Br / O double-vacancy double-bismuth-based crystal form-amorphous junction as well as synthesis method and application thereof

Abstract

The invention discloses a Br / O double-vacancy double-bismuth-based crystal form-amorphous junction as well as a synthesis method and application thereof, and belongs to the technical field of catalysts. The synthesis method comprises the following steps: taking manganese-doped bismuth oxybromide as a matrix, and forming Mn < 4 + > in a hydrothermal reaction through doping of manganese ions to promote the formation of bromine vacancies in the bismuth oxybromide, so as to obtain the manganese-doped bismuth oxybromide; amorphous bismuth tungstate partially covers the surface of a substrate of manganese-doped bismuth oxybromide in a non-continuous manner, and oxygen vacancies are formed in the amorphous bismuth tungstate through hydrothermal reaction. The special energy band structure of the catalyst can generate photo-induced electrons required for reducing Cr < 6 + > ions, and bromine vacancies are formed after manganese doping; the amorphous bismuth tungstate not only serves as an electron generation and transfer center, but also forms a heterojunction through an interface coupling effect; the optimization promotes the formation of Br / O double vacancies in the heterojunction, effectively inhibits the recombination of photon-generated carriers, and finally enables the photoreduction rate of the system to 100 mg.L <-1 > Cr < 6 + > ions under visible light to reach 8.5 times of that of a manganese-doped bismuth oxybromide material, thereby realizing the Br / O double-vacancy double-bismuth-based crystal form-amorphous junction, the synthetic method and the photoreduction effect of high-concentration Cr < 6 + > ions.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, specifically to a Br / O double-vacancy type bismuth-based crystalline-amorphous junction, its synthesis method, and its application. Background Technology

[0002] In photocatalytic water treatment technology, the physicochemical properties of semiconductors are one of the key factors determining their performance, directly affecting the material's interface structure, the separation efficiency of photogenerated carriers, and the adsorption / desorption behavior of reactants and products on the surface. Therefore, the rational design of semiconductor materials with excellent physicochemical properties is crucial.

[0003] Defect engineering, as an economical and efficient control strategy, can effectively suppress electron-hole recombination by introducing electron traps to promote the localization and aggregation of photogenerated electrons. In bismuth oxybromine, constructing metal or oxygen vacancies helps to regulate its light absorption range, enhance charge separation capability, and expand surface active sites. However, intrinsic bismuth oxybromine still faces the problem of a relatively fast photogenerated carrier recombination rate, limiting its practical application. Constructing heterojunctions is considered one of the effective strategies to overcome these limitations. By introducing photocatalytic materials with beneficial vacancies, multiple vacancy sites can be formed in the interfacial region, thereby constructing more reaction centers, controlling the band structure, and further promoting charge separation. In addition, vacancy defects can also enhance the structural asymmetry of the catalyst, induce spontaneous polarization, and form a built-in electric field, thereby accelerating the separation and migration of charge carriers.

[0004] Although crystalline / amorphous heterojunctions have shown significant potential in photocatalysis research, current research on the synthesis of dual-vacancy heterojunctions and their application in the treatment of high-concentration wastewater is still relatively scarce. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention proposes a Br / O double-vacancy type bismuth-based crystalline-amorphous junction, its synthesis method, and its application.

[0006] The objective of this invention can be achieved through the following technical solutions: A first aspect of the present invention relates to a method for synthesizing a catalyst, comprising the following steps: Using manganese-doped bismuth oxybromide as the matrix, Mn is formed in a hydrothermal reaction through manganese ion doping. 4+ This promotes the formation of bromine vacancies in bismuth oxybromine, resulting in manganese-doped bismuth oxybromine. Amorphous bismuth tungstate is used to partially cover the surface of a manganese-doped bismuth oxybromide matrix in a discontinuous manner, and oxygen vacancies are formed in the amorphous bismuth tungstate through a hydrothermal reaction.

[0007] Optionally, the raw materials for preparing the manganese-doped bismuth oxybromide include bismuth nitrate, sodium bromide, and manganese acetate tetrahydrate.

[0008] Optionally, the preparation of the amorphous bismuth tungstate includes the following steps: Manganese-doped bismuth oxybromide was prepared by adding trisodium citrate and bismuth nitrate, dispersing / dissolving in deionized water, and then adding sodium tungstate after stirring. The mixture was then transferred to a polytetrafluoroethylene high-pressure reactor for reaction. Finally, after washing and drying, a manganese-doped bismuth oxybromide-amorphous bismuth tungstate composite material was obtained.

[0009] Optionally, the molar ratio of manganese-doped bismuth oxybromide to bismuth nitrate is 1:(0.20 to 0.52).

[0010] Optionally, the concentration of manganese acetate tetrahydrate is 0.001–0.01 mol·L⁻¹. -1 .

[0011] Optionally, the concentration of bismuth nitrate in the deionized solution is 0.1–0.6 mol·L⁻¹. -1 ; Optionally, the amount of trisodium citrate added is 0 mmol to 6.25 mmol; Optionally, the reaction temperature and time for the hydrothermal reaction in forming oxygen vacancies in amorphous bismuth tungstate are 120–200 °C and 6–20 h, respectively.

[0012] A second aspect of the present invention relates to a catalyst synthesized by the above-described catalyst synthesis method.

[0013] A third aspect of the present invention relates to the application of the above-described catalyst in wastewater treatment.

[0014] The beneficial effects of this invention are: The manganese-doped bismuth oxybromide of this invention serves as a narrow-response visible light catalyst; its unique band structure can generate reduced Cr. 6+ The photogenerated electrons required for ions are generated, and bromine vacancies are formed after manganese doping. Amorphous bismuth tungstate not only serves as a center for electron generation and transfer but also forms a heterojunction through interfacial coupling. Using a simple hydrothermal process, oxygen vacancies can be formed in amorphous bismuth tungstate by adjusting parameters such as the trisodium citrate content. This optimization promotes the formation of Br / O double vacancies in the heterojunction, effectively suppressing the recombination of photogenerated carriers, ultimately enabling the system to withstand 100 mg·L⁻¹ of light under visible light. -1 Cr 6+ The photoreduction rate of ions reached 8.5 times that of manganese-doped bismuth oxybromide (pseudo-first-order kinetic constant k = 0.0297 min). -1 This led to the realization of Br / O double-vacancy bismuth-based crystalline-amorphous junction and its synthesis method, as well as the achievement of high-concentration Cr... 6+ The effect of ion light reduction. Attached Figure Description

[0015] The invention will now be further described with reference to the accompanying drawings.

[0016] Figure 1 This is a scanning electron microscope image of the product in an embodiment of the present invention.

[0017] Figure 2 This is a transmission electron microscope image of the product in an embodiment of the present invention.

[0018] Figure 3 This is an X-ray diffraction pattern of the product in an embodiment of the present invention.

[0019] Figure 4 This is a graph showing the photoreduction performance of the product in an embodiment of the present invention. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Example 1: This embodiment of the invention discloses a method for synthesizing a Br / O double-vacancy type bismuth-based crystalline-amorphous junction, comprising the following steps: A method for synthesizing a Br / O double-vacancy type bismuth-based crystalline-amorphous junction includes the following steps: Step 1: Bismuth nitrate, sodium bromide, and manganese acetate tetrahydrate are dissolved in deionized water and, after vigorous stirring, transferred to a polytetrafluoroethylene high-pressure reactor for reaction. After the reaction is complete, the product is washed and dried to obtain manganese-doped bismuth oxybromide.

[0022] Step 2: Take the manganese-doped bismuth oxybromide prepared in Step 1, add trisodium citrate and bismuth nitrate, disperse / dissolve in deionized water, stir, and then add sodium tungstate. The mixture is then transferred to a polytetrafluoroethylene high-pressure reactor for reaction. Finally, after washing and drying, the manganese-doped bismuth oxybromide-amorphous bismuth tungstate composite material is obtained.

[0023] In step one, the concentration of manganese acetate tetrahydrate is 0.003 mol·L⁻¹. -1 .

[0024] In this process, manganese acetate tetrahydrate is dissolved in deionized water and then transferred to a reaction vessel to react and obtain manganese-doped bismuth oxybromide, in which Mn is formed. 4+ Subsequently, the strong oxidizing properties produced will promote the formation of bromine vacancies. At lower concentrations of manganese acetate tetrahydrate (0.001~0.1 mol·L⁻¹), -1At this concentration, the vacancy concentration increases with increasing manganese doping, enhancing photocatalytic activity by introducing defect energy levels and promoting charge separation. However, when the concentration exceeds the optimal threshold (>0.1 mol·L⁻¹), the vacancy concentration decreases. -1 Afterwards, excessive manganese ions can lead to an over-density of bromine vacancies, which become the main recombination centers for electron-hole pairs. This can also cause lattice distortion or the formation of an inert second phase on the surface, ultimately resulting in a decline in the material's structure and photocatalytic performance. Therefore, from the perspective of subsequent photoreduction behavior, it is preferable to select a manganese acetate tetrahydrate concentration within the threshold range.

[0025] In step two, the molar ratio of manganese-doped bismuth oxybromide to bismuth nitrate is 1:0.20; the amount of trisodium citrate is 0 mmol; and the reaction temperature and time in the reactor are 120℃ and 20h, respectively.

[0026] Example 2: A Br / O double-vacancy type bismuth-based crystalline-amorphous junction, which is prepared by the synthesis method of the Br / O double-vacancy type bismuth-based crystalline-amorphous junction described in Example 1, comprising: The matrix is ​​manganese-doped bismuth oxybromide, with the chemical composition Mn-BiOBr; the manganese-doped bismuth oxybromide exhibits a micron-scale morphology. Amorphous bismuth tungstate, with the chemical composition Bi2WO6, partially covers the outer surface of the manganese-doped bismuth oxybromine matrix in a discontinuous manner; the loading of Bi2WO6 is 20% of the mass of the manganese-doped bismuth oxybromine matrix, and its surface coverage is controlled by the amount of raw materials used.

[0027] The optical absorption wavelength range of the above-mentioned Br / O double-vacancy type bismuth-based crystalline-amorphous junction is 482 nm; the photocurrent signal is 2.60 µA / cm. 2 The interface resistance is 1300Ω.

[0028] Example 3: This embodiment of the invention discloses an application of a Br / O double-vacancy type bismuth-based crystalline-amorphous junction, which is directly applied to high-concentration Cr... 6+ Ion photoreduction. Among them, the Br / O double-vacancy type bismuth-based crystalline-amorphous material exhibits ion photoreduction at 100 mg·L⁻¹ under visible light. -1 Cr 6+ The apparent kinetic constant of photoreduction of ions is increased by 3.94 times compared with that of manganese-doped bismuth oxybromide.

[0029] Currently, most photocatalysts can only effectively treat concentrations of 20-50 mg·L⁻¹. -1 Cr 6+Ionic solutions, and the Br / O double-vacancy type bismuth-based crystalline-amorphous junction prepared by this invention can efficiently process concentrations up to 0.1 g·L⁻¹ under visible light irradiation. - ¹ (i.e., 100 mg·L) - ¹) of Cr 6+ Ion-simulated wastewater demonstrates significant potential for treating high-concentration, industrial-grade organic pollutants; notably, under these concentration conditions, the material exhibits excellent resistance to Cr... 6+ The apparent kinetic constant of the photocatalytic reduction of ions was increased by 1.6 to 8.51 times compared with that of pure manganese-doped bismuth oxybromide, which significantly enhanced the separation and migration efficiency of photogenerated carriers, demonstrating the key promoting role of dual vacancies in photocatalytic performance.

[0030] The Br / O double-vacancy type bismuth-based crystalline-amorphous junction prepared by this invention can efficiently process concentrations up to 100 mg·L⁻¹ under visible light irradiation. -1 Cr 6+ Ion-simulated wastewater demonstrates significant potential for treating high-concentration, industrial-grade chromium-containing wastewater. Currently, most photocatalysts are only effective at concentrations of 20–50 mg / L. -1 Cr 6+ Ionic solutions, and the material of this invention not only increases the applicable concentration to a higher level, but also at 100 mg·L⁻¹. -1 At its initial concentration, its effect on Cr 6+ The apparent kinetic constant of photocatalytic reduction was increased by 1.6 to 8.51 times compared with that of pure manganese-doped bismuth oxybromide, indicating that the separation and migration efficiency of photogenerated carriers was significantly enhanced, which further confirms the key role of the double vacancy structure in improving photocatalytic performance.

[0031] Example 4: A method for synthesizing a Br / O double-vacancy type bismuth-based crystalline-amorphous junction, comprising the following steps: The preparation method is the same as in Example 1, except that the concentration of manganese acetate tetrahydrate in step one is 0.001 mol·L⁻¹. -1 The concentration of bismuth nitrate in deionized water is 0.6 mol·L⁻¹. -1 The reaction temperature and time in the reactor were 200℃ and 6h, respectively.

[0032] The physicochemical properties of the prepared Br / O double-vacancy type bismuth-based crystalline-amorphous junction were tested as follows: light absorption wavelength was 435 nm (tested using a Shimadzu UV-3600i Plus instrument; test method was BaSO4 pellet method); photocurrent signal was 2.31 µA / cm. 2(The testing instrument was an electrochemical workstation; the testing method was the three-electrode method, where the working electrode was a glassy carbon electrode coated with the sample, the reference electrode was a calomel electrode, and the counter electrode was a platinum electrode); the interfacial resistance was 416 Ω (The testing instrument was an electrochemical workstation; the testing method was the three-electrode method, where the working electrode was a glassy carbon electrode coated with the sample, the reference electrode was a calomel electrode, and the counter electrode was a platinum electrode); under visible light, the interfacial resistance at 100 mg·L⁻¹ was... -1 Cr 6+ The photoreduction kinetic constant of the ions was increased by 1.6 times compared with that of manganese-doped bismuth oxybromide (the instrument used for testing was a 300W xenon lamp system from Magnesium & Co.; the test method was the diphenylcarbazide method).

[0033] Example 5: A method for synthesizing a Br / O double-vacancy type bismuth-based crystalline-amorphous junction, comprising the following steps: the preparation method is the same as in Example 1, except that in step one, the concentration of manganese acetate tetrahydrate is 0.01 mol·L⁻¹. -1 In step two, the molar ratio of manganese-doped bismuth oxybromide to bismuth nitrate is 1:0.52; the amount of trisodium citrate is 0.089 mol·L⁻¹. -1 The reaction temperature and time in the reactor were 200℃ and 6h, respectively.

[0034] Citric acid molecules adsorb onto the surface of the bismuth tungstate precursor particles, forming a molecular protective layer. This protective layer generates strong steric hindrance, preventing direct contact and aggregation between particles. The end-capping effect of this protective layer effectively inhibits material growth during the hydrothermal process, resulting in smaller bismuth tungstate particles, which are thus more likely to form oxygen vacancies on the surface. Therefore, citric acid end-capping indirectly creates a more favorable surface environment for oxygen vacancy generation by promoting the formation of small grains.

[0035] The physicochemical properties of the prepared Br / O double-vacancy bismuth-based crystalline-amorphous junction were tested as follows: light absorption wavelength was 440 nm; photocurrent signal was 3.5 µA / cm. 2 The interface resistance is 1500Ω; under visible light, the resistance to 100 mg·L⁻¹ is [not specified]. -1 Cr 6+ The photoreduction kinetic constant of the ions is 2.97 times higher than that of manganese-doped bismuth oxybromide.

[0036] Example 6: A method for synthesizing a Br / O double-vacancy type bismuth-based crystalline-amorphous junction, comprising the following steps: the preparation method is the same as in Example 1, except that in step two, the molar ratio of manganese-doped bismuth oxybromide to bismuth nitrate is 1:0.52; the amount of trisodium citrate is 5.0 mmol; and the reaction temperature and time in the reactor are 150℃ and 12h, respectively.

[0037] For the pure components (as a comparative example, the optical absorption wavelengths of pure BiOBr and pure amorphous Bi2WO6 are 429 nm and 435 nm, respectively; the interface resistances are 2696 Ω and 2271 Ω, respectively; and the photocurrent signals are 0.21 µA / cm², respectively). 2 and 1.78µA / cm 2 The synthesis conditions for manganese-doped bismuth oxybromide are the same as in Step 1 of Example 1, but Step 2 is not required. The synthesis conditions for amorphous bismuth tungstate are the same as in Step 2 of Example 1, but Step 1 is not required. The difference is that the amount of bismuth nitrate in Step 2 is 0.029 mol·L⁻¹. -1 The amount of trisodium citrate was 5 mmol; the reaction temperature and time in the reactor were 150℃ and 12 h, respectively.

[0038] The physicochemical properties of the prepared Br / O double-vacancy bismuth-based crystalline-amorphous junction were tested as follows: light absorption wavelength was 460 nm; photocurrent signal was 6.90 µA / cm. 2 The interface resistance is 581Ω; under visible light, the resistance to 100 mg·L⁻¹ is [not specified]. -1 Cr 6+ The photoreduction kinetic constant of the ions is 8.5 times higher than that of manganese-doped bismuth oxybromide.

[0039] The products of the comparative example and Example 6 were analyzed and described using scanning electron microscopy, transmission electron microscopy, X-ray diffraction (XRD), and photoreduction performance diagrams.

[0040] 1. Analysis of scanning electron microscope images Figure 1 These are scanning electron microscope (SEM) results of the product; the images show that the microsheets are manganese-doped bismuth oxybromide, exhibiting a typical microsheet structure with a diameter of approximately 3 μm. The surface is adhered with amorphous bismuth tungstate, exhibiting a nanosheet structure; this morphology is attributed to the strong chelating effect of citric acid molecules. After hydrothermal treatment, these two different morphologies coexist in the images, indicating the successful preparation of a manganese-doped bismuth oxybromide-amorphous bismuth tungstate heterojunction.

[0041] 2. Transmission electron microscopy image analysis Figure 2 The transmission electron microscopy (TEM) images further confirmed the formation of the manganese-doped bismuth oxybromide-amorphous bismuth tungstate heterojunction; the obvious contrast difference between the bright and dark areas in the layered structure indicates that the heterojunction was successfully formed. Figure 2 a). High-resolution TEM (HR-TEM) images of manganese-doped bismuth oxybromine show a significant discontinuity on the (110) crystal plane. This indicates the formation of defect structures in the material, which may be attributed to manganese doping ( Figure 2 b). In Figure 2In the inset of b, no lattice fringes of bismuth tungstate were detected, indicating that bismuth tungstate exists in an amorphous state. The HR-TEM image of the heterojunction shows characteristic amorphous / crystalline interface fringes. Figure 2 c) confirms the formation of a heterogeneous interface between the components. This interfacial contact facilitates the separation and transport of photogenerated carriers.

[0042] 3. XRD pattern analysis Figure 3 The XRD patterns provide evidence of tight interfacial contact between the components. The results show that the diffraction peaks of manganese-doped bismuth oxybromide are highly consistent with the tetragonal phase standard card (JCPDS no. 078-0348), while amorphous bismuth tungstate does not exhibit characteristic diffraction peaks of orthorhombic crystal systems, displaying typical amorphous structural features. In the manganese-doped bismuth oxybromide-amorphous bismuth tungstate heterojunction, the main diffraction peak of manganese-doped bismuth oxybromide (green box) shifts towards higher angles, and the intensity of the main diffraction peak is significantly weakened. This phenomenon indicates a strong interfacial interaction between the two phases.

[0043] 4. Analysis of light reduction performance diagram Figure 4 This demonstrates heterojunctions with Cr 6+ Photoreduction activity of ions. After 120 min of visible light irradiation, pure amorphous bismuth tungstate can remove 40.37% of Cr. 6+ The removal rate of ions (removal rate = real-time concentration / initial concentration × 100%) was only 21.99% for pure manganese-doped bismuth oxybromine, indicating that a single defect structure is insufficient to effectively suppress bulk recombination of photogenerated carriers. When the two are coupled to form a manganese-doped bismuth oxybromine-amorphous bismuth tungstate heterojunction, the photoreduction efficiency increases to 97.89%, confirming that more beneficial active sites are generated between defects to accelerate the photoreduction efficiency.

[0044] In summary, in this invention, manganese-doped bismuth oxybromide serves as a narrow-response visible light catalyst, and its unique band structure can generate reduced Cr. 6+ The photogenerated electrons required for ions are generated, and bromine vacancies are formed after manganese doping. Amorphous bismuth tungstate not only serves as a center for electron generation and transfer but also forms a heterojunction through interfacial coupling. Using a simple hydrothermal process, oxygen vacancies can be formed in amorphous bismuth tungstate by adjusting parameters such as the trisodium citrate content. This optimization promotes the formation of Br / O double vacancies in the heterojunction, effectively suppressing the recombination of photogenerated carriers, ultimately enabling the system to withstand 100 mg·L⁻¹ of light under visible light. -1 Cr 6+ The photoreduction rate of ions reached 8.5 times that of manganese-doped bismuth oxybromide (pseudo-first-order kinetic constant k = 0.0297 min). -1 This led to the realization of Br / O double-vacancy bismuth-based crystalline-amorphous junction and its synthesis method, as well as the achievement of high-concentration Cr... 6+The effect of ion light reduction.

[0045] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0046] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A method for synthesizing a catalyst, comprising the steps of: Manganese-doped bismuth oxybromide is used as a matrix, manganese ions are doped, and Mn 4+ Bromine vacancies are formed in the bismuth oxybromide, and manganese-doped bismuth oxybromide is obtained; partially covering the surface of a manganese-doped bismuth oxybromide substrate with amorphous bismuth tungstate in a discontinuous manner, and forming oxygen vacancies in the amorphous bismuth tungstate through a hydrothermal reaction.

2. The method of synthesis of a catalyst according to claim 1, characterized in that, The raw materials for preparing the manganese-doped bismuth oxybromide include bismuth nitrate, sodium bromide and manganese acetate tetrahydrate.

3. The method of synthesis of a catalyst according to claim 1, characterized in that, The preparation of the amorphous bismuth tungstate comprises the steps of: adding trisodium citrate and bismuth nitrate to the manganese-doped bismuth oxybromide, dispersing / dissolving in deionized water, adding sodium tungstate after stirring, then transferring the mixed system into a polytetrafluoroethylene high-pressure reaction kettle for reaction, and finally washing and drying to obtain a manganese-doped bismuth oxybromide-amorphous bismuth tungstate composite material.

4. The method of synthesis of a catalyst according to claim 2, characterized in that, The molar ratio of the manganese-doped bismuth oxybromide to bismuth nitrate is 1: (0.20-0.52).

5. The method of claim 2, wherein the catalyst is synthesized by the process comprising: The concentration of manganese acetate tetrahydrate is 0.001-0.01 mol / L -1 .

6. The method of synthesis of a catalyst according to claim 3, characterized in that, The concentration of bismuth nitrate in deionized water is 0.1-0.6 mol / L -1 .

7. The method of synthesis of a catalyst according to claim 3, characterized in that, The amount of trisodium citrate added is 0 mmol-6.25 mmol.

8. The method of synthesis of a catalyst according to claim 1, characterized in that, The reaction temperature and time of the hydrothermal reaction for forming oxygen vacancies in the amorphous bismuth tungstate are 120-200℃ and 6-20h, respectively.

9. The catalyst synthesized by the method according to any one of claims 1-8.

10. The use of the catalyst according to claim 9 in wastewater treatment.

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