A MOF-based nano-alloy-carbon composite wave-absorbing material and a preparation method thereof

Abstract

The application belongs to the technical field of electromagnetic wave absorbing materials, and particularly relates to a MOF-based nano-alloy-carbon composite wave-absorbing material and a preparation method. The MOF-based nano-alloy-carbon composite wave-absorbing material is prepared by using terephthalic acid as an organic ligand, using a mixture of an iron source and a nickel source as a metal ion source, using a FeNi-MOF precursor adjustable metal / ligand ratio and pyrolysis derivation characteristics, and constructing a hollow nanostructure with uniform distribution of iron and nickel elements. The application can precisely control the complex permittivity and the complex permeability, optimize impedance matching, finally obtain a wide effective absorption bandwidth and strong reflection loss under a thin matching thickness, and solve the problems of single loss mechanism, and prominent contradiction between bandwidth and thickness of traditional wave-absorbing materials.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic wave absorbing materials technology, specifically relating to a MOF-based nano-alloy-carbon composite absorbing material and its preparation method. Background Technology

[0002] The rapid iteration of electronic information technology has transformed electromagnetic radiation into a hidden source of pollution that cannot be ignored behind the efficient operation of society. The proliferation of communication equipment, industrial instruments, and consumer electronics generates a large amount of unnecessary electromagnetic radiation, which not only interferes with the normal operation of precision electronic components but also poses a potential threat to the human nervous and immune systems. Currently, radar detection technology has become one of the mainstream reconnaissance methods. For example, a certain stealth aircraft has reduced its radar cross-section (RCS) to 0.001m by using ferrite absorbing materials and a multi-faceted aerodynamic shape. 2 This highlights the decisive role of stealth materials in the survivability of weapons and equipment. The complex electromagnetic environment and intelligent era of the future will place even higher demands on radar absorbing materials: they must have thin matching thickness, light weight, wide effective absorption bandwidth (EAB), and strong reflection loss (RL) to meet the urgent needs of radar stealth, electromagnetic compatibility and other fields.

[0003] However, traditional absorbing materials are limited by their structure and intrinsic properties, generally suffering from technical bottlenecks such as narrow absorption bandwidth, weak loss, and large matching thickness. Specifically, the loss mechanisms of traditional absorbing materials are singular, such as dielectric-type demagnetization response and magnetic loss-type dielectric-depletion polarization, making it difficult to simultaneously meet the dual conditions of good impedance matching (efficient electromagnetic wave incidence) and strong attenuation (rapid energy dissipation). In addition, there is a significant contradiction between the bandwidth and thickness of traditional absorbing materials; for example, a wide EAB often requires increased thickness, which conflicts with the demand for thinner and lighter materials.

[0004] Furthermore, traditional methods for preparing microwave absorbing materials struggle to precisely control elemental distribution, porosity, and interfaces, leading to uneven conductive networks, weak interfacial polarization, and limited eddy current losses. For instance, while metal-organic framework (MOF)-derived composite microwave absorbing materials exhibit excellent performance, their preparation suffers from insufficient control over precursor metal distribution and morphology at specific metal / ligand ratios and solvothermal temperatures. Moreover, calcination cannot decouple and regulate composition and structure, ultimately resulting in a technological defect where broadband bandwidth and high loss are difficult to achieve simultaneously at thin thicknesses. Summary of the Invention

[0005] To address the issues of limited loss mechanisms and difficulty in balancing bandwidth and thickness in microwave absorbing materials prepared by traditional methods, this invention provides a method for preparing MOF-based nanoalloy-carbon composite microwave absorbing materials.

[0006] This invention utilizes the tunable metal / ligand ratio and pyrolysis derivatization properties of FeNi-MOF precursors to construct hollow nanostructures with uniformly distributed iron and nickel elements. It simultaneously integrates the eddy current / resonance losses of magnetic components, the conductivity losses of carbon-based networks, and the dipole relaxation of organic ligands to achieve synergistic effects of multiple loss mechanisms. Furthermore, it precisely controls the complex permittivity and complex permeability to optimize impedance matching, ultimately achieving a wide effective absorption bandwidth and strong reflection loss with a thin matching thickness, filling the gap in existing technologies for multi-loss synergistic design.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows.

[0008] This invention provides a method for preparing MOF-based nanoalloy-carbon composite microwave absorbing materials, comprising the following steps: Using terephthalic acid as the organic ligand and a mixture of iron and nickel sources as the metal ion source, the organic ligand solution was added to the aqueous solution of the metal ion source. After ultrasonic treatment, a hydrothermal reaction was carried out to obtain the FeNi-MOF precursor. The molar ratio of the organic ligand to all metal ions was 8:2 to 4. The FeNi-MOF precursor was calcined under a protective atmosphere to obtain a hollow MOF-based nanoalloy-carbon composite microwave absorbing material.

[0009] Preferably, in the metal ion source, the molar ratio of Fe to Ni is 1:1.

[0010] Preferably, the iron source is Fe(NO3)3·9H2O or FeCl3·6H2O; the nickel source is NiCl2·6H2O, NiCl2·6H2O, Ni(NO3)2·6H2O or Ni(OAc)2·4H2O.

[0011] Preferably, the hydrothermal reaction temperature is 180℃±5℃ and the time is 20h~24h.

[0012] Preferably, the organic ligand solution is obtained by dispersing terephthalic acid in N,N-dimethylformamide (DMF); the aqueous solution of the metal ion source is obtained by dissolving an iron source and a nickel source in water at a molar ratio of Fe to Ni of 1:1.

[0013] Preferably, the calcination temperature is 800℃±15℃ and the time is 1.5h~3h.

[0014] Another aspect of the present invention provides a MOF-based nano-alloy-carbon composite microwave absorbing material, which is prepared by the method described above; the MOF-based nano-alloy-carbon composite microwave absorbing material has a hollow structure.

[0015] The beneficial effects of this invention are: 1. This invention constructs a hollow nanostructure with uniformly distributed iron-nickel elements by adjusting the molar ratio of organic ligands to all metal ions in the FeNi-MOF precursor and leveraging the pyrolysis derivatization properties of the FeNi-MOF precursor. This invention achieves synergistic effects of multiple loss mechanisms by simultaneously integrating the eddy current / resonance loss of the magnetic components, the conductivity loss of the carbon-based network, and the dipole relaxation of the organic ligands; furthermore, it precisely controls the complex permittivity and complex permeability, optimizes impedance matching, and ultimately obtains a wide effective absorption bandwidth and strong reflection loss at a thin matching thickness, solving the problems of single loss mechanisms and prominent bandwidth-thickness contradictions in traditional microwave absorbing materials.

[0016] 2. The MOF-based nano-alloy-carbon composite microwave absorbing material prepared in this invention exhibits the lowest reflection loss (RL) at a matching thickness of 1.74 mm. min The impedance reaches 33.6dB (14.3GHz), the effective absorption bandwidth (EAB) covers 6.08GHz (12GHz~18.0GHz), the impedance matching value Z approaches 1 infinitely (optimal matching), and the attenuation constant α increases steadily in the range of 2GHz~18GHz without abnormal fluctuations. Attached Figure Description

[0017] Figure 1 These are scanning electron microscope (SEM) images and EDS mapping images of the FeNi-MOF precursors prepared in Examples 1 to 3. Specifically, (a) is an SEM image of the FeNi-MOF precursor prepared in Example 1; (b) is an SEM image of the FeNi-MOF precursor prepared in Example 2; (c) is an SEM image of the FeNi-MOF precursor prepared in Example 3; (d) is an EDS mapping image of the FeNi-MOF precursor prepared in Example 1; (e) is the C element distribution map in (d); (f) is the N element distribution map in (d); (g) is the O element distribution map in (d); (h) is the Fe element distribution map in (d); and (i) is the Ni element distribution map in (d).

[0018] Figure 2These are scanning electron microscope (SEM) images and EDS mapping images of the MOF-based nano-alloy-carbon composite microwave absorbing materials prepared in Examples 1 to 3. Specifically, (a) is an SEM image of the MOF-based nano-alloy-carbon composite microwave absorbing material prepared in Example 1; (b) is an SEM image of the MOF-based nano-alloy-carbon composite microwave absorbing material prepared in Example 2; (c) is an SEM image of the MOF-based nano-alloy-carbon composite microwave absorbing material prepared in Example 3; (d) is an EDS mapping image of the MOF-based nano-alloy-carbon composite microwave absorbing material prepared in Example 1; (e) is the C element distribution map in (d); (f) is the N element distribution map in (d); (g) is the O element distribution map in (d); (h) is the Fe element distribution map in (d); and (i) is the Ni element distribution map in (d).

[0019] Figure 3 These are transmission electron microscope (TEM) images of the MOF-based nanoalloy-carbon composite microwave absorbing material prepared in Example 1. In the images, (b) is a magnified view of (a); and (c) is a magnified view of (b).

[0020] Figure 4 These are X-ray diffraction patterns of the FeNi-MOF precursor and MOF-based nano-alloy-carbon composite microwave absorbing materials prepared in Examples 1 to 3. Among them, (a) is the X-ray diffraction pattern of the FeNi-MOF precursor; (b) is the X-ray diffraction pattern of the MOF-based nano-alloy-carbon composite microwave absorbing material.

[0021] Figure 5 This is the full X-ray photoelectron spectroscopy (XPS) spectrum of the MOF-based nanoalloy-carbon composite microwave absorbing material prepared in Example 1.

[0022] Figure 6 yes Figure 5 XPS spectra of each element. Among them, (a) is the C 1s spectrum; (b) is the Fe 2p spectrum; (c) is the Ni 2p spectrum; and (d) is the O 1s spectrum.

[0023] Figure 7 These are electromagnetic parameter diagrams of the MOF-based nano-alloy-carbon composite microwave absorbing materials prepared in Examples 1 to 3. In these diagrams, (a) represents the real part of the dielectric constant; (b) represents the imaginary part of the dielectric constant; (c) represents the dielectric loss tangent; (d) represents the real part of the permeability; (e) represents the imaginary part of the permeability; and (f) represents the magnetic loss tangent.

[0024] Figure 8These are three-dimensional and corresponding two-dimensional reflection loss diagrams of the MOF-based nano-alloy-carbon composite microwave absorbing materials prepared in Examples 1 to 3. Specifically, (a) is the three-dimensional reflection loss diagram of FNC-1; (b) is the three-dimensional reflection loss diagram of FNC-2; (c) is the three-dimensional reflection loss diagram of FNC-3; (d) is the two-dimensional reflection loss diagram of FNC-1; (e) is the two-dimensional reflection loss diagram of FNC-2; and (f) is the two-dimensional reflection loss diagram of FNC-3.

[0025] Figure 9 These are the reflection loss curves of the MOF-based nano-alloy-carbon composite microwave absorbing materials prepared in Examples 1 to 3. Among them, (a) is the reflection loss curve of FNC-1; (b) is the reflection loss curve of FNC-2; and (c) is the reflection loss curve of FNC-3.

[0026] Figure 10 The corresponding relationships are for the matching thicknesses of the MOF-based nano-alloy-carbon composite microwave absorbing materials prepared in Examples 1 to 3. Among them, (d) is the corresponding relationship for the matching thickness of FNC-1; (e) is the corresponding relationship for the matching thickness of FNC-2; and (f) is the corresponding relationship for the matching thickness of FNC-3.

[0027] Figure 11 These are the impedance matching curves of the MOF-based nanoalloy-carbon composite microwave absorbing materials prepared in Examples 1 to 3. Among them, (g) is the impedance matching curve of FNC-1; (h) is the impedance matching curve of FNC-2; and (i) is the impedance matching curve of FNC-3. Detailed Implementation

[0028] 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.

[0029] Traditional absorbing materials are limited by their structure and intrinsic properties, generally suffering from bottlenecks such as narrow absorption bandwidth, weak loss capability, and large matching thickness. Classified by loss mechanism, existing solutions each have significant limitations: dielectric loss materials (such as carbon-based graphene / carbon nanotubes, ceramic SiC / MXene, conductive polymer polyaniline, etc.), while lightweight and highly conductive, suffer from insufficient impedance matching, easily leading to surface reflection due to excessively high dielectric constants, and carbon-based materials exhibit poor dispersion uniformity; magnetic loss materials (such as ferrite BaFe...) 12 O 19Nanomaterials (such as Fe / Co / Ni nanomaterials and FeSiAl magnetic alloys) exhibit excellent low-frequency absorption, but their high density limits their high-frequency response. Nanomaterials are prone to oxidation, and magnetic alloys have complex manufacturing processes. Magnetoelectric composite loss-type materials can theoretically synergistically optimize impedance matching and attenuation, but current synthesis technologies are mostly confined to the laboratory stage, resulting in high costs and complex processes, hindering industrial application. Classification by composition also has limitations: carbon-based materials have unsatisfactory impedance matching, iron-based metals are easily corroded, ceramics are brittle and have poor conductivity, and conductive polymers lack sufficient thermal stability. Single-layer coatings designed by structure have narrow high-frequency bandwidth, multi-layer structures are cumbersome to prepare, and it is difficult to balance the controllability of pore structure and mechanical properties in porous materials.

[0030] Ultimately, the common shortcomings of existing materials lie in three aspects: First, the loss mechanism is singular; dielectric materials lack magnetic response, and magnetic loss materials lack dielectric polarization, making it difficult to simultaneously meet the dual conditions of "good impedance matching (efficient electromagnetic wave incidence)" and "strong attenuation (rapid energy dissipation)." Second, there is a prominent contradiction between bandwidth and thickness; a wide EAB often requires increased thickness, which conflicts with the demand for thinner materials. For example, ferrite materials have a large matching thickness, while carbon-based materials are thin but lack bandwidth. Third, there is insufficient control over the microstructure; traditional methods cannot accurately control the element distribution, porosity, and interface, resulting in uneven conductive networks, weak interface polarization, and limited eddy current losses.

[0031] Metal-organic framework (MOF) materials offer a new approach to solving the aforementioned problems: they are formed by the self-assembly of metal ions / clusters and organic ligands into a periodic network structure, possessing high specific surface area, tunable pore size, and organic-inorganic hybrid characteristics. They can be pyrolyzed to derive magnetoelectric composite nanomaterials, achieving atomic-level uniform composites of magnetic elements such as Fe and Ni with carbon-based dielectric networks. However, existing technologies, such as the MOF-derived composite microwave absorbing materials prepared in patent application CN202111018699.0, struggle to simultaneously achieve broadband bandwidth and high loss at thinner thicknesses. The specific preparation process involves using terephthalic acid as the organic ligand and a mixture of FeCl3·6H2O and Ni(acac)2 as the metal ion source. After a solvothermal reaction at 110℃–130℃, a FeNiMIL101 precursor is obtained, which is then calcined at 600℃–800℃ under an inert atmosphere to obtain the FeNiC-X composite microwave absorbing material. The molar ratio of FeCl3·6H2O, Ni(acac)2, and organic ligands is 1:0.5:1. While the FeNiC-X composite microwave absorbing materials prepared by the aforementioned prior art exhibit excellent material properties, they suffer from insufficient control over the distribution and morphology of the precursor metals at the appropriate metal / ligand ratios and solvothermal temperatures. Furthermore, calcination cannot decouple and regulate the composition and structure, ultimately leading to a process defect where it is difficult to achieve both broadband and high-loss characteristics at thin thicknesses.

[0032] This invention achieves uniform distribution of precursor elements, controllable hollow structure, and decoupled control of calcination parameters by optimizing the metal source, especially by precisely controlling the metal / ligand ratio and solvothermal conditions. Compared with the existing processes, it achieves better impedance matching, stronger reflection loss, and wider effective absorption bandwidth at a thinner thickness, and has higher process stability and repeatability.

[0033] To address the aforementioned issues, this invention focuses on the core challenge of traditional materials, which struggle to balance wide bandwidth and high loss. Using FeNi-MOF as a precursor, a hollow FeNi nano-alloy / carbon composite material is constructed through proportioning control and pyrolysis engineering. This results in a material with excellent impedance matching, high loss, and a wide absorption bandwidth, achieving the goal of preparing a material with superior electromagnetic wave absorption performance.

[0034] The technical solution of the present invention will be further described below through specific embodiments. Unless otherwise specified, the methods described in the following embodiments are conventional methods; the reagents and materials described are commercially available unless otherwise specified.

[0035] Example 1 A method for preparing a MOF-based nanoalloy-carbon composite microwave absorbing material includes the following steps: Step 1, Preparation of FeNi-MOF precursor: Fe(NO3)3·9H2O and NiCl2·6H2O were dissolved in 15 mL of water at a 1:1 molar ratio to obtain solution A, with a concentration of 0.533 mol / L for all metal ions (Fe and Ni). Terephthalic acid was dispersed in 15 mL of DMF to obtain solution B, with a concentration of 2.134 mol / L for terephthalic acid.

[0036] Using Fe(NO3)3·9H2O and NiCl2·6H2O as metal sources and terephthalic acid as organic ligand, the molar ratio of organic ligand (terephthalic acid) to all metal ions (Fe and Ni) was set to 8:2. After injecting solution A into solution B, the mixture was stirred vigorously and sonicated at room temperature for 10 min to ensure complete dissolution, thus obtaining a mixed solution.

[0037] The mixed solution was transferred to a polytetrafluoroethylene-lined reactor and hydrothermally reacted at 180°C for 24 h. After cooling, it was washed sequentially with water and ethanol, then centrifuged at 8000 r / min for 5 min in a high-speed centrifuge, repeated 3 times. After drying under vacuum at 80°C for 12 h, and grinding, the FeNi-MOF precursor was obtained, denoted as FeNi-MOF-1.

[0038] Step 2, Preparation of MOF-based nanoalloy-carbon composite microwave absorbing material: The FeNi-MOF precursor was placed in a ceramic boat and purged with an inert protective argon gas in a tube furnace to prevent oxidation. It was then calcined at 800°C for 2 hours under a flowing nitrogen atmosphere at a heating rate of 5°C / min. After a programmed cooling process, the precursor was ground into a fine and smooth powder and stored in a sample tube. This yielded the MOF-based nano-alloy-carbon composite microwave absorbing material, denoted as FNC-1.

[0039] Example 2 A method for preparing a MOF-based nanoalloy-carbon composite microwave absorbing material differs from Example 1 in that the molar ratio of the organic ligand (terephthalic acid) to all metal ions (Fe and Ni) is 8:3. The specific preparation method includes the following steps: Step 1, Preparation of FeNi-MOF precursor: Fe(NO3)3·9H2O and NiCl2·6H2O were dissolved in 15 mL of water at a 1:1 molar ratio to obtain solution A, with a concentration of all metal ions (Fe and Ni) of 0.533 mol / L. Terephthalic acid was dispersed in 15 mL of DMF to obtain solution B, with a concentration of 1.421 mol / mL.

[0040] Using Fe(NO3)3·9H2O and NiCl2·6H2O as metal sources and terephthalic acid as organic ligand, the molar ratio of organic ligand (terephthalic acid) to all metal ions (Fe and Ni) was set to 8:3. After injecting solution A into solution B, the mixture was stirred vigorously and sonicated at room temperature for 10 min to ensure complete dissolution, thus obtaining a mixed solution.

[0041] The mixed solution was transferred to a polytetrafluoroethylene-lined reactor and hydrothermally reacted at 180°C for 24 h. After cooling, it was washed sequentially with water and ethanol, then centrifuged at 8000 r / min for 5 min in a high-speed centrifuge, repeated 4 times. After drying under vacuum at 80°C for 12 h, and grinding, the FeNi-MOF precursor was obtained, denoted as FeNi-MOF-2.

[0042] Step 2, Preparation of MOF-based nanoalloy-carbon composite microwave absorbing material: The FeNi-MOF precursor was placed in a ceramic boat and purged with an inert protective argon gas in a tube furnace to prevent oxidation. It was then calcined at 800°C for 2 hours under a flowing nitrogen atmosphere at a heating rate of 5°C / min. After programmed cooling, it was ground into a fine and smooth powder and stored in a sample tube. This yielded the MOF-based nano-alloy-carbon composite microwave absorbing material, denoted as FNC-2.

[0043] Example 3 A method for preparing a MOF-based nano-alloy-carbon composite microwave absorbing material differs from Example 1 in that the molar ratio of the organic ligand (terephthalic acid) to all metal ions (Fe and Ni) is 8:4. The specific preparation method includes the following steps: Step 1, Preparation of FeNi-MOF precursor: Fe(NO3)3·9H2O and NiCl2·6H2O were dissolved in 15 mL of water at a 1:1 molar ratio to obtain solution A, with a concentration of all metal ions (Fe and Ni) of 0.533 mol / L. Terephthalic acid was dispersed in 15 mL of DMF to obtain solution B, with a concentration of 1.066 mol / L.

[0044] Using Fe(NO3)3·9H2O and NiCl2·6H2O as metal sources and terephthalic acid as organic ligand, the molar ratio of organic ligand (terephthalic acid) to all metal ions (Fe and Ni) was set to 8:4. After injecting solution A into solution B, the mixture was stirred vigorously and sonicated at room temperature for 10 min to ensure complete dissolution, thus obtaining a mixed solution.

[0045] The mixed solution was transferred to a polytetrafluoroethylene-lined reactor and hydrothermally reacted at 180°C for 24 h. After cooling, it was washed sequentially with water and ethanol, then centrifuged at 8000 r / min for 5 min in a high-speed centrifuge, repeated 5 times. After drying under vacuum at 80°C for 12 h, and grinding, the FeNi-MOF precursor was obtained, denoted as FeNi-MOF-3.

[0046] Step 2, Preparation of MOF-based nanoalloy-carbon composite microwave absorbing material: The FeNi-MOF precursor was placed in a ceramic boat and purged with an inert protective argon gas in a tube furnace to prevent oxidation. It was then calcined at 800°C for 2 hours under a flowing nitrogen atmosphere at a heating rate of 5°C / min. After programmed cooling, it was ground into a fine and smooth powder and stored in a sample tube. This yielded the MOF-based nano-alloy-carbon composite microwave absorbing material, denoted as FNC-3.

[0047] Comparative Example 1 A method for preparing a MOF-derived composite absorbing material is disclosed, which follows the method described in Example 3 of patent application CN202111018699.0. The MOF-derived composite absorbing material prepared in Comparative Example 1 has an effective absorption bandwidth of 4.6 GHz and a minimum reflection loss of 18.6 dB.

[0048] In Example 3 of this invention, a MOF-based nano-alloy-carbon composite microwave absorbing material was prepared by using FeNiMOF as a precursor and undergoing inert pyrolysis at 800℃ with controlled proportioning. The material achieved a strong loss of 33.6dB and a wide effective absorption bandwidth of 6.08GHz with a thickness of 1.74mm. It exhibited excellent impedance matching and synergistic multiple losses, and its overall performance was significantly better than that of the material prepared by the method of Example 3 of CN202111018699.0 in Comparative Example 1.

[0049] Test method: The MOF-based nanoalloy-carbon composite microwave absorbing materials prepared in Examples 1 to 3 were used as test samples. The crystal structure was analyzed by XRD (X-ray diffraction); the spherical structure, internal hollow structure and crystal structure of the alloy were observed by SEM (scanning electron microscope, HITACHI S-5200) / TEM (transmission electron microscope, JEM-2100); the chemical state of the elements was analyzed by XPS (K-Alpha type); and the complex permittivity and complex permeability were determined by VNA (vector network analyzer).

[0050] Figure 1 These are scanning electron microscope (SEM) images and EDS mapping images of the FeNi-MOF precursors prepared in Examples 1 to 3. Figure 1 The results show that the FeNi-MOF precursor has a regular surface, with particles approximately 120 nm in diameter and a regular cubic morphology. EDS analysis reveals that Fe, Ni, C, N, and O elements are uniformly distributed on the FeNi-MOF precursor.

[0051] Figure 2 These are scanning electron microscope (SEM) images and EDS mapping images of the MOF-based nanoalloy-carbon composite microwave absorbing materials prepared in Examples 1 to 3. Figure 2 The results showed that the FeNi nanoalloy appeared as black granular spheres with obvious graphite C bonds between the metal particles. EDS analysis revealed that Fe, Ni, C, N, and O elements were uniformly distributed on it.

[0052] Figure 3 These are transmission electron microscope (TEM) images of the MOF-based nanoalloy-carbon composite microwave absorbing material prepared in Example 1. To study the crystal structure and crystal plane parameters of the FeNi nanoalloy, a typical region of the sample was selected, and the interplanar spacing was gradually locked and magnified to capture TEM images of the FeNi nanoalloy. Figure 3 (c) It can be seen that the lattice fringe spacing of 0.114 nm corresponds to the (311) crystal plane of the FeNi nano-alloy in X-ray diffraction, and the lattice fringe spacing of 0.307 nm corresponds to the (004) crystal plane of C. It can be determined that the FeNi nano-alloy forms a network structure with uniformly distributed magnetic metal ions on the surface and C-connected metal particles.

[0053] Figure 4 These are the X-ray diffraction patterns of the FeNi-MOF precursor and MOF-based nanoalloy-carbon composite microwave absorbing materials prepared in Examples 1 to 3. The crystal structures of FeNi nanoalloys and FeNi-MOF with different stoichiometric ratios were characterized by XRD, and the results are as follows: Figure 4 As shown. Figure 4 As shown in (a), all three FeNi-MOFs with different ratios exhibited characteristic peaks between 2θ = 16° and 40°. XRD patterns indicate that before calcination, the samples contained a large amount of organic ligands, and Fe and Ni exhibited extremely low crystallinity. Figure 4 As shown in (b), the characteristic peaks in the XRD pattern decreased, indicating that the impurities in the sample were significantly reduced after calcination, leaving only a small amount of C. Furthermore, the characteristic peaks of Fe and Ni became clearer, indicating that FeNi formed a crystalline structure. Comparing the XRD patterns of FeNi nanoalloys with three different ratios, the characteristic peaks became more pronounced with increasing metal ion ratio, indicating improved crystallinity, a more ordered structure, stronger crystal diffraction capabilities, and better crystallinity of the FeNi nanoalloys.

[0054] Figure 5 This is the full X-ray photoelectron spectroscopy (XPS) spectrum of the MOF-based nanoalloy-carbon composite microwave absorbing material prepared in Example 1. As shown in the XPS full spectrum, four characteristic peaks were detected in the sample: C 1s, Fe 2p, O 1s, and Ni 2p, which fully characterizes the presence of the four elements C, Fe, O, and Ni.

[0055] Figure 6 yes Figure 5 XPS spectra of each element. Figure 6 (a) shows the C 1s spectrum, where the three characteristic peaks are located at 288.75 eV, 286.47 eV, and 284.80 eV, corresponding to OC=O, COC, and CC bonds in the material. The OC=O bond indicates the presence of residual carbonyl or carboxyl groups, possibly due to surface oxidation or contamination. The COC bond represents residual ethers, possibly originating from surface oxidation or organic ligands. The CC bond represents graphitized C after calcination, consistent with the characterization in the XRD spectrum.

[0056] Figure 6 (b) shows the Fe 2p spectrum, with four characteristic peaks located at 713.70 eV, 712.20 eV, 710.70 eV, and 709.50 eV, respectively. The peaks at 713.70 eV and 709.50 eV represent Fe 2p. 3+ The satellite peaks further confirmed its oxidation state. The characteristic peaks were all concentrated near the characteristic peaks of NiFe₂O₄, corresponding to Fe... 3+The 2p3 peak in the spinel structure (NiFe2O4) indicates that Fe exists in the trivalent oxidation state, and also indicates that most of the Fe element in the material exists in the form of NiFe2O4.

[0057] Figure 6 (c) shows the Ni 2p spectrum, with five characteristic peaks located at 867.14 eV, 864.48 eV, 861.23 eV, 856.10 eV, and 855.35 eV. Among these, 856.10 eV and 855.35 eV correspond to Ni in NiFe2O4. 2+ The binding energies indicate that Ni exists in a divalent oxide state within the spinel structure (NiFe2O4). 867.14 eV, 864.48 eV, and 861.23 eV represent the binding energies of Ni. 2+ The satellite peaks further confirmed the oxidation state of Ni.

[0058] Figure 6 Image (d) shows the O 1s spectrum, with three characteristic peaks located at 533.15 eV, 533.66 eV, and 530.33 eV. The first two peaks correspond to C=O and CO bonds in the material, and as analyzed in the C 1s spectrum above, they may originate from oxygen-containing functional groups adsorbed on the surface, such as carboxyl, hydroxyl, and ether bonds. The latter peak corresponds to metal oxides in the material, specifically lattice oxygen in NiFe2O4.

[0059] Combination Figures 3 to 6 It can be seen that the specific composition of FeNi nanoalloy is Fe 0.5 Ni 0.5 / C.

[0060] Figure 7 These are electromagnetic parameter diagrams of the MOF-based nanoalloy-carbon composite microwave absorbing materials prepared in Examples 1 to 3. The complex permittivity of samples FNC-1, FNC-2, and FNC-3 is analyzed within the range of 2 GHz to 18 GHz.

[0061] like Figure 7 As shown in (a), ε′ The frequency decreases across the board, which is a result of dispersion. (FNC-1's...) ε′ The dielectric value drops from approximately 14 to around 8, indicating extremely strong dielectric properties; FNC-2's ε′ The value dropped from approximately 11 to around 8; FNC-3's ε′ The value decreased from approximately 13 to around 8. This indicates that the 8:2 FeNi nano-alloy ratio... ε′The overall value is significantly higher than that of the other two FeNi nano-alloy ratios. This is because its metal ion content is lower, and the excessive organic ligands lead to more interface defects and potentially larger porosity, which is not conducive to the formation of a conductive network through metal-to-metal contact, thus increasing eddy current losses. Simultaneously, the excessive organic ligands result in too many polar groups, leading to orientational polarization in the electric field and generating excessive high-frequency losses. This is also the reason for the higher losses in the 8:2 FeNi nano-alloy ratio. ε′ The reason for the fastest rate of value decrease is that as the ratio of metal ions increases, a conductive network is formed between metals, which increases eddy current loss. At the same time, the polar groups in the appropriate amount of organic ligands relax in the alternating electric field, which gives the 8:4 FeNi nanoalloy the characteristics of wideband strong absorption.

[0062] like Figure 7 As can be seen in (b), the three samples ε″ The value also shows a decreasing trend with increasing frequency. (FNC-1's...) ε″ The value dropped from about 8 to around 3 and then rose again to around 4, for FNC-2. ε″ The value dropped from approximately 6 to around 3, for FNC-3. ε″ The value gradually decreases from approximately 5 to around 4. Therefore, it can be concluded that FNC-1 has a higher dielectric loss capability. However, an extremely high dielectric constant does not necessarily mean excellent electromagnetic wave loss performance; on the contrary, it may lead to poor impedance matching, resulting in a reduced electromagnetic wave attenuation rate. The dielectric loss tangent represents the efficiency of converting electrical energy into heat energy within the material under the influence of an electric field. A high tan tangent... δ ε The value indicates that the material has a high energy dissipation under the action of an electric field, which manifests as greater heat generation.

[0063] Figure 7 (c) shows the dielectric loss tangent of the FeNi nano-alloy (tan φ). δ ε The relationship between dielectric loss and frequency was investigated. Results showed that the tanδε value of FNC-1 varied between approximately 0.60 and 0.40 and between 0.40 and 0.65, respectively; the tanδε value of FNC-2 varied between 0.55 and 0.35 and between 0.35 and 0.50, respectively; and the tanδε value of FNC-3 decreased from approximately 0.55 to around 0.25, then gradually increased with increasing frequency to around 0.4 and oscillated slightly. This indicates that FNC-3 has the best dielectric loss performance and a significant advantage over the other two ratios in the high-frequency range.

[0064] Figure 7In Figures (d) and (e), the curves showing the variation of the real part μ′ and the imaginary part μ″ of the complex permeability of FeNi nanoalloys with frequency are shown. It can be seen that the μ′ value of the FeNi nanoalloys generally decreases from about 1.3 to around 1.0, indicating that the differences in magnetic storage performance between materials are not significant. Comparatively, the FNC-3 sample exhibits the best performance among the samples. Similarly, the FNC-3 sample also has the highest μ″ value, indicating that it has the best magnetic loss capability. Figure 7 As shown in the magnetic loss tangent of FeNi nanoalloys in (f), the FNC-3 sample still has the best magnetic loss capability.

[0065] Figure 8 These are three-dimensional and corresponding two-dimensional reflection loss diagrams of the MOF-based nano-alloy-carbon composite microwave absorbing materials prepared in Examples 1 to 3. Figure 9 These are the reflection loss curves of the MOF-based nano-alloy-carbon composite microwave absorbing materials prepared in Examples 1 to 3.

[0066] like Figure 8 and 9 The electromagnetic wave loss performance of samples FNC-1, FNC-2, and FNC-3 is shown, demonstrating them to be high-performance absorbing materials, all of which have both low RL values ​​and wide EAB.

[0067] Among them, the FNC-1 sample exhibited RL at approximately 14.2 GHz. min -26.1dB, matching thickness (t) m With a thickness of 1.8 mm, the EAB can reach 5.68 GHz. The FNC-2 sample achieved an RL of approximately 14.5 GHz. min -58.1dB, matching thickness (t) m When the thickness is 1.84 mm, the EAB can reach 5.6 GHz. The FNC-3 sample has an RL of approximately 14.3 GHz. min -33.6dB, matching thickness (t) m When the diameter is 1.74 mm, the EAB can reach 6.08 GHz. Although the RL of the FNC-2 sample... min Although the value is the lowest, its absorption bandwidth is significantly lower than that of FNC-3, which still indicates that the material can achieve the best absorption performance when the ratio is 8:4.

[0068] Figure 10 This is the correspondence of the matching thicknesses of the MOF-based nano-alloy-carbon composite microwave absorbing materials prepared in Examples 1 to 3. Figure 11 These are the impedance matching curves of the MOF-based nanoalloy-carbon composite microwave absorbing materials prepared in Examples 1 to 3.

[0069] Figure 11The diagram shows the impedance matching values ​​corresponding to the losses within the range of 2 GHz to 18 GHz. When the impedance of a material is close to 1, electromagnetic waves can enter the material without reflection, thus achieving impedance matching and facilitating electromagnetic wave absorption. For example... Figure 10 and Figure 11 As shown, FNC-3 exhibits the best impedance matching performance, which allows electromagnetic waves to enter the material in large quantities for absorption and dissipation, thus enabling the material to achieve efficient wave absorption performance.

[0070] In summary, the MOF-based nanoalloy-carbon composite microwave absorbing material prepared in Example 3 of this invention exhibits the lowest reflection loss (RL) at a matching thickness of 1.74 mm. min The impedance reaches 33.6dB (14.3GHz), the effective absorption bandwidth (EAB) covers 6.08GHz (12GHz~18.0GHz), the impedance matching value Z approaches 1 infinitely (optimal matching), and the attenuation constant α increases steadily in the range of 2GHz~18GHz without abnormal fluctuations.

[0071] Compared with the same system FNC-1 (RL) min =26.1dB, EAB=5.68GHz) and FNC2 (RL min =58.1dB, EAB=5.6GHz), although the peak loss of FNC-3 is slightly inferior to that of FNC2, it has a bandwidth increase of 0.48GHz and a thickness reduction of 0.06mm, making it the best overall broadband performance.

[0072] Compared with the thickness and bandwidth of existing MOF-based materials (such as Ni / NPC with a thickness of 2.0 mm / EAB 4.3 GHz and Mo2C@Co / C with a thickness of 2.3 mm / EAB 5.52 GHz), the embodiments of the present invention achieve a wider bandwidth with a thinner thickness, breaking through the limitation of traditional materials that "it is difficult to achieve both thinness and wide bandwidth".

[0073] 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 a MOF-based nanoalloy-carbon composite microwave absorbing material, characterized in that, Includes the following steps: Using terephthalic acid as the organic ligand and a mixture of iron and nickel sources as the metal ion source, the organic ligand solution was added to the aqueous solution of the metal ion source. After ultrasonic treatment, a hydrothermal reaction was carried out at a temperature of 180℃±5℃ to obtain the FeNi-MOF precursor. The molar ratio of the organic ligand to all metal ions was 8:2~4. The FeNi-MOF precursor was calcined under a protective atmosphere at a temperature of 800℃±15℃ to obtain a hollow MOF-based nanoalloy-carbon composite microwave absorbing material.

2. The preparation method of the MOF-based nano-alloy-carbon composite microwave absorbing material according to claim 1, characterized in that, In the metal ion source, the molar ratio of Fe to Ni is 1:

1.

3. The preparation method of the MOF-based nano-alloy-carbon composite microwave absorbing material according to claim 1, characterized in that, The iron source is Fe(NO3)3·9H2O or FeCl3·6H2O; the nickel source is NiCl2·6H2O, Ni(NO3)2·6H2O or Ni(OAc)2·4H2O.

4. The preparation method of the MOF-based nano-alloy-carbon composite microwave absorbing material according to claim 1, characterized in that, The hydrothermal reaction takes 20 to 24 hours.

5. The method for preparing the MOF-based nano-alloy-carbon composite microwave absorbing material according to claim 1, characterized in that, The organic ligand solution was obtained by dispersing terephthalic acid in N,N-dimethylformamide; the aqueous solution of the metal ion source was obtained by dissolving an iron source and a nickel source in water at a molar ratio of Fe to Ni of 1:

1.

6. The method for preparing the MOF-based nano-alloy-carbon composite microwave absorbing material according to claim 1, characterized in that, The calcination time is 1.5h to 3h.

7. A MOF-based nanoalloy-carbon composite microwave absorbing material, characterized in that, The MOF-based nano-alloy-carbon composite microwave absorbing material is prepared by any one of claims 1 to 6; the MOF-based nano-alloy-carbon composite microwave absorbing material has a hollow structure.

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