阅读说明：本技术 一种SnO2/ZIF-8复合气敏材料的制备方法及其应用 (SnO (stannic oxide)2Preparation method and application of/ZIF-8 composite gas-sensitive material ) 是由 张现峰 吴中 李倩 邵兰芳 李昌城 程健健 于 2021-08-29 设计创作，主要内容包括：本发明公开一种SnO-(2)/ZIF-8复合气敏材料的制备方法及其应用,包括以下步骤：(1)SnO-(2)预处理：按(0.1-0.15)g：40mL的固液比将纳米SnO-(2)加入甲醇中,并进行超声分散,再将聚乙烯吡咯烷酮加入所得SnO-(2)悬浊液中,磁力搅拌24h,离心、洗涤、干燥后,再配制成2mg/mL SnO-(2)-甲醇悬浊液,备用；(2)制备SnO-(2)/ZIF-8复合材料：将Zn(NO-(3))-(2)-甲醇溶液、2-甲基咪唑-甲醇溶液加入SnO-(2)-甲醇悬浊液,磁力搅拌反应24h后,将所得乳白色溶液进行离心分离,再用无水乙醇洗涤下层沉淀3-4次,并收集白色产物；(3)产品干燥。本发明首次采用ZIF-8对纳米SnO-(2)材料进行掺杂改性,ZIF-8表面具有大量活性反应位点,可与甲酸特异性结合,同时,使其对纳米SnO-(2)提供具有较强的负载能力,提高复合稳定性。(The invention discloses SnO 2 The preparation method and the application of the/ZIF-8 composite gas-sensitive material comprise the following steps: (1) SnO 2 Pretreatment: mixing the following raw materials in a ratio of (0.1-0.15) g: 40mL of nano SnO 2 Adding into methanol, performing ultrasonic dispersion, and adding polyvinylpyrrolidone into the obtained SnO 2 Magnetically stirring the suspension for 24h, centrifuging, washing, drying, and preparing into SnO with concentration of 2mg/mL 2 -a methanol suspension for use; (2) preparation of SnO 2 ZIF-8 composite material: adding Zn (NO) 3 ) 2 Adding SnO into methanol solution or 2-methylimidazole-methanol solution 2 Magnetically stirring the methanol suspension for reaction for 24 hr, centrifuging the milky white solution, washing the lower precipitate with anhydrous ethanol for 3-4 times, and collecting the white product; (3) and (5) drying the product. The invention adopts ZIF-8 pair nano SnO for the first time 2 The material is doped and modified, and the surface of ZIF-8 has a large number of active reaction sites, can be specifically combined with formic acid, and simultaneously can be used for carrying out nano SnO 2 Provides the composite material with stronger load capacity and improved composite stability.)

1. SnO (stannic oxide)₂The preparation method of the/ZIF-8 composite gas-sensitive material is characterized by comprising the following steps of:

(1)SnO₂pretreatment: mixing the following raw materials in a ratio of (0.1-0.15) g: 40mL of nano SnO₂Adding into methanol, performing ultrasonic dispersion, and adding polyvinylpyrrolidone into the obtained SnO₂Controlling nano SnO in turbid liquid₂The mass ratio of polyvinylpyrrolidone is (1-2) to (0-2), magnetic stirring is carried out for 24 hours, centrifugation, washing and drying are carried out, and then 2mg/mL SnO is prepared₂-a methanol suspension for use;

(2) preparation of SnO₂ZIF-8 composite material:

zn (NO) is added according to the solid-to-liquid ratio of (1.6-2.0) g:38mL₃)₂·6H₂Dissolving O in methanol to obtain Zn (NO)₃)₂-a methanol solution;

dissolving 2-methylimidazole in methanol according to the solid-to-liquid ratio of (1.6-2.0) g:38mL to obtain a 2-methylimidazole-methanol solution;

adding Zn (NO)₃)₂Adding SnO into methanol solution or 2-methylimidazole-methanol solution₂Magnetically stirring the methanol suspension for reaction for 24 hr, centrifuging the milky white solution, washing the lower precipitate with anhydrous ethanol for 3-4 times, and collecting the white product;

(3) drying a product: drying at 80 deg.C for 12 hr to obtain white powdered SnO₂the/ZIF-8 composite gas-sensitive material.

2. A SnO according to claim 1₂The preparation method of the/ZIF-8 composite gas-sensitive material is characterized in that the nano SnO₂The preparation method comprises the following steps: SnCl₄·5H₂O, NaOH adding the solution and polyvinylpyrrolidone into deionized water, magnetically stirring until the solution is clear, transferring into a reaction kettle, carrying out hydrothermal reaction at constant temperature of 200 deg.C for 24h, cooling to obtain precipitate, and adding deionized waterAnd after 3 times of cross washing by ethanol, drying for 2h at 300 ℃, removing ethanol, water and unreacted polyvinylpyrrolidone, grinding and crushing to obtain a white powdery product, namely the nano SnO₂And storing for later use.

3. A SnO according to claim 2₂The preparation method of the/ZIF-8 composite gas-sensitive material is characterized in that the SnCl is₄·5H₂O, NaOH solution, polyvinylpyrrolidone and deionized water in the dosage ratio of (2-2.5) g, (8-10) mL and 50 mL.

4. A SnO according to claim 3₂The preparation method of the/ZIF-8 composite gas-sensitive material is characterized in that the concentration of the NaOH solution is 6 mol/L.

5. A SnO according to claim 1₂The preparation method of the/ZIF-8 composite gas sensitive material is characterized in that Zn (NO) is adopted₃)₂-methanol solution, 2-methylimidazole-methanol solution, SnO₂The volume ratio of the methanol suspension is (3.5-4) to 5.

6. SnO produced by the production process according to any one of claims 1 to 5₂The application of the/ZIF-8 composite gas sensitive material in the preparation of a selective formic acid gas sensitive element.

7. The application of claim 6, wherein the specific application method is as follows:

(1) preparing slurry: the SnO₂Grinding the/ZIF-8 composite gas-sensitive material for 30min, adding deionized water according to the material-liquid ratio of 1g (0.6-1.2) mL, and continuously mixing and grinding for 30min to prepare uniform pasty slurry;

(2) assembling: in Al₂O₃Two parallel annular gold electrodes are sleeved on the outer surface of the ceramic tube, two opposite platinum wire leads are welded on two sides of the annular gold electrodes, and the composite Al is assembled₂O₃A ceramic tube;

(3) coating compositionCovering: uniformly coating the obtained pasty slurry on the composite Al₂O₃Drying the surface of the ceramic tube at 80 ℃ for 5h to obtain the composite air-sensitive Al₂O₃A ceramic tube;

(3) welding: penetrating a nickel-chromium wire for controlling heating temperature into composite gas-sensitive Al₂O₃After the ceramic tube is arranged in the gas sensitive element, welding two ends of the nickel-chromium wire and four platinum wires outside the ceramic tube on the base respectively to obtain a semi-finished product of the gas sensitive element;

(4) aging: and (3) aging the semi-finished gas sensor at 300 ℃ for 3d to obtain the indirectly heated selective formic acid gas sensor.

8. The use as claimed in claim 7, wherein the indirectly heated selective formic acid gas sensor has an operating temperature of 175-325 ℃, and when the operating temperature is 260 ℃, the sensitivity value for detecting 10ppm formic acid is 20.314, and the sensitivity value for detecting 100ppm formic acid is 372.5.

Technical Field

The invention relates to the technical field of functional nano material preparation, and also relates to the technical field of gas sensing detection, in particular to SnO₂A preparation method and application of a/ZIF-8 composite gas-sensitive material are provided.

Background

With the rapid development of modern industrial production, sensors and sensing technologies enter all corners of people's life, and gas sensors are detection devices, are important tools for people to know the world, and provide great convenience for people's life. In industrial development, a wide variety of toxic and harmful gases are produced, which are directly or indirectly put into our living environment and seriously harm our health. With the increasing of the construction strength of ecological civilization, people have higher requirements on the living environment and are difficult to allow toxic gas polluting the environment. It is therefore highly desirable to be able to easily detect these toxic gases in a simple and convenient manner. Therefore, it is urgent to develop more precise and convenient gas sensitive devices and sensing technologies. Because the gas-sensitive material with a single type cannot meet the actual production and application requirements at some time, the research needs to improve various detection performances of the sensor from the aspects of the specific surface area of the material, the area of the sensing gas during the test, the manufacturing cost and the like, such as prolonging the service life, reducing the lower limit of the detection concentration, enhancing the selectivity, reducing the response/recovery time and the like, by replacing different materials, controlling and changing the appearance of the material, adding different substances to modify the material, or researching methods of a porous novel material and the like. In addition, the gas sensor developed at present is mainly applied to gases such as ethanol, formaldehyde, hydrogen, carbon monoxide, sulfur dioxide, acetone, volatile benzene and the like, but related reports on the research of the formic acid gas-sensitive material are rare. Therefore, the development of composite gas sensitive materials and sensors for selectively detecting formic acid is an urgent technical problem to be solved, and is one of the important research topics at present.

The Metal Organic Frameworks (MOFs) material is made of inorganic materialsMetal ions (e.g. Zn)²⁺、Zr⁴⁺、Cu²⁺、Fe³⁺、Ln⁴⁺、Co^{4 +}Etc.) or a porous compound having a network structure formed by coordination of metal ion clusters and organic ligands. As the MOFs have very high specific surface area, a large number of hole sites, abundant metal sites, adjustable structure, flexibility and diversity^]And the like, so the use function also has diversity, and therefore, the material is widely applied to a plurality of fields such as catalysts, gas separation, biology and medicine, ion exchange, energy storage, solar cells, sensors and the like, has great feasibility in the aspect of sensing materials, and is one of the hot spots of the performance research of the current new materials. Zeolite imidazole-like framework materials (ZIFs) are a branch of MOFs, and are novel materials which are prepared by displaying open crystals according to a certain rule. The ZIFs use Zn or Co as a metal center and coordinate with a connector of a para-position nitrogen heterocycle to form a tetrahedral three-dimensional structure. ZIFs materials have many advantages: the gas diffusion device comprises a plurality of pore passages with uniform size and shape for gas diffusion, so that the gas diffusion device has good sieving effect on gas molecules with smaller sizes; secondly, the structure is relatively simple, and various ZIFs materials with different special properties can be synthesized by changing the types of metal ions or organic ligands in the reaction; finally, the anion ligand formed by the organic ligand imidazole has stronger alkalinity and stronger coordination with metal ions, thereby having higher mechanical property. In the synthesis process, the solvent and the ligand of the ZIFs have self-assembly characteristics, the structure is multifunctional, and the surface can be flexibly regulated and controlled, so that the ZIFs have wide application prospects in the aspects of adsorbents (gas separation and storage), ion exchangers (ion removal and water softening), catalysts, sensors and the like. At present, the preparation of functionalized ZIFs materials through modification is also one of the hot spots of research in the direction.

Tin dioxide powder is generally white, but also somewhat pale grey and yellowish, and is an inorganic compound. The melting point of the tin dioxide is 1600 ℃, the boiling point is 1800-1900 ℃, and the molar mass and the density are 150.72g/mol and 6.94g/cm respectively³Is an amphoteric oxide, insoluble or poorly soluble in polar solvents such as water and alcohol, but soluble in polar solvents such as water and alcoholA hot strong base and a hot strong acid. SnO₂The crystal unit cell is a body-center orthogonal parallelepiped and has a rutile structure, the forbidden band width of the crystal unit cell is 3.54eV, and the crystal unit cell belongs to wide forbidden band metal oxide. One has measured SnO₂After the conductivity and the Hall coefficient are determined to be N-type conductivity, the main reason of the defects of the tin dioxide N-type semiconductor is researched to be that the structure contains oxygen gaps and tin interstitial atoms. SnO₂The gas-sensitive effect of (2) was found for the first time to be that in 1962, Pd and Pt-doped SnO was produced in the company Figali₂After commercialization of the gas sensor, with respect to SnO₂The research on gas sensors has been followed, and the types of gas sensors have been increasing. SnO₂The gas sensor mainly comprises a sintering type gas sensor and a thick film type gas sensor: 1) the sintering type is the most mature in the research of the current gas sensitive element, the sintering type needs to be heated during the test, and the heating modes comprise a direct heating type and an indirect heating type. Wherein, the direct heating type is to provide the working temperature needed by the element test by the heating wire embedded in the gas sensitive material, and the resistance value change of the element is tested by the measuring wire; the indirectly heated type is that the heating wire which penetrates through the ceramic tube with the surface coated with the gas-sensitive material provides working temperature, the heating wire is only used for providing temperature, the measuring wire is fixed on the ceramic tube, and the indirectly heated type is not influenced by the heating wire when the resistance value is measured, so that the indirectly heated type has higher stability. 2) The thick film type generally adopts the manufacturing technology of the silk-screen printing process, the silk-screen printing process is simpler than the manufacturing of the thin film type sensor, the cost is low, the mechanical strength of the element is improved, and the consistency is good compared with a sintering type element. However, the problems of high working temperature, poor selectivity, long response and recovery time and the like in the gas sensitive test process still exist by using single pure tin dioxide as a semiconductor gas sensitive material.

Based on the above, the invention provides a method for treating SnO by virtue of the characteristics of porous screening, large specific surface area, strong thermal stability and the like of zeolite imidazolate framework material ZIF-8₂The nano material is doped and modified, compared with pure SnO₂Modified SnO₂The gas-sensitive property is further greatly optimized and improved, and the method is used for high-sensitivity and high-selectivity detection of formic acid.

Disclosure of Invention

Aiming at the defects of the prior art, the invention aims to provide SnO₂A preparation method and application of a/ZIF-8 composite gas-sensitive material are provided.

The technical scheme of the invention is summarized as follows:

SnO (stannic oxide)₂The preparation method of the/ZIF-8 composite gas-sensitive material comprises the following steps:

(1)SnO₂pretreatment: mixing the following raw materials in a ratio of (0.1-0.15) g: 40mL of nano SnO₂Adding into methanol, performing ultrasonic dispersion, and adding polyvinylpyrrolidone into the obtained SnO₂Controlling nano SnO in turbid liquid₂The mass ratio of polyvinylpyrrolidone is (1-2) to (0-2), magnetic stirring is carried out for 24 hours, centrifugation, washing and drying are carried out, and then 2mg/mL SnO is prepared₂-a methanol suspension for use;

(2) preparation of SnO₂ZIF-8 composite material:

zn (NO) is added according to the solid-to-liquid ratio of (1.6-2.0) g:38mL₃)₂·6H₂Dissolving O in methanol to obtain Zn (NO)₃)₂-a methanol solution;

dissolving 2-methylimidazole in methanol according to the solid-to-liquid ratio of (1.6-2.0) g:38mL to obtain a 2-methylimidazole-methanol solution;

adding Zn (NO)₃)₂Adding SnO into methanol solution or 2-methylimidazole-methanol solution₂Magnetically stirring the methanol suspension for reaction for 24 hr, centrifuging the milky white solution, washing the lower precipitate with anhydrous ethanol for 3-4 times, and collecting the white product;

(3) drying a product: drying at 80 deg.C for 12 hr to obtain white powdered SnO₂the/ZIF-8 composite gas-sensitive material.

Preferably, the nano SnO₂The preparation method comprises the following steps: SnCl₄·5H₂O, NaOH adding the solution and polyvinylpyrrolidone into deionized water, magnetically stirring until the solution is clear, transferring to a reaction kettle, carrying out hydrothermal reaction at a constant temperature of 200 ℃ for 24h, cooling to obtain precipitate, and alternately washing with deionized water and ethanolWashing for 3 times, drying at 300 deg.C for 2h, removing ethanol, water and unreacted polyvinylpyrrolidone, grinding, and pulverizing to obtain white powder product, i.e. the nanometer SnO₂And storing for later use.

Preferably, the SnCl₄·5H₂O, NaOH solution, polyvinylpyrrolidone and deionized water in the dosage ratio of (2-2.5) g, (8-10) mL and 50 mL.

Preferably, the concentration of the NaOH solution is 6 mol/L.

Preferably, the Zn (NO) is₃)₂-methanol solution, 2-methylimidazole-methanol solution, SnO₂The volume ratio of the methanol suspension is (3.5-4) to 5.

SnO₂The application of the/ZIF-8 composite gas sensitive material in the preparation of a selective formic acid gas sensitive element.

Preferably, the specific application method comprises the following steps:

(1) preparing slurry: the SnO₂Grinding the/ZIF-8 composite gas-sensitive material for 30min, adding deionized water according to the material-liquid ratio of 1g (0.6-1.2) mL, and continuously mixing and grinding for 30min to prepare uniform pasty slurry;

(2) assembling: in Al₂O₃Two parallel annular gold electrodes are sleeved on the outer surface of the ceramic tube, two opposite platinum wire leads are welded on two sides of the annular gold electrodes, and the composite Al is assembled₂O₃A ceramic tube;

(3) coating: uniformly coating the obtained pasty slurry on the composite Al₂O₃Drying the surface of the ceramic tube at 80 ℃ for 5h to obtain the composite air-sensitive Al₂O₃A ceramic tube;

(3) welding: penetrating a nickel-chromium wire for controlling heating temperature into composite gas-sensitive Al₂O₃After the ceramic tube is arranged in the gas sensitive element, welding two ends of the nickel-chromium wire and four platinum wires outside the ceramic tube on the base respectively to obtain a semi-finished product of the gas sensitive element;

(4) aging: and (3) aging the semi-finished gas sensor at 300 ℃ for 3d to obtain the indirectly heated selective formic acid gas sensor.

Preferably, the working temperature of the indirect-heating type selective formic acid gas sensor is 175-325 ℃, and when the working temperature is 260 ℃, the detection sensitivity value of the indirect-heating type selective formic acid gas sensor to 10ppm formic acid reaches 20.314, and the detection sensitivity value of the indirect-heating type selective formic acid gas sensor to 100ppm formic acid reaches 372.5.

The invention has the beneficial effects that:

1. the invention adopts zeolite imidazole ester framework material ZIF-8 to nano SnO for the first time₂The material is doped and modified, ZIF-8 has the characteristics of porous screening, high specific surface area, strong thermal stability and the like, a large number of active reaction sites are arranged on the surface, the active reaction sites can be specifically combined with formic acid, the sensitivity of the gas-sensitive material to formic acid is improved, and meanwhile, the high specific surface area and the large number of active sites also enable the gas-sensitive material to nano SnO₂Provides the ZIF-8 modified SnO with stronger load capacity and improved composite stability₂The gas-sensitive property is further greatly optimized and improved, and the method is used for high-sensitivity and high-selectivity detection of formic acid.

2. SnO prepared by the invention₂the/ZIF-8 composite gas-sensitive material has high sensitivity and selectivity to formic acid, and simultaneously has higher stability and can be recycled.

Drawings

FIG. 1 is SnO of comparative example 1₂Gas sensitive Material and SnO prepared in examples 1-4₂The XRD spectrum of the/ZIF-8 composite gas-sensitive material;

FIG. 2 is SnO prepared in example 1₂SEM image of/ZIF-8 composite gas-sensitive material;

FIG. 3 is SnO prepared by comparative example 2₂Gas sensor and SnO prepared in example 5₂A ZIF-8 gas sensor detects a sensitivity change chart of 100ppm formic acid at different temperatures;

FIG. 4 is SnO prepared by comparative example 2₂Gas sensor and SnO prepared in example 5₂A ZIF-8 gas sensor detects sensitivity change graphs of formic acid with different concentrations at 260 ℃;

FIG. 5 is SnO prepared in example 5₂A ZIF-8 gas sensor detects sensitivity bar charts of 10ppm different gases at 260 ℃;

FIG. 6 is SnO prepared in example 5₂A ZIF-8 gas sensor product diagram;

FIG. 7 is SnO of the present invention₂A flow chart of a preparation method of a/ZIF-8 composite gas-sensitive material.

Detailed Description

The present invention is further described in detail below with reference to examples so that those skilled in the art can practice the invention with reference to the description.

The invention provides an embodiment of SnO₂The preparation method of the/ZIF-8 composite gas-sensitive material comprises the following steps:

(1) preparation of Nano SnO₂: SnCl₄·5H₂Adding O, 6mol/L NaOH solution and polyvinylpyrrolidone into deionized water, magnetically stirring until the solution is clarified, transferring the solution into a reaction kettle, carrying out hydrothermal reaction at a constant temperature of 200 ℃ for 24 hours, respectively washing the solution with deionized water and ethanol for 3 times after cooling the solution to obtain precipitates, drying the precipitates at 300 ℃ for 2 hours, removing ethanol, water and incompletely reacted polyvinylpyrrolidone, and grinding and crushing the precipitates to obtain a white powdery product, namely the nano SnO₂Storing for later use; the SnCl₄·5H₂O, NaOH solution, polyvinylpyrrolidone and deionized water, wherein the dosage ratio of (2-2.5) g, (8-10) mL:50 mL;

(2)SnO₂pretreatment: mixing the following raw materials in a ratio of (0.1-0.15) g: 40mL of nano SnO₂Adding into methanol, performing ultrasonic dispersion, and adding polyvinylpyrrolidone into the obtained SnO₂Controlling nano SnO in turbid liquid₂The mass ratio of polyvinylpyrrolidone is (1-2) to (0-2), magnetic stirring is carried out for 24 hours, centrifugation, washing and drying are carried out, and then 2mg/mL SnO is prepared₂-a methanol suspension for use;

(3) preparation of SnO₂ZIF-8 composite material:

zn (NO) is added according to the solid-to-liquid ratio of (1.6-2.0) g:38mL₃)₂·6H₂Dissolving O in methanol to obtain Zn (NO)₃)₂-a methanol solution;

dissolving 2-methylimidazole in methanol according to the solid-to-liquid ratio of (1.6-2.0) g:38mL to obtain a 2-methylimidazole-methanol solution;

adding Zn (NO)₃)₂-methanolAdding SnO into the solution and the 2-methylimidazole-methanol solution₂Magnetically stirring the methanol suspension for reaction for 24 hr, centrifuging the milky white solution, washing the lower precipitate with anhydrous ethanol for 3-4 times, and collecting the white product; the Zn (NO)₃)₂-methanol solution, 2-methylimidazole-methanol solution, SnO₂The volume ratio of the methanol suspension is (3.5-4) to 5;

(4) drying a product: drying at 80 deg.C for 12 hr to obtain white powdered SnO₂the/ZIF-8 composite gas-sensitive material.

SnO prepared in this example₂The application of the/ZIF-8 composite gas-sensitive material in the preparation of a selective formic acid gas-sensitive element comprises the following specific application methods:

(1) preparing slurry: the SnO₂Grinding the/ZIF-8 composite gas-sensitive material for 30min, adding deionized water according to the material-liquid ratio of 1g (0.6-1.2) mL, and continuously mixing and grinding for 30min to prepare uniform pasty slurry;

(2) assembling: in Al₂O₃Two parallel annular gold electrodes are sleeved on the outer surface of the ceramic tube, two opposite platinum wire leads are welded on two sides of the annular gold electrodes, and the composite Al is assembled₂O₃A ceramic tube;

(3) coating: uniformly coating the obtained pasty slurry on the composite Al₂O₃Drying the surface of the ceramic tube at 80 ℃ for 5h to obtain the composite air-sensitive Al₂O₃A ceramic tube;

(3) welding: penetrating a nickel-chromium wire for controlling heating temperature into composite gas-sensitive Al₂O₃After the ceramic tube is arranged in the gas sensitive element, welding two ends of the nickel-chromium wire and four platinum wires outside the ceramic tube on the base respectively to obtain a semi-finished product of the gas sensitive element;

(4) aging: and (3) aging the semi-finished gas sensor at 300 ℃ for 3d to obtain the indirectly heated selective formic acid gas sensor.

And (3) carrying out sensitivity test on the indirectly heated selective formic acid gas sensor: and inserting the obtained gas-sensitive element into a gas-sensitive tester, adding formic acid or different gases with different concentrations by adopting a static gas distribution method, opening a test system for testing, and calculating the sensitivity by using an S (Ra/Rg) formula after the resistance value is stable.

Example 1

SnO (stannic oxide)₂The preparation method of the/ZIF-8 composite gas-sensitive material comprises the following steps:

(1) preparation of Nano SnO₂: 2.2275g SnCl₄·5H₂Adding O, 8mL of 6mol/L NaOH solution, 2.1173g of polyvinylpyrrolidone (PVP, Mr 30000) into 50mL of deionized water, magnetically stirring until the solution is clarified, moving the solution into a reaction kettle, carrying out hydrothermal reaction at a constant temperature of 200 ℃ for 24h, cooling the solution to obtain precipitates, respectively washing the precipitates with deionized water and ethanol for 3 times, drying the precipitates at 300 ℃ for 2h, removing ethanol, water and unreacted polyvinylpyrrolidone, grinding and crushing to obtain a white powdery product, namely the nano SnO₂Storing for later use;

(2)SnO₂pretreatment: 0.1152g of nano SnO₂Adding into 40mL of methanol, performing ultrasonic dispersion, and adding 0.1152g of polyvinylpyrrolidone (PVP, Mr 30000) into the obtained SnO₂Controlling nano SnO in turbid liquid₂And the mass ratio of the polyvinylpyrrolidone is 1: 1, magnetically stirring for 24 hours, centrifuging, washing, drying, and preparing into 50mL of 2mg/mL SnO₂-a methanol suspension for use;

(3) preparation of SnO₂ZIF-8 composite material:

1.8563g Zn (NO)₃)₂·6H₂Dissolving O in 38mL of methanol to obtain Zn (NO)₃)₂-a methanol solution;

1.7940g of 2-methylimidazole was dissolved in 38mL of methanol to obtain a 2-methylimidazole-methanol solution;

38mL of Zn (NO)₃)₂Methanol solution, 38mL 2-methylimidazole-methanol solution 50mL SnO₂Magnetically stirring the methanol suspension for reaction for 24 hr, centrifuging the milky white solution, washing the lower precipitate with anhydrous ethanol for 3 times, and collecting the white product;

(4) drying a product: drying at 80 deg.C for 12 hr to obtain white powdered SnO₂ZIF-8 complexAnd synthesizing the gas-sensitive material.

Example 2 is the same as example 1, except that: nano SnO in example 2₂And the mass ratio of the polyvinylpyrrolidone is 1: 0.

example 3 is the same as example 1, except that: nano SnO in example 3₂And the mass ratio of the polyvinylpyrrolidone is 1: 2.

example 4 is the same as example 1, except that: nano SnO in example 3₂And the mass ratio of the polyvinylpyrrolidone is 2: 1.

comparative example 1: nano SnO₂The preparation method is the same as that of the step (1) in example 1.

SnO preparation for examples 1 to 4₂ZIF-8 composite gas-sensitive material and SnO of comparative example 1₂And (3) carrying out X-ray diffraction characterization on the gas-sensitive material:

FIG. 1 is comparative example 1SnO₂Gas sensitive Material and SnO prepared in examples 1-4₂XRD pattern of/ZIF-8 composite gas sensitive material: as shown in the figure, the prepared SnO₂All diffraction peaks correspond to and match the standard JCPDS card (JCPDS card NO. 41-1445). From the figure SnO₂The spectral line is relatively smooth, the peak shape is obviously sharp, and the coordinate base lines are relatively consistent, which shows that the crystal grain growth of the sample prepared in the experiment is relatively complete, the crystallization performance is good, and the amorphous and noncrystalline structures hardly exist. In addition, no other impurity diffraction peaks, i.e., SnO, appear in the figure₂No impurity is brought in the process of manufacturing the sample, and the obtained SnO₂The product purity is higher. Meanwhile, it is clear from the figure that when PVP and SnO are used₂The mass ratio of (1): the peak value at 1 is higher, and the full width at half maximum is larger, which shows that the crystallization is stronger, and the crystal grains are smaller, namely the crystal grains of the composite material prepared in the embodiment 1 are more complete.

SnO prepared from example 1₂SEM characterization of the/ZIF-8 composite gas-sensitive material: as can be seen from FIG. 2, in SnO₂After being compounded with ZIF-8, the sample of example 1 had irregular flower-like agglomerates composed of tiny particles supported on a spherical component, and although stacking and agglomeration occurred, the surface was smooth, and each nanoparticle had a smooth surfaceThe size is relatively uniform, which indicates that SnO is successfully prepared₂A/ZIF-8 composite material.

EXAMPLE 5 preparation of Selective formic acid gas sensor

(1) Preparing slurry: 1.5g of SnO prepared in example 1₂Grinding the/ZIF-8 composite gas-sensitive material for 30min, adding 1.2mL of deionized water, and continuously mixing and grinding for 30min to prepare uniform pasty slurry;

(2) assembling: in Al₂O₃Two parallel annular gold electrodes are sleeved on the outer surface of the ceramic tube, two opposite platinum wire leads are welded on two sides of the annular gold electrodes, and the composite Al is assembled₂O₃A ceramic tube;

(3) coating: uniformly coating the obtained pasty slurry on the composite Al₂O₃Drying the surface of the ceramic tube at 80 ℃ for 5h to obtain the composite air-sensitive Al₂O₃A ceramic tube;

(3) welding: penetrating a nickel-chromium wire for controlling heating temperature into composite gas-sensitive Al₂O₃After the ceramic tube is arranged in the gas sensitive element, welding two ends of the nickel-chromium wire and four platinum wires outside the ceramic tube on the base respectively to obtain a semi-finished product of the gas sensitive element;

(4) aging: and (3) aging the semi-finished gas sensor at 300 ℃ for 3d to obtain the indirectly heated selective formic acid gas sensor.

Comparative example 2 is the same as example 5 except that: SnO₂the/ZIF-8 composite gas-sensitive material is replaced by the nano SnO of comparative example 1₂。

The indirectly heated selective formic acid gas sensors prepared in example 5 and comparative example 2 were subjected to sensitivity test: and inserting the obtained gas-sensitive element into a gas-sensitive tester, adding formic acid or different gases with different concentrations by adopting a static gas distribution method, opening a test system for testing, and calculating the sensitivity by using an S (Ra/Rg) formula after the resistance value is stable.

FIG. 3 is SnO of comparative example 2 at different temperatures₂And SnO of example 5₂The sensitivity curve of a ZIF-8 gas sensor for detecting formic acid is as follows: as can be seen from FIG. 3, SnO at 260 ℃ is₂And SnO₂The ZIF-8 gas sensor tests the optimal working temperature of formic acid,and between 200 ℃ and 260 ℃, SnO in example 5₂The sensitivity of the/ZIF-8 gas sensor is rapidly increased, and the maximum sensitivity of 372.5 is reached at 260 ℃ while the single SnO₂The sensitivity of the gas sensor to formic acid is only 27.3, which proves that the doping modification of ZIF-8 can obviously improve SnO₂Gas-sensitive properties of the material.

FIG. 4 is SnO of comparative example 2₂And SnO of example 5₂The ZIF-8 gas sensor detects the sensitivity curves of different concentrations of formic acid: as shown in FIG. 4, SnO in example 5₂The sensitivity of the/ZIF-8 gas sensor to formic acid gas rapidly increased in the range of 60-200ppm because the reaction rate of formic acid gas with oxygen adsorbed on the surface of the material continuously increased and the response value to 10ppm formic acid was 8.5, indicating that the SnO prepared in example 5₂the/ZIF-8 composite material gas sensor has a lower detection limit which is lower than 10 ppm.

FIG. 5 is SnO of example 5₂The sensitivity of a ZIF-8 gas sensor for detecting different gases is shown as SnO₂The detection response values of the ZIF-8 gas sensor to 10ppm of methanol, ethanol, formic acid, ammonia gas, acetone, n-propanol and 1, 2-propanediol at 260 ℃ (optimum working temperature) are respectively 1.978, 1.975, 20.314, 1.189, 0.925, 0.979 and 10.632, and the sensitivity of the gas sensor to formic acid is far higher than that of other gases to be detected through sensitivity comparison, so the SnO prepared in example 5₂The ZIF-8 gas sensor has the best selectivity to formic acid, which shows that the prepared gas sensor has better selectivity.

The indirectly heated selective formic acid gas sensor prepared in example 5 was subjected to a stability test: the product made in example 5 was exposed to air and after standing for 10d and 20d, the sensitivity to formic acid reached 99.86% of the sensitivity to formic acid at 10d and 92.83% of the sensitivity to formic acid at 20d, respectively.

While embodiments of the invention have been disclosed above, it is not limited to the applications listed in the description and the embodiments, which are fully applicable in all kinds of fields of application of the invention, and further modifications may readily be effected by those skilled in the art, so that the invention is not limited to the specific details without departing from the general concept defined by the claims and the scope of equivalents.