Preparation method of MXene nanosheet with three-dimensional fold structure

Abstract

The invention provides a preparation method of a three-dimensional fold structure MXene nanosheet, which comprises the following steps: S1, carrying out etching and stripping on Ti3AlC2 MAX phase powder to obtain a Ti3C2Tx MXene colloidal solution; s2, a cationic surface active agent is added into the Ti3C2Tx MXene colloidal solution to serve as an intercalation agent, stirring is conducted for 2-12 h under the temperature condition of 20-50 DEG C, and a pre-expanded MXene intercalation compound is obtained; s3, filtering the pre-expanded MXene intercalation compound to form a wet film, and performing controllable drying to form an MXene self-supporting film with a three-dimensional fold structure; and S4, carrying out heat treatment on the self-supporting film under the protection of inert gas, and carrying out ball milling or crushing to obtain three-dimensional fold structure MXene nanosheet powder. According to the preparation method disclosed by the invention, the two-dimensional MXene nanosheet is induced to generate intrinsic self-shrinkage through intercalation-controllable drying, and a stable three-dimensional fold structure is formed through self-assembly, so that the MXene material with high specific surface area and excellent structural stability is prepared; as a hydrogen storage carrier, the material can effectively limit active particles and form catalytic sites in situ, and hydrogen absorption and desorption dynamics and cycling stability are remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of two-dimensional nanomaterials and new energy technology, specifically relating to a method for preparing three-dimensional wrinkled MXene nanosheets. Background Technology

[0002] Two-dimensional transition metal carbides / nitrides (MXenes), with their unique layered structure, high conductivity, abundant surface functional groups, and tunable interlayer spacing, have shown great application potential in energy storage and conversion, especially as nano-confined supports for hydrogen storage materials. Among them, Ti3C2T is the most representative. x Obtained by selectively etching the aluminum layer in the precursor MAX phase and then peeling it off, its intrinsic two-dimensional sheet structure theoretically provides a high specific surface area and abundant surface active sites.

[0003] However, in practical preparation and application, MXene nanosheets, due to their high surface energy and strong interlayer van der Waals forces, are prone to irreversible stacking and aggregation during drying, storage, or composite processes. This phenomenon leads to a significant reduction in the material's specific surface area and obstruction of ion or molecular transport channels, severely limiting its practical applications in multiple fields.

[0004] Current research reports have described methods to suppress the stacking of MXene nanosheets through intercalation and the construction of three-dimensional structures. For example, Chinese patent CN111153405B discloses a method for preparing Ti3C2 MXene nanosheet materials, including: Step 1, adding titanium aluminum carbon powder, hydrofluoric acid solution, and hexadecyltrimethylammonium bromide to a corrosion-resistant container and stirring at 20-60℃ for 6-60 h to obtain a CTAB-intercalated Ti3C2 mixture; Step 2, centrifuging the CTAB-intercalated Ti3C2 mixture, washing with water until the supernatant is neutral, filtering to collect the precipitate, and obtaining a CTAB-intercalated Ti3C2 multilayer material; Step 3, adding water to the CTAB-intercalated Ti3C2 multilayer material, sonicating for 30-120 min, and freeze-drying to obtain a CTAB-intercalated Ti3C2 nanosheet powder material. Although this method utilizes CTAB intercalation to increase the interlayer spacing to some extent, the solvent removal during the subsequent freeze-drying process can easily cause secondary stacking of the sheets, limiting further improvement in specific surface area and performance.

[0005] For example, Chinese patent CN114709379A discloses a three-dimensional wrinkled structure Ti3C2 MXene, its preparation method, and its application, including the following steps: (S1) obtaining a dispersion of Ti3C2 MXene; (S2) mixing a cationic surfactant with the dispersion of Ti3C2 MXene, reacting, and freeze-drying to obtain a three-dimensional wrinkled structure Ti3C2 MXene. However, this method relies on the non-covalent adsorption of the surfactant between the MXene sheets, resulting in weak interaction forces. The formed three-dimensional structure is prone to collapse or deformation during subsequent composite or processing, exhibiting insufficient structural stability and affecting its reliability and durability in various application scenarios.

[0006] Therefore, how to prepare structurally stable three-dimensional wrinkled MXene nanosheets through a simple and controllable process to prevent secondary stacking of the nanosheets during subsequent composite or processing remains a key technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] In view of the above problems, the present invention provides a method for preparing three-dimensional wrinkled MXene nanosheets, which prepares structurally stable three-dimensional wrinkled MXene nanosheets through a simple and controllable process to prevent secondary stacking of nanosheets during subsequent composite or processing.

[0008] The technical solution adopted by this invention to solve its technical problem is:

[0009] This invention provides a method for preparing three-dimensional wrinkled MXene nanosheets, comprising the following steps:

[0010] Preparation of S1.MXene colloidal solution: Ti3AlC2 MAX phase powder was etched and stripped to obtain monolayer or few-layer Ti3C2T with a concentration of 1~5 mg / ml. x MXene colloidal solution;

[0011] S2. Intercalating agent-induced pre-expansion: In the Ti3C2T x A cationic surfactant was added as an intercalating agent to an MXene colloidal solution, and the mixture was stirred at 20–50 °C for 2–12 h to allow the intercalating agent molecules to insert into Ti3C2T. x Pre-expanded MXene intercalation complexes were obtained between the MXene sheets; the amount of the cationic surfactant added was Ti3C2T. x MXene quality is 10% to 50%;

[0012] S3. Self-assembly construction of three-dimensional wrinkled structure: The pre-expanded MXene intercalation complex obtained in step S2 is filtered to form a wet film, and then controlled drying is performed to form an MXene self-supporting film with a three-dimensional wrinkled structure.

[0013] S4. Post-processing: The MXene self-supporting film with three-dimensional wrinkled structure obtained in step S3 is heat-treated at a temperature of 200~400℃ under inert gas protection and held for 1~4h. Then, it is ball-milled or crushed to obtain MXene nanosheet powder with three-dimensional wrinkled structure.

[0014] Further, in step S1, the etching and stripping process specifically involves: selectively etching the Ti3AlC2MAX phase powder with a solution of hydrofluoric acid or a mixture of lithium fluoride and hydrochloric acid to remove the aluminum layer; after washing and centrifugation to neutrality, intercalation with an organic alkali and ultrasonic stripping are performed to obtain the Ti3C2T x MXene colloidal solution; the organic base is tetramethylammonium hydroxide (TMAOH). This step selectively etches away the aluminum layer (Al) in the Ti3AlC2 MAX phase, transforming the bulk precursor (Ti3AlC2) into a monolayer or few-layer Ti3C2T with a high aspect ratio and a surface rich in functional groups (-O, -OH, -F, etc.). x Nanosheets; simultaneously, the initial intercalation using TMAOH, which has a relatively small molecular volume, not only contributes to Ti3C2T x The assisted exfoliation between MXene nanosheets promotes further dispersion of the nanosheets and the formation of an MXene colloidal solution. Moreover, it is easy to remove during subsequent washing, avoiding reagent residues that may affect material properties.

[0015] Optionally, in step S2, the cationic surfactant is at least one of hexadecyltrimethylammonium bromide (CTAB), dodecyltrimethylammonium bromide (DTAB), or octadecyltrimethylammonium bromide (OTAB). This step introduces a cationic surfactant with a long alkyl chain, utilizing its strong electrostatic interaction with the negatively charged MXene sheets to insert it between the MXene sheets, providing steric hindrance, expanding the interlayer spacing, providing initial space for the subsequent construction of the three-dimensional wrinkled structure, and preventing the nanosheets from completely stacking.

[0016] Further, in step S3, the filtration is vacuum filtration or pressure-assisted filtration; in step S3, the controllable drying is carried out in an environment with a temperature of 40~80℃ and a relative humidity of 30~60%, and the heating rate of the controllable drying is 0.5~5℃ / min. This step forms a dense wet film through vacuum filtration, followed by controllable drying in an environment with precisely controlled heating rate (0.5~5℃ / min), temperature (40~80℃), and humidity (30%~60%) to construct a three-dimensional wrinkled MXene nanosheet. Under precisely controlled humidity and heating rate, water molecules slowly evaporate from between the sheets, generating uniform capillary forces; under the control and support of the intercalating agent, the sheets generate contractile stress along the in-plane direction of the MXene nanosheets, causing the MXene sheets to spontaneously assemble into a stable three-dimensional network with abundant wrinkles and pores. In addition, by using a slow heating rate and a suitable humidity environment, the rate of water evaporation is ensured to be compatible with the relaxation speed of the layered structure, thus avoiding stress concentration, cracking or structural collapse of the three-dimensional folded structure due to excessively rapid drying.

[0017] Optionally, in step S4, the inert gas is argon or nitrogen. In this step, the heat treatment temperature is controlled at 200~400℃ to remove the cationic surfactant while retaining sufficient functional groups to maintain hydrophilicity and active sites, thereby solidifying the three-dimensional wrinkled structure, enhancing its mechanical properties and thermal stability, and optimizing the surface chemical state. Temperatures below 200℃ can easily lead to excessive cationic surfactant residue, while temperatures above 400℃ can easily damage the three-dimensional wrinkled structure of MXene. Simultaneously, the heat treatment time is controlled at 1~4h to remove the cationic surfactant. Less than 1h can easily lead to excessive cationic surfactant residue, while more than 4h can easily damage the stability of the functional groups on the MXene surface. An inert gas is used for protection to prevent MXene from oxidizing and degrading under high-temperature conditions.

[0018] This invention also provides a three-dimensional wrinkled MXene nanosheet, prepared by the above method; its specific surface area is 150~300 m². 2 / g. This MXene material can serve as a hydrogen storage carrier: on the one hand, it possesses abundant folded spaces that can effectively confine magnesium / magnesium hydride (Mg / MgH2) nanoparticles; on the other hand, the abundant defects and functional groups on the MXene surface can form highly catalytically active substances (such as TiH2) in situ, thereby improving the hydrogen adsorption / desorption kinetics and cycle stability of the material. This MXene material is not only suitable for hydrogen storage, but its unique three-dimensional conductive folded structure also has broad application potential in lithium / sodium-ion batteries, supercapacitors, electrocatalysis, and electromagnetic shielding.

[0019] Compared with the prior art, the technical solution of this application has at least the following beneficial effects:

[0020] This invention creatively induces intrinsic self-wrinkling of two-dimensional MXene nanosheets through an "intercalation-controlled drying" method, leading to self-assembly into a stable three-dimensional wrinkled structure, fundamentally solving the problem of easy stacking of MXene nanosheets. Using the method provided by this invention, nanosheets with high specific surface area (>150 m²) have been successfully prepared. 2 MXene materials, with their excellent structural stability (g / g), can effectively confine active particles and form catalytic sites in situ as hydrogen storage carriers, significantly improving hydrogen adsorption / desorption kinetics and cycle stability. They also show broad application prospects in energy storage, catalysis, and other fields. Furthermore, the process is simple and controllable, with mild reaction conditions. By adjusting the type and concentration of the intercalating agent and drying kinetic parameters (temperature, humidity, rate), the microstructure of the three-dimensional wrinkled structure can be effectively controlled, thereby optimizing the hydrogen storage performance of MXene materials. Attached Figure Description

[0021] Figure 1 These are XPS images of the three-dimensional wrinkled MXene nanosheets prepared in Example 1 and Comparative Example 1 of this invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0023] The term "comprising" as used in this application is an open-ended inclusion, meaning "including but not limited to". The term "according to" means "at least in part according to". The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment". Definitions of other terms will be given in the description below.

[0024] Example 1

[0025] This embodiment provides a method for preparing three-dimensional wrinkled MXene nanosheets, the process flow diagram of which is shown below. Figure 1 As shown, it includes the following steps:

[0026] Preparation of S1.MXene colloidal solution: 2g of Ti3AlC2 MAX phase powder was slowly added to 40ml of 10% hydrofluoric acid solution, and stirred and etched at 35℃ for 24h. After the reaction was completed, the supernatant was repeatedly centrifuged and washed until the pH of the supernatant was >6. The precipitate was dispersed in 100ml of 25% TMAOH aqueous solution, stirred and intercalated for 24h under argon protection, followed by sonication for 1h. The upper colloid was collected by centrifugation to obtain a monolayer or few-layer Ti3C2T with a concentration of 3mg / ml. x MXene colloidal solution;

[0027] S2. Intercalating agent-induced pre-expansion: Take 100ml of Ti3C2T x Add 150 mg of CTAB (i.e., the amount of cationic surfactant CTAB added is Ti3C2T) to the MXene colloidal solution. x 50% of MXene (by mass) was magnetically stirred in a 40°C water bath for 6 hours to allow the intercalating agent molecules to insert into Ti3C2T. x Between the MXene sheets, a pre-expanded MXene intercalation complex was obtained;

[0028] S3. Self-assembly construction of three-dimensional wrinkled structure: The pre-expanded MXene intercalation composite obtained in step S2 is poured into a vacuum filtration device containing a polyvinylidene fluoride filter membrane with a pore size of 0.22 μm, and vacuum filtration is performed to form a uniform wet membrane; then the wet membrane is transferred to a constant temperature and humidity chamber connected to an aluminum membrane, and heated at a programmed temperature rise rate of 2℃ / min, and controlled drying is performed at a relative humidity of 50% and a temperature of 60℃ to form an MXene self-supporting membrane with a three-dimensional wrinkled structure.

[0029] S4. Post-processing: The MXene self-supporting membrane with three-dimensional wrinkled structure obtained in step S3 is peeled off from the filter membrane, placed in a tube furnace, heated to 300°C at a heating rate of 5°C / min under argon protection, heat-treated and held at that temperature for 2 hours; after natural cooling, the film is lightly ground in an argon glove box and passed through a 400-mesh sieve to obtain MXene nanosheet powder with three-dimensional wrinkled structure.

[0030] Using the above method, a three-dimensional wrinkled MXene nanosheet with a specific surface area of ​​185 m² was prepared in this embodiment. 2 / g.

[0031] Example 2

[0032] This embodiment provides a method for preparing three-dimensional wrinkled MXene nanosheets, the process flow diagram of which is shown below. Figure 1 As shown, it includes the following steps:

[0033] S1. Same as Example 1;

[0034] S2. Intercalating agent-induced pre-expansion: Take 100ml of Ti3C2T x MXene colloidal solution, add 60 mg DTAB (i.e., the amount of cationic surfactant CTAB added is Ti3C2T) x MXene (20% by mass) was magnetically stirred in a 30°C water bath for 10 hours to allow intercalator molecules to insert into Ti3C2T. x Between the MXene sheets, a pre-expanded MXene intercalation complex was obtained;

[0035] S3. Self-assembly construction of three-dimensional wrinkled structure: The pre-expanded MXene intercalation complex obtained in step S2 is subjected to pressure-assisted filtration to form a wet film; then, it is heated at a programmed temperature rise rate of 5℃ / min and controlled drying is carried out under conditions of 40% relative humidity and 70℃ to form a self-supporting MXene film with a three-dimensional wrinkled structure.

[0036] S4. Post-processing: The MXene self-supporting film with three-dimensional wrinkled structure obtained in step S3 is heated to 250°C at a heating rate of 5°C / min under argon protection and held for 3 hours; after natural cooling, the film is lightly ground in an argon glove box and passed through a 400-mesh sieve to obtain MXene nanosheet powder with three-dimensional wrinkled structure.

[0037] Using the above method, a three-dimensional wrinkled MXene nanosheet with a specific surface area of ​​179 m² was prepared in this embodiment. 2 / g.

[0038] Comparative Example 1

[0039] Take 100 mL of the same MXene colloidal solution as in Example 1, without adding any intercalating agent, and directly perform vacuum filtration; quickly dry the resulting wet film in an oven at 120°C for 2 h; grind the resulting dense film to obtain two-dimensional stacked MXene nanosheet powder.

[0040] Using the above method, a two-dimensional stacked MXene nanosheet with a specific surface area of ​​8 m² was prepared in this comparative example. 2 / g.

[0041] Test method:

[0042] (1) The specific surface area of ​​the sample was determined by nitrogen adsorption-extraction method (BET);

[0043] (2) The surface chemical state of the sample was tested by X-ray photoelectron spectroscopy (XPS).

[0044] Results analysis:

[0045] (1) Three-dimensional wrinkled structure: As shown in Table 1, the specific surface area of ​​the three-dimensional wrinkled MXene nanosheets prepared in Example 1 of this invention is as high as 185 m², as determined by BET testing. 2 / g is the specific surface area (8m²) of the two-dimensional MXene nanosheets in Comparative Example 1. 2 The surface area of ​​the two-dimensional MXene nanosheets was more than 23 times that of the two-dimensional MXene nanosheets in Comparative Example 1, which were tightly stacked together. However, the present invention significantly increases the specific surface area by constructing the two-dimensional MXene nanosheets into a three-dimensional wrinkled structure through intercalation-controlled drying.

[0046] (2) Surface chemical state: such as Figure 1 As shown in Table 1, XPS analysis revealed that Ti in the three-dimensional wrinkled MXene nanosheets prepared in Example 1 of this invention... 3+ With Ti 4+ atomic ratio (Ti) 3+ / Ti 4+ The value was 0.35, which is much higher than the 0.08 of the two-dimensional MXene nanosheets in Comparative Example 1; at the same time, the surface oxygen-containing functional groups (-O, -OH) of the sample prepared in this invention showed a stronger signal. 3+ These are the active sites of MXene nanosheets, which typically migrate to Ti during oxidation. 4+ Transformation and inactivation, the present invention has higher Ti 3+ / Ti 4 + The results show that the controlled drying process effectively preserves the reducibility and structural integrity of MXene nanosheets.

[0047] (3) Hydrogen storage carrier performance: The MXene nanosheets prepared in Example 1 and Comparative Example 1 of this invention were used as carriers to load and hydrogenate equal amounts of magnesium nanoparticles. As shown in Table 1, the average particle size of the magnesium hydride (MgH2) particles obtained on the carrier of this invention was only 35 nm, and its initial dehydrogenation temperature was as low as 95 °C; while the MgH2 particles on the carrier of Comparative Example 1 were severely agglomerated, with an average particle size >100 nm and an initial dehydrogenation temperature as high as 280 °C. The smaller loaded particle size indicates that the three-dimensional wrinkled MXene nanosheets prepared in this invention have sufficient pores to physically isolate and confine the particles, preventing them from migrating and growing during high-temperature processing; the lower dehydrogenation temperature indicates that this invention retains the highly active surface of the MXene nanosheets, resulting in a strong catalytic interaction with the MgH2 particles. Therefore, the process provided by this invention not only realizes the construction of the microstructure of MXene nanosheets, but also endows them with the core function of serving as a high-performance micron reactor carrier.

[0048] Table 1. Comparison of MXene nanosheets in the embodiments of the present invention and comparative examples.

[0049] Specific surface area (m 2 / g)]]> Ti 3+ / Ti 4+ ]]> [Mean particle size of MgH2 (nm)] Starting dehydrogenation temperature (°C) Example 1 185 0.35 35 95 Example 2 179 0.32 51 105 Comparative Example 1 8 0.08 ＞100 280

[0050] The embodiments described above are some, but not all, embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for preparing three-dimensional wrinkled MXene nanosheets, characterized in that, Includes the following steps: Preparation of S1.MXene colloidal solution: Ti3AlC2 MAX phase powder was etched and stripped to obtain monolayer or few-layer Ti3C2T with a concentration of 1~5 mg / ml. x MXene colloidal solution; S2. Intercalating agent-induced pre-expansion: In the Ti3C2T x A cationic surfactant was added as an intercalating agent to an MXene colloidal solution, and the mixture was stirred at 20–50 °C for 2–12 h to allow the intercalating agent molecules to insert into Ti3C2T. x Pre-expanded MXene intercalation complexes were obtained between the MXene sheets; the amount of the cationic surfactant added was Ti3C2T. x MXene quality is 10% to 50%; S3. Self-assembly construction of three-dimensional wrinkled structure: The pre-expanded MXene intercalation complex obtained in step S2 is filtered to form a wet film, and then controlled drying is performed to form an MXene self-supporting film with a three-dimensional wrinkled structure. S4. Post-processing: The MXene self-supporting film with three-dimensional wrinkled structure obtained in step S3 is heat-treated at a temperature of 200~400℃ under inert gas protection and held for 1~4h. Then, it is ball-milled or crushed to obtain MXene nanosheet powder with three-dimensional wrinkled structure.

2. The method for preparing three-dimensional wrinkled MXene nanosheets according to claim 1, characterized in that, In step S1, the etching and stripping process specifically involves: selectively etching the Ti3AlC2MAX phase powder with hydrofluoric acid or a mixed solution of lithium fluoride and hydrochloric acid to remove the aluminum layer; after washing and centrifugation to neutrality, intercalation with an organic alkali and ultrasonic stripping are performed to obtain the Ti3C2T x MXene colloidal solution.

3. The method for preparing three-dimensional wrinkled MXene nanosheets according to claim 2, characterized in that, The organic base is tetramethylammonium hydroxide (TMAOH).

4. The method for preparing three-dimensional wrinkled MXene nanosheets according to claim 1, characterized in that, In step S2, the cationic surfactant is at least one of hexadecyltrimethylammonium bromide (CTAB), dodecyltrimethylammonium bromide (DTAB), or octadecyltrimethylammonium bromide (OTAB).

5. The method for preparing three-dimensional wrinkled MXene nanosheets according to claim 1, characterized in that, In step S3, the filtration is either vacuum filtration or pressure-assisted filtration.

6. The method for preparing three-dimensional wrinkled MXene nanosheets according to claim 1, characterized in that, In step S3, the controllable drying is carried out in an environment with a temperature of 40~80℃ and a relative humidity of 30~60%, and the heating rate of the controllable drying is 0.5~5℃ / min.

7. The method for preparing three-dimensional wrinkled MXene nanosheets according to claim 1, characterized in that, In step S4, the inert gas is argon or nitrogen.

8. A three-dimensional wrinkled MXene nanosheet, characterized in that, It is prepared by the preparation method described in any one of claims 1-7.

9. The three-dimensional wrinkled MXene nanosheet according to claim 8, characterized in that, Its specific surface area is 150~300m² 2 / g.

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