Visible light photocatalyst and preparation method thereof

Abstract

The invention relates to the technical field of catalytic materials, and particularly discloses a visible light photocatalyst and a preparation method thereof.The visible light photocatalyst comprises a core layer-shell layer-dynamic regulation and control layer three-stage structure; the core layer is heterojunction nano-particles formed by bismuth vanadate and bismuth oxyiodide, and the bismuth vanadate particles are uniformly dispersed on the surface of the bismuth oxyiodide to form a p-n heterojunction; the molar ratio of bismuth vanadate to bismuth oxyiodide in the core layer is 1: (0.5-2), and the particle size range is 30-80 nm; through an elaborately designed three-level structure and a dynamic regulation and control mechanism, the response efficiency and environmental adaptability of the photocatalyst to visible light are remarkably improved. A built-in electric field is formed by utilizing the energy band matching characteristic of bismuth vanadate and bismuth oxyiodide, so that the separation of photo-induced electron-hole pairs is effectively promoted, and the absorption boundary of visible light is expanded to 650nm.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalytic materials, in particular to a visible light photocatalyst and a preparation method thereof. BACKGROUND

[0002] Photocatalytic technology shows great application potential in environmental purification and energy conversion fields, such as water splitting to produce hydrogen, carbon dioxide reduction, etc., by using the photogenerated carriers generated by photocatalysts under light conditions to trigger a series of redox reactions.

[0003] However, the conventional photocatalysts on the market have the problem of insufficient light response, for example, the band gap of TiO2 is about 3.2eV, which can only respond to ultraviolet light, and the utilization rate of visible light is low, which limits its range of application in practical application; in addition, the carrier recombination rate is high, which makes the photogenerated electron-hole pairs generated by the conventional heterojunction photocatalyst under light easy to recombine, thereby reducing the quantum efficiency, in order to improve the separation efficiency, the photocatalyst needs to be additionally modified.

[0004] Another challenge is poor environmental adaptability, and the fixed band structure is difficult to adapt to the dynamic changes of different light intensities, temperatures or pollutant types, which limits the catalytic activity to only perform under a single reaction condition; in addition, the preparation process is complex, the interlayer interface regulation of the core-shell structure photocatalyst depends on precise synthesis technology, and the traditional method is difficult to achieve uniform coating at the nanoscale, which affects the stability of the catalytic performance. SUMMARY

[0005] The purpose of the present application is to provide a visible light photocatalyst and a preparation method thereof, the visible light photocatalyst prepared by the present application has high light response range and photocatalytic activity, by using special doping technology and surface modification means, the band gap of the photocatalyst is effectively reduced, so that it can respond to visible light, even part of near-infrared light, thereby greatly expanding the light absorption range.

[0006] To achieve the above purpose, the present application provides the following technical scheme: In a first aspect, a visible light photocatalyst comprises a core layer-shell layer-dynamic regulation layer three-layer structure. The core layer is formed by heterojunction nanoparticles of bismuth vanadate and bismuth oxyiodide, and the bismuth vanadate particles are uniformly dispersed on the surface of the bismuth oxyiodide to form a p-n heterojunction. The molar ratio of bismuth vanadate to bismuth oxyiodide in the core layer is 1:0.5-2, and the particle size range is 30-80nm. The shell layer is composed of rare earth doped titanium dioxide and bismuth trioxide nanosheet layer composite, the rare earth element is lanthanum, the doping amount is 0.5-3wt% of the total mass of titanium dioxide and bismuth trioxide nanometer, the sheet layer thickness is 5-20nm, and the specific surface area is greater than or equal to 15m 2 / g; The dynamic regulation layer is loaded on the surface of the shell layer and is a stimulus-responsive material, and heat-induced color change tungsten trioxide or photochromic spiropyran molecules are selected, the thickness of the dynamic regulation layer is 2-10nm, the photochromic molecules are grafted to the surface of the shell layer through amino silane coupling agent, and the response wavelength range is 380-550nm.

[0007] Further, the core layer is prepared by the following method: Step one: 10-20 parts of bismuth nitrate pentahydrate is dissolved in 50-100 parts of ethylene glycol, 2-5 parts of potassium iodide is dissolved in 20-50 parts of distilled water, and the two solutions are mixed uniformly to obtain solution A; Step two: 5-15 parts of ammonium metavanadate and 3-8 parts of citric acid are dissolved in 30-80 parts of deionized water, and heated to 60℃ to obtain solution B; Step three: solution B is stirred, and solution A is added to solution B during stirring, and stirring is continued for 2-4h, and after stirring is stopped, it is aged at room temperature for 12-24h, after completion, centrifugation, washing and drying obtain core layer heterojunction nanoparticles.

[0008] Further, the citric acid in step two is prepared by the following method: Sucrose is selected, nitrogen source and inorganic salt are added to prepare fermentation medium, aspergillus niger is inoculated, and deep fermentation is carried out at 30-50℃, and the substrate is converted into citric acid through glycolysis and tricarboxylic acid cycle.

[0009] Further, the shell layer is prepared by the following method: S1: according to the mass ratio of titanium dioxide to bismuth trioxide nanosheet 3-5:5-7, tetrabutyl titanate and bismuth nitrate are dissolved in dilute nitric acid with a concentration of 5-10wt%, then 0.1%-0.5% of cetyltrimethylammonium bromide template agent is added, and 0.5-3wt% of rare earth element lanthanum is added to the total mass of titanium dioxide and bismuth trioxide nanometer, to obtain shell layer precursor; S2: add the core layer product, the mass ratio of the core layer product to the shell layer precursor is 1:2-4, adjust the pH value to 4-5, transfer to a hydrothermal reaction kettle, stir, and heat to 180-200℃, react for 24-36h, after completion, cool, wash and dry, to obtain the shell coated heterojunction nanoparticles.

[0010] Further, the stirring time in S2 is 2-4h, and the stirring speed is 300-500rpm.

[0011] Further, the dynamic regulation layer is loaded by the following method: (1) Take 10-20 g of the shell layer product, immerse it in 100-200 mL of an ethanol solution containing 1-2 wt% of spiropyran or WO3 nanoparticles, add amino silane coupling agent, and adjust the pH value to 4-5, and perform ultrasonic treatment for 20-40 min; (2) Transfer the mixture to a tube furnace, heat to 300-350℃ at a heating rate of 1-3℃ / min under a nitrogen atmosphere, and keep the temperature for 1-3 h, and then take out after cooling.

[0012] Further, the molar ratio of the photochromic molecule to the amino silane coupling agent on the surface of the shell layer is 1:1-2.

[0013] The preparation method of the visible light photocatalyst is as follows: One: core layer synthesis: according to the molar ratio of bismuth vanadate to bismuth oxyiodide of 1:0.5-2, 10-20 parts of bismuth nitrate pentahydrate is dissolved in 50-100 parts of ethylene glycol, 2-5 parts of potassium iodide is dissolved in 20-50 parts of distilled water, the two solutions are mixed uniformly to obtain solution A, 5-15 parts of ammonium metavanadate and 3-8 parts of citric acid are dissolved in 30-80 parts of deionized water, heated to 60℃, and solution B is obtained. Stir solution B, add solution A to solution B during stirring, continue stirring for 2-4 h, and then age at room temperature for 12-24 h after stopping stirring. After completion, centrifugation, washing and drying obtain the core layer heterojunction nanoparticles, i.e. the core layer product; Two: shell coating: according to the mass ratio of titanium dioxide to bismuth oxybismuth nanoparticles of 3-5:5-7, tetrabutyl titanate and bismuth nitrate are dissolved in dilute nitric acid with a concentration of 5-10 wt%, then 0.1%-0.5% of cetyltrimethylammonium bromide template agent is added, accounting for 0.5-3 wt% of the total mass of titanium dioxide and bismuth oxybismuth nanoparticles, and 0.5-3 wt% of rare earth element lanthanum is added, to obtain a shell precursor. Add the core layer product, and the mass ratio of the core layer product to the shell precursor is 1:2-4, adjust the pH value to 4-5, transfer to a hydrothermal reaction kettle, stir at a speed of 300-500 rpm for 2-4 h, and heat to 180-200℃, react for 24-36 h, and then cool, wash and dry to obtain the shell coated heterojunction nanoparticles, i.e. the shell product; Three: dynamic layer loading: mix the shell product with 1-2 wt% of a spiropyran ethanol solution at a solid-liquid ratio of 1:8-1:12 g / mL, add 0.05-0.2 g of amino silane coupling agent, ultrasonic for 20-40 min, and calcine at 300-350℃ under a nitrogen atmosphere at a heating rate of 1-3℃ / min for 1-3 h to obtain a visible light responsive catalyst; Four: Post-processing: Visible light response catalyst grinding sieve, control particle size of 100-500nm.

[0014] Compared with the prior art, the beneficial effects of the present application are: 1. The present application, through careful design of the three-level structure and dynamic regulation mechanism, significantly improves the response efficiency of the photocatalyst to visible light and environmental adaptability. Utilizing the band matching characteristics of bismuth vanadate and bismuth oxyiodide, an internal electric field is formed, which effectively promotes the separation of photo-generated electron-hole pairs and extends the absorption boundary of visible light to 650nm; in addition, by doping lanthanum to introduce lattice defects, the scattering effect of visible light is enhanced, and the specific surface area of the material is also improved, thereby increasing the active sites for reaction.

[0015] 2. The present application relates to a dynamic band regulation technology, which can adapt to complex and variable environmental conditions. Specifically, in the case of temperature change, the distortion of WO3 lattice will cause dynamic adjustment of the band gap to adapt to the energy demand of CO2 reduction reaction at different temperatures; in addition, the change of light intensity will trigger the transformation of molecular conformation, with a response wavelength range of 380 to 550nm, thereby optimizing the absorption efficiency of visible light in real time; this technology also utilizes the synergistic effect of dynamic layer and core-shell structure, so that under AM1.5 standard light conditions, the methane selectivity of the catalyst reaches or exceeds 95%, the conversion frequency is high, and the performance is improved by more than half compared with static catalysts.

[0016] 3. The present application, the photochromic molecules are grafted to the shell layer through amino silane coupling agent, which specifically adsorbs pollutant molecules such as formaldehyde and benzene series, shortens the diffusion path, promotes the activation of intermediates, and accelerates the reaction kinetics; in addition, the photochromic molecules undergo conformational change under light, which can reversibly adjust the surface properties of the material, thereby realizing dynamic adsorption and release of pollutants under light conditions, improving the regeneration ability and cyclic use stability of the catalyst, which makes the present application have wide application prospect in air purification, indoor environmental governance and other fields.

[0017] 4. The present application, through the multi-dimensional innovation of "core-shell structure light absorption-dynamic layer intelligent regulation-interfacial efficient catalysis", breaks through the performance bottleneck of traditional photocatalysts, and provides an efficient and stable solution for visible light driven environmental governance and energy conversion. DETAILED DESCRIPTION

[0018] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0019] It should be noted that the raw materials used in the following experiments are all commercially available.

[0020] A visible light photocatalyst comprises a core-shell-dynamic regulation layer three-layer structure. The core layer is formed by heterojunction nanoparticles of bismuth vanadate and bismuth oxyiodide, and the bismuth vanadate particles are uniformly dispersed on the surface of the bismuth oxyiodide to form a p-n heterojunction. The molar ratio of bismuth vanadate to bismuth oxyiodide in the core layer is 1:0.5-2, and the particle size is 30-80 nm. The shell layer is a rare earth doped titanium dioxide and bismuth trioxide nanosheet composite material, the rare earth element is lanthanum, the doping amount is 0.5-3wt% of the total mass of titanium dioxide and bismuth trioxide nanometer, the sheet thickness is 5-20 nm, and the specific surface area is ≥150 / g; The dynamic regulation layer is a stimulus-responsive material loaded on the surface of the shell layer, and a thermochromic tungsten trioxide or a photochromic spiropyran molecule is selected, the thickness of the dynamic regulation layer is 2-10 nm, the photochromic molecule is grafted to the surface of the shell layer through an amino silane coupling agent, and the response wavelength range is 380-550 nm.

[0021] Example 1 First, 10 parts of bismuth nitrate pentahydrate are dissolved in 50 parts of ethylene glycol, then 2 parts of potassium iodide are dissolved in 20 parts of distilled water to obtain two mixed solutions, which are then uniformly mixed to obtain solution A. Secondly, 5 parts of ammonium metavanadate and 3 parts of citric acid are dissolved in 30 parts of deionized water, and the solution is heated to 60℃ to obtain solution B. Solution A is added to solution B and stirred for 2h. After stirring, the solution is aged at room temperature for 12h. After aging, the solution is placed in a centrifuge at a speed of 8000rpm for 10min. After centrifugation, the solution is washed with ethanol for 3 times, and then dried in a drying oven at 60℃ for 6h to obtain core layer heterojunction nanoparticles, i.e. the core layer product. The molar ratio of bismuth vanadate to bismuth oxyiodide in the core layer is 1:0.5, and the particle size is 30nm.

[0022] Two, shell coating is carried out, at this time, the mass ratio of titanium dioxide / bismuth trioxide nanometer 3:7, 15 g of tetrabutyl titanate and 25 g of bismuth nitrate are dissolved in 100 mL of 5 wt% dilute nitric acid, 0.1% cetyltrimethylammonium bromide template is added, about 0.05 g, and 0.5% of rare earth element lanthanum is added to the total mass of titanium dioxide and bismuth trioxide nanosheet, to obtain a shell precursor, the core layer product and the shell precursor are matched in a mass ratio of 1:2, the pH is adjusted to 4, and then transferred to a hydrothermal reaction kettle for stirring, the stirring speed is 300-500 rpm, the time is 2 h, and the temperature is raised to 180 DEG C, and the reaction is carried out for 24 h, after completion, cooling is carried out, the product is centrifuged after cooling, the centrifugal speed is 6000 rpm, and the time is 15 min, after completion, the product is washed twice with deionized water, and placed in a drying box at 80 DEG C for drying for 12 h, to obtain a shell product with a shell thickness of 5 nm and a specific surface area of 150 m 2 / g or more.

[0023] Three, dynamic layer loading is carried out, the shell product 10 g is immersed in 100 mL of ethanol solution containing 1 wt% spiropyran, 0.05 g of amino silane coupling agent is added, and the pH value is adjusted to 4, and ultrasonic is carried out for 20 min, after completion, the temperature is raised to 300 DEG C at 1 DEG C / min under nitrogen atmosphere, and calcination is carried out for 1 h, to obtain a dynamic regulation layer with a thickness of 2 nm, after completion, the product is ground and sieved until the particle size is 300 nm.

[0024] Example two One, 15 parts of bismuth nitrate pentahydrate are dissolved in 75 parts of ethylene glycol, then 3 parts of potassium iodide are dissolved in 30 parts of distilled water to obtain two mixed solutions, then the two solutions are uniformly mixed to obtain solution A, then 10 parts of ammonium metavanadate and 5 parts of citric acid are dissolved in 50 parts of deionized water, and the solution is heated to 60 DEG C to obtain solution B. Solution A is added to solution B and stirred for 3 h, and then aged at room temperature for 18 h. After completion of the aging, the solution is placed in a centrifuge at a speed of 8000 rpm for 10 min, then washed with ethanol for 3 times, and then placed in a drying box at 60 DEG C for drying for 6 h to obtain a core layer heterojunction nanoparticle, i.e. a core layer product, and the molar ratio of bismuth vanadate to bismuth oxyiodide in the core layer is 1:1.5, and the particle size is 55 nm.

[0025] Second, shell coating is performed. At this time, the mass ratio of titanium dioxide / bismuth trioxide is 4:6. 20 g of tetrabutyl titanate and 15 g of bismuth nitrate are dissolved in 150 mL of 8 wt% dilute nitric acid. 0.3% of hexadecyl trimethyl ammonium bromide template agent is added, about 0.01 g, and 1.5 wt% of rare earth element lanthanum based on the total mass of titanium dioxide and bismuth trioxide nanometer is added to obtain a shell precursor. The core layer product and the shell precursor are matched according to a mass ratio of 1:3. The lanthanum nitrate doping amount is 2 wt%. The pH is adjusted to 4.5, and then transferred to a hydrothermal reaction kettle for stirring. The stirring speed is 400 rpm, the time is 3 h, the temperature is raised to 190 DEG C, and the reaction is performed for 30 h. After completion, cooling is performed. The product is centrifuged at a speed of 6000 rpm for 15 min. After completion, the product is washed twice with deionized water, and placed in a drying box at 80 DEG C for drying for 12 h to obtain a shell product with a shell thickness of 15 nm and a specific surface area of greater than or equal to 150 m 2 / g.

[0026] Third, dynamic layer loading is performed. The shell product 15 g is immersed in 150 mL of an ethanol solution containing 1.5 wt% of spiropyran, 0.15 g of amino silane coupling agent is added, and the pH value is adjusted to 4.5. Ultrasonic treatment is performed for 30 min. After completion, the temperature is raised to 325 DEG C at a rate of 2 DEG C / min under a nitrogen atmosphere, and calcination is performed for 2 h to obtain a dynamic control layer with a thickness of 6 nm. After completion, the product is ground and sieved until the particle size is 400 nm.

[0027] Example Three 20 parts of bismuth nitrate pentahydrate are dissolved in 100 parts of ethylene glycol. Then, 5 parts of potassium iodide are dissolved in 50 parts of distilled water to obtain two mixed solutions. Then, the two solutions are uniformly mixed to obtain solution A. Then, 15 parts of ammonium metavanadate and 8 parts of citric acid are dissolved in 80 parts of deionized water to obtain solution B. The temperature of the solution is raised to 60 DEG C to obtain solution B. Solution A is added to solution B and stirred for 4 h. After stirring, the solution is aged at room temperature for 24 h. After completion of the aging, the solution is placed in a centrifuge at a speed of 8000 rpm for 10 min. After completion, the solution is washed with ethanol for 3 times, and then placed in a drying box at 60 DEG C for drying for 6 h to obtain a core layer heterojunction nanoparticle, i.e. a core layer product. The molar ratio of bismuth vanadate to bismuth oxyiodide in the core layer is 1:2, and the particle size is 80 nm.

[0028] Second, shell coating is performed, at this time, the mass ratio of titanium dioxide / bismuth trioxide nano is 5:5, 25 g of tetrabutyl titanate and 25 g of bismuth nitrate are dissolved in 200 mL of 10 wt% dilute nitric acid, 0.5% of hexadecyl trimethyl ammonium bromide template agent is added, about 0.25 g, and 3 wt% of rare earth element lanthanum based on the total mass of titanium dioxide and bismuth trioxide nano is added, to obtain a shell precursor, the core layer product and the shell precursor are matched according to a mass ratio of 1:4, the pH is adjusted to 5, and then transferred to a hydrothermal reaction kettle for stirring, and heated to 200 DEG C, and reacted for 36 h, after completion, cooling is performed, after cooling, the product is centrifuged at a speed of 6000 rpm for 15 min, after completion, washed twice with deionized water, and placed in a drying box at 80 DEG C for drying for 12 h, to obtain a shell product with a shell thickness of 20 nm and a specific surface area of 150 m 2 / g or more.

[0029] Third, dynamic layer loading is performed, the shell product 20 g is immersed in 200 mL of an ethanol solution containing 2 wt% of WO3 nano particles, 0.2 g of amino silane coupling agent is added, and the pH value is adjusted to 5, ultrasonic is performed for 40 min, after completion, heated to 350 DEG C at a rate of 3 DEG C / min under a nitrogen atmosphere, and calcined for 3 h, to obtain a dynamic regulation layer with a thickness of 10 nm, after completion, the product is ground and sieved until the particle size is 500 nm.

[0030] In the comparative example 1, it is a traditional TiO2, such as P25.

[0031] In the comparative example 2, it is a core-shell structure titanium dioxide / bismuth trioxide nano without a dynamic regulation layer.

[0032] The test data and the comparative data are shown in Table 1 as follows: Table 1 ; The test data and the comparative data are shown in Table 2 as follows: Table 2 ; In the present application, the absorption boundary is expanded to 650 nm, which is higher than 400 nm of the traditional TiO2, and then, the photoelectron-hole recombination rate of the examples is 30% to 50%, which is significantly lower than 75% and 55% of the comparative examples.

[0033] Secondly, the CH4 selectivity is all 95% or more, and the yield is 8.2 to 8.8 μmol / g / h, which is several times higher than that of the comparative examples 1 and 2.

[0034] In addition, after 5 cycles, the examples still maintain 91% or more, while the comparative examples 1 and 2 are only 65% and 80%, so that the shell uniform coating and the dynamic layer chemical stability of the present application improve the durability of the catalyst.

[0035] Finally, the application is superior to traditional photocatalysts and single core-shell structure in visible light response, carrier separation, catalytic activity and stability through the design of three-level structure and dynamic regulation mechanism, verifying the advancement and practicality of the technical scheme.

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

[0037] The preferred embodiments of the application disclosed above are only used to help explain the application. The preferred embodiments do not describe all the details and limit the application to the specific embodiments described. Obviously, many modifications and changes can be made according to the content of the present specification. The present specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the application, so that those skilled in the art can well understand and utilize the application. The application is limited only by the claims and their full scope and effects.

Claims

1. A visible light photocatalyst, characterized in that: It includes a three-level structure: core layer, shell layer, and dynamic control layer; The core layer consists of heterojunction nanoparticles formed by bismuth vanadate and bismuth oxyiodide, with the bismuth vanadate particles uniformly dispersed on the surface of bismuth oxyiodide to form a pn heterojunction. The molar ratio of bismuth vanadate to bismuth oxyiodide in the core layer is 1:0.5-2, and the particle size range is 30-80 nm. The shell is a composite material of rare-earth-doped titanium dioxide and bismuth trioxide nanosheets, wherein the rare-earth element is lanthanum, and the doping amount is 0.5-3 wt% of the total mass of the titanium dioxide and bismuth trioxide nanosheets. The sheet thickness is 5-20 nm, and the specific surface area is ≥15 m². 2 / g; The dynamic control layer is loaded with a stimulus-responsive material on the shell surface, which is selected from thermochromic tungsten trioxide or photochromic spiropyran molecules. The thickness of the dynamic control layer is 2-10 nm. The photochromic molecules are grafted to the shell surface through an aminosilane coupling agent, and the response wavelength range is 380-550 nm.

2. The visible light photocatalyst according to claim 1, characterized in that: The method for preparing the core layer is as follows: Step 1: Dissolve 10-20 parts of bismuth nitrate pentahydrate in 50-100 parts of ethylene glycol, and dissolve 2-5 parts of potassium iodide in 20-50 parts of distilled water. Mix the two solutions thoroughly to obtain solution A. Step 2: Dissolve 5-15 parts of ammonium metavanadate and 3-8 parts of citric acid in 30-80 parts of deionized water, and heat to 60°C to obtain solution B; Step 3: Stir solution B while adding solution A to solution B. Continue stirring for 2-4 hours after addition. After stopping stirring, age at room temperature for 12-24 hours. After completion, centrifuge, wash, and dry to obtain core-layer heterojunction nanoparticles.

3. A visible light photocatalyst according to claim 2, characterized in that: The citric acid in step two is prepared by the following method: Sucrose was selected, and a fermentation medium was prepared by adding nitrogen source and inorganic salt. Aspergillus niger was inoculated and deep fermentation was carried out at 30-50℃. The substrate was converted into citric acid through glycolysis and tricarboxylic acid cycle.

4. A visible light photocatalyst according to claim 1, characterized in that: The shell layer is prepared by coating using the following method: S1: According to the mass ratio of titanium dioxide to bismuth trioxide nanosheets of 3-5:5-7, tetrabutyl titanate and bismuth nitrate are dissolved in dilute nitric acid with a concentration of 5-10wt%, and then 0.1%-0.5% of hexadecyltrimethylammonium bromide template agent is added, and 0.5-3wt% of rare earth element lanthanum is added at the same time to obtain the shell precursor; S2: Add the core product, with a mass ratio of core product to shell precursor of 1:2 to 4. Adjust the pH value to 4 to 5, transfer to a hydrothermal reactor for stirring, and heat to 180 to 200°C. React for 24 to 36 hours. After completion, cool, wash, and dry to obtain shell-coated heterojunction nanoparticles.

5. A visible light photocatalyst according to claim 4, characterized in that: The stirring time in S2 is 2-4 hours, and the stirring speed is 300-500 rpm.

6. A visible light photocatalyst according to claim 1, characterized in that: The dynamic control layer is loaded through the following method: (1) Take 10-20g of shell product and immerse it in 100-200mL of ethanol solution containing 1-2wt% spiropyran or WO3 nanoparticles. At the same time, add aminosilane coupling agent and adjust the pH value to 4-5. Perform ultrasonic treatment for 20-40min. (2) Transfer the mixture to a tube furnace and heat it to 300-350°C at a heating rate of 1-3°C / min under a nitrogen atmosphere. Hold the temperature for 1-3 hours, then cool it and remove it.

7. A visible light photocatalyst according to claim 1, characterized in that: The molar ratio of the photochromic molecule to the aminosilane coupling agent on the shell surface is 1:1 to 2.

8. A method for preparing a visible light photocatalyst as described in any one of claims 1 to 7, characterized in that: The photocatalyst is prepared as follows:

1. Core Layer Synthesis: Bismuth vanadate and bismuth oxyiodide were mixed at a molar ratio of 1:0.5–2. 10–20 parts of bismuth nitrate pentahydrate were dissolved in 50–100 parts of ethylene glycol, and 2–5 parts of potassium iodide were dissolved in 20–50 parts of distilled water. The two solutions were mixed thoroughly to obtain solution A. 5–15 parts of ammonium metavanadate and 3–8 parts of citric acid were dissolved in 30–80 parts of deionized water. The mixture was heated to 60°C to obtain solution B. Solution B was stirred, and solution A was added to solution B during the stirring process. After addition, stirring was continued for 2–4 hours. After stirring was stopped, the mixture was aged at room temperature for 12–24 hours. After completion, the mixture was centrifuged, washed, and dried to obtain core layer heterojunction nanoparticles, i.e., the core layer product.

2. Shell Coating: Tetrabutyl titanate and bismuth nitrate were dissolved in dilute nitric acid with a concentration of 5-10 wt% at a titanium dioxide / bismuth trioxide nanoparticle mass ratio of 3-5:5-7. Then, 0.1%-0.5% of hexadecyltrimethylammonium bromide template agent was added, along with 0.5-3 wt% of rare earth element lanthanum, to obtain the shell precursor. The core product was then added, with a core product to shell precursor mass ratio of 1:2-4. The pH was adjusted to 4-5, and the mixture was transferred to a hydrothermal reactor for stirring at a speed of 300-500 rpm for 2-4 hours. The temperature was raised to 180-200℃ and the reaction was carried out for 24-36 hours. After completion, the mixture was cooled, washed, and dried to obtain shell-coated heterojunction nanoparticles, i.e., the shell product.

3. Dynamic layer loading: The shell product is mixed with 1-2 wt% spiropyran ethanol solution at a solid-liquid ratio of 1:8-1:12 g / mL, 0.05-0.2 g aminosilane coupling agent is added, and the mixture is sonicated for 20-40 min. Then, it is calcined in a nitrogen atmosphere at a temperature of 1-3 °C / min to 300-350 °C for 1-3 h to obtain a visible light responsive catalyst.

4. Post-processing: Grind and sieve the visible light responsive catalyst to control the particle size to 100-500 nm.