Iron-nickel alloy / nitrogen-doped carbon-based low-frequency wave-absorbing material and preparation method thereof

Abstract

The invention discloses an iron-nickel alloy / nitrogen-doped carbon-based low-frequency wave-absorbing material and a preparation method thereof, and aims at solving the problems that soft magnetic alloy is poor in impedance matching performance, large in matching thickness, high in packing ratio and the like. The preparation method comprises the following steps: step 1, preparing hollow ferroferric oxide nanospheres by a solvothermal method; step 2, preparing a hollow ferroferric oxide / nickel hydroxide / polydopamine composite assembly by a one-pot method; and step 3, performing high-temperature pyrolysis on the composite assembly in the step 2 to prepare the iron-nickel alloy / nitrogen-doped carbon-based low-frequency wave-absorbing material. The synthesis method is environmentally friendly and simple, preparation of the iron-nickel alloy and the nitrogen-doped carbon and impedance matching regulation and control can be completed by controlling pyrolysis conditions under nitrogen protection, and then the good low-frequency wave absorbing performance is obtained under the conditions of the small matching thickness and the low filling ratio.

Description

Technical Field

[0001] The present invention relates to the technical field of electromagnetic composite wave absorbing materials, and in particular to an iron-nickel alloy / nitrogen-doped carbon-based low-frequency wave absorbing material and a preparation method thereof. Background Art

[0002] With the rapid development of communications and IoT technologies, electromagnetic radiation is becoming increasingly serious, posing a serious threat to human health, the interference resistance of electronic devices, and electromagnetic compatibility. Absorbing materials are a key technology in addressing this issue. They efficiently dissipate electromagnetic energy by converting it into heat or other forms, achieving electromagnetic protection. Therefore, developing low-frequency absorbing materials that can operate within the electromagnetic frequency bands of communications and IoT technologies is of great research significance.

[0003] Low-frequency absorbing materials primarily include ferrites, carbonyl iron powders, and soft magnetic alloys. However, their practical applications face challenges such as high density, difficulty in impedance matching, and large thicknesses, making them difficult to meet the "wide, thin, light, and strong" requirements of new absorbing materials. Consequently, the development of electromagnetic composite absorbing materials that combine dielectric and magnetic loss to enhance absorbing performance through the magneto-dielectric synergistic effect has attracted widespread attention. Currently, numerous studies have reported on electromagnetic composite absorbers. For example, published patent CN114390884A reports a lightweight iron-nickel-based magnetic composite absorber whose composition, structure, and electromagnetic properties can be regulated by adjusting a polyvinylpyrrolidone-derived carbothermal reduction process. Results show that at a filling ratio of 50 wt.%, the composite exhibits a minimum reflection loss greater than -15 dB at 5.0 mm. Also, published patent CN106220247A reports a needle-shaped ferroferric oxide-coated iron-nickel alloy / graphene absorber whose electromagnetic parameters are regulated by surface modification of the iron-nickel alloy / graphene sheet, resulting in a minimum reflection loss greater than -30 dB. Given that significant room for improvement in the absorption strength, filling ratio, and matching thickness of these iron-nickel-based composite absorbers in the low-frequency electromagnetic band, it is necessary to develop a low-frequency electromagnetic composite absorber with greater absorption strength, a smaller filling ratio, and a lower matching thickness, and a method for its preparation.

[0004] The present invention provides an iron-nickel alloy / nitrogen-doped carbon-based low-frequency absorbing material and a preparation method thereof. By controlling the nitrogen doping and graphitization of carbon materials converted by pyrolysis of polydopamine, the crystal structure of the iron-nickel alloy, and the composite heterostructure of the iron-nickel alloy / nitrogen-doped carbon, etc., the magnetic-dielectric synergistic effect thereof is optimized, thereby obtaining a low-frequency electromagnetic composite absorbing material with a low filling ratio, a thin matching thickness, and strong absorbing performance. Summary of the Invention

[0005] In response to the shortcomings of the existing technology, the present invention provides an iron-nickel alloy / nitrogen-doped carbon-based low-frequency absorbing material and a preparation method thereof. The composite material not only has a simple preparation process, but also exhibits excellent low-frequency absorbing performance under conditions of low filling ratio and thin matching thickness.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for preparing an iron-nickel alloy / nitrogen-doped carbon-based low-frequency wave absorbing material comprises the following steps:

[0008] Step 1, preparing magnetic hollow ferroferric oxide (Fe3O4) nanospheres;

[0009] Step 2: Prepare hollow ferrosoferric oxide / nickel hydroxide / polydopamine (Fe3O4 / Ni(OH)2 / PDA) composite assembly by one-pot method;

[0010] Step 3: pyrolyze the composite assembly in step 2 at high temperature to prepare an iron-nickel alloy / nitrogen-doped carbon-based low-frequency absorbing material (FeNi@NC).

[0011] Preferably, step 1 is specifically as follows: dissolving ferric chloride hexahydrate, sodium acetate and sodium dodecylbenzenesulfonate in ethylene glycol in sequence, then transferring the mixed solution to a high-pressure reactor and performing a high-temperature reaction, separating the precipitate using a magnet after the reaction is completed, and finally washing the precipitate and vacuum drying to obtain the target product, hollow Fe3O4.

[0012] Preferably, the ratio of ferric chloride hexahydrate, sodium acetate, sodium dodecylbenzenesulfonate and ethylene glycol in step 1 is (1.0-2.5) g: (1.0-4.0) g: (0.5-2.0) g: 64 mL.

[0013] Preferably, the temperature of the high temperature reaction in step 1 is 150-180° C., the time of the high temperature reaction is 6-12 h, and the temperature of the vacuum drying is 50° C.

[0014] Preferably, step 2 is specifically as follows: ultrasonically dispersing ferroferric oxide in anhydrous ethanol, then adding nickel nitrate hexahydrate and urea and stirring evenly at room temperature, recorded as solution A; dissolving dopamine hydrochloride in deionized water, recorded as solution B; pouring solution B into solution A, heating to react, after the reaction is completed, filtering to obtain a precipitate, and then washing and vacuum drying the precipitate to obtain the target product Fe3O4 / Ni(OH)2 / PDA.

[0015] Preferably, the weight ratio of ferrosoferric oxide to nickel nitrate hexahydrate in step 2 is 0.1:(1.0-4.0).

[0016] Preferably, in the solution A in step 2, the concentration of urea is 10-100 mg / mL; in the solution B, the concentration of dopamine hydrochloride is 5-40 mg / mL; and the heating reaction temperature is 60-90°C.

[0017] Preferably, step 3 is specifically as follows: placing Fe3O4 / Ni(OH)2 / PDA in a tube furnace, and preparing an iron-nickel alloy / nitrogen-doped carbon-based low-frequency absorbing material by programmed temperature pyrolysis, with the protective gas being nitrogen.

[0018] Preferably, the heating rate in step 3 is 2-5°C / min, the pyrolysis temperature is 700-1000°C, and the pyrolysis time is 2-4h.

[0019] An iron-nickel alloy / nitrogen-doped carbon-based low-frequency wave absorbing material prepared by the preparation method.

[0020] Compared with the prior art, the technical effects of the present invention are embodied in the following aspects:

[0021] (1) An iron-nickel alloy / nitrogen-doped carbon-based low-frequency absorbing material was prepared by combining iron-nickel alloy with nitrogen-doped carbon material. This material can achieve good low-frequency absorbing performance at a low filling ratio and relatively thin matching thickness.

[0022] (2) The conversion of polydopamine into nitrogen-doped carbon materials by thermal decomposition can not only reduce ferroferric oxide / nickel hydroxide to iron-nickel alloy through carbon thermal reduction reaction, but also optimize the impedance matching and magneto-dielectric synergistic effect of iron-nickel alloy / nitrogen-doped carbon-based low-frequency absorbing materials, so that the minimum reflection loss (RL) at 5.6 GHz is achieved at a filling ratio of 30 wt.% and a matching thickness of 4.8 mm. min ) and effective absorption bandwidth (EAB) are -53.8dB and 2.67GHz respectively.

[0023] (3) The preparation method of the present invention is simple, low-cost, does not require complex synthesis equipment and is easy to mass produce. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 1 is the X-ray diffraction (XRD) pattern of Fe3O4, Fe3O4 / Ni(OH)2 / PDA and FeNi@NC-700 prepared in Example 1 of the present invention;

[0025] Figure 2 is a Fourier transform infrared (FT-IR) spectrum of Fe3O4 and Fe3O4 / Ni(OH)2 / PDA prepared in Example 1 of the present invention;

[0026] Figure 3is a scanning electron microscope (SEM) image of Fe3O4 and Fe3O4 / Ni(OH)2 / PDA prepared in Example 1 of the present invention;

[0027] Figure 4 is a reflection loss-frequency graph of FeNi@NC-700 prepared in Example 1 of the present invention;

[0028] Figure 5 is a reflection loss-frequency graph of FeNi@NC-800-1 prepared in Example 2 of the present invention;

[0029] Figure 6 is a reflection loss-frequency graph of FeNi@NC-900 prepared in Example 3 of the present invention;

[0030] Figure 7 This is a reflection loss-frequency diagram of FeNi@NC-800-2 prepared in Example 4 of the present invention. DETAILED DESCRIPTION

[0031] The present invention will be further described in detail below with reference to specific embodiments and drawings, which are intended to explain the present invention rather than to limit the scope of protection of the claims.

[0032] The experimental methods used in the following examples are conventional methods unless otherwise specified, and the reagents and equipment used are conventional reagents and equipment in the art unless otherwise specified.

[0033] Example 1

[0034] A method for preparing an iron-nickel alloy / nitrogen-doped carbon-based low-frequency wave absorbing material comprises the following steps:

[0035] (1) Preparation of magnetic hollow ferroferric oxide (Fe3O4) nanospheres:

[0036] 2.16 g of ferric chloride hexahydrate, 3.72 g of sodium acetate and 0.64 g of sodium dodecylbenzenesulfonate were dissolved in 64 mL of ethylene glycol in sequence. The mixed solution was then transferred to a high-pressure reactor and reacted at 180 ° C for 12 h. After the reaction, it was separated by magnetic adsorption to obtain a precipitate. Finally, the precipitate was washed three times with deionized water and ethanol respectively, and vacuum dried at 50 ° C to obtain the target product hollow Fe3O4.

[0037] (2) One-pot preparation of hollow ferroferric oxide / nickel hydroxide / polydopamine (Fe3O4 / Ni(OH)2 / PDA) composite assemblies:

[0038] 0.1 g of Fe3O4 was ultrasonically dispersed in 30 mL of anhydrous ethanol, and then 3.92 g of nickel nitrate hexahydrate and 2.4 g of urea were added and stirred evenly at room temperature, which was recorded as solution A; 400 mg of dopamine hydrochloride was dissolved in 20 mL of deionized water, which was recorded as solution B; solution B was poured into solution A, heated at 80°C for 6 h, and then filtered to obtain a precipitate. The precipitate was then washed three times with deionized water and ethanol respectively, and vacuum dried at 50°C to obtain the target product, Fe3O4 / Ni(OH)2 / PDA composite assembly.

[0039] (3) Pyrolyzing the composite assembly in step 2 at 700°C to prepare an iron-nickel alloy / nitrogen-doped carbon-based composite material (FeNi@NC-700):

[0040] Fe3O4 / Ni(OH)2 / PDA was placed in a tube furnace and pyrolyzed at high temperature to prepare iron-nickel alloy / nitrogen-doped carbon-based composite material (FeNi@NC-700). The protective gas was nitrogen, the heating rate was 2℃ / min, the pyrolysis temperature was 700℃, and the pyrolysis time was 2h.

[0041] Figure 1 Figure 2 shows the XRD patterns of Fe3O4, Fe3O4 / Ni(OH)2 / PDA, and FeNi@NC-700 in Example 1. The diffraction peaks of the prepared Fe3O4 correspond to those of the standard card, with the peaks at 30.1°, 35.6°, 43.2°, 56.9°, and 62.7° attributed to the (220), (311), (400), (511), and (440) crystal planes of Fe3O4 (PDF#88-0315), respectively. Compared to the diffraction peaks of Fe3O4, the XRD pattern of Fe3O4 / Ni(OH)2 / PDA shows no new diffraction peaks. This may be due to the low Ni(OH)2 loading or low crystallinity, while polydopamine is an amorphous polymer without diffraction peaks. In the XRD pattern of Fe3O4 / Ni(OH)2 / PDA pyrolysis-derived FeNi@NC-700 composite, the sharp peaks at 43.7°, 50.9°, and 74.9° are attributed to the (111), (200), and (220) crystal planes of FeNi alloy (PDF#47-1405), respectively, indicating that the Fe3O4 / Ni(OH)2 composite system is reduced to FeNi alloy during the process of polydopamine-derived carbon.

[0042] Figure 2 The following are the Fourier transform infrared spectra of Fe3O4 and Fe3O4 / Ni(OH)2 / PDA prepared in Example 1. Compared with Fe3O4, Fe3O4 / Ni(OH)2 / PDA has a higher FTIR value at 1260 cm -1 The characteristic peak at 1385 cm corresponds to the vibration of the C-OH bond. -1The characteristic peak at corresponds to the stretching vibration of the CN bond, proving the successful coating of PDA.

[0043] Figure 3 The following are scanning electron micrographs of Fe3O4 and Fe3O4 / Ni(OH)2 / PDA prepared in Example 1. As can be seen from the figure, the Fe3O4 is in the form of microspheres with uniform size distribution and a diameter of approximately 500-600 nm, while the Fe3O4 / Ni(OH)2 / PDA is larger in size, with more Fe3O4 coated with PDA and loaded with a large amount of flaky Ni(OH)2.

[0044] Figure 4 This is the reflection loss-frequency diagram of FeNi@NC-700 (30 wt.%) prepared in Example 1, wherein the minimum reflection loss and effective absorption bandwidth at 9.0 GHz are -10.3 dB and 0.52 GHz, respectively.

[0045] Example 2

[0046] A method for preparing an iron-nickel alloy / nitrogen-doped carbon-based low-frequency wave absorbing material comprises the following steps:

[0047] (1) Preparation of magnetic hollow ferroferric oxide (Fe3O4) nanospheres:

[0048] 2.16 g of ferric chloride hexahydrate, 3.64 g of sodium acetate and 0.60 g of sodium dodecylbenzenesulfonate were dissolved in 64 mL of ethylene glycol in sequence. The mixed solution was then transferred to a high-pressure reactor and reacted at 180 ° C for 10 hours. After the reaction, it was separated by magnetic adsorption to obtain a precipitate. Finally, the precipitate was washed three times with deionized water and ethanol respectively, and vacuum dried at 50 ° C to obtain the target product hollow Fe3O4.

[0049] (2) One-pot preparation of hollow ferroferric oxide / nickel hydroxide / polydopamine (Fe3O4 / Ni(OH)2 / PDA) composite assemblies:

[0050] 0.1 g of Fe3O4 was ultrasonically dispersed in 40 mL of anhydrous ethanol, and then 3.6 g of nickel nitrate hexahydrate and 2.4 g of urea were added and stirred evenly at room temperature, which was recorded as solution A; 500 mg of dopamine hydrochloride was dissolved in 20 mL of deionized water, which was recorded as solution B; solution B was poured into solution A, heated at 80°C for 5 h, and then filtered to obtain a precipitate. The precipitate was then washed three times with deionized water and ethanol respectively, and vacuum dried at 50°C to obtain the target product, Fe3O4 / Ni(OH)2 / PDA composite assembly.

[0051] (3) Pyrolyzing the composite assembly in step 2 at 800°C to prepare an iron-nickel alloy / nitrogen-doped carbon-based composite material (FeNi@NC-800-1):

[0052] Fe3O4 / Ni(OH)2 / PDA was placed in a tube furnace and pyrolyzed at high temperature to prepare iron-nickel alloy / nitrogen-doped carbon-based composite material (FeNi@NC-800-1). The protective gas was nitrogen, the heating rate was 2℃ / min, the pyrolysis temperature was 800℃, and the pyrolysis time was 2h.

[0053] Figure 5 This is the reflection loss-frequency diagram of FeNi@NC-800-1 (30 wt.%) prepared in Example 2, wherein the minimum reflection loss and effective absorption bandwidth at 5.6 GHz are -53.8 dB and 2.67 GHz, respectively.

[0054] Example 3

[0055] A method for preparing an iron-nickel alloy / nitrogen-doped carbon-based low-frequency wave absorbing material comprises the following steps:

[0056] (1) Preparation of magnetic hollow ferroferric oxide (Fe3O4) nanospheres:

[0057] 1.8 g of ferric chloride hexahydrate, 3.6 g of sodium acetate and 0.6 g of sodium dodecylbenzenesulfonate were dissolved in 64 mL of ethylene glycol in sequence. The mixed solution was then transferred to a high-pressure reactor and reacted at 180 ° C for 12 hours. After the reaction, it was separated by magnetic adsorption to obtain a precipitate. Finally, the precipitate was washed three times with deionized water and ethanol respectively, and vacuum dried at 50 ° C to obtain the target product hollow Fe3O4.

[0058] (2) One-pot preparation of hollow ferroferric oxide / nickel hydroxide / polydopamine (Fe3O4 / Ni(OH)2 / PDA) composite assemblies;

[0059] 0.1 g of Fe3O4 was ultrasonically dispersed in 30 mL of anhydrous ethanol, and then 3.8 g of nickel nitrate hexahydrate and 2.5 g of urea were added and stirred evenly at room temperature, which was recorded as solution A; 450 mg of dopamine hydrochloride was dissolved in 20 mL of deionized water, which was recorded as solution B; solution B was poured into solution A, heated at 80°C for 5 h, and then filtered to obtain a precipitate. The precipitate was then washed three times with deionized water and ethanol respectively, and vacuum dried at 50°C to obtain the target product, Fe3O4 / Ni(OH)2 / PDA composite assembly.

[0060] (3) Pyrolyzing the composite assembly in step 2 at 900°C to prepare an iron-nickel alloy / nitrogen-doped carbon-based composite material (FeNi@NC-900):

[0061] Fe3O4 / Ni(OH)2 / PDA was placed in a tube furnace and pyrolyzed at high temperature to prepare iron-nickel alloy / nitrogen-doped carbon-based composite material (FeNi@NC-900). The protective gas was nitrogen, the heating rate was 3℃ / min, the pyrolysis temperature was 900℃, and the pyrolysis time was 2h.

[0062] Figure 6 This is the reflection loss-frequency diagram of FeNi@NC-900 (30 wt.%) prepared in Example 3, wherein the minimum reflection loss and effective absorption bandwidth at 7.0 GHz are -28.3 dB and 3.04 GHz, respectively.

[0063] Example 4

[0064] A method for preparing an iron-nickel alloy / nitrogen-doped carbon-based low-frequency wave absorbing material comprises the following steps:

[0065] (1) Preparation of magnetic hollow ferroferric oxide (Fe3O4) nanospheres:

[0066] 2.16 g of ferric chloride hexahydrate, 3.72 g of sodium acetate and 0.64 g of sodium dodecylbenzenesulfonate were dissolved in 64 mL of ethylene glycol in sequence. The mixed solution was then transferred to a high-pressure reactor and reacted at 180 ° C for 10 hours. After the reaction, it was separated by magnetic adsorption to obtain a precipitate. Finally, the precipitate was washed three times with deionized water and ethanol respectively, and vacuum dried at 50 ° C to obtain the target product hollow Fe3O4.

[0067] (2) One-pot preparation of hollow ferroferric oxide / nickel hydroxide / polydopamine (Fe3O4 / Ni(OH)2 / PDA) composite assemblies:

[0068] 0.1 g of Fe3O4 was ultrasonically dispersed in 30 mL of anhydrous ethanol, and then 3.6 g of nickel nitrate hexahydrate and 2.2 g of urea were added and stirred evenly at room temperature, which was recorded as solution A; 450 mg of dopamine hydrochloride was dissolved in 25 mL of deionized water, which was recorded as solution B; solution B was poured into solution A, heated at 85°C for 8 hours, and then filtered to obtain a precipitate. The precipitate was then washed three times with deionized water and ethanol respectively, and vacuum dried at 50°C to obtain the target product, Fe3O4 / Ni(OH)2 / PDA composite assembly.

[0069] (3) Pyrolyzing the composite assembly in step 2 at 800°C to prepare an iron-nickel alloy / nitrogen-doped carbon-based composite material (FeNi@NC-800-2):

[0070] Fe3O4 / Ni(OH)2 / PDA was placed in a tube furnace and pyrolyzed at high temperature to prepare iron-nickel alloy / nitrogen-doped carbon-based composite material (FeNi@NC-800-2). The protective gas was nitrogen, the heating rate was 3℃ / min, the pyrolysis temperature was 800℃, and the pyrolysis time was 3h.

[0071] Figure 7 : is the reflection loss-frequency graph of FeNi@NC-800-2 (20 wt.%) prepared in Example 4. Its minimum reflection loss and effective absorption bandwidth at 9.3 GHz are -6.5 dB and 0.0 GHz, respectively.

[0072] The FeNi@NC-700, FeNi@NC-800-1, and FeNi@NC-900 prepared in the above examples were used as absorbers, and paraffin wax was used as a molding agent. The absorbers and paraffin wax were accurately weighed in a weight ratio of 3:7. The paraffin wax was then heated and melted, mixed evenly with the absorbers, and pressed into ring-shaped specimens, designated FeNi@NC-700 (30 wt.%), FeNi@NC-800-1 (30 wt.%), and FeNi@NC-900 (30 wt.%). FeNi@NC-800-2 (20 wt.%) was prepared using a similar method, with FeNi@NC-800-2 and paraffin wax weighed in a weight ratio of 1:4.

[0073] The above is only a preferred embodiment of the present invention and is not limited to the specific details of the above implementation methods. Any modifications, replacements and improvements made within the scope of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing an iron-nickel alloy / nitrogen-doped carbon-based low-frequency absorbing material, characterized in that: The following steps are involved: Step 1, preparing magnetic hollow ferroferric oxide (Fe3O4) nanospheres; Step 2: Prepare hollow ferrosoferric oxide / nickel hydroxide / polydopamine (Fe3O4 / Ni(OH)2 / PDA) composite assembly by one-pot method; Step 3: pyrolyze the composite assembly in step 2 at high temperature to prepare an iron-nickel alloy / nitrogen-doped carbon-based low-frequency absorbing material (FeNi@NC).

2. The method for preparing the iron-nickel alloy / nitrogen-doped carbon-based low-frequency absorbing material according to claim 1, characterized in that: Step 1 is specifically as follows: ferric chloride hexahydrate, sodium acetate and sodium dodecylbenzenesulfonate are dissolved in ethylene glycol in sequence, the mixed solution is then transferred to a high-pressure reactor and subjected to a high-temperature reaction, after the reaction is completed, a magnet is used to separate the precipitate, and finally the precipitate is washed and vacuum-dried to obtain the target product, hollow Fe3O4.

3. The method for preparing the iron-nickel alloy / nitrogen-doped carbon-based low-frequency absorbing material according to claim 2, characterized in that: The ratio of ferric chloride hexahydrate, sodium acetate, sodium dodecylbenzenesulfonate and ethylene glycol in step 1 is (1.0-2.5) g: (1.0-4.0) g: (0.5-2.0) g: 64 mL.

4. The method for preparing the iron-nickel alloy / nitrogen-doped carbon-based low-frequency absorbing material according to claim 2, characterized in that: In step 1, the high-temperature reaction temperature is 150-180° C., the high-temperature reaction time is 6-12 h, and the vacuum drying temperature is 50° C.

5. The method for preparing the iron-nickel alloy / nitrogen-doped carbon-based low-frequency absorbing material according to claim 1, characterized in that: Step 2 is specifically as follows: ultrasonically disperse Fe3O4 in anhydrous ethanol, then add nickel nitrate hexahydrate and urea and stir evenly at room temperature, which is recorded as solution A; Dopamine hydrochloride was dissolved in deionized water, which was recorded as solution B. Solution B was poured into solution A and heated to react. After the reaction was completed, the precipitate was filtered to obtain the precipitate, which was then washed and vacuum-dried to obtain the target product Fe3O4 / Ni(OH)2 / PDA.

6. The method for preparing the iron-nickel alloy / nitrogen-doped carbon-based low-frequency absorbing material according to claim 5, characterized in that: The weight ratio of ferrosoferric oxide to nickel nitrate hexahydrate in step 2 is 0.1:(1.0-4.0).

7. The method for preparing the iron-nickel alloy / nitrogen-doped carbon-based low-frequency absorbing material according to claim 5, characterized in that: In step 2, the concentration of urea in solution A is 10-100 mg / mL; the concentration of dopamine hydrochloride in solution B is 5-40 mg / mL; and the temperature of the heating reaction is 60-90°C.

8. The method for preparing the iron-nickel alloy / nitrogen-doped carbon-based low-frequency absorbing material according to claim 1, characterized in that: Step 3 is specifically as follows: Fe3O4 / Ni(OH)2 / PDA is placed in a tube furnace, and iron-nickel alloy / nitrogen-doped carbon-based low-frequency absorbing material is prepared by programmed temperature pyrolysis, with nitrogen as the protective gas.

9. The method for preparing the iron-nickel alloy / nitrogen-doped carbon-based low-frequency absorbing material according to claim 8, characterized in that: In step 3, the heating rate is 2-5°C / min, the pyrolysis temperature is 700-1000°C, and the pyrolysis time is 2-4h.

10. The iron-nickel alloy / nitrogen-doped carbon-based low-frequency wave absorbing material prepared by the preparation method according to any one of claims 1 to 9.

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