A method for improving conductivity and oxidation resistance of MXene

Abstract

The application discloses a method for improving the conductivity and oxidation resistance of MXene, and relates to the technical field of MXene materials, and comprises the following steps: intercalating MXene into an organic macromolecule intercalation solution, and performing washing and ultrasonic treatment to obtain a single-layer MXene nanosheet solution; adding the single-layer MXene nanosheet solution into an alkali metal salt solution, performing flocculation and spontaneous ion exchange, and then removing liquid by centrifugation to obtain MXene flocculates; and finally, adding the MXene flocculates into an alkali metal salt solution for storage, or washing the MXene flocculates with deionized water until the MXene flocculates are in a colloidal state and are not flocculated for use. The method can remove the organic macromolecules combined on the surface of the MXene through ion exchange, can effectively improve the conductivity of the MXene material, is beneficial to the storage of the MXene material, and has great application value.

Description

Technical Field

[0001] This invention relates to the field of MXene material technology, and more specifically to a method for improving the electrical conductivity and oxidation resistance of MXene. Background Technology

[0002] MXenes are a general term for a large class of layered two-dimensional transition metal carbon and / or nitrides, with the chemical formula M. n+1 X n T x In this model, M represents a transition metal element, such as Ti, V, Nb, Mo, Zr, Hf, Ta, etc., X represents C and / or N, and T represents a terminal group such as -F, -O, -OH, etc. MXenes are typically obtained by selectively etching the atom layer in the precursor MAX phase. Their unique structure and composition endow MXenes with excellent hydrophilicity, metallic conductivity, outstanding flexibility, ultra-high electrochemical specific capacity, and ease of processing. Therefore, MXenes are widely used in many fields such as electrochemical energy storage, smart sensing, electromagnetic shielding, biomedicine, and optics. For example, in the sensor field, when used as a flexible piezoresistive sensor material, MXenes exhibit ultra-high sensitivity and excellent wearable flexibility.

[0003] However, existing technologies have several problems. First, most MXene etching methods still rely on direct HF etching, in-situ HF formation, or difluorine-based etchants. However, when further processing MXene nanosheet colloidal solutions using these methods, external intercalation agents are needed to obtain high-concentration solutions (without intercalation agents, the monolayer yield after ultrasonic treatment is less than 5%). Furthermore, for MXene etched with HF acid or HF-like acids, the highest yield is often achieved using macromolecular intercalation such as tetraalkylammonium hydroxide, but current research has neglected the impact of intercalated macromolecules on MXene performance. During organic macromolecular intercalation, the macromolecules combine with MXene nanosheets through electrostatic interactions, making them difficult to remove even after multiple washes and centrifugation. Moreover, due to the strong interaction between MXene and macromolecules, this method wastes a significant amount of MXene colloid even after centrifugation and washing. Additionally, research indicates that this macromolecular intercalation leads to large interlayer spacing, and water, oxygen, and macromolecules all promote MXene degradation. Therefore, existing MXene colloids often exhibit large interlayer spacing, resulting in lower conductivity (<500 S / cm) and faster oxidation (<10 days). Thus, it is necessary to find a treatment method to remove MXene intercalated macromolecules and maintain them in water without oxidation for a long period, thereby achieving higher film conductivity and longer shelf life. Summary of the Invention

[0004] To address the aforementioned technical problems, the present invention aims to provide a method for improving the conductivity and antioxidant properties of MXene. This method removes organic macromolecules bound to the surface of MXene through ion exchange, which can effectively improve the conductivity of MXene materials and facilitate their preservation, thus possessing significant application value.

[0005] The technical solution of this invention to solve the above-mentioned technical problems is as follows: A method for improving the conductivity and antioxidant properties of MXene is provided, comprising the following steps:

[0006] (1) Add MXene to the organic macromolecular intercalation solution, heat and stir, then centrifuge to discard the supernatant and wash with water, then add water and sonicate, and finally centrifuge to collect the supernatant solution to obtain a single-layer MXene nanosheet solution.

[0007] (2) Add the monolayer MXene nanosheet solution obtained in step (1) to the alkali metal salt solution, heat and stir, wait for automatic flocculation, then let it stand to spontaneously carry out ion exchange, and then centrifuge to remove the liquid to obtain MXene flocs.

[0008] (3) Add the MXene flocculants obtained in step (2) into an alkali metal salt solution for storage;

[0009] Alternatively, the MXene flocculants obtained in step (2) can be washed with deionized water until the MXene no longer flocculates and remains in a colloidal state for use.

[0010] The beneficial effects of the technical solution of this invention are:

[0011] (1) The method of this invention first uses organic macromolecules to intercalate MXene, with a stirring time of 3-12 hours. The longer the stirring time, the higher the monolayer yield, which can reach up to 90%. After this, washing is performed 1-3 times to remove most of the organic macromolecules, and the supernatant turns black. If washing continues at this point, the monolayer MXene nanosheets will be lost. Washing is stopped, and the supernatant is collected by ultrasonic treatment to obtain monolayer MXene nanosheets. Then, an alkali metal salt solution is added. MXene will rapidly bind with the alkali metal salt. Due to the negative charge of MXene and the positive charge of the cation, it will completely precipitate within 5 minutes. In addition, the steric hindrance effect of the macromolecules also makes it easier for alkali metal ions to bind with MXene. Furthermore, the removal of organic macromolecules is achieved by replacing the macromolecules through ion exchange.

[0012] (2) This method can significantly improve the oxidation resistance of MXene materials and extend their shelf life. When inorganic salts are added to the MXene suspension, their hydration not only reduces free water molecules but also forms a protective barrier on the MXene surface by creating a hydrated ion layer. This barrier effectively isolates oxygen molecules from direct contact with MXene, thereby significantly inhibiting the oxidative attack of oxygen molecules on MXene. In addition, the presence of inorganic salts may also change the ionic strength of the solution, further affecting the solubility and diffusion rate of oxygen molecules, providing additional protection for MXene.

[0013] Furthermore, MXene is for Ti3C2T x V4C3T x Ti3CN, Mo2C, V2CT x and Nb2CT x At least one of the following. Other types of MXene materials may also be used.

[0014] Furthermore, in step (1), the organic macromolecule intercalation solution is at least one of tetramethylammonium hydroxide solution (TMAOH), tetraethylammonium hydroxide solution (TEAOH), and tetrabutylammonium hydroxide solution (TMBOH); the concentration of the organic macromolecule intercalation solution is 1-3 mol / L.

[0015] Furthermore, in step (1), the mass-to-volume ratio of MXene to the organic macromolecular intercalation solution is 1-3 g: 30-50 mL.

[0016] Furthermore, in step (1), the mixture is heated and stirred at 40-60℃ for 3-12 hours.

[0017] Furthermore, in step (2), the ultrasonic treatment lasts for 20-40 minutes.

[0018] Furthermore, in step (2), the alkali metal salt solution is at least one of sodium chloride solution, lithium chloride solution and potassium chloride solution; the concentration of the alkali metal salt solution is 1-5 mol / L.

[0019] Furthermore, in step (2), the volume ratio of the monolayer few-layer MXene nanosheet solution to the alkali metal salt solution is 0.5-1.5:5.

[0020] Furthermore, in step (2), the mixture is heated and stirred at 40-60℃ for 20-40 minutes.

[0021] Furthermore, in step (2), the sample is left to stand for 3-12 hours.

[0022] Furthermore, the centrifugation speed is 3000-4000 r / min.

[0023] The present invention has the following beneficial effects:

[0024] 1. The method of the present invention can effectively remove intercalating agent organic macromolecules bound to the surface of MXene through ion exchange, thereby increasing the conductivity of MXene by at least 10 times.

[0025] 2. The method of the present invention is under mild conditions, which can avoid the oxidation of MXene. The water and water effects of inorganic salts can also reduce the activity and coordination of dissolved oxygen in the aqueous solution.

[0026] 3. Furthermore, the MXene treated by the method of this invention can be stored for a long time without oxidation. When needed, it can be redispersed into MXene colloid by washing with deionized water multiple times for continued use. This method has advantages such as low cost, mild reaction conditions, and long shelf life. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the implementation process in Example 1;

[0028] Figure 2 This is a comparison image of flocculation before and after in Example 1;

[0029] Figure 3 This is a screenshot showing the saved MXene result after processing in Example 2.

[0030] Figure 4 XRD patterns before and after MXene removal of organic macromolecules;

[0031] Figure 5 A comparison of conductivity test results before and after MXene removal of organic macromolecules. Detailed Implementation

[0032] The principles and features of this invention are described below. The examples given are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer should be followed. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0033] Example 1

[0034] A method for improving the conductivity and antioxidant properties of MXene, the process is as follows: Figure 1 As shown, it includes the following steps:

[0035] (1) Add 2g of MXene(Ti3C2T) xAdd 40 mL of 3 mol / L tetramethylammonium hydroxide solution (TMAOH), heat and stir at 60 °C for 12 h, then centrifuge at 3500 r / min to discard the supernatant and wash with water. Add water again and sonicate for 30 min. Finally, centrifuge at 3500 r / min to collect the supernatant solution, obtaining a monolayer few-layer MXene nanosheet solution (TMAOH-Ti3C2T). x );

[0036] (2) Add 20 mL of the monolayer MXene nanosheet solution obtained in step (1) to 100 mL of 5 mol / L lithium chloride solution, heat and stir at 60 °C for 30 min, wait for automatic flocculation, then let stand for 12 h to spontaneously carry out ion exchange, and then centrifuge at 3500 r / min to remove the liquid to obtain MXene flocculents (before and after flocculation, as shown in the figure). Figure 2 (as shown);

[0037] (3) Wash the MXene flocs obtained in step (2) with deionized water until the MXene no longer flocculates and remains in a colloidal state for use.

[0038] Example 2

[0039] A method for improving the conductivity and antioxidant properties of MXene includes the following steps:

[0040] (1) Add 2g of MXene (V4C3T) x Add 40 mL of 2 mol / L tetramethylammonium hydroxide solution (TMAOH), heat and stir at 50 °C for 6 h, then centrifuge to discard the supernatant and wash with water, add water again and sonicate for 30 min, finally centrifuge to collect the supernatant solution to obtain a single-layer MXene nanosheet solution.

[0041] (2) Add 20 mL of the monolayer MXene nanosheet solution obtained in step (1) to 100 mL of 3 mol / L lithium chloride solution, heat and stir at 50 °C for 30 min, wait for automatic flocculation, then let stand for 6 h to spontaneously carry out ion exchange, and then centrifuge to remove the liquid to obtain MXene flocs.

[0042] (3) Add the MXene flocculants obtained in step (2) into an alkali metal salt solution for storage.

[0043] Example 2: After MXene was processed and stored for two months, as shown... Figure 3 As shown, it will not degrade or turn white.

[0044] Example 3

[0045] A method for improving the conductivity and antioxidant properties of MXene includes the following steps:

[0046] (1) Add 1g MXene (Ti3CN) to 50mL of 1mol / L tetraethylammonium hydroxide solution (TEAOH), heat and stir at 40℃ for 12h, then centrifuge to discard the supernatant and wash with water, add water and sonicate for 40min, and finally centrifuge to collect the supernatant solution to obtain a single-layer MXene nanosheet solution.

[0047] (2) Add 10 mL of the monolayer MXene nanosheet solution obtained in step (1) to 100 mL of 1 mol / L sodium chloride solution, heat and stir at 40 °C for 40 min, wait for automatic flocculation, then let stand for 3 h to spontaneously carry out ion exchange, and then centrifuge to remove the liquid to obtain MXene flocs.

[0048] (3) Wash the MXene flocs obtained in step (2) with deionized water until the MXene no longer flocculates and remains in a colloidal state for use.

[0049] Example 4

[0050] A method for improving the conductivity and antioxidant properties of MXene includes the following steps:

[0051] (1) Add 3g MXene (V2CT) x Add 30 mL of 3 mol / L tetrabutylammonium hydroxide solution (TMBOH), heat and stir at 60 °C for 3 h, then centrifuge to discard the supernatant and wash with water, add water again and sonicate for 20 min, finally centrifuge to collect the supernatant solution to obtain a single-layer MXene nanosheet solution.

[0052] (2) Add 30 mL of the monolayer MXene nanosheet solution obtained in step (1) to 100 mL of 5 mol / L potassium chloride solution, heat and stir at 60 °C for 20 min, wait for automatic flocculation, then let stand for 12 h to spontaneously carry out ion exchange, and then centrifuge to remove the liquid to obtain MXene flocs.

[0053] (3) Wash the MXene flocs obtained in step (2) with deionized water until the MXene no longer flocculates and remains in a colloidal state for use.

[0054] Experimental Example 1

[0055] The MXene solution (TMAOH-Ti3C2T) containing organic macromolecules from Example 1 was respectively... x ) and ion-exchanged MXene (LiCl-Ti3C2T) x The coating is applied as an MXene film.

[0056] (1) XRD detection results are as follows Figure 4As shown in the XRD pattern, the interplanar spacing decreased from 1.457 nm to 1.246 nm after ion exchange. This indicates that the macromolecules were replaced and replaced by smaller alkali metal cations intercalated between the MXene sheets.

[0057] (2) In addition, the conductivity of MXene was tested using a four-probe method, and the results are as follows: Figure 5 As shown, the conductivity increased from 200 S / cm to over 3000 S / cm after ion exchange.

[0058] Experimental Example 2

[0059] Other methods were used to test the removal effect of intercalating agents on organic macromolecules.

[0060] (1) After intercalation of organic macromolecules, solvents such as isopropanol / n-hexane were added for displacement washing. 30 mL of organic solvent was added to every 10 mL of MXene solution containing organic macromolecules. After shaking for a few minutes, it was found that due to the polar functional groups on the MXene surface, it could not dissolve well in the organic solvent, while organic molecules could dissolve in the organic solvent. Therefore, after centrifugation at 3500 r / min for 1 min and multiple washings, MXene with most of the organic solvent removed was finally obtained. However, after filtration and membrane formation, the measured conductivity was less than 800 S / cm. This indicates that although removing most of the organic molecules increased the conductivity by 4 times from 200 S / cm, it was still significantly lower than that of ion exchange. This is because solution displacement only removes macromolecules in the solution, while macromolecules bound to MXene by electrostatic forces cannot be removed. Furthermore, it was subsequently found that the MXene began to degrade in water within 20 days. Therefore, this method cannot remove macromolecules bound to the MXene surface.

[0061] (2) The second method is high-temperature degradation of organic molecules. Experiments have shown that MXene intercalated with tetramethylammonium hydroxide can completely remove organic molecules at 400℃. However, this method has a fatal flaw: both the aqueous solvent and macromolecules are removed at 400℃, resulting in the direct formation of MXene films. Due to the strong interactions between monolayers stacked together, MXene films cannot be redispersed in aqueous solutions to form colloids, and therefore cannot be processed like colloidal MXene. Furthermore, MXene is easily oxidized by water, oxygen, and high temperatures; this method operates at temperatures above 400℃, and the MXene obtained using this method is also oxidized.

[0062] In summary, washing with other solvents is difficult to completely remove the organic macromolecules bound to the surface of MXene, and MXene after high-temperature degradation is difficult to process and use, and is prone to oxidation. However, the method of the present invention can effectively remove organic macromolecules through ion exchange, which not only greatly improves the electrical conductivity of MXene, but also facilitates the preservation of MXene materials.

[0063] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for improving the conductivity and antioxidant properties of MXene, characterized in that, Includes the following steps: (1) Add MXene to the organic macromolecular intercalation solution, heat and stir, then centrifuge to discard the supernatant and wash with water, add water and sonicate, and finally centrifuge to collect the supernatant solution to obtain a single-layer MXene nanosheet solution; the organic macromolecular intercalation solution is at least one of tetramethylammonium hydroxide solution, tetraethylammonium hydroxide solution and tetrabutylammonium hydroxide solution; (2) Add the monolayer MXene nanosheet solution obtained in step (1) to the alkali metal salt solution, heat and stir, wait for automatic flocculation, then let it stand to spontaneously carry out ion exchange, and then centrifuge to remove the liquid to obtain MXene flocs; the alkali metal salt solution is at least one of sodium chloride solution, lithium chloride solution and potassium chloride solution; the concentration of the alkali metal salt solution is 1-5 mol / L; (3) Wash the MXene flocs obtained in step (2) with deionized water until the MXene no longer flocculates and remains in a colloidal state for use.

2. The method for improving the conductivity and antioxidant properties of MXene as described in claim 1, characterized in that, In step (1), the concentration of the organic macromolecule intercalation solution is 1-3 mol / L.

3. The method for improving the conductivity and antioxidant properties of MXene as described in claim 1, characterized in that, In step (1), the mass-to-volume ratio of MXene to the organic macromolecular intercalation solution is 1-3 g: 30-50 mL.

4. The method for improving the conductivity and antioxidant properties of MXene as described in claim 1, characterized in that, In step (1), heat and stir at 40-60℃ for 3-12 hours.

5. The method for improving the conductivity and antioxidant properties of MXene as described in claim 1, characterized in that, In step (2), the ultrasound treatment lasts for 20-40 minutes.

6. The method for improving the conductivity and antioxidant properties of MXene as described in claim 1, characterized in that, In step (2), the volume ratio of the monolayer few-layer MXene nanosheet solution to the alkali metal salt solution is 0.5-1.5:

5.

7. The method for improving the conductivity and antioxidant properties of MXene as described in claim 1, characterized in that, In step (2), heat and stir at 40-60℃ for 20-40 min.

8. The method for improving the conductivity and antioxidant properties of MXene as described in claim 1, characterized in that, In step (2), let it stand for 3-12 hours.

9. The method for improving the conductivity and antioxidant properties of MXene as described in claim 1, characterized in that, The centrifugation speed is 3000-4000 r / min.

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