Carbon-based microwave absorbing material with yolk-shell structure and preparation method and application thereof
By designing a carbon-based microwave absorbing material with an egg yolk-shell structure, the problems of weak magnetic loss and poor impedance matching of carbon materials have been solved, achieving high-efficiency electromagnetic wave loss performance, which is suitable for fields such as smartphones and radar signal shielding.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- FUDAN UNIVERSITY
- Filing Date
- 2023-11-02
- Publication Date
- 2026-06-26
AI Technical Summary
The microwave absorption performance of existing carbon materials is limited by weak magnetic loss and poor impedance matching, and the magnetic particles are prone to agglomeration, resulting in poor microwave absorption performance of composite materials.
A carbon-based microwave absorbing material with an egg yolk-shell structure was designed. A cobalt-nickel alloy hexahedral array nanocage coated with a carbon layer and assembled with magnetic particle arrays was prepared by calcination in an inert atmosphere. This avoided the agglomeration of magnetic materials and enhanced magnetic and dielectric loss capabilities.
It achieves excellent electromagnetic wave loss capability in the frequency range of 2.0-18.0GHz, has a simple synthesis process, and has excellent material properties, making it suitable for electromagnetic shielding of smartphones, radar signals, and microwave ovens.
Smart Images
Figure CN117693176B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of functional materials technology, specifically relating to a carbon-based microwave absorbing material with an egg yolk-eggshell structure, its preparation method, and its application. Background Technology
[0002] With the widespread use of various electronic and electrical products in today's society, electromagnetic pollution is becoming increasingly serious, making the design and synthesis of effective radiation-shielding materials an urgent priority. Electromagnetic absorbing materials are functional materials that dissipate electromagnetic waves, essentially converting them into heat or other forms of energy to weaken their effects. Carbon materials, including carbon fibers, carbon nanotubes, graphene, and mexene, have long been considered good microwave absorbing materials due to their lightweight, good chemical stability, and high dielectric loss. However, like other single-component microwave absorbing materials, their microwave absorption performance is severely limited by their lack of magnetic loss capacity and weak impedance matching characteristics. Currently, two methods are being used to address and improve the microwave absorption performance of carbon materials. One method is to combine carbon materials with magnetic materials (such as metals like iron, cobalt, and nickel) to improve the overall magnetic loss capacity of the composite material, thereby enhancing impedance matching. Another method is to rationally design the material's structure, such as porous structures, tubular structures, and core-shell structures, to form heterogeneous interfaces, thereby increasing polarization loss and creating voids or gaps to scatter microwaves.
[0003] In recent years, the structural design of magnetic carbon materials has attracted much attention from researchers. Magnetic materials possess excellent magnetic loss capabilities, and when combined with carbon materials, the magnetic carbon materials can overcome their own shortcomings such as low dielectric loss and poor impedance matching, effectively improving the microwave absorption performance of the composite material. Furthermore, utilizing structural advantages, microwave absorbing materials with an eggshell-yolk structure have been designed, effectively improving dielectric loss capabilities due to abundant interfaces and polarization factors. However, most reported composite microwave absorbing materials involve densely packing magnetic particles onto carbon materials. This packing of magnetic materials reduces the magnetic coupling effect, failing to generate strong magnetic loss. Simultaneously, the small gaps between composite materials also lead to significant impedance. To address these issues, this invention considers both the dispersion of magnetic components and the porosity problem when designing the material structure. Research shows that materials with hierarchical structures can fully utilize the advantages of each component, effectively maximizing the material's performance. Therefore, a rationally designed one-dimensional hierarchical structure is essential to effectively meet the requirements of the material in the microwave absorption direction. Summary of the Invention
[0004] The purpose of this invention is to provide a high-performance, simple-to-synthesize carbon-based microwave absorbing material with an egg yolk-shell structure, as well as its preparation method and applications.
[0005] This invention, through research, reveals that magnetic components are prone to agglomeration, a phenomenon exacerbated by high-temperature calcination. Furthermore, when combined with carbon materials, the introduction of non-magnetic components inevitably weakens the original material's magnetism. Based on these issues, this invention designs a carbon-based nanocage structure with a yolk-shell structure assembled from magnetic particle arrays, specifically a cobalt-nickel alloy hexahedron. Calcination in an inert atmosphere yields carbon-based composite materials with different magnetic components. The yolk-shell structure of the material effectively solves the agglomeration problem of magnetic materials. The magnetic and carbon components, along with the structural advantages of the core-shell, enhance the magnetic and dielectric losses of the composite material, thereby increasing the microwave absorption capability of the carbon-coated cobalt-nickel alloy hexahedron array-assembled nanocage composite.
[0006] This invention employs a simple hydrothermal and room-temperature polymerization method to synthesize polydopamine-coated iron hydroxyl oxide array-assembled microtubes. After calcination under a nitrogen atmosphere, the product structure is well preserved, and no significant agglomeration is observed. Furthermore, this yolk-shell hexahedral array-assembled carbon nanocage microwave absorbing material exhibits excellent comprehensive performance in the microwave absorption field.
[0007] The yolk-shell structured carbon-based microwave absorbing material provided by this invention is a cobalt-nickel alloy hexahedral array nanocage composite material with a carbon layer assembled from magnetic particle arrays, i.e., its inner core layer is cobalt-nickel alloy particles and its outer shell layer is a carbon layer; the specific steps of its preparation method are as follows:
[0008] (1) Weigh out nickel acetate tetrahydrate, cobalt acetate tetrahydrate, and polyvinylpyrrolidone and dissolve them in anhydrous ethanol; stir evenly, perform hydrothermal reaction, cool naturally to room temperature, collect by centrifugation, wash, and dry in a vacuum environment to obtain the cobalt nickel acetate precursor;
[0009] (2) Weigh out the cobalt nickel acetate precursor, disperse it in deionized water, add tris(hydroxymethyl)aminomethane, stir ultrasonically to obtain solution A, then continue to add dopamine hydrochloride, stir the reaction, and the obtained product is separated, washed and dried to obtain polydopamine-coated cobalt nickel acetate precursor hexahedron.
[0010] (3) Weigh out the polydopamine-coated cobalt nickel acetate precursor hexahedron, disperse it in deionized water, add deionized water, stir the reaction, and the resulting product is separated, washed and dried to obtain hollow polydopamine-coated cobalt nickel acetate precursor hexahedron.
[0011] (4) The hollow polydopamine-coated cobalt-nickel acetate precursor hexahedron is placed under nitrogen gas protection and calcined to obtain the target product.
[0012] Furthermore, in step (1), the ratio of nickel acetate tetrahydrate, cobalt acetate tetrahydrate, polyvinylpyrrolidone and anhydrous ethanol is (0.42-0.84) g: (0.42-0.84) g: (2-3) g: (140-160) mL, wherein the mass fraction of anhydrous ethanol is 98%-99%.
[0013] Furthermore, in step (1), the reaction temperature is 80-90℃ and the time is 6-8h.
[0014] Furthermore, in step (2), the ratio of the amount of cobalt nickel acetate precursor, tris(hydroxymethyl)aminomethane hydrochloride, dopamine hydrochloride and methanol solution is (100-150) mg: (25-36) mg: (30-50) mg: (100-120) mL.
[0015] Furthermore, in step (2), the ultrasonic time is 20 to 30 minutes, and the magnetic stirring time is 12 to 48 hours.
[0016] Furthermore, in step (3), the amount of deionized water is 100-500 mL.
[0017] Furthermore, in step (3), the stirring reaction time is 2–5 hours.
[0018] Furthermore, in step (4), the calcination temperature is 350–850°C, and the time is 2–4 hours. Preferably, 2 hours.
[0019] The present invention also provides a carbon-based microwave absorbing material with an egg yolk-eggshell structure obtained by the above preparation method. This material can be made into a coated outer plate and applied to smartphone radiation shielding, radar signal shielding, and microwave oven electromagnetic shielding.
[0020] The microtube material provided by this invention has the advantage of high reflection loss when applied in the field of microwave absorption. This carbon nanocage composite material exhibits excellent electromagnetic wave loss capability in the frequency range of 2.0-18.0 GHz.
[0021] The maximum reflection loss of the microtube assembled from a hexahedral array of cobalt-nickel alloy particles calcined at 850℃ (CoNi@C-850) can reach -22.1dB, the maximum reflection loss of the microtube assembled from a hexahedral array calcined at 650℃ (CoNi@C-650) can reach -46.1dB, the maximum reflection loss of the microtube assembled from a hexahedral array calcined at 450℃ (CoNi@C-850) can reach -13.1dB, and the maximum reflection loss of the sample calcined at 350℃ with a thickness of 5.5mm reaches -21.1dB.
[0022] Compared with the prior art, the present invention has the following advantages:
[0023] (1) The synthesis method of this invention is unique and successfully synthesizes hexahedral carbon nanocage material assembled from carbon-coated magnetic particle arrays.
[0024] (2) The synthesis method of the present invention has a simple synthesis process, and the characteristics such as magnetic particle array and egg yolk-eggshell structure are easy to control, and can be mass-produced.
[0025] (3) The core magnetic components of the core-shell spindle array in this invention are easy to control, thereby making it convenient to adjust the microwave absorption performance of the material. Attached Figure Description
[0026] Figure 1 A flowchart illustrating the synthesis process of hexahedral carbon-based nanocage materials with magnetic components assembled from carbon-coated arrays.
[0027] Figure 2 Scanning electron microscope images of each sample: CoNi magnetic component precursor.
[0028] Figure 3 Transmission electron microscopy (TEM) images of each sample. Among them, (a) CoNi@C-850, a hexahedral carbon-based nanocage material with a magnetic component assembled by a carbon-coated array; (b) CoNi@C-650, a hexahedral carbon-based nanocage material with a magnetic component assembled by a carbon-coated array; (c) CoNi@C-450, a hexahedral carbon-based nanocage material with a magnetic component assembled by a carbon-coated array; and CoNi@C-350, a hexahedral carbon-based nanocage material with a magnetic component assembled by a carbon-coated array.
[0029] Figure 4 X-ray diffraction pattern of an array-assembled hexahedral carbon nanocage material.
[0030] Figure 5 The values represent the reflection loss of CoNi@C-650 at different thicknesses. Detailed Implementation
[0031] The present invention will be further described below with reference to the embodiments and accompanying drawings.
[0032] In the following embodiments, unless otherwise specified, the raw materials or processing techniques are conventional commercially available materials or conventional processing techniques in the art.
[0033] Example 1:
[0034] Preparation of CoNi@C-850, a hexahedral carbon-based nanocage material with a magnetic component assembled from carbon-coated arrays: see process details. Figure 1 As shown.
[0035] First, 0.84 g of nickel acetate tetrahydrate, 0.42 g of cobalt acetate tetrahydrate, and 3 g of polyvinylpyrrolidone (K30, average molecular weight 40,000) were dissolved in 160 mL of anhydrous ethanol. After stirring thoroughly, the solutions were mixed and transferred to a 200 mL hydrothermal reactor. The mixture was reacted at 90 °C for 6 h. After naturally cooling to room temperature, the NiCo precursor precipitate was collected by centrifugation, washed three times with ethanol, and dried under vacuum to obtain the nickel-cobalt-based glycolate precursor.
[0036] Next, 100 mg of NiCo precursor and 30 mg of tris(hydroxymethyl)aminomethane hydrochloride were dissolved in methanol (10 mM, 100 mL), and sonicated for 30 minutes. 50 mg of dopamine hydrochloride was then dispersed in the homogeneous solution prepared above, and the mixture was magnetically stirred for 6, 12, and 12 hours. (This was done to obtain dopamine shells of different thicknesses, and the difference in the ability to capture metal cations was controlled by adjusting the thickness, thus regulating the size of the metal particles. Variable 1) The resulting NiCo precursor / PDA product was collected by centrifugation, washed three times with methanol, and dried under vacuum. The product, cobalt-nickel / polydopamine precursor, was obtained.
[0037] Then, 100 mg of dopamine NiCo precursor was dispersed in 200 mL of deionized water and stirred continuously for 5 h. (The hydrolysis of acetate to metal hydroxide can control the changes in the relative and absolute contents of the multi-component metals. Variable 2) Then, after centrifugation and washing with deionized water, hollow CoNi / PDA precursor was obtained.
[0038] Finally, the hollow NiCo precursor / PDA precursor obtained after vacuum drying was placed in a ceramic boat and heated to 850℃ at a heating rate of 2℃ min⁻¹, and held in a tube furnace under a nitrogen atmosphere for 1 h. (Temperature controls particle sintering size, variable 3) NiCo / NC nanocages were obtained at different temperatures.
[0039] Example 2:
[0040] Preparation of CoNi@C-650, a hexahedral carbon-based nanocage material with magnetic components assembled from carbon-coated arrays:
[0041] The majority of the results are the same as in Example 1, except that the calcination temperature is changed to 650°C.
[0042] Example 3:
[0043] Preparation of CoNi@C-450, a hexahedral carbon-based nanocage material with magnetic components assembled from carbon-coated arrays:
[0044] The majority of the results are the same as in Example 1, except that the calcination temperature is changed to 450°C.
[0045] Example 4:
[0046] Preparation of CoNi@C-350, a hexahedral carbon-based nanocage material with magnetic components assembled from carbon-coated arrays:
[0047] The majority of the results are the same as in Example 1, except that the calcination temperature is changed to 350°C.
[0048] The microstructure of the hexahedral carbon-based nanocage material with magnetic components assembled by the carbon-coated array in the above embodiments was characterized using scanning electron microscopy (SEM, Hitachi SEM S-4800). Sample preparation method: the powder sample was ultrasonically dispersed in ethanol, then dropped onto a conductive silicon wafer and dried for testing. A series of composite material microstructures were characterized using transmission electron microscopy (TEM, JEOL JEM-2100F). Sample preparation method: the powder sample was ultrasonically dispersed in ethanol, then dropped onto a carbon-supported copper mesh and dried for testing. X-ray diffraction patterns were obtained using a Bruker D8 Advance instrument. The complex relative permittivity and permeability in the range of 2.0–18.0 GHz were measured using a vector network analyzer (model N5230C).
[0049] Figure 2 These are scanning electron microscope (SEM) images of a series of carbon nanocage materials assembled from core-shell hexahedral arrays synthesized through a controlled method. Figure 2 The microstructure of the precursor in Example 1 is shown. Its outer shell has a smooth surface and is a hexahedral shape. It is a cobalt nickel hydroxyacetate.
[0050] Figure 3 These are transmission electron microscope (TEM) images of hexahedral carbon-based nanocage materials with magnetic components assembled from a series of carbon-coated arrays prepared in Examples 1-3 above. Figure 3 As shown in Figure a, the outer carbon layer of the CoNi@C-850 sample is generally a hexahedral assembly shape, while the interior consists of cobalt-nickel particles with a large number of voids; as shown in Figure a. Figure 3 As shown in b, the outer carbon layer of the CoNi@C-650 sample is generally a hexahedral assembly shape, while the interior consists of cobalt-nickel particles with a large number of voids; as Figure 3 As shown in c, the outer carbon layer of the CoNi@C-450 sample is generally a hexahedral assembly shape, while the interior consists of cobalt-nickel particles with a large number of voids; as Figure 3 As shown in d, the outer carbon layer of the CoNi@C-350 sample is an overall hexahedral assembly shape, while the interior consists of single cobalt and nickel atoms with a large number of voids; after calcination, the carbon layer and magnetic particles of the four samples were still preserved in the temperature range of 350℃ to 850℃.
[0051] Figure 4X-ray diffraction (XRD) analysis of carbon nanocages assembled from core-shell hexahedral arrays with controllable magnetic composition as described in Examples 1-4 above. In the figure, the carbon nanocage CoNi@C-400 material assembled from a carbon-coated monodisperse cobalt-nickel alloy core-shell hexahedral array in Example 1 shows a CoNi alloy peak shape.
[0052] Figure 5 The reflection loss values of the carbon nanocage material assembled from the core-shell hexahedral array obtained in Example 2 above, at frequencies of 2.0-18.0 GHz, are given at a thickness of 1.0-5.0 mm. Figure 5 As shown, when calcined at 850℃, the maximum reflection loss of the sample with a thickness of 2.5 mm reaches -22.1 dB; when calcined at 650℃, the maximum reflection loss reaches -46.1 dB; when calcined at 450℃, the maximum reflection loss reaches -13.1 dB; and when calcined at 350℃, the maximum reflection loss reaches -21.1 dB with a thickness of 5.5 mm. The carbon nanocage material assembled from a core-shell hexahedral array simultaneously meets the practical application requirements of strong absorption, wide bandwidth response, and low density, making it a potential high-performance microwave absorbing material.
[0053] In summary, the microtube material assembled from the spindle array of this invention exhibits excellent electromagnetic wave loss capability in the 2.0-18.0 GHz frequency range. This invention utilizes cobalt glycolate (nickel) as a template, coating its surface with dopamine, and by varying the calcination temperature, can produce carbon nanocage materials assembled from core-shell hexahedral arrays with different magnetic particles. The synthesis process of this invention is simple, the material properties are excellent, and it has broad application prospects in the field of microwave absorption.
[0054] Comparative Example 1:
[0055] Most of the components are the same as in Example 3, except that the dopamine coating is changed to no coating.
[0056] Without dopamine coating, it is difficult to maintain the hexahedral structure. With CoNi alloy as the main component, it is difficult to obtain carbon-based magnetic materials with a hexahedral structure, indicating that dopamine coating plays an important role in controlling the hexahedral structure.
[0057] Example 5:
[0058] Compared to Example 1, most aspects are the same, except that in this example, the ratio of nickel acetate tetrahydrate to cobalt acetate tetrahydrate is 0.4g:0.4g. Adjusting the metal ratio in the precursor allows for the control of saturation magnetization, thereby improving the intrinsic permeability of the microwave absorbing material, achieving high magnetic loss efficiency, and ultimately, higher microwave absorption reflection loss.
[0059] Example 6:
[0060] Compared to Example 1, most aspects are the same, except that in this example, the ratio of nickel acetate tetrahydrate to cobalt acetate tetrahydrate is 0.8 g: 0.4 g. Adjusting the metal ratio in the precursor allows for the control of saturation magnetization, thereby improving the intrinsic permeability of the microwave absorbing material, achieving high magnetic loss efficiency, and ultimately, higher microwave absorption reflection loss.
[0061] Example 7:
[0062] The majority of the components are the same as in Example 1, except that in this example, the oven temperature is set to 160°C and the holding time is 14 hours. Adjusting the hydrothermal time controls the size of the precursor. In constructing the conductive network, the proportion of effective absorbents in the absorbing coating can be controlled, thereby controlling the coating density to achieve high-intensity wave absorption under lighter conditions.
[0063] Example 8:
[0064] The majority of the components are the same as in Example 1, except that in this example, the oven temperature is set to 200°C and the holding time is 10 hours. Adjusting the hydrothermal time controls the size of the precursor. In constructing the conductive network, the proportion of effective absorbers in the absorbing coating can be controlled, thereby controlling the coating density to achieve high-intensity wave absorption under lighter conditions.
[0065] Example 9:
[0066] Compared to Example 1, most aspects are the same, except that in this example, the ratio of cobalt-nickel precursor to dopamine is 0.1g:1.5g. By adjusting the carbon layer thickness, the conductivity in the absorbing coating can be controlled in the construction of the conductive network, thereby controlling the conductivity loss and dielectric loss. This allows for control of the carbon layer thickness, enabling high-intensity wave absorption under lighter conditions.
[0067] Example 10:
[0068] Compared to Example 1, most aspects are the same, except that in this example, the ratio of cobalt-nickel precursor to dopamine is 0.1g:2.5g. By adjusting the carbon layer thickness, the conductivity in the absorbing coating can be controlled in the construction of the conductive network, thereby controlling the conductivity loss and dielectric loss. This allows for control of the carbon layer thickness, enabling high-intensity wave absorption under lighter conditions.
[0069] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.
Claims
1. A method for preparing a carbon-based microwave absorbing material with an egg yolk-shell structure, characterized in that, This microwave absorbing material is a carbon-coated cobalt-nickel alloy hexahedral array nanocage composite material assembled from magnetic particle arrays, i.e., its inner core layer is cobalt-nickel alloy particles, and its outer shell layer is a carbon layer; the specific preparation steps are as follows: (1) Weigh out nickel acetate tetrahydrate, cobalt acetate tetrahydrate, and polyvinylpyrrolidone and dissolve them in anhydrous ethanol; stir evenly, perform hydrothermal reaction, cool naturally to room temperature, collect by centrifugation, wash, and dry in a vacuum environment to obtain the cobalt nickel acetate precursor; (2) Weigh out the cobalt nickel acetate precursor, disperse it in deionized water, add tris(hydroxymethyl)aminomethane, and stir ultrasonically to obtain a mixed solution; then add dopamine hydrochloride and stir magnetically to react. The resulting product is separated, washed and dried to obtain polydopamine-coated cobalt nickel acetate precursor hexahedron. (3) Weigh out the polydopamine-coated cobalt nickel acetate precursor hexahedron, disperse it in deionized water, add deionized water, stir the reaction, and the resulting product is separated, washed and dried to obtain hollow polydopamine-coated cobalt nickel acetate precursor hexahedron. (4) The hollow polydopamine-coated cobalt-nickel acetate precursor hexahedron is placed under nitrogen gas protection and calcined to obtain the target product.
2. The preparation method according to claim 1, characterized in that, In step (1): The ratio of nickel acetate tetrahydrate, cobalt acetate tetrahydrate, polyvinylpyrrolidone and anhydrous ethanol is (0.42-0.84)g:(0.42-0.84)g:(2-3)g:(140-160)mL, wherein the mass fraction of anhydrous ethanol is 98%-99%. The hydrothermal reaction temperature is 80–90°C, and the hydrothermal reaction time is 6–8 hours.
3. The preparation method according to claim 2, characterized in that, In step (2): The ratio of the amounts of the cobalt nickel acetate precursor, tris(hydroxymethyl)aminomethane hydrochloride, dopamine hydrochloride, and methanol solution is (100–150) mg: (25–36) mg: (30–50) mg: (100–120) mL; The ultrasonic time is 20 to 30 minutes, and the magnetic stirring time is 12 to 48 hours.
4. The preparation method according to claim 3, characterized in that, In step (3), the amount of deionized water is 100-500 mL; the stirring reaction time is 2-5 h.
5. The preparation method according to claim 4, characterized in that, In step (4), the calcination temperature is 350-850℃ and the calcination time is 2-4h.
6. A carbon-based microwave absorbing material with an egg yolk-eggshell structure obtained by the preparation method according to any one of claims 1-5.
7. The application of the yolk-shell structured carbon-based microwave absorbing material as described in claim 6 in the field of microwave absorption.