Preparation method of Fe-Co / Zn-coated NC carbon-based composite material for absorbing high-frequency electromagnetic waves

Abstract

The invention discloses a preparation method of a Fe-Co / Zn-coated NC carbon-based composite material for absorbing high-frequency electromagnetic waves. The invention belongs to the field of preparation of carbon-based composite electromagnetic wave absorbing materials. The method comprises the following steps: uniformly mixing dimethylimidazole, zinc acetate dehydrate, cobalt nitrate hexahydrate and ferric acetylacetonate in deionized water, aging, washing, centrifuging, freeze-drying, and carrying out high-temperature treatment. The introduction of Fe leads the formation of a Fe-Co solid solution so as to drive the whole phase change process, and further mediates a gradual microstructure evolution process, so that Fe-Co / Zn-coated NC achieves compatible components and optimized configuration, and the high-frequency electromagnetic wave absorption performance is remarkably improved. When the doping ratio is 40 wt%, the reflection loss reaches-84.41 dB, and incident electromagnetic waves exceeding 99.999999% can be absorbed; the effective absorption bandwidth of 6.08 GHz can be achieved under the doping ratio of 50 wt%, namely, the frequency band of 11.92-18.00 GHz is covered, and complete absorption of high-frequency electromagnetic waves is achieved.

Description

Technical Field

[0001] The present invention belongs to the field of preparation of carbon-based composite electromagnetic wave absorption materials; specifically, it relates to a preparation method of Fe-Co / Zn@NC carbon-based composite materials for absorbing high-frequency electromagnetic waves. Background Art

[0002] With the rapid development of wireless communication technologies and electronic devices, the widespread application of high-frequency electromagnetic waves (such as the Ku band of 12 - 18 GHz) has brought electromagnetic interference and pollution problems. There is an urgent need to develop high-performance electromagnetic wave absorption materials to ensure the stable operation of devices and information security. Traditional wave-absorbing materials (such as ferrites, magnetic metals, etc.) perform well in the low-frequency band, but have defects such as poor impedance matching and insufficient attenuation ability in high-frequency environments, making it difficult to meet the comprehensive requirements of "thin, light, wide, and strong". Therefore, designing new composite materials with lightweight, wide-band, and strong absorption characteristics has become a current research hotspot.

[0003] In recent years, metal-organic framework (MOF)-derived carbon-based composite materials have shown excellent electromagnetic wave absorption potential due to their tunable microstructure, high specific surface area, and multi-component synergistic effect. By pyrolyzing multi-metal MOF precursors at high temperature, composite materials containing carbon matrix, metal nanoparticles, and heterointerfaces can be obtained, which have both dielectric loss and magnetic loss characteristics. Among them, the introduction of multi-metal systems can enhance interfacial polarization, magnetic coupling effect, and multiple scattering through component optimization and structure regulation, thereby improving the wave absorption performance. However, existing research has mostly focused on single or dual-metal systems, and there is still a lack of in-depth exploration of the precise regulation of the phase transformation mechanism and structural evolution among multi-metal components, resulting in the difficulty of adapting the electromagnetic parameters of materials to the absorption requirements in the high-frequency band.

[0004] The advantages of multi-metal MOF-derived carbon-based composite materials lie in the designability of their components and structures. By regulating the types of metals, doping ratios, and pyrolysis conditions, the balance optimization of the dielectric-magnetic properties of the materials can be achieved. At the same time, the synergistic effect between the porous carbon matrix and metal nanoparticles can effectively extend the electromagnetic wave propagation path and enhance energy dissipation. In addition, defects and dipole polarization at the heterointerfaces further improve the attenuation ability of the materials. These characteristics make them show significant potential in the field of high-frequency electromagnetic wave absorption.

[0005] However, the existing technologies still have the following deficiencies: First, the dynamic evolution mechanism of the phase composition and microstructure in the multi-metal system is not yet clear, resulting in a lack of theoretical guidance for the regulation of material properties; second, the traditional doping strategy is difficult to achieve a gradient distribution of metal components, restricting the synergistic optimization of components and structures; third, there is still room for improvement in the microwave absorption performance in the high-frequency band (such as reflection loss and effective absorption bandwidth), especially it is difficult to balance strong absorption and wide-band characteristics at low filling ratios. Therefore, developing new multi-metal MOF-derived carbon-based composites to achieve efficient absorption of high-frequency electromagnetic waves by precisely regulating the phase composition and microstructure has become a technical problem to be solved urgently. Summary of the Invention

[0006] The present invention provides a preparation method of an Fe-Co / Zn@NC carbon-based composite material for absorbing high-frequency electromagnetic waves, aiming to design and synthesize a multi-metal MOF-derived carbon-based composite material with adjustable phase composition and structure to improve the performance of absorbing high-frequency electromagnetic waves.

[0007] A preparation method of an Fe-Co / Zn@NC carbon-based composite material for absorbing high-frequency electromagnetic waves is realized according to the following steps:

[0008] 1. Put dimethylimidazole, zinc acetate dihydrate, cobalt nitrate hexahydrate and iron acetylacetonate into deionized water and mix evenly to obtain a mixed solution, and then carry out an aging reaction to obtain an aged mixed solution;

[0009] 2. Wash and centrifuge the above-aged mixed solution, and then carry out freeze-drying to obtain a purple product, namely an Fe-Co / Zn@NC-ZIF precursor;

[0010] 3. Place the above Fe-Co / Zn@NC-ZIF precursor in a ceramic crucible and carry out high-temperature heat treatment in a tube furnace. After cooling, a black product, namely an Fe-Co / Zn@NC carbon-based composite material for absorbing high-frequency electromagnetic waves, is obtained, and the preparation method is completed.

[0011] Further, in the mixed solution in step 1, the content of dimethylimidazole is 50-150 mmol, the content of zinc acetate dihydrate is 10-50 mmol, the content of cobalt nitrate hexahydrate is 10-50 mmol, the content of iron acetylacetonate is 0.1-5.0 mmol, and the amount of deionized water used is 200 ml.

[0012] Further, the aging reaction time in step 1 is 12-72 h, and the temperature is room temperature.

[0013] Further, the washing in step 2 is washing with anhydrous methanol 3-6 times.

[0014] Further, the centrifugation in step two is carried out in a high-speed centrifuge at 5000 - 12000 rpm for min.

[0015] Further, the freeze-drying in step two: freeze-dry for 12 - 72 h in a freeze-dryer at a pressure of 1 - 10 MPa and a temperature of -80 - -40 °C.

[0016] Further, the high-temperature heat treatment in step three: keep the temperature at 500 - 1000 °C for 1 - 5 h, and the heating rate is 1 - 5 °C / min.

[0017] Principle of the present invention:

[0018] Through the strategy of gradient doping of the third heterogeneous metal Fe, precise regulation of the composition and morphology of the bimetallic Co / Zn-MOF is achieved, thus achieving the goal of efficiently absorbing high-frequency electromagnetic waves. With the addition of Fe, the ternary metal MOF-derived carbon-based composite generates a disordered Fe-Co solid solution, which dominates the dynamic phase transition process of the gradual decrease in the content of the Co3ZnC intermetallic compound phase and the gradual increase in the content of the Fe3ZnC intermetallic compound phase. Secondly, the introduction of Fe makes the microstructure after heat treatment gradually continue the framework configuration of the precursor, and under the combined action of the magnetic interaction between the Fe-Co solid solution and Fe and the internal stress generated by carbon shrinkage during the heat treatment process, a step-by-step geometric optimization process is realized: from multi-level self-assembly and crossing, then to mutual cutting-segmentation-reconstruction, and finally to re-stacking and assembly. The method of gradient Fe doping can solve the problem of difficult precise control of phases and structures in multi-metal MOF-derived carbon-based composites, providing theory and guidance for customizable high-performance electromagnetic wave absorption materials.

[0019] Advantages of the present invention:

[0020] In order to design and synthesize multi-metal MOF-derived carbon-based composites with adjustable phase composition and structure and improve their performance of absorbing high-frequency electromagnetic waves, the present invention first proposes a gradient Fe doping method, successfully constructs a multi-metal MOF-derived carbon-based composite with adjustable phase composition and structure. The introduction of Fe not only dominates the formation of the Fe-Co solid solution and drives the whole phase transition process, but also mediates a step-by-step microstructure evolution process, making Fe-Co / Zn@NC reach a compatible composition and optimized configuration, thus significantly improving its performance of absorbing high-frequency electromagnetic waves.

[0021] The Fe-Co / Zn@NC carbon-based composite material prepared in the present invention for absorbing high-frequency electromagnetic waves can achieve a reflection loss of -84.41 dB at a doping ratio of 40 wt%, and can absorb more than 99.999999% of the incident electromagnetic waves; at a doping ratio of 50 wt%, it can achieve an effective absorption bandwidth of 6.08 GHz, that is, covering the frequency band of 11.92 - 18.00 GHz, realizing the complete absorption of high-frequency electromagnetic waves; the gradient doping of Fe realizes the precise regulation of the composition and microstructure in the multi-metal MOF-derived carbon-based composite material, thus showing excellent and customizable high-frequency electromagnetic wave absorption performance, and is expected to become a new generation of MOF-derived carbon-based electromagnetic wave absorption materials in the future.

[0022] The present invention is applicable to the preparation of a Fe-Co / Zn@NC carbon-based composite material for absorbing high-frequency electromagnetic waves. Description of the Drawings

[0023] Figure 1 XRD spectrum of the Fe-Co / Zn@NC carbon-based composite material for absorbing high-frequency electromagnetic waves in the embodiment;

[0024] Figure 2 SEM spectrum of the Fe-Co / Zn@NC carbon-based composite material for absorbing high-frequency electromagnetic waves in the embodiment, where part a represents Fe-Co / Zn@NC1, part b represents Fe-Co / Zn@NC2, part c represents Fe-Co / Zn@NC3, part d represents Fe-Co / Zn@NC4, and part e represents Fe-Co / Zn@NC5;

[0025] Figure 3 TEM spectrum of the Fe-Co / Zn@NC carbon-based composite material for absorbing high-frequency electromagnetic waves in the embodiment, where part a represents Fe-Co / Zn@NC1, part b represents Fe-Co / Zn@NC2, part c represents Fe-Co / Zn@NC3, part d represents Fe-Co / Zn@NC4, and part e represents Fe-Co / Zn@NC5;

[0026] Figure 4 Schematic diagram of the electromagnetic wave absorption reflection loss of the Fe-Co / Zn@NC carbon-based composite material for absorbing high-frequency electromagnetic waves in the embodiment at the same doping ratio, where part a represents Fe-Co / Zn@NC1, part b represents Fe-Co / Zn@NC2, part c represents Fe-Co / Zn@NC3, part d represents Fe-Co / Zn@NC4, and part e represents Fe-Co / Zn@NC5;

[0027] Figure 5Schematic diagram of the electromagnetic wave absorption reflection loss of the Fe-Co / Zn@NC carbon-based composite material for absorbing high-frequency electromagnetic waves in the examples at different doping ratios, where part a represents a doping ratio of 40 wt%, part b represents a doping ratio of 45 wt%, part c represents a doping ratio of 50 wt%, and part d represents a doping ratio of 55 wt%. Detailed implementation manners

[0028] The technical solution of the present invention is not limited to the following specific implementation manners listed, but also includes any combination between the specific implementation manners.

[0029] Detailed implementation manner one: A preparation method of a Fe-Co / Zn@NC carbon-based composite material for absorbing high-frequency electromagnetic waves in this implementation manner is realized according to the following steps:

[0030] 1. Put dimethylimidazole, zinc acetate dihydrate, cobalt nitrate hexahydrate and iron acetylacetonate into deionized water and mix evenly to obtain a mixed solution, and then carry out an aging reaction to obtain the aged mixed solution;

[0031] 2. Wash and centrifuge the above-aged mixed solution, and then carry out freeze-drying to obtain a purple product, namely the Fe-Co / Zn@NC-ZIF precursor;

[0032] 3. Place the above Fe-Co / Zn@NC-ZIF precursor in a ceramic crucible and carry out high-temperature heat treatment in a tube furnace. After cooling, a black product is obtained, namely the Fe-Co / Zn@NC carbon-based composite material for absorbing high-frequency electromagnetic waves, and the preparation method is completed. Detailed implementation manner two: The difference between this implementation manner and detailed implementation manner one is that the content of dimethylimidazole in the mixed solution in step 1 is 50 - 150 mmol, the content of zinc acetate dihydrate is 10 - 50 mmol, the content of cobalt nitrate hexahydrate is 10 - 50 mmol, the content of iron acetylacetonate is 0.1 - 5.0 mmol, and the amount of deionized water used is 200 ml. Other steps and parameters are the same as those in detailed implementation manner one.

[0033] Detailed implementation manner three: The difference between this implementation manner and detailed implementation manner two is that the content of dimethylimidazole in the mixed solution in step 1 is 100 mmol, the content of zinc acetate dihydrate is 25 mmol, the content of cobalt nitrate hexahydrate is 25 mmol, the content of iron acetylacetonate is 0.6 mmol, and the amount of deionized water used is 200 ml. Other steps and parameters are the same as those in detailed implementation manner two.

[0034] Detailed implementation manner four: The difference between this implementation manner and detailed implementation manner one is that the aging reaction time in step 1 is 12 - 72 h and the temperature is room temperature. Other steps and parameters are the same as those in detailed implementation manner one.

[0035] Embodiment 5: The difference between this embodiment and Embodiment 4 is that the aging reaction time in Step 1 is 48 h and the temperature is room temperature. Other steps and parameters are the same as those in Embodiment 4.

[0036] Embodiment 6: The difference between this embodiment and Embodiment 1 is that the washing in Step 2 is washing with anhydrous methanol 3 - 6 times. Other steps and parameters are the same as those in Embodiment 1.

[0037] Embodiment 7: The difference between this embodiment and Embodiment 1 is that the centrifugation in Step 2 is centrifugation in a high - speed centrifuge at 5000 - 12000 rpm for 5 - 20 min. Other steps and parameters are the same as those in Embodiment 1.

[0038] Embodiment 8: The difference between this embodiment and Embodiment 1 is that the freeze - drying in Step 2 is carried out in a freeze - dryer at a pressure of 1 - 10 MPa and a temperature of - 80 - - 40 °C for 12 - 72 h. Other steps and parameters are the same as those in Embodiment 1.

[0039] Embodiment 9: The difference between this embodiment and Embodiment 8 is that the freeze - drying in Step 2 is carried out in a freeze - dryer at a pressure of 1 MPa and a temperature of - 60 °C for 48 h. Other steps and parameters are the same as those in Embodiment 8.

[0040] Embodiment 10: The difference between this embodiment and Embodiment 1 is that the high - temperature heat treatment in Step 3 is carried out at 500 - 1000 °C for 1 - 5 h with a heating rate of 1 - 5 °C / min. Other steps and parameters are the same as those in Embodiment 1.

[0041] The beneficial effects of the present invention are verified by the following examples:

[0042] Example:

[0043] A preparation method of an Fe - Co / Zn@NC carbon - based composite material for absorbing high - frequency electromagnetic waves is realized according to the following steps:

[0044] I. Put 2 - methylimidazole, zinc acetate dihydrate, cobalt nitrate hexahydrate and iron acetylacetonate into deionized water and mix evenly to obtain a mixed solution, and then carry out an aging reaction to obtain an aged mixed solution;

[0045] II. Wash and centrifuge the above - mentioned aged mixed solution, and then carry out freeze - drying to obtain a purple product, namely the Fe - Co / Zn@NC - ZIF precursor;

[0046] 3. The above Fe-Co / Zn@NC-ZIF precursor is placed in a ceramic crucible and subjected to high-temperature heat treatment in a tube furnace. After cooling, a black product, namely the Fe-Co / Zn@NC carbon-based composite material for absorbing high-frequency electromagnetic waves, is obtained, and the preparation method is completed.

[0047] In step 1 of this example, the content of dimethylimidazole in the mixed solution is 100 mmol, the content of zinc acetate dihydrate is 25 mmol, the content of cobalt nitrate hexahydrate is 25 mmol, the contents of iron acetylacetonate are 0.6 mmol, 1.2 mmol, 1.8 mmol, 2.4 mmol, and 3.0 mmol respectively, and the amount of deionized water used is 200 ml.

[0048] In step 1 of this example, the aging reaction time is 48 h and the temperature is room temperature.

[0049] In step 2 of this example, the washing is carried out with anhydrous methanol 3 times.

[0050] In step 2 of this example, the centrifugation is carried out in a high-speed centrifuge at 8000 rpm for 10 min.

[0051] In step 2 of this example, the freeze-drying is carried out in a freeze-dryer at a pressure of 1 MPa and a temperature of -60 °C for 48 h.

[0052] In step 3 of this example, the high-temperature heat treatment is carried out at 600 °C for 3 h with a heating rate of 2 °C / min.

[0053] In this example, according to the change in the amount of iron acetylacetonate used, a total of 5 samples of the Fe-Co / Zn@NC carbon-based composite material for absorbing high-frequency electromagnetic waves are prepared, and their XRD patterns are as Figure 1 shown. From Figure 1 it can be seen that as the Fe doping content increases (the content of 0.6 mmol is denoted as Fe-Co / Zn@NC1, the content of 1.2 mmol is denoted as Fe-Co / Zn@NC2, and the content of 1.8 mmol is denoted as Fe-Co / Zn@NC3), the content of the Co3ZnC intermetallic compound gradually decreases; especially when the Fe doping content reaches 2.4 mmol (Fe-Co / Zn@NC4), the diffraction peak of the Co3ZnC intermetallic compound cannot be detected at all; while when the Fe doping content continues to increase to 3.0 mmol (Fe-Co / Zn@NC5), the diffraction peaks associated with the Fe3ZnC intermetallic compound and metallic Fe begin to appear, indicating that the gradient Fe doping method can precisely regulate the phase composition of the multi-metal MOF-derived carbon-based composite material.

[0054] The Fe-Co / Zn@NC carbon-based composite material prepared in this example for absorbing high-frequency electromagnetic waves has an SEM pattern as shown in Figure 2 shown. From Figure 2 it can be seen that as the Fe doping content increases (Figure a is denoted as Fe-Co / Zn@NC1, Figure b is denoted as Fe-Co / Zn@NC2, and so on, the same hereinafter), its microstructure gradually continues the geometric framework of the precursor. At the same time, under the action of Fe magnetism, hierarchical self-assembly and cross-behavior begin to occur. Finally, under the synergistic action of high-temperature oxidation etching of Fe and internal stress generated by carbon shrinkage, a process from cutting-segmenting-reconstructing to re-stacking and assembling occurs, indicating that the gradient Fe doping method can accurately control the microstructure of the multi-metal MOF-derived carbon-based composite material.

[0055] The Fe-Co / Zn@NC carbon-based composite material prepared in this example for absorbing high-frequency electromagnetic waves has a TEM pattern as shown in Figure 3 shown. From Figure 3 it can be seen that as the Fe doping content increases, a process of gradual dynamic structure evolution occurs, which optimizes the geometric configuration of the multi-metal MOF-derived carbon-based composite material step by step, thereby enhancing its scattering effect on electromagnetic waves and enabling it to exhibit efficient electromagnetic wave absorption performance, indicating that the gradient Fe doping method can indeed control the morphological changes of the multi-metal MOF-derived carbon-based composite material.

[0056] The Fe-Co / Zn@NC carbon-based composite material prepared in this example for absorbing high-frequency electromagnetic waves has a schematic diagram of electromagnetic wave absorption reflection loss at the same doping ratio as shown in Figure 4 shown. From Figure 4 it can be seen that as the Fe doping content increases, the effective absorption bandwidth (EAB) of the composite material gradually increases. Among them, the EAB of Fe-Co / Zn@NC4 is as high as 6.08 GHz, that is, it covers the frequency band of 11.92 - 18.00 GHz, achieving complete absorption of high-frequency electromagnetic waves, indicating that the Fe-Co / Zn@NC carbon-based composite material exhibits efficient absorption performance for high-frequency electromagnetic waves.

[0057] The Fe-Co / Zn@NC carbon-based composite material prepared in this example for absorbing high-frequency electromagnetic waves has a schematic diagram of electromagnetic wave absorption reflection loss at different doping ratios as shown in Figure 5 shown (the doping ratio in Figure a is 40 wt%, the doping ratio in Figure b is 45 wt%, the doping ratio in Figure c is 50 wt%, and the doping ratio in Figure d is 55 wt%). From Figure 5It can be seen that when the doping ratio is gradually decreased, the reflection loss of the composite material is gradually enhanced. The reflection loss can reach -84.41 dB at a doping ratio of 40 wt%, and it can absorb more than 99.999999% of the incident electromagnetic waves, indicating that the Fe-Co / Zn@NC carbon-based composite material exhibits excellent electromagnetic wave absorption performance.

[0058] In this embodiment, the Fe-Co / Zn@NC carbon-based composite material was successfully prepared. The proposed method of gradient Fe doping successfully constructed a multi-metal MOF-derived carbon-based composite material with adjustable phase composition and structure. The introduction of Fe not only dominated the formation of the Fe-Co solid solution, thus driving the entire phase transition process, but also mediated the gradual microstructure evolution process, enabling Fe-Co / Zn@NC to achieve a compatible composition and optimized configuration, thereby significantly improving its performance in absorbing high-frequency electromagnetic waves. It is expected to become a new generation of MOF-derived carbon-based electromagnetic wave absorption materials in the future.

[0059] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a Fe-Co / Zn@NC carbon-based composite material for absorbing high-frequency electromagnetic waves, characterized in that It proceeds as follows:

1. placing dimethylimidazole, zinc acetate dihydrate, cobalt nitrate hexahydrate and ferric acetylacetonate in deionized water and mixing them evenly to obtain a mixed solution, and then performing an aging reaction to obtain an aged mixed solution; 2. Washing and centrifuging the aged mixed solution, and then freeze-drying to obtain a purple product, namely, Fe-Co / Zn@NC-ZIF precursor; 3. The Fe-Co / Zn@NC-ZIF precursor is placed in a ceramic crucible and subjected to high-temperature heat treatment in a tubular furnace. After cooling, a black product is obtained, namely, a Fe-Co / Zn@NC carbon-based composite material for absorbing high-frequency electromagnetic waves, thereby completing the preparation method.

2. The method for preparing a Fe-Co / Zn@NC carbon-based composite material for absorbing high-frequency electromagnetic waves according to claim 1, characterized in that In the mixed solution in step 1, the content of dimethylimidazole is 50-150 mmol, the content of zinc acetate dihydrate is 10-50 mmol, the content of cobalt nitrate hexahydrate is 10-50 mmol, the content of ferric acetylacetonate is 0.1-5.0 mmol, and the amount of deionized water used is 200 ml.

3. The method for preparing a Fe-Co / Zn@NC carbon-based composite material for absorbing high-frequency electromagnetic waves according to claim 2, characterized in that In the mixed solution in step 1, the content of dimethylimidazole is 100 mmol, the content of zinc acetate dihydrate is 25 mmol, the content of cobalt nitrate hexahydrate is 25 mmol, the content of ferric acetylacetonate is 0.6 mmol, and the amount of deionized water used is 200 ml.

4. The method for preparing a Fe-Co / Zn@NC carbon-based composite material for absorbing high-frequency electromagnetic waves according to claim 1, characterized in that The aging reaction time in step 1 is 12 to 72 hours, and the temperature is room temperature.

5. A method for preparing a Fe-Co / Zn@NC carbon-based composite material for absorbing high-frequency electromagnetic waves according to claim 4, characterized in that The aging reaction time in step 1 is 48 hours and the temperature is room temperature.

6. The method for preparing a Fe-Co / Zn@NC carbon-based composite material for absorbing high-frequency electromagnetic waves according to claim 1, characterized in that The washing in step 2 is washing with anhydrous methanol for 3 to 6 times.

7. The method for preparing a Fe-Co / Zn@NC carbon-based composite material for absorbing high-frequency electromagnetic waves according to claim 1, characterized in that The centrifugation in step 2 is carried out in a high-speed centrifuge at 5000-12000 rpm for 5-20 minutes.

8. The method for preparing a Fe-Co / Zn@NC carbon-based composite material for absorbing high-frequency electromagnetic waves according to claim 1, characterized in that The freeze drying in step 2 is freeze drying in a freeze dryer at an air pressure of 1 to 10 MPa and a temperature of -80 to -40°C for 12 to 72 hours.

9. The method for preparing a Fe-Co / Zn@NC carbon-based composite material for absorbing high-frequency electromagnetic waves according to claim 8, characterized in that Freeze drying in step 2: freeze drying in a freeze dryer at an air pressure of 1 MPa and -60°C for 48 hours.

10. The method for preparing a Fe-Co / Zn@NC carbon-based composite material for absorbing high-frequency electromagnetic waves according to claim 1, characterized in that The high temperature heat treatment in step 3 is: keeping at 500-1000°C for 1-5h, with a heating rate of 1-5°C / min.

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