A microstructure-tunable FeCoNi@C electromagnetic wave absorbing composite material, its preparation method and application

Abstract

The application belongs to the technical field of electromagnetic wave absorption, and discloses a FeCoNi@C electromagnetic wave absorption composite material with adjustable microstructure, a preparation method and application. The application is prepared by using a coprecipitation method, an oxidation polymerization method and a high-temperature pyrolysis method. After high-temperature pyrolysis, polypyrrole can be converted into a light nitrogen-doped carbon material. Therefore, the introduction of polypyrrole not only improves the dielectric loss of the FeCoNi@C composite material, but also significantly improves the electromagnetic wave absorption performance. By changing the content of polypyrrole, the dielectric constant and magnetic permeability can be adjusted, so that the requirements of impedance matching optimization can be met. When the sample filling amount is 40%, the electromagnetic wave absorption composite material with excellent wave absorption performance can be obtained. When the matching thickness is 1.8 mm, the minimum reflection loss can reach-52.4 dB, and the corresponding effective absorption bandwidth can reach 5.18 GHz. The application has a wide application prospect in the field of electromagnetic wave absorption.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic wave absorption technology, specifically relating to a microstructure-tunable FeCoNi@C electromagnetic wave absorbing composite material derived from a polypyrrole-coated FeCoNi Prussian blue analogue, its preparation method, and its application. Background Technology

[0002] With the rapid development of science and technology, electronic communication devices have become indispensable in people's daily lives. However, the electromagnetic waves they emit also pose a serious electromagnetic pollution problem to people's living environment, which can have a negative impact on people's health and interfere with the normal operation of precision instruments.

[0003] To address this problem, researching high-performance electromagnetic wave absorbing materials that are thin, lightweight, have wide bandwidth, and strong absorption is an effective approach. In recent years, various electromagnetic wave absorbing materials, such as carbon materials, magnetic ferrites, magnetic metals and their alloys, and conductive polymers, have attracted considerable attention. However, due to their singular loss mechanisms and difficulty in controlling electromagnetic parameters, single-component electromagnetic wave absorbing materials are no longer sufficient to meet current widespread application demands. Compared to single-component electromagnetic wave absorbing materials, magnetic / dielectric composite materials offer easier electromagnetic parameter adjustment, improved impedance matching, and the ability to achieve synergistic effects between different components, making them a promising candidate for electromagnetic wave absorbing materials. Among various magnetic / dielectric composite materials, magnetic metal-carbon based composites are currently a research hotspot.

[0004] Metal-organic frameworks (MOFs), porous crystalline materials with a periodic network structure, can be transformed into magnetic metal-carbon composites through a simple high-temperature pyrolysis process. However, using these composites as microwave absorbing materials presents challenges such as particle agglomeration, morphological collapse, and difficulty in controlling the dielectric constant. To address these issues, introducing polymers as coating layers to form core-shell composites has become a common and effective approach. Polypyrrole, a traditional conductive polymer, can be transformed into a lightweight nitrogen-doped carbon material through high-temperature pyrolysis, making it an ideal candidate for combining with MOFs to create core-shell composite materials with advantages such as lightweight, structural stability, and adjustable dielectric constant. Summary of the Invention

[0005] To address the shortcomings and deficiencies in the existing technology, the primary objective of this invention is to provide a method for preparing a FeCoNi@C electromagnetic wave absorbing composite material with a tunable microstructure derived from a polypyrrole-coated FeCoNi Prussian blue analogue.

[0006] Another objective of this invention is to provide a FeCoNi@C electromagnetic wave absorbing composite material with tunable microstructure prepared by the above-described method. This material has the advantages of thinness, light weight, wide bandwidth, and strong absorption. The dielectric constant can be adjusted by changing the polypyrrole content to improve impedance matching and enhance the absorption capacity of electromagnetic waves.

[0007] Another object of the present invention is to provide the application of the above-mentioned FeCoNi@C electromagnetic wave absorbing composite material with tunable microstructure.

[0008] The objective of this invention is achieved through the following technical solution:

[0009] A method for preparing a FeCoNi@C electromagnetic wave absorbing composite material with tunable microstructure includes the following steps:

[0010] (1) Add ferricyanide and cobalt cyanide to deionized water and dissolve to obtain solution A;

[0011] (2) Add citrate and nickel salt to deionized water and dissolve to obtain solution B;

[0012] (3) Under stirring, solution A was poured into solution B and then stirred continuously to obtain solution C. After standing at room temperature, FeCoNi Prussian blue analogue was obtained.

[0013] (4) Add FeCoNi Prussian blue analogue to deionized water and sonicate to obtain solution D;

[0014] (5) Add pyrrole monomer to solution D and stir continuously to obtain solution E;

[0015] (6) Add the iron salt to deionized water and stir continuously to obtain solution F;

[0016] (7) Under stirring, solution F was added dropwise to solution E to obtain solution G. Solution G was then continuously stirred at room temperature to obtain polypyrrole-coated FeCoNi Prussian blue analogue.

[0017] (8) The FeCoNi Prussian blue analogue coated with polypyrrole was subjected to high-temperature pyrolysis to obtain FeCoNi@C electromagnetic wave absorbing composite material with tunable microstructure.

[0018] The ferricyanide mentioned in step (1) is potassium ferricyanide, and the cobalt cyanide is potassium cobalt cyanide;

[0019] The citrate in step (2) is trisodium citrate dihydrate, and the nickel salt is nickel chloride hexahydrate.

[0020] In step (3), the time for pouring solution A into solution B is 20s-40s, the time for continuous stirring is 5min, the time for standing at room temperature is 12h, and the room temperature is 30℃.

[0021] The ultrasonic treatment in step (4) takes 15 minutes;

[0022] The continuous stirring time in step (5) is 30 minutes;

[0023] The iron salt mentioned in step (6) is ferric chloride hexahydrate, and the continuous stirring time is 5 minutes;

[0024] The stirring time described in step (7) at room temperature is 24 hours.

[0025] The high-temperature pyrolysis treatment in step (8) involves heating the temperature to 600°C at a heating rate of 2°C / min, and then holding it at that temperature for 2 hours.

[0026] The mass ratio of the ferrocyanide, cobalt cyanide, citrate, and nickel salt is 1:1.009:4.020:2.166.

[0027] The molar ratio of the iron salt to the pyrrole monomer is 11:9.

[0028] The amount of FeCoNi Prussian blue analogue used in step (4) is 0.2g, and the amount of pyrrole monomer used in step (5) is >0 and ≤300μl.

[0029] A FeCoNi@C electromagnetic wave absorbing composite material with tunable microstructure prepared by the above-described method.

[0030] The aforementioned FeCoNi@C electromagnetic wave absorbing composite material with tunable microstructure can obtain different microstructures after pyrolysis, such as an egg yolk shell structure or a hollow structure, depending on the amount of pyrrole monomer used. Among them, the egg yolk shell structure FeCoNi@C is composed of FeCoNi alloy nanoparticles as the core and hollow carbon nanocubes as the outer shell; the hollow structure FeCoNi@C is composed of hollow carbon nanocubes and FeCoNi alloy nanoparticles embedded in the hollow carbon nanocubes.

[0031] The above-mentioned FeCoNi@C electromagnetic wave absorbing composite material with tunable microstructure has applications in the field of electromagnetic wave absorption.

[0032] The principle of this invention:

[0033] This invention prepares FeCoNi@C composite materials with tunable microstructure through a simple co-precipitation method, oxidative polymerization method, and high-temperature pyrolysis method. According to a specific order of raw material addition and controlled dropwise addition of solution F to solution E, polypyrrole is introduced as a coating layer of FeCoNi Prussian blue analogue to enhance the stability of the structure during high-temperature pyrolysis. After high-temperature pyrolysis, the polypyrrole-derived carbon layer connects some adjacent FeCoNi@C nanocubes, forming a unique conductive network structure that enhances electrical conductivity loss. Simultaneously, the numerous nitrogen atoms doped within the carbon layer act as polarization centers, inducing significant dipole orientation polarization. The heterogeneous interfaces between FeCoNi alloy nanoparticles and graphitized carbon layers, as well as between graphitized carbon layers and amorphous carbon layers, result in a large accumulation of space charge at the interfaces, triggering a strong interfacial polarization effect. Furthermore, the resonant loss and eddy current effect originating from the FeCoNi alloy nanoparticles play a significant role in the loss of electromagnetic wave energy. More importantly, the easily tunable microstructures, such as the yolk-shell and hollow structures, promote multiple reflections and scattering of incident electromagnetic waves, extending the propagation path and further dissipating electromagnetic wave energy. The synergistic effect between the microstructure beneficial to electromagnetic wave attenuation, electrical conductivity loss, polarization loss, and magnetic loss from the FeCoNi alloy nanoparticles gives the microstructure-tunable FeCoNi@C composite material excellent impedance matching characteristics and electromagnetic wave absorption capabilities.

[0034] The present invention has the following advantages and effects compared with the prior art:

[0035] (1) This invention introduces polypyrrole to adjust the dielectric constant of the composite material. The conductive network formed by the "bridging structure", the polarization center of the doped nitrogen atoms, the heterogeneous interface between FeCoNi alloy nanoparticles and graphitized carbon layers and between graphitized carbon layers and amorphous carbon layers, the resonance loss and eddy current effect of FeCoNi alloy nanoparticles jointly enhance the material's ability to absorb electromagnetic wave energy. The easily controllable internal microstructure, such as eggshell and hollow structure, promotes the multiple reflection and scattering behavior of incident electromagnetic waves. This gives the FeCoNi@C composite material with controllable microstructure excellent electromagnetic wave absorption performance. When the matching thickness is 1.8 mm, the minimum reflection loss can reach -52.4 dB.

[0036] (2) The preparation method of the present invention can adjust the dielectric constant by changing the content of polypyrrole to obtain the best impedance matching characteristics.

[0037] (3) The preparation method of the present invention has few steps, short time, large output, simple and convenient. When the sample filling amount is 40%, a lightweight FeCoNi@C composite material with excellent microwave absorption performance and tunable microstructure can be obtained. Attached Figure Description

[0038] Figure 1 These are scanning electron microscope (SEM) images (a, b) of the FeCoNi@C electromagnetic wave absorbing composite material with tunable microstructure prepared in Examples 1-4 before and after high-temperature pyrolysis.

[0039] Figure 2 These are transmission electron microscope (TEM) images (a, b, c, d) of the FeCoNi@C electromagnetic wave absorbing composite materials with tunable microstructure prepared in Examples 1-4.

[0040] Figure 3 The X-ray diffraction patterns (a, b) are of FeCoNi Prussian blue analogues with different polypyrrole contents prepared in Examples 1-4 and the products obtained by high-temperature pyrolysis of them.

[0041] Figure 4 These are three-dimensional images of the electromagnetic wave absorption performance of the FeCoNi@C electromagnetic wave absorbing composite materials with tunable microstructure prepared in Examples 1 to 4: FeCoNi@C-0 (a), FeCoNi@C-1 (b), FeCoNi@C-2 (c), and FeCoNi@C-3 (d).

[0042] Figure 5 The images show two-dimensional diagrams of the electromagnetic wave absorption performance of the FeCoNi@C electromagnetic wave absorbing composite materials with tunable microstructure prepared in Examples 1 to 4: FeCoNi@C-0 (a), FeCoNi@C-1 (b), FeCoNi@C-2 (c), and FeCoNi@C-3 (d).

[0043] Figure 6 These are electromagnetic impedance matching diagrams of the microstructure-tunable FeCoNi@C electromagnetic wave absorbing composite materials prepared in Examples 1-4: FeCoNi@C-0(a), FeCoNi@C-1(b), FeCoNi@C-2(c), and FeCoNi@C-3(d).

[0044] Figure 7 The electromagnetic wave attenuation constants of the FeCoNi@C electromagnetic wave absorbing composite materials with tunable microstructure prepared in Examples 1 to 4 are shown as FeCoNi@C-0(a), FeCoNi@C-1(b), FeCoNi@C-2(c), and FeCoNi@C-3(d). Detailed Implementation

[0045] The following specific embodiments further illustrate the content of the present invention, but should not be construed as limiting the present invention.

[0046] Example 1: Preparation of FeCoNi@C-0 composite material

[0047] (1) Add 0.6585g potassium ferricyanide and 0.6647g potassium cobalt cyanide to 200ml of deionized water and dissolve to obtain solution A; add 1.4261g nickel chloride hexahydrate and 2.6469g trisodium citrate dihydrate to another 200ml of deionized water and dissolve to obtain solution B;

[0048] (2) Stir solution B magnetically, then pour solution A into solution B within 20s-40s, and continue stirring for 5min to obtain solution C. Then place solution C in a room temperature environment of 30℃ for 12h, and finally obtain FeCoNi Prussian blue analogue after centrifugation and washing.

[0049] (3) The FeCoNi Prussian blue analogue was subjected to high-temperature pyrolysis treatment at 600℃ and N2 atmosphere for 2h, and the heating rate was 2℃ / min to obtain the FeCoNi@C-0 composite material.

[0050] Example 2: Preparation of FeCoNi@C-1 composite material with egg yolk shell structure

[0051] (1) Add 0.6585g potassium ferricyanide and 0.6647g potassium cobalt cyanide to 200ml of deionized water and dissolve to obtain solution A; add 1.4261g nickel chloride hexahydrate and 2.6469g trisodium citrate dihydrate to another 200ml of deionized water and dissolve to obtain solution B;

[0052] (2) Stir solution B magnetically, then pour solution A into solution B within 20s-40s, and continue stirring for 5min to obtain solution C. Then place solution C in a room temperature environment of 30℃ for 12h, and finally obtain FeCoNi Prussian blue analogue after centrifugation and washing.

[0053] (3) Add 0.20g of FeCoNi Prussian blue analogue to 30ml of deionized water and sonicate for 15min to obtain solution D;

[0054] (4) Add 100 μl of pyrrole monomer to solution D and stir continuously for 30 min to obtain solution E. Add 0.4772 g of ferric chloride hexahydrate to deionized water and stir continuously for 5 min to prepare 20 ml of solution F.

[0055] (5) Stir the solution E magnetically, then add the solution F dropwise to the solution E to obtain the solution G. Then stir the solution G continuously at room temperature of 25°C for 24 hours. After centrifugation and washing, the polypyrrole-coated FeCoNi Prussian blue analogue is obtained.

[0056] (6) The polypyrrole-coated FeCoNi Prussian blue analogue was subjected to high-temperature pyrolysis treatment at 600℃ and N2 atmosphere for 2h, and the heating rate was 2℃ / min to obtain the FeCoNi@C-1 electromagnetic wave absorbing composite material with egg yolk shell structure.

[0057] Example 3: Preparation of FeCoNi@C-2 composite material with egg yolk shell structure

[0058] (1) Add 0.6585g potassium ferricyanide and 0.6647g potassium cobalt cyanide to 200ml of deionized water and dissolve to obtain solution A; add 1.4261g nickel chloride hexahydrate and 2.6469g trisodium citrate dihydrate to another 200ml of deionized water and dissolve to obtain solution B;

[0059] (2) Stir solution B magnetically, then pour solution A into solution B within 20s-40s, and continue stirring for 5min to obtain solution C. Then place solution C in a room temperature environment of 30℃ for 12h, and finally obtain FeCoNi Prussian blue analogue after centrifugation and washing.

[0060] (3) Add 0.20g of FeCoNi Prussian blue analogue to 30ml of deionized water and sonicate for 15min to obtain solution D;

[0061] (4) Add 200 μl of pyrrole monomer to solution D and stir continuously for 30 min to obtain solution E. Add 0.9544 g of ferric chloride hexahydrate to deionized water and stir continuously for 5 min to prepare 20 ml of solution F.

[0062] (5) Stir the solution E magnetically, then add the solution F dropwise to the solution E to obtain the solution G. Then stir the solution G continuously at room temperature of 25°C for 24 hours. After centrifugation and washing, the polypyrrole-coated FeCoNi Prussian blue analogue is obtained.

[0063] (6) The polypyrrole-coated FeCoNi Prussian blue analogue was subjected to high-temperature pyrolysis treatment at 600℃ and N2 atmosphere for 2h, and the heating rate was 2℃ / min to obtain the FeCoNi@C-2 electromagnetic wave absorbing composite material with egg yolk shell structure.

[0064] Example 4: Preparation of hollow FeCoNi@C-3 composite material

[0065] (1) Add 0.6585g potassium ferricyanide and 0.6647g potassium cobalt cyanide to 200ml of deionized water and dissolve to obtain solution A; add 1.4261g nickel chloride hexahydrate and 2.6469g trisodium citrate dihydrate to another 200ml of deionized water and dissolve to obtain solution B;

[0066] (2) Stir solution B magnetically, then pour solution A into solution B within 20s-40s, and continue stirring for 5min to obtain solution C. Then place solution C in a room temperature environment of 30℃ for 12h, and finally obtain FeCoNi Prussian blue analogue after centrifugation and washing.

[0067] (3) Add 0.20g of FeCoNi Prussian blue analogue to 30ml of deionized water and sonicate for 15min to obtain solution D;

[0068] (4) Add 300 μl of pyrrole monomer to solution D and stir continuously for 30 min to obtain solution E. Add 1.4316 g of ferric chloride hexahydrate to deionized water and stir continuously for 5 min to prepare 20 ml of solution F.

[0069] (5) Stir the solution E magnetically, then add the solution F dropwise to the solution E to obtain the solution G. Then stir the solution G continuously at room temperature of 25°C for 24 hours. After centrifugation and washing, the polypyrrole-coated FeCoNi Prussian blue analogue is obtained.

[0070] (6) The FeCoNi Prussian blue analogue coated with polypyrrole was subjected to high-temperature pyrolysis treatment at 600℃ and N2 atmosphere for 2h, and the heating rate was 2℃ / min to obtain a hollow FeCoNi@C-3 electromagnetic wave absorbing composite material.

[0071] Example 5 (Effective Example):

[0072] Structural characterization and performance testing of FeCoNi@C composites with tunable microstructure:

[0073] (1) Characterization of composite material structure:

[0074] The morphology of polypyrrole-coated FeCoNi Prussian blue analogues is as follows: Figure 1 As shown in Figure a, the composite material exhibits a uniform cubic morphology with a rough surface and a distinct granular texture. After high-temperature pyrolysis, the morphology of the resulting product is as follows... Figure 1 As shown in b, the FeCoNi@C composite material can still maintain the same nanocube morphology as the precursor, and some adjacent nanocubes form a "bridging structure". Furthermore, the transmission electron microscopy (TEM) images of the products after high-temperature pyrolysis, as shown... Figure 2 As shown in Figure a, the product directly derived from the FeCoNi Prussian blue analogue, namely FeCoNi@C-0, is composed of a large number of aggregated nanoparticles with collapsed morphology and destroyed cubic structure. After the introduction of polypyrrole, as... Figure 2 As shown in b, c, and d, FeCoNi@C-1, FeCoNi@C-2, and FeCoNi@C-3 all maintain the structure of nanocubes. With the change of pyrrole monomer dosage, the thickness of the outermost carbon layer derived from polypyrrole gradually increases, and its microstructure also changes accordingly. The eggshell structure of FeCoNi@C-1 and FeCoNi@C-2 gradually transitions to the hollow structure of FeCoNi@C-3, which is beneficial to the multiple reflection and scattering behavior of incident electromagnetic waves, prolongs the propagation path of incident electromagnetic waves, and improves the attenuation ability of electromagnetic waves.

[0075] To characterize the crystal structure and phase composition of FeCoNi Prussian blue analogues, FeCoNi@C-0, FeCoNi@C-1, FeCoNi@C-2, and FeCoNi@C-3 composites with different polypyrrole contents, X-ray diffraction analysis was performed on the prepared samples. Figure 3 As shown in Figure a, after the introduction of polypyrrole, the XRD pattern of the polypyrrole-coated FeCoNi Prussian blue analog is basically consistent with that of the original FeCoNi Prussian blue analog, indicating that the introduction of polypyrrole did not have a significant impact on the crystal structure of the FeCoNi Prussian blue analog. Figure 3 As shown in b, the XRD patterns of the FeCoNi@C-0, FeCoNi@C-1, FeCoNi@C-2, and FeCoNi@C-3 composites are basically consistent, with high-resolution characteristic diffraction peaks appearing at 44°, 51°, and 75°, corresponding to the (111), (200), and (220) crystal planes of the face-centered cubic FeCoNi alloy, respectively. Furthermore, given the catalytic graphitization effect of the FeCoNi alloy on the carbon components and the absence of diffraction peaks related to the graphitized carbon (002) crystal plane in the XRD patterns, it is indicated that the carbon framework in the products mainly exists in the form of amorphous carbon.

[0076] (2) Performance characterization:

[0077] like Figure 4 and 5 As shown, the electromagnetic wave absorption performance of FeCoNi@C-0, FeCoNi@C-1, FeCoNi@C-2, and FeCoNi@C-3 was tested within a frequency range of 2.0-18.0 GHz and a thickness range of 1.0-5.0 mm. (The results were obtained through...) Figure 4From the values ​​of 'a' and 'a' in '5', we can see that when the matching thickness is 5mm, FeCoNi@C-0 has a minimum reflection loss of -12.2dB at 7.3GHz, and a maximum effective absorption bandwidth (reflection loss value less than -10dB) of 1.63GHz at a thickness of 5mm. Figure 4 From the values ​​of b and b in 5, we can see that when the matching thickness is 5mm, FeCoNi@C-1 has a minimum reflection loss of -34.6dB at 5.3GHz, and a maximum effective absorption bandwidth (reflection loss value less than -10dB) of 5.5GHz at a thickness of 2mm. Figure 4 The c in 'c' and the c in '5' indicate that FeCoNi@C-2 exhibits excellent electromagnetic wave absorption performance. With a matching thickness of 1.8 mm, the minimum reflection loss at 15.7 GHz reaches -52.4 dB, and the maximum effective absorption bandwidth (reflection loss less than -10 dB) reaches 5.84 GHz at a thickness of 1.9 mm. Figure 4 From the values ​​of d and d in 5, we can see that when the matching thickness is 1.3 mm, FeCoNi@C-3 exhibits a minimum reflection loss of -18.9 dB at 18.0 GHz and a maximum absorption bandwidth of 5.1 GHz at a thickness of 1.5 mm. These results indicate that the introduction of polypyrrole can adjust the electromagnetic parameters of the composite material and improve its electromagnetic wave absorption performance.

[0078] like Figure 6 As shown, the closer the impedance matching value is to 1, the more electromagnetic waves enter the material, and the less electromagnetic waves are reflected in the air and on the material's surface. By fixing the impedance matching values ​​to 0.8 and 1.2 respectively, where the red dashed line corresponds to an impedance matching value of 0.8 and the black dashed line corresponds to an impedance matching value of 1.2, the area enclosed by the red and black dashed lines for each sample initially increases and then decreases. This indicates that due to the introduction of polypyrrole and the increase in its dosage, the impedance matching of the samples first significantly improves and then decreases sharply. FeCoNi@C-2 achieves the best impedance matching.

[0079] like Figure 7 As shown, in this invention, the attenuation constants for pyrrole monomers introduced at amounts of 0 μl, 100 μl, 200 μl, and 300 μl are 64.62, 116.70, 148.19, and 195.65, respectively.

[0080] The above is a detailed description of the preparation of FeCoNi@C-0, FeCoNi@C-1, FeCoNi@C-2, and FeCoNi@C-3 by simple co-precipitation, oxidative polymerization, and high-temperature pyrolysis methods.

[0081] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a FeCoNi@C electromagnetic wave absorbing composite material with tunable microstructure, characterized in that... The preparation method comprises the following steps: (1) adding ferricyanide and cobalt cyanide into deionized water to dissolve and obtain solution A; (2) adding citrate and nickel salt into deionized water to dissolve and obtain solution B; (3) pouring solution A into solution B under stirring, then continuously stirring to obtain solution C, and standing at room temperature to obtain FeCoNi Prussian blue analogue; (4) adding FeCoNi Prussian blue analogue into deionized water and ultrasonic treatment to obtain solution D; (5) adding pyrrole monomer into solution D and continuously stirring to obtain solution E; (6) adding iron salt into deionized water and continuously stirring to obtain solution F; (7) adding solution F into solution E drop by drop under stirring to obtain solution G, and continuously stirring solution G at room temperature to obtain poly-pyrrole coated FeCoNi Prussian blue analogue; (8) carrying out high-temperature pyrolysis treatment on the poly-pyrrole coated FeCoNi Prussian blue analogue to obtain microstructure-controllable FeCoNi@C electromagnetic wave absorption composite material; The mass ratio of the ferricyanide, cobalt cyanide, citrate and nickel salt is 1:1.009:4.020:2.166; the molar ratio of the iron salt and pyrrole monomer is 11:9; The amount of the FeCoNi Prussian blue analogue in step (4) is 0.2 g, and the amount of the pyrrole monomer in step (5) is >0 and ≤300 μl; The high-temperature pyrolysis treatment in step (8) is heating to 600 ℃ at a heating rate of 2 ℃ / min, and then holding for 2 h.

2. The method of claim 1, wherein: The ferricyanide in step (1) is potassium ferricyanide, and the cobalt cyanide is potassium cobalt cyanide; the citrate in step (2) is trisodium citrate dihydrate, and the nickel salt is nickel chloride hexahydrate.

3. The method of claim 1, wherein: The time for pouring solution A into solution B in step (3) is 20-40 s, and the continuously stirring time is 5 min; the standing time at room temperature is 12 h, and the temperature of the room temperature is 30 ℃.

4. The method of claim 1, wherein: The ultrasonic treatment time in step (4) is 15 min; the continuously stirring time in step (5) is 30 min; the iron salt in step (6) is iron chloride hexahydrate, and the continuously stirring time is 5 min; the continuously stirring time at room temperature in step (7) is 24 h.

5. A microstructure-controllable FeCoNi@C electromagnetic wave absorption composite material prepared by the preparation method in any one of claims 1-4.

6. The microstructure-tunable FeCoNi@C electromagnetic wave absorption composite material according to claim 5, characterized in that: The composite material is yolk-shell structure or hollow structure; wherein the FeCoNi@C of the yolk-shell structure is composed of FeCoNi alloy nanoparticles as core and hollow carbon nanocubes as shell; the FeCoNi@C of the hollow structure is composed of hollow carbon nanocubes and FeCoNi alloy nanoparticles embedded in the hollow carbon nanocubes.

7. Application of the microstructure-controllable FeCoNi@C electromagnetic wave absorption composite material in claim 6 in the field of electromagnetic wave absorption.

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