Coated bismuth ferrite and bismuth oxybromide flaky water treatment catalyst as well as preparation method and application thereof

Abstract

The invention discloses a coated bismuth ferrite and bismuth oxybromide flaky water treatment catalyst and a preparation method and application thereof, and belongs to the technical field of sewage treatment.The coated bismuth ferrite and bismuth oxybromide flaky water treatment catalyst structurally comprises a two-dimensional mullite phase Bi2Fe4O9 nanosheet and a continuous film coated on the surface of the two-dimensional mullite phase Bi2Fe4O9 nanosheet, and the continuous film is composed of bismuth oxybromide nanoparticles; the side length of the two-dimensional mullite phase Bi2Fe4O9 nanosheet is 500 to 600 nm, the thickness of the two-dimensional mullite phase Bi2Fe4O9 nanosheet is 100 to 200 nm, and the particle size of the bismuth oxybromide nanoparticles is 5 to 10 nm; under visible light, the coated bismuth ferrite and bismuth oxybromide flaky water treatment catalyst removes azo dyes in wastewater by activating persulfate. The coated bismuth ferrite and bismuth oxybromide flaky water treatment catalyst provided by the invention has a compact heterogeneous interface and a relatively large specific surface area, the number of active sites is large, meanwhile, the persulfate activation capability is strong, and the coated bismuth ferrite and bismuth oxybromide flaky water treatment catalyst has a wide application prospect in the aspect of azo-containing dye wastewater treatment.

Description

Technical Field

[0001] The present invention belongs to the technical field of sewage treatment, and particularly relates to a coated bismuth ferrite@bismuth oxybromide flake water treatment catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] The textile printing and dyeing industry is a key part of traditional manufacturing, and plays an important role in economic development, technological innovation, and sustainable development. The rapid development of the textile printing and dyeing industry has brought about the extensive use of azo dyes (such as methylene blue, methyl orange, congo red, rhodamine B, etc.). However, if the wastewater containing azo dyes is directly discharged without proper treatment or complete purification, it will not only affect the aquatic environment, but also cause changes in the DNA structure of organisms and pose a carcinogenic risk. Therefore, the wastewater containing azo dyes needs to be harmlessly treated before discharge to meet the discharge standards. Traditional water treatment methods such as physical adsorption and membrane filtration can enrich and reduce the content of azo molecules in water to a certain extent, but efficient and low-energy-consuming methods for the degradation and removal of azo dyes are still closely concerned by the scientific community and the industrial community.

[0003] Based on the persulfate activation oxidation technology of semiconductor catalysts, the effective degradation of azo dyes can be achieved by activating persulfate to generate free radicals with strong oxidation ability, and harmless products to the environment are generated. Therefore, developing semiconductor catalysts with high efficiency, non-toxicity, good chemical stability, and high catalytic activity is the key to realizing the removal of azo dyes in printing and dyeing wastewater. However, the existing heterogeneous semiconductor photocatalysts have poor stability, are prone to generate Fe sludge, have a narrow pH application range, a single type of organic pollutant degradation, and are prone to losing activity during the actual catalytic process. Therefore, it is necessary to develop a highly efficient heterogeneous semiconductor photocatalyst that can remove azo dyes.

[0004] To a certain extent, constructing semiconductor composites can form heterogeneous catalysts with higher catalytic activity. In the construction of heterogeneous semiconductor catalysts, the selection and preparation methods of the two-phase materials are very important. Bismuth ferrite (Bi2Fe4O9), as a typical iron-based semiconductor oxide, has a band gap of about 2.1 eV and has good response ability to visible light, and is a typical photocatalytic material. However, the phenomenon of photo-generated carrier recombination is serious in the single-phase Bi2Fe4O9 material, and there are fewer electrons available for effective participation in photocatalysis, which greatly limits its application expansion in the field of photocatalysis. Moreover, as the light absorption center, Bi2Fe4O9 has a low light utilization rate. Therefore, if a light-responsive material rich in oxygen vacancies can be selected as the secondary structure and combined with Bi2Fe4O9 to form a tight composite interface, it is expected to enrich photo-generated electrons and holes on different surfaces of the material through the band bending of the two, effectively realizing the separation of photo-generated carriers, thereby improving the efficiency of the photocatalyst.

[0005] Bismuth oxybromide (BiOBr) is a ternary compound of group V-VI-VII, with a PbFCl-type structure in the tetragonal crystal system, belonging to the P4 / nmm space group, and the crystal structure has D4h symmetry. The crystal consists of interleaved [Bi2O2] 2+ layers and double layers of bromine atoms to form a unique layered structure, which can serve as the light absorption center for photocatalytic reactions. Chinese patent document with publication number CN116371433A discloses a flower-like TiO2 / BiOBr core-shell structure heterojunction material and its preparation method. In this invention, regular TiO2 hollow microspheres are synthesized using silica as a template, and then flaky BiOBr is loaded on the surface of TiO2 hollow microspheres by in-situ hydrothermal method to form a flower-like hierarchical core-shell structure TiO2 / BiOBr heterojunction material with strong light absorption ability. However, the synthesis process of this invention is relatively complex, requires the action of surfactants, and has a small reaction kinetic constant, so the degradation performance of organic pollutants needs to be further improved.

[0006] Based on the above analysis, if a bismuth ferrite / bismuth oxybromide heterojunction composite material can be prepared and a tight composite interface can be obtained through growth regulation, then it is expected to achieve efficient degradation of azo dyes in wastewater. Summary of the Invention

[0007] The present invention provides a coated bismuth ferrite@bismuth oxybromide flaky water treatment catalyst. This water treatment catalyst has a tight heterojunction interface and a large specific surface area, with a large number of active sites. At the same time, it has strong persulfate activation ability and has broad application prospects in the treatment of wastewater containing azo dyes.

[0008] The specific technical solutions adopted are as follows:

[0009] A coated bismuth ferrite@bismuth oxybromide flaky water treatment catalyst, the structure includes two-dimensional mullite phase Bi2Fe4O9 nanosheets and a continuous film-like coating on its surface. The continuous film-like coating is composed of bismuth oxybromide nanoparticles; the side length of the two-dimensional mullite phase Bi2Fe4O9 nanosheets is 500-600nm, the thickness is 100-200nm, and the particle size of the bismuth oxybromide nanoparticles is 5-10nm;

[0010] Under visible light, the coated bismuth ferrite@bismuth oxybromide flaky water treatment catalyst removes azo dyes in wastewater by activating persulfate.

[0011] The Fe element contained in the mullite phase Bi2Fe4O9 can effectively activate persulfate and realize the degradation of azo dyes in the advanced oxidation process. Especially when there is a valence change of the Fe element in Bi2Fe4O9, oxygen defects in the crystal (such as O v ) can not only directly activate persulfate, but also effectively induce Fe3+ / Fe 2+ Cyclic and continuous activation of persulfate, [Bi2O2] in BiOBr 2+ The strong interaction within the layer and the weak non-covalent interaction between the layers make BiOBr have a higher carrier separation efficiency after the response is generated. The present invention relates to a bismuth ferrite @ bismuth oxybromide flake catalyst, in which BiOBr with a particle size of 5-10nm is tightly coated on the surface of Bi2Fe4O9 nanosheets through in-situ growth to form a dense and continuous film-like structure. This continuous coated film-like structure formed by small-sized BiOBr nanoparticles provides more surface reaction active sites on the one hand, which can more effectively adsorb and activate PS molecules to obtain ROS (reactive groups) for catalytic reactions; on the other hand, BiOBr and Bi2Fe4O9 form a complete and continuous heterojunction interface, thereby constructing a continuous built-in electric field, which is more conducive to the migration and transport of photogenerated carriers and can greatly improve the efficiency of photocatalytic reactions. Therefore, the small-sized particles in the composite material of the present invention provide more reaction active sites, promote the absorption of light, and the built-in electric field provided by the composite interface of the two promotes carrier separation. The two aspects work synergistically to activate PDS (peroxydisulfate) and improve the photocatalytic activity.

[0012] The bismuth ferrite@bismuth oxybromide flake water treatment catalyst is suitable for activating PDS to degrade azo dyes under visible light. The principle is that PDS and Fe 2+ The reaction generates active substances and Fe 3+ At the same time, under the irradiation of visible light, photogenerated electron-hole pairs are generated inside the semiconductor. The heterogeneous interface promotes the separation of photogenerated carriers on the surface of the composite catalyst. The generated photogenerated electrons pass through Fe 3+ Reduction to Fe 2+ Accelerate the PDS activation process, effectively inhibit the recombination of photogenerated carriers, and improve the efficiency of activated PDS in degrading azo dyes.

[0013] Furthermore, in the coated bismuth ferrite@bismuth oxybromide flake water treatment catalyst, the mass percentage of bismuth oxybromide nanoparticles is 37.5-50wt%.

[0014] Optionally, the azo dye includes rhodamine b (RhB), methylene blue (MB), methyl orange (MO) or Congo red (CR).

[0015] Preferably, the persulfate is potassium persulfate.

[0016] The present invention also provides a method for preparing the coated bismuth ferrite@bismuth oxybromide flake water treatment catalyst, comprising the following steps:

[0017] (1) Using Bi(NO3)3·5H2O as bismuth source, Fe(NO3)3·9H2O as iron source, and NaOH as mineralizer, two-dimensional mullite phase Bi2Fe4O9 nanosheets were prepared by hydrothermal reaction in a solvent system of water and acetic acid.

[0018] (2) The two-dimensional mullite phase Bi2Fe4O9 nanosheets obtained in step (1) are uniformly dispersed in ethylene glycol as a substrate material, hydrobromic acid with a concentration of 40% (mass fraction) is added, and the suspension is fully stirred to obtain a suspension, and the suspension is placed in a reactor, and the suspension is kept at 120-180° C. for 2-8 hours for a solvent thermal reaction. After the reaction is completed, the suspension is cooled, washed and dried to obtain the coated bismuth ferrite@bismuth oxybromide flaky water treatment catalyst.

[0019] Preferably, the preparation method of two-dimensional mullite phase Bi2Fe4O9 nanosheets is as follows: add Bi(NO3)3·5H2O to a mixed solvent of water and acetic acid, stir magnetically until fully dissolved, then add Fe(NO3)3·9H2O, continue magnetic stirring to obtain a red mixed solution; then add NaOH to the red mixed solution to make the NaOH concentration reach 8-12 mol / L, and obtain a precursor suspension after stirring; keep the above-mentioned precursor suspension at 120-180°C for 6-12h for hydrothermal reaction, cool it with the furnace, take out the reaction product, wash it thoroughly and dry it to obtain two-dimensional mullite phase Bi2Fe4O9 nanosheets.

[0020] Preferably, the ratio of two-dimensional mullite phase Bi2Fe4O9 nanosheets, hydrobromic acid and ethylene glycol is 0.1g-0.2g: 150-250μL: 20-30mL. Under the above preferred parameters, it is conducive to the formation of small-sized bismuth oxybromide nanoparticles and continuous coating-type compact heterojunctions.

[0021] The invention uses two-dimensional mullite phase Bi2Fe4O9 nanosheets as substrate materials. On the one hand, Bi2Fe4O9, as a multi-iron oxide, is composed of a bismuth iron oxide layer, a [FeO6] octahedron layer and a [FeO4] octahedron layer, has a large internal electric field, and contains iron elements with high PDS activation activity; on the other hand, the two-dimensional Bi2Fe4O9 nanosheets have a large specific surface area and an exposed surface, which provides more active sites and can better enable BiOBr to nucleate on its surface, so that the prepared composite material has good dispersion; at the same time, according to the matching degree of the conduction band positions of the Bi2Fe4O9 and BiOBr two-phase materials, an in-situ growth technology is used to obtain a close and continuous interface, so as to obtain a composite catalyst with optimized performance, and hydrobromic acid is used as an etchant, and H + The Bi2Fe4O9 surface was etched, and BiOBr nanoparticles were in situ grown on the Bi2Fe4O9 surface to form a coated composite structure. Specifically, during the solvothermal reaction, Br- Bi on the surface of Bi2Fe4O9 3+ Anion exchange occurs in situ to form BiOBr nanoparticles with a core-shell structure, and finally a core-shell type bismuth ferrite@bismuth oxybromide flake water treatment catalyst is formed.

[0022] The bismuth ferrite@bismuth oxybromide flake water treatment catalyst has a core-shell structure. The core-shell structure can increase the area of the heterojunction contact interface, and an internal built-in electric field is easily formed at the interface; the nanoparticles have a large specific surface area and small size effect, which can provide more surface active sites; the continuous heterojunction interface can effectively reduce the transport barrier of photogenerated carriers and then exhibit better charge separation and transport characteristics. In addition, in this core-shell structure, the interface region accounts for a relatively large proportion in the total material. Therefore, the large contact area formed by the bismuth ferrite@bismuth oxybromide flake water treatment catalyst makes the interface effect dominant, providing great possibilities for the effective diffusion and transport of photogenerated charges.

[0023] In the present invention, a stable core-shell flake composite structure can be obtained by etching two-dimensional mullite phase Bi2Fe4O9 nanosheets under specific solvothermal conditions. In the specific preparation process of the present invention, a stable core-shell flake composite structure is prepared by controlling the concentration of hydrobromic acid, the concentration ratio of the substrate material, and the solvent system.

[0024] Preferably, the conditions of the solvothermal reaction are 160 °C and 6 h. Under the above reaction conditions, the solvothermal reaction can be made more sufficient.

[0025] The present invention also provides a method for treating wastewater containing azo dyes, using the core-shell type bismuth ferrite@bismuth oxybromide flake water treatment catalyst.

[0026] Exemplarily, the core-shell type bismuth ferrite@bismuth oxybromide flake water treatment catalyst is added to the wastewater containing azo dyes, and then persulfate is added, and the azo dyes are degraded under visible light conditions; the ratio of the core-shell type bismuth ferrite@bismuth oxybromide flake water treatment catalyst, persulfate and the wastewater containing azo dyes is 5 - 30 mg: 5 - 50 mg: 50 mL, and in the wastewater containing azo dyes, the concentration of azo dyes is 3×10 -5 -5×10 -5 M.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] (1) The coated bismuth ferrite@bismuth oxybromide flake water treatment catalyst provided by the present invention has good dispersibility, good stability and a large specific surface area. Bismuth oxybromide nanoparticles grow in-situ on the surface of two-dimensional mullite-phase Bi2Fe4O9 nanosheets, forming a coated composite structure with a clear heterojunction interface, which is beneficial to the adsorption of dye molecules in the degradation reaction and provides a larger number of active sites for activating PDS. Moreover, the corresponding preparation process is simple, the equipment requirements are low, and the reaction conditions are easy to control, making it suitable for large-scale industrial production.

[0029] (2) In the present invention, the coated bismuth ferrite@bismuth oxybromide flake water treatment catalyst activates PDS under visible light assistance. During the activation process, PDS reacts with Fe 2+ to generate active substances and Fe 3+ . Under visible light irradiation, the heterojunction interface of the composite catalyst effectively promotes the separation of carriers. The generated photo-generated electrons provide more Fe 2+ for the activation of PDS. At the same time, PDS can also react with photo-generated electrons to generate ·SO4 - , effectively inhibiting the recombination of photo-generated carriers and further improving the activation process of persulfate and the degradation effect on azo dyes.

[0030] (3) The coated bismuth ferrite@bismuth oxybromide flake water treatment catalyst prepared by the present invention has strong PDS activation performance. Under visible light conditions, using this composite catalyst to activate PDS, 4.2×10 -5 M of RhB, MB, MO and CR can be reduced to 98%, 84%, 70% and 91% respectively within 30 min, showing broad application prospects in the treatment of wastewater containing azo dyes. Description of the Drawings

[0031] Figure 1 are SEM images of the samples: (a) is the SEM image of two-dimensional mullite-phase Bi2Fe4O9 nanosheets, (b) is the SEM image of the sample synthesized in the aqueous phase in Comparative Example 2, and (c) is the SEM image of the coated bismuth ferrite@bismuth oxybromide flake water treatment catalyst prepared in Example 2.

[0032] Figure 2 are the XRD patterns of two-dimensional mullite-phase Bi2Fe4O9 nanosheets, the sample synthesized in the aqueous phase, and the coated bismuth ferrite@bismuth oxybromide flake water treatment catalyst in Example 2.

[0033] Figure 3 are the TEM and HRTEM images of the coated bismuth ferrite@bismuth oxybromide flake water treatment catalyst in Example 2: (a) and (b) are the TEM images and local enlarged views, and (c) is the HRTEM image.

[0034] Figure 4Degradation efficiency curve diagrams of the catalysts prepared in Example 2 and Comparative Example for degrading 20 mg / L RhB solution in different catalytic systems and the corresponding pseudo-first-order kinetic fitting curve diagrams. (a) is the degradation efficiency curve diagram, and (b) is the pseudo-first-order kinetic fitting curve diagram.

[0035] Figure 5 Degradation efficiency curve diagrams of the core-shell type bismuth ferrite@bismuth oxybromide flake water treatment catalyst in Example 2 for different azo dyes.

[0036] Figure 6 Degradation efficiency curve diagrams of the two-dimensional Bi2Fe4O9-BiOCl composite catalyst in Comparative Example 3 for different azo dyes. Detailed implementation manners

[0037] The present invention will be further illustrated below in conjunction with the examples and the accompanying drawings. It should be understood that these examples are only used to illustrate the present invention and not to limit the scope of the present invention. The operation methods without specific conditions noted in the following examples are generally in accordance with conventional conditions or in accordance with the conditions recommended by the manufacturer.

[0038] The preparation method of the two-dimensional mullite phase Bi2Fe4O9 nanosheets in the examples or comparative examples is as follows:

[0039] (1) Add 1 mmol of Bi(NO3)3·5H2O to a mixed solvent of 37.5 mL of deionized water and 2.5 mL of acetic acid, and dissolve it thoroughly by magnetic stirring. Then add 1.5 mmol of Fe(NO3)3·9H2O and continue magnetic stirring to obtain a red mixed solution. Then add NaOH to the red mixed solution to make the NaOH concentration reach 10 mol / L, and stir for 2 h to obtain a reddish-brown precursor suspension.

[0040] (2) Load the reddish-brown precursor suspension into the Teflon inner liner and then place it in a reaction kettle, seal it, and carry out a hydrothermal reaction at 180 °C for 12 h. After the reaction is completed, cool it with the furnace, take out the reaction product, wash it with deionized water and absolute ethanol until neutral, and dry it for 12 h to obtain two-dimensional mullite phase Bi2Fe4O9 nanosheets.

[0041] The SEM image of the two-dimensional mullite phase Bi2Fe4O9 (BFO) nanosheets is as Figure 1As shown in (a) therein, it can be seen that its surface is smooth, the morphology is uniform and the dispersibility is good; in the corresponding XRD pattern, the diffraction peaks are located at 14.7°, 28.2°, 28.9°, 29.8° and 33.7°, corresponding to the (001), (121), (211), (002) and (130) crystal planes of the mullite phase Bi2Fe4O9 (JCPDS: 25-0090) respectively. No impurity peaks are found in the phase of the product, indicating that the prepared Bi2Fe4O9 has high purity and good crystallinity.

[0042] The structure of the coated bismuth ferrite@bismuth oxybromide flake water treatment catalyst prepared in the example includes two-dimensional mullite phase Bi2Fe4O9 nanosheets and a continuous film-like coating on its surface. The continuous film-like coating is composed of bismuth oxybromide nanoparticles; the side length of the two-dimensional mullite phase Bi2Fe4O9 nanosheets is 500-600 nm, the thickness is 100-200 nm, and the particle size of the bismuth oxybromide nanoparticles is 5-10 nm;

[0043] Example 1

[0044] (1) Disperse 0.1 g of two-dimensional mullite phase Bi2Fe4O9 nanosheets into 20 mL of ethylene glycol, add 150 μL of 40% hydrobromic acid, and stir well to obtain a reddish-brown suspension;

[0045] (2) Load the above-mentioned reddish-brown suspension into a reaction kettle, carry out a solvothermal reaction at 160 °C for 6 h. After the reaction is completed, the reaction kettle is cooled with the furnace. Take out the sample, wash the sample with deionized water and anhydrous ethanol respectively, and dry the sample at 60 °C for 12 h. The obtained orange-yellow powder sample is the coated bismuth ferrite@bismuth oxybromide flake water treatment catalyst, denoted as BFO-BOB-1.5.

[0046] Example 2

[0047] (1) Disperse 0.1 g of two-dimensional mullite phase Bi2Fe4O9 nanosheets into 20 mL of ethylene glycol, add 200 μL of 40% hydrobromic acid, and stir well to obtain a reddish-brown suspension;

[0048] (2) Load the above-mentioned reddish-brown suspension into a reaction kettle, carry out a solvothermal reaction at 160 °C for 6 h. After the reaction is completed, the reaction kettle is cooled with the furnace. Take out the sample, wash the sample with deionized water and anhydrous ethanol respectively, and dry the sample at 60 °C for 12 h. The obtained orange-yellow powder sample is the coated bismuth ferrite@bismuth oxybromide flake water treatment catalyst, denoted as BFO-BOB-2.0.

[0049] The SEM image of the coated bismuth ferrite@bismuth oxybromide flake water treatment catalyst prepared in this example is as Figure 1As shown in (c) in [reference], it can be observed from the figure that under the etching effect of hydrobromic acid and through in-situ growth by the solvothermal method, BiOBr nanoparticles are coated on the surface of the Bi2Fe4O9 substrate and a coated flake composite structure is formed; in Figure 2 In the XRD pattern shown, it can be seen that the composite catalyst is composed of two phases, corresponding to Bi2Fe4O9 (JCPDS: 25-0090) and BiOBr (JCPDS: 73-2061) respectively, and no impurity peaks are found;

[0050] The TEM image and HRTEM image of the coated bismuth ferrite@bismuth oxybromide flake water treatment catalyst prepared in this example are as shown in Figure 3 (a)-(c) in [reference]. Under high magnification, it can be seen that a "dense" coated composite structure composed of BiOBr nanoparticles is distributed on the surface of the Bi2Fe4O9 substrate material, which also confirms that the composite structure is a coated flake composite structure; in the HRTEM image, a clear heterophase interface can be seen, and the corresponding lattice spacings of 0.384 nm and 0.426 nm correspond to the (200) and (020) crystal planes of Bi2Fe4O9, and the lattice spacing of 0.364 nm corresponds to the (011) crystal plane of BiOBr; in summary, the crystallinity of this composite structure is good, which also shows that the coated flake composite catalyst has been successfully prepared.

[0051] Example 3

[0052] (1) Disperse 0.1 g of two-dimensional mullite-phase Bi2Fe4O9 nanosheets into 20 mL of ethylene glycol, add 250 μL of hydrobromic acid with a concentration of 40%, and stir well to obtain a reddish-brown suspension;

[0053] (2) Load the above-mentioned reddish-brown suspension into a reaction kettle, carry out a solvothermal reaction at 160 °C for 6 h. After the reaction is completed, the reaction kettle is cooled with the furnace, the sample is taken out, and the sample is washed with deionized water and anhydrous ethanol respectively, and the sample is dried at 60 °C for 12 h. The obtained orange-yellow powder sample is the coated bismuth ferrite@bismuth oxybromide flake water treatment catalyst, denoted as BFO-BOB-2.5.

[0054] Example 4

[0055] (1) Disperse 0.1 g of two-dimensional mullite-phase Bi2Fe4O9 nanosheets into 30 mL of ethylene glycol, add 200 μL of hydrobromic acid with a concentration of 40%, and stir well to obtain a reddish-brown suspension;

[0056] (2) Load the above-mentioned reddish-brown suspension into a reaction kettle, carry out a solvothermal reaction at 160 °C for 6 h. After the reaction is completed, the reaction kettle is cooled with the furnace. Take out the sample, wash the sample with deionized water and absolute ethanol respectively, and dry the sample at 60 °C for 12 h. The obtained orange-yellow powder sample is the coated bismuth ferrite@bismuth oxybromide flaky water treatment catalyst, denoted as BFO-BOB-2.0-30.

[0057] Example 5

[0058] (1) Disperse 0.1 g of two-dimensional mullite-phase Bi2Fe4O9 nanosheets into 20 mL of ethylene glycol, add 200 μL of hydrobromic acid with a concentration of 40%, and stir well to obtain a reddish-brown suspension;

[0059] (2) Load the above-mentioned reddish-brown suspension into a reaction kettle, carry out a solvothermal reaction at 140 °C for 6 h. After the reaction is completed, the reaction kettle is cooled with the furnace. Take out the sample, wash the sample with deionized water and absolute ethanol respectively, and dry the sample at 60 °C for 12 h. The obtained orange-yellow powder sample is the coated bismuth ferrite@bismuth oxybromide flaky water treatment catalyst, denoted as BFO-BOB-2.0-140.

[0060] Example 6

[0061] (1) Disperse 0.1 g of two-dimensional mullite-phase Bi2Fe4O9 nanosheets into 20 mL of ethylene glycol, add 200 μL of hydrobromic acid with a concentration of 40%, and stir well to obtain a reddish-brown suspension;

[0062] (2) Load the above-mentioned reddish-brown suspension into a reaction kettle, carry out a solvothermal reaction at 180 °C for 6 h. After the reaction is completed, the reaction kettle is cooled with the furnace. Take out the sample, wash the sample with deionized water and absolute ethanol respectively, and dry the sample at 60 °C for 12 h. The obtained orange-yellow powder sample is the Bi2Fe4O9@BiOBr coated flaky composite catalyst, denoted as BFO-BOB-2.0-180.

[0063] Example 7

[0064] (1) Disperse 0.1 g of two-dimensional mullite-phase Bi2Fe4O9 nanosheets into 20 mL of ethylene glycol, add 200 μL of hydrobromic acid with a concentration of 40%, and stir well to obtain a reddish-brown suspension;

[0065] (2) Load the above-mentioned reddish-brown suspension into a reaction kettle, carry out a solvothermal reaction at 160 °C for 2 h. After the reaction is completed, the reaction kettle is cooled with the furnace. Take out the sample, wash the sample with deionized water and anhydrous ethanol respectively, and dry the sample at 60 °C for 12 h. The obtained orange-yellow powder sample is the coated bismuth ferrite@bismuth oxybromide flake water treatment catalyst, denoted as BFO-BOB-2.0-2.

[0066] Example 8

[0067] (1) Disperse 0.1 g of two-dimensional mullite-phase Bi2Fe4O9 nanosheets into 20 mL of ethylene glycol, add 200 μL of hydrobromic acid with a concentration of 40%, and stir well to obtain a reddish-brown suspension;

[0068] (2) Load the above-mentioned reddish-brown suspension into a reaction kettle, carry out a solvothermal reaction at 160 °C for 4 h. After the reaction is completed, the reaction kettle is cooled with the furnace. Take out the sample, wash the sample with deionized water and anhydrous ethanol respectively, and dry the sample at 60 °C for 12 h. The obtained orange-yellow powder sample is the coated bismuth ferrite@bismuth oxybromide flake water treatment catalyst, denoted as BFO-BOB-2.0-4.

[0069] Comparative Example 1

[0070] Use two-dimensional mullite-phase Bi2Fe4O9 nanosheets as the sample of Comparative Example 1.

[0071] Comparative Example 2

[0072] (1) Disperse 0.1 g of two-dimensional mullite-phase Bi2Fe4O9 nanosheets into 20 mL of deionized water, add 200 μL of hydrobromic acid with a concentration of 40%, and stir well to obtain a reddish-brown suspension;

[0073] (2) Load the above-mentioned reddish-brown suspension into a reaction kettle, carry out a hydrothermal reaction at 160 °C for 6 h. After the reaction is completed, the reaction kettle is cooled with the furnace. Take out the sample, wash the sample with deionized water and anhydrous ethanol respectively, and dry the sample at 60 °C for 12 h to obtain the sample synthesized in the aqueous phase.

[0074] The SEM image of the sample synthesized in the aqueous phase of Comparative Example 2 is as shown in Figure 1 (b) in. It can be seen from the figure that the morphology of the sample synthesized in the aqueous phase tends to have two different growth trends. The morphology of Bi2Fe4O9 nanosheets is not observed in the figure, and the morphology of the second phase coated on the surface of the nanosheets is not observed either. It shows that the aqueous phase synthesis method in Comparative Example 2 cannot successfully prepare a coated bismuth ferrite@bismuth oxybromide flake water treatment catalyst with a clear heterojunction interface, a large specific surface area and uniform dispersion.

[0075] Comparative Example 3

[0076] (1) Disperse 0.1 g of two-dimensional mullite-phase Bi2Fe4O9 nanosheets into 20 mL of ethylene glycol, add 2 mL of hydrochloric acid with a concentration of 2%, and stir well to obtain a reddish-brown suspension.

[0077] (2) Load the above-mentioned reddish-brown suspension into a reaction kettle, carry out a solvothermal reaction at 160 °C under a pressure of about 0.4 - 0.6 MPa for 6 h. After the reaction is completed, the reaction kettle is cooled with the furnace. Take out the sample, wash the sample with deionized water and anhydrous ethanol respectively, and dry the sample at 60 °C for 12 h. The obtained yellowish-brown powder sample is the two-dimensional Bi2Fe4O9-BiOCl composite catalyst, denoted as BFO-BOC-2.0.

[0078] Sample analysis

[0079] Add the coated bismuth ferrite@bismuth oxybromide flake water treatment catalyst (20 mg) prepared in Example 2 to 50 mL of RhB (20 mg / L) solution, stir in the dark for 30 min to reach the adsorption equilibrium, take a sample, add 30 mg of potassium persulfate, and then turn on the xenon lamp to start the photocatalytic degradation reaction. During the whole process, the solution system is maintained at about 25 °C. Take a sample every 10 min and mix it with 50 mg of Na2S2O3 to quench the reaction. After centrifugal separation, use a UV-visible spectrophotometer to test the degradation effect of different catalysts on the RhB solution.

[0080] Further determine the synergistic effect among the catalyst, visible light, and persulfate, and test the catalytic efficiency of two-dimensional mullite-phase Bi2Fe4O9 nanosheets and coated bismuth ferrite@bismuth oxybromide flake water treatment catalysts synthesized in different reaction systems on RhB. As Figure 4 shown in (a) of, in the visible light system, both Bi2Fe4O9 and BFO-BOB-2.0 act as photocatalysts to degrade RhB, and the degradation efficiencies of RhB within 30 min are 10% and 71% respectively. The heterojunction formed by the combination of Bi2Fe4O9 and BiOBr promotes the carrier separation efficiency at the interface of the composite structure and enhances the light response ability. In the PDS degradation experiment, the BFO-BOB-2.0 composite catalyst mainly acts as a PDS activator, and the degradation efficiency of RhB within 30 min reaches 60%. When visible light and PDS are introduced simultaneously, in the absence of a catalyst, the degradation efficiency of RhB is only 25%, indicating that the activation effect of visible light on PDS is poor. Then, after introducing the catalyst, both Bi2Fe4O9 and BFO-BOB-2.0 are both photocatalysts and PDS activators, and the degradation efficiencies of RhB within 30 min are 75% and 98% respectively. Further, the reaction kinetics of the degradation data is fitted, and the results are as Figure 4As shown in (b) therein, the reaction rate of the Vis / PDS / BFO-BOB-2.0 system is 0.1177 min -1 , which are 3.64, 5.45 and 2.91 times that of the Vis / BFO-BOB-2.0, PDS / BFO-BOB-2.0 and Vis / PDS / BFO systems, respectively. In addition, the performances of the coated bismuth ferrite@bismuth oxybromide flake water treatment catalyst and the two-dimensional Bi2Fe4O9-BiOCl composite catalyst were compared. The degradation reaction rate of Vis / PDS / BFO-BOB-2.0 is 1.29 times that of Vis / PDS / BFO-BOC-2.0. To sum up, the combination of Bi2Fe4O9 and BiOBr to form a coated flake composite structure improves the synergistic effect of photocatalysis and PDS. On the one hand, the Fe element on the surface of the BFO-BOB-2.0 catalyst promotes the activation of PDS; on the other hand, the BFO-BOB-2.0 composite catalyst has a clear heterojunction interface, which promotes the effective separation of carriers at the interface.

[0081] To effectively degrade azo dyes in wastewater, PDS was activated under visible light. Using azo dyes methylene blue, methyl orange and congo red as target pollutants, the degradation performance of the coated bismuth ferrite@bismuth oxybromide flake water treatment catalyst prepared in Example 2 for azo dyes was studied. As Figure 5 shown, the degradation efficiencies of azo organic pollutants methylene blue, methyl orange and congo red by activating PDS under visible light within 30 min are 84%, 70% and 91% respectively. At the same time, the degradation performance of the two-dimensional Bi2Fe4O9-BiOCl composite catalyst prepared in Comparative Example 3 for azo dyes was studied. As Figure 6 shown, the degradation efficiencies of azo organic pollutants methylene blue, methyl orange and congo red by activating PDS under visible light within 30 min are 79%, 64% and 80% respectively. And, in terms of reaction kinetics, the PDS activation catalytic degradation rate of the bismuth ferrite@bismuth oxybromide flakes involved in the present invention is higher, which is more advantageous for improving the efficiency of the catalytic reaction. To sum up, the coated bismuth ferrite@bismuth oxybromide flake water treatment catalyst prepared in Example 2 can effectively degrade various types of azo dyes. Compared with the two-dimensional Bi2Fe4O9-BiOCl composite catalyst in Comparative Example 3, the coated bismuth ferrite@bismuth oxybromide flake water treatment catalyst has stronger adaptability to the degradation of azo dyes.

[0082] The above-described embodiments have detailed the technical solutions of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, supplements or similar replacements made within the scope of the principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A coated bismuth ferrite @ bismuth oxybromide flake water treatment catalyst, characterized in that, The structure includes a two-dimensional mullite phase Bi2Fe4O9 nanosheet and a continuous film-like film coated on the surface thereof, wherein the continuous film-like film is composed of bismuth oxybromide nanoparticles; the side length of the two-dimensional mullite phase Bi2Fe4O9 nanosheet is 500-600nm, the thickness is 100-200nm, and the particle size of the bismuth oxybromide nanoparticles is 5-10nm; Under visible light, the coated bismuth ferrite@bismuth oxybromide flake water treatment catalyst removes azo dyes in wastewater by activating persulfate.

2. The coated bismuth ferrite @ bismuth oxybromide flake water treatment catalyst according to claim 1, wherein The mass percentage of bismuth oxybromide nanoparticles is 37.5-50wt%.

3. The coated bismuth ferrite @ bismuth oxybromide flake water treatment catalyst according to claim 1, characterized in that, The azo dyes include rhodamine b, methylene blue, methyl orange or Congo red.

4. The coated bismuth ferrite@bismuth oxybromide flake water treatment catalyst according to claim 1, wherein The persulfate is potassium persulfate.

5. The preparation method of the coated bismuth ferrite@bismuth oxybromide flake water treatment catalyst according to any one of claims 1-4, characterized in that, The following steps are involved: (1) Using Bi(NO3)3·5H2O as bismuth source, Fe(NO3)3·9H2O as iron source, and NaOH as mineralizer, two-dimensional mullite phase Bi2Fe4O9 nanosheets were prepared by hydrothermal reaction in a solvent system of water and acetic acid. (2) The two-dimensional mullite phase Bi2Fe4O9 nanosheets obtained in step (1) are uniformly dispersed in ethylene glycol as a substrate material, and hydrobromic acid with a concentration of 40% is added and stirred to obtain a suspension. The suspension is placed in a reactor and kept at 120-180°C for 2-8 hours for a solvent thermal reaction. After the reaction is completed, the suspension is cooled, washed and dried to obtain the coated bismuth ferrite@bismuth oxybromide flaky water treatment catalyst.

6. The preparation method of the coated bismuth ferrite @ bismuth oxybromide flake water treatment catalyst according to claim 5, characterized in that, The ratio of two-dimensional mullite phase Bi2Fe4O9 nanosheets, hydrobromic acid and ethylene glycol is 0.1g-0.2g:150-250μL:20-30mL.

7. The preparation method of the coated bismuth ferrite @ bismuth oxybromide flake water treatment catalyst according to claim 5, characterized in that, The conditions of the solvothermal reaction were 160 °C for 6 h.

8. A method for treating wastewater containing azo dyes, characterized in that, The coated bismuth ferrite@bismuth oxybromide flake water treatment catalyst described in any one of claims 1 to 4 is used.

9. The wastewater treatment method containing azo dyes according to claim 8, characterized in that, Add the described coated bismuth ferrite@bismuth oxybromide flake water treatment catalyst to the wastewater containing azo dyes, then add persulfate, and degrade the azo dyes under visible light conditions; the ratio of the coated bismuth ferrite@bismuth oxybromide flake water treatment catalyst, persulfate and the wastewater containing azo dyes is 5 - 30 mg: 5 - 50 mg: 50 mL. In the wastewater containing azo dyes, the concentration of azo dyes is 3×10 -5 -5×10 -5 M.

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