Preparation method of aerogel-based wave-absorbing material with adjustable frequency band

Abstract

The application discloses a preparation method of a frequency band magnetic control adjustable aerogel-based wave-absorbing material. First, ferromagnetic iron-cobalt nanosheets are obtained through a liquid phase reduction method, and then the nanosheets are ultrasonically mixed and dispersed with graphene oxide. The mixed system is subjected to a hydrothermal reaction to obtain a composite hydrogel precursor. After freeze-drying, a graphene aerogel-based composite wave-absorbing structure is obtained, wherein the ferromagnetic nanosheets exist in the hollow skeleton structure of the aerogel. The precursor aerogel structure is quickly immersed in a sodium alginate solution, and a hydrogel medium is formed in the structure by adding calcium ions, so that the nanosheets are suspended in the hollow skeleton of the aerogel, and an adjustable composite wave-absorbing material is obtained. By applying an external magnetic field at different angles, the nanosheets are oriented in the hollow skeleton. By changing the angle between the interface dielectric dipole array and the easy magnetization magnetic moment and the electromagnetic wave vector, respectively, the microwave electromagnetic parameters and the impedance of the material are dynamically adjusted, so that the real-time dynamic adjustment of the wave-absorbing performance and the absorption frequency band is realized.

Description

Technical Field

[0001] This invention relates to a method for preparing a dynamically adjustable aerogel-based composite microwave absorbing material with effective absorption band magnetocontrol, belonging to the field of electromagnetic functional materials. Background Technology

[0002] With the development of electronic information technology and the popularization of wireless communication technology, especially the rapid market launch of 5G communication products, electromagnetic wave technology has brought great convenience to human society. However, the electromagnetic radiation generated at the same time also threatens human health. Therefore, the development, research, and application of electromagnetic wave absorbing materials and devices are becoming increasingly important. However, facing the increasingly serious electromagnetic pollution and complex electromagnetic environment, traditional fixed-component electromagnetic wave absorbing materials can only meet the absorption requirements of electromagnetic waves in specific frequency bands and cannot effectively cope with multi-frequency and variable-frequency environments. How to adjust the microwave electromagnetic parameters and effective absorption performance of absorbing materials over a wider frequency band through external parameters has become a hot research and application issue.

[0003] Currently, existing technologies often achieve microwave absorption band control by adjusting the proportions of components in composite materials. However, composite absorbing materials obtained in this way still suffer from problems such as a relatively fixed applicable frequency band and thickness drift. Materials with fixed components only achieve performance within a fixed frequency band, making them unsuitable for the complex and variable electromagnetic interference scenarios commonly encountered in real-world applications, thus limiting their application in multiple fields. Therefore, beyond the development concept of "thin, lightweight, wide-band, and strong absorption" absorbing materials, there is an urgent need for intelligent, dynamically adjustable, and adaptive absorbing materials capable of adapting to variable electromagnetic environments. Simultaneously altering the microwave dielectric and magnetic properties of the material under external conditions is a necessary condition and development direction for achieving bidirectional dynamic adjustment of absorption performance. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing an aerogel-based microwave absorbing material with dynamically adjustable absorption band via an external magnetic field. Specifically, ferromagnetic iron-cobalt nanosheets are first obtained via liquid-phase reduction, and then the nanosheets are ultrasonically mixed and dispersed with graphene oxide. After homogenization, the mixture is subjected to a hydrothermal reaction to obtain a composite hydrogel precursor, which is then freeze-dried to obtain a graphene aerogel-based composite structure, in which the ferromagnetic nanosheets exist within the hollow framework of the aerogel. The precursor aerogel is rapidly immersed in a sodium alginate solution, and by adjusting the calcium ions, a hydrogel medium is formed within the structure, suspending the ferromagnetic nanosheets within the hollow framework of the aerogel, thus obtaining a tunable composite microwave absorbing material. By applying external magnetic fields at different angles to orient the nanosheets within the hollow framework, and by changing the angles between the interfacial dielectric dipole array and the easily magnetized magnetic moment and the electromagnetic wave vector, the microwave electromagnetic parameters and impedance of the material are dynamically adjusted, thereby achieving real-time dynamic adjustment of the absorption performance and absorption band.

[0005] The preparation method of the frequency band magnetotunable aerogel-based microwave absorbing material of the present invention includes the following steps:

[0006] Step 1: Preparation of iron-cobalt nanosheets

[0007] 1a. Dissolve 1-30 mmol ferrous sulfate and 1-25 mmol cobalt chloride in 200 ml deionized water and stir until the solution is clear. Then add 40 ml hydrazine hydrate and 9.88 g sodium hydroxide to the system and stir thoroughly at room temperature until complete precipitation to obtain the precursor mixed solution.

[0008] 1b. The precursor mixture obtained in 1a is transferred to a hydrothermal reactor for hydrothermal reaction. After the reaction is completed and cooled to room temperature, the product is repeatedly washed with deionized water and ethanol until the pH value is neutral to obtain iron-cobalt nanosheets.

[0009] In step 1a, the molar ratio of ferrous sulfate to cobalt chloride is 1–10:1–10.

[0010] In step 1b, the hydrothermal reaction temperature is 60℃ and the reaction time is 1 hour.

[0011] Step 2: Preparation of composite aerogel-based microwave absorbing materials

[0012] 2a. A certain amount of graphene oxide (single or multiple layers, with a sheet diameter of 0.5 to 10 μm) powder is added to deionized water and ultrasonically stirred to obtain a uniform dispersion. A certain amount of iron-cobalt nanosheets obtained in step 1 are then added to the dispersion and ultrasonically mixed to obtain a mixed dispersion.

[0013] 2b. The mixed dispersion obtained in 2a is transferred to a hydrothermal reactor and reacted at a certain temperature for a period of time. The product is collected and repeatedly washed with deionized water and ethanol to obtain the precursor hydrogel. The hydrogel is freeze-dried at -50 to -20℃ for 12-72 hours to obtain the iron-cobalt nanosheet / graphene composite aerogel structure framework.

[0014] 2c. The composite framework structure obtained in 2b is rapidly immersed in an aqueous solution of sodium alginate of a certain concentration, and an aqueous solution of calcium chloride of a certain concentration is added dropwise to form a hydrogel, so that the nanosheets are suspended in the hollow pores of the aerogel, thereby obtaining an aerogel-based tunable composite microwave absorbing material.

[0015] In step 2a, the concentration of the graphene oxide dispersion is 2–10 mg / mL, and the mass ratio of graphene oxide to iron-cobalt alloy nanosheets is 2:(5–20).

[0016] In step 2b, the hydrothermal reaction temperature is 180℃~200℃, the reaction time is 5~24h, and the freeze drying is specifically freeze drying at -50℃ for 48h.

[0017] In step 2c, the concentration of sodium alginate aqueous solution is 0.02-0.5 mol / L, and the concentration of calcium chloride aqueous solution is 0.1-1 mol / L.

[0018] This invention introduces a ferromagnetic iron-cobalt alloy to modulate the electromagnetic impedance of strongly polar graphene, and links the magnetic loss and dielectric loss mechanisms. Combined with the three-dimensional composite hydrogel structure constructed from two-dimensional iron-cobalt alloy nanosheets, it has a continuous porous network structure, which enhances the multiple reflections and scattering of electromagnetic waves, thus achieving excellent and tunable electromagnetic wave absorption performance.

[0019] The beneficial effects of this invention are reflected in:

[0020] 1. This invention uses a three-dimensional graphene aerogel structure as a microwave absorbing framework to package iron-cobalt nanosheets, which reduces the problem of their accumulation and aggregation under an external magnetic field, increases the adjustable space of their orientation polarization, and enhances the multiple reflection and scattering of electromagnetic waves.

[0021] 2. By introducing calcium alginate hydrogel, the present invention enables iron-cobalt magnetic nanosheets to be suspended in the hollow pores of the aerogel and to rotate only under a magnetic field, thus making the electromagnetic parameters of the composite material adjustable in real time.

[0022] 3. This invention achieves dynamic and continuous adjustment of the electromagnetic impedance and wave absorption performance of the composite material by magnetically controlling the rotation of two-dimensional iron-cobalt ferromagnetic alloy nanosheets, linking the magnetic loss in the easy magnetization direction and the dielectric loss at the two-dimensional interface.

[0023] 4. This invention comprehensively utilizes the electromagnetic loss of anisotropic reinforced structures of low-dimensional magnetic materials under microwave electromagnetic fields and the basic dielectric properties of graphene aerogels, and provides new ideas for the design of tunable electromagnetic absorbers by controlling orientation-related electromagnetic parameters through external field modulation.

[0024] 5. The hollow porous framework structure design of the present invention can be used to install low-dimensional magnetic and composite structural units at any micro-nano scale, and realize the external magnetic field magnetic control electromagnetic and wave absorption adjustable, which is suitable for future intelligent wave absorption application scenarios with adaptive electromagnetic control. Attached Figure Description

[0025] Figure 1 SEM image of the aerogel-based microwave absorbing material obtained in Example 1;

[0026] Figure 2 The complex permittivity (ε) of the aerogel-based microwave absorbing material obtained in Example 1 after applying magnetic fields of different orientations in the 2–18 GHz frequency band is given. r =ε′-jε″), complex permeability (μ) r =μ′-jμ″) and reflection loss (RL);

[0027] Figure 3 The complex permittivity (ε) of the aerogel-based microwave absorbing material obtained in Example 2 after applying magnetic fields of different orientations in the 2–18 GHz frequency band is given. r =ε′-jε″), complex permeability (μ) r =μ′-jμ″) and reflection loss (RL);

[0028] Figure 4 The complex permittivity (ε) of the aerogel-based microwave absorbing material obtained in Example 3 after applying magnetic fields of different orientations in the 2–18 GHz frequency band is given. r =ε′-jε″), complex permeability (μ) r =μ′-jμ″) and reflection loss (RL). Detailed Implementation

[0029] Example 1:

[0030] 1. Dissolve 10 mmol ferrous sulfate and 10 mmol cobalt chloride in 200 ml deionized water and stir until the solution is clear. Then add 40 ml hydrazine hydrate and 9.88 g sodium hydroxide to the system and stir for 10 min at room temperature to obtain a mixed solution. Transfer the above solution to a hydrothermal reactor for hydrothermal reaction at 60 °C for 1 h. After the reaction is completed, cool to room temperature and wash repeatedly with deionized water and ethanol until the pH value is neutral to obtain iron-cobalt alloy nanosheets.

[0031] 2. Add 20 mg of graphene oxide powder to 10 ml of deionized water and stir ultrasonically to obtain a graphene oxide dispersion. Add 0.05 g of the iron-cobalt alloy obtained in step 1 to the dispersion and mix thoroughly by ultrasonication to obtain a mixed solution. Transfer the obtained mixed solution to a hydrothermal reactor and react at 200 °C for 12 h. After cooling to room temperature, collect the product and wash it repeatedly with deionized water and ethanol to obtain a precursor hydrogel. Freeze-dry the hydrogel at -50 °C for 48 h to obtain the iron-cobalt / graphene composite aerogel structure framework.

[0032] 3. The obtained composite material was placed in a sodium alginate solution with a concentration of 0.02 mol / L, and then a calcium chloride solution with a concentration of 0.45 mol / L was added dropwise to obtain an aerogel-based microwave absorbing material.

[0033] Example 2:

[0034] 1. Dissolve 10 mmol ferrous sulfate and 10 mmol cobalt chloride in 200 ml deionized water and stir until the solution is clear. Then add 40 ml hydrazine hydrate and 9.88 g sodium hydroxide to the system and stir for 10 min at room temperature to obtain a mixed solution. Transfer the above solution to a hydrothermal reactor for hydrothermal reaction at 60 °C for 1 h. After the reaction is completed, cool to room temperature and wash repeatedly with deionized water and ethanol until the pH value is neutral to obtain iron-cobalt alloy nanosheets.

[0035] 2. Add 20 mg of graphene oxide powder to 10 ml of deionized water and stir ultrasonically to obtain a graphene oxide dispersion. Add 0.1 g of the iron-cobalt alloy obtained in step 1 to the dispersion and mix thoroughly by ultrasonication to obtain a mixed solution. Transfer the obtained mixed solution to a hydrothermal reactor and react at 200 °C for 12 h. After cooling to room temperature, collect the product and wash it repeatedly with deionized water and ethanol to obtain a precursor hydrogel. Freeze-dry the hydrogel at -50 °C for 48 h to obtain the iron-cobalt / graphene composite aerogel structure framework.

[0036] 3. The obtained composite material was placed in a sodium alginate solution with a concentration of 0.02 mol / L, and then a calcium chloride solution with a concentration of 0.45 mol / L was added dropwise to obtain an aerogel-based microwave absorbing material.

[0037] Example 3:

[0038] 1. Dissolve 10 mmol ferrous sulfate and 10 mmol cobalt chloride in 200 ml deionized water and stir until the solution is clear. Then add 40 ml hydrazine hydrate and 9.88 g sodium hydroxide to the system and stir for 10 min at room temperature to obtain a mixed solution. Transfer the above solution to a hydrothermal reactor for hydrothermal reaction at 60 °C for 1 h. After the reaction is completed, cool to room temperature and wash repeatedly with deionized water and ethanol until the pH value is neutral to obtain iron-cobalt alloy nanosheets.

[0039] 2. Add 20 mg of graphene oxide powder to 10 ml of deionized water and stir ultrasonically to obtain a graphene oxide dispersion. Add 0.2 g of the iron-cobalt alloy obtained in step 1 to the dispersion and mix thoroughly by ultrasonication to obtain a mixed solution. Transfer the obtained mixed solution to a hydrothermal reactor and react at 200 °C for 12 h. After cooling to room temperature, collect the product and wash it repeatedly with deionized water and ethanol to obtain a precursor hydrogel. Freeze-dry the hydrogel at -50 °C for 48 h to obtain the iron-cobalt / graphene composite aerogel structure framework.

[0040] 3. The obtained composite material was placed in a sodium alginate solution with a concentration of 0.02 mol / L, and then a calcium chloride solution with a concentration of 0.45 mol / L was added dropwise to obtain an aerogel-based microwave absorbing material.

[0041] Figure 1 This is a SEM image of the aerogel-based composite microwave absorbing material obtained in Example 1. As can be seen in the image, numerous iron-cobalt nanosheets are uniformly grown within the hollow pores of the graphene aerogel. Figure 2 The electromagnetic parameters and RL curves of the sample in Example 1 show that when the ratio of iron-cobalt nanosheets to graphene oxide is 5:2, the electromagnetic parameters increase with the magnetic field angle in the 2-18 GHz frequency band. Figure 2 (ab) The real part of the dielectric constant decreases in the 2-14.48 GHz frequency band, while the imaginary part decreases across the entire frequency band. Figure 2 The real part of the permeability in (cd) increases slightly in the X-band, but the imaginary part decreases in the SX-band and increases in the Ku-band. Figure 2 In (e), when the sample thickness is 2 mm, as the magnetic orientation angle increases, its absorption frequency band shifts from C to the higher frequency direction of the X band. When the magnetic orientation is 90°, RL min It reaches -11.87dB at 8.84GHz. Figure 3 The electromagnetic parameters and RL curves of the sample in Example 2 show that when the ratio of iron-cobalt nanosheets to graphene oxide is 5:1, the electromagnetic parameters increase with the magnetic field angle in the 2-18 GHz frequency band. Figure 3 (ab) The real part of the dielectric constant decreases in the 2-6 GHz frequency band, while the imaginary part decreases significantly across the entire frequency band. Figure 3 In (cd), the real part of the permeability decreases significantly in the C-Ku band, while the imaginary part increases sharply in the SX band. Figure 3 In (e), when the sample thickness is 2 mm, as the magnetic orientation angle increases, its absorption band shifts towards higher frequencies in the C-band. When the magnetic orientation is 90°, RL min At 6.52GHz, it is -6.26dB. Figure 4 The electromagnetic parameters and RL curves of the sample in Example 3 show that when the ratio of iron-cobalt magnetic nanosheets to graphene oxide is 10:1, the magnetic field angle increases with frequency in the 2-18 GHz band. Figure 4 (ab) Both the real and imaginary parts of the dielectric constant show a decreasing trend in the S-Ku band, but Figure 4 In (cd), the real part of the permeability fluctuates only in the Ku frequency band, while the imaginary part shows a slight increase. Figure 4 In (e), when the sample thickness is 2 mm, as the magnetic orientation angle increases, its absorption frequency band shifts from C to the higher frequency direction of the X band. When the magnetic orientation is 90°, RL minIt reaches -12.07dB at 8.72GHz.

Claims

1. A method for preparing a band-modulated magnetron sputtering aerogel-based microwave absorbing material, characterized in that: First, ferromagnetic iron-cobalt nanosheets were obtained via liquid-phase reduction. Then, the iron-cobalt nanosheets were ultrasonically mixed and dispersed with graphene oxide. After homogenization, the mixture was subjected to a hydrothermal reaction to obtain a composite hydrogel precursor. After freeze-drying, a graphene aerogel-based composite structure was obtained, in which the iron-cobalt nanosheets were present in the hollow framework structure of the aerogel. The precursor aerogel was rapidly immersed in a sodium alginate solution, and by adjusting the calcium ions, a hydrogel medium was formed in the structure, suspending the iron-cobalt nanosheets in the hollow framework of the aerogel, thus obtaining a tunable composite microwave absorbing material. By applying external magnetic fields at different angles to orient the nanosheets in the hollow framework, and by changing the angles between the dielectric dipole array and the easily magnetized magnetic moment at the interface and the electromagnetic wave vector, the microwave electromagnetic parameters and impedance of the material were dynamically adjusted, thereby achieving real-time dynamic adjustment of the microwave absorption performance and absorption band.

2. The preparation method according to claim 1, characterized in that... Includes the following steps: Step 1: Preparation of iron-cobalt nanosheets 1a. Dissolve 1-30 mmol ferrous sulfate and 1-25 mmol cobalt chloride in deionized water and stir until the solution is clear. Then add 40 ml hydrazine hydrate and 9.88 g sodium hydroxide to the system and stir thoroughly at room temperature until complete precipitation to obtain the precursor mixed solution. 1b. The precursor mixture obtained in 1a is transferred to a hydrothermal reactor for hydrothermal reaction. After the reaction is completed and cooled to room temperature, the product is repeatedly washed with deionized water and ethanol until the pH value is neutral to obtain iron-cobalt nanosheets. Step 2: Preparation of composite aerogel-based microwave absorbing materials 2a. A certain amount of graphene oxide powder is added to deionized water and ultrasonically stirred to obtain a uniform dispersion. A certain amount of iron-cobalt nanosheets obtained in step 1 are then added to the dispersion and ultrasonically mixed to obtain a mixed dispersion. 2b. The mixed dispersion obtained in 2a is transferred to a hydrothermal reactor and reacted at a certain temperature for a period of time. The product is collected and repeatedly washed with deionized water and ethanol to obtain the precursor hydrogel. The hydrogel is freeze-dried at -50 to -20℃ for 12-72 hours to obtain the iron-cobalt nanosheet / graphene composite aerogel structure framework. 2c. The composite framework structure obtained in 2b is rapidly immersed in an aqueous solution of sodium alginate of a certain concentration, and an aqueous solution of calcium chloride of a certain concentration is added dropwise to form a hydrogel, so that the nanosheets are suspended in the hollow pores of the aerogel, thereby obtaining an aerogel-based tunable composite microwave absorbing material.

3. The preparation method according to claim 2, characterized in that: In step 1b, the hydrothermal reaction temperature is 60-150℃ and the reaction time is 0.5-5h.

4. The preparation method according to claim 2, characterized in that: In step 2a, the concentration of the graphene oxide dispersion is 2–10 mg / mL.

5. The preparation method according to claim 2, characterized in that: In step 2a, the mass ratio of graphene oxide to iron-cobalt nanosheets is 2:(5-20).

6. The preparation method according to claim 2, characterized in that: In step 2b, the hydrothermal reaction temperature is 180℃~200℃, and the reaction time is 5~24h.

7. The preparation method according to claim 2, characterized in that: In step 2b, freeze drying specifically involves freeze drying at -50°C for 48 hours.

8. The preparation method according to claim 2, characterized in that: In step 2c, the concentration of sodium alginate aqueous solution is 0.02-0.5 mol / L, and the concentration of calcium chloride aqueous solution is 0.1-1 mol / L.

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