Methods, systems, and uses of growing MXene materials by vapor phase method

Abstract

The application discloses a method, system and use for growing MXene material by a gas phase method, and steps of the method include: mixing transition metal element powder with 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 material; the gaseous raw materials include: transition metal halide salt and X source; and / or, X source and halogen gas; the X source is a carbon source and / or a nitrogen source; the carbon source is selected from at least one of a hydrogen compound of carbon, a hydrogen halide of carbon and a halide of carbon; the nitrogen source is selected from at least one of nitrogen and a hydrogen compound of nitrogen, and preferably, the medium salt is selected from halide salt of alkali metal and / or halide salt of alkaline earth metal. The method of the application is to grow MXene at a gas-liquid phase interface in an open system, can realize continuous preparation, and / or conveniently adjust the functional group of MXene, and further provides a new technical path for efficient preparation of MXene material.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of new materials, and in particular relates to a method, system and use of growing MXene materials by a vapor phase method. BACKGROUND

[0002] Two-dimensional transition metal carbides, nitrides or carbonitrides, due to their similar two-dimensional structure to graphene, are also named as MXene, and the thickness of a single-layer MXene layer is about 1 nm, while their lateral size can reach tens of microns or more. Such unique structure and surface properties make MXene exhibit unique electrical properties, optical properties, thermal stability and other excellent properties, and have potential application prospects in the fields of energy storage, catalysis, adsorption and the like.

[0003] At present, the most classic and commonly used method for preparing MXene two-dimensional materials is a hydrofluoric acid (HF) etching method. The MAX phase material is used as a raw material, and the A component is etched away by HF to obtain two-dimensional MXene material. The MAX phase material is a layered ceramic material, M refers to a transition metal element including Sc, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta and the like; A mainly refers to elements of the third and fourth main groups, such as Al, Ga, In, Tl, Si, Ge, Sn, Pb and the like; X represents C or N; and n = 1, 2 or 3. The MAX phase material is a large category of materials, and the types of materials contained are described 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, Ti3AlC2 is immersed in a hydrofluoric acid solution (concentration 50%) for 2 h, so that 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 replaced HF with a hydrochloric acid solution + fluoride salt as an etchant to prepare MXene (Ghidiu M, Lukatskaya M R, Zhao M Q, et al. Nature, 2014, 516(7529): 78.). Similar methods are used to prepare Ti2C, Ta4C3, Ti3CN, V4C3 and other MXene two-dimensional materials.

[0005] However, this method of preparing MXene requires the direct or indirect use of highly corrosive and highly toxic HF acid, and the safety of the preparation process is difficult to guarantee. In addition, since it is a liquid phase reaction, the generated MXene is dispersed in a high concentration of acid, and the MXene powder product needs to be repeatedly cleaned, ultrasonic, centrifugal separation, drying and other steps. The complex process makes it difficult to mass-produce MXene, and the high preparation cost seriously limits the application prospect 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 a patent application (application number 202011466046.4). The precursor MAX phase material is etched by using halogen hydride and metal halide in the gas phase, which can macroscopically synthesize high-quality MXene material and avoid the steps of removing solvent and impurities in the liquid phase etching method, thereby simplifying the production process of MXene material.

[0007] However, whether based on the liquid phase etching method or the gas phase etching method, the preparation of MXene material is all based on the precursor MAX phase material as the precursor, and after etching the A layer, the accordion-shaped MXene is obtained. It is inevitable to obtain two-dimensional MXene material by stripping step, and the accordion-shaped MXene material is obtained by mechanical stripping method such as ultrasonic.

[0008] Di Wang, et al. disclosed a method for preparing MXene by gas phase growth (Science. 379, 1242-1247 (2023).). In this preparation method, MXene balls are grown on the surface of a metal titanium foil by sealing the metal titanium foil, carbon source gas and titanium chloride at a high temperature of 950℃ (closed system), and MXene two-dimensional material is obtained after stripping. This article first proposed that MXene can be synthesized by chemical vapor deposition (CVD) method, but the CVD method must be sintered at a high temperature (≥950℃) in a closed system, which has the problems of high energy consumption and low efficiency, and is difficult to be applied practically. SUMMARY

[0009] The purpose of the present application is to propose another method for preparing MXene material by gas phase growth without precursor material MAX phase. Compared with the prior art, the method of the present application is an open system, in which a molten medium salt is introduced, and the gaseous raw material is subjected to gas phase growth reaction between the gas-liquid interface to obtain MXene material.

[0010] The first aspect of the present application provides a method for growing MXene material by vapor phase method, comprising the following steps: mixing transition metal elemental powder with medium salt, heating to melt the medium salt to form a molten mixture; reacting the molten mixture with gaseous raw material at a predetermined reaction temperature to obtain MXene material; the gaseous raw material comprises: transition metal halide salt and X source; and / or, X source and halogen gas; the X source is a carbon source and / or a nitrogen source; the carbon source is selected from at least one of a carbon hydride, a carbon hydrohalide, and a carbon halide; the nitrogen source is selected from at least one of nitrogen gas and a nitrogen hydride.

[0011] In some embodiments, the medium salt is selected from alkali metal halide and / or alkaline earth metal halide.

[0012] In some embodiments, the carbon hydride in the above-mentioned carbon source is selected from one or more of methane, acetylene, propane, benzene, toluene, and petroleum gas; the carbon hydrohalide is selected from one or more of monochloromethane, dichloromethane, trichloromethane, monobromomethane, dibromomethane, and tribromomethane; and the carbon halide is selected from CCl4.

[0013] In some embodiments, the nitrogen hydride in the above-mentioned nitrogen source is selected from ammonia gas and hydrazine (N2H4).

[0014] In some embodiments, the halogen gas is selected from one or more of Cl2, Br2, and I2.

[0015] In some embodiments, the chemical formula of the above-mentioned MXene material is MXnT4-n n+1 X n T x , M represents a transition metal element; X represents carbon and / or nitrogen, T represents a surface functional group, which includes one or more of F, Cl, Br, and I, 1≤n≤4, and x is an uncertain number in the chemical formula. In the art, T x is generally used to represent that the surface of the MXene material contains functional groups, and theoretical calculations show that 0

[0016] In some embodiments, M in the above-mentioned chemical formula is selected from one or more of Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W, Y, and Sc.

[0017] In some embodiments, the medium salt is selected from one or more of sodium halide, potassium halide, lithium halide, magnesium halide, and calcium halide; preferably, the medium salt is selected from one or more of sodium chloride, potassium chloride, lithium chloride, magnesium chloride, and calcium chloride.

[0018] In some embodiments, the transition metal halide salt is selected from one or more of transition metal chloride, transition metal bromide, transition metal iodide, and transition metal fluoride.

[0019] In some embodiments, the predetermined reaction temperature is between 300°C and 1500°C; preferably, between 500°C and 900°C; more preferably, between 600°C and 800°C.

[0020] In some embodiments, the predetermined reaction time is between 1 min and 12 h.

[0021] In some embodiments, the mass ratio of the transition metal elemental powder to the medium salt is between 1:(0.1-5); preferably, between 1:(0.5-3); more preferably, between 1:(1-3).

[0022] In some embodiments, the method further comprises a purification step: washing with water to remove the medium salt, and drying to obtain the MXene material.

[0023] In some embodiments, the method further comprises a heating step: heating the transition metal halide salt and / or the X source to convert into a gaseous state to remove the metal salt therein.

[0024] In some embodiments, the method further comprises a stripping step: introducing a gas at a predetermined temperature to strip the product on the surface of the liquid phase.

[0025] In some embodiments, the method further comprises a step of introducing one or more of the gaseous raw materials into the molten mixture to form bubbles.

[0026] The second aspect of the present application provides a MXene material prepared by the above method.

[0027] The third aspect of the present application provides a system for preparing the MXene material by the above method, comprising: a heating device, a gas supply device, and an open container, wherein the open container is fixedly or detachably arranged in the heating zone of the heating device; the gas supply device is used to supply one or more of the protective gas, the X source gas, the halogen gas, and the transition metal halide salt gas to the heating device.

[0028] In some embodiments, the gas supply device is in communication with the open container through a connecting pipeline; preferably, the gas outlet of the connecting pipeline is arranged inside the open container; more preferably, arranged at the bottom of the open container.

[0029] In some embodiments, the gas supply device comprises a mixing device for mixing at least two of the protective gas, the halogen gas, the X source gas and the transition metal halide salt gas before being introduced into the heating device.

[0030] The fourth aspect of the present application provides another system for preparing MXene material by the above method, comprising: a heating device, a gas supply device and an open container; the heating device comprises a first heating temperature zone and a second heating temperature zone, the first heating temperature zone is used for placing a transition metal halide salt; the open container is fixedly or detachably arranged in the second heating temperature zone; the gas supply device is used for supplying one or more of a protective gas, an X source gas and a halogen gas to the heating device in batches or batches, and the gas supplied by the gas supply device sequentially passes through the first heating temperature zone and the second heating temperature zone.

[0031] In some embodiments, the system further comprises a stripping device for stripping the generated MXene material; preferably, the stripping device comprises at least one air jet port arranged at the opening of the open container.

[0032] In some embodiments, the system further comprises a collection device for collecting the generated MXene material.

[0033] The fifth aspect of the present application provides an application of the MXene material prepared by the above method in catalysis, sensors, electronic devices, supercapacitors, batteries, electromagnetic shielding, wave-absorbing materials, corrosion-resistant materials or superconducting materials.

[0034] Since the method of the present application is in an open system, MXene grows at the gas-liquid interface, and based on the present application, continuous preparation can be realized, and / or MXene functional group adjustment can be conveniently performed, thereby providing a new technical path for efficient preparation of MXene material. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 The XRD spectrum of the target product MXene Ti2CT x in Example 1 of the present application.

[0036] Figure 2 The SEM photo of the target product MXene Ti2CT x in Example 1 of the present application.

[0037] Figure 3 The (a) SEM photo, (b) Ti element, (c) C element and (d) Cl element distribution diagram of the target product MXene Ti2CT x in Example 1 of the present application.

[0038] Figure 4 XRD pattern of the target product MXene Ti2CT in Example 1 of the present application x (a) TEM image; (b) HRTEM and FFT image of the target product MXene Ti2CT in Example 1 of the present application.

[0039] Figure 5 XRD pattern of the target product MXene Ti2CT in Example 2 of the present application under different reaction temperatures (a) 500℃ (b) 600℃ (c) 650℃ (d) 750℃ (e) 800℃ (f) 900℃. x

[0040] Figure 6 XRD pattern of the target product MXene Ti2CT in Example 2 of the present application x

[0041] Figure 7 SEM image of the target product MXene Ti2CT in Example 2 of the present application. x

[0042] Figure 8 (a) SEM image; (b) Ti element, (c) C element and (d) Cl element distribution map of the target product MXene Ti2CT in Example 2 of the present application. x

[0043] Figure 9 (a) TEM image; (b) HRTEM and FFT image of the target product MXene Ti2CT in Example 2 of the present application. x

[0044] Figure 10 XRD pattern of the target product MXene Ti2CT in Example 4 of the present application. x

[0045] Figure 11 SEM image of the target product MXene Ti2CT in Example 4 of the present application. x

[0046] Figure 12 XRD pattern of the target product MXene Ti2NT in Example 5 of the present application. x

[0047] Figure 13 SEM image of the target product MXene Ti2NT in Example 5 of the present application. x

[0048] Figure 14 XRD pattern of the target product MXene Ti2NT in Example 5 of the present application.​​​​​​​​​x (a) TEM photograph; (b) HRTEM and FFT images; (c) elemental distribution maps of Ti, (d) elemental Cl, and (e) elemental N.

[0049] Figure 15 This is a schematic diagram of the preparation system in Embodiment 7 of the present invention.

[0050] Figure 16 This is a schematic diagram of the preparation system in Embodiment 8 of the present invention.

[0051] Explanation of annotations in the attached diagram:

[0052] 100, 200 The preparation system of the present invention;

[0053] 10 Heating device; 11 First heating zone; 12 Second heating zone; 13 Air inlet; 14 Exhaust outlet; 15 Jet pipe; 16 Transition metal halide salt; 17 Collection device;

[0054] 20 Open container; 21 Aeration device;

[0055] 30 Gas supply device; 31 Inert gas supply device; 32 X source gas supply device; 33 Mixing device; 34 Transition metal halide gasification device. Detailed Implementation

[0056] The technical solution of the present invention is illustrated below through specific embodiments. It should be understood that the one or more steps mentioned in the present invention do not preclude the existence of other methods and steps before or after the combined steps, or that other methods and steps may be inserted between these explicitly mentioned steps. It should also be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Unless otherwise stated, the numbering of each method step is only for the purpose of identifying each method step, and not for limiting the order of each method or limiting the scope of the present invention. Changes or adjustments to their relative relationships, without substantial changes to the technical content, can also be considered as within the scope of the present invention.

[0057] The raw materials and instruments used in the examples are not subject to any specific restrictions on their source; they can be purchased from the market or prepared according to conventional methods known to those skilled in the art.

[0058] This invention provides a method for growing MXene using a vapor 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, I; 1n4, 0x2. 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 application; the carbon source and / or nitrogen source are also referred to as X source in the present application.

[0059] The technical concept of the present application is that the transition metal elemental powder is dispersed in the molten medium salt to obtain a molten mixture, and gaseous raw materials (including transition metal halide salt and X source) are introduced into the molten mixture (inside or on the liquid surface), and the MXene material is formed by deposition and growth at the interface between the liquid phase and the gas phase of the molten mixture.

[0060] Since the transition metal element can react with halogen gas to generate transition metal halide salt at high temperature, in some embodiments, the gaseous raw materials introduced into the molten mixture can also be gaseous X source and / or halogen gas.

[0061] The medium salt serves to provide an interface in the liquid phase and does not participate in the gas phase deposition reaction and growth itself. Therefore, the medium salt is preferably a halide salt of an alkali metal and / or a halide salt of an alkaline earth metal, such as sodium halide, lithium halide, potassium halide, magnesium halide, calcium halide, etc., which has a low melting point and is easy to dissolve in water (conducive to water washing to remove impurities), and in some embodiments, the medium salt is selected from one or more of sodium chloride, potassium chloride, lithium chloride, magnesium chloride, calcium chloride.

[0062] In one embodiment, the present application provides a method for growing MXene by a gas phase method, wherein the X source is a component part of the gaseous raw material, and the steps include:

[0063] S01: mixing the transition metal elemental powder with the medium salt, heating to melt the medium salt to form a molten mixture;

[0064] S02: introducing gaseous raw materials into the interior and / or above the liquid surface of the molten mixture at a predetermined reaction temperature to grow MXene material; wherein the gaseous raw materials include: transition metal halide salt and X source; and / or, X source and halogen gas. The transition metal halide salt and X source in the introduced gaseous raw materials are deposited and grown on the gas-liquid interface of the molten mixture to form MXene material.

[0065] In some embodiments, the transition metal elemental powder is selected from Sc, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta elemental powder, the transition metal halide salt is selected from at least one of chloride, bromide, iodide of Sc, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta; the X source can be a carbon source and / or a nitrogen source, the carbon source is selected from at least one of a hydride of carbon, a hydrohalide of carbon, a halide of carbon; in some embodiments, the hydride of carbon is selected from one or more of methane, ethyne, propane, benzene, toluene, petroleum gas; the hydrohalide of carbon is selected from one or more of monochloromethane, dichloromethane, trichloromethane, monobromomethane, dibromomethane, tribromomethane, monoiodomethane, diiodomethane, triiodomethane; the halide of carbon is selected from CCl4; the nitrogen source is selected from at least one of nitrogen gas, a hydride of nitrogen, in some embodiments, the hydride of nitrogen is selected from ammonia (NH3) and / or hydrazine (N2H4).

[0066] More specific steps include:

[0067] S011: mixing the transition metal elemental powder and the medium salt in a certain proportion, placing in a high-temperature furnace, heating to a molten state under the protection of inert gas, forming a molten mixture, and dispersing the transition metal elemental powder in the molten medium salt; in the gas phase growth reaction, the transition metal elemental powder particles at the gas-liquid interface act as nucleation sites for MXene growth;

[0068] S012: at a predetermined reaction temperature, gaseous raw materials (transition metal halide salt and X source, and / or X source and halogen gas) are introduced into the high-temperature furnace, and after a predetermined holding time, the solid product is taken out after natural cooling to room temperature under inert gas; the gaseous raw materials can be introduced into the surface of the molten mixture or into the interior of the molten mixture, forming a bubble-shaped gas-liquid interface in the interior of the molten mixture;

[0069] S013: natural cooling to room temperature under a protective gas atmosphere, and collecting the fluffy material on the surface of the solid product; or, after water washing to remove the medium salt in the solid product, drying to obtain the target product.

[0070] The mixing ratio of the transition metal elemental powder and the medium salt in step S011 is preferably a mass ratio of 1:(0.1-5).

[0071] The predetermined reaction temperature in step S012 refers to a temperature capable of reaction, which will vary depending on the type of MXene synthesized, and is preferably between 300°C and 1500°C, and the holding time is preferably between 1 min and 12 h;

[0072] In a specific implementation, the type of medium salt is preferably capable of forming a molten salt at a temperature lower than the predetermined reaction temperature, that is, the medium salt has been molten during heating to the predetermined reaction temperature.

[0073] Example 1

[0074] This example provides a method for growing MXene Ti2CT x (or written as: Ti2CCl x , 0 < x < 2) containing chlorine (Cl) functional groups by a vapor phase method, wherein the transition metal elemental powder is titanium powder (Ti powder) and titanium tetrachloride (TiCl4); the carbon source (C source) is methane gas (CH4); and 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:

[0075] 1) Place the Ti powder and the medium salt in a mixture with a mass ratio of 1:1 in an open container device of a tube furnace, place 5 mL of TiCl4 in the upstream temperature zone of the mixture, and introduce argon into the tube furnace;

[0076] 2) Increase the temperature inside the tube furnace to 700 degrees Celsius at a rate of 10 degrees Celsius per minute, and the mixture changes from a solid powder to a molten mixture;

[0077] 3) Set the heating temperature of the upstream temperature zone where TiCl4 is placed to 100 degrees Celsius, and TiCl4 changes to a gaseous state. Then introduce a mixture of methane and argon (with a methane volume fraction of 10%) into the tube furnace, and the gaseous TiCl4 and methane enter the tube furnace under the action of the gas flow and form a gas-liquid interface contact with the molten mixture. Perform a vapor phase growth reaction at 700 degrees Celsius for 30 minutes;

[0078] 4) After the predetermined time, change the gas introduced into the tube furnace to argon, and take out the solid product after the reaction device naturally cools to room temperature;

[0079] 5) Collect the fluffy material on the surface of the solid product.

[0080] Perform X-ray diffraction (XRD) analysis on the target product, and the results are shown in Figure 1 The XRD pattern of the target product shows a strong diffraction peak at 10.5 degrees, which corresponds to the (002) plane diffraction peak of MXene Ti2CT x , which is lower than the (002) peak angle (13 degrees) of the reported MAX phase Ti2AlC, indicating that the MXene grown by the Ti source (titanium powder and TiCl4) and the C source has an expanded structure and a larger interlayer spacing, indicating that the MXene Ti2CT xthe successful preparation of the target product. As shown in Figure 2 the MXene Ti2CT x has an expanded accordion-like layered structure, which is consistent with the reported morphology of MXene, which is consistent with the XRD analysis result. The MXene Ti2CT x prepared in the example was subjected to liquid phase exfoliation and then subjected to SEM characterization, as shown in Figure 3 a, wherein there are a large number of two-dimensional ultrathin nanosheets, indicating that the accordion-like MXene Ti2CT x can be obtained by simple exfoliation, and the two-dimensional nanosheet has uniform Ti and C element distribution Figure 3 b and c), and the nanosheet also contains Cl element Figure 3 d), indicating that the target product obtained is a MXene material Ti2CT x . The MXene Ti2CT x prepared in the example was subjected to liquid phase exfoliation and then subjected to TEM characterization, as shown in Figure 4 , by comparison, it can be seen that the MXene Ti2CT x can be obtained by simple exfoliation, Figure 4 b is the HRTEM image and the diffraction spot obtained by FFT thereof, and it can be seen that the product has a hexagonal crystal structure, which is consistent with the structure of the reported MXene, which is consistent with the XRD and SEM analysis results. It can be seen that the preparation method of the present application does not need to implement the sealing tube step, and realizes the growth of MXene in an open system, simplifying the steps of preparing MXene by gas phase method.

[0081] In order to illustrate the influence of sintering temperature on the gas phase growth of MXene in the open system of the present application, under the same conditions, but changing the sintering temperature to 500℃, 600℃, 650℃, 750℃, 800℃, 900℃, the obtained product was characterized by XRD, as shown in Figure 5 , the XRD pattern appears the (002) characteristic peak of MXene Ti2CCl x , indicating that the growth of MXene can be realized at a large temperature span (500-900℃) and at a relatively low temperature.

[0082] Example 2

[0083] This example is similar to Example 1, except that the content of the medium salt is changed, more specifically, the Ti powder and the medium salt are mixed in a mass ratio of 2:1 in step 1).

[0084] The target product was subjected to XRD analysis, and the results are as followsFigure 6 As shown, a strong diffraction peak appeared at 10.5 degrees in the XRD pattern of the target product, corresponding to MXeneTi2CT. x The diffraction peak of the (002) crystal plane is lower than the angle (13 degrees) of the reported (002) peak of the MAX phase Ti2AlC, indicating that MXene grown through Ti and C sources has an expanded structure and a larger interlayer spacing, suggesting that MXeneTi2CT x The target product was successfully prepared. SEM analysis was performed on the target product, and the results are as follows: Figure 7 As shown in the comparison, MXeneTi2CT x It exhibits an inflated, accordion-like layered structure, consistent with the reported morphology of MXene and the XRD analysis results. SEM images also show that the accordion-like MXene obtained in this embodiment differs from that in Example 1 (…). Figure 2 The stacking of MXene sheets is more compact than in Example 1. This is because the morphology of the grown MXene can be controlled by adjusting the proportion of the medium salt. When the proportion of the medium salt is high, the medium salt can provide a template for MXene growth after melting, making the prepared MXene more fluffy. When the proportion of the medium salt is low, the amount of growth template provided by the medium salt is reduced, resulting in a certain degree of stacking of the prepared MXene.

[0085] The prepared MXeneTi2CT x After liquid phase stripping, SEM characterization was performed, such as... Figure 8 As shown in Figure a, it contains a large number of two-dimensional ultrathin nanosheets, indicating that the accordion's MXeneTi2CT... x Two-dimensional nanosheets with a uniform distribution of Ti and C elements can be obtained through simple exfoliation. Figure 8 (b and c), and the nanosheet also contains Cl element ( Figure 8 (d) indicates that the target product obtained is an MXene material Ti2CT containing Cl functional groups. x The prepared MXeneTi2CT x After liquid phase exfoliation, TEM characterization was performed, and the results are as follows: Figure 9 As shown in the comparison, MXene Ti2CT x Two-dimensional nanosheets can be obtained through simple exfoliation. Figure 9 Image b shows the HRTEM image and the 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 the results of XRD and SEM analysis.

[0086] Example 3

[0087] In particular, the applicant found that the gas-liquid interface grows MXene material floating on the surface of the molten mixture. Therefore, in this embodiment, the method of the application also includes a stripping step: at a predetermined sintering temperature, an inert gas stream is introduced into the tube furnace, and the gas stream blows off the MXene material floating on the surface of the molten mixture, so as to separate the MXene material from the molten mixture; after the MXene material is blown off, the liquid phase interface of the molten mixture is exposed again, and the MXene material is re-grown at the gas-liquid interface. This cycle can realize the continuous growth and collection of MXene material, improve the efficiency of gas phase growth of MXene, and the obtained MXene product does not need to be purified by solution cleaning, and has the advantage of high purity.

[0088] In the specific implementation steps, similar to embodiment 1, the difference is that: 1) an outlet is arranged near the opening of the container device, the outlet is connected to the argon supply device through a pipeline, and the outlet sprays an argon gas stream towards the liquid phase interface, so that the MXene material floating on the surface is blown off, and the flow rate of the argon gas is set to 50 mL / min to 5 L / min; 2) the reaction temperature is 700 degrees, and the temperature is kept for 12 hours; 3) after the tube furnace is naturally cooled, the MXene material blown off in the tube furnace is collected, and there is no need for a water washing and purification step.

[0089] Embodiment 4

[0090] This embodiment provides another implementation mode of introducing gaseous raw materials into the molten mixture, and the steps include:

[0091] 1) Mix Ti powder and medium salt to form a mixture, and place the mixture in a container device of an opening of a tube furnace, introduce argon into the high-temperature furnace, the container device is provided with an outlet at the bottom, and the outlet is connected to a gas pipeline; the outlet is used to introduce gaseous raw materials into the molten mixture in the container device; in this embodiment, the medium salt is a mixture of sodium chloride (NaCl) and potassium chloride (KCl) (molar ratio n NaCl :n KCl = 0.506:0.494), and the mass ratio of Ti powder to medium salt is 1:3.

[0092] 2) The inside of the high-temperature furnace is heated to a reaction temperature of 700 degrees at a rate of 10 degrees per minute, and the mixture is converted from a solid powder to a molten mixture;

[0093] 3) The heated TiCl4 (5 mL) and the mixed gas of methane / argon (the volume fraction of methane is 10%) are introduced into the bottom of the container device through the above-mentioned gas pipeline, so that the gaseous raw materials are introduced into the molten mixture to form bubbles, and the gas phase growth reaction is carried out at 700 degrees for 120 minutes;

[0094] 4) stop feeding the gaseous raw material, keep the temperature for 10 minutes, then feed argon into the tube furnace, and take out the solid product after the reaction device naturally cools to room temperature;

[0095] 5) collect the fluffy material on the surface of the solid product.

[0096] Feeding the gaseous raw material from the inside of the molten mixture can increase the gas / liquid contact interface, the reaction interface of vapor deposition, improve the vapor deposition growth efficiency, obtain a large amount of MXene material, and realize the macro preparation of MXene material. The applicant also found that during the rising of the bubbles to the liquid surface, the gas-liquid interface grows MXene material which is taken out with the bubbles and finally floats on the surface of the molten mixture. When the reaction is completed, the solid product is taken out and naturally cooled, and the surface of the solid product contains a layer of fluffy material, which is collected as MXene material.

[0097] In other embodiments, the Ti powder and the medium salt are mixed in a mass ratio of 1:(0.1-5); preferably, 1:(0.5-3); more preferably, 1:(1-3). By adjusting the ratio of transition metal elemental powder to medium salt, the morphology of the grown MXene can be controlled. When the ratio of medium salt is high, the medium salt can provide a growth template for MXene after melting, so that the prepared MXene is more fluffy and easier to peel into a sheet.

[0098] In other embodiments, the step further comprises separating the MXene from the molten mixture by adding a gas stream to strip.

[0099] In other embodiments, in order to grow MXene material in large quantities, mechanical stirring can also be added to the molten mixture to increase the contact interface between the liquid and the gas.

[0100] Example 5

[0101] This embodiment provides a method for growing MXene Ti2CT x (or written as Ti2CF x ) containing fluorine (F) functional groups by vapor phase method, wherein the transition metal elemental powder is titanium powder (Ti powder) and titanium tetrafluoride (TiF4); the carbon source (C source) is methane gas (CH4); the medium salt is a mixture of LiCl, NaCl and KCl (n LiCl :n NaCl :n KCl = 0.535:0.086:0.379). The specific preparation steps include:

[0102] 1) Put Ti powder and medium salt in a mixture with a mass ratio of 2:1 into an open container device of a tube furnace, put 1 g of TiF4 in the upstream temperature zone of the mixture, and introduce argon into the tube furnace;

[0103] 2) Increase the temperature inside the tube furnace to 380℃ at a rate of 5℃ / min, and the mixture changes from solid powder to molten mixture;

[0104] 3) Set the heating temperature of the upstream temperature zone where TiF4 is located to 300℃, introduce a mixture of methane and argon (the volume fraction of methane is 10%) into the tube furnace, and gaseous TiF4 and methane enter the tube furnace under the action of gas flow and form a gas-liquid interface contact with the molten mixture, and the gas phase growth reaction is carried out at 380℃ for 30 minutes (min);

[0105] 4) After the holding time is over, change the gas introduced into the tube furnace to argon, and take out the solid product after the reaction device naturally cools to room temperature;

[0106] 5) After the solid product is filtered and washed with water several times, the obtained solid product is freeze-dried to obtain the target product.

[0107] The target product is subjected to XRD analysis, and the results are shown in Figure 10 The XRD spectrum of the target product has strong diffraction peaks at 7.9, 15.9 and 24 degrees, which correspond to the (002), (004) and (006) crystal plane diffraction peaks of MXene Ti2CT x , wherein the position of the (002) crystal plane is lower than the angle (13 degrees) of the reported (002) peak of MAX phase Ti2AlC, which indicates that the MXene grown by the Ti source and the C source has an expanded structure and a larger interlayer spacing, indicating the successful preparation of MXene Ti2CT x . The target product is subjected to SEM test, and the results are shown in Figure 11 By comparison, it can be seen that MXene Ti2CT x has an expanded accordion-like layered structure, which is consistent with the morphology of the reported MXene and is consistent with the XRD analysis results. It is shown that the MXene is synthesized by the gas phase method of the present application.

[0108] Example 6

[0109] This example provides another gas phase method for growing MXene Ti2NT x (or written as: Ti2NCl x, 0 < x ≤ 2), wherein the transition metal element powder is titanium powder (Ti powder) and titanium tetrachloride (TiCl4); the nitrogen source (N source) is nitrogen (N2); the medium salt is a mixture (molar ratio n NaCl : KCl = 0.506:0.494). The specific preparation steps include:

[0110] 1) The Ti powder and the medium salt are mixed in a mass ratio of 1:1 and placed in an open container device of a tube furnace, 5 mL of TiCl4 is placed in the upstream temperature zone of the mixture, and argon is introduced into the tube furnace;

[0111] 2) The inside of the tube furnace is heated to a reaction temperature of 700 degrees at a rate of 10 degrees Celsius per minute, and the mixture is converted from a solid powder to a molten mixture;

[0112] 3) The heating temperature of the upstream temperature zone where TiCl4 is placed is set to 100 degrees Celsius, TiCl4 is converted into a gaseous state, nitrogen is introduced into the tube furnace, gaseous TiCl4 and nitrogen enter the tube furnace under the action of the gas flow, and form a gas-liquid interface contact with the molten mixture, and the gas phase growth reaction is carried out at 700 degrees Celsius for 30 minutes;

[0113] 4) After the predetermined time, the gas introduced into the tube furnace is changed to argon, and the solid product is taken out after the reaction device is naturally cooled to room temperature;

[0114] 5) The solid product is washed with water several times, and the obtained solid product is freeze-dried to obtain the target product.

[0115] The target product is subjected to XRD analysis, and the results are shown in Figure 12 , a strong diffraction peak appears at 10.2 degrees in the XRD spectrum of the target product, which corresponds to the (002) crystal plane diffraction peak of MXene Ti2NT x , which is lower than the (002) peak angle (13 degrees) of the reported MAX phase Ti2AlN, which indicates that the MXene grown by Ti source and N source has an expanded structure and a larger interlayer spacing, indicating the successful preparation of MXene Ti2NT x . The target product is subjected to SEM test, and the results are shown in Figure 13 , it can be seen by comparison that MXene Ti2NT x has an expanded accordion-like layered structure, which is consistent with the morphology of the reported MXene and is consistent with the XRD analysis results. The MXene Ti2NT x prepared is subjected to liquid phase exfoliation and TEM characterization, as shown in Figure 14As shown in FIG. a, there are a large number of two-dimensional ultrathin nanosheets, indicating the accordion-like MXene Ti2NT x The two-dimensional nanosheets can be obtained by simple peeling, Figure 14 FIG. b is an HRTEM image and its diffraction spots obtained by FFT, and it can be seen that the product has a hexagonal crystal structure, which is consistent with the structure of the reported MXene, and is consistent with the analysis results of XRD and SEM. The two-dimensional nanosheets have uniform Ti and N element distribution Figure 14 FIG. c and e), and the nanosheets also contain Cl element Figure 14 FIG. d), indicating that the target product obtained is a MXene material Ti2NT x .

[0116] The applicant also prepared a series of MXene materials by changing the raw materials and conditions using a method similar to that of Example 1, as shown in the following table:

[0117]

[0118]

[0119] As can be seen from the above examples, the method for gas-phase growth of MXene material of the present application does not need to seal and sinter, and can realize the growth of MXene material on the gas-liquid interface at a relatively low temperature (500-900°C) in an open system. The open synthesis system not only greatly simplifies the preparation process of gas-phase growth of MXene material, but also enables continuous production of MXene material, and more easily realizes further regulation of the surface functional groups of MXene; the relatively low synthesis temperature can reduce the energy consumption of gas-phase growth of MXene, reduce the cost of MXene material, and be more conducive to industrialized production. Surprisingly, the MXene material obtained by the method of the present application has an accordion-like structure, and the interlayer spacing of the accordion-like structure can be regulated by the content of the medium salt to obtain accordion-like MXene materials with different interlayer spacings. By controlling the content of the medium salt and further controlling the size of the interlayer spacing, accordion-like MXene materials with larger interlayer spacings can be synthesized, which are more convenient for peeling to form two-dimensional MXene nanosheets.

[0120] Example 7

[0121] The present embodiment provides a preparation system 100 for gas-phase growth of MXene, as shown in FIG. Figure 15 , comprising a heating device 10, an open container 20, and a gas supply device 30;

[0122] The gas supply device 30 is directly or indirectly communicated with the heating device 10 through a pipeline, for supplying reaction gas and / or protective gas (inert gas, such as argon) into the heating device 10; the heating device 10 is provided with a heating temperature zone, and the open container is fixedly or detachably placed in the heating temperature zone; the open container 20 is used for placing transition metal elemental powder and medium salt;

[0123] In the embodiment, two heating temperature zones are arranged in the heating device 10, which are a first heating temperature zone 11 and a second heating temperature zone 12; the first heating temperature zone 11 is close to the gas inlet 13 in the heating device 10, and the gas in the gas supply device 30 first passes through the first heating temperature zone 11 and then enters the second heating temperature zone 12, that is, according to the flow direction of the gas flow, the second heating temperature zone 12 is arranged downstream of the first heating temperature zone 11; the open container 20 is arranged in the second heating temperature zone 12.

[0124] In a specific embodiment, the first heating temperature zone 11 is used for placing transition metal halide salt 16, the open container 20 in the second heating temperature zone 12 is used for placing transition metal elemental powder and medium salt, the gas supply device 30 includes inert gas supply device 31, X source gas supply device 32 and mixing device 33, and the inert gas supply device 31 and the X source gas supply device 32 are a gas storage tank in the embodiment; the X source gas can be directly supplied into the heating device 10 through a pipeline, or the X source gas and the inert gas first enter the mixing device 33 to form mixed gas and then enter the heating device 10. The protective gas (inert gas argon) is first supplied into the heating device 10 through the gas supply device 30 to remove the air in the heating device 10, then the first heating temperature zone 11 and the second heating temperature zone 12 are respectively heated to a predetermined temperature, and the X source gas is supplied into the heating device 10; the transition metal halide salt is converted into a gas phase in the first heating temperature zone and moves to the second heating temperature zone 12 together with the X source gas along the flow of the gas flow; the medium salt is heated and melted into a liquid phase in the second heating temperature zone 12, and forms a liquid phase mixture with the transition metal elemental powder; the gas phase mixture (including the X source and the transition metal halide salt) grows on the interface of the liquid phase mixture to obtain MXene phase material, and the excess gas can be discharged through the exhaust port 14 for recycling or recycling. After the gas phase growth is completed, the input of the gas phase mixture is stopped, the protective gas is supplied into the heating device 10, and after natural cooling, the liquid phase mixture is cooled and solidified, and the MXene material is collected.

[0125] In another specific embodiment, in order to remove the air in the heating device, the vacuum treatment can be performed first.

[0126] In another preferred embodiment, the preparation system of the present application further comprises a blowing device for blowing off the MXene material grown on the surface of the liquid phase, so as to expose the surface of the liquid phase mixture to the gas phase mixture again, and grow the MXene material on the surface of the liquid phase mixture again, so as to realize the continuous growth of the MXene phase. In this embodiment, the blowing device is at least one gas injection pipeline 15, which is arranged at the opening of the open container and continuously or intermittently injects gas along the gas flow, so that the MXene material grown on the surface of the liquid phase mixture is blown off.

[0127] In another preferred embodiment, the preparation system of the present application further comprises a collecting device 17 for collecting the blown-off MXene material.

[0128] In this embodiment, two heating temperature zones are arranged in the heating device, wherein the first heating temperature zone 11 is used for heating the transition metal halide salt to form a gas phase, and the second heating temperature zone 12 is a gas phase growth MXene reaction heating temperature zone. Since the temperature for heating the transition metal halide salt to form a gas phase (50-500°C) is lower than the temperature for the gas phase reaction (500-900°C), in some embodiments, the second heating temperature zone 12 is turned on, and the transition metal halide salt placed in the first heating temperature zone 11 can be gasified by the residual heat or less auxiliary heating generated by the second heating temperature zone 12, so as to realize the comprehensive utilization of heat and further reduce energy consumption.

[0129] In some embodiments, the heating device can be a tube furnace, a box furnace or the like.

[0130] Embodiment 8

[0131] This embodiment provides another system for growing MXene in a gas phase, as shown in Figure 16 The system comprises a heating device 10, an open container 20 and a gas supply device 30. The open container 20 is arranged in a heating temperature zone in the heating device 10, and the gas supply device 30 comprises an inert gas supply device 31, an X source gas supply device 32, a mixing device 33 and a transition metal halide gasification device 34. The mixing device 33 mixes the protective gas, the X source gas and the transition metal halide gas, and then connects the mixed gas to the open container 20 through a pipeline, and the gas outlet is arranged at the bottom of the open container 20, so that the mixed gas is blown out in the form of bubbles in the liquid phase mixture, forms a gas-liquid interface, and grows MXene material at the gas-liquid interface. In this embodiment, the bottom of the open container 20 is further provided with an aeration device 21 for uniformizing and dispersing the mixed gas.

[0132] In the specific embodiment, first, the inert gas supply device 31 is used to introduce the protective gas (argon) into the heating device 10 through the pipeline to discharge the air in the heating device; then the heating temperature zone in the heating device 10 is turned on to melt the transition metal powder and the medium salt in the open container 20 to form a liquid phase mixture; then the mixed gas in the mixing device is delivered to the open container 20 through the pipeline to form bubbles in the liquid phase mixture, and the generated MXene material floats on the surface of the liquid phase mixture. After the gas phase growth is completed, the input of the mixed gas is turned off, the protective gas is introduced into the heating device, and after natural cooling, the liquid phase mixture is cooled and solidified, and the fluffy material on the surface is the MXene material.

[0133] In the present embodiment, the transition metal halide salt gasification device 34 can also be replaced by a halogen gas supply device.

[0134] In another embodiment, the present embodiment can also include a stripping device and / or a collection device to strip and collect the MXene material on the surface of the liquid phase mixture. To exclude the air inside the heating device, the vacuum treatment can be performed first.

[0135] In other embodiments, the gas supply device 30 can also include a halogen gas supply device (not shown in the figure).

[0136] Embodiment 9

[0137] The present embodiment is similar to embodiment 4, except that the gas raw material introduced in step 3) for melting and mixing is chlorine (Cl2), methane and argon (the volume fraction of chlorine and methane is 10% respectively), and at high temperature, Cl2 reacts with the transition metal elemental powder Ti to generate TiCl4 to participate in the reaction, realizing the growth of MXene at the gas-liquid interface.

[0138] The foregoing description of specific exemplary embodiments of the application is intended to be illustrative only and is not intended to limit the application to the precise forms described. Many modifications and variations are possible in light of the above teachings without departing from the spirit or essential characteristics of the application. The exemplary embodiments were chosen and described to explain the principles of the application and its practical application and to enable others skilled in the art to best utilize the application. It is intended that the scope of the application be limited only by the claims appended hereto and their equivalents.

Claims

1. A method of growing a MXene material by a vapor phase method, characterized by the steps of comprising: mixing transition metal elemental powder with medium salt, heating to melt the medium salt, forming a molten mixture; reacting the molten mixture with gaseous raw materials at a predetermined reaction temperature, to obtain MXene material; the gaseous raw materials comprising: transition metal halide salt and X source; and / or, X source and halogen gas; the X source is carbon source and / or nitrogen source; the carbon source is selected from at least one of carbon hydride, carbon hydrohalide, carbon halide; the nitrogen source is selected from at least one of nitrogen gas, nitrogen hydride.

2. The method of claim 1, wherein, the medium salt is selected from alkali metal halide salt and / or alkaline earth metal halide salt.

3. The method of claim 1, wherein, the carbon hydride in the carbon source is selected from one or more of methane, acetylene, propane, benzene, toluene, petroleum gas; the carbon hydrohalide is selected from one or more of monochloromethane, dichloromethane, trichloromethane, monobromomethane, dibromomethane, tribromomethane, monoiodomethane, diiodomethane, triiodomethane; the carbon halide is selected from CCl4; and / or, the nitrogen hydride in the nitrogen source is selected from ammonia gas, hydrazine (N2H4); and / or, the halogen gas is selected from one or more of Cl2, Br2, or I2.

4. The method of growing MXene material by vapor phase method according to any one of claims 1 to 3, characterized in that, The chemical formula of the MXene material is M n+1 X n T x , M represents a transition metal element; X represents carbon and / or nitrogen, T x represents a surface functional group, including one or more of F, Cl, Br, I, 1≤ n ≤4, 0< x ≤2.

5. The method of claim 4, wherein, the M is selected from one or more of Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W, Y, Sc.

6. The method of growing MXene material by vapor phase method according to any one of claims 1 to 3, wherein the medium salt is selected from one or more of sodium halide, potassium halide, lithium halide, magnesium halide, calcium halide; and / or, the transition metal halide salt is selected from one or more of transition metal chloride, transition metal bromide, transition metal iodide, transition metal fluoride.

7. The method of claim 6, wherein, the medium salt is selected from one or more of sodium chloride, potassium chloride, lithium chloride, magnesium chloride, calcium chloride.

8. The method of claim 1, wherein, the predetermined reaction temperature is between 300℃ and 1500℃; and / or, the predetermined reaction time is between 1min and 12h; and / or, the mass ratio of the transition metal elemental powder to the medium salt is between 1:(0.1~5).

9. The method of claim 8, wherein, the predetermined reaction temperature is between 500℃ and 900℃; and / or, the mass ratio of the transition metal elemental powder to the medium salt is between 1:(0.5~3).

10. The method of claim 8, wherein, the predetermined reaction temperature is between 600℃ and 800℃; and / or, the mass ratio of the transition metal elemental powder to the medium salt is between 1:(1~3).

11. The method of claim 1, wherein, the method further comprises a purification step: washing with water to remove the medium salt, and drying to obtain MXene material; and / or, the method further comprises a heating step: heating the transition metal halide salt and / or the X source to convert into gaseous state.

12. The method of growing MXene material by vapor deposition of claim 1, wherein, the method further comprises a stripping step: at a predetermined temperature, passing gas to strip the product on the surface of the liquid phase; and / or, the method further comprises a step: passing one or more of the gaseous raw materials into the molten mixture to form bubbles.

13. A MXene material prepared by the method of any one of claims 1 to 12.

14. A system for producing MXene material using the method of any one of claims 1 to 12, characterized by, comprising: A heating device, a gas supply device and an open container, the open container is fixedly or detachably arranged in a heating zone of the heating device; the gas supply device is used for supplying one or more of a protective gas, an X source gas, a halogen gas and a transition metal halide salt gas to the heating device in one time or in batches; The system further comprises a blowing device for blowing off the MXene material obtained by surface growth in liquid phase, so as to expose the surface of the liquid mixture to the gas mixture again.

15. The system of claim 14, wherein, The gas supply device and the open container are communicated through a connecting pipeline; And / or, the gas supply device comprises a mixing device for mixing at least two of the protective gas, the halogen gas, the X source gas and the transition metal halide salt gas before being introduced into the heating device.

16. The system of claim 15, wherein, The gas outlet of the connecting pipeline is arranged inside the open container.

17. The system of claim 15, wherein, The gas outlet of the connecting pipeline is arranged at the bottom of the open container.

18. A system for preparing a MXene material, characterized in that, Comprise: A heating device, a gas supply device and an open container; The heating device comprises a first heating zone and a second heating zone, the first heating zone is used for placing a transition metal halide salt; the open container is fixedly or detachably arranged in the second heating zone; The gas supply device is used for supplying one or more of a protective gas, an X source gas and a halogen gas to the heating device in one time or in batches, the gas supplied by the gas supply device sequentially passes through the first heating zone and the second heating zone; The system further comprises a blowing device for blowing off the MXene material obtained by surface growth in liquid phase, so as to expose the surface of the liquid mixture to the gas mixture again.

19. The system of any one of claims 14 to 18, wherein, The blowing device comprises at least one gas jet, and the gas jet is arranged at the opening of the open container; And / or, the system further comprises a collecting device for collecting the generated MXene material.

20. The use of the MXene material of claim 13 in catalysis, sensors, supercapacitors, batteries, electromagnetic shielding, wave-absorbing materials, corrosion-resistant materials, or superconducting materials.

21. The use of the MXene material of claim 13 in electronic devices.

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