JP7579550B2 - Particulate material made of novel MXene nanosheets, dispersion containing said particulate material, and method for producing said dispersion - Google Patents

Description

The present invention relates to a particulate material consisting of a novel MXene nanosheet, a dispersion containing the particulate material, and a method for producing the same.

Particle materials made of MXene layered compounds obtained by removing Al from MAX phase ceramic powder such as _{Ti3AlC2 ,} a layered compound, by acid treatment (hereinafter, these may be referred to as "MXene particle materials", "MXene nanosheets", "layered compound particle materials", or simply "particle materials") have been known (Patent Documents 1, 2, 3, and 4). These MXene layered compounds are expected to be used as negative electrode active materials for secondary batteries (storage batteries) and capacitors because Na ions and Li ions can be stored/desorbed in the void layers formed by removing the Al layers, and because they have excellent electrical conductivity, they are expected to be used in electromagnetic shielding thin films and conductive thin films.

MAX phase ceramics are layered compounds with the general formula Mn _{+ 1AXn} , where M is a transition metal (Ti, Sc, Cr, Zr, Nb, etc.), A is an A group element, X is C or [C _{(1.0-x) Nx} (0<x≦1.0)], and n is 1 to 3.

Among them, when A is Al, the bond between M-A is weaker than the bond with M-X, so the Al layer is selectively removed by acid treatment. The inventors have proposed a method to prepare MXene nanosheets by thinning the film using a bead mill with micro-sized beads (Patent Documents 5 and 6).

According to the methods of Patent Documents 5 and 6, it is disclosed that MXene particle material with an average thickness of 3.5 nm to 20 nm and an average size of 0.05 μm to 0.3 μm can be obtained by peeling using a bead mill process with beads of 10 μm to 300 μm in ethanol or isopropanol (IPA) without removing the unpeeled portions by centrifugation.

JP 2016-63171 A JP 2017-76739 A US Patent Application Publication No. 2017/0294546 US Patent Application Publication No. 2017/0088429 Patent No. 6564553 Patent No. 6564552

Here, although the methods of Patent Documents 5 and 6 provide sufficiently thin and large particles, the present inventors have conducted further studies with the aim of peeling even thinner (for example, to a monolayer level) and obtaining even larger nanosheet-like particle materials. By stacking and densely arranging thin and large nanosheet-like particle materials on a substrate, it is possible to produce extremely thin conductive thin films and electromagnetic wave shielding thin films. For example, thin films made of metal plating or metal particle ink are granular, so electromagnetic waves penetrate through the gaps when electromagnetic waves penetrate. If a dense thin film oriented and stacked along the C axis is produced using the particle material of the present invention, electromagnetic waves will penetrate from the C axis direction, and the electromagnetic waves will surely pass through the MXene, making it an effective electromagnetic wave shielding thin film. In this case, an MXene thin film may be formed on a thin film made of metal plating or metal particle ink. Alternatively, an MXene thin film may be formed on an organic film in which metal particles are dispersed.

In addition, the nanosheet particle material obtained, exfoliated to the MXene monolayer level, is easily oxidized if left as is, so it was desirable to extend its lifespan for industrial application.

The present invention was completed in consideration of the above-mentioned situation, and the problem to be solved is to provide a particulate material consisting of a novel MXene nanosheet, a dispersion containing this particulate material, and a method for producing the same.

The particulate material of the present invention that solves the above problems is a particulate material having an MXene nanosheet _material composed of _Ti3Ala ( _{CxN1 -x} ) ₂ , x=0.97-0.70, a greater than 0.02, having an average thickness of 1.0-3.5 nm, an average size of 1.5-2.0 μm, and an interlayer distance of the (002) plane of 1.350 nm-1.400 nm.

The dispersion of the present invention, which solves the above-mentioned problems, is a dispersion having the above-mentioned particulate material and a dispersion medium in which the particulate material is dispersed at 0.1% by mass to 0.4% by mass and which contains 50% by mass or more of dimethyl sulfoxide (DMSO). It is more preferable that the dispersion medium contains 100% by mass of dimethyl sulfoxide (DMSO).

The method for producing a particulate material of the present invention, which solves the above problems, is a method for producing a particulate material consisting of MXene nanosheets, which includes a peeling step in which, in a bead mill using beads of 10 μm to 300 μm, a mixture of a dispersion medium containing 50% by mass or more of water and MXene dispersed in the dispersion medium at a particle concentration of 10.0 mg/mL to 20.0 mg/mL is collided with microbeads between layers to peel off the MXene and form an exfoliated product. In particular, it is preferable that the dispersion medium contains 80% by mass or more of water. It is even more preferable that it contains 100% by mass of water.

The particulate material of the present invention has the above-mentioned configuration, thereby providing a particulate material made of large MXene with a small thickness. Furthermore, the dispersion of the present invention has the above-mentioned configuration, thereby being able to hold particulate material made of MXene in a very stable state. The method for producing the particulate material of the present invention has the above-mentioned configuration, thereby being able to obtain a particulate material made of large MXene with a small thickness.

1 shows AFM images of peeled products of Examples 1 and 2 and Comparative Example 1. 1 shows SEM photographs of peeled products of each of the Examples and Comparative Examples. 1 shows XRD profiles of Examples 1 and 2 and Comparative Examples 1 and 3. 6 shows spectra showing the wavelength dependence of transmittance of thin films obtained by spin-coating the peeled products of Examples 1 and 2 and Comparative Example 1. Note that in (a) to (c), from the top, the number of spin coats was 1, 2, 3, 4, and 5.

The particulate material of the present invention, its manufacturing method, and dispersion liquid are described in detail below based on the embodiments. The particulate material of the present embodiment is a particulate material made of MXene, which is small in thickness and large in size, and has excellent electrical properties such as electrical conductivity. Since the particulate material is small in thickness and large in size, a C-axis oriented, laminated, dense, and conductive thin film can be formed. The obtained thin film can be used as a conductive thin film, an electromagnetic wave shielding thin film, and the like. The MXene thin film can also be formed on a metal-plated substrate, on a thin film made of a metal particle ink, or on an organic film in which metal particles are dispersed.
(Particulate material)
The particulate material of this embodiment is a particulate material made of large, thin-flaked MXene for application to electromagnetic wave shielding thin films, conductive thin film materials, etc. The particulate material made of thin-flaked MXene is obtained by exfoliating MXene, which is a powdered layered compound.

In this specification, when multiple upper and lower limit values are set for a parameter, the upper and lower limit values can be combined in any way unless otherwise specified. The particulate material in this embodiment is plate-shaped, leaf-shaped, flake-shaped, sheet-shaped, etc. Collectively, they are called sheet-shaped.

The particulate material of this embodiment is MXene, a layered compound consisting of three layers of titanium and two layers of carbon, or a layered compound in which part of the carbon is replaced with nitrogen. The particulate material is made of MXene _, which is represented by the composition formula _Ti3Ala ( _{CxN1 -x} ) ₂ . Here, x=0.97-0.70, and a is greater than 0.02. The upper limit of a is preferably 0.05. (Hereinafter, this will be referred to as "MXene" where appropriate). In addition to these elements, O, OH, and halogen groups can be present as surface functional groups.

The MXene that constitutes the particulate material has a "thickness" in the direction in which the layers of the layered compound are stacked, and a direction perpendicular to that thickness is the "sheet spread direction," and the value measured in this direction is the size of the particulate material of this embodiment.

The thickness of MXene can be measured by dropping MXene onto a hydrophilized Si wafer and performing AFM analysis. The average thickness is 1.0-3.5 nm, and preferably 1.50-2.00 nm. The average thickness is calculated as the average of the values measured for 100 randomly selected particles. The size of the nanosheet can be measured by dropping MXene onto a hydrophilized Si wafer and observing it with an SEM. The average size in the spreading direction of the nanosheet is 1.5-2.0 μm, and preferably 1.50-1.70 μm. If the maximum value in the direction perpendicular to the thickness is the "long side" and the minimum value is the "short side," the average value of [(long side + short side)/2] measured by SEM for 100 randomly selected particles is taken as the average size in the spreading direction.

The interlayer distance of the (002) plane of MXene can be measured by X-ray diffraction analysis and is preferably 1.350 nm to 1.400 nm, and more preferably 1.350 nm to 1.370 nm.

The zeta potential of MXene in water at pH 6 to pH 8 is preferably in the range of −29.0 mV to −34.0 mV.
(Method of Manufacturing Particulate Material)
The method for producing a particulate material of this embodiment includes a peeling step and other necessary steps.
- Exfoliation process The exfoliation process is a process in which layered _MXene ( _Ti3Ala ( _{CxN1 -x} ) ₂ , x=0.97-0.70, a>0.02) is exfoliated by colliding microbeads between the layers in a dispersion medium to obtain sheet-like exfoliated material. The obtained exfoliated material becomes an exfoliated material suspension suspended in a dispersion medium. This exfoliated material suspension can be directly subjected to the mixing process, or the dispersion medium can be removed before being subjected to the mixing process. There is no particular limitation on the method for obtaining layered MXene as the material, but the following methods can be exemplified.

_Ti3Ala ( _{CxN1 -x} ) ₂ , x=0.97-0.70, a is greater than 0.02. MXene _is obtained by acid-treating a raw material consisting of Ti3-layer MAX phase ceramic powder to partially dissolve the Al layer. An example of a method for producing MXene is described later as a pretreatment process. The raw material used in the peeling process can have the same composition as the material constituting the particle material described above. The composition does not change much during the peeling process.

This particulate material is treated with acid to dissolve some of the Al, turning it into MXene. This MXene is then mixed into a solvent whose main component is water to form a mixture, after which a peeling process is carried out in a bead mill that rotates at high speed using beads of 10 μm to 300 μm, resulting in a suspension of exfoliated material in the form of sheets of MXene suspended in the material.

The dispersion medium used in the peeling process is not particularly limited except that it contains 50% or more by mass of water, but may also contain alcohols such as methanol, ethanol, and isopropanol, ketones such as methyl ethyl ketone and acetone, dimethylformamide, dimethyl sulfoxide, etc. In particular, the lower limit of the water content may be 60% by mass, 70% by mass, 80% by mass, 90% by mass, or 100% by mass.

The concentration of MXene in the mixture used in the peeling process is not particularly limited, but can be about 10.0 mg/mL to 20.0 mg/mL. The liquid properties of the mixture are not particularly limited, but the pH can be about 6.0 to 8.0.

The specific bead mill processing in the peeling process is explained below. Peeling is possible with a bead mill equipped with a mechanism for classifying the mixture of tiny beads and slurry by centrifugation. The peeled material peeled by bead mill processing can be separated at any time from the mixture before peeling by centrifugation, and ultimately all of the MXene can be made into the peeled material.

For example, the lower limit of the bead size can be 10 μm, 15 μm, 20 μm, 30 μm, or 40 μm, and the upper limit can be 300 μm, 200 μm, or 100 μm. If the size is 10 μm or more, it is easy to classify the beads and slurry. If beads of 300 μm or less are used, peeling can be prioritized over reducing the size of the particulate material. These lower and upper limits can be used in any combination. If the bead size is in the appropriate range, the energy applied can be large and peeling can be prioritized, so it is most preferable to use beads of 50 μm to 100 μm.

The material of the beads is not particularly limited, but ceramics such as zirconia, alumina, and silicon nitride can be used. Partially stabilized zirconia, which has high fracture toughness, is particularly preferred. On the other hand, with a commonly used bead mill that classifies beads and slurry in a micro-sized gap using beads of more than 300 μm, reducing the size of the particulate material takes precedence over peeling. Also, with a ball mill such as a planetary ball mill using beads and balls of more than 300 μm, reducing the size of the particulate material takes precedence over peeling. As a result, only a portion can be peeled off, and it becomes necessary to classify and collect some of the peeled MXene, and it is not possible to obtain peeled MXene particulate material that can be used in industry. In particular, when a planetary ball mill is used, surface oxidation progresses, making it unsuitable for MXene, and in fact it has not been considered. On the other hand, with regard to the method of irradiating ultrasonic waves to a solvent, which has been used conventionally as a method of peeling MXene, cavitation occurs when ultrasonic waves are irradiated to the solvent, and the peeling of the layers that make up the layered compound progresses through a mechanism in which the powders collide with each other due to the crushing. However, even when water, which is prone to cavitation, was used, only a small portion of the MXene nanosheets were peeled off. The nanosheets were produced by a method in which only a portion of the MXene nanosheets was extracted by classification using centrifugation, which was not at a level suitable for industrial use.

The peripheral speed in the peeling process can be 6 m/sec to 12 m/sec. A peripheral speed of 8 m/sec to 10 m/sec is preferable. A peripheral speed of 6 m/sec or more provides good peeling efficiency, while a speed of 12 m/sec or less suppresses the application of excessive energy and the temperature rise of the resulting particulate material, thereby suppressing the progression of oxidation on the surface of the resulting particulate material and reducing electrical resistance. The slurry feed rate can be 100 mL/min to 300 mL/min. The slurry particle concentration can be 20.0 mg/mL to 10.0 mg/mL. A concentration of 17.0 mg/mL to 10.0 mg/mL is more preferable. A concentration of 15.0 mg/mL to 10.0 mg/mL is even more preferable.

A concentration of 20.0 mg/mL or less is preferable because it allows sufficient peeling and reduces the need to select flaky particulate material by classification using centrifugation or other methods. In addition, it makes it possible to keep the particle size of the slurry small. A concentration of 10.0 mg/mL or more improves the efficiency of peeling.

The slurry temperature is preferably in the range of 35°C or less. Keeping it below 35°C can suppress surface oxidation and keep the electrical resistance of the particulate material low.

The bead filling amount can be between 40% and 80% by volume. A filling amount of 40% by volume or more improves the efficiency of peeling, while a filling amount of 80% by volume or less makes it easier to classify the beads and slurry. Whether or not a particulate material containing a large amount of the desired flaky particles has been produced can be determined by observation with a SEM, TEM, etc. In particular, the thickness of the particulate material can be determined by AFM analysis. The particulate material obtained in the peeling process can be classified by a method such as centrifugation before use, if necessary. The optimal conditions for the peeling process vary depending on the size of the equipment, so these values are not limited.

It is preferable that all of the MXene is exfoliated by bead milling. If the exfoliation process is completed under conditions where all of the MXene is exfoliated, it becomes possible to use the product as is without removing the unexfoliated MXene. If MXene other than the exfoliated product is to be removed, it can be separated by centrifugation, filtration, etc.

MXene in which some of the carbon sites are replaced with nitrogen is more susceptible to OH group adsorption in water, weakening the interlayer bonding force. Therefore, by changing the amount of _nitrogen substituted, the thickness and size of the resulting MXene can be controlled. Thin and large nanosheets can be obtained by setting _Ti3Ala ( _{CxN1 -x} ) ₂ , x=0.97-0.70, a greater than 0.02. It is more preferable to set x to 0.85-0.70. It is even more preferable to set x to 0.80 to 0.70. In all cases, a is greater than 0.02.

The raw material used in the pretreatment step is _a MAX phase ceramic powder having a composition represented by _Ti3Ala ( _{CxN1 -x} ) ₂ , where x=0.97-0.70 and a is 1.00. Furthermore, the amount of Al to be removed is adjusted so that the amount of Al (corresponding to x) remaining in the MAX phase ceramic powder produced by acid treatment with an acidic substance exceeds 0.02. It is also possible to remove all of the Al, and in that case, it is preferable not to proceed with the acid treatment beyond the removal of the Al.

The amount of Al removed can be adjusted by changing the contact time with the acidic substance (such as an aqueous acid solution) (the longer the contact time, the greater the amount removed), the concentration of the acidic substance (the higher the concentration, the greater the amount removed), the amount of acidic substance (the greater the absolute amount of acidic substance, the greater the amount that can be removed), and the contact temperature (the higher the temperature, the greater the amount removed).

MAX phase ceramic powder (A element is Al), which is a layered compound, is subjected to acid treatment to remove part of the Al, resulting in a layered compound having a void layer that constitutes the particle material. As the acid for removing part of the Al layer, an acidic substance combining hydrofluoric acid and hydrochloric acid is used. In order to realize the combination of hydrofluoric acid and hydrochloric acid, it is preferable to mix a salt of hydrofluoric acid (KF, LiF, etc.) with hydrochloric acid to obtain a mixture of hydrofluoric acid and hydrochloric acid.

In particular, aqueous solutions of these acids are used as the acidic substances. There are no particular limitations on the mixed concentration of hydrofluoric acid and hydrochloric acid formed when it is assumed that the fluoride salt is completely dissociated. The lower limit of the hydrofluoric acid concentration can be about 1.7 mol/L, 2.0 mol/L, or 2.3 mol/L, and the upper limit can be about 2.5 mol/L, 2.6 mol/L, or 2.7 mol/L. The lower limit of the hydrochloric acid concentration can be about 2.0 mol/L, 3.0 mol/L, or 4.0 mol/L, and the upper limit can be about 13.0 mol/L, 14.0 mol/L, or 15.0 mol/L.

There is no particular limitation on the mixing ratio (molar ratio) of hydrofluoric acid and hydrochloric acid formed when the fluoride salt is assumed to be completely dissociated, but the lower limit of hydrofluoric acid may be 1:13, 1:12, or 1:11, and the upper limit may be about 1:5, 1:6, or 1:7. The concentrations and mixing ratios of hydrofluoric acid and hydrochloric acid shown here may be combined in any desired manner. The acid treatment temperature is preferably 10°C to 30°C. More preferably, it is 10°C to 20°C.

The zeta potential of the obtained MXene nanosheet particle material was measured in water at pH 6 to 8. For _Ti3Ala ( _{CxN1 -x ) 2} , the values were -29.0 mV at X=0.97, -31.5 mV at X=0.95, -32.1 mV at X=0.90, -32.4 mV at X=0.85, -33.1 mV at X=0.75, and -34.0 mV at X=0.70. On the other hand, the values were -28.9 mV at X=1.00 and -34.5 mV at X=0.65. The zeta potentials in water at pH 6 to 8 are all negative, and hydrophilic functional groups such as OH and halogens are adsorbed by acid treatment in water and by treatment with a micro-sized bead mill in water, and a larger absolute value of the zeta potential means that more hydrophilic functional groups are adsorbed. If the absolute value of the zeta potential becomes too large, the material will be crushed into pieces by the applied physical force. It was found that thin and large MXene nanosheets can be formed by increasing the absolute value of the zeta potential from 29.0 to 34.0.

The chemical composition of the MXene nanosheets was calculated by using the atomic percentages of Ti, Al, C, and N, with Ti taken as 3, to calculate the amounts of Al, C, and N. For chemical analysis, the sample was weighed onto a platinum dish, nitric acid + sulfuric acid + hydrofluoric acid were added, and the sample was dissolved by heating (to about 120°C), and then heated at a higher temperature (300°C) to evaporate the nitric acid and hydrofluoric acid to prepare a sample solution (sulfuric acid). The sample solution was then appropriately diluted and quantitatively analyzed by ICP.

(Dispersion)
The dispersion of this embodiment is a dispersion of the particulate material of this embodiment in a dispersion medium. The particulate material dispersed in the dispersion is MXene, which is easily oxidized and cannot normally exist stably, but in this embodiment, it can exist stably for a long period of time. This makes it possible to store MXene in the form of a dispersion for a long period of time, making it possible to dramatically expand the application fields of MXene. By applying this dispersion to an appropriate substrate and drying it, it becomes possible to form a conductive thin film and an electromagnetic wave shielding thin film made of MXene on the substrate. It can also be applied when using MXene.

The dispersion medium contains 50% or more by mass of dimethyl sulfoxide, and the lower limit of the content is 60%, 70%, 80%, 90%, 95%, or 100% by mass. The higher the content of dimethyl sulfoxide, the more preferable it is. In particular, it is preferable that no dispersion medium other than dimethyl sulfoxide is contained. The composition of the dispersion medium that can be contained other than dimethyl sulfoxide is not particularly limited, but it is preferable that it contains a hydrophilic material. For example, ethanol and isopropyl alcohol can be contained. The content of dimethyl sulfoxide can be 50% by mass or more based on the mass of the entire dispersion medium, and is preferably 80% by mass or more, or 90% by mass or more. It is more preferable to make it 100% by mass. For example, it can contain no water. The content of water can be 5% by mass or less based on the mass of the entire dispersion medium, and is preferably 2% by mass or less, or 1% by mass or less. When water coexists, the surface oxidation of the MXene nanosheet particle material progresses and the conductivity deteriorates. The concentration of the particulate material in the dispersion of this embodiment is 0.1% by mass to 0.4% by mass.

The particulate material, the method for producing the same, and the dispersion of the present invention will be described in detail below with reference to examples.
Example 1
Pretreatment step 11.7 g of TiC powder (TI-30-10-0020, Rare Metallic Co., Ltd.), 0.6 g of TiN powder (TN-30-10-0020, Rare Metallic Co., Ltd.), 4.9 g of Ti powder (TIE07PB 3N, Kojundo Chemical Co., Ltd.), and 2.8 g of Al powder (ALE15PB 3NG, Kojundo Chemical Co., Ltd.) were mixed in isopropanol (IPA) for 12 hours using a ball mill, and the IPA was removed using an evaporator to obtain a uniformly mixed dry powder.

The uniformly mixed dry powder was placed in an alumina crucible and fired in a graphite resistance furnace under the conditions of 1450 ° C. in an Ar stream for 2 h (heating rate 10 ° C. / min) to obtain Ti ₃ Al (C _0.95 N _0.05 ) ₂ as a MAX phase ceramic. The obtained Ti ₃ Al (C _0.95 N _0.05 ) ₂ was coarsely ground using a mortar and pestle, and then ball milled in IPA using 5 mm zirconia balls for 24 hours. Then, planetary ball milling (200 rpm, 15 minutes, 3 times) using 0.5 mm zirconia balls was performed to obtain a suspension. The IPA was removed from the suspension using an evaporator to obtain Ti ₃ Al (C _0.95 N _0.05 ) ₂ powder ground to about 3 μm.

An acid solution was prepared _by adding 18 g of LiF to 300 mL of concentrated HCl, and 10 g of _Ti3Al ( _C0.95N0.05 ) ₂ powder was added while cooling with ice, and the mixture was stirred with a magnetic stirrer for 24 hours in an environment controlled at 20°C to 30°C to etch and remove Al, thereby obtaining a particulate _material consisting of _Ti3Al0.02 ( _C0.95N0.05 ) _2MXene . After etching, the mixture was washed with water until the pH was about 6, and finally the water was replaced with ethanol. This operation resulted in a suspension of MXene suspended in ethanol being obtained as the particulate material.

The particle concentration in the raw suspension was measured, and water was added so that the particle concentration of MXene became 15.0 mg/mL, thereby obtaining MXene (raw suspension) dispersed in water as a dispersion medium.
This raw suspension was treated in a bead mill with _ZrO2 beads of 50 μm diameter at a slurry feed rate of 150 mL/min and a _ZrO2 bead loading of 80%, to produce an exfoliated material made of MXene. By repeating this treatment three times, the particulate material made of MXene contained in the raw suspension was almost entirely converted into exfoliated material, and an exfoliated material suspension containing the exfoliated material was obtained.

The obtained suspension _of exfoliated material was dropped onto a Si substrate _that had been piranha-treated (immersed in a mixed solution of _H2SO4 : _H2O2 = 3 parts by volume: 1 part by volume), and AFM analysis was performed. The AFM image is shown in Figure 1. One hundred exfoliated materials (nanosheets) were randomly selected, and the average thickness measured by AFM was determined and shown in Table 1. Furthermore, the results of SEM observation are shown in Figure 2. One hundred exfoliated materials were randomly selected, and the vertical (maximum diameter in the direction perpendicular to the thickness direction) and horizontal (directions perpendicular to the vertical and thickness directions) dimensions were measured from the SEM photograph, and the average value was defined as the size of the exfoliated material, and the average value of the sizes of the 100 exfoliated materials is shown in Table 1.

The XRD measurements were performed on the _Ti3Al ( _C0.95N0.05 ) ₂ powder A used in the _pretreatment process and the exfoliated material (MXene nanosheets), and the results are shown in Figure 3. The interlayer distance of the (002) plane from each XRD profile is shown in Table 2.

The suspension of exfoliated material (15.0 mg/ml) was centrifuged at 37,000 G (17,000 rpm) for 30 minutes, the supernatant was discarded, and 5.0 g of dimethyl sulfoxide (DMSO) was added per 1.25 g of sediment. The material was then suspended by stirring at 140 rpm and 45 mm amplitude in a shaker for 1.5 hours. This procedure was repeated three times to replace all the dispersing medium with DMSO, and a DMSO suspension was obtained.

The resulting DMSO suspension was centrifuged at 2400G (3500rpm) and the supernatant was collected (the supernatant was named DMSO colloids). One drop of ethanol was added to two drops of DMSO colloids to prepare a spin coat sample. A piranha-treated glass plate (25 x 25 x 0.7mm) was used as a substrate, and 20μL of ethanol was added and spin coated at 4000rpm for 1 minute to produce a film.

When repeating thin film production by spin coating to control film thickness, after air drying, film production by spin coating was repeated in the same manner until the required film thickness was reached. The results of UV-vis measurement are shown in Figure 4. After vacuum drying at 200°C for 24 hours, the surface electrical resistance was measured and the results are shown in Table 3.
Example 2
The peeled material was prepared in the same manner as in Example 1, except that 9.2 g of TiC powder (TI-30-10-0020, Rare Metallic Co., Ltd.), 3.2 g of TiN powder (TN-30-10-0020, Rare Metallic Co., Ltd.), 4.9 g of Ti powder (TIE07PB 3N, Kojundo Chemical Co., Ltd.), and 2.8 g of Al powder (ALE15PB 3NG, Kojundo Chemical Co. _, Ltd.) were used as starting materials. Figure 1 shows the AFM image, Table 1 shows the average thickness and average size, Table 2 shows the interlayer distance, Figure 2 shows the SEM image, Figure 3 shows the XRD profile of the obtained _Ti3Al ( _C0.75N0.25 ) ₂ powder _{and Ti3Al0.02 ( C0.75N0.25} ) _2MXene , Figure ₄ shows the UV-vis result, and Table 3 shows the surface electrical resistance value.
(Comparative Example 1)
Except for using 12.3g of TiC powder (TI-30-10-0020, Rare Metallic Co.), 4.9g of Ti powder (TIE07PB 3N, Kojundo Chemical Co.), and 2.8g of Al powder (ALE15PB 3NG, Kojundo Chemical Co.) as starting materials, _{Ti3Al0.02C2MXene} nanosheets were prepared as exfoliated products in the same manner as in Example _1. Figure 1 shows _AFM images, Table 1 shows average thickness and average size, _Table 2 shows interlayer distance, Figure 2 shows SEM images, Figure 3 shows XRD profiles of the obtained _Ti3AlC2 powder _{and Ti3Al0.02C2MXene} , _and Table 3 shows surface electrical resistance values.
(Comparative Example 2)
Except for using 4.4g of TiC powder (TI-30-10-0020, Rare Metallic Co., Ltd.), 4.6g of TiN powder (TN-30-10-0020, Rare Metallic Co., Ltd.), 7.1g of Ti powder (TIE07PB 3N, Kojundo Chemical Co., Ltd.), and 4.0g of Al powder (ALE15PB 3NG, Kojundo Chemical Co., Ltd.) as starting materials _{, Ti3Al0.02} ( _C0.5N0.5 ) _2MXene nanosheets were prepared as exfoliated materials in the same manner as in Example 1. Figure 2 shows an _SEM image, and Figure ₃ shows the XRD profiles of _{the obtained Ti3Al(C0.5N0.5)2 powder and Ti3Al0.02 ( C0.5N0.5 ) 2MXene} .
(Comparative Example 3)
Starting materials were used: 12.3g of TiC powder (TI-30-10-0020, Rare Metallic Co.), 4.9g of Ti powder (TIE07PB 3N, Kojundo Chemical Co.), and 2.8g of Al powder (ALE15PB 3NG, Kojundo Chemical Co.), and Ti ₃ Al _0.02 C ₂ MXene nanosheets were prepared as exfoliated materials in the same manner as in Comparative Example 2, except that _ethanol was used as the dispersion medium during the exfoliation process. Figure 1 shows the AFM image, Table 1 shows the average thickness and average size, Table 2 shows the interlayer distance, Figure 2 shows the SEM image, and Figure ₃ shows the XRD profile of the obtained Ti ₃ Al ₂ powder and Ti ₃ Al _0.02 C ₂ MXene.

In comparison example 2, the particles were not crushed into sheets, and the average thickness and average size of the sheets could not be measured.

(result)
It was found that Examples 1 and 2, in which x is in the range of 0.97 to 0.7, have a thinner average thickness and a larger average size than Comparative Examples 1 and 3, in which x is 1. In Comparative Example 2, in which x is 0.5, pulverization proceeded during the peeling process, and only fine particles were generated. It is preferable to replace a part of the C site with N, since it makes it easier for hydrophilic functional groups to be adsorbed, weakens the bonding strength between layers, and facilitates peeling, but if it is replaced too much with N, the bonding strength between layers is weakened, and pulverization proceeds easily and remarkably at the same time as peeling, resulting in fine powder. It was also found that Examples 1 and 2 have better light transmittance than Comparative Example 1.

In Comparative Example 3, where the dispersion medium used in the peeling process was only ethanol, the average thickness was large and the average size was small, and sufficient peeling was not possible. Furthermore, the interlayer distance of the (002) plane was also small. Thus, it was found that using a dispersion medium containing water is preferable to performing the peeling process using a dispersion medium that does not contain water, in order to obtain thin and large nanosheets, when peeling using a bead mill method using microbeads.

MXene was exfoliated by ultrasonic irradiation, and some of the exfoliated MXene nanosheets were obtained by centrifugation, but this was not at a level suitable for industrial use. When ultrasonic waves are applied to a solvent, cavitation occurs, and the resulting collapse causes the powder particles to collide with each other, which causes the layers that make up the layered compound to peel off. However, even when water, which is prone to cavitation, is used, only some of the layers peel off. Furthermore, when using a planetary ball mill, grinding takes precedence over exfoliation, and surface oxidation progresses, so MXene has not been considered.
When some of the carbon sites of MXene are replaced with nitrogen, the hydrophilic functional groups are more strongly adsorbed, weakening the interlayer bonding strength, and by selectively applying a physical force between the MXene layers in a bead mill using microbeads, we have succeeded in obtaining MXene nanosheets with a thin average thickness and a large average size without the need for classification by centrifugation. It can be said that MXene nanosheets have reached a level where they can be used industrially.

In the peeling process, by setting the MXene particle concentration to 10 mg/mL or more, the efficiency of the peeling process was increased, and by setting it to 20 mg/mL or less, the amount of unpeeled MXene remaining was suppressed, making it easier to turn the MXene into peeled material.

By using water in the peeling process, it became possible to obtain peeled products with small average thickness, but when left as is, deterioration of MXene due to oxidation was observed. However, it was revealed that oxidation can be suppressed by replacing the dispersion medium with DMSO as in the examples. Furthermore, it was found that aggregation can be effectively suppressed by keeping the concentration in the dispersion liquid at 0.4 mass% or less.

Claims (5)

A particulate material having _MXene nanosheets composed of _Ti3Ala ( _{CxN1 -x} ) ₂ , x=0.97-0.70, a greater than 0.02, with an average thickness of 1.0-3.5 nm, an average size of 1.5-2.0 μm, and an interlayer distance of the (002) plane of 1.350 nm-1.400 nm. The particulate material described in claim 1 has a zeta potential in water at pH 6 to pH 8 in the range of -29.0 mV to -34.0 mV. A particulate material according to claim 1 or 2;
a dispersion medium in which the particulate material is dispersed at 0.1% by mass to 0.4% by mass and which contains 50% by mass or more of dimethyl sulfoxide;
A dispersion having A method for producing a particulate material consisting of MXene nanosheets, comprising a peeling step in which a mixture of a dispersion medium containing 50% or more by mass of water and MXene dispersed in the dispersion medium at a particle concentration of 10 mg/mL to 20 mg/mL is treated in a bead mill using beads of 10 μm to 300 μm to peel off the MXene and form an exfoliated material. The method for producing a particulate material according to claim 4, further comprising the steps of:
a step of replacing the water contained after the peeling step with dimethyl sulfoxide to obtain a dispersion liquid in which the particulate material is dispersed in dimethyl sulfoxide;
A method for producing a dispersion having the formula:

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