A method for laser-assisted exfoliation of MXene flakes

Abstract

This invention discloses a method for laser-assisted exfoliation of MXene flakes, comprising screening large-particle MAX phase materials, etching the MAX phase materials, preparing a fixed-concentration MXene solution, and laser-assisted ultrasonic exfoliation. This method, based on ultrasonic exfoliation, utilizes laser-assisted exfoliation to achieve high-efficiency, low-energy-consumption exfoliation of MXene flakes. Compared to conventional ultrasonic exfoliation, this method significantly shortens the exfoliation time, produces flakes with a higher surface area ratio and lower oxidation degree, and the resulting films have higher electrical conductivity.

Description

Technical Field

[0001] This invention belongs to the field of two-dimensional nanomaterials technology, and specifically relates to a method for laser-assisted exfoliation of MXene sheets. Background Technology

[0002] MXene is a two-dimensional material with a graphene-like structure, typically obtained by etching MAX phase compounds. Its specific structure is M... n+1 X n T x (n = 1, 2, 3), where M is a transition metal element (such as Ti, Zr, Nb, etc.), X is a C or N element, and Tx is the functional group linked to the M surface. Depending on the etching method, the surface is connected by functional groups such as -F, -OH, and =O in different proportions. These different surface functional groups give MXene a rich variety of surface chemical properties, resulting in excellent mechanical properties, high electrical conductivity, large surface area ratio, and high photothermal conversion capability.

[0003] Currently, the preparation of larger-sized MXenes mainly involves the following three steps: 1. Using larger-particle precursors; 2. Using intercalation agents during etching to promote separation; 3. Improving the ultrasonic exfoliation process. Differential centrifugation can pre-screen large-particle precursors Ti3AlC2. Using different intercalation agents can increase the interlayer spacing and promote the exfoliation effect, but at the same time, it will inevitably cause chemical modification of its surface functional groups. Ultrasonic exfoliation is the final and one of the most critical steps for large-sized MXenes. Ultrasonic treatment in liquids can induce phenomena such as acoustic flow and cavitation degassing. For the exfoliation process, ultrasound generates cavitation bubbles in the liquid. These bubbles generate local high temperatures of 5000 degrees Celsius and pressures of tens of thousands of Pa. During this process, water can decompose into chemically volatile H and OH ions. Therefore, cavitation can provide sufficient energy to break down the bulk and layered materials and induce a chemical reaction between the materials and water. At the same time, the ultrasonic process can remove a large amount of dissolved oxygen in the water, preventing the materials from being oxidized during the ultrasonic process.

[0004] However, simple ultrasound can damage the surface of MXene, generating more small-sized MXene particles, thus reducing its surface area ratio and negating the advantage of high surface area ratio in two-dimensional materials. Furthermore, a significant portion of the energy is dissipated into the ultrasound medium during the ultrasound process, which is detrimental to the exfoliation process. This leads to a decrease in the ultrasonic exfoliation rate and efficiency. Therefore, improving the method of MXene exfoliation is a problem worth considering. Summary of the Invention

[0005] The achievements of MXene in these different fields are inseparable from the excellent physical and chemical properties brought about by the rich variety of functional groups on its surface. A larger specific surface area of ​​MXene also means that more functional groups are attached to the surface of the same volume of MXene. In the existing technology, the ultrasonic exfoliation method typically produces a relatively small surface area ratio and is time-consuming, while the hand-cranking method is inefficient and cannot achieve mass production, and the use of intercalating agents will chemically modify the surface of the sheet.

[0006] To address the shortcomings of the prior art, this invention provides a method for laser-assisted stripping of MXene sheets.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for laser-assisted stripping of MXene sheets includes the following steps:

[0009] (1) Pour the MAX phase material powder from the top into a tube with a vertical height of 8 cm above the water surface, let it settle naturally and stand for 6 to 10 minutes;

[0010] (2) Remove the supernatant and take the bottom MAX phase material precipitate. Repeat step (1) three times to obtain MAX phase material precipitate with particles larger than 10 μm. Then dry to obtain MAX phase material particles.

[0011] (3) Add 1.6g of LiF to 15mL of HCl and 10mL of deionized water, and stir magnetically for 10min to dissolve completely;

[0012] (4) Slowly add 1g of MAX phase material particles to the solution prepared in step (3) and continuously stir magnetically at 50°C for 24 hours to perform etching;

[0013] (5) After etching, the solution was repeatedly centrifuged and washed with dilute hydrochloric acid and deionized water until neutral to obtain MXene material dispersion;

[0014] (6) The obtained MXene material dispersion was vacuum dried at 60°C for 12 hours to obtain MXene material powder;

[0015] (7) Prepare MXene material powder into a fixed concentration MXene solution and put it into a tube. Use an ultrasonic cleaner to continuously sonicate the edge of the tube. At the same time, apply a laser with a wavelength of 532nm at a distance of 5-8cm from the top of the tube and irradiate for 60 minutes to obtain MXene sheets with a high surface area ratio and low oxidation degree.

[0016] The method of this invention uses laser-assisted exfoliation on the basis of ultrasonic exfoliation, which achieves high-efficiency and low-energy exfoliation of a large number of MXene sheets. Compared with the sheets produced by ordinary ultrasonic exfoliation, the sheets produced by this method have a higher surface area ratio, a lower degree of oxidation, and the films filtered from them also have higher electrical conductivity.

[0017] Furthermore, the MAX phase material is Ti3AlC2.

[0018] Furthermore, the MXene material is Ti3C2T. x .

[0019] Furthermore, in step (3), the concentration of HCl is 8-9 mol / L. This concentration of HCl is not too high, which would cause the reaction to be too violent and destroy the Ti3AlC2 structure, nor would the reaction be too slow, which would cause the reaction time to be too long and the reaction to be incomplete.

[0020] Furthermore, in steps (1) and (4), the MAX phase material particles are 350 to 500 mesh. If the particles are too large, the etching efficiency will be affected, resulting in an increase in reaction time or incomplete reaction. If the particles are too small, it will be difficult to screen out the target 10 μm particles, resulting in a low yield.

[0021] Furthermore, in step (5), the centrifugation speed is 4000 r / min and the centrifugation time is 5 min. The purpose of washing with hydrochloric acid is to wash away excess LiF and the LiCl generated in the reaction. The purpose of washing with deionized water is to wash away hydrochloric acid. The purpose of repeating the process is to ensure that the corresponding products are completely washed away. The purpose of centrifugation is to precipitate the main product Ti3C2Tx and to remove the above-mentioned reaction byproducts directly in the supernatant.

[0022] Furthermore, in step (7), the power density of the ultrasonic cleaner is 30-45 W / L. The cavitation and turbulence effects of the ultrasonic waves promote the stripping of MXene and remove dissolved oxygen in the water, preventing MXene from being oxidized during the ultrasonic process.

[0023] Furthermore, in step (7), the concentration of the MXene solution is 3-5 mg / ml, and the choice of the concentration of the MXene solution depends on the transmittance of the solution and the power density of the laser.

[0024] Furthermore, in step (7), the power density of the laser is 15-25 W / L. The local high temperature generated by the laser irradiation on the MXene surface will promote the generation of hydroxyl groups on the MXene surface, thereby promoting peeling.

[0025] The advantages of this invention are as follows: This invention utilizes the excellent light absorption and photothermal conversion capabilities of MXene. When a laser irradiates the MXene surface through the solution, a local high temperature is generated on the MXene surface, promoting the formation of -OH functional groups and Ti-OH. These functional groups form hydrogen bonds with water, resulting in higher solubility of MXene in water and easier dispersion in water, ultimately promoting exfoliation. That is, the efficiency of laser-assisted exfoliation is relatively higher. Using this method, the exfoliation rate is increased by 100%, the energy consumption during the exfoliation process is reduced by 27%, the surface area ratio of MXene after exfoliation increases by 51%, and the oxidation degree is reduced by 33%. After filtration into a film, the conductivity increases by an average of 133%. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the laser-assisted ablation principle of the present invention;

[0027] Figure 2 This is a picture of a laser-assisted stripping process for the supernatant.

[0028] Figure 3 This is a comparison chart of the transmittance of the supernatant obtained by different stripping treatment methods using a spectrophotometer.

[0029] Figure 4 This is an electron microscope image of a thin section obtained by simple ultrasonic peeling;

[0030] Figure 5 This is an electron microscope image of a thin section obtained by laser-assisted ultrasonic ablation;

[0031] Figure 6 This is a comparative chart showing the average size of 100 slices for each exfoliation method, obtained using atomic force microscopy.

[0032] Figure 7 This is a comparative chart showing the average thickness of 100 slices for each exfoliation method, obtained using atomic force microscopy.

[0033] Figure 8 This is a comparison of the proportions of MXene functional groups obtained by different processing methods using X-ray photoelectron spectroscopy. Figure 1 ;

[0034] Figure 9 This is a comparison of the proportions of MXene functional groups obtained by different processing methods using X-ray photoelectron spectroscopy. Figure 2 ;

[0035] Figure 10 This is a comparison of the proportions of MXene functional groups obtained by different processing methods using X-ray photoelectron spectroscopy. Figure 3 ;

[0036] Figure 11This is a comparison chart of the conductivity of MXene films prepared by different processing methods. Detailed Implementation

[0037] The present invention will now be described in detail with reference to the accompanying drawings:

[0038] The essential features of the present invention can be seen from the following embodiments, but these embodiments are for illustrative purposes only and are not intended to limit this aspect.

[0039] Example 1

[0040] A method for laser-assisted stripping of MXene sheets includes the following steps:

[0041] (1) Pour 350-mesh MAX phase material powder into a tube 8 cm above the water surface from the top, let it settle naturally and stand for 6-10 minutes. Free settling and standing can screen out large particles in the MAX phase material powder.

[0042] (2) Remove the supernatant and take the bottom MAX phase material precipitate. Repeat step (1) three times to obtain MAX phase material precipitate with particles larger than 10 μm, and then dry to obtain MAX phase material particles.

[0043] (3) Add 1.6g of LiF to 15mL of 8mol / L HCl and 10mL of deionized water, stir magnetically for 10min to dissolve completely, and mix LiF and HCl thoroughly by stirring magnetically.

[0044] (4) Slowly add 1g of screened MAX phase material particles into the solution prepared in step (3) and continuously stir magnetically at 50°C for 24 hours to perform etching;

[0045] (5) After etching, the solution was washed repeatedly by centrifugation with dilute hydrochloric acid and deionized water until neutral to obtain MXene material dispersion. The centrifugation speed was 4000 r / min and the centrifugation time was 5 min.

[0046] (6) The obtained MXene material dispersion was vacuum dried at 60°C for 12 hours to obtain MXene material powder, which was then made into powder particles for easy subsequent precise preparation into a solution of the required concentration.

[0047] (7) Prepare an MXene solution with a concentration of 3 mg / ml by mixing MXene material powder and place it in a tube. Use an ultrasonic cleaner with a power density of 30 W / L to continuously sonicate the edge of the tube. At the same time, apply a laser with a wavelength of 532 nm and a power density of 15 W / L at a distance of 5 cm from the top of the tube. After continuous irradiation for 60 min, a MXene sheet with a high surface area ratio and low oxidation degree is obtained.

[0048] Example 2

[0049] (1) Pour Ti3AlC2 powder into a tube 8 cm above the water surface from the top and let it settle naturally for 6-10 minutes. Free settling and settling can filter out large particles in Ti3AlC2 powder.

[0050] (2) Remove the supernatant and take the bottom Ti3AlC2 precipitate. Repeat step (1) three times to obtain Ti3AlC2 precipitate with particles larger than 10μm. Then dry to obtain Ti3AlC2 particles.

[0051] (3) Add 1.6g of LiF to 15mL of 9mol / L HCl and 10mL of deionized water, stir magnetically for 10min to dissolve completely, and mix LiF and HCl thoroughly by stirring magnetically.

[0052] (4) Slowly add 1g of 500-mesh Ti3AlC2 particles to the solution prepared in step (3) and continuously stir magnetically at 50°C for 24 hours to perform etching;

[0053] (5) After etching, the solution was repeatedly centrifuged and washed with dilute hydrochloric acid and deionized water until neutral to obtain Ti3C2T. x The dispersion was centrifuged at 4000 r / min for 5 min.

[0054] (6) The obtained Ti3C2T x The dispersion was vacuum dried at 60°C for 12 hours to obtain Ti3C2T. x The powder is made into granules to facilitate the precise preparation of solutions of the required concentration.

[0055] (7) Ti3C2T x The powder was prepared into a concentration of 5 mg / ml for Ti3C2T. x The solution was placed in a tube, and an ultrasonic cleaner with a power density of 45 W / L was used to continuously sonicate the edge of the tube. At the same time, a laser with a wavelength of 532 nm and a power density of 25 W / L was applied 8 cm away from the top of the tube. After continuous irradiation for 60 min, Ti3C2T with a high surface area ratio and low oxidation degree was obtained. x Thin slices.

[0056] The method of this invention involves laser-assisted ultrasonic treatment of MXene after the raw material preparation is completed, which gives the two-dimensional sheet-like MXene a higher surface area ratio and a lower degree of oxidation. This superior microscopic performance results in the macroscopic film also having electrical conductivity. In other words, this method can more efficiently peel off large particles to obtain two-dimensional materials with better performance. These two-dimensional materials can form better films.

[0057] from Figure 2 It can be seen that the supernatant concentration is higher, the transmittance is lower, and the Tyndall effect is less pronounced in laser-assisted ablation. Figure 3 The results show that after standing for 24 hours, laser-assisted ultrasound (LA) produced a solution with lower transmittance than ultrasound alone (US), indicating that more of the peeled flakes remained in the supernatant. Figure 4 and Figure 5 It can be seen that laser-assisted ultrasound produces a larger sheet than ultrasound alone. Figure 6 It can be seen that laser-assisted ultrasound produces thinner slices with a more concentrated thickness distribution than ultrasound alone. Figure 7 It can be seen that laser-assisted ultrasound produces thin sheets with larger dimensions and more concentrated size distribution than ultrasound alone at the same thickness. Figure 8-10 These are XPS images of the thin sections. In the exfoliation method, the number preceding the exfoliation method represents the ultrasound duration, and the numbers following it represent US for ultrasound only and LA for laser ultrasound. It can be seen that laser-assisted ultrasound produces thin sections with a higher proportion of -OH functional groups and less oxidation than ultrasound only. From... Figure 11 It can be seen from this that the thin film conductivity of laser-assisted ultrasound has a higher conductivity.

[0058] Although the specific embodiments of the present invention have been described and illustrated in detail above, it should be noted that various changes and modifications can be made to the above embodiments without departing from the spirit of the present invention and the scope set forth in the appended claims.

Claims

1. A method for laser-assisted stripping of MXene sheets, characterized in that, Includes the following steps: (1) Pour the MAX phase material powder from the top into a tube with a vertical height of 8 cm above the water surface, let it settle naturally and stand for 6 to 10 minutes; (2) Remove the supernatant and take the bottom MAX phase material precipitate. Repeat step (1) three times to obtain MAX phase material precipitate with particles larger than 10 μm. Then dry to obtain MAX phase material particles. (3) Add 1.6g of LiF to 15mL of HCl and 10mL of deionized water, and stir magnetically for 10min to dissolve completely; (4) Slowly add 1g of MAX phase material particles to the solution prepared in step (3) and continuously stir magnetically at 50°C for 24 hours to perform etching; (5) After etching, the solution was repeatedly centrifuged and washed with dilute hydrochloric acid and deionized water until neutral to obtain MXene material dispersion; (6) The obtained MXene material dispersion was vacuum dried at 60°C for 12 hours to obtain MXene material powder; (7) Prepare MXene material powder into a fixed concentration MXene solution and put it into a tube. Use an ultrasonic cleaner to continuously sonicate the edge of the tube. At the same time, apply a laser with a wavelength of 532nm at a distance of 5-8cm from the top of the tube and irradiate for 60 minutes to obtain MXene sheets with a high surface area ratio and low oxidation degree.

2. The method for laser-assisted stripping of MXene sheets according to claim 1, characterized in that, The MAX phase material is Ti3AlC2.

3. The method for laser-assisted stripping of MXene sheets according to claim 1, characterized in that, The MXene material mentioned is Ti3C2T x .

4. The method for laser-assisted stripping of MXene sheets according to claim 1, characterized in that, In step (3), the concentration of HCl is 8-9 mol / L.

5. The method for laser-assisted stripping of MXene sheets according to claim 1, characterized in that, In step (4), the MAX phase material particles are 350-500 mesh.

6. The method for laser-assisted stripping of MXene sheets according to claim 1, characterized in that, In step (5), the centrifugation speed is 4000 r / min and the centrifugation time is 5 min.

7. The method for laser-assisted stripping of MXene sheets according to claim 1, characterized in that, The power density of the ultrasonic cleaner in step (7) is 30-45 W / L.

8. The method for laser-assisted stripping of MXene sheets according to claim 1, characterized in that, The concentration of the MXene solution in step (7) is 3-5 mg / ml.

9. The method for laser-assisted stripping of MXene sheets according to claim 1, characterized in that, The power density of the laser in step (7) is 15-25 W / L.

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