A method for one-step preparation of ternary composite materials using microwave plasma, its products and applications

Abstract

This invention proposes a one-step microwave plasma method for preparing ternary composite materials, along with its products and applications, belonging to the field of gas-sensitive materials technology. The invention places two-dimensional MXene material in a microwave plasma device, then introduces a mixed gas (including oxygen and nitrogen) for microwave plasma treatment. This process simultaneously converts the metal elements in the two-dimensional MXene material into metal nitrides and metal oxides, generating an MXene-metal nitride-metal oxide ternary composite material in situ. The ternary composite material obtained by this invention can be further fabricated into a gas sensor for the detection of low-concentration nitrogen dioxide gas. It is suitable for monitoring in environmental or industrial safety fields, fully meeting the accuracy requirements for low-concentration gas detection in these areas, and is suitable for widespread application.

Description

Technical Field

[0001] This invention belongs to the field of gas-sensitive materials technology, and particularly relates to a method for preparing ternary composite materials in one step using microwave plasma, as well as its products and applications. Background Technology

[0003] Currently, metal-oxide-semiconductor (MOS) materials, characterized by high sensitivity, low cost, and simple functionality, are widely studied as core materials for VOCs sensors. Bhati et al. (VS Bhati, D. Sheela, B. Roul, et al., "NO2 gas sensing performance enhancement based on reduced graphene oxide decorated V2O5thin films,") Nanotechnology 30 (2019) prepared V₂O₅ thin films via DC sputtering and modified their surfaces with reduced graphene oxide (rGO) using a drop-coating method to construct rGO-modified V₂O₅ thin film composites. At 150°C, the composite material exhibited a maximum response of approximately 50.7% to 100 ppm nitrogen dioxide (NO₂). Miao et al. (J. Miao, C. Chen, L. Meng and YS Lin, "Self-Assembled Monolayer of Metal Oxide Nanosheet and Structure and Gas-Sensing Property Relationship,") ACS Sensors (4 (2019): 1279-1290) CuO and ZnO nanosheet monolayer sensors were prepared via a gas-water interface self-assembly method. Compared with thick-film sensors of the same materials, the CuO nanosheet monolayer sensor exhibited enhanced gas sensing performance for 5 ppm H2S at 250 °C, while the ZnO nanosheet monolayer sensor showed approximately 100% response to 10 ppm H2. Although metal oxide semiconductor (MOS) gas sensors possess excellent sensitivity, their operating temperatures are generally high (typically >100 °C, even up to 400 °C). This characteristic significantly limits their application in wearable sensing devices. Therefore, exploring a novel material that can achieve excellent sensing performance at relatively low temperatures has become an urgent issue to be addressed.

[0004] MXene materials, with their excellent electrical conductivity, hydrophilicity, mechanical strength, tunable work function, and abundant surface functional groups, have shown great application potential in the field of gas sensing. However, the original MXene materials suffer from problems such as simple structure and insufficient stability in oxygen-containing, humid, and light-exposed environments, which limit further improvement of their performance. In particular, their low response value restricts their application in practical sensors. Among them, Ti3C2T... x As a typical representative of MXene, its gas-sensing performance can be effectively controlled and improved through modification of surface terminal groups. Current research indicates that by modifying Ti3C2T... x Ti3C2(OH) was prepared by sequentially performing KOH alkalization treatment and Ar annealing (600℃, 5h) to produce oxygen-rich terminals (-O, -OH) and expanded interlayer spacing. x / Ti3C2O x Sensing materials capable of detecting Ti3C2T x Synergistic regulation of surface endpoints and interlayer structure. Therefore, for Ti3C2T x Targeted modification of functional groups to improve oxygen affinity is important and necessary.

[0005] As a highly efficient material surface manipulation technique, plasma treatment can interact with material surfaces through high-energy ions, electrons, and free radicals to achieve surface etching, defect manipulation, and functional group introduction, thereby improving the performance of gas-sensitive materials to a certain extent. This technique has been widely studied in metal oxides and two-dimensional material systems. However, existing research shows that the manipulation mechanisms of this type of method are mostly concentrated on surface defect construction or single functional group modification, typically only achieving simple structural optimization or constructing binary composite systems, and struggling to achieve synergistic interface manipulation between multiple components. Therefore, existing microwave plasma technology still has significant limitations in the construction of gas-sensitive materials. Based on this, developing a new method that can utilize microwave plasma to achieve in-situ synergistic transformation of multiple components and construct stable ternary composite structures is of great significance for overcoming the limitations of traditional binary systems and improving the performance of MXene-based gas-sensitive materials. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention proposes a one-step microwave plasma method for preparing ternary composite materials, along with its products and applications. This invention employs microwave oxygen-nitrogen plasma technology to treat two-dimensional MXene materials, aiming to reduce their surface fluorine content and introduce abundant oxygen-containing functional groups, thereby obtaining ternary composite materials with high oxygen and low fluorine functional group characteristics. This treatment method can effectively optimize the surface chemical state of the material, thereby significantly improving its gas-sensing performance and enabling the detection of nitrogen dioxide gas.

[0007] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a one-step microwave plasma method for preparing ternary composite materials, comprising the following steps: Two-dimensional MXene material is placed in a microwave plasma device, and then a mixed gas is introduced for microwave plasma treatment, so that the metal elements in the two-dimensional MXene material are simultaneously converted into metal nitrides and metal oxides, and an MXene-metal nitride-metal oxide ternary composite material is generated in situ. The mixed gas includes oxygen (O2) and nitrogen (N2).

[0008] Furthermore, the mixed gas is excited by microwave energy to generate corresponding plasma.

[0009] Furthermore, the microwave power of the microwave plasma treatment is 700W to 1200W, and the pressure is 200Pa to 500Pa.

[0010] Furthermore, the temperature of the microwave plasma treatment is 150℃~500℃, and the treatment time is 5min~60min.

[0011] Furthermore, the mixed gas comprises nitrogen with a volume fraction of 50-90% and oxygen with a volume fraction of 10-50%.

[0012] Furthermore, the two-dimensional MXene material is selected from one of Ti3C2, Ti2C, Ti2N, Nb2C, Nb3C4, Cr2C, Cr3C2, Ta2C, Ta4C3, V2C, and V3C2.

[0013] In the preparation method of this invention, microwave plasma, under specific power (700W~1200W) and low pressure environment (200Pa~500Pa), generates high-density, highly active oxygen and nitrogen particles, achieving directional bombardment and chemical modification of the material surface within a relatively low temperature range (150℃~500℃). During the control process, the active particles competitively substitute for the original fluorine functional groups on the MXene surface, gradually transforming them into oxygen-containing functional groups, thereby achieving a surface transformation from a "high fluorine, low oxygen" state to a "high oxygen, low fluorine" state. This treatment method is characterized by in-situ, high efficiency, and adjustable parameters. By controlling conditions such as gas composition (O2, N2) and treatment time (5min~60min), the chemical state and defect density of the MXene surface can be precisely adjusted. The increase in surface oxygen functional groups not only improves the surface activity of the material but also provides more active sites for gas adsorption and reaction, thus significantly enhancing its sensitive response to gases such as nitrogen dioxide.

[0014] The present invention also provides an MXene-metal nitride-metal oxide ternary composite material, which is prepared according to the above preparation method.

[0015] The present invention also provides a gas sensor comprising the above-mentioned MXene-metal nitride-metal oxide ternary composite material.

[0016] Furthermore, the preparation method of the gas sensor includes: mixing the MXene-metal nitride-metal oxide ternary composite material with an organic solvent, coating the resulting mixture onto an Al2O3 ceramic sheet containing platinum interdigitated electrodes, and obtaining the sensor after heat treatment.

[0017] Furthermore, the organic solvent is an ethanol solution, and the ratio of the MXene-metal nitride-metal oxide ternary composite material to the organic solvent is 1g:1.5mL.

[0018] Furthermore, the heat treatment temperature is 350–550°C, and the time is 8–12 hours.

[0019] The present invention also provides an application of the above-mentioned MXene-metal nitride-metal oxide ternary composite material or the above-mentioned gas sensor in the detection of nitrogen dioxide gas.

[0020] The MXene-metal nitride-metal oxide ternary composite material obtained through the above treatment can be used to construct high-performance gas sensors. After being mixed with an organic solvent, it is coated onto an Al2O3 platinum interdigitated electrode and stabilized through medium-temperature heat treatment (350–550℃, 8–12 h), ultimately forming a structurally stable gas sensing unit with optimized surface activity, achieving high-sensitivity detection of nitrogen dioxide gas.

[0021] Compared with the prior art, the present invention has the following advantages and technical effects: 1. This invention utilizes microwave plasma as an activation method. During the nitrogen plasma bombardment stage, abundant defects are generated on and inside the MXene surface, effectively increasing the material's specific surface area. During the oxygen plasma treatment stage, the system provides an oxygen-rich environment. At high temperatures, active oxygen species in the plasma competitively replace surface fluorine functional groups, gradually replacing them with oxygen-containing functional groups. This process increases the number of oxygen adsorption sites on the material surface, providing more oxygen active centers for gas-sensitive testing, thus significantly improving the material's gas-sensitive performance.

[0022] 2. The microwave oxygen-nitrogen plasma treatment method used in this invention is clean and environmentally friendly. The resulting two-dimensional MXene material has high selectivity and stability. It can respond well to 100 ppm nitrogen dioxide gas at 25°C, with a response value of 51.10%, a gas-sensitive response rate of 35.7, and a gas-sensitive recovery rate of 37.5.

[0023] 3. The gas sensor obtained by this invention can be used for the detection of low concentration nitrogen dioxide gas, and is suitable for monitoring in fields such as environmental or industrial safety. It can fully meet the accuracy requirements for low concentration gas detection in these fields and is suitable for widespread use. Attached Figure Description

[0024] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 The image on the left is a physical picture of the TiN-TiO2-Ti3C2 ternary composite material prepared in Example 1. The image on the right is (a) the original Ti3C2MXene material, (b) the two-dimensional layered Ti3C2 material after nitrogen microwave plasma treatment in Comparative Example 5, (c) the ternary composite material obtained in Example 1, and (d) the ternary composite material obtained in Example 3. Figure 2 The images show the infrared spectra of Ti3C2MXene after treatment in the examples and comparative examples, where Ti3C2 is the original Ti3C2MXene material, TiN2-Ti3C2 is the Ti3C2 material obtained in Comparative Example 1, TiN-TiO2-Ti3C2 is the ternary composite material obtained in Example 1, TiO2-Ti3C2 (80%) is the ternary composite material obtained in Example 2, TiO2-Ti3C2 (50%) is the ternary composite material obtained in Example 3, and TiO2-Ti3C2 (70%) is the ternary composite material obtained in Example 5. Figure 3 The response cycle curve of 100 ppm nitrogen dioxide gas tested at 25°C using the sensor in Example 1; Figure 4The images show the high-resolution XPS spectra of the processed Ti3C2MXene materials in the examples and comparative examples, where (a) is the Ti 2p spectrum of TiN2-Ti3C2 obtained in Comparative Example 1, (b) is the Ti 2p spectrum of the ternary composite material TiN-TiO2-Ti3C2 obtained in Example 1, (c) is the Ti 2p spectrum of the ternary composite material TiO2-Ti3C2 (80%) obtained in Example 2, (d) is the Ti 2p spectrum of the ternary composite material TiO2-Ti3C2 (70%) obtained in Example 5, (e) is the Ti 2p spectrum of the ternary composite material TiO2-Ti3C2 (50%) obtained in Example 3; (f) are the N 1S spectra of the original Ti3C2MXene material and the ternary composite material TiN-TiO2-Ti3C2 obtained in Example 1; (g) (h) is the C1S spectrum of the processed Ti3C2MXene material in the examples and comparative examples; (h) is the O1S spectrum of the processed Ti3C2MXene material in the examples and comparative examples; Figure 5 The following are the dynamic gas-sensing performance of the gas sensors obtained from the treated Ti3C2MXene material in the examples and comparative examples at different temperatures. (a) is the response curve at 100 °C, (b) is the response curve at 150 °C, and (c) is the response-recovery behavior of the gas sensor obtained in Example 1 at 200 °C. Detailed Implementation

[0025] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0026] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0027] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0028] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0029] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0030] This invention provides a method for preparing ternary composite materials in a one-step microwave plasma method, comprising the following steps: Two-dimensional MXene material is placed in a microwave plasma device, and then a mixed gas is introduced for microwave plasma treatment, so that the metal elements in the two-dimensional MXene material are simultaneously converted into metal nitrides and metal oxides, and an MXene-metal nitride-metal oxide ternary composite material is generated in situ. The gas mixture includes oxygen (O2) and nitrogen (N2).

[0031] In some preferred embodiments of the present invention, the mixed gas is excited by microwave energy to generate the corresponding plasma.

[0032] In some preferred embodiments of the present invention, the microwave power of the microwave plasma treatment is 700W to 1200W, and the pressure is 200Pa to 500Pa.

[0033] In some preferred embodiments of the present invention, the temperature of microwave plasma treatment is 150°C to 500°C, and the treatment time is 5 min to 60 min.

[0034] In some preferred embodiments of the present invention, the mixed gas includes nitrogen with a volume fraction of 50-90% and oxygen with a volume fraction of 10-50%. For example, the mixed gas is nitrogen with a volume fraction of 90% and oxygen with a volume fraction of 10%, nitrogen with a volume fraction of 80% and oxygen with a volume fraction of 20%, nitrogen with a volume fraction of 60% and oxygen with a volume fraction of 40%, or nitrogen with a volume fraction of 50% and oxygen with a volume fraction of 50%.

[0035] In some preferred embodiments of the present invention, the two-dimensional MXene material is selected from one of Ti3C2, Ti2C, Ti2N, Nb2C, Nb3C4, Cr2C, Cr3C2, Ta2C, Ta4C3, V2C, and V3C2.

[0036] More specifically, the two-dimensional MXene material used in this embodiment of the invention is prepared by liquid-phase etching, and the specific preparation steps are as follows: The parent material was slowly added to an etching solution consisting of 1.7 g LiF, 20 mL HCl (37 wt.%), and 60 mL deionized water. The mixture was stirred at 25 °C for 5 min, and then placed in a 200 mL high-pressure hydrothermal reactor and kept at 120 °C for 120 h. After etching, the resulting solution was washed with deionized water and ethanol and centrifuged until neutral. The sample was then dried in an oven at 60 °C for 18 h to obtain the two-dimensional MXene material. When the two-dimensional MXene material used was Ti3C2, the parent material was Ti3AlC2; when the two-dimensional MXene material used was Ti2C, the parent material was Ti2AlC; and when the two-dimensional MXene material used was V3C2, the parent material was V3AlC2.

[0037] This invention also provides an MXene-metal nitride-metal oxide ternary composite material, prepared according to the above preparation method.

[0038] This invention also provides a gas sensor comprising the above-mentioned MXene-metal nitride-metal oxide ternary composite material.

[0039] In some preferred embodiments of the present invention, the preparation method of the gas sensor includes: mixing MXene-metal nitride-metal oxide ternary composite material with an organic solvent, coating the resulting mixture onto an Al2O3 ceramic sheet containing platinum interdigitated electrodes, and then heat-treating the mixture; wherein the organic solvent is an ethanol solution, the ratio of MXene-metal nitride-metal oxide ternary composite material to organic solvent is 1g:1.5mL, the heat treatment temperature is 350-550℃, and the time is 8-12h.

[0040] This invention also provides an application of the above-mentioned MXene-metal nitride-metal oxide ternary composite material or the above-mentioned gas sensor in nitrogen dioxide gas detection.

[0041] For example, this embodiment of the invention constructs a Ti3C2MXene-TiN-TiO2 ternary composite material in a one-step process. The construction process modulates the surface functional groups of Ti3C2MXene, significantly improving the gas-sensing performance of the material through multiphase synergy. Specifically, since Ti3C2MXene has a two-dimensional layered structure with abundant specific surface area and a large number of active sites, it can act as a conductive network, thus dominating the gas-sensing performance of the Ti3C2MXene-TiN-TiO2 composite material. Simultaneously, the charge modulation effect of the TiO2 heterojunction further enhances its response to gas sensing. Ti3C2MXene exhibits metal-like properties and primarily displays P-type response behavior in gas sensing tests; therefore, its conductivity mainly depends on the transport of hole carriers. In an air atmosphere, oxygen molecules first adsorb onto the surfaces of Ti3C2 and TiO2, capturing electrons to form adsorbed oxygen active molecules, leading to a decrease in the electron concentration on the surface of the composite material. Meanwhile, the Fermi level difference between Ti3C2 and TiO2 leads to band bending and an interfacial barrier, restricting carrier transport and resulting in a relatively high resistance for the sensor. When NO2 gas is introduced, it adsorbs onto Ti3C2 and TiO2. Due to its strong oxidizing properties, NO2 can plunder electrons from the material surface to form NO2. - This process further reduces the electron concentration and significantly increases the hole concentration in the material, thereby increasing its conductivity. Simultaneously, the decrease in electron concentration on the TiO2 surface causes a downward shift in the Fermi level, thus lowering the energy barrier height of Ti3C2 / TiO2 and promoting efficient hole transport at the interface. The synergistic effect of Ti3C2 and TiO2 ultimately manifests as a reduction in the overall resistance of the entire sensor system, forming a typical P-type NO2 gas-sensitive response. Furthermore, the introduction of TiN as a metallic phase can, to some extent, improve the electrical conductivity channels and interfacial charge transport efficiency of the composite material, helping to shorten response and recovery times. However, when the TiN content is too high (the TiN content can be determined by the relative peak areas of the Ti-N bonds and the N 1s peak in XPS, combined with the Ti-O / Ti-N peak area ratio and the change in gas-sensitive response; when the Ti-N peak area ratio is high and the response value decreases, it indicates that excessive TiN may form a continuous conductive channel, weakening the charge modulation effect of the Ti3C2 / TiO2 heterointerface; while an appropriate amount of TiN helps improve the charge transport efficiency of the composite material and increase the response / recovery rate), the continuous metallic conductive network formed will shield the modulation effect of the Ti3C2 / TiO2 heterointerface, thereby weakening the gas-induced resistance change and leading to a decrease in sensitivity).

[0042] All raw materials used in the embodiments of this invention were purchased.

[0043] The technical solution of the present invention will be further illustrated by the following embodiments.

[0044] Example 1 0.3g of Ti3C2MXene material obtained by liquid phase etching was placed in an alumina crucible, and then the alumina crucible was placed in a microwave plasma device. The microwave power was set to 700W and the pressure was set to 300Pa. A mixture of nitrogen and oxygen was introduced, with a nitrogen volume fraction of 90% and an oxygen volume fraction of 10%. The sample was treated in microwave nitrogen-oxygen plasma for 30min to obtain Ti3C2MXene-TiN-TiO2 ternary composite material (denoted as TiN-TiO2-Ti3C2).

[0045] 0.2 g of the obtained Ti3C2MXene-TiN-TiO2 ternary composite material was mixed with 0.3 mL of organic solvent (ethanol solution) to obtain a mixture. The mixture was then added dropwise (at a rate of 0.1 mL / cm³). 2 The platinum interdigitated electrode is applied to an Al2O3 ceramic sheet containing platinum interdigitated electrodes, and then placed in a muffle furnace for heat treatment at 350°C for 8 hours to obtain a gas sensor.

[0046] Example 2 Take 0.7g of Ti2C MXene material obtained by liquid phase etching and place it in a corundum crucible. Then place the corundum crucible in a microwave plasma device, set the microwave power to 1000W, the pressure to 500Pa, and introduce a mixed gas of nitrogen and oxygen with a nitrogen volume fraction of 80% and an oxygen volume fraction of 20%. Treat the sample in microwave nitrogen-oxygen plasma for 30min to obtain Ti2CMXene-TiN-TiO2 ternary composite material (denoted as TiO2-Ti3C2 (80%)).

[0047] 0.6 g of the obtained Ti2CMXene-TiN-TiO2 ternary composite material was mixed with 0.75 mL of organic solvent (ethanol solution), and the mixture was added dropwise (at a rate of 0.1 mL / cm³). 2 The gas sensor is obtained by applying the platinum interdigitated electrode to an Al2O3 ceramic sheet and then placing it in a muffle furnace for heat treatment at 400°C for 9 hours.

[0048] Example 3 Take 1g of V3C2MXene material obtained by liquid phase etching and place it in a corundum crucible. Then place the corundum crucible in a microwave plasma device, set the microwave power to 1200W, the pressure to 200Pa, and introduce a mixed gas of nitrogen and oxygen with a nitrogen volume fraction of 50% and an oxygen volume fraction of 50%. Treat the sample in microwave nitrogen-oxygen plasma for 60min to obtain V3C2MXene-V2O5-V2N ternary composite material (denoted as TiO2-Ti3C2 (50%)).

[0049] 0.8 g of the obtained V3C2MXene-V2O5-VO2 ternary composite material was mixed with 1.2 mL of organic solvent (ethanol solution), and the mixture was added dropwise (at a rate of 0.1 mL / cm³). 2 The gas sensor is obtained by applying the platinum interdigitated electrode to an Al2O3 ceramic sheet and then placing it in a muffle furnace for heat treatment at 450°C for 10 hours.

[0050] Example 4 0.3g of V2C MXene material obtained by liquid phase etching was placed in an alumina crucible, and then the alumina crucible was placed in a microwave plasma device. The microwave power was set to 700W and the pressure was set to 300Pa. A mixture of nitrogen and oxygen was introduced, with nitrogen volume fraction of 70% and oxygen volume fraction of 30%. The sample was treated in microwave nitrogen-oxygen plasma for 30min to obtain V2CMXene-VN-VO2 ternary composite material.

[0051] 0.2 g of the obtained Ti3C2MXene-TiN-TiO2 ternary composite material was mixed with 0.3 mL of organic solvent (ethanol solution), and the mixture was added dropwise (at a rate of 0.1 mL / cm³). 2 The gas sensor is obtained by applying the platinum interdigitated electrode to an Al2O3 ceramic sheet and then placing it in a muffle furnace for heat treatment at 500°C for 11 h.

[0052] Example 5 Take 0.3g of Ti3C2MXene material obtained by liquid phase etching and place it in a corundum crucible. Then place the corundum crucible in a microwave plasma device, set the microwave power to 700W, the pressure to 300Pa, and introduce a mixed gas of nitrogen and oxygen with a nitrogen volume fraction of 70% and an oxygen volume fraction of 30%. Treat the sample in microwave nitrogen-oxygen plasma for 30min to obtain Ti3C2MXene-TiN-TiO2 ternary composite material (denoted as TiO2-Ti3C2 (70%)).

[0053] 0.2 g of the obtained Ti3C2MXene-TiN-TiO2 ternary composite material was mixed with 0.3 mL of organic solvent (ethanol solution), and the mixture was added dropwise (at a rate of 0.1 mL / cm³). 2 The gas sensor is obtained by applying the platinum interdigitated electrode to an Al2O3 ceramic sheet and then placing it in a muffle furnace for heat treatment at 500°C for 11 h.

[0054] Comparative Example 1 Same as Example 1, except that only oxygen is introduced for microwave oxygen plasma treatment, specifically: Take 0.3g of Ti3C2MXene material obtained by liquid phase etching and place it in a corundum crucible. Then place the corundum crucible in a microwave plasma device, set the microwave power to 700W, the pressure to 300Pa, and introduce oxygen. Treat the sample in microwave oxygen plasma for 30min to obtain two-dimensional layered Ti3C2 material (denoted as TiN2-Ti3C2).

[0055] 0.2 g of the obtained two-dimensional layered Ti3C2 material was mixed with 0.3 mL of organic solvent (ethanol solution), and the mixture was added dropwise (the addition volume was 0.1 mL / cm³). 2 The platinum interdigitated electrode is applied to an Al2O3 ceramic sheet containing platinum interdigitated electrodes, and then placed in a muffle furnace for heat treatment at 350°C for 8 hours to obtain a gas sensor.

[0056] Comparative Example 2 Same as Example 1, except that nitrogen plasma treatment is performed first, followed by oxygen plasma treatment, specifically: Take 0.3g of Ti3C2MXene material obtained by liquid phase etching and place it in a corundum crucible. Then place the corundum crucible in a microwave plasma device, set the microwave power to 700W, the pressure to 300Pa, and introduce nitrogen gas to treat the sample in microwave nitrogen plasma for 30min. Then introduce oxygen gas to treat the sample in microwave oxygen plasma for 30min to obtain the composite material.

[0057] The preparation method of the gas sensor is consistent with that in Example 1.

[0058] Comparative Example 3 Same as Example 1, except that the microwave power is set to 1500W.

[0059] Comparative Example 4 Same as Example 1, except that a mixture of nitrogen and oxygen is introduced, with nitrogen comprising 40% and oxygen comprising 60% by volume.

[0060] Comparative Example 5 Same as Example 1, except that only nitrogen gas is introduced for microwave oxygen plasma treatment, specifically: Take 0.3g of Ti3C2MXene material obtained by liquid phase etching and place it in a corundum crucible. Then place the corundum crucible in a microwave plasma device, set the microwave power to 700W, the pressure to 300Pa, and introduce nitrogen gas. Treat the sample in microwave nitrogen plasma for 30min to obtain two-dimensional layered Ti3C2 material.

[0061] 0.2 g of the obtained two-dimensional layered Ti3C2 material was mixed with 0.3 mL of organic solvent (ethanol solution), and the mixture was dropped onto an Al2O3 ceramic sheet containing platinum interdigitated electrodes. The sheet was then placed in a muffle furnace and heat-treated at 350 °C for 8 h to obtain a gas sensor.

[0062] Performance testing The morphology of the obtained two-dimensional layered Ti3C2MXene material was observed using SEM electron microscopy, and the resulting morphology images are shown below. Figure 1 As shown, the left side is a physical image of the TiN-TiO2-Ti3C2 ternary composite material prepared in Example 1; the right side (a) shows the original Ti3C2MXene material; (b) shows the two-dimensional layered Ti3C2 material of Comparative Example 5 after only nitrogen microwave plasma treatment; (c) shows the ternary composite material obtained in Example 1; and (d) shows the ternary composite material obtained in Example 3. Figure 1 As can be seen from (a), the original Ti3C2MXene exhibits a typical layered stacked structure, with tightly packed layers and a relatively flat surface, displaying the "accordion-like" morphological characteristics unique to two-dimensional materials. Figure 1 In the middle (b), TiN-Ti3C2 material after nitrogen microwave plasma treatment is shown. It can be clearly observed that while maintaining the layered structure, the surface of the layers is roughened to a certain extent, accompanied by local pores and etching marks. This indicates that the high-energy bombardment of nitrogen microwave plasma, while introducing TiN, also produces corresponding etching and defect construction on the surface of Ti3C2MXene. Figure 1 Images (c) and (d) show the TiN-TiO2-Ti3C2 ternary composite material obtained under a one-step nitrogen-oxygen microwave plasma treatment. It is evident that a large number of nanoparticles are uniformly loaded onto the material surface, accompanied by more pronounced porous structures and scratch morphologies. This indicates that during the one-step nitrogen-oxygen microwave plasma treatment of Ti3C2MXene, TiO2 nanoparticles are generated in situ and uniformly anchored on the MXene sheet surface. Simultaneously, the microwave plasma etching effect is further enhanced, resulting in a porous and rough structure on the material surface.

[0063] The surface functional groups of the treated Ti3C2MXene in the examples and comparative examples were characterized by infrared spectroscopy, and the obtained infrared spectra are shown below. Figure 2 As shown in the figure (Ti3C2 is the original Ti3C2MXene material, TiN2-Ti3C2 is the Ti3C2 material obtained in Comparative Example 1, TiN-TiO2-Ti3C2 is the ternary composite material obtained in Example 1, TiO2-Ti3C2 (80%) is the ternary composite material obtained in Example 2, TiO2-Ti3C2 (50%) is the ternary composite material obtained in Example 3, and TiO2-Ti3C2 (70%) is the ternary composite material obtained in Example 5), according to Figure 2 The results show that the ternary composite material in the examples contains various functional groups such as -OH, C=O, and Ti-F on its surface, and these functional groups undergo dynamic evolution during nitriding and oxidation. These oxygen-containing functional groups preferentially anchor to coordinated unsaturated Ti sites, consistent with XPS analysis (…). Figure 4 The high-valence Ti species revealed by the study form a synergistic effect, jointly constructing an interface structure with multiple active sites, which is beneficial for the adsorption and reaction of gas molecules.

[0064] The gas-sensing performance of the gas sensors prepared in the examples and comparative examples was tested at 25℃ and 150℃ respectively. The tests were conducted on a gas-sensing testing device (SD101, Huachuang Ruike Science and Technology Wuhan Co. Ltd). A dynamic testing method was used, and the specific operation is as follows: 1. Connect the sensor to the gas-sensitive testing equipment, fill the equipment with air until it stabilizes, and the resulting value is the resistance of the device in air (Rair).

[0065] 2. Pass a test bottle containing 100 ppm nitrogen dioxide into the device until the response signal stabilizes. This value is the resistance (R) of the device in 100 ppm ethanol.

[0066] 3. Re-introduce air into the device until it stabilizes, completing one response recovery cycle. The ratio of the resistance difference ΔR between the device in air and nitrogen dioxide to the resistance in air (ΔR / Rair) is... (100%) is the device's response value to this concentration of nitrogen dioxide.

[0067] Figure 3 The image shows the response cycle curve when using the sensor from Example 1 to test 100 ppm nitrogen dioxide gas at 25°C. Figure 3It can be seen that after four response-recovery cycles, the resistance of the sample remains at its original value, thus the obtained sample has good stability. At the same time, calculations show that the sample has a very high response value, reaching 51.10%. That is, when the two-dimensional MXene material treated with microwave oxygen-nitrogen plasma at 25℃ is used to detect 100ppm of nitrogen dioxide, it exhibits high stability and response value.

[0068] Table 1 shows the response values ​​of the sensors in the examples and comparative examples at 150°C to a nitrogen dioxide concentration of 100 ppm.

[0069] Table 1. Device response values ​​for this concentration of nitrogen dioxide As can be seen from Table 1, after the two-dimensional MXene material is treated with microwave oxygen-nitrogen plasma, the response to nitrogen dioxide is significantly improved with the increase of oxygen volume fraction.

[0070] Table 2 shows the response values ​​of the sensors in the examples and comparative examples to a nitrogen dioxide concentration of 100 ppm at 25°C.

[0071] Table 2. Device response values ​​for this concentration of nitrogen dioxide As can be seen from Table 2, after the two-dimensional MXene material is treated with microwave oxygen-nitrogen plasma, it still has a high response value for a low concentration of nitrogen dioxide of 100 ppm at room temperature, and can be used for the detection of low concentration gases.

[0072] Figure 4The images show the high-resolution XPS spectra of the processed Ti3C2MXene materials in the examples and comparative examples, where (a) is the Ti 2p spectrum of TiN2-Ti3C2 obtained in Comparative Example 1, (b) is the Ti 2p spectrum of the ternary composite material TiN-TiO2-Ti3C2 obtained in Example 1, (c) is the Ti 2p spectrum of the ternary composite material TiO2-Ti3C2 (80%) obtained in Example 2, (d) is the Ti 2p spectrum of the ternary composite material TiO2-Ti3C2 (70%) obtained in Example 5, (e) is the Ti 2p spectrum of the ternary composite material TiO2-Ti3C2 (50%) obtained in Example 3; (f) are the N 1S spectra of the original Ti3C2MXene material and the ternary composite material TiN-TiO2-Ti3C2 obtained in Example 1; (g) (h) is the C1S spectrum of the Ti3C2MXene material after treatment in the examples and comparative examples; (h) is the O1S spectrum of the Ti3C2MXene material after treatment in the examples and comparative examples. It can be seen that after microwave oxygen-nitrogen plasma treatment, compared with the comparative example, the chemical composition and valence state of the Ti3C2MXene material surface in the examples have changed significantly: not only were Ti-N and Ti-O bonds successfully introduced into the material, but the number of oxygen-containing functional groups (such as -OH, C=O, etc.) on the surface also increased significantly, and the number of high-valence Ti components increased, indicating that the MXene surface has changed from "high fluorine and low oxygen" to "high oxygen and low fluorine". At the same time, the synergistic existence of multiple valence Ti species and oxygen-containing functional groups is conducive to building rich surface active sites, improving the material's adsorption and reaction capacity for gas molecules, thus providing a basis for improving gas-sensing performance.

[0073] Figure 5The figures show the dynamic gas-sensing performance of gas sensors obtained from the treated Ti3C2MXene material in the examples and comparative examples at different temperatures (TiN2-Ti3C2 is the gas sensor obtained in Comparative Example 1, TiN-TiO2-Ti3C2 is the gas sensor obtained in Example 1, TiO2-Ti3C2 (80%) is the gas sensor obtained in Example 2, TiO2-Ti3C2 (50%) is the gas sensor obtained in Example 3, and TiO2-Ti3C2 (70%) is the gas sensor obtained in Example 5), where (a) is the response curve at 100 ℃, (b) is the response curve at 150 ℃, and (c) is the response curve of the gas sensor obtained in Example 1 at 200 ℃. The response-recovery behavior at ℃ was analyzed, and the response and recovery times were labeled. It can be seen that gas sensors with different composite structures all exhibited response characteristics to NO2 gas at various temperatures. However, the gas sensor obtained from the Ti3C2MXene material treated in the examples showed significantly better response performance than the comparative sample. With the increase of the oxygen component ratio, the sensor response value generally showed an upward trend. At 200℃, the TiN-TiO2-Ti3C2 sensor prepared in Example 1 exhibited faster response and recovery speeds, indicating its excellent kinetic performance. This is mainly attributed to: Ti3C2 providing a conductive network and high specific surface area, TiO2 constructing a heterojunction to achieve charge modulation, and TiN improving conductivity and interfacial transport efficiency. The synergistic effect of these three significantly enhances gas adsorption, charge transfer, and interfacial transport processes, thereby improving the sensor's sensitivity and response speed. However, when the TiN content is too high, it can shield the heterojunction modulation, thus reducing the gas-sensing performance.

[0074] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing ternary composite materials in one step using microwave plasma, characterized in that, Includes the following steps: Two-dimensional MXene material is placed in a microwave plasma device, and then a mixed gas is introduced for microwave plasma treatment, so that the metal elements in the two-dimensional MXene material are simultaneously converted into metal nitrides and metal oxides, and an MXene-metal nitride-metal oxide ternary composite material is generated in situ. The mixed gas includes oxygen and nitrogen.

2. The method for preparing ternary composite materials by one-step microwave plasma method according to claim 1, characterized in that, The microwave plasma treatment has a microwave power of 700W to 1200W, a pressure of 200Pa to 500Pa, a temperature of 150℃ to 500℃, and a treatment time of 5min to 60min.

3. The method for preparing ternary composite materials by one-step microwave plasma method according to claim 1, characterized in that, The mixed gas comprises nitrogen with a volume fraction of 50-90% and oxygen with a volume fraction of 10-50%.

4. The method for preparing ternary composite materials by one-step microwave plasma method according to claim 1, characterized in that, The two-dimensional MXene material is selected from one of Ti3C2, Ti2C, Ti2N, Nb2C, Nb3C4, Cr2C, Cr3C2, Ta2C, Ta4C3, V2C, and V3C2.

5. A ternary composite material of MXene-metal nitride-metal oxide, characterized in that, It is prepared according to any one of claims 1 to 4.

6. A gas-sensitive sensor, characterized in that, The sensitive material is the MXene-metal nitride-metal oxide ternary composite material as described in claim 5.

7. The gas sensor according to claim 6, characterized in that, The method for preparing the gas sensor includes: mixing the MXene-metal nitride-metal oxide ternary composite material with an organic solvent, coating the resulting mixture onto an Al2O3 ceramic sheet containing platinum interdigitated electrodes, and obtaining the gas sensor after heat treatment.

8. The gas sensor according to claim 7, characterized in that, The organic solvent is an ethanol solution, and the ratio of the MXene-metal nitride-metal oxide ternary composite material to the organic solvent is 1g:1.5mL.

9. The gas sensor according to claim 7, characterized in that, The heat treatment is performed at a temperature of 350–550°C for 8–12 hours.

10. The application of the MXene-metal nitride-metal oxide ternary composite material of claim 5 or the gas sensor of any one of claims 6 to 9 in the detection of nitrogen dioxide gas.

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