A ZIF-8 / SnO2 composite, its preparation method and application

Abstract

The present application relates to a kind of ZIF-8 / SnO2 compound and its preparation method and application, the ZIF-8 / SnO2 compound is with mesoporous SnO2 nanosphere as carrier, its internal pore and surface load with ZIF-8.The diameter of the mesoporous SnO2 nanosphere is 690~720nm, pore size is 8~9nm, specific surface area is 78~80m 2 ·g ‑1 , the diameter of the ZIF-8 / SnO2 compound is 790~820nm, pore size is 7~8nm, specific surface area is 69~71m 2 ·g ‑1 It is prepared as follows: preparation mesoporous SnO2 nanosphere;Preparation SnO2 / ZIF-8 compound.Compared with prior art, the ZIF-8 / SnO2 compound prepared in the application can be applied to the field of nitrogen dioxide sensing, can be realized at lower temperature to the high electrochemical response of nitrogen dioxide, can avoid the application of MOF in electrochemical sensing due to the insulating property limit, while reducing the influence of humidity on sensing material, thereby greatly improving the selective response to nitrogen dioxide.

Description

Technical Field

[0001] This invention relates to the field of metal-organic framework materials technology, and in particular to a ZIF-8 / SnO2 composite, its preparation method and application. Background Technology

[0002] Nitrogen dioxide (NO2) is a major nitrogen pollutant in the atmosphere and a key parameter for air quality monitoring in my country. NO2 spontaneously reacts harmfully with other chemicals in the atmosphere, forming acid rain and other air pollutants, posing a significant ecological threat. For humans, even low concentrations (approximately 3 ppm) of NO2 can irritate the eyes and lungs, weaken the respiratory system, and even lead to death. High levels of NO2 exposure in pregnant women can also cause attention deficit disorders in infants and young children. Therefore, the widespread deployment and interconnection of accurate and rapid NO2 sensors are crucial for data collection, analysis, monitoring, and mitigation of air pollution.

[0003] Currently, mature methods for measuring NO2 in the atmosphere include spectrophotometry, ion chromatography, and chemiluminescence. Spectrophotometry offers high accuracy and stability, but it has strict requirements on reagent preservation and sample retention time. Ion chromatography has simple procedures, but its detection time is long, making it unsuitable for real-time monitoring. Chemiluminescence has good sensitivity and a wide linear range, but it is prone to converting other nitrogen oxides into NO during the NO2 conversion process, leading to measurement errors. Therefore, accurate detection of low-concentration NO2 remains a challenge in air quality monitoring. Further optimization based on existing research is needed to establish a simpler and more efficient method for NO2 determination.

[0004] With the advancement of nanotechnology, researchers worldwide are continuously developing air quality monitoring sensors based on novel nanomaterials. Compared to gas sensors using spectrophotometry, ion chromatography, and chemiluminescence, chemiluminescence sensors have attracted widespread research attention due to their unique advantages such as high sensitivity, small size, low cost, and ease of operation, showing great application potential in urban atmospheric environment monitoring. Among these, electrochemical sensors based on metal oxide semiconductor @MOFs composite materials have demonstrated excellent gas-sensing performance. However, their further development is still limited by drawbacks such as high operating temperature and poor selectivity.

[0005] Existing NO2 sensing materials based on metal oxides have relatively high sensing operating temperatures, reaching 150 degrees Celsius or even 300 degrees Celsius. Chinese patent CN116794118A discloses an NO2 sensor based on an In2O3 / ZIF-8 core-shell nanocube composite material and its preparation method. This method utilizes a simple solvothermal method and in-situ growth method to prepare an In2O3 nanocube composite material modified with a ZIF-8 filter film. By coating the surface with a ZIF-8 filter film, the sensor's specific sensitivity to NO2 is effectively improved. However, its optimal operating temperature of 125°C is still relatively high and requires further research. Summary of the Invention

[0006] The purpose of this invention is to provide a ZIF-8 / SnO2 complex, its preparation method, and its application. The sensor based on the ZIF-8 / SnO2 complex can achieve accurate detection of NO2 at low temperatures and has high electrochemical responsiveness and selectivity.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] On one hand, the present invention provides a ZIF-8 / SnO2 composite, using mesoporous SnO2 nanospheres as a carrier, wherein the internal channels and the surface are loaded with ZIF-8.

[0009] Preferably, the mesoporous SnO2 nanospheres have a diameter of 690–720 nm, a pore size of 8–9 nm, and a specific surface area of ​​78–80 m². 2 ·g -1 .

[0010] Preferably, the ZIF-8 / SnO2 composite has a diameter of 790–820 nm, a pore size of 7–8 nm, and a specific surface area of ​​69–71 m². 2 ·g -1 .

[0011] Preferably, the mass ratio of ZIF-8 to mesoporous SnO2 nanospheres is 1:20-30.

[0012] More preferably, the mass ratio of ZIF-8 to mesoporous SnO2 nanospheres is 1:25.

[0013] In this invention, the metal oxide semiconductor mesoporous SnO2 nanospheres have good chemical stability and high electrical conductivity, and the ZIF-8 has certain moisture resistance.

[0014] Secondly, the present invention also provides a method for preparing the ZIF-8 / SnO2 composite, comprising the following steps:

[0015] S1: Preparation of mesoporous SnO2 nanospheres;

[0016] S2: Preparation of SnO2 / ZIF-8 complex.

[0017] Preferably, step S1 comprises the following steps: preparing an F127 solution and a tannic acid aqueous solution respectively; mixing the tannic acid aqueous solution with the F127 solution, then adding a formaldehyde aqueous solution, and continuously stirring at a speed of 300-500 rpm for 20-28 hours to obtain a tannic acid-F127 mixed solution; preparing a stannous sulfate aqueous solution and mixing it with the tannic acid-F127 mixed solution, and bathing in an oil bath at 90-110 degrees Celsius for 8-16 hours to obtain a precursor solution; centrifuging, washing, drying, and calcining at 350-500 degrees Celsius for 1.5-4 hours to obtain the mesoporous SnO2 nanospheres.

[0018] More preferably, F127 refers to a triblock copolymer of polyethylene oxide and polyoxypropylene ether.

[0019] More preferably, in step S1, the concentration of F127 in the F127 solution is 4.0 to 5.5 mg / mL.

[0020] More preferably, in step S1, the F127 solution is obtained by adding F127 to a mixture of deionized water, ethanol and ammonia and stirring until dissolved, wherein the volume ratio of deionized water, ethanol and ammonia is 100:(20-30):1, and the concentration of ammonia is 25-28 wt%.

[0021] More preferably, the volume ratio of the deionized water, ethanol, and ammonia is 100:23:1.

[0022] More preferably, in step S1, the concentration of tannic acid in the tannic acid aqueous solution is 45-60 mg / mL.

[0023] More preferably, in step S1, the tannic acid aqueous solution is prepared by adding tannic acid to deionized water and dissolving it by ultrasonication.

[0024] More preferably, in step S1, the concentration of formaldehyde in the formaldehyde aqueous solution is 3.7–4.0 wt%.

[0025] More preferably, in step S1, the concentration of tannic acid in the tannic acid-F127 mixed solution is 3.0-4.5 mg / mL, and the concentration of F127 is 3.0-4.5 mg / mL.

[0026] More preferably, in step S1, the concentration of stannous sulfate in the aqueous solution is 30-40 mg / mL.

[0027] More preferably, in step S1, the stannous sulfate aqueous solution is obtained by adding stannous sulfate to deionized water and dissolving it by shaking.

[0028] More preferably, in step S1, the concentration of F127 in the precursor solution is 3.0–4.5 mg / mL, the concentration of tannic acid is 3.0–4.5 mg / mL, and the concentration of stannous sulfate is 0.9–1.5 mg / mL.

[0029] More preferably, in step S1, the mass ratio of F127, tannic acid, and stannous sulfate is 1:1:0.3-1.

[0030] More preferably, in step S1, the continuous stirring time is 24 hours and the stirring speed is 300 rpm.

[0031] More preferably, in step S1, the oil bath time is 12 hours and the oil bath temperature is 100 degrees Celsius.

[0032] More preferably, in step S1, the calcination time is 3 hours and the calcination temperature is 400 degrees Celsius.

[0033] More preferably, in step S1, the centrifugal washing uses deionized water.

[0034] More preferably, in step S1, the drying temperature is 60-70℃ and the drying time is greater than 7 hours.

[0035] Preferably, step S2 is as follows: SnO2 is added to a Zn(NO)3 methanol solution and stirred at 300-500 rpm for 200-300 minutes, then centrifuged and washed to obtain a precipitate; the precipitate is added to a 2-methylimidazolium methanol solution and stirred at 300-500 rpm for 20-28 hours, then centrifuged, washed, and dried to obtain the ZIF-8 / SnO2 complex.

[0036] More preferably, in step S2, the concentration of Zn(NO)3 in the Zn(NO)3 methanol solution is 20-30 mg / mL.

[0037] More preferably, in step S2, the Zn(NO)3 methanol solution is obtained by adding Zn(NO)3·6H2O to a methanol solution and then dissolving it by ultrasonication.

[0038] More preferably, in step S2, the mass-to-volume ratio of SnO2 to Zn(NO)3 methanol solution is 1:5 to 10.

[0039] More preferably, in step S2, the mass-to-volume ratio of SnO2 to Zn(NO)3 methanol solution is 1:9.

[0040] More preferably, in step S2, the mass-to-volume ratio of the precipitate to the 2-methylimidazole methanol solution is 1:20.

[0041] More preferably, in step S2, the concentration of 2-methylimidazole in the 2-methylimidazole methanol solution is 40-50 mg / mL.

[0042] More preferably, in step S2, the 2-methylimidazole methanol solution is obtained by adding 2-methylimidazole to a methanol solution and then dissolving it by ultrasonication.

[0043] More preferably, in step S2, the mass-to-volume ratio of the precipitate to the 2-methylimidazole methanol solution is 1:15-25.

[0044] More preferably, in step S2, the molar ratio of SnO2, Zn(NO)3·6H2O and 2-methylimidazole is (0.2-1):1:(5-10).

[0045] More preferably, in step S2, the molar ratio of SnO2, Zn(NO)3·6H2O and 2-methylimidazole is 0.2 to 1:1:7.75.

[0046] More preferably, in step S2, the centrifugal washing is performed using a methanol solution.

[0047] More preferably, in step S2, the purity of the methanol solution is 99.5%.

[0048] More preferably, in step S2, the drying temperature is 60-70℃ and the drying time is greater than 7 hours.

[0049] Thirdly, the present invention also provides an application of the above-mentioned ZIF-8 / SnO2 composite in the field of nitrogen dioxide sensing.

[0050] Preferably, the ZIF-8 / SnO2 composite can be used as a nitrogen dioxide sensor, which has electrochemical responsiveness and can detect nitrogen dioxide at low temperatures.

[0051] Preferably, the low temperature refers to 75-85°C.

[0052] More preferably, the optimal operating temperature for the nitrogen dioxide sensor is 80°C.

[0053] More preferably, the nitrogen dioxide sensor is prepared by the following method: dispersing the prepared ZIF-8 / SnO2 composite in ethanol to prepare a suspension; uniformly dropping 5-15 μL of the suspension onto a commercial ceramic tube, and then connecting it to a multimeter to obtain the nitrogen dioxide sensor.

[0054] More preferably, the concentration of the suspension is 1–3 mg / μL.

[0055] More preferably, the volume of the suspension is 10 μL.

[0056] More preferably, using the nitrogen dioxide sensor to detect ammonia includes the following steps:

[0057] (1) At the operating temperature, the nitrogen dioxide sensor is placed in a nitrogen dioxide atmosphere of known concentration, the change of resistance value over time is detected, and a standard operating curve is plotted.

[0058] (2) Place the sensor in the atmosphere to be tested, and use the standard working curve obtained in step (1) to obtain the nitrogen dioxide concentration in the atmosphere to be tested by the resistance change value.

[0059] More preferably, step (1) includes the following steps:

[0060] a. Place the nitrogen dioxide sensor in a sealed chamber;

[0061] b. Inject nitrogen dioxide into the sealed chamber using an airtight injector, while recording the resistance change (Rg) indicated by the multimeter and calculating the corresponding response value;

[0062] c. Measure the sensor's response values ​​at different concentrations of nitrogen dioxide and plot the response value as a function of concentration.

[0063] More preferably, in step b, the response value is calculated by the following method: the nitrogen dioxide sensor is placed in the chamber, and the resistance at this time is measured by a multimeter connected to the nitrogen dioxide sensor to obtain the resistance (Ra) of the sensor in the air; according to the definition formula of the response value S=Rg / Ra, the response value of the sensor at different concentrations is calculated.

[0064] More preferably, the volume of the sealed chamber is 15-20L.

[0065] More preferably, the volume of the sealed chamber is 20L.

[0066] The high-response nitrogen dioxide sensor based on ZIF-8 modified SnO2 provided by this invention can detect nitrogen dioxide at lower temperatures and has high electrochemical responsiveness. It can avoid the limitation of MOF's insulating properties in electrochemical sensing and reduce the influence of humidity on the sensing material, thereby greatly improving the selective response to nitrogen dioxide.

[0067] Compared with the prior art, the present invention has the following beneficial effects:

[0068] (1) The present invention prepares a ZIF-8 / SnO2 composite, with mesoporous SnO2 nanospheres as the carrier, and ZIF-8 loaded in the internal channels and on the surface. This composite can be used as a nitrogen dioxide sensor, and has high electrochemical responsiveness and selectivity to nitrogen dioxide at low temperature.

[0069] (2) The metal oxide semiconductor material SnO2 nanospheres prepared by this invention have mesopores and a large specific surface area, can be loaded with ZIF-8, have a simple preparation method, good chemical stability and high electrical conductivity. When combined with ZIF-8, it can overcome the limitation of the insulating properties of MOF on its application in electrochemical sensing.

[0070] (3) The ZIF-8 prepared by this invention has a large specific surface area and certain moisture resistance. When loaded onto the pores and surface of SnO2 nanospheres, it can reduce the influence of moisture in the air on the response and increase the active sites for nitrogen dioxide adsorption, thereby enhancing the gas selective response to nitrogen dioxide.

[0071] (4) The nitrogen dioxide sensor prepared based on the ZIF-8 / SnO2 composite of the present invention can detect nitrogen dioxide in the concentration range of 0.2ppm to 1ppm at a relatively low temperature of 80℃, and has good repeatability and selectivity. Attached Figure Description

[0072] Figure 1 The image shown is a scanning electron microscope image of SnO2 as shown in Example 1.

[0073] Figure 2 The image shown is a scanning electron microscope image of SnO2 / ZIF-8 as shown in Example 1.

[0074] Figure 3 The EDS elemental mapping diagram of SnO2 / ZIF-8 shown in Example 1;

[0075] Figure 4 X-ray diffraction patterns of mesoporous SnO2 nanospheres, ZIF-8, and SnO2 / ZIF-8 as shown in Example 1;

[0076] Figure 5Thermogravimetric analysis of mesoporous SnO2 nanospheres and SnO2 / ZIF-8 as shown in Example 1;

[0077] Figure 6 Raman images of mesoporous SnO2 nanospheres and SnO2 / ZIF-8 as shown in Example 1;

[0078] Figure 7 The N2 adsorption curves and pore size distribution diagrams of the mesoporous SnO2 nanospheres and SnO2 / ZIF-8 shown in Example 1 are shown.

[0079] Figure 8 The graph shows the trend of SnO2 / ZIF-8 response to 1 ppm nitrogen dioxide in the range of 36 to 130 degrees Celsius, as shown in Example 1.

[0080] Figure 9 The response diagram of SnO2 / ZIF-8 to gradient nitrogen dioxide concentrations shown in Example 1 is as follows;

[0081] Figure 10 The graph shows the linear fit between the response value of SnO2 / ZIF-8 to nitrogen dioxide and the gas concentration, as shown in Example 1.

[0082] Figure 11 The graph shows the three-cycle response recovery curve of SnO2 / ZIF-8 to 11ppb nitrogen dioxide, as shown in Example 1.

[0083] Figure 12 The diagram shows the repeated response of SnO2 / ZIF-8 to 0.5 ppm nitrogen dioxide, as shown in Example 1.

[0084] Figure 13 The image shows the gas selective response diagram of SnO2 / ZIF-8 as shown in Example 1. Detailed Implementation

[0085] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0086] Unless otherwise specified, the reagents, methods, instruments, and equipment used in this invention are conventional in the art. Unless otherwise specified, the reagents and materials used in the following examples are all commercially available.

[0087] Example 1

[0088] This embodiment provides a method for preparing a composite material based on ZIF-8 modified SnO2, including the following steps:

[0089] Preparation of S1, metal oxide semiconductor (mesoporous SnO2 nanospheres)

[0090] Weigh 200 mg of F127 and add it to a mixed solution of 35 mL of deionized water, 8 mL of ethanol, and 350 μL of ammonia (25%–28% wt). Stir until F127 is completely dissolved. Weigh 200 mg of tannic acid and add it to 2 mL of deionized water. After sonication to dissolve the tannic acid, pour the solution into the mixed solution above. Then add 3.8 mL of 3.7% wt formaldehyde aqueous solution and stir continuously (300 rpm) for 24 hours. Subsequently, weigh 70 mg of stannous sulfate and add it to 2 mL of deionized water. After shaking to dissolve the stannous sulfate, pour the solution into the mixed solution above. Incubate the solution in an oil bath at 100°C for 12 hours. Centrifuge, wash, and dry the solution (at 70°C). Finally, calcine the solution at 400°C for 3 hours to obtain SnO2.

[0091] Preparation of S2, SnO2 and ZIF-8 composite materials (SnO2 / ZIF-8 composite)

[0092] Weigh 224 mg Zn(NO)3·6H2O and add it to 10 mL of methanol. After sonication and dissolution, weigh 25 mg SnO2 and add it to the above solution. Stir for 250 minutes and wash with methanol by centrifugation. Then weigh 479 mg 2-methylimidazole and add it to 10 mL of methanol. After sonication and dissolution, add the precipitate obtained by centrifugation above. Stir at room temperature for 12 hours and let stand for 12 hours. Centrifuge, wash, and dry (60 degrees Celsius) to obtain the SnO2 complex loaded with ZIF-8.

[0093] I. Structural Characterization of SnO2 / ZIF-8

[0094] The prepared SnO2 was characterized by scanning electron microscopy, such as... Figure 1 As shown in the figure, the size of SnO2 is approximately 705 nm, with a scale bar of 5.0 μm.

[0095] The prepared SnO2 / ZIF-8 was characterized by scanning electron microscopy, such as... Figure 2 As shown in the figure, the size of SnO2 / ZIF-8 is approximately 804 nm, with a scale bar of 1.0 μm.

[0096] Figure 3 The image shows the EDS elemental mapping of SnO2 / ZIF-8. The material mainly contains C, N, O, Sn, and Zn elements. The presence of Zn and N elements is clearly visible, which is due to ZIF-8 doping in the composite material, indicating the successful preparation of SnO2 / ZIF-8.

[0097] Figure 4The X-ray diffraction patterns of mesoporous SnO2 nanospheres, ZIF-8, and SnO2 / ZIF-8 are shown in the figure. As can be seen from the figure, SnO2 has good crystallinity, and the composite product also shows the characteristic peak of ZIF-8, indicating that the materials were successfully composited.

[0098] Figure 5 The thermogravimetric curves (TG) of mesoporous SnO2 nanospheres and SnO2 / ZIF-8 are shown. The TG curves show that SnO2 and its composite material with ZIF-8 (SnO2 / ZIF-8) have small weight loss, indicating that the two materials have good thermal stability. The TG curve of the composite material is consistent with that of SnO2, but the weight loss rate is higher than that of SnO2. The loading rate of ZIF-8 is calculated to be approximately 6%.

[0099] Figure 6 Raman spectra of mesoporous SnO2 nanospheres and SnO2 / ZIF-8 were obtained. SnO2 exhibits a unique characteristic located at 480 cm⁻¹. -1 600cm -1 790cm -1 The three characteristic peaks on the left and right sides are similar to those of SnO2 / ZIF-8 and SnO2, and are located at 1500 cm⁻¹. -1 The presence of characteristic peaks for ZIF-8 on both sides indicates the successful loading of ZIF-8 onto mesoporous SnO2 nanospheres.

[0100] Figure 7 The images show the N2 adsorption curves and pore size distribution of mesoporous SnO2 nanospheres and SnO2 / ZIF-8. After loading ZIF-8, the images show the type IV N2 isothermal adsorption-desorption curves, with the pore size decreasing from 8.2 nm to 7.5 nm and the specific surface area increasing from 79.4 m² / m³. 2 / g decreased to 70.6m 2 / g indicates that the SnO2 nanospheres are indeed mesoporous, and the growth of ZIF-8 in the channels of the mesoporous SnO2 nanospheres leads to a reduction in pore size, which in turn reduces the specific surface area.

[0101] II. Electrochemical Sensing Performance of SnO2 / ZIF-8 for Nitrogen Dioxide

[0102] SnO2 / ZIF-8 powder was dispersed in ethanol to a concentration of 1 mg / μL. Then, 10 μL of the suspension was evenly dropped onto a commercial ceramic tube placed in a 20 L chamber and connected to a heater. When detecting nitrogen dioxide gas, nitrogen dioxide was injected into the sealed chamber through a gas-tight syringe, and the resistance change was observed using a multimeter. For detecting ammonia and other test liquids, a heater was also required to evaporate the ammonia and other test liquids, while the resistance change was observed using a multimeter. Unless otherwise specified, all experimental conditions were performed at a temperature of 80 degrees Celsius and with high ambient humidity (63%–85%).

[0103] Figure 8 The graph shows the response trend of SnO2 / ZIF-8 to 1 ppm nitrogen dioxide in the range of 36 to 130 degrees Celsius, indicating that the optimal operating temperature of the sensor made of SnO2 / ZIF-8 sensing material is 80 degrees Celsius.

[0104] Figure 9 The graph shows the response of SnO2 / ZIF-8 to gradient nitrogen dioxide concentrations, with nitrogen dioxide test concentrations ranging from 0.2 ppm to 1 ppm, and the responsivity ranging from R... g / R a =Rising from 10.66 to 85.95%.

[0105] Figure 10 The graph shows the linear fit between the response value of SnO2 / ZIF-8 to nitrogen dioxide and the gas concentration. The goodness of fit is greater than 0.9, indicating that the response value and the gas concentration have a good linear relationship.

[0106] Figure 11 The graph shows the three-cycle response recovery curve of SnO2 / ZIF-8 to 11 ppb nitrogen dioxide, indicating that it does indeed respond to the calculated theoretical detection limit.

[0107] Figure 12 The diagram shows the repeated response of SnO2 / ZIF-8 to 0.5 ppm nitrogen dioxide, indicating that the material maintains good repeatability and stability over six cycles.

[0108] Figure 13 The gas-selective response diagram of SnO2 / ZIF-8 is shown. The test objects are 1 ppm nitrogen dioxide, 200 ppm methanol, ethanol, isopropanol, xylene and ammonia. Among them, nitrogen dioxide, methanol, ethanol, isopropanol, xylene and ammonia are used as interfering gases. The results show that the material's response to nitrogen dioxide is much higher than that of other interfering gases.

[0109] In summary, this invention prepares a ZIF-8 / SnO2 composite with mesoporous SnO2 nanospheres as a carrier, and ZIF-8 loaded on the internal channels and surface. This composite can be used as a nitrogen dioxide sensor, exhibiting high electrochemical responsiveness and selectivity to nitrogen dioxide at low temperatures.

[0110] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A ZIF-8 / SnO2 composite, characterized in that, Mesoporous SnO2 nanospheres were used as a carrier, with ZIF-8 loaded in their internal channels and on their surface. The mesoporous SnO2 nanospheres have a diameter of 690-720 nm, a pore size of 8-9 nm, and a specific surface area of ​​78-80 m². 2 ·g -1 The ZIF-8 / SnO2 composite has a diameter of 790~820 nm, a pore size of 7~8 nm, and a specific surface area of ​​69~71 m². 2 ·g -1 .

2. The ZIF-8 / SnO2 composite according to claim 1, characterized in that, The mass ratio of ZIF-8 to mesoporous SnO2 nanospheres is 1:20~30.

3. A method for preparing the ZIF-8 / SnO2 composite as described in any one of claims 1 to 2, characterized in that, Includes the following steps: S1: Preparation of mesoporous SnO2 nanospheres; S2: Preparation of SnO2 / ZIF-8 complex.

4. The method for preparing the ZIF-8 / SnO2 composite according to claim 3, characterized in that, The specific steps of step S1 are as follows: Prepare F127 solution and tannic acid aqueous solution respectively; mix tannic acid aqueous solution and F127 solution, then add formaldehyde aqueous solution, and stir continuously at 300~500 rpm for 20~28 hours to obtain tannic acid-F127 mixed solution; prepare stannous sulfate aqueous solution and mix it with tannic acid-F127 mixed solution, and heat in an oil bath at 90~110 degrees Celsius for 8~16 hours to obtain precursor solution; after centrifugation, washing, and drying, calcine at 350~500 degrees Celsius for 1.5~4 hours to obtain the mesoporous SnO2 nanospheres.

5. The method for preparing the ZIF-8 / SnO2 composite according to claim 4, characterized in that, The concentration of F127 in the F127 solution is 4.0~5.5 mg / mL, and the concentration of tannic acid in the tannic acid aqueous solution is 45~60 mg / mL. The formaldehyde concentration in the formaldehyde aqueous solution is 3.7~4.0 wt%. In the tannic acid-F127 mixed solution, the concentration of tannic acid is 3.0~4.5 mg / mL, and the concentration of F127 is 3.0~4.5 mg / mL; The concentration of stannous sulfate in the aqueous solution is 30-40 mg / mL. In the precursor solution, the concentration of F127 is 3.0~4.5 mg / mL, the concentration of tannic acid is 3.0~4.5 mg / mL, the concentration of stannous sulfate is 0.9~1.5 mg / mL, and the mass ratio of F127, tannic acid and stannous sulfate is 1:1:0.3~1.

6. The method for preparing the ZIF-8 / SnO2 composite according to claim 4, characterized in that, The F127 solution is obtained by dissolving F127 in a mixture of deionized water, ethanol and ammonia, wherein the volume ratio of deionized water, ethanol and ammonia is 100:(20~30):1, and the concentration of ammonia is 25-28wt%.

7. The method for preparing the ZIF-8 / SnO2 composite according to claim 3, characterized in that, The specific steps of step S2 are as follows: SnO2 is added to Zn(NO)3 methanol solution, stirred at 300~500 rpm for 200~300 minutes, and centrifuged and washed to obtain the precipitate; The precipitate was added to a 2-methylimidazolium methanol solution and stirred at 300-500 rpm for 20-28 hours. After centrifugation, washing, and drying, the ZIF-8 / SnO2 complex was obtained.

8. The method for preparing the ZIF-8 / SnO2 composite according to claim 7, characterized in that, In the Zn(NO)3 methanol solution, the concentration of Zn(NO)3 is 20~30 mg / mL; The mass-to-volume ratio of the SnO2 to Zn(NO)3 methanol solution is 1:5~10; In the 2-methylimidazole methanol solution, the concentration of 2-methylimidazole is 40~50 mg / mL; The mass-to-volume ratio of the precipitate to the 2-methylimidazol methanol solution is 1:15~25; The molar ratio of SnO2, Zn(NO)3·6H2O and 2-methylimidazole is (0.2~1):1:(5~10).

9. The application of the ZIF-8 / SnO2 composite as described in any one of claims 1 to 2 in the field of nitrogen dioxide sensing.

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