Atomic dispersion palladium functional defect tungsten disulfide nanosheet and preparation method and application thereof, methanol gas sensor and preparation method and application thereof

Abstract

The invention provides an atomic dispersion palladium functionalized defective tungsten disulfide nanosheet and a preparation method and application thereof, a methanol gas sensor and a preparation method and application thereof, and relates to the technical field of sensors. The atom dispersion palladium functionalized defective tungsten disulfide nanosheet provided by the invention comprises a defective tungsten disulfide nanosheet and palladium single atoms dispersed at the defect. According to the atom dispersion palladium functional defect tungsten disulfide nanosheet provided by the invention, defects can improve surface charge transfer of a sensitive material and enhance adsorption of CH3OH, and can also be used as active sites for methanol adsorption, so that Pd monatomic atoms are more favorably stabilized, and the Pd monatomic atoms can fully mobilize each active site to participate in activation of gas molecules, so that the stability of the gas molecules is improved. And the reaction potential barrier of CH3OH and chemical adsorption oxygen is reduced. The atom dispersion palladium functionalized defect tungsten disulfide nanosheet provided by the invention is used as a gas sensor of a sensitive material, and high response to trace methanol under a room temperature condition is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of sensors, and in particular to an atomically dispersed palladium-functionalized defective tungsten disulfide nanosheet and its preparation method and application, a methanol gas sensor and its preparation method and application. Background Art

[0002] The global energy crisis is escalating, and environmental problems are becoming increasingly urgent, forcing the automotive industry to transform into the new energy field to reduce dependence on fossil fuels and environmental pollution. Methanol (CH 3 OH) has become a key energy competitor in the development of new energy vehicle technologies due to its renewable and low-carbon emission characteristics. However, CH 3 OH has extremely strong volatility and high toxicity, which can cause great harm to the human nervous system and blood system, and even damage the respiratory mucosa and eyesight in severe cases. In addition, methanol has a low flash point, and its vapor can form an explosive mixture with air within a certain range, and it is extremely easy to burn or explode when exposed to an open flame, high temperature or oxidant. Therefore, the development of high-performance room-temperature methanol sensors is crucial for the safety management of methanol fuel vehicles and the protection of personal safety. So far, the sensitive materials used for methanol detection mainly focus on metal oxide semiconductors such as ZnO, CeO 2 ,In 2 O 3 and WO 3 However, methanol sensors based on the above-mentioned sensitive materials still face challenges of high working temperature and low response. Summary of the Invention

[0003] In view of this, the purpose of the present invention is to provide an atomically dispersed palladium-functionalized defective tungsten disulfide nanosheet and its preparation method and application, a methanol gas sensor and its preparation method and application. The gas sensor using the atomically dispersed palladium-functionalized defective tungsten disulfide nanosheet (denoted as Pd SA@WS 2 NSs) provided by the present invention as the sensitive material has a high response to methanol at room temperature.

[0004] To achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0005] The present invention provides an atomically dispersed palladium-functionalized defective tungsten disulfide nanosheet, which includes a defective tungsten disulfide nanosheet and palladium single atoms dispersed at the defects.

[0006] Preferably, the mass of the palladium single atoms is 0.1-0.7% of the mass of the tungsten disulfide nanosheet.

[0007] Preferably, the thickness of the tungsten disulfide nanosheet is 3.45-4.82 nm.

[0008] The present invention also provides a method for preparing atomically dispersed palladium-functionalized defective tungsten disulfide nanosheets according to the above technical solution, comprising the following steps:

[0009] Grind tungsten disulfide powder with acetonitrile, remove the solvent, then disperse it in a mixed solvent of a low-boiling organic solvent and water, perform ultrasonic treatment, separate the solid and liquid, and remove the solvent in the obtained liquid component to obtain defective few-layer tungsten disulfide nanosheets (denoted as WS 2 NSs); the boiling point of the low-boiling organic solvent is ≤80 °C;

[0010] Mix the defective few-layer tungsten disulfide nanosheets, H 2 PdCl 4 solution and ethanol, perform ultraviolet irradiation treatment, separate the solid and liquid, to obtain atomically dispersed palladium-functionalized defective tungsten disulfide nanosheets.

[0011] Preferably, the mass-volume ratio of the tungsten disulfide powder to acetonitrile is 1 g: 0.5 - 1.5 mL;

[0012] The temperature of the grinding is room temperature and the time is 0.5 - 1 h.

[0013] Preferably, the low-boiling organic solvent includes ethanol;

[0014] The volume fraction of the low-boiling organic solvent in the mixed solvent is 20 - 40%;

[0015] The mass-volume ratio of the tungsten disulfide powder to the mixed solvent is 1 g: 100 - 300 mL;

[0016] The time of the ultrasonic treatment is 2 - 4 h.

[0017] Preferably, the mass of palladium in the H 2 PdCl 4 solution accounts for 0.1 - 1% of the mass of the defective few-layer tungsten disulfide nanosheets;

[0018] The mixing time is 10 - 12 h;

[0019] The time of the ultraviolet irradiation treatment is 10 - 20 min.

[0020] The present invention also provides a methanol gas sensor, comprising a polyimide film substrate sputtered with Au interdigital electrodes and a sensitive material layer; the sensitive material of the sensitive material layer includes the atomically dispersed palladium-functionalized defective tungsten disulfide nanosheets according to the above technical solution or the atomically dispersed palladium-functionalized defective tungsten disulfide nanosheets prepared by the preparation method according to the above technical solution.

[0021] The present invention also provides a method for preparing the methanol gas sensor described in the above technical solution, which includes the following steps: coating a sensitive material suspension on the surface of a polyimide film substrate sputtered with Au interdigital electrodes and then drying to obtain a gas sensor.

[0022] The present invention also provides the application of the atomically dispersed palladium-functionalized defective tungsten disulfide nanosheets described in the above technical solution, the atomically dispersed palladium-functionalized defective tungsten disulfide nanosheets prepared by the preparation method described in the above technical solution, the methanol gas sensor described in the above technical solution, or the methanol gas sensor prepared by the preparation method described in the above technical solution in methanol detection.

[0023] The present invention provides an atomically dispersed palladium-functionalized defective tungsten disulfide nanosheet, which includes a defective tungsten disulfide nanosheet and palladium single atoms dispersed at the defects. In the atomically dispersed palladium-functionalized defective tungsten disulfide nanosheets provided by the present invention, the defects (S defects) can not only improve the surface charge transfer of the sensitive material and enhance the adsorption of CH 3 OH, but also serve as active sites for methanol adsorption. In addition, surface defects are more conducive to stabilizing Pd single atoms. The present invention utilizes Pd single atoms to fully mobilize each active site to participate in the activation of gas molecules, reducing the reaction barrier between CH 3 OH and chemisorbed oxygen, and having a higher electron mobility in the sensing process. In addition, the strong metal-support interaction between Pd single atoms and tungsten disulfide nanosheets can further promote charge transfer in the sensing reaction process.

[0024] For the methanol gas sensor using the atomically dispersed palladium-functionalized defective tungsten disulfide nanosheets provided by the present invention as the sensitive material, it has a high response to methanol at room temperature, solves the challenges of high working temperature, low response, and difficulty in detecting low concentrations existing in existing methanol sensors, and can achieve high-performance detection of trace (ppb level) methanol at room temperature.

[0025] The present invention adopts a grinding-assisted liquid-phase exfoliation method. The introduced S defects can not only improve the surface charge transfer of the sensitive material and enhance the adsorption of CH 3 OH, but also serve as active sites for methanol adsorption. In addition, surface defects are more conducive to stabilizing Pd single atoms. The preparation method of the atomically dispersed palladium-functionalized defective tungsten disulfide provided by the present invention is simple in operation, low in production cost, green and environmentally friendly, and suitable for industrial production.

[0026] The preparation method of the gas sensor provided by the present invention is simple in process, easy to operate, strong in reliability, low in production cost, green and environmentally friendly, and suitable for industrial production. Description of the Drawings

[0027] Figure 1 For the present invention based on Pd SA@WS 2Schematic diagram of a resistive gas sensor with an NSs sensitive material layer;

[0028] Figure 2 WS prepared for Comparative Example 2 2 Atomic force microscope image of NSs;

[0029] Figure 3 WS prepared for Comparative Example 2 2 NSs and Pd SA@WS prepared in Examples 1-2 2 XRD pattern of the NSs sensitive material;

[0030] Figure 4 For WS 2 Powder (bulk WS 2 )), WS prepared for Comparative Example 2 2 NSs and 0.3 wt% Pd SA@WS prepared in Example 1 2 SEM images (a-c) of the NSs sensitive material and 0.3 wt% Pd SA@WS 2 TEM images (d-f) of the NSs sensitive material, where a is bulk WS 2 , b is WS 2 NSs, c is 0.3 wt% Pd SA@WS 2 NSs;

[0031] Figure 5 For 0.3 wt% Pd SA@WS prepared in Example 1 2 Aberration-corrected scanning transmission electron microscope image (a) and x-y line scan elemental distribution maps (b and c) of the NSs sensitive material;

[0032] Figure 6 Based on WS prepared for Comparative Example 2 2 NSs, 0.3 wt% Pd SA@WS prepared in Example 1 2 NSs and 0.5 wt% Pd SA@WS prepared in Example 2 2 Response change curves of gas sensors based on NSs to 0.1-3 ppm CH 3 OH at room temperature;

[0033] Figure 7 Based on WS prepared for Comparative Example 2 2 NSs (a) and 0.3 wt% Pd SA@WS prepared in Example 1 2 NSs (b) of gas sensors to 0.1-3 ppm CH 3 OH transient response-recovery curves at room temperature;

[0034] Figure 8For the gas sensor based on 0.3 wt% Pd SA@WS 2 NSs, the cyclic sensing transient change curve for 100 ppb CH 3 OH at room temperature.

[0035] Figure 9 For WS 2 NSs prepared based on Comparative Example 2 and 0.3 wt% Pd SA@WS 2 NSs gas sensors, the response bar chart to different interfering gases at room temperature. Detailed implementation mode

[0036] The present invention provides an atomically dispersed palladium-functionalized defective tungsten disulfide nanosheet, which includes a tungsten disulfide nanosheet with defects and palladium single atoms dispersed at the defects.

[0037] In the present invention, the mass of the palladium single atoms is 0.1-0.7% of the mass of the tungsten disulfide nanosheet, and in specific embodiments, it can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6% or 0.7%.

[0038] In the present invention, the thickness of the tungsten disulfide nanosheet is preferably 3.45-4.82 nm, and in specific implementation modes, it can be 3.45 nm, 3.8 nm, 4 nm, 4.32 nm, 4.5 nm or 4.82 nm. In the present invention, the number of layers of the tungsten disulfide nanosheet is preferably 5-10 layers, and more preferably 6-8 layers.

[0039] In the atomically dispersed palladium-functionalized defective tungsten disulfide nanosheet provided by the present invention, the defects (S defects) can not only improve the surface charge transfer of the sensitive material and enhance the adsorption of CH 3 OH, but also serve as active sites for methanol adsorption. In addition, surface defects are more conducive to stabilizing Pd single atoms. The present invention makes full use of Pd single atoms to mobilize each active site to participate in the activation of gas molecules, reducing the reaction barrier between CH 3 OH and chemisorbed oxygen, and the electron mobility participating in the sensing process is higher. In addition, the strong metal-support interaction between Pd single atoms and tungsten disulfide nanosheets can further promote charge transfer in the sensing reaction process. The present invention further improves the detection sensitivity to methanol by controlling the content of Pd single atoms in the atomically dispersed palladium-functionalized defective tungsten disulfide nanosheet.

[0040] The present invention also provides a preparation method of the atomically dispersed palladium-functionalized defective tungsten disulfide nanosheet described in the above technical solution, including the following steps:

[0041] The tungsten disulfide powder is ground with acetonitrile and then the solvent is removed. Then it is dispersed in a mixed solvent of a low-boiling organic solvent and water, ultrasonic treatment is carried out, solid-liquid separation is performed, and the solvent in the obtained liquid component is removed to obtain few-layer tungsten disulfide nanosheets with defects; the boiling point of the low-boiling organic solvent is ≤80 °C;

[0042] The few-layer tungsten disulfide nanosheets with defects, H 2 PdCl 4 solution and ethanol are mixed, and ultraviolet irradiation treatment is carried out, followed by solid-liquid separation to obtain atomically dispersed palladium-functionalized defective tungsten disulfide nanosheets.

[0043] Unless otherwise specified, the materials and equipment used in the present invention are all commercially available products in the art.

[0044] In the present invention, the tungsten disulfide powder is ground with acetonitrile and then the solvent is removed. Then it is dispersed in a mixed solvent of a low-boiling organic solvent and water, ultrasonic treatment is carried out, and solid-liquid separation is performed to obtain few-layer tungsten disulfide nanosheets with defects; the boiling point of the low-boiling organic solvent is ≤80 °C.

[0045] In the present invention, the mass-volume ratio of the tungsten disulfide powder to acetonitrile is preferably 1 g: 0.5 - 1.5 mL, and in specific embodiments, it can be 1 g: 0.5 mL, 1 g: 0.6 mL, 1 g: 0.7 mL, 1 g: 0.8 mL, 1 g: 0.9 mL, 1 g: 1 mL, 1 g: 1.1 mL, 1 g: 1.2 mL, 1 g: 1.3 mL, 1 g: 1.4 mL or 1 g: 1.5 mL. Compared with other organic solvents, acetonitrile is used as the grinding solvent in the present invention, which is easy to be completely removed from the material surface after drying. At the same time, adding an appropriate amount of acetonitrile helps to improve the exfoliation effect and yield.

[0046] In the present invention, the temperature of the grinding is preferably room temperature, and the time of the grinding is preferably 0.5 - 1 h, and in specific embodiments, it can be 30 min, 40 min, 50 min or 60 min.

[0047] In the present invention, the removal of the solvent is preferably drying, the drying is preferably vacuum drying, the temperature of the drying is preferably 50 - 80 °C, and in specific embodiments, it can be 50 °C, 60 °C, 70 °C or 80 °C; the present invention has no special limitation on the drying time, as long as the solvent can be completely removed, and the drying time can be 10 - 14 h, and in specific embodiments, it can be 10 h, 11 h, 12 h, 13 h or 14 h.

[0048] In the present invention, the low-boiling organic solvent preferably includes ethanol. In the present invention, the volume fraction of the low-boiling organic solvent in the mixed solvent is preferably 20-40%, and in specific embodiments, it can be 20%, 25%, 30%, 35% or 40%. In the present invention, due to the different solubilities of tungsten disulfide in different solvent mixtures, if the volume fraction of the low-boiling organic solvent in the mixed solvent is too large or too small, it is easy to cause incomplete dissolution of tungsten disulfide and the formed dispersion is unstable. By controlling the volume fraction of the low-boiling organic solvent in the mixed solvent to be 20-40%, the present invention helps to form a highly stable dispersion, and no precipitation is generated after storing for one week under environmental conditions.

[0049] In the present invention, the mass-volume ratio of the tungsten disulfide powder to the mixed solvent is preferably 1 g: 100-300 mL, and in specific embodiments, it can be 1 g: 100 mL, 1 g: 150 mL, 1 g: 200 mL, 1 g: 250 mL or 1 g: 300 mL.

[0050] In the present invention, the temperature of the ultrasonic treatment is preferably room temperature, and the time of the ultrasonic treatment is preferably 2-4 h, and in specific embodiments, it can be 2 h, 2.5 h, 3 h, 3.5 h or 4 h.

[0051] In the present invention, the solid-liquid separation preferably includes centrifugal separation. The rotation speed of the centrifugal separation is preferably 2500-3500 r / min, and in specific embodiments, it can be 2500 r / min, 3000 r / min or 3500 r / min; the time of the centrifugal separation is preferably 15-25 min, and in specific embodiments, it can be 15 min, 20 min or 25 min.

[0052] In the present invention, removing the solvent in the obtained liquid component preferably includes: subjecting the obtained liquid component to suction filtration and drying in sequence. In the present invention, the drying preferably includes vacuum drying. The temperature of the vacuum drying is preferably 50-80 °C, and in specific embodiments, it can be 50 °C, 60 °C, 70 °C or 80 °C; the time of the drying is preferably 10-13 h, and in specific embodiments, it can be 10 h, 11 h, 12 h or 13 h.

[0053] After obtaining few-layer tungsten disulfide nanosheets with defects, the present invention mixes the few-layer tungsten disulfide nanosheets with defects, H 2 PdCl 4 solution and ethanol, performs ultraviolet irradiation treatment, and performs solid-liquid separation to obtain atomically dispersed palladium-functionalized defective tungsten disulfide nanosheets.

[0054] In the present invention, the mass-volume ratio of the defective few-layer tungsten disulfide nanosheets to ethanol is preferably 1-3 mg: 1 mL, and in specific embodiments, it can be 1 mg: 1 mL, 1.5 mg: 1 mL, 2 mg: 1 mL, 2.5 mg: 1 mL, or 3 mg: 1 mL.

[0055] In the present invention, the H 2 PdCl 4 The mass of palladium in the solution accounts for 0.1-1% of the mass of the defective few-layer tungsten disulfide nanosheets. In specific embodiments, it can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1%.

[0056] In the present invention, the H 2 PdCl 4 The concentration of the solution is preferably 10-30 mM (mmol / L). In specific embodiments, it can be 10 mM, 15 mM, 20 mM, 25 mM, or 30 mM; the solvent in the H 2 PdCl 4 solution is preferably water. In the present invention, the mass ratio of Pd to WS 2 PdCl 4 in the atomically dispersed palladium-functionalized defective tungsten disulfide nanosheets is controlled by adjusting the addition amount of the H 2 solution.

[0057] In the present invention, the temperature of the mixing is preferably room temperature, and the mixing time is preferably 10-12 h. In specific embodiments, it can be 10 h, 11 h, or 12 h.

[0058] In the present invention, the temperature of the ultraviolet irradiation treatment is preferably room temperature; the time of the ultraviolet irradiation treatment is preferably 10-20 min. In specific embodiments, it can be 10 min, 12 min, 15 min, 18 min, or 20 min.

[0059] The present invention has no special limitation on the solid-liquid separation, and any solid-liquid separation method well-known to those skilled in the art can be used, such as filtration, suction filtration, or centrifugal separation.

[0060] In the present invention, after the solid-liquid separation, the present invention preferably further includes: washing and then drying the solid component obtained by the solid-liquid separation to obtain atomically dispersed palladium-functionalized defective tungsten disulfide nanosheets. In the present invention, the washing preferably includes alternately performing deionized water washing and ethanol washing; the number of times of deionized water washing and anhydrous ethanol washing is independently preferably 2 to 4 times. In the present invention, the drying is preferably vacuum drying, the drying temperature is preferably 50 to 80 °C, and in specific embodiments, it can be 50 °C, 60 °C, 70 °C or 80 °C; the present invention has no special limitation on the drying time, as long as the solvent can be completely removed.

[0061] The present invention adopts a grinding-assisted liquid-phase exfoliation method. The introduced S defects can not only improve the surface charge transfer of the sensitive material and enhance the adsorption of CH 3 OH, but also serve as active sites for methanol adsorption. In addition, surface defects are more conducive to stabilizing Pd single atoms. The preparation method of atomically dispersed palladium-functionalized defective tungsten disulfide provided by the present invention has a simple process, is easy to operate, has low production costs, is green and environmentally friendly, and is suitable for industrial production.

[0062] The present invention also provides a methanol gas sensor (for the structural schematic diagram, see Figure 1 ), which includes a polyimide film substrate sputtered with Au interdigital electrodes and a sensitive material layer; the sensitive material of the sensitive material layer includes the atomically dispersed palladium-functionalized defective tungsten disulfide nanosheets described in the above technical solution or the atomically dispersed palladium-functionalized defective tungsten disulfide nanosheets prepared by the preparation method described in the above technical solution.

[0063] In the present invention, the thickness of the sensitive layer is preferably 3.45 to 4.82 nm, and in specific embodiments, it can be 3.45 nm, 3.8 nm, 4 nm, 4.32 nm, 4.5 nm or 4.82 nm.

[0064] The gas sensor using the atomically dispersed palladium-functionalized defective tungsten disulfide nanosheets provided by the present invention as the sensitive material realizes a high response to trace methanol at room temperature. It solves the challenges of existing methanol sensors, such as high working temperature, low response, and difficulty in detecting low concentrations, and can achieve high-performance detection of trace methanol at room temperature.

[0065] The present invention also provides a preparation method of the methanol gas sensor described in the above technical solution, including the following steps: coating a sensitive material suspension on the surface of a polyimide film substrate sputtered with Au interdigital electrodes, and drying to obtain a methanol gas sensor.

[0066] In the present invention, the sensitive material suspension is preferably obtained by dispersing the sensitive material in a solvent. In the present invention, the solvent preferably includes water. In the present invention, the concentration of the sensitive material suspension is preferably 10 - 20 mg / mL, and in specific embodiments, it can be 10 mg / mL, 12 mg / mL, 15 mg / mL, 18 mg / mL or 20 mg / mL. In the present invention, the dispersion preferably includes ultrasonic dispersion, the temperature of the ultrasonic dispersion is preferably room temperature, and the time of the ultrasonic dispersion is preferably 5 - 15 min. In specific embodiments, it can be 5 min, 8 min, 10 min, 12 min or 15 min.

[0067] In the present invention, the coating preferably includes drop coating.

[0068] In the present invention, the temperature of the drying is preferably room temperature, and the present invention has no special limitation on the time of the drying, as long as the solvent can be completely removed.

[0069] The preparation process of the methanol gas sensor provided by the present invention is simple, the operation is easy, the reliability is strong, the production cost is low, it is green and environmentally friendly, and it is suitable for industrial production.

[0070] The present invention also provides the application of the atomically dispersed palladium-functionalized defective tungsten disulfide nanosheets described in the above technical solution, the atomically dispersed palladium-functionalized defective tungsten disulfide nanosheets prepared by the preparation method described in the above technical solution, or the methanol gas sensor described in the above technical solution in methanol detection. In the present invention, the temperature of the methanol detection is preferably room temperature.

[0071] The working principle of the methanol gas sensor provided by the present invention: O in the air 2 tends to be adsorbed at the defects of the sensitive material and is converted into chemically adsorbed oxygen ions by capturing electrons from the conduction band of the sensitive material. The above oxygen adsorption process will increase the number of the main carriers - holes on the surface of the semiconductor material, thus forming a hole accumulation layer (HAL) with a certain thickness on the surface of the sensitive material, resulting in a low-resistance state. Subsequently, when the methanol gas sensor contacts with the reducing gas CH 3 OH, CH 3 OH reacts with the chemically adsorbed oxygen ions to generate HCOOH and H 2 O. At the same time, the electrons captured in the previous stage are released and re-injected into the conduction band of the sensitive material to recombine with the holes. During this process, the number of the main carriers in the sensitive material will decrease, resulting in an increase in resistivity. The reaction process is as follows:

[0072] CH 3 OH + O 2 - →HCOOH + H 2 O + e- 。

[0073] To further illustrate the present invention, the atomically dispersed palladium-functionalized defective tungsten disulfide nanosheets provided by the present invention, their preparation methods and applications, and gas sensors and their applications will be described in detail below in conjunction with embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0074] Comparative Example 1

[0075] 1.5 g of WS 2 powder (bulk WS 2 ) and 0.5 mL of acetonitrile solvent were placed in an agate mortar and ground at room temperature for 1 h. The resulting mixture was transferred to a vacuum drying oven at 60 °C and dried for 14 h to ensure that the solvent was fully evaporated. The dried powder was dispersed in 200 mL of an ethanol aqueous solution (ethanol volume fraction of 35%), and ultrasonic treatment was carried out for 2 h to obtain a mixed solution A. The mixed solution A was centrifuged at a speed of 3000 r / min for 20 min, and then the upper suspension was taken with a pipette, filtered by suction, and dried in vacuo to constant weight to obtain few-layer tungsten disulfide nanosheets with defects (denoted as WS 2 NSs).

[0076] Comparative Example 2

[0077] 1.5 g of WS 2 powder (bulk WS 2 ) and 0.5 mL of acetonitrile solvent were placed in an agate mortar and ground at room temperature for 1 h. The resulting mixture was transferred to a vacuum drying oven at 60 °C and dried for 14 h to ensure that the solvent was fully evaporated. The dried powder was dispersed in 200 mL of an ethanol aqueous solution (ethanol volume fraction of 35%), and ultrasonic treatment was carried out for 3 h to obtain a mixed solution A. The mixed solution A was centrifuged at a speed of 3000 r / min for 20 min, and then the upper suspension was taken with a pipette, filtered by suction, and dried in vacuo to constant weight to obtain few-layer tungsten disulfide nanosheets with defects (denoted as WS 2 NSs).

[0078] Comparative Example 3

[0079] The preparation method of the WS 2 NSs sensitive material is as follows: 1.5 g of WS 2 powder (bulk WS 2) and 0.5 mL of acetonitrile solvent in an agate mortar, ground at room temperature for 1 h, and the resulting mixture was transferred to a vacuum drying oven at 60 °C and dried for 14 h to ensure that the solvent was fully evaporated. The dried powder was dispersed in 200 mL of an ethanol aqueous solution (ethanol volume fraction of 35%) and sonicated for 4 h to obtain a mixed solution A. The mixed solution A was centrifuged at 3000 r / min for 20 min, and then the upper suspension was taken with a pipette, filtered by suction, and dried to a constant weight under vacuum to obtain few-layer tungsten disulfide nanosheets with defects (denoted as WS 2 NSs).

[0080] Example 1

[0081] Disperse 1.5 g of WS 2 powder (bulk WS 2 ) and 0.5 mL of acetonitrile solvent in an agate mortar, grind at room temperature for 1 h, transfer the resulting mixture to a vacuum drying oven at 60 °C and dry for 14 h to ensure that the solvent is fully evaporated. Disperse the dried powder in 200 mL of an ethanol aqueous solution (ethanol volume fraction of 35%) and sonicate for 3 h to obtain a mixed solution A; centrifuge the mixed solution A at 3000 r / min for 20 min, take the upper suspension with a pipette and then dry to a constant weight under vacuum to obtain few-layer tungsten disulfide nanosheets with defects (WS 2 NSs). According to the mass ratio of Pd / WS 2 NSs being 0.3%, weigh out H 2 PdCl 4 solution and 30 mg of WS 2 NSs and add them to 10 mL of ethanol, stir magnetically for 12 h to obtain a mixed solution B, irradiate the mixed solution B with ultraviolet light for 15 min, wash the precipitate 3 times by centrifugation with deionized water and ethanol alternately, and dry under vacuum for 12 h to obtain atomically dispersed palladium-functionalized defective tungsten disulfide nanosheets (denoted as 0.3 wt% Pd SA@WS 2 NSs).

[0082] Example 2

[0083] Disperse 1.5 g of WS 2 powder (bulk WS 2 ) and 0.5 mL of acetonitrile solvent in an agate mortar, grind at room temperature for 1 h, transfer the resulting mixture to a vacuum drying oven at 60 °C and dry for 14 h to ensure that the solvent is fully evaporated. Subsequently, disperse the dried powder in 200 mL of an ethanol aqueous solution (ethanol volume fraction of 35%) and sonicate for 3 h to obtain a mixed solution A; centrifuge the mixed solution A at 3000 r / min for 20 min, take the upper suspension with a pipette, filter by suction and dry under vacuum to obtain WS 2NSs. According to the mass ratio of Pd / WS 2 The mass ratio of NSs is 0.5%, weigh out H 2 PdCl 4 solution and 30 mg WS 2 NSs are added to 10 mL of ethanol, and magnetically stirred for 12 h to obtain a mixed solution B. The mixed solution B is irradiated with ultraviolet light for 15 min, and the precipitate is centrifugally washed 3 times alternately with deionized water and ethanol, and vacuum dried for 12 h to obtain atomically dispersed palladium-functionalized defective tungsten disulfide nanosheets (denoted as 0.5 wt% Pd SA@WS 2 NSs).

[0084] Example 3

[0085] The Pd SA@WS 2 NSs prepared in Examples 1-2 and the WS 2 NSs prepared in Comparative Examples 1-3 are used as sensitive materials to prepare gas sensors respectively. The specific steps are as follows: The sensitive materials (4 mg) prepared in Comparative Examples 1-3 and Examples 1-2 are ultrasonically dispersed in deionized water (400 μL) for 10 min to form a uniform sensitive material suspension. The sensitive material suspension is coated onto a cleaned polyimide film substrate (thickness 20 μm, size 10 mm×10 mm) sputtered with Au interdigitated electrodes by the drop-coating method. The sensitive material layer is naturally dried at room temperature to constant weight to obtain a resistive gas sensor. The structural schematic diagram is shown in Figure 1 .

[0086] Test Example 1

[0087] Taking the Pd SA@WS 2 NSs prepared in Examples 1-2 and the WS 2 NSs prepared in Comparative Example 2 as sensitive materials for performance testing of resistive gas sensors

[0088] The gas-sensing performance test is carried out using a dynamic test system. The prepared resistive gas sensor is placed in a 150 mL closed test chamber, and the relative humidity in the test chamber is maintained at 20±5%. The gas response test process is as follows: High-purity N 2 and high-purity oxygen (purity 99.9%) are used to prepare a 25 v / v% O 2 -N 2 nitrogen-oxygen mixed gas to simulate air, and then it is introduced into the test chamber. The voltage across a known series resistor is measured using a data acquisition card (VK701N, Shenzhen Weijing Electronics Co., Ltd.) to determine the real-time resistance of the sensor under test. The computer records the resistance change of the sensor under test at 1 s intervals until it stabilizes, and the stable resistance at this time is defined as R a . By adjusting N through a digital mass flow controller2 , O 2 and the target gas - N 2 (10 ppm methanol standard gas, with nitrogen as the balance gas) to obtain target gases with different concentrations (100 ppb - 3 ppm). Subsequently, a target gas with a certain concentration was introduced into the test chamber, and finally the steady - state resistance, defined as R g . The sensor response was recorded as (R g - R a ) / R a .

[0089] Figure 2 is the atomic force microscope image of WS 2 NSs prepared in Comparative Example 2. After statistical analysis, the average thickness of the selected - area WS 2 NSs is about 4.32 nm, corresponding to 6 - 8 layers of WS 2 NSs.

[0090] Figure 3 are the XRD characterization results of the sensitive materials obtained in Comparative Example 2, Example 1, and Example 2. It can be seen that the presence of Pd was not detected in the Pd SA@WS 2 NSs sensitive material, which may be due to the low content and high dispersion of Pd.

[0091] The micro - morphologies of bulk WS 2 , WS 2 NSs, and 0.3 wt% Pd SA@WS 2 NSs were characterized using a scanning electron microscope (SEM). Compared with bulk WS 2 , it can be clearly observed that the thickness of the WS 2 nanosheets is thinner, indicating that few - layer WS 2 nanosheets were successfully prepared. The doping of noble metal Pd has no effect on the morphology and thickness of the WS 2 nanosheets ( Figure 4 a - c). The microstructure and chemical composition of the 0.3 wt% Pd SA@WS 2 NSs sample were deeply studied using a transmission electron microscope (TEM). A small number of layered flakes can be found at the edges of the WS 2 nanosheets in the TEM image, and the opaque area is caused by the overlap of multiple nanosheets ( Figure 4 d and e). It can be seen from the HRTEM image in Figure 4 f that the lattice fringe spacing of d = 0.271 nm matches well with the (100) crystal plane of 2H - WS 2 . In the circled area in the figure, WS 2Multiple defects in the nanosheets are due to sulfur vacancies generated during the exfoliation process. In WS 2 No signals of Pd nanoparticles or clusters were found on the surface of the WS flakes.

[0092] The distribution state and existence form of Pd on the 0.3 wt% Pd SA@WS 2 NSs sensitive material were further verified by aberration-corrected scanning transmission electron microscopy. Pd is highly dispersed at the atomic level on the defective-rich WS 2 nanosheets ( Figure 5 highlighted by circles in a). From Figure 5 the x-y line scan elemental distribution maps in b and c, it can be seen that the atomic-sized bright spots have significantly stronger contrast and can be considered as single-atom Pd. At the same time, as shown by the boxes, it can also be concluded that there are sulfur defects around W atoms and single-atom Pd is located at the lattice position of W.

[0093] Figure 6 The response characteristics of gas sensors based on WS 2 NSs, 0.3 wt% Pd SA@WS 2 NSs, and 0.5 wt% Pd SA@WS 2 NSs to different concentrations of CH 3 OH in the range of 0.1 - 3 ppm. Compared with WS 2 NSs, the response value of the sensor after doping with single-atom Pd is significantly improved. However, the response value of the gas sensor based on 0.5 wt% Pd SA@WS 2 NSs to methanol decreases instead. Excessive Pd doping will cause the formation of nanoparticles, gradually covering the defects on the surface of the WS 2 nanosheets, thereby reducing the active sites of the sensitive material and hindering gas adsorption, resulting in a decrease in the response value of the device. At the same concentration, the responses of each gas sensor to methanol from large to small are: 0.3 wt% Pd SA@WS 2 NSs > 0.5 wt% Pd SA@WS 2 NSs > WS 2 NSs.

[0094] Figure 7 The transient response and recovery characteristics of gas sensors based on WS 2 NSs (a) and 0.3 wt% Pd SA@WS 2 NSs (b) to different concentrations of CH 3 OH (0.1 - 3 ppm) at room temperature. It can be seen that the resistances of both sensitive materials gradually increase when exposed to the CH 3 OH atmosphere and release the CH 3When it is OH, it gradually decreases, indicating that the material prepared by the present invention has p-type semiconductor characteristics. In a low-concentration atmosphere, the gas sensor can almost return to the baseline level. However, due to the slow desorption rate of CH 3 OH at room temperature, it is difficult for the sensitive material to return to the initial state under high-concentration conditions. As the concentration of CH 3 OH increases, the response of each gas sensor to CH 3 OH shows a step-like shape.

[0095] The results of eight-cycle tests of the gas sensor based on 0.3wt% Pd SA@WS 2 NSs exposed to 100 ppb methanol atmosphere are as Figure 8 shown. During eight cycles of continuous dynamic testing, the response amplitude of the gas sensor to methanol at room temperature did not fluctuate significantly, and its average response value was 33.7%.

[0096] Figure 9 The responses of the gas sensors based on WS 2 NSs and 0.3wt% Pd SA@WS 2 NSs to 1 ppm of various interfering gases (CO, CH 3 OH, acetone (C 3 H 6 O), toluene (C 7 H 8 ), and formaldehyde (HCHO)) at room temperature are shown. It can be seen that the response of the gas sensor based on 0.3wt% PdSA@WS 2 NSs to CH 3 OH is significantly higher than that of other interfering gases. At the same time, the responses of the two gas sensors to CO and C 7 H 8 can be ignored and are interpreted as insensitive.

[0097] The above are only 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 of 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. An atomically dispersed palladium functionalized defective tungsten disulfide nanosheet, comprising a tungsten disulfide nanosheet with defects and palladium single atoms dispersed at the defects.

2. The atomically dispersed palladium functionalized defective tungsten disulfide nanosheets according to claim 1, characterized in that: The mass of the palladium single atom is 0.1-0.7% of the mass of the tungsten disulfide nanosheet.

3. The atomically dispersed palladium functionalized defective tungsten disulfide nanosheet according to claim 1 or 2, characterized in that: The thickness of the tungsten disulfide nanosheet is 3.45-4.82 nm.

4. The method for preparing the atomically dispersed palladium functionalized defective tungsten disulfide nanosheets according to any one of claims 1 to 3, comprising the following steps: The tungsten disulfide powder is ground with acetonitrile to remove the solvent, and then dispersed in a mixed solvent of a low-boiling point organic solvent and water, subjected to ultrasonic treatment, solid-liquid separation, and the solvent in the obtained liquid component is removed to obtain a defective few-layer tungsten disulfide nanosheet; the boiling point of the low-boiling point organic solvent is ≤80°C; The defective few-layer tungsten disulfide nanosheets, H2PdCl4 solution and ethanol are mixed, subjected to ultraviolet irradiation treatment, and solid-liquid separation to obtain atomically dispersed palladium functionalized defective tungsten disulfide nanosheets.

5. The preparation method according to claim 4, characterized in that: The mass volume ratio of the tungsten disulfide powder to acetonitrile is 1 g: 0.5-1.5 mL; The grinding temperature is room temperature and the grinding time is 0.5 to 1 hour.

6. The preparation method according to claim 4, characterized in that: The low boiling point organic solvent includes ethanol; The volume fraction of the low boiling point organic solvent in the mixed solvent is 20 to 40%; The mass volume ratio of the tungsten disulfide powder to the mixed solvent is 1g:100-300mL; The ultrasonic treatment time is 2 to 4 hours.

7. The preparation method according to claim 4, characterized in that: The mass of palladium in the H2PdCl4 solution accounts for 0.1-1% of the mass of the defective few-layer tungsten disulfide nanosheets; The mixing time is 10 to 12 hours; The ultraviolet irradiation treatment time is 10 to 20 minutes.

8. A methanol gas sensor, characterized in that: It comprises a polyimide film substrate sputtered with Au interdigital electrodes and a sensitive material layer; the sensitive material of the sensitive material layer comprises the atomically dispersed palladium functionalized defective tungsten disulfide nanosheets described in any one of claims 1 to 3 or the atomically dispersed palladium functionalized defective tungsten disulfide nanosheets prepared by the preparation method described in any one of claims 4 to 7.

9. The method for preparing the methanol gas sensor according to claim 8, comprising the following steps: A sensitive material suspension is coated on the surface of a polyimide film substrate on which Au interdigital electrodes are sputtered, and the surface is dried to obtain a gas sensor.

10. Use of the atomically dispersed palladium functionalized defective tungsten disulfide nanosheets as described in any one of claims 1 to 3, the atomically dispersed palladium functionalized defective tungsten disulfide nanosheets prepared by the preparation method as described in any one of claims 4 to 7, or the gas sensor as described in claim 8 or the gas sensor prepared by the preparation method as described in claim 9 in methanol detection.

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