FeCrNiCo-carbonized flammulina velutipes composite material as well as preparation method and application thereof

Abstract

The invention discloses a FeCrNiCo-carbonized flammulina velutipes composite material and a preparation method and application thereof, and the preparation method comprises the following steps: (1) immersing pretreated flammulina velutipes in a mixed metal salt solution containing Fe < 3 + >, Cr < 3 + >, Ni < 2 + > and Co < 2 + >, and loading metal ions on the flammulina velutipes under an oscillation condition; (2) adjusting the pH value of the solution to 8-9, carrying out a co-precipitation reaction to form a metal hydroxide precipitate, and then separating, washing, purifying and drying to obtain a precursor composite material; and (3) carrying out stepped heat treatment on the precursor composite material in a hydrogen-containing protective atmosphere to obtain the FeCrNiCo-carbonized flammulina velutipes composite material. Uniform loading of metal ions is achieved by means of the characteristics of biomass, carbonization and alloying are synchronously completed through multi-stage precise heat treatment, and finally the efficient microwave absorbing material with the characteristics of strong absorption and wide band is obtained.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of microwave wave-absorbing materials, and particularly relates to a preparation method of FeCrNiCo-carbonized Flammulina velutipes composite material and application of the FeCrNiCo-carbonized Flammulina velutipes composite material as a wave-absorbing material. BACKGROUND

[0002] With the wide application of 5G and Internet of Things technology, the electromagnetic environment is becoming increasingly complex, and traditional wave-absorbing materials are difficult to meet the increasingly stringent electromagnetic compatibility requirements. At the same time, the development trend of thin and light electronic devices also puts forward more stringent requirements on the thickness and weight of materials. These needs together promote the evolution of wave-absorbing materials towards ultra-thin, wideband and intelligent response, and promote the research and development of new generation of high-performance materials.

[0003] Under this background, biomass carbon materials have shown great potential in the field of microwave absorption due to their advantages of wide source, low cost and environmental friendliness. Porous carbon materials obtained by pyrolysis of natural biomass such as straw and wood not only have the characteristics of light weight, high temperature resistance and controllable dielectric properties, but also have multi-level pores and complex microstructure, which helps to improve the wave-absorbing performance. More importantly, biomass carbon materials can be combined with magnetic components to build a multi-component loss mechanism, which can synergistically optimize the impedance matching and attenuation performance, providing a new possibility for the development of high-performance and sustainable wave-absorbing materials.

[0004] However, traditional wave-absorbing materials such as ferrite and carbon-based materials still have limitations such as high density, narrow frequency band or insufficient environmental stability. SUMMARY

[0005] The technical problem to be solved by the present application is to overcome the deficiencies and shortcomings mentioned in the background, and to provide a FeCrNiCo-carbonized Flammulina velutipes composite material (denoted as FeCrNiCo-C) and a preparation method, and to use it for microwave absorption to obtain excellent microwave absorption performance.

[0006] To solve the above technical problems, the technical solution proposed by the present application is as follows: A preparation method of FeCrNiCo-carbonized Flammulina velutipes composite material, comprising the following steps: (1) immersing pretreated Flammulina velutipes in a mixed metal salt solution containing Fe 3+ , Cr 3+ , Ni 2+ , Co 2+ , and loading metal ions on the Flammulina velutipes under oscillation conditions; the Flammulina velutipes is selected from a section starting from the root to a distance of 3-4 cm from the root; the molar concentrations of Fe 3+ , Cr 3+ , Ni 2+ and Co 2+ in the mixed metal salt solution are all equal; (2) Adjust the pH of the solution to 8-9, perform co-precipitation reaction to form metal hydroxide precipitate, then separate, wash, purify, and dry to obtain the precursor composite material; (3) Perform stepwise heat treatment on the precursor composite material in a protective atmosphere containing hydrogen to carbonize the Flammulina velutipes and form a bio-carbon matrix, and at the same time form FeCrNiCo high-entropy alloy nanoparticles embedded in the bio-carbon matrix, to obtain the FeCrNiCo-carbonized Flammulina velutipes composite material; The stepwise heat treatment includes the following three stages: heating to 180-220°C and holding; heating to 650-800°C and holding; heating to 950-1100°C and holding.

[0007] As a further improvement, in the mixed metal salt solution of step (1), the molar concentrations of Fe 3+ , Cr 3+ , Ni 2+ , and Co 2+ are in the range of 0.1-0.125 mol / L; and the mass ratio of Flammulina velutipes to mixed metal salt solution is controlled at 1:(5-10).

[0008] As a further improvement, step (1) includes: soaking for 7-10 hours at an oscillation speed of 100-150 rpm to load metal ions on the Flammulina velutipes.

[0009] As a further improvement, step (2) includes: adding NaOH solution dropwise to the solution, the concentration of the NaOH solution being 0.8-1.2 mol / L, adjusting the pH to 8-9, and continuing to stir for 1.5-2.5 hours after the dropwise addition is completed to perform co-precipitation reaction.

[0010] As a further improvement, the washing, purifying, and drying of step (2) include: washing with deionized water until the washing liquid is neutral and free of residual chloride ions and sodium ions; and drying at 50-60°C under a vacuum degree of less than -0.1 MPa.

[0011] As a further improvement, the protective atmosphere in step (3) is hydrogen / argon mixed gas, and the volume fraction of H2 is 7%-10%.

[0012] As a further improvement, the stepwise heat treatment in step (3) includes the following three stages: heating to 180-220°C at a rate of 8-12°C / min, holding for 4-8 hours; heating to 650-800°C at a rate of 10-20°C / min, holding for 4-8 hours; and heating to 950-1100°C at a rate of 3-5°C / min, holding for 1.5-3 hours.

[0013] The application also provides a FeCrNiCo-carbonized Flammulina velutipes composite material prepared by the preparation method, which is composed of FeCrNiCo high-entropy alloy nanoparticles uniformly embedded in a three-dimensional porous bio-carbon matrix formed by carbonization of Flammulina velutipes.

[0014] The application also provides an application of the FeCrNiCo-carbonized Flammulina velutipes composite material as a microwave absorption material.

[0015] Compared with the prior art, the application has the following beneficial effects: The application realizes the synergistic optimization of components and structures by compounding multi-component FeCrNiCo high-entropy alloy and Flammulina velutipes derived bio-carbon matrix. The high-entropy alloy endows the material with excellent dielectric loss capability, and the three-dimensional porous fiber structure formed by carbonization of Flammulina velutipes not only provides a uniform dispersion carrier for alloy nanoparticles and constructs a hetero-interface for enhanced interface polarization, but also prolongs the electromagnetic wave propagation path through multiple reflection and scattering. The compounding of the carbon matrix with moderate conductivity and the high-loss alloy particles effectively adjusts the complex permittivity, improves the impedance matching, and makes more electromagnetic waves enter the material interior to dissipate. The preparation process is green and economical, utilizes the characteristics of biomass itself to realize uniform loading of metal ions, and synchronously completes carbonization and alloying through multi-stage precise heat treatment, so that a high-efficiency microwave absorption material with strong absorption and wide frequency band characteristics is finally obtained. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are some embodiments of the application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0017] Figure 1 is a full view of Flammulina velutipes used in the embodiment; Figure 2 is a microscopic image of a transverse section of the root of Flammulina velutipes, and the porous structure thereof can be observed; Figure 3 is a microscopic image of a transverse section of the FeCrNiCo-C composite material prepared in Example 1, and the porous structure thereof can be observed, which retains the porous structure of the transverse section of the root of Flammulina velutipes; Figure 4 is an SEM image of the FeCrNiCo-C composite material prepared in Example 1, and the carbonized Flammulina velutipes surface is covered with fine particles, i.e., FeCrNiCo alloy particles; Figure 5 is an SEM image of the FeCrNiCo-C composite material of Example 2, and the FeCrNiCo loading amount is obviously reduced and sporadically distributed, which is uneven; Figure 6 is the matching diagram of microwave absorption performance of FeCrNiCo-C composite material in Example 1 with different thicknesses (1-5 mm) and 1 / 4 wavelength theory, RL represents reflection loss, d cal represents the thickness of the wave-absorbing layer; Figure 7 is the matching diagram of microwave absorption performance of FeCrNiCo-C composite material in Example 3 with different thicknesses (1-5 mm) and 1 / 4 wavelength theory; Figure 8 is the matching diagram of microwave absorption performance of CrNiCo-C composite material in Example 4 with different thicknesses (1-5 mm) and 1 / 4 wavelength theory. DETAILED DESCRIPTION

[0018] In order to facilitate the understanding of the present application, the present application will be described more fully below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present application is not limited to the following specific embodiments.

[0019] Unless otherwise defined, all the professional terms used herein have the same meaning as understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present application.

[0020] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present application can be purchased from the market or can be prepared by existing methods.

[0021] In some embodiments, the preparation method of the FeCrNiCo-carbonized enoki mushroom composite material of the present application comprises the following steps: Step one: pretreatment of biomass precursor In some embodiments, fresh enoki mushrooms with intact and non-rotten bodies are selected, and the surface impurities are washed with deionized water and drained. The section adjacent to the root is accurately cut, preferably from the root to the section 3-4 cm away from the root (as shown in the red dashed box), which has a dense structure and abundant fibers. This part is used as a biomass template, which can effectively utilize its natural porous structure to provide a large number of active sites for the anchoring of metal ions in the subsequent steps. Figure 1

[0022] Step two: preparation of high-entropy alloy precursor solution In some embodiments, a mixed metal salt solution containing equimolar Fe 3+ , Cr 3+ , Ni 2+ and Co 2+ is prepared.

[0023] ​In some embodiments, the mixed metal salt solution is prepared from FeCl3·6H2O, CoCl2·6H2O, NiCl2·6H2O and CrCl3·6H2O. The molar concentrations of Fe 3+ , Cr 3+ , Ni 2+ and Co 2+ in the mixed metal salt solution are equal and in the range of 0.1-0.125 mol / L.

[0024] In some embodiments, each salt is dissolved in deionized water separately, stirred until completely dissolved under water bath heating, then mixed and stirred according to the principle of equal molar ratio, to ensure uniform dispersion of each metal ion, and to obtain a clear high-entropy alloy precursor mixed solution.

[0025] Step three: ion adsorption and loading In some embodiments, the pretreated shiitake mushroom segments are completely immersed in the above mixed metal salt solution, and the immersion is carried out under oscillation conditions to realize uniform loading of metal ions on the biomass template through oscillation adsorption.

[0026] In some embodiments, by controlling the amount of feed, the mass ratio of shiitake mushroom to mixed metal salt solution is strictly controlled in the range of 1:(5-10).

[0027] In some embodiments, the entire system is placed in a constant temperature shaker, and the immersion is carried out at room temperature 25±2℃ for 7-10 hours at an oscillation speed of 100-150 rpm. This process utilizes the concentration difference driving and the adsorption characteristics of the biomass itself to enable the penetration and firm loading of multiple metal ions in the microporous channels and fiber surfaces of shiitake mushroom.

[0028] Step four: co-precipitation reaction In some embodiments, an alkali solution (such as NaOH solution) is slowly added to the system loaded with metal ions under stirring, the pH value is adjusted to 8-9, and a co-precipitation reaction is carried out to generate uniformly coexisting metal hydroxide precipitates.

[0029] In some embodiments, under the condition of continuous mechanical stirring at 200-400 rpm, NaOH solution is added dropwise, the concentration of NaOH solution is 0.8-1.2 mol / L, and the pH value of the system is accurately adjusted to the weak alkaline range of 8-9. After the addition is completed, the current stirring speed is continued for 1.5-2.5 hours to ensure that the metal ions and hydroxide ions are fully reacted to generate uniformly coexisting metal hydroxide precipitates in the entire three-dimensional space network of shiitake mushroom.

[0030] Step five: washing and purification In some embodiments, the reaction product is separated and washed with deionized water until the wash is neutral and free of chloride ion, sodium ion residue. The absence of chloride ion residue is confirmed using AgNO3solution testing, and the wash is confirmed to be neutral and free of sodium ion residue using a sodium ion meter or pH paper.

[0031] Step six: vacuum drying In some embodiments, the washed sample is dried at 50-60°C under a vacuum of less than -0.1 MPa, to obtain a dried precursor composite material. This condition can effectively prevent the collapse of the sample structure and deeply remove the internal bound water, to obtain a dry, crisp precursor composite material. Preferably, the drying is continued for 20-30 hours.

[0032] Step seven: heat treatment and carbothermal reduction In some embodiments, the dried precursor composite material is subjected to programmed temperature heat treatment and carbothermal reduction in a tube furnace under a protective atmosphere.

[0033] In some embodiments, the protective atmosphere is a hydrogen / argon mixed gas with a H2volume fraction of 7-10%.

[0034] In some embodiments, the programmed temperature control is set as follows: Dehydration stage: the temperature is raised from room temperature to 180-220°C at a rate of 8-12°C / min, and the temperature is maintained at this temperature for 4-8 hours, to completely remove the physically adsorbed water and part of the bound water, and to stabilize the material skeleton.

[0035] Decomposition stage: the temperature is raised at a rate of 10-20°C / min to 650-800°C, and then maintained at this temperature for 4-8 hours. This stage allows the supported metal hydroxide to be fully thermally decomposed into the corresponding metal oxide.

[0036] Alloying and carburizing stage: the temperature is raised at a slow rate of 3-5°C / min to 950-1100°C, and the temperature is maintained at the target temperature for 1.5-3 hours. In this stage, the biomass is completely carburized into biochar, and at the same time, the metal oxide is reduced to elemental metal by H2and diffuses with each other, to finally form FeCrNiCo high-entropy alloy nanoparticles uniformly embedded in the biochar matrix. After the reaction is completed, the composite material (FeCrNiCo-carburized shiitake mushroom composite material) with a porous carbon matrix uniformly embedded with FeCrNiCo high-entropy alloy nanoparticles is obtained by natural cooling to room temperature under a hydrogen / argon atmosphere.

[0037] The FeCrNiCo-carburized shiitake mushroom composite material of the present application is composed of FeCrNiCo high-entropy alloy nanoparticles uniformly embedded in a three-dimensional porous biochar matrix formed by carburization of shiitake mushrooms. ​

[0038] This material, with its unique component synergistic effect and three-dimensional porous structure, can effectively adjust impedance matching, enhance dielectric loss and interface polarization, and achieve efficient electromagnetic wave absorption. The absorbing material prepared by this invention has the characteristics of strong absorption, wide bandwidth, lightweight and structural stability.

[0039] Example 1: Preparation of FeCrNiCo-C composite material This embodiment provides a method for preparing FeCrNiCo-C composite material.

[0040] First, select fresh enoki mushrooms, rinse them with deionized water to remove surface impurities and drain them, then cut them. Figure 1 The section within the red dashed box serves as a biological template.

[0041] Prepare a mixed solution of equimolar amounts of four metal salts: Fe, Cr, Ni, and Co (where Fe is the most abundant metal). 3+ Cr 3+ Ni 2+ and Co 2+ The molar concentration of each salt was 0.125 mol / L. Specifically, using a 0.01 g analytical balance, the required masses of FeCl3·6H2O, CoCl2·6H2O, NiCl2·6H2O, and CrCl3·6H2O crystals were accurately weighed. Each salt was dissolved in an appropriate amount of deionized water, stirred in a 50°C water bath until completely dissolved, and then diluted to volume to prepare four single metal salt stock solutions with a concentration of 0.5 mol / L. Subsequently, according to the equimolar ratio principle, equal amounts of the above stock solutions were accurately measured using a pipette, placed in beakers, mixed, and stirred using a magnetic stirrer at 300 rpm for 30 minutes to ensure uniform dispersion of the metal ions, obtaining a clear high-entropy alloy precursor mixed solution.

[0042] The enoki mushrooms and the mixed solution were mixed at a mass ratio of 1:8, and the mixture was shaken and adsorbed at 25°C and 120 rpm for 8 hours.

[0043] Subsequently, 1 mol / L NaOH solution was slowly added dropwise to pH 8.5 while stirring at 300 rpm, and the co-precipitation reaction was carried out for 2 hours. Specifically, the ion-loaded system was placed on a heated magnetic stirrer, and 1 mol / L NaOH solution was slowly and dropwise added using a constant-pressure separatory funnel while continuously stirring at 300 rpm. The pH value of the system was precisely adjusted to 8.5 by real-time monitoring with a precision pH meter.

[0044] The product was repeatedly washed with deionized water until no chloride ion residue was left. Specifically, the vacuum filtration device was used to separate the Flammulina velutipes from the solution after the reaction. Then the sample was transferred to a large amount of deionized water for soaking and washing, and was manually shaken gently every 30 minutes. The total washing time was 2-4 hours, and the deionized water was replaced 3-5 times during the washing process, until no white precipitate was detected in the supernatant using 0.1 mol / L AgNO3 solution (test ), and the washing liquid was confirmed to be neutral and free of sodium ion residue using a sodium ion meter or pH test paper, ensuring that the impurity ions were completely removed.

[0045] The wet sample was evenly spread in a petri dish and placed in a vacuum drying oven. The drying temperature was set to 60°C, and the vacuum pump was turned on to maintain the pressure in the oven below -0.1 MPa. The sample was dried for 24 hours.

[0046] Finally, the dried precursor material was placed flat in a corundum boat, which was then pushed into the constant temperature zone of a single-zone tube furnace. After sealing, high-purity argon gas (purity 99.999%) was introduced at a flow rate of 200 sccm for 30 minutes to completely remove the air in the furnace. Then the atmosphere was switched to 8% H2 / Ar, and this protective atmosphere was maintained until the end of the program. The program was set as follows: first, increase the temperature to 200°C at a rate of 10°C / min and maintain for 5 hours, then increase the temperature to 700°C at a rate of 15°C / min and maintain for 5 hours, and finally increase the temperature to 1000°C at a rate of 5°C / min and maintain for 2 hours to complete carbonization and alloying, obtaining the final product.

[0047] Figure 2 is a microscopic image of the Flammulina velutipes root cross-section, and the porous structure can be observed; Figure 3 is a microscopic image of the FeCrNiCo-C composite material prepared in Example 1, which retains the porous structure of the Flammulina velutipes root cross-section.

[0048] Figure 4 is a SEM image of the FeCrNiCo-C composite material prepared in Example 1, and the carbonized Flammulina velutipes surface is covered with fine particles, which are FeCrNiCo alloy particles.

[0049] Example 2: Effect of adsorption time This example studies the effect of ion adsorption time on microwave absorption performance. Under the premise of keeping other parameters of Example 1 unchanged, the ion adsorption time was shortened from 8 hours to 5 hours. By comparison, it was found that the change of adsorption time significantly affected the loading amount and distribution uniformity of metal ions in the carbon matrix, which in turn regulated the dielectric constant and impedance matching characteristics of the composite material, and finally reflected in the difference of microwave absorption performance. After the adsorption time was shortened to 5 hours, the microwave absorption performance was very poor and could be ignored.

[0050] Figure 5 is the SEM image of FeCrNiCo-C composite material of Example 2, FeCrNiCo loading is significantly reduced and sporadically distributed, unevenly.

[0051] Example 3: Effect of heat treatment final temperature This example studies the effect of heat treatment final temperature on microwave absorption performance. Adjust the heat treatment procedure of Example 1, set the final alloying and carbonization temperature to 900℃ (other stage parameters remain unchanged). The results show that the microwave absorption performance is relatively worse than that of Example 1, and the possible reason is that the change of final temperature not only affects the carbonization degree and graphitization degree of the mushroom, but also determines the composition of high-entropy alloy nanoparticles. These structural differences lead to different electromagnetic parameters and loss mechanisms of the composite material, thereby affecting its microwave absorption characteristics.

[0052] Example 4: Effect of reducing atmosphere This example studies the effect of hydrogen concentration in the reducing atmosphere on microwave absorption performance. Refer to the preparation process of Example 1, but adjust the protective atmosphere to 5% H2 / Ar mixed gas during the heat treatment stage. Reducing the hydrogen concentration will change the reduction kinetics and alloying process of metal oxides, affecting the interface bonding state of high-entropy alloy nanoparticles, and the microwave absorption performance is relatively worse than that of Example 1.

[0053] Comparative Example 1: Not loaded on the mushroom Except that the alloy particles are not loaded on the mushroom, the other conditions are the same as Example 1. Pure FeCrNiCo alloy particles are obtained, and the microwave absorption performance is very poor.

[0054] Each sample is pressed into a coaxial ring, and a vector network analyzer is used to test its electromagnetic parameters, and then the reflection loss (RL) value is calculated according to the electromagnetic parameters.

[0055] According to the 1 / 4 wavelength cancellation theory, when the minimum reflection loss is achieved, the calculated d cal The value of (absorbing layer thickness) is well matched with the position of the minimum RL (reflection loss) corresponding to the thickness of all samples (as shown in Figure 6-8 ).

[0056] Figure 6 is the microwave absorption performance of FeCrNiCo-C composite material in Example 1 with different thicknesses (1-5mm) and the matching diagram of 1 / 4 wavelength theory. The maximum effective bandwidth is 6.2GHz, and the minimum RL value is 52.4dB.

[0057] Figure 7is the microwave absorption performance of the FeCrNiCo-C composite material in Example 3 with different thicknesses (1-5 mm), and the matching diagram of the 1 / 4 wavelength theory. The maximum effective frequency width is 7.8 GHz, and the minimum RL value is 18.1 dB.

[0058] Figure 8 is the microwave absorption performance of the CrNiCo-C composite material in Example 4 with different thicknesses (1-5 mm), and the matching diagram of the 1 / 4 wavelength theory. The maximum effective frequency width is 9.2 GHz, and the minimum RL value is 31.6 dB.

[0059] The above is only a preferred embodiment of the present application, and does not limit the present application in any form. Therefore, any simple modification, equivalent change and modification of the above embodiment according to the technical essence of the present application, which does not deviate from the technical scheme of the present application, shall fall within the protection scope of the technical scheme of the present application.

Claims

1. A method for preparing FeCrNiCo-Flammulina velutipes composite material, characterized in that, Comprise the following steps: (1) the pretreated Flammulina velutipes is immersed in a mixed metal salt solution containing Fe 3+ , Cr 3+ , Ni 2+ , Co 2+ , and metal ions are loaded on the Flammulina velutipes under oscillation conditions; the Flammulina velutipes is selected from a section starting from the root to a distance of 3-4 cm from the root; the molar concentrations of Fe 3+ , Cr 3+ , Ni 2+ , and Co 2+ in the mixed metal salt solution are equal; (2) adjust the solution pH to 8~9, co-precipitation reaction, the formation of metal hydroxide precipitate, then separation, washing purification, drying, to get the precursor composite material; (3) the precursor composite material in the hydrogen-containing protective atmosphere stepwise heat treatment, so that the carbonization of the golden needle mushroom to form a biological carbon matrix, while forming FeCrNiCo high-entropy alloy nanoparticles embedded in the biological carbon matrix, to obtain the FeCrNiCo-carbonized golden needle mushroom composite material; The stepwise heat treatment comprises the following three stages: heating to 180~220℃ and holding; heating to 650~800℃ and holding; heating to 950~1100℃ holding.

2. The preparation method of FeCrNiCo-carbonized enoki mushroom composite material according to claim 1, characterized in that, The molar concentration of Fe 3+ , Cr 3+ , Ni 2+ and Co 2+ in the mixed metal salt solution in step (1) is in the range of 0.1-0.125 mol / L; the mass ratio of golden needle mushroom to mixed metal salt solution is controlled at 1:(5-10).

3. The preparation method of FeCrNiCo-carbonized enoki mushroom composite material according to claim 1, characterized in that, Step (1) comprises: with 100~150 revolutions per minute oscillation speed for 7-10 hours, so that the metal ions loaded on the golden needle mushroom.

4. The preparation method of the FeCrNiCo-carbonized enoki mushroom composite material according to claim 1, characterized in that, Step (2) comprises: adding NaOH solution dropwise to the solution, the concentration of NaOH solution is 0.8~1.2 mol / L, the pH value is adjusted to 8-9, after the dropwise addition is completed, continue to stir for 1.5~2.5 hours, co-precipitation reaction.

5. The preparation method of the FeCrNiCo-carbonized enoki mushroom composite material according to claim 1, characterized in that, The washing purification, drying of step (2) comprises: washing with deionized water until the washing liquid is neutral and there is no chloride ion, sodium ion residue; drying at 50-60℃, vacuum degree is less than-0.1 MPa.

6. The preparation method of FeCrNiCo-carbonized enoki mushroom composite material according to claim 1, characterized in that, The protective atmosphere of step (3) is hydrogen / argon mixed gas, the volume fraction of H2 is 7%-10%.

7. The preparation method of the FeCrNiCo-carbonized enoki mushroom composite material according to claim 1, characterized in that, The stepwise heat treatment of step (3) comprises the following three stages: heating to 180~220℃ at a rate of 8~12℃ / min, holding for 4~8 hours; heating to 650~800℃ at a rate of 10~20℃ / min, holding for 4~8 hours; heating to 950~1100℃ at a rate of 3~5℃ / min, holding for 1.5~3 hours.

8. The FeCrNiCo-Flammulina velutipes composite material prepared by the method of any one of claims 1-7, characterized in that, It is composed of FeCrNiCo high-entropy alloy nanoparticles uniformly embedded in the three-dimensional porous biological carbon matrix formed by the carbonization of the golden needle mushroom.

9. The FeCrNiCo-carbonized golden needle mushroom composite material of claim 8 as a microwave absorbing material.

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