CN109521064B - Room temperature NO2 sensor based on WO3 hollow sphere and preparation method thereof - Google Patents
Room temperature NO2 sensor based on WO3 hollow sphere and preparation method thereof Download PDFInfo
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- 238000002360 preparation method Methods 0.000 title claims abstract description 11
- 239000000919 ceramic Substances 0.000 claims abstract description 42
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 claims abstract description 24
- 229910052737 gold Inorganic materials 0.000 claims abstract description 24
- 239000010931 gold Substances 0.000 claims abstract description 24
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 claims abstract description 18
- 238000010438 heat treatment Methods 0.000 claims abstract description 17
- PNEYBMLMFCGWSK-UHFFFAOYSA-N Alumina Chemical compound [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 claims abstract description 14
- 238000000034 method Methods 0.000 claims abstract description 6
- 229910001120 nichrome Inorganic materials 0.000 claims abstract description 4
- 229910000623 nickel–chromium alloy Inorganic materials 0.000 claims abstract description 4
- 239000000758 substrate Substances 0.000 claims abstract description 3
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 46
- 239000002002 slurry Substances 0.000 claims description 31
- 239000000463 material Substances 0.000 claims description 25
- 239000008367 deionised water Substances 0.000 claims description 24
- 229910021641 deionized water Inorganic materials 0.000 claims description 24
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 24
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 claims description 22
- 238000003756 stirring Methods 0.000 claims description 22
- ZNCPFRVNHGOPAG-UHFFFAOYSA-L sodium oxalate Chemical compound [Na+].[Na+].[O-]C(=O)C([O-])=O ZNCPFRVNHGOPAG-UHFFFAOYSA-L 0.000 claims description 13
- 229940039790 sodium oxalate Drugs 0.000 claims description 13
- XMVONEAAOPAGAO-UHFFFAOYSA-N sodium tungstate Chemical compound [Na+].[Na+].[O-][W]([O-])(=O)=O XMVONEAAOPAGAO-UHFFFAOYSA-N 0.000 claims description 13
- 230000032683 aging Effects 0.000 claims description 11
- 239000011248 coating agent Substances 0.000 claims description 11
- 238000000576 coating method Methods 0.000 claims description 11
- 238000009210 therapy by ultrasound Methods 0.000 claims description 11
- 238000003466 welding Methods 0.000 claims description 11
- 238000001354 calcination Methods 0.000 claims description 9
- 238000001035 drying Methods 0.000 claims description 4
- 238000004519 manufacturing process Methods 0.000 claims description 4
- 239000000203 mixture Substances 0.000 claims description 2
- 238000005406 washing Methods 0.000 claims description 2
- 238000000643 oven drying Methods 0.000 claims 1
- 239000011224 oxide ceramic Substances 0.000 claims 1
- 229910052574 oxide ceramic Inorganic materials 0.000 claims 1
- TWNQGVIAIRXVLR-UHFFFAOYSA-N oxo(oxoalumanyloxy)alumane Chemical compound O=[Al]O[Al]=O TWNQGVIAIRXVLR-UHFFFAOYSA-N 0.000 claims 1
- 230000035945 sensitivity Effects 0.000 abstract description 17
- 238000001514 detection method Methods 0.000 abstract description 5
- 230000007613 environmental effect Effects 0.000 abstract description 3
- 238000012544 monitoring process Methods 0.000 abstract description 2
- JCXJVPUVTGWSNB-UHFFFAOYSA-N Nitrogen dioxide Chemical compound O=[N]=O JCXJVPUVTGWSNB-UHFFFAOYSA-N 0.000 description 51
- MGWGWNFMUOTEHG-UHFFFAOYSA-N 4-(3,5-dimethylphenyl)-1,3-thiazol-2-amine Chemical compound CC1=CC(C)=CC(C=2N=C(N)SC=2)=C1 MGWGWNFMUOTEHG-UHFFFAOYSA-N 0.000 description 21
- 239000007789 gas Substances 0.000 description 19
- 238000012360 testing method Methods 0.000 description 10
- OJIJEKBXJYRIBZ-UHFFFAOYSA-N cadmium nickel Chemical compound [Ni].[Cd] OJIJEKBXJYRIBZ-UHFFFAOYSA-N 0.000 description 9
- 238000007598 dipping method Methods 0.000 description 9
- 229910000925 Cd alloy Inorganic materials 0.000 description 8
- 239000004065 semiconductor Substances 0.000 description 3
- 229910052721 tungsten Inorganic materials 0.000 description 3
- 239000010937 tungsten Substances 0.000 description 3
- -1 tungsten ion Chemical class 0.000 description 3
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 description 2
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 2
- 230000006378 damage Effects 0.000 description 2
- 239000001301 oxygen Substances 0.000 description 2
- 229910052760 oxygen Inorganic materials 0.000 description 2
- 241000282414 Homo sapiens Species 0.000 description 1
- 238000003916 acid precipitation Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 239000002803 fossil fuel Substances 0.000 description 1
- 230000036541 health Effects 0.000 description 1
- 238000001027 hydrothermal synthesis Methods 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- QGLKJKCYBOYXKC-UHFFFAOYSA-N nonaoxidotritungsten Chemical compound O=[W]1(=O)O[W](=O)(=O)O[W](=O)(=O)O1 QGLKJKCYBOYXKC-UHFFFAOYSA-N 0.000 description 1
- 239000005416 organic matter Substances 0.000 description 1
- 238000011056 performance test Methods 0.000 description 1
- 230000004044 response Effects 0.000 description 1
- 238000005245 sintering Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 229910001930 tungsten oxide Inorganic materials 0.000 description 1
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- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
- G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
- G01N27/12—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a solid body in dependence upon absorption of a fluid; of a solid body in dependence upon reaction with a fluid, for detecting components in the fluid
- G01N27/125—Composition of the body, e.g. the composition of its sensitive layer
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Abstract
Based on WO3Room temperature NO of hollow sphere2A gas sensor and a preparation method thereof belong to the technical field of gas sensors. The sensor is in an indirectly heated structure and comprises an alumina ceramic tube substrate with a platinum wire and a gold electrode, and WO coated on the outer surface of the ceramic tube and the gold electrode3The hollow ball and a nickel-chromium alloy heating wire arranged in the ceramic tube; the working temperature of the sensor is provided by introducing direct current to the nichrome heating wire, and the NO is measured by measuring the resistance value of direct current resistance between two gold electrodes in different atmospheres2The function of the concentration. The preparation method is simple, and WO with uniform size and a hollow structure is utilized3For NO2The gas is detected, so that the method has high sensitivity, low working temperature and low detection lower limit, and has a good application prospect in the aspect of environmental monitoring.
Description
Technical Field
The invention belongs to the field of gas sensors, and relates to a gas sensor based on WO3Room temperature NO of hollow sphere2A sensor and a method for manufacturing the same.
Background
With the advance of industrialization, a large amount of fossil fuel is consumed, and a large amount of nitrogen dioxide (NO)2) The gas is then also discharged into the air. NO2The harm is huge, which not only can cause photochemical smog, acid rain and other environmental problems, but also can damage the health of human beings. Thus to NO2It becomes necessary to perform effective monitoring so as to control the emission thereof. Gas sensor in NO in comparison to other kinds of methods2The measurement has many unique advantages, such as low cost, rapidness, real-time performance, convenience and the like.
Currently NO2The sensitive material of the gas sensor is Si, organic matter, semiconductor oxide, etc. Based on semiconductor oxidationNO of substance2The sensor has the characteristics of good stability, good selectivity, high sensitivity and the like, so the sensor is widely concerned. Tungsten oxide (WO) in contrast to other metal semiconductor oxides3) Because the valence state of the tungsten ion is variable, the oxygen content and oxygen defects of the tungsten ion are changed along with the change of environmental factors, so that the tungsten ion has NO2、H2S、 SO2、CO、NH3High sensitivity to gases such as ethanol and acetone, especially to NO2Has excellent response characteristics and is ideal NO2A sensitive material. However, WO3Materials in detecting NO2The problems of higher working temperature, poorer selectivity, higher detection limit and the like exist in the gas. Based on the above, the invention develops a method which works at room temperature and can detect low-concentration NO2WO3A sensor.
Disclosure of Invention
The invention provides a method based on WO3Room temperature NO of hollow sphere2The prepared gas sensor has the characteristics of higher sensitivity, lower detection lower limit, better selectivity and the like, and improves the application of the gas sensor under the room temperature condition.
In order to achieve the purpose, the invention adopts the technical scheme that:
based on WO3Room temperature NO of hollow sphere2Sensor, said room temperature NO2The sensor is indirectly heated, and comprises a ceramic tube substrate with a platinum wire and a gold electrode, and WO coated on the outer surface of the alumina ceramic tube and the gold electrode3The hollow ball and a nickel-chromium alloy heating wire arranged in the ceramic tube; the working temperature of the sensor is provided by introducing direct current to the nichrome heating wire, and the NO is measured by measuring the resistance value of direct current resistance between two gold electrodes in different atmospheres2The function of the concentration. Wherein, said WO3The diameter of the hollow sphere is 2-5 mu m.
Based on WO3Room temperature NO of hollow sphere2The preparation method of the sensor comprises the following steps:
first step, preparation of WO3Hollow ball
(1) Dissolving sodium tungstate in deionized water, performing ultrasonic treatment for 10min to obtain a uniform solution, then adding sodium oxalate, stirring for 10min, dropwise adding 6M hydrochloric acid to adjust the pH value to 0.2-3.0, and then continuing stirring for 10 min; 0.40-0.60 g of sodium tungstate and 0.10-0.20 g of sodium oxalate are correspondingly added into every 25-35 ml of deionized water.
(2) Transferring the solution into a hydrothermal kettle, and then putting the hydrothermal kettle into an oven, wherein the oven parameters are set to be 150-180 ℃ for 10-24 hours;
(3) after the reaction is finished, alternately centrifuging and washing the product by using deionized water and ethanol, and drying the obtained product in an oven at the drying temperature of 40-80 ℃ for 8-12 h; then placing the mixture at 400-600 ℃ for calcining for 2-3 h to obtain WO3Materials, WO3The diameter of the hollow sphere is 2-5 mu m.
Secondly, preparing room temperature NO by adopting an indirectly heated structure2Sensor with a sensor element
(1) The WO prepared in the first step3The mass ratio of the material to ethanol is 0.2-0.4: 1, uniformly mixing to form slurry; uniformly coating the slurry on the surface of an alumina ceramic tube with a platinum wire and a gold electrode to ensure that the alumina ceramic tube completely covers the gold electrode; and a platinum wire is led out of the gold electrode;
(2) will coat with WO3Sintering the alumina ceramic tube of the hollow ball for 2-5 hours at 300-600 ℃, then enabling a nickel-cadmium heating coil to penetrate through the interior of the alumina ceramic tube, and supplying direct current to provide working temperature; welding an alumina ceramic tube on the universal indirectly heated hexagonal base through a platinum wire;
(3) finally, aging the sensor for 5-7 days in an air environment at 50-150 ℃ to obtain WO3Radical NO2A gas sensor.
Then, the gas-sensitive performance test is carried out, the test condition is room temperature, and nitrogen dioxide (NO) is tested2) The gas concentration is from 25ppb to 1000 ppb.
The invention has the beneficial effects that:
(1) the invention adopts WO synthesized by a one-step hydrothermal method3The hollow spheres have relatively uniform size distribution,simple preparation method for developing high-performance NO2Gas sensors provide an effective material.
(2) The invention uses WO of uniform size3Hollow sphere for NO2The gas has higher sensitivity.
(3) The developed sensor has lower working temperature and can be used at room temperature; the detection lower limit is lower, and can reach 25 ppb; has better stability and reliability.
(4) WO made by the present invention3Radical NO2The gas sensor has simple manufacturing process and low cost, and is suitable for industrial mass production. Has good application prospect in the aspect of environment detection.
Drawings
FIG. 1 shows WO prepared in example 3 of the present invention3SEM (a) and (b) for hollow spheres.
FIG. 2 shows WO of example 3 of the present invention at room temperature3Radical NO2Gas sensor sensitivity and NO2Graph between concentrations.
Detailed Description
The present invention will be described in further detail with reference to examples, but the present invention is not limited thereto.
Example 1
1. Firstly, dissolving 0.40g of sodium tungstate in 25ml of deionized water, carrying out ultrasonic treatment for 10min to obtain a uniform solution, then adding 0.20g of sodium oxalate, stirring for 10min, then dropping 6M hydrochloric acid to adjust the pH value to 0.2, and then continuing to stir for 10 min;
2. transferring the solution into a 50ml hydrothermal kettle, and then putting the hydrothermal kettle into an oven, wherein the oven parameters are set to be 150 ℃ and 10 hours;
3. after the reaction is finished, the product is alternately centrifugally washed by deionized water and ethanol, and the obtained product is dried in an oven and dried for 12 hours at the temperature of 60 ℃. Then calcining at 600 ℃ for 3h to obtain WO3A material.
4. 0.4mg of the prepared material was mixed with 1mg of absolute ethanol to form a slurry. And dipping a proper amount of slurry by using a brush, and coating the slurry on the outer surface of a commercial ceramic tube to completely cover the gold electrode on the outer surface.
5. The coated ceramic tube was sintered at 300 ℃ for 3h, and then a nickel cadmium alloy heating coil was passed through the inside of the ceramic tube, and direct current was applied to provide the operating temperature. Finally, welding the ceramic tube on a universal indirectly heated hexagonal base through a platinum wire to obtain WO3Radical NO2A sensor.
6. And finally, aging the sensor in an air environment at 80 ℃ for 5 days for later use.
7. Testing the sensor for 25ppb to 1000ppb NO at room temperature2The sensitivity of (2).
Example 2
1. Firstly, 0.45g of sodium tungstate is dissolved in 30ml of deionized water, a uniform solution is obtained after ultrasonic treatment for 10min, then 0.15g of sodium oxalate is added, stirring is carried out for 10min, 6M hydrochloric acid is dropped to adjust the pH value to 0.2, and then stirring is carried out for 10 min;
2. transferring the solution into a 50ml hydrothermal kettle, and then putting the hydrothermal kettle into an oven, wherein the oven parameters are set to be 160 ℃ and 12 h;
3. after the reaction is finished, the product is alternately centrifugally washed by deionized water and ethanol, and the obtained product is dried in an oven for 8 hours at 40 ℃. Then calcining at 500 ℃ for 2h to obtain WO3A material.
4. 0.4mg of the prepared material was mixed with 1mg of absolute ethanol to form a slurry. And dipping a proper amount of slurry by using a brush, and coating the slurry on the outer surface of a commercial ceramic tube to completely cover the gold electrode on the outer surface.
5. The coated ceramic tube was sintered at 500 ℃ for 2h, and then a nickel cadmium alloy heating coil was passed through the inside of the ceramic tube, and direct current was applied to provide the operating temperature. Finally, welding the ceramic tube on a universal indirectly heated hexagonal base through a platinum wire to obtain WO3Radical NO2A sensor.
6. And finally, aging the sensor in an air environment at 50 ℃ for 7 days for later use.
7. Testing the sensor for 25ppb to 1000ppb NO at room temperature2The sensitivity of (2).
Example 3
1. Firstly, 0.45g of sodium tungstate is dissolved in 30ml of deionized water, a uniform solution is obtained after ultrasonic treatment for 10min, then 0.15g of sodium oxalate is added, stirring is carried out for 10min, 6M hydrochloric acid is dropped to adjust the pH value to 0.7, and then stirring is carried out for 10 min;
2. transferring the solution into a 50ml hydrothermal kettle, and then putting the hydrothermal kettle into an oven, wherein the oven parameters are set to be 160 ℃ and 12 h;
3. after the reaction is finished, the product is alternately centrifugally washed by deionized water and ethanol, and the obtained product is dried in an oven for 8 hours at 40 ℃. Then calcining at 500 ℃ for 2h to obtain WO3A material.
4. 0.4mg of the prepared material was mixed with 1mg of ethanol to form a slurry. And dipping a proper amount of slurry by using a brush, and coating the slurry on the outer surface of a commercial ceramic tube to completely cover the gold electrode on the outer surface.
5. The coated ceramic tube was sintered at 500 ℃ for 2h, and then a nickel cadmium alloy heating coil was passed through the inside of the ceramic tube, and direct current was applied to provide the operating temperature. Finally, welding the ceramic tube on a universal indirectly heated hexagonal base through a platinum wire to obtain WO3Radical NO2A sensor.
6. And finally, aging the sensor in an air environment at 50 ℃ for 7 days for later use.
7. Testing the sensor for 25ppb to 1000ppb NO at room temperature2The sensitivity of (2).
WO prepared as shown in FIG. 1(a)3The hollow spheres are uniform in size, each hollow sphere is 2-5 microns in diameter, and careful observation shows that some broken hollow spheres are obtained. FIG. 1(b) shows an enlarged view of the hollow sphere, which is also evidence of WO3The hollow structure of (a) provides a direct proof. FIG. 2 shows the WO prepared3Radical NO2Sensitivity of gas sensor at room temperature and NO2Graph of concentration. Of note is the NO that the sensor is able to detect2The lower limit of the concentration is 25 ppb.
Example 4
1. Firstly, 0.60g of sodium tungstate is dissolved in 35ml of deionized water, a uniform solution is obtained after ultrasonic treatment is carried out for 10min, then 0.10g of sodium oxalate is added, stirring is carried out for 10min, 6M hydrochloric acid is dropped into the solution to adjust the pH value to 1.3, and then stirring is carried out for 10 min;
2. transferring the solution into a 50ml hydrothermal kettle, and then putting the hydrothermal kettle into an oven, wherein the oven parameters are set to be 180 ℃ and 24 hours; 180-24
3. After the reaction is finished, the product is alternately centrifugally washed by deionized water and ethanol, and the obtained product is dried in an oven for 10 hours at 80 ℃. Then calcining at 400 ℃ for 3h to obtain WO3A material.
4. 0.2mg of the prepared material was mixed with 1mg of ethanol to form a slurry. And dipping a proper amount of slurry by using a brush, and coating the slurry on the outer surface of a commercial ceramic tube to completely cover the gold electrode on the outer surface.
5. The coated ceramic tube was sintered at 600 ℃ for 5h, and then a nickel cadmium alloy heating coil was passed through the inside of the ceramic tube, and direct current was applied to provide the operating temperature. Finally, welding the ceramic tube on a universal indirectly heated hexagonal base through a platinum wire to obtain WO3Radical NO2A sensor.
6. And finally, aging the sensor in an air environment at 150 ℃ for 6 days for later use.
7. Testing the sensor for 25ppb to 1000ppb NO at room temperature2The sensitivity of (2).
Example 5
1. Firstly, 0.45g of sodium tungstate is dissolved in 30ml of deionized water, a uniform solution is obtained after ultrasonic treatment for 10min, then 0.15g of sodium oxalate is added, stirring is carried out for 10min, 6M hydrochloric acid is dropped to adjust the pH value to 1.3, and then stirring is carried out for 10 min;
2. transferring the solution into a 50ml hydrothermal kettle, and then putting the hydrothermal kettle into an oven, wherein the oven parameters are set to be 160 ℃ and 12 h;
3. after the reaction is finished, the product is alternately centrifugally washed by deionized water and ethanol, and the obtained product is dried in an oven for 8 hours at 40 ℃. Then calcining at 500 ℃ for 2h to obtain WO3A material.
4. 0.4mg of the prepared material was mixed with 1mg of ethanol to form a slurry. And dipping a proper amount of slurry by using a brush, and coating the slurry on the outer surface of a commercial ceramic tube to completely cover the gold electrode on the outer surface.
5. Will be coatedThe ceramic tube was sintered at 500 ℃ for 2h, and then a nichrome heating coil was passed through the inside of the ceramic tube, and direct current was applied to provide the operating temperature. Finally, welding the ceramic tube on a universal indirectly heated hexagonal base through a platinum wire to obtain WO3Radical NO2A sensor.
6. And finally, aging the sensor in an air environment at 50 ℃ for 7 days for later use.
7. Testing the sensor for 25ppb to 1000ppb NO at room temperature2The sensitivity of (2).
Example 6
1. Firstly, 0.50g of sodium tungstate is dissolved in 30ml of deionized water, a uniform solution is obtained after ultrasonic treatment is carried out for 10min, then 0.15g of sodium oxalate is added, stirring is carried out for 10min, 6M hydrochloric acid is dropped into the solution to adjust the pH value to 2.2, and then stirring is carried out for 10 min;
2. transferring the solution into a 50ml hydrothermal kettle, and then putting the hydrothermal kettle into an oven, wherein the oven parameters are set to be 160 ℃ and 18 h;
3. after the reaction is finished, the product is alternately centrifugally washed by deionized water and ethanol, and the obtained product is dried in an oven and dried for 12 hours at the temperature of 60 ℃. Then calcined at 500 ℃ for 2.5h to obtain WO3A material.
4. 0.2mg of the prepared material was mixed with 1mg of ethanol to form a slurry. And dipping a proper amount of slurry by using a brush, and coating the slurry on the outer surface of a commercial ceramic tube to completely cover the gold electrode on the outer surface.
5. The coated ceramic tube was sintered at 400 ℃ for 4h, and then a nickel cadmium alloy heating coil was passed through the inside of the ceramic tube, and direct current was applied to provide the operating temperature. Finally, welding the ceramic tube on a universal indirectly heated hexagonal base through a platinum wire to obtain WO3Radical NO2A sensor.
6. And finally, aging the sensor in an air environment at 100 ℃ for 7 days for later use.
7. Testing the sensor for 25ppb to 1000ppb NO at room temperature2The sensitivity of (2).
Example 7
1. Firstly, 0.45g of sodium tungstate is dissolved in 30ml of deionized water, a uniform solution is obtained after ultrasonic treatment is carried out for 10min, then 0.15g of sodium oxalate is added, stirring is carried out for 10min, 6M hydrochloric acid is dropped into the solution to adjust the pH value to 2.2, and then stirring is carried out for 10 min;
2. transferring the solution into a 50ml hydrothermal kettle, and then putting the hydrothermal kettle into an oven, wherein the oven parameters are set to be 160 ℃ and 12 h;
3. after the reaction is finished, the product is alternately centrifugally washed by deionized water and ethanol, and the obtained product is dried in an oven for 8 hours at 40 ℃. Then calcining at 400 ℃ for 3h to obtain WO3A material.
4. 0.4mg of the prepared material was mixed with 1mg of ethanol to form a slurry. And dipping a proper amount of slurry by using a brush, and coating the slurry on the outer surface of a commercial ceramic tube to completely cover the gold electrode on the outer surface.
5. The coated ceramic tube was sintered at 500 ℃ for 2h, and then a nickel cadmium alloy heating coil was passed through the inside of the ceramic tube, and direct current was applied to provide the operating temperature. Finally, welding the ceramic tube on a universal indirectly heated hexagonal base through a platinum wire to obtain WO3Radical NO2A sensor.
6. And finally, aging the sensor in an air environment at 50 ℃ for 7 days for later use.
7. Testing the sensor for 25ppb to 1000ppb NO at room temperature2The sensitivity of (2).
Example 8
1. Firstly, 0.45g of sodium tungstate is dissolved in 30ml of deionized water, a uniform solution is obtained after ultrasonic treatment for 5min, then 0.15g of sodium oxalate is added, stirring is carried out for 10min, 6M hydrochloric acid is dropped to adjust the pH value to 3.0, and then stirring is carried out for 10 min;
2. transferring the solution into a 50ml hydrothermal kettle, and then putting the hydrothermal kettle into an oven, wherein the oven parameters are set to be 160 ℃ and 12 h;
3. after the reaction is finished, the product is alternately centrifugally washed by deionized water and ethanol, and the obtained product is dried in an oven and dried for 12 hours at the temperature of 60 ℃. Then calcined at 500 ℃ for 2.5h to obtain WO3A material.
4. 0.2mg of the prepared material was mixed with 1mg of ethanol to form a slurry. And dipping a proper amount of slurry by using a brush, and coating the slurry on the outer surface of a commercial ceramic tube to completely cover the gold electrode on the outer surface.
5. The coated ceramic tube was sintered at 500 ℃ for 2h, and then a nickel cadmium alloy heating coil was passed through the inside of the ceramic tube, and direct current was applied to provide the operating temperature. Finally, welding the ceramic tube on a universal indirectly heated hexagonal base through a platinum wire to obtain WO3Radical NO2A sensor.
6. And finally, aging the sensor in an air environment at 80 ℃ for 7 days for later use.
7. Testing the sensor for 25ppb to 1000ppb NO at room temperature2The sensitivity of (2).
Example 9
1. Firstly, 0.45g of sodium tungstate is dissolved in 30ml of deionized water, a uniform solution is obtained after ultrasonic treatment is carried out for 10min, then 0.15g of sodium oxalate is added, stirring is carried out for 10min, 6M hydrochloric acid is dropped into the solution to adjust the pH value to 3.0, and then stirring is carried out for 10 min;
2. transferring the solution into a 50ml hydrothermal kettle, and then putting the hydrothermal kettle into an oven, wherein the oven parameters are set to be 160 ℃ and 12 h;
3. after the reaction is finished, the product is alternately centrifugally washed by deionized water and ethanol, and the obtained product is dried in an oven for 8 hours at 40 ℃. Then calcining at 500 ℃ for 2h to obtain WO3A material.
4. 0.3mg of the prepared material was mixed with 1mg of ethanol to form a slurry. And dipping a proper amount of slurry by using a brush, and coating the slurry on the outer surface of a commercial ceramic tube to completely cover the gold electrode on the outer surface.
5. The coated ceramic tube was sintered at 500 ℃ for 2h, and then a nickel cadmium alloy heating coil was passed through the inside of the ceramic tube, and direct current was applied to provide the operating temperature. Finally, welding the ceramic tube on a universal indirectly heated hexagonal base through a platinum wire to obtain WO3Radical NO2A sensor.
6. And finally, aging the sensor in an air environment at 50 ℃ for 7 days for later use.
7. Testing the sensor for 25ppb to 1000ppb NO at room temperature2The sensitivity of (2).
Table 1: gas sensor at 200ppb NO2Sensitivity to pH in the atmosphere
(sensitivity S ═ Rg/Ra, where Ra represents the resistance of the sensor in air and Rg is the resistance of the sensor in the gas to be measured)
| Examples | pH value | Sensitivity S (Rg/Ra) |
| Example 2 | 0.2 | 2.1 |
| Example 3 | 0.7 | 7.6 |
| Example 5 | 1.3 | 1.4 |
| Example 7 | 2.2 | 1.0 |
| Example 9 | 3.0 | 1.0 |
The above-mentioned embodiments only express the embodiments of the present invention, but not should be understood as the limitation of the scope of the invention patent, it should be noted that, for those skilled in the art, many variations and modifications can be made without departing from the concept of the present invention, and these all fall into the protection scope of the present invention.
Claims (4)
1. Based on WO3Room temperature NO of hollow sphere2The preparation method of the sensor is characterized in that the room temperature NO is2The sensor is indirectly heated, and comprises an alumina ceramic tube substrate with a platinum wire and a gold electrode, and WO coated on the outer surface of the alumina ceramic tube and the gold electrode3The hollow ball and a nickel-chromium alloy heating wire arranged in the alumina ceramic tube; the working temperature of the sensor is provided by introducing direct current to the nichrome heating wire, and the NO is measured by measuring the resistance value of direct current resistance between two gold electrodes in different atmospheres2The function of concentration;
the preparation method comprises the following steps:
first step, preparation of WO3Hollow ball
(1) Dissolving sodium tungstate in deionized water, performing ultrasonic treatment to obtain a uniform solution, then adding sodium oxalate, stirring, dropwise adding hydrochloric acid to adjust the pH value to 0.2-3.0, and then continuing stirring; adding 0.40-0.60 g of sodium tungstate and 0.10-0.20 g of sodium oxalate into 25-35 ml of deionized water correspondingly;
(2) transferring the solution into a hydrothermal kettle, and then putting the hydrothermal kettle into an oven, wherein the oven parameters are set to be 150-180 ℃ for 10-24 hours;
(3) after the reaction is finished, alternately centrifuging and washing the product by using deionized water and ethanol, and drying the obtained product in an oven; then placing the mixture at 400-600 ℃ for calcining for 2-3 h to obtain WO3Hollow spheres;
secondly, preparing room temperature NO by adopting an indirectly heated structure2Sensor with a sensor element
(1) The WO prepared in the first step3The hollow spheres are uniformly mixed with ethanol to form slurry; uniformly coating the slurry on the surface of an alumina ceramic tube with a platinum wire and a gold electrode to ensure that the alumina ceramic tube completely covers the gold electrode; and a platinum wire is led out of the gold electrode;
(2) will coat with WO3Alumina ceramic of hollow ballSintering the ceramic tube at 300-600 ℃ for 2-5 h, then enabling the nickel-chromium alloy heating wire to penetrate through the aluminum oxide ceramic tube, and supplying direct current to provide working temperature; then welding an alumina ceramic tube on the universal indirectly heated base through a platinum wire;
(3) aging the sensor in an air environment at 50-150 ℃ for 5-7 days to obtain WO3Basic room temperature NO2A sensor.
2. WO-based material according to claim 13Room temperature NO of hollow sphere2A method for producing a sensor, characterized in that said WO3The diameter of the hollow sphere is 2-5 mu m.
3. The preparation method according to claim 1, wherein the oven drying temperature in the first step (3) is 40-80 ℃ and the drying time is 8-12 h.
4. The process according to claim 1 or 3, wherein the WO in the second step (1)3The mass ratio of the hollow spheres to the ethanol is 0.2-0.4: 1.
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