Metal Oxide Semiconductor Porous Thin Film, Its Preparation Method and Gas Sensor

Abstract

The present invention discloses a metal oxide semiconductor porous thin film, a preparation method thereof and a gas sensor. The preparation method includes the steps of continuously heating a provided substrate and maintaining it at a first preset temperature, transferring a first predetermined volume of a metal-organic framework precursor solution onto the substrate, and then performing a first calcination. After cooling, a thin film precursor is prepared on the substrate. Continuously heating the substrate with the thin film precursor on its surface and maintaining it at the first preset temperature, transferring a second predetermined volume of the metal-organic framework precursor solution onto the thin film precursor, and then performing a second calcination to prepare the metal oxide semiconductor porous thin film on the substrate. The preparation method provided by the present invention has a simple preparation process, good film-forming quality, high efficiency, environmental friendliness, low cost, and can achieve continuous large-area production. The obtained thin film has a small contact resistance between oxide particles, excellent electronic conductivity and excellent gas sensing performance.

Description

Technical Field

[0001] The present invention relates to the field of gas sensors, and particularly to a metal oxide semiconductor porous film, a preparation method thereof, and a gas sensor. Background Art

[0002] Gas sensors based on metal oxide semiconductors have advantages such as low cost, simple operation, high sensitivity, and easy integration, and have been widely used in environmental gas monitoring, smart homes, medical diagnosis, etc. Semiconductor gas sensing depends on the adsorption and reaction of gas molecules on the material surface. To improve the sensing performance of metal oxides, it is necessary to precisely control the grain size, morphology, porosity, specific surface area, etc. of metal oxides. Mesoporous oxides have attracted much attention due to their high specific surface area and large pore size (2 - 50 nm). The gas sensing of metal oxides is a solid-gas interface reaction process. Gas molecules diffuse in the pores of the metal oxide film and then react with the oxygen species adsorbed on its surface, thereby causing a change in the conductivity of the material. However, existing preparation processes are difficult to manufacture large-area, highly crystalline metal oxide films with a mesoporous structure. For example, the soft template method creates pore structures by introducing micelles, but the volatilization of a large amount of organic matter seriously pollutes the environment, and the oxides fabricated by the soft template method have a relatively low crystallinity. The hard template method creates pores by introducing mesoporous silica or carbon spheres, and then the template is etched away with hydrofluoric acid or sodium hydroxide. The process is complex and pollutes the environment. The method of preparing mesoporous metal oxide semiconductors by pyrolysis of metal-organic frameworks can replace the above methods.

[0003] However, the existing technology first pyrolyzes metal-organic frameworks to derive metal oxides and then forms films. The process is complex, costly, and the film-forming quality is poor, making it difficult to achieve large-area and batch production. Moreover, the existing metal-organic framework-derived metal oxide materials are mainly microcrystalline powders based on metal-organic frameworks. There are a large number of grain boundary resistances between the derived metal oxide particles, which seriously affect charge transport and result in poor electronic conductivity.

[0004] Therefore, the existing technology still needs to be improved and developed. Summary of the Invention

[0005] In view of the above deficiencies in the prior art, the purpose of the present invention is to provide a metal oxide semiconductor porous film, a preparation method thereof, and a gas sensor, aiming to solve the problems of complex process, poor film-forming quality, and poor electronic conductivity of the film obtained by the existing methods for preparing metal oxide films.

[0006] The technical solution of the present invention is as follows:

[0007] In the first aspect of the present invention, a preparation method of a metal oxide semiconductor porous film is provided, which includes the steps:

[0008] Add a metal salt precursor and an organic ligand to a solvent, and after stirring, obtain a metal-organic framework precursor solution;

[0009] Provide a substrate, continuously heat the substrate and maintain it at a first preset temperature, take a first predetermined volume of the metal-organic framework precursor solution and transfer the first predetermined volume of the metal-organic framework precursor solution onto the substrate, and then perform a first calcination. After cooling, a film precursor is prepared on the substrate;

[0010] Continuously heat the substrate with the film precursor on its surface and maintain it at the first preset temperature, take a second predetermined volume of the metal-organic framework precursor solution and transfer the second predetermined volume of the metal-organic framework precursor solution onto the film precursor, and then perform a second calcination to prepare the metal oxide semiconductor porous film on the substrate.

[0011] Optionally, the metal salt precursor is selected from a zinc salt precursor, a cobalt salt precursor or a copper salt precursor;

[0012] And / or, the organic ligand is selected from an imidazole-based organic ligand or a carboxylic acid-based organic ligand;

[0013] And / or, the solvent is selected from organic solvents;

[0014] And / or, the substrate is selected from one of a glass substrate, a quartz substrate, a silicon substrate, and a ceramic substrate.

[0015] Optionally, the zinc salt precursor is selected from at least one of zinc acetate, zinc nitrate, and zinc chloride;

[0016] And / or, the cobalt salt precursor is selected from at least one of cobalt acetate, cobalt nitrate, and cobalt chloride;

[0017] And / or, the copper salt precursor is selected from at least one of copper acetate, copper sulfate, copper nitrate, and copper chloride.

[0018] Optionally, the imidazole-based organic ligand is selected from at least one of imidazole, 2-methylimidazole, 2-nitroimidazole, and benzimidazole;

[0019] And / or, the carboxylic acid-based organic ligand is selected from at least one of 1,3,5-benzenetricarboxylic acid, 1,4-terephthalic acid, 2,6-dinaphthoic acid, and 4,4'-biphenyldicarboxylic acid.

[0020] Optionally, the organic solvent is selected from methanol or ethanol.

[0021] Optionally, the ratio of the metal salt precursor to the solvent is (0.02 - 0.3) mol: 1 L, and the ratio of the organic ligand to the solvent is (0.04 - 0.6) mol: 1 L.

[0022] Optionally,

[0023] the first preset temperature is 100 to 120 °C;

[0024] and / or, the temperature of the first calcination is 350 to 550 °C, the time of the first calcination is 0.5 to 1 h, and the atmosphere of the first calcination is an air atmosphere or an inert atmosphere;

[0025] and / or, the temperature of the second calcination is 350 to 550 °C, the time of the second calcination is 2 to 5 h, and the atmosphere of the second calcination is an air atmosphere or an inert atmosphere.

[0026] Optionally,

[0027] transfer the first predetermined volume of the metal-organic framework precursor solution to the substrate by a spraying method, a dip coating method or a doctor blade coating method;

[0028] transfer the second predetermined volume of the metal-organic framework precursor solution to the thin film precursor by a spraying method, a dip coating method or a doctor blade coating method.

[0029] In a second aspect of the present invention, there is provided a metal oxide semiconductor porous thin film, which is prepared by using the preparation method of the metal oxide semiconductor porous thin film as described above in the present invention.

[0030] In a third aspect of the present invention, there is provided a gas sensor, which includes a ceramic substrate, an electrode disposed on the ceramic substrate, and the metal oxide semiconductor porous thin film as described above in the present invention disposed on the electrode.

[0031] Beneficial effects: The present invention ingeniously utilizes the permanent voids and film-forming properties of metal-organic framework materials. First, a film is formed and then calcined and derived, and a step-by-step calcination strategy is adopted to prepare a strong, dense, large-area mesoporous metal oxide semiconductor porous film. Specifically, in the first calcination stage, a thinner film is annealed to reduce stress and greatly inhibit the generation of cracks. In the second calcination stage, the second calcination can repair the cracks generated in the first calcination, thereby ensuring the continuity of the overall metal-organic framework material-derived metal oxide semiconductor film. The step-by-step calcination and derivation strategy makes the metal oxide film stronger and denser, and greatly reduces the generation of film cracks. The preparation method provided by the present invention has a simple preparation process, good film-forming quality, high efficiency (the prepared metal oxide semiconductor film has a porous structure, which is naturally generated during the calcination process without additional preparation, making the preparation method provided by the present invention more efficient), is environmentally friendly, has low cost, can realize continuous large-area film production, and is applicable to the film preparation of 4-10 inch wafer-level substrates. More importantly, the prepared metal oxide semiconductor porous film has a small contact resistance between oxide particles and excellent electronic conductivity, and exhibits excellent gas sensing performance. Description of the Drawings

[0032] Figure 1 SEM image of the metal oxide semiconductor porous film in Example 1 of the present invention.

[0033] Figure 2 SEM image of the metal oxide semiconductor porous film in Example 5 of the present invention.

[0034] Figure 3 SEM image of the metal oxide semiconductor porous film in Example 8 of the present invention.

[0035] Figure 4 Test result graph of the acetone gas sensing performance of the gas sensor in Example 12 of the present invention.

[0036] Figure 5 Test result graph of the acetone gas sensing performance of the gas sensor in Example 13 of the present invention.

[0037] Figure 6 Test result graph of the acetone gas sensing performance of the gas sensor in Example 14 of the present invention. Detailed Embodiments

[0038] The present invention provides a metal oxide semiconductor porous film, a preparation method thereof, and a gas sensor. To make the purpose, technical solution, and effects of the present invention clearer and more definite, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this invention belongs. The terms used in the description of this invention herein are for the purpose of describing specific embodiments only and are not intended to limit the invention.

[0040] Metal-organic framework (MOF) materials are a class of crystalline porous materials self-assembled from metal ions / metal clusters and organic ligands, which have advantages such as permanent voids, adjustable pore sizes, modifiable metal sites, and easy synthesis. When the metal-organic framework thin film is calcined in air, the metal ions will turn into metal oxides, and the organic part will turn into gases such as carbon dioxide and volatilize to form a mesoporous structure during the volatilization process. Then, the prior art is to first pyrolyze and derivatize the metal-organic framework material into metal oxides and then form a film. The process is complex, costly, and the film-forming quality is poor. It is difficult to achieve large-area and batch production, and there are a large number of grain boundary resistances between the derived metal oxide particles, which seriously affect charge transport and the electron conductivity is poor. Therefore, the inventors of this invention creatively proposed a method of forming a film first and then calcining and derivatizing to solve the above problems existing in derivatizing first and then forming a film. However, the inventors found in a large number of experimental studies that directly calcining the metal-organic framework thin film will cause stress problems, resulting in the film cracking, which seriously affects charge transport. Specifically, during one-step calcination, the thicker metal-organic framework thin film loses organic ligands at high temperature, the whole film shrinks, and its own stress is difficult to release, generating long cracks, which destroys the integrity and conductivity of the film. Based on this, this invention first proposes a strategy of forming a film first and then stepwise calcining and derivatizing to directly derivatize a large-area and high-quality metal oxide semiconductor porous thin film from the metal-organic framework thin film. Specifically, the embodiments of this invention provide a method for preparing a metal oxide semiconductor porous thin film, which includes the steps:

[0041] S1. Add a metal salt precursor and an organic ligand to a solvent, and after stirring, obtain a metal-organic framework precursor solution;

[0042] S2. Provide a substrate, continuously heat the substrate and maintain it at a first preset temperature, take a first predetermined volume of the metal-organic framework precursor solution and transfer the first predetermined volume of the metal-organic framework precursor solution onto the substrate, and then perform the first calcination. After cooling, a film precursor is prepared on the substrate;

[0043] S3. Continuously heat the substrate with the film precursor on its surface and maintain it at the first preset temperature, take a second predetermined volume of the metal-organic framework precursor solution and transfer the second predetermined volume of the metal-organic framework precursor solution onto the film precursor, and then perform the second calcination to prepare the metal oxide semiconductor porous thin film on the substrate.

[0044] In this embodiment, the inventor ingeniously utilized the permanent voids and easy film-forming characteristics of metal-organic framework materials, first formed a film and then calcined and derived it, and adopted a stepwise calcination strategy to prepare a strong, dense, large-area mesoporous metal oxide semiconductor porous film. Specifically, in the first calcination stage, annealing was performed on a relatively thin film, reducing stress and significantly suppressing the generation of cracks; in the second calcination stage, the second calcination could repair the cracks generated in the first calcination, thereby ensuring the continuity of the overall metal-organic framework-derived metal oxide semiconductor porous film. The stepwise calcination and derivation strategy made the metal oxide porous film stronger and denser, significantly reducing the generation of film cracks. The preparation method provided by the present invention has a simple preparation process, good film-forming quality, high efficiency (the prepared metal oxide semiconductor film has a porous structure, which is naturally generated during the calcination process without additional preparation, making the preparation method provided in this embodiment more efficient), is environmentally friendly, low-cost, can realize continuous large-area film production, and is applicable to the film preparation of 4-10 inch wafer-level substrates. More importantly, the prepared dense and continuous metal oxide semiconductor porous film has a small contact resistance between oxide particles and excellent electron conductivity, showing excellent gas sensing performance.

[0045] After the metal oxide semiconductor porous film is prepared on the substrate by the preparation method provided in this embodiment, the metal oxide semiconductor porous film together with the substrate at its bottom can be directly applied, or the substrate can be peeled off first and then the metal oxide semiconductor porous film can be applied.

[0046] In step S1, in one embodiment, the metal salt precursor is selected from zinc salt precursors, cobalt salt precursors or copper salt precursors, but is not limited thereto.

[0047] In a further embodiment, the zinc salt precursor is selected from at least one of zinc acetate, zinc nitrate, and zinc chloride.

[0048] In a further embodiment, the cobalt salt precursor is selected from at least one of cobalt acetate, cobalt nitrate, and cobalt chloride.

[0049] In a further embodiment, the copper salt precursor is selected from at least one of copper acetate, copper sulfate, copper nitrate, and copper chloride.

[0050] In one embodiment, the organic ligand is selected from imidazole-based organic ligands or carboxylic acid-based organic ligands, but is not limited thereto.

[0051] In a further embodiment, the imidazole-based organic ligand is selected from at least one of imidazole, 2-methylimidazole, 2-nitroimidazole, and benzimidazole, but is not limited thereto.

[0052] In a further embodiment, the carboxylic acid-based organic ligand is selected from at least one of 1,3,5-benzenetricarboxylic acid, 1,4-terephthalic acid, 2,6-dinaphthoic acid, 4,4'-biphenyldicarboxylic acid, but not limited thereto.

[0053] In one embodiment, the solvent is selected from organic solvents, but not limited thereto.

[0054] In a further embodiment, the organic solvent is selected from methanol or ethanol, but not limited thereto.

[0055] In one embodiment, the ratio of the metal salt precursor to the solvent is (0.02 - 0.3) mol: 1 L, and the ratio of the organic ligand to the solvent is (0.04 - 0.6) mol: 1 L.

[0056] In one embodiment, the stirring temperature is room temperature and the stirring time is 1 - 24 h.

[0057] In step S2, in one embodiment, the substrate is selected from one of a glass substrate, a quartz substrate, a silicon substrate, a ceramic substrate, but not limited thereto. These substrates have the characteristics of being easy to process and having low cost. In addition, the preparation method provided in this embodiment is applicable to a wide range of substrates, and a metal oxide semiconductor porous film can be prepared on, including but not limited to, a glass substrate, a quartz substrate, a silicon substrate, a ceramic substrate. Further, a metal oxide semiconductor porous film can be prepared on a large-area wafer-level substrate (such as a quartz wafer substrate).

[0058] In one embodiment, the first preset temperature is 100 - 120 °C. The substrate is continuously heated and maintained at 100 - 120 °C. During this process, the first predetermined volume of the metal-organic framework precursor solution is transferred onto the substrate at 100 - 120 °C. At this temperature, it is beneficial to improve the crystallinity of the metal-organic framework precursor solution during the transfer process onto the substrate.

[0059] In one embodiment, the first predetermined volume of the metal-organic framework precursor solution is transferred onto the substrate by methods including but not limited to spraying, dip coating, or blade coating.

[0060] In one embodiment, a first predetermined volume of the metal-organic framework precursor solution is taken and the first predetermined volume of the metal-organic framework precursor solution is transferred onto the substrate such that each square centimeter of the substrate contains 0.1 - 0.5 mL of the metal-organic framework precursor solution (the areal density of the metal-organic framework precursor solution on the substrate is 0.1 - 0.5 mL / cm 2 ), which can effectively ensure that during the first calcination, the stress is small and the generation of cracks is effectively inhibited.

[0061] In one embodiment, the metal-organic framework precursor solution of the first predetermined volume is transferred onto the substrate at 100-120°C. After the metal-organic framework precursor solution is dried at this temperature, the first calcination is carried out. Of course, other drying methods can also be adopted to shorten the drying time.

[0062] In one embodiment, the temperature of the first calcination is 350-550°C, the time of the first calcination is 0.5-1 h, and the atmosphere of the first calcination is an air atmosphere or an inert atmosphere. During the calcination process, the metal ions in the metal-organic framework will be transformed into metal oxides, while the organic part will be transformed into gases such as carbon dioxide and cause a mesoporous structure during the volatilization process.

[0063] In step S3, in one embodiment, the first preset temperature is 100-120°C. The substrate with the thin film precursor on its surface is continuously heated and maintained at 100-120°C. During this process, the metal-organic framework precursor solution of the second predetermined volume is transferred onto the thin film precursor at 100-120°C. This temperature is beneficial to improving the crystallinity of the metal-organic framework precursor solution during the transfer onto the thin film precursor.

[0064] In one embodiment, the metal-organic framework precursor solution of the second predetermined volume is transferred onto the thin film precursor by methods including but not limited to spraying, dip coating, or doctor blading.

[0065] In one embodiment, the metal-organic framework precursor solution of the second predetermined volume is taken and transferred onto the thin film precursor, so that each square centimeter of the thin film precursor contains 0.1-0.5 mL of the metal-organic framework precursor solution, which can effectively ensure the repair of the cracks generated during the first calcination during the second calcination, make the metal oxide porous film more solid and dense, and improve the continuity and conductivity of the metal oxide semiconductor porous film.

[0066] In one embodiment, the metal-organic framework precursor solution of the second predetermined volume is transferred onto the thin film precursor at 100-120°C. After the metal-organic framework precursor solution is dried at this temperature, the second calcination is carried out. Of course, other drying methods can also be adopted to shorten the drying time.

[0067] In one embodiment, the temperature of the second calcination is 350-550°C, the time of the second calcination is 2-5 h, and the atmosphere of the second calcination is an air atmosphere or an inert atmosphere. During the calcination process, the metal ions in the metal-organic framework will be transformed into metal oxides, while the organic part will be transformed into gases such as carbon dioxide and cause a mesoporous structure during the volatilization process. At the same time, the micro-cracks of the thin film generated during the first calcination are repaired.

[0068] An embodiment of the present invention also provides a metal oxide semiconductor porous film, which is prepared by using the preparation method of the metal oxide semiconductor porous film as described above in the embodiment of the present invention. In this embodiment, the contact resistance between oxide particles in the metal oxide semiconductor porous film is small, and it has excellent electronic conductivity, showing excellent gas sensing performance.

[0069] An embodiment of the present invention also provides a gas sensor, which includes a ceramic substrate, an electrode disposed on the ceramic substrate, and the metal oxide semiconductor porous film described in the embodiment of the present invention disposed on the electrode.

[0070] In one embodiment, the electrode is an interdigital electrode.

[0071] The following will be described in detail through specific examples.

[0072] Example 1

[0073] 12 mmol of zinc acetate was added to 100 mL of methanol, and magnetically stirred at room temperature for 10 min to completely dissolve it to obtain a clear solution. Then, 40 mmol of imidazole was added and magnetically stirred at room temperature for 12 h to obtain a metal-organic framework precursor solution (denoted as ZIF-8 precursor solution);

[0074] 40.5 mL of the ZIF-8 precursor solution was injected into a spray gun with a diameter of 200 μm. The spraying gas was high-purity argon, and the jet pressure was 0.1 MPa. A quartz wafer substrate with a diameter of 4 inches (area of 81 cm 2 ) was placed on a heating table at 100 °C and continuously heated. Then, the distance between the spray gun nozzle and the quartz wafer substrate was controlled to be 10 cm, and the switch was pressed to uniformly spray the ZIF-8 precursor solution on the quartz wafer substrate. After drying, it was calcined at 550 °C for 0.5 h in a nitrogen atmosphere. After cooling, a film precursor was prepared on the quartz wafer substrate with an area of 81 cm 2 ;

[0075] 40.5 mL of the ZIF-8 precursor solution was injected into a spray gun with a diameter of 200 μm. The spraying gas was high-purity argon, and the jet pressure was 0.1 MPa. The quartz wafer substrate with an area of 81 cm 2 containing the film precursor was placed on a heating table at 100 °C and continuously heated. Then, the distance between the spray gun nozzle and the film precursor was controlled to be 10 cm, and the switch was pressed to uniformly spray the ZIF-8 precursor solution on the film precursor. Then, it was calcined at 550 °C for 3 h in a nitrogen atmosphere. After cooling, a ZnO semiconductor porous film was prepared on the quartz wafer substrate with an area of 81 cm 2 ;

[0076] Example 2

[0077] The difference from Example 1 is only that 40 mmol of imidazole in Example 1 is replaced with 40 mmol of 2-methylimidazole.

[0078] Example 3

[0079] The difference from Example 1 is only that 40 mmol of imidazole in Example 1 is replaced with 40 mmol of 2-nitroimidazole.

[0080] Example 4

[0081] The difference from Example 1 is only that 40 mmol of imidazole in Example 1 is replaced with 40 mmol of benzimidazole.

[0082] Example 5

[0083] 10 mmol of cobalt acetate was added to 100 mL of methanol and magnetically stirred at room temperature for 10 min until it was completely dissolved to obtain a clear solution. Then, 40 mmol of 2-methylimidazole was added and the mixture was continuously magnetically stirred at room temperature for 12 h to obtain a metal-organic framework precursor solution (denoted as Co-MOF precursor solution);

[0084] 40.5 mL of the Co-MOF precursor solution was injected into a spray gun with a diameter of 200 μm. The spraying gas was high-purity argon and the jet pressure was 0.1 MPa. A quartz wafer substrate with an area of 81 cm 2 was placed on a heating table at 100 °C and continuously heated. Then, the distance between the spray gun nozzle and the quartz wafer substrate was controlled to be 10 cm. The switch was pressed to uniformly spray the Co-MOF precursor solution on the quartz wafer substrate. After drying, it was calcined in an air atmosphere at 350 °C for 0.5 h. After cooling, a film precursor was prepared on a quartz wafer substrate with an area of 81 cm 2 ;

[0085] 40.5 mL of the Co-MOF precursor solution was injected into a spray gun with a diameter of 200 μm. The spraying gas was high-purity argon and the jet pressure was 0.1 MPa. The above quartz wafer substrate with an area of 81 cm 2 containing the film precursor was placed on a heating table at 100 °C and continuously heated. Then, the distance between the nozzle and the film precursor was controlled to be 10 cm. The switch was pressed to uniformly spray the ZIF-8 precursor solution on the film precursor. After drying, it was calcined in an air atmosphere at 350 °C for 3 h. After cooling, a Co3O4 semiconductor porous film was prepared on a quartz wafer substrate with an area of 81 cm 2 ;

[0086] Example 6

[0087] The difference from Example 5 is only that 40 mmol of 2-methylimidazole in Example 5 is replaced with 40 mmol of 2-nitroimidazole.

[0088] Example 7

[0089] The difference from Example 5 is only that 40 mmol of 2-methylimidazole in Example 5 is replaced by 40 mmol of benzimidazole.

[0090] Example 8

[0091] 12 mmol of copper acetate was added to 100 mL of ethanol and magnetically stirred at room temperature for 10 min to completely dissolve it, obtaining a green solution. Then, 24 mmol of 1,3,5-benzenetricarboxylic acid was added, and the mixture was continuously shaken and ultrasonically treated at room temperature for 10 min to obtain a jelly-like gel. The gel was diluted 5 times with ethanol to obtain a metal-organic framework precursor solution (denoted as Cu-MOF precursor solution);

[0092] 40.5 mL of the Cu-MOF precursor solution was injected into a spray gun with a diameter of 200 μm. The spraying gas was high-purity argon, and the jet pressure was 0.1 MPa. A quartz wafer substrate with an area of 81 cm 2 was placed on a heating table at 100 °C and continuously heated. Then, the distance between the spray gun nozzle and the quartz wafer substrate was controlled to be 10 cm. The switch was pressed, and the Cu-MOF precursor solution was evenly sprayed on the quartz wafer substrate. After drying, it was calcined in an air atmosphere at 350 °C for 0.5 h. After cooling, a film precursor was prepared on a quartz wafer substrate with an area of 81 cm 2 ;

[0093] 40.5 mL of the Cu-MOF precursor solution was injected into a spray gun with a diameter of 200 μm. The spraying gas was high-purity argon, and the jet pressure was 0.1 MPa. The above quartz wafer substrate with an area of 81 cm 2 containing the film precursor was placed on a heating table at 100 °C and continuously heated. Then, the distance between the spray gun nozzle and the film precursor was controlled to be 10 cm. The switch was pressed, and the Cu-MOF precursor solution was evenly sprayed on the film precursor. Then, it was calcined in an air atmosphere at 350 °C for 3 h. After cooling, a CuO semiconductor porous film was prepared on a quartz wafer substrate with an area of 81 cm 2 ;

[0094] Example 9

[0095] The difference from Example 8 is only that 24 mmol of 1,3,5-benzenetricarboxylic acid in Example 8 is replaced by 24 mmol of 1,4-benzenedicarboxylic acid.

[0096] Example 10

[0097] The difference from Example 8 is only that 24 mmol of 1,3,5-benzenetricarboxylic acid in Example 8 is replaced by 24 mmol of 2,6-naphthalenedicarboxylic acid.

[0098] Example 11

[0099] The difference from Example 8 is only that 24 mmol of 1,3,5-benzenetricarboxylic acid in Example 8 is replaced by 24 mmol of 4,4'-biphenyldicarboxylic acid.

[0100] Example 12

[0101] Preparation of the gas sensor:

[0102] On the ceramic substrate, an Ag / Pd interdigital electrode is pre-prepared by screen printing (formed by screen printing the composite of Ag and Pd onto the ceramic substrate and sintered at high temperature, the same hereinafter), the interdigital spacing is 200 μm, and the number of interdigital pairs is 10 pairs;

[0103] Inject a certain volume of the ZIF-8 precursor solution in Example 1 into a spray gun with a diameter of 200 μm. The spraying gas is high-purity argon, and the jet pressure is 0.1 MPa. Place the ceramic substrate with the interdigital electrode on a heating table at 100 °C and heat continuously. Then control the distance between the spray gun nozzle and the ceramic substrate to be 10 cm, press the switch, and evenly spray the ZIF-8 precursor solution on the ceramic substrate so that each cm 2 The ceramic substrate is sprayed with 0.5 mL of the ZIF-8 precursor solution, dried and then calcined at 550 °C for 0.5 h in a nitrogen atmosphere. After cooling, a film precursor is prepared on the ceramic substrate;

[0104] Inject a certain volume of the ZIF-8 precursor solution in Example 1 into a spray gun with a diameter of 200 μm. The spraying gas is high-purity argon, and the jet pressure is 0.1 MPa. Place the above-mentioned ceramic substrate with the film precursor on a heating table at 100 °C and heat continuously. Then control the distance between the spray gun nozzle and the film precursor to be 10 cm, press the switch, and evenly spray the ZIF-8 precursor solution on the film precursor so that each cm 2 The film precursor is sprayed with 0.5 mL of the ZIF-8 precursor solution, dried and then calcined at 550 °C for 3 h in a nitrogen atmosphere. After cooling, a gas sensor is obtained.

[0105] Example 13

[0106] On the ceramic substrate, an Ag / Pd interdigital electrode is pre-prepared by screen printing, the interdigital spacing is 200 μm, and the number of interdigital pairs is 10 pairs;

[0107] Inject a certain volume of the Co-MOF precursor solution in Example 5 into a spray gun with a diameter of 200 μm. The spraying gas is high-purity argon, and the jet pressure is 0.1 MPa. Place the ceramic substrate with interdigital electrodes on a heating table at 100 °C and heat continuously. Then control the distance between the spray gun nozzle and the ceramic substrate to be 10 cm, press the switch, and evenly spray the Co-MOF precursor solution on the ceramic substrate so that per cm 2 0.5 mL of the Co-MOF precursor solution is sprayed on the ceramic substrate, and then it is calcined at 350 °C for 0.5 h in an air atmosphere. After cooling, a thin film precursor is prepared on the ceramic substrate;

[0108] Inject a certain volume of the Co-MOF precursor solution in Example 5 into a spray gun with a diameter of 200 μm. The spraying gas is high-purity argon, and the jet pressure is 0.1 MPa. Place the above-mentioned ceramic substrate with the thin film precursor on a heating table at 100 °C and heat continuously. Then control the distance between the spray gun nozzle and the thin film precursor to be 10 cm, press the switch, and evenly spray the Co-MOF precursor solution on the thin film precursor so that per cm 2 0.5 mL of the Co-MOF precursor solution is sprayed on the thin film precursor, dried, and then calcined at 350 °C for 3 h in an air atmosphere. After cooling, a gas sensor is obtained.

[0109] Example 14

[0110] Pre-prepare Ag / Pd interdigital electrodes on the ceramic substrate by screen printing, with an interdigital spacing of 200 μm and 10 pairs of interdigital electrodes;

[0111] Inject a certain volume of the Cu-MOF precursor solution in Example 8 into a spray gun with a diameter of 200 μm. The spraying gas is high-purity argon, and the jet pressure is 0.1 MPa. Place the ceramic substrate with interdigital electrodes on a heating table at 100 °C and heat continuously. Then control the distance between the spray gun nozzle and the ceramic substrate to be 10 cm, press the switch, and evenly spray the Cu-MOF precursor solution on the ceramic substrate so that per cm 2 0.5 mL of the Cu-MOF precursor solution is sprayed on the ceramic substrate, dried, and then calcined at 350 °C for 0.5 h in an air atmosphere. After cooling, a thin film precursor is prepared on the ceramic substrate;

[0112] Inject a certain volume of the Cu-MOF precursor solution in Example 8 into a spray gun with a diameter of 200 μm and a jet pressure of 0.1 MPa. Place the above-mentioned ceramic substrate with the thin film precursor on a heating table at 100 °C and heat continuously. Then control the distance between the spray gun nozzle and the thin film precursor to be 10 cm, press the switch, and evenly spray the Cu-MOF precursor solution on the thin film precursor so that per cm 2Spray 0.5 mL of the Cu-MOF precursor solution on the thin film. After drying, calcine it at 350 °C for 3 h in an air atmosphere. After cooling, a gas sensor is obtained.

[0113] Testing:

[0114] Perform SEM tests on the ZnO semiconductor porous thin film, Co3O4 semiconductor porous thin film, and CuO semiconductor porous thin film in Examples 1, 5, and 8 respectively. The results are shown in Figure 1 、 2 、and Figure 3 respectively.

[0115] Perform acetone gas sensing performance tests on the gas sensors in Examples 12, 13, and 14 respectively. The results are shown in Figure 4 、 5 、and Figure 6 respectively. It can be seen that the ZnO semiconductor porous thin film, Co3O4 semiconductor porous thin film, and CuO semiconductor porous thin film respond to acetone at a concentration level of 1 ppm, demonstrating excellent acetone gas sensing performance.

[0116] In summary, the present invention provides a metal oxide semiconductor porous thin film, its preparation method, and a gas sensor. The present invention ingeniously utilizes the permanent voids and easy film-forming characteristics of metal-organic framework materials, first forms a film and then calcines and derivatizes it, adopting a stepwise calcination strategy to prepare a strong, dense, large-area mesoporous metal oxide semiconductor porous thin film. Specifically, in the first calcination stage, annealing is performed on a relatively thin film, reducing stress and significantly suppressing the generation of cracks; in the second calcination stage, the second calcination can repair the cracks generated in the first calcination, thereby ensuring the continuity of the overall metal-organic framework-derived metal oxide semiconductor thin film. The stepwise calcination and derivatization strategy makes the metal oxide thin film stronger and denser, significantly reducing the generation of film cracks. The preparation method provided by the present invention has a simple preparation process, good film-forming quality, high efficiency (the prepared metal oxide semiconductor thin film has a porous structure, which is naturally generated during the calcination process without additional preparation, making the preparation method provided in this example more efficient), is environmentally friendly, has low cost, can realize continuous large-area film production, and is suitable for the preparation of thin films on 4-10 inch wafer-level substrates. More importantly, the prepared metal oxide semiconductor porous thin film has a small contact resistance between oxide particles and excellent electronic conductivity, demonstrating excellent gas sensing performance.

[0117] It should be understood that the application of the present invention is not limited to the above examples. For those of ordinary skill in the art, improvements or transformations can be made according to the above description. All such improvements and transformations should fall within the protection scope of the appended claims of the present invention.

Claims

1. A method for preparing a porous metal oxide semiconductor thin film, characterized in that, Including the steps: Adding a metal salt precursor and an organic ligand into a solvent, and after stirring, obtaining a metal-organic framework precursor solution; Providing a substrate, continuously heating the substrate and maintaining it at a first preset temperature, taking a first predetermined volume of the metal-organic framework precursor solution and transferring the first predetermined volume of the metal-organic framework precursor solution onto the substrate, and then performing a first calcination. After cooling, a film precursor is prepared on the substrate; Continuously heating the substrate with the film precursor on its surface and maintaining it at the first preset temperature, taking a second predetermined volume of the metal-organic framework precursor solution and transferring the second predetermined volume of the metal-organic framework precursor solution onto the film precursor, and then performing a second calcination to prepare the metal oxide semiconductor porous film on the substrate; The first preset temperature is 100 - 120 °C; The temperature of the first calcination is 350 - 550 °C, the time of the first calcination is 0.5 - 1 h, and the atmosphere of the first calcination is an air atmosphere or an inert atmosphere; The temperature of the second calcination is 350 - 550 °C, the time of the second calcination is 2 - 5 h, and the atmosphere of the second calcination is an air atmosphere or an inert atmosphere.

2. The preparation method of the metal oxide semiconductor porous thin film according to claim 1, characterized in that, The metal salt precursor is selected from a zinc salt precursor, a cobalt salt precursor or a copper salt precursor; And / or, the organic ligand is selected from an imidazole-based organic ligand or a carboxylic acid-based organic ligand; And / or, the solvent is selected from organic solvents; And / or, the substrate is selected from one of a glass substrate, a quartz substrate, a silicon substrate, and a ceramic substrate.

3. The method for preparing a metal oxide semiconductor porous thin film according to claim 2, wherein The zinc salt precursor is selected from at least one of zinc acetate, zinc nitrate, and zinc chloride; And / or, the cobalt salt precursor is selected from at least one of cobalt acetate, cobalt nitrate, and cobalt chloride; And / or, the copper salt precursor is selected from at least one of copper acetate, copper sulfate, copper nitrate, and copper chloride.

4. The method for preparing a metal oxide semiconductor porous thin film according to claim 2, wherein The imidazole-based organic ligand is selected from at least one of imidazole, 2-methylimidazole, 2-nitroimidazole, and benzimidazole; And / or, the carboxylic acid-based organic ligand is selected from at least one of 1,3,5-benzenetricarboxylic acid, 1,4-benzenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and 4,4'-biphenyldicarboxylic acid.

5. The method for preparing a metal oxide semiconductor porous thin film according to claim 2, wherein The organic solvent is selected from methanol or ethanol.

6. The preparation method of the metal oxide semiconductor porous thin film according to claim 1, characterized in that, The ratio of the metal salt precursor to the solvent is (0.02 - 0.3) mol: 1 L, and the ratio of the organic ligand to the solvent is (0.04 - 0.6) mol: 1 L.

7. The method for preparing a metal oxide semiconductor porous film according to claim 1, characterized in that The first predetermined volume of the metal-organic framework precursor solution is transferred onto the substrate by a spraying method, a dip coating method or a doctor blade method; The second predetermined volume of the metal-organic framework precursor solution is transferred onto the film precursor by a spraying method, a dip coating method or a doctor blade method.

8. A metal oxide semiconductor porous thin film, characterized in that, Prepared by using the method for preparing a metal oxide semiconductor porous film according to any one of claims 1 - 7.

9. A gas sensor, characterized in that, Including a ceramic substrate, an electrode provided on the ceramic substrate, and the metal oxide semiconductor porous film according to claim 8 provided on the electrode.

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