A bimetallic single-atom isolated nitrogen-doped porous carbon material and a preparation method and application thereof

Abstract

The application belongs to the field of microwave absorbing materials, and particularly discloses a kind of bimetallic single-atom separated nitrogen-doped porous carbon material and its preparation method and application.The material uses 2-methyl imidazole as carrier carbon-nitrogen precursor, and reacts with zinc nitrate and another metal nitrate to form a bimetallic-metal organic framework, and uses it as a core, and sequentially coats a silica layer and a dopamine layer on the core from the inside out.The dopamine layer is the outer shell, and the silica layer is the intermediate layer, wherein the outer shell is a carbon-nitrogen shell layer with zinc single atoms distributed, which is obtained by carbonizing dopamine, the core is a carbon-nitrogen base with another kind of metal single atom dispersed, which is formed by carbonizing the bimetallic-metal organic framework, and the intermediate layer is etched, so that the nitrogen-doped porous carbon material has a yolk-like shell structure.The material has high microwave absorption performance, and has the advantages of light weight, excellent electromagnetic performance, etc.

Description

Technical Field

[0001] This invention belongs to the field of microwave absorbing materials technology, specifically relating to a bimetallic single-atom separated nitrogen-doped porous carbon material, its preparation method, and its application. Background Technology

[0002] The rapid development of electrical equipment and wireless communication has brought great convenience to people. However, the electromagnetic pollution and radiation generated during the use of electronic devices not only interfere with their normal operation but also harm the environment and human health. Microwave absorbing materials can suppress the propagation, reflection, and re-polluting of electromagnetic waves. Developing new microwave absorbing materials with thin thickness, low mass density, wide effective absorption bandwidth, and high microwave loss is a common goal of researchers.

[0003] Carbon-based composite materials possess the advantage of low mass density, and through the rational design of material composition and microstructure, synergistic effects based on multiple loss mechanisms can be achieved to enhance the attenuation capability of electromagnetic waves. The size of the modifying phase in carbon-based composite materials has a significant impact on the microwave absorption performance of the material; the microwave absorption efficiency increases with the decrease in the size of the modified nanophase, which makes single-atom-doped carbon-based microwave absorbing materials the highest in microwave absorption efficiency. Furthermore, metal single-atom-doped carbon-based materials can effectively modulate the electronic structure of adjacent carbon atoms, exhibiting unique physical and chemical properties. In the field of microwave absorption, the coordination structure of metal single atoms in the carbon matrix generates local asymmetric charges, forming electric dipoles under the influence of an applied electromagnetic field. These atomic-scale polarization sites increase the dielectric loss of the material. Therefore, the development of metal single-atom-doped carbon-based microwave absorbing materials with high microwave absorption performance has become a research hotspot.

[0004] In carbon-based materials doped with metal single atoms, different types of metal single atoms with similar properties have different effects on the electrical properties and microwave absorption performance of the materials. This allows us to control the dielectric properties of the materials by separating different metal single atoms and designing their microstructures, thereby improving the conductivity loss and dielectric polarization of the materials and thus enhancing their microwave absorption performance. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a nitrogen-doped porous carbon material with bimetallic single-atom separation. A bimetallic organic framework (BOR) material is prepared by mixing dimethylimidazole, zinc nitrate, and another metal nitrate in a methanol medium. A silica layer of approximately 100 nm thickness is then coated onto the BOR, followed by a dopamine layer of approximately 100 nm thickness. After high-temperature calcination and etching of the silica layer with sodium hydroxide solution, a yolk-shell structure with a particle size of approximately 1 μm is formed. The outer shell is a carbon-nitrogen shell layer with zinc single atoms distributed by dopamine carbonization, while the core is a carbon-nitrogen substrate with dispersed other metal single atoms formed by carbonizing the BOR. This material exhibits high microwave absorption performance and possesses advantages such as lightweight and excellent electromagnetic properties.

[0006] The technical solution of this invention is as follows: This invention provides a nitrogen-doped porous carbon material with bimetallic single-atom separation. Using 2-methylimidazole as a carbon-nitrogen precursor, it reacts with zinc nitrate and another metal nitrate to form a bimetallic-metal-organic framework. The bimetallic-metal-organic framework serves as the core, and from the inside out, a silica layer and a dopamine layer are sequentially coated onto the core. The dopamine layer forms the outer shell, and the silica layer forms the intermediate layer.

[0007] The outer shell is a carbon-nitrogen shell layer with zinc single atoms distributed by carbonization of dopamine, the core is a carbon-nitrogen substrate with another metal single atom dispersed after carbonization of bimetallic-metal-organic framework, and the intermediate layer is etched to make the nitrogen-doped porous carbon material have an egg yolk-like structure.

[0008] In one preferred embodiment of the present invention, the other metal nitrate is one of ferric nitrate, cobalt nitrate, manganese nitrate, or copper nitrate.

[0009] This invention also provides a method for preparing a bimetallic single-atom separated nitrogen-doped porous carbon material, comprising the following steps:

[0010] (1) Preparation of precursor: 2-methylimidazol solution was added to bimetallic nitrate solution and reacted for 15-20 h. After centrifugation, washing and drying, bimetallic-metal-organic framework precursor was obtained.

[0011] (2) Silica coating: 0.1-0.2 g of bimetallic-metal-organic framework precursor is dispersed in a mixed solution of 200-300 mL ethanol, 50-75 mL water and 3-4 mL ammonia water, 0.6-1 mL tetraethyl orthosilicate is added, and the reaction is carried out for 5-10 h. After centrifugation, washing and drying, silica-coated carbonitriding material is obtained.

[0012] (3) Dopamine coating: 0.2-0.3g of silica-coated carbon-nitrogen material is dispersed in 40-60mL of tris(hydroxymethyl)aminomethane hydrochloride buffer solution with pH=8-9, 30-50mg of dopamine hydrochloride is added, and the reaction is carried out at 0-4℃ for 20-24h. After filtration and washing, dopamine-coated silica-coated carbon-nitrogen material is obtained.

[0013] (4) Etching silica: Dopamine-coated silica-coated carbon-nitrogen material is placed in an inert atmosphere and carbonized at 850-950℃ to obtain carbon-coated silica-coated carbon-nitrogen material. It is then dispersed in 30-50 mL of 3.5-5 M sodium hydroxide solution and reacted. After centrifugation, washing and drying, a black product is obtained. The black product is placed in an inert atmosphere and reacted at 800-950℃ for 2-2.5 h to obtain a nitrogen-doped porous carbon material with bimetallic single-atom separation.

[0014] In a preferred embodiment of the present invention, in step (1), zinc nitrate and another metal nitrate are dissolved in methanol to obtain a bimetallic salt solution; 2-methylimidazole is dissolved in methanol to obtain a carrier carbon-nitrogen precursor solution.

[0015] In a preferred embodiment of the present invention, in step (1), the carbon-nitrogen precursor solution of the carrier is rapidly added to the bimetallic salt solution under stirring, and after reacting for 18 hours, the bimetallic-metal-organic framework precursor is obtained by centrifugation, washing with methanol and drying.

[0016] In a preferred embodiment of the present invention, in step (2), the bimetallic-metal-organic framework precursor is dispersed in a mixed solvent of ethanol, water and ammonia, and then tetraethyl orthosilicate is added dropwise.

[0017] In one preferred embodiment of the present invention, in step (1), the molar ratio of 2-methylimidazole, zinc nitrate and another metal nitrate is 40:5:1.

[0018] The present invention also provides the application of the above-mentioned bimetallic single-atom separated nitrogen-doped porous carbon material in microwave absorbing materials.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] This invention discloses a nitrogen-doped porous carbon material with bimetallic single-atom separation. A simple sol-gel method and heat treatment process were used to successfully prepare this material, effectively achieving precise positional control and spatial separation of the two metal single atoms. The invention utilizes dimethylimidazole, zinc nitrate, and other nitrates to synthesize a ZIF-8-like bimetallic-organic framework precursor in a methanol environment. A silicon dioxide layer of approximately 100 nm thickness is formed on the outside through the hydrolysis of tetraethyl orthosilicate. A dopamine layer of approximately 100 nm thickness is then formed by coating with dopamine and subjected to high-temperature calcination. Finally, the intermediate silicon dioxide layer is etched away using sodium hydroxide solution, forming a yolk-shell structure: the outer shell is a carbon-nitrogen shell layer with zinc single atoms distributed by dopamine carbonization, while the core is a carbon-nitrogen substrate with dispersed other metal single atoms formed after carbonization of the bimetallic-organic framework precursor. This design achieves efficient separation and positional manipulation of two metal single atoms, significantly improving the complex permittivity of the material. The imaginary part of its permittivity exhibits a distinct polarization peak near 11 GHz, thereby enhancing its microwave absorption performance. At a thickness of 2 mm, this material achieves a broad effective absorption bandwidth (5.28 GHz) and low reflection loss (-27.8 dB), demonstrating broad application potential and technological advantages. It has the following advantages:

[0021] (1) In this invention, bimetallic single atoms are dispersed on a carbon-based support to form atomic-scale electromagnetic energy conversion sites, which improves the microwave absorption performance of the material.

[0022] (2) Metal single atoms can regulate the electronic structure and local charge distribution of adjacent carbon atoms. The separated bimetallic single atoms regulate the dielectric properties of the material. Compared with the unseparated sample, the real and imaginary parts of the composite dielectric constant are significantly improved, and a significant polarization peak appears near 11 GHz. This corresponds to the increase in conduction loss and dielectric polarization, thereby improving the microwave absorption efficiency of the material and optimizing the microwave absorption frequency and bandwidth.

[0023] (3) Bimetallic single-atom separated nitrogen-doped porous carbon materials have high specific surface area, porous structure and low density, which are beneficial to enhance microwave absorption intensity and reduce reflection loss. In addition, the eggshell structure causes microwaves to be reflected multiple times between the shell and the core, further improving its microwave absorption performance;

[0024] (4) This invention synthesizes nitrogen-doped porous carbon materials with bimetallic single-atom separation through a simple sol-gel method and heat treatment. Compared with existing technologies, this product has low equipment cost, low raw material cost, short synthesis time, and easy operation and control of the preparation process. The process of this invention has significant economic benefits and is environmentally friendly. Attached Figure Description

[0025] Figure 1 This is a SEM image of a nitrogen-doped porous carbon material with bimetallic single-atom separation according to Embodiment 1 of the present invention;

[0026] Figure 2 This is a SEM image of a nitrogen-doped porous carbon material with bimetallic single-atom separation according to Embodiment 2 of the present invention;

[0027] Figure 3 This is a TEM image of a nitrogen-doped porous carbon material with bimetallic single-atom separation according to Embodiment 1 of the present invention;

[0028] Figure 4 The electromagnetic parameters of a bimetallic nitrogen-doped porous carbon material with unseparated single atoms in the 2-18 GHz band are shown in Comparative Example 1.

[0029] Figure 5 The electromagnetic parameters of a bimetallic single-atom separated nitrogen-doped porous carbon material in the 2-18 GHz band are shown in Embodiment 1 of the present invention.

[0030] Figure 6 The reflectance test results for a bimetallic nitrogen-doped porous carbon material with unseparated single atoms, as shown in Comparative Example 1, are obtained in the 2-18 GHz band.

[0031] Figure 7 This is a reflectance test diagram of a bimetallic single-atom separated nitrogen-doped porous carbon material in the 2-18 GHz band according to Embodiment 1 of the present invention. Detailed Implementation

[0032] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0033] Numerous specific details are set forth in the following description to provide a full understanding of the invention. However, the invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0034] Example 1

[0035] A method for preparing a bimetallic single-atom separated nitrogen-doped porous carbon material according to Example 1 of the present invention includes the following steps:

[0036] (1) Preparation of precursors: 640 mg zinc nitrate and 170 mg cobalt nitrate were added to 20 mL of methanol solvent and stirred for 2 h to completely dissolve them, thus obtaining a bimetallic salt methanol solution; 526 mg 2-methylimidazole was dissolved in 10 mL of methanol solvent and stirred for 2 h to completely dissolve them, thus obtaining a carbon-nitrogen precursor solution. The carbon-nitrogen precursor solution was quickly added to the bimetallic salt solution under stirring. After stirring for five minutes, the mixture was allowed to stand for 18 h. After centrifugation and washing with methanol three times, the washed sample was placed in a hot air oven at 80 °C and dried for 6 h to obtain a zinc-cobalt-metal-organic framework.

[0037] (2) Silica coating: 0.1g of the collected zinc cobalt-metal organic framework was dispersed in a mixed solvent of 280mL ethanol, 70mL water and 4mL ammonia, and 0.8mL tetraethyl orthosilicate was added dropwise. After stirring for 8h, the silica-coated carbonitride material was obtained by centrifugation, washing and drying.

[0038] (3) Dopamine coating: 0.2g of collected silica-coated carbon-nitrogen material was added to 50mL of tris(hydroxymethyl)aminomethane hydrochloride buffer solution with pH=8.5 and stirred for 2h to disperse it evenly. 40mg of dopamine hydrochloride was slowly added and stirred for 24h under ice water bath. The dopamine-coated silica-coated carbon-nitrogen material was then obtained by filtration and washing.

[0039] (4) Etching silicon dioxide: The collected dopamine-coated silicon dioxide-coated carbonitriding material was carbonized at 900°C in an inert atmosphere for 2 hours to obtain carbon-coated silicon dioxide-coated carbonitriding material.

[0040] Carbon-coated silica-coated carbonitriding material was dispersed in a 4M sodium hydroxide solution and reacted in a water bath at 60°C for 24 hours with continuous stirring. After centrifugation, washing and drying, the black product was collected.

[0041] The collected black product was reacted at 900℃ for 2 hours under an inert atmosphere to obtain a nitrogen-doped porous carbon material with bimetallic single-atom separation.

[0042] Figure 1 This is a SEM image of a bimetallic, single-atom-separated nitrogen-doped porous carbon material from Example 1. Since SEM can only observe the surface morphology of the material, only the carbon-based shell after oxidation and self-polymerization by dopamine hydrochloride followed by high-temperature carbonization can be observed. It is clearly observed that after high-temperature carbonization, the carbon shell obtained from the pyrolysis of the dopamine coating on the surface is completely and uniformly coated, with a smooth surface and a small number of local protrusions. The morphology of the bimetallic, single-atom-separated nitrogen-doped porous carbon material remains good and there is no agglomeration.

[0043] Figure 3This is a TEM image of a nitrogen-doped porous carbon material with bimetallic single-atom separation, as shown in Example 1. It can be observed that the obtained porous carbon material has an egg yolk-like structure, with a gap of about 100 nm between the outer shell and the core.

[0044] Example 2

[0045] A method for preparing a bimetallic single-atom separated nitrogen-doped porous carbon material according to Example 2 of the present invention includes the following steps:

[0046] (1) Preparation of precursors: 640 mg zinc nitrate and 170 mg nickel nitrate were added to 20 mL methanol solvent and stirred for 2 h to completely dissolve them, thus obtaining a bimetallic salt solution; 526 mg 2-methylimidazole was dissolved in 10 mL methanol solvent and stirred for 2 h to completely dissolve them, thus obtaining a carbon-nitrogen precursor solution. The carbon-nitrogen precursor solution was quickly added to the bimetallic salt solution under stirring. After stirring for five minutes, the mixture was allowed to stand for 18 h. After centrifugation and washing with methanol three times, the washed sample was placed in a hot air oven at 80 °C and dried for 6 h to obtain a zinc-nickel-metal-organic framework.

[0047] (2) Silica coating: 0.1g of the collected zinc-nickel-metal-organic framework was dispersed in a mixed solvent of 280mL ethanol, 70mL water and 4mL ammonia, and 0.8mL tetraethyl orthosilicate was added dropwise. The mixture was stirred for 8h, and then centrifuged, washed and dried to obtain silica-coated carbonitride material.

[0048] (3) Dopamine coating: 0.2g of collected silica-coated carbon-nitrogen material was added to 50mL of tris(hydroxymethyl)aminomethane hydrochloride buffer solution with pH=8.5 and stirred for 2h to disperse it evenly. 40mg of dopamine hydrochloride was slowly added and stirred for 24h under ice water bath. The mixture was then filtered and washed to obtain dopamine-coated silica-coated carbon-nitrogen material.

[0049] (4) Etching silicon dioxide: The collected dopamine-coated silicon dioxide-coated carbonitriding material was carbonized at 900°C in an inert atmosphere for 2 hours to obtain carbon-coated silicon dioxide-coated carbonitriding material.

[0050] Carbon-coated silica-coated carbonitriding material was dispersed in a 4M sodium hydroxide solution and reacted in a water bath at 60°C for 24 hours with continuous stirring. After centrifugation, washing and drying, a black product was obtained.

[0051] The collected black product was reacted at 900℃ in an inert atmosphere for 2 hours to obtain a nitrogen-doped porous carbon material with bimetallic single-atom separation. Figure 2 This is a SEM image of the nitrogen-doped porous carbon material with bimetallic single-atom separation in Example 2; from Figure 1 and Figure 2The comparison shows that even though both Example 1 and Example 2 used zinc nitrate and metal nitrate to prepare zeolite-like imidazole frameworks with zeolite framework structures as precursors, Example 1 used a zinc-cobalt metal-organic framework as a precursor with a particle size of about 1 μm, while Example 2 used a zinc-nickel metal-organic framework as a precursor with a particle size of only tens of nanometers. This is because different metal elements replaced zinc ions during the doping process of the metal-organic framework, resulting in significant distortion of its structure. The types of metal ions introduced by the metal nitrate will significantly affect the morphological performance of the obtained bimetallic organic framework precursor and the corresponding nitrogen-doped porous carbon material with bimetallic single-atom separation obtained after treatment.

[0052] Example 3

[0053] Example 3 of this invention discloses a method for preparing a bimetallic single-atom separated nitrogen-doped porous carbon material, comprising the following steps:

[0054] (1) Preparation of precursors: 640 mg zinc nitrate and 170 mg copper nitrate were added to 20 mL methanol solvent and stirred for 2 h to completely dissolve them, thus obtaining a bimetallic salt solution; 526 mg 2-methylimidazole was dissolved in 10 mL methanol solvent and stirred for 2 h to completely dissolve them, thus obtaining a carbon-nitrogen precursor solution. The carbon-nitrogen precursor solution was quickly added to the bimetallic salt solution under stirring, and after stirring for five minutes, the mixture was allowed to stand for 18 h. After centrifugation and washing with methanol three times, the washed sample was placed in a hot air oven at 80 °C and dried for 6 h to obtain a zinc-copper-metal-organic framework.

[0055] (2) Silica coating: 0.1g of the collected zinc-copper-metal organic framework was dispersed in a mixed solvent of 280mL ethanol, 70mL water and 4mL ammonia, and 0.8mL tetraethyl orthosilicate was added dropwise. The mixture was stirred for 8h, and then centrifuged, washed and dried to obtain silica-coated carbonitride material.

[0056] (3) Dopamine coating: 0.2g of collected silica-coated carbon-nitrogen material was added to 50mL of tris(hydroxymethyl)aminomethane hydrochloride buffer solution with pH=8.5 and stirred for 2h to disperse it evenly. 40mg of dopamine hydrochloride was slowly added and stirred for 24h under ice water bath. The dopamine-coated silica-coated carbon-nitrogen material was then obtained by filtration and washing.

[0057] (4) Etching silicon dioxide: The collected dopamine-coated silicon dioxide-coated carbonitriding material was carbonized at 900°C in an inert atmosphere for 2 hours to obtain carbon-coated silicon dioxide-coated carbonitriding material.

[0058] Carbon-coated silica-coated carbonitriding material was dispersed in a 4M sodium hydroxide solution and reacted in a water bath at 60°C for 24 hours with continuous stirring. After centrifugation, washing and drying, the black product was collected.

[0059] The collected black product was reacted at 900℃ in an inert atmosphere for 2 hours to obtain a nitrogen-doped porous carbon material with bimetallic single-atom separation.

[0060] Example 4

[0061] Example 4 of this invention discloses a method for preparing a bimetallic single-atom separated nitrogen-doped porous carbon material, comprising the following steps:

[0062] (1) Precursor preparation: 640 mg zinc nitrate and 170 mg manganese nitrate were added to 20 mL of methanol solvent and stirred for 2 h to completely dissolve, thus obtaining a bimetallic salt solution; 526 mg 2-methylimidazole was dissolved in 10 mL of methanol solvent and stirred for 2 h to completely dissolve, thus obtaining a carbon-nitrogen precursor solution. The carbon-nitrogen precursor solution was quickly added to the bimetallic salt solution under stirring, and after stirring for five minutes, the mixture was allowed to stand for 18 h. After centrifugation and washing with methanol three times, the washed sample was placed in a hot air oven at 80 °C and dried for 6 h to obtain a zinc-manganese-metal-organic framework.

[0063] (2) Silica coating: 0.1g of the collected zinc-manganese-metal-organic framework was dispersed in a mixed solvent of 280mL ethanol, 70mL water and 4mL ammonia. 0.8mL tetraethyl orthosilicate was added dropwise to the mixed solution and stirred for 8h. After centrifugation, washing and drying, silica-coated carbonitriding material was obtained.

[0064] (3) Dopamine coating: 0.2g of collected silica-coated carbon-nitrogen material was added to 50mL of tris(hydroxymethyl)aminomethane hydrochloride buffer solution with pH=8.5 and stirred for 2h to disperse it evenly. 40mg of dopamine hydrochloride was slowly added and stirred for 24h under ice water bath. The dopamine-coated silica-coated carbon-nitrogen material was then obtained by filtration and washing.

[0065] (4) Etching silicon dioxide: The collected dopamine-coated silicon dioxide-coated carbonitriding material was carbonized at 900°C in an inert atmosphere for 2 hours to obtain carbon-coated silicon dioxide-coated carbonitriding material.

[0066] Carbon-coated silica-coated carbonitriding material was dispersed in a 4M sodium hydroxide solution and reacted in a water bath at 60°C for 24 hours with continuous stirring. After centrifugation, washing and drying, the black product was collected.

[0067] The collected black product was reacted at 900℃ in an inert atmosphere for 2 hours to obtain a nitrogen-doped porous carbon material with bimetallic single-atom separation.

[0068] Comparative Example 1

[0069] The present invention, Comparative Example 1, describes a method for preparing a bimetallic nitrogen-doped porous carbon material with unseparated single atoms, comprising the following steps:

[0070] (1) Precursor preparation: 640 mg zinc nitrate and 170 mg cobalt nitrate were added to 20 mL of methanol solvent and stirred for 2 h to completely dissolve them, thus obtaining a bimetallic salt solution; 526 mg 2-methylimidazole was dissolved in 10 mL of methanol solvent and stirred for 2 h to completely dissolve them, thus obtaining a carbon-nitrogen precursor solution. The carbon-nitrogen precursor solution was quickly added to the bimetallic salt solution under stirring. After stirring for five minutes, the mixture was allowed to stand for 18 h. After centrifugation and washing with methanol three times, the washed sample was placed in a hot air oven at 80 °C and dried for 6 h to obtain a zinc-cobalt-metal-organic framework.

[0071] (2) Dopamine coating:

[0072] 0.2 g of the collected zinc-cobalt-metal-organic framework was added to 50 mL of tris(hydroxymethyl)aminomethane hydrochloride buffer solution at pH 8.5 and stirred for 2 h to disperse it evenly. 40 mg of dopamine hydrochloride was slowly added and the reaction was stirred in an ice-water bath for 24 h. The resulting material was then filtered and washed to obtain dopamine-coated carbon-nitrogen material.

[0073] The collected black product was reacted at 900℃ in an inert atmosphere for 2 hours to obtain a nitrogen-doped porous carbon material with unseparated bimetallic single atoms.

[0074] The performance of the nitrogen-doped porous carbon materials of Example 1 and Comparative Example 1 was tested. Figure 4 The electromagnetic parameters of a nitrogen-doped porous carbon material in the 2-18 GHz frequency band are shown in Comparative Example 1, without separation treatment of bimetallic single atoms. Figure 5 The electromagnetic parameters of the nitrogen-doped porous carbon material in Example 1 after single-atom separation treatment in the 2-18 GHz frequency band; from Figure 4 and Figure 5 It can be clearly observed that the dielectric properties of the material obtained after the bimetallic single atoms are separated are improved. Compared with the bimetallic single atoms in Comparative Example 1 without separation treatment, the imaginary part of the dielectric constant of the bimetallic single atoms in Example 1 after separation treatment shows an obvious polarization peak near 11 GHz, while the magnetic parameters do not change significantly. This also proves that after separation treatment, zinc is still distributed in the form of single atoms inside the carbon shell and is not oxidized into metal oxide particles. Figure 6The image shows the reflectance of a nitrogen-doped porous carbon material (Comparative Example 1) in the 2-18 GHz frequency band after the bimetallic single atom was not separated. Figure 7 This is a reflectance test chart of a nitrogen-doped porous carbon material in Example 1 after single-atom separation treatment in the 2-18 GHz frequency band. Figure 7 The study showed that the bimetallic, single-atom-separated nitrogen-doped porous carbon material exhibited an effective absorption bandwidth of 5.28 GHz and a minimum reflection loss of -27.8 dB at a thickness of 2 mm. Figure 6 The comparison of reflection loss of nitrogen-doped porous carbon materials without separation treatment shows that their microwave absorption performance is significantly improved after single-atom separation treatment, and the absorption peak shifts to lower frequencies. The main reason for this is that after separation treatment, zinc exists in the form of single atoms on the inner wall of the outermost carbon coating layer. The presence of zinc single atoms regulates the electronic structure and local charge distribution of adjacent carbon atoms. The bimetallic single atoms obtained after this separation treatment enhance the dielectric properties of the material, thereby improving microwave absorption efficiency and optimizing microwave absorption frequency and bandwidth.

[0075] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A bimetallic, single-atom-separated nitrogen-doped porous carbon material, characterized in that, Using 2-methylimidazole as a carbon-nitrogen precursor, it reacts with zinc nitrate and another metal nitrate to form a bimetallic-metal-organic framework. The bimetallic-metal-organic framework serves as the core, and from the inside out, a silica layer and a dopamine layer are sequentially coated onto the core. The dopamine layer forms the outer shell, and the silica layer forms the intermediate layer. The outer shell is a carbon-nitrogen shell layer with zinc single atoms distributed by carbonization of dopamine, the core is a carbon-nitrogen substrate with another metal single atom dispersed after carbonization of bimetallic-metal-organic framework, and the intermediate layer is etched so that the nitrogen-doped porous carbon material has an egg yolk-like structure. The other metal nitrate mentioned is one of nickel nitrate, ferric nitrate, cobalt nitrate, manganese nitrate, or copper nitrate.

2. The method for preparing the bimetallic single-atom separated nitrogen-doped porous carbon material according to claim 1, characterized in that, Includes the following steps: Preparation of precursor: 2-methylimidazole solution was added to bimetallic nitrate solution and reacted for 15-20 h. After centrifugation, washing and drying, bimetallic-metal-organic framework precursor was obtained. Silica coating: 0.1~0.2g of bimetallic-metal-organic framework precursor is dispersed in a mixed solution of 200~300mL ethanol, 50~75mL water and 3~4mL ammonia water, 0.6~1mL tetraethyl orthosilicate is added, and the reaction is carried out for 5~10h. After centrifugation, washing and drying, silica-coated carbonitriding material is obtained. Dopamine coating: 0.2-0.3g of silica-coated carbon-nitrogen material was dispersed in 40-60mL of tris(hydroxymethyl)aminomethane hydrochloride buffer solution with pH=8-9, and 30-50mg of dopamine hydrochloride was added. The mixture was reacted at 0-4℃ for 20-24h, and then filtered and washed to obtain dopamine-coated silica-coated carbon-nitrogen material. Etching silica: Dopamine-coated silica-coated carbonitriding material is placed in an inert atmosphere and subjected to a carbonization reaction at 850~950℃ to obtain carbon-coated silica-coated carbonitriding material. This material is then dispersed in 30~50mL of 3.5~5M sodium hydroxide solution and reacted. After centrifugation, washing and drying, a black product is obtained. The black product is placed in an inert atmosphere and reacted at 800~950℃ for 2~2.5h to obtain a nitrogen-doped porous carbon material with bimetallic single-atom separation.

3. The method for preparing bimetallic single-atom separated nitrogen-doped porous carbon material according to claim 2, characterized in that, In step (1), zinc nitrate and another metal nitrate are dissolved in methanol to obtain a bimetallic salt solution; 2-methylimidazole is dissolved in methanol to obtain a carbon-nitrogen precursor solution.

4. The method for preparing bimetallic single-atom separated nitrogen-doped porous carbon material according to claim 3, characterized in that, In step (1), the carbon-nitrogen precursor solution of the carrier is rapidly added to the bimetallic salt solution under stirring. After reacting for 18 hours, the bimetallic-metal-organic framework precursor is obtained by centrifugation, washing with methanol and drying.

5. The method for preparing bimetallic single-atom separated nitrogen-doped porous carbon material according to claim 2, characterized in that, In step (2), the bimetallic-metal-organic framework precursor is dispersed in a mixed solvent of ethanol, water and ammonia, and then tetraethyl orthosilicate is added dropwise.

6. The method for preparing bimetallic single-atom separated nitrogen-doped porous carbon material according to claim 2, characterized in that, In step (1), the molar ratio of 2-methylimidazole, zinc nitrate and another metal nitrate is 40:5:

1.

7. The application of the bimetallic single-atom separated nitrogen-doped porous carbon material as described in claim 1 in microwave absorbing materials.

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