A FeCrNiCo-carbonized enoki mushroom composite material, its preparation method and application

Abstract

This invention discloses a FeCrNiCo-carbonized enoki mushroom composite material, its preparation method, and its application, comprising the following steps: (1) immersing pretreated enoki mushrooms in Fe... 3+ Cr 3+ Ni 2+ Co 2+ (1) In a mixed metal salt solution, metal ions are loaded onto enoki mushrooms under oscillation conditions; (2) The pH of the solution is adjusted to 8-9, and a co-precipitation reaction is carried out to form a metal hydroxide precipitate, which is then separated, washed, purified, and dried to obtain the precursor composite material; (3) The precursor composite material is subjected to a step-by-step heat treatment under a hydrogen-containing protective atmosphere to obtain the FeCrNiCo-carbonized enoki mushroom composite material. This invention utilizes the inherent characteristics of biomass to achieve uniform loading of metal ions, and simultaneously completes carbonization and alloying through multi-stage precise heat treatment, ultimately obtaining a highly efficient microwave absorbing material with strong absorption and wide bandwidth characteristics.

Description

Technical Field

[0001] This invention belongs to the field of microwave absorbing materials, and particularly relates to the preparation of a FeCrNiCo-carbonized enoki mushroom composite material and its application as a microwave absorbing material. Background Technology

[0002] With the widespread application of 5G and IoT technologies, the electromagnetic environment is becoming increasingly complex. Traditional absorbing materials are struggling to meet increasingly stringent electromagnetic compatibility requirements. Meanwhile, the trend towards thinner and lighter electronic devices is imposing stricter limitations on the thickness and weight of materials. These demands are collectively driving the evolution of absorbing materials towards ultra-thin, broadband, and intelligent response technologies, thus promoting the research and development of next-generation high-performance materials.

[0003] Against this backdrop, biomass carbon materials, with their advantages of wide availability, low cost, and environmental friendliness, have shown great potential in the field of microwave absorption. Porous carbon materials obtained through the pyrolysis of natural biomass such as straw and wood not only possess lightweight, high-temperature resistance, and tunable dielectric properties, but also exhibit hierarchical channels and complex microstructures, which contribute to improved microwave absorption performance. More importantly, biomass carbon materials can be combined with magnetic components to construct multi-element loss mechanisms, synergistically optimizing impedance matching and attenuation performance, providing new possibilities for the development of high-performance, sustainable microwave absorbing materials.

[0004] However, traditional microwave absorbing materials such as ferrite and carbon-based materials still have limitations such as high density, narrow bandwidth, or insufficient environmental stability. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the background art above, and to provide a FeCrNiCo-carbonized enoki mushroom composite material (hereinafter referred to as FeCrNiCo-C) and its preparation method, and to use it for microwave absorption to obtain excellent microwave absorption performance.

[0006] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0007] A method for preparing a FeCrNiCo-carbonized enoki mushroom composite material includes the following steps:

[0008] (1) Immerse the pretreated enoki mushrooms in a solution containing Fe 3+ Cr 3+ Ni 2+ Co 2+ In a mixed metal salt solution, metal ions are loaded onto enoki mushrooms under shaking conditions; the enoki mushrooms are selected from a section extending 3-4 cm from the root; in the mixed metal salt solution, Fe... 3+ Cr 3+ Ni 2+ and Co2+ The molar concentrations are all equal;

[0009] (2) Adjust the pH of the solution to 8-9, carry out a co-precipitation reaction to form a metal hydroxide precipitate, and then separate, wash, purify and dry to obtain the precursor composite material;

[0010] (3) The precursor composite material is subjected to step heat treatment in a hydrogen-containing protective atmosphere to carbonize the enoki mushroom to form a bio-carbon matrix. At the same time, FeCrNiCo high-entropy alloy nanoparticles are embedded in the bio-carbon matrix to obtain the FeCrNiCo-carbonized enoki mushroom composite material.

[0011] The stepped heat treatment includes the following three stages: heating to 180~220℃ and holding; heating to 650~800℃ and holding; heating to 950~1100℃ and holding.

[0012] As a further improvement, in the mixed metal salt solution described in step (1), Fe 3+ Cr 3+ Ni 2+ and Co 2+ The molar concentration is in the range of 0.1~0.125 mol / L; the mass ratio of enoki mushroom to mixed metal salt solution is controlled at 1:(5-10).

[0013] As a further improvement, step (1) includes: continuously soaking at an oscillation speed of 100~150 rpm for 7-10 hours to load metal ions onto the enoki mushrooms.

[0014] As a further improvement, step (2) includes: adding NaOH solution dropwise to the solution, with a NaOH solution concentration of 0.8~1.2 mol / L, adjusting the pH value to 8-9, and continuing to stir the reaction for 1.5~2.5 hours after the addition is complete to carry out the co-precipitation reaction.

[0015] As a further improvement, the washing, purification and drying in step (2) include: washing with deionized water until the washing solution is neutral and free of chloride and sodium ions; and drying at 50-60°C and a vacuum of less than -0.1 MPa.

[0016] As a further improvement, the protective atmosphere in step (3) is a hydrogen / argon mixture with an H2 volume fraction of 7%-10%.

[0017] As a further improvement, the stepped heat treatment in step (3) includes the following three stages: heating to 180-220°C at a rate of 8-12°C / min and holding for 4-8 hours; heating to 650-800°C at a rate of 10-20°C / min and holding for 4-8 hours; and heating to 950-1100°C at a rate of 3-5°C / min and holding for 1.5-3 hours.

[0018] The present invention also provides a FeCrNiCo-carbonized enoki mushroom composite material prepared by the above 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 enoki mushroom.

[0019] The present invention also provides an application of the FeCrNiCo-carbonized enoki mushroom composite material as a microwave absorbing material.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] This invention achieves synergistic optimization of composition and structure by compositing a multi-component FeCrNiCo high-entropy alloy with a bio-carbon matrix derived from enoki mushrooms. The high-entropy alloy endows the material with excellent dielectric loss capability, while the three-dimensional porous fiber structure formed by carbonization of enoki mushrooms not only provides a uniformly dispersed carrier for alloy nanoparticles and constructs a heterogeneous interface that enhances interfacial polarization, but also extends the electromagnetic wave propagation path through multiple reflections and scattering. The combination of the carbon matrix with moderate conductivity and the high-loss alloy particles effectively adjusts the complex dielectric constant, improves impedance matching, and allows more electromagnetic waves to enter the material for dissipation. This preparation process is green and economical, utilizing the inherent characteristics of biomass to achieve uniform loading of metal ions, and simultaneously completing carbonization and alloying through multi-stage precise heat treatment, ultimately obtaining a highly efficient microwave absorbing material with strong absorption and wide bandwidth characteristics. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention 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 the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a full view of the enoki mushrooms used in the example;

[0024] Figure 2 This is a microscopic image of a cross-section of the root of an enoki mushroom, which shows its porous structure.

[0025] Figure 3This is a cross-sectional micrograph of the FeCrNiCo-C composite material prepared in Example 1, which shows that it retains the porous structure of the cross-section of the root of the enoki mushroom.

[0026] Figure 4 The image shows a SEM image of the FeCrNiCo-C composite material prepared in Example 1. Fine particles, namely FeCrNiCo alloy particles, can be observed covering the surface of the carbonized enoki mushroom.

[0027] Figure 5 The image shows a SEM image of the FeCrNiCo-C composite material from Example 2. The FeCrNiCo loading is significantly reduced and is scattered and unevenly distributed.

[0028] Figure 6 This is a matching graph showing the microwave absorption properties of FeCrNiCo-C composite materials of different thicknesses (1-5 mm) in Example 1 and the theoretical 1 / 4 wavelength. RL represents the reflection loss, d cal Represents the thickness of the absorbing layer;

[0029] Figure 7 The image shows the microwave absorption properties of FeCrNiCo-C composite materials with different thicknesses (1-5 mm) in Example 3 and their matching with the 1 / 4 wavelength theory.

[0030] Figure 8 This is a matching diagram of the microwave absorption properties of CrNiCo-C composite materials with different thicknesses (1-5 mm) in Example 4 and the 1 / 4 wavelength theory. Detailed Implementation

[0031] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0032] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0033] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0034] In some embodiments, the preparation method of the FeCrNiCo-carbonized enoki mushroom composite material of the present invention includes the following steps:

[0035] Step 1: Biomass precursor pretreatment

[0036] In some embodiments, fresh enoki mushrooms with intact bodies and no rot are selected, rinsed with deionized water to remove surface impurities, and drained. A section adjacent to the root is precisely cut, preferably from the root to a distance of 3-4 cm (e.g., from the root). Figure 1 (As shown in the red dashed box), this part has a dense structure and is rich in fibers. Using it as a biomass template can effectively utilize its natural porous structure to provide a large number of active sites for the subsequent anchoring of metal ions.

[0037] Step 2: Preparation of high-entropy alloy precursor solution

[0038] In some embodiments, a formulation containing equimolar amounts of Fe is prepared. 3+ Cr 3+ Ni 2+ and Co 2+ A mixed metal salt solution.

[0039] In some embodiments, the mixed metal salt solution is prepared from FeCl3·6H2O, CoCl2·6H2O, NiCl2·6H2O, and CrCl3·6H2O. In the mixed metal salt solution, Fe... 3+ Cr 3+ Ni 2+ and Co 2+ The molar concentrations were all equal and ranged from 0.1 to 0.125 mol / L.

[0040] In some embodiments, each salt is dissolved in deionized water and stirred until completely dissolved under water bath heating. Then, the salts are mixed and stirred according to the principle of equimolar ratio to ensure that the metal ions are uniformly dispersed, thereby obtaining a clear high-entropy alloy precursor mixed solution.

[0041] Step 3: Ion Adsorption and Loading

[0042] In some embodiments, the pretreated enoki mushroom segments are completely immersed in the above-mentioned mixed metal salt solution and soaked under oscillation conditions to achieve uniform loading of metal ions on the biomass template through oscillation adsorption.

[0043] In some embodiments, by controlling the amount of feed, the mass ratio of enoki mushrooms to mixed metal salt solution is strictly controlled within the range of 1:(5-10).

[0044] In some embodiments, the entire system is placed in a constant-temperature shaker and continuously soaked for 7-10 hours at a shaking speed of 100-150 rpm under room temperature (25±2℃). This process utilizes the concentration difference and the adsorption characteristics of biomass itself to enable multiple metal ions to synergistically penetrate and firmly load onto the microporous channels and fiber surface of enoki mushrooms.

[0045] Step 4: Coprecipitation reaction

[0046] In some embodiments, an alkaline solution (e.g., NaOH solution) is slowly added dropwise to a system loaded with metal ions under stirring to adjust the pH to 8-9, thereby initiating a co-precipitation reaction that produces a homogeneous metal hydroxide precipitate.

[0047] In some embodiments, a NaOH solution with a concentration of 0.8–1.2 mol / L is added dropwise under continuous mechanical stirring at 200–400 rpm to precisely adjust the pH of the system to a weakly alkaline range of 8–9. After the addition is complete, the reaction is continued at the current stirring speed for 1.5–2.5 hours to ensure that the metal ions and hydroxide ions react fully, generating a uniform and coexisting metal hydroxide precipitate throughout the entire three-dimensional network of the enoki mushroom.

[0048] Step 5: Washing and Purification

[0049] In some embodiments, the reaction products are separated and washed with deionized water until the washing solution is neutral and free of chloride and sodium ions. The absence of chloride and sodium ions is confirmed by detection with AgNO3 solution. The solution was checked for residue, and a sodium ion meter or pH test paper was used to confirm that the washing solution was neutral and free of sodium ion residue.

[0050] Step Six: Vacuum Drying

[0051] In some embodiments, the washed sample is dried at 50-60°C and a vacuum degree below -0.1 MPa to obtain a dried precursor composite material. This condition effectively prevents sample structural collapse and deeply removes bound water from its interior, resulting in a dry, brittle precursor composite material. Preferably, the drying process continues for 20-30 hours.

[0052] Step 7: Heat treatment and carbonization reduction

[0053] In some embodiments, the dried precursor composite material is subjected to programmed temperature heat treatment and carbonization reduction in a tube furnace under a protective atmosphere.

[0054] In some embodiments, the protective atmosphere is a hydrogen / argon mixture with an H2 volume fraction of 7%-10%.

[0055] In some embodiments, programmed temperature control is performed according to the following settings:

[0056] Dehydration stage: The temperature is increased from room temperature to 180-220°C at a rate of 8-12°C / min, and held at this temperature for 4-8 hours to completely remove physically adsorbed water and some bound water, thereby stabilizing the material skeleton.

[0057] Decomposition stage: Increase the heating rate to 10~20℃ / min, raise the temperature to 650~800℃, and then hold for 4~8 hours. This stage allows the supported metal hydroxide to fully decompose thermally, transforming into the corresponding metal oxide.

[0058] Alloying and carbonization stage: A slow heating rate of 3-5℃ / min is used to raise the temperature to 950-1100℃, and it is held at the target temperature for 1.5-3 hours. During this stage, biomass is completely carbonized into bio-carbon. Simultaneously, metal oxides are reduced to elemental metals by H2 and interdiffusion occurs, ultimately forming FeCrNiCo high-entropy alloy nanoparticles uniformly embedded in the bio-carbon matrix. After the reaction, the mixture is naturally cooled to room temperature under a hydrogen / argon atmosphere to obtain a composite material with a porous carbon matrix uniformly embedded with FeCrNiCo high-entropy alloy nanoparticles (FeCrNiCo-carbonized enoki mushroom composite material).

[0059] The FeCrNiCo-carbonized enoki mushroom composite material of the present invention is composed of FeCrNiCo high-entropy alloy nanoparticles uniformly embedded in a three-dimensional porous bio-carbon matrix formed by carbonization of enoki mushrooms.

[0060] 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.

[0061] Example 1: Preparation of FeCrNiCo-C composite material

[0062] This embodiment provides a method for preparing FeCrNiCo-C composite material.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] The product was repeatedly washed with deionized water until no chloride ion residue remained. Specifically, the reacted enoki mushrooms were separated from the solution using a vacuum filtration device. The sample was then transferred to a large volume of deionized water for soaking and washing, with gentle manual shaking every 30 minutes. The total washing time was 2-4 hours, during which the deionized water was changed 3-5 times, until no white precipitate was found in the supernatant when tested with 0.1 mol / L AgNO3 solution (test result). Then, use a sodium ion meter or pH test paper to confirm that the washing solution is neutral and free of sodium ion residue, ensuring that impurity ions are completely removed.

[0068] Vacuum drying at 60℃ for 24 hours. Specifically: the washed, neutralized wet sample is evenly spread in a petri dish and placed in a vacuum drying oven. The drying temperature is set to 60℃, and the vacuum pump is turned on to maintain the pressure inside the oven below -0.1 MPa for 24 hours.

[0069] Finally, the dried precursor material was placed flat inside the corundum boat and then pushed into the isothermal zone of a single-zone tube furnace. After sealing, high-purity argon gas (99.999% purity) was first introduced at a flow rate of 200 sccm for 30 minutes to completely purge the air from the furnace. Then, the atmosphere was switched to 8% H2 / Ar and maintained until the program ended. The temperature was controlled according to the following settings: first, the temperature was increased to 200℃ at 10℃ / min and held for 5 hours; then, it was increased to 700℃ at 15℃ / min and held for 5 hours; finally, it was increased to 1000℃ at 5℃ / min and held for 2 hours to complete the carbonization and alloying, obtaining the final product.

[0070] Figure 2 This is a microscopic image of a cross-section of the root of an enoki mushroom, which shows its porous structure. Figure 3 This is a cross-sectional micrograph of the FeCrNiCo-C composite material prepared in Example 1, which shows that it retains the porous structure of the cross-section of the enoki mushroom root.

[0071] Figure 4 The image shows a SEM image of the FeCrNiCo-C composite material prepared in Example 1. Fine particles, namely FeCrNiCo alloy particles, can be observed covering the surface of the carbonized enoki mushroom.

[0072] Example 2: Effect of adsorption time

[0073] This embodiment investigates the effect of ion adsorption time on microwave absorption performance. While keeping other parameters unchanged from Example 1, the ion adsorption time was shortened from 8 hours to 5 hours. Comparison revealed that the change in adsorption time significantly affects the loading and distribution uniformity of metal ions in the carbon matrix, thereby regulating the dielectric constant and impedance matching characteristics of the composite material, ultimately reflected in the differences in microwave absorption performance. After shortening the adsorption time to 5 hours, the microwave absorption performance was extremely poor and negligible.

[0074] Figure 5 The image shows a SEM image of the FeCrNiCo-C composite material from Example 2. The FeCrNiCo loading is significantly reduced and is scattered and unevenly distributed.

[0075] Example 3: Effect of final heat treatment temperature

[0076] This embodiment investigates the effect of the final heat treatment temperature on microwave absorption performance. The heat treatment procedure of Example 1 was adjusted, with the final alloying and carbonization temperature set to 900℃ (other stage parameters remained unchanged). The results show that the microwave absorption performance is worse than that of Example 1. This may be because the change in final temperature not only affects the degree of carbonization and graphitization of *Flammulina velutipes*, but also determines the composition of the high-entropy alloy nanoparticles. These structural differences lead to different electromagnetic parameters and loss mechanisms in the composite material, thus affecting its microwave absorption characteristics.

[0077] Example 4: The Influence of Reducing Atmosphere

[0078] This embodiment investigates the effect of hydrogen concentration in a reducing atmosphere on microwave absorption performance. The preparation process is the same as in Example 1, but the protective atmosphere is adjusted to a 5% H2 / Ar mixture during the heat treatment stage. Reducing the hydrogen concentration alters the reduction kinetics and alloying process of the metal oxide, affecting the interfacial bonding state of the high-entropy alloy nanoparticles, resulting in a deterioration in microwave absorption performance compared to Example 1.

[0079] Comparative Example 1: Not loaded on enoki mushrooms

[0080] Except for not loading the alloy particles onto enoki mushrooms, all other conditions were the same as in Example 1. Pure FeCrNiCo alloy particles were obtained, exhibiting very poor microwave absorption performance.

[0081] Each sample was pressed into a coaxial ring, and its electromagnetic parameters were tested using a vector network analyzer. The reflection loss (RL) value was then calculated based on the electromagnetic parameters.

[0082] Based on the quarter-wavelength destructive theory, the calculated value for achieving minimum reflection loss is... d cal The (absorbing layer thickness) value matches well with the minimum RL (reflection loss) location corresponding to the thickness of all samples (e.g., Figures 6-8 (As shown).

[0083] Figure 6 This is a matching diagram of the microwave absorption properties of FeCrNiCo-C composite materials in Example 1 with different thicknesses (1-5 mm) and the theoretical 1 / 4 wavelength. The maximum effective bandwidth is 6.2 GHz, and the minimum RL value is 52.4 dB.

[0084] Figure 7 The figures show the microwave absorption properties of FeCrNiCo-C composite materials in Example 3 with different thicknesses (1-5 mm), and the matching diagrams based on the quarter-wavelength theory. The maximum effective bandwidth is 7.8 GHz, and the minimum RL value is 18.1 dB.

[0085] Figure 8 The figures show the microwave absorption properties of CrNiCo-C composite materials in Example 4 with different thicknesses (1-5 mm), and the matching diagrams based on the quarter-wavelength theory. The maximum effective bandwidth is 9.2 GHz, and the minimum RL value is 31.6 dB.

[0086] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Therefore, any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention should fall within the protection scope of the present invention.

Claims

1. A method for preparing a FeCrNiCo-carbonized enoki mushroom composite material, characterized in that, Includes the following steps: (1) Immerse the pretreated enoki mushrooms in a solution containing Fe 3+ Cr 3+ Ni 2+ Co 2+ In a mixed metal salt solution, metal ions are loaded onto enoki mushrooms under shaking conditions; the enoki mushrooms are selected from a section extending 3-4 cm from the root; in the mixed metal salt solution, Fe... 3+ Cr 3+ Ni 2+ and Co 2+ The molar concentrations are all equal; (2) Adjust the pH of the solution to 8-9, carry out a co-precipitation reaction to form a metal hydroxide precipitate, and then separate, wash, purify and dry to obtain the precursor composite material; (3) The precursor composite material is subjected to step heat treatment in a hydrogen-containing protective atmosphere to carbonize the enoki mushroom to form a bio-carbon matrix, and FeCrNiCo alloy nanoparticles are embedded in the bio-carbon matrix to obtain the FeCrNiCo-carbonized enoki mushroom composite material. The stepped heat treatment includes the following three stages: heating to 180~220℃ and holding; heating to 650~800℃ and holding; heating to 950~1100℃ and holding.

2. The preparation method of FeCrNiCo-carbonized enoki mushroom composite material according to claim 1, characterized in that, In the mixed metal salt solution described in step (1), Fe 3+ Cr 3+ Ni 2+ and Co 2+ The molar concentration is in the range of 0.1~0.125 mol / L; the mass ratio of enoki 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) includes: continuously soaking at an oscillation speed of 100~150 rpm for 7-10 hours to load metal ions onto the enoki mushrooms.

4. The preparation method of the FeCrNiCo-carbonized enoki mushroom composite material according to claim 1, characterized in that, Step (2) includes: adding NaOH solution dropwise to the solution, with a NaOH solution concentration of 0.8~1.2 mol / L, adjusting the pH value to 8-9, and continuing to stir the reaction for 1.5~2.5 hours after the addition is complete to carry out the coprecipitation reaction.

5. The preparation method of the FeCrNiCo-carbonized enoki mushroom composite material according to claim 1, characterized in that, Step (2) washing, purification and drying include: washing with deionized water until the washing solution is neutral and free of chloride and sodium ions; drying at 50-60°C and a vacuum of 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 in step (3) is a hydrogen / argon mixture with an H2 volume fraction of 7%-10%.

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

8. A FeCrNiCo-carbonized enoki mushroom composite material prepared by the preparation method according to any one of claims 1 to 7, characterized in that, It consists of FeCrNiCo alloy nanoparticles uniformly embedded in a three-dimensional porous bio-carbon matrix formed by carbonization of enoki mushrooms.

9. The application of the FeCrNiCo-carbonized enoki mushroom composite material as described in claim 8 as a microwave absorbing material.

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