A photocatalytic degradation composite material, its preparation method and application

Abstract

This invention belongs to the field of piezoelectric photocatalytic materials technology, specifically relating to a photocatalytic degradation composite material, its preparation method, and its application. In this invention, bismuth salt and tungstate are dissolved in a solvent, and a reducing agent is added. Through a solvothermal reaction, the reducing agent reduces Bi₂WO₆ to elemental Bi, forming a Bi-Bi₂WO₆ heterojunction of Bi₂WO₆ nanosheets encapsulating Bi nanospheres, yielding a Bi@Bi₂WO₆ material. The Bi@Bi₂WO₆ material is then immersed in a chemical etchant, which etches the Bi@Bi₂WO₆ material to create oxygen vacancy defects, resulting in the photocatalytic degradation composite material. The photocatalytic degradation composite material prepared by this invention has abundant oxygen vacancies, which significantly increases the active sites on the material surface, improves the piezoelectric photocatalytic performance of the material, and exhibits a significant degradation rate for 2,4-dichlorophenol.

Description

Technical Field

[0001] This invention belongs to the field of piezoelectric photocatalytic materials technology, specifically relating to a photocatalytic degradation composite material, its preparation method, and its application. Background Technology

[0002] In the field of environmental pollution control, 2,4-dichlorophenol is a common organic pollutant that poses a serious threat to the environment and human health due to its high toxicity and recalcitrant degradation. Among existing degradation methods, piezoelectric photocatalysis has attracted much attention due to its high efficiency and environmental friendliness. Introducing piezoelectric polarization into photocatalysis can enhance the separation ability of photogenerated electron-hole pairs, forming piezoelectric photocatalytic materials. Therefore, finding a material with high piezoelectric photocatalytic activity remains a research hotspot.

[0003] Bi₂WO₆ is valued for its high ferroelectricity and excellent photocatalytic performance, with a ferroelectric constant Pr of 50 μC / cm⁻¹. 2 Bandwidth E g With a photocatalytic activity of 2.76 eV, Bi₂WO₆ shows promising application potential in degrading organic pollutants and splitting water to produce hydrogen. However, its wide bandgap leads to a high photogenerated carrier recombination efficiency, resulting in low quantum utilization and thus less than ideal photocatalytic activity. Furthermore, the limited visible light response range of Bi₂WO₆ further restricts its practical application under sunlight.

[0004] Existing technologies modify Bi2WO6 through doping, heterostructure construction, and surface modification, which improve its photocatalytic performance to some extent. However, the preparation methods of existing technologies are too complex, the raw materials are not readily available, and the prepared composite photocatalytic materials have low carrier separation efficiency and poor stability, making it difficult to achieve efficient and stable photocatalytic effects. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a photocatalytic degradation composite material, its preparation method, and its applications. This invention utilizes safe and readily available raw materials, and the preparation method is simple. This invention constructs a metal-semiconductor heterojunction using a solvothermal method; then, oxygen vacancies are introduced into the lattice structure of the metal-semiconductor heterojunction through a chemical etching reaction. By optimizing the surface structure of the metal-semiconductor heterojunction, the catalytic activity of the material is enhanced. The introduction of oxygen vacancies optimizes the band structure of the material, promotes the separation of photogenerated carriers, enhances light absorption, and provides more active sites for photocatalytic reactions, thereby significantly improving piezoelectric photocatalytic performance. Under the action of an external force field, the piezoelectric photocatalytic material can induce a polarized electric field to improve the separation of photogenerated electron-hole pairs, thus significantly improving photocatalytic performance.

[0006] This invention involves dissolving bismuth salts and tungstates in a solvent to obtain a precursor solution. A reducing agent is added to the precursor solution, and through a solvothermal reaction, the reducing agent reduces Bi₂WO₆ in the precursor solution to elemental Bi, forming a Bi-Bi₂WO₆ heterojunction of Bi₂WO₆ nanosheets encapsulating Bi nanospheres, thus obtaining a Bi@Bi₂WO₆ material. The Bi@Bi₂WO₆ material is then immersed in an acidic or alkaline reagent. Under acidic conditions, hydrogen ions react with oxygen atoms in Bi₂WO₆ within the Bi@Bi₂WO₆ material, disrupting the Bi-O bond structure and causing oxygen atoms to detach from the Bi₂WO₆ lattice, thereby forming oxygen vacancies. Under alkaline conditions, hydroxide ions coordinate with Bi or W atoms on the surface of the Bi@Bi₂WO₆ material, altering the surface chemical environment, promoting lattice reorganization, and introducing oxygen vacancy defects, thus obtaining a photocatalytic degradation composite material. These structural defects significantly increase the active sites on the surface of Bi@Bi2WO6 materials. At the same time, as trapping centers for electron-hole pairs, they effectively promote the separation of photogenerated carriers, thereby significantly improving the piezoelectric photocatalytic performance of the photocatalytic degradation composite material.

[0007] The first objective of this invention is to provide a method for preparing a photocatalytic degradation composite material, comprising the following steps:

[0008] Step 1: Dissolve bismuth salt and tungstate in a solvent to obtain a precursor solution. Add a reducing agent to the precursor solution and reduce Bi2WO6 in the precursor solution to elemental Bi through a solvothermal reaction, forming a Bi-Bi2WO6 heterojunction of Bi nanospheres encapsulated by Bi2WO6 nanosheets, thus obtaining Bi@Bi2WO6 material.

[0009] It should be noted that in the solvothermal reaction process of the Bi@Bi2WO6 material prepared by this invention, the reaction temperature is the main condition. The reaction temperature directly affects Bi by controlling the activity of the reducing agent and the reaction kinetics. 3+ The reduction rate to elemental Bi. Therefore, this invention investigates the effect of solvothermal reaction temperature on the formation and growth of Bi₂WO₆ nanosheets, finding that reaction temperature plays a crucial role in the formation and growth of Bi nanospheres. When the temperature is below 220℃, insufficient reaction kinetics lead to a decrease in the reduction rate of Bi₂WO₆. 3+ The reduction rate is slow, and it is impossible to fully reduce Bi to form nanospheres; when the temperature is above 280℃, the reduction reaction rate increases significantly, allowing Bi in Bi₂WO₆ to be fully reduced. 3+ Complete reduction to elemental Bi. The preferred solvothermal reaction temperature of this invention is 220℃~280℃, and the preferred solvothermal reaction time is 12h~24h.

[0010] Preferably, the reducing agent is hexadecyltrimethylammonium bromide.

[0011] The specific preparation process of the Bi@Bi2WO6 material of the present invention is as follows: bismuth salt and tungstate are dissolved in a solvent to obtain a precursor solution; under stirring conditions, a reducing agent is added to the precursor solution, and the pH of the solution is adjusted to neutral using a 2 mol / L alkaline solution to obtain a suspension; the suspension is transferred to a reaction vessel for a solvothermal reaction; after the reaction is completed, the mixture is cooled to room temperature, washed, centrifuged, and dried to obtain the Bi@Bi2WO6 material.

[0012] It should also be noted that, since the pH of the precursor solution is 1-2, this invention investigated the effect of pH gradient on elemental Bi and Bi2WO6 nanosheets. The results showed that changes in pH affect crystal growth; both acidic and alkaline conditions inhibit the formation of Bi2WO6 nanosheets. Furthermore, the Bi@Bi2WO6 material synthesized under acidic or alkaline conditions exhibits lower activity than that synthesized under neutral conditions. Therefore, this invention adjusts the pH by adding an alkaline solution to the precursor solution, and neutral conditions are chosen for subsequent research. Preferably, the alkaline solution is one of sodium hydroxide, potassium hydroxide, or ammonia.

[0013] The molar ratio of the bismuth salt, tungstate, and reducing agent is 1–2:0.5–1:0.27–0.55.

[0014] Preferably, the bismuth salt is one of bismuth nitrate pentahydrate and bismuth chloride.

[0015] Preferably, the tungstate is one of sodium tungstate and ammonium tungstate.

[0016] Preferably, the solvent is one of ethylene glycol and ethanol.

[0017] Step 2: Immerse the Bi@Bi2WO6 material in a chemical etchant to allow the chemical etchant to etch the Bi@Bi2WO6 material to form oxygen vacancy defects, thereby obtaining a photocatalytic degradation composite material.

[0018] It should be noted that in this invention, Bi@Bi2WO6 material is immersed in a chemical etchant, which can be an acid or a base. When the chemical etchant is acidic, under acidic conditions, hydrogen ions react with oxygen atoms of Bi2WO6 in the Bi@Bi2WO6 material, disrupting the Bi-O bond structure and causing oxygen atoms of Bi2WO6 to detach from the crystal lattice, thereby forming oxygen vacancies. Furthermore, due to the high chemical reactivity of the generated metallic bismuth, once Bi is exposed to an acidic environment, partial controllable dissolution occurs, resulting in a rough, porous structure and nanoscale pores on the material surface. When the chemical etchant is base-based, under alkaline conditions, hydroxide ions coordinate with Bi or W atoms on the surface of the Bi@Bi2WO6 material, altering the surface chemical environment, promoting the reorganization of the crystal structure of the Bi@Bi2WO6 material, and introducing oxygen vacancy defects. These structural defects significantly increase the active sites on the surface of the Bi@Bi2WO6 material, which can serve as electron-hole pair trapping centers, promoting the separation of photogenerated carriers, thereby improving the photocatalytic performance of the material.

[0019] Preferably, the ratio of Bi@Bi2WO6 material to chemical etchant is 50mg to 100mg: 100mL.

[0020] Preferably, the concentration of the chemical etchant is 0.05 mol / L to 0.3 mol / L.

[0021] Preferably, the soaking time is 30 min to 240 min.

[0022] Preferably, the acid is one of hydrochloric acid, nitric acid, and phosphoric acid; and the base is one of sodium hydroxide, potassium hydroxide, and ammonium hydroxide.

[0023] The second objective of this invention is to provide a photocatalytic degradation composite material prepared by the above-described preparation method.

[0024] A third objective of this invention is to provide the application of the above-described photocatalytic degradation composite material in the degradation of 2,4-dichlorophenol.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] This invention constructs a Bi-Bi2WO6 heterojunction, consisting of Bi2WO6 nanosheets encapsulating Bi elemental nanospheres, via a solvothermal reaction. Then, oxygen vacancies are introduced into the crystal structure of the Bi-Bi2WO6 heterojunction through chemical etching. During acidic chemical etching, hydrogen ions react with oxygen atoms in the Bi2WO6 material, disrupting the Bi-O bond structure and causing oxygen atoms to detach from the Bi2WO6 lattice, thus forming oxygen vacancies. During alkaline chemical etching, hydroxide ions coordinate with Bi or W atoms on the surface of the Bi@Bi2WO6 material, altering the surface chemical environment, promoting crystal structure reorganization, and introducing oxygen vacancy defects. These structural defects significantly increase the number of active sites on the surface of Bi@Bi2WO6 materials, while also serving as trapping centers for electron-hole pairs, effectively promoting the separation of photogenerated carriers. Secondly, they modulate the band structure of Bi@Bi2WO6 materials, reducing the recombination rate of photogenerated electrons and holes and enhancing the material's absorption capacity for visible light, thereby significantly improving the piezoelectric photocatalytic performance of the composite material. Under piezoelectric polarization, the migration of photogenerated electron-hole pairs to the material surface is accelerated, thereby continuously enhancing the catalytic degradation process of 2,4-dichlorophenol.

[0027] This invention employs a simple solvothermal method to synthesize Bi@Bi2WO6 heterojunctions, and then combines this with a chemical etching method to immerse the Bi@Bi2WO6 material in a chemical etchant, allowing the chemical etchant to etch the Bi@Bi2WO6 material to form oxygen vacancy defects, thereby obtaining a photocatalytic degradation composite material. The preparation process is simple, green and pollution-free, and the solvothermal method combined with chemical etching is easy to operate, uses inexpensive and readily available raw materials, and is suitable for large-scale production.

[0028] This invention enables precise control of the oxygen defect concentration on the surface of photocatalytic degradation composite materials through chemical etching, thereby providing more active sites and effectively enhancing the activity of the photocatalytic reaction. Attached Figure Description

[0029] Figure 1 The XRD characterization diagrams are of the photocatalytic degradation composite materials prepared in Examples 1 to 3 of this invention and the Bi@Bi2WO6 material prepared in Comparative Example 7.

[0030] Figure 2 The XRD characterization diagrams are of the photocatalytic degradation composite materials prepared in Examples 5 to 7 of this invention and the Bi@Bi2WO6 material prepared in Comparative Example 7.

[0031] Figure 3 The images show the XRD characterization of the Bi2WO6 materials prepared in Comparative Examples 1 to 7 and the Bi@Bi2WO6 material prepared in Comparative Example 8 of this invention.

[0032] Figure 4 SEM images of the Bi2WO6 material prepared in Comparative Example 1, the Bi@Bi2WO6 material prepared in Comparative Example 7, and the photocatalytic degradation composite materials prepared in Examples 1 to 8 of this invention are shown below; where (a) is Comparative Example 1, (b) is Comparative Example 7, (c) is Example 2, (d) is Example 1, (e) is Example 3, (f) is Example 4, (g) is Example 7, (h) is Example 6, (i) is Example 5, and (j) is Example 8.

[0033] Figure 5 The removal rates of 2,4-DCP by the Bi2WO6 material prepared in Comparative Example 1, the Bi@Bi2WO6 material prepared in Comparative Example 7, and the photocatalytic degradation composite materials prepared in Examples 1 to 3 of this invention are shown.

[0034] Figure 6 The removal rates of 2,4-DCP by the Bi2WO6 material prepared in Comparative Example 1, the Bi@Bi2WO6 material prepared in Comparative Example 7, and the photocatalytic degradation composite materials prepared in Examples 5 to 7 are shown.

[0035] Figure 7 Electron paramagnetic resonance characterization diagrams of the Bi2WO6 material prepared in Comparative Example 1, the Bi@Bi2WO6 material prepared in Comparative Example 7, and the photocatalytic degradation composite materials prepared in Examples 1 and 5 of this invention. Detailed Implementation

[0036] To enable those skilled in the art to better understand and implement the technical solutions of this invention, the invention will be further described below with reference to specific embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0037] Unless otherwise specified, all reagents used in this invention are commercially available, and all methods used are conventional techniques in the art.

[0038] The following specific examples will provide further details.

[0039] Example 1

[0040] This embodiment provides a method for preparing a photocatalytic degradation composite material.

[0041] Step 1: Preparation of Bi@Bi2WO6 material:

[0042] 1.1) Dissolve 2 mmol of Bi(NO3)3·5H2O and 1 mmol of Na2WO4·2H2O in 60 mL of ethylene glycol to obtain a precursor solution.

[0043] 1.2) Under stirring conditions, 0.27 mmol of hexadecyltrimethylammonium bromide was added to the precursor solution, and 2 mol / L KOH was added to adjust the pH to 7.00. The mixture was stirred for 30 min to obtain a suspension.

[0044] 1.3) The suspension was transferred to a 100 mL polytetrafluoroethylene reaction vessel and kept at a constant temperature of 240 °C for 24 h. After cooling to room temperature, the precipitate generated by the reaction was thoroughly washed three times with deionized water and anhydrous ethanol, respectively. After drying at 60 °C for 24 h, the Bi@Bi2WO6 material was obtained by grinding.

[0045] Step 2: Preparation of photocatalytic degradation composite material:

[0046] 50 mg of Bi@Bi2WO6 material was immersed in 100 mL of 0.1 mol / L sodium hydroxide solution and stirred for 30 min to carry out a chemical etching reaction, resulting in a photocatalytic degradation composite material, denoted as 0.1_Alk_BBW.

[0047] Example 2

[0048] This embodiment provides a method for preparing a photocatalytic degradation composite material.

[0049] The difference between this embodiment and Embodiment 1 is as follows:

[0050] In this embodiment, the concentration of sodium hydroxide solution is 0.05 mol / L; the photocatalytic degradation composite material obtained in this embodiment is denoted as 0.05_Alk_BBW.

[0051] Example 3

[0052] This embodiment provides a method for preparing a photocatalytic degradation composite material.

[0053] The difference between this embodiment and Embodiment 1 is as follows:

[0054] In this embodiment, the concentration of sodium hydroxide solution is 0.2 mol / L; the photocatalytic degradation composite material obtained in this embodiment is denoted as 0.2_Alk_BBW.

[0055] Example 4

[0056] This embodiment provides a method for preparing a photocatalytic degradation composite material.

[0057] The difference between this embodiment and Embodiment 1 is as follows:

[0058] In this embodiment, the concentration of sodium hydroxide solution is 0.3 mol / L; the photocatalytic degradation composite material obtained in this embodiment is denoted as 0.3_Alk_BBW.

[0059] Example 5

[0060] This embodiment provides a method for preparing a photocatalytic degradation composite material.

[0061] The difference between this embodiment and Embodiment 1 is as follows:

[0062] The chemical etching reagent in this embodiment is a hydrochloric acid solution with a concentration of 0.2 mol / L; the photocatalytic degradation composite material obtained in this embodiment is denoted as 0.2_Aci_BBW.

[0063] Example 6

[0064] This embodiment provides a method for preparing a photocatalytic degradation composite material.

[0065] The difference between this embodiment and Embodiment 1 is as follows:

[0066] The chemical etching reagent in this embodiment is a hydrochloric acid solution with a concentration of 0.1 mol / L; the photocatalytic degradation composite material obtained in this embodiment is denoted as 0.1_Aci_BBW.

[0067] Example 7

[0068] This embodiment provides a method for preparing a photocatalytic degradation composite material.

[0069] The difference between this embodiment and Embodiment 1 is as follows:

[0070] The chemical etching reagent in this embodiment is a hydrochloric acid solution with a concentration of 0.05 mol / L; the photocatalytic degradation composite material obtained in this embodiment is denoted as 0.05_Aci_BBW.

[0071] Example 8

[0072] This embodiment provides a method for preparing a photocatalytic degradation composite material.

[0073] The difference between this embodiment and Embodiment 1 is as follows:

[0074] The chemical etching reagent in this embodiment is a hydrochloric acid solution with a concentration of 0.3 mol / L; the photocatalytic degradation composite material obtained in this embodiment is denoted as 0.3_Aci_BBW.

[0075] Comparative Example 1

[0076] This comparative example provides a method for preparing Bi2WO6 material.

[0077] 1.1) Dissolve 2 mmol of Bi(NO3)3·5H2O and 1 mmol of Na2WO4·2H2O in 60 mL of ethylene glycol to obtain a precursor solution.

[0078] 1.2) Under stirring conditions, 0.55 mmol of cetyltrimethylammonium bromide was added to the precursor solution, and 2 mol / L KOH was added to adjust the pH to 7.00. The mixture was stirred for 30 min to obtain a suspension.

[0079] 1.3) The suspension was transferred to a 100 mL polytetrafluoroethylene reaction vessel and kept at a constant temperature of 180 °C for 24 h. After cooling to room temperature, the precipitate generated by the reaction was thoroughly washed three times with deionized water and anhydrous ethanol, respectively. After drying at 60 °C for 24 h, the Bi2WO6 material was obtained after grinding, denoted as BW.

[0080] The difference between this comparative example and Example 1 is as follows:

[0081] This comparative example did not involve immersing the Bi2WO6 material in a chemical etchant for chemical etching.

[0082] Comparative Example 2

[0083] This comparative example provides a method for preparing Bi2WO6 material.

[0084] The difference between this comparative example and Comparative Example 1 is as follows:

[0085] The temperature of the solvothermal reaction in this comparative example is 120℃.

[0086] Comparative Example 3

[0087] This comparative example provides a method for preparing Bi2WO6 material.

[0088] The difference between this comparative example and Comparative Example 1 is as follows:

[0089] The temperature of the solvothermal reaction in this comparative example is 140℃.

[0090] Comparative Example 4

[0091] This comparative example provides a method for preparing Bi2WO6 material.

[0092] The difference between this comparative example and Comparative Example 1 is as follows:

[0093] The temperature of the solvothermal reaction in this comparative example is 160℃.

[0094] Comparative Example 5

[0095] This comparative example provides a method for preparing Bi2WO6 material.

[0096] The difference between this comparative example and Comparative Example 1 is as follows:

[0097] The temperature of the solvothermal reaction in this comparative example is 200℃.

[0098] Comparative Example 6

[0099] This comparative example provides a method for preparing Bi2WO6 material.

[0100] The difference between this comparative example and Comparative Example 1 is as follows:

[0101] The temperature of the solvothermal reaction in this comparative example was 220℃.

[0102] Comparative Example 7

[0103] This comparative example provides a method for preparing Bi@Bi2WO6 material.

[0104] The difference between this comparative example and Comparative Example 1 is as follows:

[0105] The solvothermal reaction temperature in this comparative example was 240℃. The Bi@Bi2WO6 material obtained in this comparative example was denoted as BBW.

[0106] Comparative Example 8

[0107] This embodiment provides a method for preparing Bi@Bi2WO6 material.

[0108] The difference between this comparative example and Comparative Example 1 is as follows:

[0109] The temperature of the solvothermal reaction in this comparative example is 280℃.

[0110] Experimental Section

[0111] I. Material Characterization

[0112] 1. XRD characterization

[0113] Figure 1 The images show the XRD characterization patterns of the photocatalytic degradation composite materials prepared in Examples 1-3 and the Bi@Bi2WO6 material prepared in Comparative Example 7. Figure 1 It can be seen that BBW without NaOH etching exhibits strong Bi₂WO₆ and Bi diffraction signals. When the NaOH concentration increases from 0.05M to 0.2M, the diffraction peak intensity of elemental Bi gradually decreases, while the diffraction peak intensity of Bi₂WO₆ significantly increases. This indicates that the crystal structure of the material undergoes significant changes during alkaline etching, suggesting that the etching process with NaOH in this invention causes slight lattice disruption of the photocatalytic degradation composite material and introduces oxygen vacancies.

[0114] Figure 2The XRD characterization images are of the photocatalytic degradation composite materials prepared in Examples 5-7 and the Bi@Bi2WO6 material prepared in Comparative Example 7. The XRD patterns show that the unetched BBW exhibits strong Bi2WO6 and Bi diffraction signals. After etching with different concentrations of hydrochloric acid, the diffraction peaks of these etched photocatalytic degradation composite materials show that Bi and Bi2WO6 remain the main crystalline phases with increasing hydrochloric acid concentration. Compared with BBW, the diffraction peak intensity of the photocatalytic degradation composite materials gradually decreases, indicating that the etching with HCl causes slight lattice disruption of the photocatalytic degradation composite material and introduces oxygen defects. Furthermore, when the hydrochloric acid concentration is greater than 0.1 M, characteristic diffraction peaks of BiOCl appear, indicating that moderate concentration acid etching triggers surface chemical reactions, partially destroying Bi. 3+ After ion hydrolysis, BiOCl is generated, which distorts the structure of the material, but the main body of the material is still Bi@Bi2WO6.

[0115] Figure 3 The images show the XRD characterization patterns of the Bi@Bi2WO6 materials prepared in Comparative Examples 1 to 8. Figure 3 As shown, the crystal structure of Bi₂WO₆ material changed significantly as the reaction temperature gradually increased from 120℃ to 280℃. Below 220℃, the Bi₂WO₆ material mainly consisted of the Bi₂WO₆ crystalline phase, and the diffraction peaks were consistent with the standard card JCPDS No. 79-2381. However, when the temperature increased to 240℃ and above, diffraction peaks of elemental Bi began to appear, indicating that the reducing agent reacted with Bi₂WO₆ to generate elemental Bi. With a further increase in temperature to 280℃, the diffraction peak signal of Bi₂WO₆ disappeared, and only diffraction peaks of elemental Bi were observed, indicating that Bi₂WO₆ had been completely reduced. Therefore, the preferred solvothermal reaction temperature of this invention is 220℃~280℃.

[0116] 2. SEM characterization

[0117] Figure 4 SEM images of the Bi2WO6 material prepared in Comparative Example 1, the Bi@Bi2WO6 material prepared in Comparative Example 7, and the photocatalytic degradation composite materials prepared in Examples 1 to 8; wherein, (a) is Comparative Example 1, (b) is Comparative Example 7, (c) is Example 2, (d) is Example 1, (e) is Example 3, (f) is Example 4, (g) is Example 7, (h) is Example 6, (i) is Example 5, and (j) is Example 8. Figure 4 This shows the changes in the material during the etching process. (By...) Figure 4 In (a), it was observed that BW consists of an irregular microsphere structure formed by the aggregation of nanosheets; Figure 4(b) shows that BBW consists of nanosheets and microspheres, with the microspheres mainly composed of reduced Bi and the nanosheets primarily composed of Bi₂WO₆. Figure 4 Images (c) to (f) show the alkaline etching process, where the microspheres gradually lose their regular morphology, and petal-like structures appear within the clustered nanosheets. Furthermore, the number of these petals gradually increases with increasing NaOH concentration. In contrast, during acidic etching, as... Figure 4 As shown in (g) to (j), with the increase of HCl concentration, the microsphere structure in the material is gradually destroyed and its number decreases, while the size of the nanosheets covering the surface of the microspheres becomes smaller and their number increases significantly.

[0118] 3. Degradation test

[0119] In this invention, 50 mg of Bi₂WO₆ material prepared in Comparative Example 1, Bi@Bi₂WO₆ material prepared in Comparative Example 7, and photocatalytic degradation composite materials prepared in Examples 1-3 were weighed out and dispersed in 100 mL of 10 mg / L 2,4-dichlorophenol solution, respectively. The solutions were stirred in the dark for 30 min to obtain a reaction solution and establish an adsorption-desorption equilibrium. 5 mL of the reaction solution was extracted every 10 min and centrifuged. The results were then measured at a wavelength of 284 nm using a UV-Vis spectrophotometer. Figure 5 and Figure 6 As shown, a 300W xenon lamp was used to simulate natural light conditions during the degradation process, and the ultrasonic equipment had a power of 100W and a frequency of 45kHz.

[0120] Figure 5 The removal rates of 2,4-dichlorophenol by the Bi2WO6 material prepared in Comparative Example 1, the Bi@Bi2WO6 material prepared in Comparative Example 7, and the photocatalytic degradation composite materials prepared in Examples 1 to 3 are shown. Figure 5 It can be seen that the unetched BW and BBW materials exhibited low degradation efficiencies of 64.79% and 78.11%, respectively. In the alkaline etching system, the degradation efficiencies of 0.05 Alk BBW, 0.1 Alk BBW, and 0.2 Alk BBW were 90.64%, 95.51%, and 87.45%, respectively. The removal of 2,4-DCP by alkaline etching of Bi@Bi2WO6 material first increased and then decreased, reaching a maximum of 95.51% when the sodium hydroxide concentration was 0.1 mol / L.

[0121] Figure 6 The removal rates of 2,4-dichlorophenol by the Bi2WO6 material prepared in Comparative Example 1, the Bi@Bi2WO6 material prepared in Comparative Example 7, and the photocatalytic degradation composite materials prepared in Examples 5 to 7 are shown. Figure 5It can be seen that in the acid etching system, the degradation efficiencies of 0.05_Aci_BBW, 0.1_Aci_BBW and 0.2_Aci_BBW are 75.32%, 83.65% and 86.067%, respectively; the removal rate of 2,4-dichlorophenol by acid etching of Bi@Bi2WO6 material is positively correlated with the concentration of added HCl.

[0122] This demonstrates that the present invention can significantly improve the removal efficiency of 2,4-dichlorophenol by Bi@Bi2WO6 material through both acid and alkali etching processes.

[0123] 4. Degradation mechanism

[0124] This invention characterizes the surface states of BW, BBW, 0.1_Alk_BBW, and 0.2_Aci_BBW materials using electron paramagnetic resonance (EPR), and the results are as follows: Figure 7 As shown. Electron paramagnetic resonance (EPR) is a technique where the g-factor, or Landes g-factor, is a crucial parameter describing the response of electrons or other particles with magnetic moments in a sample to an applied magnetic field. It reflects the relationship between the particle's magnetism and the external magnetic field, particularly its total angular momentum and magnetic moment.

[0125] Figure 7 Electron paramagnetic resonance (EPR) characterization images of the Bi2WO6 material prepared in Comparative Example 1, the Bi@Bi2WO6 material prepared in Comparative Example 7, and the photocatalytic degradation composite materials prepared in Examples 1 and 5 are shown. Except for the BW material, significant oxygen vacancy signals were observed in BBW, 0.1_Alk_BBW, and 0.2_Aci_BBW materials at a g-factor of 2.004, with 0.1_Alk_BBW exhibiting the strongest signal, followed by 0.2_Aci_BBW. This pattern is consistent with the observation that 0.1_Alk_BBW showed the highest degradation efficiency in the degradation experiments. On BW, the EPR signal was almost negligible, while the signal intensity on 0.1_Alk_BBW was significantly higher than that on 0.2_Aci_BBW, and twice that of the latter. This indicates that the acid-base environment does indeed affect the formation of oxygen vacancies during sample preparation: NaOH may disrupt WO bonds, causing a disordered crystal structure and generating more oxygen vacancies on the surface, while HCl preferentially reacts with elemental Bi to form BiOCl, resulting in a lower oxygen vacancy content. The increase in oxygen vacancies is beneficial for improving the catalytic activity of the material because oxygen vacancies provide more active sites, promote the separation of photogenerated electron-hole pairs, enhance photocatalytic performance, and simultaneously improve the material's electronic conductivity and light absorption capacity, thereby increasing the efficiency of photocatalytic degradation of pollutants.

[0126] Obviously, the above embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for preparing a photocatalytic degradation composite material, characterized in that, Includes the following steps: Bismuth salt and tungstate are dissolved in a solvent to obtain a precursor solution; hexadecyltrimethylammonium bromide is added to the precursor solution, and a Bi-Bi2WO6 heterojunction of Bi nanospheres encapsulated in Bi2WO6 nanosheets is formed through a solvothermal reaction to obtain Bi@Bi2WO6 material; the solvent is one of ethylene glycol and ethanol; the temperature of the solvothermal reaction is ≥240℃ and <280℃. Bi@Bi2WO6 material was immersed in a chemical etchant to form oxygen vacancy defects in the Bi@Bi2WO6 material, thus obtaining a photocatalytic degradation composite material. The ratio of Bi@Bi2WO6 material to chemical etchant is 50mg~100mg:100mL; The concentration of the chemical etchant is 0.05 mol / L to 0.3 mol / L; The soaking time is 30 min to 240 min; The chemical etching agent is acid; The acid is one of hydrochloric acid, nitric acid, and phosphoric acid.

2. The method for preparing the photocatalytic degradation composite material according to claim 1, characterized in that, The molar ratio of the bismuth salt, tungstate, and hexadecyltrimethylammonium bromide is 1~2:0.5~1:0.27~0.

55.

3. The method for preparing the photocatalytic degradation composite material according to claim 1, characterized in that, The solvothermal reaction takes 12 to 24 hours.

4. A photocatalytic degradation composite material prepared by the preparation method according to any one of claims 1 to 3.

5. The application of the photocatalytic degradation composite material according to claim 4 in the photocatalytic degradation of 2,4-dichlorophenol.

Images