A green, safe, efficient and universal method for preparing MXenes

Abstract

The present invention discloses a method for green, safe, efficient and universal preparation of MXenes, which relates to the technical field of MXenes preparation. The method successively comprises the following steps: (1) adding ammonium bifluoride and MAX phase precursor into a reaction kettle, mixing evenly and sealing; (2) heating the reaction kettle to 60-200 °C under stirring conditions for reaction for 1-8 h, cooling to room temperature, and then washing, centrifuging and drying to obtain accordion-shaped MXenes. The present invention does not use any solvent in the etching preparation process, has the characteristics of green safety, low cost, etc., and effectively solves the problems in the prior art such as great harm to experimental operators and the environment, long etching period, easy promotion of oxidation by solvents, low universality and being not conducive to large-scale industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of MXenes preparation, and particularly relates to a green, safe, efficient and universal method for preparing MXenes. Background Art

[0002] MXenes is a general term for a large class of layered two-dimensional transition metal carbides or / and nitrides. The research groups of Professor Naguib and Professor Gogotsi at Drexel University in the United States first obtained a two-layer Ti3C2T x -MXene by selectively etching the precursor MAX phase in 2011. Since then, MXenes has gradually developed into a popular material favored by researchers. The chemical general formula of MXenes is M n+1 X n T x , where M represents transition metal elements such as Ti, V, Nb, Mo, Zr, Hf, Ta, etc., X represents C or / and N elements, and T x represents terminal groups such as -F, -O, -OH, etc. Usually, MXenes is obtained by selectively etching the A atomic layer in the precursor MAX phase. The unique structure and composition endow MXenes with excellent hydrophilicity, metallic conductivity, outstanding flexibility, ultra-high specific electrochemical capacitance and easy processing, etc. Therefore, MXenes is widely used in many fields such as electrochemical energy storage, intelligent sensing, electromagnetic shielding, biomedicine, optics, etc. For example, in the field of electrochemical energy storage, when MXenes is used as the electrode material of a flexible supercapacitor, it can exhibit ultra-high pseudocapacitance response, ultra-long electrochemical cycle stability and excellent wearable flexibility.

[0003] Currently, the preparation method of MXenes is mainly to selectively etch the precursor by directly using or in-situ generating HF. Among them, the most widely used method at present is to in-situ generate HF in an aqueous solution with LiF / HCl to etch the precursor to obtain MXenes products. Specifically, different MXenes are achieved by adjusting the process to change the etching temperature and time.

[0004] However, the existing technologies have the following prominent problems: The existing MXenes etching technologies directly or indirectly use HF, which poses great hazards to experimental operators and the environment, and their safety and environmental friendliness need to be improved; The existing MXenes etching technologies generally take 12 - 196 hours, and most methods are still in the laboratory stage, with a long etching cycle and troublesome post-treatment processes; Existing MXenes etching is usually carried out in the presence of solvents (aqueous solvents or organic solvents). Aqueous solvents are extremely likely to promote the oxidation of MXenes, and organic solvents are costly and have high environmental hazards; The existing MXenes etching technologies are only applicable to some MAX phases, with low universality; Existing molten salt method and Lewis acid method for etching MXenes have high temperature and large energy consumption. The supercritical carbon dioxide assisted method requires a high-pressure atmosphere and has high requirements for equipment (high pressure and corrosion resistance), which is not conducive to actual industrial large-scale production and application. Summary of the Invention

[0005] In order to solve the above technical problems, the object of the present invention is to provide a method for green, safe, efficient and universal preparation of MXenes, which does not use any solvents during the etching preparation process, has the characteristics of green safety and low cost, and effectively solves the problems in the existing technologies such as great hazards to experimental operators and the environment, long etching cycle, easy promotion of oxidation by solvents, low universality, and unfavorable for industrial large-scale production.

[0006] The technical solution of the present invention to solve the above technical problems is as follows: Provide a method for green, safe, efficient and universal preparation of MXenes, including the following steps: successively including the following steps:

[0007] (1) Add ammonium bifluoride and MAX phase precursor into a reaction kettle, mix evenly, and seal.

[0008] (2) Under stirring conditions, heat the reaction kettle to 60 - 200 °C and react for 1 - 8 hours, cool to room temperature, and then wash, centrifuge and dry to obtain accordion-shaped MXenes.

[0009] Further, in step (1), the MAX phase is Ti3AlC2, Ti2AlC, Ti3AlCN, Nb4AlC3, Mo2TiAlC2, V4AlC3 or Mo2Ga2C.

[0010] Further, in step (1), the mass ratio of ammonium bifluoride to MAX phase is 1 - 11:1.

[0011] Further, in step (1), after mixing evenly, use argon or nitrogen to wash the gas multiple times to discharge the air in the reaction kettle.

[0012] Further, in step (2), magnetic stirring is carried out under the condition of 700 - 900 rpm.

[0013] Further, in step (2), deionized water, ethanol, hydrochloric acid or isopropanol is used for cleaning.

[0014] Further, it is washed at 3500 rpm for 2 - 4 min and dried at 40 - 50 °C for 18 h.

[0015] The accordion - shaped MXenes prepared by the above - mentioned green, safe, efficient and universal method for preparing MXenes.

[0016] The present invention has the following beneficial effects:

[0017] 1. In the etching preparation process of the present invention, no solvents (including deionized water) are used, which has the characteristics of being green, safe and low - cost, effectively solving the problems in the prior art such as great harm to experimental operators and the environment, long etching cycle, easy promotion of oxidation by solvents, low universality and being not conducive to large - scale industrial production.

[0018] 2. The present invention realizes the rapid large - batch etching of MXenes under relatively low temperature (compared with the molten salt method) and ultra - low pressure conditions of 0 MPa, and the shortest time only needs 1 h.

[0019] 3. The present invention prepares MXenes under normal pressure of inert gas, realizes accelerating the etching reaction by increasing the temperature while avoiding the oxidation of MXenes, and the used NH4HF2 etchant decomposes to produce HF and NH3 during the heating process, avoiding the direct use of HF. Precise control of the ratio of the etchant to the precursor can minimize the generation of reaction waste residues (NH3 and other gases can be discharged by pressure relief).

[0020] 4. The preparation method of the present invention has universality and can realize the etching of various MAX phases, such as various precursors like Ti3AlC2, Ti2AlC, Ti3AlCN, Nb4AlC3, Mo2TiAlC2, V4AlC3 or Mo2Ga2C, etc.

[0021] 5. The preparation method of the present invention has a short required time, low cost, low equipment requirements, environmental friendliness, high safety, simple post - treatment of products, and can carry out large - scale preparation of MXenes at relatively low temperature and normal pressure, which is more conducive to the commercial production and industrial application of MXenes. Description of the Drawings

[0022] Figure 1 is the XRD spectrum of V4C3T x -MXene;

[0023] Figure 2 is the SEM image of V4C3T x -MXene.

[0024] Among them,Figure 1 In Figure a from top to bottom are large - batch V4C3T x -MXene, small - batch V4C3T x -MXene and V4AlC3; Figures b and c are Ti3C2T x and Ti3CNT x . Specific implementation manners

[0025] The principles and features of the present invention are described below. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention. For those not specified in the examples, the operations are carried out according to conventional conditions or the conditions recommended by the manufacturer. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0026] Example 1

[0027] A method for green, safe, efficient and universal preparation of MXenes, comprising the following steps: successively including the following steps:

[0028] (1) Add ammonium bifluoride and V4AlC3 precursor into the inner liner of a polytetrafluoroethylene reaction kettle according to a mass ratio of 11.4:1, mix evenly, use argon or nitrogen to purge the air in the reaction kettle 3 times, and seal it;

[0029] (2) Stir magnetically at 800 rpm, heat the reaction kettle to 170 °C and react for 1 h, cool to room temperature, wash for 3 min at 3500 rpm, and dry at 45 °C for 18 h to obtain accordion - shaped MXenes.

[0030] Example 2

[0031] A method for green, safe, efficient and universal preparation of MXenes, comprising the following steps: successively including the following steps:

[0032] (1) Add ammonium bifluoride and Ti3AlC2 precursor into the inner liner of a polytetrafluoroethylene reaction kettle according to a mass ratio of 5.7:1, mix evenly, use argon or nitrogen to purge the air in the reaction kettle 3 times, and seal it;

[0033] (2) Stir magnetically at 800 rpm, heat the reaction kettle to 120 °C and react for 1 h, cool to room temperature, wash for 3 min at 3500 rpm, and dry at 45 °C for 18 h to obtain accordion - shaped MXenes.

[0034] Example 3

[0035] A method for green, safe, efficient and universal preparation of MXenes, comprising the following steps: successively including the following steps:

[0036] (1) Add ammonium bifluoride and the Ti3AlCN precursor into the inner liner of a polytetrafluoroethylene reaction kettle at a mass ratio of 11.4:1, mix evenly, use argon or nitrogen to purge the air in the reaction kettle three times, and seal it.

[0037] (2) Stir magnetically at 800 rpm, heat the reaction kettle to 120 °C and react for 3 h, cool to room temperature, wash for 3 min at 3500 rpm, and dry at 45 °C for 18 h to obtain accordion-shaped MXenes.

[0038] Example 4

[0039] A method for green, safe, efficient and universal preparation of MXenes, comprising the following steps: successively including the following steps:

[0040] (1) Add ammonium bifluoride and the Nb4AlC3 precursor into the inner liner of a polytetrafluoroethylene reaction kettle at a mass ratio of 5.7:1, mix evenly, use argon or nitrogen to purge the air in the reaction kettle three times, and seal it.

[0041] (2) Stir magnetically at 800 rpm, heat the reaction kettle to 160 °C and react for 1 h, cool to room temperature, wash for 3 min at 3500 rpm, and dry at 45 °C for 18 h to obtain accordion-shaped MXenes.

[0042] Example 5

[0043] A method for green, safe, efficient and universal preparation of MXenes, comprising the following steps: successively including the following steps:

[0044] (1) Add ammonium bifluoride and the Ti2AlC precursor into the inner liner of a polytetrafluoroethylene reaction kettle at a mass ratio of 11.4:1, mix evenly, use argon or nitrogen to purge the air in the reaction kettle three times, and seal it.

[0045] (2) Stir magnetically at 800 rpm, heat the reaction kettle to 100 °C and react for 5 h, cool to room temperature, wash for 3 min at 3500 rpm, and dry at 45 °C for 18 h to obtain accordion-shaped MXenes.

[0046] Example 6

[0047] A method for green, safe, efficient and universal preparation of MXenes, comprising the following steps: successively including the following steps:

[0048] (1) Add ammonium bifluoride and the Mo2TiAlC2 precursor into the inner liner of a polytetrafluoroethylene reaction kettle at a mass ratio of 11.4:1, mix evenly, use argon or nitrogen to purge the air in the reaction kettle three times, and seal it.

[0049] (2) Stir magnetically at 800 rpm, heat the autoclave to 150 °C and react for 5 h, cool to room temperature, wash for 3 min at 3500 rpm, and dry at 45 °C for 18 h to obtain accordion-like MXenes.

[0050] Example 7

[0051] A method for green, safe, efficient and universal preparation of MXenes, comprising the following steps: successively including the following steps:

[0052] (1) Add ammonium bifluoride and Mo2Ga2C precursor into the inner liner of a polytetrafluoroethylene autoclave according to a mass ratio of 11.4:1, mix evenly, use argon or nitrogen to purge the air in the autoclave 3 times, and seal it;

[0053] (2) Stir magnetically at 800 rpm, heat the autoclave to 180 °C and react for 1 h, cool to room temperature, wash for 3 min at 3500 rpm, and dry at 45 °C for 18 h to obtain accordion-like MXenes.

[0054] Experimental example

[0055] Conduct tests according to the following process:

[0056] 1. Preparation of V4C3Tx-MXene

[0057] (1) Reaction raw materials:

[0058] MAX phase (Jilin Yiyi Technology Co., Ltd.), the main raw material, as the precursor of the product;

[0059] Ammonium bifluoride (AR, Macklin), the main raw material, as the etchant;

[0060] Propylene carbonate (abbreviated as PC, AR, Kelong Chemical Industry);

[0061] Deionized water, the secondary raw material, as the detergent;

[0062] (2) Experimental method:

[0063] Etching: Add 5.7 g of NH4HF2 and 0.5 g of V4C3T x -MAX precursor V4AlC3 into the inner liner of a polytetrafluoroethylene autoclave, put its inner liner into a high-pressure autoclave, mechanically shake for 5 min to mix evenly, then lock and seal the stainless steel autoclave shell, introduce Ar or N2 into the autoclave for 3 times to purge the air, heat up to 170 °C, and react for 1 h under magnetic stirring at 800 rpm.

[0064] Product cleaning and drying: After the reaction, slowly release the residual pressure. Transfer the reaction product to a centrifuge tube, and wash it by centrifugation with deionized water 5 times. Before each centrifugation, shake it with a vortex oscillator for 60 s. The centrifugation speed is 3500 rpm for 3 min. Discard the supernatant and collect the precipitate each time. After collecting the precipitate, perform suction filtration and then dry it at 45 °C under vacuum for 18 h.

[0065] The results are as Figure 1 shown in Figure 1 Figure a in x is the XRD pattern of the V4C3T Figure 2 -MXene prepared in small batches, and

[0066] As can be seen from the figure, Figure 1 in a, the strong peak at 6.02° is the XRD characteristic peak of MXene, while the XRD characteristic peak of the V4AlC3-MAX phase at 39.72° almost completely disappears, indicating that V4AlC3 has been completely transformed into V4C3T x -MXene, Figure 2 and a shows the typical accordion structure of MXene.

[0067] 2. Batch preparation of V4C3T x -MXene

[0068] Etching: In a high-pressure reactor, add 2300 g of NH4HF2 and 500 g of the V4C3T x -MAX precursor V4AlC3. Quickly seal the reactor and purge the air in the reactor with Ar or N2 three times. Keep the mechanical stirring on throughout the process at a speed of 300 rpm. Heat up to 160 °C and maintain this condition for 6 h.

[0069] Product cleaning and drying: After the reaction, slowly release the residual pressure. Transfer the reaction product to a centrifuge tube, and wash it by centrifugation with deionized water 5 times. Before each centrifugation, shake it with a vortex oscillator for 60 s. The centrifugation speed is 3500 rpm for 3 min. Discard the supernatant and collect the precipitate each time. After collecting the precipitate, perform suction filtration and then dry it at 45 °C under vacuum for 18 h.

[0070] The results are as Figure 1 shown in Figure 1 Figure a in x is the XRD pattern of the V4C3T Figure 2 -MXene prepared in large batches, and

[0071] As can be seen from the figure, Figure 1In a, the strong peak at 6.02° is the XRD characteristic peak of MXene, while the XRD characteristic peak of the V4AlC3-MAX phase at 39.72° almost completely disappears, indicating that V4AlC3 has been completely transformed into V4C3T x -MXenes.

[0072] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A green, safe, efficient and universal method for preparing MXenes, characterized in that, It successively includes the following steps: (1) Add ammonium bifluoride and MAX phase precursor into a reaction kettle, mix evenly, and seal it; (2) Under stirring conditions, heat the reaction kettle to 60 - 200 °C and react at normal pressure for 1 - 8 h, cool to room temperature, and then wash, centrifuge, and dry to obtain accordion-like MXenes.

2. The method for preparing MXenes in a green, safe, efficient and universal manner as described in claim 1, wherein, In step (1), the MAX phase is Ti3AlC2, Ti2AlC, Ti3AlCN, Nb4AlC3, Mo2TiAlC2, V4AlC3, or Mo2Ga2C.

3. The method for preparing MXenes in a green, safe, efficient and universal manner according to claim 1, wherein In step (1), the mass ratio of ammonium bifluoride to the MAX phase is 1 - 11:

1.

4. The method for preparing MXenes in a green, safe, efficient and universal manner according to claim 1, characterized in that, In step (1), after mixing evenly, use argon or nitrogen to wash the air in the reaction kettle out for multiple times.

5. The method for preparing MXenes in a green, safe, efficient and universal manner according to claim 1, wherein In step (2), stir magnetically under the condition of 700 - 900 rpm.

6. The method for preparing MXenes in a green, safe, efficient and universal manner as claimed in claim 1, wherein In step (2), use deionized water, ethanol, hydrochloric acid, or isopropanol for cleaning.

7. The method for preparing MXenes in a green, safe, efficient and universal manner according to claim 1, wherein Wash at 3500 rpm for 2 - 4 min and dry at 40 - 50 °C for 18 h.

8. Accordion-like MXenes prepared by the method for green, safe, efficient, and universal preparation of MXenes according to any one of claims 1 - 7.

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