Preparation method and application of Co@G / CNT nanorod composite material with super-wide electromagnetic wave absorption performance

Abstract

The application discloses a preparation method and application of Co@G / CNT nanorod composite material with super-wide electromagnetic wave absorption performance. The preparation of the composite material is as follows: Co and Zn acetate solutions are added into a mixed solution of dimethyl imidazole and CTAB, stirring is carried out at room temperature, a hydrothermal synthesis reaction is carried out on the obtained solution, the synthesized product is washed, dried, and then calcined under Ar / H2 atmosphere, so that the target product is obtained. In the application, the in-situ growth method is used to directly induce the growth of carbon nanotubes on a carbon rod base, the generated carbon nanotubes can form a continuous conductive network, which is beneficial to adjusting the electromagnetic parameters of the material, such as dielectric constant and magnetic permeability, so that effective absorption can be realized in a wider frequency band. The magnetic metal for generating the carbon nanotubes also provides magnetic loss, and the good synergistic effect of the dielectric loss and the magnetic loss of the composite material further improves the wave absorption performance.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic wave absorbing materials technology, specifically to a method for preparing and applying a Co@G / CNT nanorod composite material with ultrawide electromagnetic wave absorption performance. Background Technology

[0002] Electromagnetic radiation pollution generated by the widespread use of electronic devices, from household appliances to wireless base stations and military radar, seriously threatens human health and national defense security. Therefore, the demand for high-performance electromagnetic wave absorbing (EWA) materials is urgent. Magnetic materials, including metals (Co, Ni, Fe) and metal alloys (FeCo, CoNi, etc.), are generally used as microwave absorbers due to their high magnetic loss capacity. Carbonaceous materials, due to their lightweight, high dielectric loss, low cost, large surface area, and strong affinity for magnetic particles, are frequently used as matrices to support magnetic components. The combination of carbon-based materials with magnetic components improves absorption performance by increasing dielectric loss and improving impedance matching due to the synergistic effect between their dielectric and magnetic components. Researchers typically use multi-component composite materials, obtained by combining doped carbon nanotubes with magnetic metals, but the preparation process is complex. In summary, the combination of carbon-based materials with magnetic metals provides new ideas and methods for designing and developing lightweight and efficient electromagnetic wave absorbing materials. The ingenious combination will give full play to the advantages of both, providing strong support for solving the problems of traditional wave absorbing materials and promoting the research and application of electromagnetic wave absorbing materials. Summary of the Invention

[0003] In view of the above-mentioned technical problems existing in the prior art, the purpose of this application is to provide a Co@G / CNT nanorod composite microwave absorbing material with ultra-wide electromagnetic wave absorption performance, its preparation method and application.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] The method for preparing a Co@G / CNT nanorod composite material with ultrawide electromagnetic wave absorption performance includes the following steps:

[0006] 1) Dissolve Co(CH3COO)2·4H2O and Zn(CH3COO)2·2H2O in ultrapure water to prepare solution a;

[0007] 2) Mix and dissolve dimethylimidazole and CTAB in ultrapure water to obtain solution b;

[0008] 3) Quickly add solution a to solution b, stir at room temperature, transfer the mixture to a stainless steel reactor with a Teflon liner and hydrothermally react at 100-140℃ for 24-50h. After the reaction is complete, cool to room temperature, centrifuge, wash and dry to obtain the CoZn-ZIF precursor.

[0009] 4) The CoZn-ZIF precursor was calcined in an Ar / H2 atmosphere to obtain a Co@G / CNT nanorod composite material with ultrawide electromagnetic wave absorption performance.

[0010] Further, in step 1), the molar ratio of Co(CH3COO)2·4H2O and Zn(CH3COO)2·2H2O is 1:1-5, preferably 1:2-3.

[0011] Further, in step 2), the mass of CTAB is 2-10% of the mass of dimethylimidazole, preferably 4-6%.

[0012] Furthermore, in step 1), the total amount of Co(CH3COO)2·4H2O and Zn(CH3COO)2·2H2O in the ratio of the mass of dimethylimidazole in step 2) is 1:2-5, preferably 1:2.5-3.

[0013] Further, the concentration of dimethylimidazole in the mixture in step 3) is 40-200 mg / mL, preferably 70-80 mg / mL.

[0014] Furthermore, in step 3), the temperature of the hydrothermal reaction is 110-120℃, and the reaction time is 40-48h.

[0015] Further, in step 4), the volume fraction of H2 in the Ar / H2 atmosphere is 2-10%, preferably 5-6%; the calcination in step 4) is carried out in two steps, the first step of calcination is calcination at 300-400℃ for 1-2 hours, and the second step of calcination is calcination at 700-900℃ for 2-5 hours.

[0016] Furthermore, the first calcination temperature is 350℃ and the calcination time is 1.5-2 hours, while the second calcination temperature is 800℃ and the calcination time is 3-4 hours.

[0017] The present invention relates to the application of a Co@G / CNT nanorod composite material with ultrawide electromagnetic wave absorption performance, wherein the material is used to absorb electromagnetic waves in the frequency range of 2 to 18 GHz.

[0018] This application discloses a Co@G / CNT nanorod composite microwave absorbing material with ultrawide electromagnetic wave absorption performance. The synthesis mechanism involves a simple synthesis strategy: cobalt and zinc salts are hydrothermally synthesized under the action of the surfactant CTAB to obtain a rod-shaped bimetallic organic framework precursor. Due to the catalytic effect of Co metal, carbon nanotubes can be directly induced to grow on the carbon rod substrate under a specific hydrogen atmosphere. This in-situ growth method avoids complex mixing, dispersion, and subsequent processing steps, greatly simplifying the preparation process, improving production efficiency, and reducing production costs. The carbon nanotubes can form a continuous conductive network, which is beneficial for adjusting the electromagnetic parameters of the material, such as dielectric constant and permeability, and improving impedance matching, thereby achieving effective microwave absorption over a wider frequency range. Furthermore, the magnetic metal that induces the carbon nanotubes provides magnetic loss; the synergistic effect of good magnetic loss and dielectric loss further enhances the microwave absorption performance. This invention uses ultrapure water as a solvent, the preparation process is simple, energy-saving and environmentally friendly, and the reagents used are inexpensive, enabling large-scale production.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] 1) This invention prepares a Co@G / CNT nanorod composite microwave absorbing material with ultra-wide electromagnetic wave absorption performance through in-situ growth of carbon nanotubes. The method allows for the controllable distribution of carbon nanotubes on a carbon rod substrate. The high-temperature sublimation of zinc generates numerous and uniform pores in the material, reducing its density. The magnetic metal cobalt, which induces the growth of carbon nanotubes, provides magnetic loss. The carbon nanotubes form a continuous conductive network, which facilitates the adjustment of the material's electromagnetic parameters, such as dielectric constant and permeability, thereby achieving effective microwave absorption over a wider frequency range. This invention uses water as a solvent, has a simple preparation process, is relatively energy-efficient and environmentally friendly, and uses inexpensive reagents, while exhibiting excellent microwave absorption performance.

[0021] 2) In the Co@G / CNT nanorod composite microwave absorbing material with ultrawide electromagnetic wave absorption performance prepared by in-situ growth of carbon nanotubes in this invention, the Co content is adjusted... 2+ and Zn 2+ The molar ratio of ions is carefully controlled to rationally manage the content and distribution of Co NPs in the Co@G / CNT composite material. Zn atoms effectively block adjacent Co atoms, significantly reducing the aggregation of magnetic Co. Co NPs can be uniformly distributed inside and on the surface of CoZn nanorods and carbon nanotubes. Good compositional control and ingenious structural design result in enhanced multiple losses, multiple interface polarizations, and good impedance matching, achieving a reflection loss of -40.36 dB. A relatively thin thickness of 3.2 mm with a 15 wt% filler load achieves a wide bandwidth of 9.6 GHz. Its acceptable bandwidth reaches 13.2 GHz, achieving electromagnetic wave absorption exceeding 99.9999%.

[0022] 3) In the preparation of Co@G / CNT nanorod composite microwave absorbing material with ultra-wide electromagnetic wave absorption performance by the method of in-situ growth of carbon nanotubes in this invention, the large outer surface area causes multiple reflections and scatterings of electromagnetic waves between the nanorods and the carbon nanotubes on the surface, which prolongs the propagation path of electromagnetic waves and enhances the attenuation ability. Attached Figure Description

[0023] Figure 1 Comparison of X-ray electron diffraction (XRD) images of Co@G / CNT-1, Co@G / CNT-2 and Co@G / CNT-3 materials prepared in Example 1.

[0024] Figure 2 The image shows the scanning electron microscope (SEM) test results of the Co@G / CNT composite material in Example 1.

[0025] Figure 3 The image shows the scanning electron microscope (SEM) test results of the Co@G / CNT composite material in Example 2.

[0026] Figure 4 The image shows the scanning electron microscope (SEM) test results of the Co@G / CNT composite material in Example 3.

[0027] Figure 5 The image shows the transmission electron microscopy (TEM) test results of the Co@G / CNT composite material in Example 1.

[0028] Figure 6 The image shows the transmission electron microscopy (TEM) test results of the Co@G / CNT composite material in Example 2.

[0029] Figure 7 The image shows the transmission electron microscopy (TEM) test results of the Co@G / CNT composite material in Example 3.

[0030] Figure 8 The image shows the reflection loss (RL) curve of the Co@G / CNT composite material in Example 1.

[0031] Figure 9 The image shows the reflection loss (RL) curve of the Co@G / CNT composite material in Example 2.

[0032] Figure 10 The image shows the reflection loss (RL) curve of the Co@G / CNT composite material in Example 3. Detailed Implementation

[0033] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0034] Example 1

[0035] A method for preparing Co@G / CNT nanorod composite materials with ultrawide electromagnetic wave absorption properties via in-situ growth includes the following steps:

[0036] 1) At room temperature, disperse 0.249g Co(CH3COO)2·4H2O (1mmol) into 4ml of ultrapure water, sonicate until completely dissolved, then add 0.219g Zn(CH3COO)2·2H2O (1mmol) and continue sonicating until completely dissolved. Label this solution as solution a.

[0037] 2) Disperse 4.927g of dimethylimidazole in 60ml of ultrapure water, sonicate until completely dissolved, then add 0.241g of CTAB and continue sonicating until completely dissolved. The resulting solution is labeled as solution b.

[0038] 3) Quickly add the prepared solution a to solution b, stir at room temperature for 5 min, transfer the solution to a Teflon-lined stainless steel container and heat at 120℃ for 48 hours to obtain CoZn-MOF. After cooling to room temperature, collect the purple powder by centrifugation. Wash several times with methanol and ethanol, centrifuge, and dry at 70℃ overnight to obtain the CoZn-ZIF precursor;

[0039] 4) After drying, the CoZn-ZIF precursor sample was calcined in a tube furnace at a heating rate of 2℃ / min to 350℃ for 1.5h under an Ar / H2 atmosphere with a H2 volume fraction of 5%. The furnace temperature was then further increased to 800℃ and held for 3.5h. A Co@G / CNT nanorod composite material with ultrawide electromagnetic wave absorption properties was obtained and labeled Co@G / CNT-2.

[0040] X-ray electron diffraction (XRD) was performed on the Co@G / CNT-2 composite material prepared in Example 1. The test results are as follows: Figure 1 As shown, the XRD pattern of the Co@G / CNT-2 composite material prepared in this invention matches well with the crystallographic data simulation results of composite materials synthesized with different proportions of cobalt-zinc salts. The materials all have three obvious peaks at 2θ = 44.21°, 51.41° and 75.71°, which can be corresponding to the (111), (200) and (220) planes of Co NPs, respectively, indicating the presence of high-purity cobalt crystals.

[0041] The preparation method of Co@G / CNT nanorod composite material in steps 1)-4) of Example 1 is followed, except that the amount of Co(CH3COO)2·4H2O and Zn(CH3COO)2·2H2O added in step 1) is adjusted to maintain the total amount of both at 2 mmol, so that Co2+ and Zn 2+ The molar ratio of ions was changed to 3:1 and 1:3, and the final microwave absorbing materials were labeled as Co@G / CNT-1 and Co@G / CNT-3, respectively.

[0042] The Co@G / CNT-1, Co@G / CNT-2, and Co@G / CNT-3 materials prepared in Example 1 were all subjected to X-ray electron diffraction (XRD) analysis. The test results are as follows: Figure 1 As shown, the XRD pattern of the Co@G / CNT nanorod composite material with ultra-wide electromagnetic wave absorption properties prepared by the in-situ growth method of this invention matches well with the results of crystallographic data simulation. The material also exhibits a relatively weak but broad peak near 2θ = 25.01°, corresponding to the (002) crystal plane of carbon. This is due to the reduced content of CoNPs and the decreased graphitization degree of carbon. No diffraction peaks for zinc and zinc oxide were found in the figure, indicating that the presence of zinc is at a very low level or in an amorphous state.

[0043] The scanning electron microscopy (SEM) test results of the Co@G / CNT-2 composite material in Example 1 are as follows: Figure 2 As shown, from Figure 2 The obvious rod-like structure and the uniform distribution of carbon nanotubes on the carbon rods demonstrate the successful synthesis of the Co@G / CNT-2 composite material, which is consistent with the XRD test results.

[0044] The transmission electron microscopy (TEM) results of the Co@G / CNT-2 material prepared in Example 1 are as follows: Figure 5 As shown, from Figure 5 It can be seen that Co NPs are distributed on the surface and inside the carbon framework of Co@G / CNT-3, with metal nanoparticles wrapped at the end of each carbon nanotube. These nanoparticles are encapsulated by many graphitic carbon layers, which are formed by the catalytic graphitization of Co NPs during carbonization. Carbon nanotubes can form a continuous conductive network, which is beneficial for adjusting the electromagnetic parameters of the material, allowing more electromagnetic waves to enter the interior of the absorbing material, thereby enhancing electromagnetic wave absorption.

[0045] The electromagnetic wave absorption performance of the Co@G / CNT-2 material prepared in Example 1 was tested. The sample was mixed with paraffin wax, with the Co@G / CNT-2 sample comprising 15 wt% of the mixture. After thorough dispersion in cyclohexane, the solvent was completely evaporated by water bath heating. The resulting solidified material was pressed into sheets using a mold and then tested. The reflection loss (RL) curves of the material at thicknesses of 1.0–5.5 mm and frequencies of 2–18 GHz are shown below. Figure 8 As shown. Generally, an RL value below -10dB indicates that 90% of electromagnetic waves are absorbed. For example... Figure 8As shown, the RLmin value of Co@G / CNT-2 material is -41.23dB when the thickness is 3.0mm, and the effective absorption bandwidth (RL value < -10dB) is 5.20GHz (9.69~14.89GHz) when the thickness is 2.5mm.

[0046] The superior microwave absorption performance of the Co@G / CNT-2 material in this invention can be attributed to the excellent synergistic effect of magnetic loss and dielectric loss. Traditional methods often involve doping carbon nanotubes into a magnetic material matrix. However, this method suffers from complex fabrication processes, high costs, and difficulty in precisely controlling the distribution of carbon nanotubes in the composite material, leading to poor impedance matching. This invention cleverly utilizes a simple synthesis strategy to directly induce the growth of carbon nanotubes (CNTs) on a carbon rod substrate. By precisely controlling the ratio of cobalt salt to zinc salt, the number and length of the generated carbon nanotubes are effectively controlled, thereby effectively adjusting and optimizing the microwave absorption performance of the material. Compared to traditional doping methods, this in-situ growth method avoids complex mixing, dispersion, and subsequent processing steps, greatly simplifying the fabrication process, improving production efficiency, and reducing production costs. CNTs can form a continuous conductive network, which not only enhances the electromagnetic shielding performance of the material but also facilitates the adjustment of electromagnetic parameters such as dielectric constant and permeability, thereby achieving effective microwave absorption over a wider frequency range. Furthermore, the magnetic metal that induces carbon nanotubes provides magnetic loss. This additional property, combined with enhanced dielectric loss, forms a dual-loss mechanism that further improves wave absorption performance. Therefore, this invention provides a new design approach and technical support for the preparation of broadband electromagnetic wave absorbing materials.

[0047] This invention prepares a Co@G / CNT-2 nanorod composite material with ultra-wide electromagnetic wave absorption performance. Ring-forming tests were conducted on a sample of Co@G / CNT-2 mixed with paraffin. The sample exhibited excellent wave absorption performance even with a Co@G / CNT-2 content of only 15 wt%, reducing the material filler content and achieving the goal of "lightweight" materials. By controlling the proportion of metal salts, this invention achieves the preparation of a Co@G / CNT nanorod composite material with ultra-wide electromagnetic wave absorption performance through in-situ growth. Water is used as the solvent, the preparation process is simple and environmentally friendly, and the reagents used are inexpensive.

[0048] Example 2

[0049] A method for preparing Co@G / CNT nanorod composite materials with ultra-wide electromagnetic wave absorption properties by in-situ growth at room temperature includes the following steps:

[0050] 1) At room temperature, disperse 0.374g Co(CH3COO)2·4H2O (1.5mmol) in 4ml of ultrapure water, sonicate until completely dissolved, then add 0.110g Zn(CH3COO)2·2H2O (0.5mmol) and continue sonicating until completely dissolved. Label this solution as solution a.

[0051] 2) Disperse 4.927g of dimethylimidazole in 60ml of ultrapure water, sonicate until completely dissolved, then add 0.241g of CTAB and continue sonicating until completely dissolved. The resulting solution is labeled as solution b.

[0052] 3) Quickly add the prepared solution a to solution b, stir at room temperature for 5 min, transfer the solution to a Teflon-lined stainless steel container and heat at 120℃ for 48 hours to obtain CoZn-MOF. After cooling to room temperature, collect the purple powder by centrifugation. Wash several times with methanol and ethanol, centrifuge, and dry at 70℃ overnight to obtain the CoZn-ZIF precursor;

[0053] 4) After drying, the CoZn-ZIF precursor sample was calcined in a tube furnace at a heating rate of 2℃ / min to 350℃ for 1.5h under an Ar / H2 atmosphere with a H2 volume fraction of 5%. The furnace temperature was then further increased to 800℃ and held for 3.5h. A Co@G / CNT nanorod composite material with ultrawide electromagnetic wave absorption properties was obtained and labeled as Co@G / CNT-1.

[0054] The scanning electron microscope (SEM) and transmission electron microscope (TEM) test results of the Co@G / CNT-1 material prepared in Example 2 are as follows: Figure 3 and Figure 6 As shown, from Figure 6 It can be seen that Co NPs exhibit significant aggregation on the surface and inside the carbon framework.

[0055] The electromagnetic wave absorption performance of the Co@G / CNT-1 material prepared in Example 2 was tested. The sample was mixed with paraffin wax for testing, and the test conditions were the same as in Example 1. The reflection loss (RL) curves of the material at a thickness of 1.0–5.5 mm and a frequency of 2–18 GHz are shown below. Figure 9 As shown, it exhibits good electromagnetic wave absorption capability at a thickness of 2.5 mm, with the optimal RL... min The value is -30.23dB, and the corresponding effective absorption bandwidth is a maximum bandwidth of 5.04GHz (12.96~18.0GHz) when the thickness is 2.0mm.

[0056] Compared with Example 1, the microwave absorption performance of the microwave absorbing material synthesized in Example 2 is reduced. This is because the amount of zinc salt added is less than that in Example 1, which greatly increases the agglomeration of magnetic metal Co, which is not conducive to obtaining good impedance matching, resulting in poor microwave absorption performance of Co@G / CNT-1 composite material.

[0057] Example 3

[0058] A method for preparing Co@G / CNT nanorod composite materials with ultra-wide electromagnetic wave absorption properties by in-situ growth at room temperature includes the following steps:

[0059] 1) At room temperature, disperse 0.125g Co(CH3COO)2·4H2O (0.5mmol) in 4ml of ultrapure water, sonicate until completely dissolved, then add 0.329g Zn(CH3COO)2·2H2O (1.5mmol) and continue sonicating until completely dissolved. Label this solution as solution a.

[0060] 2) Disperse 4.927g of dimethylimidazole in 60ml of ultrapure water, sonicate until completely dissolved, then add 0.241g of CTAB and continue sonicating until completely dissolved. The resulting solution is labeled as solution b.

[0061] 3) Quickly add the prepared solution a to solution b, stir at room temperature for 5 min, transfer the solution to a Teflon-lined stainless steel container and heat at 120℃ for 48 hours to obtain CoZn-MOF. After cooling to room temperature, collect the purple powder by centrifugation. Wash several times with methanol and ethanol, centrifuge, and dry at 70℃ overnight to obtain the CoZn-ZIF precursor;

[0062] 4) After drying, the CoZn-ZIF precursor sample was calcined in a tube furnace at 350℃ for 1.5h at a heating rate of 2℃ / min under an Ar / H2 atmosphere with a H2 volume fraction of 5%. The furnace temperature was then further increased to 800℃ and held for 3.5h. A Co@G / CNT nanorod composite material with ultrawide electromagnetic wave absorption properties was obtained and labeled as Co@G / CNT-3.

[0063] The scanning electron microscope (SEM) and transmission electron microscope (TEM) test results of the Co@G / CNT-3 material prepared in Example 3 are as follows: Figure 4 and Figure 7 As shown, from Figure 7 It can be seen that Co NPs are more evenly distributed on the surface and inside the carbon skeleton of Co@G / CNT-3.

[0064] The electromagnetic wave absorption performance of the Co@G / CNT-3 material prepared in Example 3 was tested. The sample was mixed with paraffin wax for testing, and the test conditions were the same as in Example 1. The reflection loss (RL) curves of the material at a thickness of 1.0–5.5 mm and a frequency of 2–18 GHz are shown below. Figure 10 As shown. It exhibits excellent electromagnetic wave absorption capability at a thickness of 3.0 mm, with optimal RL. min The value is -40.36dB, and the corresponding effective absorption bandwidth reaches a maximum bandwidth of 9.61GHz (8.39~18.0GHz).

[0065] Compared to Example 1, the microwave absorbing material synthesized in Example 3 exhibits improved microwave absorption performance. This is because the amount of zinc salt added is greater than that in Example 1, which significantly reduces the agglomeration of magnetic metal Co, allowing Co NPs to be evenly distributed, thereby increasing the porosity of the material and contributing to good impedance matching. Good compositional control and ingenious structural design give the Co@G / CNT-3 composite material better microwave absorption performance.

[0066] Compare with Example 1:

[0067] The preparation steps of Example 1 were repeated, except that the calcination atmosphere in "step 4) was replaced with N2". All other conditions remained the same, and the CoZn-ZIF composite material was finally obtained.

[0068] Electromagnetic wave absorption performance was tested using the CoZn-ZIF composite material as described in Example 1. The sample was mixed with paraffin wax, and the test conditions were the same as in Example 1. The optimal RL was achieved at a thickness of 3.0 mm. min The value is -24.02dB, and the effective absorption bandwidth (RL value < -10dB) is 2.80GHz (8.87~11.67GHz). Since the magnetic metal Co cannot generate more carbon nanotubes under N2 atmosphere, the reduction of carbon nanotubes makes it impossible to form a conductive network on the surface, and the conductivity loss is weakened. The reduction of surface defects weakens the attenuation ability, which ultimately leads to the poor wave absorption performance of the material.

[0069] The contents described in this specification are merely an enumeration of the implementation forms of the inventive concept, and the scope of protection of this invention should not be regarded as limited to the specific forms described in the embodiments.

Claims

1. A method for preparing a Co@G / CNT nanorod composite material with ultrawide electromagnetic wave absorption performance, characterized in that... Includes the following steps: 1) Dissolve Co(CH3COO)2·4H2O and Zn(CH3COO)2·2H2O in ultrapure water to prepare solution a; 2) Mix and dissolve dimethylimidazole and CTAB in ultrapure water to obtain solution b; 3) Quickly add solution a to solution b, stir at room temperature, transfer the mixture to a stainless steel reactor with a Teflon liner and hydrothermally react at 100-140℃ for 24-50h. After the reaction is complete, cool to room temperature, centrifuge, wash and dry to obtain the CoZn-ZIF precursor. 4) The CoZn-ZIF precursor was calcined in an Ar / H2 atmosphere to obtain a Co@G / CNT nanorod composite material with ultrawide electromagnetic wave absorption performance. In step 1), the molar ratio of Co(CH3COO)2·4H2O and Zn(CH3COO)2·2H2O is 1:1-5; In step 2), the mass of CTAB is 2-10% of the mass of dimethylimidazole; The ratio of the total amount of Co(CH3COO)2·4H2O and Zn(CH3COO)2·2H2O in step 1) to the mass of dimethylimidazole in step 2) is 1:2-5; In step 4), the volume fraction of H2 in the Ar / H2 atmosphere is 2-10%.

2. The method for preparing a Co@G / CNT nanorod composite material with ultrawide electromagnetic wave absorption performance as described in claim 1, characterized in that... In step 1), the molar ratio of Co(CH3COO)2·4H2O and Zn(CH3COO)2·2H2O is 1:2-3.

3. The method for preparing a Co@G / CNT nanorod composite material with ultrawide electromagnetic wave absorption performance as described in claim 1, characterized in that... In step 2), the mass of CTAB is 4-6% of the mass of dimethylimidazole.

4. The method for preparing a Co@G / CNT nanorod composite material with ultrawide electromagnetic wave absorption performance as described in claim 1, characterized in that... In step 1), the total amount of Co(CH3COO)2·4H2O and Zn(CH3COO)2·2H2O is in a mass ratio of 1:2.5-3 to that of dimethylimidazole in step 2).

5. The method for preparing a Co@G / CNT nanorod composite material with ultrawide electromagnetic wave absorption performance as described in claim 1, characterized in that... Step 3) The concentration of dimethylimidazole in the mixture is 40-200 mg / mL.

6. The method for preparing a Co@G / CNT nanorod composite material with ultrawide electromagnetic wave absorption performance as described in claim 5, characterized in that... Step 3) The concentration of dimethylimidazole in the mixture is 70-80 mg / mL.

7. The method for preparing a Co@G / CNT nanorod composite material with ultrawide electromagnetic wave absorption performance as described in claim 1, characterized in that... In step 3), the hydrothermal reaction temperature is 110-120℃ and the reaction time is 40-48h.

8. The method for preparing a Co@G / CNT nanorod composite material with ultrawide electromagnetic wave absorption performance as described in claim 1, characterized in that... In step 4), the volume fraction of H2 in the Ar / H2 atmosphere is 5-6%; the calcination in step 4) is carried out in two steps. The first step of calcination is carried out at 300-400℃ for 1-2 hours, and the second step of calcination is carried out at 700-900℃ for 2-5 hours.

9. The method for preparing a Co@G / CNT nanorod composite material with ultrawide electromagnetic wave absorption performance as described in claim 8, characterized in that... The first calcination step is performed at a temperature of 350℃ for 1.5-2 hours, and the second calcination step is performed at a temperature of 800℃ for 3-4 hours.

10. A Co@G / CNT nanorod composite material with ultrawide electromagnetic wave absorption properties prepared by the method described in any one of claims 1-9.

11. The application of the Co@G / CNT nanorod composite material with ultrawide electromagnetic wave absorption performance as described in claim 10, characterized in that... The material is used to absorb electromagnetic waves in the frequency range of 2–18 GHz.

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