All-carbon aerogel and its preparation method and wave absorption application

Abstract

The application relates to a kind of all-carbon aerogel and its preparation method and wave-absorbing application, and belongs to the technical field of functional materials.The application solves the technical problems of existing wave-absorbing material preparation, such as complexity, large density, low wave-absorbing intensity and poor corrosion resistance.The technical solution points: functionalized graphene oxide and carbon quantum dots are used as catalysts and unit materials, and an all-carbon aerogel with a nanometer sandwich structure is prepared by a sol-gel method, the sandwich structure includes a graphene sandwich layer and a phenolic carbon particle surface layer containing carbon quantum dots.The all-carbon aerogel is based on the dielectric property difference between the phenolic carbon particle layer and graphene, generates a large number of heterojunction interfaces and rich surface groups, strengthens interface polarization, improves impedance matching, the porous structure gives lightweight characteristics, and has high-temperature stability and corrosion resistance.The application is mainly used for electromagnetic wave absorption and electromagnetic radiation protection.

Description

Technical Field

[0001] This invention relates to the field of functional materials technology, and more specifically, to an all-carbon aerogel, its preparation method, and its microwave absorption applications. Background Technology

[0002] With the rapid development of electronic technology, the hazards of electromagnetic radiation are becoming increasingly prominent: it not only interferes with the normal operation of electronic devices and causes electromagnetic environmental pollution, but also has adverse effects on human health. Absorbing materials can convert electromagnetic radiation into non-radiative energy and dissipate it, avoiding secondary pollution, thus becoming a research hotspot. The current demand for integrated intelligent and multifunctional electronic devices is driving the development of absorbing materials towards wider absorption bands, lighter weight, lower cost, higher thermal stability, and corrosion resistance.

[0003] Carbon aerogel is a typical lightweight microwave absorbing material with low electrical loss, but its high dielectric constant results in poor impedance matching and unsatisfactory absorption performance when not combined with other materials. Existing technologies often combine nano-carbon materials with conductive polymers, magnetic metals (alloys), metal oxides, etc., to control electromagnetic properties. Although this can improve impedance matching and enhance microwave absorption performance, it suffers from problems such as complex preparation processes, poor thermal stability, and poor corrosion resistance. For example, the nitrogen-doped reduced oxide aerogel / nickel nanoparticle composite material disclosed in the literature "Carbon, 2019, 152, 575-586" achieves a minimum reflection loss (RLmin) of -60.8 dB and an effective absorption bandwidth of 5.1 GHz at a coating thickness of 2.1 mm and a frequency of 13.7 GHz; the three-dimensional MoS2 / RGO / NC wrinkled microspheres disclosed in the literature "Composites, 2022, 161A: 107119" achieve a minimum reflection loss of -60.4 dB at a thickness of 3.1 mm; and the ternary composite material disclosed in patent "CN 110205097 B, 2022" achieves a minimum reflection loss of -47.9 dB at a thickness of 3 mm. These composite systems have not solved the core problems of complex preparation and insufficient stability. Single carbon aerogels (graphene, carbon nanotubes, carbon fibers), relying solely on dielectric loss, fail to meet the required microwave absorption performance. Summary of the Invention

[0004] (a) Technical problems to be solved This invention aims to solve the technical problems of existing microwave absorbing materials, such as complex preparation process, high density, low microwave absorption intensity, poor high temperature stability, and insufficient corrosion resistance. It provides an all-carbon aerogel with adjustable dielectric properties, simple preparation process, easy operation, and low production cost, as well as its preparation method, while ensuring that it has excellent microwave absorption performance, high temperature stability, and corrosion resistance.

[0005] (II) Technical Solution The core idea of ​​this invention is to utilize functionalized graphene oxide and carbon quantum dots as catalysts and unit materials to prepare an all-carbon aerogel with a nano-sandwich structure via a sol-gel method. The graphene sandwich layer and the surface layer of phenolic carbon particles containing carbon quantum dots form a heterogeneous interface. By controlling electromagnetic parameters, impedance matching is improved, and microwave absorption performance is enhanced. The specific technical solution is as follows: A fully carbon aerogel, made from graphene oxide, carbon quantum dots, formaldehyde, and resorcinol, possesses a nano-sandwich structure. This structure includes a graphene core layer and a surface layer of phenolic carbon particles containing carbon quantum dots. The graphene core layer is composed of graphene oxide, and the phenolic carbon particle surface layer is formed by the condensation of resorcinol and formaldehyde under the catalysis of carbon quantum dots. The fully carbon aerogel exhibits electromagnetic wave absorption capabilities, high-temperature stability, and corrosion resistance.

[0006] Graphene oxide can be one or more of carboxylated graphene oxide, graphene oxide, and hydroxylated graphene oxide. Carbon quantum dots can be one or more of aminated graphene quantum dots and aminated carbon dots, with a size of 2~10 nm.

[0007] A method for preparing an all-carbon aerogel includes the following steps: Step 1: Prepare a mixture by uniformly dispersing resorcinol, formaldehyde solution, and graphene oxide aqueous solution in water; Step 2: Seal and let the mixed solution from Step 1 stand at 20~60℃ for 1~4 hours; Step 3: Add the aminated carbon quantum dot solution to the aqueous solution in Step 2, disperse it evenly, and then seal and let it stand at 40~80℃ for 5~240 min to carry out sol-gelation to obtain hydrogel; Step 4: Heat the hydrogel from Step 3 to 60-80℃ at a rate of 0.5-5℃ / min for 1-2 days; Step 5: The hydrogel aged in Step 4 is subjected to solvent replacement and supercritical drying to obtain a dry aerogel. Step 6: Heat the dried gel from Step 5 to 600-1200℃ at a rate of 1-5℃ / min and carbonize for 1-3 hours. After cooling, a fully carbonized aerogel is obtained.

[0008] Preferably, in step 1, the molar ratio of resorcinol to formaldehyde is 1:1.5-2.5, and the mass fraction of resorcinol and formaldehyde in the total solution is 5-15%. The pH value of the graphene oxide aqueous solution is 1-5, and the concentration of graphene oxide in the total solution is 1-5 mg / mL. The graphene oxide can be monolayer or multilayer, preferably monolayer graphene oxide. In step 3, the concentration of aminated carbon quantum dots in the total solution is 0.1-2 mg / mL. In step 5, supercritical drying is performed using ethanol supercritical drying or carbon dioxide supercritical drying. In step 6, carbonization is carried out under an inert atmosphere, and the heating rate is preferably 1-3 °C / min.

[0009] Figure 1 Images of a sample of the all-carbon aerogel precursor (before carbonization) prepared according to the present invention are provided. Figure 2-3 Its electronic scan image is provided. Figure 4-5 Images of its microwave absorption performance are provided. Compared with existing phenolic carbon aerogel preparation technologies, this invention does not require alkaline catalysts such as Na2CO3, K2CO3, Ca(OH)2, or hydrochloric acid, but utilizes the acidification effect of functional groups on the graphene surface and the amino catalytic condensation of phenolic resin on the carbon quantum dot surface to form a nano-sandwich structure.

[0010] (III) Beneficial Effects This invention relates to an all-carbon aerogel that leverages the dielectric property difference between phenolic carbon particles and graphene to generate numerous heterogeneous interfaces and abundant surface functional groups, effectively enhancing interfacial polarization and improving impedance matching. The porous structure endows the all-carbon aerogel with lightweight properties, as well as high-temperature stability and corrosion resistance. Impedance matching can be adjusted by controlling the electromagnetic parameters of the aerogel, thereby significantly improving its microwave absorption performance. Furthermore, the preparation process is simple and efficient, facilitating industrial-scale production. Attached Figure Description

[0011] Figure 1 Images of all-carbon aerogel precursor samples prepared according to this invention; Figure 2 This is an electron scanning image of the all-carbon aerogel sample from Example 1; Figure 3 This is an electron scanning image of the all-carbon aerogel sample from Example 2; Figure 4 These are images of the electromagnetic absorption properties of the all-carbon aerogel sample from Example 1; Figure 5 This is an image showing the electromagnetic absorption performance of the all-carbon aerogel sample from Example 2. Detailed Implementation

[0012] To make the objectives, technical solutions, and advantages of this invention clearer, the following description is provided in conjunction with the appendix. Figure 1-5The present invention will be further described in detail with reference to the embodiments. The described embodiments are only used to explain the present invention and are not intended to limit the present invention.

[0013] Example 1 1. Preparation method Step 1: Disperse 0.24g resorcinol, 0.34mL formaldehyde solution and 0.5mL graphene oxide aqueous solution (concentration 10mg / mL, pH 2.1) evenly in 1.5mL of water to prepare a mixed solution; Step 2: Seal and let the mixture stand at 40°C for 4 hours; Step 3: Add 2.5 mL of amino-graphene quantum dot solution (concentration 1 mg / mL) to the above aqueous solution, disperse evenly, seal and let stand at 60℃ for 120 min to perform sol-gelation to obtain hydrogel; Step 4: Heat the hydrogel to 80℃ at a heating rate of 2℃ / min and age for 2 days; Step 5: The aged hydrogel is replaced with ethanol solvent and dried by supercritical drying to obtain a dry aerogel; Step 6: Heat the dried gel to 850℃ at a heating rate of 5℃ / min, carbonize for 1 hour, and then cool to obtain a fully carbonized aerogel.

[0014] 2. Performance Testing The electron scanning image of the full carbon aerogel prepared in this embodiment is as follows: Figure 2 As shown in the image, the electromagnetic absorption performance is as follows: Figure 4 As shown, its nano-sandwich structure and excellent wave absorption performance can be observed.

[0015] Example 2 1. Preparation method Step 1: Disperse 0.40g resorcinol, 0.57mL formaldehyde solution and 0.5mL graphene oxide aqueous solution (concentration 10mg / mL, pH 2.1) evenly in 2mL of water to prepare a mixed solution; Step 2: Seal and let the mixture stand at 40°C for 4 hours; Step 3: Add 1.5 mL of amino-graphene quantum dot solution (concentration 1 mg / mL) to the above aqueous solution, disperse evenly, seal and let stand at 40℃ for 60 min, and perform sol-gelation to obtain hydrogel; Step 4: Heat the hydrogel to 60°C at a heating rate of 2°C / min and age it for 2 days; Step 5: The aged hydrogel is replaced with ethanol solvent and dried by supercritical drying to obtain a dry aerogel; Step 6: Heat the dried gel to 850℃ at a heating rate of 5℃ / min, carbonize for 1 hour, and then cool to obtain a fully carbonized aerogel.

[0016] 2. Performance Testing The electron scanning image of the full carbon aerogel prepared in this embodiment is as follows: Figure 3 As shown in the image, the electromagnetic absorption performance is as follows: Figure 5 As shown, the stability of its structure and wave absorption performance is verified.

[0017] Example 3 0.32 g resorcinol, 0.46 mL formaldehyde solution, and 0.5 mL carboxylated graphene oxide aqueous solution were uniformly dispersed in 2.5 mL of water to prepare a mixed solution. The concentration of the graphene oxide aqueous solution was 10 mg / mL, and the pH value was 4.5. The prepared mixed solution was sealed and allowed to stand for 4 h at 40 °C. 1.5 mL of aminated carbon quantum dot solution (concentration 1 mg / mL) was added to the above-prepared aqueous solution and uniformly dispersed. The solution was then sealed and allowed to stand for 60 min at 60 °C to perform sol-gelation to obtain a hydrogel. The prepared hydrogel was heated to 80 °C at a heating rate of 2 °C / min and aged for 2 days. The aged hydrogel was subjected to ethanol solvent replacement and supercritical drying to obtain a dried aerogel. The dried gel was directly heated to 950 °C at a heating rate of 5 °C / min and carbonized for 1.5 h. After cooling, a fully carbonized aerogel was obtained.

[0018] Example 4 0.24 g resorcinol, 0.34 mL formaldehyde solution, and 0.5 mL graphene oxide aqueous solution were uniformly dispersed in 2.9 mL of water to prepare a mixed solution. The concentration of the graphene oxide aqueous solution was 10 mg / mL, and the pH value was 2.1. The prepared mixed solution was sealed and allowed to stand for 2 h at 40 °C. 1.0 mL of aminated graphene quantum dot solution (concentration 5 mg / mL) was added to the above-prepared aqueous solution and uniformly dispersed. The solution was then sealed and allowed to stand for 20 min at 60 °C to perform sol-gelation to obtain a hydrogel. The prepared hydrogel was heated to 80 °C at a heating rate of 2 °C / min and aged for 2 days. The aged hydrogel was subjected to ethanol solvent replacement and supercritical drying to obtain a dried aerogel. The dried gel was directly heated to 850 °C at a heating rate of 5 °C / min and carbonized for 1 h. After cooling, a fully carbonized aerogel was obtained.

[0019] The above description, in conjunction with specific embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A fully carbon aerogel, characterized in that... Made from graphene oxide, carbon quantum dots, formaldehyde, and resorcinol, this nanostructured aerogel comprises a graphene core layer and a phenolic carbon particle surface layer containing carbon quantum dots. The graphene core layer is composed of graphene oxide, and the phenolic carbon particle surface layer is formed by the condensation of resorcinol and formaldehyde under the catalysis of carbon quantum dots. The all-carbon aerogel exhibits electromagnetic wave absorption capability, high-temperature stability, and corrosion resistance.

2. The all-carbon aerogel according to claim 1, characterized in that... The graphene oxide is one or more of carboxylated graphene oxide, graphene oxide, and hydroxylated graphene oxide.

3. The all-carbon aerogel according to claim 1, characterized in that... The carbon quantum dots are one or more of aminated graphene quantum dots and aminated carbon dots, with a size of 2~10 nm.

4. A method for preparing an all-carbon aerogel, characterized in that... Includes the following steps: Step 1: Prepare a mixture by uniformly dispersing resorcinol, formaldehyde solution, and graphene oxide aqueous solution in water; Step 2: Seal and let the mixed solution from Step 1 stand at 20~60℃ for 1~4 hours; Step 3: Add the aminated carbon quantum dot solution to the aqueous solution in Step 2, disperse it evenly, and then seal and let it stand at 40~80℃ for 5~240 min to carry out sol-gelation to obtain hydrogel; Step 4: Heat the hydrogel from Step 3 to 60-80℃ at a rate of 0.5-5℃ / min for 1-2 days; Step 5: The hydrogel aged in Step 4 is subjected to solvent replacement and supercritical drying to obtain a dry aerogel. Step 6: Heat the dried gel from Step 5 to 600-1200℃ at a rate of 1-5℃ / min and carbonize for 1-3 hours. After cooling, a fully carbonized aerogel is obtained.

5. The method for preparing all-carbon aerogel according to claim 4, characterized in that... In step 1, the molar ratio of resorcinol to formaldehyde is 1:1.5~2.5, and the mass fraction of resorcinol and formaldehyde in the total solution is 5~15%.

6. The method for preparing all-carbon aerogel according to claim 4, characterized in that... In step 1, the pH value of the graphene oxide aqueous solution is 1~5, and the concentration of graphene oxide in the total solution is 1~5 mg / mL.

7. The method for preparing all-carbon aerogel according to claim 4, characterized in that... In step 3, the concentration of aminated carbon quantum dots in the total solution is 0.1~2 mg / mL.

8. The method for preparing all-carbon aerogel according to claim 4, characterized in that... In step 5, supercritical drying is performed using either ethanol supercritical drying or carbon dioxide supercritical drying.

9. The method for preparing all-carbon aerogel according to claim 4, characterized in that... In step 6, carbonization is carried out under an inert atmosphere, with a heating rate of 1~3℃ / min.

10. The all-carbon aerogel according to claim 1, characterized in that... The all-carbon aerogel is used in the fields of electromagnetic wave absorption and electromagnetic radiation protection.

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