Preparation method of lightweight hollow Co / C-coated SnO2 nanowire composite wave-absorbing material with adjustable internal and external interface impedance

Abstract

The invention discloses a preparation method of a light hollow Co / C-coated SnO2 nanowire composite wave-absorbing material with adjustable internal and external interface impedance. The preparation method comprises the following steps: synthesizing a hollow light dodecahedron metal organic framework ZIF-67, carrying out heat treatment in an inert atmosphere to obtain a dodecahedron hollow porous carbon derivative structure embedded with Co nanocrystals, inducing Sn < 4 + > to be anchored on the external surface of the hollow dodecahedron framework by using glycine, and carrying out in-situ growth of SnO2 nanowires. And finally, the Co / C-coated SnO2 nanowire hollow dodecahedron light composite wave-absorbing material of which the outer surface is coated with one-dimensional nanowires and the inner interface is embedded with ferromagnetic nanocrystals is obtained. On the basis of the dodecahedron carbon framework, the internal and external interface impedance of the hollow structure is cooperatively regulated and controlled through ferromagnetic nanocrystal embedding and semiconductor nanowire coating, and the electromagnetic wave absorption performance of the material is remarkably improved through the double-interface design.

Description

Technical Field

[0001] The present invention belongs to the field of electromagnetic functional materials, and particularly relates to a preparation method of a lightweight hollow Co / C@SnO2 nanowire composite absorbing material with adjustable internal and external interface impedance. Background Art

[0002] The progress of electronic technology and the popularization of communication networks have brought convenience to life, but also introduced continuous electromagnetic interference and electromagnetic radiation into the environment. In view of the current complex multi-frequency and variable-frequency electromagnetic pollution problems, the single-component absorbing materials have disadvantages such as narrow absorption bandwidth, high interface impedance, thick coating, and high density, and can no longer meet the requirements of existing devices for absorbing performance. Therefore, the design of composite absorbing materials with multiple loss mechanisms to achieve broadband absorption has attracted much attention.

[0003] The preparation of lightweight absorbing materials with multiple heterogeneous interfaces by material compounding is a research hotspot in the industry. For example, the patent application with the application number CN202411078569.X discloses a Ti3C2T x MXene / Co / C composite material, which uses two-dimensional MXene material as the matrix, synthesizes Co metal particles with different dimensions through pH value adjustment and composites them, providing a favorable interface for the composite absorbing material. The patent application with the application number CN202210715672.5 discloses a three-dimensional cubic hollow framework NiCo2O4@C absorbing material, with pores with a diameter of 200 nm distributed on its six surfaces, and NiCo2O4 nanoparticles formed due to structural decomposition inside, and the particles and the hollow structure form an interface to improve the overall absorbing performance. The patent application with the application number CN202211558769.6 discloses a novel woven Ni-MOF absorbing material, and the composite of Ni nanoparticles and the woven structure provides multiple heterogeneous interfaces. However, the modulation of heterogeneous interfaces only targets the input impedance of electromagnetic waves, and its loss is still limited by the intrinsic electromagnetic properties of the material.

[0004] Considering the decisive role of the input electromagnetic impedance in the incident rate and reflectivity of electromagnetic waves, the modulation of interface impedance combined with structural design to form multiple reflections, scatterings and absorptions can break away from the limitations of the material's own electromagnetic properties and greatly improve the electromagnetic loss and absorbing performance. If a three-dimensional hollow structure can be used as the matrix framework, the internal interface is modulated by compounding magnetic nanoparticles for electromagnetic loss mechanism, and the external interface is optimized by heterogeneous structure growth to enhance the incident rate of electromagnetic waves at the external interface, combined with multiple scatterings and absorptions at the internal interface, then the absorbing performance and effective absorption bandwidth of the material will be greatly improved. Summary of the Invention

[0005] In view of the deficiencies of the above-mentioned existing technologies, the present invention provides a method for preparing a lightweight hollow Co / C@SnO2 nanowire composite absorbing material with adjustable internal and external interface impedance. The absorbing material designed by the present invention has the characteristics of high absorbing performance, wide absorbing frequency band, thin matching thickness, adjustable frequency conversion absorption, etc.

[0006] The method for preparing the lightweight hollow Co / C@SnO2 nanowire composite absorbing material with adjustable internal and external interface impedance of the present invention first synthesizes dodecahedral metal-organic framework ZIF-67 by liquid-phase chemical method, and performs high-temperature heat treatment for precursor carbonization to obtain a dodecahedral hollow porous carbon derivative embedded with Co nanocrystals; then in-situ grows SnO2 nanowires on the outer interface of the hollow structure by hydrothermal method, uses the amino (-NH2) and carboxyl (-COOH) groups in glycine to guide the one-dimensional growth of the nanowires, and uses the interfacial polar groups of the dodecahedral carbon derivative for in-situ deposition to obtain the lightweight hollow Co / C@SnO2 nanowire composite absorbing material. The three-dimensional porous carbon skeleton of the ZIF-67 derivative has extremely high dielectric properties, which cooperate with the magnetic permeability of the Co nanocrystals embedded therein. At the same time, by using the in-situ deposition method, SnO2 nanowires are grown on the outer interface of the matrix, so that the internal and external interface impedance of the composite material is modulated; the interfacial coating growth of the SnO2 nanowires passivates the extremely strong interfacial dipole of the carbon derivative, and the dielectric properties are partially sacrificed, but the electromagnetic impedance is improved, enabling more electromagnetic waves to enter the dodecahedral hollow structure, and through multiple reflections and scattering at the internal interface, the electromagnetic loss performance is improved.

[0007] The preparation process of the hollow Co / C@SnO2 nanowire composite material specifically includes the following steps:

[0008] Step 1: Synthesize the metal-organic framework ZIF-67 by liquid-phase chemical method;

[0009] Step 2: Perform high-temperature heat treatment on the material obtained in Step 1 to obtain a dodecahedral porous carbon particle composite embedded with Co nanocrystals, which is a derivative of ZIF-67;

[0010] Step 3: In-situ grow SnO2 nanowires on the outer interface of the dodecahedral derivative obtained in Step 2 by hydrothermal method to obtain the hollow Co / C@SnO2 nanowire composite material.

[0011] Furthermore:

[0012] In Step 1, weigh 3.5 - 7 g of cobalt nitrate hexahydrate (Co(NO3)2·6H2O) and dissolve it in 100 mL of methanol by stirring to prepare a uniform solution A; weigh 4.1 g of 2 - methylimidazole and also dissolve it in 100 mL of methanol by stirring to prepare a uniform solution B; add solution B to solution A under vigorous stirring to make them fully mixed; stir the mixed solution at room temperature for 24 h, after centrifuging and washing with alcohol 3 times, dry it at 60 °C to obtain ZIF - 67 with a particle size of 400 - 800 nm.

[0013] In Step 2, take 0.75 - 1.5 g of ZIF - 67 powder and place it in a crucible, heat it to 600 - 700 °C at a rate of 2 °C / min under a nitrogen atmosphere protection, and keep it warm for 2 - 3 h to obtain Co / C hollow derivatives.

[0014] In Step 3, weigh 100 - 300 mg of tin tetrachloride pentahydrate (SnCl4·5H2O) and add it to a mixed solvent containing 20 mL of oleic acid, 0.5 - 1.25 mL of oleylamine and 20 - 60 μL of deionized water, keep it warm and stir at 80 °C for 6 h in a nitrogen atmosphere until uniformly mixed; add 10 mL of absolute ethanol, 10 - 20 mg of glycine, 100 mg of Co / C hollow derivatives to the mixed solution, ultrasonically disperse for 30 min and then quickly add it to a 50 mL Teflon - lined autoclave, put it in an oven and heat to 180 °C and keep it warm for 3 - 8 h; after natural cooling, collect it by magnetic absorption and wash with alcohol, and obtain the hollow Co / C@SnO2 nanowire composite microwave absorption material after vacuum drying.

[0015] The present invention synthesizes dodecahedral metal - organic framework ZIF - 67 by a liquid - phase chemical method and carbonizes it to obtain a hollow - structured MOF derivative, that is, a Co / C derivative embedded with ferromagnetic Co nanocrystals and hollow - porous, and at the same time, guides the one - dimensional growth of Sn by glycine complexation through a hydrothermal method 4+ and in - situ deposits it on the outer interface of the Co / C hollow structure. The combination of the hollow matrix and the one - dimensional nanowires endows it with the characteristics of a lightweight hollow microwave absorption material with adjustable double - interface impedance.

[0016] The beneficial effects of the present invention are as follows:

[0017] 1. The lightweight hollow composite microwave absorption structure synthesized by the present invention has a large number of heterogeneous interfaces. Although the MOF derivative of the hollow matrix has strong dielectric properties, by coating weakly polar SnO2 nanowires on the outer interface, its interface impedance is effectively adjusted, which is beneficial to the incidence of electromagnetic waves; at the same time, the inner interface of the hollow structure is modified by ferromagnetic Co nanocrystals, forming multiple scattering and loss of the incident electromagnetic waves, so that the material meets the requirements of improving microwave absorption performance, wide - band and lightweight from the structure.

[0018] 2. The present invention uses the hydrothermal method to in-situ grow SnO2 nanowires on the outer interface. Through the complexation of Sn 4+ with carboxyl and amino groups to form a long-chain precursor, which is beneficial to the one-dimensional growth of SnO2. At the same time, oleic acid and oleylamine can also prevent further growth and agglomeration.

[0019] 3. During the in-situ deposition of SnO2 nanowires in the present invention, by utilizing the affinity between the porous defects and polar functional groups on the outer interface of the Co / C framework and the amino (-NH2) and carboxyl (-COOH) groups in glycine, Sn 4+ is anchored on the outer interface to form the in-situ composite growth of one-dimensional nanowires, thereby uniformly reducing the interfacial impedance of the polar outer interface. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0021] Figure 1 It is the TEM image of the Co / C derivative in Example 1.

[0022] Figure 2 It is the SEM image of the Co / C derivative in Example 2.

[0023] Figure 3 It is the TEM image of the hydrothermally synthesized SnO2 nanowires.

[0024] Figure 4 It is the SEM image of the Co / C@SnO2 nanowire composite structure.

[0025] Figure 5 It is the HRTEM image of the interface of the Co / C@SnO2 nanowire composite structure.

[0026] Figure 6 It is the reflection loss (RL) curve of samples with different thicknesses in the 2 - 18 GHz range in Example 3.

[0027] Figure 7 It is the reflection loss (RL) curve of samples with different thicknesses in the 2 - 18 GHz range in Example 4.

[0028] Figure 8 It is the reflection loss (RL) curve of samples with different thicknesses in the 2 - 18 GHz range in Example 5.

[0029] Figure 9Reflection loss (RL) curves of samples with different thicknesses in Example 6 at 2 - 18 GHz.

[0030] Figure 10 Reflection loss (RL) curves of samples with different thicknesses in Example 7 at 2 - 18 GHz. Detailed implementation manners

[0031] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, only some embodiments of the present invention are shown herein, rather than all embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0032] Example 1:

[0033] The preparation method of the Co / C composite derivative material in this example includes the following steps:

[0034] 1. Weigh 3.5 g of cobalt nitrate hexahydrate (Co(NO3)2·6H2O), dissolve it in 100 mL of methanol by magnetic stirring to prepare a uniform solution A; weigh 4.1 g of 2-methylimidazole, also dissolve it in 100 mL of methanol by magnetic stirring to prepare a uniform solution B; under vigorous stirring, add solution B to solution A to make them fully mixed; stir the mixed solution at room temperature for 24 h, after centrifuging and washing with alcohol 3 times, dry it at 60 °C to obtain ZIF-67 with a particle size of 400 - 800 nm.

[0035] 2. Take 1 g of ZIF-67 powder and place it in a crucible, heat it to 600 °C at a rate of 2 °C / min under nitrogen atmosphere protection, and keep it at this temperature for 2 h to obtain Co / C hollow derivatives.

[0036] Figure 1 This is the TEM image of the Co / C derivative in this example. The geometric morphology and the relatively low contrast in the center of the Co / C derivative prepared in this example indicate that it has a unique dodecahedron hollow structure. The reflection loss (RL) of a solid paraffin sample containing 40 wt% of the Co / C derivative was tested in the range of 2 - 18 GHz by the transmission / reflection coaxial method. The results show that the minimum value of its RL is only -12.51 dB at 17.8 GHz when the thickness is 1.375 mm, which is caused by the relatively high dielectric constant of this carbon derivative resulting in more electromagnetic wave reflections due to the high electromagnetic impedance at the interface.

[0037] Example 2:

[0038] The preparation method of the Co / C composite derivative material in this example includes the following steps:

[0039] 1. Weigh 7 g of cobalt nitrate hexahydrate (Co(NO3)2·6H2O), dissolve it in 100 mL of methanol by magnetic stirring to prepare a uniform solution A; weigh 4.1 g of 2-methylimidazole, also dissolve it in 100 mL of methanol by magnetic stirring to prepare a uniform solution B; under vigorous stirring, add solution B to solution A to make them fully mixed; stir the mixed solution at room temperature for 24 h, after centrifuging and washing with alcohol three times, dry it at 60 °C to obtain ZIF-67 with a particle size of 400 - 800 nm.

[0040] 2. Take 1 g of ZIF-67 powder and place it in a crucible, heat it to 700 °C at a rate of 2 °C / min under nitrogen atmosphere protection, and keep it at this temperature for 3 h to obtain Co / C hollow derivative.

[0041] Figure 2 This is the SEM image of the Co / C derivative in this example. The geometric morphology of the Co / C derivative prepared in this example does not show a regular dodecahedron structure. The reflection loss (RL) of a solid paraffin sample containing 40 wt% of the Co / C derivative was measured from 2 to 18 GHz by the transmission / reflection coaxial method. The results show that the minimum value of its RL is only -6.45 dB at 17.28 GHz when the thickness is 0.925 mm, and no effective electromagnetic wave absorption is formed. This indicates that the excessive addition of Co leads to the collapse of the hollow carbon skeleton, further weakening the wave absorption performance of the composite material.

[0042] Example 3:

[0043] The preparation method of the Co / C@SnO2 nanowire composite material in this example includes the following steps:

[0044] 1. Weigh 3.5 g of cobalt nitrate hexahydrate (Co(NO3)2·6H2O), dissolve it in 100 mL of methanol by magnetic stirring to prepare a uniform solution A; weigh 4.1 g of 2-methylimidazole, also dissolve it in 100 mL of methanol by magnetic stirring to prepare a uniform solution B; under vigorous stirring, add solution B to solution A to make them fully mixed; place the mixed solution at room temperature and stir for 24 h, after centrifuging and washing with alcohol three times, dry it at 60 °C to obtain ZIF-67 with a particle size of 400 - 800 nm.

[0045] 2. Take 1 g of ZIF-67 powder and place it in a crucible, heat it to 600 °C at a rate of 2 °C / min under nitrogen atmosphere protection, and keep it at this temperature for 2 h to obtain Co / C hollow derivative.

[0046] 3. Weigh 100 mg of tin(IV) chloride pentahydrate (SnCl4·5H2O), and add it to a mixed solvent containing 20 mL of oleic acid, 0.5 mL of oleylamine, and 20 μL of deionized water. Under nitrogen protection, stir and mix evenly and heat to 80 °C, and keep warm for 6 h. After that, add 10 mL of absolute ethanol, 10 mg of glycine, and 100 mg of Co / C hollow derivative to the solution. After ultrasonic treatment for 30 min until evenly dispersed, quickly add the mixed solution to a 50 mL Teflon-lined reaction kettle, and heat to 180 °C and keep warm for 3 h. After the reaction is completed, magnetically separate the mixed solution and wash it with alcohol 3 times to obtain the Co / C@SnO2 nanowire composite material.

[0047] Figure 3 Figure 4 is the TEM image of SnO2 nanowires synthesized by the hydrothermal method alone. It can be seen from the figure that the nanowires are monodisperse one-dimensional structures with a length of about 20 - 40 nm. Figure 4 and Figure 5 Figures 5(a) and 5(b) are the SEM and HRTEM images of the interface of the Co / C@SnO2 nanowire composite material in this example, respectively. As shown in the figure, the composite material shows a dodecahedron structure. The interface image shows that SnO2 nanowires grow uniformly on the outer interface of the dodecahedron derivative. The fringe image of the nanowires indicates that the loaded material is SnO2. Figure 6 Figure 6 is the reflection loss (RL) curve of the paraffin sample containing 40 wt% of the Co / C@SnO2 nanowires in this example in the range of 2 - 18 GHz. It can be seen that the Co / C@SnO2 nanowire composite material obtains a minimum RL value of -17.05 dB at 16.24 GHz when the thickness is 5.7 mm, and forms double absorption peaks in the C and Ku bands. When the thickness is 8.95 mm, triple absorption peaks in the S, X, and Ku bands appear.

[0048] Example 4:

[0049] The preparation method of the Co / C@SnO2 nanowire composite material in this example includes the following steps:

[0050] 1. Weigh 3.5 g of cobalt(II) nitrate hexahydrate (Co(NO3)2·6H2O), dissolve it in 100 mL of methanol by magnetic stirring to prepare a uniform solution A; weigh 4.1 g of 2-methylimidazole, and also dissolve it in 100 mL of methanol by magnetic stirring to prepare a uniform solution B; under vigorous stirring, add solution B to solution A to make them fully mixed; place the mixed solution at room temperature and stir for 24 h. After centrifuging and washing with alcohol 3 times, dry it at 60 °C to obtain ZIF-67 with a particle size of 400 - 800 nm.

[0051] 2. Weigh 1 g of ZIF-67 powder and place it in a crucible. Under the protection of a nitrogen atmosphere, heat it to 600 °C at a rate of 2 °C / min and hold for 2 h to obtain a Co / C hollow derivative.

[0052] 3. Weigh 100 mg of tin(IV) chloride pentahydrate (SnCl4·5H2O) and add it to a mixed solvent containing 20 mL of oleic acid, 0.5 mL of oleylamine, and 20 μL of deionized water. Stir and mix evenly under nitrogen protection and heat to 80 °C, then hold for 6 h. After that, add 10 mL of absolute ethanol, 10 mg of glycine, and 100 mg of the Co / C hollow derivative to the solution. Ultrasonic for 30 min until evenly dispersed, then quickly add the mixed solution to a 50 mL Teflon-lined autoclave and heat to 180 °C and hold for 8 h. After the reaction, magnetically separate the mixed solution and wash it with alcohol three times to obtain the Co / C@SnO2 nanowire composite material.

[0053] Figure 7 It is the reflection loss (RL) curve of the paraffin sample containing 40 wt% of the Co / C@SnO2 nanowires of this example in the range of 2 - 18 GHz. It can be seen that the Co / C@SnO2 nanowire composite material obtains a minimum RL value of -58.94 dB at 10.72 GHz in the Ku band when the thickness is 2.475 mm, and the effective absorption bandwidth is 3.76 GHz. When the thickness is 1.8 mm, the effective absorption bandwidth reaches a maximum of 4.76 GHz.

[0054] Example 5:

[0055] The preparation method of the Co / C@SnO2 nanowire composite material in this example includes the following steps:

[0056] 1. Weigh 3.5 g of cobalt(II) nitrate hexahydrate (Co(NO3)2·6H2O) and dissolve it in 100 mL of methanol by magnetic stirring to prepare a uniform solution A; weigh 4.1 g of 2-methylimidazole and also dissolve it in 100 mL of methanol by magnetic stirring to prepare a uniform solution B; under vigorous stirring, add solution B to solution A to make them fully mixed; place the mixed solution at room temperature and stir for 24 h, then after centrifuging and washing with alcohol three times, dry it at 60 °C to obtain ZIF-67 with a particle size of 400 - 800 nm.

[0057] 2. Take 1 g of ZIF-67 powder and place it in a crucible. Under the protection of a nitrogen atmosphere, heat it to 700 °C at a rate of 2 °C / min and hold for 3 h to obtain a Co / C hollow derivative.

[0058] 3. Weigh 100 mg of tin(IV) chloride pentahydrate (SnCl4·5H2O) and add it to a mixed solvent containing 20 mL of oleic acid, 0.5 mL of oleylamine, and 20 μL of deionized water. Stir and mix evenly under nitrogen protection and heat to 80 °C, then keep the temperature for 6 h. After that, add 10 mL of absolute ethanol, 10 mg of glycine, and 100 mg of Co / C hollow derivative to the solution. Ultrasonicate for 30 min until evenly dispersed, then quickly add the mixed solution to a 50 mL Teflon-lined reactor and heat to 180 °C and keep the temperature for 3 h. After the reaction, magnetically separate the mixed solution and wash it with alcohol three times to obtain the Co / C@SnO2 nanowire composite material.

[0059] Figure 8 It is the reflection loss (RL) curve of the paraffin sample containing 40 wt% of the Co / C@SnO2 nanowires of this example in the range of 2 - 18 GHz. It can be seen that the Co / C@SnO2 nanowire composite material obtains a minimum RL value of -23.26 dB at 18 GHz in the Ku band when the thickness is 1.325 mm, and the effective absorption bandwidth is 2.56 GHz. When the thickness is 1.525 mm, it obtains an effective absorption bandwidth of up to 5.04 GHz in the Ku band, almost covering most of the Ku band. In this example, the annealing temperature during the carbonization of the ZIF-67 derivative is increased and the holding time is extended, resulting in an effective enhancement of the basic dielectric loss of the material due to the improved graphitization degree catalyzed by Co nanocrystals in the matrix.

[0060] Example 6:

[0061] The preparation method of the Co / C@SnO2 nanowire composite material in this example includes the following steps:

[0062] 1. Weigh 3.5 g of cobalt(II) nitrate hexahydrate (Co(NO3)2·6H2O) and dissolve it in 100 mL of methanol by magnetic stirring to prepare a uniform solution A; weigh 4.1 g of 2-methylimidazole and also dissolve it in 100 mL of methanol by magnetic stirring to prepare a uniform solution B. Under vigorous stirring, add solution B to solution A to make them fully mixed. Place the mixed solution at room temperature and stir for 24 h. After centrifuging and washing with alcohol three times, dry it at 60 °C to obtain ZIF-67 with a particle size of 400 - 800 nm.

[0063] 2. Take 1 g of ZIF-67 powder and place it in a crucible. Under nitrogen atmosphere protection, heat it to 600 °C at a rate of 2 °C / min and keep the temperature for 2 h to obtain the Co / C hollow derivative.

[0064] 3. Weigh 300 mg of tin(IV) chloride pentahydrate (SnCl4·5H2O) and add it to a mixed solvent containing 20 mL of oleic acid, 1.25 mL of oleylamine, and 60 μL of deionized water. Stir and mix evenly under nitrogen protection and heat to 80 °C, then keep the temperature for 6 h. After that, add 10 mL of absolute ethanol, 10 mg of glycine, and 100 mg of Co / C hollow derivative to the solution. Ultrasonic for 30 min until evenly dispersed, then quickly add the mixed solution to a 50 mL Teflon-lined reaction kettle and heat to 180 °C for 8 h. After the reaction, magnetically separate the mixed solution and wash it with alcohol three times to obtain the Co / C@SnO2 nanowire composite material.

[0065] Figure 9 It is the reflection loss (RL) curve of the paraffin sample containing 40 wt% of the Co / C@SnO2 nanowires of this example in the range of 2 - 18 GHz. It can be seen that the Co / C@SnO2 nanowire composite material obtains an effective absorption bandwidth of up to 4.16 GHz in the X-band and Ku-band when the thickness is 2.275 mm, and obtains a minimum RL value of -45.37 dB at 11.88 GHz in the Ku-band when the thickness is 2.475 mm, and the effective absorption bandwidth at this time is 3.84 GHz. As the thickness increases to 4.9 mm, double absorption peaks appear in the C-band and Ku-band. In this example, by increasing the composite ratio of SnO2 nanowires, the interfacial polarization of the composite material is weakened due to interfacial coating, resulting in a decrease in dielectric constant but an improvement in impedance, effectively broadening the effective absorption bandwidth of each frequency band.

[0066] Example 7:

[0067] The preparation method of the Co / C@SnO2 nanowire composite material in this example includes the following steps:

[0068] 1. Weigh 3.5 g of cobalt(II) nitrate hexahydrate (Co(NO3)2·6H2O), dissolve it in 100 mL of methanol by magnetic stirring to prepare a uniform solution A; weigh 4.1 g of 2-methylimidazole, also dissolve it in 100 mL of methanol by magnetic stirring to prepare a uniform solution B; under vigorous stirring, add solution B to solution A to make them fully mixed; place the mixed solution at room temperature and stir for 24 h, after centrifuging and washing with alcohol three times, dry it at 60 °C to obtain ZIF-67 with a particle size of 400 - 800 nm.

[0069] 2. Take 1 g of ZIF-67 powder and place it in a crucible. Under the protection of a nitrogen atmosphere, heat it to 600 °C at a rate of 2 °C / min and keep the temperature for 2 h to obtain the Co / C hollow derivative.

[0070] 3. Weigh 300 mg of tin(IV) chloride pentahydrate (SnCl4·5H2O) and add it to a mixed solvent containing 20 mL of oleic acid, 1.25 mL of oleylamine, and 60 μL of deionized water. Stir and mix evenly under nitrogen protection and heat to 80 °C, then keep the temperature for 6 h. After that, add 10 mL of absolute ethanol, 20 mg of glycine, and 100 mg of Co / C hollow derivative to the solution. Ultrasonicate for 30 min until evenly dispersed, then quickly add the mixed solution to a 50 mL Teflon-lined autoclave and heat to 180 °C and keep the temperature for 8 h. After the reaction is completed, magnetically separate the mixed solution and wash it with alcohol three times to obtain the Co / C@SnO2 nanowire composite material.

[0071] Figure 10 It is the reflection loss (RL) curve of the paraffin sample containing 40 wt% of the Co / C@SnO2 nanowires of this example in the range of 2 - 18 GHz. It can be seen that the Co / C@SnO2 nanowire composite material reaches the minimum RL value of -28.31 dB in the Ku band when the thickness is 5.775 mm, and the effective absorption bandwidth can reach 4.5 GHz in the Ku band when the thickness is 6.775 mm. In this example, by increasing the proportion of the glycine complexing agent, the coating degree of SnO2 nanowires on the outer interface of the Co / C hollow derivative is further improved. However, the too-thick shell layer overly weakens the interfacial polarization of the composite material, and compared with Example 6, it weakens the RL and the effective bandwidth instead.

[0072] In summary, by changing the ratio of the metal ion to the ligand of the MOF matrix, the annealing temperature and time, the hydrothermal time, and the ratio of the complexing agent, the internal and external interfacial impedance and the microwave electromagnetic loss performance of the Co / C@SnO2 nanowire hollow structure can be modulated, enabling the adjustment of the electromagnetic wave absorption performance and the effective absorption bandwidth in the electromagnetic frequency band, which has good application value.

[0073] The above embodiments are all relatively typical embodiments of the present invention and do not impose any limitations on the present invention. For example, the hydrothermal temperature, hydrothermal time, heat treatment temperature, heat treatment time, the ratio and content of materials, etc. can all be further adjusted. Therefore, according to the general idea of the present invention, those skilled in the art of this technical field who make adjustments and modifications to the process parameters described, as long as they do not deviate from the concept of the invention or exceed the scope defined by this claim book, should fall within the protection scope of the present invention.

[0074] The above content is only an example and explanation of the structure of the present invention. Those skilled in the art of this technical field can make various modifications or supplements to the described specific embodiments or use similar methods for substitution, as long as they do not deviate from the structure of the present invention or exceed the scope defined by this claim book, they should fall within the protection scope of the present invention.

Claims

1. A preparation method of a lightweight hollow Co / C@SnO2 nanowire composite microwave absorbing material with adjustable impedance at the inner and outer interfaces, characterized in that: First, dodecahedral metal-organic framework ZIF-67 was synthesized by a liquid-phase chemical method, and the precursor was carbonized by high-temperature heat treatment to obtain a dodecahedral hollow porous carbon derivative embedded with Co nanocrystals; then, SnO2 nanowires were in-situ grown on the outer interface of the hollow structure by a hydrothermal method, and the complexation of amino and carboxyl groups in glycine with Sn 4+ was used to guide the one-dimensional growth of SnO2, and in-situ deposition was carried out using the polar groups on the outer interface of the dodecahedral derivative, and finally a lightweight hollow Co / C@SnO2 nanowire composite microwave absorbing material was obtained.

2. The preparation method according to claim 1, characterized in that It includes the following steps: Step 1: Synthesize metal-organic framework ZIF-67 by a liquid-phase chemical method; Step 2: Perform high-temperature heat treatment on the precursor obtained in Step 1 to obtain a dodecahedral porous carbon hollow structure embedded with Co nanocrystals, which is a derivative of ZIF-67; Step 3: In-situ grow SnO2 nanowires on the outer interface of the dodecahedral derivative obtained in Step 2 by a hydrothermal method to obtain a hollow Co / C@SnO2 nanowire composite material.

3. The preparation method according to claim 2, characterized in that: In Step 1, 3.5 - 7 g of cobalt nitrate hexahydrate is dissolved in methanol and continuously stirred to prepare a uniform solution A; 4.1 g of 2-methylimidazole is also stirred and dissolved in methanol to prepare a uniform solution B; solution B is added to solution A under stirring to make them fully mixed; the mixed solution is stirred at room temperature for 24 h, centrifuged, washed with alcohol, and dried to obtain ZIF-67 with a particle size of 400 - 800 nm.

4. The preparation method according to claim 2, characterized in that: In Step 2, the ZIF-67 powder obtained in Step 1 is placed in a crucible, heated to 600 °C at a rate of 2 °C / min under a nitrogen atmosphere protection, and kept warm for 2 h to obtain a Co / C hollow derivative framework.

5. The preparation method according to claim 2, characterized in that: In Step 3, tin chloride pentahydrate is added to a mixed solvent containing oleic acid, oleylamine, and deionized water, and stirred at 80 °C for 6 h in a nitrogen atmosphere until uniformly mixed; absolute ethanol, glycine, and the Co / C hollow derivative are added to the mixed solution, ultrasonically dispersed evenly, and then quickly transferred to a high-pressure reaction kettle lined with Teflon, placed in an oven and heated to 180 °C and kept warm for 3 - 8 h; after natural cooling, it is magnetically collected, washed with alcohol, and vacuum dried to obtain a hollow Co / C@SnO2 nanowire composite microwave absorbing material.

6. The preparation method according to claim 5, characterized in that: In Step 3, the addition amount of tin chloride pentahydrate is 100 - 300 mg, the addition amount of oleic acid is 20 mL, the addition amount of oleylamine is 0.5 - 1.25 mL, the addition amount of deionized water is 20 - 60 μL, the addition amount of absolute ethanol is 10 mL, the addition amount of glycine is 10 - 20 mg, and the addition amount of the Co / C derivative is 100 mg.

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