A method for preparing MXene in a low-temperature medium-pressure molten alkali system

Abstract

The application is suitable for the technical field of two-dimensional nanometer new material preparation, and provides a method for preparing MXene in a low-temperature medium-pressure molten alkali system, comprising the following steps: uniformly dispersing a MAX phase and an inorganic alkali in an agate mortar, transferring the mixed sample into a silver tube, injecting ammonia gas into the silver tube and sealing the silver tube; transferring the silver tube into a high-pressure reaction kettle filled with water, installing the reaction kettle on a LECO high-pressure hydrothermal reaction device to perform two-stage reactions of low-temperature low-pressure and low-temperature medium-pressure; washing inorganic salts and excessive alkali in the product with deionized water, so that the final MXene water dispersion is neutral, placing the dispersion in a beaker, treating with ultrasonic waves, then performing low-speed centrifugal separation, and then drying, so that single-layer MXene material is obtained. The method has mild reaction conditions, the obtained MXene material does not contain halogen functional groups, the sample has high purity, the cost is low, the method is green and pollution-free, and mass production can be performed.

Description

Technical Field

[0001] This invention belongs to the field of two-dimensional nanomaterial preparation technology, and particularly relates to a method for preparing MXene using a low-temperature, medium-pressure molten alkali system. Background Technology

[0002] MXene, a novel two-dimensional material, is primarily a transition metal carbide or nitride. It is generally synthesized by selectively etching the atom layer (A) of the MAX phase (where M is an early transition metal, A is mainly a group IIIA or IVA element, and X is C or N). MXene possesses excellent metallic conductivity and abundant surface functional groups, and is currently widely used in the research and development of supercapacitors. In summary, MXene, as a novel two-dimensional material, possesses many properties not found in traditional materials, and has a wide range of applications. In the MAX phase, the MX bond exhibits a strong mixed covalent / metallic / ionic character, while the MA bond is a weak metallic bond; therefore, most methods obtain MXene by selectively etching away the A atoms.

[0003] The invention patent CN106495210A, entitled "A Method for Preparing MXene Colloid," describes a method for preparing MXene colloid comprising the following steps: (1) mixing H2SO4 solution with NH4HF2 to prepare an etching solution containing HF and (NH4)2SO4; (2) adding MAX phase ceramic to the etching solution, etching it first, then washing it with deionized water by centrifugation until pH>6, and finally vacuum drying to obtain MXene powder; (3) adding deionized water to the MXene powder, sonicating it, and then centrifuging it to obtain MXene colloid. This synthesis method uses HF to etch the MAX phase. Although HF can effectively remove the A layer in the MAX phase, HF is highly corrosive, posing a significant health hazard and being environmentally unfriendly. Furthermore, the MXene synthesized by HF etching not only lacks control over the types of surface end groups, but the presence of F-functional groups also affects the electrochemical performance of the material.

[0004] The invention patent CN112194135A, entitled "A Method for Preparing MXene Materials from Molten Salt," describes a method that uses a halide salt as a salt bed. The method involves heating and melting the MAX phase, Lewis acid salt, and halide salt. After cooling, byproducts are washed away with deionized water and an oxidizing agent, followed by filtration and drying to obtain the MXene material. This method introduces halogen-containing functional groups, leading to poor performance of the synthesized MXene in certain applications. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing MXene using a low-temperature, medium-pressure molten alkali system, thereby addressing the problems mentioned in the background section.

[0006] The present invention is implemented as follows: a method for preparing MXene using a low-temperature, medium-pressure molten alkali system includes the following steps:

[0007] Step 1: Mix the MAX phase and inorganic base evenly in an agate mortar, transfer the mixed sample to a silver tube, inject ammonia into the silver tube and seal it.

[0008] Step 2: Transfer the silver tube to a high-pressure reactor filled with water, and install the reactor on the LECO high-pressure hydrothermal reactor to carry out two-stage reactions: low temperature and low pressure, and high temperature and high pressure.

[0009] Step 3: Wash away the inorganic salts and excess alkali in the product with deionized water to make the final aqueous dispersion of MXene neutral. Place the dispersion in a beaker, treat it with ultrasound, then separate it by low-speed centrifugation, and then dry it to obtain a single layer of MXene material.

[0010] In a further technical solution, in step 1, the MAX phase is one of Ti3AlC2, Ti2AlC, Ti2SnC, V2AlC, Ti3SiC2, or Ti3AlCN.

[0011] In a further technical solution, in step 1, the inorganic alkali is NaOH or KOH, the molar ratio of the MAX phase to the inorganic alkali is 1:5 to 20, and the grinding time is 1 to 10 minutes.

[0012] In a further technical solution, the ammonia pressure in step 1 is 5-10 MPa.

[0013] In a further technical solution, in step 2, the reaction temperature of the low-temperature and low-pressure reaction is 200–400°C, the reaction pressure is 50–100 MPa, and the reaction time is 2–4 hours; the reaction temperature of the low-temperature and medium-pressure reaction is 400–600°C, the reaction pressure is 100–150 MPa, and the reaction time is 6–12 hours.

[0014] In a further technical solution, in step 3, the ultrasonic treatment time is 20 min to 60 min, the drying temperature is 80 to 140℃, and the drying time is 1 to 4 hours.

[0015] The present invention provides a method for preparing MXene using a low-temperature, medium-pressure molten alkali system, the advantages of which are as follows:

[0016] (1) This method uses inorganic base and ammonia to treat the MAX phase to obtain MXene material. Compared with the MXene material obtained by traditional aqueous HF etching, the reaction conditions are mild, the obtained MXene material does not contain halogen functional groups, the sample has high purity, low cost and is green and pollution-free, and can be mass-produced.

[0017] (2) In this method, when reacting at low temperature and low pressure, the inorganic base reacts with the MAX phase, which weakens the metal bond strength in MA. When reacting at low temperature and medium pressure, the molten inorganic base is more conducive to the removal of group IIIA or IVA element A.

[0018] (3) This method involves injecting ammonia gas into a silver tube. The addition of an alkaline atmosphere helps to remove group IIIA or IVA elements in the MAX phase. At the same time, it can also achieve in-situ nitrogen doping of MXene materials and improve the electrical conductivity of the materials. Attached Figure Description

[0019] Figure 1 The X-ray diffraction pattern of Example 1;

[0020] Figure 2 This is a scanning electron microscope (SEM) image of Example 1;

[0021] Figure 3 This is an XPS test graph from Example 1;

[0022] Figure 4 This is another XPS test graph from Example 1;

[0023] Figure 5 This is another XPS test graph from Example 1;

[0024] Figure 6 The X-ray diffraction pattern is shown in Comparative Example 1.

[0025] Figure 7 The image shown is a scanning electron microscope (SEM) image of Comparative Example 1.

[0026] Figure 8 This is a comparison chart of the electrochemical performance of Example 1 and Comparative Example 1. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0028] The specific implementation of the present invention will be described in detail below with reference to specific embodiments.

[0029] An embodiment of the present invention provides a method for preparing MXene using a low-temperature, medium-pressure molten alkali system, comprising the following steps:

[0030] Step 1: Disperse the MAX phase and inorganic base evenly in an agate mortar and grind them. Transfer the ground sample to a silver tube, inject ammonia into the silver tube and seal it.

[0031] Step 2: Transfer the silver tube to a high-pressure reactor filled with water, and install the reactor on the LECO high-pressure hydrothermal reactor to carry out two-stage reactions: low temperature and low pressure, and high temperature and high pressure.

[0032] Step 3: Wash away the inorganic salts and excess alkali in the product with deionized water to make the final aqueous dispersion of MXene neutral. Place the dispersion in a beaker, treat it with ultrasound, then separate it by low-speed centrifugation, and then dry it to obtain a single layer of MXene material.

[0033] In a preferred embodiment of the present invention, in step 1, the MAX phase is one or a mixture of several of Ti3AlC2, Ti2AlC, Ti2SnC, V2AlC, Ti3SiC2, or Ti3AlCN.

[0034] In a preferred embodiment of the present invention, in step 1, the inorganic base is NaOH or KOH, the molar ratio of the MAX phase to the inorganic base is 1:5 to 1:20, and the grinding time is 1 to 10 minutes.

[0035] In a preferred embodiment of the present invention, the ammonia pressure in step 1 is 5-10 MPa.

[0036] In a preferred embodiment of the present invention, in step 2, the reaction temperature of the low-temperature and low-pressure reaction is 200-400°C, the reaction pressure is 50-100 MPa, and the reaction time is 2-4 hours; the reaction temperature of the low-temperature and medium-pressure reaction is 400-600°C, the reaction pressure is 100-150 MPa, and the reaction time is 6-12 hours.

[0037] In a preferred embodiment of the present invention, in step 3, the ultrasonic treatment time is 20 min to 60 min, the drying temperature is 80 to 140°C, and the drying time is 1 to 4 hours.

[0038] The following are several specific embodiments to verify the effectiveness of this method.

[0039] Example 1

[0040] (1) Disperse Ti3AlC2 phase and NaOH evenly in an agate mortar at a molar ratio of 1:20 and grind for 5 minutes. Transfer the ground medicine to a glove box filled with argon atmosphere. Transfer the medicine to a silver tube in the glove box and purge the silver tube with ammonia gas for 1 minute. Then seal one end of the silver tube and continue to purge with ammonia gas until the pressure of ammonia gas in the silver tube is 6.5 MPa. Then seal the silver tube.

[0041] (2) Transfer the silver tube to a high-pressure reactor filled with water. Install the reactor on the LECO high-pressure hydrothermal reactor. After the initial pressure of 50 MPa is supplied by the gas cylinder, close the main valve and raise the temperature to 300°C. React for 2.5 hours. Then, after the pressure is controlled to 100 MPa by the gas cylinder, raise the temperature to 400°C and react for 12 hours before cooling to room temperature.

[0042] (3) The inorganic salts and excess NaOH in the product were washed away with deionized water to make the pH of the final MXene aqueous dispersion neutral. The resulting black aqueous dispersion was placed in a beaker and treated with an ultrasonic cleaner for 60 min. Then, the sample was separated by centrifugation at 3500 r. The separated sample was dried at 120 °C for 2 h to obtain monolayer MXene material M1. The X-ray diffraction (XRD) pattern of the prepared material is shown in [reference needed]. Figure 1 Scanning electron microscope image (see) Figure 2 XPS chart Figure 3 , Figure 4 and Figure 5 .

[0043] Example 2

[0044] Same as Example 1, except that in step (1), Ti3AlC2 is replaced with Ti3SnC2, NaOH is replaced with KOH, and the molar ratio of Ti3SnC2 to KOH is 1:10. The pressure of ammonia gas is 7.5 MPa. The low-temperature, low-pressure reaction temperature is 500℃, the reaction pressure is 115 MPa, and the reaction time is 3 hours. The low-temperature, medium-pressure reaction temperature is 600℃, the reaction pressure is 180 MPa, and the reaction time is 10 hours, thus obtaining the monolayer MXene material M2 prepared by this invention.

[0045] Example 3

[0046] Same as Example 1, except that Ti3AlC2 in step (1) is replaced with Ti2AlC, and the molar ratio of Ti2AlC to NaOH is 1:15. The pressure of ammonia gas is 9 MPa. The low-temperature, low-pressure reaction temperature is 400℃, the reaction pressure is 100 MPa, and the reaction time is 4 hours. The low-temperature, medium-pressure reaction temperature is 650℃, the reaction pressure is 190 MPa, and the reaction time is 7 hours. The monolayer MXene material M3 prepared by this invention is obtained.

[0047] Example 4

[0048] Same as Example 1, except that Ti3AlC2 in step (1) is replaced with V2AlC, and the molar ratio of V2AlC to NaOH is 1:6. The pressure of ammonia gas is 5.5 MPa. The low-temperature reaction temperature is 550℃, the reaction pressure is 145 MPa, and the reaction time is 3 hours. The high-temperature reaction temperature is 550℃, the reaction pressure is 160 MPa, and the reaction time is 11 hours. The monolayer MXene material M4 prepared by this invention is obtained.

[0049] Comparative Example 1

[0050] Synthesis of Ti3C2 by HF method: HF (20% concentration) and MAX were heated in an oil bath at 35℃ for 24 h. The mixture was then washed with deionized water by centrifugation to remove acid and other salts, and finally dried to obtain a black powder. The XRD pattern of the prepared material is shown below. Figure 6 Scanning electron microscope image (see) Figure 7 .

[0051] High-voltage performance evaluation: The Ti3C2 prepared under high voltage was used to modify the zinc anode of an aqueous zinc-ion battery. The modified zinc anode was assembled into a symmetrical battery, and its cycle stability was observed. Figure 8 As shown, at 1mA cm -2 1mAh cm -2 Under the conditions, the symmetric cell modified with high-voltage Ti3C2 can maintain stability for 500 hours, while the symmetric cell modified with Ti3C2 etched by HF acid short-circuited after 300 hours. This indicates that the surface coating with high-voltage Ti3C2 effectively weakens the zinc dendrite phenomenon and avoids short circuits.

[0052] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for the production of MXene in a low-temperature, medium-pressure molten alkali system, characterized by, The method comprises the following steps: Step 1, uniformly mixing MAX phase and inorganic base in an agate mortar, transferring the mixed sample into a silver tube, injecting ammonia gas into the silver tube and sealing the silver tube; Step 2, transferring the silver tube into a high-pressure reaction kettle filled with water, installing the reaction kettle on a LECO high-pressure hydrothermal reaction device to perform two-stage reactions of low-temperature and low-pressure and high-temperature and high-pressure; Step 3, washing inorganic salt and excess base in the product with deionized water, making the final MXene water dispersion liquid neutral, placing the dispersion liquid in a beaker, treating with ultrasonic, then performing low-speed centrifugal separation, and then drying to obtain a single-layer MXene material; In the step 2, the reaction temperature of the low-temperature and low-pressure reaction is 200-400 DEG C, the reaction pressure is 50-100 MPa, and the reaction time is 2-4 hours; the reaction temperature of the low-temperature and medium-pressure reaction is 400-600 DEG C, the reaction pressure is 100-150 MPa, and the reaction time is 6-12 hours.

2. The method of claim 1, wherein the low-temperature, moderate-pressure molten alkali system preparation of MXene is characterized by, In the step 1, the MAX phase is one of Ti3AlC2, Ti2AlC, Ti2SnC, V2AlC, Ti3SiC2 or Ti3AlCN.

3. The method of claim 2, wherein the low-temperature, moderate-pressure molten alkali system preparation of MXene is characterized by, In the step 1, the inorganic base is NaOH or KOH, the molar ratio of the MAX phase to the inorganic base is 1:5-20, and the grinding time is 1-10 minutes.

4. The method of claim 1, wherein the low-temperature, moderate-pressure molten alkali system preparation of MXene is characterized by, In the step 1, the ammonia gas pressure is 5-10 MPa.

5. The method of claim 2, wherein the low-temperature, moderate-pressure molten alkali system preparation of MXene is characterized by, In the step 3, the ultrasonic treatment time is 20 min-60 min, the drying temperature is 80-140 DEG C, and the drying time is 1-4 hours.

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