Gas type detection method, disease detection method based thereon, and mxene production methodd

Abstract

Provided are: a gas type detection method comprising bringing a plurality of gas sensors into contact with a gas to be detected and, on the basis of a gas response pattern of the plurality of gas sensors, detecting the presence or absence of a specific gas type in the gas to be detected, wherein the plurality of gas sensors have gas-responsive materials that contain MXenes differing in gas responsiveness from each other; a disease detection method; and a MXene production method.

Description

Gas species detection method, disease detection method based thereon, and Maxine manufacturing method

[0001] The present invention relates to a gas species detection method, a disease detection method based thereon, and a method for manufacturing Maxine.

[0002] The main gases contained in exhaled breath are nitrogen, carbon dioxide, oxygen, and water vapor, which account for approximately 99% of exhaled breath. The remaining approximately 1% contains a variety of other gases. It is known that the gas species present in exhaled breath vary depending on the disease. For example, abnormalities in intestinal anaerobic bacteria increase hydrogen gas in exhaled breath, colonic polyps increase hydrogen sulfide gas in exhaled breath, liver cirrhosis increases ammonia and ethanol gas in exhaled breath, diabetes increases acetone gas in exhaled breath, cancer increases acetaldehyde gas in exhaled breath, and asthma increases nitrogen dioxide gas in exhaled breath. Therefore, selective detection of gas species causally related to disease using gas sensors can enable disease prediction. In the medical field, gas sensors are expected to be used as wearable devices aimed at early diagnosis.

[0003] Metal oxide semiconductors (MOS) are known as gas-responsive materials (see, for example, Non-Patent Document 1). In n-type semiconductors, where electrical conduction occurs through free electrons, electrical resistance decreases when exposed to electron-donating gases such as acetone gas, and increases when exposed to electron-withdrawing gases such as nitrogen dioxide gas. Conversely, in p-type semiconductors, electrical resistance increases when exposed to electron-donating gases, and decreases when exposed to electron-withdrawing gases such as nitrogen dioxide gas. Existing gas sensors using MOS generally operate at fairly high temperatures, around 300°C, and problems such as moisture reducing gas detection sensitivity have been pointed out (see, for example, Non-Patent Document 2).

[0004] Recently, a two-dimensional layered compound called MXene has been attracting attention due to its unique electrical conductivity properties. ｎ＋１ X ｎ T ｘwhere n is 1 to 4, M is an early transition metal such as Ti, V, or Nb, and X is C and / or N, T ｘ indicates a terminal functional group on the surface (typically O, OH, Cl, and / or F; hereafter, simply referred to as "terminal functional group"). Maxine functions as a gas-responsive material with excellent gas detection sensitivity (e.g., gas detection sensitivity in the range of approximately 1 to 700 ppm) even at low temperatures such as room temperature. Therefore, its application to gas sensors is expected; however, basic data is currently scarce, and the details of Maxine's gas detection mechanism are unclear. Maxine is synthesized by selectively etching away the A-site element from the MAX phase precursor material, where the M in the n+1 layer covers the X in the n layer in a [MX]nM configuration. A is primarily Al, but can also be Si or Ga. This etching process is generally performed using hydrogen fluoride (HF). However, HF itself is highly dangerous, and problems have been pointed out, such as the possibility of MAX phase residue and limited variation in the surface terminal functional groups. Also known is an etching process using a mixed solution of a fluoride salt such as sodium fluoride, potassium fluoride, lithium fluoride, or ammonium fluoride with hydrochloric acid (HCl). This etching process is a type of in-situ HF generation method, and is safer and does not damage the terminal functional group T of Maxine. ｘ This allows for the creation of variations in the MAXIN phase, contributing to the diversification of MAXIN species. Another proposed etching technique is hydrothermal-assisted etching, in which in-situ HF etching is performed under high temperature and pressure. Hydrothermal-assisted etching is an etching method that generates HF by reacting hydrochloric acid with the above-mentioned fluoride salts under high temperature and pressure. Because hydrothermal-assisted etching provides a closed reaction environment under high temperature and pressure, it can achieve high conversion efficiency from the MAX phase to MAXIN in a short time and also enables the use of reagents with low solubility at room temperature (e.g., LiF). Furthermore, the molten salt method shortens the reaction time and is safer because it does not use HF.

[0005] Kim HJ, Lee JH. Sens Actuators B Chem. 2014, Vol. 192, pp. 607-627. Dey A. Semiconductor metal oxide gas sensors, a review. Mater Sci Eng B Solid State Mater Adv Technol. 2018, Vol. 29, pp. 206-217.

[0006] An object of the present invention is to provide a gas species detection method that detects the presence or absence of a specific gas species in a target gas using multiple gas sensors that employ Maxine gas sensors with different gas responsiveness as the gas-responsive material. Another object of the present invention is to provide a disease detection method that includes detecting the presence or absence of a specific gas species in a target gas using the gas species detection method. Another object of the present invention is to provide a new method for manufacturing Maxine gas sensors.

[0007] As described above, there are a wide variety of Maxin types due to factors such as their elemental composition and the type of terminal functional group. As a result of extensive research conducted by the present inventors, including conventional knowledge, it has become clear that Maxin types exhibit unique gas responsiveness depending on their type, and that even the same type of Maxin can exhibit diverse gas responsiveness depending on differences in manufacturing method, etc. The present invention was completed based on these findings and further research.

[0008] The above-mentioned object of the present invention has been achieved by the following means: [1] A gas species detection method comprising bringing a plurality of gas sensors into contact with a gas to be detected and detecting the presence or absence of a specific gas species in the gas to be detected based on the gas response patterns of the plurality of gas sensors, wherein the gas-responsive materials of the plurality of gas sensors include MXenes with different gas responsiveness from each other. [2] The gas species detection method according to [1], wherein two or more of the plurality of gas sensors have the same type of MXene, and the gas responsiveness of the same type of MXenes is different from each other. [3] The same type of MXenes with different gas responsiveness from each other are Nb ２ CT ｘ or Nb ２ CTｘ The gas species detection method according to [2], wherein the compound of T ｘ represents a terminal functional group. [4] As the same type of maxine having different gas responsiveness, V ２ CT ｘ or V ２ CT ｘ The gas species detection method according to [2] or [3], wherein the compound of T ｘ represents a terminal functional group. [5] As the same type of maxine having different gas responsiveness, Ti ３ C ２ T ｘ or Ti ３ C ２ T ｘ The gas species detection method according to [2] or [3], wherein the compound of T ｘ represents a terminal functional group. [6] The same type of Nb having different gas responsiveness ２ CT ｘ or Nb ２ CT ｘ The gas species detection method according to [3], wherein at least one of the compounds is a product that has been subjected to hydrothermal-assisted etching or etching by a molten salt method. [7] The gas species detection method according to any one of [2] to [6], wherein the same type of maxines having different gas responsiveness from each other include maxines whose electrical resistance increases upon contact with gas species X and maxines whose electrical resistance decreases upon contact with the gas species X. [8] The gas species detection method according to [7], wherein the gas species X is a gas selected from hydrogen gas, hydrogen sulfide gas, ammonia gas, ethanol gas, acetone gas, toluene gas, and nitrogen dioxide gas. [9] The gas species detection method according to any one of [1] to [8], wherein a plurality of gas sensors are brought into contact with a gas to be detected at 10 to 50°C.

[10] A disease detection method comprising detecting the presence or absence of a specific gas species by the gas species detection method according to any one of [1] to [9], and detecting the presence or absence of a disease associated with the presence of the specific gas species.

[11] A method for producing maxine, comprising introducing a halogen-based terminal functional group onto the surface of an etched maxine product obtained by the molten salt method.

[0009] In the present invention, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0010] According to the gas species detection method of the present invention, the presence or absence of a specific gas species in a gas to be detected can be detected using multiple gas sensors that employ Maxine, each with a different gas response, as the gas-responsive material. Furthermore, according to the disease detection method of the present invention, the presence or absence of a specific gas species in a gas to be detected by the gas species detection method can be linked to the presence or absence of a disease, thereby detecting the presence or absence of a disease. Furthermore, the method for producing Maxine of the present invention provides a novel method for producing Maxine.

[0011] Nb ２ AlC, LiF-Nb ２ CT ｘ , N.H. ４ F-Nb ２ CT ｘ and HF-Nb ２ CT ｘ 1(a) shows the XRD pattern at 2θ=5 to 60°, and FIG. 1(b) shows the XRD pattern at 2θ=6 to 14°. ２ 2(a) and 2(b) are SEM images of AlC and HF-Nb. ２ CT ｘ 2(c) is the SEM image of LiF—Nb ２ CT ｘ 2(d) is an SEM image of NH ４ F-Nb ２ CT ｘ The SEM image of Fig. 3(a) is LiF-Nb ２ CT ｘ 3(b) is the HRTEM image of LiF—Nb ２ CT ｘ The electron diffraction pattern of LiF-Nb is shown in Fig. 4(a). ２ CT ｘ 4(b) to (e) are SEI images of LiF-Nb ２ CT ｘ Element mapping (in order: O, F, Al, Nb). ４ F-Nb ２ CTｘ 4(g) to (j) are the SEI images of NH ４ F-Nb ２ CT ｘ Elemental mapping (in order: O, F, Al, Nb) of LiF—Nb ２ CT ｘ The results of XPS analysis are shown in Fig. 5(a) and Fig. 5(b) to (d) respectively show the high-resolution spectra of the Nb3d, C1s, and O1s regions and the results of Gaussian fitting of these spectra. ４ F-Nb ２ CT ｘ 6(a) shows the overall spectrum, and Fig. 6(b) to (d) show the high-resolution spectra of the Nb3d, C1s, and O1s regions, respectively, and the results of Gaussian fitting of these spectra. ２ CT ｘ 7(a) is a graph showing the results of gas response to various gas species. ２ 7(b) to (d) are graphs showing the change in gas response value over time during gas flow (0.5 ppm) and after gas flow has stopped. Graphs 7(b) to (d) are graphs showing the change in gas response value after 10 minutes of exposure to gas species at various concentrations. Graph 7(e) shows the gas detection response reproducibility Rr calculated by formula (B) after 10 minutes of exposure to the highest concentration of each gas shown in FIG. 7(b). ２ AlC, LiF-Nb ２ CT ｘ , N.H. ４ F-Nb ２ CT ｘ and HF—Nb obtained in Synthesis Example 1 above. ２ CT ｘ 8(a) shows the XRD pattern at 2θ=5 to 60°, and FIG. 8(b) shows the XRD pattern at 2θ=5 to 10°. The top row of FIG. 9 shows the XRD pattern of LiF—Nb ２ CT ｘ The SEI image (left end) and element mapping (O, F, Nb, Al, from the left) are shown. ４ F-Nb ２ CT ｘThe SEI image (left end) and elemental mapping (O, F, Nb, Al, from the left) of the LiF-Nb sample (autoclaved at 180°C for 24 hours and vacuum dried at 60°C) are shown. The results of elemental analysis of the sample surface are shown below each elemental mapping. ２ CT ｘ 10(b) to 10(d) show the high-resolution spectrum of the O1s region and the results of Gaussian fitting of the spectrum. ２ CT ｘ , N.H. ４ F-Nb ２ CT ｘ (autoclaved at 180°C for 24 hours, dried in vacuum at 60°C), NH ４ F-Nb ２ CT ｘ (autoclaved at 180°C for 24 hours, then vacuum-frozen and dried). ２ CT ｘ and N.H. ４ F-Nb ２ CT ｘ 11 is a graph showing the results of gas response to various gas species after exposure to acetone gas (50 ppm) for 10 minutes, and the right side of FIG. 11 is a graph showing the change in gas response after exposure to ammonia gas (12 ppm) for 10 minutes. ２ AlC, Nb ２ CT ｘ (molten salt method) and NH ４ F-Nb ２ CT ｘ The left side of Figure 13 shows the XRD pattern of NH ４ F-Nb ２ CT ｘ The right side of FIG. 13 is an SEM image of Nb ２ CT ｘ (molten salt method). ４ F-Nb ２ CT ｘ (In situ) and Nb ２ CT ｘ15(a) and (b) show the results of XPS analysis of NH ４ F-Nb ２ CT ｘ 15(c) and (d) are graphs showing the results of gas response to various gas species (in situ). ２ CT ｘ 15(a) and (c) are graphs showing the change in resistance when exposed to acetone gas at 15-minute intervals, and FIGS. 15(b) and (d) are graphs showing the change in resistance when exposed to ammonia gas at 15-minute intervals. FIG. 16(a) is a schematic diagram of the gas sensor produced in the example, and FIG. 16(b) is a schematic diagram of the gas sensing device. Nb ２ AlC, Nb ２ CT ｘ (MS-HF) and Nb ２ CT ｘ 17(a) shows the XRD pattern of Nb (HF). FIG. 17(a) shows the XRD pattern at 2θ=5 to 60°, and FIG. 17(b) shows the XRD pattern at 2θ=8 to 12°. ２ 18(b) is an SEM image of AlC, and FIG. 18(b) is an SEM image of Nb ２ CT ｘ (HF) and Fig. 18(c) shows the SEM image of Nb using an aqueous HF solution with a concentration of 0 mass%. ２ CT ｘ (MS-HF) and Fig. 18(d) shows the SEM image of Nb using an HF aqueous solution with a concentration of 34 mass%. ２ CT ｘ (MS-HF) SEM image. ２ CT ｘ The results of XPS analysis of (MS-HF) show the spectrum in the binding energy range of 681 to 695 eV where the F1s peak is observed. ２ CT ｘ (MS-HF) and Nb ２ CT ｘ 1 is a bar graph showing the results of quantitative analysis of Nb (HF) by SEM EDS, from the left, using an aqueous HF solution with a concentration of 0 mass %. ２ CTｘ (MS-HF), Nb using an aqueous HF solution with a concentration of 43 mass% ２ CT ｘ (MS-HF), Nb ２ CT ｘ Fig. 21 shows the data for Nb (HF) using an aqueous HF solution with a concentration of 0 mass%. ２ CT ｘ (MS-HF), Nb using an aqueous HF solution with a concentration of 43 mass% ２ CT ｘ (MS-HF) and Nb ２ CT ｘ 21 is a graph showing the results of acetone gas response of Nb (HF), which is a graph showing the gas detection response ΔR calculated by formula (A) when exposed to acetone gas for 20 minutes. The upper part of FIG. 21 shows the concentration of the supplied acetone gas. FIG. 22 is a graph showing the results of acetone gas response of Nb (HF) when exposed to acetone gas for 20 minutes. ２ CT ｘ 22 shows the gas detection response ΔR calculated by formula (A) when exposed to acetone gas for 20 minutes, and the concentration of the supplied acetone gas is shown at the top of FIG. 22. FIG. 23 shows the results of the acetone gas response of Nb (HF) using an aqueous solution of HF with a concentration of 0 mass %. ２ CT ｘ (MS-HF), Nb using an aqueous HF solution with a concentration of 43 mass% ２ CT ｘ (MS-HF) and Nb ２ CT ｘ 23 is a graph showing the ammonia gas response of (HF), which is a graph showing the gas detection response ΔR calculated by formula (A) when exposed to ammonia gas for 20 minutes. The upper part of FIG. 23 shows the concentration of the supplied ammonia gas.

[0012] Preferred embodiments of the present invention will be described below, but the present invention is not limited to the following embodiments except as defined in the present invention.

[0013] [Gas Species Detection Method] The gas species detection method of the present invention uses multiple gas sensors. The multiple gas sensors may exist as individual gas sensors or as a gas sensor array. These multiple gas sensors are brought into contact with a target gas, and the presence or absence of a specific gas species in the target gas is detected based on the gas response patterns of the multiple gas sensors. In this invention, "detection" does not mean determining the presence or absence of a specific gas species, but also means predicting (estimating) the presence or absence of a specific gas species with a desired accuracy. Furthermore, in this invention, the "presence" in the "presence or absence" of a specific gas species may mean the simple presence of the specific gas species, or it may mean that the mere presence of the specific gas species is not sufficient but that a certain amount (a certain concentration) or more of the specific gas species is present. Similarly, "absence" may mean the complete absence of the specific gas species (below the detection limit) or that the amount (concentration) of the specific gas species is below a certain amount (a certain concentration). In this way, the criteria for "presence or absence" are appropriately set depending on the purpose.

[0014] The specific gas species can be appropriately set depending on the purpose. For example, a gas species causally related to a disease or the like can be set as the specific gas species. As an example, hydrogen gas in breath can be detected as a specific gas species for testing for abnormalities in intestinal anaerobic bacteria. Furthermore, hydrogen sulfide gas in breath can be detected as a specific gas species for testing for colon polyps. Furthermore, ammonia gas or ethanol gas in breath can be detected as a specific gas species for testing for liver cirrhosis. Furthermore, acetone gas in breath can be detected as a specific gas species for testing for diabetes. Furthermore, acetaldehyde gas in breath can be detected as a specific gas species for testing for cancer. Furthermore, nitrogen dioxide gas in breath can be detected as a specific gas species for testing for asthma. In the present invention, "disease" refers to a state in which some abnormality occurs in the living body. For example, benign tumors such as polyps are also considered to be a type of disease in the present invention.

[0015] In the gas species detection method of the present invention, the gas-responsive materials of the plurality of gas sensors contain MXenes with different gas responsiveness. That is, at least two of the plurality of gas sensors have MXenes with different gas responsiveness as gas-responsive materials. MXenes with different gas responsiveness mean gas sensors that exhibit different gas responsiveness in their form. In the gas species detection method of the present invention, all of the gas-responsive materials of the plurality of gas sensors may be MXenes with different gas responsiveness.

[0016] The types of maxins that the plurality of gas sensors have are as described above. ｎ＋１ X ｎ T ｘ There are no particular limitations as long as it is represented by the composition formula. M can be, for example, Ti, V, or Nb. X can be, for example, C. T, which represents a terminal functional group on the surface ｘ can be selected from, for example, O, OH, Cl, and F. Furthermore, n is an integer of 1 to 4. A preferred example of the maxin possessed by the plurality of gas sensors is Nb ２ CT ｘ , Nb ３ C ２ T ｘ , V ２ CT ｘ , V ３ C ２ T ｘ , Ti ２ CT ｘ , Ti ３ C ２ T ｘ , Mo ２ CT ｘ , Mo ３ C ２ T ｘ However, the present invention is not limited to the use of these maxines. ２ CT ｘWhen particles containing Nb were administered to mice, they showed negligible side effects, suggesting excellent biocompatibility. ２ CT ｘ In the present invention, when simply referring to "Maxine", it is ｎ＋１ X ｎ T ｘ In addition to that, M ｎ＋１ X ｎ T ｘ and M ｎ＋１ X ｎ T ｘ Compounds with oxides of M ｎ＋１ X ｎ T ｘ and metal particles composite, and M ｎ＋１ X ｎ T ｘ and M ｎ＋１ X ｎ T ｘ A composite of an oxide of the present invention and metal particles (hereinafter, these composites are collectively referred to as "M ｎ＋１ X ｎ T ｘ It is also called a "compound of." ｎ＋１ X ｎ T ｘ and M ｎ＋１ X ｎ T ｘ The composition formula of the composite with the oxide of Nb is, for example, ２ CT ｘ -Nb ２ O ５ , Nb ３ C ２ T ｘ -Nb ２ O ５ , V ２ CT ｘ -V ２ O ５ , V ２ CT ｘ -V ３ O ７ , V ３ C ２ T ｘ -V ２ O ５ , V ３ C ２ T ｘ -V ３ O７ , Ti ２ CT ｘ -TiO ２ , Ti ３ C ２ T ｘ -TiO ２ Examples include: ｎ＋１ X ｎ T ｘ and M ｎ＋１ X ｎ T ｘ There is no particular limitation on the chemical structure (form) of the composite with the oxide of M. ｎ＋１ X ｎ T ｘ and nanoparticle M ｎ＋１ X ｎ T ｘ The composite may be, for example, a composite with an oxide of M ｎ＋１ X ｎ T ｘ In the synthesis process of M ｎ＋１ X ｎ T ｘ The oxide nanoparticles are grown. ｎ＋１ X ｎ T ｘ As a composite of metal particles, M ｎ＋１ X ｎ T ｘ Examples of the material include those in which spherical or rod-shaped particles of metals such as Au and Pt are added to the above-mentioned material. For example, Au / Nb ２ CT ｘ Examples include: ｎ＋１ X ｎ T ｘ and M ｎ＋１ X ｎ T ｘ Examples of composites of oxides of M and metal particles include M ｎ＋１ X ｎ T ｘ and M ｎ＋１ X ｎ T ｘ Examples of the composite include a composite in which the above-mentioned metal particles are further added to the composite with the oxide of Pt / Ti. ３ C ２ T ｘ -TiO ２At least one of the maxines possessed by the plurality of gas sensors is preferably a maxine obtained by introducing a halogen-based terminal functional group onto the surface of an article that has been etched by the molten salt method described below.

[0017] For example, an example of the gas species detection method of the present invention will be described in which the target gas is the breath of a subject suspected of having diabetes, and the specific gas species is acetone gas. Gas sensor A has, as a gas-responsive material, Maxine, whose electrical resistance increases upon contact with acetone gas, and gas sensor B has, as a gas-responsive material, Maxine, whose electrical resistance decreases conversely. These gas sensors are then exposed to the subject's breath. If the electrical resistance of gas sensor A increases and the electrical resistance of gas sensor B decreases, the presence of acetone gas, a specific gas species, in the breath can be detected. On the other hand, when exposed to a subject's breath, if the electrical resistance of gas sensor A increases but the electrical resistance of gas sensor B does not decrease (i.e., if the gas resistance increases or does not change), if the electrical resistance of gas sensor A does not increase (i.e., if the gas resistance decreases or does not change) but the electrical resistance of gas sensor B decreases, or if the electrical resistance of gas sensor A does not increase but the electrical resistance of gas sensor B does not decrease, the presence of the specific gas species, acetone gas, in the breath can be detected. By using two gas sensors, A and B, which have different responsiveness to acetone gas, the presence or absence of acetone gas can be detected with higher accuracy than when using a single gas sensor. Furthermore, by using three or more gas sensors with different responsiveness, acetone gas can be detected with higher accuracy. The gas species detection method of the present invention described above is also applicable when the specific gas species is a gas species other than acetone gas.

[0018] In the gas species detection method of the present invention, a specific gas species (gas species to be detected) that may be contained in the gas to be detected is preferably preset, and the presence or absence of this specific gas species is detected. That is, rather than identifying the gas species in the gas to be detected, the presence or absence of which is unknown, is preferably determined. For example, in the above example, the specific gas species is set as acetone gas, and the presence or absence of this acetone gas species is detected. The specific gas species to be preset may be one or more. Examples of specific gas species that may be preset include hydrogen gas, hydrogen sulfide gas, ammonia gas, ethanol gas, acetone gas, acetaldehyde gas, toluene gas, and nitrogen dioxide gas. When the specific gas species is set as hydrogen gas, the gas to be detected may be, for example, the breath of a subject suspected of having an abnormality in intestinal anaerobic bacteria. When the specific gas species is set as hydrogen sulfide gas, the gas to be detected may be, for example, the breath of a subject suspected of having a colon polyp. When the specific gas species is set to ammonia gas, the gas to be detected can be, for example, the breath of a subject suspected of having cirrhosis. When the specific gas species is set to ethanol gas, the gas to be detected can be, for example, the breath of a subject suspected of having cirrhosis. When the specific gas species is set to acetone gas, the gas to be detected can be, for example, the breath of a subject suspected of having diabetes. When the specific gas species is set to acetaldehyde gas, the gas to be detected can be, for example, the breath of a subject suspected of having cancer. When the specific gas species is set to nitrogen dioxide gas, the gas to be detected can be, for example, the breath of a subject suspected of having asthma.

[0019] In the gas species detection method of the present invention, two or more of the plurality of gas sensors (preferably 2 to 10 gas sensors, more preferably 2 to 4 gas sensors, and even more preferably 2 or 3 gas sensors) can have the same type of maxine, and the gas responsiveness of the maxine of the same type can be different from each other. In the present invention, "the same type of maxine" means a gas sensor having a composition formula: M ｎ＋１ X ｎ T ｘIt means a maxine in which M, X and n are the same. ｎ＋１ X ｎ T ｘ Even when a compound of M is included, ｎ＋１ X ｎ T ｘ If M, X and n are the same in the part, they are the same maxine. ２ CT ｘ They are the same species of maxine, Ti ３ C ２ T ｘ On the other hand, Nb ２ CT ｘ and Nb ３ C ２ T ｘ is the heterogeneous maxine, and Nb ２ CT ｘ and V ２ CT ｘ is the heterogeneous maxine, and Nb ３ C ２ T ｘ and Ti ３ C ２ T ｘ are also different species of maxines. ｘThe unique characteristic of Maxin as a gas-responsive material is that it can exhibit different gas responsiveness depending on the state of the material. By using Maxin, it is possible to create Maxin molecules with the same M, X, and n in the composition formula but different gas responsiveness (same type of Maxin) by changing the reagent (etchant) or adjusting the manufacturing method (e.g., by changing the reaction time, reaction temperature, reagent concentration, solvent, drying conditions, reaction method, etc.) while using the same raw materials and reducing costs. Furthermore, even when using the exact same Maxin, gas sensors containing Maxin molecules with different gas responsiveness can be created by adjusting the film thickness of the Maxin molecules contained in the gas sensor. In this way, by adjusting the synthesis method, etc., it is possible to obtain Maxin molecules with different gas responsiveness even if they are the same type of Maxin. For example, even if the raw materials are the same, by adjusting various conditions during synthesis (e.g., temperature, time, solvent, reagent concentration), the concentration of the terminal functional group of Maxin can be gradually controlled. By understanding the relationship between the concentration of the terminal functional group and the responsiveness to various gases, gas species can be more easily identified. For this reason, it is preferable that two or more gas sensors among multiple gas sensors contain the same type of Maxin. More specifically, in the method for synthesizing maxine by selectively etching away A-site elements from the MAX phase, which is a precursor material, the type of etching treatment is selected from among etching treatment using HF, in-situ HF etching, etching treatment in which in-situ HF etching is performed under high temperature and pressure (hydrothermal-assisted in-situ HF etching), and etching treatment by a molten salt method, so that the obtained maxine can be made to exhibit different gas responsiveness while being of the same type. Furthermore, by performing a terminal functional group control operation on maxine obtained by etching, it is possible to obtain the same type of maxine that exhibits a different gas responsiveness from the maxine before the terminal functional group control operation.

[0020] In-situ HF etching is a process using hydrochloric acid (HCl) and sodium fluoride (NaF), potassium fluoride (KF), lithium fluoride (LiF), or ammonium fluoride (NH ４The etching process uses a mixed solution of HCl and fluoride salts such as LiF. The chemical reaction in the in-situ HF etching process is ４ F and Nb ２ In the case of using AlC, HF generated by the reaction of the following formula (1) or (2) is converted into Nb ２ It reacts with AlC to produce Maxine through the chemical reactions expressed by the following formulas (3) to (5). In addition, in the etching process using HF, Maxine is obtained through the reactions expressed by the following formulas (3) to (5). LiF + HCl → HF + LiCl (1) NH ４ F + H ２ O → HF + NH ３ ・H ２ O (2) Nb ２ AlC + 3HF → AlF ３ + 3 / 2H ２ + Nb ２ C (3) Nb ２ C + 2H ２ O → Nb ２ C(OH) ２ +H ２ (4) Nb ２ C + 2HF → Nb ２ CF ２ +H ２ (5)

[0021] The pressure and temperature conditions in the hydrothermal-assisted in-situ HF etching treatment are not particularly limited. For example, the pressure can be in the range of 0.1 to 2.3 MPa using an autoclave, and the temperature can be in the range of 100 to 220°C.

[0022] The etching process using the molten salt method is an etching process that utilizes oxidation of the A-site elements in the MAX layer, which is a precursor material, by cations with high redox potential of a Lewis acid molten salt. The Lewis acid molten salt is not particularly limited, and may be CuCl ２ , NiCl ２ , FeCl ２ , AgCl, CdCl ２ , SnCl２ Molten salts containing the above Lewis acidic molten salts (e.g., CuCl ２ The above-mentioned CuCl (containing molten salt) can also be used. ２ The contained molten salt is, for example, CuCl ２ -NaCl-based molten salt, CuCl ２ -KCl-based molten salt, CuCl ２ -NaCl-KCl based molten salt (e.g., CuCl ２ : NaCl: KCl = 3:2:2). ２ When the molten salt contains two or more components, each component (e.g., CuCl ２ - In NaCl-KCl molten salt, CuCl ２ The molten salt can be formed by mixing three components (Nb, NaCl, and KCl) in a predetermined ratio and then heating them at a high temperature of about 600°C or higher (preferably 650 to 800°C) in an inert gas atmosphere such as Ar gas. Regarding the method for forming a molten salt including a Lewis acidic molten salt, see, for example, Dong, Hanyu, et al., Molten salt derived Nb2CT x MXene anode for Li-ion batteries, ChemElectroChem, 2021, Vol. 8, No. 5, pp. 957-962. The mixture of the components constituting the above molten salt is Nb ２ This may be done at the same time as mixing with a precursor material such as AlC. ２ This may be done separately before mixing with AlC. ２ The etching process can be performed by the molten salt method by mixing a precursor material such as AlC with each component constituting the molten salt and then heating the mixture. ２ and Nb ２ In an example using AlC, Nb is produced by the reaction of the following formula (6): ２After etching Al in AlC, the remaining Cu is removed to obtain Maxine. Cu(0), a by-product of the reaction of the following formula (6), can be oxidized to Cu(II) using an oxidizing agent such as an aqueous solution of ammonium persulfate, and then removed in the purification step described below. ２ CuCl in molten salt containing ２ The other components (NaCl and KCl) are CuCl ２ CuCl ２ It is a component that contributes to adjusting the melting temperature of the contained molten salt, and Nb ｎ＋１ AlX ｎ It is not a component that directly participates in the reaction with precursor materials such as 2Nb ｎ＋１ AlX ｎ + 3CuCl ２ → 2Nb ｎ＋１ X ｎ +2AlCl ３ + 3Cu (6)

[0023] In the various etching processes, the step of purifying Maxine from the resulting product can be carried out by a conventional method, using an appropriate combination of washing, filtration, drying, etc. Drying methods include vacuum drying while heating in the range of 60 to 120°C, vacuum freeze drying, etc.

[0024] By controlling the terminal functional groups, the interplanar spacing (interlayer distance) of Maxin is maintained at a constant distance due to the etching process, while the terminal functional groups (T ｘ In other words, depending on whether or not the terminal functional group control operation is performed on maxines obtained by the same etching process, it is possible to adjust the composition ratio of the functional groups constituting the terminal functional groups (T ｘ ) can be obtained. In addition, the terminal functional groups (T ｘBy adjusting the composition ratio of the functional groups constituting maxine, it is believed that the types and amounts of impurities in maxine resulting from various etching processes can be approximately the same for each maxine obtained. The terminal functional group control operation may be performed on maxine obtained by the above-mentioned etching process either before or after the purification of maxine obtained by the etching process. It is also preferable to purify maxine after the terminal functional group control operation. The description of the process for purifying maxine from the product obtained by the above-mentioned various etching processes can be applied to the purification of maxine after the terminal functional group control operation. An example of the terminal functional group control operation for maxine obtained by etching is a treatment using hydrofluoric acid. Treatment with hydrofluoric acid can remove the terminal functional group T of maxine. ｘ In the method for producing Maxine of the present invention, the terminal functional group control operation is carried out on the etched product, and the terminal functional groups (T ｘ ) is controlled. Specifically, a preferred method is to produce Maxine obtained by the molten salt method, in which an etched Maxine product obtained by the molten salt method is subjected to a terminal functional group control operation using hydrofluoric acid (for example, an operation of immersing the etched Maxine product in hydrofluoric acid), thereby producing Maxine obtained by the molten salt method, in which halogen-based terminal functional groups (F and Cl) are introduced onto the surface of Maxine obtained by the molten salt method. An etched Maxine product obtained by the molten salt method, before being subjected to a terminal functional group control operation using hydrofluoric acid, is subjected to a terminal functional group control operation using hydrofluoric acid to introduce terminal functional groups (T ｘ ) and increasing the content ratio of halogen-based terminal functional groups (F and Cl) constituting the terminal functional groups (T ｘ As the hydrofluoric acid, for example, an aqueous solution of hydrofluoric acid having a concentration of 20 to 60% by mass (preferably a concentration of 25 to 55% by mass, and more preferably a concentration of 30 to 50% by mass) can be used.

[0025] Details will be described later, but examples of using the same type of maxin with different gas responsiveness include the combinations shown below, which can detect the presence or absence of a specific gas species. However, the present invention is not limited to these combinations. As the same type of maxin with different gas responsiveness, Nb ２ CT ｘ or Nb ２ CT ｘ When the compound contains the compound, it is possible to detect the presence or absence of at least one gas selected from the group consisting of hydrogen sulfide gas, ammonia gas, and acetone gas. ２ CT ｘ or V ２ CT ｘ When the compound contains the compound, it is possible to detect the presence or absence of at least one gas species selected from the group consisting of hydrogen gas, ammonia gas, ethanol gas, and acetone gas. ３ C ２ T ｘ or Ti ３ C ２ T ｘ When the compound contains the compound, it is possible to detect the presence or absence of at least one gas species among ammonia gas, acetone gas, etc. ２ CT ｘ or Ti ２ CT ｘ In the case where the compound contains the compound, it is possible to detect the presence or absence of at least one gas species selected from hydrogen gas, ethanol gas, etc. It is preferable that at least one of the same type of maxins having different gas responsiveness is a product that has been subjected to hydrothermal etching or etching by a molten salt method, and the same type of Nb ２ CT ｘ or Nb ２ CT ｘIt is more preferable that at least one of the composites is a product that has been subjected to hydrothermal etching or etching by a molten salt method. Furthermore, at least one of the same type of Maxine compounds having different gas responsiveness can be a product that has been subjected to etching by a molten salt method as described above. In this case, it is also preferable that the product that has been subjected to etching by a molten salt method is a Maxine compound having a halogen-based terminal functional group introduced on its surface. Furthermore, in this case, the Maxine compound is Nb ２ CT ｘ or Nb ２ CT ｘ It is preferred that the compound contains a compound of the formula:

[0026] To explain the basis for the above combinations, for example, the following combinations are given based on data disclosed in conventional literature.

[0027] (Nb ２ CT ｘ or Nb ２ CT ｘ In fact, for example, Nb ２ CT ｘ (HF) and Nb described in D2 ２ CT ｘ (HF) and Au / Nb described in D3 ２ CT ｘ (Hydrothermal-assisted in-situ HF etching process, HCl + LiF) are the same maxima as each other, but the Nb described in D1 is different from the ammonia gas. ２ CT ｘ (HF) and Au / Nb described in D3 ２ CT ｘ (Hydrothermal-assisted in-situ HF etching treatment, HCl + LiF) reduces the electrical resistance and ２ CT ｘ (HF) has been shown to increase the electrical resistance. ２ CT ｘ The difference in the responsiveness of Nb (HF) to ammonia gas is thought to be due to the terminal functional group, interplanar spacing, number of layers stacked, particle size, electrode state depending on the manufacturing process, etc. ２ CTｘ (hydrothermal-assisted in-situ HF etching treatment, HCl+LiF), Nb in Synthesis Example 2 described later ２ CT ｘ (Hydrothermal-assisted in-situ HF etching process, HCl + NH ４ F), Nb in Synthesis Example 3 described below ２ CT ｘ (molten salt method) and Nb ２ CT ｘ (Hydrothermal-assisted in-situ HF etching process, HCl + NH ４ F), Nb in Synthesis Example 4 described below ２ CT ｘ The combination of the molten salt method and the terminal functional group control is as described in the examples below.

[0028] (V ２ CT ｘ or V ２ CT ｘ Compound of V described in D5 ２ CT ｘ (HF), V described in D6 ２ CT ｘ (HCl + HF) and V as described in D7 ２ CT ｘ -V ２ O ５ (HCl + LiF) increases the electrical resistance to hydrogen gas, and V described in D6 ２ CT ｘ -V ３ O ７ (HCl + HF) has a lower electrical resistance to hydrogen gas, and although they are the same type of maxine, they show different responsiveness to hydrogen gas. ２ CT ｘ (HF), V described in D5 ２ CT ｘ (HF), V described in D6 ２ CT ｘ (HCl + HF) and V as described in D6 ２ CT ｘ -V ３ O ７ (HCl + HF) increases the electrical resistance to ammonia gas, and V ２ CT ｘ(HCl+LiF) and V ２ CT ｘ The electrical resistance of (HCl + NaF) decreases with respect to ammonia gas. That is, although these Maxines are the same type, they show different responses to ammonia gas. ２ CT ｘ (HF), V described in D5 ２ CT ｘ (HF), V described in D6 ２ CT ｘ (HCl + HF) and V as described in D7 ２ CT ｘ -V ２ O ５ (HCl + LiF) increases the electrical resistance against ethanol gas, and V ２ CT ｘ (HCl+LiF) and V ２ CT ｘ (HCl + NaF) and V as described in D6 ２ CT ｘ -V ３ O ７ The electrical resistance of (HCl + HF) decreases with ethanol gas. That is, although these maxines are the same type, they show different responses to ethanol gas. ２ CT ｘ (HF) and V described in D5 ２ CT ｘ (HF) increases the electrical resistance to acetone gas, and V ２ CT ｘ (HCl+LiF) and V ２ CT ｘ The electrical resistance of (HCl+NaF) decreases with acetone gas. That is, although these maxines are the same type, they exhibit different responses to acetone gas.

[0029] (Ti ３ C ２ T ｘ or Ti ３ C ２ T ｘ D8) Ti composite ３ C ２T ｘ (HCl + LiF), Ti as described in D9 ３ C ２ T ｘ (HCl + LiF), Ti according to D10 ３ C ２ T ｘ (HCl + NaF), Ti as described in D11 ３ C ２ T ｘ (HF), Ti ３ C ２ T ｘ -TiO ２ (HF) and Pt / Ti ３ C ２ T ｘ -TiO ２ (HF) increases the electrical resistance to ammonia gas, and Ti described in D4 ３ C ２ T ｘ (Molten salt method) shows a decrease in electrical resistance to ammonia gas. Although these Maxine are the same type of Maxine, they show different responses to ammonia gas. ３ C ２ T ｘ (HCl + LiF) and Ti as described in D9 ３ C ２ T ｘ (HCl + LiF) increases the electrical resistance against acetone gas, and Ti described in D4 ３ C ２ T ｘ The electrical resistance of the molten salt method does not change with acetone gas. Although these Maxine are the same type of Maxine, they show different responses to acetone gas.

[0030] (Ti ２ CT ｘ or Ti ２ CT ｘ In fact, for example, Ti described in D12 ２ CT ｘ (HCl + NaF) and Ti described in D12 ２ CT ｘ -TiO ２(HCl + NaF) are the same type of maxine, but the Ti described in D12 is ２ CT ｘ (HCl + NaF) reduces the electrical resistance, and Ti described in D12 ２ CT ｘ -TiO ２ It has been shown that (HCl+NaF) increases electrical resistance. In this paragraph, the description in parentheses after Maxine indicates the manufacturing method, with "HF" indicating an etching treatment using HF, "HCl+LiF," "HCl+NaF," and "HCl+HF" indicating in-situ HF etching treatment, "hydrothermal-assisted in-situ HF etching treatment," and "molten salt method" indicating etching treatment using a molten salt method.

[0031] The above D1 to D12 are the following documents: D1: "Amine-functionalized stable Nb ２ CT ｘ MXene tower room temperature ultrasensitive NO ２ gas sensor”, Mater. Adv., 2022, Vol. 3, No. 12, pp. 5151-5162 D2: “Fabrication of Delaminated 2D Metal Carbide MXenes (Nb ２ CT ｘ ) by CTAB-based NO ２ Gas Sensor with Enhanced Stability”, Adv. Mater. Interfaces, 2022, Vol. 9, No. 22, 202200415 D3: “Light-driven, ultra-sensitive and multifunctional ammonia wireless sensing system by plasmonic-functionalized Nb ２ CT ｘMXenes towards smart agriculture”, Nano Energy. 2023, Vol. 108, 108216 D4: “V ２ CT ｘ　 and Ti ３ C ２ T ｘ　 D5: “Two-Dimensional Vanadium Carbide MXene for Gas Sensors with Ultrahigh Sensitivity Toward Nonpolar Gases”, ACS Sens., 2019, Vol. 4, No. 6, pp. 1603-1611 D6: “Chemoresistive Properties of V ２ CT ｘ MXene and the V ２ CT ｘ / V ３ O ７ Nanocomposite Based on It”, Chemosensors, 2023, Volume 11, No. 2, p. 142 D7: “V ２ CT ｘ MXene-based hybrid sensor with high selectivity and ppb-level detection for acetone at room temperature”, Sci Rep. 2023, Volume 13, 3114 D8: “Metallic Ti ３ C ２ T ｘD9: “Room Temperature Gas Sensing of Two-Dimensional Titanium Carbide (MXene),” ACS Appl. Mater. Interfaces, 2017, Vol. 9, No. 42, pp. 37184-37190 D10: “Ti ３ C ２ MXene-Based Sensors with High Selectivity for NH ３ Detection at Room Temperature”, ACS Sens., 2019, Volume 4, p.2763-2770 D11: “Enhanced ammonia sensing response based on Pt-decorated Ti ３ C ２ T ｘ / TiO ２ "Composite at room temperature," Nanotechnology, 2023, Vol. 34, 205501

[0032] In the gas species detection method of the present invention, the maxines of the same type but with different gas responsiveness preferably include a maxine whose electrical resistance increases upon contact with gas species X and a maxine whose electrical resistance decreases upon contact with gas species X. Gas species X may be one of the specific gas species. When there are multiple specific gas species, one of the specific gas species is gas species X, and when there is only one specific gas species, the specific gas species itself is gas species X. In the gas species detection method of the present invention, gas species X is preferably a gas selected from hydrogen gas, hydrogen sulfide gas, ammonia gas, ethanol gas, acetone gas, toluene gas, and nitrogen dioxide gas.

[0033] The gas sensor itself used in the gas species detection method of the present invention can be obtained by a conventional method. For example, Maxine is added to a solvent such as ethanol and dispersed ultrasonically to prepare a slurry. A comb-shaped electrode sheet is then placed on a heated magnetic stirrer set to 70 to 120°C, and the slurry is dropped onto the comb-shaped electrode using a pipette or the like so that it spreads evenly over the comb-shaped electrode. The dropped slurry is then dried in a drying oven at 60 to 100°C to remove the solvent, thereby obtaining a gas sensor. The gas species detection method of the present invention typically uses two or more gas sensors, each containing one Maxine. More specifically, it is preferable that the gas-responsive materials of the two or more gas sensors contain Maxine molecules with different gas responsiveness.

[0034] In the gas species detection method of the present invention, contact between the target gas and the multiple gas sensors can be achieved by allowing the target gas to reach the gas sensors by natural diffusion. Contact between the multiple gas sensors and the target gas can be achieved at 10 to 50°C. Furthermore, in the gas species detection method of the present invention, the detectable concentration of a specific gas species in the target gas varies depending on the gas species and the maxine used, but gas species can be detected in the range of, for example, 1 to 700 ppm.

[0035] [Disease Detection Method] As described above, the gas species detection method of the present invention can be applied to disease detection. That is, according to the present invention, there is provided a disease detection method that includes detecting the presence or absence of a specific gas species using the gas species detection method of the present invention and detecting the presence or absence of a disease associated with the presence of the specific gas species. Examples of the disease include abnormalities of intestinal anaerobic bacteria, colon polyps, liver cirrhosis, diabetes, cancer, and asthma.

[0036] Below, we will introduce an example of the excellent properties of Maxin's gas-responsive material, Nb ２ CT ｘ , Nb synthesized by the molten salt method ２ CT ｘ Nb synthesized by the molten salt method and terminal functional group control ２ CT ｘThe test results are shown below as an example. This example does not represent a specific embodiment of the present invention, but experimentally demonstrates the properties of one example of Maxine that can be used in the present invention. The present invention should not be construed as being limited by the following examples except as defined in the present invention. Note that room temperature means 20 to 30°C, min means minutes, and wt% means mass %.

[0037] Synthesis example 1: Nb ２ CT ｘ Synthesis of Maxine Nb ２ A powder of AlC (98%, 400 mesh, manufactured by Jilin 11 Technology Co., Ltd.) was subjected to a hydrothermal-assisted in-situ HF etching process or an HF-based etching process using one of the following fluorine solutions: (Fluorine Solution) NH ４ F + HCl:H ２ 30 mL of HCl, 10 mL of an aqueous HCl solution (35 to 37% by mass, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and NH ４ LiF+HCl:H ２ The sample consisted of 30 mL of HF, 10 mL of an aqueous HCl solution (35-37% by mass, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and 3 g of LiF (99.0% by mass or more, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.). HF: The sample consisted of 30 mL of an aqueous HF solution (46-48% by mass, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.). Specifically, Nb ２ 2 g of AlC powder was added to the fluorine solution and stirred at room temperature for 30 minutes, and then the mixture was placed in a Teflon-lined stainless steel autoclave. ４ When LiF+HCl or LiF+HCl was used, the mixture was kept at 180°C for 24 hours, and when HF was used, the mixture was kept at 35°C for 72 hours, and then naturally cooled to room temperature. The obtained powder was then washed with 6M HCl and deionized water, and centrifuged several times until the pH value was 6 or higher. Finally, the powder was washed with ethanol, and the precipitate obtained by filtration was vacuum dried at 60°C overnight to obtain a sample. In the following description related to Synthesis Example 1, the sample prepared using LiF+HCl was converted to LiF-Nb by hydrothermal-assisted in-situ HF etching. ２ CTｘ , N.H. ４ The sample prepared using F + HCl was ４ F-Nb ２ CT ｘ The samples prepared by etching using HF are called HF-Nb ２ CT ｘ and are called respectively.

[0038] (Identification) The obtained samples were identified using an X-ray diffractometer (XRD, Bruker, D2 Phaser). The morphology, microstructure, and state of the surface terminal functional groups were examined using a field emission scanning electron microscope (FE-SEM, JSM-7800F, JEOL Ltd.) equipped with an energy dispersive X-ray spectrometer (EDS). The crystalline phase was determined using a high-resolution transmission electron microscope (HRTEM, EM-002B, TOPCON Corporation). Furthermore, X-ray photoelectron spectroscopy (XPS, PHI5600, ULVAC-PHI) was performed using a focused monochromatic Al Kα (200 W) 20 eV X-ray source. The binding energy was based on the C1s peak at 284.8 eV on the irregular carbon surface to correct for shifts due to charge effects. The samples obtained in the following Synthesis Examples 2 to 4 were also identified based on the description in this paragraph.

[0039] In FIG. ２ AlC, LiF-Nb ２ CT ｘ , N.H. ４ F-Nb ２ CT ｘ and HF-Nb ２ CT ｘ After etching, the XRD pattern of Nb ２ The peak of AlC disappears, and the two-dimensional layered compound Nb ２ CT ｘ The characteristic (002) peak of LiF—Nb ２ CT ｘ At 2θ = 7.05°, NH ４ F-Nb ２ CT ｘ At 2θ=7.22° and HF-Nb ２ CT ｘ and 2θ = 8.61°.４ F-Nb ２ CT ｘ AlF was identified as an impurity in the vicinity of 2θ=25°. ３ It is known that LiF—Nb precipitates depending on the ionic strength in the solution. ２ CT ｘ , N.H. ４ F-Nb ２ CT ｘ and HF-Nb ２ CT ｘ shows a typical accordion-type structure of maxine, and furthermore, the LiF—Nb ２ CT ｘ The HRTEM image and electron diffraction pattern of the LiF-Nb alloy confirmed that it exhibited a typical hexagonal crystal structure and interlayer spaces. ２ CT ｘ , N.H. ４ F-Nb ２ CT ｘ and HF-Nb ２ CT ｘ In both cases, Nb ２ CT ｘ It was confirmed that this is the case.

[0040] In addition, EDS analysis was performed to compare the influence of the etching solution (fluorine solution) on the surface state and the presence or absence of impurities. ２ CT ｘ and N.H. ４ F-Nb ２ CT ｘ The secondary electron image (SEI) and elemental mapping of the sample are shown in Table 1, and the results of elemental analysis of the sample surface are shown in Table 2.

[0041]

[0042] From FIG. 4 and Table 1, LiF—Nb ２ CT ｘ The difference in the ratio of Cl is NH ４ F-Nb ２ CT ｘ The ratio of O, Al and F is 1.08 wt% between them, which is about the same ratio, while the ratio of O, Al and F is NH ４ F-Nb ２ CTｘ It was shown that the surface element concentration differs depending on the etching solution. ４ F-Nb ２ CT ｘ Regarding the points with high O concentration on the surface of ４ In the hydrothermal-assisted etching method using F + HCl, many O / -OH groups were formed on the surface as a result of hydrolysis based on the above-mentioned chemical reaction formula (4), and the residual adsorbed H ２ The presence of O or Nb oxidized at high temperature during synthesis ２ CT ｘ This may suggest the presence of Nb-oxides due to NH ４ Because F has a relatively high solubility, it can be etched in a shorter time than LiF, even at a relatively low temperature. If the etched material is exposed to a hydrothermal environment for a long time, oxidation of the surface may progress. In addition, because it contains a large amount of Al and F, AlF is present as an impurity. ３ The formation of LiF—Nb ２ CT ｘ The results of XPS analysis are shown in FIG. ４ F-Nb ２ CT ｘ As shown in Figures 5 and 6, the results of XPS analysis of LiF-Nb ２ CT ｘ and N.H. ４ F-Nb ２ CT ｘ In any of the above, Nb ２ CT ｘ It was shown that the surface of the NH ４ F-Nb ２ CT ｘ In the O1s region of the XPS spectrum, residual adsorbed H ２ O was detected. ４ F-Nb ２ CT ｘ is LiF-Nb ２ CT ｘ Etching starts earlier (at a lower temperature) than H ２This is thought to be due to the long exposure time to oxidizing species in the form of O. Thus, the results of the XPS analysis were in good agreement with the results of the elemental mapping analysis.

[0043] (Fabrication and Analysis of Gas Sensing Device) As shown in the schematic diagram in Figure 16(a), 10 mg of sample was added to 200 µL of ethanol and dispersed by ultrasonic waves. The interdigitated electrode sheet was placed on a heated magnetic stirrer set at 70 °C, and 15 µL of the slurry was pipetted onto the interdigitated electrode (area 55 mm2). ２ ) was dropped onto the electrode. Once the slurry had spread over the electrode, the next 15 μL was dropped. After all the slurry had been dropped, the dropped slurry was dried overnight in a drying oven at 60°C to prepare a gas sensor, which was then fixed to the chamber for the gas sensing device. The gas sensing properties of the sample were evaluated using a data collection device (Agilent 34970A, manufactured by Agilent Technologies) by the two-point probe method. H ２ Gas, H ２ S gas, NH ３Various target gases containing gases such as ethanol, acetone, or toluene (target gases) at predetermined concentrations in room-temperature dry air (base gas) were introduced into the sensor device for each gas type, and the sensor's response and selectivity to each target gas in room-temperature dry air were measured. Specifically, room-temperature dry air (base gas) and a target gas mixture of the target gas and room-temperature dry air (base gas) to a predetermined concentration were flowed at a total flow rate of 200 mL / min. The target gas concentration was calculated from the target gas flow rate during the 200 mL / min flow rate. The target gas injection time was 10 minutes, with a 10-minute interval for reintroducing the air atmosphere. During this interval, the target gas was not flowed, and only room-temperature dry air (base gas) was flowed. The gas detection response ΔR was calculated from the following formula (A) as the ratio of the electrical resistance (Ra) of the sensor in dry air at room temperature immediately before the flow of each concentration of the target gas to the electrical resistance (Rg) of the sensor in a mixed gas of dry air at room temperature and the target gas: ΔR={(Rg-Ra) / Ra}×100% Formula (A) The gas detection response reproducibility Rr was calculated from the following formula (B): Rr={(ΔRn-ΔRi) / ΔRi}×100% Formula (B) In the above formula, ΔRi is the initial electrical resistance, and ΔRn is the electrical resistance at the time of cycling. The recovery time (t ｒｅｃ The recovery time was defined as the time required for the sensor resistance to recover to within ±10% of the baseline resistance. The fabrication and analysis of gas sensing devices for the samples obtained in the following Synthesis Examples 2 to 4 were also carried out based on the description in this paragraph.

[0044] - Evaluation of gas responsiveness - Among the above samples, LiF-Nb, which has the widest interplanar spacing, ２ CT ｘ The gas sensing performance of the SiO2 nanoparticles was evaluated in the presence of a target gas in dry air at room temperature. The gas response results are shown in Figure 7. As shown in Figure 7(a), H ２ When gas was passed through the electrode, the electrical resistance increased. The gas detection response ΔR was calculated using the above formula (A). ２ CT ｘAfter 10 minutes of exposure to the target gas, the response values ​​showed positive responses to all six gases: hydrogen gas, hydrogen sulfide gas, ammonia gas, ethanol gas, acetone gas, and toluene gas. The gas detection response ΔR increased with increasing gas concentration (Fig. 7(b)). This is because carrier transport was inhibited by gas adsorption, and Nb ２ CT ｘ This is due to an increase in the electrical resistance of ２ The gas was detected at the lowest concentration (0.5 ppm) of the six gases mentioned above (Fig. 7(b)). When exposed to the gas concentration (10 ppm), LiF-Nb ２ CT ｘ showed the highest response to ammonia gas compared to ethanol, toluene, and acetone gases (Figure 7(c)). When exposed to a gas concentration of 50 ppm, the sensor responded to toluene and acetone gases but not significantly to ethanol gas (Figure 7(d)). When gases of the same concentration were added four times, responses were observed that were less than 15% different from the initial response, except for ammonia gas, demonstrating its applicability as a gas sensor with reasonable reproducibility (Figure 7(e)). Note that the recovery time is required for the sensor resistance to recover to within ±10% of the baseline resistance (Figure 7(a)). The average recovery times for four cycles at the maximum gas concentration shown in Figure 7(b) were 21, 28, 35, and 27 seconds for hydrogen gas, hydrogen sulfide gas, toluene gas, and acetone gas, respectively. For ethanol gas, the response did not recover even after 10 minutes. This rapid response recovery is due to physical adsorption rather than chemical adsorption, suggesting that electrical conduction is significantly affected by physical adsorption. If detection is possible through physical adsorption, the recovery time required for the gas sensor is short, and it can be used sufficiently for repeated gas species detection measurements. ２ CT ｘ It has been reported that Nb exhibits metallic behavior, and the electrical resistance values ​​obtained in this study are relatively high (Fig. 7(a)). This is due to the presence of Nb on the surface, as shown by XPS. ２ O ５ Therefore, the LiF—Nb obtained as above ２ CT ｘ is Nb２ CT ｘ and Nb ２ O ５ This point is considered to be a composite of Nb. ２ O ５ is an n-type semiconductor with a work function of 4.0 eV. ２ CT ｘ The terminal functional groups (terminations) on the surface of Nb control the work function of the maxine. ２ CT ｘ All surfaces of T were covered with —OH groups (i.e., T ｘ are all —OH) Nb ２ CT ｘ The work function of LiF—Nb is 2.5 eV, and the work function increases as the ratio of the surface substituted with functional groups other than —OH increases relative to this maximum. ２ CT ｘ is Nb ２ CT ｘ In-situ grown Nb on the surface ２ O ５ The presence of nanoparticles allows electrons to ２ CT ｘ From the conduction band of n-type Nb ２ O ５ As a result, both (Nb ２ CT ｘ and Nb ２ O ５ ) a Schottky barrier and a depletion layer are formed at the interface. The existence of the depletion layer and the Schottky barrier is due to the ２ CT ｘ hinders the movement of charge carriers in LiF—Nb ２ CT ｘ In order to increase the electrical resistance of the LiF—Nb ２ CT ｘ It is thought that the electrical resistance value of

[0045] Synthesis example 2: Nb ２ CT ｘ Synthesis of Maxine Nb ２A powder of AlC (98%, 400 mesh, manufactured by Jilin 11 Technology Co., Ltd.) was subjected to hydrothermal-assisted in-situ HF etching using one of the following fluorine solutions: (Fluorine Solution) NH ４ F + HCl:H ２ 30 mL of HCl, 10 mL of an aqueous HCl solution (35 to 37% by mass, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and NH ４ LiF+HCl:H ２ The solution was composed of 30 mL of fluorine dioxide, 10 mL of an aqueous HCl solution (35 to 37% by mass, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and 3 g of LiF (99.0% by mass or more, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.). Specifically, the fluorine solution was stirred at room temperature for 30 minutes to homogenize the components in the solution, and then Nb ２ 2 g of AlC powder was added, and the mixture was stirred at room temperature for another 10 minutes, and then sealed in a Teflon (registered trademark)-lined stainless steel autoclave. After being held at a predetermined temperature of 180 to 200°C for 24 hours, it was naturally cooled (allowed to cool) to room temperature. The obtained powder was then washed with 6M HCl and deionized water, and centrifuged several times until the pH value reached 6 or higher. Finally, the powder was washed with ethanol, and the precipitate obtained by filtration was vacuum-dried at 60°C overnight or freeze-dried in vacuum to obtain a sample. In the following description related to Synthesis Example 2, the sample prepared using LiF+HCl was referred to as LiF-Nb ２ CT ｘ , N.H. ４ The sample prepared using F + HCl was ４ F-Nb ２ CT ｘ 8, 10 and 11, the sample prepared using LiF+HCl is referred to as LiF, NH ４ The sample prepared using F + HCl was ４ These are written as F, respectively.

[0046] (Identification) In FIG. ２ AlC, LiF-Nb ２ CT ｘ , N.H. ４ F-Nb ２ CT ｘand HF—Nb obtained in Synthesis Example 1 above. ２ CT ｘ After etching, the XRD pattern of Nb ２ The peak of AlC disappears, and the two-dimensional layered compound Nb ２ CT ｘ The characteristic (002) peaks of the respective samples were observed at low angles of 2θ = 10° or less. ２ CT ｘ NH ４ F is NH ４ F-Nb ２ CT ｘ HF is HF-Nb ２ CT ｘ ), the heating temperature and heating time in the autoclave (HF-Nb ２ CT ｘ The usual heating reaction conditions are listed below, followed by the drying conditions (vacuum means vacuum drying at 60°C, and freeze means vacuum freeze drying). For example, the top XRD pattern is LiF-Nb ２ CT ｘ This means that the sample was autoclaved at 180°C for 24 hours and vacuum dried at 60°C. SEM observation confirmed that the sample exhibited an accordion-type structure typical of Maxine. From these results, the obtained LiF-Nb ２ CT ｘ and N.H. ４ F-Nb ２ CT ｘ In both cases, Nb ２ CT ｘ It was confirmed that this is the case.

[0047] In addition, EDS analysis was performed to compare the influence of the etching solution (fluorine solution) on the surface state and the presence or absence of impurities. ２ CT ｘ and N.H. ４ F-Nb ２ CT ｘThe secondary electron image (SEI) and elemental mapping of the LiF—Nb sample (autoclaved at 180° C. for 24 hours and dried in a vacuum at 60° C.) are shown in FIG. 9, as well as the results of elemental analysis of the sample surface. ２ CT ｘ is NH ４ F-Nb ２ CT ｘ The ratio of Cl is about the same, while the ratios of O, Al, and F are relatively low, indicating that the element concentrations on the surface differ depending on the etching solution. ２ CT ｘ 10(b) to 10(d) show the high-resolution spectrum of the O1s region and the results of Gaussian fitting of the spectrum of LiF—Nb ２ CT ｘ , N.H. ４ F-Nb ２ CT ｘ (autoclaved at 180°C for 24 hours, dried in vacuum at 60°C), NH ４ F-Nb ２ CT ｘ (autoclaved at 180°C for 24 hours, then vacuum freeze-dried). ４ In the example using F+HCl solution, the H on the surface was removed by freeze-drying. ２ It was found that the residual O was suppressed.

[0048] - Nb ２ CT ｘ Gas detection devices were prepared in the same manner as in Synthesis Example 1 above, and analyses were carried out in the same manner as in Synthesis Example 1 above, except for the matters described below. ２ CT ｘ and N.H. ４ F-Nb ２ CT ｘThe gas sensing performance of the LiF-Nb electrode (autoclaved at 180°C for 24 hours, freeze-dried) was evaluated at room temperature in air using various gases containing target gases (ammonia gas or acetone gas) at predetermined concentrations in room temperature dry air (base gas) as the target gas. The results of gas response to 12 ppm ammonia gas and 50 ppm acetone gas are shown in Figure 11. As shown in Figure 11, the response value after 10 minutes of exposure to the target gas was 1.0 MPa. ２ CT ｘ showed a positive response to both ammonia gas and acetone gas, whereas NH ４ F-Nb ２ CT ｘ (autoclaved at 180°C for 24 hours, freeze-dried in vacuum) showed a negative response to ammonia gas and a positive response to acetone gas.

[0049] Synthesis example 3: Nb ２ CT ｘ Synthesis of Maxine Nb ２ A powder of AlC (98%, 400 mesh, manufactured by Jilin 11 Technology Co., Ltd.) was subjected to etching treatment by the molten salt method. ２ AlC:CuCl ２ The mixture was mixed in a molar ratio of 1:3:2:2, transferred to an alumina crucible, and kept at 750°C in an Ar atmosphere for 5 hours, and then allowed to cool naturally (stand to cool) to room temperature. Then, a 0.5M aqueous solution of ammonium persulfate was added to convert Cu to Cu. ２＋ The resulting powder was centrifuged at 12,000 rpm for 3 minutes and washed several times with deionized water and ethanol. After washing, it was washed several times with ethanol and dried overnight in vacuum at 60°C to obtain a sample. ２ A powder of AlC (98%, 400 mesh, manufactured by Jilin 11 Technology Co., Ltd.) was subjected to hydrothermal-assisted in-situ HF etching treatment using the following fluorine solution: (Fluorine Solution) NH ４ F + HCl:H ２ 10 mL of HCl solution (9 M, Fujifilm Wako Pure Chemical Industries, Ltd.) and 30 mL of NH ４2 g of F (97.0 mass % or more, manufactured by Kanto Chemical Co., Ltd.). ２ 1 g of AlC powder was added to the fluorine solution and stirred at room temperature for 10 minutes, then sealed in a Teflon-lined stainless steel autoclave, kept at 180°C for 24 hours, and then naturally cooled (cooled) to room temperature. The obtained powder was then washed with 6M HCl and deionized water, and centrifuged several times until the pH value reached 6 or more. Finally, the powder was washed with ethanol, and the precipitate obtained by filtration was vacuum-dried at 60°C overnight to obtain a sample. In the following description related to Synthesis Example 3, the sample prepared by etching using the molten salt method was treated with Nb ２ CT ｘ (molten salt method), NH ４ The sample prepared using F + HCl was ４ F-Nb ２ CT ｘ 12 to 14, the samples prepared by etching using the molten salt method are referred to as molten salt method and NH ４ The samples prepared using F+HCl are referred to as In situ HF.

[0050] (Identification) In FIG. ２ AlC, Nb ２ CT ｘ (molten salt method) and NH ４ F-Nb ２ CT ｘ The XRD pattern of the Nb (in situ) was obtained by etching. ２ The peak of AlC disappears, and the two-dimensional layered compound Nb ２ CT ｘ The characteristic (002) peaks of the respective XRD patterns were observed at low angles of 2θ=10° or less. The upper right corner of each XRD pattern in FIG. 12 indicates the type of sample (In situ HF, NH ４ F-Nb ２ CT ｘ (In situ), and the molten salt method is Nb ２ CT ｘ (molten salt method). ２ CT ｘ (molten salt method) and NH４ F-Nb ２ CT ｘ In both cases, SEM observation confirmed that the accordion-type structure typical of maxine was observed. ２ CT ｘ (molten salt method) and NH ４ F-Nb ２ CT ｘ (In situ) are all Nb ２ CT ｘ It was confirmed that this is the case.

[0051] The results of XPS analysis to compare the surface state and the presence or absence of impurities are shown in FIG. ４ F-Nb ２ CT ｘ In the in situ study, peaks of F1s and FKLL were observed, indicating the presence of F groups on the sample surface. ２ CT ｘ In the molten salt method, no peaks due to F were observed, indicating that no F groups were present on the sample surface.

[0052] - Nb ２ CT ｘ A gas detection device was prepared in the same manner as in Synthesis Example 1 above, and analysis was carried out in the same manner as in Synthesis Example 1 above, except for the matters described below. ２ CT ｘ (molten salt method) and NH ４ F-Nb ２ CT ｘ The gas sensing performance of the in situ gas sensor was evaluated at room temperature in dry air using various analyte gases, each containing a target gas (ammonia gas or acetone gas) at a predetermined concentration in room temperature dry air (base gas). The analyte gas was injected for 15 minutes, with a 15-minute interval between each gas injections to reintroduce the air atmosphere. During this interval, the analyte gas was not flowed, and only room temperature dry air was flowed. The gas response results obtained are shown in Figure 15. The response value after exposing the sample to the analyte gas for 15 minutes was NH ４ F-Nb２ CT ｘ (In situ) showed a negative response to both ammonia gas and acetone gas (Figs. 15(a) and (b)), and Nb ２ CT ｘ The molten salt method also showed a negative response to both ammonia gas and acetone gas (FIGS. 15(c) and (d)).

[0053] Synthesis example 4: Nb ２ CT ｘ Synthesis of Maxine Nb ２ A powder of AlC (98%, 400 mesh, manufactured by Jilin 11 Technology Co., Ltd.) was subjected to etching treatment by a molten salt method, and then terminal functional groups were controlled using hydrofluoric acid. ２ AlC:CuCl ２ The mixture was mixed in a molar ratio of 1:3:2:2, transferred to an alumina crucible, and kept at 750°C in an Ar atmosphere for 5 hours, and then allowed to cool naturally (stand to cool) to room temperature. Then, a 0.5M aqueous solution of ammonium persulfate was added to convert Cu to Cu. ２＋ The powder was oxidized to 1000 rpm, and the resulting powder was centrifuged at 12,000 rpm for 3 minutes and immersed in an aqueous HF solution (terminal functional group control). After terminal functional group control using the aqueous HF solution, the powder was washed several times with ethanol and vacuum dried overnight at 60°C to obtain a sample. The aqueous HF solution used had a concentration of 5 mass%, 16 mass%, 34 mass%, or 43 mass%. Also, a sample was prepared by etching using HF. Specifically, Nb ２ 1 g of AlC (98%, 400 mesh, manufactured by Jilin 11 Technology Co., Ltd.) powder was added to a 43% by mass HF aqueous solution, stirred at 70°C for 5 days, and then naturally cooled (allowed to cool) to room temperature. The obtained powder was then washed with deionized water and centrifuged several times until the pH value reached 6 or higher. Finally, the powder was washed with ethanol and filtered to obtain a precipitate, which was then vacuum dried overnight at 60°C to obtain a sample. In the following description related to Synthesis Example 4, a sample prepared by etching using the molten salt method and controlling the terminal functional groups with hydrofluoric acid was used to prepare a Nb ２ CTｘ (MS-HF), the sample prepared by etching using HF was Nb ２ CT ｘ 17 to 22, the samples prepared by etching using the molten salt method and then controlling the terminal functional groups using hydrofluoric acid are referred to as MS (HF 5 wt%), MS (HF 16 wt%), MS (HF 34 wt%), and MS (HF 43 wt%), respectively, depending on the concentration of the hydrofluoric acid aqueous solution, and the sample prepared by etching using HF is referred to as HF Etching. Note that MS (HF 0 wt%) refers to a sample prepared without controlling the terminal functional groups using an HF aqueous solution after the etching using the molten salt method. Specifically, the samples were prepared in the same manner except that immersion in an HF aqueous solution (controlling the terminal functional groups) was not performed after the etching using the molten salt method.

[0054] (Identification) In FIG. ２ AlC, Nb ２ CT ｘ (MS-HF) and Nb ２ CT ｘ The XRD pattern of Nb (HF) is shown. The type of sample is indicated at the top right of each XRD pattern in Figure 17. ２ The peak of AlC disappears, and the two-dimensional layered compound Nb ２ CT ｘ The characteristic (002) peak of Nb ２ CT ｘ (MS-HF) and Nb ２ CT ｘ In both cases, the lattice angle was observed at a low angle of 2θ=10° or less. ２ CT ｘ In the case of (MS-HF), regardless of the concentration of the hydrofluoric acid solution, Nb ２ CT ｘ A characteristic (002) peak of Nb ２ CT ｘ (MS-HF) interplanar spacing (d ｉｎｔｅｒ ) was 8.9 Å. ２ CT ｘXRD pattern of (MS-HF) and Nb ２ CT ｘ From the comparison with the XRD pattern of (HF), Nb ２ CT ｘ (MS-HF) is Nb ２ CT ｘ It can be seen that the impurities are less than those of Nb (HF). ２ CT ｘ (MS-HF) and Nb ２ CT ｘ In both cases, Nb (HF) was observed by SEM. ２ The gap structure between layers (the structure indicated by the arrow in Figure 18) was observed, which is evidence of Al being removed from AlC, and it was confirmed that Maxine exhibited a typical accordion-type structure. ２ CT ｘ (MS-HF) and Nb ２ CT ｘ (HF) is Nb ２ CT ｘ It was confirmed that this is the case.

[0055] Nb ２ CT ｘ As the analysis results of the terminal functional groups on the surface of Maxine (MS-HF), the observation results of the F1s peak by XPS analysis are shown in Figure 19, the results of the XPS quantitative analysis are shown in Table 2, and the results of the quantitative analysis by SEM EDS are shown in Figure 20. As shown in Figure 19, the Nb ２ CT ｘ (MS-HF) in which the concentration of hydrofluoric acid in aqueous solution is 34 mass % ２ CT ｘ (MS-HF 34 wt%) and Nb with a hydrofluoric acid aqueous solution concentration of 43 mass% ２ CT ｘIn the case of (MS-HF 43 wt%), an F1s peak was observed (MS (HF 34 wt%) and MS (HF 43 wt%) in Figure 19). This indicates that by performing the terminal functional group control operation using hydrofluoric acid on the etched product of Maxin obtained by the molten salt method, F groups could be introduced as terminal functional groups on the Maxin surface. Furthermore, the results of quantitative analysis by SEM EDS shown in Figure 20 indicate that the Nb ２ CT ｘ (MS-HF 0 wt%) and Nb ２ CT ｘ In the MS-HF 43 wt % (MS-HF 43 wt %), F was observed as a terminal functional group, and the ratio of Cl as a terminal functional group also increased (MS (HF 43 wt %) versus MS (HF 0 wt %) in FIG. 20). From this result, it was found that the terminal functional group (T ｘ ) and increasing the content ratio of halogen-based terminal functional groups (F and Cl) constituting the terminal functional groups (T ｘ The results of the XPS quantitative analysis shown in Table 2 show that the ratio of F in the total of F and O / OH is 0% by mass in the Nb ２ CT ｘ (MS-HF 0 wt%) and Nb ２ CT ｘ It was shown that the concentration of the terminal functional group (T) was higher in MS (43 wt%) than in MS (0 wt%) (MS (43 wt%) in Table 2). Thus, the results of the XPS quantitative analysis were in agreement with the results of the SEM EDS quantitative analysis. ｘ ) tendencies in the ratios of the atoms that make up the crystals were generally consistent.

[0056]

[0057] - Nb ２ CT ｘA gas detection device was prepared in the same manner as in Synthesis Example 1 above, and analysis was carried out in the same manner as in Synthesis Example 1 above, except for the matters described below. ２ CT ｘ (MS-HF 0 wt%) and Nb with a hydrofluoric acid aqueous solution concentration of 43 mass% ２ CT ｘ (MS-HF 43 wt%) and Nb as a reference example ２ CT ｘ The gas sensing performance of (HF) was evaluated by measuring the target gas (ammonia gas or acetone gas) with N ２ The gases contained in the gas (base gas) at predetermined concentrations were used as the various analysis target gases. ２ Gas is used, N ２ The analysis was performed at room temperature in N gas. ２ A 20-minute interval was allowed for the reintroduction of the gas atmosphere. During this interval, the analyte gas was not flowing, and N ２ Only the base gas was flowed. The initial electrical resistance (ΔRi) was measured for the Nb ２ CT ｘ (HF) is 226kΩ, Nb ２ CT ｘ (MS-HF 43 wt%) is 2.93 kΩ, Nb ２ CT ｘ (MS-HF 0 wt%) is 6.58 MΩ, and in the case of ammonia gas sensing, Nb ２ CT ｘ (HF) is 272kΩ, Nb ２ CT ｘ (MS-HF 43 wt%) is 2.97 kΩ, Nb ２ CT ｘ The gas response results obtained are shown in Figures 21 to 23. After exposing the sample to the target gas for 20 minutes, the response value was 11.7 MΩ. ２ CT ｘ (MS-HF 0 wt%) showed a negative response to both ammonia gas and acetone gas, and Nb２ CT ｘ (MS-HF 43 wt%) and Nb ２ CT ｘ (HF) showed a positive response to both ammonia gas and acetone gas (as shown in the enlarged view of FIG. 22, Nb ２ CT ｘ (HF) showed a positive response to acetone gas at a concentration of 20 ppm or more. Furthermore, Nb SiO 2 ... ２ CT ｘ (MS-HF 34 wt%) also contains Nb ２ CT ｘ It is believed that, like MS-HF 43 wt%, it shows a positive response to both ammonia gas and acetone gas. Thus, the Nb MAXINs with the same interplanar spacing obtained by the same etching treatment using the molten salt method, but differing in the presence or absence of terminal functional group control using hydrofluoric acid, are ２ CT ｘ (MS-HF 0 wt%) and Nb ２ CT ｘ (MS-HF 43 wt%), the terminal functional group (T ｘ It was shown that the composition ratio of functional groups constituting the SiO2 (particularly the content ratio of halogen-based terminal functional groups (F and Cl)) may be significantly involved in gas responsiveness.

[0058] [Gas species detection method] LiF—Nb prepared in Synthesis Example 1 ２ CT ｘ (Nb ２ CT ｘ and Nb ２ O ５ The composite (hydrothermal-assisted in-situ HF etching treatment) showed a positive response to all six gases: hydrogen gas, hydrogen sulfide gas, ammonia gas, ethanol gas, acetone gas, and toluene gas. ４ F-Nb ２ CT ｘThe Nb SiO2 nanoparticles prepared in Synthesis Example 3 (hydrothermal-assisted in-situ HF etching, autoclaving at 180°C for 24 hours, and vacuum freeze-drying) showed a negative response to ammonia gas and a positive response to acetone gas. ２ CT ｘ (molten salt method) and NH ４ F-Nb ２ CT ｘ (In situ) showed a negative response to ammonia gas and acetone gas. ２ CT ｘ (MS-HF 43 wt%) and Nb ２ CT ｘ (HF) showed a positive response to ammonia gas and acetone gas, and the Nb ２ CT ｘ (MS-HF 0 wt%) showed a negative response to ammonia gas and acetone gas. Therefore, it can be used to detect the presence or absence of specific gas species by combining it with Maxine Nb, which has a different gas response from the Maxine Nb reported so far, or by combining it with the Maxine Nb obtained in each of the synthesis examples above. ２ CT ｘ As a gas type detection method by combining the above, the presence or absence of at least one gas selected from hydrogen sulfide gas, ammonia gas, acetone gas, etc. can be detected by the following combination.

[0059] For example, LiF—Nb prepared in Synthesis Example 1 ２ CT ｘ (Nb ２ CT ｘ and Nb ２ O ５ (composite of Nb as described in D1 above, hydrothermal assisted in-situ HF etching treatment) ２ CT ｘ Although it is the same type of maxine as (HF), it shows a different response to hydrogen sulfide gas. ２ CT ｘ (Nb ２ CT ｘ and Nb２ O ５ The composite (hydrothermal-assisted in-situ HF etching treatment) exhibits increased electrical resistance, and the Nb ２ CT ｘ (HF) reduces electrical resistance.

[0060] In addition, although it is the same type of maxine, the LiF—Nb ２ CT ｘ (Nb ２ CT ｘ and Nb ２ O ５ (composite, hydrothermal-assisted in-situ HF etching treatment), Nb prepared in Synthesis Example 4 ２ CT ｘ (MS-HF 43 wt%) and Nb ２ CT ｘ (HF) and Nb as described in D2 above ２ CT ｘ (HF) increases the electrical resistance, and NH ４ F-Nb ２ CT ｘ (Hydrothermal-assisted in-situ HF etching treatment, autoclaving at 180°C for 24 hours, freeze-drying in vacuum), Nb prepared in Synthesis Example 3 ２ CT ｘ (molten salt method) and NH ４ F-Nb ２ CT ｘ (In situ) Nb prepared in Synthesis Example 4 ２ CT ｘ (MS-HF 0 wt%), Nb as described in D1 above ２ CT ｘ (HF) and the Au / Nb described in D3 above ２ CT ｘ (Hydrothermal assisted in-situ HF etching process, HCl+LiF) reduces the electrical resistance.

[0061] In addition, although it is the same type of maxine, the LiF—Nb ２ CT ｘ (Nb ２ CT ｘ and Nb ２ O ５(a) a composite of (a) and (b) (b) (c) (d) (e) (f) (g) (h) (h) (i) (i) (ii) (iii) (iv) (iv) (iv) (v ... ４ F-Nb ２ CT ｘ (Hydrothermal-assisted in-situ HF etching treatment, autoclaving at 180°C for 24 hours, freeze-drying in vacuum), Nb prepared in Synthesis Example 4 ２ CT ｘ (MS-HF 43 wt%) and Nb ２ CT ｘ (HF) and Nb as described in D1 above ２ CT ｘ (HF) and Nb as described in D2 above ２ CT ｘ (HF) increases the electrical resistance, and Nb ２ CT ｘ (molten salt method) and NH ４ F-Nb ２ CT ｘ (In situ) and Nb prepared in Synthesis Example 4 ２ CT ｘ (MS-HF 0 wt %) reduces the electrical resistance.

[0062] While the present invention has been described in connection with embodiments thereof, we do not intend to limit our invention to any of the details of the description unless otherwise specified, and believe that the claims should be construed broadly without departing from the spirit and scope of the invention as set forth in the appended claims.

[0063] This application claims priority based on Japanese Patent Application No. 2024-086544, filed on May 28, 2024, the contents of which are incorporated herein by reference as part of the present specification.

Claims

1. A gas species detection method comprising contacting a plurality of gas sensors with a gas to be detected and detecting the presence or absence of a specific gas species in the gas to be detected based on the gas response patterns of the plurality of gas sensors, wherein the gas-responsive materials possessed by the plurality of gas sensors include MXene, each of which has a different gas response.

2. The gas species detection method according to claim 1, wherein two or more of the plurality of gas sensors have the same type of maxin, and the gas responsiveness of the same type of maxin is different from each other.

3. As the same type of maxine with different gas responsiveness, Nb ２ CT ｘ or Nb ２ CT ｘ 3. The method of claim 2, wherein the T ｘ indicates a terminal functional group.

4. V as the same type of maxine with different gas responsiveness ２ CT ｘ or V ２ CT ｘ 3. The method of claim 2, wherein the T ｘ indicates a terminal functional group.

5. As the same type of maxine with different gas responsiveness, Ti ３ C ２ T ｘ or Ti ３ C ２ T ｘ 3. The method of claim 2, wherein the T ｘ indicates a terminal functional group.

6. The same type of Nb with different gas responsiveness ２ CT ｘ or Nb ２ CT ｘ 4. The method for detecting a gas species according to claim 3, wherein at least one of the compounds is hydrothermally assisted etched or etched by a molten salt method.

7. A gas species detection method according to claim 2, wherein the maxins of the same type but with different gas responsiveness include a maxin whose electrical resistance increases upon contact with gas species X and a maxin whose electrical resistance decreases upon contact with said gas species X.

8. The gas species detection method according to claim 7, wherein the gas species X is a gas selected from the group consisting of hydrogen gas, hydrogen sulfide gas, ammonia gas, ethanol gas, acetone gas, toluene gas, and nitrogen dioxide gas.

9. The gas species detection method according to claim 8, wherein the plurality of gas sensors are brought into contact with the gas to be detected at 10 to 50°C.

10. A disease detection method, comprising detecting the presence or absence of a specific gas species using the gas species detection method according to any one of claims 1 to 9, and detecting the presence or absence of a disease associated with the presence of the specific gas species.

11. A method for producing maxine, which comprises introducing halogen-based terminal functional groups onto the surface of an etched maxine product obtained by the molten salt method.

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