Two-dimensional particle, two-dimensional particle-containing film, and two-dimensional particle-containing dispersion liquid

Abstract

This two-dimensional particle has one or more layers. In the two-dimensional particle, each of the layers includes: a layer main body represented by the formula MmXn (in the formula, M is at least one metal belonging to groups 3, 4, 5, 6 and 7, X is a carbon atom, a nitrogen atom or a combination of these, n is 1-4, and m is greater than n and not more than 5); and a modification or terminal T present at the surface of the layer main body (T is at least one type selected from the group consisting of a hydroxyl group, a fluorine atom, a chlorine atom, an oxygen atom and a hydrogen atom). The two-dimensional particle has a structure in which an oxygen atom derived from a hydroxyl group that is the modification or terminal T is bonded to a phosphorus atom in a nitrogen-containing phosphonic acid.

Description

Two-dimensional particles, two-dimensional particle-containing film, and two-dimensional particle-containing dispersion

[0001] The present disclosure relates to two-dimensional particles, two-dimensional particle-containing films, and two-dimensional particle-containing dispersions.

[0002] In recent years, MXene has been attracting attention as a new material. MXene is a type of so-called two-dimensional material, and is a layered material having the form of one or more layers. ｍ X ｎ T s It is a layered compound represented by the following composition, and is obtained by etching the precursor MAX. Due to the etching of the MAX, modifications or terminations such as -OH, =O, and -F are generated on the surface of MXene. These modifications or terminations impart hydrophilic properties to MXene. Therefore, MXene has excellent water dispersion properties. MXene also exhibits excellent electrical conductivity.

[0003] The surface of MXene is rich in modified or terminated functional groups derived from the etchant used in precursor treatment. In recent years, ligand substitution, in which other ligands are substituted via hydroxyl groups by dehydration condensation or other methods, has attracted attention as a technique that can impart various new functional groups not originally present to MXene and thereby impart new properties.

[0004] For example, Patent Document 1 discloses two-dimensional MXene particles surface-modified with functional groups containing saturated or unsaturated hydrocarbons, and passivated two-dimensional MXene particles having an organic protective film formed on the surface of the surface-modified two-dimensional MXene particles, the functional groups being selected from the group consisting of phosphonates and amines, and the two-dimensional MXene particles surface-modified with functional groups containing saturated or unsaturated hydrocarbons are dispersed in an organic solvent that forms a protective film. Patent Document 1 also discloses that the two-dimensional MXene particles are easily dispersible in organic solvents, making it easy to prepare polymer composites containing the particles, as well as having advantageous properties for application in films and coating products with various performances.

[0005] In addition, Non-Patent Document 1 reports that Ti is bonded to the silane ligand spacer through coordination interactions. ３ C ２ A method for covalently bonding lipase to the surface of a TX nanosheet has been described. Non-Patent Document 1 also shows that the catalytic activity of immobilized lipase for the hydrolysis of p-nitrophenyl palmitate (pNPP) was improved by near-infrared light irradiation, and that immobilized lipase exhibits good pH and thermal stability and reusability, which are important for the practical application of enzymes.

[0006] Japanese Patent Application Laid-Open No. 2020-93971

[0007] Chaoying Ding et al., "Photothermal enhanced enzymatic activity of lipase covalently immobilized on functionalized Ti3C2TX nanosheets", Chemical Engineering Journal 2019, 378, 122205.

[0008] The MXene particles of Patent Document 1 can only be dispersed in organic dispersion media that are immiscible with water (solubility in water <10% w / w), and are therefore limited in the dispersion media in which they can be dispersed. Furthermore, the MXene particles of Patent Document 1 have the problem of low dispersion stability in organic dispersion media.

[0009] Furthermore, in Non-Patent Document 1, substitution with a ligand having an amino group is carried out, but the ligand-substituted MXene shown in Non-Patent Document 1 has the problem of insufficient conductivity.

[0010] The present disclosure has been made in consideration of the above circumstances, and its purpose is to provide two-dimensional particles whose surfaces are modified with a nitrogen-containing phosphonic acid having a saturated hydrocarbon group or an unsaturated hydrocarbon group and a nitrogen-containing functional group, and which are well dispersible in various dispersion media; a two-dimensional particle-containing film that contains the two-dimensional particles and exhibits high conductivity; and a two-dimensional particle-containing dispersion liquid in which the two-dimensional particles have high dispersion stability.

[0011] According to one aspect of the present disclosure, there is provided a two-dimensional particle comprising one or more layers, wherein said layers are of the following formula: M ｍ X ｎ (wherein M is at least one metal of Group 3, 4, 5, 6 or 7; X is a carbon atom, a nitrogen atom or a combination thereof; n is 1 or more and 4 or less; and m is greater than n and 5 or less), and modified or terminal T (wherein T is at least one selected from the group consisting of a hydroxyl group, a fluorine atom, a chlorine atom, an oxygen atom and a hydrogen atom) present on the surface of the layer body, wherein the oxygen atom derived from the hydroxyl group, which is the modified or terminal T, is bonded to a phosphorus atom of a nitrogen-containing phosphonic acid having a saturated or unsaturated hydrocarbon group and a nitrogen-containing functional group.

[0012] According to the present disclosure, it is possible to provide two-dimensional particles whose surfaces are modified with a nitrogen-containing phosphonic acid having a saturated hydrocarbon group or an unsaturated hydrocarbon group and a nitrogen-containing functional group, and which are well dispersible in various dispersion media; a two-dimensional particle-containing film that contains the two-dimensional particles and exhibits high electrical conductivity; and a two-dimensional particle-containing dispersion liquid that exhibits high dispersion stability of the two-dimensional particles.

[0013] 1-1. This figure shows the results of XRD measurement of the ligand-substituted MXene film of Example 1-1. It is a diagram showing the results of ultraviolet-visible spectrophotometric measurement (ultraviolet-visible absorption spectrum) of the ligand-substituted MXene particle-containing dispersion of Example 2-1. It is a photograph of the ligand-substituted MXene particle-containing dispersion at the initial stage and after standing for 89 hours in Example 2-1. It is a diagram showing the relationship between the standing time and the ratio of absorbance to initial absorbance in Example 2-1. 1A and 1B are diagrams schematically showing the dispersion states of conventional and present embodiment ligand-substituted MXene particle-containing dispersions, and the state of films formed using the dispersions.

[0014] The present inventors focused on the usefulness of two-dimensional particles in which the surface of MXene is modified with a compound having a nitrogen-containing functional group, allowing for the immobilization of heterogeneous materials on the MXene surface via the nitrogen-containing functional group, and conducted extensive research to obtain such two-dimensional particles. Non-Patent Document 1 first explored a substitution reaction using APTES as a ligand, utilizing the hydroxyl groups on MXene. This technology can be considered to impart amino groups to MXene. However, upon further investigation of this technology, it was discovered that when this silane coupling agent is used as a ligand, polymerization reactions occur not only between MXene and the silane coupling agent, but also between the silane coupling agents themselves, resulting in the presence of a polysiloxane having Si-O-Si bonds on MXene. Furthermore, the presence of this polysiloxane on MXene poses the problem of preventing uniform and thin ligand substitution on MXene. The inability to achieve uniform and thin ligand substitution results in a significantly lower conductivity, so low that the conductivity of the resulting film cannot be measured, potentially preventing the excellent electrical properties of MXene from being exhibited.

[0015] Furthermore, it is generally known that electron transfer occurs more easily when MXene is bonded to a different material when the distance between the MXene and the different material is short. However, as mentioned above, the presence of polysiloxane on the MXene increases the distance between the materials. As a result, the efficiency of electron transfer between the MXene and the different material becomes very poor, making it difficult to use MXene in electronic devices that utilize its electrical conductivity.

[0016] The inventors have therefore conducted extensive research to develop ligand-substituted MXene particles whose surfaces are ligand-substituted, which exhibit high conductivity, particularly when formed into films, and which are easily dispersible in various dispersion media. The inventors have found that the distance between MXene particles in the z-axis direction (stacking direction) is a factor influencing electrical conductivity, an important characteristic of MXene. The shorter the distance between MXene flakes, the higher the electron transfer efficiency, resulting in higher electrical conductivity when stacked in a film structure. Furthermore, factors other than the distance between MXene flakes, such as the type of ligand on MXene, also affect electrical conductivity. As a result, they have found that when MXene particles (e.g., single-layer or small-layer MXene flakes) are ligand-substituted with a nitrogen-containing phosphonic acid having a nitrogen-containing functional group, the resulting two-dimensional particles disperse well in various dispersion media, and that two-dimensional particle-containing films formed using the two-dimensional particles exhibit good electrical conductivity.

[0017] The two-dimensional particles, the two-dimensional particle-containing dispersion, and the two-dimensional particle-containing film according to the present disclosure will be described below.

[0018] (Embodiment 1: Two-dimensional particles) Hereinafter, two-dimensional particles according to one embodiment of the present invention will be described in detail, but the present disclosure is not limited to such an embodiment.

[0019] The two-dimensional particle in this embodiment is a two-dimensional particle comprising one or more layers, wherein said layers have the following formula: M ｍ X ｎ(wherein M is at least one Group 3, 4, 5, 6, or 7 metal; X is a carbon atom, a nitrogen atom, or a combination thereof; n is 1 or more and 4 or less; and m is greater than n and 5 or less), and a modified or terminated T (wherein T is at least one selected from the group consisting of a hydroxyl group, a fluorine atom, a chlorine atom, an oxygen atom, and a hydrogen atom) present on the surface of the layer body, wherein the oxygen atom derived from the hydroxyl group, which is the modified or terminated T, has a structure bonded to a phosphorus atom of a nitrogen-containing phosphonic acid having a saturated or unsaturated hydrocarbon group and a nitrogen-containing functional group. As a result, the two-dimensional particles in this embodiment can be well dispersed in various dispersion media, and when a two-dimensional particle-containing film is formed using the two-dimensional particles, a highly conductive two-dimensional particle-containing film can be realized.

[0020] In this specification, when an "atom" refers to a certain element, the oxidation number of the element is not limited to 0, but may be any number within the range of oxidation numbers that the element can take.

[0021] First, MXene, which constitutes the two-dimensional particles of this embodiment (or precursor particles used to produce the two-dimensional particles of this embodiment), will be described.

[0022] The one or more layers may be understood as a layered compound and referred to as "M ｍ X ｎ T ｓ ", where s is any number, and conventionally, x or z may be used instead of s. Typically, n can be 1, 2, 3, or 4, but is not limited thereto.

[0023] In the above formula for MXene, M is preferably at least one selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and Mn, more preferably at least one selected from the group consisting of Ti, V, Cr, and Mo. Most preferably, M contains Ti. M may be only Ti.

[0024] MXene is a compound represented by the formula: M ｍ X ｎHowever, it is known that it can be expressed as follows: Sc ２ C, Ti ２ C, Ti ２ N, Zr ２ C, Zr ２ N, Hf ２ C, Hf ２ N.V. ２ C.V. ２ N, Nb ２ C, Ta ２ C, Cr ２ C, Cr ２ N, Mo ２ C, Mo １．３ C, Cr １．３ C, (Ti, V) ２ C, (Ti, Nb) ２ C.W. ２ C.W. １．３ C, Mo ２ N, Nb １．３ C, Mo １．３ Y ０．６ C (in the above formula, "1.3" and "0.6" mean approximately 1.3 (= 4 / 3) and approximately 0.6 (= 2 / 3), respectively), Ti ３ C ２ , Ti ３ N ２ , Ti ３ (CN), Zr ３ C ２ , (Ti, V) ３ C ２ , (Ti ２ Nb)C ２ , (Ti ２ Ta) C ２ , (Ti ２ Mn)C ２ , Hf ３ C ２ , (Hf ２ V) C ２ , (Hf ２ Mn)C ２ , (V ２ Ti)C ２ , (Cr ２ Ti)C ２ , (Cr ２ V) C ２ , (Cr ２ Nb)C ２ , (Cr ２ Ta) C ２、(Mo ２ Sc)C ２ 、(Mo ２ Ti)C ２ 、(Mo ２ Zr)C ２ 、(Mo ２ Hf)C ２ 、(Mo ２ V)C ２ 、(Mo ２ Nb)C ２ 、(Mo ２ Ta)C ２ 、(W ２ Ti)C ２ 、(W ２ Zr)C ２ 、(W ２ Hf)C ２ 、 Ti ４ N ３ 、V ４ C ３ 、Nb ４ C ３ 、Ta ４ C ３ 、(Ti,Nb) ４ C ３ 、(Nb,Zr) ４ C ３ 、(Ti ２ Nb ２ )C ３ 、(Ti ２ Ta ２ )C ３ 、(V ２ Ti ２ )C ３ 、(V ２ Nb ２ )C ３ 、(V ２ Ta ２ )C ３ 、(Nb ２ Ta ２ )C ３ 、(Cr ２ Ti ２ )C ３ 、(Cr ２ V ２ )C ３ 、(Cr ２ Nb ２ )C ３ 、(Cr ２ Ta ２ )C ３ 、(Mo２ Ti ２ ) C ３ , (Mo ２ Zr ２ ) C ３ , (Mo ２ Hf ２ ) C ３ , (Mo ２ V ２ ) C ３ , (Mo ２ Nb ２ ) C ３ , (Mo ２ Ta ２ ) C ３ , (W ２ Ti ２ ) C ３ , (W ２ Zr ２ ) C ３ , (W ２ Hf ２ ) C ３ , (Mo ２．７ V １．３ ) C ３ (In the above formula, "2.7" and "1.3" mean approximately 2.7 (= 8 / 3) and approximately 1.3 (= 4 / 3), respectively.)

[0025] Typically, in the above formula, M can be titanium or vanadium, and X can be a carbon atom or a nitrogen atom. For example, the MAX phase can be Ti ３ AlC ２ and MXene is Ti ３ C ２ T ｓ (In other words, the layer body is Ti ３ C ２ wherein M is Ti, X is C, n is 2, and m is 3. Preferably, the layer body is Ti. ３ C ２ In this case, the MXene particles obtained have high dispersion stability in the dispersion medium and exhibit high electrical conductivity when formed into a film.

[0026] In this embodiment, MXene may contain a relatively small amount of A atoms derived from the precursor MAX phase, for example, 10% by mass or less of the original A atoms. The residual amount of A atoms is preferably 8% by mass or less, more preferably 6% by mass or less. However, even if the residual amount of A atoms exceeds 10% by mass, this may not be a problem depending on the application and use conditions of the two-dimensional particles.

[0027] MXene constituting the two-dimensional particles of this embodiment (or precursor particles used to produce the two-dimensional particles of this embodiment) will be described below with reference to Figure 1. Note that Figures 1(a) and 1(b) below do not show the substituents derived from the nitrogen-containing phosphonic acid on the surface of the layer body.

[0028] The MXene constituting the two-dimensional particles of this embodiment is an aggregate including one layer of MXene particles (hereinafter simply referred to as "MXene particles") 10a (single-layer MXene particles) as illustrated in Fig. 1(a). More specifically, the MXene particles 10a are ｍ X ｎ The layer body (M ｍ X ｎ The MXene layer 7a has a main layer 1a and modifications or terminations T3a, 5a present on the surface of the main layer 1a (more specifically, on at least one of the two opposing surfaces of each layer). ｍ X ｎ T ｓ ", where s is an arbitrary number.

[0029] The two-dimensional particles of this embodiment may contain one or more layers. Examples of MXene particles with multiple layers (multilayer MXene particles) include, but are not limited to, two-layer MXene particles 10b, as shown schematically in FIG. 1(b). 1b, 3b, 5b, and 7b in FIG. 1(b) are the same as 1a, 3a, 5a, and 7a in FIG. 1(a). Two adjacent MXene layers (e.g., 7a and 7b) in a multilayer MXene particle do not necessarily need to be completely separated and may be partially in contact. The MXene particle 10a may be a mixture of the single-layer MXene particle 10a and the multilayer MXene particle 10b, with the multilayer MXene particles 10b remaining unseparated.

[0030] Although this embodiment is not limited thereto, the thickness of each layer (corresponding to the above-described MXene layers 7a and 7b) contained in the MXene particle is, for example, 0.8 nm to 5 nm, particularly 0.8 nm to 3 nm (this thickness may vary mainly depending on the number of M atomic layers contained in each layer). The interlayer distance (or gap dimension, shown as Δd in FIG. 1(b)) of each stack of the multilayer MXene particle that may be contained may be, for example, 0.8 nm to 10 nm, particularly 0.8 nm to 5 nm, more particularly about 1 nm, and the total number of layers may be 2 to 20,000.

[0031] The MXene constituting the two-dimensional particles of this embodiment is preferably a multilayer MXene particle with a small number of layers obtained by a delamination process. The term "small number of layers" refers to, for example, a stacked number of MXene layers of 10 or less, preferably 6 or less. Furthermore, the thickness of the multilayer MXene particle with a small number of layers in the stacking direction is preferably 15 nm or less, more preferably 10 nm or less. Hereinafter, these "multilayer MXene particles with a small number of layers" may be referred to as "small-layer MXene particles." Furthermore, single-layer MXene particles and small-layer MXene particles may be collectively referred to as "single-layer / small-layer MXene particles."

[0032] The MXene constituting the two-dimensional particles of this embodiment preferably contains a large amount of single-layered and few-layered MXene. By including a large amount of single-layered and few-layered MXene, the specific surface area of ​​MXene can be made larger than that of multi-layered MXene, which is thought to result in a larger contact area with the ligand during the substitution reaction and a higher ligand coverage. For example, the layered material particles of this embodiment have 10 or fewer MXene stacks and a thickness of 15 nm or less, preferably 10 nm or less, and the single-layered and few-layered MXene preferably accounts for 80 vol% or more, more preferably 90 vol% or more, and even more preferably 95 vol% or more of the total MXene. Furthermore, it is more preferable that the volume of single-layered MXene is greater than the volume of few-layered MXene. Because the true density of these MXenes does not vary significantly depending on their form, it can also be said that it is more preferable that the mass of single-layered MXene is greater than the mass of few-layered MXene. When these relationships are satisfied, the specific surface area can be further increased, resulting in, for example, improved dispersion stability and, for example, when the two-dimensional particles of this embodiment are used in electrodes, sufficient suppression of deterioration of conductivity over time. Most preferably, the MXene constituting the two-dimensional particles of this embodiment is formed solely of a single layer of MXene.

[0033] The two-dimensional particles according to this embodiment have a structure in which, due to the above reaction, an oxygen atom derived from the hydroxyl group, which is the modified or terminal T, is bonded to the phosphorus atom of a phosphonic acid having a saturated or unsaturated hydrocarbon group and a nitrogen-containing functional group. In this specification, a phosphonic acid having a saturated or unsaturated hydrocarbon group and a nitrogen-containing functional group is referred to as a "nitrogen-containing phosphonic acid." Nitrogen-containing phosphonic acids have a phosphorus oxoacid as a parent compound and a general formula of R-P(=O)X ２ (R is an organic group having a saturated or unsaturated hydrocarbon group and a nitrogen-containing functional group, and at least one of the two Xs is an oxygen atom derived from the hydroxyl group that is the modification of MXene or the terminal T).

[0034] The bond between the oxygen atom derived from the hydroxyl group of the modified or terminal T and the phosphorus atom may be, for example, a covalent bond or an ionic bond. Confirmation of the bond between the oxygen atom derived from the hydroxyl group of the main body and the phosphorus atom, i.e., whether phosphonic acid is substituted on MXene or whether an amino group (nitrogen atom) is present, can be confirmed using, for example, XRD, TG-DTA, XPS, solid-state NMR, TG-MS, or conductivity measurement.

[0035] In the manufacturing process of the two-dimensional particles according to this embodiment, the substitution reaction of the multiple hydroxyl groups present on the surface of the MXene particle (precursor particle) layer body with the nitrogen-containing phosphonic acid proceeds, increasing the number of bonds between the oxygen atoms derived from the hydroxyl groups on the body and the phosphorus atoms, thereby increasing the amount of ligand present on the MXene.

[0036] There is no limitation on the length of the carbon chain of the saturated or unsaturated hydrocarbon group of the nitrogen-containing phosphonic acid. Examples include methylphosphonic acid (C1), propylphosphonic acid (C3), hexylphosphonic acid (C6), octylphosphonic acid (C8), decylphosphonic acid (C10), and dodecylphosphonic acid (C12). Furthermore, since the unpaired electron on the nitrogen atom is important for the nitrogen-containing functional group, any functional group containing a nitrogen element in the molecule, such as pyridine, pyrrole, aniline, pyrrolidine, pyrimidine, a cyano group, a nitro group, an amino group, or an imino group, may be used.

[0037] The nitrogen-containing functional group is preferably an amino group. This allows for the formation of highly conductive aminated MXene (especially when the layer itself is Ti). ３ C ２ As the phosphonic acid containing a saturated hydrocarbon group or an unsaturated hydrocarbon group and an amino group, for example, aminomethylphosphonic acid (C1) (aminophosphonic acid having an alkyl chain length of 1: hereinafter referred to as NH ２ -C1PA), aminopropylphosphonic acid (C3) (aminophosphonic acid with an alkyl chain length of 3: hereinafter referred to as NH ２ -C3PA), aminohexylphosphonic acid (C6) (aminophosphonic acid with an alkyl chain length of 6: hereinafter referred to as NH ２-C6PA) can be used. The phosphonic acid is preferably aminomethylphosphonic acid (C1).

[0038] The two-dimensional particles can be obtained by, for example, the manufacturing method recommended below. The bonded structure can be formed during the manufacturing process of the two-dimensional particles according to this embodiment by a dehydration condensation reaction between hydroxyl groups present on the surface of the MXene particle (precursor particle) layer and the nitrogen-containing phosphonic acid ligand. This reaction can also be described as a reaction in which hydroxyl groups (particularly hydrogen atoms) present on the surface of the MXene particle (precursor particle) layer are substituted with nitrogen-containing phosphonic acid. As mentioned above, the reaction in which the MXene surface modification or terminal is substituted with nitrogen-containing phosphonic acid is sometimes referred to as "ligand substitution" in this specification.

[0039] In conventional ligand-substituted MXene particles using a silane coupling agent, as shown in FIG. 2A, the ligand exists on the MXene in the form of a bulky polymer such as siloxane, whereas in the two-dimensional particles according to the present embodiment, the phosphonic acids do not react with each other, and therefore the ligand can be present almost uniformly on the MXene, as shown in FIG. 2B. As a result, in a film formed using conventional ligand-substituted MXene particles, as shown in FIG. 3, the distance between MXene particles is large as indicated by the double arrows, and it is believed that the conductive efficiency is low. On the other hand, in a film formed using the two-dimensional particles according to the present embodiment, as shown in FIG. 4, the distance between MXene particles is short as indicated by the double arrows, and it is believed that the conductive efficiency is increased and excellent conductivity can be ensured.

[0040] (Embodiment 2: Two-dimensional particle-containing dispersion) The two-dimensional particle-containing dispersion according to this embodiment contains the two-dimensional particles and a dispersion medium. The two-dimensional particle-containing dispersion according to this embodiment contains two-dimensional particles that are ligand-substituted with nitrogen-containing phosphonic acid (particularly, aminated MXene particles, particularly those having a layer body of Ti). ３ C ２The particles are (2-dimensional particles) and have excellent dispersion stability. The two-dimensional particles contained in the two-dimensional particle-containing dispersion are as described above (Embodiment 1: Two-dimensional particles). In the two-dimensional particle-containing dispersion according to this embodiment, the dispersion stability of the MXene dispersion is quantified using absorbance in the ultraviolet-visible absorption spectrum, as shown in the examples described below, and the time it takes for the initial absorbance to decrease by half is 87 hours or more. As a result, the range of applicable dispersion media is expanded.

[0041] The dispersion medium may be water (pure water), an organic dispersion medium compatible with water (solubility in water > 10% w / w), or an organic dispersion medium that is incompatible with water. Unlike Patent Document 1 and the like, this embodiment allows dispersion in an organic dispersion medium compatible with water (solubility in water > 10% w / w), providing a wider selection of organic dispersion mediums than conventional methods. It also allows dispersion in alcohol dispersion mediums, which were previously incompatible with MXene, reducing the energy consumption required for removing the dispersion medium during film formation processes such as spray coating.

[0042] As the organic dispersion medium, for example, one or more selected from the group consisting of ethanol, 2-propanol, ethylene glycol, methanol, acetone, acetonitrile, DMF, NMF, DMSO, and NMP can be used. Examples of organic dispersion media that are not compatible with water include 1-hexanol, chloroform, and toluene. The dispersion medium is preferably one or more selected from the group consisting of pure water, ethanol, and 2-propanol. Two-dimensional particle-containing dispersions using these dispersion media have high dispersion stability of the two-dimensional particles, as evaluated in the examples described below.

[0043] (Embodiment 3: Two-dimensional particle-containing film) The two-dimensional particle-containing film according to this embodiment contains the two-dimensional particles described above (Embodiment 1: Two-dimensional particles). As a result, the two-dimensional particle-containing film exhibits high conductivity, as will be shown in the examples described later.

[0044] The two-dimensional particles contained in the two-dimensional particle-containing film according to this embodiment are believed to have high dispersion stability in a dispersion medium because the ligand contained in the two-dimensional particles is a nitrogen-containing phosphonic acid. Therefore, the two-dimensional particle-containing dispersion medium has high dispersibility of the two-dimensional particles, and two-dimensional particle-containing films, such as filtration membranes and spray membranes, obtained using the two-dimensional particle-containing dispersion are believed to have high film quality. As a result, the conductivity of the two-dimensional particle-containing film is believed to be high. For example, the conductivity of the two-dimensional particle-containing film, as measured by the method described in the Examples below, is preferably 5 S / cm or higher (5.00 S / cm or higher), preferably 10 S / cm or higher, more preferably 1000 S / cm or higher, and can achieve 20,000 S / cm or lower. The two-dimensional particle-containing film according to this embodiment has such high conductivity that it is suitable for use, for example, in electrodes.

[0045] Next, a method for producing a two-dimensional particle-containing film will be described. For example, two-dimensional particles can be applied to a substrate to form a film containing the two-dimensional particles on the substrate surface. The two-dimensional particles can be applied to a substrate using, for example, the two-dimensional particle-containing dispersion described above. The two-dimensional particle-containing dispersion may be a suspension. The method for forming a two-dimensional particle-containing film using the two-dimensional particle-containing dispersion is not particularly limited. The two-dimensional particle-containing dispersion may be applied to a substrate as is or after appropriate adjustment (e.g., dilution with a medium liquid or addition of a binder). Examples of application methods include spray coating using a nozzle such as a one-fluid nozzle, a two-fluid nozzle, or an airbrush; slit coating using a table coater, comma coater, or bar coater; screen printing; metal mask printing; spin coating; dip coating; and dripping. The dispersion medium constituting the dispersion can be one or more of pure water and organic dispersion mediums. The organic dispersion medium is not limited. According to this embodiment, as the organic dispersion medium, an organic dispersion medium that is compatible with water (solubility in water > 10% w / w) as described above (Embodiment 2: two-dimensional particle-containing dispersion liquid) may be used, or an organic dispersion medium that is not compatible with water may be used.

[0046] When a two-dimensional particle-containing film is obtained by spraying, a slurry containing two-dimensional particles in a dispersion medium is first prepared. The thus-prepared slurry is then sprayed to produce a two-dimensional particle-containing film. The two-dimensional particle-containing film may contain, or may not substantially contain, liquid components derived from the dispersion medium of the slurry. The two-dimensional particle-containing film may not contain a so-called binder.

[0047] The substrate is not particularly limited and can be made of any appropriate material. The substrate may be, for example, a resin film, a metal foil, a printed wiring board, a mounted electronic component, a metal pin, a metal wiring, a metal wire, or the like. For example, a substrate formed of a metal material suitable for an electrode, a resin, or the like can be appropriately employed. A two-dimensional particle-containing film can be formed on any appropriate substrate (which may constitute a predetermined component together with the two-dimensional particle-containing film or may ultimately be separated from the two-dimensional particle-containing film) by coating the two-dimensional particle-containing film on the substrate.

[0048] Instead of the coating method, suction filtration can be used to form a two-dimensional particle-containing film without a binder. Furthermore, a two-dimensional particle-containing film can be formed without using a substrate. Even in the case of suction filtration, the two-dimensional particle-containing film may contain or may be substantially free of liquid components derived from the liquid medium of the slurry.

[0049] Drying may be performed under mild conditions such as natural drying (typically, placing the film in an air atmosphere at room temperature and pressure) or air drying (blowing air), or under relatively active conditions such as hot air drying (blowing heated air), heat drying, and / or vacuum drying. In this embodiment, "drying" refers to removing a dispersion medium, such as an organic dispersion medium, that may be present in the film. The drying may be performed, for example, at a temperature of 400°C or less using a normal pressure oven or a vacuum oven.

[0050] The formation and drying of the two-dimensional particle-containing film may be appropriately repeated until a desired thickness of the two-dimensional particle-containing film is obtained. For example, a combination of spraying and drying may be repeated multiple times.

[0051] (Embodiment 4: Method for Producing Two-Dimensional Particles) Hereinafter, a method for producing two-dimensional particles according to one embodiment of the present invention will be described in detail, but the present disclosure is not limited to this embodiment.

[0052] The method for producing two-dimensional particles according to this embodiment comprises: (a) a precursor particle comprising one or more layers, wherein the layers are represented by the following formula: M ｍ X ｎ (wherein M is at least one Group 3, 4, 5, 6 or 7 metal; X is a carbon atom, a nitrogen atom or a combination thereof; n is 1 or more and 4 or less; and m is greater than n and 5 or less), and a modified or terminal T (T is at least one selected from the group consisting of a hydroxyl group, a fluorine atom, a chlorine atom, an oxygen atom and a hydrogen atom, and includes at least a hydroxyl group) present on the surface of the layer body; (b) preparing an aqueous dispersion containing the precursor particles and a solution containing a nitrogen-containing phosphonic acid having a saturated or unsaturated hydrocarbon group and a nitrogen-containing functional group; and (c) mixing and stirring the aqueous dispersion containing the precursor particles, the solution containing the nitrogen-containing phosphonic acid and an inorganic acid to obtain a structure in which the oxygen atom derived from the hydroxyl group, which is the modified or terminal T, is bonded to the phosphorus atom of the nitrogen-containing phosphonic acid. According to this method, aggregation of precursor particles (MXene particles) is suppressed, and two-dimensional particles with good ligand substitution can be obtained.

[0053] Each step of the above-mentioned production method will be described in detail below. Step (a) Preparing predetermined MXene particles (precursor particles). The production of the MXene particles (precursor particles) is not limited, and they can be produced, for example, by the following method.

[0054] Etching of MAX Phases Particles of a given layered material (MXene particles, precursor particles) can be synthesized by selectively etching (removing and optionally layer-separating) A atoms (and optionally some of the M atoms) from a MAX phase. The MAX phase has the following formula: ｍ AX ｎ(wherein M, X, n and m are as defined above, A is at least one element of Groups 12, 13, 14, 15 and 16, and is usually an element of Group A, typically Group IIIA and Group IVA, and more particularly may contain at least one element selected from the group consisting of Al, Ga, In, Tl, Si, Ge, Sn, Pb, P, As, S and Cd, and is preferably Al), and M ｍ X ｎ (each X may have a crystal lattice in which it is located in an octahedral array of M) and a layer composed of A atoms is located between them. In the MAX phase, typically when m=n+1, one layer of X atoms is arranged between each of the n+1 layers of M atoms (these are collectively referred to as "M ｍ X ｎ The repeating unit has a layer of A atoms (also referred to as an "A atom layer") arranged as the next layer after the n+1th layer of M atoms, but is not limited thereto.

[0055] Etching is performed to remove at least some of the A atoms from the precursor using an etching solution. The etching solution is HF, H ３ P.O. ４ , HCl, HI and H ２ SO ４ The etching solution preferably contains at least one of HF (hydrofluoric acid) and H ３ P.O. ４ It is more preferable that the etching solution contains at least one of the following: (phosphoric acid). For example, etching can be performed by the so-called MILD method, in which HCl and LiF contained in the etching solution are reacted in the system to generate HF; however, it is preferable to perform etching using an etching solution containing HF (hydrofluoric acid), the so-called ACID method, or an etching solution containing phosphoric acid. These methods are preferable because they make it easier to obtain flake-shaped layered material particles (MXene particles) with a large planar area than the MILD method. Other etching conditions are not particularly limited, and known conditions can be adopted. As the etching solution, a mixture of the above acid and, for example, pure water as a solvent can be used. As the etching solution, a solution with an HF concentration of 1.5M or more and 14M or less, and H ３ P.O.４ concentration of 5.5M or more, HCl concentration of 6.0M or more, HI concentration of 5.0M or more, and H ２ SO ４ An etching solution having a concentration of at least one selected from the group consisting of 5.0 M or more can be used. In the etching of the A atoms, in addition to the A atoms, some of the M atoms may also be selectively etched in some cases. An example of the etched product obtained by the above etching is a slurry.

[0056] The MAX phase can be produced by a known method. For example, TiC powder, Ti powder, and Al powder are mixed in a ball mill, and the resulting mixed powder is sintered in an Ar atmosphere to obtain a sintered body (a block of the MAX phase). The sintered body is then pulverized with an end mill to obtain the powdered MAX phase for the next step.

[0057] The A atoms (and possibly some of the M atoms) are selectively etched (removed and possibly layer separated) from the MAX phase, thereby removing the A atom layer (and possibly some of the M atoms) to expose the M ｍ X ｎ The surface of the layer is modified with hydroxyl groups, fluorine atoms, chlorine atoms, oxygen atoms, hydrogen atoms, etc. present in the etching solution (usually, an aqueous solution of fluorine-containing acid is used, but this is not limited to this) to terminate the surface.

[0058] The etching solution may contain a metal compound containing a monovalent metal ion, and an intercalation treatment of the monovalent metal ion may be carried out simultaneously with the etching. Examples of metal compounds containing monovalent metal ions include those used in the intercalation treatment described below. The content of the metal compound containing monovalent metal ions in the etching solution is preferably 0.001% by mass or more. The content is more preferably 0.01% by mass or more, and even more preferably 0.1% by mass or more. On the other hand, from the viewpoint of dispersibility in the solution, the content of the metal compound containing monovalent metal ions in the etching solution is preferably 10% by mass or less, more preferably 1% by mass or less.

[0059] (Water Washing) The etched product obtained by the etching is washed with water. By washing with water, the acid used in the etching can be sufficiently removed. The amount of water to be mixed with the etched product and the washing method are not particularly limited. For example, water may be added and the mixture may be stirred or centrifuged. Stirring methods include stirring using a hand shake, an automatic shaker, a shear mixer, a pot mill, or the like. The degree of stirring, such as the stirring speed and stirring time, may be adjusted depending on the amount and concentration of the material to be treated. The water washing may be performed one or more times. Preferably, the water washing is performed multiple times. For example, steps (i) to (iv) of (i) adding water (to the etched product or the remaining precipitate obtained in (iii) below), (ii) stirring, (iii) centrifuging the stirred product, and (iv) discarding the supernatant after centrifugation and recovering the remaining precipitate may be performed two or more times, for example, 15 or less times.

[0060] [MXene Layer Separation] The treated product (water-washed product) obtained by the water washing may be used to promote layer separation of MXene (delamination, separating multilayer MXene into single-layer MXene) by any appropriate post-treatment (e.g., ultrasonic treatment, hand shaking, automatic shaker, etc.). Since ultrasonic treatment can destroy MXene due to excessive shear force, if it is desired to obtain two-dimensional MXene particles with a larger aspect ratio (preferably single-layer MXene), it is preferable to apply an appropriate shear force using a hand shake or automatic shaker, etc. The intercalation treatment and delamination are described below.

[0061] (Intercalation Treatment) For example, a monovalent metal ion intercalation treatment may be performed, which includes a step of mixing the etched product obtained by the etching treatment with a metal compound containing a monovalent metal ion. Examples of the monovalent metal ion constituting the metal compound containing a monovalent metal ion include alkali metal ions such as lithium ions, sodium ions, and potassium ions, copper ions, silver ions, and gold ions. Examples of the metal compound containing a monovalent metal ion include ionic compounds in which the above metal ions are bonded to cations. Examples include iodides, phosphates, sulfide salts including sulfates, nitrates, acetates, and carboxylates of the above metal ions. As described above, lithium ions are preferred as the monovalent metal ion, and metal compounds containing lithium ions are preferred as metal compounds containing lithium ions, more preferably ionic compounds of lithium ions, and even more preferably one or more of iodides, phosphates, and sulfide salts of lithium ions. If lithium ions are used as the metal ion, it is thought that water hydrated with lithium ions has the most negative dielectric constant, making it easier to form a monolayer.

[0062] The content of the metal compound containing a monovalent metal ion in the formulation for intercalation treatment of a monovalent metal ion is preferably 0.001% by mass or more. The content is more preferably 0.01% by mass or more, and even more preferably 0.1% by mass or more. On the other hand, from the viewpoint of dispersibility in the solution, the content of the metal compound containing a monovalent metal ion is preferably 10% by mass or less, more preferably 1% by mass or less.

[0063] The specific method of intercalation is not particularly limited. For example, a metal compound containing a monovalent metal ion may be mixed with the MXene water medium clay, and the mixture may be stirred or left to stand. For example, stirring at room temperature may be used. Examples of the stirring method include a method using a stirring bar such as a stirrer, a method using a stirring blade, a method using a mixer, and a method using a centrifugal device. The stirring time can be set depending on the production scale of the two-dimensional particles, and may be set, for example, between 12 and 24 hours.

[0064] (Delamination) Delamination may be performed using the intercalation-treated product obtained by intercalation. For example, delamination may involve centrifuging the intercalation-treated product, discarding the supernatant, and then washing the remaining precipitate with water. The conditions for the delamination treatment are not particularly limited. The dispersion medium used for delamination is also not particularly limited, and examples include using one or more polar organic dispersion mediums and aqueous dispersion mediums. This process may be repeated at least once, preferably at least twice, but not more than 10 times, to obtain a supernatant containing single-layered and / or few-layered MXene as the delamination-treated product. Alternatively, the supernatant may be centrifuged, and the resulting supernatant may be discarded to obtain a single-layered and / or few-layered MXene-containing clay as the delamination-treated product. The resulting delamination-treated product may be used as an aqueous dispersion containing precursor particles.

[0065] The delamination-treated product, ie, the supernatant containing the single-layer / few-layer MXene and the single-layer / few-layer MXene-containing clay, may be subjected to removal of the dispersion medium to obtain dried precursor particles.

[0066] Step (b) Prepare an aqueous dispersion containing the precursor particles and a solution containing nitrogen-containing phosphonic acid, for example, a solution containing nitrogen-containing phosphonic acid dissolved in pure water. The solution containing nitrogen-containing phosphonic acid can be prepared using not only pure water but also any of ethanol, 2-propanol, ethylene glycol, methanol, acetone, acetonitrile, DMF, NMF, DMSO, NMP, and the like, which are capable of dissolving nitrogen-containing phosphonic acid, and one or more of these can be used.

[0067] The aqueous dispersion containing the precursor particles may be the single-layered or few-layered MXene-containing clay obtained by the delamination process, or the aqueous dispersion may be prepared by adjusting the water content. Alternatively, the aqueous dispersion may be prepared by dispersing the precursor particles (dried product) obtained by the above method in water. The proportion of the precursor particles contained in the aqueous dispersion containing the precursor particles may be, for example, in the range of 0.01% by mass to 1% by mass (solid content).

[0068] The reaction solution obtained by mixing the aqueous dispersion containing the precursor particles, the solution containing the nitrogen-containing phosphonic acid (e.g., an aqueous solution containing a nitrogen-containing phosphonic acid), and an inorganic acid such as hydrochloric acid may have a pH of 4 or less.

[0069] Step (c) An aqueous dispersion containing precursor particles, a solution containing the nitrogen-containing phosphonic acid (e.g., an aqueous solution of the nitrogen-containing phosphonic acid), and an inorganic acid are mixed and stirred to obtain a structure in which an oxygen atom derived from the hydroxyl group, which is the modifying or terminal T, is bonded to a phosphorus atom of the nitrogen-containing phosphonic acid.

[0070] The method for mixing and stirring the aqueous dispersion containing precursor particles and the solution containing the nitrogen-containing phosphonic acid is not particularly limited. The stirring can be performed, for example, for a period of 6 hours or more and 24 hours or less. According to this embodiment, the aqueous dispersion containing precursor particles and the solution containing the nitrogen-containing phosphonic acid are mixed and stirred. This is a reaction mode in which the precursor particles (MXene particles) and the ligand are contained in the same system, rather than a phase-separation type interfacial reaction as in Patent Document 1. Therefore, the contact frequency between the hydroxyl groups on MXene and the ligand is increased compared to the phase-separation type interfacial reaction, thereby accelerating the substitution reaction. As a result, the substitution rate of the ligand on the surface of the precursor particles (MXene particles) can be improved.

[0071] The proportion of the nitrogen-containing phosphonic acid in the precursor particles is preferably high, and the molar ratio of the precursor particles to the nitrogen-containing phosphonic acid is preferably 1: (3 to 50). ３ C ２ (OH) ２ The nitrogen-containing phosphonic acid is aminomethylphosphonic acid (NH ２-C1PA), the blending ratio may be precursor particles:aminomethylphosphonic acid (molar ratio) = 1: (3 to 20), and further may be precursor particles:aminomethylphosphonic acid (molar ratio) = 1: (6 to 10).

[0072] The method for producing two-dimensional particles according to this embodiment may include at least the above steps (a) to (c) in this order, and other steps are not limited. For example, after step (c), a step of washing the ligand-substituted MXene particles obtained by the reaction may be included.

[0073] The present disclosure will be described in more detail below with reference to examples. The present disclosure is not limited to the following examples, and appropriate modifications can be made within the scope of the above-mentioned and below-mentioned aims, and all such modifications are within the technical scope of the present disclosure. For example, the present disclosure is not limited to the preparation methods described below, and any preparation method that can modify MXene or react with the terminal functional group can be used.

[0074] [Example 1-1] In this example, NH was used as a ligand (a nitrogen-containing phosphonic acid having a saturated hydrocarbon group or an unsaturated hydrocarbon group and a nitrogen-containing functional group, a surface modifier). ２ Aminophosphonic acid-substituted MXene particles were produced as two-dimensional particles (ligand-substituted MXene particles) using -C1PA (aminophosphonic acid with an alkyl chain length of 1 (C1)). Although aminophosphonic acid was used in this example, the ligand is not limited to this. Since the unpaired electron on the nitrogen atom is important, any phosphonic acid containing a nitrogen element in the molecule will suffice. If the raw materials are changed, the weight to be added may change, taking into account the molecular weight of each.

[0075] (Preparation of MXene particles (precursor particles)) First, the following steps were carried out in order: (1) preparation of precursor (MAX), (2) etching of precursor, (3) cleaning after etching, (4) Li intercalation, and (5) delamination, as detailed below, to obtain precursor particles (single-layer / few-layer MXene-containing samples, MXene particles) to be subjected to treatments such as ligand substitution.

[0076] [1] Preparation of Precursor (MAX) TiC powder, Ti powder, and Al powder (all manufactured by Kojundo Chemical Laboratory Co., Ltd.) were mixed in a molar ratio of 2:1:1 in a ball mill containing zirconia balls for 24 hours. The resulting mixed powder was fired at 1350°C for 2 hours in an Ar atmosphere. The fired body (block-shaped MAX) was then crushed with an end mill to a maximum size of 40 μm or less. This resulted in the preparation of TiC powder as a precursor (powdered MAX). ３ AlC ２ particles were obtained.

[0077] [2] Etching of precursor (MAX) Ti prepared by the above method ３ AlC ２ Using particles (powder), etching was performed under the following etching conditions to remove Ti ３ AlC ２ A solid-liquid mixture (slurry) containing solid components derived from the powder was obtained. (Etching conditions) Precursor: Ti ３ AlC ２ (Sieved through a 45 μm mesh) Etching solution composition: 49% HF 6 mL H ２ O 18 mL HCl (12 M) 36 mL Precursor input amount: 3.0 g Etching container: 100 mL Eye Boy Etching temperature: 35°C Etching time: 24 h Stirrer rotation speed: 400 rpm

[0078] [3] Post-etching cleaning The above slurry was divided into two parts and placed in two 50 mL centrifuge tubes. Then, after centrifuging at 3500 G for 5 minutes using a centrifuge, the supernatant was discarded. Thereafter, (i) 40 mL of pure water was added to the remaining precipitate in each centrifuge tube, (ii) centrifugation was again carried out at 3500 G for 5 minutes, and (iii) the supernatant was separated and removed. This procedure from (i) to (iii) was repeated 11 times. After the final centrifugation, the supernatant was discarded, and Ti ３ AlC ２ T ｘ - Water medium clay was obtained.

[0079] [4] Li intercalation Ti prepared by the above method ３ AlC２ T ｘ The clay was subjected to Li intercalation using LiCl as a Li-containing compound under the following conditions: the clay was stirred at 20°C to 25°C for 12 hours. (Li intercalation conditions) ３ AlC ２ T ｘ - Water medium clay (MXene after washing): solid content 0.75 g LiCl: 0.75 g Intercalation container: 100 mL Eye Boy Temperature: 20 ° C or higher and 25 ° C or lower (room temperature) Time: 12 hours Stirrer rotation speed: 800 rpm

[0080] [5] Delamination The slurry obtained by Li intercalation was placed in a 50 mL centrifuge tube and centrifuged at 3500 G using a centrifuge. The supernatant was then discarded. Next, (i) 40 mL of pure water was added to the remaining precipitate, followed by stirring for 15 minutes on a shaker. (ii) The mixture was centrifuged at 3500 G. (iii) The supernatant was recovered as a single-layer / sparse-layer MXene-containing solution. These steps (i) to (iii) were repeated four times to obtain a single-layer / sparse-layer MXene-containing supernatant. Furthermore, this supernatant was centrifuged at 4300 G for 2 hours using a centrifuge. The supernatant was then discarded, and the remaining precipitate, a single-layer / sparse-layer MXene-containing clay (hereinafter simply referred to as MXene clay), was obtained as a clay containing MXene particles (precursor particles).

[0081] In this example, clay (MXene clay) containing MXene particles (precursor particles) obtained in the preparation of the MXene particles (precursor particles) described above was used to obtain a ligand-substituted MXene particle-containing dispersion by carrying out the following steps in sequence: (1) synthesis of ligand-substituted MXene particles, (2) washing of the ligand-substituted MXene particles, and (3) preparation of a ligand-substituted MXene particle-containing dispersion, as described in detail below. Then, using the ligand-substituted MXene particle-containing dispersion, (4) a ligand-substituted MXene particle-containing film was formed. Furthermore, using the resulting ligand-substituted MXene particle-containing film, (5) evaluation of the interlayer distance of the ligand-substituted MXene particle-containing film and (6) evaluation of the conductivity of the ligand-substituted MXene particle-containing film were performed. In this example, the ligand-substituted MXene particles refer to aminated MXene particles whose amino groups have been modified. Each step is described below.

[0082] (1) Synthesis of Ligand-Substituted MXene Particles MXene clay was dispersed in pure water to prepare an aqueous dispersion containing MXene particles, with the MXene solids concentration adjusted to 1 mg / mL. 20 mL of this aqueous dispersion containing MXene particles was prepared and transferred to a 50 mL vial containing a stirrer. NH ２ 73.5 mg (0.660 mmol) of -C1PA (manufactured by Aldrich) was weighed and dissolved in 1.32 mL of pure water. ２ - As long as C1PA dissolves, the water is not limited to pure water.

[0083] 10 μL of hydrochloric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and NH ２ 1.32 mL of -C1PA was added, and the mixture was stirred at a room temperature of 20 to 25°C using a magnetic stirrer at a stirring speed of 800 rpm for 24 hours.

[0084] Patent Document 1 describes a technology in which an alkylphosphonic acid ligand is substituted for the hydroxyl group on MXene by dehydration condensation. Because the alkylphosphonic acid has only one reactive site, the phosphonic acid (the alkyl group is unreactive), no matter how the reaction is conducted, the hydroxyl group on MXene will inevitably react with the phosphonic acid. In contrast, in this example, there are two functional groups that can react with MXene: an amino group and a phosphonic acid. Selective reaction with the hydroxyl group on MXene on the phosphonic acid side was technically difficult. However, by controlling the pH of the reaction solution, we succeeded in achieving reaction with MXene on the phosphonic acid side. As long as the pH of the reaction solution is 4 or less, inorganic acids other than hydrochloric acid can be used, such as sulfuric acid and phosphoric acid. The pH is preferably in the range of 1 to 2.5.

[0085] (2) Washing of Ligand-Substituted MXene Particles After stirring, the sample solution was transferred to a 50 mL centrifuge tube and centrifuged at room temperature, 8000 rpm, and for 8 minutes, after which the supernatant was discarded. Next, 20 mL of pure water was added to the precipitate to redisperse it. This procedure of adding pure water to the precipitate, centrifuging, and discarding the supernatant was repeated two more times (a total of three times) to remove unreacted NH ２ -C1PA was removed.

[0086] (3) Preparation of a dispersion containing ligand-substituted MXene particles After discarding the supernatant resulting from the third centrifugation in (2) above, 20 mL of pure water was added to the precipitate as a dispersion medium to prepare a dispersion in which the ligand-substituted MXene particles were dispersed in pure water. Note that there are no limitations on the dispersion medium used to disperse the ligand-substituted MXene particles, and any dispersion medium other than those listed above can be used. In this example, pure water was used as the dispersion medium, but this is not a limitation.

[0087] The aminophosphonic acid-substituted MXene prepared in this example was analyzed by XPS (Quantes, manufactured by ULVAC-PHI, Inc.), solid-state NMR (NMR AVAVCE400, measurement conditions: 9.4 T magnetic field, ３１ P measurement and １ Using 1H measurement, it was confirmed that phosphonic acid was substituted on MXene and that it had an amino group (nitrogen atom).

[0088] (4) Formation of Ligand-Substituted MXene Particle-Containing Film 80 mL of the ligand-substituted MXene particle-containing dispersion prepared in (3) above was prepared. While there are no limitations on the dispersion medium used to prepare the dispersion, pure water was selected in this example. The ligand-substituted MXene particle-containing dispersion was applied to a glass substrate using a spray coater (Muramatsu: M1822J) as follows: First, a 3 cm square glass substrate (SCHOTT: Tempax) was cleaned with oxygen plasma for 1 minute and placed on the stage of the spray coater. Next, the ligand-substituted MXene particle-containing dispersion was applied to the glass substrate under the following spray coating conditions to form a film. The resulting spray film was dried in a vacuum dryer at 80°C for 16 hours to obtain a ligand-substituted MXene particle-containing film (a ligand-substituted MXene film). (Spray coating conditions) Syringe flow rate: 5.0 mL / min Atomization pressure: 0.5 MPa Distance between nozzle tip and substrate: 15 cm Sweep speed: 15 cm / s Stage temperature: 25° C.

[0089] (5) Evaluation of Interlayer Distance of Ligand-Substituted MXene Particle-Containing Films The interlayer distance was estimated by evaluating the XRD of the ligand-substituted MXene film (ligand-substituted MXene spray film) prepared in (4) above. XRD was measured using an X-ray diffractometer (Rigaku: SmartLab) (Figure 5). Focusing on the 2θ value of the (002) peak, which is characteristic of MXene, the interlayer distance of MXene was calculated using a Cu Kα X-ray source (λ = 1.5418 Å). As a result, the 2θ value of (002) was 6.44°, and the interlayer distance calculated from this value was 13.7 Å, as shown in Table 1. Note that the interlayer distance here refers to the distance from one MXene flake to another. Therefore, when ligands are substituted on the MXene flakes, the interlayer distance increases depending on the type and amount of ligand substituted.

[0090] (6) Evaluation of the Conductivity of Ligand-Exchanged MXene Films The conductivity (σ) of the ligand-exchanged MXene film (ligand-exchanged MXene spray film) prepared in (4) above was calculated according to the following formula (1) using the surface resistance and film thickness measurements of the ligand-exchanged MXene film, as described in detail below. The surface resistance of the ligand-exchanged MXene film was measured using a Loresta (MCP-T370, manufactured by Nitto Seiko Co., Ltd.), and the film thickness of the ligand-exchanged MXene film was measured using a stylus-type surface profiler (Dektak8, manufactured by ULVAC Co., Ltd.). The film thickness was measured at three locations per sample, and the average value was used. The conductivity (σ) of the ligand-exchanged MXene film was calculated using the following formula (1). Since the surface resistance was 8.5 Ω / square and the film thickness was 0.21 μm, the conductivity of this ligand-exchanged MXene film was 5660 S / cm. Since the conductivity of MXene before ligand substitution was approximately 10,000 S / cm, the conductivity did not decrease significantly: σ = 1 / ρ = 1 / (Rs·t) (1) In equation (1), σ [S / cm] is the conductivity of the film, ρ [Ω·m] is the resistivity, Rs [Ω / square] is the surface resistance, and t [m] is the film thickness.

[0091]

[0092] [Example 1-2] In this example, in (1) of Example 1-1, NH was used as the aminophosphonic acid. ２ - Instead of C1PA, NH ２ -C3PA or NH ２ Ligand-substituted MXene was prepared in the same manner as above, except that 0.660 mmol of -C6PA was weighed out, and the interlayer distance and electrical conductivity were evaluated in the same manner as in (5) and (6) of Example 1-1. The results are shown in Table 2.

[0093] NH as a ligand ２ XRD analysis of the ligand-substituted MXene prepared using -C3PA revealed that the 2θ of (002) was 6.30° and the interlayer distance was 14.0 Å. The surface resistance was 2210 Ω / square and the film thickness was 0.88 μm, giving a conductivity of 5.14 S / cm. The NH ２XRD analysis of the ligand-substituted MXene prepared using -C6PA revealed that the 2θ of (002) was 6.34° and the interlayer distance was 13.9 Å. The surface resistance was 60.9 Ω / square and the film thickness was 0.11 μm, giving a conductivity of 1510 S / cm. NH ２ The conductivity of the ligand-substituted MXene prepared using -C3PA was 5.14 S / cm, and NH ２ -C1PA and NH ２ The conductivity was lower than that of the ligand-substituted MXene prepared using -C6PA, presumably because aggregation of MXene in the dispersion state affected the quality of the film when it was made into a film.

[0094]

[0095] [Comparative Example 1-1] In Comparative Example 1-1, a ligand-substituted MXene film was prepared using the same silane coupling agent as in Non-Patent Document 1. Non-Patent Document 1 does not provide an evaluation of conductivity, but when the conductivity evaluation was performed in the same manner as in Example 1-1, the surface resistance was 1600 Ω / square, and the film thickness was 1.26 μm, resulting in a conductivity of 4.95 S / cm. Furthermore, when XRD was measured for the ligand-substituted MXene using the silane coupling agent described in Non-Patent Document 1, the 2θ of (002) was 4.4° and the interlayer distance was 19.9 Å. Table 3 shows the interlayer distance and conductivity measured in Comparative Example 1-1. As described above, the interlayer distance in Comparative Example 1-1 is significantly larger than that in Example 1-1, etc. This suggests that a polymerization reaction between the silane coupling agents occurred, resulting in the presence of a polymer such as siloxane on the MXene frame.

[0096]

[0097] The results of Examples 1-1 and 1-2 and Comparative Example 1-1 above indicate that in ligand substitution using a silane coupling agent (APTES), the polymerization reaction between APTES and the ligand substitution reaction with MXene occur in competition, resulting in the ligand being present on MXene in the form of a bulky polymer similar to siloxane. As a result, the interlayer distance between MXene flakes increases, making electron transfer between MXene flakes less likely, resulting in a decrease in conductivity. On the other hand, in this example, phosphonic acid was used as the ligand rather than a silane coupling agent. Compared to silane coupling agents, phosphonic acid is a very stable reagent that does not self-polymerize and only reacts with functional groups on MXene, which is thought to be the reason for the uniform ligand substitution. Therefore, in this example, the ligand was uniformly immobilized on MXene while suppressing polymerization between the ligands, which is thought to have resulted in maintaining a narrow interlayer distance between MXene flakes. It is known that the conductivity of an MXene film is determined in part by the ease of electron transfer in the z-axis direction of the stacked MXene flakes. In this example, the distance between the MXene layers was kept short, as described above. As a result, electron transfer between the MXene flakes became easier, and an aminated MXene film with high conductivity was achieved.

[0098] Example 2 In Example 2, dispersions prepared in the same manner as in Example 1-1 and Comparative Example 1-1 above, and a dispersion of MXene that had not undergone ligand substitution, were used to evaluate the dispersion stability of ligand-substituted MXene and the like in dispersion media.

[0099] [Example 2-1] In this example, the same compound as in Example 1-1 (ligand is NH ２ The dispersion stability of the ligand-substituted MXene dispersion obtained in the same manner as in (1) synthesis of ligand-substituted MXene, (2) washing of the ligand-substituted MXene, and (3) preparation of the ligand-substituted MXene dispersion (C1PA) was evaluated as follows.

[0100] (Evaluation of Dispersion Stability) The dispersion stability of the prepared ligand-substituted MXene particle-containing dispersion was evaluated. Although there are no restrictions on the dispersion medium in which the ligand-substituted MXene is dispersed, in this example, pure water, ethanol, and 2-propanol were selected for evaluation.

[0101] 30 mL of the dispersion containing ligand-substituted MXene particles was added to a 50 mL vial. As shown in Figure 6, an ultraviolet-visible spectrophotometer (Shimadzu Corporation: UV1800) was used to adjust the absorbance at the MXene-specific wavelength of 780 nm to approximately 0.5 (this procedure was performed to roughly equalize the ligand-substituted MXene particle concentration). Hereinafter, the absorbance value at a wavelength of 780 nm is used as the absorbance of the ligand-substituted MXene particles.

[0102] The dispersion was sonicated for 10 minutes to thoroughly disperse the ligand-substituted MXene particles, and then allowed to stand. The supernatant was then removed and its absorbance was measured using a UV-visible spectrophotometer. The supernatant was collected gently to avoid stirring up the precipitate. This procedure of removing the supernatant and measuring its absorbance was repeated at regular intervals to evaluate the sedimentation rate (i.e., dispersion stability) of the ligand-substituted MXene particles over time. The results are shown in Figures 7 and 8. Figure 7 shows the results of the NH ２8 is a photograph showing the dispersion state of a dispersion containing ligand-substituted MXene particles (dispersion medium: water) ligand-substituted with -C1PA immediately after ultrasonic treatment and after 89 hours. FIG. 8 is a graph showing the ratio of absorbance at 24 hours and 89 hours to the initial absorbance (also referred to as "absorbance (normalized)" or "normalized absorbance"), where the absorbance at a wavelength of 780 nm at 0 hours of standing time (immediately after ultrasonic treatment) is set to 1.0 (initial absorbance). In this example, the relationship between the measured standing time and the ratio of absorbance to initial absorbance (absorbance (normalized)) was calculated from the measurement results, or the time at which the ratio of absorbance to initial absorbance reached 0.5 was determined by directly reading the graph. The longer this time, the more suppressed sedimentation was, indicating better dispersion and superior dispersion stability. In this example, the time required for the normalized absorbance to reach 0.5 was calculated to be 173 hours for pure water, 87 hours for ethanol, and 99 hours for 2-propanol.

[0103]

[0104] As in Comparative Example 1-1, ligand-substituted MXene was prepared using a silane coupling agent as described in Non-Patent Document 1, and the dispersion stability was investigated in the same manner as in Example 2-1. As a result, the time required for the normalized absorbance to reach 0.5 when the dispersion was left to stand at room temperature was calculated to be 8 hours for pure water, 17 hours for ethanol, and 17 hours for 2-propanol.

[0105]

[0106] Comparative Example 2-2: The dispersion stability of MXene without ligand substitution was also evaluated with reference to Example 2-1. Specifically, the MXene clay obtained in [5] delamination of Example 1-1 was dispersed in pure water, ethanol, or IPA to prepare an aqueous dispersion containing MXene particles, adjusted to an MXene solids concentration of 1 mg / mL. Using this aqueous dispersion containing MXene particles, dispersion stability was evaluated in the same manner as in Example 2-1. As a result, the time required for the normalized absorbance to reach 0.5 when the dispersion was allowed to stand at room temperature was calculated to be 693 hours in pure water, but the dispersion medium was barely dispersed in ethanol or 2-propanol.

[0107]

[0108] The results of Example 2-1 and Comparative Examples 2-1 and 2-2 above reveal the following. First, while non-ligand-substituted MXene exhibited high dispersion stability in water, it was hardly dispersed in alcoholic dispersion media such as ethanol. In contrast, as in this example, substituting the surface of MXene with aminophosphonic acid changed the hydrophilicity / hydrophobicity of the surface, making it possible to disperse MXene in alcoholic dispersion media (ethanol, IPA), which conventional MXene could not. Furthermore, it was confirmed that ligand-substituted MXene using aminophosphonic acid had improved dispersion stability in water and alcoholic organic dispersion media compared to conventional ligand-substituted MXene using a silane coupling agent. As shown schematically in Figure 9A, conventional ligand-substituted MXene is bulky and does not form a uniform film, suggesting that the film quality is poor. In contrast, as shown schematically in FIG. 9B, the two-dimensional particles of this embodiment have improved dispersion stability in a dispersion medium, which improves the film quality of a two-dimensional particle-containing film, such as a spray film, produced using the particles. As a result, it is assumed that the conductivity of the film is improved, as can be seen from the comparison between Example 1-1, Example 1-2, and Comparative Example 1-1 described above.

[0109] This application claims priority from Japanese Patent Application No. 2024-030286, which is incorporated herein by reference.

[0110] The two-dimensional particles, two-dimensional particle-containing films, and two-dimensional particle-containing dispersions of the present disclosure can be used in any suitable applications, and can be particularly preferably used, for example, in electrodes in electrical devices and in the manufacture thereof.

[0111] The disclosure of the present specification may include the following aspects: <1> A two-dimensional particle including one or more layers, wherein the layers are represented by the following formula: M ｍ X ｎ (wherein M is at least one metal of Group 3, 4, 5, 6 or 7, X is a carbon atom, a nitrogen atom or a combination thereof, n is 1 or more and 4 or less, and m is greater than n and 5 or less), and modified or terminated T (the T is at least one selected from the group consisting of a hydroxyl group, a fluorine atom, a chlorine atom, an oxygen atom and a hydrogen atom) present on the surface of the layer body, wherein the oxygen atom derived from the hydroxyl group, which is the modified or terminated T, is bonded to a phosphorus atom of a nitrogen-containing phosphonic acid having a saturated hydrocarbon group or an unsaturated hydrocarbon group and a nitrogen-containing functional group. <2> The layer body is Ti ３ C ２ <3> The two-dimensional particle according to <1>, wherein the nitrogen-containing functional group is an amino group. <4> A two-dimensional particle-containing film comprising the two-dimensional particle according to any one of <1> to <3>. <5> A two-dimensional particle-containing dispersion comprising the two-dimensional particle according to any one of <1> to <3> and a dispersion medium. <6> The two-dimensional particle-containing dispersion according to <5>, wherein the dispersion medium is one or more selected from the group consisting of pure water, ethanol, and 2-propanol.

[0112] 1a, 1b Layer body (M ｍ X ｎ Layer) 3a, 5a, 3b, 5b Modified or terminated T 7a, 7b MXene layer 10a, 10b, 10c MXene particle 21 Conventional ligand 23 Ligand of this embodiment

Claims

1. A two-dimensional particle comprising one or more layers, wherein said layers have the following formula: M ｍ X ｎ (wherein M is at least one metal of Group 3, 4, 5, 6 or 7, X is a carbon atom, a nitrogen atom or a combination thereof, n is 1 or more and 4 or less, and m is greater than n and 5 or less), and modified or terminated T (said T is at least one selected from the group consisting of a hydroxyl group, a fluorine atom, a chlorine atom, an oxygen atom and a hydrogen atom) present on the surface of said layer body, wherein the oxygen atom derived from the hydroxyl group, which is said modified or terminated T, is bonded to a phosphorus atom of a nitrogen-containing phosphonic acid having a saturated or unsaturated hydrocarbon group and a nitrogen-containing functional group.

2. The layer body is Ti ３ C ２ The two-dimensional particle of claim 1 , 3. The two-dimensional particle according to claim 1 or 2, wherein the nitrogen-containing functional group is an amino group.

4. A two-dimensional particle-containing film comprising the two-dimensional particles according to any one of claims 1 to 3.

5. A two-dimensional particle-containing dispersion liquid comprising the two-dimensional particles according to any one of claims 1 to 3 and a dispersion medium.

6. The two-dimensional particle-containing dispersion liquid according to claim 5, wherein the dispersion medium is one or more selected from the group consisting of pure water, ethanol, and 2-propanol.

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