Preparation method of nitrogen-doped carbon / reduced graphene oxide / magnetic metal composite absorbing material

Abstract

The present invention provides a method for preparing a nitrogen-doped carbon / reduced graphene oxide / magnetic metal composite absorbing material, belonging to the field of absorbing material preparation. The preparation method comprises the following steps: first, separately preparing a sodium alginate solution, a protonated aramid nanofiber solution, a graphene oxide solution, and a polyphenol-magnetic metal salt solution; then, mixing and stirring the above solutions at room temperature; then, pouring the stirred solution into a mold, directionally freezing, and freeze-drying it; and finally, carbonizing the dried sample under an inert atmosphere to obtain the nitrogen-doped carbon / reduced graphene oxide / magnetic metal composite absorbing material. The present invention is environmentally friendly and simple to operate, and the prepared composite material has good absorbing, hydrophobic, and mechanical properties.

Description

Technical Field

[0001] The present invention relates to the technical field of wave-absorbing material preparation, and in particular to a method for preparing a nitrogen-doped carbon / reduced graphene oxide / magnetic metal composite wave-absorbing material. Background Art

[0002] The rapid development of the military, communications, and aerospace sectors has led to an increase in electromagnetic radiation. Low-frequency electromagnetic radiation will become particularly prominent with the advancement of 5G and, in the future, 6G technologies. Therefore, effective microwave absorbing and shielding materials are crucial for addressing this issue. Furthermore, given the harsh environments in which various facilities requiring microwave absorbing materials, such as communications equipment, aircraft, and military structures, operate, higher requirements are placed on the hydrophobicity and thermal insulation properties of microwave absorbing materials. Therefore, the development of multifunctional absorbing materials, designed to meet the demands of complex environments, is crucial.

[0003] A material's impedance matching and electromagnetic attenuation capabilities determine its microwave absorption and shielding properties. Materials with porous structures, such as aerogels, can enhance lightweight properties and optimize impedance matching by increasing the air volume, thereby promoting effective microwave penetration. Two-dimensional carbon-based materials, such as graphene, graphene oxide (GO), and reduced graphene oxide (rGO), are the most promising candidates due to their light weight, stability, high aspect ratio, and good electronic properties.

[0004] Although progress has been made in aerogels made from two-dimensional carbon-based materials, such as the MXeneTi3C2T prepared by Wang et al. X @rGO aerogel, but due to the single energy dissipation mechanism, there are still performance limitations (Journal of Alloys and Compounds, 2020, 828, 154251).

[0005] By linking organic ligands with biomass polyphenols (tannic acid, chlorogenic acid) to form a metal polyphenol framework (MPN), this material exhibits a similar structure to metal-organic frameworks (MOFs). The raw materials are abundant, environmentally friendly, and inexpensive. This invention also uses protonated aramid nanofibers and graphene sheets to enhance the mechanical properties of sodium alginate to prepare a nitrogen-doped carbon / reduced graphene oxide / magnetic metal composite absorber. The magnetic metal formed by carbonization of the metal polyphenol framework is evenly distributed within the nitrogen-doped carbon gel network derived from sodium alginate and aramid nanofibers, effectively regulating the material's impedance matching to achieve broadband, strong absorption performance. The combination of the nitrogen-doped carbon framework, magnetic metal, and reduced graphene oxide enables the composite to exhibit multiple loss mechanisms and achieve excellent impedance matching, significantly enhancing its absorption performance. The presence of reduced graphene oxide and protonated aramid nanofibers imparts excellent mechanical and hydrophobic properties to the carbonized aerogel, significantly expanding the composite's application areas. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for preparing a nitrogen-doped carbon / reduced graphene oxide / magnetic metal composite absorbing material. The material has excellent microwave absorption performance and good mechanical properties, the preparation process is simple and green, the raw materials are easily available, and the equipment requirements are low.

[0007] In order to achieve the above objectives, the present invention is implemented by the following technical solution: a method for preparing a nitrogen-doped carbon / reduced graphene oxide / magnetic metal composite absorbing material, comprising the following steps:

[0008] S1: Separately prepare a sodium alginate solution with a concentration of 50-120 mg / mL, a protonated aramid nanofiber solution with a concentration of 5-12 mg / mL, a graphene oxide solution with a concentration of 5-10 mg / mL, and a polyphenol-magnetic metal salt solution with a concentration of 8-20 mg / mL, wherein the mass ratio of polyphenol to magnetic metal salt is 1:1; the volume of the sodium alginate solution: the volume of the aramid nanofiber solution: the volume of the graphene oxide solution: the volume of the polyphenol-magnetic metal salt solution is 4:2:1:1 to 8:4:2:1;

[0009] S2: Mix the above solutions at room temperature and stir for 3 h to make them evenly dispersed;

[0010] S3: Pour the dispersed sodium alginate / graphene oxide / polyphenol-magnetic metal salt / aramid nanofiber solution into a mold and freeze it at -40 °C for 1 hour and freeze-dry it for 48 hours;

[0011] S4: The dried sample is carbonized under an inert atmosphere to obtain a nitrogen-doped carbon / reduced graphene oxide / magnetic metal composite absorbing material.

[0012] Preferably, the polyphenol is one or a combination of tannic acid, catechin, and chlorogenic acid, and the metal salt is a water-soluble salt, wherein the metal ion is Fe 3+ 、Fe 2+ 、Co 2+ 、Ni 2+ One or a combination of the following, wherein the metal salt is one of chloride, sulfate, and nitrate.

[0013] Preferably, the volume of the sodium alginate solution: the volume of the aramid nanofiber solution: the volume of the graphene oxide solution: the volume of the polyphenol-magnetic metal salt solution = 4:2:1:1 to 8:4:2:1

[0014] Preferably, the polyphenol-magnetic metal salt solution is Fe 3+ -Tannic acid, Fe 2+ -Tannic acid, Co 2+ -Tannic acid, Ni 2+ -Tannic acid, Fe 3+ -Catechin, Fe 2+ -Catechin, Co 2+ -Catechin, Ni 2+ -Catechin, Fe 3+ -Chlorogenic acid, Fe 2+ -Chlorogenic acid, Co 2+ -Chlorogenic acid, Ni 2+ - One or a combination of chlorogenic acids.

[0015] Preferably, the inert atmosphere is nitrogen or argon, the heating rate is 10-20°C / min, the temperature range is 600-900°C, and the carbonization time is 2-4h.

[0016] Preferably, the metal is one or a combination of Fe, Co, and Ni.

[0017] The present invention has at least the following excellent effects:

[0018] (1) The nitrogen-doped carbon / reduced graphene oxide / magnetic metal composite absorber provided by the present invention is made of sodium alginate, graphene oxide, biomass polyphenol, soluble metal salt and protonated aramid nanofiber as raw materials, and water as solvent. The mechanical properties of sodium alginate can be enhanced by hydrogen bonding between the amide group (-NH-OH) of the protonated aramid nanofiber and the hydroxyl group (-OH) of sodium alginate. The biomass polyphenol reacts with the metal salt to form a metal-polyphenol skeleton and is connected to the sodium alginate through hydrogen bonding. Finally, carbonization is performed to obtain the nitrogen-doped carbon / reduced graphene oxide / magnetic metal composite material. The polyphenol used is a biomass raw material, which is green and environmentally friendly and can be repeatedly operated, meeting the current green and environmental protection requirements.

[0019] (2) The nitrogen-doped carbon / reduced graphene oxide / magnetic metal composite absorber provided by the present invention, wherein the nitrogen-doped carbon can promote the reduction of metal ions to magnetic metals to provide magnetic loss, and the reduction of graphene oxide to reduced graphene oxide. Moreover, the heterogeneous interface formed by the magnetic metal and the nitrogen-doped carbon is conducive to promoting interface polarization. On the other hand, defects will form in the composite material after carbonization, which will enhance the polarization and dipole polarization caused by the defects under the alternating magnetic field. The nitrogen-doped carbon network structure formed by the carbonization of sodium alginate and aramid nanofibers can promote the migration and jumping of electrons and enhance the conduction loss. Finally, the impedance matching of the composite material is improved through the synergistic effect of the various components, so that electromagnetic waves can enter the interior of the absorber as much as possible.

[0020] (3) The nitrogen-doped carbon / reduced graphene oxide / magnetic metal composite absorbing material provided by the present invention has good mechanical properties (capable of bearing 600-1200 times its own weight), hydrophobic properties and excellent absorbing properties.

[0021] (4) The nitrogen-doped carbon / reduced graphene oxide / magnetic metal composite absorbing material provided by the present invention can achieve broadband strong absorption (effective absorption bandwidth is between 2 and 6 GHz, and the minimum reflection loss is between -20 and -72 dB) at a relatively low filling rate (20-30 wt%).

[0022] (5) The nitrogen-doped carbon / reduced graphene oxide / magnetic metal composite absorbing material provided by the present invention can regulate the microstructure and size of the carbon / reduced graphene oxide / metal / protonated aramid nanofiber composite material by adjusting the ratio of sodium alginate, graphene oxide, polyphenol-magnetic metal salt, protonated aramid nanofiber, carbonization temperature, carbonization time and other conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a scanning electron microscope image of the nitrogen-doped carbon / rGO / Co composite absorbing material prepared in Example 1 of the present invention.

[0024] Figure 2 This is the X-ray diffraction pattern of the nitrogen-doped carbon / rGO / Co composite absorbing material prepared in Example 1 of the present invention.

[0025] Figure 3 This is a reflection loss diagram of the nitrogen-doped carbon / rGO / Co composite absorbing material prepared in Example 1 of the present invention.

[0026] Figure 4 This is a diagram showing that the nitrogen-doped carbon / rGO / Co composite absorbing material prepared in Example 1 of the present invention can withstand 806 times its own weight. DETAILED DESCRIPTION

[0027] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. After understanding the embodiments of the present invention, any person skilled in the art may make changes and modifications based on the techniques taught by the present invention without departing from the spirit and scope of the present invention.

[0028] Test Method

[0029] Micromorphology was observed using a SU-3500 scanning electron microscope; the phases of the nitrogen-doped carbon / reduced graphene oxide / magnetic metal composite absorber were analyzed using a Shimadzu XRD-6100 X-ray diffractometer; and the electromagnetic parameters of the samples were measured using a N5230A vector network analyzer using the coaxial method. The sample was mixed with paraffin wax in a uniform ratio and pressed into a ring with an inner diameter of 3 mm, an outer diameter of 7 mm, and a thickness of 2 mm. The electromagnetic parameters were measured in the 2-18 GHz range and fitted and analyzed using Matlab.

[0030] Embodiment 1:

[0031] S1: Prepare 20 mL of 50 mg / mL sodium alginate solution, 10 mL of 7.5 mg / mL protonated aramid nanofiber solution, 5 mL of 8 mg / mL graphene oxide solution, and 5 mL of 10 mg / mL tannic acid-cobalt chloride solution;

[0032] S2: Mix the above solutions at room temperature and stir for 3 h to make them evenly dispersed;

[0033] S3: Dispersed sodium alginate / graphene oxide / Co 2+ The tannic acid / protonated aramid nanofiber solution was poured into a mold and directionally frozen at -40°C for 1 hour and freeze-dried for 48 hours;

[0034] S4: The dried sample was carbonized at 700°C for 2 h in a nitrogen atmosphere at a heating rate of 10°C / min to obtain a nitrogen-doped carbon / rGO / Co composite absorber material;

[0035] Figure 1 This is a scanning electron microscope image of the nitrogen-doped carbon / rGO / Co composite absorbing material prepared in Example 1. Figure 2 This is the X-ray diffraction pattern of the nitrogen-doped carbon / rGO / Co composite absorbing material prepared in Example 1. Figure 3 This is a reflection loss diagram of the nitrogen-doped carbon / rGO / Co composite absorbing material prepared in Example 1 with 20 wt% added to paraffin wax. Figure 4This is a diagram showing that the nitrogen-doped carbon / rGO / Co composite absorbing material prepared in Example 1 can withstand 806 times its own weight. The hydrophobic angle of the nitrogen-doped carbon / rGO / Co composite absorbing material is 115°, which has good hydrophobic properties. Figure 1 It can be seen that the composite material exhibits a rich three-dimensional porous structure, with Co metal particles distributed in the porous network skeleton and rGO sheets. Figure 2 It can be seen that the XRD diffraction peak of the composite absorber has obvious Co (PDF#15-0806) characteristic peaks, which are basically consistent with the standard card. The diffraction peak at 25.2° corresponds to the carbon peak. Figure 3 It can be seen that when the addition amount of the composite material to paraffin is 20wt%, the minimum reflection loss with a matching thickness of 3.85mm is -70.3dB, and when the matching thickness is 1.93mm, the effective absorption bandwidth is 5.84GHz. Figure 4 It shows that nitrogen-doped carbon / rGO / Co composite material can withstand 806 times of its own weight and exhibits good mechanical properties.

[0036] Example 2:

[0037] S1: Prepare 20 mL of 50 mg / mL sodium alginate solution, 10 mL of 7.5 mg / mL protonated aramid nanofiber solution, 5 mL of 5 mg / mL graphene oxide solution, and 2.5 mL of 8 mg / mL tannic acid-ferrous sulfate solution;

[0038] S2: Mix the above solutions at room temperature and stir for 3 h to make them evenly dispersed;

[0039] S3: Dispersed sodium alginate / graphene oxide / Fe 2+ The tannic acid / protonated aramid nanofiber solution was poured into a mold and directionally frozen at -40°C for 1 hour and freeze-dried for 48 hours;

[0040] S4: The dried sample was carbonized at 700°C for 2 h in a nitrogen atmosphere at a heating rate of 10°C / min to obtain a nitrogen-doped carbon / rGO / Fe composite absorber material;

[0041] The nitrogen-doped carbon / rGO / Fe composite absorber has a filling rate of 25wt% in paraffin and a matching thickness of 2.8mm. The minimum reflection loss is -35dB, the effective absorption bandwidth is 3.24GHz, it can withstand 900 times its own weight, and the hydrophobic angle is 108°.

[0042] Example 3:

[0043] S1: Prepare 20 mL of 60 mg / mL sodium alginate solution, 5 mL of 5 mg / mL protonated aramid nanofiber solution, 2.5 mL of 10 mg / mL graphene oxide solution, and 2.5 mL of 15 mg / mL catechin-nickel nitrate solution;

[0044] S2: Mix the above solutions at room temperature and stir for 3 h to make them evenly dispersed;

[0045] S3: Dispersed sodium alginate / graphene oxide / Ni 2+ The catechin / protonated aramid nanofiber solution was poured into a mold and directionally frozen at -40°C for 1 hour and freeze-dried for 48 hours;

[0046] S4: The dried sample was carbonized at 800°C for 3 h in an argon atmosphere at a heating rate of 15°C / min to obtain a nitrogen-doped carbon / rGO / Ni composite absorber material;

[0047] The nitrogen-doped carbon / rGO / Ni composite absorber has a filling rate of 25wt% in paraffin and a matching thickness of 3mm. The minimum reflection loss is -25dB, the effective absorption bandwidth is 3.08GHz, it can withstand 600 times its own weight, and the hydrophobic angle is 116°.

[0048] Embodiment 4:

[0049] S1: Prepare 20 mL of 80 mg / mL sodium alginate solution, 10 mL of 12 mg / mL protonated aramid nanofiber solution, 5 mL of 10 mg / mL graphene oxide solution, 2.5 mL of 10 mg / mL tannic acid solution-ferric chloride solution, and 2.5 mL of 10 mg / mL chlorogenic acid-ferric chloride hexahydrate solution;

[0050] S2: Mix the above solutions at room temperature and stir for 3 h to make them evenly dispersed;

[0051] S3: Dispersed sodium alginate / graphene oxide / Fe 3+ -Tannic acid / Fe 3+ The chlorogenic acid / protonated aramid nanofiber solution was poured into a mold and directionally frozen at -40°C for 1 hour and freeze-dried for 48 hours;

[0052] S4: The dried sample was carbonized at 600°C for 4 h in a nitrogen atmosphere at a heating rate of 10°C / min to obtain a nitrogen-doped carbon / rGO / Fe composite absorber material;

[0053] The nitrogen-doped carbon / rGO / Fe composite absorber has a filling rate of 30wt% in paraffin and a matching thickness of 3.9mm. The minimum reflection loss is -29dB, the effective absorption bandwidth is 3.2GHz, it can withstand 1000 times its own weight, and the hydrophobic angle is 127°.

[0054] Example 5:

[0055] S1: Prepare 24 mL of 100 mg / mL sodium alginate solution, 12 mL of 10 mg / mL protonated aramid nanofiber solution, 4 mL of 7.5 mg / mL graphene oxide solution, 3 mL of 20 mg / mL catechin-nickel chloride solution, and 3 mL of 20 mg / mL catechin-cobalt chloride solution;

[0056] S2: Mix the above solutions at room temperature and stir for 3 h to make them evenly dispersed;

[0057] S3: Dispersed sodium alginate / graphene oxide / Ni 2+ -Catechin / Co 2+ The catechin / aramid nanofiber solution was poured into a mold and directionally frozen at -40°C for 1 hour and freeze-dried for 48 hours;

[0058] S4: The dried sample was carbonized at 800°C for 3 h in a nitrogen atmosphere at a heating rate of 20°C / min to obtain a nitrogen-doped carbon / rGO / CoNi composite absorber material;

[0059] The nitrogen-doped carbon / rGO / CoNi composite absorber has a filling rate of 25wt% in paraffin and a matching thickness of 2mm. The minimum reflection loss is -47dB, the effective absorption bandwidth is 4.3GHz, it can withstand 1200 times its own weight, and the hydrophobic angle is 133°.

Claims

1. A method for preparing a nitrogen-doped carbon / reduced graphene oxide / magnetic metal composite absorbing material, characterized by comprising the following steps: S1: Separately prepare a sodium alginate solution with a concentration of 50-120 mg / mL, a protonated aramid nanofiber solution with a concentration of 5-12 mg / mL, a graphene oxide solution with a concentration of 5-10 mg / mL, and a polyphenol-magnetic metal salt solution with a concentration of 8-20 mg / mL (the mass ratio of polyphenol to magnetic metal salt is 1:2); the volume of the sodium alginate solution: the volume of the aramid nanofiber solution: the volume of the graphene oxide solution: the volume of the polyphenol-magnetic metal salt solution is 4:2:1:1 to 8:4:2:1; S2: Mix the above solutions at room temperature and stir for 3 h to make them evenly dispersed; S3: Pour the dispersed sodium alginate / graphene oxide / polyphenol-magnetic metal salt / aramid nanofiber solution into a mold and freeze it at -40 °C for 1 hour and freeze-dry it for 48 hours; S4: carbonizing the dried sample under an inert atmosphere to obtain a nitrogen-doped carbon / reduced graphene oxide / magnetic metal composite absorbing material; The density of the nitrogen-doped carbon / reduced graphene oxide / magnetic metal composite absorbing material is between 0.2-0.5 g / cm 3 When used as an absorbing material, the minimum reflection loss is between -20~-72dB, the effective absorbing bandwidth is between 2~6GHz, the mechanical properties can withstand 600-1200 times its own weight, and the hydrophobic angle is 100-135°.

2. The method for preparing the nitrogen-doped carbon / reduced graphene oxide / magnetic metal composite absorbing material according to claim 1, wherein: The polyphenol is one or a combination of tannic acid, catechin, and chlorogenic acid, and the metal salt is a water-soluble salt, wherein the metal ion is Fe 3+ 、Fe 2+ 、Co 2+ 、Ni 2+ One or a combination of the foregoing metal salts, wherein the metal salt is one of the chlorides, sulfates, and nitrates of the foregoing metal ions.

3. The method for preparing the nitrogen-doped carbon / reduced graphene oxide / magnetic metal composite absorbing material according to claim 1, wherein: The polyphenol-magnetic metal salt solution is Fe 3+ -Tannic acid, Fe 2+ -Tannic acid, Co 2+ -Tannic acid, Ni 2+ -Tannic acid, Fe 3+ -Catechin, Fe 2+ -Catechin, Co 2+ -Catechin, Ni 2+ -Catechin, Fe 3+ -Chlorogenic acid, Fe 2+ -Chlorogenic acid, Co 2+ -Chlorogenic acid, Ni 2+ - One or a combination of chlorogenic acids.

4. The method for preparing the nitrogen-doped carbon / reduced graphene oxide / magnetic metal composite absorbing material according to claim 1, wherein: The inert atmosphere is nitrogen. During carbonization, the heating rate is 10-20°C / min, the temperature range is 600-900°C, and the carbonization time is 2-4h.

5. The method for preparing the nitrogen-doped carbon / reduced graphene oxide / magnetic metal composite absorbing material according to claim 1, wherein: The magnetic metal is one or a combination of Fe, Co, and Ni.

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