A broadband CoNiFe-MOF composite microwave absorbing material, its preparation method and application

Abstract

The present invention discloses a broadband CoNiFe-MOF composite microwave absorbing material and a preparation method thereof. The broadband microwave absorbing material prepared by using this method has a core-shell structure, which is conducive to multiple random reflections and scatterings of electromagnetic waves inside it. At the same time, the rich defect polarization, dipole polarization and interfacial polarization on its surface are conducive to enhancing the polarization loss, so that the absorbed electromagnetic waves are converted into heat energy.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation of microwave absorbing and electromagnetic shielding materials, and particularly relates to a broadband CoNiFe-MOF composite microwave absorbing material and a preparation method thereof. Background Art

[0002] With the rapid development of modern technology, from household appliances and mobile phones in daily life to radar detection and electromagnetic wave interference technologies in the military field, the application of electromagnetic waves has been everywhere. The application of electromagnetic waves has greatly improved the efficiency of social development, but it has also brought more hidden dangers to current information security and health. Long-term exposure to an electromagnetic radiation environment will pose a threat to human health, and the propagation of electromagnetic waves between digital devices will also reduce the service life of electronic devices. In order to effectively reduce the harm caused by electromagnetic wave radiation, the research and development of a new generation of thin, wideband, and strong microwave absorbing materials is extremely urgent.

[0003] Both theory and experiments have confirmed that after the material is anisotropized, due to the fact that electromagnetic waves can undergo multiple random reflections and scatterings inside it, and there are abundant defect polarizations, dipole polarizations, and interfacial polarizations, which are conducive to enhancing polarization loss and converting the absorbed electromagnetic waves into heat energy, thereby improving the microwave absorbing performance. Metal-organic frameworks (MOFs) composed of metal atoms and high-surface-area organic ligands have a high metal content and a stable carbon skeleton. During high-temperature annealing, the organic ligands are carbonized to form a carbon skeleton, and metal ions will nucleate and grow to form metal compounds. Under certain conditions, a carbon-based composite material with a highly anisotropic core-shell structure dispersed in the carbon texture can be formed. At the same time, by adjusting the types and ratios of metals and organic ligands during the preparation process and changing the technological process, MOFs with different morphologies and properties can be obtained, and thus in-situ pyrolyzed into carbon-based magnetic composite microwave absorbing materials for application in different fields.

[0004] Now, in order to meet the requirements of microwave absorbing materials with a thin matching thickness, a wide absorption band, and a high absorption rate, a broadband CoNiFe-MOF composite microwave absorbing material is provided. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a multi-element composite broadband CoNiFe-MOF microwave absorbing material and a preparation method thereof. The preparation of this microwave absorbing material can be carried out in a low-oxygen environment, and the prepared microwave absorbing material has the characteristics of a relatively thin matching thickness, low density, and strong absorption.

[0006] When the matching thickness of this material is 2.2 mm, it has an effective electromagnetic wave absorption of more than 70% in the frequency band of 6.27 - 18 GHz, and when the matching thickness is 1.5 mm, it has an effective electromagnetic wave absorption of more than 90% in the frequency band of 15.28 - 18 GHz.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] A preparation method of a broadband CoNiFe-MOF composite microwave absorbing material, comprising the following steps:

[0009] (1) Preparation of CoNiFe-MOF precursor:

[0010] Dissolve Prussian blue (PB) in oxalic acid solution, and then dissolve cobalt nitrate hexahydrate, nickel nitrate hexahydrate, and 2-methylimidazole in methanol respectively; subsequently, pour the 2-methylimidazole solution into the cobalt-nickel composite solution, and pour in the Prussian blue solution, and react under magnetic stirring; after centrifugal washing and drying of the reacted mixed solution, CoNiFe-MOF precursor powder is obtained;

[0011] (2) Preparation of broadband CoNiFe-MOF composite microwave absorbing material:

[0012] Place the CoNiFe-MOF precursor powder in a muffle furnace under a low-oxygen environment, and after completion, cool it to room temperature with the furnace, to obtain the broadband CoNiFe-MOF composite microwave absorbing material.

[0013] Optionally, in step (1), the molar ratio of Prussian blue to oxalic acid is 1:9.5, and the molar ratio of cobalt nitrate hexahydrate, nickel nitrate hexahydrate, and 2-methylimidazole is 1:1:21.2.

[0014] It should be noted that the oxalic acid solution is prepared by adding an appropriate amount of oxalic acid to deionized water and stirring until the oxalic acid is completely dissolved; and when pouring the 2-methylimidazole solution into the cobalt-nickel composite solution and pouring in the Prussian blue solution, the 2-methylimidazole solution should be poured evenly into the cobalt-nickel composite solution placed on a magnetic stirring table and in a stirring state.

[0015] Moreover, the washing method is to place the uniformly stirred composite solution in a centrifuge tube, pour in methanol solution, shake the centrifuge tube until there is no obvious precipitate remaining at the bottom, and then centrifuge and wash at 12000 r / min for 10 minutes, pour off the upper solution, only retain the precipitate, and repeat the operation 3 times or more until the color of the upper solution is lighter.

[0016] Furthermore, the magnetic stirring reaction temperature is 16 °C, the reaction time is 24 h; the drying temperature is 70 °C, and the drying time is 24 h.

[0017] Optionally, the calcination process parameters in step (2) are as follows:

[0018] Heat up to 600-700 °C and hold for 4 h, and the heating rate of the muffle furnace is 5 °C / min.

[0019] Further, the container for placing the CoNiFe-MOF precursor powder is a closed crucible, but not airtight. Specifically, the CoNiFe-MOF precursor powder is placed in the crucible, and the crucible containing the powder is completely covered with a lid that can completely cover the lower crucible to achieve a low-oxygen environment during the sintering process.

[0020] The second technical object of the present invention is to provide a broadband CoNiFe-MOF composite absorbing material prepared by the above method.

[0021] The third technical object of the present invention is to provide the application of the broadband CoNiFe-MOF composite absorbing material in absorbing electromagnetic waves in the frequency range of 1-18 GHz.

[0022] It should be noted that this material shows a high electromagnetic wave absorption efficiency in the frequency range of 6.27-18 GHz. As Figure 3 shown, after incorporating 4%wt of paraffin into the composite material and pressing it into a ring with a thickness of 2 mm, using the coaxial method in the frequency range of 1-18 GHz, when the matching thickness is 2.2 mm, the frequency range where the electromagnetic wave absorption reaches -5 dB reaches 11.73 GHz, and 70% of the electromagnetic wave effective absorption can be achieved. When the matching thickness is 1.5 mm, the frequency range where the absorption reaches -10 dB (90% of the electromagnetic wave effective absorption can be achieved) is greater than 2.72 GHz. It is a good electromagnetic wave attenuation functional material and can be used for the radar stealth of military equipment or the prevention and control of electromagnetic pollution in civil buildings.

[0023] From the above technical solutions, compared with the prior art, a broadband CoNiFe-MOF composite absorbing material, its preparation method and application provided by the present invention have the following excellent effects:

[0024] (1) The sintering process adopted by the present invention does not need to be carried out in an inert or vacuum environment. Only when sintering, the CoNiFe-MOF precursor powder is placed in a closed but not airtight crucible, so that the precursor powder is in a low-oxygen environment during the sintering process;

[0025] (2) The CoNiFe-MOF composite absorbing material prepared by the present invention has a highly anisotropic core-shell structure. The formation of this structure is conducive to the multiple random reflections and scatterings of electromagnetic waves inside it, forming rich defect polarization, dipole polarization and interface polarization, which is conducive to enhancing polarization loss, converting the absorbed electromagnetic waves into heat energy, and thus improving the wave absorption performance;

[0026] (3) When the matching thickness of the composite material prepared by the present invention is 1.5 mm, it has more than 70% of the electromagnetic wave effective absorption in the frequency band of 6.27-18 GHz. When the matching thickness is 2.2 mm, it has more than 90% of the electromagnetic wave effective absorption in the frequency band of 15.28-18 GHz. Brief Description of the Drawings

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to the provided drawings.

[0028] Figure 1 (a1-a2) SEM images and (b) TEM images of the CoNiFe-MOF composite microwave absorbing material prepared in Example 2.

[0029] Figure 2 Schematic diagram of microwave reflection loss of the CoNiFe-MOF composite microwave absorbing material prepared in Example 1 at 1-18 GHz and different thicknesses.

[0030] Figure 3 Schematic diagram of (a) dielectric constant and (b) magnetic permeability of the CoNiFe-MOF composite microwave absorbing material prepared in Example 2 at 1-18 GHz.

[0031] Figure 4 Schematic diagram of microwave reflection loss of the CoNiFe-MOF composite microwave absorbing material prepared in Example 2 at 1-18 GHz and different thicknesses.

[0032] Figure 5 Schematic diagram of microwave reflection loss of the CoNiFe-MOF composite microwave absorbing material prepared in Example 3 at 1-18 GHz and different thicknesses. Detailed Embodiments

[0033] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the embodiments of the present invention and the accompanying drawings of the specification. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0034] The embodiments of the present invention disclose a preparation method of a broadband CoNiFe-MOF composite microwave absorbing material.

[0035] To better understand the present invention, the following will further specifically elaborate on the present invention through the following embodiments. However, it should not be construed as a limitation of the present invention. For those skilled in the art, some non-essential improvements and adjustments made according to the above invention content are also considered to fall within the scope of protection of the present invention.

[0036] Next, in combination with specific embodiments, the technical solution of the present invention will be further described.

[0037] Example 1

[0038] A preparation method of CoNiFe-MOF composite microwave absorbing material, comprising the following steps:

[0039] (1) Preparation of CoNiFe-MOF precursor:

[0040] Dissolve 2 g of oxalic acid in deionized water to prepare an oxalic acid solution, and then pour 2 g of Prussian blue powder into the oxalic acid solution and stir to dissolve it; dissolve 2.5 g of cobalt nitrate hexahydrate and 2.5 g of nickel nitrate hexahydrate in 200 ml of methanol, and dissolve another 15 g of dimethylimidazole in 200 ml of methanol. Slowly pour the dimethylimidazole solution into the cobalt-nickel solution that is being magnetically stirred, and magnetically stir for 24 h. Place the reaction solution in a centrifuge tube and shake the centrifuge tube until no obvious precipitate remains at the bottom. Centrifuge and wash for 10 minutes at a rotation speed of 12,000 r / min, pour out the upper solution and only retain the precipitate, and repeat the washing with methanol solution 3 times or more until the color of the upper solution is lighter. Place the washed precipitate in a vacuum drying oven at 70 °C and dry for 24 h until all the residual methanol solution has evaporated. After taking it out, CoNiFe-MOF precursor powder is obtained.

[0041] (2) Preparation of CoNiFe-MOF composite microwave absorbing material:

[0042] Place the CoNiFe-MOF precursor powder in a crucible, and use a lid that can completely cover the lower crucible to completely cover the crucible containing the powder. Then send it into a muffle furnace, set the temperature to 600 °C, the heating rate is 5 °C per minute, and keep it warm for 4 h. After the reaction is completed, cool it to room temperature with the furnace to obtain the CoNiFe-MOF composite microwave absorbing material.

[0043] Example 2

[0044] A preparation method of broadband CoNiFe-MOF composite microwave absorbing material, comprising the following steps:

[0045] (1) Preparation of CoNiFe-MOF precursor:

[0046] Dissolve 2 g of oxalic acid in deionized water to prepare an oxalic acid solution, and then pour 2 g of Prussian blue powder into the oxalic acid solution and stir to dissolve it. Dissolve 2.5 g of cobalt nitrate hexahydrate and 2.5 g of nickel nitrate hexahydrate in 200 ml of methanol. Separately, dissolve 15 g of dimethylimidazole in 200 ml of methanol. Slowly pour the dimethylimidazole solution into the cobalt-nickel solution that is being magnetically stirred, and magnetically stir for 24 h. Place the reacted solution in a centrifuge tube and shake the centrifuge tube until no obvious precipitate remains at the bottom. Centrifuge and wash at a speed of 12,000 r / min for 10 minutes. Pour off the upper solution and only retain the precipitate. Add methanol solution and repeat the washing 3 times or more until the color of the upper solution is lighter. Place the washed precipitate in a vacuum drying oven at 70 °C and dry for 24 h until all the residual methanol solution has evaporated. After taking it out, obtain the CoNiFe-MOF precursor powder.

[0047] (2) Preparation of broadband CoNiFe-MOF composite microwave absorbing material

[0048] Place the CoNiFe-MOF precursor powder in a crucible and cover the crucible containing the powder completely with a lid that can completely cover the lower crucible. Send it into a muffle furnace, set the temperature to 650 °C, increase the temperature at a rate of 5 °C per minute, and keep it at this temperature for 4 h. After the reaction is completed, cool it to room temperature with the furnace to obtain the broadband CoNiFe-MOF composite microwave absorbing material.

[0049] Example 3

[0050] A preparation method of a CoNiFe-MOF composite microwave absorbing material, comprising the following steps:

[0051] (1) Preparation of CoNiFe-MOF precursor:

[0052] Dissolve 2 g of oxalic acid in deionized water to prepare an oxalic acid solution, and then pour 2 g of Prussian blue powder into the oxalic acid solution and stir to dissolve it. Dissolve 2.5 g of cobalt nitrate hexahydrate and 2.5 g of nickel nitrate hexahydrate in 200 ml of methanol. Separately, dissolve 15 g of dimethylimidazole in 200 ml of methanol. Slowly pour the dimethylimidazole solution into the cobalt-nickel solution that is being magnetically stirred, and magnetically stir for 24 h. Place the reacted solution in a centrifuge tube and shake the centrifuge tube until no obvious precipitate remains at the bottom. Centrifuge and wash at a speed of 12,000 r / min for 10 minutes. Pour off the upper solution and only retain the precipitate. Add methanol solution and repeat the washing 3 times or more until the color of the upper solution is lighter. Place the washed precipitate in a vacuum drying oven at 70 °C and dry for 24 h until all the residual methanol solution has evaporated. After taking it out, obtain the CoNiFe-MOF precursor powder;

[0053] (2) Preparation of CoNiFe-MOF composite microwave absorbing material:

[0054] Place the CoNiFe-MOF precursor powder in a crucible, and use a lid that can completely cover the crucible below to completely cover the crucible containing the powder. Then send it into a muffle furnace, set the temperature to 700 °C, the heating rate to 5 °C per minute, and keep it warm for 4 h. After the reaction is completed, cool it to room temperature with the furnace to obtain the CoNiFe-MOF composite microwave absorption material.

[0055] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A preparation method of a broadband CoNiFe-MOF composite microwave absorbing material, characterized in that, It includes the following steps: (1) Preparation of CoNiFe-MOF precursor: Dissolve Prussian blue (PB) in oxalic acid solution, and dissolve cobalt nitrate hexahydrate, nickel nitrate hexahydrate, and dimethylimidazole in methanol respectively; then pour the dimethylimidazole solution into the cobalt-nickel composite solution, and pour in the Prussian blue solution, and stir magnetically for reaction; after centrifuging, washing, and drying the reaction mixture solution, obtain CoNiFe-MOF precursor powder; (2) Preparation of broadband CoNiFe-MOF composite absorbing material: Calcine the CoNiFe-MOF precursor powder in a muffle furnace under a low-oxygen environment, and cool it to room temperature with the furnace after completion to obtain the broadband CoNiFe-MOF composite absorbing material.

2. The preparation method of the broadband CoNiFe-MOF composite microwave absorption material according to claim 1, characterized in that, In step (1), the molar ratio of Prussian blue to oxalic acid is 1:9.5, and the molar ratio of cobalt nitrate hexahydrate, nickel nitrate hexahydrate, and dimethylimidazole is 1:1:21.

2.

3. The preparation method of the broadband CoNiFe-MOF composite microwave absorbing material according to claim 1 or 2, characterized in that, In step (1), the dimethylimidazole solution is poured into the cobalt-nickel solution that is being magnetically stirred at a constant speed. The temperature of the magnetic stirring reaction is 16°C, and the reaction time is 24 h; the drying temperature after washing is 70°C, and the drying time is 24 h.

4. The preparation method of the broadband CoNiFe-MOF composite microwave absorption material according to claim 3, wherein The washing method in step (1) is to place the reaction solution in a centrifuge tube, shake until there is no obvious precipitate at the bottom, centrifuge and wash for 10 minutes in a centrifuge at a speed of 12,000 r / min, retain the precipitate, and repeat washing 3 times or more with methanol solution.

5. The preparation method of the broadband CoNiFe-MOF composite microwave absorbing material according to claim 1, characterized in that, The calcination process in step (2) is as follows: Place the powder in a crucible that can be completely covered with a lid; Heat up to 600-700°C and keep it warm for 4 h, and the heating rate of the muffle furnace is 5°C / min.

6. A broadband CoNiFe-MOF composite microwave absorbing material prepared by the method according to claim 1, characterized in that, The material has a highly anisotropic core-shell structure.

7. Application of a broadband CoNiFe-MOF composite absorbing material prepared by the method according to claim 1 or the broadband CoNiFe-MOF composite absorbing material according to claim 6 in absorbing electromagnetic waves in the frequency range of 1-18 GHz.

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