Multidimensional composite electromagnetic absorbing material, preparation method and application thereof

Abstract

The application belongs to the technical field of electromagnetic functional materials, and specifically discloses a multi-dimensional composite electromagnetic absorbing material and a preparation method and application thereof. A multi-dimensional synergistic composite material composed of multi-walled carbon nanotubes, molybdenum disulfide and manganese metal organic frameworks is synthesized by a hydrothermal method. The material forms an interface barrier at numerous heterogeneous interfaces, promotes the accumulation and relaxation of space charges, and thus enhances the interface polarization. The synergistic effect of molybdenum disulfide and multi-walled carbon nanotubes improves impedance matching and forms a three-dimensional conductive network to increase conductive loss. The lowest reflection loss of 55.9 dB is achieved at a thickness of 1.92 mm, and the effective absorption bandwidth is 4.02 GHz, almost covering the X-band. RCS simulation shows that the attenuation reaches 33.09 dB·m 2 at a polarization angle of 0°, which proves the strong radar signal suppression capability of the material. The application provides a theoretical basis and practical guidance for designing and optimizing low-frequency, thin-layer and high-efficiency absorbers.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic functional materials technology, and in particular to a multidimensional composite electromagnetic absorbing material, its preparation method, and its application. Background Technology

[0002] The rapid development of intelligent communication and electronic devices has exacerbated electromagnetic radiation pollution, making the development of high-performance electromagnetic wave absorbing materials an urgent priority. Traditional single-component absorbers, such as carbon materials, magnetic metals, or conductive polymers, typically exhibit poor impedance matching, high density, or a single loss mechanism, making it difficult to simultaneously meet the comprehensive requirements of being "thin, lightweight, wide-bandwidth, and strong." Constructing multidimensional composite materials through multi-component synergistic design has become an effective strategy to overcome the performance limitations of single-component systems.

[0003] Microwave absorbing materials are generally classified into carbon-based, dielectric ceramic-based, conductive polymer-based, and metal-based categories. Two-dimensional materials such as graphene, MXene, and molybdenum disulfide (MoS2) are widely used in this field due to their high specific surface area, suitable band gap, and excellent structural processability. MoS2, as an intrinsic p-type semiconductor, exhibits moderate conductivity that is beneficial for electron migration loss. Its layered S-Mo-S structure is held together by van der Waals forces; this two-dimensional stacking extends the propagation path of electromagnetic waves and enhances attenuation through multiple reflections and scattering. MoS2 primarily exhibits a single loss mechanism, thus mainly serving as a dielectric loss-type electromagnetic wave absorber. Combining MoS2 with other dielectrics or magnets is an effective way to introduce additional loss channels and improve electromagnetic wave performance. Several research groups have modified the dielectric properties of MoS2 and improved the impedance matching of MoS2-based composites by combining magnetic or other dielectric loss components with MoS2. For example, Ma et al. synthesized Fe3O4 / MoS2 composites by embedding magnetic Fe3O4 nanoclusters into MoS2 nanosheets using a simple solvothermal method. This composite material exhibits multi-band absorption, with a minimum reflection loss (RLmin) of -87.24 dB (approximately four times that of the original MoS2 nanosheets) and an effective absorption bandwidth (EAB) of 5.52 GHz. Luo et al. synthesized the MoS2 / Ni3S2 composite material via a one-step hydrothermal method. By controlling the thickness of the MoS2 coating, they optimized the complex dielectric constant of the binary composite material, ultimately achieving an absorption bandwidth exceeding 4.8 GHz. These works confirm the synergistic effect between dielectric loss and magnetic loss and demonstrate that multi-component composite materials can significantly improve microwave absorption performance.

[0004] Therefore, how to design low-frequency, thin-layer, high-performance microwave absorbing materials through synergistic optimization of structure and composition is a topic worthy of research. Summary of the Invention

[0005] The purpose of this invention is to address the aforementioned shortcomings of existing technologies by providing a multidimensional composite electromagnetic absorbing material, its preparation method, and its applications. This method utilizes Mn... 2+ Using metal coordination centers, a Mn-MOF / MoS2 / MWCNTs composite material with abundant heterostructures was synthesized via a hydrothermal method. Optimal impedance matching was achieved by controlling the doping amount of MWCNTs. Under the influence of an alternating electromagnetic field, the space charge at the component interfaces redistributed, resulting in significant interfacial polarization relaxation, thereby enhancing electromagnetic energy dissipation and significantly suppressing radar reflection.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A first aspect of the present invention is to provide a method for preparing a multidimensional composite electromagnetic absorbing material, the method comprising: Obtain the Mn-MOF precursor solution; MoS2 powder was dissolved in the Mn-MOF precursor solution to obtain a suspension; The suspension was subjected to a first hydrothermal reaction. After the reaction solution was cooled and centrifuged, the Mn-MOF / MoS2 composite material was obtained. Multi-walled carbon nanotubes were dispersed in water to obtain a multi-walled carbon nanotube dispersion. The Mn-MOF / MoS2 composite material was added to the dispersion and mixed evenly. A second hydrothermal reaction was carried out. After the reaction solution was cooled and centrifuged, the Mn-MOF / MoS2 / MWCNTs composite material, i.e., the multidimensional composite electromagnetic absorbing material, was obtained.

[0007] Furthermore, the multi-walled carbon nanotubes account for 10% to 40% of the mass fraction of the Mn-MOF / MoS2 / MWCNTs composite material.

[0008] Furthermore, the molar ratio of the MoS2 powder to the Mn-MOF precursor solution is (1.0~1.5):1.

[0009] Furthermore, the preparation process of the Mn-MOF precursor solution involves adding imidazole-4,5-dicarboxylic acid and manganese source to deionized water at a molar ratio of 1:(0.8~1.2), then adding an alkaline solution to adjust the pH, and stirring to form a homogeneous Mn-MOF precursor solution.

[0010] Furthermore, the manganese source includes at least one of manganese chloride tetrahydrate, manganese sulfate, or manganese acetate.

[0011] Furthermore, the molar ratio of the alkaline solution to imidazole-4,5-dicarboxylic acid is (1.5~2.5):1.

[0012] Furthermore, the alkaline solution includes any one of sodium hydroxide, potassium hydroxide, or ammonia water.

[0013] Furthermore, the temperature of the first hydrothermal reaction is 180~220℃, and the reaction time is 12~24h; the temperature of the second hydrothermal reaction is 180~220℃, and the reaction time is 12~24h.

[0014] A second aspect of the present invention is to provide a multidimensional composite electromagnetic absorbing material prepared by the method described above.

[0015] A third aspect of the present invention is to provide the application of the above-described multidimensional composite electromagnetic absorbing material in the fabrication of electromagnetic functional devices, wherein the electromagnetic functional devices are selected from: a) Stealth coatings, used to reduce the radar cross-section of targets; b) Millimeter-wave radar absorber, used to eliminate clutter interference from intelligent driving systems; c) Flexible electromagnetic shielding film, used to suppress near-field coupling interference between electronic components; d) Microwave thermistor, used to efficiently convert electromagnetic energy into thermal energy.

[0016] Compared with the prior art, the beneficial effects of the present invention are: (1) This invention provides a multidimensional composite electromagnetic absorbing material by introducing one-dimensional tubular MWCNTs into a Mn-MOF / MoS2 matrix; forming interfacial barriers at numerous heterogeneous interfaces, promoting the accumulation and relaxation of space charge, thereby enhancing interfacial polarization. At the same time, the semiconductor properties of MoS2 complement the high conductivity of MWCNTs, improving impedance matching and forming a three-dimensional conductive network, introducing an additional polarization mechanism, thereby improving microwave absorption performance.

[0017] (2) The present invention uses Mn 2+ Using metal coordination centers, a Mn-MOF / MoS2 / MWCNTs composite material with abundant heterostructures was synthesized via a hydrothermal method. Optimal impedance matching was achieved by controlling the doping amount of MWCNTs. Under the action of an alternating electromagnetic field, the space charge at the component interfaces redistributed, resulting in significant interfacial polarization relaxation, thereby enhancing electromagnetic energy dissipation. When the MWCNT content was 20 wt%, the composite material exhibited the best impedance matching at a thickness of 1.92 mm, with a minimum reflection loss of -55.9 dB and a wide effective absorption bandwidth of 4.02 GHz (7.80–11.82 GHz).

[0018] (3) This invention introduces the square of the product of the dielectric constant and the permeability ( με ) 2As an indicator for evaluating the inherent absorption performance of the material, the results show that with a loading of 20 wt% multi-walled carbon nanotubes, the composite material achieves a minimum reflection loss (RLmin) of -55.9 dB at a matched thickness of 1.92 mm, and an effective absorption bandwidth (EAB) of 4.02 GHz (7.80–11.82 GHz), almost covering the entire X-band. Radar cross section (RCS) simulations show its signal suppression capability of -19.67 dB·m. 2 MSW-2 average ( με ) 2 The value was 14.57, significantly higher than other samples, confirming its excellent inherent electromagnetic properties.

[0019] (4) This invention provides new design ideas and theoretical basis for the development of high-performance, lightweight MOF-based absorber materials. Attached Figure Description

[0020] Figure 1 RCS simulation model of the absorber and PEC layer; Figure 2 shows the structural characterization of the multidimensional composite electromagnetic absorbing material provided by the present invention. In the figure, (a) is a schematic diagram of the MSW preparation process, (b, c) are X-ray diffraction patterns, (d) are Raman spectra, and (e) are Fourier transform infrared spectra. Figure 3 (a) is a scanning electron microscope (SEM) image of Mn-MOF, (b) is a scanning electron microscope (SEM) image of MoS2, (c) is a scanning electron microscope (SEM) image of Mn-MOF / MoS2 / MWCNTs, (d) is an EDS mapping image of MSW-2, (e)-(g) are transmission electron microscope (TEM) images of Mn-MOF / MoS2 / MWCNTs, Mn-MOF, MoS2 and Mn-MOF / MoS2, and (h)-(j) are high-resolution transmission electron microscope (HRTEM) images of Mn-MOF, MoS2 and MWCNTs; Figure 4 The figure shows the electromagnetic parameter test results of the multidimensional composite electromagnetic absorbing material provided by the present invention. In the figure, (a) and (b) are the ε' values ​​of the multidimensional composite electromagnetic absorbing material. ε'' Values, (c) is the tanδε value, (d) is... μ' Value, (e) is μ'' The value, (f) is tanδμ Values, (g)-(j) are Cole-Cole curves; Figure 5 The figure shows the electromagnetic wave absorption performance results of the multidimensional composite electromagnetic absorbing material provided by the present invention. In the figure, (a)-(a) MSW-1, (b)-(b) MSW-2, (c)-(c) MSW-3, and (d)-(d) MSW-4; Figure 6 (a) shows the Z values ​​of MSW-1 (a), MSW-2 (b), MSW-3 (c), and MSW-4 (d) in the 2.0–18.0 GHz band when the thickness is 1.0–5.0 mm; (e) shows the frequency dependence of the attenuation constant of MSW-1, MSW-2, MSW-3, and MSW-4; and (f) shows the comprehensive comparison results based on absorbent content, tm, and RLmin. Figure 7 (a) is a schematic diagram of radar aircraft target detection; (b) is a CST simulation model; (c) is the RCS reduction at a specific angle; compared with a pure PEC substrate, the 3D RCS simulation curves covering (d) MSW-1, (e) MSW-2, and (f) MSW-3 are shown; the 2D projection diagram of the PEC substrate covering (g) MSW-1, (h) MSW-2, and (i) MSW-3 is shown; and (j)-(l) are the RCS reduction values ​​of the prepared MSW at different angles. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the specific embodiments and accompanying drawings are described in further detail below. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0022] This invention provides a method for preparing a multidimensional composite electromagnetic absorbing material, specifically including: Obtain the Mn-MOF precursor solution; MoS2 powder was dissolved in the Mn-MOF precursor solution to obtain a suspension; The suspension was subjected to a first hydrothermal reaction. After the reaction solution was cooled and centrifuged, the Mn-MOF / MoS2 composite material was obtained. Multi-walled carbon nanotubes were dispersed in water to obtain a multi-walled carbon nanotube dispersion. The Mn-MOF / MoS2 composite material was added to the dispersion and mixed evenly. A second hydrothermal reaction was carried out. After the reaction solution was cooled and centrifuged, the Mn-MOF / MoS2 / MWCNTs composite material, i.e., the multidimensional composite electromagnetic absorbing material, was obtained.

[0023] In some embodiments, the multi-walled carbon nanotubes account for 10% to 40% of the mass fraction of the Mn-MOF / MoS2 / MWCNTs composite material.

[0024] In some embodiments, the molar ratio of the MoS2 powder to the Mn-MOF precursor solution is (1.0~1.5):1.

[0025] In some embodiments, the preparation process of the Mn-MOF precursor solution involves adding imidazole-4,5-dicarboxylic acid and a manganese source to deionized water at a molar ratio of 1:(0.8~1.2), then adding an alkaline solution to adjust the pH, and stirring to form a homogeneous Mn-MOF precursor solution. The manganese source includes at least one of manganese chloride tetrahydrate, manganese sulfate, or manganese acetate. The molar ratio of the alkaline solution to imidazole-4,5-dicarboxylic acid is (1.5~2.5):1, and the alkaline solution includes any one of sodium hydroxide, potassium hydroxide, or ammonia solution.

[0026] The multidimensional composite electromagnetic absorbing material prepared by the above method involves MWCNTs penetrating into the Mn-MOF / MoS2 matrix to form a conductive network, promoting the uniform dispersion of Mn-MOF. This structure forms a hierarchical "moss-flower" structure, increasing the interface area and enhancing the multiple reflections and scattering of electromagnetic waves. It can be used to fabricate electromagnetic functional devices, which are selected from: a) Stealth coatings, used to reduce the radar cross-section of targets; b) Millimeter-wave radar absorber, used to eliminate clutter interference from intelligent driving systems; c) Flexible electromagnetic shielding film, used to suppress near-field coupling interference between electronic components; d) Microwave thermistor, used to efficiently convert electromagnetic energy into thermal energy.

[0027] The following will provide a detailed description of a multidimensional composite electromagnetic absorbing material and its preparation method according to the present invention, in conjunction with embodiments, comparative examples, and experimental data.

[0028] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0029] In embodiments of the present invention, the phase composition and crystal structure of the samples were characterized using an X-ray diffractometer (XRD, D2-AXS, USA) and a Raman spectrometer (Raman, WITec Alpha 300 R). The Raman spectroscopy measurement range was 300-2500 cm⁻¹. -¹. Raman analysis also determined the content and spatial distribution of amorphous carbon and graphitic carbon. Fourier transform infrared spectroscopy (FTIR, Nicolet 10, TFS, USA) was used in the range of 4000–400 cm⁻¹. - ¹The molecular structure and chemical composition, including functional groups, of the samples were investigated within the spectral range. The microstructure of the samples was observed using scanning electron microscopy (SEM, JEOL JSM-7800 F) and transmission electron microscopy (TEM, JEM-ARM 300 F, JEOL). Elemental composition was determined using integrated energy-dispersive X-ray spectrometry (EDS), and elemental states were analyzed using X-ray photoelectron spectroscopy (XPS, Axis Ultra DLD, UK). Magnetic properties were measured using a vibrating sample magnetometer. Electromagnetic parameters were acquired in the frequency range of 1 GHz to 18 GHz using a vector network analyzer (VNA, N5222A, KEYSIGHT) to evaluate the electromagnetic behavior of the materials. For measurements, the samples were mixed with 30 wt% paraffin and molded into toroidal specimens with an outer diameter Φout = 7.00 mm and an inner diameter Φin = 3.04 mm. The electromagnetic properties were then determined using a VNA.

[0030] Electromagnetic simulations of the RCS were performed using CST Studio Suite software. The model consisted of a single-layer uniform absorber. All simulations used open boundary conditions. The bottom layer of the model measures 120 × 120 × 1 mm. 3 Ideal conductor (PEC), top layer with dimensions of 120×120×1.92 mm. 3 MSW-x composite material, used as an electromagnetic absorption layer (such as...) Figure 1 (As shown). Electromagnetic parameters of all samples were measured using a vector network analyzer (VNA), and these parameters were imported into CST for simulation. The model plate was located in the XOY plane, and linearly polarized plane waves propagated along the x-axis from +z to -z. The θ scan range was -90° to +90°, and the far-field RCS monitoring frequency was fixed at 11.44 GHz. The RCS value was calculated using the following formula:

[0031] in S λ represents the area of ​​the simulation model, λ represents the wavelength of the incident electromagnetic wave, and Es and Ei represent the electric field strengths of the scattered wave and the incident wave, respectively.

[0032] Example 1 This embodiment provides a multidimensional composite electromagnetic absorbing material MSW-1 and its preparation method.

[0033] 4.25 mmol of sodium molybdate dihydrate (Na₂MoO₄·2H₂O) and 25 mmol of thiourea (CH₄N₂S) were dissolved in a mixture of 20 mL of ethanol and 50 mL of deionized water. The mixture was sonicated for 30 minutes, followed by stirring at room temperature for another 30 minutes. The suspension was transferred to a polytetrafluoroethylene-lined autoclave and hydrothermally synthesized at 210 °C for 24 hours. After cooling to room temperature, the black precipitate was collected by centrifugation and washed three times with ethanol. The obtained MoS₂ material was dried in an oven at 60 °C for 12 hours to obtain MoS₂ powder. 0.5 mmol of imidazole-4,5-dicarboxylic acid (4,5-IDA) and 0.5 mmol of manganese chloride tetrahydrate (MnCl₂·4H₂O) were weighed and dissolved in 20 mL of deionized water. 1 mmol (1 mL) of NaOH solution was added, and the mixture was magnetically stirred for 30 minutes to form a homogeneous precursor solution. 0.625 mmol of dry MoS2 powder was dissolved in a Mn-MOF precursor solution and sonicated for 30 minutes to obtain a homogeneous suspension. The suspension was transferred to a 50 mL polytetrafluoroethylene (PTFE) autoclave and subjected to hydrothermal treatment at 200 °C for 16 hours. After cooling, the black precipitate was collected by centrifugation, washed successively with deionized water and ethanol, dried, and ground to obtain a black powdery Mn-MOF / MoS2 composite material. Mn-MOF was also prepared separately using the same method.

[0034] 0.011 g of multi-walled carbon nanotubes (MWCNTs) were dispersed in 25 mL of deionized water and sonicated for 30 minutes. 0.1 g of Mn-MOF / MoS2 composite powder was added to the dispersion and stirred until a uniform black suspension was formed. The suspension was transferred to a PTFE-lined autoclave and hydrothermally treated at 200 °C for 16 hours. After the reaction, the autoclave was allowed to cool naturally to room temperature, and the black precipitate was recovered. The Mn-MOF / MoS2 / MWCNTs composite material was obtained by centrifugation and washing. The final composite material was labeled MSW-1, with a MWCNTs mass fraction of 10%.

[0035] Example 2 This embodiment provides a multidimensional composite electromagnetic absorbing material MSW-2 and its preparation method.

[0036] The procedure was essentially the same as in Example 1, except that 0.025 g of multi-walled carbon nanotubes (MWCNTs) were dispersed in 25 mL of deionized water and sonicated for 30 minutes. The final composite material contained 20% MWCNTs by mass.

[0037] Example 3 This embodiment provides a multidimensional composite electromagnetic absorbing material MSW-3 and its preparation method.

[0038] The procedure was essentially the same as in Example 1, except that 0.043 g of multi-walled carbon nanotubes (MWCNTs) were dispersed in 25 mL of deionized water and sonicated for 30 minutes. The final composite material contained 30% MWCNTs by mass.

[0039] Example 4 This embodiment provides a multidimensional composite electromagnetic absorbing material MSW-4 and its preparation method.

[0040] The procedure was essentially the same as in Example 1, except that 0.067 g of multi-walled carbon nanotubes (MWCNTs) were dispersed in 25 mL of deionized water and sonicated for 30 minutes. The final composite material contained 40% MWCNTs by mass.

[0041] Structural and performance studies were conducted on Examples 1-4: refer to Figure 2 (a) illustrates the preparation of the MSW composite material and its petal-like structure. A three-dimensional layered structure was prepared using a MnCl2-derived MOF precursor as a template. In the presence of NaOH, imidazole-4,5-dicarboxylic acid (4,5-IDA) underwent carboxyl deprotonation, promoting the formation of MnCl2-derived MOFs. 2+ Dissociation from MnCl2·4H2O. Released Mn 2+ Mo atoms form coordination bonds with carboxyl oxygen and imidazole nitrogen. Magnetic stirring increases the diffusion and collision frequency between coordination units, driving ligand bridging and growth, ultimately forming an ordered three-dimensional Mn-MOF precursor. Under hydrothermal conditions, Mo atoms at the MoS2 edge combine with Mn atoms in the MOF. 2+ Mo-O-Mn bonds are formed, generating a "MOF-layer" heterostructure. This interface structure enhances interfacial polarization, thereby increasing dielectric loss; the semiconductor MoS2 dissipates electromagnetic energy through electronic transitions and lattice vibrations. Meanwhile, Mn... 2+ The weak magnetic response provides a small magnetic loss channel, causing the Mn-MOF / MoS2 intermediate to exhibit combined dielectric and magnetic loss characteristics. After ultrasonic dispersion, MWCNTs form a three-dimensional conductive network under hydrothermal conditions through the π-π stacking interaction between their surface π electron clouds and the intermediate.

[0042] refer to Figure 2In (b) and (c), the composition and crystal structure of the samples were characterized by X-ray diffraction (XRD). The diffraction peaks at 2θ = 9.8°, 32.3°, 34.6°, and 57.9° correspond to the (002), (100), (102), and (110) crystal planes of MoS2, respectively (PDF card number: 98-000-0313). The Mn-MOF sample showed strong diffraction peaks at 2θ = 14.6°, 18.1°, 25.7°, 33.3°, and 38.7°, indicating good crystallinity. The dominant phase is Mn-MOF. In the Mn-MOF / MoS2 sample, the characteristic peaks of Mn-MOF were significantly weakened and broadened. The XRD pattern of the Mn-MOF / MoS2 / MWCNTs composite material showed a peak at 2θ = 25.8°, which is attributed to the (002) crystal plane of MWCNTs. XRD patterns of MSW-1, MSW-2, MSW-3, and MSW-4 show that their characteristic peaks originate from MoS2, Mn-MOF, and MWCNTs, respectively, confirming the successful synthesis of the Mn-MOF / MoS2 / MWCNT composite material. With increasing MWCNT loading, the diffraction peaks of Mn-MOF and MoS2 further weaken and broaden, while the diffraction peaks of MWCNT gradually strengthen. These results indicate that the addition of MWCNTs does not change the original phase composition, but rather reduces long-range crystal order through interfacial interactions, thereby generating additional defects and interfacial sites. The shift in characteristic peaks indicates the formation of chemical bonds between the components, while the overall structure of the composite material remains intact during synthesis. In the XRD patterns, the MSW-2 sample exhibits an optimal balance between crystallinity and interfacial coupling. This balance provides sufficient heterogeneous interfaces, thereby enhancing polarization relaxation while avoiding agglomeration and impedance mismatch associated with excessive MWCNT loading.

[0043] refer to Figure 2 In the middle (d), Raman spectroscopy was used to characterize the disorder of the samples. All samples were within the range of 1331 cm⁻¹. -1 and 1586 cm -1 Peaks appear at the points corresponding to the D-band (defects or amorphous carbon) and the G-band (in-plane vibrations of graphitic carbon), respectively. The D-band reflects the structural disorder and defect content of carbon nanocrystals, while the G-band indicates the degree of graphitization of the material. The intensity ratio ID / IG is used to quantify disorder; a higher ratio indicates greater disorder and a higher defect concentration. The ID / IG values ​​of MSW-1, MSW-2, MSW-3, and MSW-4 are 1.57, 0.83, 1.51, and 1.14, respectively. These values ​​indicate that at a MWCNT loading of 20 wt%, the samples exhibit the fewest carbon structural defects, the highest degree of graphitization, and the most complete sp.2 The carbon framework, this phenomenon stems from the "optimal defect balance point." When the multi-walled carbon nanotube (MWCNT) content is too low (MSW-1), the nanotubes exist as isolated island-like regions in the matrix, which reduces interfacial contact and promotes local micro-agglomeration; therefore, the inherent defects of Mn-MOF and MoS2 dominate the Raman response and increase the ID / IG ratio. When the MWCNT content is 20 wt% (MSW-2), the nanotubes form a uniform three-dimensional conductive network, whose highly graphitized sp... 2 Carbon becomes the primary Raman contributor, thus reducing the ID / IG ratio. When the MWCNT content exceeds this value, it surpasses the dispersion capability of Mn-MOF / MoS2 and promotes extensive entanglement and stacking to form dense tubular aggregates, thereby causing sp24-fold distortion and breakage. 2 The lattice is formed, resulting in numerous structural defects. In MSW-2, MWCNTs are highly graphitized and have intact sp2 crystals. 2 The carbon framework maintains a continuous conductive network, thereby achieving efficient energy dissipation and making the material's characteristic impedance closer to that of free space.

[0044] refer to Figure 2 Image (e) shows the FT-IR spectra of Mn-MOF, Mn-MOF / MoS2, and Mn-MOF / MoS2 / MWCNTs. (3200-3500 cm⁻¹) -1 The broad absorption band at 1587 cm⁻¹ originates from the OH stretching vibration of coordinated water in the Mn-MOF. -1 and 1378 cm -1 The absorption bands at 1454 cm⁻¹ correspond to the asymmetric and symmetric stretching vibrations of -COOH, respectively, indicating that the carboxylate ligands underwent deprotonation after coordination with Mn ions. -1 and 1238 cm -1 The peaks at 1494 cm⁻¹ are attributed to C=C and CC stretching vibrations, respectively, while the peaks at 1494 cm⁻¹ are attributed to C=C and CC stretching vibrations, respectively. -1 and 1083 cm -1 The signal at [location missing] reflects the CN and C=N stretching vibrations of the imidazole ring, confirming the successful synthesis of Mn-MOF from imidazole-4,5-dicarboxylic acid. The Mn-O stretching vibration mode appears in the spectra of Mn-MOF / MoS2 and Mn-MOF / MoS2 / MWCNTs, located at 798 cm⁻¹, respectively. -1 and 659 cm -1 In the spectrum of Mn-MOF / MoS2 / MWCNTs, the characteristic peaks of MoS2 and MWCNTs were not clearly distinguishable, which may be because the strong absorption of Mn-MOF masked the weaker characteristic peaks of these components.

[0045] refer to Figure 3In Figures (a)-(c), the microstructure and morphology of MSW-1 were characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Mn-MOF formed layered sheets, MoS2 exhibited a petal-like morphology, and MWCNTs appeared as fibrous tubular structures. After subsequent hydrothermal treatment, the petal-like MoS2 adhered tightly to the Mn-MOF / MWCNT composite material. MWCNTs penetrated into the Mn-MOF / MoS2 matrix, forming a conductive network and promoting the uniform dispersion of Mn-MOF. This structure formed a hierarchical "moss-flower" structure, increasing the interfacial area and enhancing the multiple reflections and scattering of electromagnetic waves. The elemental mapping diagram of MSW-2 is also shown. Figure 3 (d) confirmed the uniform distribution of C, N, O, S, Mn and Mo. Figure 3 Images (e)-(g) show TEM images of Mn-MOF / MoS2 / MWCNTs, Mn-MOF, MoS2, and Mn-MOF / MoS2 composites. High-resolution TEM (HRTEM) images ( Figure 3 The crystal structures of each component were confirmed in (h)-(j). The 0.655 nm lattice fringes match the (102) crystal plane of Mn-MOF, indicating that its structure was retained after composite formation. The lattice spacings of 0.615 nm and 0.345 nm correspond to the (002) crystal planes of MoS2 and MWCNTs, respectively, verifying the successful synthesis and high crystallinity of each component. This carefully designed multi-component, multi-scale microstructure enables the composite material to couple multiple microwave absorption mechanisms: dielectric loss, magnetic loss, and conduction loss, while simultaneously improving impedance matching, thereby jointly producing excellent microwave absorption performance.

[0046] Research on electromagnetic parameters and electromagnetic wave absorption performance: The electromagnetic wave absorption performance of MSW composites depends on their complex permittivity. ε r = ε ' - jε '',in ε 'Quantitative energy storage,' ε Quantify electrical energy dissipation. Figure 4 Figures (a)-(b) show the frequency-dependent dielectric parameters of the MSW sample. ε ', ε ''). ε 'and ε The frequency dispersion characteristics observed in the MSW samples all monotonically decrease within the 2-18 GHz range, reflecting the typical frequency dispersion properties of dielectric materials, i.e., the polarization mechanism gradually lags behind changes in the external electric field. The higher frequency dispersion observed in the MSW samples... ε 'and εThe value originates from the high conductivity of MWCNTs. In composite materials, MWCNTs form a conductive network, enhancing interfacial polarization and introducing a conductive loss mechanism. In particular, MSW-2 exhibits a wide conductivity range between 8-12 GHz. ε The peak coincides with its efficient absorption bandwidth in the X-band. To quantify the material's ability to dissipate electromagnetic energy, the dielectric loss tangent is defined. tanδ ε = ε '' / ε Its frequency dependence is as follows: Figure 4 As shown in (c). tanδ ε The curves show that MSW-4 has the highest value, reflecting its excellent conductivity loss. Figure 4 Figures (d)-(e) show that the real part of the complex permeability of all MSW samples is ( μ ') and the imaginary part ( μ The frequency remains extremely low throughout the 2-18 GHz band. Therefore, as... Figure 4 As shown in (f), the magnetic loss tangent ( tan δ μ = μ '' / μ The value is much less than 1 and remains below the dielectric loss tangent throughout the entire frequency range. tanδ ε This phenomenon originates from the paramagnetic Mn in Mn-MOF. 2+ Due to their limited content and the non-magnetic nature of MoS2 and MWCNTs, their combined effect produces only a weak macroscopic magnetic response. Therefore, dielectric loss dominates electromagnetic attenuation in MSW composites. According to the free electron relation... ε " = σ / (2 πε 0 f ), where σ represents conductivity and ε0 represents vacuum permittivity. f In terms of frequency, dielectric loss in MSW composite materials primarily arises from two mechanisms. First, there is conduction loss: the three-dimensional conductive network formed by MWCNTs allows charge carriers to migrate under alternating electric fields, dissipating electromagnetic energy as Joule heat. Second, there is polarization loss: abundant heterointerfaces (Mn-MOF / MoS2, MoS2 / MWCNT, Mn-MOF / MWCNT) promote space charge accumulation and interfacial polarization, while intrinsic defects act as polarization centers, generating dipole polarization. These processes are typically described using Debye relaxation; the relevant Cole-Cole equation is as follows:

[0047] in, εs and ε ∞ represents the dielectric constant at static and infinite frequencies, respectively. In the 2.00–18.00 GHz range, dipole polarization and interfacial polarization are the main sources of polarization losses. Under alternating electromagnetic fields, both mechanisms produce Debye relaxation. In the Cole-Cole diagram, each downward-opening semicircle corresponds to a polarization relaxation process, while the low-frequency straight line reflects conduction losses. Figure 4 Tables (g)-(j) show the Cole-Cole curves of the MSW samples. In MSW-1, the MWCNT loading is too low to form a continuous conductive network, thus suppressing carrier migration. Therefore, the conductive loss is negligible, and the dielectric loss mainly originates from the limited polarization relaxation at the Mn-MOF / MoS2 interface. MSW-2 exhibits multiple semicircles, indicating the presence of several different polarization relaxations; its low-frequency straight line indicates the presence of measurable conductive loss. In MSW-3 and MSW-4, the low-frequency semicircular features gradually disappear and are replaced by steep low-frequency straight lines. Excessive MWCNTs cover many interfacial polarization sites, thus weakening polarization relaxation; at the same time, the overly dense conductive network enhances conductive loss and partially shields the internal electric field, which further suppresses the polarization mechanism.

[0048] The reflection loss value directly reflects the microwave absorption (MWA) characteristics of the composite material. Its calculation formula is as follows:

[0049] Where f represents the frequency of the incident electromagnetic wave, d Indicates the matching thickness of the absorbing material. c Speed ​​of light Z in and Z 0 represents input impedance matching and space impedance matching, respectively. A reflection loss below -10 dB indicates effective electromagnetic wave absorption, corresponding to the absorption of more than 90% of the incident power. The frequency range that meets this condition is defined as the effective absorption region (EAB). Figure 5 Two-dimensional and three-dimensional reflection loss maps of samples with different matching thicknesses are shown. Figure 5 in (a)-(a MSW-1 achieved a minimum reflection loss of -18.1 dB at a thickness of 2.73 mm and a frequency of 12.88 GHz. The low MWCNT content in MSW-1 hindered the formation of a continuous conductive network, thus limiting conduction loss; furthermore, the fewer heterostructures reduced interfacial polarization. These factors combined to produce only moderate absorption. In contrast, Figure 5 (b)-(b) The MSW-2 exhibits the best performance, achieving a minimum reflection loss (RL) of -55.9 dB at 1.92 mm and 11.44 GHz. Its effective absorption bandwidth (EAB, RL < -10 dB) extends to 4.02 GHz (7.80–11.82 GHz), covering almost the entire X-band. Its superior performance stems from a moderate MWCNT content, establishing an optimal dielectric constant ratio and achieving effective impedance matching. Simultaneously, MWCNTs form a three-dimensional conductive network, generating conduction losses, while multiple heterogeneous interfaces—Mn-MOF / MoS2, MoS2 / MWCNT, and Mn-MOF / MWCNT—generate interfacial polarization losses. The synergistic effect of these loss mechanisms allows the MSW-2 to maintain high attenuation efficiency over a wide frequency range. In contrast, the MSW-3 ( Figure 5 (c)-(c) The minimum reflection loss (RLmin) of the MSW-4 is only -15.7 dB, and the maximum effective absorption frequency (EAB) is 2.93 GHz, while the MSW-4 ( Figure 5 (d)-(d) The RLmin of the composite material is only -10.15 dB. This performance degradation is likely due to the excessively high MWCNT content, which significantly increases the dielectric constant of the composite (especially its real part), leading to a severe mismatch between the characteristic impedance and free-space impedance. Consequently, most incident electromagnetic waves are reflected at the surface and cannot penetrate the material for absorption. The dense conductive network also prevents electric fields from penetrating the material, thus suppressing interfacial and dipole polarization. Furthermore, excessive MWCNT aggregation in the composite material can disrupt network uniformity, reducing the number of heterogeneous interfaces per unit volume and thus decreasing the contribution of polarization loss to dielectric loss.

[0050] Impedance matching, with |Z in / Z0| represents the value that plays a crucial role in the efficiency of incident electromagnetic waves penetrating the absorber. Ideally, |Z in / Z0|= 1, the incident wave can completely penetrate the absorber without being reflected. Figure 6 Figures (a)-(d) depict the |Z| of MSW-1, MSW-2, and MSW-4 at different thicknesses. in / Z0| value. MSW-1 exhibits poor impedance matching: its impedance is excessively increased and fluctuates wildly, leading to reverse mismatch. These characteristics stem from its discontinuous conductive network and insufficient polarization relaxation, which also contributes to its weak absorption capability. In contrast, MSW-2 demonstrates the widest and most concentrated impedance matching region. Within a thickness of 1.5–2.5 mm and a frequency range of 8–14 GHz, |Z0| value. in / Z0| Normally, |Z in The / Z0| value is close to 1. A clear matching center (|Z0|) appears at a thickness of 1.92 mm and a frequency close to 11.44 GHz. in The impedance matching is approximately 1 / Z0, indicating optimal impedance matching and minimal reflection loss. In contrast, the MSW-3 exhibits significantly poor impedance matching, while the MSW-4 performs even worse. Throughout the thickness-frequency range, the MSW-4 rarely achieves |Z0|. in / Z0|≈ 1 level; |Z in / Z0| values ​​are mostly below 0.6. This phenomenon indicates that excessive multi-walled carbon nanotube (MWCNT) loading leads to an overly dense conductive network, giving the material conductor-like properties and high reflectivity, thus causing impedance matching failure. Attenuation constant α It is also a key parameter for controlling attenuation performance, and can be calculated as follows:

[0051] α A higher value generally indicates a stronger inherent attenuation capability of the material for electromagnetic waves. Figure 6(e) shows the frequency correlation of the MSW composite material. α Curves. All samples α The values ​​all increase with increasing frequency, with MSW-4 showing the highest value. α The value is the highest. However, the poor impedance matching of the MSW-4 limits its overall absorption performance. Conversely, the MSW-2, although... αWhile not the highest value, its impedance matching performance is excellent, achieving the best electromagnetic wave absorption performance among all samples. These results indicate that optimal electromagnetic wave absorption requires a balance between good impedance matching and a moderate attenuation constant. Figure 6(f) illustrates the absorption mechanism of the Mn-MOF / MoS2 / MWCNTs composite. The synergistic effect of the multidimensional and multi-component structure generates a multilayer loss mechanism, coupled with good impedance matching, enabling the composite to effectively absorb electromagnetic waves. When incident electromagnetic waves irradiate the material surface, some energy is reflected, while the remaining energy penetrates into the material interior. Inside the composite, the three-dimensional Mn-MOF framework and the petal-like MoS2 structure form a tortuous propagation network. This structure promotes multiple reflections and scattering of the incident wave, thereby increasing its effective path length and the opportunity for energy dissipation. At the microscale, Schottky defects at the interfaces of Mn-MOF / MoS2, MoS2 / MWCNTs, and Mn-MOF / MWCNTs increase the interfacial resistance. The space charge accumulated at these interfaces is reconstructed under the influence of alternating electromagnetic fields, resulting in significant interfacial polarization relaxation, thereby converting electromagnetic energy into thermal energy. Simultaneously, inherent defects such as sulfur vacancies in MoS2 nanosheets, as well as the metal nodes and organic ligands of Mn-MOF, can all serve as polarization centers. Defects induce strong dipole polarization, increasing dielectric loss. Under the influence of alternating electric fields, the local charge redistribution caused by defect-induced polarization further dissipates energy. The introduced multi-walled carbon nanotubes (MWCNTs) form a three-dimensional interlaced conductive network, promoting carrier migration and transitions, thereby increasing conductivity and attenuating electromagnetic waves. Furthermore, MWCNTs improve the impedance matching between the composite material and free space, enhancing wave penetration and reducing surface reflection. Interfacial polarization, dipole polarization, conductivity loss, and multiple reflections collectively explain the excellent broadband electromagnetic wave absorption performance of the Mn-MOF / MoS2 / MWCNTs composite material.

[0052] Example 5 To improve stealth performance, metallic components are typically coated with electromagnetic wave absorbing materials to reduce their radar cross section (RCS). To evaluate MSW composite materials (… Figure 7 To assess the actual stealth potential of the sample (a), this embodiment uses CST and far-field response calculations to simulate the RCS of the sample at 11.44 GHz. Simulation model ( Figure 7 (b) is constructed based on experimentally measured electromagnetic parameters (as shown in Tables 1-6) and includes an ideal conductive plane (PEC) substrate coated with different MSW absorbers. Figure 7 (c) shows the RCS reduction at the selected angle. Figure 7(d)-(i) demonstrate the overall stealth performance. Compared to the bare PEC substrate, the MSW coating significantly reduces the RCS intensity; changes in the radiation pattern distribution and color scale indicate significant electromagnetic energy dissipation. Figure 7 Figures (j)-(l) illustrate the difference in radar scattering intensity between the MSW-coated sample and the PEC substrate within the angular range of -90° < θ < 90°. MSW-x significantly reduces the radar scattering intensity of the pure PEC board, demonstrating the practicality of this material. In particular, the PEC substrate coated with MSW-2 exhibits the best electromagnetic attenuation performance, with a radar cross section (RCS) below -20 dB·m across the entire detection angle range. 2 At a scattering angle of 0°, the RCS of the PEC plate coated with MSW-2 decreased by -33.09 dB·m. 2 These results demonstrate that the MSW-x composite material possesses strong electromagnetic absorption capabilities and effective wide-angle radar stealth performance. The simulation results are consistent with previously measured excellent absorption performance, validating the potential application value of the MSW composite material in the field of wide-angle radar stealth.

[0053] Table 1. Dielectric constants used in MSW-1 RCS simulations.

[0054] Table 2. Permeability used in MSW-1 RCS simulations.

[0055] Table 3. Dielectric constants used in MSW-2 RCS simulations.

[0056] Table 4. Permeability used in MSW-2 RCS simulation.

[0057] Table 5. Dielectric constants used in MSW-3 RCS simulations.

[0058] Table 6. Permeability used in MSW-3 RCS simulations.

[0059] For any points not covered above, existing technologies shall apply.

[0060] Although specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, without departing from the direction of the invention or exceeding the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc., made to the above embodiments based on the technical essence of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a multidimensional composite electromagnetic absorbing material, characterized in that, The method includes: Obtain the Mn-MOF precursor solution; MoS2 powder was dissolved in the Mn-MOF precursor solution to obtain a suspension; The suspension was subjected to a first hydrothermal reaction. After the reaction solution was cooled and centrifuged, the Mn-MOF / MoS2 composite material was obtained. Multi-walled carbon nanotubes were dispersed in water to obtain a multi-walled carbon nanotube dispersion. The Mn-MOF / MoS2 composite material was added to the dispersion and mixed evenly. A second hydrothermal reaction was carried out. After the reaction solution was cooled and centrifuged, the Mn-MOF / MoS2 / MWCNTs composite material, i.e., the multidimensional composite electromagnetic absorbing material, was obtained.

2. The method according to claim 1, characterized in that, The multi-walled carbon nanotubes account for 10% to 40% of the mass fraction of the Mn-MOF / MoS2 / MWCNTs composite material.

3. The method according to claim 1, characterized in that, The molar ratio of the MoS2 powder to the Mn-MOF precursor solution is (1.0~1.5):

1.

4. The method according to claim 3, characterized in that, The preparation process of the Mn-MOF precursor solution is as follows: imidazole-4,5-dicarboxylic acid and manganese source are added to deionized water at a molar ratio of 1:(0.8~1.2), and then an alkaline solution is added to adjust the pH. The mixture is stirred to form a homogeneous Mn-MOF precursor solution.

5. The method according to claim 4, characterized in that, The manganese source includes at least one of manganese chloride tetrahydrate, manganese sulfate, or manganese acetate.

6. The method according to claim 4, characterized in that, The molar ratio of the alkaline solution to imidazole-4,5-dicarboxylic acid is (1.5~2.5):

1.

7. The method according to claim 6, characterized in that, The alkaline solution includes any one of sodium hydroxide, potassium hydroxide, or ammonia water.

8. The method according to claim 1, characterized in that, The temperature of the first hydrothermal reaction is 180~220℃, and the reaction time is 12~24h; the temperature of the second hydrothermal reaction is 180~220℃, and the reaction time is 12~24h.

9. A multidimensional composite electromagnetic absorbing material prepared by the method according to any one of claims 1-8.

10. The application of the multidimensional composite electromagnetic absorbing material according to claim 9 in the preparation of electromagnetic functional devices, characterized in that, The electromagnetic functional devices are selected from: a) Stealth coatings, used to reduce the radar cross-section of targets; b) Millimeter-wave radar absorber, used to eliminate clutter interference from intelligent driving systems; c) Flexible electromagnetic shielding film, used to suppress near-field coupling interference between electronic components; d) Microwave thermistor, used to efficiently convert electromagnetic energy into thermal energy.

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