Novel microwave absorbing material of magnetic CoFe / C bamboo-like carbon nanotube core-shell nanocomposite and preparation method of novel microwave absorbing material

Abstract

The invention discloses a design and preparation of a novel microwave absorbing material of a magnetic CoFe / C at bamboo-like carbon nanotube (CoFe / C at bamboo-like CNTs) core-shell nanocomposite. The material has a hollow core-shell structure, an inner core of the core-shell structure is made of CoFe magnetic alloy, and an outer shell layer of the core-shell structure is made of bamboo-like carbon nanotubes. The magnetic CoFe / C and bamboo-like CNTs core-shell nano composite microwave absorbing material disclosed by the invention shows excellent electromagnetic wave loss capability in a frequency range of 2.0 to 18.0 GHz. The preparation method comprises the following steps: uniformly mixing a metal-nitrilotriacetic acid chelate precursor with dicyandiamide according to a certain ratio, and annealing in argon, so as to prepare the magnetic CoFe / C bamboo-like CNTs core-shell nano composite microwave absorbing material with multiple components and rich heterogeneous interfaces.

Description

Technical Field

[0001] The present invention belongs to the technical field of microwave absorption material design and development, and in particular relates to the design and preparation of a new type of microwave absorption material of magnetic CoFe / C@bamboo-shaped carbon nanotubes (CoFe / C@bamboo-shaped CNTs) core-shell nanocomposite. Background Art

[0002] With the popularization of electronic and electrical equipment and the rapid development of wireless communication technology, electromagnetic radiation pollution has become a global problem that threatens human health and interferes with the operation of precision equipment. The development of efficient microwave absorbing materials is the key to achieving electromagnetic protection. Its core goal is to convert the incident electromagnetic wave energy into heat energy or other forms of energy through the unique physical and chemical mechanisms within the material, thereby weakening the reflection and transmission of electromagnetic waves. Ideal microwave absorbing materials must have the characteristics of lightweight, broadband absorption, strong attenuation ability and environmental stability. Carbon-based materials (such as carbon fibers, carbon nanotubes, and graphene) should have low density, high specific surface area, excellent conductivity and dielectric loss properties, and are considered to be highly promising candidate materials. However, single carbon materials rely on dielectric loss mechanisms and have bottlenecks such as high electromagnetic wave reflectivity and poor impedance matching, resulting in narrow absorption bandwidth and low efficiency, making it difficult to meet the needs of complex application scenarios. Therefore, optimizing the electromagnetic parameters of materials through multi-component collaboration and structural design has become an important direction to break through the performance limitations of single-component materials.

[0003] Improving microwave absorption performance relies on the efficient synergy of magnetic and dielectric losses. Although single dielectric materials (such as pure carbon) possess high dielectric constants, excessive dielectric polarization can easily lead to surface impedance mismatch, causing significant electromagnetic wave reflection at the material interface. Magnetic materials (such as ferrites and magnetic metals) can achieve magnetic loss through mechanisms such as natural resonance and domain wall displacement, but their high density and narrow bandwidth limit their applications. By constructing magnetic-dielectric composite systems, the complex permittivity and complex permeability can be synergistically manipulated to improve impedance matching and broaden the loss mechanism. Carbon nanotubes (CNTs), due to their unique bamboo-like hollow structure, offer significant advantages in composite design: first, the heterojunction formed by the bamboo-like tube walls can induce interfacial polarization, enhancing dielectric loss. Second, the one-dimensional tubular structure can construct a three-dimensional conductive network, extending the electromagnetic wave propagation path through multiple reflections. Third, their high specific surface area and chemical activity facilitate the loading of magnetic nanoparticles (such as Fe3O4 and CoNi alloys) to form a magnetic-dielectric heterojunction, simultaneously introducing a magnetic loss mechanism. For example, embedding Fe3O4 nanoparticles into the cavity of carbon nanotubes or modifying their surfaces can effectively adjust the material's electromagnetic parameters, utilizing hysteresis and eddy current losses to enhance low-frequency absorption performance, while the high conductivity of carbon nanotubes enhances high-frequency dielectric loss, thereby achieving efficient broadband absorption. This type of hierarchical structural design provides innovative ideas for the development of new microwave absorbing materials that are lightweight, strong, and compatible with broadband performance. Summary of the Invention

[0004] The purpose of the present invention is to provide a design and preparation process of a new type of magnetic CoFe / C@bamboo-shaped carbon nanotube (CoFe / C@bamboo-shaped CNTs) core-shell nanocomposite composite material, which has a simple synthesis process and excellent performance.

[0005] The technical solution of the present invention is: a preparation method of a novel microwave absorbing material of a magnetic CoFe / C@bamboo-shaped carbon nanotube core-shell nanocomposite, comprising the following steps: (1) dispersing equimolar amounts of ferrous chloride and cobalt chloride with nitrilotriacetic acid in isopropyl alcohol and deionized water, stirring to form a uniform solution, then placing the solution in a reactor for hydrothermal reaction, and centrifugally drying to obtain a CoFe-nitrilotriacetic acid chelate; (2) weighing the CoFe-nitrilotriacetic acid chelate and dicyandiamide, mixing them uniformly, and placing them in a quartz boat; (3) placing the quartz boat containing the sample in a tube furnace, introducing argon gas, and performing high-temperature carbonization annealing treatment. After the reaction is completed, the solution is cooled to room temperature and then placed in an air environment to obtain the target product.

[0006] In the step (1), the ratio of the added amounts of ferrous chloride, cobalt chloride, nitrilotriacetic acid, isopropyl alcohol and deionized water is 3 mmol:3 mmol:1.2 g:30 mL:40 mL.

[0007] The stirring time in step (1) is 1-2 hours, and the temperature of the hydrothermal reaction is set to 160-180° C. for 6-8 hours.

[0008] In the step (2), the ratio of the added amount of CoFe nitrilotriacetic acid chelate and dicyandiamide is 500 mg:(1000-2000) mg.

[0009] In the step (3), the carbonization temperature is 700-900°C, the time is 1-3h, and the heating rate is 3°C / min.

[0010] A novel microwave absorbing material of magnetic CoFe / C@bamboo-shaped carbon nanotube core-shell nanocomposite prepared by the preparation method.

[0011] Beneficial effects of the present invention: Through research, the present invention has found that the synthesis process of multi-component composites is very complicated. However, the present application utilizes magnetic metals to catalyze the growth of carbon nanotubes. By mixing a metal-nitrilotriacetic acid chelate with dicyandiamide in a certain proportion and then subjecting it to high-temperature treatment under argon, it is possible to synthesize a magnetic CoFe / C@bamboo-shaped carbon nanotube (CoFe / C@bamboo-shaped CNTs) core-shell nanocomposite. Because the magnetic CoFe alloy and the bamboo-shaped carbon nanotubes have rich heterogeneous interfaces, the magnetic loss and dielectric loss capabilities of the material are greatly improved, thereby making the magnetic CoFe / C@bamboo-shaped carbon nanotube (CoFe / C@bamboo-shaped CNTs) core-shell nanocomposite exhibit excellent electromagnetic wave absorption performance.

[0012] (1) The novel microwave absorbing material of the magnetic CoFe / C@bamboo-shaped carbon nanotubes (CoFe / C@bamboo-shaped CNTs) core-shell nanocomposite provided by the present invention has the advantages of wide bandwidth, low matching thickness, and broadband response. At a low thickness of 2.27 mm, it can achieve a wide bandwidth of 6.80 GHz. This type of composite material exhibits excellent electromagnetic wave absorption performance in the entire test frequency band: S (2-4 GHz), C (4-8 GHz), X (8-12 GHz), and Ku (12-18 GHz).

[0013] (2) The synthesis process and method of the present invention are novel, simple, and easy to promote to synthesize other types of novel CoFe / C@bamboo-shaped carbon nanotube core-shell nanocomposites.

[0014] (3) The microstructure parameters of the inner and outer shell materials in the present invention are adjustable, which can effectively realize the regulation and optimization of the electromagnetic parameters of the material, thereby obtaining adjustable and excellent electromagnetic wave absorption performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 (a) X-ray diffraction spectra and (b) Raman spectra of the microwave absorbing materials of Comparative Example 1, Example 2, and Example 1;

[0016] Figure 2 The scanning electron microscopy and transmission electron microscopy images of the samples are as follows: (a1), (a2) comparative example 1; (b1), (b2) example 2; (c1), (c2) example 1;

[0017] Figure 3 The effective absorption bandwidth curves of the samples are: (a) Comparative Example 1; (b) Example 2; (c) Example 1. DETAILED DESCRIPTION

[0018] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0019] The following are examples of the present invention. Unless otherwise specified, raw materials or processing techniques are conventional commercially available raw materials or conventional processing techniques in the art.

[0020] Example 1:

[0021] (1) 3 mmol of cobalt chloride, 3 mmol of ferrous chloride, and 1.2 g of nitrilotriacetic acid were weighed and added to a mixed solution of 30 mL of isopropanol and 40 mL of deionized water, and stirred for 90 min to form a homogeneous solution. The homogeneous solution was added to a 100 mL reactor for hydrothermal reaction, and the temperature was set to 180°C for 7 hours. After cooling, the solution was washed, centrifuged, and dried to obtain a metal-nitrilotriacetic acid chelate.

[0022] (2) Weigh 500 mg of metal-nitrilotriacetic acid chelate and 2 g of dicyandiamide, grind and mix them evenly, place them in a tube furnace and carbonize and anneal them at 900°C under argon atmosphere for 2 h at a heating rate of 3°C / min. After cooling to room temperature, the target product can be obtained.

[0023] Example 2:

[0024] Without changing other steps, the carbonization temperature of step (2) is set to 800° C., and a magnetic CoFe / C@bamboo-shaped CNTs core-shell nanocomposite absorbing material with slightly poor crystallinity can be obtained.

[0025] Example 3:

[0026] Without changing other steps, the carbonization temperature of step (2) is set to 700° C., and a magnetic CoFe / C@bamboo-shaped CNTs core-shell nanocomposite absorbing material with worse crystallinity can be obtained.

[0027] Example 4:

[0028] Without changing other steps, the mass of dicyandiamide added in step (2) is changed to 1.5 g, and a magnetic CoFe / C@bamboo-shaped CNTs core-shell nanocomposite absorbing material with slightly less bamboo-shaped carbon nanotubes can be obtained.

[0029] Example 5:

[0030] Without changing other steps, by changing the mass of dicyandiamide added in step (2) to 1g, a magnetic CoFe / C@bamboo-shaped CNTs core-shell nanocomposite absorbing material with fewer bamboo-shaped carbon nanotubes can be obtained.

[0031] Comparative Example 1:

[0032] Compared with Example 2, without changing other steps, the mass of dicyandiamide added in step (2) was changed to 0g.

[0033] Characterization and performance testing experiments

[0034] Figure 1 The X-ray diffraction (XRD) pattern analysis results of the samples of Example 1, Example 2 and Comparative Example 1 are shown. As shown in the figure, the three samples all show characteristic diffraction peaks at 2θ=44.87°, 65.31° and 82.74°, corresponding to the (110), (200) and (211) crystal planes of the CoFe alloy (JCPDS No.49-1568), respectively, indicating that a CoFe crystal phase with a BCC structure has been successfully formed in the sample. It is worth noting that compared with Comparative Example 1, the intensity of the CoFe characteristic peak of Example 2 is significantly reduced, which is attributed to the increase in the relative carbon content in the composite material, resulting in a weakening of the metal phase diffraction signal. Under the same carbon content conditions, the intensity of the CoFe diffraction peak of Example 1 is significantly enhanced due to the increase in the carbonization temperature to 900°C, indicating that the high temperature treatment effectively promotes the growth of the CoFe alloy grains and the improvement of the crystallinity. In order to further confirm the composition of the composite material, we analyzed the structural characteristics of the carbon component by Raman spectroscopy ( Figure 2 All samples were at about 1350cm -1 and 1585cm -1 A distinct double-peak structure is observed near the D and G bands of the carbon material, respectively. Combined XRD phase analysis and Raman spectroscopy confirm the successful preparation of a CoFe alloy-carbon composite structure. XRD data clearly defines the crystal structure of the metallic phase, while Raman spectroscopy reveals the structural evolution of the carbon component at the molecular vibrational level. The two characterization methods complement each other effectively, providing sufficient evidence for the composition and structure of the composite material.

[0035] Figure 2 The micromorphology of different samples was characterized by SEM and TEM systems. The a1 and a2 images of comparative example 1 (CoFe / C, carbonized at 800℃) show ( Figure 2 a1, a2), the material retains a one-dimensional rod-like structure, and its surface is densely packed with carbon-coated CoFe nanoparticles to form a significantly rough surface. This morphology is due to the heterogeneous nucleation and restricted growth of metal particles during the carbothermal reaction. When the bamboo-like carbon nanotube construction strategy is introduced, Example 2 (CoFe / C@bamboo-like CNTs, 800℃) and Example 1 (CoFe / C@bamboo-like CNTs, 900℃) show significantly different structural characteristics ( Figure 2 b1-b2,c1-c2):

[0036] (1) CNTs exhibit a typical bamboo-like segmented structure, and the uniformity of tube diameter increases with increasing carbonization temperature;

[0037] (2) High-angle TEM images ( Figure 2 c2 insert) clearly shows that CoFe nanoparticles (black contrast area) are confined and encapsulated in the internode cavity of carbon nanotubes, forming a unique "bead-chain" composite structure;

[0038] (3) The self-assembly characteristics of the three-dimensional conductive network are particularly prominent in Example 1. The bamboo-shaped carbon nanotubes form a through-type conductive path through topological winding, which provides an ideal carrier for multiple reflections and dielectric loss of electromagnetic waves.

[0039] Figure 3 The effective absorption bandwidth (EAB, RL<-10dB) of different samples at matching thicknesses of 1.0-10.0mm was compared. Comparative Example 1 (CoFe / C) only obtained an EAB of 3.20GHz at a thickness of 7.39mm. Figure 3 a), while the structurally modified Example 2 and Example 1 exhibit significantly optimized broadband absorption characteristics:

[0040] (1) Example 2 (800°C) EAB reaches 6.00 GHz at 2.34 mm thickness ( Figure 3 b) Compared with Comparative Example 1, the thickness is reduced by 68% while the bandwidth is increased by 87.5%;

[0041] (2) Example 1 (900°C) further optimizes the interface coupling by high-temperature carbonization, and extends the EAB to 6.80 GHz ( Figure 3 c) Covering the 12.4-18.0GHz frequency band (full Ku-band coverage).

[0042] Comparing Example 1 and Example 2 with Comparative Example 1, the wave absorption performance of the CoFe / C sample has been greatly improved. Its superior performance is attributed to the construction of rich heterojunction surfaces, which is conducive to the optimization of impedance matching and enhances polarization loss. In addition, CoFe alloy is beneficial to magnetic loss, and the introduction of bamboo-like CNTs can extend the transmission path of electrons and further enhance dielectric loss.

[0043] The above description of the embodiments and comparative examples is intended to facilitate understanding and use of the invention by those skilled in the art. Those skilled in the art can readily modify these embodiments and apply the general principles described herein to other embodiments without resorting to creative discovery. Therefore, the present invention is not limited to the above embodiments, and 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 present invention should be within the scope of protection of the present invention.

Claims

1. A method for preparing a novel microwave absorbing material of a magnetic CoFe / C@bamboo-shaped carbon nanotube core-shell nanocomposite, characterized by: The method comprises the following steps: (1) dispersing equimolar amounts of ferrous chloride and cobalt chloride with nitrilotriacetic acid in isopropyl alcohol and deionized water, stirring the mixture to form a uniform solution, placing the mixture in a reactor for hydrothermal reaction, and centrifuging and drying the mixture to obtain a CoFe-nitrilotriacetic acid chelate; (2) weighing the CoFe-nitrilotriacetic acid chelate and dicyandiamide, mixing the mixture uniformly, and placing the mixture in a quartz boat; (3) placing the quartz boat containing the sample in a tube furnace, introducing argon gas, and performing high-temperature carbonization annealing treatment. After the reaction is completed, the mixture is cooled to room temperature and then placed in an air environment to obtain the target product.

2. The method for preparing a novel microwave absorbing material of a magnetic CoFe / C@bamboo-shaped carbon nanotube core-shell nanocomposite according to claim 1, characterized in that: In step (1), the ratio of the added amounts of ferrous chloride, cobalt chloride, nitrilotriacetic acid, isopropyl alcohol and deionized water is 3 mmol:3 mmol:1.2 g:30 mL:40 mL.

3. The method for preparing a novel microwave absorbing material of a magnetic CoFe / C@bamboo-shaped carbon nanotube core-shell nanocomposite according to claim 1, characterized in that: The stirring time in step (1) is 1-2 hours, and the temperature of the hydrothermal reaction is set to 160-180° C. for 6-8 hours.

4. The method for preparing a novel microwave absorbing material of a magnetic CoFe / C@bamboo-shaped carbon nanotube core-shell nanocomposite according to claim 1, characterized in that: In step (2), the ratio of the added amount of CoFe nitrilotriacetic acid chelate to dicyandiamide is 500 mg:(1000-2000) mg.

5. The method for preparing a novel microwave absorbing material of a magnetic CoFe / C@bamboo-shaped carbon nanotube core-shell nanocomposite according to claim 1, characterized in that: In step (3), the carbonization temperature is 700-900°C, the time is 1-3h, and the heating rate is 3°C / min.

6. A novel microwave absorbing material comprising a magnetic CoFe / C@bamboo-shaped carbon nanotube core-shell nanocomposite prepared by the method according to any one of claims 1 to 5.

Images