Preparation method of composite wave-absorbing material

Abstract

The invention relates to the technical field of microwave absorbing materials, and discloses a composite wave absorbing material preparation method, which comprises: carrying out ultrasonic dispersion treatment on graphene oxide to obtain a graphene oxide dispersion liquid; the method comprises the following steps: carrying out surface positive electrification treatment on Fe3O4 nanospheres by using an organic solvent, washing the positively electrified Fe3O4 nanospheres by using ethanol and deionized water, removing excessive organic solvent on the surfaces of the Fe3O4 nanospheres, and drying to obtain positively electrified Fe3O4 nanospheres; ultrasonically dispersing the positively electrified Fe3O4 nanospheres in deionized water, and mixing with a graphene oxide dispersion liquid to obtain a mixed solution; and adding the conductive two-dimensional material solution into the mixed solution, uniformly mixing, and then freeze-drying to obtain the three-dimensional magnetic composite wave-absorbing material. The three-dimensional porous composite structure with the graphene oxide as a framework, the Fe3O4 nanospheres as magnetic units and the conductive two-dimensional material as the conductive wrapping layer enables the material to show excellent broadband wave-absorbing performance in the frequency band of 2-18 GHz, and the lowest reflection loss of the material can reach-39.24 dB at 17.76 GHz.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of microwave absorbing materials, and particularly relates to a preparation method of a composite wave-absorbing material and particularly relates to a light-weight and high-efficiency three-dimensional porous composite wave-absorbing material and a preparation method thereof. BACKGROUND

[0002] With the rapid development of the electronic communication industry, the wide application of the fifth generation (5G) mobile communication technology, the large-scale construction of radar base stations, and the universal use of various communication equipment and related intelligent electronic products, electromagnetic pollution derived therefrom not only interferes with the normal operation of precision electronic equipment, but also endangers human health. Meanwhile, with the rapid development of modern military information technology, electronic countermeasures will inevitably become an important form of future warfare, and electromagnetic wave signal leakage in electronic countermeasures will endanger national security and even cause significant losses of national interests. Therefore, it is of great significance to develop microwave absorbing materials with high performance. Meanwhile, with the gradual development of electronic equipment towards miniaturization, light weight, flexibility and other directions, the highly integrated form characteristics and portable application requirements of the electronic equipment put forward performance requirements such as flexibility, light weight, multi-band and strong absorption on the wave-absorbing material.

[0003] Traditional wave-absorbing materials, such as ferrite, carbon black and metal powder, are difficult to meet the above core requirements. In order to meet the application requirements of future electronic equipment electromagnetic wave absorption, it is urgent to develop new wave-absorbing materials with flexibility, light weight, multi-band and strong absorption. SUMMARY

[0004] The application aims to provide a preparation method of a composite wave-absorbing material, and realize the effects of flexibility, light weight, multi-band and strong absorption.

[0005] According to the above idea, the technical scheme adopted by the application is as follows: According to a first aspect of an embodiment of the application, a preparation method of a composite wave-absorbing material is provided, comprising the following steps: S1: performing ultrasonic dispersion treatment on graphene oxide to obtain a graphene oxide dispersion liquid; S2: performing surface positive electrochemical treatment on Fe3O4 nanospheres using an organic solvent; S3: washing the positively charged Fe3O4 nanospheres with ethanol and deionized water to remove excess organic solvent on the surface of the Fe3O4 nanospheres, and drying to obtain positively charged Fe3O4 nanospheres; S4: ultrasonically dispersing the positively charged Fe3O4 nanospheres in deionized water, and mixing with the graphene oxide dispersion liquid at room temperature to obtain a mixed solution; S5: adding a conductive two-dimensional material solution to the mixed solution, mixing uniformly, and then performing freeze-drying to obtain a three-dimensional magnetic composite wave-absorbing material.

[0006] In some embodiments, the concentration of the graphene oxide in step S1 is 1-5 mg / ml.

[0007] In some embodiments, the concentration of the conductive two-dimensional material solution in step S5 is 10-20 mg / ml.

[0008] In some embodiments, the mass ratio of the Fe3O4 nanospheres to graphene is 1:1 to 1:5.

[0009] In some embodiments, the organic solvent is hexadecyl trimethyl ammonium bromide.

[0010] In some embodiments, the conductive two-dimensional material comprises at least one of MXene, graphene, and transition metal dichalcogenide.

[0011] Further, the conductive two-dimensional material is preferably a MXene material.

[0012] In some embodiments, step S4 specifically comprises: after mixing the positively charged Fe3O4 nanospheres with the graphene oxide dispersion, oscillating treatment at room temperature for 10-24 hours, so that the positively charged Fe3O4 nanospheres spontaneously and orderly adhere to the surface of the negatively charged graphene oxide by electrostatic attraction.

[0013] According to a second aspect of the embodiments of the present application, a composite wave-absorbing material is provided, which is composed of a conductive two-dimensional material, graphene oxide, and Fe3O4, and has a three-dimensional porous structure; wherein the Fe3O4 is in the form of nanospheres attached to the surface of the graphene oxide, and the outer surface of the Fe3O4 nanospheres is further wrapped with nanosheets of the conductive two-dimensional material.

[0014] According to a third aspect of the embodiments of the present application, the composite wave-absorbing material is used as a flexible film, a structural patch, or a wave-absorbing component filled in a cavity.

[0015] The present application has the following advantages: 1. The present application successfully constructs a three-dimensional porous composite structure with graphene oxide as the skeleton, Fe3O4 nanospheres as the magnetic unit, and a conductive two-dimensional material (especially a MXene material) as the wrapping layer through electrostatic self-assembly and freeze-drying process. The structure effectively synergizes the magnetic loss, dielectric loss, and conductive loss mechanisms, so that the material exhibits excellent broadband wave-absorbing performance in the frequency range of 2-18 GHz, with the lowest reflection loss of -39.24 dB at 17.76 GHz.

[0016] 2. This invention combines the high specific surface area and flexibility of graphene oxide, the magnetism of iron oxide, and the high conductivity of conductive two-dimensional materials, resulting in a microwave absorbing material with high efficiency and flexibility. This high-performance composite microwave absorbing material has significant market potential and value in 5G communication equipment, electromagnetic countermeasures, and electromagnetic compatibility and protection in the low-altitude economy. Attached Figure Description

[0017] Figure 1 This is a flowchart of the main process of the composite absorbing material of the present invention; Figure 2 This is a diagram illustrating the lightweight properties of the composite microwave absorbing material of the present invention; Figure 3 This is a scanning electron microscope image of the composite absorbing material of the present invention; Figure 4 This is a microwave absorption test diagram of the composite absorbing material of the present invention; Figure 5 This is a diagram showing the minimum reflection loss of the composite absorbing material of the present invention. Detailed Implementation

[0018] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of apparatuses and methods consistent with some aspects of the invention as detailed in the appended claims.

[0019] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. Unless otherwise defined, the technical or scientific terms used in this application should be understood in their ordinary sense by one of ordinary skill in the art to which this invention pertains. The words “a” or “one” and similar terms used in this application specification and claims do not indicate a limitation of quantity, but rather indicate the presence of at least one. “A plurality” means two or more. The words “comprising” or “including” and similar terms mean that the element or object preceding “comprising” or “including” covers the element or object listed following “comprising” or “including” and its equivalents, and does not exclude other elements or objects. The words “connected” or “linked” and similar terms are not limited to physical or mechanical connections and can include electrical connections, whether direct or indirect. The words “above” and / or “below” and similar terms are for ease of description only and are not limited to a location or spatial orientation. The singular forms “a,” “the,” and “the” used in this application specification and appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more associated listed items.

[0020] The technical concept of this invention includes: To address the challenge that current absorbing materials struggle to simultaneously meet the comprehensive performance requirements of flexibility, lightweight, wide bandwidth, and strong absorption, especially given the high integration of 5G communication, electronic countermeasures, and portable electronic devices, where traditional ferrite, carbon black, and other materials are no longer adequate for modern electromagnetic compatibility and protection needs, this invention proposes a multi-component composite system based on conductive two-dimensional materials, graphene oxide, and iron oxide. Through controllable electrostatic self-assembly and low-temperature freeze-drying processes, a lightweight composite absorbing material with an "egg-shaped" core-shell unit and a three-dimensional porous structure is constructed.

[0021] The advantages of this approach are as follows: Firstly, by attaching ferromagnetic Fe3O4 nanospheres to the surface of high-specific-surface-area, flexible graphene oxide, and further coating the outer layer with highly conductive two-dimensional nanosheets, an effective synergy of magnetic loss, dielectric loss, and multiple interface polarization effects is achieved. Secondly, by using freeze-drying to form a stable three-dimensional porous structure at low temperatures, the material density is significantly reduced, giving it good flexibility and structural stability, thereby achieving efficient electromagnetic wave absorption over a wide frequency range.

[0022] Therefore, through the integrated concept of "structural design-component composite-process matching", this invention has successfully constructed a new generation of microwave absorbing materials that combine lightweight, flexibility, strong absorption and wideband response characteristics, providing a feasible material basis and process path for their practical application in flexible electronics, stealth technology and electromagnetic protection.

[0023] This application provides a method for preparing a composite microwave absorbing material, including the following steps: S1: Ultrasonic dispersion of graphene oxide is performed to obtain graphene oxide dispersion. S2: Fe3O4 nanospheres were positively electrolyzed using organic solvents; S3: The positively charged Fe3O4 nanospheres were washed with ethanol and deionized water to remove excess organic solvent from the surface of the Fe3O4 nanospheres. After drying, positively charged Fe3O4 nanospheres were obtained. S4: The positively charged Fe3O4 nanospheres were ultrasonically dispersed in deionized water and mixed with graphene oxide dispersion at room temperature to obtain a mixed solution; S5: Add the conductive two-dimensional material solution to the above mixed solution, mix evenly, and then freeze-dry to obtain a three-dimensional magnetic composite absorbing material.

[0024] This invention provides a lightweight and efficient three-dimensional porous composite microwave absorbing material and its preparation method. A high-concentration graphene oxide dispersion is obtained through ultrasonic oscillation. Then, Fe3O4 nanospheres are attached to the surface of the graphene oxide as a framework via electrostatic self-assembly. A conductive two-dimensional material solution is then added, further encapsulating the Fe3O4 nanospheres with conductive two-dimensional material nanosheets to form a "fried egg" structure. Finally, freeze-drying effectively avoids oxidation caused by high temperatures, resulting in a lightweight microwave absorbing material with a three-dimensional porous structure. The combination of the high specific surface area and flexibility of graphene oxide, the magnetism of iron(III) oxide, and the high conductivity of the conductive two-dimensional material gives the provided microwave absorbing material high-efficiency microwave absorption performance and lightweight flexibility. This high-performance composite microwave absorbing material has significant market potential and value in 5G communication equipment, electromagnetic countermeasures, and electromagnetic compatibility and protection in the low-altitude economy.

[0025] The following is in conjunction with the appendix Figures 1 to 5 This application provides a detailed description of a method for preparing a composite microwave absorbing material.

[0026] Example 1 Take 46 ml of concentrated sulfuric acid and add 3.2 g of sodium nitrate, stirring until completely dissolved. After complete dissolution, transfer the beaker containing the reactants to an ice bath and stir continuously. Then, slowly add 2 g of graphite powder and stir evenly for 45 min. Slowly add 6 g of potassium permanganate, always keeping the reaction system temperature below 5°C. After all the reagents are added, continue stirring for 60 min. Then, transfer the reaction vessel to an oil bath at 40°C and stir continuously for 90 min. Slowly add 92 ml of deionized water to the reaction system. After the water addition is complete, transfer the system to an oil bath at 100°C and continue reacting for 20 min. Remove the system and let it cool to 60°C. Slowly add 180 ml of deionized water, then slowly add 30 ml of hydrogen peroxide. The reaction turns golden yellow, indicating the reaction is terminated. After standing for 10 h, remove the precipitated colloid and place it in a dialysis bag for dialyzing until the pH is neutral. Remove the material and freeze-dry it to obtain graphene oxide.

[0027] 30 mg of graphene oxide was added to 20 mL of deionized water and sonicated at 300 W for 1 h. 25 mg of Fe3O4 nanospheres were added to 5 mL of a 1 mg / mL cetyltrimethylammonium bromide solution and sonicated for 60 minutes. Afterwards, the nanospheres were centrifuged, washed repeatedly with deionized water and ethanol, and then vacuum-dried in a vacuum drying oven to obtain positively charged Fe3O4 nanospheres. Finally, 6 mg of positively charged Fe3O4 nanospheres were weighed and added to the graphene oxide solution. The mixture was vibrated in a shaking bed for 20 hours to ensure good electrostatic assembly of the positively charged Fe3O4 and negatively charged graphene oxide. Then, 20 mL of a 15 mg / mL MXene solution was added to the above solution, stirred thoroughly, and then freeze-dried for 72 h. Based on the amount of graphene oxide used, the absorbing material was designated GMF-30.

[0028] Example 2 The mass of graphene oxide is 40 mg, and the mass of positively charged Fe3O4 nanospheres is 10 mg.

[0029] Take 46 ml of concentrated sulfuric acid and add 3.2 g of sodium nitrate, stirring until completely dissolved. After complete dissolution, transfer the beaker containing the reactants to an ice bath and stir continuously. Then, slowly add 2 g of graphite powder and stir evenly for 45 min. Slowly add 6 g of potassium permanganate, always keeping the reaction system temperature below 5°C. After all the reagents are added, continue stirring for 60 min. Then, transfer the reaction vessel to an oil bath at 40°C and stir continuously for 90 min. Slowly add 92 ml of deionized water to the reaction system. After the water addition is complete, transfer the system to an oil bath at 100°C and continue reacting for 20 min. Remove the system and let it cool to 60°C. Slowly add 180 ml of deionized water, then slowly add 30 ml of hydrogen peroxide. The reaction turns golden yellow, indicating the reaction is terminated. After standing for 10 h, remove the precipitated colloid and place it in a dialysis bag for dialyzing until the pH is neutral. Remove the material and freeze-dry it to obtain graphene oxide.

[0030] 40 mg of graphene oxide was added to 20 mL of deionized water and sonicated at 300 W for 1 h. 25 mg of Fe3O4 nanospheres were added to 5 mL of a 1 mg / mL cetyltrimethylammonium bromide solution and sonicated for 60 minutes. Afterwards, the mixture was centrifuged, washed repeatedly with deionized water and ethanol, and then vacuum-dried in a vacuum drying oven to obtain positively charged Fe3O4 nanospheres. Finally, 10 mg of positively charged Fe3O4 nanospheres were weighed and added to the graphene oxide solution. The prepared mixture was vibrated on a shaking bed for 20 hours to ensure good electrostatic assembly of the positively charged Fe3O4 and negatively charged graphene oxide. Then, 20 mL of a 15 mg / mL MXene solution was added to the above solution, stirred thoroughly, and then freeze-dried for 72 h. Based on the amount of graphene oxide used, the absorbing material was designated GMF-40.

[0031] Example 3 The mass of graphene oxide is 50 mg, and the mass of positively charged Fe3O4 nanospheres is 25 mg.

[0032] Take 46 ml of concentrated sulfuric acid and add 3.2 g of sodium nitrate, stirring until completely dissolved. After complete dissolution, transfer the beaker containing the reactants to an ice bath and stir continuously. Then, slowly add 2 g of graphite powder and stir evenly for 45 min. Slowly add 6 g of potassium permanganate, always keeping the reaction system temperature below 5°C. After all the reagents are added, continue stirring for 60 min. Then, transfer the reaction vessel to an oil bath at 40°C and stir continuously for 90 min. Slowly add 92 ml of deionized water to the reaction system. After the water addition is complete, transfer the system to an oil bath at 100°C and continue reacting for 20 min. Remove the system and let it cool to 60°C. Slowly add 180 ml of deionized water, then slowly add 30 ml of hydrogen peroxide. The reaction turns golden yellow, indicating the reaction is terminated. After standing for 10 h, remove the precipitated colloid and place it in a dialysis bag for dialyzing until the pH is neutral. Remove the material and freeze-dry it to obtain graphene oxide.

[0033] 50 mg of graphene oxide was added to 20 mL of deionized water and sonicated at 300 W for 1 h. 25 mg of Fe3O4 nanospheres were added to 5 mL of a 1 mg / mL cetyltrimethylammonium bromide solution and sonicated for 60 minutes. Afterwards, the mixture was centrifuged, washed repeatedly with deionized water and ethanol, and then vacuum-dried in a vacuum drying oven to obtain positively charged Fe3O4 nanospheres. Finally, 25 mg of positively charged Fe3O4 nanospheres were weighed and added to the graphene oxide solution. The prepared mixture was vibrated on a shaking bed for 20 hours to ensure good electrostatic assembly of the positively charged Fe3O4 and negatively charged graphene oxide. Then, 20 mL of a 15 mg / mL MXene solution was added to the above solution, stirred thoroughly, and then freeze-dried for 72 h. Based on the amount of graphene oxide used, the absorbing material was designated GMF-50.

[0034] Example 4 Take 46 ml of concentrated sulfuric acid and add 3.2 g of sodium nitrate, stirring until completely dissolved. After complete dissolution, transfer the beaker containing the reactants to an ice bath and stir continuously. Then, slowly add 2 g of graphite powder and stir evenly for 45 min. Slowly add 6 g of potassium permanganate, always keeping the reaction system temperature below 5°C. After all the reagents are added, continue stirring for 60 min. Then, transfer the reaction vessel to an oil bath at 40°C and stir continuously for 90 min. Slowly add 92 ml of deionized water to the reaction system. After the water addition is complete, transfer the system to an oil bath at 100°C and continue reacting for 20 min. Remove the system and let it cool to 60°C. Slowly add 180 ml of deionized water, then slowly add 30 ml of hydrogen peroxide. The reaction turns golden yellow, indicating the reaction is terminated. After standing for 10 h, remove the precipitated colloid and place it in a dialysis bag for dialyzing until the pH is neutral. Remove the material and freeze-dry it to obtain graphene oxide.

[0035] 30 mg of graphene oxide was added to 20 mL of deionized water and sonicated at 300 W for 1 h. 25 mg of Fe3O4 nanospheres were added to 5 mL of a 1 mg / mL cetyltrimethylammonium bromide solution and sonicated for 60 minutes. Afterwards, the mixture was centrifuged, washed repeatedly with deionized water and ethanol, and then vacuum-dried in a vacuum drying oven to obtain positively charged Fe3O4 nanospheres. Finally, 6 mg of positively charged Fe3O4 nanospheres were weighed and added to the graphene oxide solution. The mixture was shaken in a vibrating bed for 20 hours to ensure good electrostatic assembly of the positively charged Fe3O4 and negatively charged graphene oxide. Then, 30 mL of 1 mg / mL 1T phase molybdenum disulfide nanosheets were added to the above solution, stirred until homogeneous, and then freeze-dried for 72 h.

[0036] Comparative Example 1 30 mg of graphene oxide was added to 20 mL of deionized water and sonicated at 200 W for 0.5 h. 25 mg of Fe3O4 nanospheres were added to 5 mL of a 1 mg / mL cetyltrimethylammonium bromide solution and sonicated for 60 min. Afterwards, the mixture was centrifuged, washed repeatedly with deionized water and ethanol, and then vacuum-dried in a vacuum drying oven to obtain positively charged Fe3O4 nanospheres. Finally, 6 mg of positively charged Fe3O4 nanospheres were added to the graphene oxide solution. The prepared mixture was vibrated on a shaking bed for 20 h to ensure good electrostatic assembly of the positively charged Fe3O4 and the negatively charged graphene oxide. Then, 20 mL of a 15 mg / mL conductive carbon black solution was added to the above solution, stirred until homogeneous, and then freeze-dried for 72 h. The absorbing material is denoted as GMF based on the amount of graphene oxide used.

[0037] Based on the core concept proposed in this invention, those skilled in the art will understand that the scope of protection for the composite absorbing material and its preparation method is not limited to the combination of the three materials explicitly listed in the embodiments: MXene, graphene oxide, and iron oxide. As long as the concept of constructing a composite system of "conductive two-dimensional material + magnetic nanoparticles + porous three-dimensional framework" is adopted, and a lightweight absorbing material with a multi-level loss structure is achieved through electrostatic self-assembly and freeze-drying processes, then the technical solution falls within the scope of protection of this invention.

[0038] Regardless of any reasonable adjustments made to the specific types, microstructures, or proportions of the components based on the principles of this invention, or any equivalent changes to process parameters such as ultrasonic power, dispersion time, and freeze-drying time within the scope disclosed in this invention—for example, partially replacing MXene with other highly conductive two-dimensional materials (such as graphene or transition metal sulfides), or replacing Fe3O4 with other magnetic nanoparticles—all fall under the category of equivalent transformations or simple extensions of the material system and process methods described in this invention. This design, by achieving a unity of magnetic-electric synergy and porous lightweighting at the material composition and structural levels, further broadens the performance boundaries and application scenarios of microwave absorbing materials, and should all be covered by the patent scope of this invention.

[0039] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the disclosure herein. The invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of the invention are indicated by the following claims.

[0040] It should be understood that the present invention is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A method for preparing a composite wave-absorbing material, characterized in that, The method comprises the following steps: S1: ultrasonic dispersion treatment is performed on graphene oxide to obtain a graphene oxide dispersion liquid; S2: surface positive electrochemical treatment is performed on Fe3O4 nanospheres using an organic solvent; S3: the positively charged Fe3O4 nanospheres are washed with ethanol and deionized water to remove excess organic solvent on the surface of the Fe3O4 nanospheres, and after drying, positively charged Fe3O4 nanospheres are obtained; S4: the positively charged Fe3O4 nanospheres are ultrasonically dispersed in deionized water, mixed with the graphene oxide dispersion liquid at room temperature, and a mixed solution is obtained; S5: a conductive two-dimensional material solution is added to the mixed solution, mixed uniformly, and then freeze-dried to obtain a three-dimensional magnetic composite wave-absorbing material.

2. The method according to claim 1, wherein, In the step S1, the concentration of the graphene oxide is 1-5 mg / ml.

3. The method of claim 1, wherein the composite wave-absorbing material is prepared by the steps of: mixing the carbon nanotubes and the magnetic material to form a mixture; and mixing the mixture with the polymer to form the composite wave-absorbing material. In the step S5, the concentration of the conductive two-dimensional material solution is 10-20 mg / ml.

4. The method of claim 1, wherein the composite wave-absorbing material is prepared by the steps of: preparing a solution of a metal salt and a polymer; coating a substrate with the solution; and drying the coated substrate. The mass ratio of the Fe3O4 nanospheres to graphene is 1:1 to 1:

5.

5. The method of claim 1, wherein the composite wave-absorbing material is prepared by the steps of: mixing the carbon nanotubes and the magnetic material to form a mixture; and mixing the mixture with the polymer to form the composite wave-absorbing material. The organic solvent is hexadecyl trimethyl ammonium bromide.

6. The method of claim 1, wherein the composite wave-absorbing material is prepared by the steps of: The step S4 specifically comprises: after the positively charged Fe3O4 nanospheres are mixed with the graphene oxide dispersion liquid, oscillation treatment is performed at room temperature for 10-24 hours, so that the positively charged Fe3O4 nanospheres spontaneously and orderly adhere to the surface of the negatively charged graphene oxide through electrostatic attraction.

7. The method of claim 1, wherein the composite wave-absorbing material is prepared by the steps of: mixing the absorbing material and the dielectric material to form a mixture; and mixing the mixture with the magnetic material to form the composite wave-absorbing material. In the step S5, the conductive two-dimensional material comprises at least one of MXene, graphene, and transition metal dichalcogenide.

8. The composite wave-absorbing material prepared by the method of claims 1-7, characterized in that, The composite wave-absorbing material is composed of a conductive two-dimensional material, graphene oxide, and ferroferric oxide, and has a three-dimensional porous structure; wherein Fe3O4 is in the form of nanospheres attached to the surface of graphene oxide, and the outer surface of the Fe3O4 nanospheres is further wrapped with conductive two-dimensional material nanosheets.

9. Use of a composite wave-absorbing material, characterized in that, The composite wave-absorbing material is a flexible film, a structural patch, or a wave-absorbing assembly filled in a cavity.

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