Lightweight and efficient Fe3O4-CNTs / polymer composite aerogel wave-absorbing material and preparation method thereof

Abstract

The invention provides a lightweight high-efficiency Fe3O4-CNTs / polymer composite aerogel wave-absorbing material and a preparation method thereof, and the method comprises the following steps: modifying CNTs with a silane coupling agent to obtain silane coupling agent modified CNTs; the silane coupling agent modified CNTs are dispersed into triethylene glycol to react with ferric acetylacetonate, and Fe3O4-CNTs are obtained; the preparation method comprises the following steps: mixing Fe3O4-CNTs with deionized water, adding acrylic acid, acrylamide, a cross-linking agent and an initiator to obtain a pre-polymerization solution, carrying out a polymerization reaction for 2 hours to obtain hydrogel, soaking the hydrogel in deionized water for 24 hours, and carrying out freeze drying to obtain the Fe3O4-CNTs / polymer composite aerogel. According to the composite aerogel disclosed by the invention, the magnetic loss unit and the dielectric loss unit are effectively integrated into an aerogel skeleton, so that the wave-absorbing material has magnetic loss and dielectric loss at the same time, and has excellent electromagnetic wave absorbing capacity.

Description

Technical Field

[0001] This application relates to the field of functional composite materials technology, and in particular to a lightweight and efficient Fe3O4-CNTs / polymer composite aerogel microwave absorbing material and its preparation method. Background Technology

[0002] The rapid development of electronic communication technology has brought unprecedented convenience to modern society, but it has also led to increasingly serious electromagnetic pollution and interference problems. The resulting electromagnetic radiation not only interferes with the normal operation of precision electronic equipment but also poses a potential threat to human health, drawing widespread attention to electromagnetic protection technologies worldwide. Advanced electromagnetic wave absorbing (EMWA) materials are crucial and a key national strategic priority. These materials can convert the energy of incident electromagnetic waves into heat energy for dissipation, thus absorbing electromagnetic waves and preventing secondary electromagnetic pollution. Given the current trend towards miniaturization, integration, and portability of electronic devices, exploring lightweight and efficient electromagnetic wave absorbing materials is of significant research importance.

[0003] Despite their potential, traditional single-component EMWA materials face obstacles that limit their practical applications. While pure carbon-based materials possess excellent dielectric loss properties, their excessively high conductivity leads to impedance mismatch, resulting in strong electromagnetic wave reflection rather than absorption. Conversely, purely magnetic materials exhibit good magnetic loss characteristics, but often suffer from high density, limited effective absorption bandwidth, and poor environmental stability. These materials struggle to balance the trade-off between impedance matching and attenuation capability, resulting in narrow absorption bandwidths and limited practical applicability.

[0004] Research has found that constructing multi-component heterogeneous structures can effectively synergize electrical, dielectric, and magnetic loss mechanisms, with carbon-based / magnetic material composite systems attracting particular attention. For example, introducing magnetic materials onto one-dimensional conductive carbon nanotubes (CNTs) can significantly improve the impedance matching and attenuation performance of CNTs. However, effectively integrating magnetic and dielectric loss units into an aerogel framework to achieve synergistic effects remains a technical challenge in this field. Summary of the Invention

[0005] This application provides a lightweight and efficient Fe3O4-CNTs / polymer composite aerogel microwave absorbing material and its preparation method, in order to solve the problems mentioned in the background art.

[0006] In a first aspect, this application provides a method for preparing a lightweight and efficient Fe3O4-CNTs / polymer composite aerogel microwave absorbing material, the method comprising the following steps: (1) Silane coupling agent modified CNTs: CNTs were nitrated with a mixed pickling solution of H2SO4 and HNO3 to obtain hydroxylated CNTs. The hydroxylated CNTs were then added to ethanol and ultrasonically dispersed. The pH of the system was adjusted to 3-4 with acid. An ethanol solution of silane coupling agent was added dropwise and a condensation reaction was carried out under stirring to obtain silane coupling agent modified CNTs. (2) Fe3O4 nanoparticle loading: Silane coupling agent modified CNTs were dispersed in triethylene glycol, and then acetylacetone iron was added. The mixture was ultrasonically treated for 30 min to obtain a mixed suspension. The mixed suspension was reacted, and the resulting reactants were washed and dried to obtain modified CNTs loaded with Fe3O4 nanoparticles, namely Fe3O4-CNTs. (3) Preparation of composite aerogel: Fe3O4-CNTs were mixed with deionized water to obtain a Fe3O4-CNTs dispersion. Acrylic acid and acrylamide were added to the dispersion, followed by a crosslinking agent and an initiator. The mixture was stirred to obtain a prepolymer solution. The prepolymer solution was polymerized at 80°C for 2 hours to obtain a hydrogel. The hydrogel was soaked in deionized water for 24 hours and then freeze-dried to obtain a Fe3O4-CNTs / polymer composite aerogel.

[0007] Optionally, in the step of modifying CNTs with silane coupling agents: The weight ratio of hydroxylated CNTs to ethanol is 1:100, the mass concentration of the ethanol solution of the silane coupling agent is 5wt%, and the weight ratio of hydroxylated CNTs to silane coupling agent is 1:(5-25).

[0008] Optionally, in the step of modifying CNTs with silane coupling agents, the condensation reaction conditions are: stirring in an oil bath at 70°C for 12 hours.

[0009] Optionally, in the Fe3O4 nanoparticle loading step: The mass-to-volume ratio of silane coupling agent-modified CNTs to triethylene glycol is 0.2 g / 100 mL, and the mass ratio of silane coupling agent-modified CNTs to iron acetylacetone is 1:2-6.

[0010] Optionally, in the Fe3O4 nanoparticle loading step, the mixed suspension reaction conditions are 200℃ for 2-6 hours.

[0011] Optionally, in the preparation steps of the composite aerogel: The prepolymer solution, by mass concentration, comprises: 2-6% Fe3O4-CNTs, 0.16% crosslinking agent, 0.16% initiator, 2% acrylic acid, 8% acrylamide, and the balance being the deionized water.

[0012] Optionally, the preparation steps of hydroxylated CNTs include: H2SO4 and HNO3 were mixed in a volume ratio of 3:1 to obtain a mixed pickling solution. CNTs were added to the mixed pickling solution, and the mixture was ultrasonically dispersed for 30 min. The solution was then heated and stirred at 60 °C for 3 h to obtain a reaction solution containing hydroxylated CNTs. The reaction solution containing hydroxylated CNTs was filtered, washed, and dried to obtain hydroxylated CNTs.

[0013] Optionally, the mass-to-volume ratio of CNTs to the mixed pickling solution is 1 g / 100 mL.

[0014] Secondly, this application provides a Fe3O4-CNTs / polymer composite aerogel microwave absorbing material, which is prepared by the above-mentioned method.

[0015] Thirdly, this application provides an application of Fe3O4-CNTs / polymer composite aerogel absorbing material, which is the aforementioned composite aerogel absorbing material, and is applied in the field of electromagnetic wave absorption.

[0016] This application provides a lightweight and efficient Fe3O4-CNTs / polymer composite aerogel microwave absorbing material and its preparation method. It achieves the preparation of Fe3O4-CNTs / polymer composite aerogel microwave absorbing material, successfully integrating magnetic loss units (Fe3O4) and dielectric loss units (CNTs) into the aerogel framework and realizing a synergistic effect. Compared with existing technologies, it has the following beneficial effects: (1) This application utilizes a comprehensive approach combining hydrothermal synthesis, copolymerization, and freeze-drying techniques to construct a layered porous ternary composite aerogel. A Fe3O4-CNTs heterostructure was successfully prepared by surface modification of CNTs and in-situ hydrothermal growth of Fe3O4 nanoparticles. This heterostructure was then copolymerized with acrylic acid (AA) and acrylamide (AM) to form a three-dimensional porous network, and freeze-dried to obtain the Fe3O4-CNTs / P(AA-AM) composite aerogel. Simultaneously, the electromagnetic wave absorption performance of the composite aerogel was controlled by varying the amount of Fe3O4-CNTs added. When the amount of Fe3O4-CNTs added was 5%, the EAB was 5.04 GHz, and the RL... min With a voltage rating of -35.5dB, it possesses multiple electromagnetic loss mechanisms and is a novel, highly efficient microwave absorbing material.

[0017] (2) The Fe3O4-CNTs / polymer composite aerogel provided in this application has excellent electromagnetic wave absorption capability. The modified CNTs loaded with Fe3O4 nanoparticles enable the absorbing material to simultaneously possess magnetic loss (Fe3O4) and dielectric loss (CNTs and interfaces). This dual-loss mechanism allows the absorbing material to effectively respond to electromagnetic waves of different frequency bands over a wider frequency range. The Fe3O4 nanoparticles are anchored on the surface of CNTs or uniformly dispersed in the polymer matrix, creating a large number of Fe3O4 / CNTs and Fe3O4 / CNTs-polymer heterojunction interfaces. These interfaces greatly enhance the dielectric loss and dissipate into heat through interfacial polarization relaxation, thus achieving the absorption of electromagnetic waves. The polymer matrix prevents the tight aggregation of Fe3O4-CNTs, allowing them to exist in a more dispersed and active form, exposing a larger specific surface area, thereby generating more interfaces.

[0018] (3) This application effectively integrates magnetic loss units (Fe3O4) and dielectric loss units (CNTs) into the aerogel framework to achieve a synergistic effect. Fe3O4 particles create extremely dense Fe3O4 / CNTs and Fe3O4 / polymer heterostructures on the surface of CNTs and in the polymer matrix. These interfaces are "active sites" for generating interfacial polarization. At the same time, the Fe3O4-CNTs / polymer composite aerogel provided by this application has a unique "high specific surface area-small pore size" structure, which maximizes the interfacial polarization effect and significantly enhances the electromagnetic wave scattering effect. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 A schematic diagram illustrating the preparation process and chemical synthesis of Fe3O4-CNTs / polymer composite aerogel provided in an embodiment of this application; Figure 2 XRD patterns of modified CNTs loaded with Fe3O4 nanoparticles provided in Examples 1-5; Figure 3 TEM images of CNTs, Fe3O4-CNTs-6 provided in Example 5 and Fe3O4-CNTs-2 provided in Example 3. Figure 3 (a) is a TEM image of the CNTs provided in Example 5. Figure 3(b) is a TEM image of Fe3O4-CNTs-2- calcined as provided in Example 3. Figure 3 (c) is a TEM image of Fe3O4-CNTs-6 provided in Example 5. Figure 3 (d) is a partially enlarged TEM image of Fe3O4-CNTs-6 provided in Example 5; Figure 4 SEM and EDS images of Fe3O4-CNTs / P(AA-AM)-5 at different magnifications provided in Example 9. Figure 4 Images (a)-(d) are SEM images of Fe3O4-CNTs / P(AA-AM)-5 at different magnifications provided in Example 9. Figure 4 (e)-(i) in the figure are the EDS diagrams of Fe3O4-CNTs / P(AA-AM)-5 provided in Example 9; Figure 5 Specific surface area and pore structure diagrams of the Fe3O4-CNTs / polymer composite aerogel absorbing materials provided in Examples 6, 9, and 10. Figure 5 (a) is the N2 adsorption / desorption isotherm of the Fe3O4-CNTs / polymer composite aerogel absorbing materials provided in Examples 6, 9, and 10. Figure 5 (b) is a pore size distribution diagram of the Fe3O4-CNTs / polymer composite aerogel absorbing materials provided in Examples 6, 9 and 10; Figure 6 The microwave absorption performance diagrams of the Fe3O4-CNTs / polymer composite aerogel absorbing materials provided in Examples 6-10 are shown. Figure 6 (a1) and (a2) are two-dimensional and three-dimensional RL contour plots of Fe3O4-CNTs / P(AA-AM)-2 provided in Example 6. Figure 6 (b1) and (b2) are two-dimensional and three-dimensional RL contour plots of Fe3O4-CNTs / P(AA-AM)-3 provided in Example 7. Figure 6 (c1) and (c2) are two-dimensional and three-dimensional RL contour plots of Fe3O4-CNTs / P(AA-AM)-4 provided in Example 8. Figure 6 (d1) and (d2) are two-dimensional and three-dimensional RL contour plots of Fe3O4-CNTs / P(AA-AM)-5 provided in Example 9. Figure 6 (e1) and (e2) are two-dimensional and three-dimensional RL contour plots of Fe3O4-CNTs / P(AA-AM)-6 provided in Example 10; Figure 7The graphs show the relationship between absorption intensity and frequency of the Fe3O4-CNTs / polymer composite aerogel absorbing materials provided in Examples 6-10. Figure 7 (a1)-(e1) are the RL-frequency curves of the Fe3O4-CNTs / polymer composite aerogel absorbing materials provided in Examples 6-10. Figure 7 (a2)-(e2) are the 1 / 4 wavelength matching diagrams of the Fe3O4-CNTs / polymer composite aerogel absorbing materials provided in Examples 6-10. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application are described clearly and completely below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are also within the scope of protection of this application.

[0022] like Figure 1 As shown, in a first aspect, this application provides a method for preparing a lightweight and efficient Fe3O4-CNTs / polymer composite aerogel microwave absorbing material, the method comprising the following steps: (1) Silane coupling agent modified CNTs: CNTs were nitrated with a mixed pickling solution of H2SO4 and HNO3 to obtain hydroxylated CNTs. The hydroxylated CNTs were then added to ethanol and ultrasonically dispersed. The pH of the system was adjusted to 3-4 with hydrochloric acid. An ethanol solution of silane coupling agent was added dropwise and a condensation reaction was carried out under stirring to obtain silane coupling agent modified CNTs.

[0023] (2) Fe3O4 nanoparticle loading: Silane coupling agent modified CNTs were dispersed in triethylene glycol, and then acetylacetone iron was added. The mixture was ultrasonically treated for 30 min to obtain a mixed suspension. The mixed suspension was reacted, and the resulting reactants were washed and dried to obtain modified CNTs loaded with Fe3O4 nanoparticles, namely Fe3O4-CNTs.

[0024] (3) Preparation of composite aerogel: Fe3O4-CNTs were mixed with deionized water to obtain a Fe3O4-CNTs dispersion. Acrylic acid and acrylamide were added to the dispersion, followed by a crosslinking agent and an initiator. The mixture was stirred to obtain a prepolymer solution. The prepolymer solution was polymerized at 80°C for 2 hours to obtain a hydrogel. The hydrogel was soaked in deionized water for 24 hours and then freeze-dried to obtain a Fe3O4-CNTs / polymer composite aerogel.

[0025] Specifically, CNTs are first nitrated with a mixed acid washing solution of concentrated H2SO4 and concentrated HNO3. The mixed acid generates oxygen-containing hydroxyl groups on the CNT surface, resulting in hydroxylated CNTs. Then, a condensation reaction is performed between a silane coupling agent and the surface hydroxyl groups. The hydrolyzed silane coupling agent (containing -Si(OH)3) undergoes a dehydration condensation reaction with the hydroxyl groups (-OH) on the CNT surface, forming a strong covalent bond -Si-OC-, yielding silane coupling agent-modified CNTs. By covalently grafting organic molecules with specific reactivity onto the CNT surface, copolymerization reactions can occur with subsequent monomers, thereby efficiently embedding CNTs into the polymer matrix, which is beneficial for the preparation of composite aerogels.

[0026] In the modification of CNTs with silane coupling agents, hydroxylated CNTs are added to ethanol and ultrasonically dispersed. The cavitation effect of ultrasound provides significant energy, breaking up the CNT aggregates and dispersing them uniformly in ethanol in single or small quantities, thus exposing more reaction sites and promoting efficient reaction. The pH of the system is adjusted to 3-4 with acid. The silane coupling agent needs to be hydrolyzed into active silanol (-SiOH) before the reaction. Acidic conditions effectively catalyze the hydrolysis of the silane coupling agent. Simultaneously, the acidic environment protonates the -OH groups on the CNT surface, allowing them to interact with the silanol through hydrogen bonding, further facilitating the efficient condensation reaction. The silane coupling agent is added dropwise under stirring. To control the local concentration of the silane coupling agent in the reaction system and prevent excessively high local concentrations from causing rapid self-aggregation of silane molecules and forming large amounts of siloxane oligomers, which would physically adsorb onto the CNT surface, affecting the modification effect and product purity.

[0027] The concentration of concentrated H₂SO₄ is 18.4 mol / L, and the concentration of concentrated HNO₃ is 15 mol / L. The pH of the system is adjusted to 3-4 using an acid, which can be any one of hydrochloric acid, nitric acid, or sulfuric acid, with hydrochloric acid being preferred.

[0028] Furthermore, the silane coupling agent is selected from KH-570.

[0029] Furthermore, after the condensation reaction is completed, the reaction product is filtered and washed at least three times with deionized water and anhydrous ethanol, and then dried under vacuum at 80°C for 24 h to obtain silane coupling agent modified CNTs.

[0030] In the Fe3O4 nanoparticle loading step, Fe3O4-CNTs composite material was synthesized via a one-step hydrothermal method. Triethylene glycol served as both a solvent and a reducing agent and a protective agent. Under high heat, acetylacetone iron was decomposed and reduced on the surface of the modified CNTs, generating uniformly attached Fe3O4 nanoparticles in situ. After the reaction, the product was washed several times with anhydrous ethanol, then washed with distilled water until neutral. The solid product was then separated from the water using a magnet. The solid product was dried in a vacuum drying oven at 60-80℃ for 12 hours, finally yielding magnetic modified CNTs loaded with Fe3O4 nanoparticles, namely Fe3O4-CNTs.

[0031] In another embodiment, after the hydrothermal reaction is completed, the product is calcined at 700°C for 2 hours under a nitrogen atmosphere.

[0032] In the preparation of composite aerogels, a novel aerogel with magnetic properties (from Fe3O4), electrical conductivity (from CNTs), and high specific surface area is obtained by uniformly immobilizing Fe3O4-CNTs nanocomposite materials within a three-dimensional polymer network. Acrylamide provides amide functional groups, participating in the formation of hydrogen bonds and enhancing the mechanical strength of the gel. The initiator decomposes upon heating to generate free radicals, initiating a chain polymerization reaction of monomers. The heat causes the initiator to decompose, and the free radicals attack the C=C double bonds, initiating a chain growth reaction. Simultaneously, under the action of a crosslinking agent, a huge, water-insoluble three-dimensional network (hydrogel) is formed, in which Fe3O4-CNTs are captured and immobilized within the polymer network.

[0033] After immersing the hydrogel in deionized water for 24 hours, it was freeze-dried. Immersion in deionized water washes away unreacted monomers, oligomers, and excess initiators, resulting in a purer product. It also promotes swelling equilibrium, allowing the hydrogel to reach a balance between network elasticity and osmotic pressure, leading to a more stable structure and facilitating the formation of regular pores during subsequent freeze-drying. During freeze-drying, the water-filled hydrogel was rapidly frozen, causing the water to crystallize. The sample was then placed in a vacuum environment, where the ice crystals sublimated directly into water vapor and were removed, creating interconnected pores within the gel, thus yielding the Fe3O4-CNTs / polymer composite aerogel.

[0034] The crosslinking agent is selected from N,N'-methylenebisacrylamide (MBA), and the initiator is selected from potassium persulfate (KPS).

[0035] This invention proposes a novel strategy for constructing layered porous ternary composite aerogels by combining hydrothermal synthesis, copolymerization, and freeze-drying techniques. A Fe3O4-CNTs heterostructure was successfully prepared by surface modification of CNTs and in-situ hydrothermal growth of Fe3O4 nanoparticles. This structure was then copolymerized with acrylic acid (AA) and acrylamide (AM) to form a three-dimensional porous network, and freeze-dried to obtain a Fe3O4-CNTs / polymer composite aerogel microwave absorbing material (Fe3O4-CNTs / P(AA-AM)).

[0036] The Fe3O4-CNTs / polymer composite aerogel provided in this application exhibits excellent electromagnetic wave absorption capabilities. The modified CNTs loaded with Fe3O4 nanoparticles enable this absorbing material to simultaneously possess magnetic loss (Fe3O4) and dielectric loss (CNTs and interfaces). This dual-loss mechanism allows the absorbing material to effectively respond to electromagnetic waves of different frequency bands over a wider frequency range. The Fe3O4 nanoparticles are anchored on the CNTs surface or uniformly dispersed in the polymer matrix, creating numerous Fe3O4 / CNTs and Fe3O4 / CNTs-polymer heterojunction interfaces, which significantly enhance dielectric loss. The polymer matrix prevents the tight aggregation of Fe3O4-CNTs, allowing them to exist in a more separated and active form, exposing a larger specific surface area and thus generating more interfaces. When applied to electromagnetic wave absorption, the porous structure of aerogel is first used to achieve good impedance matching, so that the electromagnetic wave is reflected as little as possible and enters the interior of the material more. Then, the electromagnetic wave undergoes multiple reflections and scattering in the three-dimensional porous network inside the material, and the path is greatly extended. During the long propagation path, the electromagnetic wave is converted into heat by Fe3O4 through magnetic resonance and eddy current loss, and is converted into Joule heat by CNTs through conductivity loss. At the numerous heterogeneous interfaces between the components, the electromagnetic wave is dissipated into heat through interface polarization relaxation, thus achieving the absorption of electromagnetic waves.

[0037] Optionally, in the step of modifying CNTs with silane coupling agents: The weight ratio of hydroxylated CNTs to ethanol is 1:100, the mass concentration of the ethanol solution of the silane coupling agent is 5wt%, and the weight ratio of hydroxylated CNTs to silane coupling agent is 1:(5-25).

[0038] Optionally, in the step of modifying CNTs with silane coupling agents, the condensation reaction conditions are: stirring in an oil bath at 70°C for 12 hours.

[0039] Optionally, in the Fe3O4 nanoparticle loading step: The mass-to-volume ratio of silane coupling agent-modified CNTs to triethylene glycol is 0.2 g / 100 mL, and the mass ratio of silane coupling agent-modified CNTs to iron acetylacetone is 1:2-6.

[0040] Specifically, the higher the ratio of silane coupling agent-modified CNTs to iron acetylacetone, the greater the loading of Fe3O4 nanoparticles. Controlling the ratio of the two can achieve a high loading while avoiding excessive agglomeration of nanoparticles.

[0041] Optionally, in the Fe3O4 nanoparticle loading step, the mixed suspension reaction conditions are 200℃ for 2-6 hours.

[0042] Optionally, in the preparation steps of the composite aerogel: The prepolymer solution, by mass concentration, comprises: 2-6% Fe3O4-CNTs, 0.16% crosslinking agent, 0.16% initiator, 2% acrylic acid, 8% acrylamide, and the balance being the deionized water.

[0043] Optionally, the preparation steps of hydroxylated CNTs include: H2SO4 and HNO3 were mixed in a volume ratio of 3:1 to obtain a mixed pickling solution. CNTs were added to the mixed pickling solution, and the mixture was ultrasonically dispersed for 30 min. The solution was then heated and stirred at 60 °C for 3 h to obtain a reaction solution containing hydroxylated CNTs. The reaction solution containing hydroxylated CNTs was filtered, washed with deionized water until neutral, and dried in a vacuum drying oven at 70-80 °C to constant weight to obtain hydroxylated CNTs.

[0044] Optionally, the mass-to-volume ratio of CNTs to the mixed pickling solution is 1 g / 100 mL.

[0045] Secondly, this application provides a Fe3O4-CNTs / polymer composite aerogel microwave absorbing material, which is prepared by the above-mentioned method.

[0046] Thirdly, this application provides an application of Fe3O4-CNTs / polymer composite aerogel absorbing material, which is the aforementioned composite aerogel absorbing material, and is applied in the field of electromagnetic wave absorption.

[0047] The technical solution of this application will be illustrated in detail below with specific embodiments. Example 1

[0048] Preparation of modified CNTs loaded with Fe3O4 nanoparticles: The preparation method includes: (1) Hydroxylated CNTs: H2SO4 and HNO3 were mixed in a volume ratio of 3:1 to obtain a mixed pickling solution. CNTs were added to the mixed pickling solution, and the mixture was ultrasonically dispersed for 30 min. The solution was then heated and stirred at 60 °C for 3 h to obtain a reaction solution containing hydroxylated CNTs. The reaction solution containing hydroxylated CNTs was filtered, washed with deionized water until neutral, and dried in a vacuum drying oven at 70-80 °C to constant weight to obtain hydroxylated CNTs.

[0049] The mass-to-volume ratio of CNTs to the mixed pickling solution is 1 g / 100 mL.

[0050] (2) Silane coupling agent modified CNTs: 2g of hydroxylated CNTs were added to 200g of anhydrous ethanol and ultrasonically dispersed. The pH of the system was adjusted to 3-4 with hydrochloric acid. A 5 wt% KH570 ethanol solution was added dropwise. The mixture was then stirred in an oil bath at 70℃ for 12 h to carry out the condensation reaction. After the reaction was completed, the mixture was washed multiple times with deionized water and ethanol, and then dried under vacuum at 80℃ for 24 h to finally obtain KH570 modified CNTs (CNTs-KH570).

[0051] The weight ratio of hydroxylated CNTs to silane coupling agent is 1:5.

[0052] (3) Fe3O4 nanoparticle loading: 0.1 g of CNTs-KH570 was dispersed in 50 mL of triethylene glycol, and 0.2 g of ferric acetylacetone was added. The mixture was sonicated for 30 min to obtain a mixed suspension. The mixed suspension was transferred to a high-pressure reactor and heated at 200 °C for 4 h. The resulting product was washed several times with ethanol to remove surfactants, and then washed with distilled water until neutral. Finally, the product was separated from water using a magnet and then dried in a vacuum drying oven (60-80 °C) for 12 h to obtain modified CNTs loaded with Fe3O4 nanoparticles, named Fe3O4-CNTs-2. Example 2

[0053] Preparation of modified CNTs loaded with Fe3O4 nanoparticles: The preparation method includes: The difference from Example 1 is that: (3) Fe3O4 nanoparticle loading: The hydrothermal reaction conditions were: heating at 200℃ for 2 hours to obtain modified CNTs loaded with Fe3O4 nanoparticles, named Fe3O4-CNTs-2-1. Example 3

[0054] Preparation of modified CNTs loaded with Fe3O4 nanoparticles: The preparation method includes: The difference from Example 1 is that: (3) Fe3O4 nanoparticle loading: The hydrothermal reaction conditions were: heating at 200℃ for 2 hours and calcining at 700℃ for 2 hours under a nitrogen atmosphere to obtain modified CNTs loaded with Fe3O4 nanoparticles, named: Fe3O4-CNTs-2-calcined. Example 4

[0055] Preparation of modified CNTs loaded with Fe3O4 nanoparticles: The preparation method includes: The difference from Example 1 is that: (3) Fe3O4 nanoparticle loading: Different reactant addition ratios: 0.1 g CNTs-KH570 was dispersed in 50 mL of triethylene glycol, and then 0.4 g of acetylacetone iron was added; The hydrothermal reaction yielded modified CNTs loaded with Fe3O4 nanoparticles, named Fe3O4-CNTs-4. Example 5

[0056] Preparation of modified CNTs loaded with Fe3O4 nanoparticles: The preparation method includes: The difference from Example 1 is that: (3) Fe3O4 nanoparticle loading: Different reactant addition ratios: 0.1 g CNTs-KH570 was dispersed in 50 mL of triethylene glycol, and then 0.6 g of acetylacetone iron was added; The hydrothermal reaction yielded modified CNTs loaded with Fe3O4 nanoparticles, named Fe3O4-CNTs-6.

[0057] Experimental Example 1 Examples 1 to 5 successfully prepared modified CNTs loaded with Fe3O4 nanoparticles. The phase composition and crystal structure of the modified CNTs loaded with Fe3O4 nanoparticles provided in Examples 1 to 5 were tested by XRD (X-ray diffraction), and compared with the original CNTs. The XRD patterns are shown below. Figure 2 As shown. Figure 2 XRD patterns of modified CNTs loaded with Fe3O4 nanoparticles provided in Examples 1 to 5.

[0058] observe Figure 2The XRD patterns of the Fe3O4-CNTs composite material showed distinct characteristic diffraction peaks at 2θ angles of 30.1, 35.5, 43.4, 57.2, and 62.9. These diffraction peaks correspond to the (220), (311), (400), (511), and (440) crystal planes of standard Fe3O4 (PDF#72-2303), respectively, fully confirming the successful synthesis of Fe3O4 crystals after the hydrothermal reaction.

[0059] Experiment Example 2 Taking the CNTs and Fe3O4-CNTs-6 provided in Example 5 and the Fe3O4-CNTs-2-calcined sample provided in Example 3 as examples, transmission electron microscopy (TEM) tests were performed on each sample, and the results are as follows. Figure 3 As shown, Figure 3 TEM images of CNTs, Fe3O4-CNTs-6 provided in Example 5 and Fe3O4-CNTs-2 provided in Example 3. Figure 3 (a) is a TEM image of the CNTs provided in Example 5. Figure 3 (b) is a TEM image of Fe3O4-CNTs-2- calcined as provided in Example 3. Figure 3 (c) is a TEM image of Fe3O4-CNTs-6 provided in Example 5. Figure 3 (d) is a partial magnified view of the TEM image of Fe3O4-CNTs-6 provided in Example 5.

[0060] observe Figure 3 The study confirmed the successful loading of Fe3O4 nanoparticles onto the surface of CNTs after hydrothermal reaction, and the particle loading density was also low when the amount of iron acetylacetone (Fe(acac)3) was small. The average particle size of the Fe3O4 nanoparticles was measured to be approximately 3.5 nm, with the particle size distribution mainly concentrated in a narrow range of 2-6 nm. Figure 3In (c), the particle size distribution of Fe3O4 nanoparticles was observed, exhibiting an approximately normal distribution with particles ranging from 3.5 to 4 nm accounting for the largest proportion. This small and uniform size characteristic indicates that the hydrothermal synthesis method has good controllability. Furthermore, the fine particle size can significantly enhance the interfacial polarization effect of the composite material through two synergistic pathways: "maximizing interfacial density" and "optimizing polarization relaxation efficiency," thereby improving the microwave absorption performance. The intensity of interfacial polarization is directly related to the number of heterojunction interfaces. The reduction in particle size leads to a sharp increase in specific surface area. Fe3O4 particles create extremely dense Fe3O4 / CNTs and Fe3O4 / polymer heterojunction interfaces on the CNTs surface and in the polymer matrix. These interfaces are the "active sites" for interfacial polarization. Simultaneously, the fine and uniform particle size distribution makes the charge / dipole distribution at the interface more uniform and consistent. Under the action of an alternating electromagnetic field, these charges confined at the nanoscale interface can undergo faster and more synergistic relaxation. This efficient and vigorous charge movement leads to stronger relaxation losses, thus converting electromagnetic energy more effectively into heat energy for dissipation. In contrast, excessively large or non-uniform particles result in decreased polarization relaxation efficiency due to uneven distribution of interfacial charges.

[0061] Example 6 A method for preparing a Fe3O4-CNTs / polymer composite aerogel microwave absorbing material includes: Composite aerogels were prepared using the Fe3O4-CNTs-6 provided in Example 5: Fe3O4-CNTs-6 was mixed with deionized water to obtain a Fe3O4-CNTs-6 dispersion. Acrylic acid and acrylamide were added to the dispersion, followed by a crosslinking agent and an initiator. The mixture was stirred to obtain a prepolymer solution. The prepolymer solution was polymerized at 80°C for 2 hours to obtain a hydrogel. The hydrogel was soaked in deionized water for 24 hours and then freeze-dried to obtain a Fe3O4-CNTs / polymer composite aerogel, named Fe3O4-CNTs / P(AA-AM)-2.

[0062] The prepolymer solution comprises, by mass concentration: 2% Fe3O4-CNTs, 0.16% crosslinking agent, 0.16% initiator, 2% acrylic acid, 8% acrylamide, and the balance being the deionized water.

[0063] Example 7 A method for preparing a Fe3O4-CNTs / polymer composite aerogel microwave absorbing material includes: The difference from Example 6 is that: The prepolymer solution contains, by mass concentration, 3% Fe3O4-CNTs, named Fe3O4-CNTs / P(AA-AM)-3.

[0064] Example 8 A method for preparing a Fe3O4-CNTs / polymer composite aerogel microwave absorbing material includes: The difference from Example 6 is that: The prepolymer solution contains, by mass concentration, 4% Fe3O4-CNTs, named Fe3O4-CNTs / P(AA-AM)-4.

[0065] Example 9 A method for preparing a Fe3O4-CNTs / polymer composite aerogel microwave absorbing material includes: The difference from Example 6 is that: The prepolymer solution contains, by mass concentration, 5% Fe3O4-CNTs, named Fe3O4-CNTs / P(AA-AM)-5.

[0066] Example 10 A method for preparing a Fe3O4-CNTs / polymer composite aerogel microwave absorbing material includes: The difference from Example 6 is that: The prepolymer solution contains, by mass concentration, 6% Fe3O4-CNTs, named Fe3O4-CNTs / P(AA-AM)-6.

[0067] Experimental Example 3 Fe3O4-CNTs / polymer composite aerogel microwave absorbing materials were successfully prepared through Examples 6-10. Taking Fe3O4-CNTs / P(AA-AM)-5 provided in Example 9 as an example, its cross-section was analyzed by scanning electron microscopy and energy dispersive spectroscopy, and the results are as follows: Figure 4 As shown. Figure 4 The images and local energy dispersive spectroscopy (EDS) plots of Fe3O4-CNTs / P(AA-AM)-5 at different magnifications provided in Example 9 are shown. Figure 4 Images (a)-(d) are SEM images of Fe3O4-CNTs / P(AA-AM)-5 at different magnifications provided in Example 9. Figure 4 (e)-(i) in the figure are the EDS diagrams of Fe3O4-CNTs / P(AA-AM)-5 provided in Example 9.

[0068] Depend on Figure 4It is evident that the Fe3O4-CNTs / P(AA-AM)-5 aerogel possesses a typical loose and porous structure. High-magnification observation reveals that the Fe3O4-CNTs / P(AA-AM)-5 aerogel provided in Example 9 exhibits a three-dimensional interconnected porous network structure with an average pore size reaching the micrometer level. This well-developed porous framework, formed by the polymerization of Fe3O4-CNTs with acrylic polymers, enables the construction of a highly efficient three-dimensional conductive network within the aerogel. Furthermore, the energy dispersive spectroscopy (EDS) analysis of Fe3O4-CNTs / P(AA-AM)-5 clearly shows the uniform distribution of Fe elements within the material. Combined with these characterization results, it is demonstrated that nanoscale Fe3O4 particles have been successfully loaded onto the CNT surface and effectively anchored within the pore structure of the acrylic-acrylamide copolymer aerogel matrix through a copolymerization reaction.

[0069] Experiment Example 4 The specific surface area and pore structure of the Fe3O4-CNTs / polymer composite aerogel absorbing materials provided in Examples 6 (Fe3O4-CNTs / P(AA-AM)-2), 9 (Fe3O4-CNTs / P(AA-AM)-5), and 10 (Fe3O4-CNTs / P(AA-AM)-6) were tested, and the results are as follows: Figure 5 As shown.

[0070] Simultaneously, the pore size characteristics of the Fe3O4-CNTs / polymer composite aerogel absorbing materials provided in Example 6 (Fe3O4-CNTs / P(AA-AM)-2), Example 9 (Fe3O4-CNTs / P(AA-AM)-5), and Example 10 (Fe3O4-CNTs / P(AA-AM)-6) were tested, and the specific surface area (S) was measured by the BET method. BET The total pore volume (V) was measured by the BJH adsorption method. total The average pore size was measured by the BJH adsorption method, and the results are shown in Table 1.

[0071] Figure 5 Specific surface area and pore structure diagrams of the Fe3O4-CNTs / polymer composite aerogel absorbing materials provided in Examples 6, 9, and 10. Figure 5 (a) is the N2 adsorption / desorption isotherm of the Fe3O4-CNTs / polymer composite aerogel absorbing materials provided in Examples 6, 9, and 10. Figure 5 (b) is a pore size distribution diagram of the Fe3O4-CNTs / polymer composite aerogel absorbing material provided in Examples 6, 9 and 10.

[0072] like Figure 5As shown in (a), all samples exhibited type IV isotherms and type H3 hysteresis loops, further confirming the existence of slit-like mesopores formed by the stacking of sheet-like structures. Figure 5 In (b), the pore size distribution of Fe3O4-CNTs / P(AA-AM)-5 is concentrated within 50 nm, indicating that its structure is dominated by micropores / mesopores. In contrast, the pore size distribution of Fe3O4-CNTs / P(AA-AM)-2 and Fe3O4-CNTs / P(AA-AM)-6 is uneven, with micropores, mesopores and macropores present simultaneously.

[0073] Table 1

[0074] As shown in Table 1, the three aerogels exhibit significant differences in specific surface area and pore structure, indicating that the loading of Fe3O4-CNTs plays a decisive role in the porosity of the aerogels. Specifically, the specific surface area of ​​Fe3O4-CNTs / P(AA-AM)-5 (93.05 m² / g) is significantly higher than that of Fe3O4-CNTs / P(AA-AM)-2 (38.60 m² / g) and Fe3O4-CNTs / P(AA-AM)-6 (41.33 m² / g). This suggests that a 5% loading of Fe3O4-CNTs promotes the formation of richer micro / mesoporous structures in the three-dimensional network, providing more interfaces for electromagnetic wave scattering and polarization. A high specific surface area helps to construct a denser Fe3O4-CNTs-polymer heterostructure interface, thereby enhancing the interfacial polarization effect. Although Fe3O4-CNTs / P(AA-AM)-6 exhibits the highest total pore volume (0.13 cm³ / g) and the largest average pore size (20.38 nm), combined with its low specific surface area, this suggests that excessive filler content (Fe3O4-CNTs) (6%) leads to partial structural collapse or pore fusion of the aerogel framework, resulting in large macropores. While this increases the total pore volume, it reduces the effective interfaces required for polarization, weakening the scattering effect. Fe3O4-CNTs / P(AA-AM)-5 exhibits a medium pore volume (0.07 cm³ / g). 3The high specific surface area ( / g) of Fe3O4-CNTs / P(AA-AM)-5, consistent with its high pore size, indicates that its predominantly small-to-medium-sized mesopore structure is more conducive to multiple scattering of electromagnetic waves. Fe3O4-CNTs / P(AA-AM)-5 has the smallest average pore size (4.31 nm), falling within the typical mesoporous range, which is highly consistent with its high specific surface area. The small pore size helps to extend the propagation path of electromagnetic waves within the pores, enhancing energy attenuation through repeated scattering / reflection. The dense mesoporous structure significantly improves interfacial polarization because the space charge accumulated on the pore walls is more easily relaxed within the nanoscale confined space. In summary, Fe3O4-CNTs / P(AA-AM)-5 exhibits optimal pore characteristics. Its unique "high specific surface area-small pore size" structure maximizes both interfacial polarization and significantly enhances electromagnetic wave scattering.

[0075] Experimental Example 5 Wave absorption performance test The microwave absorption performance of the Fe3O4-CNTs / polymer composite aerogel absorbing materials provided in Examples 6-10 was tested, and the results were as follows: Figure 6 The results are shown. Figure 6 (a1) and (a2) are two-dimensional and three-dimensional RL contour plots of Fe3O4-CNTs / P(AA-AM)-2 provided in Example 6. Figure 6 (b1) and (b2) are two-dimensional and three-dimensional RL contour plots of Fe3O4-CNTs / P(AA-AM)-3 provided in Example 7. Figure 6 (c1) and (c2) are two-dimensional and three-dimensional RL contour plots of Fe3O4-CNTs / P(AA-AM)-4 provided in Example 8. Figure 6 (d1) and (d2) are two-dimensional and three-dimensional RL contour plots of Fe3O4-CNTs / P(AA-AM)-5 provided in Example 9. Figure 6 (e1) and (e2) are two-dimensional and three-dimensional RL contour plots of Fe3O4-CNTs / P(AA-AM)-6 provided in Example 10.

[0076] analyze Figure 6 It can be seen that Fe3O4-CNTs / P(AA-AM)-2 aerogel exhibits only weak absorption performance, and its RL min The value was -10.25 dB, attributed to the minimal electromagnetic loss due to insufficient Fe3O4-CNTs content. The absorption performance of Fe3O4-CNTs / P(AA-AM)-3 aerogel was improved, RL min The value reached -20.5 dB, and the EAB was 1.92 GHz at a thickness of approximately 4.8 mm. The performance of Fe3O4-CNTs / P(AA-AM)-4 aerogel was further improved (RL). min=-22.2dB, EAB=2.12GHz), the Fe3O4-CNTs / P(AA-AM)-5 aerogel achieved optimal absorption performance, exhibiting significant RL. min The values ​​(-35.5 dB) and EAB (5.04 GHz) are mainly due to the increased dielectric and magnetic losses caused by the high Fe3O4-CNT content. However, when the addition amount reaches 6%, the RL of the aerogel... min The value decreased, while EAB did not change much. This may be due to impedance mismatch caused by an excessively high dielectric constant, which in turn leads to a decrease in absorption capacity.

[0077] Experimental Example 6 The relationship between absorption intensity and frequency of the Fe3O4-CNTs / polymer composite aerogel absorbing materials provided in Examples 6-10 was tested. The results are as follows: Figure 7 As shown, Figure 7 (a1)-(e1) are the RL-frequency curves of the Fe3O4-CNTs / polymer composite aerogel absorbing materials provided in Examples 6-10. Figure 7 (a2)-(e2) are the 1 / 4 wavelength matching diagrams of the Fe3O4-CNTs / polymer composite aerogel absorbing materials provided in Examples 6-10.

[0078] like Figure 7 As shown in (a1)-(e1), the RL values ​​of all samples increased with increasing Fe3O4-CNTs / polymer composite aerogel thickness. min The values ​​gradually shift towards lower frequencies. This phenomenon is closely related to the wavelength characteristics of electromagnetic waves: in the low-frequency range, longer wavelengths enhance the material's sensitivity to absorption and reflection. As the thickness of the Fe3O4-CNTs / polymer composite aerogel increases, its absorption efficiency at these frequencies also increases accordingly. The thickness variation at different frequencies was analyzed in detail using the following formula; the results are as follows: Figure 7 As shown in (a2)-(e2).

[0079]

[0080] Where λ represents the wavelength, f m Represents frequency, t m To match the thickness, the phase difference and interference effect in the EMW propagation path reach their maximum when the incident wave passes through a material layer with a thickness equal to 1 / 4λ. This causes a phase reversal between the reflected wave and the incident wave, resulting in the energy of the two waves canceling each other out, thereby reducing reflectivity and increasing absorption efficiency. The RL values ​​for all five samples... min The vertical coordinates of the curves are in high agreement with the theoretical thickness trajectory, indicating that the best absorption effect can be achieved when the absorber thickness meets the λ / 4 matching condition.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for preparing a lightweight and efficient Fe3O4-CNTs / polymer composite aerogel wave-absorbing material, characterized in that, The preparation method comprises the following steps: (1) silane coupling agent modified CNTs: Through nitration reaction of mixed acid washing solution of H2SO4 and HNO3 with CNTs, hydroxylated CNTs are obtained, the hydroxylated CNTs are added into ethanol for ultrasonic dispersion, the pH value of the system is adjusted to 3-4 by acid, the silane coupling agent ethanol solution is added drop by drop, and condensation reaction is carried out under stirring to obtain silane coupling agent modified CNTs; (2) Fe3O4 nanoparticle loading: The silane coupling agent modified CNTs are dispersed into triethylene glycol, and then acetylacetone iron is added and ultrasonic treated to obtain a mixed suspension, and the mixed suspension is reacted, and the obtained reaction product is washed and dried to obtain modified CNTs loaded with Fe3O4 nanoparticles, namely Fe3O4-CNTs; (3) composite aerogel preparation: The Fe3O4-CNTs are mixed with deionized water to obtain a Fe3O4-CNTs dispersion, acrylic acid and acrylamide are added to the dispersion, and then a crosslinking agent and an initiator are added, and the pre-polymer liquid is obtained by stirring, and the pre-polymer liquid is polymerized at 80°C for 2h to obtain a hydrogel, and the hydrogel is soaked in deionized water for 24h and then freeze-dried to obtain a Fe3O4-CNTs / polymer composite aerogel.

2. The preparation method of the lightweight and efficient Fe3C>4-CNTs / polymer composite aerogel wave-absorbing material according to claim 1, characterized in that, In the step of silane coupling agent modified CNTs: The weight ratio of the hydroxylated CNTs to ethanol is 1:100, the mass concentration of the silane coupling agent ethanol solution is 5wt%, and the weight ratio of the hydroxylated CNTs to the silane coupling agent is 1:(5-25).

3. The preparation method of the lightweight and efficient Fe304-CNTs / polymer composite aerogel wave-absorbing material according to claim 1, characterized in that, In the step of silane coupling agent modified CNTs, the condensation reaction is carried out under the following conditions: stirring in an oil bath at 70°C for 12h.

4. The preparation method of the lightweight and efficient Fe3C>4-CNTs / polymer composite aerogel wave-absorbing material according to claim 1, characterized in that, In the step of Fe3O4 nanoparticle loading: The mass-volume ratio of the silane coupling agent modified CNTs to triethylene glycol is 0.2g / 100mL, and the mass ratio of the silane coupling agent modified CNTs to the acetylacetone iron is 1:2-6.

5. The method according to claim 1, wherein the method is characterized in that, In the step of Fe3O4 nanoparticle loading, the mixed suspension is reacted at 200°C for 2-6h.

6. The method according to claim 1, wherein the method is characterized by, In the step of composite aerogel preparation: In the pre-polymer liquid, the Fe3O4-CNTs, the crosslinking agent, the initiator, the acrylic acid, the acrylamide and the deionized water are included in the following mass concentrations: 2-6%, 0.16%, 0.16%, 2%, 8% and the balance, respectively.

7. The method of claim 1-6, wherein the method of preparing lightweight and efficient Fe304-CNTs / polymer composite aerogel wave-absorbing material is characterized in that, The preparation step of the hydroxylated CNTs comprises: H2SO4 and HNO3 are mixed in a volume ratio of 3:1 to obtain a mixed acid washing solution, CNTs are added into the mixed acid washing solution, ultrasonic dispersion is carried out for 30min, and then heating and stirring are carried out at 60°C for 3h to obtain a reaction liquid containing hydroxylated CNTs, and the reaction liquid containing hydroxylated CNTs is filtered, washed and dried to obtain the hydroxylated CNTs.

8. The method according to claim 6, wherein the method is characterized by, The mass-volume ratio of the CNTs to the mixed acid washing solution is 1g / 100mL.

9. A lightweight and efficient Fe304-CNTs / polymer composite aerogel wave-absorbing material, characterized in that, The composite aerogel wave-absorbing material is prepared by the method of any one of claims 1-8.

10. Use of a lightweight and efficient Fe3O4-CNTs / polymer composite aerogel wave-absorbing material, characterized in that, The composite aerogel wave-absorbing material is prepared by the method of any one of claims 1-8 or is the composite aerogel wave-absorbing material of claim 9, and is applied to the field of electromagnetic wave absorption.

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