Preparation method of anti-ultraviolet modified starch-based composite material and application thereof in pesticide

Abstract

This invention discloses a method for preparing UV-resistant modified starch-based composite materials and their application in pesticides, belonging to the field of pesticide technology. The method involves synthesizing UV-resistant mesoporous nanospheres from zinc and aluminum salts using a hydrothermal method, followed by the preparation of photoresponsive modified powder. The UV-resistant mesoporous nanospheres and the photoresponsive modified powder are then combined via a grafting method to obtain photoresponsive UV-resistant mesoporous nanospheres. Subsequently, under alkaline conditions, the photoresponsive UV-resistant mesoporous nanospheres are firmly deposited on the surface of starch microspheres prepared from corn starch using dopamine oxidative self-polymerization and chemical bonding, ultimately yielding a UV-resistant modified starch-based composite material. This material exhibits high pesticide loading capacity, high encapsulation efficiency, excellent UV resistance, and photoresponsive sustained-release properties.

Description

Technical Field

[0001] This invention belongs to the field of pesticide technology, specifically relating to the preparation method of UV-resistant modified starch-based composite materials and their application in pesticides. Background Technology

[0002] Starch is widely available, inexpensive, biodegradable, and safe for humans and animals. Furthermore, the numerous hydroxyl groups in its molecular structure readily bind to the active ingredients in pesticides, making it an excellent choice for pesticide carriers. Starch-based composite materials have broad application prospects in pesticides, replacing traditional non-degradable carriers to reduce agricultural non-point source pollution. They can also achieve controlled-release of pesticides to extend their effective period, improve utilization, and precisely meet agricultural needs. However, starch generally suffers from problems such as high water solubility, structural instability, and poor mechanical properties, leading to rapid pesticide loss and easy breakage of formulations, which can affect the application effect and shelf life of pesticides.

[0003] Chinese invention patent application CN110622965A discloses a method for preparing leaf-affinity pesticide nanocapsules based on tannic acid modification. The capsule core is formed by nanospheres formed by modified starch as pesticide carrier, and the capsule wall is a chelate of tannic acid and ferric chloride. The advantage is that tannic acid has adhesive properties on the surface of various materials, which helps to reduce the rolling off of pesticide molecules.

[0004] However, in the above scheme, no ultraviolet absorbers or reflective components were added to the tannic acid-ferric chloride complex in the capsule wall material and the modified starch in the capsule core. In field applications, some pesticides are exposed to sunlight, and ultraviolet light irradiation can easily lead to the degradation of the active ingredients of pesticides, thereby reducing efficacy and shortening the duration of effect. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing UV-resistant modified starch-based composite materials and their application in pesticides. Using starch microspheres as a carrier, photoresponsive UV-resistant mesoporous nanospheres are firmly loaded onto the carrier surface using polydopamine to construct a synergistic UV-resistant system. This overcomes the deficiency of existing organic carriers lacking UV protection and ensures that pesticides can fully exert their efficacy.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] The preparation method of UV-resistant modified starch-based composite material includes the following steps:

[0008] Step 1: Anti-UV mesoporous nanospheres are synthesized by hydrothermal method, and then photoresponsive modified powder is combined with anti-UV mesoporous nanospheres by grafting method to obtain photoresponsive anti-UV mesoporous nanospheres.

[0009] Step 2: Photoresponsive UV-resistant mesoporous nanospheres are loaded onto the surface of starch microspheres in an alkaline buffer solution using the oxidative polymerization and chemical bonding of polydopamine, resulting in a UV-resistant modified starch-based composite material.

[0010] Furthermore, the specific preparation process of the UV-resistant mesoporous nanospheres is as follows:

[0011] Add zinc salt and aluminum salt to deionized water and stir for 30-40 min. Then add urea and ammonium fluoride and stir magnetically for 30-40 min. Transfer the reaction mixture to a stainless steel high-pressure reactor lined with polytetrafluoroethylene and heat at 120-130℃ for 24-26 h. Allow it to cool naturally to room temperature, centrifuge, filter, and wash the filter cake 3-5 times with deionized water and anhydrous ethanol. Dry to constant weight to obtain UV-resistant mesoporous nanospheres.

[0012] Furthermore, the ratio of zinc salt, aluminum salt, deionized water, urea and ammonium fluoride is 1.78-2.28g: 0.75-1.1g: 120-150mL: 3-4g: 0.6-1g.

[0013] Furthermore, the zinc salt is either zinc chloride or zinc nitrate hexahydrate, and the aluminum salt is either aluminum chloride or aluminum nitrate nonahydrate.

[0014] Furthermore, the specific preparation process of the photoresponsive modified powder is as follows:

[0015] Propyltriethoxysilane isocyanate and 4-carboxyazobenzene were added to a three-necked flask containing tetrahydrofuran that had been dehydrated by 4 Å molecular sieves. The mixture was heated to 75-85 °C under a nitrogen atmosphere, stirred, and reacted in the dark for 12-14 h. Then, n-hexane was added, and the mixture was allowed to stand overnight at -20--10 °C. The crystals were collected by filtration through a microporous membrane, washed with a large amount of n-hexane, dried under vacuum to constant weight, and ground into a fine powder to obtain the photoresponsive modified powder.

[0016] Furthermore, the ratio of propyltriethoxysilane isocyanate, 4-carboxyazobenzene, tetrahydrofuran, and n-hexane is 2.05-3.85 g : 1.58-2.88 g : 12-15 mL : 40-50 mL.

[0017] Furthermore, the specific preparation process of the photoresponsive UV-resistant mesoporous nanospheres is as follows:

[0018] UV-resistant mesoporous nanospheres were activated under vacuum at 110℃ for 2-3 hours, added to a round-bottom flask containing anhydrous methanol, sonicated for 5-10 minutes, and then photoresponsive modified powder was added. The mixture was stirred at 60-70℃ under nitrogen protection for 12-14 hours, centrifuged, filtered, and the filter cake was washed 3-5 times alternately with a large amount of tetrahydrofuran and anhydrous methanol. The mixture was then freeze-dried to obtain photoresponsive UV-resistant mesoporous nanospheres.

[0019] Furthermore, the ratio of UV-resistant mesoporous nanospheres, anhydrous methanol, and photoresponsive modified powder is 500-800 mg: 50-60 mL: 50-70 mg.

[0020] Furthermore, the specific preparation process of starch microspheres is as follows:

[0021] Corn starch was added to a 1 mol / L sodium hydroxide solution and stirred at 60-80℃ for 30-40 min. After cooling to room temperature, it was used as the aqueous phase. Soybean oil was heated to 60-70℃, Span 80 was added, and stirred for 10-20 min. After cooling to 40-50℃, it was used as the oil phase. The aqueous phase was added to the oil phase at a rate of 1-1.5 mL / min and stirred continuously for 30-40 min to emulsify. Then epichlorohydrin was added and stirred for 3-5 h. The upper oil phase was removed by centrifugation. The precipitate was washed 3-5 times each with ethyl acetate, anhydrous ethanol, and acetone. After centrifugation, it was vacuum dried to constant weight to obtain starch microspheres.

[0022] Furthermore, the ratio of corn starch, 1 mol / L sodium hydroxide solution, soybean oil, and Span 80 is 18-25 g: 200-300 mL: 1-1.5 L: 3-4 g.

[0023] Furthermore, the volume ratio of the aqueous phase, oil phase, and epichlorohydrin is 40-60:200-300:2-3.

[0024] Furthermore, the specific preparation process of the UV-resistant modified starch-based composite material is as follows:

[0025] A 2 mg / mL dopamine hydrochloride solution was prepared using 0.01 mol / L Tris-HCl solution (pH=8.5) as the solvent. Then, photoresponsive UV-resistant mesoporous nanospheres were added, and the mixture was sonicated for 20-30 min to obtain a mixed dispersion. Starch microspheres were then added, and the mixture was allowed to settle in the dark at 37-41℃ for 24-26 h. After filtration, the filter cake was ultrasonically washed 3-5 times with deionized water and vacuum dried to constant weight to obtain the UV-resistant modified starch-based composite material.

[0026] Furthermore, the ratio of 2 mg / mL dopamine hydrochloride solution, photoresponsive UV-resistant mesoporous nanospheres, and starch microspheres is 500-800 mL: 500-600 mg: 10-15 g.

[0027] The present invention also provides an application of UV-resistant modified starch-based composite material in pesticides, which serves as a carrier for pesticides that are easily degraded by ultraviolet light.

[0028] The beneficial effects of this invention are:

[0029] 1. The UV-resistant modified starch-based composite material prepared in this invention uses biodegradable corn starch microspheres as the core, and firmly loads photoresponsive UV-resistant mesoporous nanospheres through a polydopamine coating. This constructs a dual UV protection system with high specific surface area for drug loading, UV-resistant mesoporous nanospheres, and photoresponsive modified powder. The azophenyl groups grafted into the photoresponsive UV-resistant mesoporous nanospheres further endow the material with intelligent light-controlled release, realizing controllable pesticide delivery from slow release in the dark to rapid release under light. Polydopamine not only enhances interfacial bonding, but its own UV absorption and adhesion, along with the rough structure formed on the coating surface, also improve the pesticide carrier's resistance to rain erosion. Ultimately, this results in a pesticide carrier that integrates high load capacity, excellent UV resistance, intelligent controlled release, and strong environmental adaptability.

[0030] 2. The starch microspheres in this invention completely overcome the defects of natural corn starch, such as easy water absorption, poor mechanical strength, and insufficient temperature and acid / alkali resistance. They possess excellent structural stability and environmental tolerance, and can maintain their morphology integrity in subsequent processing and applications to prevent functional components from falling off. The spherical morphology with an average size of 30 μm combines a moderate specific surface area with good dispersibility. This provides abundant loading sites for the photoresponsive UV-resistant mesoporous nanospheres, ensuring uniform coverage of functional components. At the same time, the hydroxyl groups retained on their surface have good interaction with the polydopamine coating, which can promote uniform deposition and firm adhesion of polydopamine, thereby achieving stable loading of functional components to ensure the durability of UV resistance.

[0031] 3. The UV-resistant mesoporous nanospheres in this invention have high specific surface area due to their mesoporous channels, providing a large number of adsorption sites for pesticide molecules, which is the basis for achieving high drug loading rate and slow release behavior. The synergistic effect of the mesoporous spherical structure and zinc ions endows the material with UV shielding function. The abundant metal hydroxyl active sites on the surface become ideal sites for grafting photoresponsive molecules. The regular spherical morphology ensures size matching and uniform loading with starch microsphere carriers. Furthermore, the increased surface roughness enhances the material's adhesion to leaf surfaces and its resistance to rain erosion.

[0032] 4. The photoresponsive UV-resistant mesoporous nanospheres of this invention covalently bond azobenzene photosensitive groups to the UV-resistant mesoporous nanospheres, constructing a light-controlled intelligent release switch. This enables the pesticide carrier to undergo a reversible configurational change under light irradiation, actively regulating pore flow resistance and achieving precise switching between slow release in the dark and rapid release under light. In conjunction with the UV protection system, the UV shielding effect of the UV-resistant mesoporous nanospheres and the light quenching effect of azobenzene mutually enhance each other, jointly constructing a synergistic UV defense line. Stable chemical bonding ensures functional durability, prevents the loss of photosensitive components, and ensures that the intelligent release behavior remains effective in complex environments. Detailed Implementation

[0033] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments in the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0034] Example 1: A method for preparing a UV-resistant modified starch-based composite material, comprising the following steps:

[0035] S1: Add 18g of corn starch to 200mL of 1mol / L sodium hydroxide solution, stir at 60℃ for 30min, cool to room temperature and use as the aqueous phase. Heat 1L of soybean oil to 60℃, add 3g of Span 80, stir for 10min, cool to 40℃ and use as the oil phase. Add 200mL of the aqueous phase to 1L of the oil phase at a rate of 1mL / min, stir continuously, emulsify for 30min, then add 10mL of epichlorohydrin, stir for 3h, centrifuge to remove the upper oil phase, wash the precipitate three times each with ethyl acetate, anhydrous ethanol and acetone, centrifuge, and vacuum dry at 40℃ for 20h to obtain starch microspheres with an average particle size of 30μm.

[0036] By using reverse emulsification, corn starch is dissolved under alkaline conditions as the aqueous phase, and an oil-in-water droplet template is formed under the action of an emulsifier. Then, epichlorohydrin, a crosslinking agent, is added to allow it to crosslink with starch molecules inside the droplet, forming a three-dimensional network structure solidified microsphere.

[0037] S2: Add 1.78g zinc nitrate hexahydrate and 0.75g aluminum nitrate nonahydrate to 120mL of deionized water and stir for 30min. Then add 3g urea and 0.6g ammonium fluoride and stir magnetically for 30min. Transfer the reaction mixture to a stainless steel high-pressure reactor lined with polytetrafluoroethylene and heat at 120℃ for 24h. After cooling naturally to room temperature, centrifuge and filter. Wash the filter cake three times with deionized water and anhydrous ethanol and dry at 60℃ for 12h to obtain UV-resistant mesoporous nanospheres with an average particle size of 8μm.

[0038] Using a hydrothermal method, urea is used as a slow hydrolysis precipitant to uniformly release hydroxide ions at high temperature, which promotes the co-precipitation of zinc and aluminum ions to form primary LDH (layered hydroxide) crystal nuclei. Then, fluoride ions are used to inhibit the growth of specific crystal faces, guiding the primary nanosheets to self-assemble into a three-dimensional mesoporous microsphere structure with a high specific surface area, composed of countless nanosheets.

[0039] S3: 2.05 g of propyltriethoxysilane isocyanate and 1.58 g of 4-carboxyazobenzene were added to a three-necked flask containing 12 mL of tetrahydrofuran dehydrated by 4 Å molecular sieves. The mixture was heated to 75 °C and stirred under a nitrogen atmosphere and reacted in the dark for 12 h. Then 40 mL of n-hexane was added and the mixture was allowed to stand overnight at -20 °C. The crystals were collected by filtration through a microporous membrane, washed with a large amount of n-hexane, dried under vacuum to constant weight, and ground into a fine powder to obtain the photoresponsive modified powder.

[0040] Using the photosensitive compound 4-carboxyazobenzene and the silane coupling agent isocyanate-based triethoxysilane as reactants and dehydrated tetrahydrofuran as solvent, the isocyanate group of propyltriethoxysilane undergoes an addition reaction with the carboxyl group of 4-carboxyazobenzene, thereby covalently linking the photoresponsive azophenyl group to the triethoxysilane coupling agent.

[0041] S4: 500 mg of UV-resistant mesoporous nanospheres were vacuum activated at 110 °C for 2 h, added to a round-bottom flask containing 50 mL of anhydrous methanol, sonicated for 5 min, and then 50 mg of photoresponsive modified powder was added. The mixture was stirred at 60 °C under nitrogen protection for 12 h, centrifuged, filtered, and the filter cake was washed three times alternately with a large amount of tetrahydrofuran and anhydrous methanol. The mixture was then freeze-dried to obtain photoresponsive UV-resistant mesoporous nanospheres.

[0042] By grafting, water molecules on the LDH surface are first removed and the active sites of metal hydroxyl groups are exposed. The triethoxysilyl groups at the end of the photoresponsive modified powder are hydrolyzed to generate highly active silanols, which undergo condensation reactions with the hydroxyl groups on the LDH surface to form Si-OM covalent bonds, thus constructing a composite material with LDH carrier structure and photoresponsive function.

[0043] S5: Using 0.01 mol / L Tris-HCl solution (pH=8.5) as solvent, prepare 500 mL of 2 mg / mL dopamine hydrochloride solution, then add 500 mg of photoresponsive UV-resistant mesoporous nanospheres, sonicate for 20 min to obtain a mixed dispersion, then add 10 g of starch microspheres, let stand at 37℃ in the dark for 24 h to deposit, filter, ultrasonically wash the filter cake three times with deionized water, vacuum dry to constant weight, and obtain a UV-resistant modified starch-based composite material with an average coating thickness of 5 μm.

[0044] In a Tris-HCl buffer solution with a pH of 8.5, dopamine can spontaneously polymerize on the surface of various materials to form a polydopamine coating. The oxidative polymerization properties of polydopamine are used to coat and modify starch microspheres. At the same time, the catechol groups in the dopamine molecule form stable coordination bonds with the metal-hydroxyl groups (M–OH) on the surface of the photoresponsive UV-resistant mesoporous nanospheres, thus depositing on the surface of the photoresponsive UV-resistant mesoporous nanospheres. Then, under alkaline conditions, dopamine generates quinones through an oxidative self-polymerization reaction, which then form covalent bonds with other dopamine molecules or polydopamine on the starch microspheres, thereby anchoring LDH particles to the surface of the starch microspheres, resulting in a UV-resistant modified starch-based composite material.

[0045] Example 2: A method for preparing a UV-resistant modified starch-based composite material, comprising the following steps:

[0046] S1: Add 21.5g of corn starch to 250mL of 1mol / L sodium hydroxide solution, stir at 70℃ for 35min, cool to room temperature to obtain the aqueous phase. Heat 1.25L of soybean oil to 65℃, add 3.5g of Span 80, stir for 15min, cool to 45℃ to obtain the oil phase. Add 250mL of the aqueous phase to the 1.25L oil phase at a rate of 1.25mL / min, stir continuously, emulsify for 35min, then add 12.5mL of epichlorohydrin, stir for 4h, centrifuge to remove the upper oil phase, wash the precipitate four times each with ethyl acetate, anhydrous ethanol, and acetone, centrifuge, and vacuum dry at 45℃ for 22h to obtain starch microspheres.

[0047] S2: Add 2.03g zinc nitrate hexahydrate and 0.93g aluminum nitrate nonahydrate to 135mL of deionized water and stir for 35min. Then add 3.5g urea and 0.8g ammonium fluoride and stir magnetically for 35min. Transfer the reaction mixture to a stainless steel high-pressure reactor lined with polytetrafluoroethylene and heat at 125℃ for 25h. After cooling naturally to room temperature, centrifuge and filter. Wash the filter cake four times with deionized water and anhydrous ethanol and dry at 65℃ for 13.5h to obtain UV-resistant mesoporous nanospheres.

[0048] S3: 2.95 g of propyltriethoxysilane isocyanate and 2.23 g of 4-carboxyazobenzene were added to a three-necked flask containing 13.5 mL of tetrahydrofuran dehydrated by 4 Å molecular sieves. The mixture was heated to 80 °C and stirred under a nitrogen atmosphere and reacted in the dark for 13 h. Then 45 mL of n-hexane was added and the mixture was allowed to stand overnight at -15 °C. The crystals were collected by filtration through a microporous membrane, washed with a large amount of n-hexane, dried under vacuum to constant weight, and ground into a fine powder to obtain the photoresponsive modified powder.

[0049] S4: 650 mg of UV-resistant mesoporous nanospheres were vacuum activated at 110 °C for 2.5 h, added to a round-bottom flask containing 55 mL of anhydrous methanol, sonicated for 7.5 min, and then 60 mg of photoresponsive modified powder was added. The mixture was stirred at 65 °C under nitrogen protection for 13 h, centrifuged, filtered, and the filter cake was washed 4 times alternately with a large amount of tetrahydrofuran and anhydrous methanol. The mixture was then freeze-dried to obtain photoresponsive UV-resistant mesoporous nanospheres.

[0050] S5: Using 0.01 mol / L Tris-HCl solution (pH=8.5) as solvent, prepare 650 mL of 2 mg / mL dopamine hydrochloride solution, then add 550 mg of photoresponsive UV-resistant mesoporous nanospheres, sonicate for 25 min to obtain a mixed dispersion, then add 12.5 g of starch microspheres, let stand at 39 °C in the dark for 25 h to deposit, filter, ultrasonically wash the filter cake 4 times with deionized water, and vacuum dry to constant weight to obtain UV-resistant modified starch-based composite material.

[0051] Example 3: A method for preparing a UV-resistant modified starch-based composite material, comprising the following steps:

[0052] S1: Add 25g of corn starch to 300mL of 1mol / L sodium hydroxide solution, stir at 80℃ for 40min, cool to room temperature to obtain the aqueous phase. Heat 1.5L of soybean oil to 70℃, add 4g of Span 80, stir for 20min, cool to 50℃ to obtain the oil phase. Add 300mL of the aqueous phase to the 1.5L oil phase at a rate of 1.5mL / min, stir continuously, emulsify for 40min, then add 15mL of epichlorohydrin, stir for 5h, centrifuge to remove the upper oil phase, wash the precipitate 5 times each with ethyl acetate, anhydrous ethanol, and acetone, centrifuge, and vacuum dry at 50℃ for 24h to obtain starch microspheres.

[0053] S2: Add 2.28g zinc nitrate hexahydrate and 1.1g aluminum nitrate nonahydrate to 150mL of deionized water and stir for 40min. Then add 4g urea and 1g ammonium fluoride and stir magnetically for 40min. Transfer the reaction mixture to a stainless steel high-pressure reactor lined with polytetrafluoroethylene and heat at 130℃ for 26h. After cooling naturally to room temperature, centrifuge and filter. Wash the filter cake 5 times with deionized water and anhydrous ethanol and dry at 70℃ for 15h to obtain UV-resistant mesoporous nanospheres.

[0054] S3: 3.85 g of propyltriethoxysilane isocyanate and 2.88 g of 4-carboxyazobenzene were added to a three-necked flask containing 15 mL of tetrahydrofuran dehydrated by 4 Å molecular sieves. The mixture was heated to 85 °C and stirred under a nitrogen atmosphere and reacted in the dark for 14 h. Then, 50 mL of n-hexane was added and the mixture was allowed to stand overnight at -10 °C. The crystals were collected by filtration through a microporous membrane, washed with a large amount of n-hexane, dried under vacuum to constant weight, and ground into a fine powder to obtain the photoresponsive modified powder.

[0055] S4: 800 mg of UV-resistant mesoporous nanospheres were vacuum activated at 110 °C for 3 h, added to a round-bottom flask containing 60 mL of anhydrous methanol, sonicated for 10 min, and then 70 mg of photoresponsive modified powder was added. The mixture was stirred at 70 °C under nitrogen protection for 14 h, centrifuged, filtered, and the filter cake was washed 5 times alternately with a large amount of tetrahydrofuran and anhydrous methanol. The mixture was then freeze-dried to obtain photoresponsive UV-resistant mesoporous nanospheres.

[0056] S5: Using 0.01 mol / L Tris-HCl solution (pH=8.5) as solvent, prepare 800 mL of 2 mg / mL dopamine hydrochloride solution, then add 600 mg of photoresponsive UV-resistant mesoporous nanospheres, sonicate for 30 min to obtain a mixed dispersion, then add 15 g of starch microspheres, let stand at 41℃ in the dark for 26 h to deposit, filter, ultrasonically wash the filter cake 5 times with deionized water, and vacuum dry to constant weight to obtain UV-resistant modified starch-based composite material.

[0057] Example 4: This example provides a method for preparing an anti-ultraviolet modified starch-based composite material. The difference from Example 1 is that zinc chloride and aluminum chloride are used instead of zinc nitrate hexahydrate and aluminum nitrate nonahydrate in step S2 to prepare the anti-ultraviolet modified starch-based composite material.

[0058] In Examples 1-4, the corn starch was selected from Jinan Xinyuchengtai Chemical Technology Co., Ltd., brand name Xinyuchengtai Chemical, with an average particle size of 2μm; the soybean oil was selected from Jiangxi Huanqiu Natural Flavors Co., Ltd., CAS No. 8001-22-7; the urea was selected from Jinan Ausli Chemical Co., Ltd., CAS No. 57-13-6; the 4-carboxylated azobenzene was selected from Guangdong Wengjiang Chemical Reagent Co., Ltd., CAS No. 586-91-4; and the remaining raw materials were commercially available products.

[0059] Comparative Example 1: The difference from Example 1 is that step S2 is omitted, and the UV-resistant mesoporous nanospheres in step S4 are replaced with commercially available mesoporous silica with an average particle size of 8 μm. The remaining steps remain unchanged, and a UV-resistant modified starch-based composite material is prepared.

[0060] Comparative Example 2: The difference from Example 1 is that steps S3 and S4 are omitted, and the photoresponsive UV-resistant mesoporous nanospheres in step S5 are replaced with UV-resistant mesoporous nanospheres in step S2. The remaining steps remain unchanged, and a UV-resistant modified starch-based composite material is prepared.

[0061] Comparative Example 3: The difference from Example 1 is that steps S2, S3 and S4 are omitted, and photoresponsive UV-resistant mesoporous nanospheres are not added in step S5. The remaining steps remain unchanged, and a UV-resistant modified starch-based composite material is prepared.

[0062] Application example: Dissolve 2g of azoxystrobin in 2L of water, add 10g of UV-resistant modified starch-based composite material, stir magnetically at room temperature for 12h, irradiate with UV light at 0.4W / cm2 and 365nm for 2min, centrifuge at 8000rpm for 10min, filter, wash three times with excess methanol by centrifugation, and vacuum dry the product to constant weight to obtain pesticide-loaded UV-resistant modified starch-based composite material powder.

[0063] The pesticide pyraclostrobin in the application example can also be any of the following pesticides that are easily photodegraded or require photocontrolled release: diquat, glufosinate, cypermethrin, and chlorpyrifos.

[0064] The performance of the UV-resistant modified starch-based composite materials prepared in Examples 1-4 and Comparative Examples 1-3 was tested. Samples loaded with azoxystrobin were prepared according to the methods described in the application examples. The specific test methods for each sample are as follows:

[0065] Encapsulation efficiency: The drug loading and encapsulation efficiency of the microspheres were determined by HPLC. The detection conditions were: Amethyst C18-H column (4.6 mm × 250 mm), UV detector, column temperature 25 ℃, flow rate 1 mL / min, detection wavelength 289 nm, injection volume 20 μL, and mobile phase 90% methanol aqueous solution.

[0066] Actual drug loading (%) = (mass of azoxystrobin in microspheres / total mass of microspheres) × 100%;

[0067] Theoretical drug loading (%) = (actual mass of azoxystrobin / actual mass of azoxystrobin + actual mass of UV-modified starch-based composite material) × 100%;

[0068] Encapsulation efficiency (%) = (actual drug loading / theoretical drug loading) × 100%.

[0069] UV photolysis resistance test: Referring to GB / T31270.1-2014 "Criteria for Environmental Safety Evaluation of Chemical Pesticides Part 1: UV Photolysis Test in Soil", according to the application example, pyraclostrobin was used, and the composite materials prepared in Examples 1-5 and Comparative Examples 1-3 were loaded to obtain pesticide-loaded samples. The samples were transferred to a UV lamp (36W, 254nm) for irradiation, and the pesticide residue rate at 20h time point was quantitatively determined by high performance liquid chromatography.

[0070] Calculation formula: Pesticide residual rate (%) = (pesticide mass measured at the current time point / pesticide mass of the initial load) × 100%.

[0071] Slow-release performance test: Refer to GB / T34763-2017 "Determination of controlled-release performance of coating materials for water-soluble fertilizers". The sample preparation is the same as above. The sample is subjected to dynamic dialysis. Equal load samples are placed in dialysis bags and immersed in phosphate buffer at pH=7.0 to simulate the release medium in the natural environment. The mixture is stirred at a constant speed at 25℃ and alternated between light and dark. First, it is dark for 5 hours, then irradiated with ultraviolet light (365nm) for 5 hours, and then dark for 5 hours. This cycle is repeated to measure the pesticide concentration in the sampling medium each time and calculate the cumulative release rate at each time point.

[0072] The performance test results are shown in Table 1:

[0073] Table 1: Performance Test Results of UV-Resistant Modified Starch-Based Composite Materials

[0074] project Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Drug loading rate / % 45.4 43.8 42.6 43.1 35.2 44.3 28.4 Encapsulation rate / % 36.1 35.6 35.2 34.7 28.6 35.4 22.3 Pesticide retention rate after 20 hours of UV irradiation / % 52.2 51.7 51.4 50.8 15.3 35.1 9.1 10-hour cumulative release rate / % 45.3 46.7 47.2 47.5 55.2 50.3 65.3 20h cumulative release rate / % 63.4 64.3 64.8 65.1 70.1 68.3 85.2 30h cumulative release rate / % 76.8 77.1 77.6 78.3 82.3 80.8 90.7

[0075] As can be seen from Table 1, the UV-resistant modified starch-based composite materials prepared in Examples 1-4 are significantly superior to those in Comparative Examples 1-3. The UV-resistant mesoporous nanospheres synthesized by hydrothermal method have excellent UV shielding ability and high specific surface area to achieve efficient drug loading. Photoresponsive azophenyl groups are grafted onto the UV-resistant mesoporous nanospheres by silane coupling agent, and then polydopamine is used to firmly load them onto the surface of starch microspheres, giving the material high drug loading rate, high encapsulation rate, excellent UV resistance and photoresponsive sustained release characteristics.

[0076] In Comparative Example 1, the drug loading rate, encapsulation rate, and pesticide retention rate after 20 hours of UV irradiation significantly decreased. This may be because ordinary mesoporous silica was used instead of UV-resistant mesoporous nanospheres. Although mesoporous silica has a certain porous structure and drug loading capacity, it does not have the same adsorption effect of metal ions on drug molecules as UV-resistant mesoporous nanospheres. It cannot provide UV shielding function and has limited loading capacity for photoresponsive modified powder, ultimately resulting in the deterioration of drug loading performance, UV protection, and photocontrolled release capability.

[0077] In Comparative Example 2, the pesticide retention rate was significantly reduced after 20 hours of UV irradiation. This may be because although the group retained the structure and drug loading capacity of the UV-resistant mesoporous nanospheres, it did not graft photoresponsive modified powder, resulting in the material lacking the photoresponsive synergistic effect of azobenzene molecules and thus reducing its UV protection capability.

[0078] Comparative Example 3 showed the lowest drug loading rate, encapsulation rate, and pesticide retention rate after 20 hours of UV irradiation, but the highest cumulative release rate, indicating the worst overall performance. The simple starch microsphere carrier lacked a high specific surface area mesoporous structure to efficiently load the drug, did not have any UV-resistant components to protect the photosensitive pesticide, and also lacked the response effect to regulate drug release, resulting in poor performance in actual field use.

[0079] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A method for preparing UV-resistant modified starch-based composite materials, characterized in that, Includes the following steps: Step 1: Anti-UV mesoporous nanospheres are synthesized by hydrothermal method, and then photoresponsive modified powder is combined with anti-UV mesoporous nanospheres by grafting method to obtain photoresponsive anti-UV mesoporous nanospheres; The process involves adding zinc salt and aluminum salt to deionized water and stirring for 30-40 minutes. Then, urea and ammonium fluoride are added and the mixture is magnetically stirred for 30-40 minutes. The reaction mixture is then transferred to a stainless steel high-pressure reactor lined with polytetrafluoroethylene and heated at 120-130°C for 24-26 hours. After naturally cooling to room temperature, the mixture is centrifuged, filtered, and the filter cake is washed 3-5 times with deionized water and anhydrous ethanol. The cake is then dried to constant weight to obtain UV-resistant mesoporous nanospheres. Propyltriethoxysilane isocyanate and 4-carboxyazobenzene were added to a three-necked flask containing tetrahydrofuran that had been dehydrated by 4Å molecular sieves. The mixture was heated to 75-85°C under a nitrogen atmosphere and stirred. The reaction was carried out in the dark for 12-14 hours. Then, n-hexane was added and the mixture was allowed to stand overnight at -20--10°C. The crystals were collected by filtration through a microporous membrane, washed with a large amount of n-hexane, dried under vacuum to constant weight, and ground into a fine powder to obtain a photoresponsive modified powder. UV-resistant mesoporous nanospheres were activated under vacuum at 110℃ for 2-3 hours, added to a round-bottom flask containing anhydrous methanol, sonicated for 5-10 minutes, and then photoresponsive modified powder was added. The mixture was stirred at 60-70℃ under nitrogen protection for 12-14 hours, centrifuged, filtered, and the filter cake was washed 3-5 times alternately with a large amount of tetrahydrofuran and anhydrous methanol. The mixture was then freeze-dried to obtain photoresponsive UV-resistant mesoporous nanospheres. Step 2: Photoresponsive UV-resistant mesoporous nanospheres were loaded onto the surface of starch microspheres in an alkaline buffer solution using the oxidative polymerization and chemical bonding of polydopamine to obtain a UV-resistant modified starch-based composite material. In this process, corn starch was added to a 1 mol / L sodium hydroxide solution and stirred at 60-80℃ for 30-40 min. After cooling to room temperature, the aqueous phase was obtained. Soybean oil was heated to 60-70℃, Span 80 was added, and the mixture was stirred for 10-20 min. After cooling to 40-50℃, the oil phase was obtained. The aqueous phase was added to the oil phase at a rate of 1-1.5 mL / min, and the mixture was stirred continuously for 30-40 min to emulsify. Then epichlorohydrin was added, and the mixture was stirred for 3-5 h. The upper oil phase was removed by centrifugation. The precipitate was washed 3-5 times each with ethyl acetate, anhydrous ethanol, and acetone. After centrifugation, the precipitate was vacuum dried to constant weight to obtain starch microspheres. A 2 mg / mL dopamine hydrochloride solution was prepared using 0.01 mol / L Tris-HCl solution as the solvent. Then, photoresponsive UV-resistant mesoporous nanospheres were added, and the mixture was sonicated for 20-30 min to obtain a mixed dispersion. Starch microspheres were then added, and the mixture was allowed to settle in the dark at 37-41℃ for 24-26 h. After filtration, the filter cake was ultrasonically washed 3-5 times with deionized water and vacuum dried to constant weight to obtain a UV-resistant modified starch-based composite material.

2. The method for preparing the UV-resistant modified starch-based composite material according to claim 1, characterized in that, The ratio of zinc salt, aluminum salt, deionized water, urea and ammonium fluoride used is 1.78-2.28g: 0.75-1.1g: 120-150mL: 3-4g: 0.6-1g; The zinc salt is either zinc chloride or zinc nitrate hexahydrate, and the aluminum salt is either aluminum chloride or aluminum nitrate nonahydrate.

3. The method for preparing the UV-resistant modified starch-based composite material according to claim 1, characterized in that, The ratio of propyltriethoxysilane isocyanate, 4-carboxyazobenzene, tetrahydrofuran, and n-hexane is 2.05-3.85g: 1.58-2.88g: 12-15mL: 40-50mL.

4. The method for preparing the UV-resistant modified starch-based composite material according to claim 1, characterized in that, The ratio of the UV-resistant mesoporous nanospheres, anhydrous methanol, and photoresponsive modified powder is 500-800 mg: 50-60 mL: 50-70 mg.

5. The method for preparing the UV-resistant modified starch-based composite material according to claim 1, characterized in that, The ratio of corn starch, 1 mol / L sodium hydroxide solution, soybean oil and Span 80 is 18-25 g: 200-300 mL: 1-1.5 L: 3-4 g; The volume ratio of the aqueous phase, oil phase, and epichlorohydrin is 40-60:200-300:2-3.

6. The method for preparing the UV-resistant modified starch-based composite material according to claim 1, characterized in that, The ratio of the 2 mg / mL dopamine hydrochloride solution, the photoresponsive UV-resistant mesoporous nanospheres, and the starch microspheres is 500-800 mL: 500-600 mg: 10-15 g.

7. The application of UV-resistant modified starch-based composite materials in pesticides, characterized in that, The UV-resistant modified starch-based composite material is prepared by the method for preparing the UV-resistant modified starch-based composite material according to any one of claims 1-6.