Method for synthesizing Mo2CTx MXene by phosphoric acid-assisted hydrothermal method and application of Mo2CTx MXene

Abstract

The invention relates to the field of material science and chemical engineering, in particular to a method for synthesizing Mo2CTx MXene by a phosphoric acid-assisted hydrothermal method. The preparation method comprises the following steps: mixing Mo2Ga2C with a phosphoric acid aqueous solution, putting the mixture into a hydrothermal reaction kettle for hydrothermal reaction, after the reaction is completed, filtering and washing a solid product to remove unreacted phosphoric acid and Ga < 3 + > ions, and drying to obtain Mo2CTx MXene. The Mo2CTx obtained through the method has the advantages of being high in purity, free of functional groups such as F and Cl on the surface and extremely low in P element residue, and compared with a traditional HF etching method, the Mo2CTx has remarkable advantages in the aspects of operation safety, production convenience and large-scale potential, and the method is suitable for industrial production. Good application prospects are shown in various application fields of catalytic materials, batteries, supercapacitors, photoelectric devices and the like.

Description

Technical Field

[0001] The present invention relates to the fields of material science and chemical engineering, and in particular to a phosphoric acid-assisted hydrothermal method for synthesizing Mo 2 CT x Methods and applications of MXene. Background Art

[0002] Two-dimensional transition metal carbides or nitrides are also called MXenes. n X n+1 T x The general structural formula of MXene is MXene, where M represents transition metal carbide, X represents carbon or nitrogen, and T represents surface functional groups. Due to the advantages of MXene such as large-spaced two-dimensional layered structure, rich and adjustable surface functional groups and excellent conductivity, it has shown excellent application prospects in the fields of batteries, supercapacitors, optoelectronic devices and catalysis, and has received extensive attention and research. Studies have shown that the type and distribution of surface functional groups of MXene-based materials have an important influence on the electronic band structure of MXene, which is ultimately reflected in the physical and chemical properties and performance of MXene in various application scenarios.

[0003] At present, the mainstream method for synthesizing MXene is to use HF or a strong acid solution containing F to etch the corresponding precursor MAX phase. For example, using high concentration HF to etch Mo under heating conditions 2 Ga 2 C obtains Mo with F functional groups on the surface 2 CT x Although MXene can be successfully etched by using fluoride salts and hydrochloric acid, it does not substantially avoid the use of dangerous HF. The development of safe MXene synthesis methods is of great significance to promote the development of MXene-based materials, especially the safe synthesis of F-free MXene.

[0004] Researchers have conducted preliminary explorations in the development of F-free MXenes, such as the method of etching with concentrated hydrochloric acid published in the patent (CN 111732103A), and the method of etching with concentrated NaOH reported in the paper (Angew.Chem.Int.Ed.2018,57,6115-6119). However, the use of HCl requires the use of 37wt% concentrated hydrochloric acid, and the use of highly volatile HCl for hydrothermal reaction is somewhat dangerous, and the obtained MXene surface contains -Cl functional groups. Although NaOH etching can obtain halogen-free MXene, it requires hydrothermal reaction at 270°C, which is far beyond the maximum operating temperature of 220°C of polytetrafluoroethylene-lined hydrothermal reactors commonly used in laboratories and industry. The excessively high hydrothermal temperature limits the application of this method. Therefore, it is of great significance to develop a method for preparing MXene under mild conditions. Summary of the invention

[0005] The purpose of the present invention is to provide a phosphoric acid-assisted hydrothermal method for synthesizing Mo 2 Method and application of CTx MXene, using phosphoric acid as an etchant and synthesizing multilayer Mo by hydrothermal reaction 2 CT x MXene, and further processed to obtain single-layer and few-layer Mo 2 CT x MXene. The method of the present invention is safe and environmentally friendly, and provides high-quality basic materials for applications such as electrochemical energy storage devices and catalysts.

[0006] In order to achieve the above object, the technical solution of the present invention is as follows:

[0007] On the one hand, the present invention provides a phosphoric acid-assisted hydrothermal method for synthesizing Mo 2 CT x MXene method, Mo 2 Ga 2 C is mixed with a phosphoric acid aqueous solution and placed in a hydrothermal reactor for hydrothermal reaction. After the reaction is completed, the solid product is filtered and washed to remove unreacted phosphoric acid and Ga 3+ ions, and Mo is obtained after drying 2 CT x MXene.

[0008] In the above technical scheme, further, the hydrothermal reaction temperature is 120-220°C, and the hydrothermal reaction time is greater than 2 hours. High temperature can reduce the hydrothermal reaction time, but the risk increases. In order to improve the reaction efficiency and ensure safety, preferably, the hydrothermal reaction temperature is 160-180°C, and the hydrothermal reaction time is 8-24 hours.

[0009] In the above technical solution, further, Mo 2 Ga 2 The molar ratio of C to phosphoric acid is greater than 1:1.5, preferably, for every 1-10 g of Mo etched 2 Ga 2 C used 50 mL of 10% phosphoric acid aqueous solution.

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

[0011] In the above technical solution, further, Mo 2 CT x MXene was mixed with an intercalation agent, and then ultrasonically treated in a closed container and washed to remove the intercalation agent to obtain single-layer and few-layer Mo 2 CT x MXene.

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

[0013] Another aspect of the present invention provides a Mo prepared by the above method 2 CT x MXene materials.

[0014] The present invention also provides a kind of above-mentioned Mo 2 CT x Applications of MXene materials in electrochemistry, catalysis, rechargeable batteries and supercapacitors.

[0015] The beneficial effects of the present invention are:

[0016] (1) The phosphoric acid used in the present invention is a medium-strong acid and a non-volatile acid. The method can be implemented using a conventional hydrothermal reactor. The preparation conditions are mild and the equipment requirements are low. Even after a short contact with the human body, no serious harm will be caused. The harm caused by the use of hydrofluoric acid, high-concentration hydrochloric acid or high-concentration sodium hydroxide is avoided, and it is safer.

[0017] (2) The phosphoric acid used in the present invention is removed in the washing operation and measured by EDS. After 3 times of filtration and water washing, Mo is obtained. 2 CT x The residual phosphorus content in MXene powder is only 0.1%, and the residual P element is extremely low, which is of great significance for controlling the surface functional groups of MXene.

[0018] (3) Mo prepared by the present invention2 CT x The surface of MXene does not contain halogen functional groups such as F and Cl, and the main functional groups are -O and -OH, which improves its application prospects in catalysis, adsorption and energy storage. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Mo in Example 1 2 CT x - SEM image of P10-24 sample;

[0020] Figure 2 Mo in Example 1 2 CT x -HRTEM image of the P10-24 sample, (a) is magnified 340,000 times, (b) is magnified 1 million times, and (c) is a selected area diffraction image;

[0021] Figure 3 is the XRD spectra of the samples in Examples 1-4 and Comparative Examples 1-2, (a) is the Mo in Example 1 2 Ga 2 C sample, (b) is the multilayer Mo in Example 1-4 2 CT x MXene sample, (c) is the multilayer Mo in Comparative Example 1-2 2 CT x MXene samples;

[0022] Figure 4 Mo in Example 1 2 CT x -1 XRD spectrum of sample;

[0023] Figure 5 Mo in Example 1 2 CT x -1 sample of CO 2 Hydrogenation performance diagram. DETAILED DESCRIPTION

[0024] In view of the bottleneck problem of MXene preparation and the many defects of the prior art, the inventor of this case has proposed the technical solution of the present invention after long-term research and extensive practice. The technical solution, its implementation process and principle, etc. will be further explained as follows. However, it should be understood that within the scope of the present invention, the above-mentioned technical features of the present invention and the various technical features specifically described in the following (embodiments) can be combined with each other to form a new or preferred technical solution.

[0025] Example 1

[0026] Will 1g Mo 2 Ga 2C powder and 50 mL of 10% phosphoric acid aqueous solution were added to a 100 mL polytetrafluoroethylene-lined hydrothermal reactor, and the hydrothermal reaction was carried out at 180°C for 24 h. After the hydrothermal reactor was cooled to room temperature, the liquid was filtered out, and the solid was washed with deionized water until the pH of the filtrate was about 7, and then dried in a vacuum drying oven at 60°C overnight to obtain Mo 2 CT x MXene, denoted as Mo 2 CT x -P10-24.

[0027] Mo 2 Ga 2 Preparation of C powder: Add 5g of β-Mo in a crucible 2 C and 8g of metallic gallium were added, and then the lid was covered. Then, the sample was calcined at 750°C in a tube furnace under vacuum for 72h. After the sample was cooled, it was poured into 100mL of 10% hydrochloric acid and stirred until no bubbles were generated. Then, the gallium-containing solution and Mo were separated by filtration. 2 Ga 2 The solid powder was washed with deionized water until the pH was about 7, and then dried in a forced air drying oven at 80°C overnight to obtain Mo 2 Ga 2 C powder.

[0028] This example obtains Mo 2 CT x - P10-24 powder 0.71 g.

[0029] Figure 1 Mo obtained in Example 1 2 CT x -SEM image of P10-24, Figure 2 Mo obtained in Example 1 2 CT x -HRTEM image of P10-24, showing the successful conversion of Mo into 2 Ga 2 C is etched into flake Mo 2 CT x MXene, Mo 2 CT x Mo atoms in MXene are arranged in a hexagonal close-packed pattern; Figure 1 The XRD diffraction spectrum in the figure shows that the multilayer Mo obtained by phosphoric acid etching 2 CT x MXene contains some Mo with larger interlayer spacing. 2 CT x According to literature reports, a larger interlayer spacing is beneficial to the application of MXene in electrochemistry, energy storage devices, and optoelectronic materials.

[0030] The multilayer Mo prepared in Example 1 2 CT x -P10-24 exfoliation to few-layer and single-layer Mo 2 CT x Mxene was used to test the performance of carbon dioxide hydrogenation reaction. The stripping method was as follows: 0.5gMo 2 CT x -P10-24 was added into a flask containing 5 mL of 5% tetrapropylammonium hydroxide ethanol solution, sealed and ultrasonically treated in an ultrasonic cleaner for 1 h. The sample after ultrasonication was centrifuged to separate the solid precipitate, then washed with anhydrous ethanol for 3 times, and vacuum dried at 60 °C to obtain a few layers and a single layer of d-Mo 2 CT x MXene, denoted as Mo 2 CT x -1.

[0031] Figure 4 for Mo 2 CT x -1's XRD spectrum shows few-layer and single-layer d-Mo 2 CT x The (002) interplanar spacing of MXene increases to 1.55 nm, indicating that the d-Mo 2 CT x The interlayer spacing of MXene is 1.55nm, which is conducive to the application of MXene in catalysis, rechargeable batteries and other fields.

[0032] Take 20mg Mo 2 CT x -1 in fixed bed CO 2 Testing CO in a hydrogenation reactor 2 Hydrogenation reaction performance. Before the reaction, the 2 The reaction was pretreated at 450 °C for 2 h; the temperature was increased from 200 °C to 600 °C, and 24 ml / min CO was introduced. 2 +72mL / min H 2 and 4 mL / min N 2 Test reaction, reaction space velocity is 300000ml g cat. -1 h -1 , the test results are as follows Figure 5 shown.

[0033] Example 2

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

[0035] Take 1g Mo2 Ga 2 C powder and 50 mL of 5% phosphoric acid aqueous solution were added to a 100 mL polytetrafluoroethylene-lined hydrothermal reactor, and the hydrothermal reaction was carried out at 180 ° C for 24 h. After the hydrothermal reactor cooled to room temperature, the upper liquid was poured out. After the hydrothermal reactor cooled to room temperature, the liquid was filtered out, and the solid was washed with deionized water until the pH of the filtrate was about 7, and then dried in a vacuum drying oven at 60 ° C overnight to obtain Mo 2 CT x MXene, denoted as Mo 2 CT x -P5-24, this example obtains Mo 2 CT x -P5-24 powder 0.71 g.

[0036] Example 3

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

[0038] Take 1g Mo 2 Ga 2 C and 50 mL of 10% phosphoric acid solution were added to a 100 mL polytetrafluoroethylene-lined hydrothermal reactor, and the hydrothermal reaction was carried out at 160°C for 24 h. After the hydrothermal reactor was cooled to room temperature, the liquid was filtered out, and the solid was washed with deionized water until the pH of the filtrate was about 7, and then dried in a vacuum drying oven at 60°C overnight to obtain Mo 2 CT x MXene, denoted as Mo 2 CT x -P10-160. This example obtains Mo 2 CT x MXene powder 0.71g.

[0039] Example 4

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

[0041] Take 1g Mo 2 Ga 2 C and 50 mL of 10% phosphoric acid solution were added to a 100 mL polytetrafluoroethylene-lined hydrothermal reactor, and the hydrothermal reaction was carried out at 180 ° C for 8 h. After the hydrothermal reactor was cooled to room temperature, the liquid was filtered out, and the solid was washed with deionized water until the pH of the filtrate was about 7, and then dried in a vacuum drying oven at 60 ° C overnight to obtain Mo 2 CT x MXene, denoted as Mo 2 CT x -P10-8. This example obtains Mo2 CT x MXene powder 0.71g.

[0042] Example 5

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

[0044] Take 1g Mo 2 Ga 2 C and 50 mL of 10% phosphoric acid solution were added to a 100 mL polytetrafluoroethylene-lined hydrothermal reactor, and the hydrothermal reaction was carried out at 120°C for 72 h. After the hydrothermal reactor was cooled to room temperature, the liquid was filtered out, and the solid was washed with deionized water until the pH of the filtrate was about 7, and then dried in a vacuum drying oven at 60°C overnight to obtain Mo 2 CT x MXene. This example obtains Mo 2 CT x MXene powder 0.68g.

[0045] Example 6

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

[0047] Take 1g Mo 2 Ga 2 C and 50 mL of 10% phosphoric acid solution were added to a 100 mL polytetrafluoroethylene-lined hydrothermal reactor, and the hydrothermal reaction was carried out at 200 ° C for 6 h. After the hydrothermal reactor was cooled to room temperature, the liquid was filtered out, and the solid was washed with deionized water until the pH of the filtrate was about 7, and then dried in a vacuum drying oven at 60 ° C overnight to obtain Mo 2 CT x MXene. This example obtains Mo 2 CT x MXene powder 0.68g.

[0048] Comparative Example 1

[0049] Take 1g Mo 2 Ga 2 C and 50 mL of 40% hydrofluoric acid solution were added to a 100 mL polytetrafluoroethylene-lined hydrothermal reactor, and the hydrothermal reaction was carried out at 180 ° C for 24 h. After the hydrothermal reactor was cooled to room temperature, the precipitate was collected by centrifugation, and the precipitate was washed with deionized water until the pH of the filtrate was about 7, and then dried in a vacuum drying oven at 60 ° C overnight to obtain Mo 2 CT x MXene, denoted as Mo 2 CTx -F10-24, this comparative example obtains Mo 2 CT x MXene powder 0.68g.

[0050] Comparative Example 2

[0051] Take 1g Mo 2 Ga 2 C and 50 mL of 37% hydrochloric acid solution were added to a 100 mL polytetrafluoroethylene-lined hydrothermal reactor, and the hydrothermal reaction was carried out at 180 ° C for 24 h. After the hydrothermal reactor was cooled to room temperature, the precipitate was collected by centrifugation, and the precipitate was washed with deionized water until the filtrate pH was ~7, and then dried in a vacuum drying oven at 60 ° C overnight to obtain Mo 2 CT x MXene, denoted as Mo 2 CT x -Cl10-24, this comparative example obtains Mo 2 CT x MXene powder 0.69g.

[0052] Table 1 Parameter control list of Examples 1-6 and Comparative Examples 1-2

[0053]

[0054]

[0055] As shown in Table 1, Example 3 shows that Mo can be completely etched at 160°C. 2 Ga 2 C, Example 4 shows that Mo can be completely etched within 8 hours. 2 Ga 2 C, Example 5 shows that Mo can also be etched at 120°C 2 Ga 2 C, but it takes longer time. Example 6 shows that increasing the reaction temperature can significantly reduce the time required. However, in order to improve the synthesis efficiency and ensure safety, 160-180°C is usually used. Comparative Examples 1-2 show that Mo can also be obtained by etching with hydrofluoric acid and hydrochloric acid 2 CT x MXene, but the yield is slightly lower than that of the phosphoric acid etching method.

[0056] The above embodiments are only preferred embodiments of the present invention and are not intended to limit the implementation methods. The protection scope of the present invention shall be subject to the scope defined in the claims. Other different forms of changes or modifications may be made based on the above description. Obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A phosphoric acid-assisted hydrothermal method for the synthesis of Mo2CT x The method of MXene, characterized in that Mo2Ga2C is mixed with a phosphoric acid aqueous solution and placed in a hydrothermal reactor for hydrothermal reaction. After the reaction is completed, the solid product is filtered, washed and dried to obtain Mo2CT x MXene.

2. The method according to claim 1, wherein the hydrothermal reaction temperature is 120-220°C and the hydrothermal reaction time is greater than 2 hours.

3. The method according to claim 1, wherein the hydrothermal reaction temperature is 160-180°C.

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

5.

5. The method according to claim 1, characterized in that The mass concentration of phosphoric acid in the phosphoric acid aqueous solution is less than 85%.

6. The method according to claim 1, characterized in that Mo2CT x MXene was mixed with an intercalation agent, treated with ultrasound in a closed container, and washed to remove the intercalation agent to obtain single-layer and few-layer Mo2CT x MXene.

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

8. Mo2CT prepared by the method according to any one of claims 1 to 7 x MXene materials.

9. Mo2CT according to claim 8 x Applications of MXene materials in electrochemistry, catalysis, rechargeable batteries and supercapacitors.

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