Preparation method of gas sensitive material, gas sensor and preparation method of gas sensor

Abstract

The invention discloses a preparation method of a gas sensitive material, a gas sensor and a preparation method of the gas sensor, and relates to the field of sensors. The method comprises the following steps: mixing a hydrofluoric acid solution with an MAX phase material to prepare an MXene solution; the preparation method comprises the following steps: mixing a graphene oxide solution, a tungsten ion compound, ascorbic acid and an MXene solution, so that graphene oxide in the graphene oxide solution is reduced by the ascorbic acid, and an rGO / MXene / WO3 mixed solution is prepared; the rGO / MXene / WO3 mixed solution is subjected to a hydrothermal reaction, and the rGO / MXene / WO3 gas sensitive material is prepared. The invention aims to solve the problem that NO2 cannot be accurately and rapidly detected due to poor gas-sensitive performance of the existing gas-sensitive material.

Description

Technical Field

[0001] The present invention relates to the field of sensor technology, and in particular to a method for preparing a gas-sensitive material, a gas sensor and a method for preparing the same. Background Art

[0002] Nitrogen dioxide (NO2) is a toxic and harmful gas with a pungent odor. Its emission mainly comes from motor vehicle exhaust and fossil fuel combustion. When the NO2 content in the atmosphere is too high, it will cause pollution events such as acid rain, photochemical smog, and near-ground ozone. At the same time, NO2 will cause serious damage to human skin, eyes, and respiratory system. For the sake of human health and environmental protection, it is urgent to achieve accurate and rapid detection of NO2.

[0003] In the related technologies, semiconductor oxides such as ZnO, SnO2, In2O3 and other materials have been widely used in the field of NO2 detection. However, traditional gas-sensitive materials can generally only meet the detection requirements of NO2 under high temperature conditions, while under low temperature conditions, the gas-sensitive properties (such as sensitivity, selectivity, stability, etc.) of gas-sensitive materials still cannot meet the detection requirements of NO2, especially under room temperature conditions (about 25°C), the gas-sensitive properties of gas-sensitive materials prepared in the related technologies are poor. Summary of the invention

[0004] The present invention provides a method for preparing a gas-sensitive material, a gas sensor and a method for preparing the same, aiming to solve the problem that the existing gas-sensitive materials have poor gas-sensitive properties and thus cannot accurately and quickly detect NO2.

[0005] In a first aspect, the present invention provides a method for preparing a gas-sensitive material, the method comprising:

[0006] Mixing a hydrofluoric acid solution with a MAX phase material to prepare a MXene solution;

[0007] Mixing a graphene oxide solution, a tungsten ion compound, ascorbic acid and the MXene solution, so that the ascorbic acid reduces the graphene oxide in the graphene oxide solution to obtain a rGO / MXene / WO3 mixed solution;

[0008] The rGO / MXene / WO3 mixed solution is subjected to a hydrothermal reaction to obtain an rGO / MXene / WO3 gas-sensitive material.

[0009] In a second aspect, the present invention provides a method for preparing a gas sensor, the method comprising:

[0010] The rGO / MXene / WO3 gas-sensitive material is prepared by the above-mentioned preparation method of the gas-sensitive material;

[0011] Adding the rGO / MXene / WO3 gas-sensitive material into a dispersant solution to obtain a gas-sensitive material ink;

[0012] Printing using the gas-sensitive material ink to form a gas-sensitive film on the surface of the micro-hotplate;

[0013] The micro-hotplate formed with the gas sensitive film is packaged to obtain a gas sensor.

[0014] In a third aspect, the present invention provides a gas sensor, which is prepared by using the above-mentioned method for preparing the gas sensor.

[0015] The present application provides a method for preparing a gas-sensitive material, a gas sensor and a method for preparing the same, wherein a MXene solution is prepared by mixing a hydrofluoric acid solution with a MAX phase material; a graphene oxide solution, a tungsten ion compound, ascorbic acid and a MXene solution are mixed so that ascorbic acid reduces the graphene oxide in the graphene oxide solution to prepare a rGO / MXene / WO3 mixed solution; and a hydrothermal reaction is performed on the rGO / MXene / WO3 mixed solution to prepare a rGO / MXene / WO3 gas-sensitive material. Thus, a tungsten ion compound can be introduced during the preparation of the gas-sensitive material to form a rGO / MXene / WO3 gas-sensitive material having a loose porous structure, which can provide more active sites for the gas-sensitive material to contact with the gas. At the same time, the presence of tungsten trioxide can also promote the adsorption of surface oxygen molecules and increase the surface chemical adsorption oxygen content, thereby facilitating the gas-sensitive reaction, so that the prepared gas sensor exhibits excellent gas-sensitive performance to NO2 gas, has excellent selectivity and stability, and has a simple manufacturing process and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying any creative work.

[0017] Figure 1 It is a schematic flow chart of the steps of a method for preparing a gas-sensitive material provided by an embodiment of the present invention;

[0018] Figure 2 A scanning electron microscope schematic diagram of an rGO / MXene / WO3 gas-sensitive material provided in an embodiment of the present invention;

[0019] Figure 3 A schematic flow chart of the steps of a method for preparing a gas sensor provided by an embodiment of the present invention;

[0020] Figure 4 A schematic diagram of a response recovery curve of a gas sensor provided in each embodiment and a comparative example of the present invention in a 10ppm NO2 gas environment;

[0021] Figure 5 A schematic diagram of a response value variation curve of a gas sensor prepared in Example 1 to 10 ppm NO2 gas at different operating temperatures provided in an embodiment of the present invention;

[0022] Figure 6 A schematic diagram of a response recovery curve of a gas sensor prepared in Example 1 provided in an embodiment of the present invention in an environment of NO2 gas with different concentrations. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] It should be understood that when used in this specification and the appended claims, the terms "include" and "comprises" indicate the presence of described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

[0025] It should also be understood that the terms used in this specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the specification of the present invention and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include plural forms.

[0026] It should be further understood that the term "and / or" used in the present description and the appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0027] In conjunction with the accompanying drawings, some embodiments of the present application are described in detail below. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0028] As environmental issues become increasingly prominent, air pollution has become a focus of social attention. Among many pollutants, nitrogen dioxide (NO2) has attracted much attention due to its serious impact on human health and the environment. This gas mainly comes from industrial combustion, transportation emissions, and coal mining processes. People who are exposed to high concentrations of NO2 for a long time face a variety of health risks such as respiratory diseases, cardiovascular diseases, and lung cancer. Therefore, effective monitoring of NO2 levels is crucial to maintaining the ecological environment and public health.

[0029] See also Figure 1 , Figure 1 The present invention provides a schematic flow chart of a method for preparing a gas-sensitive material. The method for preparing the gas-sensitive material introduces a tungsten ion compound during the preparation process to form a rGO / MXene / WO3 gas-sensitive material with a loose porous structure, which can provide more active sites for the gas-sensitive material to contact with the gas. At the same time, the presence of tungsten trioxide can also promote the adsorption of surface oxygen molecules and increase the surface chemical adsorption oxygen content, which is conducive to the gas-sensitive reaction.

[0030] Among them, gas-sensitive materials can be used in the fields of gas sensors, supercapacitors, lithium battery electrode materials, and heat storage materials, etc., without specific limitation here.

[0031] For example, since the rGO / MXene / WO3 gas-sensitive material has a loose porous structure, it can provide more active sites for the contact between the gas-sensitive material and the gas. The presence of tungsten trioxide can also promote the adsorption of surface oxygen molecules and increase the surface chemically adsorbed oxygen content, which is beneficial to the gas-sensitive reaction. Therefore, the rGO / MXene / WO3 gas-sensitive material provided in this application can be used in the field of gas sensors.

[0032] For example, since the rGO / MXene / WO3 gas-sensitive material also has the characteristics of being porous, having a high specific surface area and having good conductivity, the rGO / MXene / WO3 gas-sensitive material provided in the present application can also be applied to the field of supercapacitors and the field of lithium battery electrode materials, thereby improving the specific capacitance and conductivity, and enhancing the energy density and power density of lithium batteries.

[0033] For example, since MXene and rGO have good thermal conductivity, the thermal conductivity of the material can be improved after compounding. WO3, as a thermally stable material, can improve the application ability of rGO / MXene / WO3 composite materials at high temperatures. Therefore, the rGO / MXene / WO3 gas-sensitive material provided in this application can also be used in the field of heat storage materials.

[0034] The following is a detailed description taking the application of gas sensitive materials in the field of gas sensors as an example.

[0035] like Figure 1 As shown, the method for preparing the gas-sensitive material includes: steps S101 to S103.

[0036] Step S101: Mix a hydrofluoric acid solution with a MAX phase material to prepare a MXene solution.

[0037] Among them, MAX phase material is a type of layered high-performance ceramic material with a close-packed hexagonal structure, and it has the excellent properties of both metals and ceramics. At the same time, MAX phase material performs well in high-temperature oxidation resistance, high electrical and thermal conductivity, and excellent radiation resistance.

[0038] In the embodiment of the present application, the MAX phase material may be a titanium-based MAX phase material, a niobium-based MAX phase material, or the like.

[0039] For example, the MXene solution can be a solution prepared from a hydrofluoric acid solution and a MAX phase material. MXene has a graphene-like structure and novel properties, and has excellent flexibility, good electronic conductivity and excellent mechanical properties. It is composed of metal carbides or nitrides, and the chemical formula is M n+1 X n T X , where n = 1, 2 or 3, representing three common structures. "M" represents metal elements, mainly transition metals (such as Ti, V, Nb, Ta, Cr, Mo, etc.); "X" represents carbon or nitrogen elements; "T" represents functional groups on the surface of the material, such as hydroxyl (-OH), halogen groups (-F, -Cl), etc.

[0040] In some embodiments, a method for preparing a hydrofluoric acid solution is provided, wherein a fluoride ion compound is mixed with an acidic solvent so that the fluoride ions of the fluoride ion compound react with the hydrogen ions of the acidic solvent to obtain a hydrofluoric acid solution. Thus, a hydrofluoric acid solution for reacting with a MAX phase material can be prepared by using the fluoride ion compound and the acidic solvent.

[0041] Exemplarily, the fluoride ion compound may be lithium fluoride (LiF), sodium fluoride (NaF), ammonium fluoride (NH4F) or other fluoride ion-containing compounds, which are not specifically limited herein.

[0042] For example, the acidic solvent may be a strong acid solution such as hydrochloric acid or sulfuric acid to provide hydrogen ions and fluorine ions to react, which is not specifically limited here.

[0043] For example, 1 g of lithium fluoride is mixed with 20 mL of 9 mol / L hydrochloric acid and stirred for 20 min to allow fluoride ions of the lithium fluoride to react with hydrogen ions of the hydrochloric acid to produce a hydrofluoric acid solution.

[0044] In some embodiments, the MAX phase material is added to a hydrofluoric acid solution to obtain a MXene suspension, and the MXene suspension is filtered to obtain a MXene solution. Thus, a MXene solution can be obtained by reacting the MAX phase material with the hydrofluoric acid solution.

[0045] In the embodiments of the present application, a conductive two-dimensional material matrix (MXene) is introduced in the preparation process of the gas-sensitive material, so that the performance of detecting harmful gases can be improved by preparing nano-composite materials. MXene materials are highly favored due to their excellent electron mobility and huge specific surface area. In addition, the adsorption capacity of NO2 gas can be effectively controlled by adjusting its surface chemical properties.

[0046] Exemplarily, the MAX phase material may be titanium aluminum carbide (Ti3AlC2, Ti4AlN3), niobium aluminum carbide (Nb2AlC, Nb3AlC2), etc., without specific limitation herein.

[0047] For example, 1 g of Ti3AlC2 powder can be weighed and added to the hydrofluoric acid solution, and stirred. After stirring, the solution is transferred to a water bath at a temperature of 40-60° C. to react for 8 h to 24 h, thereby obtaining Ti3AlT X MXene suspension.

[0048] In some embodiments, the MXene suspension is cleaned, ultrasonically treated, and dried to obtain a MXene powder; the MXene powder is ultrasonically dispersed in a mixed solvent to prepare a MXene solution, wherein the ratio of deionized water to ethanol in the mixed solvent is 1:(1-10), and the concentration of the MXene solution is 0.5-10 mg / g.

[0049] The MXene powder is a powder extracted from a MXene suspension, such as Ti3AlT X MXene powder.

[0050] For example, the MXene suspension is repeatedly washed with deionized water until the pH value of the supernatant in the MXene suspension is close to 6, so as to wash away the residual acidic solvent in the MXene suspension; then the precipitate after the last washing is dispersed in ethanol and ultrasonically treated for 120 minutes to increase the stratification and evaporation rate of MXene; finally, it is transferred to a vacuum oven at a temperature of 60°C for drying for 12 hours, thereby obtaining Ti3AlT X MXene powder.

[0051] Exemplarily, the mixed solvent can be formed by deionized water and ethanol, and the ratio of deionized water to ethanol in the mixed solvent can be set according to actual conditions. For example, the ratio of deionized water to ethanol in the mixed solvent can be 1:1-1:10. For example, the ratio of deionized water to ethanol in the mixed solvent can be 1:1, 1:2, 1:5, 1:10, etc. Preferably, the ratio of deionized water to ethanol in the mixed solvent can be 1:2, so that the dispersion effect of MXene powder in the mixed solvent is better.

[0052] Exemplarily, the concentration of the MXene solution can be prepared according to actual conditions. For example, the concentration of the MXene solution can be 0.5-10 mg / g. For example, the concentration of the MXene solution can be 0.5 mg / g, 1 mg / g, 5 mg / g and 10 mg / g, etc. Preferably, the concentration of the MXene solution is 1 mg / g, so that the dispersion effect of the MXene powder in the mixed solvent is better.

[0053] For example, a mixed solvent can be prepared according to the ratio of deionized water: ethanol = 1:2, and then a certain amount of MXene powder is ultrasonically dispersed in the mixed solution so that the concentration of MXene in the mixed solution is 1 mg / g, that is, a MXene solution is prepared.

[0054] Step S102: mixing the graphene oxide solution, the tungsten ion compound, ascorbic acid and the MXene solution, so that the ascorbic acid reduces the graphene oxide in the graphene oxide solution to obtain a rGO / MXene / WO3 mixed solution.

[0055] The graphene oxide solution is a liquid formed by dispersing graphene oxide (GO) in a solvent. The tungsten ion compound can be any compound containing tungsten ions, and the valence of the tungsten ions in the tungsten ion compound can be +2, +4, +5, or +6, which is not specifically limited here. Ascorbic acid can adjust the pH value of the solution and can be used as a reducing agent to reduce the graphene oxide solution.

[0056] Specifically, a graphene oxide solution, a tungsten ion compound and ascorbic acid can be mixed so that the ascorbic acid reduces the graphene oxide in the graphene oxide solution to obtain a rGO / WO3 mixed solution; and a MXene solution is added to the rGO / WO3 mixed solution to obtain a rGO / MXene / WO3 mixed solution.

[0057] The rGO / WO3 mixed solution is a mixed solution of reduced graphene oxide and tungsten trioxide. The rGO / MXene / WO3 mixed solution is a mixed solution of reduced graphene oxide, MXene solution and tungsten trioxide.

[0058] In some embodiments, a graphene oxide solution is added to deionized water to obtain a graphene oxide mixed solution; a tungsten ion compound and ascorbic acid are added to the graphene oxide mixed solution to obtain an rGO / WO3 mixed solution, and the mass ratio of the graphene oxide solution to the tungsten ion compound is 1:1-5:1.

[0059] Wherein, the graphene oxide mixed solution is a mixed solution of graphene oxide solution and deionized water.

[0060] Exemplarily, the tungsten ion compound can be a tungstate, tungstic acid, tungsten carbide and other compounds, such as sodium tungstate (Na2WO4·2H2O), calcium tungstate (CaWO4), cobalt tungstate (CoWO4), cadmium tungstate (CdWO4), ferrous tungstate (FeWO4), zinc tungstate (5ZnO·12WO3), tungsten dioxide (WO2) and tungsten chlorides such as tungsten hexachloride (WCl6), tungsten pentachloride (WCl5), tungsten tetrachloride (WCl4), tungsten dichloride (WCl2), etc.

[0061] Exemplarily, 1 mL of a 10 mg / mL graphene oxide (GO) solution is dispersed in 40 mL of deionized water, and then 0.032 g of Na2WO4·2H2O and 0.053 g of ascorbic acid are added. At this time, ascorbic acid can reduce the graphene oxide (GO) in the graphene oxide solution to reduced graphene oxide (rGO), thereby preparing an rGO / WO3 mixed solution.

[0062] Exemplarily, the mass ratio of graphene oxide solution to tungsten ion compound can be 1:1-5:1. If the tungsten ion compound is excessive, a large amount of WO3 is easily formed in the rGO / WO3 mixed solution, thereby destroying the 3D porous structure. Therefore, the mass ratio of graphene oxide solution to tungsten ion compound is at least 1:1. Preferably, it is necessary to control the added mass of graphene oxide solution to be greater than the added mass of graphene oxide solution, such as the mass ratio of graphene oxide solution to tungsten ion compound is 3:1.

[0063] In the embodiment of the present application, the valence of the tungsten ion in the tungsten ion compound can be +2, +4, +5, or +6. If the tungsten ion compound is any one of WO2, WCl5, WCl4, or WCl2, the valence of the tungsten ion in the above tungsten ion compound is +2, +4, or +5. Therefore, in the process of preparing the rGO / WO3 mixed solution, an oxidant needs to be added to the tungsten ion compound to increase the valence of W to +6, thereby forming WO3 to obtain the rGO / WO3 mixed solution.

[0064] Preferably, the valence of the tungsten ion in the tungsten ion compound is +6.

[0065] Since the valence of W in the rGO / WO3 mixed solution is +6, if the valence of tungsten ions in the tungsten ion compound is +6, such as Na2WO4·2H2O, CaWO4, etc., the valence of W remains unchanged during the formation of WO3, and there is no need to use an oxidant for oxidation reaction to increase the valence of W, which is more conducive to the preparation of WO3 and can reduce the preparation cost of gas-sensitive materials to a certain extent.

[0066] In some embodiments, under an acidic environment, a MXene solution is added to a rGO / WO3 mixed solution to prepare a rGO / MXene / WO3 mixed solution, and the mass ratio of reduced graphene oxide to the MXene solution is 1:1-5:1.

[0067] The acidic environment may be an environment with a pH value of 1-5. In an acidic environment, it is more conducive to the reaction between the MXene solution and the rGO / WO3 mixed solution.

[0068] Exemplarily, a MXene solution is added to a rGO / WO3 mixed solution, and the pH value of the solution is adjusted to about 2. After being fully stirred for 15 minutes, an rGO / MXene / WO3 mixed solution is obtained.

[0069] It should be noted that the pH value of the solution can be adjusted by controlling the amount of ascorbic acid added, or by adding another acidic solvent, which is not specifically limited here.

[0070] Exemplarily, the mass ratio of reduced graphene oxide (rGO) to MXene solution can be 1:1-5:1. Since the role of graphene oxide (GO) reduction to form reduced graphene oxide (rGO) is to enter the MXene interlayer to form a 3D layered structure, and a curled 3D network structure will be formed during the drying process, therefore, the mass ratio of reduced graphene oxide (rGO) to MXene solution is at least 1:1. Preferably, the mass of rGO needs to be controlled to be much larger than the mass of the MXene solution, such as the mass ratio of rGO to MXene solution is 3:1, to ensure that all rGO enters the MXene interlayer to form a 3D layered structure.

[0071] Step S103, subjecting the rGO / MXene / WO3 mixed solution to a hydrothermal reaction to obtain an rGO / MXene / WO3 gas-sensitive material.

[0072] Among them, the rGO / MXene / WO3 gas-sensitive material is a composite material formed by reduced graphene oxide (rGO), two-dimensional material (MXene) and tungsten trioxide (WO3). The rGO / MXene / WO3 gas-sensitive material significantly improves the overall conductivity of the gas-sensitive material by combining the characteristics of MXene and rGO. At the same time, due to the synergistic effect between the multilayer structure of MXene and the high porosity of rGO, the rGO / MXene / WO3 gas-sensitive material has the characteristics of fast response speed and high sensitivity.

[0073] In the embodiment of the present application, WO3 in the rGO / MXene / WO3 gas-sensitive material, as an N-type semiconductor, can form a PN junction after being compounded with P-type rGO and MXene. Since WO3 has a higher work function, electrons will flow from rGO and MXene to WO3, thereby increasing the surface electron density of WO3, which in turn can promote the adsorption of surface oxygen molecules, increase the surface chemically adsorbed oxygen content, and is beneficial to the gas-sensitive reaction.

[0074] In some embodiments, the reaction conditions of the hydrothermal reaction include: a hydrothermal temperature of 120-240°C, a hydrothermal time of 8-24h, and a capacity of a hydrothermal container of 20-120mL. This can provide a high temperature and high pressure reaction environment for the rGO / MXene / WO3 mixed solution reaction, thereby improving the orderliness of atomic arrangement and crystallinity, and can also control the crystal surface of the outer surface of the crystal, thereby improving the binding force with gas molecules and catalytic efficiency.

[0075] The hydrothermal container may be a container such as a reactor that can be used for hydrothermal reactions. The capacity of the hydrothermal container can control the pressure of the hydrothermal container. In order to make the pressure of the hydrothermal container higher and more stable, the capacity of the selected hydrothermal container is as small as possible.

[0076] For example, the rGO / MXene / WO3 mixed solution is transferred to a reactor with a capacity of 50mL and reacted at a temperature of 180°C for 12h. Selecting a reactor with a smaller volume can effectively control the pressure in the reactor, thereby improving the orderliness of atomic arrangement and crystallinity, and can also control the crystal surface of the outer surface of the crystal, thereby improving the binding force with gas molecules and catalytic efficiency. Then, the reaction product after the hydrothermal reaction is repeatedly washed with deionized water and ethanol, and then the rGO / MXene / WO3 gas-sensitive material is separated from impurities such as deionized water and ethanol in a centrifuge, and finally dried at a temperature of 60°C for 24h to obtain the rGO / MXene / WO3 gas-sensitive material.

[0077] See also Figure 2 , Figure 2 A scanning electron microscope schematic diagram of an rGO / MXene / WO3 gas-sensitive material provided in an embodiment of the present invention.

[0078] like Figure 2 As shown in the figure, the rGO / MXene composite material forms a porous network structure, and the flaky WO3 grows evenly in the porous network structure, that is, there are a large number of active sites for the gas-sensitive material to contact the gas, indicating that the rGO / MXene / WO3 gas-sensitive material can promote the adsorption of surface oxygen molecules, increase the surface chemically adsorbed oxygen content, and is conducive to the gas-sensitive reaction.

[0079] The present application provides a method for preparing a gas-sensitive material. By introducing a tungsten ion compound during the preparation of the gas-sensitive material, an rGO / MXene / WO3 gas-sensitive material with a loose porous structure is formed, which can provide more active sites for the contact between the gas-sensitive material and the gas. At the same time, the presence of tungsten trioxide can also promote the adsorption of surface oxygen molecules and increase the surface chemically adsorbed oxygen content, which is beneficial to the gas-sensitive reaction.

[0080] See also Figure 3 , Figure 3 The present invention provides a schematic flow chart of a method for preparing a gas sensor. The method for preparing the gas sensor has a simple manufacturing process and low cost, and can enable the prepared gas sensor to exhibit excellent gas-sensitive performance to NO2 gas, and has excellent selectivity and stability.

[0081] like Figure 3 As shown, the method for preparing the gas sensor includes: steps S201 to S204.

[0082] Step S201: prepare rGO / MXene / WO3 gas-sensitive material by adopting the preparation method of gas-sensitive material.

[0083] Since the preparation method of the gas-sensitive material has been described above, the specific steps of preparing the rGO / MXene / WO3 gas-sensitive material by the preparation method of the gas-sensitive material can be referred to the above embodiment, and will not be repeated here.

[0084] Step S202: adding rGO / MXene / WO3 gas-sensitive material into the dispersant solution to obtain gas-sensitive material ink.

[0085] Among them, the dispersant solution mainly plays the role of reducing viscosity, dispersing and wetting. Gas-sensitive material ink generally contains gas-sensitive materials, which are highly sensitive to specific gases (such as nitrogen dioxide and ammonia) and can maintain stable performance under different humidity environments.

[0086] Exemplarily, the dispersant may be one or more of Tuyile DS-195L polymer dispersant, isopropyl alcohol, polyvinyl alcohol, polyethylene glycol, sodium polyacrylate and polyacrylamide, which are not specifically limited herein.

[0087] For example, 0.1 g of rGO / MXene / WO3 gas-sensitive material, 10 mL of isopropanol, 2 mL of propylene glycol (used as a stabilizer), and 0.6 g of a surfactant can be taken, mixed evenly, and subjected to ultrasonic dispersion treatment to form a gas-sensitive material ink with uniform dispersion of the rGO / MXene / WO3 gas-sensitive material and stable and non-agglomerated particles.

[0088] Step S203: Printing with gas-sensitive material ink to form a gas-sensitive film on the surface of the micro-hotplate.

[0089] Among them, micro-hotplate (MHP) is made by using integrated circuit technology and micromachining technology on silicon substrate. Micro-hotplate has the advantages of low heating power, fast response time, small heat loss, compatibility with CMOS technology, and easy integration with other microelectronic devices. Therefore, it has great development potential in the fields of gas sensors, infrared emitters, gas flow meters, etc. Gas sensitive films can be used to prepare gas sensors.

[0090] Exemplarily, the printing method may include inkjet printing, electrohydrodynamic (EHD) printing, etc., which are not specifically limited here.

[0091] For example, it can be printed onto a MEMS micro-hotplate by inkjet printing and dried and sintered at a temperature of 200-400° C. for 0.5-4 hours to remove solvents and organic matter in the gas-sensitive material ink, thereby improving the stability of the gas sensor.

[0092] In some embodiments, electrohydrodynamic printing is performed using gas-sensitive material ink to form a gas-sensitive film on the surface of the micro-hotplate.

[0093] Among them, electrohydrodynamic (EHD) printing controls droplet ejection through electric field force, has high printing precision, and is suitable for film formation on a micro-hotplate at the hundred-micron level; highly programmed printing can ensure film formation efficiency and batch consistency. Therefore, the embodiment of the present application uses EHD printing to form a film on a micro-hotplate using gas-sensitive material ink.

[0094] Step S204: packaging the micro-hotplate formed with the gas sensitive film to obtain a gas sensor.

[0095] Among them, the gas sensor can accurately and quickly detect NO2 gas. At the same time, the gas sensor made of rGO / MXene / WO3 gas-sensitive material can operate at room temperature, so it can show extremely high sensitivity to ultra-low concentration of NO2 gas.

[0096] Specifically, a micro-hotplate with a gas-sensitive film formed on the surface is pasted into a ceramic tube shell, and wire welding and capping are performed to form a gas sensor. Since the gas-sensitive film has high film forming accuracy, good film forming effect, and good gas-sensing performance, the gas sensor made of the gas-sensitive film exhibits excellent gas-sensing performance for NO2 gas, has excellent selectivity and stability, and has a simple manufacturing process and low cost, and has broad application prospects in the large-scale preparation of gas sensors.

[0097] The following is a specific example to illustrate the preparation method and performance of the gas sensor of the embodiment of the present application. Specifically, the gas sensor prepared in each of the following embodiments can be connected to a circuit, the heating voltage can be adjusted to make the working temperature between 25°C and 80°C, and the aging treatment can be performed for 48 hours. After the aging is completed, the gas sensing performance test can be performed respectively.

[0098] Embodiment 1:

[0099] (1) Mix 1 g of lithium fluoride with 20 mL of 9 mol / L hydrochloric acid and stir for 20 min. Then weigh 1 g of Ti3AlC2 powder and add it to the above solution and continue stirring. Then transfer the above solution to a water bath at 40 °C and react for 24 h to obtain Ti3AlC2. X MXene suspension. The above solution was repeatedly washed with deionized water until the pH value of the supernatant was close to 6, and then the precipitate from the last wash was dispersed in ethanol and ultrasonically treated for 120 min at a temperature of 100 °C and finally dried in a vacuum oven at 60 °C for 12 h to obtain Ti3AlT X MXene powder.

[0100] (2) Ti3AlT X MXene powder was ultrasonically dispersed in a mixed solvent of deionized water and ethanol to make Ti3AlT X The concentration of MXene powder in the mixed solvent was 1 mg / g, and Ti3AlT X MXene solution.

[0101] (3) Take 3 mL of 10 mg / mL graphene oxide (GO) solution and disperse it in 40 mL of deionized water. Then add 0.032 g of Na2WO4·2H2O, 0.011 g of ascorbic acid and 0.043 g of sodium chloride. Then add 3 mL of Ti3AlT XMXene solution, and adjust the pH value to about 2. After fully stirring for 15 minutes, the mixed solution was transferred to a reactor and reacted at 180°C for 12 hours. The reaction product was repeatedly washed with deionized water and ethanol, and then the rGO / MXene / WO3 gas-sensitive material was separated from impurities such as deionized water and ethanol in a centrifuge. Finally, it was dried at 60°C for 24 hours to obtain rGO / MXene / WO3 gas-sensitive material.

[0102] (4) 0.1 g of rGO / MXene / WO3 gas-sensitive material, 10 mL of isopropanol, 2 mL of propylene glycol and 0.6 g of a surfactant were mixed and ultrasonically dispersed to form an ink with uniform dispersion and stable particles without agglomeration of the rGO / MXene / WO3 gas-sensitive material. Finally, the ink was printed onto a MEMS micro-hotplate by inkjet printing and dried and sintered at 400 °C for 2 h. Finally, the MEMS micro-hotplate was bonded to a ceramic shell, and wire binding and packaging were performed to form a gas sensor.

[0103] Embodiment 2:

[0104] (1) Mix 1 g of lithium fluoride with 20 mL of 9 mol / L hydrochloric acid and stir for 20 min. Then weigh 1 g of Ti3AlC2 powder and add it to the above solution and continue stirring. Then transfer the above solution to a water bath at 40 °C and react for 24 h to obtain Ti3AlC2. X MXene suspension. The above solution was repeatedly washed with deionized water until the pH value of the supernatant was close to 6, and then the precipitate from the last wash was dispersed in ethanol and ultrasonically treated for 120 min at a temperature of 100 °C and finally dried in a vacuum oven at 60 °C for 12 h to obtain Ti3AlT X MXene powder.

[0105] (2) Ti3AlT X MXene powder was ultrasonically dispersed in a mixed solvent of deionized water and ethanol to make Ti3AlT X The concentration of MXene powder in the mixed solvent was 1 mg / g, and Ti3AlT X MXene solution.

[0106] (3) Take 3 mL of 10 mg / mL graphene oxide (GO) solution and disperse it in 40 mL of deionized water. Then add 0.032 g of Na2WO4·2H2O, 0.011 g of ascorbic acid and 0.043 g of sodium chloride, and add 30 mL of Ti3AlT XMXene solution, and adjust the pH value to about 2. After fully stirring for 15 minutes, the mixed solution was transferred to a reactor and reacted at 180°C for 12 hours. The reaction product was repeatedly washed with deionized water and ethanol, and then the rGO / MXene / WO3 gas-sensitive material was separated from impurities such as deionized water and ethanol in a centrifuge. Finally, it was dried at 60°C for 24 hours to obtain rGO / MXene / WO3 gas-sensitive material.

[0107] (4) 0.1 g of rGO / MXene / WO3 gas-sensitive material, 10 mL of isopropanol, 2 mL of propylene glycol and 0.6 g of a surfactant were mixed and ultrasonically dispersed to form an ink with uniform dispersion and stable particles without agglomeration of the rGO / MXene / WO3 gas-sensitive material. Finally, the ink was printed onto a MEMS micro-hotplate by inkjet printing and dried and sintered at 400 °C for 2 h. Finally, the MEMS micro-hotplate was bonded to a ceramic shell, and wire binding and packaging were performed to form a gas sensor.

[0108] Embodiment 3:

[0109] (1) Mix 1 g of lithium fluoride with 20 mL of 9 mol / L hydrochloric acid and stir for 20 min. Then weigh 1 g of Ti3AlC2 powder and add it to the above solution and continue stirring. Then transfer the above solution to a water bath at 40 °C and react for 24 h to obtain Ti3AlC2. X MXene suspension. The above solution was repeatedly washed with deionized water until the pH value of the supernatant was close to 6, and then the precipitate from the last wash was dispersed in ethanol and ultrasonically treated for 120 min at a temperature of 100 °C and finally dried in a vacuum oven at 60 °C for 12 h to obtain Ti3AlT X MXene powder.

[0110] (2) Ti3AlT X MXene powder was ultrasonically dispersed in a mixed solvent of deionized water and ethanol to make Ti3AlT X The concentration of MXene powder in the mixed solvent was 1 mg / g, and Ti3AlT X MXene solution.

[0111] (3) Take 3 mL of 10 mg / mL graphene oxide (GO) solution and disperse it in 40 mL of deionized water. Then add 0.096 g of Na2WO4·2H2O, 0.011 g of ascorbic acid and 0.043 g of sodium chloride, and add 3 mL of Ti3AlT XMXene solution, and adjust the pH value to about 2. After fully stirring for 15 minutes, the mixed solution was transferred to a reactor and reacted at 180°C for 12 hours. The reaction product was repeatedly washed with deionized water and ethanol, and then the rGO / MXene / WO3 gas-sensitive material was separated from impurities such as deionized water and ethanol in a centrifuge. Finally, it was dried at 60°C for 24 hours to obtain rGO / MXene / WO3 gas-sensitive material.

[0112] (4) 0.1 g of rGO / MXene / WO3 gas-sensitive material, 10 mL of isopropanol, 2 mL of propylene glycol and 0.6 g of a surfactant were mixed and ultrasonically dispersed to form an ink with uniform dispersion and stable particles without agglomeration of the rGO / MXene / WO3 gas-sensitive material. Finally, the ink was printed onto a MEMS micro-hotplate by inkjet printing and dried and sintered at 400 °C for 2 h. Finally, the MEMS micro-hotplate was bonded to a ceramic shell, and wire binding and packaging were performed to form a gas sensor.

[0113] Comparative Example:

[0114] (1) Mix 1 g of lithium fluoride with 20 mL of 9 mol / L hydrochloric acid and stir for 20 min. Then weigh 1 g of Ti3AlC2 powder and add it to the above solution and continue stirring. Then transfer the above solution to a water bath at 40 °C and react for 24 h to obtain Ti3AlC2. X MXene suspension. The above solution was repeatedly washed with deionized water until the pH value of the supernatant was close to 6, and then the precipitate from the last wash was dispersed in ethanol and ultrasonically treated for 120 min at a temperature of 100 °C and finally dried in a vacuum oven at 60 °C for 12 h to obtain Ti3AlT X MXene powder.

[0115] (2) Ti3AlT X MXene powder was ultrasonically dispersed in a mixed solvent of deionized water and ethanol to make Ti3AlT X The concentration of MXene powder in the mixed solvent was 1 mg / g, and Ti3AlT X MXene solution.

[0116] (3) Take 3 mL of 10 mg / mL graphene oxide (GO) solution and disperse it in 40 mL of deionized water. Then add 0.011 g of ascorbic acid and 0.043 g of sodium chloride, and add 3 mL of Ti3AlT XMXene solution, and adjust the pH value to about 2. After fully stirring for 15 minutes, the mixed solution was transferred to a reactor and reacted at 180°C for 12 hours. The reaction product was repeatedly washed with deionized water and ethanol, and then the rGO / MXene / WO3 gas-sensitive material was separated from impurities such as deionized water and ethanol in a centrifuge. Finally, it was dried at 60°C for 24 hours to obtain rGO / MXene / WO3 gas-sensitive material.

[0117] (4) 0.1 g of rGO / MXene / WO3 gas-sensitive material, 10 mL of isopropanol, 2 mL of propylene glycol and 0.6 g of a surfactant were mixed and ultrasonically dispersed to form an ink with uniform dispersion and stable particles without agglomeration of the rGO / MXene / WO3 gas-sensitive material. Finally, the ink was printed onto a MEMS micro-hotplate by inkjet printing and dried and sintered at 400 °C for 2 h. Finally, the MEMS micro-hotplate was bonded to a ceramic shell, and wire binding and packaging were performed to form a gas sensor.

[0118] like Figure 4 As shown, Figure 4 The response recovery curves of the gas sensors prepared in the above-mentioned embodiments and comparative examples in a 10ppmNO2 gas environment are shown. It can be seen that, when the tungsten ion compound is controlled not to be excessive, the gas sensors corresponding to Embodiment 1 and Embodiment 2 both exhibit better response speed and recovery speed in a 1ppmNO2 gas environment, and are both better than the gas sensors corresponding to the comparative examples, that is, the gas sensors provided in the embodiments of the present application exhibit excellent gas-sensing performance.

[0119] like Figure 5 As shown, Figure 5 The response value change curve of the gas sensor prepared in Example 1 to 10ppm NO2 gas at different working temperatures is shown, from which it can be seen that the gas sensor prepared in Example 1 has the highest response value to NO2 gas at 25°C, which means that the gas sensor provided in the embodiment of the present application can work at room temperature.

[0120] like Figure 6 As shown, Figure 6 The response recovery curve of the gas sensor prepared in Example 1 in an environment of NO2 gas with different concentrations is shown, from which it can be seen that the gas sensor prepared in Example 1 exhibits better response speed and recovery speed in an environment of NO2 gas with different concentrations, which means that the gas sensor provided in the embodiment of the present application has a higher working stability.

[0121] In summary, the gas sensor provided in the embodiment of the present application exhibits excellent gas-sensitive performance for NO2 gas, and can realize NO2 detection under low temperature or room temperature conditions. The operating temperature can be 25°C. When the test concentration is 10ppm, the response value [(Ra-Rg) / Rg] is 311%, the response recovery time is 164s / 95s, and the detection lower limit reaches 0.5ppm. In terms of detecting NO2 gas, it has excellent selectivity and long-term stability.

[0122] An embodiment of the present application also provides a gas sensor, which is prepared by using the preparation method provided by any of the above embodiments.

[0123] The specific method of preparing the gas sensor can refer to the corresponding embodiment recorded in the specification of this application, and this embodiment will not be repeated here. The gas sensor provided in the embodiment of this application exhibits excellent gas-sensing performance for NO2 gas, and has excellent selectivity and stability.

[0124] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A method for preparing a gas-sensitive material, characterized in that: The method comprises: Mixing a hydrofluoric acid solution with a MAX phase material to prepare a MXene solution; Mixing a graphene oxide solution, a tungsten ion compound, ascorbic acid and the MXene solution, so that the ascorbic acid reduces the graphene oxide in the graphene oxide solution to obtain a rGO / MXene / WO3 mixed solution; The rGO / MXene / WO3 mixed solution is subjected to a hydrothermal reaction to obtain an rGO / MXene / WO3 gas-sensitive material.

2. The method according to claim 1, characterized in that The step of mixing the hydrofluoric acid solution with the MAX phase material to prepare the MXene solution comprises: Adding the MAX phase material to the hydrofluoric acid solution to prepare a MXene suspension; The MXene suspension is filtered to obtain the MXene solution.

3. The method according to claim 2, characterized in that The filtering treatment of the MXene suspension to obtain the MXene solution comprises: The MXene suspension is cleaned, ultrasonicated and dried to obtain MXene powder; The MXene powder is ultrasonically dispersed in a mixed solvent to prepare the MXene solution, wherein the ratio of deionized water to ethanol in the mixed solvent is 1:(1-10), and the concentration of the MXene solution is 0.5-10 mg / g.

4. The method according to claim 1, characterized in that The reaction conditions of the hydrothermal reaction include: hydrothermal temperature of 120-240° C., hydrothermal time of 8-24 h, and a capacity of the hydrothermal container of 20-120 mL.

5. The method according to claim 1, characterized in that The step of mixing a graphene oxide solution, a tungsten ion compound, ascorbic acid and the MXene solution so that the ascorbic acid reduces the graphene oxide in the graphene oxide solution to obtain a rGO / MXene / WO3 mixed solution comprises: Mixing a graphene oxide solution, a tungsten ion compound and ascorbic acid, so that the ascorbic acid reduces the graphene oxide in the graphene oxide solution to obtain a rGO / WO3 mixed solution; The MXene solution is added to the rGO / WO3 mixed solution to prepare the rGO / MXene / WO3 mixed solution.

6. The method according to claim 5, characterized in that The step of mixing a graphene oxide solution, a tungsten ion compound and ascorbic acid so that the ascorbic acid reduces the graphene oxide in the graphene oxide solution to obtain a rGO / WO3 mixed solution comprises: Adding the graphene oxide solution into deionized water to obtain a graphene oxide mixed solution; The tungsten ion compound and the ascorbic acid are added to the graphene oxide mixed solution to prepare the rGO / WO3 mixed solution, and the mass ratio of the graphene oxide solution to the tungsten ion compound is 1:1-5:

1.

7. The method according to claim 5, characterized in that The step of adding the MXene solution to the rGO / WO3 mixed solution to obtain the rGO / MXene / WO3 mixed solution comprises: In an acidic environment, the MXene solution is added to the rGO / WO3 mixed solution to prepare an rGO / MXene / WO3 mixed solution, and the mass ratio of reduced graphene oxide to the MXene solution is 1:1-5:

1.

8. The method according to any one of claims 1 to 7, characterized in that: The valence of the tungsten ion in the tungsten ion compound is +6.

9. A method for preparing a gas sensor, characterized in that: The method comprises: The rGO / MXene / WO3 gas-sensitive material is prepared by the preparation method of the gas-sensitive material according to any one of claims 1 to 8; Adding the rGO / MXene / WO3 gas-sensitive material into a dispersant solution to obtain a gas-sensitive material ink; Printing using the gas-sensitive material ink to form a gas-sensitive film on the surface of the micro-hotplate; The micro-hotplate formed with the gas sensitive film is packaged to obtain a gas sensor.

10. A gas sensor, characterized in that: The gas sensor is prepared by using the method for preparing a gas sensor according to claim 9.

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