A few-layer MXenes material and its fluorine-free simultaneous etching-exfoliation preparation method

Abstract

This invention provides a few-layer MXenes material and its green, fluorine-free, simultaneous cleavage preparation method, comprising the following steps: reacting the MAX phase material at high temperature in a functional composite salt to achieve simultaneous etching and exfoliation; and obtaining the few-layer MXenes material after washing. This invention develops a functional composite salt for preparing few-layer MXenes materials, avoiding the use of fluorine-containing etchants. It achieves MXene cleavage simultaneously with the etching of A-site atoms, providing a one-step preparation method for few-layer MXenes materials. This method is highly efficient, environmentally friendly, and suitable for industrial production.

Description

Technical Field

[0001] This invention relates to the field of two-dimensional material preparation technology, and in particular to a few-layer MXenes material and its fluorine-free synchronous etching-exfoliation preparation method. Background Technology

[0002] Two-dimensional transition metal carbides, nitrides, and carbonitrides, also known as MXenes, are a new type of two-dimensional material with the molecular formula M. n+1 X n T x In this model, M represents an early transition metal, primarily Ti, Nb, V, Cr, Mo, etc.; X represents C, N, or CN; and T represents surface functional groups, primarily =O, -F, -OH, and -Cl, etc. Due to their excellent electrical conductivity, tunable structure, rich surface chemical properties, optical properties, and magnetic properties, MXenes are considered highly promising two-dimensional materials with wide applications in energy storage, catalysis, electromagnetic interference shielding, optoelectronics, sensing, and medicine.

[0003] Currently, MXenes materials are typically prepared by selectively etching the A atom layer in the MAX phase, where A is a Group 3 or 4 element, such as Al, Si, or Ga (M and X represent the corresponding elements in the MXenes).

[0004] Traditional preparation methods require fluorine-containing solutions, which are not environmentally friendly and make it difficult to control the functional groups on the material surface. Currently developed fluorine-free preparation routes, such as high-concentration sodium or potassium hydroxide, acidic, halogenated, and electrochemical etching, still rely on aqueous systems, making it difficult to control the functional groups on the MXene surface, and requiring harsh operating conditions and hazardous experimental procedures. Although high-temperature molten salt etching has paved the way for non-aqueous fluorine-free MXene preparation, it yields multilayer MXenes, requiring the subsequent addition of intercalating agents to exfoliate the material into few-layer or monolayer materials. Current fluorine-free etching methods rarely achieve few-layer MXene materials in a single step, requiring two steps of etching and delamination, which is complex, and the introduction of intercalating agents may damage the MXene structure and introduce defects. Therefore, there is an urgent need to develop methods suitable for green, efficient, and large-scale preparation of few-layer MXene materials, and to develop a one-step fluorine-free preparation system to achieve efficient preparation of few-layer MXene materials. Summary of the Invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide a few-layer MXenes material and a fluorine-free synchronous etching-stripping preparation method thereof, so as to realize the etching and layering of MAX materials in one step.

[0006] The present invention provides a few-layer MXenes material, wherein the few-layer MXenes material has ≤20 layers and comprises a single layer of MXene material.

[0007] In this invention, the limitation on the number of layers mentioned above refers to Ti3C2T x An atomic layer is defined as one layer. It can be 2 to 20 layers, or it can be a single layer of MXene material.

[0008] Preferably, the few-layer MXenes material of the present invention comprises a single-layer MXene material.

[0009] The presence of monolayer MXene materials improves the overall electrochemical performance of the few-layer MXenes materials, and is expected to expand the application fields of MXenes materials in the future.

[0010] In this invention, the surface of the few-layer MXenes material carries a positive charge.

[0011] In this invention, the surface functional groups of the few-layer MXenes material include -Cl, =O and -N.

[0012] The few-layer MXenes material provided by this invention differs from the current multilayer MXenes with -Cl and =O functional groups. Its surface functional groups include -Cl, =O and -N, among which the introduction of -N significantly improves the electrochemical performance of the material.

[0013] Furthermore, the few-layer MXenes material provided by this invention has a positively charged surface, unlike the currently used negatively charged MXenes. The positively charged few-layer MXenes material is expected to expand its application areas.

[0014] This invention provides a method for preparing few-layer MXenes materials using fluorine-free simultaneous etching-exfoliation, comprising the following steps:

[0015] The MAX phase material is subjected to a high-temperature reaction in a functional composite salt, simultaneously achieving etching and stripping, and after washing, a few-layer MXenes material is obtained.

[0016] In this invention, a functional composite salt is used to achieve simultaneous etching and stripping. Preferably, the functional composite salt is a deep eutectic solvent.

[0017] In this invention, the cleavage refers to simultaneous etching-stripping.

[0018] The etching process described above specifically refers to using an etchant to etch the A atom layer in the MAX phase to obtain two-dimensional MXenes materials.

[0019] The aforementioned stripping specifically refers to the stripping agent decomposing at high temperatures to generate a large amount of gas, which expands the material.

[0020] The etching mechanism of this invention is as follows:

[0021] Lewis acid etchants with higher redox potentials etch A elements from the MAX phase;

[0022] M1H x +M2AX→M2X+M1+AH y ↑

[0023] This invention applies a functional composite salt to the preparation of few-layer MXenes, utilizing the metal salt as an etchant and the stripping agent as a swelling agent. Due to the interaction between the etchant and the swelling agent, the etchant carries the swelling agent into the interlayer space during the etching of the A-atom layer. At high temperatures, the swelling agent decomposes into a large amount of gas, which can expand the interlayer space. Therefore, the etching and delamination processes of the MAX phase in the reaction system are completed in one step, efficiently achieving simultaneous etching and delamination during the reaction, simplifying the preparation process, and directly obtaining few-layer MXenes in one step, thus improving the preparation efficiency.

[0024] Preferably, the functional composite salt includes an etchant and a stripping agent.

[0025] Preferably, the etchant comprises any one or more metal salts.

[0026] The metal salt is preferably any one or a combination of two or more of the following, including but not limited to SnCl4, GeCl4, InCl3, MnCl2, CdCl2, FeCl2, CoCl2, CuCl2, NiCl2, ZnCl2, AgCl, SnBr4, GeBr4, InBr3, MnBr2, CdBr2, FeBr, CoBr2, CuBr2, NiBr2, ZnBr2, AgBr, SnI4, GeI4, InI3, MnI2, CdI2, FeI2, CoI2, CuI2, NiI2, ZnI2, and AgI.

[0027] Preferably, the stripping agent includes, but is not limited to, any one or a combination of two or more of the following: quaternary ammonium salts, urea, thiourea, N-methylurea, dimethylurea, acetamide, bis(trifluoromethanesulfonyl)imide, glycerol, adipic acid, citric acid, oxalic acid, ethylenediaminetetraacetic acid, sodium bicarbonate, and ammonium chloride.

[0028] The quaternary ammonium salt is preferably one or more of choline chloride and chlormequat chloride.

[0029] The preferred molar ratio of the MAX material to the etchant is 1:(2-10). If the proportion of the etchant is too low, it will hinder the complete reaction; if it is too high, it will cause the material to oxidize. The above ratio range can ensure that the reaction proceeds smoothly and that the material is not oxidized.

[0030] The molar ratio of the etchant to the stripper is preferably 1:(0.5-5).

[0031] This invention uses MAX material as raw material. This invention does not have any special limitations on the MAX material. Experimental results show that the method provided by this invention is applicable to most MAX materials.

[0032] Preferably, the molecular formula of the MAX phase material is M n+1 AX n M is preferably any one or a combination of two or more elements from Sc, Ti, V, Cr, Mn, Y, Zr, Nb, Mo, La, Hf, Ta, and W; A is preferably an element from group VIIB, VIII, IB, IIB, IIIA, IVA, VA, or VIA; X is preferably any one or a combination of two elements from C and N; and n is preferably 1, 2, 3, or 4.

[0033] More preferably, the MAX material includes, but is not limited to, any one or a combination of two or more of the following: Ti2AlC, Ti2SnC, Ti2GaC, Ti2AlN, Ti3AlC2, Ti3AlN3, Ti3AlCN, Ti3SiC2, Ti3SnC2, Ti4AlN3, Ta2AlC, Ta3AlC2, Ta4AlC3, Nb2AlC, Nb4AlC3, V2AlC, V2GaC, V2GeC, V2ZnC, V2SnC, V4AlC3, VCrAlC, Cr2AlC, Cr2GaC, Cr2GaN, Sc2AlC, Zr2AlC, Zr2SnC, Mo2AlC, Mo2Ga2C, Mo2GaC, Mo2GaN, Mo2Ti2AlC3, Mo2Ti2AlC3, Hf2AlC, and Hf2AlN.

[0034] In a preferred embodiment of the present invention, the MAX material and the metal salt are first mixed to obtain mixture A, and then mixture A is mixed with a stripping agent to obtain mixture B.

[0035] Then, mixture B was placed in a crucible, which was then placed in a quartz glass tube. An inert gas was introduced, and the mixture was calcined at high temperature for a certain period of time to obtain sample C.

[0036] The preferred temperature for high-temperature calcination is 400-800℃, and in some specific embodiments of the present invention, the temperature for high-temperature calcination is 500℃.

[0037] If the high-temperature calcination temperature is too low, it will be detrimental to the reaction kinetics, causing the material to fail to react or to react incompletely. If the temperature is too high, it will cause the material to oxidize or even break chemical bonds.

[0038] The high-temperature calcination time is 30 min to 24 h, and in some specific embodiments of the present invention, the high-temperature calcination time is 1 h.

[0039] If the reaction time is too short, it will not be conducive to a complete reaction; if it is too long, it will cause oxidation of the material.

[0040] The high-temperature calcination is preferably carried out in an inert gas atmosphere, and the inert gas is preferably argon.

[0041] After high-temperature calcination, sample C is cooled to room temperature and then a detergent is added to remove impurities. The present invention does not have any special limitation on the detergent, which can be an oxidant known to those skilled in the art, including but not limited to one or more of ferric chloride, ammonium persulfate, and hydrochloric acid. The detergent can effectively remove the byproducts obtained from the reaction.

[0042] Preferably, the present invention further includes drying after washing and removing impurities.

[0043] The present invention does not specifically limit the drying method, but preferably one or more of vacuum oven drying and freeze dryer drying, thereby preventing the material from being overexposed to air and causing oxidation.

[0044] This invention also provides a few-layer MXenes material prepared by the above preparation method. The above method can bring new physicochemical properties to MXenes materials, thereby expanding the storage methods and application fields of the materials to a certain extent.

[0045] The few-layer MXenes material prepared by this invention can be applied in a variety of fields, such as supercapacitors, alkali metal ion secondary batteries (lithium-ion batteries, sodium-ion batteries, etc.), catalysis, etc. The prepared few-layer MXenes material can be used as an electrode material in supercapacitors, or as a negative electrode material in alkali metal ion batteries, or as an effective carrier of active materials in lithium-sulfur batteries and lithium-air batteries, or as a catalytic material.

[0046] Based on this, the present invention provides a supercapacitor or alkali metal ion secondary battery, comprising the few-layer MXenes material prepared by the above preparation method.

[0047] Compared with existing technologies, this invention provides a fluorine-free simultaneous etching-exfoliation method for preparing few-layer MXenes materials, comprising the following steps: reacting the MAX phase material at high temperature in a functional composite salt to achieve simultaneous etching and exfoliation, followed by washing to obtain the few-layer MXenes material. This invention applies a functional composite salt to the preparation of few-layer MXenes, allowing etching and delamination to occur simultaneously without the need for fluorine-containing solutions, thus achieving a one-step preparation method for few-layer MXenes materials. This method is highly efficient, environmentally friendly, and suitable for industrial production. Attached Figure Description

[0048] Figure 1 Scanning electron microscope (SEM) and transmission electron microscope (TEM) images of few-layer and multi-layer MXenes;

[0049] Figure 2 An atomic force microscope image of a single-layer MXenes;

[0050] Figure 3 EDS spectra of Cl, O, and N for few-layer MXenes;

[0051] Figure 4 The rate performance diagrams for few-layer and multi-layer MXenes are shown.

[0052] Figure 5 Long-cycle performance graphs for few-layer and multi-layer MXenes;

[0053] Figure 6 Zeta potential diagrams for few-layer and multi-layer MXenes. Detailed Implementation

[0054] To further illustrate the present invention, the method for preparing few-layer MXenes using a green, fluorine-free solvent in a one-step process, as provided by the present invention, is described in detail below with reference to embodiments. However, it should be understood that these descriptions are merely for further illustrating the features and advantages of the present invention and are not intended to limit the scope of the claims.

[0055] There are no particular restrictions on the source of any raw materials used in this invention; they can be purchased from the market or prepared using conventional methods known to those skilled in the art.

[0056] Example 1

[0057] (1) The etching raw materials Ti3AlC2 and CuCl2 are mixed evenly in a 1:2 molar ratio to obtain mixture A. Then, mixture A is mixed evenly with 1 molar ratio of urea to obtain mixture B.

[0058] (2) Place mixture B into a crucible, then place the crucible into a quartz glass tube, introduce argon gas, and calcine at 500℃ for 1 hour to obtain sample C;

[0059] (3) After cooling sample C to room temperature, add 1 mole of ferric chloride to wash and remove impurities to obtain sample D. Then, dry sample D with a freeze dryer to obtain a few-layer MXene material.

[0060] The prepared few-layer MXene material was tested, and the results are as follows: Figure 1As shown in Figure a, where the left image is a scanning electron microscope (SEM) image and the right image is a transmission electron microscope (TEM) image, it can be seen that this embodiment prepared a few-layer MXene material containing monolayer MXene, as shown in the figure. Figure 2 As shown.

[0061] The prepared few-layer MXene material was analyzed by EDS energy dispersive spectroscopy, and the results are as follows: Figure 3 As shown, the surface functional groups of the few-layer MXene material prepared by this invention include -Cl, =O and -N.

[0062] Example 2

[0063] The implementation method is the same as in Example 1, except that in step (1), Ti3AlC2 and CuCl2 are mixed uniformly in a ratio of 1:3 to prepare a few-layer MXene material.

[0064] Example 3

[0065] The implementation method is the same as in Example 1, except that in step (1), Ti3AlC2 and CuCl2 are mixed uniformly in a ratio of 1:4 to prepare a few-layer MXene material.

[0066] Example 4

[0067] The implementation method is the same as in Example 1, except that in step (1), Ti3AlC2 and CuCl2 are mixed uniformly in a ratio of 1:6 to prepare a few-layer MXene material.

[0068] Example 5

[0069] The implementation method is the same as in Example 1, except that in step (1), Ti3AlC2 and ZnCl2 are mixed uniformly in a ratio of 1:2 to prepare a few-layer MXene material.

[0070] Example 6

[0071] The implementation method is the same as in Example 1, except that in step (1), Ti3AlC2 and ZnCl2 are mixed uniformly in a ratio of 1:4 to prepare a few-layer MXene material.

[0072] Example 7

[0073] The implementation method is the same as in Example 1, except that in step (1), Ti3AlC2 and ZnCl2 are mixed uniformly in a ratio of 1:6 to prepare a few-layer MXene material.

[0074] Example 8

[0075] The implementation method is the same as in Example 1, except that in step (1), Ti3AlC2 and FeCl2 are mixed uniformly in a ratio of 1:3 to prepare a few-layer MXene material.

[0076] Example 9

[0077] The implementation method is the same as in Example 1, except that in step (1), Ti3AlC2 and FeCl2 are mixed uniformly in a ratio of 1:6 to prepare a few-layer MXene material.

[0078] Example 10

[0079] The implementation method is the same as in Example 1, except that in step (1), Ti3AlC2 and CoCl2 are mixed uniformly in a ratio of 1:3 to prepare a few-layer MXene material.

[0080] Example 11

[0081] The implementation method is the same as in Example 1, except that in step (1), Ti3AlC2 and CoCl2 are mixed uniformly in a ratio of 1:6 to prepare a few-layer MXene material.

[0082] Example 12

[0083] The implementation method is the same as in Example 1, except that in step (1), Ti3AlC2 and CoCl2 are mixed uniformly in a ratio of 1:9 to prepare a few-layer MXene material.

[0084] Example 13

[0085] The implementation method is the same as in Example 1, except that in step (1), mixture A is mixed with N-methylurea to obtain mixture B, and a few-layer MXene material is prepared.

[0086] Example 14

[0087] The implementation method is the same as in Example 1, except that in step (1), mixture A is mixed with acetamide to obtain mixture B, and a few-layer MXene material is prepared.

[0088] Example 15

[0089] The implementation method is the same as in Example 1, except that in step (1), mixture A is mixed with bis(trifluoromethanesulfonyl)imide to obtain mixture B, and a few-layer MXene material is prepared.

[0090] Example 16

[0091] The implementation method is the same as in Example 1, except that in step (1), mixture A is mixed with glycerol to obtain mixture B, and a few-layer MXene material is prepared.

[0092] Example 17

[0093] The implementation method is the same as in Example 1, except that in step (1), mixture A is mixed with adipic acid to obtain mixture B, and a few-layer MXene material is prepared.

[0094] Example 18

[0095] The implementation method is the same as in Example 1, except that in step (1), mixture A is mixed with sodium bicarbonate to obtain mixture B, and a few-layer MXene material is prepared.

[0096] Example 19

[0097] The implementation method is the same as in Example 1, except that in step (1), the high-temperature calcination temperature is 700°C to prepare a few-layer MXene material.

[0098] Example 20

[0099] The implementation method is the same as in Example 1, except that in step (1), the high-temperature calcination time is 4 hours to prepare a few-layer MXene material.

[0100] Example 21

[0101] The implementation method is the same as in Example 1, except that in step (1), the reaction raw material is V2AlC, and a few-layer MXene material is prepared.

[0102] Example 22

[0103] The implementation method is the same as in Example 1, except that in step (1), the reaction raw material is Ta2AlC, and a few-layer MXene material is prepared.

[0104] Comparative Example 1

[0105] The implementation method is the same as in Example 1, except that no stripping agent is added, and a multilayer MXene material is finally obtained.

[0106] The prepared multilayer MXene material was tested, and the results are as follows: Figure 1 As shown in Figure b, the left image is a transmission electron microscope (TEM) image, and the right image is a scanning electron microscope (SEM) image. It can be seen that multilayer MXene materials were prepared in the system without the addition of a release agent, while adding a release agent resulted in few-layer MXene.

[0107] Electrochemical performance testing

[0108] The target materials prepared in Examples 1-21 and Comparative Example 1 were applied to lithium-ion batteries, and the specific steps for preparing lithium-ion batteries are as follows:

[0109] The target material was uniformly mixed with acetylene black and PVDF in a ratio of 70:15:15 (wt.%), coated onto a 2cm×2cm copper foil current collector, and dried at 100℃.

[0110] The prepared electrode sheets are placed in the order of negative electrode shell, spring sheet, gasket, negative electrode, separator, positive electrode, and positive electrode shell. After adding a certain amount of electrolyte, the assembled capacitor is sealed under a pressure of 50 MPa using a sealing machine to obtain a coin cell. After standing for 24 hours, electrochemical performance is tested. In this embodiment, the electrolyte used is one mole of lithium hexafluorophosphate (LiPF6) dissolved in an organic solution of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC).

[0111] Test results are as follows Figure 4 and Figure 5 As shown. Figure 4 This is a rate performance graph for few-layer MXene and multi-layer MXene. Figure 5 This is a long-cycle performance graph for few-layer and multi-layer MXene.

[0112] It can be seen that the rate performance and long-cycle performance of fewer-layer MXene are better than those of multi-layer MXene.

[0113] Figure 6 The figures show the Zeta potential diagrams of few-layer MXene and multi-layer MXene. It can be seen that, unlike existing multi-layer MXene which has a negative surface charge, the few-layer MXene material prepared in this invention has a positive surface charge.

[0114] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing few-layer MXenes materials by fluorine-free simultaneous etching-exfoliation, comprising the following steps: The MAX phase material is subjected to a high-temperature reaction in a functional composite salt to achieve simultaneous etching and stripping, and after washing, a few-layer MXenes material is obtained. The functional composite salt includes an etchant and a stripping agent; The etching agent includes any one or more metal salts; The stripping agent includes any one or a combination of two or more of the following: quaternary ammonium salt, urea, thiourea, N-methylurea, dimethylurea, acetamide, bis(trifluoromethanesulfonyl)imide, glycerol, adipic acid, citric acid, oxalic acid, ethylenediaminetetraacetic acid, sodium bicarbonate, and ammonium chloride. The metal salt includes any one or a combination of two or more of SnCl4, GeCl4, InCl3, MnCl2, CdCl2, FeCl2, CoCl2, CuCl2, NiCl2, ZnCl2, AgCl, SnBr4, GeBr4, InBr3, MnBr2, CdBr2, FeBr, CoBr2, CuBr2, NiBr2, ZnBr2, AgBr, SnI4, GeI4, InI3, MnI2, CdI2, FeI2, CoI2, CuI2, NiI2, ZnI2, and AgI; The high-temperature reaction is carried out at a temperature of 400-800℃ for a duration of 30 min to 24 h.

2. The preparation method according to claim 1, characterized in that, The molecular formula of the MAX phase material is M n+1 AX n Where M is any one or more of the elements Sc, Ti, V, Cr, Mn, Y, Zr, Nb, Mo, La, Hf, Ta, and W; A is an element of group VIIB, VIII, IB, IIB, IIIA, IVA, VA, or VIA; X is any one or two of the elements C and N; and n is 1, 2, 3, or 4.

3. The preparation method according to claim 2, characterized in that, The MAX material includes any one or a combination of two or more of the following: Ti2AlC, Ti2SnC, Ti2GaC, Ti2AlN, Ti3AlC2, Ti3AlN3, Ti3AlCN, Ti3SiC2, Ti3SnC2, Ti4AlN3, Ta2AlC, Ta3AlC2, Ta4AlC3, Nb2AlC, Nb4AlC3, V2AlC, V2GaC, V2GeC, V2ZnC, V2SnC, V4AlC3, VCrAlC, Cr2AlC, Cr2GaC, Cr2GaN, Sc2AlC, Zr2AlC, Zr2SnC, Mo2AlC, Mo2Ga2C, Mo2GaC, Mo2GaN, Mo2Ti2AlC3, Mo2Ti2AlC3, Hf2AlC, and Hf2AlN.

4. The preparation method according to claim 1, characterized in that, The molar ratio of the MAX material to the etchant is 1:(2-10); The molar ratio of the etchant to the stripper is 1:(0.5-5).

5. The preparation method according to claim 1, characterized in that, The high-temperature reaction is carried out in an inert gas atmosphere.

6. The few-layer MXenes material prepared by the preparation method according to any one of claims 1 to 5, characterized in that, The few-layer MXenes material has ≤20 layers, and the few-layer MXenes material includes a single-layer MXene material.

7. The few-layer MXenes material according to claim 6, characterized in that, The few-layer MXenes material has a positively charged surface, and the surface functional groups include -Cl, =O and -N.

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