Preparation method of micron-sized large-size monolithic layer MXene

Abstract

The invention provides a preparation method of micron-sized large-size monolithic MXene, and belongs to the field of preparation of a two-dimensional layered material MXene. An MAX phase is used as a precursor, lithium fluoride, lithium chloride and concentrated hydrochloric acid are used as etching agents, etching is performed in an HF etching solution generated in situ by LiF / HCl, excessive lithium ions provided by lithium chloride are used for assisting in stripping of multi-lamellar MXene, and the MXene is prepared. And finally, the micron-sized large-size monolithic layer MXene is prepared. The monolithic MXene prepared by the method has a micron-sized large transverse size, and has more surface active groups compared with common MXene, so that the monolithic MXene has a wide application prospect in the field of modified separation.

Description

Technical Field

[0001] The present invention relates to the technical field of MXene preparation, and in particular to a method for preparing a micron-sized single-layer MXene. Background Art

[0002] MXene is a class of metallic carbon or nitrides that are graphene-like materials with a structure similar to graphene, belonging to the same two-dimensional crystalline material. It is prepared by reacting hydrofluoric acid or other chemical reagents with the raw material MAX under certain conditions. In 2011, Professor Yury of Drexel University in the United States, inspired by experiments showing that 3C cubic silicon carbide (3C-SiC) could be immersed in a mixture of hydrofluoric acid and nitric acid to produce layered silicon carbide nanosheets with a thickness of 5-10 nm, used hydrofluoric acid to selectively etch Ti3AlC2 (MAX) powder, successfully preparing Ti3C2 two-dimensional nanomaterials (MXene) with a layered structure. The resulting materials were then ultrasonicated and centrifuged to obtain few-layer or single-layer MXene nanosheets. MXene nanomaterials have numerous surface groups and attachment sites, allowing for the customization of the type and number of surface groups. Two-dimensional MXene films exhibit regular nanoscale interlayer channels. Consequently, MXene has garnered widespread attention in fields such as capacitors, lithium batteries, and membrane separations. MXene, a two-dimensional material, has become a hot topic in the membrane separation field due to its significant research value, as its nano-interlayer channels and numerous surface-modifiable functional groups demonstrate significant research value. However, traditional etching methods, such as hydrofluoric acid etching and in-situ etching, require prolonged ultrasonic treatment to exfoliate the resulting single-layer MXene nanosheets. This results in the lateral dimensions of the MXene sheets becoming increasingly smaller under ultrasonic treatment. Furthermore, small-sized MXenes exhibit poor selectivity in membrane separations, a limited number of surface active groups, numerous non-selective surface defects, and short material transfer pathways, all of which severely impact MXene's application in membrane separations. This method adds lithium chloride to the traditional in-situ etching method to assist in the exfoliation of multi-layer MXene. The addition of lithium chloride can significantly increase the concentration of lithium ions in the etching system. Excess lithium ions can be inserted into the interlayer domain of MXene through electrochemical drive, which can effectively weaken the interaction force between MXene layers and create a favorable interlayer environment for the subsequent exfoliation of single-layer MXene. In addition, the insertion of excess lithium ions into the interlayer channels of MXene will form a double-layer structure, which inhibits the restacking of layers through the electrostatic repulsion between lithium ions. Summary of the Invention

[0003] In response to the problem in the prior art that the lateral size of MXene nanosheets obtained by cyclic ultrasonic centrifugal exfoliation is too small, the present invention aims to provide a method for preparing large-scale monolayer MXene on the micron scale. This method uses concentrated hydrochloric acid and lithium fluoride to in-situ etch the large-particle MAX phase powder material after screening, and then cooperates with lithium chloride intercalation to assist in exfoliation. A short-term cyclic ultrasonic centrifugation method is used to produce monolayer MXene with large lateral size on the micron scale.

[0004] To achieve the above object, the technical solutions adopted by the present invention are as follows:

[0005] A method for preparing a micron-sized single-layer MXene comprises the following steps:

[0006] (1) MAX phase screening: Based on the principle of Stokes sedimentation dynamics, the hydraulic classification method is used to selectively separate the particle size of the MAX phase powder material. The MAX phase powder material is dispersed in a deionized water medium according to a certain solid-liquid ratio. The MAX phase powder material is fully dispersed in the deionized water medium by magnetic uniform stirring to eliminate the particle agglomeration effect. Subsequently, under the action of the gravity field, the terminal sedimentation velocity difference of particles of different particle sizes is used to perform graded separation. The large-particle MAX phase powder material is preferentially sedimented and separated, and the unsettled small-particle MAX phase powder material is poured out and removed together with the deionized water. After multiple separations, the sediment is centrifuged to obtain a large-particle enriched phase. The final product is dried at a constant temperature in a vacuum drying oven to obtain a large-particle MAX phase powder material;

[0007] (2) MAX phase etching: Use hydrochloric acid, lithium fluoride, and lithium chloride to etch the MAX phase powder material to etch away the main group element Al in the MAX phase. The addition of lithium chloride can significantly increase the concentration of lithium ions in the etching system. Excess lithium ions can be inserted into the interlayer domain of MXene by electrochemical drive, which can effectively weaken the interaction force between MXene layers and create a favorable interlayer environment for the subsequent peeling of single-layer MXene. Excess lithium ions inserted into the interlayer channel of MXene will form a double-layer structure, which inhibits the restacking of the layers through the electrostatic repulsion between lithium ions. After the etching is completed, the etching solution is repeatedly centrifuged and washed until it is neutral and redispersed to obtain a MXene multi-layer solution;

[0008] (3) Cyclic ultrasonic centrifugation: The multi-layer MXene obtained in step (2) is treated alternately with an ultrasonic machine and a centrifuge. After cyclic ultrasonic centrifugation, the supernatant in the centrifuge tube is collected to obtain a large lateral size single-layer MXene.

[0009] Furthermore, in step (1), during the screening process of the MAX phase powder material, the MAX phase powder material is dispersed in deionized water at a solid-liquid ratio of 1:25 to 1:50 g / mL, the stirring rate of the magnetic stirring is greater than 400 rpm, the stirring time is controlled within 1-3 min, and the sedimentation rate in the screening container is controlled to be greater than 1.25 cm / min.

[0010] First, add the MAX phase powder material into a screening container filled with deionized water, place the screening container on a magnetic stirrer and stir evenly, then turn off the magnetic stirring and let it settle freely. Repeat the sedimentation and screening three times to obtain a precipitate. After the precipitate is vacuum dried, a large-particle MAX phase powder material with a size greater than 10 microns is obtained.

[0011] Furthermore, in step (2), the weight ratio of the MAX phase powder material and lithium fluoride is 1:1, the weight ratio of the MAX phase powder material to lithium chloride is less than or equal to 2:1, the concentration of concentrated hydrochloric acid is 12M, and the amount of hydrochloric acid used is 0.12 mol of hydrochloric acid for 1 g of MAX phase powder material.

[0012] Furthermore, during the etching process of step (2), lithium fluoride, lithium chloride and concentrated hydrochloric acid are sequentially added into a polytetrafluoroethylene bottle, placed in a magnetic stirring water bath and stirred evenly, and then the MAX phase powder material is slowly added in batches and stirred at 30-40° C. for 24-48 hours.

[0013] Furthermore, the repeated centrifugation and washing process in step (2) is as follows: first, the rotation speed is controlled at 452.8-676.4×g, the supernatant is removed after centrifugation, and deionized water is added and shaken sufficiently to redisperse the precipitate, and centrifuged again. This process is repeated 5-10 times to remove the by-products of the etching reaction and dilute the acid solution until the pH of the solution is neutral. Finally, the centrifuged mixture is dispersed again with deionized water to obtain a multi-layer MXene solution.

[0014] Furthermore, during the cyclic ultrasonic centrifugation in step (3), the multi-layer MXene solution is added to the ultrasonic machine and ultrasonic treatment is started. After the ultrasonic treatment, the multi-layer solution is taken out and placed in a centrifuge for centrifugal treatment. The supernatant obtained after centrifugation is collected, and the obtained precipitate is further dispersed by adding deionized water and the above steps are repeated to collect the supernatant to obtain a solution containing a large-sized single-layer MXene. The ultrasonic power is controlled at 120-160 W, the ultrasonic time is controlled at 5-10 min, the centrifugal force of the centrifuge is controlled at 50.3-89.4 x g, and the centrifugation time is controlled at 5-10 min.

[0015] The micron-scale large-size single-layer MXene prepared by the above method in the present invention has the characteristics of large lateral size and rich surface active sites.

[0016] Compared with the prior art, the design mechanism and beneficial effects of the present invention are as follows:

[0017] 1. This method uses wet in-situ etching, which is safer and more environmentally friendly than direct hydrofluoric acid etching. In addition, the MXene obtained by wet etching contains rich functional groups on its surface, providing abundant active sites for subsequent grafting of functional groups.

[0018] 2. During etching, an excess of lithium chloride is added to assist intercalation and exfoliation. The mass ratio of MAX phase powder material to lithium chloride is less than or equal to 2:1. The lithium ions in the added lithium chloride make the lithium ions in the etching solution excessive. The excess lithium ions can be inserted into the interlayer domain of MXene by electrochemical drive, which can effectively weaken the interaction force between MXene layers and create a favorable interlayer environment for the subsequent exfoliation of single-layer MXene. The insertion of excess lithium ions into the interlayer channel of MXene will form a double-layer structure, and the electrostatic repulsion between lithium ions will inhibit the restacking of the layers, greatly shortening the time required for ultrasonic exfoliation. After centrifugation at low power ultrasound, a single-layer MXene with a large lateral size of micrometer level with good performance is obtained.

[0019] 3. The preparation method of the present invention uses in-situ generated hydrofluoric acid etching, which is safer than direct use of hydrofluoric acid etching, simpler to operate, and has a short ultrasonic centrifugation time. The MXene produced has a large lateral size, which has the advantage of becoming the mainstream preparation method for single-layer MXene with large lateral size at the micron level. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a comparison chart of the particle size distribution of the MAX phase powder material before and after screening in Example 1;

[0021] Figure 2 TEM image of the multilayer MXene powder after assisted intercalation prepared in Example 1;

[0022] Figure 3 This is an AFM image of the micron-sized monolithic MXene prepared in Example 1;

[0023] Figure 4 The XRD patterns of micron-scale large lateral size single-layer MXene prepared with different lithium chloride addition amounts. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is described in detail below in conjunction with the embodiments. The specific embodiments described herein are intended to explain the present invention and are not intended to limit the present invention.

[0025] Example 1:

[0026] This embodiment provides a method for preparing a large-scale single-layer MXene at the micron level. The preparation process is as follows:

[0027] 1. Screening of large-particle MAX phase powder material: Weigh 10g of 200-mesh MAX phase Ti3AlC2 powder, disperse the MAX phase powder material in deionized water at a solid-liquid ratio of 1:25g / mL, control the deionized water height in the beaker at 15cm, place the beaker on a magnetic stirrer and stir at a rate of 500rpm for 1min, stop stirring and let the MAX phase powder settle freely for 12min, immediately pour out the suspension containing small particles in the beaker after sedimentation, repeat screening 3 times, and place the resulting precipitate in a vacuum oven at 70℃ and dry for 8h to obtain large-particle MAX phase powder material.

[0028] 2. Etching of Large-Particle MAX Phase Powder Material: Weigh 5g of LiCl powder and 5g of LiF powder into a polytetrafluoroethylene bottle and add 50mL of 12M concentrated hydrochloric acid to prepare an etching solution. Then weigh 5g of large-particle MAX phase powder. After the etching solution is evenly stirred, add the large-particle MAX phase powder in batches. Stir at 35°C for 36 hours to etch away the Al element to obtain the etched MAX phase. The resulting etched product is repeatedly centrifuged and washed 5-10 times until the pH reaches 7. The resulting precipitate is then redispersed in deionized water. Specifically, the repeated centrifugation and washing method is as follows: first, control the centrifugal force to 559xg for 5 minutes. After centrifugation, remove the supernatant, add deionized water and shake thoroughly to redisperse the precipitate. Centrifuge again at 559xg for 5 minutes. Repeat this washing process 5-10 times to remove etching reaction byproducts and dilute the acid solution until the final pH is neutral. The resulting precipitate is redispersed in deionized water.

[0029] 3. Multi-layer MXene exfoliation: The dispersed suspension is placed in an ultrasonic machine for ultrasonication with an ultrasonic power of 140 W and an ultrasonic time of 10 minutes. After the ultrasonication, it is transferred to a centrifuge for centrifugation with a centrifugal force of 68.5xg and a centrifugal time of 10 minutes. After centrifugation, the supernatant in the centrifuge tube is collected. This cycle of ultrasonic centrifugation is repeated 4 times, and the supernatant collected is the required single-layer MXene with a large lateral size of micrometers. After collection, the obtained MXene is sealed and refrigerated with inert gas.

[0030] Example 2:

[0031] This embodiment provides a method for preparing a large-scale single-layer MXene at the micron level. The preparation process is as follows:

[0032] 1. Screening of large-particle MAX phase powder material: Weigh 10g of 200-mesh MAX phase Ti3AlC2 powder, disperse the MAX phase powder material in deionized water at a solid-liquid ratio of 1:30g / mL, control the deionized water height in the beaker at 15cm, place the beaker on a magnetic stirrer and stir at 400rpm for 2min, stop stirring and let the MAX phase powder settle freely for 10min, immediately pour out the suspension containing small particles in the beaker after sedimentation, repeat screening 3 times, and place the resulting precipitate in a vacuum oven at 100℃ and dry for 6h to obtain large-particle MAX phase powder material.

[0033] 2. Etching of large-particle MAX phase powder materials: Weigh 3g of LiCl powder and 5g of LiF powder into a polytetrafluoroethylene bottle and add 50mL of 12M concentrated hydrochloric acid to prepare an etching solution. Then weigh 5g of large-particle MAX phase powder. After the etching solution is stirred evenly, add the large-particle MAX phase powder in batches. Stir at 30°C for 48h to etch away the Al element to obtain the etched MAX phase.

[0034] The obtained etched product is repeatedly centrifuged and washed 5-10 times until the pH reaches 7, and the resulting precipitate is redispersed in deionized water. Specifically, the repeated centrifugation and washing method is as follows: first, the centrifugal force is controlled at 452.8xg for 8 minutes, the supernatant is removed after centrifugation, and deionized water is added and shaken thoroughly to redisperse the precipitate, and the product is centrifuged again at 452.8xg for 8 minutes. This washing process is repeated 5-10 times to remove etching reaction byproducts and dilute the acid solution until the final pH value is neutral, and the resulting precipitate is redispersed in deionized water.

[0035] 3. Multi-layer MXene exfoliation: The dispersed suspension is placed in an ultrasonic machine for ultrasonication with an ultrasonic power of 120 W and an ultrasonic time of 8 minutes. After the ultrasonication, the suspension is transferred to a centrifuge for centrifugation with a centrifugal force of 50.3xg and a centrifugal time of 8 minutes. After centrifugation, the supernatant in the centrifuge tube is collected. This cycle of ultrasonic centrifugation is repeated three times, and the supernatant collected is the required single-layer MXene with a large lateral size in the micron range. After collection, the obtained MXene is sealed and refrigerated with an inert gas.

[0036] Example 3:

[0037] This embodiment provides a method for preparing a large-scale single-layer MXene at the micron level. The preparation process is as follows:

[0038] 1. Screening of large-particle MAX phase powder material: Weigh 10g of 200-mesh MAX phase Ti3AlC2 powder, disperse the MAX phase powder material in deionized water at a solid-liquid ratio of 1:50g / mL, control the deionized water height in the beaker at 15cm, place the beaker on a magnetic stirrer and stir at a rate of 400rpm for 3min, stop stirring and let the MAX phase powder settle freely for 12min, immediately pour out the suspension containing small particles in the beaker after sedimentation, repeat screening 3 times, place the resulting precipitate in a vacuum oven at 120℃ and dry for 6h to obtain large-particle MAX phase powder material.

[0039] 2. Etching of large-particle MAX phase powder materials: Weigh 7g of LiCl powder and 5g of LiF powder into a polytetrafluoroethylene bottle and add 50ml of 12M concentrated hydrochloric acid to prepare an etching solution. Then weigh 5g of large-particle MAX phase powder. After the etching solution is evenly stirred, add the large-particle MAX phase powder in batches. Stir at 40°C for 24h to etch away the Al element to obtain the etched MAX phase.

[0040] The obtained etched product is repeatedly centrifuged and washed 5-10 times until the pH reaches 7, and the resulting precipitate is redispersed in deionized water. Specifically, the repeated centrifugation and washing method is as follows: first, the centrifugal force is controlled at 676.4xg for 10 minutes, the supernatant is removed after centrifugation, deionized water is added and shaken thoroughly to redisperse the precipitate, and the product is centrifuged again at 676.4xg for 10 minutes. This washing process is repeated 5-10 times to remove etching reaction byproducts and dilute the acid solution until the final pH value is neutral, and the resulting precipitate is redispersed in deionized water.

[0041] 3. Multi-layer MXene exfoliation: The dispersed suspension is placed in an ultrasonic machine for ultrasonication with an ultrasonic power of 160 W and an ultrasonic time of 5 minutes. After the ultrasonication, it is transferred to a centrifuge for centrifugation with a centrifugal force of 89.4xg and a centrifugal time of 5 minutes. After centrifugation, the supernatant in the centrifuge tube is collected. This cycle of ultrasonic centrifugation is repeated 5 times, and the supernatant collected is the required single-layer MXene with a large lateral size of micrometers. After collection, the obtained MXene is sealed and refrigerated with inert gas.

Claims

1. A method for preparing a large-scale monolithic MXene in the micrometer scale, characterized by: The method comprises the following steps: (1) MAX phase screening: MAX phase powder material was dispersed in deionized water at a solid-liquid ratio of 1:25 to 1:50 g / mL, magnetically stirred and allowed to settle, particles with a sedimentation rate greater than 1.25 cm / min were separated, and large-particle MAX phase powder was obtained after centrifugal drying; (2) MAX phase etching: The MAX phase powder obtained in step (1) is mixed with hydrochloric acid, lithium fluoride and lithium chloride, wherein the mass ratio of lithium chloride to MAX phase is ≤2:1, and centrifuged and washed until neutral to obtain a MXene multi-layer solution; (3) Circular Ultrasonic Centrifugation: The solution obtained in step (2) was ultrasonically treated for 5-10 min, followed by centrifugation at 50.3-89.4 x g for 5-10 min, and the supernatant was collected. Repeat the above steps 3-5 times to collect the supernatant to obtain a monolayer MXene solution.

2. The method for preparing a micron-sized monolithic MXene according to claim 1, characterized in that MAX phase is Ti n+1 AlC n , n is 1-3.

3. The method for preparing a large-scale monolithic MXene in the micrometer scale according to claim 1, characterized in that: During the screening process of step (1), the mesh size of the MAX phase powder material is less than or equal to 200 meshes. A smaller mesh size ensures that the MAX phase powder material has MAX phase particles with larger particle sizes. During the screening process, the solid-liquid ratio of the MAX phase material to deionized water is controlled at 1:25-1:50 g / mL. The MAX phase powder material is stirred evenly in deionized water and then screened. The stirring rate is greater than 400 rpm, and the stirring time is controlled at 1-3 minutes. During the screening process, the sedimentation rate in the screening container is controlled to be greater than 1.25 cm / min. After screening, MAX phase powder material with a particle size of less than 10 microns can be removed.

4. The method for preparing a large-scale monolithic MXene in the micrometer scale according to claim 1, characterized in that: During the etching process of step (2), the mass ratio of the MAX phase powder material to lithium chloride is less than or equal to 2:

1.

5. The method for preparing a large-scale monolithic MXene in the micrometer scale according to claim 1, characterized in that: The cyclic ultrasonic centrifugation process in step (3) is as follows: the multi-layer MXene solution prepared by etching in step (2) is ultrasonically treated for 5-10 minutes. After the ultrasonic treatment, the solution is removed and placed in a centrifuge for centrifugation, the centrifugal force of the centrifuge is controlled at 50.3-89.4xg, the centrifugation time is 5-10 minutes, and the supernatant obtained after centrifugation is collected. The lower precipitate is further dispersed by adding deionized water and the above steps are repeated 3-5 times. The collected supernatant is the prepared micron-sized single-layer MXene solution.

6. A micron-sized monolithic MXene prepared by the method of claim 1, characterized in that: The MXene nanosheets have a lateral size greater than or equal to 5 μm and are characterized by rich active sites.

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