Hydrogen-induced reconstructed nickel-based MOF-derived microwave absorbing materials, their preparation methods and applications

Abstract

This invention discloses a hydrogen-induced reconfiguration nickel-based MOF-derived microwave absorbing material, its preparation method, and its applications, belonging to the field of electromagnetic wave absorption and shielding materials technology. The preparation method includes: using nickel salt and trimesic acid as metal and organic ligands, polyvinylpyrrolidone as a morphology modifier, and N,N-dimethylformamide, ethanol, and water as a mixed solvent to prepare a nickel-based MOF precursor via a solvothermal reaction; subsequently, the precursor is subjected to a programmed temperature reduction treatment in an argon-hydrogen mixed atmosphere, utilizing hydrogen to induce structural reconstruction and phase transition, ultimately obtaining a nickel-based derived microwave absorbing material with a multi-level structure and heterogeneous interfaces. This method is simple and structurally controllable. The prepared material exhibits excellent electromagnetic wave absorption and shielding performance in the 2–18 GHz frequency band, characterized by strong absorption, wide bandwidth, and thin thickness, and can be widely used in electromagnetic protection, stealth technology, and microwave compatibility fields for electronic information equipment.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic functional composite materials technology, and specifically provides a hydrogen-induced reconfigurable nickel-based MOF-derived microwave absorbing material, its preparation method, and its application. Background Technology

[0002] With the rapid development and widespread adoption of 5G / 6G communication, radar detection, aerospace, smart wearables, and precision electronic equipment, electromagnetic waves, as the core carrier of information transmission and energy interaction, have found applications covering multiple fields, including civilian, industrial, and defense sectors. However, the uncontrolled radiation of electromagnetic waves has also triggered a series of pressing problems: on the one hand, excessive electromagnetic radiation can cause severe electromagnetic interference, affecting the normal operation of precision electronic components, reducing equipment measurement and control accuracy, and even causing equipment failures in critical areas such as aerospace and rail transportation, creating safety hazards; on the other hand, electromagnetic radiation can lead to information leakage, threatening national defense security, commercial secrets, and personal privacy, while also posing potential health hazards to the human nervous and cardiovascular systems. Furthermore, in the field of stealth defense, the demand for broadband, high-absorption, and lightweight electromagnetic wave absorbing materials is becoming increasingly urgent. Therefore, developing high-performance electromagnetic wave absorbing materials that combine lightweight, thinness, broadband, high efficiency, and good environmental stability has become a core means to solve electromagnetic pollution and achieve electromagnetic protection and stealth, and is also a current research focus and urgent need in the field of materials science and engineering. Metal-organic frameworks (MOFs) are a class of crystalline porous materials formed by the coordination bonds between metal ion clusters and organic ligands. Due to their high porosity, large specific surface area, precise design of composition and microstructure, and the ability to achieve synergistic regulation of the metal and carbon-based phases after pyrolysis, they have become ideal precursors for the preparation of high-performance electromagnetic wave absorbing materials. Nickel-based MOFs, as typical magnetic MOF materials, can form a nickel / C composite structure with uniformly dispersed nickel particles in a carbon matrix after pyrolysis. This structure possesses multiple excellent electromagnetic loss characteristics: nickel exhibits good ferromagnetism, achieving magnetic loss attenuation of electromagnetic waves through hysteresis loss and eddy current loss; the carbon matrix provides both conductive and dielectric polarization losses, and its porous structure also enables multiple scattering, reflection, and diffuse reflection of electromagnetic waves, effectively extending the propagation path of electromagnetic waves within the material and further improving energy attenuation efficiency. Based on these unique advantages, nickel / carbon composite microwave absorbing materials derived from nickel-based MOFs have become a research hotspot in the field of microwave absorbing materials and are considered one of the most promising high-performance microwave absorbing materials. Currently, performance optimization for this type of material mainly focuses on precursor design, element doping, or composite modification. However, research on the precise control of electromagnetic and microwave absorption properties by introducing specific regulators to participate in the pyrolysis process to achieve directional reconstruction of the material's microstructure is still in the exploratory stage. Among these, there are no reports on innovative methods that use hydrogen as a pyrolysis regulator to reconstruct the microstructure of nickel-based MOFs and optimize their microwave absorption performance through hydrogen-induced effects.

[0003] Patent CN115322744B discloses a nickel-carbon composite material for absorbing electromagnetic waves and its preparation method. A nickel-based MOF precursor is prepared using nickel salts and terephthalic acid as raw materials, and then pyrolyzed and carbonized in an inert gas atmosphere to obtain the nickel-carbon composite microwave absorbing material. The porous structure of the carbon matrix and the magnetic properties of metallic nickel synergistically achieve electromagnetic wave attenuation. The preparation process is simple and low-cost. However, the absorption performance of this patent has significant limitations: the effective absorption bandwidth is only 1.0~2.5 GHz, the absorption frequency band is narrow, and the dispersion of nickel particles after pyrolysis is not controlled, making agglomeration easy and leading to a decrease in magnetic loss capability, which cannot meet the practical application requirements of wideband and high efficiency.

[0004] Patent CN115926182B discloses a novel method for preparing a braided nickel-based MOF microwave absorbing material. The method involves preparing a braided nickel precursor powder using a solvent method, followed by pyrolysis in a low-oxygen environment to obtain an anisotropic nickel-based MOF microwave absorbing material. This method leverages the braided structure to achieve multiple scattering of electromagnetic waves and polarization loss, and simplifies sintering conditions, eliminating the need for a strictly inert or vacuum environment. However, this patent relies solely on a low-oxygen atmosphere for MOF pyrolysis and carbonization, without actively controlling the material's microstructure. The crystallinity, dispersibility, and graphitization degree of the carbon matrix all evolve naturally with pyrolysis, making it impossible to precisely adjust the material's electromagnetic parameters. Therefore, the improvement in microwave absorption performance depends solely on the morphology and structure, lacking core control methods to support controllable performance optimization.

[0005] Patent CN114501966B discloses a zero-dimensional / one-dimensional / two-dimensional composite nanostructure absorbing material containing a nickel MOF-derived phase. This material combines a nickel-based MOF-derived nickel / carbon nanophase with other dimensional absorbing units, utilizing the synergistic effect of the multi-dimensional structure to enhance electromagnetic wave loss and broaden the absorption frequency band. However, this patent treats the nickel-based MOF as a single derived phase without optimizing the microstructure of the nickel-based MOF itself. The electromagnetic properties of the derived nickel / carbon phase are not fully explored, and the multi-dimensional composite process is complex, resulting in weak interfacial bonding between phases. This makes it prone to phase separation under complex environments, leading to a decrease in the stability of the absorption performance. Summary of the Invention

[0006] With the rapid development of 5G / 6G communications, radar detection, smart electronics, and defense stealth, the development of electromagnetic wave absorbing materials that combine broadband, high efficiency, lightweight, and structurally controllable characteristics has become an urgent need. In existing technologies, conventional nickel-based MOF-derived absorbing materials often struggle to achieve both excellent electromagnetic wave attenuation and precise electromagnetic parameter control. Nickel-based MOFs, as ideal precursors for high-performance absorbing materials, exhibit good application potential due to the designability of their composition and structure. However, how to achieve directional reconstruction of their microstructure through simple and efficient methods, and thus precisely control their absorption performance, still requires further exploration.

[0007] The purpose of this invention is to provide a hydrogen-induced nickel-based MOF-derived microwave absorbing material, its preparation method, and its applications. This method uses hydrogen as the core structure modulator, featuring a simple and highly controllable process that can prepare nickel / carbon composite microwave absorbing materials with stable phases, tunable electromagnetic parameters, and no complex post-processing required. The prepared microwave absorbing material exhibits excellent electromagnetic wave absorption performance in the 2–18 GHz microwave frequency band.

[0008] This invention also provides a method for preparing hydrogen-induced reconstructed nickel-based MOF-derived microwave absorbing materials, comprising the following steps: S1. Preparation of nickel-based MOF precursor: Nickel nitrate hexahydrate and trimesic acid were weighed according to the ratio and dissolved in a DMF / ethanol / water mixed solvent. After solvothermal reaction, washing and drying, nickel-based MOF precursor powder was obtained. S2. Hydrogen-induced pyrolysis reconstruction: The nickel-based MOF precursor powder obtained in step S1 is placed in a tube furnace, and an argon-hydrogen mixed gas is introduced. The temperature is increased at a rate of 2–15 °C / min for pyrolysis reduction treatment. After treatment, argon gas is introduced for passivation. After programmed temperature pyrolysis and cooling, the hydrogen-induced reconstructed nickel-based MOF microwave absorbing material is obtained. By systematically adjusting parameters such as hydrogen concentration (to control the crystallinity of metallic nickel, material morphology, and degree of graphitization) and pyrolysis temperature, the electromagnetic wave absorption performance of the absorbing material in the 2–18 GHz frequency band can be effectively controlled.

[0009] In step S1, the amounts of each raw material are: 1.5~2.5 g nickel nitrate hexahydrate, 0.3~0.8 g trimesic acid, and 0.5~3 g PVP; the mixed solvent is a mixture of 20~60 mL DMF, 20~60 mL ethanol, and 20~60 mL water.

[0010] In step S1, the solvothermal reaction conditions are: constant temperature reaction at 150~250 ℃ for 6~12 h; washing method is alternating centrifugal washing with deionized water and anhydrous ethanol; drying conditions are vacuum drying at 40~80 ℃.

[0011] In step S2, the volume concentration of hydrogen in the argon-hydrogen mixed gas is 0% to 30%.

[0012] In step S2, the pyrolysis reduction temperature is 400–900 °C, the holding time is 1–4 h, and the heating rate is 2–10 / min.

[0013] In step S2, the total gas velocity inside the tubular furnace is 50–200 sccm.

[0014] In step S2, the material needs to be passivated with an inert gas for 8–24 h after pyrolysis to protect it.

[0015] A hydrogen-induced remodeling nickel-based MOF-derived microwave absorbing material prepared by the preparation method described above.

[0016] The application of the hydrogen-induced remodeling nickel-based MOF-derived microwave absorbing material in the preparation of electromagnetic wave shielding materials.

[0017] The beneficial effects of this invention are as follows: The process is simple and highly controllable: Nickel-based MOF precursors are prepared using a conventional solvothermal method, combined with a hydrogen atmosphere pyrolysis reconstruction process. No expensive reagents or complex equipment are required, the hydrogen concentration can be easily controlled, the reaction conditions are mild, safe and reliable, and it is suitable for large-scale preparation.

[0018] Controllable structure and excellent performance: By using hydrogen for directional regulation, the microstructure of nickel-based MOF derivatives can be precisely reconstructed. The resulting nickel / carbon composite material exhibits good morphological dispersion and phase stability, with excellent synergy between metallic nickel and the carbon matrix in terms of electromagnetic loss. The material prepared with a 5% hydrogen concentration has an effective absorption bandwidth of up to 8.2 GHz, exhibiting wideband and high-efficiency electromagnetic wave absorption characteristics in the 2–18 GHz frequency band.

[0019] Flexible control and strong adaptability: By fine-tuning process parameters such as hydrogen concentration and pyrolysis temperature, the crystallinity, graphitization degree and magnetic properties of the material can be controlled in a directional manner, so as to realize the customized absorption performance on demand. It can be adapted to the needs of different application scenarios such as wide frequency coverage and high efficiency attenuation, solving the problems of single performance and poor adaptability of traditional absorption materials. Attached Figure Description

[0020] Figure 1 Reflection loss diagrams of nickel-based MOF derivatives with different thicknesses at 5% hydrogen concentration; Figure 2 XRD of the nickel-based MOF derivative in Example 1; Figure 3 Magnetization curves of the nickel-based MOF derivative in Example 1; Figure 4 Scanning electron microscope image of the nickel-based MOF derivative in Example 1; Figure 5 Reflection loss diagrams of nickel-based MOF derivatives at different thicknesses in the range of 2–18 GHz in Example 1; Figure 6 XRD of the nickel-based MOF derivative in Comparative Example 1; Figure 7 Magnetization curves of the nickel-based MOF derivative in Comparative Example 1; Figure 8 Scanning electron microscope image of the nickel-based MOF derivative in Comparative Example 1; Figure 9 Reflection loss diagrams of nickel-based MOF derivatives at different thicknesses in the range of 2–18 GHz in Comparative Example 1; Figure 10 XRD of the nickel-based MOF derivative in Comparative Example 2; Figure 11 Magnetization curves of the nickel-based MOF derivative in Comparative Example 2; Figure 12 Scanning electron microscope image of the nickel-based MOF derivative in Comparative Example 2; Figure 13 Reflection loss diagrams of nickel-based MOF derivatives at different thicknesses in the range of 2–18 GHz in Comparative Example 2; Figure 14 XRD of the nickel-based MOF derivatives in Comparative Example 3; Figure 15 Magnetization curves of nickel-based MOF derivatives in Comparative Example 3; Figure 16 The image shows a scanning electron microscope (SEM) image of the material prepared in Comparative Example 3. Figure 17 Reflection loss diagrams of nickel-based MOF derivatives at different thicknesses in the range of 2–18 GHz in Comparative Example 3. Detailed Implementation

[0021] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the specific embodiments, structures, features, and effects according to the present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments. In the following description, different "embodiments" or "embodiments" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0022] Example 1 This embodiment provides a method for preparing a hydrogen-induced reconstructed nickel-based MOF microwave absorbing material, the steps of which are as follows: (1) Preparation of nickel-based MOF precursor: Weigh 1.745 g nickel nitrate hexahydrate and 0.51 g trimesic acid, and dissolve them together in a mixed solvent consisting of 40 mL DMF, 40 mL anhydrous ethanol and 40 mL deionized water. Stir magnetically for 30 min until the raw materials are completely dissolved to obtain a homogeneous mixed solution. Transfer the mixed solution into a 200 mL polytetrafluoroethylene reaction vessel, seal it and place it in an oven. Perform a solvothermal reaction at 200 °C for 8 h. After the reaction is completed, allow it to cool naturally to room temperature. Wash the green precipitate in the vessel three times by alternating centrifugation with deionized water and anhydrous ethanol. Then dry it in a vacuum drying oven at 60 °C for 12 h. After grinding, obtain nickel-based MOF precursor powder.

[0023] (2) Hydrogen-induced pyrolysis reconstruction: Take 0.5 g of nickel-based MOF precursor powder obtained in step (1) and put it into a tube furnace; after pumping out the gas in the furnace tube, argon gas is then introduced to atmospheric pressure and then a hydrogen-argon mixed gas with a hydrogen volume concentration of 0% is introduced to maintain a total gas flow rate of 100 sccm; set the heating program of the tube furnace and heat it to 600 ℃ at a heating rate of 10 ℃ / min, and hold it at the temperature for pyrolysis for 3 h; after the pyrolysis is completed, turn off the heating device, purge the gas in the tube, and then introduce argon gas again for 12 h to derive the nickel-based MOF absorbing material.

[0024] Figure 2 The image shows the XRD pattern of the nickel-based MOF-derived microwave absorbing material prepared in this embodiment. Figure 2 As can be seen, nickel-based MOF-derived microwave absorbing materials have been successfully synthesized.

[0025] Figure 3 This is the room-temperature hysteresis loop spectrum of the absorbing material prepared in this embodiment. From... Figure 3 As can be seen, the material is ferromagnetic, with a coercivity of 17 Oe and a saturation magnetization of 47.48 emu / g, and has the potential for magnetic loss.

[0026] Figure 4 This is a scanning electron microscope (SEM) image of the absorbing material prepared in this embodiment. From... Figure 4 As can be seen, the material is spherical with a rough surface.

[0027] Figure 5 This diagram shows the reflection loss of the absorbing material prepared in this embodiment at different thicknesses within the range of 2–18 GHz. Figure 5 As can be seen, the obtained absorbing material has an effective absorption bandwidth of up to 2.6 GHz with a thickness of 2.5 mm.

[0028] Comparative Example 1 The only difference between this comparative example and Example 1 is that pure argon gas is introduced in step (2), and the hydrogen volume concentration is 5%. The remaining steps and process parameters are exactly the same as those in Example 1.

[0029] Figure 6 The image shows the XRD pattern of the nickel-based MOF-derived microwave absorbing material prepared in this embodiment. Figure 6 As can be seen, nickel-based MOF-derived microwave absorbing materials have been successfully synthesized.

[0030] Figure 7 The room-temperature hysteresis loop spectrum of the absorbing material prepared in this comparative example. Figure 7 As can be seen, the material is ferromagnetic, with a coercivity of 3 Oe and a saturation magnetization of 43.09 emu / g, and its magnetic properties are weaker than those of Example 1.

[0031] Figure 8 This is a scanning electron microscope (SEM) image of the absorbing material prepared in this embodiment. From... Figure 8 As can be seen, the material is spherical and has a relatively rough surface.

[0032] Figure 9 This diagram shows the reflection loss of the absorbing material prepared in this embodiment at different thicknesses within the range of 2–18 GHz. Figure 9 As can be seen, the prepared absorbing material exhibits excellent broadband absorption performance in the microwave band, with an effective absorption bandwidth of up to 8.2 GHz at a thickness of 2.5 mm, which is the best among all embodiments and comparative examples.

[0033] Comparative Example 2 The only difference between this comparative example and Example 1 is that in step (2), an argon-hydrogen mixed gas with a hydrogen volume concentration of 10% is introduced. The remaining steps and process parameters are exactly the same as in Example 1.

[0034] Figure 10 The image shows the XRD pattern of the nickel-based MOF-derived microwave absorbing material prepared in this embodiment. Figure 10 As can be seen, nickel-based MOF-derived microwave absorbing materials have been successfully synthesized.

[0035] Figure 11 The room-temperature hysteresis loop spectrum of the absorbing material prepared in this comparative example. Figure 11As can be seen, the material is ferromagnetic, with a coercivity of 30 Oe and a saturation magnetization of 43.09 emu / g, which is the highest among all embodiments and comparative examples, but the magnetic loss and dielectric loss have poor matching.

[0036] Figure 12 This is a scanning electron microscope (SEM) image of the absorbing material prepared in this embodiment. From... Figure 12 As can be seen, the material is spherical and has a relatively rough surface.

[0037] Figure 13 The reflection loss diagrams for the absorbing material prepared in this comparative example at different thicknesses within the range of 2–18 GHz show that the effective absorption bandwidth can reach 4.6 GHz at a thickness of 2.5 mm. Comparative Example 3 The only difference between this comparative example and Example 1 is that in step (2), an argon-hydrogen mixed gas with a hydrogen volume concentration of 30% is introduced. The remaining steps and process parameters are exactly the same as in Example 1.

[0038] Figure 14 The image shows the XRD pattern of the nickel-based MOF-derived material prepared in this embodiment. Figure 14 As can be seen, nickel-based MOF-derived materials have been successfully synthesized.

[0039] Figure 15 The room-temperature hysteresis loop spectrum of the material prepared for this comparative example. Figure 15 As can be seen, the material is ferromagnetic, with a coercivity of 18 Oe and a saturation magnetization of 58.69 emu / g, which is the highest among all embodiments and comparative examples, but the magnetic loss and dielectric loss have poor matching.

[0040] Figure 16 This is a scanning electron microscope (SEM) image of the material prepared in this embodiment. From... Figure 2 As can be seen, the material is in the form of spherical aggregates, and its surface is the smoothest compared to the comparative example.

[0041] Figure 17 The image shows the reflection loss of the material prepared in this comparative example at different thicknesses within the range of 2 to 18 GHz. The prepared material no longer has wave absorption properties.

[0042] The above description is merely a preferred embodiment of the present invention and is 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. The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the protection scope of the present invention.

Claims

1. A method for preparing a hydrogen-induced reconstructed nickel-based MOF-derived microwave absorbing material, characterized in that, Includes the following steps: S1. Preparation of nickel-based MOF derivative precursors: Nickel nitrate hexahydrate, trimesic acid, and polyvinylpyrrolidone were added to a mixed solvent of N,N-dimethylformamide, ethanol, and water. After stirring and dissolving, a solvothermal reaction was carried out. The product was washed and dried to obtain nickel-based MOF powder. S2. Hydrogen atmosphere pyrolysis reduction: The powder obtained in step S1 is placed in a tube furnace, and an argon-hydrogen mixed gas is introduced. The temperature is increased at a rate of 2~15℃ / min for pyrolysis reduction treatment. After treatment, argon gas is introduced for passivation.

2. The method for preparing hydrogen-induced reconstructed nickel-based MOF-derived microwave absorbing material according to claim 1, characterized in that, In step S1, the amounts of each raw material are: 1.5~2.5 g nickel nitrate hexahydrate, 0.3~0.8 g trimesic acid, and 0.5~3 g PVP; the mixed solvent is a mixture of 20~60 mL DMF, 20~60 mL ethanol, and 20~60 mL water.

3. The method for preparing hydrogen-induced reconstructed nickel-based MOF-derived microwave absorbing material according to claim 1, characterized in that, In step S1, the solvothermal reaction conditions are: constant temperature reaction at 150~250 ℃ for 6~12 h; washing method is alternating centrifugal washing with deionized water and anhydrous ethanol; drying conditions are vacuum drying at 40~80 ℃.

4. The method for preparing hydrogen-induced reconfiguration nickel-based MOF-derived microwave absorbing material according to claim 1, characterized in that, In step S2, the volume concentration of hydrogen in the argon-hydrogen mixed gas is 0% to 30%.

5. The method for preparing hydrogen-induced reconstructed nickel-based MOF-derived microwave absorbing material according to claim 1, characterized in that, In step S2, the pyrolysis reduction temperature is 400–900 °C, the holding time is 1–4 h, and the heating rate is (2–10) / min.

6. The method for preparing hydrogen-induced reconfiguration nickel-based MOF-derived microwave absorbing material according to any one of claims 1 and 5, characterized in that, In step S2, the total gas velocity inside the tubular furnace is 50–200 sccm.

7. In the preparation method of hydrogen-induced reconstructed nickel-based MOF-derived microwave absorbing material according to claim 1, in step S2, the material needs to be passivated with an inert gas for 8-24 hours after pyrolysis to protect it.

8. A hydrogen-induced reconfiguration nickel-based MOF-derived microwave absorbing material prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the hydrogen-induced reconfiguration nickel-based MOF-derived microwave absorbing material according to claim 8 in the preparation of electromagnetic wave shielding materials.

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