Alpha-FeOOH gel composite material and preparation method thereof

Abstract

The invention relates to the field of functional gel composite material preparation and application thereof, in particular to an alpha-FeOOH gel composite material and a preparation method thereof.The preparation method includes the steps that 1, mixed solid powder is prepared and added into humic acid to be mixed to obtain gel, and the gel is added into a FeSO4 solution to be stirred and mixed; 2, a NaOH solution is dropwise added into the mixture, the mass ratio of FeSO4 to NaOH and the pH value of the NaOH solution are controlled, air is introduced for oxidation, and a supported alpha-FeOOH seed crystal suspension compound is obtained; 3, dispersing chitosan in a mixed aqueous solution of humic acid and acetic acid to obtain a mixed aqueous solution of chitosan and humic acid; 4, mixing the suspension compound with the mixed aqueous solution to obtain a cross-linked mixture solution; and 5, adding the FeSO4 solution again, introducing air to oxidize, and dropwise adding the NaOH solution to control the pH value of the cross-linked mixture solution, so that alpha-FeOOH is precipitated and grows on the seed crystal, and the alpha-FeOOH-gel slow-release composite material is obtained. The humic acid enables the degradable plastic to age, exposes functional groups, and is easier to mix.

Description

Technical Field

[0001] The present invention relates to the preparation and application fields of functional gel composite materials, and in particular to an α-FeOOH gel composite material and a preparation method thereof. Background Art

[0002] Slow-release fertilizers are playing an increasingly important role in modern agriculture. They can improve fertilizer utilization efficiency. They slowly release nutrients, meeting crop nutrient needs at different growth stages, extending fertilizer effectiveness, and enhancing nutrient utilization. Compared to traditional fertilizers, slow-release fertilizers do not release all their nutrients immediately, giving plants more time to absorb them and reducing nutrient loss. The use of slow-release fertilizers can reduce nutrient loss and mitigate the risk of eutrophication. Furthermore, by controlling nutrient release, slow-release fertilizers reduce greenhouse gas emissions and help maintain the health of soil ecosystems. Slow-release fertilizers can increase crop yields, reduce fertilizer costs, and improve labor productivity. Because of their extended shelf life, slow-release fertilizers can reduce fertilization frequency and labor intensity, thereby saving labor. By continuously releasing nutrients, slow-release fertilizers improve soil structure and fertility, promote microbial activity and root development, and enhance the soil's ability to retain nutrients and water. This is crucial for long-term soil health and sustainable agricultural development.

[0003] Soil pollution is a global problem. Over the past few decades, due to the acceleration of industrialization and urbanization, rapidly developing countries have faced serious soil pollution problems. The main pollutants causing soil pollution include chemicals, pesticides, dyes, organic pollutants (such as polycyclic aromatic hydrocarbons), and heavy metals (Acosta-Dacal et al. 2022; Bhandari et al. 2020; Issaka et al. 2022). These pollutants accumulate in the soil, affecting soil quality, disrupting ecological balance, and posing a threat to human health through the food chain. Therefore, timely remediation of contaminated soil is essential. Soil remediation methods include physical remediation, chemical remediation, and bioremediation (Zhai et al., 2018). Physical remediation methods include filtration, sedimentation, centrifugation, magnetic separation, and flotation. Physical remediation is generally suitable for the remediation of inorganic pollutants and is particularly suitable for treating small-scale contaminated soil. Chemical remediation involves the addition of chemicals to induce chemical reactions in harmful substances in the soil, converting them into harmless substances or reducing their toxicity. Common chemical remediation methods include the addition of adsorbents, reducing agents, and precipitants. Bioremediation refers to the use of organisms such as plants and microorganisms to repair soil pollution by absorbing, decomposing or transforming harmful substances.

[0004] Adsorption is an effective method for removing pollutants from soil, particularly heavy metals, organic solvents, dyes, and pesticides. Due to its high efficiency, strong selectivity, ease of operation, environmental friendliness, compatibility with a wide range of soil types, ease of subsequent treatment, and sustainability, adsorption has become an important soil remediation technology with broad application prospects (Manna et al., 2021; Shrestha et al., 2021). The selection of appropriate adsorbents, such as activated carbon, biochar, and nanomaterials, can significantly improve pollutant removal efficiency. To date, a variety of adsorbents and passivators have been developed for soil remediation. These include clay materials, carbon-based materials, metal-organic frameworks, and hydrogels (Ding et al., 2023; Gao et al., 2023). Hydrogels, due to their unique three-dimensional network structure and diverse active functional groups, have broad applications in soil pollution control. α-FeOOH has a high specific surface area, a fine particle structure, and stable physical and chemical properties. It exhibits superior environmental compatibility and chemical stability compared to other materials, and plays an important role in purifying pollutants in the soil environment (Jaiswal et al., 2013). Currently, methods for preparing α-FeOOH nanoparticles primarily include sol-gel, chemical precipitation, microemulsion, sonochemical, hydrothermal synthesis, gel-grid precipitation, air oxidation, and room-temperature solid-phase methods. Chemical precipitation and hydrothermal synthesis are the most widely studied methods for synthesizing α-FeOOH nanoparticles.

[0005] However, in the existing waste slow-release and soil pollution remediation processes, the two are independent of each other: slow-release fertilizer is slow-release fertilizer, and pollution remediation is pollution remediation, and they are not combined in a targeted manner. Therefore, the utilization rate of soil in agricultural use is reduced. Summary of the Invention

[0006] In response to the problems existing in the prior art, the purpose of the present invention is to provide a functional material that combines soil pollution remediation with fertilizer slow release, which can improve agricultural utilization efficiency. α-FeOOH gel is prepared using biomass materials as raw materials by chemical precipitation method, and composite materials are prepared by combining nutrients. The α-FeOOH gel composite material based on degradable plastic and its preparation method are studied for its adsorption and catalytic degradation ability of pollutants in the soil environment and fertilizer slow release performance.

[0007] To achieve the above object, the technical solution adopted by the present invention is: a method for preparing an α-FeOOH gel composite material, comprising the following steps: Step 1: preparing a mixed solid powder based on biodegradable plastic, fly ash, and phosphate rock powder, adding the mixed solid powder to humic acid to obtain a gel, and adding the gel to a FeSO4 solution and stirring to mix; Step 2: Slowly add NaOH solution dropwise to the mixture in step 1 while stirring, control the mass ratio of FeSO4 to NaOH and the pH value of the NaOH solution, and oxidize under air to obtain a supported α-FeOOH seed crystal suspension complex; Step 3: Dispersing chitosan in a mixed aqueous solution of humic acid and acetic acid, stirring and dissolving the mixture evenly, so that the chitosan macromolecules and the humic acid molecular chains are cross-linked and fixed, thereby obtaining a mixed aqueous solution of chitosan and humic acid; Step 4: mixing the supported α-FeOOH seed suspension complex with the mixed aqueous solution of chitosan and humic acid, and adding a cross-linking agent to cross-link them to obtain a cross-linked mixture solution; Step 5: FeSO4 solution is added to the cross-linked mixture solution again, and NaOH solution is added dropwise while oxidizing with air to control the pH value of the cross-linked mixture solution, so that α-FeOOH is precipitated in situ in the unit space inside the gel and on the surface, and grows on the supported α-FeOOH seed crystals to obtain an α-FeOOH-gel sustained-release composite material.

[0008] The preparation method of the above-mentioned α-FeOOH gel composite material, said step 1 comprises: Step 1-1: cooling the fly ash heated in a high-temperature muffle furnace and washing it in dilute sulfuric acid to obtain high-temperature acid-washed fly ash; Step 1-2: Grind and sieve the biodegradable plastic, high-temperature acid-washed fly ash, and phosphate rock powder according to the mass ratio, and then evenly mix them so that the high-temperature acid-washed fly ash and phosphate rock powder adhere to the pores of the biodegradable plastic to obtain a basic mixed powder; Step 1-3: Mix the basic mixed powder and humic acid according to the mass ratio, and mechanically stir until the liquid evaporates completely, exposing the functional groups of the degradable plastic to obtain a gel.

[0009] In the above-mentioned method for preparing the α-FeOOH gel composite material, in step 1: the temperature of the high-temperature muffle furnace is 500-800 degrees Celsius, the heating time is 1-2 hours, and the concentration of dilute sulfuric acid is 0.1%-0.5%; Use a 200-mesh sieve to screen, and the mass ratio of biodegradable plastic, fly ash, and phosphate rock powder is 2:1:0.5; The mass ratio of the basic mixed powder to humic acid is 1:0.5.

[0010] In the preparation method of the above-mentioned α-FeOOH gel composite material, in step 1, the FeSO4 content in the FeSO4 solution is 25%, and the mass ratio of the weight of the mixed solid powder in the gel to the FeSO4 solution is 1:2. During mixing, the gel is slowly added to the FeSO4 solution step by step and batch by batch, while mechanically stirring, and mixing for 2-4 hours to allow the iron ions to infiltrate the solid powder.

[0011] In the above-mentioned method for preparing the α-FeOOH gel composite material, in step 2, the mixture is kept in a stirring state during oxidation by air so as to keep the mixed liquid in suspension.

[0012] In the above-mentioned method for preparing the α-FeOOH gel composite material, in step 3, the concentration of chitosan is 2%, the concentration of humic acid is 2%, and the concentration of acetic acid is 0.5%, and they are dissolved by mechanical stirring at room temperature.

[0013] In the above-mentioned method for preparing the α-FeOOH gel composite material, in step 4, the mass ratio of the supported α-FeOOH seed crystal suspension composite to the mixed aqueous solution of chitosan and humic acid is 3:1, and glutaraldehyde is used as the cross-linking agent.

[0014] In the above-mentioned method for preparing the α-FeOOH gel composite material, in step 5, the FeSO4 solution is added again at a mass ratio of 1%.

[0015] An α-FeOOH gel composite material comprises a supported α-FeOOH seed crystal suspension compound, chitosan, humic acid, acetic acid, a crosslinking agent, a FeSO4 solution, and a NaOH solution, wherein the chitosan is dispersed in a mixed aqueous solution of humic acid and acetic acid, and the supported α-FeOOH seed crystal suspension compound comprises degradable plastic, fly ash, phosphate rock powder, humic acid, a FeSO4 solution, and a NaOH solution.

[0016] In the above-mentioned α-FeOOH gel composite material, the mass ratio of degradable plastic, fly ash and phosphate rock powder is 2:1:0.5, the mass ratio of the total solid mass of degradable plastic, fly ash and phosphate rock powder to FeSO4 solution is 1:2, the mass ratio of FeSO4 to NaOH is 4:1, and the mass ratio of the mixed aqueous solution obtained by dispersing chitosan in a mixed aqueous solution of humic acid and acetic acid to the α-FeOOH seed crystal suspension complex is 3:1.

[0017] The beneficial effects of the α-FeOOH gel composite material and the preparation method of the present invention are as follows: the α-FeOOH gel composite material based on degradable plastic is magnetic and recyclable, can adsorb heavy metals, catalytically degrade organic pollutants, and slowly release nutrients, and has the dual characteristics of pollution repair and slow-release fertilizer. During the preparation process, the high-temperature pickling fly ash generates fewer impurities and can have more pores, which increases the efficiency and effect of pickling harmful metals; humic acid causes the degradable plastic to age, exposing functional groups, and further dissolving the fly ash and phosphate rock powder to obtain small particles, which are easier to mix. The addition of degradable plastic can increase the specific surface area, increase the attachment sites of nanoparticles, make the material looser, and make it easier to obtain high-quality composite materials. By adding FeSO4 for the second time, better cross-linking is achieved, and it is easier to obtain seed crystals and cultivate different crystal forms. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a scanning electron microscope surface image in an embodiment of the present invention; Figure 2 This is a scanning electron microscope hole image in an embodiment of the present invention; Figure 3 (a) is a pseudo-first-order kinetic diagram of the adsorption of MO by the composite hydrogel in an embodiment of the present invention, and (b) is a pseudo-first-order kinetic diagram of the adsorption of Cr by the composite hydrogel in an embodiment of the present invention. 6+ Schematic diagram of pseudo-first-order kinetics; Figure 4 (c) is a pseudo-second-order kinetic diagram of the adsorption of MO by the composite hydrogel in an embodiment of the present invention, and (d) is a pseudo-second-order kinetic diagram of the adsorption of Cr by the composite hydrogel in an embodiment of the present invention. 6+ Schematic diagram of pseudo-second-order kinetics; Figure 5 (e) is a schematic diagram of the adsorption isotherm model of MO adsorbed by the composite hydrogel in the embodiment of the present invention, and (f) is a schematic diagram of the adsorption isotherm model of Cr adsorbed by the composite hydrogel in the embodiment of the present invention. 6+ Schematic diagram of the adsorption isotherm model. DETAILED DESCRIPTION

[0019] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention is described below in conjunction with specific implementation methods and drawings.

[0020] Example 1 An α-FeOOH gel composite material comprises a supported α-FeOOH seed suspension compound, chitosan, humic acid, acetic acid, a crosslinking agent, a FeSO4 solution, and a NaOH solution. The chitosan is dispersed in a mixed aqueous solution of humic acid and acetic acid. The supported α-FeOOH seed suspension compound comprises degradable plastic, fly ash, phosphate rock powder, humic acid, a FeSO4 solution, and a NaOH solution.

[0021] The mass ratio of degradable plastic, fly ash and phosphate rock powder is 2:1:0.5, the mass ratio of the total solid mass of degradable plastic, fly ash and phosphate rock powder to FeSO4 solution is 1:2, the mass ratio of FeSO4 to NaOH is 4:1, and the mass ratio of the mixed aqueous solution obtained by dispersing chitosan in a mixed aqueous solution of humic acid and acetic acid to the α-FeOOH seed suspension complex is 3:1.

[0022] Specifically, waste degradable plastics include but are not limited to biodegradable polyesters, such as polylactic acid, biodegradable PET, polybutylene succinate / caproate, polyhydroxybutyrate / valerate, polyethylene succinate, polyester amide and polycaprolactone / mixture; starch and its mixture, etc., which can interpenetrate and cross-link hydrogels to make them more stable, increase the specific surface area, increase the attachment sites of nanoparticles, make the material looser, and make it easier to obtain high-quality composite materials.

[0023] High temperature pickling of fly ash increases porosity and mechanical strength of the material, making it easier to use and recycle.

[0024] Phosphate rock powder can dissolve and slowly release nutrients. After dissolution, some of the vacancies can adsorb pollutants through displacement.

[0025] Humic acid provides slow-release fertilizer raw materials, promotes the dissolution of phosphate rock powder, and increases the cross-linking degree of gel.

[0026] The obtained α-FeOOH nanoparticles can adsorb heavy metals, catalytically degrade organic pollutants, and provide magnetism, allowing the composite material to be recycled after use.

[0027] Example 2 A method for preparing an α-FeOOH gel composite material comprises the following steps.

[0028] Step 1: Prepare a mixed solid powder based on biodegradable plastic, fly ash, and phosphate rock powder, add the mixed solid powder to humic acid to obtain a gel, add the gel to a FeSO4 solution, and stir to mix.

[0029] Step 2: Slowly add NaOH solution dropwise to the mixture in step 1 while stirring, control the mass ratio of FeSO4 to NaOH and the pH value of the NaOH solution, and oxidize with air to obtain a supported α-FeOOH seed crystal suspension complex.

[0030] Step 3: Disperse chitosan in a mixed aqueous solution of humic acid and acetic acid, stir and dissolve evenly, so that chitosan macromolecules and humic acid molecular chains are cross-linked and fixed, and obtain a mixed aqueous solution of chitosan and humic acid.

[0031] Step 4: Mix the supported α-FeOOH seed crystal suspension complex with the mixed aqueous solution of chitosan and humic acid, add a cross-linking agent to cross-link them, and obtain a cross-linked mixture solution.

[0032] Step 5: Add FeSO4 solution to the cross-linked mixture solution again, and add NaOH solution dropwise to control the pH value of the cross-linked mixture solution while oxidizing with air, so that α-FeOOH is in situ precipitated in the unit space inside the gel and on the surface, and grows on the supported α-FeOOH seed crystals to obtain an α-FeOOH-gel sustained-release composite material. Figure 1 and Figure 2 shown.

[0033] Specifically, fly ash is heated in a muffle furnace at 500-800 degrees Celsius for 1-2 hours. After cooling, it is washed in 0.1%-0.5% dilute sulfuric acid to produce high-temperature acid-washed fly ash, which is then dried and used in the subsequent hydrogel preparation. At this temperature, the fly ash produces fewer impurities and has more pores, increasing the efficiency and effectiveness of acid washing for harmful metals.

[0034] Degradable plastic, fly ash, and phosphate rock are pulverized separately and passed through a 200-mesh sieve. Mix them uniformly in a mass ratio of 2:1:0.5. Grind in a mortar to ensure thorough mixing, allowing the solid fly ash and phosphate rock to adhere to the pores of the degradable plastic and resulting in the smallest possible particles. The powders are then mixed with humic acid (mass ratio of 1:0.5) and mechanically stirred until the liquid evaporates completely. This allows the degradable plastic to age, exposing its functional groups, and further dissolving the fly ash and phosphate rock to form small particles that are easier to mix.

[0035] Add the above-mentioned mixed solid powder to a 25% FeSO₄ solution (the total mass of the biodegradable plastic, fly ash, and phosphate rock solids to the FeSO₄ solution is 1:2). Add the mixture gradually and slowly, stirring mechanically, for 2-4 hours to allow the iron ions to fully penetrate the solid powder. Then, slowly add a 5% NaOH solution dropwise, with a FeSO₄:NaOH mass ratio of 4:1, stirring while adding. Control the solution pH to 5-6. Air oxidation is performed to obtain a supported α-FeOOH seed suspension. Maintain stirring to keep the mixture suspended.

[0036] 2% chitosan was dispersed in a mixed aqueous solution of 2% humic acid and 0.5% acetic acid. The mixture was mechanically stirred at room temperature to dissolve the chitosan macromolecules uniformly, allowing the chitosan macromolecules to fully crosslink and fix the humic acid chains. This resulted in a chitosan-humic acid mixed aqueous solution. The chitosan-humic acid mixed aqueous solution was then mixed with an α-FeOOH seed suspension, with the chitosan solution and α-FeOOH seed suspension composite at a mass ratio of 3:1. The mixture was stirred until thoroughly mixed, and a crosslinking agent (glutaraldehyde) was added to effect crosslinking. Simultaneously, 1% FeSO₄ (25%) was added to the mixture. The mixture was then oxidized with air while NaOH solution was added dropwise to control the solution pH to 5-6. α-FeOOH precipitated in situ within the gel's internal unit spaces and on its surface, growing on the seed crystals to form α-FeOOH of a specific crystalline form. This resulted in an α-FeOOH-gel sustained-release composite material. The material is magnetic and recyclable, can adsorb heavy metals, catalytically degrade organic pollutants, and slowly release nutrients. It has the dual characteristics of pollution repair and slow-release fertilizer.

[0037] After use, the prepared material is recovered, crushed, mixed with 5% phosphate rock powder, and the above steps are repeated to obtain a reusable gel material, which can be repeated many times and save energy.

[0038] In this embodiment, the addition of degradable plastic can increase the specific surface area, increase the attachment sites of nanoparticles, make the material looser, and make it easier to obtain high-quality composite materials.

[0039] The addition of high-temperature pickled fly ash can increase the strength of the material, and the voids in the fly ash can increase the specific surface area and increase the attachment of nanoparticles.

[0040] Reuse waste and avoid wasting resources.

[0041] Phosphate rock powder can dissolve and slowly release nutrients. After dissolution, some of the vacancies can adsorb pollutants through displacement.

[0042] Humic acid provides slow-release fertilizer raw materials, promotes the dissolution of phosphate rock powder, and increases the cross-linking degree of gel.

[0043] By adding FeSO4 for the second time, better cross-linking is achieved, crystal seeds are more easily obtained, and different crystal forms can be cultivated.

[0044] The obtained α-FeOOH-gel sustained-release composite material has high strength and can be recycled after use.

[0045] It has a wide range of applications and can be applied to water and soil.

[0046] Adsorption and catalytic degradation properties coexist.

[0047] Adsorption experiments. Gel adsorption of methyl orange (MO) and Cr(VI) solutions.

[0048] Ten milligrams of α-FeOOH composite hydrogel were used to adsorb 10 mL of 50 mg / L methyl orange (MO) and Cr(VI) solutions, respectively. Adsorption experiments were performed in 50 mL centrifuge tubes, shaken at 150 rpm in a water bath, and sampled at intervals of 1, 3, 5, 10, 20, 40, 80, 120, and 120 minutes. The resulting pollutant solutions were filtered through a 0.45 nm filter membrane and then measured using a UV-visible spectrophotometer. The pollutant removal rate reached 95%, and the material recovery rate reached 97%.

[0049] The analysis results of gel adsorption capacity by adsorption kinetics fitting are as follows: Figure 3 As shown in Table 1, the adsorption kinetics fitting parameters are shown in Table 1. Figure 3 (a) and Figure 4 As shown in (c), the linear fitting correlation coefficient R of the pseudo-second-order kinetics of the composite hydrogel for the adsorption of methyl orange is 2 The value of 0.99893 is closer to 1, and the qmax of the pseudo-second-order kinetic fitting is 39.55 mg / g, which is closer to the adsorption amount at the actual adsorption equilibrium. Compared with the above, it can be seen that the pseudo-second-order kinetic linear fitting correlation coefficient of the gel for methyl orange is better, which is more consistent with the pseudo-second-order adsorption kinetic model. Therefore, the adsorption kinetics of methyl orange is mainly controlled by chemical reactions. Figure 3 Middle (b), Figure 4 In (d), it can be seen that the gel adsorbs Cr 6+ The linear fitting correlation coefficient R of pseudo-second-order kinetics 2 The value of 0.99957 is closer to 1, and the qmax of the pseudo-second-order kinetic fitting is 35.05 mg / g, which is closer to the adsorption amount at the actual adsorption equilibrium. 6+ The linear fitting correlation coefficient of pseudo-second-order kinetics is better, indicating that the adsorption process is also dominated by chemical adsorption, supplemented by physical adsorption.

[0050] Table 1: Adsorption of MO and Cr by gel alone 6+ Adsorption kinetics fitting parameters .

[0051] The results are as follows: Figure 5 As shown in (e) and (f), the adsorption isotherm parameters are shown in Table 2. Figure 5 As shown in (e), the Langmuir and Freundlich adsorption isotherms of methyl orange adsorbed on gel are fitted with the correlation coefficient R2 The results are 0.96529 and 0.92713 respectively. The comparison of the two models shows that the Langmuir R² is closer to 1. The maximum saturated adsorption capacity simulated by the Langmuir model is 619.35 mg / g. Therefore, the Langmuir model can better describe the adsorption process of methyl orange by the hydrogel, indicating that the adsorption of MO by the gel is a monolayer adsorption, and most of the MO is adsorbed on the active sites on the surface of the composite hydrogel. Figure 5 As shown in (f), the gel adsorbs Cr 6+ The correlation coefficient R between the Langmuir and Freundlich adsorption isotherms 2 The results of the two models are 0.99491 and 0.98483 respectively. The Langmuir R² is closer to 1. The maximum saturated adsorption capacity simulated by the Langmuir model is 93.63 mg / g, which is closer to the actual maximum adsorption capacity. Therefore, the hydrogel has a good adsorption effect on Cr 6+ The adsorption process of the gel is more consistent with the Langmuir model, indicating that the gel can absorb Cr 6+ The adsorption is monolayer adsorption, most of Cr 6+ Adsorbed on the active sites on the surface of the composite hydrogel.

[0052] Table 2: Gel adsorption of methyl orange and Cr 6+ Langmuir and Freundilich adsorption isotherm parameters .

[0053] Gel adsorption of antibiotics and remediation of contaminated soil: 10 mg of α-FeOOH composite hydrogel was used to adsorb 1-5 mg / L antibiotic solution. The removal rate was 99% and the material recovery rate was 96.5%.

[0054] By adding the composite material (dosage of one thousandth) into Cd (0.6%) contaminated soil and cultivating the soil for one week, the pollutant removal rate was 54.4% and the material recovery rate was 87%.

[0055] Fertilizer slow-release effect of gel composite material: 1g of α-FeOOH composite hydrogel was placed in 1000 mL of aqueous solution to verify the slow-release effect of fertilizer. The slow-release period was 30 days, and the slow-release amount of phosphorus increased day by day, reaching 0.13g / L.

[0056] 10 g of α-FeOOH composite hydrogel was placed in 20 kg of soil to verify the slow-release effect of fertilizer. The slow-release period was 30 days, and the slow-release amount of soil phosphorus increased day by day, with an increase of 11% in 30 days.

[0057] The above embodiments are intended only to illustrate the structural concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the present invention and implement it accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made based on the essence of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing an α-FeOOH gel composite material, characterized in that: The following steps are involved: Step 1: preparing a mixed solid powder based on biodegradable plastic, fly ash, and phosphate rock powder, adding the mixed solid powder to humic acid to obtain a gel, and adding the gel to a FeSO4 solution and stirring to mix; Step 2: Slowly add NaOH solution dropwise to the mixture in step 1 while stirring, control the mass ratio of FeSO4 to NaOH and the pH value of the NaOH solution, and oxidize under air to obtain a supported α-FeOOH seed crystal suspension complex; Step 3: Dispersing chitosan in a mixed aqueous solution of humic acid and acetic acid, stirring and dissolving the mixture evenly, so that the chitosan macromolecules and the humic acid molecular chains are cross-linked and fixed, thereby obtaining a mixed aqueous solution of chitosan and humic acid; Step 4: mixing the supported α-FeOOH seed suspension complex with the mixed aqueous solution of chitosan and humic acid, and adding a cross-linking agent to cross-link them to obtain a cross-linked mixture solution; Step 5: FeSO4 solution is added to the cross-linked mixture solution again, and NaOH solution is added dropwise while oxidizing with air to control the pH value of the cross-linked mixture solution, so that α-FeOOH is precipitated in situ in the unit space inside the gel and on the surface, and grows on the supported α-FeOOH seed crystals to obtain an α-FeOOH-gel sustained-release composite material.

2. The method for preparing the α-FeOOH gel composite material according to claim 1, characterized in that: The step 1 comprises: Step 1-1: cooling the fly ash heated in a high-temperature muffle furnace and washing it in dilute sulfuric acid to obtain high-temperature acid-washed fly ash; Step 1-2: Grind and sieve the biodegradable plastic, high-temperature acid-washed fly ash, and phosphate rock powder according to the mass ratio, and then evenly mix them so that the high-temperature acid-washed fly ash and phosphate rock powder adhere to the pores of the biodegradable plastic to obtain a basic mixed powder; Step 1-3: Mix the basic mixed powder and humic acid according to the mass ratio, and mechanically stir until the liquid evaporates completely, exposing the functional groups of the degradable plastic to obtain a gel.

3. The method for preparing the α-FeOOH gel composite material according to claim 2, characterized in that: In step 1: the temperature of the high-temperature muffle furnace is 500-800 degrees Celsius, the heating time is 1-2 hours, and the concentration of dilute sulfuric acid is 0.1%-0.5%; Use a 200-mesh sieve to screen, and the mass ratio of biodegradable plastic, fly ash, and phosphate rock powder is 2:1:0.5; The mass ratio of the basic mixed powder to humic acid is 1:0.

5.

4. The method for preparing the α-FeOOH gel composite material according to claim 1, characterized in that: In step 1, the FeSO4 content in the FeSO4 solution is 25%, and the mass ratio of the weight of the mixed solid powder in the gel to the FeSO4 solution is 1:

2. During mixing, the gel is slowly added to the FeSO4 solution step by step and batch by batch while mechanically stirring for 2-4 hours to allow the iron ions to infiltrate the solid powder.

5. The method for preparing the α-FeOOH gel composite material according to claim 1, characterized in that: In the step 2, the stirring state is maintained during the oxidation with air so that the mixed liquid remains suspended.

6. The method for preparing the α-FeOOH gel composite material according to claim 1, characterized in that: In step 3, the concentration of chitosan is 2%, the concentration of humic acid is 2%, and the concentration of acetic acid is 0.5%, and mechanical stirring and dissolution are performed at room temperature.

7. The method for preparing the α-FeOOH gel composite material according to claim 1, characterized in that: In the step 4, the mass ratio of the supported α-FeOOH seed suspension complex to the mixed aqueous solution of chitosan and humic acid is 3:1, and glutaraldehyde is used as the cross-linking agent.

8. The method for preparing the α-FeOOH gel composite material according to claim 1, characterized in that: In step 5, the mass ratio of the FeSO4 solution added again is 1%.

9. An α-FeOOH gel composite material, characterized in that: The invention comprises a supported α-FeOOH crystal suspension complex, chitosan, humic acid, acetic acid, a crosslinking agent, a FeSO4 solution, and a NaOH solution. The chitosan is dispersed in a mixed aqueous solution of humic acid and acetic acid. The supported α-FeOOH crystal suspension complex comprises degradable plastic, fly ash, phosphate rock powder, humic acid, a FeSO4 solution, and a NaOH solution.

10. The α-FeOOH gel composite material according to claim 1, characterized in that: The mass ratio of degradable plastic, fly ash and phosphate rock powder is 2:1:0.5, the mass ratio of the total solid mass of degradable plastic, fly ash and phosphate rock powder to FeSO4 solution is 1:2, the mass ratio of FeSO4 to NaOH is 4:1, and the mass ratio of the mixed aqueous solution obtained by dispersing chitosan in a mixed aqueous solution of humic acid and acetic acid to the α-FeOOH seed suspension complex is 3:1.

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