A method for preparing large-size MXene nanosheets

Abstract

The application provides a preparation method of large-size MXene nanosheets, which first screens large-size MAX phase single crystal particles through self-settling, prepares multilayer MXene through liquid phase etching and disperses the multilayer MXene in a mixed solution of water, C1-3 alcohol and amino acid type surfactant to obtain a suspension, then mechanically exfoliates the suspension, and then performs cascade centrifugal separation, and finally obtains a large-size MXene aqueous solution. Compared with other methods, the application has the remarkable advantages of high efficiency and speed, green environmental protection, small danger coefficient, wide application, easy batch production and the like, and the prepared large-size MXene nanosheets have excellent conductivity, high infrared reflection, larger specific surface area and more active sites, and are widely applied in flexible electronic devices, electromagnetic shielding, supercapacitors and the like.

Description

Technical Field

[0001] This invention belongs to the field of MXene material technology, specifically relating to a method for preparing large-size MXene nanosheets. Background Technology

[0002] MXene is a newly emerging graphene-like two-dimensional material. In 2011, Gogotsi's team synthesized this transition metal carbide / nitride MXene using hydrofluoric acid (HF), providing researchers in various fields with a novel research direction. MXene is generally produced from M... n+1 AX n The ternary MAX phase can be fabricated by selectively etching out the A layer in the phase, and its structure can be described as a two-dimensional M layer. n+1 AX n MXene is a layered material composed of alternating MX and A atomic layers, where M is a transition metal (Sc, Ti, V, Cr, Nb, Mo, etc.), A is a Group 3 or 4 element, and X is C and / or N. The MX phase has a hexagonal layered structure, consisting of alternating MX and A atomic layers. The MX layers are primarily characterized by mixed covalent / metallic bonds, while the MA layers exhibit weak metallic bonds. Under specific chemical conditions, the A atomic layers can be selectively etched to form stable MX layers. The etched surface adsorbs terminal functional groups such as -OH, -O, and -F, resulting in a two-dimensional material called MXene.

[0003] MXene, as a novel class of two-dimensional materials, possesses inherent nanolayered structure, large specific surface area, good hydrophilicity, excellent conductivity, and catalytic activity, making it a promising candidate for applications in numerous fields such as chemical sensing, supercapacitors, photocatalysts (electrocatalysts), transparent conductive films, electromagnetic shielding, electronic devices, energy, and flexible high-strength composite materials. Large-size MXene nanosheets exhibit significant advantages in several aspects: fewer grain boundary defects and a continuous conductive network improve electrical conductivity while enhancing mechanical strength and flexibility, meeting the demands of high-performance flexible composite materials; in electrochemical applications, large-size sheets provide a larger active surface and a more stable structure, which is beneficial for improving energy storage performance and cycle stability; furthermore, large-size MXene is easy to form uniform thin films, suitable for large-area device fabrication, and exhibits higher transmittance and uniformity in optical applications; its abundant surface active sites also make it promising in the field of catalysis. Overall, large-size MXene demonstrates excellent electrical, mechanical, electrochemical, optical, and catalytic properties, making it suitable for a variety of high-performance applications.

[0004] Currently, conventional methods for preparing MXenes include acid etching (hydrofluoric acid or corresponding fluorohydrochloric acid solutions), alkaline etching, and electrochemical stripping. A suitable etchant is used to selectively etch the alumina (A) element in the MAX phase, followed by ultrasonic and oscillatory stripping. The preparation of large-size MXenes presents three main challenges: the synthesis of the MAX phase is prone to grain boundary defects or small grains; the concentration, time, and temperature of the etchant (such as HF or a fluoride / acid mixture) must be precisely controlled; excessively high temperatures or long times can lead to over-etching of the MXene layer, while insufficient time results in incomplete etching; and large-size MXenes are susceptible to shear damage during ultrasonic stripping or mechanical stirring, leading to lamellar breakage or size reduction. Furthermore, ultrasonic stripping of bulk MAX phases can generate nanoscale bulks, affecting the quality of the MXenes.

[0005] CN115353108A discloses a method for preparing large-sized MXene nanosheets with a size of 5-10 μm, including the following steps: a) dispersing MAX material in a lithium fluoride hydrochloric acid solution and stirring at 35°C for 24 h; washing the etching product with deionized water until the pH of the supernatant after centrifugation is 6±1, and collecting the bottom precipitate; b) dispersing the etched material in a solvent to obtain a solution of a certain concentration; placing the solution in an Erlenmeyer flask and shaking it in a shaker for a period of time to perform exfoliation; c) finally centrifuging and collecting the supernatant to obtain large-sized MXene nanosheets. However, the MXene size obtained by this patent is still limited.

[0006] CN110615440A discloses a method for preparing large-sized, oxygen-functionalized MXene nanosheets. The nanosheets are MXene micron-scale films formed by stacking multiple monolayers, with a lateral dimension greater than 50 μm and a thickness of 10 nm to 30 nm. The method includes the following steps: 1. Centrifuging a two-dimensional MXene nanosheet suspension, discarding the supernatant to obtain a mud-like precipitate; 2. First, adding deionized water to the mud-like precipitate and stirring evenly to obtain a viscous MXene nanosheet slurry; then freezing the viscous MXene nanosheet slurry in a -80°C ultra-low temperature freezer for 2-3 hours, and finally freeze-drying it in a freeze dryer to obtain a lyophilized product; 3. Sonicating the lyophilized product in a solvent to obtain large-sized, oxygen-functionalized MXene nanosheets dispersed in the solvent; the mass ratio of the lyophilized product to the volume ratio of the solvent in step 3 is (1 mg to 5 mg):(1 mL to 10 mL). This patent actually yields a micron-scale MXene film. Figure 3 The medium- and low-magnification transmission electron microscopy images show that the size of each piece is less than 10 μm, and it requires ultra-low temperature operation, resulting in a low yield and high cost. Summary of the Invention

[0007] This invention overcomes the size limitations and technical complexity of existing MXene monolayer fabrication techniques. Through a simple method, it successfully fabricates two-dimensional MXene nanosheets with grain sizes close to those of the MAX phase, solving the problem of small sheet size. The reaction conditions are mild, the operation is simple, and it is environmentally friendly. The monolayer MXene nanosheets prepared by this invention show promising applications in flexible electronic devices, electromagnetic shielding, infrared stealth, energy storage, lubrication, adsorption, and catalysts. Specifically, this invention achieves the above objectives through the following technical solutions:

[0008] A method for preparing large-size MXene nanosheets includes the following steps:

[0009] (S1) Disperse the MAX phase material in hydrochloric acid solution, stir, wash with water until the pH of the supernatant after centrifugation is 5-7, collect the bottom precipitate, repeat the sedimentation with water, dry, and obtain the purified MAX material with uniform particle size.

[0010] (S2) The purified MAX material was dispersed in a mixed solution of lithium fluoride and hydrochloric acid, stirred under heating, and the etching product was washed until the pH of the supernatant was 5-7. The bottom precipitate was collected to obtain the etched material, which was dispersed in a mixed solution of water, C1-3 alcohol and amino acid surfactant, shaken to peel off, and washed by centrifugation to obtain the peeling solution.

[0011] (S3) The stripping solution is centrifuged at low speed, and the supernatant is taken to obtain a mixed MXene solution. After multiple high-speed centrifugations, the precipitate is dried to obtain large-sized MXene nanosheets.

[0012] Furthermore, the large-sized MXene nanosheets have a lateral dimension of 20-50 μm and a thickness of 1-3 nm, forming a single-layer sheet structure.

[0013] Further, in step (S1), the MAX phase material is selected from at least one of Ti3AlC2, Ti2AlC, V2AlC, Ta4AlC3, Ti3AlCN, and Nb2AlC.

[0014] Further, in step (S1), the concentration of hydrochloric acid solution is 1-2 mol / L, the mass-to-volume ratio of MAX phase material to hydrochloric acid solution is 1 g: 10-20 mL, and the stirring conditions are stirring at 20-30℃ for 5-10 h.

[0015] Furthermore, in step (S1), repeated sedimentation involves dispersing the precipitate in water, allowing it to stand, and then collecting the precipitate again, repeating this process 3-5 times.

[0016] Further, in step (S2), the concentration of lithium fluoride in the mixed solution of lithium fluoride and hydrochloric acid is 0.05-0.1 g / mL, and the concentration of hydrochloric acid is 5-9 mol / L.

[0017] Further, in step (S2), the mass-to-volume ratio of the MAX material and the mixed solution of lithium fluoride and hydrochloric acid is 1g:10-30mL, preferably 1g:20-25mL.

[0018] Furthermore, in step (S2), the stirring under heating conditions is carried out at a speed of 400-800 rpm and a temperature of 40-60℃ for 20-30 hours; the ratio of the etched material to the mixed solution is 1g:30-50mL.

[0019] Further, in step (S2), the ratio of water, C1-3 alcohol, and amphiphilic surfactant mixed solution is 30-50ml: 10-20ml: 5-8g, shake for 2-5 hours to complete the stripping.

[0020] Furthermore, the C1-3 alcohol is selected from at least one of methanol, ethanol, isopropanol, ethylene glycol, propylene glycol, and glycerol; the amino acid-type surfactant is selected from at least one of sodium lauroyl sarcosinate, sodium lauroyl glutamate, cocoyl glutamate, disodium cocoyl glutamate, triethanolamine cocoyl glutamate, sodium cocoyl sarcosinate, triethanolamine cocoyl alanine, aminosulfonic acid betaine, potassium cocoyl glycinate, sodium cocoyl hydroxyethyl sulfonate, sodium lauroyl aspartate, disodium lauroyl aspartate, sodium lauroyl sarcosinate, lauroyl lysine, sodium lauroyl glycinate, potassium lauroyl glycinate, sodium myristoyl glutamate, sodium myristoyl sarcosinate, potassium myristoyl glycinate, and sodium myristoyl hydroxyethanesulfonate.

[0021] The inventors discovered that, in a specific ratio of water, C1-3 alcohol, and amino acid-based surfactant, large-sized MXene nanosheets can be rapidly, efficiently, and with a high yield through simple agitation and exfoliation. However, this method has only been observed with amino acid-based surfactants; conventional anionic or nonionic surfactants cannot achieve the same result.

[0022] Further, in step (S3), the first low-speed centrifugation is performed at 2000-3500 rpm for 10-20 min; the high-speed centrifugation is performed at 5000-8000 rpm for 5-10 min, and the precipitate is redispersed in water. This high-speed centrifugation is repeated 4-8 times. Finally, the obtained precipitate is freeze-dried to obtain the product, large-sized MXene nanosheets.

[0023] This invention discloses a method for preparing ultra-large MXene nanosheets with near-MAX phase grain size using self-sedimentation screening and cascade centrifugation. The method involves removing MAX phase impurities through acid washing and removing small grains through self-sedimentation screening to obtain pure, large-grain MAX phase precursor material. The nanosheets are then exfoliated by shaking in a mixed solution of water, C1-3 alcohol, and amino acid-based surfactant, followed by low-speed centrifugation to remove multilayered and unetched MAX phase, and high-speed centrifugation to separate and break down small-sized MXene nanosheets, thus yielding high-quality, large-sized, low-defect MXene nanosheets. The instruments and reagents used in this invention are inexpensive and widely available. The reaction conditions are mild, requiring no ice bath sonication or inert atmosphere protection. The operation is simple, and the nanosheet size reaches over 20 μm. Attached Figure Description

[0024] Figure 1 An optical microscope image of the large-size two-dimensional MXene nanosheets prepared in Example 1.

[0025] Figure 2 An atomic force microscope image of the large-size two-dimensional MXene nanosheets prepared in Example 1.

[0026] Figure 3 This is a scanning electron microscope image of the upper surface of the MXene film prepared in Example 1.

[0027] Figure 4 The X-ray diffraction spectrum of the MXene thin film prepared in Example 1.

[0028] Figure 5 An optical microscope image of the two-dimensional MXene nanosheets prepared in Example 2.

[0029] Figure 6 An optical microscope image of the two-dimensional MXene nanosheets prepared in Example 3.

[0030] Figure 7 An optical microscope image of the two-dimensional MXene nanosheets prepared for Comparative Example 1. Detailed Implementation

[0031] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to the following embodiments.

[0032] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; unless otherwise specified, the reagents and materials are commercially available.

[0033] Example 1

[0034] (S1) First, add 5g of 400-mesh Ti3AlC2 powder to 50ml of 1M hydrochloric acid solution and mix and stir at room temperature for 10h. Take out the mixed solution and centrifuge and wash it with deionized water until the pH>6. Then disperse it in 50ml of deionized water, let it stand at room temperature of 25℃ for 100s and remove the upper layer solution. Repeat the operation 5 times. Take the precipitate and vacuum dry it at 60℃ for 2h to obtain large-grain Ti3AlC2 powder.

[0035] (S2) Add 1.6g of lithium fluoride to 20ml of 9M hydrochloric acid solution and mix well to obtain a mixed solution. Then, slowly add 1g of large-grained Ti3AlC2 powder to the mixed solution and heat at 45℃ and 400rpm for 24h. Then, centrifuge and wash until pH>6. Disperse 1g of precipitate into 50ml of a mixed solution of water, ethanol, and sodium lauroyl glutamate in a ratio of 40ml:10ml:5.6g and shake for 2h.

[0036] (S3) After shaking, the solution was centrifuged at 3000 rpm for 15 min. The supernatant was centrifuged at 4500 rpm for 5 min. The precipitate was then dispersed in 50 ml of deionized water. The high-speed centrifugation at 4500 rpm was repeated 4 times. The precipitate was then dried to obtain large-sized MXene nanosheets.

[0037] Figure 1 An optical microscope image of the large-size two-dimensional MXene nanosheets prepared in Example 1, with a lateral dimension of over 25 μm.

[0038] Figure 2 This is an atomic force microscope image of the large-size two-dimensional MXene nanosheets prepared in Example 1. The thickness is 2.2 nm, indicating that the obtained two-dimensional MXene nanosheets are monolayer sheet structures.

[0039] (S4): Take 3 ml of MXene nanosheet solution and filter it under vacuum to obtain MXene film.

[0040] Figure 3 This is a scanning electron microscope image of the upper surface of the MXene film obtained in Example 1, which clearly shows the orderly stacking of large-sized MXene sheets.

[0041] Figure 4 The X-ray diffraction pattern of the MXene thin film obtained in Example 1 can be identified as Ti3C2T. X And it contains no other impurities.

[0042] Example 2

[0043] The other conditions are the same as in Example 1, except that in step (S2), the mixed solution is changed to a mixed solution of water, ethanol, and disodium cocoyl glutamate in a ratio of 40 ml: 10 ml: 7.2 g. Figure 5 An optical microscope image of the two-dimensional MXene nanosheets prepared in Example 2. The obtained MXene nanosheets have a lateral dimension of 32 μm.

[0044] Example 3

[0045] The other conditions are the same as in Example 1, except that in step (S2), the mixed solution is changed to a mixed solution of water, ethanol, and potassium myristoyl glycinate in a ratio of 40 ml: 10 ml: 6.6 g. Figure 6 An optical microscope image of the two-dimensional MXene nanosheets prepared in Example 3. The obtained MXene nanosheets have a lateral dimension of 31 μm.

[0046] Comparative Example 1

[0047] 3.2 g of lithium fluoride was added to 40 ml of 9 M hydrochloric acid solution and mixed thoroughly to obtain a mixed solution. Then, 2 g of large-grained Ti3AlC2 powder was slowly added to the mixed solution. The mixture was heated at 45 °C and 400 rpm for 24 h, followed by centrifugation and washing until the pH was > 6. The precipitate was dispersed in 100 ml of deionized water and ultrasonically vibrated at 80 W for 30 min under an argon atmosphere and an ice bath at 10 °C. The precipitate was then centrifuged, freeze-dried, and MXene nanosheets were obtained.

[0048] Figure 7 The image shows an optical microscope image of the two-dimensional MXene nanosheets obtained in Comparative Example 1. It can be seen that their lateral dimensions are 0.5-3 nm.

[0049] Comparative Example 2

[0050] The other conditions were the same as in Example 1, except that in step (S2), the mixed solution was changed to a mixture of water, ethanol, and sodium dodecylbenzenesulfonate in a ratio of 40 ml: 10 ml: 5.6 g. The resulting MXene nanosheets had a lateral size of 2 μm.

[0051] Comparative Example 3

[0052] The other conditions were the same as in Example 1, except that in step (S2), the mixed solution was changed to a mixture of water and sodium lauroyl glutamate in a ratio of 40 ml: 5.6 g. The resulting MXene nanosheets had a lateral size of 8 μm.

[0053] Comparative Example 4

[0054] The other conditions were the same as in Example 1, except that in step (S2), the mixed solution was changed to a mixture of water, ethanol, and Tween 80 in a ratio of 40 ml: 10 ml: 5.6 g. The resulting MXene nanosheets had a lateral size of 5 μm.

Claims

1. A method for preparing large-size MXene nanosheets, characterized in that, Includes the following steps: (S1) Disperse the MAX phase material in hydrochloric acid solution, stir, wash with water until the pH of the supernatant after centrifugation is 5-7, collect the bottom precipitate, repeat the sedimentation with water, dry, and obtain the purified MAX material with uniform particle size. (S2) The purified MAX material was dispersed in a mixed solution of lithium fluoride and hydrochloric acid, stirred under heating, and the etching product was washed until the pH of the supernatant was 5-7. The bottom precipitate was collected to obtain the etched material, which was dispersed in a mixed solution of water, C1-3 alcohol and amino acid surfactant, shaken to peel off, and washed by centrifugation to obtain the peeling solution. (S3) The stripping solution is centrifuged at low speed, and the supernatant is taken to obtain a mixed MXene solution. After multiple high-speed centrifugations, the precipitate is dried to obtain large-sized MXene nanosheets.

2. The preparation method according to claim 1, characterized in that, The large-sized MXene nanosheets have a lateral dimension of 20-50 μm and a thickness of 1-3 nm, and are a single-layer sheet structure.

3. The preparation method according to claim 1, characterized in that, In step (S1), the MAX phase material is selected from at least one of Ti3AlC2, Ti2AlC, V2AlC, Ta4AlC3, Ti3AlCN, and Nb2AlC.

4. The preparation method according to claim 1, characterized in that, In step (S1), the concentration of hydrochloric acid solution is 1-2 mol / L, and the mass-to-volume ratio of MAX phase material to hydrochloric acid solution is 1 g: 10-20 mL; the stirring conditions are 20-30℃ for 5-10 h.

5. The preparation method according to claim 1, characterized in that, In step (S2), the concentration of lithium fluoride in the mixed solution of lithium fluoride and hydrochloric acid is 0.05-0.1 g / mL and the concentration of hydrochloric acid is 5-9 mol / L.

6. The preparation method according to claim 1, characterized in that, In step (S2), the mass-to-volume ratio of the MAX material and the mixed solution of lithium fluoride and hydrochloric acid is 1g:10-30mL, preferably 1g:20-25mL.

7. The preparation method according to claim 1, characterized in that, In step (S2), stirring under heating conditions is carried out at a speed of 400-800 rpm and a temperature of 40-60℃ for 20-30 hours; the ratio of etched material to mixed solution is 1g:30-50mL.

8. The preparation method according to claim 1, characterized in that, In step (S2), the ratio of water, C1-3 alcohol, and amphiphilic surfactant mixed solution is 30-50ml: 10-20ml: 5-8g. Shake for 2-5 hours to complete the stripping.

9. The preparation method according to claim 1, characterized in that, The C1-3 alcohol is selected from at least one of methanol, ethanol, isopropanol, ethylene glycol, propylene glycol, and glycerol; the amino acid-type surfactant is selected from at least one of sodium lauroyl sarcosinate, sodium lauroyl glutamate, cocoyl glutamate, disodium cocoyl glutamate, triethanolamine cocoyl glutamate, sodium cocoyl sarcosinate, triethanolamine cocoyl alanine, aminosulfonic acid betaine, potassium cocoyl glycinate, sodium cocoyl hydroxyethyl sulfonate, sodium lauroyl aspartate, disodium lauroyl aspartate, sodium lauroyl sarcosinate, lauroyl lysine, sodium lauroyl glycinate, potassium lauroyl glycinate, sodium myristoyl glutamate, sodium myristoyl sarcosinate, potassium myristoyl glycinate, and sodium myristoyl hydroxyethanesulfonate.

10. The preparation method according to claim 1, characterized in that, In step (S3), the first low-speed centrifugation is performed at 2000-3500 rpm for 10-20 min; the high-speed centrifugation is performed at 5000-8000 rpm for 5-10 min, and the precipitate is dispersed in the water again. The high-speed centrifugation is repeated 4-8 times.

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