A hollow hierarchical nano-wire sensing material, a preparation method thereof, and an ammonia gas sensor

Abstract

This application discloses a hollow hierarchical nanowire sensitive material, its preparation method, and an ammonia sensor. The preparation method includes the following steps: (1) adding hollow carbon nanofibers to a mixture of ethanol and water and mixing evenly, then adding nickel salt and urea sequentially, and reacting at 70-90°C. The resulting precipitate is washed and dried, and then calcined at 300-400°C to obtain nickel oxide nanowires; (2) adding the nickel oxide nanowires obtained in the above steps to water and dispersing evenly, then adding aniline, protic acid, and an initiator sequentially, and reacting at 0-4°C. The resulting precipitate is washed and dried to obtain the hollow hierarchical nanowire sensitive material. This application can improve the sensitivity of ammonia sensor monitoring.

Description

Technical Field

[0001] This application relates to the technical field of ammonia sensors, and in particular to a hollow hierarchical nanowire sensitive material, its preparation method, and an ammonia sensor. Background Technology

[0002] Sensors, as the source of sensing, acquiring, and monitoring information, are widely used in environmental monitoring, biomedicine, and other fields. Gas sensors are an important branch of the sensor field. With the rapid development of industrial production technology, the problem of air pollution, such as the leakage of industrial toxic gases, has also attracted attention. Ammonia is an important industrial raw material that has a strong irritant effect on skin tissue and is also highly corrosive. Furthermore, ammonia has extremely high solubility and can irritate and even corrode the upper respiratory tract of humans and animals, seriously threatening human health. Therefore, it is essential to use sensors to monitor ammonia in production and daily life.

[0003] Compared to traditional monitoring technologies such as gas chromatography, liquid chromatography, and mass spectrometry, semiconductor gas sensors currently offer advantages such as low cost and real-time monitoring, leading to their increasingly widespread application in health and environmental monitoring, safe industrial production, and assisting medical diagnosis. Semiconductor gas sensors primarily use high-temperature resistant ceramics as a substrate and metal oxides or conductive polymers as gas-sensitive materials. They utilize the oxidation or reduction reaction of the target gas on the surface of the gas-sensitive material, causing changes in its electrical properties. The purpose of gas monitoring is achieved by measuring these changes in electrical properties. While this ammonia gas sensor can basically meet the requirements for real-time gas safety monitoring, metal oxide-based gas-sensitive materials typically require high operating temperatures, which can easily affect the sensor's stability; conductive polymer-based gas-sensitive materials suffer from short lifespans. Therefore, the development of sensors with high stability and long service life remains a key research focus. Summary of the Invention

[0004] To improve the lifespan of an ammonia sensor and enable sensitive monitoring of ammonia at room temperature, this application provides a hollow hierarchical nanowire sensitive material.

[0005] The technical solution adopted in this application is as follows:

[0006] A hollow hierarchical nanowire sensitive material includes a carbon nanofiber layer, a nickel oxide layer, and a polyaniline layer, wherein the nickel oxide layer is located between the polyaniline layer and the carbon nanofiber layer, and the carbon nanofiber layer has a hollow structure.

[0007] Hollow carbon nanofibers possess a hollow structure with nickel oxide coating the surface, followed by a polyaniline layer. The hollow carbon nanofibers provide a high surface area and high porosity, facilitating ammonia gas entry and thus enhancing sensitivity. Nickel oxide exhibits unique adsorption properties and a wide band gap, resulting in high stability and rapid recovery. The outermost polyaniline layer, with its π-π stacking interaction between the hollow carbon nanofibers and polyaniline, traps the nickel oxide in the middle layer, forming a hierarchical structure. The disordered arrangement of nickel oxide and polyaniline particles significantly improves gas diffusion paths, increases active sites, and enhances electron enrichment and heterogeneous structures on the outer surface, thereby promoting ammonia adsorption and desorption and improving ammonia monitoring capabilities. The nickel oxide and polyaniline layers, loaded onto the carbon nanofiber surface, maintain contact and prevent cracking, enhancing structural stability and enabling more durable ammonia monitoring.

[0008] Secondly, this application provides a method for preparing the nanowire sensitive material in the above-mentioned scheme.

[0009] A method for preparing a hollow hierarchical nanowire sensing material includes the following steps:

[0010] (1) Hollow carbon nanofibers were added to a mixture of ethanol and water and mixed evenly. Then nickel salt and urea were added in sequence and reacted at 70-90℃. The precipitate was washed and dried and then calcined at 300-400℃ to obtain nickel oxide nanowires.

[0011] (2) Add the nickel oxide nanowires 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 nanowire sensitive material.

[0012] Hollow carbon nanofibers are first uniformly mixed in a solution, reacted, and then calcined. This allows nickel oxide particles to be loaded onto the surface of the hollow carbon nanofibers. The reaction then proceeds in a solution of aniline monomers. Due to the π-π stacking interaction between the hollow carbon nanofibers and polyaniline, as well as the hydrogen bonding between the surface groups of the carbon nanofibers and the aniline monomers, the aniline monomers can be positioned on the carbon fiber surface before polymerization. Therefore, hollow carbon nanofibers can serve as polymerization templates, improving the microstructure of the organic polymer, allowing polyaniline particles to be loaded onto the surface of the hollow carbon nanofibers, and increasing the active sites in contact with gases. This results in a relatively large adsorption capacity for ammonia, thereby shortening the reaction time and improving sensitivity.

[0013] Optionally, in step (1), the nickel salt is selected from nickel acetate.

[0014] Optionally, the molar ratio of nickel acetate to urea is (2-3):(5-7).

[0015] Optionally, the molar ratio of nickel acetate to urea is 3:6.

[0016] By adopting the above technical solution and further controlling the molar ratio of nickel acetate and urea, the nickel oxide particles become more uniform, and the resistance changes rapidly after contacting ammonia, thus making the ammonia monitoring more sensitive.

[0017] Optionally, in step (1), the volume ratio of ethanol to water is 1:1.

[0018] By adopting the above technical solution and controlling the volume ratio of ethanol and water, dispersion and reaction are facilitated, and the formation of agglomerates during the later drying and calcination processes can be reduced, thereby maintaining the sensitivity of ammonia monitoring.

[0019] Optionally, the protic acid is selected from hydrochloric acid.

[0020] Thirdly, this application provides an ammonia sensor.

[0021] An ammonia sensor includes a nanowire sensitive material prepared using the above-described preparation method, and a ceramic plate, wherein the nanowire sensitive material is disposed on the surface of the ceramic plate.

[0022] By adopting the above technical solution, the above-mentioned nanowire sensitive material is made into a gas-sensitive material. In the process of monitoring ammonia, it can react quickly to ammonia and change its own resistance, thereby achieving the effect of ammonia monitoring. It also has high sensitivity and long service life.

[0023] In summary, this application includes at least one of the following beneficial effects:

[0024] 1. The hollow carbon nanofiber layer, nickel oxide layer and polyaniline layer form a layered structure, forming a nanofiber structure with carbon nanofiber as template and nanoparticles coated on the surface. The prepared nanowire sensitive material is used as a gas sensitive material. The hollow carbon nanofibers can be stacked and built together to form a multi-pore nanofiber structure, which increases the specific surface area of ​​ammonia gas in contact with the material, which is beneficial to the adsorption and desorption of gas.

[0025] 2. The existence of π bonds between hollow carbon nanofibers and polyaniline alters the distribution of π electrons within the system, thereby affecting the conjugation effect and reducing the electron cloud density in the molecular chain of polyaniline. This increases the delocalization effect in the molecular chain, greatly enhancing the charge transfer capability and thus exhibiting higher sensitivity to ammonia. Attached Figure Description

[0026] Figure 1 This is an electron microscope image of the nanowire sensitive material obtained in Example 1 of this application;

[0027] Figure 2 This is a simplified structural diagram of the ammonia sensor in Application Example 1 of this application. Detailed Implementation

[0028] The following is in conjunction with the appendix Figure 1-2 This application will be described in further detail.

[0029] Example 1

[0030] A method for preparing a hollow hierarchical nanowire sensing material includes the following steps:

[0031] (1) Mix 50 mL of ethanol and 50 mL of water, then add 0.2 g of hollow carbon nanofibers to the mixture and ultrasonically disperse and mix them evenly at room temperature. The average diameter of the hollow carbon nanofibers is 100 nm-200 nm and the average length is 5-20 μm. Then add 2 mmol of nickel acetate and 5 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 nanowires.

[0032] (2) Add the nickel oxide nanowires obtained in step (1) to deionized water and stir continuously. Then add 1 mmol of polyaniline, 2.5 mL of hydrochloric acid and 57 mg of ammonium persulfate in sequence, and stir continuously at 4 °C for 2 hours. After the reaction is completed, the precipitate is washed by centrifugation with deionized water and ethanol multiple times, and dried to obtain a hollow hierarchical nanowire sensitive material.

[0033] Reference Figure 1In this embodiment, the hollow hierarchical structure primarily uses hollow carbon nanofibers as a template, with a nickel oxide layer and a polyaniline layer loaded on the surface of the hollow carbon nanofibers. The voids at the ends of the hollow carbon nanofibers can also be seen in the figure. The surface layered, plate-like particle stacking structure of the hollow hierarchical structure, based on hollow carbon nanofibers, results in a sensitive material with a higher specific surface area, thus providing more active sites. Consequently, the nanowire sensitive material described in this application exhibits higher sensitivity in ammonia monitoring.

[0034] Example 2

[0035] A method for preparing a hollow hierarchical nanowire sensing material includes the following steps:

[0036] (1) Mix 50 mL of ethanol and 50 mL of water, then add 0.2 g of hollow carbon nanofibers to the mixture and ultrasonically disperse and mix them evenly at room temperature. The average diameter of the hollow carbon nanofibers is 100 nm-200 nm and the average length is 5-20 μm. Then add 3 mmol of nickel acetate and 7 mmol of urea in sequence and mix them evenly. Then react the resulting solution at 90 °C for 6 hours. After cooling to room temperature, wash the precipitate with deionized water and ethanol several times and dry it at 60 °C. After drying, calcine the precipitate at 400 °C for 2 hours to obtain hollow nickel oxide nanowires.

[0037] (2) Add the nickel oxide nanowires obtained in step (1) to deionized water and stir continuously. Then add 1.5 mmol of polyaniline, 2.5 mL of hydrochloric acid and 60 mg of ammonium persulfate in sequence, and stir continuously at 0 °C for 2 hours. After the reaction is completed, the precipitate is washed by centrifugation with deionized water and ethanol multiple times, and dried to obtain a hollow hierarchical nanowire sensitive material.

[0038] Example 3

[0039] A method for preparing a hollow hierarchical nanowire sensing material includes the following steps:

[0040] (1) Mix 50 mL of ethanol and 50 mL of water, then add 0.2 g of hollow carbon nanofibers to the mixture and ultrasonically disperse and mix them evenly at room temperature. The average diameter of the hollow carbon nanofibers is 100 nm-200 nm and the average length is 5-20 μm. Then add 3 mmol of nickel acetate and 6 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 nanowires.

[0041] (2) Add the nickel oxide nanowires obtained in step (1) to deionized water and stir continuously. Then add 1.5 mmol of polyaniline, 2.5 mL of hydrochloric acid and 60 mg of ammonium persulfate in sequence, and stir continuously at 0 °C for 2 hours. After the reaction is completed, the precipitate is washed by centrifugation with deionized water and ethanol multiple times, and dried to obtain a hollow hierarchical nanowire sensitive material.

[0042] Comparative Preparation Example 1

[0043] The difference between this comparative preparation example 1 and example 1 is that the 50 mL of ethanol in step (1) is replaced with water, while the remaining process steps and raw materials are the same as in example 1.

[0044] Comparative Preparation Example 2

[0045] The difference between this comparative preparation example and Example 1 is that the hollow carbon nanofibers in step (1) are replaced with solid carbon nanofibers, while the remaining process steps and raw materials are the same as in Example 1.

[0046] Comparative preparation example 3

[0047] The difference between this comparative preparation example and Example 1 is that polyaniline was not loaded onto the surface of the nickel oxide nanowires.

[0048] Comparative preparation example 4

[0049] The difference between this comparative preparation example and Example 1 is that hollow carbon nanofibers were added to deionized water and stirred continuously. Then, 1 mmol of polyaniline, 2.5 mL of hydrochloric acid and 57 mg of ammonium persulfate were added sequentially, and the mixture was stirred continuously at 4 °C for 2 hours. After the reaction was completed, the precipitate was washed by centrifugation with deionized water and ethanol multiple times, and dried to obtain a hollow hierarchical nanowire sensitive material.

[0050] Application Example 1

[0051] Take 0.1g of the hollow hierarchical nanowire sensitive material prepared in Example 1 and mix it with 0.1% of the polyvinyl alcohol adhesive solution of the nanowire sensitive material to form a paste. Then, use a fine brush to evenly coat the paste on the front side of the ceramic plate to form a gas-sensitive material on the surface of the ceramic plate. Ammonia gas sensor is formed by connecting leads, and its resistance value is measured with a gold electrode.

[0052] Reference Figure 2 The ammonia sensor in this application mainly includes a ceramic plate and a gas-sensitive material disposed on the ceramic plate. The gas-sensitive material is connected by an electrode, thereby enabling the monitoring of the resistance of the gas-sensitive material. The electrode is located between the surface of the ceramic plate and the gas-sensitive material layer.

[0053] Application Example 2

[0054] Take 0.1g of the hollow hierarchical nanowire sensitive material prepared in Example 2 and mix it with 0.1% of the nanowire sensitive material by mass in a polyvinyl alcohol binder solution to form a paste. Then, use a fine brush to evenly coat the paste on the front side of the ceramic plate to form a gas-sensitive material on the surface of the ceramic plate. Ammonia gas sensor is formed by connecting leads, and its resistance value is measured with a gold electrode.

[0055] Application Example 3

[0056] Take 0.1g of the hollow hierarchical nanowire sensitive material prepared in Example 3 and mix it with 0.1% of the nanowire sensitive material by mass in a polyvinyl alcohol binder solution to form a paste. Then, use a fine brush to evenly coat the paste on the front side of the ceramic plate to form a gas-sensitive material on the surface of the ceramic plate. Ammonia gas sensor is formed by connecting leads, and its resistance value is measured with a gold electrode.

[0057] Application Example 4

[0058] The nanowire-sensitive material in Comparative Preparation Example 1 was used, and the remaining steps were the same as in Application Example 1.

[0059] Application Example 5

[0060] The nanowire-sensitive material used in Comparative Preparation Example 2 was prepared, and the remaining steps were the same as in Application Example 1.

[0061] Application Example 6

[0062] The nanowire-sensitive material used in Comparative Preparation Example 3 was prepared, and the remaining steps were the same as in Application Example 1.

[0063] Application Example 7

[0064] The nanowire-sensitive material in Comparative Preparation Example 4 was used, and the remaining steps were the same as in Application Example 1.

[0065] Performance testing

[0066] In the sensor performance test, the static method was used to measure the resistance value of the sensor under room temperature conditions. During the test, the test chamber was purged with gas, and then the sensor was placed in the test chamber. Ammonia gas of different concentrations was injected into the test chamber through a micro-syringe, and then the resistance value was read.

[0067] Sensitivity: The output resistance value of the sensor in the gas to be measured is denoted as Rg, and the resistance value of the sensor in air is Ra. Sensitivity = Rg / Ra.

[0068] Sensitivity retention rate: The difference in sensitivity change after the sensor has been placed for 50 days, divided by the original sensitivity.

[0069] Table 1. Test results for Application Examples 1-7 under 1 ppm ammonia conditions.

[0070]

[0071] Table 2 shows the test results for Application Examples 1-7 under 100 ppm ammonia conditions.

[0072]

[0073] Table 3 shows the sensitivity reduction rate of application examples 1-7 after 50 days of storage under 100 ppm ammonia conditions.

[0074]

[0075] A comparison of Application Examples 1 and 4 shows that the nanowire sensitive material prepared in step 1 with a 1:1 volume ratio of ethanol to water exhibits better sensitivity. This is mainly because the evaporation of water during the drying stage affects the porosity between particles; adjusting the ratio of ethanol to water can reduce the occurrence of agglomeration.

[0076] By comparing Application Example 1 and Application Example 5, it can be seen that hollow carbon nanofibers play an important role in improving the sensitivity of sensitive materials. The porous carbon nanofiber structure can provide enough pores, which greatly increases the specific surface area of ​​the sensitive material and is beneficial to improving sensitivity.

[0077] By comparing Application Example 1 with Application Examples 6 and 7, it can be seen that the hollow hierarchical sensitive material prepared in this application can increase the contact area between the material and the gas to be measured, increase more active sites, and thus enhance the sensitivity in ammonia monitoring.

[0078] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A method for preparing a hollow hierarchical nanowire sensitive material, characterized in that: The nanowire sensitive material includes a carbon nanofiber layer, a nickel oxide layer, and a polyaniline layer, wherein the nickel oxide layer is located between the polyaniline layer and the carbon nanofiber layer, and the carbon nanofiber layer has a hollow structure. The method for preparing the nanowire-sensitive material includes the following steps: (1) Hollow carbon nanofibers are added to a mixture of ethanol and water and mixed evenly. Then, nickel salt and urea are added in sequence and reacted at 70-90°C. The resulting precipitate is washed and dried, and then calcined at 300-400°C to obtain nickel oxide nanowires. The nickel salt is selected from nickel acetate. The molar ratio of nickel acetate to urea is 3:

6. The volume ratio of ethanol to water is 1:

1. (2) Add the nickel oxide nanowires 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 nanowire sensitive material. The protic acid is selected from hydrochloric acid.

2. An ammonia gas sensor, characterized in that: The invention includes a nanowire sensitive material prepared using the preparation method of claim 1, and a ceramic plate, wherein the nanowire sensitive material is disposed on the surface of the ceramic plate.

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