A kind of microplastic-based ferroferric oxide / manganese dioxide magnetic core-shell composite material and its preparation method and application

Abstract

This invention belongs to the field of environmental functional materials and waste resource utilization technology, specifically disclosing a magnetic core-shell composite material based on microplastics, including an iron(III) oxide / manganese(II) oxide composite material, its preparation method, and its applications. Addressing the problems of traditional inorganic carriers' tendency to sink and difficulty in contacting upper-middle-layer pollutants, and the poor interfacial bonding and easy peeling of organic carriers with inorganic components, this invention mixes and stirs an iron salt with a microplastic suspension to load iron ions onto the microplastic surface. Iron(III) oxide is then generated through in-situ co-precipitation nucleation, followed by the construction of a porous manganese(II) oxide shell using a hydrothermal method, resulting in the core-shell composite material. This invention utilizes the low-density characteristics of waste microplastics, enabling the material to float or suspend in the upper layers of water, increasing the efficiency of contact and reaction with pollutants, while also endowing the product with adsorption-catalytic activity and magnetic separation function. This invention is mainly applied in environmental remediation fields such as wastewater treatment.

Description

Technical Field

[0001] This invention belongs to the field of environmental functional materials and waste resource utilization technology, specifically relating to a magnetic core-shell composite material based on microplastics, including its preparation method and application. Background Technology

[0002] Microplastics (MPs) generally refer to plastic fibers, particles, or films with a diameter of less than 5 mm in the environment. Microplastic pollution is ubiquitous in the daily environment, and due to their low density and strong hydrophobicity, they easily float and remain suspended in the upper and middle layers and on the surface of water bodies for extended periods, acting as ideal attachment sites for hydrophobic organic matter and heavy metals, threatening ecological security and human health. Therefore, achieving efficient removal and resource recycling of microplastics floating in the upper and middle layers of water bodies is of great significance.

[0003] Manganese dioxide, a strong natural oxidant, is commonly used in environmental remediation processes. However, it is prone to decreased catalytic efficiency after reaction due to reduced surface area and burying of active sites. While introducing iron oxide (Fe3O4) can increase specific surface area and impart magnetic separation properties to the material, existing preparation processes often rely on purchasing ready-made inorganic nanoparticles and physically agitating them to adhere to the carrier surface. Catalysts prepared by these methods generally have a significantly higher density than water in their inorganic components, making them prone to self-sinking and accumulating in large quantities at the bottom of the reactor in actual wastewater treatment. Because they are difficult to react fully with suspended microplastics and non-polar organic pollutants that commonly float or float on the surface of water, continuous, energy-intensive, and forceful mechanical agitation is usually required to maintain their suspension, significantly increasing the operating costs of water treatment.

[0004] Furthermore, when attempting to directly modify non-polar polymeric waste microplastics collected from water bodies using them as the core framework, the low interfacial affinity between organic polymers and inorganic magnetic components makes traditional physical mixing and attachment processes prone to weak bonding. The shell layer is easily peeled off and broken under the hydraulic scouring of actual wastewater treatment, leading to a rapid loss of catalytic activity and magnetic response efficiency. Therefore, constructing a magnetic core-shell composite material that combines excellent adsorption and catalytic activity, high bonding strength, and adaptability to the surface pollution distribution characteristics of waste microplastics is a key challenge for achieving high-efficiency, low-energy-consumption solid waste resource recovery. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a magnetic core-shell composite material based on microplastics, including its preparation method and application.

[0006] The purpose of this invention is specifically reflected in the following three aspects: 1. A technical approach is provided for the resource utilization of waste microplastics and the reduction of water treatment stirring energy consumption. By utilizing the natural suspension characteristics of microplastics, the technical defects of traditional inorganic catalysts, which require continuous mechanical stirring to maintain suspension due to their high density and self-sinking, are solved. 2. A method for improving the bonding strength of organic-inorganic composite interfaces is provided, which utilizes stepwise in-situ chemical reactions to construct a robust core-shell structure on the surface of microplastics, thereby solving the technical problems of weak bonding between magnetic components and microplastics and easy detachment and breakage of the shell under water scouring. 3. Develop a multifunctional core-shell composite material that combines catalytic degradation and magnetic separation properties. Utilize the synergistic effect of iron tetroxide and manganese dioxide on the carrier to improve the degradation efficiency of pollutants, and achieve solid-liquid magnetic separation and efficient recovery under conventional conditions by applying an external magnetic field.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: 1. A magnetic core-shell composite material based on microplastics (Fe3O4 / Mn2O4), its preparation method, and its application, characterized by comprising the following steps: (1) Preparation of microplastic suspension: Disperse microplastic powder in deionized water and sonicate for 10-30 minutes to obtain a uniform suspension; (2) Iron source surface modification and loading: Add iron salt or its solution to the microplastic suspension and stir for 1-3 hours; (3) Coprecipitation in-situ nucleation reaction: Ammonia water is added dropwise to the system obtained in step (2) as an alkaline solution to adjust the pH of the system to 9. The reaction is carried out at 70-90℃ for 6-12 hours to generate Fe3O4 nanoparticles in-situ on the surface of the microplastics, forming a preliminary coated core-shell structure. After the reaction, solid-liquid separation is carried out. The solid is washed 1-3 times with deionized water and anhydrous ethanol and dried at 60℃ for 6-12 hours to obtain the microplastic@Fe3O4 preliminary core-shell material. (4) Hydrothermal construction of manganese dioxide shell: The microplastic@iron tetroxide core-shell material and potassium permanganate were added to deionized water, and a 37% hydrochloric acid solution was slowly added dropwise. After mixing evenly, the mixture was transferred to a reaction vessel and subjected to hydrothermal reaction at 90-130℃ for 6-24 hours. After the reaction, solid-liquid separation was performed, and the solid was washed 1-3 times with deionized water and anhydrous ethanol. The solid was dried at 60℃ for 6-12 hours to obtain microplastic@iron tetroxide / manganese dioxide magnetic core-shell composite material.

[0008] Furthermore, the microplastic particles have a particle size ranging from 0.4 μm to 4 mm and are made of polyethylene (PE).

[0009] Furthermore, the iron salt is a mixture of ferric chloride and ferrous chloride, and the concentration of the iron salt solution is 0.1-1 mol / L.

[0010] Furthermore, the concentration of ammonia in step (3) is 10-25%.

[0011] Furthermore, the mass ratio of the iron salt to the microplastics is 3.3-4.5:1.

[0012] Furthermore, the mass ratio of potassium permanganate to the microplastic@ferric oxide preliminary core-shell material is 0.7-0.9:1.

[0013] Furthermore, the solid-liquid separation in steps (3) and (4) is carried out by vacuum filtration or centrifugation.

[0014] Another object of the present invention is to provide a microplastic@iron tetroxide / manganese dioxide magnetic core-shell composite material prepared by the preparation method described in any one of the preceding claims.

[0015] Another object of the present invention is to provide the application of the microplastic@iron tetroxide / manganese dioxide magnetic core-shell composite material in the adsorption or catalytic degradation of water pollutants, wastewater treatment and solid-liquid magnetic separation and recovery. Attached Figure Description

[0016] Figure 1 Scanning electron microscope (SEM) images of microplastics, microplastics@Fe3O4, and microplastics@Fe3O4 / Mn2O4, where a is microplastic (PE), b is microplastics@Fe3O4, and c is microplastics@Fe3O4 / Mn2O4. Figure 2 This is the Fourier transform infrared (FTIR) spectrum of the composite material prepared in Example 1 of this invention; Figure 3 This is a comparison diagram of the degradation performance of the composite material prepared in Example 1 of the present invention and the comparative material on tetracycline solution; Figure 4 This is a vibrational magnetic signature (VSM) spectrum of the composite material prepared in Example 1 of this invention; Figure 5 This is a scanning electron microscope image of the composite material sample prepared in Example 1 of the present invention after a cyclic experiment; Figure 6 This is a magnetic display image of the composite material sample prepared in Example 1 of the present invention after a cyclic experiment. Detailed Implementation

[0017] The present invention will be described in detail below with reference to the embodiments. However, the scope of protection of the present invention is not limited to the following embodiments. Any simple changes made in accordance with the scope of the patent application and the contents of the specification of the present invention shall fall within the scope of protection of the present invention.

[0018] Example 1 In this example, the preparation steps of the microplastic@iron(II)O3 / manganese(II)O3 catalyst are as follows: (1) Weigh 1g of microplastic powder into 100ml of deionized water, sonicate for 10 minutes, then add 2.72g of ferric chloride and 1g of ferrous chloride, stir for 1 hour, so that iron ions are adsorbed on the surface of microplastics. (2) Add ammonia water dropwise to the system obtained in step (1) to adjust pH=9, react at 80℃ for 12 hours to generate Fe3O4 nanoparticles on the surface of microplastics. After the reaction, wash, filter and dry in an oven at 60℃ for 12 hours to obtain microplastics@Fe3O4. (3) Weigh 0.3g of microplastic@iron tetroxide into 35ml of deionized water, add 0.25g of potassium permanganate, and then slowly add 0.9ml of hydrochloric acid solution with a mass fraction of 37%. After mixing evenly, transfer to the reaction vessel and hydrothermally react at 110℃ for 9 hours. (4) After the reaction is completed, solid-liquid separation is performed, and the product is washed and dried to obtain the microplastic@iron tetroxide / manganese dioxide magnetic core-shell composite material; wherein the composite material has a microplastic core and a composite shell formed by Fe3O4 and MnO2 sequentially wrapped on the surface.

[0019] After preparation, the above materials were characterized in terms of morphology and properties, and the test and analysis results are as follows: Figures 1-4 As shown.

[0020] Figure 1 a is a SEM image of microplastics (PE); Figure 1 b is the SEM image of the microplastic@Fe3O4; Figure 1 Figure c shows the SEM image of the microplastic@Fe3O4 / Mn2O4. As can be seen from the figure, the initial polyethylene (PE) core is smooth and spherical (Figure a), while the surface becomes rough after loading Fe3O4 (Figure b), which intuitively confirms the initial formation of the core-shell structure. Figure c shows that the final composite material surface forms a flower-like porous structure, which is a typical morphology of δ-MnO2. Its high specific surface area is beneficial to the subsequent catalytic reaction. Figure 2 It can be seen that the MPs@Fe3O4 / MnO2 sample simultaneously exhibits the -CH2 and CC characteristic peaks of MPs and the 573 cm⁻¹ peak of Fe3O4. -1 Fe-O characteristic peaks and MnO2 at 502 cm⁻¹ -1 The characteristic peaks of Mn-O indicate that the MPs@Fe3O4 / MnO2 magnetic core-shell material was successfully prepared.

[0021] Example 2: The MPs@Fe3O4 / MnO2 prepared in Example 1, along with the materials from each control group, were added to a 20 mg / L tetracycline solution. The concentration of each material added was 0.3 g / L. Then, 3 ml of 10% hydrogen peroxide was added, and the reaction was allowed to proceed for 48 h. Samples were taken at 0.5, 1, 2, 3, 4, 6, 9, 24, and 48 hours to calculate the degradation rate of the tetracycline solution. The experimental results are as follows: Figure 3 As shown, MPs@Fe3O4 / MnO2 effectively improves the degradation rate and exhibits good degradation performance on the target compound. This composite material achieves a 98% degradation rate for tetracycline within 48 hours. However, the degradation performance of MPs, MnO2, and MPs@Fe3O4 is significantly inferior to that of MPs@Fe3O4 / MnO2. This is because the core-shell structure formed by Fe3O4 and MnO2 on the MPs support produces a synergistic effect, which cannot be achieved by MPs, MnO2, or Fe3O4 alone. Furthermore, the degradation processes of different systems are as follows... Figure 3 As shown, the degradation rate of MnO2 was relatively fast in the early stage of the reaction (0-10h), but the degradation rate and final degradation rate of the MPs@Fe3O4 / MnO2 system were significantly higher in the later stage. This is because the core-shell structure of MPs@Fe3O4 / MnO2 not only retains the active sites of the catalyst, but also improves the reaction efficiency through the dispersion effect of the support, thus achieving synergistic effect.

[0022] Example 3 Figure 4 The image shows the vibrational sample magnetometer (VSM) spectrum. While the saturation magnetization (Ms) of MPs@Fe3O4 / MnO2 decreased to 22 emu / g compared to MPs@Fe3O4 (35 emu / g), it is still significantly higher than the paramagnetic threshold (<5 emu / g). This magnetic intensity is sufficient to drive rapid separation—under a conventional magnetic field gradient (∇H ~ 104 Oe / cm), the magnetic force (F∝Ms·∇H) for particle migration meets the kinetic requirements of second-level solid-liquid separation in wastewater treatment. The slope of its low-to-mid-range (0-104 Oe) magnetization curve also confirms its rapid magnetic response capability: even with MnO2 coating, the domain flipping resistance of the Fe3O4 core is extremely small, ensuring that particle separation is triggered instantaneously upon application of the magnetic field. Meanwhile, the regular decrease in magnetic moment and the smooth and continuous magnetization curve provide double evidence: the former is consistent with the expectation of the dilution of magnetic moment in the non-magnetic MnO2 shell, and the latter indirectly proves the uniformity of the coating, which together support the successful construction of the core-shell structure.

[0023] Example 4 Figure 5 Scanning electron microscopy (SEM) images showed that the catalyst after the reaction maintained its complete spherical morphology, with no signs of breakage or etching. This morphological evidence directly confirms the good structural stability of the microplastic support itself, indicating that no decomposition occurred. Meanwhile, [the following text appears to be incomplete and requires further context: "by..."] Figure 6As shown in the magnetic field diagram, the recycled material can be completely separated from the water with an efficiency exceeding 99%. Therefore, this system fundamentally eliminates the risk of secondary pollution from microplastics.

[0024] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, all technical solutions obtained through equivalent substitution or transformation fall within the protection scope of the present invention.

Claims

1. A magnetic core-shell composite material based on microplastics (Fe3O4 / Mn2O4), its preparation method, and its application, characterized in that, Includes the following steps: Preparation of microplastic suspension: Disperse microplastic powder in deionized water and sonicate for 10-30 minutes to obtain a uniform suspension; Iron source surface modification and loading: Add iron salt or its solution to the microplastic suspension and stir for 1-3 hours; Coprecipitation in-situ nucleation reaction: Ammonia water was added dropwise at a uniform rate to the system obtained in step (2) as an alkaline solution to adjust the pH of the system to 9. The reaction was carried out at 70-90℃ for 6-12 hours to generate Fe3O4 nanoparticles in situ on the surface of the microplastics, forming a preliminary coated core-shell structure. After the reaction, solid-liquid separation was carried out, and the solid was washed 1-3 times with deionized water and anhydrous ethanol. It was then dried at 60℃ for 6-12 hours to obtain the microplastic@Fe3O4 preliminary core-shell material. Hydrothermal construction of manganese dioxide shell: The microplastic@iron tetroxide core-shell material and potassium permanganate were added to deionized water, and a 37% hydrochloric acid solution was slowly added dropwise. After mixing evenly, the mixture was transferred to a reaction vessel and subjected to hydrothermal reaction at 90-130℃ for 6-24 hours. After the reaction, solid-liquid separation was performed, and the solid was washed 1-3 times with deionized water and anhydrous ethanol. The solid was then dried at 60℃ for 6-12 hours to obtain the microplastic@iron tetroxide / manganese dioxide magnetic core-shell composite material.

2. The preparation method according to claim 1, characterized in that: The microplastic particles have a particle size ranging from 0.4 μm to 4 mm and are made of polyethylene (PE).

3. The preparation method according to claim 1, characterized in that: The iron salt is a mixture of ferric chloride and ferrous chloride, and the concentration of the iron salt solution is 0.1-1 mol / L.

4. The preparation method according to claim 1, characterized in that: The concentration of ammonia in step (3) is 10-25%.

5. The preparation method according to claim 1, characterized in that: In step (2), the mass ratio of the iron salt to the microplastic is 3.3-4.5:1; in step (4), the mass ratio of the potassium permanganate to the microplastic@ferric oxide preliminary core-shell material is 0.7-0.9:

1.

6. The preparation method according to claim 1, characterized in that: The solid-liquid separation in steps (3) and (4) is performed by vacuum filtration or centrifugation.

7. The microplastic@iron(II)O3 / manganese(II)O3 magnetic core-shell composite material prepared by the preparation method according to any one of claims 1-6.

8. The application of the microplastic@iron tetroxide / manganese dioxide magnetic core-shell composite material according to claim 7 in the adsorption or catalytic degradation of water pollutants, wastewater treatment and solid-liquid magnetic separation and recovery.

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