Preparation method of high-yield single-layer MXene dispersion liquid

Abstract

The invention provides a preparation method of a high-yield single-layer MXene dispersion liquid, and relates to the field of preparation of MXene materials. The technology comprises the following steps: firstly, corroding Ti3AlC2MAX phase powder by adopting HCl and HF to obtain multilayer MXene, then adding LiCl for intercalation, and finally, ultrasonically destroying the limitation of a hydrogen bond cage structure in the multilayer MXene at 60-80 DEG C under the assistance of ethanol, so that a multilayer MXene dispersion liquid is stripped into a single layer. According to the technology, the yield of the single-layer MXene can be increased to 95.0% or above, the average nanometer size of the MXene is 1.8 microns, and the MXene can be applied to functional materials such as conductive materials, electromagnetic shielding materials and printing materials. The obtained single-layer MXene dispersion liquid has the advantages of being high in yield, large in size, simple and efficient in preparation method, capable of being prepared on a large scale and the like, and has good industrial potential and application value in the field of MXene materials.

Description

Technical Field

[0001] The present invention relates to the field of MXene material preparation, and particularly relates to a method for preparing a high-yield single-layer MXene dispersion. Background Art

[0002] MXene (Ti 3 C 2 T x ) is well-known for its excellent electrical conductivity and hydrophilicity, and shows great market value in the fields of energy storage, electromagnetic shielding, communication, etc. So far, wet etching using HF / HCl or LiF / HCl, etc. to remove Al from Ti 3 AlC 2 MAX phase, and then performing exfoliation and delamination has become a relatively mature method for preparing single-layer MXene dispersion. This process mainly involves two steps, namely etching and exfoliation. Obtaining multi-layer MXene by HF / HCl etching and exfoliating to obtain single-layer MXene nanosheets after ion intercalation has become the preferred method for most researchers.

[0003] Generally, ultrasonic treatment is used during the exfoliation process to accelerate the multi-layer Ti 3 C 2 T xStratification is carried out to produce a higher proportion of single-layer MXene sheets. However, the yield of single-layer MXene finally obtained in this way is usually less than 40%, severely limiting the large-scale application of MXene. To solve the problem of the preparation efficiency of MXene, Zhang et al. (ZHANG Q X, FAN R Z, CHENG W H, et al. Synthesis of Large-Area MXenes with High Yields through Power-Focused Delamination Utilizing Vortex Kinetic Energy[J]. Advanced Science, 2022, 9(28).) designed a power-focused scheme to obtain single-layer MXene by focusing the impact force generated by the vortex motion of water flow to shear the surface delamination of multi-layer MXene without any ultrasonic treatment, but the obtained MXene yield is only 61.2%. Huang et al. (HUANG X W, WU P Y. A Facile, High-Yield, and Freeze-and-Thaw-Assisted Approach to Fabricate MXene with Plentiful Wrinkles and Its Application in On-Chip Micro-Supercapacitors[J]. Advanced Functional Materials, 2020, 30(12)) proposed a freeze-thaw-assisted method. Through the expansion phenomenon during the water freezing process, the yield of MXene nanosheets can be effectively improved through simple repeated freeze-thaw cycles. At a relatively slow freezing rate, after several freeze-thaw cycles, the obtained MXene nanosheets are larger in size and obvious micro-wrinkles appear on the surface, but the yield is only 39%. Extending the ultrasonic treatment time can further increase the yield of single-layer MXene within a certain limit, but it will significantly increase the defects on the surface of MXene and reduce the sheet size, thereby causing the loss of its excellent properties. Therefore, finding an efficient and rapid delamination method to prepare single-layer MXene with a high yield is of great significance for the development and application of MXene-based materials. Summary of the Invention

[0004] Based on the problems of preparation efficiency and MXene size existing in the preparation of single-layer MXene dispersions reported above, the purpose of the present invention is to provide a method for preparing a single-layer MXene dispersion with a high yield, in order to improve the preparation efficiency of the single-layer MXene dispersion.

[0005] The concept of the present invention is as follows:

[0006] Ti3 AlC 2 After the MAX phase is etched with HF and HCl, multi-layer MXene is obtained. At this time, the multi-layer MXene cannot be exfoliated and an intercalating agent (such as LiCl) needs to be used for ion intercalation. The multi-layer MXene treated by intercalation is usually ultrasonically exfoliated in ice water. However, the inventor found during the research that low temperature is the main reason for the inefficient exfoliation of multi-layer MXene during the ultrasonic process. By controlling the ultrasonic exfoliation temperature, the hydrogen bonds between the oxygen-containing functional groups in the multi-layer MXene and the surrounding water molecules can be effectively broken, thereby significantly increasing the yield of single-layer MXene without damaging the quality of MXene. In addition, to enhance the exfoliation effect, a small amount of ethanol is added to increase the cavitation bubble density and enhance the exfoliation effect on MXene. The inventor's research found that within a specific ultrasonic temperature range, adding a small amount of ethanol, MXene has an extremely high yield of single-layer MXene during the exfoliation process.

[0007] Therefore, the invention uses a method of appropriately increasing the temperature of MXene during ultrasonic exfoliation to effectively solve the problem of low yield in the preparation of single-layer MXene.

[0008] Based on the above concept, the present invention provides the following technical solutions:

[0009] (1) Mix 12 wt% HF and 38 wt% HCl solutions evenly according to a volume ratio of 1:1.5 - 2.0 to obtain a mixed solution;

[0010] (2) Add Ti 3 AlC 2 MAX phase powder to make its concentration within 40 - 60 mg / mL, and stir at 25 - 35 °C for 18 - 36 hours.

[0011] (3) Centrifuge the obtained mixed solution at a speed of 3500 revolutions per minute for 5 minutes, and repeat the operation until the precipitate is washed to pH = 6 to obtain multi-layer MXene;

[0012] (4) Disperse the multi-layer MXene obtained in step (3) in water, and add LiCl according to the mass ratio of multi-layer MXene to LiCl of 1:1 - 1.2. Stir at 25 - 35 °C for 15 - 18 hours to perform ion intercalation of multi-layer MXene.

[0013] (5) Centrifuge the mixed solution obtained in step (4) at a speed of 3000 revolutions per minute for 5 minutes, retain the precipitate and redisperse it in water, and repeat the operation 3 - 5 times to obtain the intercalated multi-layer MXene;

[0014] (6) Disperse the intercalated multi-layer MXene obtained in step (5) with an ethanol solution, place it in a bath-type ultrasonic machine at a temperature of 60-80 °C for ultrasonic treatment for 3-5 minutes, with a power of 240-400 W, and introduce an argon gas flow during the entire exfoliation process.

[0015] (7) Centrifuge the mixture obtained in step (6) at a speed of 3500 revolutions per minute for 30 minutes, collect the supernatant to obtain a monolayer MXene dispersion;

[0016] Preferably, the stirring temperature in step (2) is 35 °C and the time is 24 hours;

[0017] Preferably, the Ti 3 AlC 2 MAX concentration in step (2) is 50 mg / mL;

[0018] Preferably, the stirring temperature in step (4) is 35 °C and the time is 16 hours;

[0019] Preferably, the ultrasonic temperature in step (6) is 70 °C;

[0020] Preferably, the ethanol concentration in step (6) is 1-3%;

[0021] Preferably, the ultrasonic time in step (6) is 5 minutes;

[0022] Preferably, the ultrasonic power in step (6) is 240 W;

[0023] The present invention provides a method for preparing a high-yield monolayer MXene dispersion, mainly including three steps: preparation of a multi-layer MXene dispersion, intercalation of multi-layer MXene, and exfoliation of a monolayer MXene dispersion ( Figure 1 ), and this process mainly improves the yield of the MXene dispersion by regulating the temperature of the water bath during ultrasonic treatment in step (6), realizing the efficient preparation of a monolayer MXene dispersion ( Figure 2 ).

[0024] As is well known in the industry, MXene is extremely prone to oxidation in the presence of oxygen and water, especially under high-temperature conditions. Due to wave attenuation and energy loss during ultrasonic treatment, the liquid temperature may rise significantly. Researchers usually introduce ice to cool the system during the ultrasonic treatment of multi-layer Ti 3 AlC 2 to prevent MXene oxidation. However, the inventor found during the research process that low temperature is the main reason for the inefficient exfoliation of multi-layer MXene during ultrasonic treatment.

[0025] Here, the inventors proposed a strategy to significantly improve the monolayer yield by breaking the restriction of the hydrogen-bonded cage structure in multi-layer MXene through high-temperature ultrasound, challenging the traditional view that monolayer MXene can only be prepared at low temperatures. At about 70 °C, the hydrogen bonds between the oxygen-containing end groups of multi-layer MXene and surrounding water molecules are weakened, and the restraint of the hydrogen-bonded cage structure is weakened. At the same time, since the surface tension of ethanol is much lower than that of water, a small amount of ethanol added can reduce the surface tension of the dispersion. The lower surface tension will reduce the energy barrier for bubble formation and promote the generation of more cavitation bubbles. This enables ultrasonic cavitation to generate more microbubbles, which penetrate into the interlayers of multi-layer MXene, thereby achieving efficient exfoliation under mild conditions and obtaining larger monolayer nanosheets.

[0026] Therefore, the inventors first prepared a multi-layer MXene dispersion by etching with HCl and HF in steps (1) to (5), and then appropriately increased the temperature during ultrasonic exfoliation of MXene to 60 - 80 °C in step (6). It was found that a higher ultrasonic exfoliation temperature can effectively break the hydrogen bonds between the oxygen-containing functional groups in multi-layer MXene and surrounding water molecules, thereby significantly increasing the yield of monolayer MXene without damaging the quality of MXene. Part of the reason is that ultrasonic treatment usually induces cavitation effects in liquids. Cavitation includes the formation, growth, and violent collapse of microbubbles in a liquid medium under the influence of ultrasound. At the same time, a small amount of ethanol added can reduce the energy barrier for bubble formation and promote the generation of more cavitation bubbles. The violent collapse of these bubbles generates extremely high temperatures and pressures, accompanied by strong local liquid flow and microjets. These forces strongly impact and shear the interlayers of multi-layer Ti 3 AlC 2 to further overcome the van der Waals forces and hydrogen bonds, thereby exfoliating it into monolayer or few-layer nanosheets. Another part of the reason is that at 15 °C, many water molecules surround multi-layer Ti 3 C 2 to form extensive hydrogen bonds with the oxygen-containing functional groups on Ti 3 AlC 2 to produce a strong hydrogen-bond cage effect. This hydrogen-bond cage tightly wraps and restricts multi-layer Ti 3 AlC 2 and prevents the penetration of external water molecules. As the temperature increases, the number of hydrogen bonds decreases significantly, resulting in a significant reduction in the restriction of the hydrogen-bond cage. Therefore, external water molecules can more easily penetrate into multi-layer Ti 3 AlC 2Between the layers. When ultrasonic treatment is applied at this point, the bubbles formed by water molecules are also more likely to penetrate into the interlayers, further promoting the delamination process. It is worth noting that the formation of bubbles usually begins with nucleation. In a high-temperature liquid medium, the nucleation threshold decreases, resulting in an increase in nucleation points. These nuclei then form microbubbles under the repeated influence of sinusoidal ultrasonic waves. Therefore, compared with a low-temperature ice bath (about 15 °C), the MXene dispersion under the condition of high-temperature ultrasonic treatment at 70 °C with 3 wt% ethanol added can contain more microbubbles. From a thermodynamic perspective, temperature is a key factor affecting the intensity of molecular thermal motion. A higher temperature leads to an increase in the average kinetic energy of molecules, thus resulting in an enhanced interaction between them. During the ultrasonic delamination process, a higher temperature not only reduces the nucleation threshold and increases the nucleation points but also enhances the mobility of water molecules. This helps water molecules penetrate more effectively into the interlayers of MXene and promotes interlayer separation.

[0027] Therefore, step (6) can achieve a monolayer MXene yield of over 95% in just 3 - 5 minutes, and the properties of these nanosheets are comparable to those prepared by the traditional ice bath method. In addition, the MXene films prepared by this high-yield method are indistinguishable from the films prepared by ice bath ultrasound in terms of morphology, conductivity, and electromagnetic shielding performance. The high-concentration MXene ink prepared by large-scale production exhibits excellent printing and processing capabilities, and the prepared products demonstrate superior infrared stealth and Joule heating characteristics. This study has solved the key technical bottleneck in MXene production and paved the way for its extensive technical and industrial applications.

[0028] To ensure the product quality of the monolayer MXene dispersion prepared by the technology provided by the present invention, it is found by scanning electron microscopy that the morphology of the monolayer MXene obtained by traditional ice bath ultrasonic delamination and the heating ultrasonic delamination of the present invention both maintain a consistent hexagonal crystal structure ( Figure 3 ), indicating that the high-temperature treatment does not change the microscopic configuration of MXene ( Figure 4 ). After measurement, the average size of the monolayer MXene obtained by ice bath ultrasonic delamination is 1.7 μm, which is basically equal to the size (1.8 μm) of the monolayer MXene obtained by the heating ultrasonic delamination of the present invention ( Figure 5 ). Obviously, the heating ultrasonic delamination technology will not cause serious damage to the size of MXene.

[0029] The beneficial effects of the present invention are:

[0030] 1. The operation of the process for delaminating MXene in the present invention is simple;

[0031] 2. The yield of the MXene dispersion prepared by the present invention is over 95%;

[0032] 3. The size of MXene in the monolayer MXene dispersion prepared by the present invention is relatively complete;

[0033] 4. The film prepared from the monolayer MXene dispersion prepared by the present invention has excellent conductivity and electromagnetic shielding performance. Description of the Drawings

[0034] Figure 1 is the preparation process of the monolayer MXene dispersion;

[0035] Figure 2 are the photos of the MXene dispersion before and after dilution;

[0036] Figure 3 is the scanning electron microscopy image of the MXene nanosheets;

[0037] Figure 4 is the transmission electron microscopy image of the MXene nanosheets;

[0038] Figure 5 is the nano-size distribution diagram of the MXene nanosheets;

[0039] Figure 6 is the conductivity diagram of the MXene nanosheets;

[0040] Figure 7 is the electromagnetic shielding effectiveness diagram of the MXene nanosheets. Detailed Embodiments

[0041] The technical solutions provided by the present invention will be described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0042] Example 1

[0043] Mix 12 wt% HF and 38 wt% HCl solutions evenly according to a volume ratio of 1:1.5 to obtain a mixed solution. Add 2 g of Ti 3 AlC 2 MAX phase powder into 40 mL of the mixed solution and stir at 35 °C for 24 hours. Centrifuge the obtained mixed solution at a speed of 3500 revolutions per minute for 5 minutes, and repeat the operation until the precipitate is washed to pH = 6 to obtain multi-layer MXene. Subsequently, disperse the obtained multi-layer MXene in water, and add LiCl according to a mass ratio of multi-layer MXene to LiCl of 1:1.1. Stir at 35 °C for 16 hours to perform ion intercalation of the multi-layer MXene. Centrifuge the obtained mixed solution at a speed of 3000 revolutions per minute for 5 minutes, retain the precipitate, redisperse it in water, and repeat the operation 4 times to obtain the intercalated multi-layer MXene.

[0044] Disperse the intercalated multi-layer MXene in 150 mL of an ethanol solution with a mass fraction of 3 wt%, place it in a bath-type ultrasonic machine at a temperature of 70 °C, and ultrasonically treat it for 5 minutes with a power of 240 W. Introduce an argon gas flow during the entire exfoliation process. Centrifuge the mixture at a speed of 3500 revolutions per minute for 30 minutes, collect the supernatant, and obtain a monolayer MXene dispersion.

[0045] Example 2

[0046] The difference between this example and Example 1 is that the ultrasonic temperature is an ice bath (5 °C), and the MXene dispersion yield is 35.8%.

[0047] Example 3

[0048] The difference between this example and Example 1 is that the mass ratio of multi-layer MXene to LiCl is 10:1, and the MXene dispersion yield is 10.3%.

[0049] Example 4

[0050] The difference between this example and Example 1 is that the ultrasonic temperature is 60 °C, and the MXene dispersion yield is 80.3%.

[0051] Example 5

[0052] The difference between this example and Example 1 is that the ultrasonic temperature is 80 °C, and the MXene dispersion yield is 93.3%.

[0053] Example 6

[0054] The difference between this example and Example 1 is that the ultrasonic time is 30 minutes, and the MXene dispersion yield is 81.5%

[0055] Example 7

[0056] The difference between this example and Example 1 is that the stirring temperature in step (4) is 25 °C, and the MXene dispersion yield is 95.0%

[0057] Example 8

[0058] The difference between this example and Example 1 is that in step (6), it is dispersed in 150 mL of water, and the MXene dispersion yield is 78%

[0059] Example 9

[0060] The difference between this example and Example 1 is that the ultrasonic power in step (6) is 400 W, and the MXene dispersion yield is 90%.

[0061] Example 10

[0062] The difference between this example and Example 1 is that: the stirring time in step (2) is 36 h, and the yield of the MXene dispersion is 92.0%

[0063] Example 11

[0064] The difference between this example and Example 1 is that: the mixed solution added in step (2) is 200 mL, and the Ti 3 AlC 2 MAX phase powder is 10 g, and the yield of the MXene dispersion is 93% - 95%.

[0065] Example 12

[0066] The difference between this example and Example 1 is that: the mixed solution added in step (2) is 200 mL, and the Ti 3 AlC 2 MAX phase powder is 100 g, and the yield of the MXene dispersion is 90% - 93%. This example shows that this technology can still maintain a high MXene yield under an enlarged production system.

[0067] Example 13

[0068] Take the MXene monolayer dispersions prepared in Examples 1 and 2, and assemble the monolayer MXene dispersions prepared by the two processes into a self - supported MXene film through vacuum - assisted suction filtration.

[0069] The tensile strength of the film obtained from the dispersion of Example 1 is 49 MPa, and the tensile strength of the film obtained from the dispersion of Example 2 is 51 MPa, which are almost the same; the conductivity of the 30 - mg films obtained from the dispersions of Examples 1 and 2 is about 6500 S / cm ( Figure 6 ), and they are also very close in terms of electromagnetic shielding efficiency ( Figure 7 ). This example shows that the heating - ultrasonic technology has a high yield of monolayer MXene, and when applied to MXene materials, it can effectively maintain various excellent physical and chemical properties of MXene itself.

[0070] Example 14

[0071] Take the MXene monolayer dispersion in Example 1, centrifuge it at a speed of 10,000 revolutions per minute for 30 minutes, and collect the precipitate. Heat and stir the obtained precipitate at 60 °C, and high-concentration MXene ink with a solid content of 22-26 wt% can be obtained by adding different volumes of deionized water. Coat the MXene ink on the silk screen, use a squeegee to evenly press the ink through the mesh holes, and transfer the pattern to different substrates (PDMS, Paper, Glass, and PET) that have been pretreated with plasma. The required printed pattern is formed on the substrate. Place the printed pattern on a hot plate at 80 °C, and the temperature on the surface of the pattern is only 35 °C. Even when the heating temperature reaches 120 °C, the temperature on the surface of the pattern remains in the range of 46 °C - 47 °C during the continuous heating time of 10 min. This example shows that the prepared MXene can be applied to printing materials.

[0072] Example 15

[0073] Take the MXene monolayer dispersion in Example 1, centrifuge it at a speed of 10,000 revolutions per minute for 30 minutes, and collect the precipitate. Heat and stir the obtained precipitate at 60 °C, and MXene ink with a concentration of 20 mg / mL can be obtained by adding different volumes of deionized water. Stir and mix it with cotton fabric for 2 minutes, and dry it to obtain an MXene-based fabric with a loading of 19.48 wt%. At a voltage of 1.5 V, the surface temperature of the fabric reaches 34.8 °C, and at a voltage of 5 V, the surface temperature of the fabric reaches 160.6 °C. This example shows that the prepared MXene can be applied to temperature control materials.

[0074] Although the above examples have described the present invention in detail, they are only a part of the embodiments of the present invention, not all embodiments. People can also obtain other embodiments according to these embodiments without creative efforts, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing a high-yield single-layer MXene dispersion, characterized in that: The following steps are involved: (1) mixing 12 wt % HF and 38 wt % HCl solution in a volume ratio of 1:1.5-2.0 to obtain a mixed solution; (2) adding Ti3AlC2 MAX phase powder to the mixed solution of step (1) to a concentration of 40 to 60 mg / mL, and stirring at 25 to 35° C. for 18 to 36 hours; (3) centrifuging the resulting mixture at a rotation speed of 3500 rpm for 5 minutes, and repeating the operation until the precipitate is washed to pH = 6 to obtain multilayer MXene; (4) dispersing the multilayer MXene obtained in step (3) in water, adding LiCl in a mass ratio of 1:1 to 1.2 between the multilayer MXene and LiCl; stirring at 25 to 35° C. for 15 to 18 hours to perform Li + Ion intercalation; (5) centrifuging the mixture obtained in step (4) at a speed of 3000 rpm for 5 minutes, retaining the precipitate and redispersing it with water, repeating the operation 3 to 5 times to obtain the intercalated multilayer MXene; (6) adding the intercalated multilayer MXene obtained in step (5) to an ethanol solution for dispersion, placing it in a bath ultrasonic machine at a temperature of 60 to 80° C. and an ultrasonic treatment of 240 to 400 W for 3 to 5 minutes, and introducing an argon gas flow during the entire stripping process; (7) The mixed solution obtained in step (6) was centrifuged at 3500 rpm for 30 min, and the supernatant was collected to obtain a monolayer MXene dispersion.

2. The method according to claim 1, characterized in that The ethanol concentration in step (6) is 1 to 3 wt%.

3. The method according to claim 1, characterized in that In step (6), the concentration of the monolayer MXene dispersion is controlled within the range of 10 to 25 mg / mL.

4. The method according to claim 1, characterized in that In the single-layer MXene dispersion of step (6), 80% of the MXene has a size of 1.0 to 3.0 μm, and the MXene conductivity and electromagnetic shielding properties are unchanged.

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