A flower-shaped MXene nanomaterial with high electromagnetic wave absorption performance and its preparation method and application

Abstract

This invention relates to the field of absorbing materials technology and discloses a flower-shaped MXene nanomaterial with high electromagnetic wave absorption performance, its preparation method, and application. The preparation process comprises the following steps: Step 1: etching MAX phase ceramic powder to obtain multilayer MXene; Step 2: washing the MAX precursor and dispersing it in water, ultrasonicating it under inert gas protection, and subjecting the dispersion to low-speed centrifugation to obtain a supernatant; Step 3: subjecting the supernatant obtained in Step 2 to high-speed centrifugation, collecting the supernatant, and freeze-drying it to obtain the flower-shaped MXene nanomaterial. The present invention separates low-aspect-ratio, small-sized MXene from MXene through a simple fractional exfoliation method. The small-sized MXene, rich in hydrophilic groups on its surface, self-assembles into a stable three-dimensional flower-shaped structure, resulting in a MXene material with excellent absorbing performance. This simple and efficient preparation method solves the cumbersome MXene modification and preparation process in conventional technologies.

Description

Technical Field

[0001] The present invention relates to the technical field of absorbing materials, and in particular to a flower-shaped MXene nanomaterial with high electromagnetic wave absorption performance, a preparation method thereof, and applications thereof. Background Art

[0002] With the advent of the 5G era, the widespread use of electronic devices has led to an increasingly serious problem of electromagnetic radiation pollution. Electromagnetic wave absorbing materials can convert incident electromagnetic waves into other forms of energy, thereby achieving the purpose of electromagnetic protection.

[0003] In recent years, MXene has been considered a potential candidate for excellent microwave-absorbing materials due to its low density and strong conductivity. However, excessively strong dielectric properties can lead to impedance mismatch, causing incident electromagnetic waves to be re-reflected into the air and difficult to penetrate the material. Structural design of MXene to improve impedance matching and enhance electromagnetic wave absorption has become a research hotspot in recent years. However, the difficulty of structural design caused by re-stacking has limited the application of MXene in this field.

[0004] Patent CN116621172A discloses a method for preparing lightweight MXene powder. This involves etching MAX with a fluorine-containing etchant in a high-viscosity reaction system, followed by vacuum drying to obtain a low-density MXene powder. This invention inevitably introduces new impurities into the MXene material and does not address the problem of MXene sheet reaccumulation.

[0005] Patent CN114655957A discloses a corallite-structured magnetic MXene absorber composite material. MXene / PMMA microspheres are prepared using a polymethyl methacrylate (PMMA) template method. Magnetic Fe₃O₄ particles are introduced into the MXene / PMMA structure to balance the high dielectric properties of the MXene. Annealing then removes the PMMA template, resulting in a corallite-structured MXene absorber with a maximum reflection loss of only -42.48 dB. This invention is complex and difficult to control, and the materials used offer limited improvement in absorber performance.

[0006] CN 114314678 A discloses a flower-shaped Fe3O4 / Ti3C2T x Composite absorber and preparation method thereof, wherein Ti3AlC2 powder is etched by HF solution to obtain multilayer MXene-Ti3C2T x Powder. Ti3C2T x Powder, FeCl3·6H2O and urea were dissolved in ethylene glycol solution, and black powder was prepared by solvothermal method. Then, the black powder was placed in a tubular atmosphere furnace and heat treated under atmosphere protection to obtain flower-like Fe3O4 / Ti3C2T xComposite absorbers. This material has a unique structure that effectively improves the scattering of electromagnetic waves in composite materials, enhancing the material's absorption properties. However, its preparation method is also cumbersome, and the improvement in absorption performance is limited, making it difficult to achieve industrial production and promotion. Summary of the Invention

[0007] In response to the problems in the prior art of MXene-based composite materials, such as difficult structural design, complicated preparation process steps, and weak improvement in product absorption performance, the present invention provides a method for preparing flower-shaped MXene nanomaterials. By simple fractional centrifugation, small-sized MXene flakes are obtained to obtain a flower-shaped MXene material with a rich mesoporous structure. This material has excellent electromagnetic wave absorption performance.

[0008] To achieve the above object, the technical solution adopted by the present invention is:

[0009] A method for preparing a flower-shaped MXene nanomaterial with high electromagnetic wave absorption performance comprises the following steps:

[0010] Step 1: etching MAX phase ceramic powder in an acidic solution using a fluorine-containing etchant to obtain multilayer MXene;

[0011] Step 2: The multilayer MXene is washed and dispersed in water, ultrasonicated under inert gas protection, and the dispersion is centrifuged at a low speed to obtain a supernatant; the low-speed centrifugation speed is 700-1200 rpm, and the centrifugation time is 5-10 min;

[0012] Step 3: collect the supernatant obtained in step 2 by high-speed centrifugation, and freeze-dry to obtain the flower-shaped MXene nanomaterial; the high-speed centrifugation speed is 3500-5500 rpm, and the centrifugation time is 30-90 min.

[0013] In the present invention, the MAX phase ceramic powder is first etched, and then ultrasonically treated to peel off the multilayer MXene into a few-layer MXene sheets. The large-sized sheets are further removed by low-speed centrifugation to obtain small-sized sheets. Subsequently, high-speed centrifugation is performed, and the hydrogen bonding between the surface hydrophilic functional groups of the low-aspect ratio sheets and water is utilized to make the small-sized MXene self-assemble to obtain a three-dimensional flower-like structure material. The rich mesoporous structure has the function of coordinating the impedance of air and the absorption material, thereby achieving the effect of adjusting impedance matching. The obtained material has excellent electromagnetic wave absorption performance, and the minimum reflection loss value can reach -66.9dB.

[0014] The fluorine-containing etching solution includes any one or more of lithium fluoride, sodium fluoride, and potassium fluoride.

[0015] The MAX phase ceramic powder source includes any one or more of Ti3AlC2, V2AlC, and Nb3AlC3.

[0016] The acidic solution is an aqueous solution of any one or more of hydrochloric acid, nitric acid, and sulfuric acid;

[0017] The acid molar concentration of the acid solution is 5-15 mol / L. If the concentration of the acid solution is too low, MAX cannot be completely etched, and if the concentration is too high, the washing efficiency will be affected.

[0018] Preferably, the acid molar concentration in the acidic solution is 8-10 mol / L, more preferably 9 mol / L.

[0019] The mass ratio of the etchant to the MAX phase ceramic powder is 1-3:1;

[0020] In step 1, the etching temperature is 25-60°C and the etching time is 24-72h. The low temperature and short etching time result in unsatisfactory etching effect, and the MAX is not completely etched. The high temperature and long etching time affect the etching efficiency.

[0021] Preferably, the etching temperature is 35-50° C., and the etching time is 30-40 h, more preferably 36 h.

[0022] Preferably, the MAX precursor in step 2 is washed with deionized water, ethanol or any one or more solvents until the pH of the solution is 5-6.

[0023] To avoid oxidation of the MAX precursor, ultrasonic treatment is performed under the protection of an inert gas. More preferably, the ultrasonic temperature in step 2 is -5-5°C. Performing the treatment at a low temperature is more conducive to protecting the material from oxidation.

[0024] The mass concentration of MAX precursor in the dispersion during ultrasound is 2-6 mg / mL. A high concentration of the dispersion causes the sheets to stretch into two dimensions, making it impossible to self-assemble into three-dimensional flower-like materials. Too low a concentration affects the yield.

[0025] The ultrasonic treatment time is 30-90 minutes, such as 40 minutes, 50 minutes, 60 minutes, 70 minutes, 80 minutes, or any value therebetween. The purpose of ultrasonic treatment is to exfoliate the multilayer MXene, using ultrasound to assist in the production of a large number of small flakes. The resulting MXene material is uniform in size, effectively producing a three-dimensional, flower-like MXene material with richer mesopores and a larger specific surface area.

[0026] The preferred ultrasonic time is 60-90 minutes. Too short an ultrasonic time will affect the uniformity of small-sized sheets, affect the local impedance matching of the material, and further affect the absorbing performance.

[0027] Preferably, the low-speed centrifugation speed is 900-1100 rpm, and the centrifugation time is 5 minutes. Too high a speed will cause small-sized flaky materials to be filtered out, thereby reducing the final material yield.

[0028] Preferably, the high-speed centrifugation speed is 3500-4500 rpm, and the centrifugation time is 30-60 min.

[0029] The present invention also provides a flower-shaped MXene nanomaterial with high electromagnetic wave absorption performance prepared according to the preparation method. The microscopic morphology of the flower-shaped MXene nanomaterial is a flower-shaped sphere, the particle size is 200-500nm, contains 2-50nm mesopores, and has a specific surface area of ​​30-70m 2 / g, pore volume of 0.2-0.8cm 3 / g.

[0030] The reflection loss value of the flower-shaped Mxene nanomaterial is below -50dB, and the bandwidth is 2-4GHz.

[0031] The present invention also provides that the flower-shaped MXene nanomaterial has excellent wave absorbing properties and can be used in the fields of electromagnetic wave absorption, electrochemical energy storage, electromagnetic interference shielding, pollutant adsorption, antistatic, etc.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) This invention separates low-aspect-ratio, small-sized MXene from MXene via a graded exfoliation method. By utilizing the abundant hydrophilic groups on the surface of the small-sized MXene, a uniform MXene aqueous solution is prepared. Under the multidimensional hydrogen bonding between the sheets and the sheet / water molecules, the nanoscale MXene self-assembles into a stable three-dimensional flower-like structure. This simple and efficient preparation method solves the cumbersome MXene modification and preparation process in previous technologies.

[0034] (2) The present invention controls the particle size of the flower-shaped MXene material by controlling the ultrasonic time process parameters. The prepared flower-shaped MXene has a rich mesoporous structure, which can effectively improve the material impedance matching and enhance the wave absorption performance. It solves the inherent problem of impedance mismatch caused by the high dielectric property of MXene, and the obtained material has excellent wave absorption performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a scanning electron microscope image of the MXene layer prepared in Comparative Example 1.

[0036] Figure 2 This is the pore size distribution diagram of the MXene layer prepared in Comparative Example 1.

[0037] Figure 3 This is the reflection loss of the two-dimensional layered MXene prepared in Comparative Example 1.

[0038] Figure 4 This is the scanning electron microscope image of the two-dimensional MXene prepared in Comparative Example 2.

[0039] Figure 5 This is a scanning electron microscope image of the three-dimensional MXene prepared in Example 1.

[0040] Figure 6 This is the pore size distribution diagram of the flower-shaped MXene prepared in Example 1.

[0041] Figure 7 This is the reflection loss of the flower-shaped MXene prepared in Example 1.

[0042] Figure 8 This is a scanning electron microscope image of the three-dimensional MXene prepared in Example 2.

[0043] Figure 9 This is the reflection loss of the flower-shaped MXene prepared in Example 2.

[0044] Figure 10 This is a scanning electron microscope image of the three-dimensional MXene prepared in Example 3.

[0045] Figure 11 This is the reflection loss of the flower-shaped MXene prepared in Example 3. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with embodiment. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Those skilled in the art will make modifications or equivalent substitutions based on understanding the technical solution of the present invention, without departing from the spirit and scope of the technical solution of the present invention, and all should be encompassed within the protection scope of the present invention.

[0047] Unless otherwise specified, the raw materials used in the following specific embodiments were purchased from the market.

[0048] Comparative Example 1

[0049] Step 1, etching of the MAX precursor: First, 0.5 g of LiF was magnetically stirred with 10 mL of 9 M HCl at room temperature for 10 minutes to fully dissolve it. 0.25 g of Ti3AlC2(MAX) was slowly added to the solution and stirred continuously at 35°C for 72 hours. Finally, the solution was centrifuged at 3500 rpm for 5 minutes and centrifuged several times until the pH of the supernatant reached approximately 6.

[0050] Step 2: Add 90 mL of deionized water to the precipitate obtained in step 1 to form a stable dispersion. Then, under N2 protection, the dispersion was placed in an ice bath and ultrasonicated for 30 min. The resulting colloidal solution was centrifuged at 1000 rpm for 5 min, and the black supernatant was freeze-dried to obtain a two-dimensional MXene sheet. The scanning electron microscopy of the MXene sheet is shown in FIG. Figure 1As shown, it is a two-dimensional large-layer morphology with a specific surface area of ​​only 3.7m 2 / g, pore volume 0.0244cm 3 / g, pore size distribution diagram as shown Figure 2 As shown, there are basically macropores and a small number of micropores.

[0051] Absorption performance test: A vector network analyzer (VNA, N5234A) was used to measure electromagnetic parameters in the range of 2 to 18 GHz using the coaxial method. 50 wt% of MXene material was mixed with paraffin to form a coaxial ring (R = 7.00 mm, R = 3.04 mm, d = 2 mm) to prepare a test sample. The minimum reflection loss RL value was -2.86 dB, which did not achieve the ideal absorption effect. Figure 3 shown.

[0052] Comparative Example 2

[0053] Step 1, etching of the precursor MAX: the implementation method is the same as that of Comparative Example 1.

[0054] Step 2: Add 90 mL of deionized water to the precipitate obtained in step 1 to form a stable dispersion. Under N2 protection, the dispersion was placed in an ice bath and ultrasonicated for 30 min. The obtained colloidal solution was centrifuged at 600 rpm for 5 min, and then the supernatant was centrifuged at 3500 rpm for 30 min to obtain a black supernatant, which was freeze-dried to obtain a two-dimensional MXene sheet. The scanning electron microscopy of the MXene sheet is shown in FIG. Figure 4 As shown in the figure, when the centrifugal speed is too low, MXene presents a two-dimensional lamellar morphology.

[0055] Example 1

[0056] Step 1, etching of the MAX precursor: First, magnetically stir 0.5 g of LiF with 10 mL of 9 M HCl at room temperature for 10 minutes to fully dissolve it. Slowly add 0.5 g of Ti3AlC2(MAX) to the solution and stir continuously at 35°C for 36 hours. Finally, wash the solution by centrifugation at 3500 rpm for 5 minutes. Repeat the centrifugation several times until the pH of the supernatant approaches 6.

[0057] Step 2: Add 90 mL of deionized water to the precipitate obtained in step 1 to form a stable dispersion. Then, under N2 protection, the dispersion was placed in an ice bath for ultrasonic treatment for 30 minutes to prevent oxidation. The resulting colloidal solution was centrifuged at 800 rpm for 5 minutes. Subsequently, the supernatant was centrifuged at 4000 rpm for 30 minutes. After two centrifugations, a dark green liquid supernatant was obtained, which was freeze-dried to obtain a three-dimensional flower-like MXene. Its scanning electron microscopy is as follows: Figure 5 As shown, it has a three-dimensional flower-like morphology and contains rich pore structures with a diameter of about 500nm and a specific surface area of ​​45.1m 2 / g, pore volume 0.2492cm 3 / g, contains a large number of mesopores with a diameter of 2-50 nm, and the pore size distribution is shown in the figure Figure 6 shown.

[0058] The absorption test shows that the minimum reflection loss RL value is -58.7dB, the effective absorption bandwidth EAB is 2.8GHz, and the reflection loss is as follows: Figure 7 shown.

[0059] Example 2

[0060] Step 1, etching of the MAX precursor: First, 1.5 g of LiF was magnetically stirred in 10 mL of 9 M HCl at room temperature for 10 minutes to fully dissolve it. 0.5 g of Ti3AlC2(MAX) was slowly added to the solution and stirred continuously at 35°C for 36 hours. Finally, the solution was centrifuged at 3500 rpm for 5 minutes and centrifuged several times until the pH of the supernatant reached approximately 6.

[0061] Step 2: Add 90 mL of deionized water to the precipitate obtained in step 1 to form a stable dispersion. Then, under N2 protection, the dispersion was placed in an ice bath and ultrasonicated for 60 min. The resulting colloidal solution was centrifuged at 1000 rpm for 5 min to remove the unetched MAX. Subsequently, the supernatant was centrifuged at 4000 rpm for 30 min. After two centrifugations, a dark green liquid supernatant was obtained, which was freeze-dried to obtain a three-dimensional flower-like MXene. The scanning electron microscopy of the MXene is shown in FIG. Figure 8 As shown, it can be seen that it has a three-dimensional flower-like morphology and its diameter is reduced to about 400nm.

[0062] The absorption test shows that the minimum reflection loss RL value is -58dB, the effective absorption bandwidth EAB is 3.1GHz, and the reflection loss is as follows: Figure 9 shown.

[0063] Example 3

[0064] Step 1, etching of the MAX precursor: First, 1.5 g of LiF was magnetically stirred in 10 mL of 9 M HCl at room temperature for 10 minutes to fully dissolve it. 0.5 g of Ti3AlC2(MAX) was slowly added to the solution and stirred continuously at 35°C for 36 hours. Finally, the solution was centrifuged at 3500 rpm for 5 minutes and centrifuged several times until the pH of the supernatant reached approximately 6.

[0065] Step 2: Add 90 mL of deionized water to the precipitate obtained in step 1 to form a stable dispersion. Then, under N2 protection, the dispersion was placed in an ice bath and ultrasonicated for 90 min. The resulting colloidal solution was centrifuged at 1000 rpm for 5 min, and the supernatant was centrifuged at 4000 rpm for 30 min to obtain a dark green liquid supernatant. The three-dimensional flower-like MXene was obtained by freeze-drying. The scanning electron microscopy of the MXene is shown in FIG. Figure 10 As shown, it can be seen that it has a three-dimensional flower-like morphology and its diameter is reduced to about 300nm.

[0066] The absorption test shows that the minimum reflection loss RL value is -66.9dB, the effective absorption bandwidth EAB is 3.04GHz, and the reflection loss is as follows: Figure 11 shown.

[0067] By comparing the morphology images of the comparative example and the embodiment, it can be found that the MXene prepared by only one centrifugation is a two-dimensional layer. The differential centrifugation method adopted in the present invention can effectively prepare flower-like MXene, and then the size of the flower-like microspheres can be controlled by controlling the ultrasonic time to optimize the absorption performance.

[0068] As can be seen from Comparative Example 2, if the centrifugal speed in step 2 is too low, large-sized flake materials cannot be removed, making it difficult to effectively self-assemble to form a flower-like structure in step 3. Only large flake structures can be obtained, which is not conducive to improving its absorbing performance.

[0069] Table 1 compares the performance of MXene absorbing materials prepared in the comparative examples and the examples. It shows that the flower-like structure exhibits significantly superior absorbing performance compared to lamellar MXene. By controlling the ultrasonication time and reducing the particle size of the flower-like microspheres, longer ultrasonication times and smaller material sizes lead to richer mesopores in the resulting flower-like structured absorbing material, resulting in superior absorbing performance. This indicates that the MXene nanoflower material obtained by the method of the present invention exhibits improved absorbing performance in terms of minimum reflection loss, effective absorption bandwidth, and thickness.

[0070] Table 1 MXene absorbing material properties of the examples and comparative examples

[0071]

[0072] In summary, the graded exfoliation method adopted in the present invention can effectively separate MXene flakes of different sizes, and obtain self-assembled three-dimensional MXene through subsequent freeze-drying. Compared with two-dimensional lamellae MXene, the three-dimensional MXene has greatly improved wave absorption performance.

[0073] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent variation made to the above embodiment based on the essence of the invention technology shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing a flower-shaped MXene nanomaterial with high electromagnetic wave absorption performance, characterized in that: Including steps: Step 1: etching the MAX phase ceramic powder in an acidic solution using a fluorine-containing etching solution to obtain a multilayer MXene; the fluorine-containing etching solution includes any one or more of lithium fluoride, sodium fluoride, and potassium fluoride; Step 2: The multilayer MXene is washed and dispersed in water, ultrasonicated under inert gas protection, and the dispersion is centrifuged at a low speed to obtain a supernatant; the low-speed centrifugation speed is 700-1200 rpm, and the centrifugation time is 5-10 min; Step 3: collect the supernatant obtained in step 2 by high-speed centrifugation, and freeze-dry to obtain the flower-shaped MXene nanomaterial; the high-speed centrifugation speed is 3500-5500 rpm, and the centrifugation time is 30-90 min.

2. The method for preparing a flower-shaped MXene nanomaterial with high electromagnetic wave absorption performance according to claim 1, characterized in that: The mass ratio of the fluorine-containing etching solution to the MAX phase ceramic powder is 1-3:

1.

3. The method for preparing the flower-shaped MXene nanomaterial with high electromagnetic wave absorption performance according to claim 1, characterized in that: The MAX phase ceramic powder source includes any one or more of Ti3AlC2, V2AlC, and Nb3AlC3.

4. The method for preparing a flower-shaped MXene nanomaterial with high electromagnetic wave absorption performance according to claim 1, characterized in that: The acidic solution is an aqueous solution of any one or more of hydrochloric acid, nitric acid, and sulfuric acid; And / or, the acid molar concentration in the acidic solution is 5-15 mol / L.

5. The method for preparing a flower-shaped MXene nanomaterial with high electromagnetic wave absorption performance according to claim 1, characterized in that: In step 1, the etching temperature is 25-60° C., and the etching time is 24-72 hours.

6. The method for preparing a flower-shaped MXene nanomaterial with high electromagnetic wave absorption performance according to claim 1, characterized in that: The ultrasonic temperature in step 2 is -5-5°C; and / or, the mass concentration of the multilayer MXene in the dispersion during ultrasound is 2 to 6 mg / mL.

7. The method for preparing a flower-shaped MXene nanomaterial with high electromagnetic wave absorption performance according to claim 1, characterized in that: The ultrasound time is 30-90 minutes.

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