CoFe-coated CoFe2O4 / C composite material with aerogel structure and preparation method of CoFe-coated CoFe2O4 / C composite material

Abstract

The invention discloses a CoFe-coated CoFe2O4 / C composite material with an aerogel structure and a preparation method of the CoFe-coated CoFe2O4 / C composite material, and belongs to the technical field of material preparation. According to the method, g-C3N4 is prepared in the first step, chitosan / g-C3N4 aerogel is prepared in the second step, Co / Fe / chitosan / g-C3N4 hydrogel is prepared in the third step, and the Co / Fe / chitosan / g-C3N4 hydrogel is converted into CoFe-CoFe2O4 / C aerogel in the fourth step. In the preparation process, chitosan is used as an intermediate'medium ', and the surface has abundant functional groups, so that CoFe adsorbed in the g-C3N4 aerogel in the infiltration process can be dispersed in the porous aerogel. CoFe can grow in the aerogel in situ in the subsequent carbonization process, and a core-shell coating structure is formed after carbonization. The method is simple in synthesis process, good in repeatability, high in practicability and economical efficiency and high in reference and application value in the field of electromagnetic wave absorption and heat insulation.

Description

Technical Field

[0001] The present invention belongs to the technical field of material preparation, and in particular relates to a CoFe@CoFe2O4 / C composite material with an aerogel structure and a preparation method thereof. Background Art

[0002] Electromagnetic protection technologies primarily include electromagnetic shielding and electromagnetic absorption. Electromagnetic shielding achieves targeted protection by preventing electromagnetic waves from entering the shielded area through reflection and absorption on the surface of a shielding material. Electromagnetic absorption, on the other hand, requires that electromagnetic waves can smoothly penetrate the interior of the absorbing material. By utilizing the dielectric and magnetic loss mechanisms of the material, the electromagnetic wave energy is converted into heat or other forms of energy, thereby reducing reflection and transmission of the electromagnetic wave and achieving efficient attenuation. Electromagnetic absorption technology reduces reflection, avoids secondary pollution, and eliminates electromagnetic waves at their source. Electromagnetic protection technology plays an indispensable role in modern science and military fields. Shielding and absorption technologies for electromagnetic waves, particularly those in the radar frequency band (2-18 GHz), have become a research focus. Both technologies rely heavily on the development of thin, lightweight, wide-band, and high-absorption electromagnetic wave absorbing materials. However, common problems with electromagnetic wave absorbing materials in their applications include high density, poor impedance matching, and a narrow effective absorption bandwidth. Summary of the Invention

[0003] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide a CoFe@CoFe2O4 / C composite material with an aerogel structure and a preparation method thereof, so as to solve the problems of high density, poor impedance matching and narrow effective absorption bandwidth commonly existing in the application of electromagnetic wave materials in the prior art.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions:

[0005] A method for preparing a CoFe@CoFe2O4 / C composite material having an aerogel structure comprises the following steps:

[0006] S1, obtaining bulk g-C3N4 by pyrolysis of urea; ultrasonically treating the bulk g-C3N4 to obtain g-C3N4 nanosheets;

[0007] S2, dispersing chitosan in water, adding glacial acetic acid and the g-C3N4 nanosheets obtained in S1, and mixing them evenly by magnetic stirring to obtain chitosan / g-C3N4 hydrogel, and freeze-drying the chitosan / g-C3N4 hydrogel to obtain chitosan / g-C3N4 aerogel;

[0008] S3, Fe(NO3)3·9H2O and Co(NO3)2·6H2O were dispersed in water and mixed evenly by magnetic stirring to obtain Co / Fe solution, chitosan / g-C3N4 aerogel was immersed in the Co / Fe solution and stirred until saturated to obtain Co / Fe / chitosan / g-C3N4 hydrogel;

[0009] S4, the Co / Fe / chitosan / g-C3N4 hydrogel was vacuum freeze-dried to obtain the dry Co / Fe / chitosan / g-C3N4 aerogel, and the dry Co / Fe / chitosan / g-C3N4 aerogel was carbonized to obtain the CoFe@CoFe2O4 / C aerogel.

[0010] A further improvement of the present invention is:

[0011] Preferably, in S1, the pyrolysis temperature is 500° C. and the pyrolysis time is 3 h.

[0012] Preferably, in S2, the mixing mass ratio of chitosan and glacial acetic acid is 3:4.

[0013] Preferably, the mixing mass ratio of chitosan and g-C3N4 nanosheets is 8:1.

[0014] Preferably, in S2, the freeze-drying temperature is -80°C, and the vacuum freeze-drying time is 48 hours.

[0015] Preferably, in S3, the mixing molar ratio of Fe(NO3)3·9H2O and Co(NO3)2·6H2O is 2:1.

[0016] Preferably, in S4, the vacuum freezing temperature is -80°C and the vacuum freezing time is 24 hours.

[0017] Preferably, in S4, the carbonization temperature is 700° C. and the carbonization time is 2 h.

[0018] A CoFe@CoFe2O4 / C composite material with an aerogel structure prepared by any of the above preparation methods, wherein the composite material has a porous carbon aerogel skeleton as the main structure, and nanoparticles are attached inside and on the surface of the carbon aerogel skeleton. The nanoparticles are a core-shell structure, the core is a CoFe alloy, and the shell is CoFe2O4.

[0019] Preferably, the size of the nanoparticles is 50-60 nm.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention discloses a method for preparing a CoFe@CoFe2O4 / C composite material having an aerogel structure. The method uses g-C3N4 as a chelating agent and uses freeze-drying, infiltration absorption, and high-temperature annealing processes to composite CoFe2O4 with a carbon material. The method first prepares g-C3N4 by pyrolyzing urea in an argon environment to synthesize bulk g-C3N4, which is then ultrasonically treated to obtain g-C3N4 nanosheets. The second step is to prepare chitosan / g-C3N4 aerogel by completely dispersing chitosan, glacial acetic acid, and g-C3N4 powder in deionized water and freeze-drying to obtain the chitosan / g-C3N4 aerogel. The third step is to prepare a Co / Fe / chitosan / g-C3N4 hydrogel. Ferric nitrate nonahydrate and cobalt nitrate hexahydrate are mixed and dissolved in deionized water to form a Co / Fe solution. The chitosan / g-C3N4 aerogel is then infiltrated into the Co / Fe solution and stirred until saturated to obtain the Co / Fe / chitosan / g-C3N4 hydrogel. The fourth step is to prepare a CoFe@CoFe2O4 / C aerogel. The Co / Fe / chitosan / g-C3N4 hydrogel is vacuum freeze-dried to produce a Co / Fe / chitosan / g-C3N4 aerogel, which is then annealed to obtain the CoFe@CoFe2O4 / C aerogel. In the preparation process of the present invention, chitosan is used as an intermediate "medium." Its surface is rich in functional groups, allowing the CoFe adsorbed within the g-C3N4 aerogel during the infiltration process to diffuse within the porous aerogel. During the subsequent carbonization process, the CoFe is able to grow in situ within the aerogel, forming a core-shell structure after carbonization. The synthesis process of the invention is simple, has good repeatability, is highly practical and economical, and has high reference and application value in the fields of electromagnetic wave absorption and heat insulation.

[0022] Furthermore, the present invention provides a freeze-drying-high temperature annealing synergistic strategy to prepare a CoFe@CoFe2O4 / C composite material with an aerogel structure. By precisely controlling the annealing temperature, a balance is achieved between the crystal structure evolution of the magnetic particles and the degree of graphitization of the carbon skeleton. The prepared aerogel has one-dimensional / three-dimensional composite structural characteristics, and realizes the in-situ growth of one-dimensional core-shell structured magnetic nanoparticles (CoFe2O4 shell and CoFe alloy core) on a three-dimensional cross-linked carbon nanosheet skeleton. The preparation process of the present invention is simple, the operation process is safe, and the cost is low. The prepared aerogel composite material has a rich pore structure and has potential application value in the fields of electromagnetic wave absorption and heat insulation.

[0023] The CoFe@CoFe2O4 / C composite material with an aerogel structure prepared by the present invention not only has a carbon aerogel skeleton with electromagnetic wave absorption capacity, but also because CoFe@CoFe2O4 has a core-shell structure and is multi-layered, the layered core-shell structure is more conducive to the absorption and loss of electromagnetic waves. CoFe2O4, as a magnetic loss-type absorbing material, has the characteristics of high stability and corrosion resistance. The core-shell structure is a multi-layer structure, and the multi-layer structure has a stronger electromagnetic wave absorption capacity, which can optimize impedance matching performance while enhancing dielectric loss. The composite aerogel material has a rich pore structure, which not only can achieve the synergy of multiple attenuation mechanisms and improve the material's electromagnetic wave absorption performance, but also has excellent thermal insulation properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of SEM characterization of CoFe@CoFe2O4 / C aerogel obtained in Examples 1, 2, and 3;

[0025] Wherein, Figures (a) and (b) are schematic diagrams of Example 1; Figures (c) and (d) are schematic diagrams of Example 2; Figures (e) and (f) are schematic diagrams of Example 3;

[0026] Figure 2 Schematic diagram of TEM and EDX characterization of CoFe@CoFe2O4 / C aerogel obtained in Example 1.

[0027] Wherein, (a), (b) and (c) are transmission electron microscopy diagrams of the magnetic particles in Example 1; (d) is a schematic diagram of element distribution of the magnetic particles in Example 11;

[0028] Figure 3 Schematic diagram of XRD characterization of CoFe@CoFe2O4 / C aerogel obtained in Examples 1, 2, and 3.

[0029] Figure 4 Schematic diagram of Raman spectroscopy characterization of CoFe@CoFe2O4 / C aerogels obtained in Examples 1, 2, and 3.

[0030] Figure 5 Schematic diagram of electromagnetic parameters measured at 300K using the coaxial method after the CoFe@CoFe2O4 / C aerogel obtained in Examples 1, 2, and 3 was mixed with paraffin.

[0031] Wherein, (a) is a schematic diagram of Example 1; (b) is a schematic diagram of Example 2; (c) is a schematic diagram of Example 3;

[0032] Figure 6Schematic diagram of the effective absorption bandwidth of CoFe@CoFe2O4 / C aerogels obtained in Examples 1, 2, and 3. (a) is a schematic diagram of Example 1; (b) is a schematic diagram of Example 2; (c) is a schematic diagram of Example 3;

[0033] Figure 7 This is a thermal infrared schematic diagram of the CoFe@CoFe2O4 / C aerogel obtained in Example 1. DETAILED DESCRIPTION

[0034] The present invention is described in further detail below with reference to the accompanying drawings:

[0035] To facilitate understanding of the features and effects of the present invention by those skilled in the art, the following provides a general description and definition of the terms and expressions used in the specification and claims. Unless otherwise indicated, all technical and scientific terms used herein have the ordinary meanings as understood by those skilled in the art regarding the present invention. In the event of conflict, the definitions in this specification shall prevail.

[0036] In this document, unless otherwise specified, “include,” “including,” “contains,” “has” or similar terms cover the meanings of “consisting of” and “mainly consisting of,” for example, “A includes a” covers the meanings of “A includes a and other” and “A only includes a.”

[0037] Below in conjunction with specific embodiment, further set forth the present invention.Should be understood that these embodiments are only used to illustrate the present invention and are not used in limiting the scope of the present invention.In addition, should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall equally within the scope limited by the appended claims of the application.

[0038] The following examples were prepared using conventional instruments and equipment in the art. Experimental methods in the following examples, where specific conditions are not specified, were generally performed under conventional conditions or according to the conditions recommended by the manufacturer. The various raw materials used in the following examples, unless otherwise specified, were conventional commercially available products, with specifications conventional in the art. In the present specification and the following examples, unless otherwise specified, "%" indicates percentage by weight, "part" indicates parts by weight, and "ratio" indicates weight ratio.

[0039] The first aspect of the present invention discloses a method for preparing a CoFe@CoFe2O4 / C composite material having an aerogel structure, the preparation method comprising the following steps:

[0040] S1. Preparation of g-C3N4 nanosheets: Urea was first ground into a powder and placed in a corundum boat. Pyrolysis was then performed at 500°C for 3 h under argon to obtain yellow g-C3N4 blocks. The blocks were then ultrasonically treated to obtain pale yellow g-C3N4 nanosheets approximately 100 nm thick.

[0041] S2, Preparation of Chitosan / g-C3N4 Aerogel: Chitosan powder was completely dispersed in deionized water. Glacial acetic acid and the g-C3N4 nanosheets prepared in S1 were then added. The chitosan / acetic acid mass ratio was 3:4, and the chitosan / g-C3N4 nanosheet mass ratio was 8:1. The mixture was magnetically stirred to obtain a chitosan / g-C3N4 hydrogel. The hydrogel was then frozen at -80°C for 24 hours and then freeze-dried under vacuum for 48 hours to obtain a pale yellow chitosan / g-C3N4 aerogel ready for use.

[0042] S3, preparation of Co / Fe / chitosan / g-C3N4 hydrogel: Fe(NO3)3·9H2O and Co(NO3)2·6H2O with a molar ratio of 2:1 were dispersed in deionized water and mixed evenly by magnetic stirring to synthesize Co / Fe solution. When the solute was completely dissolved, the solution turned dark red. Subsequently, the chitosan / g-C3N4 aerogel in S2 was immersed in the Co / Fe solution and stirred continuously until saturated, so that the Co / Fe solution and the chitosan / g-C3N4 aerogel were evenly mixed and the Co / Fe solution was fully absorbed by the chitosan / g-C3N4 aerogel, thereby obtaining a light red Co / Fe / chitosan / g-C3N4 hydrogel. In this process, the amino (-NH2) and hydroxyl (-OH) groups in chitosan act as "claws" to capture and anchor the positively charged Fe 3+ and Co 2+ Layered g-C3N4 nanosheets act as chelating agents within the chitosan colloid, fragmenting the spatial distribution of metal ions and inhibiting aggregation of magnetic particles during annealing. Finally, the hydrogel was placed in a vacuum drying oven at room temperature and low pressure for 2 hours to eliminate air bubbles before use.

[0043] S4, preparation of CoFe@CoFe2O4 / C aerogel: The hydrogel in step 3 was frozen at -80℃ for 24h, and then vacuum freeze-dried for 48h to obtain light red Co / Fe / chitosan / g-C3N4 aerogel, which was then annealed at 700℃ for 2h under argon protection to carbonize the chitosan. In this process, the O2 released during the carbonization of chitosan can promote the crystallization of the edge of the Co / Fe precursor to form CoFe2O4, while the interior of the Co / Fe precursor crystallized to form CoFe alloy, and finally formed CoFe@CoFe2O4 core-shell structured magnetic particles, thereby obtaining black CoFe@CoFe2O4 / C aerogel.

[0044] A second aspect of the present invention discloses a CoFe@CoFe2O4 / C composite material prepared by the aforementioned placement. The composite material comprises a porous aerogel skeleton formed of carbon sheets approximately 100 nm thick. Nanoparticles are attached to the interior and surface of the carbon aerogel skeleton. The nanoparticles have a core-shell structure, with the core being a CoFe alloy and the shell being CoFe2O4. The nanoparticles are 50-60 nm in size.

[0045] The composite structure of the present invention has the following advantages: (1) There is a difference in work function between the core (CoFe alloy) and the shell (CoFe2O4), which makes the charge distribution at the interface uneven. Under the action of electromagnetic waves, it can induce a large amount of interface polarization, increasing the loss of electromagnetic waves. (2) The metallic phase of CoFe alloy has ferromagnetism and can produce a certain amount of magnetic loss, but it is very easy to induce eddy currents, causing material impedance mismatch. Therefore, the CoFe2O4 shell is wrapped around the outside of the CoFe alloy core, effectively suppressing the eddy current effect. (3) The metallic CoFe alloy is easily oxidized in the air, resulting in a decrease in magnetic properties. (4) As a stable oxide, the CoFe2O4 shell can improve the chemical stability of the material. Therefore, after entering the shell, the electromagnetic wave can be reflected and scattered at the core-shell interface, extending the loss path of the electromagnetic wave inside the material.

[0046] The following is further described in conjunction with specific embodiments. Specific implementation method:

[0048] Example 1

[0049] First, 10g of urea was weighed and ground into a powder, placed in a corundum boat, and pyrolyzed at 500°C for 3 hours under an argon atmosphere to synthesize yellow bulk g-C3N4. The bulk g-C3N4 was then ultrasonically treated to obtain pale yellow g-C3N4 nanosheets for later use.

[0050] Disperse 0.8g of chitosan powder in 20mL of deionized water, then add 1.2mL of glacial acetic acid and 100mg of g-C3N4 nanosheets. Mix thoroughly with magnetic stirring to synthesize chitosan / g-C3N4 hydrogel. Freeze-dry the hydrogel under vacuum to obtain a pale yellow chitosan / g-C3N4 aerogel for later use.

[0051] 2.02g of Fe(NO3)3·9H2O and 0.73g of Co(NO3)2·6H2O were dispersed in deionized water and mixed thoroughly by magnetic stirring. A deep red Co / Fe solution was synthesized after the solute was completely dissolved. Chitosan / g-C3N4 aerogel was then immersed in the Co / Fe solution and stirred until saturated, yielding a light red Co / Fe / chitosan / g-C3N4 hydrogel. The hydrogel was then placed in a vacuum drying oven at room temperature and low pressure for 2 hours to eliminate bubbles before use.

[0052] Finally, the Co / Fe / chitosan / g-C3N4 hydrogel was vacuum freeze-dried to obtain light red Co / Fe / chitosan / g-C3N4 aerogel, which was then carbonized at 700 °C for 2 h under argon protection to obtain black CoFe@CoFe2O4 / C aerogel.

[0053] The SEM image of the CoFe@CoFe2O4 / C aerogel prepared in Example 1 is shown in FIG. Figure 1 As shown in Figures (a) and (b), it can be clearly seen that the aerogel is composed of carbon sheets with a thickness of about 100nm, showing a highly interconnected three-dimensional porous network structure. Figure 2 As shown in Figure 2, the magnetic particles are evenly dispersed on the carbon sheets, with a size of about 50-60 nm, showing a clear CoFe@CoFe2O4 core-shell structure. Figure 3 As shown in Figure 2, the diffraction peak at 44.7° corresponds to the (110) crystal plane of CoFe alloy. The diffraction peak at 35.4° corresponds to the (311) crystal plane of CoFe2O4. There is no diffraction peak of graphite, indicating that the main component of the carbon sheet is amorphous carbon. Figure 4 As shown, the lower degree of graphitization in the aerogel is demonstrated.

[0054] 0.3g of the prepared CoFe@CoFe2O4 / C aerogel was mixed with 0.7g of paraffin wax in a molten state and pressed into a ring with an outer diameter of 0.7mm and an inner diameter of 0.3mm using a tableting mold. Electromagnetic parameter tests were then performed at 300K using the coaxial method. Figure 5 As shown in (a), the electromagnetic parameters have obvious dispersion behavior, indicating that the prepared CoFe@CoFe2O4 / C aerogel has a strong interaction with electromagnetic waves. Subsequently, the electromagnetic wave absorption performance was calculated using the transmission line theory based on the metal backplane, as shown in Figure 6 As shown in (a), at a matching thickness of 2.63 mm, it has an effective absorption bandwidth of 7.84 GHz (10.16-18 GHz). Finally, the thermal insulation performance test was carried out. Figure 7 As shown in Figure 3, the surface temperature of the aerogel only rises by 1.5°C after being placed on a heating platform at 90°C for 30 minutes.

[0055] Example 2

[0056] First, 10g of urea was weighed and ground into a powder. The powder was then placed in a corundum boat and pyrolyzed at 500°C for 3 hours under an argon atmosphere to synthesize yellow bulk g-C3N4. The bulk g-C3N4 was then ultrasonically treated to obtain pale yellow g-C3N4 nanosheets for later use.

[0057] Disperse 0.64g of chitosan powder in 20mL of deionized water, then add 1.05mL of glacial acetic acid and 80mg of g-C3N4 nanosheets. Mix thoroughly with magnetic stirring to synthesize chitosan / g-C3N4 hydrogel. Freeze-dry the hydrogel under vacuum to obtain a pale yellow chitosan / g-C3N4 aerogel for later use.

[0058] 2.02g of Fe(NO3)3·9H2O and 0.73g of Co(NO3)2·6H2O were dispersed in deionized water and mixed uniformly by magnetic stirring. A deep red Co / Fe solution was synthesized after the solute was completely dissolved. Chitosan / g-C3N4 aerogel was then immersed in the Co / Fe solution and stirred continuously until saturated, yielding a light red Co / Fe / chitosan / g-C3N4 hydrogel. The hydrogel was then placed in a vacuum drying oven at room temperature and low pressure for 2 hours to eliminate bubbles before use.

[0059] Finally, the Co / Fe / chitosan / g-C3N4 hydrogel was vacuum freeze-dried to obtain light red Co / Fe / chitosan / g-C3N4 aerogel, which was then carbonized at 700 °C for 2 h under argon protection to obtain black CoFe@CoFe2O4 / C aerogel.

[0060] The SEM image of the CoFe@CoFe2O4 / C aerogel prepared in Example 2 is shown in FIG. Figure 1 As shown in Figures (c) and (d), it can be clearly seen that the aerogel is composed of carbon sheets with a thickness of about 100 nm, showing a highly interconnected three-dimensional porous network structure. Figure 3 As shown, the diffraction peak at 4.7° corresponds to the (110) crystal plane of CoFe alloy. The diffraction peak at 35.4° corresponds to the (311) crystal plane of CoFe2O4. There is no diffraction peak of graphite, indicating that the main component of the carbon sheet is amorphous carbon. Raman spectrum is shown Figure 4 As shown, the lower degree of graphitization in the aerogel is demonstrated.

[0061] 0.3g of the prepared CoFe@CoFe2O4 / C aerogel was mixed evenly with 0.7g of paraffin wax in a molten state and pressed into a ring with an outer diameter of 7mm and an inner diameter of 3mm using a tableting mold. The electromagnetic parameters were then tested at 300K using the coaxial method, as shown in the following example. Figure 5 As shown in (b), the electromagnetic parameters have obvious dispersion behavior, indicating that the prepared CoFe@CoFe2O4 / C aerogel has a strong interaction with electromagnetic waves. Subsequently, the electromagnetic wave absorption performance was calculated using the transmission line theory based on the metal backplane, as shown in Figure 6 As shown in (b), at a matching thickness of 2.35 mm, it has an effective absorption bandwidth of 6.96 GHz (11.04-18 GHz).

[0062] Example 3

[0063] First, 10g of urea was weighed and ground into a powder. The powder was then placed in a corundum boat and pyrolyzed at 500°C for 3 hours under an argon atmosphere to synthesize yellow bulk g-C3N4. The bulk g-C3N4 was then ultrasonically treated to obtain pale yellow g-C3N4 nanosheets for later use.

[0064] Disperse 0.48g of chitosan powder in 20mL of deionized water, then add 0.9mL of glacial acetic acid and 60mg of g-C3N4 nanosheets. Mix thoroughly with magnetic stirring to synthesize chitosan / g-C3N4 hydrogel. Freeze-dry the hydrogel under vacuum to obtain a pale yellow chitosan / g-C3N4 aerogel for later use.

[0065] 2.02g of Fe(NO3)3·9H2O and 0.73g of Co(NO3)2·6H2O were dispersed in deionized water and mixed thoroughly by magnetic stirring. A deep red Co / Fe solution was synthesized after the solute was completely dissolved. Chitosan / g-C3N4 aerogel was then immersed in the Co / Fe solution and stirred until saturated, yielding a light red Co / Fe / chitosan / g-C3N4 hydrogel. The hydrogel was then placed in a vacuum drying oven at room temperature and low pressure for 2 hours to eliminate bubbles before use.

[0066] Finally, the Co / Fe / chitosan / g-C3N4 hydrogel was vacuum freeze-dried to obtain light red Co / Fe / chitosan / g-C3N4 aerogel, which was then carbonized at 700 °C for 2 h under argon protection to obtain black CoFe@CoFe2O4 / C aerogel.

[0067] The SEM image of the CoFe@CoFe2O4 / C aerogel prepared in Example 3 is shown in FIG. Figure 1As shown in (e, f), it can be clearly seen from the figure that the aerogel is composed of carbon sheets with a thickness of about 100 nm, showing a highly interconnected three-dimensional porous network structure. Figure 3 As shown, the diffraction peak at 4.7° corresponds to the (110) crystal plane of CoFe alloy. The diffraction peak at 35.4° corresponds to the (311) crystal plane of CoFe2O4. There is no diffraction peak of graphite, indicating that the main component of the carbon sheet is amorphous carbon. Raman spectrum is shown Figure 4 As shown, the lower degree of graphitization in the aerogel is demonstrated.

[0068] 0.3g of the prepared CoFe@CoFe2O4 / C aerogel was mixed with 0.7g of paraffin wax in a molten state and pressed into a ring with an outer diameter of 0.7mm and an inner diameter of 0.3mm using a tableting mold. The electromagnetic parameters were then tested at 300K using the coaxial method. Figure 5 As shown in (c), the electromagnetic parameters have obvious dispersion behavior, indicating that the prepared CoFe@CoFe2O4 / C aerogel has a strong interaction with electromagnetic waves. Subsequently, the electromagnetic wave absorption performance was calculated using the transmission line theory based on the metal backplane, as shown in Figure 6 As shown in (c), at a matching thickness of 1.95 mm, it has an effective absorption bandwidth of 5.92 GHz (12.08–18 GHz).

[0069] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a CoFe@CoFe2O4 / C composite material having an aerogel structure, characterized in that: The following steps are involved: S1, obtaining bulk g-C3N4 by pyrolysis of urea; ultrasonically treating the bulk g-C3N4 to obtain g-C3N4 nanosheets; S2, dispersing chitosan in water, adding glacial acetic acid and the g-C3N4 nanosheets obtained in S1, and mixing them evenly by magnetic stirring to obtain chitosan / g-C3N4 hydrogel, and freeze-drying the chitosan / g-C3N4 hydrogel to obtain chitosan / g-C3N4 aerogel; S3, Fe(NO3)3·9H2O and Co(NO3)2·6H2O were dispersed in water and mixed evenly by magnetic stirring to obtain Co / Fe solution, chitosan / g-C3N4 aerogel was immersed in the Co / Fe solution and stirred until saturated to obtain Co / Fe / chitosan / g-C3N4 hydrogel; S4, the Co / Fe / chitosan / g-C3N4 hydrogel was vacuum freeze-dried to obtain the dry Co / Fe / chitosan / g-C3N4 aerogel, and the dry Co / Fe / chitosan / g-C3N4 aerogel was carbonized to obtain the CoFe@CoFe2O4 / C aerogel.

2. The method for preparing a CoFe@CoFe2O4 / C composite material having an aerogel structure according to claim 1, characterized in that: In S1, the pyrolysis temperature is 500°C and the pyrolysis time is 3 h.

3. The method for preparing a CoFe@CoFe2O4 / C composite material having an aerogel structure according to claim 1, characterized in that: In S2, the mixing mass ratio of chitosan and glacial acetic acid is 3:

4.

4. The method for preparing a CoFe@CoFe2O4 / C composite material having an aerogel structure according to claim 1, characterized in that: The mixing mass ratio of chitosan and g-C3N4 nanosheets is 8:

1.

5. The method for preparing a CoFe@CoFe2O4 / C composite material having an aerogel structure according to claim 1, characterized in that: In S2, the freeze-drying temperature is -80°C and the freeze-drying time is 48 h.

6. The method for preparing a CoFe@CoFe2O4 / C composite material having an aerogel structure according to claim 1, characterized in that: In S3, the mixing molar ratio of Fe(NO3)3·9H2O and Co(NO3)2·6H2O is 2:

1.

7. The method for preparing a CoFe@CoFe2O4 / C composite material having an aerogel structure according to claim 1, characterized in that: In S4, the vacuum freezing temperature is -80°C and the vacuum freezing time is 24 h.

8. The method for preparing a CoFe@CoFe2O4 / C composite material having an aerogel structure according to claim 1, characterized in that: In S4, the carbonization temperature is 700°C and the carbonization time is 2 h.

9. A CoFe@CoFe2O4 / C composite material having an aerogel structure prepared by the preparation method according to any one of claims 1 to 8, characterized in that: The composite material has a porous carbon aerogel skeleton as the main structure, with nanoparticles attached inside and on the surface of the carbon aerogel skeleton. The nanoparticles are a core-shell structure, the core is CoFe alloy, and the shell is CoFe2O4.

10. The CoFe@CoFe2O4 / C composite material with an aerogel structure according to claim 9, characterized in that The size of the nanoparticles is 50-60 nm.

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