Preparation method of acrylic acid copolymer composite ZrMOF aerogel fertilizer slow-release material

Abstract

The present invention relates to a preparation method of an acrylic copolymer composite ZrMOF aerogel fertilizer slow-release material, which comprises the following steps: (1) dissolving a zirconium salt and pyromellitic acid in a mixed solvent at room temperature, subsequently adding concentrated HCl, and reacting after ultrasonic dissolution; after the reaction product is cooled to room temperature, centrifugation, washing, and drying overnight to obtain a mesoporous ZrMOF powder; (2) uniformly mixing the mesoporous ZrMOF powder with nitrogen fertilizer and distilled water to obtain a ZrMOF / nitrogen fertilizer mixed solution; (3) adding the ZrMOF / nitrogen fertilizer mixed solution and a polysaccharide natural polymer to a container in sequence and stirring at room temperature; simultaneously adding a water-soluble initiator, an acrylic acid monomer mixed solution, and a cross-linking agent aqueous solution from different bottle openings; after stirring the reaction, the product is washed and freeze-dried to obtain an acrylic copolymer composite ZrMOF aerogel fertilizer slow-release material. The present invention has a simple process, readily available raw materials, low cost, mild preparation conditions, and the obtained material is eco-friendly, safe, and reliable, and can be applied to the agricultural field, especially in arid and semi-arid areas.

Description

Technical Field

[0001] The present invention relates to the fields of functional polymer materials and agricultural materials, and in particular to a method for preparing an acrylic acid copolymer composite ZrMOF aerogel fertilizer slow-release material. Background Art

[0002] With the rapid development of industry and agriculture and the growing world population, food security has become a major concern. The large-scale production and application of chemical fertilizers has placed a severe burden on the environment and soil. Improving fertilizer utilization and increasing food production is crucial for selecting fertilization methods. Agricultural production is inseparable from soil nutrients, which are both the foundation of agricultural production and the material prerequisite for sustainable agricultural development. However, depending on the application method and climatic conditions, up to 90% of applied fertilizers fail to reach the target plants, leading to adverse biological reactions, cyclical application, rising costs, and environmental hazards. Therefore, while traditional fertilizers promote plant growth, they also suffer from drawbacks such as severe pollution, high costs, and diminishing returns. Slow-release fertilizers offer an alternative solution to this problem.

[0003] Slow-release fertilizers, or controlled-release fertilizers, are carriers of fertilizer ingredients that gradually release nutrients needed by crops, thereby improving soil safety and productivity, accelerating plant growth, and increasing fertilizer utilization efficiency. Using slow-release fertilizers can reduce the loss of fertilizer nutrients, particularly nitrogen, in the soil, reduce the number of fertilization operations, save labor and costs, and avoid damage to seeds or seedlings caused by excessive fertilization. For example, invention patent CN 112608188 A discloses a method for preparing a loess-based geopolymer composite slow-release fertilizer. However, conventional slow-release fertilizers still have shortcomings in use. For example, Gil-OrtizR, et. al. (Enhanced Agronomic Efficiency Using a New Controlled-Released, Polymeric-Coated Nitrogen Fertilizer in Rice [J]. Plants, 2020, 9(9): 1183.) combined byproducts of wood pulp production with urease inhibitors and natural biostimulants and coated them with polymers to obtain a coating material with a slow-release effect of urea. Although this slow-release fertilizer has a low cost, the membrane material and carrier residues still have negative effects. Guo Y, et. al. (Effects of HumicAcid Added to Controlled-Release Fertilizer on Summer Maize Yield, Nitrogen Use Efficiency and Greenhouse Gas Emission [J]. Agriculture, 2022, 12 (4): 448.) By adding humic acid to controlled-release fertilizer to increase crop yield and nitrogen absorption, this controlled-release fertilizer increased crop yield, but it had the problem of insufficient initial nutrient release rate. Invention patent CN 116410028 A discloses a starch-based anti-floating hydrogel slow-release fertilizer and its preparation method. This material is physically cross-linked with cationic starch and anionic polyacrylic acid to prepare a starch-based hydrogel slow-release fertilizer. This prevents the slow-release fertilizer from floating on the water surface, achieving uniform slow-release of the fertilizer, and exhibiting good water retention and biodegradability. However, this slow-release fertilizer suffers from high processing costs and cumbersome procedures. Therefore, developing a fertilizer-carrying system with high nutrient loading and good slow-release performance is an effective way to reduce fertilizer losses and improve fertilizer utilization.

[0004] Metal-organic frameworks (MoFs) have numerous applications in catalytic degradation, adsorption and separation, gas storage, and drug delivery due to their large surface area, diverse ligands, high porosity, and flexible, tunable structure. However, their application in agriculture is relatively limited. For example, invention patent CN 112546222 A discloses a metal-organic framework microwave-sensitizing microsphere and its preparation method; invention patent CN 112129818 A discloses a Cu-ZrMOF-based multimodal signal detection method for chlorpyrifos in vegetables. Despite these advantages, the inherent microporous structure of most reported MOFs limits their functionality in practical applications. Therefore, the preparation of MOFs with mesoporous structures holds great promise. Most existing studies have synthesized mesoporous MOFs by modifying the pore structure of MOFs through the introduction of templates or large organic ligands. For example, invention patent CN 113231102 A discloses a glutaric acid-selective polyacid catalyst based on a micro-mesoporous Zr-MOF material, its preparation method, and application; invention patent CN 114307975 A discloses a micro-mesoporous UiO-metal-organic framework material for the reverse-selective adsorption separation of isoparaffins; invention patent CN 112111478 A discloses a mesoporous Me / UIO-66-ZrMOF material, its preparation method, and application; and invention patent CN 107008507 A discloses a mesoporous Fe-based MOF@AgI high-efficiency composite visible light photocatalytic material, its preparation method, and application. However, large-sized organic ligands often require multi-step synthesis, resulting in cumbersome preparation processes and low yields. Template-based preparation, from the initial introduction of the template to the final removal of the template, is a lengthy and time-consuming process, making it unsuitable for large-scale production. Therefore, the facile synthesis of mesoporous MOFs remains an area of ​​research.

[0005] MOFs are emerging porous materials for fertilizer delivery, providing a new carrier for the slow release of nutrients and potentially serving as a nutrient source for crop growth. Wang Y, et al. (Synthesis of a pH-responsive nano-cellulose / sodium alginate / MOFs hydrogel and its application in the regulation of water and N-fertilizer [J]. International Journal of Biological Macromolecules, 2021, 187: 262-271.) designed a pH-sensitive cellulose / MOFs hydrogel by combining a cellulose-based hydrogel with MIL-100(Fe). This material exhibits excellent water-holding capacity, losing total water after 30 days, 18 days longer than pure soil. The resulting MOF-based slow-release fertilizer exhibits excellent performance and can be used in green agriculture. Lin X, et al. (A TEMPO-oxidized cellulose nanofibers / MOFs hydrogel with temperature and pH responsiveness for fertilizers slow-release [J]. International Journal of Biological Macromolecules, 2021, 191: 483-491.) used a free radical polymerization method to prepare a MOF-Fe@CNFs hydrogel based on oxidized cellulose nanofibers (CNFs). After loading urea, a temperature- and pH-sensitive slow-release fertilizer was prepared. The addition of MOF-Fe enhanced the hydrogel's urea loading capacity and slow-release ability, while also improving its water retention. Guo L, et al. (Synthesis of bio-based MIL-100(Fe)@CNF-SA composite hydrogel and its application in slow-release N-fertilizer [J]. Journal of Cleaner Production, 2021, 324: 129274.) A novel cellulose-based hydrogel (MOF-(Fe)@CNF-SA) was synthesized in situ by combining metal organic frameworks (MOFs) with nanocellulose (CNFs) and sodium alginate (SA).Due to the synergistic effect of the porous structure of the hydrogel and the high specific surface area of ​​MOFs, the application of slow-release fertilizer achieves the slow release of urea. In addition, after applying MOF-(Fe)@CNF-SA slow-release fertilizer, the germination rate and chlorophyll content of wheat were doubled compared to those without slow-release fertilizer. However, current research has mainly focused on FeMOF, CuMOF, and AlMOF due to their inherent pore structure and specific surface area, as well as Cu. 2+ and Al 3+ The dissolution of metal organic frameworks limits their function (Wang Zhengxian. Preparation and performance research of slow-release fertilizers based on metal organic framework materials [D]. Hubei University for Nationalities, Enshi, 2022.).

[0006] UiO-66 has the potential to be used as a drug and pesticide carrier due to its excellent chemical stability, non-toxicity, and large-scale production advantages. For example, Isabel L, et. al. (Surface-Functionalization of Zr-FumarateMOF for Selective Cytotoxicity and Immune System Compatibility inNanoscale Drug Delivery [J]. ACS Appl. Mater. Interfaces, 2018, 10(37):31146-31157.) first synthesized the Zr-fum carrier material and then loaded the drug dichloroacetic acid, which can be used in the medical field. Meng W, et al. (Preparation of a novel sustained-release system for pyrethroids by using metal-organic frameworks (MOFs) nanoparticles [J]. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2020, 604, 125266.) encapsulated cyhalothrin (LC) in nanostructured UiO-66 (LC@UiO-66), demonstrating high drug loading and excellent sustained-release properties. Therefore, optimizing the porosity, specific surface area, and biotoxicity of MOFs to make them suitable for agricultural applications is currently a hot topic.

[0007] In summary, the performance of slow-release fertilizers varies significantly under different environmental conditions. It is worth exploring how to achieve intelligent slow-release fertilizers and fully utilize the porous structure and trace elements of MOFs to enable them to make greater contributions to modern agriculture. Furthermore, while there are numerous methods for preparing slow-release fertilizers, relatively few reports have been published using metal-organic frameworks.

[0008] Zirconium, primarily present in mineral form in nature, possesses exceptional stability, biocompatibility, non-toxicity, and excellent corrosion resistance, finding applications in a wide range of fields. For example, zirconium dioxide is the primary component of ceramics, knives, and decorative items essential to everyday life. High-performance zirconium oxide is commonly used in dental materials, artificial joints, pacemakers, and other biomedical applications. Nanozirconia can be made into a range of clinical chemistry reagents, bioseparation materials, and biomedical materials for tissue and organ repair and replacement. Zircon is commonly used in cosmetic additives, bracelet ornaments, paints, abrasives, the glass industry, and in the manufacture of refractory materials. Zirconium and its alloys are found in rocket launcher nozzles, lunar rover brackets, spacecraft heat shields, and submarine engines. Within China's zirconium material manufacturing industry, metallic zirconium is expected to have the greatest potential, brightest spots, and greatest development prospects. Therefore, this paper designs and synthesizes zirconium-based MOFs (ZrMOFs) with the goal of developing new agricultural materials for agricultural applications. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to provide a method for preparing an acrylic copolymer composite ZrMOF aerogel fertilizer slow-release material with simple preparation process, low cost and environmental friendliness.

[0010] To solve the above problems, the present invention provides a method for preparing an acrylic acid copolymer composite ZrMOF aerogel fertilizer slow-release material, comprising the following steps:

[0011] ⑴ At room temperature, zirconium salt and trimesic acid are dissolved in a mixed solvent, followed by adding concentrated HCl and sonicating for 20 to 50 minutes to fully dissolve them; then, the resulting solution is transferred to a polytetrafluoroethylene autoclave and reacted at 100 to 140°C for 15 to 25 hours to obtain a reaction product; after the reaction product is cooled to room temperature, it is centrifuged, washed with a polar solvent 3 to 6 times, and dried at 60°C overnight to obtain a mesoporous ZrMOF powder;

[0012] ⑵ The mesoporous ZrMOF powder is mixed with nitrogen fertilizer and distilled water in a mass ratio of 0.1:1:3 to 0.7:2:6 to obtain a ZrMOF / nitrogen fertilizer mixture;

[0013] ⑶ In a container equipped with a heating bath, a magnetic stirring device, and a reflux condenser, ZrMOF / nitrogen fertilizer mixture and polysaccharide natural polymer are added in sequence and stirred at room temperature for 10 to 30 minutes; then, a water-soluble initiator, an acrylic acid monomer mixture, and a cross-linking agent aqueous solution are added dropwise from different bottle openings at 50°C under uniform stirring; after the addition is completed, the temperature is raised to 70°C and the reaction is stirred for 2 to 6 hours to obtain a gel product. The product is washed three times with anhydrous ethanol and freeze-dried to obtain an acrylic acid copolymer composite ZrMOF aerogel fertilizer slow-release material.

[0014] In step (1), the zirconium salt refers to one of zirconium tetrachloride, zirconium oxychloride octahydrate, and zirconium dioxide; the trimesic acid refers to 2-amino-1,3,5-benzenetricarboxylic acid or 1,3,5-benzenetricarboxylic acid; and the mass ratio of the zirconium salt to the trimesic acid is 1.0:1.0 to 1.0:4.0.

[0015] The mixed solvent in step (1) is one of N,N-methyleneformamide / ethanol, N,N-methyleneformamide / water, and N,N-methyleneformamide / methanol mixed solvents; the ratio of zirconium salt to mixed solvent is 80-114:10-40 (mg / mL); and the volume ratio of mixed solvent to concentrated HCl is 10-40:1-3 (mL / mL).

[0016] The polar solvent in step (1) is one of methanol, N,N-methyleneformamide and water.

[0017] In the step (2), the nitrogen fertilizer is one of urea, ammonium chloride, ammonium nitrate and ammonium bicarbonate.

[0018] In step (3), the amount of the ZrMOF / nitrogen fertilizer mixture is 85-135% of the mass of the acrylic acid monomer mixture.

[0019] The polysaccharide natural polymer in step (3) is one of starch, cellulose, and xanthan gum; the amount of the polysaccharide natural polymer is 1-15% of the mass of the acrylic acid monomer mixture.

[0020] The water-soluble initiator in step (3) refers to a solution obtained by uniformly mixing the initiator and water in a mass ratio of 1:20 to 1:100; the initiator is potassium persulfate or ammonium persulfate, and its amount is 0.75 to 5% of the total monomer mass.

[0021] The acrylic acid monomer mixture in step (3) refers to a solution obtained by uniformly mixing acrylic acid and a dibasic organic acid in a mass ratio of 1:0.2 to 3:0.7; the neutralization degree of the acrylic acid is 65 to 85%; and the dibasic organic acid is itaconic acid or fumaric acid.

[0022] The crosslinking agent aqueous solution in step (3) refers to a solution obtained by uniformly mixing the crosslinking agent and water in a mass ratio of 1:40 to 1:160; the crosslinking agent is one of N,N-methylenebisacrylamide, boric acid, and sodium perborate, and its amount is 0.1 to 2% of the total monomer mass.

[0023] The freeze-drying conditions in step (3) are a temperature of -30 to -58°C and a freezing time of 10 to 20 h.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] 1. This invention uses a solvothermal method to prepare a mesoporous ZrMOF by adjusting the solvent ratio. The ZrMOF is used as a carrier to load the nutrient source, which is then added to a mixture of acrylic acid monomers to initiate a polymerization reaction, endowing the polymer aerogel fertilizer with water-retention and slow-release properties.

[0026] 2. The acrylic copolymer composite ZrMOF aerogel fertilizer slow-release material prepared by the present invention exhibits a rich macroporous structure. These interconnected pores create a favorable environment for effectively loading fertilizer into the aerogel.

[0027] 3. The present invention adds ZrMOF to the acrylic acid monomer mixture to increase the pore structure and specific surface area of ​​the material, thereby giving the aerogel fertilizer slow-release material more excellent water retention and slow-release properties.

[0028] 4. The present invention applied an acrylic copolymer composite ZrMOF aerogel fertilizer slow-release material to soil water retention and slow-release experiments, as well as to corn growth. The material demonstrated excellent water retention, maintaining a 30.7% water retention rate over 50 days. Furthermore, the aerogel fertilizer slow-release material exhibited good slow-release properties, with a cumulative nitrogen leaching rate of 52.5% over 40 days, positively promoting the growth of corn roots and leaves.

[0029] 5. The process of the present invention is simple, the raw materials are readily available, the cost is low, the preparation conditions are mild, and the prepared materials are eco-friendly, safe and reliable, and can be applied in the agricultural field, especially in arid and semi-arid areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0031] Figure 1 This is a scanning electron microscope image of the acrylic acid copolymer composite ZrMOF aerogel fertilizer slow-release material prepared in Example 2 of the present invention. The left image is an acrylic acid copolymer composite ZrMOF aerogel fertilizer slow-release material; the right image is an enlarged image of the acrylic acid copolymer composite ZrMOF aerogel fertilizer slow-release material.

[0032] Figure 2 This is a surface scan of the element distribution of the acrylic acid copolymer composite ZrMOF aerogel fertilizer slow-release material prepared in Example 2 of the present invention.

[0033] Figure 3 This is an infrared spectrum of the acrylic acid copolymer composite ZrMOF aerogel fertilizer slow-release material prepared in Example 2 of the present invention.

[0034] Figure 4 The maximum water holding capacity result graph (left) and water retention performance result graph (right) of the acrylic acid copolymer composite ZrMOF aerogel fertilizer slow-release material prepared in Example 2 of the present invention are shown.

[0035] Figure 5 The graphs show the slow-release performance of the acrylic acid copolymer composite ZrMOF aerogel fertilizer slow-release material prepared in Example 2 of the present invention. The left graph shows the slow-release of the aerogel material in water; the right graph shows the slow-release of the aerogel material in soil.

[0036] Figure 6 This is a diagram showing the effect of the acrylic copolymer composite ZrMOF aerogel fertilizer slow-release material prepared in Example 2 of the present invention on corn growth. DETAILED DESCRIPTION

[0037] A method for preparing an acrylic acid copolymer composite ZrMOF aerogel fertilizer slow-release material comprises the following steps:

[0038] ⑴ At room temperature, zirconium salt and trimesic acid are dissolved in a mixed solvent, followed by adding concentrated HCl and ultrasonication for 20-50 minutes to fully dissolve them; then, the resulting solution is transferred to a polytetrafluoroethylene high-pressure reactor and reacted at 100-140°C for 15-25 hours to obtain the reaction product; after the reaction product is cooled to room temperature, it is centrifuged, washed with a polar solvent 3-6 times, and dried at 60°C overnight to obtain mesoporous ZrMOF powder.

[0039] Wherein: the zirconium salt refers to one of zirconium tetrachloride, zirconium oxychloride octahydrate, and zirconium dioxide; the trimesic acid refers to 2-amino-1,3,5-benzenetricarboxylic acid or 1,3,5-benzenetricarboxylic acid; and the mass ratio (mg / mg) of the zirconium salt to the trimesic acid is 1.0:1.0 to 1.0:4.0.

[0040] The mixed solvent refers to one of N,N-methyleneformamide / ethanol, N,N-methyleneformamide / water, and N,N-methyleneformamide / methanol mixed solvents, and the volume ratio of the two raw materials in the mixed solvent is 2:1~6:1 (mL / mL); the ratio of zirconium salt to mixed solvent is 80~114:10~40 (mg / mL); and the volume ratio of the mixed solvent to concentrated HCl is 10~40:1~3 (mL / mL).

[0041] The polar solvent is one of methanol, N,N-methyleneformamide and water.

[0042] (2) The mesoporous ZrMOF powder is uniformly mixed with nitrogen fertilizer and distilled water at a mass ratio (g / g) of 0.1:1:3 to 0.7:2:6 to obtain a ZrMOF / nitrogen fertilizer mixture. The nitrogen fertilizer is selected from the group consisting of urea, ammonium chloride, ammonium nitrate, and ammonium bicarbonate.

[0043] ⑶ In a container equipped with a heating bath, magnetic stirring apparatus, and reflux condenser, add the ZrMOF / nitrogen fertilizer mixture and polysaccharide natural polymer in sequence and stir at room temperature for 10-30 minutes. Then, at 50°C and with constant stirring, simultaneously add a water-soluble initiator, acrylic acid monomer mixture, and crosslinker aqueous solution dropwise from different bottle openings. The initiator should be added within 3-10 minutes, and the acrylic acid monomer mixture and crosslinker aqueous solution should be added within 10-30 minutes. After the addition is complete, raise the temperature to 70°C and stir for 2-6 hours to obtain a gel-like product. This product is washed three times with anhydrous ethanol and freeze-dried at -30 to -58°C for 10-20 hours to obtain an acrylic acid copolymer composite ZrMOF aerogel fertilizer slow-release material.

[0044] The amount of the ZrMOF / nitrogen fertilizer mixture is 85-135% of the mass of the acrylic acid monomer mixture.

[0045] The polysaccharide natural polymer refers to one of starch, cellulose and xanthan gum; the amount of the polysaccharide natural polymer is 1-15% of the mass of the acrylic acid monomer mixture.

[0046] The water-soluble initiator refers to a solution obtained by uniformly mixing the initiator and water at a mass ratio (g / g) of 1:20 to 1:100; the initiator is potassium persulfate or ammonium persulfate, and its usage is 0.75 to 5% of the total monomer mass.

[0047] The acrylic acid monomer mixture refers to a solution obtained by uniformly mixing acrylic acid and a dibasic organic acid in a mass ratio (g / g) of 1:0.2 to 3:0.7; the neutralization degree of the acrylic acid is 65 to 85%; and the dibasic organic acid refers to itaconic acid or fumaric acid.

[0048] The crosslinking agent aqueous solution refers to a solution obtained by uniformly mixing the crosslinking agent and water at a mass ratio (g / g) of 1:40 to 1:160; the crosslinking agent is one of N,N-methylenebisacrylamide, boric acid, and sodium perborate, and its usage is 0.1 to 2% of the total monomer mass.

[0049] Example 1 A method for preparing an acrylic acid copolymer composite ZrMOF aerogel fertilizer slow-release material comprises the following steps:

[0050] At room temperature, 100 mg of ZrCl₄ and 125 mg of 2-amino-1,3,5-benzenetricarboxylic acid were dissolved in 30 mL of a 2:1 N,N-methyleneformamide / ethanol mixture. 1 mL of concentrated HCl was then added and sonicated for 20 minutes to fully dissolve the mixture. The resulting solution was then transferred to a 50 mL polytetrafluoroethylene autoclave and reacted at 100°C for 25 hours to obtain the product. After cooling to room temperature, the product was centrifuged, washed four times with water, and dried overnight at 60°C to yield 150 mg of mesoporous ZrMOF powder.

[0051] ⑵ Place 0.1 g of ZrMOF, 1.0 g of ammonium chloride, and 3.0 mL of distilled water in a 10 mL centrifuge tube and shake at a constant temperature for 12 h to obtain a ZrMOF / ammonium chloride mixture.

[0052] (3) In a container equipped with a heating bath, magnetic stirring apparatus, and reflux condenser, the ZrMOF / ammonium chloride mixture and 0.45 g of starch were added sequentially and stirred at room temperature for 10 minutes. Subsequently, at 50°C and with constant stirring, 4.0 mL of an aqueous solution containing 0.05 g of ammonium persulfate, 3.0 g of 65% neutralized acrylic acid, 0.5 g of fumaric acid, and 0.8 mL of a solution containing 0.01 g of boric acid were simultaneously added dropwise from different vials. After the additions were complete, the temperature was raised to 70°C and stirred for 2 hours to yield a gel-like product. This product was then washed three times with anhydrous ethanol and freeze-dried at -30°C for 20 hours to obtain an acrylic acid copolymer-composite ZrMOF aerogel fertilizer slow-release material.

[0053] An acrylic acid copolymer-composite ZrMOF aerogel fertilizer slow-release material was applied to soil water retention, slow-release, and maize growth experiments. The material demonstrated excellent water retention, maintaining over 25% of its water retention rate for 50 days. The aerogel fertilizer slow-release material also exhibited good slow-release properties, reducing cumulative nitrogen leaching by over 50% within 40 days. Furthermore, maize growth experiments demonstrated that the acrylic acid copolymer-composite ZrMOF aerogel fertilizer slow-release material positively promoted maize root and leaf growth.

[0054] Example 2 A method for preparing an acrylic acid copolymer composite ZrMOF aerogel fertilizer slow-release material comprises the following steps:

[0055] At room temperature, 95.5 mg of ZrOCl2·8H2O and 113.1 mg of 1,3,5-benzenetricarboxylic acid were dissolved in 20.0 mL of a 3:1 N,N-methyleneformamide / water mixture. 1.5 mL of concentrated HCl was then added and sonicated for 30 minutes to fully dissolve the mixture. The resulting solution was then transferred to a 100 mL polytetrafluoroethylene autoclave and reacted at 120°C for 24 hours to obtain the product. After cooling to room temperature, the product was centrifuged, washed six times with N,N-methyleneformamide, and dried overnight at 60°C to yield 135 mg of mesoporous ZrMOF powder.

[0056] ⑵ Place 0.4 g of ZrMOF, 1.0 g of urea and 2.0 mL of distilled water in a 10 mL centrifuge tube in sequence and oscillate at a constant temperature in a shaker for 12 h to obtain a ZrMOF / urea mixture.

[0057] (3) In a container equipped with a heating bath, magnetic stirring apparatus, and reflux condenser, the ZrMOF / urea mixture and 0.3 g of xanthan gum were added sequentially and stirred at room temperature for 20 min. Subsequently, at 50°C and with constant stirring, 3.0 mL of an aqueous solution containing 0.08 g of potassium persulfate, 2.5 g of 70% neutralized acrylic acid, 0.5 g of itaconic acid, and 3.0 mL of an aqueous solution containing 0.03 g of N,N-methylenebisacrylamide were simultaneously added dropwise from different vials. After the additions were complete, the temperature was raised to 70°C and stirred for 3 h to yield a gel-like product. This product was then washed three times with anhydrous ethanol and freeze-dried at -45°C for 17 h to obtain an acrylic acid copolymer-composite ZrMOF aerogel fertilizer slow-release material.

[0058] The acrylic acid copolymer composite ZrMOF aerogel fertilizer slow-release material prepared in the present invention was characterized, analyzed, and tested for performance using the following methods.

[0059]

Microscopic morphology

[0060] The morphological analysis of the aerogel fertilizer slow-release material prepared by the present invention was performed using a scanning electron microscope. Figure 1 (Left) The surface of the aerogel fertilizer slow-release material exhibits a rich macroporous structure. These interconnected pores create a favorable environment for the efficient loading of fertilizers into the aerogel. These irregular pores vary in density and size, and the presence of cavities demonstrates the aerogel's excellent adsorption capacity for water and urea. The formation of these macropores is attributed to the large surface area of ​​ZrMOF and the freeze-drying process.

[0061] Figure 1(Right) is an enlarged view of the left image, showing the presence of numerous flower-like structures composed of stacked octahedral ZrMOFs within the voids of the aerogel fertilizer slow-release material. Furthermore, the image reveals a polyhedral structure with distinct defects in the ZrMOF. Compared to traditional ZrMOF octahedra, this morphology has changed significantly, likely due to solvent effects. Therefore, adjusting the ratio of the mixed solvents can lead to defects on the MOF surface, indicating the successful composite of ZrMOF and acrylic acid copolymer, and demonstrating the successful synthesis of the acrylic acid copolymer-composite ZrMOF aerogel fertilizer slow-release material.

[0062]

EDS elemental analysis

[0063] The distribution of elements in the selected area of ​​the aerogel fertilizer slow-release material prepared by the present invention was analyzed by EDS, and the results are as follows: Figure 2 As shown in the figure, the presence of C, Zr, O, Cl, and Na in the aerogel fertilizer slow-release material is clearly observed. Zr, Cl, and Na primarily originate from the ZrMOF. Furthermore, the distinct Zr granules and the uniform distribution of C and O in the selected area demonstrate clear elemental profiles and uniform distribution within the functional material. This demonstrates the successful composite of ZrMOF and acrylic acid copolymer.

[0064]

Infrared spectroscopy analysis

[0065] Figure 3 This is the infrared spectrum of acrylic acid copolymer composite ZrMOF aerogel fertilizer slow-release material. As can be seen from the figure, 3442 cm -1 The broad absorption peak at 2923 cm is attributed to the stretching vibration of ZrMOF and acrylic acid monomer OH. -1 and 2849 cm -1 The peak at 1720 cm corresponds to the asymmetric stretching vibration of -CH2 in the acrylic acid monomer in the aerogel structure. -1 The peak near 713 cm corresponds to the C=O stretching vibration of -COOH. -1 and 646 cm -1 The characteristic peak of Zr-O bond appeared at , proving the existence of ZrMOF. This shows that ZrMOF and acrylic acid copolymer have been successfully compounded, and also shows that acrylic acid copolymer-composite ZrMOF aerogel fertilizer slow-release material has been successfully prepared.

[0066] Maximum water holding capacity and water retention performance

[0067] In some arid and semi-arid regions, the expansion of cultivated areas is restricted due to water shortage. This has prompted people to seek the use of water-retaining agents with high water-holding properties. In order to reveal the effect of not adding ZrMOF on water retention and nutrient release in the preparation process of the present invention, the soil without aerogel was used as a control group, and its maximum water holding capacity and water retention capacity were studied. The results are as follows: Figure 4 shown.

[0068] Compared with the control group, there was a significant difference in the water holding capacity of the soil after treatment with aerogel fertilizer slow-release material ( Figure 4 Left). The maximum water holding capacity of the soil after applying the aerogel fertilizer slow-release material was 46.1%, compared to 33.3% in the control group. This indicates that the aerogel fertilizer slow-release material improved soil quality, increasing its water holding capacity by 12.8%. The aerogel fertilizer slow-release material's excellent water-holding capacity is attributed to the aerogel's macroporous structure and abundant hydrophilic groups.

[0069] Figure 4 (Right) A graph shows the water retention performance of the aerogel fertilizer slow-release material in soil. The blank (pure soil) exhibits the lowest water retention, with virtually no water lost within 15 days. In contrast, the soil treated with the aerogel fertilizer slow-release material maintained a 30.7% water retention rate after 50 days. This improved water retention is attributed to the aerogel's three-dimensional network structure, abundant hydrophilic groups, and the high specific surface area and porous structure of ZrMOF. This indicates that the acrylic copolymer-composite ZrMOF aerogel fertilizer slow-release material, as an environmentally friendly water-retaining agent, can meet plant water needs while providing water for growth. Therefore, it has potential for application in arid and semi-arid regions.

[0070]

Sustained release performance

[0071] In order to evaluate the application of aerogel materials in controlled release chemical systems, the slow-release performance of acrylic acid copolymer composite ZrMOF aerogel fertilizer slow-release material was studied. The results are as follows Figure 5 As shown. Figure 5 (Left) As can be seen, the cumulative release rate of the control (urea) in water is significantly faster than that of the aerogel fertilizer slow-release material, reaching 100% nutrient release in a very short time. However, the nutrient release rate in the aerogel is significantly slower, with cumulative nutrient leaching reaching 61.9% within 150 minutes. This indicates that the aerogel significantly reduces cumulative nitrogen leaching in water.

[0072] In addition, the slow-release performance of acrylic acid copolymer composite ZrMOF aerogel fertilizer slow-release material in soil was studied. Figure 5As can be seen in the figure (right), there is a significant difference in the release rates of fertilizer nutrients in soil and water, with the cumulative nutrient release rate in soil being significantly slower than that in water. This is largely due to the reduced diffusion of nutrients in the soil environment, which leads to a decrease in the dynamic exchange rate between water and the nutrient-loaded aerogel. The cumulative N leaching rate in the control group reached 100% within 10 days, significantly higher than that in the aerogel-applied group. Within 40 days, the aerogel fertilizer slow-release material achieved a cumulative N leaching rate of 52.5%. This is attributed to the porous structure of the ZrMOF, where the fertilizer is loaded into the ZrMOF pores. The polymer network then encapsulates the fertilizer-containing ZrMOF, slowing nutrient release. These results demonstrate that the acrylic copolymer-composite ZrMOF aerogel fertilizer slow-release material exhibits excellent slow-release properties, attributed to the synergistic effect of the aerogel's porous structure and the high surface area of ​​the ZrMOF. This slows nutrient leaching from soil and effectively reduces the environmental threat posed by groundwater.

[0073] [Pot experiment]

[0074] The speed of nutrient release from fertilizer has a significant impact on corn growth indicators, such as Figure 6 The figure shows the effects of the blank control, urea application, control group (without ZrMOF), commercial compound fertilizer, and acrylic acid copolymer-composite ZrMOF aerogel fertilizer slow-release material on corn plant growth. The figure shows that the corn plants in the blank and commercial compound fertilizer groups were smaller, while the corn treated with acrylic acid copolymer-composite ZrMOF aerogel fertilizer slow-release material exhibited a significant growth advantage over the other groups. This was primarily manifested in wider leaves, larger plants, and longer leaves. Furthermore, the corn treated with the aerogel fertilizer slow-release material exhibited more robust root development and thicker roots. This indicates that the addition of the aerogel fertilizer slow-release material positively promotes plant growth and root nourishment, releasing water and nutrients retained in the polymer network for absorption by the corn. This suggests that the acrylic acid copolymer-composite ZrMOF aerogel fertilizer slow-release material can reduce the rate of nutrient release, providing nutrients to the plant's roots and growth, resulting in better plant growth indicators.

[0075] In summary, the acrylic acid copolymer-composite ZrMOF aerogel fertilizer slow-release material was applied to soil water retention, slow-release, and maize growth experiments. It demonstrated excellent water retention, maintaining a 30.7% water retention rate over 50 days. Furthermore, the aerogel fertilizer slow-release material exhibited good slow-release properties, with a cumulative nitrogen leaching rate of 52.5% over 40 days. Furthermore, maize growth experiments demonstrated that the acrylic acid copolymer-composite ZrMOF aerogel fertilizer slow-release material positively promoted maize root and leaf growth.

[0076] Example 3 A method for preparing an acrylic acid copolymer composite ZrMOF aerogel fertilizer slow-release material comprises the following steps:

[0077] At room temperature, 80.0 mg of ZrO2 and 120.0 mg of 1,3,5-benzenetricarboxylic acid were dissolved in 15.0 mL of a 5:1 N,N-methyleneformamide / ethanol mixture. 1.0 mL of concentrated HCl was then added and sonicated for 20 minutes to fully dissolve the mixture. The resulting solution was then transferred to a 50 mL polytetrafluoroethylene autoclave and reacted at 130°C for 20 hours to obtain the reaction product. After cooling to room temperature, the product was centrifuged, washed four times with methanol, and dried at 60°C overnight to yield 113 mg of mesoporous ZrMOF powder.

[0078] ⑵ Place 0.7 g of ZrMOF, 2.0 g of ammonium nitrate, and 6.0 mL of distilled water in a 10 mL centrifuge tube and shake at a constant temperature for 12 h to obtain a ZrMOF / ammonium nitrate mixture.

[0079] (3) In a container equipped with a heating bath, magnetic stirring apparatus, and reflux condenser, the ZrMOF / ammonium nitrate mixture and 0.6 g of cellulose were added sequentially and stirred at room temperature for 30 minutes. Subsequently, at 50°C and with constant stirring, 8.0 mL of an aqueous solution containing 0.1 g of ammonium persulfate, 6.0 g of 70% neutralized acrylic acid, 1.0 g of itaconic acid, and 1.6 mL of an aqueous solution containing 0.04 g of boric acid were simultaneously added dropwise from different vials. After the additions were complete, the temperature was raised to 70°C and stirred for 6 hours to yield a gel-like product. This product was then washed three times with anhydrous ethanol and freeze-dried at -45°C for 14 hours to obtain an acrylic acid copolymer-composite ZrMOF aerogel fertilizer slow-release material.

[0080] An acrylic acid copolymer-composite ZrMOF aerogel fertilizer slow-release material was applied to soil water retention, slow-release, and maize growth experiments. The material demonstrated excellent water retention, maintaining a 28% water retention rate over 50 days. The aerogel fertilizer slow-release material also exhibited good slow-release properties, reducing cumulative nitrogen leaching by over 55% within 40 days. Furthermore, maize growth experiments demonstrated that the acrylic acid copolymer-composite ZrMOF aerogel fertilizer slow-release material positively promoted maize root and leaf growth.

[0081] Example 4 A method for preparing an acrylic acid copolymer composite ZrMOF aerogel fertilizer slow-release material comprises the following steps:

[0082] At room temperature, 113.5 mg of ZrCl₄ and 133.9 mg of 1,3,5-benzenetricarboxylic acid were dissolved in 40 mL of a 6:1 N,N-methyleneformamide / methanol mixture. 2 mL of concentrated HCl was then added and dispersed by sonication for 40 minutes. The resulting solution was then transferred to a 100 mL polytetrafluoroethylene autoclave and reacted at 140°C for 15 hours to obtain the reaction product. After cooling to room temperature, the reaction product was centrifuged, washed five times with methanol, and dried at 60°C overnight to yield 185 mg of mesoporous ZrMOF powder.

[0083] ⑵ Place 0.5 g of ZrMOF, 2.0 g of ammonium bicarbonate, and 4.0 mL of distilled water in a 10 mL centrifuge tube and shake at a constant temperature for 12 h to obtain a ZrMOF / ammonium bicarbonate mixture.

[0084] (3) In a container equipped with a heating bath, magnetic stirring apparatus, and reflux condenser, the ZrMOF / ammonium bicarbonate mixture and 0.5 g of cellulose were added sequentially and stirred at room temperature for 25 minutes. Subsequently, at 50°C and with constant stirring, 1.0 mL of an aqueous solution containing 0.04 g of potassium persulfate, 4.0 g of 75% neutralized acrylic acid, 0.9 g of fumaric acid, and 2.0 mL of an aqueous solution containing 0.03 g of sodium borate were simultaneously added dropwise from different vials. After the additions were complete, the temperature was raised to 70°C and stirred for 5 hours to yield a gel-like product. This product was then washed three times with anhydrous ethanol and freeze-dried at -58°C for 12 hours to obtain an acrylic acid copolymer-composite ZrMOF aerogel fertilizer slow-release material.

[0085] An acrylic acid copolymer-composite ZrMOF aerogel fertilizer slow-release material was applied to soil water retention and slow-release experiments, as well as to corn growth. The material demonstrated excellent water retention, maintaining approximately 35% of its water retention rate over 50 days. The aerogel fertilizer slow-release material also exhibited good slow-release properties, reducing cumulative nitrogen leaching by approximately 45% over 40 days. Furthermore, corn growth experiments demonstrated that the acrylic acid copolymer-composite ZrMOF aerogel fertilizer slow-release material positively promoted root and leaf growth.

Claims

1. A method for preparing an acrylic acid copolymer composite ZrMOF aerogel fertilizer slow-release material, comprising the following steps: ⑴ At room temperature, a zirconium salt and trimesic acid are dissolved in a mixed solvent, followed by adding concentrated HCl and ultrasonically dissolving them for 20 to 50 minutes to fully dissolve them; then, the resulting solution is transferred to a polytetrafluoroethylene autoclave and reacted at 100 to 140°C for 15 to 25 hours to obtain a reaction product; after the reaction product is cooled to room temperature, it is centrifuged, washed with a polar solvent 3 to 6 times, and dried at 60°C overnight to obtain a mesoporous ZrMOF powder; the zirconium salt is one of zirconium tetrachloride, zirconium oxychloride octahydrate, and zirconium dioxide; the trimesic acid is 2-amino-1,3,5-benzenetricarboxylic acid or 1,3,5-benzenetricarboxylic acid; the mass ratio of the zirconium salt to the trimesic acid is 1.0:1.0 to 1.0:4.0; ⑵ The mesoporous ZrMOF powder is mixed with nitrogen fertilizer and distilled water in a mass ratio of 0.1:1:3 to 0.7:2:6 to obtain a ZrMOF / nitrogen fertilizer mixture; ⑶ In a container equipped with a heating bath, a magnetic stirring device, and a reflux condenser, ZrMOF / nitrogen fertilizer mixture and polysaccharide natural polymer are added in sequence and stirred at room temperature for 10 to 30 minutes; then, a water-soluble initiator, acrylic acid monomer mixture, and crosslinker aqueous solution are added dropwise from different bottle openings at 50°C under uniform stirring; after the addition is completed, the temperature is raised to 70°C and stirred for reaction for 2 to 6 hours to obtain a gel product, which is washed three times with anhydrous ethanol and freeze-dried to obtain an acrylic copolymer composite ZrMOF aerogel fertilizer slow-release material; the polysaccharide natural polymer is one of starch, cellulose, and xanthan gum; the amount of the polysaccharide natural polymer is 1 to 15% of the mass of the acrylic acid monomer mixture; the acrylic acid monomer mixture is a solution obtained by uniformly mixing acrylic acid and a dibasic organic acid in a mass ratio of 1:0.2 to 3:0.7; the neutralization degree of the acrylic acid is 65 to 85%; the dibasic organic acid is itaconic acid or fumaric acid.

2. The method for preparing an acrylic acid copolymer composite ZrMOF aerogel fertilizer slow-release material according to claim 1, characterized in that: The mixed solvent in step (1) is one of N,N-methyleneformamide / ethanol, N,N-methyleneformamide / water, and N,N-methyleneformamide / methanol mixed solvents; the ratio of zirconium salt to mixed solvent is 80-114:10-40 (mg / mL); and the volume ratio of mixed solvent to concentrated HCl is 10-40:1-3 (mL / mL).

3. The method for preparing an acrylic acid copolymer composite ZrMOF aerogel fertilizer slow-release material according to claim 1, characterized in that: The polar solvent in step (1) is one of methanol, N,N-methyleneformamide and water.

4. The method for preparing an acrylic acid copolymer composite ZrMOF aerogel fertilizer slow-release material according to claim 1, characterized in that: In the step (2), the nitrogen fertilizer is one of urea, ammonium chloride, ammonium nitrate and ammonium bicarbonate.

5. The method for preparing an acrylic acid copolymer composite ZrMOF aerogel fertilizer slow-release material according to claim 1, characterized in that: In step (3), the amount of the ZrMOF / nitrogen fertilizer mixture is 85-135% of the mass of the acrylic acid monomer mixture.

6. The method for preparing an acrylic acid copolymer composite ZrMOF aerogel fertilizer slow-release material according to claim 1, characterized in that: The water-soluble initiator in step (3) refers to a solution obtained by uniformly mixing the initiator and water in a mass ratio of 1:20 to 1:100; the initiator is potassium persulfate or ammonium persulfate, and its amount is 0.75 to 5% of the total monomer mass.

7. The method for preparing an acrylic acid copolymer composite ZrMOF aerogel fertilizer slow-release material according to claim 1, characterized in that: The crosslinking agent aqueous solution in step (3) refers to a solution obtained by uniformly mixing the crosslinking agent and water in a mass ratio of 1:40 to 1:160; the crosslinking agent is one of N,N-methylenebisacrylamide, boric acid, and sodium borate, and its amount is 0.1 to 2% of the total monomer mass.

8. The method for preparing an acrylic acid copolymer composite ZrMOF aerogel fertilizer slow-release material according to claim 1, characterized in that: The freeze-drying conditions in step (3) are a temperature of -30 to -58°C and a freezing time of 10 to 20 h.

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