A NO 2 Sensor and method for preparing the same

Abstract

The present invention provides a NO 2 Sensor and preparation method thereof, wherein Ni / Co bimetallic oxide synthesized using MOF as template detects NO 2 The method comprises the following steps: the Ni / Co bimetallic oxide in the method has a better NO conversion than conventional semiconductor metal oxides. 2 It shows a relatively sensitive response, a fast response time, a low response temperature, and no obvious response to common volatile organic compounds, showing good selectivity. This method is expected to be used in the low-temperature NO 2 It is widely used in sensing.

Description

Technical Field

[0001] The present invention belongs to the field of sensing methods, and specifically relates to a method for preparing Ni / Co bimetallic oxide for NO by using MOF as a template. 2 Sensing method. Background Art

[0002] In recent years, the synthesis of nanomaterials and the research on their properties have made great progress. Among them, semiconductor metal oxides, as a major type of important functional materials, have been widely used in the field of gas sensing. Although semiconductor metal oxides have good sensing effects on common toxic and harmful gases, and can achieve high sensitivity and low detection limits, most semiconductor metal oxides need to work at high temperatures above 250°C, which not only wastes energy but also greatly limits their practical applications. Therefore, it has become a very important topic to reduce the working temperature of semiconductor metal oxides while retaining their good sensing performance.

[0003] As we all know, NO 2 It is a common toxic and harmful gas, mainly from automobile exhaust, boiler exhaust, etc. It is one of the causes of acid rain. Therefore, NO 2 The present invention introduces a Ni / Co bimetallic oxide synthesized based on the template method for low-temperature detection of NO 2 This method has high sensitivity and can achieve 1ppm NO 2 The method has good selectivity and no obvious response to common volatile organic compounds. The method has good stability and the results of three repetitions have no obvious deviation, which is a good indicator of low concentration NO 2 It lays the foundation for quantitative detection. More importantly, the working temperature of the sensor in this method is 80°C, which is much lower than the working temperature of common semiconductor metal oxides. It saves energy and is easier to meet the needs of portable detection, providing new possibilities for the design of low-temperature sensors. Summary of the invention

[0004] The purpose of the present invention is to make up for the shortcomings of existing semiconductor metal oxide high temperature sensors and propose a Ni / Co bimetallic oxide low temperature detection NO 2 new method.

[0005] The present invention provides a NO 2 The sensor comprises a sensing film made of Ni / Co bimetallic oxide.

[0006] Preferably, the thickness of the sensing film is 0.1-1 mm.

[0007] Another aspect of the present invention is a NO 2The preparation method of the sensing film comprises the following steps: preparing a Ni / Co bimetallic oxide and an alcohol reagent into a suspension to prepare a film-like material.

[0008] Preferably, the concentration of the suspension is 1-10 mg / ml.

[0009] The present invention also provides NO 2 Sensing method: Use an external DC power supply to NO 2 The sensor is heated to a specific temperature; a certain amount of air is opened through the flow control system to make the sensor resistance reach a stable value in dry air. Under the premise of keeping the total flow constant, adjust the NO 2 and air flow rate to achieve changes in NO 2 The effect of concentration. Start the timer and make different concentrations of NO 2 After a certain period of time, the sensor will react and close the NO 2 Adjust the air flow to the initial value, and let the resistance recover for a period of time in the air atmosphere; then change the air and NO 2 Flow rate, test different NO 2 The response of the sensor to the concentration of air atmosphere and NO 2 The difference in the ambient resistance ΔR divided by the initial resistance R 0 As the response value of the sensor, a working curve of response value and concentration is drawn. The test steps for other common interferences are the same as NO 2 .

[0010] Preferably, the DC power supply is used to heat the sensor at a heating temperature of 80-300°C.

[0011] Preferably, the total flow rate of the gas is 50-500 ml / min.

[0012] Preferably, the sensor is used in combination with different concentrations of NO 2 The reaction time is 5-10 minutes, and the resistance recovery time in the air is 10-20 minutes.

[0013] Preferably, the interfering substance is selected from water, acetone, methanol, ethanol, chlorobenzene, ethyl acetate, toluene or carbon tetrachloride.

[0014] The present invention has the following advantages:

[0015] (1) This method is easy to operate and has high sensitivity, and can detect 1 ppm NO 2 , good selectivity, no obvious interference from water and common VOCs.

[0016] (2) This method detects NO 2It has good stability, and the signal has no obvious attenuation after one week of testing; it has good reproducibility, and there is no obvious deviation in the results of three consecutive tests (see Figure 3 ).

[0017] (3) This method overcomes the shortcomings of most semiconductor metal oxides in high-temperature sensing and can achieve a relatively low temperature of 80°C for NO 2 High selectivity and high sensitivity sensing. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of the working of the sensor in a homemade sealed bottle;

[0019] Figure 2 The Ni / Co bimetallic oxide prepared in Example 4 is used as the sensing membrane to detect different concentrations of NO 2 Resistance response change curve;

[0020] Figure 3 The Ni / Co bimetallic oxide sensor membrane prepared in Example 4 is sensitive to different concentrations of NO 2 Working curve of response value and concentration;

[0021] Figure 4 The Ni / Co bimetallic oxide prepared in Example 5 has a 2 Comparison of the response values ​​with those of the interferents. DETAILED DESCRIPTION

[0022] The present invention will be further described in the following examples, but the present invention is not limited thereto.

[0023] A MOF-based Ni / Co bimetallic oxide for NO 2 The sensing method has the following specific steps:

[0024] (1) Preparation of sensor: Prepare Ni / Co bimetallic oxide into a suspension with anhydrous ethanol and disperse it evenly by ultrasonic. Use a pipette to transfer an appropriate amount and evenly coat it on the surface of the ceramic tube to form a thin film. After thorough drying, fix the coated ceramic tube with a wire in a homemade sealed bottle and check the sealing of the entire gas path.

[0025] (2) NO 2 Sensor: Use an external DC power supply to heat the sensor to a specific temperature. Open a certain flow of air through the flow control system to make the sensor resistance reach a stable value in dry air. Under the premise of controlling the total flow rate unchanged, adjust the NO 2 and air flow rate to achieve changes in NO 2 The effect of concentration. Start the timer and make different concentrations of NO 2 After a certain period of time, the sensor will react and close the NO2 Adjust the air flow to the initial value, and let the resistance recover for a period of time in the air atmosphere. Then change the air and NO 2 Flow rate, test different NO 2 The response of the sensor to the concentration of air atmosphere and NO 2 The difference in the ambient resistance ΔR divided by the initial resistance R 0 As the response value of the sensor, a working curve of response value and concentration is drawn. The test steps for other common interfering substances VOCs are the same as those for NO 2 .

[0026] In step (1), the concentration of the suspension is 1-10 mg / ml, and the ultrasonic dispersion time is 10-30 min;

[0027] The volume of the suspension applied in step (1) is 10-50 μL, and the thickness of the formed sensing film is 0.1-1 mm;

[0028] In the step (2), the DC power supply is used to heat the sensor at a heating temperature of 80-300° C.;

[0029] The total flow rate of the gas in step (2) is 50-500 ml / min;

[0030] In the step (2), the sensor is exposed to different concentrations of NO 2 The reaction time is 5-10 minutes, and the resistance recovery time in the air is 10-20 minutes;

[0031] The interfering substances in step (2) include water, acetone, methanol, ethanol, chlorobenzene, ethyl acetate, toluene and carbon tetrachloride.

[0032] Ni / Co bimetallic oxide was prepared by template method. Specifically, 125 mg of terephthalic acid was weighed in a 100 ml beaker, 15 ml of N,N-dimethylformamide, 2 ml of anhydrous ethanol, and 2 ml of water were added, and stirred to mix well. Then 90 mg of NiCl 2 6H 2 O,90mg CoCl 2 6H 2O, 0.5g polyvinyl pyrrolidone, stir at room temperature for 20min until the solution is clear and transparent, transfer the solution into a 50ml polytetrafluoroethylene-lined reactor, react at 150℃ for 10h, cool naturally to room temperature, wash three times with anhydrous ethanol, and dry in a 60℃ vacuum oven for 6h to obtain Ni / Co bimetallic MOF. The prepared Ni / Co bimetallic MOF is placed in a quartz boat and calcined in a tube furnace in an air atmosphere with a starting temperature of 20℃, and the temperature is programmed to 600℃ at a rate of 2℃ / min, maintained for 20min, and then cooled naturally to room temperature to obtain the product Ni / Co bimetallic oxide.

[0033] like Figure 1 As shown, the volume of the homemade sealed bottle is 100-500ml, and the bottle cap is punched with holes to connect the wires, two of which are connected to the sensor at one end and connected to the multimeter at the other end to record the change in resistance value, and the other two wires are connected to the sensor at one end and connected to the DC power supply at the other end to heat the sensor. The wires make the sensor hang in the bottle, and the gap between the hole and the wire is sealed with epoxy resin glue.

[0034] Example 1 Preparation of sensor

[0035] Prepare a 1 mg / ml suspension of Ni / Co bimetallic oxide with anhydrous ethanol and disperse it evenly by ultrasonication for 30 minutes. Take an appropriate amount of 20 μL with a pipette and evenly coat it on the surface of the ceramic tube to form a 0.2 mm film. After thoroughly drying at room temperature for 12 hours, fix the coated ceramic tube with a wire in a homemade sealed bottle, such as Figure 1 As shown, one end of two wires is connected to the metal column of the sensor base, and the other end is connected to the multimeter. One end of the other two wires is also connected to the metal column of the sensor base, and the other end is connected to the DC power supply. After the line connection is completed, check the sealing of the entire gas circuit.

[0036] Example 2 Preparation of sensor

[0037] Prepare a 1 mg / ml suspension of Ni / Co bimetallic oxide with anhydrous ethanol and disperse it evenly by ultrasonication for 30 minutes. Take an appropriate amount of 50 μL with a pipette and evenly coat it on the surface of the ceramic tube to form a 0.5 mm film. After thoroughly drying at room temperature for 12 hours, fix the coated ceramic tube with a wire in a homemade sealed bottle, such as Figure 1 As shown, one end of two wires is connected to the metal column of the sensor base, and the other end is connected to the multimeter. One end of the other two wires is also connected to the metal column of the sensor base, and the other end is connected to the DC power supply. After the line connection is completed, check the sealing of the entire gas circuit.

[0038] Example 3 Preparation of sensor

[0039] Prepare a 10 mg / ml suspension of Ni / Co bimetallic oxide with anhydrous ethanol and disperse it evenly by ultrasonication for 30 minutes. Take an appropriate amount of 10 μL with a pipette and evenly coat it on the surface of the ceramic tube to form a 1 mm film. After thoroughly drying at room temperature for 12 hours, fix the coated ceramic tube with a wire in a homemade sealed bottle, such as Figure 1 As shown, one end of two wires is connected to the metal column of the sensor base, and the other end is connected to the multimeter. One end of the other two wires is also connected to the metal column of the sensor base, and the other end is connected to the DC power supply. After the line connection is completed, check the sealing of the entire gas circuit.

[0040] Example 4 NO 2 Sensor

[0041] Use an external DC power supply to heat the sensor until the reaction temperature reaches 80°C. Open the air through the flow control system to a flow rate of 80ml / min, and let the sensor resistance reach a stable value in dry air. Under the premise of keeping the total flow constant, adjust the NO in the gas cylinder to 80ppm. 2 The flow rate is 2ml / min, and the air flow rate is 78ml / min. 2 The concentration of NO is 2ppm. Start the timer, then 2ppm NO 2 After reacting with the sensor for 10 minutes, turn off NO 2 Adjust the air flow to the initial value of 80ml / min, and let the resistance recover in the air atmosphere for 15 minutes. Then change the air and NO 2 The flow rate makes NO 2 The flow rate of NO in the sealed bottle is 3 ml / min and the flow rate of air is 77 ml / min. 2 The concentration is 3ppm, and the reaction time and recovery time are the same as 2ppm NO 2 The same is true for other concentrations. 2 The difference in the ambient resistance ΔR divided by the initial resistance R 0 As the response value of the sensor, draw a working curve of response value and concentration, such as Figure 2 and Figure 3 shown.

[0042] Example 5 Testing of Interfering Substances

[0043] like Figure 4As shown, use an external DC power supply to heat the sensor until the reaction temperature reaches 80°C. Open the air through the flow control system to a flow rate of 100ml / min, and make the resistance of the sensor reach a stable value in dry air. Under the premise of controlling the total flow rate unchanged, adjust the flow rate of 100ppm methanol in the gas cylinder to 50ml / min, and the flow rate of air to 50ml / min, then the concentration of methanol in the sealed bottle is 50ppm. Turn on the timer, and after 50ppm of methanol reacts with the sensor for 10min, close the methanol gas line, adjust the flow rate of the air gas line to the initial value of 100ml / min, and restore the resistance in the air atmosphere for 15min. The remaining interferences - ethanol, acetone, carbon tetrachloride, toluene, chlorobenzene, ethyl acetate, water and methanol are tested in the same process. The results show that the sensor is sensitive to NO 2 There is good response, but almost no noticeable response to interferers.

Claims

1. A NO 2 sensor, Features: The material composition of the sensing film of the sensor includes Ni / Co bimetallic oxide; The Ni / Co bimetallic oxide is prepared by calcining Ni / Co bimetallic MOF; The NO 2 The working process of the sensor is as follows: Use an external DC power supply to supply NO 2 The sensor is heated to a specific temperature; a certain flow of air is opened through the flow control system to make the sensor resistance reach a stable value in dry air; while the total flow remains unchanged, the NO 2 and air flow rate to achieve changes in NO 2 The effect of concentration; start the timer and make different concentrations of NO 2 After a certain period of time, the sensor will react and close the NO 2 Adjust the air flow to the initial value, and let the resistance recover for a period of time in the air atmosphere; then change the air and NO 2 Flow rate, test different NO 2 The response of the sensor to the concentration of air atmosphere and NO 2 The difference in the ambient resistance ΔR divided by the initial resistance R 0 As the response value of the sensor, a working curve of response value and concentration is drawn; the test steps for other common interferences are the same as NO 2 ; The heating temperature of the direct current power supply for heating the sensor is 80-300°C.

2. NO according to claim 1 2 sensor, Features: The thickness of the sensing film is 0.1-1 mm.

3. NO according to claim 1 2 sensor, Features: The total flow rate of gas is 50-500ml / min.

4. NO according to claim 1 2 sensor, Features: The sensor reacts with different concentrations of NO 2 The reaction time is 5-10 minutes, and the resistance recovery time in the air is 10-20 minutes.

5. NO according to claim 1 2 sensor, Features: The interfering substance is selected from water, acetone, methanol, ethanol, chlorobenzene, ethyl acetate, toluene or carbon tetrachloride.

6. A NO according to claim 1 2 NO in Sensors 2 Preparation method of sensing film, It is characterized in that The Ni / Co bimetallic oxide and an alcohol reagent are prepared into a suspension to prepare a film-like material.

7. The preparation method according to claim 6, Features: The concentration of the suspension is 1-10 mg / ml.

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