Method for synthesizing MXene material from low-temperature molten salt in solvent-free manner and application

Abstract

The invention relates to a low-temperature molten salt solvent-free synthesis method of an MXene material and application. The method comprises the following steps: firstly, synthesizing various precursor MAX phases through a high-temperature solid-phase method; then, various MAX carbides are mixed with ammonium fluoride and a solid micromolecule intercalator, and various MXene materials are successfully prepared through a solvent-free reaction in a reaction kettle. According to the invention, hydrofluoric acid (HF) with strong corrosivity and high toxicity commonly used in the traditional method is abandoned in the aspect of etching agent selection, and ammonium fluoride is adopted as the etching agent, so that not only is the danger of HF acid avoided, but also the green and environment-friendly properties of the reaction are ensured. Besides, compared with a traditional etching process depending on a liquid-phase strong acid system, the method has the advantages that efficient selective etching of the MAX phase A layer is achieved at the low temperature through the solid-state fused salt system, operation is easy and convenient, conditions are mild, process control is easy, no organic solvent is needed in the whole process, and clean solvent-free preparation is truly achieved.

Description

Technical Field

[0001] This invention relates to the field of nanomaterials, specifically to a method for low-temperature solvent-free synthesis of MXene materials and its application. Background Technology

[0002] MXenes are a class of two-dimensional layered materials composed of transition metal carbides, nitrides, or carbonitrides, with the general formula Mx. n+1 AX n T x , where M is a transition metal, X is C and / or N, and T is T. x It has surface groups such as -F, -O, and -OH. Due to its excellent conductivity, specific surface area, and tunable surface chemistry, MXene has broad application prospects in energy storage devices, electromagnetic shielding, catalysis, and sensing.

[0003] Existing methods for preparing MXene mainly include wet etching with hydrofluoric acid and Lewis acid molten salt etching. The former method uses solutions such as HF or LiF / HCl to etch the A layer of the MAX phase to obtain MXene. This method has high etching efficiency, but it suffers from problems such as strong corrosivity, significant safety hazards, severe environmental pollution, and difficulty in waste liquid treatment. The latter method uses Lewis acid molten salts (such as ZnCl2) to etch the A layer of the MAX phase in a molten state, but the reaction temperature is usually high (e.g., above 500℃), and some processes still require the addition of solvents or complex post-processing steps.

[0004] Therefore, developing a new method for preparing MXene that is solvent-free, low-temperature, simple, and environmentally friendly is of great practical significance and application value. Summary of the Invention

[0005] The purpose of this invention is to provide a method and application for the low-temperature molten salt solventless synthesis of MXene materials to achieve selective etching of the A layer in the MAX phase at a lower temperature, thereby obtaining sheet-expandable and easily peelable MXene two-dimensional materials.

[0006] To achieve the above objectives, this invention involves uniformly mixing ammonium fluoride, a solid small molecule intercalating agent, and the MAX phase without using HF or organic solvents, then transferring the mixture into a Teflon-lined stainless steel reactor and heating it in an oven. After the reaction is complete, MXene two-dimensional materials are obtained.

[0007] The specific preparation includes the following steps: 1) Mix and grind the MAX precursor powder to obtain a precursor mixture; 2) The precursor mixture is transferred to a tube furnace. Under inert gas protection, the tube furnace is heated from room temperature to 1350-1600℃ at a heating rate of 2-6℃ / min and kept at the temperature for 2-8 h to obtain MAX phase powder. 3) Take 0.25-1g of MAX phase powder, 1.5-6g of ammonium fluoride and 1.5-6g of solid small molecules, shake well to obtain a mixture; 4) Transfer the mixture to a Teflon-lined stainless steel reactor and etch it in an oven at 100-240℃ for 2-24 hours; 5) Wash the precipitate obtained by etching with anhydrous ethanol, then add ultrapure water for washing and vacuum drying to obtain MXene.

[0008] The MAX precursor powder in step 1) is an analytically pure raw material, which is composed of at least one of the transition metals Ti, Zr, Hf, V, Nb, Ta, Cr, and Mo, at least one of the group III and IV main elements Al, Sn, Ga, and Si, and carbon powder.

[0009] Step 1) involves wet grinding with ethanol and drying after grinding to obtain a precursor mixture.

[0010] In step 2), the inert gas used is argon gas with a pressure of 0.02-0.08 MPa and a flow rate of 20-100 cc / min.

[0011] The general formula of the MAX phase powder is M n+1 AX n M represents Ti, Zr, Hf, V, Nb, Ta, Cr, or Mo, A represents Group IIIA elements (Al and Ga) or Group IVA elements (Sn and Si), and X represents C and / or N.

[0012] The solid small molecules in step 3) are urea, oxalic acid, boric acid, thiourea, ethylene glycol, glycine, acetamide, propionamide, or pyrrole.

[0013] In step 5), the precipitate is washed 2-3 times with anhydrous ethanol.

[0014] The MXene material prepared by the above method is used as a hydrogen storage, catalyst support, lithium-ion battery electrode, and supercapacitor electrode material.

[0015] Compared with existing technologies, this invention does not use highly corrosive liquid acids such as HF during the etching process, nor does it require the preparation of organic solvent systems, significantly reducing operational safety risks and environmental burden. By forming a low-melting-point molten salt system with ammonium fluoride and solid small molecules, effective selective etching of the A layer in the MAX phase can be completed under relatively mild conditions, which is beneficial to maintaining the crystal structure integrity of MXene. Solid small molecules can achieve in-situ expansion and intercalation between layers in the molten salt, resulting in MXene with larger interlayer spacing and better exfoliation performance, making it easier to obtain high-concentration, stable two-dimensional sheet dispersions. At the same time, the overall process only includes solid mixing, furnace heating, and subsequent washing steps, without the need for complex equipment and cumbersome operations. The process is simple, the conditions are easy to control, and it is suitable for large-scale and continuous preparation. Attached Figure Description

[0016] Figure 1 The Ti3AlC2MAX and Ti3C2T prepared in Example 1 of this invention x XRD pattern of MXene; Figure 2 The Ti3AlC2MAX and Ti3C2T prepared in Example 1 of this invention x SEM image of MXene; Figure 3 The Ti3AlC2MAX and Ti3C2T prepared in Example 1 of this invention x XPS graph of MXene; Detailed Implementation The present invention will be further explained and described below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0017] The present invention will now be described in detail through specific embodiments.

[0018] Example 1: 1) Analytical grade titanium powder, aluminum powder and graphite powder with a particle size of 200 mesh were mixed in a molar ratio of 3:1:2 and wet-milled with ethanol, and then dried after milling to obtain the precursor mixture. 2) The precursor mixture was transferred to a tube furnace and heated from room temperature to 1350°C at a rate of 4°C / min under argon protection at a pressure of 0.05 MPa and a flow rate of 80 cc / min. The mixture was kept at the same temperature for 2 h to obtain Ti3AlC2MAX powder, which was then ground through a 40-micron sieve. 3) Shake 0.25 g Ti3AlC2MAX, 1.6 g ammonium fluoride and 1.6 g thiourea well; 4) Transfer the mixture to a Teflon-lined stainless steel reactor and etch it in an oven at 200°C for 2 hours; 5) The precipitate obtained from etching was washed by centrifugation with anhydrous ethanol at 3500 rpm for 3 min. The supernatant was discarded, and the washing process was repeated three times. After washing with ultrapure water, the precipitate was dried under vacuum at 60℃ to obtain Ti3C2T. x MXene.

[0019] The Ti3AlC2 and Ti3C2T prepared in Example 1 x For XRD analysis of MXene materials, see [link to documentation]. Figure 1 ,from Figure 1 As can be seen from the original Ti3AlC2, the Al layer was etched, and the (002) peak was significantly shifted, thus successfully obtaining MXene.

[0020] The Ti3AlC2 and Ti3C2T prepared in Example 1 x For SEM analysis of MXene materials, see [link to documentation]. Figure 2 ,from Figure 2 As can be seen, MXene exhibits a distinct accordion-like layered structure.

[0021] The Ti3AlC2 and Ti3C2T prepared in Example 1 x For XPS analysis of MXene materials, see [link to relevant documentation]. Figure 3 ,from Figure 3 As can be seen, the Al layer of MXene is etched, and there is no Al 2p signal.

[0022] Example 2: 1) Analytical grade molybdenum powder, titanium powder, aluminum powder and graphite powder, all with a particle size of 200 mesh, were mixed in a molar ratio of 2:1:1.3:2 and wet-milled with ethanol. After milling, the mixture was dried to obtain a precursor mixture. 2) The precursor mixture was transferred to a tube furnace and heated from room temperature to 1600℃ at a rate of 4℃ / min under argon protection at a pressure of 0.02 MPa and a flow rate of 20 cc / min. The mixture was kept at the same temperature for 4 h to obtain Mo2TiAlC2MAX powder, which was then ground through a 40-micron sieve. 3) Shake 0.25 g Mo2TiAlC2MAX, 1.6 g ammonium fluoride and 1.6 g thiourea well; 4) Transfer the mixture to a Teflon-lined stainless steel reactor and etch it in an oven at 200°C for 24 hours; 5) The precipitate obtained from etching was washed by centrifugation with anhydrous ethanol at 3500 rpm for 3 min. The supernatant was discarded, and the process was repeated three times by centrifugation. After washing with ultrapure water, the precipitate was dried under vacuum at 60℃ to obtain Mo2TiC2T. x MXene.

[0023] Example 3: 1) Analytical grade vanadium powder, aluminum powder and graphite powder with a particle size of 200 mesh were mixed in a molar ratio of 4:1:2.7 and wet-milled with ethanol. After milling, the mixture was dried to obtain the precursor mixture. 2) The precursor mixture was transferred to a tube furnace and heated from room temperature to 1600℃ at a rate of 4℃ / min under argon protection at a pressure of 0.08 MPa and a flow rate of 100 cc / min. The mixture was kept at the same temperature for 4 h to obtain V4AlC3MAX powder, which was then ground through a 40-micron sieve. 3) Shake 0.25 g V4AlC3MAX, 1.6 g ammonium fluoride and 1.6 g urea well; 4) Transfer the mixture to a Teflon-lined stainless steel reactor and etch it in an oven at 200°C for 24 hours; 5) The precipitate obtained from etching was washed by centrifugation with anhydrous ethanol at 3500 rpm for 3 min. The supernatant was discarded. The washing process was repeated twice by centrifugation. After washing with ultrapure water, the precipitate was dried under vacuum at 60℃ to obtain V4C3T. x MXene.

[0024] Example 4: 1) Niobium powder, aluminum powder and graphite powder of analytical grade with a particle size of 200 mesh were mixed in a molar ratio of 2:1:0.9 and wet-milled with ethanol, and then dried after milling to obtain the precursor mixture. 2) The precursor mixture was transferred to a tube furnace and heated from room temperature to 1500℃ at a rate of 4℃ / min under argon protection at a pressure of 0.04 MPa and a flow rate of 50 cc / min. The mixture was kept at the same temperature for 4 h to obtain Nb2AlC MAX powder, which was then ground through a 40-micron sieve. 3) Shake 0.25 g Nb2AlC MAX, 1.6 g ammonium fluoride and 1.6 g oxalic acid well; 4) Transfer the mixture to a Teflon-lined stainless steel reactor and etch it in an oven at 200°C for 6 hours; 5) The precipitate obtained from etching was washed by centrifugation with anhydrous ethanol at 3500 rpm for 3 min. The supernatant was discarded, and the process was repeated three times by centrifugation. After washing with ultrapure water, the precipitate was dried under vacuum at 60℃ to obtain Nb2CT. x MXene.

[0025] Example 5: 1) Analytical grade vanadium powder, aluminum powder and graphite powder with a particle size of 200 mesh were mixed in a molar ratio of 2:1:1 and wet-milled with ethanol, and then dried after milling to obtain the precursor mixture. 2) The precursor mixture was transferred to a tube furnace and heated from room temperature to 1500℃ at a rate of 5℃ / min under argon protection at a pressure of 0.06 MPa and a flow rate of 60 cc / min. The mixture was kept at the same temperature for 8 h to obtain V2AlC MAX powder, which was then ground through a 40-micron sieve. 3) Shake 0.25 g V2AlC MAX, 1.6 g ammonium fluoride and 1.6 g thiourea well; 4) Transfer the mixture to a Teflon-lined stainless steel reactor and etch it in an oven at 200°C for 6 hours; 5) The precipitate obtained from etching was washed by centrifugation with anhydrous ethanol at 3500 rpm for 3 min. The supernatant was discarded, and the process was repeated three times by centrifugation. After washing with ultrapure water, the precipitate was dried under vacuum at 60°C to obtain V2CT. x MXene.

[0026] Example 6: 1) Analytical grade titanium powder, aluminum powder and graphite powder with a particle size of 200 mesh were mixed in a molar ratio of 3:1:2 and wet-milled with ethanol, and then dried after milling to obtain the precursor mixture. 2) The precursor mixture was transferred to a tube furnace and heated from room temperature to 1350°C at a rate of 4°C / min under argon protection at a pressure of 0.05 MPa and a flow rate of 80 cc / min. The mixture was kept at the same temperature for 2 h to obtain Ti3AlC2MAX powder, which was then ground through a 40-micron sieve. 3) Shake 1 g Ti3AlC2MAX, 6 g ammonium fluoride and 6 g thiourea well; 4) Transfer the mixture to a Teflon-lined stainless steel reactor and etch it in an oven at 200°C for 2 hours; 5) The precipitate obtained from etching was washed by centrifugation with anhydrous ethanol at 3500 rpm for 3 min. The supernatant was discarded, and the washing process was repeated three times. After washing with ultrapure water, the precipitate was dried under vacuum at 60℃ to obtain Ti3C2T. xMXene.

[0027] Example 7: 1) Analytical grade vanadium powder, tin powder and graphite powder with a particle size of 200 mesh were mixed in a molar ratio of 2:1:1 and wet-milled with ethanol, and then dried after milling to obtain the precursor mixture. 2) The precursor mixture was transferred to a tube furnace and heated from room temperature to 1500℃ at a rate of 4℃ / min under argon protection at a pressure of 0.05 MPa and a flow rate of 80 cc / min. The mixture was kept at the same temperature for 2 h to obtain V2SnC MAX powder, which was then ground through a 40-micron sieve. 3) Shake 1 g V2SnC MAX, 6 g ammonium fluoride and 6 g thiourea well; 4) Transfer the mixture to a Teflon-lined stainless steel reactor and etch it in an oven at 200°C for 2 hours; 5) The precipitate obtained from etching was washed by centrifugation with anhydrous ethanol at 3500 rpm for 3 min. The supernatant was discarded, and the process was repeated three times by centrifugation. After washing with ultrapure water, the precipitate was dried under vacuum at 60°C to obtain V2CT. x MXene.

[0028] Example 8: 1) Titanium powder, titanium nitride, aluminum powder and graphite powder of analytical grade with a particle size of 200 mesh were mixed in a molar ratio of 2:1:1:1 and wet-milled with ethanol, and dried after milling to obtain the precursor mixture. 2) The precursor mixture was transferred to a tube furnace and heated from room temperature to 1500℃ at a rate of 4℃ / min under argon protection at a pressure of 0.05 MPa and a flow rate of 80 cc / min. The mixture was kept at the same temperature for 2 h to obtain Ti3AlCN MAX powder, which was then ground through a 40-micron sieve. 3) Shake 1 g Ti3AlCN MAX, 6 g ammonium fluoride and 6 g oxalic acid until well mixed; 4) Transfer the mixture to a Teflon-lined stainless steel reactor and etch it in an oven at 200°C for 2 hours; 5) The precipitate obtained from etching was washed by centrifugation with anhydrous ethanol at 3500 rpm for 3 min. The supernatant was discarded, and the washing process was repeated three times. After washing with ultrapure water, the precipitate was dried under vacuum at 60℃ to obtain Ti3CNT. x MXene.

[0029] This invention involves uniformly mixing a MAX phase compound with a solvent-free, low-temperature molten salt, reacting the mixture in a Teflon-lined stainless steel reactor, then washing with anhydrous ethanol and ultrapure water. The washed sample is then dried under vacuum at a specific temperature for a certain period to obtain MXene material. This invention provides a method for preparing MXene that does not involve toxic or harmful HF acids, completely etching away Al in the MAX phase to obtain MXene. The method is green, environmentally friendly, pollution-free, and the reaction is mild, easy to control, and simple to operate, making it suitable for large-scale production. Therefore, it has significant application prospects in many fields, such as hydrogen storage, catalyst supports, lithium-ion battery electrodes, and supercapacitor electrode materials.

[0030] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for low-temperature solvent-free synthesis of MXene materials using molten salt, characterized in that: Ammonium fluoride, solid small molecule intercalating agent and MAX phase are uniformly mixed and transferred into a Teflon-lined stainless steel reactor. The mixture is then heated in an oven. After the reaction is complete, MXene two-dimensional material is obtained.

2. The method for low-temperature molten salt solvent-free synthesis of MXene materials according to claim 1, characterized in that... Includes the following steps: 1) Mix and grind the MAX precursor powder to obtain a precursor mixture; 2) The precursor mixture is transferred to a tube furnace. Under inert gas protection, the tube furnace is heated from room temperature to 1350-1600℃ at a heating rate of 2-6℃ / min and kept at the temperature for 2-8 h to obtain MAX phase powder. 3) Take 0.25-1 g of MAX phase powder, 1.5-6 g of ammonium fluoride and 1.5-6 g of solid small molecules, shake well to obtain a mixture; 4) Transfer the mixture to a Teflon-lined stainless steel reactor and etch it in an oven at 100-240℃ for 2-24 hours; 5) Wash the precipitate obtained by etching with anhydrous ethanol, then add ultrapure water for washing and vacuum drying to obtain MXene.

3. The method for low-temperature molten salt solvent-free synthesis of MXene materials according to claim 2, characterized in that: The MAX precursor powder in step 1) is an analytically pure raw material, which is composed of at least one of the transition metals Ti, Zr, Hf, V, Nb, Ta, Cr, and Mo, at least one of the group III and IV main elements Al, Sn, Ga, and Si, and carbon powder.

4. The method for low-temperature molten salt solvent-free synthesis of MXene materials according to claim 2, characterized in that: Step 1) involves wet grinding with ethanol and drying after grinding to obtain a precursor mixture.

5. The method for low-temperature molten salt solvent-free synthesis of MXene materials according to claim 2, characterized in that: In step 2), the inert gas used is argon gas with a pressure of 0.02-0.08 MPa and a flow rate of 20-100 cc / min.

6. The method for low-temperature molten salt solvent-free synthesis of MXene materials according to claim 2, characterized in that: The general formula of the MAX phase powder is M n+1 AX n M represents Ti, Zr, Hf, V, Nb, Ta, Cr, or Mo, A represents Group IIIA elements (Al and Ga) or Group IVA elements (Sn and Si), and X represents C and / or N.

7. The method for low-temperature molten salt solvent-free synthesis of MXene materials according to claim 2, characterized in that: The solid small molecules in step 3) are urea, oxalic acid, boric acid, thiourea, ethylene glycol, glycine, acetamide, propionamide, or pyrrole.

8. The method for low-temperature molten salt solvent-free synthesis of MXene materials according to claim 2, characterized in that: In step 5), the precipitate is washed 2-3 times with anhydrous ethanol.

9. The application of an MXene material prepared by the method according to any one of claims 1 to 8 as a hydrogen storage, catalyst support, lithium-ion battery electrode, and supercapacitor electrode material.

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