Preparation method of MXene / g-C3N4 composite material, product, gas sensor and application thereof

Abstract

The application discloses a kind of preparation method of MXene / g-C3N4 composite material, product and a kind of gas sensor and its application, it is characterized in that, belong to gas-sensitive material technical field, comprising the following steps: (1) the preparation of MXene material;(2) the preparation of MXene / g-C3N4 composite material.Simultaneously disclosed the MXene / g-C3N4 composite material prepared by the above preparation method, and the gas sensor and its application prepared by the material.The composite material provided by the application can exhibit high gas sensitivity to different gases at low and high temperatures, and also shows good gas sensitivity selectivity and stability to NH3 and NO2, which can be used to prepare a dual-gas gas sensor for detecting NH3 and NO2.

Description

Technical Field

[0001] This invention relates to the field of gas-sensitive materials, and in particular to a method for preparing an MXene / g-C3N4 composite material, a product thereof, a gas-sensitive sensor thereof, and its application. Background Technology

[0002] With the continuous progress of human society and the constant innovation of science and technology, NH3 and NO2 have gradually become major harmful gases that pollute the air and damage human health. Long-term inhalation of NH3 can cause pulmonary edema, acute respiratory distress syndrome, and other diseases. When the concentration of NO2 exceeds 1 ppm, it will damage the respiratory system and aggravate respiratory diseases. At the same time, NH3 and NO2 cause serious pollution to rivers, land, vegetation, and air. Therefore, the development of gas sensors that can accurately detect NO2 and NH3 is imperative.

[0003] Currently, gas-sensitive materials for NO2 and NH3 detection are mainly concentrated in metal oxide semiconductors such as SnO2, ZnO, Co3O4, and WO3. Although metal oxide semiconductor gas-sensitive materials exhibit excellent gas-sensing properties, they often require high operating temperatures, and the fabricated gas sensors can only detect one gas. This not only leads to material waste but also increases energy consumption.

[0004] Therefore, how to provide a sensor that can operate under low-temperature conditions, has high gas sensitivity, and can detect dual gases is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing MXene / g-C3N4 composite materials with different F / O ratios, products, and a gas sensor and its application, in order to solve the problems existing in the prior art. This composite material can exhibit high gas sensitivity performance for different gases at low and high temperatures, and at the same time, it exhibits good gas sensitivity selectivity and stability for NH3 and NO2. It can be used to prepare a dual-gas gas sensor for the detection of NH3 and NO2.

[0006] To achieve the above objectives, the present invention provides the following solution:

[0007] A method for preparing an MXene / g-C3N4 composite material includes the following steps:

[0008] (1) MAX was placed in a mixed solution of fluoride salt and HCl, and liquid phase etching was performed by stirring under hydrothermal conditions. After cleaning, the material was dried to obtain MXene material.

[0009] (2) The MXene material is mixed with g-C3N4 and sintered under gas conditions to obtain the MXene / g-C3N4 composite material.

[0010] Preferably, the MAX precursor in step (1) is selected from one of V2AlC, V3AlC2, Cr2AlC, Cr3AlC2, Ti2AlC, and Ti3AlC2;

[0011] The fluoride salt is one of NaF and LiF;

[0012] The HCl concentration in the mixed solution is 6 mol / L, and the fluoride salt concentration is 3.85 mol / L;

[0013] The stirring rate is 450-550 rpm, the hydrothermal temperature is 100-120℃, and the hydrothermal time is 5-7 days;

[0014] The cleaning process involves using deionized water and anhydrous ethanol until the solution is neutral.

[0015] The drying temperature is 60-80℃, and the drying time is 7-12 hours;

[0016] The MXene material is V2CT. x V3C2T x Cr2CT x Cr3C2T x Ti2CT x Ti3C2T x One of them.

[0017] Beneficial effects: The preparation process of MXene uses a mixed solution of HCl and fluoride salts, which avoids the toxic and high-risk system of HF and yields pure layered MXene materials.

[0018] Preferably, the mass ratio of MXene material to g-C3N4 in step (2) is (3-5):(10-15);

[0019] The gas conditions are argon or air;

[0020] The sintering temperature is 200℃-300℃, and the sintering time is 0.5-1h;

[0021] The chemicals used in the g-C3N4 material are melamine or urea, the instrument is a muffle furnace, and the preparation temperature is 450℃-560℃.

[0022] Preferably, the step between (1) and (2) further includes:

[0023] (1-1) The MXene material is dispersed in an alkaline solution and stirred, and then washed, dried and sintered in sequence to obtain a high hydroxyl (-OH)MXene material;

[0024] Preferably, the alkaline solution in step (1-1) is a NaOH solution or a KOH solution;

[0025] The concentration of the alkaline solution is 1.8 mol / L;

[0026] The stirring rate is 700 rpm, and the stirring time is 4-6 hours.

[0027] The cleaning process involves washing with deionized water 5-8 times, and the drying temperature is 70-90℃, with a drying time of 8-12 hours.

[0028] The sintering is carried out under an argon atmosphere at a temperature of 400-500℃ for 2-3 hours.

[0029] An MXene / g-C3N4 composite material prepared by the above preparation method.

[0030] A gas sensor comprising the above-mentioned MXene / g-C3N4 composite material, wherein the preparation method includes the following steps:

[0031] The MXene / g-C3N4 composite material was mixed with an ethanol solution, ground, and then printed onto a ceramic sheet with a platinum-plated electrode. The mixture was then placed in a tube furnace and sintered under an Ar protective atmosphere to obtain a gas sensor.

[0032] In this invention, the ethanol solution is used as the grinding medium. Those skilled in the art can adjust the ethanol concentration and amount added according to the actual grinding conditions. Furthermore, this invention does not impose any special limitations on the grinding particle size. Those skilled in the art can select the grinding time and the final grinding particle size according to the printing state.

[0033] The sintering temperature is 350℃-550℃, and the time is 2-4 hours.

[0034] Application of a gas sensor in the detection of NO2 and / or NH3 gases.

[0035] This invention discloses a method for preparing an MXene / g-C3N4 composite material, the product, and a gas sensor and its application. By regulating the functional groups of MXene and combining it with g-C3N4, this invention effectively reduces the content of F functional groups on the MXene surface, providing more oxygen active sites for gas-sensing performance testing and improving gas-sensing performance. Secondly, by regulating the functional groups of MXene and combining it with g-C3N4, this invention alters the energy level structure of the MXene material, causing it to exhibit different semiconductor properties for different gases at different temperatures, thereby enabling the detection of different gases. Furthermore, the MXene / g-C3N4 gas-sensing material obtained by this invention exhibits excellent gas-sensing characteristics, achieving a gas-sensing response value of 84.2% for 100ppm NH3 at 25℃, while also showing good gas-sensing selectivity and stability for NH3 and NO2, allowing for the fabrication of a dual-gas gas sensor. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 To utilize the hyperoxia V2CT obtained in Example 1 x The response cycle curves of a gas sensor prepared from the -g-C3N4 composite when testing different concentrations of NO2 gas at 250℃;

[0038] Figure 2 The gas-sensitive response values ​​of different samples to 100ppm NO2 at different operating temperatures;

[0039] Figure 3 The images shown are scanning electron microscope (SEM) images of the obtained products.

[0040] Wherein, (b) is the V2CT obtained in Example 1. x Scanning electron micrograph of -g-C3N4-O2, (d) is the V2CT obtained in Example 2. x Scanning electron microscope image of -g-C3N4-KOH-Ar. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0043] Example 1

[0044] A method for preparing an MXene / g-C3N4 composite material includes the following steps:

[0045] (1) Preparation of two-dimensional layered MXene powder:

[0046] The parent material V2AlC was added to a mixed solution of 0.05M sodium fluoride (NaF) and 6M HCl in 40 ml. The mixture was stirred at 450 rpm using a magnetic stirrer until homogeneous. The homogeneous solution was then poured into a 100 ml polytetrafluoroethylene stainless steel reactor and hydrothermally treated at 120°C for 5 days. After the reaction was complete, the mixture was allowed to cool naturally to room temperature. The resulting solution was washed several times with deionized water and anhydrous ethanol until the pH reached 7. The resulting black precipitate was then dried in a 60°C oven for 12 hours to obtain two-dimensional layered V2CT. x powder;

[0047] (2) Preparation of g-C3N4:

[0048] Melamine was placed in a covered ceramic crucible and sintered in a muffle furnace at 550°C for 2 hours. The furnace was then cooled to obtain a yellow powder g-C3N4.

[0049] (3) Hyperoxia V2CT x -g-C3N4 complex:

[0050] Take the V2CT obtained in step (1) x The mixture was prepared by mixing g-C3N4 at a mass ratio of 3:10, and after thorough mixing, it was placed in a conventional muffle furnace and sintered at 200°C for 1 hour in air atmosphere to obtain high-oxygen V2CT. x -g-C3N4 complex.

[0051] Example 2

[0052] A method for preparing an MXene / g-C3N4 composite material, which differs from Example 1, is as follows:

[0053] Step (3) is: take the V2CT obtained in step (1). x 3g of powder was placed in 60ml of 1.8M KOH solution and stirred at 700rpm for 6h to obtain a homogeneous solution. The solution was washed repeatedly with deionized water 8 times and then filtered. The resulting black precipitate was placed in an oven and dried at 90℃ for 10h. The sample was then placed in a tube furnace and sintered at 450℃ under argon protection for 4h. After cooling to room temperature with the furnace, high (-OH)MXene V2CT was obtained. x Black powder, high (-OH)MXene V2CT x g-C3N4 was mixed with g-C3N4 at a mass ratio of 5:10. After thorough mixing, the mixture was placed in a conventional tube furnace and sintered at 300°C for 0.5 h under argon protection to obtain high (-OH)V2CT. x -g-C3N4 complex.

[0054] Example 3

[0055] A method for preparing an MXene / g-C3N4 composite material, which differs from Example 1, is as follows:

[0056] The parent material in step (1) is Ti2AlC, and Ti2CT is finally obtained. x powder;

[0057] Step (3) is: Take the Ti2CT obtained in step (1) x The powder and g-C3N4 were mixed at a mass ratio of 3:15. After thorough mixing, the mixture was placed in a conventional tube furnace / muffle furnace and sintered at 300°C for 1 hour in air atmosphere to obtain high-oxygen Ti2CT. x -g-C3N4 complex.

[0058] Example 4

[0059] A method for preparing an MXene / g-C3N4 composite material, which differs from Example 1, is as follows:

[0060] The parent material in step (1) is Cr3AlC2, and the final product is Cr3C2T. x powder;

[0061] Step (3) is: Take the Cr3C2T obtained in step (1) x 3g was placed in 60ml of KOH solution and stirred at 700rpm for 4h to obtain a homogeneous solution. The solution was washed repeatedly with deionized water 5 times, filtered, and the resulting black precipitate was placed in an oven and dried at 70℃ for 10h. The sample was then placed in a tube furnace and sintered at 400℃ under argon protection for 3h, followed by furnace cooling to room temperature to obtain high (-OH)MXene Cr3C2T. xBlack powder containing high (-OH)MXene Cr3C2T x The mixture was prepared by mixing g-C3N4 at a mass ratio of 5:15, and after thorough mixing, it was placed in a conventional tube furnace and sintered at 200°C for 1 hour under argon protection to obtain high (-OH)Cr3C2T. x -g-C3N4 complex.

[0062] Example 5

[0063] A gas sensor comprising an MXene / g-C3N4 composite material, and the preparation method comprising the following steps:

[0064] The obtained MXene / g-C3N4 composite material was mixed with a 50% ethanol solution and ground for 10 min to a particle size of 580 nm. The mixture was then printed onto a ceramic sheet with a platinum-plated electrode and sintered in a tube furnace at 550 °C under an Ar protective atmosphere for 2 h to obtain a gas sensor.

[0065] Comparative Example 1

[0066] A method for preparing a composite material, differing from Example 1 in that the etched V2CT... x It does not combine with g-C3N4 to form a composite material.

[0067] Comparative Example 2

[0068] A method for preparing a composite material, which differs from Example 2 in that, in step (3), high (-OH)V2CT is used. x Replace with pure V2CT x To perform compounding.

[0069] Technical effect

[0070] I. XPS Spectrum Analysis

[0071] Table 1 shows the XPS peak fitting results for each element in different samples:

[0072] Table 1

[0073] C N F O V F / O <![CDATA[V2CT x ]]> 32.30 - 11.24 28.18 28.28 0.39 <![CDATA[V2CT x -NaOH]]> 17.89 - 4.00 26.83 51.27 0.14 <![CDATA[V2CT x -KOH]]> 13.08 - 5.02 26.66 55.24 0.18 <![CDATA[V2CT x -g-C3N4-O2]]> 26.64 28.98 4.02 14.24 26.11 0.28 <![CDATA[V2CT x -g-C3N4-Ar]]> 34.26 31.13 7.29 15.99 11.32 0.45 <![CDATA[V2CT x -g-C3N4-NaOH-Ar]]> 27.91 29.22 3.43 14.18 25.27 0.24 <![CDATA[V2CT x -g-C3N4-KOH-Ar]]> 28.00 26.77 4.04 13.76 27.43 0.29

[0074] As shown in Table 1, V2CT after alkali treatment x The F / O ratio decreases significantly, which is due to the reaction between the -OH group in the base and V2CT. x The -F functional groups on the surface compete for energy, and -F is gradually replaced. Furthermore, the sintering atmosphere affects V2CT. x -g-C3N4 has a significant impact on the F / O ratio; an aerobic environment is conducive to V2CT. xThe removal of -F in -g-C3N4 materials, similar to that of -OH, also competes with -F, leading to a decrease in -F content. x The increased O content in the -g-C3N4 material facilitates the adsorption of gas molecules in the gas-sensitive reaction, allowing more oxygen molecules to adsorb onto the material surface, increasing the resistance difference before and after the target gas is introduced, and improving the gas-sensitive performance of the material.

[0075] II. Gas Sensing Performance Test

[0076] Using the materials obtained in Examples 1-2 and Comparative Examples 1-2, gas sensors were prepared using the method in Example 5. The gas-sensing performance of the sensitive material used in the sensors was tested at 250°C and 25°C, respectively. The tests were conducted on a gas-sensing testing device (KLUM-QM-104) using a dynamic testing method, and the specific operation is as follows:

[0077] 1. Connect the gas sensor to the gas-sensitive testing equipment, fill the gas-sensitive testing equipment with air until it stabilizes, and measure the resistance value (Rair) of the gas sensor in the air;

[0078] 2. Introduce NO2 or NH3 at a concentration of 100 ppm into the gas-sensitive testing equipment until the response signal stabilizes, and measure the resistance (R) of the gas sensor in 100 ppm NO2 and 100 ppm NH3 respectively;

[0079] 3. Re-introduce air into the gas-sensitive testing equipment until it stabilizes, and then allow the gas sensor to complete one response recovery process. The ratio of the resistance difference ΔR between the gas sensor and NO2 or NH3 in air to the resistance value in air (ΔR / Rair*100%) is the response value of the gas sensor to that concentration of NO2 or NH3.

[0080] Figure 1 The response cycle curves of the sensor in Example 1 when testing different concentrations of NO2 gas at 250°C are shown.

[0081] Depend on Figure 1 As can be seen, the product provided by this invention can detect NO2 at different concentrations, with a gas-sensitive response value of 90.3% for 100ppm NO2, indicating that the product provided by this invention has good gas-sensitive response and stability.

[0082] Table 2 shows the ratio of the difference between the resistance values ​​of the gas sensors prepared using the products provided in Examples 1-2 and Comparative Examples 1-2 in 100ppm NH3 and in air, respectively, to the resistance value of air, measured at 25°C.

[0083] Table 2

[0084]

[0085] As shown in Table 2, the combination of MXene and g-C3N4 can regulate the functional groups on the surface of MXene, forming oxygen-rich / -OH-rich MXene / g-C3N4 composite materials, which can effectively improve the gas-sensitive response of MXene materials to NH3.

[0086] Table 3 shows the ratio of the difference between the resistance values ​​of the sensors in Examples 1-2 and Comparative Examples 1-2 in 100ppm NO2 and in air to the air resistance value at 250℃.

[0087] Table 3

[0088]

[0089] As shown in Table 3, the combination of MXene and g-C3N4, as well as the regulation of the functional groups on the surface of MXene to form oxygen-rich / -OH-rich MXene / g-C3N4 composite materials, can effectively improve the gas-sensitive response of MXene materials to NO2.

[0090] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing an MXene / g-C3N4 composite material, characterized in that, Includes the following steps: (1) MAX was placed in a mixed solution of fluoride salt and HCl, and liquid phase etching was performed by stirring under hydrothermal conditions. After cleaning, the material was dried to obtain MXene material. Optional: Between steps (1) and (2) there is also: (1-1) The MXene material is dispersed in an alkaline solution and stirred, and then washed, dried and sintered in sequence to obtain a high hydroxyl (-OH)MXene material; (2) The MXene material is mixed with g-C3N4 and sintered under gaseous conditions to obtain the MXene / g-C3N4 composite material; When step (1-1) is included; the gas condition is argon; When step (1-1) is not included; the gas condition is air condition.

2. The method for preparing an MXene / g-C3N4 composite material according to claim 1, characterized in that, The MAX precursor mentioned in step (1) is selected from one of V2AlC, V3AlC2, Cr2AlC, Cr3AlC2, Ti2AlC, and Ti3AlC2; The fluoride salt is one of NaF and LiF; The HCl concentration in the mixed solution is 6 mol / L, and the fluoride salt concentration is 3.85 mol / L; The stirring rate is 450-550 rpm, the hydrothermal temperature is 100-120℃, and the hydrothermal time is 5-7 days; The cleaning process involves using deionized water and anhydrous ethanol until the solution is neutral. The drying temperature is 60-80℃, and the drying time is 7-12 hours; The MXene material is V2CT. x V3C2T x Cr2CT x Cr3C2T x Ti2CT x Ti3C2T x One of them.

3. The method for preparing an MXene / g-C3N4 composite material according to claim 1, characterized in that, The mass ratio of MXene material to g-C3N4 in step (2) is (3-5):(10-15); The sintering temperature is 200℃-300℃, and the sintering time is 0.5-1h; The chemicals used in the g-C3N4 material are melamine or urea, the instrument is a muffle furnace, and the preparation temperature is 450℃-560℃.

4. The method for preparing an MXene / g-C3N4 composite material according to claim 1, characterized in that, The alkaline solution mentioned in step (1-1) is a NaOH solution or a KOH solution; The concentration of the alkaline solution is 1.8 mol / L; The stirring rate is 700 rpm, and the stirring time is 4-6 hours. The cleaning process involves washing with deionized water 5-8 times, and the drying temperature is 70-90℃, with a drying time of 8-12 hours. The sintering is carried out under an argon atmosphere at a temperature of 400-500℃ for 2-3 hours.

5. An MXene / g-C3N4 composite material prepared by the preparation method according to any one of claims 1-4.

6. A gas-sensitive sensor, characterized in that, The preparation method of the MXene / g-C3N4 composite material according to claim 5 includes the following steps: The MXene / g-C3N4 composite material was mixed with an ethanol solution, ground, and then printed onto a ceramic sheet with a platinum-plated electrode. The mixture was then placed in a tube furnace and sintered under an Ar protective atmosphere to obtain a gas sensor.

7. A gas sensor according to claim 6, characterized in that, The sintering temperature is 350℃-550℃, and the time is 2-4 hours.

8. The application of a gas sensor as described in claim 6 or 7 in the detection of NO2 and / or NH3 gases.

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