Preparation method and application of a magnetic bifunctional modified graphene oxide composite material

Abstract

The application discloses a preparation method and application of a magnetic bifunctional modified graphene oxide composite material. The material is prepared by sequentially performing the following steps on graphene oxide: p-phenylenediamine-mediated surface positive modification (amino functional group is introduced), ascorbic acid-induced mild reduction (hydrophobicity and pi-pi interaction are restored), and magnetic loading by a chemical co-precipitation method, so as to form a composite material with a multi-layer pore structure (the pore size is mainly mesoporous with a size of 2-50 nm) and rich surface functional groups (-NH2, -COOH and the like). Potted plant tests show that the material realizes complexation / adsorption (amino coordination, electrostatic attraction) of Cd and Pb heavy metal ions and interface adsorption (pi-pi stacking, electrostatic attraction and hydrophobic interaction) of PS-NPs through pore interception and functional group synergistic effect, significantly reduces the content of available pollutants in soil, and inhibits the migration of the available pollutants to the roots of food and vegetable crops and the transportation of the available pollutants to the aboveground parts.

Description

Technical Field

[0001] This invention belongs to the field of environmental functional materials and contaminated soil remediation technology, specifically relating to a method for preparing a magnetic bifunctional modified graphene oxide composite material and its application. Background Technology

[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.

[0003] The combined pollution of heavy metals and micro / nanoplastics (PS-NPs) in soil environments is becoming increasingly common, especially in farmland ecosystems. On the one hand, heavy metals such as Cd and Pb, as typical inorganic pollutants, are frequently detected in soil environmental quality surveys; on the other hand, with the long-term application of plastic film mulching and chemical fertilizers and pesticides, the accumulation of PS-NPs in farmland soils has increased significantly, becoming a new type of pollutant that has attracted widespread attention in recent years. These two types of pollutants easily coexist and interact in the environment, forming a complex pollution system that alters their environmental chemical behavior and bioavailability. This type of complex pollution may not only inhibit the growth and reproduction of soil organisms, reducing crop yield and quality, but may also pose a potential threat to human health through bioaccumulation in the food chain. Therefore, it is urgent to pay attention to the problem of combined heavy metal and PS-NP pollution in arable land soils to ensure arable land quality and sustainable agricultural development.

[0004] Currently, there are relatively abundant technologies for remediating single heavy metal or micro / nanoplastics pollution in soil, but research and related technologies for combined pollution by both are relatively scarce. Adsorption and immobilization using environmentally functional materials is a common method for addressing the current challenges of remediating combined pollutants. However, in combined pollution systems, micro / nanoplastics can interact with heavy metals, potentially altering their form and occupying active sites on adsorbent materials, thus weakening the adsorption performance of traditional high specific surface area materials (such as graphene, activated carbon, aerogels, porous aluminosilicates, and biochar). Therefore, existing materials often have limited effectiveness in dealing with combined pollution, making it difficult to achieve efficient synergistic removal. Against this backdrop, there is an urgent need to develop functional materials or remediation methods that are easy to prepare, stable in performance, and capable of simultaneously and efficiently removing micro / nanoplastics and heavy metals to meet the practical needs of remediating combined polluted soils.

[0005] Graphene oxide, an oxidized derivative of graphene, is a single-layer or multi-layer carbon material obtained by introducing oxygen-containing functional groups into graphite raw materials through strong acid oxidation and subsequent exfoliation. As an important branch of graphene-based materials, graphene oxide retains some of the excellent properties of graphene (such as high specific surface area and good mechanical strength), while gaining more reactive chemical properties and processability through the introduction of oxygen-containing functional groups, making it a research hotspot in materials science in recent years. The structure of graphene oxide is based on the layered structure of graphite, with oxygen-containing functional groups introduced onto its surface and edges, such as hydroxyl (-OH), epoxy (-O-), carboxyl (-COOH), and carbonyl (-C=O). The introduction of these functional groups gives it a higher adsorption capacity for removing heavy metals and nanoplastics from polluted soil. However, the limited number of adsorption sites on the surface of graphene oxide restricts its application in practical engineering. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing a magnetically bifunctional modified graphene oxide composite material and its application. This invention loads amino groups onto the surface of graphene oxide to enhance its adsorption capacity for negatively charged nanoplastics and heavy metals, while retaining its inherent hydrophobic / π–π interactions. Then, the material is magnetized through magnetic modification, enabling convenient material recycling. When the resulting modified material is applied to crop soils with varying degrees of pollution, it demonstrates excellent removal effects for both heavy metals and PS-NPs.

[0007] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a method for preparing a magnetic bifunctional modified graphene oxide composite material, comprising the following steps: S1, graphene oxide is dispersed in water, p-phenylenediamine is added, and the mixture is sonicated and then heated under reflux to obtain amino-modified graphene oxide (aGO) with positively charged surface. S2. After preparing a dispersion of the amino-modified graphene oxide (aGO) obtained in step S1, the pH value is adjusted to 6-7, and the sheets are completely dispersed by sonication. Ascorbic acid is added while stirring, and the reaction is heated to obtain bifunctional modified graphene oxide (arGO). S3. The bifunctional modified graphene oxide (arGO) obtained in step S2 is sieved, dispersed in water, and a mixed solution of ferric salt and ferrous salt is added. The mixture is heated and stirred, and an alkaline solution is added dropwise to adjust the pH value to 10-11. The mixture is stirred continuously, and then the suspension is sealed and allowed to stand. After solid-liquid separation and drying, magnetic bifunctional modified graphene oxide (M-arGO) is obtained.

[0008] In step S1, water is added to the graphene oxide, followed by ultrasonic treatment to disperse the graphene oxide as much as possible. After the reflux reaction is complete, unreacted p-phenylenediamine is removed by centrifugation with anhydrous ethanol and water. The centrifuge parameters are 8000~10000 rpm, and the single centrifugation time is 10~20 min.

[0009] In step S1, the concentration of graphene oxide in water is 0.7~1.5 mg / mL.

[0010] In step S1, take 200-300 mg of graphene oxide (GO), add 200-300 mL of deionized water, and then sonicate for 1.5-2.5 h to disperse the graphene oxide as much as possible. After adding p-phenylenediamine, the sonication time is 0.75–1.25 h; the reflux reaction conditions are 70–90 °C, and the reflux reaction time is 18–30 h. For water bath reactions, the beaker mouth must be sealed to prevent excessive oxidation.

[0011] In step S1, the mass ratio of p-phenylenediamine to graphene oxide is 2 to 4:1, preferably 3:1.

[0012] Preferably, during the magnetic stirring reaction in step S2, the color change of the solution should be observed in real time. Suitable process parameters for the magnetic stirring reaction are: the mass ratio of ascorbic acid to amino-modified graphene oxide (aGO) should be controlled within the range of (5~7):1; the reaction time should be controlled within 1.5~2.5 hours; and the reaction temperature should be 50~70℃. Within this range, ascorbic acid moderately and controllably reduces aGO. At the end of the reaction, the dispersion should be a uniform dark gray, indicating that the material has been successfully reduced to a light gray. If it turns black, it indicates over-reduction, and the reaction should be terminated immediately.

[0013] In step S2, the stirring speed is 200~400 rpm.

[0014] In step S2, the pH is adjusted to neutral using 0.1 mol / L HCl or NaOH. Under neutral conditions, the ascorbic acid reduction efficiency is moderate, and strong acids and bases are avoided from damaging the aGO sheets.

[0015] Preferably, in step S3, either ferric salt or ferrous salt can be selected from at least one of chloride salt and nitrate salt.

[0016] Preferably, in step S3, the ferric salt is FeCl3·6H2O and the ferrous salt is FeCl2·4H2O; the mass ratio of FeCl3·6H2O to FeCl2·4H2O is 1~3:1.

[0017] This material is produced by sequentially modifying graphene oxide with p-phenylenediamine-mediated surface positive charge (introducing amino functional groups), ascorbic acid-induced mild reduction (restoring hydrophobicity and π-π interactions), and magnetic loading via chemical coprecipitation. This process creates a composite material with a multilayered porous structure (primarily mesopores with pore sizes of 2-50 nm) and abundant surface functional groups (-NH2, -COOH, etc.). Pot experiments demonstrate that this material, through pore trapping and synergistic effects of functional groups, achieves complexation / adsorption of Cd and Pb heavy metal ions (amino coordination, electrostatic attraction) and interfacial adsorption of PS-NPs (π-π stacking, electrostatic attraction, and hydrophobic interactions), significantly reducing the content of available pollutants in the soil and inhibiting their migration to the roots and translocation to the aboveground parts of food and vegetable crops. Furthermore, the material exhibits magnetic responsiveness, allowing for rapid recovery and reducing the risk of secondary pollution. It possesses clear technical advantages and application value in the remediation of combined heavy metal and microplastic pollution in soil.

[0018] In a second aspect, the present invention provides a magnetically bifunctional modified graphene oxide composite material prepared by the preparation method of the magnetically bifunctional modified graphene oxide composite material described in the first aspect.

[0019] The surface of the magnetic bifunctional modified graphene oxide composite material has stacked sheets and pores, wrinkles, and is also loaded with Fe3O4 particles.

[0020] The pore size is mainly mesopores of 2-50 nm.

[0021] Thirdly, the application of the magnetic bifunctional modified graphene oxide composite material described in the second aspect of the present invention in the removal of heavy metals and / or microplastics.

[0022] Furthermore, the present invention provides the application of the magnetic bifunctional modified graphene oxide composite material described in the second aspect in the removal of heavy metals and PS-NPs composite pollution in soil environments.

[0023] Furthermore, the present invention provides the application of the magnetic bifunctional modified graphene oxide composite material described in the second aspect in the remediation of farmland soil contaminated with heavy metals and / or nanoplastics.

[0024] Pot experiments have confirmed that applying the aforementioned magnetic bifunctional modified graphene oxide composite material to contaminated soil containing Cd, Pb, and PS-NPs, leverages its unique multilayered porous structure and surface functional groups to simultaneously achieve complexation / adsorption of heavy metal ions and interfacial adsorption of micro / nanoplastics, significantly reducing the content of available pollutants in the soil. Simultaneously, due to the material's pollutant immobilization effect, it effectively inhibits the migration of Cd, Pb, and PS-NPs to the roots and translocation to the aboveground parts of grain and vegetable crops, thereby reducing the accumulation level of pollutants within the crops. Compared with existing technologies, the composite material of this invention, through the synergistic effect of introducing magnetic components and functionalized graphene oxide, achieves both high adsorption capacity for heavy metals and micro / nanoplastics while enabling magnetically responsive separation. After adsorption, the material can be rapidly recovered under an external magnetic field, thereby improving material utilization efficiency and reducing the risk of secondary pollution. Therefore, this material has clear technical advantages and application value in the remediation of soil pollution caused by combined heavy metals and microplastics.

[0025] Fourthly, the present invention provides a method for remediating farmland soil contaminated with heavy metals and / or nanoplastics, by adding the magnetic bifunctional modified graphene oxide composite material described in the second aspect to the contaminated soil.

[0026] The beneficial effects achieved by one or more embodiments of the present invention described above are as follows: 1. The method for preparing magnetic bifunctional modified graphene oxide composite material provided by this invention loads more amino groups on the surface of graphene oxide, improving its adsorption capacity for negatively charged nanoplastics. Simultaneously, the coordination effect promotes the accumulation of heavy metals. Furthermore, this invention restores the sp² structure of GO through mild reduction, maintaining the aromaticity of GO and enhancing the π–π stacking interaction with nanoplastics. The mild reduction treatment does not destroy the basic structure of GO. After bifunctional modification, this invention magnetizes the material, enabling portable separation and recycling.

[0027] 2. The method for preparing the magnetic bifunctional modified graphene oxide composite material provided by this invention involves loading magnetic iron oxide nanoparticles onto bifunctional modified graphene oxide, thereby imparting superparamagnetism to the final product (M-arGO). This property enables rapid and thorough solid-liquid separation and recovery of the material after adsorption of soil pollutants using an external magnetic field. The preparation process is relatively simple, and the modifying materials FeCl3·6H2O and FeCl2·4H2O are both common chemical raw materials on the market, resulting in low cost.

[0028] 3. The method for preparing the magnetic bifunctional modified graphene oxide composite material provided by this invention can simultaneously and efficiently adsorb heavy metal ions (such as Cd) in soil. 2+ Pb 2+It exhibits synergistic remediation potential for both ) and nanoplastic pollutants, overcoming the challenges posed by heavy metal ions (such as Cd) and nanoplastic pollutants. 2+ Pb 2+ When combined with nanoplastics, the single amination-modified or mildly reduced-modified materials have poor mitigation effects in reducing pollution. Attached Figure Description

[0029] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0030] Figure 1 This is a scanning electron microscope (SEM) schematic diagram of graphene oxide in Example 1 of the present invention; Figure 2 This is a scanning electron microscope (SEM) schematic diagram of bifunctional modified graphene oxide (arGO) in Example 1 of the present invention. Figure 3 This is a scanning electron microscope (SEM) schematic diagram of the magnetic bifunctional modified graphene oxide (M-arGO) in Example 1 of the present invention. Detailed Implementation

[0031] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0032] The present invention will be further described below with reference to the embodiments.

[0033] Example 1 Preparation of magnetic bifunctional modified graphene oxide composite materials: 200 mg of graphene oxide (GO) was placed in a 500 mL beaker, and 200 mL of deionized water was added. The mixture was then sonicated for 2 h to disperse the graphene oxide as much as possible. Next, 600 mg of p-phenylenediamine (PPD) was added, and the mixture was sonicated for 30 min. The mixture was then refluxed in a water bath at 80 °C for 24 h. After the reaction was complete, the reaction solution was washed six times with anhydrous ethanol and deionized water by centrifugation to remove unreacted p-phenylenediamine. The resulting product was then freeze-dried at -40 °C for 12 h. After drying, the product was ground to obtain surface-modified graphene oxide (aGO).

[0034] The amino-modified graphene oxide (aGO) was re-dispersed ultrasonically in deionized water. 100 mL of the amino-modified graphene oxide dispersion (1 mg / mL, containing 100 mg aGO, with deionized water as the dispersion solvent) was placed in a 100 mL beaker, and the pH was adjusted to 6-7 with 0.1 mol / L HCl or NaOH. The beaker was placed in an ultrasonic cleaner, set to 90 W, and ultrasonicated for 40 min. After ultrasonication, the dispersion should show no obvious precipitation and be a uniform brownish-yellow color, indicating that the aGO sheets were completely dispersed. After ultrasonication, the dispersion was transferred to a thermostatic magnetic stirrer, set to 200 rpm, and pre-stirred for 10 min to ensure that the aGO sheets were uniformly distributed in the solution. Weigh 500 mg of ascorbic acid and add it evenly to the above dispersion. Adjust the parameters of the constant temperature magnetic stirrer: reaction temperature 60℃, stirring speed 300 rpm, reaction time 2 h. After the reaction is completed, wash the reaction solution with anhydrous ethanol and deionized water alternately by centrifugation 6 times to obtain bifunctional modified graphene oxide (arGO).

[0035] Graphene oxide (GO) and the resulting bifunctional modified graphene oxide (arGO) were characterized by scanning electron microscopy (SEM).

[0036] The arGO used was 200 mesh. It was dissolved in 200 mL of deionized water and ultrasonically dispersed for 2 h. 1.8 g of FeCl3·6H2O and 0.9 g of FeCl2·4H2O were dissolved in 50 mL of deionized water and quickly added to the above arGO dispersion. The mixture was stirred at 80 °C for 30 min, and then 5 mol·L⁻¹ was added dropwise. -1 NaOH solution (volume 50 mL, dropping rate 10 mL / min) -1 To ensure a constant dripping rate, the pH of the suspension was adjusted to 10.0-11.0, and mechanical stirring was continued for 1 h. The suspension was then sealed with a sealing film and allowed to stand for 12 h. After centrifugation and washing, the magnetic bifunctional modified graphene oxide (M-arGO) was obtained by freeze-drying. The obtained magnetic bifunctional modified graphene oxide (M-arGO) was characterized by scanning electron microscopy (SEM).

[0037] Figure 1 and Figure 2 These are scanning electron microscope (SEM) schematic diagrams of graphene oxide and bifunctional modified graphene oxide, respectively. Figure 2 It can be seen that the surface of graphene oxide is loaded with a large number of modified particles after bifunctional modification, and the stacked sheets and rich pores and wrinkles on the material surface provide a crucial roughness basis for creating a hydrophobic surface. Figure 3 This is a scanning electron microscope (SEM) schematic diagram of magnetically bifunctional modified graphene oxide (M-arGO). Figure 3It can be seen that the magnetized bifunctional modified graphene oxide has a large number of Fe3O4 particles uniformly loaded on its surface on the original basis.

[0038] Example 2 Adsorption applications of magnetic bifunctional modified graphene oxide composites A pot experiment was set up to examine the adsorption and removal efficiency of modified graphene oxide for Cd, Pb, and PS-NPs. Lettuce was used as the potted plant. The background soil concentrations in the experimental pots were 1.5 mg / kg Cd, 600 mg / kg Pb, and 0.01% PS-NPs. The amount of adsorbent added in the experimental group was 0.5%. Potted lettuce plants were divided into five groups (A1, A2, A3, A4, and A5). A1 was the control group without adsorption material, A2 was the experimental group with unmodified graphene oxide, A3 was the experimental group with amination-modified graphene oxide, A4 was the experimental group with bifunctional modified graphene oxide, and A5 was the experimental group with magnetic bifunctional modified graphene oxide. After 45 days of cultivation, the available Cd content in the soil, the available Pb content in the soil, the Cd content in the lettuce roots, the Cd content in the aboveground parts of the lettuce, the Pb content in the lettuce roots, the Pb content in the aboveground parts of the lettuce, the Ps-NPs content in the lettuce roots, and the Ps-NPs content in the aboveground parts of the lettuce were measured. The reduction rate and blocking rate were calculated based on the content data.

[0039] The formulas for calculating the reduction rate and the blocking rate are as follows:

[0040]

[0041] In formula 1-1, C represents the pollutant reduction rate (%). X C1 represents the content of different pollutants after the addition of modified materials, and C0 represents the content of pollutants without the addition of modified materials; in Formula 1-2, C represents the percentage (%) of the rate at which pollutants are blocked from the plant roots to the aboveground parts. R C indicates the pollutant content in the roots of potted plants. L The table shows the content of pollutants in the aboveground parts of potted plants. Table 1 shows the reduction rates of Cd, Pb, and PS-NPs in different experimental groups based on the content determination results; Table 2 shows the pollutant blocking rate from the lettuce roots to the aboveground parts.

[0042] Table 1. Reduction rates (%) of Cd, Pb, and PS-NPs in different experimental groups

[0043] Table 2. Interception rate of pollutants from lettuce roots to above-ground parts (%)

[0044] The results in Tables 1 and 2 confirm that the magnetic bifunctional modified graphene oxide composite material possesses excellent pollution remediation and blocking properties. On the one hand, its removal efficiency for Cd, Pb, and PS-NPs in soil is significantly improved compared to the unmodified material (Table 1); on the other hand, it can more effectively inhibit the migration of pollutants from the roots to the edible parts of lettuce (Table 2). This material simultaneously achieves efficient soil remediation and effective protection of crop safety.

[0045] Example 3 Effect of different amounts of modified materials on pollutant reduction rate The adsorption and removal effects of different amounts of magnetic bifunctional modified graphene oxide composite material on Cd, Pb, and PS-NPs were evaluated through pot experiments. Lettuce was used as the test plant, and the background value of the potting soil was the same as in Example 2. The lettuce pots were divided into four groups (B1, B2, B3, and B4), each with magnetic bifunctional modified graphene oxide composite material added at amounts of 0.5%, 1%, 2%, and 4%, respectively. The cultivation time and measurement items were the same as in Example 2. Based on the measurement results, the reduction rates of Cd, Pb, and PS-NPs in different experimental groups were calculated, as shown in Table 3.

[0046] Table 3. Reduction rates (%) of Cd, Pb, and PS-NPs under different material addition amounts

[0047] As shown in Table 3, the reduction rates of Cd, Pb, and PS-NPs all increased with the increase of the modified material addition. The reduction rate increased rapidly when the addition amount was 0.5%–2%; however, when the addition amount increased to 2%–4%, the increase in the reduction rate slowed significantly and gradually stabilized. This indicates that when the material addition amount reached above 2%, the reduction effect on the three pollutants was close to the optimal level.

[0048] Example 4 Comparative analysis of pollutant reduction rates under different concentration conditions Building upon Example 2, this experiment further analyzed the adsorption and removal effects of modified materials on Cd, Pb, and PS-NPs in soil and plants under different pollution levels by varying the background concentration of soil pollutants. Lettuce was used as the potted plant in the experiment, and four treatment groups (C1, C2, C3, and C4) were set up. C1 and C2 were low-pollution groups (Cd 1.5 mg / kg, Pb 600 mg / kg, PS-NPs 0.01%), with C1 receiving no adsorbent and C2 receiving 2% modified material. C3 and C4 were high-pollution groups (Cd 2 mg / kg, Pb 1000 mg / kg, PS-NPs 0.02%), with C3 receiving no adsorbent and C4 receiving 2% modified material. The cultivation time and measurement items were the same as in Example 2. The pollutant concentrations and reduction rates are shown in Table 4.

[0049] Table 4. Cd, Pb, and PS-NPs Pollutant Content and Reduction Rate

[0050] As shown in Table 4, the reduction rates of Cd, Pb, and PS-NPs by the magnetic bifunctional modified graphene oxide composite material remained above 80% under both low and high pollution concentrations. Even at higher pollutant concentrations, the reduction rate did not decrease significantly and remained at a high level. This indicates that the material can still exert a stable and significant remediation effect even under severe soil pollution.

[0051] Example 5 Analysis of the reduction of Cd, Pb and PS-NPs pollutants by modified materials in wheat crops Building upon Example 2, this study further analyzed the adsorption and removal effects of different graphene oxide materials on Cd, Pb, and PS-NPs using wheat as the test plant through pot experiments. Five treatment groups were set up (D1, D2, D3, D4, D5): D1 was a blank control group without adsorption material; D2 was treated with unmodified graphene oxide; D3 with aminated graphene oxide; D4 with bifunctional modified graphene oxide; and D5 with magnetic bifunctional modified graphene oxide. The cultivation time and measurement items were the same as in Example 2. Based on the measurement results, the reduction rates of Cd, Pb, and PS-NPs in each treatment group were calculated (Table 5), as well as the blocking rate of pollutants from the wheat roots to the aboveground parts (Table 6).

[0052] Table 5. Reduction rates (%) of Cd, Pb, and PS-NPs in different experimental groups

[0053] Table 6. Interception rate of pollutants from wheat roots to above-ground parts (%)

[0054] As shown in Table 5, compared with the control group without adsorbent material, the reduction rates of Cd, Pb, and PS-NPs in the experimental group with modified material were significantly increased, and the reduction rate showed a further increasing trend with the increase of functional component loading in the material. This indicates that the adsorption and removal effect of magnetic bifunctional modified graphene oxide composite material on pollutants remains significant in grain crops such as wheat. As shown in Table 6, compared with the control group (D1), the migration of pollutants to the aboveground edible tissues was significantly inhibited after adding the modified material, and the blocking rate was improved. This indicates that the material can effectively control the transfer of pollutants from the roots to edible parts, thereby helping to reduce the safety risks of agricultural products.

[0055] Example 6 Effects of different amounts of modified materials added to wheat crops on pollutant reduction rates Based on Example 3, this experiment investigated the removal effects of different amounts of magnetic bifunctional modified graphene oxide composite material on Cd, Pb, and PS-NPs in wheat using a pot experiment. The tested wheat was cultivated in contaminated soil with the same background values ​​as in Example 3, and four treatment groups (E1, E2, E3, E4) were set up, with composite material addition amounts of 0.5%, 1%, 2%, and 4%, respectively. The cultivation time and measurement items were the same as in Example 3. Based on the measurement results, the reduction rates of Cd, Pb, and PS-NPs in each group were calculated, as shown in Table 7.

[0056] Table 7. Reduction rates (%) of Cd, Pb, and PS-NPs in wheat crops under different material addition levels.

[0057] As shown in Table 7, all dosages of the modified materials exhibited reduction effects on Cd, Pb, and PS-NPs. When the M-arGO addition was between 0.5% and 2%, the pollutant reduction rate increased significantly; as the addition increased to 2%–4%, the rate of increase slowed and gradually stabilized. This indicates that in the wheat system, the reduction effect on the three pollutants approached the optimal level after the M-arGO addition reached 2%, a trend consistent with the results of the lettuce pot experiment.

[0058] Example 7 Comparative analysis of pollutant reduction rates under different concentrations in wheat crops To verify the remediation effect of M-arGO on different pollution levels in a wheat system, based on Example 4, wheat was used as the test plant to analyze the removal effect of this material on Cd, Pb, and PS-NPs in soil and plants at different pollutant concentrations. Four treatment groups (F1, F2, F3, F4) were set up: F1 and F2 were low-pollution groups (Cd 1.5 mg / kg, Pb 600 mg / kg, PS-NPs 0.01%), with F1 receiving no adsorbent and F2 receiving 2% M-arGO; F3 and F4 were high-pollution groups (Cd 2 mg / kg, Pb 1000 mg / kg, PS-NPs 0.02%), with F3 receiving no adsorbent and F4 receiving 2% M-arGO. The culture conditions and measurement items were the same as in Example 4. The pollutant concentration and reduction rate results are shown in Table 8.

[0059] Table 8. Content and Reduction Rate of Cd, Pb and PS-NPs Pollutants in Potted Wheat

[0060] As shown in Table 8, under both low and high pollution conditions set in this experiment, M-arGO exhibited good removal effects on Cd, Pb, and PS-NPs in the wheat system, with reduction rates consistently above 80%. Even under high pollution loads, its reduction efficiency did not decrease significantly and remained at a high level. This indicates that M-arGO possesses stable and efficient remediation performance in farmland soils with varying degrees of pollution, demonstrating strong environmental adaptability and broad-spectrum remediation potential for combined heavy metal and microplastic pollution, providing material support for the safe utilization of farmland in practice.

[0061] Comparative Example 1 Analysis of the effect of single-modification and multi-functional modification on pollutant reduction in materials To investigate the differences in the individual treatment effects of different modified graphene oxide materials on Cd, Pb, and PS-NPs, this study compared the pollutant reduction effects of amination-modified, mildly reduced-modified, and magnetically bifunctional modified graphene oxide on lettuce and wheat under the same background pollutant concentration through pot experiments. Two crop groups, lettuce and wheat, were set up in pots, each containing four treatments. Wheat samples: G1 was a blank control without adsorbent material; G2 was treated with amination-modified graphene oxide; G3 was treated with mildly reduced-modified graphene oxide; G4 was treated with magnetically bifunctional modified graphene oxide. Lettuce samples: H1 was a blank control without adsorbent material; H2 was treated with amination-modified graphene oxide; H3 was treated with mildly reduced-modified graphene oxide; H4 was treated with magnetically bifunctional modified graphene oxide. The incubation time and measurement items were set according to the soil pollutant background value settings in Example 2. The calculated results of pollutant reduction for each treatment are shown in Tables 9 and 10.

[0062] Table 9 Pollutant Reduction Rates of Single-Modified and Multi-Modified Materials in Wheat Pots

[0063] Table 10 Pollutant Reduction Rates of Single and Multifunctional Modified Materials in Potted Lettuce

[0064] The data in the table above shows that single amination modification or mild reduction modification treatments both have a certain reduction effect on pollutants in lettuce and potted wheat. However, after adding magnetic bifunctional modified graphene oxide, the reduction rates of Cd, Pb, and PS-NPs in both plants increased by 45% to 70% compared to single modification. The results indicate that magnetic bifunctional modified graphene oxide has a significantly better effect on reducing pollutants in crops than single modification methods, thus demonstrating the outstanding advantages of this patented material in dealing with complex pollution situations.

[0065] Comparative Example 2 Comparative Study on the Influence Mechanisms of Different Modified Materials on Pollutant Removal under Single and Combined Pollution Conditions To investigate the differences in pollutant types and concentrations in the soil environment, this experiment verified the reduction effects of single-modification materials and patented-modification materials on single and compound pollutants. The experiment included two potted plant groups: lettuce and wheat, with six experimental subgroups in each group. The wheat potted plant group consisted of: ammoniation-modified experimental groups (J1, J2), mild reduction-modified experimental groups (J3, J4), and patented-material groups (J5, J6). The lettuce potted plant group consisted of: ammoniation-modified experimental groups (K1, K2), mild reduction-modified experimental groups (K3, K4), and patented-material groups (K5, K6). The soil pollutant concentrations for J1, J3, and J5 were 1.5 mg / kg for Cd and 600 mg / kg for Pb, with an adsorption material addition of 0.5% in the experimental group. The soil pollutant concentrations for J2, J4, and J6 were 1.5 mg / kg for Cd and 600 mg / kg for Pb, with an adsorption material addition of 0.5% in the experimental group and a PS-NPs addition of 0.01%, with an adsorption material addition of 0.5% in the experimental group. The concentrations of pollutants after treatment of each component and the inhibition of adsorption effect by PS-NPs are shown in Tables 11 and 12.

[0066] Table 11 Pollutant content in wheat under different treatment groups and the inhibition of adsorption effect by PS-NPs

[0067] Table 12. Pollutant content in different treatment groups of lettuce and the inhibition of adsorption effect by PS-NPs.

[0068] The data in the table above show that when polystyrene nanoplastics (PS-NPs) are present in the soil, the adsorption efficiency of single amination-modified or mildly reduced modified materials for Cd and Pb is significantly reduced, with a reduction rate of only 18%~30%. However, when using the magnetic bifunctional graphene oxide material of this patent, the effect of PS-NPs on heavy metal reduction is controlled within 10%. This indicates that PS-NPs significantly inhibit the adsorption of heavy metals by single modified materials in the soil environment. In contrast, the magnetic bifunctional graphene oxide developed in this study maintains excellent adsorption performance under the coexistence of micro / nanoplastics and heavy metals. Its core mechanism lies in the electrostatic attraction between the positively charged functional group (-NH2) introduced by the amino modification and the negatively charged PS-NPs, while the mildly reduced sp... 2 The hybrid structure enhances the π-π stacking interaction, and the two work together to directly anchor PS-NPs, effectively reducing their competitive occupation of heavy metal adsorption sites, thereby significantly weakening the inhibitory effect of PS-NPs on heavy metal removal.

[0069] Comparative Example 3 Preparation and properties of comparative materials for over-reduction caused by excessive ascorbic acid Take 100 mL of amino-modified graphene oxide (aGO) dispersion (concentration 1 mg / mL, containing 100 mg aGO) in a 100 mL beaker, and adjust the pH to 6-7 with 0.1 mol / L HCl or NaOH. After ultrasonic dispersion at 90 W for 45 min, transfer the dispersion to a thermostatic magnetic stirrer and pre-stir at 200 rpm for 10 min. Weigh 1000 mg of ascorbic acid (ratio 10:1) and add it evenly to the dispersion. Perform a reduction reaction with magnetic stirring at 60 °C and 300 rpm. About 1 hour after the start of the reaction, the solution color changes from brownish-yellow to dark gray, and then gradually deepens, turning pitch black after 2 hours. The reaction is then terminated. The reaction solution is washed 6 times by alternating centrifugation with anhydrous ethanol and deionized water (9000 rpm, 15 min) to obtain over-reduced graphene oxide. Pot experiments were conducted on the above materials, with two groups of potted plants, one for wheat and one for lettuce. Two groups were set up for each material. The wheat group consisted of L1 (with added aminated graphene oxide), L2 (with added mildly reduced graphene oxide), and L3 (with added excessively reduced graphene oxide). The lettuce group consisted of M1 (with added aminated graphene oxide), M2 (with added mildly reduced graphene oxide), and M3 (with added excessively reduced graphene oxide). The other conditions were the same as in Example 2. The pollutant reduction effects of the two materials were measured and are shown in Tables 13 and 14.

[0070] Table 13 Pollutant reduction rate (%) of two materials in wheat

[0071] Table 14. Pollutant reduction rate (%) of two materials in lettuce

[0072] The data above show that, compared with mildly reduced modified materials, the reduction rates of Cd, Pb, and PS-NPs in wheat and lettuce decreased by 30% to 60% overall after extensive reduction. This is mainly attributed to the overly vigorous reduction reaction, which resulted in the removal of a large number of oxygen-containing functional groups (such as -COOH and -OH) on the graphene oxide sheets, leading to a significant reduction in Pb content. 2 Excessive structural recovery. This not only resulted in the loss of the amino functional groups introduced in the early stage, weakening the effect of amination modification, but also significantly reduced the positive charge of the material surface and its ability to complex heavy metal ions.

[0073] Meanwhile, although excessive reduction enhances the overall hydrophobicity of the material, the resulting severe lamellar aggregation leads to a sharp decrease in the effective adsorption specific surface area, and the densified structure also hinders the full contact between PS-NPs and the active interface of the material, thus significantly reducing the adsorption efficiency of PS-NPs.

[0074] In summary, excessive reduction caused by adding far more ascorbic acid than the appropriate ratio disrupts the dual-functional synergistic mechanism of "amino-complexed heavy metals" and "hydrophobic / π-π adsorption of nanoplastics" in the material. This significantly reduces its simultaneous removal efficiency of heavy metals and nanoplastics in the complex pollution system, failing to achieve the design objectives of this invention. Therefore, a ratio of surface-positively modified graphene oxide (aGO) to ascorbic acid of 1:5 to 1:7 results in a more reasonable mild reduction effect.

[0075] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a magnetic bifunctional modified graphene oxide composite material, characterized in that, Includes the following steps: S1, dispersing graphene oxide in water, adding p-phenylenediamine, sonicating and then heating under reflux to react, to obtain amino-modified graphene oxide with positively charged surface. S2, after preparing the amino-modified graphene oxide obtained in step S1 into a dispersion, the pH value is adjusted to 6-7, the sheets are completely dispersed by sonication, ascorbic acid is added while stirring, and the reaction is heated to obtain bifunctional modified graphene oxide. S3. The bifunctional modified graphene oxide obtained in step S2 is sieved, dispersed in water, and a mixed solution of ferric salt and ferrous salt is added. The mixture is heated and stirred, and an alkaline solution is added dropwise to adjust the pH value to 10-11. The mixture is stirred continuously, and then the suspension is sealed and allowed to stand. After solid-liquid separation and drying, magnetic bifunctional modified graphene oxide is obtained.

2. The method for preparing the magnetic bifunctional modified graphene oxide composite material according to claim 1, characterized in that, In step S1, water is added to graphene oxide and then ultrasonic treatment is performed to disperse the graphene oxide as much as possible; after the reflux reaction is completed, unreacted p-phenylenediamine is removed by centrifugation and washing with anhydrous ethanol and water. Preferably, the centrifuge parameters are 8000~10000 rpm, and the single centrifugation time is 10~20 min.

3. The method for preparing the magnetic bifunctional modified graphene oxide composite material according to claim 1, characterized in that, After adding p-phenylenediamine, the sonication time was 0.75~1.25 h; the reflux reaction conditions were 70~90℃, and the reflux reaction time was 18~30 h.

4. The method for preparing the magnetic bifunctional modified graphene oxide composite material according to claim 1, characterized in that, In step S1, the concentration of graphene oxide in water is 0.7~1.5 mg / mL; Alternatively, the mass ratio of p-phenylenediamine to graphene oxide is 2 to 4:1, preferably 3:

1.

5. The method for preparing the magnetic bifunctional modified graphene oxide composite material according to claim 1, characterized in that, During the magnetic stirring reaction in step S2, the color change of the solution should be observed in real time. The suitable process parameters for the magnetic stirring reaction are: the mass ratio of ascorbic acid to amino-modified graphene oxide is 5~7:1, the reaction time is 1.5~2.5 h, and the reaction temperature is 50~70℃. In this process, ascorbic acid moderately and controllably reduces aGO, and the dispersion should be a uniform dark gray color at the end of the reaction.

6. The method for preparing the magnetic bifunctional modified graphene oxide composite material according to claim 1, characterized in that, In step S3, the ferric salt or ferrous salt is selected from at least one of chloride salts and nitrate salts; Furthermore, in step S3, the ferric salt is FeCl3·6H2O, and the ferrous salt is FeCl2·4H2O; the mass ratio of FeCl3·6H2O to FeCl2·4H2O is 1~3:

1.

7. The magnetically bifunctional modified graphene oxide composite material prepared by the method according to any one of claims 1 to 6, characterized in that, The surface of the magnetic bifunctional modified graphene oxide composite material has stacked sheets and pores, wrinkles, and is also loaded with Fe3O4 particles. Preferably, the pore size is mainly mesopores of 2-50 nm.

8. The application of the magnetic bifunctional modified graphene oxide composite material of claim 7 in the removal of heavy metals and / or microplastics.

9. The application of the magnetic bifunctional modified graphene oxide composite material according to claim 8 in the removal of heavy metals and / or microplastics, characterized in that, The magnetic bifunctional modified graphene oxide composite material is used for the removal of heavy metals and PS-NPs composite pollution in soil environments; Furthermore, the aforementioned magnetic bifunctional modified graphene oxide composite material is used for the remediation of farmland soil contaminated with heavy metals and / or nanoplastics.

10. A method for remediating arable land contaminated with heavy metals and / or nanoplastics, characterized in that, The magnetic bifunctional modified graphene oxide composite material of claim 8 is added to contaminated soil.

Images