NiCo-MOF derived carbon nanotube wave-absorbing material with core-shell structure and preparation method of NiCo-MOF derived carbon nanotube wave-absorbing material

Abstract

The invention discloses a NiCo-MOF derived carbon nanotube wave-absorbing material with a core-shell structure and a preparation method of the NiCo-MOF derived carbon nanotube wave-absorbing material, and relates to the technical field of wave-absorbing materials. According to the method, NiCo-MOF with a core-shell structure is obtained by controlling the solvent proportion, then a carbon nano tube grows on the surface of the NiCo-MOF in situ, the prepared MOF-derived carbon nano tube has a hollow core-shell structure, and the surface of the MOF-derived carbon nano tube is covered with a layer of dense carbon nano tube. By adopting the structure, the conductivity of the material is greatly improved, the types of interface polarization are enriched, and good wave absorbing performance is shown in the frequency band of 2-18 GHz; the hollow structure is beneficial to multiple reflection of electromagnetic waves inside, and when the matching thickness is 2.5 mm, the effective absorption bandwidth can reach 5.7 GHz, and the minimum absorption peak reaches 4.8 GHz. The method is simple in technological process, low in cost and suitable for large-scale preparation, and has wide application prospects in the fields of light broadband wave absorption, thermal protection and the like.

Description

Technical Field

[0001] This invention relates to the field of microwave absorbing materials technology, specifically to a NiCo-MOF-derived carbon nanotube microwave absorbing material with a core-shell structure and its preparation method. Background Technology

[0002] With the rapid development of modern electronic technology and wireless communication, the application of electromagnetic waves in civilian, industrial, and defense fields is constantly deepening. The accompanying problems of electromagnetic interference and information leakage are becoming increasingly serious, placing higher demands on high-performance electromagnetic wave absorbing materials. An ideal absorbing material needs to achieve strong absorption over a wide frequency band, while also possessing characteristics such as thinness, light weight, environmental resistance, and good stability, to meet the stringent performance requirements of fifth-generation communication systems, high-frequency radar, stealth technology, and flexible electronic devices.

[0003] Among various microwave absorbing materials, carbon-based materials have attracted much attention due to their low density, tunable dielectric properties, and good chemical stability. Carbon nanotubes, in particular, not only possess high conductivity and a large aspect ratio but also exhibit significant dielectric loss capacity, which is beneficial for the conversion and dissipation of electromagnetic energy. However, single carbon nanotubes suffer from problems such as easy aggregation, poor impedance matching, and weak magnetism, which limit their absorption performance and practical applications in the low-frequency range.

[0004] Metal-organic frameworks (MOFs) have been extensively studied in recent years because of their porosity, high specific surface area, and diversity of metal centers. After pyrolysis, they can be used to derive carbon / metal composite microwave absorbing materials with controllable structures.

[0005] Currently, although some studies have focused on the application of MOF-derived carbon materials in the field of microwave absorption, systematic and in-depth research on specific composite strategies and precise controllable preparation is still lacking. Exploration of directional composite methods between MOFs and other functional components at the molecular or nanoscale is limited. Furthermore, how to design and prepare MOF-derived composite materials with specific compositional gradients, core-shell structures, or hierarchical channels to meet absorption requirements in different frequency bands requires further experimental and mechanistic research. Therefore, deepening the understanding of the structure-property relationship of MOF-derived carbon-based microwave absorbing materials and developing directional composite and preparation methods are crucial for improving the low-frequency absorption performance of these materials and promoting their practical applications. Summary of the Invention

[0006] The purpose of this invention is to provide a NiCo-MOF-derived carbon nanotube microwave absorbing material with a core-shell structure and its preparation method, thereby solving the aforementioned problems. The preparation process is simple and low-cost, and the prepared material exhibits excellent microwave absorption performance.

[0007] To achieve the above objectives, this invention provides a method for preparing a NiCo-MOF-derived carbon nanotube microwave absorbing material with a core-shell structure, comprising the following steps: (1) Dissolve PVP in a mixture of deionized water and DMF, then add tricarboxylic acid. After the tricarboxylic acid dissolves, add nickel nitrate hexahydrate and cobalt nitrate hexahydrate to obtain a mixed solution. Wash and dry the powder obtained after hydrothermal treatment of the mixed solution. (2) Place the powder obtained in (1) into the middle position of the tube furnace. Perform staged dynamic atmosphere control during the heating, reaction and cooling stages. After the tube furnace cools naturally to room temperature, open the tube furnace lid to obtain the NiCo-MOF-derived carbon nanotube microwave absorbing material with core-shell structure.

[0008] Preferably, in the mixed solution of step (1), the concentration of PVP is 50-100 g / mL, the concentration of tricarboxylic acid is 5-10 mg / mL, the concentration of cobalt hexanitrate is 10-50 mg / mL, the concentration of nickel hexanitrate is 10-20 mg / mL, and the ratio is 1-5:1.

[0009] In the mixture of step (1), the volume ratio of DMF to deionized water is 6:1 to 1:1.

[0010] Preferably, the concentration of cobalt hexanitrate is 10-20 mg / mL.

[0011] Preferably, in step (1), the mixed solution is placed in a hydrothermal reactor with a polytetrafluoroethylene liner to transfer the precursor solution for hydrothermal reaction, the hydrothermal reaction temperature is 120-180℃, and the time is 3-24h. The powder is washed several times with deionized water and then rinsed with anhydrous ethanol. The drying time is 4-24 hours and the drying temperature is 30-90℃.

[0012] Preferably, in step (2), the heating rate is 5℃ / min-15℃ / min; the temperature of the reaction stage is 550℃-1000℃; the reaction time is 5-60min; and the cooling stage is natural cooling.

[0013] Preferably, in step (2), the dynamic atmosphere includes: a protective gas, a reducing gas and a carbon source gas, with volumetric flow rates of 400-500 mL / min, 60-100 mL / min and 5-40 mL / min, respectively; The protective gas is any one or more of nitrogen or argon; the reducing gas is any one or more of hydrogen or nitric oxide; and the carbon source gas is any one or more of acetylene or methane.

[0014] Preferably, in step (2), the phased dynamic atmosphere control includes the following processes: (2-1) Initially, a protective gas is introduced during the heating stage, and a reducing gas is introduced when the temperature reaches 200-400℃; (2-2) After heating to the reaction temperature of the reaction stage, stabilize for 5 min-20 min, and then introduce carbon source gas; (2-3) After the carbon source gas has been introduced for 5-60 minutes, close the carbon source gas channel, turn off the injection pump, and turn off the temperature control program of the tube furnace. The tube furnace will then begin to cool naturally. (2-4) Close the reducing gas passage when the tubular furnace cools to 500℃; (2-5) Close the protective gas passage when the tubular furnace cools down to 100°C.

[0015] The present invention also provides a NiCo-MOF-derived carbon nanotube microwave absorbing material with a core-shell structure prepared by the above-described preparation method. This NiCo-MOF-derived carbon nanotube microwave absorbing material uses carbon as the shell and a nickel-cobalt core, with carbon nanotubes grown in situ on the nickel-cobalt core.

[0016] Therefore, the present invention employs the above-mentioned NiCo-MOF-derived carbon nanotube microwave absorbing material with a core-shell structure and its preparation method, which has the following beneficial effects: 1. The NiCo-MOF precursor in this invention is transformed into a magnetic metal / carbon composite structure through heat treatment, while inheriting the porous characteristics of MOF, which is beneficial to enhance dielectric / magnetic synergistic loss, improve impedance matching, and enhance oxidation resistance and high temperature stability.

[0017] 2. The NiCo-MOF in this invention has a core-shell structure. The change in the content of Ni and Co in the MOF can effectively affect the growth of carbon nanotubes. It has a significant electromagnetic wave absorption effect in the 2-18 GHz frequency band, with an effective absorption bandwidth of up to 5.7 GHz and a matching thickness of only 2.5 mm.

[0018] 3. In this invention, the growth of carbon nanotubes improves the conductivity of the material and enriches the types of interfacial polarization. At the same time, the hollow core-shell structure is conducive to the entry of electromagnetic waves and multiple reflections after entry, which synergistically optimizes impedance matching and establishes a multi-element dissipation system of "conductive loss-dielectric loss-interfacial polarization", which significantly broadens the absorption bandwidth and enhances the absorption intensity.

[0019] Furthermore, the growth of carbon nanotubes not only improves the conductivity and dielectric constant of the material, but also, to some extent, prevents the collapse and breakage of the MOF structure due to in-situ growth. Different ratios of Ni and Co can induce dipole polarization. Simultaneously, changes in the solvent during hydrothermal treatment can effectively regulate the size of the MOF, which can improve impedance matching to some extent. The hollow core-shell structure allows for multiple reflections of incoming electromagnetic waves within the structure.

[0020] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0021] Figure 1 SEM image of the sample material prepared in Example 1; Figure 2 The images shown are SEM images of the sample material prepared in Comparative Example 1, where a is an SEM image with a scale bar of 2 μm, b is an SEM image with a scale bar of 20 μm, and c is an SEM image with a scale bar of 10 μm. Figure 3 SEM images of the sample material prepared in Comparative Example 2; Figure 4 The images shown are SEM images of the sample material prepared in Comparative Example 3, where a is an SEM image with a scale bar of 20 μm and b is an SEM image with a scale bar of 50 μm. Figure 5 SEM images of the samples prepared in Examples 2-4 are shown below, where a is the SEM image of the sample in Example 2, b is the SEM image of the sample in Example 3, and c is the SEM image of the sample in Example 4. Figure 6 The images show the XRD patterns of the sample materials prepared in Example 1 and Comparative Examples 1-3. Figure 7 The image shows the microwave absorption performance of the sample material prepared in Example 1 at a thickness of 2-5 mm. Figure 8 The microwave absorption performance of the sample material prepared in Comparative Example 1 at a thickness of 2-5 mm is shown in the figure. Figure 9 The microwave absorption performance of the sample material prepared in Comparative Example 2 at a thickness of 2-5 mm is shown in the figure. Figure 10 The image shows the microwave absorption performance of the sample material prepared for Comparative Example 3 at a thickness of 2-5 mm. Detailed Implementation

[0022] This invention provides a NiCo-MOF-derived carbon nanotube microwave absorbing material with a core-shell structure, wherein carbon nanotubes are grown in situ on the surface of a core-shell NiCo-MOF. The preparation method includes the following steps: (1) Dissolve a certain amount of PVP in a mixture of deionized water and DMF, then add benzotricarboxylic acid to dissolve it, then add nickel nitrate hexahydrate and cobalt nitrate hexahydrate. Transfer the solution to a polytetrafluoroethylene liner and hydrothermally heat it at 120-180℃ for 3-24 hours. Wash the obtained powder several times with deionized water, rinse it with anhydrous ethanol, and dry it at 30-90℃ for 4-24 hours.

[0023] In this step, the concentrations of each component in the mixed solution are as follows: PVP concentration is 50-100 g / mL, tricarboxylic acid concentration is 5-10 mg / mL, and cobalt hexanitrate concentration is 10-20 mg / mL; the volume ratio of DMF to deionized water in the mixed solution is 6:1-1:1.

[0024] (2) Place the powder obtained in (1) into the middle position of the tube furnace, set the temperature control program of the tube furnace, and perform phased dynamic atmosphere control in the heating stage, reaction stage and cooling stage. After the tube furnace cools naturally to room temperature, open the tube furnace lid to obtain the NiCo-MOF-derived carbon nanotube microwave absorbing material with core-shell structure.

[0025] In this step, the heating rate is 5℃ / min-15℃ / min; the reaction temperature is 550℃-1000℃, and the reaction time is 5-60min; the cooling stage is natural cooling.

[0026] The dynamic atmosphere includes: a protective gas, a reducing gas, and a carbon source gas, with volumetric flow rates of 400-500 mL / min, 60-100 mL / min, and 5-40 mL / min, respectively; the protective gas is any one or more of nitrogen or argon; the reducing gas is any one or more of hydrogen or nitric oxide; and the carbon source gas is any one or more of acetylene or methane.

[0027] In step (2), the phased dynamic atmosphere control includes the following processes: (2-1) Initially, a protective gas is introduced during the heating stage, and a reducing gas is introduced when the temperature rises to 200-400℃.

[0028] (2-2) After heating to the reaction temperature of the reaction stage, stabilize for 5 min-20 min and then introduce carbon source gas.

[0029] (2-3) After the carbon source gas has been introduced for 5-60 minutes, close the carbon source gas channel, turn off the injection pump, and turn off the temperature control program of the tube furnace. The tube furnace will then begin to cool naturally.

[0030] (2-4) Close the reducing gas passage when the tubular furnace cools down to 500°C.

[0031] (2-5) Close the protective gas passage when the tubular furnace cools down to 100°C.

[0032] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0033] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can be appropriately combined to form other embodiments that can be understood by those skilled in the art. These other embodiments are also covered within the scope of protection of this invention.

[0034] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0035] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0036] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can be appropriately combined to form other embodiments that can be understood by those skilled in the art. These other embodiments are also covered within the scope of protection of this invention.

[0037] Example 1 This embodiment provides a method for preparing NiCo-MOF-derived carbon nanotubes with a core-shell structure, including the following steps: (1) Dissolve 3g of PVP in a mixture of deionized water and DMF in a volume ratio of 2:1. Then add 0.63g of tricarboxylic acid to dissolve it, followed by 0.291g of nickel nitrate hexahydrate and 0.582g of cobalt nitrate hexahydrate. Transfer the solution to a polytetrafluoroethylene liner and hydrothermally heat it in a 150°C hydrothermal tank for 6 hours. Wash the obtained powder several times with deionized water, rinse it with anhydrous ethanol, and dry it at 60°C for 5 hours.

[0038] (2) Place the powder obtained in step (1) into the middle position of the tube furnace, set the temperature control program of the tube furnace, that is, heat for 40 minutes to raise the temperature inside the tube furnace to 750°C, and then maintain it at 750°C for 1 hour. After setting, start heating and simultaneously introduce argon gas at the set rate of 400 mL / min. When the temperature rises to 200°C, introduce hydrogen gas at 90 mL / min. When the temperature rises to 750°C, wait for the temperature to stabilize for 5 minutes, then start introducing acetylene at a rate of 20 mL / min to carry out the reaction and start timing. After introducing acetylene for 15 minutes, close the acetylene channel, turn off the injection pump, and turn off the temperature control program of the tube furnace. After that, the tube furnace begins to cool naturally. When the tube furnace cools naturally to 500°C, close the hydrogen channel. When the tube furnace cools naturally to 100°C, close the argon channel. After the tube furnace cools naturally to room temperature, open the tube furnace lid and take out the sample. In this embodiment, the sample is named Ni1Co2-MOF according to the nickel / cobalt ratio.

[0039] Comparative Example 1 This comparative example provides a method for preparing Ni-MOF-derived carbon nanotubes with a core-shell structure, including the following steps: (1) Dissolve 3g of PVP in a mixture of deionized water and DMF 2:1, then add 0.63g of tricarboxylic acid to dissolve it, then add 0.873g of nickel nitrate hexahydrate, transfer the solution to a polytetrafluoroethylene liner, and hydrothermally heat it at 150°C for a period of time. Wash the obtained powder and dry it at 60°C for 6 hours.

[0040] (2) The steps (2) of this comparative example are the same as those of Example 1. The sample prepared in this comparative example is named Ni-MOF.

[0041] Comparative Example 2 This comparative example provides a method for preparing NiCo-MOF-derived carbon nanotubes with a core-shell structure, including the following steps: (1) Dissolve 3g of PVP in a mixture of deionized water and DMF 2:1, then add 0.63g of tricarboxylic acid to dissolve it, then add 0.582g of nickel nitrate hexahydrate and 0.291g of cobalt nitrate hexahydrate. Transfer the solution to a polytetrafluoroethylene liner and heat it in a hydrothermal tank at 150°C for a period of time. Wash the obtained powder and dry it at 60°C for 6 hours.

[0042] (2) Step (2) of this comparative example is the same as step (2) of Example 1. The sample of this comparative example is named Ni2Co1-MOF according to the nickel / cobalt ratio.

[0043] Comparative Example 3 This comparative example provides a method for preparing Co-MOF-derived carbon nanotubes with a core-shell structure, including the following steps: (1) Dissolve 3g of PVP in a mixture of deionized water and DMF 2:1, then add 0.63g of tricarboxylic acid to dissolve it, and then add 0.873g of cobalt nitrate hexahydrate. Transfer the solution to a polytetrafluoroethylene liner and heat it in a hydrothermal tank at 150°C for a period of time. Wash the obtained powder and dry it at 60°C for 6 hours.

[0044] (2) The steps (2) of this comparative example are the same as those of Example 1. The sample prepared in this comparative example is named Co-MOF.

[0045] Example 2 This embodiment provides a method for preparing NiCo-MOF-derived carbon nanotubes with a core-shell structure, including the following steps: (1) Dissolve 3g of PVP in a mixture of deionized water and DMF in a volume ratio of 2:1. Then add 0.63g of tricarboxylic acid to dissolve it, followed by 0.291g of nickel nitrate hexahydrate and 0.582g of cobalt nitrate hexahydrate. Transfer the solution to a polytetrafluoroethylene liner and hydrothermally heat it in a 150°C hydrothermal tank for 6 hours. Wash the obtained powder several times with deionized water, rinse it with anhydrous ethanol, and dry it at 60°C for 5 hours.

[0046] (2) Place the powder obtained in step (1) into the middle position of the tube furnace, set the temperature control program of the tube furnace to heat for 40 minutes, raise the temperature inside the tube furnace to 700℃, and then maintain 700℃ for 1 hour. After setting, start heating and simultaneously introduce argon gas at the set rate of 400 mL / min. When the temperature rises to 200℃, introduce hydrogen gas at 90 mL / min. When the temperature rises to 750℃, wait for the temperature to stabilize for 5 minutes, then start introducing acetylene at a rate of 20 mL / min to carry out the reaction and start timing. After introducing acetylene for 15 minutes, close the acetylene channel, turn off the injection pump, and turn off the temperature control program of the tube furnace. After that, the tube furnace begins to cool naturally. When the tube furnace cools naturally to 500℃, close the hydrogen channel. When the tube furnace cools naturally to 100℃, close the argon channel. After the tube furnace cools naturally to room temperature, open the tube furnace lid and take out the sample. In this embodiment, the sample is named Ni1Co2-MOF-2 according to the nickel / cobalt ratio.

[0047] Example 3 This embodiment provides a method for preparing NiCo-MOF-derived carbon nanotubes with a core-shell structure, including the following steps: (1) Dissolve 3g of PVP in a mixture of deionized water and DMF in a volume ratio of 2:1. Then add 0.63g of tricarboxylic acid to dissolve it, followed by 0.291g of nickel nitrate hexahydrate and 0.582g of cobalt nitrate hexahydrate. Transfer the solution to a polytetrafluoroethylene liner and hydrothermally heat it in a 150°C hydrothermal tank for 6 hours. Wash the obtained powder several times with deionized water, rinse it with anhydrous ethanol, and dry it at 60°C for 5 hours.

[0048] (2) Place the powder obtained in step (1) into the middle position of the tube furnace, set the temperature control program of the tube furnace, that is, heat for 40 minutes to raise the temperature inside the tube furnace to 800℃, and then maintain it at 750℃ for 1 hour. After setting, start heating and simultaneously introduce argon gas at the set rate of 400 mL / min. When the temperature rises to 200℃, introduce hydrogen gas at 90 mL / min. When the temperature rises to 750℃, wait for the temperature to stabilize for 5 minutes, then start introducing acetylene at a rate of 20 mL / min to carry out the reaction and start timing. After introducing acetylene for 15 minutes, close the acetylene channel, turn off the injection pump, and turn off the temperature control program of the tube furnace. After that, the tube furnace begins to cool naturally. When the tube furnace cools naturally to 500℃, close the hydrogen channel. When the tube furnace cools naturally to 100℃, close the argon channel. After the tube furnace cools naturally to room temperature, open the tube furnace lid and take out the sample. In this embodiment, the sample is named Ni1Co2-MOF-3 according to the nickel / cobalt ratio.

[0049] Example 4 This embodiment provides a method for preparing NiCo-MOF-derived carbon nanotubes with a core-shell structure, including the following steps: (1) Dissolve 3g of PVP in a mixture of deionized water and DMF in a volume ratio of 2:1. Then add 0.63g of tricarboxylic acid to dissolve it, followed by 0.291g of nickel nitrate hexahydrate and 0.582g of cobalt nitrate hexahydrate. Transfer the solution to a polytetrafluoroethylene liner and hydrothermally heat it in a 150°C hydrothermal tank for 6 hours. Wash the obtained powder several times with deionized water, rinse it with anhydrous ethanol, and dry it at 60°C for 5 hours.

[0050] (2) Place the powder obtained in step (1) into the middle position of the tube furnace, set the temperature control program of the tube furnace, that is, heat for 40 minutes to raise the temperature inside the tube furnace to 750°C, and then maintain it at 750°C for 1 hour. After setting, start heating and simultaneously introduce argon gas at the set rate of 400 mL / min. When the temperature rises to 200°C, introduce hydrogen gas at 95 mL / min. When the temperature rises to 750°C, wait for the temperature to stabilize for 5 minutes, then start introducing acetylene at a rate of 15 mL / min to carry out the reaction and start timing. After introducing acetylene for 20 minutes, close the acetylene channel, turn off the injection pump, and turn off the temperature control program of the tube furnace. After that, the tube furnace begins to cool naturally. When the tube furnace cools naturally to 500°C, close the hydrogen channel. When the tube furnace cools naturally to 100°C, close the argon channel. After the tube furnace cools naturally to room temperature, open the tube furnace lid and take out the sample. In this embodiment, the sample is named Ni1Co2-MOF-4 according to the nickel / cobalt ratio.

[0051] The samples prepared in Examples 1-4 and Comparative Examples 1-3 were respectively prepared into coaxial ring samples (the inner diameter of the coaxial ring sample was 3 mm and the outer diameter was 7 mm). The electromagnetic parameters of the samples were measured by a vector network analyzer, and the microwave absorption performance of the materials was calculated by CSTSTUDIOSUITE software.

[0052] The SEM images of the above samples are as follows: Figure 1-5 As shown, Figure 1 The morphological structure of Ni1Co2-MOF-derived carbon nanotubes is shown in the figure. The figure shows that the sample has a core-shell structure and that carbon nanotubes grow vigorously on the surface of the core-shell structure. Figure 2 The image shows the morphology and structure of Ni-MOF-derived carbon nanotubes. The image clearly shows significant aggregation, making it difficult to discern the core-shell structure. Furthermore, the growth of carbon nanotubes is relatively small. Figure 3 The morphological structure of Ni2Co1-MOF-derived carbon nanotubes is shown. Although the figure shows a core-shell structure, the growth of carbon nanotubes is relatively small. Figure 4 The image shows the morphological structure of Co-MOF-derived carbon nanotubes. The image shows that although a large number of carbon nanotubes are grown, the growth of carbon nanotubes disrupts the original MOF core and shell. Figure 5 The images show SEM images of carbon nanotubes grown on Ni1Co2-MOF prepared in Examples 2-4. The images show that carbon nanotubes were grown in all samples prepared in Examples 2-4.

[0053] The XRD patterns of the above samples are as follows: Figure 6 As shown, the sample in Example 1 has a distinct (002) carbon characteristic peak compared to the comparative example, proving the successful generation of carbon nanotubes.

[0054] The absorption performance of the above samples at a thickness of 2-5 mm is as follows: Figure 7-10 As shown. Figure 7 The microwave absorption performance of Ni1Co2-MOF-derived carbon nanotubes in the 2-5 mm range is shown in the figure. The bandwidth reaches 5.7 GHz and the minimum absorption peak position is -48.9 dB. Figure 8 The microwave absorption performance of Ni-MOF-derived carbon nanotubes in the 2-5 mm range is shown in the figure. The figure shows that the bandwidth is small and the microwave absorption performance is poor. Figure 9 The microwave absorption performance of Ni2Co1-MOF-derived carbon nanotubes in the 2-5 mm range is shown. The figure shows that the sample has the same absorption trend as Ni-MOF, with a smaller bandwidth, but a lower minimum absorption peak. Figure 10 The microwave absorption performance of Ni2Co1-MOF-derived carbon nanotubes at 2-5 mm is shown. It can be clearly seen that they exhibit the same absorption trend as Ni-MOF, with a smaller bandwidth but a lower minimum absorption peak. Therefore, the Ni1Co2-MOF-derived carbon nanotubes prepared in Example 1 show a significant improvement in microwave absorption performance compared to other samples.

[0055] As can be seen, in Comparative Example 1, the Ni-MOF-derived carbon nanotubes are difficult to maintain their basic morphology, and the spherical particles are not uniform in size. Although adding carbon source can grow abundant carbon nanotubes on MOF, which can improve the material's loss capacity, it sacrifices the material's impedance matching ability and makes it difficult to achieve the ideal absorption effect.

[0056] In Comparative Example 2, the addition of Co maintained the core-shell structure of the material, but the growth of carbon nanotubes was limited. This resulted in good impedance matching, but poor loss capability. In Comparative Example 3, Co-MOF facilitated the growth of carbon nanotubes, but the core-shell structure collapsed, with a large amount of carbon coating around the Co particles, which improved the loss capability.

[0057] In contrast, the core-shell structured Ni2Co1-MOF-derived carbon nanotubes provided in this invention achieve the growth of a layer of fluffy carbon nanotubes on a hollow structure through optimized preparation methods. This material exhibits excellent electromagnetic wave absorption performance in the 2–18 GHz frequency band, with an effective absorption bandwidth of 5.7 GHz and a matching thickness of only 2.5 mm. The growth of carbon nanotubes on the MOF enhances both conductivity and polarization losses; the heterogeneous interface formed between NiCo particles and carbon nanotubes induces a significant interfacial polarization effect. The synergistic effect of these three factors optimizes impedance matching, constructing a multi-factor loss mechanism of "conductivity loss + dielectric loss + interfacial polarization," thereby significantly broadening the absorption bandwidth and enhancing absorption performance.

[0058] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and does not limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a NiCo-MOF-derived carbon nanotube microwave absorbing material with a core-shell structure, characterized in that, Includes the following steps: (1) Dissolve PVP in a mixture of deionized water and DMF, then add tricarboxylic acid. After the tricarboxylic acid dissolves, add nickel nitrate hexahydrate and cobalt nitrate hexahydrate to obtain a mixed solution. Wash and dry the powder obtained after hydrothermal treatment of the mixed solution. (2) Place the powder obtained in (1) into the middle position of the tube furnace. Perform staged dynamic atmosphere control during the heating, reaction and cooling stages. After the tube furnace cools naturally to room temperature, open the tube furnace lid to obtain the NiCo-MOF-derived carbon nanotube microwave absorbing material with core-shell structure.

2. The method for preparing a NiCo-MOF-derived carbon nanotube microwave absorbing material with a core-shell structure according to claim 1, characterized in that, In the mixed solution of step (1), the concentration of PVP is 50-100 g / mL, the concentration of tricarboxylic acid is 5-10 mg / mL, the concentration of cobalt nitrate hexahydrate is 10-50 mg / mL, and the concentration of nickel nitrate hexahydrate is 10-20 mg / mL. In the mixture of step (1), the volume ratio of DMF to deionized water is 6:1 to 1:

1.

3. The method for preparing a NiCo-MOF-derived carbon nanotube microwave absorbing material with a core-shell structure according to claim 1, characterized in that, In step (1), the mass ratio of nickel hexanitrate and cobalt hexanitrate is 1-5:

1.

4. The method for preparing a NiCo-MOF-derived carbon nanotube microwave absorbing material with a core-shell structure according to claim 1, characterized in that, In step (1), the mixed solution is placed in a hydrothermal reactor with a polytetrafluoroethylene liner to conduct a hydrothermal reaction. The hydrothermal reaction temperature is 120-180℃ and the time is 3-24h. The powder is washed several times with deionized water and then rinsed with anhydrous ethanol. The drying time is 4-24 hours and the drying temperature is 30-90℃.

5. The method for preparing a NiCo-MOF-derived carbon nanotube microwave absorbing material with a core-shell structure according to claim 1, characterized in that, In step (2), the heating rate is 5℃ / min-15℃ / min; the temperature of the reaction stage is 550℃-1000℃; the reaction time is 5-60min; and the cooling stage is natural cooling.

6. The method for preparing a NiCo-MOF-derived carbon nanotube microwave absorbing material with a core-shell structure according to claim 1, characterized in that, In step (2), the dynamic atmosphere includes: protective gas, reducing gas and carbon source gas, with volumetric flow rates of 400-500 mL / min, 60-100 mL / min and 5-40 mL / min, respectively; The protective gas is any one or more of nitrogen or argon; the reducing gas is any one or more of hydrogen or nitric oxide; and the carbon source gas is any one or more of acetylene or methane.

7. The method for preparing a NiCo-MOF-derived carbon nanotube microwave absorbing material with a core-shell structure according to claim 1, characterized in that, In step (2), the phased dynamic atmosphere control includes the following processes: (2-1) Initially, a protective gas is introduced during the heating stage, and a reducing gas is introduced when the temperature reaches 200-400℃; (2-2) After heating to the reaction temperature of the reaction stage, stabilize for 5 min-20 min, and then introduce carbon source gas; (2-3) After the carbon source gas has been introduced for 5-60 minutes, close the carbon source gas channel, turn off the injection pump, and turn off the temperature control program of the tube furnace. The tube furnace will then begin to cool naturally. (2-4) Close the reducing gas passage when the tubular furnace cools to 500℃; (2-5) Close the protective gas passage when the tubular furnace cools down to 100°C.

8. A NiCo-MOF-derived carbon nanotube microwave absorbing material with a core-shell structure, characterized in that, It is prepared by the preparation method according to any one of claims 1-7.

9. The NiCo-MOF-derived carbon nanotube microwave absorbing material with a core-shell structure according to claim 8, characterized in that, The NiCo-MOF-derived carbon nanotube microwave absorbing material has a carbon shell and a nickel-cobalt core, with carbon nanotubes grown in situ on the surface.

Images