SnO2 quantum dot-sulfide composite gas sensitive material, preparation method thereof and application thereof in NH3 sensor

Abstract

The application relates to a SnO2 quantum dot-sulfide composite gas-sensitive material, a preparation method thereof and application thereof in NH3 sensors, and belongs to the field of gas sensors. The SnO2 quantum dot-sulfide composite gas-sensitive material has the micro-morphology that SnO2 quantum dots are uniformly grown on the surface of sulfide, wherein the crystal structure of the SnO2 quantum dots is a tetragonal phase crystal structure; the sulfide is a hierarchical porous flower-shaped structure assembled by sulfide nanosheets, the sulfide is MoS2 or SnS2, and the crystal structure is a hexagonal phase crystal structure. The SnO2 quantum dot-sulfide composite gas-sensitive material solves the problems of low sensitivity of the NH3 sensor under room temperature conditions and slow response / recovery rate through the high activity of the SnO2 quantum dots, the rich nucleation sites on the surface of the sulfide, the high carrier migration rate and the synergistic effect of the heterostructure formed between the SnO2 quantum dots and the sulfide.

Description

TECHNICAL FIELD

[0001] The present application relates to a SnO2 quantum dot-sulfide composite gas sensitive material, a preparation method thereof and application thereof in an NH3 sensor, and belongs to the field of gas sensors. BACKGROUND

[0002] With the rapid development of human society and the continuous development and utilization of resources, the harm of toxic and harmful gases to public health and the ecological environment is also increasing. The demand for high-performance gas sensors in the fields of environmental protection, medicine, food, military, etc. is also increasing.

[0003] NH3 is easily produced in the processes of chemical fertilizer industry, bacterial nitrogen fixation and fuel combustion, and thus diffuses into the air. Since NH3 has a high solubility in water, NH3 in the air can burn the mucous membranes of the human body and cause the human body to have weakened immunity to microorganisms. If a human being inhales a large amount of high-concentration NH3, various symptoms such as tearing, coughing and difficulty in breathing will occur. In addition, the mixture of NH3 and air is also explosive. However, most of the existing NH3 sensors require a high working temperature and have a very slow response / recovery speed (for example, document 1: Materials science and Engineering: B, vol. 224, pages 163-170). Document 1 discloses a WO3 and SnO2 composite gas sensitive thin film synthesized by a sputtering method, which realizes the detection of NH3 under high temperature conditions. However, the high working temperature not only brings high power consumption, which is not conducive to the portability of the device, but also has certain safety hazards. In addition, the working temperature of the NH3 sensor based on the WO3 / SnO2 thin film is as high as 300℃, which greatly increases the power consumption of the sensor and also has certain safety hazards. Therefore, it is necessary to realize effective monitoring of NH3 at a relatively low temperature.

[0004] Quantum dots have unique properties, including adjustable band gap, high specific surface area and rich active sites, because the movement of carriers in each direction is limited. The electrical characteristics of quantum dots are very suitable for gas sensing and detection, and in particular, the quantum dot-based gas sensor exhibits good performance at a low working temperature. Due to the unique effect of quantum dots, the band gap of SnO2 quantum dots is much larger than that of bulk SnO2 (3.6-3.8 eV), and more dangling bonds are exposed on the surface, which greatly improves the surface activity of SnO2 quantum dots. MoS2 and SnS2 and other sulfides have extremely high specific surface area and high carrier mobility, and have been applied to the field of gas sensors in recent years.

[0005] Studies have shown that SnO2 quantum dots and sulfide composite will form a heterojunction to improve the gas sensing performance of SnO2 quantum dot-sulfide composite gas sensing material. In addition, the large specific surface area of the sulfide can provide nucleation sites for quantum dots, and the high carrier mobility rate helps to improve the poor conductivity of quantum dots, quickly transferring the electrons generated in the gas sensing reaction process to the electrode, thereby improving the response-recovery rate of SnO2 quantum dot-sulfide composite gas sensing material. In addition, the effective combination of sulfide and SnO2 quantum dots can realize gas sensing at room temperature. However, under room temperature conditions, the SnO2 quantum dot-sulfide composite gas sensor still has the shortcomings of long recovery time. Therefore, it is necessary to continue to develop new SnO2 quantum dot-sulfide composite gas sensor to improve its recovery characteristics at room temperature. SUMMARY

[0006] The technical problem solved by the present application is to provide a SnO2 quantum dot-sulfide composite gas sensing material and an NH3 room temperature gas sensor prepared by using the material.

[0007] A SnO2 quantum dot-sulfide composite gas sensing material, the micro-morphology of the SnO2 quantum dot-sulfide composite gas sensing material is that SnO2 quantum dots are uniformly grown on the surface of sulfide, wherein,

[0008] The crystal structure of the SnO2 quantum dots is a tetragonal crystal structure; the sulfide is a hierarchical porous flower-like structure assembled by sulfide nanosheets, the sulfide is MoS2 or SnS2, and the crystal structure is a hexagonal crystal structure.

[0009] Further, the molar ratio of the sulfide to the SnO2 quantum dots is 0.2-2:1.

[0010] Further, the diameter of the SnO2 quantum dots is 2-4 nm; and the sulfide is a hierarchical porous flower-like structure assembled by sulfide nanosheets with a thickness of 20 nm or less.

[0011] Another object of the present application is to provide a preparation method of SnO2 quantum dot-sulfide composite gas sensing material.

[0012] A preparation method of SnO2 quantum dot-sulfide composite gas sensing material, raw materials required for preparing SnO2 quantum dots and sulfide nanosheets are added to a reaction container and heated, or SnO2 quantum dots and sulfide nanosheets are added to a reaction container and ultrasonically reacted, then mechanically stirred for a period of time, washed, separated, and SnO2 quantum dot-sulfide composite gas sensing material is obtained,

[0013] The raw material for preparing the SnO2 quantum dots is SnCl4·5H2O and oleic acid, wherein the mass ratio of SnCl4·5H2O to oleic acid is 1:30.

[0014] Further, the raw material for preparing the SnO2 quantum dots and the sulfide nanosheet are added to the reaction container and heated at 80℃ for 3-6h, or the SnO2 quantum dots and the sulfide nanosheet are added to the reaction container and subjected to ultrasonic reaction at a frequency of 40kHz for 10-20min and mechanical stirring for 3-12h.

[0015] Further, the MoS2 nanosheet is prepared by the following method: at room temperature, cetyltrimethylammonium bromide is added to a mixed solution of sodium molybdate dihydrate and thioacetamide; the formed solution is loaded into a reaction kettle and reacted at 160-200℃ for 12-24h, and then cooled to room temperature; the obtained product is separated, washed and dried, and then heated to 700℃ at a rate of 5℃ / min under Ar atmosphere in a tube furnace, and then cooled to room temperature after heat treatment for 1-3h, to obtain the MoS2 nanosheet, wherein the mass ratio of sodium molybdate dihydrate, thioacetamide and cetyltrimethylammonium bromide is 1:1:0.3.

[0016] Preferably, the preparation method of the MoS2 comprises the following steps:

[0017] ① at room temperature, sodium molybdate dihydrate and thioacetamide are added to deionized water and stirred for 15min; cetyltrimethylammonium bromide is added to the formed solution and stirred for another 30min; the formed solution is loaded into a reaction kettle and reacted at 160-200℃ for 12-24h, and then cooled to room temperature; wherein the mass ratio of sodium molybdate dihydrate, thioacetamide and cetyltrimethylammonium bromide is 1:1:0.3.

[0018] ② the supernatant is removed after centrifugation of the product of step ①, and the product is washed and dried, and then heated to 700℃ at a rate of 5℃ / min under Ar atmosphere in a tube furnace, and then cooled to room temperature after heat treatment for 1-3h, to obtain the MoS2 nanosheet.

[0019] Further, the SnS2 nanosheet is prepared by the following method: at room temperature, tin tetrachloride pentahydrate and thioacetamide are added to anhydrous ethanol to form a uniform transparent solution; the formed solution is loaded into a reaction kettle and reacted at 120-180℃ for 8-20h, and then cooled to room temperature; the obtained product is separated, washed and dried to obtain the SnS2 nanosheet, wherein the molar ratio of tin tetrachloride pentahydrate to thioacetamide is 1:4.

[0020] Preferably, the preparation method of the SnS2 comprises the following steps:

[0021] ① Under room temperature, tin tetrachloride pentahydrate and thioacetamide are added into anhydrous ethanol, stirred for 30 min until a uniform transparent solution is formed; the formed solution is loaded into a reaction kettle and reacted at 120-180℃ for 8-20 h, and then cooled to room temperature; wherein the molar ratio of tin tetrachloride pentahydrate and thioacetamide is 1:1-1:5.

[0022] ② After centrifugation, the supernatant of the product of step ① is removed, washed, and vacuum dried in a vacuum drying oven for 12 h to obtain SnS2 nanosheets.

[0023] The synthesis method of SnO2 quantum dots in the application can refer to the reported method, and the characterization means mainly include spectrum, energy spectrum, high-magnification scanning electron microscope, transmission electron microscope and X-ray diffraction, etc.

[0024] Another object of the application is to provide a room temperature NH3 sensor prepared by using the above SnO2 quantum dot-sulfide composite gas sensitive material and a preparation method of the room temperature NH3 sensor.

[0025] A room temperature NH3 sensor based on SnO2 quantum dot-sulfide composite gas sensitive material, wherein the gas sensor mainly consists of an electrode element and a SnO2 quantum dot-sulfide composite gas sensitive material thin film uniformly spin-coated on the surface of the electrode element.

[0026] Further, the detection range of the gas sensor for NH3 gas is 25-500 ppm, and the working temperature is 25℃.

[0027] A preparation method of a room temperature NH3 sensor based on SnO2 quantum dot-sulfide composite gas sensitive material, comprising the following process steps:

[0028] ① 100-150 μL of SnO2 quantum dot-sulfide composite gas sensitive material solution is added dropwise on the surface of Ag-Pd interdigital electrode by using a pipette, and spin-coated at a speed of 500-1500 rpm for 30-60 s; 100-120 μL of CuCl2 methanol solution is further added dropwise on the surface of Ag-Pd interdigital electrode by using a pipette, and spin-coated at a speed of 500-1500 rpm for 30-60 s; 100-120 μL of methanol is further added dropwise on the surface of Ag-Pd interdigital electrode by using a pipette, and spin-coated twice to clean the surface of the thin film, and the spin-coating time of each time is 30-60 s;

[0029] ② The above step ① is repeated for 2-4 times;

[0030] ③ The Ag-Pd interdigitated electrode with a SnO2 quantum dot-sulfide composite gas-sensitive material gas-sensitive film spin-coated on its surface is subjected to heat treatment under the following conditions: heating to 100-200℃ at a heating rate of 2℃ / min and holding for 2-6h to obtain the electrode.

[0031] Furthermore, the SnO2 quantum dot-sulfide composite gas-sensitive material is prepared at a concentration of 0.01–0.2 mol / ml, with n-hexane as the solvent.

[0032] The features and beneficial effects of this invention are as follows: The SnO2 quantum dot-sulfide composite gas-sensitive material of this invention solves the problems of low sensitivity and slow response / recovery rate of NH3 sensors at room temperature by utilizing the high activity of SnO2 quantum dots, the abundant nucleation sites and high carrier migration rate on the sulfide surface, and the synergistic effect of the heterostructure formed between the two. Furthermore, the gas sensor based on the SnO2 quantum dot-sulfide composite gas-sensitive material exhibits good selectivity, reproducibility, long-term stability, and moisture resistance, demonstrating good application value and development prospects. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of a room temperature NH3 sensor based on SnO2 quantum dot-sulfide composite gas-sensitive material.

[0034] Figure 2 X-ray diffraction pattern of SnO2 quantum dot-MoS2 composite gas-sensitive material;

[0035] Figure 3 Scanning electron microscope image of MoS2 material;

[0036] Figure 4 (a) Transmission electron microscope image and (b) high-resolution transmission electron microscope image of SnO2 quantum dot-MoS2 composite gas-sensitive material;

[0037] Figure 5 X-ray diffraction pattern of SnO2 quantum dot-SnS2 composite gas-sensitive material;

[0038] Figure 6 Scanning electron microscope image of SnS2 material;

[0039] Figure 7 (a) Transmission electron microscope image and (b) high-resolution transmission electron microscope image of SnO2 quantum dot-SnS2 composite gas-sensitive material;

[0040] Figure 8 The figures for (a) the response-recovery curves of the room temperature NH3 sensor of Embodiment 1 of the present invention at a room temperature of 25°C and a humidity of 19%RH to different concentrations of NH3 and (b) the relationship between sensitivity and NH3 gas concentration are shown.

[0041] Figure 9 Response-recovery curve of the room temperature NH3 sensor of Example 1 of the present application for 100 ppm NH3 at 25℃ under different humidity conditions; and (b) the relationship between sensitivity and humidity.

[0042] Figure 10 Reproducibility investigation graph of the room temperature NH3 sensor of Example 1 of the present application for 100 ppm NH3 at 25℃ under 19% RH;

[0043] Figure 11 Selectivity investigation graph of the room temperature NH3 sensor of Example 1 of the present application for different kinds of gases at 25℃ under 19% RH.

[0044] Figure 12 Long-term stability investigation graph of the room temperature NH3 sensor of Example 1 of the present application within 30 days;

[0045] Figure 13 Response-recovery curve of the room temperature NH3 sensor of Example 2 of the present application for different concentrations of NH3 at 25℃ under 23% RH; and (b) the relationship between sensitivity and NH3 gas concentration.

[0046] Figure 14 Response-recovery curve of the room temperature NH3 sensor of Example 2 of the present application for 100 ppm NH3 at 25℃ under different humidity conditions; and (b) the relationship between sensitivity and humidity.

[0047] Figure 15 Reproducibility investigation graph of the room temperature NH3 sensor of Example 2 of the present application for 100 ppm NH3 at 25℃ under 23% RH;

[0048] Figure 16 Selectivity investigation graph of the room temperature NH3 sensor of Example 2 of the present application for different kinds of gases at 25℃ under 23% RH.

[0049] Figure 17 Long-term stability investigation graph of the room temperature NH3 sensor of Example 2 of the present application within 30 days. DETAILED DESCRIPTION

[0050] The following non-limiting examples can provide a more complete understanding of the application to those of ordinary skill in the art, but do not limit the application in any way.

[0051] The test methods in the following examples are the conventional methods unless otherwise specified; the reagents and materials are commercially available unless otherwise specified.

[0052] A preparation method of SnO2 quantum dot-sulfide composite gas sensitive material, comprising the following steps:

[0053] ①The raw materials required for preparing SnO2 quantum dots and sulfides are added to a reaction container and heated, or SnO2 quantum dots and sulfides are added to a reaction container and subjected to ultrasonic reaction and then mechanically stirred for a period of time to obtain SnO2 quantum dot-sulfide composite gas sensitive material.

[0054] ②The composite gas sensitive material obtained in step ① is centrifuged and washed, the supernatant is removed, and then dispersed in a certain volume of n-hexane.

[0055] Preferably, the molar ratio of sulfides and SnO2 quantum dots is in the range of 0.2-2, and the gas sensitive performance of the composite material is optimal.

[0056] Preferably, the period of time in step ① is 3-12h.

[0057] Preferably, the centrifugal speed in step ② is 8000rpm-10000rpm.

[0058] A room temperature gas sensor based on SnO2 quantum dot-sulfide composite gas sensitive material, which realizes high sensitivity detection of NH3 at room temperature. The preparation method of the gas sensor based on SnO2 quantum dot-sulfide composite gas sensitive material comprises the following process steps:

[0059] ①100-150μL of SnO2 quantum dot-sulfide composite gas sensitive material solution is added dropwise on the surface of Ag-Pd interdigital electrode by using a pipette, and spin-coated at a speed of 500-1500rpm for 30-60s; 100-120μL of CuCl2 methanol solution is added dropwise on the surface of Ag-Pd interdigital electrode by using a pipette, and spin-coated at a speed of 500-1500rpm for 30-60s; 100-120μL of methanol is added dropwise on the surface of Ag-Pd interdigital electrode by using a pipette, and spin-coated twice to clean the surface of the film, and the spin-coating time for each time is 30-60s.

[0060] ②The above step ① is repeated for 2-4 times;

[0061] ③The Ag-Pd interdigital electrode with SnO2 quantum dot-sulfide composite gas sensitive material gas sensitive film spin-coated on the surface is subjected to heat treatment, and the condition is that heated to 100-200℃ at a heating rate of 2℃ / min and kept for 2-6h, and thus obtained.

[0062] Preferably, the gas sensor has a detection range of 25-500ppm for NH3 gas and a working temperature of 25℃.

[0063] The structure of the room temperature NH3 sensor based on SnO2 quantum dot-MoS2 composite gas sensitive material of the present embodiment is shown in Figure 1 The room temperature NH3 sensor based on SnO2 quantum dot-MoS2 composite gas sensitive material is made by coating the SnO2 quantum dot-MoS2 gas sensitive material film 2 on the surface of the Ag-Pd electrode 1 and the ceramic substrate 3, contacting the measuring probe 4 on the surface of the Ag-Pd electrode 1, and connecting the circuit.

[0064] The X-ray diffraction pattern of the SnO2 quantum dot-MoS2 composite gas sensitive material is shown in Figure 2 The X-ray diffraction peaks of the SnO2 quantum dot-MoS2 composite gas sensitive material include the diffraction peaks of SnO2 and MoS2, SnO2 is a tetragonal crystal structure, MoS2 is a hexagonal crystal structure, and there is no diffraction peak of other impurities. The scanning electron microscope photo of MoS2 is shown in Figure 3 The flower-like MoS2 with multi-level structure is assembled by nanosheets with a thickness of about 7nm. The transmission electron microscope photo of the SnO2 quantum dot-MoS2 composite gas sensitive material is shown in Figure 4 Figure 4 (a) is a transmission electron microscope photo, Figure 4 (b) is a high-resolution transmission electron microscope photo, which can find that the SnO2 quantum dots are uniformly distributed on MoS2, and the diameter of the SnO2 quantum dots is 2-4nm.

[0065] A preparation method of a room temperature NH3 sensor based on SnO2 quantum dot-MoS2 composite gas sensitive material is as follows:

[0066] ①Under room temperature conditions, 1g of sodium molybdate dihydrate and 1g of thioacetamide are added to deionized water and stirred for 15min; 0.3g of cetyltrimethylammonium bromide is added to the formed solution and continues to be stirred for 30min; the formed solution is loaded into a reaction kettle and reacted at 180℃ for 24h, and then cooled to room temperature;

[0067] ②The supernatant is removed after centrifugation of the product obtained in step ①, and the centrifugation and washing are each 2 times, the centrifugal speed is 8000rpm, and the product is placed in a drying box at 60℃ for drying for 10h. The product is placed in a tube furnace and heated to 700℃ at 5℃ / min under Ar atmosphere, heat-treated for 2h, and then cooled to room temperature to obtain MoS2.

[0068] ​③ 0.0544 g of the heat-treated MoS2 was added to a mixed solvent of 20 ml of oleic acid and 2.5 ml of oleylamine, and ultrasonic treatment was performed for 15 min; 1.7 mmol of tin tetrachloride pentahydrate was added to the mixed solution, and heating was performed at 80°C for 6 h under an Ar atmosphere, and then the temperature was lowered to room temperature; 10 ml of ethanol was added to the obtained solution, and the solution was loaded into a reaction kettle and reacted at 180°C for 3 h, and then the temperature was lowered to room temperature;

[0069] ④ After centrifugation, the supernatant was removed, and centrifugation and washing were performed at a speed of 10,000 rpm, and the bottom precipitate was dispersed in a n-hexane solution to obtain the SnO2 quantum dot-MoS2 composite gas-sensitive material.

[0070] ⑤ 100 μL of the SnO2 quantum dot-MoS2 composite gas-sensitive material solution was added dropwise to the surface of the Ag-Pd interdigital electrode by using a pipette, and spin coating was performed at a speed of 1,200 rpm for 45 s; 100 μL of a CuCl2 methanol solution was added dropwise to the surface of the Ag-Pd interdigital electrode by using a pipette, and spin coating was performed at a speed of 1,200 rpm for 45 s; 100 μL of methanol was added dropwise to the surface of the Ag-Pd interdigital electrode by using a pipette, and spin coating was performed at a speed of 1,200 rpm for 45 s.

[0071] ⑥ The above step ⑤ was repeated three times;

[0072] ⑦ The Ag-Pd interdigital electrode on which the SnO2 quantum dot-MoS2 composite gas-sensitive material gas-sensitive thin film was spin coated was subjected to heat treatment, and the heat treatment was performed at a heating rate of 2°C / min to 200°C and maintained for 6 h to obtain the SnO2 quantum dot-MoS2-based room-temperature NH3 sensor.

[0073] The response-recovery curve of the SnO2 quantum dot-MoS2 composite gas-sensitive material gas sensor in this embodiment to 25-500 ppm NH3 at a temperature of 25°C and a humidity of 19% RH is shown in Figure 8 (a), and the sensitivity change curve with the NH3 concentration is shown in Figure 8 (b). As can be seen from Figure 8 (a), the response and recovery time of the gas sensor to 25-500 ppm NH3 are short; as can be seen from Figure 8 (b), the sensitivity of the SnO2 quantum dot-MoS2 composite gas-sensitive material gas sensor to 25-500 ppm NH3 is 2.3, 3.8, 8.6, 16.1 and 48.2, respectively. The above results show that the gas sensor of the present application can effectively monitor a large range of NH3 concentrations at room temperature, and the fitting equation is close to linear, which is conducive to determining the concentration of the detected gas according to the sensitivity in the future.

[0074] The response-recovery curves of the gas sensor of the SnO2 quantum dot-MoS2 composite gas sensitive material in this embodiment to 100 ppm NH3 under different humidity conditions are as shown in Figure 9 (a), and the sensitivity change curve with humidity is as shown in Figure 9 (b). It can be seen from the figure that the sensitivity of the gas sensor under different humidity conditions is relatively high, and the response-recovery is fast. With the increase of humidity, the sensitivity of the gas sensor gradually decreases, but the decrease is not large, indicating that the anti-humidity performance is excellent.

[0075] The continuous 6-time response-recovery curves of the gas sensor of the SnO2 quantum dot-MoS2 composite gas sensitive material in this embodiment to 100 ppm NH3 at a temperature of 25°C and a humidity of 19% RH are as shown in Figure 10 . It can be seen from Figure 10 that in the continuous 6-time detection, the resistance change of the gas sensor of the SnO2 quantum dot-MoS2 composite gas sensitive material is very small, and the response time and recovery time are similar, indicating that the gas sensor has good reproducibility and reaction reversibility, and can meet the requirements of practical application.

[0076] The sensitivity results of the gas sensor of the SnO2 quantum dot-MoS2 composite gas sensitive material in this embodiment to NH3 with a concentration of 100 ppm, H2 with a concentration of 1000 ppm, CH3CH2OH with a concentration of 100 ppm, CH4 with a concentration of 1000 ppm, and NO2 with a concentration of 1 ppm at a temperature of 25°C and a humidity of 19% RH are as shown in Figure 11 . Among them, the sensitivity of the gas sensor of the SnO2 quantum dot-MoS2 composite gas sensitive material to NH3 is much higher than that to other gases, indicating that the gas sensor has good gas selectivity to NH3, and is less affected by other gases in practical application, and has good application prospect.

[0077] The results of the gas sensor of the SnO2 quantum dot-MoS2 composite gas sensitive material in this embodiment to NH3 with a concentration of 100 ppm within 30 days are as shown in Figure 12 . Among them, the sensitivity of the gas sensor of the SnO2 quantum dot-MoS2 composite gas sensitive material to NH3 only decreases slightly within 30 days, indicating that the gas sensor can maintain excellent performance for a long time, and has good application prospect.

[0078] Example 2

[0079] The room temperature NH3 gas sensor based on the SnO2 quantum dot-SnS2 composite gas sensitive material of this embodiment has the same structure as that of Example 1. The specific characterization results are as shown in Figures 5-7 , which is similar to Example 1.

[0080] A preparation method of an NH3 gas sensor based on a SnO2 quantum dot-SnS2 composite gas sensitive material, which is carried out according to the following steps:

[0081] ① Under room temperature conditions, 1.5 mmol of tin tetrachloride pentahydrate and 6 mmol of thioacetamide are added to 40 ml of anhydrous ethanol and stirred for 30 min until a uniform transparent solution is formed. The formed solution is transferred to a reaction kettle, reacted at 180 in conditions for 16 h, and then naturally cooled to room temperature.

[0082] ② After centrifugation of the product obtained in step ①, the supernatant is removed, and centrifugation and washing are each performed twice, with a centrifugal speed of 6000 rpm, and the product is placed in a vacuum drying box at 60°C for vacuum drying for 12 h.

[0083] ③ After mixing 20 ml of oleic acid and 2.5 ml of oleylamine, 1.7 mmol of tin tetrachloride pentahydrate is added to the mixed solution, which is heated at 80°C for 6 h under Ar atmosphere and then cooled to room temperature. 10 ml of ethanol is added to the obtained solution, and the formed solution is loaded into a reaction kettle and reacted at 180°C for 3 h, and then cooled to room temperature.

[0084] ④ After centrifugation of the product, the supernatant is removed, and centrifugation and washing are performed, with a speed of 10000 rpm, and the bottom precipitate is dispersed into a n-hexane solution to obtain SnO2 quantum dots. Subsequently, 0.311 g of SnS2 material is weighed and mixed with the SnO2 quantum dots, and then ultrasonic reaction is performed for 15 min, and mechanical stirring is performed for 12 h, to obtain a SnO2 quantum dot-SnS2 composite gas sensitive material.

[0085] ⑤ A 150 μL SnO2 quantum dot-SnS2 composite gas sensitive material solution is added dropwise on the surface of an Ag-Pd interdigital electrode by using a pipette, and spin coating is performed at a speed of 700 rpm for 45 s; a 100 μL CuCl2 methanol solution is continuously added dropwise on the surface of the Ag-Pd interdigital electrode by using a pipette, and spin coating is performed at a speed of 700 rpm for 45 s; a 100 μL methanol is continuously added dropwise on the surface of the Ag-Pd interdigital electrode by using a pipette, and spin coating is performed at a speed of 700 rpm for 2 times, with a spin time of 45 s each time.

[0086] ⑥ The above step ⑤ is repeated three times;

[0087] ⑦ The Ag-Pd interdigital electrode with the SnO2 quantum dot-SnS2 composite gas sensitive material gas sensitive thin film spin-coated on the surface is subjected to heat treatment, with a heating rate of 2°C / min to 100°C for 6 h, to obtain a SnO2 quantum dot-SnS2 based room temperature NH3 sensor.

[0088] In this embodiment, the response-recovery curves of the SnO2 quantum dot-SnS2 composite gas sensor to 25–500 ppm NH3 at a temperature of 25°C and a humidity of 23% RH are shown below. Figure 13 As shown in (a), the sensitivity curve as a function of NH3 concentration is as follows: Figure 13 As shown in (b). Figure 13 (a) It can be seen that the gas sensor has a short response and recovery time for 25–500 ppm NH3; Figure 13 (b) It can be seen that the sensitivities of the SnO2 quantum dot-SnS2 composite gas sensor for NH3 ranging from 25 to 500 ppm are 5.1, 8.3, 13.5, 23.6, and 47.8, respectively. These results indicate that the gas sensor of the present invention can effectively monitor a wide range of NH3 concentrations at room temperature, and the fitting equation is nearly linear, which is beneficial for determining the concentration of the detected gas based on the sensitivity in the future.

[0089] In this embodiment, the gas sensor made of SnO2 quantum dot-SnS2 composite gas-sensitive material exhibits response-recovery curves for 100ppm NH3 under different humidity conditions, as shown below. Figure 14 As shown in (a), the sensitivity variation curve with humidity is as follows: Figure 14 As shown in (b), humidity has a slight effect on the sensor's sensitivity, but the effect is not significant.

[0090] In this embodiment, the response-recovery curves of the SnO2 quantum dot-SnS2 composite gas sensor to 100ppm NH3 at a temperature of 25℃ and a humidity of 23%RH are shown in the figure below. Figure 15 As shown. By Figure 15 It can be seen that the gas sensor has good reproducibility.

[0091] In this embodiment, the SnO2 quantum dot-SnS2 composite gas sensor exhibits the following sensitivity results at a temperature of 25°C and a humidity of 23%RH for concentrations of 100 ppm NH3, 1000 ppm H2, 100 ppm CH3CH2OH, 1000 ppm CH4, and 1 ppm NO2: Figure 16 As shown in the figure, the SnO2 quantum dot-SnS2 composite gas sensor achieved a sensitivity of 11.1 for NH3, while the sensitivity for other gases did not exceed 3, indicating that the gas sensor has good gas selectivity for NH3.

[0092] In this embodiment, the SnO2 quantum dot-SnS2 composite gas sensor was used to test NH3 at a concentration of 100 ppm over 30 days, and the results are as follows. Figure 17The results show that the SnO2 quantum dots-SnS2 composite gas sensor has good long-term stability.

Claims

1. A method for preparing a SnO2 quantum dot-sulfide composite gas-sensitive material, characterized in that: The raw materials and SnS2 nanosheets required for the preparation of SnO2 quantum dots are added to a reaction vessel and heated, or the SnO2 quantum dots and SnS2 nanosheets are added to a reaction vessel, ultrasonically reacted, and then mechanically stirred for a period of time. After washing and separation, the SnO2 quantum dot-sulfide composite gas-sensitive material is obtained. The raw materials required for the preparation of SnO2 quantum dots are SnCl4·5H2O and oleic acid, wherein the mass ratio of SnCl4·5H2O to oleic acid is 1:

30.

2. The method according to claim 1, characterized in that: The raw materials and SnS2 nanosheets required for the preparation of SnO2 quantum dots are added to a reaction vessel and heated at 80°C for 3-6 h, or SnO2 quantum dots and SnS2 nanosheets are added to a reaction vessel and ultrasonically reacted at a frequency of 40 kHz for 10-20 min, followed by mechanical stirring for 3-12 h.

3. The method according to claim 1, characterized in that: The SnS2 nanosheets were prepared by the following method: at room temperature, tin tetrachloride pentahydrate and thioacetamide were added to anhydrous ethanol to form a homogeneous and transparent solution; the solution was placed in a reaction vessel and reacted at 120-180°C for 8-20 h, and then cooled to room temperature; the obtained product was separated, washed and dried to obtain SnS2 nanosheets, wherein the molar ratio of tin tetrachloride pentahydrate to thioacetamide was 1:

4.

4. A SnO2 quantum dot-sulfide composite gas-sensitive material prepared by the method according to any one of claims 1 to 3, wherein the microstructure of the SnO2 quantum dot-sulfide composite gas-sensitive material is characterized by SnO2 quantum dots uniformly grown on the sulfide surface, wherein... The crystal structure of SnO2 quantum dots is a tetragonal phase crystal structure; the sulfide is a hierarchical porous flower-like structure assembled from sulfide nanosheets, and the sulfide is SnS2 with a hexagonal phase crystal structure.

5. The material according to claim 4, characterized in that: The molar ratio of the sulfide to SnO2 quantum dots is 0.2 to 2:

1.

6. The material according to claim 4, characterized in that: The SnO2 quantum dots have a diameter of 2-4 nm; the sulfide is a hierarchical porous flower-like structure assembled from sulfide nanosheets with a thickness of less than 20 nm.

7. A room temperature NH3 sensor based on the SnO2 quantum dot-sulfide composite gas-sensitive material as described in claim 4, characterized in that: The sensor includes electrode elements and a SnO2 quantum dot-sulfide composite gas-sensitive material film uniformly spin-coated on the surface of the electrode elements.

8. The NH3 sensor according to claim 7, characterized in that: The sensor has a detection range of 25~500ppm for NH3 gas and an operating temperature of 25°C.

9. A method for preparing a room temperature NH3 sensor based on SnO2 quantum dot-sulfide composite gas-sensitive material as described in claim 7, characterized in that: The process includes the following steps: S1. Using a pipette, 100-150 μL of SnO2 quantum dot-sulfide composite gas-sensitive material solution is dropped onto the surface of the Ag-Pd interdigitated electrode and spin-coated at 500-1500 rpm for 30-60 s. Then, using a pipette, 100-120 μL of CuCl2 methanol solution is dropped onto the surface of the Ag-Pd interdigitated electrode and spin-coated at 500-1500 rpm for 30-60 s. Finally, using a pipette, 100-120 μL of methanol is dropped onto the surface of the Ag-Pd interdigitated electrode and spin-coated twice at 500-1500 rpm to clean the film surface, with each spin lasting 30-60 s. S2, repeat step S1 2 to 4 times; S3. The Ag-Pd interdigitated electrode with a SnO2 quantum dot-sulfide composite gas-sensitive material gas-sensitive film spin-coated on its surface is subjected to heat treatment under the following conditions: heating to 100~200°C at a heating rate of 2 °C / min and holding for 2~6 hours to obtain the product.

10. The method according to claim 9, characterized in that: The concentration of the SnO2 quantum dot-sulfide composite gas-sensitive material solution is 0.01~0.2 mol / ml, and the solvent is n-hexane.

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