Preparation method of modified corn straw nanocellulose-based dual-response controlled-release pesticide

Abstract

The invention discloses a preparation method of a modified corn straw nanocellulose-based dual-response controlled-release pesticide, and relates to the technical field of resource utilization of agricultural wastes and environmental protection. The method comprises the following steps: extracting nano-cellulose from corn straws, modifying the nano-cellulose with zein, preparing a modified corn straw nano-cellulose-based emulsion carrier, and preparing and evaluating the modified corn straw nano-cellulose-based dual-response controlled-release pesticide. The method verifies the effectiveness of the EDC / NHS cross-linking agent in an alcohol-soluble system, successfully modifies the corn straw nano-cellulose, realizes efficient utilization of waste resources, solves the problems of low utilization rate of traditional pesticides, combustion waste of corn straw and performance limitation of conventional cellulose, and has a wide application prospect. Meanwhile, a novel efficient, environment-friendly and economical dual-response controlled-release pesticide can be obtained, and important guiding significance is achieved for solving the bottleneck problem in the field of pesticide preparations.

Description

Technical Field

[0001] The invention belongs to the technical field of resource utilization and environmental protection of agricultural waste, and specifically relates to a method for preparing a modified corn straw nanocellulose-based dual-response controlled-release pesticide. Background Art

[0002] Traditional pesticide formulations generally have problems such as rapid decomposition of active ingredients and low target retention rate during application, resulting in a pesticide utilization rate of less than 30%. This not only causes a waste of resources, but also leads to serious environmental problems such as soil pollution and water eutrophication.

[0003] The soil environment of saline-alkali land is special, with high concentration of soluble salts in the soil, imbalanced pH (high pH value of alkaline soil), and alkaline soil. Traditional pesticides have poor stability in such an environment, resulting in a large amount of pesticides being fixed or lost in the soil, unable to effectively act on pests and diseases, and low utilization rate. It is easy to aggravate the soil compaction in saline-alkali land, which is not conducive to water penetration and gas exchange, and hinders the improvement process of saline-alkali land. For example, some organophosphorus pesticides may accelerate hydrolysis and reduce the efficacy in saline-alkali land due to the high pH value. Due to the low utilization rate of pesticides, in order to achieve the prevention and control effect, farmers often need to increase the amount of pesticides used, which not only increases the cost of agricultural production, but also the long-term and large-scale use of pesticides will destroy the fertility and ecological function of saline-alkali soil, further aggravating soil degradation. In addition, a large amount of pesticides remain in the soil, water bodies and agricultural products, causing harm to the entire ecosystem, destroying the ecological balance of saline-alkali land, and posing a serious threat to the ecological environment and human health. In addition, the drainage performance of saline-alkali soil itself is poor, and pesticide residues are more likely to accumulate in the soil and pollute groundwater through leaching.

[0004] In order to meet this challenge, the development of efficient and environmentally friendly dual-responsive controlled-release pesticides has emerged. Dual-responsive controlled-release pesticides can respond quickly to specific conditions and achieve precise control of pesticide release, thereby improving the efficiency of pesticide use, increasing crop yields and quality in saline-alkali land, and reducing environmental pollution. It is of great significance to promote the green development of agriculture. At present, the preparation of dual-responsive controlled-release pesticides mainly adopts microcapsule encapsulation, hydrogel loading or organic polymer blending methods, but there are defects such as non-degradable carrier materials (such as polyvinyl alcohol), complex preparation processes (such as interfacial polymerization methods require multiple steps of reaction) or single controlled-release responsiveness.

[0005] In recent years, with the popularization of the concept of sustainable development and the advancement of technology, the use of natural renewable resources as dual-responsive controlled-release pesticide carrier materials has become a research hotspot. Nanocellulose is regarded as an excellent controlled-release pesticide carrier material because of its high specific surface area, unique physical and chemical properties and environmental friendliness, which can significantly improve the dispersibility, stability and penetration ability of pesticides. Among the raw materials for extracting nanocellulose, corn stalks stand out. Corn stalks are a common agricultural waste that is often burned and wasted, but corn stalks not only contain a large amount of cellulose components, but also because of their unique structural characteristics, they have become an ideal raw material for extracting high-quality nanocellulose. At the same time, the surface of nanocellulose has abundant modified hydroxyl groups, and modification of nanocellulose will further enhance the functional properties.

[0006] The present invention aims to provide a method for preparing a modified corn straw nanocellulose-based dual-responsive controlled-release pesticide, which can effectively utilize agricultural waste, reduce environmental pollution, and improve the economy and effectiveness of pesticide use. Through the technical solution of the present invention, a high-performance modified nanocellulose controlled-release pesticide system based on agricultural waste can be obtained, which has both environmental friendliness and dual release characteristics, which has important guiding significance for solving the bottleneck problem in the field of pesticide formulation. Summary of the invention

[0007] The purpose of the present invention is to solve the problems of low utilization rate of traditional pesticides, wasteful burning of corn straw and limited performance of conventional cellulose, and to provide a method for preparing a modified corn straw nanocellulose-based dual-responsive controlled-release pesticide, thereby improving the targeted utilization rate of pesticides, and making the production process simpler and the production cost lower.

[0008] A method for preparing a modified corn straw nanocellulose-based dual-responsive controlled-release pesticide, wherein the controlled-release pesticide prepared by the method can achieve pH-redox dual-responsive release, and the method comprises: step 1, extracting nanocellulose from corn straw: step 1.1, preparing corn straw cellulose powder: drying untreated corn straw to remove moisture, then crushing and sieving with a blender, alkali washing and bleaching the obtained powder to remove hemicellulose, lignin and other impurities, and obtaining purified corn straw cellulose powder; step 1.2, nano-processing: mixing the purified corn straw cellulose powder with an aqueous solution containing 2,2,6,6-tetramethylpiperidin-1-oxyl free radical, i.e., TEMPO, and sodium bromide, then adding a sodium hypochlorite aqueous solution to start a nano-processing reaction, continuously stirring during the reaction, while maintaining the pH value of the solution at 10.5, adding ethanol after the reaction is completed to completely quench, filtering and collecting the precipitate, and washing the precipitate with deionized water for multiple times, and vacuum drying to obtain corn straw nanocellulose, i.e., CNF ; Step 2, Zein modified nanocellulose: Step 2.1, preparation of nanocellulose aqueous solution: dissolve CNF powder in deionized water, stir at room temperature to obtain CNF aqueous dispersion system; Step 2.2, preparation of zein ethanol solution: dissolve zein, i.e., Zein, in anhydrous ethanol to obtain Zein ethanol dispersion system; Step 2.3, amidation covalent modification: prepare 1-(3-(dimethylamino)propyl)-3-ethylcarbodiimide hydrochloride, i.e., EDC and N-hydroxysuccinimide, i.e., NHS, is a covalent crosslinking agent. The aqueous solution containing EDC and NHS is added to the CNF aqueous dispersion system in step 2.1, and the pH value of the mixed solution is adjusted to 5.5-6.0. Then, the Zein ethanol dispersion system in step 2.1 is added, and the pH value of the mixed solution is adjusted to 8.0. The reaction is carried out at room temperature. After the reaction is completed, the pH value of the reaction solution is reduced to 1-2 to quench the amidation reaction. The reaction solution is then centrifuged and washed with distilled water. The reaction mixture is washed with a molecular weight cutoff of 8000. Da was dialyzed through a dialysis membrane and freeze-dried to obtain a covalently coupled CNF / Zein powder; Step three, preparation of a modified corn straw nanocellulose-based emulsion carrier: Step 3.1, preparation of an aqueous phase and an oil phase: dissolving the covalently coupled CNF / Zein powder in water to form a suspension as the aqueous phase, and measuring medium-chain triglycerides, i.e., MCT, as the oil phase; Step 3.2, preparation of a Pickering emulsion: mixing the aqueous phase and the oil phase in proportion so that the volume fraction of the oil phase φ=0.4, and emulsifying under a high-speed shear machine to form a Pickering emulsion; Step four, preparation of a modified corn straw nanocellulose-based dual-responsive controlled-release pesticide: Step 4.1, pesticide loading: dissolving avermectin, i.e., AVM, in the Pickering emulsion in step three, and mixing well to obtain a dual-responsive controlled-release pesticide AVM@CNF / Zein.

[0009] Optionally, after step 2.3, the method further comprises: step 2.4, experimental verification of covalent conjugate properties: using the OPA method to quantify the content of free amino groups in the covalent conjugate CNF / Zein, and the grafting degree of the conjugate is evaluated using the following formula: ; Among them, A s and A c The free amino groups of the conjugate and native zein were expressed as follows: -1 The microscopic morphology was obtained by electron microscope.

[0010] Optionally, after step 3.2, the method further includes: step 3.3, experimental verification of Pickering emulsion properties: the morphology of the emulsion droplets is recorded with a camera and an optical microscope, the rheological properties of the emulsion are analyzed using a TA rheometer, and the mechanism of the conjugate stabilizing the emulsion is analyzed by confocal microscopy imaging, wherein MCT, Zein and CNF are stained with Nile red, Nile blue and fluorescein calcium white dyes, respectively.

[0011] Optionally, after step 4, the method further includes: step 5, evaluation of modified corn straw nanocellulose-based dual-responsive controlled-release pesticides: step 5.1, controlled-release experimental verification: AVM@CNF / Zein is placed in a dialysis bag with a molecular weight cutoff of 5000 Da, and the dialysis bag is immersed in a brown conical flask containing an ethanol aqueous solution to form a culture medium system, sodium hydroxide or hydrochloric acid is used to adjust the pH value of the culture medium, and a culture medium sample is taken at each pH value and the absorbance of AVM in the culture medium is measured by ultraviolet absorption spectrophotometry to verify the pH responsiveness of the controlled-release pesticide, wherein each pH value covers three categories: acidic, alkaline and neutral; glutathione is added to the culture medium to make the glutathione concentration of 2 mM and 8 mM, and a culture medium sample is taken at a specific concentration and the absorbance of AVM in the culture medium is measured by ultraviolet absorption spectrophotometry to verify the redox responsiveness of the controlled-release pesticide; the data obtained from the pH responsiveness verification and the redox responsiveness verification are substituted into the following formula to calculate the cumulative release ratio R of AVM n , which represents the controlled release response mechanism of controlled release pesticides: ; in, C n is the concentration of AVM at a specific pH or glutathione concentration (mg / L), m AVM is the total mass of AVM in the culture medium, n represents the number of experiments; The difference between the cumulative release ratios is determined by the difference factor f 1 and similarity factor f 2. Evaluate when f 1 is greater than 15 and f 2When it is less than 50, it is considered that there is a difference, indicating that the responsiveness under different conditions can be achieved, among which, f 1 and f 2The calculation formula is as follows: ; ; in, t Represents an index variable, m represents the number of experimental intervals in the sustained-release curve, R t represents the cumulative release rate of controlled-release pesticides, T t It represents the cumulative release rate of the control conventional pesticide; Step 5.2, efficacy evaluation experimental verification: After the controlled release pesticide AVM@CNF / Zein was centrifuged at a speed of 1000 rpm, the supernatant was placed in a dark volumetric flask, the volume was adjusted with ethanol, and the concentration of free AVM in the supernatant was measured at a wavelength of 245 nm using a UV-visible spectrophotometer. The encapsulation efficiency of AVM in the responsive carrier was calculated using the following formula: ; in, m AVM is the mass of AVM in the controlled-release pesticide before centrifugation, m 上清液AVM is the mass of unencapsulated AVM in the supernatant after centrifugation; The insecticidal activity of the dual-responsive controlled-release pesticide was tested by leaf dipping experiments. Cabbage leaves were dipped in the AVM@CNF / Zein formulation and dried at room temperature. Cabbage leaves soaked in deionized water were used as a control group. The treated leaves were transferred to a petri dish containing Plutella xylostella to investigate the mortality of Plutella xylostella and evaluate the insecticidal effect of AVM@CNF / Zein.

[0012] Optionally, the step 1.1 is to place the untreated corn stalks in a 105°C drying oven and dry them for 24 hours to remove moisture, then crush and sieve them with a blender, and mix the obtained powder with a 4% (w / v) NaOH solution at a mass volume ratio of 1:25 (w / v), heat it in a 100°C water bath for 4 hours to remove hemicellulose, lignin and other impurities, filter and collect the precipitate and dry it, mix the dried powder with a bleaching solution at a mass volume ratio of 1:25 (w / v), and stir it continuously in a water bath at 80°C for 6 hours. The bleaching solution consists of: 0.85% (w / v) NaClO2, 3.75% (v / v) glacial acetic acid and 1.35% (w / v) NaOH, wash the bleached solution with water 4 times and then dry it to obtain purified corn stalk cellulose powder.

[0013] Optionally, in the step 1.2, the purified corn straw cellulose powder is mixed with an aqueous solution containing 2,2,6,6-tetramethylpiperidin-1-oxyl free radical, i.e., TEMPO, and sodium bromide at a mass volume ratio of 1:100 (w / v), wherein the concentration of TEMPO in the aqueous solution is 1 mmol / L, and the concentration of sodium bromide is 10 mmol / L, and then an aqueous solution of sodium hypochlorite is added, wherein 10 mmol of sodium hypochlorite is added per gram of purified corn straw cellulose powder, and the nano-reaction is started, and stirring is continued for 2 h.

[0014] Optionally, the step 2.1 is to dissolve 0.4 g of CNF powder in 50 mL of deionized water and stir at room temperature to obtain a CNF aqueous dispersion system; the step 2.2 is to dissolve 0.2-0.8 g of Zein in 100 mL of anhydrous ethanol to obtain a Zein ethanol dispersion system; the step 2.3 is to add 50 mL of an aqueous solution containing 0.38 g of EDC and 0.22 g of NHS to the CNF aqueous dispersion system in step 2.1.

[0015] Optionally, in step 3.1, the mass ratio of the solute solution of the suspension formed by dissolving the covalent coupling CNF / Zein powder in water is 1.0%; in step 3.2, the Pickering emulsion is formed by emulsifying at a speed of 12000 rpm on a FB-110J high-speed shearing machine for 3 min.

[0016] Optionally, the step 4.1 is to dissolve 10 mg of avermectin, i.e. AVM, in 6 mL of the Pickering emulsion in step 3, and mix well to obtain the dual-responsive controlled-release pesticide AVM@CNF / Zein.

[0017] Optionally, in step 5.1, the dialysis bag is immersed in 50 mL of ethanol-water solution with a concentration of 40%; in step 5.2, the controlled-release pesticide AVM@CNF / Zein is centrifuged at 12,000 rpm for 10 min. After centrifugation, 1 mL of the supernatant is placed in a dark volumetric flask and the volume is adjusted to 25 mL with ethanol; in the leaf immersion experiment, cabbage leaves with a diameter of 3 cm are immersed in the AVM@CNF / Zein formula for 10 minutes, and the mortality rate of the diamondback moth is investigated after 48 hours.

[0018] The beneficial effects of the present invention are: 1. The present invention verifies the effectiveness of EDC / NHS crosslinking agent in an alcohol-soluble system and successfully modifies corn straw nanocellulose, broadening its application value. The preparation method is simple to operate, low in cost, and easy to scale up production. 2. The present invention "takes from agriculture and uses it for agriculture", and provides a new type of dual-response controlled-release pesticide that is efficient, environmentally friendly and economical for the pesticide industry. The controlled-release pesticide has a pH-redox dual-response characteristic. In the alkaline environment of the pest's intestine (high pH value) and the presence of glutathione (a redox agent), the controlled-release pesticide can quickly release the active ingredients of the pesticide to achieve precise killing of pests, while in other non-target environments, the pesticide is released slowly, thereby improving the precise utilization rate of the pesticide. It is expected to be widely used in agricultural production, improve crop yield and quality, and promote agricultural production and income increase; 3. The controlled-release pesticide prepared by the present invention has a pH-redox dual response release characteristic, and releases more active ingredients of the pesticide in the alkaline soil environment of saline-alkali land, thereby significantly improving the utilization rate of pesticides in saline-alkali land, reducing pesticide waste, and reducing the negative impact on saline-alkali soil improvement.

[0019] 4. The present invention uses corn straw agricultural waste as raw material, which not only solves the environmental pollution problem caused by corn straw burning, but also realizes the recycling of resources, conforms to the concept of green chemistry and sustainable development, has good environmental benefits and social value, and belongs to "turning waste into treasure". BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the overall method steps of the present invention; Figure 2 The schematic diagram of the chemical structure of the nano-cellulose of corn stalks and the nano-cellulose modified by zein of the present invention; Figure 3 The finished powder images of three covalent conjugates of zein-modified nanocellulose prepared in Examples 1, 2, and 3 of the present invention; Figure 4The data diagram of free amino groups and grafting degrees of three covalent conjugates prepared in Examples 1, 2 and 3 of the present invention; Figure 5 The infrared spectra of three covalent conjugates prepared in Examples 1, 2 and 3 of the present invention; Figure 6 This is a microscopic transmission electron microscope morphology image of the covalent conjugate prepared in Example 1 of the present invention; Figure 7 This is an apparent diagram of the Pickering emulsions stabilized by three covalent conjugates prepared in Examples 1, 2, and 3 of the present invention; Figure 8 Optical microscope images of three covalently coupled stabilized Pickering emulsions prepared in Examples 1, 2, and 3 of the present invention; Fig. 9 The rheological properties of the three covalently coupled Pickering emulsions stabilized by Examples 1, 2 and 3 of the present invention are shown in FIG. Fig.10 This is a confocal microscopy image of the covalently coupled compound-stabilized Pickering emulsion prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0021] Traditional pesticides lack intelligent response mechanisms and are indiscriminately released in the environment, resulting in low utilization rates and easily causing ecological risks. Existing controlled-release pesticides mostly rely on a single environmental signal and can only identify one, such as pH value, with low accuracy. The present invention proposes a preparation method for a dual-response controlled-release pesticide targeting the biological characteristics of the alkaline environment of the pest intestine and the high concentration of glutathione in the body. The controlled-release pesticide prepared by the method of the present invention can achieve dual responses to pH value and redox environment. Under the conditions of the alkaline environment of the pest intestine (high pH value) and glutathione (a redox agent), the controlled-release pesticide can quickly release the active ingredients of the pesticide to achieve precise killing of pests, thereby improving the precise utilization rate of the pesticide. The pesticide prepared by the present invention reduces the residue and loss of pesticides in the environment through precise release, improves the utilization rate in saline-alkali land, reduces pesticide waste, reduces pollution to soil, water and air, and is beneficial to the protection of the ecological environment.

[0022] The present invention will be further described below with reference to the embodiments and experimental verification drawings: Example 1: A method for preparing a modified corn straw nanocellulose-based dual-responsive controlled-release pesticide, see Attachment Figure 1 , including the following steps: Step 1: extracting nanocellulose from corn stalks, specifically including: Step 1.1, preparation of corn straw cellulose powder: pretreatment, put the untreated corn straw into a 105 ℃ drying oven for 24 h to remove moisture, then crush and sieve with a blender, and mix the obtained powder with 4% (w / v) NaOH solution at a mass ratio of 1:25 (w / v), and heat it in a 100 ℃ water bath for 4 h to remove hemicellulose, lignin and other impurities. Bleaching, filter the pretreated solution, collect the precipitate and dry it, mix the dried powder with the bleaching solution at a mass ratio of 1:25 (w / v), and stir it in a water bath at 80 ℃ for 6 h. The bleaching solution consists of: 0.85% (w / v) NaClO2, 3.75% (v / v) glacial acetic acid and 1.35% (w / v) NaOH. The bleached solution was washed with water 4 times and dried to obtain purified corn straw cellulose powder.

[0023] It should be noted that the corn stalks used in the present invention are available to the public through conventional channels. In addition, a series of specific operating data are provided in the embodiments of the present invention, such as drying in a drying oven at 105°C for 24 hours, heating in a water bath at 100°C for 4 hours, etc. These parameters are optimal settings determined based on experience and multiple experiments. It can be understood that those skilled in the art can flexibly select existing technologies according to specific circumstances in actual operations under the overall technical framework of this case to achieve the same operating effect. For example, according to the scale of the controlled-release pesticide to be prepared, the amount of corn stalks or the degree of dryness and wetness, and the equipment conditions, a suitable drying method is selected, such as natural drying, vacuum drying or hot air circulation drying, etc., and the drying time is appropriately extended for high-water content stalks, and the drying time is appropriately shortened for low-water content stalks. Those skilled in the art should understand that the purpose of the present invention is to provide an overall preparation process and technical principle with universal applicability, and to cover as many different applicable scenarios and conditions as possible (such as different raw material characteristics, production scales, product requirements, etc.). Therefore, some specific operations in the embodiments of the present invention can be flexibly adjusted during actual implementation, as long as the expected or the same or similar technical effects as those in the embodiments of the present invention can be achieved. The specific operation values ​​in the following steps, such as temperature, time, material ratio, etc., all follow the above principles in the same way and will not be repeated here.

[0024] Step 1.2, nano-treatment: The purified corn straw cellulose powder was mixed with an aqueous solution containing 2,2,6,6-tetramethylpiperidin-1-oxyl free radical (TEMPO, 1 mmol / L) and sodium bromide (10 mmol / L) at a mass ratio of 1:100 (w / v), and then an aqueous solution of sodium hypochlorite (10 mmol / g purified corn straw cellulose powder) was added. The nano-treatment reaction was started and stirred for 2 h while maintaining the pH value of the solution at 10.5. After the reaction was completed, 800 mL of ethanol was added to completely quench the reaction, the precipitate was collected by filtration, and the precipitate was washed with deionized water several times, and finally vacuum dried for 72 h to obtain corn straw nanocellulose (CNF).

[0025] Step 2: Modification of nanocellulose with zein, see Appendix Figure 2 , 3 , 4, 5, 6, specifically including: Step 2.1, preparation of nanocellulose aqueous solution: CNF powder (0.4 g) was dissolved in 50 mL of deionized water and stirred at room temperature to obtain a CNF aqueous dispersion system.

[0026] Step 2.2, prepare zein ethanol solution: dissolve Zein (0.2 g) in 100 mL of anhydrous ethanol to obtain a Zein ethanol dispersion system.

[0027] Step 2.3, amidation covalent modification: First, prepare 1-(3-(dimethylamino)propyl)-3-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) covalent crosslinkers. Add 50 mL of aqueous solution containing EDC (0.38 g) and NHS (0.22 g) to 50 mL of CNF aqueous dispersion in step 2.1, and adjust the pH value of the mixture to 5.5-6.0. Then, add 100 mL of Zein ethanol dispersion in step 2.2 to the mixture to form a reaction volume of 200 mL. Adjust the pH value of the mixture to 8.0 and react at room temperature for 24 h. After the reaction, reduce the pH value of the reaction solution to 1-2 to quench the amidation reaction, then centrifuge with distilled water, dialyze (Mw = 8000 Da), and finally freeze-dry for 72 h to obtain the covalent conjugate (CNF / Zein) powder, which is labeled as CNF / Zein 2 according to the mass ratio of CNF to Zein.

[0028] Step 2.4, experimental verification of covalent conjugate properties: The content of free amino groups was quantified using the OPA (o-phthalaldehyde) method. The degree of grafting of the conjugate was evaluated using the following formula: ; Among them, A s and A cRepresent the free amino content of the conjugate and native zein, respectively.

[0029] Chemical group changes were analyzed using Fourier transform infrared spectroscopy (FT-IR) between 4000 and 400 cm -1 The microstructure was captured by a HT7820 transmission electron microscope at 100 kV.

[0030] Step 3, preparation of modified corn straw nanocellulose based emulsion carrier, see attached Figure 7 , 8 , 9, 10, specifically including: Step 3.1, preparing the water phase and the oil phase: firstly, the covalent conjugate (CNF / Zein) powder was dissolved in water to form a suspension (1.0%, w / w) to obtain the water phase. Then, medium chain triglyceride (MCT) was measured as the oil phase.

[0031] Step 3.2, prepare the Pickering emulsion, mix the water phase and the oil phase in proportion, so that the final volume fraction of the oil phase is φ=0.4, and then emulsify at 12000 rpm on a FB-110J high-speed shearing machine for 3 min to form a Pickering emulsion.

[0032] Step 3.3, experimental verification of Pickering emulsion properties, the morphology of the emulsion droplets was recorded with a camera and an optical microscope. The rheological properties of the emulsion were analyzed using a TA rheometer. The mechanism of the conjugate stabilizing the emulsion was analyzed by confocal microscopy imaging, where MCT oil, Zein, and CNF were stained with Nile red, Nile blue, and fluorescein calcium white dyes, respectively.

[0033] Step 4, preparation of modified corn straw nanocellulose-based dual-responsive controlled-release pesticide, specifically comprising: Step 4.1, pesticide loading, dissolve 10 mg of avermectin (AVM) in 6 mL of the Pickering emulsion in step 3 and mix thoroughly to obtain a dual-responsive controlled-release pesticide (AVM@CNF / Zein).

[0034] Step 5: Evaluation of modified corn straw nanocellulose-based dual-responsive controlled-release pesticides, including: Step 5.1, controlled release experimental verification: AVM@CNF / Zein (5 mL) was placed in a dialysis bag (Mw=5000 Da), and then the dialysis bag was placed in a brown conical flask containing 50 mL of 40% ethanol aqueous solution to form a culture medium system. The pH value of the culture medium was adjusted with sodium hydroxide / hydrochloric acid, and culture medium samples (1 mL) were taken under acidic, alkaline and neutral conditions (such as pH 3, pH 7, pH 9, pH 12) and the absorbance of AVM in the culture medium was measured by UV absorption spectrophotometry to verify the pH responsiveness of the controlled release pesticide.

[0035] Glutathione was added to the culture medium to make the glutathione concentration (pH 7) 2 mM and 8 mM. The culture medium samples (1 mL) were taken at specific concentrations (i.e., 2 mM and 8 mM) and the absorbance of AVM in the culture medium was measured by UV absorption spectrophotometry to verify the redox responsiveness of the controlled-release pesticide. Optionally, in order to enrich the number of groups, a group with a glutathione concentration of 12 mM can also be added for experimental verification.

[0036] The data obtained from the above two types of responsiveness are substituted into the following formula to calculate the cumulative release ratio (Rn) of AVM, which represents the controlled release response mechanism of the controlled release pesticide: ; in C n is the concentration of AVM at a specific pH / glutathione concentration (mg / L), m AVM is the total mass of AVM in the culture medium, n Indicates the number of experiments.

[0037] The difference between the cumulative release ratios is determined by the difference factor f 1 and similarity factor f 2. Evaluate when f 1 is greater than 15 and f 2When it is less than 50, it is considered that there is a difference, which means that the responsiveness under different conditions can be achieved, among which, f 1 and f 2The calculation formula is as follows: ; ; in, t Represents an index variable, m represents the number of experimental intervals in the sustained-release curve, R t represents the cumulative release rate of controlled-release pesticides, T t It represents the cumulative release rate of the control conventional pesticide; Step 5.2, efficacy evaluation experimental verification: The controlled release pesticide AVM@CNF / Zein was centrifuged at 12000 rpm for 10 min. After centrifugation, 1 mL of the supernatant was taken out and placed in a dark volumetric flask, and the volume was adjusted to 25 mL with ethanol. The free AVM concentration in the supernatant was measured by UV-visible spectrophotometer at a wavelength of 245 nm. The encapsulation efficiency of AVM in the responsive carrier was calculated using the following formula: ; in, m AVM is the mass of AVM in the controlled-release pesticide before centrifugation, m 上清液AVM is the mass of unencapsulated AVM in the supernatant after centrifugation.

[0038] The insecticidal activity of the dual-response controlled-release pesticide was tested by leaf dipping experiments. Cabbage leaves with a diameter of 3 cm were immersed in the AVM@CNF / Zein formulation for 10 minutes and dried at room temperature. Cabbage leaves immersed in deionized water were used as a control group. The treated leaves were transferred to a petri dish containing diamondback moths, and the mortality rate (pest control rate) of diamondback moths was investigated after 48 hours to evaluate the insecticidal effect of AVM@CNF / Zein.

[0039] In step 5, all treatments were repeated three times, and three parallel experiments were performed. The mean of the three experimental results was taken as the final test result, and the experimental error was calculated.

[0040] Example 2: This example is different from Example 1 in that in the preparation of the nanocellulose solution and the zein solution in step 2, the amount of Zein used is different, 0.4 g of Zein is weighed, and the mass ratio of Zein to CNF is 1:1, and the covalent conjugate is labeled as CNF / Zein 1. The other steps and parameters are the same as those in Example 1.

[0041] Example 3: This example is different from Example 1 in that in the preparation of the nanocellulose solution and the zein solution in step 2, the amount of Zein used is different, 0.8 g of Zein is weighed, the mass ratio of Zein to CNF is 1:2, and the covalent conjugate is labeled as CNF / Zein 0.5. The other steps and parameters are the same as those in Example 1.

[0042] Figure 1 It is a schematic diagram of the overall method steps, showing the overall flow chart of the extraction of corn straw nanocellulose (CNF) from corn straw, the modification of corn straw nanocellulose with zein (Zein) to form covalent conjugates (CNF / Zein), the stabilization of Pickering emulsions by covalent conjugates, and the preparation and evaluation of dual-responsive controlled-release pesticides.

[0043] Figure 2 This is a schematic diagram of the chemical structure of corn straw cellulose nanofiber and zein-modified nanocellulose, which shows that the hydroxyl group (-OH) of corn straw cellulose is oxidized by TEMPO to become nanocellulose containing carboxyl groups (-COOH), and then undergoes an amidation reaction with the amino group (-NH2) of zein (Zein) under the action of EDC / NHS covalent crosslinking agent to form a covalent conjugate (CNF / Zein).

[0044] Figure 3 The finished powder pictures of the three covalent conjugates of zein-modified nanocellulose prepared in Examples 1, 2, and 3 show that the three finished powders have excellent physical properties as a whole, are fine in quality, and have good morphology, and can be used as excellent substrates for controlled-release pesticides.

[0045] Figure 4 The experimental data of free amino groups and grafting degree of three covalent conjugates prepared in Examples 1, 2, and 3 are shown in Figure 1. The free amino groups in the three covalent conjugates (CNF / Zein 2, CNF / Zein 1, and CNF / Zein 0.5) are significantly reduced compared to the control Zein content, indicating that the amino groups are consumed to generate new covalent bonds. As the polymer ratio is adjusted from CNF / Zein 0.5 to CNF / Zein 2, the grafting degree increases from 38±0.4% to 65.7±0.2%, showing higher reactivity and more effective chemical bonding.

[0046] Figure 5 The infrared spectra of the three covalent conjugates prepared in Examples 1, 2, and 3 are shown in Figure 1. The infrared spectra of the three covalent conjugates (CNF / Zein 2, CNF / Zein 1, and CNF / Zein 0.5) at 1600 cm -1 The disappearance of the CNF carboxyl band C=O at 1645 cm -1 and 1540 cm -1 The decrease of amide I band (C=O) and amide II band (N–H) in Zein indicated the success of modified nanocellulose and its application in controlled release of pesticides.

[0047] Figure 6 The microscopic transmission electron microscopy morphology of the covalent conjugate prepared in Example 1 clearly shows the successful covalent modification of CNF and Zein to form Zein-CNF core-shell particles.

[0048] Figure 7 The surface diagrams of the Pickering emulsions stabilized by the three covalent conjugates prepared in Examples 1, 2, and 3 show that the three covalent conjugates have superior stability properties compared to the CNF and Zein stabilized emulsions alone, thereby improving the stability of the controlled-release pesticide.

[0049] Figure 8 The optical microscopy images of the Pickering emulsions stabilized by the three covalent conjugates prepared in Examples 1, 2, and 3 show that the emulsion droplets of the three covalent conjugates are smaller, more uniform and dense than those of the emulsions stabilized by CNF and Zein alone, thereby making the droplets of the controlled-release pesticide finer and more uniform.

[0050] Fig. 9 The rheological properties of the Pickering emulsions stabilized by the three covalent conjugates prepared in Examples 1, 2, and 3 show that the three covalent conjugates have better rheological properties than the emulsions stabilized by CNF and Zein alone, and can improve the adhesion of controlled-release pesticides on leaves.

[0051] Fig.10 The confocal microscopy image of the covalently coupled Pickering emulsion stabilized by Example 1 clearly shows that Zein forms an interfacial protective layer on the surface of the oil droplets, while CNF cleverly adheres to the protein particles and is evenly dispersed in the continuous phase to play a bridging role. Through this unique structural combination of "interfacial adsorption-network wrapping", the two components work together to create a highly stable controlled-release pesticide carrier system and achieve dual-responsive release.

[0052] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a modified corn straw nanocellulose-based dual-responsive controlled-release pesticide, characterized in that: The controlled-release pesticide prepared by the method can achieve pH-redox dual response release, and the method comprises: Step 1: Extracting nanocellulose from corn stalks: Step 1.1, preparing corn straw cellulose powder: drying the untreated corn straw to remove moisture, then crushing and sieving with a blender, and alkali washing and bleaching the obtained powder to remove hemicellulose, lignin and other impurities to obtain purified corn straw cellulose powder; Step 1.2, nano-processing: the purified corn straw cellulose powder is mixed with an aqueous solution containing 2,2,6,6-tetramethylpiperidin-1-oxyl free radical, i.e., TEMPO, and sodium bromide, and then an aqueous solution of sodium hypochlorite is added to start a nano-processing reaction, and stirring is continued during the reaction while maintaining the pH value of the solution at 10.

5. After the reaction is completed, ethanol is added to completely quench, and the precipitate is collected by filtration, and the precipitate is washed with deionized water for multiple times, and vacuum dried to obtain corn straw nanocellulose, i.e., CNF; Step 2: Zein modified nanocellulose: Step 2.1, preparing a nanocellulose aqueous solution: dissolving CNF powder in deionized water and stirring at room temperature to obtain a CNF aqueous dispersion system; Step 2.2, preparing a zein ethanol solution: dissolving zein in anhydrous ethanol to obtain a Zein ethanol dispersion system; Step 2.3, amidation covalent modification: prepare 1-(3-(dimethylamino)propyl)-3-ethylcarbodiimide hydrochloride, namely EDC, and N-hydroxysuccinimide, namely NHS, a covalent crosslinking agent, add the aqueous solution containing EDC and NHS to the CNF aqueous dispersion system in step 2.1, adjust the pH value of the mixed solution to 5.5-6.0, then add the Zein ethanol dispersion system in step 2.1, and then adjust the pH value of the mixed solution to 8.0, react at room temperature, and after the reaction is completed, reduce the pH value of the reaction solution to 1-2 to quench the amidation reaction, then centrifuge and wash the reaction solution with distilled water, dialyze using a dialysis membrane with a molecular weight cutoff of 8000 Da, and freeze-dry to obtain a covalent conjugate CNF / Zein powder; Step 3, preparation of modified corn straw nanocellulose-based emulsion carrier: Step 3.1, preparing the water phase and the oil phase: dissolving the covalent conjugate CNF / Zein powder in water to form a suspension as the water phase, and measuring medium chain triglycerides, i.e., MCT, as the oil phase; Step 3.2, preparing a Pickering emulsion: mixing the water phase and the oil phase in a proportion such that the volume fraction of the oil phase φ=0.4, and emulsifying under a high-speed shearing machine to form a Pickering emulsion; Step 4: Preparation of modified corn straw nanocellulose-based dual-responsive controlled-release pesticides: Step 4.1, pesticide loading: AVM was dissolved in the Pickering emulsion in step 3 and mixed to obtain the dual-responsive controlled-release pesticide AVM@CNF / Zein.

2. The method for preparing the modified corn straw nanocellulose-based dual-responsive controlled-release pesticide according to claim 1, characterized in that: After step 2.3, the method further comprises: Step 2.4, experimental verification of covalent conjugate properties: The OPA method was used to quantify the content of free amino groups in the covalent conjugate CNF / Zein, and the grafting degree of the conjugate was evaluated using the following formula: ； Among them, A s and A c The free amino groups of the conjugate and native zein were expressed as follows: -1 The microscopic morphology was obtained by electron microscope.

3. The method for preparing the modified corn straw nanocellulose-based dual-responsive controlled-release pesticide according to claim 1, characterized in that: After step 3.2, the method further comprises: Step 3.3, experimental verification of Pickering emulsion properties: the morphology of the emulsion droplets was recorded with a camera and an optical microscope, the rheological properties of the emulsion were analyzed using a TA rheometer, and the mechanism of the conjugate stabilizing the emulsion was analyzed by confocal microscopy imaging, in which MCT, Zein and CNF were stained with Nile red, Nile blue and fluorescein calcium white dyes, respectively.

4. The method for preparing the modified corn straw nanocellulose-based dual-responsive controlled-release pesticide according to claim 1, characterized in that: After step 4, the method further comprises: Step 5: Evaluation of modified corn straw nanocellulose-based dual-responsive controlled release pesticides: Step 5.1, controlled release experimental verification: AVM@CNF / Zein was placed in a dialysis bag with a molecular weight cutoff of 5000 Da, and the dialysis bag was immersed in a brown conical flask containing an ethanol aqueous solution to form a culture medium system. The pH value of the culture medium was adjusted using sodium hydroxide or hydrochloric acid. The culture medium sample was taken at each pH value and the absorbance of AVM in the culture medium was measured by ultraviolet absorption spectrophotometry to verify the pH responsiveness of the controlled release pesticide, wherein each pH value covered three categories: acidic, alkaline and neutral; Glutathione was added to the culture medium to make the concentration of glutathione 2 mM and 8 mM, and the culture medium samples were taken at specific concentrations and the absorbance of AVM in the culture medium was measured by UV absorption spectrophotometry to verify the redox responsiveness of the controlled-release pesticide; The data obtained from pH responsiveness verification and redox responsiveness verification were substituted into the following formula to calculate the cumulative release ratio R of AVM: n , which represents the controlled release response mechanism of controlled release pesticides: ； in, C n is the concentration of AVM at a specific pH or glutathione concentration (mg / L), m AVM is the total mass of AVM in the culture medium, n represents the number of experiments; The difference between the cumulative release ratios is determined by the difference factor f 1 and similarity factor f 2. Evaluate when f 1 is greater than 15 and f 2When it is less than 50, it is considered that there is a difference, indicating that the responsiveness under different conditions can be achieved, among which, f 1 and f 2The calculation formula is as follows: ； ； in, t Represents an index variable, m represents the number of experimental intervals in the sustained-release curve, R t represents the cumulative release rate of controlled-release pesticides, T t It represents the cumulative release rate of the control conventional pesticide; Step 5.2, efficacy evaluation experimental verification: After the controlled release pesticide AVM@CNF / Zein was centrifuged at a speed of 1000 rpm, the supernatant was placed in a dark volumetric flask, the volume was adjusted with ethanol, and the concentration of free AVM in the supernatant was measured at a wavelength of 245 nm using a UV-visible spectrophotometer. The encapsulation efficiency of AVM in the responsive carrier was calculated using the following formula: ； in, m AVM is the mass of AVM in the controlled-release pesticide before centrifugation, m 上清液AVM is the mass of unencapsulated AVM in the supernatant after centrifugation; The insecticidal activity of the dual-responsive controlled-release pesticide was tested by leaf dipping experiments. Cabbage leaves were dipped in the AVM@CNF / Zein formulation and dried at room temperature. Cabbage leaves soaked in deionized water were used as a control group. The treated leaves were transferred to a petri dish containing Plutella xylostella to investigate the mortality of Plutella xylostella and evaluate the insecticidal effect of AVM@CNF / Zein.

5. The method for preparing the modified corn straw nanocellulose-based dual-responsive controlled-release pesticide according to claim 1, characterized in that: The step 1.1 is to put the untreated corn stalks into a 105°C drying oven and dry them for 24 hours to remove moisture, then crush and sieve them with a blender, and mix the obtained powder with a 4% (w / v) NaOH solution at a mass volume ratio of 1:25 (w / v), heat it in a 100°C water bath for 4 hours to remove hemicellulose, lignin and other impurities, collect the precipitate by filtration and dry it, mix the dried powder with a bleaching solution at a mass volume ratio of 1:25 (w / v), and continue stirring in a water bath at 80°C for 6 hours. The bleaching solution is composed of: 0.85% (w / v) NaClO2, 3.75% (v / v) glacial acetic acid and 1.35% (w / v) NaOH, wash the bleached solution with water 4 times and then dry it to obtain purified corn stalk cellulose powder.

6. The method for preparing the modified corn straw nanocellulose-based dual-responsive controlled-release pesticide according to claim 1, characterized in that: In the step 1.2, the purified corn straw cellulose powder is mixed with an aqueous solution containing 2,2,6,6-tetramethylpiperidin-1-oxyl free radical, i.e., TEMPO, and sodium bromide at a mass volume ratio of 1:100 (w / v), wherein the concentration of TEMPO in the aqueous solution is 1 mmol / L, and the concentration of sodium bromide is 10 mmol / L, and then an aqueous solution of sodium hypochlorite is added, wherein 10 mmol of sodium hypochlorite is added per gram of purified corn straw cellulose powder, and the nano-reaction is started, and stirring is continued for 2 h.

7. The method for preparing the modified corn straw nanocellulose-based dual-responsive controlled-release pesticide according to claim 1, characterized in that: The step 2.1 is to dissolve 0.4 g of CNF powder in 50 mL of deionized water and stir at room temperature to obtain a CNF water dispersion system; The step 2.2 is to dissolve 0.2-0.8 g of Zein in 100 mL of anhydrous ethanol to obtain a Zein ethanol dispersion system; The step 2.3 is to add 50 mL of an aqueous solution containing 0.38 g of EDC and 0.22 g of NHS into the CNF aqueous dispersion system in step 2.

1.

8. The method for preparing the modified corn straw nanocellulose-based dual-responsive controlled-release pesticide according to claim 1, characterized in that: In the step 3.1, the mass ratio of the solute solution of the suspension formed by dissolving the covalent coupling CNF / Zein powder in water is 1.0%; In the step 3.2, the Pickering emulsion is formed by emulsifying for 3 minutes at a speed of 12000 rpm on a FB-110J high-speed shearing machine.

9. The method for preparing the modified corn straw nanocellulose-based dual-responsive controlled-release pesticide according to claim 1, characterized in that: The step 4.1 is to dissolve 10 mg of avermectin, i.e. AVM, in 6 mL of the Pickering emulsion in step 3, and mix well to obtain the dual-responsive controlled-release pesticide AVM@CNF / Zein.

10. The method for preparing the modified corn straw nanocellulose-based dual-responsive controlled-release pesticide according to claim 4, characterized in that: In step 5.1, the dialysis bag is immersed in 50 mL of ethanol aqueous solution with a concentration of 40%; In step 5.2, the controlled-release pesticide AVM@CNF / Zein was centrifuged at 12,000 rpm for 10 min. After centrifugation, 1 mL of the supernatant was placed in a dark volumetric flask and the volume was adjusted to 25 mL with ethanol. In the leaf immersion experiment, cabbage leaves with a diameter of 3 cm were immersed in the AVM@CNF / Zein formula for 10 minutes, and the mortality rate of the diamondback moth was investigated after 48 hours.

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