End-group-adjustable few-layer MXene as well as preparation and application thereof

Abstract

The invention relates to the technical field of preparation and stripping of MXene, in particular to end-group-adjustable few-layer MXene as well as preparation and application thereof. The preparation method comprises the following steps: firstly, uniformly mixing MAX, conductive carbon black, PVDF (Polyvinylidene Fluoride) and NMP (N-Methyl Pyrrolidone), coating an interlayer wrapped by carbon cloth, and compacting to obtain an etched anode; a spectrum pure graphite rod is used as a counter electrode; then uniformly mixing the alkali metal halide fused salt and halogenated aluminum salt, placing the mixture in an electrolytic bath, and carrying out heating treatment to obtain a melt electrolyte containing polyanion clusters; inserting an etching anode and a counter electrode into the melt electrolyte, applying a constant voltage between the two electrodes to carry out etching treatment, and collecting a product from the etching anode; taking out the product, washing, and performing ultrasonic stripping to obtain a black suspension; and finally, carrying out vacuum filtration and ultrasonic treatment on the obtained black suspension, centrifuging, and collecting supernate to obtain the end-group-adjustable few-layer MXene. According to the invention, an expandable non-destructive way is established for controlling surface chemical and interlayer stripping of MXene.

Description

Technical Field

[0001] The present invention relates to the technical field of MXene preparation, and in particular to a oligolayer MXene with adjustable end groups and its preparation and application. Background Art

[0002] Since the first report of Ti3C2Tx in 2011, the family of two-dimensional (2D) transition metal carbides / nitrides known as MXenes has been greatly expanded and has had a significant impact in the fields of energy storage, electromagnetic interference shielding, optoelectronics, biomedicine, and future quantum technology. n+1 X n T x (n=1-4), where M represents a transition metal, X represents carbon or nitrogen or both, and Tx represents surface termination. MXene is usually prepared by synthesizing MAX phase precursors (i.e., M n+1 AX n ) is synthesized by selectively etching away the A atomic layer. n+1 X n While the backbone is inherited from the MAX precursor, its surface terminal groups are largely determined by the etching process. Generally, wet chemical etching in fluorinated aqueous solutions yields MXenes with a randomly mixed surface pattern of oxygen-containing terminal groups (e.g., -OH, -O, -F, and -Cl). Although these MXenes can be readily exfoliated into monolayers in aqueous solution with the aid of intercalation agents (e.g., LiCl), the mixed and oxidative nature of the terminal groups limits the manipulation of surface chemistry. The Lewis acid molten salt method (LAMS) offers promise for the preparation of MXenes with uniform halogen terminal groups. Through covalent surface modification, MXenes containing -Cl or -Br groups can be substituted with various inorganic functional groups (e.g., -S, -Se, -Te) or organic functional groups (e.g., alkylamines, diamines). However, due to the necessary metal impurity treatment steps, some halogen groups are replaced with -O during the manufacturing process. Furthermore, these halogen-dominated MXenes are inherently hydrophobic and exhibit strong interlayer interactions, necessitating the use of hazardous organic chemicals (e.g., n-butyllithium) for intercalation-assisted exfoliation. Moreover, these organic solvents are difficult to remove and can cause structural degradation and severely reduce electrical conductivity.

[0003] Therefore, exploring methods to tailor the surface chemical properties of MXene and non-destructive exfoliation is of great significance but quite challenging, and developing a method that can achieve both of the above controls simultaneously is even more challenging. Summary of the Invention

[0004] In order to solve the above problems, the purpose of the present invention is to provide a oligolayer MXene with adjustable end groups and its preparation and application.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] The first object of the present invention is to provide a method for preparing end-group-adjustable oligolayer MXene, comprising the following steps:

[0007] (S1) MAX, conductive carbon black, PVDF, and NMP are mixed and coated between the carbon cloth-wrapped interlayers, and compacted to obtain an etching anode;

[0008] A spectroscopically pure graphite rod was used as the counter electrode;

[0009] (S2) mixing an alkali metal halide molten salt and an aluminum halide salt and placing the mixture in an electrolytic cell, and heating the mixture to obtain a molten electrolyte containing polyanion clusters;

[0010] The polyanion cluster is Al n X 3n+1 - , X is Cl, Br or I (which is embedded in the MXene interlayer during the electrolysis process and is the key to the subsequent effective exfoliation into single-layer and few-layer MXene flakes);

[0011] (S3) inserting the etching anode and the counter electrode obtained in step (S1) into the molten electrolyte obtained in step (S2), applying a constant voltage between the two electrodes to perform etching, and collecting a product from the etching anode;

[0012] (S4) taking out the product obtained in step (S3), washing it, and then performing ultrasonic peeling to obtain a black suspension;

[0013] (S5) The black suspension obtained in (S4) is vacuum filtered, ultrasonicated, and centrifuged to collect the supernatant to obtain an end-group-tunable oligolayer MXene.

[0014] Unlike aqueous solutions, the eutectic melting point of alkali metal-aluminum halide melts (such as AlCl3-NaCl-KCl) is about 91°C, which has excellent thermochemical stability and a wide electrochemical window, and can effectively avoid the impact of electrolyte oxidation and decomposition on MXene terminal groups during electrochemical etching. In addition, a large number of "naked" ions (L) in the molten salt can easily combine with the metal elements in the MAX phase during the reaction process, promoting the deintercalation of the A atomic layer (forming A x L y Compounds), and the exposed M layer atomic surface is covered with uniform terminal groups (ML). In particular, the melt also contains a large number of polyanion clusters (Al n Cl 3n+1 - ), such as Al2Cl7 - 、Al3Cl 10- and Al4Cl 13 - , which will help to reduce the exfoliation energy after intercalation between MXene layers and promote their subsequent effective exfoliation.

[0015] In one embodiment of the present invention, in step (S1), the MAX is selected from Ti3AlC2, Ti3SiC2, Ti2AlC, V2AlC, Nb2AlC or Ti2AlN.

[0016] In one embodiment of the present invention, in step (S1), the mass ratio of MAX, conductive carbon black, PVDF and NMP is 1-15:0.1-2:0.1-3:80-98.8.

[0017] In one embodiment of the present invention, in step (S2), the alkali metal halide molten salt is selected from one or more of LiCl, NaCl, KCl, LiBr, NaBr, KBr, LiI, NaI or KI;

[0018] The aluminum halide salt is selected from one or more of AlCl3, AlBr3 or AlI3.

[0019] In one embodiment of the present invention, the molar ratio of the alkali metal halide molten salt to the aluminum halide salt is 10-50:50-90;

[0020] During the heating treatment, the temperature is 110-300°C.

[0021] In one embodiment of the present invention, in step (S3), during the etching process, the constant voltage is 1.0 to 3.0 V, and the time is 6 to 12 hours.

[0022] In one embodiment of the present invention, steps (S1) to (S3) are all carried out in a high-temperature heating furnace glove box integrated device (O2<0.01ppm, H2O<0.01ppm).

[0023] In one embodiment of the present invention, in step (S4), washing is performed using deionized water.

[0024] In one embodiment of the present invention, in step (S5), the solution is placed in ethanol for ultrasonic treatment at a temperature of 0 to 4° C. for 20 to 40 minutes;

[0025] During the centrifugation process, the rotation speed is 4000-6000 rpm and the time is 10-20 minutes.

[0026] The second object of the present invention is to provide a oligolayer MXene with adjustable end groups, which is prepared by the above method.

[0027] The third object of the present invention is to provide an application of end-group-adjustable oligolayer MXene in the fields of energy, catalysis or electronic information.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] (1) Compared with traditional ionic crystalline molten salts (such as LiCl, NaCl, CaCl2, KCl, etc., whose melting points are usually above 600°C), the low-temperature characteristics of alkali metal-aluminum halide molten salts can effectively inhibit the self-oxidation reaction of MXene;

[0030] (2) Compared with the smaller halogen ions (such as Cl - ), alkali metal-aluminum halide molten salts are rich in inorganic polyanions (such as Al n Cl 3n+1 - ), which helps to embed into the MXene interlayer under electric field driving mode to destroy its van der Waals force and promote the separation of layers. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The SEM and corresponding EDS of the etched product in Example 1;

[0032] Figure 2 XRD patterns and microscopic strain diagrams of MXene prepared in Example 1 and Comparative Example 1;

[0033] Figure 3 The SEM and corresponding EDS images of the etched product in Example 2;

[0034] Figure 4 Ti3C2NH in Example 2 x SEM image after delamination;

[0035] Figure 5 The SEM and corresponding EDS images of the etched product in Example 3;

[0036] Figure 6 Ti3C2Br in Example 3 x SEM image after delamination. DETAILED DESCRIPTION

[0037] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0038] In the following examples, unless otherwise specified, all reagents used are commercially available reagents, and all detection means and methods used are conventional detection means and methods in the art.

[0039] Example 1

[0040] This embodiment provides a method for preparing a oligolayer MXene with adjustable end groups, comprising the following steps:

[0041] (S1) Ti3AlC2 powder (1 g), conductive carbon, PVDF, and NMP were mixed in a mass ratio of 9.5:0.2:0.3:50 to form a thick slurry. The mixed slurry was then evenly applied to four pieces of carbon cloth (2 cm*1 cm). The carbon cloths were then stacked and compacted to form a MAX electrode. The MAX electrode was then embedded in an electrode holder and fixed as an etching anode. A high-purity graphite rod was used as a cathode.

[0042] (S2) In a high-temperature heating furnace glove box integrated equipment (O2 <0.01 ppm, H2O <0.01 ppm), anhydrous AlCl3, NaCl, and KCl were first ground uniformly in a molar ratio of 63:12:25 and added to a glass electrolytic cell. The electrolytic cell was then placed in a heating mantle and heated to 170°C for 2 hours to obtain a uniform and transparent molten electrolyte;

[0043] (S3) inserting the etching anode and the counter electrode obtained in step (S1) into the molten electrolyte obtained in step (S2), etching for 12 hours under a constant voltage of 2.5 V, and collecting the etching product;

[0044] (S4) taking out the product prepared in step (S3), washing the sample with deionized water, and then performing ultrasonic stripping to peel the MXene from the carbon cloth to obtain a black suspension;

[0045] (S5) The mixture of step (S4) was ultrasonicated in ethanol in an ice bath for 30 minutes, and then centrifuged at 5000 rpm for 15 minutes, and the supernatant was collected to obtain a layered Ti3C2Cl x MXene, its morphology SEM characterization is as follows Figure 1 Its XRD pattern and microscopic strain diagram are shown in Figure 2 shown.

[0046] pass Figure 1 It can be found that the obtained product is basically a few-layer MXene sheet with a low number of layers, and is mainly composed of Cl surface functional groups.

[0047] Example 2

[0048] This embodiment provides a method for preparing a oligolayer MXene with adjustable end groups, comprising the following steps:

[0049] (S1) Ti3AlC2 powder (0.5 g), conductive carbon, PVDF, and NMP were mixed in a mass ratio of 8.5:0.5:1:42 to form a thick slurry. The mixed slurry was then evenly applied to four pieces of carbon cloth (2 cm*1 cm). The carbon cloths were then stacked and compacted to form a MAX electrode. The MAX electrode was then embedded in an electrode holder and fixed as an etching anode. A high-purity graphite rod was used as the cathode.

[0050] (S2) In a high-temperature heating furnace glove box integrated equipment (O2 <0.01 ppm, H2O <0.01 ppm), anhydrous AlCl3, NaCl, and KCl were first ground uniformly in a molar ratio of 59:25:26 and added to a glass electrolytic cell. The electrolytic cell was then placed in a heating mantle and heated to 230°C for 2 hours to obtain a uniform and transparent melt electrolyte;

[0051] (S3) inserting the etching anode and the counter electrode obtained in step (S1) into the molten electrolyte obtained in step (S2), etching for 12 hours under a constant voltage of 2.5 V, adding 0.5 g of NaNH2 to the molten salt after etching to modify the surface end groups, and then collecting the etching products;

[0052] (S4) taking out the product prepared in step (S3), washing the sample with deionized water, and then performing ultrasonic stripping to peel the MXene from the carbon cloth to obtain a black suspension;

[0053] (S5) The mixture of step (S4) was ultrasonicated in ethanol in an ice bath for 30 minutes, and then centrifuged at 5000 rpm for 10 minutes to collect the supernatant to obtain layered Ti3C2NH x MXene, its morphology SEM characterization is as follows Figure 2 、 3 shown.

[0054] pass Figure 3 and Figure 4 It can be found that the surface end groups of the obtained MXene product are mainly N, and can be easily peeled off into thin flakes.

[0055] Example 3

[0056] This embodiment provides a method for preparing a oligolayer MXene with adjustable end groups, comprising the following steps:

[0057] (S1) Ti3AlC2 powder (0.5 g), conductive carbon, PVDF, and NMP were mixed in a mass ratio of 8.5:1:1.5:70 to form a thick slurry. The mixed slurry was then evenly applied to three pieces of carbon cloth (2 cm*1 cm). The carbon cloths were then stacked and compacted to form a MAX electrode. The MAX electrode was then embedded in an electrode holder and fixed as an etching anode. A high-purity graphite rod was used as the cathode.

[0058] (S2) In a high-temperature heating furnace glove box integrated equipment (O2 <0.01 ppm, H2O <0.01 ppm), anhydrous AlBr3, LiBr, NaBr, and KBr were first ground uniformly in a molar ratio of 60:11:12:17 and added to a glass electrolytic cell. The electrolytic cell was then placed in a heating mantle and heated to 200°C for 1.5 hours to obtain a uniform and transparent melt electrolyte;

[0059] (S3) inserting the etching anode and the counter electrode obtained in step (S1) into the molten electrolyte obtained in step (S2), etching for 12 hours under a constant voltage of 2.5 V, and collecting the etching product;

[0060] (S4) taking out the product prepared in step (S3), washing the sample with deionized water, and then performing ultrasonic stripping to peel the MXene from the carbon cloth to obtain a black suspension;

[0061] (S5) The mixture of step (S4) was ultrasonicated in ethanol in an ice bath for 30 minutes, and then centrifuged at 5000 rpm for 20 minutes to collect the supernatant to obtain a layered Ti3C2Br x MXene, its morphology SEM characterization is as follows Figure 4 、 5 shown.

[0062] pass Figure 5 and Figure 6 It can be found that the surface end groups of the obtained MXene product are mainly Br, and can be easily peeled off into thin flakes.

[0063] Example 4

[0064] This embodiment provides a method for preparing a oligolayer MXene with adjustable end groups, comprising the following steps:

[0065] (S1) Ti3AlC2 powder (1 g), conductive carbon, PVDF, and NMP were mixed in a mass ratio of 8.5:1:1.5:68 to form a thick slurry. The mixed slurry was then evenly applied to three pieces of carbon cloth (2 cm*1 cm). The carbon cloths were then stacked and compacted to form a MAX electrode. The MAX electrode was then embedded in an electrode holder and fixed as an etching anode. A high-purity graphite rod was used as the cathode.

[0066] (S2) In a high-temperature heating furnace glove box integrated equipment (O2 <0.01 ppm, H2O <0.01 ppm), anhydrous AlI3, NaI, and KI were first ground uniformly in a molar ratio of 60:14:26 and added to a glass electrolytic cell. The electrolytic cell was then placed in a heating mantle and heated to 230°C for 1.5 hours to obtain a uniform and transparent melt electrolyte;

[0067] (S3) inserting the etching anode and the counter electrode obtained in step (S1) into the molten electrolyte obtained in step (S2), etching for 9 hours under a constant voltage of 2.5 V, and collecting the etching product;

[0068] (S4) taking out the product prepared in step (S3), washing the sample with deionized water, and then performing ultrasonic stripping to peel the MXene from the carbon cloth to obtain a black suspension;

[0069] (S5) The mixture of step (S4) was ultrasonicated in ethanol in an ice bath for 30 minutes, and then centrifuged at 5000 rpm for 20 minutes to collect the supernatant to obtain a layered Ti3C2I x MXene.

[0070] Comparative Example 1

[0071] This comparative example provides a method for preparing MXene, which specifically includes the following steps:

[0072] This embodiment provides a method for preparing a oligolayer MXene with adjustable end groups, comprising the following steps:

[0073] (S1) Ti3AlC2 powder (1 g), conductive carbon, PVDF, and NMP were mixed in a mass ratio of 9.5:0.2:0.3:50 to form a thick slurry. The mixed slurry was then evenly applied to four pieces of carbon cloth. The carbon cloths were then stacked and compacted to form a MAX electrode. The MAX electrode was then embedded in an electrode holder and fixed as an etching anode. A high-purity graphite rod was used as a cathode.

[0074] (S2) In a high-temperature heating furnace glove box integrated equipment (O2 <0.01 ppm, H2O <0.01 ppm), NaCl and KCl were first ground uniformly in a molar ratio of 1:1 and added to a glass electrolytic cell. The electrolytic cell was then placed in a heating mantle and heated to 700°C for 2 hours to obtain a uniform and transparent melt electrolyte;

[0075] (S3) inserting the etching anode and the counter electrode obtained in step (S1) into the molten electrolyte obtained in step (S2), etching for 12 hours under a constant voltage of 2.5 V, and collecting the etching product;

[0076] (S4) taking out the product prepared in step (S3), washing the sample with deionized water, and then performing ultrasonic stripping to peel the MXene from the carbon cloth to obtain a black suspension;

[0077] (S5) The product of step (S4) was ultrasonicated in ethanol in an ice bath for 30 minutes, and then centrifuged at 5000 rpm for 15 minutes, and the supernatant was collected to obtain MXene. Its XRD pattern and microstrain diagram are shown in FIG. Figure 2 shown.

[0078] pass Figure 2 It can be found that the microscopic strain value ε of the MXene prepared in Example 1 calculated by the Williamson-Hall formula based on XRD is 6 times the microscopic strain value of the MXene prepared in Comparative Example 1.

[0079] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the explanations of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for preparing end-group-adjustable oligolayer MXene, characterized in that: The following steps are involved: (S1) MAX, conductive carbon black, PVDF, and NMP are mixed and coated between the carbon cloth-wrapped interlayers, and compacted to obtain an etching anode; A spectroscopically pure graphite rod was used as the counter electrode; (S2) mixing an alkali metal halide molten salt and an aluminum halide salt and placing the mixture in an electrolytic cell, and heating the mixture to obtain a molten electrolyte containing polyanion clusters; The polyanion cluster is Al n X 3n+1 - , X is Cl, Br or I; (S3) inserting the etching anode and the counter electrode obtained in step (S1) into the molten electrolyte obtained in step (S2), applying a constant voltage between the two electrodes to perform etching, and collecting a product from the etching anode; (S4) taking out the product obtained in step (S3), washing it, and then performing ultrasonic peeling to obtain a black suspension; (S5) The black suspension obtained in step (S4) is vacuum filtered, ultrasonicated and then centrifuged, and the supernatant is collected to obtain an end-group-adjustable oligolayer MXene.

2. The method for preparing a oligolayer MXene with adjustable end groups according to claim 1, wherein: In step (S1), the MAX is selected from Ti3AlC2, Ti3SiC2, Ti2AlC, V2AlC, Nb2AlC or Ti2AlN.

3. The method for preparing a oligolayer MXene with adjustable end groups according to claim 1, wherein: In step (S1), the mass ratio of MAX, conductive carbon black, PVDF and NMP is 1-15:0.1-2:0.1-3:80-98.

8.

4. The method for preparing a oligolayer MXene with adjustable end groups according to claim 1, wherein: In step (S2), the alkali metal halide molten salt is selected from one or more of LiCl, NaCl, KCl, LiBr, NaBr, KBr, LiI, NaI or KI; The aluminum halide salt is selected from one or more of AlCl3, AlBr3 or AlI3.

5. The method for preparing a oligolayer MXene with adjustable end groups according to claim 4, characterized in that: The molar ratio of the alkali metal halide molten salt to the aluminum halide salt is 10-50:50-90; During the heating treatment, the temperature is 110-300°C.

6. The method for preparing a oligolayer MXene with adjustable end groups according to claim 1, characterized in that: In step (S3), during the etching process, the constant voltage is 1.0 to 3.0 V and the time is 6 to 12 hours.

7. The method for preparing a oligolayer MXene with adjustable end groups according to claim 1, wherein: In step (S4), washing is performed using deionized water.

8. The method for preparing a oligolayer MXene with adjustable end groups according to claim 1, wherein: In step (S5), the mixture is placed in ethanol for ultrasonic treatment at a temperature of 0 to 4° C. for 20 to 40 minutes; During the centrifugation process, the rotation speed is 4000-6000 rpm and the time is 10-20 minutes.

9. A oligolayer MXene with adjustable end groups, characterized in that: It is prepared by the method according to any one of claims 1 to 8.

10. Use of the end-group-adjustable oligolayer MXene according to claim 9 in the fields of energy, catalysis or electronic information.

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