A novel multi-band responsive Mo-TiC MXene / MoC-Mo2N electromagnetic absorbing material preparation method and product

Abstract

This invention discloses a method for preparing a novel multi-band responsive Mo-TiC MXene / MoC-Mo2N electromagnetic absorbing material and the resulting product. Using Mo2TiAlC2MAX as a precursor, a multilayer Mo-TiC MXene is exfoliated through an etching process. A TMAOH intercalation process is then used to transform the multilayer Mo-TiC MXene into a few-layer Mo-TiC MXene. An in-situ pre-oxidation strategy is employed to introduce a large number of oxygen-containing functional groups, and an in-situ heat treatment strategy is used to anchor MoC and Mo2N nanoparticles onto the Mo-TiC MXene matrix, thereby achieving multi-band responsive electromagnetic absorbing performance. This invention not only expands the types of electromagnetic absorbing materials and develops a new variety of electromagnetic absorbing materials with high efficiency absorption in multiple frequency bands and ultra-thin matching thickness, but also enables the control of dielectric loss of Mo-TiC MXene / MoC-Mo2N materials by MoC and Mo2N nanoparticles. It effectively overcomes the problems of poor impedance matching, weak absorption capacity, large matching thickness, and difficulty in achieving multi-frequency absorption in existing electromagnetic absorbing materials, and provides a brand-new method for the formation of MoC and Mo2N.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic microwave absorption technology, and in particular to a method for preparing a novel multi-band responsive Mo-TiCMXene / MoC-Mo2N electromagnetic absorbing material and the product obtained therefrom. Background Technology

[0002] Stealth technology is a key focus of research and development in the defense and military field today, as it can effectively improve the survivability, breakthrough capabilities, and combat effectiveness of military equipment. Therefore, stealth technology has become a research priority for major military powers worldwide. Furthermore, with the development of 5G / 6G technology and the continuous evolution of electronic devices, electromagnetic pollution is becoming increasingly serious. Therefore, the development of advanced and efficient electromagnetic absorbing materials is of significant strategic importance in both defense and civilian applications.

[0003] Carbides, as typical dielectric loss materials, have attracted considerable attention from researchers due to their excellent thermal stability, high mechanical strength, oxidation resistance, and corrosion resistance. Among them, molybdenum carbide is one of the most widely used metallic carbides, possessing excellent dielectric properties, chemical stability, and controllable composition and structure, making it widely applicable in the field of electromagnetic wave absorption. However, excessive conductivity and impedance mismatch caused by agglomeration remain obstacles to the application of molybdenum carbide alone. Molybdenum nitride, as another molybdenum-based metal compound with good conductivity, is considered one of the ideal dielectric materials. Currently, it is generally believed that the performance of a material is highly correlated with its microstructure. Therefore, constructing molybdenum-based compounds with different crystal structures may be a feasible method to optimize impedance matching and may also provide additional interfacial polarization and dipole polarization for the material. Furthermore, research indicates that Mo atoms occupy the outermost layer of Mo-TiC MXene formed by etching Mo2TiAlC2 MAX, which facilitates the in-situ formation of molybdenum-based compounds, such as sulfides, oxides, nitrides, and carbides, on the Mo-TiC MXene surface through specialized processes, while preserving the inherent structure of Mo-TiC MXene. Therefore, utilizing Mo atoms in Mo-TiC MXene to synthesize molybdenum-based compounds is feasible and helps address the aggregation problem. However, since Mo-TiC MXene itself is a two-dimensional layered structure, it is susceptible to van der Waals forces, potentially leading to stacking issues. This affects the large-scale synthesis of molybdenum-based compounds and the electromagnetic wave absorption performance of the material. Current technologies for addressing the stacking problem in Mo-TiC MXene primarily involve transforming multilayer structures into few-layer or single-layer structures using methods such as ultrasound, intercalation, and molten salt. Therefore, developing Mo-TiC MXene / MoC-Mo2N electromagnetic wave absorbing materials with superior performance using few-layer Mo-TiC MXene is of great significance. In addition, discovering a low-cost, high-yield method for preparing few-layer Mo-TiC MXene materials, and finding a simple and effective process for synthesizing molybdenum-based compounds are also among the technical challenges in the synthesis of this material. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a novel method for preparing multi-band responsive Mo-TiCMXene / MoC-Mo2N electromagnetic absorbing materials. Through in-situ pre-oxidation and in-situ heat treatment processes, a large number of MoC and Mo2N nanoparticles are formed on the surface of a few-layer Mo-TiCMXene, thereby utilizing an in-situ phase transition strategy to adjust the dielectric loss capability. This provides an important technical approach and method for the design of multi-band responsive electromagnetic absorbing materials. Another objective of this invention is to provide products prepared using the aforementioned novel multi-band responsive Mo-TiCMXene / MoC-Mo2N electromagnetic absorbing material preparation method.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] This invention provides a method for preparing a novel multi-band responsive Mo-TiC MXene / MoC-Mo2N electromagnetic absorbing material, comprising the following steps:

[0007] (1) Preparation of multilayer Mo-TiC MXene

[0008] Using Mo2TiAlC2MAX as raw material and 40% hydrofluoric acid as etching agent, the raw material: etching agent = 0.5-1g: 20-60mL were stirred and mixed together, and then collected by centrifugation and washed to obtain undried multilayer Mo-TiCMXene.

[0009] (2) Preparation of few-layer Mo-TiC MXene

[0010] (2-1) Using the undried multilayer Mo-TiC MXene as the material and TMAOH with a concentration of 5wt% as the intercalating agent, the materials are mixed together at a mass-volume ratio of material:intercalating agent = 0.5-1.2g: 20-40mL. After centrifugation and washing, a few-layer Mo-TiC MXene precursor with TMAOH removed is obtained.

[0011] (2-2) The few-layer Mo-TiC MXene precursor was dispersed again in deionized water and mixed together according to the mass-volume ratio of few-layer Mo-TiC MXene precursor: deionized water = 0.7-1.5g: 20-30mL. The supernatant was collected by centrifugation. The supernatant collection process was repeated, and the combined supernatants were the few-layer Mo-TiC MXene solution.

[0012] (3) Preparation of few-layer Mo-TiC MXene-O powder

[0013] The few-layer Mo-TiC MXene solution was stirred and refluxed in a constant temperature environment, and then freeze-dried to obtain few-layer Mo-TiC MXene-O powder. In this way, the few-layer Mo-TiC MXene-O was obtained by in-situ pre-oxidation process, which provides a molybdenum oxide intermediate phase for the formation of MoC and Mo2N in the next in-situ heat treatment process.

[0014] (4) Preparation of Mo-TiC MXene / MoC-Mo2N

[0015] According to the mass ratio of few-layer Mo-TiC MXene-O to dicyandiamide = 1-2-0.5-4, the few-layer Mo-TiC MXene-O powder and dicyandiamide are placed at both ends of a ceramic boat and placed in a tube furnace, with dicyandiamide at the inlet end and the few-layer Mo-TiC MXene-O powder at the outlet end. Argon gas is introduced at a flow rate of 200-400 mL / min, and the temperature is increased to 350-550℃ at 2℃ / min for 1-4 hours, followed by heat treatment at 700-850℃ at 5℃ / min for 1-4 hours, thus obtaining a Mo-TiC MXene / MoC-Mo2N electromagnetic absorbing material with multi-band response. Dicyandiamide provides gaseous carbon and nitrogen sources for the formation of MoC and Mo2N, while molybdenum in the few-layer Mo-TiC MXene-O provides a molybdenum source for the formation of MoC and Mo2N. The few-layer Mo-TiC MXene-O undergoes a two-stage heat treatment process to first form a molybdenum oxide mesophase, which then reacts with gaseous carbon and nitrogen sources to form MoC and Mo2N, respectively.

[0016] Further, in step (1) of the present invention, the stirring and mixing time is 72-96 h; the centrifugation speed is 3000-8000 r / min, and the centrifugation time is 5-30 min; the washing solution is deionized water, and the washing is performed until the pH value is ≥7. In step (2-1), the stirring and mixing time is 12-24 h; the centrifugation speed is 10000-13000 r / min, and the centrifugation time is 5-30 min; the washing solution is deionized water, and the washing is performed until the pH value is ≥7; in step (2-2), the centrifugation speed is 3000-4000 r / min, and the centrifugation time is 30-60 min; the supernatant collection process is repeated 3-6 times. In step (3), the stirring and reflux temperature is 40-50℃, and the time is 48-72 h; the freeze-drying time is 48-72 h.

[0017] The product prepared by the above-mentioned novel multi-band response Mo-TiC MXene / MoC-Mo2N electromagnetic absorbing material has a reflection loss of -14.8 to -65.2 dB with a matching thickness of 1.565 to 5 mm in the frequency range of 2 to 18 GHz.

[0018] The present invention has the following beneficial effects:

[0019] (1) This invention uses Mo2TiAlC2MAX and dicyandiamide as raw materials, combined with etchants and intercalating agents, and employs in-situ pre-oxidation and heat treatment processes to synthesize MoC and Mo2N nanoparticles in situ on the surface of few-layer Mo-TiC MXene nanosheets, thereby regulating the overall dielectric properties of the material. This invention not only expands the types of electromagnetic absorbing materials, but also develops a new variety of electromagnetic absorbing materials with multi-band absorption (reflection loss of -14.8 to -65.2 dB) and ultra-thin matching thickness (1.565 to 5 mm). Through the synergistic effect of conduction loss and multiple interface polarization mechanisms, the dielectric loss capability of the material is adjusted, overcoming the problems of poor impedance matching, weak absorption capability, and large matching thickness of existing electromagnetic absorbing materials.

[0020] (2) In this invention, hydrofluoric acid is used as an etchant to etch away the Al layer in Mo2TiAlC2 MAX to form a multilayer Mo-TiC MXene, which provides the required multilayer MXene structure for TMAOH intercalation of Mo-TiC MXene and provides the prerequisite for the formation of few-layer Mo-TiC MXene nanosheets.

[0021] (3) In this invention, TMAOH is used as an intercalating agent, and TMAOH is introduced by magnetic stirring. + Ions are intercalated into the interlayer spaces of multilayer Mo-TiCMXene, expanding the interlayer spacing and further transforming the multilayer structure of Mo-TiCMXene into a few-layer structure. The few-layer Mo-TiCMXene nanosheets prepared by the TMAOH intercalation process have a large specific surface area and relatively large inter-sheet spacing, providing space for the in-situ synthesis of MoC and Mo2N nanoparticles. Furthermore, the synthesis of nanoparticles can effectively inhibit the re-aggregation of few-layer Mo-TiCMXene.

[0022] (4) The present invention employs an in-situ pre-oxidation process to introduce a large number of oxygen-containing functional groups into the few-layer Mo-TiC MXene, providing oxygen for the subsequent heat treatment process. This ensures that after heat treatment, the few-layer Mo-TiC MXene-O preferentially forms a molybdenum oxide mesophase, which then undergoes a phase transformation with carbon and nitrogen elements in dicyandiamide to form MoC and Mo2N, respectively. The present invention demonstrates that the in-situ pre-oxidation strategy is indispensable in the entire process; only after the pre-oxidation process is performed can MoC and Mo2N be formed.

[0023] (5) In the reaction system of this invention, dicyandiamide is used to provide the carbon and nitrogen elements required for the synthesis of molybdenum-based compounds. The purpose is to transform the molybdenum oxide mesophase preferentially formed in the in-situ heat treatment process into MoC and Mo2N. Therefore, the Mo-TiC MXene / MoC-Mo2N heterostructure can be precisely controlled by adjusting the in-situ heat treatment and in-situ pre-oxidation process parameters. This is beneficial for expanding the loss path, promoting interface polarization and improving dielectric loss capability, achieving efficient multi-band response, and effectively overcoming the problems of poor impedance matching, weak absorption capability, large matching thickness and difficulty in taking into account multi-band absorption of existing electromagnetic absorbing materials. This provides a new method for the formation of MoC and Mo2N.

[0024] (6) The process of this invention has high repeatability, is easy to control, has low cost, and is easy to promote and use. Attached Figure Description

[0025] The present invention will now be described in further detail with reference to the embodiments and accompanying drawings:

[0026] Figure 1 This is a scanning electron microscope image of the novel multi-band responsive Mo-TiC MXene / MoC-Mo2N electromagnetic absorbing material prepared according to an embodiment of the present invention;

[0027] Figure 2 This is an X-ray diffraction pattern of the novel multi-band responsive Mo-TiC MXene / MoC-Mo2N electromagnetic absorbing material prepared according to an embodiment of the present invention;

[0028] Figure 3 This is a graph showing the relationship between reflection loss and frequency of the novel multi-band response Mo-TiC MXene / MoC-Mo2N electromagnetic absorbing material prepared according to embodiments of the present invention at different matching thicknesses;

[0029] Figure 4 This is a graph showing the optimal reflection loss versus frequency relationship of the electromagnetic absorbing materials in the embodiments and comparative examples of the present invention. Detailed Implementation

[0030] Example:

[0031] This invention discloses a method for preparing a novel multi-band responsive Mo-TiC MXene / MoC-Mo2N electromagnetic absorbing material, the steps of which are as follows:

[0032] (1) Preparation of multilayer Mo-TiC MXene

[0033] Using Mo2TiAlC2 MAX as raw material and 40% hydrofluoric acid as etching agent, 30 mL of etching agent was measured into a 100 mL Teflon liner, and 1 g of Mo2TiAlC2 MAX was slowly added. After mixing with magnetic stirring at 55 °C for 72 h, the resulting suspension was collected by centrifugation at 6000 r / min for 5 min and washed with deionized water until the pH value was ≥7 to obtain undried multilayer Mo-TiC MXene.

[0034] (2) Preparation of few-layer Mo-TiC MXene

[0035] (2-1) Using 5wt% TMAOH as an intercalating agent, 0.8g of the above-mentioned undried multilayer Mo-TiCMXene was added to 40mL of intercalating agent, and the mixture was magnetically stirred at room temperature for 12h to intercalate the TMAOH. + Ions are inserted into the interlayer space of Mo-TiC MXene, expanding the interlayer spacing; the resulting solution is collected by centrifugation at 10000 r / min for 10 min, and washed with deionized water until the pH value is ≥7, to obtain a few-layer Mo-TiC MXene precursor with TMAOH removed;

[0036] (2-2) Disperse 0.8g of the above few-layer Mo-TiC MXene precursor again into 25mL of deionized water. After shaking and mixing for 5min at room temperature, the resulting suspension is centrifuged at 3500r / min for 60min to obtain the supernatant. The supernatant collection process is repeated 4 times to increase the yield. The combined supernatant of about 100mL is the few-layer Mo-TiC MXene solution.

[0037] (3) Preparation of few-layer Mo-TiC MXene-O powder

[0038] 40 mL of the above few-layer Mo-TiC MXene solution was taken, magnetically stirred and refluxed in an oil bath at 50 °C for 72 h, and then freeze-dried at -90 °C for 48 h to obtain few-layer Mo-TiC MXene-O powder. In this way, few-layer Mo-TiC MXene-O was obtained by in-situ pre-oxidation process, which provides a molybdenum oxide intermediate phase for the formation of MoC and Mo2N in the next in-situ heat treatment process.

[0039] (4) Preparation of Mo-TiC MXene / MoC-Mo2N

[0040] According to the mass ratio of few-layer Mo-TiC MXene-O to dicyandiamide = 1:1, the above-mentioned few-layer Mo-TiC MXene-O powder and dicyandiamide were placed at both ends of a ceramic boat and placed in the middle of a quartz tube furnace, with dicyandiamide placed at the inlet end and few-layer Mo-TiC MXene-O powder placed at the outlet end; argon gas was introduced at a flow rate of 200 mL / min, and the temperature was first increased to 400℃ at 2℃ / min for 2 hours, and then increased to 750℃ at 5℃ / min for 2 hours, thus obtaining a Mo-TiC MXene / MoC-Mo2N electromagnetic absorbing material with multi-band response (see...). Figure 1 and Figure 2 ).

[0041] The Mo-TiC MXene / MoC-Mo2N multi-band electromagnetic absorbing material prepared in this embodiment exhibits reflection losses of -65.2dB, -52.2dB, -22.8dB, -14.8dB, -27.2dB, -47.2dB, -17.0dB, -15.1dB, and -15.0dB at matching thicknesses of 1.565mm, 1.7mm, 2.0mm, 2.245mm, 3.0mm, 3.165mm, 3.975mm, 4.5mm, and 5.0mm within the frequency range of 2–18GHz, respectively. All these reflection losses are less than -10dB, achieving effective and multi-band electromagnetic absorption. The optimal reflection loss is -65.2dB with a matching thickness of 1.565mm (see...). Figure 3 ).

[0042] Comparative Example 1:

[0043] This comparative example uses the preparation method of the present invention, and the few-layer Mo-TiC MXene-O obtained in step (3) is used as an electromagnetic absorbing material.

[0044] The electromagnetic absorbing material prepared in this comparative example is Mo-TiC MXene-O. Within the frequency range of 2–18 GHz and with a matching thickness of 1.565–5 mm, the optimal reflection loss is -13.6 dB, with a matching thickness of 5 mm (see...). Figure 4 ).

[0045] Comparative Example 2:

[0046] This comparative example uses the preparation method of the present invention, but differs from the example in that 0g of dicyandiamide is added in step (4).

[0047] The electromagnetic absorbing material prepared in this comparative example is Mo-TiC MXene-OP. Within the frequency range of 2–18 GHz and with a matching thickness of 1.565–5 mm, the optimal reflection loss is -12 dB, with a matching thickness of 5 mm (see...). Figure 4 ).

[0048] Comparative Example 3:

[0049] This comparative example uses the preparation method of the embodiment of the present invention. The difference from the embodiment is that the few-layer Mo-TiC MXene solution obtained in step (2) is freeze-dried to obtain few-layer Mo-TiC MXene powder; the few-layer Mo-TiC MXene powder and dicyandiamide are used in step (4) for preparation.

[0050] The electromagnetic absorbing material prepared in this comparative example is Mo-TiC MXene-CN-P. Within the frequency range of 2–18 GHz and with a matching thickness of 1.565–5 mm, the optimal reflection loss is -5.4 dB, and the matching thickness is 3 mm (see...). Figure 4 ).

[0051] The Mo-TiC MXene / MoC-Mo2N multi-band electromagnetic absorbing material prepared in the embodiments of the present invention, such as... Figure 1 and 3 As shown, a large number of MoC and Mo2N nanoparticles were synthesized in situ on the surface of few-layer Mo-TiC MXene, and the dielectric loss capability of the material was tuned to achieve efficient multi-band electromagnetic wave absorption; Figure 4 As shown, compared with the electromagnetic absorbing materials of Comparative Examples 1, 2, and 3, the embodiments of the present invention have stronger electromagnetic absorbing capabilities, thinner matching thickness, and wider effective absorption bandwidth.

Claims

1. A method for preparing a novel multi-band response Mo-TiC MXene / MoC-Mo2N electromagnetic absorbing material, characterized in that... Includes the following steps: (1) Preparation of multilayer Mo-TiC MXene Using Mo2TiAlC2MAX as raw material and 40% hydrofluoric acid as etching agent, the raw material: etching agent = 0.5-1g: 20-60mL were stirred and mixed together, and then collected by centrifugation and washed to obtain undried multilayer Mo-TiCMXene. (2) Preparation of few-layer Mo-TiC MXene (2-1) Using the undried multilayer Mo-TiC MXene as the material and TMAOH with a concentration of 5wt% as the intercalating agent, the materials are mixed together at a mass-volume ratio of material:intercalating agent = 0.5-1.2g: 20-40mL. After centrifugation and washing, a few-layer Mo-TiC MXene precursor with TMAOH removed is obtained. (2-2) The few-layer Mo-TiC MXene precursor was dispersed again in deionized water and mixed together according to the mass-volume ratio of few-layer Mo-TiC MXene precursor: deionized water = 0.7-1.5g: 20-30mL. The supernatant was collected by centrifugation. The supernatant collection process was repeated, and the combined supernatants were the few-layer Mo-TiC MXene solution. (3) Preparation of few-layer Mo-TiC MXene-O powder The few-layer Mo-TiC MXene solution was stirred and refluxed in a constant temperature environment, and then freeze-dried to obtain few-layer Mo-TiC MXene-O powder; (4) Preparation of Mo-TiC MXene / MoC-Mo2N According to the mass ratio of few-layer Mo-TiC MXene-O : dicyandiamide = 1~2 : 0.5~4, the few-layer Mo-TiC MXene-O powder and dicyandiamide are placed at both ends of a ceramic boat and placed in a tube furnace, with the dicyandiamide placed at the inlet end and the few-layer Mo-TiC MXene-O powder placed at the outlet end; argon gas is introduced at a flow rate of 200~400 mL / min, and the temperature is increased to 350~550℃ at 2℃ / min for 1~4 h, and then the temperature is increased to 700~850℃ at 5℃ / min for 1~4 h, thus obtaining a Mo-TiC MXene / MoC-Mo2N electromagnetic absorbing material with multi-band response.

2. The preparation method of the novel multi-band response Mo-TiC MXene / MoC-Mo2N electromagnetic absorbing material according to claim 1, characterized in that: In step (1), the stirring time is 72-96 hours; the centrifugation speed is 3000-8000 r / min and the centrifugation time is 5-30 minutes; the washing solution is deionized water and the washing is performed until the pH value is ≥7.

3. The preparation method of the novel multi-band response Mo-TiC MXene / MoC-Mo2N electromagnetic absorbing material according to claim 1, characterized in that: In step (2-1), the stirring and mixing time is 12-24 hours, the centrifugation speed is 10000-13000 r / min, the centrifugation time is 5-30 minutes, and the washing solution is deionized water, and the washing is performed until the pH value is ≥7; in step (2-2), the centrifugation speed is 3000-4000 r / min, the centrifugation time is 30-60 minutes; the supernatant collection process is repeated 3-6 times.

4. The preparation method of the novel multi-band response Mo-TiC MXene / MoC-Mo2N electromagnetic absorbing material according to claim 1, characterized in that: The stirring and reflux in step (3) are carried out at a temperature of 40-50°C for 48-72 hours; the freeze-drying time is 48-72 hours.

5. A product prepared using the method for preparing the novel multi-band response Mo-TiC MXene / MoC-Mo2N electromagnetic absorbing material according to any one of claims 1-4.

6. The product according to claim 5, characterized in that: The multi-band electromagnetic absorbing material has a reflection loss of -14.8 to -65.2 dB when matched with a thickness of 1.565 to 5 mm within the frequency range of 2 to 18 GHz.

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