A method for preparing a low-detection-limit ammonia gas sensor

Abstract

The application discloses a preparation method of a low-detection-limit ammonia gas sensor, which comprises the following steps: firstly, synthesizing niobium oxide coated cerium oxide nanoparticles through a hydrothermal method; then adding the dried powder into rosin; finally, uniformly applying the rosin containing the sensing material on a ceramic tube and welding the ceramic tube to prepare a gas sensitive sensor. The gas sensitive sensor prepared by the method is composed of two kinds of semiconductor oxides, and the two kinds of oxides have a higher contact area and carrier mobility due to the fact that the niobium oxide is a composite nanoparticle material prepared on the surface of the cerium oxide through in-situ reduction, so that the gas sensitive sensing performance of the material is improved; and the electrons are redistributed to form an electron depletion layer and an electron enrichment layer, so that the material is more likely to react with oxygen to generate oxygen negative ions, thereby improving the gas sensitive performance of the material to VOCs gas.

Description

Technical Field

[0001] This invention relates to a method for preparing a low detection limit ammonia gas sensor, belonging to the field of gas concentration detection technology. Background Technology

[0002] Currently, the main types of sensors for detecting gaseous pollutants on the market include PID photoionization gas sensors, electrochemical gas sensors, and semiconductor gas sensors. These are used in various applications to detect specific pollutant gases. PID photoionization gas sensors primarily utilize ultraviolet light to break down organic matter into positive and negative ions, generating a weak current under an electric field to reflect the concentration of the substance. Electrochemical gas sensors oxidize or reduce the measured gas at electrodes; during the chemical reaction, the carrier concentration in the sensing material changes, causing a change in current. Semiconductor gas sensors typically use semiconductor oxides as the gas-sensitive material, which is made by utilizing the change in resistance of the gas-sensitive material caused by the oxidation-reduction reaction of gas on the semiconductor surface.

[0003] The defects of the above-mentioned gas sensors are as follows:

[0004] 1) Currently available PID gas sensors can detect VOCs gas at concentrations of ppb (parts per billion), but their high price limits their large-scale application.

[0005] 2) Currently, commercially available electrochemical and semiconductor gas sensors are relatively inexpensive, but their detection limits for VOCs are mostly at the ppm (parts per million) level, which is significantly lower than the extremely low VOC concentrations (ppb or even ppt) required for semiconductor manufacturing environments. This limits the application of such sensors in the semiconductor manufacturing field. Summary of the Invention

[0006] The present invention aims to provide a method for preparing a low-detection-limit ammonia gas sensor. This method involves synthesizing niobium oxide-encapsulated cerium oxide nanoparticles via a hydrothermal method and fabricating the gas sensor. The gas sensor prepared by this method consists of two nanoscale semiconductor oxides. Since niobium oxide is prepared as a composite nanoparticle material through in-situ reduction on the surface of cerium oxide, the two oxides have a higher contact area and carrier mobility, thereby improving the gas-sensing performance of the material. Electrons are redistributed to form an electron depletion layer and an electron enrichment layer, making the material more readily react with oxygen to generate oxygen anions, thus enhancing the material's gas-sensing performance for VOCs gases.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing a low detection limit ammonia gas sensor, comprising the following steps:

[0009] Step 1: Synthesize niobium oxide-encapsulated cerium oxide nanoparticles:

[0010] (1) Synthesis of cerium oxide nanoparticles: First, cerium nitrate hexahydrate (Ce(NO3)3·6H2O), poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer (P123) and sodium hydroxide were dissolved in distilled water. Then, the mixture was reacted at 100-140℃ for 13-20 hours. After that, it was washed three times with ethanol and deionized water. Finally, it was heated in air for a certain period of time. After the reaction was completed, it was cooled to room temperature.

[0011] (2) Synthesis of niobium oxide nanoparticles: Niobium oxalate (C10H5NbO20) was added to ultrapure water, followed by cerium oxide nanoparticles as seed crystals. The mixed solution was then heated at a certain temperature. After cooling, water was added to dilute the solution to a niobium content of 0.01-0.02 mol / L. Finally, the solution was added to a polytetrafluoroethylene container and reacted at 150-250℃ for 1-3 hours. After the reaction was completed, the solution was rinsed with deionized water and dried at a certain temperature.

[0012] Step 2: Add the dried powder to the rosin, and finally evenly coat the rosin containing the sensing material onto the ceramic tube and weld the ceramic tube to make a gas sensor.

[0013] Furthermore, in the synthesis of cerium oxide nanoparticles in step one, 4 parts of cerium nitrate hexahydrate, 0.8 parts of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer, and 1 part of sodium hydroxide are dissolved in 30 parts of distilled water.

[0014] Furthermore, in the synthesis of cerium oxide nanoparticles in step one, after rinsing, the nanoparticles are heated in air at a temperature of 350-500°C for 1-2 hours, with a heating rate of 0.5°C / min.

[0015] Furthermore, it is preferable to heat at 450°C for 2 hours.

[0016] Furthermore, in the synthesis of niobium oxide nanoparticles in step one, 26-27 parts of niobium oxalate are added to 100 parts of ultrapure water, followed by the addition of 1 part of cerium oxide nanoparticles as seed crystals.

[0017] Furthermore, in the synthesis of niobium oxide nanoparticles in step one, the mixed solution is heated at 100-140℃ for 3-6 hours, and after cooling, it is diluted with water to a niobium content of about 0.01-0.02 mol / L. Finally, 5-10 parts of the solution are added to a polytetrafluoroethylene container.

[0018] Furthermore, it is preferable to heat the mixed solution at 120°C for 5 hours, and after cooling, dilute it with water to a niobium content of 0.015 mol / L; after adding it into a polytetrafluoroethylene container, react it at 200°C for 2 hours.

[0019] A low detection limit ammonia gas sensor is prepared using the method described above.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] (1) This invention patent prepares a niobium oxide-encapsulated niobium oxide nanoparticle ammonia sensor by hydrothermal synthesis using cerium oxide as a seed crystal. Its detection limit is as low as 1 ppb, which is beneficial for quickly and accurately evaluating the filtration efficiency of the filter for ammonia and the concentration of ammonia in the environment.

[0022] (2) The gas sensor prepared by this invention is an oxide semiconductor device. The sensing principle is that after the adsorption of pollutant gas (ammonia), the pollutant gas undergoes an oxidation-reduction reaction on the material surface, causing a change in the resistance of the gas sensor. The prepared sensor has a simple structure, low cost, and is suitable for large-scale manufacturing and application. Attached Figure Description

[0023] Figure 1 This is a schematic diagram illustrating the gas-sensing performance test principle of the ammonia gas sensor of this invention.

[0024] Figure 2 This is a response graph of the ammonia gas sensor of the present invention to different concentrations of ammonia gas;

[0025] Figure 3 These are response curves of different types of ammonia gas sensors to 0.5 ppb ammonia. Detailed Implementation

[0026] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0027] Example 1

[0028] A method for preparing a low detection limit ammonia gas sensor, comprising the following steps:

[0029] Step 1: Synthesis of cerium oxide nanoparticles coated with niobium oxide:

[0030] (1) Synthesis of cerium oxide nanoparticles: 4 parts of cerium nitrate hexahydrate (Ce(NO3)3·6H2O), 0.8 parts of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123), and 1 part of sodium hydroxide were dissolved in 30 parts of distilled water. The mixture was then reacted at 100-140℃ for 13-20 hours, followed by rinsing with ethanol and deionized water. Finally, the mixture was heated in air at 350-500℃ for 1-2 hours (heating rate of 0.5℃ / min), and then cooled to room temperature after the reaction was completed.

[0031] (2) Synthesis of niobium oxide nanoparticles: 26-27 parts of niobium oxalate (C10H5NbO20) were added to 100 parts of ultrapure water, followed by 1 part of cerium oxide nanoparticles as seed crystals. The mixed solution was then heated at 100-140℃ for 3-6 hours. After cooling, water was added to dilute the solution to a niobium content of about 0.01-0.02 mol / L. Finally, 5-10 parts of the solution were added to a polytetrafluoroethylene container and reacted at 150-250℃ for 1-3 hours. After the reaction was completed, the solution was rinsed with deionized water and dried at 60℃.

[0032] Step 2: After synthesizing niobium oxide-coated cerium oxide nanoparticles by the above hydrothermal method, the dried powder is added to rosin. Finally, the rosin containing the sensing material is evenly coated on the ceramic tube and the ceramic tube is welded to form a gas sensor.

[0033] Example 2

[0034] This embodiment provides a low detection limit ammonia gas sensor, which is prepared using the preparation method described in Embodiment 1 above.

[0035] Example 3

[0036] This embodiment performs a gas-sensing test on the ammonia gas sensor prepared in the first embodiment above: specifically, the prepared ceramic tube is aged at 300°C to remove rosin, and then the prepared gas sensor is connected to the circuit for gas-sensing test. Since niobium oxide is a composite nanoparticle material prepared by in-situ reduction on the surface of cerium oxide, the two oxides have a higher contact area and carrier mobility, thereby improving the gas-sensing performance of the material.

[0037] The gas sensitivity test system includes: gas cylinder, test container, DC power supply, wires, fixed resistor (R0), voltmeter, computer, and gas sensor (Rx).

[0038] Gas-sensitive performance testing process:

[0039] (1) The concentration of ammonia in the gas cylinder can be calculated by passing a certain amount of ammonia into the sealed gas cylinder.

[0040] (2) Adjust the working voltage of the gas sensor in the empty bottle, and transfer it to the gas cylinder containing ammonia after it is balanced.

[0041] (3) Record the voltage readings of the external fixed resistor R0 of the gas sensor in gases of different concentrations. For example... Figure 1 The fixed resistor and the gas sensor are connected in series. Under stable external power supply voltage, when the resistance of the gas sensor exposed to ammonia gas changes, the voltage across the fixed resistor also changes. Therefore, measuring the voltage across the fixed resistor yields the change in the gas sensor's resistance. The series connection of the fixed resistor serves two purposes: first, to prevent sudden changes in the gas sensor's resistance over a short period from affecting the circuit; and second, to simplify the structure of the gas sensor section.

[0042] (4) The resistance of the gas sensor under different concentrations of ammonia was calculated, and the relationship between the resistance and the ammonia concentration was obtained.

[0043] The testing system uses ammonia atmospheres of different known concentrations as test conditions, measures the voltage change of a fixed resistor and saves the data to a computer, and finally calculates the resistance change of the gas sensor. The results are as follows. Figure 2 As shown, the formula for calculating the response value is response value S=(Rg-Ra) / Ra, where Ra is the resistance value of the fixed resistor R0 when the gas-sensitive material is in air, and Rg is the resistance value of the fixed resistor R0 when the gas-sensitive material is in the gas to be measured.

[0044] Furthermore, niobium oxide nanoparticles and cerium oxide nanoparticles were synthesized using a hydrothermal synthesis method, and then fabricated into gas sensors. Gas-sensing performance was tested at specific ammonia concentrations using the same testing method, and the comparative results are shown below. Figure 3 As shown.

[0045] In summary, the sensing principle of this low detection limit ammonia gas sensor is as follows: When the oxide semiconductor material is exposed to air, oxygen in the air diffuses to the surface of the material. When energized, this oxygen on the surface of the semiconductor gas-sensitive material gains electrons to generate oxygen negative ions (O-). When the material reaches equilibrium and comes into contact with pollutant gases (such as ammonia), the oxygen negative ions on the surface of the semiconductor gas-sensitive material undergo an oxidation-reduction reaction with the pollutant gases, thereby taking away or donating electrons, causing a change in the concentration of charge carriers in the material, which in turn causes a change in the resistance of the oxide material.

[0046] This invention utilizes a hydrothermal method to prepare composite nanoparticles by in-situ reduction of niobium oxide onto the surface of cerium oxide. These nanoparticles are then coated onto the surface of a ceramic tube to fabricate a gas sensor. The raw materials are inexpensive, resulting in low cost. The prepared sensor has a detection limit as low as 1 ppb, which is beneficial for rapidly and accurately assessing the filtration efficiency of filters for ammonia and the concentration of ammonia in the environment.

[0047] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the above embodiments do not limit the scope of protection of the present invention in any way, and all technical solutions obtained by equivalent substitution or other means fall within the scope of protection of the present invention. Parts not covered in this invention are the same as or can be implemented using existing technology.

Claims

1. A method for preparing a low detection limit ammonia gas sensor, characterized in that... The preparation steps are as follows: Step 1: Synthesize niobium oxide-encapsulated cerium oxide nanoparticles: (1) Synthesis of cerium oxide nanoparticles: First, cerium nitrate hexahydrate (Ce(NO3)3·6H2O), poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer (P123) and sodium hydroxide were dissolved in distilled water. Then, the mixture was reacted at 100-140℃ for 13-20 hours. After that, it was washed three times with ethanol and deionized water. Finally, it was heated in air for a certain period of time. After the reaction was completed, it was cooled to room temperature. (2) Synthesis of niobium oxide nanoparticles: Niobium oxalate (C10H5NbO20) was added to ultrapure water, followed by cerium oxide nanoparticles as seed crystals. The mixed solution was then heated at a certain temperature. After cooling, water was added to dilute the solution to a niobium content of 0.01-0.02 mol / L. Finally, the solution was added to a polytetrafluoroethylene container and reacted at 150-250℃ for 1-3 hours. After the reaction was completed, the solution was rinsed with deionized water and dried at a certain temperature. Step 2: Add the dried powder to the rosin, and finally evenly coat the rosin containing the sensing material onto the ceramic tube and weld the ceramic tube to make a gas sensor.

2. The method for preparing a low detection limit ammonia gas sensor according to claim 1, characterized in that, The synthesis of cerium oxide nanoparticles in step one involves dissolving 4 parts of cerium nitrate hexahydrate, 0.8 parts of polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer, and 1 part of sodium hydroxide in 30 parts of distilled water.

3. The method for preparing a low detection limit ammonia gas sensor according to claim 2, characterized in that, In the synthesis of cerium oxide nanoparticles in step one, after rinsing, the nanoparticles are heated in air at a temperature of 350-500℃ for 1-2 hours, with a heating rate of 0.5℃ / min.

4. The method for preparing a low detection limit ammonia gas sensor according to claim 3, characterized in that, Heat at 450℃ for 2 hours.

5. The method for preparing a low detection limit ammonia gas sensor according to claim 1, characterized in that, In the synthesis of niobium oxide nanoparticles in step one, 26-27 parts of niobium oxalate are added to 100 parts of ultrapure water, followed by the addition of 1 part of cerium oxide nanoparticles as seed crystals.

6. The method for preparing a low detection limit ammonia gas sensor according to claim 4, characterized in that, In the synthesis of niobium oxide nanoparticles in step one, the mixed solution is heated at 100-140℃ for 3-6 hours. After cooling, water is added to dilute the solution to a niobium content of about 0.01-0.02 mol / L. Finally, 5-10 portions of the solution are added to a polytetrafluoroethylene container.

7. The method for preparing a low detection limit ammonia gas sensor according to claim 6, characterized in that, The mixed solution was heated at 120°C for 5 hours, and after cooling, it was diluted with water to a niobium content of 0.015 mol / L. After being added to a polytetrafluoroethylene container, it was reacted at 200°C for 2 hours.

8. A low detection limit ammonia gas sensor, characterized in that, It is prepared by any one of claims 1 to 7.

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