Method for preparing room-temperature MXene-based ethanol sensor material by using supercritical carbon dioxide

Abstract

The invention belongs to the technical field of preparation of gas sensor materials, and particularly relates to a method for preparing a room-temperature MXene-based ethanol sensor material by using supercritical carbon dioxide. The method comprises the following steps: firstly, carrying out hydrothermal reaction on titanium dioxide powder to obtain titanium nanotubes (TNTs); then carrying out high-temperature calcination on the TNTs; and then the calcined titanium nanotube and MXene are stirred to react under the supercritical COC condition, and finally MXene composite material powder is obtained. The material shows excellent response performance to ethanol gas at room temperature, including short response and recovery time (lt: 5 seconds) and resistance change rate as high as 42%. According to the invention, the electrical conductivity of MXene and the gas sensitivity of TiOnanotubes are fully exerted, the supercritical treatment means is combined, the preparation process is simple, convenient, green and environment-friendly, and the method has a good industrial application prospect and is especially suitable for the field of VOCs gas sensors which are low in power consumption and operate at room temperature.

Description

Technical Field

[0001] The present invention belongs to the technical field of gas sensor material preparation, and particularly relates to a method for preparing a room-temperature MXene-based ethanol sensor material by using supercritical carbon dioxide. Background Art

[0002] Volatile organic compounds (VOCs) widely exist in daily life, such as air fresheners, paints, wood preservatives, and automotive products. These compounds not only pollute the environment but also can enter the human body through the respiratory tract or skin, causing acute or chronic health problems. As a typical VOC, ethanol can affect a person's judgment and reaction ability when its concentration increases in human blood, and may even lead to safety accidents such as drunk driving in severe cases. In recent years, the number of traffic accidents caused by this has been on the rise.

[0003] For the detection of VOCs, common methods include Raman spectroscopy, electrochemical sensors, and amperometric biosensors, etc. However, these methods have problems such as high cost, slow response, or limited detection environment. In contrast, semiconductor gas sensors have become an important research direction in the field of VOCs detection due to their advantages of fast response, high sensitivity, low cost, and simple manufacturing, especially having significant advantages in achieving sensitive detection at the ppb level and integrating portable devices.

[0004] In recent years, the interdigital electrode structure has been widely used to construct planar nano or micro gas sensor devices to improve the sensing performance. MXene materials have shown great potential in the field of gas sensing due to their excellent electrical conductivity, rich surface functional groups, tunable chemical activity, and good structural stability. However, most current gas-sensitive materials still need to work at high temperatures of 200 - 400 °C, which not only increases energy consumption and equipment complexity but also limits their promotion in low-power and environmentally friendly application scenarios. Therefore, developing a high-performance ethanol sensor material that can operate at room temperature is one of the important challenges faced by current gas sensing technologies.

[0005] As a typical n-type semiconductor material, TiO2 is widely used in gas sensing due to its high electron mobility, wide bandgap, chemical stability, and non-toxicity. If TiO2 is compounded with layered MXene, the specific surface area of the composite material can be significantly increased, providing more ethanol adsorption and reaction sites. At the same time, by virtue of the excellent electrical conductivity of MXene, the rapid migration of carriers can be effectively promoted, thereby improving the response speed and recovery performance.

[0006] In addition, supercritical carbon dioxide (scCO2), as a green and environmentally friendly reaction medium, has characteristics such as non-polarity, low viscosity, and high permeability, and has shown good application prospects in material synthesis and modification. However, there is currently no publicly reported scheme for using supercritical CO2 technology to assist in the preparation of MXene / TiO2 composites for room-temperature ethanol gas sensing. Therefore, developing a preparation method for room-temperature MXene-based ethanol sensing materials based on supercritical carbon dioxide treatment technology has important scientific research value and application prospects. Summary of the Invention

[0007] The object of the present invention is to provide a method for preparing a room-temperature MXene-based ethanol sensor material using supercritical carbon dioxide, so as to solve the problems that existing gas-sensitive materials need to work at high temperatures, have complex composite processes, and slow response speeds.

[0008] To achieve the above object, the present invention provides the following technical solutions: A method for preparing a room-temperature MXene-based ethanol sensor material using supercritical carbon dioxide, comprising the following steps: (1) Dispersing titanium dioxide powder in an aqueous sodium hydroxide solution to obtain a dispersion, and subjecting the dispersion to a hydrothermal reaction to obtain titanium nanotubes; (2) Calcining the titanium nanotubes in an air atmosphere; (3) Mixing the calcined titanium nanotubes with MXene and a solvent to obtain a dispersion, transferring the dispersion to a supercritical device, injecting carbon dioxide into the supercritical device, stirring and reacting, cooling and depressurizing after the reaction ends, and drying the product to obtain the room-temperature MXene-based ethanol sensor material.

[0009] Further, in step (1), the concentration of the aqueous sodium hydroxide solution is 0.5 - 2 mol / L, and the mass-volume ratio of the titanium dioxide powder to the aqueous sodium oxide solution is 1 g:20 mL - 1 g:40 mL.

[0010] Further, before the hydrothermal reaction in step (1), the dispersion is stirred at a rotation speed of 600 - 1000 r / min at room temperature for 36 - 72 h.

[0011] Further, in step (1), the temperature of the hydrothermal reaction is 100 - 200 °C, and the time is 36 - 72 h.

[0012] Further, in step (1), the titanium nanotubes are successively subjected to pickling, water washing, and alcohol washing, and the acid used for pickling is 0.1 - 0.5 mol / L nitric acid.

[0013] Further, in step (2), the temperature of the calcination is 300 - 500 °C, and the time is 60 - 120 min.

[0014] Further, the MXene described in step (3) is selected from Ti3C2T x MXene.

[0015] All the MXene used in the present invention is commercially available and does not need to be modified.

[0016] Further, the solvent described in step (3) is ethanol at 30 - 70 v%.

[0017] Further, the mass ratio of the titanium nanotubes to the MXene described in step (3) is 2:1 - 1:3.

[0018] Further, the mass - volume ratio of the titanium nanotubes to the solvent described in step (3) is 1 g:10 mL - 1 g:50 mL.

[0019] Further, the temperature of the reaction described in step (3) is 40 - 100 °C, the pressure is 10 - 20 MPa, and the time is 2 - 4 h.

[0020] The present invention synergistically improves the gas - sensing performance and response rate by reasonably designing the material structure and interface regulation means. The present invention selects TiO2 as the basic gas - sensing material because of its high electron mobility, wide bandgap, and good chemical stability as an n - type semiconductor, which can provide abundant gas adsorption and reaction sites; the TiO2 nanotubes (TNTs) synthesized by the alkaline hydrothermal method have a high specific surface area and a one - dimensional electron transport path, which helps to improve the sensitivity and reaction speed, while the high - temperature calcination treatment can further stabilize its crystal phase and enhance its conductivity. Ti3C2T x MXene, due to its layered structure and excellent conductivity, acts as a fast electron - transport channel in the composite material. At the same time, its surface functional groups can also participate in gas - molecule adsorption, improving the response intensity. CO2 in the supercritical state has low surface tension, high diffusivity, and good solubility, and can effectively penetrate into the microporous structures of TNTs and MXene, promoting uniform composite and tight coupling at the nanoscale, thereby optimizing the electron path and interface synergistic effect at the microscopic level. The finally obtained composite material can exhibit excellent gas - sensing performance with fast response, fast recovery, and high resistance change rate at room temperature, not only realizing low - energy - consumption operation, but also taking into account the greenness and high efficiency of the preparation process, and having significant theoretical value and application prospects.

[0021] Compared with the prior art, the advantages and beneficial effects of the present invention are: The composite material prepared by the present invention can achieve highly sensitive and fast-response detection of ethanol gas at room temperature. Compared with the defects of traditional gas-sensitive materials that need to work at high temperatures and have high energy consumption, the sensor material prepared by the present invention has the advantages of short response time, rapid recovery, high resistance change rate, etc. In addition, this method has simple process, environmental friendliness, non-toxic and pollution-free, is suitable for large-scale preparation and industrial promotion, and is especially suitable for VOCs gas sensing applications in intelligent wearables, portable detection and low-power electronic devices. Description of the Drawings

[0022] Figure 1 Transmission electron microscope image of titanium nanotubes TNTs prepared in Example 1.

[0023] Figure 2 XPS spectrum of C 1s of the sensor material prepared in Example 1.

[0024] Figure 3 XPS spectrum of Ti 2p of the sensor material prepared in Example 1.

[0025] Figure 4 Dynamic response-recovery curve of the sensor material prepared in Example 1 to ethanol.

[0026] Figure 5 Dynamic response-recovery curves of the sensor materials prepared in Comparative Example 1 - Comparative Example 4 to ethanol. Detailed Description of the Invention

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0028] Unless otherwise specified, the raw materials used in the examples are all ordinary commercially available products. The following sources are for illustrative purposes: Titanium dioxide was purchased from Shanghai Macklin Biochemical Co., Ltd., anatase TiO2, AR grade.

[0029] Ti3C2T x MXene was purchased from Foshan Newene Technology Co., Ltd., monolayer specification.

[0030] Example 1: This example provides a method for preparing a room-temperature MXene-based ethanol sensor material using supercritical carbon dioxide, including the following steps:

[0031] (1) The titanium dioxide powder was dispersed in an aqueous sodium hydroxide solution with a concentration of 1 mol / L at a mass-to-volume ratio of 1 g:30 mL. The resulting dispersion was stirred at a speed of 600 r / min for 48 hours at room temperature. After stirring, the dispersion was transferred to a hydrothermal reaction kettle lined with polytetrafluoroethylene and subjected to a hydrothermal reaction at 150 °C for 48 hours. Then, the product was pickled with 0.1 mol / L nitric acid 12 times, washed with deionized water 4 times, and washed with absolute ethanol 1 time. Subsequently, it was placed in a blast drying oven and dried at 50 °C for 6 hours to obtain titanium nanotube (TNTs) powder; (2) The dried titanium nanotube powder was placed in a porcelain boat and calcined at 400 °C for 120 minutes in an air atmosphere to further oxidize and stabilize its structure; (3) The calcined titanium nanotube powder, Ti3C2T x MXene was mixed with a solvent at a mass-to-volume ratio of 1 g:1 g:10 mL. The solvent was 50 v% ethanol. After mixing evenly, a dispersion was formed. The dispersion was transferred to a supercritical reaction kettle, and carbon dioxide was introduced into it. It was stirred and reacted under supercritical conditions of a temperature of 80 °C and a pressure of 15 MPa for 3 hours; after the reaction, it was naturally cooled to room temperature. After depressurization, the reactant was taken out and the reactant was dried to finally obtain Ti3C2T x MXene-based ethanol sensor composite material powder.

[0032] The transmission electron microscope image of the titanium nanotube TNTs prepared in this example is shown in Figure 1 , and it can be seen that the diameter of the titanium oxide nanotubes is about 10 nm, and the size and distribution are relatively uniform.

[0033] The XPS spectrum of C 1s of the sensor material prepared in this example is shown in Figure 2 , and C 1s peaks can be observed at 281.3, 282.6, 284.8, 286.6, and 288.5 eV, which are attributed to C-Ti (carbide in MXene), C-Ti-O, C-C, C-O (surface functional group), and C=C (aliphatic carbon group), respectively.

[0034] The XPS spectrum of Ti 2p of the sensor material prepared in this example is shown in Figure 3 , and it can be seen that Ti exists in multiple oxidation states; it can be deconvoluted into five peaks at 455.5, 457, 459.5, 461.8, and 465 eV, which are attributed to Ti + (Ti-C), Ti 2+ (Ti-X), Ti 3+ (Ti x O y )、Ti4+ (Ti-O2) and TiO 2-X F X 。

[0035] The sensor materials prepared in this example were characterized for gas sensor performance, as shown in Figure 4 , which showed the ability to rapidly respond to and recover from different concentrations of ethanol at room temperature. Both the response and recovery times were within 5 s, and the resistance change rate (R g -R a / R a ) could reach up to 42% at 120 ppm. Here, R g represents the resistance of the sensor after adding the gas to be measured in dry air, and R a is the initial resistance of the sensor in dry air.

[0036] Comparative Example 1: The difference between this comparative example and Example 1 is that steps (1) and (2) were not carried out, and titanium dioxide powder was directly used to compound with Ti3C2T x MXene.

[0037] Comparative Example 2: The difference between this comparative example and Example 1 is that step (2) was not carried out, and the titanium nanotube (TNTs) powder prepared in step (1) was compounded with Ti3C2T x MXene.

[0038] Comparative Example 3: The difference between this comparative example and Example 1 is that the supercritical treatment in step (3) was not carried out, and the titanium nanotube (TNTs) powder prepared in step (1) was simply stirred and compounded with Ti3C2T x MXene in solution.

[0039] Comparative Example 4: The difference between this comparative example and Example 1 is that step (3) is as follows: The calcined titanium nanotube powder was mixed with Ti3C2T x MXene and a solvent at a mass-to-volume ratio of 4 g:1 g:10 mL in solution. The solvent was 50 v% ethanol. After mixing evenly to form a dispersion, the dispersion was transferred to a supercritical reaction kettle, carbon dioxide was introduced into it, and it was stirred and reacted under supercritical conditions of a temperature of 80 °C and a pressure of 15 MPa for 3 hours. After the reaction ended, the reactants were dried to obtain MXene-based composite material powder.

[0040] The sensor materials prepared in Comparative Examples 1-4 were characterized for gas sensor performance, as shown in Figure 5。Comparing its ability to show rapid response and recovery to ethanol at different concentrations at room temperature, it is found that the response and recovery time and the resistance change rate index parameters of all comparative examples are worse than those of Example 1. Among them, the materials of Comparative Example 1 and Comparative Example 4 have no obvious response signal to ethanol and are unstable, and the resistance change rates of the materials of Comparative Example 2 and Comparative Example 3 are significantly weaker than those of Example 1.

[0041] The above are the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle described in the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a room-temperature MXene-based ethanol sensor material using supercritical carbon dioxide, comprising the following steps: (1) Dispersing titanium dioxide powder in an aqueous sodium hydroxide solution to obtain a dispersion, and subjecting the dispersion to a hydrothermal reaction to obtain titanium nanotubes; (2) Calcining the titanium nanotubes in an air atmosphere; (3) Mixing the calcined titanium nanotubes with MXene and a solvent to obtain a dispersion, transferring the dispersion to a supercritical device, injecting carbon dioxide into the supercritical device, stirring and reacting, cooling and depressurizing after the reaction ends, and drying the product to obtain the room-temperature MXene-based ethanol sensor material; The mass ratio of the titanium nanotubes to MXene is 2:1 - 1:

3.

2. The method according to claim 1, wherein: In step (1), the concentration of the aqueous sodium hydroxide solution is 0.5 - 2 mol / L, and the mass-volume ratio of the titanium dioxide powder to the aqueous sodium hydroxide solution is 1 g:20 mL - 1 g:40 mL.

3. The method according to claim 1, characterized in that: In step (1), before the hydrothermal reaction, the dispersion is stirred at a rotation speed of 600 - 1000 r / min at room temperature for 36 - 72 h, the temperature of the hydrothermal reaction is 100 - 200 °C, and the time is 36 - 72 h.

4. The method according to claim 1, characterized in that: In step (1), the titanium nanotubes are successively subjected to pickling, washing with water, and washing with alcohol, and the acid used for pickling is 0.1 - 0.5 mol / L nitric acid.

5. The method according to claim 1, wherein: In step (2), the calcination temperature is 300 - 500 °C, and the time is 60 - 120 min.

6. The method according to claim 1, wherein: The MXene described in step (3) is selected from Ti3C2T x MXene.

7. The method according to claim 1, wherein: In step (3), the solvent is 30 - 70 v% ethanol.

8. The method according to claim 1, characterized in that: In step (3), the mass-volume ratio of the titanium nanotubes to the solvent is 1 g:10 mL - 1 g:50 mL.

9. The method according to claim 1, characterized in that: In step (3), the reaction temperature is 40 - 100 °C, the pressure is 10 - 20 MPa, and the time is 2 - 4 h.

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