Methylbenzene steam detection gas sensor and preparation method thereof

Abstract

The invention discloses a toluene steam detection gas sensor and a preparation method thereof, the sensor takes a porous Co3O4 material synthesized by a mixture of a cobalt compound, urea and a solvent through hydrothermal and annealing as a sensitive body, and the interaction of gas on the surface of the sensor is improved through a surface pore-forming technology. The gas sensor is deposited on the surface of a planar gold interdigital electrode through a coating process to prepare a gas sensitive element. The obtained sensitive element has good response to toluene steam, and the detectable actual concentration is as low as 1 ppm. In addition, the sensor also has the capability of resisting interference of other organic steam, and has better selective response to toluene steam. The kit can be used as a beneficial tool for preliminary diagnosis of lung cancer clinically.

Description

Technical Field

[0001] The present application relates to a toluene vapor detection gas sensor and a preparation method thereof, belonging to the technical field of gas sensors. Background Art

[0002] Studies have shown that the toluene content in the exhaled gas of lung cancer patients is as high as 1ppm. Therefore, the high sensitivity and high selectivity of toluene vapor detection in clinical practice is of great significance in the preliminary diagnosis of lung cancer. Gas sensors based on semiconductor metal oxides have been widely used in various fields such as industry, environmental monitoring, and food testing due to their advantages such as small size, low energy consumption, and good stability. However, due to the limitations of the gas-sensing mechanism, most metal oxide gas sensors respond to almost all gases. When detecting mixed gases or in the presence of interfering gases, it is difficult to effectively identify and detect the target component.

[0003] The key to developing high-performance sensors lies in the research of sensitive materials with high selectivity and high sensitivity. Summary of the invention

[0004] Based on the above problems, the purpose of the present invention is to provide a porous Co3O4 material synthesized by hydrothermal and annealing a mixture of cobalt compounds, urea and solvents as a sensitive body, and to prepare a sensitive layer with appropriate film thickness and uniform distribution by a coating process, so as to prepare a highly selective and highly sensitive toluene sensitive element.

[0005] Toluene molecules can undergo a specific catalytic oxidation reaction on the surface of the catalytically active Co3O4 material. The present application further enhances the activity of the catalytic oxidation reaction by pore-forming on the surface of Co3O4, thereby increasing its detection sensitivity. The porous Co3O4 material prepared in this way is used as a sensitive body to prepare a gas sensor, thereby achieving efficient detection of toluene vapor in exhaled breath.

[0006] According to one aspect of the present application, a toluene vapor detection gas sensor is provided, wherein the toluene vapor detection gas sensor uses a porous Co3O4 nanomaterial as a sensitive body;

[0007] The pore size of the porous Co3O4 nanomaterial is 2 to 10 nm;

[0008] The length of the porous Co3O4 nanomaterial is 200-200nm, and the width is 50-200nm.

[0009] Optionally, the operating temperature of the toluene vapor detection gas sensor is 100-200°C.

[0010] Optionally, the resistance value of the toluene vapor detection gas sensor is 10 to 200 KΩ.

[0011] Optionally, the resistance value of the toluene vapor detection gas sensor is selected from any value of 10KΩ, 20KΩ, 30KΩ, 50KΩ, 100KΩ, 150KΩ, 200KΩ or a range between any two of the above values.

[0012] Optionally, the toluene vapor detection gas sensor can detect a toluene concentration of 1 to 100 ppm.

[0013] According to another aspect of the present application, a method for preparing the above-mentioned toluene vapor detection gas sensor is provided, the preparation method comprising:

[0014] A solution containing porous Co3O4 nanomaterials is drop-coated on the surface of the ceramic tube interdigital electrode, and infrared baking is performed until the solution is completely volatilized to obtain the toluene vapor detection gas sensor.

[0015] Optionally, the solvent in the solution is selected from at least one of water, ethanol, methanol, acetone, acetonitrile, toluene, ethylene glycol, and n-hexane.

[0016] Optionally, the mass volume ratio of the porous Co3O4 nanomaterial to the solvent is: 2-100 mg: 0.2-10 mL.

[0017] Optionally, the infrared baking temperature is 40-90°C.

[0018] Optionally, the infrared baking temperature is selected from any value of 40°C, 50°C, 60°C, 70°C, 80°C, 90°C or a range between any two of the above values.

[0019] Optionally, the number of dripping is 2 to 6 times.

[0020] Optionally, the method for preparing the porous Co3O4 nanomaterial comprises:

[0021] In a sealed container, a mixture containing cobalt compounds, urea and a solvent is reacted and annealed to obtain the porous Co3O4 nanomaterial.

[0022] Optionally, the cobalt compound is selected from cobalt chloride and / or cobalt nitrate.

[0023] Optionally, the molar ratio of the cobalt compound to urea is 1:5-10.

[0024] Optionally, the molar ratio of the cobalt compound to urea is selected from any value of 1:5, 1:6, 1:7, 1:8, 1:9, 1:10 or a range between any two of the above values.

[0025] Optionally, the solvent comprises water, ethanol and oleic acid.

[0026] Optionally, the volume ratio of water, ethanol and oleic acid is 15:11:3 to 15:5:1.

[0027] Optionally, the reaction temperature is 160-200° C., and the reaction time is 6-12 hours.

[0028] Optionally, the annealing temperature is 300-400° C., and the annealing time is 2-6 hours.

[0029] As a specific implementation, the present application is implemented through the following technical solutions:

[0030] Porous Co3O4 material is synthesized by using a mixture of cobalt compounds, urea and solvent, hydrothermal treatment and annealing, and the appropriate material morphology is obtained by controlling the reaction temperature and the amount of reagents.

[0031] Preparation of a porous Co3O4 material, the specific steps are as follows

[0032] 1) The volume ratio of deionized water, ethanol and oleic acid is 15:11:3;

[0033] 2) The molar ratio of the cobalt compound to urea is 1:5-10;

[0034] 3) Transfer the entire solution into a 50 mL polytetrafluoroethylene-lined autoclave and maintain at 160-200° C. for 9 hours;

[0035] 4) The precipitate was collected by centrifugation and washed with deionized water several times. Finally, it was dried at 60°C overnight and annealed at 300-400°C in air for 3 hours to obtain the product.

[0036] Using porous Co3O4 material as the sensitive body, the thickness of the gas-sensitive film is controlled through a coating process to optimize the material's response to toluene gas, thereby achieving high-sensitivity detection of toluene gas.

[0037] The porous Co3O4 material is one or more of nanowires, nanosheets, nanoflower-shaped microspheres, and the like.

[0038] The gas sensor is prepared by coating process, the specific steps are as follows:

[0039] 1) Take a certain mass of porous Co3O4 material and evenly disperse it in a suitable solvent;

[0040] 2) Take a certain volume of the dispersed porous Co3O4 material described in step 1) and drop it on the surface of N planar interdigital electrodes. In order to make the sensitive body evenly deposited on the surface of the planar interdigital electrodes, it is necessary to place it under an infrared lamp at a certain temperature for baking treatment until the organic solvent is completely volatilized to form a layer of gas sensitive film; by dropping the sensitive body dispersion liquid on different planar interdigital electrodes for different times and baking temperatures, multiple sensitive films with different thicknesses and film consistency will be obtained;

[0041] 3) The front side of the planar interdigitated electrode described in step 2) is connected to the measuring circuit by two wires respectively, and the heating wire on the back side is connected to the heating circuit; the sensor works at 200° C., and the resistance value is 10 to 200 KΩ.

[0042] In the present application, the toluene vapor sensor is a porous Co3O4 material synthesized by hydrothermal and annealing of a mixture of cobalt compounds, urea and solvents as a sensitive body, and the surface pore-making technology is used to enhance the interaction of gases on its surface. It is deposited on the surface of a planar gold interdigitated electrode through a coating process to prepare a gas sensitive element. The obtained sensitive element has a good response to toluene vapor, and the actual concentration that can be detected is as low as 1ppm. In addition, the sensor has the ability to resist interference from other organic vapors and has a good selective response to toluene vapor. It can be used as a useful tool for the preliminary diagnosis of lung cancer in clinical practice.

[0043] The beneficial effects of this application include:

[0044] 1) The toluene vapor detection gas sensor provided in the present application starts with the chemical properties of the target gas and selects the Co3O4 material with catalytic oxidation activity to it, thereby ensuring the selectivity of the sensitive element.

[0045] 2) The toluene vapor detection gas sensor provided in the present application achieves high sensitivity response of Co3O4 to toluene vapor through pore-forming surface structure enhancement, improves its detection limit, and is more conducive to ppb response in the actual detection process.

[0046] 3) The toluene vapor detection gas sensor provided in this application is affected by many factors, such as the difference in electronic conductivity between gas-sensitive material layers, the diffusion rate and concentration drop caused by the diffusion of gas between different layers, the pore size of semiconductor metal oxide materials, the contact resistance of semiconductor metal oxides, etc. Therefore, as the number of layers increases, the response to the target gas can be improved by optimizing the thickness of the sensitive layer and the consistency of the film layer;

[0047] 4) The sensor and the preparation method thereof provided in the present application are simple, reliable and have good practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 This is the response curve of the sensitive element in Example 2 of the present application when testing 1 ppm toluene vapor.

[0049] Figure 2 This is a scanning electron microscope characterization image of the mesoporous Co3O4 nanoplate material in Example 1 of the present application.

[0050] Figure 3 The sensitive element in Example 2 of the present application is used to test toluene vapor ((a) sensor response of Co3O4 nanoplate at different temperatures; (b) transient response for detecting 1 to 100 ppm toluene; (c) linear curve fitting for different toluene concentrations). DETAILED DESCRIPTION

[0051] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0052] Unless otherwise specified, the raw materials in the examples of this application were purchased through commercial channels.

[0053] In this application, each gas sensor uses a porous Co3O4 material as a sensitive membrane. The thickness of the sensing membrane and the surface properties of the membrane layer in each sensor are different, and the response to toluene gas is different, so as to optimize the toluene sensitivity performance of the sensor and achieve high-sensitivity detection of low-concentration (1ppm) toluene vapor.

[0054] Preparation of a porous Co3O4 material, the specific steps are as follows

[0055] 1) The volume ratio of deionized water, ethanol and oleic acid is 15:11:3;

[0056] 2) The molar ratio of the cobalt compound to urea is 1:5-10;

[0057] 3) Transfer the entire solution into a 50 mL polytetrafluoroethylene-lined autoclave and maintain at 160-200° C. for 9 hours;

[0058] 4) The precipitate was collected by centrifugation and washed with deionized water several times. Finally, it was dried at 60°C overnight and annealed at 300-400°C in air for 3 hours to obtain the product.

[0059] A single sensor is prepared by spin coating, and the specific steps are as follows:

[0060] 1) 2-100 mg of a porous Co3O4 material is uniformly dispersed in 0.2-10 mL of a solvent (one or more mixtures of ultrapure water, ethanol, methanol, acetone, acetonitrile, toluene, ethylene glycol, and n-hexane);

[0061] 2) taking a certain volume of the dispersed porous Co3O4 material described in step 1), dripping it on the surface of N planar interdigital electrodes, and baking it under an infrared lamp at 40-90°C for 2 hours until the organic solvent is completely volatilized to form a layer of porous Co3O4 sensitive film; dripping the dispersion liquid on the surfaces of different planar interdigital electrodes for different times, and controlling the baking temperature under the infrared lamp at the same time, to obtain multiple sensitive films with different thicknesses and surface densities;

[0062] 3) The sensor works at 150-300℃, and the resistance in the air is 10-200KΩ;

[0063] 4) Test the response performance of porous Co3O4 devices with different thicknesses and surface densities to toluene, and select the most selective and sensitive sensitive elements for real-time detection of low concentration (1ppm) toluene.

[0064] Embodiment 1:

[0065] 1) a homogeneous solution was obtained by mixing deionized water (15 mL), ethanol (11 mL) and oleic acid (3 mL);

[0066] 2) Urea (387 mg) and Co(NO3)2·6H2O (188 mg) were fully dispersed into the solution under magnetic stirring for 1 hour;

[0067] 3) The entire solution was transferred into a 50 mL polytetrafluoroethylene-lined autoclave and maintained at 160 °C for 9 hours;

[0068] 4) The precipitate was collected by centrifugation and washed with deionized water several times. Finally, it was dried at 60 °C overnight and annealed at 300 °C in air for 3 h to obtain the product porous Co3O4 nanomaterial. Figure 2 It can be seen that the prepared Co3O4 nanomaterial presents a plate-like structure with a length of about 1500nm, a width of about 500nm, and a thickness of about 100nm.

[0069] Embodiment 2:

[0070] 1) 5 mg of the porous Co3O4 nanosheets prepared in Example 1 were uniformly dispersed in 5 mL of ethanol by ultrasound. The morphology and structure of the porous Co3O4 nanosheets are as follows: Figure 1 As shown;

[0071] 2) Take 5 μL of the dispersed porous Co3O4 nanosheet dispersion, drop it on the surface of a planar interdigital electrode, and bake it under an infrared lamp at 60°C for 1 hour until the organic solvent is completely volatilized to form a sensitive film; 5 μL of the dispersion is dripped on different planar interdigital electrodes 1-10 times in sequence to obtain 10 sensors with Co3O4 gas-sensitive films of 1 layer, 2 layers, 3 layers, 4 layers, 5 layers, 6 layers, 7 layers, 8 layers, 9 layers, and 10 layers;

[0072] 3) When the sensor is heated at 250℃, the resistance value is between 10 and 100KΩ;

[0073] Define the sensor response value as S = R g / R a , where R a is the resistance of the sensor in air, R g is the resistance of the sensor in the gas to be measured.

[0074] The prepared gas sensor was tested for its toluene sensitivity response performance. The sensitive body had the best response to toluene after being spin-coated for about 2 times. The toluene vapor content in the exhaled gas of lung cancer patients is less than 1ppm, so the sensor is required to have excellent recognition performance for 1ppm toluene. Figure 2 As shown, the sensor with optimized film thickness has a higher response value to 1ppm toluene vapor, which can achieve preliminary diagnosis of lung cancer patients.

[0075] The developed sensor showed obvious response to toluene vapor of different concentrations (1ppm, 2ppm, 5ppm, 10ppm, 20ppm, 50ppm, 100ppm) at 140℃, see Figure 3 In addition, the responses of toluene at concentrations of 1ppm, 2ppm, 5ppm, 10ppm, 20ppm, and 50ppm also have good linear relationships.

[0076] The above are only a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Any technician familiar with the profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A toluene vapor detection gas sensor, characterized in that: The toluene vapor detection gas sensor uses porous Co3O4 nanomaterial as a sensitive body; The pore size of the porous Co3O4 nanomaterial is 2 to 10 nm; The length of the porous Co3O4 nanomaterial is 200-200nm, and the width is 50-200nm.

2. The toluene vapor detection gas sensor according to claim 1, characterized in that: The operating temperature of the toluene vapor detection gas sensor is 100-200°C; Preferably, the resistance value of the toluene vapor detection gas sensor is 10 to 200 KΩ; Preferably, the toluene vapor detection gas sensor can detect toluene at a concentration of 1 to 100 ppm.

3. The method for preparing a toluene vapor detection gas sensor according to any one of claims 1 to 2, characterized in that: The preparation method comprises: A solution containing porous Co3O4 nanomaterials is drop-coated on the surface of the ceramic tube interdigital electrode, and infrared baking is performed until the solution is completely volatilized to obtain the toluene vapor detection gas sensor.

4. The preparation method according to claim 3, characterized in that: The solvent in the solution is selected from at least one of water, ethanol, methanol, acetone, acetonitrile, toluene, ethylene glycol, and n-hexane; Preferably, the mass volume ratio of the porous Co3O4 nanomaterial to the solvent is: 2-100 mg: 0.2-10 mL.

5. The preparation method according to claim 3, characterized in that: The temperature of the infrared baking is 40-90°C; Preferably, the number of dripping is 2 to 6 times.

6. The preparation method according to claim 3, characterized in that: The preparation method of the porous Co3O4 nanomaterial comprises: In a sealed container, a mixture containing cobalt compounds, urea and a solvent is reacted and annealed to obtain the porous Co3O4 nanomaterial.

7. The preparation method according to claim 6, characterized in that: The cobalt compound is selected from cobalt chloride and / or cobalt nitrate; Preferably, the molar ratio of the cobalt compound to urea is 1:5-10.

8. The preparation method according to claim 6, characterized in that: The solvent includes water, ethanol and oleic acid; Preferably, the volume ratio of water, ethanol and oleic acid is 15:11:3 to 15:5:

1.

9. The preparation method according to claim 6, characterized in that: The reaction temperature is 160-200° C., and the reaction time is 6-12 hours.

10. The preparation method according to claim 6, characterized in that: The annealing temperature is 300-400° C., and the annealing time is 2-6 hours.

Images