A core-shell catalyst, its preparation method and application

Abstract

The embodiment of the application provides a core-shell catalyst and a preparation method and application thereof, wherein the core-shell catalyst comprises: an inner core comprising I-doped BiOI; and a film layer comprising BiOI, which is arranged on the surface of the inner core. The heterojunction formed by the core-shell structure of the I-doped BiOI coated by BiOI can not only efficiently remove algae under light, but also promote the piezoelectric activation of persulfate without light, so as to realize all-weather algae removal. Moreover, due to the closer interface contact and larger contact area of the heterojunction in the core-shell structure, the photo-generated charge transfer and separation can be improved, the stability can be ensured, the active sites can be protected to resist harsh environmental conditions, and the deactivation speed of the catalyst can be effectively slowed down. In addition, since the BiOI has good piezoelectric properties, the built-in electric field and piezoelectric polarization electric field in the heterojunction interface generated by the core-shell catalyst can significantly reduce the carrier interface recombination to enhance the charge separation efficiency and significantly improve the photocatalytic reaction activity.

Description

Technical Field

[0001] This application relates to the field of catalytic algae removal technology, and in particular to a core-shell catalyst, its preparation method, and its application. Background Technology

[0002] With the increasing eutrophication of water bodies, the ecological security crisis caused by cyanobacterial blooms is becoming increasingly severe. The explosive proliferation of algae not only leads to decreased water transparency, depletion of dissolved oxygen, and decline in biodiversity, but also releases secondary pollutants such as microcystins and anabatin, posing a direct threat to drinking water safety. Photocatalysis technology, with its green and energy-saving characteristics, uses sunlight to drive catalysts to generate reactive oxygen species, thereby inactivating algal cells and degrading toxins, and is considered a revolutionary solution in the field of environmental remediation.

[0003] However, existing photocatalytic algae removal systems still face multiple technical bottlenecks: ① Narrow spectral response range, with conventional semiconductor materials utilizing less than 5% of the solar spectrum (ultraviolet band); ② Photogenerated carrier recombination rate (picosecond level) is much faster than migration rate (hundreds of picoseconds level), resulting in low quantum efficiency; ③ Solvation of the catalyst surface by a water film causes energy level mismatch, hindering interfacial electron transfer; ④ Intermittent light-dependent characteristics lead to catalytic failure at night and during cloudy / rainy weather; ⑤ In traditional non-contact catalysis, the transport distance of reactive oxygen species is limited, making them susceptible to quenching by the water matrix and difficult to contact algal cells. These bottlenecks severely restrict the large-scale application of photocatalytic technology in actual algal bloom control, necessitating the development of novel photocatalytic systems with broad-spectrum response, efficient carrier separation, and all-day catalytic algae removal capabilities. Summary of the Invention

[0004] This application provides a core-shell catalyst, its preparation method, and its application, aiming to improve the problems of low photon utilization, low catalytic activity, and inability to catalyze throughout the entire time period of existing photocatalysts.

[0005] To solve the above problems, this application provides the following technical solution:

[0006] This application proposes a core-shell catalyst, comprising:

[0007] The core, including I-doped BiOI;

[0008] A film layer, including BiOI, is disposed on the surface of the core.

[0009] In the core-shell catalyst provided in this application, the heterojunction formed by coating I-doped BiOI with BiOI not only efficiently removes algae under light, but also promotes the piezoelectric activation of persulfate in the absence of light, thus achieving all-weather algae removal. Moreover, due to the tighter interfacial contact and larger contact area of ​​the heterojunction in the core-shell structure, it can not only improve photogenerated charge transfer and separation, but also ensure stability, providing strict protection for active sites to resist harsh environmental conditions and effectively slowing down the deactivation rate of the catalyst. At the same time, since BiOI has good piezoelectric properties, the built-in electric field and piezoelectric polarization field of the heterojunction interface generated by this core-shell catalyst can significantly reduce carrier interfacial recombination to enhance charge separation efficiency, thereby significantly improving photocatalytic reaction activity. In addition, this material can form a complex with algal blooms, thereby achieving in-situ algae removal and significantly improving the algae removal effect.

[0010] Furthermore, in the core-shell catalyst, the catalyst is spherical.

[0011] Furthermore, in the core-shell catalyst, the diameter of the catalyst is 0.8~2 μm.

[0012] Furthermore, in the core-shell catalyst, the diameter of the core is 0.1~0.75 μm, and the thickness of the film is 0.1~0.5 μm.

[0013] Furthermore, the core-shell catalyst is prepared in situ using a one-pot method.

[0014] This application discloses a method for preparing a core-shell catalyst, comprising:

[0015] Bismuth nitrate dissolves in ethylene glycol methyl ether to form the first solution;

[0016] Potassium iodide is dissolved in ethylene glycol methyl ether to form a second solution;

[0017] Under stirring conditions, the second solution is added dropwise to the first solution, then sealed and heated to react, then cooled, washed and dried to obtain a core-shell catalyst, wherein the heating reaction temperature is 120℃~200℃ and the time is 5 h~20 h.

[0018] The preparation method provided in this application first prepares a KI ethylene glycol methyl ether solution and a bismuth nitrate ethylene glycol methyl ether solution as ion liquids containing I. Taking advantage of the miscibility of KI and bismuth nitrate in ethylene glycol methyl ether, when the KI solution is added dropwise to the bismuth nitrate ethylene glycol methyl ether solution, an emulsion is formed under stirring, achieving a droplet domain similar to that in traditional oil-in-liquid ion liquids. The tiny KI microemulsion is then absorbed by the Bi... 3+ The ethylene glycol methyl ether surrounds the reaction chamber, thus forming a micro-reaction chamber, while under heating conditions, Bi... 3+The ions react with I ions at the microemulsion interface to form a BiOI shell; at the same time, a large amount of KI glycol methyl ether solution inside the microemulsion reacts with a small amount of bismuth nitrate glycol methyl ether solution that has infiltrated to generate I-rich BiOI, thus obtaining a core-shell catalyst of I-doped BiOI coated with BiOI.

[0019] Furthermore, in the preparation method, the reaction temperature is 160°C and the reaction time is 12 h.

[0020] Furthermore, in the preparation method, the concentration of bismuth nitrate is 0.005~0.5 mmol / mL; and the concentration of potassium iodide in the second solution is 0.005~0.5 mmol / mL.

[0021] Furthermore, in the preparation method, during the process of adding the second solution dropwise to the first solution, the molar ratio of bismuth nitrate to potassium iodide is controlled to be 1:1.

[0022] Furthermore, in the preparation method, during the process of adding the second solution dropwise to the first solution, the stirring speed is controlled at 200 r / min to 1000 r / min and the stirring time is 5 to 20 min; and / or

[0023] During the dissolution of bismuth nitrate in ethylene glycol methyl ether, the stirring speed is controlled at 100 r / min to 500 r / min, and the stirring time is 25 to 60 min; and / or

[0024] During the process of dissolving potassium iodide in ethylene glycol methyl ether, the stirring speed is controlled at 100 r / min to 500 r / min, and the stirring time is 5 to 60 min.

[0025] Furthermore, in the preparation method, the drying temperature is less than or equal to 80°C.

[0026] This application also proposes an application of the above-mentioned core-shell catalyst, wherein the core-shell catalyst is used to inactivate algae. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the core-shell catalyst provided in the embodiments of this application;

[0028] Figure 2 This is a flowchart of a method for preparing a core-shell catalyst provided in an embodiment of this application;

[0029] Figure 3 These are electron micrographs of the core-shell catalysts in the embodiments of this application;

[0030] Figure 4These are XRD patterns of the core-shell catalysts in the embodiments of this application;

[0031] Figure 5 These are XPS test images of the core-shell catalyst in the embodiments of this application;

[0032] Figure 6 This is a KPFM test diagram of the core-shell catalyst in the embodiments of this application;

[0033] Figure 7 This is a UV diffuse reflectance test pattern of the core-shell catalyst in the embodiments of this application;

[0034] Figure 8 These are transient photocurrent response and impedance test diagrams of the core-shell catalyst in the embodiments of this application;

[0035] Figure 9 This is a piezoelectric photocatalytic activity test diagram of the core-shell catalyst in the embodiments of this application;

[0036] Figure 10 This is a test diagram of the in-situ all-weather degradation performance of the core-shell catalyst in the embodiments of this application;

[0037] Figure 11 This is a cycle performance test diagram of the core-shell catalyst in the embodiments of this application;

[0038] Figure 12 These are in-situ infrared and Raman spectra of the core-shell catalyst in the embodiments of this application.

[0039] Figure 13 These are scanning electron microscope images of algal cell morphology under different treatment durations;

[0040] Figure 14 This is a quenching experiment test diagram from an embodiment of this application. Detailed Implementation

[0041] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0042] With the increasing eutrophication of water bodies, the ecological security crisis caused by cyanobacterial blooms is becoming increasingly severe. Photocatalysis technology, with its green and energy-saving characteristics, uses sunlight to drive catalysts to generate reactive oxygen species, thereby inactivating algal cells and degrading toxins, and is regarded as a revolutionary solution in the field of environmental governance.

[0043] However, existing photocatalytic algae removal systems still face multiple technical bottlenecks: ① Narrow spectral response range, with conventional semiconductor materials utilizing less than 5% of the solar spectrum (ultraviolet band); ② The migration of charge carriers from the bulk to the catalytically active sites on the catalyst surface takes hundreds of picoseconds, while charge recombination in the bulk takes only a few picoseconds, resulting in high recombination rates and low quantum efficiency; ③ Solvation of the water film on the catalyst surface causes energy level mismatch, hindering interfacial electron transfer; ④ Intermittent light-dependent characteristics lead to catalytic failure at night and during cloudy / rainy weather; ⑤ In traditional non-contact catalysis, the transport distance of reactive oxygen species is limited, making them susceptible to quenching by the water matrix and difficult to contact algal cells. These bottlenecks severely restrict the large-scale application of photocatalytic technology in actual algal bloom control, necessitating the development of novel photocatalytic systems with broad-spectrum response, efficient charge carrier separation, and all-day catalytic algae removal capabilities.

[0044] The applicant discovered that, regarding the numerous problems associated with photocatalytic algae removal, simply constructing a semiconductor heterojunction through heteroatom doping results in a low efficiency in promoting carrier separation due to its built-in electric field, leading to low algae removal efficiency. The applicant also found that areas with severe algal bloom pollution generally experience mechanical disturbances in the water flow, and piezoelectric materials can utilize these disturbances to generate a localized polarized electric field, effectively promoting carrier migration and separation. Compared to traditional methods such as defect modification and heteroatom doping, photocatalytic coupling with piezoelectric materials significantly suppresses carrier recombination. Furthermore, the band bending under piezoelectric potential can increase the valence band potential, reducing the energy required for electron transitions and thus improving spectral utilization. Moreover, the polarized electric field generated by piezoelectricity can promote persulfate activation, continuously generating various reactive oxygen species even at night without light, enabling all-weather inactivation of algal blooms.

[0045] However, traditional piezoelectric materials still suffer from problems such as low mechanical sensitivity, low energy conversion efficiency, and narrow spectral absorption. For example, current piezoelectric catalytic reactions generally utilize high-frequency ultrasound, resulting in low utilization of low-frequency natural energy sources such as water flow; non-lead-based environmentally friendly piezoelectric materials have low piezoelectric coefficients; common single piezoelectric materials (such as molybdenum disulfide MoS2 and zinc oxide ZnO) have wide band gaps, limiting their absorption of visible light; and persulfate activation requires matching the electronic structure of the material to promote the generation of reactive oxygen species.

[0046] Based on the above findings, this application provides a core-shell catalyst 100 to address the problems of narrow spectral response range, low catalytic activity, and inability to catalyze algae removal throughout the entire time period associated with existing photocatalysts. Figure 1 As shown in Figure 2, the material 100 includes a core 11 comprising I-doped BiOI; and a film layer 12 comprising BiOI disposed on the surface of the core 11.

[0047] In the core-shell catalyst provided in this application, a heterojunction with a core-shell structure is formed by coating I-doped BiOI (IBiOI). This not only integrates the chemical composition, electronic structure, and microstructure of piezoelectric and photocatalytic materials, promoting the piezoelectric activation of persulfate under no-light conditions, thus achieving all-weather algae removal, but also, due to the tighter interfacial contact and larger contact area of ​​the heterojunction in the core-shell structure, significantly improving photogenerated charge transfer and separation, ensuring stability, and providing robust protection for active sites to resist harsh environmental conditions, thereby effectively slowing down the deactivation rate of the catalyst. Simultaneously, due to the good piezoelectric properties of BiOI, the built-in electric field and piezoelectric polarization field generated by the heterojunction interface of this core-shell catalyst can significantly reduce carrier interfacial recombination to enhance charge separation efficiency, thereby significantly improving photocatalytic reaction activity. Furthermore, this material can form a complex with algal blooms, thereby achieving in-situ algae removal and significantly improving the algae removal effect.

[0048] Alternatively, given that the catalyst can utilize solar and mechanical energy to generate highly oxidizing reactive oxygen species, it can also be used to degrade pollutants such as phenol, bisphenol A, and antibiotics; and can also be used to inactivate pathogenic microorganisms.

[0049] Optionally, in one embodiment, the core-shell catalyst is spherical in shape, which not only makes the heterojunction formed therewith a tighter interfacial contact and a larger contact area, thereby improving photogenerated charge transfer and separation, but also makes the structure more stable, thereby effectively slowing down the deactivation rate of the catalyst.

[0050] Optionally, in one embodiment, the diameter of the core-shell catalyst is 0.8~2 μm. At this particle size, the catalyst particles not only have a larger specific surface area, but are also more uniformly distributed and less prone to agglomeration.

[0051] Optionally, in one specific embodiment, the diameter of the core in the above-mentioned core-shell catalyst is 0.25~0.75 μm, and the thickness of the film layer is 0.1~0.5 μm, which can effectively balance the structural strength and catalytic performance of the material and more rationally match BiOI and IBiOI.

[0052] In the preparation of core-shell catalysts, the size ratio of the film layer to the core can be controlled by adjusting the droplet size, the concentration of KI and bismuth nitrate, the temperature, and the stirring rate in the system.

[0053] This application provides a method for preparing a core-shell catalyst, such as... Figure 2 As shown, the method includes steps 201 to 203:

[0054] Step 201: Bismuth nitrate is dissolved in ethylene glycol methyl ether to form the first solution;

[0055] Step 202: Dissolve potassium iodide in ethylene glycol monomethyl ether to form a second solution;

[0056] Step 202: Under stirring conditions, the second solution is added dropwise to the first solution, then sealed and heated to react, then cooled, washed and dried to obtain a core-shell catalyst, wherein the heating reaction temperature is 120℃~200℃ and the time is 5 h~20 h.

[0057] In this embodiment, a KI ethylene glycol methyl ether solution containing I ionic liquid and a bismuth nitrate ethylene glycol methyl ether solution containing Bi ionic liquid are first prepared. Taking advantage of the limited miscibility of the KI and bismuth nitrate ionic liquids in ethylene glycol methyl ether, an emulsion is formed under stirring, achieving a droplet domain similar to that in traditional oil-in-liquid ionic liquids. When the KI ionic liquid is added dropwise to the bismuth nitrate ethylene glycol methyl ether solution, the tiny KI microemulsion is absorbed by the Bi-containing emulsion. 3+ The ethylene glycol methyl ether surrounds the reaction chamber, thus forming a micro-reaction chamber, while under heating conditions, Bi... 3+ The ions react with the I ions on the microemulsion interface to form a BiOI shell; at the same time, the KI glycol methyl ether solution inside the microemulsion reacts with a small amount of bismuth nitrate glycol methyl ether solution that has permeated in to generate I-doped BiOI (IBiOI), thus obtaining a core-shell catalyst with BiOI coated with IBiOI.

[0058] In step 201 above, stirring is performed during the dissolution of bismuth nitrate in ethylene glycol methyl ether to promote the dissolution of bismuth nitrate. Optionally, the bismuth nitrate mentioned above can be bismuth nitrate pentahydrate, and the stirring speed is controlled at 100 r / min to 500 r / min, and the stirring time is 25 to 60 min, which can effectively promote the dissolution of bismuth nitrate while avoiding excessive oxygen mixing.

[0059] In step 201 above, the stirring speed can be one or any two of the following: 100 r / min, 200 r / min, 300 r / min, 400 r / min, 500 r / min, and the stirring time can be one or any two of the following: 25 min, 30 min, 40 min, 50 min, 60 min.

[0060] Optionally, the concentration of bismuth nitrate in the first solution can be 0.01~0.2 mmol / mL, for example, it can be one or any two of the following values: 0.01 mmol / mL, 0.02 mmol / mL, 0.05 mmol / mL, 0.8 mmol / mL, 0.1 mmol / mL, 0.15 mmol / mL, 0.2 mmol / mL. The concentration is moderate, which is convenient for contact reaction with KI, thereby improving the piezoelectric photocatalytic performance of the product, and avoids the precipitation of bismuth nitrate, which would cause material waste.

[0061] For example, 0.3 mmol Bi(NO3)3 can be added with stirring. 5H2O was dissolved in 30 mL of ethylene glycol methyl ether, with the stirring speed controlled at 300 r / min and the stirring time at 40 min, which resulted in better piezoelectric photocatalytic performance of the BiOI prepared subsequently.

[0062] In step 202 above, stirring is performed during the dissolution of KI in ethylene glycol methyl ether to promote KI dissolution. Optionally, in the above step, the stirring speed is controlled at 100 r / min to 500 r / min, and the stirring time is 5 to 60 min, which can effectively promote bismuth nitrate dissolution while avoiding excessive oxygen incorporation that could cause KI oxidation.

[0063] In step 201 above, the stirring speed can be one or any two of the following: 100 r / min, 200 r / min, 300 r / min, 400 r / min, 500 r / min, and the stirring time can be one or any two of the following: 5 min, 10 min, 20 min, 30 min, 40 min, 50 min, 60 min.

[0064] Optionally, the concentration of potassium iodide in the first solution can be 0.01~0.2 mmol / mL, for example, it can be one or any two of the following values: 0.01 mmol / mL, 0.02 mmol / mL, 0.05 mmol / mL, 0.8 mmol / mL, 0.1 mmol / mL, 0.15 mmol / mL, 0.2 mmol / mL. The concentration is moderate, which is convenient for contact reaction with bismuth nitrate, thereby improving the piezoelectric photocatalytic performance of the product, and avoids the precipitation of potassium iodide, which would cause material waste.

[0065] For example, 0.3 mmol KI can be dissolved in 30 mL of ethylene glycol methyl ether with stirring, wherein the stirring speed is controlled at 300 r / min and the stirring time is 40 min, so that the BiOI prepared subsequently has better piezoelectric photocatalytic performance.

[0066] In step 203 above, under stirring conditions, the second solution is slowly added dropwise to the first solution, so that the tiny KI microemulsions are contained in Bi. 3+ The mixture is surrounded by ethylene glycol methyl ether, thus forming a micro-reaction chamber, which is then sealed and heated at 120°C to 200°C. 3+ The ions react with the I ions on the microemulsion interface to form a BiOI shell. At the same time, the KI glycol methyl ether solution inside the microemulsion reacts with a small amount of bismuth nitrate glycol methyl ether solution that has permeated in to generate IBiOI, thus obtaining a core-shell catalyst with BiOI coated with IBiOI. After cooling, washing and drying, the final product can be obtained.

[0067] Optionally, in one embodiment, during the process of adding the second solution dropwise to the first solution, the stirring speed is controlled to be 200 r / min to 1000 r / min and the stirring time is 5 to 20 min; and / or

[0068] The reaction temperature can be any one or any two of the following: 120℃, 150℃, 160℃, 170℃, 180℃, and 200℃. The reaction time can be any one or any two of the following: 5 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, and 20 h.

[0069] Optionally, in one embodiment, the reaction temperature is controlled at 160°C and the reaction time is controlled at 12 h.

[0070] Optionally, in one embodiment, during the process of adding the second solution to the first solution, the molar ratio of bismuth nitrate to potassium iodide is controlled to be 1:1, so that the energy levels of BiOI and IBiOI in the core-shell structure product are reasonably matched, and the piezoelectric photocatalytic performance is particularly good.

[0071] In step 203 above, after cooling the reaction product to room temperature, it can be washed multiple times with deionized water and ethanol, and then dried at a temperature of less than or equal to 80°C to avoid oxidation of the product.

[0072] Alternatively, in one embodiment, the product can be dried in a vacuum drying oven at 60°C.

[0073] To make the inventive objectives, technical solutions, and beneficial effects of this invention clearer, the invention is further described below with reference to embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0074] The present invention will be described in detail below through embodiments.

[0075] Example 1

[0076] (1) Under stirring conditions, 0.3 mmol Bi(NO3)3 5H2O was dissolved in 30 mL of ethylene glycol methyl ether to obtain the first solution; wherein the stirring speed was controlled at 300 r / min and the stirring time was 40 min.

[0077] (2) Under stirring conditions, 0.3 mmol KI was dissolved in 30 mL of ethylene glycol methyl ether to obtain a second solution; wherein the stirring speed was controlled at 300 r / min and the stirring time was 40 min.

[0078] (3) Under stirring conditions, the second solution is added dropwise to the first solution, then sealed and heated to react, then cooled, cleaned and dried in a vacuum drying oven at 60°C to obtain a core-shell catalyst, wherein the reaction temperature is 160°C and the reaction time is 12h.

[0079] Examples 2-6

[0080] The difference between Examples 2-6 and Example 1 is that, in step (3), the stirring speed is adjusted to 200 r / min, 400 r / min, 600 r / min, 800 r / min and 1000 r / min respectively.

[0081] Test Example 1

[0082] The catalyst prepared in Example 1 was subjected to scanning electron microscopy, and the results are as follows: Figure 3 As shown in (a). By Figure 3 As can be seen in (a), the prepared catalyst has a spherical nanostructure with obvious epitaxial wrinkles.

[0083] The catalyst prepared in Example 1 was subjected to high-angle annular dark-field scanning transmission electron microscopy (PES) testing, and the results are as follows: Figure 3 As shown in (b) to (f), where, Figure 3 Images (b) to (c) are high-angle annular dark-field scanning transmission electron microscopy (STEM) results, while images (d) to (f) are energy-dispersive X-ray spectroscopy (EDS) elemental distribution maps for Bi, I, and O, respectively. It can be seen that Bi, I, and O are distributed in the outer layer of the spherical particles, while the inner layer is mainly composed of IBiOI. This indicates that the catalyst prepared in Example 1 is a spherical nanomaterial with a core-shell structure.

[0084] Test Example 2

[0085] The catalyst prepared in Example 1 was subjected to XRD testing, and the results are as follows: Figure 4As shown, the XRD peaks of the prepared catalyst show obvious (102), (110), (004), and (212) crystal planes compared with the BiOI (PDF#10-0445) standard card, indicating that BiOI was successfully prepared. The XRD peaks of BiOI shift to higher angles, further suggesting that it may have a core-shell structure.

[0086] Test Example 3

[0087] The catalyst prepared in Example 1, the algae-catalyst mixture, and the algae were tested by XPS, and the results are as follows: Figure 5 As shown in (a) to (c), the algae-catalyst mixture is prepared by mixing the catalyst with algae solution and stirring for 20 minutes, then freezing the mixture and placing it in a freeze-drying oven for 48 hours.

[0088] in, Figure 5 In (a), the Bi 4f peaks at 160.3 eV and 165.6 eV are attributed to Bi 4f of BiOI, respectively. 7 / 2 and Bi4f 5 / 2 (Bi) 3+ );Depend on Figure 5 As can be seen in (b), after BiOI is mixed with algae, Bi 4f 7 / 2 and Bi 4f 5 / 2 The voltages shifted to 159.0 and 164.3 eV respectively, which may be due to the Bi on the BiOI surface. 3+ This is due to coordination with the abundant carboxyl (-COOH), hydroxyl (-OH), and amino (-NH2) functional groups on the algal surface, forming Bi-OC or Bi-N complex structures; Figure 5 There is also a significant I3d peak shift in (c), and the I3d peak of BiOI is... 5 / 2 (619.7 eV) and I 3d 3 / 2 (631.2 eV) After mixing with algae, the energy levels shift to lower levels, reaching 619.9 eV and 630.5 eV; furthermore, in O 1s, 530.7 eV and 532 eV represent Bi-O and OH bonds, respectively. In summary, a core-shell catalyst was successfully prepared, and this catalyst can coordinate with the abundant functional groups on the algal surface.

[0089] Test Example 4

[0090] The catalyst prepared in Example 1 was subjected to KPFM testing, and its morphology, amplitude, phase, and butterfly displacement-voltage curves are shown below. Figure 6 As shown in (a) to (d).

[0091] Among them, the image comparisons of the morphology diagram, amplitude diagram, and phase diagram are obvious, indicating that the catalyst is a piezoelectric material; at the same time, combined with Figure 6 The typical butterfly-shaped displacement-voltage curve in (d) further demonstrates the piezoelectric properties of the material. The maximum effective piezoelectric coefficient d33 of the sample was determined to be 1 mV / V by calculating the slope of the displacement-voltage curve. In summary, the prepared catalyst is a piezoelectric material with good piezoelectric properties.

[0092] Test Example 5

[0093] The catalyst prepared in Example 1 was subjected to ultraviolet diffuse reflectance testing. The ultraviolet diffuse reflectance spectrum and band gap are as follows: Figure 7 As shown. The bandgap width is calculated based on the ultraviolet diffuse reflectance spectrum using the following formula: αhν = A(E g -hν) n / 2 In the formula, α, h, ν, A and E g These represent the absorption coefficient, Planck's constant, incident light frequency, constant, and bandgap, respectively. In this equation, for a direct bandgap semiconductor, n equals 1.

[0094] pass Figure 7 It can be seen that the absorption boundary of the prepared catalyst is about 545 nm, indicating that the material has good visible light absorption performance and a band gap of 1.96 eV.

[0095] Test Example 6

[0096] The catalyst prepared in Example 1 was subjected to transient photocurrent response and impedance tests, and the results are as follows: Figure 8 As shown in (a) and (b).

[0097] The test method is as follows: Nafion solution (5.0 wt%, 0.1 mL) and BiOI (10 mg) were mixed with ethanol (1 mL) and ultrasonically dispersed for 3 h to obtain a suspension. 20 μL of the suspension was dropped onto a conductive glass surface and dried at 60 °C for 8 h to obtain an electrode sheet. Photocurrent and impedance tests were performed using an electrochemical workstation (Chenhua CHI660E, Shanghai) equipped with a conventional three-electrode configuration. A 300 W xenon lamp was used as the light source, and 0.1 M Na2SO4 solution was used as the electrolyte. During the test, 0.01 mmol / L PMS was added to form the BiOI / PMS system, and vice versa for the BiOI system.

[0098] pass Figure 8It can be seen that the prepared catalyst can generate a significant photocurrent under light irradiation, indicating that the catalyst has a good photoelectric effect. In addition, compared with the BiOI system, the catalyst / persulfate system (BiOI / PMS system) has a stronger photocurrent, which indicates that BiOI promotes the activation of PMS under light irradiation.

[0099] Test Example 7

[0100] The catalysts prepared in each embodiment were subjected to piezoelectric photocatalytic activity testing, and the results are as follows: Figure 9 As shown, the specific testing method is as follows:

[0101] The catalyst was placed in a piezoelectric photocatalytic reactor to degrade Microcystis aeruginosa. During the photocatalytic reaction, an LED light was used as the light source, and 40 mL of algal suspension was used. The reactor was prepared with / without a catalyst (0.5 g / L), and the light source was turned on / off (20 W / m²). 2 Place the reactor under ultrasonic / non-ultrasonic conditions and add / do not add persulfate.

[0102] Based on the different reaction conditions in the above experiments: with / without catalyst (BiOI), on / off light source (Vis), with / without ultrasound (US), and with / without persulfate (PMS), the following reaction systems can be obtained: persulfate (PMS) system; ultrasound / visible light (US / Vis) system; persulfate / ultrasound (PMS / US) system; persulfate / visible light (PMS / Vis) system; persulfate / ultrasound / visible light (PMS / US / Vis) system; catalyst / persulfate (BiOI / PMS) system; catalyst / ultrasound / visible light (BiOI / US / Vis) system; catalyst / persulfate / ultrasound (BiOI / PMS / US) system; catalyst / persulfate / visible light (BiOI / PMS / Vis) system; catalyst / persulfate / ultrasound / visible light (BiOI / PMS / US / Vis) system.

[0103] At preset time intervals, 8 mL of reaction solution was taken to measure its chlorophyll a content. A 0.45 μm filter membrane was then placed on a filtration instrument, and 8 mL of sample was filtered. The filter membrane was placed in a test tube and frozen for 12 h. The test tube was then removed, and 8 mL of 90% acetone solution was added, along with a small amount of magnesium carbonate powder to protect the chlorophyll from damage. The sample was then disrupted using an ultrasonic cell disruptor (ultrasonic time 3 s, interval 2 s) for 3 min, and treated at 4500 r / min for 10 minutes. The supernatant was collected, and using 90% acetone as a reference, the chlorophyll a content was measured using OD0.05. 630 OD 647 OD 664 and OD750 The formula for calculating the chlorophyll a content is shown below:

[0104]

[0105] In the formula:

[0106] OD 630 OD 647 OD 664 OD 750 V1 represents the absorbance values ​​of the sample at wavelengths of 630 nm, 647 nm, 664 nm, and 750 nm, respectively; V2 represents the sample volume in mL; V3 represents the volume of 90% acetone in mL.

[0107] The removal rate of Microcystis aeruginosa was calculated as C / C0, where C0 and C are the chlorophyll a contents at 0 and t min, respectively.

[0108] Depend on Figure 9 As shown in (a), the catalyst in Example 1 exhibits superior piezoelectric photocatalytic algae removal effect. Furthermore, under ultrasonic and piezoelectric action, the chlorophyll in algal cells is significantly destroyed, indicating that the BiOI / US / Vis system can achieve 100% inactivation of algal cells, far exceeding the catalysts prepared in other examples. Figure 9 As shown in (b), the US / Vis system, PMS / US system, and PMS / US / Vis system do not cause algal death, indicating that the core-shell structure catalyst prepared by optimizing the experimental preparation method has a better algae removal effect.

[0109] Test Example 8

[0110] The catalyst prepared in Example 1 was subjected to in-situ all-weather degradation performance testing, and the results are as follows: Figure 10 As shown, the specific test method is the same as that in Test Example 7, except that 0.01 mM permonosulfate (PMS) is added as an oxidant in this test example.

[0111] Depend on Figure 10The BiOI / PMS / US / Vis system exhibits superior algae removal performance, indicating that BiOI material possesses excellent photocatalytic and piezoelectric properties. Under mechanical action, this material generates a polarized electric field, promoting carrier separation and subsequently generating a large number of reactive oxygen species, thus achieving highly efficient algal inactivation. The BiOI / PMS / Vis system can inactivate 90% of Microcystis aeruginosa within 150 minutes, demonstrating that the core-shell catalyst BiOI possesses excellent photocatalytic performance and can utilize light to generate a large number of reactive oxygen species, achieving highly efficient algal cell inactivation. Meanwhile, the BiOI / PMS / US / Vis system exhibits higher algae removal efficiency, indicating that under piezoelectric and photocatalytic action, PMS activation can be promoted, generating reactive oxygen species such as sulfate radicals and hydroxyl radicals, thus promoting algal bloom removal. In addition, the BiOI / PMS / US system can inactivate 60% of algae in 150 min, demonstrating that the prepared catalyst can generate a polarized electric field by utilizing the mechanical disturbance of water flow at night without light, generating a large number of reactive oxygen species to inactivate algal cells. In other words, the catalyst can achieve all-weather in-situ inactivation of algal blooms.

[0112] Test Example 9

[0113] The catalyst prepared in Example 1 was subjected to cycle performance testing, and the results are as follows: Figure 11 As shown, the specific testing method is as follows:

[0114] After the first degradation reaction is completed, the catalyst is separated from the solution by filtration, and the filtered catalyst is washed with deionized water and ethanol and then dried in a freeze dryer for 48 hours for later use. The second degradation reaction is carried out using the above-mentioned spare material, and the reaction conditions are kept the same as the first time except for the material. After the second reaction is completed, the above steps are repeated to carry out the third, fourth and fifth degradation experiments.

[0115] Depend on Figure 11 It can be seen that the BiOI / PMS / US / Vis system has good cycling stability. After 5 cycles, it can still completely inactivate algal cells within 150 min, indicating that the material has good cycling stability.

[0116] Test Case 10

[0117] The catalyst prepared in Example 1 was subjected to in-situ infrared spectroscopy and in-situ Raman spectroscopy, and the results are as follows: Figure 12 As shown in (a) to (b), the specific test methods are as follows:

[0118] In-situ Raman spectroscopy: The surface chemical changes of the catalyst during PMS activation were studied using a 532 nm laser confocal Raman spectroscopy system. Specifically, 10 mg of catalyst was loaded onto a glass slide and pressed into a thin slice approximately 1 mm thick. PMS solution (0.01–2 mmol / L) was then dropped onto the slice, and the sample was analyzed at 50–1500 cm⁻¹. -1 Scan within the range.

[0119] In-situ infrared spectroscopy: The changes in surface functional groups of the catalyst during PMS activation were studied using Fourier transform infrared spectroscopy. Specifically, 10 mg of catalyst was added to the infrared spectrometer stage, and PMS solution (0.01-2 mmol / L) was added dropwise. Then, the sample was analyzed at 500-2500 cm⁻¹. -1 Scan within the range.

[0120] Depend on Figure 12 As shown in (a), compared with the system without PMS, the Bi-O bond of BiOI disappears after the addition of PMS. This indicates that PMS can react with Bi on BiOI and further generate reactive oxygen species, enabling BiOI to continuously remove algae at night when there is no light.

[0121] Depend on Figure 12 As shown in (b), compared with the system without PMS, the Bi-I bond of BiOI is significantly shifted after the addition of PMS; in addition, the OO bond peak of PMS is broadened. Combined with the in-situ infrared results, it can be seen that PMS can interact with Bi of BiOI in the absence of light, so that BiOI can continue to remove algae at night in the absence of light.

[0122] Test Example 11

[0123] The catalyst prepared in Example 1 was tested for algae removal in a BiOI / PMS / US / Vis system for 10 min, 20 min, and 30 min, with a PMS / US / Vis system algae removal test for 1.5 h serving as a control. Algal cell morphology was then observed using biological SEM, and the results are as follows: Figure 13 As shown in (a) to (d).

[0124] Depend on Figure 13 It can be seen that in the BiOI / PMS / US / Vis system, algal cells gradually shrink and break down as the reaction proceeds, while in the control group PMS / US / Vis system, algal cells remain plump. This indicates that the BiOI / PMS / US / Vis system can significantly damage algal cell membranes, leading to algal cell damage and death.

[0125] Test Example 12

[0126] The catalyst prepared in Example 1 was used to investigate the main reactive oxygen species in the all-weather algae removal system under light through quenching experiments. The test results are as follows: Figure 14 As shown, the specific test methods are as follows: The experimental methods are the same as those in Test Example 8, except that different amounts of quenchers are added to the system at the beginning of the reaction. Ethanol is used to quench sulfate radicals and hydroxyl radicals, disodium ethylenediaminetetraacetate (EDTA-2Na, 1 mmol / L) is used to quench holes, furfuryl alcohol (FFA, 1 mmol / L) is used to quench singlet oxygen, tert-butanol (TBA, 3 mmol / L) is used to quench hydroxyl radicals, and p-benzoquinone (BQ, 3 mmol / L) is used to quench superoxide radicals.

[0127] Depend on Figure 14 It was found that after adding BQ, the BiOI / PMS / US / Vis system could only remove 10% of the algae (150 min); under the quenching of FFA, the algae removal efficiency of the BiOI / PMS / US / Vis system decreased to 80%, and EDTA-2Na could also significantly inhibit the inactivation of algal blooms, with the BiOI / PMS / US / Vis system only inactivating 70% of the algae. These results indicate that the main reactive oxygen species in the BiOI / PMS / US / Vis system are superoxide radicals, singlet oxygen, and holes, suggesting that the prepared catalyst can efficiently absorb photons, causing valence band electrons to transition to the conduction band and generate holes in the valence band. Simultaneously, the built-in electric field of the core-shell structure and the piezoelectric polarization field promote carrier separation, and photogenerated electrons further activate the surface-adsorbed PMS and oxygen, generating superoxide radicals and singlet oxygen.

[0128] In summary, the core-shell catalyst provided in this application, in which BiOI-coated I-doped BiOI forms a core-shell heterojunction, not only integrates the chemical composition, electronic structure, and microstructure of piezoelectric and photocatalytic materials, promoting piezoelectric activation of persulfate under no-light conditions, thus achieving all-weather algae removal; but also, due to the tighter interfacial contact and larger contact area of ​​the heterojunction in the core-shell structure, it can not only improve photogenerated charge transfer and separation, but also ensure stability, providing strict protection for active sites to resist harsh environmental conditions and effectively slowing down the deactivation rate of the catalyst; at the same time, because BiOI has good piezoelectric properties, the built-in electric field and piezoelectric polarization field of the heterojunction interface generated by this core-shell catalyst can significantly reduce carrier interfacial recombination to enhance charge separation efficiency, thereby significantly improving photocatalytic reaction activity; in addition, this material can form a complex with algal blooms, thereby achieving in-situ algae removal and significantly improving the algae removal effect.

[0129] Terminology Explanation

[0130] In this application, "multiple" refers to two or more.

[0131] 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.

[0132] In this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, in this application, the character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0133] Unless otherwise specified, all steps in this application may be performed sequentially or randomly. For example, if the method includes steps A and B, it means that the method may include steps A and B performed sequentially, or it may include steps B and A performed sequentially. For example, if the method may also include step C, it means that step C may be added to the method in any order. For example, the method may include steps A, B, and C, or it may include steps A, C, and B, or it may include steps C, A, and B, etc.

[0134] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for producing a core-shell catalyst, characterized by, The application relates to a preparation method of a core-shell type catalyst. Dissolve bismuth nitrate in ethylene glycol dimethyl ether to form a first solution, wherein the concentration of bismuth nitrate in the first solution is 0.005-0.5 mmol / mL; Dissolve potassium iodide in ethylene glycol dimethyl ether to form a second solution; The concentration of potassium iodide in the second solution is 0.005-0.5 mmol / mL; Under stirring, the second solution is added dropwise to the first solution, then the reaction is sealed and heated, and after cooling, cleaning and drying, a core-shell type catalyst is obtained; wherein the molar ratio of bismuth nitrate to potassium iodide is controlled to be 1:1 during the process of adding the second solution to the first solution; the heating temperature is 120-200 DEG C, and the heating time is 5-20 h; The core-shell type catalyst comprises: An inner core comprising I-doped BiOI; A film layer comprising BiOI, arranged on the surface of the inner core; The core-shell type catalyst is spherical; the diameter of the core-shell type catalyst is 0.8-2 mu m; the diameter of the inner core is 0.25-0.75 mu m, and the thickness of the film layer is 0.1-0.5 mu m.

2. The production method according to claim 1, characterized by, The heating temperature is 160 DEG C, the heating time is 12 h, and / or The drying temperature is less than or equal to 80 DEG C.

3. The preparation method according to claim 1, characterized in that, During the process of adding the second solution to the first solution, the stirring speed is controlled to be 400-800 r / min, and the stirring time is 5-20 min; and / or During the process of dissolving bismuth nitrate in ethylene glycol dimethyl ether, the stirring speed is controlled to be 100-500 r / min, and the stirring time is 25-60 min; and / or During the process of dissolving potassium iodide in ethylene glycol dimethyl ether, the stirring speed is controlled to be 100-500 r / min, and the stirring time is 5-60 min.

4. Use of a core-shell catalyst prepared according to any one of claims 1 to 3, characterized in that The core-shell type catalyst is used for inactivating at least one of algae, pathogenic microorganisms and pollutants, wherein the pollutants comprise at least one of phenol, bisphenol A and antibiotics.

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