CN111230140A

CN111230140A - Preparation method of dielectric adjustable three-dimensional grading nanocapsule wave-absorbing material

Info

Publication number: CN111230140A
Application number: CN202010090501.9A
Authority: CN
Inventors: 汪嘉恒; 吕楠; 吴玉程; 张勇; 鲍智勇
Original assignee: Hefei University of Technology
Current assignee: Hefei University of Technology
Priority date: 2020-02-13
Filing date: 2020-02-13
Publication date: 2020-06-05
Anticipated expiration: 2040-02-13
Also published as: CN111230140B

Abstract

The invention discloses a preparation method of a dielectric adjustable three-dimensional hierarchical nanocapsule wave-absorbing material, which comprises the steps of reducing nickel salt by a one-step polyalcohol solvothermal method, preparing a three-dimensional hierarchical nanostructure formed by random crossing of nickel (Ni) nanosheets, and coating a Polystyrene (PS) shell layer which is embedded and modified by Graphene Quantum Dots (GQDs) on the surface of a magnetic hierarchical Ni core by utilizing in-situ polymerization, so as to obtain the Ni/GQDs/PS three-dimensional hierarchical nanocapsule wave-absorbing material. According to the invention, multiple scattering and microwave magnetic conductivity of the easy-to-magnetize surface are improved through the geometrical effect and anisotropy of the Ni hierarchical structure, and three-dimensional magnetic loss enhancement is realized; the graded Ni core is coated with a GQDs/PS shell layer, and the composite of polar and nonpolar materials is utilized to realize the adjustability of microwave dielectric constant, so as to modulate dielectric loss, impedance matching and absorption frequency band, effectively prevent the oxidation of the Ni core and realize the adjustable wave-absorbing performance of the material.

Description

Preparation method of dielectric adjustable three-dimensional grading nanocapsule wave-absorbing material

Technical Field

The invention relates to a preparation method of a composite wave-absorbing material with adjustable performance, in particular to a preparation method of a dielectric adjustable three-dimensional graded nanocapsule wave-absorbing material, belonging to the field of wave-absorbing functional materials.

Background

With the miniaturization and high-frequency development of electronic devices, electromagnetic interference and electromagnetic radiation have seriously affected social production and human health, and electromagnetic shielding and electromagnetic absorption have become hot problems concerned in the relevant fields of civil use and military affairs. In the last decade, ferromagnetic metals and alloys have become hot research points in the related industries of wave-absorbing materials due to their characteristics of high saturation magnetization, small hysteresis expansion coefficient, high microwave permeability, etc. However, with the improvement of the electromagnetic compatibility standard of scientific and technological products, the wave-absorbing material gradually tends to be thin-layered, wide-frequency and light-weight, and ferromagnetic metal and alloy-based wave-absorbing materials cause very large input impedance due to relatively high dielectric constant and relatively low magnetic permeability which are difficult to match with the material under the electromagnetic wave frequency band, increase the reflection of the electromagnetic wave on the surface, and make it difficult to form effective absorption in a wide frequency band and a thin thickness. The microwave absorbing application oriented to a specific frequency band, and the limitation of microwave electromagnetic parameters of the material also makes the effective absorption frequency band difficult to adjust in a targeted manner. Therefore, the adjustability of the input impedance of the wave-absorbing material has become a hot research point in the field of absorption band modulation.

The key of the impedance modulation is to realize the adjustability of microwave electromagnetic parameters. The magnetic/dielectric composite nano capsule structure is an effective means for adjusting and improving electromagnetic impedance and matching electromagnetic parameters, the dielectric loss of the material can be improved while the magnetic loss is not lost, a new physical loss mechanism can be introduced by the interface polarization and electromagnetic coupling effect brought by the magnetic/dielectric composite nano capsule structure, the wave absorbing performance of the material is enhanced, and the magnetic/dielectric composite nano capsule structure is widely promoted by related researches. According to the transmission line theory, the improvement of the microwave permeability is more beneficial to the improvement of the broadband of the electromagnetic impedance, and the microwave dielectric constant is reasonably matched and adjusted according to the permeability of the corresponding frequency band. Ferromagnetic metals and alloys are used as cores, the microwave magnetic permeability and magnetic loss are difficult to be greatly improved by nanocrystalline magnetic domains and grain boundaries, and the method of emphasizing the easily magnetized magnetic moment by shape anisotropy and improving the magnetic permeability is more concerned by research. The microwave dielectric loss regulation of the dielectric shell layer also has the problems of single shell layer performance limitation, difficult preparation of double shell layers, compatibility of composite materials and the like, is difficult to form effective electromagnetic matching with a magnetic core, and is also the key point for solving impedance modulation. Therefore, the nanocapsule composite material which is stable and efficient and can realize flexible adjustment of dielectric property on the basis of higher magnetic permeability is prepared by a simple and rapid method and becomes a focus in the field of electromagnetic wave absorption.

Disclosure of Invention

The invention aims to provide a preparation method of a dielectric adjustable three-dimensional grading nanocapsule wave-absorbing material, which is characterized in that a three-dimensional grading nanostructure formed by randomly crossing nickel (Ni) nanosheets is prepared by using polyol reduction as a core, and then a Graphene Quantum Dot (GQDs) layer is coated on the core and embedded in a modified Polystyrene (PS) shell layer, so that the impedance matching performance of the core is further improved, and finally the three-dimensional grading nanocapsule wave-absorbing material with wide frequency band, high absorption and adjustable microwave dielectric performance is formed, and the absorption performance and the frequency band are adjustable.

The three-dimensional hierarchical nanocapsule wave-absorbing material is a core-shell structure which takes a three-dimensional hierarchical nano structure of Ni as a core and takes a PS polymer embedded and modified with GQDs as a shell layer.

The preparation method of the dielectric adjustable three-dimensional grading nanocapsule wave-absorbing material comprises the following steps of firstly, preparing a Ni grading nanostructure with uniform size and shape by a one-step solvothermal method through polyol reduction; and then coating a layer of GQDs embedded modified PS shell layer on the surface of the magnetic grading core by an in-situ polymerization method, thereby obtaining the Ni/GQDs/PS three-dimensional grading nanocapsule composite wave-absorbing material. The method specifically comprises the following steps:

step 1: preparation of nickel (Ni) graded nanocore

1a, dissolving 3mmol of nickel salt in 20ml of polyhydric alcohol, simultaneously adding 0.25-1 mmol of surfactant, and heating and stirring until the nickel salt is completely dissolved to obtain a clear solution 1;

in step 1a, the nickel salt is selected from nickel nitrate, nickel acetate, nickel chloride or the like.

In step 1a, the polyol is selected from ethylene glycol, propylene glycol, glycerol, tetraethylene glycol, and the like.

In step 1a, the surfactant is selected from polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), cetyltrimethylammonium bromide (CTAB), or the like.

In the step 1a, the heating temperature is controlled to be 60-100 ℃.

1b, dissolving 0.045-0.05 mol of sodium hydroxide in 10ml of same polyhydric alcohol, and heating and stirring until the sodium hydroxide is completely dissolved to obtain a clear solution 2;

in the step 1b, the heating temperature is controlled to be 60-80 ℃.

1c, fully mixing and uniformly stirring the solution 1 and the solution 2, transferring the mixture into a lining of a 50ml polytetrafluoroethylene reaction kettle, filling a stainless steel shell, reacting for 2-8 h at 200 ℃, taking out after cooling to room temperature, separating a product by using a magnetic field, and washing 3 times by using distilled water and absolute ethyl alcohol respectively to obtain a Ni grading nano core;

step 2: modification of reduced graphene oxide quantum dots (GQDs)

2a, re-dispersing the Ni graded nano core prepared in the step 1 into deionized water, adding 0.017-0.022 mmol of surfactant, and performing ultrasonic treatment and uniform dispersion;

in step 2a, the surfactant is polyvinylpyrrolidone (PVP).

2b, separating the product subjected to ultrasonic dispersion in the step 2a by using a magnetic field, transferring the product into a flask, adding 20-50 ml of aqueous solution containing 4-9 mg of graphene oxide quantum dots, putting the flask into a water bath, heating to 95 ℃, continuously and mechanically stirring, adding 2-5 ml of hydrazine hydrate, and continuously reacting for 2-6 hours in a nitrogen atmosphere to obtain a GQDs modified Ni hierarchical structure precursor solution;

in the step 2b, the water bath heating rate is controlled to be 1-5 ℃/min.

In the step 2b, the dropping speed of hydrazine hydrate should be controlled to be 0.5-1.25 ml/h.

In the step 2b, the rotating speed of the mechanical stirring paddle should be controlled to be 300-600 rpm.

In the step 2b, the graphene oxide quantum dots are obtained from markets, and the specific parameters are water solution with the size less than 15nm and the concentration of 0.5-2 mg/ml.

And step 3: in situ polymerization coating of Polystyrene (PS)

3a, dispersing 30 vt.% of oleic acid into the precursor aqueous solution obtained in the step 2, performing ultrasonic treatment at 65 ℃ for 5-60 min, and performing high-speed centrifugal separation at the speed of 6000-12000 rpm;

3b, dispersing the separated product into 4-20 mmol/L styrene aqueous solution, adding 1mmol surfactant, performing ultrasonic dispersion, transferring the mixture into a flask, mechanically stirring the flask in a 70 ℃ water bath, measuring 0.5-2 ml of 0.15mol/L persulfate aqueous solution by using a microsyringe, dripping the solution into the flask, and reacting the mixed solution for 2-8 hours under the nitrogen atmosphere;

in step 3b, the surfactant is Sodium Dodecyl Benzene Sulfonate (SDBS).

In step 3b, the persulfate is selected from ammonium persulfate, potassium persulfate, sodium persulfate, etc.

And 3c, separating the product obtained in the step 3b by using a magnetic field, washing the product for 3 times by using deionized water and absolute ethyl alcohol respectively, and drying the product in a vacuum drying oven for 6-8 hours to obtain the core-shell Ni/GQDs/PS three-dimensional graded nanocapsule composite wave-absorbing material.

In step 3c, the parameters of vacuum drying are as follows: the pressure is lower than 0.01MPa, and the temperature is 60 ℃.

The invention has the beneficial effects that:

1. the invention utilizes the three-dimensional hierarchical nano structure formed by the random crossing of the Ni nano sheets as a magnetic core, promotes the microwave magnetic loss of the magnetic moment of the easy-to-magnetize surface through the geometric effect, the shape and the magnetocrystalline anisotropy, enhances the multiple scattering among the nano sheets and realizes the enhancement of the microwave magnetic conductivity.

2. According to the invention, the Ni graded nano core is reduced by using the polyhydric alcohol at high temperature and high pressure in one step, the anisotropic growth of the Ni easy-to-magnetize surface can be effectively promoted in a strong alkaline environment, and meanwhile, the Ni graded nano structure with high yield, uniform size and consistent shape is obtained by combining modification and control of the surfactant.

3. According to the invention, the surface of the magnetic nano core is coated with the GQDs embedded and modified PS shell layer, and the adjustability of microwave dielectric constant and dielectric loss is realized by utilizing the compounding and interface regulation of polar and nonpolar dielectric materials, so that the adjustability of the absorption band of the material is enhanced, and the oxidation of the inner Ni core is effectively prevented.

4. The microwave dielectric property of the nanocapsule can be simply adjusted by adjusting the component ratio of GQDs to PS, so that the impedance matching of the material in each frequency band can be flexibly adjusted, and the enhanced microwave absorption property can be obtained.

5. The invention has the advantages of simple operation, short production period, good repeatability, adjustable electromagnetic wave absorption frequency band and performance and wide application value.

Drawings

FIG. 1 is a TEM image of the core-shell Ni/GQDs/PS three-dimensional hierarchical nanocapsule obtained in example 1;

FIG. 2 is an HRTEM image of the core-shell Ni/GQDs/PS three-dimensional hierarchical nanocapsule obtained in example 1;

FIG. 3 shows the complex dielectric constant (. epsilon.) of the core-shell Ni/GQDs/PS three-dimensional hierarchical nanocapsule obtained in example 1 in the frequency band of 1-18GHz_r＝ε_r′-jε_r") and (b) complex permeability (. mu.)_r＝μ_r′-jμ_r″)；

FIG. 4 is a graph showing the Reflection Loss (RL) of the core-shell Ni/GQDs/PS three-dimensional hierarchical nanocapsule obtained in example 1 in the frequency band of 1-18GHz and the thickness of the nanocapsule being 0-10 mm;

FIG. 5 is a TEM image of the core-shell Ni/GQDs/PS three-dimensional hierarchical nanocapsule obtained in example 2;

FIG. 6 shows the complex dielectric constant (. epsilon.) of the core-shell Ni/GQDs/PS three-dimensional hierarchical nanocapsule obtained in example 2 in the frequency band of 1-18GHz_r＝ε_r′-jε_r") and (b) complex permeability (. mu.)_r＝μ_r′-jμ_r″)；

FIG. 7 shows the Reflection Loss (RL) of the core-shell Ni/GQDs/PS three-dimensional hierarchical nanocapsule obtained in example 2 in the frequency band of 1-18GHz and the thickness of 0-10 mm;

FIG. 8 is a TEM image of the core-shell Ni/GQDs/PS three-dimensional hierarchical nanocapsule obtained in example 3;

FIG. 9 shows the complex dielectric constant (. epsilon.) of the core-shell Ni/GQDs/PS three-dimensional hierarchical nanocapsule obtained in example 3 in the frequency band of 1-18GHz_r＝ε_r′-jε_r") and (b) complex permeability (. mu.)_r＝μ_r′-jμ_r″)；

FIG. 10 shows the Reflection Loss (RL) of the core-shell Ni/GQDs/PS three-dimensional hierarchical nanocapsule obtained in example 3 in the frequency band of 1-18GHz and the thickness of 0-10 mm.

Detailed Description

The technical solution of the present invention is further illustrated by the following specific examples.

Example 1:

1. dissolving 3mmol of nickel acetate tetrahydrate and 1g of polyethylene glycol 4000 in 20mL of ethylene glycol, and stirring for 20min at 80 ℃ by using magnetic force until the nickel acetate and the polyethylene glycol are completely dissolved to obtain a clear solution 1;

2. adding 0.045mol of sodium hydroxide into 10mL of ethylene glycol, and stirring for 20min at 80 ℃ by using magnetic force until the sodium hydroxide is completely dissolved to obtain a clear solution 2;

3. fully mixing and uniformly stirring the solution 1 and the solution 2, transferring the mixture into a lining of a 50ml polytetrafluoroethylene reaction kettle, filling a stainless steel shell, reacting for 8 hours at 200 ℃, taking out after cooling to room temperature, separating a product by using a magnetic field, and washing the product for 3 times by using distilled water and absolute ethyl alcohol respectively to obtain a Ni grading nano core;

4. re-dispersing the graded nano Ni prepared in the step 3 into deionized water, adding 1g of polyvinylpyrrolidone (PVP) and carrying out ultrasonic treatment and uniformly dispersing;

5. separating the product subjected to ultrasonic dispersion in the step 4 by using a magnetic field, transferring the product into a flask, adding 50ml of aqueous solution containing 9mg of graphene oxide quantum dots, putting the flask into a water bath, heating to 95 ℃, continuously and mechanically stirring, adding 4ml of hydrazine hydrate, and continuously reacting for 4 hours in a nitrogen atmosphere to obtain a GQDs modified Ni hierarchical structure precursor solution;

6. dispersing 30 vt.% of oleic acid into the precursor aqueous solution obtained in the step 5, performing ultrasonic treatment at 65 ℃ for 60min, and performing high-speed centrifugal separation at a speed of 7500 rpm;

7. dispersing the product obtained in the step 6 into 45mL of a 5mmol/L styrene aqueous solution, adding 0.03g of Sodium Dodecyl Benzene Sulfonate (SDBS), ultrasonically mixing, transferring into a flask, mechanically stirring the flask in a 70 ℃ water bath, slowly and uniformly dropping 0.5mL of 0.15mmol/mL ammonium persulfate solution at the heating rate of 5 ℃/min, and reacting the mixed solution for 4 hours in a nitrogen atmosphere;

8. and (3) separating the product obtained in the step (7) by using a magnetic field, washing the product by using deionized water and absolute ethyl alcohol for 3 times respectively, and drying the product in a vacuum drying oven for 8 hours to obtain the core-shell Ni/GQDs/PS three-dimensional graded nanocapsule composite wave-absorbing material.

The TEM image of the core-shell Ni/GQDs/PS three-dimensional hierarchical nanocomposite structure obtained in this example is shown in FIG. 1. FIG. 1 shows that magnetic metal Ni is a three-dimensional hierarchical structure formed by random crossing of nanosheets, the diameter of the magnetic metal Ni is about 1 μm, the magnetic metal Ni is uniform in shape and size, and PS is coated on the outer layer of a Ni core to form a uniform shell layer. FIG. 2HRTEM shows that the PS shell layer of the Ni core outer layer is a typical amorphous phase image, the thickness is about 30-35 nm, and the size of the embedded GQDs is uniform and about 3-5 nm. FIG. 3 shows that the real part value of the complex dielectric constant of the Ni/GQDs/PS composite structure is 8.2-9.1, and the imaginary part value is 0.7-1.7, which indicates that the microwave dielectric property of the composite structure is remarkably improved by the interface polarization of the GQDs. The complex permeability value is also kept at a higher level due to the shape anisotropy of Ni, the real part value is 0.95-1.34, and the imaginary part value is 0.01-0.2. FIG. 4 is a reflection loss curve of a paraffin-based absorber containing 40 wt.% Ni/GQDs/PS nanocapsules measured at a thickness of 0-10mm in a frequency band of 1-18 GHz. As can be seen from FIG. 4, when the thickness of the X-Ku frequency band is 4-8 mm, the electromagnetic wave absorption capacity of the material is remarkably enhanced, when the frequency is 14.04GHz and the thickness is 5.8mm, the reflection loss of the material reaches-44.3 dB, the wave-absorbing performance is best, and when the thickness of the material is 7.7mm, the effective absorption bandwidth (RL < -10dB) reaches 2.1 GHz.

Example 2:

2. adding 0.045mol of flaky sodium hydroxide into 10mL of ethylene glycol, and stirring for 20min at 80 ℃ by using magnetic force until the flaky sodium hydroxide is completely dissolved to obtain a clear solution 2;

7. dispersing the product obtained in the step 6 into 45mL of 10mmol/L styrene aqueous solution, adding 0.03g of Sodium Dodecyl Benzene Sulfonate (SDBS), ultrasonically mixing, transferring into a flask, mechanically stirring the flask in a 70 ℃ water bath, slowly and uniformly dropping 1mL of 0.15mmol/mL ammonium persulfate solution at the heating rate of 5 ℃/min, and reacting the mixed solution for 4 hours in the nitrogen atmosphere;

The TEM image of the core-shell Ni/GQDs/PS three-dimensional hierarchical nanocomposite structure obtained in this example is shown in FIG. 5. FIG. 5 shows that magnetic metal Ni is a three-dimensional hierarchical structure formed by random crossing of nanosheets, the diameter is about 1 μm, the shape is uniform, the size is consistent, PS is coated on the outer layer of a Ni core to form a relatively uniform shell layer, and the thickness is about 35-40 nm. FIG. 6 shows that the real part of the complex dielectric constant of the Ni/GQDs/PS composite structure is 7.8-8.7, the imaginary part is 0.68-1.9, which is reduced by about 3% compared with the average value of example 1, and the thickened amorphous PS shell layer can weaken the interface dipole of the GQDs and Ni. The real part value of the complex permeability is 0.9-1.3, and the imaginary part value is 0.009-0.2, which has a small amplitude reduction compared with example 1, because the proportion of the magnetic component is relatively reduced due to the increase of the PS content. This example illustrates that, based on the higher dielectric properties of the composite structure brought by GQDs, the increase of PS can flexibly fine-tune the input impedance of the composite material by reducing the dielectric constant of the material by a small margin. As shown in FIG. 7, in the X-Ku frequency band, the effective absorption peak of the material has a little displacement towards the high thickness direction, when the frequency is 13.58GHz and the thickness is 6.1mm, the electromagnetic wave absorption performance of the material is best and reaches-42.5 dB, and when the thickness of the material is 7.6mm, the effective absorption bandwidth (RL < -10dB) reaches 2.3 GHz.

Example 3:

7. dispersing the product obtained in the step 6 into 45mL of a 20mmol/L styrene aqueous solution, adding 0.03g of Sodium Dodecyl Benzene Sulfonate (SDBS), ultrasonically mixing, transferring into a flask, mechanically stirring the flask in a 70 ℃ water bath, slowly and uniformly dropping 2mL of 0.15mmol/mL ammonium persulfate solution at the heating rate of 5 ℃/min, and reacting the mixed solution for 4 hours in a nitrogen atmosphere;

FIG. 8 is a TEM image of the core-shell Ni/GQDs/PS three-dimensional hierarchical nano-composite structure obtained in the present embodiment, where the image shows that the magnetic metal Ni is a three-dimensional hierarchical structure formed by crossing nano-sheets, the diameter is about 1 μm, and the thickness of the PS coating on the outer layer is about 40-45 nm. FIG. 9 shows that the real part of the complex dielectric constant of the Ni/GQDs/PS composite structure is 5.1-6.3, which is reduced by 26% compared with example 1, and the imaginary part is between 0.28-1.7, because the polarization of the interface dipole is further weakened by the thickening of the amorphous PS shell layer. The real part value of the complex permeability is 0.9-1.3, the imaginary part value is 0.01-0.18, and the reduction of the complex permeability is small compared with the embodiment 1, because the proportion of the magnetic components is relatively reduced due to the increase of the PS content, the permeability of the material is reduced. Compared with

embodiments

1 and 2, in the present embodiment, while the GQDs increases the dielectric constant, the further increase of the PS content further reduces the dielectric constant of the material in the full frequency band, thereby adjusting the input impedance. As shown in FIG. 10, the effective absorption peak of the material in the X-Ku frequency band continues to move in the high-frequency and high-thickness direction, when the frequency is 10.14GHz and the thickness is 9mm, the electromagnetic wave absorption performance of the material is best and reaches-52.6 dB, and when the thickness is 9.4mm, the effective absorption bandwidth (RL < -10dB) reaches 2.1 GHz.

Claims

1. A preparation method of a dielectric adjustable three-dimensional grading nanocapsule wave-absorbing material is characterized by comprising the following steps:

firstly, preparing a magnetic metal Ni three-dimensional hierarchical nano structure which is formed by randomly crossing nano sheets and has a uniform size and shape by a one-step solvothermal method through polyol reduction; and then coating a layer of GQDs embedded and modified PS shell layer on the surface of the magnetic Ni hierarchical core by an in-situ polymerization method, thereby obtaining the Ni/GQDs/PS three-dimensional hierarchical nanocapsule composite wave-absorbing material.

2. The method of claim 1, comprising the steps of:

step 1: preparation of Ni hierarchical nanocore

1b, dissolving 0.045-0.05 mol of sodium hydroxide in 10ml of the same polyhydric alcohol in the step 1a, and heating and stirring until the sodium hydroxide is completely dissolved to obtain a clear solution 2;

1c, fully mixing and uniformly stirring the solution 1 and the solution 2, transferring the mixture into a lining of a 50ml polytetrafluoroethylene reaction kettle, filling a stainless steel shell, reacting for 2-8 h at 200 ℃, cooling to room temperature, taking out, separating a product by using a magnetic field, and sequentially washing by using distilled water and absolute ethyl alcohol to obtain a Ni graded nano core;

step 2: modification of GQDs

2b, separating the product subjected to ultrasonic dispersion in the step 2a by using a magnetic field, transferring the product into a flask, adding 20-50 ml of aqueous solution containing 4-9 mol of graphene oxide quantum dots, putting the flask into a water bath, heating to 95 ℃, continuously and mechanically stirring, adding 2-5 ml of hydrazine hydrate, and continuously reacting for 2-6 h under a nitrogen atmosphere to obtain a GQDs modified Ni hierarchical structure precursor solution;

and step 3: in situ polymerization coating of PS

3a, dispersing 30 vt% of oleic acid into the precursor solution obtained in the step 2, performing ultrasonic treatment at 65 ℃ for 5-60 min, and performing high-speed centrifugal separation at the speed of 6000-12000 rpm;

and 3c, separating the product obtained in the step 3b by using a magnetic field, sequentially washing by using deionized water and absolute ethyl alcohol, and drying the product in a vacuum drying oven for 6-8 hours to obtain the core-shell Ni/GQDs/PS three-dimensional graded nanocapsule composite wave-absorbing material.

3. The method of claim 2, wherein:

in step 1a, the nickel salt is selected from nickel nitrate, nickel acetate or nickel chloride; the polyhydric alcohol is selected from ethylene glycol, propylene glycol, glycerol or tetraethylene glycol; the surfactant is selected from polyethylene glycol, polyvinylpyrrolidone or cetyl trimethyl ammonium bromide.

4. The method of claim 2, wherein:

in step 2a, the surfactant is polyvinylpyrrolidone.

5. The method of claim 2, wherein:

in the step 2b, the water bath heating rate is controlled to be 1-5 ℃/min.

6. The method of claim 2, wherein:

in the step 2b, the dropping speed of hydrazine hydrate is controlled to be 0.5-1.25 ml/h.

7. The method of claim 2, wherein:

in step 3b, the surfactant is sodium dodecyl benzene sulfonate.

8. The method of claim 2, wherein:

in step 3b, the persulfate is selected from ammonium persulfate, potassium persulfate, or sodium persulfate.

9. The method of claim 2, wherein:

10. The method of claim 2, wherein:

by changing the proportion of GQDs to PS, the real part of the complex dielectric constant of the obtained composite wave-absorbing material is within 5-12, and the imaginary part of the composite wave-absorbing material is within 0.2-2, so that the corresponding effective absorption peak of electromagnetic waves is adjusted within the ranges of f 1-18GHz and d 1-10 mm.