Thin film with exposed anatase titanium dioxide (111) crystal face and preparation method thereof

Abstract

The invention provides a thin film with the exposed anatase titanium dioxide (111) crystal face and a preparation method thereof.The preparation method prepares the thin film with the exposed anatase titanium dioxide (111) crystal face by controlling the proportion of hydrochloric acid and a titanium source, according to the method, sodium fluoride is added into hydrochloric acid, the titanium source is added after stirring, and a mixture is obtained; then placing the mixture and a substrate in a reaction device, and after crystallization treatment, growing a thin film exposing the crystal face of anatase titanium dioxide (111) on the surface of the substrate; wherein the mass ratio of the sodium fluoride to the hydrochloric acid to the titanium source is 1: (45-55): (3.5-4.5). The invention further provides a thin film for exposing the crystal face of anatase titanium dioxide (111), and the exposure proportion of the crystal face of the thin film (111) is larger than or equal to 60%.

Description

Technical Field

[0001] The present invention belongs to the technical field of titanium dioxide thin film preparation, and particularly relates to a thin film exposing anatase titanium dioxide (111) crystal plane and a preparation method thereof. Background Art

[0002] Anatase titanium dioxide (TiO2) has important application values in the fields of photocatalytic catalysis, electrochemical sensing, and self-cleaning surfaces due to its excellent photoelectrocatalytic performance. At present, there are mainly two processes for preparing TiO2 thin films exposing specific crystal planes: one is to first synthesize TiO2 powder exposing specific crystal planes, and then form films through post-treatment processes such as coating, drying, and calcination (powder film formation method); the other is to in-situ grow TiO2 thin films exposing specific crystal planes on a substrate (in-situ film formation method). However, the powder film formation method has obvious defects, such as uneven film thickness, poor transparency, and high-temperature calcination is likely to introduce carbon impurities, affecting the purity of TiO2. In addition, it is difficult to achieve large-area uniform film formation by this method, limiting its application in industry.

[0003] Although the in-situ film formation method can avoid some problems of the powder film formation, it can currently only grow on limited substrates (such as FTO, ITO), and relies on fluorine sources such as hydrogen fluoride (HF) or ammonium hexafluorotitanate (NH4)2TiF6 as crystal plane control agents. Since the introduction of fluorine sources may bring side reactions, and the release efficiency of F - ions is unstable, resulting in uncontrollable crystal plane regulation. In addition, the existing technologies are mainly limited to the exposure of crystal planes such as (001), (101), and (010), while the exposure ratio of the highly active (111) crystal plane is relatively low. More critically, the existing methods have strict requirements for the lattice matching degree of the substrate, with limited applicability, and it is difficult to grow high-quality TiO2 thin films on non-lattice matching substrates such as carbon cloth.

[0004] Therefore, the current technology still lacks a preparation method for anatase TiO2 thin films with strong universality, simple process, and efficient regulation of (111) crystal plane exposure. In particular, how to achieve a high proportion of (111) crystal plane exposure on non-lattice matching substrates (such as carbon cloth) while avoiding the use of complex fluorine sources is a technical problem to be solved urgently. The present invention aims to break through the limitation of the traditional dodecahedron structure by optimizing the ratio of hydrochloric acid to the titanium source, and achieve high (111) crystal plane exposure of hexahedral TiO2, so as to provide a more stable and efficient thin film preparation technology. Summary of the Invention

[0005] The present invention aims to at least solve one of the above technical problems existing in the prior art. For this reason, the present invention provides a preparation method for a thin film exposing anatase titanium dioxide (111) crystal plane. The anatase titanium dioxide thin film prepared by the method of the present invention has a high exposure ratio of the (111) crystal plane.

[0006] The present invention also provides a thin film exposing the (111) crystal plane of anatase titanium dioxide.

[0007] In a first aspect of the present invention, there is provided a method for preparing a thin film exposing the (111) crystal plane of anatase titanium dioxide. The preparation method controls the ratio of hydrochloric acid to a titanium source to prepare a thin film exposing the (111) crystal plane of anatase titanium dioxide, and includes the following steps:

[0008] S1: Add sodium fluoride to hydrochloric acid, stir and then add the titanium source to obtain a mixture.

[0009] S2: Place the mixture and a substrate in a reaction device. After crystallization treatment, a thin film exposing the (111) crystal plane of anatase titanium dioxide grows on the surface of the substrate.

[0010] The mass ratio of the sodium fluoride, hydrochloric acid, and titanium source is 1:(45 - 55):(3.5 - 4.5).

[0011] One technical solution in the method for preparing a thin film exposing the (111) crystal plane of anatase titanium dioxide according to the present invention has at least the following beneficial effects:

[0012] For the anatase titanium dioxide thin film prepared by the method of the present invention, the exposure ratio of the (111) crystal plane is ≥60%. Compared with the traditional method that mainly exposes crystal planes such as (001) and (101), this (111) crystal plane shows higher reaction activity and product selectivity in photocatalysis (such as ammonia synthesis reaction).

[0013] The prior art usually relies on specific substrates such as FTO and ITO, while the method of the present invention can stably grow a TiO2 thin film with a high exposure of the (111) crystal plane on various substrates (including carbon cloth with non-lattice matching), expanding the application scenarios of the material.

[0014] The traditional method needs to rely on complex fluorine sources such as hydrogen fluoride (HF) or ammonium hexafluorotitanate, while the present invention only needs to optimize the ratio of hydrochloric acid to the titanium source and combine with low-concentration sodium fluoride to achieve efficient crystal plane regulation, avoiding the side reaction problems caused by the introduction of fluorine sources, and improving the process stability and repeatability.

[0015] Compared with the powder film-forming method, the present invention adopts an in-situ hydrothermal growth technique, avoiding the carbon doping problem caused by high-temperature roasting. The obtained thin film has high purity, strong adhesion, uniform thickness, and excellent transparency and photoelectrochemical stability. This method has a simple process, low cost, strong scalability, and can achieve large-area uniform film formation, and has broad application prospects in the fields of photocatalysis, electrochemical sensing, self-cleaning coatings, etc.

[0016] According to some embodiments of the present invention, the mass ratio of the sodium fluoride, hydrochloric acid, titanium source, and water is 1:(50 - 55):(4 - 4.5):70.

[0017] According to some embodiments of the present invention, the mass ratio of sodium fluoride, hydrochloric acid, titanium source and water is 1:50:4:70.

[0018] According to some embodiments of the present invention, the stirring speed ≥ 1000 rpm.

[0019] According to some embodiments of the present invention, the titanium source includes tetrabutyl titanate.

[0020] According to some embodiments of the present invention, the temperature of the crystallization treatment is 140°C - 180°C.

[0021] According to some embodiments of the present invention, the temperature of the crystallization treatment is any value among 140°C, 150°C, 160°C, 170°C, 180°C, such as 150°C, or a range value formed by any two of them, such as 150°C - 160°C.

[0022] According to some embodiments of the present invention, the time of the crystallization treatment ≥ 6 h.

[0023] According to some embodiments of the present invention, the time of the crystallization treatment is 6 h - 16 h.

[0024] According to some embodiments of the present invention, the substrate includes one of conductive glass, indium tin oxide, carbon cloth, polytetrafluoroethylene and polyvinyl chloride.

[0025] The second aspect of the present invention provides anatase titanium dioxide thin film, which is prepared by the method of the first aspect of the present invention.

[0026] One technical solution in the technical solution of the present invention regarding anatase titanium dioxide thin film has at least the following beneficial effects:

[0027] This thin film has a high proportion of (111) crystal plane exposure ≥ 67%. Compared with traditional crystal planes such as (001) and (101), the (111) crystal plane shows higher surface activity and reaction selectivity in photocatalysis (such as ammonia synthesis, CO2 reduction) and electrochemical sensing, which can significantly improve the photoelectrocatalytic performance of the material and provide new ideas for the design of a new generation of high-efficiency catalytic materials.

[0028] According to some embodiments of the present invention, the exposure ratio of the (111) crystal plane in the anatase titanium dioxide thin film ≥ 60%.

[0029] According to some embodiments of the present invention, the exposure ratio of the (111) crystal plane in the anatase titanium dioxide thin film ≥ 66%.

[0030] According to some embodiments of the present invention, the thickness of the anatase titanium dioxide thin film is 1.20 - 1.30 μm.

[0031] The thickness of the anatase titanium dioxide thin film is less than 1.20 μm, and the compactness of the thin film is poor; when it is greater than 1.30 μm, the thin film is easy to fall off. Description of the Drawings

[0032] Figure 1 It is the X-ray powder diffraction test result of the thin film prepared in Example 1.

[0033] Figure 2 It is the microscopic morphology of the thin film prepared in Example 1.

[0034] Figure 3 It is the ammonia production rate diagram of ammonia synthesis by thin films with different crystal planes under different hydrogen treatment durations. Detailed Description of the Invention

[0035] The following will clearly and completely describe the concept and technical effects of the present invention in combination with the embodiments to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative efforts shall fall within the scope of protection of the present invention.

[0036] In the description of the present invention, the description referring to terms such as "one embodiment", "some embodiments", "schematic embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0037] Unless otherwise specified, "room temperature" in the present invention means 25°C ± 5°C.

[0038] Unless otherwise specified, "about" in the present invention means that the allowable error is within ±2%.

[0039] For those conditions not specified in the examples, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments whose manufacturers are not specified, they are all conventional products that can be obtained through commercial purchase.

[0040] Example 1

[0041] An anatase titanium dioxide thin film with an exposed ratio of (111) crystal plane ≥ 66% was prepared. The method is as follows:

[0042] S1: Add sodium fluoride to hydrochloric acid, and then add a titanium source after stirring to obtain a mixture.

[0043] S2: Place the mixture and the substrate in a reaction device. After crystallization treatment, a film exposing the (111) crystal plane of anatase titanium dioxide grows on the surface of the substrate.

[0044] The mass ratio of sodium fluoride, hydrochloric acid, titanium source, and water is 1:50:4:70.

[0045] The stirring speed is 1000 rpm.

[0046] The titanium source is tetrabutyl titanate (Aladdin reagent, purity 98%). Hydrochloric acid is purchased from Changtai Chemical Industry, analytical grade. Sodium fluoride is purchased from Macklin reagent, analytical grade.

[0047] The temperature of the crystallization treatment is 150 °C.

[0048] The time of the crystallization treatment is 12 h.

[0049] The substrate is FTO (Lige Technology).

[0050] Example 2

[0051] The difference from Example 1 is that the mass ratio of sodium fluoride, hydrochloric acid, titanium source, and water is 1:45:3.5:70.

[0052] Example 3

[0053] The difference from Example 1 is that the mass ratio of sodium fluoride, hydrochloric acid, titanium source, and water is 1:55:4.5:70.

[0054] Comparative Example 1

[0055] The difference from Example 1 is that the mass ratio of sodium fluoride, hydrochloric acid, titanium source, and water is 1:100:5.8:100.

[0056] Comparative Example 2

[0057] The difference from Example 1 is that the fluorine source is replaced with a chlorine source, specifically sodium chloride. The mass ratio of the chlorine source, hydrochloric acid, titanium source, and water is 1:550:15:500.

[0058] Product Performance Characterization

[0059] The film prepared in Example 1 was tested by X-ray powder diffraction. The 2θ angle range was 20° - 70°, and the scanning speed was 10° / min. As Figure 1 shown. It can be seen from Figure 1 that the film is anatase-phase titanium dioxide, corresponding to the standard Anatase PDF#(21 - 1272) card.

[0060] The microscopic morphology of the thin film prepared in Example 1 was observed by scanning electron microscopy, as Figure 2 shown. It can be seen from Figure 2 that the morphology of the prepared thin film is uniform and the thickness can be controlled.

[0061] Among Examples 1 to 3, the thin film of Example 1 has a uniform thickness of about 1.25 μm, and the proportion of exposed (111) crystal planes is the highest, about 66.7%.

[0062] The thin film of Example 2 has a thickness of about 1.05 μm, and the proportion of exposed (111) crystal planes is about 61%.

[0063] The thin film of Example 3 has a thickness of about 1.60 μm, and the proportion of exposed (111) crystal planes is about 60.2%.

[0064] The thin film of Comparative Example 1 has a small proportion of exposed (001) crystal planes and no (111) crystal planes at all.

[0065] The thin film of Comparative Example 2 is a rutile-phase TiO2 thin film, with a high proportion of exposed (110) crystal planes, about 90%. There is no (111) crystal plane.

[0066] Furthermore, the ammonia production rate diagrams of thin films with (110), (101), (001), and (111) crystal planes were tested under different hydrogen treatment duration conditions.

[0067] The test method is as follows:

[0068] Using TiO2 as the working electrode and a 0.3 M K2SO4 solution containing 200 ppm NO3 - as the catholyte, the electrolytic reduction reaction was carried out for 3 hours at the optimal potential (-0.75 V vs. RHE). The A{111} electrode has the best ammonia production efficiency under hydrogen treatment. Specifically, the Faraday efficiency of NH4 + is 74.9%, the conversion rate of NO3 - reaches 88.5%, and the generation rate of NH4 + is 3.49 μmol h - 1 cm -2 .

[0069] The results are as Figure 3 shown.

[0070] The present invention has been described in detail above in conjunction with the embodiments. However, the present invention is not limited to the above embodiments. Various changes can be made without departing from the spirit of the present invention within the knowledge scope of those of ordinary skill in the art.

Claims

1. A method for preparing a thin film exposing the (111) crystal plane of anatase titanium dioxide, characterized in that, The preparation method prepares a film exposing the anatase titanium dioxide (111) crystal plane by controlling the ratio of hydrochloric acid to titanium source, and comprises the following steps: S1: Add sodium fluoride into hydrochloric acid, and add the titanium source after stirring to obtain a mixture; S2: Place the mixture and the substrate in a reaction device. After crystallization treatment, a film exposing the anatase titanium dioxide (111) crystal plane grows on the surface of the substrate; The mass ratio of the sodium fluoride, hydrochloric acid and titanium source is 1:(45-55):(3.5-4.5).

2. According to the method described in claim 1, the mass ratio of the sodium fluoride, hydrochloric acid, titanium source and water is 1:(50-55):(4-4.5):

70.

3. The preparation method according to claim 1, characterized in that, The stirring speed is ≥1000 rpm.

4. The preparation method according to claim 1, characterized in that, The titanium source includes tetrabutyl titanate.

5. The preparation method according to claim 1, characterized in that, The temperature of the crystallization treatment is 140°C - 180°C.

6. The preparation method according to claim 5, characterized in that, The time of the crystallization treatment is ≥6 h.

7. The preparation method according to claim 1, characterized in that, The time of the crystallization treatment is 6 h - 16 h.

8. The preparation method according to claim 1, characterized in that, The substrate includes one of conductive glass, indium tin oxide, carbon cloth, polytetrafluoroethylene and polyvinyl chloride.

9. A thin film exposing the anatase titanium dioxide (111) crystal plane, characterized in that, Prepared by the preparation method described in any one of claims 1 to 7.

10. The thin film according to claim 9, characterized in that, The exposure ratio of the (111) crystal plane in the film is ≥60%.

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