Preparation method and product of a new type of high-efficiency ultra-thin Mo2TiC2 MXene / MoS2 electromagnetic wave absorption material

Abstract

The present invention discloses a method for preparing a novel, highly efficient, ultra-thin Mo2TiC2MXene / MoS2 electromagnetic wave absorbing material and a product obtained thereof. The method comprises the following steps: using Mo2TiAlC2MAX ceramic as a precursor, peeling off the precursor into multi-layer Mo2TiC2MXene through an etching process, and then using the precursor as a matrix material. A molten salt method and a hydrothermal synthesis method are used to convert the multi-layer Mo2TiC2MXene into a single-layer Mo2TiC2MXene. A two-dimensional ultra-thin MoS2 nanosheet is grown on the surface interface of the two-dimensional single-layer Mo2TiC2MXene to form a double two-dimensional heterostructure with tight surface interface bonding and rich heterogeneous interfaces, which can be efficiently applied to electromagnetic wave absorption. The present invention not only expands the types of electromagnetic wave absorbing materials and develops a new type of electromagnetic wave absorbing material with high efficiency absorption and ultra-thin matching thickness, but also achieves adjustable specific surface area of Mo-based MXene nanosheets and thickness of ultra-thin MoS2 nanosheets, controllable morphology and interface of the heterostructure, and tight interface bonding, effectively overcoming the problems of poor impedance matching, weak absorption, and large matching thickness of electromagnetic wave absorbing materials in the prior art.

Description

Technical Field

[0001] The present invention relates to the field of electromagnetic microwave absorption technology, and in particular to a method for preparing a novel high-efficiency ultra-thin Mo2TiC2MXene / MoS2 electromagnetic wave absorption material and a product obtained therefrom. Background Art

[0002] With the rapid development of the 5G era, many high-power mobile communications and electronic devices are widely used in civil, medical and other fields, but the electromagnetic radiation and pollution they cause are becoming increasingly serious, threatening human health and the normal use of electronic equipment. At the same time, various national defense and military weapons and equipment are constantly being upgraded, which puts forward more stringent requirements on stealth technology. Coating electromagnetic wave absorbing materials on military equipment is an effective means of anti-detection. Therefore, the development of high reflection loss (R L ), wide effective bandwidth (R L <-10dB), thin matching thickness and low density high-quality electromagnetic wave absorbing materials are crucial and are also the main development direction of electromagnetic functional materials.

[0003] Two-dimensional (2D) nanomaterials, with their high specific surface area, excellent flexibility, and unique electrical properties, have become the preferred materials for lightweight and high-performance electromagnetic wave absorption. Among them, transition metal carbonitrides Ti3C2 (MXene), a new class of 2D nanomaterials, and Mo-based MXene (Mo2TiC2 MXene), in particular, have been developed as highly effective electromagnetic wave absorbers due to their excellent mechanical properties, multilayer structure, hydrophilicity, tunable conductivity, and abundant surface functional groups. However, the high conductivity of dense MXene ceramics leads to strong surface reflection, which can easily lead to impedance mismatch. Furthermore, due to the stacking effect, adjacent synthesized MXene ceramic nanosheets are prone to reaggregation, which severely reduces electromagnetic wave absorption capacity. Most importantly, due to the limited number of components and absorption mechanisms, single 2D materials are difficult to achieve excellent impedance matching and electromagnetic loss performance, resulting in large matching thicknesses and a narrow effective absorption band. Therefore, the development of Mo-based MXene ceramic-based electromagnetic wave absorbers with ultra-thin matching thicknesses and high absorption capacity is of great significance. In addition, it is very necessary to develop a preparation method for Mo-based MXene ceramic-based electromagnetic wave absorption materials with low cost and high yield for application in the field of electromagnetic wave absorption, which is also one of the technical difficulties in the field of electromagnetic wave absorption materials. Summary of the Invention

[0004] The present invention aims to overcome the shortcomings of the prior art and provide a method for preparing a novel, highly efficient, ultrathin Mo2TiC2MXene / MoS2 electromagnetic wave absorbing material. Using processes such as molten salt and hydrothermal synthesis, two-dimensional ultrathin MoS2 nanosheets are grown on the surface interface of a two-dimensional monolayer of Mo2TiC2MXene, forming a dual two-dimensional heterostructure with tightly bonded surfaces and abundant heterogeneous interfaces. This structure is applied to electromagnetic wave absorption, effectively meeting the requirements of novel electromagnetic wave absorption technologies. Another object of the present invention is to provide products produced using this method for preparing the novel, highly efficient, ultrathin electromagnetic wave absorbing material.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] The present invention provides a method for preparing a novel, high-efficiency, ultra-thin Mo2TiC2 MXene / MoS2 electromagnetic wave absorbing material, comprising the following steps:

[0007] (1) Preparation of multilayer Mo2TiC2 MXene

[0008] Using Mo2TiAlC2 MAX bulk ceramic as raw material and 40% concentrated hydrofluoric acid as etchant, the material was magnetically stirred at room temperature according to the mass volume ratio of Mo2TiAlC2 MAX: etchant = 0.5-1g: 20-60mL, and then collected by centrifugation, washed, and dried to obtain multilayer Mo2TiC2 MXene.

[0009] (2) Preparation of single-layer Mo2TiC2 MXene

[0010] The multilayer Mo2TiC2 MXene is used as a raw material and combined with a metal salt, and the mixture is mixed according to a mass ratio of multilayer Mo2TiC2 MXene: metal salt = 0.5-2:5-20. After grinding, the mixture is placed in a tube furnace, nitrogen is introduced at a flow rate of 200-400 mL / min, and the temperature is increased by 2°C / min to 350-550°C for heat treatment for 1-4 hours, and then the temperature is increased by 5°C / min to 600-900°C for heat treatment for 1-4 hours to obtain a heat-treated powder; the heat-treated powder is used as a raw material and combined with an acid solution, magnetically stirred at room temperature, and then centrifuged, washed, and dried to obtain a single-layer Mo2TiC2 MXene;

[0011] (3) Preparation of precursor reaction solution

[0012] Deionized water is used as a solvent, a molybdenum source, a sulfur source and the monolayer Mo2TiC2 MXene are used as raw materials, and a chelating agent is combined. The mixture is mixed according to a molar ratio of deionized water: molybdenum source: sulfur source: monolayer Mo2TiC2 MXene: chelating agent = 1000-1200: 0.2-0.5: 5-15: 0.2-0.5: 0.1-0.4, and then stirred and ultrasonicated to form a precursor reaction liquid;

[0013] (4) Preparation of dual two-dimensional Mo2TiC2 MXene / MoS2 heterostructures

[0014] The precursor reaction liquid is subjected to a hydrothermal reaction at a temperature of 160 to 220° C. for 10 to 24 hours. The obtained suspension is collected by centrifugation, washed and dried to obtain an electromagnetic wave absorption material having a double two-dimensional Mo2TiC2 MXene / MoS2 heterostructure.

[0015] Furthermore, in step (1) of the present invention, the magnetic stirring time is 48 to 96 hours; the rotation speed of the centrifugal collection is 3000 to 8000 r / min, and the centrifugal collection time is 5 to 30 minutes; the washing solution is deionized water, and the washing is performed to a pH value ≥ 6; the drying temperature is 50 to 80° C., and the drying time is 12 to 48 hours.

[0016] Furthermore, in step (2) of the present invention, the metal salt is LiCl or KCl. The acid solution is 0.5 mol / L sulfuric acid; the grinding time is 0.5 to 2 hours; the centrifugal collection speed is 5000 to 9000 r / min, and the centrifugal collection time is 5 to 20 minutes; the washing solution is deionized water, and the number of washings is 3 to 6 times; the drying temperature is 60 to 80°C, and the drying time is 6 to 36 hours.

[0017] Furthermore, the stirring and ultrasonicating process in step (3) of the present invention is to first sequentially add a sulfur source and a molybdenum source, stir for 10 to 30 minutes, then sequentially add the monolayer Mo2TiC2 MXene and a chelating agent, stir for 20 to 60 minutes, and ultrasonicate for 5 to 30 minutes. The sulfur source is thiourea, the molybdenum source is ammonium molybdate tetrahydrate, and the chelating agent is citric acid monohydrate.

[0018] Furthermore, in step (4) of the present invention, the rotation speed of the centrifugal collection is 4000-8000 r / min, and the centrifugal collection time is 3-15 min; the washing solution is deionized water and anhydrous ethanol, and the number of washing times is 2-5 times; the drying temperature is 70-90° C., and the drying time is 6-18 h.

[0019] The product prepared using the above-mentioned new high-efficiency ultra-thin Mo2TiC2 MXene / MoS2 electromagnetic wave absorption material preparation method has a reflection loss of -12.76 to -65.98 dB at a matching thickness of 1.58 to 5 mm within the frequency range of 2 to 18 GHz.

[0020] The present invention has the following beneficial effects:

[0021] (1) The present invention uses Mo2TiAlC2 MAX, a sulfur source, and a molybdenum source as raw materials, and combines an etchant, a metal salt, and a chelating agent. The molten salt method and the hydrothermal synthesis method are used to construct a two-dimensional ultrathin MoS2 nanosheet on the surface of a two-dimensional single-layer Mo2TiC2 MXene nanosheet, forming a double two-dimensional heterostructure with tight surface interface bonding and rich heterogeneous interfaces. The present invention not only expands the types of electromagnetic wave absorption materials and develops a new type of electromagnetic wave absorption material with high efficiency absorption (reflection loss of -12.76 to -65.98 dB) and ultrathin matching thickness (1.58 to 5 mm), but also can achieve adjustable specific surface area of Mo-based MXene nanosheets and thickness of ultrathin MoS2 nanosheets, controllable morphology and interface of heterostructures, and tight interface bonding, effectively overcoming the problems of poor impedance matching, weak absorption, and large matching thickness of electromagnetic wave absorption materials in the prior art.

[0022] (2) The present invention uses concentrated hydrofluoric acid as an etchant to effectively etch away the Al layer in Mo2TiAlC2 MAX, forming a multilayer Mo2TiC2 MXene structure, which opens the possibility of forming a single-layer Mo2TiC2 MXene. The multilayer Mo2TiC2 MXene prepared by the hydrofluoric acid etching process has a relatively large specific surface area and rich surface functional groups (hydroxyl groups, terminal oxygen, etc.).

[0023] (3) The present invention uses LiCl and KCl as metal salts to form molten salts at high temperatures, which can further peel off the multilayer Mo2TiC2 MXene and effectively form a single-layer Mo2TiC2 MXene structure. The single-layer Mo2TiC2 MXene obtained by the molten salt method is very thin and has a large specific surface area, which provides sufficient space for the growth of ultra-thin MoS2 nanosheets, and the grown MoS2 nanosheets can effectively inhibit the re-aggregation of the single-layer Mo2TiC2 MXene. In addition, the surface of the single-layer Mo2TiC2 MXene obtained by the molten salt method contains abundant defects (vacancy defects and heterogeneous atom doping defects), which promote dipole polarization, thereby improving the dielectric loss capability of the heterostructure.

[0024] (4) Citric acid is added as a chelating agent in the reaction system of the present invention to regulate the fine growth (thickness and direction) of ultrathin MoS2 nanosheets on the monolayer Mo2TiC2 MXene. Therefore, by adjusting the chelating agent content and the hydrothermal synthesis process parameters, a dual-dimensional Mo2TiC2MXene / MoS2 heterostructure with tight surface interface bonding and rich heterogeneous interfaces is achieved, which is beneficial for expanding loss paths, promoting interfacial polarization, and improving magnetic loss capacity.

[0025] (5) The process of the present invention has high repeatability, is easy to control, has low cost, and is easy to promote and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention will be described in further detail below with reference to the embodiments and accompanying drawings:

[0027] Figure 1 This is a scanning electron microscope image of the new high-efficiency ultra-thin Mo2TiC2 MXene / MoS2 electromagnetic wave absorption material prepared in an embodiment of the present invention;

[0028] Figure 2 This is a graph showing the relationship between reflection loss and frequency of the new high-efficiency ultra-thin Mo2TiC2 MXene / MoS2 electromagnetic wave absorption material prepared in Example 1 of the present invention at different matching thicknesses;

[0029] Figure 3 1 is a graph showing the relationship between the optimal reflection loss and frequency of the electromagnetic wave absorbing materials of Example 1 of the present invention and various comparative examples. DETAILED DESCRIPTION

[0030] Example 1:

[0031] This embodiment provides a method for preparing a novel, highly efficient, ultra-thin Mo2TiC2 MXene / MoS2 electromagnetic wave absorbing material, the steps of which are as follows:

[0032] (1) Preparation of multilayer Mo2TiC2 MXene

[0033] Measure 30 mL of 40% concentrated hydrofluoric acid and transfer it to a 100 mL Teflon-lined container. Slowly add 0.7 g of Mo2TiAlC2 MAX and magnetically stir at room temperature for 72 h. The resulting suspension is centrifuged at 5000 r / min for 10 min and washed with deionized water to a pH ≥ 6. Then, dry it at 70 ° C for 24 h to obtain multilayer Mo2TiC2 MXene powder.

[0034] (2) Preparation of single-layer Mo2TiC2 MXene

[0035] 1 g of the above-mentioned multilayer Mo2TiC2 MXene powder was weighed and transferred to an agate mortar. 2 g of LiCl and 8 g of KCl were added in sequence and ground at room temperature for 1 h. Then, the mixed powder was placed in a porcelain boat and placed in the middle of a quartz tube furnace. Nitrogen was then introduced at a flow rate of 300 mL / min, and the mixture was first heat-treated at 400 °C for 2 h (heating rate of 2 °C / min), and then heat-treated at 800 °C for 2 h (heating rate of 5 °C / min) to obtain heat-treated powder. Then, the heat-treated powder was ground and placed in 50 mL of 0.5 mol / L sulfuric acid, magnetically stirred at room temperature for 12 h, and the resulting suspension was centrifuged at 6000 r / min for 10 min, washed 4 times with deionized water, and dried at 70 °C for 24 h to obtain a single-layer Mo2TiC2 MXene powder.

[0036] (3) Preparation of Mo2TiC2 MXene / MoS2 precursor reaction solution

[0037] Measure 20 mL of deionized water and transfer it to a 50 mL beaker. Then, add 0.6518 g of thiourea and 0.3322 g of ammonium molybdate tetrahydrate in sequence, and magnetically stir at room temperature for 20 min. Then, add 0.075 g of the above-mentioned single-layer Mo2TiC2MXene powder and 0.0413 g of citric acid in sequence, and magnetically stir at room temperature for 45 min and ultrasonicate for 30 min to obtain a Mo2TiC2MXene / MoS2 precursor reaction solution.

[0038] (4) Preparation of dual two-dimensional Mo2TiC2 MXene / MoS2

[0039] The precursor reaction solution was transferred to a Teflon-lined container with a volume of 50 mL and placed in a high-pressure reactor. The reaction was hydrothermally reacted at 200 ° C for 18 h. The obtained suspension was centrifuged at 6000 r / min for 5 min, washed with deionized water and anhydrous ethanol 4 times each, and dried at 80 ° C for 12 h to obtain an electromagnetic wave absorption material with a double two-dimensional Mo2TiC2 MXene / MoS2 heterostructure (see Figure 1 ).

[0040] The reflection losses of the Mo2TiC2 MXene / MoS2 electromagnetic wave absorption material prepared in this embodiment at the matching thicknesses of 1.58 mm, 2 mm, 2.21 mm, 3 mm, 3.23 mm, 3.5 mm, 4 mm and 5 mm within the frequency range of 2 to 18 GHz are -57.66 dB, -33.14 dB, -65.98 dB, -18.88 dB, -43.13 dB, -19.39 dB, -13.82 dB and -12.76 dB, that is, the optimal reflection loss is -65.98 dB, and the matching thickness is 2.21 mm (see Figure 2 ).

[0041] Comparative Example 1:

[0042] Using the preparation method of the embodiment of the present invention, the multilayer Mo2TiC2 MXene prepared in step (1) is used as an electromagnetic wave absorbing material.

[0043] The electromagnetic wave absorbing material prepared in this comparative example is a multilayer Mo2TiC2 MXene. In the frequency range of 2 to 18 GHz and the matching thickness of 1.58 to 5 mm, the optimal reflection loss is -4.44 dB, and the matching thickness is 3 mm (see Figure 3 ).

[0044] Comparative Example 2:

[0045] Using the preparation method of the embodiment of the present invention, the single-layer Mo2TiC2 MXene prepared in step (2) is used as the electromagnetic wave absorbing material.

[0046] The electromagnetic wave absorbing material prepared in this comparative example is a single-layer Mo2TiC2 MXene. In the frequency range of 2 to 18 GHz and the matching thickness of 1.58 to 5 mm, the optimal reflection loss is -3.2 dB, and the matching thickness is 5 mm (see Figure 3 ).

[0047] Comparative Example 3:

[0048] The preparation method of the embodiment of the present invention is adopted, which is different from the embodiment in that: 0g of single-layer Mo2TiC2 MXene is added in step (3).

[0049] The electromagnetic wave absorbing material prepared in this comparative example is MoS2. In the frequency range of 2 to 18 GHz and the matching thickness of 1.58 to 5 mm, the optimal reflection loss is -7.82 dB. The matching thickness is 5 mm (see Figure 3 ).

[0050] The Mo2TiC2 MXene / MoS2 electromagnetic wave absorbing material prepared in the embodiment of the present invention is as follows Figure 1As shown in Figure 2, two-dimensional ultrathin MoS2 nanosheets are grown on the surface of a two-dimensional single-layer Mo2TiC2 MXene, forming a double two-dimensional heterostructure with tight surface interface and rich heterogeneous interface. Figure 3 As shown, the embodiment of the present invention has stronger electromagnetic wave absorption capability and thinner matching thickness compared with the electromagnetic wave absorption materials of Comparative Examples 1, 2 and 3.

Claims

1. A method for preparing a novel, highly efficient, ultra-thin Mo2TiC2 MXene / MoS2 electromagnetic wave absorbing material, characterized in that The following steps are involved: (1) Preparation of multilayer Mo2TiC2 MXene Using Mo2TiAlC2 MAX bulk ceramic as raw material and 40% concentrated hydrofluoric acid as etchant, the material was magnetically stirred at room temperature according to the mass volume ratio of Mo2TiAlC2 MAX: etchant = 0.5-1g: 20-60mL, and then collected by centrifugation, washed, and dried to obtain multilayer Mo2TiC2 MXene. (2) Preparation of single-layer Mo2TiC2 MXene The multilayer Mo2TiC2 MXene is used as a raw material and combined with a metal salt, and the mixture is mixed according to a mass ratio of multilayer Mo2TiC2 MXene: metal salt = 0.5-2:5-20. After grinding, the mixture is placed in a tube furnace, nitrogen is introduced at a flow rate of 200-400 mL / min, and the temperature is increased by 2°C / min to 350-550°C for heat treatment for 1-4 hours, and then the temperature is increased by 5°C / min to 600-900°C for heat treatment for 1-4 hours to obtain a heat-treated powder; the heat-treated powder is used as a raw material and combined with an acid solution, magnetically stirred at room temperature, and then centrifuged, washed, and dried to obtain a single-layer Mo2TiC2 MXene; (3) Preparation of precursor reaction solution Deionized water is used as a solvent, a molybdenum source, a sulfur source and the monolayer Mo2TiC2 MXene are used as raw materials, and a chelating agent is combined. The mixture is mixed according to a molar ratio of deionized water: molybdenum source: sulfur source: monolayer Mo2TiC2 MXene: chelating agent = 1000-1200: 0.2-0.5: 5-15: 0.2-0.5: 0.1-0.4, and then stirred and ultrasonicated to form a precursor reaction liquid; (4) Preparation of dual two-dimensional Mo2TiC2 MXene / MoS2 heterostructures The precursor reaction liquid is subjected to a hydrothermal reaction at a temperature of 160 to 220° C. for 10 to 24 hours. The obtained suspension is collected by centrifugation, washed and dried to obtain an electromagnetic wave absorption material having a double two-dimensional Mo2TiC2 MXene / MoS2 heterostructure.

2. The method for preparing the novel high-efficiency ultrathin Mo2TiC2 MXene / MoS2 electromagnetic wave absorbing material according to claim 1 is characterized in that: In the step (1), the magnetic stirring time is 48 to 96 hours; the centrifugal collection speed is 3000 to 8000 r / min, and the centrifugal collection time is 5 to 30 minutes; the washing solution is deionized water, and the washing is performed to a pH value ≥ 6; the drying temperature is 50 to 80° C., and the drying time is 12 to 48 hours.

3. The method for preparing the novel high-efficiency ultrathin Mo2TiC2 MXene / MoS2 electromagnetic wave absorbing material according to claim 1 is characterized in that: The metal salt in step (2) is LiCl or KCl.

4. The method for preparing the novel high-efficiency ultrathin Mo2TiC2 MXene / MoS2 electromagnetic wave absorbing material according to claim 1 or 3, characterized in that: In the step (2), the acid solution is sulfuric acid with a concentration of 0.5 mol / L; the grinding time is 0.5 to 2 hours; the rotation speed of the centrifugal collection is 5000 to 9000 r / min, and the centrifugal collection time is 5 to 20 minutes; the washing solution is deionized water, and the number of washing times is 3 to 6 times; the drying temperature is 60 to 80° C., and the drying time is 6 to 36 hours.

5. The method for preparing the novel high-efficiency ultrathin Mo2TiC2 MXene / MoS2 electromagnetic wave absorbing material according to claim 1, characterized in that: The stirring and ultrasonic operation process in step (3) is to first add the sulfur source and the molybdenum source in sequence, stir for 10 to 30 minutes, then add the single-layer Mo2TiC2 MXene and the chelating agent in sequence, and then stir for 20 to 60 minutes and ultrasonicate for 5 to 30 minutes.

6. The method for preparing the novel high-efficiency ultrathin Mo2TiC2 MXene / MoS2 electromagnetic wave absorbing material according to claim 1 or 5, characterized in that: In the step (3), the sulfur source is thiourea, the molybdenum source is ammonium molybdate tetrahydrate, and the chelating agent is citric acid monohydrate.

7. The method for preparing the novel high-efficiency ultrathin Mo2TiC2 MXene / MoS2 electromagnetic wave absorbing material according to claim 1, characterized in that: The rotation speed of the centrifugal collection in the step (4) is 4000-8000 r / min, and the centrifugal collection time is 3-15 min; the washing solution is deionized water and anhydrous ethanol, and the number of washing times is 2-5 times; the drying temperature is 70-90° C., and the drying time is 6-18 h.

8. A product obtained by the method for preparing the novel high-efficiency ultra-thin Mo2TiC2 MXene / MoS2 electromagnetic wave absorbing material according to any one of claims 1 to 7.

9. The product according to claim 8, characterized in that: The electromagnetic wave absorbing material has a reflection loss of -12.76 to -65.98 dB at a matching thickness of 1.58 to 5 mm within a frequency range of 2 to 18 GHz.

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