Preparation method of lignin-based slow-release nano-pesticide

Abstract

The present application relates to the technical field of agricultural biomass pesticide, and particularly relates to a preparation method of a lignin-based slow-release nano-pesticide. The method is used for preparing a cationic surfactant-corn straw lignin nano-pesticide with PH and enzyme double responses through self-assembly. The material is modified lignin prepared by using cetyltrimethylammonium bromide (CTAB) as a cationic surfactant and corn straw, and further forms the cationic surfactant-corn straw lignin nano-pesticide through the self-assembly method. The preparation method has the advantages of simple process, low cost and environmental friendliness, and the obtained slow-release nano-pesticide product has excellent performances in terms of ultraviolet light shielding performance, slow-release performance and insecticidal activity, can precisely target pesticide delivery, significantly reduces the possibility of pesticide residues and environmental pollution, and promotes the sustainable development of agriculture.

Description

Technical Field

[0001] This invention relates to the field of agricultural biomass pesticide preparation technology, specifically to a method for preparing a lignin-based slow-release nanopesticide. Background Technology

[0002] The development and application of pesticides are closely related to the sustainable development of agriculture in my country, and the rational use of pesticides is of great significance for agricultural production and ecological environmental protection. However, there are many types of pesticides, and most pesticide technical materials are poorly soluble solids with poor dispersibility. Furthermore, they are prone to dust drift during application, affecting their efficacy and making direct application difficult under normal circumstances. Excessive and inefficient use of pesticides has led to a series of problems, including food safety, ecological environment, and human health issues. Therefore, improving the effective utilization rate of pesticides and reducing pesticide transfer to non-target organisms and the environment, as well as residual pollution, is crucial.

[0003] Nanoplatforms have been widely reported due to their unique physicochemical properties, flexibility in loading therapeutic biomolecules or drugs, and ability to employ targeting strategies. Many materials have been developed as carriers for nanopesticides, such as silica nanoparticles, polymer systems, carbon nanotubes, and viral particles. However, research on nanotechnology in agriculture started relatively late and is still relatively weak. Therefore, the research and application of nanopesticides still face several unresolved issues, such as: most reported nanopesticides are still in the laboratory research stage, with complex and diverse preparation methods, limited product quantities, and difficulty in ensuring process and product stability; nanoparticles are prone to spontaneous aggregation due to their small size and specific surface area, leading to reduced stability and requiring the selection of appropriate adjuvants; complex and time-consuming synthesis processes, uncontrolled diffusion and release of substances, and environmental pollution caused by nanocarriers. Therefore, there is an urgent need for a nanoplatform that can be prepared through a simple process with minimal environmental pollution, ensuring the biocontrol efficacy of pesticides on the target while extending the duration of drug efficacy, reducing drug toxicity, and achieving green and environmentally friendly practices.

[0004] Lignin, as the most abundant high-molecular-weight organic substance in nature after cellulose, not only possesses rich chemical structures and biological activities, but also plays a dual role of support and protection in plants. Furthermore, as an abundant biomass resource, lignin is widely available, inexpensive, and naturally hydrophobic and renewable. Developing lignin as a coating material for nanopesticides not only has significant social and economic value, but also plays a vital role in promoting sustainable agricultural development.

[0005] However, the current industrial application rate of lignin is relatively low, with a large amount of lignin being treated as waste during production. This not only wastes resources but also poses a potential threat to the environment. To date, lignin from the Poaceae family has rarely been used in slow-release pesticides.

[0006] Corn stalks are a significant byproduct of agricultural production. Extracting lignin from them allows for the high-value utilization of this resource, enhancing both its economic and environmental value. Studies have shown that lignin extracted from corn stalks undergoes thermal decomposition within the temperature range of 130–500℃, and the cross-linking of some functional groups results in high thermal stability, making lignin potentially valuable for high-temperature applications. Therefore, extracting lignin from corn stalks not only increases the economic value of the stalks but also promotes environmental protection and sustainable agricultural development, possessing significant practical importance and broad application prospects.

[0007] Currently, the application of lignin from grasses in pesticides is not widespread. Therefore, this study, considering the chemical structure and bioactivity of lignin, as well as the sustainable supply of lignin from corn stalks, explored its application potential in the pesticide field. Developing slow-release nanopesticides based on corn stalk lignin can not only improve the environmental friendliness and efficiency of pesticides but also promote sustainable agricultural development. Summary of the Invention

[0008] To address the problems mentioned above, the present invention aims to provide a cationic surfactant with both pH and enzyme responsiveness – corn stalk lignin nanopesticide.

[0009] Specifically, this is achieved through the following technical solutions:

[0010] This invention provides a method for preparing lignin-based slow-release nanopesticides, comprising the following steps:

[0011] Weigh out lignin and hexadecyltrimethylammonium bromide, dissolve them in 0.3 mol / L tetrahydrofuran solution a, and sonicate them to fully disperse them to obtain mixture a, wherein the mass ratio of lignin to hexadecyltrimethylammonium bromide is 3:1;

[0012] The mixture a is rotary evaporated to obtain concentrated solution b. The concentrated solution b is slowly dripped into distilled water and stirred thoroughly to disperse it evenly to obtain suspension c.

[0013] The suspension c was centrifuged to remove the supernatant, and the solid precipitate was freeze-dried to obtain lignin modified with cationic surfactant.

[0014] Weigh the lignin modified with the cationic surfactant and the pesticide component, disperse them in tetrahydrofuran solution b, and sonicate them to fully disperse them to obtain a mixture d;

[0015] Distilled water is slowly added to the mixture d and stirred thoroughly to obtain suspension e;

[0016] The suspension e is centrifuged to remove the supernatant, and the solid precipitate is freeze-dried. The final product is the lignin-based slow-release nano-pesticide.

[0017] As a preferred embodiment of the present invention, the pesticide component is abamectin or abscisic acid.

[0018] As a preferred embodiment of the present invention, the mass ratio of the lignin modified by the cationic surfactant to the pesticide component is 1:1 to 3:1.

[0019] As a preferred technical solution of the present invention, the lignin is corn stalk lignin, and its preparation steps include: collecting and crushing corn stalks, placing them in a hydrothermal reactor and adding anhydrous ethanol, deionized water and acetic acid to form a mixed solution, heating to 200 ℃ and keeping warm, after the reaction is completed, filtering the mixed solution under reduced pressure to obtain a solid residue and washing it with anhydrous ethanol, removing the solid residue to obtain a concentrated solution f, adding distilled water to the concentrated solution f and stirring, centrifuging and freeze-drying to form a solid product, which is the corn stalk lignin.

[0020] As a preferred embodiment of the present invention, the heat preservation time is not less than 9 hours.

[0021] As a preferred embodiment of the present invention, the washing with anhydrous ethanol is performed no less than three times.

[0022] As a preferred technical solution of the present invention, when centrifuging the suspension c and the suspension e, the centrifugation speed is 8000 rpm.

[0023] As a preferred embodiment of the present invention, distilled water is slowly added to the concentrate b and the mixture d at a rate of 40 mL / min.

[0024] As a preferred technical solution of the present invention, the stirring conditions in the step of slowly adding distilled water to the mixture d and stirring it fully with magnetic force to obtain the suspension e are to continuously stir for 30 minutes under magnetic stirring at 450 rpm.

[0025] As a preferred embodiment of the present invention, in the freeze-drying step of the solid precipitate, the solid precipitate is washed with water at least three times before freeze-drying.

[0026] The lignin-based slow-release nanopesticides prepared by the above method can be used as slow-release pesticides for the control of crop diseases and pests. They achieve slow release of pesticides, thereby reducing problems such as pesticide degradation and leaching, and improving pesticide utilization efficiency. Simultaneously, the slow-release technology allows the pesticide to continue to work for a longer period, prolonging the control effect and reducing the number of applications. This approach achieves both the resource utilization of waste and the reduction of environmental risks, demonstrating significant application and promotion value.

[0027] By adopting the above technical solution, the beneficial effects of this invention are as follows: This invention, through an innovative technical solution, utilizes corn straw lignin, hexadecyltrimethylammonium bromide (CTAB), and abamectin (AVM) to successfully develop a novel bio-slow-release nanopesticide, AVM@L-CTAB. Hexadecyltrimethylammonium bromide (CTAB), as a cationic surfactant, can improve the yield of nanopesticides and enhance their encapsulation and loading rates. Through a self-assembly method, lignin-based nanopesticides loaded with abamectin are formed, achieving the purpose of slow-release abamectin. Simultaneously, abamectin is easily photodegraded, and lignin has excellent UV shielding effects, which can improve the utilization rate of abamectin. The prepared lignin-based slow-release nanopesticide can be used as a slow-release pesticide for the control of crop diseases and pests, achieving slow release of the pesticide, thereby reducing problems such as pesticide degradation and leaching, and improving pesticide utilization efficiency. At the same time, the slow-release technology allows the pesticide to continue to act for a longer period, prolonging the pesticide's control effect and reducing the number of applications. It achieves both the resource utilization of waste and the reduction of environmental risks, and has good application and promotion value.

[0028] Furthermore, the raw materials for this invention are widely available and inexpensive, and the materials prepared are easily degradable and environmentally friendly, thus having a significant effect on improving pesticide utilization, promoting carbon sequestration and emission reduction, and reducing environmental pollution.

[0029] The preparation method of this invention is simple, green, safe, easy to operate and control, and exhibits high stability and broad application prospects, demonstrating great development potential and market value as a pesticide. This technology not only has important reference value in the field of agricultural applications, but also opens up new avenues for the high-value-added application of lignin in the biological field. Attached Figure Description

[0030] Figure 1 This is an electron microscope image of the lignin-based slow-release nanopesticide in Example 1 of the present invention;

[0031] Figure 2 This is an electron microscope image of the lignin-based slow-release nanopesticide in Example 2 of this invention;

[0032] Figure 3 This is an electron microscope image of the lignin-based slow-release nanopesticide in Example 3 of this invention;

[0033] Figure 4 The standard curve of abamectin of the present invention and the cumulative release rate of AVM of different pesticides in Examples 1, 2, 3 and Comparative Example 1 within 180 h are shown.

[0034] Figure 5 The mortality rate of diamondback moth larvae in a one-week insecticidal activity test of Examples 1, 2, and 3 and Comparative Examples 1 and 2 of the present invention. Detailed Implementation

[0035] The technical solution of the present invention will be further described in detail below through specific embodiments. Example

[0036] A method for preparing a lignin-based slow-release nanopesticide specifically includes the following steps:

[0037] 1) Experimental method for lignin extraction: 5 g of corn stalk powder, 29.1 mL of anhydrous ethanol, 41.6 mL of deionized water, and 6.66 mL of acetic acid were added to the inner liner of a 100 mL hydrothermal reactor. The reactor was placed in a constant temperature vacuum oven at 200℃ for 9 h, then removed from the reactor and cooled to room temperature. The solid-liquid mixture was filtered and washed to separate the solid residue. The liquid was evaporated and concentrated in a vacuum rotary evaporator (50℃). The concentrated solution was slowly added dropwise to distilled water (166.6 mL) with stirring to wash the precipitated lignin. The mixture was centrifuged at 9000 rpm for 7 min, and the lower precipitate was retained. After 24 h of freeze-drying, the obtained lignin was a light brown powder, which was sealed and stored.

[0038] Tetrahydrofuran was used as an organic solvent for the large-scale preparation of AVM@L-CTAB.

[0039] 2) Synthesis of cationic surfactant-modified lignin (L-CTAB): A lignin (0.908148228 g)-tetrahydrofuran solution (20 mL) with a concentration of 0.3 mol / L (0.454074114 g / mL) was prepared; then, 0.364 g of hexadecyltrimethylammonium bromide (CTAB) was dissolved and added to the above solution, and then distilled water was slowly added to the mixture and stirred thoroughly to obtain a suspension; the concentrated solution was obtained by rotary evaporation, and then slowly added dropwise to 600 mL of distilled water and stirred magnetically to disperse it evenly to obtain a suspension; the suspension was centrifuged at 8000 rpm to remove the supernatant, and the solid precipitate was freeze-dried to prepare cationic surfactant-modified lignin (L-CTAB).

[0040] 3) Synthesis of nano-pesticides

[0041] Cationic surfactant-modified lignin (L-CTAB) and free abamectin (AVM) were dissolved in 75 mL of tetrahydrofuran at a ratio of 60 mg:60 mg (1:1) and dispersed by ultrasonication to obtain a mixture. Under magnetic stirring, 200 mL of deionized water was added uniformly to the mixture at a rate of 40 mL / min (5 min). After continuous stirring at 450 rpm for 30 min, a lignin-based slow-release nanopesticide (AVM@L-CTAB) was obtained, with the structure shown below. Figure 1 As shown. Example

[0042] The method is the same as in Example 1, except that the mass ratio of cationic surfactant-modified lignin (L-CTAB) to free abamectin (AVM) is 120 mg:60 mg (2:1), and its structure is as follows. Figure 2 As shown. Example

[0043] The method is the same as in Example 1, except that the mass ratio of cationic surfactant-modified lignin (L-CTAB) to free abamectin (AVM) is 180 mg:60 mg (3:1), and its structure is as follows. Figure 3 As shown.

[0044] To verify the beneficial effects of the above embodiments of the present invention, the following comparative examples are made and compared with the above embodiments:

[0045] Comparative Example 1 was the concentration of abamectin CK (AVM).

[0046] Comparative Example 2 is lignin

[0047] Then, the drug loading rate and encapsulation efficiency of abamectin (AVM) in Examples 1, 2, and 3 were determined.

[0048] 1. Determination of drug loading capacity (LC) (%)

[0049] Add 2 / 3 methanol solution to a 25 mL volumetric flask, and accurately weigh a certain amount of microcapsule sample (m c The abamectin was dissolved in a volumetric flask, sonicated for 2 hours, cooled, and then diluted to volume with methanol. The solution was shaken well to obtain the desired test solution. The absorbance of the solution at 245 nm was measured using a UV-2700 UV-Vis spectrophotometer, and the abamectin content was calculated (m). s ), calculate the average value of three parallel experiments.

[0050] The formula for calculating drug loading LC (%) is shown in equation (1-1):

[0051]

[0052] Where: m s This indicates the mass of the active ingredient ivermectin in the sample; m c This indicates the mass of the sample taken.

[0053] 2. Encapsulation efficiency (EE) determination

[0054] ① Determination of the maximum ultraviolet absorption wavelength of avermectin

[0055] Add 2 / 3 methanol solution to a 100 mL volumetric flask, and accurately weigh 0.0050 g of avermectin technical grade into the flask and dissolve it. Then, sonicate, cool, shake well, and dilute to volume with methanol to prepare a mother liquor. Accurately measure 3 mL of the mother liquor and add it to a 10 mL volumetric flask, and dilute to volume with methanol to obtain a 0.0150 g / L avermectin test solution. Scan the avermectin test solution in the wavelength range of 200–400 nm (according to the UV-Vis spectrophotometry method in the Appendix of the 2010 Chinese Pharmacopoeia), and determine that the maximum absorption wavelength of avermectin technical grade is 245 nm.

[0056] ② Determination of the standard curve of avermectin

[0057] A series of avermectin standard solutions with concentrations of 5.0 mg / L, 7.5 mg / L, 10.0 mg / L, 12.5 mg / L, 15.0 mg / L, 17.5 mg / L, and 20.0 mg / L were prepared. The absorbance of the solutions at a wavelength of 245 nm was then measured using a UV-2700 UV-Vis spectrophotometer, and a standard curve was plotted.

[0058] ③ Determination of encapsulation efficiency (EE) (%) of AVM@L-CTAB

[0059] Accurately weigh a certain amount of sample (m) into a 10 mL centrifuge tube. c The sample was washed with n-hexane and centrifuged (4000 rpm) three times. The precipitate obtained from the centrifuge tube was dissolved in methanol, washed several times, transferred to a 25 mL volumetric flask, and then an appropriate amount of methanol was added. The mixture was sonicated for 2 h, and after cooling, it was diluted to volume with methanol and shaken well to obtain the sample solution. The absorbance was measured at 245 nm using a UV-Vis spectrophotometer to analyze the content of the effective component (m). n The average value was calculated from three parallel experiments. The formulas for calculating the quality of avermectin in the microcapsule-encapsulated sample are shown in equation (1-2), and the formulas for calculating the encapsulation efficiency EE (%) are shown in equation (1-3).

[0060]

[0061]

[0062] Where: m n This indicates the mass of the avermectin active ingredient encapsulated inside the sample; m c This indicates the mass of the sample taken.

[0063] The drug loading rate and encapsulation efficiency of Examples 1, 2, and 3 are shown in Table 1.

[0064]

[0065] As can be seen from Table 1, Example 3, which prepared the lignin-based slow-release nanopesticide AVM@L-CTAB with a mass ratio of cationic surfactant-modified lignin (L-CTAB) and free abamectin (AVM) of 180 mg:60 mg (3:1), had the highest drug loading rate and encapsulation efficiency.

[0066] Sustained-release performance test:

[0067] The cumulative release of AVM under different environments was measured using a UV spectrophotometer:

[0068] Take 100 mg of sample into a dialysis bag (MWCO=5000 Da), add 5 mL of 60% ethanol aqueous solution, place the dialysis bag into a brown conical flask containing 45 mL of 60% ethanol aqueous solution at different pH values, and then place the brown conical flask in a shaker at 30℃. Take 1 mL of solution at specific time points and make up to 10 mL. Measure the absorbance of AVM in each sample using a UV spectrophotometer. Calculate the cumulative release rate R of AVM using the standard curve of AVM and formula (2-1) to obtain the sustained-release cumulative curve of the sample.

[0069]

[0070] Where Ci represents the AVM concentration (mg / L) at different time intervals, and m represents the sample mass.

[0071] As shown in Figure 4, this invention provides a lignin-based nanopesticide with excellent slow-release properties. Compared with the comparative example, the cumulative release rate of the lignin-based nanopesticides in the three different embodiments within the first 5 hours is similar to that of Comparative Example 1, ensuring that the active ingredient of the pesticide reaches a certain concentration in a short period of time, initially killing pests or inhibiting the growth and reproduction of pathogens. In contrast, Comparative Example 1 reaches its maximum release after 80 hours, and then the pesticide concentration drops rapidly, failing to provide sustained control for subsequent pest and disease control. Within the same time period, the cumulative release rate of the three different embodiments slows down from 5 to 60 hours, and is even slower from 60 to 180 hours. The lower cumulative release rate can maintain a certain pesticide concentration for a long time, allowing the pesticide to continuously release the active ingredient for a longer period of time, continuously controlling the pest population, reducing the development of pest resistance, and providing long-term protection.

[0072] Insecticidal activity test – leaf dipping experiment

[0073] Nanocapsule ethanol solutions and AVM ethanol solutions were directly dispersed in aqueous solutions at AVM concentrations of 5.0, 2.0, 1.0, 0.4, and 0.2 mg·L⁻¹. Fresh cabbage leaves with a diameter of 3.5 cm were soaked in the corresponding formulations for 10 minutes and then dried at room temperature. All treated leaves were transferred to petri dishes containing 10 third-instar larvae as a pest model. The petri dishes were placed in an incubator at 26°C–27°C and 60% humidity. The mortality rate of the diamondback moth was calculated after 2 days.

[0074] As shown in Figure 5, the lignin-based slow-release nanopesticide AVM@L-CTAB of the present invention exhibits significant insecticidal activity. Example 1 describes the preparation of the lignin-based slow-release nanopesticide AVM@L-CTAB using a mass ratio of cationic surfactant-modified lignin (L-CTAB) and free abamectin (AVM) of 60 mg:60 mg (1:1). Its insecticidal performance was most excellent and exhibited the strongest insecticidal activity at AVM concentrations of 5.0, 2.0, 1.0, and 0.4 mg·L⁻¹.

[0075] The above experiments demonstrate that this invention successfully prepared a nano-pesticide for agricultural production using corn straw lignin, hexadecyltrimethylammonium bromide, and abamectin. This nano-pesticide exhibits excellent slow-release properties, UV resistance, and insecticidal activity. It provides valuable insights for the application of lignin in agriculture and offers new ideas for the high-value utilization of lignin in the biological field.

[0076] The purpose, technical solution and beneficial effects of the present invention have been further described in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a lignin-based slow-release nanopesticide, characterized in that, Includes the following steps: Weigh out lignin and hexadecyltrimethylammonium bromide, dissolve them in 0.3 mol / L tetrahydrofuran solution a, and sonicate them to fully disperse them to obtain mixture a, wherein the mass ratio of lignin to hexadecyltrimethylammonium bromide is 3:1; The mixture a is rotary evaporated to obtain concentrated solution b. The concentrated solution b is slowly dripped into distilled water and stirred thoroughly to disperse it evenly to obtain suspension c. The suspension c was centrifuged to remove the supernatant, and the solid precipitate was freeze-dried to obtain lignin modified with cationic surfactant. Weigh the lignin modified with the cationic surfactant and the pesticide component, disperse them in tetrahydrofuran solution b, and sonicate them to fully disperse them to obtain a mixture d; Distilled water is slowly added to the mixture d and stirred thoroughly to obtain suspension e; The suspension e is centrifuged to remove the supernatant, and the solid precipitate is freeze-dried. The final product is the lignin-based slow-release nano-pesticide. The pesticide component is abamectin; The mass ratio of the lignin modified with the cationic surfactant to the pesticide component is 1:1 to 3:

1. The lignin is corn stalk lignin, and its preparation steps include: collecting and crushing corn stalks, placing them in a hydrothermal reactor and adding anhydrous ethanol, deionized water, and acetic acid to form a mixed solution, heating to 200 ℃ and keeping warm, after the reaction is completed, filtering the mixed solution under reduced pressure to obtain a solid residue and washing it with anhydrous ethanol, removing the solid residue to obtain a concentrated solution f, adding distilled water to the concentrated solution f and stirring, centrifuging, and freeze-drying to form a solid product, which is the corn stalk lignin.

2. The method for preparing lignin-based slow-release nanopesticides according to claim 1, characterized in that, The heat preservation time shall not be less than 9 hours.

3. The method for preparing lignin-based slow-release nanopesticides according to claim 1, characterized in that, The washing process with anhydrous ethanol shall be performed no less than three times.

4. The method for preparing lignin-based slow-release nanopesticides according to claim 1, characterized in that, When centrifuging the suspensions c and e, the centrifugation speed is 8000 rpm.

5. The method for preparing lignin-based slow-release nanopesticides according to claim 1 or 3, characterized in that, Distilled water is slowly added to the concentrate b and the mixture d at a rate of 40 mL / min.

6. The method for preparing lignin-based slow-release nanopesticides according to claim 1, characterized in that, Distilled water is slowly added to the mixture d and the mixture is stirred magnetically to obtain the suspension e. The stirring conditions in this step are continuous stirring at 450 rpm for 30 minutes.

7. The method for preparing lignin-based slow-release nanopesticides according to claim 1, characterized in that, In the freeze-drying step of the solid precipitate, the solid precipitate is washed with water at least three times before freeze-drying.

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