Piezoelectric coupling photocatalyst, preparation method and application thereof

Abstract

The application provides a piezoelectric coupling photocatalyst, a preparation method and application thereof, wherein the piezoelectric coupling photocatalyst can couple piezoelectric materials and semiconductor characteristics, combines the photocatalysis and piezoelectric catalysis principles, can realize all-weather algae inhibition with efficiency improvement and speed increase, can couple the wind energy, water wave energy, vibration and solar energy in nature, and provides a new principle and new idea for multi-path utilization of natural energy, energy saving and emission reduction, and has great potential in future energy environment applications.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalytic algae removal, and particularly relates to a piezoelectric coupling photocatalyst and a preparation method and application thereof. BACKGROUND

[0002] With the aggravation of water eutrophication, the ecological safety crisis caused by cyanobacterial blooms is becoming increasingly serious. Algal explosive proliferation not only causes water transparency to decline, dissolved oxygen to be exhausted, and biodiversity to be attenuated, but also releases secondary pollutants such as microcystins and fishy algae toxins, which directly threaten drinking water safety. Photocatalytic advanced oxidation is considered one of the most effective technologies for algae inactivation and organic matter degradation due to its low cost, environmental sustainability and high efficiency. When photocatalytic algae removal is performed, solar energy commonly existing in algal bloom growth waters is used to efficiently inactivate algal cells and oxidize metabolic products such as algal toxins through the generation of strong oxidizing free radicals and other active oxygen species by photocatalysts under daytime light.

[0003] However, although the current photocatalytic oxidation technology shows potential in terms of algae inactivation and organic matter degradation, it is severely restricted in terms of application performance in actual water treatment engineering due to low spectral utilization rate, low charge separation efficiency, low orbital matching degree and easy environmental light influence. SUMMARY

[0004] Embodiments of the present application provide a piezoelectric coupling photocatalyst and a preparation method and application thereof, aiming to improve the problem of narrow spectral response range, low catalytic reaction activity and inability to catalyze at all times of the existing photocatalyst.

[0005] To solve the above problems, the present application is realized through the following technical solutions:

[0006] The present application provides a piezoelectric coupling photocatalyst, which comprises Bi4NbO8Br2-Bi2Sn2O7.

[0007] Further, the molar ratio of Bi4NbO8Br to Bi2Sn2O7 in the catalyst is 2:1-1:4.

[0008] Further, the molar ratio of Bi4NbO8Br to Bi2Sn2O7 in the catalyst is 1:1.5.

[0009] Further, in the catalyst, Bi4NbO8Br is in a sheet shape.

[0010] The present application provides a preparation method of a piezoelectric coupling photocatalyst, which comprises:

[0011] providing a monomer BiOBr;

[0012] Bi2O3, Nb2O5 and BiOBr are mixed in a molten salt, calcined and washed to obtain Bi4NbO8Br;

[0013] Bi2Sn2O7 is compounded on Bi4NbO8Br to obtain a piezoelectric coupling photocatalyst.

[0014] Further, in the preparation method, the monomer BiOBr is prepared by:

[0015] Bi(NO3)3 is dissolved in ethylene glycol to obtain a first solution;

[0016] KBr is dissolved in water to form a second solution;

[0017] The second solution is added dropwise to the first solution under stirring, and then washed with water, filtered and dried to obtain the monomer BiOBr.

[0018] Further, in the preparation method, the molten salt comprises NaCl and KCl, the calcination temperature is 720-780°C, and the time is 3-5 h.

[0019] Further, in the preparation method, Bi2Sn2O7 is compounded on Bi4NbO8Br, comprising:

[0020] Bi4NbO8Br, Bi(NO3)3, polyvinylpyrrolidone are added into mannitol and mixed, a tin salt mannitol solution is added dropwise, and a strong base is added to obtain a third solution, wherein the tin salt comprises at least one of sodium stannate and potassium stannate;

[0021] The third solution is heated by a hydrothermal method to obtain a piezoelectric coupling photocatalyst.

[0022] Further, in the preparation method, during the heating of the third solution by the hydrothermal method, the temperature of the hydrothermal heating is 200°C, and the time is 24 h.

[0023] Further, in the preparation method, during the process of adding Bi4NbO8Br, Bi(NO3)3 and polyvinylpyrrolidone into mannitol and mixing, and then adding the tin salt mannitol solution dropwise, the molar ratio of Bi4NbO8Br, Bi(NO3)3 and the tin salt is controlled to be (0.12-0.48):1:1.

[0024] Further, in the preparation method, during the process of adding Bi4NbO8Br, Bi(NO3)3 and polyvinylpyrrolidone into mannitol and mixing, and then adding the tin salt mannitol solution dropwise, the molar ratio of polyvinylpyrrolidone and the tin salt is controlled to be 0.3:1.

[0025] The application further provides application of the piezoelectric coupling photocatalyst, and the piezoelectric coupling photocatalyst is used to inactivate algae.

[0026] The piezoelectric coupling photocatalyst provided in the embodiments of the application is composed of Bi4NbO8Br2 and Bi2Sn2O7, wherein Bi2Sn2O7 is a full-spectrum photocatalytic material, has two kinds of interpenetrating metal Bi and Sn arranged in tetrahedral and octahedral coordination, is beneficial to the separation of photo-generated charges, can further improve the photocatalytic performance through defect engineering, and has obvious piezocatalytic performance; in addition, the conduction band and the valence band of Bi4NbO8Br are-0.88 eV and 1.60 eV respectively, the conduction band and the valence band of Bi2Sn2O7 are-1.29 eV and 0.71 eV respectively, the band gap of Bi2Sn2O7 is relatively small, and can absorb visible and infrared light; at the same time, the energy band positions of Bi4NbO8Br and Bi2Sn2O7 enable them to construct a Z-type heterojunction through compounding, thereby greatly promoting the transfer of photo-generated carriers and retaining high potential; in addition, in the daytime or in an environment with sufficient light, Bi4NbO8Br-Bi2Sn2O7 can absorb ultraviolet, visible light and most of the infrared light, generate ROS to inhibit the reproduction of algae and inactivate algae cells, at the same time, the piezoelectric effect utilizes the mechanical vibration in the water body to generate a polarization electric field, promotes the separation and transport of photo-generated carriers, and improves the photocatalytic performance; and in the night or in the absence of light, the piezoelectric material Bi4NbO8Br in the Bi4NbO8Br-Bi2Sn2O7 heterojunction can utilize the tidal vibration mechanical energy of the water body to generate various ROS to continuously inhibit the reproduction of algae cells, and realize all-weather algae removal. Therefore, the piezoelectric coupling photocatalyst provided in the embodiments of the application can couple the piezoelectric material and the semiconductor characteristics, combine the photocatalytic and piezocatalytic principles, achieve all-weather algae inhibition with improved efficiency and speed, and couple the wind energy, water wave energy, vibration and solar energy in nature, thereby providing a new principle and a new idea for the multi-way utilization of natural energy and energy saving and emission reduction, and playing a great potential in future energy and environmental applications. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is an electron microscope test diagram of the piezoelectric coupling photocatalyst provided in the embodiments of the application;

[0028] Figure 2 is an XRD test diagram of the piezoelectric coupling photocatalyst in the embodiments of the application;

[0029] Figure 3 is a Raman spectrum test diagram of the piezoelectric coupling photocatalyst in the embodiments of the application;

[0030] Figure 4 is a KPFM test diagram of the piezoelectric coupling photocatalyst in the embodiments of the application;

[0031] Figure 5 is the ultraviolet diffuse reflection test graph of the piezoelectric coupling photocatalyst in the embodiment of the present application;

[0032] Figure 6 is the piezoelectric photocatalytic activity test graph of the piezoelectric coupling photocatalyst in the embodiment of the present application;

[0033] Figure 7 is the piezoelectric catalytic activity test graph of the piezoelectric coupling photocatalyst in the embodiment of the present application;

[0034] Figure 8 is the cycle performance test graph of the piezoelectric coupling photocatalyst in the embodiment of the present application. DETAILED DESCRIPTION

[0035] In order to make the technical problems, technical solutions and beneficial effects solved by the present application clearer, the present application will be further described in detail below in combination with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not to limit the present application.

[0036] With the aggravation of water body eutrophication, the ecological safety crisis caused by water bloom is becoming increasingly serious. The photocatalytic technology is regarded as an innovative solution in the field of environmental governance due to its green and energy-saving characteristics, which realizes the inactivation of algal cells and the degradation of toxins by producing active oxygen species through sunlight-driven catalyst.

[0037] The principle of photocatalytic algae removal is to utilize the sunlight energy commonly existing in algal bloom growth water area, to efficiently inactivate algal cells and oxidize algal toxins and other by-products through the production of strong oxidizing free radicals and other active oxygen species by photocatalysts under daylight illumination. However, photocatalytic process still faces the following four technical problems in actual algae removal applications: (1) the spectral range absorbed and utilized is too narrow; (2) the charge separation efficiency is too low; (3) the orbital matching degree is too low; (4) the algae removal efficiency is greatly affected by environmental illumination.

[0038] In view of the above problems existing in photocatalytic algae removal, the applicant found that the nanostructure of piezoelectric material can utilize the mechanical force of water flow disturbance in water body to generate a local polarization electric field. Under the action of the internal electric field, the valence band (VB) and the conduction band (CB) will tilt, thereby effectively separating the photo-induced electron-hole pairs generated by photocatalysis (piezophotonic effect). Secondly, piezoelectric effect can make the semiconductor band bend, increase the valence band potential, and promote the transition of electrons, thereby improving the utilization rate of photons. In addition, when the energy source is lost at night, piezoelectric materials can still generate a polarization electric field through piezoelectric effect, thereby generating strong oxidizing ROS.

[0039] Based on the above findings, in order to solve the problems of narrow spectral response range, low catalytic activity and inability to catalyze and remove algae at all times of the existing photocatalyst, the application provides a piezoelectric coupling photocatalyst including Bi4NbO8Br-Bi2Sn2O7, that is, the piezoelectric coupling photocatalyst provided by the application is composed of Bi4NbO8Br and Bi2Sn2O7.

[0040] In the piezoelectric coupling photocatalyst provided by the application, firstly, Bi2Sn2O7 has two interpenetrating metal Bi and Sn arranged in tetrahedral and octahedral coordination, which is beneficial to the separation of photo-generated charges, not only can further improve the photocatalytic performance through defect engineering, and Bi4NbO8Br has obvious piezoelectric catalytic performance; secondly, the conduction band and valence band positions of Bi4NbO8Br are-0.88 eV and 1.60 eV respectively, and the conduction band and valence band positions of Bi2Sn2O7 are-1.29 eV and 0.71 eV respectively, and the band gap of Bi2Sn2O7 is smaller, which can absorb visible and infrared light; at the same time, the energy band positions of Bi4NbO8Br and Bi2Sn2O7 enable them to construct a Z-type heterojunction through compounding, thereby greatly promoting the transfer of photo-generated carriers and retaining their high potential; in addition, in the daytime or in an environment with sufficient light, Bi4NbO8Br-Bi2Sn2O7 can absorb ultraviolet, visible light and most of the infrared light to generate ROS to inhibit the reproduction of algae and inactivate algal cells, in addition, the piezoelectric effect utilizes the mechanical vibration in the water body to generate a polarization electric field, promotes the separation and transmission of photo-generated carriers, and improves the photocatalytic performance; and in the night or in the absence of light, the piezoelectric material Bi4NbO8Br in the Bi4NbO8Br-Bi2Sn2O7 heterojunction can utilize the tidal vibration mechanical energy of the water body to generate various ROS to continuously inhibit the reproduction of algal cells, thereby achieving all-weather algae removal.

[0041] Therefore, the piezoelectric coupling photocatalyst provided by the application optimizes the composition, coordination structure and electronic energy state of the heterojunction, not only strengthens the built-in electric field in the heterojunction interface, but also enhances the piezoelectric polarization electric field, reduces the carrier interface recombination to enhance the charge separation efficiency, not only significantly improves the photocatalytic reaction activity and the algae removal efficiency, but also couples the piezoelectric material and semiconductor characteristics, combines the principles of photocatalysis and piezoelectric catalysis, can not only achieve all-weather algae inhibition with improved efficiency and speed, but also can integrate the wind energy, water wave energy, vibration and solar energy in nature, provides a new principle and new idea for the multi-way utilization of natural energy and energy saving and emission reduction, and plays a great potential in future energy and environmental applications.

[0042] Optionally, in view of the fact that the catalyst can generate strong oxidizing active oxygen species by utilizing solar energy and mechanical energy, the catalyst can also be used for degrading pollutants such as phenol, bisphenol A and antibiotics; and can also be used for inactivating pathogenic microorganisms.

[0043] Optionally, in an embodiment, the molar ratio of Bi4NbO8Br to Bi2Sn2O7 in the catalyst is 2:1-1:4, which can ensure that Bi4NbO8Br has excellent photocatalytic and piezoelectric properties, and Bi2Sn2O7 can broaden the light absorption range of the material.

[0044] In practical applications, the amount of Nb and Sn can be determined by X-ray photoelectron spectroscopy (XPS) analysis of the catalyst, and the molar ratio of Bi4NbO8Br to Bi2Sn2O7 can be determined.

[0045] Optionally, in an embodiment, the molar ratio of Bi4NbO8Br to Bi2Sn2O7 in the catalyst is 1:1.5, which has excellent comprehensive performance.

[0046] Optionally, in an embodiment, the molar ratio of Bi4NbO8Br to Bi2Sn2O7 in the catalyst is 1:1.5, which has excellent comprehensive performance.

[0047] Bi4NbO8Br is a Sillen-Aurivillius structure of a perovskite, which is composed of a single-layer NbO6 octahedral sheet and a (Bi2O2)2Br block, has a sheet shape, and has photocatalytic and piezoelectric properties.

[0048] Optionally, in an embodiment, the catalyst provided by the present application has Bi2Sn2O7 covering the surface of Bi4NbO8Br.

[0049] The present application provides a preparation method of a piezoelectric coupling photocatalyst, which comprises steps 201-203.

[0050] Step 201, providing monomer BiOBr;

[0051] Step 202, mixing Bi2O3, Nb2O5 and BiOBr in a molten salt, calcining and then washing to obtain Bi4NbO8Br;

[0052] Step 203, compounding Bi2Sn2O7 on Bi4NbO8Br to obtain a piezoelectric coupling photocatalyst.

[0053] In the embodiment of the present application, monomer BiOBr is prepared first, and then Bi2O3, Nb2O5 and BiOBr are calcined by a molten salt system to form Bi4NbO8Br, and then Bi2Sn2O7 is uniformly prepared on Bi4NbO8Br by a hydrothermal method, so that a piezoelectric coupling photocatalyst capable of coupling piezoelectric material and semiconductor characteristics can be obtained, which can not only realize efficiency improvement, speed increase and all-weather algae inhibition, but also can couple wind energy, water wave energy, vibration and solar energy in nature, and can effectively improve the problems of narrow spectral response range, low catalytic reaction activity and inability to catalyze at all times of the existing photocatalyst.

[0054] Optionally, in an embodiment, the step of providing monomer BiOBr includes steps 111-113:

[0055] In step 111, bismuth nitrate is dissolved in ethylene glycol to obtain a first solution.

[0056] In step 111, stirring is performed during the process of dissolving bismuth nitrate in ethylene glycol to promote the dissolution of bismuth nitrate. Optionally, the above-mentioned bismuth nitrate can be bismuth nitrate pentahydrate, and the stirring speed is controlled to be 100 r / min-500 r / min and the stirring time is controlled to be 25-120 min, which can effectively promote the dissolution of bismuth nitrate while avoiding excessive oxygen mixing.

[0057] Specifically, the bismuth nitrate can be Bi(NO3)3·5H2O.

[0058] Optionally, in the first solution, the concentration of bismuth nitrate can be 0.1-1 mmol / mL, for example, it can be one of 0.1 mmol / mL, 0.2 mmol / mL, 0.4 mmol / mL, 0.8 mmol / mL and 1 mmol / mL or a range value of any two thereof, which has a moderate concentration, which not only facilitates the contact reaction with potassium bromide to improve the piezoelectric photocatalytic performance of the product, but also avoids the waste of materials caused by the precipitation of bismuth nitrate.

[0059] For example, 10 mmol of Bi(NO3)3·5H2O can be dissolved in 25 mL of ethylene glycol under stirring, wherein the stirring speed is controlled to be 300 r / min and the stirring time is controlled to be 40 min, so that the piezoelectric photocatalytic performance of the subsequently prepared Bi4NbO8Br is better.

[0060] In step 112, potassium bromide is dissolved in water to form a second solution.

[0061] In the step 112, the stirring is performed during the process of dissolving potassium bromide in water to promote the dissolution of potassium bromide. Alternatively, in the above step, the stirring speed is controlled to be 100 r / min-500 r / min, and the stirring time is 5-120 min, which can effectively promote the dissolution of potassium bromide while avoiding excessive oxygen mixing to cause oxidation of potassium bromide.

[0062] In the above step 112, the stirring speed can be one or a range value of any two of 100 r / min, 200 r / min, 300 r / min, 400 r / min, and 500 r / min, and the stirring time can be one or a range value of any two of 5 min, 10 min, 20 min, 30 min, 40 min, 50 min, and 60 min.

[0063] Alternatively, in the above first solution, the concentration of potassium bromide can be 0.1-1 mmol / mL, for example, one or a range value of any two of 0.1 mmol / mL, 0.2 mmol / mL, 0.4 mmol / mL, 0.8 mmol / mL, and 1 mmol / mL, which is moderate in concentration, facilitating the contact reaction with bismuth nitrate to improve the piezoelectric photocatalytic performance of the product, and avoiding the waste of materials caused by the precipitation of potassium bromide.

[0064] For example, 10 mmol of KBr can be dissolved in 25 mL of deionized water under stirring, wherein the stirring speed is controlled to be 300 r / min and the stirring time is 40 min, so that the piezoelectric photocatalytic performance of the subsequently prepared Bi4NbO8Br is better.

[0065] In step 113, the second solution is added dropwise to the first solution under stirring, and then washed with water, filtered, and dried to obtain monomer BiOBr.

[0066] In the step 113, the KBr solution is slowly dropped into the Bi(NO3)3 ethylene glycol solution at room temperature of 20-30°C, and stirred for 0.5-2 h by magnetic stirring or the like, and then the filter residue is collected by washing with deionized water and drying treatment, to obtain monomer BiOBr.

[0067] Alternatively, when the filter residue is dried, the drying temperature can be 60°C, and the drying time can be 10 h.

[0068] Alternatively, Bi2O3, Nb2O5, and BiOBr are mixed in a molten salt including NaCl and KCl during calcination, the calcination temperature is 720-780°C, and the time is 3-5 h.

[0069] In the preparation method provided by the embodiments of the present application, the NaCl-KCl eutectic system is used as a fluxing agent, which significantly improves the synthesis efficiency and product quality of Bi4NbO8Br; wherein, the molten salt forms a liquid phase at high temperature, providing a solution-like environment that is conducive to the diffusion and migration of reactant ions, thereby effectively reducing the reaction activation energy and promoting the formation of the target phase; at the same time, the molten salt can up-regulate the growth rate of the crystal, which helps to obtain a product with higher crystallinity and more complete structure; in addition, since NaCl and KCl have good water solubility, they can be easily removed by water washing after the reaction without introducing impurities, and subsequent purification treatment is also facilitated. Therefore, the molten salt method not only has significant advantages in promoting the reaction and regulating the morphology, but also ensures the high purity and repeatability of the product.

[0070] Optionally, in the molten salt system, the molar ratio of NaCl and KCl is 1:1, and slow heating is performed during the calcination process to form a molten salt to provide reaction conditions for the formation of Bi4NbO8Br. The heating rate can be in the range of one of or any two of 1℃ / min -1 , 3℃ / min -1 , 5℃ / min -1 .

[0071] Optionally, the calcination temperature can be one of or in the range of any two of 720℃, 730℃, 740℃, 750℃, 760℃, 770℃, 780℃, and the calcination time can be one of or in the range of any two of 3h, 4h, 5h.

[0072] Optionally, in one embodiment, Bi2Sn2O7 is compounded on Bi4NbO8Br, including steps 211-212:

[0073] Step 211, Bi4NbO8Br, bismuth nitrate, and polyvinylpyrrolidone are added to mannitol and mixed uniformly, then a tin salt mannitol solution is added dropwise, and NaOH is added to a pH of 11.5-12.5 to obtain a third solution; the tin salt includes at least one of sodium stannate and potassium stannate.

[0074] In this step 211, the materials Bi4NbO8Br, bismuth nitrate, and polyvinylpyrrolidone are added to mannitol and mixed thoroughly by ultrasonic, shaking, or the like.

[0075] In this step 211, the bismuth nitrate can be Bi(NO3)3·5H2O, and the sodium stannate crystal can be Na2SnO3·3H2O.

[0076] In step 211, the Bi2Sn2O7 is adjusted to a small size by a polyvinylpyrrolidone-assisted solvothermal method, which is easy to be loaded on the surface of Bi4NbO8Br, and at the same time, more low-coordination surface atoms are exposed and lost to form vacancies, which not only promotes the photocatalytic carrier separation, but also is beneficial to the formation of a heterojunction with Bi4NbO8Br.

[0077] Optionally, in step 211, the molar ratio of polyvinylpyrrolidone to stannate is controlled to be 0.3:1, which can effectively adjust the Bi2Sn2O7 formed to a small size and load it on the surface of Bi4NbO8Br.

[0078] Optionally, in step 211, the molar ratio of Bi4NbO8Br, bismuth nitrate, and stannate is controlled to be (0.12-0.48):1:1, so that the Bi2Sn2O7 formed on the surface of Bi4NbO8Br forms a moderate thickness of the covering layer, which is beneficial to the diffusion of carriers to the heterojunction interface and avoids the recombination of carriers.

[0079] In step 211, after the monomers Bi4NbO8Br and bismuth nitrate are sequentially added, they are fully mixed by ultrasonic, shaking, or the like, and then a strong alkali solution is added dropwise to adjust the pH to 11.5-12.5, for example, one of 11.5, 12, and 12.5 or a range value of any two thereof, so as to utilize the etching effect of the alkali to inhibit the Bi 3+ The reduction produces Bi atoms.

[0080] Optionally, the strong alkali can be NaOH, KOH, or the like. Optionally, the strong alkali solution can be a NaOH solution with a concentration of 2 mol / L, which is moderate, can quickly adjust the pH of the system, and does not damage the crystal structure of the material due to too strong alkalinity.

[0081] In step 212, the third solution is subjected to a hydrothermal method to obtain a piezoelectric coupling photocatalyst.

[0082] In step 212, the third solution is placed in a sealed reaction device for hydrothermal heating, which can fully disperse the reaction substances and uniformly heat them to react to obtain a precipitate, and then the precipitate is taken out by centrifugation and washed with water, so as to obtain a piezoelectric coupling photocatalyst with Bi4NbO8Br and Bi2Sn2O7. The above-mentioned sealed reaction device can be a reaction kettle.

[0083] Optionally, in the process of hydrothermal heating of the third solution, the temperature of the hydrothermal heating is one or a range value of any two of 180°C, 190°C, 200°C, 210°C, 220°C, and the time is one or a range value of any two of 12 h, 24 h, 36 h, which is conducive to promoting the full conversion of the reactants and the purification of the crystal phase, and can effectively balance the yield, purity and product performance.

[0084] In order to make the invention purposes, technical solutions and beneficial effects of the present application clearer, the present application will be further described below in conjunction with examples. It should be understood that these examples are only used to illustrate the present application and not used to limit the scope of the present application.

[0085] The present application will be described in detail below through examples.

[0086] Example 1

[0087] (1) 10 mmol of Bi(NO3)3·5H2O was dissolved in 25 mL of ethylene glycol, 10 mmol of KBr was dissolved in 25 mL of deionized water, then the KBr solution was slowly dropped into the Bi(NO3)3 ethylene glycol solution under room temperature 25°C, and was magnetically stirred for 1 h, then was washed with deionized water, and the filter residue was collected and dried at 60°C for 10 h to prepare monomer BiOBr;

[0088] (2) 60.5 mmol of NaCl and 60.5 mmol of KCl were mixed as flux with 3 mmol of Bi2O3 and 2 mmol of prepared monomer BiOBr, 1 mmol of Nb2O5; then the mixture was put into a muffle furnace and heated in air at 750°C for 4 h, with a heating rate of 3°C / min -1 After cooling at room temperature 25°C, the block solid was washed with deionized water and dried in an oven at 60°C for 24 h to prepare Bi4NbO8Br;

[0089] (3) 0.16 mmol Bi4NbO8Br, 1 mmol Bi(NO3)3·5H2O and 0.3 mmol polyvinylpyrridone were added into 15 mL mannitol (0.1 M) and ultrasonically dispersed to obtain solution A; 1 mmol Na2SnO3·3H2O was dissolved in 5 mL mannitol to obtain solution B, under strong stirring, solution B was slowly dropped into solution A by using a dropper, and after stirring for 30 min, the pH was adjusted to 12 by using NaOH (2 M), and after stirring for another 30 min, the solution was placed in a 100 ml reaction kettle, heated at 200 ℃ for 24 h, after the reaction kettle was cooled to room temperature, washing and drying were performed, and a catalyst Bi4NbO8Br-Bi2Sn2O7 (1:3) with a molar ratio of Bi4NbO8Br to Bi2Sn2O7 of about 1:1.5 was prepared.

[0090] Examples 2-4

[0091] Examples 2-4 are different from Example 1 in that in step (3), the amount of Bi4NbO8Br added was adjusted to 0.48 mmol, 0.32 mmol and 0.12 mmol respectively, and catalysts Bi4NbO8Br-Bi2Sn2O7 (1:1), Bi4NbO8Br-Bi2Sn2O7 (1:2) and Bi4NbO8Br-Bi2Sn2O7 (1:4) with molar ratios of Bi4NbO8Br to Bi2Sn2O7 of 2:1, 1:1 and 1:2 respectively were obtained.

[0092] Example 5

[0093] 1 mmol Bi(NO3)3·5H2O and 0.3 mmol polyvinylpyrridone were added into 15 mL mannitol (0.1 M) and ultrasonically dispersed to obtain solution A. 1 mmol Na2SnO3·4H2O was dissolved in 5 mL mannitol to obtain solution B. Under strong stirring, solution B was slowly dropped into solution A by using a dropper, and after stirring for 30 min, the pH was adjusted to 12 by using NaOH (2 M), and after stirring for another 30 min, the solution was placed in a 100 ml reaction kettle, heated at 200 ℃ for 24 h. After the reaction kettle was cooled to room temperature, washing and drying were performed, and Bi2Sn2O7 was prepared.

[0094] Test Example 1

[0095] Bi4NbO8Br prepared in Example 1 and catalyst Bi4NbO8Br-Bi2Sn2O7 (1:3) were respectively subjected to scanning electron microscope test, and the results are shown in FIGS. (a), (b) and (c) of Figure 1 Figure 1 ​It can be seen that Bi2Sn2O7 is in blocky nanostructure, while Bi4NbO8Br is in nanosheet structure, and Bi4NbO8Br-Bi2Sn2O7 (1:3) is in blocky material coating nanosheet material, which indicates that Bi2Sn2O7 and Bi4NbO8Br are successfully compounded.

[0096] Test Example 2

[0097] Bi2Sn2O7, Bi4NbO8Br prepared in Example 1, and catalyst Bi4NbO8Br-Bi2Sn2O7 (1:3) were respectively subjected to X-ray diffraction (XRD) test, and a German PANalytical Aeris type desktop diffractometer was used for the test, with the test conditions set as: scanning range 5-90°, scanning rate 2° / min, and then the obtained spectrum was compared with a standard card library, and the results are shown in Figure 2

[0098] From Figure 2 It can be seen that the XRD peaks of Bi2Sn2O7 are consistent with the standard card (PDF #432-6954), indicating that Bi2Sn2O7 is successfully prepared; the peak position of Bi4NbO8Br is consistent with PDF #054-0818, indicating that Bi4NbO8Br has a good crystal structure; and the characteristic peaks of Bi2Sn2O7 and Bi4NbO8Br are obviously observed in Bi4NbO8Br-Bi2Sn2O7 (1:3), which indicates that Bi2Sn2O7 and Bi4NbO8Br are successfully compounded.

[0099] Test Example 3

[0100] Bi2Sn2O7, Bi4NbO8Br prepared in Example 1, and catalyst Bi4NbO8Br-Bi2Sn2O7 (1:3) were respectively subjected to Raman spectrum test, and the results are shown in Figure 3

[0101] Raman test: a laser confocal Raman spectrometer was used at an excitation wavelength of 532 nm, the sample was loaded on a glass slide and pressed into a thin piece of about 1 millimeter thick, and then scanned in the range of 50-1500 cm -1 .

[0102] From Figure 3 The peaks of [Bi2O2] 2+ , Bi-O-Bi, Nb-O-Nb and Nb-O-Bi-O-Bi can be detected, which indicates that Bi4NbO8Br is successfully prepared, and in addition, weak [Bi2O2]​​2+ , peaks of Bi-O-Bi, Nb-O-Nb and Nb-O-Bi-O-Bi, which indicates that Bi4NbO8Br-Bi2Sn2O7 successfully composites Bi2Sn2O7 and Bi4NbO8Br.

[0103] Test Example 4

[0104] The Bi4NbO8Br prepared in Example 1 was subjected to KPFM test, and the morphology image, amplitude image, phase image and butterfly-shaped displacement-voltage curve of the Bi4NbO8Br are shown in Figs. 8(a)~(d), respectively. Figure 4

[0105] Among them, the image contrast of the morphology image, amplitude image and phase image is obvious, indicating that the Bi4NbO8Br is a piezoelectric material; at the same time, combined with the typical butterfly-shaped displacement-voltage curve in Fig. 8(d), it is further indicated that the material has piezoelectric properties. The maximum effective piezoelectric coefficient d33 of the sample is determined to be 7 mV / V by calculating the slope of the displacement-voltage curve. In summary, the prepared Bi4NbO8Br is a piezoelectric material and has good piezoelectric properties. Figure 4

[0106] Test Example 5

[0107] Bi2Sn2O7 and the Bi4NbO8Br prepared in Example 1, and the catalyst Bi4NbO8Br-Bi2Sn2O7 (1:3) were subjected to ultraviolet diffuse reflectance (Diffuse Reflectance Spectroscopy, DRS) test. The test was performed by using a Lambda 1050 N / W spectrometer of PerkinElmer Company, USA, and the scanning wavelength range was 200~2500 nm. The obtained ultraviolet diffuse reflectance spectrum and band gap are shown in Fig. 5. It can be seen from Fig. 5 that the absorption boundary of the prepared catalyst Bi4NbO8Br-Bi2Sn2O7 (1:3) is about 580 nm, indicating that the material has good visible light absorption performance. Figure 5 Figure 5

[0108] Test Example 6

[0109] The catalysts prepared in each example were subjected to piezoelectric photocatalytic activity test, and the results are shown in Fig. 6. The specific test method is as follows: Figure 6

[0110] The catalyst was placed in a piezoelectric light reaction device to degrade Microcystis aeruginosa. In the process of photocatalytic reaction, LED lamp was used as light source, 40 mL of algal suspension was used, and the reactor was placed with / without catalyst (0.5 g / L) and the light source was turned on / off (20 W / m 2 ​​​​​), the reactor was placed under ultrasound / no ultrasound.

[0111] According to different reaction conditions in the above experiments: standing (Bi4NbO8Br, Bi2Sn2O7or Bi4NbO8Br-Bi2Sn2O7), turning on / off light source (Vis), with / without ultrasound (US), the following reaction systems can be obtained: ultrasound / visible light (US / Vis) system; visible light (Vis) system; catalyst / ultrasound / visible light (Bi4NbO8Br-Bi2Sn2O7 / US / Vis) system; catalyst / visible light (Bi4NbO8Br-Bi2Sn2O7 / Vis) system.

[0112] Every preset time, 8 mL of the reaction solution was taken to measure the content of chlorophyll a, then a 0.45 μm filter membrane was placed on the filtration instrument, and then 8 mL of the sample was filtered, the filter membrane was placed in a test tube and refrigerated for 12 h, the test tube was taken out, 8 mL of 90% acetone solution was added, a small amount of magnesium carbonate powder was added to protect the chlorophyll from being destroyed, and the sample was treated by an ultrasonic cell disrupter (ultrasonic time 3 s, interval time 2 s) for 3 min at a speed of 4500 r / min for 10 min, and the supernatant was taken, 90% acetone was used as a reference, and OD 630 , OD 647 , OD 664 and OD 750 were used to measure the content of chlorophyll a, and the calculation formula was as follows:

[0113]

[0114] In the formula:

[0115] OD 630 , OD 647 , OD 664 , OD 750 are absorbance values of the sample at wavelengths of 630 nm, 647 nm, 664 nm and 750 nm respectively; V1 is the sample volume, mL; V2 is the volume of 90% acetone, mL;

[0116] The removal rate of Microcystis aeruginosa was calculated as C / C0, wherein C0and C are the contents of chlorophyll a at 0 and t min respectively.

[0117] From the above experiments, the following conclusions can be drawn: Figure 6As can be known from (a), the catalyst in Example 1 has a better piezoelectric photocatalytic algae removal effect, and under the action of ultrasound and piezoelectricity, the chlorophyll of the algae cells is significantly destroyed, and 72% of the algae is removed within 4.5 h, which is much higher than 30% of Bi4NbO8Br and 10% of Bi2Sn2O7, because the composite material can promote the absorption of visible light, the photo-generated electrons can be more efficiently separated under the double action of the built-in electric field and the polarization electric field, and then a higher concentration of active oxygen species is generated to achieve efficient inactivation of the algae cells. In addition, the algae removal performance of the Bi4NbO8Br-Bi2Sn2O7 (1:3) / US / Vis system is better than that of the Bi4NbO8Br-Bi2Sn2O7 (1:3) / Vis system, which shows that the polarization electric field generated by the piezoelectric material Bi4NbO8Br can promote the separation of carriers and improve the algae removal efficiency. From (b), it can be known that in the US / Vis system and the Vis system, the algae will not die, which shows that the catalyst prepared by optimizing the experimental preparation method has better algae removal effect. Figure 6

[0118] Test Example 7

[0119] The phenol piezoelectric degradation reaction was carried out in a 100 mL quartz beaker, and the constant temperature of the reaction system was controlled to be 25°C by a cooling water circulation system. The quartz beaker was placed in a 200 W ultrasonic machine and shielded from light. 1 mL of reaction solution was taken at intervals and filtered through a 0.25 µm cellulose acetate filter membrane, and the filtrate was detected by liquid chromatography to determine the peak signal of phenol. Each experiment was designed in triplicate. The phenol degradation curve was determined by measuring the ratio of real-time concentration to initial concentration (C / C0). The concentration of phenol was detected by high performance liquid chromatography at a characteristic wavelength of 223 nm, and the mobile phase was acetonitrile:water = 20:80, and the flow rate was 0.8 mL / min.

[0120] With 10 ppm of phenol as the target pollutant, the piezoelectric degradation performance of the catalyst prepared in Example 1 under the action of ultrasound was investigated, and the results are shown in Figure 7 As can be seen, under ultrasound, Bi4NbO8Br-Bi2Sn2O7 (1:3) can degrade 37% of phenol in 4.5 h, which shows that Bi4NbO8Br-Bi2Sn2O7 (1:3) can generate a polarization electric field under the action of ultrasound, and then generate active oxygen species to degrade the pollutants.

[0121] Test Example 8

[0122] The catalyst prepared in Example 1 was subjected to a cycle performance test, and the results are shown in Figure 8 As shown in the table, the specific test method is as follows:

[0123] ​After the first degradation reaction (1st) is completed, the catalyst is separated from the solution by filtration, and the filtered catalyst is washed with deionized water and ethanol and dried in a freeze dryer for 48 hours for later use. The second degradation reaction (2st) is carried out using the above-mentioned spare material. Except for the material, the other reaction conditions are the same as the first one. After the second reaction is completed, the above steps are repeated to carry out the third (3st), fourth (4st), and fifth (5th) degradation experiments.

[0124] Depend on Figure 8 It can be seen that the Bi4NbO8Br-Bi2Sn2O7 (1:3) / US / Vis system has good cycling stability. After 5 cycles, the algae removal effect only decreased by 10%, indicating that the material has good cycling stability and good application prospects.

[0125] In summary, this application, through the application of heterojunction construction, designs and synthesizes highly efficient, all-weather piezoelectric-photocatalytic algae-removing materials by utilizing the characteristics of piezoelectric and photocatalytic materials and the band structure of semiconductors. In experiments, simulating actual aquatic environments using light, ultrasound, and stirring, the efficiency of the composite material in algae removal and intermediate product processing was studied. The surface characteristics and mechanism of action of the material were investigated, including the active sites of reactive oxygen species involved in algae removal and various algae removal indicators, to obtain a detailed understanding of the material's algae removal mechanism. Furthermore, through material characterization, a comprehensive understanding of the material's physicochemical properties, optical properties, and piezoelectric properties was achieved, providing new principles and ideas for multi-pathway utilization and energy conservation and emission reduction in the field of photocatalysis, enabling it to play a greater role in future energy and environmental applications.

[0126] Furthermore, the voltage-coupled photocatalytic material Bi4NbO8Br2-Bi2Sn2O7 prepared in this application optimizes the composition, coordination structure, and electronic energy state of the heterojunction by first preparing Bi4NbO8Br and then introducing Bi2Sn2O7 into the preparation of Bi4NbO8Br. This strengthens both the built-in electric field at the heterojunction interface and the piezoelectric polarization field, reduces carrier recombination at the interface to enhance charge separation efficiency, thereby significantly improving photocatalytic reaction activity and algae removal efficiency.

[0127] Terminology Explanation

[0128] In this application, "multiple" refers to two or more.

[0129] The terms “first,” “second,” “third,” “fourth,” etc., in this application (if present) are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0130] The term "and / or", within the context of the present application, is used to associate associated objects, and means that three relationships can exist, for example, A and / or B can mean that A exists alone, A and B exist together, and B exists alone. In addition, the character " / " within the present application generally means that the associated objects before and after are in an "or" relationship.

[0131] If not specifically stated, all steps in the present application can be performed in sequence or randomly. For example, the method comprises steps A and B, which means that the method can comprise steps A and B performed in sequence, or steps B and A performed in sequence. For example, the method can further comprise step C, which means that step C can be added to the method in any order, for example, the method can comprise steps A, B and C, or steps A, C and B, or steps C, A and B, etc.

[0132] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a piezoelectrically coupled photocatalyst, characterized by, The application relates to a piezoelectric coupling photocatalyst. BiOBr is provided; Bi2O3, Nb2O5 and BiOBr are mixed in a molten salt, calcined and washed to obtain Bi4NbO8Br; Bi2Sn2O7 is compounded on Bi4NbO8Br to obtain the piezoelectric coupling photocatalyst, wherein the piezoelectric coupling photocatalyst comprises Bi4NbO8Br-Bi2Sn2O7, the energy band position of Bi4NbO8Br and Bi2Sn2O7 is constructed into a Z-type heterojunction through compounding, and the molar ratio of Bi4NbO8Br to Bi2Sn2O7 in the catalyst is 2:1-1:4; Bi2Sn2O7 is compounded on Bi4NbO8Br, which comprises: Bi4NbO8Br, bismuth nitrate and polyvinylpyrrolidone are mixed in mannitol, a tin salt mannitol solution is added dropwise, and a strong base is added to obtain a third solution, wherein the tin salt comprises at least one of sodium stannate and potassium stannate; The piezoelectric coupling photocatalyst is obtained by hydrothermal heating of the third solution.

2. The production method according to claim 1, characterized by, The molar ratio of Bi4NbO8Br to Bi2Sn2O7 in the catalyst is 1:1.

5.

3. The preparation method according to claim 1, characterized in that, The application further provides a preparation method of the piezoelectric coupling photocatalyst. Bismuth nitrate is dissolved in ethylene glycol to obtain a first solution; Potassium bromide is dissolved in water to form a second solution; The second solution is added dropwise to the first solution under stirring, and then water washing, filtration and drying are carried out to obtain monomer BiOBr.

4. The method of claim 1, wherein, The molten salt comprises NaCl and KCl, the calcination temperature is 720-780 DEG C, and the time is 3-5 h.

5. The preparation method according to claim 1, characterized in that, During the hydrothermal heating of the third solution, the temperature of the hydrothermal heating is 200 DEG C, and the time is 24 h.

6. The method of claim 1, wherein, During the mixing of Bi4NbO8Br, bismuth nitrate and polyvinylpyrrolidone in mannitol, the molar ratio of Bi4NbO8Br, bismuth nitrate and tin salt is controlled to be (0.12-0.48):1:1; and / or During the mixing of Bi4NbO8Br, bismuth nitrate and polyvinylpyrrolidone in mannitol, the molar ratio of polyvinylpyrrolidone to tin salt is controlled to be 0.3:

1.

7. Use of a piezo-coupled photocatalyst prepared according to the method of any one of claims 1 to 6. The piezoelectric coupling photocatalyst is used for inactivating algae.

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