A thin-walled porous magnetic / carbon composite material and its preparation method and application

Abstract

The present invention relates to a thin-walled porous magnetic / carbon composite material, its preparation method, and its application. The thin-walled porous magnetic / carbon composite material has a three-dimensional honeycomb porous structure, with pore walls composed of two-dimensional magnetic / carbon nanosheets. The two-dimensional magnetic / carbon nanosheets are composited from magnetic nanoparticles and a carbon-based material, wherein the magnetic nanoparticles are uniformly dispersed within the two-dimensional magnetic / carbon nanosheets. The thin-walled porous magnetic / carbon composite material provided by the present invention has uniform magnetic nanoparticle distribution and is firmly bound within the porous material. The thin pore walls provide excellent and stable electromagnetic wave absorption performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of applied materials, and in particular relates to a thin-walled porous magnetic / carbon composite material and a preparation method and application thereof. Background Art

[0002] With the rapid development of absorbing materials, the demand for high-performance absorbers is increasing. High-performance absorbers must meet the following basic requirements: a wide effective absorption bandwidth, low reflection loss, a thin matching thickness, and low weight. Currently, porous magnetic / carbon composite absorbers have become a mainstream focus of electromagnetic wave absorber research due to their combination of light weight and high performance. Recent studies have demonstrated that porous structures can effectively reduce the dielectric constant while providing additional propagation paths for electromagnetic waves. Furthermore, thinner pore walls allow for easier entry of incident electromagnetic waves into the absorber, improving impedance matching and enhancing the absorber's performance. Current methods for preparing porous magnetic / carbon composite absorbers primarily rely on template methods. The introduction of pore structure typically depends on the size and morphology of the sacrificial template, resulting in uncontrollable pore size and structure. Furthermore, template removal requires the use of corrosive agents and is extremely time-consuming. Therefore, current preparation processes for porous magnetic / carbon absorbers fail to meet the practical needs of high-performance absorbers. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a thin-walled porous magnetic / carbon composite material and its preparation method and application in response to the above-mentioned deficiencies in the prior art. The magnetic material in the thin-walled porous magnetic / carbon composite material is evenly distributed, has strong microwave absorption capacity, and stable microwave absorption performance.

[0004] In order to solve the above technical problems, the technical solution provided by the present invention is:

[0005] Provided is a thin-walled porous magnetic / carbon composite material, which has a three-dimensional honeycomb porous structure, wherein the pore walls are composed of two-dimensional magnetic / carbon nanosheets, and the two-dimensional magnetic / carbon nanosheets are obtained by compounding magnetic nanoparticles with carbon-based materials, wherein the magnetic nanoparticles are uniformly dispersed in the two-dimensional magnetic / carbon nanosheets.

[0006] According to the above scheme, the thin-walled porous magnetic / carbon composite material has a specific surface area of ​​280 to 350 m 2 / g, and the pore wall thickness is 1 to 200 nm.

[0007] According to the above scheme, the size of the two-dimensional magnetic / carbon nanosheet is 5 to 10 μm.

[0008] According to the above solution, the magnetic nanoparticles are one of CoNi alloy nanoparticles, Fe nanoparticles, Co nanoparticles, Ni nanoparticles, and Fe oxide nanoparticles, and the particle size is 20 to 50 nm.

[0009] According to the above solution, the mass percentage of magnetic nanoparticles in the thin-walled porous magnetic / carbon composite material is 20-60%.

[0010] According to the above solution, the reflection loss of the thin-walled porous magnetic / carbon composite material is -15 to -60 dB, and the effective absorption bandwidth is 2.5 to 7 GHz.

[0011] The present invention also includes a method for preparing the thin-walled porous magnetic / carbon composite material, which comprises the following steps:

[0012] 4) uniformly dispersing the polymer (carbon source) in deionized water, adding metal nitrate (used as a metal source for magnetic nanoparticles), ultrasonically dispersing, and then stirring to obtain a precursor solution;

[0013] 5) drying and grinding the precursor solution obtained in step 1) to obtain a precursor powder;

[0014] 6) placing the precursor powder obtained in step 2) in a tube furnace for carbonization treatment to obtain a thin-walled porous magnetic / carbon composite material.

[0015] According to the above scheme, the polymer in step 1) is one of polyvinyl pyrrolidone, glucose, and ammonium citrate.

[0016] According to the above scheme, the metal nitrate in step 1) is one or more of nickel nitrate hexahydrate, cobalt nitrate hexahydrate, and ferric nitrate nonahydrate. Nitrate hydrate can also serve as a foaming agent to form a porous structure in the precursor during the carbonization process.

[0017] According to the above scheme, the mass ratio of the polymer to the metal nitrate in step 1) is 1 to 17:1.

[0018] According to the above scheme, the mass concentration of the polymer in the precursor solution in step 1) is 7-8%.

[0019] According to the above scheme, the carbonization treatment process conditions in step 3) are: starting from room temperature under argon atmosphere, heating to 600-800°C at a heating rate of 5-10°C / min, and keeping warm for 2-3h.

[0020] The present invention also includes the application of the thin-walled porous magnetic / carbon composite material in the field of electromagnetic wave absorbing materials.

[0021] The present invention uses a polymer and a metal nitrate to form a precursor powder. During the heating process in a tube furnace, the nitrate decomposes and releases a large amount of gas, blowing the molten polymer into bubbles. The higher the gas release and the internal pressure of the polymer, the thinner the bubble walls. As the temperature rises, the bubble walls carbonize at high temperatures to form pore walls. Simultaneously, metal ions adsorbed within the polymer are carbon-thermally reduced in situ and evenly anchored to the carbon walls. Furthermore, by varying the metal nitrate content and the heating rate during carbonization, the present invention can regulate the gas content and pressure released within the polymer, thereby controlling the structure and pore wall thickness of the porous magnetic / carbon composite absorber. This results in strong reflection loss and a wide effective absorption band, making its morphology easier to control than with traditional template methods.

[0022] The present invention has the following beneficial effects: 1. The magnetic nanoparticles in the thin-walled porous magnetic / carbon composite material provided by the present invention are uniformly distributed and firmly bound within the porous material. The thin pore walls provide excellent and stable electromagnetic wave absorption. 2. The preparation method of the present invention is highly safe, environmentally friendly, simple in steps, and employs mild reaction conditions, making it amenable to large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a SEM image of the thin-walled porous magnetic / carbon composite material prepared in Example 1 of the present invention;

[0024] Figure 2 TEM image of the thin-walled porous magnetic / carbon composite material prepared in Example 1;

[0025] Figure 3 The X-ray diffraction pattern of the thin-walled porous magnetic / carbon composite material prepared in Example 1;

[0026] Figure 4 This is the reflection loss spectrum of the thin-walled porous magnetic / carbon composite material prepared in Example 1;

[0027] Figure 5 This is a SEM photo of the thin-walled porous magnetic / carbon composite material prepared in Example 2;

[0028] Figure 6 This is a SEM photo of the thin-walled porous magnetic / carbon composite material prepared in Example 3;

[0029] Figure 7 This is a SEM photo of the thin-walled porous magnetic / carbon composite material prepared in Comparative Example 1;

[0030] Figure 8 This is an SEM photograph of the thin-walled porous magnetic / carbon composite material prepared in Comparative Example 2. DETAILED DESCRIPTION

[0031] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below with reference to the accompanying drawings.

[0032] Example 1

[0033] A thin-walled porous magnetic / carbon composite material, the specific preparation method is as follows:

[0034] 4.5 g of polyvinyl pyrrolidone (K88-96, average molecular weight 1300000) was weighed and dispersed in 50 mL of deionized water. 1.5 g of cobalt nitrate hexahydrate and 1.5 g of nickel nitrate hexahydrate were then added in sequence. The mixture was ultrasonically dispersed at room temperature for 20 min and stirred for 60 min until transparent to obtain a precursor solution. The precursor solution was placed in an oven at 80°C for 30 h. After drying, it was ground into gravel using a mortar to obtain a precursor powder.

[0035] The precursor powder was placed in a porcelain boat and put into a tubular furnace for carbonization treatment. The carbonization treatment process conditions were as follows: starting from room temperature under argon atmosphere, the temperature was increased to 700°C at a heating rate of 10°C / min, kept warm for 2 hours, and cooled to room temperature with the furnace to obtain a thin-walled porous magnetic / carbon composite material.

[0036] The porous magnetic / carbon composite material prepared in this embodiment was tested by nitrogen adsorption, and its BET specific surface area was 346 m 2 Thermogravimetric analysis showed that the mass percentage of magnetic nanoparticles in the porous magnetic / carbon composite material prepared in this embodiment was 50.2%.

[0037] The SEM image of the porous magnetic / carbon composite material prepared in this embodiment is shown in FIG. Figure 1 As shown in the figure, the composite material has a three-dimensional honeycomb porous structure, with the pore walls composed of two-dimensional magnetic / carbon nanosheets with a size of 5 to 10 μm. The porous magnetic / carbon composite prepared in this example was ultrasonically dispersed in water, and atomic force microscopy testing showed that the pore wall thickness of the composite material was within the range of 1 to 2 nm.

[0038] like Figure 2 The TEM image of the porous magnetic / carbon composite material prepared in this example is shown. It can be seen that the magnetic nanoparticles are evenly embedded in the ultra-thin nanosheets, and the particle size of the magnetic nanoparticles is 20 to 50 nm.

[0039] Figure 3 From the X-ray diffraction pattern of the porous magnetic / carbon composite material prepared in this embodiment, it can be seen that the characteristic peaks of the magnetic nanoparticles (CoNi) correspond one-to-one with the standard card, indicating that the magnetic nanoparticles are CoNi alloys with good crystallinity. At the same time, the characteristic peaks of carbon can also be seen, indicating that the carbon-based material in the composite material is amorphous carbon.

[0040] like Figure 4 The figure shows the reflection loss spectrum of the thin-walled porous magnetic / carbon composite material prepared in this embodiment. When the matching thickness is 2.4 mm, the effective bandwidth of this composite material can reach 6.6 GHz. When the matching thickness is 3.5 mm, the reflection loss value reaches -55.7 dB, which meets the requirements of "strong absorption" and "broadband" for high-performance absorbers.

[0041] Example 2

[0042] A thin-walled porous magnetic / carbon composite material, the specific preparation method is as follows:

[0043] 4.5 g of polyvinyl pyrrolidone was weighed and dispersed in 50 mL of deionized water. 0.73 g of cobalt nitrate hexahydrate and 0.73 g of nickel nitrate hexahydrate were then added in sequence. The mixture was ultrasonically dispersed at room temperature for 20 min and stirred for 60 min until transparent to obtain a precursor solution. The precursor solution was dried in an oven and then ground into gravel using a mortar to obtain a precursor powder.

[0044] The precursor powder was placed in a porcelain boat and put into a tubular furnace for carbonization treatment. The carbonization treatment process conditions were as follows: starting from room temperature under argon atmosphere, the temperature was increased to 700°C at a heating rate of 10°C / min, kept warm for 2 hours, and cooled to room temperature with the furnace to obtain a thin-walled porous magnetic / carbon composite material.

[0045] like Figure 5 The SEM image of the porous magnetic / carbon composite material prepared in this example shows a honeycomb-like three-dimensional porous structure with pore wall thicknesses ranging from 100 to 200 nm. The minimum reflection loss reached -15.7 dB at 16.5 GHz, with a matching thickness of 1.3 mm, and a maximum effective bandwidth of 2.5 GHz.

[0046] Example 3

[0047] A thin-walled porous magnetic / carbon composite material, the specific preparation method is as follows:

[0048] 4.5 g of polyvinyl pyrrolidone was weighed and dispersed in 50 mL of deionized water. 1.5 g of cobalt nitrate hexahydrate and 1.5 g of nickel nitrate hexahydrate were then added in sequence. The mixture was ultrasonically dispersed at room temperature for 20 min and stirred for 60 min until transparent to obtain a precursor solution. The precursor solution was dried in an oven and then ground into gravel using a mortar to obtain a precursor powder.

[0049] The precursor powder was placed in a porcelain boat and put into a tubular furnace for carbonization treatment. The carbonization treatment process conditions were as follows: starting from room temperature under argon atmosphere, the temperature was increased to 700°C at a heating rate of 5°C / min, kept warm for 2 hours, and cooled to room temperature with the furnace to obtain a thin-walled porous magnetic / carbon composite material.

[0050] The SEM image of the porous magnetic / carbon composite material prepared in this embodiment is shown in FIG. Figure 6 The results show that it has a honeycomb-like three-dimensional porous structure with a pore wall thickness ranging from 50 to 100 nm. The lowest reflection loss was measured at 4.6 GHz, reaching -20.2 dB. The matching thickness was 5 mm, and the widest effective bandwidth was 6.3 GHz.

[0051] Comparative Example 1

[0052] A thin-walled porous magnetic / carbon composite material, the specific preparation method is as follows:

[0053] 4.5 g of polyvinyl pyrrolidone was weighed and dispersed in 50 mL of deionized water. 3.0 g of cobalt nitrate hexahydrate and 3.0 g of nickel nitrate hexahydrate were then added in sequence. The mixture was ultrasonically dispersed at room temperature for 20 min and stirred for 60 min until transparent to obtain a precursor solution. The precursor solution was dried in an oven and then ground into gravel using a mortar to obtain a precursor powder.

[0054] The precursor powder was placed in a porcelain boat and put into a tubular furnace for carbonization treatment. The carbonization treatment process conditions were as follows: starting from room temperature under argon atmosphere, the temperature was increased to 700°C at a heating rate of 10°C / min, kept warm for 2 hours, and cooled to room temperature with the furnace to obtain a thin-walled porous magnetic / carbon composite material.

[0055] The SEM image of the porous magnetic / carbon composite material prepared in this comparative example is as follows: Figure 7 As shown, the composite material has an irregular structure, with fragmented carbon nanosheets and a thickness ranging from 5 to 20 nm. This is likely due to the excessive amount of gas released by the decomposition of excess nitrate at high temperatures, which causes the porous structure to collapse. The lowest reflection loss measured was -13.8 dB at 7.8 GHz, with a matching thickness of 4.7 mm and a maximum effective bandwidth of 3.5 GHz.

[0056] Comparative Example 2

[0057] A thin-walled porous magnetic / carbon composite material, the specific preparation method is as follows:

[0058] 4.5 g of polyvinyl pyrrolidone was weighed and dispersed in 50 mL of deionized water. 1.5 g of cobalt nitrate hexahydrate and 1.5 g of nickel nitrate hexahydrate were then added in sequence. The mixture was ultrasonically dispersed at room temperature for 20 min and stirred for 60 min until transparent to obtain a precursor solution. The precursor solution was dried in an oven and then ground into gravel using a mortar to obtain a precursor powder.

[0059] The precursor powder was placed in a porcelain boat and put into a tubular furnace for carbonization treatment. The carbonization treatment process conditions were as follows: starting from room temperature under argon atmosphere, the temperature was increased to 700°C at a heating rate of 15°C / min, kept warm for 2 hours, and cooled to room temperature with the furnace to obtain a thin-walled porous magnetic / carbon composite material.

[0060] The SEM image of the porous magnetic / carbon composite material prepared in this comparative example is as follows: Figure 8 As shown, the composite material exhibits an irregular structure, with fragmented carbon nanosheets. This is likely due to the rapid heating rate during carbonization, which resulted in excessive pressure from the gas accumulated within the polymer, causing the bubble walls to rupture and the three-dimensional porous structure to break apart. The thickness of the two-dimensional carbon nanosheets ranged from 5 to 20 nm. The lowest reflection loss was measured at 17.9 GHz, at a matching thickness of 1.5 mm. There was no effective absorption bandwidth at -10 dB, indicating a lack of significant absorption performance.

[0061] The results of the above examples show that the thin-walled porous magnetic / carbon composite material prepared by the embodiment of the present invention has excellent wave absorption performance as an absorber. This is because the thin carbon nanosheets can increase the incident path of electromagnetic waves. At the same time, the three-dimensional porous structure is conducive to multiple absorption or scattering of electromagnetic waves in the pore channels, thereby greatly enhancing the attenuation ability of the absorber to electromagnetic waves. The introduction of magnetic nanoparticles not only generates magnetic loss, but also can cause interfacial polarization effect at the interface between the magnetic nanoparticles and the carbon-based material, further improving the wave absorption ability. The synergistic effect of multiple loss mechanisms ultimately makes the thin-walled porous magnetic / carbon composite material have strong reflection loss and wide effective bandwidth, which meets the requirements of practical applications.

[0062] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A thin-walled porous magnetic / carbon composite material, characterized in that: The thin-walled porous magnetic / carbon composite material has a three-dimensional honeycomb porous structure, the pore walls are composed of two-dimensional magnetic / carbon nanosheets, and the two-dimensional magnetic / carbon nanosheets are obtained by compounding magnetic nanoparticles and carbon-based materials, wherein the magnetic nanoparticles are uniformly dispersed in the two-dimensional magnetic / carbon nanosheets; The preparation method of the thin-walled porous magnetic / carbon composite material is as follows: 1) uniformly dispersing a polymer in deionized water, adding a metal nitrate, ultrasonically dispersing, and then stirring to obtain a precursor solution, wherein the polymer is one of polyvinyl pyrrolidone, glucose, and ammonium citrate; and the metal nitrate is one or more of nickel nitrate hexahydrate, cobalt nitrate hexahydrate, and ferric nitrate nonahydrate; 2) drying and grinding the precursor solution obtained in step 1) to obtain a precursor powder; 3) The precursor powder obtained in step 2) is placed in a tube furnace for carbonization treatment to obtain a thin-walled porous magnetic / carbon composite material.

2. The thin-walled porous magnetic / carbon composite material according to claim 1, characterized in that The thin-walled porous magnetic / carbon composite material has a specific surface area of ​​280-350 m 2 / g, and the pore wall thickness is 1~200nm.

3. The thin-walled porous magnetic / carbon composite material according to claim 1, characterized in that: The size of the two-dimensional magnetic / carbon nanosheet is 5-10 μm, and the magnetic nanoparticles are one of CoNi alloy nanoparticles, Fe nanoparticles, Co nanoparticles, Ni nanoparticles, and Fe oxide nanoparticles, with a particle size of 20-50 nm.

4. The thin-walled porous magnetic / carbon composite material according to claim 1, characterized in that: The mass percentage of magnetic nanoparticles in the thin-walled porous magnetic / carbon composite material is 20-60%.

5. The thin-walled porous magnetic / carbon composite material according to claim 1, characterized in that: The thin-walled porous magnetic / carbon composite material has a reflection loss of -15 to -60 dB and an effective absorption bandwidth of 2.5 to 7 GHz.

6. The thin-walled porous magnetic / carbon composite material according to claim 1, characterized in that: The preparation method comprises the following steps: 1) the mass ratio of the polymer to the metal nitrate is 1-17:1; and 1) the mass concentration of the polymer in the precursor solution is 7-8%.

7. The thin-walled porous magnetic / carbon composite material according to claim 1, characterized in that: The carbonization treatment process conditions in step 3 of the preparation method are: starting from room temperature under argon atmosphere, heating to 600-800°C at a heating rate of 5-10°C / min, and keeping the temperature for 2-3 hours.

8. Use of the thin-walled porous magnetic / carbon composite material according to any one of claims 1 to 7 in the field of electromagnetic absorbing materials.

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