A cobalt-iron alloy carbon magnetoelectric composite microwave absorbing material, its preparation method and application

Abstract

This invention relates to the field of microwave absorbing materials technology, specifically to an iron-cobalt alloy carbon magnetoelectric composite microwave absorbing material, its preparation method, and its applications. The specific preparation method includes the following steps: using potassium ferricyanide as the carbon and nitrogen source, a co-precipitation reaction is carried out with a Co source and sodium citrate in a solvent system to prepare a Prussian blue analog; then, under a protective atmosphere, the Prussian blue analog is pyrolyzed at 400–600℃, causing Co nanoparticles to be loaded onto the surface of a carbon-nitrogen matrix, resulting in the iron-cobalt alloy carbon magnetoelectric composite microwave absorbing material. This invention mainly uses the C≡N groups in the metal coordination bonds as the carbon and nitrogen sources, and Co nanoparticles as magnetic particles. By controlling the pyrolysis temperature, the microstructure and internal structure of the product are altered, thereby controlling the electromagnetic parameters of the material and obtaining an absorbing material with good impedance matching and attenuation performance.

Description

Technical Field

[0001] This invention relates to the field of microwave absorbing materials technology, specifically to an iron-cobalt alloy carbon magnetoelectric composite microwave absorbing material, its preparation method, and its application. Background Technology

[0002] Driven by the wave of electronification and informatization, the number of electronic and communication devices has increased dramatically, significantly improving the convenience of people's daily lives. However, as these devices become increasingly concentrated in limited spaces, electromagnetic energy density continues to rise, leading to a significant deterioration of the electromagnetic environment and consequently, electromagnetic pollution. When electronic and communication devices are operating, the electromagnetic waves they release can adversely affect other electronic instruments in the vicinity, interfering with their normal operation and even causing performance degradation or complete failure. Furthermore, strong electromagnetic radiation can pose a threat to human health; studies have shown that it can have varying degrees of negative effects on the central nervous system and other systems. Therefore, electromagnetic radiation has become another major source of pollution, in addition to air pollution, water pollution, and light pollution.

[0003] As an indispensable basic material for modern aircraft and weaponry, electromagnetic wave absorbing materials, or simply absorbing materials, now have applications far beyond military stealth and anti-stealth, and countermeasures and countermeasures. They are widely used in various fields, including human safety protection, interference elimination in microwave anechoic chambers, and electromagnetic interference protection for communication and navigation systems. Undoubtedly, absorbing materials play a crucial role in both civilian and defense fields such as electromagnetic radiation protection, microwave communication, and military stealth. Therefore, research on absorbing materials is not only related to people's lives but also to national security.

[0004] Electromagnetic wave absorbing materials absorb electromagnetic waves by dissipating the energy of the electromagnetic waves entering the material as heat or other forms of energy. Traditional absorbing materials are relatively mature, but they generally suffer from drawbacks such as narrow absorption bandwidth and weak absorption performance. Therefore, the development of highly efficient electromagnetic wave absorbing materials with high reflection loss, thin matching thickness, wide effective absorption bandwidth, and lightweight properties is a research hotspot in the field of electromagnetic functional materials both domestically and internationally.

[0005] Electromagnetic wave loss mechanisms include dielectric loss, conductive loss, and magnetic loss. Magnetic loss absorbing materials are typically Fe, Co, and Ni-based ferrites and their doped systems. Electrical loss absorbing materials are divided into resistive loss absorbing materials and dielectric loss absorbing materials, including conductive polymers and carbon-based materials such as graphene, carbon nanotubes, and carbon fibers. Both dielectric loss and magnetic loss absorbing materials have certain drawbacks in the preparation of high-performance absorbing materials due to their singular electromagnetic wave absorption mechanisms, including poor impedance matching and excessively high density. Dielectric absorbing materials suffer from excessively high dielectric properties, leading to poor impedance matching and hindering effective electromagnetic wave absorption, while magnetic loss absorbing materials are characterized by high density. Combining magnetic and dielectric loss mechanisms can avoid many of these drawbacks and produce highly efficient absorbing materials with stable absorption performance.

[0006] Metal-organic frameworks (MOFs) are a hot research topic in magnetoelectric composite absorbing materials. MOFs are self-assembled from metal ions and organic ligands, exhibiting a periodic network crystal structure, large specific surface area, and high porosity. The MOF structure plays a crucial role in material synthesis, serving not only as an excellent source of metals and carbon but also enabling the simultaneous occurrence of reduction and pyrolysis processes due to their unique microstructure. This synchronization mechanism ensures that the composite absorbing materials retain a series of advantageous properties of the MOF precursor after annealing, including the high dispersion of metal nanoparticles, the orderly microstructure, and the uniformity of chemical composition. These advantages enable MOF-derived composite absorbing materials to exhibit superior performance in multiple application areas. However, the problems of narrow bandwidth and weak loss in absorbing agents still exist; therefore, enhancing loss and broadening bandwidth remain urgent problems to be solved. Summary of the Invention

[0007] To address the problems of narrow effective absorption bandwidth and weak electromagnetic wave loss capability of existing microwave absorbing materials, the present invention aims to provide an iron-cobalt alloy carbon magnetoelectric composite microwave absorbing material, its preparation method, and its application.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows.

[0009] The first aspect of this invention provides a method for preparing an iron-cobalt alloy-carbon magnetoelectric composite microwave absorbing material, comprising the following steps:

[0010] Prussian blue analogues were prepared by co-precipitation reaction of potassium ferricyanide as carbon and nitrogen source and iron source with Co source and sodium citrate in a solvent system.

[0011] Then, under a protective atmosphere, the Prussian blue analogue was pyrolyzed at 400–600 °C to load Co nanoparticles onto the surface of a carbon-nitrogen matrix, thus obtaining an iron-cobalt alloy carbon magnetoelectric composite microwave absorbing material.

[0012] This invention primarily utilizes a co-precipitation method to obtain Prussian blue analogues. The C≡N groups in the metal coordination bonds serve as carbon and nitrogen sources, while Co and Fe magnetic elements act as magnetic components. Through pyrolysis, a composite material is obtained where an iron-cobalt alloy is uniformly distributed on a carbon-nitrogen matrix. Further control of the pyrolysis temperature alters the microstructure and internal structure of the product, thereby controlling the electromagnetic parameters of the material and yielding a microwave absorbing material with excellent impedance matching and attenuation properties. Sodium citrate plays a role in combining with the Co source, enabling a coordination reaction in the system.

[0013] Preferably, the pyrolysis temperature is 500℃, and the pyrolysis time is 1h to 3h. Subsequent experiments show that the pyrolysis temperature is between 400℃ and 600℃, and specifically at 500℃, the pyrolysis can achieve a wide effective absorption bandwidth of 7.76GHz with a relatively thin thickness of 2.5mm, and the minimum reflection loss at a thickness of 2.5mm is -43.2dB. This provides theoretical guidance for the preparation of magnetoelectric composite absorbing materials with wide bandwidth and strong absorption characteristics.

[0014] Preferably, the Co source is Co(NO3)2·6H2O or CoCl2·6H2O.

[0015] More preferably, the molar ratio of Co source to sodium citrate is approximately 3:4 to 5. For example, 3:4, 3:4.5, 3:5, etc.

[0016] Preferably, the specific reaction process is as follows:

[0017] Co source, sodium citrate, and a portion of solvent are mixed evenly to obtain solution A;

[0018] Mix potassium ferricyanide with the remaining solvent until homogeneous to obtain solution B;

[0019] Solution B and solution were mixed and allowed to stand for co-precipitation to form a precipitate; after washing and drying, a Prussian blue analogue was obtained.

[0020] Under a protective atmosphere, Prussian blue analogues are pyrolyzed at 400℃~600℃ to load Co and Fe nanoparticles onto the surface of a carbon-nitrogen matrix, resulting in an iron-cobalt alloy carbon magnetoelectric composite microwave absorbing material.

[0021] Preferably, the solvent is water.

[0022] More preferably, the ratio of the total volume of the solvent to the amount of the Co source is 150 mL to 200 mL: 3 mmol.

[0023] Preferably, the protective atmosphere is an argon atmosphere.

[0024] Preferably, the coprecipitation reaction is carried out at room temperature for 20 to 24 hours. The room temperature is 20°C to 30°C.

[0025] A second aspect of the present invention provides an iron-cobalt alloy-carbon magnetoelectric composite microwave absorbing material prepared by the preparation method described in the first aspect.

[0026] A third aspect of the present invention provides an application of the iron-cobalt alloy-carbon magnetoelectric composite absorbing material described in the second aspect in electromagnetic wave absorbing materials.

[0027] Preferably, the specific application method is as follows: mixing a nitrogen-doped carbon / cobalt-based microwave absorbing agent with a polymer matrix to prepare an electromagnetic wave absorbing coating material; wherein the polymer matrix is ​​polyurethane or epoxy resin. The polymer matrix is ​​not limited to polyurethane or epoxy resin, and can be selected according to actual needs.

[0028] Preferably, the nitrogen-doped carbon / cobalt-based microwave absorbing agent has a mass percentage of 40% in the electromagnetic wave absorbing material.

[0029] The beneficial effects of this invention are:

[0030] 1. This invention mainly uses C≡N groups in metal coordination bonds as carbon and nitrogen sources, and Co nanoparticles as magnetic particles. By controlling the pyrolysis temperature, the microstructure and internal structure of the product are changed, thereby controlling the electromagnetic parameters of the material and obtaining a microwave absorbing material with good impedance matching and attenuation performance.

[0031] 2. The Co and Fe nanoparticles of the present invention can be uniformly dispersed in a carbon matrix to form a rich heterogeneous interface, thereby greatly enhancing the interface polarization effect and optimizing electromagnetic impedance matching.

[0032] 3. This invention obtains an iron-cobalt alloy carbon magnetoelectric composite absorbing material by pyrolysis of a Prussian blue analogue. This absorbing material has excellent performance, with a minimum reflection loss of -43.2dB and an effective absorption bandwidth of 7.76GHz at a thickness of 2.5mm. This provides theoretical guidance for the preparation of magnetoelectric composite absorbing materials with wide bandwidth and strong absorption characteristics. Attached Figure Description

[0033] Figure 1 Co prepared in Example 1 0.7 Fe 0.3 Transmission electron microscope image of @C-400.

[0034] Figure 2 Co prepared in Example 1 0.7 Fe 0.3 EDS image of @C-400.

[0035] Figure 3Co prepared in Example 2 0.7 Fe 0.3 Transmission electron microscope image of @C-500.

[0036] Figure 4 Co prepared in Example 2 0.7 Fe 0.3 @C-500 EDS image.

[0037] Figure 5 Co prepared in Example 3 0.7 Fe 0.3 Transmission electron microscope image of @C-600.

[0038] Figure 6 Co prepared in Example 3 0.7 Fe 0.3 EDS chart for @C-600.

[0039] Figure 7 Co prepared in Examples 1 to 3 0.7 Fe 0.3 @C-400、Co 0.7 Fe 0.3 @C-500, Co 0.7 Fe 0.3 XRD pattern of @C-600.

[0040] Figure 8 Co prepared in Examples 1 to 3 0.7 Fe 0.3 @C-400、Co 0.7 Fe 0.3 @C-500, Co 0.7 Fe 0.3 Raman spectrum (a), XPS full spectrum (b), C 1s spectrum (c), N 1s spectrum (d), Fe 2p spectrum (e), and Co 2p spectrum (f) of @C-600.

[0041] Figure 9 Co prepared in Examples 1 to 3 0.7 Fe 0.3 @C-400、Co 0.7 Fe 0.3 @C-500, Co 0.7 Fe 0.3 N2 adsorption-desorption isotherms (a) and pore size distribution curves (b) of @C-600.

[0042] Figure 10 Co prepared in Examples 1 to 3 0.7 Fe 0.3 @C-400、Co 0.7Fe 0.3 @C-500, Co 0.7 Fe 0.3 @C-600 hysteresis loop at room temperature (a) and locally magnified hysteresis loop at room temperature (b).

[0043] Figure 11 Co prepared in Examples 1 to 3 0.7 Fe 0.3 @C-400、Co 0.7 Fe 0.3 @C-500, Co 0.7 Fe 0.3 Electromagnetic parameter diagram of @C-600. Among them, (a) is the real part of dielectric; (b) is the imaginary part of dielectric; (c) is the dielectric loss tangent; (d) is the real part of permeability; (e) is the imaginary part of permeability; (f) is the magnetic loss tangent.

[0044] Figure 12 Co prepared in Examples 1 to 3 0.7 Fe 0.3 @C-400、Co 0.7 Fe 0.3 @C-500, Co 0.7 Fe 0.3 The reflection loss diagram of @C-600 and the corresponding matching thickness and impedance matching performance diagram are shown. Among them, (a) is Co 0.7 Fe 0.3 @C-400 reflection loss diagram; (b) is Co 0.7 Fe 0.3 @C-500 reflection loss diagram; (c) is Co 0.7 Fe 0.3 @C-600 reflection loss diagram; (d) is Co 0.7 Fe 0.3 @C-400 matching thickness; (e) is Co 0.7 Fe 0.3 @C-500 matching thickness; (f) is Co 0.7 Fe 0.3 @C-600 matching thickness; (g) is Co 0.7 Fe 0.3 @C-400 impedance matching performance diagram; (h) is Co 0.7 Fe 0.3 @C-500 impedance matching performance diagram; (i) is Co 0.7 Fe 0.3 Impedance matching performance diagram of @C-600. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0046] The physicochemical properties of MOF-derived composite microwave absorbing materials can typically be customized by precisely controlling high-temperature annealing conditions and adjusting the ratio of metal ions to organic ligands in the precursor. Compared to other microwave absorbing agents, a major advantage of MOF-derived composite microwave absorbing materials is their ability to maintain the integrity of the carbon framework, thereby endowing the material with high conductivity, which greatly improves the efficiency of conductivity loss. Furthermore, by adjusting the annealing temperature, we can flexibly control the degree of graphitization in the material, further optimizing conductivity loss. It is worth noting that defects within the carbon matrix can also induce dipole polarization. In addition, carbon has low density, high mechanical strength, and high stability, which is not only beneficial for reducing the density of nanocomposite microwave absorbing materials but also improves the material's environmental adaptability. Another significant characteristic of MOF-derived materials is their high dispersibility. This characteristic allows metal oxides, metal nanoparticles, or other components to be uniformly dispersed in the carbon matrix, forming rich heterogeneous interfaces, thereby greatly enhancing the interfacial polarization effect and optimizing electromagnetic impedance matching. Given these numerous advantages, MOF-derived composite microwave absorbing materials show broad application prospects in the field of microwave absorbing materials.

[0047] Prussian blue analogues and their derivatives, abbreviated as PBA, are typical MOFs containing CN groups, denoted as -MII-CN-MIII-. They possess abundant porosity, large specific surface area, excellent intrinsic magnetic properties, and diverse structures and functions. They utilize the C≡N groups in the metal coordination bonds as carbon and nitrogen sources, and the cobalt-iron elements present in the system as magnetic metal sources. By controlling the pyrolysis temperature to alter the microstructure and internal structure of the products, the electromagnetic parameters of the material can be controlled, resulting in microwave absorbing materials with good impedance matching and attenuation performance.

[0048] To address the challenges in electromagnetic wave absorption, this invention primarily focuses on preparing an iron-cobalt alloy / carbon composite absorbing material obtained from the pyrolysis of Prussian blue. By adjusting the temperature to control the dielectric properties of Co0.7Fe0.3@C, its impedance matching frequency band is broadened, enabling the absorbing material to achieve high reflection loss and a wide effective absorption bandwidth with a relatively low matching thickness.

[0049] The technical solution of the present invention will be analyzed below through specific embodiments. Unless otherwise specified, the methods described in the following embodiments are conventional methods; unless otherwise specified, the reagents and materials can be purchased commercially.

[0050] In the following examples, C6H5Na3O7 is sodium citrate. K3[Fe(CN)6] is potassium ferricyanide. The room temperature is 20℃~30℃.

[0051] Example 1

[0052] A method for preparing an iron-cobalt alloy-carbon magnetoelectric composite microwave absorbing material includes the following steps:

[0053] Dissolve 3 mmol Co(NO3)2·6H2O and 4.5 mmol C6H5Na3O7 in 100 mL of deionized water and stir for 5 minutes to form solution A.

[0054] Dissolve 2 mmol of K3[Fe(CN)6] in 100 mL of deionized water to form solution B.

[0055] Solution B was added to solution A and stirred for 10 minutes. The resulting mixture was allowed to stand at room temperature for 24 hours, then thoroughly washed with ethanol and dried at 60°C for 12 hours. The obtained compound was heated to 400°C in an Ar atmosphere at a heating rate of 5°C / min, and then pyrolyzed at 400°C for two hours to obtain an iron-cobalt alloy carbon magnetoelectric composite microwave absorbing agent, named Co. 0.7 Fe 0.3 @C-400.

[0056] Example 2

[0057] A method for preparing an iron-cobalt alloy-carbon magnetoelectric composite microwave absorbing material includes the following steps:

[0058] Dissolve Co(NO3)2·6H2O (3 mmol) and C6H5Na3O7 (4.5 mmol) in 100 mL of deionized water and stir for 5 minutes to form solution A.

[0059] Dissolve K3[Fe(CN)6] (2 mmol) in 100 mL of deionized water to form solution B.

[0060] Solution B was added to solution A and stirred for 10 minutes. The resulting mixture was allowed to stand at room temperature for 24 hours, then thoroughly washed with ethanol and dried at 60°C for 12 hours. The obtained compound was heated to 500°C in an Ar atmosphere at a heating rate of 5°C / min, and then pyrolyzed at 500°C for two hours to obtain an iron-cobalt alloy carbon magnetoelectric composite microwave absorbing agent, named Co. 0.7 Fe 0.3 @C-500.

[0061] Example 3

[0062] A method for preparing an iron-cobalt alloy-carbon magnetoelectric composite microwave absorbing material includes the following steps:

[0063] Dissolve Co(NO3)2·6H2O (3 mmol) and C6H5Na3O7 (4.5 mmol) in 100 mL of deionized water and stir for 5 minutes to form solution A.

[0064] Dissolve K3[Fe(CN)6] (2 mmol) in 100 mL of deionized water to form solution B.

[0065] Solution B was added to solution A and stirred for 10 minutes. The resulting mixture was allowed to stand at room temperature for 24 hours, then thoroughly washed with ethanol and dried at 60°C for 12 hours. The obtained compound was heated to 600°C in an Ar atmosphere at a heating rate of 5°C / min, and then pyrolyzed at 600°C for two hours to obtain an iron-cobalt alloy carbon magnetoelectric composite microwave absorbing agent, named Co. 0.7 Fe 0.3 @C-600.

[0066] Example 4

[0067] A method for preparing an iron-cobalt alloy-carbon magnetoelectric composite microwave absorbing material includes the following steps:

[0068] Dissolve 3 mmol Co(NO3)2·6H2O and 4 mmol C6H5Na3O7 in 80 mL of deionized water and stir for 5 minutes to form solution A.

[0069] Dissolve 2 mmol of K3[Fe(CN)6] in 70 mL of deionized water to form solution B.

[0070] Solution B was added to solution A and stirred for 10 minutes. The resulting mixture was allowed to stand at room temperature for 20 hours, then thoroughly washed with ethanol and dried at 60°C for 12 hours. The resulting compound was heated to 500°C in an Ar atmosphere at a heating rate of 5°C / min, and then pyrolyzed at 500°C for 1 hour to obtain an iron-cobalt alloy-carbon magnetoelectric composite microwave absorber. SEM and TEM images showed that the iron-cobalt alloy-carbon magnetoelectric composite microwave absorber formed a hollow structure with uniformly distributed magnetic metal particles on its surface.

[0071] Example 5

[0072] A method for preparing an iron-cobalt alloy-carbon magnetoelectric composite microwave absorbing material includes the following steps:

[0073] Dissolve 3 mmol Co(NO3)2·6H2O and 5 mmol C6H5Na3O7 in 90 mL of deionized water and stir for 5 minutes to form solution A.

[0074] Dissolve 2 mmol of K3[Fe(CN)6] in 100 mL of deionized water to form solution B.

[0075] Solution B was added to solution A and stirred for 10 minutes. The resulting mixture was allowed to stand at room temperature for 24 hours, then thoroughly washed with ethanol and dried at 60°C for 12 hours. The resulting compound was heated to 500°C in an Ar atmosphere at a heating rate of 5°C / min, and then pyrolyzed at 500°C for 3 hours to obtain an iron-cobalt alloy carbon magnetoelectric composite microwave absorber. SEM and TEM images showed that the iron-cobalt alloy carbon magnetoelectric composite microwave absorber formed a hollow structure with uniformly distributed magnetic metal particles on its surface.

[0076] In the above embodiments of the present invention, the iron-cobalt alloy carbon magnetoelectric composite microwave absorbing agent is simply referred to as Co. 0.7 Fe 0.3 @C. Among them, Co 0.7 Fe 0.3 @C-400、Co 0.7 Fe 0.3 @C-500, Co 0.7 Fe 0.3 @C-600 are iron-cobalt alloy carbon magnetoelectric composite microwave absorbing agents obtained at different pyrolysis temperatures. The above embodiments of the present invention mainly utilize temperature changes to regulate the Co... 0.7 Fe 0.3 The dielectric properties of @C broaden its impedance matching frequency band, making Co 0.7 Fe 0.3 @C achieves higher reflection loss and wider effective absorption bandwidth with lower matching thickness.

[0077] The following describes the Co prepared in Examples 1-3 above. 0.7 Fe 0.3 @C-400、Co 0.7 Fe 0.3 @C-500, Co 0.7 Fe 0.3 The @C-600 was used for X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, BET aperture and specific surface area measurement, hysteresis loop, electromagnetic parameters, and electromagnetic wave absorption performance tests and characterization.

[0078] Test 1: Transmission electron microscopy and energy dispersive spectroscopy analysis.

[0079] Co prepared in Examples 1-3 0.7 Fe 0.3@C-400, Co 0.7 Fe 0.3 @C-500, Co 0.7 Fe 0.3 Transmission electron microscopy analysis and energy spectrum analysis were carried out on @C-600 respectively to study the crystal structure and crystal plane parameters of Co 0.7 Fe 0.3 @C, and high-resolution transmission electron microscopy and characterization were further carried out on it. The results are shown in Figures 1 to 6 . The TEM image is a transmission electron microscopy image; the EDS image is an energy spectrum image. The HRTEM image is a high-resolution transmission electron microscopy image; the SAED image is a selected area electron diffraction image.

[0080] Figure 1 The transmission electron microscopy image of Co 0.7 Fe 0.3 @C-400 prepared in Example 1. Among them, (a1) is the TEM image; (b1) is the HRTEM image; (c1) is the SAED image.

[0081] Figure 2 The EDS image (d1) of Co 0.7 Fe 0.3 @C-400 prepared in Example 1.

[0082] Figure 3 The transmission electron microscopy image of Co 0.7 Fe 0.3 @C-500 prepared in Example 2. Among them, (a2) is the TEM image; (b2) is the HRTEM image; (c2) is the SAED image.

[0083] Figure 4 The EDS image (d2) of Co 0.7 Fe 0.3 @C-500 prepared in Example 2.

[0084] Figure 5 The transmission electron microscopy image of Co 0.7 Fe 0.3 @C-600 prepared in Example 3. Among them, (a3) is the TEM image; (b3) is the HRTEM image; (c3) is the SAED image.

[0085] Figure 6 The EDS image (d3) of Co 0.7 Fe 0.3 @C-600 prepared in Example 3. [[ID=​​​​​​​​As can be seen from the EDS diagram, Co, Fe, C, N and O elements are evenly distributed on it.

[0087] Depend on Figure 3 As can be seen, at a pyrolysis temperature of 500℃, Co 0.7 Fe 0.3 The morphology of @C-500 is closer to that of rounded microcubes with non-uniform dimensions, and due to the increased pyrolysis temperature, the size of the rounded microcubes is ~50 nm. For example... Figure 3 The lattice fringe spacing of 0.202 nm corresponds to the crystal Co in the X-ray diffraction pattern. 0.7 Fe 0.3 The (110) crystal plane, with a lattice fringe spacing of 0.351 nm, corresponds to the (004) crystal plane of C, which determines that Co 0.7 Fe 0.3 @C-500 forms a hollow structure with uniformly distributed magnetic metal particles on its surface. The magnetic metal particles are Co. 0.7 Fe 0.3 ; combination Figure 4 The EDS diagram shows that it contains Co, Fe, C, N and O elements.

[0088] For Co 0.7 Fe 0.3 The C-600 was characterized using SEM and TEM, such as... Figure 5 and Figure 6 As shown, the microcubic structure is further disrupted compared to Co. 0.7 Fe 0.3 @C-500, Co 0.7 Fe 0.3 The rounded hollow structure of @C-600 collapsed, and its morphology evolved into a spherical shape, forming uniformly distributed magnetic metal particles (Co). 0.7 Fe 0.3 The carbon network; the lattice fringe spacing of 0.202 nm corresponds to the crystal Co in the X-ray diffraction pattern. 0.7 Fe 0.3 The (110) crystal plane, with a lattice fringe spacing of 0.334 nm, corresponds to the (004) crystal plane of C.

[0089] Test 2: XRD analysis.

[0090] Co prepared in Examples 1-3 0.7 Fe 0.3 @C-400、Co 0.7 Fe 0.3 @C-500, Co 0.7 Fe 0.3 X-ray diffraction analysis was performed on @C-600, and the results are shown below. Figure 7JCPDS#86-0502, JCPDS#26-1080, and JCPDS#48-1818 were used as controls. The XRD pattern is an X-ray diffraction pattern; the XRD analysis is an X-ray diffraction analysis.

[0091] Figure 7 Co prepared in Examples 1 to 3 0.7 Fe 0.3 @C-400、Co 0.7 Fe 0.3 @C-500, Co 0.7 Fe 0.3 XRD pattern of @C-600.

[0092] pass Figure 7 It can be seen that Co 0.7 Fe 0.3 The C-400 sample exhibits three diffraction peaks at 24.4°, 34.8°, and 39.0°, primarily corresponding to Co[Fe(CN)6]. 0.667 ·(H2O) 3.333 (JCPDS#86-0502). Co 0.7 Fe 0.3 @C-500 and Co 0.7 Fe 0.3 @C-600 all show diffraction peaks at 2θ = 44.9° and 65.5°, corresponding to Co 0.7 Fe 0.3 (JCPDS#48-1818) indicates that highly crystalline magnetic cobalt-iron alloy particles have formed in the material, and Co can be observed. 0.7 Fe 0.3 The increased intensity of the @C-600 diffraction peak indicates that a higher pyrolysis temperature is beneficial to improving the crystallization behavior of metal particles. In addition, Co... 0.7 Fe 0.3 @C-500 and Co 0.7 Fe 0.3 The presence of a diffraction peak at 2θ = 26° (JCPDS#26-1080) in the C-600 indicates the presence of graphitic carbon.

[0093] Test 3: Raman spectroscopy and XPS analysis.

[0094] Co prepared in Examples 1-3 0.7 Fe 0.3 @C-400、Co 0.7 Fe 0.3 @C-500, Co 0.7 Fe 0.3 Raman spectroscopy and X-ray photoelectron spectroscopy were performed using the C-600, and the results are shown below. Figure 8 XPS stands for X-ray photoelectron spectroscopy.

[0095] Figure 8 Co prepared in Examples 1 to 3 0.7 Fe 0.3 @C-400、Co 0.7 Fe 0.3 @C-500, Co 0.7 Fe 0.3 Raman spectrum (a), XPS full spectrum (b), C 1s spectrum (c), N 1s spectrum (d), Fe 2p spectrum (e), and Co 2p spectrum (f) of @C-600.

[0096] pass Figure 8 The results show that it is located at approximately 1350 cm⁻¹ in the Raman spectrum. -1 and 1580cm -1 The two typical broad peaks belong to the D band (disordered carbon) and the G band (graphite carbon), respectively. Generally, the G band reflects the degree of crystallinity and graphitization of carbon; a higher G band peak indicates better crystallinity and graphitization. The D band, on the other hand, reflects the lattice distortion / defects of carbon materials; a higher D band peak indicates more defects in the material. D / I G That is, the peak intensity of D (I) D ) and G peak intensity (I G The ratio of I to 2π provides important information about the defect density and graphitization degree in the material: D / I G A higher ratio indicates a higher proportion of defective or amorphous carbon structures relative to ordered or graphitized graphite structures in the sample. Conversely, a lower ratio indicates a lower proportion of defects or amorphous carbon structures relative to ordered graphite or graphitized structures. D / I G A smaller ratio indicates that the material is relatively pure, has fewer defects, and a higher degree of graphitization.

[0097] Depend on Figure 8 It can be seen that Co 0.7 Fe 0.3 The D-band and G-band peaks of @C-400 are not obvious. 0.7 Fe 0.3 @C-500, Co 0.7 Fe 0.3 The strength ratio of the D-band to the G-band of the @C-600 (I) D / I G The values ​​were 1.01 and 0.77 respectively, indicating that Co... 0.7 Fe 0.3 @C-500 contains a relatively large amount of amorphous carbon structures, while Co 0.7 Fe 0.3@C-600 has a better degree of graphitization and fewer defects.

[0098] The XPS full spectrum detected four characteristic peaks: C1s, N1s, O1s, Fe 2p, and Co 2p, indicating the presence of five elements: C, N, O, Fe, and Co. From the C1s spectrum, three peaks are located at ~284.6, 285.8, and 288.7 eV, corresponding to C-C, CN, and C=O bonds, respectively. Analysis of the N1s spectrum shows that Co... 0.7 Fe 0.3 In @C-400, nitrogen (N) mainly exists in the form of pyridine nitrogen, while Co... 0.7 Fe 0.3 @C-500 contains pyridine nitrogen, pyrrole nitrogen, and a small amount of nitrogen oxides. As the pyrolysis temperature increases, the heteroatom content decreases, indicating that Co... 0.7 Fe 0.3 The N1s spectral intensity of @C-600 decreases, and the diffraction peaks are weaker.

[0099] Test 4: N2 adsorption-desorption isotherms and pore size distribution curves.

[0100] Figure 9 Co prepared in Examples 1 to 3 0.7 Fe 0.3 @C-400、Co 0.7 Fe 0.3 @C-500, Co 0.7 Fe 0.3 N2 adsorption-desorption isotherms (a) and pore size distribution curves (b) of @C-600.

[0101] Isotherms can be further divided into six types, by Figure 9 It can be seen that the samples all belong to the rare Type III curves, with the isotherm curves concave and no inflection point. Co 0.7 Fe 0.3 The significant upward movement of the high-pressure portion of the @C-400 curve indicates uneven particle packing in the sample. Further observation of the hysteresis loop isotherm reveals that none of the three curves show a clear saturation adsorption plateau, suggesting a highly irregular pore structure. Co 0.7 Fe 0.3 @C-400、Co 0.7 Fe 0.3 @C-500, Co 0.7 Fe 0.3 The specific surface area of ​​@C-600 is 43.3007 m². 2 / g、28.7863m 2 / g and 26.1997m 2 / g, the specific surface area of ​​the material mainly depends on the particle size; the smaller the particle size, the larger the specific surface area. This indicates that the particle size gradually increases with increasing pyrolysis temperature. From the pore size distribution curves of the three samples, Co 0.7 Fe 0.3 @C-500 and Co 0.7 Fe 0.3 @C-600 exhibits a typical mesoporous structure, with pore sizes mostly around 3 nm, approaching the dimensions of microporous structures. In particular, Co... 0.7 Fe 0.3 @C-500 has some mesopores distributed around 40nm. According to Table 3-2, Co 0.7 Fe 0.3 @C-400、Co 0.7 Fe 0.3 @C-500, Co 0.7 Fe 0.3 The average pore sizes of @C-600 are 38.7615 nm, 24.1365 nm and 21.1758 nm, respectively, indicating that as the pyrolysis temperature increases, the porosity within the material is continuously improved and the pore size gradually decreases.

[0102] Test 5: Hysteresis loop diagram.

[0103] Figure 10 Co prepared in Examples 1 to 3 0.7 Fe 0.3 @C-400、Co 0.7 Fe 0.3 @C-500, Co 0.7 Fe 0.3 @C-600 hysteresis loop at room temperature (a) and locally magnified hysteresis loop at room temperature (b).

[0104] Depend on Figure 10 It can be seen that Co 0.7 Fe 0.3 The hysteresis loop of @C-400 is nearly flat, therefore it does not exhibit significant magnetism, while for Co... 0.7 Fe 0.3 @C-500 and Co 0.7 Fe 0.3 The @C-600 hysteresis loop exhibits characteristics typical of soft magnetic materials. Its Ms are 20.4802 emu / g and 112.3817 emu / g, respectively. Therefore, this indicates that Co... 0.7 Fe 0.3 @C-600 has strong magnetism, while Co 0.7 Fe 0.3 @C-500 compared to Co 0.7 Fe 0.3@C-600 has weak magnetism.

[0105] Test 6: Electromagnetic parameters.

[0106] Figure 11 Co prepared in Examples 1 to 3 0.7 Fe 0.3 @C-400、Co 0.7 Fe 0.3 @C-500, Co 0.7 Fe 0.3 Electromagnetic parameter diagram of @C-600. Among them, (a) is the real part of dielectric; (b) is the imaginary part of dielectric; (c) is the dielectric loss tangent; (d) is the real part of permeability; (e) is the imaginary part of permeability; (f) is the magnetic loss tangent.

[0107] Depend on Figure 11 It can be seen that ε′ represents the dielectric constant contributed by the polarization process, while ε″ includes conductivity loss and relaxation polarization loss. The higher the conductivity and polarization relaxation of the carbon dielectric, the larger ε″. As shown in Figure (a), ε′ decreases with increasing frequency, but ε′ increases significantly with increasing pyrolysis temperature. Excessively high ε′ can cause impedance mismatch in the material, preventing electromagnetic waves from effectively absorbing into the material. In Figure (b), Co... 0.7 Fe 0.3 The ε″ curve of the @C-400 composite material remains relatively stable, and the value tends to 0. Co 0.7 Fe 0.3 The decrease in ε″ of @C500 with increasing frequency can be attributed to the polarization relaxation process. 0.7 Fe 0.3 The ε″ of @C-600 increases with increasing frequency because higher pyrolysis temperatures lead to more structural defects, triggering more dipole polarization; therefore, ε″ increases with increasing temperature. As shown in Figure (c), Co... 0.7 Fe 0.3 @C-600's tanδ ε The highest value indicates that it has the strongest dielectric loss capability.

[0108] like Figure 11 μ′ represents the real part of the complex permeability; μ″ represents the imaginary part of the complex permeability. Figures (d) and (e) are the curves showing the variation of the real part μ′ and the imaginary part μ″ of the complex permeability with frequency, respectively. It can be seen that Co 0.7 Fe 0.3 The μ′ values ​​of @C all fluctuate around 1.0, indicating that their magnetic storage performance differences are small. In contrast, Co 0.7 Fe 0.3 @C-500 is superior. Co... 0.7 Fe 0.3@C-500 has the highest μ″ value, indicating that it has the best magnetic loss capability for Co. 0.7 Fe 0.3 @C-400、Co 0.7 Fe 0.3 The μ″ of @C-600 shows a negative value, which may be caused by the Fabry-Perot resonance of the material during the test. (f) In the figure, tanδ μ This represents magnetic loss. The tanδ of the three samples was analyzed. μ It can be seen that Co 0.7 Fe 0.3 @c-500 has the best magnetic loss capability.

[0109] Test 7: Wave absorption performance analysis.

[0110] Co prepared in Examples 1 to 3 0.7 Fe 0.3 @C-400、Co 0.7 Fe 0.3 @C-500, Co 0.7 Fe 0.3 The absorption performance of the C-600 samples was analyzed. Electromagnetic parameters for each sample were input into MATLAB, with a thickness of 1-5 mm and a frequency range of 2-18 GHz. Reflection loss diagrams for these three samples were obtained through calculation; the results are shown below. Figure 12 .

[0111] Figure 12 Co prepared in Examples 1 to 3 0.7 Fe 0.3 @C-400、Co 0.7 Fe 0.3 @C-500, Co 0.7 Fe 0.3 The reflection loss diagram of @C-600 and the corresponding matching thickness and impedance matching performance diagram are shown. Among them, (a) is Co 0.7 Fe 0.3 @C-400 reflection loss diagram; (b) is Co 0.7 Fe 0.3 @C-500 reflection loss diagram; (c) is Co 0.7 Fe 0.3 @C-600 reflection loss diagram; (d) is Co 0.7 Fe 0.3 @C-400 matching thickness; (e) is Co 0.7 Fe 0.3 @C-500 matching thickness; (f) is Co 0.7 Fe 0.3 @C-600 matching thickness; (g) is Co0.7 Fe 0.3 @C-400 impedance matching performance diagram; (h) is Co 0.7 Fe 0.3 @C-500 impedance matching performance diagram; (i) is Co 0.7 Fe 0.3 Impedance matching performance diagram of @C-600. RL represents reflection loss. min This represents the minimum reflection loss. m To simulate thickness. Z m For impedance matching.

[0112] Depend on Figure 12 It can be seen that the Co prepared in Example 2 0.7 Fe 0.3 The C-500 magnetoelectric composite absorbing material, with a thickness of 2.5 mm, exhibits a minimum reflection loss of -43.2 dB and an effective absorption bandwidth of 7.76 GHz. This demonstrates that the embodiments of the present invention have successfully prepared a absorbing material with excellent performance, providing theoretical guidance for the preparation of magnetoelectric composite absorbing materials with wide bandwidth and strong absorption characteristics.

[0113] In summary, the above-described embodiments of the present invention primarily utilize the C≡N groups in metal coordination bonds as carbon and nitrogen sources, and Co nanoparticles as magnetic particles. By controlling the pyrolysis temperature, the microstructure and internal structure of the products are altered, thereby controlling the electromagnetic parameters of the material and obtaining a microwave absorbing material with excellent impedance matching and attenuation performance. This not only provides a novel design approach for the research of high-loss, broadband microwave absorbing materials but also offers necessary innovative technical support and theoretical backing for the simple preparation of efficient microwave absorbing agents, possessing significant academic and practical value.

[0114] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing an iron-cobalt alloy-carbon magnetoelectric composite microwave absorbing material, characterized in that, Includes the following steps: Prussian blue analogues were prepared by co-precipitation reaction of potassium ferricyanide, a Co source, and sodium citrate in a solvent system, using potassium ferricyanide as the carbon and nitrogen source and iron source; the molar ratio of Co source to sodium citrate was 3:4-5; the Co source was Co(NO3)2·6H2O. Then, under a protective atmosphere, the Prussian blue analogue was pyrolyzed at 500℃, causing Co nanoparticles to be loaded onto the surface of a carbon-nitrogen matrix, forming a hollow structure with uniformly distributed magnetic metal particles. The magnetic metal particles are Co. 0.7 Fe 0.3 Iron-cobalt alloy carbon magnetoelectric composite microwave absorbing material was obtained.

2. The preparation method of the iron-cobalt alloy carbon magnetoelectric composite microwave absorbing material according to claim 1, characterized in that, The pyrolysis time is 1 hour to 3 hours.

3. The preparation method of the iron-cobalt alloy carbon magnetoelectric composite microwave absorbing material according to claim 1, characterized in that, The specific reaction process is as follows: Co source, sodium citrate, and a portion of solvent are mixed evenly to obtain solution A; Mix potassium ferricyanide with the remaining solvent until homogeneous to obtain solution B; Solution B and solution A were mixed and allowed to stand for co-precipitation to form a precipitate; after washing and drying, a Prussian blue analogue was obtained. Under a protective atmosphere, a Prussian blue analogue was pyrolyzed at 500℃ to load Co nanoparticles onto the surface of a carbon-nitrogen matrix, forming a hollow structure with uniformly distributed magnetic metal particles. The magnetic metal particles were Co. 0.7 Fe 0.3 Iron-cobalt alloy carbon magnetoelectric composite microwave absorbing material was obtained.

4. The preparation method of the iron-cobalt alloy carbon magnetoelectric composite microwave absorbing material according to claim 3, characterized in that, The solvent is water; the protective atmosphere is argon.

5. The preparation method of the iron-cobalt alloy carbon magnetoelectric composite microwave absorbing material according to claim 4, characterized in that, The ratio of the total volume of solvent to the amount of Co source used is 150 mL to 200 mL: 3 mmol.

6. The preparation method of the iron-cobalt alloy carbon magnetoelectric composite microwave absorbing material according to claim 3, characterized in that, The coprecipitation reaction was carried out at room temperature for 20 to 24 hours.

7. A cobalt-iron alloy carbon magnetoelectric composite microwave absorbing material prepared by the preparation method according to any one of claims 1 to 6, characterized in that, The iron-cobalt alloy carbon magnetoelectric composite absorbing material has a hollow structure with uniformly distributed magnetic metal particles on its surface. The magnetic metal particles are Co. 0.7 Fe 0.3 .

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