A porous reduced graphene oxide aerogel / resin microwave absorbing material and its preparation method

Abstract

This invention discloses a porous reduced graphene oxide aerogel / resin microwave absorbing material and its preparation method, belonging to the category of resin-based microwave absorbing materials. The method involves placing ferric nitrate nonahydrate in graphene oxide, and by controlling the solution potential, forming a uniform dispersion of graphene oxide based on electrostatic stability. At high temperature, iron-carbon solid solution is generated to produce Fe3C, and the graphene oxide is then heat-treated to generate reduced graphene oxide. After etching to remove Fe3C, nanoscale pores are generated on the reduced graphene oxide. The porous graphene oxide is then encapsulated by resin, and under the action of the resin, some of the nanoscale pores are transformed into microscale pores. Finally, a reduced graphene oxide aerogel / resin microwave absorbing material with hierarchical pores is formed. The nanopores can enhance the polarization relaxation ability of the material, and the microscale pore structure can improve the impedance matching characteristics of the material, inducing multiple reflections of electromagnetic waves, extending the propagation path of electromagnetic waves within the material, thereby enhancing its electromagnetic wave attenuation.

Description

Technical Field

[0001] This invention belongs to the field of resin-based microwave absorbing materials technology, specifically relating to a porous reduced graphene oxide aerogel / resin microwave absorbing material and its preparation method. Background Technology

[0002] With the increasing collaborative strike capabilities of multi-site radar network detection and interception systems, stealth performance has become crucial for the battlefield survival and penetration of future aircraft. Electromagnetic absorbing materials are an important means of achieving radar stealth for aircraft. Most existing electromagnetic absorbing materials used in medium / high temperatures are dielectric loss materials, which suffer from significant temperature fluctuations in dielectric properties and require large material thicknesses to achieve effective electromagnetic absorption, greatly limiting their engineering applications. Therefore, researching thin electromagnetic absorbing materials with temperature-insensitive dielectric properties is of great significance.

[0003] Compared to dense magnetic and semiconductor ceramic materials, carbon materials offer advantages such as low density, high chemical stability, and low manufacturing cost, making them the most widely studied microwave absorbing material system. Among them, graphene, with its unique two-dimensional planar structure, low density, high specific surface area, and excellent carrier mobility, can achieve superior electromagnetic absorption performance with relatively low filler content, making it a key candidate for developing high-performance microwave absorbing materials. However, when facing increasingly demanding service environments in the future, graphene suffers from poor impedance matching, high conductivity loss, insufficient dielectric stability over a wide temperature range, and a narrow effective absorption bandwidth (reflection loss RL < 10 dB), making it difficult to meet the requirements of engineering applications. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a porous reduced graphene oxide aerogel / resin microwave absorbing material and its preparation method. This method combines freeze-drying and resin impregnation processes to prepare a wide-temperature-range microwave absorbing composite material, thereby solving the problems of poor impedance matching performance, high conductivity loss, and strong dielectric temperature dependence.

[0005] To achieve the above objectives, the present invention employs the following technical solution:

[0006] A method for preparing a porous reduced graphene oxide aerogel / resin microwave absorbing material includes the following steps:

[0007] Step 1: Place the graphene oxide slurry in deionized water and obtain an aqueous solution of graphene oxide by magnetic stirring;

[0008] Step 2: Ferric nitrate nonahydrate was placed in an aqueous solution of graphene oxide, mixed thoroughly, and then ammonia was added to adjust the pH of the solution. After freeze-drying, Fe was obtained. 3+ Graphene oxide aerogel;

[0009] Step 3, load Fe 3+ After heat treatment of graphene oxide aerogel, reduced graphene oxide aerogel loaded with Fe3C is obtained. The reduced graphene oxide aerogel loaded with Fe3C is then soaked in hydrochloric acid and dried to obtain porous reduced graphene oxide aerogel.

[0010] Step 4: Place the porous reduced graphene oxide aerogel in a resin solution, impregnate it under normal pressure, and then cure it to obtain the porous reduced graphene oxide aerogel / resin microwave absorbing material.

[0011] A further improvement of the present invention is that:

[0012] Preferably, in step 1, the concentration of the graphene oxide aqueous solution is 3-5 mg / mL.

[0013] Preferably, in step 2, the mass ratio of graphene oxide in the ferric nitrate nonahydrate and the graphene oxide aqueous solution is 0.1 to 0.3.

[0014] Preferably, in step 2, the pH of the solution is adjusted to 7-10.

[0015] Preferably, in step 3, the heat treatment temperature is 900–1200℃ and the heat treatment time is 1–3 hours.

[0016] Preferably, in step 3, the hydrochloric acid concentration is 10-30 wt.%, the soaking time is 24 h, the drying temperature is 80 °C, and the drying time is 2 h.

[0017] Preferably, in step 4, the solvent of the resin solution is anhydrous ethanol, and the concentration of the resin solution is 0.1–0.3 g / mL.

[0018] Preferably, in step 4, the atmospheric pressure impregnation time is 0.5 to 1 hour.

[0019] Preferably, in step 4, the curing temperature is 160°C and the curing time is 1 hour.

[0020] A porous reduced graphene oxide aerogel / resin microwave absorbing material prepared by any of the above preparation methods includes graphene sheets, wherein the graphene sheets are coated with resin, and nanoscale pores and microscale pores are distributed on the graphene sheets.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] This invention discloses a method for preparing porous reduced graphene oxide aerogel / resin microwave absorbing material. The method involves placing ferric nitrate nonahydrate in graphene oxide and using ferric nitrate nonahydrate as a pore-forming agent. Fe metal has high catalytic activity for decomposing carbon precursors, moderate carbon solubility, and moderate binding ability with carbon. At the same time, ferric nitrate exhibits strong oxidizing properties towards oxygen-containing functional groups, reacting with oxygen-containing functional groups such as hydroxyl and carbonyl groups in graphene oxide, thereby leading to the removal of oxygen atoms. At high temperature, iron-carbon solid solution is formed to form Fe3C. After removing Fe3C by etching with hydrochloric acid, corresponding pores can be formed.

[0023] In the preparation process, the adsorption efficiency of metal cations and the zeta potential are adjusted by controlling the pH value of the solution. Based on electrostatic stability, a uniform dispersion of graphene is formed. At the same time, under the action of electrostatic attraction, metal cations preferentially combine with oxygen-containing functional groups in graphene oxide, ensuring the uniform dispersion of metal cations on graphene sheets.

[0024] This method utilizes freeze-drying technology to fix a uniformly dispersed graphene, avoiding the accumulation of graphene sheets caused by van der Waals effects during the reduction process. It then uses an iron-carbon solid solution reaction to etch the graphene sheets, and after removing Fe3C, synthesizes a porous reduced graphene oxide aerogel. In step 3, the pores in the formed porous graphene oxide aerogel are nanoscale. After impregnation with resin, the surface tension of the resin solution increases the size of the nanoscale pores, with some becoming micrometer-scale, forming a porous reduced graphene oxide aerogel / resin composite material with a hierarchical pore structure. The nano / micrometer-scale pores are uniformly distributed on the graphene sheets, enhancing the wide-temperature-range microwave absorption performance of the composite material. Furthermore, the resin, as an insulating phase, coats the reduced graphene oxide sheets, disrupting the three-dimensional conductive network structure formed by the overlapping reduced graphene oxide sheets, hindering electron transport, further reducing conductivity, and improving impedance matching. After curing, the resin enhances the hardness and stability of the entire microwave absorbing material. The synergistic effect of the heterogeneous phase and hierarchical pores improves the interfacial polarization loss and reduces the electrical conductivity loss, thus obtaining a wide-temperature absorbing material with low dielectric temperature dependence.

[0025] Furthermore, the heat treatment process reduces graphene oxide. During the high-temperature heat treatment reduction process, iron-carbon solid solution reaction can occur simultaneously, simplifying the process. By adjusting the heat treatment temperature, the degree of iron-carbon solid solution can be effectively controlled. When the iron content is low, the heat treatment temperature can be increased to accelerate iron-carbon solid solution, improve the etching degree, and increase the pore size. When the iron content is high, the heat treatment temperature can be decreased to avoid over-etching.

[0026] Furthermore, this invention prepares hierarchical pores (nano / micro pores). The nanopores can reduce the conductivity of graphene oxide, improve impedance matching performance, increase the specific surface area of ​​the material, and reduce the conductivity of reduced graphene oxide, thus improving impedance matching performance. Simultaneously, the nanopores can be considered as gas / solid interfaces, where loads easily accumulate, leading to interfacial polarization and enhancing the material's polarization relaxation ability. In addition, the nanopores help resist the redeposition of reduced graphene oxide. The micropore structure can act as an "effective medium" to improve the material's impedance matching characteristics, induce multiple reflections of electromagnetic waves, and prolong the propagation path of electromagnetic waves within the material, thereby enhancing its electromagnetic wave attenuation.

[0027] This invention also discloses a porous reduced graphene oxide aerogel / resin microwave absorbing material, which is a porous reduced graphene oxide aerogel / resin composite material with wide-temperature-range microwave absorption performance. At a thickness of 2.75 mm, it has an effective absorption bandwidth of 4.2 GHz, covering the entire X-band, with a minimum reflection loss of -41.6 dB. It exhibits excellent X-band microwave absorption performance in the 323–523 K range, almost always covering the entire X-band. It achieves the performance requirements of being thin, wide-range, lightweight, strong, and having low dielectric temperature dependence. Attached Figure Description

[0028] Figure 1 Optical photographs of the aerogel materials prepared in Examples 1-3: (a) is the graphene oxide aerogel in Example 1, (b) is the porous reduced graphene oxide aerogel in Example 1, (c) is the porous reduced graphene oxide aerogel in Example 2, and (d) is the porous reduced graphene oxide aerogel in Example 3.

[0029] Figure 2 The images are scanning electron microscope (SEM) images of the aerogel materials prepared in Examples 1-3. (a) is graphene oxide in Example 1, (b) is porous reduced graphene oxide in Example 1, (c) is porous reduced graphene oxide in Example 2, and (d) is porous reduced graphene oxide in Example 3.

[0030] Figure 3 This is a scanning electron microscope image of the porous reduced graphene oxide aerogel / phenolic resin composite material prepared in Example 2.

[0031] Figure 4 The diagram shows the wide-temperature-range microwave absorption performance of different porous reduced graphene oxide aerogel / phenolic resin composites prepared in Example 2.

[0032] The thickness of (a) figure is 2.75 mm; the thickness of (b) figure is 3.05 mm; the thickness of (c) figure is 2.95 mm; the thickness of (d) figure is 2.85 mm; and the thickness of (e) figure is 2.80 mm. Detailed Implementation

[0033] The present invention will now be described in further detail with reference to the accompanying drawings:

[0034] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0035] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0036] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0037] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0038] This invention discloses a method for preparing a porous reduced graphene oxide aerogel / resin composite material with wide temperature range microwave absorption properties, specifically including the following steps:

[0039] Step 1, Preparation of graphene oxide solution: Weigh the graphene oxide slurry, add it to deionized water, and obtain a uniformly dispersed graphene oxide aqueous solution by magnetic stirring.

[0040] The process uses graphene oxide slurry as a raw material, which results in good dispersibility of the graphene oxide aqueous solution.

[0041] Step 2, Preparation of graphene oxide aerogel: Ferric nitrate nonahydrate was added to the graphene oxide aqueous solution prepared in Step 1, and the mixture was magnetically stirred until homogeneous. Ammonia was then added to adjust the pH of the solution, and the solution was freeze-dried to obtain Fe-loaded aerogel. 3+ Graphene oxide aerogel;

[0042] Step 3, Preparation of porous reduced graphene oxide aerogel: The graphene oxide aerogel prepared in the previous step is placed in a tube furnace, heated and held at a temperature under an argon atmosphere to obtain Fe-loaded aerogel. 3+ Reduced graphene oxide aerogel, followed by immersion in hydrochloric acid to remove Fe. 3+ After drying at 80℃ for 2 hours, porous reduced graphene oxide aerogel was obtained.

[0043] Step 4, preparation of resin solution: Weigh a certain amount of resin, add it to anhydrous ethanol, and then obtain a uniformly dispersed resin solution by magnetic stirring.

[0044] Step 5, Preparation of porous reduced graphene oxide aerogel / resin composite material with wide temperature range microwave absorption performance: The porous reduced graphene oxide aerogel prepared in step 3 is immersed in the resin solution prepared in step 4 under normal pressure for 0.5 to 1 hour, then taken out and heated to cure to obtain the porous reduced graphene oxide aerogel / resin composite material with wide temperature range microwave absorption performance.

[0045] In some embodiments of the present invention, in step 1, the concentration of the graphene oxide solution is 3-5 mg / mL.

[0046] In some embodiments of the present invention, in step 1, the magnetic stirring time is 1 hour.

[0047] In some embodiments of the present invention, in step 2, the mass ratio of the ferric nitrate nonahydrate to the graphene oxide in the graphene oxide solution is 0.1 to 0.3. The amount of ferric nitrate nonahydrate used should not be excessive, as this will cause the metal salt to agglomerate.

[0048] In some embodiments of the present invention, in step 2, the magnetic stirring time is 1 to 2 hours; the pH value of the solution is 7 to 10; the freezing time is 6 hours; and the drying time is 48 hours.

[0049] In some embodiments of the present invention, the protective atmosphere in step 3 is argon, the heating rate is 5-10℃ / min, the heat treatment temperature is 900-1200℃, the heat treatment time is 1-3h, the hydrochloric acid concentration is 10-30wt.%, the soaking time is 24h, the drying temperature is 80℃, and the drying time is 2h.

[0050] In some embodiments of the present invention, in step 4, the resin is one of phenolic resin, epoxy resin, polyimide resin, bismaleimide resin, silicone resin or cyanate ester resin.

[0051] It should be noted that different resins require different curing temperatures and times during the curing process.

[0052] As a preferred embodiment, the resin is phenolic resin, with a curing temperature of 160℃ and a curing time of 1 hour.

[0053] In some embodiments of the present invention, the resin in step 4 is a phenolic resin, and the concentration of the resin solution is 0.1 to 0.3 g / mL.

[0054] A porous reduced graphene oxide aerogel / resin composite material with wide temperature range microwave absorption performance is prepared by the above preparation method. The prepared composite material has a hierarchical pore structure, with nano / micron-sized pores uniformly distributed on the reduced graphene oxide sheets, and resin uniformly coated on the graphene surface. The composite material still has a sheet structure, and some graphene is bonded together.

[0055] The preparation process of this invention utilizes the fact that graphene oxide is rich in various oxygen-containing active groups such as ether bonds, carboxyl groups, hydroxyl groups, and carbonyl groups, making it easier to hybridize with other materials. Graphene oxide can provide active sites for metal cations and can serve as a two-dimensional support for anchoring and dispersing metal oxide nanoparticles. Therefore, metal salts can be candidate materials for pore-forming agents on the graphene surface. Currently, there are still two main problems in preparing porous reduced graphene oxide microwave absorbing materials by metal salts. First, the uniform dispersion of the metal salt / graphene mixed solution. Pure graphene oxide solution carries a high negative charge due to the ionization of carboxyl and phenolic hydroxyl groups, which can form a stable colloid under the action of electrostatic repulsion, thereby avoiding the aggregation of graphene sheets. However, the combination of metal cations with graphene will inevitably affect the surface charge of graphene, thus affecting the dispersibility of graphene. Therefore, this problem is solved in this invention by controlling the amount of metal salt added and the pH value. Second, the strong van der Waals interactions between reduced graphene oxide sheets can lead to the accumulation of graphene sheets. Both of these factors make it difficult to control the conductivity of graphene, which is not conducive to impedance matching and microwave absorption.

[0056] This invention modulates the electrical properties of graphene by controlling its preparation process, adjusting its distribution morphology, and combining it with composite heterogeneous materials, thereby enabling it to simultaneously possess strong loss capacity and good impedance matching. This invention introduces pores into graphene, which are considered gas / solid interfaces that easily accumulate charge, leading to interfacial polarization. Creating pores on the graphene surface enhances this interfacial polarization. Furthermore, interfacial relaxation exists in heterogeneous systems; combining graphene with other materials further increases the heterogeneous interface.

[0057] Regarding the dispersibility issue of metal salt / graphene mixed solutions: The dispersibility of metal salt solutions is affected by factors such as ion concentration, temperature, and solution pH, among which Fe... 3+It is extremely unstable and readily hydrolyzes in aqueous solution to form Fe(OH)3 precipitate, leading to aggregation. Typically, precipitation begins at pH 2.7. Adjusting the concentration of graphene oxide can increase the acidity of the solution, inhibiting Fe... 3+ Hydrolysis of Fe followed by electrostatic interactions of oxygen-containing functional groups such as hydroxyl, carboxyl, and epoxy groups caused Fe to... 3+ Cations are uniformly adsorbed on graphene oxide sheets. Experiments show that the dispersibility of graphene oxide solutions strongly depends on pH, ionic strength, ion species, and the number of oxygen-containing functional groups on the surface. The Zeta potential of the graphene oxide solution decreases with increasing pH, which is beneficial for graphene dispersion. However, high pH accelerates metal adsorption, reduces the electrostatic repulsion between graphene oxides, and thus causes Zeta potential reversal. Furthermore, graphene adsorption capacity is weak when the oxygen content is low, requiring an increase in pH to enhance the adsorption of metal cations. Based on charge screening, deprotonation of oxygen-containing functional groups under different pH conditions, and the adsorption between functional groups and metal cations, under the coupled effects of multiple influencing factors, appropriate ammonia should be added until the solution pH stabilizes between 7 and 10 to ensure uniform dispersion of graphene oxide. At this point, Fe... 3+ In-situ formation of Fe(OH)3 crystals by cations. Regarding the stacking problem of reduced graphene oxide: constructing a three-dimensional porous microstructure is an effective strategy to alleviate the stacking of reduced graphene oxide. Aerogel materials prepared by freeze-drying technology possess excellent properties such as high porosity, low density, abundant pore structure, and high specific surface area. This three-dimensional porous structure has unique advantages in optimizing impedance matching, constructing conductive networks, and increasing multiple reflections. Therefore, freeze-drying can be used to stabilize graphene dispersions. The reduction of graphene oxide is completed by combining heat treatment processes, and the etching of graphene sheets is achieved using an iron-carbon solid solution reaction.

[0058] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0059] Example 1

[0060] S1. Preparation of graphene oxide solution: Weigh 150mg of graphene oxide slurry and add it to 30mL of deionized water. Stir magnetically for 1h to obtain a uniformly dispersed graphene oxide solution with a concentration of 5mg / mL.

[0061] S2. Preparation of graphene oxide aerogel: 15 mg of ferric nitrate nonahydrate was weighed and added to the graphene oxide aqueous solution prepared in S1. The solution was magnetically stirred for 1 h to obtain a uniformly mixed solution. Then, ammonia was added to adjust the pH of the solution to 9. After magnetic stirring for 0.5 h, the mixed solution was poured into a self-made polytetrafluoroethylene mold and placed in a freeze dryer to freeze for 6 h. Then, it was dried at low temperature for 48 h to obtain graphene oxide aerogel.

[0062] S3. Preparation of porous reduced graphene oxide aerogel: The graphene oxide aerogel prepared in S2 was placed in a tube furnace and heated to 1100℃ for 2 hours under an argon atmosphere at a heating rate of 5℃ / min. During the heat treatment, graphene oxide came into contact with and reacted with iron oxide nanoparticles, and was catalyzed by iron to form Fe3C, forming pores around the Fe3C. Then, the aerogel was soaked in 20wt% hydrochloric acid for 24 hours to remove iron oxide / iron carbide particles and obtain porous reduced graphene oxide aerogel.

[0063] S4. Preparation of resin solution: Weigh 10g of phenolic resin and add it to 50mL of anhydrous ethanol. Stir magnetically for 1h to obtain a uniformly dispersed phenolic resin solution.

[0064] S5. Preparation of porous reduced graphene oxide aerogel / phenolic resin composite material: The porous reduced graphene oxide aerogel prepared in step S3 is immersed in the phenolic resin solution prepared in step S4 under normal pressure for 1 hour, and then removed and cured at 160℃ for 1 hour to obtain the porous reduced graphene oxide aerogel / phenolic resin composite material.

[0065] Example 2

[0066] S1 is the same as S1 in Example 1;

[0067] S2. Preparation of graphene oxide aerogel: 30 mg of ferric nitrate nonahydrate was weighed and added to the graphene oxide aqueous solution prepared in S1. The solution was magnetically stirred for 1 h to obtain a uniformly mixed solution. Then, ammonia was added to adjust the pH of the solution to 8. After magnetic stirring for 0.5 h, the mixed solution was poured into a self-made polytetrafluoroethylene mold and placed in a freeze dryer to freeze for 6 h. Then, it was dried at low temperature for 48 h to obtain graphene oxide aerogel.

[0068] S3 is the same as S3 in Example 1;

[0069] S4 is the same as S4 in Example 1;

[0070] S5 is the same as S5 in Example 1.

[0071] The wide-temperature-range absorption performance of the porous reduced graphene oxide aerogel / phenolic resin composite material prepared in Example 2 was tested using a vector network analyzer paired with a high-temperature waveguide cavity. The results showed that the composite material achieved effective absorption across the entire X-band when the thickness was 2.75 mm, and the minimum reflection loss value was -41.6 dB@9.15 GHz when the thickness was 3.00 mm.

[0072] Example 3

[0073] S1 is the same as S1 in Example 1;

[0074] S2. Preparation of graphene oxide aerogel: 45 mg of ferric nitrate nonahydrate was weighed and added to the graphene oxide aqueous solution prepared in S1. The solution was magnetically stirred for 1 h to obtain a uniformly mixed solution. Then, ammonia was added to adjust the pH of the solution to 7. After magnetic stirring for 0.5 h, the mixed solution was poured into a self-made polytetrafluoroethylene mold and placed in a freeze dryer to freeze for 6 h. Then, it was dried at low temperature for 48 h to obtain graphene oxide aerogel.

[0075] S3. Preparation of porous reduced graphene oxide aerogel: The graphene oxide aerogel prepared in S2 was placed in a tube furnace and heated to 1000℃ for 2 hours under an argon atmosphere at a heating rate of 5℃ / min. During the heat treatment, graphene oxide came into contact with and reacted with iron oxide nanoparticles, and was catalyzed by iron to form Fe3C, forming pores around the Fe3C. Then, the aerogel was soaked in 20wt% hydrochloric acid for 24 hours to remove iron oxide / iron carbide particles and obtain porous reduced graphene oxide aerogel.

[0076] S4 is the same as S4 in Example 1;

[0077] S5 is the same as S5 in Example 1.

[0078] Figure 1 Optical photographs of the aerogel materials prepared in Examples 1-3 are shown. (a) is the graphene oxide aerogel in Example 1, (b) is the porous reduced graphene oxide aerogel in Example 1, (c) is the porous reduced graphene oxide aerogel in Example 2, and (d) is the porous reduced graphene oxide aerogel in Example 3. All four samples are three-dimensional porous aerogel materials.

[0079] Figure 2The images show scanning electron microscope (SEM) images of the graphene aerogel sheets prepared in Examples 1-3. (a) shows the graphene oxide in Example 1, (b) shows the porous reduced graphene oxide in Example 1, (c) shows the porous reduced graphene oxide in Example 2, and (d) shows the porous reduced graphene oxide in Example 3. As can be seen from the images, the surface of the graphene oxide sheets is smooth before the addition of the pore-forming agent. In Example 1, the porous reduced graphene oxide surface has a relatively uniform distribution of a small number of pores, ranging in size from 25-80 nm, with an average size of 50 nm. In Example 2, the porous reduced graphene oxide surface has a large number of pores, with pore diameters ranging from 20-90 nm and an average diameter of 60 nm. In Example 3, the number of pores on the surface of the porous reduced graphene oxide is significantly reduced, with pore sizes ranging from 20-100 nm and an average size of 65 nm. The amount of pore-forming agent added affects the diameter and number distribution of pores. With increasing agent content, the number of pores on the graphene surface first increases and then decreases, while the pore diameter range gradually increases. This is because during heat treatment, metal salt nanoparticles aggregate to form larger particles due to Ostwald curing, resulting in larger pores after heat treatment. Therefore, it can be concluded that when the mass ratio of ferric nitrate nonahydrate particles to graphene oxide in the aqueous graphene oxide solution is 0.2, the number of pores generated is the highest, and the pore-forming effect is the best.

[0080] Figure 3 This is a scanning electron microscope (SEM) image of the porous reduced graphene oxide aerogel / phenolic resin composite material prepared in Example 2. Under the influence of surface tension, the pore diameter range expands to 0.4–7.0 μm, forming a hierarchical pore (nano / micro pore) structure. The nanopores help resist the recombination of reduced graphene oxide, reduce its conductivity, improve impedance matching performance, and easily accumulate loads at the interface, leading to interfacial polarization and improving the material's polarization relaxation capability. The micropore structure can induce multiple reflections of electromagnetic waves, prolonging the propagation path of electromagnetic waves within the material, thereby enhancing the material's electromagnetic wave attenuation.

[0081] Figure 4The image shows the wide-temperature-range absorption performance of the porous reduced graphene oxide aerogel / phenolic resin composite material prepared in Example 2. At 323 K, the composite material achieves minimum absorption with a thickness of 3 mm, with a minimum reflection loss of -41.60 dB@9.15 GHz. With a thickness of 2.75 mm, the effective absorption bandwidth is 4.2 GHz, achieving full-band X-band absorption. As the test temperature increases to 373 K, the minimum reflection loss is -46.61 dB@10.45 GHz with a thickness of 3 mm, and the effective absorption bandwidth is 4.01 GHz with a thickness of 3.05 mm, covering the 8.39-12.4 GHz range. When the temperature rises to 423 K, the minimum reflection loss is... At a thickness of 2.95 mm, the effective absorption bandwidth is 4.2 GHz, covering the entire X-band, with a minimum reflection loss of -41.74 dB at 10.53 GHz and a minimum reflection loss of -45.21 dB at 8.2 GHz. Similarly, at a thickness of 2.85 mm, the effective absorption bandwidth remains at 4.2 GHz, covering the entire X-band. Furthermore, at a temperature of 523 K, the minimum reflection loss is -62.78 dB at 8.77 GHz, and at a thickness of 2.8 mm, the effective absorption bandwidth remains at 4.2 GHz, also covering the entire X-band. The porous reduced graphene oxide aerogel / phenolic resin composite exhibits excellent X-band absorption performance in the 323 k to 523 k range, almost consistently covering the entire X-band, indicating that the composite has low dielectric temperature dependence.

[0082] Example 4

[0083] In this embodiment, the heat treatment temperature in S3 is 900℃ and the heat treatment time is 3h, and the rest is the same as in Embodiment 1.

[0084] Example 5

[0085] In this embodiment, the heat treatment temperature in S3 is 1200℃ and the heat treatment time is 1h, and the rest is the same as in Embodiment 1.

[0086] Example 6

[0087] In this embodiment, in step S4, 5g of epoxy resin is weighed and added to 50mL of anhydrous ethanol, and the rest is the same as in Example 1.

[0088] Example 7

[0089] In this embodiment, in step S4, 15g of organosilicon resin is weighed and added to 50mL of anhydrous ethanol, and the rest is the same as in Example 1.

[0090] Example 8

[0091] In this embodiment, the impregnation time under normal pressure in step S5 is 0.5 hours, and the rest is the same as in embodiment 1.

[0092] Example 9

[0093] In this embodiment, the amount of graphene oxide slurry added in S1 is 0 mg, and the rest is the same as in Example 1.

[0094] Example 10

[0095] In this embodiment, the amount of graphene oxide slurry added in S1 is 120 mg, and the rest is the same as in Example 1.

[0096] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a porous reduced graphene oxide aerogel / resin microwave absorbing material, characterized in that, Includes the following steps: Step 1: Place the graphene oxide slurry in deionized water and obtain an aqueous graphene oxide solution by magnetic stirring; the concentration of the aqueous graphene oxide solution is 3~5 mg / mL; Step 2: Ferric nitrate nonahydrate was placed in an aqueous solution of graphene oxide, mixed thoroughly, and then ammonia was added to adjust the pH of the solution. After freeze-drying, Fe was obtained. 3+ The graphene oxide aerogel; the mass ratio of graphene oxide in the ferric nitrate nonahydrate and the graphene oxide aqueous solution is 0.1~0.3; the pH of the solution is adjusted to 7~10; Step 3, load Fe 3+ After heat treatment, reduced graphene oxide aerogel loaded with Fe3C was obtained. The reduced graphene oxide aerogel loaded with Fe3C was then soaked in hydrochloric acid and dried to obtain porous reduced graphene oxide aerogel. The heat treatment temperature was 900~1200 ℃ and the heat treatment time was 1~3 h. Step 4: Place the porous reduced graphene oxide aerogel in a resin solution, impregnate it under normal pressure, and then cure it to obtain the porous reduced graphene oxide aerogel / resin microwave absorbing material. The resin in the resin solution is one of phenolic resin, epoxy resin, polyimide resin, bismaleimide resin, silicone resin, or cyanate ester resin.

2. The method for preparing a porous reduced graphene oxide aerogel / resin microwave absorbing material according to claim 1, characterized in that, In step 3, the hydrochloric acid concentration is 10~30 wt.%, the soaking time is 24 h, the drying temperature is 80 ℃, and the drying time is 2 h.

3. The method for preparing a porous reduced graphene oxide aerogel / resin microwave absorbing material according to claim 1, characterized in that, In step 4, the solvent of the resin solution is anhydrous ethanol, and the concentration of the resin solution is 0.1~0.3g / mL.

4. The method for preparing a porous reduced graphene oxide aerogel / resin microwave absorbing material according to claim 1, characterized in that, In step 4, the atmospheric pressure impregnation time is 0.5~1h.

5. The method for preparing a porous reduced graphene oxide aerogel / resin microwave absorbing material according to claim 1, characterized in that, In step 4, the curing temperature is 160℃ and the curing time is 1 hour.

6. A porous reduced graphene oxide aerogel / resin microwave absorbing material prepared by any one of claims 1-5, characterized in that, It includes graphene sheets coated with resin, and the graphene sheets have nanoscale pores and microscale pores distributed on them.

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