High-entropy double hydroxide / carbon fiber aerogel electromagnetic wave-absorbing material and preparation method thereof

Abstract

The invention discloses a high-entropy double hydroxide / carbon fiber aerogel electromagnetic wave-absorbing material and a preparation method thereof, and the method specifically comprises the following steps: (1) activating green algae to obtain carbon fibers, and freeze-drying the carbon fibers to obtain aerogel carbon fibers; (2) immersing the aerogel carbon fiber subjected to heat treatment into a high-entropy layered double hydroxide precursor solution for hydrothermal reaction, and obtaining a high-entropy double hydroxide / carbon fiber aerogel material after the reaction; wherein the temperature of the hydrothermal reaction is 115-120 DEG C, and the reaction time is not less than 5 hours; and (3) freeze-drying the aerogel material obtained in the step (2) to obtain a target product. The high-entropy double hydroxide / carbon fiber aerogel electromagnetic wave-absorbing material disclosed by the invention can realize low-frequency absorption of 2.46 GHz under 2 to 8 GHz, and can realize broadband absorption of 12.44 GHz under 2 to 18 GHz.

Description

Technical Field

[0001] The present invention relates to a high entropy double hydroxide / carbon fiber aerogel electromagnetic wave absorbing material and also relates to a preparation method of the electromagnetic wave absorbing material. Background Art

[0002] Electromagnetic wave absorbing materials have important applications in many fields, including communications, military, drones, aerospace, and medical devices. These materials can absorb or reflect electromagnetic waves and are used to isolate signals, reduce electromagnetic radiation, improve stealth, and enhance electromagnetic compatibility. Therefore, the development of efficient electromagnetic wave absorbing materials has become crucial, ensuring the proper operation of precision electronic equipment while also helping to protect human health. Traditional powder-based electromagnetic wave absorbing materials no longer meet the diverse needs of practical applications. Aerogel products prepared from biomass raw materials have attracted research attention due to their simple preparation process, ultra-light solid-state properties, excellent thermal insulation properties, and extremely low thermal conductivity. Carbon fiber aerogel, as a lightweight conductive material, has excellent dielectric loss capacity and a porous structure. However, when used alone as an electromagnetic wave absorbing material, it suffers from poor impedance matching, a single absorption mechanism, and insufficient polarization loss, resulting in high reflectivity, a narrow absorption bandwidth, and low minimum reflection loss. Summary of the Invention

[0003] Purpose of the invention: The purpose of the present invention is to provide a high-entropy double hydroxide / carbon fiber aerogel electromagnetic absorbing material with good electromagnetic absorbing performance in a wide frequency band; another purpose of the present invention is to provide a method for preparing the above-mentioned electromagnetic absorbing material.

[0004] Technical solution: The method for preparing the high entropy double hydroxide / carbon fiber aerogel electromagnetic absorbing material of the present invention comprises the following steps:

[0005] (1) Activating green algae to obtain carbon fibers (biomass-based carbon fibers), freeze-drying the carbon fibers to obtain aerogel carbon fibers with a three-dimensional network structure;

[0006] (2) immersing the heat-treated aerogel carbon fiber in a high-entropy layered double hydroxide precursor solution for a hydrothermal reaction, thereby obtaining a high-entropy double hydroxide / carbon fiber aerogel material; wherein the hydrothermal reaction temperature is 115-120° C., and the reaction time is not less than 5 hours;

[0007] (3) freeze-drying the aerogel material of step (2) (freeze-drying can not only prevent the structural damage of the sample during the drying process, but also retain the morphology and composition stability of the sample, form ice crystals, and provide conditions for subsequent sublimation) to obtain the target product.

[0008] Among them, in step (1), the specific process of activating the green algae is as follows: immersing the green algae in a NaClO-H2SO4 mixed solution, taking it out after ultrasonic treatment for 0.5h, and then immersing it in an ethanol aqueous solution for 1h to obtain carbon fiber; NaClO and H2SO4 react to obtain hypochlorous acid (3H2SO4+6NaClO=3Na2SO4+2HCl+2H2O+2Cl2+2O2; Cl2+H2O=HCl+HClO), and the hypochlorous acid formed is used to destroy the chlorophyll on the surface of the green algae; then immersing it in an ethanol solution can remove impurities on the one hand and activate the carbon fiber on the other hand; in the NaClO-H2SO4 mixed solution, the concentration of NaClO is 2.7mol / L, and the concentration of H2SO4 is 0.6mol / L.

[0009] In step (1), in order to ensure that the water in the sample can be completely crystallized into ice before sublimation drying, so as to facilitate subsequent effective sublimation dehydration in a vacuum, the sample is pre-frozen for 12 h using a cold trap of a freeze dryer, and then freeze-dried for 24 h at a freezing temperature of -60°C.

[0010] In step (2), the heat treatment is carried out in an argon atmosphere at a temperature of 700°C to 750°C for 1 hour, and a heating rate of 2°C / min. The optimal heat treatment temperature for the original carbon fiber is 700°C. When the temperature is lower than 700°C, the carbon fiber cannot be completely carbonized, resulting in extremely poor electrical conductivity, which is not conducive to electromagnetic wave absorption performance. When the temperature is higher than 750°C, the structure of the carbon fiber surface is gradually destroyed, which is not conducive to serving as a growth substrate for the subsequent high-entropy layered double hydroxide.

[0011] In step (2), in the high entropy layered double hydroxide precursor solution, the molar ratio of Ni(NO3)2·6H2O, Fe(NO3)2·9H2O, Co(NO3)2·6H2O, Mn(NO3)2·4H2O and Cu(NO3)2·3H2O is 1:1:1:1:1. 2+ 、Mn 2+ 、Cu 2+ can be stably inserted into the layered double hydroxide layer, and Fe 3+ Providing trivalent ions can maintain layer charge balance. They have good compatibility in size and can be jointly stabilized between the layers of layered double hydroxides.

[0012] In step (2), a stainless steel autoclave is used to ensure that the carbon fiber aerogel is completely immersed in the high-entropy layered double hydroxide precursor solution. The autoclave is sealed and placed in an oven preheated to 120°C for a hydrothermal reaction lasting 5 hours. Maintaining a stable temperature during the reaction is crucial to ensure the formation of high-entropy layered double hydroxide nanosheet arrays. After the reaction is completed, the autoclave is allowed to cool naturally to room temperature, and the high-entropy double hydroxide / carbon fiber aerogel material is removed.

[0013] In step (3), the product was washed three times with deionized water and three times with ethanol, and then placed in a vacuum freeze dryer for pre-freezing for 12 hours and freeze-drying for 24 hours, with the freezing temperature being -60°C.

[0014] The high-entropy double hydroxide / carbon fiber aerogel electromagnetic absorbing material prepared by the present invention uses one-dimensional carbon fiber as a substrate, and high-entropy double hydroxide nanosheets are uniformly loaded on the carbon fiber substrate; the mass ratio of the carbon fiber substrate to the high-entropy double hydroxide nanosheets is 1.8-3.7:1.

[0015] The present invention introduces high entropy double hydroxide on the basis of biomass-based carbon fiber aerogel, and utilizes the ultra-high specific surface area of ​​the two-dimensional high entropy double hydroxide nanosheet array and the characteristics of biomass-based carbon fiber to combine, thereby having excellent electromagnetic wave absorption performance.

[0016] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: the high-entropy double hydroxide / carbon fiber aerogel electromagnetic absorbing material of the present invention, the biomass carbon fiber has good electrical conductivity. When electromagnetic waves pass through the material, the electric field drives the flow of free electrons, which leads to conductivity loss. The multiple interfaces between the high-entropy double hydroxide and the biomass carbon fiber can cause multiple reflections and refractions of electromagnetic waves, increasing the scattering and absorption of energy. The high-entropy double hydroxide / carbon fiber aerogel electromagnetic absorbing material of the present invention achieves low-frequency absorption of 2.46 GHz at 2 to 8 GHz (with low-frequency absorption capability) and achieves broadband absorption of 12.44 GHz at 2 to 18 GHz. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a SEM image of the high entropy double hydroxide nanosheets prepared in Example 1 at the 1 μm scale;

[0018] Figure 2 These are SEM images of the high entropy double hydroxide / carbon fiber aerogel electromagnetic absorbing materials prepared in Example 1 and Comparative Examples 1-2; wherein a is HELC-1, b is HELC-2, and c is HELC-3;

[0019] Figure 3 The BET diagrams of the high entropy double hydroxide / carbon fiber aerogel electromagnetic absorbing materials prepared in Example 1 and Comparative Examples 1-2;

[0020] Figure 4 This is the X-ray diffraction pattern of the high entropy double hydroxide / carbon fiber aerogel electromagnetic absorbing material prepared in Example 1;

[0021] Figure 5 This is the XPS analysis spectrum of the high entropy double hydroxide / carbon fiber aerogel electromagnetic absorbing material prepared in Example 1;

[0022] Figure 6 This is the FTIR analysis spectrum of the high entropy double hydroxide / carbon fiber aerogel electromagnetic absorbing material prepared in Example 1;

[0023] Figure 7 Graph showing the electromagnetic absorption performance of the high entropy double hydroxide / carbon fiber aerogel electromagnetic absorption materials prepared in Example 1 and Comparative Examples 1-2;

[0024] Figure 8 This is a physical picture of the high entropy double hydroxide / carbon fiber aerogel electromagnetic absorbing material prepared in Example 1;

[0025] Figure 9 This is an infrared thermal imaging image of the high entropy double hydroxide / carbon fiber aerogel electromagnetic absorbing material prepared in Example 1. DETAILED DESCRIPTION

[0026] Example 1

[0027] The preparation method of the high entropy double hydroxide / carbon fiber aerogel electromagnetic absorbing material of the present invention comprises the following steps:

[0028] (1) 4 g of the initial green algae raw material was placed in a NaClO-H2SO4 mixed solution, in which the concentration of NaClO was 2.7 mol / L and the concentration of H2SO4 was 0.6 mol / L. Ultrasonic stirring was performed for 0.5 h to achieve full activation. The sample was then taken out and transferred to an ethanol solution and soaked for 1 h to remove residual impurities. After treatment, carbon fibers were obtained. The obtained carbon fibers were placed in molds of different shapes (such as a cuboid or a cylinder) and freeze-dried (pre-frozen for 12 h, then freeze-dried for 24 h, and the freezing temperature was -60 ° C) to obtain a formed carbon fiber aerogel material.

[0029] (2) heat treating the carbon fiber aerogel material of step (1) in an argon atmosphere at a temperature of 700° C. for 1 h and a heating rate of 2° C. / min;

[0030] (3) Weigh equimolar (0.50 mmol) amounts of Mn(NO3)2·4H2O, Cu(NO3)2·3H2O, Ni(NO3)2·6H2O, Fe(NO3)2·9H2O and Co(NO3)2·6H2O, add them into 35 mL of deionized water in sequence, and stir them with a magnetic stirrer until the metal salts are completely dissolved to form a uniform metal ion solution; then, gradually add NH4F (4.44 mmol) and urea (11.11 mmol) into the above solution, and continue stirring until all reagents are completely dissolved to obtain a transparent mixed precursor solution; place the carbon fiber aerogel material after heat treatment in step (2) in a stainless steel high-pressure reactor, and inject the above mixed precursor solution into the reactor to ensure that the carbon fiber aerogel is completely immersed in the solution to provide a uniform reaction environment for subsequent reactions;

[0031] (4) The autoclave containing the reaction mixture was sealed and placed in an oven preheated to 120°C for a 5-hour hydrothermal reaction. Maintaining a stable temperature during the reaction was crucial for the orderly growth and structural quality of the high-entropy layered double hydroxide nanosheet arrays. After the reaction, the autoclave was naturally cooled to room temperature. After cooling, the generated high-entropy double hydroxide / carbon fiber aerogel material was removed and placed in a PDMS mold for 48 hours of freeze-drying (pre-freezing for 12 hours at -60°C). The resulting sample was named HELC-2.

[0032] Example 2

[0033] The preparation method of the high entropy double hydroxide / carbon fiber aerogel electromagnetic absorbing material of the present invention comprises the following steps:

[0034] (1) 4 g of the initial green algae raw material was placed in a NaClO-H2SO4 mixed solution, in which the concentration of NaClO was 2.7 mol / L and the concentration of H2SO4 was 0.6 mol / L. Ultrasonic stirring was performed for 0.5 h to achieve full activation. The sample was then taken out and transferred to an ethanol solution and soaked for 1 h to remove residual impurities. After treatment, carbon fibers were obtained. The obtained carbon fibers were placed in molds of different shapes (such as a cuboid or a cylinder) and freeze-dried (pre-frozen for 12 h, then freeze-dried for 24 h, and the freezing temperature was -60 ° C) to obtain a formed carbon fiber aerogel material.

[0035] (2) heat treating the carbon fiber aerogel material of step (1) in an argon atmosphere at a temperature of 720° C. for 1 h and a heating rate of 2° C. / min;

[0036] (3) Weigh equimolar (0.50 mmol) amounts of Mn(NO3)2·4H2O, Cu(NO3)2·3H2O, Ni(NO3)2·6H2O, Fe(NO3)2·9H2O and Co(NO3)2·6H2O, add them into 35 mL of deionized water in sequence, and stir them with a magnetic stirrer until the metal salts are completely dissolved to form a uniform metal ion solution; then, gradually add NH4F (4.44 mmol) and urea (11.11 mmol) into the above solution, and continue stirring until all reagents are completely dissolved to obtain a transparent mixed precursor solution; place the carbon fiber aerogel material after heat treatment in step (2) in a stainless steel high-pressure reactor, and inject the above mixed precursor solution into the reactor to ensure that the carbon fiber aerogel is completely immersed in the solution to provide a uniform reaction environment for subsequent reactions;

[0037] (4) The autoclave containing the reaction mixture was sealed and placed in an oven preheated to 120°C for a 5-hour hydrothermal reaction. Maintaining a stable temperature during the reaction was crucial for the orderly growth and structural quality of the high-entropy layered double hydroxide nanosheet arrays. After the reaction was completed, the autoclave was naturally cooled to room temperature. After cooling, the generated high-entropy double hydroxide / carbon fiber aerogel material was removed and placed in a PDMS mold. The aerogel was freeze-dried for 48 hours (pre-frozen for 12 hours at -60°C) to obtain the target product.

[0038] Example 3

[0039] The preparation method of the high entropy double hydroxide / carbon fiber aerogel electromagnetic absorbing material of the present invention comprises the following steps:

[0040] (1) 4 g of the initial green algae raw material was placed in a NaClO-H2SO4 mixed solution, in which the concentration of NaClO was 2.7 mol / L and the concentration of H2SO4 was 0.6 mol / L. Ultrasonic stirring was performed for 0.5 h to achieve full activation. The sample was then taken out and transferred to an ethanol solution and soaked for 1 h to remove residual impurities. After treatment, carbon fibers were obtained. The obtained carbon fibers were placed in molds of different shapes (such as a cuboid or a cylinder) and freeze-dried (pre-frozen for 12 h, then freeze-dried for 24 h, and the freezing temperature was -60 ° C) to obtain a formed carbon fiber aerogel material.

[0041] (2) heat treating the carbon fiber aerogel material of step (1) in an argon atmosphere at a temperature of 750° C. for 1 h and a heating rate of 2° C. / min;

[0042] (3) Weigh equimolar (0.50 mmol) amounts of Mn(NO3)2·4H2O, Cu(NO3)2·3H2O, Ni(NO3)2·6H2O, Fe(NO3)2·9H2O and Co(NO3)2·6H2O, add them into 35 mL of deionized water in sequence, and stir them with a magnetic stirrer until the metal salts are completely dissolved to form a uniform metal ion solution; then, gradually add NH4F (4.44 mmol) and urea (11.11 mmol) into the above solution, and continue stirring until all reagents are completely dissolved to obtain a transparent mixed precursor solution; place the carbon fiber aerogel material after heat treatment in step (2) in a stainless steel high-pressure reactor, and inject the above mixed precursor solution into the reactor to ensure that the carbon fiber aerogel is completely immersed in the solution to provide a uniform reaction environment for subsequent reactions;

[0043] (4) The autoclave containing the reaction mixture was sealed and placed in an oven preheated to 120°C for a 5-hour hydrothermal reaction. Maintaining a stable temperature during the reaction was crucial for the orderly growth and structural quality of the high-entropy layered double hydroxide nanosheet arrays. After the reaction was completed, the autoclave was naturally cooled to room temperature. After cooling, the generated high-entropy double hydroxide / carbon fiber aerogel material was removed and placed in a PDMS mold. The aerogel was freeze-dried for 48 hours (pre-frozen for 12 hours at -60°C) to obtain the target product.

[0044] Comparative Example 1

[0045] A method for preparing a high entropy double hydroxide / carbon fiber aerogel electromagnetic absorbing material comprises the following steps:

[0046] (1) 4 g of the initial green algae raw material was placed in a NaClO-H2SO4 mixed solution, in which the concentration of NaClO was 2.7 mol / L and the concentration of H2SO4 was 0.6 mol / L. Ultrasonic stirring was performed for 0.5 h to achieve full activation. The sample was then taken out and transferred to an ethanol solution and soaked for 1 h to remove residual impurities. After treatment, carbon fibers were obtained. The obtained carbon fibers were placed in molds of different shapes (such as a cuboid or a cylinder) and freeze-dried (pre-frozen for 12 h, then freeze-dried for 24 h, and the freezing temperature was -60 ° C) to obtain a formed carbon fiber aerogel material.

[0047] (2) heat treating the carbon fiber aerogel material of step (1) in an argon atmosphere at a temperature of 700° C. for 1 h and a heating rate of 2° C. / min;

[0048] (3) Weigh equimolar (0.50 mmol) amounts of Mn(NO3)2·4H2O, Cu(NO3)2·3H2O, Ni(NO3)2·6H2O, Fe(NO3)2·9H2O and Co(NO3)2·6H2O, add them into 35 mL of deionized water in sequence, and stir them with a magnetic stirrer until the metal salts are completely dissolved to form a uniform metal ion solution; then, gradually add NH4F (4.44 mmol) and urea (11.11 mmol) into the above solution, and continue stirring until all reagents are completely dissolved to obtain a transparent mixed precursor solution; place the carbon fiber aerogel material after heat treatment in step (2) in a stainless steel high-pressure reactor, and inject the above mixed precursor solution into the reactor to ensure that the carbon fiber aerogel is completely immersed in the solution to provide a uniform reaction environment for subsequent reactions;

[0049] (4) The autoclave containing the reaction mixture was sealed and placed in an oven preheated to 100°C for a 5-hour hydrothermal reaction. Maintaining a stable temperature during the reaction was crucial for the orderly growth and structural quality of the high-entropy layered double hydroxide nanosheet arrays. After the reaction, the autoclave was naturally cooled to room temperature. After cooling, the resulting high-entropy double hydroxide / carbon fiber aerogel material was removed and placed in a PDMS mold for 48 hours of freeze-drying (pre-freezing for 12 hours at -60°C). The resulting sample was named HELC-1.

[0050] Comparative Example 2

[0051] A method for preparing a high entropy double hydroxide / carbon fiber aerogel electromagnetic absorbing material comprises the following steps:

[0052] (1) 4 g of the initial green algae raw material was placed in a NaClO-H2SO4 mixed solution, in which the concentration of NaClO was 2.7 mol / L and the concentration of H2SO4 was 0.6 mol / L. Ultrasonic stirring was performed for 0.5 h to achieve full activation. The sample was then taken out and transferred to an ethanol solution and soaked for 1 h to remove residual impurities. After treatment, carbon fibers were obtained. The obtained carbon fibers were placed in molds of different shapes (such as a cuboid or a cylinder) and freeze-dried (pre-frozen for 12 h, then freeze-dried for 24 h, and the freezing temperature was -60 ° C) to obtain a formed carbon fiber aerogel material.

[0053] (2) heat treating the carbon fiber aerogel material of step (1) in an argon atmosphere at a temperature of 700° C. for 1 h and a heating rate of 2° C. / min;

[0054] (3) Weigh equimolar (0.50 mmol) amounts of Mn(NO3)2·4H2O, Cu(NO3)2·3H2O, Ni(NO3)2·6H2O, Fe(NO3)2·9H2O and Co(NO3)2·6H2O, add them into 35 mL of deionized water in sequence, and stir them with a magnetic stirrer until the metal salts are completely dissolved to form a uniform metal ion solution; then, gradually add NH4F (4.44 mmol) and urea (11.11 mmol) into the above solution, and continue stirring until all reagents are completely dissolved to obtain a transparent mixed precursor solution; place the carbon fiber aerogel material after heat treatment in step (2) in a stainless steel high-pressure reactor, and inject the above mixed precursor solution into the reactor to ensure that the carbon fiber aerogel is completely immersed in the solution to provide a uniform reaction environment for subsequent reactions;

[0055] (4) The autoclave containing the reaction mixture was sealed and placed in an oven preheated to 140°C for a 5-hour hydrothermal reaction. Maintaining a stable temperature during the reaction was crucial for the orderly growth and structural quality of the high-entropy layered double hydroxide nanosheet arrays. After the reaction was completed, the autoclave was naturally cooled to room temperature. After cooling, the generated high-entropy double hydroxide / carbon fiber aerogel material was removed and placed in a PDMS mold for 48 hours of freeze-drying (pre-freezing for 12 hours at -60°C). The resulting sample was named HELC-3.

[0056] The micromorphology and performance of the high entropy double hydroxide / carbon fiber aerogel materials prepared in Example 1 and Comparative Examples 1-2 were characterized:

[0057] from Figure 1 It can be seen that the high entropy double hydroxide nanosheets prepared in Example 1 are ultra-thin two-dimensional nanosheets. Figure 2 As can be seen in a, when the carbon fiber substrate surface is loaded with high entropy double hydroxide nanosheets, the surface of the carbon fiber substrate becomes rough. When the reaction temperature is 100 ° C, the loaded high entropy double hydroxide nanosheets are few and uneven. Figure 2 As can be seen in Figure b, when the reaction temperature is 120°C, the loaded high entropy double hydroxide nanosheets are uniformly loaded on the carbon fiber substrate. Figure 2 As can be seen from Figure c, when the reaction temperature is 140°C, the high entropy double hydroxide nanosheets form large particles after the reaction is intense. Figure 3It can be seen that the specific surface area of ​​the high entropy double hydroxide / carbon fiber aerogel prepared in Example 1 is HELC-2, HELC-1, and HELC-3, respectively. This is because at low temperatures (100°C), primary nucleation is dominant, crystal growth is slow, the morphology is unstable, and the lamellae are not fully expanded. At medium temperatures (120°C), nucleation and crystal growth are in dynamic equilibrium, the two-dimensional lamellae are fully expanded, and the specific surface area is the largest. At high temperatures (140°C), the crystals grow rapidly, the granules aggregate, the lamellae collapse or fuse, and the porosity and specific surface area are reduced. The nanosheet structure enriches the energy dissipation mechanism by amplifying the effects of the microscopic interface, electromagnetic wave path, and dielectric loss, so the wave absorption performance is significantly better than that of the granular structure.

[0058] from Figure 4 It can be seen that the high entropy double hydroxide / carbon fiber aerogel prepared in Example 1 includes characteristic peaks of carbon fiber and high entropy double hydroxide, corresponding to the hexagonal hydrotalcite structure, proving that the synthesized material is high entropy double hydroxide. Figure 5 and Figure 6 It can be seen that the product prepared in Example 1 contains elements such as C, O, Fe, Co, Ni, Mn and Cu.

[0059] from Figure 7 It can be seen from the ac that the high-entropy double hydroxide / carbon fiber aerogel with a perfect high-entropy structure has excellent microwave absorption performance under the conditions of strong attenuation and high impedance matching. At a thickness of 1.9 mm, the broadband EAB of HELC-2 reaches 5.9 GHz; the maximum RL value of -45.79 dB is achieved at 10.24 GHz, which means that more than 99.999% of the energy is dissipated. In the 5G frequency band, the total absorption bandwidth (Δf) of HELC-1, HELC-2 and HELC-3 reaches 1.0 GHz, 2.46 GHz and 0.24 GHz, respectively. In particular, at a thickness of 3.7 mm, the EAB of HELC-2 reaches 2.44 GHz. In the range of 2-18 GHz, the Δf of HELC-1, HELC-2 and HELC-3 are 2.28 GHz, 12.44 GHz and 10.44 GHz, respectively.

[0060] from Figure 8 It can be seen that the high entropy double hydroxide / carbon fiber aerogel prepared in Example 1 has the characteristics of light weight. Figure 9As can be seen in Example 1, the high-entropy double hydroxide / carbon fiber aerogel exhibits excellent thermal insulation properties under infrared thermal radiation conditions. When the heating platform temperature is 200°C, the aerogel surface temperature hardly increases significantly within 65 minutes of continuous heating, showing good thermal insulation and stealth effects. At the same time, the infrared emissivity of the aerogel is 0.69. The present invention uses high-entropy layered double hydroxide / carbon fiber for compounding to construct a multiphase interface aerogel structure, which not only significantly improves the interface polarization, but also achieves coordinated regulation of electromagnetic parameters, improves impedance matching, and enhances multiple scattering and energy dissipation of electromagnetic waves, thereby obtaining better absorption performance over a wider frequency band.

Claims

1. A method for preparing a high entropy double hydroxide / carbon fiber aerogel electromagnetic absorbing material, characterized in that: The steps include: (1) activating green algae to obtain carbon fibers, and freeze-drying the carbon fibers to obtain aerogel carbon fibers; (2) immersing the heat-treated aerogel carbon fiber in a high-entropy layered double hydroxide precursor solution for a hydrothermal reaction, thereby obtaining a high-entropy double hydroxide / carbon fiber aerogel material; wherein the hydrothermal reaction temperature is 115-120° C., and the reaction time is not less than 5 hours; (3) freeze-drying the aerogel material of step (2) to obtain the target product.

2. The preparation method according to claim 1, wherein: In step (1), the specific process of activating the green algae is as follows: immersing the green algae in a NaClO-H2SO4 mixed solution, taking it out after ultrasonic treatment, and then immersing it in an ethanol aqueous solution to obtain carbon fibers.

3. The preparation method according to claim 2, wherein: The ultrasonic treatment time is 0.5 to 1 hour; the soaking time in the ethanol aqueous solution is 0.5 to 1 hour.

4. The preparation method according to claim 2, wherein: Na In the ClO-H2SO4 mixed solution, the concentration of NaClO is 2.7~3.0mol / L, and the concentration of H2SO4 is 0.6~0.8mol / L.

5. The preparation method according to claim 1, wherein: In step (1), the product is pre-frozen for 12 to 14 hours and then freeze-dried for 22 to 24 hours, with the freezing temperature being no higher than -60°C.

6. The preparation method according to claim 1, wherein: In step (2), the heat treatment is carried out in an argon atmosphere, the heat treatment temperature is 700°C to 750°C, the holding time is 1 to 1.5 hours, and the heating rate is 2 to 2.5°C / min.

7. The preparation method according to claim 1, wherein: In step (2), Ni(NO3)2·6H2O, Fe(NO3)2·9H2O, Co(NO3)2·6H2O, Mn(NO3)2·4H2O and Cu(NO3)2·3H2O are mixed in equimolar amounts in a high entropy layered double hydroxide precursor solution.

8. The preparation method according to claim 1, wherein: In step (3), the product is washed with deionized water and ethanol in sequence, and then placed in a vacuum freeze dryer for pre-freezing for 12 to 14 hours and then freeze-dried for 24 to 48 hours, with the freezing temperature being no higher than -60°C.

9. The high entropy double hydroxide / carbon fiber aerogel electromagnetic absorbing material prepared by the preparation method of claim 1, characterized in that: With one-dimensional carbon fiber as the substrate, high entropy double hydroxide nanosheets are evenly loaded on the carbon fiber substrate.

10. The electromagnetic absorbing material according to claim 9, wherein: The mass ratio of the carbon fiber substrate to the high entropy double hydroxide nanosheets is 1.8 to 3.7:1.

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