Preparation method and application of cobaltosic oxide / titanium dioxide composite structure carbon monoxide gas sensor

Abstract

The invention relates to the technical field of gas sensors, and provides a preparation method and application of a cobaltosic oxide / titanium dioxide composite structure gas sensor. The gas sensor material provided by the invention comprises cobaltosic oxide and titanium dioxide to form a heterojunction, and has good response to carbon monoxide gas at room temperature. The gas sensor provided by the invention comprises a substrate, a cobaltosic oxide nano prism / titanium dioxide nano rod composite structure layer and an interdigital electrode which are sequentially contacted from bottom to top. Aiming at the problem of difficulty in room-temperature detection of carbon monoxide at present, in-situ growth cobaltosic oxide nano prisms are introduced to the surfaces of titanium dioxide nanorods, response to carbon monoxide is greatly improved at room temperature, and sensitivity to carbon monoxide is effectively improved by modification of precious metal of cobaltosic oxide. The problem of room-temperature detection of carbon monoxide can be well solved. The preparation method provided by the invention is simple in steps, low in cost, high in repeatability and simple and convenient in process, and can be used for large-scale synthesis.

Description

Technical Field

[0001] The present invention relates to the technical field of gas sensors, and provides a preparation method and application of a cobalt tetroxide / titanium dioxide composite structure gas sensor. Background Art

[0002] Carbon monoxide is a colorless and odorless poisonous gas. After entering the human body, carbon monoxide can combine with hemoglobin to form carboxyhemoglobin, thus hindering the combination of hemoglobin and oxygen, causing poisoning and endangering life in severe cases. The incomplete combustion of industrial fuels, vehicle exhaust, etc. will all release a large amount of carbon monoxide. Therefore, effective monitoring of carbon monoxide is very necessary. Metal oxide semiconductor sensors have been widely studied due to their advantages such as low cost, high sensitivity, fast response and recovery. However, a large amount of research work has focused on improving the sensitivity of the sensor and reducing its detection limit, etc., and rarely mentions its working performance at room temperature. For the commercial application of sensors, the two factors of response and sensitivity at room temperature are crucial. Therefore, it is still extremely challenging to prepare a metal oxide semiconductor carbon monoxide gas sensor with response and high sensitivity at room temperature.

[0003] TiO2 is an important wide-bandgap (3.2 eV for anatase and 3.0 eV for rutile) semiconductor functional material. As a common n-type semiconductor oxide material, it has abundant reserves, low price, non-toxic, stable chemical properties, and environmental protection, and many people have widely applied it to the research of gas sensors. However, most TiO2-based gas sensors still have the disadvantages of low sensitivity at room temperature (the optimal working temperature of most TiO2 gas sensors is 100 - 200 °C) and long response and recovery times, which to a certain extent limit their practical applications.

[0004] Therefore, those skilled in the art have proposed a preparation method and application of a cobalt tetroxide / titanium dioxide composite structure carbon monoxide gas sensor to solve the problems raised in the background art. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a preparation method and application of a cobalt tetroxide nanoprism / titanium dioxide nanorod composite structure gas sensor. The gas sensor provided by the present invention has high sensitivity and stable performance at room temperature.

[0006] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0007] A cobalt tetroxide nanorod / titanium dioxide nanorod composite structure gas sensor, which includes a substrate, a cobalt tetroxide nanorod / titanium dioxide nanorod composite structure layer disposed on the surface of the substrate, and interdigital electrodes disposed on the surface of the cobalt tetroxide nanorod / titanium dioxide nanorod composite structure layer from bottom to top; the cobalt tetroxide nanorod / titanium dioxide nanorod composite structure layer is composed of cobalt tetroxide nanorods and titanium dioxide nanorods.

[0008] Preferably, the cobalt tetroxide nanorod / titanium dioxide nanorod composite structure layer includes a titanium dioxide nanorod layer and a cobalt tetroxide nanorod layer on the upper surface of the titanium dioxide nanorod layer;

[0009] Or it includes a silver-modified cobalt tetroxide nanorod layer on the upper surface of the titanium dioxide nanorod layer.

[0010] Preferably, when the cobalt tetroxide nanorod / titanium dioxide nanorod composite structure layer includes a titanium dioxide nanorod layer and a cobalt tetroxide nanorod layer grown on the upper surface of the titanium dioxide nanorod layer, the thickness of the cobalt tetroxide nanorod / titanium dioxide nanorod composite structure layer is 5.51 μm, and the thickness of the cobalt tetroxide nanorod layer is 2.76 μm;

[0011] When the cobalt tetroxide nanorod / titanium dioxide nanorod composite structure layer includes a titanium dioxide nanorod layer and a silver-modified cobalt tetroxide nanorod layer grown on the upper surface of the titanium dioxide nanorod layer, the thickness of the cobalt tetroxide nanorod / titanium dioxide nanorod composite structure layer is 5.43 μm, and the thickness of the silver-modified cobalt tetroxide nanorod layer is 2.15 μm.

[0012] Preferably, the substrate is an FTO substrate; the interdigital electrodes are platinum interdigital electrodes.

[0013] The present invention provides a preparation method for the above gas sensor, including the following steps:

[0014] (1) Prepare a titanium dioxide nanorod thin film on the surface of the substrate by a hydrothermal method and perform the first annealing;

[0015] (2) Grow cobalt tetroxide nanorods or silver-modified cobalt tetroxide nanorods on the titanium dioxide nanorod thin film after the first annealing, and then perform the second annealing to obtain a cobalt tetroxide nanorod / titanium dioxide nanorod composite structure layer or a silver-modified cobalt tetroxide nanorod / titanium dioxide nanorod composite structure layer;

[0016] (3) Prepare interdigitated electrodes on the surface of the cobalt ferrite nanorod / titanium dioxide nanorod composite structure or the silver-modified cobalt ferrite nanorod / titanium dioxide nanorod composite structure layer to obtain a gas sensor based on the cobalt ferrite nanorod / titanium dioxide nanorod composite structure or the silver-modified cobalt ferrite nanorod / titanium dioxide nanorod composite structure layer.

[0017] Preferably, in step (1), the hydrothermal temperature of the hydrothermal method is 150 °C and the hydrothermal time is 8 h; the solvent used in the hydrothermal method is a mixed solvent of water and ethanol.

[0018] Preferably, the first annealing temperature is 400 °C, the time is 20 min, and the annealing atmosphere is air.

[0019] Preferably, in step (2), the method for growing cobalt ferrite nanorods or silver-modified cobalt ferrite is the hydrothermal method; the hydrothermal temperature of the hydrothermal method is 95 °C and the hydrothermal time is 24 h.

[0020] Preferably, the temperature of the second annealing is 450 °C, the time is 240 min, and the annealing atmosphere is air.

[0021] The present invention provides the application of the gas sensor based on the cobalt ferrite nanorod / titanium dioxide nanorod composite structure described in the above solution or the gas sensor based on the silver-modified cobalt ferrite nanorod / titanium dioxide nanorod composite structure prepared by the preparation method described in the above solution in gas testing.

[0022] The present invention provides a gas sensor based on a cobalt ferrite nanorod / titanium dioxide nanorod composite structure, comprising a substrate, a cobalt ferrite nanorod / titanium dioxide nanorod composite structure layer, and interdigitated electrodes that are in contact with each other from bottom to top. The gas sensor provided by the present invention includes a cobalt ferrite nanorod / titanium dioxide nanorod composite structure layer, in which cobalt ferrite and titanium dioxide form a heterojunction, greatly increasing the response to carbon monoxide. The sensor provided by the present invention can be carried out at room temperature, has a high sensitivity to carbon monoxide, and has good selectivity for carbon monoxide.

[0023] The present invention also provides a preparation method for the gas sensor based on the cobalt ferrite nanorod / titanium dioxide nanorod composite structure described in the above solution. The preparation method provided by the present invention has simple steps, low cost, strong operability, low requirements for equipment, and can be used for large-scale synthesis.

[0024] The present invention also provides the application of the gas sensor based on the cobalt ferrite nanorod / titanium dioxide nanorod composite structure described in the above solution in gas detection. The sensor provided by the present invention can be carried out at room temperature, has a high sensitivity to carbon monoxide and good selectivity for the target gas.

[0025] The results of the examples show that when the amount of ethanol in the hydrothermal growth of titanium dioxide nanorods is 2 - 5 ml, the first annealing temperature is 400 °C, the time is 20 min, the temperature of the hydrothermal growth of cobalt tetroxide nanoplates is 95 °C, and the time is 24 h, the resulting gas sensor has a high sensitivity to carbon monoxide at room temperature. Description of the Drawings

[0026] Figure 1 It is the resistance-time change curve of the TiO2 nanorod gas sensor to the response of carbon monoxide in Comparative Example 1;

[0027] Figure 2 It is the surface FESEM image of the Co3O4 / TiO2 composite structure gas sensor in Example 1;

[0028] Figure 3 It is the cross-sectional FESEM image of the Co3O4 / TiO2 composite structure gas sensor in Example 1;

[0029] Figure 4 It is the resistance-time change curve of the Co3O4 / TiO2 composite structure gas sensor to the response of carbon monoxide in Example 1;

[0030] Figure 5 It is the surface FESEM image of the Ag-Co3O4 / TiO2 nanorod composite structure gas sensor in Example 2;

[0031] Figure 6 It is the cross-sectional FESEM image of the Ag-Co3O4 / TiO2 nanorod composite structure gas sensor in Example 2;

[0032] Figure 7 It is the resistance-time change curve of the Ag-Co3O4 / TiO2 nanorod composite structure gas sensor to the response of carbon monoxide in Example 2. Detailed Embodiments

[0033] The present invention provides a cobalt tetroxide nanoprism / titanium dioxide nanorod composite structure gas sensor, including a substrate, a cobalt tetroxide nanoprism / titanium dioxide nanorod composite structure layer disposed on the surface of the substrate, and interdigital electrodes disposed on the surface of the cobalt tetroxide nanoprism / titanium dioxide nanorod composite structure layer.

[0034] The gas sensor provided by the present invention includes a substrate. In the present invention, the substrate is preferably an FTO substrate, and the size of the FTO substrate is preferably 2.5 cm × 2.5 cm; the present invention has no special requirements for the thickness of the FTO substrate, and an FTO substrate well-known to those skilled in the art can be used.

[0035] The gas sensor provided by the present invention includes a cobalt tetroxide nanorod / titanium dioxide nanorod composite structure layer disposed on the upper surface of a substrate. In the present invention, the cobalt tetroxide nanorod / titanium dioxide nanorod composite structure layer is obtained by growing cobalt tetroxide nanorods on the surface of a titanium dioxide nanorod layer. Due to different preparation conditions (which will be specifically described in the subsequent introduction of the preparation method), the cobalt tetroxide nanorod layer varies, and thus the specific structure of the cobalt tetroxide nanorod / titanium dioxide nanorod composite structure layer can be divided into the following two cases:

[0036] I. When growing a cobalt tetroxide nanorod layer on the surface of titanium dioxide nanorods, and the cobalt tetroxide nanorod / titanium dioxide nanorod composite structure layer includes a titanium dioxide nanorod layer and a cobalt tetroxide nanorod layer grown on the upper surface of the titanium dioxide nanorod layer, the thickness of the cobalt tetroxide nanorod / titanium dioxide nanorod composite structure layer is 5.51 μm, and the thickness of the cobalt tetroxide nanorod layer is 2.76 μm;

[0037] II. When growing a silver-modified cobalt tetroxide nanorod layer on the surface of titanium dioxide nanorods, and the silver-modified cobalt tetroxide nanorod / titanium dioxide nanorod composite structure layer includes a titanium dioxide nanorod layer and a silver-modified cobalt tetroxide nanorod layer grown on the upper surface of the titanium dioxide nanorod layer, the thickness of the silver-modified cobalt tetroxide nanorod / titanium dioxide nanorod composite structure layer is 5.56 μm, and the thickness of the silver-modified cobalt tetroxide nanorod layer is 2.47 μm.

[0038] In the present invention, the morphology of the cobalt tetroxide nanorods in the cobalt tetroxide nanorod / titanium dioxide nanorod composite structure layer is defined as a tetragonal prism shape.

[0039] The gas sensor provided by the present invention includes interdigital electrodes disposed on the upper surface of the cobalt tetroxide nanorod / titanium dioxide nanorod composite structure layer. In the present invention, the interdigital electrodes are preferably platinum interdigital electrodes, and the thickness of the interdigital electrodes is preferably 800 - 900 nm.

[0040] The present invention provides a preparation method for the above gas sensor, including the following steps:

[0041] (1) Prepare a titanium dioxide nanorod thin film on the surface of a substrate by a hydrothermal method, and then perform the first annealing;

[0042] (2) Grow cobalt tetroxide nanorods on the titanium dioxide nanorod thin film after the first annealing, and then perform the second annealing to obtain a cobalt tetroxide nanorod / titanium dioxide nanorod composite structure layer;

[0043] (3) A interdigital electrode is prepared on the surface of the cobalt ferrite nanorod / titanium dioxide nanorod composite structure to obtain a cobalt ferrite nanorod / titanium dioxide nanorod composite structure gas sensor.

[0044] In the present invention, a titanium dioxide nanorod thin film is prepared on the surface of a substrate by a hydrothermal method, and then dried and annealed for the first time. In the present invention, the substrate is preferably cleaned and dried before use; the cleaning is preferably carried out successively in ethanol, glass cleaning agent, deionized water, acetone and ethanol.

[0045] In the present invention, the hydrothermal temperature for preparing the titanium dioxide nanorod thin film by the hydrothermal method is preferably 150 °C, and the hydrothermal time is preferably 8 h; the solvent used in the hydrothermal method is preferably water or a mixed solvent of water and ethanol, and the ethanol is preferably anhydrous ethanol. In a specific embodiment of the present invention, the volume of the solvent used in the hydrothermal method is preferably fixed at 30 ml. Specifically, a mixed solvent of 25 - 28 ml of water and 2 - 5 ml of ethanol is used; in the present invention, adding ethanol to the solvent can enhance the condensation kinetics, thereby promoting nucleation and growth and providing more crystal seeds.

[0046] In a specific embodiment of the present invention, the preparation of the titanium dioxide nanorod thin film by the hydrothermal method specifically includes the following steps:

[0047] (a) Mix water, ethanol, concentrated hydrochloric acid and a titanium source to obtain a titanium dioxide precursor solution;

[0048] (b) Place two substrates with the conductive surfaces facing down and lean them against the inner wall of the reaction kettle in a V shape, and transfer the titanium dioxide precursor solution to the reaction kettle for hydrothermal reaction.

[0049] In the present invention, the concentrated hydrochloric acid is used to provide an acidic environment to inhibit the hydrolysis of the titanium source, and the pH value of the acidic environment is specifically 2; the titanium source is preferably tetrabutyl titanate; the volume fraction of the titanium source in the titanium dioxide precursor solution is preferably 1.5% - 5%.

[0050] After the hydrothermal reaction is completed, in the present invention, the substrate with the grown titanium dioxide nanorods is preferably washed and dried successively to obtain a titanium dioxide nanorod thin film on the substrate. In the present invention, the detergent used for washing is preferably deionized water, and the specific washing method is: soak the substrate of the titanium dioxide nanorod thin film in deionized water for 6 h and change the water every 3 h; the drying temperature is preferably 60 - 90 °C.

[0051] After obtaining the titanium dioxide nanorod film, the present invention performs the first annealing on the nanorod film. In the present invention, the temperature of the first annealing is preferably 400 °C, and the time of the first annealing is preferably 20 min. The annealing atmosphere is preferably air. The present invention improves the crystallinity of TiO2 nanorods and the adhesion to FTO through the first annealing.

[0052] After the first annealing is completed, the present invention grows cobalt tetroxide nanorods on the titanium dioxide nanorod film after the first annealing, and then performs the second annealing to obtain a cobalt tetroxide nanorod / titanium dioxide nanorod composite structure layer. In the present invention, the method for growing cobalt tetroxide nanorods is preferably the hydrothermal method; when using the hydrothermal method, the hydrothermal temperature of the hydrothermal method is preferably 95 °C, and the hydrothermal time is preferably 24 h.

[0053] In the present invention, the hydrothermal method for growing cobalt tetroxide nanorods preferably includes the following steps:

[0054] (i) Mix a cobalt source, ammonium fluoride, hexamethylenetetramine, and water to obtain a cobalt tetroxide nanorod precursor solution;

[0055] (ii) Place the titanium dioxide nanorod film surfaces of two substrates with grown titanium dioxide nanorod films facing down and lean them against the inner wall of the reaction kettle in a V shape, and transfer the cobalt tetroxide nanorod precursor solution to the reaction kettle for hydrothermal reaction.

[0056] In the present invention, the cobalt source is preferably cobalt nitrate hexahydrate; the dosage ratio of the cobalt source, ammonium fluoride, hexamethylenetetramine, and water is preferably 0.727 g:0.185 g:0.7 g:50 mL; the water is preferably deionized water. The present invention regulates the cobalt tetroxide nanostructure by adding fluoride ions.

[0057] After the hydrothermal reaction is completed, the present invention takes out the sample with grown cobalt tetroxide nanorod hydrate, and then performs washing and drying in sequence to obtain cobalt tetroxide nanorod hydrate grown on the titanium dioxide nanorod film; the detergent for washing is preferably deionized water; the drying temperature is preferably 60-90 °C.

[0058] In the present invention, the temperature of the second annealing is preferably 450 °C, and the time of the second annealing is preferably 240 min; the annealing atmosphere is preferably air. The present invention dehydrates and converts the cobalt tetroxide nanorod hydrate through the second annealing to obtain crystalline cobalt tetroxide nanorods and enhances the contact between the cobalt tetroxide nanorods and the titanium dioxide nanorods.

[0059] After obtaining the Co₃O₄ nanorod prism / TiO₂ nanorod composite structure layer, the present invention prepares interdigital electrodes on the surface of the Co₃O₄ nanorod prism / TiO₂ nanorod composite structure to obtain a Co₃O₄ nanorod prism / TiO₂ nanorod composite structure gas sensor. The present invention preferably uses DC magnetron sputtering to prepare the interdigital electrodes; the parameters of the DC magnetron sputtering preferably include: the background vacuum degree is 6×10 -4 Pa, the Ar flow rate is 10-20 sccm, the working gas pressure is 0.5-1 Pa, the DC sputtering power is 40-60 W, and the sputtering time is 20 min.

[0060] The present invention also provides the application of the Co₃O₄ nanorod prism precursor / TiO₂ nanorod composite structure gas sensor described in the above solution in gas testing. In the present invention, the gas is specifically carbon monoxide; the temperature of the application is preferably room temperature; the present invention has no special requirements for the specific method of the application, and the application can be carried out according to the methods well-known to those skilled in the art.

[0061] The following is a detailed description of the solution provided by the present invention in combination with the embodiments, but they cannot be understood as a limitation to the protection scope of the present invention.

[0062] Comparative Example 1

[0063] The FTO substrate was leaned against the inner wall of the PTFE of the hydrothermal reactor in a V shape, and the precursor solution prepared from 28 ml of deionized water, 2 ml of absolute ethanol, 30 ml of concentrated hydrochloric acid and 1 ml of tetrabutyl titanate was poured in. TiO₂ nanorod thin films were obtained by hydrothermal reaction at 150 °C for 8 h. After the reactor was cooled to room temperature, the thin films were washed with deionized water, soaked in deionized water for 3 hours, dried at a constant temperature at 60 °C, and annealed in a tube furnace in an air atmosphere at 400 °C for 20 min and then reserved.

[0064] A Pt target with a purity of 99.99% was installed at the cathode target position of the magnetron sputtering system. The distance between the fixed target and the substrate was 60 mm. An interdigital mask was covered on the surface of the titanium dioxide thin film. The mechanical pump and the solenoid valve molecular pump pumping system were respectively turned on. When the background vacuum degree was pumped to 6×10 -4 Pa, the argon flow rate was set to 14.4 sccm, the chamber working gas pressure was maintained at 1 Pa, the DC sputtering power was set to 40 W, and the target was sputtered and coated for 20 min to prepare metal Pt interdigital electrodes.

[0065] The obtained titanium dioxide nanorod thin film gas sensor was tested for carbon monoxide at room temperature, and the obtained results are as Figure 1 shown. According to Figure 1 it can be seen that the obtained gas sensor has a very low response to carbon monoxide.

[0066] Example 1

[0067] The FTO substrate was leaned against the inner wall of the PTFE of the hydrothermal reactor in a V shape, and the precursor solution prepared from 28 ml of deionized water, 2 ml of absolute ethanol, 30 ml of concentrated hydrochloric acid and 1 ml of tetrabutyl titanate was poured in. A titanium dioxide nanorod film was obtained by hydrothermal reaction at 150 °C for 8 h. After the reactor cooled to room temperature, the film was washed with deionized water, soaked in deionized water for 3 hours, dried at a constant temperature at 70 °C, and annealed in a tube furnace in air atmosphere at 400 °C for 20 min and then reserved for use.

[0068] The precursor solution (prepared from 0.727 g of cobalt nitrate hexahydrate, 0.185 g of ammonium fluoride, 0.7 g of hexamethylenetetramine and 50 ml of deionized water) was placed in a beaker. Two pieces of FTO (with the surface of the titanium dioxide nanorod film facing down) were placed in a V shape on the inner wall of the PTFE reactor for a water bath reaction to grow cobalt tetroxide nanoprisms with the titanium dioxide nanorods as the substrate; the hydrothermal reaction was carried out at 95 °C for 24 h. Then the reactor was taken out and cooled to room temperature. The film was washed with deionized water, soaked in deionized water, and after soaking for 3 h, dried at a constant temperature at 60 °C, and annealed in a tube furnace in air atmosphere at 450 °C for 240 min and then reserved for use.

[0069] The Pt target with a purity of 99.99% was installed at the cathode target position of the magnetron sputtering system. The distance between the fixed target and the substrate was 60 mm. An interdigital mask was covered on the surface of the cobalt tetroxide / titanium dioxide film. The mechanical pump and the solenoid valve molecular pump pumping system were turned on respectively. When the background vacuum reached 6×10 -4 Pa, the argon gas flow rate was set to 14.4 sccm, the chamber working pressure was maintained at 1 Pa, the DC sputtering power was set to 40 W, and the target was sputtered for 20 min to deposit a metal Pt interdigital electrode.

[0070] According to Figures 2-3 It can be seen that in Example 1, a cobalt tetroxide / titanium dioxide composite structure was successfully synthesized. The composite structure specifically includes titanium dioxide nanorods and cobalt tetroxide nanoprisms on the titanium dioxide nanorods (i.e., the above-mentioned situation 1), and the thickness of the composite structure is 5.51 μm.

[0071] At room temperature, the obtained cobalt tetroxide / titanium dioxide composite structure gas sensor was detected in a carbon monoxide atmosphere, and the obtained results are as Figure 4 shown. The results show that the sensor has good sensitivity to carbon monoxide, and the sensitivity of the sensor to carbon monoxide is improved compared with the pure titanium dioxide nanorod structure.

[0072] Example 2

[0073] The FTO substrate was leaned against the inner wall of the PTFE hydrothermal reactor in a V shape, and the precursor solution prepared from 25 ml of deionized water, 5 ml of absolute ethanol, 30 ml of concentrated hydrochloric acid, and 1 ml of tetrabutyl titanate was poured in. A titanium dioxide nanorod film was obtained by hydrothermal reaction at 150 °C for 8 h. After the reactor cooled to room temperature, the film was washed with deionized water, soaked in deionized water for 3 hours, dried at a constant temperature at 60 °C, and annealed at 400 °C for 20 min in a tube furnace under an air atmosphere for standby.

[0074] The precursor solution (prepared from 0.727 g of cobalt nitrate hexahydrate, 0.185 g of ammonium fluoride, 0.7 g of hexamethylenetetramine, 221 μL of 0.1% silver nitrate solution, and 50 mL of deionized water) was placed in a PTFE reactor with two pieces of FTO (the side with the titanium dioxide nanorod film facing down) in a V shape on the inner wall for a water bath reaction to grow silver-modified cobalt tetroxide with the titanium dioxide nanorods as the substrate; the hydrothermal reaction was carried out at 95 °C for 24 h, then the reactor was taken out and cooled to room temperature, the film was washed with deionized water, soaked in deionized water, and after soaking for 3 h, dried at a constant temperature at 60 °C, and annealed at 450 °C for 240 min in a tube furnace under an air atmosphere for standby.

[0075] The Pt target with a purity of 99.99% was installed at the cathode target position of the magnetron sputtering system, the distance between the fixed target and the substrate was 60 mm, an interdigital mask was covered on the surface of the silver-modified cobalt tetroxide / titanium dioxide film, the mechanical pump and the solenoid valve molecular pump pumping system were respectively turned on, and when the base vacuum reached 6×10 -4 Pa, the argon gas flow rate was set to 14.4 sccm, the chamber working pressure was maintained at 1 Pa, the DC sputtering power was set to 40 W, and the target was sputtered and coated for 20 min to prepare a metal Pt interdigital electrode.

[0076] The obtained silver-modified cobalt tetroxide / titanium dioxide composite structure gas sensor was detected in a carbon monoxide atmosphere at room temperature, and the obtained results are as Figure 7 shown. The results show that the sensor has a high sensitivity to carbon monoxide at room temperature and has good repeatability.

[0077] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc. means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms are not necessarily directed to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0078] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A cobalt tetroxide / titanium dioxide composite structure carbon monoxide gas sensor, characterized in that: The gas sensor includes, from bottom to top, a substrate, a cobalt tetroxide nanorod / titanium dioxide nanorod composite structure layer disposed on the surface of the substrate, and interdigital electrodes disposed on the surface of the cobalt tetroxide nanorod / titanium dioxide nanorod composite structure layer; the cobalt tetroxide nanorod / titanium dioxide nanorod composite structure layer is composed of cobalt tetroxide nanorods and titanium dioxide nanorods.

2. The cobalt tetroxide / titanium dioxide composite structure carbon monoxide gas sensor according to claim 1, characterized in that: The cobalt tetroxide nanorod / titanium dioxide nanorod composite structure layer includes a titanium dioxide nanorod layer and a cobalt tetroxide nanorod layer grown on the upper surface of the titanium dioxide nanorod layer; or includes a titanium dioxide nanorod layer and a silver-modified cobalt tetroxide nanorod layer grown on the upper surface of the titanium dioxide nanorod layer.

3. The cobalt tetroxide / titanium dioxide composite structure carbon monoxide gas sensor according to claim 1, wherein: When the cobalt tetroxide nanorod / titanium dioxide nanorod composite structure layer includes a titanium dioxide nanorod layer and a cobalt tetroxide nanorod layer grown on the upper surface of the titanium dioxide nanorod layer, the thickness of the cobalt tetroxide nanorod / titanium dioxide nanorod composite structure layer is 5.51 μm, and the thickness of the cobalt tetroxide nanorod layer is 2.76 μm; When the cobalt tetroxide nanorod / titanium dioxide nanorod composite structure layer includes a titanium dioxide nanorod layer and a silver-modified cobalt tetroxide nanorod layer grown on the upper surface of the titanium dioxide nanorod layer, the thickness of the cobalt tetroxide nanorod / titanium dioxide nanorod composite structure layer is 5.43 μm, and the thickness of the silver-modified cobalt tetroxide nanorod layer is 2.15 μm.

4. The cobalt tetroxide / titanium dioxide composite structure carbon monoxide gas sensor according to claim 1, wherein: The substrate is an FTO substrate; the interdigital electrodes are platinum interdigital electrodes.

5. The preparation method of a cobalt tetroxide / titanium dioxide composite structure carbon monoxide gas sensor according to any one of claims 1-4, characterized in that: It includes the following steps: (1) Prepare a titanium dioxide nanorod thin film on the surface of the substrate by hydrothermal method and perform the first annealing; (2) Grow cobalt tetroxide nanorods on the titanium dioxide nanorod thin film after the first annealing and perform the second annealing to obtain a cobalt tetroxide nanorod / titanium dioxide nanorod composite structure layer; (3) Prepare interdigital electrodes on the surface of the cobalt tetroxide nanorod / titanium dioxide nanorod composite structure to obtain a cobalt tetroxide nanorod / titanium dioxide nanorod composite structure gas sensor.

6. The preparation method of a cobalt tetroxide / titanium dioxide composite structure carbon monoxide gas sensor according to claim 5, characterized in that: In the step (1), the hydrothermal temperature of the hydrothermal method is 150 °C, and the hydrothermal time is 8 h; the solvent used in the hydrothermal method is a mixed solvent of water and ethanol.

7. The preparation method of a cobalt tetroxide / titanium dioxide composite structure carbon monoxide gas sensor according to claim 6, characterized in that: The temperature of the first annealing is 400 °C, the time is 20 min, and the annealing atmosphere is air.

8. The preparation method of a cobalt tetroxide / titanium dioxide composite structure carbon monoxide gas sensor according to claim 5, characterized in that: In the step (2), the method for growing cobalt tetroxide nanorods is the hydrothermal method; the hydrothermal temperature of the hydrothermal method is 95 °C, and the hydrothermal time is 24 h.

9. The preparation method and application of a cobalt tetroxide / titanium dioxide composite structure carbon monoxide gas sensor according to claim 8, characterized in that: The temperature of the second annealing is 450 °C, the time is 240 min, and the annealing atmosphere is air.

10. Application of the cobalt tetroxide nanorod / titanium dioxide nanorod composite structure gas sensor according to any one of claims 1 to 4 in gas testing.

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