Melamine sponge-based nitrogen-doped CoO / Co / C composite material and preparation method and application thereof

Abstract

The present invention belongs to the technical field of absorbing materials, and specifically relates to a melamine sponge-based nitrogen-doped CoO / Co / C composite material, its preparation method, and application. The invention comprises the following steps: dissolving a soluble cobalt salt and 2-methylimidazole in an alcohol solvent to prepare a mixed solution; placing a melamine sponge in the mixed solution for compounding to prepare a melamine sponge / ZIF-67 composite material; and heat-treating the melamine sponge / ZIF-67 composite material at 700-900°C, followed by natural cooling to room temperature to obtain the melamine sponge-based nitrogen-doped CoO / Co / C composite material. The dielectric constant of the composite material is adjusted to a low-frequency range by utilizing the adjustable composition and microstructure of ZIF-67. The unique structure of the melamine sponge and the carbon nanotubes grown on its surface generate multiple losses, enabling the absorbing material to achieve high reflection loss and a wide effective absorption bandwidth at a low matching thickness.

Description

Technical Field

[0001] The present invention belongs to the technical field of wave-absorbing materials, and in particular relates to a melamine sponge-based nitrogen-doped CoO / Co / C composite material, a preparation method thereof, and applications thereof. Background Art

[0002] With the rapid development and application of cutting-edge electronic technologies such as 5G and self-driving cars, the environmental hazards posed by electromagnetic radiation are becoming increasingly severe. Complex and disordered electromagnetic waves can interfere with communication signals, affect electronic equipment, and harm human health. Furthermore, electromagnetic wave absorption has important applications in national defense and the military. Therefore, the research of absorbing materials is crucial. Currently, electromagnetic wave absorbing materials are gradually developing towards matching thin thickness, lightweight, wide effective absorption bandwidth (EAB), and strong reflection loss (RL).

[0003] The loss mechanisms of electromagnetic waves include dielectric loss, conductive loss, and magnetic loss. Currently, combining electrical loss materials with magnetic loss materials is a common strategy for preparing absorbing materials. This allows the absorbing materials to obtain a magneto-electric synergistic loss mechanism, greatly improving the material's ability to dissipate electromagnetic waves. Magnetic loss absorbing materials are typically Fe, Co, Ni-based ferrites and their doping systems. Electrical loss absorbing materials are divided into two categories: resistive loss absorbing materials and dielectric loss absorbing materials, including carbon-based materials such as graphene, carbon nanotubes, and carbon fibers, as well as conductive polymers. Combining magnetic materials with carbon-based materials can form magneto-electric composite loss absorbing materials, which also greatly improves the material's electromagnetic wave loss capacity.

[0004] Improving low-frequency radar absorption requires materials with high magnetic loss and good dielectric constant frequency response. Research on optimizing the absorption performance of low-frequency absorbers primarily focuses on regulating the complex dielectric constant and complex magnetic permeability. By adjusting the composition and micromorphology of the absorber, the electromagnetic parameters of the absorber are adjusted to a reasonable range. Research has found that the magneto-electric synergistic attenuation mechanism generated by combining magnetic and dielectric materials can effectively control the electromagnetic parameters and optimize overall performance. Therefore, some researchers have combined lightweight and stable high-electron mobility carbon materials with nanomagnetic materials to enhance the material's electromagnetic loss capability. Professor Chen Yujin's team at Harbin Engineering University prepared nitrogen-doped graphene-coated nickel nanoparticles, which exhibit an effective absorption bandwidth of 8.5 GHz at a thickness of 3 mm. Professor Tong Guoxiu's team at Zhejiang Normal University prepared Fe3O4@C nanoring composites, which exhibit an electromagnetic wave reflectivity of -61.54 dB at a thickness of 1.50 mm. These studies have proved that the composite material can effectively improve the microwave loss capability of magnetic materials and broaden the absorption band.

[0005] However, there are currently few reports on how to enhance the loss and broaden the absorption bandwidth of highly efficient, low-frequency, broadband absorbing materials. In particular, there is no research on how to manipulate the dielectric constant and impedance matching characteristics of these materials to low frequencies. The difficulty lies in the fact that the precise construction of composite materials with easily tunable components and structures is the foundation, while the key is to manipulate the dielectric constant and impedance matching characteristics of the materials to low frequencies. Summary of the Invention

[0006] In order to solve the above technical problems, the present invention provides a melamine sponge-based nitrogen-doped CoO / Co / C composite material and its preparation method and application. First, a structure with adjustable components and structure is constructed, and Co 2+ The components and microstructure of the coordinated MOFs structure are adjustable, adjusting the dielectric constant of the composite material to the low-frequency range. At the same time, the special structure of the melamine sponge and the carbon nanotubes grown on its surface produce multiple losses, enabling the absorbing material of the present invention to achieve higher reflection loss and wider effective absorption bandwidth at a lower matching thickness.

[0007] The present invention is specifically achieved through the following technical solutions.

[0008] The present invention first provides a method for preparing a melamine sponge-based nitrogen-doped CoO / Co / C composite material, comprising the following steps:

[0009] S1. Dissolving a soluble cobalt salt and 2-methylimidazole in an alcohol solvent to prepare a mixed solution; placing a melamine sponge in the mixed solution for compounding, and drying to prepare a melamine sponge / ZIF-67 composite material;

[0010] S2. Under a protective gas atmosphere, the melamine sponge / ZIF-67 composite material prepared in S1 was heat-treated at 700-900° C., and then naturally cooled to room temperature to obtain a melamine sponge-based nitrogen-doped CoO / Co / C composite material.

[0011] Preferably, in S1, the compounding temperature is 70-75° C., and the reaction is carried out for 1-2 hours under stirring.

[0012] Preferably, in S1, the soluble cobalt salt is cobalt nitrate hexahydrate, cobalt acetate, cobalt sulfate or cobalt chloride.

[0013] Preferably, in S1, the alcohol solvent is methanol.

[0014] Preferably, in S1, the mass ratio of the soluble cobalt salt to 2-methylimidazole is 0.96:1.2.

[0015] Preferably, in S2, the holding time is 2-3 hours.

[0016] Preferably, in S2, the heating rate is 4-6°C / min.

[0017] The present invention also provides a melamine sponge-based nitrogen-doped CoO / Co / C composite material prepared by the preparation method.

[0018] The present invention also provides application of the melamine sponge-based nitrogen-doped CoO / Co / C composite material in the field of wave-absorbing materials.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. The present invention combines melamine sponge with MOF through reasonable composition, interface regulation and multi-level structure design to construct a structural and functional integrated absorbing material with light weight, low frequency and broadband characteristics. For the first time, by using Co 2+ A melamine sponge-based nitrogen-doped CoO / Co / C composite material was prepared using a coordinated MOF structure (ZIF-67) and used for electromagnetic wave absorption applications. The melamine sponge promotes multiple reflections of electromagnetic waves within the material, increasing the number of reflection paths and achieving multiple losses. Furthermore, the Co magnetic particles and carbon nanotubes on the surface of the melamine sponge-based nitrogen-doped CoO / Co / C composite material induce magnetic and conduction losses, further contributing to electromagnetic wave losses. These multiple losses enable the absorber material to achieve high reflection losses and a wide effective absorption bandwidth at a relatively low matching thickness. The use of melamine sponge and structurally diverse MOFs to prepare magnetic transition metal-doped carbon composites is expected to yield highly efficient absorbers.

[0021] 2. The present invention uses melamine sponge as a template and, through ingenious design, prepares a series of melamine sponge-based nitrogen-doped CoO / Co / C composites. These studies provide a model system and rich experience for a deeper understanding of the regulation of the composition and microstructure of transition metal-doped hierarchical carbon composites. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Scanning electron micrographs of CoO / Co / N / C-700 (A), CoO / Co / N / C-800 (B), and CoO / Co / N / C-900 (C), transmission electron micrographs of CoO / Co / N / C-800 (D), (E), and high-resolution transmission electron micrograph (with built-in selected area electron diffraction pattern) (F);

[0023] Figure 2 Scanning electron microscope image of CoO / Co / N / C-800 (A), EDS mapping images of CoO / Co / N / C-800 (B)-(E);

[0024] Figure 3XRD spectrum of CoO / Co / N / C-700 / 800 / 900 (A), Raman spectrum of CoO / Co / N / C-700 / 800 / 900 (B), N2 adsorption-desorption curve of CoO / Co / N / C-700 / 800 / 900 (C) and pore size distribution diagram of CoO / Co / N / C-700 / 800 / 900 (D);

[0025] Figure 4 XPS spectra of CoO / Co / N / C-700 / 800 / 900: full spectrum (A); C 1s spectrum (B); N 1s spectrum (C) and Co 2p spectrum (D);

[0026] Figure 5 Electromagnetic parameters of CoO / Co / N / C-700 / 800 / 900 samples: real part of dielectric constant (A), imaginary part of dielectric constant (B), dielectric loss tangent (C), real part of magnetic permeability (D), imaginary part of magnetic permeability (E) and magnetic loss tangent (F);

[0027] Figure 6 (A) and (D) 3D images and contour maps of the absorbing performance of CoO / Co / N / C-700, (B) and (E) 3D images and contour maps of the absorbing performance of CoO / Co / N / C-800, and (C) and (F) 3D images and contour maps of the absorbing performance of CoO / Co / N / C-900.

[0028] Figure 7 Reflection loss and matching thickness of CoO / Co / N / C-700 / 800 / 900 (A)-(C). DETAILED DESCRIPTION

[0029] In order to enable those skilled in the art to better understand and implement the technical solution of the present invention, the present invention is further described below with reference to specific embodiments and drawings, but the embodiments are not intended to limit the present invention.

[0030] The experimental methods and detection methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials are commercially available unless otherwise specified.

[0031] A method for preparing a melamine sponge-based nitrogen-doped CoO / Co / C composite material comprises the following steps:

[0032] S1. Dissolving a soluble cobalt salt and 2-methylimidazole in an alcohol solvent to prepare a mixed solution; placing a melamine sponge in the mixed solution for compounding, and drying to prepare a melamine sponge / ZIF-67 composite material;

[0033] S2. Under a protective gas atmosphere, the melamine sponge / ZIF-67 composite material prepared in S1 was heat-treated at 700-900° C., and then naturally cooled to room temperature to obtain a melamine sponge-based nitrogen-doped CoO / Co / C composite material.

[0034] The soluble cobalt salt is cobalt nitrate hexahydrate, cobalt acetate, cobalt sulfate or cobalt chloride.

[0035] The present invention will be specifically described below through the following examples.

[0036] Example 1

[0037] A method for preparing a melamine sponge-based nitrogen-doped CoO / Co / C composite material comprises the following steps:

[0038] S1. Preparation of melamine sponge / ZIF-67 composite materials

[0039] Cut the melamine sponge into cubes of appropriate size and place them in a flask. Dissolve 0.96g of cobalt nitrate hexahydrate and 1.2g of 2-methylimidazole in 120ml of anhydrous methanol. Pour each solution into the flask containing the melamine sponge. Place the flask on a magnetic stirrer and stir at 70°C for 1 hour. Dry the resulting product in a vacuum drying oven at 60°C for 12 hours to obtain the product.

[0040] S2. Preparation of melamine sponge-based nitrogen-doped CoO / Co / C composites

[0041] The resulting melamine sponge / ZIF-67 composite was placed in a tube furnace, purged with argon, and heated at 900°C for two hours at a heating rate of 5°C / min. The resulting sample was then naturally cooled to room temperature. The resulting sample was named CoO / Co / N / C-900.

[0042] Example 2

[0043] A method for preparing a melamine sponge-based nitrogen-doped CoO / Co / C composite material comprises the following steps:

[0044] S1. Preparation of melamine sponge / ZIF-67 composite materials

[0045] Cut the melamine sponge into cubes of appropriate size and place them in a flask. Dissolve 0.96g of cobalt nitrate hexahydrate and 1.2g of 2-methylimidazole in 120ml of anhydrous methanol. Pour each solution into the flask containing the melamine sponge. Place the flask on a magnetic stirrer and stir at 70°C for 1 hour. Dry the resulting product in a vacuum drying oven at 60°C for 12 hours to obtain the product.

[0046] S2. Preparation of melamine sponge-based nitrogen-doped CoO / Co / C composites

[0047] The resulting melamine sponge / ZIF-67 composite was placed in a tube furnace, purged with argon, heated at a rate of 5°C / min, and held at 700°C for two hours before naturally cooling to room temperature. The resulting sample was named CoO / Co / N / C-700.

[0048] Example 3

[0049] A method for preparing a melamine sponge-based nitrogen-doped CoO / Co / C composite material comprises the following steps:

[0050] S1. Preparation of melamine sponge / ZIF-67 composite materials

[0051] Cut the melamine sponge into cubes of appropriate size and place them in a flask. Dissolve 0.96g of cobalt nitrate hexahydrate and 1.2g of 2-methylimidazole in 120ml of anhydrous methanol. Pour each solution into the flask containing the melamine sponge. Place the flask on a magnetic stirrer and stir at 70°C for 1 hour. Dry the resulting product in a vacuum drying oven at 60°C for 12 hours to obtain the product.

[0052] S2. Preparation of melamine sponge-based nitrogen-doped CoO / Co / C composites

[0053] The resulting melamine sponge / ZIF-67 composite was placed in a tube furnace, purged with argon, and heated at 800°C for two hours at a heating rate of 5°C / min. The resulting sample was then naturally cooled to room temperature. The resulting sample was named CoO / Co / N / C-800.

[0054] The pyrolyzed samples were tested and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman, specific surface area, and electromagnetic wave absorption performance.

[0055] Depend on Figure 1 It can be seen that after pyrolysis, carbon nanotube structures are generated on the CoO / Co / N / C material. The formation of carbon nanotubes is beneficial to promoting conduction losses, and the CoO / Co metal particles on the top of the carbon nanotubes can induce magnetic losses and promote impedance matching. The HRTEM image and SAED image show the (111) crystal plane of Co and the (200) crystal plane of Co, with interplanar spacings of 0.198nm and 0.214nm, respectively, which can indicate that the crystalline structure of Co and CoO has been successfully produced in the material.

[0056] Figure 2SEM image (A) of CoO / Co / N / C-800, EDS mapping images (B)-(E) of CoO / Co / N / C-800, Figure 2 It can be seen that the four elements C, N, O, and Co are evenly distributed in the material.

[0057] Depend on Figure 3 It can be seen that the X-ray diffraction pattern of CoO / Co / N / C-700 / 800 / 900 composite material is as follows Figure 3 (A) shows the crystal structure of the materials. All three composite materials have diffraction peaks at 2θ = 26°, indicating the presence of graphitic carbon. In addition, the diffraction peaks of Co appear at 2θ = 44.2°, 51.5°, and 75.8°, and the intensity of the diffraction peaks increases with the increase of pyrolysis temperature, indicating that the increase of pyrolysis temperature is conducive to the growth of Co metal particles. CoO / Co / N / C-800 has a diffraction peak of CoO at 2θ = 42.4°, indicating that CoO is produced after pyrolysis of the material at 800°C. Figure 3 (B) is the Raman spectrum. As the temperature increases, I D / I G The value of decreases accordingly, indicating that the degree of graphitization of the material increases with increasing temperature. Figure 3 (C) and (D) are the N2 adsorption-desorption curves and pore distribution curves of CoO / Co / N / C-700 / 800 / 900 composite materials. It can be seen that the specific surface areas of CoO / Co / N / C-700 / 800 / 900 are 144.245m 2 / g, 169.706m 2 / g and 222.228m 2 / g, and the pore size of CoO / Co / N / C-700 / 800 / 900 is about 6 nm.

[0058] Depend on Figure 4 It can be seen that the chemical state and elemental composition of CoO / Co / N-CNTs-3-700 / 800 / 900 were analyzed by X-ray photoelectron spectroscopy, indicating the presence of four elements: C, N, O, and Co. The characteristic peaks in the C 1s spectrum indicate the presence of CC bonds, CN bonds, CO bonds, and CO=C bonds. The N 1s spectrum shows the presence of pyridinic nitrogen, pyrrolic nitrogen, and graphitic nitrogen, and the intensity of the N1s spectrum gradually decreases with increasing pyrolysis temperature, indicating that the content of graphitic carbon gradually increases. And the Co 2p spectrum shows that Co 2+ and Co 3+ existence.

[0059] Depend on Figure 5As can be seen, as is normal for dielectrics, the real part of the dielectric constant gradually decreases with increasing frequency, while the real part of the dielectric constant increases as the pyrolysis temperature increases from 700°C to 900°C. The ε″ of the materials pyrolyzed at 800°C and 900°C shows a decreasing trend with increasing frequency, while the ε″ curve for the material pyrolyzed at 700°C remains relatively stable, with a resonant peak observed. Furthermore, this series of materials has a low complex permeability parameter, and magnetic loss has a minimal impact on the EMW loss capability of this material. Therefore, the contribution of dielectric loss plays a major role in this process.

[0060] Depend on Figure 6 and Figure 7 As can be seen, by entering the electromagnetic parameters of each sample into MATLAB, fitting thicknesses between 1 and 5 mm and frequencies between 2 and 18 GHz, we can calculate the reflectivity plots for the three samples. At a matching thickness of 2.0 mm, the CoO / Co / N / C-800 sample achieves a maximum reflection loss of -52.3 dB, with an effective absorption bandwidth of 4.88 GHz. At virtually all thicknesses, the RL value is less than -10 dB, indicating that the sample absorbs 90% of electromagnetic waves at these thicknesses. The reflection loss values of the CoO / Co / N / C-700 and CoO / Co / N / C-900 samples are both lower than the -52.3 dB of CoO / Co / N / C-800. This demonstrates that the CoO / Co / N / C-800 sample has the best absorption performance of the three samples, and that this series of absorbers exhibits excellent absorption properties.

[0061] From the above results, it can be seen that the present invention first constructs a structure with adjustable components and structure, and utilizes Co 2+ The components and microstructure of the coordinated MOFs structure are adjustable, adjusting the dielectric constant of the composite material to the low-frequency range. At the same time, the special structure of the melamine sponge and the carbon nanotubes grown on its surface produce multiple losses, enabling the absorbing material of the present invention to achieve higher reflection loss and wider effective absorption bandwidth at a lower matching thickness.

[0062] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications of the present invention fall within the scope of the claims and their equivalents, such changes and modifications are intended to be included.

Claims

1. A method for preparing a melamine sponge-based nitrogen-doped CoO / Co / C composite material, characterized in that: The following steps are involved: S1. Dissolving a soluble cobalt salt and 2-methylimidazole in an alcohol solvent to prepare a mixed solution; placing a melamine sponge in the mixed solution for compounding, and drying to prepare a melamine sponge / ZIF-67 composite material; S2. In a protective gas atmosphere, the melamine sponge / ZIF-67 composite material prepared in S1 was heat-treated at 700-900° C., and then naturally cooled to room temperature to obtain a melamine sponge-based nitrogen-doped CoO / Co / C composite material; In S1, the compounding temperature is 70-75°C, and the reaction is carried out for 1-2 hours under stirring; The pore size of the melamine sponge-based nitrogen-doped CoO / Co / C composite is 6 nm.

2. The preparation method according to claim 1, characterized in that In S1, the soluble cobalt salt is cobalt nitrate hexahydrate, cobalt acetate, cobalt sulfate or cobalt chloride.

3. The preparation method according to claim 1, characterized in that In S1, the alcohol solvent is methanol.

4. The preparation method according to claim 1, characterized in that In S1, the mass ratio of soluble cobalt salt to 2-methylimidazole is 0.96:1.

2.

5. The preparation method according to claim 1, characterized in that In S2, the holding time is 2-3h.

6. The preparation method according to claim 1, characterized in that In S2, the heating rate is 4-6°C / min.

7. A melamine sponge-based nitrogen-doped CoO / Co / C composite material prepared according to the preparation method according to any one of claims 1 to 6.

8. Use of the melamine sponge-based nitrogen-doped CoO / Co / C composite material according to claim 7 in the field of microwave absorbing materials.

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