagnetic wave absorption diagram of the magnetic nitrogen-doped porous carbon aerogel absorbing material prepared in Example 4 of this invention;

[0028] Figure 7a Temperature graph of the magnetic nitrogen-doped porous carbon aerogel microwave absorbing material prepared in Example 3 of this invention at 0 minutes during thermal insulation testing;

[0029] Figure 7b Temperature graph of the magnetic nitrogen-doped porous carbon aerogel microwave absorbing material prepared in Example 3 of this invention during a 10-minute thermal insulation test;

[0030] Figure 7c Temperature graph of the magnetic nitrogen-doped porous carbon aerogel microwave absorbing material prepared in Example 3 of this invention during a 20-minute thermal insulation test;

[0031] Figure 7d Temperature graph of the magnetic nitrogen-doped porous carbon aerogel microwave absorbing material prepared in Example 3 of this invention during a 30-minute thermal insulation test;

[0032] Figure 7e Temperature graph of the magnetic nitrogen-doped porous carbon aerogel microwave absorbing material prepared in Example 3 of this invention during a 40-minute thermal insulation test;

[0033] Figure 7f Temperature graph of the magnetic nitrogen-doped porous carbon aerogel microwave absorbing material prepared in Example 3 of this invention during a 60-minute thermal insulation test. Detailed Implementation

[0034] Example 1

[0035] Step 1: In a glass bottle containing 4 mL of N,N-dimethylformamide, add 0.0268 g of terephthalaldehyde, 0.01 g of scandium trifluoromethanesulfonate, and 0.0468 g of 1,3,5-tris(4-aminophenyl)benzene in sequence. Then, sonicate the mixture until homogeneous. After sonication for 5 min, allow it to stand and crystallize to form a COF gel. The formed COF gel is then subjected to solvent exchange with N,N-dimethylformamide, acetone, ethanol, methanol, and water in sequence, with each solvent exchange being 2-3 times. The last solvent exchange is performed with water 4-5 times to obtain a COF hydrogel.

[0036] Step 2: Dissolve 0.0861 g of nickel chloride hexahydrate and 0.0098 g of ferric chloride hexahydrate in 4 mL of deionized water. Add the above salt solution of nickel chloride hexahydrate and ferric chloride hexahydrate to the COF hydrogel from Step 1. The nickel and iron metal ions in the solution are adsorbed by the porous structure of the COF hydrogel. Let stand for 4–5 days until the solution becomes colorless. Then freeze-dry overnight to obtain FeNi. 10 @COF aerogel.

[0037] Step 3: Add FeNi 10 The COF aerogel was placed on a quartz boat and transferred into a tube furnace. It was then heated at 800°C under a nitrogen atmosphere for 2 hours, with a heating rate of 2°C / min. -1 FeNi was obtained by calcination and pyrolysis. 10 @NCA-1 aerogel, namely magnetic nitrogen-doped porous carbon aerogel microwave absorbing material.

[0038] Step 4: Place the petals on the prepared FeNi 10 @NCA-1 aerogel was heated with an alcohol lamp, and the changes in the petals were recorded using a mobile phone. After heating with an alcohol lamp for 0, 30, 60, and 120 seconds, there was no significant change in the shape of the petals, proving that the aerogel has good thermal insulation properties.

[0039] Step 5: Use CST electromagnetic field simulation software to simulate FeNi 10 The radar stealth performance of @NCA-1 aerogel was simulated, and its radar cross-section was calculated using the following formula:

[0040] ;

[0041] Step 6: The prepared FeNi 10 @NCA-1 aerogel material was made into rings by impregnating a substrate of molten paraffin. The density of the aerogel was calculated to give it a percentage of 10 wt.% of the total mass of the rings. The electromagnetic parameters of this material were measured using a vector network analyzer. Based on transmission line theory, the formula for calculating the reflection loss of electromagnetic waves by the material is as follows:

[0042] .

[0043] Example 2

[0044] Step 1: In a glass bottle containing 4 mL of N,N-dimethylformamide, add 0.0268 g of terephthalaldehyde, 0.01 g of scandium trifluoromethanesulfonate, and 0.0468 g of 1,3,5-tris(4-aminophenyl)benzene in sequence. Then, sonicate the mixture until homogeneous. After sonication for 5 min, allow it to stand and crystallize to form a COF gel. The formed gel is then subjected to solvent exchange with N,N-dimethylformamide, acetone, ethanol, methanol, and water in sequence, with each solvent exchange being 2-3 times. The last solvent exchange is performed with water 4-5 times to obtain the COF hydrogel.

[0045] Step 2: Dissolve 0.1728 g of nickel chloride hexahydrate and 0.0197 g of ferric chloride hexahydrate in 4 mL of deionized water. Add the above salt solution of nickel chloride hexahydrate and ferric chloride hexahydrate to the COF hydrogel from Step 1. The nickel and iron metal ions in the solution are adsorbed by the porous structure of the COF hydrogel. Let stand for 4–5 days until the solution becomes colorless. Then freeze-dry overnight to obtain FeNi. 10 @COF aerogel.

[0046] Step 3: Add FeNi 10 The COF aerogel was placed on a quartz boat and transferred into a tube furnace. It was then heated at 800°C under a nitrogen atmosphere for 2 hours, with a heating rate of 2°C / min. -1 FeNi was obtained by calcination and pyrolysis. 10 @NCA-2 aerogel, namely magnetic nitrogen-doped porous carbon aerogel microwave absorbing material.

[0047] Step 4: Place the petals on the prepared FeNi 10 @NCA-2 aerogel, heated with an alcohol lamp, and the changes in the petals were recorded with a mobile phone.

[0048] Step 5: Use CST electromagnetic field simulation software to simulate FeNi 10 The radar stealth performance of @NCA-2 aerogel was simulated, and its radar cross-section was calculated using the following formula:

[0049] ;

[0050] Step 6: The prepared FeNi 10 The @NCA-2 aerogel material was impregnated with molten paraffin as a substrate to form a ring. The density of the aerogel was calculated, revealing that this material constituted 10 wt.% of the total mass of the ring. The electromagnetic parameters of this material were measured using a vector network analyzer. Based on transmission line theory, the formula for calculating the reflection loss of the material to electromagnetic waves is as follows:

[0051] .

[0052] Example 3

[0053] Step 1: In a glass bottle containing 4 mL of N,N-dimethylformamide, add 0.0268 g of terephthalaldehyde, 0.01 g of scandium trifluoromethanesulfonate, and 0.0468 g of 1,3,5-tris(4-aminophenyl)benzene in sequence. Then, sonicate the mixture until homogeneous. After sonication for 5 min, allow it to stand and crystallize to form a COF gel. The formed gel is then subjected to solvent exchange with N,N-dimethylformamide, acetone, ethanol, methanol, and water in sequence, with each solvent exchange being 2-3 times. The last solvent exchange is performed with water 4-5 times to obtain the COF hydrogel.

[0054] Step 2: Dissolve 0.2593 g of nickel chloride hexahydrate and 0.0295 g of ferric chloride hexahydrate in 4 mL of deionized water. Add the salt solution of nickel chloride hexahydrate and ferric chloride hexahydrate to the COF hydrogel from Step 1. Nickel and iron ions are adsorbed by the porous structure of the COF hydrogel. Let stand for 4–5 days until the solution becomes colorless. Then freeze-dry overnight to obtain FeNi. 10 @COF aerogel.

[0055] Step 3: Add FeNi 10 @COF aerogel was placed on a quartz boat, transferred into a tube furnace, and calcined and pyrolyzed at 800℃ under a nitrogen atmosphere for 2 h at a heating rate of 2 ℃ / min to obtain FeNi@NCA-3 aerogel.

[0056] Step 4: Place the petals on the prepared FeNi 10 Heat the petals on an NCA-3 aerogel with an alcohol lamp and record the changes with your phone.

[0057] Step 5: Use CST electromagnetic field simulation software to simulate FeNi 10 The radar stealth performance of @NCA-3 aerogel was simulated, and its radar cross-section was calculated using the following formula:

[0058] ;

[0059] Step 6: The prepared FeNi 10 The @NCA-3 aerogel material was impregnated with molten paraffin as a substrate to form a ring. The density of the aerogel was calculated, revealing that this material constituted 10 wt.% of the total mass of the ring. The electromagnetic parameters of this material were measured using a vector network analyzer. Based on transmission line theory, the formula for calculating the reflection loss of the material to electromagnetic waves is as follows:

[0060] .

[0061] Example 4

[0062] Step 1: In a glass bottle containing 4 mL of N,N-dimethylformamide, add 0.0268 g of terephthalaldehyde, 0.01 g of scandium trifluoromethanesulfonate, and 0.0468 g of 1,3,5-tris(4-aminophenyl)benzene in sequence. Then, sonicate the mixture until homogeneous. After sonication for 5 min, allow it to stand and crystallize to form a COF gel. The formed COF gel is then subjected to solvent exchange with N,N-dimethylformamide, acetone, ethanol, methanol, and water in sequence, with each solvent exchange being 2-3 times. The last solvent exchange is performed with water 4-5 times to obtain a COF hydrogel.

[0063] Step 2: Dissolve 0.3457 g of nickel chloride hexahydrate and 0.0393 g of ferric chloride hexahydrate in 4 mL of deionized water. Add the salt solution of nickel chloride hexahydrate and ferric chloride hexahydrate to the gel from Step 1. Nickel and iron metal ions are adsorbed by the porous structure of the COF hydrogel. Let stand for 4–5 days until the solution becomes colorless. Then freeze-dry overnight to obtain FeNi@COF aerogel.

[0064] Step 3: Add FeNi 10 The COF aerogel was placed on a quartz boat and transferred into a tube furnace. It was then heated at 800°C under a nitrogen atmosphere for 2 hours, with a heating rate of 2°C / min. -1 FeNi@NCA-4 aerogel was prepared by pyrolysis.

[0065] Step 4: Place the petals on the prepared FeNi@NCA-4 aerogel, heat with an alcohol lamp, and record the changes in the petals with a mobile phone.

[0066] Step 5: Use CST electromagnetic field simulation software to simulate FeNi 10 The radar stealth performance of @NCA-4 aerogel was simulated, and its radar cross-section was calculated using the following formula:

[0067]

[0068] Step 6: The prepared FeNi@NCA-4 aerogel material was impregnated with molten paraffin as the substrate to form a ring. The density of the aerogel was calculated to determine that the material constituted 10 wt.% of the total mass of the ring. The electromagnetic parameters of the material were measured using a vector network analyzer. Based on transmission line theory, the formula for calculating the reflection loss of the material to electromagnetic waves is as follows:

[0069] .

[0070] Figure 1 The X-ray diffraction patterns of the COF-derived magnetic nitrogen-doped porous carbon aerogel microwave absorbing materials provided in Examples 1, 2, 3 and 4 of this invention show that the diffraction peaks at 44.3°, 51.6° and 76.2° of the four samples are the (111), (200) and (220) crystal planes of FeNi alloy. The diffraction peak at 26.3° is derived from graphite carbon obtained by COF pyrolysis, which corresponds to the characteristic diffraction peak of graphite (002) crystal plane. This indicates that the FeNi@NCA aerogel has high purity and stable product, which is conducive to industrial production and promotion.

[0071] Figure 2This is a scanning electron microscopy image of the COF-derived magnetic nitrogen-doped porous carbon aerogel absorbing material provided in Example 3 of the present invention. The COF-derived magnetic nitrogen-doped porous carbon aerogel is composed of regular nanospheres assembled into a porous structure with a size of approximately 320 nm, uniformly distributed on the surface of the carbon microspheres and in the pores.

[0072] Figure 3 This is a transmission electron microscope (TEM) image of the COF-derived magnetic nitrogen-doped porous carbon aerogel absorbing material provided in Embodiment 3 of the present invention. Numerous black cubic blocks are uniformly dispersed on a gray material composed of stacked spherical particles. The gray spherical material is carbon aerogel, and the black cubic blocks are FeNi. 10 Nanoparticles. Results show that metal ions are thermally reduced within the aerogel channels to uniformly distributed cubic FeNi nanoparticles. 10 Alloy nanoparticles.

[0073] Figures 4a-4b The figures show the nitrogen adsorption-desorption isotherms and pore size distributions of the COF-derived magnetic nitrogen-doped porous carbon aerogel microwave absorbing materials provided in Examples 1, 2, 3, and 4 of this invention. The isotherms of all samples exhibit typical Type IV characteristics, indicating the coexistence of micropores and mesopores, consistent with their pore size distributions. Micropores / mesopores can generate more interfaces, providing numerous active centers for multiple reflections and absorption of electromagnetic waves.

[0074] Figure 5 Vibrational sample magnetometer (VSM) images of the COF-derived magnetic nitrogen-doped porous carbon aerogel absorbing materials provided in Examples 1, 2, 3, and 4 of this invention. FeNi 10 @NCA-1、FeNi 10 @NCA-2、FeNi 10 @NCA-3 and FeNi 10 @NCA-4 saturation magnetization ( M s The values ​​were 32.4, 23.5, 13.7 and 8.9 emu / g, respectively. M s Improving the magnetic loss helps to achieve better absorption performance.

[0075] Figures 6a to 6d The electromagnetic wave absorption diagrams are shown for the COF-derived magnetic nitrogen-doped porous carbon aerogel absorbing materials provided in Embodiments 1, 2, 3, and 4 of this invention. Figure 6a The electromagnetic reflection loss of the sample provided in Example 1, Figure 6b The electromagnetic reflection loss of the sample provided in Example 2, Figure 6c The electromagnetic reflection loss of the sample provided in Example 3, Figure 6dElectromagnetic reflection loss of the sample provided in Example 4. When the filling ratio is 10%, FeNi 10 @NCA-1、FeNi 10 @NCA-2 and FeNi 10 @NCA-4's RL min The polarization values ​​can reach -22.1 dB, -57.9 dB, and -55.1 dB, respectively, with matching thicknesses of 2.10 mm, 3.30 mm, and 4.11 mm, respectively. FeNi can be observed. 10 @NCA-3 at a frequency of 17.36 GHz, RL min It has a gain of −63.8 dB, a matching thickness of only 2.09 mm, and the largest EAB is 6.56 GHz (11.44-18 GHz) with a thickness of 2.28 mm.

[0076] Figures 7a to 7f This image shows the thermal insulation test results of the COF-derived magnetic nitrogen-doped porous carbon aerogel microwave absorbing material provided in Example 3 of the present invention. The heating platform temperature was 120°C. Figure 7a The initial temperature was 42℃. Figure 7b After ten minutes of testing, the temperature was 46℃. Figure 7c After 20 minutes of testing, the temperature was 49℃. Figure 7d After 30 minutes of testing, the temperature was 52℃. Figure 7e After 40 minutes of testing, the temperature was 54℃. Figure 7f After 60 minutes of testing, the temperature reached 57℃. The thermal insulation test showed that the COF-derived magnetically doped porous carbon aerogel microwave absorbing material has excellent thermal insulation performance.

[0077] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

[0078] Note: This patent was supported by the Natural Science Foundation of Jiangxi Province (No. 20232BAB212004), the China Aerospace Science Foundation (No. 2020Z056056003), and the National Natural Science Foundation of China (No. 22265021).

Claims

1. A method for preparing a magnetic nitrogen-doped porous carbon aerogel microwave absorbing material, characterized in that: The preparation method described above involves obtaining COF hydrogel through an ultrasound-assisted self-crosslinking reaction under the catalysis of scandium trifluoromethanesulfonate. A metal salt solution is then in situ immersed in the COF hydrogel, followed by freeze-drying and external thermal drive to produce a magnetic nitrogen-doped porous carbon aerogel microwave absorbing material. The specific steps are as follows: Step 1: Add terephthalaldehyde, 1,3,5-tris(4-aminophenyl)benzene and scandium trifluoromethanesulfonate to N,N-dimethylformamide. After ultrasonic-assisted self-crosslinking reaction, allow it to stand and crystallize to form COF gel. Then, use N,N-dimethylformamide, acetone, ethanol, methanol and water in sequence for solvent exchange to obtain COF hydrogel. Step 2: Add solutions of nickel chloride (II) hexahydrate and ferric chloride (III) hexahydrate to the COF hydrogel to allow metal ions to be in situ immersed in the hydrogel. Then freeze-dry overnight to obtain FeNi. 10 @COF aerogel; Step 3: Calcine and pyrolyze the COF aerogel under a protective atmosphere to obtain FeNi. 10 @NCA aerogel, namely magnetic nitrogen-doped porous carbon aerogel microwave absorbing material.

2. The method for preparing a magnetic nitrogen-doped porous carbon aerogel microwave absorbing material according to claim 1, characterized in that: In step 1, the ratio of terephthalaldehyde, 1,3,5-tris(4-aminophenyl)benzene, scandium trifluoromethanesulfonate, and N,N-dimethylformamide is 0.0134–0.0268 g: 0.0234–0.0468 g: 0.05–0.1 g: 4 mL, and the ultrasonic-assisted self-crosslinking reaction takes 5–10 minutes.

3. The method for preparing a magnetic nitrogen-doped porous carbon aerogel microwave absorbing material according to claim 1, characterized in that: In step 2, the ratio of nickel chloride hexahydrate (II) to ferric chloride hexahydrate (III) is 0.0862~0.3457g : 0.0098~0.0393g.

4. The method for preparing a magnetic nitrogen-doped porous carbon aerogel microwave absorbing material according to claim 1, characterized in that: In step 3, the protective gas is nitrogen or argon, the calcination pyrolysis temperature is 600~900℃, the holding time is 2~3 h, and the heating rate is 2~3 ℃ / min.

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