阅读说明：本技术 一种钒离子空位型钒酸铋光阳极薄膜及其制备方法 (Vanadium ion vacancy type bismuth vanadate photo-anode film and preparation method thereof ) 是由 黄爱彬 朱莹 包山虎 金平实 于 2019-10-16 设计创作，主要内容包括：本发明公开了一种钒离子空位型钒酸铋光阳极薄膜及其制备方法。所述钒离子空位钒酸铋光阳极薄膜包括透明导电基底和位于透明导电基底上的钒酸铋薄膜,所述薄膜至少上表面存在钒离子空位。本发明的制备方法中,通过调节钒酸铋靶材化学计量比,借助磁控溅射制备化学计量比的钒酸铋薄膜,调整能带位置,提高载流子浓度；另外,高真空环境中高温快速退火促使薄膜表面微结构重构,提高钒酸铋光生载流子分离效率。(The invention discloses a vanadium ion vacancy type bismuth vanadate photo-anode film and a preparation method thereof. The vanadium ion vacancy bismuth vanadate photo-anode film comprises a transparent conductive substrate and a bismuth vanadate film positioned on the transparent conductive substrate, wherein vanadium ion vacancies exist on at least the upper surface of the film. According to the preparation method, the stoichiometric ratio of the bismuth vanadate target is adjusted, the bismuth vanadate film with the stoichiometric ratio is prepared by means of magnetron sputtering, the energy band position is adjusted, and the carrier concentration is improved; in addition, the high-temperature rapid annealing in a high vacuum environment promotes the reconstruction of the microstructure on the surface of the film, and improves the separation efficiency of bismuth vanadate photon-generated carriers.)

1. The bismuth vanadate photo-anode film with the vanadium ion vacancies is characterized by comprising a transparent conductive substrate and a bismuth vanadate film positioned on the transparent conductive substrate, wherein at least the upper surface of the film has the vanadium ion vacancies.

2. The bismuth vanadate photo-anode film according to claim 1, wherein the thickness of the bismuth vanadate film is 50-500 nm.

3. The bismuth vanadate photo-anode film according to claim 1 or 2, wherein the concentration of vanadium ion vacancies is gradually decreased in the direction from the surface of the film to the conductive substrate, and the distribution depth of the vanadium ion vacancies is 0-200 nm.

4. The bismuth vanadate photoanode thin film according to any one of claims 1 to 3, wherein the concentration of the vanadium ion vacancies is 0 to 20 at%.

5. A method for preparing a bismuth vanadate photo-anode film according to any one of claims 1 to 4, comprising the steps of:

(1) using a conductive substrate as a substrate and bismuth vanadate Bi_xV_yO_zAnd (3) taking the ceramic target as a target material, carrying out direct-current magnetron sputtering, and depositing a film on the surface of the substrate: wherein, the bismuth vanadate Bi_xV_yThe stoichiometric ratio of the O ceramic target is x, y, z = (0.8-1.2), 0.8-1.2 and 3.5-4.5;

(2) and then carrying out high-temperature rapid annealing treatment on the deposited film: wherein the annealing temperature is 500-1200 ℃, the heating rate is 10-50 ℃/S, and the heat preservation time is 5-500S.

6. The method according to claim 5, wherein in the step (1), the sputtering gas is argon gas or a mixed gas of argon gas and oxygen gas, the total pressure is 0.5 to 2.5Pa, and the partial pressure of oxygen in the mixed gas is 0 to 50%.

7. The production method according to claim 5 or 6, wherein in the step (1), the temperature of the substrate is from room temperature to 500 ℃.

8. The method according to any one of claims 5 to 7, wherein in the step (1), the distance between the target and the substrate is 7 to 20cm, the power of the DC power supply applied to the target is 50 to 500W or the power density is 0.6 to 6.4W/cm²The deposition time is 5-60 minutes.

9. The method according to any one of claims 5 to 8, wherein the degree of vacuum in the step (2) is 0.5 to 50 Pa.

10. The production method according to any one of claims 5 to 9, wherein the conductive substrate comprises at least one of a transparent conductive electrode, a porous electrode, and a metal nanowire electrode.

Technical Field

The invention relates to the technical field of functional materials, in particular to a bismuth vanadate photo-anode film with a surface vanadium ion vacancy and a preparation method thereof.

Background

With the rapid development of social economy and industry, the demand of human beings on resources and energy is increasingly urgent, which draws attention to the problems of energy shortage, environmental pollution and the like. Solar energy has become one of the first-choice alternative energy sources as an emerging renewable clean energy source, and therefore, the efficient utilization of solar energy has become the focus and difficulty of current research. Experimental research shows that the photocatalytic oxidation technology can effectively utilize clean and reproducible solar energy, carry out photocatalytic decomposition on water to produce hydrogen and oxygen, carry out photocatalytic degradation on water and organic pollutants in the atmosphere, and has mild reaction conditions, so that the energy consumption can be effectively reduced, and the possibility of byproducts and secondary pollution is reduced. The method can not only relieve the problem of energy shortage, but also solve the problem of environmental pollution, and is a high-efficiency oxidation technology with good development prospect.

The photocatalytic material can directly absorb and convert solar energy into chemical energy, and is considered as a promising strategy for solving the current environmental and energy crisis. BiVO₄The yellow pigment is widely applied and has the main characteristics of bright color, regular appearance and pure color. The material has wide sources of the constituent elements, has the characteristics of good chemical and thermal stability, no toxicity, environmental friendliness and the like, and BiVO (BiVO) is prepared from the material with narrow forbidden band width and proper valence band position₄The semiconductor photocatalytic material has excellent photocatalytic degradation capability on organic pollutants and water, and has good thermal stability and photostability. It is now found that BiVO is found in nature₄There are three crystal forms of (a): tetragonal zircon type, monoclinic scheelite type and tetragonal scheelite type. Wherein, monoclinic phase BiVO₄Having a forbidden band width Eg equal to 2.4eV, in violetThe photocatalyst has better absorption in the external-visible light region, and shows the best photocatalytic activity in the aspects of degrading organic pollutants by visible light and photolyzing water to produce hydrogen and oxygen. BiVO under AM1.5 solar spectrum₄The maximum photocurrent theoretically generated is 7.6mA/cm²The conversion efficiency of the maximum theoretical light hydrogen production can reach 9.3 percent, and in addition, the monoclinic BiVO₄The bottom of the conduction band is positioned near the reversible hydrogen electrode, and water can be cracked when a lower bias voltage is loaded, which means that the hydrogen production energy consumption of BiVO4 is less than that of other visible light semiconductors in the complete photocatalytic water splitting process.

At present, BiVO is synthesized₄The methods for the thin film are various. Chemical and physical methods can be classified according to whether a chemical reaction occurs. Among them, the most widely used and effective synthetic chemical method is the decomposition method of metal organic matter, and then the film is prepared by using the spin coating method; and the physical laws include physical vapor deposition, pulsed laser deposition, etc. Because the methods have complex processes, harsh conditions, high cost and general performance, the methods have many difficulties in the practical application of the bismuth vanadate film, and other materials have to be loaded to assist in improving the separating capability of the photon-generated carriers.

At present, various patents for preparing bismuth vanadate films have been disclosed, and CN108408776A discloses a method for preparing a bismuth vanadate film, which comprises depositing a bismuth film on an FTO conductive glass substrate; then reacting the bismuth film with vanadyl acetylacetonate at 450 ℃ to obtain a film; CN102949991A discloses a sol-gel method for preparing BiVO with photocatalytic performance₄Method for making thin film, bismuth nitrate pentahydrate (Bi (NO)₃)₃·5H₂O), ammonium metavanadate (NH)₄VO₃) Preparing precursor solutions A and B by using citric acid as a solvent as a raw material, and mixing the precursor solutions A and B to prepare BiVO₄Sol, and then forming uniform BiVO on the surface of the FTO substrate by a spin coating method₄A film. CN105463396A discloses a method for preparing a bismuth vanadate film for photolysis of water by direct current magnetron sputtering, which comprises the steps of taking conductive glass as a substrate and metal bismuth and metal vanadium as targets, carrying out direct current magnetron sputtering in a mixed atmosphere of argon and oxygen, and then annealing the grown film in air at the annealing temperature of 500-600 ℃. On the upper partThe methods have many problems, such as complex process, harsh conditions, high cost and general efficiency, and are not beneficial to the market popularization and practical application of the bismuth vanadate film. We believe that there is a need to continue to develop a bismuth vanadate thin film with excellent rapid synthesis properties.

Disclosure of Invention

In view of the above problems, the present invention provides a vanadium ion vacancy type bismuth vanadate photo-anode film and a preparation method thereof.

In a first aspect, the invention provides a vanadium ion vacancy bismuth vanadate photo-anode film, which comprises a transparent conductive substrate and a bismuth vanadate film positioned on the transparent conductive substrate, wherein at least the upper surface (the upper surface refers to the surface relatively far away from the transparent conductive substrate) of the film has vanadium ion vacancies.

Preferably, the thickness of the bismuth vanadate film is 50-500 nm.

Preferably, the concentration of the vanadium ion vacancies is gradually decreased in the direction of the conductive substrate on the upper surface of the film, and the distribution depth of the vanadium ion vacancies is 0-200 nm. The bismuth vanadate film based on the transparent conductive glass substrate has the vacancy concentration gradually reduced from the upper surface to the lower surface (towards the direction of the conductive substrate), the vacancy concentration of the upper surface is the highest, and the vacancy existence depth is 0-200 nm.

Preferably, the concentration of the vanadium ion vacancy is 0 to 20 at%.

The bismuth vanadate film prepared by the invention has excellent photon-generated carrier separation and transport capacity, generates a large amount of free electrons and holes, and has wide application in the fields of photocatalysis, photoelectrocatalysis, electrocatalysis and the like.

In a second aspect, the present invention provides a method for preparing a bismuth vanadate photo-anode thin film, including the following steps:

(1) using a conductive substrate as a substrate and bismuth vanadate Bi_xV_yO_zAnd (3) taking the ceramic target as a target material, carrying out direct-current magnetron sputtering, and depositing a film on the surface of the substrate: wherein the stoichiometric ratio of x, y, z (0.8-1.2), 0.8-1.2 and 3.5-4.5) is the ratio of bismuth vanadate ceramic target;

(2) and then carrying out high-temperature rapid annealing treatment on the deposited film: wherein the heat treatment temperature is 500-1200 ℃, the heating rate is 10-50 ℃/S, and the heat preservation time is 5-500S.

The invention designs the stoichiometric ratio of the target material according to the difference of atom volatility. Sputtering the bismuth vanadate film with an ideal stoichiometric ratio by magnetron sputtering, and improving the integral crystallinity of the film by a post annealing process and constructing defects on the surface of the film. Vanadium ion vacancies with different gradient concentrations can be formed on the surface of the bismuth vanadate film according to different annealing time and temperature.

Preferably, in the step (1), the sputtering gas is argon or a mixed gas of argon and oxygen, the total pressure is 0.5 to 2.5Pa, and the partial pressure of oxygen in the mixed gas is 0 to 50%.

Preferably, in the step (1), the temperature of the substrate is between room temperature and 500 ℃.

Preferably, in the step (1), the distance between the target and the substrate is 7-20 cm, and the power of the DC power supply applied to the target is 50-500W or the power density is 0.6-6.4W/cm²The deposition time is 5-60 minutes.

Preferably, in the step (2), the vacuum degree is 0.5 to 50 Pa.

Preferably, the initial background vacuum of the sputtering system is less than 10^-4Pa。

Preferably, the pure titanium target is pre-sputtered before sputtering the bismuth vanadate target; the technological conditions of the pre-sputtering are as follows: the power is 50-400W, the time is 5-30 minutes, the atmosphere is pure argon, and the gas pressure is 0.5-1.5 Pa.

Preferably, the conductive substrate comprises at least one of a transparent conductive electrode, a porous electrode, and a metal nanowire electrode.

Compared with a widely used solution method, the preparation method has the advantages of better efficiency, simpler preparation process, capability of being prepared at room temperature, more compact and flat film and effective reduction of the interface resistance of the film.

The invention has the following beneficial effects:

1) the magnetron sputtering process has mild conditions, simple process and short period, can be continuously prepared and is not limited by the size, the texture and the shape of the substrate.

2) By controlling the target material metering ratio, the film with the optimal stoichiometric ratio reasonable can be obtained, the defects in the film body are reduced, and the photoelectrochemical property of the film is improved.

3) The high vacuum rapid annealing can rapidly improve the crystallinity of the film, simultaneously promote the change of the surface microstructure to form vanadium ion vacancies as active sites to improve the performance of the film as a photo-anode.

Drawings

FIG. 1 is a scanning electron micrograph of the surface and cross section of a bismuth vanadate thin film obtained by magnetron sputtering deposition of example 1, wherein (A) is the surface and (B) is the cross section.

FIG. 2 is a scanning electron micrograph of the surface and cross section of a bismuth vanadate thin film after the high vacuum rapid annealing treatment of example 1, wherein a drawing (A) is the surface and a drawing (B) is the cross section.

FIG. 3 is a photo current curve of the neutral electrolyte after different heat treatment modes of the bismuth vanadate thin film. In the example 1 corresponding to the curve A, the heat treatment mode is 800 ℃, 40s and the vacuum degree is 5 mTorr; curve B corresponds to comparative example 1, the heat treatment was carried out in air at 500 ℃ for 2 h; curve C corresponds to comparative example 2 with a heat treatment in air at 350℃ for 0.5h, followed by a vacuum of 5mTorr, 500℃ for 270 s.

FIG. 4 is XPS spectra of vanadium element obtained from example 1 when etching bismuth vanadate film for different periods of time.

FIG. 5 is an XRD pattern of a bismuth vanadate film subjected to different heat treatment modes, wherein a is an XRD pattern of a bismuth vanadate film subjected to atmospheric pressure heat treatment in comparative example 1; and the diagram B is an XRD diagram of the high-vacuum rapid heat treatment bismuth vanadate thin film in the example 1.

Detailed Description

The present invention is further illustrated by the following examples, which are to be understood as merely illustrative and not restrictive.

The invention designs a high-performance bismuth vanadate photo-anode film rich in vanadium ion vacancies, which comprises a transparent conductive substrate and a bismuth vanadate film positioned on the transparent conductive substrate, wherein controllable gradient vanadium ion vacancies exist on at least the upper surface of the film, and because the surface is in contact with a liquid phase in a catalytic reaction tank, the purpose of designing gradient concentration vacancies is to reduce the contact potential difference between the solid phase and the liquid phase and improve the separation and transmission efficiency of a photo-generated carrier vacancy-electron pair. The vanadium ion vacancy of the surface structure is beneficial to the separation of photon-generated carriers, and the performance of the photo-anode is greatly improved.

In some embodiments, the thickness of the bismuth vanadate thin film can be 50-500 nm. The concentration of the vanadium ion vacancies is gradually decreased from the upper surface of the film to the direction of the conductive substrate to form the gradient depth of the vanadium ion vacancies, and the gradient depth of the vanadium ion vacancies can be 0-200nm, and is preferably 20-50 nm. An appropriate amount of vacancies can improve the carrier separation efficiency, but the presence of too many vacancies necessarily affects the crystallinity of the bismuth vanadate thin film as a whole. Since the reduction in crystallinity of the thin film itself lowers the photon absorption ability of the thin film itself, there is inevitably a balanced depth, and both the crystallinity of the thin film itself and the carrier separation efficiency can be achieved. Meanwhile, the gradient concentration can not only reduce the number of vacancies existing but also gradually bend the energy band, thereby reducing the contact resistance with the liquid surface, as compared with a thin film in which the vacancy concentration is uniform.

The gradient concentration of the vanadium ion vacancies is 0 to 20%, preferably 5 to 10%. The concentration gradient of the vanadium ion vacancy can be adjusted according to different treatment methods. The existence of the gradient vacancy can cause the surface energy band of the bismuth vanadate film to bend, thereby reducing the liquid electrical resistance with the solution, improving the separation efficiency of photo-generated electrons and vacancies at the interface and finally improving the capability of the film for decomposing water by photoelectrocatalysis.

The method is based on that the bond and the capability between bismuth vanadate molecules are not strong, and part of atoms are easy to volatilize in the magnetron sputtering process to form a large number of vacancy and gap filling defects. These defects are recombination centers of photogenerated carriers, which greatly impair the performance of the film as a photoanode. Therefore, the bismuth vanadate target with non-stoichiometric ratio is designed, and the bismuth vanadate film with ideal ratio is expected to be obtained. In addition, compared with the film prepared by the solution method, the magnetron sputtering method has the advantages of high compactness, low surface roughness, continuously adjustable thickness, no influence of the area of the substrate and easier obtainment of the high-quality film. The crystallinity of the film is improved through a post annealing process, and simultaneously the high vacuum rapid annealing is beneficial to promoting the surface to form vanadium ion vacancies which are active centers and promote the separation of photo-generated electron-hole pairs.

The following shows a method for preparing a bismuth vanadate photo-anode film.

Firstly, depositing and growing a film on a conductive substrate by adopting a direct current magnetron sputtering method.

The conductive substrate is not limited by its material. The conductive substrate may use, without limitation, a transparent conductive electrode, a porous electrode, and a metal nanowire electrode. Transparent conductive electrodes include, but are not limited to, FTO, ITO, AZO, ATO. Porous electrodes include, but are not limited to, nickel foam. The metal nanowire electrode includes, but is not limited to, Cu, Au, Ag, Al.

The bismuth vanadate (BixVyOz) ceramic target is prepared by using a bismuth vanadate ceramic target with a special metering ratio, wherein the metering ratio x, y, z is (0.8-1.2): 3.5-4.5). Compared with the use of two metal targets of metal vanadium and metal bismuth, the bismuth vanadate ceramic target has the advantages that the composition of the obtained film is more accurate, and the defects in a bulk phase structure are fewer. Moreover, the reactive sputtering deposition efficiency of the two metal targets is low, and the deposition efficiency of the bismuth vanadate ceramic target is relatively high. Because of slight decomposition of bismuth vanadate in the deposition process, the film integrally contains a proper amount of metal ion vacancies. By slightly adding more metal elements when preparing the target material, the bismuth vanadate film meeting the stoichiometric ratio can be obtained. If the proportion exceeds the proportion provided by the invention, the film is excessively doped with certain elements, becomes a recombination position of a photon-generated carrier, and influences the photoelectrochemical property of the film.

According to the invention, the stoichiometric ratio of the bismuth vanadate target is adjusted, the bismuth vanadate film with the stoichiometric ratio is prepared by magnetron sputtering, the energy band position is adjusted, and the carrier concentration is improved.

During sputtering, the sputtering gas may be pure argon. The sputtering gas may be a mixed gas of argon and oxygen. The total pressure is 0.5-2.5 Pa, preferably 0.5-2 Pa. The oxygen partial pressure in the mixed gas is 0 to 50%, preferably 0 to 20%. For example, the purity of argon and oxygen may be 99.99% and above. When argon is used, direct sputtering is adopted; when a mixed gas of argon and oxygen is used, it is a reaction gas, and oxygen vacancies which may exist in the film can be eliminated.

In some embodiments, the distance between the target and the substrate is 7-20 cm. The sputtering distance is too short, and the film grows too fast, which can result in the film not being dense enough. If the sputtering distance is too long, the film is insufficiently crystallized.

The temperature in the film deposition process is controlled according to actual needs, and the bismuth vanadate nano film can be rapidly prepared by deposition. The initial temperature of the substrate is room temperature, and can be 15-35 ℃ generally. In the whole process, the substrate can be heated, and the heating temperature range is room temperature to 500 ℃. The substrate is heated, so that the migration capability of the deposited nano particles on the surface of the substrate can be improved, the film is more compact, and the crystallinity of the film can be improved.

The power of the DC power supply applied to the target can be 50-500W or the power density can be 0.6-6.4W/cm²Wherein the deposition time is 5-60 minutes, preferably 10-30 minutes.

In the scheme, the initial background vacuum degree (namely the initial vacuum degree of the deposition chamber) of the whole system is lower than 10^{- 4}Pa。

In some embodiments, the pre-sputtering is performed prior to sputtering the bismuth vanadate target. The technological conditions of the pre-sputtering are as follows: the power is 50-400W, the time is 5-30 minutes, the atmosphere is pure argon, and the gas pressure is 0.5-1.5 Pa.

The deposited film is then heat treated to improve the crystallinity of the film and to produce graded defects as active centers. Wherein the heat treatment temperature is 500-1200 ℃, the heating rate is 10-50 ℃/S, and the heat preservation time is 5-500S.

In the scheme, the vacuum is kept constant in the heat treatment process, and the length of the annealing time is adjusted according to the temperature. The degree of vacuum of the heat treatment may be 0.5 to 50 Pa.

According to the method, the bismuth vanadate film with a special metering ratio is deposited through magnetron sputtering, the energy band position is adjusted, the carrier concentration is improved, and the reconstruction of the microstructure of the film surface is promoted through ultrahigh-temperature rapid annealing in a high-vacuum environment.

The following shows a method for preparing a bismuth vanadate photo-anode thin film according to an embodiment of the present invention.

The dc magnetron sputtering system used for deposition may include a deposition chamber, a sample introduction chamber, a target carrying plate at an angle to the substrate plate (the angle is the angle formed by the target carrying plate and the normal of the substrate plate, and is typically 37 °), a substrate plate, a dc power supply connected to the target carrying plate, and a series of vacuum pumps.

The high vacuum rapid annealing furnace system used for the heat treatment comprises a mechanical pump, a molecular pump, a controller, a barometer, a quartz chamber, an infrared heating wire and a silicon carbide objective table.

Ultrasonically cleaning conductive base material, respectively ultrasonically cleaning the base material with acetone and anhydrous ethanol for 30min, sequentially fixing on a substrate plate, placing into a sample chamber, opening a gate, and loading until vacuum degree (background vacuum degree) reaches 10^-4Pa in the following deposition chamber.

In the specific deposition process, a high-purity argon and oxygen mixed gas is introduced into a deposition chamber, the purity of the argon and the oxygen can be more than 99.99%, the total pressure and the oxygen partial pressure are controlled within the ranges of 0.5-2.5 Pa and 0-50%, the total pressure is preferably 0.5-2 Pa, and the oxygen partial pressure is preferably 0-20%. The distance between the target and the base material is controlled to be 7-20 cm, and the initial base temperature is room temperature. Starting a direct current power supply, controlling the power of the direct current power supply to be 50-500W, wherein the sputtering target material is a bismuth vanadate ceramic target material, the deposition time can be 5-60 minutes, and the substrate temperature is 50-500 ℃, wherein the metering ratio x, y, z of the bismuth vanadate (BixVyOz) ceramic target is (0.8-1.2) to (3.5-4.5). And after the deposition is finished, cooling the substrate to room temperature, and taking out the base material. Then the sample is sent into a rapid annealing furnace, the air pressure is pumped to be below 50Pa by a mechanical pump, and the molecular pump is turned on to continuously reduce the air pressure. And after the air pressure reaches the specified requirement, carrying out heat treatment on the sample according to the set parameters. And after the annealing is finished, firstly closing the molecular pump, then closing the mechanical pump, and finally, taking out the sample after the temperature of the sample is reduced to the room temperature. The sample is a bismuth vanadate photo-anode film with a gradient vanadium ion vacancy on the surface.

According to the method, the bismuth vanadate film with a special metering ratio is deposited through magnetron sputtering, the energy band position is adjusted, the carrier concentration is improved, and the reconstruction of the microstructure of the film surface is promoted through ultrahigh-temperature rapid annealing in a high-vacuum environment. The process has the advantages of simple preparation process, low cost, small pollution, short period and good performance, and is easy to realize commercial popularization, and the bismuth vanadate photo-anode film prepared by the method can be widely applied to the fields of photocatalysis, photoelectrocatalysis and electrocatalysis, including oxygen evolution, hydrogen evolution, nitrogen fixation, carbon oxide reduction, olefin hydrogenation and the like.

The present invention will be described in detail by way of examples. It is also to be understood that the following examples are illustrative of the present invention and are not to be construed as limiting the scope of the invention, and that certain insubstantial modifications and adaptations of the invention by those skilled in the art may be made in light of the above teachings. The specific time, temperature, pressure, power, and other process parameters described in the following examples are also only one example of suitable ranges, i.e., those skilled in the art can select the appropriate ranges through the description herein, and are not limited to the specific values described in the following examples.

The sheet resistance of the FTO glass substrate used in each example was 10 to 30. omega./cm²。