An electromagnetic shielding aerogel doped with coal-based carbon and its preparation method

Abstract

This invention discloses a coal-based carbon-doped electromagnetic shielding aerogel and its preparation method, belonging to the field of aerogel technology. The aerogel uses lignite as the main carbon source, and prepares a coal-based carbon oxide precursor with rich surface functional groups through oxidation extraction. Iron-cobalt bimetallic ions are loaded through chelation, followed by gradient gelation, solvent replacement, freeze-drying, and high-temperature carbonization using a segmented heating process. In-situ alloy reduction, mesoporous etching, and graphitized carbon nanofiber growth are then completed to construct a hierarchical porous structure. The prepared aerogel is lightweight and high-strength, exhibiting excellent X-band shielding effectiveness primarily through absorption loss. It effectively improves the problems of weak conductivity, low shielding effectiveness, and severe secondary electromagnetic pollution associated with existing coal-based carbon aerogels. Simultaneously, it enhances the graphitization degree of the carbon skeleton and the continuity of the conductive network, fully releasing the magnetic loss efficiency of magnetic particles and strengthening the material's ability to dissipate electromagnetic waves. It is suitable for various electromagnetic protection scenarios.

Description

Technical Field

[0001] This invention relates to the field of aerogel materials technology, specifically to an electromagnetic shielding aerogel doped with coal-based carbon and its preparation method. Background Technology

[0002] Aerogels are nanoscale porous solid materials formed by replacing the liquid phase in a gel with gas through a sol-gel method and a specific drying process. Common aerogels are silica aerogels. Aerogels possess gel properties such as expansion, thixotropy, and slurry separation, and also have characteristics such as low density, low thermal conductivity, high porosity, high temperature resistance, and non-flammability. Electromagnetic shielding aerogels are porous composite materials that combine ultra-low density, high porosity, and excellent electromagnetic interference (EMI) shielding performance with aerogels. By constructing a three-dimensional conductive network, they achieve a shielding mechanism based on absorption, effectively solving the problems of heavy weight, easy corrosion, and secondary reflection pollution of traditional metal shielding materials.

[0003] Currently, coal-based carbon aerogels are an important development direction for low-cost electromagnetic shielding materials. However, because coal-based carbon precursors are mostly amorphous carbon structures after high-temperature carbonization, with low graphitization and weak intrinsic conductivity, the modification of magnetic components often adopts physical blending and simple impregnation loading methods. Metal particles tend to agglomerate and grow, resulting in weak interfacial bonding with the carbon skeleton. Consequently, coal-based carbon aerogels generally suffer from insufficient electrical conductivity loss, inadequate magnetic loss efficiency, high electromagnetic wave surface reflection ratio, and few internal multiple scattering loss paths. This leads to low overall electromagnetic shielding efficiency, with reflection loss being the main factor. It is difficult to meet the high shielding performance requirements of high-end electronic equipment and communication scenarios, and it is also prone to causing secondary electromagnetic radiation pollution. At the same time, the material has high mechanical brittleness and insufficient structural stability, which further limits the large-scale promotion and application of coal-based carbon aerogels in the field of electromagnetic protection. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides an electromagnetic shielding aerogel doped with coal-based carbon and its preparation method, thus solving the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing an electromagnetic shielding aerogel doped with coal-based carbon, comprising the following steps: S1. Select lignite as raw material, ball mill lignite, and pass it through a 200-mesh sieve to obtain coal powder; S2. Coal powder is oxidized by hydrogen peroxide, then extracted by alkali dissolution and acid precipitation, washed and dried to obtain coal-based carbon dioxide precursor powder with oxygen-containing functional groups on the surface. S3. Disperse the coal-based carbon oxide precursor in anhydrous ethanol, add soluble iron salt and soluble cobalt salt for ultrasonic dispersion, achieve uniform loading of metal ions through chelation, then add resorcinol, formaldehyde and pH adjuster, and stir to obtain a homogeneous sol. S4. The sol is injected into a sealed mold and subjected to gradient gelation and aging treatment in sequence to obtain a wet gel. The wet gel is then replaced with anhydrous ethanol solvent and freeze-dried to obtain a dry gel. S5. The dry gel is placed in a tube furnace and carbonized in stages under an argon protective atmosphere. During the high-temperature holding stage, the iron-cobalt alloy reduction, directional migration etching for pore formation and catalytic graphitization of carbon nanofibers are completed simultaneously. After natural cooling with the furnace, an electromagnetic shielding aerogel doped with coal-based carbon is obtained.

[0006] Preferably, step S2 specifically includes: According to the solid-liquid ratio of 1g of coal powder to 10-20mL of hydrogen peroxide, add 30% hydrogen peroxide solution to the coal powder, oxidize at 60-80℃ for 4-8h, and filter to collect the filtrate. Adjust the pH to 10-12 with alkaline solution and stir to dissolve. After centrifugation to remove insoluble matter, take the supernatant. The pH of the supernatant was adjusted to 2-3 with dilute acid to precipitate the precipitate. After washing until neutral, the precipitate was freeze-dried to obtain coal-based carbon oxide precursor powder.

[0007] Preferably, in step S3, the total molar amount of iron and cobalt is 0.5-2 mmol:1g in mass ratio to the coal-based carbon dioxide precursor powder, and the molar ratio of iron salt to cobalt salt is 1-3:3-1. The molar ratio of resorcinol to formaldehyde is 1:2, and the mass ratio of coal-based carbon precursor powder to resorcinol is 3-8:1; after adjusting the pH to 7-8, the mixture is stirred to form a homogeneous sol.

[0008] Preferably, the soluble iron salt in step S3 is any one of ferric nitrate, ferric chloride, or ferric acetylacetone; The soluble cobalt salt is any one of cobalt nitrate, cobalt chloride, or cobalt acetylacetonate; The ultrasonic dispersion time of the soluble iron salt and the soluble cobalt salt is 30-60 min.

[0009] Preferably, the gradient gelation in step S4 specifically involves: First, let it stand at 40-50℃ for 6-12 hours to form a concentration gradient from the surface to the core by utilizing the difference in diffusion rate of iron and cobalt ions. Then, raise the temperature to 60-80℃ and let it stand for 12-24 hours to complete gel solidification. After the gel is formed, continue to age it at 80℃ for 24-48 hours to complete gradient gelation.

[0010] Preferably, in step S4, the solvent replacement is carried out by multiple immersions in anhydrous ethanol, with each immersion lasting 6-12 hours and repeated 3-5 times. Freeze-drying involves pre-freezing at a temperature of -40 to -60°C for 4 to 8 hours, followed by drying under a vacuum of 10 to 50 Pa and a cold trap temperature not exceeding -55°C for 24 to 48 hours.

[0011] Preferably, the segmented heating in step S5 adopts a three-stage heating method: The first stage involves heating from room temperature to 300℃ at a rate of 5℃ / min, followed by holding at this temperature to remove residual solvents and small molecules. The second stage involves heating from 300℃ to 600℃ at a rate of 2℃ / min, followed by heat preservation to complete pre-carbonization and skeleton curing. The third stage involves heating from 600℃ to the target carbonization temperature at a rate of 3℃ / min.

[0012] Preferably, the target carbonization temperature in step S5 is 800-1100℃, and the high-temperature holding time is 1-3 hours; During the heat preservation process, iron and cobalt ions are reduced by carbon to iron and cobalt alloy nanoparticles. The particles migrate in a directional manner to etch continuous mesoporous channels, while simultaneously catalyzing the growth of surrounding amorphous carbon into graphitized carbon nanofibers.

[0013] Preferably, the total mass of the iron-cobalt alloy in the prepared coal-doped carbon electromagnetic shielding aerogel accounts for 5%-20% of its total mass, and the density of the coal-doped carbon electromagnetic shielding aerogel is controlled at 15-50 mg / cm3.

[0014] Preferably, the electromagnetic shielding aerogel doped with coal-based carbon is prepared according to the preparation method described above.

[0015] This invention provides an electromagnetic shielding aerogel doped with coal-based carbon and its preparation method. It has the following beneficial effects: (1) The aerogel adopts the process of iron-cobalt bimetallic ion chelation loading combined with high-temperature in-situ catalytic graphitization. It relies on the rich oxygen-containing functional groups on the surface of the coal-based carbon oxide precursor to achieve uniform anchoring of metal ions, avoiding the problems of particle agglomeration and weak interface bonding that are easy to occur in traditional physical blending methods. During the carbonization process, it is reduced in situ to form well-dispersed alloy particles, and simultaneously catalyzes the growth of surrounding amorphous carbon into graphitized carbon nanofibers that are tightly bound to the carbon skeleton, thereby improving the graphitization degree of the carbon skeleton and the continuity of the conductive network, fully releasing the magnetic loss efficiency of magnetic particles, strengthening the material's ability to dissipate electromagnetic waves, and improving the insufficient shielding efficiency of pure coal-based carbon materials.

[0016] (2) By utilizing the process design of gradient gelation and in-situ migration etching to create holes, a gradient distribution structure of metal components along the thickness direction is formed by gradient temperature control during the gel solidification stage. At the same time, the directional migration etching effect of alloy particles at high temperature is used to construct fully connected hierarchical channels, so that the surface impedance of the material is well matched with the free space, reducing the direct reflection of electromagnetic waves on the material surface. The internal multi-level connected channels provide sufficient multiple reflection and scattering paths and interface polarization sites for electromagnetic waves, achieving a balance between impedance matching characteristics and internal loss capability, greatly increasing the absorption loss ratio, effectively reducing the harm of secondary electromagnetic radiation, and forming an absorption-dominant green electromagnetic protection effect.

[0017] (3) This aerogel uses abundant coal as the main carbon source and prepares soluble coal-based carbon precursors through an oxidation extraction process. It does not require the addition of expensive nanofillers and template reagents. Furthermore, the graphitized carbon nanofibers grown in situ form covalent bonds with the carbon skeleton, which can effectively transfer and disperse stress, improve the mechanical toughness and structural stability of the material, and significantly reduce the preparation cost while ensuring the excellent shielding performance of the material. This enhances the structural reliability and environmental adaptability of the product and promotes the application of coal-based carbon aerogels in the fields of electromagnetic protection and flexible wearable devices.

[0018] (4) During the catalytic graphitization process, the iron-cobalt alloy particles are tightly covered by the graphitized carbon layer grown in situ and are anchored inside the carbon skeleton, which isolates the magnetic particles from the direct erosion of the external environment. At the same time, the continuous carbon phase structure avoids the problems of easy detachment of external fillers and easy failure of interfaces, which improves the material's resistance to moisture, corrosion and aging. It can be used stably for a long time in complex environments such as outdoor, high humidity and industrial corrosion, breaking through the limitations of traditional magnetic composite materials that are easy to oxidize and fail and have rapid performance decay, and broadening the application of coal-based carbon aerogel in complex electromagnetic protection scenarios. Attached Figure Description

[0019] Figure 1 This diagram illustrates the steps of the method for preparing the electromagnetic shielding aerogel doped with coal-based carbon according to the present invention. Detailed Implementation

[0020] 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. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Example 1 See Figure 1 The specific steps for preparing coal-doped carbon electromagnetic shielding aerogels are as follows: S1. Select lignite as raw material, crush it in a ball mill and pass it through a 200-mesh standard sieve to obtain coal powder for later use; S2. Add 30% hydrogen peroxide solution to coal powder at a solid-liquid ratio of 1g:20mL, and oxidize it in a water bath at 80℃ for 8h. After the reaction is complete, filter the filtrate, adjust the pH of the filtrate to 12 with sodium hydroxide solution, stir until the soluble components are fully dissolved, centrifuge to remove insoluble matter, collect the supernatant, adjust the pH of the supernatant to 3 with dilute hydrochloric acid, precipitate humic acid, centrifuge to collect the precipitate and wash it to neutral, and freeze-dry to obtain coal-based carbon dioxide precursor powder with oxygen-containing functional groups on the surface. S3. Disperse the coal-based carbon oxide precursor in anhydrous ethanol. Add ferric nitrate and cobalt nitrate at a ratio of 2 mmol:1 g of total iron and cobalt molar amount to precursor mass ratio, and control the molar ratio of iron salt to cobalt salt to be 3:1. Sonicate for 60 min to achieve uniform loading of metal ions through the chelation effect of oxygen-containing functional groups on the precursor surface. Then add resorcinol and formaldehyde, and control the mass ratio of coal-based carbon precursor to resorcinol to be 8:1 and the molar ratio of resorcinol to formaldehyde to be 1:2. Add sodium carbonate adjuster to adjust the pH of the system to 8 and continue stirring until a homogeneous sol is formed. S4. Inject the sol into a sealed mold and let it stand at 50°C for 12 hours to form a concentration gradient by utilizing the difference in ion diffusion rates. Then, raise the temperature to 80°C and let it stand for 24 hours to complete gel solidification. After the gel is formed, continue to age it at 80°C for 48 hours to strengthen the three-dimensional skeleton structure. Replace the aged wet gel with anhydrous ethanol, soaking for 12 hours each time, repeating 5 times. After the replacement is completed, freeze-dry it: first, pre-freeze it at -40°C for 8 hours, and then dry it at a vacuum of 10 Pa and a cold trap temperature not higher than -55°C for 48 hours to obtain a dry gel. S5. Place the dry gel in a tube furnace and introduce argon gas as a protective atmosphere. Use a three-stage programmed temperature rise for carbonization: the first stage is to heat from room temperature to 300℃ at a rate of 5℃ / min, and hold at this temperature to remove residual solvent and small molecules; the second stage is to heat from 300℃ to 600℃ at a rate of 2℃ / min, and hold at this temperature to complete pre-carbonization and skeleton solidification; the third stage is to heat from 600℃ to 1100℃ at a rate of 3℃ / min, and hold at 1100℃ for 3 hours. During the high-temperature stage, the iron-cobalt alloy reduction, directional migration etching for pore formation, and catalytic graphitization of carbon nanofibers are completed simultaneously. The gel is then naturally cooled to room temperature with the furnace to obtain an electromagnetic shielding aerogel doped with coal-based carbon.

[0022] Example 2 The specific steps for preparing coal-doped carbon electromagnetic shielding aerogels are as follows: S1. Select lignite as raw material, crush it in a ball mill and pass it through a 200-mesh standard sieve to obtain coal powder for later use; S2. Add 30% hydrogen peroxide solution to coal powder at a solid-liquid ratio of 1g:15mL, and oxidize it in a 70℃ water bath for 6 hours. After the reaction is complete, filter the filtrate, adjust the pH of the filtrate to 11 with sodium hydroxide solution, stir until the soluble components are fully dissolved, centrifuge to remove insoluble matter, collect the supernatant, adjust the pH of the supernatant to 2.5 with dilute hydrochloric acid, precipitate humic acid, centrifuge to collect the precipitate and wash it to neutral, and freeze-dry to obtain coal-based carbon dioxide precursor powder. S3. Disperse the coal-based carbon oxide precursor in anhydrous ethanol. Add ferric nitrate and cobalt nitrate at a ratio of 1.25 mmol:1 g of total iron and cobalt molar amount to precursor mass ratio, and control the molar ratio of iron salt to cobalt salt to be 1:1. Sonicate for 45 min to complete chelation loading. Then add resorcinol and formaldehyde, and control the mass ratio of coal-based carbon precursor to resorcinol to be 5.5:1 and the molar ratio of resorcinol to formaldehyde to be 1:2. Add sodium carbonate adjuster to adjust the pH of the system to 7.5 and continue stirring until a homogeneous sol is formed. S4. Inject the sol into a sealed mold, let it stand at 45℃ for 9 hours to form an ion concentration gradient, then raise the temperature to 70℃ and let it stand for 18 hours to complete gel solidification. After the gel is formed, continue to age it at 80℃ for 36 hours. Replace the aged wet gel with anhydrous ethanol, soaking for 9 hours each time, repeating 4 times. After the replacement is completed, freeze dry it: first pre-freeze it at -50℃ for 6 hours, then dry it at a vacuum of 30Pa and a cold trap temperature not higher than -55℃ for 36 hours to obtain a dry gel. S5. Place the dry gel in a tube furnace and purge it with argon gas. Use a three-stage temperature program: heating rate of 5℃ / min from room temperature to 300℃, heating rate of 2℃ / min from 300℃ to 600℃, and heating rate of 3℃ / min from 600℃ to 950℃. Hold at 950℃ for 2 hours and allow to cool naturally in the furnace to obtain an electromagnetic shielding aerogel doped with coal-based carbon.

[0023] Example 3 The specific steps for preparing coal-doped carbon electromagnetic shielding aerogels are as follows: S1. Select lignite as raw material, crush it in a ball mill and pass it through a 200-mesh standard sieve to obtain coal powder for later use; S2. Add 30% hydrogen peroxide solution to coal powder at a solid-liquid ratio of 1g:10mL, oxidize for 4 hours in a 60℃ water bath, filter after the reaction, adjust the pH of the filtrate to 10 with sodium hydroxide solution, stir until the soluble components are fully dissolved, centrifuge to remove insoluble matter and collect the supernatant, adjust the pH of the supernatant to 2 with dilute hydrochloric acid to precipitate humic acid, centrifuge to collect the precipitate and wash until neutral, freeze dry to obtain coal-based carbon dioxide precursor powder; S3. Disperse the coal-based carbon oxide precursor in anhydrous ethanol. Add ferric nitrate and cobalt nitrate at a ratio of 0.5 mmol:1 g of total iron and cobalt molar amount to precursor mass ratio, and control the molar ratio of iron salt to cobalt salt to be 1:3. Sonicate for 30 min to complete chelation loading. Then add resorcinol and formaldehyde, and control the mass ratio of coal-based carbon precursor to resorcinol to be 3:1 and the molar ratio of resorcinol to formaldehyde to be 1:2. Add sodium carbonate adjuster to adjust the pH of the system to 7 and continue stirring until a homogeneous sol is formed. S4. Inject the sol into a sealed mold, let it stand at 40℃ for 6 hours to form an ion concentration gradient, then raise the temperature to 60℃ and let it stand for 12 hours to complete gel solidification. After the gel is formed, continue to age it at 80℃ for 24 hours. Replace the aged wet gel with anhydrous ethanol, soaking for 6 hours each time, repeating 3 times. After the replacement is completed, freeze dry it: first pre-freeze it at -60℃ for 4 hours, then dry it at a vacuum of 50Pa and a cold trap temperature not higher than -55℃ for 24 hours to obtain a dry gel. S5. Place the dry gel in a tube furnace and purge it with argon gas. Use a three-stage temperature program: heating rate of 5℃ / min from room temperature to 300℃, heating rate of 2℃ / min from 300℃ to 600℃, and heating rate of 3℃ / min from 600℃ to 800℃. Hold at 800℃ for 1 hour and allow it to cool naturally in the furnace to obtain an electromagnetic shielding aerogel doped with coal-based carbon.

[0024] Comparative Example 1 Comparative Example 1 The preparation steps are the same as in Example 1, except that ferric nitrate and cobalt nitrate are not added in step S3, and the other process parameters are the same as in Example 1.

[0025] Comparative Example 2 The preparation steps are the same as in Example 1, except that in step S3, after the iron salt and cobalt salt are added, they are only mechanically stirred and mixed, without ultrasonic chelation and dispersion treatment. The other process parameters are the same as in Example 1.

[0026] Comparative Example 3 The preparation steps are the same as in Example 1, except that the low temperature gradient standing step is omitted in step S4. Instead, the sol is placed in a 70°C water bath and kept at a constant temperature for 18 hours to complete gel solidification. The remaining process parameters are the same as in Example 1.

[0027] Comparative Example 4 The preparation steps are the same as in Example 1, except that only ferric nitrate is added in step S3, the total molar amount of iron is equal to the total molar amount of iron and cobalt in Example 1, no cobalt salt is added, and the other process parameters are the same as in Example 1.

[0028] Comparative Example 5 The preparation steps are the same as in Example 1, except that only cobalt nitrate is added in step S3, the total molar amount of cobalt is equal to the total molar amount of iron and cobalt in Example 1, no iron salt is added, and the other process parameters are the same as in Example 1.

[0029] Comparative Example 6 The preparation steps are the same as in Example 1, except that the final carbonization temperature in step S5 is set to 750℃ and the holding time is still 2h. The other process parameters are the same as in Example 1.

[0030] Comparative Example 7 The preparation steps are the same as in Example 1, except that: in step S4, after solvent replacement, freeze drying is not performed, but instead, hot air drying at 60°C and atmospheric pressure is performed for 24 hours to obtain a dry gel. The remaining process parameters are the same as in Example 1.

[0031] Comparative Example 8 The preparation steps are the same as in Example 1, except that the oxidation extraction step S2 is omitted, and 200-mesh coal powder is directly dispersed in anhydrous ethanol to prepare the subsequent sol. The remaining process parameters are the same as in Example 1.

[0032] Comparative Example 9 The preparation steps are the same as in Example 1, except that in step S5, the temperature is directly raised to 950°C at a rate of 5°C / min and held for 2 hours, without using the three-stage segmented heating program. The other process parameters are the same as in Example 1.

[0033] Test case Bulk density: The volume of the sample was calculated by measuring its geometric dimensions with vernier calipers and then by weighing it using an analytical balance. Conductivity: The conductivity of the samples was tested at room temperature using a four-probe resistivity meter. Each group of samples was tested in parallel for 3 times and the average value was taken. Electromagnetic shielding effectiveness: The average electromagnetic shielding effectiveness of the samples in the X-band (8.2-12.4 GHz) was tested using a vector network analyzer and the waveguide method. Specific surface area: The specific surface area of ​​the sample was calculated using a nitrogen adsorption-desorption tester and the BET model. Compressive strength: The compressive strength of the sample under 10% strain was tested using a universal testing machine at a loading rate of 1 mm / min. ; As shown in Table 1, compared with Comparative Example 1, the in-situ catalysis of iron-cobalt bimetallic alloy can improve the conductivity of coal-based carbon aerogel and the electromagnetic shielding efficiency by more than 2 times, thus improving the defect of insufficient conductivity loss of pure coal-based amorphous carbon. Compared with Comparative Example 2, the chelation loading method enables the metal particles to achieve molecular-level dispersion, avoiding the decline in catalytic efficiency and magnetic loss capacity caused by agglomeration and growth. The shielding efficiency is improved by more than 50% under the same metal dosage. Compared with Comparative Examples 4 and 5, the catalytic activity and magnetic loss capacity of the iron-cobalt bimetallic alloy are significantly better than those of a single metal. The synergy between the two is more conducive to the growth of graphitized carbon and the construction of multi-loss mechanism, which fully verifies the technical effect of magnetic-dielectric synergistic enhancement. Comparative examples and Comparative Example 3 show that the metal content gradient structure along the thickness direction can significantly optimize the impedance matching characteristics of the material, increase the absorption loss ratio by nearly 10 percentage points, greatly reduce electromagnetic wave surface reflection, effectively reduce the risk of secondary electromagnetic radiation, and combined with the fully connected hierarchical channels formed by in-situ migration etching, can provide sufficient multiple reflection and scattering paths and interface polarization sites for incident electromagnetic waves, further enhancing the internal dissipation capability. The aerogel of this invention has an absorption loss ratio of over 70%, realizing absorption-dominant electromagnetic shielding, which is in line with the development direction of green electromagnetic protection. As can be seen from the comparison of the examples and Comparative Example 1, the in-situ grown graphitized carbon nanofibers and the coal-based carbon skeleton are covalently bonded continuous carbon phases, which can efficiently transfer and disperse stress, increasing the compressive strength of the material by more than 40%, significantly improving the defects of pure coal-based carbon aerogels such as high brittleness and easy breakage. At the same time, the metal alloy particles are in-situ coated and anchored by the graphitized carbon layer, which is different from the surface adhesion method of physical blending. It can effectively resist the erosion of the external environment, avoid particle shedding and performance degradation, and improve the service stability and service life of the material under complex working conditions. This solution uses abundant and inexpensive lignite as the main carbon source and prepares soluble precursors through a mild oxidative extraction process. The core catalytic graphitization, hierarchical pore construction, and gradient structure formation are all achieved through in-situ control of process parameters, eliminating the need for expensive nano-carbon fillers and template reagents, thus significantly reducing raw material and process costs. Examples 1-3 show a clear performance gradient: as the metal loading and carbonization temperature increase, the material's shielding effectiveness and mechanical strength gradually increase, while the density increases synchronously. The material's performance can be flexibly controlled by adjusting process parameters to meet the lightweight and shielding requirements of different scenarios such as consumer electronics, communication base stations, and aerospace, demonstrating good process versatility and product adaptability.

[0034] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A method for preparing a coal-doped carbon-based electromagnetic shielding aerogel, characterized in that: Includes the following steps: S1. Select lignite as raw material, ball mill lignite, and pass it through a 200-mesh sieve to obtain coal powder; S2. Coal powder is oxidized by hydrogen peroxide, then extracted by alkali dissolution and acid precipitation, washed and dried to obtain coal-based carbon dioxide precursor powder with oxygen-containing functional groups on the surface. S3. Disperse the coal-based carbon oxide precursor in anhydrous ethanol, add soluble iron salt and soluble cobalt salt for ultrasonic dispersion, achieve uniform loading of metal ions through chelation, then add resorcinol, formaldehyde and pH adjuster, and stir to obtain a homogeneous sol. S4. The sol is injected into a sealed mold and subjected to gradient gelation and aging treatment in sequence to obtain a wet gel. The wet gel is then replaced with anhydrous ethanol solvent and freeze-dried to obtain a dry gel. S5. The dry gel is placed in a tube furnace and carbonized in stages under an argon protective atmosphere. During the high-temperature holding stage, the iron-cobalt alloy reduction, directional migration etching for pore formation and catalytic graphitization of carbon nanofibers are completed simultaneously. After natural cooling with the furnace, an electromagnetic shielding aerogel doped with coal-based carbon is obtained.

2. The electromagnetic shielding aerogel doped with coal-based carbon and its preparation method according to claim 1, characterized in that: Step S2 is as follows: According to the solid-liquid ratio of 1g of coal powder to 10-20mL of hydrogen peroxide, add 30% hydrogen peroxide solution to the coal powder, oxidize at 60-80℃ for 4-8h, and filter to collect the filtrate. Adjust the pH to 10-12 with alkaline solution and stir to dissolve. After centrifugation to remove insoluble matter, take the supernatant. The pH of the supernatant was adjusted to 2-3 with dilute acid to precipitate the precipitate. After washing until neutral, the precipitate was freeze-dried to obtain coal-based carbon oxide precursor powder.

3. The electromagnetic shielding aerogel doped with coal-based carbon and its preparation method according to claim 1, characterized in that: In step S3, the total molar amount of iron and cobalt is 0.5-2 mmol:1 g to the mass ratio of the coal-based carbon dioxide precursor powder, and the molar ratio of iron salt to cobalt salt is 1-3:3-1. The molar ratio of resorcinol to formaldehyde is 1:2, and the mass ratio of coal-based carbon precursor powder to resorcinol is 3-8:1; after adjusting the pH to 7-8, the mixture is stirred to form a homogeneous sol.

4. The electromagnetic shielding aerogel doped with coal-based carbon and its preparation method according to claim 1, characterized in that: The soluble iron salt mentioned in step S3 is any one of ferric nitrate, ferric chloride, or ferric acetylacetone; The soluble cobalt salt is any one of cobalt nitrate, cobalt chloride, or cobalt acetylacetonate; The ultrasonic dispersion time of the soluble iron salt and the soluble cobalt salt is 30-60 min.

5. The electromagnetic shielding aerogel doped with coal-based carbon and its preparation method according to claim 1, characterized in that: The gradient gelation in step S4 is specifically as follows: First, let it stand at 40-50℃ for 6-12 hours to form a concentration gradient from the surface to the core by utilizing the difference in diffusion rate of iron and cobalt ions. Then, raise the temperature to 60-80℃ and let it stand for 12-24 hours to complete gel solidification. After the gel is formed, continue to age it at 80℃ for 24-48 hours to complete gradient gelation.

6. The electromagnetic shielding aerogel doped with coal-based carbon and its preparation method according to claim 1, characterized in that: In step S4, solvent replacement is performed by multiple immersions in anhydrous ethanol, with each immersion lasting 6-12 hours, repeated 3-5 times. Freeze-drying involves pre-freezing at a temperature of -40 to -60°C for 4 to 8 hours, followed by drying under a vacuum of 10 to 50 Pa and a cold trap temperature not exceeding -55°C for 24 to 48 hours.

7. The electromagnetic shielding aerogel doped with coal-based carbon and its preparation method according to claim 1, characterized in that: Step S5 uses a three-stage heating method: The first stage involves heating from room temperature to 300℃ at a rate of 5℃ / min, followed by holding at this temperature to remove residual solvents and small molecules. The second stage involves heating from 300℃ to 600℃ at a rate of 2℃ / min, followed by heat preservation to complete pre-carbonization and skeleton curing. The third stage involves heating from 600℃ to the target carbonization temperature at a rate of 3℃ / min.

8. The electromagnetic shielding aerogel doped with coal-based carbon and its preparation method according to claim 1, characterized in that: In step S5, the target carbonization temperature is 800-1100℃, and the high-temperature holding time is 1-3 hours. During the heat preservation process, iron and cobalt ions are reduced by carbon to iron and cobalt alloy nanoparticles. The particles migrate in a directional manner to etch continuous mesoporous channels, while simultaneously catalyzing the growth of surrounding amorphous carbon into graphitized carbon nanofibers.

9. The electromagnetic shielding aerogel doped with coal-based carbon and its preparation method according to claim 1, characterized in that: The total mass of the iron-cobalt alloy in the prepared coal-doped carbon electromagnetic shielding aerogel accounts for 5%–20% of its total mass, and the density of the coal-doped carbon electromagnetic shielding aerogel is controlled at 15–50 mg / cm³. 3 .

10. The preparation method according to claim 1 yields an electromagnetic shielding aerogel doped with coal-based carbon.

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