A composite material for degrading microplastics and a method of making the same

Abstract

This application relates to a composite material for degrading microplastics and its preparation method. The composite material is La-BiFeO3 / AgNPs, and its preparation method includes the following steps: dissolving Bi source, Fe source, La source, and tartaric acid in an ethylene glycol-ethanol mixed solvent, stirring evenly, and then transferring the solution to a polytetrafluoroethylene high-pressure reactor for solvothermal reaction to obtain La-BiFeO3; dissolving AgNO3 and sodium citrate in deionized water to obtain a mixed solution, then dispersing La-BiFeO3 in the mixed solution, and reacting the mixed solution in a microwave reactor to obtain La-BiFeO3 / AgNPs. This application involves lanthanum doping of BiFeO3, which readily substitutes Bi sites, introducing lattice strain to enhance polarization effects. Combining BiFeO3 with nano-Ag suppresses electron-hole recombination, improves carrier lifetime, and the porous La-BiFeO3 provides abundant channels and surface areas, increasing photocatalytic active sites. La-BiFeO3 / AgNPs exhibit high efficiency in degrading microplastics as a photocatalyst.

Description

Technical Field

[0001] This invention belongs to the field of microplastic degradation, specifically relating to a composite material for degrading microplastics and its preparation method. Background Technology

[0002] Microplastics refer to plastic particles with a diameter of less than 5 mm, which can be divided into primary microplastics and secondary microplastics. They are widely present in the environment and pose a potential threat to ecology and health. The harms of microplastics are mainly reflected in the following aspects: (1) Environmental pollution: About 8 million tons of plastic enter the ocean every year, most of which degrade into microplastics, threatening the survival of marine life (such as fish, seabirds, and corals). In addition, microplastics in agricultural mulch film and sludge fertilizer change the soil structure, affecting the microbial community and crop growth; (2) Biological ingestion: Microplastics are easily ingested by plankton, shellfish, etc., and are transmitted to higher organisms such as humans through the food chain; (3) Harm to human health: Microplastics enter the respiratory system through the nasal cavity, causing respiratory diseases; or enter the digestive system through the mouth. Microplastics that enter the digestive tract with food may be transferred to other tissues and organs and become a route for the transmission of toxic chemicals.

[0003] Currently, microplastic degradation technologies mainly include biodegradation, thermal decomposition, and photocatalytic degradation. Among these, photocatalytic degradation technology has attracted much attention from researchers due to its green and environmentally friendly nature and low cost. Existing technology CN112023713A discloses a method for preparing a bifunctional oxide-carbon fiber membrane that simultaneously adsorbs and degrades microplastics. The method involves reacting an aminooxime-modified polyacrylonitrile fiber membrane (with an aminooxime group content of 0.5–15 wt%) with a metal salt at a mass ratio of 1:0.01–0.5 under hydrothermal conditions through a self-assembly reaction, followed by calcination to obtain the bifunctional oxide-carbon fiber membrane. The interwoven carbon fibers in the carbon fiber membrane form numerous pores, which can capture microplastics in the water. The highly dispersed small-sized metal oxide nanoparticles have a large specific surface area and can expose a sufficient number of active sites, which is beneficial for improving photocatalytic efficiency. CN119588353A discloses a method for degrading microplastics using a composite semiconductor photocatalyst. In the preparation process, transition metal copper powder is first mixed and dispersed with the semiconductor material titanium dioxide in anhydrous ethanol, ensuring thorough and uniform mixing of the copper powder and titanium dioxide. After filtration and drying, they are calcined together to obtain a composite semiconductor material of copper oxide and titanium dioxide. Using the composite semiconductor photocatalyst, the CuO / TiO2 composite material can efficiently degrade microplastics under visible light irradiation. Compared with traditional single semiconductor catalysts, the composite material has a wider light absorption range and significantly improved catalytic activity, thus achieving a faster degradation process. However, the photocatalysts in the aforementioned two papers still have low degradation rates for microplastics and are not suitable for the degradation and transformation of microplastics in actual water bodies. Furthermore, the preparation process is complex and difficult to industrialize. Therefore, seeking a photocatalytic composite material with a simple preparation process and high degradation performance is of great practical significance for the control of microplastic pollution. Summary of the Invention

[0004] To address the aforementioned technical problems, the purpose of this application is to develop a photocatalytic composite material with a simple preparation process, mild reaction conditions, and high degradation performance to degrade microplastics.

[0005] A method for preparing a composite material for degrading microplastics, characterized in that the composite material is La-BiFeO3 / AgNPs, and the preparation method includes the following steps:

[0006] (1) Dissolve Bi source, Fe source, La source and tartaric acid in ethylene glycol-ethanol mixed solvent, the volume ratio of ethylene glycol-ethanol is (2-3):1, and the molar ratio of Bi source, Fe source, La source and tartaric acid is 1:1:(0.05-0.1):(0.2-0.5); stir evenly, transfer to polytetrafluoroethylene high pressure reactor, solvothermal reaction, filter, and wash 1-2 times with deionized water and ethanol respectively;

[0007] (2) Dissolve AgNO3 and sodium citrate in deionized water to obtain a mixture, then disperse La-BiFeO3 in the mixture, place the mixture in a microwave reactor to react, control the microwave power to be 300-400W, and the microwave radiation time to be 10-20min; to obtain La-BiFeO3 / AgNPs.

[0008] Furthermore, the Bi source is bismuth nitrate pentahydrate, bismuth chloride, or bismuth citrate.

[0009] Furthermore, the Fe source is ferric nitrate or ferric chloride;

[0010] Furthermore, the La source is lanthanum nitrate or lanthanum chloride;

[0011] Furthermore, the solvothermal reaction temperature is 160-200℃; the reaction time is 12-24h.

[0012] Furthermore, the molar ratio of AgNO3 to sodium citrate is 1:2;

[0013] The present invention also provides a La-BiFeO3 / AgNPs composite material prepared by the above method.

[0014] This invention also provides an application of the La-BiFeO3 / Ag NPs composite material prepared by the above method in the photocatalytic degradation of microplastics.

[0015] This application has the following advantages and beneficial effects:

[0016] (1) In this invention, lanthanum doping of BiFeO3 is used to easily replace Bi sites, introduce lattice strain, enhance polarization effect, and promote photogenerated charge separation. The oxygen vacancies introduced by La doping can serve as electron trapping centers, which can excite more charge carriers under visible light and improve the degradation rate of microplastics.

[0017] (2) In this invention, nano-silver is combined with BiFeO3. The introduction of nano-Ag promotes the formation of oxygen vacancies on the surface of BiFeO3, enhances the adsorption of O2, and promotes the generation of superoxide radicals. In addition, since the Fermi level of Ag is lower than the conduction band of BiFeO3, photogenerated electrons will migrate rapidly to AgNPs, while holes remain in the valence band of BiFeO3, thereby inhibiting electron-hole recombination and improving carrier lifetime.

[0018] (3) The porous structure of La-BiFeO3 provides abundant pores and surface, increases photocatalytic active sites, and promotes the adsorption and interfacial reaction of microplastics; nanoscale microplastics can enter the interior of the pores and fully contact the catalyst, shortening the diffusion path of the degradation reaction.

[0019] (4) The composite material preparation process of the present invention is simple, the conditions are mild, there is no environmental pollution, and it is easy to apply to industrial production. Attached Figure Description

[0020] Figure 1 The images shown are SEM and TEM images of La-BiFeO3 / AgNPs from this application.

[0021] Figure 2 These are characterization diagrams of the degradation performance of microplastic polystyrene in Examples 1-3 and Comparative Examples 1-2 of this application.

[0022] Figure 3 These are characterization graphs of the degradation performance of microplastic polyethylene in Examples 1-3 and Comparative Examples 1-2 of this application. Detailed Implementation

[0023] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0024] Example 1

[0025] A method for preparing a composite material for degrading microplastics, comprising the following steps:

[0026] (1) Dissolve 4.85g bismuth nitrate pentahydrate, 2.41g ferric nitrate, 0.16g lanthanum nitrate and 0.45g tartaric acid in 80ml ethylene glycol-ethanol mixed solvent with a volume ratio of 3:1; stir evenly, transfer to a polytetrafluoroethylene high-pressure reactor, react at 180℃ for 12h in a solvothermal environment, filter, and wash twice with deionized water and ethanol respectively.

[0027] (2) Dissolve 0.85g of AgNO3 and 2.58g of sodium citrate in 50ml of deionized water to obtain a mixture. Then disperse La-BiFeO3 in the mixture and place the mixture in a microwave reactor to react. Control the ultrasonic power to 300W and the microwave radiation time to 20min to obtain La-BiFeO3 / AgNPs.

[0028] Example 2

[0029] A method for preparing a composite material for degrading microplastics, comprising the following steps:

[0030] (1) Dissolve 4.85g bismuth nitrate pentahydrate, 2.41g ferric nitrate, 0.16g lanthanum nitrate and 0.45g tartaric acid in 80ml ethylene glycol-ethanol mixed solvent; the volume ratio of ethylene glycol to ethanol is 3:1; stir evenly, transfer to a polytetrafluoroethylene high-pressure reactor, react at 180℃ for 12h in a solvothermal environment, filter, and wash twice with deionized water and ethanol respectively;

[0031] (2) Dissolve 0.85g of AgNO3 and 2.58g of sodium citrate in 50ml of deionized water to obtain a mixture. Then disperse La-BiFeO3 in the mixture and place the mixture in a microwave reactor to react. Control the ultrasonic power to 400W and the microwave radiation time to 10min; obtain La-BiFeO3 / AgNPs.

[0032] Example 3

[0033] A method for preparing a composite material for degrading microplastics, comprising the following steps:

[0034] (1) Dissolve 4.85g bismuth nitrate pentahydrate, 2.41g ferric nitrate, 0.16g lanthanum nitrate and 0.45g tartaric acid in 60ml ethylene glycol-ethanol mixed solvent, with a volume ratio of ethylene glycol-ethanol of 2:1; stir evenly, transfer to a polytetrafluoroethylene high-pressure reactor, react at 190℃ for 12h in a solvothermal environment, filter, and wash once with deionized water and once with ethanol respectively;

[0035] (2) Dissolve 0.85g of AgNO3 and 2.58g of sodium citrate in 50ml of deionized water to obtain a mixture. Then disperse La-BiFeO3 in the mixture and place the mixture in a microwave reactor to react. Control the microwave power to be 400W and the microwave radiation time to be 10min; obtain La-BiFeO3 / AgNPs.

[0036] Comparative Example 1

[0037] (1) Add 4.85g of bismuth nitrate pentahydrate, 2.41g of ferric nitrate and 0.45g of tartaric acid to a solution dissolved in 80ml of ethylene glycol-ethanol mixed solvent; the volume ratio of ethylene glycol to ethanol is 3:1; stir evenly, transfer to a polytetrafluoroethylene high-pressure reactor, react at 180℃ for 12h in a solvothermal environment, filter, and wash once with deionized water and once with ethanol respectively;

[0038] (2) Dissolve 0.85g of AgNO3 and 2.58g of sodium citrate in 50ml of deionized water to obtain a mixture. Then disperse La-BiFeO3 in the mixture and place the mixture in a microwave reactor to react. Control the ultrasonic power to be 300W and the microwave radiation time to be 20min; obtain BiFeO3 / Ag NPs.

[0039] Comparative Example 2

[0040] 4.85 g of bismuth nitrate pentahydrate, 2.41 g of ferric nitrate, 0.16 g of lanthanum nitrate, and 0.45 g of tartaric acid were dissolved in 80 ml of a mixed solvent of ethylene glycol and ethanol (volume ratio of ethylene glycol to ethanol: 3:1). The mixture was stirred until homogeneous and then transferred to a polytetrafluoroethylene high-pressure reactor. The reactor was subjected to a solvothermal reaction at 180 °C for 12 h. The mixture was then filtered and washed once with deionized water and once with ethanol, respectively, to obtain La-BiFeO3.

[0041] Figure 1 The images show SEM and TEM images of the La-BiFeO3 / Ag NPs composite material prepared in Example 1. It can be seen that the La-BiFeO3 / Ag NPs exhibit a micron-sized porous spherical structure, with nano-Ag particles uniformly dispersed on the La-BiFeO3 surface. This porous spherical structure provides abundant channels and surface area, increasing photocatalytic active sites and promoting the adsorption of microplastics and interfacial reactions. The nano-sized microplastics can penetrate into the pores, ensuring sufficient contact with the catalyst and shortening the diffusion path of the degradation reaction.

[0042] The microplastic degradation performance of the catalytic materials in Examples 1-3 and Comparative Examples 1-2 was studied.

[0043] Polystyrene and polyethylene microplastics with an average particle size of 0.5-1 mm were used as degradation targets. Under the reaction conditions of 25℃, 50 mg of catalyst and 20 mg of microplastics were dispersed in 50 mL of water and stirred continuously. The photodegradation experiment was carried out by irradiation with a 300 W xenon lamp as a visible light source. The degradation rate of polystyrene and polyethylene microplastics was tested after 12 h.

[0044] from Figure 2-3 It can be seen that the degradation rates of polystyrene and polyethylene microplastics by the catalytic materials in Examples 1-3 are significantly higher than those in Comparative Examples 1-2. Examples 1 and Comparative Example 1 can fully demonstrate that La doping can effectively improve the photocatalytic degradation rate. The main reason is that lanthanum doping introduces lattice strain, which enhances the polarization effect and promotes the separation of photogenerated charges. In addition, the oxygen vacancies introduced by La doping can serve as electron trapping centers, which can excite more charge carriers under visible light and improve the degradation rate of microplastics. As shown in Example 1 and Comparative Example 2, the degradation performance of plastics is further improved after La-BiFeO3 and nano-Ag are combined. The reasons are as follows: the reaction process of La-BiFeO3 and nano-Ag forms a heterojunction structure. The introduction of nano-Ag promotes the formation of oxygen vacancies on the surface of BiFeO3, enhances the adsorption of O2, and promotes the generation of superoxide radicals. In addition, since the Fermi level of Ag is lower than the conduction band of BiFeO3, photogenerated electrons will migrate rapidly to Ag NPs, while holes remain in the valence band of BiFeO3, thereby inhibiting electron-hole recombination, improving carrier lifetime, and thus improving the photocatalytic degradation performance of microplastics.

[0045] Specific embodiments have been used to illustrate the principles and implementation methods of this invention. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of this invention. At the same time, for those skilled in the art, there will be changes in the scope of specific implementation methods based on the ideas of this invention. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. The application of a micron-porous spherical La-BiFeO3 / Ag NPs composite material in the degradation of microplastics, characterized in that, The method for preparing this composite material includes the following steps: (1) Add Bi source, Fe source, La source and tartaric acid to a mixed solvent of ethylene glycol-ethanol, the volume ratio of ethylene glycol-ethanol is (2-3):1, and the molar ratio of Bi source, Fe source, La source and tartaric acid is 1:1:(0.05-0.1):(0.2-0.5); stir evenly, transfer to a polytetrafluoroethylene high-pressure reactor, solvothermal reaction, filter, wash with deionized water and ethanol 1-2 times respectively; the solvothermal reaction temperature is 160-200℃; the reaction time is 12-24h; (2) AgNO3 and sodium citrate were dissolved in deionized water to obtain a mixture. Then, La-BiFeO3 was dispersed in the mixture. The mixture was placed in a microwave reactor and reacted. The microwave power was controlled at 300-400W and the microwave irradiation time was 10-20min. La-BiFeO3 / Ag NPs were obtained. The porous structure provides abundant pores and surface, increases photocatalytic active sites, promotes the adsorption and interfacial reaction of microplastics, and shortens the diffusion path of degradation reaction.

2. The application of the micron-porous spherical La-BiFeO3 / Ag NPs composite material according to claim 1 in the degradation of microplastics, wherein the Bi source is bismuth nitrate pentahydrate, bismuth chloride, or bismuth citrate.

3. The application of the micron-porous spherical La-BiFeO3 / Ag NPs composite material according to claim 1 in the degradation of microplastics, wherein the Fe source is ferric nitrate or ferric chloride.

4. The application of the micron-porous spherical La-BiFeO3 / Ag NPs composite material according to claim 1 in the degradation of microplastics, wherein the La source is lanthanum nitrate or lanthanum chloride.

5. The application of the micron-porous spherical La-BiFeO3 / Ag NPs composite material according to claim 1 in the degradation of microplastics, wherein the molar ratio of AgNO3 to sodium citrate is 1:2.

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