Iron-cobalt alloy carbon magnetoelectric composite wave-absorbing material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of wave-absorbing materials, in particular to an iron-cobalt alloy carbon magnetoelectric composite wave-absorbing material and a preparation method and application thereof. The specific preparation method comprises the following steps: by taking potassium ferricyanide as a carbon source and a nitrogen source, carrying out a co-precipitation reaction with a Co source and sodium citrate in a solvent system to prepare the Prussian blue analogue; and then under a protective atmosphere, pyrolyzing the Prussian blue analogue at 400-600 DEG C, so that the Co nanoparticles are loaded on the surface of the carbon-nitrogen matrix to obtain the iron-cobalt alloy carbon magnetoelectric composite wave-absorbing material. According to the invention, C = N groups in metal coordinate bonds are mainly used as a carbon source and a nitrogen source, Co nanoparticles are used as magnetic particles, and the pyrolysis temperature is regulated to change the microstructure and the internal structure of the product, so that the regulation of electromagnetic parameters of the material is realized, and the wave-absorbing material with good impedance matching and attenuation performance is obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of wave absorbing materials, and in particular to an iron-cobalt alloy carbon magneto-electric composite wave absorbing material and a preparation method and application thereof. Background Art

[0002] Driven by the wave of electronicization 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 continue to concentrate in a limited space, the electromagnetic energy density continues to rise, leading to a significant deterioration of the electromagnetic environment, which in turn causes the problem of electromagnetic pollution. When electronic and communication equipment are running, the electromagnetic waves they release will have an adverse effect on other surrounding electronic instruments, interfere with their normal operation, and even cause performance degradation or complete failure. In addition, strong electromagnetic radiation may also pose a threat to human health. Studies have shown that it will have varying degrees of negative effects on the human central nervous system. 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 weapons and equipment, electromagnetic wave absorbing materials, or absorbing materials for short, have now been applied far beyond the fields of military stealth and anti-stealth, confrontation and anti-confrontation, and have been widely used in human safety protection, microwave darkroom equipment interference elimination, communication and navigation system electromagnetic interference protection and other aspects. Undoubtedly, absorbing materials play a vital role in civil and national defense fields such as electromagnetic radiation protection, microwave communications, and military stealth. Therefore, the research on absorbing materials is not only related to people's lives, but also to the security of a country.

[0004] Electromagnetic wave absorbing materials achieve the purpose of absorbing electromagnetic waves by dissipating the electromagnetic wave energy entering the material as heat or other forms of energy. Traditional absorbing materials are relatively mature, but they generally have shortcomings such as narrow absorption bandwidth and weak absorption performance. Therefore, the preparation of efficient electromagnetic wave absorbing materials with strong reflection loss, thin matching thickness, wide effective absorption bandwidth and light weight is a research hotspot in the field of electromagnetic functional materials at home and abroad.

[0005] The loss mechanism of electromagnetic waves includes dielectric loss, conductive loss and magnetic loss. Magnetic loss absorbing materials are usually 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 conductive polymers and carbon-based materials such as graphene, carbon nanotubes, and carbon fibers. Dielectric loss absorbing materials and magnetic loss absorbing materials have certain defects in the preparation of high-performance absorbing materials due to their single electromagnetic wave absorption mechanism, including poor impedance matching performance and excessive density. Dielectric absorbing materials have the problem of too high dielectric, resulting in poor impedance matching and the inability to achieve effective electromagnetic wave absorption, while magnetic loss absorbing materials have the common problem of high density. Combining the magnetic loss and dielectric loss mechanisms can avoid many defects and prepare high-efficiency absorbing materials with relatively stable absorbing performance.

[0006] Metal organic framework, referred to as MOF, is one of the hot spots in the research of magnetoelectric composite absorbers. MOF is self-assembled by metal ions and organic ligands. It is a material with periodic network crystal structure, large specific surface area and high porosity. MOF structure plays a key role in material synthesis. It is not only a good provider of metal source and carbon source, but also its unique microstructure enables the reduction reaction and pyrolysis process to proceed simultaneously. This synchronization mechanism ensures that the composite absorber can retain a series of advantageous properties of MOF precursor after annealing, including the high dispersion of metal nanoparticles, the regularity and orderliness of microstructure, and the uniformity of chemical composition. These advantages make MOF-derived composite absorbers show excellent performance in multiple application fields. However, the problem of narrow bandwidth and weak loss of absorbers still exists, so enhancing loss and broadening bandwidth are still urgent problems to be solved. Summary of the invention

[0007] In order to solve the problems of narrow effective absorption bandwidth and weak electromagnetic wave loss capacity of existing absorbing materials, the purpose of the present invention is to provide an iron-cobalt alloy carbon magneto-electric composite absorbing material and a preparation method and application thereof.

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

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

[0010] Potassium ferrocyanide was used as a carbon, nitrogen and iron source, and coprecipitated with a Co source and sodium citrate in a solvent system to prepare a Prussian blue analogue.

[0011] Then, the Prussian blue analogue is pyrolyzed at 400-600 DEG C under a protective atmosphere to load Co nanoparticles on the surface of the carbon-nitrogen matrix to obtain an iron-cobalt alloy carbon magneto-electric composite wave absorbing material.

[0012] The invention mainly obtains a Prussian blue analogue by a coprecipitation method, wherein the C≡N group in the metal coordination bond is used as a carbon source and a nitrogen source, and Co and Fe magnetic elements are used as magnetic components, and a composite material in which an iron-cobalt alloy is uniformly distributed on a carbon-nitrogen matrix is ​​obtained by pyrolysis, and the pyrolysis temperature is further controlled to change the microscopic morphology and internal structure of the product, so as to realize the control of the electromagnetic parameters of the material, and obtain an absorbing material with good impedance matching and attenuation performance. The role of sodium citrate is to combine with the Co source so that the system can undergo a coordination reaction.

[0013] Preferably, the pyrolysis temperature is preferably 500°C, and the pyrolysis time is 1h to 3h. Subsequent experiments show that the pyrolysis temperature is 400°C to 600°C, wherein at 500°C, pyrolysis can obtain a wider effective absorption bandwidth of 7.76GHz for electromagnetic wave absorption performance at a thinner 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 the Co source to sodium citrate is about 3:4 to 5. For example, 3:4, 3:4.5, 3:5, etc.

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

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

[0018] Mix potassium ferrocyanide and the remaining solvent evenly to obtain solution B;

[0019] The solution B and the solution are mixed and allowed to stand for a coprecipitation reaction to form a precipitate; after washing and drying, a Prussian blue analogue is obtained;

[0020] Under a protective atmosphere, a Prussian blue analogue is pyrolyzed at 400-600°C to load Co and Fe nanoparticles on the surface of a carbon-nitrogen matrix to obtain an iron-cobalt alloy carbon magneto-electric composite wave absorbing material.

[0021] Preferably, the solvent is water.

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

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

[0024] Preferably, the coprecipitation reaction temperature is room temperature, the coprecipitation reaction time is 20h to 24h, and the room temperature is 20°C to 30°C.

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

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

[0027] Preferably, the specific application method is: mixing the nitrogen-doped carbon / cobalt-based absorber 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 also be selected according to actual needs.

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

[0029] Beneficial effects of the present invention:

[0030] 1. The present invention mainly uses the C≡N group in the metal coordination bond as the carbon source and nitrogen source, and Co nanoparticles as the magnetic particles. By adjusting the pyrolysis temperature, the microscopic morphology and internal structure of the product are changed to achieve the regulation of the electromagnetic parameters of the material, and obtain an absorbing material with good impedance matching and attenuation performance.

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

[0032] 3. The present invention obtains an iron-cobalt alloy carbon magneto-electric composite absorbing material by pyrolyzing a Prussian blue analogue. The absorbing material has excellent performance. At a thickness of 2.5 mm, the minimum reflection loss is -43.2 dB, and the effective absorption bandwidth is 7.76 GHz. This provides theoretical guidance for the preparation of magneto-electric composite absorbing materials with wide-band and strong absorption characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0034] Figure 2 The Co prepared in Example 1 0.7 Fe 0.3 @EDS diagram 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 @EDS graph of C-500.

[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 diagram of 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] Fig. 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 isotherm (a) and pore size distribution curve (b) of @C-600.

[0042] Fig.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 a partially enlarged hysteresis loop at room temperature (b).

[0043] Fig.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 @C-600 electromagnetic parameter diagram. Among them, (a) is the real part of dielectric, (b) is the imaginary part of dielectric, (c) dielectric loss tangent, (d) real part of magnetic permeability, (e) imaginary part of magnetic permeability, and (f) magnetic loss tangent.

[0044] Fig.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 @C-600 reflection loss diagram and corresponding matching thickness and impedance matching performance diagram. Among them, (a) is Co 0.7 Fe 0.3 @C-400 reflection loss diagram; (b) 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 @C-600 impedance matching performance diagram. DETAILED DESCRIPTION

[0045] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present invention.

[0046] The physical and chemical properties of MOF-derived composite absorbers can usually be customized by precisely controlling high-temperature annealing conditions and adjusting the ratio of metal ion types and organic ligands in the precursor. Compared with other absorbers, a major advantage of MOF-derived composite absorbers is that they can maintain the integrity of the carbon skeleton, thereby giving the material a higher conductivity, which greatly promotes the efficiency of conductivity loss. In addition, by adjusting the annealing temperature, we can flexibly control the degree of graphitization of the material, thereby further optimizing the conductivity loss. It is worth noting that defects inside the carbon matrix can also induce dipole polarization. In addition, carbon has the characteristics of low density, high mechanical strength and high stability, which is not only beneficial to reducing the density of nanocomposite absorbers, but also can improve the environmental adaptability of materials. Another significant feature of MOF-derived materials is their high dispersibility, which enables metal oxides, metal nanoparticles or other components to be evenly dispersed in the carbon matrix, forming a rich heterogeneous heterogeneous interface, thereby greatly enhancing the interface polarization effect and optimizing the electromagnetic impedance matching. In view of the above advantages, MOF-derived composite absorbers have shown broad application prospects in the field of absorbers.

[0047] Among them, Prussian blue analogs and their derivatives, referred to as PBA, are a typical MOF containing CN groups, which are expressed as -MII-CN-MIII-. They have rich pore structures, large specific surface areas, good inherent magnetic properties, and diverse structures and functions. They use the C≡N groups in metal coordination bonds as carbon and nitrogen sources, and use the cobalt and iron elements contained in the system as magnetic metal sources. By adjusting the pyrolysis temperature to change the microscopic morphology and internal structure of the product, the electromagnetic parameters of the material can be adjusted to obtain an absorbing material with good impedance matching and attenuation performance.

[0048] In view of the difficulties faced in the field of electromagnetic wave absorption, the present invention mainly prepares an iron-cobalt alloy / carbon composite absorbing material obtained by pyrolyzing Prussian blue. By changing the temperature to control the dielectric properties of Co0.7Fe0.3@C, its impedance matching frequency band is broadened, so that the absorbing material achieves higher reflection loss and wider effective absorption bandwidth at a lower matching thickness.

[0049] The technical solution of the present invention is analyzed by specific examples. The methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials are commercially available unless otherwise specified.

[0050] In the following examples, C6H5Na3O7 is sodium citrate. K3[Fe(CN)6] is potassium ferrocyanide. The room temperature is 20°C to 30°C.

[0051] Example 1

[0052] A method for preparing an iron-cobalt alloy carbon magneto-electric composite wave absorbing material comprises the following steps:

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

[0054] 2 mmol K3[Fe(CN)6] was dissolved in 100 ml 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 fully washed with ethanol and dried at 60°C for 12 hours. The resulting compound was heated to 400°C at a heating rate of 5°C / min in an Ar atmosphere, and then pyrolyzed at 400°C for two hours to obtain an iron-cobalt alloy carbon magnetoelectric composite absorber. The resulting product was named Co 0.7 Fe 0.3 @C-400.

[0056] Example 2

[0057] A method for preparing an iron-cobalt alloy carbon magneto-electric composite wave absorbing material comprises the following steps:

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

[0059] K3[Fe(CN)6] (2 mmol) was dissolved 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 fully washed with ethanol and dried at 60°C for 12 hours. The resulting compound was heated to 500°C at a heating rate of 5°C / min in an Ar atmosphere, and then pyrolyzed at 500°C for two hours to obtain an iron-cobalt alloy carbon magnetoelectric composite absorber. The resulting product was named Co 0.7 Fe 0.3 @C-500.

[0061] Example 3

[0062] A method for preparing an iron-cobalt alloy carbon magneto-electric composite wave absorbing material comprises the following steps:

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

[0064] K3[Fe(CN)6] (2 mmol) was dissolved 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 fully washed with ethanol and dried at 60°C for 12 hours. The resulting compound was heated to 600°C at a heating rate of 5°C / min in an Ar atmosphere, and then pyrolyzed at 600°C for two hours to obtain an iron-cobalt alloy carbon magnetoelectric composite absorber. The resulting product was named Co 0.7 Fe 0.3 @C-600.

[0066] Example 4

[0067] A method for preparing an iron-cobalt alloy carbon magneto-electric composite wave absorbing material comprises the following steps:

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

[0069] 2 mmol K3[Fe(CN)6] was dissolved in 70 ml 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 fully washed with ethanol and dried at 60°C for 12 hours. The resulting compound was heated to 500°C at a heating rate of 5°C / min in an Ar atmosphere, and then pyrolyzed at 500°C for 1 hour to obtain an iron-cobalt alloy carbon magneto-electric composite absorber. The SEM and TEM images showed that the iron-cobalt alloy carbon magneto-electric composite absorber formed a hollow structure with uniformly distributed magnetic metal particles on the surface.

[0071] Example 5

[0072] A method for preparing an iron-cobalt alloy carbon magneto-electric composite wave absorbing material comprises the following steps:

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

[0074] 2 mmol K3[Fe(CN)6] was dissolved in 100 ml 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 fully washed with ethanol and dried at 60°C for 12 hours. The resulting compound was heated to 500°C at a heating rate of 5°C / min in an Ar atmosphere, and then pyrolyzed at 500°C for 3 hours to obtain an iron-cobalt alloy carbon magneto-electric composite absorber. The SEM and TEM images showed that the iron-cobalt alloy carbon magneto-electric composite absorber formed a hollow structure with uniformly distributed magnetic metal particles on the surface.

[0076] In the above embodiment of the present invention, the iron-cobalt alloy carbon magneto-electric composite absorber is 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 absorbers obtained at different pyrolysis temperatures. The above embodiments of the present invention mainly use the change of temperature to control the Co 0.7 Fe 0.3 @C's dielectric properties broaden its impedance matching frequency band, making Co 0.7 Fe 0.3 @C can achieve higher reflection loss and wider effective absorption bandwidth at lower matching thickness.

[0077] The following is the 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 performs X-ray diffraction, X-ray photoelectron spectroscopy, Raman, BET aperture test and specific surface area test, hysteresis loop, electromagnetic parameters, electromagnetic wave absorption performance and other tests and characterizations.

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

[0079] The 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 were used for transmission electron microscopy analysis and energy spectrum analysis to study Co 0.7 Fe 0.3 The crystal structure and crystal plane parameters of @C were further characterized by high-resolution transmission electron microscopy. Figures 1 to 6 TEM is a transmission electron microscope image; EDS is an energy spectrum image; HRTEM is a high-resolution transmission electron microscope image; SAED is a selected area electron diffraction image.

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

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

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

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

[0084] Figure 5 Co prepared in Example 3 0.7 Fe 0.3 @C-600 transmission electron microscope images. (a3) ​​is the TEM image; (b3) is the HRTEM image; (c3) is the SAED image.

[0085] Figure 6 Co prepared in Example 3 0.7 Fe 0.3 @EDS pattern of C-600 (d3).

[0086] like Figure 1 As shown, Co 0.7 Fe 0.3 @C-400 is a hollow cube structure. Figure 2From the EDS image, it can be seen that Co, Fe, C, N and O elements are evenly distributed on it.

[0087] Depend on Figure 3 It can be seen that at the pyrolysis temperature of 500 °C, Co 0.7 Fe 0.3 The morphology of @C-500 is closer to rounded microcubes with uneven sizes, and due to the increase in pyrolysis temperature, the size of the rounded microcubes is ∼50 nm. Figure 3 , the lattice fringe spacing of 0.202nm corresponds to the crystal Co in the X-ray diffraction pattern 0.7 Fe 0.3 The (110) crystal plane of Co, with a lattice fringe spacing of 0.351 nm, corresponds to the (004) crystal plane of C. 0.7 Fe 0.3 @C-500 forms a hollow structure with uniformly distributed magnetic metal particles on the surface. The magnetic metal particles are Co 0.7 Fe 0.3 ; Combine Figure 4 From the EDS diagram, it can be seen that it contains Co, Fe, C, N and O elements.

[0088] About Co 0.7 Fe 0.3 @C-600 was characterized by SEM and TEM, such as Figure 5 and Figure 6 As shown, the microcube structure is further destroyed 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 the morphology developed into a spherical shape, forming a uniformly distributed magnetic metal particle Co 0.7 Fe 0.3 The carbon network; the lattice fringe spacing of 0.202nm corresponds to the X-ray diffraction pattern of crystalline Co 0.7 Fe 0.3 The (110) crystal plane and the lattice fringe spacing of 0.334nm correspond to the (004) crystal plane of C.

[0089] Test 2: XRD analysis.

[0090] The 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 were subjected to X-ray diffraction analysis, the results are shown in Figure 7Among them, JCPDS#86-0502, JCPDS#26-1080, and JCPDS#48-1818 are used as controls. XRD pattern is X-ray diffraction pattern; XRD analysis is 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 @C-400 sample 2θ shows three diffraction peaks at 24.4°, 34.8°, and 39.0°, mainly corresponding to Co[Fe(CN)6] 0.667 ·(H2O) 3.333 (JCPDS#86-0502). 0.7 Fe 0.3 @C-500 and Co 0.7 Fe 0.3 @C-600 has diffraction peaks at 2θ=44.9° and 65.5°, corresponding to Co 0.7 Fe 0.3 (JCPDS#48-1818), indicating that magnetic cobalt-iron alloy particles with high crystallinity are formed in the material. At the same time, Co 0.7 Fe 0.3 The diffraction peak intensity of @C-600 increases, indicating that higher pyrolysis temperature is conducive to the improvement of the crystallization behavior of metal particles. 0.7 Fe 0.3 @C-500 and Co 0.7 Fe 0.3 @C-600 has a diffraction peak at 2θ=26° (JCPDS#26-1080), indicating the presence of graphite carbon.

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

[0094] The 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 Raman spectroscopy and X-ray photoelectron spectroscopy were performed respectively. The results are shown in Figure 8 . XPS is 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 showed that the Raman spectrum was located at about 1350 cm -1 and 1580cm -1 The two typical broad peaks belong to the D band (disordered carbon) and the G band (graphite carbon). Generally, the G band reflects the degree of crystallization and graphitization of carbon. The higher the peak value of the G band, the better the crystallinity and graphitization of the sample; while the D band reflects the lattice distortion / defects of the carbon material. The higher the peak value in the D band, the more defects there are in the material. D / I G That is, the D peak intensity (I D ) and G peak intensity (I G ) provides important information about the defect density and degree of graphitization in the material: I D / I G The larger the ratio, the higher the proportion of defects or amorphous carbon structures relative to ordered graphite or graphitized structures in the sample. 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 @C-400's D-band and G-band peaks are not obvious. 0.7 Fe 0.3 @C-500, Co 0.7 Fe 0.3 @C-600 D-band and G-band intensity ratio (I D / I G ) were 1.01 and 0.77, which indicates that Co 0.7 Fe 0.3 @C-500 has relatively more amorphous carbon structure, while Co 0.7 Fe 0.3@C-600 has better graphitization and fewer defects.

[0098] Four characteristic peaks, C1s, N 1s, O 1s, Fe 2p, and Co 2p, were detected in the XPS spectrum, 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 CC, CN, and C=O bonds. By analyzing the N1s spectrum, it can be seen that Co 0.7 Fe 0.3 @C-400 N element mainly exists in the form of pyridine nitrogen, Co 0.7 Fe 0.3 @C-500 contains pyridinic nitrogen, pyrrolic nitrogen and a small amount of nitrogen oxide. As the pyrolysis temperature increases, the heteroatom content decreases. 0.7 Fe 0.3 The N1s spectrum intensity of @C-600 decreases and the diffraction peak is weak.

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

[0100] Fig. 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 isotherm (a) and pore size distribution curve (b) of @C-600.

[0101] Isotherms can be divided into six types, Fig. 9 It can be seen that the samples all belong to the rare type III curve, with the isotherms concave and no inflection point. 0.7 Fe 0.3 @C-400 The high pressure part rises significantly, which indicates that the sample particles are not evenly packed. Further observation of the hysteresis loop isotherms shows that none of the three curves have an obvious saturated adsorption platform, which indicates that the pore structure is very irregular. 0.7 Fe 0.3 @C-400, Co 0.7 Fe 0.3 @C-500, Co 0.7 Fe 0.3 @C-600 has a specific surface area of ​​43.3007m 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 shows that as the pyrolysis temperature increases, the particle size gradually increases. 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 is a typical mesoporous structure, with pore sizes mostly distributed around 3nm, close to the microporous structure. 0.7 Fe 0.3 @C-500 has some mesopores with a size of about 40 nm. 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 38.7615nm, 24.1365nm and 21.1758nm, respectively, which indicates that as the pyrolysis temperature increases, the voids in the material continue to improve and the pore size gradually decreases.

[0102] Test 5: Hysteresis loop plot.

[0103] Fig.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 a partially enlarged hysteresis loop at room temperature (b).

[0104] Depend on Fig.10 It can be seen that Co 0.7 Fe 0.3 @C-400's hysteresis loop is close to straight, so it does not have obvious magnetism. 0.7 Fe 0.3 @C-500 and Co 0.7 Fe 0.3 @C-600 hysteresis loop shows the characteristics of typical soft magnetic materials. Its Ms is 20.4802emu / g and 112.3817emu / g respectively. Therefore, it shows that Co 0.7 Fe 0.3 @C-600 has strong magnetic properties, and Co 0.7 Fe 0.3 @C-500 vs Co 0.7 Fe 0.3@C-600 has weaker magnetism.

[0105] Test 6: Electromagnetic parameters.

[0106] Fig.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 @C-600 electromagnetic parameter diagram. Among them, (a) is the real part of dielectric, (b) is the imaginary part of dielectric, (c) dielectric loss tangent, (d) real part of magnetic permeability, (e) imaginary part of magnetic permeability, and (f) magnetic loss tangent.

[0107] Depend on Fig.11 It can be seen that ε′ represents the dielectric constant contributed by the polarization process, and ε″ includes conductivity loss and relaxation polarization loss. The higher the conductivity and polarization relaxation of the carbon medium, the larger the ε″. As shown in Figure (a), ε′ decreases with increasing frequency, but ε′ increases significantly with increasing pyrolysis temperature. Too high ε′ will cause material impedance mismatch, resulting in the inability of electromagnetic waves to enter the material for effective absorption. In Figure (b), Co 0.7 Fe 0.3 The ε″ curve of @C-400 composite material remains relatively stable, and its value tends to 0. 0.7 Fe 0.3 The ε″ of @C500 decreases with increasing frequency, which can be attributed to the polarization relaxation process. 0.7 Fe 0.3 @C-600's ε″ increases with increasing frequency. This is because high pyrolysis temperature leads to more structural defects, which triggers more dipole polarization. Therefore, ε″ increases with increasing temperature. As can be seen from Figure (c), Co 0.7 Fe 0.3 @tanδ of C-600 ε The highest value indicates that it has the strongest dielectric loss capability.

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

[0109] Test 7: Wave absorbing performance analysis.

[0110] The 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 were used to analyze the absorption performance. The electromagnetic parameters of each sample were input into MATLAB, and the fitting thickness was between 1-5mm and the frequency range was between 2-18GHz. The reflection loss diagrams of the three samples can be obtained by calculation. The results are shown in Fig.12 .

[0111] Fig.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 @C-600 reflection loss diagram and corresponding matching thickness and impedance matching performance diagram. Among them, (a) is Co 0.7 Fe 0.3 @C-400 reflection loss diagram; (b) 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 @C-600 impedance matching performance diagram. RL is the reflection loss. min is the minimum reflection loss. m is the simulated thickness. m For impedance matching.

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

[0113] The above analysis shows that the above embodiments of the present invention mainly use the C≡N group in the metal coordination bond as the carbon source and nitrogen source, use Co nanoparticles as magnetic particles, and adjust the pyrolysis temperature to change the microscopic morphology and internal structure of the product, so as to achieve the regulation of the electromagnetic parameters of the material and obtain an absorbing material with good impedance matching and attenuation performance. This can not only provide a new design idea for the research of high-loss and broadband absorbing materials, but also provide the necessary innovative technical support and theoretical support for the simple preparation of efficient absorbing agents, which has important academic significance and practical value.

[0114] The above are only 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 in the protection scope of the present invention.

Claims

1. A method for preparing an iron-cobalt alloy carbon magnetoelectric composite absorbing material, characterized in that: The following steps are involved: Potassium ferrocyanide was used as a carbon, nitrogen and iron source, and coprecipitated with a Co source and sodium citrate in a solvent system to prepare a Prussian blue analogue. Then, the Prussian blue analogue is pyrolyzed at 400-600 DEG C in a protective atmosphere to load Co nanoparticles on the surface of the carbon-nitrogen matrix to obtain an iron-cobalt alloy carbon magneto-electric composite wave absorbing material.

2. The method for preparing the iron-cobalt alloy carbon magneto-electric composite absorbing material according to claim 1, characterized in that: The pyrolysis temperature is preferably 500° C., and the pyrolysis time is 1 h to 3 h.

3. The method for preparing the iron-cobalt alloy carbon magneto-electric composite absorbing material according to claim 1, characterized in that: The Co source is Co(NO3)2·6H2O or CoCl2·6H2O.

4. The method for preparing the iron-cobalt alloy carbon magneto-electric composite absorbing material according to claim 3, characterized in that: The molar ratio of the Co source to sodium citrate is about 3:4-5.

5. The method for preparing the iron-cobalt alloy carbon magneto-electric composite absorbing material according to claim 1, characterized in that: The specific reaction process is as follows: The Co source, sodium citrate and a portion of the solvent are uniformly mixed to obtain a solution A; Mix potassium ferrocyanide and the remaining solvent evenly to obtain solution B; The solution B and the solution A are mixed and allowed to stand for a coprecipitation reaction to form a precipitate; after washing and drying, a Prussian blue analogue is obtained; Under a protective atmosphere, a Prussian blue analogue is pyrolyzed at 400-600°C to load Co nanoparticles on the surface of a carbon-nitrogen matrix to obtain an iron-cobalt alloy carbon magneto-electric composite wave absorbing material.

6. The method for preparing the iron-cobalt alloy carbon magneto-electric composite absorbing material according to claim 5, characterized in that: The solvent is water; the protective atmosphere is argon atmosphere.

7. The method for preparing the iron-cobalt alloy carbon magneto-electric composite absorbing material according to claim 5, characterized in that: The temperature of the coprecipitation reaction is room temperature, and the time of the coprecipitation reaction is 20 h to 24 h.

8. The method for preparing the iron-cobalt alloy carbon magneto-electric composite absorbing material according to claim 6, characterized in that: The total volume of the solvent and the amount of the Co source used are in a ratio of 150 mL to 200 mL: 3 mmol.

9. An iron-cobalt alloy carbon magneto-electric composite absorbing material prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the iron-cobalt alloy-carbon magneto-electric composite wave absorbing material according to claim 9 in the preparation of electromagnetic wave absorbing materials.

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