Preparation method and application of a multi-layer carbon sphere material

Abstract

The application discloses a preparation method and application of a multilayer carbon sphere material. Hollow carbon spheres are obtained by a hard template method, silica is used as a core, and phenolic resin (RF) is used as a shell. The multilayer hollow carbon spheres can be obtained by repeatedly and alternately wrapping the silica and the phenolic resin and then carbonizing and removing the core. By adjusting the particle size of the silica, multilayer carbon spheres with different particle sizes can be obtained. By adjusting the number of layers covered by the phenolic resin, the number of layers of the multilayer hollow carbon spheres can be adjusted. The hollow structure of the hollow carbon spheres reflects and scatters electromagnetic waves, and the interface polarization between the multilayer shells makes the multilayer hollow carbon spheres have excellent absorption effect on electromagnetic waves. The application provides a new preparation method for the multilayer hollow carbon spheres, successfully prepares single-layer, double-layer and three-layer carbon spheres with different particle sizes, the synthesis method is simple, raw material prices are low, and the obtained material has a wide application prospect in stealth technology.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wave-absorbing materials, and particularly relates to a preparation method of a multi-layer carbon sphere material and application thereof. BACKGROUND

[0002] With the rapid development of modern electronic technology, electromagnetic radiation pollution is becoming increasingly serious. Meanwhile, in the military field, in order to counter radar detection, the demand for high-performance wave-absorbing materials is extremely urgent. Carbon materials have great application potential in the field of wave-absorbing materials due to their unique electrical, magnetic and chemical properties. However, traditional carbon materials still have some deficiencies in wave-absorbing performance, such as narrow absorption frequency band and insufficient absorption intensity. Therefore, it is of great significance to develop new carbon-based wave-absorbing materials.

[0003] So far, breakthrough progress has been made in the preparation method of hollow carbon spheres. The internal structure of the synthesized material is controlled by changing the size and shape of the internal pore space through the structure guiding effect and order of the template. According to the different templates selected, it can be divided into hard template method, soft template method and template-free method. The hard template method is a method for preparing hollow carbon spheres by using a hard material as a template. In the process of preparing hollow carbon spheres, the template needs to be synthesized first, and the carbon precursor is filled on the surface and in the channel of the template. After high-temperature carbonization, according to the chemical properties of the template, the template is removed by calcination, decomposition or etching, and hollow carbon spheres with reverse replicated template structure can be obtained. In an ideal state, the material can maintain the original channel structure and morphology after the template is removed. The soft template method refers to a method for preparing hollow carbon spheres by using a soft material as a template. The soft template refers to an organic molecule or supramolecule with high amphiphilic molecules, such as block copolymer, surfactant micelle, emulsion droplet, bubble, etc., which can be used as a soft template for preparing ordered structure carbon materials. The advantage of the soft template preparation method is that the template is relatively easy to remove. However, due to the deformation of the soft template, it may cause uneven dispersion of the morphology and size of the hollow carbon spheres. The template-free method does not add a prepared template in the preparation process, so there is no need to remove the template later, and the preparation process is relatively simple. However, this method requires a strict reaction system, and a trace amount of impurities may affect the self-assembly behavior, which makes its practical application more difficult. SUMMARY

[0004] The present application aims to provide a preparation method of multi-layer carbon spheres. The three-layer carbon spheres prepared by the method have unique structure and excellent wave-absorbing performance. Another object of the present application is to provide the application of the multi-layer carbon spheres in wave-absorbing materials.

[0005] In order to achieve the above-mentioned objects, the present application adopts the following technical solutions:

[0006] A preparation method of a multi-layer carbon sphere material, which is obtained by repeatedly wrapping silica and phenolic resin, carbonizing and then removing the silica core.

[0007] The particle size of the silica is 70-1000 nm.

[0008] The specific steps of the preparation method of the multi-layer carbon sphere material are as follows:

[0009] (1) Synthesis of silica: a mixture of anhydrous ethanol, deionized water, tetraethyl orthosilicate, ammonia and potassium chloride is stirred to obtain a silica emulsion;

[0010] (2) Synthesis of SiO2@RF: resorcinol and formaldehyde are added to the silica emulsion obtained in step (1), and after stirring for 18 h, the obtained solid is centrifuged and dried at 80°C for 12 h, and then crushed to obtain SiO2@RF powder;

[0011] (3) Polyacrylic acid modified SiO2@RF: after the SiO2@RF powder is dissolved in deionized water, polyacrylic acid is added for reaction, and after the reaction is completed, the solution is centrifuged, and the washed solid is redissolved in deionized water to obtain a polyacrylic acid modified SiO2@RF solution;

[0012] (4) Synthesis of SiO2@RF@SiO2: anhydrous ethanol, ammonia and tetraethyl orthosilicate are added to the solution obtained in step (3) and stirred for 30 min to obtain an emulsion;

[0013] (5) Synthesis of SiO2@RF@SiO2@RF: resorcinol and formaldehyde are added to the emulsion obtained in step (4) and stirred for 18 h, and then centrifuged, and the obtained solid is dried at 80°C for 12 h, and then crushed to obtain SiO2@RF@SiO2@RF powder;

[0014] (6) Carbonization to form SiO2@C@SiO2@C: the powder obtained in step (5) is placed in a tube furnace, heated to 1000°C at a heating rate of 5°C / min under nitrogen atmosphere, and reacted for 2 hours, and then cooled to room temperature to obtain SiO2@C@SiO2@C;

[0015] (7) The SiO2@C@SiO2@C obtained in step (6) is placed in a sodium hydroxide aqueous solution and reacted at 80°C for 24 h, and then filtered and washed to neutral, and dried to obtain double-layer hollow carbon spheres;

[0016] (8) The SiO2@RF@SiO2@RF obtained in step (7) is repeated in steps (3)-(7) to obtain triple-layer hollow carbon spheres.

[0017] Furthermore, in step (1), the amounts of anhydrous ethanol, deionized water, tetraethyl orthosilicate, ammonia, and potassium chloride are 1500mL: 210mL: 68.4mL: (20-200mL): (0.2-4.4g).

[0018] Furthermore, in step (2), the amount of hydroquinone and formaldehyde used is 12g:16.8mL.

[0019] Furthermore, in step (3), the ratio of SiO2@RF powder to polyacrylic acid is 1:1.

[0020] Furthermore, in step (4), the ratio of anhydrous ethanol, ammonia, and tetraethyl orthosilicate is 200 mL: 10 mL: 1 mL.

[0021] Furthermore, in step (7), the concentration of the sodium hydroxide solution is 0.5 g / mL.

[0022] The present invention also provides multilayer hollow carbon spheres obtained by the above preparation method.

[0023] The present invention also provides a method for adjusting the particle size of silica, the specific steps of which are as follows:

[0024] (1) Synthesis of silica with particle size of 70-450nm: 1500ml of anhydrous ethanol, 210ml of deionized water, 68.4ml of tetraethyl orthosilicate and ammonia were added to a beaker and stirred for 30 minutes. After the reaction was completed, a white silica emulsion was obtained. The amount of ammonia was adjusted from 20ml to 200ml, and the silica particle size was adjusted from 70nm to 450nm.

[0025] (2) Synthesis of silica with particle size of 450-800nm: 1500mL of anhydrous ethanol, 210mL of deionized water, 68.4mL of tetraethyl orthosilicate, 800mL of ammonia and potassium chloride were added to a beaker and mixed and stirred for 30 minutes to obtain a white silica emulsion. The amount of potassium chloride was adjusted from 0.2 to 1.4g, and the silica particle size was adjusted from 450nm to 800nm.

[0026] (3) Synthesis of silica with a particle size of 800-1000nm: 750mL of anhydrous ethanol, 105mL of deionized water, 34.2mL of tetraethyl orthosilicate, 400mL of ammonia and 0.75g of potassium chloride were added to a beaker and mixed and stirred for 30 minutes. Then, another 750mL of anhydrous ethanol, 105mL of deionized water, 34.2mL of tetraethyl orthosilicate and 0.75g of potassium chloride were added to another beaker and added to the first beaker at a rate of 1mL / min. The dropping time was adjusted from 0 to 900min, and the silica particle size was changed from 800nm ​​to 1000nm.

[0027] In this invention, to obtain hollow carbon spheres of different sizes, it is first necessary to obtain silica of different sizes. This invention designs a sol-gel method for producing silica, by adjusting the amount of ammonia, adding potassium chloride, and using a seed growth method to obtain silica of different sizes, with the particle size adjustment range being 70 nanometers to 1000 nanometers.

[0028] Phenolic resin is synthesized from resorcinol and formaldehyde. When resorcinol and formaldehyde are added to a silica gel solution, the resulting phenolic resin adheres to the silica surface, forming a core-shell structure SiO2@RF with silica as the core and phenolic resin as the shell. The thickness of the phenolic resin shell can be easily altered by changing the amounts of resorcinol and formaldehyde, thus yielding hollow carbon spheres with varying shell thicknesses. Carbonizing the SiO2@RF core-shell structure at high temperature in a nitrogen atmosphere transforms the phenolic resin shell into a carbon shell. Finally, removing the silica with excess sodium hydroxide yields the hollow carbon spheres.

[0029] In order to enable silica to repeatedly coat the surface of phenolic resin without forming its own nucleation, this paper adopts a surface modification method to modify the phenolic resin with polyacrylic acid to achieve this effect.

[0030] The beneficial effects of this invention are as follows:

[0031] This invention provides a method for preparing hollow carbon spheres of different particle sizes, as well as novel methods for preparing double-layer and triple-layer hollow carbon spheres. In conventional sol-gel methods, adjusting the ammonia concentration only allows for silica particle sizes of 450 nm. However, this invention, by adding potassium chloride, utilizes the positively charged potassium ions adsorbed on the silica surface. This neutralizes the surface charge of silica, reducing the repulsive forces between silica particles and promoting silica aggregation and growth. During seed particle growth, the formation of secondary particles often leads to a distribution of different particle sizes. To suppress this, the supersaturation consumption rate of seed particle growth should be sufficient to deplete the generation rate. The seed growth method employs a low feed rate to reduce the supersaturation generation rate, allowing silica to continue growing instead of forming secondary particles. Furthermore, the phenolic resin shell surface is negatively charged, and the grown silica also carries a negative charge. Adding polyacrylic acid can modify the surface of the negatively charged silica, allowing silica to subsequently grow on the phenolic resin surface. This multi-layer coating method enables the preparation of multi-layer carbon spheres. Because multilayer carbon spheres have better impedance matching and interface polarization performance than single-layer carbon spheres, the 500nm double-layer hollow carbon spheres finally selected, with a paraffin filling ratio of 20% and a thickness of 2.5mm, achieved a minimum reflection loss RLmin of -43.87dB at 9.60GHz and an effective absorption bandwidth EAB of 6.00GHz (8.64-14.64GHz). Attached Figure Description

[0032] Figure 1 SEM images of hollow carbon spheres with different particle sizes: (a) 70 nm, (b) 300 nm, (c) 500 nm, (d) 650 nm, (e) 1000 nm; (f) TEM image of a 300 nm hollow carbon sphere.

[0033] Figure 2 TEM image of 500nm hollow carbon spheres modified with polyacrylic acid (a), and TEM image of 500nm hollow carbon spheres without polyacrylic acid modification (b);

[0034] Figure 3 TEM images of 500nm hollow carbon spheres with different numbers of layers: single layer (a), double layer (b), and triple layer (c).

[0035] Figure 4 Fourier transform infrared spectra of SiO2@RF before and after modification with polyacrylic acid;

[0036] Figure 5 The RL curves are for 70nm diameter monolayer hollow carbon spheres with a 20% filler ratio in the 2-18GHz frequency range.

[0037] Figure 6 The RL curves are for monolayer hollow carbon spheres with a particle size of 300 nm and a filler ratio of 20% in the 2-18 GHz frequency range.

[0038] Figure 7 The RL curves for 500nm diameter monolayer hollow carbon spheres with a 20% filler ratio are shown in the frequency range of 2-18GHz.

[0039] Figure 8 The RL curves are for 650nm diameter monolayer hollow carbon spheres with a 20% filler ratio in the 2-18GHz frequency range.

[0040] Figure 9 The RL curves are for monolayer hollow carbon spheres with a particle size of 1000 nm and a filler ratio of 20% in the 2-18 GHz frequency range.

[0041] Figure 10 RL curves for 500nm diameter double-layer hollow carbon spheres with a 20% filler ratio in the 2-18GHz frequency range;

[0042] Figure 11 The RL curves are for 500nm diameter three-layer hollow carbon spheres with a 20% filler ratio in the 2-18GHz frequency range. Detailed Implementation

[0043] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0044] Example 1

[0045] (1) Synthesis of silica: 1500 mL of anhydrous ethanol, 210 mL of deionized water, 68.4 mL of tetraethyl orthosilicate and 20 mL of ammonia were added to a beaker and mixed and stirred for 30 minutes to obtain a white silica emulsion with a silica particle size of 70 nm.

[0046] (2) Synthesis of SiO2@RF: 12g of resorcinol and 16.8mL of formaldehyde were added to the silica emulsion synthesized in step (1). After stirring and reacting for 18 hours, the solid was centrifuged and dried in an oven at 80°C for 12 hours. The resulting yellow SiO2@RF was then ground into powder using a mortar and pestle.

[0047] (3) Carbonization to form SiO2@C: The powder ground in step (2) is placed in an alumina square ceramic boat, which is then placed in a tube furnace. Nitrogen gas is connected, and the temperature is raised to 1000℃ at a rate of 5℃ / min. The carbonization reaction is carried out at 1000℃ for 2 hours. After the temperature in the tube furnace naturally cools down to room temperature, black SiO2@C is obtained.

[0048] (4) Removal of silica core: Dissolve 60g of sodium hydroxide in 120mL of deionized water to obtain sodium hydroxide solution. Then add 30g of SiO2@C obtained in step (3) to 120mL of sodium hydroxide solution. Heat to 80℃ and stir for 24 hours. After the reaction is completed, filter the solution and wash it several times until the filtrate is neutral. After washing, dry the solid obtained in an oven at 80℃ for 12 hours. After drying, grind the solid into powder to obtain a single-layer hollow carbon ball with a particle size of 70 nm.

[0049] like Figure 5 As shown, the sample exhibits the lowest reflection loss RL when the paraffin filling ratio is 20% and the thickness is 2.5 mm. min It reaches -16.81dB at 13.20GHz, with an effective absorption bandwidth (EAB) of 3.04GHz (11.44-14.48GHz).

[0050] Example 2

[0051] The other steps are the same as in Example 1, except that the amount of ammonia used is 90 mL, and the resulting monolayer hollow carbon spheres have a particle size of 300 nm. Figure 6 As shown, the sample exhibits the lowest reflection loss RL when the paraffin filling ratio is 20% and the thickness is 2 mm.min It reaches -14.27dB at 13.20GHz, with an effective absorption bandwidth (EAB) of 4.00GHz (12.00-16.00GHz).

[0052] Example 3

[0053] (1) Synthesis of silica: 1500mL of anhydrous ethanol, 210mL of deionized water, 68.4mL of tetraethyl orthosilicate, 800mL of ammonia and 0.4g of potassium chloride were added to a beaker and mixed and stirred for 30 minutes to obtain a white silica emulsion with a silica particle size of 500nm; Steps (2)-(4) are the same as in Example 1.

[0054] like Figure 7 As shown, the sample exhibits the lowest reflection loss RL when the paraffin filling ratio is 20% and the thickness is 2 mm. min It reaches -19.87dB at 11.84GHz, with an effective absorption bandwidth (EAB) of 4.00GHz (14.56-14.56GHz).

[0055] Example 4

[0056] The other steps are the same as in Example 3, except that when the amount of potassium chloride is 1.0g, the resulting silica particle size is 650nm.

[0057] like Figure 8 As shown, the sample exhibits the lowest reflection loss RL when the paraffin filling ratio is 20% and the thickness is 2.5 mm. min It reaches -8.17dB at 13.28GHz, with an effective absorption bandwidth (EAB) of 0.

[0058] Example 5

[0059] (1) Synthesis of silica: 750 mL of anhydrous ethanol, 105 mL of deionized water, 34.2 mL of tetraethyl orthosilicate, 400 mL of ammonia and 0.75 g of potassium chloride were added to a beaker and mixed and stirred for 30 minutes. Then, another 750 mL of anhydrous ethanol, 105 mL of deionized water, 34.2 mL of tetraethyl orthosilicate and 0.75 g of potassium chloride were added to another beaker and mixed evenly. The mixture was then added to the first beaker at a rate of 1 mL / min for 900 min. The silica particle size was 1000 nm. Steps (2) to (4) were the same as in Example 1.

[0060] like Figure 9 As shown, the sample exhibits the lowest reflection loss RL when the paraffin filling ratio is 20% and the thickness is 2.5 mm. min It reaches -8.32dB at 12.48, with an effective absorption bandwidth (EAB) of 0.

[0061] SEM images of monolayer hollow carbon spheres of different particle sizes obtained in Examples 1-5 are shown below. Figure 1 As shown.

[0062] Example 6

[0063] (1) Synthesis of 500nm silica particles: 1500mL of anhydrous ethanol, 210mL of deionized water, 68.4mL of tetraethyl orthosilicate, 400mL of ammonia and 0.5g of potassium chloride were added to a beaker and mixed and stirred for 30 minutes to obtain a white silica emulsion.

[0064] (2) Synthesis of SiO2@RF: 12g of resorcinol and 16.8mL of formaldehyde were added to the silica emulsion obtained in step (1), and the reaction was continued for 18 hours. After centrifugation, the solid was dried in an oven at 80°C for 12 hours. Then the yellow SiO2@RF was ground into powder using a mortar and pestle.

[0065] (3) Polyacrylic acid modified SiO2@RF: Add 60mL of deionized water to 1g of SiO2@RF powder ground in step (2) and stir evenly. Then add 1g of polyacrylic acid and continue stirring for 3 hours. After the reaction is completed, centrifuge the solution and wash it with deionized water. Dissolve the solid after centrifugation in 60mL of deionized water to obtain the polyacrylic acid modified solution. Figure 4 These are the Fourier transform infrared spectra of SiO2@RF before and after polyacrylic acid modification. As shown in the figure, the SiO2@RF spectrum before polyacrylic acid modification is at 1456 cm⁻¹. -1 1540cm -1 1612cm -1 The absorption peak at 800 cm⁻¹ can be attributed to the skeletal vibration of the benzene ring in the phenolic resin, while the peak at 800 cm⁻¹ is at 800 cm⁻¹. -1 The absorption peak at 1101 cm⁻¹ is attributed to the out-of-plane bending vibration of CH₄ on the benzene ring in the phenolic resin; -1 The absorption peak at 3205 cm⁻¹ can be attributed to the stretching vibration of the CO-C bond in the phenolic resin; while the absorption peak at 3205 cm⁻¹ can be attributed to the stretching vibration of the CO-C bond in the phenolic resin. -1 The absorption peak at [location missing] is caused by the stretching vibration of the OH bond in the phenolic hydroxyl group of the phenolic resin. In addition to the absorptions observed at the aforementioned locations, polyacrylic acid-modified SiO2@RF also exhibits a peak at 3414 cm⁻¹. -1 Located at 1718cm -1 The absorption peaks appearing at these points can be attributed to the stretching vibrations of the OH bond in the carboxyl group and the C=O bond in the carboxyl group, respectively. These are characteristic peaks in the infrared spectrum of polyacrylic acid, proving that the modification of polyacrylic acid was successful.

[0066] (4) Synthesis of SiO2@RF@SiO2: The solution modified by polyacrylic acid in step (3) was added to 400 mL of ethanol, and then 20 mL of ammonia and 2 mL of tetraethyl orthosilicate were added in sequence. The mixture was stirred for 30 minutes to obtain an emulsion.

[0067] (5) Synthesis of SiO2@RF@SiO2@RF: 1.2g of resorcinol and 1.68mL of formaldehyde were added to the emulsion synthesized in step (4). After stirring for 18 hours, the solid was centrifuged and dried in an oven at 80°C for 12 hours. The resulting solid was then ground into powder using a mortar and pestle.

[0068] (6) Carbonization to form SiO2@C@SiO2@C: The powder ground in step (5) is placed in an alumina square ceramic boat, which is then placed in a tube furnace. Nitrogen gas is connected, and the temperature is raised to 1000℃ at a rate of 5℃ / min. The carbonization reaction is carried out at 1000℃ for 2 hours. After the temperature in the tube furnace naturally cools down to room temperature, black SiO2@C is obtained.

[0069] (7) Removal of silica cores: Dissolve a slightly excess amount of sodium hydroxide in deionized water to obtain a sodium hydroxide solution of 0.5 g / ml. Then add the SiO2@C@SiO2@C obtained in step (6) to the sodium hydroxide solution. The mass ratio of sodium hydroxide to SiO2@C@SiO2@C is 2:1. Heat to 80°C and stir for 24 hours. After the reaction is complete, filter the solution and wash it several times until the filtrate is neutral. After washing, dry the solid obtained in an oven at 80°C for 12 hours. After drying, grind the solid into powder to obtain double-layer hollow carbon spheres. TEM image is shown below. Figure 3 As shown in b.

[0070] like Figure 10 As shown, the sample exhibits the lowest reflection loss RL when the paraffin filling ratio is 20% and the thickness is 2.5 mm. min It reaches -43.87dB at 9.60GHz, with an effective absorption bandwidth (EAB) of 6.00GHz (8.64-14.64GHz).

[0071] Example 7

[0072] Take 1g of the powder obtained in step 5 of Example 4 and follow the steps (3)-(7) of Example 4 to obtain three-layer hollow carbon spheres. The TEM image is shown below. Figure 3 As shown in c.

[0073] like Figure 11 As shown, the sample exhibits the lowest reflection loss RL when the paraffin filling ratio is 20% and the thickness is 2.0 mm. minIt reaches -20.49dB at 11.76GHz, with an effective absorption bandwidth (EAB) of 4.00GHz (10.08-14.08GHz).

[0074] Comparative Example 1

[0075] The specific steps are the same as in Example 6, except that polyacrylic acid is not added in step (3); the results are as follows Figure 2 As shown, a double-layered hollow structure cannot be obtained without the addition of polyacrylic acid modification.

[0076] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A method for preparing a multilayer carbon sphere material, characterized in that: The multilayer carbon sphere material uses silicon dioxide as the core and polyacrylic acid modified phenolic resin as the shell. Multilayer hollow carbon spheres can be obtained by repeatedly and alternately wrapping silicon dioxide and phenolic resin, carbonizing, and then removing the silicon dioxide core. The specific steps of the preparation method are as follows: (1) Synthesis of silica: Anhydrous ethanol, deionized water, tetraethyl orthosilicate, ammonia and potassium chloride were mixed and stirred to obtain silica emulsion; (2) Synthesis of SiO2@RF: Resorcinol and formaldehyde were added to the silica emulsion obtained in step (1), and the mixture was stirred for 18 hours and then centrifuged. The resulting solid was dried at 60-80℃ for 12 hours and then pulverized to obtain SiO2@RF powder. (3) Polyacrylic acid modified SiO2@RF: After dissolving SiO2@RF powder in deionized water, polyacrylic acid is added to react. After the reaction is completed, the solution is centrifuged and the washed solid is redissolved in deionized water to obtain polyacrylic acid modified SiO2@RF solution. (4) Synthesis of SiO2@RF@SiO2: Anhydrous ethanol, ammonia and tetraethyl orthosilicate were added to the solution obtained in step (3) and stirred for 30 min to obtain an emulsion; (5) Synthesis of SiO2@RF@SiO2@RF: Add resorcinol and formaldehyde to the emulsion obtained in step (4), stir and react for 18 hours, then centrifuge. Dry the obtained solid at 60-80℃ for 12 hours, and then pulverize to obtain SiO2@RF@SiO2@RF powder. (6) Carbonization to form SiO2@C@SiO2@C: The powder obtained in step (5) is placed in a tube furnace and heated to 1000°C at a heating rate of 5°C / min under a nitrogen atmosphere. The reaction is carried out for 2 hours and SiO2@C@SiO2@C is obtained after cooling to room temperature. (7) Place the SiO2@C@SiO2@C obtained in step (6) in an aqueous sodium hydroxide solution and react at 80°C for 24 hours. After the reaction, filter and wash the solution until it is neutral and then dry it to obtain double-layer hollow carbon spheres.

2. The preparation method according to claim 1, characterized in that: The silicon dioxide has a particle size of 70-1000 nm.

3. The preparation method according to claim 1, characterized in that: In step (1), the amounts of anhydrous ethanol, deionized water, tetraethyl orthosilicate, ammonia, and potassium chloride are 1500mL: 210mL: 68.4mL: (20-200mL): (0.2-1.4g).

4. The preparation method according to claim 1, characterized in that: In step (2), the amount of hydroquinone and formaldehyde used is 12g:16.8mL.

5. The preparation method according to claim 1, characterized in that: In step (3), the ratio of SiO2@RF powder to polyacrylic acid is 1:

1.

6. The preparation method according to claim 1, characterized in that: In step (4), the ratio of anhydrous ethanol, ammonia, and tetraethyl orthosilicate is 200 mL: 10 mL: 1 mL.

7. The preparation method according to claim 1, characterized in that: In step (7), the concentration of sodium hydroxide solution is 0.5 g / mL.

8. The multilayer hollow carbon spheres obtained by the preparation method according to any one of claims 1-7.

Images