CoNi-C-doped aramid framework aerogel, preparation method and application of CoNi-C-doped aramid framework aerogel

Abstract

The invention discloses CoNi-C-doped aramid skeleton aerogel, a preparation method and application thereof. The CoNi-C-doped aramid skeleton aerogel is prepared from the following raw materials: CoNi-C, carboxylated multi-walled carbon nanotubes and aramid nanofiber gel in a mass ratio of (1-4): (0-40): 500. The preparation method comprises the following steps: preferably selecting aramid fiber nanofiber gel, carboxylated multi-walled carbon nanotubes and CoNi-coated C as raw materials, preparing aramid fiber skeleton aerogel with uniform pore size as a microwave absorbing matrix and carboxylated multi-walled carbon nanotubes and CoNi-coated C as main microwave absorbents, and carrying out pre-freezing, freeze-drying and other steps to obtain the high-temperature-resistant microwave absorbing material. The aramid framework aerogel which is thin, light, strong in absorption and wide in effective absorption wave band is prepared; the aramid skeleton aerogel prepared by the invention has a hierarchical pore structure, can enhance the electromagnetic wave absorption capacity under different scales, and has multiple loss mechanisms such as magnetic loss and dielectric loss and relatively strong electromagnetic wave absorption capacity.

Description

Technical Field

[0001] The invention relates to the fields of aramid composite aerogel, stealth material and electronic communication technology, and in particular to a CoNi@C-doped aramid skeleton aerogel, a preparation method and application thereof. Background Art

[0002] With the development of national defense and the large-scale deployment of 5G base stations, the popularity of personal electronic communication devices has made electronic devices based on electromagnetic waves an indispensable part of daily life, greatly improving the convenience of human communication. However, while bringing convenience to people, the electromagnetic radiation problems caused by it have had an adverse impact on many fields such as military, manufacturing, information security and health care. Long-term exposure to electromagnetic radiation may cause irreversible damage to the human reproductive system and immune system; at the same time, electromagnetic wave pollution will also affect the normal operation of precision equipment. Electromagnetic radiation pollution has become an urgent concern for people around the world, and effective control of electromagnetic pollution is urgent.

[0003] At present, common commercial electromagnetic shielding absorbers are usually made of metal materials or metal filler composite materials, and play a microwave absorption role by covering the parts that need to be protected. However, due to the high density of metal, this type of absorber increases the weight of the equipment. In addition, they also face problems such as easy oxidation, easy corrosion, difficult to adjust the absorption performance and inconvenient use. In some special occasions, metal materials may even cause internal short circuits in precision instruments, causing unnecessary losses. These problems seriously limit the practical application of metal materials in the field of microwave absorption. Therefore, there is an urgent need for a lightweight, low-cost, corrosion-resistant, flexible material with excellent absorption performance.

[0004] Aramid skeleton aerogel is a porous aerogel obtained by pyrolysis, protonation and freeze-drying of para-aramid short fibers. It has a rich pore structure, which is not only conducive to the loss of electromagnetic waves entering the material, but also makes the aramid skeleton aerogel have a lower density (20mg / cm 3 ). The rigid chain structure and extremely strong amide bond (305kJ / mol) between the para-aramid fiber molecules are retained during the preparation of the aramid skeleton aerogel, which makes it also have strong strength. However, the aramid skeleton aerogel itself does not have the ability to absorb electromagnetic waves, and the unlimited growth of ice crystals during the preparation of the aerogel leads to its irregular and disordered porous structure, which greatly limits its application in the field of microwave absorption.

[0005] The patent application with application number CN202311024360.0 discloses a method for preparing an iron sulfide / porous carbon fiber @ aramid composite aerogel material that integrates wave absorption, heat insulation, and hydrophobic functions. Iron sulfide and porous carbon fiber are blended by an electrospinning process, and then mixed with aramid nanofibers and freeze-dried to prepare an iron sulfide / porous carbon fiber @ aramid composite aerogel material that integrates wave absorption, heat insulation, and hydrophobic functions. However, the invention has problems such as complex preparation process. The patent application with application number CN202310613428.2 discloses a multi-metal MOF-derived composite nitrogen-doped carbon material film, preparation method, and application thereof. FeCoNi@C hollow spheres and NC@Co / NC carbon nanocages are prepared by a solvothermal method, and then the ratio of the two is adjusted and mixed with PVDF to form a film. However, the invention has problems such as poor reflection loss and excessively high magnetic permeability.

[0006] Carbon material is a common resistive electromagnetic wave absorber. It has the advantages of adjustable surface properties, corrosion resistance, high thermal conductivity, etc., and has attracted much attention from researchers at home and abroad. Carbon materials exist in various forms, such as carbon spheres, porous carbon, carbon nanotubes, etc., which have the advantages of large specific surface area, light weight and high conductivity loss. However, a single type of carbon material is still difficult to meet the needs of the wave absorption field, and the wave absorption performance is not ideal (the effective absorption frequency band is narrow and the absorption intensity is weak). Therefore, it is often compounded with other magnetic materials, semiconductors, sulfides, etc. to improve the wave absorption performance. Carbon nanotubes are a one-dimensional quantum material with a special structure. Its radial size is nanometer-level and its axial size is micrometer-level. It has excellent electrical conductivity and thermal conductivity, but its poor impedance matching and single loss mechanism hinder its application in the field of wave absorption. Metal organic framework materials (MOFs) are crystalline porous materials with periodic network structures formed by self-assembly of transition metal ions and organic ligands. MOFs have the characteristics of adjustable structure, low density, rich surface functional groups, large specific surface area and high porosity. It is favored by scientific researchers in the field of radar absorption because of its stable three-dimensional structure and uniform distribution of metal particles. Summary of the invention

[0007] In order to overcome the problems of high density, easy corrosion and difficult adjustment of absorbing performance of electromagnetic shielding absorbers in the prior art, the purpose of the present invention is to provide a CoNi@C doped aramid skeleton aerogel, a preparation method and an application thereof. By selecting aramid nanofiber gel, zeolite imidazolate skeleton structure material (ZIF material, a kind of MOF), and carboxylated multi-walled carbon nanotube raw materials, cracked aramid nanofibers are used as a supporting skeleton, and zeolite imidazolate skeleton structure material derivative CONi@C and carboxylated multi-walled carbon nanotubes are used as microwave absorbers. The aramid skeleton aerogel is prepared by freezing the mixed gel system and then freeze-drying it, and an ultra-light CoNi@C doped aramid skeleton aerogel with strong absorption, wide bandwidth and high impedance matching is prepared. The present invention has the advantages of simple process and efficient preparation.

[0008] In order to achieve the above object, the technical solution adopted by the present invention is:

[0009] A CoNi@C doped aramid skeleton aerogel, the raw material components of which include CoNi@C, carboxylated multi-walled carbon nanotubes and aramid nanofiber gel, wherein the mass ratio of CoNi@C:carboxylated multi-walled carbon nanotubes:aramid nanofiber gel is [1-4]:[0-40]:500.

[0010] The carboxylated multi-walled carbon nanotubes have a length of 40 to 60 μm and a diameter of 8 to 15 nm, a dispersion system of water, and a carbon nanotube content of 1.8 to 2.2 wt%.

[0011] The water content of the aramid nanofiber gel is 90-95%; the raw material is para-aramid short-cut fiber with a diameter of 50-100nm and a length of 3-7mm, which is prepared by a potassium hydroxide and dimethyl sulfoxide system.

[0012] A method for preparing CoNi@C-doped aramid skeleton aerogel comprises the following steps:

[0013] Step 1, dissolving cobalt nitrate hexahydrate (CoNO3·6H2O) and 2-methylimidazole (2-MI) in methanol for 10 to 60 minutes respectively, to obtain cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution and 2-methylimidazole (2-MI) methanol solution respectively, the mass concentration of cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution is 29.10 to 116.41 g / L, and the mass concentration of 2-methylimidazole (2-MI) methanol solution is 16.42 to 65.68 g / L; dissolving the same volume of cobalt nitrate hexahydrate (CoNO3·6H2O) in methanol for 10 to 60 minutes respectively, to obtain cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution and 2-methylimidazole (2-MI) methanol solution respectively. The alcohol solution and the 2-methylimidazole (2-MI) methanol solution are mixed, stirred for 5 to 30 minutes, aged for 12 to 36 hours, and the purple precipitate zeolite imidazole ester framework material ZIF-67 is collected, washed with ethanol for 2 to 5 times, and dried for later use; when the cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution and the 2-methylimidazole (2-MI) methanol solution are mixed, the mass concentration ratio of the cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution: 2-methylimidazole (2-MI) methanol solution = [29.10 to 116.41]: [16.42 to 65.68];

[0014] The dried zeolite imidazolate framework material ZIF-67 and nickel nitrate hexahydrate (NiNO3·6H2O) were dissolved in ethanol to obtain solution A and solution B, respectively. The mass concentration of solution A was 7.05-14.10 g / L, and the mass concentration of solution B was 14.54-29.08 g / L. The solution A and solution B were mixed evenly, reacted in a water bath at 20-40° C. for 18-36 h, and the dark green precipitate CoNi@C precursor was collected, washed with ethanol for 2-5 times, and dried for later use. When the solution A and solution B were mixed, the mass concentration ratio of solution A to solution B was [7.05-14.10]: [14.54-29.08];

[0015] Step 2, carbonizing the dark green precipitate CoNi@C precursor obtained in step 1 under inert gas protection at 700-900° C. for 1-3 h at a heating rate of 5-10° C. / min to obtain gray-black solid CoNi@C;

[0016] Step 3, the gray-black solid CoNi@C, carboxylated multi-walled carbon nanotubes and aramid nanofiber gel obtained in step 2 are mixed evenly to obtain a mixed system A, and the mixed system A is placed in a mold for shaping and placed in a low-temperature environment device for freezing for 5 to 60 minutes until the mixed system A is frozen; in terms of mass ratio, the gray-black solid CoNi@C: carboxylated multi-walled carbon nanotubes: aramid nanofiber gel = [1 to 4]: [0 to 40]: 500;

[0017] Step 4, placing the sample frozen in step 3 in a freeze dryer at a temperature of -60 to -40°C and a pressure of 2 to 10 Pa for freeze drying for 24 to 48 hours to obtain CoNi@C-doped aramid skeleton aerogel.

[0018] In the step 1, when the cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution and the 2-methylimidazole (2-MI) methanol solution are mixed, the 2-methylimidazole (2-MI) methanol solution is added to the cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution, so that the 2-methylimidazole molecules enter a large amount of the cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution.

[0019] In step 2, the inert gas is argon or helium.

[0020] In step 3, the mold is a circular, square or pentagonal shape that can be used to shape the gel.

[0021] In step 3, the low-temperature environment equipment includes a refrigerator, an ultra-low temperature refrigerator, or a device that can generate a low-temperature environment using liquid nitrogen.

[0022] An application of CoNi@C doped aramid skeleton aerogel. The prepared CoNi@C doped aramid skeleton aerogel can be applied to the fields of aerospace material weight reduction, stealth weapons and electromagnetic protection.

[0023] Compared with the prior art, the present invention has the following beneficial technical effects:

[0024] 1. The present invention preferably uses aramid skeleton aerogel as the core fiber skeleton of the absorbing material. Aramid skeleton aerogel is made of para-aramid chopped fibers as raw materials, and is prepared by chemical cracking, protonation, freeze-drying and molding of the raw materials. It has a porous structure, low density, high strength and large specific surface area. Aramid skeleton aerogel, as the main absorbing matrix, is more conducive to the incidence, multiple reflections and diffraction of electromagnetic waves than traditional absorbing materials. At the same time, it increases the loading amount of the absorber, which can effectively improve the absorbing performance of aramid skeleton aerogel.

[0025] 2. The present invention introduces CoNi@C as the main electromagnetic wave absorber. The zeolite imidazolate skeleton structure material ZIF-67 is first prepared by step 1, and then replaced with free nickel ions in an ethanol solution in step 2 to obtain a CoNi@C precursor, and then CoNi@C is prepared by high-temperature carbonization of the organic framework 2-methylimidazole (sacrificial template method) in a tubular furnace in step 2. The CoNi@C material prepared by the present invention has a hollow porous structure, which is conducive to multiple reflections of electromagnetic waves, extends the transmission distance of electromagnetic waves, and promotes the absorption of electromagnetic waves. After the electromagnetic wave absorber is added, the magnetic permeability of the aramid skeleton aerogel can be effectively improved, and the wave absorbing performance of the aramid skeleton aerogel can be improved while maintaining the strength. The presence of metal particles and organic ligands can balance dielectric loss and magnetic loss and optimize impedance matching.

[0026] 3. In the process of the present invention, the calcination process in step 2 is preferably carried out at a temperature of 700-900°C, a heating rate of 5-10°C / min, and a holding time of 1-3h, so that the 2-methylimidazole organic framework in the CoNi@C precursor is partially carbonized, so that CoNi@C has a larger saturation magnetization intensity, which is beneficial to enhance the electromagnetic wave absorption ability of CoNi@C, and dissipate electromagnetic waves through magnetic loss methods such as eddy current loss and natural resonance.

[0027] 4. The present invention preferably uses carboxylated multi-walled carbon nanotubes as another electromagnetic wave absorber, and introduces carboxyl (-COOH) functional groups on the surface of multi-walled carbon nanotubes to increase their solubility, dispersibility and compatibility with aramid nanofibers. The interweaving of carbon nanotubes forms a structural conductive network, which greatly improves the conductivity of the material and can increase the dielectric constant of the material, thereby reducing the reflection and Joule loss of electromagnetic waves inside the material, which is more conducive to the absorption of electromagnetic waves in principle.

[0028] 5. The present invention uses low-temperature environment equipment with high heat exchange efficiency during the pre-freezing process, so that the mixed aramid nanofiber gel and the freezing medium undergo intense heat exchange and the freezing speed is extremely fast, thereby producing small and evenly distributed ice crystals inside the gel. After freeze-drying, the ice crystals sublime, leaving behind a pore structure with smaller pore size and narrower pore size distribution, thereby improving the ability of electromagnetic waves to enter the aramid skeleton aerogel.

[0029] 6. The present invention preferably adopts freeze-drying process in terms of process, that is, cold drying for 36 to 60 hours at a temperature of -60 to -40°C and a pressure of 0 to 10 Pa, so that small and evenly distributed ice crystals can be quickly dissipated during the sublimation process and the original pore structure will not be destroyed.

[0030] 7. The present invention, through the limitation of process steps and process parameters, only uses simple process means such as solution preparation, mechanical stirring, centrifugation, drying, high-temperature calcination, freeze drying, etc., through the macroscopic pore structure of the aramid skeleton aerogel itself and the mesoporous structure of CoNi@C, to achieve a multi-level pore construction of CoNi@C-doped aramid skeleton aerogel. In the process of electromagnetic waves being absorbed by the material, they first enter the material through the macroscopic pore structure, and multiple reflections and scattering processes occur inside the material; then, the mesoporous structure of CoNi@C increases the pore volume of the material, making the propagation distance of electromagnetic waves inside the material longer, causing multiple reflections of electromagnetic waves.

[0031] 8. The present invention changes the dielectric constant and magnetic permeability of the aramid skeleton aerogel by regulating the ratio of CoNi@C to carboxylated multi-walled carbon nanotubes to obtain appropriate impedance matching, which is beneficial for electromagnetic waves to be incident on the inside of the material rather than reflected on the surface of the material; at the same time, the magneto-electric synergy also causes the electromagnetic waves to undergo multiple reflections and scattering inside the material, resulting in conductivity losses on the carbon nanotubes or magnetic losses on CoNi@C.

[0032] In summary, the process of the present invention is simple and the preparation is efficient, and an aramid skeleton aerogel with thinness, lightness, strong absorption and wide effective absorption band is obtained, which has broad application prospects in the fields of microwave absorption, aircraft stealth, material weight reduction, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 ] are the hysteresis loop diagrams of ZIF-67, CoNi@C precursor, and CoNi@C in the embodiments of the present invention.

[0034] Figure 2 This is a scanning electron microscope image of Example 1 of the present invention.

[0035] Figure 3 This is a 3D absorption loss diagram of Example 3 of the present invention.

[0036] Figure 4 This is a 3D absorption loss diagram of Example 4 of the present invention.

[0037] Figure 5 It is a bar graph of the absorption loss values ​​of the comparative example and embodiments 1-5 of the present invention. DETAILED DESCRIPTION

[0038] The present invention is further described in detail below in conjunction with specific embodiments, which are intended to explain the present invention rather than to limit it.

[0039] A CoNi@C doped aramid skeleton aerogel, the raw material components of which include CoNi@C, carboxylated multi-walled carbon nanotubes and aramid nanofiber gel, wherein the mass ratio of CoNi@C:carboxylated multi-walled carbon nanotubes:aramid nanofiber gel is [1-4]:[0-40]:500.

[0040] The carboxylated multi-walled carbon nanotubes are preferably 50 μm in length and 8-15 nm in diameter. The dispersion system is water, and the carbon nanotube content is preferably 2.0 wt %.

[0041] The aramid nanofiber gel was purchased from Shaanxi Xingnuo Paper-based New Material Technology Co., Ltd., with a water content of 90-95%; the raw material is para-aramid chopped fibers with a diameter of 50-100 nm and a length of 3-7 mm, which are prepared by a potassium hydroxide and dimethyl sulfoxide system (chemical cracking method).

[0042] A method for preparing CoNi@C-doped aramid skeleton aerogel comprises the following steps:

[0043] Step 1, dissolving cobalt nitrate hexahydrate (CoNO3·6H2O) and 2-methylimidazole (2-MI) in methanol for 10 to 60 minutes respectively, to obtain cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution and 2-methylimidazole (2-MI) methanol solution respectively, the mass concentration of cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution is 29.10 to 116.41 g / L, and the mass concentration of 2-methylimidazole (2-MI) methanol solution is 16.42 to 65.68 g / L; dissolving the same volume of cobalt nitrate hexahydrate (CoNO3·6H2O) in methanol for 10 to 60 minutes respectively, to obtain cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution and 2-methylimidazole (2-MI) methanol solution respectively. The alcohol solution and the 2-methylimidazole (2-MI) methanol solution are mixed, stirred for 5 to 30 minutes, aged for 12 to 36 hours, and the purple precipitate zeolite imidazole ester framework material ZIF-67 is collected, washed with ethanol for 2 to 5 times, and dried for later use; when the cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution and the 2-methylimidazole (2-MI) methanol solution are mixed, the mass concentration ratio of the cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution: 2-methylimidazole (2-MI) methanol solution = [29.10 to 116.41]: [16.42 to 65.68];

[0044] The dried zeolite imidazolate framework material ZIF-67 and nickel nitrate hexahydrate (NiNO3·6H2O) were dissolved in ethanol to obtain solution A and solution B, respectively. The mass concentration of solution A was 7.05-14.10 g / L, and the mass concentration of solution B was 14.54-29.08 g / L. The solution A and solution B were mixed evenly, reacted in a water bath at 20-40° C. for 18-36 h, and the dark green precipitate CoNi@C precursor was collected, washed with ethanol for 2-5 times, and dried for later use. When the solution A and solution B were mixed, the mass concentration ratio of solution A to solution B was [7.05-14.10]: [14.54-29.08];

[0045] Step 2, placing the dark green precipitate CoNi@C precursor obtained in step 1 in a tube furnace, carbonizing at 700-900° C. for 1-3 h under inert gas protection, with a heating rate of 5-10° C. / min, to obtain gray-black solid CoNi@C;

[0046] Step 3, the gray-black solid CoNi@C, carboxylated multi-walled carbon nanotubes and aramid nanofiber gel obtained in step 2 are mixed evenly to obtain a mixed system A, and the mixed system A is placed in a mold for shaping and placed in a low-temperature environment device for freezing for 5 to 60 minutes until the mixed system A is frozen; in terms of mass ratio, the gray-black solid CoNi@C: carboxylated multi-walled carbon nanotubes: aramid nanofiber gel = [1 to 4]: [0 to 40]: 500;

[0047] Step 4, placing the sample frozen in step 3 in a freeze dryer at a temperature of -60 to -40°C and a pressure of 2 to 10 Pa for freeze drying for 24 to 48 hours to obtain CoNi@C-doped aramid skeleton aerogel.

[0048] In the step 1, when the cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution and the 2-methylimidazole (2-MI) methanol solution are mixed, the 2-methylimidazole (2-MI) methanol solution is added to the cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution, so that the 2-methylimidazole molecules enter a large amount of the cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution.

[0049] In step 2, the inert gas is argon or helium.

[0050] In step 3, the mold is a circular, square or pentagonal shape that can be used to shape the gel.

[0051] In step 3, the low-temperature environment equipment includes a refrigerator, an ultra-low temperature refrigerator, or a device that can generate a low-temperature environment using liquid nitrogen.

[0052] An application of CoNi@C doped aramid skeleton aerogel. The prepared CoNi@C doped aramid skeleton aerogel can be applied to the fields of aerospace material weight reduction, stealth weapons and electromagnetic protection.

[0053] Example 1

[0054] A CoNi@C doped aramid skeleton aerogel, the raw material components of which include CoNi@C and aramid nanofiber gel, and the mass ratio of CoNi@C:aramid nanofiber gel is 1:500.

[0055] A method for preparing CoNi@C-doped aramid skeleton aerogel comprises the following steps:

[0056] Step 1, dissolving cobalt nitrate hexahydrate (CoNO3·6H2O) and 2-methylimidazole (2-MI) in methanol for 30 minutes respectively, to obtain cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution and 2-methylimidazole (2-MI) methanol solution respectively, the mass concentration of cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution is 58.20 g / L, and the mass concentration of 2-methylimidazole (2-MI) methanol solution is 16.42 g / L; dissolving the same volume of cobalt nitrate hexahydrate in methanol for 30 minutes respectively, to obtain cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution and 2-methylimidazole (2-MI) methanol solution respectively, the mass concentration of cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution is 58.20 g / L, and the mass concentration of 2-methylimidazole (2-MI) methanol solution is 16.42 g / L; (CoNO3·6H2O) methanol solution and 2-methylimidazole (2-MI) methanol solution were mixed, stirred for 5 minutes, aged for 12 hours, and the purple precipitate zeolite imidazole ester framework material ZIF-67 was collected, washed with ethanol for 5 times, and dried for use; when the cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution was mixed, the mass concentration ratio of cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution: 2-methylimidazole (2-MI) methanol solution = 58.20: 16.42;

[0057] The dried zeolite imidazolate framework material ZIF-67 and nickel nitrate hexahydrate (NiNO3·6H2O) were dissolved in ethanol to obtain solution A and solution B, respectively. The mass concentration of solution A was 7.05 g / L, and the mass concentration of solution B was 29.08 g / L. Solution A and solution B were mixed evenly, reacted in a water bath at 20°C for 18 hours, and the dark green precipitate CoNi@C precursor was collected, washed twice with ethanol, and dried for later use. When solution A and solution B were mixed, the mass concentration ratio of solution A to solution B was 7.05:29.08.

[0058] Step 2, placing the dark green precipitate CoNi@C precursor obtained in step 1 in a tube furnace, carbonizing at 700°C for 1 h with helium protection, and heating at a rate of 5°C / min to obtain a gray-black solid CoNi@C;

[0059] Step 3, the gray-black solid CoNi@C obtained in step 2 is mixed evenly with the aramid nanofiber gel to obtain a mixed system A, and the mixed system A is placed in a mold for shaping and placed in a refrigerator for freezing for 5 minutes until the mixed system A is frozen; in terms of mass ratio, the gray-black solid CoNi@C: aramid nanofiber gel = 1:500;

[0060] Step 4, placing the sample frozen in step 3 in a freeze dryer at a temperature of -50°C and a pressure of 2 Pa for freeze drying for 24 hours to obtain CoNi@C-doped aramid skeleton aerogel.

[0061] The CoNi@C doped aramid skeleton aerogel prepared by the above method has the strongest reflection loss of -21.50dB and the effective absorption band reaches 0.96GHz.

[0062] Example 2

[0063] A CoNi@C doped aramid skeleton aerogel, the raw material components of which include CoNi@C, carboxylated multi-walled carbon nanotubes and aramid nanofiber gel, wherein the mass ratio of CoNi@C:carboxylated multi-walled carbon nanotubes:aramid nanofiber gel is 1:40:500.

[0064] A method for preparing CoNi@C-doped aramid skeleton aerogel comprises the following steps:

[0065] Step 1, dissolving cobalt nitrate hexahydrate (CoNO3·6H2O) and 2-methylimidazole (2-MI) in methanol for 20 minutes respectively, to obtain cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution and 2-methylimidazole (2-MI) methanol solution respectively, the mass concentration of cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution is 29.10 g / L, and the mass concentration of 2-methylimidazole (2-MI) methanol solution is 32.84 g / L; dissolving the same volume of cobalt nitrate hexahydrate (CoNO3·6H2O) in methanol for 20 minutes respectively, to obtain cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution and 2-methylimidazole (2-MI) methanol solution respectively, the mass concentration of cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution is 29.10 g / L, and the mass concentration of 2-methylimidazole (2-MI) methanol solution is 32.84 g / L; 2O) methanol solution and 2-methylimidazole (2-MI) methanol solution were mixed, stirred for 30 minutes, aged for 24 hours, and the purple precipitate zeolite imidazolate framework material ZIF-67 was collected, washed with ethanol for 5 times, and dried for use; when the cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution and the 2-methylimidazole (2-MI) methanol solution were mixed, the mass concentration ratio of cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution: 2-methylimidazole (2-MI) methanol solution = 29.10: 32.84;

[0066] The dried zeolite imidazolate framework material ZIF-67 and nickel nitrate hexahydrate (NiNO3·6H2O) were dissolved in ethanol to obtain solution A and solution B, respectively. The mass concentration of solution A was 14.10 g / L, and the mass concentration of solution B was 14.54 g / L. Solution A and solution B were mixed evenly, reacted in a 30°C water bath for 24 hours, and the dark green precipitate CoNi@C precursor was collected, washed with ethanol for 5 times, and dried for later use. When solution A and solution B were mixed, the mass concentration ratio of solution A to solution B was 14.10:14.54.

[0067] Step 2, placing the dark green precipitate CoNi@C precursor obtained in step 1 in a tube furnace, carbonizing at 900° C. for 3 h with helium protection, and heating at a rate of 5° C. / min to obtain a gray-black solid CoNi@C;

[0068] Step 3, the gray-black solid CoNi@C, carboxylated multi-walled carbon nanotubes and aramid nanofiber gel obtained in step 2 are uniformly mixed to obtain a mixed system A, and the mixed system A is placed in a mold for final shaping and placed in an ultra-low temperature refrigerator for freezing for 60 minutes until the mixed system A is frozen; in terms of mass ratio, the gray-black solid CoNi@C: carboxylated multi-walled carbon nanotubes: aramid nanofiber gel = 1:40:500;

[0069] Step 4, placing the sample frozen in step 3 in a freeze dryer at a temperature of -60°C and a pressure of 6 Pa for freeze drying for 36 hours to obtain CoNi@C-doped aramid skeleton aerogel.

[0070] The CoNi@C doped aramid skeleton aerogel prepared by the above method has the strongest reflection loss of -31.25dB and the effective absorption band reaches 7.53GHz.

[0071] Example 3

[0072] A CoNi@C doped aramid skeleton aerogel, the raw material components of which include CoNi@C, carboxylated multi-walled carbon nanotubes and aramid nanofiber gel, wherein the mass ratio of CoNi@C:carboxylated multi-walled carbon nanotubes:aramid nanofiber gel is 2:40:500.

[0073] A method for preparing CoNi@C-doped aramid skeleton aerogel comprises the following steps:

[0074] Step 1, dissolving cobalt nitrate hexahydrate (CoNO3·6H2O) and 2-methylimidazole (2-MI) in methanol for 10 minutes respectively, to obtain cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution and 2-methylimidazole (2-MI) methanol solution respectively, the mass concentration of cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution is 58.20 g / L, and the mass concentration of 2-methylimidazole (2-MI) methanol solution is 65.68 g / L; dissolving the same volume of cobalt nitrate hexahydrate (CoNO3·6H2O) in methanol for 10 minutes respectively, to obtain cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution and 2-methylimidazole (2-MI) methanol solution respectively, the mass concentration of cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution is 58.20 g / L, and the mass concentration of 2-methylimidazole (2-MI) methanol solution is 65.68 g / L; 2O) methanol solution and 2-methylimidazole (2-MI) methanol solution were mixed, stirred for 10 min, aged for 30 h, and the purple precipitate zeolite imidazolate framework material ZIF-67 was collected, washed with ethanol for 4 times, and dried for later use; when cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution and 2-methylimidazole (2-MI) methanol solution were mixed, the mass concentration ratio of cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution: 2-methylimidazole (2-MI) methanol solution = 58.20: 65.68;

[0075] The dried zeolite imidazolate framework material ZIF-67 and nickel nitrate hexahydrate (NiNO3·6H2O) were dissolved in ethanol to obtain solution A and solution B, respectively. The mass concentration of solution A was 14.10 g / L, and the mass concentration of solution B was 14.54 g / L. Solution A and solution B were mixed evenly, reacted in a 30°C water bath for 18 hours, and the dark green precipitate CoNi@C precursor was collected, washed with ethanol for 3 times, and dried for later use. When solution A and solution B were mixed, the mass concentration ratio of solution A to solution B was 14.10:14.54.

[0076] Step 2, placing the dark green precipitate CoNi@C precursor obtained in step 1 in a tube furnace, carbonizing at 900°C for 1 h with argon protection, and heating at a rate of 10°C / min to obtain a gray-black solid CoNi@C;

[0077] Step 3, the gray-black solid CoNi@C, carboxylated multi-walled carbon nanotubes and aramid nanofiber gel obtained in step 2 are uniformly mixed to obtain a mixed system A, and the mixed system A is placed in a mold for final shaping and placed in an ultra-low temperature refrigerator for freezing for 60 minutes until the mixed system A is frozen; in terms of mass ratio, the gray-black solid CoNi@C: carboxylated multi-walled carbon nanotubes: aramid nanofiber gel = 2:40:500;

[0078] Step 4, placing the sample frozen in step 3 in a freeze dryer at a temperature of -50°C and a pressure of 8 Pa for freeze drying for 36 hours to obtain CoNi@C-doped aramid skeleton aerogel.

[0079] The CoNi@C doped aramid skeleton aerogel prepared by the above method has the strongest reflection loss of -47.40dB and the effective absorption band reaches 7.96GHz.

[0080] Example 4

[0081] A CoNi@C doped aramid skeleton aerogel, the raw material components of which include CoNi@C, carboxylated multi-walled carbon nanotubes and aramid nanofiber gel, wherein the mass ratio of CoNi@C: carboxylated multi-walled carbon nanotubes: aramid nanofiber gel is 3:40:500.

[0082] A method for preparing a CoNi@C-doped aramid skeleton aerogel comprises the following steps:

[0083] Step 1, dissolving cobalt nitrate hexahydrate (CoNO3·6H2O) and 2-methylimidazole (2-MI) in methanol for 50 minutes respectively, to obtain cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution and 2-methylimidazole (2-MI) methanol solution respectively, the mass concentration of cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution is 29.10 g / L, and the mass concentration of 2-methylimidazole (2-MI) methanol solution is 65.68 g / L; dissolving the same volume of cobalt nitrate hexahydrate (CoNO3·6H2O) in methanol for 50 minutes respectively, to obtain cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution and 2-methylimidazole (2-MI) methanol solution respectively, the mass concentration of cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution is 29.10 g / L, and the mass concentration of 2-methylimidazole (2-MI) methanol solution is 65.68 g / L; 2O) methanol solution and 2-methylimidazole (2-MI) methanol solution were mixed, stirred for 5 minutes, aged for 18 hours, and the purple precipitate zeolite imidazolate framework material ZIF-67 was collected, washed with ethanol for 5 times, and dried for use; when cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution and 2-methylimidazole (2-MI) methanol solution were mixed, the mass concentration ratio of cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution: 2-methylimidazole (2-MI) methanol solution = 29.10: 65.68;

[0084] The dried zeolite imidazolate framework material ZIF-67 and nickel nitrate hexahydrate (NiNO3·6H2O) were dissolved in ethanol to obtain solution A and solution B, respectively. The mass concentration of solution A was 7.05 g / L, and the mass concentration of solution B was 29.08 g / L. Solution A and solution B were mixed evenly, reacted in a water bath at 20°C for 36 hours, and the dark green precipitate CoNi@C precursor was collected, washed with ethanol for 3 times, and dried for later use. When solution A and solution B were mixed, the mass concentration ratio of solution A to solution B was 7.05:29.08.

[0085] Step 2, placing the dark green precipitate CoNi@C precursor obtained in step 1 in a tube furnace, carbonizing at 800°C for 2h with helium protection, and heating at a rate of 10°C / min to obtain a gray-black solid CoNi@C;

[0086] Step 3, the gray-black solid CoNi@C, carboxylated multi-walled carbon nanotubes and aramid nanofiber gel obtained in step 2 are uniformly mixed to obtain a mixed system A, and the mixed system A is placed in a mold for shaping and placed in liquid nitrogen for freezing for 10 minutes until the mixed system A is frozen; in terms of mass ratio, the gray-black solid CoNi@C: carboxylated multi-walled carbon nanotubes: aramid nanofiber gel = 3:40:500;

[0087] Step 4, placing the sample frozen in step 3 in a freeze dryer at a temperature of -60°C and a pressure of 4 Pa ​​for freeze drying for 48 hours to obtain CoNi@C-doped aramid skeleton aerogel.

[0088] The CoNi@C doped aramid skeleton aerogel prepared by the above method has the strongest reflection loss of -59.66dB and the effective absorption band reaches 8.31GHz.

[0089] Example 5

[0090] A CoNi@C doped aramid skeleton aerogel, the raw material components of which include CoNi@C, carboxylated multi-walled carbon nanotubes and aramid nanofiber gel, wherein the mass ratio of CoNi@C: carboxylated multi-walled carbon nanotubes: aramid nanofiber gel is 4:40:500.

[0091] A method for preparing CoNi@C-doped aramid skeleton aerogel comprises the following steps:

[0092] Step 1, dissolving cobalt nitrate hexahydrate (CoNO3·6H2O) and 2-methylimidazole (2-MI) in methanol for 40 minutes respectively, to obtain cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution and 2-methylimidazole (2-MI) methanol solution respectively, the mass concentration of cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution is 116.41 g / L, and the mass concentration of 2-methylimidazole (2-MI) methanol solution is 65.68 g / L; dissolving the same volume of cobalt nitrate hexahydrate (CoNO3·6H2O) in methanol for 40 minutes respectively, to obtain cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution and 2-methylimidazole (2-MI) methanol solution respectively, the mass concentration of cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution is 116.41 g / L, and the mass concentration of 2-methylimidazole (2-MI) methanol solution is 65.68 g / L; 2O) methanol solution and 2-methylimidazole (2-MI) methanol solution were mixed, stirred for 15 min, aged for 36 h, and the purple precipitate zeolite imidazolate framework material ZIF-67 was collected, washed with ethanol for 3 times, and dried for later use; when cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution and 2-methylimidazole (2-MI) methanol solution were mixed, the mass concentration ratio of cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution: 2-methylimidazole (2-MI) methanol solution = 116.41: 65.68;

[0093] The dried zeolite imidazolate framework material ZIF-67 and nickel nitrate hexahydrate (NiNO3·6H2O) were dissolved in ethanol to obtain solution A and solution B, respectively. The mass concentration of solution A was 7.05 g / L, and the mass concentration of solution B was 14.54 g / L. Solution A and solution B were mixed evenly, reacted in a 40°C water bath for 36 hours, and the dark green precipitate CoNi@C precursor was collected, washed twice with ethanol, and dried for later use. When solution A and solution B were mixed, the mass concentration ratio of solution A to solution B was 7.05:14.54.

[0094] Step 2, placing the dark green precipitate CoNi@C precursor obtained in step 1 in a tube furnace, carbonizing at 700°C for 3 hours with argon protection, and heating at a rate of 5°C / min to obtain a gray-black solid CoNi@C;

[0095] Step 3, the gray-black solid CoNi@C, carboxylated multi-walled carbon nanotubes and aramid nanofiber gel obtained in step 2 are uniformly mixed to obtain a mixed system A, and the mixed system A is placed in a mold for shaping and placed in liquid nitrogen for freezing for 5 minutes until the mixed system A is frozen; in terms of mass ratio, the gray-black solid CoNi@C: carboxylated multi-walled carbon nanotubes: aramid nanofiber gel = 4:40:500;

[0096] Step 4, placing the sample frozen in step 3 in a freeze dryer at a temperature of -40°C and a pressure of 6 Pa for freeze drying for 48 hours to obtain CoNi@C-doped aramid skeleton aerogel.

[0097] The CoNi@C doped aramid skeleton aerogel prepared by the above method has the strongest reflection loss of -52.53dB and the effective absorption band reaches 8.58GHz.

[0098] The above embodiments demonstrate that the CoNi@C doped aramid skeleton aerogel prepared by the present invention has a relatively strong reflection loss value and a relatively wide effective absorption band.

[0099] Depend on Figure 1 It can be seen that the magnetization saturation values ​​of ZIF-67 and CoNi@C precursors are small and almost non-magnetic; the magnetization saturation value of CoNi@C after calcination is large and has certain magnetism. The high-temperature carbonization of the organic framework 2-methylimidazole part in the tubular furnace in step 2 makes the central metal ions (cobalt and nickel ions) exposed to the outside, and the valence state changes to form a metal element, which has certain magnetism.

[0100] like Figure 2 The scanning electron microscope image of Example 1 of the present invention is shown. Figure 2It can be seen that there are more wrinkles inside the aramid skeleton aerogel, which makes it have a larger specific surface area and provides attachment points for CoNi@C and carboxylated multi-walled carbon nanotubes; in addition, CoNi@C and carboxylated multi-walled carbon nanotubes are evenly distributed inside the aramid skeleton aerogel, which can effectively balance the dielectric loss and magnetic loss and optimize the impedance matching.

[0101] like Figure 3 The 3D absorption loss diagram of Example 3 of the present invention is shown. Figure 3 It can be seen that Example 3 of the present invention achieves the strongest reflection loss (RL min ) is -47.40dB, and the reflection loss at many frequencies and thicknesses is <-10dB.

[0102] like Figure 4 The 3D absorption loss diagram of Example 4 of the present invention is shown. Figure 4 It can be seen that Example 4 of the present invention achieves the strongest reflection loss (RL min ) is -59.66dB, that is, it can absorb 99.9% of electromagnetic waves and only reflect 0.1% of electromagnetic waves, which can effectively reduce the reflection area of ​​the material in the radar; and compared with Example 3, there are more reflection losses under more frequencies and thicknesses <-10dB. When the thickness is 2.94mm, the frequency band with reflection loss ≤-10dB can reach 7.96GHz, which can effectively cover the entire Ku band (12-18GHz) and most of the X band (8-12GHz).

[0103] Comparative Example

[0104] A method for preparing a CoNi@C-doped aramid skeleton aerogel comprises the following steps:

[0105] Step 1, mixing carboxylated multi-walled carbon nanotubes and aramid nanofiber gel evenly to obtain a mixed system A, placing the mixed system A in a mold for shaping and placing it in a refrigerator for freezing for 15 minutes until the mixed system A is frozen; in terms of mass ratio, the carboxylated multi-walled carbon nanotubes: aramid nanofiber gel = 40:500;

[0106] Step 2, placing the sample frozen in step 1 in a freeze dryer at a temperature of -40°C and a pressure of 10 Pa for freeze drying for 24 hours to obtain CoNi@C-doped aramid skeleton aerogel.

[0107] The aramid skeleton aerogel prepared by the above method has the strongest reflection loss of -12.12dB and the effective absorption band reaches 2.98GHz.

[0108] Figure 5 The figure is a bar graph of the absorption loss values ​​of the comparative example and embodiments 1-5 of the present invention. Figure 5It can be seen that in the comparative example, the reflection loss value reaches -12.12dB by adding carboxylated multi-walled carbon nanotubes inside the aramid skeleton aerogel. In Example 1, only CoNi@C is added inside the aramid skeleton aerogel, and the reflection loss value reaches -21.5dB. In Examples 2 to 5, the mass proportion of CoNi@C gradually increases, and the reflection loss value is greatly enhanced. This is because the introduction of CoNi@C and carboxylated multi-walled carbon nanotubes causes the aramid skeleton aerogel to have a variety of loss mechanisms such as conductive loss, polarization loss, and magnetic loss, thereby enhancing the electromagnetic wave absorption capacity of the aramid skeleton aerogel. In Examples 2 to 5, the reflection loss value shows a trend of first increasing and then decreasing. In Example 4, the strongest reflection loss value of the present invention, -59.66dB, is reached. Compared with the comparative example, the reflection loss value is increased by 492%. Example 4 can absorb 99.9% of electromagnetic waves in a specific band and thickness. The highest reflection loss value in Example 4 occurs because the change in the ratio of CoNi@C to carboxylated multi-walled carbon nanotubes causes changes in the dielectric constant and magnetic permeability of the aramid skeleton aerogel, achieving optimal impedance matching, which is beneficial for electromagnetic waves to enter the interior of the material rather than be reflected on the surface of the material; at the same time, the magneto-electric synergy also causes the electromagnetic waves to undergo multiple reflections and scattering inside the material, resulting in conductivity losses on the carbon nanotubes or magnetic losses on CoNi@C.

Claims

1. A CoNi@C doped aramid skeleton aerogel, characterized in that: The raw material components include CoNi@C, carboxylated multi-walled carbon nanotubes and aramid nanofiber gel, and the mass ratio is CoNi@C: carboxylated multi-walled carbon nanotubes: aramid nanofiber gel = [1-4]: [0-40]:

500.

2. The CoNi@C doped aramid skeleton aerogel according to claim 1, characterized in that: The carboxylated multi-walled carbon nanotubes have a length of 40 to 60 μm and a diameter of 8 to 15 nm, a dispersion system of water, and a carbon nanotube content of 1.8 to 2.2 wt%.

3. The CoNi@C doped aramid skeleton aerogel according to claim 1, characterized in that: The water content of the aramid nanofiber gel is 90-95%; the raw material is para-aramid short-cut fiber with a diameter of 50-100nm and a length of 3-7mm, which is prepared by a potassium hydroxide and dimethyl sulfoxide system.

4. A CoNi@C doped aramid skeleton aerogel, characterized in that: The raw material components include CoNi@C, carboxylated multi-walled carbon nanotubes, and aramid nanofiber gel, and the mass ratio of CoNi@C: carboxylated multi-walled carbon nanotubes: aramid nanofiber gel is 3:40:

500. The preparation method includes the following steps: Step 1, dissolving cobalt nitrate hexahydrate (CoNO3·6H2O) and 2-methylimidazole (2-MI) in methanol for 50 minutes respectively, to obtain cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution and 2-methylimidazole (2-MI) methanol solution respectively, the mass concentration of cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution is 29.10 g / L, and the mass concentration of 2-methylimidazole (2-MI) methanol solution is 65.68 g / L; dissolving the same volume of cobalt nitrate hexahydrate (CoNO3·6H2O) in methanol for 50 minutes respectively, to obtain cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution and 2-methylimidazole (2-MI) methanol solution respectively, the mass concentration of cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution is 29.10 g / L, and the mass concentration of 2-methylimidazole (2-MI) methanol solution is 65.68 g / L; 2O) methanol solution and 2-methylimidazole (2-MI) methanol solution were mixed, stirred for 5 minutes, aged for 18 hours, and the purple precipitate zeolite imidazolate framework material ZIF-67 was collected, washed with ethanol for 5 times, and dried for use; when cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution and 2-methylimidazole (2-MI) methanol solution were mixed, the mass concentration ratio of cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution: 2-methylimidazole (2-MI) methanol solution = 29.10: 65.68; The dried zeolite imidazolate framework material ZIF-67 and nickel nitrate hexahydrate (NiNO3·6H2O) were dissolved in ethanol to obtain solution A and solution B, respectively. The mass concentration of solution A was 7.05 g / L, and the mass concentration of solution B was 29.08 g / L. Solution A and solution B were mixed evenly, reacted in a water bath at 20°C for 36 hours, and the dark green precipitate CoNi@C precursor was collected, washed with ethanol for 3 times, and dried for later use. When solution A and solution B were mixed, the mass concentration ratio of solution A to solution B was 7.05:29.

08. Step 2, placing the dark green precipitate CoNi@C precursor obtained in step 1 in a tube furnace, carbonizing at 800°C for 2h with helium protection, and heating at a rate of 10°C / min to obtain a gray-black solid CoNi@C; Step 3, the gray-black solid CoNi@C, carboxylated multi-walled carbon nanotubes and aramid nanofiber gel obtained in step 2 are uniformly mixed to obtain a mixed system A, and the mixed system A is placed in a mold for shaping and placed in liquid nitrogen for freezing for 10 minutes until the mixed system A is frozen; in terms of mass ratio, the gray-black solid CoNi@C: carboxylated multi-walled carbon nanotubes: aramid nanofiber gel = 3:40:500; Step 4, placing the sample frozen in step 3 in a freeze dryer at a temperature of -60°C and a pressure of 4 Pa ​​for freeze drying for 48 hours to obtain CoNi@C-doped aramid skeleton aerogel.

5. A method for preparing CoNi@C doped aramid skeleton aerogel, characterized in that: The following steps are involved: Step 1, dissolving cobalt nitrate hexahydrate (CoNO3·6H2O) and 2-methylimidazole (2-MI) in methanol for 10 to 60 minutes respectively, to obtain cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution and 2-methylimidazole (2-MI) methanol solution respectively, the mass concentration of cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution is 29.10 to 116.41 g / L, and the mass concentration of 2-methylimidazole (2-MI) methanol solution is 16.42 to 65.68 g / L; dissolving the same volume of cobalt nitrate hexahydrate (CoNO3·6H2O) in methanol for 10 to 60 minutes respectively, to obtain cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution and 2-methylimidazole (2-MI) methanol solution respectively. The alcohol solution and the 2-methylimidazole (2-MI) methanol solution are mixed, stirred for 5 to 30 minutes, aged for 12 to 36 hours, and the purple precipitate zeolite imidazole ester framework material ZIF-67 is collected, washed with ethanol for 2 to 5 times, and dried for later use; when the cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution and the 2-methylimidazole (2-MI) methanol solution are mixed, the mass concentration ratio of the cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution: 2-methylimidazole (2-MI) methanol solution = [29.10 to 116.41]: [16.42 to 65.68]; The dried zeolite imidazolate framework material ZIF-67 and nickel nitrate hexahydrate (NiNO3·6H2O) were dissolved in ethanol to obtain solution A and solution B, respectively. The mass concentration of solution A was 7.05-14.10 g / L, and the mass concentration of solution B was 14.54-29.08 g / L. The solution A and solution B were mixed evenly, reacted in a water bath at 20-40° C. for 18-36 h, and the dark green precipitate CoNi@C precursor was collected, washed with ethanol for 2-5 times, and dried for later use. When the solution A and solution B were mixed, the mass concentration ratio of solution A to solution B was [7.05-14.10]: [14.54-29.08]; Step 2, carbonizing the dark green precipitate CoNi@C precursor obtained in step 1 under inert gas protection at 700-900° C. for 1-3 h at a heating rate of 5-10° C. / min to obtain gray-black solid CoNi@C; Step 3, the gray-black solid CoNi@C, carboxylated multi-walled carbon nanotubes and aramid nanofiber gel obtained in step 2 are mixed evenly to obtain a mixed system A, and the mixed system A is placed in a mold for shaping and placed in a low-temperature environment device for freezing for 5 to 60 minutes until the mixed system A is frozen; in terms of mass ratio, the gray-black solid CoNi@C: carboxylated multi-walled carbon nanotubes: aramid nanofiber gel = [1 to 4]: [0 to 40]: 500; Step 4, placing the sample frozen in step 3 in a freeze dryer at a temperature of -60 to -40°C and a pressure of 2 to 10 Pa for freeze drying for 24 to 48 hours to obtain CoNi@C-doped aramid skeleton aerogel.

6. The method for preparing a CoNi@C doped aramid skeleton aerogel according to claim 5, characterized in that: In the step 1, when the cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution and the 2-methylimidazole (2-MI) methanol solution are mixed, the 2-methylimidazole (2-MI) methanol solution is added to the cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution, so that the 2-methylimidazole molecules enter a large amount of the cobalt nitrate hexahydrate (CoNO3·6H2O) methanol solution.

7. The method for preparing a CoNi@C doped aramid skeleton aerogel according to claim 5, characterized in that: In step 2, the inert gas is argon or helium.

8. The method for preparing a CoNi@C doped aramid skeleton aerogel according to claim 5, characterized in that: In step 3, the mold is a circular, square or pentagonal shape that can be used to shape the gel.

9. The method for preparing a CoNi@C doped aramid skeleton aerogel according to claim 5, characterized in that: In step 3, the low-temperature environment equipment includes a refrigerator, an ultra-low temperature refrigerator, or a device that can generate a low-temperature environment using liquid nitrogen.

10. An application of CoNi@C doped aramid skeleton aerogel, characterized in that: The CoNi@C doped aramid skeleton aerogel according to any one of claims 1 to 4 and the CoNi@C doped aramid skeleton aerogel prepared according to any one of claims 5 to 9 can be applied to the fields of aerospace material weight reduction, stealth weapons and electromagnetic protection.

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