Preparation Method of Modified Corn Straw Nanocellulose-based Dual-responsive Controlled-release Pesticide

Abstract

The invention discloses a preparation method of a modified corn straw nanocellulose-based dual-responsive controlled-release pesticide, which relates to the technical field of resource utilization of agricultural waste and environmental protection. The method includes: extracting nanocellulose from corn straw, modifying nanocellulose with zein, preparing a modified corn straw nanocellulose-based emulsion carrier, and preparing and evaluating a modified corn straw nanocellulose-based dual-responsive controlled-release pesticide. The invention verifies the effectiveness of the EDC / NHS cross-linking agent in an alcohol solution system, successfully modifies corn straw nanocellulose, realizes the efficient utilization of waste resources, solves the problems of low utilization rate of traditional pesticides, burning waste of corn straw and limitations of the performance of conventional cellulose, and at the same time, a new type of dual-responsive controlled-release pesticide that is efficient, environmentally friendly and economical can be obtained, which has important guiding significance for solving the bottleneck problems in the field of pesticide formulations.

Description

Technical Field

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

[0002] In the application of traditional pesticide formulations, problems such as rapid decomposition of active ingredients and low target retention rate are common, resulting in a pesticide utilization rate of less than 30%. This not only causes 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 a high concentration of soil soluble salts, pH imbalance (higher pH value in alkaline soil), and the soil is alkaline. 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, diseases, and weeds, with low utilization rate, and it is easy to exacerbate soil compaction in saline-alkali land, which is not conducive to water infiltration and gas exchange, and hinders the improvement process of saline-alkali land. For example, some organophosphorus pesticides may accelerate hydrolysis due to a relatively high pH value in saline-alkali land, reducing the efficacy. Due to the low utilization rate of pesticides, in order to achieve the control effect, farmers often need to increase the amount of pesticides used. This not only increases the agricultural production cost, but also the long-term and large-scale use of pesticides will damage the fertility and ecological functions of the saline-alkali land soil, further exacerbating 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, posing a serious threat to the ecological environment and human health. Coupled with the poor drainage performance of the saline-alkali land soil itself, pesticide residues are more likely to accumulate in the soil and pollute groundwater through leaching.

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

[0005] In recent years, with the popularization of the concept of sustainable development and the progress of technology, using natural renewable resources as dual-responsive controlled-release pesticide carrier materials has become a research hotspot. Nano-cellulose, due to its high specific surface area, unique physical and chemical properties, and environmental friendliness, can significantly improve the dispersibility, stability, and penetration ability of pesticides, and is regarded as an excellent controlled-release pesticide carrier material. Among the raw materials for extracting nano-cellulose, corn straw stands out. Corn straw is a common agricultural waste, often burned and wasted. However, corn straw not only contains a large amount of cellulose components, but also, due to its unique structural characteristics, has become an ideal raw material for extracting high-quality nano-cellulose. At the same time, the surface of nano-cellulose has abundant modified hydroxyl groups, and modifying nano-cellulose will further enhance its functional properties.

[0006] The purpose of the present invention is to provide a preparation method of modified corn straw nano-cellulose-based dual-responsive controlled-release pesticide, which can effectively utilize agricultural waste, reduce environmental pollution, and improve the economy and effectiveness of pesticide use at the same time. Through the technical solution of the present invention, a high-performance modified nano-cellulose controlled-release pesticide system based on agricultural waste can be obtained, which has both environmental friendliness and dual-release characteristics, and has important guiding significance for solving the bottleneck problems in the field of pesticide formulations. Summary of the Invention

[0007] The purpose of the present invention is to solve the problems of low utilization rate of traditional pesticides, waste of burning corn straw, and limitations of the performance of conventional cellulose, and to provide a preparation method of modified corn straw nano-cellulose-based dual-responsive controlled-release pesticide, which can improve the targeted utilization rate of pesticides, and the production process is simpler and the production cost is lower.

[0008] A preparation method of a modified corn straw nanocellulose-based dual-responsive controlled-release pesticide. The controlled-release pesticide prepared by this method can achieve dual-responsive release of pH-redox. The method includes: 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 it 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, nanosizing treatment: mixing the purified corn straw cellulose powder with an aqueous solution containing 2,2,6,6-tetramethylpiperidine-1-oxyl radical, i.e., TEMPO, and sodium bromide, then adding an aqueous solution of sodium hypochlorite to start the nanosizing reaction, continuously stirring during the reaction, and simultaneously maintaining the pH value of the solution at 10.5. After the reaction, add ethanol to completely quench, filter and collect the precipitate, and wash the precipitate with deionized water multiple times, and vacuum-dry to obtain corn straw nanocellulose, i.e., CNF; Step 2, modifying nanocellulose with zein: Step 2.1, preparing an aqueous solution of nanocellulose: dissolving CNF powder in deionized water and stirring at room temperature to obtain a CNF aqueous dispersion system; Step 2.2, preparing an ethanol solution of zein: dissolving zein, i.e., Zein, in absolute ethanol to obtain a Zein ethanol dispersion system; Step 2.3, amidation covalent modification: preparing a covalent cross-linking agent of 1-(3-(dimethylamino)propyl)-3-ethylcarbodiimide hydrochloride, i.e., EDC, and N-hydroxysuccinimide, i.e., NHS, adding the aqueous solution containing EDC and NHS to the CNF aqueous dispersion system in Step 2.1, adjusting the pH value of the mixture to 5.5-6.0, then adding the Zein ethanol dispersion system in Step 2.2, and then adjusting the pH value of the mixture to 8.0, reacting at room temperature, and after the reaction, lowering the pH value of the reaction solution to 1-2 to quench the amidation reaction, then centrifugally washing the reaction solution with distilled water, dialyzing with a dialysis membrane with a molecular weight cut-off of 8000 Da, and freeze-drying to obtain a covalent conjugate CNF / Zein powder; Step 3, preparing a modified corn straw nanocellulose-based emulsion carrier: Step 3.1, preparing an aqueous phase and an oil phase: dissolving the covalent conjugate 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, preparing a Pickering emulsion: mixing the aqueous phase and the oil phase in a certain proportion so that the volume fraction φ of the oil phase is 0.4, and emulsifying to form a Pickering emulsion with a high-speed shear mixer; Step 4, preparing a modified corn straw nanocellulose-based dual-responsive controlled-release pesticide: Step 4.1, pesticide loading: dissolving abamectin, i.e., AVM, in the Pickering emulsion in Step 3 and mixing evenly to obtain a dual-responsive controlled-release pesticide AVM@CNF / Zein.

[0009] Optionally, after step 2.3, the method further includes: step 2.4, experimental verification of the properties of the covalent conjugate: quantifying the content of free amino groups in the covalent conjugate CNF / Zein using the OPA method, and evaluating the grafting degree of the conjugate using the following formula:

[0010] ;

[0011] wherein, A s and A c respectively represent the content of free amino groups in the conjugate and native zein, the chemical group changes are detected using a Fourier transform infrared spectrometer in the range of 4000 to 400 cm -1 range, and the microscopic morphology is obtained by photographing with an electron microscope.

[0012] Optionally, after step 3.2, the method further includes: step 3.3, experimental verification of the properties of Pickering emulsion: the morphology of 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 conjugate-stabilized emulsion is analyzed by confocal microscopy imaging, wherein MCT, Zein, and CNF are stained with Nile red, Nile blue, and fluorescein calcein dyes, respectively.

[0013] Optionally, after step four, the method further includes: step five, evaluation of the modified corn straw nanocellulose-based dual-responsive controlled-release pesticide: step 5.1, controlled-release experiment verification: putting AVM@CNF / Zein into a dialysis bag with a molecular weight cut-off of 5000 Da, immersing the dialysis bag into a brown conical flask containing an ethanol aqueous solution to form a culture medium system, adjusting the pH value of the culture medium using sodium hydroxide or hydrochloric acid, taking culture medium samples at each pH value and measuring the absorbance of AVM in the culture medium using ultraviolet absorption spectrophotometry to verify the pH responsiveness of the controlled-release pesticide, wherein each pH value covers three categories of acidic, alkaline, and neutral; adding glutathione to the culture medium to make the glutathione concentration 2 mM and 8 mM, taking culture medium samples at a specific concentration and measuring the absorbance of AVM in the culture medium using ultraviolet absorption spectrophotometry to verify the redox responsiveness of the controlled-release pesticide; substituting the data obtained from the pH responsiveness verification and the redox responsiveness verification into the following formula to calculate the cumulative release ratio R n , which represents the controlled-release response mechanism of the controlled-release pesticide:

[0014] ;

[0015] wherein, C n is the concentration of AVM (mg / L) at a specific pH or glutathione concentration, m AVMis the total mass of AVM in the culture medium, n represents the number of experiments;

[0016] The difference between the cumulative release ratios is evaluated by the difference factor f f1 and the similarity factor f f2. When f f1 is greater than 15 and f f2 is less than 50, it is considered that there is a difference, indicating that the responsiveness under different conditions can be achieved. Among them, f f1 and f f2 are calculated as follows:

[0017] ;

[0018] ;

[0019] Among them, t i represents the index variable, m n represents the number of experimental intervals in the sustained-release curve, R t Qn represents the cumulative release rate of the controlled-release pesticide, T t Q0 represents the cumulative release rate of the control traditional pesticide;

[0020] Step 5.2, Utility evaluation experiment verification: After centrifuging the controlled-release pesticide AVM@CNF / Zein at a certain speed, take the supernatant and place it in a dark volumetric flask, adjust the volume with ethanol, and measure the concentration of free AVM in the supernatant at a wavelength of 245 nm using a UV-visible spectrophotometer. Calculate the encapsulation efficiency of AVM by the responsive carrier using the following formula:

[0021] ;

[0022] Among them, m AVM m0 is the mass of AVM in the controlled-release pesticide before centrifugation, m 上清液AVM m1 is the mass of unencapsulated AVM in the supernatant after centrifugation;

[0023] Test the insecticidal activity of the dual-responsive controlled-release pesticide through the leaf-dipping experiment. Immerse the cabbage leaves in the AVM@CNF / Zein formulation and dry them at room temperature. Use the cabbage leaves soaked in deionized water as the control group. Transfer the treated leaves to a petri dish containing Plutella xylostella, investigate the mortality rate of Plutella xylostella, and evaluate the insecticidal effect of AVM@CNF / Zein.

[0024] Optionally, in step 1.1, the untreated corn straw is placed in a drying oven at 105 °C for 24 h to remove moisture, and then pulverized and sieved with a blender. The obtained powder is mixed with a 4% w / v NaOH solution at a mass-to-volume ratio of 1:25 and heated in a water bath at 100 °C for 4 h to remove hemicellulose, lignin, and other impurities. The precipitate is filtered, collected, and dried. The dried powder is mixed with a bleaching solution at a mass-to-volume ratio of 1:25 and continuously stirred in a water bath at 80 °C 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 is washed with water 4 times and then dried to obtain purified corn straw cellulose powder.

[0025] Optionally, in step 1.2, the purified corn straw cellulose powder is mixed with an aqueous solution containing 2,2,6,6-tetramethylpiperidine-1-oxyl radical, namely TEMPO, and sodium bromide at a mass-to-volume ratio of 1:100. The concentration of TEMPO in the aqueous solution is 1 mmol / L, and the concentration of sodium bromide is 10 mmol / L. Subsequently, an aqueous solution of sodium hypochlorite is added, with 10 mmol of sodium hypochlorite added per gram of the purified corn straw cellulose powder, and the nanonization reaction is started, with continuous stirring for 2 h.

[0026] Optionally, in step 2.1, 0.4 g of CNF powder is dissolved in 50 mL of deionized water and stirred at room temperature to obtain a CNF aqueous dispersion system; in step 2.2, 0.2 - 0.8 g of Zein is dissolved in 100 mL of absolute ethanol to obtain a Zein ethanol dispersion system; in step 2.3, 50 mL of an aqueous solution containing 0.38 g of EDC and 0.22 g of NHS is added to the CNF aqueous dispersion system in step 2.1.

[0027] Optionally, in step 3.1, the mass ratio of the solute in the suspension formed by dissolving the covalent conjugate CNF / Zein powder in water is 1.0%; in step 3.2, emulsification is carried out at a speed of 12000 rpm for 3 min with a FB-110J high-speed shear machine to form a Pickering emulsion.

[0028] Optionally, in step 4.1, 10 mg of abamectin, namely AVM, is dissolved in 6 mL of the Pickering emulsion in step three, and mixed evenly to obtain the dual-responsive controlled-release pesticide AVM@CNF / Zein.

[0029] Optionally, the ethanol aqueous solution into which the dialysis bag is immersed in Step 5.1 is 50 mL 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 taken and placed in a dark volumetric flask, and the volume is adjusted to 25 mL with ethanol; for the leaf dipping experiment, a cabbage leaf with a diameter of 3 cm is soaked in the AVM@CNF / Zein formulation for 10 minutes, and the mortality rate of Plutella xylostella is investigated after 48 hours.

[0030] The beneficial effects of the present invention are as follows:

[0031] 1. The present invention verifies the effectiveness of the EDC / NHS cross-linking agent in an alcohol-soluble system, successfully modifies corn straw nanocellulose, broadens the application value, and at the same time, the preparation method is simple to operate, low in cost, and easy to scale up production;

[0032] 2. The present invention "takes from agriculture and uses it in agriculture", providing a new type of highly efficient, environmentally friendly, and economical dual-responsive controlled-release pesticide for the pesticide industry. This controlled-release pesticide has pH-redox dual-responsive characteristics. In the alkaline environment (higher pH value) of the pest intestine and in the presence of glutathione (an oxidation-reducing agent), the controlled-release pesticide can quickly release the pesticide active ingredient to achieve precise killing of pests. 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 to increase crop yield and quality and promote agricultural production increase and income increase;

[0033] 3. The controlled-release pesticide prepared by the present invention has pH-redox dual-responsive release characteristics, releasing more pesticide active ingredients 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 the improvement of saline-alkali soil.

[0034] 4. The present invention uses corn straw agricultural waste as a 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 concepts of green chemistry and sustainable development, has good environmental benefits and social values, and belongs to "turning waste into treasure". Brief Description of the Drawings

[0035] Figure 1 It is a schematic diagram of the overall method steps of the present invention;

[0036] Figure 2 It is a schematic diagram of the chemical structure of corn straw cellulose nanonization and modification of nanocellulose with corn zein in the present invention;

[0037] Figure 3Powder diagrams of three covalent conjugates of zein-modified nanocellulose prepared in Examples 1, 2, and 3 of the present invention;

[0038] Figure 4 Data diagrams of free amino groups and grafting degrees of three covalent conjugates prepared in Examples 1, 2, and 3 of the present invention;

[0039] Figure 5 Infrared spectra diagrams of three covalent conjugates prepared in Examples 1, 2, and 3 of the present invention;

[0040] Figure 6 Microscopic transmission electron microscopy morphology diagram of the covalent conjugate prepared in Example 1 of the present invention;

[0041] Figure 7 Apparent diagrams of Pickering emulsions stabilized by three covalent conjugates prepared in Examples 1, 2, and 3 of the present invention;

[0042] Figure 8 Optical microscopy diagrams of Pickering emulsions stabilized by three covalent conjugates prepared in Examples 1, 2, and 3 of the present invention;

[0043] Figure 9 Rheological property diagrams of Pickering emulsions stabilized by three covalent conjugates prepared in Examples 1, 2, and 3 of the present invention;

[0044] Figure 10 Confocal microscopy diagram of a Pickering emulsion stabilized by the covalent conjugate prepared in Example 1 of the present invention. Detailed implementation manners

[0045] Due to the lack of an intelligent response mechanism, traditional pesticides are released indiscriminately in the environment, resulting in low utilization rates and easy ecological risks. Existing controlled-release pesticides mostly rely on a single environmental signal and can only recognize one, such as only being able to recognize the pH value, with low accuracy. In view of the biological characteristics of the alkaline environment in the intestines of pests and the high concentration of glutathione in their bodies, the present invention proposes a preparation method for a dual-responsive controlled-release pesticide. The controlled-release pesticide prepared by the method of the present invention can achieve dual responses to the pH value and the redox environment. Under the alkaline environment (higher pH value) in the intestines of pests and the condition containing glutathione (an oxidation-reducing agent), the controlled-release pesticide can rapidly release the pesticide active ingredient to achieve precise killing of pests, thereby improving the precise utilization rate of pesticides. The pesticide prepared by the present invention reduces the residue and loss of pesticides in the environment through precise release, and also improves the utilization rate in saline-alkali land, reduces pesticide waste, and reduces pollution to the soil, water body, and air, which is beneficial to the protection of the ecological environment.

[0046] The following further illustrates the present invention in conjunction with examples and experimental verification drawings:

[0047] Example 1: A preparation method of a modified corn straw nanocellulose-based dual-responsive controlled-release pesticide. Refer to the appendix Figure 1 , which includes the following steps:

[0048] Step 1, extracting nanocellulose from corn straw, specifically including:

[0049] Step 1.1, preparing corn straw cellulose powder: Pretreatment, putting the untreated corn straw into a 105 °C drying oven to dry for 24 h to remove moisture, then crushing and sieving it with a blender. The obtained powder is mixed with a 4% (w / v) NaOH solution according to a mass ratio of 1:25 (w / v) and heated in a water bath at 100 °C for 4 h to remove hemicellulose, lignin, and other impurities. Bleaching, filtering the pretreated solution, collecting the precipitate and drying it. The dried powder is mixed with a bleaching solution according to a mass ratio of 1:25 (w / v) and continuously stirred in a water bath at 80 °C for 6 h. The bleaching solution composition is: 0.85% (w / v) NaClO2, 3.75% (v / v) glacial acetic acid, and 1.35% (w / v) NaOH. Washing the bleached solution 4 times with water and then drying it to obtain purified corn straw cellulose powder.

[0050] It should be supplemented that the corn straw used in the present invention is publicly available through conventional channels. In addition, a series of specific operation data are provided in the embodiments of the present invention, such as drying in a 105 °C drying oven for 24 h, heating in a water bath at 100 °C for 4 h, etc. These parameters are relatively 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 the overall technical framework of this case to achieve the same operation effect. For example, according to the scale of the controlled-release pesticide to be prepared, the amount of corn straw used, or its dry-wet degree, and equipment conditions, select a suitable drying method, such as natural drying, vacuum drying, or hot air circulation drying, etc., and appropriately extend the drying time for high-moisture straw and shorten the drying time for low-moisture straw. Those skilled in the art should understand that the purpose of the present invention is to provide a general overall preparation process and technical principle, and 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 elaborated here.

[0051] Step 1.2, Nanonization treatment: The purified corn straw cellulose powder is mixed with an aqueous solution containing 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO, 1 mmol / L) and sodium bromide (10 mmol / L) at a mass ratio of 1:100 (w / v). Subsequently, an aqueous solution of sodium hypochlorite (10 mmol / g of the purified corn straw cellulose powder) is added. The nanonization reaction is initiated and continuously stirred for 2 h while maintaining the pH value of the solution at 10.5. After the reaction, 800 mL of ethanol is added to completely quench the reaction. The precipitate is collected by filtration, washed multiple times with deionized water, and finally dried under vacuum for 72 h to obtain corn straw nanocellulose (CNF).

[0052] Step two, modification of nanocellulose with zein, refer to Appendix Figure 2 、 3 、4, 5, 6, specifically including:

[0053] Step 2.1, Preparation of an aqueous solution of nanocellulose: Dissolve CNF powder (0.4 g) in 50 mL of deionized water and stir at room temperature to obtain a CNF aqueous dispersion system.

[0054] Step 2.2, Preparation of an ethanol solution of zein: Dissolve Zein (0.2 g) in 100 mL of absolute ethanol to obtain a Zein ethanol dispersion system.

[0055] Step 2.3, Amidation covalent modification: First, prepare 1-(3-(dimethylamino)propyl)-3-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) covalent crosslinking agents. Add 50 mL of an aqueous solution containing EDC (0.38 g) and NHS (0.22 g) to the 50 mL CNF aqueous dispersion system in Step 2.1, and adjust the pH value of the mixture to 5.5 - 6.0. Subsequently, continue to add the 100 mL Zein ethanol dispersion system 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, lower the pH value of the reaction solution to 1 - 2 to quench the amidation reaction, then centrifuge with distilled water and dialyze (Mw = 8000 Da), and finally freeze-dry for 72 h to obtain a covalent conjugate (CNF / Zein) powder, labeled as CNF / Zein 2 according to the mass ratio of CNF and Zein.

[0056] Step 2.4, Experimental verification of the properties of the covalent conjugate: The content of free amino groups is quantified using the OPA (o-phthalaldehyde) method. The grafting degree of the conjugate is evaluated using the following formula:

[0057] ;

[0058] Among them, A s and A c Represent the free amino content of the conjugate and native zein, respectively.

[0059] 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.

[0060] Step 3, preparation of modified corn straw nanocellulose based emulsion carrier, see attached Figure 7 , 8 , 9, 10, specifically including:

[0061] 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.

[0062] 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.

[0063] 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.

[0064] Step 4, preparation of modified corn straw nanocellulose-based dual-responsive controlled-release pesticide, specifically comprising:

[0065] 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).

[0066] Step 5: Evaluation of modified corn straw nanocellulose-based dual-responsive controlled-release pesticides, including:

[0067] Step 5.1, Controlled release experiment verification: Put AVM@CNF / Zein (5 mL) into a dialysis bag (Mw = 5000 Da), and then place the dialysis bag in a brown conical flask containing 50 mL of 40% ethanol aqueous solution to form a culture medium system. Adjust the pH value of the culture medium with sodium hydroxide / hydrochloric acid, and take culture medium samples (1 mL) under acidic, alkaline, and neutral conditions (such as pH 3, pH 7, pH 9, pH 12), and measure the absorbance of AVM in the culture medium by ultraviolet absorption spectrophotometry to verify the pH responsiveness of the controlled release pesticide.

[0068] Add glutathione to the culture medium so that the glutathione concentration (pH 7) is 2 mM and 8 mM. Take culture medium samples (1 mL) at specific concentrations (i.e., 2 mM and 8 mM), and measure the absorbance of AVM in the culture medium by ultraviolet absorption spectrophotometry to verify the redox responsiveness of the controlled release pesticide. Optionally, to enrich the number of groups, a group with a glutathione concentration of 12 mM can also be added for experimental verification.

[0069] Substitute the data obtained from the above two types of responsiveness 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:

[0070] ;

[0071] where C n is the concentration of AVM (mg / L) at a specific pH / glutathione concentration, m AVM is the total mass of AVM in the culture medium, n represents the number of experiments.

[0072] The difference between the cumulative release ratios is evaluated by the difference factor f 1 and the similarity factor f 2. When f 1 is greater than 15 and f 2 is less than 50, it is considered that there is a difference, which means that the responsiveness under different conditions can be achieved. Among them, f 1 and f 2 are calculated as follows:

[0073] ;

[0074] ;

[0075] where, t represents the index variable, m represents the number of experimental intervals in the sustained release curve, R t represents the cumulative release rate of the controlled release pesticide,T t represents the cumulative release rate compared with traditional pesticides;

[0076] Step 5.2, Utility evaluation experiment verification: The controlled-release pesticide AVM@CNF / Zein was centrifuged at 12,000 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 concentration of free AVM in the supernatant was measured using a UV-visible spectrophotometer at a wavelength of 245 nm. The encapsulation efficiency of AVM by the responsive carrier was calculated using the following formula:

[0077] ;

[0078] where, 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.

[0079] The insecticidal activity of the dual-responsive controlled-release pesticide was tested through a leaf-dipping experiment. Cabbage leaves with a diameter of 3 cm were soaked in the AVM@CNF / Zein formulation for 10 minutes and dried at room temperature. Cabbage leaves soaked in deionized water were used as the 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.

[0080] All treatments in Step 5 were repeated three times to conduct three parallel repeated experiments. The mean value of the results of the three experiments was used as the final test result, and the experimental error was calculated.

[0081] Example 2: The difference between this example and Example 1 is that in the preparation of the nanocellulose solution and zein solution in Step 2, the amount of Zein used is different. 0.4 g of Zein was weighed, and the mass ratio with CNF was 1:1. The covalent conjugate was labeled as CNF / Zein 1. Other steps and parameters were the same as those in Example 1.

[0082] Example 3: The difference between this example and Example 1 is that in the preparation of the nanocellulose solution and zein solution in Step 2, the amount of Zein used is different. 0.8 g of Zein was weighed, and the mass ratio with CNF was 1:2. The covalent conjugate was labeled as CNF / Zein 0.5. Other steps and parameters were the same as those in Example 1.

[0083] Figure 1It is a schematic diagram of the overall method steps, showing the overall flow chart of extracting corn straw nanocellulose (CNF) from corn straw, modifying corn straw nanocellulose with zein to form a covalent conjugate (CNF / Zein), stabilizing Pickering emulsion with the covalent conjugate, and preparing and evaluating the dual-responsive controlled-release pesticide.

[0084] Figure 2 It is a schematic diagram of the chemical structure of corn straw cellulose nanonization and zein-modified nanocellulose, showing that the hydroxyl group (-OH) of corn straw cellulose becomes nanocellulose containing carboxyl group (-COOH) after TEMPO oxidation, and then undergoes carboxamide condensation amidation reaction with the amino group (-NH2) of zein under the action of EDC / NHS covalent cross-linking agent to generate a covalent conjugate (CNF / Zein).

[0085] Figure 3 It is a picture of the finished powder of three covalent conjugates of zein-modified nanocellulose prepared in Examples 1, 2, and 3. It can be seen that the three finished powders as a whole show excellent physical properties, with fine powder quality and good morphology, and can be used as excellent substrates for controlled-release pesticides.

[0086] Figure 4 It is an experimental data chart of the free amino groups and grafting degrees of the three covalent conjugates prepared in Examples 1, 2, and 3. The free amino groups in the three covalent conjugates (CNF / Zein 2, CNF / Zein 1, and CNF / Zein 0.5) are significantly reduced compared with the content of zein in the control group, indicating that the amino groups are consumed to form 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.

[0087] Figure 5 It is an infrared spectrum chart of the three covalent conjugates prepared in Examples 1, 2, and 3. In the three covalent conjugates (CNF / Zein 2, CNF / Zein 1, and CNF / Zein 0.5), the disappearance of the C=O of the CNF carboxyl band at 1600 cm -1 and the decrease of the amide I band (C=O) and amide II band (N–H) in zein at 1645 cm -1 and 1540 cm -1 both illustrate the success of the modified nanocellulose and can be better applied to controlled-release pesticides.

[0088] Figure 6The transmission electron microscopy (TEM) image of the covalent conjugate prepared in Example 1 clearly shows the successful covalent modification of CNF with Zein, forming Zein-CNF core-shell particles.

[0089] Figure 7 Appearance images of Pickering emulsions stabilized by the three covalent conjugates prepared in Examples 1, 2, and 3, showing that the three covalent conjugates have excellent emulsion stabilization performance compared to CNF and Zein alone, thus improving the stability of controlled-release pesticides.

[0090] Figure 8 Optical microscopy images of Pickering emulsions stabilized by the three covalent conjugates prepared in Examples 1, 2, and 3, showing that the emulsion droplets of the three covalent conjugates are smaller, more uniform, and denser compared to the emulsions stabilized by CNF and Zein alone, thus making the droplets of the controlled-release pesticides finer and more uniform.

[0091] Figure 9 Rheological property diagrams of Pickering emulsions stabilized by the three covalent conjugates prepared in Examples 1, 2, and 3, showing that the three covalent conjugates have better emulsion rheological properties compared to the emulsions stabilized by CNF and Zein alone, which can improve the adhesion of the controlled-release pesticides to the leaves.

[0092] Figure 10 Confocal microscopy images of Pickering emulsions stabilized by the covalent conjugate prepared in Example 1 clearly show that Zein forms an interfacial protective layer on the surface of the oil droplets, while CNF cleverly adheres around the protein particles and is uniformly dispersed in the continuous phase, playing a bridging role. Through this unique structural combination of "interfacial adsorption-network encapsulation", the two components work together to create a highly stable controlled-release pesticide carrier system and achieve dual-responsive release.

[0093] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill 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 present invention, and 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 2.2, 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, 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, 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.

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, 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 a sodium hypochlorite aqueous solution 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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