Fe3O4@Bi@BiOBr composite photocatalyst, preparation method of catalyst and application thereof

Abstract

The application relates to an Fe3O4@Bi@BiOBr composite photocatalyst, a preparation method of the catalyst and application of the catalyst, raw materials of the application include the following: 1-2 mmol of bismuth nitrate pentahydrate, 1-2 mmol of sodium bromide, 1.0-2.0 g of polyvinylpyrrolidone, 1-2 mmol of sodium borohydride, 60-210 mg of ammonium ferric sulfate, 40-140 mg of ammonium ferrous sulfate, and the composite photocatalyst prepared by the application contains elemental bismuth, BiOBr and Fe3O4, wherein the BiOBr is synthesized by a hydrothermal method, the elemental bismuth is loaded on the BiOBr by in-situ reduction, the Fe3O4 is generated by a chemical reaction, the elemental bismuth is loaded on the BiOBr by in-situ reduction, the prepared BiOBr precursor has high crystallinity and a larger specific surface area, so that more active sites are formed and the performance is stable, and the photocatalytic reaction is facilitated; the loading of the elemental bismuth can improve the conductivity of the BiOBr, and the existence of the bismuth can optimize the energy band structure of the composite catalyst; the Fe3O4 in the prepared Fe3O4@Bi@BiOBr composite photocatalyst is in the form of powder and is attached to the surface of the BiOBr, which is favorable for the transmission of photo-generated electrons, effectively reduces the recombination of photo-generated electron-hole pairs, and makes the prepared photocatalyst have high catalytic activity.

Description

Technical Field

[0001] This invention belongs to the field of environmental chemical photocatalytic treatment technology, and particularly relates to a Fe3O4@Bi@BiOBr composite photocatalyst, the preparation method of the catalyst and its application. Background Technology

[0002] Photocatalysis, due to its ability to convert solar energy into chemical energy that promotes the oxidative degradation of organic pollutants, and its advantages such as low cost, good degradation effect, and no secondary pollution, has been identified as one of the best methods for degrading organic pollutants. In 1972, Fujishima et al. first discovered that TiO2 could catalyze the decomposition of water to produce hydrogen under ultraviolet light irradiation; in 1976, Carey et al. reported that TiO2 aqueous turbidity could dechlorinate polychlorinated biphenyls under near-ultraviolet light irradiation; in 1977, Frank et al. used TiO2 powder to photocatalyze the degradation of CN- containing solutions, thus initiating the application research of semiconductor photocatalysis technology in the field of environmental remediation. However, because TiO2 has a band gap of 3.0-3.2 eV, the excitation wavelength needs to be limited to the ultraviolet light region (accounting for only about 4% of solar energy), and under visible light radiation, the photon yield is low and the catalytic activity is not high, thus limiting its widespread application in the degradation and removal of pollutants in aquatic environments. In order to effectively utilize solar energy and expand the visible light response range of catalysts, the development of new narrow band gap photocatalytic materials has become a focus of attention. BiOBr, as a novel semiconductor photocatalytic material, can narrow its band gap and broaden its visible light wavelength response due to the dipoles generated by orbital hybridization, thereby enhancing its absorption performance for visible light. It is a new type of photocatalytic material that can replace TiO2.

[0003] However, BiOBr alone exhibits a high recombination rate of photogenerated carriers, requiring further optimization to improve its photocatalytic activity. Therefore, a small amount of elemental bismuth is loaded onto its surface through an in-situ reduction process. On one hand, elemental bismuth can act as a bridge between two semiconductors, thus improving conductivity; on the other hand, the surface of elemental bismuth exhibits a plasmon effect, both of which promote the photocatalytic degradation process. However, Bi@BiOBr is a powder particle, which presents certain limitations in practical applications. Many researchers have focused on photocatalytic membrane systems by loading photocatalysts onto inorganic materials such as glass, stainless steel, carbon fiber, activated carbon, or organic matrices through sintering, impregnation, spraying, or bonding. Unfortunately, compared to powder catalysts, the catalytic activity has not been significantly improved, and the photocatalytic membrane is easily corroded by active carriers after light radiation, leading to membrane detachment. Therefore, it is necessary to incorporate a magnetic material to impart magnetic properties, facilitating the effective utilization of its powder catalytic activity and efficient recycling. Liu et al. successfully prepared Fe3O4 / BiOBr composite photocatalysts by chemical precipitation. Characterization and degradation experiments showed that the photocatalytic performance of Fe3O4 / BiOBr was superior to that of pure BiOBr. Furthermore, magnetic experiments demonstrated that Fe3O4 / BiOBr had good magnetic properties, and the magnetic material could be recycled within 30 seconds.

[0004] Chinese patent CN111686770B discloses a BiOBr photocatalyst co-doped with Fe and Cd metal ions. The co-doped catalyst material was prepared using a simple hydrothermal synthesis method. Its catalytic performance was evaluated by catalytically degrading organic pollutants such as dyes and antibiotics in wastewater under simulated sunlight irradiation, demonstrating that the co-doped catalyst material possesses highly efficient degradation and removal capabilities. However, like other catalysts prepared in this way, it faces a common problem: how to apply the powdered / particulate catalyst in practical industrial fields. Catalyst recovery remains a significant challenge for its conversion and application.

[0005] Chinese patent CN110560136A discloses a photocatalytic thin film, its preparation method, and its application. The paper describes the preparation of a photocatalytic thin film composed of two TiO layers sandwiching a CuN layer, and studies have shown a significant degradation and removal effect on methyl orange. However, issues such as how to fix the membrane material onto the support, whether the membrane can withstand the water pressure of actual wastewater, and whether the membrane will become clogged remain unresolved. Furthermore, effective technologies and methods have yet to be found to address the problems of membrane detachment, breakage, and clogging in practical applications. Summary of the Invention

[0006] To overcome the shortcomings of the prior art, the present invention aims to provide a Fe3O4@Bi@BiOBr composite photocatalyst, a method for preparing the catalyst, and its application. A simple in-situ reduction method is used to reduce elemental bismuth to the surface of bismuth oxybromide, thereby improving the structure of bismuth oxybromide. Furthermore, the resulting Fe3O4@Bi@BiOBr composite significantly slows down the electron transport rate, thus rapidly improving the performance of the composite photocatalyst. It features high photocatalytic activity, good stability, and easy recycling.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A Fe3O4@Bi@BiOBr composite photocatalyst, the raw materials of which include: 1-2 mmol of bismuth nitrate pentahydrate, 1-2 mmol of sodium bromide, 1.0-2.0 g of polyvinylpyrrolidone, 1-2 mmol of sodium borohydride, 60-210 mg of ferric ammonium sulfate, and 40-140 mg of ferrous ammonium sulfate (analytical grade).

[0009] A Fe3O4@Bi@BiOBr composite photocatalyst and its preparation method, specifically including the following steps:

[0010] 1) Under stirring conditions, dissolve 1-2 mmol of bismuth nitrate pentahydrate in 15-20 mL of deionized water to obtain solution A, and dissolve 1-2 mmol of sodium bromide in 15-20 mL of deionized water to obtain solution B;

[0011] 2) Mix solution A and solution B and stir continuously until a white suspension is obtained;

[0012] 3) The white suspension obtained in step 2) is subjected to hydrothermal treatment to obtain the BiOBr precursor;

[0013] 4) Dissolve 1.0-2.0g of polyvinylpyrrolidone in 80-120mL of deionized water to obtain solution C, and dissolve 1-2mmol of sodium borohydride in 30-50mL of deionized water to obtain solution D;

[0014] 5) Disperse the BiOBr precursor obtained in step 3) uniformly into solution C, and then add solution D dropwise under stirring. After the suspension is aged and allowed to stand at room temperature for 5-8 hours, centrifuge at 3000-10000 r / min for about 3-10 minutes. Wash the obtained solid with deionized water and anhydrous ethanol alternately 3-5 times, and dry at 70-90℃ for 8-12 hours to obtain Bi@BiOBr.

[0015] 6) Take 60-210 mg of ferric ammonium sulfate and 40-140 mg of ferrous ammonium sulfate into a three-necked flask continuously purged with nitrogen, and add 50-150 mL of deionized water to dissolve them;

[0016] 7) Take 0.4-0.6g of Bi@BiOBr obtained in step 5) and add it to a three-necked flask. Stir and disperse evenly, then heat to 70-90℃ and add 5-10ml of ammonia water with a concentration of 10%-20% to the three-necked flask;

[0017] 8) Continue heating to 90-120℃. After 30-40 minutes, stop heating and allow to cool naturally. Centrifuge the reaction solution in the three-necked flask at 3000-10000 r / min for about 3-10 minutes. Wash the obtained solid several times with deionized water and filter out the liquid. Dry at 70-90℃ for 8-12 hours to obtain the Fe3O4@Bi@BiOBr composite photocatalyst.

[0018] In step 1), the molar ratio of bismuth nitrate pentahydrate to sodium bromide is 1:1 to 2.

[0019] The stirring time in step 2) is 30-50 minutes.

[0020] The hydrothermal treatment in step 3) is as follows: the white suspension is heated to 180-220℃ at a heating rate of 3-5℃ / min, kept at this temperature for 16-24h, and then naturally cooled to room temperature. The resulting solid is centrifuged at 3000-10000r / min for 3-10min. The resulting solid is then washed alternately with deionized water and anhydrous ethanol 3-5 times and dried at a temperature of 65-95℃ for 8-12h.

[0021] In step 6), the molar ratio of ferric ammonium sulfate to ferrous ammonium sulfate is 1:0.2 to 1.6, and nitrogen must be continuously introduced to ensure an oxygen-free condition, so that Fe3O4 is generated in the reaction.

[0022] The washing and drying process in step 8) includes washing with deionized water until neutral.

[0023] An application of a Fe3O4@Bi@BiOBr composite photocatalyst for photocatalytic degradation of organic wastewater; and for improving the conductivity of optical coatings, battery electrodes, and gas sensors.

[0024] Compared with the prior art, the present invention has the following beneficial technical effects:

[0025] The composite photocatalyst prepared in this invention contains elemental bismuth, BiOBr, and Fe3O4. BiOBr is synthesized via a hydrothermal method, with elemental bismuth supported on BiOBr through in-situ reduction. Fe3O4 is generated through a chemical reaction, and BiOBr is synthesized via a hydrothermal method, with elemental bismuth supported on BiOBr through in-situ reduction. The prepared BiOBr precursor exhibits high crystallinity, indicating a larger specific surface area, thus providing more active sites and stable performance, which is beneficial for photocatalytic reactions. Furthermore, the bismuth support improves the conductivity of BiOBr, and the presence of bismuth optimizes the band structure of the composite catalyst. Moreover, in the prepared Fe3O4@Bi@BiOBr composite photocatalyst, Fe3O4 is attached to the BiOBr surface in powder form along bismuth nanowires, which facilitates the transfer of photogenerated electrons and effectively mitigates the recombination of photogenerated electron-hole pairs, resulting in high catalytic activity of the photocatalyst prepared in this invention.

[0026] This invention utilizes a hydrothermal method to prepare BiOBr nanosheets in a one-step process. These nanosheets possess a larger surface area and more active sites, thus enhancing photocatalytic performance. The invention employs a simple in-situ reduction method to reduce elemental bismuth onto the surface of the BiOBr precursor (BiOBr nanosheets), improving the structure of the BiOBr nanosheets. After being composited with Fe3O4, the electron transport rate is significantly slowed, thereby rapidly improving the performance of the composite photocatalyst.

[0027] This invention uses hydrothermal synthesis, in-situ reduction and chemical synthesis techniques to prepare the composite photocatalyst. The method is simple and easy to implement, the equipment process is simple, which is conducive to large-scale production and preparation, and solves the problem of recycling and application of powder materials. It can be widely used in the field of photocatalytic water treatment. Attached Figure Description

[0028] Figure 1 The images show the XRD patterns of Fe3O4@Bi@BiOBr prepared by the preparation methods of this invention with different Fe3O4 ratios. Detailed Implementation

[0029] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0031] A Fe3O4@Bi@BiOBr composite photocatalyst, the raw materials of which include: 1-2 mmol of bismuth nitrate pentahydrate, 1-2 mmol of sodium bromide, 1.0-2.0 g of polyvinylpyrrolidone, 1-2 mmol of sodium borohydride, 60-210 mg of ferric ammonium sulfate, and 40-140 mg of ferrous ammonium sulfate (analytical grade).

[0032] A Fe3O4@Bi@BiOBr composite photocatalyst and its preparation method, specifically including the following steps:

[0033] 1) Under stirring conditions, dissolve 1-2 mmol of bismuth nitrate pentahydrate in 15-20 mL of deionized water to obtain solution A, and dissolve 1-2 mmol of sodium bromide in 15-20 mL of deionized water to obtain solution B;

[0034] 2) Mix solution A and solution B and stir continuously until a white suspension is obtained;

[0035] 3) The white suspension obtained in step 2) is transferred to a stainless steel reactor for hydrothermal treatment to obtain the BiOBr precursor (BiOBr nanosheets);

[0036] 4) Dissolve 1.0-2.0g of polyvinylpyrrolidone in 80-120mL of deionized water to obtain solution C, and dissolve 1-2mmol of sodium borohydride in 30-50mL of deionized water to obtain solution D;

[0037] 5) The BiOBr precursor obtained in step 3) is uniformly dispersed in solution C, and then D is added dropwise under stirring. After the suspension is aged and allowed to stand for 5-8 hours, it is centrifuged at 3000-10000 r / min for about 3-10 min. The obtained solid is washed with deionized water and anhydrous ethanol alternately 3-5 times, and dried at 70-90℃ for 8-12 hours to obtain Bi@BiOBr (elemental bismuth is reduced and loaded onto bismuth oxybromide).

[0038] 6) Take 60-210 mg of ferric ammonium sulfate and 40-140 mg of ferrous ammonium sulfate into a three-necked flask continuously purged with nitrogen, and add 100-150 mL of deionized water to dissolve them;

[0039] 7) Take the Bi@BiOBr obtained in step 5) and add it to a three-necked flask. Stir and disperse it evenly. Then place the three-necked flask in an oil bath and heat it to 70-90℃. Add 5-10 ml of ammonia water with a concentration of 10%-20% to the three-necked flask.

[0040] 8) Continue heating the oil bath to 90-120℃ for 30-40 minutes, then stop heating and allow it to cool naturally. Centrifuge the reaction solution in the three-necked flask at 3000-10000 r / min for about 3-10 minutes. Wash the obtained solid several times with deionized water and filter out the liquid. Dry the solid at 70-90℃ for 8-12 hours to obtain the Fe3O4@Bi@BiOBr composite photocatalyst.

[0041] In step 1), the molar ratio of bismuth nitrate pentahydrate to sodium bromide is 1:1 to 2.

[0042] The stirring time in step 2) is 30-50 minutes.

[0043] The hydrothermal treatment in step 3) is as follows: the white suspension is heated to 180-220℃ at a heating rate of 3-5℃ / min, kept at this temperature for 16-24h, and then naturally cooled to room temperature. The resulting solid is centrifuged at 3000-10000r / min for 3-10min. The resulting solid is then washed alternately with deionized water and anhydrous ethanol 3-5 times and dried at a temperature of 65-95℃ for 8-12h.

[0044] In step 6), the molar ratio of ferric ammonium sulfate to ferrous ammonium sulfate is 1:0.2 to 1.6, and nitrogen must be continuously introduced to ensure an oxygen-free condition, so that Fe3O4 is generated in the reaction.

[0045] The washing and drying process in step 8) includes washing with deionized water until neutral.

[0046] Example 1

[0047] 1) Under stirring conditions, 1 mmol of bismuth nitrate pentahydrate was dissolved in 15 mL of deionized water to obtain solution A, and 1 mmol of sodium bromide was dissolved in 15 mL of deionized water to obtain solution B.

[0048] 2) Mix solution A and solution B and stir continuously until a white suspension is obtained;

[0049] 3) Transfer the white suspension obtained in step 2) to the reaction vessel, heat it to 180°C at a heating rate of 3°C / min, keep it at this temperature for 24 hours, and then let it cool naturally to room temperature. Centrifuge the obtained solid at 3000 r / min for 10 min, wash the obtained solid three times with deionized water and anhydrous ethanol alternately, and dry it at 80°C for 12 hours until it is dry, thus obtaining the BiOBr precursor.

[0050] 4) Dissolve 1.0 g of polyvinylpyrrolidone in 100 mL of deionized water to obtain solution C, and dissolve 1.5 mmol of 40 mmol / L sodium borohydride in 30 mL of deionized water to obtain solution D;

[0051] 5) The BiOBr precursor obtained in step 3) is uniformly dispersed in solution C, and then solution D is added dropwise under stirring. The suspension is aged and allowed to stand at room temperature for 5 hours, and then centrifuged at 3000 r / min for about 10 minutes. The obtained solid is washed three times alternately with deionized water and anhydrous ethanol, and dried at 80℃ for 8 hours to obtain Bi@BiOBr.

[0052] 6) Take 69.4 mg of ferric ammonium sulfate and 45.2 mg of ferrous ammonium sulfate into a container continuously purged with nitrogen, and add 50 mL of deionized water to dissolve them;

[0053] 7) Take 0.5g of Bi@BiOBr obtained in step 5) and add it to the container in step 6) and stir to disperse it evenly. Then heat it to 80℃ and add 5ml of 10% ammonia water to the container.

[0054] 8) Continue heating to 100℃. After 30 minutes, stop heating and allow to cool naturally. Centrifuge the reaction liquid in the container at 3000 r / min for about 10 minutes. Wash the obtained solid several times with deionized water and filter out the liquid. Dry at 80℃ for 12 hours to obtain the Fe3O4@Bi@BiOBr composite photocatalyst.

[0055] It is denoted as Fe3O4@Bi@BiOBr-1. The photocatalytic performance of the catalyst Fe3O4@Bi@BiOBr-1 in this example was studied using norfloxacin as a degradation substrate.

[0056] Example 2

[0057] 1) Under stirring conditions, 2 mmol of bismuth nitrate pentahydrate was dissolved in 20 mL of deionized water to obtain solution A, and 2 mmol of sodium bromide was dissolved in 20 mL of deionized water to obtain solution B.

[0058] 2) Mix solution A and solution B and stir continuously until a white suspension is obtained;

[0059] 3) Transfer the white suspension obtained in step 2) to the reaction vessel, heat it to 200°C at a heating rate of 5°C / min, keep it at this temperature for 22 hours, and then let it cool naturally to room temperature. Centrifuge the obtained solid at 3000 r / min for 18 min, wash the obtained solid with deionized water and anhydrous ethanol alternately 4 times, and dry it at 70°C for 10 hours until it is dry, thus obtaining the BiOBr precursor.

[0060] 4) Dissolve 1.2g of polyvinylpyrrolidone in 50mL of deionized water to obtain solution C, and dissolve 2mmol of 40mmol / L sodium borohydride in 50mL of deionized water to obtain solution D;

[0061] 5) The BiOBr precursor obtained in step 3) is uniformly dispersed in solution C, and then solution D is added dropwise under stirring. The suspension is aged and allowed to stand at room temperature for 8 hours, and then centrifuged at 8000 r / min for about 8 minutes. The obtained solid is washed 5 times alternately with deionized water and anhydrous ethanol, and dried at 90℃ for 8 hours to obtain Bi@BiOBr.

[0062] 6) Take 104.1 mg of ferric ammonium sulfate and 67.8 mg of ferrous ammonium sulfate into a container continuously purged with nitrogen, and add 100 mL of deionized water to dissolve them;

[0063] 7) Take 0.5g of Bi@BiOBr obtained in step 5) and add it to the container in step 6) and stir to disperse it evenly. Then heat it to 70℃ and add 8ml of 10% ammonia water to the container.

[0064] 8) Continue heating to 100℃. After 40 minutes, stop heating and allow to cool naturally. Centrifuge the reaction solution in the container at 5000 r / min for about 6 minutes. Wash the obtained solid several times with deionized water and filter out the liquid. Dry at 90℃ for 10 hours to obtain the Fe3O4@Bi@BiOBr composite photocatalyst.

[0065] Example 3

[0066] 1) Under stirring conditions, 1.5 mmol of bismuth nitrate pentahydrate was dissolved in 20 mL of deionized water to obtain solution A, and 1.5 mmol of sodium bromide was dissolved in 20 mL of deionized water to obtain solution B;

[0067] 2) Mix solution A and solution B and stir continuously until a white suspension is obtained;

[0068] 3) Transfer the white suspension obtained in step 2) to the reaction vessel, heat it to 220°C at a heating rate of 5°C / min, keep it at this temperature for 18 hours, and then let it cool naturally to room temperature. Centrifuge the obtained solid at 10000 r / min for 3 minutes. Wash the obtained solid with deionized water and anhydrous ethanol alternately 4 times and dry it at 90°C for 9 hours until it is dry, thus obtaining the BiOBr precursor.

[0069] 4) Dissolve 1.1g of polyvinylpyrrolidone in 110mL of deionized water to obtain solution C, and dissolve 1.6mmol of 40mmol / L sodium borohydride in 40mL of deionized water to obtain solution D;

[0070] 5) The BiOBr precursor obtained in step 3) is uniformly dispersed in solution C, and then solution D is added dropwise under stirring. The suspension is aged and allowed to stand at room temperature for 8 hours, and then centrifuged at 3000 r / min for about 6 minutes. The obtained solid is washed 5 times alternately with deionized water and anhydrous ethanol, and dried at 70℃ for 10 hours to obtain Bi@BiOBr.

[0071] 6) Take 138.8 mg of ferric ammonium sulfate and 90.4 mg of ferrous ammonium sulfate into a container continuously purged with nitrogen, and add 150 mL of deionized water to dissolve them;

[0072] 7) Take 0.5g of Bi@BiOBr obtained in step 5) and add it to the container in step 6) and stir to disperse it evenly. Then heat it to 70℃ and add 8ml of 10% ammonia water to the container.

[0073] 8) Continue heating to 90℃. After 35 minutes, stop heating and allow to cool naturally. Centrifuge the reaction liquid in the container at 3000 r / min for about 5 minutes. Wash the obtained solid several times with deionized water and filter out the liquid. Dry at 70℃ for 12 hours to obtain the Fe3O4@Bi@BiOBr composite photocatalyst.

[0074] Example 4

[0075] 1) Under stirring conditions, 1 mmol of bismuth nitrate pentahydrate was dissolved in 15 mL of deionized water to obtain solution A, and 1 mmol of sodium bromide was dissolved in 15 mL of deionized water to obtain solution B.

[0076] 2) Mix solution A and solution B and stir continuously until a white suspension is obtained;

[0077] 3) Transfer the white suspension obtained in step 2) to the reaction vessel, heat it to 180°C at a heating rate of 3°C / min, keep it at this temperature for 24 hours, and then let it cool naturally to room temperature. Centrifuge the obtained solid at 3000 r / min for 10 min, wash the obtained solid three times with deionized water and anhydrous ethanol alternately, and dry it at 80°C for 12 hours until it is dry, thus obtaining the BiOBr precursor.

[0078] 4) Dissolve 1.0 g of polyvinylpyrrolidone in 100 mL of deionized water to obtain solution C, and dissolve 1.5 mmol of 40 mmol / L sodium borohydride in 30 mL of deionized water to obtain solution D;

[0079] 5) The BiOBr precursor obtained in step 3) is uniformly dispersed in solution C, and then solution D is added dropwise under stirring. The suspension is aged and allowed to stand at room temperature for 5 hours, and then centrifuged at 3000 r / min for about 10 minutes. The obtained solid is washed three times alternately with deionized water and anhydrous ethanol, and dried at 80℃ for 8 hours to obtain Bi@BiOBr.

[0080] 6) Take 173.5 mg of ferric ammonium sulfate and 113 mg of ferrous ammonium sulfate into a container continuously purged with nitrogen, and add 80 mL of deionized water to dissolve them;

[0081] 7) Take 0.5g of Bi@BiOBr obtained in step 5) and add it to the container in step 6) and stir to disperse it evenly. Then heat it to 80℃ and add 6ml of 10% ammonia water to the container.

[0082] 8) Continue heating to 100℃. After 35 minutes, stop heating and allow to cool naturally. Centrifuge the reaction liquid in the container at 3000 r / min for about 10 minutes. Wash the obtained solid several times with deionized water and filter out the liquid. Dry at 90℃ for 8 hours to obtain the Fe3O4@Bi@BiOBr composite photocatalyst.

[0083] Example 5

[0084] 1) Under stirring conditions, 2 mmol of bismuth nitrate pentahydrate was dissolved in 20 mL of deionized water to obtain solution A, and 2 mmol of sodium bromide was dissolved in 20 mL of deionized water to obtain solution B.

[0085] 2) Mix solution A and solution B and stir continuously until a white suspension is obtained;

[0086] 3) Transfer the white suspension obtained in step 2) to the reaction vessel, heat it to 200°C at a heating rate of 5°C / min, keep it at this temperature for 22 hours, and then let it cool naturally to room temperature. Centrifuge the obtained solid at 3000 r / min for 18 min, wash the obtained solid with deionized water and anhydrous ethanol alternately 4 times, and dry it at 70°C for 10 hours until it is dry, thus obtaining the BiOBr precursor.

[0087] 4) Dissolve 1.2g of polyvinylpyrrolidone in 120mL of deionized water to obtain solution C, and dissolve 2mmol of 40mmol / L sodium borohydride in 50mL of deionized water to obtain solution D.

[0088] 5) The BiOBr precursor obtained in step 3) is uniformly dispersed in solution C, and then solution D is added dropwise under stirring. The suspension is aged and allowed to stand at room temperature for 8 hours, and then centrifuged at 8000 r / min for about 8 minutes. The obtained solid is washed 5 times alternately with deionized water and anhydrous ethanol, and dried at 90℃ for 8 hours to obtain Bi@BiOBr.

[0089] 6) Take 208.2 mg of ferric ammonium sulfate and 135.6 mg of ferrous ammonium sulfate into a container continuously purged with nitrogen, and add 120 mL of deionized water to dissolve them;

[0090] 7) Take 0.5g of Bi@BiOBr obtained in step 5) and add it to the container in step 6) and stir to disperse it evenly. Then heat it to 80℃ and add 5ml of 10% ammonia water to the container.

[0091] 8) Continue heating to 100℃. After 30 minutes, stop heating and allow to cool naturally. Centrifuge the reaction solution in the container at 3000 r / min for about 5 minutes. Wash the obtained solid several times with deionized water and filter out the liquid. Dry at 90℃ for 12 hours to obtain the Fe3O4@Bi@BiOBr composite photocatalyst.

[0092] See Figure 1 The XRD patterns of the prepared Fe3O4@Bi@BiOBr series samples showed that the samples had high crystallinity and no impurity peaks, indicating that the Fe3O4@Bi@BiOBr series samples were successfully prepared.

[0093] Referring to Table 1, a 500W xenon lamp was used as the visible light simulation source. Continuous circulating cooling water was used to reduce the heat generated by the xenon lamp, maintaining it at room temperature and improving the accuracy of the experiment. Taking the photocatalytic degradation of organic wastewater as an example, 50mg of catalyst was weighed and added to 50mL of a 20mg / L norfloxacin solution. The solution was stirred in the dark for 30min to ensure uniform dispersion and full adsorption of the catalyst. Then, the light source was turned on, and the circulating cooling water system was activated. The concentration change of norfloxacin in the solution was measured using a UV-Vis spectrometer. The norfloxacin degradation rate was calculated using the formula: (c0-c t ) / c0×100%.

[0094] Table 1 Catalytic degradation rate of norfloxacin by Fe3O4@Bi@BiOBr

[0095]

Claims

1. A method for preparing a Fe3O4@Bi@BiOBr composite photocatalyst, characterized in that, Includes the following steps: 1) Under stirring conditions, dissolve 1-2 mmol of bismuth nitrate pentahydrate in 15-20 mL of deionized water to obtain solution A, and dissolve 1-2 mmol of sodium bromide in 15-20 mL of deionized water to obtain solution B; 2) Mix solution A and solution B and stir continuously until a white suspension is obtained; 3) The white suspension obtained in step 2) is subjected to hydrothermal treatment to obtain the BiOBr precursor; 4) Dissolve 1.0-2.0g of polyvinylpyrrolidone in 80-120mL of deionized water to obtain solution C, and dissolve 1-2mmol of sodium borohydride in 30-50mL of deionized water to obtain solution D; 5) The BiOBr precursor obtained in step 3) is uniformly dispersed in solution C, and then solution D is added dropwise under stirring. The suspension is aged at room temperature for 5-8 hours and then centrifuged at 3000-10000 r / min for 3-10 min. The obtained solid is washed alternately with deionized water and anhydrous ethanol 3-5 times and dried at 70-90℃ for 8-12 hours to obtain Bi@BiOBr. 6) Take 60-210 mg of ferric ammonium sulfate and 40-140 mg of ferrous ammonium sulfate into a container continuously purged with nitrogen, and add 50-150 mL of deionized water to dissolve them; 7) Take 0.4-0.6g of Bi@BiOBr obtained in step 5) and add it to the container in step 6). Stir and disperse evenly, then heat to 70-90℃ and add 5-10ml of ammonia water with a concentration of 10%-20% to the container. 8) Continue heating to 90-120℃. After 30-40 minutes, stop heating and allow to cool naturally. Centrifuge the reaction solution in the container at 3000-10000 r / min for 3-10 minutes. Wash the obtained solid several times with deionized water and filter out the liquid. Dry at 70-90℃ for 8-12 hours to obtain the Fe3O4@Bi@BiOBr composite photocatalyst.

2. The preparation method of the Fe3O4@Bi@BiOBr composite photocatalyst according to claim 1, characterized in that, In step 1), the molar ratio of bismuth nitrate pentahydrate to sodium bromide is 1:1~2.

3. The preparation method of the Fe3O4@Bi@BiOBr composite photocatalyst according to claim 1, characterized in that, The stirring time in step 2) is 30-50 minutes.

4. The preparation method of the Fe3O4@Bi@BiOBr composite photocatalyst according to claim 1, characterized in that, The hydrothermal treatment in step 3) is as follows: the white suspension is heated to 180-220℃ at a heating rate of 3-5℃ / min, kept at this temperature for 16-24h, and then naturally cooled to room temperature. The resulting solid is centrifuged at 3000-10000r / min for 3-10min. The resulting solid is then washed alternately with deionized water and anhydrous ethanol 3-5 times and dried at a temperature of 65-95℃ for 8-12h.

5. The preparation method of the Fe3O4@Bi@BiOBr composite photocatalyst according to claim 1, characterized in that, In step 6), the molar ratio of ferric ammonium sulfate to ferrous ammonium sulfate is 1:0.2~1.6, and nitrogen must be continuously introduced to ensure an oxygen-free condition, so that Fe3O4 is generated in the reaction.

6. The preparation method of the Fe3O4@Bi@BiOBr composite photocatalyst according to claim 1, characterized in that, The washing and drying process in step 8) includes washing with deionized water until neutral.

7. The preparation method of the Fe3O4@Bi@BiOBr composite photocatalyst according to claim 1, characterized in that, The specific method is as follows: 1) Under stirring conditions, 1 mmol of bismuth nitrate pentahydrate was dissolved in 15 mL of deionized water to obtain solution A, and 1 mmol of sodium bromide was dissolved in 15 mL of deionized water to obtain solution B. 2) Mix solution A and solution B and stir continuously until a white suspension is obtained; 3) Transfer the white suspension obtained in step 2) to the reaction vessel, heat it to 180°C at a heating rate of 3°C / min, keep it at this temperature for 24 hours, and then let it cool naturally to room temperature. Centrifuge the obtained solid at 3000 r / min for 10 min, wash the obtained solid three times alternately with deionized water and anhydrous ethanol, and dry it at 80°C for 12 hours until it is dry, thus obtaining the BiOBr precursor. 4) Dissolve 1.0 g of polyvinylpyrrolidone in 100 mL of deionized water to obtain solution C, and dissolve 1.5 mmol of 40 mmol / L sodium borohydride in 30 mL of deionized water to obtain solution D; 5) The BiOBr precursor obtained in step 3) is uniformly dispersed in solution C, and then solution D is added dropwise under stirring. The suspension is aged and allowed to stand at room temperature for 5 hours, and then centrifuged at 3000 r / min for 10 minutes. The obtained solid is washed three times alternately with deionized water and anhydrous ethanol, and dried at 80℃ for 8 hours to obtain Bi@BiOBr. 6) Take 69.4 mg of ferric ammonium sulfate and 45.2 mg of ferrous ammonium sulfate into a container continuously purged with nitrogen, and add 50 mL of deionized water to dissolve them; 7) Take 0.5g of Bi@BiOBr obtained in step 5) and add it to the container in step 6) and stir to disperse it evenly. Then heat it to 80℃ and add 5ml of 10% ammonia water to the container. 8) Continue heating to 100℃. After 30 minutes, stop heating and allow to cool naturally. Centrifuge the reaction solution in the container at 3000 r / min for 10 minutes. Wash the obtained solid several times with deionized water and filter out the liquid. Dry at 80℃ for 12 hours to obtain the Fe3O4@Bi@BiOBr composite photocatalyst.

8. The application of the Fe3O4@Bi@BiOBr composite photocatalyst prepared by the preparation method according to any one of claims 1 to 7, characterized in that, Applications include photocatalytic degradation of organic wastewater; and improving the conductivity of optical coatings, battery electrodes, and gas sensors.

Images