Method for rapidly preparing two-dimensional MXene material through dry ball milling

Abstract

The invention belongs to the technical field of preparation of two-dimensional materials, and discloses a method for rapidly preparing a two-dimensional MXene material by dry ball milling, which comprises the following steps: 1) mixing parent phase MAX powder and ammonium bifluoride, and loading into a ball milling tube in an argon environment; 2) performing oscillating high-energy ball milling according to a ball-to-material ratio of (5-20): 1 to realize dry etching; and 3) grinding the ball-milled product, washing with deionized water until the product is neutral, and standing or centrifugally layering to obtain a two-dimensional MXene material on the upper layer and unreacted MAX on the lower layer. Dry etching is adopted, friction spontaneous heating generated in the ball milling process is utilized, an external heat source is not needed for heating, energy loss is reduced, the equipment requirement is lowered, and the particle size of the MXene material and the interlayer spacing of the accordion-shaped structure can be regulated and controlled through ball milling parameters.

Description

Technical Field

[0001] The present invention belongs to the technical field of two-dimensional material preparation, and relates to a method for rapidly preparing two-dimensional MXene materials by dry ball milling. Background Art

[0002] In recent years, two-dimensional transition metal carbon / nitride (MXene) has shown great application potential in energy storage (such as lithium-ion batteries, supercapacitors), electromagnetic shielding, catalysis and sensors due to its unique layered structure, high conductivity, excellent chemical stability and adjustable surface functional groups. As an emerging two-dimensional material, MXene material is composed of MAX phase (where M represents transition metal, such as titanium, niobium, vanadium, etc., A represents aluminum or silicon, and X represents carbon and nitrogen) by selectively etching the A-layer elements, followed by ion intercalation and exfoliation treatment.

[0003] Traditionally, MXenes are prepared by selectively etching the aluminum layer in a MAX phase (such as Ti3AlC2) with hydrofluoric acid (HF) or its precursors (such as ammonium bifluoride, NH4HF2), followed by exfoliation to obtain single or multilayer MXene nanosheets. However, traditional liquid-phase etching methods have significant drawbacks: First, the extensive use of high-concentration hydrofluoric acid or fluorine-containing solutions presents strong corrosiveness, high toxicity, and challenges with waste disposal. Second, uncontrolled accumulation between MXene layers can occur during the etching process, leading to a reduction in specific surface area and active sites. Third, the multi-step liquid-phase treatment process is complex, costly, and difficult to achieve continuous production. To overcome these challenges, researchers have explored new methods such as molten salt etching and electrochemical exfoliation, but these methods still face challenges such as high-temperature energy consumption, complex equipment requirements, and uneven product morphology. Therefore, a dry, safe, and continuous method is urgently needed to achieve the large-scale production of MXenes. Summary of the Invention

[0004] The present invention addresses the technical problems of high energy consumption, complex equipment, and uncontrollable products in the preparation of two-dimensional MXene materials, and provides a method for rapidly preparing two-dimensional MXene materials by dry ball milling. Dry etching is adopted, and the frictional self-heating generated during the ball milling process is utilized. No external heat source is required for heating, which reduces energy loss and equipment requirements. The particle size of the MXene material and the interlayer spacing of the accordion-like structure can be controlled by ball milling parameters (frequency, time, ball-to-material ratio).

[0005] To achieve the above object, the present invention adopts the following technical solutions: The present invention provides a method for rapidly preparing two-dimensional MXene materials by dry ball milling, comprising the following steps: 1) Mix the parent phase MAX powder and ammonium bifluoride and place them into a ball mill under argon atmosphere; 2) Perform oscillating high-energy ball milling at a ball-to-material ratio of 5 to 20:1 to achieve dry etching; 3) The ball-milled product is ground and washed with deionized water until neutral, and then allowed to stand or centrifuge for separation. The upper layer is the two-dimensional MXene material, and the lower layer is the unreacted MAX.

[0006] In the above technical solution, the parent phase MAX powder is selected from one of titanium aluminum carbide (Ti3AlC2), vanadium aluminum carbide (V2AlC), niobium aluminum carbide (Nb4AlC3), titanium silicon carbide (Ti3SiC2), titanium aluminum carbonitride (Ti3AlCN) or titanium tin carbide (Ti3SnC).

[0007] In the above technical solution, the mass ratio of the parent phase MAX powder to ammonium bifluoride is 1:1~8.

[0008] In the above technical solution, the ball milling frequency is 5~30 Hz (preferably 15~30 Hz), and the ball milling time is 15 min~10 h.

[0009] In the above technical solution, the unreacted MAX is recovered by drying and then subjected to oscillating high-energy ball milling etching to achieve recycling of raw materials.

[0010] Combine Figure 1 The schematic diagram of the material force during the oscillating ball milling process is shown in FIG. The main technical concepts of the present invention are as follows: 1. Ammonium bifluoride can mildly corrode Al and achieve etching Solid ammonium bifluoride is used as the etching material. The key to etching from the parent phase MAX to MXene is to destroy the MA bond. The decomposition temperature range of ammonium bifluoride is 125.6℃ to 239.5℃. During the ball milling process, it will gradually decompose into hydrogen fluoride and ammonia, thereby achieving the effect of dry etching A atoms. Although the effect is weaker than directly using hydrogen fluoride, it is safer and gentler than directly using hydrogen fluoride gas. The ammonia produced in the decomposition reaction can also destroy the interlayer van der Waals force. The friction and pressure converted by mechanical ball milling in a closed environment promote the rapid movement of gas molecules, which can also achieve the effect of expanding the interlayer.

[0011] 2. Oscillating ball milling accelerates the etching reaction and realizes controllable adjustment of morphology parameters The high energy input and uniform mixing characteristics of oscillating ball milling enable the etching reaction to be completed within a few hours (traditional methods require dozens of hours), and the particle size of the MXene material and the interlayer spacing of the accordion-like structure can be controlled by ball milling parameters (frequency, time, ball-to-material ratio).

[0012] 3. Ball milling shear stress destroys weak ionic bonds, while local high temperature achieves etching Compared to conventional aqueous etching, the shear stress provided by dry ball milling is more likely to cause lattice defects in intact, robust MAX phase crystals. Since MA bonds are weak metallic bonds, they are more easily damaged by high-energy impact. Ammonium bifluoride decomposes at around 200°C. The instantaneous impact of ball milling can cause the local temperature to rise to nearly 100°C, accelerating the ammonium bifluoride's corrosion of A atoms. Furthermore, localized high temperature and pressure can promote atomic diffusion or activate chemical reactions, indirectly leading to bond breakage and recombination.

[0013] 4. Provide higher extrusion pressure to allow gas molecules to diffuse between layers Since the decomposition of ammonium bifluoride is accompanied by the generation of trace amounts of NH3 and H2 gases during the reaction, the ball milling process provides a large compressive stress that allows the gas to shuttle between the materials. The reaction system becomes weakly acidic due to the decomposition of ammonium bifluoride. NH3 and H2 escape between the accordion-shaped MXene layers and come into contact with H + Converted into NH4 + Staying between layers has the effect of expanding the distance between layers.

[0014] 5. Provide a pure ionic environment to achieve a large number of fluorine end groups Thanks to the ease of solid-phase mixing, inert gas can be injected into a sealed ball mill or directly mixed and sealed in an inert gas environment. The subsequent ball milling process does not involve the complex ion environment of liquid-phase etching. By adjusting the ratio of ammonium bifluoride, MXene with high fluorine end groups can be prepared, greatly simplifying the process.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention employs dry etching, using ammonium bifluoride as the etchant. This avoids the use of highly concentrated strong acids and bases required during wet etching, simplifies the ionic environment, and reduces unnecessary chemical reactions and the formation of byproducts. Compared to high-concentration hydrofluoric acid, ammonium bifluoride is more mild in chemical properties, reducing both equipment corrosiveness and safety risks during operation, thereby lowering equipment requirements. Furthermore, the use of ammonium bifluoride promotes the formation of high-fluorine end groups, enhancing the electrical and mechanical properties of MXene and providing a better foundation for its application in energy storage, electromagnetic shielding, and other fields.

[0016] 2. The present invention utilizes the extrusion force generated during the ball milling process to make the gas generated by the decomposition of ammonium bifluoride diffuse between the layers and convert it into NH4 + Staying between the layers is conducive to obtaining MXene materials with larger interlayer spacing.

[0017] 3. This invention utilizes the frictional self-heating generated during ball milling, eliminating the need for an external heat source for temperature increase. This reduces energy loss and improves utilization, offering a degree of controllability, relative safety, and reliability, making it suitable for mass production. Furthermore, byproducts generated during ball milling (such as (NH4)3AlF6) are readily soluble in water and easy to remove.

[0018] 4. The shear and impact forces generated during the ball milling process not only help break MA bonds but also promote the exfoliation of MXene layers, thereby obtaining MXene materials with large interlayer spacing. Furthermore, dry ball milling reduces chemical reagent waste, aligning with the concepts of green chemistry and sustainable development. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic diagram of the forces acting on materials during the oscillating ball milling process.

[0020] Figure 2 These are the X-ray diffraction (XRD) images and scanning electron microscope images of the sample of Comparative Example 1 after being sealed and placed for 30 minutes and 5 hours after mixing.

[0021] Figure 3 It is a flow chart of the operation process of Example 1.

[0022] Figure 4 1 is the XRD image of the sample after ball milling and mixing at different vibration frequencies in Example 1.

[0023] Figure 5 1 is the XRD pattern of samples prepared by ball milling at a selected speed of 15 Hz for 15 min at different mixing ratios in Examples 1-6.

[0024] Figure 6 These are the electronic photographs and XRD images of the by-products obtained after the upper layer of waste liquid was dried when the product was washed away with deionized water in Example 1, where (a) is a photo of the recovered by-products (NH4)3AlF6 and NH4Cl; (b) is the XRD image of (NH4)3AlF6 harvested by water washing; and (c) is the XRD image of NH4Cl harvested after acid washing.

[0025] Figure 7 This is a scanning electron microscope image of the two-dimensional MXene material with edge etching obtained in Example 1.

[0026] Figure 8 (a) Electron photo; (b) SEM image of the product obtained by ball milling when the mass ratio of Ti3AlC2 to NH4HF2 is 1:8 in Example 5.

[0027] Figure 9 These are the XRD images of the products after ball milling at different ball milling times in Examples 7 and 8.

[0028] Figure 10 This is a scanning electron microscope image of the MXene material obtained in the initial stage of ball milling (within 1 h) in Example 7. The substance covering the surface is decomposed ammonium bifluoride particles.

[0029] Figure 11 The scanning electron microscope images of the MXene material at different magnifications were obtained when the ball milling time was 6 h in Example 8; Figure 12 is an XRD image of the MXene material collected after washing with hydrochloric acid and then washing with deionized water in Example 9.

[0030] Figure 13 These are the XRD images of the MXene material collected by two different schemes: the sample ball-milled for 1 h in Example 10 was washed only with deionized water and the sample was washed with acid first and then with water in Example 9.

[0031] Figure 14 These are the XRD and SEM images of MXene obtained in Example 11 after ball milling the sample for 6 h with an overall mass ratio of MAX and ammonium bifluoride of 1:6 and then washing with water.

[0032] Figure 15 (a) Transmission electron microscope image of the MXene material prepared by solid-phase ball milling in Example 11; (b) high-resolution transmission electron microscope image.

[0033] Figure 16 This is the X-ray photoelectron spectrum of the high fluorine end group content MXene material prepared by ball milling and then washed with water in Example 11, where (a) Ti 2p; (b) C 1s; (c) Al 2p; and (d) F 1s are fine spectra.

[0034] Figure 17 (a) XRD image; (b) scanning electron microscope image of the MXene material obtained by mixed ball milling of trititanium aluminum carbon nitride (Ti3AlCN) and ammonium bifluoride in Example 12.

[0035] Figure 18 (a) XRD image; (b) scanning electron microscope image of the MXene material obtained by mixed ball milling of niobium aluminum carbide (Nb4AlC3) and ammonium bifluoride in Example 13.

[0036] Figure 19 (a) XRD image and (b) scanning electron microscope image of the MXene material obtained by mixed ball milling of titanium silicon carbide (Ti3SiC2) and ammonium bifluoride in Example 14. DETAILED DESCRIPTION

[0037] The following examples are used to illustrate the present invention but are not intended to limit the scope of protection of the present invention. Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art. The test methods in the following examples are all conventional methods unless otherwise specified.

[0038] Comparative Example 1: Preparation of Ammonium Bifluoride Mixed MAX Ti3AlC2 (0.2 g) and ammonium bifluoride (1.2 g) were mixed and placed in a plastic tube, which was then filled with inert gas and sealed. The mixture was then placed at room temperature for 30 min and 5 h, respectively. The products were characterized by X-ray diffraction and scanning electron microscopy. Figure 2 As shown. Figure 2 It can be seen that after the initial mixture is placed for a short time, MAX does not react with ammonium bifluoride and still maintains the original MAX structure; after a long time, ammonium bifluoride will react with the aluminum and titanium elements in Ti3AlC2 through its acidity and strong coordination ability of fluoride ions to form fluorides or complexes, and slightly reduce the intensity of the (104) peak belonging to Ti3AlC2 at around 38°, and shift the (002) peak at 9.6° to the left, indicating an expansion of the interlayer spacing. The edge corrosion delamination phenomenon is also shown by scanning electron microscopy.

[0039] Example 1 like Figure 3 As shown in the process flow chart, 0.2 g of Ti₃AlC₂ and 0.2 g of NH₄HF₂ were mixed and placed in a plastic ductile iron tube. 4 g of zirconia balls (80% 5 mm and 20% 10 mm) were added. In a glove box, inert Ar gas was introduced into the tube and the tube was sealed with parafilm. The mixture was then placed in a ball mill (Ant Source Scientific Instruments AM100S) and oscillated for 15 minutes at frequencies of 5, 10, 15, 20, 25, and 30 Hz. The milled product was then removed.

[0040] Comparison of XRD analysis of products after ball milling at different vibration frequencies, such as Figure 4 The results show that effective etching occurs at a ball milling frequency of 15 Hz. After balancing the equipment and experimental efficiency, the ball milling frequency of 15 Hz was determined to be the ball milling frequency for subsequent studies.

[0041] When the mass ratio of Ti3AlC2 to NH4HF2 in this embodiment is 1:1, the product after ball milling at 15 Hz for 15 min is subjected to X-ray diffraction (XRD) to verify the phase information, as shown in FIG. Figure 5 As shown. Figure 5 It was found that the characteristic peak of MXene (002) (the (002) peak of 9.6°MAX shifted to the left), indicating the expansion between layers; and the (104) peak of MAX decreased, but there were still many MAX phases, which was sufficient to prove the etching and stripping of Al.

[0042] For the ball-milled product, the fluoride produced by the reaction and the unreacted etchant were first washed with deionized water, and the upper waste liquid was collected and dried to obtain the by-product (such as Figure 6 -a), and from the XRD analysis results (such as Figure 6 -b) was analyzed and confirmed to be (NH4)3AlF6. If dilute hydrochloric acid is used for cleaning in this step, NH4Cl (such as Figure 6 -c).

[0043] The lower layer product after washing with deionized water was then placed in dilute hydrochloric acid (20 mL, 1 mol / L) for dispersion and washing, and then washed with deionized water until neutral, and allowed to stand for stratification to obtain edge-etched and layered two-dimensional MXene materials, such as Figure 7 shown.

[0044] Example 2 This embodiment is basically the same as embodiment 1, except that the mass ratio of Ti3AlC2 to NH4HF2 is 1:2, and the oscillating ball milling is performed at a frequency of 15 Hz for 15 min.

[0045] From the X-ray diffraction (XRD) analysis results, it was found that when the amount of ammonium bifluoride increased, a slightly stronger MXene (002) characteristic peak appeared than in Example 1, such as Figure 5 shown.

[0046] From this embodiment, it can be found that the decomposition of ammonium bifluoride will cause a portion of the etchant to become ineffective, so an appropriate excess of ammonium bifluoride should be added during the ball milling process to supplement it, thereby obtaining a higher etching efficiency.

[0047] Example 3 This embodiment is basically the same as embodiment 2, except that the mass ratio of Ti3AlC2 to NH4HF2 is 1:4, and the oscillating ball milling is performed at a frequency of 15 Hz for 15 min.

[0048] From the X-ray diffraction (XRD) analysis results, it was found that when the amount of ammonium bifluoride increased, the characteristic peak of MXene (002) was slightly stronger than that of Example 2, such as Figure 5 shown.

[0049] Example 4 This embodiment is basically the same as embodiment 2, except that the mass ratio of Ti3AlC2 to NH4HF2 is 1:6, and the oscillating ball milling is performed at a frequency of 15 Hz for 15 min.

[0050] The XRD analysis of the ball-milled product revealed that the characteristic peak of the (002) crystal plane, which was originally located at around 9.6°, had shifted left to 7.1°, proving that the etching reaction occurred relatively completely, and the peak intensity belonging to ammonium bifluoride was further enhanced. Figure 5 shown.

[0051] Example 5 This embodiment is basically the same as embodiment 2, except that the mass ratio of Ti3AlC2 to NH4HF2 is 1:8, and the oscillating ball milling is performed at a frequency of 15 Hz for 15 min.

[0052] The photo of the product after ball milling is as follows Figure 8 As shown in the figure, it can be seen that the morphology of the sample has changed seriously, from the original gray-black to yellow-brown. Figure 5 In the XRD data of phase characterization, there is a large amount of unreacted ammonium bifluoride residue.

[0053] Example 6 This embodiment is basically the same as embodiment 2, except that the mass ratio of Ti3AlC2 to NH4HF2 is 1:10, and the oscillating ball milling is performed at a frequency of 15 Hz for 15 min.

[0054] like Figure 5 As shown in the figure, the original lattice structure of the product is destroyed after ball milling, and the Ti in Ti3AlC2 is also corroded to form (NH4)2TiF6. This shows that appropriately increasing the amount of ammonium bifluoride selected during the ball milling process can accelerate the etching efficiency, but using too much will destroy the MAX phase structure, making it impossible to obtain a two-dimensional MXene material.

[0055] Example 7 This embodiment is basically the same as embodiment 4, except that the ball milling time is extended to 30, 45, and 60 minutes, respectively, that is, the ball milling time is proportionally extended within 1 hour.

[0056] like Figure 9 The XRD phase characterization results of the ball-milled product show that the unstable lattice of ammonium bifluoride was destroyed in the early stage of ball milling, causing it to decompose.

[0057] like Figure 10 Scanning electron microscopy analysis and elemental distribution spectroscopy (EDS) of the MXene material shown in the figure show that the surface is covered with decomposed ammonium bifluoride particles in the early stage of ball milling (within 1 h), while a layered morphology gradually emerges.

[0058] Example 8 This embodiment is basically the same as embodiment 4, except that the ball milling time is extended to 2, 4, 6, and 8 hours, respectively.

[0059] like Figure 9The XRD phase characterization results of the ball-milled product shown in the figure show that the intensity of the (104) peak at around 38° belonging to Ti3AlC2 decreases sharply, proving that ammonium bifluoride further corrodes Al. When the ball-milling time reaches 6 h, a conversion rate of 90.62% can be obtained (calculated using the integral area ratio of the MXene (002) bun peak at around 7.1° and the sum of the peak area at 9.6° belonging to MAX (002)).

[0060] like Figure 11 The morphological characterization shown in the figure shows that most of the three-dimensional MAX phase is converted into accordion or few-layer MXene structures, proving that a very high etching conversion rate can be achieved with a ball milling preparation time of 6 h.

[0061] Example 9 This example is essentially the same as Examples 7 and 8, except that the products obtained after ball milling for 0.5, 1, 2, 4, 6, and 8 h were washed with 1 mol / L dilute hydrochloric acid and then with deionized water until neutral. The separated MXene solutions were collected and freeze-dried to obtain MXene powder.

[0062] like Figure 12 As shown, XRD analysis of MXene powder revealed that after washing, three peaks appeared between 5 and 10°, of which 9.1° represented the (002) crystal plane of Ti3AlC2, while 7.1° and 8.6° represented the (002) crystal plane of Ti3C2MXene with two different interlayer spacings. This is because during the ball milling process, some NH3 remained between the material layers and was converted into NH4 + The form of NH4 + was removed, resulting in the partial interlayer spacing being restored to 8.6°.

[0063] Example 10 This example is basically the same as Example 9, except that the sample obtained by ball milling for 1 h was washed only with deionized water until neutral, and then the upper layer solution after stratification was collected and freeze-dried to obtain MXene powder.

[0064] Compared with the hydrochloric acid cleaning solution used in Example 9, Figure 13 XRD analysis shows that only using deionized water to wash can avoid intercalation of NH4 + The problem of being cleaned up.

[0065] Example 11 This example is basically the same as Example 9, except that the sample with a ball milling time of 6 h was washed only with deionized water until it was neutral, and then processed to obtain dry MXene powder.

[0066] like Figure 14 The XRD and SEM analysis shown also revealed that the (104) characteristic peak of the MAX phase has completely disappeared, proving that this method can be used to obtain well-etched MXene materials.

[0067] Through Figure 15 The TEM analysis shown in the figure shows that the interlayer spacing of the MXene material is 1.23 nm, which is consistent with the result obtained by XRD test calculated using the Bragg equation (the (002) in XRD corresponds to an angle of 7.1°, and the Bragg equation is: d=λ / (2sinθ)=1.5406 / (2*sin(3.55°)≈12.46 Å).

[0068] X-ray photoelectron spectroscopy (XPS) was used to analyze the surface functional group composition of the material, such as Figure 16 The results show that thanks to the pure ion environment (F - ), the sample surface has a high number of fluorine end groups.

[0069] Example 12 This embodiment is basically the same as embodiment 1, except that Ti3AlC2 in the raw material is replaced by Ti3AlCN, the mass ratio of MAX to ammonium bifluoride is 1:6, and the oscillating ball milling is performed at a frequency of 15 Hz for 4 h.

[0070] pass Figure 17 The XRD and scanning electron microscopy shown in the figure prove that by using Ti3AlCN instead, a successfully etched Ti3CN MXene phase can also be obtained.

[0071] Example 13 This embodiment is basically the same as embodiment 1, except that Ti3AlC2 in the raw material is replaced by Nb4AlC3, the mass ratio of MAX to ammonium bifluoride is 1:8, and the oscillating ball milling is performed at a frequency of 15 Hz for 6 h.

[0072] pass Figure 18 The XRD and scanning electron microscopy shown in the figure prove that by using Nb4AlC3 instead, the Nb4C3MXene phase can also be successfully etched.

[0073] Example 14 This embodiment is basically the same as embodiment 1, except that Ti3AlC2 in the raw material is replaced by Ti3SiC2, the mass ratio of MAX to ammonium bifluoride is 1:6, and the oscillating ball milling is performed at a frequency of 15 Hz for 4 h.

[0074] pass Figure 19The XRD and scanning electron microscopy shown in the figure prove that by using Ti3SiC2 instead, the Ti3C2MXene phase can also be successfully etched.

[0075] The embodiments described above are only preferred embodiments of the present invention and are only used to explain the present invention, not to limit the scope of implementation of the present invention. For those skilled in the art, it is of course possible to easily make other implementation methods by replacing or changing the technical content disclosed in this specification. Therefore, all changes and improvements made on the principles of the present invention should be included in the scope of the patent application of the present invention.

Claims

1. A method for rapidly preparing two-dimensional MXene materials by dry ball milling, characterized in that: The following steps are involved: 1) Mix the parent phase MAX powder and ammonium bifluoride and place them into a ball mill under argon atmosphere; 2) Perform oscillating high-energy ball milling at a ball-to-material ratio of 5 to 20:1 to achieve dry etching; 3) The ball-milled product is ground and washed with deionized water until neutral, and then allowed to stand or centrifuge for separation. The upper layer is the two-dimensional MXene material, and the lower layer is the unreacted MAX.

2. The method according to claim 1, characterized in that The parent phase MAX powder is selected from titanium aluminum carbide, vanadium aluminum carbide, niobium aluminum carbide, titanium silicon carbide, titanium aluminum carbonitride or titanium tin carbide.

3. The method according to claim 1, characterized in that The mass ratio of the parent phase MAX powder to ammonium bifluoride is 1:1-8.

4. The method according to claim 1, wherein The ball milling frequency is 5-30 Hz, and the ball milling time is 15 min-10 h.

5. The method according to claim 1, wherein The unreacted MAX is recovered by drying and then subjected to oscillating high-energy ball milling etching.

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