CN118026363B

CN118026363B - Preparation and piezoelectric photocatalytic application of unsaturated tungsten oxide-coated bismuth ferrite nanomaterials

Info

Publication number: CN118026363B
Application number: CN202410354979.6A
Authority: CN
Inventors: 刘丹青; 岳志浩; 陈前; 邹鹏飞; 李娜
Original assignee: Harbin University of Science and Technology
Current assignee: Harbin University of Science and Technology
Priority date: 2024-03-26
Filing date: 2024-03-26
Publication date: 2025-11-18
Anticipated expiration: 2044-03-26
Also published as: CN118026363A

Abstract

本发明属于纳米材料压电光催化领域，涉及一种缺陷态氧化钨包覆铁酸铋纳米材料(WO_3‑x/BiFeO₃)的制备及压电光催化领域的应用。本发明通过水热法合成了WO_3‑x/BiFeO₃，WO_3‑x在可见到近红外光区优良的光吸收能力，增强了复合材料对太阳光的有效利用，BiFeO₃在超声作用下能形成压电场，为光诱导电荷提供驱动力，抑制光生电子‑空穴复合，同时能带弯曲，带隙变窄，有助于压电光催化分解有机污染物和分解水制氢。WO_3‑x/BiFeO₃压电光催化降解亚甲基蓝的效率是BiFeO₃的3.29倍，压电光催化产氢量是BiFeO₃的4.86倍，压电光催化性能显著提升。本发明阐述了一种缺陷态氧化钨包覆铁酸铋纳米材料的制备方法及其在压电光催化降解有机污染物和分解水制氢的应用，制备工艺流程简单，具有广阔的应用前景。This invention belongs to the field of piezoelectric photocatalysis of nanomaterials, and relates to the preparation of a defect-state tungsten oxide-coated bismuth ferrite nanomaterial (WO3 _-x / _BiFeO3 ) and its application in piezoelectric photocatalysis. This invention synthesizes WO3 _-x / _BiFeO3 via a hydrothermal method. _WO3-x exhibits excellent light absorption in the visible and near-infrared regions, enhancing the composite material's efficient utilization of sunlight. _BiFeO3 can form a piezoelectric field under ultrasonic irradiation, providing a driving force for photoinduced charges and inhibiting photogenerated electron-hole recombination. Simultaneously, it exhibits band bending and band gap narrowing, which facilitates the piezoelectric photocatalytic decomposition of organic pollutants and water splitting for hydrogen production. The efficiency of _WO3-x / _BiFeO3 in piezoelectric photocatalytic degradation of methylene blue is 3.29 times that of _BiFeO3 , and the hydrogen production is 4.86 times that of _BiFeO3 , demonstrating a significant improvement in piezoelectric photocatalytic performance. This invention describes a method for preparing defect-state tungsten oxide-coated bismuth ferrite nanomaterials and their application in piezoelectric photocatalytic degradation of organic pollutants and water splitting for hydrogen production. The preparation process is simple and has broad application prospects.

Description

Preparation and piezoelectric photocatalysis application of unsaturated tungsten oxide coated bismuth ferrite nano material

Technical field:

The preparation method belongs to the technical field of piezoelectric photocatalysis, and particularly relates to preparation of a defect-state tungsten oxide coated bismuth ferrite nano material and application of the composite material in piezoelectric photocatalysis.

The background technology is as follows:

With the rapid development of the Chinese printing and dyeing industry, the environmental pollution problem caused by dye wastewater is particularly serious. The dye has stable molecular structure, difficult degradation, complex components and high heavy metal content, and the characteristics lead to difficult treatment of dye wastewater. The treatment methods in the scientific paper such as adsorption and precipitation cannot thoroughly solve the problem. For example, adsorption simply transfers contaminants from one system to another, and requires additional degradation treatments. The precipitation method is to precipitate the wastewater, and does not fundamentally solve pollutants. Thus, there is a strong need for a low cost, low energy and efficient method of treating wastewater.

As an advanced oxidation technology, the photocatalytic oxidation technology has the advantages of mild reaction conditions, easiness in application, no secondary pollution and the like, and has the unique advantage in the aspect of environmental pollutant control. The basic principle of photocatalysis is that under illumination, a semiconductor photocatalysis material absorbs photons to generate free electrons and holes, and electron-hole pairs migrate to the surface of the material to participate in redox reaction to generate active oxygen species for degradation of various pollutants. However, the present photocatalysis technology is mostly focused on basic research of nano materials, and one of the core problems is low quantum efficiency caused by rapid recombination of electron hole pairs. Electron-hole pairs generated by the semiconductor under the excitation of light under the action of coulomb force are easily recombined in the bulk phase or the surface, and only a small part of carriers can get rid of the coulomb force and migrate to the surface of the semiconductor particles to participate in the photocatalytic reaction. Therefore, effective enhancement of the spatial separation of electron-hole pairs is one of the key issues that photocatalytic technology needs to address. Recently, researchers have found that piezoelectric polarization can be coupled with light excitation, semiconductor characteristics, and effectively regulate carrier generation, separation, transport, and recombination processes through polarized electric fields. For photocatalysis, the presence of a polarizing electric field can inhibit carrier recombination. The free electrons and the holes have opposite charges, and under the action of external stress, the polarized electric field generated by the directional migration of the polarized charges in the piezoelectric material can effectively promote the migration of the electron holes to opposite directions, so that the separation efficiency of photo-generated carriers is greatly improved.

Among various metal oxide semiconductors, n-type semiconductor unsaturated valence state tungsten oxide (WO _3-x) exhibits a wide light absorption characteristic in the ultraviolet to near infrared band due to its large number of oxygen vacancies. The valence band is close to 2.8eV, has higher hole oxidation capability, and has excellent photocatalytic performance in the aspects of photocatalytic organic pollutant degradation, antibacterial property, photocatalytic water oxidation, selective alcohol oxidation and the like. However, the internal recombination of photoexcited charges still severely inhibits catalytic activity. In order to solve the problem of photoexcitation charge recombination, a series of methods have been developed, such as heterojunction preparation, element doping, co-catalyst modification, and the like.

The ferroelectric perovskite type material can improve the photocatalysis performance through a built-in internal electric field of polarization modulation, and effectively control the separation of photoexcited electron/hole pairs. Multiferroic bismuth ferrite (BiFeO ₃, BFO) with perovskite structure is a prominent p-type semiconductor in solar drive applications, which has rhombohedral distorted perovskite structure with R3c space groups, which can form good interface contact with other semiconductors. It is well known for its light absorption capability (narrow bandgap of 2.1-2.7 eV), non-toxicity, low cost, chemical stability and spontaneous polarization.

The invention comprises the following steps:

The invention aims to solve the problem of low efficiency of degrading organic pollutants by piezophotocatalysis due to the energy band structure of BiFeO ₃ and the limitation of piezophotocatalysis performance. The formation of composite semiconductor nanomaterials by constructing heterojunctions is one of the main methods to improve the material properties. The P-type narrow bandgap semiconductor BiFeO ₃ and the N-type semiconductor WO _3-x are compounded with each other to form a P-N heterojunction, so that the energy band structure of the material is changed. When light and ultrasound are applied, photon-generated carriers are generated in WO _3-x、BiFeO₃, and under the action of ultrasound, the BiFeO ₃ nano material generates a spontaneous polarization electric field, which can inhibit the recombination of electron and hole pairs in the photon-generated carriers, so as to improve the catalytic performance of organic pollutants. Meanwhile, the unsaturated valence tungsten oxide has excellent light absorption capacity in a visible near infrared region, so that the effective utilization of the composite material to sunlight is enhanced, and the photocatalytic performance is improved. The invention relates to preparation of a defect-state tungsten oxide coated bismuth ferrite nano material and application of the composite material in the field of piezoelectric photocatalysis.

The invention relates to preparation and piezoelectric photocatalysis application of a defect-state tungsten oxide coated bismuth ferrite nano material, which mainly relate to characterization of the defect-state tungsten oxide coated bismuth ferrite nano material and research on piezoelectric photocatalysis degradation of organic pollutants and piezoelectric photocatalysis hydrogen production of the nano material, and specifically comprise the following steps:

dissolving bismuth nitrate and ferric nitrate in a dilute nitric acid solution, performing ultrasonic treatment to form a uniform transparent colorless solution, adjusting the pH value to enable the solution to be alkaline, centrifuging the solution to obtain a precipitate, and drying to obtain a certain amount of solid;

Grinding the solid obtained in the first step, and placing the ground powder into a tube furnace for calcination to obtain calcined solid powder;

Step three, washing the solid powder calcined in the step two with acid washing water, centrifuging, alternately carrying out three times, finally washing with ethanol, and drying in vacuum to obtain bismuth ferrite nano particles;

step four, dissolving tungsten ethoxide in ethanol, heating in water bath until the tungsten ethoxide is completely dissolved, adding the dried bismuth ferrite nano particles in the step three, and carrying out ultrasonic treatment to uniformly disperse the bismuth ferrite nano particles;

Transferring the mixed solution in the step four into a liner of a reaction kettle for hydrothermal reaction, centrifuging turbid liquid after the hydrothermal reaction, washing with water, centrifuging, alternately repeating the steps for three times, finally washing with ethanol, and vacuum drying to obtain defective tungsten oxide coated bismuth ferrite nano particles;

The molar ratio of bismuth nitrate to ferric nitrate is 1:1.1;

the dilute nitric acid solution is prepared by preparing concentrated nitric acid and water in a volume ratio of 1:30-40;

The pH value is alkaline and is 9-10;

The drying condition in the first step is that the temperature is 50-70 ℃, preferably 60 ℃, and the time is 9-14 hours, preferably 12 hours;

step two, the temperature rising rate is 4-8 ℃ per minute, preferably 5 ℃ per minute;

The calcination temperature in the second step is 300-500 ℃, preferably 500 ℃;

the calcination time in the second step is 30-60 min, preferably 60min;

The vacuum drying conditions are that the temperature is 50-70 ℃, preferably 60 ℃, the vacuum degree is-25 to-30 kpa, preferably-30 kpa, and the time is 9-14 h, preferably 12h;

Fourthly, the concentration of tungsten ethoxide is 1-10 mM/L, and the ultrasonic time is 20-40 min;

the water bath heating temperature is 50-70 ℃, preferably 60 ℃;

fifthly, the hydrothermal reaction temperature is 150-200 ℃, preferably 200 ℃;

fifthly, the hydrothermal reaction time is 18-24 hours, preferably 22 hours;

and the centrifugal speed in the third step and the fifth step is 9000r/min.

Uniformly dispersing the defect-state tungsten oxide coated bismuth ferrite nano material in an organic pollutant methylene blue aqueous solution, measuring the absorbance change of the methylene blue aqueous solution under the conditions of mechanical force and illumination by an ultraviolet-visible spectrophotometer, and finally converting the degradation rate of the methylene blue aqueous solution;

Step six, the concentration of the Methylene Blue (MB) solution is 5mg/L;

step seven, the application of the defect-state tungsten oxide coated bismuth ferrite nano material in generating hydrogen by piezoelectricity photocatalysis decomposition of water comprises the following steps of uniformly dispersing the defect-state tungsten oxide coated bismuth ferrite nano material in Na ₂SO₃ solution, introducing N ₂, removing oxygen, and measuring the generated hydrogen by gas chromatography under the conditions of mechanical force and illumination;

the mechanical force and the illumination are specifically generated by carrying out ultrasonic and xenon lamp irradiation on a reaction solution containing the defect-state tungsten oxide coated bismuth ferrite nano material.

Preferably, the ultrasonic frequency is 20-40 kHz, more preferably 40kHz, the xenon lamp power is preferably 300W, and the optical filter is lambda >420nm.

The invention characterizes the defect state tungsten oxide coated bismuth ferrite nano material and tests the piezoelectric photocatalysis performance by an X-ray powder diffractometer, a transmission electron microscope, an ultraviolet visible spectrophotometer and a gas chromatograph.

The invention has the advantages and effects that:

The preparation method is simple to operate, and the heterojunction modified bismuth ferrite is formed by coating the defect-state tungsten oxide with the bismuth ferrite nano material through hydrothermal synthesis, so that a piezoelectric field can be formed under the action of mechanical force, driving force is provided for photoinduction charge, separation is enhanced, and recombination is inhibited. The energy bands of bismuth ferrite and trapped tungsten oxide are also bent, and the band gap is narrowed. Because of the existence of the oxygen vacancy of the trapped tungsten oxide, the material has wide light absorption characteristics in the ultraviolet to near infrared band, and can realize the maximum utilization of sunlight spectrum. Compared with pure-phase bismuth ferrite, the degradation efficiency of the defect-state tungsten oxide coated bismuth ferrite nano material for piezoelectricity photocatalytic degradation of organic pollutants is 3.29 times that of pure-phase bismuth ferrite, and the hydrogen production amount of piezoelectricity photocatalysis is 4.86 times that of the pure-phase bismuth ferrite material, so that the degradation effect and the hydrogen production efficiency of the organic pollutants are effectively improved.

The invention has simple process, easily obtained materials and lower cost, and is beneficial to industrial production.

Description of the drawings:

FIG. 1 is an X-ray powder diffraction pattern of a defective tungsten oxide coated bismuth ferrite nanomaterial, defective tungsten oxide, and bismuth ferrite nanomaterial

FIG. 2 is a transmission electron microscope image of a defect-state tungsten oxide coated bismuth ferrite nanomaterial

FIG. 3 is a fluorescence spectrum of a defective tungsten oxide coated bismuth ferrite nanomaterial and a pure phase bismuth ferrite material

FIG. 4 is an ultraviolet-visible diffuse reflection absorption spectrum of a defective tungsten oxide coated bismuth ferrite nanomaterial, a defective tungsten oxide, and a bismuth ferrite nanomaterial

FIG. 5 is a comparative bar graph of the piezoelectric photocatalytic degradation rate of defective tungsten oxide coated bismuth ferrite nanomaterial and bismuth ferrite nanomaterial

FIG. 6 is a graph showing hydrogen production versus histogram of defective tungsten oxide coated bismuth ferrite nanomaterial and bismuth ferrite nanomaterial

The specific embodiment is as follows:

Embodiment 1:

Dissolving 0.5336g of bismuth nitrate and 0.4040g of ferric nitrate in 33mL of dilute nitric acid solution, performing ultrasonic treatment to form a uniform transparent colorless solution, adjusting the pH value of the solution to 9.8, centrifuging, and drying in a drying oven at 60 ℃ for 12 hours to obtain solid powder;

step two, after the solid is cooled to room temperature, grinding the solid into powder by a mortar, putting the powder into a tube furnace, heating the powder to 300 ℃ at a heating rate of 5 ℃ per minute, calcining the powder for 40 minutes, heating the powder to 500 ℃ and calcining the powder for 60 minutes to obtain calcined powder;

Step three, the calcined powder is alternately centrifugally washed for 3 times by dilute nitric acid and deionized water, washed twice by absolute ethyl alcohol, and dried in vacuum for 12 hours at 60 ℃ to obtain bismuth ferrite nano particles;

Fourthly, 0.09008g of tungsten ethoxide is dissolved in ethanol, water bath heating is carried out until the tungsten ethoxide is completely dissolved, 400mg of bismuth ferrite nano-particles obtained in the third step are added, and the bismuth ferrite nano-particles are uniformly dispersed by ultrasonic;

Transferring the mixed solution in the step four into a liner of a reaction kettle, performing hydrothermal reaction for 22 hours at 200 ℃, centrifuging turbid liquid after the hydrothermal reaction to obtain a precipitate, washing with water, centrifuging, alternately repeating the steps for three times, washing with ethanol, and vacuum drying in a vacuum drying oven at 60 ℃ for 12 hours to obtain defective tungsten oxide coated bismuth ferrite nano particles;

step six, weighing 25mg of the defect-state tungsten oxide coated bismuth ferrite nano material, uniformly dispersing the defect-state tungsten oxide coated bismuth ferrite nano material into 25mL of 5mg/L MB solution, and measuring the absorbance change of the MB solution through an ultraviolet-visible spectrophotometer from the 0 th minute under the conditions of ultrasonic vibration and illumination, wherein the absorbance change is measured once every 10 minutes, and the total measurement time is 60 minutes;

And step seven, uniformly dispersing 100mg of the obtained defect-state tungsten oxide coated bismuth ferrite nano particles into 100mL of Na ₂SO₃ solution, introducing nitrogen into a sealed reactor for 30 minutes to remove oxygen, and then measuring the hydrogen amount above the reactor from the 0 th hour under ultrasonic vibration and illumination, wherein the measurement is carried out once every 1 hour for 5 hours.

The following tests are adopted to verify the effects of the invention:

1. preparation and characterization of defect-state tungsten oxide coated bismuth ferrite nano material

And carrying out crystal phase structure analysis on the prepared defect-state tungsten oxide coated bismuth ferrite nano material, unsaturated tungsten oxide and pure-phase bismuth ferrite nano material by X-ray powder diffraction (XRD). The XRD patterns of defective tungsten oxide coated bismuth ferrite nanomaterial, pure phase bismuth ferrite nanomaterial, and unsaturated tungsten oxide are shown in FIG. 1, corresponding to standard cards for bismuth ferrite (PDF # 01-075-6667) and unsaturated tungsten oxide (PDF # 00-005-0392). As shown, diffraction peaks of the defect-state tungsten oxide coated bismuth ferrite nanomaterial at 2θ=22.4°, 31.8 ° 32.0 °, 39.5 °, 45.8 °, 51.3 ° and 57.0 ° correspond to (012), (104), (110), (202), (024), (116) and (214) crystal planes of bismuth ferrite, respectively, and diffraction peaks at 2θ=23.1 °, 27.2 °, 34.6 ° and 48.1 ° correspond to (010), (211), (014) and (020) crystal planes of unsaturated tungsten oxide, respectively. The XRD diffraction pattern of the bismuth ferrite nano material is consistent with a standard PDF card (PDF#01-075-6667), and no other impurity phase appears in the bismuth ferrite, so that the prepared bismuth ferrite is proved to be of a standard rhombic perovskite structure. The XRD pattern of the defect-state tungsten oxide coated bismuth ferrite nano material is basically consistent with that of bismuth ferrite and unsaturated tungsten oxide, and diffraction peaks of other impurity phases are not found in the pattern. The result shows that the defect-state tungsten oxide coated bismuth ferrite nano material is successfully prepared.

The morphology of the prepared defect-state tungsten oxide coated bismuth ferrite nano material is observed through a transmission electron microscope, as shown in fig. 2, the prepared defect-state tungsten oxide coated bismuth ferrite nano material has an irregular square-like sheet morphology, and the average particle size is about 40-160 nm.

The separation efficiency of the photo-generated carriers of the bismuth ferrite nano material coated by the bismuth ferrite and the defective tungsten oxide is compared and studied through fluorescence spectrum (PL). As shown in FIG. 3, the PL intensity of the defect-state tungsten oxide coated bismuth ferrite nano material is obviously lower than that of bismuth ferrite, and the fluorescence quenching phenomenon shows that the prepared defect-state tungsten oxide coated bismuth ferrite nano material effectively improves the separation efficiency of photogenerated electrons and holes.

The light absorption characteristics of bismuth ferrite, unsaturated tungsten oxide and defective tungsten oxide coated bismuth ferrite nanomaterial were studied using solid uv-vis diffuse reflection absorption spectroscopy, as shown in fig. 4. Bismuth ferrite mainly shows intrinsic absorption in ultraviolet region and small visible light region, and unsaturated tungsten oxide has strong light absorption capacity in visible light to near infrared region and infrared region due to a large amount of oxygen vacancies. After the bismuth ferrite is coated with the unsaturated tungsten oxide, the composite nano material has excellent light absorption capacity in ultraviolet, visible and near infrared light areas, which shows that the introduction of the unsaturated tungsten oxide successfully widens the light absorption capacity of the bismuth ferrite in the visible and near infrared light areas.

2. Catalytic degradation efficiency study

The degradation performance of the bismuth ferrite and defect-state tungsten oxide coated bismuth ferrite nano material under ultrasonic vibration and visible light is detected by using an ultraviolet-visible spectrophotometer, and a degradation experiment is carried out for 60 minutes under mechanical vibration (40 kHz) and xenon lamp irradiation (300W, lambda >420 nm). Fig. 5 shows the comparison of the degradation efficiency of bismuth ferrite and the bismuth ferrite nanomaterial coated with the defective tungsten oxide, and as shown in the figure, the bismuth ferrite nanomaterial can degrade 52.8% of MB in 60min under the excitation of mechanical vibration and visible light irradiation, the degradation rate constant k= 0.01184min ^-1, and under the same condition, the degradation rate of MB is 91.2% when the bismuth ferrite nanomaterial is coated with the defective tungsten oxide in 60min, and the degradation rate constant k= 0.03893min ^-1 is 3.29 times that of the pure iron acid nanomaterial.

3. Research on hydrogen production performance

The hydrogen production performance of bismuth ferrite and defect-state tungsten oxide coated bismuth ferrite nano materials under ultrasonic vibration and visible light irradiation is detected by using a gas chromatograph, and hydrogen production tests are carried out for 5 hours under mechanical vibration (40 kHz) and xenon lamp irradiation (300W, lambda >420 nm). The hydrogen yield of the bismuth ferrite and the defective tungsten oxide coated bismuth ferrite nano material is compared in FIG. 6, and the hydrogen yield of the bismuth ferrite nano material in 5 hours is only 4.02 mmol.g ^-1, and under the same conditions, the hydrogen yield of the defective tungsten oxide coated bismuth ferrite nano material in 5 hours is about 19.55 mmol.g ^-1, which is 4.86 times of that of the pure bismuth ferrite nano material, so that the hydrogen yield efficiency is remarkably improved.

In summary, the invention uses the coprecipitation method and uses bismuth nitrate, ferric nitrate and tungsten ethoxide as reactants to successfully synthesize the defect tungsten oxide coated bismuth ferrite nano material. The piezoelectric photocatalytic degradation organic pollutant and hydrogen production performance of the defect-state tungsten oxide coated bismuth ferrite nano material are both obviously improved. The method for degrading organic pollutants and decomposing water into hydrogen by utilizing mechanical energy and natural light through piezoelectric photocatalysis has the advantages of simple process flow, strong operability and wide application prospect. The source of mechanical energy is wide, the mechanical energy and solar energy are effectively utilized and converted, and the generation of organic pollutants and hydrogen energy has important significance for the sustainable development of future society.

Claims

1. The preparation method of the unsaturated tungsten oxide coated bismuth ferrite nano material is characterized by comprising the following steps of:

Transferring the mixed solution in the step four into a liner of a reaction kettle for hydrothermal reaction, centrifuging turbid liquid after the hydrothermal reaction to obtain a precipitate, washing with water, centrifuging, alternating for three times, washing with ethanol, and vacuum drying to obtain the unsaturated tungsten oxide coated bismuth ferrite nano particles.

2. The method according to claim 1, characterized in that:

the molar ratio of bismuth nitrate to ferric nitrate in the first step is 1:1.1;

The dilute nitric acid solution in the first step is prepared by preparing concentrated nitric acid and water in a volume ratio of 1:30-40;

the pH value in the first step is alkaline 9-10;

the drying condition in the first step is that the temperature of the oven is 50-70 ℃ and the time is 9-14 h.

3. The method according to claim 1, characterized in that:

The temperature rising rate in the second step is 4-8 ℃ per minute;

the calcination temperature in the second step is 300-500 ℃;

and in the second step, the calcination time is 30-60 min.

4. The method according to claim 1, characterized in that:

The centrifugal speed in the third step is 9000r/min;

And step three, vacuum drying is carried out under the conditions that the temperature is 50-70 ℃, the vacuum degree is minus 25 to minus 30kpa, and the time is 9-12 hours.

5. The method according to claim 1, characterized in that:

in the fourth step, the concentration of tungsten ethanol is 1-10 mmol/L;

The water bath temperature in the fourth step is 50-70 ℃;

and in the fourth step, the ultrasonic time is 20-40 min.

6. The method according to claim 1, characterized in that:

the hydrothermal reaction condition in the fifth step is that the temperature is 150-200 ℃ and the time is 18-24 h;

The centrifugal speed in the fifth step is 9000r/min;

and fifthly, the vacuum drying condition is that the temperature is 50-70 ℃, the vacuum degree is-25 to-30 kpa, and the time is 9-12 h.

7. An unsaturated tungsten oxide coated bismuth ferrite nanomaterial prepared by the method of any one of claims 1 to 6.

8. An application of the unsaturated tungsten oxide coated bismuth ferrite nano material according to claim 7 in the aspects of piezoelectric photocatalytic degradation of organic pollutants and piezoelectric light synergistic hydrogen production.

9. The method according to claim 8, wherein the unsaturated tungsten oxide coated bismuth ferrite nanomaterial is used for degrading organic pollutants under piezophotocatalysis, and is characterized by comprising the specific steps of uniformly dispersing the unsaturated tungsten oxide coated bismuth ferrite nanomaterial in a methylene blue solution of 5mg/L, measuring the absorbance change of the methylene blue aqueous solution under the conditions of mechanical force and illumination by an ultraviolet-visible spectrophotometer, and calculating the degradation rate.

10. The application of the method according to claim 9, wherein the mechanical force and the illumination are specifically generated by carrying out ultrasonic and xenon lamp illumination on a solution containing the unsaturated tungsten oxide coated bismuth ferrite nano material, wherein the ultrasonic frequency is 20-60 kHz, the xenon lamp power is 300W, and the optical filter is lambda >420nm.

11. The application of the unsaturated tungsten oxide coated bismuth ferrite nano material in piezoelectricity photocatalysis decomposition of water to produce hydrogen, according to claim 8, wherein the specific steps are that the unsaturated tungsten oxide coated bismuth ferrite nano material is uniformly dispersed in Na ₂SO₃ solution, nitrogen is introduced to remove oxygen, and the produced hydrogen is measured by gas chromatography under the conditions of mechanical force and illumination.

12. The application of the method according to claim 11, wherein the mechanical force and the illumination are specifically generated by carrying out ultrasonic and xenon lamp illumination on a solution containing the unsaturated tungsten oxide coated bismuth ferrite nano material, wherein the ultrasonic frequency is 20-60 kHz, the xenon lamp power is 300W, and the optical filter is lambda >420nm.