A magnetic carbon nanosheet assembly absorbing material and its preparation method

Abstract

The present invention discloses a magnetic carbon nanosheet assembly absorbing material and a preparation method thereof, which includes nano-iron, nano-nickel and a flaky carbon matrix. The nano-iron and nano-nickel are coated within the flaky carbon matrix, and a number of irregular nano-protrusions are formed on the surface of the flaky carbon matrix. The present invention overcomes the deficiencies of the prior art, avoids the formation of iron-nickel alloy within the magnetic carbon nanosheet assembly, and can adjust the ratio of iron and nickel within the magnetic carbon nanosheet assembly absorbing material. The prepared magnetic carbon nanosheet assembly absorbing material has good electromagnetic wave absorption performance.

Description

Technical Field

[0001] The present invention relates to the technical field of electromagnetic wave absorption materials, and specifically belongs to a wave-absorbing material of a magnetic carbon nanosheet assembly and a preparation method thereof. Background Art

[0002] Electromagnetic wave absorption materials, abbreviated as wave-absorbing materials, can absorb electromagnetic waves in specific frequency bands. Among them, metal-organic frameworks (MOF) derivatives have been widely studied in the fields of energy, catalysis, electromagnetics, electromagnetic shielding, and microwave absorption due to their advantages such as structural diversity, adjustable components, and controllable electromagnetic properties. In order to meet the impedance matching characteristics and strong loss requirements of electromagnetic wave absorption, MOF-derived magnetic-dielectric synergistic functional composites have been intensively studied and developed in microwave absorption and radar stealth, and have shown excellent electromagnetic wave energy absorption capabilities. Composites of strongly magnetic substances and conductive carbon components derived from MOF have become a research hotspot for microwave absorption materials. By adjusting the microstructure and material composition, the electromagnetic properties and impedance matching of the composite materials can be effectively adjusted to achieve strong absorption and broadband response to incident electromagnetic waves. Summary of the Invention

[0003] The purpose of the present invention is to provide a wave-absorbing material of a magnetic carbon nanosheet assembly and a preparation method thereof, which overcomes the deficiencies of the prior art, avoids the formation of iron-nickel alloy in the magnetic carbon nanosheet assembly, and can adjust the ratio of iron and nickel in the wave-absorbing material of the magnetic carbon nanosheet assembly. The prepared wave-absorbing material of the magnetic carbon nanosheet assembly has good electromagnetic wave absorption performance.

[0004] To solve the above problems, the technical solutions adopted by the present invention are as follows:

[0005] A wave-absorbing material of a magnetic carbon nanosheet assembly, comprising nano-iron, nano-nickel, and a flaky carbon matrix. The nano-iron and nano-nickel are coated in the flaky carbon matrix, and a number of irregular nano-protrusions are formed on the surface of the flaky carbon matrix.

[0006] Among them, the particle size of the nano-iron is 50-200 nm, and the particle size of the nano-nickel is 50-200 nm.

[0007] A method for preparing a wave-absorbing material of a magnetic carbon nanosheet assembly, comprising the following steps:

[0008] S1. Dissolve 0.10 g - 0.40 g of diaminoterephthalic acid, 0.06 g - 0.25 g of Ni(NO3)2·6H2O, 0.10 g - 0.50 g of FeCl3·6H2O, and 0.9 g of polyvinylpyrrolidone K-30 in 30 mL of a mixed solution of N,N-dimethylformamide and ethanol. After uniform dissolution and dispersion, seal the obtained mixed solution and react it at 120 °C for 12 h. After cooling, wash it with the solvent and dry it under vacuum to obtain Fe-Ni-MOF precursor powder;

[0009] S2. Heat the Fe-Ni-MOF powder from room temperature to 450 °C - 750 °C under a hydrogen-argon atmosphere and hold the reaction for 200 min - 400 min to obtain a magnetic carbon nanosheet assembly.

[0010] Among them, the volume ratio of N,N-dimethylformamide to ethanol in the mixed solution of N,N-dimethylformamide and ethanol is 3 - 27:27 - 3.

[0011] Among them, the solvent is ethanol.

[0012] Among them, the heating rate of the Fe-Ni-MOF powder under a protective atmosphere is 2 - 4 °C / min.

[0013] Compared with the prior art, the implementation effects of the present invention are as follows:

[0014] 1. The present invention uses solvothermal preparation of a bimetallic organic framework (Fe-Ni-MOF) as a precursor, and through carbothermal reduction treatment, magnetic iron / nickel nanoparticles are uniformly dispersed in carbon nanosheets to assemble into a magnetic carbon nanosheet assembly, avoiding the formation of iron-nickel nanoalloys;

[0015] 2. The present invention realizes the adjustment of the iron and nickel ratios in the microwave absorption material of the magnetic carbon nanosheet assembly by adjusting the volume ratio of N,N-dimethylformamide to ethanol in the mixed solution of N,N-dimethylformamide and ethanol;

[0016] 3. The microwave absorption material of the magnetic carbon nanosheet assembly of the present invention exhibits excellent electromagnetic wave absorption performance, and its reflection loss value can reach -57.5 dB; and when the thickness is 2.0 mm, its effective absorption bandwidth (< -10 dB) can reach 5.6 GHz (11.2 GHz - 16.8 GHz). BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is the X-ray diffraction pattern of the magnetic carbon nanosheet assembly of Examples 5 - 7 of the present invention;

[0018] Figure 2 It is the electromagnetic parameter diagram of the magnetic carbon nanosheet assembly of Examples 5 - 7 of the present invention;

[0019] Figure 3 Raman spectra of the magnetic carbon nanosheet assemblies of Embodiments 5-7 of the present invention;

[0020] Figure 4 Scanning electron micrographs of the magnetic carbon nanosheet assemblies of Embodiments 5-7 of the present invention;

[0021] Figure 5 Transmission electron micrographs of the magnetic carbon nanosheet assemblies of Embodiment 6 of the present invention;

[0022] Figure 6 Transmission electron micrographs of the magnetic carbon nanosheet assemblies of Embodiment 6 of the present invention;

[0023] Figure 7 Electromagnetic parameter diagrams of the magnetic carbon nanosheet assemblies of Embodiments 5-7 of the present invention;

[0024] Figure 8 Microwave absorption loss diagrams of the magnetic carbon nanosheet assemblies of Embodiments 5-7 of the present invention. Detailed implementation manners

[0025] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0026] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention.

[0027] In the description of the present invention, it should be noted that unless otherwise clearly defined and limited, the terms "installation", "connection", and "connection" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0028] Testing instruments and parameters of the materials of the present invention: An X-ray diffractometer (XRD, XD-3, Beijing Purkinje General Instrument Co., Ltd.) was used to characterize the phase composition of the samples. A vibrating sample magnetometer (VSM, HH-20, Instrument Factory of Nanjing University) was used to test the hysteresis loop of the samples; a laser Raman spectrometer (inVia, Renishaw Co., Ltd., UK) was used to characterize the carbon arrangement structure of the samples; a scanning electron microscope (SEM, S-4800, Hitachi, Japan) and a transmission electron microscope (TEM, JEOL-2010, JEOL Ltd., Japan) were used to characterize the microscopic morphology and composition of the samples. The samples were uniformly mixed with paraffin at a mass ratio of 1:1 to form coaxial rings with an inner diameter of 3.04 mm and an outer diameter of 7.00 mm, and the thickness of the coaxial rings was polished to 2.00 mm with fine sandpaper. A vector network analyzer (VNA, AV3629D, China Electronics Technology Group Corporation) was used to measure the electromagnetic parameters (complex permittivity and complex permeability) of the samples in the range of 2-18 GHz.

[0029] Example 1

[0030] (1) 0.40 g of diamino terephthalic acid, 0.25 g of Ni(NO3)2·6H2O, 0.5 g of FeCl3·6H2O and 0.9 g of polyvinylpyrrolidone K-30 were dissolved in 30 mL of a mixed solution of N,N-dimethylformamide and ethanol with a volume ratio of 27 mL:3 mL; after ultrasonic dispersion for 10 min, magnetic stirring was carried out for 20 min; the uniformly dispersed solution was transferred to a high-pressure reaction kettle with a polytetrafluoroethylene lining and maintained at 120 °C for 12 h; the obtained precipitate was collected through ethanol washing and centrifugation processes and vacuum dried at 50 °C for 12 h to obtain Fe-Ni-MOF precursor powder.

[0031] (2) The Fe-Ni-MOF powder was placed in a crucible, and a hydrogen-argon atmosphere (the volume percentage of hydrogen was 5%) was introduced, and calcination annealing treatment was carried out at a temperature of 750 °C for 200 min with a heating rate of 2 °C / min to obtain a black powder of Fe-Ni-MOF-derived magnetic carbon nanosheet assembly.

[0032] Example 2

[0033] (1) Dissolve 0.10 g of diaminoterephthalic acid, 0.06 g of Ni(NO3)2·6H2O, 0.10 g of FeCl3·6H2O, and 0.9 g of polyvinylpyrrolidone K-30 in 30 mL of a mixed solution of N,N-dimethylformamide and ethanol with a volume ratio of 3 mL:27 mL; after ultrasonic dispersion for 10 min, then magnetic stirring for 20 min; transfer the uniformly dispersed solution to a high-pressure reaction kettle with a polytetrafluoroethylene lining and maintain it at 120 °C for 12 h; collect the obtained precipitate through ethanol washing and centrifugation processes, and vacuum dry it at 50 °C for 12 h to obtain Fe-Ni-MOF precursor powder.

[0034] (2) Place the Fe-Ni-MOF powder in a crucible, introduce a hydrogen-argon atmosphere (the volume percentage of hydrogen is 5%), perform calcination annealing treatment at a temperature of 450 °C for 400 min, and the heating rate is 4 °C / min to obtain a black powder of Fe-Ni-MOF-derived magnetic carbon nanosheet assembly.

[0035] Example 3

[0036] (1) Dissolve 0.32 g of diaminoterephthalic acid, 0.18 g of Ni(NO3)2·6H2O, 0.20 g of FeCl3·6H2O, and 0.9 g of polyvinylpyrrolidone K-30 in 30 mL of a mixed solution of N,N-dimethylformamide and ethanol with a volume ratio of 25 mL:5 mL; after ultrasonic dispersion for 10 min, then magnetic stirring for 20 min; transfer the uniformly dispersed solution to a high-pressure reaction kettle with a polytetrafluoroethylene lining and maintain it at 120 °C for 12 h; collect the obtained precipitate through ethanol washing and centrifugation processes, and vacuum dry it at 50 °C for 12 h to obtain Fe-Ni-MOF precursor powder.

[0037] (2) Place the Fe-Ni-MOF powder in a crucible, introduce a hydrogen-argon atmosphere (the volume percentage of hydrogen is 5%), perform calcination annealing treatment at a temperature of 650 °C for 350 min, and the heating rate is 2 °C / min to obtain a black powder of Fe-Ni-MOF-derived magnetic carbon nanosheet assembly.

[0038] Example 4

[0039] (1) Dissolve 0.18 g of diaminoterephthalic acid, 0.10 g of Ni(NO3)2·6H2O, 0.40 g of FeCl3·6H2O and 0.9 g of polyvinylpyrrolidone K-30 in 30 mL of a mixed solution of N,N-dimethylformamide and ethanol with a volume ratio of 5 mL:25 mL; after ultrasonic dispersion for 10 min, then magnetic stirring for 20 min; transfer the uniformly dispersed solution to a high-pressure reaction kettle with a polytetrafluoroethylene lining and maintain it at 120 °C for 12 h; collect the obtained precipitate through ethanol washing and centrifugation processes and vacuum dry it at 50 °C for 12 h to obtain Fe-Ni-MOF precursor powder.

[0040] (2) Place the Fe-Ni-MOF powder in a crucible, introduce a hydrogen-argon atmosphere (the volume percentage of hydrogen is 5%), perform calcination and annealing treatment at a temperature of 500 °C for 250 min with a heating rate of 2 °C / min to obtain a black powder of Fe-Ni-MOF-derived magnetic carbon nanosheet assembly.

[0041] Example 5

[0042] (1) Dissolve 0.24 g of diaminoterephthalic acid, 0.13 g of Ni(NO3)2·6H2O, 0.24 g of FeCl3·6H2O and 0.9 g of polyvinylpyrrolidone K-30 in 30 mL of a mixed solution of N,N-dimethylformamide and ethanol with a volume ratio of 15 mL:15 mL; after ultrasonic dispersion for 10 min, then magnetic stirring for 20 min; transfer the uniformly dispersed solution to a high-pressure reaction kettle with a polytetrafluoroethylene lining and maintain it at 120 °C for 12 h; collect the obtained precipitate through ethanol washing and centrifugation processes and vacuum dry it at 50 °C for 12 h to obtain Fe-Ni-MOF precursor powder.

[0043] (2) Place the Fe-Ni-MOF powder in a crucible, introduce a hydrogen-argon atmosphere (the volume percentage of hydrogen is 5%), perform calcination and annealing treatment at a temperature of 600 °C for 300 min with a heating rate of 2 °C / min to obtain a black powder of Fe-Ni-MOF-derived magnetic carbon nanosheet assembly.

[0044] Example 6

[0045] The difference from Example 5 is that 0.24 g of diaminoterephthalic acid, 0.13 g of Ni(NO3)2·6H2O, 0.24 g of FeCl3·6H2O and 0.9 g of polyvinylpyrrolidone K-30 are dissolved in 30 mL of a mixed solution of N,N-dimethylformamide and ethanol with a volume ratio of 15 mL:15 mL, and the subsequent steps are exactly the same as those in Example 5 to obtain a black powder of Fe-Ni-MOF-derived magnetic carbon nanosheet assembly.

[0046] Example 7

[0047] The difference from Example 5 is that 0.24 g of diaminoterephthalic acid, 0.13 g of Ni(NO3)2·6H2O, 0.24 g of FeCl3·6H2O, and 0.9 g of polyvinylpyrrolidone K-30 were dissolved in 30 mL of a mixed solution of N,N-dimethylformamide and ethanol with a volume ratio of 25 mL:5 mL. The subsequent steps were exactly the same as those in Example 5, and a black powder of Fe-Ni-MOF-derived magnetic carbon nanosheet assembly was obtained.

[0048] The magnetic carbon nanosheet assemblies obtained in Examples 5-7 were analyzed and tested using an X-ray diffractometer, a vibrating sample magnetometer, a laser Raman spectrometer, a scanning electron microscope, a transmission electron microscope, and a vector network analyzer, respectively. The results are as Figure 1-8 shown.

[0049] As Figure 1 shown, the magnetic carbon nanosheet assembly is composed of elemental iron, elemental nickel, and carbon components. The diffraction peaks at 2θ = 44.7° and 65° correspond to the (110) and (200) crystal planes of Fe, respectively; the diffraction peaks at 2θ = 43.6°, 50.8°, and 65.0° correspond to the (111), (200), and (220) crystal planes of elemental Ni, respectively; the diffraction peak at 2θ = 26° belongs to the (002) crystal plane of carbon in the component, which is due to the transformation of the organic ligand into a highly graphitized carbon layer during the carbothermal reduction process. The XRD pattern also shows that as the volume ratio of N,N-dimethylformamide in the mixed solution of N,N-dimethylformamide and ethanol increases, the content of elemental iron in the magnetic carbon nanosheet assembly composite is continuously increasing. Because N,N-dimethylformamide is more polar than ethanol, as the content of DMF increases, more Fe 3+ ions can participate in the reaction in the solution, resulting in an increase in the content of elemental iron in the composite and an increase in the intensity of the XRD-derived peak.

[0050] As Figure 2 shown, the hysteresis loops of the magnetic carbon nanosheet assemblies of Examples 5-7 were measured at room temperature using a magnetic property measurement system. From Figure 2 it can be seen that the magnetic carbon nanosheet assemblies of Examples 5-7 all have a high magnetic response ability and a high saturation magnetization value. The saturation magnetization values of the magnetic carbon nanosheets of Examples 5-7 are 38.7 emu / g, 64.1 emu / g, and 71.7 emu / g, respectively.

[0051] As Figure 3 shown, at 1345.7 and 1593.8 cm -1Two Raman characteristic peaks appear at the respective positions, which are respectively attributed to the D-peak and the G-peak. The D-peak represents the lattice defects of carbon atoms, while the G-peak represents the in-plane stretching vibration and regular arrangement degree of sp2 hybridization of C atoms. Usually, the intensity ratio (I D / I G ) of the D-peak and the G-peak is used to illustrate the graphitization degree of the carbon component in the composite. As can be seen from Figure 3 , the I D / I G intensity ratios of the magnetic carbon nanosheets in Examples 5-7 are 1.01, 0.98, and 0.93 respectively. Raman data confirms that during the preparation of the magnetic carbon nanosheets, the defects of the carbon component decrease with the increase of the content of elemental iron, thereby improving the sp2 hybridization arrangement degree of its carbon atoms.

[0052] As Figure 4-6 shown, Figure 4 the magnetic carbon nanosheets in Examples 5-7 of Figure 5 and Figure 6 are all in a sheet stacking structure. There are obvious gaps between the nanosheets instead of being completely adhered together. And with the continuous increase of the volume ratio of N,N-dimethylformamide in the mixed solution of N,N-dimethylformamide and ethanol, the sheet structure of the magnetic carbon nanosheets gradually increases, and the irregular protrusions of the nanostructures formed on the surface of the sheet structure also become larger and show a disordered distribution state. The particle size of the nanostructure protrusions is mainly distributed in the range of 50-500 nm; while the transmission electron microscope images ( Figure 5 and Figure 6 ) of the magnetic carbon nanosheets prepared in Example 6 show that the prepared nanoiron and nanonickel are both coated in the sheet-like carbon matrix. The particle size of the nanoiron is 50-200 nm, and the particle size of the nanonickel is 50-200 nm; it shows that in the carbothermal reduction process of the present invention, the magnetic particles with reducibility are used as the center to catalyze the transformation of adjacent carbon-containing organic ligands, so that the ligands are transformed into highly graphitized carbon layers, and under the action of the MOF matrix of the present invention, the formation of iron-nickel alloy is avoided, and the assembled magnetic carbon nanosheets are composed of elemental iron, elemental nickel, and carbon components.

[0053] As Figure 7-8 shown, the electromagnetic parameters of the composite material were characterized by using a vector network analyzer. The electromagnetic parameters are composed of the complex dielectric constant (ε r = ε′-jε″) and the relative complex magnetic permeability (μ r = μ′-jμ″). According to the microwave absorption performance calculation formulas (Equations 1 and 2), the electromagnetic wave reflection loss value (the negative sign represents absorption, and the value represents the absorption intensity) curve of the assembled magnetic carbon nanosheet composite was fitted. The reflection loss calculation formula is as follows:

[0054]

[0055] RL = 20 log|(Z in - Z0) / (Z in + Z0)| (2)

[0056] where Z in is the normalized input impedance of the absorber, Z0 is the impedance of free space, ε r is the complex permittivity, μ r is the complex permeability, f is the given frequency, c is the speed of light, and d is the fitted thickness of the absorber. Figure 8 It can be seen that when the thicknesses are 2.0, 2.5, and 3.0 mm respectively, the reflection loss values of the magnetic carbon nanosheets in Example 5 are -14.1, -15.8, and -15.9 dB( Figure 8 a); the corresponding effective absorption bandwidths (RL ≤ -10 dB) are 3.9, 3.4, and 2.7 GHz( Figure 8 b). As the fitted thickness of the magnetic carbon nanosheets in Example 7 increases, its strongest absorption peak shifts towards the low-frequency region; when the thickness is 1.5 mm, its strongest reflection loss value reaches -24.7 dB at 15.5 GHz( Figure 8 e); its effective absorption bandwidth can reach 5.1 GHz from 12.9 GHz to 18 GHz( Figure 8 f). The magnetic carbon nanosheets in Example 6 exhibit the strongest absorption intensity. When the thicknesses are 2.0, 2.5, and 3.0 mm respectively, their reflection loss values can reach -43.6, -39.5, and -57.5 dB( Figure 8 c); when the thickness is 2.0 mm, its effective absorption bandwidth can cover 5.6 GHz from 11.2 to 16.8 GHz( Figure 8 d). By adjusting the content of the magnetic components in the magnetic carbon nanosheets, not only can the electromagnetic response ability of the composite be changed, but also the effective absorption band range of the composite at low thickness can be enhanced.

[0057] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. An electromagnetic wave absorbing material of a magnetic carbon nanosheet assembly, characterized in that It includes nano-iron, nano-nickel and a flaky carbon matrix. The nano-iron and nano-nickel are coated within the flaky carbon matrix, and a number of irregular nano-protrusions are formed on the surface of the flaky carbon matrix; A preparation method of a magnetic carbon nanosheet assembly absorbing material, comprising the following steps: S1, Dissolve 0.10 g - 0.40 g of terephthalic diamine, 0.06 g - 0.25 g of Ni(NO3)2·6H2O, 0.10 g - 0.50 g of FeCl3·6H2O and 0.9 g of polyvinylpyrrolidone K-30 in a 30 mL mixed solution of N,N-dimethylformamide and ethanol. After dissolving and dispersing evenly, seal the obtained mixed solution and react at 120 °C for 12 h. After cooling, wash with a solvent and dry under vacuum to obtain Fe-Ni-MOF precursor powder; S2, Heat the Fe-Ni-MOF precursor powder from room temperature to 450 °C - 750 °C in a hydrogen-argon atmosphere, and keep the temperature for reaction for 200 min - 400 min to obtain the magnetic carbon nanosheet assembly absorbing material.

2. The electromagnetic wave absorbing material of the magnetic carbon nanosheet assembly according to claim 1, wherein The particle size of the nano-iron is 50 - 200 nm, and the particle size of the nano-nickel is 50 - 200 nm.

3. The electromagnetic wave absorbing material of the magnetic carbon nanosheet assembly according to claim 1, wherein In the mixed solution of N,N-dimethylformamide and ethanol, the volume ratio of N,N-dimethylformamide to ethanol is 3 - 27:27 - 3.

4. The electromagnetic wave absorbing material of the magnetic carbon nanosheet assembly according to claim 1, wherein The solvent is ethanol.

5. The electromagnetic wave absorbing material of the magnetic carbon nanosheet assembly according to claim 1, wherein The heating rate of the Fe-Ni-MOF precursor powder in a hydrogen-argon atmosphere is 2 - 4 °C / min.

Images