CN117548684A - Co@SiO with hollow core-shell structure 2 Preparation method and application of @ PPy - Google Patents

Abstract

Co@SiO with hollow core-shell structure ₂ A preparation method and application of @ PPy, which belong to the technical field of electromagnetic wave absorbing materials. Firstly, preparing monodisperse Co microspheres with a hollow structure by a solvothermal method, wherein the hollow structure reduces the weight of Co without losing the magnetic loss performance of Co; then coating SiO on the surface of Co microsphere by modified STber method ₂ ，SiO ₂ The introduction of the layer can not only enhance the interfacial polarization of the composite material, but also prevent Co cores from being corroded by acidic solution, and has no obvious negative influence on the magnetic loss capacity of Co; finally by in situ polymerizationSiO ₂ PPy is coated on the surface of the layer; PPy has very strong conductivity loss due to its high conductivity, and high dielectric loss can be obtained without high temperature calcination. Co@SiO with hollow core-shell structure ₂ The @ PPy is used as an electromagnetic wave absorbing material.

Description

Preparation method and application of hollow core-shell structure Co@SiO2@PPy

Technical field

The invention belongs to the technical field of electromagnetic wave absorbing materials, and specifically relates to a preparation method and application of a hollow core-shell structure Co@SiO ₂ @PPy.

Background technique

While electromagnetic waves bring great convenience to human life, they also produce a large amount of electromagnetic pollution. Electromagnetic wave absorbing materials are one of the important methods to solve electromagnetic pollution. An ideal electromagnetic wave absorbing material should have the characteristics of high absorption intensity, effective absorption bandwidth, thin matching thickness and light weight. Research shows that the composite and reasonable structural design of magnetic materials and dielectric materials is an important method to obtain excellent electromagnetic wave absorption performance. Soft magnetic materials (Fe, Co, Ni, CIP, Fe ₃ O ₄ , etc.) are widely used in the field of electromagnetic wave absorption due to their high saturation magnetization and large magnetic loss. However, magnetic metals such as Fe and Co have disadvantages such as high density and poor corrosion resistance. The introduction of dielectric materials can protect magnetic metals and increase dielectric losses. Conductive polymers PPy and PANI have strong dielectric loss, and have many advantages such as low density, simple synthesis method, and low cost. Based on the above two considerations, researchers tend to design core-shell structure magnetic metal/carbon composite materials with cavities. On the one hand, electromagnetic waves are absorbed through the combined action of strong magnetic loss and dielectric loss. On the other hand, the introduction of the carbon shell can not only increase the dielectric loss, but also protect the internal magnetic metal from corrosion. Normally, when preparing PPy and PANI using APS and FeCl ₃ as initiators, acidic solutions will corrode Co and Fe. Therefore, most studies use phenolic resin or polydopamine as a precursor and obtain dielectric loss through high-temperature calcination. However, these methods not only increase the energy-consuming calcination process, but high-temperature calcination may also adversely affect the magnetic loss of magnetic materials.

Contents of the invention

In order to overcome the above-mentioned shortcomings of existing materials, the present invention provides a preparation method and application of hollow core-shell structure Co@SiO ₂ @PPy.

The present invention first prepares monodisperse hollow structure Co microspheres through a solvothermal method. The hollow structure reduces the weight of Co without losing its magnetic loss performance; then the surface of the Co microspheres is coated with SiO ₂ through the modified Stober method. The introduction of the SiO ₂ layer can not only enhance the interfacial polarization of the composite material, but also prevent the Co core from being corroded by the acidic solution, and has no obvious negative impact on the magnetic loss capability of Co; finally, the surface of the SiO ₂ layer is coated through in-situ polymerization PPy; PPy has strong conductivity loss due to its high conductivity, and high dielectric loss can be obtained without high-temperature calcination; the hollow core-shell structure Co@SiO ₂ @PPy prepared by the present invention has excellent electromagnetic wave absorption performance .

A preparation method of hollow core-shell structure Co@SiO ₂ @PPy is specifically completed according to the following steps:

1. Dissolve PVP, CoCl ₂ ·6H ₂ O, and N ₂ H ₄ ·H ₂ O in ethylene glycol to obtain solution A;

2. Stir solution A evenly and then transfer it to a hydrothermal kettle, and then place it in a hydrothermal reaction at 180°C for a period of time to obtain reaction product I;

3. After the hydrothermal kettle is cooled to room temperature, the reaction product I is separated by magnetic adsorption in sequence, and the solid product is washed and vacuum dried to obtain hollow structure Co microspheres;

4. Disperse the hollow structure Co microspheres in a mixed solution of deionized water, ammonia water, and absolute ethanol to obtain suspension B;

5. Add TEOS to suspension B, then stir evenly to obtain suspension C;

6. React suspension C at room temperature for a period of time to obtain suspension D;

7. The suspension D is subjected to magnetic adsorption separation in sequence, and the solid product is washed and vacuum dried to obtain hollow structure Co@SiO ₂ microspheres;

8. Disperse the hollow structure Co@SiO ₂ microspheres in deionized water to obtain suspension E;

9. Disperse pyrrole in suspension E to obtain suspension F;

10. Add the oxidizing agent to the suspension F under ice bath conditions to obtain the suspension G;

11. React suspension G under ice bath conditions for a period of time to obtain suspension H;

12. The suspension H is subjected to magnetic adsorption separation in sequence, and the obtained solid product is washed and vacuum dried to obtain the hollow core-shell structure Co@SiO ₂ @PPy.

A hollow core-shell structure Co@SiO ₂ @PPy is used as an electromagnetic wave absorbing material.

Compared with the prior art, the present invention has the following beneficial effects:

The hollow structure reduces the weight of Co, and the introduction of the _SiO2 layer not only enhances the interface polarization of the composite material, but also prevents the Co core from being corroded by acidic solutions, and has no obvious negative impact on the magnetic loss capability of Co. PPy has strong conductivity losses due to its high conductivity, and does not require an energy-consuming high-temperature calcination process to obtain high dielectric losses. The hollow core-shell structure Co@SiO ₂ @PPy composite material prepared has excellent electromagnetic wave absorption properties and has good application potential in the fields of electromagnetic wave absorption and electromagnetic shielding.

Description of the drawings

Figure 1 is an SEM image of the hollow core-shell structure Co@SiO ₂ @PPy composite material prepared in Example 1;

Figure 2 is an electromagnetic wave absorption performance diagram of the hollow core-shell structure Co@SiO ₂ @PPy composite material prepared in Example 1;

Figure 3 is an SEM image of the hollow core-shell structure Co@SiO ₂ @PPy composite material prepared in Example 2;

Figure 4 is an electromagnetic wave absorption performance diagram of the hollow core-shell structure Co@SiO ₂ @PPy composite material prepared in Example 2;

Figure 5 is an SEM image of the hollow core-shell structure Co@SiO ₂ @PPy composite material prepared in Example 3;

Figure 6 is an electromagnetic wave absorption performance diagram of the hollow core-shell structure Co@SiO ₂ @PPy composite material prepared in Example 3;

Figure 7 is an SEM image of the hollow structure Co microspheres described in Examples 1 to 3 after being etched with 0.1 mol/L HCl for 1 hour.

Detailed ways

Specific Embodiment 1: This embodiment is a preparation method of hollow core-shell structure Co@SiO ₂ @PPy. Specifically, it is completed according to the following steps:

1. Dissolve PVP, CoCl ₂ ·6H ₂ O, and N ₂ H ₄ ·H ₂ O in ethylene glycol to obtain solution A;

2. Stir solution A evenly and then transfer it to a hydrothermal kettle, and then place it in a hydrothermal reaction at 180°C for a period of time to obtain reaction product I;

3. After the hydrothermal kettle is cooled to room temperature, the reaction product I is separated by magnetic adsorption in sequence, and the solid product is washed and vacuum dried to obtain hollow structure Co microspheres;

4. Disperse the hollow structure Co microspheres in a mixed solution of deionized water, ammonia water, and absolute ethanol to obtain suspension B;

5. Add TEOS to suspension B, then stir evenly to obtain suspension C;

6. React suspension C at room temperature for a period of time to obtain suspension D;

7. The suspension D is subjected to magnetic adsorption separation in sequence, and the solid product is washed and vacuum dried to obtain hollow structure Co@SiO ₂ microspheres;

8. Disperse the hollow structure Co@SiO ₂ microspheres in deionized water to obtain suspension E;

9. Disperse pyrrole in suspension E to obtain suspension F;

10. Add the oxidizing agent to the suspension F under ice bath conditions to obtain the suspension G;

11. React suspension G under ice bath conditions for a period of time to obtain suspension H;

12. The suspension H is subjected to magnetic adsorption separation in sequence, and the obtained solid product is washed and vacuum dried to obtain the hollow core-shell structure Co@SiO ₂ @PPy.

Specific Embodiment 2: The difference between this embodiment and Specific Embodiment 1 is that the concentration of PVP in solution A described in step one is 15g/L ~ 60g/L; the CoCl ₂ · in solution A described in step one is The concentration of 6H ₂ O is 15g/L ~ 60g/L; the concentration of N ₂ H ₄ ·H ₂ O in solution A described in step 1 is 50mL/L ~ 150mL/L. Other steps are the same as the first embodiment.

Specific Embodiment 3: The difference between this embodiment and Specific Embodiment 1 or 2 is that the hydrothermal reaction time described in step 2 is 4h to 48h. Other steps are the same as the first or second embodiment.

Specific embodiment four: The difference between this embodiment and one of the specific embodiments one to three is that the concentration of the hollow structure Co microspheres in the suspension B described in step four is 0.25g/L ~ 25g/L; step four The volume ratio of ammonia water, deionized water and absolute ethanol in the mixed solution of deionized water, ammonia water and absolute ethanol is (10~20): (40~60): (300~400); The mass fraction of ammonia water is 25% to 28%. Other steps are the same as the specific embodiments one to three.

Specific Embodiment 5: The difference between this embodiment and one of Specific Embodiments 1 to 4 is that the concentration of TEOS in the turbid liquid C described in step 5 is 5 mL/L to 50 mL/L. Other steps are the same as the specific embodiments one to four.

Specific Embodiment 6: The difference between this embodiment and one of Specific Embodiments 1 to 5 is that the reaction time described in step 6 is 0.5h to 12h. Other steps are the same as the specific embodiments 1 to 5.

Specific Embodiment 7: The difference between this embodiment and one of Specific Embodiments 1 to 6 is that the concentration of hollow structure Co@SiO ₂ microspheres in the suspension E described in step 8 is 0.25g/L ~ 25g/L ; The concentration of pyrrole in the suspension F described in step nine is 0.12mL/L ~ 50mL/L. Other steps are the same as the specific embodiments one to six.

Specific Embodiment 8: The difference between this embodiment and one of Specific Embodiments 1 to 7 is that: the oxidizing agent described in step 10 is APS, FeCl ₃ or FeCl ₃ ·6H ₂ O; the oxidizing agent in the suspension G is The concentration is 0.12g/L~150g/L. Other steps are the same as the specific embodiments one to seven.

Specific Embodiment 9: The difference between this embodiment and one of Specific Embodiments 1 to 8 is that in step 1, the reaction time of suspension G under ice bath conditions is 4h to 24h. Other steps are the same as the specific embodiments 1 to 8.

Specific Embodiment 10: In this embodiment, a hollow core-shell structure Co@SiO ₂ @PPy is used as an electromagnetic wave absorbing material.

The following examples are used to verify the beneficial effects of the present invention:

Example 1: A method for preparing a hollow core-shell structure Co@SiO ₂ @PPy, which is characterized in that the preparation method is specifically completed according to the following steps:

1. Dissolve 3g polyvinylpyrrolidone (PVP, k29-32, Mw=58000), 3g CoCl ₂ ·6H ₂ O, and 10mL N ₂ H ₄ ·H ₂ O in 100mL ethylene glycol to obtain solution A;

2. Stir solution A evenly and then transfer it to a hydrothermal kettle and place it at 180°C to react for 6 hours to obtain reaction product I;

3. After the hydrothermal kettle is cooled to room temperature, the reaction product I is sequentially adsorbed and separated with a magnet, washed 3 times with deionized water and absolute ethanol, and dried at 60°C for 12 hours in a vacuum to obtain a hollow structure Co microstructure. ball;

4. Disperse 1.5g hollow Co microspheres in a mixed solution of 350mL absolute ethanol, 50mL ionized water, and 15mL ammonia water to obtain suspension B; the mass fraction of the ammonia water is 28%;

5. Add 5mL TEOS to suspension B, and then stir evenly to obtain suspension C;

6. React suspension C at room temperature for 5 hours to obtain suspension D;

7. Use a magnet to adsorb and separate the suspension D product, wash it with deionized water and absolute ethanol three times each, and dry it in a vacuum at 60°C for 12 hours to obtain hollow structure Co@SiO ₂ microspheres;

8. Disperse 0.5g of hollow structure Co@SiO ₂ microspheres in 100 mL of deionized water to obtain suspension E;

9. Disperse 600 μL of pyrrole in suspension E to obtain suspension F;

10. Add 0.60g ammonium persulfate to suspension F under ice bath conditions to obtain suspension G;

11. React suspension G under ice bath conditions for 10 hours to obtain suspension H;

12. Use a magnet to adsorb and separate the suspension H, wash it three times with deionized water and absolute ethanol, and dry it in a vacuum at 50°C for 24 hours to obtain a hollow core-shell structure Co@SiO ₂ @PPy composite material.

Figure 1 is an SEM image of the hollow core-shell structure Co@SiO ₂ @PPy composite material prepared in Example 1;

It can be seen from Figure 1 that the Co@SiO ₂ @PPy composite has a double-layer shell, with the inner layer being SiO ₂ and the outer layer being PPy.

The detection method of the electromagnetic wave absorption performance in the present invention: mix the sample powder and paraffin evenly at a mass ratio of 1:1, then press it into a ring-shaped sample, use vector network analysis to test the electromagnetic parameters of the sample, and then calculate the electromagnetic wave absorption performance.

Figure 2 is an electromagnetic wave absorption performance diagram of the hollow core-shell structure Co@SiO ₂ @PPy composite material prepared in Example 1;

It can be seen from Figure 2 that the hollow core-shell structure Co@SiO ₂ @PPy composite material prepared in Example 1 has an effective absorption bandwidth of 4.48GHz in the high-frequency region, and the minimum reflection loss reaches -25.14dB.

Example 2: A method for preparing hollow core-shell structure Co@SiO ₂ @PPy, which is characterized in that the preparation method is specifically completed according to the following steps:

1. Dissolve 3g polyvinylpyrrolidone (PVP, k29-32, Mw=58000), 3g CoCl ₂ ·6H ₂ O, and 10mL N ₂ H ₄ ·H ₂ O in 100mL ethylene glycol to obtain solution A;

2. Stir solution A evenly and then transfer it to a hydrothermal kettle and place it at 180°C to react for 6 hours to obtain reaction product I;

3. After the hydrothermal kettle is cooled to room temperature, the reaction product I is sequentially adsorbed and separated with a magnet, washed 3 times with deionized water and absolute ethanol, and dried at 60°C for 12 hours in a vacuum to obtain a hollow structure Co microstructure. ball;

4. Disperse 1.5g hollow Co microspheres in a mixed solution of 350mL absolute ethanol, 50mL ionized water, and 15mL ammonia water to obtain suspension B; the mass fraction of the ammonia water is 28%;

5. Add 5mL TEOS to suspension B, and then stir evenly to obtain suspension C;

6. React suspension C at room temperature for 5 hours to obtain suspension D;

7. Use a magnet to adsorb and separate the suspension D product, wash it with deionized water and absolute ethanol three times each, and dry it in a vacuum at 60°C for 12 hours to obtain hollow structure Co@SiO ₂ microspheres;

8. Disperse 0.5g of hollow structure Co@SiO ₂ microspheres in 100 mL of deionized water to obtain suspension E;

9. Disperse 660 μL of pyrrole in suspension E to obtain suspension F;

10. Add 0.66g ammonium persulfate to suspension F under ice bath conditions to obtain suspension G;

11. React suspension G under ice bath conditions for 10 hours to obtain suspension H;

12. Use a magnet to adsorb and separate the suspension H, wash it three times with deionized water and absolute ethanol, and dry it in a vacuum at 50°C for 24 hours to obtain a hollow core-shell structure Co@SiO ₂ @PPy composite material.

Figure 3 is an SEM image of the hollow core-shell structure Co@SiO ₂ @PPy composite material prepared in Example 2;

It can be seen from Figure 3 that the hollow core-shell structure Co@SiO ₂ @PPy composite material was successfully prepared. Compared with Example 1, this example has fewer broken shells and more discrete PPy due to the increased added pyrrole content.

Figure 4 is an electromagnetic wave absorption performance diagram of the hollow core-shell structure Co@SiO ₂ @PPy composite material prepared in Example 2;

It can be seen from Figure 4 that the hollow core-shell structure Co@SiO ₂ @PPy composite material prepared in Example 2 has a maximum effective absorption bandwidth of 5.2GHz, and the minimum reflection loss reaches -65.83dB, and has excellent electromagnetic wave absorption effect.

Example 3: A method for preparing hollow core-shell structure Co@SiO ₂ @PPy, which is characterized in that the preparation method is specifically completed according to the following steps:

1. Dissolve 3g polyvinylpyrrolidone (PVP, k29-32, Mw=58000), 3g CoCl ₂ ·6H ₂ O, and 10mL N ₂ H ₄ ·H ₂ O in 100mL ethylene glycol to obtain solution A;

2. Stir solution A evenly and then transfer it to a hydrothermal kettle and place it at 180°C to react for 6 hours to obtain reaction product I;

3. After the hydrothermal kettle is cooled to room temperature, the reaction product I is sequentially adsorbed and separated with a magnet, washed 3 times with deionized water and absolute ethanol, and dried at 60°C for 12 hours in a vacuum to obtain a hollow structure Co microstructure. ball;

4. Disperse 1.5g hollow Co microspheres in a mixed solution of 350mL absolute ethanol, 50mL ionized water, and 15mL ammonia water to obtain suspension B; the mass fraction of the ammonia water is 28%;

5. Add 5mL TEOS to suspension B, and then stir evenly to obtain suspension C;

6. React suspension C at room temperature for 5 hours to obtain suspension D;

7. Use a magnet to adsorb and separate the suspension D product, wash it with deionized water and absolute ethanol three times each, and dry it in a vacuum at 60°C for 12 hours to obtain hollow structure Co@SiO ₂ microspheres;

8. Disperse 0.5g of hollow structure Co@SiO ₂ microspheres in 100 mL of deionized water to obtain suspension E;

9. Disperse 760 μL of pyrrole in suspension E to obtain suspension F;

10. Add 0.76g of ammonium persulfate to suspension F under ice bath conditions to obtain suspension G;

11. React suspension G under ice bath conditions for 10 hours to obtain suspension H;

12. Use a magnet to adsorb and separate the suspension H, wash it three times with deionized water and absolute ethanol, and dry it in a vacuum at 50°C for 24 hours to obtain a hollow core-shell structure Co@SiO ₂ @PPy composite material.

Figure 5 is an SEM image of the hollow core-shell structure Co@SiO ₂ @PPy composite material prepared in Example 3;

It can be seen from Figure 5 that the hollow core-shell structure Co@SiO ₂ @PPy composite material was successfully prepared. Compared with Examples 1 and 2, this example has more pyrrole content and more discrete PPy, so the coating is relatively complete. But the core-shell structure can also be seen.

Figure 6 is an electromagnetic wave absorption performance diagram of the hollow core-shell structure Co@SiO ₂ @PPy composite material prepared in Example 3;

It can be seen from Figure 6 that the hollow core-shell structure Co@SiO ₂ @PPy composite material has excellent electromagnetic wave absorption properties. When the thickness is 1.66mm, the effective absorption bandwidth is 3.96GHz, and the minimum reflection loss reaches -61.66dB. When the thickness is 1.83mm, the effective absorption bandwidth reaches 5.4GHz, and the minimum reflection loss reaches -50.70dB, achieving a wider absorption effect at a thinner thickness.

Example 4: A method for preparing a hollow core-shell structure Co@SiO ₂ @PPy composite material. Specifically, it is completed according to the following steps:

1. Dissolve 0.5g PVP (k29-32, Mw=58000), 1g CoCl ₂ ·6H ₂ O, 6mL N ₂ H ₄ ·H ₂ O in 100mL ethylene glycol to obtain solution A;

2. Stir solution A evenly and then transfer it to a hydrothermal kettle and react it at 180°C for 20 hours to obtain reaction product I;

3. After the hydrothermal kettle is cooled to room temperature, the reaction product I is sequentially adsorbed and separated with a magnet, washed three times with deionized water and absolute ethanol, and dried in a vacuum at 50°C for 24 hours to obtain hollow structure Co microspheres. ;

4. Disperse 0.5g hollow Co microspheres in a mixed solution of 120mL absolute ethanol, 40mL ionized water, and 10mL ammonia water to obtain suspension B; the mass fraction of the ammonia water is 28%;

5. Add 1mL TEOS to suspension B, and then stir evenly to obtain suspension C;

6. React suspension C at room temperature for 2 hours to obtain suspension D;

7. Use a magnet to adsorb and separate the suspension D product, wash it 4 times each with deionized water and absolute ethanol, and dry it in a vacuum at 60°C for 24 hours to obtain hollow structure Co@SiO ₂ microspheres;

8. Disperse 1.0g hollow structure Co@SiO ₂ microspheres in 100mL deionized water to obtain suspension E;

9. Disperse 1000 μL pyrrole in suspension E to obtain suspension F;

10. Add 1.0g of ammonium persulfate to suspension F under ice bath conditions to obtain suspension G;

11. React suspension G under ice bath conditions for 6 hours to obtain suspension H;

12. Use a magnet to adsorb and separate the suspension H, wash it three times with deionized water and absolute ethanol, and dry it in a vacuum at 50°C for 12 hours to obtain a hollow core-shell structure Co@SiO ₂ @PPy composite material.

Example 5: A method for preparing a hollow core-shell structure Co@SiO ₂ @PPy composite material. Specifically, it is completed according to the following steps:

1. Dissolve 1g PVP (k29-32, Mw=58000), 1.5g CoCl ₂ ·6H ₂ O, and 12mL N ₂ H ₄ ·H ₂ O in 100mL ethylene glycol to obtain solution A;

2. Stir solution A evenly and then transfer it to a hydrothermal kettle and place it at 180°C for reaction for 24 hours to obtain reaction product I;

3. After the hydrothermal kettle is cooled to room temperature, the reaction product I is sequentially adsorbed and separated with a magnet, washed 4 times with deionized water and absolute ethanol, and dried in a vacuum at 50°C for 20 hours to obtain hollow structure Co microspheres. ;

4. Disperse 2 g of hollow Co microspheres in a mixed solution of 300 mL of absolute ethanol, 40 mL of ionized water, and 10 mL of ammonia water to obtain suspension B; the mass fraction of the ammonia water is 28%;

5. Add 10mL TEOS to suspension B, and then stir evenly to obtain suspension C;

6. React suspension C at room temperature for 3 hours to obtain suspension D;

7. Use a magnet to adsorb and separate the suspension D product, wash it with deionized water and absolute ethanol 5 times each, and dry it in a vacuum at 55°C for 24 hours to obtain hollow structure Co@SiO ₂ microspheres;

8. Disperse 2.0g hollow structure Co@SiO ₂ microspheres in 400mL deionized water to obtain suspension E;

9. Disperse 2000 μL pyrrole in suspension E to obtain suspension F;

10. Add 6.0g of ammonium persulfate to suspension F under ice bath conditions to obtain suspension G;

11. React suspension G under ice bath conditions for 8 hours to obtain suspension H;

12. Use a magnet to adsorb and separate the suspension H, wash it 5 times with deionized water and absolute ethanol, and dry it in a vacuum at 50°C for 24 hours to obtain a hollow core-shell structure Co@SiO ₂ @PPy composite material.

Figure 7 is an SEM image of the hollow structure Co microspheres described in Examples 1 to 3 after being etched with 0.1 mol/L HCl for 1 hour. It can be seen from Figure 7 that the center of the Co microspheres is a hollow structure, and the hollow volumes of different microspheres are Slightly different.

Claims (10)

1. A method for preparing hollow core-shell structure Co@SiO ₂ @PPy, which is characterized in that the preparation method is specifically completed according to the following steps: 1. Dissolve PVP, CoCl ₂ ·6H ₂ O, and N ₂ H ₄ ·H ₂ O in ethylene glycol to obtain solution A; 2. Stir solution A evenly and then transfer it to a hydrothermal kettle, and then place it in a hydrothermal reaction at 180°C for a period of time to obtain reaction product I; 3. After the hydrothermal kettle is cooled to room temperature, the reaction product I is separated by magnetic adsorption in sequence, and the solid product is washed and vacuum dried to obtain hollow structure Co microspheres; 4. Disperse the hollow structure Co microspheres in a mixed solution of deionized water, ammonia water, and absolute ethanol to obtain suspension B; 5. Add TEOS to suspension B, then stir evenly to obtain suspension C; 6. React suspension C at room temperature for a period of time to obtain suspension D; 7. The suspension D is subjected to magnetic adsorption separation in sequence, and the solid product is washed and vacuum dried to obtain hollow structure Co@SiO ₂ microspheres; 8. Disperse the hollow structure Co@SiO ₂ microspheres in deionized water to obtain suspension E; 9. Disperse pyrrole in suspension E to obtain suspension F; 10. Add the oxidizing agent to the suspension F under ice bath conditions to obtain the suspension G; 11. React suspension G under ice bath conditions for a period of time to obtain suspension H; 12. The suspension H is subjected to magnetic adsorption separation in sequence, and the obtained solid product is washed and vacuum dried to obtain the hollow core-shell structure Co@SiO ₂ @PPy. 2. A method for preparing hollow core-shell structure Co@SiO ₂ @PPy according to claim 1, characterized in that the concentration of PVP in solution A described in step 1 is 15g/L ~ 60g/L; step The concentration of CoCl ₂ ·6H ₂ O in solution A described in step 1 is 15g/L ~ 60g/L; the concentration of N ₂ H ₄ ·H ₂ O in solution A described in step 1 is 50mL/L ~ 150mL /L. 3. A method for preparing hollow core-shell structure Co@SiO ₂ @PPy according to claim 1, characterized in that the hydrothermal reaction time in step two is 4h to 48h. 4. The preparation method of a hollow core-shell structure Co@SiO ₂ @PPy according to claim 1, characterized in that the concentration of the hollow structure Co microspheres in the suspension B described in step 4 is 0.25g/ L～25g/L; the volume ratio of ammonia water, deionized water and absolute ethanol in the mixed solution of deionized water, ammonia water and absolute ethanol described in step 4 is (10～20): (40～60): (300～400); the mass fraction of ammonia water is 25%～28%. 5. A method for preparing hollow core-shell structure Co@SiO ₂ @PPy according to claim 1, characterized in that the concentration of TEOS in the turbid liquid C described in step five is 5 mL/L to 50 mL/L. 6. A method for preparing hollow core-shell structure Co@SiO ₂ @PPy according to claim 1, characterized in that the reaction time in step six is 0.5h to 12h. 7. A method for preparing hollow core-shell structure Co@SiO ₂ @PPy according to claim 1, characterized in that the concentration of hollow structure Co@SiO ₂ microspheres in the suspension E described in step eight is 0.25g/L～25g/L; the concentration of pyrrole in the suspension F described in step nine is 0.12mL/L～50mL/L. 8. A method for preparing hollow core-shell structure Co@SiO ₂ @PPy according to claim 1, characterized in that the oxidant described in step ten is APS, FeCl ₃ or FeCl ₃ ·6H ₂ O; The concentration of the oxidant in the suspension G is 0.12g/L ~ 150g/L. 9. A method for preparing hollow core-shell structure Co@SiO ₂ @PPy according to claim 1, characterized in that the reaction time of suspension G in step 1 under ice bath conditions is 4h to 24h. 10. Application of a hollow core-shell structure Co@SiO ₂ @PPy prepared by the preparation method according to claim 1, characterized in that a hollow core-shell structure Co@SiO ₂ @PPy is used as an electromagnetic wave absorbing material.