A stannous α-tungstate thin film, a preparation method thereof, and an application thereof

Abstract

The present invention discloses an α-stannous tungstate thin film, a preparation method thereof and an application thereof. The preparation method includes: under a vacuum condition, making a tungsten oxide thin film contact and react with a vapor stream containing a stannous source, thereby preparing the α-stannous tungstate thin film. The α-stannous tungstate thin film prepared by the stannous vapor method of the present invention has an excellent optical band gap and can be preferably applied to fields such as photoelectrocatalysis, photocatalysis or gas sensors. At the same time, the stannous vapor method of the present invention is simple in operation and low in cost, and can realize large-scale commercial application.

Description

Technical Field

[0001] The invention belongs to the technical field of thin films, and in particular relates to an α-stannous tungstate thin film and a preparation method and application thereof. Background Art

[0002] At present, it is difficult to obtain α-stannous tungstate thin films with excellent crystallinity and purity. Among them, there are only three methods for preparing α-stannous tungstate thin films: hydrothermal conversion, reactive magnetron sputtering, and laser pulse deposition. Among them, the hydrothermal conversion method is difficult to obtain materials with good crystallinity, and it also has many unfavorable defect states and impurity phases, which limits further development and utilization. It is also difficult to ensure that the thin film material has good purity for reactive magnetron sputtering and laser pulse deposition. At the same time, the equipment is expensive, which is not conducive to widespread promotion and research. Therefore, how to provide a simple and efficient method for preparing α-stannous tungstate thin films is an urgent problem to be solved. Summary of the Invention

[0003] The main purpose of the present invention is to provide an α-stannous tungstate film and a preparation method and application thereof, so as to overcome the deficiencies of the prior art.

[0004] To achieve the aforementioned object of the invention, the technical solutions adopted by the present invention include:

[0005] An embodiment of the present invention provides a method for preparing an α-stannous tungstate thin film, which includes:

[0006] The tungsten oxide film is contacted with a vapor flow containing a stannous source under vacuum conditions to react, thereby preparing an α-stannous tungstate film.

[0007] Furthermore, the preparation method includes: placing the tungsten oxide film and the stannous source in a reaction chamber, forming a vacuum environment in the reaction chamber, and then raising the temperature in the reaction chamber to 300-550°C so that the stannous source forms a vapor flow and contacts and reacts with the tungsten oxide film, thereby preparing the α-stannous tungstate film.

[0008] The embodiment of the present invention also provides an α-stannous tungstate thin film prepared by any of the aforementioned methods.

[0009] The embodiment of the present invention further provides the use of the aforementioned α-stannous tungstate thin film in photoelectrocatalytic reactions, photocatalytic reactions, or the preparation of gas sensors.

[0010] An embodiment of the present invention further provides an n-type semiconductor material, which includes the aforementioned α-stannous tungstate thin film.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention uses stannous chloride vapor to react with tungsten oxide thin films, providing a low-cost and easy-to-operate method for preparing stannous tungstate (α-SnWO4) thin films, and enabling large-scale commercial applications. At the same time, the prepared α-SnWO4 thin films have excellent crystallization properties, optical band gaps, and uniformity, showing good application prospects in fields such as photoelectrocatalysis, photocatalysis, or gas sensors. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments recorded in the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0013] Figure 1a It is a schematic diagram of the preparation of α-SnWO4 by the stannous vapor method in Example 1 of the present invention;

[0014] Figure 1b-Figure 1e It is the SEM image and XRD pattern of the WO3 thin film and the α-SnWO4 thin film prepared from the WO3 thin film in Example 1 of the present invention;

[0015] Figure 1f - FIG. li is the SEM image and XRD pattern of the WO3·H2O thin film and the α-SnWO4 thin film prepared from the WO3·H2O thin film in Example 1 of the present invention;

[0016] Figure 2a It is a photograph of the α-SnWO4 thin film prepared from the WO3 thin film in Example 1 of the present invention;

[0017] Figure 2b-2f It is the XRD pattern, light transmittance spectrum, light absorption spectrum, direct band gap diagram, and indirect band gap diagram of the α-SnWO4 thin film prepared from the WO3 thin film in Example 1 of the present invention;

[0018] Figure 3a-Figure 3b It is a schematic diagram of the preparation of α-SnWO4 by the stannous vapor method in Example 2 of the present invention;

[0019] Figure 3c-3k It is the surface SEM image, cross-section SEM image, and XRD pattern of the WO3 thin film and the α-SnWO4 thin films prepared with different reaction times in Example 2 of the present invention;

[0020] Figure 4a-4c It is a schematic diagram of the preparation of α-SnWO4 with different reaction times by the stannous vapor method in Example 3 of the present invention;

[0021] Figure 4d-4oThey are the surface SEM images, cross-section SEM images, and XRD patterns of the WO3 thin film and the α-SnWO4 thin films prepared with different reaction times in Example 3 of the present invention;

[0022] Figure 5a-5c It is a schematic diagram of preparing α-SnWO4 with different amounts of SnCl2 by the stannous vapor method in Example 4 of the present invention;

[0023] Figure 5d They are the XRD patterns of the WO3 thin film and the α-SnWO4 thin films prepared with different amounts of SnCl2 in Example 4 of the present invention;

[0024] Figure 6a It is a schematic diagram of preparing α-SnWO4 by the stannous vapor method in Example 5 of the present invention;

[0025] Figure 6b-6c They are the surface SEM images and cross-section SEM images of the α-SnWO4 thin film prepared in Example 5 of the present invention;

[0026] Figure 7 It is a schematic diagram of preparing α-SnWO4 by the stannous vapor method in Example 6 of the present invention;

[0027] Figure 8a It is a schematic diagram of preparing α-SnWO4 from a 50-nm WO3 thin film in Example 7 of the present invention;

[0028] Figure 8b-8c They are the surface SEM images and cross-section SEM images of the α-SnWO4 thin film prepared from a 50-nm WO3 thin film in Example 7 of the present invention;

[0029] Figure 8d It is a schematic diagram of preparing α-SnWO4 from a 100-nm WO3 thin film in Example 7 of the present invention;

[0030] Figure 8e-8f They are the surface SEM images and cross-section SEM images of the α-SnWO4 thin film prepared from a 100-nm WO3 thin film in Example 7 of the present invention;

[0031] Figure 8g It is a schematic diagram of preparing α-SnWO4 from a 200-nm WO3 thin film in Example 7 of the present invention;

[0032] Figure 8h-8i They are the surface SEM images and cross-section SEM images of the α-SnWO4 thin film prepared from a 200-nm WO3 thin film in Example 7 of the present invention;

[0033] Figure 9a It is a schematic diagram of preparing α-SnWO4 from a 50-nm WO3 thin film in Example 8 of the present invention;

[0034] Figure 9b-9c It is the surface SEM image and cross-sectional SEM image of the α-SnWO4 thin film prepared from the 50-nm WO3 thin film in Example 8 of the present invention;

[0035] Figure 9d It is a schematic diagram of preparing α-SnWO4 from the 100-nm WO3 thin film in Example 8 of the present invention;

[0036] Figure 9e-9f It is the surface SEM image and cross-sectional SEM image of the α-SnWO4 thin film prepared from the 100-nm WO3 thin film in Example 8 of the present invention;

[0037] Figure 9g It is a schematic diagram of preparing α-SnWO4 from the 200-nm WO3 thin film in Example 8 of the present invention;

[0038] Figure 9h-9i It is the surface SEM image and cross-sectional SEM image of the α-SnWO4 thin film prepared from the 200-nm WO3 thin film in Example 8 of the present invention.

[0039] Figure 10a It is a schematic diagram of preparing α-SnWO4 from the 200-nm WO3 thin film in Example 9 of the present invention;

[0040] Figure 10b-Figure 10c It is the surface SEM image and cross-sectional SEM image of the α-SnWO4 thin film prepared from the 200-nm WO3 thin film in Example 9 of the present invention;

[0041] Figure 10d-10g It is the XRD pattern, optical absorption rate spectrum, indirect bandgap diagram, and direct bandgap diagram of the α-SnWO4 thin film prepared from the 200-nm WO3 thin film in Example 9 of the present invention;

[0042] Figure 10h It is the UPS test result and corresponding work function of the α-SnWO4 thin film in Example 9 of the present invention

[0043] Figure 11a It is the linear sweep voltammogram of the α-SnWO4 thin film electrode and the α-SnWO4 thin film loaded with cobalt oxide (CoO x ) electrode in a 1 M potassium borate buffer electrolyte (pH = 9) and containing 0.2 M Na2SO3 as a sacrificial agent;

[0044] Figure 11b-Figure 11c It is the stability test of the pure α-SnWO4 thin film or the α-SnWO4 thin film loaded with cobalt oxide (CoO x ) electrode in a 1 M potassium borate buffer electrolyte (pH = 9) and containing 0.2 M Na2SO3 as a sacrificial agent;

[0045] Figure 11d-Figure 11f The pure α-SnWO4 film, the α-SnWO4 film after the photoelectrocatalytic stability test and the α-SnWO4 film / CoO film in Example 10 of the present invention are x X-ray photoelectron spectroscopy (XPS). DETAILED DESCRIPTION

[0046] In view of the shortcomings of the prior art, the inventors of this case, after long-term research and extensive practice, have proposed the technical solution of the present invention. The technical solution of the present invention will be clearly and completely described below. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making any creative effort shall fall within the scope of protection of the present invention.

[0047] One aspect of an embodiment of the present invention provides a method for preparing an α-stannous tungstate thin film, comprising:

[0048] The tungsten oxide film is contacted with a vapor flow containing a stannous source under vacuum conditions to react, thereby preparing an α-stannous tungstate film.

[0049] Specifically, the method for preparing the α-stannous tungstate film includes:

[0050] Providing tungsten oxide thin films;

[0051] Furthermore, under vacuum conditions, the tungsten oxide film is reacted with a vapor flow obtained by controlling a stannous source of different masses in a certain space to produce α-stannous tungstate films with different morphologies and transmittances.

[0052] In some more specific embodiments, the preparation method includes: placing the tungsten oxide film and the stannous source in a reaction chamber, forming a vacuum environment in the reaction chamber, and then raising the temperature in the reaction chamber to 300-550°C so that the stannous source forms a vapor flow and contacts and reacts with the tungsten oxide film, thereby preparing the α-stannous tungstate film.

[0053] Furthermore, the certain space contains a quartz tube with a length of 600 mm and a diameter of 60 mm to a length of 300 mm and a diameter of 30 mm.

[0054] Furthermore, before the reaction chamber is evacuated to form the vacuum environment, the reaction chamber is in an oxygen-free environment or an inert gas atmosphere.

[0055] Furthermore, the air pressure of the vacuum environment is 0-10 Pa.

[0056] Further, the distance between the tungsten oxide thin film and the stannous source in the reaction cavity is 0 to 10 cm, preferably 3 to 10 cm.

[0057] Further, the reaction time is 0.2 to 2 h.

[0058] Further, the amount of the stannous source used in the reaction is in excess.

[0059] In some more specific embodiments, the tungsten oxide thin film includes a WO3 thin film or a tungsten oxide thin film containing crystal water, and is not limited thereto.

[0060] Further, the tungsten oxide thin film containing crystal water includes a WO3·H2O thin film, and is not limited thereto.

[0061] Further, the thickness of the tungsten oxide thin film is greater than 0 and less than or equal to 200 nm, and is not limited thereto, and is preferably any one of 50 nm, 100 nm, and 200 nm.

[0062] Further, the stannous source includes SnCl2 or SnF2, and is not limited thereto.

[0063] In some more specific embodiments, the preparation method further includes: preparing a tungsten oxide thin film on the surface of a substrate by a hydrothermal method and / or a thermal evaporation method to obtain a WO3 thin film / substrate or a WO3·H2O thin film / substrate.

[0064] Further, the substrate includes FTO conductive glass, a silicon wafer, or a titanium sheet, and is not limited thereto.

[0065] Further, the preparation method further includes: calcining the WO3 thin film / substrate or the WO3·H2O thin film / substrate at a high temperature (300 to 600 °C, for improving the crystallinity or dehydration of the material, and is not limited thereto) to obtain a WO3 thin film / substrate.

[0066] In some more specific embodiments, the preparation method further includes: after the reaction is completed, cleaning the obtained reaction product with an inorganic acid and water.

[0067] Further, the inorganic acid includes any one or a combination of two or more of dilute hydrochloric acid, dilute nitric acid, and dilute sulfuric acid, and is not limited thereto.

[0068] In some more specific embodiments, the method for preparing the α-stannous tungstate film may include: using a tungsten oxide (containing or not containing crystalline water) film as a precursor material to react with stannous vapor to obtain an α-stannous tungstate film material. A certain amount of stannous raw material is placed in a non-reactive container and placed in a heating device, and then the tungsten oxide film is also placed in a non-reactive container and placed near the stannous source. The heating device is then heated to a vaporization temperature under vacuum conditions and reacts with the precursor. Finally, the sample is washed with dilute hydrochloric acid and deionized water to obtain a reddish-brown α-SnWO4 film material.

[0069] Specifically, 0.1 to 2 g of stannous oxide is placed in a quartz crucible and placed in a heating device. The prepared WO3 / FTO sample is then placed in another quartz crucible 3 to 10 cm apart. The reaction chamber is then evacuated to a pressure of 0 to 10 Pa and heated to 300°C to 550°C to allow the stannous oxide vapor flow to react with the tungsten oxide film for 0.2 to 2 hours. Finally, the remaining reactants are washed with dilute hydrochloric acid and deionized water to obtain a reddish-brown SnWO4 thin film material.

[0070] In the present invention, the scheme for preparing WO3·H2O film / FTO and WO3 film / FTO by hydrothermal method includes:

[0071] (1) A layer of tungsten oxide containing crystalline water (WO3·H2O) was obtained on the conductive surface of FTO conductive glass (fluorine-doped SnO2) by hydrothermal reaction at 120°C for 30 minutes, namely WO3·H2O film / FTO. The hydrothermal reaction solution was 15ml deionized water + 3ml 3M dilute hydrochloric acid + 0.115g sodium tungstate (Na2WO4) + 0.1g ammonium oxalate ((NH4)2C2O4);

[0072] (2) The obtained WO3·H2O film / FTO is calcined at a high temperature of 500°C to obtain tungsten oxide (WO3) without crystalline water, namely WO3 film / FTO.

[0073] In the present invention, the method of preparing WO3 thin film / FTO by thermal evaporation includes: obtaining a tungsten oxide film of corresponding thickness on the conductive surface of FTO conductive glass (fluorine-doped SnO2) by thermal evaporation of tungsten oxide powder, and then improving the crystallinity by high temperature calcination at 500℃.

[0074] Another aspect of the embodiments of the present invention further provides an α-stannous tungstate thin film prepared by any of the aforementioned methods.

[0075] Furthermore, the indirect band gap of the α-stannous tungstate film is 1.9-2.1 eV.

[0076] Further, the XRD diffraction peaks of the stannous α-tungstate thin film are distinct, and there are no diffraction peaks of tungsten oxide and other impurity phases.

[0077] Further, the work function of the stannous α-tungstate thin film is 4.4 - 4.5 eV.

[0078] Further, the thickness of the stannous α-tungstate thin film is 200 - 800 nm.

[0079] Another aspect of the embodiments of the present invention also provides the use of the aforementioned stannous α-tungstate thin film in photoelectrocatalytic reactions, photocatalytic reactions, or the preparation of gas sensors.

[0080] For example, the potential use of the stannous α-tungstate thin film in the field of photoelectrocatalytic water splitting.

[0081] Another aspect of the embodiments of the present invention also provides an n-type semiconductor material, which comprises the aforementioned stannous α-tungstate thin film.

[0082] The technical solutions of the present invention will be further described in detail below in conjunction with several preferred embodiments and the accompanying drawings. These embodiments are implemented on the premise of the technical solutions of the invention, and detailed implementation manners and specific operation processes are given. However, the protection scope of the present invention is not limited to the following embodiments.

[0083] In the following embodiments, the experimental materials used can be obtained from conventional biochemical reagent companies without special instructions.

[0084] Example 1

[0085] (1) A layer of tungsten oxide containing crystal water (WO3·H2O), i.e., WO3·H2O thin film / FTO, was obtained on the conductive surface of FTO conductive glass (fluorine-doped SnO2) by hydrothermal reaction at 120 °C for 30 min. The hydrothermal reaction solution was 15 ml of deionized water + 3 ml of 3M dilute hydrochloric acid + 0.115 g of sodium tungstate (Na2WO4) + 0.1 g of ammonium oxalate ((NH4)2C2O4); the obtained WO3·H2O thin film / FTO was calcined at 500 °C to obtain tungsten oxide without crystal water (WO3), i.e., WO3 thin film / FTO;

[0086] (2) 1 g of SnCl2 was placed in a quartz crucible and placed in the reaction cavity of the heating device. Then, the prepared WO3 / FTO or WO3·H2O / FTO sample was placed in another quartz crucible 7.5 cm apart. Subsequently, the reaction cavity was evacuated to a pressure of 5 Pa and heated to 350 °C to allow the stannous vapor flow to react with the tungsten oxide thin film for 1 h. Finally, the residual reactants were washed with dilute hydrochloric acid and deionized water to obtain two reddish-brown SnWO4 thin film materials.

[0087] Performance characterization:

[0088] Figure 1a Schematic diagram of preparing α-SnWO4 by stannous vapor method; Figure 1b-Figure 1c SEM images and XRD patterns of WO3 thin film samples respectively; Figures Id - Ie are SEM images and XRD patterns of α-SnWO4 thin film samples prepared from WO3 thin film samples respectively; Figure 1f-1g SEM images and XRD patterns of WO3·H2O thin film samples; Figure Ih - Figure 1i SEM images and XRD patterns of α-SnWO4 thin film samples prepared from WO3·H2O thin film samples respectively;

[0089] Figure 2a Photo of α-SnWO4 thin film sample prepared from WO3 thin film sample, Figure 2b-2f XRD pattern, light transmittance spectrum, light absorption spectrum, direct bandgap diagram, and indirect bandgap diagram of α-SnWO4 thin film samples prepared from WO3 thin film samples respectively; Through calculation, the direct bandgap of the α-SnWO4 thin film sample is 2.27 eV, and the indirect bandgap is 2.06 eV; It shows that this bandgap has good sunlight utilization rate and has great development potential in the field of solar water splitting.

[0090] Example 2

[0091] (1) By thermally evaporating tungsten oxide powder, a tungsten oxide thin film with a corresponding thickness is obtained on the conductive surface of FTO conductive glass (fluorine-doped SnO2), and then the crystallinity is improved by calcining at 500 °C to obtain a tungsten oxide thin film with a thickness of 200 nm, which is also denoted as WO3 thin film / FTO (the thickness of the WO3 thin film is 200 nm);

[0092] (2) Place 1 g of SnCl2 in a quartz crucible and put it in a heating device. Then place the prepared WO3 thin film / FTO in another quartz crucible 6 cm away. Subsequently, evacuate to make the pressure in the reaction chamber 5 Pa, heat to 350 °C, and allow the stannous vapor flow to react with the tungsten oxide thin film for 1 h or 2 h. Finally, wash the residual reactants with dilute hydrochloric acid and deionized water to obtain two reddish-brown SnWO4 thin film materials.

[0093] Figure 3a-Figure 3b Schematic diagrams of preparing α-SnWO4 by stannous vapor method with reaction times of 1 h and 2 h in this example respectively; Figure 3c-Figure 3e Surface SEM images of WO3 thin film, α-SnWO4 thin film prepared with a reaction time of 1 h, and α-SnWO4 thin film prepared with a reaction time of 2 h respectively; Figure 3f-3hCross-sectional SEM images of WO3 film, α-SnWO4 film prepared with a reaction time of 1 h, and α-SnWO4 film prepared with a reaction time of 2 h; Figure 3i-3k These are the XRD patterns of WO3 film, α-SnWO4 film prepared with a reaction time of 1h, and α-SnWO4 film prepared with a reaction time of 2h.

[0094] Example 3

[0095] (1) WO3 thin film / FTO (WO3 film thickness is 200 nm) was prepared by the same method as in Example 2;

[0096] (2) 1g of SnCl2 was placed in a quartz crucible and placed in a heating device. The prepared WO3 film / FTO was then placed in another quartz crucible 6cm apart. The reaction chamber was then evacuated to a pressure of 5Pa and heated to 450℃. The stannous vapor flow was allowed to react with the tungsten oxide film for 0.2h, 1h, or 2h. Finally, the residual reactants were washed with dilute hydrochloric acid and deionized water to obtain three reddish-brown SnWO4 thin film materials.

[0097] Figure 4a-4c Schematic diagrams of preparing α-SnWO4 by the stannous vapor method with reaction times of 0.2h, 1h, and 2h in this embodiment respectively; Figure 4d-4g Surface SEM images of WO3 film, α-SnWO4 film prepared with a reaction time of 0.1h, α-SnWO4 film prepared with a reaction time of 1h, and α-SnWO4 film prepared with a reaction time of 2h; Figure 4h-4k The cross-sectional SEM images of WO3 film, α-SnWO4 film prepared with a reaction time of 0.2h, α-SnWO4 film prepared with a reaction time of 1h, and α-SnWO4 film prepared with a reaction time of 2h are shown in FIG4I- Figure 4o These are the XRD patterns of WO3 film, α-SnWO4 film prepared with a reaction time of 0.2h, α-SnWO4 film prepared with a reaction time of 1h, and α-SnWO4 film prepared with a reaction time of 2h.

[0098] Example 4

[0099] (1) WO3 thin film / FTO (WO3 film thickness is 200 nm) was prepared by the same method as in Example 2;

[0100] (2) 0.1g, 0.7g, and 1.5g of SnCl2 were placed in a quartz crucible, respectively, and placed in a heating device. The prepared WO3 film / FTO was then placed in another quartz crucible 5cm apart. The reaction chamber was then evacuated to a pressure of 5Pa and heated to 450°C. The stannous vapor flow reacted with the tungsten oxide film for 1h. Finally, the residual reactants were washed with dilute hydrochloric acid and deionized water to obtain three reddish-brown SnWO4 thin film materials.

[0101] Figure 5a-5c Schematic diagrams of preparing α-SnWO4 by the stannous vapor method with different SnCl2 amounts in this embodiment; Figure 5d XRD patterns of WO3 thin film and α-SnWO4 thin film prepared with SnCl2 amounts of 0.1g and 1.5g.

[0102] Example 5

[0103] (1) WO3 thin film / FTO (WO3 film thickness is 100 nm) was prepared by the same method as in Example 2;

[0104] (2) 2 g of SnCl2 was placed in a quartz crucible and placed in a heating device. The prepared WO3 film / FTO was then placed in another quartz crucible 6 cm apart. The reaction chamber was then evacuated to a pressure of 5 Pa and heated to 350 ° C. The stannous vapor flow reacted with the tungsten oxide film for 2 h. Finally, the residual reactants were washed with dilute hydrochloric acid and deionized water to obtain a reddish-brown SnWO4 thin film material.

[0105] Figure 6a Schematic diagram of the preparation of α-SnWO4 by the stannous vapor method in this embodiment; Figure 6b-6c These are the surface SEM images and cross-sectional SEM images of the prepared α-SnWO4 thin films.

[0106] Example 6

[0107] (1) WO3 thin film / FTO (WO3 film thickness is 200 nm) was prepared by the same method as in Example 2;

[0108] (2) 0.5 g of SnCl2 was placed in a quartz crucible and placed in a heating device. The prepared WO3 film / FTO was then placed in another quartz crucible 3 cm apart. The reaction chamber was then evacuated to a pressure of 5 Pa and heated to 450 ° C. The stannous vapor flow reacted with the tungsten oxide film for 1 hour. Finally, the residual reactants were washed with dilute hydrochloric acid and deionized water to obtain a reddish-brown SnWO4 thin film material.

[0109] Figure 7 Schematic diagram of the preparation of α-SnWO4 by the stannous vapor method in this embodiment.

[0110] Example 7

[0111] (1) WO3 thin films / FTO with different WO3 film thicknesses (50 nm, 100 nm, 200 nm) were prepared using the same method as in Example 2;

[0112] (2) 1g of SnC12 was placed in a quartz crucible and placed in a heating device. The prepared WO3 film / FTO of different thicknesses was then placed in another quartz crucible 5cm apart. The reaction chamber was then evacuated to a pressure of 5Pa and heated to 500℃ to allow the stannous vapor flow to react with the tungsten oxide film for 2h. Finally, the residual reactants were washed with dilute hydrochloric acid and deionized water to obtain three reddish-brown SnWO4 thin film materials.

[0113] Figure 8a Schematic diagram of preparing α-SnWO4 of 50nm WO3 thin film in this embodiment; Figure 8b-8c Surface SEM images and cross-sectional SEM images of α-SnWO4 thin films prepared from 50nm WO3 thin films; Figure 8d Schematic diagram of preparing α-SnWO4 with a 100nm WO3 thin film in this embodiment; Figure 8e-8f Surface SEM images and cross-sectional SEM images of α-SnWO4 thin films prepared with 100 nm WO3 thin films; Figure 8g Schematic diagram of preparing α-SnWO4 with a 200nm WO3 thin film in this embodiment; Figure 8h-8i Surface SEM images and cross-sectional SEM images of α-SnWO4 thin films prepared with 200 nm WO3 thin films;

[0114] Example 8

[0115] (1) WO3 thin films / FTO with different WO3 film thicknesses (50 nm, 100 nm, 200 nm) were prepared using the same method as in Example 2;

[0116] (2) 1.5 g of SnCl2 was placed in a quartz crucible and placed in a heating device. The prepared WO3 film / FTO of different thicknesses was then placed in another quartz crucible 7.5 cm apart. The reaction chamber was then evacuated to a pressure of 5 Pa and heated to 300 ° C. The stannous vapor flow was allowed to react with the tungsten oxide film for 1 hour. Finally, the residual reactants were washed with dilute hydrochloric acid and deionized water to obtain three reddish-brown SnWO4 thin film materials.

[0117] Figure 9a Schematic diagram of preparing α-SnWO4 of 50nm WO3 thin film in this embodiment; Figure 9b-9c Surface SEM images and cross-sectional SEM images of α-SnWO4 thin films prepared from 50nm WO3 thin films; Figure 9dSchematic diagram of preparing α-SnWO4 with a 100nm WO3 thin film in this embodiment; Figure 9e-9f Surface SEM images and cross-sectional SEM images of α-SnWO4 thin films prepared with 100 nm WO3 thin films; Figure 9g Schematic diagram of preparing α-SnWO4 with a 200nm WO3 thin film in this embodiment; Figure 9h-9i Surface SEM images and cross-sectional SEM images of α-SnWO4 thin films prepared with 200nm WO3 thin films respectively.

[0118] Example 9

[0119] (1) WO3 thin films / FTO with different WO3 film thicknesses (200 nm) were prepared using the same method as in Example 2;

[0120] (2) 0.5 g of SnCl2 was placed in a quartz crucible and placed in a heating device. The prepared WO3 films / FTO of different thicknesses were then placed in another quartz crucible 4.5 cm apart. The reaction chamber was then evacuated to a pressure of 5 Pa and heated to 450 ° C. The stannous vapor flow reacted with the tungsten oxide film for 1 hour. Finally, the residual reactants were washed with dilute hydrochloric acid and deionized water to obtain a reddish-brown SnWO4 thin film material.

[0121] Figure 10a Schematic diagram of preparing α-SnWO4 from 200nm WO3 thin film in this embodiment; Figure 10b-Figure 10c Surface SEM images and cross-sectional SEM images of α-SnWO4 thin films prepared with 200 nm WO3 thin films; Figure 10d-10g They are XRD pattern, optical absorptivity spectrum, indirect band gap diagram, and direct band gap diagram; Figure 10h UPS test results and corresponding work function of α-SnWO4 thin film Calculations show that the indirect band gap of the α-SnWO4 film sample is 1.99 eV, and the direct band gap is 2.52 eV. The 4.44 eV work function implies that the Fermi level of the α-SnWO4 film is located at -0.06 V vs. NHE. These results indicate that the valence band and conduction band positions of the α-SnWO4 film span the oxidation and reduction potentials of water, respectively, and therefore have great potential for development in the field of solar water splitting.

[0122] Example 10

[0123] (1) α-SnWO4 film / FTO prepared by the same method as in Example 9;

[0124] (2) Generally, photocatalytic water splitting involves highly efficient oxygen evolution cocatalysts that match the photoanode materials. Currently, there is no suitable oxygen evolution cocatalyst that can be applied to α-SnWO4 materials. Therefore, we deposited a cobalt oxide material (CoOx) with a hole transport layer on the α-SnWO4 thin film to further verify the potential application of the α-SnWO4 thin film / FTO in the field of photocatalytic water splitting. Among them, the loading of CoO x was achieved by placing the α-SnWO4 thin film / FTO into 100 mL of an aqueous solution (the aqueous solution contained 10 mM of Co(NO3)2·6H2O and 100 mM of urea), and reacting at 80 °C for 1 h by hydrothermal method. Then, the reacted sample was rinsed with deionized water, dried and placed into a tubular furnace. Finally, it was calcined in air at 573 K for 20 min.

[0125] (3) The photocatalytic performance test was carried out in a three-electrode system (CS150H), in 1.0 M potassium borate buffer electrolyte (pH = 9) and 0.2 M Na2SO3. A saturated Ag / AgCl electrode and a platinum wire were used as the reference electrode and the counter electrode, respectively. The test voltage range of the linear sweep voltammogram was from -0.828 V to 0.502 V vs Ag / AgCl (the scan rate was 20 mV / s). The calculation formula for the reversible hydrogen electrode (RHE) is: E RHE = E Ag / AgCl + 0.197 + 0.059PH.

[0126] Figure 11a is the linear sweep voltammogram (scan rate: 20 mV / s, light source: 455 nm LED lamp, light intensity: 39 mW / cm x ) of the α-SnWO4 thin film electrode and the α-SnWO4 thin film loaded with cobalt oxide (CoO 2 ) electrode in 1 M potassium borate buffer electrolyte (pH = 9) and containing 0.2 M Na2SO3 as a sacrificial agent in Example 10 of the present invention;

[0127] Figure 11b-Figure 11c is the stability test (potential: 1.1 V vs RHE, light source: 455 nm LED lamp (light intensity: 39 mW / cm x ) or simulated sunlight AM1.5 (light intensity: 100 mW / cm 2 ) of the pure α-SnWO4 thin film or the α-SnWO4 thin film loaded with cobalt oxide (CoO 2 ) electrode in 1 M potassium borate buffer electrolyte (pH = 9) and containing 0.2 M Na2SO3 as a sacrificial agent prepared in Example 10 of the present invention; The results show that CoO xThe α-SnWO4 thin film / FTO electrode exhibits excellent photoelectrocatalytic stability. The lower photocurrent and increased dark-state current observed with pure α-SnWO4 thin film are primarily due to the lack of a suitable co-catalyst, which leads to unfavorable surface states. Therefore, we believe that further development of efficient oxygen evolution co-catalysts based on α-SnWO4 thin film materials has great potential for achieving photoelectrocatalytic water decomposition to produce oxygen.

[0128] Figure 11d-Figure 11f The pure α-SnWO4 film in Example 10 of the present invention, the α-SnWO4 film after the photoelectrocatalytic stability test and the CoO x X-ray photoelectron spectroscopy (XPS) of / α-SnWO4 thin film. The results show that after the photoelectrocatalytic reaction, α-SnWO4 thin film and CoO x The Sn elements in the Sn / α-SnWO4 thin films all maintain a +2 valence state, further revealing that the α-SnWO4 thin films we prepared have good antioxidant properties in photoelectrocatalytic reactions.

[0129] In addition, the inventors of this case also referred to the aforementioned embodiments and conducted experiments using other raw materials, process operations, and process conditions described in this specification, and obtained relatively ideal results.

[0130] It should be understood that the technical solution of the present invention is not limited to the above-mentioned specific implementation cases. Any technical variations made according to the technical solution of the present invention without departing from the scope of protection of the purpose of the present invention and the claims shall fall within the scope of protection of the present invention.

Claims

1. A method for preparing an α-stannous tungstate thin film, characterized in that Comprising: Placing a tungsten oxide thin film and a stannous source in a reaction chamber, creating a vacuum environment in the reaction chamber, and then raising the temperature in the reaction chamber to 300 - 550 °C to form a vapor stream of the stannous source and make it contact and react with the tungsten oxide thin film, thereby preparing a stannous tungstate (α-SnWO₄) thin film; Among them, the stannous source includes SnCl2 and / or SnF2; the indirect band gap of the stannous α-tungstate thin film is 1.99 to 2.1 eV; the work function of the stannous α-tungstate thin film is 4.44 to 4.5 eV.

2. The preparation method according to claim 1, characterized in that: Before the reaction chamber is evacuated to form the vacuum environment, the reaction chamber is in an anaerobic environment or an inert gas atmosphere.

3. The preparation method according to claim 1, wherein: The air pressure of the vacuum environment is 0 - 10 Pa.

4. The preparation method according to claim 1, characterized in that: The distance between the tungsten oxide thin film and the stannous source in the reaction chamber is 0 - 10 cm.

5. The preparation method according to claim 4, characterized in that: The distance between the tungsten oxide thin film and the stannous source in the reaction chamber is 3 - 10 cm.

6. The preparation method according to claim 1, wherein: The reaction time is 0.2 - 2 h.

7. The preparation method according to claim 1, characterized in that: The tungsten oxide thin film includes a WO₃ thin film or a tungsten oxide thin film containing crystal water; wherein, the tungsten oxide thin film containing crystal water includes a WO₃·H₂O thin film; the thickness of the tungsten oxide thin film is greater than 0 and less than or equal to 200 nm.

8. The preparation method according to claim 1, characterized in that Also comprising: preparing a tungsten oxide thin film on the surface of a substrate by a hydrothermal method and / or a thermal evaporation method to obtain a WO₃ thin film / substrate or a WO₃·H₂O thin film / substrate; Wherein, the substrate includes FTO conductive glass, a silicon wafer or a titanium sheet.

9. The preparation method according to claim 8, wherein Also comprising: Roasting the WO₃ thin film / substrate or the WO₃·H₂O thin film / substrate at 300 - 600 °C to obtain a WO₃ thin film / substrate.

10. The preparation method according to claim 1, wherein Also comprising: After the reaction is completed, cleaning the obtained reaction product with an inorganic acid and water; wherein, the inorganic acid includes any one or a combination of two or more of dilute hydrochloric acid, dilute nitric acid, and dilute sulfuric acid.

11. A stannous tungstate (α-SnWO₄) thin film prepared by the method according to any one of claims 1 - 10, wherein the thickness of the stannous tungstate (α-SnWO₄) thin film is 200 - 800 nm.

12. Use of the stannous tungstate (α-SnWO₄) thin film according to claim 11 in a photoelectrocatalytic reaction, a photocatalytic reaction or the preparation of a gas sensor.

13. An n-type semiconductor material, characterized in that Comprising the stannous tungstate (α-SnWO₄) thin film according to claim 11.

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