A method for preparing a MoSe2 / nitrogen-doped expanded graphite composite electromagnetic wave absorbing material

Abstract

This application discloses a method for preparing a MoSe2 / nitrogen-doped expanded graphite composite electromagnetic wave absorbing material. Melamine is used as the nitrogen source, and after mixing and grinding with expandable graphite, nitrogen-doped expanded graphite is obtained by high-temperature annealing. Sodium molybdate dihydrate and selenium powder are dissolved in hydrazine hydrate to obtain solution A. The nitrogen-doped expanded graphite is dispersed in a mixture of deionized water and ethanol to obtain mixture B. Solution A and mixture B are mixed and transferred to a high-pressure reactor for hydrothermal reaction. After filtration, washing, and drying, the composite material is obtained. In this material, MoSe2 is uniformly grown in flower-shaped nanosheets between the layers and on the surface of the three-dimensional porous worm-like nitrogen-doped expanded graphite. The preparation process of this application is simple and low-cost. The resulting composite material achieves a minimum reflection loss of -43.6 dB at a 5% filler content and an effective absorption bandwidth of 8.2 GHz, which can be applied in the fields of radar stealth, electromagnetic compatibility protection, and electromagnetic radiation absorption.

Description

Technical Field

[0001] This application belongs to the field of electromagnetic wave absorbing materials technology, specifically relating to a method for preparing a MoSe2 / nitrogen-doped expanded graphite composite electromagnetic wave absorbing material. Background Technology

[0002] With the rapid development of modern electronic information technology, especially the widespread adoption of 5G, digital applications such as artificial intelligence, autonomous driving, and holographic communication have enabled the Internet of Things. On the one hand, portable wireless electronic devices based on electromagnetic waves have become an important part of our daily lives, bringing great convenience. On the other hand, as the main carrier for information transmission and interconnection of electronic devices, electromagnetic waves generate a large amount of electromagnetic radiation during propagation, causing serious electromagnetic pollution problems. Meanwhile, in the modern military field, electronic equipment and electronic countermeasures technology are crucial to national defense. With the continuous upgrading of radar detection and satellite guidance technologies, fighter jets, missiles, and military defense systems face increased exposure risks and are more vulnerable to attack, placing higher demands on the radar stealth capabilities of weapons and equipment. Therefore, the development and research of new and efficient electromagnetic wave absorbing materials is essential.

[0003] Compared to traditional microwave absorbing materials such as ferrites and ceramics, graphite-based carbon materials, with their tunable dielectric properties, lightweight structure, and high loss capacity, have become the core system of next-generation high-performance electromagnetic wave absorbing materials. Expanded graphite (EG), as a unique graphite-based carbon material, possesses a three-dimensional layered porous structure, combining large specific surface area, high conductivity, and low density. Furthermore, it has low toxicity and low cost, making it suitable for mass production. In terms of absorption mechanism, due to EG's multilayered structure, electromagnetic waves can be reflected multiple times, thereby enhancing its ability to attenuate electromagnetic waves. EG's porous layered structure also provides numerous conductive interfaces, forming a conductive network that increases conductivity loss and enhances absorption performance. However, similar to most carbon materials, pure expanded graphite has a high dielectric constant, which can easily lead to impedance mismatch and limit its electromagnetic wave absorption performance.

[0004] Transition metal chalcogenides (TMDs) are a class of typical dielectric materials composed of transition metals and chalcogen elements. Due to their tunable conductivity and easily designed interface and defect structures, these materials exhibit considerable potential in the field of electromagnetic wave absorption. Among the many TMDs, MoSe2 has attracted much attention due to its excellent physical and chemical properties. MoSe2 has a graphene-like layered structure, a large specific surface area, and low weight. Its unique structure facilitates electron migration along the molecular backbone, generating induced currents in electromagnetic fields. Furthermore, MoSe2 has a triatomic structure with Se–Mo–Se covalent bonds within its layers, while the layers are connected by relatively weak van der Waals forces. This characteristic makes it easy to construct heterojunctions, thereby promoting polarization relaxation processes and facilitating electromagnetic energy dissipation. However, MoSe2 itself is a semiconductor with low intrinsic conductivity and insufficient structural stability, making it prone to interlayer aggregation. This results in its pure-phase absorption performance failing to meet practical application requirements.

[0005] In recent years, composite electromagnetic wave absorbing materials, with the synergistic effect of dielectric materials and graphite-carbon-based materials as their core, have shown great promise for application due to their advantages such as tunable multidimensional structure and excellent impedance matching. However, current technical routes still suffer from problems such as complex operation, time-consuming preparation methods, easy material agglomeration, and difficulty in controlling electromagnetic parameters. Therefore, exploring simpler composite preparation processes and achieving precise control of the electromagnetic parameters of composite materials has become an important research direction. Summary of the Invention

[0006] To overcome the shortcomings of existing expanded graphite, such as poor impedance matching due to excessively high dielectric constant, easy agglomeration of molybdenum diselenide, and difficulty in constructing conductive networks, this application provides a method for preparing MoSe2 / nitrogen-doped expanded graphite composite electromagnetic wave absorbing materials. By controlling the electronic structure of graphite through nitrogen doping and inducing MoSe2 to grow uniformly in situ between its layers, the method achieves synergistic control of dielectric properties and construction of multiple loss mechanisms, significantly improving the electromagnetic wave absorption capability of the material.

[0007] To achieve the above technical objectives, this application specifically adopts the following technical solution: In one aspect of this application, a method for preparing a MoSe2 / nitrogen-doped expanded graphite composite electromagnetic wave absorbing material is provided, comprising the following steps: S1. Nitrogen source and expandable graphite are mixed and ground, then subjected to high-temperature annealing in a nitrogen atmosphere, and cooled to obtain nitrogen-doped expandable graphite. S2. Dissolve the molybdenum source and selenium source in a solvent and stir to obtain solution A; disperse the prepared nitrogen-doped expanded graphite in a mixture of deionized water and ethanol and stir to obtain mixture B; add solution A to mixture B and stir evenly to obtain mixture C. S3. Place the mixture C in a high-pressure reactor for hydrothermal reaction. After the reaction is completed, filter, wash and dry to obtain MoSe2 / nitrogen-doped expanded graphite composite electromagnetic wave absorbing material.

[0008] In one embodiment, the nitrogen source is melamine, and the mass ratio of melamine to expandable graphite is 1:8 to 10.

[0009] In one embodiment, the high-temperature annealing temperature in step S1 is 700-900°C, the holding time is 2 hours, and the heating rate is 10°C / min.

[0010] In one embodiment, the molybdenum source in step S2 is sodium molybdate dihydrate, the selenium source is selenium powder, and the solvent is 80% hydrazine hydrate; the mass ratio of sodium molybdate dihydrate to selenium powder is 1:0.55 to 0.65.

[0011] In one embodiment, the mass ratio of nitrogen-doped expanded graphite to final MoSe2 in step S2 is 3:1 to 1:1; and the volume ratio of deionized water to ethanol is 1:1 to 3.

[0012] In one embodiment, in step S2, the stirring speed of mixture B and mixture C is 500-600 rpm, and the stirring time is 1-2 hours.

[0013] In one embodiment, the temperature of the hydrothermal reaction in step S3 is 180–200°C, and the reaction time is 18–20 h.

[0014] In one embodiment, the washing in step S3 is to wash three times each with deionized water and ethanol alternately; the drying is to dry under vacuum at a temperature of 80°C for 24 hours.

[0015] In another aspect of this application, a MoSe2 / nitrogen-doped expanded graphite composite electromagnetic wave absorbing material prepared by the above method is provided. The electromagnetic wave absorbing material has a three-dimensional porous worm-like structure, and flower-shaped MoSe2 nanosheets are uniformly grown between the layers of nitrogen-doped expanded graphite.

[0016] Compared with the prior art, this application has the following beneficial effects: 1) This application prepares a three-dimensional porous worm-like MoSe2 / nitrogen-doped expanded graphite composite material through one-step thermal expansion and hydrothermal reaction. The preparation process is simple, the raw material cost is low, and the morphology is unique, with good repeatability and potential for large-scale production.

[0017] 2) The composite material prepared in this application not only exhibits good impedance matching but also retains the conductive loss and multiple reflection / scattering mechanism of expanded graphite, as well as the dipole polarization and interfacial polarization loss of MoSe2. Furthermore, by constructing abundant heterointerfaces, it introduces strong interfacial polarization relaxation. Nitrogen doping further increases defect dipoles and enhances dipole polarization. The synergistic effect of multiple loss mechanisms significantly improves the electromagnetic wave energy conversion efficiency.

[0018] 3) In this application, the low-density characteristics of expanded graphite are maintained, and the nanosheet structure of MoSe2 also contributes to the high specific surface area. The resulting composite material has a low overall density, which is beneficial for achieving lightweight and thin-layer microwave absorbing coatings, meeting the stringent requirements of modern weaponry and high-end electronic equipment for weight reduction and compact spatial layout.

[0019] Thanks to the synergy of optimized impedance matching and multiple loss mechanisms, the composite material prepared in this application achieves a minimum reflection loss of -43.6dB and an effective absorption bandwidth of up to 8.2GHz when the filler content is only 5%, demonstrating excellent broadband electromagnetic wave absorption performance. Attached Figure Description

[0020] Figure 1 The microstructure diagrams of MoSe2 / NEG-2 in Example 2 of this application are shown; (a) 50 μm, (b) 3 μm; Figure 2 The X-ray diffraction (XRD) patterns of the MoSe2 / nitrogen-doped expanded graphite composite materials in Examples 1-3 of this application are shown. Figure 3 The electromagnetic wave absorption performance diagrams of the MoSe2 / nitrogen-doped expanded graphite composite materials in Examples 1-3 of this application are shown; (a) MoSe2 / NEG-1, (b) MoSe2 / NEG-2, (c) MoSe2 / NEG-3. Detailed Implementation

[0021] The technical solution of this application will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are only some embodiments of this application, not all embodiments, and are only used to illustrate this application, and should not be regarded as limiting the scope of this application. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0022] To address the technical bottlenecks of poor impedance matching due to the high dielectric constant of expanded graphite and the difficulty in forming an effective conductive network due to the interlayer aggregation of MoSe2, this application proposes using nitrogen-doped expanded graphite as a three-dimensional conductive framework. Utilizing the confined space and active sites provided by its worm-like porous structure, MoSe2 is induced to grow in situ on its surface and between layers, forming a flower-shaped nanosheet composite structure. Nitrogen doping not only optimizes the electronic structure and surface properties of graphite and improves the guidance for MoSe2 growth, but also introduces additional defect dipoles. The introduction of MoSe2 constructs rich heterogeneous interfaces, enhancing interfacial polarization relaxation. Through the synergistic design of composition and structure, an organic integration of conductive loss, interfacial polarization, dipole polarization, and multiple reflection mechanisms is achieved, significantly improving electromagnetic wave attenuation while improving impedance matching.

[0023] In one embodiment, the preparation method of the MoSe2 / nitrogen-doped expanded graphite composite electromagnetic wave absorbing material of this application includes the following steps: S1. Nitrogen source and expandable graphite are mixed and ground, then subjected to high-temperature annealing in a nitrogen atmosphere, and cooled to obtain nitrogen-doped expandable graphite.

[0024] A nitrogen source and expandable graphite are mixed in a certain proportion and then mechanically ground to ensure full contact between the two. The nitrogen source is selected from melamine, and the mass ratio of melamine to expandable graphite is 1:8-10. The grinding time can be controlled at about 30 minutes to ensure uniformity of the mixture. The ground mixture is placed in a ceramic boat and sent into a tube furnace for high-temperature annealing under a nitrogen atmosphere. The annealing temperature is 700-900℃, the holding time is 2 hours, and the heating rate is set at 10℃ / min. During this process, the expandable graphite undergoes volume expansion at high temperature, forming a worm-like three-dimensional porous structure. At the same time, nitrogen atoms generated from the decomposition of melamine dop into the graphite lattice, resulting in nitrogen-doped expanded graphite. After the reaction is complete, the mixture is naturally cooled to room temperature to obtain the nitrogen-doped expanded graphite product. This step achieves graphite expansion and nitrogen doping simultaneously through a one-step thermal expansion method, which is simple and produces uniform doping.

[0025] S2. Dissolve the molybdenum source and selenium source in a solvent and stir to obtain solution A; disperse the prepared nitrogen-doped expanded graphite in a mixture of deionized water and ethanol and stir to obtain mixture B; add solution A to mixture B and stir evenly to obtain mixture C.

[0026] The molybdenum source is sodium molybdate dihydrate, the selenium source is selenium powder, and the solvent is 80% hydrazine hydrate. Specifically, sodium molybdate dihydrate and selenium powder are weighed in a mass ratio of 1:0.55 to 0.65. The weighed sodium molybdate dihydrate and selenium powder are added to the 80% hydrazine hydrate solvent and magnetically stirred for 30 minutes to fully dissolve the solids, obtaining a homogeneous solution A. The nitrogen-doped expanded graphite obtained in step S1 is then dispersed in a mixture of deionized water and ethanol, with a volume ratio of deionized water to ethanol of 1:1 to 3. The amount of nitrogen-doped expanded graphite used is determined based on the mass ratio of nitrogen-doped expanded graphite to MoSe2 in the target product, which is 3:1 to 1:1. The mixture is magnetically stirred at 500 to 600 rpm for 1 to 2 hours to uniformly disperse the nitrogen-doped expanded graphite, forming a mixture B. Solution A was then slowly poured into mixture B, and the mixture was stirred at the same speed for 1–2 hours to ensure thorough mixing of the two solutions, resulting in mixture C. This step, through liquid-phase blending, uniformly mixes the molybdenum source, selenium source, and nitrogen-doped expanded graphite, providing a foundation for the in-situ growth of MoSe2 on the graphite surface and between layers in the subsequent hydrothermal reaction.

[0027] S3. Place the mixture C in a high-pressure reactor for hydrothermal reaction. After the reaction is completed, filter, wash and dry to obtain MoSe2 / nitrogen-doped expanded graphite composite electromagnetic wave absorbing material.

[0028] Specifically, the mixture C prepared in step S2 was transferred to a high-pressure reactor lined with polytetrafluoroethylene (PTFE), with a reactor volume of 80 ml. After sealing, the reactor was placed in an electrically heated drying oven for hydrothermal reaction, with the reaction temperature controlled at 180–200 °C and the reaction time at 18–20 hours. Under these temperature and pressure conditions, the molybdenum source and selenium source reacted chemically, generating MoSe2 crystals in situ on the surface and interlayer of nitrogen-doped expanded graphite, forming a flower-shaped nanosheet structure. After the reaction, the reactor was naturally cooled to room temperature, and the product was removed. The obtained product was subjected to solid-liquid separation by vacuum filtration. The filter cake was washed alternately with deionized water and ethanol, and dried after each wash, repeated three times to remove unreacted reactants and byproducts. The washed product was placed in a vacuum drying oven and dried at 80 °C for 24 hours to obtain a MoSe2 / nitrogen-doped expanded graphite composite electromagnetic wave absorbing material. In this material, MoSe2 is uniformly grown in a nano-flower-like shape on the three-dimensional porous framework of nitrogen-doped expanded graphite, forming a structurally stable composite system.

[0029] Example 1 S1. First, weigh melamine and expandable graphite at a mass ratio of 1:10, and grind them thoroughly in a mortar for 30 minutes. Then, place the mixture in a ceramic boat and anneal it at 800°C for 2 hours in a tube furnace under a nitrogen atmosphere, maintaining a heating rate of 10°C / min. Finally, cool the mixture to room temperature to obtain nitrogen-doped expanded graphite (N-EG).

[0030] S2. Weigh 19.36 mg of sodium molybdate dihydrate and 12.63 mg of selenium powder and dissolve them in 8 ml of 80% hydrazine hydrate. Stir magnetically for 30 min to obtain a homogeneous solution A. Weigh 0.05 g of N-EG and place it in a mixture of 25 ml of deionized water and 15 ml of ethanol. Stir magnetically at 550 rpm for 1 h to form a mixture B. Slowly pour solution A into mixture B and stir evenly to form mixture C.

[0031] S3. The obtained mixture C was placed in an 80ml polytetrafluoroethylene high-pressure reactor and subjected to hydrothermal reaction at 180℃ for 20h in an electric heating drying oven. After the reaction, the mixture was repeatedly filtered and washed with water and ethanol. Finally, it was dried at 80℃ for 24h in a vacuum drying phase to obtain the MoSe2 / nitrogen-doped expanded graphite composite electromagnetic wave absorbing material, labeled as MoSe2 / NEG-1. The tested MoSe2 / NEG-1 material showed a minimum reflection loss of -34.41 dB and an effective absorption bandwidth of 5.25 GHz.

[0032] Example 2 S1. First, weigh melamine and expandable graphite at a mass ratio of 1:10, and grind them thoroughly in a mortar for 30 minutes. Then, place the mixture in a ceramic boat and anneal it at 900°C for 2 hours in a tube furnace under a nitrogen atmosphere, maintaining a heating rate of 10°C / min. Finally, cool the mixture to room temperature to obtain nitrogen-doped expanded graphite (N-EG).

[0033] S2. Weigh 48.39 mg of sodium molybdate dihydrate and 31.6 mg of selenium powder and dissolve them in 10 ml of 80% hydrazine hydrate. Stir magnetically for 30 min to obtain a homogeneous solution A. Weigh 0.05 g of N-EG and place it in a mixture of 20 ml of deionized water and 20 ml of ethanol. Stir magnetically at 550 rpm for 1 h to form a mixture B. Slowly pour solution A into mixture B and stir evenly to form mixture C.

[0034] S3. The obtained mixture C was placed in an 80ml polytetrafluoroethylene high-pressure reactor and subjected to hydrothermal reaction at 200℃ in an electric heating drying oven for 20h. After the reaction, the mixture was repeatedly filtered and washed with water and ethanol. Finally, it was dried in a vacuum drying phase at 80℃ for 24h to obtain the MoSe2 / nitrogen-doped expanded graphite composite electromagnetic wave absorbing material, labeled as MoSe2 / NEG-2. The tested MoSe2 / NEG-2 material showed a minimum reflection loss of -43.6 dB and an effective absorption bandwidth of 8.2 GHz.

[0035] Example 3 S1. First, weigh melamine and expandable graphite at a mass ratio of 1:10, and grind them thoroughly in a mortar for 30 minutes. Then, place the mixture in a ceramic boat and anneal it at 900°C for 2 hours in a tube furnace under a nitrogen atmosphere, maintaining a heating rate of 10°C / min. Finally, cool the mixture to room temperature to obtain nitrogen-doped expanded graphite (N-EG).

[0036] S2. Weigh 24.2 mg of sodium molybdate dihydrate and 15.8 mg of selenium powder and dissolve them in 10 ml of 80% hydrazine hydrate. Stir magnetically for 30 min to obtain a homogeneous solution A. Weigh 0.05 g of N-EG and place it in a mixture of 15 ml of deionized water and 35 ml of ethanol. Stir magnetically at 550 rpm for 1 h to form a mixture B. Slowly pour solution A into mixture B and stir evenly to form mixture C.

[0037] S3. The obtained mixture C was placed in an 80ml polytetrafluoroethylene high-pressure reactor and subjected to hydrothermal reaction at 200℃ for 18h in an electric heating drying oven. After the reaction, the mixture was repeatedly filtered and washed with water and ethanol. Finally, it was dried at 80℃ for 24h in a vacuum drying phase to obtain the MoSe2 / nitrogen-doped expanded graphite composite electromagnetic wave absorbing material, labeled as MoSe2 / NEG-3.

[0038] The tested MoSe2 / NEG-3 material showed a minimum reflection loss of -34.61 dB and an effective absorption bandwidth of 6.22 GHz.

[0039] N-doped hollow carbon foam coated with magnetic metal@carbon nanotubes was prepared by a simple one-step high-temperature process. Figure 1 This is a microstructure image of Co@CNT / NCF-CL2 from Example 2. Figure 1 (ab) It can be seen that the ends of the carbon nanotubes are encapsulated with cobalt nanoparticles, which are uniformly distributed on the N-doped hollow carbon foam. This indicates that the preparation method proposed in this scheme can effectively reduce the size of magnetic nanoparticles.

[0040] Figure 2The image shows the XRD patterns of the composite materials in Examples 1-3. The diffraction peak at 26.5° corresponds to the (002) crystal plane of carbon nanotubes (PDF#26-1079). The peaks at 44.3°, 51.5°, and 75.8° correspond to the (111), (200), and (220) crystal planes of Co, respectively (PDF#15-0806).

[0041] Figure 3 The graph shows the electromagnetic wave absorption performance of the composite materials in Examples 1-3. It is worth noting that the effective absorption bandwidth of Co@CNT / NCF-CL1 can reach 5.92 GHz. By adjusting the thickness of the composite material, effective electromagnetic wave absorption of 7.52~17.28 GHz can be achieved.

[0042] Although the embodiments of this application have been described above in conjunction with the accompanying drawings, this application is not limited to the specific embodiments and application fields described above. The specific embodiments described above are merely illustrative and instructive, not restrictive. Those skilled in the art can make many other forms based on the guidance of this specification and without departing from the scope of protection of the claims of this application, and these are all within the scope of protection of this application.

Claims

1. A method for preparing a MoSe2 / nitrogen-doped expanded graphite composite electromagnetic wave absorbing material, characterized in that, Includes the following steps: S1. Nitrogen source and expandable graphite are mixed and ground, then subjected to high-temperature annealing in a nitrogen atmosphere, and cooled to obtain nitrogen-doped expandable graphite. S2. Dissolve the molybdenum source and selenium source in a solvent and stir to obtain solution A; disperse the prepared nitrogen-doped expanded graphite in a mixture of deionized water and ethanol and stir to obtain mixture B; add solution A to mixture B and stir evenly to obtain mixture C. S3. Place the mixture C in a high-pressure reactor for hydrothermal reaction. After the reaction is completed, filter, wash and dry to obtain MoSe2 / nitrogen-doped expanded graphite composite electromagnetic wave absorbing material.

2. The preparation method of the MoSe2 / nitrogen-doped expanded graphite composite electromagnetic wave absorbing material according to claim 1, characterized in that, The nitrogen source is melamine, and the mass ratio of melamine to expandable graphite is 1:8 to 10.

3. The preparation method of the MoSe2 / nitrogen-doped expanded graphite composite electromagnetic wave absorbing material according to claim 1, characterized in that, The high-temperature annealing in step S1 is performed at a temperature of 700–900°C, a holding time of 2 hours, and a heating rate of 10°C / min.

4. The preparation method of the MoSe2 / nitrogen-doped expanded graphite composite electromagnetic wave absorbing material according to claim 1, characterized in that, In step S2, the molybdenum source is sodium molybdate dihydrate, the selenium source is selenium powder, and the solvent is 80% hydrazine hydrate; the mass ratio of sodium molybdate dihydrate to selenium powder is 1:0.55 to 0.

65.

5. The preparation method of the MoSe2 / nitrogen-doped expanded graphite composite electromagnetic wave absorbing material according to claim 1, characterized in that, In step S2, the mass ratio of nitrogen-doped expanded graphite to final MoSe2 is 3:1 to 1:1; the volume ratio of deionized water to ethanol is 1:1 to 3.

6. The preparation method of the MoSe2 / nitrogen-doped expanded graphite composite electromagnetic wave absorbing material according to claim 1, characterized in that, In step S2, the stirring speed of mixture B and mixture C is 500-600 rpm, and the stirring time is 1-2 hours.

7. The preparation method of the MoSe2 / nitrogen-doped expanded graphite composite electromagnetic wave absorbing material according to claim 1, characterized in that, The hydrothermal reaction in step S3 is carried out at a temperature of 180–200°C for 18–20 hours.

8. The preparation method of the MoSe2 / nitrogen-doped expanded graphite composite electromagnetic wave absorbing material according to claim 1, characterized in that, The washing in step S3 involves alternating between deionized water and ethanol three times each; the drying is vacuum drying at a temperature of 80°C for 24 hours.

9. The MoSe2 / nitrogen-doped expanded graphite composite electromagnetic wave absorbing material prepared by the preparation method according to any one of claims 1-8, characterized in that, The electromagnetic wave absorbing material has a three-dimensional porous worm-like structure, with flower-shaped MoSe2 nanosheets growing between the layers of nitrogen-doped expanded graphite.

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