Flower-shaped Ni-MOFs derived spherical porous carbon composite nickel microwave absorbent and preparation method thereof

Abstract

The invention discloses a flower-like Ni-MOFs derived spherical porous carbon composite nickel microwave absorbent and a preparation method thereof, flower-like Ni-MOFs is used as a raw material, and a microwave absorbing material is formed on a micro-nano scale through a high-temperature carbonization method. The composite nickel microwave absorbent is of a spherical porous carbon structure, the whole preparation process is safe and environmentally friendly, the preparation cost is low, the yield of the composite nickel microwave absorbent is high, the effective absorption bandwidth and the dot frequency absorption strength are higher than those of MOFs derived porous carbon materials with other morphologies as absorbents, and the composite nickel microwave absorbent is suitable for microwave absorption.

Description

Technical Field

[0001] The present invention belongs to the technical field of ultra-wideband microwave absorbing materials, and in particular relates to a flower-shaped Ni-MOFs-derived spherical porous carbon composite nickel microwave absorber and a preparation method thereof. Background Art

[0002] With the rapid development of electronic information technology, the pollution caused by electronic equipment is also increasing rapidly. The harm of electromagnetic waves generated by electronic equipment to equipment and human health is becoming more and more serious. Therefore, the research and exploration of absorbing materials is in line with the trend of the times.

[0003] As an absorbing material, it must meet two necessary conditions: one is that it has a strong loss capacity for electromagnetic waves, including electrical loss and magnetic loss; the other is that it has a strong impedance matching effect to ensure that electromagnetic waves can enter the material more, which requires the impedance value of the absorbing material to be close to that of free space.

[0004] Existing absorbing materials can be divided into the following three types according to the loss type of the absorbing material: resistive loss type, electrical loss type and magnetic loss type absorbing materials; Resistive materials: porous carbon (PC), graphene (GO), carbon nanotubes (CNTs), etc. have high electrical conductivity, which leads to a fast electron migration rate and thus a strong loss capacity for electromagnetic waves. However, the impedance matching effect is poor, which makes it impossible for electromagnetic waves to effectively enter the interior of the material.

[0005] Electrically lossy materials: zirconium dioxide (ZrO2), silicon dioxide (SiO2), gallium arsenide (GaAs), etc. have stable mechanical properties, but their ability to attenuate electromagnetic waves is weak.

[0006] Magnetic loss type materials: alloy particles Fe, Ni, Co, metal oxides Co3O4, Fe2O3, Fe3O4 have strong magnetic loss capacity, but their tap density is large, which does not meet the requirements of "thin, light, wide, and strong", and the cutoff frequency is low, which limits practical applications.

[0007] As can be seen from the above classification, materials with a single absorption mechanism, due to their low absorption strength and narrow absorption bandwidth, cannot meet the requirements of wide bandwidth, thin thickness, light weight, and strong absorption. Therefore, combining absorbing materials with different loss mechanisms has become a viable solution. However, existing composite absorbing materials have a narrow effective bandwidth and low loss strength in the microwave frequency band due to the complex and variable synthesis steps, uncontrollable size, and severe particle agglomeration during the reaction process.

[0008] Metal-organic frameworks (MOFs) are a newly emerging class of porous materials composed of metal salts and organic ligands, primarily used in gas adsorption, environmental purification, and lithium-ion batteries. MOFs possess multi-level tunable pores (micropores, mesopores, and macropores) and thermal stability. The porous carbon materials obtained after high-temperature pyrolysis can maintain their multi-level pore structure. Furthermore, the central metals of MOFs can be reduced to metal alloy particles after high-temperature pyrolysis, with the Co, Fe, and Ni particles possessing strong magnetic properties. When MOF-derived porous carbon materials are used in microwave-absorbing materials, their unique pore structure allows for greater penetration of electromagnetic waves. The carbon conductive network formed after pyrolysis facilitates conductivity losses, while the presence of magnetic alloy particles fosters eddy current losses and resonance effects. The contact between the magnetic particles and the carbon conductive network provides more opportunities for polarization effects.

[0009] MOF-derived carbon is a simple material to prepare and has controllable size, making it a promising new absorber. However, there are thousands of different MOFs, and their shape, structure, pore structure, and pyrolysis temperature all influence their absorbing properties. For example, a pyrolysis temperature that is too low can lead to incomplete carbonization of the MOFs, resulting in low electrical conductivity and impacting their electrical loss capacity. A high temperature, on the other hand, can damage the carbon material's pore structure, increasing electrical loss but also negating the impedance matching effect, causing electromagnetic waves to be completely reflected at the material's surface.

[0010] Therefore, the selection of MOFs material type and the regulation of pyrolysis temperature are important factors affecting its excellent microwave absorbing performance. Summary of the Invention

[0011] In view of the problem that there are tens of thousands of types of MOFs in the prior art and that their shape structure, pore structure and pyrolysis temperature all affect their microwave absorption performance, the present invention provides a flower-shaped Ni-MOFs-derived spherical porous carbon composite nickel microwave absorber and a preparation method thereof. Flower-shaped Ni-MOFs are used as raw materials, and a microwave absorbing material is formed on a micro-nano scale by a high-temperature carbonization method to obtain a flower-shaped Ni-MOFs-derived spherical porous carbon composite nickel microwave absorber. The flower-shaped Ni-MOFs-derived spherical porous carbon composite nickel microwave absorber is a spherical porous carbon structure. The entire preparation process is safe and environmentally friendly, the preparation cost is low, the yield of the composite nickel microwave absorber is high, and the effective absorption bandwidth and point frequency absorption intensity are stronger than those of MOFs-derived porous carbon materials with other morphologies as absorbers, and the composite nickel microwave absorber is suitable for microwave absorption.

[0012] This invention studies the use of Ni-MOFs-derived porous carbon materials as microwave absorbers, mainly involving the screening of Ni-MOFs types (flower-shaped, rod-shaped, sheet-shaped) and pyrolysis temperatures (600°C, 700°C, 800°C).

[0013] The technical solutions of the present invention are as follows: A method for preparing a flower-like Ni-MOFs-derived spherical porous carbon composite nickel microwave absorber comprises the following steps: S1. After mixing the nickel salt and the organic ligand, the mixture is dispersed in a container containing an organic solvent and deionized water by stirring for 20 min-30 min and ultrasonicating for 20 min-30 min, wherein the nickel salt, the organic ligand, the organic solvent and the deionized water are in the order of Molar ratio of (0.001~0.01)mol:(0.0015~0.003)mol:(0.5~0.6)mol; The nickel salt is selected from nickel nitrate hexahydrate (Ni(NO3)2•6H2O); The organic ligand is selected from one of trimesic acid (H3BTC), 2,5-dihydroxyterephthalic acid (H2DOBDC), and biphenyldicarboxylic acid (BPDC); The organic solvent is selected from dimethylformamide (DMF) or anhydrous ethanol (CH3CH2OH); S2. After the nickel salt and organic ligand are fully dissolved, place the container in a heat-insulating drying oven and dry it at 100°C to 150°C for 10 hours to 24 hours before taking it out; S3. The dried container is naturally cooled to room temperature, and centrifuged using dimethylformamide (DMF) 1 to 3 times, each centrifugation time being 2 to 5 minutes; S4. Pour off the supernatant after centrifugation and place in an 80°C oven to dry for 10-12 hours to obtain a yellow-brown flower-like Ni-MOFs powder; S5. The yellow-brown flower-shaped Ni-MOFs powder obtained in the previous step is placed in a tubular furnace filled with protective gas for pyrolysis. The pyrolysis temperature is set to 600°C~800°C, the heating rate is 5°C / min, the holding time is 2h, and the powder is naturally cooled to room temperature and then taken out to obtain a flower-shaped Ni-MOFs-derived spherical porous carbon composite nickel microwave absorber.

[0014] Furthermore, the stirring time in S1 is 30 minutes; the ultrasonication time is 30 minutes; and the container is a hydrothermal reactor.

[0015] Furthermore, the placing in the heat preservation drying oven described in S2 is selected to be kept warm at 100°C for 24 hours, or kept warm at 120°C for 12 hours, or kept warm at 150°C for 10 hours.

[0016] Furthermore, the "filled with protective gas" in S5 refers to a nitrogen atmosphere; the pyrolysis temperature is 600°C, 700°C or 800°C; and the "natural cooling to room temperature" refers to cooling to 21°C.

[0017] The present invention also relates to a flower-shaped Ni-MOFs-derived spherical porous carbon composite nickel microwave absorber, which is obtained by adopting the preparation method of the above-mentioned flower-shaped Ni-MOFs-derived spherical porous carbon composite nickel microwave absorber. The flower-shaped Ni-MOFs-derived spherical porous carbon composite nickel microwave absorber is a spherical porous carbon composite nickel microwave absorber, which uses flower-shaped Ni-MOFsNi-DOBDC as raw material and forms Ni-DOBDC-700 spherical porous carbon composite nickel microwave absorber after high-temperature carbonization. The composite nickel microwave absorber has a spherical porous structure, and nickel alloy particles cover the outside of the spherical structure.

[0018] Furthermore, the Ni-MOFs-derived spherical porous carbon composite nickel microwave absorber also has shapes such as rods, spheres, and sheets.

[0019] In addition, the present invention also provides an application of the above-mentioned flower-shaped Ni-MOFs-derived spherical porous carbon composite nickel microwave absorber in the microwave frequency band, comprising the following steps: The prepared flower-like Ni-MOFs-derived spherical porous carbon composite nickel microwave absorber was fully mixed with a binder and an organic solvent in an organic solvent at a mass ratio of 4:6:1 to form a coaxial ring, and the microwave absorption test was carried out using the coaxial method.

[0020] Furthermore, the binder is selected from paraffin, and the organic solvent is selected from n-hexane.

[0021] Furthermore, the coaxial ring mentioned above refers to a coaxial ring with an outer diameter of 7 mm, an inner diameter of 3.05 mm, and a thickness of 2.6 mm. The wave absorption test is performed using the coaxial method, which means that the sample is assembled and calibrated with coaxial parts, and the test frequency band is 2GHz-18GHz.

[0022] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention describes a flower-shaped Ni-MOFs-derived spherical porous carbon composite nickel microwave absorber. Ni-MOFs are used as precursor materials. Ni-MOFs offer a rich structure, diverse and adjustable pores, and a simple and accessible preparation process, demonstrating significant potential in fields such as gas adsorption and environmental purification. The present invention compares flower-shaped, rod-shaped, and sheet-shaped Ni-MOFs precursors, studying the applications of the composite nickel microwave absorbers obtained by pyrolysis of these precursors in microwave absorption and identifying the absorber with the optimal morphology.

[0023] 2. The carbon materials obtained by this invention are available in spherical, rod-shaped, and flake-shaped forms. Physical and chemical performance testing of the materials revealed that, compared to rod-shaped and flake-shaped structures, the spherical structure enhances the impedance matching effect between the composite nickel microwave absorber and electromagnetic waves, facilitating electron transfer and transitions, and improving the material's electrical conductivity. When used as a microwave absorber, this structure increases the material's dielectric loss capacity, effectively enhancing absorption intensity at a single point frequency.

[0024] 3. The spherical, rod-shaped and sheet-shaped composite nickel microwave absorbers obtained by the one-step pyrolysis method of the present invention are 2+ Being reduced to a nickel alloy increases the magnetic permeability of the composite nickel microwave absorber. By combining carbon materials with high electrical conductivity losses with magnetic materials and regulating the pyrolysis temperature, the dielectric constant and magnetic permeability of the composite nickel microwave absorber are altered, effectively changing the impedance matching between the composite nickel microwave absorber and free space. In addition to the dielectric losses caused by the spherical, rod-shaped, and flaky carbon materials and the magnetic losses caused by the magnetic nickel particles, the interfacial polarization and dipole polarization effects at the interfaces between the various components of the composite nickel microwave absorber also increase the absorption capacity of electromagnetic waves. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention.

[0026] Figure 1 X-ray diffraction patterns of spherical, rod-shaped and sheet-shaped porous carbon materials and flower-shaped, rod-shaped and sheet-shaped Ni-MOFs prepared in the examples and comparative examples of the present invention (wherein: Figure 1 (a) is the XRD diffraction pattern of Ni-DOBDC-700 spherical porous carbon composite nickel microwave absorber, Ni-BTC-700 rod-shaped porous carbon composite nickel microwave absorber, and Ni-BPDC-700 sheet-shaped porous carbon composite nickel microwave absorber; Figure 1 (b) XRD diffraction patterns of Ni-DOBDC, Ni-BPDC and Ni-BTC); Figure 2 The scanning electron micrographs of spherical, rod-shaped, and sheet-shaped Ni-MOFs prepared in the comparative example of the present invention (wherein: Figure 2 (a) is Ni-BTC; Figure 2 (d) is Ni-BTC-600 rod-shaped porous carbon composite nickel microwave absorber; Figure 2 (g) is Ni-BTC-700 rod-shaped porous carbon composite nickel microwave absorber; Figure 2 (j) is Ni-BTC-800 rod-shaped porous carbon composite nickel microwave absorber; Figure 2 (b) is Ni-DOBDC; Figure 2 (e) is Ni-DOBDC-600 spherical porous carbon composite nickel microwave absorber; Figure 2 (h) is Ni-DOBDC-700 spherical porous carbon composite nickel microwave absorber; Figure 2 (k) is Ni-DOBDC-800 spherical porous carbon composite nickel microwave absorber; Figure 2 (c) Ni-BPDC; Figure 2 (f) is Ni-BPDC-600 flaky porous carbon composite nickel microwave absorber; Figure 2 (i) Ni-BPDC-700 flaky porous carbon composite nickel microwave absorber; Figure 2 (1) is a SEM image of Ni-BPDC-800 flaky porous carbon composite nickel microwave absorber); Figure 3 Comparison of the microwave absorption performance of several composite nickel microwave absorbers, including Ni-BTC-700 rod-shaped porous carbon composite nickel microwave absorber, Ni-DOBDC-700 spherical porous carbon composite nickel microwave absorber, and Ni-BPDC-700 sheet-shaped porous carbon composite nickel microwave absorber, prepared in the examples of the present invention and the comparative examples (wherein: Figure 3 (a) Ni-BTC-700 rod-shaped porous carbon composite nickel microwave absorber; Figure 3 (b) is Ni-DOBDC-700 spherical porous carbon composite nickel microwave absorber; Figure 3 (c) Ni-BPDC-700; Figure 3 (d) is Ni-BTC-600 rod-shaped porous carbon composite nickel microwave absorber; Figure 3 (e) is Ni-DOBDC-600 spherical porous carbon composite nickel microwave absorber; Figure 3 (g) is Ni-BTC-800 rod-shaped porous carbon composite nickel microwave absorber; Figure 3 (h) is the absorption curve of Ni-DOBDC-800 spherical porous carbon composite nickel microwave absorber; Figure 3 (f) Figure 3 (i) Two-dimensional absorption bandwidth diagram of Ni-DOBDC-700 spherical porous carbon composite nickel microwave absorber and Ni-BTC-700 rod-shaped porous carbon composite nickel microwave absorber). DETAILED DESCRIPTION

[0027] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0028] It should be noted that the professional terms used in the present invention are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention. Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in the following embodiments of the present invention can be purchased from the market or prepared by existing methods.

[0029] Example 1: A flower-shaped Ni-MOFs-derived spherical porous carbon composite nickel microwave absorber. The composite nickel microwave absorber is made of flower-shaped Ni-MOFs and Ni-DOBDC as raw materials, and is formed into a Ni-DOBDC-700 spherical porous carbon composite nickel microwave absorber after high-temperature carbonization. The composite nickel microwave absorber has a spherical porous structure. The preparation method of the Ni-DOBDC-700 composite nickel microwave absorber comprises the following steps: S1. Weigh 1.503 g Ni(NO3)2•6H2O and 0.502 g H2DOBDC and add them to 10.5 mL DMF, 10.5 mL CH3CH2OH and 10.5 mL H2O. Ultrasonicate for 20 min, stir for 30 min and transfer to a 50 mL hydrothermal reactor. S2. Transfer the hydrothermal reactor to a 150°C heat-insulating drying oven for 20 hours; S3. The reactor after drying was cooled naturally to room temperature and centrifuged once with DMF for 5 min. S4. The supernatant after the centrifugation was discarded and placed in an 80°C oven to dry for 12 hours to obtain a yellow-brown flower-like Ni-MOFs powder; S5. The yellow-brown flower-like Ni-MOFs powder obtained above was placed in a nitrogen-filled tubular furnace for pyrolysis. The pyrolysis temperature was set to 700°C, the heating rate was 5°C / min, the holding time was 2h, and the powder was naturally cooled to room temperature and then taken out to obtain Ni-DOBDC-700 spherical porous carbon composite nickel microwave absorber.

[0030] Example 2: A flower-shaped Ni-MOFs-derived spherical porous carbon composite nickel microwave absorber. The composite nickel microwave absorber is made of flower-shaped Ni-MOFs and Ni-DOBDC as raw materials, and is formed into a Ni-DOBDC-600 spherical porous carbon composite nickel microwave absorber after high-temperature carbonization. The composite nickel microwave absorber has a spherical porous structure. The preparation method of the Ni-DOBDC-600 composite nickel microwave absorber comprises the following steps: S1. Weigh 1.503 g Ni(NO3)2•6H2O and 0.502 g H2DOBDC and add them to 10.5 mL DMF, 10.5 mL CH3CH2OH and 10.5 mL H2O. Ultrasonicate for 20 min, stir for 30 min and transfer to a 50 mL hydrothermal reactor. S2. Transfer the hydrothermal reactor to a 150°C heat-insulating drying oven for 12 hours; S3. The reactor after drying was cooled naturally to room temperature and centrifuged twice with DMF, each time for 4 minutes; S4. The supernatant after the centrifugation was discarded and placed in an 80°C oven to dry for 10 h, to obtain a yellow-brown flower-like Ni-MOFs powder; S5. The yellow-brown flower-like Ni-MOFs powder obtained above was placed in a tubular furnace filled with nitrogen for pyrolysis. The pyrolysis temperature was set to 600°C, the heating rate was 5°C / min, the holding time was 2h, and the powder was naturally cooled to room temperature and then taken out to obtain Ni-DOBDC-600 spherical porous carbon composite nickel microwave absorber.

[0031] Example 3: A flower-shaped Ni-MOFs-derived spherical porous carbon composite nickel microwave absorber. The microwave absorber is made of flower-shaped Ni-MOFs and Ni-DOBDC as raw materials, and is carbonized at high temperature to form a Ni-DOBDC-800 spherical porous carbon composite nickel microwave absorber. The composite nickel microwave absorber has a spherical porous structure. The preparation method of the Ni-DOBDC-800 composite nickel microwave absorber comprises the following steps: S1. Weigh 1.503 g Ni(NO3)2•6H2O and 0.502 g H2DOBDC and add them to 10.5 mL DMF, 10.5 mL CH3CH2OH and 10.5 mL H2O. Ultrasonicate for 30 min, stir for 20 min and transfer to a 50 mL hydrothermal reactor. S2. Transfer the hydrothermal reactor to a 150°C heat-insulating drying oven for 16 hours; S3. The reactor after drying was cooled naturally to room temperature and centrifuged with DMF three times, each time for 3 minutes; S4. The supernatant after the centrifugation was discarded and placed in an 80°C oven to dry for 12 hours to obtain a yellow-brown flower-like Ni-MOFs powder; S5. The yellow-brown flower-like Ni-MOFs powder obtained above was placed in a nitrogen-filled tubular furnace for pyrolysis. The pyrolysis temperature was set to 800°C, the heating rate was 5°C / min, the holding time was 2h, and the powder was naturally cooled to room temperature and then taken out to obtain Ni-DOBDC-800 spherical porous carbon composite nickel microwave absorber.

[0032] Comparative Example 1: A rod-shaped porous carbon composite nickel microwave absorber, wherein the microwave absorber is made of rod-shaped Ni-MOFs and Ni-BTC as raw materials, and is formed into Ni-BTC-700 rod-shaped porous carbon composite nickel microwave absorber after high-temperature carbonization. The composite nickel microwave absorber has a rod-shaped porous structure; The preparation method of the Ni-BTC-700 composite nickel microwave absorber comprises the following steps: S1. Weigh 3.4896 g Ni(NO3)2•6H2O, 1.68 g H3BTC and 0.96 g NaOH and add them to 100 mL H2O and 100 mL CH3CH2OH, sonicate for 30 min, and stir for 20 min. S2. Transfer the hydrothermal reactor to a 100°C heat-insulating drying oven for 24 hours; S3, centrifuging the sample after ultrasonication and stirring with DMF three times, each time for 2 minutes; S4. The supernatant after the centrifugation was discarded and placed in an 80°C oven to dry for 10 h to obtain a light green rod-shaped Ni-MOFs powder; S5. The light green rod-shaped Ni-MOFs powder obtained above was placed in a tubular furnace filled with nitrogen for pyrolysis. The pyrolysis temperature was set to 700°C, the heating rate was 5°C / min, the holding time was 2h, and the powder was naturally cooled to room temperature and then taken out to obtain Ni-BTC-700 rod-shaped porous carbon composite nickel microwave absorber.

[0033] Comparative Example 2: A flaky porous carbon composite nickel microwave absorber, wherein the microwave absorber is made of flaky Ni-MOFs and Ni-BPDC as raw materials, and is formed into a Ni-BPDC-700 flaky porous carbon composite nickel microwave absorber after high-temperature carbonization. The composite nickel microwave absorber has a flaky porous structure; The preparation method of the Ni-BPDC-700 composite nickel microwave absorber comprises the following steps: S1. Weigh 0.095 g Ni(NO3)2·6H2O and 0.165 g BPDC, add them to 20 mL DMF and 2 mL 1 mol / L NaOH, sonicate for 25 min, stir for 25 min, and then transfer to a 50 mL hydrothermal reactor; S2. Transfer the hydrothermal reactor to a 100°C heat-insulating drying oven for 24 hours; S3. The reactor after drying was cooled naturally to room temperature and centrifuged twice with DMF, each time for 3 minutes; S4. The supernatant after the centrifugation was discarded and placed in an 80°C oven for drying for 11 hours to obtain a light green flaky Ni-MOFs powder; S5. The light green flaky Ni-MOFs powder obtained above was placed in a tubular furnace filled with nitrogen for pyrolysis. The pyrolysis temperature was set to 700°C, the heating rate was 5°C / min, the holding time was 2h, and the powder was naturally cooled to room temperature and then taken out to obtain Ni-BPDC-700 flaky porous carbon composite nickel microwave absorber.

[0034] Comparative Example 3: A rod-shaped porous carbon composite nickel microwave absorber, wherein the microwave absorber is made of rod-shaped Ni-MOFs and Ni-BTC as raw materials, and is formed into Ni-BTC-600 rod-shaped porous carbon composite nickel microwave absorber after high-temperature carbonization. The composite nickel microwave absorber has a rod-shaped porous structure; The preparation method of the Ni-BTC-600 composite nickel microwave absorber comprises the following steps: S1. Weigh 3.4896 g Ni(NO3)2•6H2O, 1.68 g H3BTC and 0.96 g NaOH and add them to 100 mL H2O and 100 mL CH3CH2OH, sonicate for 25 min, and stir for 25 min. S2. Transfer the hydrothermal reactor to a 120°C heat-insulating drying oven for 20 hours; S3, centrifuging the sample after ultrasonication and stirring with DMF three times, each time for 2 minutes; S4. The supernatant after the centrifugation was discarded and placed in an 80°C oven to dry for 10 h to obtain a light green rod-shaped Ni-MOFs powder; S5. The light green rod-shaped Ni-MOFs powder obtained above was placed in a tubular furnace filled with nitrogen for pyrolysis. The pyrolysis temperature was set to 600°C, the heating rate was 5°C / min, the holding time was 2h, and the powder was naturally cooled to room temperature and then taken out to obtain Ni-BTC-600 rod-shaped porous carbon composite nickel microwave absorber.

[0035] Comparative Example 4: A rod-shaped porous carbon composite nickel microwave absorber, wherein the microwave absorber is made of rod-shaped Ni-MOF and Ni-BTC as raw materials, and is formed into Ni-BTC-800 rod-shaped porous carbon composite nickel microwave absorber after high-temperature carbonization. The composite nickel microwave absorber has a rod-shaped porous structure; The preparation method of the Ni-BTC-800 composite nickel microwave absorber comprises the following steps: S1. Weigh 3.4896 g Ni(NO3)2•6H2O, 1.68 g H3BTC and 0.96 g NaOH, add them to 100 mL H2O and 100 mL CH3CH2OH, sonicate for 30 min, and stir for 20 min. S2. Transfer the hydrothermal reactor to a 120°C heat-insulating drying oven for 16 hours; S3, centrifuging the sample after sonication and stirring with DMF three times, each centrifugation time is 4 minutes; S4. The supernatant after the centrifugation was discarded and placed in an 80°C oven to dry for 12 hours to obtain a light green rod-shaped Ni-MOFs powder; S5. The light green rod-shaped Ni-MOFs powder obtained above was placed in a tubular furnace filled with nitrogen for pyrolysis. The pyrolysis temperature was set to 800°C, the heating rate was 5°C / min, the holding time was 2h, and the powder was naturally cooled to room temperature and then taken out to obtain Ni-BTC-800 rod-shaped porous carbon composite nickel microwave absorber.

[0036] Results and Discussion The following combination Figure 1-3 The morphology characteristics and microwave absorbing properties of the microwave absorbing materials prepared in Examples 1-3 and Comparative Examples 1-4 are described.

[0037] Figure 1 The X-ray diffraction patterns of the Ni-DOBDC-700 spherical porous carbon composite nickel microwave absorber, the Ni-BTC-700 rod-shaped porous carbon composite nickel microwave absorber, and the Ni-BPDC-700 sheet-shaped porous carbon composite nickel microwave absorber prepared in Example 1, Comparative Example 1, and Comparative Example 2 are as follows: Figure 1 (a) is the XRD diffraction pattern of Ni-DOBDC-700 spherical porous carbon composite nickel microwave absorber, Ni-BTC-700 rod-shaped porous carbon composite nickel microwave absorber, and Ni-BPDC-700 sheet-shaped porous carbon composite nickel microwave absorber; Figure 1 (b) is the XRD diffraction pattern of Ni-DOBDC, Ni-BPDC and Ni-BTC; the abscissa is 2 times the diffraction angle (2-Theta), unit is degree; the ordinate is the X-ray diffraction intensity, unit is au; Depend on Figure 1It can be seen that after pyrolysis at 700°C, all three materials become a composite of carbon material and nickel alloy particles, and the diffraction peak intensity of the Ni-DOBDC-700 spherical porous carbon composite nickel microwave absorber at 44° is stronger than that of the Ni-BTC-700 rod-shaped porous carbon composite nickel microwave absorber and the Ni-BPDC-700 sheet-shaped porous carbon composite nickel microwave absorber. This shows that the Ni-DOBDC-700 spherical porous carbon composite nickel microwave absorber of Example 1 has a strong magnetic loss characteristic, which will be beneficial to enhance its impedance matching effect and improve the absorption efficiency.

[0038] Figure 2 Scanning electron microscope images (SEM) of the Ni-DOBDC-700 spherical porous carbon composite nickel microwave absorber, Ni-BTC-700 rod-shaped porous carbon composite nickel microwave absorber, Ni-BPDC-700 sheet-shaped porous carbon composite nickel microwave absorber, Ni-DOBDC-600 spherical porous carbon composite nickel microwave absorber, Ni-DOBDC-800 spherical porous carbon composite nickel microwave absorber, Ni-BTC-600 rod-shaped porous carbon composite nickel microwave absorber, and Ni-BTC-800 rod-shaped porous carbon composite nickel microwave absorber prepared in Example 1, Comparative Example 1, Comparative Example 2, Example 2, Example 3, Comparative Example 3, and Comparative Example 4, wherein: Figure 2 (a) is Ni-BTC; Figure 2 (d) is Ni-BTC-600 rod-shaped porous carbon composite nickel microwave absorber; Figure 2 (g) is Ni-BTC-700 rod-shaped porous carbon composite nickel microwave absorber; Figure 2 (j) is Ni-BTC-800 rod-shaped porous carbon composite nickel microwave absorber; Figure 2 (b) is Ni-DOBDC; Figure 2 (e) is Ni-DOBDC-600 spherical porous carbon composite nickel microwave absorber; Figure 2 (h) is Ni-DOBDC-700 spherical porous carbon composite nickel microwave absorber; Figure 2 (k) is Ni-DOBDC-800 spherical porous carbon composite nickel microwave absorber; Figure 2 (c) Ni-BPDC; Figure 2 (f) is Ni-BPDC-600 flaky porous carbon composite nickel microwave absorber; Figure 2 (i) Ni-BPDC-700 flaky porous carbon composite nickel microwave absorber; Figure 2 (l) is the SEM image of Ni-BPDC-800 flaky porous carbon composite nickel microwave absorber; Figure 2 (a)- Figure 2(c) These three Ni-MOFs materials with different structures, it can be seen that rod-shaped, flower-shaped and sheet-shaped Ni-MOFs are respectively displayed in SEM; Figure 2 (d)- Figure 2 (f) shows the carbon materials obtained by pyrolysis of three Ni-MOFs at 600 °C. It can be seen that the rod-shaped, flower-shaped and sheet-shaped structures are still retained. Figure 2 (b) Some particles are exposed but not fully formed, which are nickel alloy particles; Figure 2 (e)- Figure 2 There are almost no magnetic particles in (f), which indicates that the pyrolysis temperature is not high enough to make Ni 2+ Completely reduced to nickel alloy; Figure 2 (g)- Figure 2 (i) is the porous carbon material obtained by pyrolysis of the three materials at 700°C. Figure 2 (g) and Figure 2 (i) Some magnetic particles were exposed while retaining the rod-like and sheet-like structures, and the particle size was uniform and evenly distributed; a complete spherical structure appeared in Figure 2 (h) This is obtained by pyrolysis of flower-like Ni-MOFs at 700°C. The size of the spherical particles is approximately 3μm-4μm, the size is uniform and there is not much agglomeration. The petal-like structure is retained on the surface of the spherical particles, which will help increase the impedance matching effect and thus enhance the dissipation capacity of electromagnetic waves.

[0039] Figure 2 (j)- Figure 2 (l) is the porous carbon material obtained by pyrolysis of three types of Ni-MOFs at 800℃. It can be seen that regardless of the morphology of Ni-MOFs, their particles showed varying degrees of agglomeration at the high temperature of 800℃. Among them, the agglomeration phenomenon of Ni-BTC-800 rod-shaped porous carbon composite nickel microwave absorber and Ni-BPDC-800 sheet-shaped porous carbon composite nickel microwave absorber was more serious, which will reflect more electromagnetic waves on the material surface, resulting in impedance matching failure.

[0040] Figure 3The microwave absorber reflection loss curves of the Ni-DOBDC-700 spherical porous carbon composite nickel microwave absorber, Ni-BTC-700 rod-shaped porous carbon composite nickel microwave absorber, Ni-BPDC-700 sheet-shaped porous carbon composite nickel microwave absorber, Ni-DOBDC-600 spherical porous carbon composite nickel microwave absorber, Ni-DOBDC-800 spherical porous carbon composite nickel microwave absorber, Ni-BTC-600 rod-shaped porous carbon composite nickel microwave absorber, and Ni-BTC-800 rod-shaped porous carbon composite nickel microwave absorber prepared in Example 1, Comparative Example 1, Comparative Example 2, Example 2, Example 3, Comparative Example 3, and Comparative Example 4, and the two-dimensional effective bandwidth diagram of the Ni-DOBDC-700 spherical porous carbon composite nickel microwave absorber and Ni-BTC-700 rod-shaped porous carbon composite nickel microwave absorber prepared in Example 1 and Comparative Example 1, wherein: Figure 3 (a) Ni-BTC-700 rod-shaped porous carbon composite nickel microwave absorber; Figure 3 (b) is Ni-DOBDC-700 spherical porous carbon composite nickel microwave absorber; Figure 3 (c) Ni-BPDC-700; Figure 3 (d) is Ni-BTC-600 rod-shaped porous carbon composite nickel microwave absorber; Figure 3 (e) is Ni-DOBDC-600 spherical porous carbon composite nickel microwave absorber; Figure 3 (g) is Ni-BTC-800 rod-shaped porous carbon composite nickel microwave absorber; Figure 3 (h) is the absorption curve of Ni-DOBDC-800 spherical porous carbon composite nickel microwave absorber; Figure 3 (f) Figure 3 (i) Two-dimensional absorption bandwidth diagram of Ni-DOBDC-700 spherical porous carbon composite nickel microwave absorber and Ni-BTC-700 rod-shaped porous carbon composite nickel microwave absorber; It can be seen that the rod-shaped, flower-shaped, and sheet-shaped Ni-MOFs structures exhibited significantly different microwave absorption properties after pyrolysis at 700°C. Among them, the Ni-DOBDC-700 spherical porous carbon composite nickel microwave absorber had the best performance. Although the strongest point frequency absorption intensity was only -20 dB, under the premise of matching thickness of 2.2 mm, the effective bandwidth could reach 6.7 GHz (11.1GHz-17.8GHz), far exceeding the effective absorption bandwidth of Ni-BTC-700 (4.6GHz) rod-shaped porous carbon composite nickel microwave absorber and Ni-BPDC-700 (0GHZ) rod-shaped porous carbon composite nickel microwave absorber. Among them, the Ni-BTC-700 rod-shaped porous carbon composite nickel microwave absorber can also effectively absorb electromagnetic waves due to its unique rod-shaped structure. However, compared with spherical porous carbon, its space occupation ratio is smaller, and the space for electromagnetic waves to enter its interior is limited. In addition, the loss of electromagnetic waves by the material itself is less than that of spherical porous carbon, so it cannot achieve the strongest absorption effect. and Figure 3 (d)- Figure 3 (e) and Figure 3 (g)- Figure 3 (h) The reflection loss curves of the porous carbon composite nickel microwave absorbers obtained by pyrolysis of flower-shaped and rod-shaped Ni-MOFs at 600℃ and 800℃, respectively. It can be seen that compared with the porous carbon composite nickel microwave absorber obtained by pyrolysis at 700℃, the carbonization temperatures of 600℃ and 800℃ are insufficient or too high, which affects the absorbing performance of the porous carbon composite nickel microwave absorber.

[0041] In summary, the porous carbon-composite nickel microwave absorber with spherical particle morphology exhibits the best microwave absorption performance at 700°C.

[0042] It should be noted that when numerical ranges are designed in the present invention, it should be understood that both endpoints of each numerical range and any value between the two endpoints may be selected. Since the steps and methods used are the same as those in the embodiments, in order to avoid redundancy, the present invention describes preferred embodiments. Although preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they understand the basic inventive concepts. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0043] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A method for preparing a flower-like Ni-MOFs-derived spherical porous carbon composite nickel microwave absorber, characterized by: The following steps are involved: S1. After mixing the nickel salt and the organic ligand, the mixture is dispersed in a container containing an organic solvent and deionized water by stirring for 20 min-30 min and ultrasonicating for 20 min-30 min, wherein the nickel salt, the organic ligand, the organic solvent and the deionized water are in the order of Molar ratio of (0.001~0.01)mol:(0.0015~0.003)mol:(0.5~0.6)mol; The nickel salt is selected from nickel nitrate hexahydrate; The organic ligand is selected from one of trimesic acid, 2,5-dihydroxyterephthalic acid, and biphenyl dicarboxylic acid; The organic solvent is selected from dimethylacetamide or anhydrous ethanol; S2. After the nickel salt and organic ligand are fully dissolved, place the container in a heat-insulating drying oven and dry it at 100°C to 150°C for 10 hours to 24 hours before taking it out; S3. The dried container is naturally cooled to room temperature, and centrifuged using dimethylformamide for 1 to 3 times, each centrifugation time being 2 to 5 minutes; S4. Pour off the supernatant after centrifugation and place in an 80°C oven to dry for 10-12 hours to obtain a yellow-brown flower-like Ni-MOFs powder; S5. The yellow-brown flower-shaped Ni-MOFs powder obtained in the previous step is placed in a tubular furnace filled with protective gas for pyrolysis. The pyrolysis temperature is set to 600°C~800°C, the heating rate is 5°C / min, the holding time is 2h, and the powder is naturally cooled to room temperature and then taken out to obtain a flower-shaped Ni-MOFs-derived spherical porous carbon composite nickel microwave absorber.

2. The method for preparing a flower-like Ni-MOFs-derived spherical porous carbon composite nickel microwave absorber according to claim 1, characterized in that: The stirring time in S1 is 30 minutes; the ultrasonic time is 30 minutes; and the container is a hydrothermal reactor.

3. The method for preparing a flower-like Ni-MOFs-derived spherical porous carbon composite nickel microwave absorber according to claim 1, characterized in that: The placing in the heat preservation drying oven described in S2 is selected to be kept warm at 100°C for 24 hours, or kept warm at 120°C for 12 hours, or kept warm at 150°C for 10 hours.

4. The method for preparing a flower-like Ni-MOFs-derived spherical porous carbon composite nickel microwave absorber according to claim 1, characterized in that: The "filled with protective gas" mentioned in S5 refers to a nitrogen atmosphere; the pyrolysis temperature is 600°C, 700°C or 800°C; and the "natural cooling to room temperature" refers to cooling to 21°C.

5. A flower-like Ni-MOFs-derived spherical porous carbon composite nickel microwave absorber, characterized by: The invention discloses a spherical porous carbon composite nickel microwave absorber derived from a flower-shaped Ni-MOFs by the preparation method of any one of claims 1 to 4. The flower-shaped Ni-MOFs-derived spherical porous carbon composite nickel microwave absorber is a spherical porous carbon composite nickel microwave absorber. The flower-shaped Ni-MOFs Ni-DOBDC is used as a raw material, and a Ni-DOBDC-700 spherical porous carbon composite nickel microwave absorber is formed after high-temperature carbonization. The composite nickel microwave absorber has a spherical porous structure, and nickel alloy particles cover the outside of the spherical structure.

6. The use of the flower-like Ni-MOFs-derived spherical porous carbon composite nickel microwave absorber in the microwave frequency band according to claim 5, characterized in that: The steps include: The prepared flower-shaped Ni-MOFs-derived spherical porous carbon composite nickel microwave absorber is fully mixed with a binder and an organic solvent in an organic solvent at a mass ratio of 4:6:1 to form a coaxial ring, and the absorption test is performed using the coaxial method; the binder is selected from paraffin, and the organic solvent is selected from n-hexane.

7. The use of a flower-like Ni-MOFs-derived spherical porous carbon composite nickel microwave absorber in the microwave frequency band according to claim 6, characterized in that: The coaxial ring mentioned above refers to a coaxial ring with an outer diameter of 7 mm, an inner diameter of 3.05 mm, and a thickness of 2.6 mm. The wave absorption test is performed using the coaxial method, which means that the sample is assembled and calibrated with coaxial parts. The test frequency band is 2 GHz-18 GHz.

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