Preparation method of lignin-based slow-release nano pesticide

Abstract

The invention relates to the technical field of agricultural biomass pesticides, in particular to a preparation method of a lignin-based slow-release nano pesticide. According to the method, the cationic surface active agent-corn straw lignin nano pesticide with pH and enzyme double responsiveness is prepared through self-assembly. According to the material, cetyltrimethylammonium bromide (CTAB) is adopted as a cationic surface active agent to be prepared into modified lignin with corn straw, and the cationic surface active agent-corn straw lignin nano pesticide is further formed through a self-assembly method. The preparation method has the advantages of being simple in process, low in cost, environmentally friendly and the like, the obtained slow-release nano pesticide product is excellent in ultraviolet shielding performance, slow-release performance and insecticidal activity, pesticide can be accurately conveyed in a target spot mode, the possibility of pesticide residues and environmental pollution is remarkably reduced, and sustainable development of agriculture is promoted.

Description

Technical Field

[0001] The invention relates to the field of agricultural biomass pesticide preparation technology, and in particular to a method for preparing a lignin-based slow-release nano pesticide. Background Art

[0002] The creation and application of pesticides are closely related to the sustainable development of my country's agriculture. The rational use of pesticides is of great significance to agricultural production and ecological environmental protection. However, there are many types of pesticides. Most pesticide raw materials are insoluble solids with poor dispersibility. In addition, they are prone to dust drift during application, which affects the full play of the efficacy of the pesticides. They are usually difficult to apply directly. Excessive and inefficient use of pesticides has led to a series of problems, including food safety, ecological environment and human health. Therefore, it is crucial to improve the effective utilization rate of pesticides and reduce the transfer and residual pollution of pesticides in non-target organisms and the environment.

[0003] Nanoplatforms have been widely reported due to their unique physicochemical properties, flexibility in loading therapeutic biomolecules or drugs, and the ability of targeted strategies. Many materials have been developed as carriers of nanopesticides, such as silica nanoparticles, polymer systems, carbon nanotubes, and virus particles. However, the research on nanotechnology in agriculture started late and is weak, so there are still some urgent problems to be solved in the research and application of nanopesticides, such as: most of the reported nanopesticides are only in the laboratory research stage, the preparation methods are complex and diverse, the number of products is limited, and it is difficult to ensure the stability of the process and products; due to the small size and specific surface area effect, nanoparticles are prone to spontaneous agglomeration, resulting in reduced stability, and the need to select suitable adjuvants; complex and time-consuming synthesis process, uncontrolled cargo diffusion release, and environmental pollution caused by nanocarriers. Therefore, there is an urgent need for a nanoplatform that can be prepared by a simple process with minimal environmental pollution, which can extend the drug's effective period, reduce drug toxicity, and achieve green environmental protection while ensuring the pesticide's control effect on target organisms.

[0004] Lignin, as a high molecular organic substance second only to cellulose in nature, not only has rich chemical structure and biological activity, but also plays a dual role of support and protection in plants. In addition, as a rich biomass resource, lignin has a wide range of sources, low cost, and natural hydrophobicity and renewability. Developing it into a coating material for nanopesticides not only has significant social and economic value, but also has important significance for promoting sustainable agricultural development.

[0005] However, the current industrial application rate of lignin is relatively low, and a large amount of lignin is treated as waste during the production process, which not only causes a waste of resources, but also poses a potential threat to the environment. So far, lignin in the Poaceae family has rarely been used in slow-release pesticides.

[0006] Corn straw is a large byproduct of agricultural production. By extracting lignin, we can achieve high-value utilization of straw resources and improve its economic and environmental value. Studies have shown that lignin extracted from corn straw undergoes thermal decomposition reactions within 130-500°C, and some functional groups have high thermal stability after cross-linking, which makes lignin potentially valuable in high-temperature applications. It can be seen that extracting lignin from corn straw can not only improve the economic value of straw, but also promote environmental protection and sustainable development of agriculture, which has important practical significance and broad application prospects.

[0007] At present, the application of lignin in grass plants in pesticides is not widespread. Therefore, this study took into account the chemical structure and biological activity of lignin, as well as the sustainable supply of corn straw lignin, and conducted in-depth research and exploration of its application potential in the field of pesticides. By developing slow-release nanopesticides based on corn straw lignin, it is possible to improve the environmental protection and efficiency of pesticides and promote the sustainable development of agriculture. Summary of the invention

[0008] In order to solve the problems arising from the above-mentioned background technology, the object of the present invention is to provide a cationic surfactant-corn straw lignin nanopesticide with dual responsiveness to pH and enzyme.

[0009] This is achieved specifically through the following technical solutions: The present invention provides a method for preparing a lignin-based slow-release nanopesticide, comprising the following steps: Weigh lignin and cetyltrimethylammonium bromide, dissolve them in 0.3 mol / L tetrahydrofuran solution a, and fully disperse them by ultrasonication to obtain a mixed solution a, wherein the mass ratio of the lignin to the cetyltrimethylammonium bromide is 3:1; Rotary evaporation of the mixed solution a to obtain a concentrated solution b, slowly dropping the concentrated solution b into distilled water and fully stirring it to uniformly disperse it to obtain a suspension c; The suspension c is centrifuged to remove the supernatant, and the solid precipitate is freeze-dried to obtain lignin modified by a cationic surfactant; Weigh the cationic surfactant-modified lignin and the pesticide component, disperse them in tetrahydrofuran solution b, and fully disperse them by ultrasonication to obtain a mixed solution d; Slowly adding distilled water to the mixed solution d and stirring thoroughly to obtain a suspension e; The suspension e is centrifuged to remove the supernatant, and the solid precipitate is freeze-dried, and the final product is the lignin-based slow-release nanopesticide.

[0010] As a preferred technical solution of the present invention, the pesticide component is avermectin or abscisic acid.

[0011] As a preferred technical solution 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.

[0012] As a preferred technical solution of the present invention, the lignin is corn straw lignin, and its preparation steps include: collecting and crushing corn straw, placing it in a hydrothermal kettle and adding anhydrous ethanol, deionized water, and acetic acid to form a mixture solution, heating it to 200°C for insulation, and after the reaction, the mixture solution is decompressed and filtered to obtain a solid residue and washed with anhydrous ethanol, and after removing the solid residue, a concentrated solution f is obtained, and distilled water is added to the concentrated solution f and stirred, centrifuged, and freeze-dried to form a solid product, that is, the corn straw lignin.

[0013] As a preferred technical solution of the present invention, the insulation time is not less than 9 hours.

[0014] As a preferred technical solution of the present invention, the washing with anhydrous ethanol is performed no less than 3 times.

[0015] As a preferred technical solution of the present invention, when the suspension c and the suspension e are centrifuged, the centrifugal speed is 8000 rpm.

[0016] As a preferred technical solution of the present invention, the speed of slowly adding distilled water into the concentrated solution b and the mixed solution d is 40 mL / min.

[0017] As a preferred technical solution of the present invention, distilled water is slowly added to the mixed solution d and the mixture is fully stirred by magnetic force to obtain the suspension e. The stirring condition in step e is continuous stirring at 450 rpm for 30 minutes.

[0018] As a preferred technical solution of the present invention, in the step of freeze-drying the solid precipitate, the solid precipitate is washed with water at least three times before freeze-drying.

[0019] The lignin-based slow-release nanopesticide prepared by the above method can be used as a slow-release pesticide for the prevention and control of crop diseases and insect pests, and can achieve the slow release of pesticides, thereby reducing the degradation and leaching of pesticide originals and other related problems, and improving the utilization efficiency of pesticides; at the same time, the slow-release technology allows the pesticide to continue to play a role for a long time, prolonging the control effect of the pesticide and reducing the number of times the pesticide is applied. It not only realizes the resource utilization of waste, but also reduces environmental risks, and has good application and promotion value.

[0020] By adopting the above technical scheme, the beneficial effects of the present invention are as follows: the present invention successfully develops a new type of biological slow-release nanopesticide AVM@L-CTAB by using corn straw lignin, hexadecyltrimethylammonium bromide (CTAB) and avermectin (AVM) through an innovative technical scheme. Hexadecyltrimethylammonium bromide (CTAB) as a cationic surfactant can improve the yield of nanopesticides and improve their encapsulation rate and drug loading rate. By a self-assembly method, a lignin nanopesticide loaded with avermectin is formed to achieve the purpose of slow release of avermectin. At the same time, avermectin is easily photodegraded, and lignin has a good ultraviolet shielding effect, which can improve the utilization rate of avermectin. The prepared lignin-based slow-release nanopesticide can be used as a slow-release pesticide for the prevention and control of plant diseases and insect pests, and the slow release of pesticides is achieved, thereby reducing the degradation and leaching of the original pesticide and other related problems, and improving the utilization efficiency of pesticides; at the same time, the slow-release technology allows the pesticide to continue to play a role for a long time, prolonging the control effect of the pesticide and reducing the number of times of application. It not only realizes the resource utilization of waste, but also reduces environmental risks, and has good application and promotion value.

[0021] In addition, the raw materials of the invention are widely available and low in cost, and the prepared materials are easily degraded and environmentally friendly, thus having a significant effect in improving the utilization rate of pesticides, promoting carbon fixation and emission reduction, and reducing environmental pollution.

[0022] The preparation method of the present invention is simple, green and safe, easy to operate and control, and has high stability and broad application prospects, showing great development potential and market value as a pesticide. The technology not only has important reference value in the field of agricultural applications, but also opens up a new way for the high value-added application of lignin in the biological field. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is an electron microscope photograph of the lignin-based slow-release nanopesticide in Example 1 of the present invention; Figure 2 This is an electron microscope photo of the lignin-based slow-release nanopesticide in Example 2 of the present invention; Figure 3 This is an electron microscope photo of the lignin-based slow-release nanopesticide in Example 3 of the present invention; Figure 4 It is the standard curve of avermectin 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 hours.

[0024] Figure 5 It is the mortality rate of Plutella xylostella larvae in the one-week insecticidal activity test of Examples 1, 2, 3 of the present invention and Comparative Examples 1 and 2. DETAILED DESCRIPTION

[0025] The technical solution of the present invention is further described in detail below through specific embodiments. Example

[0026] A method for preparing a lignin-based slow-release nanopesticide comprises the following steps: 1) Experimental method for lignin extraction: 5 g corn straw powder, 29.1 mL anhydrous ethanol, 41.6 mL deionized water and 6.66 mL acetic acid were added to the inner tank of a 100 mL hydrothermal reactor, and the reactor was placed in a constant temperature vacuum oven at 200°C for 9 h, then taken out of the reactor and cooled to room temperature. The solid-liquid mixture was filtered and washed to separate the solid residue, and the liquid was evaporated and concentrated in a vacuum rotary evaporator (50°C). The concentrated solution was slowly dripped into distilled water (166.6 mL) under stirring to wash and precipitate lignin. After the mixture was centrifuged in a high-speed centrifuge (9000 rpm) for 7 min, the lower precipitate was retained. After 24 h of freezing and drying, the obtained lignin was light brown powder and sealed for storage.

[0027] Tetrahydrofuran was used as the organic solvent for the large-scale preparation of AVM@L-CTAB.

[0028] 2) Synthesis of cationic surfactant modified lignin (L-CTAB): A 0.3 mol / L (0.454074114 g / mL) lignin (0.908148228 g)-tetrahydrofuran solution (20 mL) was prepared; subsequently, 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; rotary evaporation was performed to obtain a concentrated solution, which was slowly dripped into 600 mL of distilled water and stirred magnetically to be uniformly dispersed to obtain a suspension; the suspension was centrifuged at a speed of 8000 rmp to remove the supernatant, and the solid precipitate was freeze-dried to prepare a cationic surfactant modified lignin (L-CTAB).

[0029] 3) Nanopesticide synthesis Cationic surfactant modified lignin (L-CTAB) and free avermectin (AVM) were dissolved in 75 mL of tetrahydrofuran at a ratio of 60 mg:60 mg (1:1), and ultrasonically dispersed to obtain a mixed solution; under magnetic stirring, 200 mL of deionized water was uniformly added to the mixture at 40 mL / min (5 min). After continuous stirring at 450 rpm for 30 minutes, a lignin-based slow-release nanopesticide (AVM@L-CTAB) was obtained, and its structure is as follows Figure 1 shown. Example

[0030] The method is the same as that of Example 1, except that the mass ratio of cationic surfactant modified lignin (L-CTAB) to free avermectin (AVM) is 120 mg:60 mg (2:1), and its structure is as follows: Figure 2 shown. Example

[0031] The method is the same as that of Example 1, except that the mass ratio of cationic surfactant modified lignin (L-CTAB) to free avermectin (AVM) is 180 mg:60 mg (3:1), and its structure is as follows: Figure 3 shown.

[0032] In order to verify the beneficial effects of the above embodiments of the present invention, the following comparative examples are compared with the above embodiments, and the comparative examples are: Comparative Example 1 is the concentration of Avermectin CK (AVM) Comparative Example 2 is lignin Then the drug loading rate and encapsulation rate of AVM in Examples 1, 2 and 3 were determined. 1. Drug loading LC (%) determination Add 2 / 3 of methanol solution into a 25 mL volumetric flask and accurately weigh a certain amount of microcapsule sample (m c ) was placed in a volumetric flask and dissolved, ultrasonically broken for 2 h, and after cooling, methanol was added to the volume and shaken to obtain the required test solution. The absorbance of the solution at a wavelength of 245 nm was measured using a UV-2700 ultraviolet-visible spectrophotometer to calculate the content of avermectin (m s ), and the average value was calculated from three parallel experiments.

[0033] The calculation formula of drug loading LC (%) is shown in formula (1-1):

[0034] Where: m s Indicates the mass of the active ingredient of avermectin in the sample; m c Indicates the mass of the sample weighed.

[0035] 2. Determination of encapsulation efficiency EE (%) ① Determination of the maximum ultraviolet absorption wavelength of avermectin Add 2 / 3 of methanol solution to a 100 mL volumetric flask, accurately weigh 0.0050 g of avermectin technical drug using an analytical balance and dissolve it in the volumetric flask. Then ultrasonicate the solution, cool it, shake it evenly, and dilute it with methanol to prepare a mother solution. Accurately measure 3 mL of the mother solution and add it to a 10 mL volumetric flask, dilute it 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-visible spectrophotometry in the appendix of the 2010 edition of the Chinese Pharmacopoeia), and determine that the maximum absorption wavelength of avermectin technical drug is 245 nm.

[0036] ② Determination of avermectin standard curve 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, and the absorbance of the solutions at a wavelength of 245 nm was measured using a UV-2700 ultraviolet-visible spectrophotometer to draw a standard curve.

[0037] ③ Determination of encapsulation efficiency EE (%) of AVM@L-CTAB In a 10 mL centrifuge tube, accurately weigh a certain amount of sample (m c ), washed with n-hexane and centrifuged (4000 rpm) 3 times. The precipitate obtained in the centrifuge tube was dissolved in methanol, washed several times and transferred to a 25 mL volumetric flask, and then an appropriate amount of methanol was added, ultrasonically broken for 2 h, and after the solution was cooled, it was fixed to volume with methanol and shaken to obtain the sample solution. The absorbance was measured at a wavelength of 245 nm using a UV-visible spectrophotometer to analyze the active ingredient content (m n ), and the average value was calculated by three parallel experiments. The calculation formula of the quality of Avermectin encapsulated in the microcapsule sample is shown in formula (1-2) and the calculation formula of the encapsulation efficiency EE (%) is shown in formula (1-3):

[0038]

[0039] Where: m n Indicates the mass of the active ingredient of avermectin encapsulated in the sample; m c Indicates the mass of the sample weighed.

[0040] The drug loading rate and encapsulation efficiency of Examples 1, 2 and 3 were measured and shown in Table 1.

[0041]

[0042] As can be seen from Table 1, in Example 3, when the mass ratio of cationic surfactant modified lignin (L-CTAB) and free avermectin (AVM) was 180 mg:60 mg (3:1), the lignin-based sustained-release nanopesticide AVM@L-CTAB was prepared, and its drug loading rate and encapsulation efficiency were the highest.

[0043] Sustained release performance test: Use UV spectrophotometer to test the cumulative release of AVM in different environments: Take 100 mg of sample and put it in a dialysis bag (MWCO=5 000 Da), inject 5 mL of 60% ethanol aqueous solution, put the dialysis bag into a brown conical flask containing 45 mL of 60% ethanol aqueous solution with different pH values, then put the brown conical flask in a shaker at 30°C for shaking, and draw 1 mL of solution at specific time and make the volume 10 mL. The absorbance of AVM in each sample was measured by ultraviolet spectrophotometer, and the cumulative release rate R of AVM was calculated by the standard curve of AVM and formula (2-1) to obtain the sustained release cumulative curve of the sample.

[0044]

[0045] Where Ci represents the AVM concentration (mg / L) at different time intervals, and m represents the mass of the sample.

[0046] As can be seen from Figure 4, the present invention provides a lignin-based nanopesticide with excellent slow-release performance. Compared with the comparative example, the cumulative release rate of the lignin-based nanopesticides in the first 5 hours of the three different embodiments is similar to that of comparative example 1, ensuring that the active ingredients of the pesticide reach a certain concentration in a relatively short time, preliminarily killing pests or inhibiting the growth and reproduction of pathogens. However, comparative example 1 reaches the maximum release after 80 hours, and then the concentration of the agent drops rapidly, and it cannot play a continuous control role in the subsequent pest control; in the same time period, the cumulative release rate of the three different embodiments slows down in 5~60 hours, and is slower than before in 60~180 hours. The lower cumulative release rate can maintain a certain concentration of the agent for a long time, so that the pesticide can continuously release the active ingredient for a long time, which can continuously control the number of pest populations, reduce the generation of pest resistance, and play a long-term protective role.

[0047] Insecticidal activity test - leaf dip test Nanocapsule ethanol solution and AVM ethanol solution were directly dispersed in aqueous solution, and the AVM concentrations were 5.0, 2.0, 1.0, 0.4 and 0.2 mg·L-1, respectively. 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 a petri dish containing 10 third-instar larvae as a pest model. The petri dish was placed in an incubator at 26°C-27°C and 60% humidity. The mortality of Plutella xylostella was calculated after 2 days.

[0048] As can be seen from Figure 5, the lignin-based slow-release nanopesticide AVM@L-CTAB of the present invention has significant insecticidal activity. Example 1 When the mass ratio of cationic surfactant-modified lignin (L-CTAB) and free avermectin (AVM) is 60 mg:60 mg (1:1), the lignin-based slow-release nanopesticide AVM@L-CTAB is prepared, and its insecticidal performance is the best when the AVM concentration is 5.0, 2.0, 1.0, and 0.4 mg·L-1, respectively, and the insecticidal activity is the strongest.

[0049] Through the above experiments: It is shown that the present invention uses corn straw lignin, hexadecyltrimethylammonium bromide and avermectin to successfully prepare nanopesticides for agricultural production, which have excellent slow-release performance, UV resistance and insecticidal activity. It has reference value for the application of lignin in the agricultural field and also provides new ideas for the high value-added utilization of lignin in the biological field.

[0050] The objectives, technical solutions and beneficial effects of the present invention are further described in detail. It should be understood that the above are only specific implementation methods 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 in the scope of protection of the present invention.

Claims

1. A method for preparing a lignin-based slow-release nanopesticide, characterized in that: The steps include: Weigh lignin and cetyltrimethylammonium bromide, dissolve them in 0.3 mol / L tetrahydrofuran solution a, and fully disperse them by ultrasonication to obtain a mixed solution a, wherein the mass ratio of the lignin to the cetyltrimethylammonium bromide is 3:1; Rotary evaporation of the mixed solution a to obtain a concentrated solution b, slowly dropping the concentrated solution b into distilled water and fully stirring it to uniformly disperse it to obtain a suspension c; The suspension c is centrifuged to remove the supernatant, and the solid precipitate is freeze-dried to obtain lignin modified by a cationic surfactant; Weigh the cationic surfactant-modified lignin and the pesticide component, disperse them in tetrahydrofuran solution b, and fully disperse them by ultrasonication to obtain a mixed solution d; Slowly adding distilled water to the mixed solution d and stirring thoroughly to obtain a suspension e; The suspension e is centrifuged to remove the supernatant, and the solid precipitate is freeze-dried, and the final product is the lignin-based slow-release nanopesticide.

2. The method for preparing the lignin-based slow-release nanopesticide according to claim 1, characterized in that: The pesticide component is avermectin or abscisic acid.

3. The method for preparing the lignin-based slow-release nanopesticide according to claim 1, characterized in that: The mass ratio of the lignin modified by the cationic surfactant to the pesticide component is 1:1 to 3:

1.

4. The method for preparing the lignin-based slow-release nanopesticide according to claim 1, characterized in that: The lignin is corn straw lignin, and its preparation steps include: collecting and crushing corn straw, placing it in a hydrothermal kettle and adding anhydrous ethanol, deionized water and acetic acid to form a mixture solution, heating it to 200°C for heat preservation, after the reaction, vacuum filtering the mixture solution 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, stirring, centrifuging, and freeze-drying to form a solid product, that is, the corn straw lignin.

5. The method for preparing the lignin-based slow-release nanopesticide according to claim 4, characterized in that: The insulation time is not less than 9 h.

6. The method for preparing the lignin-based slow-release nanopesticide according to claim 4, characterized in that: The washing with anhydrous ethanol is performed no less than 3 times.

7. The method for preparing the lignin-based slow-release nanopesticide according to claim 1, characterized in that: When the suspension c and the suspension e are centrifuged, the centrifugal speed is 8000 rpm.

8. The method for preparing the lignin-based slow-release nanopesticide according to claim 2 or 6, characterized in that: Distilled water was slowly added to the concentrated solution b and the mixed solution d at a rate of 40 mL / min.

9. The method for preparing the lignin-based slow-release nanopesticide according to claim 2, characterized in that: Distilled water was slowly added to the mixed solution d and the mixture was fully stirred by magnetic force to obtain the suspension e. The stirring condition in step e was continuous stirring at 450 rpm for 30 minutes.

10. The method for preparing the lignin-based slow-release nanopesticide according to claim 2, characterized in that: In the step of freeze-drying the solid precipitate, the solid precipitate is washed with water at least three times before freeze-drying.

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