Porous carbon-rich siocn nanospheres with excellent wave-absorbing performance and a preparation method thereof

Abstract

The application discloses porous carbon-rich SiOCN nanospheres with excellent wave-absorbing performance and a preparation method thereof, and comprises the following steps: S1, dropping SiOC ceramic precursor into a hydrolysis solution and stirring to obtain a SiOC ceramic precursor mixed solution; S2, adding an acid catalyst into the mixed solution and stirring to hydrolyze the SiOC ceramic precursor; S3, continuously adding an alkali catalyst after the hydrolysis and stirring to form a SiOC nanosphere particle mixed solution through polycondensation; S4, adding a carbon phase precursor into the SiOC nanosphere particle mixed solution and stirring, centrifuging and drying to obtain porous carbon-rich nanosphere precursors; and S5, pyrolyzing the porous carbon-rich nanosphere precursors under a protective atmosphere to obtain the porous carbon-rich SiOCN nanospheres; and the weight ratio of the SiOC ceramic precursor, the acid catalyst, the alkali catalyst and the carbon phase precursor is (5-15):(0.5-2.0):(1-10):(2-6).

Description

Technical Field

[0001] This invention relates to the fields of precursor ceramic conversion for preparing ceramic powder and electromagnetic protection technology, specifically to a SiOCN nanosphere with excellent microwave absorption properties and its preparation method. Background Technology

[0002] Precursor ceramic conversion methods offer the advantage of on-demand design of ceramic powders at the atomic level, enabling functional applications and thus finding wide application across various fields. Electromagnetic waves, due to their advantages in long-distance, wireless, and high-speed transmission, have ushered in the 5G era. While this era brings convenience, electromagnetic pollution problems such as electromagnetic interference and radiation are becoming increasingly serious. Electromagnetic pollution not only affects the normal operation of electronic devices but also significantly threatens information security in the scientific community and harms human health. Therefore, developing a thin, lightweight, strong, and wide-bandgap high-efficiency absorbing material is an urgent problem to be solved.

[0003] SiOC precursor ceramics can be viewed as products of oxygen atoms being replaced by carbon atoms in the SiO2 network, leading to increased bond density and improved mechanical properties and thermal stability. Simultaneously, the presence of free carbon in the SiOC matrix helps reduce infrared radiation heat transfer, making it a promising high-temperature insulation material. However, due to the low content of SiC nanocrystals and free carbon in SiOC ceramics, their microwave absorption performance is not ideal. Therefore, improving the microwave absorption performance of SiOC ceramics while simultaneously maintaining their thermal insulation properties has become a hot research topic.

[0004] As is well known, in addition to the composition of materials affecting microwave absorption performance, the control of material structure and morphology is also an important parameter affecting microwave absorption performance. Porous nanospheres have abundant specific surface area and mesopores. Incident electromagnetic waves undergo multiple reflections within the mesopores, thus dissipating electromagnetic energy. Meanwhile, the unique free carbon network layer facilitates the transport of free electrons, forming a conductive network within the ceramic matrix surface to enhance conductivity loss. Summary of the Invention

[0005] The purpose of this invention is to address the problem of unsatisfactory microwave absorption performance of SiOC ceramics by proposing a method for preparing porous carbon-rich SiOCN nanospheres, thereby achieving excellent microwave absorption performance in the obtained material.

[0006] This invention is achieved through the following technical solution:

[0007] This invention provides a method for preparing porous carbon-rich SiOCN nanospheres with excellent microwave absorption properties, the method comprising the following steps:

[0008] S1. Provide SiOC ceramic precursor and add it dropwise to the hydrolysate, stirring to obtain SiOC ceramic precursor mixture;

[0009] S2. Add an acid catalyst dropwise to the SiOC ceramic precursor mixture and stir to promote the hydrolysis of the SiOC ceramic precursor;

[0010] S3. After hydrolysis, continue to add alkaline catalyst to the system, stir, and condense to form a mixed solution of SiOC nanospheres;

[0011] S4. Add a carbon phase precursor to the SiOC nanosphere particle mixed solution, stir, centrifuge, and dry to obtain a porous carbon-rich nanosphere precursor.

[0012] S5. Under a nitrogen atmosphere, the porous carbon-rich nanosphere precursor is pyrolyzed to obtain porous carbon-rich SiOCN nanospheres.

[0013] The weight ratio of the SiOC ceramic precursor, acid catalyst, base catalyst and carbon phase precursor is (5-15):(0.5-2.0):(1-10):(2-6).

[0014] Furthermore, a method for preparing porous carbon-rich SiOCN nanospheres with excellent microwave absorption properties: Step S1, providing a SiOC ceramic precursor and adding it dropwise to a hydrolysate, stirring for 10-15 minutes to obtain a SiOC ceramic precursor mixture; wherein: the hydrolysate is composed of deionized water and anhydrous ethanol in a weight ratio of (10-20):(80-120); the weight ratio of the SiOC ceramic precursor to the hydrolysate is (5-15):(90-140).

[0015] Furthermore, a method for preparing porous carbon-rich SiOCN nanospheres with excellent microwave absorption properties is provided: the SiOC ceramic precursor is selected from at least one of tetraethyl orthosilicate, methyltrimethoxysilane, dimethyldimethoxysilane, and phenyltriethoxysilane.

[0016] Furthermore, a method for preparing porous carbon-rich SiOCN nanospheres with excellent microwave absorption properties: Step S2, add an acid catalyst dropwise to the SiOC ceramic precursor mixture and stir for 2 to 8 hours to promote the hydrolysis of the SiOC ceramic precursor; the acid catalyst is selected from nitric acid, hydrochloric acid, and acetic acid.

[0017] Furthermore, a method for preparing porous carbon-rich SiOCN nanospheres with excellent microwave absorption properties is as follows: Step S3, after hydrolysis, an alkaline catalyst is added to the system and stirred for 12-24 hours to condense and form a mixed solution of SiOC nanosphere particles; the alkaline catalyst is selected from KOH, NaOH, and ammonia water.

[0018] Furthermore, a method for preparing porous carbon-rich SiOCN nanospheres with excellent microwave absorption properties: Step S4, add a carbon phase precursor to the SiOC nanosphere particle mixed solution, stir for 12-24 hours, centrifuge at a speed of 3000-10000 rpm for 2-5 minutes, and dry to obtain a porous carbon-rich nanosphere precursor; wherein: the carbon phase precursor is resorcinol and formaldehyde; by weight, the weight ratio between the SiOC ceramic precursor, resorcinol and formaldehyde is (5-15):(1-3):(1-3).

[0019] Furthermore, a method for preparing porous carbon-rich SiOCN nanospheres with excellent microwave absorption properties: Step S5, under a nitrogen atmosphere, the temperature is increased from room temperature to 1200-1500℃ at a rate of 1-5℃ / min and maintained for 2-4 hours to perform high-temperature pyrolysis on the porous carbon-rich nanosphere precursor, thereby obtaining porous carbon-rich SiOCN nanospheres.

[0020] The present invention also provides a porous carbon-rich SiOCN nanosphere with excellent microwave absorption performance, which is prepared by the above-described preparation method.

[0021] To address the issue of unsatisfactory microwave absorption performance of standalone SiOC ceramics, this invention proposes a solution: SiOC ceramic precursors are used to form spherical SiOC structures under alkaline conditions. Resorcinol and formaldehyde are then introduced as carbon-phase precursors, leading to in-situ polymerization on the surface of the SiOC nanospheres to form a free carbon network structure. The composition and structure of the porous carbon-rich SiOCN nanospheres are controlled by adjusting the proportion of SiOC ceramic precursors, process parameters, and the amount of carbon-phase precursors added. The large specific surface area of ​​the porous SiOCN nanospheres increases the reflection and scattering of incident electromagnetic waves, thereby improving the absorption capacity. Furthermore, the free carbon network layer constructs an excellent conductive network to enhance electrical conductivity. After pyrolysis, the in-situ generated SiC, Si3N4, and free carbon form abundant heterogeneous interfaces with the SiOC ceramic matrix, causing interfacial polarization and enhancing electromagnetic wave dissipation. The synergistic effect of multiple loss mechanisms results in excellent microwave absorption performance of the obtained material.

[0022] The porous carbon-rich SiOCN nanospheres obtained in this invention exhibit a maximum reflection coefficient of -60.74 dB at a material thickness of 1.62 mm and a maximum effective absorption bandwidth of 5.14 GHz at a material thickness of 2.51 mm. Furthermore, by adjusting the material thickness, the effective absorption bandwidth can cover the entire C, X, and Ku frequency bands. The porous carbon-rich SiOCN nanospheres prepared in this invention demonstrate superior reflection coefficient and effective bandwidth compared to most current SiOC-based absorbing materials.

[0023] The beneficial effects of this invention are:

[0024] (1) The method of this invention combines the advantages of porous nanosphere structure and free carbon network conductive layer to prepare porous carbon-rich SiOCN nanospheres as microwave absorbing materials. During the preparation process, it is necessary to precisely control the SiOC ceramic precursor ratio, process parameters, and carbon phase precursor introduction amount. The SiOC ceramic precursor ratio and process parameters affect the attenuation ability of SiOC ceramic to electromagnetic waves, while the carbon phase precursor introduction amount seriously affects the impedance matching and attenuation coefficient of SiOC ceramic. Improper impedance matching control will be detrimental to the improvement of microwave absorption performance. Therefore, to obtain porous carbon-rich SiOCN nanospheres with excellent microwave absorption performance, it is necessary to precisely control the SiOC ceramic precursor ratio, process parameters, and carbon phase precursor introduction amount.

[0025] (2) The preparation method of the present invention is a method for preparing porous carbon-rich SiOCN nanospheres by precursor conversion. This method has the advantages of high preparation yield, short cycle, controllable composition and structure, and the raw materials used are widely available and inexpensive.

[0026] (3) The method of the present invention controls the proportion of SiOC ceramic precursors through chemical composition design to prepare porous carbon-rich SiOCN nanospheres. The large specific surface area of ​​the porous nanospheres increases the reflection and scattering of incident electromagnetic waves to improve the absorption of electromagnetic waves. The free carbon network layer constructs an excellent conductive network to enhance the conductivity loss. The SiC or Si3N4 produced by pyrolysis forms a rich heterogeneous interface with the free carbon and SiOC ceramic matrix, causing interface polarization to enhance the electromagnetic wave dissipation capability. The synergistic effect of multiple loss mechanisms realizes the absorption performance of C, X and Ku bands, so that the obtained material has excellent wave absorption performance.

[0027] (4) The porous carbon-rich SiOCN nanospheres prepared in this invention exhibit the strongest reflectance coefficient of -60.74 dB at a thickness of 1.62 mm; and the widest effective absorption bandwidth reaches 5.14 GHz at a thickness of 2.51 mm. Furthermore, by adjusting the material thickness, the effective absorption bandwidth can cover the entire C, X, and Ku frequency bands. The absorption intensity and bandwidth of these porous carbon-rich SiOCN nanospheres are superior to most current SiOC ceramic matrix composites, and they are expected to have good application prospects in the field of high-temperature electromagnetic protection. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 SEM images of porous carbon-rich SiOCN nanospheres prepared in Example 1 and curves showing the relationship between microwave absorption performance and frequency and thickness in the 2-18 GHz frequency band.

[0030] Figure 2 SEM images of porous carbon-rich SiOCN nanospheres prepared in Example 2 and curves showing the relationship between microwave absorption performance and frequency and thickness in the 2-18 GHz frequency band.

[0031] Figure 3 SEM images of porous carbon-rich SiOCN nanospheres prepared in Example 3 and curves showing the relationship between microwave absorption performance and frequency and thickness in the 2-18 GHz frequency band.

[0032] Figure 4 The image shows the SEM morphology of the porous carbon-rich SiOCN nanospheres prepared in Example 4 and the curves showing the relationship between the absorption performance and the frequency and thickness in the 2-18 GHz frequency band. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0034] Example 1

[0035] A method for preparing porous carbon-rich SiOCN nanospheres with excellent microwave absorption properties is provided, the method comprising the following specific steps:

[0036] S1. Weigh 12.0g of SiOC ceramic precursor (which includes 10.0g of tetraethyl orthosilicate and 2.0g of dimethyldimethoxysilane) and add it dropwise to a hydrolysate consisting of 100.0g of anhydrous ethanol and 18.0g of deionized water. Stir for 15 minutes to obtain a SiOC ceramic precursor mixture.

[0037] S2. Add 0.5g of nitric acid (acid catalyst) dropwise to the above SiOC ceramic precursor mixture and stir for 5 hours to promote the hydrolysis of the SiOC ceramic precursor.

[0038] S3. After hydrolysis, add 5.0g of ammonia (alkaline catalyst) to the system and stir for 15 hours to condense and form a mixed solution of SiOC nanospheres.

[0039] S4. Add 1.0 g of resorcinol and 1.4 g of methanol as carbon phase precursors to the obtained SiOC nanosphere particle mixed solution, stir for 24 hours, then place in a centrifuge and centrifuge at 5000 rpm for 3 minutes, and dry after centrifugation to obtain porous carbon-rich nanosphere precursors.

[0040] S5. Under the protection of argon atmosphere, the temperature is increased from room temperature to 1450℃ at a rate of 5℃ / min and maintained at this temperature for 2 hours to perform high-temperature pyrolysis of the porous carbon-rich nanosphere precursor. Then, it is cooled to room temperature to prepare porous carbon-rich SiOCN nanospheres.

[0041] The microwave absorption performance of the porous carbon-rich SiOCN nanospheres obtained in Example 1 in the 2–18 GHz frequency band was tested using the coaxial testing method of a Detech vector network analyzer. During the test, the porous carbon-rich SiOCN nanospheres from Example 1 were uniformly mixed with solid paraffin at a mass ratio of 1:1 at 70°C, and then pressed into a coaxial ring with an inner diameter of 3.04 mm, an outer diameter of 7.0 mm, and a thickness of 2.0 mm for testing. The test results are as follows: Figure 1 As shown, Figure 1 These are SEM images of the porous carbon-rich SiOCN nanospheres obtained in Example 1, and curves showing the relationship between the reflectance coefficient and frequency and thickness; Figure 1 It can be seen that when the material thickness is 1.81mm, the minimum reflection coefficient is -50.43dB, indicating that it can dissipate 99.999% of electromagnetic energy, and its absorption performance is excellent. When the material thickness is 2.51mm, the frequency band with a reflection coefficient less than -10dB can cover 10.99~16.13GHz, and its effective absorption bandwidth can reach about 5.14GHz. However, the frequency band coverage with a reflection coefficient less than -10dB is smaller at other thicknesses.

[0042] Example 2

[0043] A method for preparing porous carbon-rich SiOCN nanospheres with excellent microwave absorption properties is provided, the method comprising the following specific steps:

[0044] S1. Weigh 7.0g of tetraethyl orthosilicate and 1.0g of phenyltriethoxysilane, and add them dropwise to a hydrolysate consisting of 80.0g of anhydrous ethanol and 15.0g of deionized water. Stir for 12 minutes to obtain a SiOC ceramic precursor mixture.

[0045] S2. Add 0.6g of hydrochloric acid dropwise to the above SiOC ceramic precursor mixture and stir for 7 hours to promote the hydrolysis of the SiOC ceramic precursor.

[0046] S3. After hydrolysis, add 3.0 g of NaOH to the system and stir for 24 hours to condense and form a mixed solution of SiOC nanospheres.

[0047] S4. Add 2.0 g of resorcinol and 2.8 g of methanol as carbon phase precursors to the obtained SiOC nanosphere particle mixed solution, stir for 18 hours, then place in a centrifuge and centrifuge at 3000 rpm for 5 minutes, and dry after centrifugation to obtain porous carbon-rich nanosphere precursors.

[0048] S5. Under nitrogen atmosphere protection, the temperature is increased from room temperature to 1500℃ at a rate of 5℃ / min and maintained at this temperature for 2 hours to perform high-temperature pyrolysis of the porous carbon-rich nanosphere precursor. Then, it is cooled to room temperature to prepare porous carbon-rich SiOCN nanospheres.

[0049] The microwave absorption performance of the porous carbon-rich SiOCN nanospheres obtained in Example 2 in the 2–18 GHz frequency band was tested using the coaxial testing method of a Detech vector network analyzer. During the test, the porous carbon-rich SiOCN nanospheres from Example 2 were uniformly mixed with solid paraffin at a mass ratio of 7:3 at 70°C, and then pressed into a coaxial ring with an inner diameter of 3.04 mm, an outer diameter of 7.0 mm, and a thickness of 2.0 mm for testing. The test results are as follows: Figure 2 As shown, Figure 2 These are SEM images of the porous carbon-rich SiOCN nanospheres obtained in Example 2, and curves showing the relationship between the reflectance coefficient and frequency and thickness; Figure 2 It can be seen that when the material thickness is 1.51 mm, the minimum reflection coefficient is -38.46 dB, indicating that it can dissipate 99.9% of electromagnetic energy, demonstrating excellent absorption performance. When the material thickness is 2.01 mm, the frequency band with a reflection coefficient less than -10 dB can cover 11.29–15.30 GHz, with an effective absorption bandwidth of approximately 4.01 GHz. At other thicknesses, the frequency band coverage with a reflection coefficient less than -10 dB is smaller. Furthermore, by adjusting the material thickness, a reflection coefficient less than -10 dB can cover the C, X, and Ku frequency bands.

[0050] Example 3

[0051] A method for preparing porous carbon-rich SiOCN nanospheres with excellent microwave absorption properties is provided, the method comprising the following specific steps:

[0052] S1. Weigh 8.0g of tetraethyl orthosilicate and 2.0g of dimethyldimethoxysilane, and add them dropwise to a hydrolysate consisting of 100.0g of anhydrous ethanol and 15.0g of deionized water. Stir for 15 minutes to obtain a SiOC ceramic precursor mixture.

[0053] S2. Add 0.5g of nitric acid dropwise to the above SiOC ceramic precursor mixture and stir for 6 hours to promote the hydrolysis of the SiOC ceramic precursor.

[0054] S3. After hydrolysis, add 5.0g of ammonia water to the system and stir for 24 hours to condense and form a mixed solution of SiOC nanospheres.

[0055] S4. Add 2.0 g of resorcinol and 2.8 g of methanol as carbon phase precursors to the obtained SiOC nanosphere particle mixed solution, stir for 24 hours, then place in a centrifuge and centrifuge at 10000 rpm for 2 minutes, and dry after centrifugation to obtain porous carbon-rich nanosphere precursors.

[0056] S5. Under nitrogen atmosphere protection, the temperature is increased from room temperature to 1250℃ at a rate of 3℃ / min and maintained at this temperature for 4 hours to perform high-temperature pyrolysis of the porous carbon-rich nanosphere precursor. Then, it is cooled to room temperature to prepare porous carbon-rich SiOCN nanospheres.

[0057] The microwave absorption performance of the porous carbon-rich SiOCN nanospheres obtained in Example 3 in the 2–18 GHz frequency band was tested using the coaxial testing method of a Detech vector network analyzer. During the test, the porous carbon-rich SiOCN nanospheres of Example 3 were uniformly mixed with solid paraffin at a mass ratio of 7:3 at 70°C, and then pressed into a coaxial ring with an inner diameter of 3.04 mm, an outer diameter of 7.0 mm, and a thickness of 2.0 mm for testing. The test results are as follows: Figure 3 As shown, Figure 3 These are SEM images of the porous carbon-rich SiOCN nanospheres obtained in Example 3, and curves showing the relationship between the reflectance coefficient and frequency and thickness; Figure 3 It can be seen that when the material thickness is 3.85mm, the minimum reflection coefficient is -54.55dB, indicating that it can dissipate 99.999% of electromagnetic energy, demonstrating excellent absorption performance. When the material thickness is 3.05mm, the frequency band with a reflection coefficient less than -10dB can cover 6.60~10.73GHz, with an effective absorption bandwidth of approximately 4.13GHz. Furthermore, by adjusting the material thickness, a reflection coefficient less than -10dB can cover the C, X, and Ku frequency bands.

[0058] Example 4

[0059] A method for preparing porous carbon-rich SiOCN nanospheres with excellent microwave absorption properties is provided, the method comprising the following specific steps:

[0060] S1. Weigh 10.0g of tetraethyl orthosilicate and 2.0g of methyltrimethoxysilane, and add them dropwise to a hydrolysate consisting of 90.0g of anhydrous ethanol and 15.0g of deionized water. Stir for 10 minutes to obtain a SiOC ceramic precursor mixture.

[0061] S2. Add 0.7g of nitric acid dropwise to the above SiOC ceramic precursor mixture and stir for 5 hours to promote the hydrolysis of the SiOC ceramic precursor.

[0062] S3. After hydrolysis, add 7.0g of ammonia water to the system and stir for 12 hours to condense and form a mixed solution of SiOC nanospheres.

[0063] S4. Add 1.0 g of resorcinol and 1.4 g of methanol as carbon phase precursors to the obtained SiOC nanosphere particle mixed solution, stir for 24 hours, then place in a centrifuge and centrifuge at 5000 rpm for 2 minutes, and dry after centrifugation to obtain porous carbon-rich nanosphere precursors.

[0064] S5. Under nitrogen atmosphere protection, the temperature is increased from room temperature to 1350℃ at a rate of 3℃ / min and maintained at this temperature for 3 hours to perform high-temperature pyrolysis of the porous carbon-rich nanosphere precursor. Then, it is cooled to room temperature to prepare porous carbon-rich SiOCN nanospheres.

[0065] The microwave absorption performance of the porous carbon-rich SiOCN nanospheres obtained in Example 4 in the 2–18 GHz frequency band was tested using the coaxial testing method of a Detech vector network analyzer. During the test, the porous carbon-rich SiOCN nanospheres from Example 4 were uniformly mixed with solid paraffin at a mass ratio of 7:3 at 70°C, and then pressed into a coaxial ring with an inner diameter of 3.04 mm, an outer diameter of 7.0 mm, and a thickness of 2.0 mm for testing. The test results are as follows: Figure 4 As shown, Figure 4 These are SEM images of the porous carbon-rich SiOCN nanospheres obtained in Example 4, and curves showing the relationship between the reflectance coefficient and frequency and thickness; Figure 4 It can be seen that when the material thickness is 1.62mm, the minimum reflection coefficient is -60.74dB, indicating that it can dissipate 99.9999% of electromagnetic energy, and its wave absorption performance is excellent. When the material thickness is 2.52mm, the frequency band with a reflection coefficient of less than -10dB can cover 7.81~12.37GHz, and its effective wave absorption bandwidth is about 4.56GHz.

[0066] The test results from Examples 1-4 above show that the porous carbon-rich SiOCN nanospheres prepared in this invention exhibit a maximum reflection coefficient of -60.74 dB at a thickness of 1.62 mm; and a maximum effective absorption bandwidth of approximately 5.14 GHz at a thickness of 2.51 mm. Furthermore, by adjusting the material thickness, the effective absorption bandwidth can cover the entire C, X, and Ku frequency bands. The absorption intensity and bandwidth of the porous carbon-rich SiOCN nanospheres prepared in this invention are superior to most current SiOC ceramic matrix composites, and they are expected to have good application prospects in the field of high-temperature electromagnetic protection.

[0067] The above-described preferred embodiments of the present invention are for illustrative purposes only and are not intended to limit the scope of the invention. Any obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A method for preparing porous carbon-rich SiOCN nanospheres with excellent microwave absorption properties, characterized in that, The method includes the following steps: S1. Provide SiOC ceramic precursor and add it dropwise to the hydrolysate, stirring to obtain SiOC ceramic precursor mixture; S2. Add an acid catalyst dropwise to the SiOC ceramic precursor mixture and stir to promote the hydrolysis of the SiOC ceramic precursor; S3. After hydrolysis, continue to add alkaline catalyst to the system, stir, and condense to form a mixed solution of SiOC nanospheres; S4. Add a carbon phase precursor to the SiOC nanosphere particle mixed solution, stir, centrifuge, and dry to obtain a porous carbon-rich nanosphere precursor. S5. Under a nitrogen atmosphere, the porous carbon-rich nanosphere precursor is pyrolyzed to obtain porous carbon-rich SiOCN nanospheres. The weight ratio of the SiOC ceramic precursor, acid catalyst, base catalyst and carbon phase precursor is (5-15):(0.5-2.0):(1-10):(2-6). The carbon phase precursor is resorcinol and formaldehyde, and the weight ratio of the SiOC ceramic precursor, resorcinol and formaldehyde is (5-15):(1-3):(1-3).

2. The method for preparing porous carbon-rich SiOCN nanospheres with excellent microwave absorption properties according to claim 1, characterized in that: Step S1: Provide SiOC ceramic precursor and add it dropwise to the hydrolysate, stir for 10-15 minutes to obtain SiOC ceramic precursor mixture; The hydrolysate is composed of deionized water and anhydrous ethanol in a weight ratio of (10-20):(80-120); the weight ratio of the SiOC ceramic precursor to the hydrolysate is (5-15):(90-140).

3. The method for preparing porous carbon-rich SiOCN nanospheres with excellent microwave absorption properties according to claim 1 or 2, characterized in that: The SiOC ceramic precursor is selected from at least one of tetraethyl orthosilicate, methyltrimethoxysilane, dimethyldimethoxysilane, and phenyltriethoxysilane.

4. The method for preparing porous carbon-rich SiOCN nanospheres with excellent microwave absorption properties according to claim 1, characterized in that: Step S2: Add an acid catalyst dropwise to the SiOC ceramic precursor mixture and stir for 2 to 8 hours to promote the hydrolysis of the SiOC ceramic precursor; the acid catalyst is selected from nitric acid, hydrochloric acid, and acetic acid.

5. The method for preparing porous carbon-rich SiOCN nanospheres with excellent microwave absorption properties according to claim 1, characterized in that: Step S3: After hydrolysis, continue to add an alkaline catalyst to the system and stir for 12-24 hours to condense and form a mixed solution of SiOC nanospheres; the alkaline catalyst is selected from KOH, NaOH, and ammonia water.

6. The method for preparing porous carbon-rich SiOCN nanospheres with excellent microwave absorption properties according to claim 1, characterized in that: Step S4: Add a carbon phase precursor to the SiOC nanosphere particle mixed solution, stir for 12-24 hours, centrifuge at 3000-10000 rpm for 2-5 minutes, and dry to obtain a porous carbon-rich nanosphere precursor.

7. The method for preparing porous carbon-rich SiOCN nanospheres with excellent microwave absorption properties according to claim 1, characterized in that: Step S5: Under a nitrogen atmosphere, the temperature is increased from room temperature to 1200-1500°C at a rate of 1-5°C / min and maintained for 2-4 hours to perform high-temperature pyrolysis on the porous carbon-rich nanosphere precursor, thereby obtaining porous carbon-rich SiOCN nanospheres.

8. A porous carbon-rich SiOCN nanosphere with excellent microwave absorption properties, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 7.

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