Hollow silicon carbide-based nano-microsphere, preparation method and application

Abstract

The invention discloses a hollow silicon carbide-based nano-microsphere, a preparation method and application, and belongs to the technical field of wave absorbing, and the preparation method comprises the following steps: 1, adding an alkaline solution into a mixed solution of ethanol and water, uniformly mixing, respectively adding a silicon source, a pore forming agent and a functional reagent, stirring, adding a catalyst, a phenolic compound and an aldehyde compound, and uniformly stirring, so as to obtain a hollow silicon carbide-based nano-microsphere; heating and reacting to obtain SiO2 (at) RF nano-microspheres with a hollow structure; wherein the catalyst is ferric nitrate or nickel nitrate; and 2, pyrolyzing the SiO2 (at) RF nano-microspheres obtained in the step 1 to obtain the hollow SiC (at) C nano-microspheres which do not need to be etched. According to the preparation method disclosed by the invention, etching is not needed, the problem of potential safety hazards caused by the use of a large amount of strongly corrosive acid-base solution when a hard template is etched is avoided, and meanwhile, the prepared hollow silicon carbide-based nano-microspheres have good electromagnetic wave absorption performance.

Description

Technical Field

[0001] The invention belongs to the field of wave absorbing technology and relates to a wave absorbing material, in particular to a hollow silicon carbide-based nano-microsphere, a preparation method and an application thereof. Background Art

[0002] With the advent of the 5G era, the dense deployment of 5G base stations and equipment has become the norm, and the risk of electromagnetic wave pollution caused by this has increased significantly. This phenomenon is not only reflected in the mutual interference between electronic devices, affecting the stable operation of the equipment, but also in the potential threat to human health and environmental safety. In the face of this challenge, the application of electromagnetic shielding technology and absorbing materials has become particularly critical.

[0003] As a typical dielectric absorbing material, silicon carbide has attracted widespread attention due to its outstanding thermal conductivity, high temperature resistance and excellent corrosion resistance, and has shown broad application prospects. In the field of microwave absorption, the microstructure of the material plays a key role in its absorbing performance. At present, researchers have developed various forms of silicon carbide absorbing materials, including fibrous, porous, core-shell structures, etc. These different microstructures provide rich design space for improving absorbing performance.

[0004] The traditional preparation technology of hollow nano-microspheres is mainly based on the template synthesis method, which is divided into two paths: soft template method and hard template method. In the preparation process of hollow silicon carbide nano-microspheres, the commonly used method is to use silicon dioxide as a hard template, wrap phenolic resin on its surface, and then perform carbonization treatment and remove the template. However, in the process of removing the template, it is often necessary to use highly corrosive acids and alkalis such as hydrofluoric acid (HF), hydrochloric acid (HCl), and sodium hydroxide (NaOH), which not only makes the operation process more cumbersome, but also poses safety hazards. Summary of the invention

[0005] In view of the problems in the prior art, the present invention provides a hollow silicon carbide-based nano-microsphere, a preparation method and an application thereof, which directly realizes the hollowing of silicon carbide / carbon nano-microspheres through a two-step method without etching, and is a more environmentally friendly and safe preparation method.

[0006] Specifically, the present invention adopts the following technical solutions:

[0007] In the first aspect, a method for preparing hollow silicon carbide-based nanospheres comprises the following steps: step 1, adding an alkaline solution to a mixed solution of ethanol and water, mixing evenly, respectively adding a silicon source, a pore-forming agent and a functionalizing agent, stirring, adding a catalyst, a phenolic compound and an aldehyde compound, heating and reacting, and obtaining a hollow structured SiO2 nanosphere. 2 @RF nanospheres; wherein the catalyst is iron nitrate or nickel nitrate; step 2, the SiO2 @RF nanospheres are pyrolyzed to achieve the effect of full reaction between silicon dioxide and carbon materials under the action of catalyst through the coordinated coordination of pyrolysis temperature and time, and finally hollow SiC@C nanospheres are obtained without etching.

[0008] Furthermore, in step one, the alkaline solution is ammonia water; the silicon source is tetraethyl orthosilicate (TEOS) or tetrabutoxysilane (TPOS); the pore-forming agent is (11-mercaptoundecyl)-N,N,N-trimethylammonium bromide; the functionalizing agent is A-1120 or 3-mercaptopropyltrimethoxysilane; the volume ratio of ethanol, water, ammonia water, silicon source and functionalizing agent is 20-25:1-5:0.5-2:0.5-1.5:0.05-0.2, preferably 22:3:1.3:1:0.1; the molar ratio of the pore-forming agent to the functionalizing agent is 1:0.5-1.5, preferably 1:1.05.

[0009] Furthermore, in step 1, the phenolic compound is resorcinol; the aldehyde compound is formaldehyde; the molar ratio of formaldehyde to resorcinol is 3 to 8:1, preferably 5:1; the volume ratio of formaldehyde to silicon source is 1:3 to 8, preferably 1:5.

[0010] Furthermore, in step 1, the ferric nitrate is ferric nitrate nonahydrate, and the nickel nitrate is nickel nitrate hexahydrate; and the molar ratio of the catalyst to the silicon source is 0.0015 to 0.03:1.

[0011] Furthermore, in step 1, the stirring time is 20 to 30 minutes.

[0012] Furthermore, in step 1, the heating temperature of the heating reaction is 120 to 180° C., and the reaction time is 24 to 60 hours.

[0013] Furthermore, in step 2, the pyrolysis is carried out under a nitrogen atmosphere.

[0014] Furthermore, in step 2, the pyrolysis temperature is 1300-1600° C., the time is 2-10 h, and the heating rate is 2-5° C. / min.

[0015] In a second aspect, the present invention also provides hollow silicon carbide-based nano-microspheres prepared by the above-mentioned preparation method.

[0016] In a third aspect, the present invention also provides the use of the above-mentioned hollow silicon carbide-based nano-microspheres in wave absorption.

[0017] The beneficial effects of the present invention are:

[0018] 1. The preparation method of the present invention adopts a one-step method to preferentially form a hollow structure of SiO 2@RF nanospheres, that is, in the long hydrothermal process, the in-situ coating of phenolic formaldehyde and the hollowing of the inner core can be achieved simultaneously. In this process, the pore-forming agent "kills two birds with one stone". In the process of high temperature and high pressure, the voids continue to expand and merge from the inner core with a lower degree of polymerization, making the inner core gradually hollow. The cations generated by the pore-forming agent in the solution can promote the co-assembly of phenolic formaldehyde outside the silica through heterogeneous nucleation, and gradually tend to be uniform under a long hydrothermal environment, maintaining the stability of the overall spherical particle morphology and avoiding mutual adhesion between phenolic formaldehydes.

[0019] 2. The preparation method of the present invention uses a functional reagent to give SiO 2 @RF The weaker bonding between the networks makes SiO 2 @RF nanospheres can form thinner hollow sphere walls when facing pressure.

[0020] 3. The preparation method of the present invention adds a certain amount of catalyst during the precursor preparation process. At high temperature, the metal salt is converted into metal particles. During the carbon thermal reduction process, the metal particles melt to form a liquid phase distributed between the carbon layer and the silicon dioxide interface, providing good active sites for the growth of silicon carbide. Under the synergistic effect of temperature and time, the inner thin-walled hollow silicon dioxide reacts completely with carbon, achieving the excellent effect of preparing hollow silicon carbide-based materials without etching.

[0021] 4. The preparation method of the present invention avoids the potential safety hazard caused by using a large amount of highly corrosive acid and alkali solutions to etch away the hard template during the carbon thermal reduction preparation of silicon carbide-based materials. It not only significantly improves the safety of the preparation process, but also greatly reduces the complexity of the preparation method, and is suitable for industrial production.

[0022] 5. The hollow silicon carbide-based nanospheres of the present invention show excellent performance in the field of electromagnetic wave absorption. Specifically, due to the difference in work function at the interface between silicon carbide and carbon, the positive and negative charges at the interface are rearranged in the alternating electric field, resulting in strong interface polarization; in addition, the hollow morphology gives the material a large specific surface area, and the hollow structure promotes multiple scattering and reflection of electromagnetic waves in the cavity, further promoting the conversion of electromagnetic energy into heat energy and dissipation. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a TEM image of the hollow silicon carbide-based nanospheres prepared in Example 1;

[0024] Figure 2 is the reflection loss curve of the hollow silicon carbide-based nano-microspheres prepared in Example 1 at a thickness of 3.8 mm;

[0025] Figure 3 This is the reflection loss curve of the hollow silicon carbide-based nano-microspheres prepared in Example 1 at a thickness of 1.58 mm. DETAILED DESCRIPTION

[0026] The present invention is further described below in conjunction with specific embodiments.

[0027] Example 1

[0028] This embodiment provides a hollow silicon carbide-based nanosphere for absorbing microwaves, and the preparation method thereof comprises the following steps:

[0029] Step 1: Add ammonia water to the mixed solution of ethanol and water, mix well, and then add TEOS, (11-mercaptoundecyl)-N,N,N-trimethylammonium bromide and A-1120 respectively. Among them, the volume ratio of ethanol, water, ammonia water and TEOS is 22:3:1.3:1, the molar ratio of (11-mercaptoundecyl)-N,N,N-trimethylammonium bromide and A-1120 is 1:1.05, and the volume ratio of silicon source and functionalization reagent is 10:1. After stirring the mixed solution for 20 minutes, add ferric nitrate nonahydrate, and the molar ratio of ferric nitrate nonahydrate to silicon source is 0.003:1. After being fully mixed, add formaldehyde and resorcinol with a molar ratio of 5:1, and the volume ratio of formaldehyde to silicon source is 1:5. Then transfer the precursor solution to a high-pressure reactor and keep it at 150°C for 40 hours. After the reaction was completed, the precursor was cooled to room temperature, centrifuged at 9000 r / min, and dried to obtain hollow SiO 2 @RF nanospheres;

[0030] Step 2: SiO obtained in step 1 2 The @RF nanospheres were heated to 1450°C at a heating rate of 2°C / min in a nitrogen atmosphere and kept at this temperature for 4 hours. After cooling to room temperature, the powder was collected to obtain hollow silicon carbide-based nanospheres that did not require etching.

[0031] The TEM images of the hollow silicon carbide-based nanospheres are as follows: Figure 1 As shown in the figure, it can be seen that the inner hollow structure and the outer silicon carbide / carbon shell thickness are up to 17nm, which indicates that the template can be removed without the aid of additional acid and alkali etching, proving the successful implementation and effectiveness of the preparation scheme.

[0032] The vector network test of the hollow silicon carbide-based nanospheres was carried out, and the results were as follows Figure 2 and Figure 3As shown. From the reflection loss curve, it can be seen that at a thickness of 3.8mm, the maximum reflection loss reaches -68.3dB; at a thickness of 1.58mm, the effective absorption bandwidth below -10dB is 4.44GHz. Due to the difference in work function at the interface between silicon carbide and carbon, the positive and negative charges at the interface are rearranged in the alternating electric field, resulting in strong interface polarization; in addition, the hollow morphology gives the material a large specific surface area, and the hollow structure promotes multiple scattering and reflection of electromagnetic waves in the cavity, further promoting the conversion of electromagnetic energy into heat energy and dissipation.

[0033] Example 2

[0034] This embodiment provides a hollow silicon carbide-based nanosphere for absorbing microwaves, and the preparation method thereof comprises the following steps:

[0035] Step 1: Add ammonia water to the mixed solution of ethanol and water, mix well, and then add TEOS, (11-mercaptoundecyl)-N,N,N-trimethylammonium bromide and A-1120 respectively. Among them, the volume ratio of ethanol, water, ammonia water and TEOS is 22:3:1.3:1, the molar ratio of (11-mercaptoundecyl)-N,N,N-trimethylammonium bromide and A-1120 is 1:1.05, and the volume ratio of silicon source and functionalization reagent is 10:1. After stirring the mixed solution for 20 minutes, nickel nitrate hexahydrate is added, and the molar ratio of nickel nitrate hexahydrate to silicon source is 0.003:1. After being fully mixed, formaldehyde and resorcinol with a molar ratio of 5:1 are added, and the volume ratio of formaldehyde to silicon source is 1:5. The precursor solution is then transferred to a high-pressure reactor and kept at 150°C for 40 hours. After the reaction was completed, the precursor was cooled to room temperature, centrifuged at 9000 r / min, and dried to obtain hollow SiO 2 @RF nanospheres;

[0036] Step 2: SiO obtained in step 1 2 The @RF nanospheres were heated to 1450°C at a heating rate of 2°C / min in a nitrogen atmosphere and kept at this temperature for 4 hours. After cooling to room temperature, the powder was collected to obtain hollow silicon carbide-based nanospheres that did not require etching.

[0037] Example 3

[0038] This embodiment provides a hollow silicon carbide-based nanosphere for absorbing microwaves, and the preparation method thereof comprises the following steps:

[0039] Step 1: Add ammonia water to the mixed solution of ethanol and water, mix well, and then add TEOS, (11-mercaptoundecyl)-N,N,N-trimethylammonium bromide and 3-mercaptopropyltrimethoxysilane respectively. Among them, the volume ratio of ethanol, water, ammonia water and TEOS is 22:3:1.3:1, the molar ratio of (11-mercaptoundecyl)-N,N,N-trimethylammonium bromide and 3-mercaptopropyltrimethoxysilane is 1:1.05, and the volume ratio of silicon source and functionalization reagent is 10:1. After stirring the mixed solution for 20 minutes, nickel nitrate hexahydrate is added, and the molar ratio of nickel nitrate hexahydrate to silicon source is 0.003:1. After being fully mixed, formaldehyde and resorcinol with a molar ratio of 5:1 are added, and the volume ratio of formaldehyde to silicon source is 1:5. The precursor solution is then transferred to a high-pressure reactor and kept at 150°C for 40 hours. After the reaction was completed, the precursor was cooled to room temperature, centrifuged at 9000 r / min, and dried to obtain hollow SiO 2 @RF nanospheres;

[0040] Step 2: SiO obtained in step 1 2 The @RF nanospheres were heated to 1450°C at a heating rate of 2°C / min in a nitrogen atmosphere and kept at this temperature for 4 hours. After cooling to room temperature, the powder was collected to obtain hollow silicon carbide-based nanospheres that did not require etching.

[0041] In the present invention, unless otherwise specified, the scientific and technical terms used herein have the meanings commonly understood by those skilled in the art. In addition, the reagents, materials and operating procedures used herein are reagents, materials and conventional procedures widely used in the corresponding fields.

[0042] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing hollow silicon carbide-based nanospheres, characterized in that: The following steps are involved: Step 1: add an alkaline solution to a mixed solution of ethanol and water, mix well, add a silicon source, a pore-forming agent and a functionalizing agent respectively, stir, add a catalyst, a phenolic compound and an aldehyde compound, heat and react, and obtain SiO2@RF nano-microspheres with a hollow structure; Wherein, the catalyst is iron nitrate or nickel nitrate; Step 2: Pyrolyze the SiO2@RF nanospheres obtained in step 1 to obtain hollow SiC@C nanospheres.

2. The method for preparing hollow silicon carbide-based nanospheres according to claim 1, characterized in that: In step 1, the alkaline solution is aqueous ammonia; The silicon source is ethyl orthosilicate or tetrabutoxysilane; The pore-forming agent is (11-mercaptoundecyl)-N,N,N-trimethylammonium bromide; The functionalizing agent is A-1120 or 3-mercaptopropyltrimethoxysilane; The volume ratio of ethanol, water, ammonia water, silicon source and functional reagent is 20-25: 1-5: 0.5-2: 0.5-1.5: 0.05-0.2; the molar ratio of pore-forming agent and functional reagent is 1: 0.5-1.

5.

3. The method for preparing hollow silicon carbide-based nanospheres according to claim 1, characterized in that: In step 1, the phenolic compound is resorcinol; the aldehyde compound is formaldehyde; the molar ratio of formaldehyde to resorcinol is 3-8:1; and the volume ratio of formaldehyde to silicon source is 1:3-8.

4. The method for preparing hollow silicon carbide-based nanospheres according to claim 1, characterized in that: In step 1, the ferric nitrate is ferric nitrate nonahydrate, and the nickel nitrate is nickel nitrate hexahydrate; the molar ratio of the catalyst to the silicon source is 0.0015-0.03:

1.

5. The method for preparing hollow silicon carbide-based nanospheres according to claim 1, characterized in that: In step 1, the stirring time is 20 to 30 minutes.

6. The method for preparing hollow silicon carbide-based nanospheres according to claim 1, characterized in that: In step 1, the heating temperature of the heating reaction is 120-180° C., and the reaction time is 24-60 hours.

7. The method for preparing hollow silicon carbide-based nanospheres according to claim 1, characterized in that: In step 2, the pyrolysis is carried out under a nitrogen atmosphere.

8. The method for preparing hollow silicon carbide-based nanospheres according to claim 1, characterized in that: In step 2, the pyrolysis temperature is 1300-1600° C., the time is 2-10 hours, and the heating rate is 2-5° C. / min.

9. Hollow silicon carbide-based nanospheres prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the hollow silicon carbide-based nanospheres as claimed in claim 9 in wave absorption.

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