A method for preparing Ti2CCl2 MXene

Abstract

This invention discloses a method for preparing Ti₂CCl₂MXene. The method involves using titanium chloride precursor or a mixture of Ti or TiH₂ and TiCl₄ in a specific ratio as a titanium source precursor, reacting it with a carbon source gas to synthesize Ti₂CCl₂MXene. Compared with traditional selective etching methods, this invention not only solves the problem of obtaining high-purity, low-defect, high-quality MXene using traditional etching methods, but also has the advantages of high synthesis efficiency and low cost, resulting in significant economic and social benefits.

Description

Technical Field

[0001] This invention belongs to the fields of chemical engineering and materials, and specifically relates to a method for preparing Ti2CCl2 MXene. Background Technology

[0002] MXene is a novel class of two-dimensional layered compounds with the general chemical formula M. n+1 X n T x Where (n = 1 to 3), M is a transition metal, such as Ti, Zr, V, Mo, etc.; X is a C or N element; T x MXenes are surface functional groups, such as -OH, -O, F, and -Cl. Compared to other two-dimensional materials, MXenes' most significant advantage is their greater freedom in controlling their physicochemical properties. For example, the type and number of transition metal core layers can be controlled within the layers, and surface groups can be modified or recombined between layers. This provides more possibilities for designing materials on demand or tailoring their performance. Due to this tunable characteristic, MXenes show great promise in optoelectronics, separation, catalysis, electromagnetic shielding, and energy storage. Typically, at a specific n value, the performance of MXenes is closely related to parameters such as impurities, defects, and specific surface area. High-quality MXenes need to meet requirements such as high purity, few defects, and a small number of layers. However, since 2011, Ti3C2T... x Since its initial report, the low-cost preparation of high-quality MXene still faces significant challenges.

[0003] The current mainstream method for preparing MXene is selective etching, which involves first synthesizing M... n+1 AX n Phase, where A represents elements such as Al, Si, P, S, and Ga, and the A atomic layer is located in M. n+1 AX n M in crystal structure n+1 X n Between atomic layers, therefore, it is only necessary to selectively erode away the A atomic layer and then M. n+1 X n Functional group T is attached between atomic layers x MXene can then be synthesized. Based on different etching methods, it can be broadly divided into the following two categories:

[0004] (I) Etching method using HF or F-based compounds

[0005] As the name suggests, the etching solution used in this method is an HF solution or a compound containing F ions, such as LiF + HCl, NH4HF2, KHF2, etc. Its core principle is that F ions preferentially interact with M... n+1 AX nThe reaction of the A atom in the solution produces a soluble liquid fluoride or a volatile solid fluoride. Simultaneously, -F, -O, or -OH groups in the solution are grafted onto the M atom. MXene is then obtained through multiple centrifugation separations. This method is the most commonly used, and more than 30 MXenes have been prepared using this method (Science. 2021, 327, 1165), such as Ti3C2T. x Zr3C2T x Nb4C3T x V4C3T x And so on. However, this method struggles to obtain a single T. x MXene, because in solution T x The MXene prepared by this method typically consists of a mixture of -F, -O, and -OH groups, making it difficult to obtain pure -Cl-stopping groups (Nat. Commun., 2021, 12, 5085). Furthermore, the MXene prepared by this method contains numerous defects because some M atoms are etched away during the etching process, causing structural collapse. This results in poor stability of the MXene, making it difficult to store for extended periods even at room temperature; it typically requires storage in a dark, frozen environment (Chem. Mater., 2017, 29, 7633-7644).

[0006] (II) Lewis acid molten salt etching method

[0007] The principle of this method is based on Lewis acids (such as ZnCl2, CuCl2, FeCl3). 2, NiCl2 selectively etches away M in molten salt (LiCl / KCl / NaCl) medium. n+1 AX n The A-layer atoms in the phase generate A chlorides and metallic elements (Zn, Cu, Fe, Ni), and in the M phase... n+1 X nCl groups are grafted onto the main structure (Angew. Chem. Int. Ed. 2021, 133, 27219-27224). Although this method can solve the problem of not being able to obtain -Cl groups, it still cannot synthesize high-purity MXene with pure -Cl groups. This is because after etching, MXene is mixed with molten salt, requiring multiple impurity removal processes, as well as multiple washing and centrifugation to obtain MXene. However, in all reports to date, the impurity content is still very high, for example, Al: 0.22-1.90 atom%, Zn: 0.7-1.8 atom%, Cu: 0.5-4.9 atom% (ACS Nano. 2016, 10, 9193-9200; J. Mater. Chem. A. 2017, 5, 21663–21668). Most of these impurities remain in the crystal lattice, and even repeated acid washing is insufficient to further reduce the impurity content. Furthermore, during the washing and separation process, approximately 10 atom% of Cl groups are replaced by -O and -OH groups, making it impossible to synthesize pure -Cl groups. Additionally, the prepared MXene still contains a large number of defects.

[0008] Among all MXenes, high-quality M2XT is synthesized. x The most difficult part is the synthesis of pure-phase M2XT using an etching method. x First, it is necessary to synthesize pure-phase M. n+1 AX n Precursor. However, in MAX systems, such as the Ti-Al-C system, the smaller the n value, the more pronounced the M2XT effect. x The lower the stability of the Ti-Al-C system, the more difficult it is to synthesize pure-phase M2AX precursors. From a thermodynamic perspective, the Ti-Al-C system reaction is very complex, generating not only Ti2AlC but also byproducts such as Ti3AlC2, Ti4AlC3, Ti2C, TiC, Al4C3, AlTi, and Al3Ti. Furthermore, the regions for Ti2AlC and Ti3AlC2 formation are relatively small, resulting in a narrow synthesis window (J. Ceram. Sci. Technol. 2016, 7, 301-306). From a kinetic perspective, the presence of kinetic mass transfer barriers during the reaction process easily leads to local reaction ratio mismatches, resulting in Ti3AlC2 and TiC impurities, as well as residual C, frequently appearing in Ti2AlC (Nanoscale Adv. 2019, 1, 3680). Based on the above analysis, it is clear that preparing high-quality MXene using the etch-exfoliation method remains quite challenging.

[0009] Chemical vapor deposition (CVD) is considered an effective method for synthesizing high-quality two-dimensional materials, and numerous high-quality graphene, BN, MoS2, and Siene have been synthesized. However, there are no reports of preparing MXene using CVD. To date, only ultrathin two-dimensional carbides without functional groups, Mo2C, have been prepared using CVD (Nat. Mater. 2015, 14, 1135–1141, Adv. Mater. 2017, 29, 1700072). The preparation process involves: laying a layer of Cu foil on a Mo substrate, introducing methane at 1000°C, and under the catalysis of Cu, decomposing methane on the Cu foil surface to generate graphene. Simultaneously, Mo atoms diffuse into the Cu foil and react with the graphene to form the two-dimensional material Mo2C. Due to the fewer defects in CVD-prepared two-dimensional materials, Mo2C exhibits exceptionally good stability. However, the deposition temperature is much higher than that of Mo2CT. x The stable temperature of the two-dimensional Mo2C means that the surface of the two-dimensional Mo2C does not contain functional groups. Furthermore, the two-dimensional Mo2C prepared by this method is inefficient and costly.

[0010] In summary, due to inherent limitations of the etching method, it is difficult to synthesize high-quality MXenes that are defect-free and low in impurities. Although chemical vapor deposition (CVD) can prepare high-quality two-dimensional materials, the preparation of Ti₂CCl₂ MXenes by CVD still faces significant challenges. Therefore, there is an urgent need in this field to develop a method for synthesizing Ti₂CCl₂ MXenes. Summary of the Invention

[0011] To address the above problems, this invention proposes a method for preparing Ti2CCl2 MXene. This method solves the problem that etching methods are difficult to obtain high-purity, low-defect, high-quality MXene, and also overcomes the barrier that traditional chemical vapor deposition cannot synthesize MXene containing surface functional groups.

[0012] To achieve the above objectives, the present invention adopts the following technical solution:

[0013] A method for preparing Ti2CCl2 MXene, the method comprising the following steps:

[0014] Do not use M n+1 AX n Instead of using titanium chloride as a precursor, a mixture of Ti or TiH2 as a solid titanium source and TiCl4 or HCl in a certain proportion is used as a precursor. The precursor is reacted with a carbon source gas at 600-830℃ to synthesize Ti2CCl2 MXene. The titanium chloride precursor is TiCl3 or a mixture of TiCl3 and TiCl2 in any proportion.

[0015] When the precursor is a mixture of Ti or TiH₂ and TiCl₄, the molar ratio of TiCl₄ to Ti or TiH₂ satisfies 0.3 < n(TiCl₄) / n(TiCl₄ + Ti or TiCl₄ + TiH₂) < 1.

[0016] When the precursor is a mixture of Ti or TiH₂ and HCl, the molar ratio of HCl to Ti or TiH₂ satisfies 1 ≤ n(HCl) / n(Ti) ≤ 5.

[0017] When the solid titanium source is Ti, it can be any one of titanium powder, titanium mesh, titanium felt or titanium fiber.

[0018] The carbon source gas is any one of carbon sources such as CH₄, C₂H₄, C₂H₂ or a mixed gas with any proportion.

[0019] In the reaction for synthesizing Ti₂CCl₂ MXene, the molar amount of Ti in the precursor titanium source and the molar amount of C in the carbon source gas satisfy 0.5 ≤ n(Ti) / n(C) ≤ 6.

[0020] The temperature range for synthesizing Ti₂CCl x MXene is 600 - 830 °C. For example, it can be selected as 600 - 650 °C, 620 - 670 °C, 640 - 700 °C, 680 - 750 °C, 700 - 780 °C, 760 - 820 °C, 780 - 830 °C, etc. Further preferably, it is 680 - 780 °C, and most preferably 770 °C.

[0021] The reaction time is greater than 5 min. For example, it can be selected as 5 - 10 min, 8 - 16 min, 10 - 20 min, 15 - 30 min, 18 - 36 min, 25 - 45 min, 30 - 60 min, 60 - 80 min, 70 - 90 min, 80 - 100 min, 90 - 120 min, etc. Further preferably, it is 30 - 90 min, and most preferably 60 min.

[0022] The present invention has the following advantages compared with the prior art:

[0023] The present invention provides a method for synthesizing Ti₂CCl₂ MXene, which solves the problem that it is difficult to obtain high-quality MXene with high purity and few defects by the etching method. Brief Description of the Drawings

[0024] The drawings are used to provide further explanation of the present invention, and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention, and do not constitute a limitation to the present invention.

[0025] Figure 1The image shows a SEM image of the Ti2CCl2 MXene prepared according to Example 1 of this invention.

[0026] Figure 2 The image shows a SEM image of the Ti2CCl2 MXene prepared according to Example 2 of this invention.

[0027] Figure 3 The image shows the XRD pattern of Ti2CCl2 MXene prepared according to Example 3 of this invention. Detailed Implementation

[0028] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. However, the examples described below are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims. To better illustrate the present invention and facilitate understanding of the technical solution, typical but non-limiting embodiments of the present invention are as follows:

[0029] Example 1

[0030] 1 g of a mixture of TiCl3 and TiCl2 precursors in a molar ratio of 2:1 was weighed under an inert atmosphere and placed in a quartz tube reactor. After cleaning and treatment under Ar inert gas for 30 min, methane was introduced and the temperature was raised to 700 °C. The molar ratio of TiCl3 to methane was 0.8. After reacting for 120 min, the temperature was lowered to room temperature to obtain Ti2CCl2MXene. Figure 1 The SEM image of Ti2CCl2 MXene shows a polygonal morphology, and the EDS composition analysis shows that the molar ratio of Ti, C and Cl is 2:1:2. No other metal impurities were found, indicating that high-quality Ti2CCl2 MXene was obtained.

[0031] Example 2

[0032] 2g of titanium mesh was weighed and placed in the isothermal zone of the reactor. Then, TiCl4 gas carrying Ar was introduced into the reactor. During the reaction, the molar ratio of TiCl4 to titanium in the Ti mesh satisfied n(TiCl4) / n(TiCl4+Ti)=0.4. C2H4 gas was then introduced, and the molar amount of Ti in the titanium source precursor (TiCl4 and Ti mesh) and the molar amount of C in the carbon source gas satisfied n(Ti) / n(C)=0.55. The reaction temperature was 790℃, and the reaction time was 30min. The furnace was then cooled to room temperature to obtain Ti2CCl2MXene grown on titanium wire. Figure 2 To prepare the SEM image of Ti₂CCl₂ MXene, EDS compositional analysis showed that it contained Ti, C, and Cl elements, with no other metal impurities detected. XRD patterns showed that the main diffraction peaks matched the characteristic diffraction peaks of Ti₂CCl₂.

[0033] Example 3

[0034] 0.5 g of TiCl3 precursor was weighed under an inert atmosphere and placed in a quartz tube reactor. The reactor was then cleaned with Ar and heated to 820 °C. Subsequently, C2H2 was introduced. The molar amount of Ti in the titanium source precursor and the molar amount of C in the carbon source gas satisfied n(Ti) / n(C) = 5.5. After reacting for 5 min, the reactor was cooled to room temperature to obtain Ti2CCl2MXene. Figure 3 The XRD pattern of Ti2CCl2 MXene shows that all peaks in the figure match the characteristic diffraction peaks of Ti2CCl2, and no other impurity phases are present, indicating that pure Ti2CCl2 MXene has been obtained.

[0035] Example 4

[0036] 2g of TiH2 was weighed and placed in the isothermal zone of the reactor. Dry HCl was then introduced into the reactor using Ar to carry it. During the reaction, the molar ratio of TiH2 to HCl satisfied n(HCl) / n(Ti) = 1.5. C2H4 gas was also introduced, and the molar amounts of Ti in the titanium source precursor and C in the carbon source gas satisfied n(Ti) / n(C) = 3. The reaction temperature was 650℃, and the reaction time was 40 min to obtain Ti2CCl. x The powder, according to compositional analysis, contains Ti, C, and Cl elements, with no other metallic impurities found. XRD patterns show that the main diffraction peak matches the characteristic diffraction peaks of Ti₂CCl₂.

[0037] Example 5

[0038] 1 g of TiH2 was weighed and placed in the isothermal zone of the reactor. Dry HCl was then introduced into the reactor using Ar to carry it. During the reaction, the molar ratio of TiH2 to HCl satisfied n(HCl) / n(Ti) = 5. C2H2 gas was also introduced. The molar amount of Ti in the titanium source precursor and the molar amount of C in the carbon source gas satisfied n(Ti) / n(C) = 4.5. The reaction temperature was 830℃, and the reaction time was 30 min to obtain Ti2CCl2 powder. Compositional analysis showed that it contained Ti, C, and Cl elements, with no other metallic impurities found. XRD patterns showed that the main diffraction peak matched the characteristic diffraction peaks of Ti2CCl2.

[0039] The upper and lower limits of the process parameters (such as temperature, time, etc.) and the range values ​​of the present invention can all achieve the method, and examples are not listed here.

[0040] All aspects not described in detail in this invention can be covered using conventional technical knowledge in the field.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing Ti2CCl2 MXene, the method comprising the steps of: using titanium subchloride as a precursor or a mixture of a certain proportion of solid titanium source and TiCl4 or HCl as a precursor, the precursor being reacted with a carbon source gas at 600-830℃ to synthesize Ti2CCl2 MXene; the titanium subchloride precursor is TiCl3 or a mixture of TiCl3 and TiCl2 in any proportion; when the precursor is a mixture of solid titanium source and TiCl4, the molar ratio of TiCl4 to solid titanium source satisfies 0.3 < n(TiCl4) / n(TiCl4 + solid titanium source) < 1; when the precursor is a mixture of solid titanium source and HCl, the molar ratio of solid titanium source to HCl satisfies 1 ≤ n(HCl) / n(Ti) ≤ 5; in the synthesis of Ti2CCl2 MXene reaction, the molar amount of Ti in the precursor and the molar amount of C in the carbon source gas satisfy 0.5 ≤ n(Ti) / n(C) ≤ 6.

2. The method of claim 1, wherein, the solid titanium source is Ti or TiH2.

3. The method of claim 2, wherein, when the solid titanium source is Ti, the solid titanium source is any one of titanium powder, titanium mesh, titanium felt or titanium fiber.

4. The method of claim 1, wherein, the carbon source gas is any one of CH4, C2H4, C2H2 or a mixed gas in any proportion.

5. The method of claim 1, wherein, the reaction time of the synthesis of Ti2CCl2 MXene reaction is greater than 5 min.

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