Method for growing MXene material by molten salt method and its use

Abstract

The present invention discloses a method for growing MXene materials by molten salt method and its use, wherein the method includes: mixing transition metal elemental powder, X-source powder and a medium salt, heating to melt the medium salt to form a molten mixture; reacting the molten mixture with gaseous raw materials at a predetermined reaction temperature to obtain MXene materials; the gaseous raw materials include: transition metal halide salts; and / or, halogen gases; the X-source powder is one or more of a carbon source, a carbon-nitrogen source, and a nitrogen source; the carbon source is selected from carbon materials; the carbon-nitrogen source is selected from: carbon nitride, melamine, dicyandiamide, urea; the nitrogen source is boron nitride; the medium salt is selected from: halide salts of alkali metals and / or halide salts of alkaline earth metals. The method of the present invention can be carried out in an open system at a relatively reduced synthesis temperature, reducing the reaction synthesis temperature, reducing the synthesis energy consumption, and simplifying the gas-phase growth process, providing a new technical path for the efficient preparation of MXene materials.

Description

Technical Field

[0001] The present invention belongs to the field of new materials, and particularly relates to a method for growing MXene materials by molten salt method and its uses. Background Art

[0002] Two-dimensional transition metal carbides, nitrides or carbonitrides, due to their two-dimensional structure similar to that of graphene, are also named MXene. The thickness of a single MXene layer is about 1 nm, while their lateral size can reach more than dozens of micrometers. This unique structure and surface properties endow MXene with excellent properties such as unique electrical properties, optical properties, and thermal stability, and have potential application prospects in the fields of energy storage, catalysis, adsorption, etc.

[0003] Currently, the most classic and commonly used method for preparing MXene two-dimensional materials is the hydrofluoric acid (HF) etching method. Using MAX phase materials as raw materials, the A component is etched away by HF to obtain two-dimensional MXene materials. Among them, MAX phase materials are layered ceramic materials, M refers to transition metal elements, including Sc, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, etc.; A mainly refers to elements in the third main group and the fourth main group, such as Al, Ga, In, Tl, Si, Ge, Sn, Pb, etc.; X represents C or N; n = 1, 2, or 3. MAX phase materials are a large class of materials, and the types of materials included can be seen in the literature (Maxim S, Varun N, Sankalp K, et al. Trends in Chemistry, 2019, 1(2): 210 - 223.).

[0004] Taking Ti3AlC2 MAX phase as an example, by immersing Ti3AlC2 in a hydrofluoric acid solution (concentration 50%) for 2 h, the Al atoms in Ti3AlC2 are etched to prepare Ti3C2, (Naguib M, Kurtoglu M, Presser V, et al. Advanced Materials, 2011, 23(37): 4248 - 4253.). Since direct use of HF has strong corrosiveness and high toxicity, researchers have used hydrochloric acid solution + fluoride salt to replace HF as an etchant to prepare MXene (Ghidiu M, Lukatskaya M R, Zhao M Q, et al. Nature, 2014, 516(7529): 78.). Using a similar method, MXene two-dimensional materials such as Ti2C, Ta4C3, Ti3CN, V4C3, etc. have also been prepared.

[0005] However, this method for preparing MXene requires the direct or indirect use of highly corrosive and toxic hydrofluoric acid solution, and the safety during the preparation process is difficult to guarantee. At the same time, since it is a liquid-phase reaction, the generated MXene is dispersed in a high-concentration acid solution, and obtaining the MXene powder product also requires repeated washing, ultrasonic treatment, centrifugal separation, drying and other steps. The complex process steps make it difficult to achieve large-scale preparation of MXene, and the preparation cost is extremely high, seriously limiting the application prospects of MXene. At present, the preparation and application of MXene are still in the laboratory research stage.

[0006] The applicant proposed a gas-phase etching method for preparing MXene in the patent application (application number 202011466046.4). By using gaseous hydrogen halides and metal halide salts to etch the precursor MAX phase material, high-quality MXene materials can be synthesized in large quantities, avoiding the steps of desolvation and impurity removal in the liquid-phase etching method and simplifying the production process of MXene materials.

[0007] However, whether based on the liquid-phase etching method or the gas-phase etching method above, the preparation of MXene materials uses the precursor MAX phase material as the precursor. After etching the A layer therein, accordion-shaped MXene is obtained. Inevitably, to obtain two-dimensional MXene materials, a peeling step is required, and the accordion-shaped MXene material is mechanically peeled by ultrasonic treatment and other methods to obtain two-dimensional MXene materials. Summary of the Invention

[0008] The object of the present invention is to propose another method for preparing MXene materials by the molten salt method without using the precursor material MAX phase. Compared with the prior art, the method of the present invention is an open system, in which a molten medium salt is introduced, and transition metal elemental powder and X-source powder are dispersed in the molten medium salt. The molten medium salt is used to improve the reaction activity of the reactants, and MXene materials are grown by gas phase with the transition metal elemental and X-source powder as the nucleation sites.

[0009] The first aspect of the present invention provides an MXene material grown by the molten salt method. The preparation method of the MXene material includes: mixing transition metal elemental powder, X-source powder and medium salt, heating to melt the medium salt to form a molten mixture; at a predetermined reaction temperature, reacting the molten mixture with gaseous raw materials to obtain MXene materials; the gaseous raw materials include: transition metal halide salts; and / or, halogen gases; the X-source powder is one or more of a carbon source, a carbon-nitrogen source, and a nitrogen source; the carbon source is selected from carbon materials; the carbon-nitrogen source is selected from: carbon nitride, melamine, dicyandiamide, urea; the nitrogen source is boron nitride; the medium salt is selected from: halide salts of alkali metals and / or halide salts of alkaline earth metals.

[0010] In some embodiments, the above carbon material is selected from one or more of graphite, graphene, expanded graphite, carbon nanotubes, carbon nanofibers, and carbon nanobelts.

[0011] In some embodiments, the chemical formula of the above MXene material is M n+1 X n T x , where M represents a transition metal element; X represents carbon and / or nitrogen, and T represents a surface functional group including one or more of F, Cl, Br, and I, and 1 ≤ n ≤ 4.

[0012] In some embodiments, M in the above chemical formula is selected from one or more of Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W, Y, and Sc.

[0013] In some embodiments, the above medium salt is selected from one or several of sodium chloride, potassium chloride, and lithium chloride.

[0014] In some embodiments, the above transition metal halide salt is selected from one or more of transition metal chlorides, transition metal bromides, transition metal iodides, and transition metal fluorides.

[0015] In some embodiments, the above predetermined reaction temperature is between 300°C and 1500°C.

[0016] In some embodiments, the above predetermined reaction temperature is between 500°C and 900°C.

[0017] In some embodiments, the above predetermined reaction temperature is between 600°C and 850°C.

[0018] In some embodiments, the time of the above predetermined reaction is between 1 min and 12 h.

[0019] In some embodiments, the above MXene material has one or several of an expanded morphology, a hollow tubular morphology, and a one-dimensional morphology.

[0020] In some embodiments, the mass ratio of the mixture of the above transition metal elemental powder and X-source powder to the medium salt ≥ 1; more preferably, the mass ratio ≥ 2.

[0021] In some embodiments, the above method further includes a purification step: washing with water to remove the medium salt, and drying to obtain the MXene material.

[0022] In some embodiments, the above method further includes: a heating step of heating the above transition metal halide salt to convert it into a gaseous state.

[0023] In some embodiments, the above method further includes the step of introducing the gaseous raw material into the molten mixture to form bubbles.

[0024] In some embodiments, the above method further includes a stripping step. At a predetermined sintering temperature, an inert gas is introduced into the tubular furnace to strip the floating substances on the surface of the molten mixture.

[0025] The second aspect of the present invention provides an MXene material prepared by the above method.

[0026] The third aspect of the present invention provides an application of the above MXene material in catalysis, sensors, electronic devices, supercapacitors, batteries, electromagnetic shielding, microwave absorbing materials, corrosion-resistant materials, or superconducting materials.

[0027] The method of the present invention can be carried out at a relatively reduced synthesis temperature in an open system, reducing the reaction synthesis temperature, reducing the synthesis energy consumption, simplifying the vapor-phase growth process. The MXene prepared by the open system can also facilitate the adjustment of MXene functional groups. The present invention provides a new technical route for the efficient preparation of MXene materials. Description of the Drawings

[0028] Figure 1 It is the XRD pattern of the product MXene prepared in Example 1 of the present invention.

[0029] Figure 2 SEM photograph of the product MXene prepared in Example 1 of the present invention.

[0030] Figure 3 SEM photograph of the tubular MXene prepared in Example 1 of the present invention.

[0031] Figure 4 TEM photographs (a) and HRTEM (b) of the MXene prepared in Example 1 of the present invention.

[0032] Figure 5 It is the XRD pattern of the product MXene prepared in Example 2 of the present invention.

[0033] Figure 6 SEM photograph of the product MXene prepared in Example 2 of the present invention.

[0034] Figure 7 It is the XRD pattern of the product MXene prepared in Example 3 of the present invention.

[0035] Figure 8 SEM photograph of the product MXene prepared in Example 3 of the present invention.

[0036] Figure 9XRD pattern of the product MXene prepared in Example 4 of the present invention.

[0037] Figure 10 XRD pattern of the product MXene prepared in Example 4 of the present invention.

[0038] Figure 11 XRD pattern of the product MXene prepared in Example 5 of the present invention.

[0039] Figure 12 SEM photograph of the product MXene prepared in Example 5 of the present invention.

[0040] Figure 13 XRD pattern of the product obtained in Comparative Example 1 of the present invention. Detailed implementation manners

[0041] The technical solutions of the present invention are illustrated by the following specific examples. It should be understood that one or more steps mentioned in the present invention do not exclude the existence of other methods and steps before and after the combined steps, or other methods and steps can be inserted between these explicitly mentioned steps. It should also be understood that these examples are only used to illustrate the present invention and not to limit the scope of the present invention. Unless otherwise specified, the numbers of each method step are only for the purpose of identifying each method step, rather than limiting the arrangement order of each method or defining the implementation scope of the present invention. The change or adjustment of their relative relationship can also be regarded as the implementable scope of the present invention under the condition of no substantial change in technical content.

[0042] There is no specific limitation on the sources of the raw materials and instruments used in the examples, and they can be purchased in the market or prepared by the conventional methods well-known to those skilled in the art.

[0043] The sources of the raw materials and instruments used in the examples are as follows: Ti powder, TiCl4, expanded graphite, carbon nanotubes, and melamine are all purchased from InnoChem Technology Co., Ltd. C3N4 is prepared by thermal polymerization by laboratory personnel using melamine as the raw material, and graphene is prepared by laboratory personnel using expanded graphite as the raw material by the airflow pulverization method.

[0044] The present invention provides a method for growing MXene by a gas phase method, wherein the chemical formula of the MXene is represented as M n+ 1X n T x, M represents a transition metal element; X represents carbon and / or nitrogen; T represents a surface functional group including one or more of F, Cl, Br, and I; 1 ≤ n ≤ 4, 0 < x ≤ 2. The raw materials include: transition metal elemental powder, transition metal halide salt, carbon source and / or nitrogen source, and medium salt; wherein, the transition metal elemental powder and the transition metal halide salt are also referred to as transition metal source or M source in the present invention; the carbon source, nitrogen source, and carbon-nitrogen source are also referred to as X source in the present invention.

[0045] In some embodiments, the transition metal elemental powder is selected from Sc, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta elemental powders, and the transition metal halide salt is selected from at least one of chlorides, bromides, and iodides of Sc, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta;

[0046] The technical concept of the present invention is that the transition metal elemental powder and the X-source powder are dispersed in the molten medium salt to obtain a molten mixture, and gaseous transition metal halide salt is introduced into the molten mixture (inside or on the liquid surface), and MXene material is formed by vapor-phase growth.

[0047] Since at high temperature, the transition metal element can react with the halogen gas to generate transition metal halide salt, therefore, in some embodiments, the gas introduced into the molten mixture can also be gaseous halogen gas.

[0048] The role of the medium salt is to provide a molten liquid phase environment for the reactants of the transition metal element, X source, and gas source raw materials, and it does not participate in the vapor deposition reaction growth itself. Therefore, the medium salt is preferably a halide salt of an alkali metal and / or an alkaline earth metal with a low melting point and easy solubility in water (conducive to washing and impurity removal). In some embodiments, the medium salt is selected from one or several of sodium chloride, potassium chloride, and lithium chloride.

[0049] In one embodiment, the method for growing MXene by the gas phase method of the present invention includes the steps of:

[0050] S01: Mix the transition metal elemental powder, the X-source powder, and the medium salt, and heat to melt the medium salt to form a molten mixture;

[0051] S02: At a predetermined reaction temperature, introduce gaseous raw materials into the inside and / or above the liquid surface of the molten mixture to grow MXene material; wherein, the gaseous raw materials include: transition metal halide salt; and / or, halogen gas. The transition metal halide salt and / or halogen gas in the introduced gaseous raw materials deposit and grow MXene material in the molten mixture. The generated MXene material is fluffy and has a low density, and gradually floats on the surface of the molten mixture (liquid phase), and can be blown off and collected from the liquid surface by introducing gas.

[0052] Among them, in some embodiments, the transition metal elemental powder is selected from Sc, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta elemental powders, and the transition metal halide salt is selected from at least one of chlorides, bromides, and iodides of Sc, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta; the X source can be a carbon source, a nitrogen source, or a carbon-nitrogen source; the carbon source is selected from carbon materials; the carbon-nitrogen source is selected from: carbon nitride, melamine, dicyandiamide, urea; the nitrogen source is boron nitride.

[0053] In some embodiments, the carbon material is selected from one or more of graphite, graphene, expanded graphite, carbon nanotubes, carbon nanofibers, and carbon nanobelts. The present invention finds that the generated MXene can retain the morphological characteristics of the X source to a certain extent. Therefore, by selecting a carbon material with a specific morphology, MXene with a specific morphology that is difficult to obtain by other methods can be obtained. For example, when using carbon nanotubes as the X source, the synthesized MXene retains a one-dimensional morphology.

[0054] More specific steps include:

[0055] S11: Mix the transition metal elemental powder, the X source powder, and the medium salt in a certain proportion, place them in a high-temperature furnace, and under the protection of an inert gas, heat to a molten state of the medium salt to form a molten mixture, and the transition metal elemental powder and the X source powder are dispersed in the molten medium salt; in the vapor-phase growth reaction, the contact part of the gaseous raw material with the transition metal elemental particles and the X source in the molten mixture is the nucleation site for the growth of MXene.

[0056] S12: At a predetermined reaction temperature, introduce a gaseous raw material (transition metal halide salt, and / or halogen gas) into the high-temperature furnace. After maintaining the temperature for a predetermined time, introduce an inert gas and naturally cool to room temperature, and then take out the solid product; the way of introducing the gaseous raw material can be to introduce it onto the surface of the molten mixture or into the interior of the molten mixture to form a bubble-like gas-liquid interface inside the molten mixture;

[0057] S13: Collect the product; optional collection methods include one or more of the following methods: blowing off the floating matter on the surface of the molten mixture; or, collecting the product on the surface of the solid product after the molten mixture cools and solidifies; or, washing with water to remove the medium salt in the solid product and then drying to obtain the target product; or, heating the product in an inert gas to vaporize and discharge the transition metal halide salt.

[0058] In the above step S12, the predetermined reaction temperature refers to the temperature at which the reaction can occur, which varies depending on the type of MXene synthesized. Preferably, the predetermined reaction temperature ranges from 300°C to 1500°C, and the holding time preferably ranges from 1 minute to 12 hours; more preferably, the predetermined reaction temperature ranges from 600°C to 850°C, and the holding time preferably ranges from 10 minutes to 1 hour; that is, the molten salt vapor phase method of the present invention can achieve the vapor phase growth of MXene at a relatively low temperature and in an open system, reducing the energy consumption and process difficulty of MXene vapor phase growth.

[0059] In a specific implementation, the type of the medium salt is preferably a salt that can form a molten state when the temperature is lower than the predetermined reaction temperature, that is, during the heating process to the predetermined reaction temperature, the medium salt has melted.

[0060] Example 1

[0061] This example provides a method for growing MXene Ti2C containing chlorine (Cl) functional groups y N 1-y T x (or written as: Ti2C y N 1-y Cl x , 0 < x ≤ 2, 0 < y < 1), wherein the transition metal elemental powder is titanium powder (Ti powder) and titanium tetrachloride (TiCl4); the carbon and nitrogen source (CN source) is carbon nitride (C3N4); the medium salt is a mixture of sodium chloride (NaCl) and potassium chloride (KCl) (molar ratio n NaCl :n KCl = 0.506:0.494). The specific preparation steps include:

[0062] 1) After uniformly mixing Ti powder and C3N4 according to a molar ratio of 12:1, the mixture is uniformly mixed with the medium salt at a mass ratio of 1:1 to obtain a reactant, which is placed in a tubular furnace;

[0063] 2) Place 5 mL of TiCl4 in the upstream temperature zone of the reactant, and introduce argon into the tubular furnace;

[0064] 3) Heat the inside of the tubular furnace to the reaction temperature of 700 degrees at a rate of 10°C / min, and the mixture changes from a solid powder to a molten reactant; set the heating temperature of the upstream temperature zone where TiCl4 is placed to 100°C, and TiCl4 changes to a gas state. Then introduce argon into the tubular furnace, and the gaseous TiCl4 enters the tubular furnace under the action of the gas flow and contacts the molten reactant to form a gas-liquid interface. Hold for 30 minutes at 700°C to carry out the gas phase growth reaction;

[0065] 4) After the reaction is completed, wait for the reaction device to cool naturally to room temperature, and collect the fluff on the surface of the solid product to obtain the target product.

[0066] The target product was analyzed by X-ray diffraction (XRD), and the results are as Figure 1 shown. A strong diffraction peak appeared at 10 degrees in the XRD pattern of the target product, corresponding to the diffraction peak of the (002) crystal plane of MXene Ti2C y N 1-y T x . The angle of the (002) peak of the reported MAX phase Ti2AlC 1 / 2 N 1 / 2 is 13 degrees, which is lower than that of the (002) peak of the reported MAX phase Ti2AlC. This indicates that the MXene grown from the Ti source (titanium powder and TiCl4) and C3N4 has an expanded structure and a larger interlayer spacing, indicating the successful preparation of MXene Ti2C y N 1-y T x . The target product was tested by scanning electron microscopy (SEM) respectively, and the results are as Figure 2 shown. MXene Ti2C y N 1-y T x has an expanded layered structure, similar to the reported morphology of MXene, which is consistent with the XRD analysis results. In addition, products with a tubular morphology also appeared in the SEM characterization ( Figure 3 ), which may be related to the slow decomposition of C3N4 to produce gas at high temperature.

[0067] The target product was tested by TEM, and the results are as Figure 4 shown in a. By comparison, it can be seen that MXene Ti2C y N 1-y Cl x can be simply exfoliated to obtain two-dimensional nanosheets. Figure 4 b is the HRTEM image and its diffraction spots obtained by FFT. It can be seen that the product has a hexagonal crystal structure, which is consistent with the reported structure of MXene and is consistent with the XRD and SEM analysis results.

[0068] It can be seen that the present invention also provides a technical solution for preparing tubular MXene, that is, using transition metal elemental powder, transition metal halide, and C3N4 as raw materials in a molten medium salt environment, a technical solution for preparing tubular MXene can be obtained.

[0069] Example 2

[0070] This example is similar to Example 1, except that in step 1, the ratio of the Ti powder and C3N4 mixture to the medium salt was adjusted, and the mixture was mixed evenly with the medium salt in a mass ratio of 2:1 and reacted under the same conditions to collect the target product.

[0071] XRD analysis was performed on the target product, and the results are as follows Figure 5 shown. Similar to Example 1, a strong diffraction peak appeared at 10 degrees in the XRD pattern of the target product, corresponding to the diffraction peak of the (002) crystal plane of MXene Ti2C y N 1-y T x , which is lower than the angle (13 degrees) of the (002) peak of the reported MAX phase Ti2AlC 1 / 2 N 1 / 2 . This indicates that the MXene grown from the Ti source (titanium powder and TiCl4) and C3N4 has an expanded structure and a larger interlayer spacing, demonstrating the successful preparation of MXene Ti2C y N 1-y T x . It can also be seen from the SEM photos that there are expanded layered structures ( Figure 6 a) and hollow tubular structures ( Figure 6 b) in the product.

[0072] In this example, the content of the medium salt was reduced. It can be seen from the XRD pattern that the miscellaneous peaks of the product are fewer than those in Example 1 Figure 1 , indicating that there are relatively fewer impurities in the product. This is related to the more sufficient contact between the reactants (transition metal elemental particles and X source) after the reduction of the medium salt. Therefore, it is preferred that the mass ratio of the mixture (transition metal element and X source) to the medium salt is ≥1, and more preferably ≥2.

[0073] Example 3

[0074] This example provides a method for growing MXene Ti3C2T containing chlorine (Cl) functional groups ( x (or written as: Ti3C2Cl x , 0 < x ≤ 2)) by the molten salt vapor phase method. In this example, carbon nanotubes (CNTs) were used as the carbon source, similar to Example 1. The difference is that in step 1, C3N4 was replaced by CNTs. After Ti powder and CNTs were uniformly mixed at a molar ratio of 3:2, they were uniformly ground with the medium salt at a mass ratio of 1:1 and placed in a tubular furnace; under the same reaction conditions, the reaction was carried out under the same conditions, and the target product was collected.

[0075] XRD analysis was performed on the target product, and the results are as follows Figure 7 shown. A strong diffraction peak appeared at 8.2 degrees in the XRD pattern of the target product, corresponding to MXene Ti3C2T xThe diffraction peak of the (002) crystal plane is lower than the angle (9.5 degrees) of the (002) peak of the reported MAX phase Ti3AlC2, indicating that the MXene grown from the Ti source (titanium powder and TiCl4) and CNTs has an expanded structure and a larger interlayer spacing, suggesting the successful preparation of MXeneTi3C2T x In particular, from the XRD pattern of the product, it can also be seen that there are no characteristic peaks of CNTs and transition metal elements. Other characteristic peaks correspond to the by-product titanium carbide, indicating that both CNTs and transition metal elements participated in the reaction. From the SEM photograph ( Figure 8 ), it can be seen that the product retains the one-dimensional morphology of CNTs, which is related to the fact that CNTs provide a template for chemical vapor deposition. It can be seen that the present invention also provides a technical solution for preparing one-dimensional MXene, that is, a technical solution capable of preparing one-dimensional MXene by using transition metal elemental powder, transition metal halide, and one-dimensional carbon material as raw materials in a molten medium salt environment.

[0076] Example 4

[0077] This example is similar to Example 3, except that CNTs are replaced by expanded graphite. After uniformly mixing titanium powder and expanded graphite in a molar ratio of 2:1, they are uniformly ground with the medium salt in a mass ratio of 1:1 and placed in a tube furnace; under the same reaction conditions, the reaction is carried out under the same conditions, and the target product is collected.

[0078] XRD analysis was performed on the target product, and the results are as Figure 9 shown. A strong diffraction peak appears at 10.2 degrees in the XRD pattern of the target product, corresponding to the diffraction peak of the (002) crystal plane of MXene Ti2CT x which is lower than the angle (13 degrees) of the (002) peak of the reported MAX phase Ti3AlC2, indicating that the MXene grown from the Ti source (titanium powder and TiCl4) and expanded graphite has an expanded structure and a larger interlayer spacing, suggesting the successful preparation of MXene Ti2CT x From the SEM photograph ( Figure 10 ), it can be seen that the product retains the morphology of expanded graphite, which is related to the fact that expanded graphite provides a template for chemical vapor deposition.

[0079] Example 5

[0080] This example is similar to Example 3, except that CNTs are replaced by graphene. After uniformly mixing titanium powder and graphene in a molar ratio of 2:1, the reaction is carried out under the same reaction conditions, and the target product is collected.

[0081] XRD analysis was performed on the target product, and the results are as Figure 11As shown, a strong diffraction peak appears at 10.1 degrees in the XRD pattern of the target product, corresponding to the diffraction peak of the (002) crystal plane of MXene Ti2CT x The diffraction peak of the (002) peak of MAX phase Ti2AlC reported is at an angle of 13 degrees. This indicates that the MXene grown from Ti sources (titanium powder and TiCl4) and graphene has an expanded structure and a larger interlayer spacing, demonstrating the successful preparation of MXene Ti2CT x From the SEM images ( Figure 12 ), it can be seen that the product retains the morphology of the ultrathin two-dimensional sheets of graphene, which is related to the fact that graphene provides a template for chemical vapor deposition.

[0082] Comparative Example 1

[0083] This comparative example uses a method similar to that of Example 1, except that no medium salt is used. Instead, the transition metal elemental powder is directly mixed with X source C3N4 and then reacted with TiCl4 under the same conditions. The target product is collected to verify the role of the medium salt in this reaction.

[0084] XRD analysis was performed on the target product, and the results are as Figure 13 shown. In the XRD pattern of the target product, almost no diffraction peaks of the (002) crystal plane of MXene appear, and only the diffraction peaks of the raw material Ti powder and the by-product titanium carbide are present. This indicates that in the absence of the medium salt, the reaction is difficult to occur at 700 degrees. It shows that the medium salt plays a role in increasing the reaction activity of the reactants, enabling the reaction to occur at a lower temperature.

[0085] The applicant also prepared a series of MXene materials by using a method similar to that of Example 1 and changing the reaction raw materials and conditions, as shown in the following table:

[0086]

[0087]

[0088]

[0089] The foregoing description of the specific exemplary embodiments of the present invention is for purposes of illustration and exemplification. These descriptions are not intended to limit the invention to the precise forms disclosed, and it is obvious that many changes and variations are possible in light of the above teachings. The purpose of selecting and describing the exemplary embodiments is to explain the specific principles of the present invention and its practical applications, so that those skilled in the art can implement and utilize various different exemplary embodiments of the present invention, as well as various different selections and changes. The scope of the present invention is intended to be defined by the claims and their equivalents.

Claims

1. A method for growing MXene materials by molten salt method, characterized in that, The method includes: Mixing a transition metal elemental powder, an X-source powder, and a medium salt, heating to melt the medium salt to form a molten mixture; at a predetermined reaction temperature, reacting the molten mixture with a gaseous raw material to obtain a MXene material; the gaseous raw material includes: a transition metal halide salt; and / or, a halogen gas; The X-source powder is one or more of a carbon source, a carbon-nitrogen source, and a nitrogen source; the carbon source is selected from carbon materials; the carbon-nitrogen source is selected from: carbon nitride, melamine, dicyandiamide, urea; the nitrogen source is boron nitride; the medium salt is selected from: halide salts of alkali metals and / or halide salts of alkaline earth metals; The carbon material is selected from one or more of graphite, graphene, carbon nanotubes, carbon nanofibers, and carbon nanobelts.

2. The method for growing MXene materials by the molten salt method according to claim 1, characterized in that, The graphite is selected from expanded graphite.

3. The method for growing MXene materials by the molten salt method according to claim 1, characterized in that, The chemical formula of the MXene material is M n+1 X n T x , where M represents a transition metal element; X represents carbon and / or nitrogen, and T represents a surface functional group including one or more of F, Cl, Br, and I, and 1 ≤ n ≤ 4.

4. The method for growing MXene materials by the molten salt method according to claim 3, characterized in that, The M is selected from one or more of Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W, Y, and Sc.

5. The method for growing MXene materials by the molten salt method according to claim 1, characterized in that, The medium salt is selected from one or several of sodium chloride, potassium chloride, and lithium chloride; and / or, the transition metal halide salt is selected from one or more of transition metal chlorides, transition metal bromides, transition metal iodides, and transition metal fluorides.

6. The method for growing MXene materials by molten salt method according to claim 1, characterized in that, The predetermined reaction temperature is between 300°C and 1500°C; and / or, the time of the predetermined reaction is between 1 min and 12 h.

7. The method for growing MXene materials by molten salt method according to claim 6, characterized in that, The predetermined reaction is between 500°C and 900°C.

8. The method for growing MXene materials by molten salt method according to claim 6, characterized in that, The predetermined reaction is between 600°C and 800°C.

9. The method for growing MXene materials by the molten salt method according to claim 1, wherein The MXene material has one or more of an expanded morphology, a hollow tubular morphology, and a one-dimensional morphology.

10. The method for growing MXene materials by the molten salt method according to claim 1, wherein, The mass ratio of the mixture of the transition metal elemental powder and the X-source powder to the medium salt is ≥1.

11. The method for growing MXene materials by the molten salt method according to claim 1, characterized in that, The mass ratio of the mixture of the transition metal elemental powder and the X-source powder to the medium salt is ≥2.

12. The method for growing MXene materials by molten salt method according to any one of claims 1 to 11, characterized in that, The preparation method further includes a purification step: washing with water to remove the medium salt, and drying to obtain the MXene material; and / or, the preparation method further includes: a heating step of heating the transition metal halide salt to convert it into a gas state; and / or, the preparation method further includes a step of introducing the gaseous raw material into the molten mixture to form bubbles.

13. The method for growing MXene materials by molten salt method according to any one of claims 1 to 11, characterized in that, The preparation method further includes a blowing-off step. At a predetermined sintering temperature, introducing an inert gas into a tubular furnace to blow off the floating matter on the surface of the molten mixture.

14. A MXene material prepared by the method according to any one of claims 1 to 13.

15. An application of the MXene material according to claim 14 in catalysis, sensors, electronic devices, supercapacitors, batteries, electromagnetic shielding, microwave absorbing materials, corrosion-resistant materials, or superconducting materials.

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