A TiO2 homogeneous heterogeneous junction film and its preparation method and application, hydrogen sensor

Abstract

The present invention provides a TiO2 heterojunction thin film, a preparation method and application thereof, and a hydrogen sensor, and relates to the technical field of gas sensors. The TiO2 heterojunction thin film of the present invention comprises rutile TiO2 nanopillars and branched anatase TiO2 dispersed on the surface of the rutile TiO2 nanopillars. The branched anatase TiO2 of the present invention grows on the (110) surface of the columnar rutile TiO2 to expose the (101) surface, forming a (110) / (101) heterojunction structure. The hydrogen sensor prepared by the TiO2 heterojunction thin film of the present invention has a sensitivity of 1.28 to 4.87 when detecting a 1ppm H2 concentration at room temperature, having a low detection concentration limit; when detecting a 1200ppm H2 concentration, the sensitivity can reach 85.18, having the characteristics of high sensitivity and excellent long-term stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of gas sensors, and in particular relates to a TiO2 homogeneous heterogeneous junction thin film, a preparation method and application thereof, and a hydrogen sensor. Background Art

[0002] TiO2 has been widely studied due to its low cost, non-toxicity, and simple and convenient fabrication process, and is commonly used in gas sensors. However, single-phase TiO2-based semiconductor gas sensors currently suffer from technical drawbacks such as low sensitivity, long response recovery time, narrow detection range, and high operating temperature. For example, Zhou et al. synthesized a single rutile-phase titanium dioxide nanorod array. The resulting TiO2 gas sensor exhibited a sensitivity of only 2.56 and a response time exceeding 40 seconds at room temperature and a H2 concentration of 1 to 1000 ppm (doi:10.1021 / acsami.8b07816), making it difficult to meet the market's high gas detection requirements.

[0003] To address these shortcomings, existing technologies have sought to improve the sensing properties (sensitivity, selectivity, and response recovery time) of TiO2-based semiconductor gas sensors by constructing TiO2 homojunction structures. For example, Jin et al. synthesized equal amounts of Ni-doped TiO2 nanoparticles in anatase and rutile forms using a coprecipitation method. Ni-doped TiO2 homojunction sensors prepared from these powders were tested for H2 at 600°C (doi:10.3390 / s20215992). Bhowmik et al. prepared p-TiO2 NPs and coated them on n-TiO2 NPs grown by electrochemical anodization. The two formed a stable homojunction, resulting in a high interfacial Schottky barrier. This enhanced the device's sensitivity to ethanol gas and enabled the device to detect ethanol at room temperature (doi:10.1109 / TED.2018.2885360). However, during the long-term operation of the above-mentioned sensor device with a TiO2 homojunction structure, the p-TiO2 NPs sample has poor response selectivity to volatile gases, cannot achieve accurate detection, and has low sensitivity; the Ni-doped TiO2 homojunction operates at a temperature of up to 600°C during hydrogen detection. Long-term high-temperature operation is not conducive to the long-term stability of the sensor device and seriously limits the application range of the sensor device, thereby affecting the sensor device's detection sensitivity to the target gas. Summary of the Invention

[0004] The purpose of the present invention is to provide a TiO2 heterogeneous junction thin film, its preparation method and application, and a hydrogen sensor. The hydrogen sensor device prepared using the TiO2 heterogeneous junction thin film of the present invention has the characteristics of high sensitivity and excellent long-term stability.

[0005] In order to achieve the purpose of the present invention, the present invention provides the following technical solutions:

[0006] A TiO2 isomorphous heterogeneous junction film comprises rutile TiO2 nanocolumns and branched anatase TiO2 dispersed on the surfaces of the rutile TiO2 nanocolumns.

[0007] Preferably, the diameter of the rutile phase TiO2 nanocolumns is 50 to 200 nm, and the length is 1.5 to 4 μm; the length of the branched anatase TiO2 is 0.06 to 0.1 μm.

[0008] The present invention provides a method for preparing the TiO2 homogeneous heterojunction thin film described in the above technical solution, comprising the following steps:

[0009] Placing a substrate in a hydrothermal reaction precursor solution to perform a hydrothermal reaction, and then performing a first annealing treatment to load rutile phase TiO2 nanorods on the substrate surface to obtain a TiO2 isojunction thin film precursor; the hydrothermal reaction precursor solution includes ethanol, hydrochloric acid, a first titanium compound, and water;

[0010] The TiO2 isojunction thin film precursor is placed in an immersion treatment precursor solution for immersion treatment, and then subjected to a second annealing treatment to grow branched anatase TiO2 on the surface of the rutile phase TiO2 nanocolumns, thereby obtaining a TiO2 isojunction thin film on the surface of the substrate; the immersion treatment precursor solution includes boric acid, a second titanium compound and water.

[0011] Preferably, the ethanol content in the hydrothermal reaction precursor solution is 0.0825-8.25wt%, the hydrochloric acid content is 30-65wt%, and the first titanium compound content is 0.8-4.8wt%; the boric acid content in the immersion treatment precursor solution is 1.4-9.8wt%, and the second titanium compound content is 1.4-9.8wt%.

[0012] Preferably, the first titanium compound includes tetrabutyl titanate, titanium tetrachloride or titanium isopropoxide; and the second titanium compound includes ammonium hexafluorotitanate or titanium oxysulfide.

[0013] Preferably, the temperature of the hydrothermal reaction is 120-180° C., and the time is 4-18 hours; the temperature of the immersion treatment is 60-90° C., and the time is 4-12 hours.

[0014] Preferably, the annealing treatment is performed at a temperature of 300 to 500° C. and for a time of 10 to 180 minutes.

[0015] The present invention provides the application of the TiO2 homogeneous heterojunction thin film described in the above technical solution or the TiO2 homogeneous heterojunction thin film prepared by the preparation method described in the above technical solution in hydrogen detection.

[0016] The present invention provides a hydrogen sensor, comprising a substrate, a TiO2 homogeneous heterojunction film and an electrode stacked in sequence; the TiO2 homogeneous heterojunction film is the TiO2 homogeneous heterojunction film described in the above technical solution or a TiO2 homogeneous heterojunction film prepared by the preparation method described in the above technical solution.

[0017] The present invention provides a TiO2 heterojunction film, comprising rutile TiO2 nanopillars and branched anatase TiO2 dispersed on the surface of the rutile TiO2 nanopillars. The branched anatase TiO2 grows on the (110) surface of the columnar rutile TiO2 to expose the (101) surface, forming a (110) / (101) heterojunction structure. Compared with single-phase TiO2, the heterojunction increases the interface adsorption sites and amplifies the carrier concentration barrier modulation effect. On the other hand, after the heterojunction is formed, the Fermi levels of the two crystalline phases of TiO2 at the interface between the branched anatase TiO2 and the columnar rutile TiO2 are balanced, and a continuous band bending and a well-matched lattice are formed at the interface, so that the film has excellent carrier transport and diffusion paths. At the same time, by constructing a branched structure, the specific surface area of ​​the film can be increased, which is beneficial to the diffusion, adsorption and reaction of gases on the surface of the film; and the electrons in the homogeneous heterojunction are transferred from the rutile phase TiO2 nanocolumns to the branched anatase phase TiO2, generating a built-in electric field at the heterojunction interface, and forming a wider depletion layer and charge accumulation layer, thereby obtaining a TiO2 homogeneous heterojunction film with a high resistance value. The strong interaction at the heterojunction interface is beneficial to the adsorption, analysis and desorption of oxygen in the air and the target gas hydrogen. The present invention improves the response sensitivity of the TiO2 homogeneous heterojunction film to gas by changing the Schottky barrier height at the heterojunction interface and then changing the depletion layer width.

[0018] The present invention provides a method for preparing the TiO2 isojunction thin film described in the above technical solution. The present invention vertically grows columnar rutile TiO2 on the surface of a substrate by a hydrothermal method, and then grows branched anatase phase TiO2 on the surface of the columnar rutile TiO2 by an immersion method to construct a TiO2 isojunction thin film of branched anatase phase and columnar rutile phase. The preparation method described in the present invention has the advantages of simple process and low cost.

[0019] The present invention also provides a hydrogen sensor. The results of the embodiments of the present invention show that the gas sensor of the present invention has a sensitivity of 1.28 to 4.87 when detecting a 1 ppm H2 concentration at room temperature, and has a low detection concentration limit; when detecting a 1200 ppm H2 concentration, the sensitivity can reach 85.18, and it has excellent selectivity and stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0021] Figure 1 The structural diagram of TiO2 homogeneous heterojunction film and hydrogen sensor;

[0022] Figure 2 The SEM images of the surfaces and cross sections of the samples obtained in Examples 1 to 4, Comparative Example 1 and Comparative Example 3 are shown;

[0023] Figure 3 The XRD patterns of the samples obtained in Examples 1 to 4, Comparative Example 1 and Comparative Example 2 are shown;

[0024] Figure 4 The Raman spectra of the samples obtained in Examples 1 to 4, Comparative Example 1 and Comparative Example 2 are shown;

[0025] Figure 5 This is the H2 sensing characteristic test diagram of the hydrogen sensor H2-A / R-TiO2-1;

[0026] Figure 6 This is the H2 sensing characteristic test diagram of the hydrogen sensor H2-A / R-TiO2-3;

[0027] Figure 7 This is the H2 sensing characteristic test diagram of the hydrogen sensor H2-A / R-TiO2-5;

[0028] Figure 8 This is the H2 sensing characteristic test diagram of the hydrogen sensor H2-A / R-TiO2-7;

[0029] Figure 9 This is the H2 sensing characteristic test diagram of the hydrogen sensor H2-A / R-TiO2-9;

[0030] Figure 10 This is the H2 sensing characteristic test diagram of the hydrogen sensor H2-R-TiO2;

[0031] Figure 11 This is a comparison chart of the response sensitivity of the hydrogen sensor described in Application Example 1 when the H2 concentration range is 1 to 1600 ppm;

[0032] Figure 12 This is a comparison chart of the response time of the hydrogen sensor described in Application Example 1 when the H2 concentration range is 1 to 1600 ppm;

[0033] Figure 13This is the long-term stability test chart of the hydrogen sensor H2-A / R-TiO2-5. DETAILED DESCRIPTION

[0034] The present invention provides a TiO2 isomorphous heterogeneous junction thin film, comprising rutile phase TiO2 nanocolumns and branched anatase TiO2 dispersed on the surface of the rutile phase TiO2 nanocolumns.

[0035] In the present invention, the diameter of the rutile phase TiO2 nanocolumns is preferably 50-200 nm, more preferably 100-120 nm; the length is preferably 1.5-4.5 μm, more preferably 2.9 μm; the length of the branched anatase TiO2 is preferably 0.06-0.1 μm, more preferably 0.08 μm.

[0036] In the present invention, the thickness of the TiO2 heterojunction thin film is preferably 1.5 to 4.5 μm, more preferably 2.9 μm.

[0037] The present invention provides a method for preparing the TiO2 homogeneous heterojunction thin film described in the above technical solution, comprising the following steps:

[0038] Placing a substrate in a hydrothermal reaction precursor solution to perform a hydrothermal reaction, and then performing a first annealing treatment to load rutile phase TiO2 nanorods on the substrate surface to obtain a TiO2 isojunction thin film precursor; the hydrothermal reaction precursor solution includes ethanol, hydrochloric acid, a first titanium compound, and water;

[0039] The TiO2 isojunction thin film precursor is placed in an immersion treatment precursor solution for immersion treatment, and then subjected to a second annealing treatment to grow branched anatase TiO2 on the surface of the rutile phase TiO2 nanocolumns, thereby obtaining a TiO2 isojunction thin film on the surface of the substrate; the immersion treatment precursor solution includes boric acid, a second titanium compound and water.

[0040] In the present invention, unless otherwise specified, all preparation raw materials are preferably commercially available products.

[0041] The present invention places a substrate in a hydrothermal reaction precursor solution to undergo a hydrothermal reaction, followed by a first annealing treatment to load rutile TiO2 nanorods on the substrate surface, thereby obtaining a TiO2 homogeneous heterogeneous junction thin film precursor. In the present invention, the substrate is preferably a fluorine-doped tin oxide substrate (FTO) or an indium tin oxide substrate (ITO).

[0042] In the present invention, the hydrothermal reaction precursor solution comprises ethanol, hydrochloric acid, a first titanium compound, and water. In the present invention, the content of ethanol in the hydrothermal reaction precursor solution is preferably 0.0825 to 8.25 wt %, more preferably 3.3 wt %. In the present invention, the ethanol is preferably anhydrous ethanol, and the purity of the anhydrous ethanol (analytical grade) is preferably ≥99.7%. In the present invention, the addition of the ethanol can increase the condensation kinetics during the reaction, promote the nucleation and growth of rutile phase TiO2, and provide more seed crystals.

[0043] In the present invention, the hydrochloric acid content in the hydrothermal reaction precursor solution is preferably 30-65 wt %, more preferably 49 wt %. In the present invention, the mass fraction of the hydrochloric acid (analytical grade) is preferably 36-38 wt %, more preferably 37 wt %. In the present invention, the hydrochloric acid is used to provide an acidic environment and inhibit the hydrolysis of the first titanium compound, such as tetrabutyl titanate.

[0044] In the present invention, the content of the first titanium compound in the hydrothermal reaction precursor solution is preferably 0.8-4.8 wt%, more preferably 1.6 wt%. In the present invention, the first titanium compound preferably comprises tetrabutyl titanate, titanium tetrachloride, or titanium isopropoxide, more preferably tetrabutyl titanate. In the present invention, the purity of the tetrabutyl titanate is preferably ≥99.0%. In the present invention, the water is preferably deionized water.

[0045] In the present invention, the conductive surface of the substrate is preferably immersed in a hydrothermal reaction precursor solution to undergo a hydrothermal reaction, followed by a first annealing treatment, so that the conductive surface of the substrate is loaded with rutile TiO2 nanopillars. In the present invention, the substrate is preferably ultrasonically cleaned using ethanol, glass cleaner, deionized water, and acetone in that order before use.

[0046] In the present invention, the hydrothermal reaction temperature is preferably 120-180°C, more preferably 150-160°C, and the reaction time is preferably 4-18 hours, more preferably 8-12 hours. During the hydrothermal reaction of the present invention, the first titanium compound is first hydrolyzed, and then dehydration polymerization and dealcoholization polymerization are carried out on the conductive surface of the FTO substrate to grow columnar rutile titanium dioxide, so that the substrate surface is loaded with rutile phase TiO2 nanocolumns.

[0047] In the present invention, after the hydrothermal reaction, the hydrothermal reaction product is preferably cooled, cleaned and dried in sequence, and then subjected to a first annealing treatment. The present invention does not specifically limit the cooling method of the hydrothermal reaction product, and cooling to room temperature is sufficient. In the present invention, the cleaning is preferably performed by ultrapure water; the drying is preferably performed by natural air drying. In the present invention, the temperature of the first annealing treatment is preferably 300-500°C, more preferably 400°C; the time is preferably 10-180 minutes, more preferably 20-60 minutes. In the present invention, the first annealing treatment is preferably performed in an air atmosphere. The first annealing treatment of the present invention can improve the crystallinity of the rutile phase TiO2 nanocolumns, thereby improving the gas-sensing performance of the device; at the same time, annealing reduces surface stress, so that the TiO2 isojunction thin film precursor is better bonded to the FTO substrate.

[0048] After obtaining the TiO2 isojunction thin film precursor, the present invention places the TiO2 isojunction thin film precursor in an immersion treatment precursor solution for immersion treatment, and then undergoes a second annealing treatment to grow branched anatase TiO2 on the surface of the rutile phase TiO2 nanocolumns, thereby obtaining a TiO2 isojunction thin film on the surface of the substrate.

[0049] In the present invention, the impregnation precursor solution comprises boric acid, a second titanium compound, and water. The boric acid content in the impregnation precursor solution is preferably 1.4 to 9.8 wt%, more preferably 7 wt%. The boric acid concentration is preferably 1 to 8% w / v, more preferably 4% w / v. Boric acid regulates the crystalline morphology of anatase-phase titanium dioxide.

[0050] In the present invention, the content of the second titanium compound in the immersion treatment precursor solution is preferably 0.5-2%, more preferably 1%. In the present invention, the second titanium compound preferably comprises ammonium hexafluorotitanate or titanium oxysulfide, more preferably ammonium hexafluorotitanate. In the present invention, the purity of the ammonium hexafluorotitanate is preferably 98%.

[0051] In the present invention, the impregnation treatment temperature is preferably 60-90°C, more preferably 70-80°C, and the time is preferably 4-12 hours, more preferably 8-10 hours. The impregnation process of the present invention can promote ligand replacement between the titanium ions in the second titanium compound and water molecules, accelerate the reaction between boric acid and free fluoride ions, and thus drive the hydrolysis rate to accelerate the synthesis of anatase TiO2.

[0052] In the present invention, after the impregnation treatment, the impregnation treatment product is preferably cooled, cleaned and dried in sequence, and then subjected to a second annealing treatment. In the present invention, the cooling, cleaning and drying methods are preferably consistent with the above-mentioned cooling, cleaning and drying methods, and are not repeated here. In the present invention, the temperature of the second annealing treatment is preferably 300-500°C, more preferably 400°C; the time is preferably 10-180min, more preferably 60-120min. In the present invention, the second annealing treatment is preferably carried out in an air atmosphere. The second annealing treatment of the present invention can keep the anatase phase from undergoing phase transformation, while removing residual boron and fluoride ion impurities on the surface of the TiO2 isojunction film, improving the crystallinity, and reducing the number of oxygen defects.

[0053] The present invention provides the application of the TiO2 homogeneous heterojunction thin film described in the above technical solution or the TiO2 homogeneous heterojunction thin film prepared by the preparation method described in the above technical solution in hydrogen detection.

[0054] In the present invention, a hydrogen sensor is preferably used to detect hydrogen.

[0055] The present invention provides a hydrogen sensor, comprising a substrate, a TiO2 homogeneous heterojunction film and an electrode stacked in sequence; the TiO2 homogeneous heterojunction film is the TiO2 homogeneous heterojunction film described in the above technical solution or a TiO2 homogeneous heterojunction film prepared by the preparation method described in the above technical solution.

[0056] The hydrogen sensor provided by the present invention includes a substrate, which is preferably consistent with the above-mentioned substrate.

[0057] The hydrogen sensor provided by the present invention comprises a TiO2 heterojunction thin film disposed on a substrate surface. In the present invention, the TiO2 heterojunction thin film is preferably the same as the TiO2 heterojunction thin film described above.

[0058] The hydrogen sensor provided by the present invention includes an electrode disposed on the surface of a TiO2 homogeneous heterojunction thin film. In the present invention, the electrode is preferably an interdigitated electrode; the electrode is preferably a Pt electrode, a silver electrode, or an Al electrode, and more preferably a Pt electrode.

[0059] The method for preparing the hydrogen sensor of the present invention preferably includes the following steps:

[0060] The hydrogen sensor is obtained by preparing an electrode on the surface of the TiO2 homogeneous heterojunction film on a substrate loaded with the TiO2 homogeneous heterojunction film by a magnetron sputtering method.

[0061] In the present invention, the magnetron sputtering method preferably includes: installing an electrode target material at the cathode target position of the magnetron sputtering system, setting the distance between the electrode target material and the substrate, and fixing an interdigitated electrode mask on the thin surface of the TiO2 isojunction film; respectively opening the mechanical pump, solenoid valve, and molecular pump pumping system to vacuum the chamber, and then introducing argon gas to maintain the working pressure of the chamber, sputtering the electrode target material, preparing an electrode on the surface of the TiO2 isojunction film, and obtaining the hydrogen sensor.

[0062] In the present invention, the purity of the electrode target material is preferably 99.99%.

[0063] In the present invention, the distance between the electrode target and the substrate is preferably 80 to 120 mm, more preferably 100 mm.

[0064] In the present invention, the vacuum degree of the chamber is preferably evacuated to 6.0×10 -4 Pa~6.9×10 -4 Pa, more preferably to 6.6×10 -4 Pa.

[0065] In the present invention, the flow rate of the argon gas is preferably 14-15 sccm, more preferably 14.4 sccm.

[0066] In the present invention, the chamber working pressure is preferably 0.3-1 Pa, more preferably 0.5 Pa.

[0067] In the present invention, the sputtering power is preferably 36 to 44 W, more preferably 40 W; and the sputtering time is preferably 5 to 20 min.

[0068] In order to further illustrate the present invention, the TiO2 isojunction thin film provided by the present invention is described in detail below with reference to the accompanying drawings and examples, but they should not be construed as limiting the scope of protection of the present invention.

[0069] The parameters for preparing the raw materials described in the following implementation of the present invention are as follows:

[0070] Anhydrous ethanol: analytical grade ≥99.7%;

[0071] Hydrochloric acid: analytical grade 36-38%;

[0072] Tetrabutyl titanate: ≥99.0%;

[0073] Boric acid solution: concentration 4% w / v;

[0074] Ammonium hexafluorotitanate: chemically pure 98%;

[0075] Glycerol: purity ≥99.5%;

[0076] Titanium oxysulfide: Ti (as TiO2) basis, purity ≥ 29%.

[0077] Example 1

[0078] The FTO substrate was cleaned with ethanol, glass cleaner, deionized water and acetone in sequence under ultrasonic conditions, and then dried in an oven at 60°C to obtain a pretreated FTO substrate;

[0079] 28 mL of deionized water, 2 mL of anhydrous ethanol, 30 mL of hydrochloric acid and 1 mL of tetrabutyl titanate were mixed to obtain a hydrothermal reaction precursor solution; the two pretreated FTO substrates were placed with the conductive surface facing down in a "V" shape against the inner lining wall of a polytetrafluoroethylene-lined hydrothermal reactor containing the hydrothermal reaction precursor solution, the pretreated FTO substrates were immersed in the hydrothermal reaction precursor solution, and the hydrothermal reaction was carried out at 150° C. for 8 hours. After cooling, the FTO substrates after the hydrothermal reaction were washed with ultrapure water in turn and naturally air-dried, and then a first annealing treatment was carried out in an air atmosphere at 400° C. for 20 minutes to load rutile phase TiO2 nanorods (R-TiO2) on the substrate surface, and a TiO2 isojunction thin film precursor was obtained on the substrate surface, which was recorded as an R-TiO2 thin film precursor;

[0080] 60mL of deionized water, 1mL of boric acid solution and 0.26g of ammonium hexafluorotitanate are mixed to obtain an immersion treatment precursor solution; a substrate loaded with the above-mentioned R-TiO2 thin film precursor is tilted against the inner lining wall of a beaker containing the immersion treatment precursor solution, so that the above-mentioned R-TiO2 thin film precursor is immersed in the immersion treatment precursor solution; the immersion treatment is carried out at 80°C for 8h, and after cooling, the immersion-treated film is washed with ultrapure water, soaked and naturally air-dried, and then a second annealing treatment is carried out in an air atmosphere at 500°C for 120min to grow branched anatase TiO2 (A-TiO2) on the surface of the rutile phase TiO2 nanocolumns, and a TiO2 isojunction thin film is obtained on the surface of the substrate, which is recorded as A / R-TiO2-1. The structure of the TiO2 isojunction thin film is shown in FIG. Figure 1 As shown in (b) in .

[0081] Example 2

[0082] A TiO2 heterojunction thin film was prepared by referring to the preparation method of Example 1, except that the amount of boric acid solution used was 3 mL. The obtained TiO2 heterojunction thin film was recorded as A / R-TiO2-3.

[0083] Example 3

[0084] A TiO2 heterojunction thin film was prepared by referring to the preparation method described in Example 1, except that the amount of boric acid solution used was 5 mL. The obtained TiO2 heterojunction thin film was recorded as A / R-TiO2-5.

[0085] Example 4

[0086] A TiO2 heterojunction thin film was prepared by referring to the preparation method described in Example 1, except that the amount of boric acid solution used was 7 mL. The obtained TiO2 heterojunction thin film was recorded as A / R-TiO2-7.

[0087] Comparative Example 1

[0088] The FTO substrate was cleaned with ethanol, glass cleaner, deionized water and acetone in sequence under ultrasonic conditions, and then dried in an oven at 60°C to obtain a pretreated FTO substrate;

[0089] Mix 28 mL of deionized water, 2 mL of anhydrous ethanol, 30 mL of hydrochloric acid and 1 mL of tetrabutyl titanate to obtain a hydrothermal reaction precursor solution; place the two pretreated FTO substrates with their conductive surfaces facing down in a "V" shape against the inner lining wall of a polytetrafluoroethylene-lined hydrothermal reactor containing the hydrothermal reaction precursor solution, immerse the pretreated FTO substrates in the hydrothermal reaction precursor solution, and keep them warm at 150°C for 8 hours for a hydrothermal reaction. After cooling, take out the FTO substrates after the hydrothermal reaction, wash and soak them with ultrapure water, and air-dry them naturally to obtain a thin film sample; subject the thin film sample to a first annealing treatment in an air atmosphere at 400°C for 20 minutes to load rutile phase TiO2 nanocolumns on the substrate surface, and obtain a rutile phase TiO2 thin film on the substrate surface, which is recorded as R-TiO2.

[0090] Comparative Example 2

[0091] 60 mL of deionized water, 1 mL of boric acid solution, and 0.26 g of ammonium hexafluorotitanate were mixed to obtain an impregnation precursor solution. The solution was kept warm at 80°C for 8 h. After cooling, the impregnation solution was filtered to obtain a white powder. The powder was washed three times by centrifugation with ultrapure water, dried in an oven at 60°C, and then annealed in air at 500°C for 120 min to obtain anatase phase TiO2 powder, which was designated as A-TiO2.

[0092] Comparative Example 3

[0093] The FTO substrate was cleaned with ethanol, glass cleaner, deionized water and acetone in sequence under ultrasonic conditions, and then dried in an oven at 60°C to obtain a pretreated FTO substrate;

[0094] 28 mL of deionized water, 2 mL of anhydrous ethanol, 30 mL of hydrochloric acid and 1 mL of tetrabutyl titanate were mixed to obtain a first hydrothermal reaction precursor solution; the two pretreated FTO substrates were placed with the conductive surface facing down in a "V" shape against the inner lining wall of a polytetrafluoroethylene-lined hydrothermal reactor containing the hydrothermal reaction precursor solution, the pretreated FTO substrates were immersed in the hydrothermal reaction precursor solution, and the hydrothermal reaction was carried out at 150° C. for 8 hours. After cooling, the FTO substrates after the hydrothermal reaction were washed with ultrapure water, soaked and naturally air-dried, and then subjected to a first annealing treatment in an air atmosphere at 400° C. for 20 minutes to load rutile phase TiO2 nanocolumns on the substrate surface, and a TiO2 isojunction thin film precursor was obtained on the substrate surface, which was recorded as R-TiO2 thin film precursor;

[0095] Mix 12mL of deionized water, 20mL of anhydrous ethanol, 6mL of glycerol and 0.22g of titanium oxysulfide to obtain a second hydrothermal reaction precursor solution; tilt the substrate loaded with the above-mentioned R-TiO2 thin film precursor against the inner lining wall of the beaker containing the second hydrothermal reaction precursor solution, and immerse the above-mentioned R-TiO2 thin film precursor in the second hydrothermal reaction precursor solution; carry out a second hydrothermal reaction at 180°C for 9h, and after cooling, wash the film after the second hydrothermal reaction with ultrapure water, soak it and air-dry it naturally, and then perform a second annealing treatment in an air atmosphere at 400°C for 20min to grow branched anatase TiO2 on the surface of the rutile phase TiO2 nanocolumns to obtain a wrapped TiO2 isojunction thin film.

[0096] Comparative Example 4

[0097] A TiO2 heterojunction thin film was prepared by referring to the preparation method described in Example 1, except that the amount of boric acid solution used was 9 mL. The obtained TiO2 heterojunction thin film was recorded as A / R-TiO2-9.

[0098] Application Examples

[0099] 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 target and the FTO substrate was fixed at 100 mm. An interdigital electrode mask was fixed on the thin surface of the TiO2 isomorphous and heterogeneous junction film. The mechanical pump, solenoid valve, and molecular pump were opened to evacuate the chamber. The vacuum was pumped to 6.6×10 -4Pa, argon gas is introduced (the argon flow rate is set to 14.4 sccm), the chamber working pressure is maintained at 0.5 Pa, the DC sputtering power is set to 40 W, the Pt target is sputtered for 5 minutes, and a metal Pt interdigital electrode is prepared on the surface of the TiO2 heterogeneous junction film to obtain the hydrogen sensor. In this application example, the TiO2 heterogeneous junction films are the TiO2 heterogeneous junction films described in Examples 1 to 4 and Comparative Example 4, and the rutile phase TiO2 film described in Comparative Example 1. The hydrogen sensors finally obtained are respectively recorded as H2-A / R-TiO2-1, H2-A / R-TiO2-3, H2-A / R-TiO2-5, H2-A / R-TiO2-7, H2-A / R-TiO2-9 and H2-R-TiO2; the structural diagram of the hydrogen sensor is shown in FIG. Figure 1 As shown in (a) in .

[0100] Test Example 1

[0101] The surfaces, cross-sections, and structures of the TiO2 isojunction films described in Examples 1 to 4 and the rutile phase TiO2 films described in Comparative Examples 1 and 3 were characterized, and the results are shown below.

[0102] Figure 2 SEM images of the surface and cross-section of the samples obtained in Examples 1 to 4, Comparative Example 1 (R-TiO2), and Comparative Example 3 (wrapped type); Figure 2 a, b, c, d, and e are surface SEM images of R-TiO2, A / R-TiO2-1, A / R-TiO2-3, A / R-TiO2-5, and A / R-TiO2-7, respectively; g and h are cross-sectional SEM images of R-TiO2 and A / R-TiO2-5, respectively; f is a surface SEM image of the wrapped TiO2 heterojunction film described in Comparative Example 3; i is a cross-sectional SEM image of the wrapped TiO2 heterojunction film described in Comparative Example 3, Figure 2 The R-TiO2 grows vertically on the FTO substrate, forming columnar nanorods approximately 2.9 μm in height. After immersion treatment, the sides of the nanorods are covered with flaky, branched A-TiO2, revealing a distinct hierarchical structure, demonstrating the successful construction of an A / R-TiO2 heterojunction. Furthermore, as the amount of boric acid increases from 1 to 5 mL, the branched A-TiO2 growing on the sides of the R-TiO2 gradually becomes denser. At 7 mL of boric acid, the branched A-TiO2 grows atop the columnar R-TiO2, forming a dense dendritic layer on the surface.

[0103] Figure 3 The XRD patterns of the samples obtained in Examples 1 to 4, Comparative Example 1 (R-TiO2), and Comparative Example 2 (A-TiO2) are shown in FIG. Figure 3It can be seen that, except for the peak of FTO, all other peaks correspond to the standard card of rutile tetragonal system (JCPDS No. 21-1276) and the standard card of anatase tetragonal system (JCPDS No. 21-1272). The peak appearing at 2θ = 25.6° corresponds to the (101) plane of the anatase phase, and the peaks appearing at 2θ = 36.1° and 62.7° correspond to the (101) and (002) planes of the rutile phase. With the increase of the amount of boric acid, the intensity of the diffraction peak relative to the (101) plane of the anatase phase gradually increases, which is consistent with the SEM test results.

[0104] Figure 4 The Raman spectra of the samples obtained in Examples 1 to 4, Comparative Example 1 (R-TiO2), and Comparative Example 2 (A-TiO2) are shown below. Figure 4 It can be seen that in the Raman spectrum of R-TiO2 film, the -1 The Raman peak at corresponds to E g Vibration mode, located at 608cm -1 The Raman peak at corresponds to A 1g Vibration mode; and located at 239cm -1 The broad band hump at 143 cm is mainly due to the large difference in lattice disorder within rutile. Compared with R-TiO2, R / A-TiO2 has a broad band hump at 143 cm -1 The peaks at are all E of R-TiO2 g The results show that the present invention successfully prepared a TiO2 isojunction film with branched anatase TiO2 dispersed on the surface of the rutile phase TiO2 nanorods.

[0105] Test Example 2

[0106] The sensing characteristics of the hydrogen sensor described in Example 1 were tested for response curves of different hydrogen concentrations under a relative humidity of 40% and room temperature (25° C.). The results are shown below.

[0107] Figure 5 This is the H2 sensing characteristic test diagram of the sensor H2-A / R-TiO2-1. Figure 6 This is the H2 sensing characteristic test diagram of the sensor H2-A / R-TiO2-3. Figure 7 This is the H2 sensing characteristic test diagram of the sensor H2-A / R-TiO2-5. Figure 8 This is the H2 sensing characteristic test diagram of the sensor H2-A / R-TiO2-7. Figure 9 This is the H2 sensing characteristic test diagram of the sensor H2-A / R-TiO2-9. Figure 10 This is the H2 sensing characteristic test diagram of the sensor H2-R-TiO2. Figures 5-10It can be seen that the initial resistance of single-phase H2-R-TiO2 is only about 3KΩ. After the preparation of the homogeneous heterojunction, as the amount of boric acid increases, the initial resistance first increases and then decreases. When the amount of boric acid is 9mL, the initial resistance of H2-A / R-TiO2-9 described in Comparative Example 4 is even lower than that of single-phase H2-R-TiO2. Figure 2 The SEM images have a consistent structure. As the number of heterojunctions increases, the resistance increases. When the surface is completely covered with anatase TiO2, the resistance decreases. Figure 5 It shows that the initial resistance value of sample H2-A / R-TiO2-1 cannot be restored at high concentration. Figure 6 It can be seen that the recovery time of the H2-A / R-TiO2-3 sample increases after 400ppm, while the responses of the H2-A / R-TiO2-7 and H2-A / R-TiO2-9 samples reach saturation and low response at a hydrogen concentration of 800ppm. Compared with the R-TiO2 sample, the hydrogen detection range of the homogeneous heterojunction samples is increased to 1600ppm, and the hydrogen sensitivity performance is greatly improved. Among them, the H2-A / R-TiO2-5 sample has the best performance.

[0108] The response sensitivity of the hydrogen sensor described in Example 1 was tested in the H2 concentration range of 1 to 1600 ppm, and the results are shown below.

[0109] Figure 11 This is a comparison chart of the response sensitivity of the hydrogen sensor described in Application Example 1 when the H2 concentration range is 1 to 1600 ppm. Figure 11 It can be seen that the maximum detection limit of the H2-R-TiO2 sample is 1200ppm, while the detection range of the hydrogen sensor with homogeneous heterogeneous junction prepared by the present invention is increased to 1600ppm, and it has a higher response at each concentration point. For H2-A / R-TiO2-1, H2-A / R-TiO2-3 and H2-A / R-TiO2-7 sensors, the response sensitivity of the H2-A / R-TiO2-5 sensor is improved by orders of magnitude.

[0110] The response time of the hydrogen sensor described in Example 1 was tested when the H2 concentration range was 1 to 1600 ppm. The results are shown below.

[0111] Figure 12 This is a comparison chart of the response time of the hydrogen sensor described in Application Example 1 when the H2 concentration range is 1 to 1600 ppm. Figure 12 It can be seen that H2-A / R-TiO2-5 has the fastest response time, which is 6.5s and 9.0s at hydrogen concentrations of 100ppm and 800ppm, respectively, while the response time of H2-R-TiO2 is 9.4s and 20.8s at concentrations of 100ppm and 800ppm, respectively.

[0112] After H2-A / R-TiO2-5 was placed at 25±2℃ for 60 days, the sensing characteristics were tested at H2 concentrations of 200ppm, 400ppm and 1200ppm, and the results are shown below.

[0113] Figure 13 This is the long-term stability test diagram of the hydrogen sensor H2-A / R-TiO2-5, as shown in Figure 13 As shown in the figure, at a H2 concentration of 200 ppm, the average sensitivity is 11.79, at 400 ppm it is 19.32, and at a 1200 ppm H2 atmosphere it is 78.61, which are very close to the initial sensitivities (11.83, 23.02, and 85.18) measured in the same environment. Moreover, the response of the sensor after three cycles at a single concentration is still very stable, indicating that the hydrogen sensor prepared by the present invention has excellent signal reproducibility and long-term stability.

[0114] The sensitivity of the hydrogen sensor described in Example 1 was tested at H2 concentrations of 1 to 1600 ppm. The test results are shown in Table 1. Sensitivity S = R a / R g , where R a and R g are the resistance values ​​of the device in air and in H2 atmosphere, respectively.

[0115] Table 1 Response sensitivity of the hydrogen sensor described in Application Example 1 at 1 to 1600 ppm H2 concentration

[0116]

[0117] Note: In Table 1, “×” indicates that the sensor response value was not measured under the corresponding hydrogen concentration conditions, and “ / ” indicates that the response of the hydrogen sensor has reached saturation and the response sensitivity has almost stopped increasing, so no test was performed.

[0118] The data comparison in Table 1 clearly shows that at 1 ppm, the response sensitivity of the single-phase H2-R-TiO2 sample is only 1.05, while the response sensitivity of the H2-A / R-TiO2-5 sample is 3.03, demonstrating that the response of the hydrogen sensor increases nearly threefold after constructing the homogeneous heterojunction. As the hydrogen concentration increases, at 1200 ppm, the response sensitivity of the single-phase H2-R-TiO2 sample is 1.98, while the response sensitivity of the hydrogen sensor with the homogeneous heterojunction structure of the present invention is 85.18, a nearly 42-fold increase, representing an order of magnitude increase in sensitivity.

[0119] The response time of the hydrogen sensor described in Example 1 was tested at H2 concentrations of 1 to 1600 ppm. The test results are shown in Table 2.

[0120] Table 2 Response time of the hydrogen sensor described in Application Example 1 at 1 to 1600 ppm H2 concentration

[0121]

[0122] Note: In Table 2, “×” indicates that the sensor response value was not measured under the corresponding hydrogen concentration conditions, and “ / ” indicates that the response of the hydrogen sensor has reached saturation and the response sensitivity has almost stopped increasing, so no test was performed.

[0123] From the data comparison in Table 2, it can be seen intuitively that at 50ppm, the response time of the single-phase H2-R-TiO2 sample is 15.3s, while the response time of H2-A / R-TiO2-5 is 8.4s; and as the hydrogen concentration increases, at 1200ppm, the response time of H2-R-TiO2 is 68.0s, and the response time of the hydrogen sensor H2-A / R-TiO2-5 with the homogeneous heterojunction structure of the present invention is 13.8s, which is nearly 5 times shorter. From the overall comparison, the response time of the single-phase H2-R-TiO2 sample gradually increases with the increase of hydrogen concentration, while the response time of the H2-A / R-TiO2-5 sample changes little with the concentration and is stable at around 10s. The long response time at 1ppm may be due to the slow initial reaction of the sample. In general, the response time of the hydrogen sensor constructed with the homogeneous heterojunction of the present invention is shortened.

[0124] Although the above embodiment provides a detailed description of the present invention, it is only a part of the embodiments of the present invention, not all of the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. A TiO2 heterojunction thin film, characterized in that: It includes rutile phase TiO2 nanopillars and branched anatase TiO2 dispersed on the surface of the rutile phase TiO2 nanopillars; The method for preparing the TiO2 homogeneous heterojunction thin film comprises the following steps: Placing a substrate in a hydrothermal reaction precursor solution to perform a hydrothermal reaction, and then performing a first annealing treatment to load rutile phase TiO2 nanorods on the substrate surface to obtain a TiO2 isojunction thin film precursor; the hydrothermal reaction precursor solution includes ethanol, hydrochloric acid, a first titanium compound, and water; The TiO2 isojunction thin film precursor is placed in an immersion treatment precursor solution for immersion treatment, followed by a second annealing treatment to grow branched anatase TiO2 on the surface of the rutile phase TiO2 nanocolumns, thereby obtaining the TiO2 isojunction thin film on the surface of the substrate; the immersion treatment precursor solution includes boric acid, a second titanium compound, and water; The content of boric acid in the precursor solution for the immersion treatment is 1.4-9.8 wt %; the temperature for the immersion treatment is 60-90° C., and the time is 4-12 hours.

2. The TiO2 homogeneous heterojunction thin film according to claim 1, characterized in that: The diameter of the rutile phase TiO2 nanocolumn is 50 to 200 nm, and the length is 1.5 to 4 μm; the length of the branched anatase TiO2 is 0.06 to 0.1 μm.

3. The method for preparing the TiO2 isojunction thin film according to any one of claims 1 to 2, characterized in that: The steps are: Placing a substrate in a hydrothermal reaction precursor solution to perform a hydrothermal reaction, and then performing a first annealing treatment to load rutile phase TiO2 nanorods on the substrate surface to obtain a TiO2 isojunction thin film precursor; the hydrothermal reaction precursor solution includes ethanol, hydrochloric acid, a first titanium compound, and water; The TiO2 isojunction thin film precursor is placed in an immersion treatment precursor solution for immersion treatment, followed by a second annealing treatment to grow branched anatase TiO2 on the surface of the rutile phase TiO2 nanocolumns, thereby obtaining the TiO2 isojunction thin film on the surface of the substrate; the immersion treatment precursor solution includes boric acid, a second titanium compound, and water; The content of boric acid in the precursor solution for the immersion treatment is 1.4-9.8 wt %; the temperature for the immersion treatment is 60-90° C., and the time is 4-12 hours.

4. The preparation method according to claim 3, characterized in that The hydrothermal reaction precursor solution contains 0.0825-8.25 wt% of ethanol, 30-65 wt% of hydrochloric acid, and 0.8-4.8 wt% of the first titanium compound. The immersion treatment precursor solution contains 1.4-9.8 wt% of the second titanium compound.

5. The preparation method according to claim 3 or 4, characterized in that The first titanium compound includes tetrabutyl titanate, titanium tetrachloride or titanium isopropoxide; the second titanium compound includes ammonium hexafluorotitanate or titanium oxysulfide.

6. The preparation method according to claim 3, characterized in that The temperature of the hydrothermal reaction is 120-180° C., and the time is 4-18 hours.

7. The preparation method according to claim 3, characterized in that The first annealing treatment and the second annealing treatment are independently performed at a temperature of 300 to 500° C. and for a time of 10 to 180 minutes.

8. Use of the TiO2 heterojunction thin film according to any one of claims 1 to 2 or the TiO2 heterojunction thin film prepared by the preparation method according to any one of claims 3 to 7 in hydrogen detection.

9. A hydrogen sensor comprising a substrate, a TiO2 heterojunction film, and an electrode stacked in sequence; the TiO2 heterojunction film is the TiO2 heterojunction film according to any one of claims 1 to 2 or a TiO2 heterojunction film prepared by the preparation method according to any one of claims 3 to 7.

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