Hollow hierarchical structure metal oxide microsphere gas sensitive material, and preparation method and application thereof

Abstract

The application discloses a kind of hollow hierarchical structure metal oxide microsphere gas sensitive material and its preparation method and application.The preparation method includes the following steps: (1) preparation PVP microsphere;(2) the prepared PVP microsphere is added to the mixed solution of ethanol and water and mixed uniformly, then nickel salt and urea are sequentially added, and reaction is carried out under the condition of 80 DEG C, the generated precipitate is washed and dried, then calcination is carried out under the condition of 300-400 DEG C, and hollow nickel oxide microsphere is obtained;(3) the spherical nanomaterial of nickel oxide obtained in the above step is added to water and dispersed uniformly, then aniline, proton acid and initiator are sequentially added, and reaction is carried out at 0-4 DEG C, and the generated precipitate is washed and dried, to obtain the hollow hierarchical structure metal oxide microsphere gas sensitive material.The application can effectively improve the sensitivity of ammonia gas sensor monitoring.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of ammonia gas sensors, and particularly relates to a preparation method of a hollow hierarchical structure metal oxide microsphere gas-sensitive material and an ammonia gas sensor. BACKGROUND

[0002] In the modern era of highly developed industrial production, the ecological environment is deteriorating, and ammonia is a common colorless, toxic, and irritating odor pollutant gas, mainly derived from industrial production, biological metabolism, and tail gas emission. Studies have shown that when the ammonia concentration is greater than 300 ppm, it can damage human cells and cause serious damage to the eyes, skin, and respiratory tract. At present, the technologies for identifying gas concentration mainly include gas chromatography, liquid chromatography, and mass spectrometry. These methods have the advantages of accurate analysis of gas components and low detection limit, but they are generally expensive, large in size, and complex to operate, and cannot be monitored in real time, which cannot meet people's demand for miniaturization, portability, and real-time monitoring. Gas sensors can identify the type or concentration of a specific gas in a certain area in real time, and convert it into an electrical signal according to a certain physical and chemical reaction, and then realize real-time monitoring, analysis, and alarm of the specific gas through the collection and processing of the electrical signal, so as to facilitate timely evacuation or processing.

[0003] In recent years, the development of ammonia gas sensors has attracted widespread attention, and the sensitive materials involve metal oxides and organic conductive polymers. For example, nickel oxide as a p-type semiconductor has high sensitivity to ammonia; polyaniline (PANI) as a conductive polymer has adjustable ammonia sensing properties at room temperature. However, both types of gas sensors have obvious defects. The main defects of the nickel oxide sensor are high working temperature, high energy consumption, and easy agglomeration of metal oxide particles, which reduces the selectivity to ammonia. Although the conductive polymer can realize room temperature sensing, it has poor sensitivity and selectivity to ammonia. Therefore, further research is needed to solve the problems in the technology of ammonia gas sensors. SUMMARY

[0004] In view of the defects of existing ammonia gas sensors, in order to improve the service life of the ammonia gas sensor and monitor ammonia at room temperature, the application provides a hollow hierarchical structure metal oxide microsphere gas-sensitive material.

[0005] The application adopts the following technical solution:

[0006] A hollow hierarchical structure metal oxide microsphere gas-sensitive material includes nickel oxide microspheres with a hollow structure and a polyaniline layer polymerized in situ on the surface of the nickel oxide microspheres.

[0007] The preparation method of the hollow hierarchical structure metal oxide microsphere gas-sensitive material includes the following steps:

[0008] (1) mixing methyl methacrylate, azobisisobutyronitrile and polyvinyl pyrrolidone in a solution of methanol and water, reacting at 70℃ under nitrogen atmosphere to obtain PVP microspheres;

[0009] (2) mixing the PVP microspheres in a mixture of ethanol and water, then adding nickel salt and urea in sequence, and reacting at 80℃, washing and drying the generated precipitate, and calcining at 300-400℃ to obtain hollow nickel oxide microspheres;

[0010] (3) adding the nickel oxide microspheres obtained in step (2) into water and dispersing uniformly, then adding aniline, protonic acid and initiator in sequence, and reacting at 0-4℃, washing and drying the generated precipitate to obtain hollow hierarchical structure spherical metal oxide nano gas sensitive material.

[0011] Further, in step (1), the amount ratio of methyl methacrylate, azobisisobutyronitrile and polyvinyl pyrrolidone is 10ml:0.01g:2g.

[0012] Further, in step (1), the volume ratio of methanol and water is 1:1.

[0013] Further, in step (2), the volume ratio of ethanol and water is 1:1.

[0014] Further, in step (2), the nickel salt is selected from nickel nitrate hexahydrate.

[0015] Further, the molar ratio of the above nickel nitrate hexahydrate and urea is 1:2.

[0016] Further, in step (3), the protonic acid is selected from concentrated hydrochloric acid.

[0017] Further, in step (3), the initiator is ammonium persulfate.

[0018] Application of the above hollow hierarchical structure metal oxide microsphere gas sensitive material in ammonia detection.

[0019] An ammonia sensor made of the above hollow hierarchical structure metal oxide microsphere gas sensitive material.

[0020] Further, the ammonia sensor comprises hollow hierarchical structure metal oxide microsphere gas sensitive material and gold electrode, and the hollow hierarchical structure spherical metal oxide nano gas sensitive material is arranged on the surface of the gold electrode.

[0021] By adopting the technical scheme, the hollow hierarchical structure metal oxide microsphere gas sensitive material is made into a sensor, which can quickly respond to ammonia gas and change its resistance during ammonia gas monitoring, thereby achieving the effect of ammonia gas monitoring, and having high sensitivity and long service life.

[0022] Technical principles of the present application:

[0023] The nickel oxide microspheres have a hollow structure, and then a polyaniline layer is coated thereon. The stable spherical structure and the hollow morphology of the micro material provide a high surface area and porosity, which is beneficial to the entry of ammonia gas, improves the utilization rate of the sensitive body of the material, and is beneficial to the improvement of the response value. Nickel oxide is a p-type metal oxide semiconductor material with a wide band gap (3.6e-4.2eV). Due to its thermodynamic stability and unique optical, magnetic and chemical properties, it has become an attractive material. It has been applied in many fields such as lithium ion batteries, supercapacitors, electrode material preparation and chemical sensing. And because aniline can polymerize in situ on the surface of the nickel oxide microspheres to form a surface rough core-shell composite material, compared with the previous single nickel oxide microspheres, it has more gas diffusion channels, which can further improve the sensitivity of the sensor. The nickel oxide particles and polyaniline particles are arranged in disorder, the pores between the particles greatly improve the gas diffusion path, increase the active sites, enrich the outer surface electrons and increase the heterostructure, thereby promoting the adsorption and desorption of ammonia gas, and improving the ammonia gas monitoring capability.

[0024] In the preparation method of the hollow hierarchical structure metal oxide microsphere gas sensitive material, the PVP microspheres are mixed uniformly in the mixed solution, and then reacted and calcined, so that the nickel oxide particles can be loaded on the surface of the microspheres, and then reacted in the aniline monomer solution. Due to the π-π stacking effect between the hollow nickel oxide microspheres and polyaniline, the aniline monomer can polymerize on the surface of the hollow nickel oxide microspheres. Therefore, the hollow nickel oxide microspheres can be used as a polymerization template to improve the micro morphology of the organic polymer, so that the polyaniline particles are loaded on the surface of the hollow nickel oxide microspheres, and the active sites in contact with the gas are increased, thereby having a relatively large adsorption capacity for ammonia gas, thereby shortening the reaction time and improving the sensitivity. By further controlling the molar ratio of nickel nitrate hexahydrate and urea, the nickel oxide particles are more uniform, and the resistance changes fast after contacting with ammonia gas, thereby making the sensitivity of ammonia gas monitoring higher. By controlling the volume ratio of methanol and water, it is beneficial to dispersion and reaction, and can reduce the formation of agglomerates during the drying and calcination process in the later stage, thereby maintaining the sensitivity of ammonia gas monitoring.

[0025] The hollow hierarchical metal oxide microsphere gas sensitive material is made into a sensor, which can quickly respond to ammonia gas and change its resistance during ammonia gas monitoring, thereby achieving the effect of ammonia gas monitoring, and has high sensitivity and long service life.

[0026] The present application has the following advantages:

[0027] 1. The hollow nickel oxide microsphere layer and the polyaniline layer form a hierarchical structure, and the hierarchical structure with the hollow nickel oxide microsphere as a template and the polyaniline particles coated on the surface is formed, and the prepared hollow hierarchical spherical metal oxide nano sensitive material as a gas sensitive material increases the specific surface area of ammonia gas in contact with the material, which is beneficial to the adsorption and desorption of the gas.

[0028] 2. There is a π bond between the hollow nickel oxide microsphere layer and the polyaniline, so that the distribution of π electrons in the system changes, thereby affecting the conjugation effect, and the electron cloud density in the molecular chain of polyaniline is reduced, the delocalization effect in the molecular chain is increased, the charge transfer capacity is greatly improved, and higher sensitivity to ammonia gas is exhibited. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is an electron microscope image of the hollow hierarchical metal oxide microsphere gas sensitive material obtained in Example 1 of the present application.

[0030] Figure 2 is a response test diagram of the ammonia gas sensor obtained in Application Example 1 of the present application under room temperature conditions, for different concentrations of ammonia gas. DETAILED DESCRIPTION

[0031] In order to make the content of the present application more convenient to understand, the technical solutions of the present application will be further described below in combination with specific embodiments, but the present application is not limited thereto.

[0032] Example 1

[0033] A preparation method of a hollow hierarchical metal oxide microsphere gas sensitive material, comprising the following steps:

[0034] (1) 10 mL of methyl methacrylate, 0.01 g of azobisisobutyronitrile and 2 g of polyvinylpyrrolidone are mixed in a solution of 100 mL of methanol and 100 mL of water, and reacted under a nitrogen atmosphere at 70℃ for 70 hours to obtain PVP microspheres.

[0035] (2) Mix 50 mL of ethanol and 50 mL of water, then add 0.2 g of the prepared PVP microspheres to the mixture and ultrasonically disperse and mix them evenly at room temperature. Then add 2 mmol of nickel nitrate hexahydrate and 4 mmol of urea in sequence and mix them evenly. Then react the resulting solution at 80 °C for 6 hours. After cooling to room temperature, wash the generated precipitate with deionized water and ethanol several times and dry it at 60 °C. After drying, calcine the precipitate at 300 °C for 2 hours to obtain hollow nickel oxide microspheres.

[0036] (3) The hollow nickel oxide microspheres obtained in step (2) were added to deionized water and stirred continuously. Then, 1 mmol of polyaniline, 2.5 mL of concentrated hydrochloric acid and 57 mg of ammonium persulfate were added in sequence and stirred continuously at 4 °C for 2 hours. After the reaction was completed, the precipitate was washed by centrifugation with deionized water and ethanol several times and dried to obtain hollow hierarchical spherical metal oxide nanosensitive materials.

[0037] like Figure 1 As shown, the hollow hierarchical structure in this embodiment mainly uses hollow nickel oxide microspheres as templates and loads a polyaniline layer on the surface of the hollow nickel oxide microspheres. The surface layer of the hollow hierarchical structure has a sheet-like particle stacking structure, and the surface of the obtained sensitive material has a higher specific surface area, thereby providing more active sites. As a result, the spherical metal oxide nanosensitive material with hollow hierarchical structure in this application has higher sensitivity when used as a gas-sensitive material for ammonia monitoring.

[0038] Example 2

[0039] A method for preparing a hollow hierarchical metal oxide microsphere gas-sensitive material includes the following steps:

[0040] (1) Mix 10 mL of methyl methacrylate, 0.01 g of azobisisobutyronitrile and 2 g of polyvinylpyrrolidone in a solution of 100 mL of methanol and 100 mL of water, and react at 70 °C for 70 hours under a nitrogen atmosphere to obtain PVP microspheres.

[0041] (2) Mix 100 mL of ethanol and 100 mL of water, then add 0.3 g of the prepared PVP microspheres to the mixture and ultrasonically disperse and mix them evenly at room temperature. Then add 2 mmol of nickel nitrate hexahydrate and 4 mmol of urea in sequence and mix them evenly. Then react the resulting solution at 80 °C for 6 hours. After cooling to room temperature, wash the generated precipitate with deionized water and ethanol several times and dry it at 60 °C. After drying, calcine the precipitate at 300 °C for 2 hours to obtain hollow nickel oxide microspheres.

[0042] (3) The hollow nickel oxide microspheres obtained in step (2) are added to deionized water, and stirring is continuously performed, then 1 mmol of polyaniline, 2.5 mL of concentrated hydrochloric acid and 57 mg of ammonium persulfate are sequentially added, and stirring is continuously performed at 4°C for 2 hours. After the reaction is completed, the generated precipitate is washed with deionized water and ethanol multiple times through centrifugation, and after drying, a hollow hierarchical structure spherical metal oxide nano-sensitive material is obtained.

[0043] Example 3

[0044] A method for preparing a hollow hierarchical structure metal oxide microsphere gas-sensitive material, comprising the following steps:

[0045] (1) 10 mL of methyl methacrylate, 0.01 g of azobisisobutyronitrile and 2 g of polyvinylpyrrolidone are mixed in a solution of 100 mL of methanol and 100 mL of water, and reaction is performed at 70°C under a nitrogen atmosphere for 70 hours to obtain PVP microspheres.

[0046] (2) 50 mL of ethanol and 50 mL of water are mixed, then 0.2 g of the prepared PVP microspheres are added to the mixed solution, and ultrasonic dispersion is performed at room temperature until the mixture is uniformly mixed, then 1 mmol of nickel nitrate hexahydrate and 2 mmol of urea are sequentially added, and the mixture is uniformly mixed, then the obtained solution is reacted at 80°C for 6 hours, and after cooling to room temperature, the generated precipitate is washed with deionized water and ethanol multiple times, and drying is performed at 60°C. After drying, the obtained precipitate is calcined at 300°C for 2 hours to obtain hollow nickel oxide microspheres.

[0047] (3) The hollow nickel oxide microspheres obtained in step (2) are added to deionized water, and stirring is continuously performed, then 1 mmol of polyaniline, 2.5 mL of concentrated hydrochloric acid and 57 mg of ammonium persulfate are sequentially added, and stirring is continuously performed at 4°C for 2 hours. After the reaction is completed, the generated precipitate is washed with deionized water and ethanol multiple times through centrifugation, and after drying, a hollow hierarchical structure spherical metal oxide nano-sensitive material is obtained.

[0048] Comparative Preparation Example 1

[0049] The difference between the present comparative preparation example 1 and example 1 is that ethanol in step (2) is replaced by water, and the remaining process steps and raw materials are the same as those of example 1.

[0050] Comparative Preparation Example 2

[0051] The difference between the present comparative preparation example and example 1 is that the microspheres in step (2) are not dispersed, and the remaining process steps and raw materials are the same as those of example 1.

[0052] Comparative Preparation Example 3

[0053] The difference between the present comparative preparation example and example 1 is that polyaniline is not loaded on the surface of the hollow nickel oxide microspheres.

[0054] Comparative example 4

[0055] The difference between the present comparative example and example 1 is that the PVP microspheres are added to deionized water and stirring is continued, then 3 mmol of polyaniline, 2.5 mL of hydrochloric acid and 57 mg of ammonium persulfate are sequentially added, and the reaction is continuously stirred at 4°C for 2 hours. After the reaction is completed, the generated precipitate is washed multiple times by centrifugation with deionized water and ethanol, and the hollow hierarchical structured spherical metal oxide nano-sensitive material is obtained after drying.

[0056] Application example 1

[0057] 0.1 g of the hollow hierarchical structured spherical metal oxide nano-sensitive material prepared in example 1 and a terpineol adhesive solution are mixed to form a paste slurry, and then the slurry is uniformly coated on the surface of a gold electrode using a fine brush to form a gas-sensitive material on the surface of the gold electrode, and an ammonia gas sensor is formed by connecting a lead wire.

[0058] As shown in Figure 2 application example 1, the ammonia gas sensor obtained is tested for response to different concentrations (5 ppm, 10 ppm, 20 ppm, 50 ppm, 100 ppm) of ammonia gas at room temperature to investigate the response performance of the ammonia gas sensor to different concentrations of ammonia gas. It can be seen that the prepared sensor can quickly respond to different concentrations of ammonia gas, and the response has good reversibility.

[0059] Application example 2

[0060] 0.1 g of the hollow hierarchical structured spherical metal oxide nano-sensitive material prepared in example 2 and a terpineol adhesive solution are mixed to form a paste slurry, and then the slurry is uniformly coated on the surface of a gold electrode using a fine brush to form a gas-sensitive material on the surface of the gold electrode, and an ammonia gas sensor is formed by connecting a lead wire.

[0061] Application example 3

[0062] 0.1 g of the hollow hierarchical structured spherical metal oxide nano-sensitive material prepared in example 3 and a terpineol adhesive solution are mixed to form a paste slurry, and then the slurry is uniformly coated on the surface of a gold electrode using a fine brush to form a gas-sensitive material on the surface of the gold electrode, and an ammonia gas sensor is formed by connecting a lead wire.

[0063] Application example 4

[0064] The hollow hierarchical structured spherical metal oxide nano-sensitive material in comparative example 1 is used, and the remaining steps are the same as in application example 1.

[0065] Application Example 5

[0066] The remaining steps and application example 1 are the same, using the hollow hierarchical structure of spherical metal oxide nano-sensitive material in Comparative Example 2.

[0067] Application Example 6

[0068] The remaining steps and application example 1 are the same, using the hollow hierarchical structure of spherical metal oxide nano-sensitive material in Comparative Example 3.

[0069] Application Example 7

[0070] The remaining steps and application example 1 are the same, using the hollow hierarchical structure of spherical metal oxide nano-sensitive material in Comparative Example 4.

[0071] Performance Test

[0072] In the sensor performance test, the static method is used to measure at room temperature, and the resistance value of the sensor is collected. The test box is purged with air during the test, and then the sensor is placed in the test box. Different concentrations of ammonia gas are injected into the test box through a micro-sampler, and then the resistance value is read.

[0073] Sensitivity: The output resistance value of the sensor in the gas to be measured is recorded as Rg, and the resistance value of the sensor in the air is Ra, and the sensitivity = Rg / Ra.

[0074] Table 1 Test table of application examples 1-7 under the condition of 10 ppm ammonia

[0075] Application Example 1 Application Example 2 Application Example 3 Application Example 4 Application Example 5 Application Example 6 Application Example 7 Sensitivity 1.25 1.41 1.73 1.12 1.44 1.11 1.14

[0076] Table 2 Test table of application examples 1-7 under the condition of 100 ppm ammonia

[0077] Application Example 1 Application Example 2 Application Example 3 Application Example 4 Application Example 5 Application Example 6 Application Example 7 Sensitivity 2.17 2.36 2.97 1.89 2.22 1.83 1.91

[0078] As can be seen by comparing application example 1 and application example 4, the hollow hierarchical structure of spherical metal oxide nano-sensitive material prepared in step 1 using a volume ratio of ethanol and water of 1:1 has better sensitivity. Mainly in the drying stage, the water is evaporated, which has an effect on the pores between the particles. By adjusting the ratio of ethanol and water, the agglomeration can be reduced.

[0079] As can be seen by comparing application example 1 and application example 5, the hollow structure of nickel oxide microspheres plays an important role in improving the sensitivity of the sensitive material, providing enough pores and greatly improving the specific surface area of the sensitive material, which is beneficial to the improvement of the sensitivity.

[0080] As can be seen by comparing application example 1 and application examples 6 and 7, the hollow hierarchical structure sensitive material prepared in the present application can increase the contact area of the material with the gas to be detected, increase more active sites, and thus enhance the sensitivity in ammonia monitoring.

[0081] The above are preferred embodiments of the present application, and are not intended to limit the protection scope of the present application, and thus: any equivalent changes made in structure, shape, principle, etc. according to the present application should be encompassed within the protection scope of the present application.

Claims

1. A method for preparing a hollow hierarchical nickel oxide microsphere gas-sensitive material, characterized in that: Includes the following steps: (1) Methyl methacrylate, azobisisobutyronitrile, and polyvinylpyrrolidone were mixed in a solution of methanol and water and reacted at 70°C under a nitrogen atmosphere to obtain PVP microspheres. (2) PVP microspheres were added to a mixture of ethanol and water and mixed evenly. Then nickel salt and urea were added in sequence and reacted at 80°C. The resulting precipitate was washed and dried, and then calcined at 300-400°C to obtain hollow nickel oxide microspheres. (3) Add the hollow nickel oxide microspheres obtained in the above steps to water and disperse them evenly. Then add aniline, protic acid and initiator in sequence and react at 0-4℃. Wash and dry the generated precipitate to obtain the hollow hierarchical structured nickel oxide microsphere gas-sensitive material. In step (1), the ratio of the amounts of methyl methacrylate, azobisisobutyronitrile, and polyvinylpyrrolidone is 10 ml: 0.01 g: 2 g; in step (2), the nickel salt is selected from nickel nitrate hexahydrate; the molar ratio of nickel nitrate hexahydrate to urea is 1:2; in step (1), the volume ratio of methanol to water is 1:1; in step (2), the volume ratio of ethanol to water is 1:1; in step (3), the protic acid is selected from concentrated hydrochloric acid; in step (3), the initiator is ammonium persulfate.

2. The hollow hierarchical nickel oxide microsphere gas-sensitive material prepared by the preparation method described in claim 1.

3. The application of the hollow hierarchical nickel oxide microsphere gas-sensitive material as described in claim 2 in ammonia detection.

4. The ammonia sensor made of the hollow hierarchical nickel oxide microsphere gas-sensitive material as described in claim 2, characterized in that: It includes a hollow hierarchical nickel oxide microsphere gas-sensitive material and a gold electrode; the hollow hierarchical nickel oxide microsphere gas-sensitive material is coated on the surface of the gold electrode.

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