Doped modified bismuth ferrite-based heterojunction and application thereof in photocatalytic degradation of organic wastewater

Abstract

The invention discloses a doped modified bismuth ferrite-based heterojunction and application thereof in photocatalytic degradation of organic wastewater. The doped modified bismuth ferrite-based heterojunction is prepared by the following steps: S1, preparing carboxylated graphene oxide; s2, preparing acousto-optic dual-response carbon dots; and S3, preparing the doped modified bismuth ferrite-based heterojunction by a hydrothermal method. According to the preparation method disclosed by the invention, the bismuth ferrite-based heterojunction is compounded and doped by adopting the rare earth gadolinium, the carboxylated graphene oxide and the acousto-optic double-response carbon dots, so that the photocatalytic activity of the bismuth ferrite-based heterojunction can be remarkably improved; due to the introduction of the acousto-optic dual-response carbon dots, the doped and modified bismuth ferrite-based heterojunction can be endowed with catalytic activity under the ultrasonic action, so that when the doped and modified bismuth ferrite-based heterojunction is used for organic wastewater treatment under the simultaneous action of visible light and ultrasonic, higher wastewater degradation efficiency can be obtained.

Description

Technical Field

[0001] The invention relates to the field of bismuth-based heterojunction materials and water treatment, and in particular to a doped modified bismuth ferrite-based heterojunction and application thereof in photocatalytic degradation of organic wastewater. Background Art

[0002] At present, the problem of water environmental pollution has received increasing attention, and the degradation and treatment of organic matter in water bodies is related to human health and the sustainable development of society.

[0003] Among many pollutant treatment technologies, semiconductor photocatalyst degradation of organic pollutants has attracted widespread attention due to its advantages such as no secondary pollution and simple operation. The semiconductor photocatalytic reaction mainly includes the following process: when the semiconductor absorbs energy greater than or equal to its bandgap width (hν), the electrons in its valence band will absorb energy and jump across the bandgap to the conduction band, and holes will be generated in the valence band at the same time. When the generated photogenerated electrons and holes are transferred to the semiconductor surface, they react with oxygen, water, etc. in the environment to generate active substances such as superoxide free radicals and hydroxyl free radicals; these active substances with strong oxidizing properties react with pollutant macromolecules, thereby playing a role in degrading pollutants (Yang Xue1, Huang Rui1, Rao Zeping2, Wang Zhenhua2,3, Cai Wei2,3*. Research progress of bismuth ferrite-based heterojunction photocatalysts for degradation of organic pollutants [J]. New Chemical Materials, 2024(002):052.).

[0004] As a semiconductor photocatalytic material, bismuth ferrite is often used in wastewater treatment, water purification and water pollution remediation, and can effectively convert organic pollutants into harmless substances. In terms of photocatalysis, bismuth ferrite has good photocatalytic activity in the visible light region, which enables it to effectively use visible light for photocatalytic reactions.

[0005] However, the catalytic efficiency of the traditional bismuth ferrite-based heterojunction is not high. For example, in the literature "Ding Liuliu, Jiang Guojian, Li Wenjun, et al. Preparation of bismuth ferrite by hydrothermal method and study of its photocatalytic performance [J]. Journal of Synthetic Crystals, 2013, 42(8): 1607-1610, 1615.", the degradation rate of methyl orange by the bismuth ferrite catalyst prepared therein is only 72.847%. Therefore, it is necessary to improve the existing technology to further improve the organic matter degradation efficiency of the bismuth ferrite-based heterojunction catalyst. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a doped modified bismuth ferrite-based heterojunction in view of the deficiencies in the above-mentioned prior art.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is: in the first aspect of the present invention, a doped modified bismuth ferrite-based heterojunction and its application in photocatalytic degradation of organic wastewater are provided, which is prepared by the following steps: S1. preparing carboxylated graphene oxide; S2. Preparation of acousto-optic dual-responsive carbon dots: Benzoic acid, 4-aminobenzoic acid, tetraphenylporphyrin, silver nitrate and copper nitrate are added to an ethanol aqueous solution, and the resulting mixture is subjected to a hydrothermal reaction to synthesize the acoustic-optical dual-responsive carbon dots; S3. Preparation of doped modified bismuth ferrite-based heterojunction by hydrothermal method: S3-1, dispersing the carboxylated graphene oxide prepared in step S1 in deionized water to prepare a dispersion 1; S3-2, dispersing the acousto-optic dual-responsive carbon dots prepared in step S2 in deionized water to prepare dispersion 2; S3-3, adding iron nitrate, bismuth nitrate and gadolinium nitrate to a nitric acid aqueous solution, and then sequentially adding dispersion 1 and dispersion 2, and then adjusting the pH value of the mixed system to obtain a precursor solution; S3-4, subjecting the precursor solution to a hydrothermal reaction to prepare the doped modified bismuth ferrite-based heterojunction.

[0008] Preferably, step S1 specifically comprises: Take graphene oxide and add it to deionized water, stir it, add sodium hydroxide and sodium chloroacetate while stirring, then treat it under ultrasonication for 1.5-6h, adjust the pH to neutral with hydrochloric acid, then wash it with water repeatedly by centrifugation until it is neutral, and dry it to obtain carboxylated graphene oxide.

[0009] Preferably, step S1 specifically comprises: Take 0.5-2g of graphene oxide and add it to 500-1000mL of deionized water, stir at 1000-8000rpm for 5-30min, add 7.5-30g of sodium hydroxide and 6-24g of sodium chloroacetate while stirring, then treat under ultrasonic action for 1.5-6h, adjust the pH to neutral with hydrochloric acid, then repeatedly centrifuge and wash with water to neutral, and dry at 60-90°C for 6-24h to obtain carboxylated graphene oxide.

[0010] Preferably, step S2 specifically comprises: Benzoic acid, 4-aminobenzoic acid, tetraphenylporphyrin, silver nitrate and copper nitrate were added to a hot ethanol aqueous solution and dispersed by ultrasonication. The obtained mixture was transferred to a reactor and reacted under heating. After the reaction, the mixture was cooled to room temperature and filtered with a filter membrane. The filtrate was dialyzed in deionized water with a dialysis bag. The dialysate in the dialysis bag was freeze-dried to obtain the acousto-optic dual-responsive carbon dots.

[0011] Preferably, step S2 specifically comprises: 366-1464 mg of benzoic acid, 283-576 mg of citric acid, 205-822 mg of 4-aminobenzoic acid, 153-615 mg of tetraphenylporphyrin, 127-510 mg of silver nitrate, and 141-564 mg of copper nitrate were added to an ethanol aqueous solution composed of 100-400 mL of deionized water and 50-200 mL of ethanol at 50-70°C, and ultrasonically dispersed for 15-60 min. The resulting mixture was transferred to a polytetrafluoroethylene-lined reactor, reacted at 170-205°C for 6-18 h, cooled to room temperature, filtered with a 0.22 μm filter membrane, and the filtrate was dialyzed in deionized water for 6-27 h using a dialysis bag with a molecular weight cutoff of 1000-2000 Da. The dialysate in the dialysis bag was freeze-dried to obtain acoustic-optical dual-responsive carbon dots.

[0012] Preferably, step S3 specifically comprises: S3-1, adding the carboxylated graphene oxide prepared in step S1 into deionized water, and performing ultrasonic dispersion to obtain dispersion 1; S3-2, adding the acousto-optic dual-responsive carbon dots prepared in step S2 into deionized water, and performing ultrasonic dispersion to obtain dispersion 2; S3-3, adding iron nitrate, bismuth nitrate and gadolinium nitrate hexahydrate to a nitric acid aqueous solution, stirring for 2-15 minutes, adding dispersion 1 to the obtained mixed solution under stirring, maintaining stirring for 2-15 minutes, and then continuing to add dispersion 2 under continuous stirring, ultrasonically dispersing, and dropping ammonia water into the obtained mixed solution until the pH value of the mixed system reaches 7.5-8.5 to obtain a precursor solution; S3-4. The obtained precursor solution is transferred to a reactor, and the reaction is carried out at 190-210° C. for 6-16 hours. After the reaction is completed, the mixture is cooled to room temperature, filtered, and the solid product is washed with deionized water and ethanol in sequence, and vacuum dried to obtain a doped modified bismuth ferrite-based heterojunction.

[0013] Preferably, step S3 specifically comprises: S3-1, taking 0.9-3.6 g of the carboxylated graphene oxide prepared in step S1, adding it to 50-200 mL of deionized water, and ultrasonically dispersing it for 15-60 min to obtain dispersion 1; S3-2, taking 0.35-1.5 g of the acousto-optic dual-responsive carbon dots prepared in step S2, adding them into 50-200 mL of deionized water, and ultrasonically dispersing them for 15-60 min to obtain dispersion 2; S3-3, 1.21-4.84 g of ferric nitrate, 1.975-7.9 g of bismuth nitrate, and 0.2255-0.902 g of gadolinium nitrate hexahydrate are added to 150-600 mL of a nitric acid aqueous solution having a mass concentration of 10-20%, and stirred for 2-15 min. Dispersion liquid 1 is added to the obtained mixed solution under stirring, and stirring is maintained for 2-15 min. Then, dispersion liquid 2 is added under continuous stirring, and ultrasonic dispersion is performed for 30-90 min. Ammonia water having a concentration of 20-25 wt % is added dropwise to the obtained mixed solution until the pH value of the mixed system reaches 7.5-8.5 to obtain a precursor solution; S3-4. Transfer the obtained precursor solution to a reactor, react at 190-210°C for 6-16 hours, cool to room temperature after the reaction, filter, wash the solid product with deionized water and ethanol in turn, and vacuum dry at 70-90°C for 4-12 hours to obtain a doped modified bismuth ferrite-based heterojunction.

[0014] The second aspect of the present invention provides an application of the doped modified bismuth ferrite-based heterojunction as described above in photocatalytic degradation of organic wastewater.

[0015] Preferably, the application method is: putting the doped modified bismuth ferrite-based heterojunction into organic wastewater, and then performing degradation treatment of the organic wastewater under the combined action of visible light irradiation and ultrasound.

[0016] Preferably, the application method is: putting the doped modified bismuth ferrite-based heterojunction into organic wastewater, controlling the concentration of the doped modified bismuth ferrite-based heterojunction in the organic wastewater to be 0.2-5 g / L, stirring for 5-30 minutes, and then treating for 10-90 minutes under visible light irradiation and ultrasound assistance; Among them, the ultrasonic power is 50-500W and the ultrasonic frequency is 30-100kHz.

[0017] The beneficial effects of the present invention are: The present invention provides a doped modified bismuth ferrite-based heterojunction and an application thereof in photocatalytic degradation of organic wastewater. The present invention adopts rare earth gadolinium, carboxylated graphene oxide and acousto-optic dual-responsive carbon dots to perform composite doping on the bismuth ferrite-based heterojunction, thereby significantly improving the photocatalytic activity of the bismuth ferrite-based heterojunction. The introduction of the acousto-optic dual-responsive carbon dots can endow the doped modified bismuth ferrite-based heterojunction with catalytic activity under ultrasound, so that when the doped modified bismuth ferrite-based heterojunction is used for organic wastewater treatment under the simultaneous action of visible light and ultrasound, a higher wastewater degradation efficiency can be obtained.

[0018] In the doped modified bismuth ferrite-based heterojunction provided by the present invention, by constructing a multi-component composite structure system GO@BFO@AgCu-CDs of "carboxylated graphene oxide + gadolinium-doped bismuth ferrite + acoustic-optic dual-responsive carbon dots", the ability of the bismuth ferrite-based heterojunction to catalyze the degradation of organic matter can be greatly improved through the synergistic effect between the various components, and the acoustic-optic dual catalytic activity can be given to it, which will be very beneficial for improving its treatment effect on organic wastewater. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is the degradation performance test result; Figure 2 is the infrared spectrum of the acousto-optic dual-response carbon dots synthesized in Example 1; Figure 3 This is the result of the singlet oxygen production ability test. DETAILED DESCRIPTION

[0020] The present invention is further described in detail below in conjunction with embodiments so that those skilled in the art can implement the invention with reference to the description.

[0021] It should be understood that the terms such as “having”, “including” and “comprising” used herein do not exclude the existence or addition of one or more other elements or combinations thereof.

[0022] The test methods used in the following examples are conventional methods unless otherwise specified. The materials and reagents used in the following examples are all commercially available unless otherwise specified. In the following examples, if no specific conditions are specified, the experiments were carried out under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used, if the manufacturer is not specified, are all conventional products that can be purchased commercially.

[0023] The present invention provides a doped modified bismuth ferrite-based heterojunction, which is prepared by the following steps: S1. Preparation of carboxylated graphene oxide: Take 0.5-2g of graphene oxide and add it to 500-1000mL of deionized water, stir at 1000-8000rpm for 5-30min, add 7.5-30g of sodium hydroxide and 6-24g of sodium chloroacetate while stirring, then treat under ultrasonic action for 1.5-6h, adjust the pH to neutral with hydrochloric acid, then repeatedly centrifuge and wash with water to neutral, and dry at 60-90°C for 6-24h to obtain carboxylated graphene oxide.

[0024] S2. Preparation of acousto-optic dual-responsive carbon dots: 366-1464 mg of benzoic acid, 283-576 mg of citric acid, 205-822 mg of 4-aminobenzoic acid, 153-615 mg of tetraphenylporphyrin, 127-510 mg of silver nitrate, and 141-564 mg of copper nitrate were added to an ethanol aqueous solution composed of 100-400 mL of deionized water and 50-200 mL of ethanol at 50-70°C, and ultrasonically dispersed for 15-60 min. The resulting mixture was transferred to a polytetrafluoroethylene-lined reactor, reacted at 170-205°C for 6-18 h, cooled to room temperature, filtered with a 0.22 μm filter membrane, and the filtrate was dialyzed in deionized water for 6-27 h using a dialysis bag with a molecular weight cutoff of 1000-2000 Da. The dialysate in the dialysis bag was freeze-dried to obtain acoustic-optical dual-responsive carbon dots.

[0025] S3. Preparation of doped modified bismuth ferrite-based heterojunction by hydrothermal method: S3-1, taking 0.9-3.6 g of the carboxylated graphene oxide prepared in step S1, adding it to 50-200 mL of deionized water, and ultrasonically dispersing it for 15-60 min to obtain dispersion 1; S3-2, taking 0.35-1.5 g of the acousto-optic dual-responsive carbon dots prepared in step S2, adding them into 50-200 mL of deionized water, and ultrasonically dispersing them for 15-60 min to obtain dispersion 2; S3-3, 1.21-4.84 g of ferric nitrate, 1.975-7.9 g of bismuth nitrate, and 0.2255-0.902 g of gadolinium nitrate hexahydrate are added to 150-600 mL of a nitric acid aqueous solution having a mass concentration of 10-20%, and stirred for 2-15 min. Dispersion liquid 1 is added to the obtained mixed solution under stirring, and stirring is maintained for 2-15 min. Then, dispersion liquid 2 is added under continuous stirring, and ultrasonic dispersion is performed for 30-90 min. Ammonia water having a concentration of 20-25 wt % is added dropwise to the obtained mixed solution until the pH value of the mixed system reaches 7.5-8.5 to obtain a precursor solution; S3-4. Transfer the obtained precursor solution to a reactor, react at 190-210°C for 6-16 hours, cool to room temperature after the reaction, filter, wash the solid product with deionized water and ethanol in turn, and vacuum dry at 70-90°C for 4-12 hours to obtain a doped modified bismuth ferrite-based heterojunction.

[0026] The present invention also provides an application of the above-mentioned doped modified bismuth ferrite-based heterojunction in photocatalytic degradation of organic wastewater.

[0027] In a preferred embodiment, the application method is: putting the doped modified bismuth ferrite-based heterojunction into organic wastewater, and then degrading the organic wastewater under the combined action of visible light irradiation and ultrasound.

[0028] In a more preferred embodiment, the application method is: putting the doped modified bismuth ferrite-based heterojunction into organic wastewater, controlling the concentration of the doped modified bismuth ferrite-based heterojunction in the organic wastewater to be 0.2-5 g / L, stirring for 5-30 min, and then treating for 10-90 min under visible light irradiation and ultrasound assistance; Among them, the ultrasonic power is 50-500W and the ultrasonic frequency is 30-100kHz.

[0029] The present invention uses rare earth gadolinium, carboxylated graphene oxide and acousto-optic dual-responsive carbon dots to compound-dope the bismuth ferrite-based heterojunction, which can significantly improve the photocatalytic activity of the bismuth ferrite-based heterojunction, and the introduction of the acousto-optic dual-responsive carbon dots can give the doped modified bismuth ferrite-based heterojunction catalytic activity under ultrasound, so that when the doped modified bismuth ferrite-based heterojunction is used for organic wastewater treatment under the simultaneous action of visible light and ultrasound, a higher wastewater degradation efficiency can be obtained than that of the traditional bismuth ferrite-based heterojunction catalyst. The main mechanism of the present invention is described below.

[0030] The present invention firstly performs carboxylation treatment on graphene oxide, and introduces abundant oxygen-containing functional groups such as carboxyl groups on its surface to improve its dispersibility and facilitate modification treatment. At the same time, it can be beneficial to generate more active oxygen (such as hydroxyl free radicals • OH) and singlet oxygen in the system under the stimulation of visible light and ultrasound by virtue of the effect of carbon dots. 1 O2); Then, 4-aminobenzoic acid, citric acid, benzoic acid with oxidation properties, and tetraphenylporphyrin with acoustic sensitivity were used as carbon sources, and silver nitrate and copper nitrate were used as doping components to prepare a Ag-Cu co-doped carbon dot with acoustic-optical dual response characteristics. The surface of the carbon dot is rich in functional groups such as carboxyl, hydroxyl, and amino groups, and the carbon dot can show the degradation effect on organic matter by generating active oxygen under visible light and ultrasonic excitation. After being doped into a bismuth ferrite-based heterojunction system, the organic matter degradation ability of the system can be greatly improved. Finally, through a pot of hot water reaction, graphene oxide, acoustic-optic dual-responsive carbon dots, and rare earth gadolinium were co-doped into the bismuth ferrite-based heterojunction system to obtain the final doped-modified bismuth ferrite-based heterojunction; in the reaction process, iron nitrate, bismuth nitrate, and gadolinium nitrate hexahydrate were first mixed with the dispersion of carboxylated graphene oxide, and the iron ions, bismuth ions, and gadolinium ions were combined with the carboxyl and hydroxyl functional groups on the surface of carboxylated graphene oxide through coordination and electrostatic adsorption energy. After the dispersion of acoustic-optic dual-responsive carbon dots was added, the carbon dots The carboxyl, hydroxyl, amino and other functional groups on the surface can also coordinate and / or electrostatically adsorb with the iron ions, bismuth ions, gadolinium ions, etc. adsorbed on the carboxylated graphene oxide, thereby connecting to form a structural system of "carboxylated graphene oxide-iron, bismuth ions, gadolinium ions-acoustic-optical dual-responsive carbon dots". Finally, through a hydrothermal reaction, a strong chemical bond is formed to obtain a bismuth ferrite-based heterojunction of a composite doped carboxylated graphene oxide, acoustic-optical dual-responsive carbon dots and rare earth gadolinium: GO@BFO@AgCu-CDs.

[0031] In the GO@BFO@AgCu-CDs system: (1) Acousto-optic dual-response carbon dots AgCu-CDs can generate reactive oxygen species (ROS) under the action of visible light. On the other hand, they also inherit the sonosensitive properties of tetraphenylporphyrin, which enables them to generate reactive oxygen species under ultrasound, showing excellent ability to oxidize and degrade organic matter. The doping of Cu and Ag can increase the electron cloud density and enhance the acousto-optic dual-response activity of carbon dots. On the other hand, the CuO formed by the doped Cu ions in the system can form a P-N heterojunction with bismuth ferrite (BFO), which can effectively promote the separation and transfer of photogenerated electron-hole pairs, thereby improving the catalytic activity (Niu F, Chen D, Qin LS, et al. Facile Synthesis of Highly Efficient PGN Heterojunction CuO / BiFeO3 Composite Photocatalysts with Enhanced Visible GLight Photocatalytic Activity[J]. ChemCatChem, 2015, 7(20): 3279G3289. ); and the doped Ag can help to further improve the photocatalytic activity by enhancing the conversion between Fe3+ and Fe2+.

[0032] (2) Doped Gd can reduce the recombination rate of electrons and holes, and can also act as a capture center for holes or electrons, which can not only effectively improve the charge transfer rate, but also significantly enhance the separation efficiency of photogenerated carriers, thereby greatly improving the photocatalytic activity of the system. Moreover, the function of Gd in reducing the recombination rate of electrons and holes can also act on the acousto-optic dual-response carbon dots, and at the same time can enhance the catalytic activity of the carbon dots, ultimately playing a superimposed effect on the improvement of the catalytic activity of the system.

[0033] (3) Carboxylated graphene oxide provides a large number of oxygen-containing functional groups such as carboxyl, which is conducive to the generation of more active oxygen. At the same time, it can form a network structure in the structural system to collect and transfer electrons generated by the BFO valence band, which will reduce the recombination rate of photogenerated electron holes and allow more remaining holes to participate in the oxidation reaction, thereby improving the catalytic degradation activity (Liu, Y., Zuo, RZ and Qi, SS (2013) Controllable Preparation of BiFeO3 Carbon Core / Shell Nanofibers with Enhanced Visible Photocatalytic Activity. Journal of Molecular Catalysis A: Chemical, 376, 1-6.). In addition, the introduction of carboxylated graphene oxide can also enhance its physical adsorption by increasing the specific surface area of ​​the system, which can also play a positive role in its ability to degrade organic matter.

[0034] In summary, in the doped modified bismuth ferrite-based heterojunction provided by the present invention, by constructing a multi-component composite structure system GO@BFO@AgCu-CDs of "carboxylated graphene oxide + gadolinium-doped bismuth ferrite + acoustic-optical dual-responsive carbon dots", the ability of the bismuth ferrite-based heterojunction to catalyze the degradation of organic matter can be greatly improved through the synergistic cooperation between the various components therein, and it can be endowed with acoustic-optical dual catalytic activity, which will be very beneficial for improving its treatment effect on organic wastewater.

[0035] The above is the overall concept of the present invention, and detailed embodiments and comparative examples are provided below on the basis of the overall concept of the present invention to further illustrate the present invention.

[0036] Example 1 A doped modified bismuth ferrite-based heterojunction is prepared by the following steps: S1. Preparation of carboxylated graphene oxide: Take 1g of graphene oxide and add it to 700mL of deionized water. Stir at 5000rpm for 15min, add 15g of sodium hydroxide and 12g of sodium chloroacetate while stirring, and then treat it under 850W, 45kHz ultrasound for 3h, adjust the pH to neutral with 15wt% hydrochloric acid, then repeatedly centrifuge and wash with water to neutral, and dry at 70℃ for 12h to obtain carboxylated graphene oxide.

[0037] S2. Preparation of acousto-optic dual-responsive carbon dots: 732 mg of benzoic acid, 475 mg of citric acid, 411 mg of 4-aminobenzoic acid, 307.5 mg of tetraphenylporphyrin, 255 mg of silver nitrate, and 282 mg of copper nitrate were added to a mixed solution of 200 mL of deionized water and 100 mL of ethanol at 65°C, and ultrasonically dispersed for 30 min. The resulting mixture was transferred to a polytetrafluoroethylene-lined reactor and reacted at 180°C for 10 h. The mixture was cooled to room temperature and filtered through a 0.22 μm filter membrane. The filtrate was dialyzed in deionized water for 12 h using a dialysis bag with a molecular weight cutoff of 1500 Da. The dialysate in the dialysis bag was freeze-dried to obtain acoustic-optical dual-responsive carbon dots.

[0038] S3. Preparation of doped modified bismuth ferrite-based heterojunction by hydrothermal method: S3-1, taking 1.8 g of the carboxylated graphene oxide prepared in step S1, adding it to 100 mL of deionized water, and ultrasonically dispersing it for 30 min to obtain dispersion 1; S3-2, taking 0.75 g of the acousto-optic dual-responsive carbon dots prepared in step S2, adding it into 50 mL of deionized water, and ultrasonically dispersing it for 30 min to obtain dispersion 2; S3-3, add 2.42g of ferric nitrate, 3.95g of bismuth nitrate, and 0.451g of gadolinium nitrate hexahydrate into 300mL of 15% nitric acid aqueous solution, stir for 5min, add dispersion 1 to the obtained mixed solution under stirring, keep stirring for 10min, then continue to add dispersion 2 under continuous stirring, ultrasonically disperse for 45min, and dropwise add 25wt% ammonia water to the obtained mixed solution until the pH value of the mixed system is 8, to obtain a precursor solution; S3-4. The obtained precursor solution was transferred to a reactor and reacted at 200°C for 8 hours. After the reaction was completed, the mixture was cooled to room temperature and filtered. The solid product was washed with deionized water and ethanol in turn and dried in vacuo at 80°C for 6 hours to obtain a doped modified bismuth ferrite-based heterojunction.

[0039] Example 2 A doped modified bismuth ferrite-based heterojunction is prepared by the following steps: S1. Preparation of carboxylated graphene oxide: Take 1g of graphene oxide and add it to 700mL of deionized water. Stir at 5000rpm for 15min, add 15g of sodium hydroxide and 12g of sodium chloroacetate while stirring, and then treat it under 850W, 45kHz ultrasound for 3h, adjust the pH to neutral with 15wt% hydrochloric acid, then repeatedly centrifuge and wash with water to neutral, and dry at 70℃ for 12h to obtain carboxylated graphene oxide.

[0040] S2. Preparation of acousto-optic dual-responsive carbon dots: 732 mg of benzoic acid, 475 mg of citric acid, 411 mg of 4-aminobenzoic acid, 307.5 mg of tetraphenylporphyrin, 255 mg of silver nitrate, and 282 mg of copper nitrate were added to a mixed solution of 200 mL of deionized water and 100 mL of ethanol at 65°C, and ultrasonically dispersed for 30 min. The resulting mixture was transferred to a polytetrafluoroethylene-lined reactor and reacted at 180°C for 10 h. The mixture was cooled to room temperature and filtered through a 0.22 μm filter membrane. The filtrate was dialyzed in deionized water for 12 h using a dialysis bag with a molecular weight cutoff of 1500 Da. The dialysate in the dialysis bag was freeze-dried to obtain acoustic-optical dual-responsive carbon dots.

[0041] S3. Preparation of doped modified bismuth ferrite-based heterojunction by hydrothermal method: S3-1, taking 1.65 g of the carboxylated graphene oxide prepared in step S1, adding it to 100 mL of deionized water, and ultrasonically dispersing it for 30 min to obtain dispersion 1; S3-2, taking 0.7 g of the acousto-optic dual-responsive carbon dots prepared in step S2, adding them into 50 mL of deionized water, and ultrasonically dispersing them for 30 min to obtain dispersion 2; S3-3, add 2.42g of ferric nitrate, 3.95g of bismuth nitrate, and 0.451g of gadolinium nitrate hexahydrate into 300mL of 15% nitric acid aqueous solution, stir for 5min, add dispersion 1 to the obtained mixed solution under stirring, keep stirring for 10min, then continue to add dispersion 2 under continuous stirring, ultrasonically disperse for 45min, and dropwise add 25wt% ammonia water to the obtained mixed solution until the pH value of the mixed system is 8, to obtain a precursor solution; S3-4. The obtained precursor solution was transferred to a reactor and reacted at 190°C for 8 hours. After the reaction was completed, the mixture was cooled to room temperature and filtered. The solid product was washed with deionized water and ethanol in sequence and vacuum dried at 80°C for 6 hours to obtain a doped modified bismuth ferrite-based heterojunction.

[0042] Example 3 A doped modified bismuth ferrite-based heterojunction is prepared by the following steps: S1. Preparation of carboxylated graphene oxide: Take 1g of graphene oxide and add it to 700mL of deionized water. Stir at 5000rpm for 15min, add 15g of sodium hydroxide and 12g of sodium chloroacetate while stirring, and then treat it under 850W, 45kHz ultrasound for 3h, adjust the pH to neutral with 15wt% hydrochloric acid, then repeatedly centrifuge and wash with water to neutral, and dry at 70℃ for 12h to obtain carboxylated graphene oxide.

[0043] S2. Preparation of acousto-optic dual-responsive carbon dots: 732 mg of benzoic acid, 475 mg of citric acid, 411 mg of 4-aminobenzoic acid, 307.5 mg of tetraphenylporphyrin, 255 mg of silver nitrate, and 282 mg of copper nitrate were added to a mixed solution of 200 mL of deionized water and 100 mL of ethanol at 65°C, and ultrasonically dispersed for 30 min. The resulting mixture was transferred to a polytetrafluoroethylene-lined reactor and reacted at 180°C for 10 h. The mixture was cooled to room temperature and filtered through a 0.22 μm filter membrane. The filtrate was dialyzed in deionized water for 12 h using a dialysis bag with a molecular weight cutoff of 1500 Da. The dialysate in the dialysis bag was freeze-dried to obtain acoustic-optical dual-responsive carbon dots.

[0044] S3. Preparation of doped modified bismuth ferrite-based heterojunction by hydrothermal method: S3-1, taking 1.9 g of the carboxylated graphene oxide prepared in step S1, adding it to 100 mL of deionized water, and ultrasonically dispersing it for 30 min to obtain dispersion 1; S3-2, taking 0.8 g of the acousto-optic dual-responsive carbon dots prepared in step S2, adding them into 50 mL of deionized water, and ultrasonically dispersing them for 30 min to obtain dispersion 2; S3-3, add 2.42g of ferric nitrate, 3.95g of bismuth nitrate, and 0.451g of gadolinium nitrate hexahydrate into 300mL of 15% nitric acid aqueous solution, stir for 5min, add dispersion 1 to the obtained mixed solution under stirring, keep stirring for 10min, then continue to add dispersion 2 under continuous stirring, ultrasonically disperse for 45min, and dropwise add 25wt% ammonia water to the obtained mixed solution until the pH value of the mixed system is 8, to obtain a precursor solution; S3-4. The obtained precursor solution is transferred to a reactor and reacted at 210°C for 6 hours. After the reaction is completed, it is cooled to room temperature and filtered. The solid product is washed with deionized water and ethanol in sequence and vacuum dried at 80°C for 6 hours to obtain a doped modified bismuth ferrite-based heterojunction.

[0045] Comparative Example 1 A doped modified bismuth ferrite-based heterojunction is prepared by the following steps: S1, preparing carboxylated graphene oxide, the same as in Example 1; S2. Preparation of doped modified bismuth ferrite-based heterojunction by hydrothermal method: S2-1, taking 1.8 g of the carboxylated graphene oxide prepared in step S1, adding it to 100 mL of deionized water, and ultrasonically dispersing it for 30 min to obtain dispersion 1; S2-2, add 2.42g of ferric nitrate, 3.95g of bismuth nitrate, and 0.451g of gadolinium nitrate hexahydrate into 300mL of 15% nitric acid aqueous solution, stir for 5min, add dispersion 1 to the obtained mixed solution under stirring, keep stirring for 10min, ultrasonically disperse for 45min, and dropwise add 25wt% ammonia water to the obtained mixed solution until the pH value of the mixed system is 8, to obtain a precursor solution; S2-3. The obtained precursor solution was transferred to a reactor and reacted at 200°C for 8 hours. After the reaction was completed, it was cooled to room temperature and filtered. The solid product was washed with deionized water and ethanol in turn, and vacuum dried at 80°C for 6 hours to obtain a doped modified bismuth ferrite-based heterojunction.

[0046] Comparative Example 2 A doped modified bismuth ferrite-based heterojunction is prepared by the following steps: S1, preparing carboxylated graphene oxide, the same as in Example 1; S2. Preparation of acousto-optic dual-responsive carbon dots: 732 mg of benzoic acid, 475 mg of citric acid, 411 mg of 4-aminobenzoic acid, 307.5 mg of tetraphenylporphyrin, and 282 mg of copper nitrate were added to a mixed solution of 200 mL of deionized water and 100 mL of ethanol at 65°C, and ultrasonically dispersed for 30 min. The resulting mixture was transferred to a polytetrafluoroethylene-lined reactor and reacted at 180°C for 10 h. The mixture was cooled to room temperature and filtered through a 0.22 μm filter membrane. The filtrate was dialyzed in deionized water for 12 h using a dialysis bag with a molecular weight cutoff of 1500 Da. The dialysate in the dialysis bag was freeze-dried to obtain acoustic-optical dual-responsive carbon dots.

[0047] S3. Prepare a doped modified bismuth ferrite-based heterojunction by a hydrothermal method, which is the same as in Example 1.

[0048] Comparative Example 3 A doped modified bismuth ferrite-based heterojunction is prepared by the following steps: S1, preparing carboxylated graphene oxide, the same as in Example 1; S2. Preparation of acousto-optic dual-responsive carbon dots: 732 mg of benzoic acid, 475 mg of citric acid, 411 mg of 4-aminobenzoic acid, 307.5 mg of tetraphenylporphyrin, and 255 mg of silver nitrate were added to a mixed solution of 200 mL of deionized water and 100 mL of ethanol at 65°C, and ultrasonically dispersed for 30 min. The resulting mixture was transferred to a polytetrafluoroethylene-lined reactor, reacted at 180°C for 10 h, cooled to room temperature, filtered through a 0.22 μm filter membrane, and the filtrate was dialyzed in deionized water for 12 h using a dialysis bag with a molecular weight cutoff of 1500 Da. The dialysate in the dialysis bag was freeze-dried to obtain the acoustic-optical dual-responsive carbon dots. S3. Prepare a doped modified bismuth ferrite-based heterojunction by a hydrothermal method, which is the same as in Example 1.

[0049] Comparative Example 4 A doped modified bismuth ferrite-based heterojunction is prepared by the following steps: S1, preparing carboxylated graphene oxide, the same as in Example 1; S2, preparing acousto-optic dual-responsive carbon dots, the same as in Example 1; S3. Preparation of doped modified bismuth ferrite-based heterojunction by hydrothermal method: S3-1, taking 1.65 g of the carboxylated graphene oxide prepared in step S1, adding it to 100 mL of deionized water, and ultrasonically dispersing it for 30 min to obtain dispersion 1; S3-2, taking 0.7 g of the acousto-optic dual-responsive carbon dots prepared in step S2, adding them into 50 mL of deionized water, and ultrasonically dispersing them for 30 min to obtain dispersion 2; S3-3, take 2.42g of ferric nitrate and 3.95g of bismuth nitrate, add them to 300mL of 15% nitric acid aqueous solution, stir for 5min, add dispersion 1 to the obtained mixed solution under stirring, keep stirring for 10min, then continue to add dispersion 2 under continuous stirring, ultrasonically disperse for 45min, add 25wt% ammonia water to the obtained mixed solution until the pH value of the mixed system is 8, to obtain a precursor solution; S3-4. The obtained precursor solution was transferred to a reactor and reacted at 190°C for 8 hours. After the reaction was completed, the mixture was cooled to room temperature and filtered. The solid product was washed with deionized water and ethanol in sequence and vacuum dried at 80°C for 6 hours to obtain a doped modified bismuth ferrite-based heterojunction.

[0050] Comparative Example 5 A doped modified bismuth ferrite-based heterojunction is prepared by the following steps: S1, preparing carboxylated graphene oxide, the same as in Example 1; S2, preparing acousto-optic dual-responsive carbon dots, the same as in Example 1; S3. Preparation of doped modified bismuth ferrite-based heterojunction by hydrothermal method: S3-1, taking 0.7 g of the acousto-optic dual-responsive carbon dots prepared in step S2, adding them into 50 mL of deionized water, and ultrasonically dispersing them for 30 min to obtain dispersion 1; S3-2, add 2.42g of ferric nitrate, 3.95g of bismuth nitrate, and 0.451g of gadolinium nitrate hexahydrate into 300mL of 15% nitric acid aqueous solution, stir for 5min, then continue to add dispersion 1 under continuous stirring, ultrasonically disperse for 45min, and dropwise add 25wt% ammonia water into the obtained mixed solution until the pH value of the mixed system is 8, to obtain a precursor solution; S3-3. The obtained precursor solution is transferred to a reactor and reacted at 190°C for 8 hours. After the reaction is completed, it is cooled to room temperature and filtered. The solid product is washed with deionized water and ethanol in sequence and vacuum dried at 80°C for 6 hours to obtain a doped modified bismuth ferrite-based heterojunction.

[0051] 1. Degradation performance test The doped modified bismuth ferrite-based heterojunctions prepared in Examples 1-3 and Comparative Examples 1-5 were respectively subjected to degradation tests of organic wastewater according to the following method.

[0052] A 50 mg / L methyl orange solution (volume 200 mL) was used as the target degradation product to simulate organic wastewater. A doped modified bismuth ferrite-based heterojunction was added at an addition amount of 2 g / L. After stirring for 15 minutes under light protection, the mixture was transferred to a xenon lamp and irradiated with visible light (power 500 W, λ>400 nm). Ultrasonic action was applied during the process, with an ultrasonic power of 400 W and an ultrasonic frequency of 80 kHz. Samples were taken every 5 minutes, and the absorbance of the solution was tested with a UV-visible spectrophotometer (464 nm) to obtain the methyl orange concentration and calculate the degradation rate of methyl orange: In addition, a control example is set up. The control example uses the doped modified bismuth ferrite-based heterostructure prepared in Example 1. No ultrasonic action is applied during the test, and the rest is the same as above.

[0053] Test results such as Figure 1 (Example 2 and Example 3 are not shown in the figure), the degradation rate results after 60 minutes of treatment are shown in the following Table 1: Table 1 According to the test results, it can be seen that the doped modified bismuth ferrite-based heterojunction prepared in Examples 1-3 can achieve efficient degradation of methyl orange under the simultaneous action of sound and light; ultrasound was not applied in the control example, resulting in a significant decrease in the degradation efficiency; the degradation ability of the undoped sound-optic dual-responsive carbon dots in Comparative Example 1 was greatly reduced; the decrease in the degradation rate of Comparative Examples 2 and 3 illustrates the effect of silver and copper doping in the carbon dots; the decrease in the degradation rate of Comparative Example 4 is attributed to the undoped gadolinium in the bismuth ferrite-based heterojunction; the decrease in the degradation rate of Comparative Example 5 is due to the undoped carboxylated graphene oxide in the system.

[0054] 2. Performance Characterization 1. Reference Figure 2 , is the infrared spectrum of the acoustic-optic dual-responsive carbon dots synthesized in Example 1. It can be seen that the surface of the carbon dots contains abundant amino, carboxyl, hydroxyl and other functional groups, 748cm -1 The peak at 505 cm is derived from the absorption peak of =CH on the pyrrole ring, combined with the stretching vibration peak of the Ag-O bond (505 cm -1 Nearby), the stretching vibration peak of Cu-O bond (440cm -1 The appearance of ) and the like indicates the successful synthesis of the carbon dots.

[0055] 2. Singlet oxygen production capacity detection The carbon dots synthesized in Example 1 and Comparative Examples 2-3 were used to prepare carbon dot solutions with a concentration of 0.1 mg / mL, and then a singlet oxygen green fluorescent probe (SOSG, Product No.: KM0040, Beijing Biolab Technology Co., Ltd.) was used to detect the singlet oxygen content in the carbon dot solution at different times under the following test conditions.

[0056] (1) Visible light illumination (power 500 W, λ>400 nm) and ultrasound (ultrasonic power 400 W, ultrasonic frequency 80 kHz) were applied simultaneously to test the singlet oxygen content generated by the carbon dots synthesized in Example 1 and Comparative Examples 2-3 at different times; Example 1 was recorded as AgCu-CDs-1 (HV+US), and Comparative Examples 2-3 were recorded as CDs-2 (HV+US) and CDs-3 (HV+US) respectively; (2) Only visible light illumination (power 500 W, λ>400 nm) was used to test the singlet oxygen content generated by the carbon dots synthesized in Example 1 at different times, which was recorded as AgCu-CDs-1 (HV).

[0057] Test results such as Figure 3 As shown, it can be seen that for the carbon dots prepared in Example 1, applying ultrasound can produce more singlet oxygen than not applying ultrasound, which verifies the acousto-optic dual response characteristics of the carbon dots. The results of CDs-2 (HV+US) and CDs-3 (HV+US) show that the doping of Ag and Cu in the carbon dots is beneficial to improving the singlet oxygen yield of the carbon dots.

[0058] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and the implementation modes. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to specific details.

Claims

1. A doped modified bismuth ferrite-based heterojunction, characterized in that: It is prepared by the following steps: S1. preparing carboxylated graphene oxide; S2. Preparation of acousto-optic dual-responsive carbon dots: Benzoic acid, 4-aminobenzoic acid, tetraphenylporphyrin, silver nitrate and copper nitrate are added to an ethanol aqueous solution, and the resulting mixture is subjected to a hydrothermal reaction to synthesize the acoustic-optical dual-responsive carbon dots; S3. Preparation of doped modified bismuth ferrite-based heterojunction by hydrothermal method: S3-1, dispersing the carboxylated graphene oxide prepared in step S1 in deionized water to prepare a dispersion 1; S3-2, dispersing the acousto-optic dual-responsive carbon dots prepared in step S2 in deionized water to prepare dispersion 2; S3-3, adding iron nitrate, bismuth nitrate and gadolinium nitrate to a nitric acid aqueous solution, and then sequentially adding dispersion 1 and dispersion 2, and then adjusting the pH value of the mixed system to obtain a precursor solution; S3-4, subjecting the precursor solution to a hydrothermal reaction to prepare the doped modified bismuth ferrite-based heterojunction.

2. The doped modified bismuth ferrite-based heterojunction according to claim 1, characterized in that: Step S1 is specifically as follows: Take graphene oxide and add it to deionized water, stir it, add sodium hydroxide and sodium chloroacetate while stirring, then treat it under ultrasonication for 1.5-6h, adjust the pH to neutral with hydrochloric acid, then wash it with water repeatedly by centrifugation until it is neutral, and dry it to obtain carboxylated graphene oxide.

3. The doped modified bismuth ferrite-based heterojunction according to claim 2, characterized in that: Step S1 is specifically as follows: Take 0.5-2g of graphene oxide and add it to 500-1000mL of deionized water, stir at 1000-8000rpm for 5-30min, add 7.5-30g of sodium hydroxide and 6-24g of sodium chloroacetate while stirring, then treat under ultrasonic action for 1.5-6h, adjust the pH to neutral with hydrochloric acid, then repeatedly centrifuge and wash with water to neutral, and dry at 60-90°C for 6-24h to obtain carboxylated graphene oxide.

4. The doped modified bismuth ferrite-based heterojunction according to claim 1, characterized in that: Step S2 is specifically as follows: Benzoic acid, 4-aminobenzoic acid, tetraphenylporphyrin, silver nitrate and copper nitrate were added to a hot ethanol aqueous solution and dispersed by ultrasonication. The obtained mixture was transferred to a reactor and reacted under heating. After the reaction, the mixture was cooled to room temperature and filtered with a filter membrane. The filtrate was dialyzed in deionized water with a dialysis bag. The dialysate in the dialysis bag was freeze-dried to obtain the acousto-optic dual-responsive carbon dots.

5. The doped modified bismuth ferrite-based heterojunction according to claim 4, characterized in that: Step S2 is specifically as follows: 366-1464 mg of benzoic acid, 283-576 mg of citric acid, 205-822 mg of 4-aminobenzoic acid, 153-615 mg of tetraphenylporphyrin, 127-510 mg of silver nitrate, and 141-564 mg of copper nitrate were added to an ethanol aqueous solution composed of 100-400 mL of deionized water and 50-200 mL of ethanol at 50-70°C, and ultrasonically dispersed for 15-60 min. The resulting mixture was transferred to a polytetrafluoroethylene-lined reactor, reacted at 170-205°C for 6-18 h, cooled to room temperature, filtered with a 0.22 μm filter membrane, and the filtrate was dialyzed in deionized water for 6-27 h using a dialysis bag with a molecular weight cutoff of 1000-2000 Da. The dialysate in the dialysis bag was freeze-dried to obtain acoustic-optical dual-responsive carbon dots.

6. The doped modified bismuth ferrite-based heterojunction according to claim 1, characterized in that: Step S3 is specifically as follows: S3-1, adding the carboxylated graphene oxide prepared in step S1 into deionized water, and performing ultrasonic dispersion to obtain dispersion 1; S3-2, adding the acousto-optic dual-responsive carbon dots prepared in step S2 into deionized water, and performing ultrasonic dispersion to obtain dispersion 2; S3-3, adding iron nitrate, bismuth nitrate and gadolinium nitrate hexahydrate to a nitric acid aqueous solution, stirring for 2-15 minutes, adding dispersion 1 to the obtained mixed solution under stirring, maintaining stirring for 2-15 minutes, and then continuing to add dispersion 2 under continuous stirring, ultrasonically dispersing, and dropping ammonia water into the obtained mixed solution until the pH value of the mixed system reaches 7.5-8.5 to obtain a precursor solution; S3-4. The obtained precursor solution is transferred to a reactor, and the reaction is carried out at 190-210° C. for 6-16 hours. After the reaction is completed, the mixture is cooled to room temperature, filtered, and the solid product is washed with deionized water and ethanol in sequence, and vacuum dried to obtain a doped modified bismuth ferrite-based heterojunction.

7. The doped modified bismuth ferrite-based heterojunction according to claim 6, characterized in that: Step S3 is specifically as follows: S3-1, taking 0.9-3.6 g of the carboxylated graphene oxide prepared in step S1, adding it to 50-200 mL of deionized water, and ultrasonically dispersing it for 15-60 min to obtain dispersion 1; S3-2, taking 0.35-1.5 g of the acousto-optic dual-responsive carbon dots prepared in step S2, adding them into 50-200 mL of deionized water, and ultrasonically dispersing them for 15-60 min to obtain dispersion 2; S3-3, 1.21-4.84 g of ferric nitrate, 1.975-7.9 g of bismuth nitrate, and 0.2255-0.902 g of gadolinium nitrate hexahydrate are added to 150-600 mL of a nitric acid aqueous solution having a mass concentration of 10-20%, and stirred for 2-15 min. Dispersion liquid 1 is added to the obtained mixed solution under stirring, and stirring is maintained for 2-15 min. Then, dispersion liquid 2 is added under continuous stirring, and ultrasonic dispersion is performed for 30-90 min. Ammonia water having a concentration of 20-25 wt % is added dropwise to the obtained mixed solution until the pH value of the mixed system reaches 7.5-8.5 to obtain a precursor solution; S3-4. Transfer the obtained precursor solution to a reactor, react at 190-210°C for 6-16 hours, cool to room temperature after the reaction, filter, wash the solid product with deionized water and ethanol in turn, and vacuum dry at 70-90°C for 4-12 hours to obtain a doped modified bismuth ferrite-based heterojunction.

8. Use of the doped modified bismuth ferrite-based heterojunction as claimed in any one of claims 1 to 7 in photocatalytic degradation of organic wastewater.

9. The use according to claim 8, characterized in that: The application method is: putting the doped modified bismuth ferrite-based heterojunction into organic wastewater, and then degrading the organic wastewater under the combined action of visible light irradiation and ultrasound.

10. The use according to claim 9, characterized in that: The application method is as follows: putting the doped modified bismuth ferrite-based heterojunction into organic wastewater, controlling the concentration of the doped modified bismuth ferrite-based heterojunction in the organic wastewater to be 0.2-5 g / L, stirring for 5-30 minutes, and then treating for 10-90 minutes under visible light irradiation and ultrasound assistance; Among them, the ultrasonic power is 50-500W and the ultrasonic frequency is 30-100kHz.

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