A method for preparing two-dimensional transition metal carbide

Abstract

The present invention provides a method for preparing a two-dimensional transition metal carbide, which belongs to the technical field of two-dimensional materials. The present invention mixes Ti3AlC2 powder, an organic intercalant and a fluorine-free inorganic acid etchant, and performs etching treatment in the presence of supercritical carbon dioxide to obtain a two-dimensional transition metal carbide. The present invention uses Ti3AlC2 powder as a raw material and utilizes supercritical carbon dioxide to assist in etching treatment, which can achieve green, gentle and efficient preparation of two-dimensional transition metal carbides (specifically MXene‑Ti3C2). At the same time, the method provided by the present invention has simple requirements on the device structure and is easy to operate, which provides a new idea for the green and gentle preparation of MXene‑Ti3C2 and has great application prospects. Furthermore, the present invention can prepare a single / few layer of MXene‑Ti3C2 (≤10 layers) by washing and stripping after etching.

Description

Technical Field

[0001] The present invention relates to the technical field of two-dimensional nanomaterials, and in particular to a method for preparing two-dimensional transition metal carbides. Background Art

[0002] With the rapid development of inorganic nanomaterial preparation, many two-dimensional inorganic nanomaterials have been discovered. Mxene-Ti3C2, a new type of two-dimensional transition metal carbide, has a similar lamellar structure to graphene and exhibits excellent electrical conductivity. Research has shown that its electrical conductivity and charge storage capacity surpass those of graphene and carbon nanotubes, suggesting promising application prospects in lithium batteries.

[0003] MXene-Ti3C2 is typically obtained by chemically etching Al from MAX phase materials (Ti3AlC2). Common etchants include HF, NH4HF2, and a mixture of HCl and LiF. Intercalation agents include dimethyl sulfoxide (DMSO), tetrabutylammonium hydroxide (TBAOH), isopropylamine (IPA), and hydrazine hydrate. However, these etchants do not effectively strip Al and produce AlF3 as a byproduct. AlF3 adheres to the surface of MXene-Ti3C2 and is difficult to remove. Furthermore, the resulting fluorine capping affects the performance of MXene-Ti3C2 (e.g., capacitance). Fluorine-free methods can also be used to prepare MXene-Ti3C2, but these methods typically require high temperatures and concentrated acid or base conditions. For example, etching with Lewis acid salts (CuCl2, ZnCl2, etc.) requires temperatures above 750°C; etching with concentrated HCl (12MHCl) requires temperatures above 140°C; and etching with the Bayer process (27.5MNaOH) requires temperatures above 270°C. These methods require harsh etching conditions and do not meet environmental protection requirements, resulting in significant risks and environmental pollution. Currently, the only method for preparing MXene-Ti3C2 under fluorine-free conditions at room temperature is electrochemical etching, but this cannot be widely implemented due to equipment limitations, and this method is also inefficient in removing the Al interlayer. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for preparing two-dimensional transition metal carbides. The present invention uses Ti3AlC2 powder as raw material and utilizes supercritical carbon dioxide to assist in etching treatment, which can achieve green, mild and efficient preparation of two-dimensional transition metal carbides.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for preparing a two-dimensional transition metal carbide, comprising the following steps:

[0007] Ti3AlC2 powder, an organic intercalation agent and a fluorine-free inorganic acid etchant are mixed and etched in the presence of supercritical carbon dioxide to obtain a two-dimensional transition metal carbide.

[0008] Preferably, the organic intercalant comprises one or more of dimethyl sulfoxide, ethanol and methanol.

[0009] Preferably, the fluorine-free inorganic acid etchant includes one or more of hydrochloric acid, nitric acid and sulfuric acid; and the concentration of the fluorine-free inorganic acid etchant is 0.1-2.5 mol / L.

[0010] Preferably, the volume ratio of the organic intercalant to the fluorine-free inorganic acid etchant is (1-3): (0.5-1.5); the ratio of the mass of the Ti3AlC2 powder to the total volume of the organic intercalant and the fluorine-free inorganic acid etchant is (3-10) mg: 1 mL.

[0011] Preferably, the etching treatment conditions include: temperature of 32 to 55° C., pressure of 8 to 30 MPa, and time of 0.5 to 24 h.

[0012] Preferably, after the etching treatment, the method further comprises: washing the etching material obtained after the etching treatment.

[0013] Preferably, after the washing, the method further comprises: mixing the washed material obtained after washing with a stripping agent to perform a stripping treatment.

[0014] Preferably, the stripping agent includes one or more of dimethyl sulfoxide, methanol and hydrazine hydrate.

[0015] Preferably, the ratio of the washing material to the stripping agent is (1-20) mg:1 mL.

[0016] Preferably, the stripping treatment is performed under ultrasonic conditions, the temperature of the stripping treatment is 0 to 26° C., and the time is 0.5 to 2 hours.

[0017] The present invention provides a method for preparing a two-dimensional transition metal carbide, comprising the following steps: mixing Ti3AlC2 powder, an organic intercalating agent and a fluorine-free inorganic acid etchant, and performing an etching treatment in the presence of supercritical carbon dioxide (scCO2) to obtain a two-dimensional transition metal carbide. The present invention uses Ti3AlC2 powder as a raw material and utilizes scCO2 to assist in the etching treatment, thereby being able to achieve a green, mild and efficient preparation of a two-dimensional transition metal carbide (specifically MXene-Ti3C2). Specifically, the present invention adopts a method comprising combining an organic phase, an inorganic acid phase and scCO2 to construct an scCO2 homogeneous system to selectively etch the Al element. scCO2 can create a solvent environment system with high diffusivity and high permeability, so that the formed homogeneous system can have a better binding and etching effect on the Al element. The method provided by the present invention is mild and green and environmentally friendly, avoiding high-temperature environments, metal ion escape and the use of toxic and highly corrosive hydrofluoric acid. The preparation process is safe and stable, the preparation flow is simple, and the prepared MXene-Ti3C2 does not contain fluorine and is fluorine-terminated, which is beneficial to reducing the generation of defect structures and improving the electron transfer efficiency of the material. At the same time, the method provided by the present invention has simple requirements on the device structure and is easy to operate, providing a new idea for the green and mild preparation of MXene-Ti3C2, and has great application prospects.

[0018] Furthermore, the present invention can prepare a single / few layers of Mxene-Ti3C2 (≤10 layers) by washing and stripping after etching. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The device and principle diagram of the present invention for preparing two-dimensional transition metal carbides using supercritical carbon dioxide as an aid;

[0020] Figure 2 The scanning electron microscope images of the Ti3AlC2 powder and the multilayer MXene-Ti3C2 prepared after supercritical assisted etching in Example 1;

[0021] Figure 3 The scanning electron microscope image and elemental analysis characterization image of the multilayer MXene-Ti3C2 prepared in Example 1;

[0022] Figure 4 The scanning electron microscope image and elemental analysis characterization image of the material obtained by etching without the participation of an organic intercalant in Comparative Example 1;

[0023] Figure 5 The dispersion photo and transmission electron micrograph of the single / few-layer (≤10 layers) MXene-Ti3C2 prepared in Example 2;

[0024] Figure 6Material characterization diagrams (including X-ray diffraction diagram, ultraviolet-visible spectrum diagram, Fourier transform infrared spectrum diagram and X-ray photoelectron spectrum diagram) of single / few layer (≤10 layers) MXene-Ti3C2 prepared in Example 2;

[0025] Figure 7 The performance characterization diagram of the MXene-Ti3C2 working electrode prepared in Example 3 (including cyclic voltammetry curve, constant current charge and discharge curve, cycle rate diagram and cycle curve). DETAILED DESCRIPTION

[0026] The present invention provides a method for preparing a two-dimensional transition metal carbide, comprising the following steps:

[0027] Ti3AlC2 powder, an organic intercalation agent and a fluorine-free inorganic acid etchant are mixed and etched in the presence of supercritical carbon dioxide to obtain a two-dimensional transition metal carbide.

[0028] In the present invention, unless otherwise specified, the raw materials used are commercially available products well known to those skilled in the art.

[0029] The present invention combines Ti3AlC2 powder, an organic intercalant, and a fluorine-free inorganic acid etchant to produce a mixed liquid. The Ti3AlC2 powder preferably has a particle size of 200 mesh. The organic intercalant preferably includes one or more of dimethyl sulfoxide, ethanol, and methanol, with dimethyl sulfoxide being more preferred. The present invention preferably utilizes these organic intercalants, which improves the permeation efficiency of the homogeneous system and, in turn, enhances the etching process. In the present invention, the fluorine-free inorganic acid etchant preferably includes one or more of hydrochloric acid, nitric acid and sulfuric acid, more preferably hydrochloric acid; the concentration of the fluorine-free inorganic acid etchant is preferably 0.1-2.5 mol / L, more preferably 0.3-1.5 mol / L, and further preferably 0.5-1.5 mol / L; in the present invention, the volume ratio of the organic intercalant to the fluorine-free inorganic acid etchant is preferably (1-3):(0.5-1.5), more preferably (1.5-2.5):(0.8-1.2), and further preferably 2:1; the ratio of the mass of the Ti3AlC2 powder to the total volume of the organic intercalant and the fluorine-free inorganic acid etchant is preferably (3-10) mg:1 mL, more preferably (6-7) mg:1 mL.

[0030] After obtaining the mixed liquid, the present invention etches the mixed liquid in the presence of supercritical carbon dioxide to obtain a two-dimensional transition metal carbide. In the present invention, the conditions for the etching treatment preferably include: a temperature of preferably 32 to 55°C, more preferably 32 to 45°C; a pressure of preferably 8 to 30 MPa, more preferably 14 to 20 MPa; a time of preferably 0.5 to 24 hours, more preferably 18 to 24 hours. In the present invention, the etching treatment is preferably carried out in a supercritical carbon dioxide kettle; specifically, the mixed liquid is placed in a supercritical carbon dioxide kettle, and then carbon dioxide is introduced to form supercritical carbon dioxide under the above conditions for etching. In the present invention, during the etching process, the organic intercalant and supercritical carbon dioxide carry the fluorine-free inorganic acid etchant to the reaction site, selectively react with the interlayer Al element of the Ti3AlC2 powder, etch away the Al layer, and the remaining components are subsequently washed and separated to collect a multilayer two-dimensional transition metal carbide (denoted as multilayer MXene-Ti3C2, with a layer number >10 layers).

[0031] Supercritical carbon dioxide (scCO2) is a fluid in which the interface between liquid and gas disappears when CO2 exceeds a specific critical point temperature and pressure condition (31.26°C, 7.18MPa). It has the characteristics of both liquid and gas, and therefore has the characteristics of a large diffusion coefficient, low viscosity, and good permeability. In addition, CO2 is stable in nature and has good physical and chemical properties such as being odorless, tasteless, non-toxic, non-flammable and non-explosive. The present invention uses Ti3AlC2 powder as raw material and utilizes scCO2 to assist in etching treatment, which can achieve green and gentle preparation of two-dimensional transition metal carbides (specifically MXene-Ti3C2). Specifically, the present invention adopts a method comprising combining an organic phase, an inorganic acid phase and scCO2 to construct a scCO2 homogeneous system to selectively etch the Al element. scCO2 can create a solvent environment system with high diffusivity and high permeability, so that the formed homogeneous system can have a better binding and etching effect on the Al element. The method provided by the present invention is mild and green and environmentally friendly, avoiding high-temperature environments, metal ion escape and the use of toxic and highly corrosive hydrofluoric acid. The prepared MXene-Ti3C2 does not contain fluorine and is fluorine-terminated, which is beneficial to reducing the generation of defect structures and improving the electron transfer efficiency of the material. At the same time, the method provided by the present invention is simple to operate, providing a new idea for the green and mild preparation of MXene-Ti3C2, and has great application prospects.

[0032] In the present invention, after the etching treatment, the etching material obtained after the etching treatment is further included: washing the etched material. The present invention preferably performs solid-liquid separation on the material liquid obtained after the etching treatment, and washes the obtained solid material; the present invention does not specifically limit the method of solid-liquid separation, and can adopt a method well known to those skilled in the art, such as centrifugation; the speed of the centrifugation is preferably 3000-4000r / min, more preferably 3500r / min, and the time is preferably 5-15min, more preferably 10-15min. In the present invention, the reagent used for the washing is preferably ultrapure water; the washing method is preferably ultrasonic washing, and the number of washings is preferably 4-6 times; after each ultrasonic washing, solid-liquid separation is preferably performed, and then the next washing is performed. The method of solid-liquid separation is preferably consistent with the above technical solution, which will not be repeated here; the present invention preferably washes until the supernatant is pure and the pH value of the supernatant is 5-6, at which time the corresponding solid material is multilayer MXene-Ti3C2 (number of layers>10 layers).

[0033] In the present invention, after washing, the step preferably further comprises: mixing the washing material obtained after washing with a stripping agent for stripping treatment. In the present invention, the stripping agent preferably comprises one or more of dimethyl sulfoxide, methanol and hydrazine hydrate, more preferably dimethyl sulfoxide. In the present invention, the amount ratio of the washing material to the stripping agent is preferably (1-20) mg:1 mL, more preferably (5-10) mg:1 mL; the washing material is the multilayer MXene-Ti3C2. In the present invention, the stripping treatment is preferably carried out under ultrasonic conditions; the temperature of the stripping treatment is preferably 0-26°C, more preferably 0-10°C, and further preferably 0-5°C. In an embodiment of the present invention, the stripping treatment is specifically carried out under ice bath conditions; the stripping treatment time is preferably 0.5-2h, more preferably 1-1.5h. In the present invention, multilayer MXene-Ti3C2 is stripped to form a single / few-layer two-dimensional transition metal carbide (denoted as a single / few-layer MXene-Ti3C2, with a layer number ≤10 layers) through stripping treatment. After the stripping treatment, the present invention preferably centrifuges the obtained liquid and freeze-dries the obtained supernatant to obtain a single / few-layer MXene-Ti3C2 (number of layers ≤ 10 layers); the centrifugal speed is preferably 3000-4000 r / min, more preferably 3500 r / min, and the time is preferably 15-60 min, more preferably 30-60 min.

[0034] Figure 1This is a schematic diagram of the apparatus and principle for preparing two-dimensional transition metal carbides using supercritical carbon dioxide as an aid in the present invention. The present invention is based on the preparation of two-dimensional transition metal carbides with the aid of supercritical carbon dioxide. During the etching process, the organic intercalant and the fluorine-free inorganic acid etchant captured by scCO2 enter the layer structure of the Ti3AlC2 powder and break the Ti-Al bond (this depends on the dependent interface formed by the organic intercalant and scCO2). The increase in local density leads to enhanced permeability, allowing the reaction to continue. The obtained multilayer MXene-Ti3C2 is then ultrasonically stripped to form a single / few-layer MXene-Ti3C2. In addition, due to the fluorine-free etching, the stripped Ti3C2 flakes do not include fluorine ends. However, simple fluorine-free inorganic acid etchants such as hydrochloric acid cannot successfully prepare a wide range of MXene systems. When etching is performed only by scCO2 and hydrochloric acid without using an organic intercalant, it cannot achieve a good etching effect because of its low affinity for intermediate elements. At the same time, the organic intercalating agent such as dimethyl sulfoxide (DMSO) in the present invention can significantly enhance the activity energy of the MXene surface. The high permeability of scCO2 can successfully penetrate the material layers and destroy the interlayer van der Waals force, thereby successfully preparing MXene-Ti3C2.

[0035] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0036] Example 1

[0037] 200 mg Ti3AlC2 powder (200 mesh), 20 mL dimethyl sulfoxide and 10 mL 1.5 mol / L hydrochloric acid were mixed evenly, and the resulting mixture was transferred to a supercritical carbon dioxide autoclave and etched at a pressure of 20 MPa and a temperature of 32°C for 24 hours. After the etching, the resulting liquid was collected and centrifuged at a speed of 3500 r / min for 15 minutes. Ultrapure water was added to the resulting precipitate for ultrasonic dispersion and centrifugation again. The dispersion and centrifugation operations were repeated 4 times to achieve sufficient washing until pure multilayer MXene-Ti3C2 with a supernatant pH of 5 to 6 was obtained.

[0038] Figure 2 The scanning electron microscope images of Ti3AlC2 powder and multilayer MXene-Ti3C2 prepared after supercritical assisted etching in Example 1, where (A) is the scanning electron microscope image of Ti3AlC2 powder and (B) is the scanning electron microscope image of multilayer Ti3C2. Figure 2The layered behavior of Ti3AlC2 can be seen, indicating that the etching of interlayer aluminum elements increases the interlayer freedom.

[0039] Figure 3 The scanning electron microscope image and elemental analysis characterization image of the multilayer MXene-Ti3C2 prepared in Example 1. Figure 3 It can be seen that the etching behavior of Ti3AlC2 is accompanied by a corresponding decrease in the number of aluminum atoms, forming multilayer MXene-Ti3C2.

[0040] Comparative Example 1

[0041] The method of Example 1 was followed, except that dimethyl sulfoxide was omitted, that is, Ti3AlC2 powder was directly mixed with hydrochloric acid for subsequent treatment.

[0042] Figure 4 The scanning electron microscope image and elemental analysis characterization image of the material obtained by etching without the participation of organic intercalation agent in comparative example 1. Figure 4 It can be explained that when Ti3AlC2 powder is supercritically etched without the participation of organic intercalants, the number of aluminum atoms decreases accordingly, but the complete etching of aluminum atoms and the stratification behavior of the material are not achieved.

[0043] Example 2

[0044] 200 mg of multilayer MXene-Ti3C2 prepared in Example 1 was mixed with 20 mL of exfoliation reagent (specifically DMSO), ultrasonically exfoliated for 1 h in an ice bath (0°C), and then centrifuged at 3500 r / min for 60 min. The supernatant was freeze-dried to prepare single / few-layer (≤10 layers) MXene-Ti3C2.

[0045] Figure 5 The dispersion of single / few layers (≤10 layers) of MXene-Ti3C2 obtained after ultrasonic exfoliation in an ice bath in Example 2 and the transmission electron microscope image are shown. Figure 5 It can be shown that after ultrasonic exfoliation of multilayer MXene-Ti3C2, single / few layers (≤10 layers) MXene-Ti3C2 with good dispersion can be prepared.

[0046] Ti3AlC2 powder and MXene-Ti3C2 prepared in Example 2 were characterized by X-ray diffraction (XRD), ultraviolet-visible spectroscopy (UV), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) (black: Ti3AlC2; red: Ti3C2). Figure 6 As shown, (A) is the XRD, Raman, UV and IR characterization diagram, (B) is the XPS characterization diagram. Figure 6It can be seen that compared with Ti3AlC2, no characteristic peaks and groups of fluorine were found in Ti3C2 prepared by supercritical assisted etching, indicating that fluorine-free MXene-Ti3C2 was successfully prepared by supercritical assisted etching.

[0047] Example 3

[0048] The MXene-Ti3C2 sheet prepared in Example 2, acetylene black and polytetrafluoroethylene (PTFE) were mixed in a mass ratio of 8:1:1, the resulting mixture was pressed into a film, and then dried at 80°C in a vacuum overnight; after drying, the film was cut into discs and pressed onto carbon writing paper to form a working electrode.

[0049] The MXene-Ti3C2 working electrode prepared in Example 3 was used to test the supercapacitor performance. Figure 7 shown. Figure 7 (A) is the cyclic voltammetry curve of the MXene-Ti3C2 working electrode as a capacitor device. It is calculated that at a scan rate of 2 mV / s, the maximum mass capacity of the capacitor can reach 320 F / g. Figure 7 Middle (B) is the constant current charge and discharge curve of the capacitor. It can be seen that as the charging current increases, the time span of the curve gradually decreases, and the symmetry is good, that is, the Coulomb efficiency reaches 100%, and the energy is well utilized. Figure 7 Middle (C) is the cycle rate diagram of the MXene-Ti3C2 working electrode. It can be seen that the performance of the electrode is stable during the cycle process with different charging currents, and the capacity is not much different from that at the beginning of the cycle, indicating that this capacitor has good rate performance and stability. Figure 7 Middle (D) is a cycle curve of 10,000 cycles under 5A / g discharge conditions using a constant current charge and discharge method. After 10,000 cycles, the capacity of the capacitor can still reach 96% of the original capacity, showing good electrochemical stability.

[0050] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing a two-dimensional transition metal carbide, comprising the following steps: Ti3AlC2 powder, an organic intercalation agent and a fluorine-free inorganic acid etchant are mixed and etched in the presence of supercritical carbon dioxide to obtain a two-dimensional transition metal carbide. The fluorine-free inorganic acid etchant includes one or more of hydrochloric acid, nitric acid and sulfuric acid; The concentration of the fluorine-free inorganic acid etchant is 0.1 to 1.5 mol / L; The etching treatment conditions include: temperature of 32° C., pressure of 8-20 MPa, and time of 0.5-24 h.

2. The preparation method according to claim 1, characterized in that The organic intercalant includes one or more of dimethyl sulfoxide, ethanol and methanol.

3. The preparation method according to claim 1 or 2, characterized in that The volume ratio of the organic intercalant to the fluorine-free inorganic acid etchant is (1-3): (0.5-1.5); the ratio of the mass of the Ti3AlC2 powder to the total volume of the organic intercalant and the fluorine-free inorganic acid etchant is (3-10) mg: 1 mL.

4. The preparation method according to claim 1, characterized in that After the etching process, the method further comprises: washing the etching material obtained after the etching process.

5. The preparation method according to claim 4, characterized in that After the washing, the method further comprises: mixing the washed material obtained after washing with a stripping agent to perform a stripping treatment.

6. The preparation method according to claim 5, characterized in that The stripping agent includes one or more of dimethyl sulfoxide, methanol and hydrazine hydrate.

7. The preparation method according to claim 5 or 6, characterized in that: The usage ratio of the washing material to the stripping agent is (1-20) mg:1 mL.

8. The preparation method according to claim 5, characterized in that The stripping treatment is performed under ultrasonic conditions, the temperature of the stripping treatment is 0 to 26° C., and the time is 0.5 to 2 hours.

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