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

Abstract

The invention provides a preparation method of a nitrogen-doped carbon / reduced graphene oxide / magnetic metal composite wave-absorbing material, and belongs to the field of wave-absorbing material preparation.The preparation method comprises the following steps that firstly, a sodium alginate solution, a protonated aramid nanofiber solution, a graphene oxide solution and a polyphenol-magnetic metal salt solution are prepared; the preparation method comprises the following steps: firstly, preparing a magnetic metal composite wave-absorbing material, then mixing and uniformly stirring the solutions at room temperature, pouring the uniformly stirred solution into a mold for directional freezing and freeze drying, and finally, carbonizing a dried sample in an inert atmosphere to obtain the nitrogen-doped carbon / reduced graphene oxide / magnetic metal composite wave-absorbing material. The preparation method is green, environment-friendly and simple to operate, and the prepared composite material has good wave-absorbing property, hydrophobic property and mechanical property.

Description

Technical Field

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

[0002] Due to the rapid development of the military, communication, and aerospace fields, electromagnetic radiation has been increasing continuously. Especially with the advancement of 5G and future 6G technologies, low-frequency electromagnetic radiation will become particularly prominent. Therefore, effective microwave absorption and shielding materials are the key to dealing with electromagnetic radiation problems. At the same time, considering that various facilities requiring microwave absorbing materials, such as communication equipment, airplanes, and military buildings, will face relatively harsh application environments, higher requirements are put forward for the hydrophobicity and heat insulation functions of microwave absorbing materials. Therefore, based on the application requirements in complex environments, the research and development of multifunctional microwave absorbing materials are particularly important.

[0003] The impedance matching and electromagnetic attenuation ability of materials determine the microwave absorption and shielding performance of materials. Materials with porous structures, such as aerogels, can enhance the lightweight performance 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), have become 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 of two-dimensional carbon-based materials, such as the MXeneTi3C2T X @rGO aerogel prepared by Wang et al., there are still performance limitations due to the single energy dissipation mechanism (Journal of Alloys and Compounds, 2020, 828, 154251).

[0005] By connecting organic ligands with biomass polyphenols (tannic acid, chlorogenic acid) to form a metal polyphenol framework (MPN), which has a structure similar to that of metal-organic frameworks, the raw materials have the advantages of rich sources, environmental friendliness, and low price. In the present invention, a nitrogen-doped carbon / reduced graphene oxide / magnetic metal composite microwave absorbing material is prepared by protonating aramid nanofibers and graphene sheets to enhance the mechanical properties of sodium alginate. The magnetic metal formed by the carbonization of the metal polyphenol framework is uniformly distributed in the nitrogen-doped carbon gel network framework derived from sodium alginate and aramid nanofibers, and effectively regulates the impedance matching of the material to achieve broadband strong absorption performance. The combination of the nitrogen-doped carbon framework, magnetic metal, and reduced graphene oxide enables the composite material to have multiple loss mechanisms and achieve excellent impedance matching, greatly enhancing the microwave absorption performance of the composite material. The presence of reduced graphene oxide and protonated aramid nanofibers endows the carbonized aerogel with excellent mechanical properties and hydrophobic properties, greatly expanding the application fields of the composite material. Summary of the Invention

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

[0007] To achieve the above object, the present invention is realized through the following technical solutions: A method for preparing a nitrogen-doped carbon / reduced graphene oxide / magnetic metal composite microwave absorbing material, comprising the following steps: S1: 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 ratio of the sodium alginate solution: aramid nanofiber solution: graphene oxide solution: polyphenol-magnetic metal salt solution = 4:2:1:1 - 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, freeze it directionally at -40 °C for 1 hour, and perform freeze-drying for 48 h; S4: Carbonize the dried sample in an inert atmosphere to obtain a nitrogen-doped carbon / reduced graphene oxide / magnetic metal composite microwave absorbing material.

[0008] Preferably, the polyphenol is one or a combination of tannic acid, catechuic acid, chlorogenic acid, etc., and the metal salt is a water-soluble salt, wherein the metal ion is Fe 3+ 、Fe2+ 、Co 2+ 、Ni 2+ One or a combination of several of them, and the metal salt is one of chloride, sulfate, and nitrate.

[0009] Preferably, the volume ratio of the sodium alginate solution: the aramid nanofiber solution: the graphene oxide solution: the polyphenol-magnetic metal salt solution = 4:2:1:1 to 8:4:2:1 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+ - catechuic acid, Fe 2+ - catechuic acid, Co 2+ - catechuic acid, Ni 2+ - catechuic acid, Fe 3+ - chlorogenic acid, Fe 2+ - chlorogenic acid, Co 2+ - chlorogenic acid, Ni 2+ - One or a combination of several of chlorogenic acids.

[0010] Preferably, the inert atmosphere is one of nitrogen or argon, the heating rate is 10-20 °C / min, the temperature range is 600-900 °C, and the carbonization time is 2-4 h.

[0011] Preferably, the metal is one or a combination of several of Fe, Co, and Ni.

[0012] The present invention has at least the following excellent effects: (1) The nitrogen-doped carbon / reduced graphene oxide / magnetic metal composite microwave absorbing material provided by the present invention uses sodium alginate, graphene oxide, biomass polyphenol, soluble metal salt, and protonated aramid nanofibers as raw materials and water as a solvent. Through the hydrogen bond interaction between the protonated amide group (-NH-OH) of the aramid nanofiber and the hydroxyl group (-OH) of sodium alginate, the mechanical properties of sodium alginate can be enhanced. The biomass polyphenol reacts with the metal salt to form a metal-polyphenol skeleton and is connected to sodium alginate through hydrogen bonds. Finally, a nitrogen-doped carbon / reduced graphene oxide / magnetic metal composite material is obtained by carbonization. The polyphenol used is a biomass raw material, which is green and environmentally friendly, can be operated repeatedly, and meets the requirements of today's green environmental protection.

[0013] (2) The nitrogen-doped carbon / reduced graphene oxide / magnetic metal composite microwave absorbing material provided by the present invention, wherein the nitrogen-doped carbon can promote the reduction of metal ions into magnetic metals to provide magnetic loss, and the graphene oxide is reduced to reduced graphene oxide. Moreover, the heterojunction formed by the magnetic metal and the nitrogen-doped carbon is conducive to promoting interfacial polarization. On the other hand, defects will be formed after the composite material is carbonized, enhancing 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 hopping of electrons and enhance the conduction loss. Finally, through the synergistic effect of each component, the impedance matching of the composite material is improved, enabling electromagnetic waves to enter the microwave absorbing material as much as possible.

[0014] (3) The nitrogen-doped carbon / reduced graphene oxide / magnetic metal composite microwave absorbing material provided by the present invention has good mechanical properties (able to withstand 600 - 1200 times its own weight), hydrophobic properties, and excellent microwave absorbing properties.

[0015] (4) The nitrogen-doped carbon / reduced graphene oxide / magnetic metal composite microwave absorbing material provided by the present invention can achieve broadband strong absorption (the effective microwave absorption bandwidth ranges from 2 to 6 GHz, and the minimum reflection loss ranges from -20 to -72 dB) at a relatively low filling rate (20 - 30 wt%).

[0016] (5) The nitrogen-doped carbon / reduced graphene oxide / magnetic metal composite microwave 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 ratios of sodium alginate, graphene oxide, polyphenol-magnetic metal salt, protonated aramid nanofibers, the carbonization temperature, and the carbonization time, etc. Description of the Drawings

[0017] Figure 1 It is the scanning electron microscope image of the nitrogen-doped carbon / rGO / Co composite microwave absorbing material prepared in Example 1 of the present invention.

[0018] Figure 2 It is the X-ray diffraction pattern of the nitrogen-doped carbon / rGO / Co composite microwave absorbing material prepared in Example 1 of the present invention.

[0019] Figure 3 It is the reflection loss diagram of the nitrogen-doped carbon / rGO / Co composite microwave absorbing material prepared in Example 1 of the present invention.

[0020] Figure 4 It is the effect diagram that the nitrogen-doped carbon / rGO / Co composite microwave absorbing material prepared in Example 1 of the present invention can withstand 806 times its own weight. Detailed Embodiments

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. After any person skilled in the relevant technical field understands the embodiments of the present invention, the technologies taught by the present invention can be changed and modified without departing from the spirit and scope of the present invention.

[0022] Testing method A SU-3500 scanning electron microscope was used for microscopic morphology observation; a Shimadzu XRD-6100 X-ray diffractometer was used to analyze the phase of the nitrogen-doped carbon / reduced graphene oxide / magnetic metal composite microwave absorbing material; an N5230A vector network analyzer was used to test the electromagnetic parameters of the sample, and the testing method was the coaxial method. The sample to be tested was uniformly mixed with paraffin in a certain proportion and pressed into a ring with an inner diameter of 3 mm, an outer diameter of 7 mm, and a thickness of 2 mm. Its electromagnetic parameters were tested in the range of 2-18 GHz, and analyzed by fitting with Matlab; Example 1:

[0023] S1: Prepare 20 mL of a sodium alginate solution with a concentration of 50 mg / mL, 10 mL of a protonated aramid nanofiber solution with a concentration of 7.5 mg / mL, 5 mL of a graphene oxide solution with a concentration of 8 mg / mL, and 5 mL of a tannic acid-cobalt chloride solution with a concentration of 10 mg / mL; 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 / Co 2+ -tannic acid / protonated aramid nanofiber solution into a mold, freeze it directionally at -40 °C for 1 hour, and perform freeze-drying for 48 h; S4: Carbonize the dried sample in a nitrogen atmosphere at a heating rate of 10 °C / min and 700 °C for 2 h to obtain a nitrogen-doped carbon / rGO / Co composite microwave absorbing material; Figure 1 is the scanning electron microscope image of the nitrogen-doped carbon / rGO / Co composite microwave absorbing material prepared in Example 1, Figure 2 is the X-ray diffraction pattern of the nitrogen-doped carbon / rGO / Co composite microwave absorbing material prepared in Example 1, Figure 3 is the reflection loss diagram of the nitrogen-doped carbon / rGO / Co composite microwave absorbing material prepared in Example 1 with an addition amount of 20 wt% in paraffin, Figure 4 is the effect diagram that the nitrogen-doped carbon / rGO / Co composite microwave absorbing material can withstand 806 times its own weight. The hydrophobic angle of the nitrogen-doped carbon / rGO / Co composite microwave absorbing material is 115°, showing good hydrophobic performance. It can be seen that Figure 1 the composite material exhibits a rich three-dimensional porous structure, and Co metal particles are distributed in the porous network skeleton and rGO sheets. It can be seen fromFigure 2 It can be seen that the XRD diffraction peaks of the composite absorbing material have obvious characteristic peaks of Co (PDF#15-0806), which basically conform to the standard card. The diffraction peak at 25.2° corresponds to the carbon peak. From Figure 3 it can be known that when the addition amount of the composite material in paraffin is 20wt%, the minimum reflection loss at a matching thickness of 3.85mm is -70.3dB, and when the matching thickness is 1.93mm, the effective absorption frequency bandwidth is 5.84GHz. Figure 4 It shows that the nitrogen-doped carbon / rGO / Co composite material can withstand 806 times its own weight, showing good mechanical properties.

[0024] Example 2:

[0025] S1: Prepare 20 mL of sodium alginate solution with a concentration of 50 mg / mL, 10 mL of protonated aramid nanofiber solution with a concentration of 7.5 mg / mL, 5 mL of graphene oxide solution with a concentration of 5 mg / mL, and 2.5 mL of tannic acid-ferrous sulfate solution with a concentration of 8 mg / mL; 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 / Fe 2+ -tannic acid / protonated aramid nanofiber solution into a mold, freeze it directionally at -40°C for 1 hour and perform freeze-drying for 48 h; S4: Carbonize the dried sample in a nitrogen atmosphere at a heating rate of 10°C / min at 700°C for 2 h to obtain a nitrogen-doped carbon / rGO / Fe composite absorbing material; When the filling rate of the nitrogen-doped carbon / rGO / Fe composite absorbing material in paraffin is 25wt% and the matching thickness is 2.8mm, the minimum reflection loss is -35dB, the effective absorption frequency bandwidth is 3.24GHz, it can withstand 900 times its own weight, and the hydrophobic angle is 108°.

[0026] Example 3:

[0027] S1: Prepare 20 mL of sodium alginate solution with a concentration of 60 mg / mL, 5 mL of protonated aramid nanofiber solution with a concentration of 5 mg / mL, 2.5 mL of graphene oxide solution with a concentration of 10 mg / mL, and 2.5 mL of catechol-nickel nitrate solution with a concentration of 15 mg / mL; 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 / Ni 2+ -catechol / protonated aramid nanofiber solution into a mold, freeze it directionally at -40°C for 1 hour and perform freeze-drying for 48 h; S4: Carbonize the dried sample in an argon atmosphere at a heating rate of 15 °C / min for 3 h at 800 °C to obtain a nitrogen-doped carbon / rGO / Ni composite microwave absorption material; When the filling ratio of the nitrogen-doped carbon / rGO / Ni composite microwave absorption material in paraffin is 25 wt% and the matching thickness is 3 mm, the minimum reflection loss is -25 dB, the effective absorption bandwidth is 3.08 GHz, it can withstand 600 times its own weight, and the hydrophobic angle is 116°.

[0028] Example 4:

[0029] S1: Prepare 20 mL of a sodium alginate solution with a concentration of 80 mg / mL, 10 mL of a protonated aramid nanofiber solution with a concentration of 12 mg / mL, 5 mL of a graphene oxide solution with a concentration of 10 mg / mL, 2.5 mL of a tannic acid - ferric chloride solution with a concentration of 10 mg / mL, and 2.5 mL of a chlorogenic acid - ferric chloride hexahydrate solution with a concentration of 10 mg / mL; S2: Mix the above solutions at room temperature and stir for 3 h to disperse them evenly; S3: Pour the dispersed sodium alginate / graphene oxide / Fe 3+ - tannic acid / Fe 3+ - chlorogenic acid / protonated aramid nanofiber solution into a mold, freeze it directionally at -40 °C for 1 h, and perform freeze-drying for 48 h; S4: Carbonize the dried sample in a nitrogen atmosphere at a heating rate of 10 °C / min for 4 h at 600 °C to obtain a nitrogen-doped carbon / rGO / Fe composite microwave absorption material; When the filling ratio of the nitrogen-doped carbon / rGO / Fe composite microwave absorption material in paraffin is 30 wt% and the matching thickness is 3.9 mm, the minimum reflection loss is -29 dB, the effective absorption bandwidth is 3.2 GHz, it can withstand 1000 times its own weight, and the hydrophobic angle is 127°.

[0030] Example 5:

[0031] S1: Prepare 24 mL of a sodium alginate solution with a concentration of 100 mg / mL, 12 mL of a protonated aramid nanofiber solution with a concentration of 10 mg / mL, 4 mL of a graphene oxide solution with a concentration of 7.5 mg / mL, 3 mL of a catechol - nickel chloride solution with a concentration of 20 mg / mL, and 3 mL of a catechol - cobalt chloride solution with a concentration of 20 mg / mL; S2: Mix the above solutions at room temperature and stir for 3 h to disperse them evenly; S3: Pour the dispersed sodium alginate / graphene oxide / Ni 2+ - catechol / Co 2+- Pour the catechin / aramid nanofiber solution into a mold, directionally freeze it at -40 °C for 1 hour, and then perform freeze-drying for 48 hours; S4: Carbonize the dried sample in a nitrogen atmosphere at a heating rate of 20 °C / min and 800 °C for 3 hours to obtain a nitrogen-doped carbon / rGO / CoNi composite microwave absorbing material; When the filling ratio of the nitrogen-doped carbon / rGO / CoNi composite microwave absorbing material in paraffin is 25 wt% and the matching thickness is 2 mm, the minimum reflection loss is -47 dB, the effective absorption bandwidth is 4.3 GHz, it can withstand 1200 times its own weight, and the hydrophobic angle is 133°.

Claims

1. A preparation method of a nitrogen-doped carbon / reduced graphene oxide / magnetic metal composite microwave absorbing material, characterized by the following steps: S1: 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, where the mass ratio of polyphenol to magnetic metal salt is 1:1; the volume ratio of the sodium alginate solution: aramid nanofiber solution: graphene oxide solution: polyphenol-magnetic metal salt solution = 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, directionally freeze it at -40 °C for 1 hour, and perform freeze-drying for 48 h; S4: Carbonize the dried sample in an inert atmosphere to obtain a nitrogen-doped carbon / reduced graphene oxide / magnetic metal composite microwave absorbing material; Among them, the density of the nitrogen-doped carbon / reduced graphene oxide / magnetic metal composite microwave absorbing material is between 0.2-0.5 g / cm 3 , when used as a microwave absorbing material, the minimum reflection loss is between -20~-72 dB, the effective microwave absorption bandwidth is between 2~6 GHz, the mechanical properties can withstand 600-1200 times its own weight, and the hydrophobic angle is 100-135°.

2. The preparation method of the nitrogen-doped carbon / reduced graphene oxide / magnetic metal composite microwave absorbing material according to claim 1, characterized in that, The polyphenol is one or a combination of several of tannic acid, catechuic acid, and chlorogenic acid, and the metal salt is a water-soluble salt, where the metal ion is Fe 3+ , Fe 2+ , Co 2+ , Ni 2+ or a combination of several of them, and the metal salt is one of chloride, sulfate, and nitrate.

3. The preparation method of the nitrogen-doped carbon / reduced graphene oxide / magnetic metal composite microwave absorption material according to claim 1, characterized in that, 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+ -catechuic acid, Fe 2+ -catechuic acid, Co 2+ -catechuic acid, Ni 2+ -catechuic acid, Fe 3+ -chlorogenic acid, Fe 2+ -chlorogenic acid, Co 2+ -chlorogenic acid, Ni 2+ -one or a combination of several of chlorogenic acid.

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

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

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