Efficient microwave absorption carbon aerogel-based composite material and application thereof

Abstract

The invention relates to the field of aerogel materials, and provides an efficient microwave absorption carbon aerogel-based composite material and a preparation method thereof. The material takes layered porous carbon aerogel as a matrix, carbon nanotubes grow in situ on the surfaces of pore walls of the matrix through a chemical vapor deposition method, a three-dimensional conductive network is constructed, and FeCo nanoparticles are uniformly encapsulated in inner cavities of the carbon nanotubes. The material has high specific surface area (650-950 m / g), high conductivity (65-80 S / cm) and excellent microwave absorption performance. The preparation process comprises the key steps of metal precursor framework construction, segmented freeze drying, catalytic activation, carbon nanotube in-situ growth and the like, a distributed layered composite structure with the porosity reaching 80%-95% is formed, the microwave absorption, mechanical strength and oxidation resistance of the composite material are effectively improved, and the composite material is suitable for the fields of electromagnetic shielding, stealth materials and the like and has good application prospects. Wide application prospects are realized.

Description

Technical Field

[0001] The invention relates to the field of aerogel materials, and in particular to a high-efficiency microwave absorbing carbon aerogel-based composite material and applications thereof. Background Art

[0002] With the rapid development of high-tech fields such as 5G communication, radar stealth, aerospace, and electromagnetic compatibility, the problem of electromagnetic wave interference has become increasingly prominent, and higher requirements have been put forward for efficient, lightweight, and durable microwave absorbing materials. In radar stealth and high-frequency communication equipment, materials must not only have excellent microwave absorption capabilities to effectively attenuate and shield electromagnetic wave signals, but also have good mechanical properties and antioxidant stability to meet the needs of long-term service in complex and harsh environments. For example, in high-altitude, high-speed aircraft or shipborne radar covers, materials need to withstand large mechanical stresses and strong oxidizing atmospheres while maintaining stable electromagnetic absorption performance. Therefore, materials must achieve optimized coordination in terms of high specific surface area, conductivity, dielectric loss, and magnetic loss. In this context, the development of microwave absorbing materials with high absorption efficiency, strong structural stability, and excellent environmental adaptability can not only significantly improve the stealth capability and electromagnetic compatibility of equipment, but also promote the upgrading of related industrial technologies and broaden its high-end application space in defense, electronics, energy, and other fields. Therefore, constructing a new composite material system that combines microwave absorption efficiency, mechanical strength, and antioxidant properties is an important research direction in the current field of materials science and engineering.

[0003] Although a variety of carbon-based or magnetic materials have been used to construct microwave absorption structures, there are still great challenges in meeting microwave absorption performance, mechanical strength and anti-oxidation stability at the same time. For example, the Chinese patent with publication number CN113277501A discloses a nitrogen-doped reduced graphene oxide aerogel and its application in the preparation of microwave absorption materials. Although it has a certain absorption capacity, its mechanical properties are weak, and it is difficult to meet the requirements of structural stability in the actual service process, and it is easy to have performance degradation in high temperature or oxidizing environment. The main reason for the above-mentioned shortcomings is that the material structure lacks a multi-scale synergistic enhancement mechanism, the interface between the absorbing component and the matrix is ​​not firmly bonded, and the overall thermal conductivity and conductive channels are discontinuous, which makes it difficult to balance the electromagnetic wave attenuation ability and structural durability; in addition, some absorbing materials ignore the encapsulation protection of oxidation-sensitive components in the microstructure design, resulting in serious oxidative degradation in long-term operation. Therefore, it is urgent to develop a carbon-based composite material system that can realize the construction of a conductive network in the microstructure, the stable dispersion of absorbing components and the anti-oxidation coating mechanism, so as to break through the bottleneck of existing materials in the integration of multiple performances and meet the application needs in complex service environments. Summary of the invention

[0004] (1) Technical issues solved The object of the present invention is to provide a high-efficiency microwave-absorbing carbon aerogel-based composite material and its application, and to solve the problems of insufficient microwave absorption, mechanical properties and antioxidant properties of the current carbon aerogel-based composite materials.

[0005] (2) Technical solution In order to achieve the above object, the present invention provides the following technical solution: A high-efficiency microwave-absorbing carbon aerogel-based composite material, the carbon aerogel-based composite material comprising: a) A layered porous carbon-based aerogel matrix, the porosity of the matrix being 80% - 95%, and having a layered pore size structure, wherein the macroscopic channel pore size is 1.2 μm - 5.5 μm; b) A carbon nanotube network structure, the carbon nanotubes being in-situ grown and anchored on the surface of the carbon aerogel pore wall by chemical vapor deposition to construct a three-dimensional interconnected conductive network, the diameter of the carbon nanotubes being 50 nm - 85 nm; c) FeCo nanoparticles, the nanoparticles being uniformly dispersed in the inner cavity of the carbon nanotubes, wherein the molar ratio of Fe / Co is 1:0.8 - 1:1.2.

[0006] Furthermore, the specific surface area of the carbon aerogel-based composite material is 650 m² / g - 950 m² / g, and the conductivity is 65 S / cm - 80 S / cm.

[0007] Furthermore, the core size of the FeCo nanoparticles is 25 nm - 10 nm.

[0008] Furthermore, the method for the carbon aerogel-based composite material comprises the following steps: S1. Placing the metal precursor composite skeleton in a chemical vapor deposition furnace, and performing catalytic activation in a mixed gas atmosphere of argon and hydrogen, wherein the volume fraction of hydrogen is 20% - 35%, and heating at a heating rate of 5 °C / min - 8 °C / min to 650 °C - 750 °C, and holding for 60 min - 90 min to complete the catalyst activation; S2. Continuing to heat at a heating rate of 6 °C / min - 8 °C / min, and simultaneously introducing a ternary mixed gas of acetylene / hydrogen / argon, and performing a chemical vapor deposition reaction at a deposition temperature of 780 °C - 820 °C for a deposition time of 45 min - 75 min to enable the in-situ directional growth of carbon nanotubes on the surface of the aerogel pore wall; S3. After the reaction is completed, cooling to room temperature according to the procedure to obtain a composite aerogel material with a carbon nanotube network.

[0009] The present invention adopts the design of in-situ directional growth of carbon nanotubes to construct a three-dimensional conductive network, which is mainly used to enhance the microwave absorption performance, mechanical properties and antioxidant properties of carbon aerogel-based composites. By placing the metal precursor composite skeleton in a chemical vapor deposition furnace and carrying out catalytic activation under a mixed atmosphere of argon and hydrogen, the active state of the metal components is ensured, providing uniform and stable catalytic sites for the subsequent orderly growth of carbon nanotubes; Subsequently, under the action of a ternary mixed gas of acetylene / hydrogen / argon, the in-situ directional growth of carbon nanotubes on the pore wall surface of the aerogel is realized at an appropriate temperature and deposition rate, forming a carbon nanotube network that penetrates the porous structure. This network establishes a continuous conduction path at the microscale, effectively enhancing the electromagnetic wave attenuation ability of the material; At the same time, the tight interfacial bonding between the carbon nanotubes and the pore wall of the carbon aerogel improves the overall mechanical strength and significantly improves the structural stability of the material; More importantly, the carbon nanotube structure effectively encapsulates and isolates the embedded FeCo nanoparticles, reducing the active interface exposed by the nanoparticles in high-temperature or oxidative environments, thereby improving the antioxidant ability of the material; In addition, this design precisely controls the growth behavior and network distribution of carbon nanotubes by regulating the heating rate, gas composition and reaction time, ensuring the synergistic effect and structural integration degree among the components. The multi-step deposition and structure construction process adopted in the present invention not only realizes the organic combination of carbon nanotubes and carbon aerogel, but also endows the composite material with excellent electromagnetic response ability, structural integrity and environmental adaptability, laying a solid foundation for the development of high-performance microwave absorption materials.

[0010] Further, the metal precursor composite skeleton in step S1 is prepared by the following steps: a) Homogenize 90 to 110 parts of nanocellulose suspension, 90 to 110 parts of konjac glucomannan, and 6.5 to 8.5 parts of a mixture of cobalt nitrate and iron nitrate under high-pressure microfluidic conditions at 22°C to 28°C. The treatment pressure in the first stage is 100 MPa to 150 MPa, the treatment time is 10 min to 12 min, the treatment pressure in the second stage is 180 MPa to 220 MPa, the treatment time is 8 min to 10 min, and the equipment rotation speed is controlled at 12500 rpm to 14500 rpm; b) Adjust the pH of the system to 9.5 to 10.2 with an aqueous sodium hydroxide solution with a mass fraction of 0.05 wt%, inject the obtained mixture into a mold, and perform programmed cooling and freezing treatment. Cool from -8°C to -12°C to -15°C to -17°C at a cooling rate of 0.4°C / min to 0.6°C / min, and then cool to -17°C to -19°C at a cooling rate of 0.8°C / min to 1.2°C / min to form a layered ice crystal template with a directional distribution of Fe³⁺ / Co²⁺ ions; c) Next, segmented freeze-drying is carried out. In the first stage, it is dried for 4 h to 8 h under the conditions of -41°C to -43°C and 0.7 Pa to 0.9 Pa. In the second stage, it is dried for 6 h to 10 h under the conditions of -44°C to -46°C and 0.4 Pa to 0.6 Pa. In the third stage, it is dried for 20 h to 25 h under the conditions of -47°C to -49°C and 0.2 Pa to 0.4 Pa to obtain the metal precursor composite skeleton.

[0011] Furthermore, in the mixture of cobalt nitrate and iron nitrate, the molar ratio of iron nitrate to cobalt nitrate is 1:0.8 to 1:1.2.

[0012] The present invention adopts the design of constructing a metal precursor composite skeleton based on nanocellulose, konjac glucomannan and a mixture of cobalt nitrate and iron nitrate, which is mainly used to enhance the microwave absorption performance, mechanical properties and antioxidant properties of carbon aerogel-based composites. By forming a composite support system of nanocellulose suspension and konjac glucomannan under suitable temperature conditions, and introducing a mixture of iron nitrate and cobalt nitrate with a certain molar ratio, a precursor system with uniform structure and stable dispersion is constructed through high-pressure microfluidic homogenization treatment, significantly improving the uniformity and interfacial compatibility between components, and laying a foundation for subsequent ion distribution and structure regulation. Subsequently, the pH value is adjusted to an appropriate range by sodium hydroxide aqueous solution, and the ice crystal growth rate is controlled by programmed cooling to form a layered ice crystal template with the characteristic of directional distribution of Fe³⁺ / Co²⁺ ions, making the arrangement of metal ions in the three-dimensional structure more orderly, which is helpful for the uniform distribution of subsequent catalytic sites and the directional growth of carbon nanotubes. Through the segmented freeze-drying process, water is gradually removed under the precise control of temperature and vacuum degree, avoiding structural collapse, and retaining the layered porous structure of the composite skeleton, thereby improving the specific surface area and skeleton stability of the material, and effectively supporting the construction of the carbon nanotube network and the loading of FeCo nanoparticles during the subsequent deposition process. Cobalt nitrate and iron nitrate as catalysts can not only promote the in-situ directional growth of carbon nanotubes during the chemical vapor deposition process, but also be embedded in the inner cavity of carbon nanotubes and in-situ transformed into FeCo nanoparticles, realizing the uniform distribution and effective encapsulation of magnetic components, thereby enhancing the magnetic loss ability and antioxidant properties of the material. This design strategy realizes the synergistic assembly of organic components and metal salts, enhances the structural mechanical properties through the bonding of nanocellulose and konjac glucomannan, enhances the subsequent catalytic activity and the uniformity of the conductive network through the ion template to guide the spatial orderly distribution of metal ions, and at the same time provides a precursor structure basis for the uniform dispersion and stable encapsulation of FeCo nanoparticles, thereby synergistically improving the microwave absorption ability, mechanical strength and antioxidant stability of the material as a whole, reflecting the core role of the precursor structure design in multi-property regulation.

[0013] Furthermore, the preparation method of the nanocellulose suspension includes the following steps: a) Treat the poplar raw materials in a high-speed shearing crusher for 30 min to 60 min, control the blade rotation speed at 1500 rpm to 2500 rpm, and obtain wood chips with a length of 1 mm to 5 mm; b) Conduct wet ball milling on the obtained wood chips for 4 to 8 h, with the ball milling medium diameter being 5 mm to 10 mm, and control the material-to-ball ratio at 1:8 to 1:12 to obtain woody crude fibers with a particle size of 80 mesh to 200 mesh; c) Take 100 parts to 120 parts of the obtained woody crude fibers and immerse them in a mixed alkali solution containing 85 parts to 145 parts of sodium hydroxide and 14 parts to 17 parts of sodium sulfite to form a suspension system with a solid-to-liquid ratio of 1:18 to 1:22; d) Under the condition of 45 °C to 55 °C, use a nano-grinder to conduct three-stage gradient mechanochemical grinding on the suspension system. The gap of the first-stage grinding disc is 0.03 mm to 0.05 mm, and the rotation speed is 2800 rpm to 3000 rpm. The gap of the second-stage grinding disc is 0.02 mm to 0.04 mm, and the rotation speed is 2900 rpm to 3100 rpm. The gap of the third-stage grinding disc is 0.01 mm to 0.03 mm, and the rotation speed is 3000 rpm to 3200 rpm. The grinding time for each stage is 4 h to 5 h to obtain a nano-cellulose suspension with a particle size of 20 nm to 50 nm. Then, wash the obtained nano-cellulose suspension 6 to 7 times with boiling water to remove the residual alkali solution, and at the same time adjust the solid content to 1.8 wt% to 2.2 wt% to make the absolute value of the Zeta potential of the suspension 30 mV to 50 mV to improve the stability of the suspension.

[0014] The design of the present invention for preparing nano - cellulose suspension based on mechanochemistry is mainly used to enhance the dispersion stability, structural uniformity and mechanical properties of carbon aerogel - based composites. By subjecting poplar raw materials to high - speed shearing and wet ball - milling treatment, the natural wood structure is gradually dissociated into lignocellulose fibers with appropriate particle sizes, providing a good reaction basis for subsequent alkali impregnation and nano - grinding; in the mixed alkali solution composed of sodium hydroxide and sodium sulfite, the lignocellulose fibers undergo delignification and cellulose swelling reactions, which contribute to the separation and nano - sizing of cellulose chains during the subsequent grinding process; by gradually reducing the gap between the grinding discs and increasing the rotation speed through a three - stage gradient nano - grinder, efficient depolymerization of cellulose is achieved at a mild temperature, thereby obtaining a nano - cellulose suspension with uniform particle size and controllable dimensions; further, through multiple boiling - water washes to remove residual alkali solution and adjusting its solid content and Zeta potential, the suspension has good colloidal stability driven by electric potential, avoiding particle aggregation and sedimentation. During the subsequent construction of the metal precursor composite framework, this nano - cellulose suspension not only provides good mechanical enhancement as a three - dimensional framework support material, but also forms a hydrogen - bond network with konjac glucomannan molecules through its abundant hydroxyl functional groups, enhancing the adhesiveness and structural integrity of the solution system; at the same time, its stable dispersion ensures the uniform distribution of cobalt nitrate and iron nitrate in the system, providing support for the orderly and directional laying of metal ions during the low - temperature freezing process, thereby strengthening the construction effect of the subsequent ice - crystal template structure. This design realizes the precise transformation of cellulose from raw wood to the nano - scale by controlling raw material size, alkali hydrolysis modification, nano - grinding parameters and colloidal stability adjustment, and synergistically interacts with other components at the micro - structure level, ultimately enhancing the structural stability, component uniformity and mechanical properties of the composite material, laying a solid foundation for realizing the multi - performance integrated carbon aerogel structure.

[0015] Further, during the chemical vapor deposition process in step S2, the flow rate of acetylene gas in the acetylene / hydrogen / argon ternary mixed gas is controlled at 10 sccm - 20 sccm, the flow rate of hydrogen gas is 150 sccm - 300 sccm, and the flow rate of argon gas is 50 sccm - 100 sccm.

[0016] Further, the programmed temperature reduction in step S3 adopts a multi - step temperature reduction strategy. In the first stage, the temperature is reduced to 480 °C - 520 °C at a temperature reduction rate of 4 °C / min - 6 °C / min. In the second stage, the temperature is reduced to 280 °C - 320 °C at a temperature reduction rate of 1.5 °C / min - 2.5 °C / min, and then the temperature is reduced to room temperature at a temperature reduction rate of 0.5 °C / min - 1.5 °C / min.

[0017] The present invention also provides an application of the high - efficiency microwave - absorbing carbon aerogel - based composite material in electromagnetic wave shielding, radar stealth, electromagnetic interference prevention devices and high - performance structural - functional integrated materials.

[0018] (3) Beneficial technical effects 1. The present invention constructs a conductive network in situ and directionally with carbon nanotubes to synergistically embed FeCo particles, significantly improving the electromagnetic attenuation, structural strength and antioxidant stability of carbon aerogels, solving the problems of discontinuous conductivity, fragile structure and poor environmental adaptability of existing materials, and having excellent engineering application prospects.

[0019] 2. The present invention constructs an ordered porous framework through the synergy of nanocellulose, konjac glucomannan and metal salts, realizes uniform regulation of catalytic activity and stable embedding of FeCo particles, significantly improves the microwave absorption, mechanical strength and antioxidant properties of carbon aerogels, and solves the key problems such as unstable structure and poor performance coupling of existing materials.

[0020] 3. The present invention precisely regulates the size and dispersion stability of nanocellulose by mechanochemical method, synergistically with the hydrogen bond network of konjac glucomannan and the technology of directional distribution of metal ions, breaks through the bottleneck of uneven mechanical properties and distribution of functional components in traditional aerogels. Its three-dimensional interpenetrating structure endows the material with both high porosity and compression resilience, and can effectively solve the industry problem of synergistic optimization of lightweight and broadband absorption of electromagnetic shielding materials for 5G base stations, promoting the development of microwave absorption materials towards the direction of multi-performance integration. Description of the drawings

[0021] Figure 1 is the microscopic morphology of the carbon aerogel-based composite material prepared in Example 1 of the present invention.

[0022] Figure 2 is the elemental distribution map of surface scanning of carbon nanotubes prepared in Example 1 of the present invention. Detailed implementation manners

[0023] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention.

[0024] Example 1 A high-efficiency microwave absorption carbon aerogel-based composite material, the carbon aerogel-based composite material comprising: a) A layered porous carbon-based aerogel matrix, the porosity of the matrix is 80%, and it has a layered pore size structure, wherein the macroscopic channel pore size is 1.2 μm; b) A carbon nanotube network structure, the carbon nanotubes are in-situ grown and anchored on the surface of the carbon aerogel pore wall by chemical vapor deposition method to construct a three-dimensional interconnected conductive network, and the diameter of the carbon nanotubes is 50 nm; c) FeCo nanoparticles, the nanoparticles are uniformly dispersed in the inner cavity of the carbon nanotubes, wherein the molar ratio of Fe / Co is 1:0.8.

[0025] The specific surface area of the carbon aerogel-based composite material is 650 m² / g, and the conductivity is 65 S / cm. The core size of the FeCo nanoparticles is 25 nm.

[0026] The method for the carbon aerogel-based composite material of this embodiment includes the following steps: S1. Place the metal precursor composite skeleton in a chemical vapor deposition furnace, and carry out catalytic activation under the atmosphere of a mixed gas of argon and hydrogen, where the volume fraction of hydrogen is 20%. Heat it up to 650 °C at a heating rate of 5 °C / min and keep it warm for 60 min to complete the catalyst activation; S2. Continue to heat up at a heating rate of 6 °C / min, and at the same time introduce a ternary mixed gas of acetylene / hydrogen / argon. Carry out a chemical vapor deposition reaction at a deposition temperature of 780 °C for 45 min to enable the in-situ directional growth of carbon nanotubes on the surface of the aerogel pore wall; the flow rate of acetylene gas in the ternary mixed gas of acetylene / hydrogen / argon is controlled at 10 sccm, the hydrogen flow rate is 150 sccm, and the argon flow rate is 50 sccm.

[0027] S3. After the reaction is completed, cool it down to room temperature according to the program to obtain a composite aerogel material with a carbon nanotube network; the programmed cooling adopts a multi-step cooling strategy. In the first stage, cool it down to 480 °C at a cooling rate of 4 °C / min, in the second stage, cool it down to 280 °C at a cooling rate of 1.5 °C / min, and then cool it down to room temperature at a cooling rate of 0.5 °C / min.

[0028] The metal precursor composite skeleton described in step S1 of this embodiment is prepared through the following steps: a) Subject 90 parts of nanocellulose suspension, 90 parts of konjac glucomannan, and a mixture of 6.5 parts of cobalt nitrate and iron nitrate to high-pressure microfluidic homogenization treatment at 22 °C. The treatment pressure in the first stage is 100 MPa, the treatment time is 10 min, the treatment pressure in the second stage is 180 MPa, the treatment time is 8 min, and the equipment rotation speed is controlled at 12,500 rpm; b) Add an aqueous sodium hydroxide solution with a mass fraction of 0.05 wt% to adjust the pH of the system to 9.5. Inject the obtained mixture into a mold and carry out programmed cooling and freezing treatment. Cool it down from -8 °C to -15 °C at a cooling rate of 0.4 °C / min, and then cool it down to -17 °C at a cooling rate of 0.8 °C / min to form a layered ice crystal template with a directional distribution of Fe³⁺ / Co²⁺ ions; c) Next, carry out segmented freeze-drying. In the first stage, dry it at -41 °C and 0.7 Pa for 4 h, in the second stage, dry it at -44 °C and 0.4 Pa for 6 h, and in the third stage, dry it at -47 °C and 0.2 Pa for 20 h to obtain the metal precursor composite skeleton In the mixture of cobalt nitrate and iron nitrate in this embodiment, the molar ratio of iron nitrate to cobalt nitrate is 1:0.8; The preparation method of the nanocellulose suspension in this embodiment includes the following steps: a) Treat poplar raw materials in a high-speed shear crusher for 39 min, control the blade speed at 1800 rpm, and obtain wood chips with a length of 2.2 mm; b) Perform wet ball milling on the obtained wood chips for 5 h, with a ball milling medium diameter of 6.5 mm and a material-to-ball ratio controlled at 1:9, to obtain woody coarse fibers with a particle size of 116 mesh; c) Take 106 parts of the obtained woody coarse fibers and immerse them in a mixed alkali solution containing 103 parts of sodium hydroxide and 14.9 parts of sodium sulfite to form a suspension system with a solid-to-liquid ratio of 1:19; d) At 48 °C, use a nano-grinder to perform three-stage gradient mechanochemical grinding on the suspension system. The gap of the first-stage grinding disc is 0.036 mm, the rotation speed is 2860 rpm, the gap of the second-stage grinding disc is 0.026 mm, the rotation speed is 2960 rpm, the gap of the third-stage grinding disc is 0.016 mm, the rotation speed is 3060 rpm, and the grinding time for each stage is 4.3 h to obtain a nanocellulose suspension with a particle size of 29 nm; Then, wash the obtained nanocellulose suspension with boiling water 6 times to remove residual alkali solution, and at the same time adjust the solid content to 1.92 wt% to make the absolute value of the Zeta potential of the suspension 36 mV to improve the stability of the suspension.

[0029] Figure 1 This is the microscopic morphology of the carbon aerogel-based composite material prepared in Example 1 of the present invention, which clearly shows the three-dimensional topological structure of the layered porous carbon-based aerogel matrix and the characteristics of the macroscopic channels arranged in an orderly manner inside it. At the same time, the effectiveness of constructing a three-dimensional interconnected conductive network by chemical vapor deposition is verified through the in-situ growth of the carbon nanotube network structure; Figure 2 Through elemental surface scanning analysis, the spatial distribution characteristics of FeCo nanoparticles in the inner cavity of carbon nanotubes and their elemental composition ratio relationship are intuitively revealed, confirming the regulation effect of the metal precursor composite skeleton design and the freeze-casting template process on the encapsulation uniformity of magnetic components.

[0030] Example 2 A highly efficient microwave-absorbing carbon aerogel-based composite material, the carbon aerogel-based composite material comprising: a) A layered porous carbon-based aerogel matrix with a porosity of 85% and a layered pore size structure, where the macroscopic channel pore size is 2.5 μm; b) A carbon nanotube network structure, where the carbon nanotubes are in-situ grown and anchored on the surface of the carbon aerogel pore wall by chemical vapor deposition to construct a three-dimensional interconnected conductive network, and the diameter of the carbon nanotubes is 61 nm; c) FeCo nanoparticles, the nanoparticles are uniformly dispersed in the inner cavity of the carbon nanotubes, where the molar ratio of Fe / Co is 1:0.9.

[0031] The specific surface area of the carbon aerogel-based composite material is 740 m² / g, and the conductivity is 70 S / cm. The core size of the FeCo nanoparticles is 20 nm.

[0032] The method for the carbon aerogel-based composite material of this embodiment includes the following steps: S1. Place the metal precursor composite skeleton in a chemical vapor deposition furnace, and carry out catalytic activation under the atmosphere of a mixed gas of argon and hydrogen, where the volume fraction of hydrogen is 25%, heat up to 680 °C at a heating rate of 6 °C / min, and keep the temperature for 69 min to complete the catalyst activation; S2. Continue to heat up at a heating rate of 7 °C / min, and at the same time introduce a ternary mixed gas of acetylene / hydrogen / argon, and carry out a chemical vapor deposition reaction at a deposition temperature of 792 °C for a deposition time of 54 min to realize in-situ directional growth of carbon nanotubes on the surface of the aerogel pore wall; the flow rate of acetylene gas in the ternary mixed gas of acetylene / hydrogen / argon is controlled at 13 sccm, the hydrogen flow rate is 195 sccm, and the argon flow rate is 65 sccm.

[0033] S3. After the reaction is completed, cool down to room temperature according to the program to obtain a composite aerogel material with a carbon nanotube network; the programmed cooling adopts a multi-step cooling strategy. In the first stage, cool down to 492 °C at a cooling rate of 4.6 °C / min, in the second stage, cool down to 292 °C at a cooling rate of 1.8 °C / min, and then cool down to room temperature at a cooling rate of 0.8 °C / min.

[0034] The metal precursor composite skeleton in step S1 of this embodiment is prepared by the following steps: a) Subject 96 parts of nanocellulose suspension, 96 parts of konjac glucomannan, and a mixture of 7.1 parts of cobalt nitrate and iron nitrate to high-pressure microfluidic homogenization treatment at 24 °C, where the treatment pressure in the first stage is 115 MPa, the treatment time is 11 min, the treatment pressure in the second stage is 192 MPa, the treatment time is 9 min, and the equipment rotation speed is controlled at 13100 rpm; b) Add an aqueous sodium hydroxide solution with a mass fraction of 0.05 wt% to adjust the pH of the system to 9.7, inject the obtained mixture into a mold, and perform programmed cooling and freezing treatment. Cool down from -9 °C to -15.6 °C at a cooling rate of 0.46 °C / min, and then cool down to -17.6 °C at a cooling rate of 0.92 °C / min to form a layered ice crystal template with a directional distribution of Fe³⁺ / Co²⁺ ions; c) Next, segmented freeze-drying is carried out. In the first stage, it is dried at -41.6°C and 0.76 Pa for 5 h. In the second stage, it is dried at -44.6°C and 0.46 Pa for 7 h. In the third stage, it is dried at -47.6°C and 0.26 Pa for 21.5 h to obtain the metal precursor composite skeleton.

[0035] In the mixture of cobalt nitrate and iron nitrate in this example, the molar ratio of iron nitrate to cobalt nitrate is 1:0.9; The preparation method of the nanocellulose suspension in this example includes the following steps: a) Treat poplar raw materials in a high-speed shear crusher for 30 min, control the blade speed at 1500 rpm to obtain wood chips with a length of 1 mm; b) Carry out wet ball milling on the obtained wood chips for 4 h, with the diameter of the ball milling medium being 5 mm and the material-ball ratio controlled at 1:8 to obtain woody coarse fibers with a particle size of 80 mesh; c) Take 100 parts of the obtained woody coarse fibers and immerse them in a mixed alkali solution containing 85 parts of sodium hydroxide and 14 parts of sodium sulfite to form a suspension system with a solid-liquid ratio of 1:18; d) At 45°C, use a nanogrinder to carry out three-stage gradient mechanochemical grinding on the suspension system. The gap of the first-stage grinding disc is 0.03 mm and the rotation speed is 2800 rpm. The gap of the second-stage grinding disc is 0.02 mm and the rotation speed is 2900 rpm. The gap of the third-stage grinding disc is 0.01 mm and the rotation speed is 3000 rpm. The grinding time for each stage is 4 h to obtain a nanocellulose suspension with a particle size of 20 nm. Then, wash the obtained nanocellulose suspension with boiling water 6 times to remove the residual alkali solution, and at the same time adjust the solid content to 1.8 wt% to make the absolute value of the Zeta potential of the suspension 30 mV to improve the stability of the suspension.

[0036] Example 3 A high-efficiency microwave-absorbing carbon aerogel-based composite material, the carbon aerogel-based composite material comprising: a) A layered porous carbon-based aerogel matrix, the porosity of the matrix is 89%, and it has a layered pore size structure, where the macroscopic channel pore size is 3.8 μm; b) A carbon nanotube network structure, the carbon nanotubes are in-situ grown and anchored on the surface of the carbon aerogel pore wall by chemical vapor deposition to construct a three-dimensional interconnected conductive network, and the diameter of the carbon nanotubes is 71 nm; c) FeCo nanoparticles, the nanoparticles are uniformly dispersed in the inner cavity of the carbon nanotubes, where the molar ratio of Fe / Co is 1:1.

[0037] The specific surface area of the carbon aerogel-based composite material is 950 m² / g, and the conductivity is 80 S / cm. The core size of the FeCo nanoparticles is 10 nm.

[0038] The method for the carbon aerogel-based composite material of this embodiment includes the following steps: S1. Place the metal precursor composite skeleton in a chemical vapor deposition furnace, and carry out catalytic activation under the atmosphere of a mixed gas of argon and hydrogen, where the volume fraction of hydrogen is 29%. Heat it at a heating rate of 7 °C / min to 710 °C, and keep it warm for 78 min to complete the catalyst activation; S2. Continue to heat at a heating rate of 7 °C / min, and at the same time introduce a ternary mixed gas of acetylene / hydrogen / argon. Carry out a chemical vapor deposition reaction at a deposition temperature of 804 °C for a deposition time of 63 min to enable in-situ directional growth of carbon nanotubes on the surface of the aerogel pore wall; the flow rate of acetylene gas in the ternary mixed gas of acetylene / hydrogen / argon is controlled at 16 sccm, the hydrogen flow rate is 240 sccm, and the argon flow rate is 80 sccm.

[0039] S3. After the reaction is completed, cool it down to room temperature according to the program to obtain a composite aerogel material with a carbon nanotube network; the programmed cooling adopts a multi-step cooling strategy. In the first stage, cool it down to 504 °C at a cooling rate of 5.2 °C / min, in the second stage, cool it down to 304 °C at a cooling rate of 2.1 °C / min, and then cool it down to room temperature at a cooling rate of 1.1 °C / min.

[0040] The metal precursor composite skeleton described in step S1 of this embodiment is prepared through the following steps: a) Subject 102 parts of nanocellulose suspension, 102 parts of konjac glucomannan, and a mixture of 7.7 parts of cobalt nitrate and iron nitrate to high-pressure microfluidic homogenization treatment at 26 °C. The treatment pressure in the first stage is 130 MPa, the treatment time is 11 min, the treatment pressure in the second stage is 204 MPa, the treatment time is 9 min, and the equipment rotation speed is controlled at 13700 rpm; b) Add an aqueous sodium hydroxide solution with a mass fraction of 0.05 wt% to adjust the pH of the system to 9.9. Inject the obtained mixture into a mold, and carry out programmed cooling and freezing treatment. Cool it down from -10 °C to -16.2 °C at a cooling rate of 0.52 °C / min, and then cool it down to -18.2 °C at a cooling rate of 1.04 °C / min to form a layered ice crystal template with a directional distribution of Fe³⁺ / Co²⁺ ions; c) Next, carry out segmented freeze-drying. In the first stage, dry it at -42.2 °C and 0.82 Pa for 6 h, in the second stage, dry it at -45.2 °C and 0.52 Pa for 8 h, and in the third stage, dry it at -48.2 °C and 0.32 Pa for 23 h to obtain the metal precursor composite skeleton.

[0041] In the mixture of cobalt nitrate and iron nitrate in this embodiment, the molar ratio of iron nitrate to cobalt nitrate is 1:1; The preparation method of the nanocellulose suspension in this embodiment includes the following steps: a) Treat poplar raw materials in a high-speed shear crusher for 48 min, control the blade speed at 2100 rpm, and obtain wood chips with a length of 3.4 mm; b) Perform wet ball milling on the obtained wood chips for 6 h, with a ball milling medium diameter of 8 mm and a material-to-ball ratio controlled at 1:10, to obtain woody coarse fibers with a particle size of 152 mesh; c) Take 112 parts of the obtained woody powder fibers and immerse them in a mixed alkali solution containing 121 parts of sodium hydroxide and 15.8 parts of sodium sulfite to form a suspension system with a solid-to-liquid ratio of 1:20; d) At 51 °C, use a nano grinder to perform three-stage gradient mechanochemical grinding on the suspension system. The gap of the first-stage grinding disc is 0.042 mm, the rotation speed is 2920 rpm, the gap of the second-stage grinding disc is 0.032 mm, the rotation speed is 3020 rpm, the gap of the third-stage grinding disc is 0.022 mm, the rotation speed is 3120 rpm, and the grinding time for each stage is 4.6 h to obtain a nanocellulose suspension with a particle size of 38 nm; then wash the obtained nanocellulose suspension with boiling water 7 times to remove residual alkali solution, and at the same time adjust the solid content to 2.04 wt% to make the absolute value of the Zeta potential of the suspension 42 mV to improve the stability of the suspension.

[0042] Example 4 A high-efficiency microwave-absorbing carbon aerogel-based composite material, the carbon aerogel-based composite material includes: a) A layered porous carbon-based aerogel matrix, the porosity of the matrix is 95%, and it has a layered pore size structure, where the macrochannel pore size is 5.5 μm; b) A carbon nanotube network structure, the carbon nanotubes are in-situ grown and anchored on the pore wall surface of the carbon aerogel by chemical vapor deposition to construct a three-dimensional interconnected conductive network, and the diameter of the carbon nanotubes is 85 nm; c) FeCo nanoparticles, the nanoparticles are uniformly dispersed in the inner cavity of the carbon nanotubes, where the molar ratio of Fe / Co is 1:1.2.

[0043] The specific surface area of the carbon aerogel-based composite material is 830 m² / g, and the conductivity is 74 S / cm. The core size of the FeCo nanoparticles is 16 nm.

[0044] The method for the carbon aerogel-based composite material in this embodiment includes the following steps: S1. Place the metal precursor composite framework in a chemical vapor deposition furnace and perform catalytic activation under a mixed gas atmosphere of argon and hydrogen, where the volume fraction of hydrogen is 35%. Heat it to 750 °C at a heating rate of 8 °C / min and hold for 90 min to complete the catalyst activation. S2. Continue heating at a heating rate of 8 °C / min while introducing a ternary mixed gas of acetylene / hydrogen / argon. Perform chemical vapor deposition reaction at a deposition temperature of 820 °C for 75 min to achieve in-situ directional growth of carbon nanotubes on the surface of the aerogel pore walls. The flow rate of acetylene gas in the acetylene / hydrogen / argon ternary mixed gas is controlled at 20 sccm, the hydrogen flow rate is 300 sccm, and the argon flow rate is 100 sccm.

[0045] S3. After the reaction is completed, cool it to room temperature according to the program to obtain a composite aerogel material with a carbon nanotube network. The programmed cooling adopts a multi-step cooling strategy. In the first stage, cool it to 520 °C at a cooling rate of 6 °C / min. In the second stage, cool it to 320 °C at a cooling rate of 2.5 °C / min, and then cool it to room temperature at a cooling rate of 1.5 °C / min.

[0046] In step S1 of this example, the metal precursor composite framework is prepared through the following steps: a) Perform high-pressure microfluidic homogenization treatment on 110 parts of nano-cellulose suspension, 110 parts of konjac glucomannan, and a mixture of 8.5 parts of cobalt nitrate and iron nitrate at 28 °C. The treatment pressure in the first stage is 150 MPa, the treatment time is 12 min, the treatment pressure in the second stage is 220 MPa, the treatment time is 10 min, and the equipment rotation speed is controlled at 14,500 rpm. b) Add an aqueous sodium hydroxide solution with a mass fraction of 0.05 wt% to adjust the pH of the system to 10.2. Inject the obtained mixture into a mold and perform programmed cooling and freezing treatment. Cool it from -12 °C to -17 °C at a cooling rate of 0.6 °C / min, and then cool it to -19 °C at a cooling rate of 1.2 °C / min to form a layered ice crystal template with a directional distribution of Fe³⁺ / Co²⁺ ions. c) Next, perform segmented freeze-drying. In the first stage, dry it at -43 °C and 0.9 Pa for 8 h. In the second stage, dry it at -46 °C and 0.6 Pa for 10 h. In the third stage, dry it at -49 °C and 0.4 Pa for 25 h to obtain the metal precursor composite framework.

[0047] In the mixture of cobalt nitrate and iron nitrate in this example, the molar ratio of iron nitrate to cobalt nitrate is 1:1.2. The preparation method of the nano-cellulose suspension in this example includes the following steps: a) Treat the poplar raw materials in a high-speed shear crusher for 60 min, control the blade rotation speed at 2500 rpm, and obtain wood chips with a length of 5 mm; b) Conduct wet ball milling on the obtained wood chips for 8 h, with the diameter of the ball milling medium being 10 mm and the material-to-ball ratio controlled at 1:12, to obtain woody crude fiber with a particle size of 200 mesh; c) Take 120 parts of the obtained woody crude fiber and immerse it in a mixed alkali solution containing 145 parts of sodium hydroxide and 17 parts of sodium sulfite to form a suspension system with a solid-to-liquid ratio of 1:22; d) At 55 °C, use a nano-grinder to conduct three-stage gradient mechanochemical grinding on the suspension system. The gap of the first-stage grinding disc is 0.05 mm and the rotation speed is 3000 rpm. The gap of the second-stage grinding disc is 0.04 mm and the rotation speed is 3100 rpm. The gap of the third-stage grinding disc is 0.03 mm and the rotation speed is 3200 rpm. The grinding time for each stage is 5 h to obtain a nano-cellulose suspension with a particle size of 50 nm; then conduct 7 times of boiling water washing on the obtained nano-cellulose suspension to remove the residual alkali solution, and at the same time adjust the solid content to 2.2 wt% to make the absolute value of the Zeta potential of the suspension 50 mV to improve the stability of the suspension.

[0048] Comparative Example 1 Basically the same as Example 1, except that the hydrogen volume fraction in step S1 is 15%, which is lower than the range of 20% - 35% in the claims, resulting in incomplete activation of the catalyst.

[0049] Comparative Example 2 Basically the same as Example 1, except that the deposition temperature in step S2 is 760 °C, which is lower than the range of 780 °C - 820 °C in the claims, resulting in a decrease in the growth density of carbon nanotubes.

[0050] Comparative Example 3 Basically the same as Example 1, except that the heating rate in step S1 is 3 °C / min, which is much lower than the range of 5 °C - 8 °C in the claims, and the agglomeration size of metal particles reaches 50 nm.

[0051] Comparative Example 4 Basically the same as Example 1, except that the acetylene flow rate in step S2 is 5 sccm, which is lower than the range of 10 sccm - 20 sccm in the claims, and the carbon nanotube diameter increases to 120 nm.

[0052] Comparative Example 5 Basically the same as Example 1, except that the rate of the first stage of programmed cooling in step S3 is 8 °C / min, which exceeds the range of 4 °C - 6 °C in the claims, and the internal crack density of the material increases.

[0053] Comparative Example 6 Basically the same as Example 1, except that in step S1, the molar ratio of iron nitrate to cobalt nitrate is 1:1.5, exceeding 1:0.8 - 1:1.2 of the claim, and the FeCo particle distribution is uneven.

[0054] Comparative Example 7 Basically the same as Example 1, except that in step S1, the heating rate is 3 °C / min, much lower than 5 °C - 8 °C / min of the claim, and the agglomeration size of metal particles reaches 50 nm.

[0055] Comparative Example 8 Basically the same as Example 1, except that in step S5, the freeze-drying time in the second stage is 4 h, lower than 6 h - 10 h of claim 5, and the residual moisture results in a reduction in porosity after carbonization.

[0056] Comparative Example 9 Basically the same as Example 1, except that in step S7, the solid content of the nanocellulose suspension is 1.0 wt%, lower than 1.8 wt% - 2.2 wt% of the claim, and the skeleton strength decreases.

[0057] Comparative Example 10 Basically the same as Example 1, except that in step S5, the freezing cooling rate is 2 °C / min, exceeding 0.8 °C - 1.2 °C / min of claim 5, and the uneven ice crystal size causes pore blockage.

[0058] Comparative Example 11 Basically the same as Example 1, except that konjac glucomannan is not added, lacking a synergistic bonding network, resulting in an increase in skeleton brittleness and a decrease in structural integrity.

[0059] Performance test: Microwave absorption performance test (reflection loss and effective bandwidth): The reflection loss of the material is tested in the 8 - 18 GHz band using the bow-tie method (ASTM D5568). The sample is processed into a coaxial ring (outer diameter 7.0 mm, inner diameter 3.0 mm), and the S parameters are measured by a vector network analyzer (Keysight N5224B) to calculate the reflection loss (RL) and the effective absorption bandwidth (RL ≤ -10 dB).

[0060] Mechanical property test (compressive strength and resilience rate): A universal testing machine (Instron 5967) is used for quasi-static compression testing (strain rate 2 mm / min), the compressive strength at 50% strain is recorded, and the resilience rate is calculated through 10 cycles of compression (strain 50%).

[0061] Analysis of electrical conductivity and impedance matching: The in-plane electrical conductivity was measured by the four-probe method. The complex dielectric constants (ε', ε'') and complex magnetic permeabilities (μ', μ'') were tested by combining with the coaxial probe method (ASTM D5568), and the normalized impedance was calculated using the transmission line theory.

[0062] Evaluation of antioxidant stability: The samples were placed in a constant temperature and humidity chamber at 80 °C / 85% RH for accelerated aging for 240 h. The peak position shifts of Fe 2p and Co 2p were analyzed by X-ray photoelectron spectroscopy (XPS, Thermo Scientific K-Alpha) to quantify the metal oxidation ratio.

[0063] The properties of the aerogel-based composites of Examples 1-4 and Comparative Examples 1-11 are summarized in Table 1.

[0064] Table 1 Summary of the properties of the aerogel-based composites of Examples 1-4 and Comparative Examples 1-11 As can be seen from Table 1, the material properties are synergistically affected by multiple factors: the porosity and pore size distribution determine the specific surface area and the multiple scattering effect of electromagnetic waves. High porosity improves the wave absorption performance but may weaken the mechanical strength; the diameter and aspect ratio of carbon nanotubes regulate the density of the conductive network and the carrier mobility. A small diameter and high aspect ratio are beneficial for forming a permeable conductive path; the size and distribution state of FeCo nanoparticles affect the magnetic loss ability and antioxidant property. Small size and uniform dispersion enhance the interfacial polarization loss; the hydrogen bond network of konjac glucomannan and nanocellulose determines the structural toughness and the metal ion anchoring effect; the chemical vapor deposition parameters (temperature, gas flow rate, cooling rate) affect the dielectric loss by regulating the crystallinity and defect density of CNTs; the freeze-drying process parameters determine the integrity of the pore structure, and the ice crystal growth rate and drying gradient affect the orientation and mechanical stability of the layered structure; the precursor ratio and the homogenization treatment intensity are directly related to the uniformity of metal ion dispersion, and thus affect the spatial distribution of magnetic groups and the matching degree of electromagnetic parameters.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that any equivalent structural transformation made under the concept of the present invention using the content of the specification and drawings of the present invention should be covered by the protection scope of the claims of the present invention.

Claims

1. A highly efficient microwave absorbing carbon aerogel-based composite material, characterized in that: The carbon aerogel-based composite material comprises: a) a layered porous carbon-based aerogel matrix, wherein the matrix has a porosity of 80% to 95% and a layered distributed pore size structure, wherein the macroscopic channel pore size is 1.2 μm to 5.5 μm; b) a carbon nanotube network structure, wherein the carbon nanotubes are in-situ grown and anchored on the surface of the carbon aerogel pore wall by chemical vapor deposition to construct a three-dimensional interconnected conductive network, and the diameter of the carbon nanotubes is 50nm to 85nm; c) FeCo nanoparticles, wherein the nanoparticles are uniformly dispersed in the inner cavity of the carbon nanotubes, wherein the molar ratio of Fe / Co is 1:0.8-1:1.

2.

2. A high-efficiency microwave absorbing carbon aerogel-based composite material as described in claim 1, wherein the specific surface area of ​​the carbon aerogel-based composite material is 650m² / g~950m² / g, and the electrical conductivity is 65S / cm~80S / cm.

3. The high-efficiency microwave absorbing carbon aerogel-based composite material according to claim 1, characterized in that: The core size of the FeCo nanoparticles is 25nm-10nm.

4. The high-efficiency microwave absorbing carbon aerogel-based composite material according to claim 1, characterized in that: The method for the carbon aerogel-based composite material comprises the following steps: S1. placing the metal precursor composite skeleton in a chemical vapor deposition furnace, catalytically activating the catalyst in a mixed gas atmosphere of argon and hydrogen, wherein the hydrogen volume fraction is 20% to 35%, heating the temperature to 650°C to 750°C at a heating rate of 5°C / min to 8°C / min, and keeping the temperature for 60min to 90min to complete the catalyst activation; S2. Continue to increase the temperature at a heating rate of 6°C / min~8°C / min, and introduce a ternary mixed gas of acetylene / hydrogen / argon at the same time, and perform a chemical vapor deposition reaction at a deposition temperature of 780°C~820°C for a deposition time of 45min~75min, so that the carbon nanotubes can be grown in situ on the pore wall surface of the aerogel; S3. After the reaction is completed, the temperature is lowered to room temperature according to the procedure to obtain a composite aerogel material with a carbon nanotube network.

5. The high-efficiency microwave absorbing carbon aerogel-based composite material according to claim 4, characterized in that: The metal precursor composite skeleton in step S1 is prepared by the following steps: a) 90 to 110 parts of nanocellulose suspension, 90 to 110 parts of konjac glucomannan, 6.5 to 8.5 parts of a mixture of cobalt nitrate and ferric nitrate are subjected to high pressure microfluidization homogenization at 22 to 28° C., wherein the first stage treatment pressure is 100 MPa to 150 MPa, the treatment time is 10 min to 12 min, the second stage treatment pressure is 180 MPa to 220 MPa, the treatment time is 8 min to 10 min, and the equipment speed is controlled at 12500 rpm to 14500 rpm; b) adding a sodium hydroxide aqueous solution with a mass fraction of 0.05wt% to adjust the pH of the system to 9.5-10.2, injecting the obtained mixture into a mold, and subjecting the mold to a programmed cooling and freezing treatment, cooling the temperature from -8°C to -12°C to -15°C to -17°C at a cooling rate of 0.4°C / min-0.6°C / min, and then cooling the temperature to -17°C to -19°C at a cooling rate of 0.8°C / min-1.2°C / min, to form a layered ice crystal template with directional distribution of Fe³⁺ / Co²⁺ ions; c) Next, freeze-drying is carried out in stages, wherein the first stage is dried at -41°C~-43°C and 0.7Pa~0.9Pa for 4h~8h, the second stage is dried at -44°C~-46°C and 0.4Pa~0.6Pa for 6h~10h, and the third stage is dried at -47°C~-49°C and 0.2Pa~0.4Pa for 20h~25h to obtain a metal precursor composite skeleton.

6. The high-efficiency microwave absorbing carbon aerogel-based composite material according to claim 5, characterized in that: The molar ratio of ferric nitrate to cobalt nitrate in the mixture of cobalt nitrate and ferric nitrate is 1:0.8-1:1.

2.

7. The high-efficiency microwave absorbing carbon aerogel-based composite material according to claim 5, characterized in that: The method for preparing the nanocellulose suspension comprises the following steps: a) processing the poplar wood raw material in a high-speed shear crusher for 30 min to 60 min, controlling the blade speed at 1500 rpm to 2500 rpm, and obtaining sawdust with a length of 1 mm to 5 mm; b) subjecting the obtained sawdust to wet ball milling for 4-8 hours, with the ball milling medium having a diameter of 5 mm-10 mm and a material-ball ratio controlled at 1:8-1:12, to obtain wood crude fiber with a particle size of 80 meshes to 200 meshes; c) taking 100 to 120 parts of the obtained wood crude fiber, and immersing them in a mixed alkali solution containing 85 to 145 parts of sodium hydroxide and 14 to 17 parts of sodium sulfite to form a suspension system with a solid-liquid ratio of 1:18 to 1:22; d) At 45°C to 55°C, a nano-grinder is used to perform three-stage gradient mechanical chemical grinding on the suspension system, wherein the gap between the first-stage grinding discs is 0.03mm to 0.05mm, the rotation speed is 2800rpm to 3000rpm, the gap between the second-stage grinding discs is 0.02mm to 0.04mm, the rotation speed is 2900rpm to 3100rpm, the gap between the third-stage grinding discs is 0.01mm to 0.03mm, the rotation speed is 3000rpm to 3200rpm, and the grinding time for each stage is 4h to 5h to obtain a nanocellulose suspension with a particle size of 20nm to 50nm; then the obtained nanocellulose suspension is washed with boiling water for 6 to 7 times to remove residual alkali solution, and the solid content is adjusted to 1.8wt% to 2.2wt% so that the absolute value of the Zeta potential of the suspension is 30mV to 50mV to improve the stability of the suspension.

8. The high-efficiency microwave absorbing carbon aerogel-based composite material according to claim 4, characterized in that: During the chemical vapor deposition process in step S2, the flow rate of acetylene gas in the acetylene / hydrogen / argon ternary mixed gas is controlled at 10 sccm-20 sccm, the flow rate of hydrogen is 150 sccm-300 sccm, and the flow rate of argon is 50 sccm-100 sccm.

9. The high-efficiency microwave absorbing carbon aerogel-based composite material according to claim 4, characterized in that: The programmed cooling described in step S3 adopts a multi-step cooling strategy. In the first stage, the temperature is cooled to 480°C~520°C at a cooling rate of 4°C / min~6°C / min, and in the second stage, the temperature is cooled to 280°C~320°C at a cooling rate of 1.5°C / min~2.5°C / min, and then cooled to room temperature at a cooling rate of 0.5°C / min~1.5°C / min.

10. Application of a high-efficiency microwave absorbing carbon aerogel-based composite material as claimed in claim 1 in electromagnetic wave shielding, radar stealth, anti-electromagnetic interference devices and high-performance structural functional integrated materials.

Images