Method for safely and efficiently preparing double-transition metal MXene material

Abstract

The invention discloses a method for safely and efficiently preparing a double-transition metal MXene material, and belongs to the technical field of preparation of MXene materials. Comprising the following steps: slowly adding Mo2TiAlC2 powder into a lithium hydroxide solution, performing continuous ultrasonic stirring uniformly, and performing etching under a heating condition of 150-200 DEG C; centrifuging and washing the mixed solution until the pH value of the mixed solution reaches 6-7; adding into a tetrabutyl ammonium hydroxide solution, and ultrasonically stirring at 50 DEG C; centrifuging after the ultrasonic treatment is finished, and retaining supernate to obtain an MXene material; by changing the original etching solution, the etching process is safer, the atomic activity is increased, the etching is more efficient and more sufficient, and the conductivity, thermoelectric conversion rate and other properties of the material are effectively increased. Meanwhile, an ultrasonic field is introduced and reaction conditions are optimized, so that a two-dimensional layered structure of a main body is not damaged while sufficient material contact is ensured, the overall time is greatly shortened, and the yield and the product purity are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of new material preparation, and in particular relates to a method for safely and efficiently preparing dual transition metal MXene two-dimensional nanosheets. Background Art

[0002] MXene is a new type of two-dimensional material, typically composed of metal carbides, obtained by chemically exfoliating multiple layers of metal carbides. It possesses excellent thermoelectric and mechanical properties, and has broad application prospects in fields such as energy harvesting and sensors. Currently, the most common method for preparing MXene is hydrofluoric acid etching, but this method has the following problems: 1) Hydrogen fluoride is highly corrosive to metals, glass, and other materials, and can corrode production equipment; 2) Hydrogen fluoride can cause irreversible damage to human skin, and exposure to even 2% of the skin can be fatal, necessitating stringent safety precautions during production; 3) The hydrofluoric acid etching method does not thoroughly etch certain MAXs (e.g., V2AlC), resulting in residual MAX residues in the resulting product, resulting in low yield and poor purity.

[0003] Therefore, it is of great significance to develop a safe, simple and efficient method to prepare MXene. Summary of the Invention

[0004] The present invention addresses the aforementioned issues with the existing technologies by providing a safer and more efficient method for preparing dual-transition metal MXene two-dimensional nanosheets. By replacing the original etching solution with lithium hydroxide, the etching process is made safer, while increasing atomic activity and resulting in more efficient and complete etching, effectively improving the material's electrical conductivity, thermoelectric conversion rate, and other properties. Furthermore, the introduction of an ultrasonic field and optimized reaction conditions ensure adequate material contact without disrupting the underlying two-dimensional layered structure, significantly reducing overall processing time and improving yield and product purity.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a method for safely and efficiently preparing a dual transition metal MXene material, the method comprising the following steps:

[0006] Step 1: slowly add Mo2TiAlC2 powder into lithium hydroxide solution, stir evenly by continuous ultrasonication, and etch under heating conditions of 150-200°C;

[0007] Step 2: After etching, the mixed solution is centrifuged and washed until the pH value of the mixed solution reaches 6-7;

[0008] Step 3, adding the mixed solution after centrifugation and washing into tetrabutylammonium hydroxide solution and stirring with ultrasound at 50° C.;

[0009] Step 4: After the ultrasound in step 3, centrifuge and retain the supernatant to obtain the MXene material.

[0010] Preferably, the molar ratio of Mo2TiAlC2, lithium hydroxide and tetrabutylammonium hydroxide is 1:9:0.4-1:10:0.5.

[0011] Preferably, the concentration of lithium hydroxide in step 1 is 1.25-1.3M.

[0012] Preferably, the ultrasonic power in step 1 is 27-29 kHz, and the ultrasonic time is 3-5 minutes.

[0013] Preferably, the centrifugation condition in step 2 is: centrifugation at 4000-6000 rpm for 2-5 minutes.

[0014] Preferably, the centrifugation condition in step 4 is: centrifugation at 4000-6000 rpm for 30 minutes.

[0015] Preferably, the concentration of the tetrabutylammonium hydroxide solution is 0.29-0.31M.

[0016] The beneficial effects of the present invention are as follows: compared with the original method, the introduction of lithium hydroxide provides a fluorine-free and safer alternative to traditional etching technology, greatly reducing the experimental safety hazards caused by hydrofluoric acid. At the same time, the introduction of an ultrasonic field and the optimization of reaction conditions ensure sufficient material contact without destroying the two-dimensional layered structure of the main body, thereby greatly reducing the overall time, improving the yield and product purity.

[0017] The present invention has the characteristics of simple operation, low cost and strong practicality, and achieves the goal of preparing double transition metal MXene two-dimensional nanosheets in a short time and with high quality. The prepared two-dimensional nanosheets have better performance and higher quality and have very great potential application value.

[0018] The present invention can be widely applied to Mo2TiC2T x 、Mo2Ti2C3T x As well as the preparation of V-based, Ti-based and other double transition metal MXenes, the emergence of this high-yield, large-size, ultra-thin two-dimensional nanosheet has significantly improved the thermoelectric properties of two-dimensional MXene, greatly promoted the development of nanotechnology and the practical application of two-dimensional MXene, and the development and application of high-performance human body thermoelectric devices can greatly reduce the use of batteries, and provide an effective alternative method for maintaining an effective and convenient sustainable environmental energy supply, which has an important impact on my country's sustainable development. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 SEM image of unetched Mo2TiAlC2.

[0020] Figure 2 These are SEM images of the MXene materials obtained after etching (a is the MXene material prepared in Example 1, and b is the MXene material prepared in Example 2).

[0021] Figure 3 The changes in the Seebeck coefficient (S) of the MXene materials obtained in Examples 1-2 and Comparative Examples 1-4.

[0022] Figure 4 The electrical conductivity (σ) of the MXene materials obtained in Examples 1-2 and Comparative Examples 1-4 was measured.

[0023] Figure 5 Power factor (PF) analysis of the MXene materials obtained in Examples 1-2 and Comparative Examples 1-4. DETAILED DESCRIPTION

[0024] The contents and drawings of the present invention will be described in detail below. This embodiment is implemented based on the technical solution of the present invention and involves detailed implementation plans and operating procedures. However, the scope of protection of the present invention is not limited to the following specific embodiments. The terms used in the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0025] Example 1:

[0026] A method for safely and efficiently preparing dual transition metal MXene materials comprises the following steps:

[0027] (1) First, 0.8 g of Mo2TiAlC2 powder was slowly added to 20 ml of 1.25 M lithium hydroxide solution, and ultrasonic stirring was continued at 28 kHz for 5 minutes, and the mixture was heated at 150 °C for 5 hours.

[0028] (2) After etching, the mixture was centrifuged and washed twice, each time at 6000 rpm for 2 minutes, until the pH value reached 6-7.

[0029] (3) Add 4 ml of 0.3 M tetrabutylammonium hydroxide solution to the neutral solution and stir ultrasonically at 50°C for 45 minutes.

[0030] (4) Dilute the intercalation mixture and transfer it to a 100 mL centrifuge tube. Add deionized water to the centrifuge tube until the mixed solution reaches 80 mL. Centrifuge at 6000 rpm for 30 minutes and collect the supernatant.

[0031] Example 2:

[0032] A method for safely and efficiently preparing dual transition metal MXene materials comprises the following steps:

[0033] (1) First, 0.8 g of Mo2TiAlC2 powder was slowly added to 20 ml of 1.25 M lithium hydroxide solution, stirred continuously at 28 kHz for 5 minutes, and reacted at 200 °C for 30 minutes.

[0034] (2) After etching, the mixture was centrifuged and washed twice, each time at 6000 rpm for 2 minutes, until the pH value reached 6-7.

[0035] (3) Add 4 ml of 0.3 M tetrabutylammonium hydroxide solution to the neutral solution and stir ultrasonically at 50°C for 30 minutes.

[0036] (4) Dilute the intercalation mixture and transfer it to a 100 mL centrifuge tube. Add deionized water to the centrifuge tube until the mixed solution reaches 80 mL. Centrifuge at 6000 rpm for 30 minutes and collect the supernatant.

[0037] Comparative Example 1:

[0038] Compared with Example 1, in step (1), lithium hydroxide is replaced by hydrofluoric acid, the ultrasonic step is omitted, and the heating temperature is 40° C.;

[0039] The specific steps include:

[0040] (1) First, 1 gram of Mo2TiAlC2 powder was slowly added to 40 milliliters of 1.25M hydrofluoric acid solution, stirred for 15 minutes, and heated at 40°C for 72 hours for etching.

[0041] (2) After etching, the mixture was centrifuged and washed three times, each time at 6000 rpm for 5 minutes, until the pH value reached 6-7.

[0042] (3) Add 4 ml of 0.3 M tetrabutylammonium hydroxide solution to the neutral solution and stir evenly at room temperature for 48 hours.

[0043] (4) Dilute the intercalation mixture and transfer it to a 100 mL centrifuge tube. Add deionized water to the centrifuge tube until the mixed solution is 80 mL. Centrifuge at 6000 rpm for 1 hour to remove the supernatant. Wash twice or more. Transfer the dispersion to a 100 mL centrifuge tube and centrifuge at 5000 rpm for 60 minutes. Collect the resulting supernatant.

[0044] Comparative Example 2:

[0045] Compared with Example 1, in step (1), lithium hydroxide is replaced by hydrofluoric acid, and the heating temperature is 40° C.;

[0046] The specific steps include:

[0047] (1) First, 1 gram of Mo2TiAlC2 powder was slowly added to 40 ml of 1.25 M hydrofluoric acid solution, and ultrasonic stirring was continued at 28 kHz for 5 minutes. The mixture was heated at 40 °C for 48 hours for etching.

[0048] (2) After etching, the mixture was centrifuged and washed twice, each time at 6000 rpm for 2 minutes, until the pH value reached 6-7.

[0049] (3) 4 ml of 0.3 M tetrabutylammonium hydroxide solution was added to the deionized solution and ultrasonically stirred at room temperature for 10 hours.

[0050] (4) Dilute the intercalation mixture and transfer it to a 100 mL centrifuge tube. Add deionized water to the centrifuge tube until the mixed solution is 80 mL. Centrifuge at 6000 rpm for 30 minutes to remove the supernatant. Wash twice or more. Transfer the dispersion to a 100 mL centrifuge tube and centrifuge at 5000 rpm for 45 minutes. Collect the resulting supernatant.

[0051] Comparative Example 3:

[0052] Compared with Example 1, the ultrasonic step was omitted in step (1), and the heating temperature was 40°C;

[0053] The specific steps include:

[0054] (1) First, 0.8 g of Mo2TiAlC2 powder was slowly added to 20 ml of 1.25 M lithium hydroxide solution, stirred for 15 minutes, and etched in a 40°C water bath for 48 hours.

[0055] (2) After etching, the mixture was centrifuged and washed twice, each time at 6000 rpm for 5 minutes, until the pH value reached 6-7.

[0056] (3) Add 4 ml of 0.3 M tetrabutylammonium hydroxide solution to the neutral solution and stir evenly at room temperature for 48 hours.

[0057] (4) Dilute the intercalation mixture and transfer it to a 100 mL centrifuge tube. Add deionized water to the centrifuge tube until the mixed solution reaches 80 mL. Centrifuge at 6000 rpm for 1 hour to remove the supernatant. Transfer the dispersion to a 100 mL centrifuge tube and centrifuge at 5000 rpm for 1 hour to collect the resulting supernatant.

[0058] Comparative Example 4: Compared with Example 1, the heating temperature in step (1) is 40°C;

[0059] The specific steps include:

[0060] (1) First, 0.8 g of Mo2TiAlC2 powder was slowly added to 20 ml of 1.25 M lithium hydroxide solution, ultrasonically stirred for 5 minutes, and etched in a 40 °C water bath for 24 hours.

[0061] (2) After etching, the mixture was centrifuged and washed twice, each time at 6000 rpm for 5 minutes, until the pH value reached 6-7.

[0062] (3) Add 4 ml of 0.3 M tetrabutylammonium hydroxide solution to the neutral solution and stir under ultrasonication at 50°C for 1 hour.

[0063] (4) Dilute the intercalation mixture and transfer it to a 100 mL centrifuge tube. Add deionized water to the centrifuge tube until the mixed solution reaches 80 mL. Centrifuge at 6000 rpm for 30 minutes to remove the supernatant. Transfer the dispersion to a 100 mL centrifuge tube and centrifuge at 5000 rpm for 45 minutes to collect the resulting supernatant.

[0064] The dual transition metal MXene films obtained above were measured using a micrometer and all had specifications of 45 mm in diameter and 0.2 mm in thickness. The yields varied: Example 1 produced a total of 41 MXene films; Example 2 produced a total of 45 MXene films; Comparative Example 1 produced a total of 30 MXene films; Comparative Example 2 produced a total of 32 MXene films; Comparative Example 3 produced a total of 33.5 MXene films; and Comparative Example 4 produced a total of 37 MXene films. The yield increased by 36.67% compared to Example 1, and by 50% compared to Example 2. The yield increased by 10.81% compared to Example 1, and by approximately 21.62% compared to Example 2.

[0065] Figure 2 In contrast, the surface in Figure b appears rougher, with noticeable wrinkles and irregular textures. Generally speaking, materials with higher surface roughness exhibit higher thermoelectric performance. The particles in Figure a are smaller and more evenly distributed than those in Figure b. Evenly distributed small particles increase phonon scattering, which helps improve the material's thermoelectric performance. The structure in Figure a is more complete than that in Figure b. Structurally complete materials exhibit lower defect scattering and better thermoelectric performance.

[0066] Use a thermoelectric performance tester to measure the voltage difference of different MXene materials at the same temperature difference, using the formula:

[0067]

[0068] Where S is the Seebeck coefficient; ΔT is the temperature difference; ΔV is the output voltage at a specific temperature difference. Calculate the Seebeck coefficient (S).

[0069] According to the proportional relationship between voltage and current using the four-probe method, the formula is:

[0070]

[0071] Where I is the current; V is the voltage; σ is the conductivity. Calculate the conductivity (σ) of the material.

[0072] The power factor (PF) of MXene materials is calculated using the formula:

[0073] PF=S 2 σ

[0074] Where PF is the power factor; S is the Seebeck coefficient; and σ is the conductivity.

[0075] Final drawing Figure 3-5 .

[0076] according to Figure 3-5 According to the data of Comparative Examples 1 and 2, the Seebeck coefficient and power factor of the MXene material prepared with lithium hydroxide as the etching solution are worse than those of the MXene material prepared with hydrofluoric acid as the etching solution. Although the conductivity has improved, it is not obvious.

[0077] From Comparative Examples 3 and 4, the introduction of an ultrasonic field during etching can significantly improve the Seebeck coefficient, conductivity, and power factor of the MXene material, but the performance improvement is not obvious compared with Comparative Example 2;

[0078] Comparative Example 4, Examples 1, and 2 show that ultrasound combined with temperature not only significantly improves the Seebeck coefficient, conductivity, and power factor of the MXene material, but also increases efficiency and significantly shortens reaction time. At 200°C, the MXene material exhibits relatively superior performance.

[0079] The foregoing is merely an embodiment of the present invention and is not intended to limit the present invention. It will be apparent to those skilled in the art that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are intended to be included within the scope of the claims of the present invention.

Claims

1. A method for safely and efficiently preparing dual transition metal MXene materials, characterized in that: The method comprises the following steps: Step 1: slowly add Mo2TiAlC2 powder into lithium hydroxide solution, stir evenly by continuous ultrasonication, and etch under heating conditions of 150-200°C; Step 2: After etching, the mixed solution is centrifuged and washed until the pH value of the mixed solution reaches 6-7; Step 3, adding the mixed solution after centrifugation and washing into tetrabutylammonium hydroxide solution and stirring with ultrasound at 50° C.; Step 4: After the ultrasound in step 3, centrifuge and retain the supernatant to obtain the MXene material.

2. The method for safely and efficiently preparing dual transition metal MXene materials according to claim 1, characterized in that: The molar ratio of Mo2TiAlC2, lithium hydroxide and tetrabutylammonium hydroxide is 1:9:0.4-1:10:0.

5.

3. The method for safely and efficiently preparing dual transition metal MXene materials according to claim 1, characterized in that: The concentration of lithium hydroxide in step 1 is 1.25-1.3M.

4. The method for safely and efficiently preparing dual transition metal MXene materials according to claim 1, characterized in that: The ultrasonic power in step 1 is 27-29 kHz, and the ultrasonic time is 3-5 minutes.

5. The method for safely and efficiently preparing dual transition metal MXene materials according to claim 1, characterized in that: The centrifugation conditions in step 2 are: centrifugation at a rotation speed of 4000-6000 rpm for 2-5 minutes.

6. The method for safely and efficiently preparing dual transition metal MXene materials according to claim 1, characterized in that: The centrifugation conditions in step 4 are: centrifugation at 4000-6000 rpm for 30 minutes.

7. The method for safely and efficiently preparing dual transition metal MXene materials according to claim 1, characterized in that: The concentration of the tetrabutylammonium hydroxide solution is 0.29-0.31M.

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