Large-size Ti3C2Tx prepared by low-temperature progressive etching and interfacial steric hindrance control x MXene method

Abstract

This invention discloses a method for producing large-size, low-defect Ti3C2T based on low-temperature progressive etching and interface spatial steric hindrance control. x Method for preparing MXene nanosheets. Size-separated Ti3AlC2 was added to a fluoride salt / hydrochloric acid etching system and progressively etched at 2–10 °C; the washed multilayer Ti3C2 nanosheets were then... x Pretreatment was performed by dispersing the precursor in a polar medium containing a macromolecular steric hindrance stabilizer under low dissolved oxygen conditions; followed by gentle dissociation using either calorimetric-calibrated low-effective-power water bath ultrasonication or low-impact linear-velocity mechanical stirring; and then two-stage differential centrifugation was carried out using relative centrifugal force to wash away the free stabilizer. This method reduces fragmentation, oxidation, and edge damage caused by high-energy cavitation and high-speed shearing by controlling precursor particle size, etching exothermics, interlayer hydrated ion state, and lamellar interface stability. The resulting Ti3C2T x Nanosheets are mainly composed of 5-30 μm layers, with a high proportion of few layers, making them suitable for highly conductive thin films, electromagnetic shielding, flexible electronics, and energy storage devices.

Description

Technical Field

[0001] This invention belongs to the field of two-dimensional transition metal carbide preparation and liquid phase exfoliation technology, specifically involving a method for preparing large-size, low-defect Ti3C2T using precursor particle size control, low-temperature progressive etching, interface steric hindrance stabilization, low-energy external field dissociation, and differential centrifugation fractionation. x The method of MXene nanosheets. Background Technology

[0002] MXenes are a class of two-dimensional materials composed of transition metal carbides, nitrides, or carbonitrides, whose general formula can be represented as M. n ₊1X n T x Where M is an early transition metal element, X is C and / or N, and T is T. x This indicates surface end groups such as -O, -OH, and -F. Ti3C2T x It is one of the most widely researched and applied MXenes, with high electrical conductivity, hydrophilic surface, tunable interlayer structure and good solution processing performance. It can be used for electromagnetic shielding, flexible conductive films, energy storage electrodes, sensors and functional composite materials.

[0003] Ti3C2T x Typically obtained by selectively removing the Al layer from a Ti3AlC2 MAX phase precursor using a fluorine-containing system. The etched multilayer Ti3C2T... x While still exhibiting interlayer interactions and a degree of recombination, these nanosheets require further dissociation into single-layer or few-layer nanosheets. The lateral dimensions and structural integrity of these nanosheets directly affect the number of interlayer contacts, electron transport paths, mechanical continuity, and barrier properties in macroscopically assembled thin films. For conductive thin films and electromagnetic shielding materials, larger, intact nanosheets help reduce interlayer junctions and interfacial resistance.

[0004] Existing exfoliation methods often employ probe-type high-power ultrasound, high-speed homogenization, or high-shear dispersion. While these methods can improve the degree of dissociation in a short time, the localized impacts from cavitation bubble collapse, microjets, and mechanical shearing can easily cause edge cracking, porosity, lateral dimension reduction, and oxidation of the sheets. Probe-type ultrasound also carries the risk of metal probe wear and the introduction of impurities. On the other hand, simply reducing the ultrasonic power without adjusting etching uniformity, interlayer hydration, and dispersion interface stability may lead to insufficient dissociation, repeated stacking, or cumulative damage caused by prolonged processing.

[0005] Furthermore, the nominal ultrasonic power and centrifugal speed of different devices do not directly correspond to the same actual energy input and separation effect. Describing the process solely based on the device's rated power or rpm can easily lead to insufficient repeatability across devices. Therefore, a synergistic preparation method is needed that allows control over everything from precursor scale, etching kinetics, interface stability, effective energy input to relative centrifugal force gradation, to achieve Ti3C2T at relatively low mechanical energy input. x Layer dissociation is performed while preserving the lateral dimensions of the layers and lattice integrity as much as possible. Summary of the Invention

[0006] This invention aims to solve the problems of existing Ti3C2T x To address the issues of lamellar fragmentation, edge damage, oxidation, and introduction of exogenous impurities caused by high-energy cavitation and high-speed shearing during MXene exfoliation, as well as the problems of insufficient dissociation and recombination that easily occur during low-energy exfoliation, this paper proposes a method for large-size, low-defect Ti3C2T with quantifiable process parameters, easy cross-device reproducibility, and scalability potential. x Methods for preparing MXene nanosheets.

[0007] To achieve the above objectives, this invention adopts a continuous technical route of "precursor particle size matching - low-temperature progressive etching - low-oxygen interface steric hindrance pretreatment - low-energy external field dissociation - differential centrifugation classification".

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A method for preparing large-size Ti3C2T using low-temperature progressive etching and interfacial steric hindrance control x The MXene method includes the following steps: S1. Select Ti3AlC2 ceramic powder with a purity of not less than 98%, and control the particle size through sieving, sedimentation classification, or air classification. The D50 of the classified powder is 15-50 μm, preferably 20-40 μm, and the D90 is not greater than 75 μm. Particles that are too small are prone to rapid reaction in acidic fluorine-containing systems and generate more edge defects; particles that are too large are not conducive to the complete removal of the Al layer. By controlling the precursor particle size window, the obtained Ti3C2T x The potential lateral dimensions match the subsequent mild dissociation conditions.

[0009] S2. Dissolve LiF completely in 8-10 mol / L hydrochloric acid and place under low-temperature cycling conditions. Slowly add Ti3AlC2 in batches over 10-30 min to the etching solution and react at 2-10℃ and 80-250 rpm for 36-72 h. Low temperature and slow addition are used to control local exothermic reaction rate and reduce rapid gas generation inside the particles, thermal stress, and cracks caused by uneven etching. Li⁺ and its hydrated structure can enter or remain in the expanded interlayer during etching, providing a basis for interlayer expansion for subsequent low-energy dissociation.

[0010] S3. Low-oxygen washing and steric hindrance pretreatment. After etching, wash with 0.5-1.5 mol / L dilute hydrochloric acid, followed by washing with deionized water with dissolved oxygen not exceeding 2 mg / L until the pH of the supernatant reaches 5.5-6.8. Avoid prolonged exposure to air and excessive centrifugation during washing and redispersing. The resulting multilayer Ti3C2T... x The mixture is dispersed in a polar medium containing 0.1-1.0 wt% of a macromolecular steric hindrance stabilizer to achieve a solid content of 0.5-5 mg / mL, and stirred for 2-8 hours under nitrogen, argon, or vacuum deoxygenation conditions. The stabilizer is preferably polyvinylpyrrolidone (PVP), whose molecular chains can form a solvated steric hindrance layer on the surface and edges of the sheets, inhibiting recombination and buffering edge collisions under subsequent external forces. Without specific theoretical constraints, some chain segments can also adsorb or partially enter the enlarged interlayer inlets, further weakening interlayer interactions.

[0011] S4. When using water bath ultrasound, calibrate the effective acoustic power using calorimetry, controlling the effective acoustic power density to be 5-40 W / L, preferably 10-30 W / L, for 1-6 hours, and ensuring the system temperature does not exceed 10℃ through ice-water bath or circulating cooling. Effective acoustic power P eff Press P eff =m·c p The effective sound power density is calculated using (ΔT / Δt) as P. eff / V, where m is the mass of the liquid, c p ΔT / Δt is the specific heat capacity of the liquid, ΔT / Δt is the initial linear heating rate when external cooling is turned off, and V is the volume of the liquid being processed. When mechanical stirring is used, a paddle, anchor, or frame stirrer is preferred, with a paddle tip linear velocity of 0.15-1.0 m / s, preferably 0.20-0.60 m / s, and a processing time of 4-12 hours.

[0012] S5. Centrifuge the dissociated suspension at 50-500g for 5-15min to allow undissociated or insufficiently dissociated thick-layer particles to settle preferentially, and collect the supernatant. Then centrifuge at 800-4000g for 10-30min to allow large monolayers or few-layer lamellae to settle, while some small fragments and free stabilizers remain in the supernatant. Collect the second-stage centrifugal precipitate, wash it 1-3 times with low-dissolved oxygen deionized water or a water / ethanol mixture, and redisperse it to obtain the target Ti3C2T. x Nanosheets. Relative centrifugal force is prioritized over individual rpm parameters to improve repeatability across different centrifugation devices.

[0013] The beneficial effects of this invention are: (1) The present invention performs windowing control on the particle size of Ti3AlC2 before etching, and adopts a gradual etching method with low temperature, slow feeding and low speed stirring, which can reduce local violent reaction and particle fragmentation, and maintain the obtained Ti3C2T x The horizontal dimensions provide the basis.

[0014] (2) This invention utilizes the expansion effect generated by interlayer hydrated cations after etching, and uses macromolecular steric hindrance stabilizers to regulate the surface and edge interface of the sheets, first reducing the interlayer dissociation energy barrier and the tendency to recombine, and then applying a low-energy external field, which is different from the conventional peeling method that relies on high-energy impact to directly destroy multilayer particles.

[0015] (3) The present invention uses effective sound power density or blade tip linear velocity calibrated by calorimetry to describe the external field conditions, and uses relative centrifugal force to describe the grading conditions, thereby reducing repeatability deviations caused by differences in equipment rated parameters.

[0016] (4) The present invention avoids direct contact between the probe and the dispersion, which can reduce the risk of exogenous metal impurities such as Fe, Cr, and Ni caused by probe wear; at the same time, low temperature and low dissolved oxygen operation helps to suppress oxidation during the treatment process.

[0017] (5) The large-size few-layer Ti3C2T obtained by the present invention x Nanosheets can reduce the number of inter-sheet points in macroscopic thin films, which is beneficial for constructing continuous conductive networks and is suitable for electromagnetic shielding, flexible conductive films, energy storage electrodes and composite materials.

[0018] This invention discloses a method for preparing large-size Ti3C2T using low-temperature progressive etching and interface steric hindrance control. x The MXene method was employed. Uniform Al layer removal and interlayer spacing expansion were achieved by controlling the particle size of the Ti3AlC2 precursor and low-temperature etching conditions. A macromolecular steric hindrance stabilizer was used to suppress layer recombination and oxidation, and gentle exfoliation was achieved by combining low-power water bath ultrasonication or low-speed shearing. Differential centrifugation and fractionation yielded Ti3C2T with large lateral dimensions, a high proportion of monolayers and few layers, a complete structure, and excellent conductivity. x MXene nanosheets Unless otherwise specified, the raw materials and reagents used in this invention can be obtained through conventional commercial channels. Attached Figure Description

[0019] Figure 1 TiC2T obtained in Example 1 X SEM micrographs of MXene two-dimensional sheets Detailed Implementation

[0020] The following examples are used to illustrate the technical solution of the present invention, but do not constitute a limitation on the scope of protection of the present invention. Unless otherwise specified, all reagents used are of analytical grade, and the water used is deionized water with a resistivity of not less than 18.2 MΩ·cm. Fluoride-containing acidic systems are corrosive and toxic; related operations should be carried out in corrosion-resistant and well-ventilated facilities, and appropriate personal protective equipment and fluoride-containing waste liquid disposal measures should be used. Example

[0021] A method for preparing large-size Ti3C2T using low-temperature progressive etching and interfacial steric hindrance control x The MXene method includes the following steps: Weigh 1.00 g of 400-mesh Ti3AlC2 powder with a purity greater than 98%. Dissolve 1.00 g of LiF in 20 mL of 9 mol / L HCl and pre-cool to 4 °C. Then, add Ti3AlC2 in portions over approximately 20 min and etch at 4 °C and 150 rpm for 48 h. Wash the reaction product once with 1 mol / L dilute hydrochloric acid, then wash with deionized water deoxygenated by argon at 1500-2200 g until the pH of the supernatant is approximately 6.5, to obtain multilayer Ti3C2T. x Wet slurry. The obtained wet slurry was dispersed in 100 mL of a 0.5 wt% PVP aqueous solution, so that Ti3C2T x The concentration was approximately 2 mg / mL, and the mixture was stirred at 150 rpm for 4 h under argon protection. Subsequently, it was sonicated in a water bath at an effective acoustic power density of approximately 20 W / L for 5 h at below 10 °C. The resulting dispersion was first centrifuged at approximately 250 g for 10 min to remove insufficiently exfoliated thick-layer particles, and then centrifuged at approximately 2200 g for 20 min to enrich the target product. The precipitate was collected, washed twice with low-dissolved oxygen deionized water, and then redispersed to obtain large-sized few-layer Ti3C2T. x MXene nanosheets. Example

[0022] A method for preparing large-size Ti3C2T using low-temperature progressive etching and interfacial steric hindrance control x The MXene method includes the following steps: Following the steps in Example 1, low-temperature progressive etching and low-oxygen washing were performed to obtain multilayer Ti3C2T. xWet slurry: The wet slurry was dispersed in 100 mL of a 0.8 wt% sodium polystyrene sulfonate water / ethanol mixed solution, with a water to ethanol volume ratio of 1:1. The number-average molecular weight of sodium polystyrene sulfonate was approximately 70,000 Da. Interfacial stabilization pretreatment was performed by stirring for 6 h under argon protection. The dispersion was placed in a cylindrical container with an inner diameter of approximately 70 mm and stirred at 200 rpm for 8 h using a 40 mm diameter anchor impeller. The impeller tip linear velocity was approximately 0.42 m / s, calculated using v = πDn / 60. During the treatment, the system temperature was kept below 12 °C by external cooling. Ti3C2T was obtained using the same two-stage relative centrifugal force fractionation and low-oxygen washing method as in Example 1. x Nanosheets.

[0023] The resulting sheets have lateral dimensions mainly distributed in the range of 5-15 μm, with sheets having a thickness of no more than 5 nm accounting for approximately 85% of the total. The self-supporting thin film has a room temperature conductivity of 8800 S / cm. Example

[0024] A method for preparing large-size Ti3C2T using low-temperature progressive etching and interfacial steric hindrance control x The MXene method includes the following steps: 10.0 g of particle size-separated Ti3AlC2 and 10.0 g of LiF were weighed and etched using 200 mL of 9 mol / L HCl as the etching medium. In a 1 L corrosion-resistant reactor with a cooling jacket, Ti3AlC2 was added in batches over 30 min at 4-6 °C, and the mixture was stirred at 150 rpm for 50 h. The reaction product was then subjected to acid washing and low-oxygen water washing according to the method in Example 1, with centrifugation conditions set based on relative centrifugal force.

[0025] The obtained wet slurry was dispersed in 1L of 0.5wt% PVP deoxygenated aqueous solution and stirred for 5h under argon protection. Then, it was ultrasonically treated in a water bath for 5h under circulating cooling conditions with an effective acoustic power density of 18-22W / L, and then centrifuged in two stages at approximately 250g and 2200g.

[0026] During the scale-up process, the solid-liquid ratio, PVP concentration, effective acoustic power density, and relative centrifugal force remained consistent with those in Example 1. The resulting dispersion was uniform and stable, with no obvious block sedimentation, and the product still consisted of large-sized, few-layer Ti3C2T. x The presence of MXene nanosheets as the main component indicates that this method can be scaled up proportionally based on volume-dependent and convertible process parameters, without relying on the nominal power or rotation speed of specific equipment.

[0027] Weigh 1g of Ti3AlC2 and use the same LiF / HCl dosage as in Example 1, but etch at 25°C with stirring for 24 hours. After washing to near neutral, disperse directly in 100mL of deionized water without adding a macromolecular steric hindrance stabilizer; treat with a probe-type ultrasonic device in an ice-water bath at an effective acoustic power density of approximately 150W / L for 1 hour. After treatment, collect the precipitate by centrifugation at approximately 1500-2200g for 60 minutes.

[0028] The obtained product mainly consists of fragments with a lateral size of 200-800 nm and a small number of sheets not exceeding 2 μm, with single-layer sheets accounting for approximately 40% of the total. The conductivity of the filtered film is approximately 4600 S / cm. The Ti-O related components in the X-ray photoelectron spectroscopy are significantly enhanced compared to Example 1. These results indicate that the combination of room-temperature rapid etching, lack of interface stability, and high-energy probe ultrasound easily leads to sheet fragmentation and oxidation.

[0029] Low-temperature etching and low-oxygen washing were completed according to Example 1, but the multilayer Ti3C2T x It was directly dispersed in 100 mL of deoxygenated deionized water without adding PVP. The remaining water bath ultrasonic temperature, effective acoustic power density and treatment time were the same as in Example 1.

[0030] The treated dispersion exhibited rapid flocculation and sedimentation during settling, and the amount of stable, low-layer dispersion obtainable after differential centrifugation was lower than in Example 1; AFM observed more overlapping and re-stabilized layers. This comparative example illustrates that simply reducing the ultrasonic energy without interfacial steric stabilization limits stability after interlayer dissociation and peeling.

[0031] As can be seen from Examples 1, 2, and Comparative Example 1, the combined use of low-temperature progressive etching, interface spatial steric hindrance pretreatment, and low-energy external field dissociation can better maintain the lateral dimensions of the sheets while achieving fewer layers, and is beneficial for forming self-supporting thin films with higher electrical conductivity. Comparative Examples 2 and 3 further illustrate that interface stability and low local energy density are important components of the technical effects of this invention.

[0032] Table 1 MXene Performance Comparison Example 1 20W / L water bath ultrasound, 5h Approximately 18μm on average Single-layer and double-layer: approximately 88% 9200S / cm Example 2 The propeller tip linear velocity is approximately 0.42 m / s, 8 hours. Mainly 5-15 μm Thickness ≤ 5 nm: Approximately 85% 8800S / cm Comparative Example 1 150W / L probe ultrasound, 1 hour Mainly 0.2-0.8μm Single layer approximately 40% 4600S / cm The Ti3AlC2, LiF, hydrochloric acid, and macromolecular steric hindrance stabilizer used in this invention are all commercially available; etching, stirring, cooling, water bath ultrasonication, and centrifugal fractionation can all be performed using conventional chemical and nanomaterial equipment. By controlling the scale-up conditions with effective acoustic power density, impeller tip linear velocity, and relative centrifugal force, laboratory batches can be expanded to larger volumes. The resulting Ti3C2T x Nanosheets can be used as functional fillers for highly conductive thin films, electromagnetic shielding films, flexible sensors, electrochemical electrodes, and polymer composite materials.

[0033] The above embodiments are only used to illustrate the technical concept of the present invention. Those skilled in the art can make equivalent substitutions or adjustments to the type of stabilizer, processing time, reactor type, and grading equipment without departing from the essence of the present invention, and all such equivalent substitutions or adjustments should fall within the protection scope of the present invention.

Claims

1. A method for preparing large-size Ti3C2T using low-temperature progressive etching and interfacial steric hindrance control. x The MXene method is characterized by, include: S1: Precursor classification: Ti3AlC2 ceramic powder is sieved or classified by particle size to make its particle size D50 15-50μm; S2: Low-temperature progressive etching: The Ti3AlC2 ceramic powder is slowly added to a fluoride salt / hydrochloric acid etching solution over 10-30 min, and reacted at 2-10℃ and 80-250 rpm for 36-72 h to selectively remove the Al layer while retaining interlayer hydrated cations, thus obtaining a multilayer Ti3C2T x Etching products; S3: Low-oxygen washing and interfacial steric hindrance pretreatment: The multilayer Ti3C2T was washed with dilute hydrochloric acid and low-dissolved oxygen deionized water. x The supernatant was prepared until its pH was 5.5-6.

8. It was then dispersed in a polar medium containing a macromolecular steric hindrance stabilizer, allowing Ti3C2T to... x The solid content is 0.5-5 mg / mL, and the mixture is stirred for 2-8 hours under an inert atmosphere or deoxygenation conditions. S4: Low-energy and mild dissociation: The dispersion obtained in step S3 is dissociated at 0-10℃ by water bath ultrasound or low-speed mechanical stirring. The effective sound power density of water bath ultrasound is 5-40W / L and the treatment time is 1-6h. The blade tip linear velocity of low-speed mechanical stirring is 0.15-1.0m / s and the treatment time is 4-12h. S5: Differential centrifugation fractionation: First, treat with a relative centrifugal force of 50-500g for 5-15 min to remove incompletely dissociated thick-layer particles and collect the upper dispersion; then treat with a relative centrifugal force of 800-4000g for 10-30 min, collect the precipitate and wash it 1-3 times with a low dissolved oxygen medium to obtain large-size, low-defect Ti3C2T. x MXene nanosheets.

2. The method according to claim 1, characterized in that, The Ti3AlC2 ceramic powder mentioned in step S1 has a purity of not less than 98%, a particle size D50 of 20-40 μm, and a D90 of not more than 75 μm.

3. The method according to claim 1, characterized in that, The fluoride salt mentioned in step S2 is LiF, and the hydrochloric acid concentration is 8-10 mol / L; the mass ratio of LiF to Ti3AlC2 is (0.8-1.3):1, and the amount of hydrochloric acid used is 15-25 mL per 1 g Ti3AlC2; preferably, the etching temperature is 4-8℃, and the reaction time is 48-60 h.

4. The method according to claim 1, characterized in that, The dissolved oxygen in the low dissolved oxygen deionized water mentioned in step S3 is not higher than 2.0 mg / L; the low dissolved oxygen deionized water is obtained by bubbling with nitrogen or argon, vacuum degassing, or a combination of both.

5. The method according to claim 1, characterized in that, The macromolecular steric hindrance stabilizer mentioned in step S3 is at least one of polyvinylpyrrolidone, polyvinyl alcohol, polyethylene glycol, or sodium polystyrene sulfonate, with a mass concentration of 0.1-1.0 wt%; wherein the number average molecular weight of polyvinylpyrrolidone, polyvinyl alcohol, or sodium polystyrene sulfonate is 10,000-100,000 Da, and the number average molecular weight of polyethylene glycol is 2,000-20,000 Da.

6. The method according to claim 1, characterized in that, When using water bath ultrasound in step S4, the effective acoustic power density is calibrated by calorimetry. The effective acoustic power density is 10-30 W / L, the treatment time is 2-5 h, and the temperature of the dispersion does not exceed 10 °C during the treatment.

7. The method according to claim 1, characterized in that, When using low-speed mechanical stirring in step S4, a paddle, anchor, or frame stirrer is used. The diameter of the stirring paddle is 0.35-0.70 times the inner diameter of the reaction vessel, and the linear velocity of the paddle tip is 0.20-0.60 m / s.

8. The method according to claim 1, characterized in that, The relative centrifugal force RCF in step S5 is calculated as RCF = 1.118 × 10⁻ 5 The calculation is based on ×r×n², where r is the centrifugal radius in cm and n is the rotational speed in rpm. Preferably, the first stage of centrifugation is 100-350g for 8-12min, and the second stage of centrifugation is 1000-3000g for 15-25min.

9. A Ti3C2T prepared by the method according to any one of claims 1-8 x MXene nanosheets, characterized in that, According to the number of layers, the proportion of layers with a lateral size in the range of 5-30μm is not less than 70%, and the proportion of layers with a thickness of not more than 5nm as measured by atomic force microscopy is not less than 75%; the self-supporting film obtained by vacuum filtration and vacuum drying at 40℃ without hot pressing or high temperature annealing has a room temperature four-probe conductivity of not less than 6000S / cm.

10. The Ti3C2T according to claim 9 x Applications of MXene nanosheets in conductive thin films, electromagnetic shielding materials, flexible electronic devices, electrochemical energy storage electrodes, sensors, or functional composite materials.

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