A Phosphoric Acid-Assisted Hydrothermal Synthesis of Mo2CT x MXene methods and applications

Abstract

This invention relates to the fields of materials science and chemical engineering, specifically to a phosphoric acid-assisted hydrothermal synthesis method for Mo2CT. x The MXene method involves mixing Mo₂Ga₂C with an aqueous solution of phosphoric acid and conducting a hydrothermal reaction in a hydrothermal reactor. After the reaction is complete, the solid product is filtered and washed to remove unreacted phosphoric acid and Ga. 3+ Ions, after drying, yield Mo2CT x MXene. Mo2CT obtained by the method of this invention. x It has the advantages of high purity, no functional groups such as F and Cl on its surface, and extremely low residual P element. Compared with the traditional HF etching method, it shows significant advantages in terms of operational safety, production convenience and scalability potential. It has shown good application prospects in a variety of application fields such as catalytic materials, batteries, supercapacitors, and optoelectronic devices.

Description

Technical Field

[0001] This invention relates to the fields of materials science and chemical engineering, specifically to a phosphoric acid-assisted hydrothermal synthesis method for Mo2CT. x MXene methods and applications. Background Technology

[0002] Two-dimensional transition metal carbides or nitrides, also known as MXenes, have M n X n+1 T x The general structural formula for MXene is given by M, where M represents a transition metal carbide, X represents carbon or nitrogen, and T represents a surface functional group. Due to its large-spaced two-dimensional layered structure, abundant and tunable surface functional groups, and excellent conductivity, MXene has shown great promise in batteries, supercapacitors, optoelectronic devices, and catalysis, attracting widespread attention and research. Studies have shown that the type and distribution of surface functional groups in MXene-based materials significantly influence the electronic band structure of MXene, ultimately affecting its physicochemical properties and performance in various application scenarios.

[0003] The current mainstream method for synthesizing MXenes is to etch the corresponding precursor MAX phase using HF or a strong acid solution containing fluorine (F). For example, etching Mo2Ga2C with high concentrations of HF under heating conditions yields Mo2CT with F-functionalized surfaces. x While MXene can be successfully etched using fluoride salts and hydrochloric acid, this method does not eliminate the need for hazardous HF. Developing safe MXene synthesis methods is crucial for advancing MXene-based materials, especially for the safe synthesis of fluorine-free MXene.

[0004] Researchers have made initial explorations in developing halogen-free MXenes, such as the etching method using concentrated hydrochloric acid disclosed in patent (CN 111732103A) and the etching method using concentrated NaOH reported in the paper (Angew. Chem. Int. Ed. 2018, 57, 6115-6119). However, using HCl requires 37wt% concentrated hydrochloric acid, and using highly volatile HCl for hydrothermal reactions poses certain risks, and the resulting MXene surface contains -Cl functional groups. While etching with NaOH can yield halogen-free MXenes, it requires a hydrothermal reaction at 270°C, which far exceeds the maximum operating temperature of 220°C for commonly used PTFE-lined hydrothermal reactors in laboratories and industries. This excessively high hydrothermal temperature limits the application of this method. Therefore, developing a method for preparing MXenes under mild conditions is of great significance. Summary of the Invention

[0005] The purpose of this invention is to provide a method and application for the synthesis of Mo2CTx MXene via a phosphoric acid-assisted hydrothermal method, utilizing phosphoric acid as an etching agent and synthesizing multilayer Mo2CTx MXene through a hydrothermal reaction. x MXene was further processed to obtain monolayer and few-layer Mo2CT. x MXene. The method of this invention is safe and environmentally friendly, providing a high-quality basic material for applications such as electrochemical energy storage devices and catalysts.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] This invention provides a phosphoric acid-assisted hydrothermal method for the synthesis of Mo2CT. x MXene's method involves mixing Mo₂Ga₂C with an aqueous solution of phosphoric acid and conducting a hydrothermal reaction in a hydrothermal reactor. After the reaction is complete, the solid product is filtered and washed to remove unreacted phosphoric acid and Ga. 3+ Ions, after drying, yield Mo2CT x MXene.

[0008] In the above technical solution, the hydrothermal reaction temperature is 120-220℃ and the hydrothermal reaction time is greater than 2 hours. Higher temperatures can reduce the hydrothermal reaction time, but increase the risk. In order to improve reaction efficiency and ensure safety, the preferred hydrothermal reaction temperature is 160-180℃ and the hydrothermal reaction time is 8-24 hours.

[0009] In the above technical solution, the molar ratio of Mo2Ga2C to phosphoric acid is greater than 1:1.5. Preferably, 50 mL of 10% phosphoric acid aqueous solution is used for each 1 to 10 g of Mo2Ga2C etched.

[0010] In the above technical solution, the mass concentration of phosphoric acid in the phosphoric acid aqueous solution is less than 85%.

[0011] In the above technical solution, further, Mo2CT x MXene is mixed with an intercalating agent and subjected to ultrasonic treatment in a sealed container. The intercalating agent is then washed away to obtain monolayer and few-layer Mo2CT. x MXene.

[0012] In the above technical solution, the intercalating agent further includes one or more of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, and ethylenediamine. The solution for dissolving the intercalating agent includes, but is not limited to, one or more of ethanol and water. Preferably, an aqueous solution of tetrapropylammonium hydroxide is used.

[0013] Another aspect of the present invention provides a Mo2CT prepared by the above method.x MXene material.

[0014] The present invention also provides the above-mentioned Mo2CT x Applications of MXene materials in electrochemistry, catalysis, rechargeable batteries and supercapacitors.

[0015] The beneficial effects of this invention are as follows:

[0016] (1) The phosphoric acid used in this invention is a moderately strong acid and a non-volatile acid. The method can be achieved using a conventional hydrothermal reactor. The preparation conditions are mild, the equipment requirements are low, and it will not cause serious harm even after brief human contact. It avoids the harm caused by using hydrofluoric acid, high-concentration hydrochloric acid or high-concentration sodium hydroxide, making it safer.

[0017] (2) The phosphoric acid used in this invention is removed during the washing process and measured by EDS. After three filtrations and washings, Mo2CT is obtained. x The residual phosphorus content in MXene powder is only 0.1%, and the extremely low residual P content is of great significance for controlling the functional groups on the surface of MXene.

[0018] (3) Mo2CT prepared by the present invention x MXene surfaces do not contain halogen functional groups such as F and Cl; their main functional groups are -O and -OH, which improves their application prospects in catalysis, adsorption, and energy storage. Attached Figure Description

[0019] Figure 1 Mo2CT in Example 1 x SEM image of sample P10-24;

[0020] Figure 2 Mo2CT in Example 1 x -HRTEM images of sample P10-24, (a) magnified 340,000 times, (b) magnified 1,000,000 times, (c) selected area diffraction image;

[0021] Figure 3 The XRD spectra of the samples in Examples 1-4 and Comparative Examples 1-2 are shown. (a) is the Mo2Ga2C sample in Example 1, and (b) is the multilayer Mo2CT sample in Examples 1-4. x MXene samples, (c) are multilayer Mo2CT samples from Comparative Examples 1-2. x MXene samples;

[0022] Figure 4 Mo2CT in Example 1 x XRD spectrum of sample -1;

[0023] Figure 5Mo2CT in Example 1 x -1. CO2 hydrogenation performance diagram of sample. Detailed Implementation

[0024] To address the bottlenecks in MXene preparation and the numerous shortcomings of existing technologies, the inventors of this invention, through long-term research and extensive practice, have proposed the technical solution of this invention. The following will further explain and illustrate this technical solution, its implementation process, and its principles. However, it should be understood that within the scope of this invention, the above-mentioned technical features of this invention and the various technical features specifically described below (Examples) can be combined with each other to constitute new or preferred technical solutions.

[0025] Example 1

[0026] 1 g of Mo₂Ga₂C powder and 50 mL of 10% phosphoric acid aqueous solution were added to a 100 mL hydrothermal reactor lined with polytetrafluoroethylene. The reactor was hydrothermally reacted at 180 °C for 24 h. After the reactor cooled to room temperature, the liquid was removed by filtration. The solid was washed with deionized water until the pH of the filtrate was approximately 7. Then, it was dried overnight at 60 °C in a vacuum drying oven to obtain Mo₂CT. x MXene, denoted as Mo2CT x -P10-24.

[0027] Preparation of Mo2Ga2C powder: 5g of β-Mo2C and 8g of metallic gallium were added sequentially to a crucible, which was then covered and calcined at 750℃ for 72h under vacuum in a tube furnace. After the sample cooled, it was poured into 100mL of 10% hydrochloric acid and stirred until no bubbles were generated. Then, the gallium-containing solution and Mo2Ga2C solid were separated by filtration. The solid powder was washed with deionized water until the pH was about 7, and then dried overnight in an 80℃ forced-air drying oven to obtain Mo2Ga2C powder.

[0028] This embodiment obtains Mo2CT x -P10-24 powder 0.71g.

[0029] Figure 1 Mo2CT prepared in Example 1 x SEM image of P10-24, Figure 2 Mo2CT prepared in Example 1 x The HRTEM image at P10-24 shows that Mo2Ga2C was successfully etched into sheet-like Mo2CT using phosphoric acid. x MXene, Mo2CT x In MXene, Mo atoms are arranged in a hexagonal close-packed configuration; and through Figure 1 The XRD diffraction pattern shows that the multilayer Mo2CT obtained by phosphoric acid etching... xMXene contains some Mo2CT with larger interlayer spacing. x According to literature reports, a larger interlayer spacing is beneficial for the application of MXene in electrochemistry, energy storage devices and optoelectronic materials.

[0030] The multilayer Mo2CT prepared in Example 1 x -P10-24 was dissected into few-layer and single-layer Mo2CT. x Mxene was tested for its performance in carbon dioxide hydrogenation reaction. The stripping method was as follows: 0.5g Mo2CT was added... x -P10-24 was added to a flask containing 5 mL of 5% tetrapropylammonium hydroxide ethanol solution, sealed, and ultrasonically treated for 1 hour in an ultrasonic cleaner. The sample was then centrifuged to separate the solid precipitate, washed three times with anhydrous ethanol, and vacuum dried at 60°C to obtain few-layer and monolayer d-Mo2CT. x MXene, denoted as Mo2CT x -1.

[0031] Figure 4 Mo2CT x The XRD pattern at -1 allows for the observation of few-layer and monolayer d-Mo2CT. x The (002) interplanar spacing of MXene increased to 1.55 nm, indicating that d-Mo2CT x The MXene interlayer spacing is 1.55 nm, which is beneficial for the application of MXene in catalysis, rechargeable batteries and other fields.

[0032] Take 20mg Mo2CT x -1 The performance of CO2 hydrogenation reaction was tested in a fixed-bed CO2 hydrogenation reactor. Before the reaction, the reactor was pretreated in 40 mL / min H2 at 450 °C for 2 h. During the reaction, the temperature was increased stepwise from 200 °C to 600 °C, and the reactor was tested by introducing 24 mL / min CO2 + 72 mL / min H2 and 4 mL / min N2. The reaction space velocity was 300,000 mL / g. cat. -1 h -1 The test results are as follows Figure 5 As shown.

[0033] Example 2

[0034] The preparation process is similar to that in Example 1, except that the concentration of the phosphoric acid aqueous solution is 5%.

[0035] 1 g of Mo₂Ga₂C powder and 50 mL of 5% phosphoric acid aqueous solution were added to a 100 mL hydrothermal reactor lined with polytetrafluoroethylene. The reaction was carried out at 180 °C for 24 h. After the hydrothermal reactor cooled to room temperature, the supernatant was poured off. After the hydrothermal reactor cooled to room temperature, the liquid was filtered off. The solid was washed with deionized water until the pH of the filtrate was approximately 7. Then, it was dried overnight at 60 °C in a vacuum drying oven to obtain Mo₂CT. x MXene, denoted as Mo2CT x -P5-24, This embodiment obtains Mo2CT x -P5-24 powder 0.71g.

[0036] Example 3

[0037] The preparation process is similar to that in Example 1, except that the hydrothermal reaction temperature is 160°C.

[0038] 1 g of Mo₂Ga₂C and 50 mL of 10% phosphoric acid solution were added to a 100 mL hydrothermal reactor lined with polytetrafluoroethylene. The reactor was hydrothermally reacted at 160 °C for 24 h. After the reactor cooled to room temperature, the liquid was removed by filtration. The solid was washed with deionized water until the pH of the filtrate was approximately 7. The solid was then dried overnight at 60 °C in a vacuum drying oven to obtain Mo₂CT. x MXene, denoted as Mo2CT x -P10-160. This embodiment yields Mo2CT. x 0.71g of MXene powder.

[0039] Example 4

[0040] The preparation process is similar to that in Example 1, except that the hydrothermal reaction time is 8 hours.

[0041] 1 g of Mo₂Ga₂C and 50 mL of 10% phosphoric acid solution were added to a 100 mL hydrothermal reactor lined with polytetrafluoroethylene. The reactor was hydrothermally reacted at 180 °C for 8 h. After the reactor cooled to room temperature, the liquid was removed by filtration. The solid was washed with deionized water until the pH of the filtrate was approximately 7. The solid was then dried overnight at 60 °C in a vacuum drying oven to obtain Mo₂CT. x MXene, denoted as Mo2CT x -P10-8. This embodiment yields Mo2CT. x 0.71g of MXene powder.

[0042] Example 5

[0043] The preparation process is similar to that in Example 1, except that the hydrothermal reaction temperature is 120°C and the hydrothermal reaction time is 72 h.

[0044] 1 g of Mo₂Ga₂C and 50 mL of 10% phosphoric acid solution were added to a 100 mL hydrothermal reactor lined with polytetrafluoroethylene. The reactor was hydrothermally reacted at 120 °C for 72 h. After the reactor cooled to room temperature, the liquid was removed by filtration. The solid was washed with deionized water until the pH of the filtrate was approximately 7. The solid was then dried overnight at 60 °C in a vacuum drying oven to obtain Mo₂CT. x MXene. This embodiment yields Mo2CT. x 0.68g of MXene powder.

[0045] Example 6

[0046] The preparation process is similar to that in Example 1, except that the hydrothermal reaction temperature is 200°C and the hydrothermal reaction time is 6 hours.

[0047] 1 g of Mo₂Ga₂C and 50 mL of 10% phosphoric acid solution were added to a 100 mL hydrothermal reactor lined with polytetrafluoroethylene. The reactor was hydrothermally reacted at 200 °C for 6 h. After the reactor cooled to room temperature, the liquid was removed by filtration. The solid was washed with deionized water until the pH of the filtrate was approximately 7. The solid was then dried overnight at 60 °C in a vacuum drying oven to obtain Mo₂CT. x MXene. This embodiment yields Mo2CT. x 0.68g of MXene powder.

[0048] Comparative Example 1

[0049] 1 g of Mo₂Ga₂C and 50 mL of 40% hydrofluoric acid solution were added to a 100 mL hydrothermal reactor lined with polytetrafluoroethylene. The reactor was hydrothermally reacted at 180 °C for 24 h. After the reactor cooled to room temperature, the precipitate was collected by centrifugation. The precipitate was washed with deionized water until the pH of the filtrate was approximately 7. Then, it was dried overnight at 60 °C in a vacuum drying oven to obtain Mo₂CT. x MXene, denoted as Mo2CT x -F10-24, this comparative example yields Mo2CT x 0.68g of MXene powder.

[0050] Comparative Example 2

[0051] 1 g of Mo₂Ga₂C and 50 mL of 37% hydrochloric acid solution were added to a 100 mL hydrothermal reactor lined with polytetrafluoroethylene. The reactor was hydrothermally reacted at 180 °C for 24 h. After the reactor cooled to room temperature, the precipitate was collected by centrifugation. The precipitate was washed with deionized water until the pH of the filtrate was ~7. Then, it was dried overnight at 60 °C in a vacuum drying oven to obtain Mo₂CT. x MXene, denoted as Mo2CT x -Cl10-24, this comparative example yields Mo2CT xMXene powder 0.69g.

[0052] Table 1. Overview of parameter control in Examples 1-6 and Comparative Examples 1-2

[0053]

[0054]

[0055] As shown in Table 1, Example 3 demonstrates that Mo2Ga2C can be completely etched at 160°C; Example 4 demonstrates that Mo2Ga2C can be completely etched within 8 hours; Example 5 demonstrates that Mo2Ga2C can be etched at 120°C, but requires a longer time; and Example 6 demonstrates that increasing the reaction temperature can significantly reduce the required time. However, to improve synthesis efficiency and ensure safety, 160-180°C is typically used. Comparative Examples 1-2 demonstrate that Mo2CT can also be obtained using etching with hydrofluoric acid and hydrochloric acid. x MXene, but the yield is slightly lower than that of the phosphoric acid etching method.

[0056] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the implementation. The scope of protection of the present invention should be determined by the scope defined in the claims. Other variations or modifications can be made based on the above description. Obvious variations or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A phosphoric acid-assisted hydrothermal synthesis of Mo2CT x MXene's method is characterized by, Mo₂Ga₂C was mixed with an aqueous solution of phosphoric acid and placed in a hydrothermal reactor for hydrothermal reaction. After the reaction was completed, the solid product was filtered, washed, and dried to obtain Mo₂CT. x MXene; The hydrothermal reaction temperature is 160~180 ℃.

2. The method according to claim 1, wherein the hydrothermal reaction time is greater than 2 h.

3. The method according to claim 1, characterized in that, The molar ratio of Mo2Ga2C to phosphoric acid is greater than 1:1.

5.

4. The method according to claim 1, characterized in that, The phosphoric acid aqueous solution has a phosphoric acid mass concentration of less than 85%.

5. The method according to claim 1, characterized in that, Mo2CT x MXene is mixed with an intercalating agent and subjected to ultrasonic treatment in a sealed container. The intercalating agent is then washed away to obtain monolayer and few-layer Mo2CT. x MXene.

6. The method according to claim 5, characterized in that, The intercalating agent includes one or more of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, and ethylenediamine.

7. A Mo2CT prepared by the method according to any one of claims 1-6 x MXene material.

8. A Mo2CT as described in claim 7 x Applications of MXene materials in electrochemistry, catalysis, rechargeable batteries and supercapacitors.

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