Method for preparing two-dimensional MXene by high-energy shock wave assisted metal salt replacement without fluorine

Abstract

The application belongs to the technical field of two-dimensional MXene materials, and discloses a method for preparing two-dimensional MXene by high-energy electric shock assisted metal salt replacement without fluorine, which comprises the following steps: after grinding and mixing mother phase MAX powder and metal salt, the mixture is loaded into a quartz tube of a high-energy electric shock device, graphite electrodes are inserted into two ends of the quartz tube, and the material is compacted to make it closely contact with the electrodes; after the capacitor of the high-energy electric shock device is charged, a discharge button is opened to perform high-energy electric shock, the reaction is completed after flash phenomenon occurs, and the electric shock is repeated once after the metal salt is supplemented; the product after electric shock is ground and washed with acid, and after washing with deionized water until neutral, standing or centrifugal layering is performed, and the MXene two-dimensional material is obtained from the upper layer. According to the application, the A atom is accelerated to escape from the MAX interlayer by high-energy electric shock, so that the MXene material is quickly obtained, the fluorine-free rapid etching of MXene is realized, and the problems of slow Lewis acid salt etching reaction and high cost are solved.

Description

Technical Field

[0001] This invention belongs to the field of two-dimensional MXene material technology, and relates to a method for preparing two-dimensional MXene without fluorine by high-energy electrostatic discharge assisted metal salt replacement. Background Technology

[0002] MXene materials are produced by selectively etching the A-layer elements of a parent MAX material (where M represents transition metals such as titanium, niobium, and vanadium, A represents aluminum or silicon, and X represents carbon or nitrogen) and then intercalating them to obtain MXene two-dimensional nanosheets. Unlike other two-dimensional materials, MXenes exhibit diversity and controllable end groups, making them applicable in various fields such as electrochemical energy storage, electromagnetic shielding, and environmental protection. Currently, the method of etching the intermediate A-layer atoms is called the top-down etching method, which is universal and capable of mass production. However, current methods often require strong acids or bases to etch the MAX phase. While hydrofluoric acid is a commonly used etching agent with high etching efficiency, its strong corrosiveness and harmfulness to humans make it difficult to industrialize, thus affecting the large-scale application of MXene materials. In contrast, the method of using molten Lewis acid salts to etch the MAX phase has become more popular in recent years. It has a certain degree of safety and less environmental harm, but high energy consumption and long reaction times remain obstacles to the industrial-scale preparation of MXenes. Therefore, there is an urgent need for a green, environmentally friendly, low-cost, fluorine-free, and efficient preparation method to promote the large-scale preparation and application of MXene materials. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides a method for preparing fluorine-free two-dimensional MXene using a high-energy electrostatic discharge (HEED) assisted metal salt substitution. This method rapidly breaks the MA bonds in the MAX layer through high-energy electrostatic discharge and accelerates the escape of A atoms from the MAX interlayer by utilizing a redox reaction between molten metal salt and A atoms. This allows for the rapid acquisition of MXene material, achieving rapid fluorine-free etching of MXene and solving the problems of slow and costly Lewis acid salt etching reactions.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] This invention provides a method for preparing two-dimensional MXene by high-energy electrostatic discharge assisted metal salt displacement without fluorine, comprising the following steps:

[0006] 1) After grinding and mixing the parent phase MAX powder and metal salt, the mixture is loaded into the quartz tube of the high-energy electric shock device. Graphite electrodes are inserted into both ends of the quartz tube, and the material is compacted to make it in close contact with the electrodes.

[0007] 2) After the capacitor of the high-energy electric shock device is fully charged, turn on the discharge button to perform a high-energy electric shock. After a flash phenomenon occurs, the reaction ends. After replenishing the metal salt, repeat the electric shock 1 to 2 times.

[0008] 3) The product after electrolysis is ground and washed with acid. After washing with deionized water until neutral, it is allowed to stand or centrifuged to separate into layers. The upper layer is MXene two-dimensional material.

[0009] Preferably, the parent phase MAX powder is selected from titanium aluminum carbide, vanadium aluminum carbide, niobium aluminum carbide, titanium silicon carbide or titanium tin carbide.

[0010] Preferably, the metal salt is selected from copper chloride, zinc chloride, ferrous chloride, copper bromide, or ammonium sulfite. Under high-energy electric shock, a high temperature of 3000K is generated within 0.1s. Copper chloride has a melting point of 620℃, zinc chloride 283℃, ferrous chloride 670℃, copper bromide 498℃, and ammonium sulfite 60℃. All of these can be melted instantly upon Joule heating. The molten metal salt undergoes metal bond dissociation and exists in ionic form. Atoms react with it in redox reactions (e.g., Ti3AlC2 + 1.5CuCl2 = Ti3C2 + 1.5Cu + AlCl3↑, Ti3C2 + Cu = Ti3CuC2), generating ionic compounds of A, making the A atoms easier to strip.

[0011] Preferably, the mass ratio of the parent phase MAX powder to the total amount of metal salt is 1:1 to 2.5.

[0012] Preferably, the electric shock energy corresponding to each 100mg of raw material is 50-800J.

[0013] It is worth noting that the high-energy electric shock device used in this invention is a device for regenerating lithium-ion battery electrode materials disclosed in application publication number CN 113258159 A. The dimensions of the quartz tube are adjusted as follows: diameter 4mm, wall thickness 2mm, and length 60mm. Through experiments, this device can be used to perform high-energy electric shock on the parent phase MAX material to obtain MXene two-dimensional material. The energy required for this reaction is calculated based on the energy required for the mass of reactants during high-energy electric shock, using the formula... The charging voltage and the number of capacitors can be set. The high-energy electric shock device can select n capacitors to adjust the reaction voltage in series or parallel. When the amount of reactant increases, a larger reactor can be selected for the reaction. Since high temperature can easily cause the MAX phase to decompose and change phase, in order to prevent the reactor from breaking due to instantaneous high temperature and the occurrence of uncontrollable side reactions, the energy should be controlled below 800J.

[0014] The technical features of this invention are as follows:

[0015] 1. Instantaneous high-energy current and voltage affect the connection of chemical bonds.

[0016] The key to etching from the parent phase MAX to MXene is to break the MA bonds, thereby enabling subsequent layering and stripping. Under the impact of high voltage and high-energy electrons, the weaker MA bonds will be broken. The breaking of MA bonds can be achieved by controlling the voltage field and the magnitude of the high-energy current.

[0017] 2. Reducing metal salts facilitate the rapid escape of A atoms.

[0018] Even after the MA bond is broken, the A atom will still exist in the interlayer. The Joule heat generated by internal resistance alone cannot achieve complete separation of the A atom. Selecting a reducing metal salt with lower metal reactivity than the A atom can achieve a redox reaction in the molten state, thereby replacing the A atom. By adjusting the mixing ratio, the A atom can be assisted to escape from the interlayer and form a new ionic compound, so as to achieve low-temperature vaporization and subsequent separation by washing.

[0019] 3. Instantaneous high temperatures can trigger microscopic explosive reactions between layers.

[0020] In the instantaneous (second-level) reaction process, due to the drastic temperature change, the selected reducing metal salt will generate gas in the redox reaction with A atoms in the interlayer. In a closed environment, the gas is generated explosively in the material, which can easily lead to micro-explosion phenomena. This can effectively increase the interlayer spacing of the MAX phase and accelerate further reactions.

[0021] 4. Instantaneous high-energy electrical shocks result in faster etching efficiency.

[0022] Because the reaction is completed instantaneously and can be rapidly repeated, a large yield of MXene material can be obtained through stepped electrochemical screening. Furthermore, the energy required for the electrochemical shock is stored in a capacitor, requiring only a momentary high-energy current pulse. Compared to currently common etching methods, this method has significantly lower overall energy consumption.

[0023] 5. The selection of reducing metal salts can control the functional groups of the generated MXene. Currently, most MXene etching is fluorine-containing etching, which is very harmful to human health and the environment. Different metal salts can be tried during the reaction process, such as copper chloride (CuCl2), copper oxide (CuO), copper bromide (CuBr2), ferrous chloride (FeCl2), and sulfites. High-energy electrochemical discharge (EED) is used to destroy the macromolecular atom (MA), and then the metal salt is used to replace the atom in the macromolecular atom, achieving fluorine-free etching. Unlike Lewis acid salt melting etching, the high-energy electrochemical discharge method has the advantages of fast reaction, high efficiency, and low power consumption.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1. This invention rapidly breaks the MA bonds in MAX by high-energy electric shock and accelerates the escape of A atoms from the MAX interlayer by utilizing the redox reaction between molten metal salt and A atoms, thereby quickly obtaining MXene material, realizing fluorine-free rapid etching of MXene, and solving the problems of slow and costly Lewis acid salt etching reactions.

[0026] 2. Compared with common chemical solvent etching methods, the method of the present invention does not require the use of high-energy acids for solution etching and does not use fluorine-containing raw materials; compared with Lewis acid molten salt etching, the method of the present invention reacts rapidly and can achieve rapid repeated etching to improve yield; the method of the present invention is applicable to a variety of MAX phase materials, and due to the fast reaction time, it can effectively suppress the high-temperature oxidation of MXene.

[0027] 3. The method of the present invention has a certain degree of controllability, is relatively safe and reliable, has the advantage of mass production, and the waste gas generated during the electric shock process is easy to collect. Compared with the solution etching method, it is less harmful, and compared with the molten salt method, it has the advantages of fast speed, high efficiency and safety.

[0028] 4. This invention can match different MAX materials by adjusting the input energy and the metal salts added. At the same time, the fully mixed metal salts and MAX phase materials react in a molten state at high temperature, which can replace A atoms by redox reaction. Furthermore, the anions in the molten salt combine with A atoms to form ionic compounds that are easier to vaporize, effectively inhibiting the decomposition of MAX crystals and showing better application prospects. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the material manufacturing process of the present invention.

[0030] Figure 2 The image shows the SEM images of MAX before and after pickling in Comparative Example 1. Figure 2 -a is the SEM image of MAX before pickling. Figure 2 -b is the SEM image of MAX after acid washing.

[0031] Figure 3 The XRD patterns are shown for the materials obtained by acid washing in Comparative Example 1 and by electrostatic discharge in Examples 1-6. Figure 3 -a is the XRD pattern of the materials in Comparative Example 1 and Examples 1-6. Figure 3 -b is a magnified XRD pattern of the material and the parent phase MAX obtained by electrolysis in Example 2.

[0032] Figure 4 This is a screenshot from a video recording of the experimental phenomena during the electric shock process in Example 2.

[0033] Figure 5The images show SEM images of multilayer MXene and multilayer MXene with large interlayer spacing obtained in Example 2.

[0034] Figure 6 This is a TEM image of the few-layer MXene obtained in Example 2.

[0035] Figure 7 The MXene obtained in Example 2 and the acid-washed MAX from Comparative Example 1 were used as lithium-ion battery anode materials in 0.1 A g. -1 Electrochemical performance under cycling at current density.

[0036] Figure 8 The images show the SEM images and elemental distribution diagrams of the product from Example 6.

[0037] Figure 9 This is a TEM image of the product obtained in Example 7.

[0038] Figure 10 The reaction process is shown in Example 8.

[0039] Figure 11 This is a SEM image of the MXene material obtained in Example 9.

[0040] Figure 12 This is a SEM image of the MXene material obtained in Example 10.

[0041] Figure 13 The images show the XRD patterns of the MXene materials obtained in Examples 9 and 10.

[0042] Figure 14 This is a SEM image of the MXene material obtained in Example 11.

[0043] Figure 15 This is a SEM image of the MXene material obtained in Example 12.

[0044] Figure 16 This is a SEM image of the MXene material obtained in Example 13. Detailed Implementation

[0045] The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of protection of the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, the test methods in the following embodiments are conventional methods.

[0046] Example 1

[0047] According to such Figure 1The diagram shows the material preparation process of this invention. 75 mg of aluminum carbide and 15 mg of copper chloride are ground and mixed, then placed into a glass quartz tube. Both ends are sealed with conductive grinding rods and compacted using external force to ensure close contact with the electrodes. The quartz tube is placed in a reactor, and both ends are fixed with grooved copper rods. The input voltage is adjusted to 150V, and two capacitors (Hitachi HCGHA series 400V 5600UF 5600MFD 400VDC capacitors) are activated, with a discharge energy of 126J. After the capacitors are fully charged, the discharge button is turned on, and a single discharge occurs. A flash of light and significant gas evolution are observed during the reaction. After the reaction is complete, the sample is removed, ground, and pulverized. Then, 10 mg of copper chloride is added, ground, mixed, and placed back into the quartz tube, which is then compacted with conductive grinding rods. The voltage is maintained at 150V, with two capacitors activated, and the discharge energy is 126J. A single discharge occurs. Finally, the reactants were removed, ground, and placed in dilute hydrochloric acid (20 ml, 1 mol / L) for ultrasonic dispersion and washing. Then, they were washed with deionized water until neutral, allowed to stand and separate into layers. The upper layer was MXene material (5 mg).

[0048] Example 2

[0049] This embodiment is basically the same as Embodiment 1, except that: 50mg of aluminum carbide is mixed with 30mg of copper chloride, and after one electric shock, 20mg of copper chloride is added, while maintaining the same voltage of 150V. Two capacitors are used in both embodiments, and the electric shock energy is 126J. Then, another electric shock is performed. The upper layer yields MXene material (15mg).

[0050] Example 3

[0051] This embodiment is basically the same as embodiment 1, except that: 40mg of aluminum carbide is mixed with 40mg of copper chloride, and after one electric shock, 20mg of copper chloride is added, and the voltage is kept the same at 150V. Two capacitors are used, the electric shock energy is 126J, and then another electric shock is performed.

[0052] Example 4

[0053] This embodiment is basically the same as embodiment 1, except that: 34mg of aluminum carbide is mixed with 40mg of copper chloride, and after one electric shock, 26mg of copper chloride is added, and the voltage is kept the same at 150V. Two capacitors are used, the electric shock energy is 126J, and then another electric shock is performed.

[0054] Example 5

[0055] This embodiment is basically the same as embodiment 1, except that: 28mg of aluminum carbide is mixed with 40mg of copper chloride, and after one electric shock, 32mg of copper chloride is added, and the voltage is kept the same at 150V. Two capacitors are used, the electric shock energy is 126J, and then another electric shock is performed.

[0056] Example 6

[0057] This embodiment is basically the same as embodiment 1, except that: 25mg of aluminum carbide is mixed with 40mg of copper chloride, and after one electric shock, 35mg of copper chloride is added, and the voltage is kept the same at 150V. Two capacitors are used, the electric shock energy is 126J, and then another electric shock is performed.

[0058] Comparative Example 1: Preparation of Acid Washing MAX

[0059] Aluminum titanate carbide (Ti3AlC2) and copper chloride (CuCl2) were mixed at a mass ratio of 1:1 and then added to dilute hydrochloric acid (20 ml, 9 mol / L) in a plastic container. The mixture was stirred at room temperature. After the final solution was centrifuged and washed multiple times until it approached neutral, the precipitate was dispersed in an aqueous solution and ultrasonically dispersed for 30 min. Finally, it was freeze-dried to obtain the acid-washed MAX dry powder.

[0060] Figure 2 The image shows SEM images of MAX before and after acid washing in Comparative Example 1. As can be seen from the image, only copper chloride was partially dissolved in the acid solution. After acid washing, MAX retained its original MAX structure and was randomly distributed with the undissolved copper chloride, indicating that the two did not react.

[0061] Figure 3 The X-ray diffraction patterns are shown for MAX after acid washing in Comparative Example 1 and the materials obtained by electroporation in Examples 1-6. It can be seen that MAX did not exhibit etching behavior after acid washing; when the overall mass ratio of MAX to CuCl2 was 3:1 (Example 1), no MXene (002) characteristic peak appeared, only the (104) peak of MAX decreased, indicating that no etching behavior occurred; when the overall mass ratio of MAX to CuCl2 was 1:1 (Example 2), from... Figure 3 In -b, a weaker MXene(002) characteristic peak can be observed more clearly, indicating that only etching behavior occurred; while according to Figure 3As shown in -a, when the overall mass ratio of MAX to CuCl2 is 1:1.5 to 2.5 (Examples 3 to 5), a characteristic peak of Cu appears, and it gradually increases with the increase of the proportion of copper chloride, indicating that the MAX phase has a transformation trend; when the overall mass ratio of MAX to CuCl2 is 1:3 (Example 6), the characteristic (002) peak of the MAX phase shifts to the left, and the characteristic peak of Cu grows to the highest, which should be the formation of Ti3CuC2 phase, indicating that copper chloride is in excess.

[0062] Figure 4 The image shown is a screenshot from a video recording of the experimental phenomena during the electric shock process in Example 2. It can be seen that gas expansion occurred during the electric shock process. Furthermore, because CuCl2 readily absorbs water, a small amount of water vapor was released during the electric shock. The repeated gas expansion also indicates the occurrence of a redox reaction.

[0063] Figure 5 The images show SEM images of the multilayer MXene and the multilayer MXene with larger interlayer spacing obtained in Example 2. It can be seen that high-energy electric shock can produce accordion-shaped MXene materials with larger interlayer spacing. When used as a negative electrode material in lithium-ion batteries, it provides more vacancies for lithium-ion intercalation, thereby providing greater capacity.

[0064] In addition, the product obtained in Example 2 also contains a small amount of few-layer MXene (such as... Figure 6 (As shown), this is due to the multiple layers of MXene being shaken off and broken during the micro-explosion.

[0065] Take 50 mg each of MXene obtained in Example 2 and MAX material after acid washing in Comparative Example 1, mix them with binder polyvinylidene fluoride (PVDF) and conductive carbon black (Super P) in a ratio of 8:1:1, prepare a slurry using N-methylpyrrolidone (NMP) as solvent, stir evenly, coat it on copper foil, and place it in an oven at 80°C for 10 hours. After drying, cut it into circular active material electrodes with a diameter of 12 mm. Assemble CR2032 button-type lithium-ion half-cells in a glove box filled with argon atmosphere in the following order: negative electrode shell, active material electrode, separator, lithium sheet, gasket, and spring sheet, using lithium hexafluorophosphate (LiPF6) as electrolyte.

[0066] Figure 7 The MXene obtained in Example 2 and the acid-washed MAX from Comparative Example 1 were used as lithium-ion battery anode materials in 0.1 A g. -1 Electrochemical performance under cycling at current density. This electrochemically demonstrates the successful etching of MXene in Example 2, where the interlayer serves as lithium-ion insertion sites, thus increasing capacity.

[0067] Figure 8The images show the SEM image and elemental distribution of the product from Example 6. The precipitation of Al and the substitution of Cu indicate the formation of a new substance, Ti3CuC2.

[0068] Example 7

[0069] This embodiment is basically the same as embodiment 2, except that the charging voltage is 200V and the number of activated capacitors is 3, that is, the energy of the high-energy electric shock is 336J.

[0070] Figure 9 This is a TEM image of the product obtained in Example 7. The image shows that amorphous carbon appeared after the decomposition of Ti3AlC2, while titanium and aluminum volatilized at high temperatures, resulting in the decomposition of the MAX phase structure due to excessive energy.

[0071] Example 8

[0072] This embodiment is basically the same as embodiment 2, except that the charging voltage is 250V, the number of activated capacitors is 5, and the energy of the high-energy electric shock is 875J.

[0073] Figure 10 The reaction process in Example 8 is shown. It can be seen that due to excessive energy, a severe explosion occurred during the electric shock process. This explosion was caused by the escape of gas generated during the electric shock; therefore, the energy should be controlled below 800J.

[0074] Example 9

[0075] This embodiment is basically the same as Embodiment 2, except that the copper chloride (CuCl2) material is replaced with zinc chloride (ZnCl2). The upper layer yields MXene material (12 mg).

[0076] Figure 11 The image shows a SEM image of the MXene material obtained in Example 9. It can be seen that even after replacing the metal salt with ZnCl2, MXene material with etched edges can still be obtained.

[0077] Example 10

[0078] This embodiment is basically the same as Embodiment 2, except that the copper chloride (CuCl2) material is replaced with ferrous chloride (FeCl2). The upper layer yields MXene material (5 mg).

[0079] Figure 12 This is a SEM image of the MXene material obtained in Example 10. It can be seen that even after changing the metal salt to FeCl2, MXene material with etched edges can still be obtained.

[0080] Figure 13The images show the XRD patterns of the MXene materials obtained in Examples 9 and 10.

[0081] Example 11

[0082] This embodiment is basically the same as Embodiment 2, except that copper chloride (CuCl2) is replaced with copper bromide (CuBr2). The upper layer yields MXene material (7 mg).

[0083] Figure 14 This is a SEM image of the MXene material obtained in Example 11. It can be seen that even after replacing the metal salt with CuBr2, MXene material with etched edges can still be obtained.

[0084] Example 12

[0085] This embodiment is basically the same as Embodiment 2, except that the aluminum titanate carbide (Ti3AlC2) material is replaced with ammonium sulfite ((NH4)2SO3). The upper layer yields MXene material (6 mg).

[0086] Figure 15 This is a SEM image of the MXene material obtained in Example 12. It can be seen that even after changing the metal salt to (NH4)2SO3, MXene material with etched edges can still be obtained.

[0087] Example 13

[0088] This embodiment is basically the same as Embodiment 2, except that the aluminum titanate carbide (Ti3AlC2) material is replaced with vanadium aluminum carbide (V2AlC). The upper layer yields MXene material (9 mg).

[0089] Figure 16 This is a SEM image of the MXene material obtained in Example 13. It can be seen that even after replacing the parent phase MAX material, MXene material with etched edges can still be obtained.

[0090] The embodiments described above are merely preferred embodiments of the present invention and are only used to explain the present invention. They are not intended to limit the scope of the present invention. For those skilled in the art, other implementation methods can be easily made by substitution or modification based on the technical content disclosed in this specification. Therefore, all changes and improvements made on the principle of the present invention should be included within the scope of the patent application of the present invention.

Claims

1. A method for preparing two-dimensional MXene by high-energy electroporation-assisted metal salt displacement without fluorine, characterized in that, Includes the following steps: 1) After grinding and mixing the parent phase MAX powder and metal salt, the mixture is loaded into the quartz tube of the high-energy electric shock device. Graphite electrodes are inserted into both ends of the quartz tube, and the material is compacted to ensure close contact with the electrodes. The mass ratio of the parent phase MAX powder to the metal salt is 1:1~2.

5. 2) After the capacitor of the high-energy electric shock device is fully charged, turn on the discharge button to perform a high-energy electric shock. The reaction ends after a flash phenomenon occurs. After replenishing the metal salt, repeat the electric shock 1-2 times. The electric shock energy corresponding to each 100mg of raw material is 50-800 J. 3) The product after electrolysis is ground and washed with acid. After washing with deionized water until neutral, it is allowed to stand or centrifuged to separate into layers. The upper layer is MXene two-dimensional material.

2. The method according to claim 1, characterized in that, The parent phase MAX powder is selected from titanium aluminum carbide, vanadium aluminum carbide, niobium aluminum carbide, titanium silicon carbide or titanium tin carbide.

3. The method according to claim 1, characterized in that, The metal salt is selected from copper chloride, zinc chloride, ferrous chloride, copper bromide, or ammonium sulfite.

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