Doping modified bismuth ferrite-based heterojunction and its application in photocatalytic degradation of organic wastewater

Abstract

This invention discloses a doped and modified bismuth ferrite-based heterojunction and its application in the photocatalytic degradation of organic wastewater. The doped and modified bismuth ferrite-based heterojunction is prepared through the following steps: S1, preparing carboxylated graphene oxide; S2, preparing acousto-optic dual-response carbon dots; S3, preparing the doped and modified bismuth ferrite-based heterojunction via a hydrothermal method. This invention significantly enhances the photocatalytic activity of the bismuth ferrite-based heterojunction by using rare earth gadolinium, carboxylated graphene oxide, and acousto-optic dual-response carbon dots for co-doping. The introduction of acousto-optic dual-response carbon dots endows the doped and modified bismuth ferrite-based heterojunction with catalytic activity under ultrasonic irradiation, enabling it to achieve higher wastewater degradation efficiency when used for organic wastewater treatment under both visible light and ultrasonic irradiation.

Description

Technical Field

[0001] This invention relates to the fields of bismuth-based heterojunction materials and water treatment, and particularly to a doped and modified bismuth ferrite-based heterojunction and its application in the photocatalytic degradation of organic wastewater. Background Technology

[0002] Currently, the problem of water pollution is receiving increasing attention, and the degradation and treatment of organic matter in water is related to human health and the sustainable development of society.

[0003] Among numerous pollutant treatment technologies, semiconductor photocatalysis for the 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 a semiconductor absorbs energy greater than or equal to its band gap (hν), electrons in its valence band will absorb energy and jump across the band gap to the conduction band, while generating holes in the valence band. 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 radicals and hydroxyl 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 on degradation of organic pollutants by bismuth ferrite-based heterojunction photocatalysts [J]. New Chemical Materials, 2024(002):052.).

[0004] Bismuth ferrite, as a semiconductor photocatalyst, is commonly used in wastewater treatment, water purification, and water pollution remediation, effectively converting organic pollutants into harmless substances. In terms of photocatalysis, bismuth ferrite exhibits excellent photocatalytic activity in the visible light region, enabling it to effectively utilize visible light for photocatalytic reactions.

[0005] However, the catalytic efficiency of traditional bismuth ferrite-based heterojunctions 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 on photocatalytic performance [J]. Journal of Synthetic Crystals, 2013, 42(8):1607-1610,1615," the bismuth ferrite catalyst prepared by them only achieved a degradation rate of 72.847% for methyl orange. Therefore, it is necessary to improve the existing technology to further enhance the organic matter degradation efficiency of bismuth ferrite-based heterojunction catalysts. Summary of the Invention

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

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: In its first aspect, the present invention provides a doped and modified bismuth ferrite-based heterojunction and its application in the photocatalytic degradation of organic wastewater, which is prepared through the following steps:

[0008] S1. Preparation of carboxylated graphene oxide;

[0009] S2. Preparation of acousto-optic dual-response carbon dots:

[0010] Benzoic acid, 4-aminobenzoic acid, tetraphenylporphyrin, silver nitrate, and copper nitrate were added to an aqueous ethanol solution, and the resulting mixture was subjected to a hydrothermal reaction to synthesize acousto-optic dual-response carbon dot.

[0011] S3. Preparation of doped and modified bismuth ferrite-based heterojunctions by hydrothermal method:

[0012] S3-1. Disperse the carboxylated graphene oxide prepared in step S1 in deionized water to prepare dispersion 1.

[0013] S3-2. Disperse the acoustic-optic dual-response carbon dots prepared in step S2 in deionized water to prepare dispersion 2.

[0014] S3-3. Add ferric nitrate, bismuth nitrate, and gadolinium nitrate to an aqueous nitric acid solution, then add dispersion 1 and dispersion 2 in sequence, and adjust the pH value of the mixture to obtain the precursor solution.

[0015] S3-4. The precursor solution is subjected to a hydrothermal reaction to prepare the doped modified bismuth ferrite-based heterojunction.

[0016] Preferably, step S1 specifically includes:

[0017] Add graphene oxide to deionized water and stir. While stirring, add sodium hydroxide and sodium chloroacetate, then treat with ultrasound for 1.5-6 hours. Adjust the pH to neutral with hydrochloric acid, then repeatedly centrifuge and wash with water until neutral, and dry to obtain carboxylated graphene oxide.

[0018] Preferably, step S1 specifically includes:

[0019] Add 0.5-2g of graphene oxide to 500-1000mL of deionized water and stir at 1000-8000rpm for 5-30min. While stirring, add 7.5-30g of sodium hydroxide and 6-24g of sodium chloroacetate. Then treat under sonication for 1.5-6h. Adjust the pH to neutral with hydrochloric acid, then repeatedly centrifuge and wash with water until neutral. Dry at 60-90℃ for 6-24h to obtain carboxylated graphene oxide.

[0020] Preferably, step S2 specifically includes:

[0021] Benzoic acid, 4-aminobenzoic acid, tetraphenylporphyrin, silver nitrate, and copper nitrate were added to a hot aqueous ethanol solution and ultrasonically dispersed. The resulting mixture was transferred to a reaction vessel and reacted under heating. After the reaction was completed, the mixture was cooled to room temperature and filtered through a filter membrane. The filtrate was dialyzed in deionized water using a dialysis bag. The dialysate in the dialysis bag was then freeze-dried to obtain acousto-optic dual-response carbon dots.

[0022] Preferably, step S2 specifically includes:

[0023] Take 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 and add them to an ethanol-water solution consisting of 100-400 mL of deionized water and 50-200 mL of ethanol at 50-70℃. Disperse the mixture ultrasonically for 15-60 min. Transfer the resulting mixture to a reaction vessel lined with polytetrafluoroethylene and react at 170-205℃ for 6-18 h. Cool to room temperature and filter with a 0.22 μm filter membrane. Dialyze the filtrate in deionized water for 6-27 h using a dialysis bag with a molecular weight cutoff of 1000-2000 Da. Take the dialysate in the dialysis bag and freeze-dry it to obtain acousto-optic dual-response carbon dots.

[0024] Preferably, step S3 specifically includes:

[0025] S3-1. Take the carboxylated graphene oxide prepared in step S1 and add it to deionized water, then disperse it by ultrasonication to obtain dispersion 1.

[0026] S3-2. Take the acousto-optic dual-response carbon dots prepared in step S2, add them to deionized water, and disperse them by ultrasonication to obtain dispersion 2.

[0027] S3-3. Add ferric nitrate, bismuth nitrate, and gadolinium hexahydrate to an aqueous nitric acid solution and stir for 2-15 minutes. While stirring, add dispersion 1 to the resulting mixture and continue stirring for 2-15 minutes. Then, continue to add dispersion 2 while stirring continuously and sonicate. Add ammonia dropwise to the resulting mixture until the pH of the mixture is 7.5-8.5 to obtain the precursor solution.

[0028] S3-4. Transfer the obtained precursor solution to a reaction vessel and react at 190-210℃ for 6-16 hours. After the reaction is completed, cool to room temperature, filter, wash the solid product with deionized water and ethanol in sequence, and dry under vacuum to obtain a doped modified bismuth ferrite-based heterojunction.

[0029] Preferably, step S3 specifically includes:

[0030] S3-1. Take 0.9-3.6g of the carboxylated graphene oxide prepared in step S1 and add it to 50-200mL of deionized water. Disperse it ultrasonically for 15-60min to obtain dispersion 1.

[0031] S3-2. Take 0.35-1.5g of the acousto-optic dual-response carbon dots prepared in step S2 and add them to 50-200mL of deionized water. Disperse them ultrasonically for 15-60min to obtain dispersion 2.

[0032] S3-3: Take 1.21-4.84g of ferric nitrate, 1.975-7.9g of bismuth nitrate, and 0.2255-0.902g of gadolinium hexahydrate and add them to 150-600mL of nitric acid aqueous solution with a mass concentration of 10-20%. Stir for 2-15min. Add dispersion 1 to the resulting mixture while stirring, and continue stirring for 2-15min. Then, continue adding dispersion 2 while stirring continuously. Sonicate and disperse for 30-90min. Add 20-25wt% ammonia water to the resulting mixture until the pH value of the mixture is 7.5-8.5 to obtain the precursor solution.

[0033] S3-4. Transfer the obtained precursor solution to a reaction vessel and react at 190-210℃ for 6-16 hours. After the reaction is completed, cool to room temperature, filter, wash the solid product with deionized water and ethanol in sequence, and dry under vacuum at 70-90℃ for 4-12 hours to obtain a doped modified bismuth ferrite-based heterojunction.

[0034] In a second aspect, the present invention provides an application of the doped and modified bismuth ferrite-based heterojunction as described above in the photocatalytic degradation of organic wastewater.

[0035] Preferably, the application method is as follows: the doped and modified bismuth ferrite-based heterojunction is added to the organic wastewater, and then the organic wastewater is degraded under the combined action of visible light irradiation and ultrasound.

[0036] Preferably, the application method is as follows: the doped modified bismuth ferrite-based heterojunction is added to organic wastewater, the concentration of the doped modified bismuth ferrite-based heterojunction in the organic wastewater is controlled at 0.2-5 g / L, stirred for 5-30 min, and then treated for 10-90 min under visible light irradiation and ultrasonic assistance.

[0037] The ultrasonic power ranges from 50 to 500W, and the ultrasonic frequency ranges from 30 to 100kHz.

[0038] The beneficial effects of this invention are:

[0039] This invention provides a doped and modified bismuth ferrite-based heterojunction and its application in the photocatalytic degradation of organic wastewater. By using rare earth gadolinium, carboxylated graphene oxide, and acousto-optic dual-response carbon dots to co-dope the bismuth ferrite-based heterojunction, the photocatalytic activity of the bismuth ferrite-based heterojunction can be significantly improved. The introduction of acousto-optic dual-response carbon dots can endow the doped and modified bismuth ferrite-based heterojunction with catalytic activity under ultrasonic irradiation, 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 ultrasound, higher wastewater degradation efficiency can be obtained.

[0040] The doped and modified bismuth ferrite-based heterojunction provided by this invention, through the construction of a multi-component composite structure system GO@BFO@AgCu-CDs consisting of "carboxylated graphene oxide + gadolinium-doped bismuth ferrite + acousto-optic dual-response carbon dots", can significantly enhance the catalytic degradation ability of the bismuth ferrite-based heterojunction for organic matter through the synergistic effect between its components, and endow it with acousto-optic dual-catalytic activity, which will be very beneficial for improving its treatment effect on organic wastewater. Attached Figure Description

[0041] Figure 1 These are the results of degradation performance tests;

[0042] Figure 2 The infrared spectrum of the acousto-optic dual-response carbon dots synthesized in Example 1;

[0043] Figure 3 The results are from the test of singlet oxygen production capacity. Detailed Implementation

[0044] The present invention will be further described in detail below with reference to embodiments, so that those skilled in the art can implement it based on the description.

[0045] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0046] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials and reagents used in the following examples are commercially available. For examples where specific conditions are not specified, conventional conditions or conditions recommended by the manufacturer are followed. For reagents or instruments whose manufacturers are not specified, they are all commercially available products.

[0047] This invention provides a doped and modified bismuth ferrite-based heterojunction, which is prepared by the following steps:

[0048] S1. Preparation of carboxylated graphene oxide:

[0049] Add 0.5-2g of graphene oxide to 500-1000mL of deionized water and stir at 1000-8000rpm for 5-30min. While stirring, add 7.5-30g of sodium hydroxide and 6-24g of sodium chloroacetate. Then treat under sonication for 1.5-6h. Adjust the pH to neutral with hydrochloric acid, then repeatedly centrifuge and wash with water until neutral. Dry at 60-90℃ for 6-24h to obtain carboxylated graphene oxide.

[0050] S2. Preparation of acousto-optic dual-response carbon dots:

[0051] Take 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 and add them to an ethanol-water solution consisting of 100-400 mL of deionized water and 50-200 mL of ethanol at 50-70℃. Disperse the mixture ultrasonically for 15-60 min. Transfer the resulting mixture to a reaction vessel lined with polytetrafluoroethylene and react at 170-205℃ for 6-18 h. Cool to room temperature and filter with a 0.22 μm filter membrane. Dialyze the filtrate in deionized water for 6-27 h using a dialysis bag with a molecular weight cutoff of 1000-2000 Da. Take the dialysate in the dialysis bag and freeze-dry it to obtain acousto-optic dual-response carbon dots.

[0052] S3. Preparation of doped and modified bismuth ferrite-based heterojunctions by hydrothermal method:

[0053] S3-1. Take 0.9-3.6g of the carboxylated graphene oxide prepared in step S1 and add it to 50-200mL of deionized water. Disperse it ultrasonically for 15-60min to obtain dispersion 1.

[0054] S3-2. Take 0.35-1.5g of the acousto-optic dual-response carbon dots prepared in step S2 and add them to 50-200mL of deionized water. Disperse them ultrasonically for 15-60min to obtain dispersion 2.

[0055] S3-3: Take 1.21-4.84g of ferric nitrate, 1.975-7.9g of bismuth nitrate, and 0.2255-0.902g of gadolinium hexahydrate and add them to 150-600mL of nitric acid aqueous solution with a mass concentration of 10-20%. Stir for 2-15min. Add dispersion 1 to the resulting mixture while stirring, and continue stirring for 2-15min. Then, continue adding dispersion 2 while stirring continuously. Sonicate and disperse for 30-90min. Add 20-25wt% ammonia water to the resulting mixture until the pH value of the mixture is 7.5-8.5 to obtain the precursor solution.

[0056] S3-4. Transfer the obtained precursor solution to a reaction vessel and react at 190-210℃ for 6-16 hours. After the reaction is completed, cool to room temperature, filter, wash the solid product with deionized water and ethanol in sequence, and dry under vacuum at 70-90℃ for 4-12 hours to obtain a doped modified bismuth ferrite-based heterojunction.

[0057] This invention also provides an application of the above-mentioned doped and modified bismuth ferrite-based heterojunction in the photocatalytic degradation of organic wastewater.

[0058] In a preferred embodiment, the application method is as follows: the doped and modified bismuth ferrite-based heterojunction is added to organic wastewater, and then the organic wastewater is degraded under the combined action of visible light irradiation and ultrasound.

[0059] In a more preferred embodiment, the application method is as follows: the doped modified bismuth ferrite-based heterojunction is added to organic wastewater, the concentration of the doped modified bismuth ferrite-based heterojunction in the organic wastewater is controlled to be 0.2-5 g / L, stirred for 5-30 min, and then treated for 10-90 min under visible light irradiation and ultrasonic assistance.

[0060] The ultrasonic power ranges from 50 to 500W, and the ultrasonic frequency ranges from 30 to 100kHz.

[0061] This invention significantly enhances the photocatalytic activity of bismuth ferrite-based heterojunctions by employing rare-earth gadolinium, carboxylated graphene oxide, and acousto-optically responsive carbon dots in a composite doping process. The introduction of acousto-optically responsive carbon dots endows the doped bismuth ferrite-based heterojunction with catalytic activity under ultrasonic irradiation. This results in a higher wastewater degradation efficiency compared to traditional bismuth ferrite-based heterojunction catalysts when used for organic wastewater treatment under both visible light and ultrasound. The main mechanism of this invention is explained below.

[0062] This invention first carboxylates graphene oxide, introducing abundant carboxyl groups and other oxygen-containing functional groups onto its surface to improve its dispersibility and facilitate modification. Simultaneously, it allows for the generation of more reactive oxygen species (such as hydroxyl radicals •OH) and singlet oxygen under visible light and ultrasonic excitation, facilitated by carbon dots within the system. 1 O2);

[0063] Then, using 4-aminobenzoic acid, citric acid, oxidizing benzoic acid, and tetraphenylporphyrin with acoustic properties as carbon sources, and silver nitrate and copper nitrate as doping components, an Ag-Cu co-doped carbon dot with acoustic and optical dual-response characteristics was prepared. The surface of this carbon dot is rich in functional groups such as carboxyl, hydroxyl, and amino groups. Under visible light and ultrasonic excitation, this carbon dot can exhibit the degradation effect on organic matter by generating active oxygen. After being doped into the bismuth ferrite-based heterojunction system, it can greatly enhance the organic matter degradation ability of the system.

[0064] Finally, graphene oxide, acousto-optic dual-response carbon dots, and rare-earth gadolinium were co-doped into a bismuth ferrite-based heterojunction system via a hot water reaction, resulting in the final doped and modified bismuth ferrite-based heterojunction. During this reaction, ferric nitrate, bismuth nitrate, and gadolinium hexahydrate were first mixed with a dispersion of carboxylated graphene oxide. Ferric, bismuth, and gadolinium ions then bonded to the carboxyl and hydroxyl groups on the surface of the carboxylated graphene oxide through coordination and electrostatic adsorption. After the addition of a dispersion of acousto-optic dual-response carbon dots, the carbon dots... The surface functional groups such as carboxyl, hydroxyl, and amino groups can also coordinate and / or interact with iron ions, bismuth ions, gadolinium ions, etc. adsorbed on carboxylated graphene oxide, thereby forming a structural system of "carboxylated graphene oxide-iron, bismuth ions, gadolinium ions-acoustic and optically responsive carbon dots". Finally, through hydrothermal reaction, strong chemical bonds are formed to obtain a composite doped carboxylated graphene oxide, acousto-optically responsive carbon dots, and rare earth gadolinium bismuth ferrite-based heterojunction: GO@BFO@AgCu-CDs.

[0065] In the GO@BFO@AgCu-CDs system:

[0066] (1) Acousto-optic dual-response carbon dots AgCu-CDs can generate reactive oxygen species (ROS) under visible light. On the other hand, they also inherit the acoustic properties of tetraphenylporphyrin, enabling them to generate ROS under ultrasound, thus exhibiting excellent ability to oxidize and degrade organic matter. Cu and Ag doping can increase electron cloud density and enhance the acousto-optic dual-response activity of carbon dots. On the other hand, CuO formed by doped Cu ions in the system can form a PGN heterojunction with bismuth ferrite (BFO), which can effectively promote the separation and transfer of photogenerated electron-hole pairs, thereby improving catalytic activity (Niu F, Chen D, Qin LS, et al. Facilitated synthesis of highly efficient PGN heterojunction CuO / BiFeO3 Composite Photocatalysts with Enhanced Visible G Light Photocatalytic). Activity[J]. ChemCatChem,2015,7(20):3279G3289. ); while doped Ag can help to further improve photocatalytic activity by enhancing the conversion between Fe3+ and Fe2+.

[0067] (2) Doped Gd can reduce the electron-hole recombination rate and can also act as a hole or electron trapping center, 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 electron-hole recombination rate can also act on the acousto-optic dual-response carbon dots, and at the same time enhance the catalytic activity of the carbon dots, ultimately playing a synergistic effect on improving the catalytic activity of the system.

[0068] (3) Carboxylated graphene oxide provides a large number of oxygen-containing functional groups such as carboxyl groups, 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 valence band of BFO. This will reduce the recombination rate of photogenerated electrons and holes, allowing 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 BiFeO3Carbon 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 also plays a positive role in its ability to degrade organic matter.

[0069] In summary, the doped and modified bismuth ferrite-based heterojunction provided by this invention, through the construction of a multi-component composite structure system GO@BFO@AgCu-CDs consisting of "carboxylated graphene oxide + gadolinium-doped bismuth ferrite + acousto-optic dual-response carbon dots", can significantly enhance the catalytic degradation ability of the bismuth ferrite-based heterojunction by the synergistic effect between its components, and endow it with acousto-optic dual-catalytic activity, which will be very beneficial for improving its treatment effect on organic wastewater.

[0070] The above is the general concept of the present invention. Based on this, detailed embodiments and comparative examples are provided below to further illustrate the present invention.

[0071] Example 1

[0072] A doped and modified bismuth ferrite-based heterojunction is prepared by the following steps:

[0073] S1. Preparation of carboxylated graphene oxide:

[0074] Add 1g of graphene oxide to 700mL of deionized water and stir at 5000rpm for 15min. While stirring, add 15g of sodium hydroxide and 12g of sodium chloroacetate. Then, treat with ultrasound at 850W and 45kHz for 3h. Adjust the pH to neutral with 15wt% hydrochloric acid. Then, repeatedly centrifuge and wash with water until neutral. Dry at 70℃ for 12h to obtain carboxylated graphene oxide.

[0075] S2. Preparation of acousto-optic dual-response carbon dots:

[0076] 732 mg benzoic acid, 475 mg citric acid, 411 mg 4-aminobenzoic acid, 307.5 mg tetraphenylporphyrin, 255 mg silver nitrate, and 282 mg copper nitrate were added to a mixed solution of 200 mL deionized water and 100 mL 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. After cooling to room temperature, the mixture was 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 removed and freeze-dried to obtain acousto-optic dual-response carbon dots.

[0077] S3. Preparation of doped and modified bismuth ferrite-based heterojunctions by hydrothermal method:

[0078] S3-1. Take 1.8g of the carboxylated graphene oxide prepared in step S1 and add it to 100mL of deionized water. Disperse it by ultrasonication for 30min to obtain dispersion 1.

[0079] S3-2. Take 0.75g of the acousto-optic dual-response carbon dots prepared in step S2 and add them to 50mL of deionized water. Disperse them by ultrasonication for 30min to obtain dispersion 2.

[0080] S3-3. Take 2.42g of ferric nitrate, 3.95g of bismuth nitrate, and 0.451g of gadolinium hexahydrate and add them to 300mL of 15% nitric acid aqueous solution. Stir for 5min. Add dispersion 1 to the resulting mixture while stirring and keep stirring for 10min. Then add dispersion 2 while stirring continuously and sonicate for 45min. Add 25wt% ammonia water to the resulting mixture until the pH of the mixture is 8 to obtain the precursor solution.

[0081] S3-4. The obtained precursor solution was transferred to a reaction vessel and reacted at 200°C for 8 hours. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the solid product was washed sequentially with deionized water and ethanol. It was then dried under vacuum at 80°C for 6 hours to obtain a doped and modified bismuth ferrite-based heterojunction.

[0082] Example 2

[0083] A doped and modified bismuth ferrite-based heterojunction is prepared by the following steps:

[0084] S1. Preparation of carboxylated graphene oxide:

[0085] Add 1g of graphene oxide to 700mL of deionized water and stir at 5000rpm for 15min. While stirring, add 15g of sodium hydroxide and 12g of sodium chloroacetate. Then, treat with ultrasound at 850W and 45kHz for 3h. Adjust the pH to neutral with 15wt% hydrochloric acid. Then, repeatedly centrifuge and wash with water until neutral. Dry at 70℃ for 12h to obtain carboxylated graphene oxide.

[0086] S2. Preparation of acousto-optic dual-response carbon dots:

[0087] 732 mg benzoic acid, 475 mg citric acid, 411 mg 4-aminobenzoic acid, 307.5 mg tetraphenylporphyrin, 255 mg silver nitrate, and 282 mg copper nitrate were added to a mixed solution of 200 mL deionized water and 100 mL 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. After cooling to room temperature, the mixture was 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 removed and freeze-dried to obtain acousto-optic dual-response carbon dots.

[0088] S3. Preparation of doped and modified bismuth ferrite-based heterojunctions by hydrothermal method:

[0089] S3-1. Take 1.65g of the carboxylated graphene oxide prepared in step S1 and add it to 100mL of deionized water. Disperse it by ultrasonication for 30min to obtain dispersion 1.

[0090] S3-2. Take 0.7g of the acousto-optic dual-response carbon dots prepared in step S2 and add them to 50mL of deionized water. Disperse them by ultrasonication for 30min to obtain dispersion 2.

[0091] S3-3. Take 2.42g of ferric nitrate, 3.95g of bismuth nitrate, and 0.451g of gadolinium hexahydrate and add them to 300mL of 15% nitric acid aqueous solution. Stir for 5min. Add dispersion 1 to the resulting mixture while stirring and keep stirring for 10min. Then add dispersion 2 while stirring continuously and sonicate for 45min. Add 25wt% ammonia water to the resulting mixture until the pH of the mixture is 8 to obtain the precursor solution.

[0092] S3-4. The obtained precursor solution was transferred to a reaction vessel and reacted at 190°C for 8 hours. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the solid product was washed sequentially with deionized water and ethanol. It was then dried under vacuum at 80°C for 6 hours to obtain a doped and modified bismuth ferrite-based heterojunction.

[0093] Example 3

[0094] A doped and modified bismuth ferrite-based heterojunction is prepared by the following steps:

[0095] S1. Preparation of carboxylated graphene oxide:

[0096] Add 1g of graphene oxide to 700mL of deionized water and stir at 5000rpm for 15min. While stirring, add 15g of sodium hydroxide and 12g of sodium chloroacetate. Then, treat with ultrasound at 850W and 45kHz for 3h. Adjust the pH to neutral with 15wt% hydrochloric acid. Then, repeatedly centrifuge and wash with water until neutral. Dry at 70℃ for 12h to obtain carboxylated graphene oxide.

[0097] S2. Preparation of acousto-optic dual-response carbon dots:

[0098] 732 mg benzoic acid, 475 mg citric acid, 411 mg 4-aminobenzoic acid, 307.5 mg tetraphenylporphyrin, 255 mg silver nitrate, and 282 mg copper nitrate were added to a mixed solution of 200 mL deionized water and 100 mL 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. After cooling to room temperature, the mixture was 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 removed and freeze-dried to obtain acousto-optic dual-response carbon dots.

[0099] S3. Preparation of doped and modified bismuth ferrite-based heterojunctions by hydrothermal method:

[0100] S3-1. Take 1.9g of the carboxylated graphene oxide prepared in step S1 and add it to 100mL of deionized water. Disperse it by ultrasonication for 30min to obtain dispersion 1.

[0101] S3-2. Take 0.8g of the acousto-optic dual-response carbon dots prepared in step S2 and add them to 50mL of deionized water. Disperse them by ultrasonication for 30min to obtain dispersion 2.

[0102] S3-3. Take 2.42g of ferric nitrate, 3.95g of bismuth nitrate, and 0.451g of gadolinium hexahydrate and add them to 300mL of 15% nitric acid aqueous solution. Stir for 5min. Add dispersion 1 to the resulting mixture while stirring and keep stirring for 10min. Then add dispersion 2 while stirring continuously and sonicate for 45min. Add 25wt% ammonia water to the resulting mixture until the pH of the mixture is 8 to obtain the precursor solution.

[0103] S3-4. The obtained precursor solution was transferred to a reaction vessel and reacted at 210°C for 6 hours. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the solid product was washed sequentially with deionized water and ethanol. It was then dried under vacuum at 80°C for 6 hours to obtain a doped and modified bismuth ferrite-based heterojunction.

[0104] Comparative Example 1

[0105] A doped and modified bismuth ferrite-based heterojunction is prepared by the following steps:

[0106] S1. Preparation of carboxylated graphene oxide, same as in Example 1;

[0107] S2. Preparation of doped and modified bismuth ferrite-based heterojunctions by hydrothermal method:

[0108] S2-1. Take 1.8g of the carboxylated graphene oxide prepared in step S1 and add it to 100mL of deionized water. Disperse it by ultrasonication for 30min to obtain dispersion 1.

[0109] S2-2. Take 2.42g of ferric nitrate, 3.95g of bismuth nitrate, and 0.451g of gadolinium hexahydrate and add them to 300mL of 15% nitric acid aqueous solution. Stir for 5min. Add dispersion 1 to the resulting mixture while stirring. Keep stirring for 10min and sonicate for 45min. Add 25wt% ammonia water to the resulting mixture until the pH of the mixture is 8 to obtain the precursor solution.

[0110] S2-3. The obtained precursor solution was transferred to a reaction vessel and reacted at 200℃ for 8 hours. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the solid product was washed with deionized water and ethanol in sequence. It was then dried under vacuum at 80℃ for 6 hours to obtain a doped and modified bismuth ferrite-based heterojunction.

[0111] Comparative Example 2

[0112] A doped and modified bismuth ferrite-based heterojunction is prepared by the following steps:

[0113] S1. Preparation of carboxylated graphene oxide, same as in Example 1;

[0114] S2. Preparation of acousto-optic dual-response carbon dots:

[0115] 732 mg benzoic acid, 475 mg citric acid, 411 mg 4-aminobenzoic acid, 307.5 mg tetraphenylporphyrin, and 282 mg copper nitrate were added to a mixed solution of 200 mL deionized water and 100 mL 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. After cooling to room temperature, the mixture was 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 removed and freeze-dried to obtain acousto-optic dual-response carbon dots.

[0116] S3. Prepare doped modified bismuth ferrite-based heterojunctions by hydrothermal method, the same as in Example 1.

[0117] Comparative Example 3

[0118] A doped and modified bismuth ferrite-based heterojunction is prepared by the following steps:

[0119] S1. Preparation of carboxylated graphene oxide, same as in Example 1;

[0120] S2. Preparation of acousto-optic dual-response carbon dots:

[0121] 732 mg benzoic acid, 475 mg citric acid, 411 mg 4-aminobenzoic acid, 307.5 mg tetraphenylporphyrin, and 255 mg silver nitrate were added to a mixed solution of 200 mL deionized water and 100 mL 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. After cooling to room temperature, the mixture was 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 removed and freeze-dried to obtain acousto-optic dual-response carbon dots.

[0122] S3. Prepare doped modified bismuth ferrite-based heterojunctions by hydrothermal method, the same as in Example 1.

[0123] Comparative Example 4

[0124] A doped and modified bismuth ferrite-based heterojunction is prepared by the following steps:

[0125] S1. Preparation of carboxylated graphene oxide, same as in Example 1;

[0126] S2. Prepare acousto-optic dual-response carbon dots, the same as in Example 1;

[0127] S3. Preparation of doped and modified bismuth ferrite-based heterojunctions by hydrothermal method:

[0128] S3-1. Take 1.65g of the carboxylated graphene oxide prepared in step S1 and add it to 100mL of deionized water. Disperse it by ultrasonication for 30min to obtain dispersion 1.

[0129] S3-2. Take 0.7g of the acousto-optic dual-response carbon dots prepared in step S2 and add them to 50mL of deionized water. Disperse them by ultrasonication for 30min to obtain dispersion 2.

[0130] S3-3. Take 2.42g of ferric nitrate and 3.95g of bismuth nitrate and add them to 300mL of 15% nitric acid aqueous solution. Stir for 5min. Add dispersion 1 to the resulting mixture while stirring and keep stirring for 10min. Then add dispersion 2 while stirring continuously and sonicate for 45min. Add 25wt% ammonia water to the resulting mixture until the pH of the mixture is 8 to obtain the precursor solution.

[0131] S3-4. The obtained precursor solution was transferred to a reaction vessel and reacted at 190°C for 8 hours. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the solid product was washed sequentially with deionized water and ethanol. It was then dried under vacuum at 80°C for 6 hours to obtain a doped and modified bismuth ferrite-based heterojunction.

[0132] Comparative Example 5

[0133] A doped and modified bismuth ferrite-based heterojunction is prepared by the following steps:

[0134] S1. Preparation of carboxylated graphene oxide, same as in Example 1;

[0135] S2. Prepare acousto-optic dual-response carbon dots, the same as in Example 1;

[0136] S3. Preparation of doped and modified bismuth ferrite-based heterojunctions by hydrothermal method:

[0137] S3-1. Take 0.7g of the acousto-optic dual-response carbon dots prepared in step S2 and add them to 50mL of deionized water. Disperse them by ultrasonication for 30min to obtain dispersion 1.

[0138] S3-2. Take 2.42g of ferric nitrate, 3.95g of bismuth nitrate, and 0.451g of gadolinium hexahydrate and add them to 300mL of 15% nitric acid aqueous solution. Stir for 5min, then continue to add dispersion 1 while stirring continuously. Sonicate for 45min, and add 25wt% ammonia water to the resulting mixture until the pH of the mixture is 8 to obtain the precursor solution.

[0139] S3-3. The obtained precursor solution was transferred to a reaction vessel and reacted at 190°C for 8 hours. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the solid product was washed sequentially with deionized water and ethanol. It was then dried under vacuum at 80°C for 6 hours to obtain a doped and modified bismuth ferrite-based heterojunction.

[0140] I. Degradation Performance Test

[0141] The doped and modified bismuth ferrite-based heterojunctions prepared in Examples 1-3 and Comparative Examples 1-5 were subjected to degradation tests on organic wastewater according to the following methods.

[0142] A 200 mL solution of 50 mg / L methyl orange was used as the target degradation product to simulate organic wastewater. A doped bismuth ferrite-based heterojunction was added at a concentration of 2 g / L. After stirring for 15 min in the dark, the solution was transferred to a xenon lamp and irradiated with visible light (500 W, λ > 400 nm) while simultaneously subjected to ultrasound at a power of 400 W and a frequency of 80 kHz. Samples were taken every 5 min, and the absorbance (464 nm) of the solution was measured using a UV-Vis spectrophotometer to obtain the methyl orange concentration. The degradation rate η of methyl orange was then calculated.

[0143]

[0144] In addition, a control example was set up, which used the doped modified bismuth ferrite-based heterostructure prepared in Example 1. No ultrasonic treatment was applied during the test, and the rest was the same as above.

[0145] Test results are as follows Figure 1 (Examples 2 and 3 are not shown in the figure) The degradation rate results after 60 minutes of treatment are shown in Table 1 below:

[0146] Table 1

[0147]

[0148] The test results show that the doped and modified bismuth ferrite-based heterojunctions prepared in Examples 1-3 can achieve efficient degradation of methyl orange under the combined action of acousto-optic and acoustic effects. In the control examples, no ultrasound was applied, resulting in a significant decrease in degradation efficiency. In Comparative Example 1, the lack of doped acousto-optic dual-response carbon dots led to a substantial decrease in degradation ability. The decrease in degradation rate in Comparative Examples 2 and 3 indicates the role of silver and copper doping in the carbon dots. The decrease in degradation rate in Comparative Example 4 is attributed to the lack of gadolinium doping in the bismuth ferrite-based heterojunction. The decrease in degradation rate in Comparative Example 5 is due to the lack of carboxylated graphene oxide doping in the system.

[0149] II. Performance Characterization

[0150] 1. Reference Figure 2 The image shows the infrared spectrum of the acousto-optic dual-response carbon dots synthesized in Example 1. It can be seen that the surface of these carbon dots contains abundant functional groups such as amino, carboxyl, and hydroxyl groups. (748 cm⁻¹) -1 The peak at that position originates from the absorption peak of =CH on the pyrrole ring, combined with the stretching vibration peak of the Ag-O bond (505 cm⁻¹). -1Nearby, the tensile vibration peak of the Cu-O bond (440 cm⁻¹) -1 The presence of carbon dots (nearby) indicates the successful synthesis of this carbon dot.

[0151] 2. Singlet oxygen production capacity detection

[0152] Carbon dot solutions with a concentration of 0.1 mg / mL were prepared using the carbon dots synthesized in Example 1 and Comparative Examples 2-3, respectively. Then, the singlet oxygen content in the carbon dot solutions at different times was detected under the following test conditions using a singlet oxygen green fluorescent probe (SOSG, catalog number: KM0040, Beijing Bio-Lab Technology Co., Ltd.).

[0153] (1) Visible light irradiation (power 500W, λ>400nm) and simultaneous ultrasound (ultrasound power 400W, ultrasound frequency 80kHz) were applied to test the singlet oxygen content of the carbon dots synthesized in Example 1 and Comparative Examples 2-3 at different times; Example 1 was denoted as AgCu-CDs-1(HV+US), and Comparative Examples 2-3 were denoted as CDs-2(HV+US) and CDs-3(HV+US) respectively.

[0154] (2) Under visible light irradiation (power 500W, λ>400nm), the singlet oxygen content generated by the carbon dots synthesized in Example 1 at different times was tested and recorded as AgCu-CDs-1 (HV).

[0155] Test results as follows Figure 3 As shown, it can be seen that for the carbon dots prepared in Example 1, applying ultrasound can generate 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) indicate that the doping of Ag and Cu in the carbon dots is beneficial to improving the singlet oxygen yield of the carbon dots.

[0156] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details.

Claims

1. A doped and modified bismuth ferrite-based heterojunction, characterized in that, It is prepared through the following steps: S1. Preparation of carboxylated graphene oxide, specifically: Add graphene oxide to deionized water and stir. While stirring, add sodium hydroxide and sodium chloroacetate. Then treat under ultrasonication for 1.5-6 hours. Adjust the pH to neutral with hydrochloric acid. Then repeatedly centrifuge and wash with water until neutral. Dry to obtain carboxylated graphene oxide. S2. Preparation of acousto-optic dual-response carbon dots, specifically: Benzoic acid, 4-aminobenzoic acid, tetraphenylporphyrin, silver nitrate, and copper nitrate were added to a hot aqueous ethanol solution and ultrasonically dispersed. The resulting mixture was transferred to a reaction vessel and reacted under heating. After the reaction was completed, the mixture was cooled to room temperature and filtered through a filter membrane. The filtrate was dialyzed in deionized water using a dialysis bag. The dialysate in the dialysis bag was freeze-dried to obtain acousto-optic dual-response carbon dots. S3. Preparation of doped and modified bismuth ferrite-based heterojunctions by hydrothermal method, specifically: S3-1. Take the carboxylated graphene oxide prepared in step S1 and add it to deionized water, then disperse it by ultrasonication to obtain dispersion 1. S3-2. Take the acousto-optic dual-response carbon dots prepared in step S2, add them to deionized water, and disperse them by ultrasonication to obtain dispersion 2. S3-3. Add ferric nitrate, bismuth nitrate, and gadolinium hexahydrate to an aqueous nitric acid solution and stir for 2-15 minutes. While stirring, add dispersion 1 to the resulting mixture and continue stirring for 2-15 minutes. Then, while continuing to stir, add dispersion 2 and sonicate. Add ammonia dropwise to the resulting mixture until the pH of the mixture is 7.5-8.5 to obtain the precursor solution. S3-4. Transfer the obtained precursor solution to a reaction vessel and react at 190-210℃ for 6-16 hours. After the reaction is completed, cool to room temperature, filter, wash the solid product with deionized water and ethanol in sequence, and dry under vacuum to obtain a doped modified bismuth ferrite-based heterojunction.

2. The doped and modified bismuth ferrite-based heterojunction according to claim 1, characterized in that, Step S1 is as follows: Add 0.5-2g of graphene oxide to 500-1000mL of deionized water and stir at 1000-8000rpm for 5-30min. While stirring, add 7.5-30g of sodium hydroxide and 6-24g of sodium chloroacetate. Then treat under sonication for 1.5-6h. Adjust the pH to neutral with hydrochloric acid, then repeatedly centrifuge and wash with water until neutral. Dry at 60-90℃ for 6-24h to obtain carboxylated graphene oxide.

3. The doped and modified bismuth ferrite-based heterojunction according to claim 1, characterized in that, Step S2 is as follows: Take 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 and add them to an ethanol-water solution consisting of 100-400 mL of deionized water and 50-200 mL of ethanol at 50-70℃. Disperse the mixture ultrasonically for 15-60 min. Transfer the resulting mixture to a reaction vessel lined with polytetrafluoroethylene and react at 170-205℃ for 6-18 h. Cool to room temperature and filter with a 0.22 μm filter membrane. Dialyze the filtrate in deionized water for 6-27 h using a dialysis bag with a molecular weight cutoff of 1000-2000 Da. Take the dialysate in the dialysis bag and freeze-dry it to obtain acousto-optic dual-response carbon dots.

4. The doped and modified bismuth ferrite-based heterojunction according to claim 1, characterized in that, Step S3 is as follows: S3-1. Take 0.9-3.6g of the carboxylated graphene oxide prepared in step S1 and add it to 50-200mL of deionized water. Disperse it ultrasonically for 15-60min to obtain dispersion 1. S3-2. Take 0.35-1.5g of the acousto-optic dual-response carbon dots prepared in step S2 and add them to 50-200mL of deionized water. Disperse them ultrasonically for 15-60min to obtain dispersion 2. S3-3: Take 1.21-4.84g of ferric nitrate, 1.975-7.9g of bismuth nitrate, and 0.2255-0.902g of gadolinium hexahydrate and add them to 150-600mL of nitric acid aqueous solution with a mass concentration of 10-20%. Stir for 2-15min. Add dispersion 1 to the resulting mixture while stirring, and continue stirring for 2-15min. Then, continue to add dispersion 2 while stirring continuously. Sonicate and disperse for 30-90min. Add 20-25wt% ammonia water to the resulting mixture until the pH value of the mixture is 7.5-8.5 to obtain the precursor solution. S3-4. Transfer the obtained precursor solution to a reaction vessel and react at 190-210℃ for 6-16 hours. After the reaction is completed, cool to room temperature, filter, wash the solid product with deionized water and ethanol in sequence, and dry under vacuum at 70-90℃ for 4-12 hours to obtain a doped modified bismuth ferrite-based heterojunction.

5. The application of a doped and modified bismuth ferrite-based heterojunction as described in any one of claims 1-4 in the photocatalytic degradation of organic wastewater.

6. The application according to claim 5, characterized in that, The application method is as follows: the doped and modified bismuth ferrite-based heterojunction is added to the organic wastewater, and then the organic wastewater is degraded under the combined action of visible light irradiation and ultrasound.

7. The application according to claim 6, characterized in that, The application method is as follows: add the doped and modified bismuth ferrite-based heterojunction into the organic wastewater, control the concentration of the doped and modified bismuth ferrite-based heterojunction in the organic wastewater to be 0.2-5 g / L, stir for 5-30 min, and then treat for 10-90 min under visible light irradiation and ultrasonic assistance. The ultrasonic power ranges from 50 to 500W, and the ultrasonic frequency ranges from 30 to 100kHz.

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