A graphene-containing wave-absorbing material and its preparation method

Abstract

The present invention relates to the field of graphene materials, and specifically provides a wave-absorbing material containing graphene and a preparation method thereof. Magnetic metal salts are used to prepare FeCoNi Prussian blue nano-precursor particles (FeCoNi PBAs). An organic carbon coating layer is coated on the surface of FeCoNi PBAs through a self-polymerization coating strategy. After carbonization, FeCoNi-C with a magnetic FeCoNi core and nano-carbon cages is obtained. Utilizing the catalytic characteristics of the magnetic core metal elements, pyridine is used as a carbon source for the catalytic growth of nitrogen-doped graphene, and a graphene-based carbon cage composite material with a FeCoNi-N-Gr@C magnetic core is obtained. A wave-absorbing material and a preparation method thereof provided by the present invention are broadband electromagnetic absorption materials with both magnetism and high conductivity, which can absorb low-frequency and high-frequency electromagnetic waves simultaneously. By using the catalytic action of the magnetic alloy core, flocculent nitrogen-doped graphene rich in pyridine N is grown inside the carbon cage, greatly improving the conductivity of the composite material.

Description

Technical Field

[0001] The present invention relates to the field of graphene materials, and particularly to a wave-absorbing material containing graphene and a preparation method thereof. Background Art

[0002] With the rapid development of electronic technology, while bringing convenience to our work and life, it also brings increasingly serious electromagnetic pollution. Electromagnetic pollution not only interferes with the normal operation of electronic devices, but also causes serious harm to the health of living organisms. Electromagnetic protection technology has gradually received extensive attention from people in all walks of life. The development of materials with excellent electromagnetic protection performance has extremely important strategic significance for the development of multiple fields such as military, biology, medicine, and industry. Currently, electromagnetic protection materials are mainly divided into electromagnetic shielding materials and electromagnetic wave absorption materials. Electromagnetic shielding materials mainly achieve electromagnetic protection by reflecting incident electromagnetic waves, and have no attenuation effect on electromagnetic waves. Moreover, the reflected electromagnetic waves will cause secondary electromagnetic pollution. Electromagnetic wave absorption materials mainly absorb electromagnetic waves and convert the electromagnetic energy of the incident electromagnetic waves into thermal energy or energy of other properties, so as to achieve the purpose of eliminating the incident electromagnetic waves. According to its working principle, it can be divided into dielectric loss and magnetic loss. Dielectric loss mainly relies on highly conductive materials, and magnetic loss mainly relies on magnetic materials. Highly conductive electromagnetic absorption materials mainly rely on dielectric loss and are suitable for high-frequency electromagnetic wave protection. When high-frequency electromagnetic waves are incident, free electrons migrate in the electromagnetic field to form an induced current, and the induced current converts the electromagnetic energy of the high-frequency electromagnetic waves into thermal energy through the Joule effect to achieve electromagnetic absorption. In addition, due to the skin effect usually formed by high-frequency electromagnetic waves, the design of dielectric loss type electromagnetic wave absorption materials requires a large porosity and effective absorption area. Magnetic electromagnetic wave absorption materials mainly relying on magnetic loss are suitable for low-frequency electromagnetic wave protection. The magnetic loss mechanism mainly includes hysteresis loss, domain wall resonance loss, eddy current loss, and ferromagnetic resonance loss. The design of magnetic electromagnetic wave absorption materials mainly focuses on factors such as magnetic strength, magnetic core size, anisotropic equivalent field, and effective absorption area. Currently, the electromagnetic wave absorption materials in use usually focus on high frequency or low frequency, and there are few that are compatible with both high frequency and low frequency, and the effective absorption bandwidth is limited. A graphene-based carbon cage with a magnetic core provided by the present invention is a composite electromagnetic wave absorption material combining a small-sized magnetic alloy core and a highly conductive graphene-based carbon cage. Summary of the Invention

[0003] A preparation method of a graphene-based carbon cage with a magnetic core provided by the present invention can be briefly summarized into three stages: construction of a small-sized magnetic core, carbonization treatment, and growth of a nitrogen-doped graphene-based carbon cage.

[0004] The primary object of the present invention is to provide a graphene-based carbon cage with a magnetic core;

[0005] It includes a carbon cage and multiple aggregated wave-absorbing monomers inside the carbon cage. The wave-absorbing monomer includes a magnetic core, graphene grows on the surface of the magnetic core, a hard carbon layer is wrapped outside the core, and there is a gap between the core and the hard carbon layer; the resistivity of the wave-absorbing material is less than 3 mΩ·cm.

[0006] In a further technical solution, the carbon cage is an amorphous carbon layer. Specifically, the carbon cage is an amorphous carbon layer formed by the high-temperature catalytic reaction of polydopamine with the magnetic core.

[0007] In a further technical solution, the magnetic core is selected as a ternary metal alloy; specifically, the ternary metal alloy is an alloy formed by the coordination of three magnetic elements, Fe, Co, and Ni.

[0008] Another object of the present invention is to provide a preparation method of a graphene-based carbon cage of a magnetic core.

[0009] The object of the present invention is achieved by the following technical solutions. The specific steps include:

[0010] S1. Preparation of FeCoNi PBAs precursor: Under the condition of magnetic stirring at 50-80 °C, an aqueous solution A of 0.01-0.1 M potassium ferricyanide (K3Fe(CN)6) is prepared, and an aqueous solution B containing 0.01-0.1 M nickel acetate hexahydrate (Ni(OAc)2·6H2O) and 0.01-0.1 M cobalt acetate tetrahydrate (Co(OAc)2·4H2O) is prepared; the precursor solutions A and B are mixed in equal volume, and precursor solution A is added dropwise to precursor solution B under the condition of magnetic stirring to obtain suspension C; suspension C is placed for 24-48 h under the condition of magnetic stirring in an atmosphere of 5-25 °C, and then centrifuged, washed, and dried with deionized water to obtain FeCoNi PBAs powder.

[0011] In this step, the aqueous solution of potassium ferricyanide decomposes under visible light to obtain an aqueous solution of basic iron hydroxide, and solution B is an acidic aqueous solution, thus forming a comprehensive reaction of acid-base addition reaction and coordination reaction, so as to produce a precursor in a state of insoluble, slightly soluble, and precipitate, which is convenient for precursor collection.

[0012] S2. Prepare an aqueous solution of 0.1-0.5 M hydrochloric acid dopamine (DA) under the condition of magnetic stirring, add the FeCoNi PBAs powder obtained in S1 and disperse it evenly, and then use

[0013] Adjust the pH value of the solution to ≥8 to cause DA to self-polymerize under alkaline conditions; after 5 - 10 h, centrifuge, wash, and dry with deionized water to obtain FeCoNi PBAs@PDA powder; in an alkaline environment, DA monomers undergo a self-polymerization reaction to form a long-chain polymer, polydopamine. Therefore, the solution is adjusted to alkaline by a tris(hydroxymethyl)aminomethane buffer. When pH≥8, DA monomers are loaded on the surface of the FeCoNi PBAs precursor as the core and self-polymerize to form a PDA coating layer; in addition, PDA can polymerize a large number of small-sized precursors to form large-sized secondary aggregates.

[0014] S3. Load it in a graphite crucible and carbonize it in a tube furnace at 600 - 750 °C for 2 - 4 h. During this period, use high-purity nitrogen as the protective gas. During carbonization, the internal pressure of the quartz tube is maintained at about 1 Torr. During the carbonization stage, the self-carbon source reduces the positively charged metal to elemental metal to form a magnetic core. Due to the catalytic effect of the ternary metal alloy magnetic core, the self-carbon source of FeCoNi PBAs forms a highly graphitized carbon layer. There will be a certain mass loss and voids during the carbonization process. The PDA self-polymerized coating layer self-polymerizes with FeCoNi PBAs as the core. Due to the strong adhesion of PDA, multiple FeCoNi PBAs can be polymerized to form secondary aggregates. Therefore, the PDA carbon layer is in close contact with the graphitized hard carbon layer of the magnetic core, and the structure is stable, but there is a distance from the alloy core source. The PDA self-polymerized coating layer is far from the metal core and lacks effective catalysis to form an amorphous carbon cage, obtaining FeCoNi@C@C samples.

[0015] S4. After the reaction in step S3 is completed, raise the temperature to 900 - 1000 °C, use high-purity nitrogen as the carrier gas, and bring the liquid pyridine in the pyridine tank into the quartz tube by the bubbling method for reaction. The reaction time is 20 - 60 min. During the reaction, the internal pressure of the quartz tube is maintained at 0.4 - 0.8 Torr by regulating the carrier gas flow rate. The purpose of reducing the carrier gas flow rate is to avoid a large amount of pyridine being carried out by the excessive air flow and affecting the reaction. During the reaction, the magnetic metal core acts as a catalyst. Pyridine is used as the carbon source and grows into flocculent graphene with a large amount of pyridine N doping inside the carbon cage, increasing the conductivity of the composite material and the specific surface area of the composite material at the same time. After the reaction is completed, stop heating and naturally cool to room temperature to obtain FeCoNi-N-Gr@C black powder samples.

[0016] Pyridine has a six-membered ring structure with alternating C and N atoms. Its structure is similar to the C six-membered ring structure of graphene, enabling high doping and not damaging the long-range ordered six-membered ring structure of graphene. Additionally, pyridine N-doped graphite has a higher electron conductivity, which can be attributed to the fact that the doped N has a surplus non-bonding electron. It uses a metal alloy core as a catalyst and starts catalytic growth on the surface of the metal alloy core and finally fills the voids of the nanocarbon cage, increasing the overall conductivity of the composite material while increasing the effective surface area. The magnetic metal alloy core can absorb short-frequency electromagnetic waves and convert them into heat energy. At the same time, the heat energy can diffuse through the N-doped graphene and be absorbed by the free electrons on the N-doped graphene. The free electrons absorb energy, which can further improve its conductivity to a certain extent. The carbon layer of the non-alloy core with high conductivity absorbs high-frequency electromagnetic waves. N-doped graphene can enhance the absorption and loss of high-frequency electromagnetic waves because of its high conductivity and high specific surface area. The high-frequency electromagnetic waves are reflected and refracted multiple times within the material and finally consume the energy of the incident electromagnetic waves.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] A graphene-based carbon cage composite material with a magnetic core provided by the present invention is a composite carbon material with a magnetic alloy core, which is a broadband electromagnetic absorption material with both magnetism and high conductivity, and can absorb low-frequency and high-frequency electromagnetic waves simultaneously. By using the catalytic effect of the magnetic alloy core, flocculent nitrogen-doped graphene rich in pyridine N is grown inside the carbon cage, greatly improving the conductivity of the composite material.

[0019] A preparation method of a graphene-based carbon cage with a magnetic core provided by the present invention uses an organometallic source to obtain a double-layer carbon structure. The highly graphitized carbon near the magnetic alloy can serve as the growth active site for subsequent nitrogen-doped graphene. By using the growth strategy inside the carbon cage, the specific surface area of the composite material is increased. When used as an electromagnetic absorption material, a larger effective absorption area of electromagnetic waves can be obtained, weakening the skin effect caused by high-frequency electromagnetic waves.

[0020] A preparation method of a graphene-based carbon cage with a magnetic core provided by the present invention can obtain highly conductive graphene with a large amount of pyridine N doping, and construct an ideal 3D conductive network inside the carbon cage, making up for the deficiency of the conductive performance of the amorphous carbon cage. Description of the Drawings

[0021] Figure 1 SEM image of the FeCoNi PBAs@PDA sample obtained in step 2 of Example 1.

[0022] Figure 2 SEM image of the FeCoNi-N-Gr@C obtained in step 4 of Example 1.

[0023] Figure 3 Magnetic test effect diagram. Detailed implementation manners

[0024] The content of the present invention will be further described below in conjunction with specific embodiments, but it should not be construed as a limitation to the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the technical field. Example 1

[0025] This example briefly outlines a preparation method of a graphene-based carbon cage with a magnetic core provided by the present invention. The specific steps are as follows:

[0026] S1. Preparation of FeCoNi PBAs precursor: An aqueous solution A of 0.05 M potassium ferricyanide (K3Fe(CN)6) was prepared under magnetic stirring at 70 °C, and an aqueous solution B containing 0.05 M nickel acetate hexahydrate (Ni(OAc)2˙6H2O) and 0.02 M cobalt acetate tetrahydrate (Co(OAc)2˙4H2O) was prepared; the precursor solutions A and B were mixed in equal volumes, and precursor solution A was added dropwise to precursor solution B under magnetic stirring to obtain suspension C; suspension C was placed in a refrigerator at 10 °C under magnetic stirring for 24 h, centrifuged and washed with deionized water, and dried in a forced-air oven at 60 °C to obtain FeCoNi PBAs powder.

[0027] S2. An aqueous solution containing 0.2 M dopamine hydrochloride (DA) was prepared under magnetic stirring, the FeCoNi PBAs powder obtained in S1 was added and dispersed evenly, and then the

[0028] pH value of the solution was adjusted to 8.5 using a tris(hydroxymethyl)aminomethane buffer to cause DA to self-polymerize under alkaline conditions; after stirring at room temperature for 8 h, it was centrifuged and washed with deionized water, and then dried in a forced-air oven at 60 °C to obtain FeCoNi PBAs@PDA powder.

[0029] S3. Using a graphite crucible as a carrier, carbonization was carried out in a tube furnace at 700 °C for 3 h. High-purity nitrogen was used as a protective gas during carbonization, and the internal pressure of the quartz tube was maintained at about 1 Torr during carbonization. The positive-valent metal was reduced to elemental metal by its own carbon source during the carbonization stage to form a magnetic metal alloy core. The FeCoNi PBAs formed a highly graphitized carbon layer by its own carbon source. The PDA self-polymerized coating was far from the metal core and lacked effective catalysis to form an amorphous carbon cage, and the FeCoNi@C@C sample was obtained.

[0030] After the reactions in steps S4 and S3 are completed, the temperature is raised to 950 °C. Using high-purity nitrogen as the carrier gas, the liquid pyridine in the pyridine tank is introduced into the quartz tube by the bubbling method for reaction. The reaction time is 30 min. During the reaction, the internal pressure of the quartz tube is maintained at 0.6 Torr by regulating the carrier gas flow rate. The purpose of reducing the carrier gas flow rate is to avoid excessive air flow from carrying out a large amount of pyridine and affecting the reaction. During the reaction, the magnetic metal core acts as a catalyst. Pyridine serves as a carbon source and grows into flocculent graphene with a large amount of pyridine N doping inside the carbon cage, increasing the conductivity of the composite material while increasing the specific surface area of the composite material. After the reaction is completed, heating is stopped and it is naturally cooled to room temperature to obtain the FeCoNi-N-Gr@C black powder sample.

[0031] S5. Use a rubidium magnet to verify whether the target powder obtained in S4 has magnetism. Use a magnetic rod of 10,000 gauss to conduct an adsorption test on the powder sample of the example. As Figure 3 shown, it is found that the black powder sample is adsorbed on the magnetic rod, indicating that the sample obtained in Example 1 has good magnetism. Use a specific surface area tester to test the specific surface area of the sample, and use a four-probe resistivity tester to test the conductivity of the sample after powder pressing. The test results show that the target powder obtained in step S4 has very good magnetism, the BET test value is 230 m 2 / g, and the resistivity of the powder sample is 2.33 mΩ·cm, indicating that the sample has the characteristics of high magnetism, high conductivity, and large effective electromagnetic wave absorption area required for an ideal electromagnetic absorption material. Example 2

[0032] Steps S1 to S3 are the same as those in Example 1 and will not be elaborated here.

[0033] S4. After the reaction in step S3 is completed, the temperature is raised to 950 °C, and a methane / argon mixed gas is introduced into the quartz tube for reaction. The reaction time is 30 min. During the reaction, the internal pressure of the quartz tube is maintained at 0.6 Torr by regulating the carrier gas flow rate.

[0034] The difference between this example and Example 1 is that in step 4, methane is used instead of pyridine as the carbon source for graphene growth, and the other steps are the same as those in Example 1 and will not be elaborated. The purpose is to explore the influence of graphene growth conditions on the material properties. The results show that the resistivity of the obtained powder tested is 6.72 Ω·cm, and the other test results are similar to those in Example 1. After analysis, it is considered that using pyridine as the growth carbon source in Example 1 can greatly improve the conductivity of the sample, which can be attributed to the fact that when pyridine is used as the growth carbon source, the grown graphite contains abundant pyridine N. Example 3

[0035] The difference between this embodiment and Embodiment 1 is that step 4 is absent, and the other steps are the same as those in Embodiment 1 and will not be elaborated here. Its purpose is to explore the influence of graphene growth on the material properties. The results show that the obtained powder is magnetic, and the measured BET value is 47m 2 / g, and the measured resistivity value is 55.08 Ω·cm. Through analysis, it is considered that since graphene is not grown on the magnetic core, the internal resistance of the material has increased significantly, indicating that the growth of graphene can greatly improve the physical and electrical properties of the material. Therefore, the resistivity in Embodiment 3 has increased significantly. Embodiment 4

[0036] S1. Preparation of FeCoNi PBAs precursor: Under the condition of magnetic stirring at 70 °C, an aqueous solution A of 0.05 M potassium ferricyanide (K3Fe(CN)6) is prepared, and an aqueous solution B containing 0.05 M nickel acetate hexahydrate (Ni(OAc)2·6H2O) and 0.02 M cobalt acetate tetrahydrate (Co(OAc)2·4H2O) is prepared; the precursor solutions A and B are mixed in equal volumes, and precursor solution A is added dropwise to precursor solution B under the condition of magnetic stirring to obtain suspension C; suspension C is stirred for 24 h at 50 °C under the condition of magnetic stirring, centrifuged and washed with deionized water, and dried in a blast drying oven at 60 °C to obtain FeCoNi PBAs powder.

[0037] The difference between this embodiment and Embodiment 1 is that in step 1, solution C is stirred for 24 h at 50 °C, and the other steps are the same as those in Embodiment 1 and will not be elaborated here. Its purpose is to explore the influence of the reaction temperature in step S1 on the material properties. The results show that the measured BET value of the obtained powder is 57.11m 2 / g, and the other test results are similar to those in Embodiment 1, which can be attributed to the aging treatment at a relatively high temperature, resulting in a relatively large growth of the alloy core of the composite material, which is not conducive to improving the BET value of the material.

[0038] More specifically, although the exemplary embodiments of the present invention have been described herein, the present invention is not limited to these embodiments, but includes any and all embodiments that those skilled in the art can recognize through the foregoing detailed description, including modifications, omissions, for example, combinations between various embodiments, adaptive changes, and / or substitutions. The limitations in the claims can be broadly interpreted according to the language used in the claims and are not limited to the examples described in the foregoing detailed description or during the implementation of this application, and these examples should be considered non-exclusive. Any steps recited in any method or process claim can be executed in any order and are not limited to the order set forth in the claims. Therefore, the scope of the present invention should be determined only by the appended claims and their legal equivalents, rather than by the descriptions and examples given above.

Claims

1. An electromagnetic wave absorbing material containing graphene, characterized in that, It includes a carbon cage and multiple aggregated wave-absorbing monomers inside the carbon cage. The wave-absorbing monomer includes a magnetic core, graphene grows on the surface of the magnetic core, a layer of hard carbon layer is wrapped outside the core and there is a gap between the core and the hard carbon layer; the resistivity of the wave-absorbing material is less than 3 mΩ·cm; the wave-absorbing material containing graphene is prepared by the following method, including the following steps, 1) Prepare a magnetic ternary metal alloy precursor containing a carbon source; 2) Coating polydopamine outside the precursor; 3) Carry out carbonization treatment on the precursor coated with polydopamine; 4) After the carbonization treatment, raise the temperature and introduce a carbon source gas to grow graphene, and obtain the graphene-containing wave-absorbing material after cooling.

2. The absorbing material containing graphene according to claim 1, wherein: The carbon cage is an amorphous carbon layer. Specifically, the carbon cage is an amorphous carbon layer formed by the high-temperature catalytic reaction of polydopamine through the magnetic core.

3. The microwave absorbing material containing graphene according to claim 1, wherein: The magnetic core is selected as a ternary metal alloy; specifically, the ternary metal alloy is an alloy formed by the coordination of three magnetic elements, Fe, Co, and Ni.

4. A preparation method of a graphene-containing wave-absorbing material, characterized in that: Including the following steps, 1) Prepare a magnetic ternary metal alloy precursor containing a carbon source; 2) Coating polydopamine outside the precursor; 3) Carry out carbonization treatment on the precursor coated with polydopamine; 4) After the carbonization treatment, raise the temperature and introduce a carbon source gas to grow graphene, and obtain the graphene-containing wave-absorbing material after cooling; In step 1), an aqueous solution A of potassium ferricyanide (K3Fe(CN)6) with a concentration of 0.01 - 0.1 M is prepared under magnetic stirring conditions at 50 - 80 °C, and an aqueous solution B containing 0.01 - 0.1 M nickel acetate hexahydrate (Ni(OAc)2·6H2O) and 0.01 - 0.1 M cobalt acetate tetrahydrate (Co(OAc)2·4H2O) is prepared; the precursor solutions A and B are mixed in equal volumes, and precursor solution A is added dropwise to precursor solution B under magnetic stirring conditions to obtain suspension C; suspension C is placed for 24 - 48 h under magnetic stirring conditions in an atmosphere of 5 - 25 °C, and then centrifuged, washed, and dried with deionized water to obtain the magnetic ternary metal alloy precursor FeCoNi PBAs powder containing a carbon source.

5. The preparation method of a graphene-containing wave-absorbing material according to claim 4, characterized in that: In step 2), an aqueous solution of dopamine hydrochloride with a concentration of 0.1 - 0.5 M is prepared under magnetic stirring conditions, the FeCoNi PBAs powder obtained in S1 is added and dispersed evenly, and then the pH value of the solution is adjusted to ≥8 using a tris(hydroxymethyl)aminomethane buffer to cause the self-polymerization of dopamine hydrochloride under alkaline conditions; after 5 - 10 h, it is centrifuged, washed, and dried with deionized water to achieve the coating of polydopamine outside the FeCoNi PBAs powder, and FeCoNi PBAs@PDA powder is obtained.

6. The preparation method of a graphene-containing wave-absorbing material according to claim 4, characterized in that: In step 3), the FeCoNi PBAs@PDA powder is loaded into a graphite crucible and carbonized in a tube furnace for 2 - 4 h. During this period, high-purity nitrogen is used as a protective gas, and the internal pressure of the quartz tube is maintained at 1 Torr during carbonization. The positive-valent metal is reduced to elemental metal by the self-carbon source during the carbonization stage to form a magnetic metal alloy core, and the PDA self-polymerized coating forms an amorphous carbon cage.

7. The preparation method of a graphene-containing wave-absorbing material according to claim 6, characterized in that: In step 3), the temperature of the carbonization treatment in the tube furnace is set to 600 - 750 °C.

8. The preparation method of a graphene-containing wave-absorbing material according to claim 4, wherein: In step 4), the temperature is raised, and high-purity nitrogen is used as the carrier gas. The liquid pyridine in the pyridine tank is brought into the quartz tube by the bubbling method for reaction. The reaction time is 20 - 60 minutes. During the reaction, the internal pressure of the quartz tube is maintained at 0.4 - 0.8 Torr by regulating the carrier gas flow rate. The purpose of reducing the carrier gas flow rate is to avoid excessive airflow from carrying out a large amount of pyridine and affecting the reaction. During the reaction, the magnetic metal core acts as a catalyst. Pyridine serves as the carbon source and grows into flocculent graphene with a large amount of pyridine N-doping inside the carbon cage, increasing the conductivity of the composite material while increasing the specific surface area of the composite material. After the reaction, heating is stopped and the temperature is naturally cooled to room temperature to obtain a black powder sample of the microwave absorption material.

9. The preparation method of a graphene-containing wave-absorbing material according to claim 8, characterized in that: In step 4), the temperature is raised to 900 - 1000 °C for growing graphene.

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