An electromagnetic wave absorbing material based on in-situ growth of carbon nanotubes on FeCoNi alloy and a preparation method thereof

Abstract

This invention discloses an electromagnetic wave absorbing material based on in-situ grown carbon nanotubes from FeCoNi alloy and its preparation method. First, an iron-based metal-organic framework is synthesized via a hydrothermal reaction, followed by ultrasonication, washing, and drying to obtain iron-based metal-organic framework nanoparticles. Then, the surface of the iron-based metal-organic framework nanoparticles is modified using polyvinylpyrrolidone, and Co is adsorbed onto them. 2+ and Ni 2+ Polyvinylpyrrolidone (MOF)-modified iron-cobalt-nickel (FeCoNi)-based metal-organic framework (MOF) nanoparticles were obtained. Finally, melamine and the cobalt-nickel-adsorbed MOF-modified FeCoNi-based MOF nanoparticles were subjected to a carbothermal reduction reaction under a nitrogen atmosphere to obtain the electromagnetic wave absorbing material. This invention relies on MOF porous templates and metal nanoparticles to catalyze the growth of carbon nanotubes, improving conductivity loss. Simultaneously, the interfacial polarization between the generated FeCoNi nanoparticles and the carbon matrix optimizes impedance matching and enhances electromagnetic wave absorption performance.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic wave absorbing materials technology, specifically relating to an electromagnetic wave absorbing material based on in-situ grown carbon nanotubes of FeCoNi alloy and its preparation method. Background Technology

[0002] Electromagnetic wave absorbing materials are widely used in communications, radar systems, and military technology to mitigate electromagnetic interference, protect electronic equipment, and improve signal quality. Developing thin, lightweight, wide-bandwidth, and strong electromagnetic wave absorbing materials is a pressing issue. Fe-MOFs, with their high specific surface area, tunable pore structure, and abundant active sites, exhibit excellent performance in electromagnetic wave absorbing materials. However, limited effective absorption bandwidth, susceptibility to corrosion, and high density requirements severely restrict the further application of MOF materials. Designing novel multifunctional MOF composites to achieve superior electromagnetic absorption performance is receiving increasing attention.

[0003] Constructing composite materials with multiple losses provides a mainstream approach to further enhance electromagnetic wave absorption capabilities. Typical traditional microwave absorbing materials exhibit excellent absorption performance, such as magnetic materials, semiconductor-based metal oxide nanoparticles, MXene, and conductive polymers. These materials face common problems such as impedance mismatch and poor stability of single components, hindering their practical applications. Constructing multiple heterogeneous interfaces in different composite materials can improve the overall effect of magnetic-dielectric synergy, enriching the mechanisms and pathways of electromagnetic wave loss. The structural and compositional diversity of metal-organic frameworks (MOFs) has attracted great attention for their derived electromagnetic wave absorbing materials, as these variations can effectively control their electromagnetic absorption performance. Organic ligands in MOF structures gradually pyrolyze to form carbon, and magnetic nanoparticles are often encapsulated in graphitic carbon. This core-shell structure is beneficial for impedance matching and dielectric loss through heterogeneous interfaces. Among various MOF derivatives, Fe-MOF stands out due to its inherent magnetism and tunable structure, which facilitates the formation of magnetic nanoparticles and conductive carbon matrices, further optimizing impedance matching and loss mechanisms. Carbon-based materials, due to their low density, excellent chemical stability, and conductivity, significantly influence dielectric loss, making them advanced candidates for potential microwave absorbers. Carbon nanotubes, with their excellent conductivity, high surface area, and lightweight properties, are ideal electromagnetic wave absorbing materials. Therefore, designing carbon nanotube composites with Fe-MOFs is an important strategy for optimizing impedance matching and effective absorption bandwidth. Summary of the Invention

[0004] This invention is proposed to solve the problems existing in the prior art, and its purpose is to provide an electromagnetic wave absorbing material based on in-situ grown carbon nanotubes of FeCoNi alloy and its preparation method.

[0005] This invention is achieved through the following technical solution: An electromagnetic wave absorbing material based on in-situ grown carbon nanotubes of FeCoNi alloy and its preparation method include the following steps: S1. Preparation of iron-based metal-organic framework nanoparticles: Iron-based metal-organic frameworks (Fe-MOF) are synthesized by hydrothermal reaction, and then uniform iron-based metal-organic framework nanoparticles (Fe-MOF nanoparticles) are obtained by ultrasonication, washing and drying. The specific preparation method is as follows: terephthalic acid and FeCl3·6H2O are dissolved in N,N-dimethylformamide (DMF), mixed and poured into a high-pressure reactor, heated at 110℃ for 20h, allowed to stand at room temperature for 1h, and then washed and freeze-dried to obtain Fe-MOF nanoparticles. The ratio of phthalic acid, FeCl3·6H2O and DMF is 1 mol: (1.5~2.5) mol: (10~15) mL, preferably 1 mol: 2 mol: 12 mL; S2, Metal Ion Adsorption: First, the iron-based metal-organic framework nanoparticles prepared in step S1 are surface-modified using polyvinylpyrrolidone. Then, Co ions are adsorbed using cobalt and nickel salts. 2+ and Ni 2+ Polyvinylpyrrolidone-modified iron-cobalt-nickel-based metal-organic framework nanoparticles were adsorbed onto the surface of the nanoparticles to obtain polyvinylpyrrolidone-modified iron-cobalt-nickel-based metal-organic framework nanoparticles. The specific preparation method is as follows: S21. The Fe-MOF nanoparticles obtained in step S1 are dispersed in a polyvinylpyrrolidone (PVP) aqueous solution and stirred for 1 h. The Fe-MOF nanoparticles prepared in step S1 are surface modified with polyvinylpyrrolidone (PVP). After centrifugation, washing and freeze-drying, PVP-modified Fe-MOF nanoparticle powder (Fe-MOF@PVP) is obtained. The mass ratio of the Fe-MOF nanoparticles to polyvinylpyrrolidone (PVP) is 1:1; The mass concentration of the polyvinylpyrrolidone (PVP) aqueous solution is 0.67%. S22. Under stirring conditions, add Co(NO3)2·6H2O and Ni(NO3)2·6H2O to deionized water to prepare a mixed salt solution, and continue stirring. Add the PVP-modified Fe-MOF nanoparticles obtained in step S21 to the mixed salt solution, and stir for 4-6 hours to allow the Co... 2+ and Ni 2+The Fe-MOF nanoparticles were fully adsorbed in ionic form on the surface of PVP-modified Fe-MOF nanoparticles. After washing with ethanol and deionized water and centrifuging 3-5 times respectively, the Fe-MOF nanoparticles were freeze-dried for 24 hours to obtain Co / Ni adsorbed PVP-modified FeCoNi-MOF nanoparticles (CoNi / Fe-MOF@PVP), thus achieving surface modification and stabilization of Fe-MOF nanoparticles. The mass ratio of the PVP-modified Fe-MOF nanoparticles, Co(NO3)2·6H2O and Ni(NO3)2·6H2O obtained in step S21 is 2:1:1. The mass concentrations of both Co(NO3)2·6H2O and Ni(NO3)2·6H2O in the mixed salt solution were 22.7%. S3, Carbothermic reduction reaction: Melamine and the PVP-modified Fe-MOF nanoparticles with adsorbed Co / Ni obtained in step S2 were placed in the upstream and downstream of a tube furnace, respectively, and carbothermic reduction reaction was carried out under a nitrogen atmosphere to obtain nitrogen-doped carbon nanotube composite material (FeCoNi@NCNTs) grown in situ on the surface of Fe-MOF derivative, i.e. FeCoNi alloy encapsulated in situ by carbon nanotubes. The specific preparation method is as follows: The PVP-modified Fe-MOF nanoparticles with adsorbed Co / Ni obtained in step S2 were placed in a quartz boat and placed downstream of a tube furnace. Then, a quartz boat containing melamine was placed upstream of the tube furnace. A carbothermic reduction reaction was carried out in the tube furnace under a nitrogen atmosphere. After the reaction, nitrogen-doped carbon nanotube composite material with in-situ growth on the surface of Fe-MOF derivative was obtained, namely, carbon nanotube in-situ encapsulated FeCoNi alloy (FeCoNi@NCNTs). The carbothermic reduction reaction is carried out at a temperature of 750℃~850℃ for 1h~2h. The mass ratio of the melamine to the PVP-modified FeCoNi-MOF nanoparticles with adsorbed Co / Ni obtained in step S2 is (8~12):1, preferably 10:1; A quartz boat containing PVP-modified Fe-MOF nanoparticles adsorbed with Co / Ni and a quartz boat containing melamine are placed symmetrically around the center of a tube furnace, with a distance of 5 cm between their adjacent end faces. During the carbothermic reduction reaction, melamine, as a reaction substrate, volatilizes upon heating and travels downstream with the gas flow to participate in subsequent reactions. Metal nanoparticles catalyze the formation of carbon nanotubes, resulting in the growth of a large number of carbon nanotubes on the surface of Fe-MOF derivatives, forming a composite material of nitrogen-doped carbon nanotubes. S4. Testing the electromagnetic wave absorption performance of FeCoNi alloy encapsulated in situ with carbon nanotubes: The FeCoNi alloy encapsulated in situ with carbon nanotubes and paraffin wax were thoroughly stirred and then placed in a compression mold to press into a ring with an outer diameter of 7.0 mm, an inner diameter of 3.04 mm, and a thickness of 2.0 mm. The electromagnetic wave absorption performance of the sample was tested in the 2 GHz to 18 GHz band using a vector network analyzer (VAN, Ceyear 3656D). The mass of the FeCoNi alloy encapsulated in situ with carbon nanotubes accounted for 18% of the total mass of the FeCoNi alloy encapsulated in situ with carbon nanotubes and paraffin wax.

[0006] Tests revealed that the in-situ grown nitrogen-doped carbon nanotube composite material on the surface of the prepared Fe-MOF derivative exhibits excellent magnetic properties and dielectric loss as an electromagnetic wave absorbing material, synergistically promoting electromagnetic wave absorption performance. The porous structure with interwoven carbon nanotubes promotes multiple reflections and absorptions of electromagnetic waves, further improving loss efficiency.

[0007] The beneficial effects of this invention are: This invention provides an electromagnetic wave absorbing material based on in-situ grown carbon nanotubes of FeCoNi alloy and its preparation method. It innovatively constructs a lightweight and porous composite nanostructure through a nano-constraint strategy and in-situ carbothermal reduction reaction, and effectively improves the electromagnetic wave absorption performance by achieving synergistic loss of conductivity and dielectric properties, thus meeting the high-performance requirements of modern electronic devices for electromagnetic wave absorbing materials.

[0008] The carbon nanotube-encapsulated FeCoNi alloy prepared by this invention has a hierarchical composite structure. It relies on MOF porous templates and metal nanoparticles to catalyze the growth of carbon nanotubes, thereby improving conductivity loss. At the same time, the interfacial polarization between the FeCoNi nanoparticles and the carbon matrix can optimize impedance matching and improve electromagnetic wave absorption performance. This invention provides a new research strategy for obtaining materials with high electromagnetic wave absorption performance. Attached Figure Description

[0009] Figure 1 These are scanning electron microscope images of Fe-MOF nanoparticles prepared in Example 1 of this invention; Figure 2 These are scanning electron microscope images of FeCoNi@NCNT prepared in Example 1 of this invention; Figure 3 These are transmission electron microscope images of FeCoNi@NCNT prepared in Example 1 of this invention; Figure 4 This is a graph showing the electromagnetic wave absorption performance of the Fe-MOF nanoparticles prepared in the comparative example of this invention after heating at 800℃. Figure 5 These are electromagnetic wave absorption performance diagrams of FeCoNi@NCNT prepared in Examples 1-3 of this invention.

[0010] For those skilled in the art, other related figures can be obtained from the above figures without any creative effort. Detailed Implementation

[0011] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. Example 1

[0012] A method for preparing electromagnetic wave absorbing materials based on in-situ grown carbon nanotubes from FeCoNi alloy includes the following steps: S1. Dissolve 5 mmol of terephthalic acid and 10 mmol of FeCl3·6H2O in 60 mL of DMF and stir thoroughly for 3 h. Transfer the stirred solution to a high-pressure reactor and place the high-pressure reactor in an oven at 110 °C for 20 h. After the oven is heated, centrifuge at 8000 r / min for 3 min to collect the Fe-MOF precipitate. Wash the precipitate three times with DMF and ethanol respectively to remove unreacted compounds. Then dry the precipitate in a freeze dryer for 24 h to obtain Fe-MOF nanoparticles. S2. Dissolve 200 mg of PVP in 30 mL of deionized water and stir until completely dissolved. Then add 200 mg of Fe-MOF nanoparticles prepared in step S1 to the solution and stir for 2 h. After centrifugation, washing and freeze-drying, PVP-modified Fe-MOF nanoparticle powder is obtained. S3. Dissolve 100 mg of Co(NO3)2·6H2O and 100 mg of Ni(NO3)2·6H2O in 40 mL of deionized water, and add 200 mg of the PVP-modified Fe-MOF nanoparticles prepared in step S2. Mix well, centrifuge to remove excess unadsorbed ions, and then freeze-dry to obtain PVP-modified Fe-MOF nanoparticles adsorbing Co / Ni. S4. Place the PVP-modified Fe-MOF nanoparticles with adsorbed Co / Ni into a quartz boat located downstream of the tube furnace. Weigh 10 times the mass of melamine with adsorbed Co / Ni PVP-modified Fe-MOF nanoparticles and place it into the quartz boat upstream. Pyrolyze the material in the tube furnace at 750℃ for 1.5h under a nitrogen atmosphere to obtain an electromagnetic wave absorbing material (FeCoNi@NCNT) based on in-situ grown carbon nanotubes of FeCoNi alloy. Example 2

[0013] A method for preparing electromagnetic wave absorbing materials based on in-situ grown carbon nanotubes from FeCoNi alloy includes the following steps: The preparation of S1 and Fe-MOF nanoparticles is the same as in Example 1; The process of surface modification of Fe-MOF by S2 and PVP is the same as in Example 1; S3, Co 2+ and Ni 2+ The adsorption process on PVP-modified Fe-MOF is the same as in Example 1; S4. The temperature of the tubular furnace is increased to 800°C, and its parameters are the same as in Example 1. Example 3

[0014] A method for preparing electromagnetic wave absorbing materials based on in-situ grown carbon nanotubes from FeCoNi alloy includes the following steps: The preparation of S1 and Fe-MOF nanoparticles is the same as in Example 1; The process of surface modification of Fe-MOF by S2 and PVP is the same as in Example 1; S3, Co 2+ and Ni 2+ The adsorption process on PVP-modified Fe-MOF is the same as in Example 1; S4. The temperature of the tubular furnace is increased to 850°C, and its parameters are the same as in Example 1.

[0015] Comparative Example 1 This comparative example involves heating the unmodified Fe-MOF (the product prepared in step S1) in a tube furnace. The specific method is as follows: The preparation of S1 and Fe-MOF nanoparticles is the same as in Example 1; S2. Place the Fe-MOF nanoparticles into a quartz boat located downstream of the tube furnace, weigh melamine at 10 times the mass of the Fe-MOF nanoparticles and place it into the quartz boat upstream, and pyrolyze it in the tube furnace at 800℃ for 1.5h under a nitrogen atmosphere.

[0016] To provide a detailed description of the material properties and parameters in the embodiments, the following section will begin... Figures 1 to 5 Further explanations are given regarding the material's cross-sectional morphology and electromagnetic shielding performance.

[0017] Depend on Figure 1 It was found that Fe-MOF nanoparticles can be prepared well by hydrothermal reaction. Scanning electron microscopy (SEM) shows that the Fe-MOF nanoparticles are octahedral pyramids and uniform in size.

[0018] Depend on Figure 2 It was found that Fe-MOF nanoparticles, after modification and heating in a tube furnace, exhibit the formation of tubular nanotubes on their surface. This demonstrates that under high-temperature conditions, upstream melamine is vaporized and undergoes an in-situ carbothermic reaction with downstream precursors.

[0019] Depend on Figure 3 It was learned that Figure 3Transmission electron microscopy images a and 3b provide a more microscopic view of FeCoNi@NCNT. Numerous carbon nanotubes are grown on the surface, and the formation of a large number of metal nanoparticles is also observed. Iron, cobalt, and nickel nanoparticles, as well as nitrogen released during pyrolysis, provide abundant catalytically active sites, which are not only reduced to metal nanoparticles but also promote the formation of carbon nanotubes.

[0020] Depend on Figure 4 The diagram displayed shows the electromagnetic wave absorption performance of Fe-MOF under heating conditions at 800℃ (two-dimensional graph). Observations indicate that in the 2-18 GHz band, the minimum reflection loss (RL) is -18.8 dB at a thickness of 5 mm. At a thickness of 2 mm, the maximum effective absorption bandwidth (EAB) is 2.32 GHz.

[0021] Depend on Figure 5 It was learned that Figure 5 Figures a through 5c show two-dimensional graphs of electromagnetic wave absorption performance under heating conditions of 750°C, 800°C, and 850°C. It was observed that the sample heated to 800°C exhibited a minimum RL value of -44.0 dB at a thickness of 2.0 mm. Under this condition, the EAB reached 5.3 GHz. When the temperature was further increased to 850°C, an EAB of approximately 4.3 GHz was observed at a thickness of 3.0 mm, almost covering the X-band (8.2–12.4 GHz).

[0022] Compared with existing technologies, this invention employs a nano-confined strategy during carbothermal reduction to achieve the growth of multidimensional nanostructures, thereby improving the material's uniformity and stability. Through the synergistic effect of lightweight nitrogen-doped carbon nanotubes and magnetic components, impedance matching characteristics are optimized, and the multi-level structure provides abundant interfacial polarization and multiple scattering effects, thus achieving efficient microwave absorption. The FeCoNi@NCNTs composite material exhibits excellent electromagnetic wave absorption performance, achieving an ultra-high reflection loss of -59.5 dB in a wide frequency range of 2 GHz to 18 GHz. The composite material prepared by this invention achieves a maximum effective absorption bandwidth of 5.3 GHz with a thickness of only 2.0 mm and a filler loading of 18%, combining lightweight design with efficient microwave attenuation characteristics.

[0023] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A preparation method of an electromagnetic wave absorbing material based on FeCoNi alloy in-situ grown carbon nanotubes, characterized by comprising the following steps: Includes the following steps: ​ S1. Iron-based metal-organic frameworks are synthesized through hydrothermal reaction, and then iron-based metal-organic framework nanoparticles are obtained by ultrasonication, washing and drying. S2, first surface modification of the iron-based metal-organic framework nanoparticles prepared in step S1 using polyvinylpyrrolidone, and then adsorption of Co 2+ and Ni 2+ on the surface of the polyvinylpyrrolidone-modified iron-based metal-organic framework nanoparticles using cobalt and nickel salts to obtain polyvinylpyrrolidone-modified iron-cobalt-nickel-based metal-organic framework nanoparticles; S3. Melamine and polyvinylpyrrolidone-modified iron-cobalt-nickel-based metal-organic framework nanoparticles with adsorbed cobalt and nickel obtained in step S2 are placed in the upstream and downstream of a tube furnace, respectively, and carbothermic reduction reaction is carried out under a nitrogen atmosphere to obtain carbon nanotube-encapsulated FeCoNi alloy. 2.The electromagnetic wave absorption material based on FeCoNi alloy in-situ grown carbon nanotubes according to claim 1, characterized in that: The specific preparation method of step S1 is as follows: terephthalic acid and FeCl3·6H2O are dissolved in N,N-dimethylformamide to obtain a mixed solution, and then the mixed solution is heated at 110℃ for 20h. After standing at room temperature, it is washed and freeze-dried to obtain iron-based metal-organic framework nanoparticles. 3.The electromagnetic wave absorption material based on FeCoNi alloy in-situ grown carbon nanotubes according to claim 2, characterized in that: The ratio of phthalic acid, FeCl3·6H2O and N,N-dimethylformamide is 1 mol: (1.5~2.5) mol: (10~15) mL. 4.The electromagnetic wave absorption material based on FeCoNi alloy in-situ grown carbon nanotubes according to claim 1, characterized in that: The specific preparation method for step S21 is as follows: S21. The iron-based metal-organic framework nanoparticles obtained in step S1 are dispersed in an aqueous solution of polyvinylpyrrolidone, stirred, and then centrifuged, washed, and freeze-dried to obtain polyvinylpyrrolidone-modified iron-based metal-organic framework nanoparticles. S22. Under stirring conditions, Co(NO3)2·6H2O and Ni(NO3)2·6H2O are added to deionized water to prepare a mixed salt solution. The mixture is stirred continuously. Polyvinylpyrrolidone modified iron-based metal-organic framework nanoparticles obtained in step S21 are added to the mixed salt solution. The mixture is stirred for 4 to 6 hours, and then washed and freeze-dried to obtain polyvinylpyrrolidone modified iron-based metal-organic framework nanoparticles that adsorb Co / Ni. 5.The electromagnetic wave absorption material based on FeCoNi alloy in-situ grown carbon nanotubes according to claim 4, characterized in that: The mass ratio of the iron-based metal-organic framework nanoparticles to polyvinylpyrrolidone is 1:1; the mass concentration of the polyvinylpyrrolidone aqueous solution is 0.67%. The mass ratio of the polyvinylpyrrolidone-modified iron-based metal-organic framework nanoparticles, Co(NO3)2·6H2O and Ni(NO3)2·6H2O is 2:1:1; The mass concentrations of both Co(NO3)2·6H2O and Ni(NO3)2·6H2O in the mixed salt solution were 22.7%. 6.The electromagnetic wave absorption material based on FeCoNi alloy in-situ grown carbon nanotubes according to claim 1, characterized in that: The temperature of the carbothermic reduction reaction in step S3 is 750℃~850℃, and the reaction time is 1h~2h; the mass ratio of the melamine and the polyvinylpyrrolidone modified iron-based metal-organic framework nanoparticles obtained in step S2 is 10:

1.

7. An electromagnetic wave absorbing material based on in-situ growth of carbon nanotubes on FeCoNi alloy, characterized in that: Prepared by the method described in any one of claims 1 to 6.

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