Full-biomass-based abamectin sustained and controlled release pesticide preparation and preparation method thereof

Abstract

The invention belongs to the technical field of environment-friendly pesticide preparations, and discloses a full-biomass-based abamectin controlled release agent and a preparation method thereof. The preparation method comprises the following steps: firstly, loading abamectin on biochar, and then alternately depositing chitosan and sodium lignin sulfonate with opposite charges on the surface of the biochar through a layer-by-layer self-assembly technology to form a stable coating layer; the coating layer can effectively coat abamectin and reduce the specific surface area and pore volume of the carrier, so that the release rate is delayed. By regulating and controlling the number of deposition layers, customization and precise regulation and control of the abamectin release rate can be achieved, meanwhile, the light degradation rate of the abamectin is remarkably reduced, and the pesticide utilization rate is increased. The raw materials are green and degradable, the preparation process is simple, the condition is mild, the release performance is controllable, and a sustainable technical scheme is provided for green and precise application of pesticides.

Description

Technical Field

[0001] This invention belongs to the field of slow-release pesticides, specifically relating to a whole biomass-based avermectin slow-release pesticide formulation and its preparation method. Background Technology

[0002] The steady increase in grain production is the core foundation for ensuring global food security. Pesticides, as a key means of controlling crop pests and diseases, play an irreplaceable role in ensuring stable and increased grain production and reducing post-harvest losses. However, in actual production, soil-borne diseases pose a serious threat to crop yield and quality. Effective control of these diseases often requires the application of large quantities of pesticides, which not only leads to low pesticide utilization rates but also easily causes environmental problems such as soil pollution and pesticide residues. To address this pain point, controlled-release pesticide formulations have been gradually developed in recent years, providing an important technological path to improve pesticide utilization, reduce environmental risks, and achieve precise pesticide application.

[0003] In the development of controlled-release pesticide formulations, the selection of carrier materials is crucial in determining the formulation's performance, directly impacting pesticide loading efficiency, release rate, and environmental compatibility. Biomass-based materials, derived from natural plants and animals, possess excellent biodegradability, biocompatibility, soil compatibility, and low environmental toxicity, eliminating concerns about secondary pollution. Therefore, they exhibit enormous application potential in controlled-release formulations and have become a current research hotspot. Specifically, biochar, as a carbon material prepared from biomass pyrolysis, not only boasts advantages such as wide availability of raw materials, simple and stable preparation processes, low production costs, and environmental friendliness, but also, due to its high specific surface area, well-developed pore structure, and abundant oxygen-containing functional groups, can efficiently load pesticides, making it an ideal core material for pesticide carriers. Lignin, as a natural biomass component, possesses UV resistance, antioxidant, and antibacterial properties, effectively protecting sensitive pesticides from environmental damage. It is an excellent pesticide encapsulation material and is widely used in pesticide encapsulation systems. Furthermore, lignin typically carries a negative charge, allowing for flexible control of the coating thickness through electrostatic interactions with positively charged materials, providing a structural basis for achieving controlled-release pesticides. Complementing this, chitosan, one of the few natural cationic polysaccharides, combines the advantages of being non-toxic, antibacterial, biodegradable, sustainable, and economical. Its own UV absorption capacity further enhances the photostability of pesticides, making it suitable as a protective coating for sensitive pesticides, forming a complementary and compatible encapsulation system with lignin.

[0004] However, abamectin, a commonly used and effective pesticide for soil-borne diseases, has obvious performance defects: it has poor chemical stability, is easily degraded under ultraviolet irradiation, and is easily leached away by rainwater, resulting in a short field duration of effectiveness and low pesticide utilization, which makes it difficult to meet the needs of green prevention and control and precision application.

[0005] Considering the outstanding advantages of biomass-based carriers and the shortcomings of existing avermectin formulations, developing an avermectin sustained-release formulation with controllable release rate and high photostability has become a key technical problem that urgently needs to be solved. Summary of the Invention

[0006] This invention provides a biomass-based avermectin controlled-release pesticide formulation and its preparation method, aiming to solve the technical problems of high carrier cost, easy secondary pollution, difficulty in accurately controlling avermectin release rate, poor photostability, and low utilization rate in existing controlled-release pesticide formulations, and to achieve controllable controlled release and green and efficient application of avermectin.

[0007] The objective of this invention can be achieved through the following technical solutions: This invention provides a method for preparing a fully biomass-based abamectin sustained-release pesticide formulation, comprising the following steps: (1) Chitosan was added to a formic acid solution with a volume concentration of 0.5%~1.5%, and sodium lignosulfonate was added to deionized water. The solutions were then subjected to ultrasonic treatment until completely dissolved to obtain chitosan solution and sodium lignosulfonate solution with a concentration of 2~6 mg / mL. (2) Add biochar to water and disperse it evenly by ultrasonication to obtain a biochar suspension with a concentration of 0.3g~0.6g / 100mL; add 10~20mg / mL avermectin methanol solution to the biochar suspension according to the mass ratio of avermectin to biochar of 1~2:3, then adjust the pH value to 2~4 with 2mol / L sulfuric acid solution, centrifuge, discard the supernatant to remove unloaded avermectin, collect the precipitate, and obtain avermectin-loaded biochar; (3) Disperse the biochar loaded with abamectin in the chitosan solution and stir at a speed of 400-600 rpm for 1-3 hours; centrifuge, discard the supernatant to remove unadsorbed chitosan, collect the precipitate, and obtain chitosan-coated biochar. (4) Disperse the chitosan-coated biochar in the sodium lignosulfonate solution and stir at a speed of 400-600 rpm for 1-3 hours; centrifuge, discard the supernatant to remove unadsorbed sodium lignosulfonate, collect the precipitate, and complete the single deposition of chitosan and sodium lignosulfonate. (5) Repeat steps (3) to (4) to adjust the number of deposition layers, and finally vacuum dry to obtain the whole biomass-based abamectin slow-release pesticide formulation.

[0008] As a preferred embodiment, in steps (2) to (4), the centrifugation speed is 7000-9000 rpm and the centrifugation time is 1-3 minutes.

[0009] Compared with the prior art, the beneficial effects of the present invention are reflected in: 1. This invention first loads abamectin onto biochar, and then uses a layer-by-layer self-assembly technique to deposit heteroelectrochemical chitosan and sodium lignin sulfonate on the surface of the biochar to form a coating layer. This coating layer can effectively encapsulate abamectin while significantly reducing the specific surface area and pore volume of the biochar, thereby effectively slowing down the release rate of abamectin. In addition, the synergistic effect of chitosan and lignin can significantly reduce the photodegradation rate of abamectin, greatly prolong its field retention period, thereby improving the utilization rate of abamectin, reducing pesticide application, and reducing pesticide residues and pollution in the soil and environment.

[0010] 2. This invention can precisely control the thickness of the coating layer by flexibly adjusting the deposition times of chitosan and sodium lignin sulfonate, thereby achieving predictable and controllable release rate of abamectin, and adapting to the control needs of different crops and different soil-borne diseases.

[0011] 3. The reaction conditions of this invention are mild, the preparation steps are simple, the requirements for instruments and equipment are low, the operation is convenient, and it is easy to prepare in large quantities and industrial production. At the same time, the carriers used (biochar, chitosan, sodium lignosulfonate) are all derived from biomass, which are safe, non-toxic, and naturally degradable. They are not only inexpensive, but also avoid secondary pollution caused by carrier residues, thus taking into account both economic efficiency and environmental compatibility.

[0012] 4. This invention combines biomass carriers with layer-by-layer self-assembly technology to construct a fully biomass-based controlled-release system. This not only solves the problems of poor environmental performance, high cost, and uncontrollable release of existing controlled-release formulation carriers, but also overcomes the industry challenges of easy photodegradation and low utilization rate of abamectin. It provides a reliable and sustainable technical solution for precise pesticide release and green pest control, and has important practical application value for promoting technological progress in the field of controlled-release pesticides, ensuring food security, and protecting the ecological environment. Attached Figure Description

[0013] Figure 1 This is a SEM image of the controlled-release pesticide formulation prepared in Example 4 of the present invention; Figure 2 This is a TEM image of the controlled-release pesticide formulation prepared in Example 4 of the present invention; Figure 3 The encapsulation efficiency of the controlled-release pesticide formulations prepared in Examples 1-4 of this invention; Figure 4 The controlled release curves of the sustained-release pesticide formulations prepared in Examples 1-4 of this invention are shown. Figure 5 The photodegradation curves of the controlled-release pesticide formulations prepared in Examples 1-4 of this invention are shown. Detailed Implementation

[0014] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below.

[0015] Example 1: Preparation of a monolayer biomass-based abamectin sustained-release pesticide formulation (1) Chitosan was added to 1% formic acid solution and sodium lignosulfonate was added to deionized water. The mixture was sonicated until completely dissolved to obtain chitosan solution and sodium lignosulfonate solution with a concentration of 4 mg / mL. (2) Add 0.3g of biochar to 50mL of water and sonicate for 30 minutes to disperse evenly to obtain a biochar suspension; add 10mL of 10mg / mL avermectin methanol solution to the suspension and adjust the pH to about 3 with 2mol / L sulfuric acid solution; centrifuge at 8000rpm for 2 minutes, discard the supernatant to remove unloaded avermectin, collect the precipitate, and obtain avermectin-loaded biochar; (3) Disperse the biochar loaded with abamectin in 50 mL of chitosan solution and stir at 500 rpm for 2 hours; centrifuge at 8000 rpm for 2 minutes, discard the supernatant to remove unadsorbed chitosan, collect the precipitate, and obtain chitosan-coated biochar. (4) Disperse the chitosan-coated biochar in 50 mL of sodium lignosulfonate solution and stir at 500 rpm for 2 hours; centrifuge at 8000 rpm for 2 minutes, discard the supernatant to remove unadsorbed sodium lignosulfonate, collect the precipitate, and complete one deposition. (5) The mixture was dried under vacuum at 60°C for 12 hours without repeated cycles to obtain a monolayer biomass-based avermectin slow-release pesticide formulation.

[0016] Example 2: Preparation of a three-layer biomass-based abamectin sustained-release pesticide formulation (1) Same as step (1) in Example 1; (2) Same as step (2) in Example 1; (3) Same as step (3) in Example 1; (4) Same as step (4) in Example 1; (5) Repeat steps (3) to (4) twice more to complete a total of three depositions. Vacuum dry to obtain a three-layer biomass-based avermectin slow-release pesticide formulation.

[0017] Example 3: Preparation of a five-layer biomass-based abamectin sustained-release pesticide formulation (1) Same as step (1) in Example 1; (2) Same as step (2) in Example 1; (3) Same as step (3) in Example 1; (4) Same as step (4) in Example 1; (5) Repeat steps (3) to (4) 4 times to complete a total of 5 depositions. Vacuum dry to obtain a five-layer biomass-based avermectin slow-release pesticide formulation.

[0018] Example 4: Preparation of a seven-layer biomass-based abamectin sustained-release pesticide formulation (1) Same as step (1) in Example 1; (2) Same as step (2) in Example 1; (3) Same as step (3) in Example 1; (4) Same as step (4) in Example 1; (5) Repeat steps (3) to (4) 6 times to complete a total of 7 depositions. Vacuum dry to obtain a seven-layer biomass-based avermectin slow-release pesticide formulation.

[0019] The biomass-based abamectin controlled-release pesticide formulations prepared in Examples 1-4 were used as samples to systematically characterize their performance. The specific test methods and results are as follows: 1. Morphological determination Take an appropriate amount of the controlled-release pesticide formulation sample prepared in Example 4, adhere it to conductive adhesive, and observe its surface morphology using a scanning electron microscope (SEM). Figure 1 As shown, the surface of the controlled-release pesticide formulation is uniformly covered with a large number of tiny particles composed of chitosan and sodium lignosulfonate, indicating that the coating layer has been successfully deposited on the surface of biochar.

[0020] Take an appropriate amount of the sample prepared in Example 4, dilute it, and drop it onto an ultrathin carbon film copper grid. Observe its internal structure using a transmission electron microscope (TEM). Figure 2 As shown, approximately seven layers of coating structure can be clearly observed in the edge region of the controlled-release pesticide formulation, which perfectly matches the seven-deposition process set in Example 4, verifying the reliability and stability of the layer-by-layer self-assembly preparation method of the present invention.

[0021] 2. Encapsulation ratio calculation Accurately weigh 10 mg of the controlled-release pesticide formulation sample and dissolve it in 2 mL of methanol solution. Sonicate the solution for 30 minutes to fully extract the abamectin loaded onto the sample. Filter the extract through a 0.22 μm organic filter membrane and determine the concentration of abamectin in the filtrate using a UV spectrophotometer. Calculate the encapsulation efficiency using the following formula: Encapsulation efficiency = (Mass of loaded abamectin / Total mass of added abamectin) × 100% like Figure 3As shown, calculations revealed that the encapsulation efficiencies of the controlled-release pesticide formulations prepared in Examples 1, 2, 3, and 4 were 49.25%, 47.04%, 47.23%, and 48.58%, respectively, remaining consistently within the range of 47% to 50%. These results indicate that altering the deposition frequency of chitosan and sodium lignin sulfonate does not significantly affect the loading effect of abamectin, further demonstrating the stability of the preparation process of this invention.

[0022] 3. Determination of sustained-release performance Accurately weigh 50 mg of the controlled-release pesticide formulation sample and place it in a dialysis bag. Add 2 mL of ethanol-water solution (ethanol:water = 2:8, volume ratio) to the bag. Immerse the dialysis bag in a container containing 98 mL of the same ethanol-water solution and place it in a shaking incubator at 30°C and 200 rpm. At set time intervals, take 2 mL of the external solution each time and detect the concentration of abamectin using a UV spectrophotometer. Then, add 2 mL of fresh ethanol-water solution to maintain the total volume of the system at 100 mL.

[0023] like Figure 4 As shown, the release rate of pure abamectin was relatively fast, and it was almost completely released within 72 hours. Only the sample loaded on biochar showed a reduced release rate. The release rate of the controlled-release pesticide formulations prepared in Examples 1-4 gradually slowed down with the increase of the number of coating layers. Among them, the abamectin release rate of the sample in Example 4 (7-layer deposition) was only about 31% after 72 hours. The above results indicate that by controlling the number of deposition layers of chitosan and sodium lignin sulfonate, the release rate of abamectin can be effectively controlled, and precise controlled-release of abamectin can be achieved.

[0024] 4. Light stability measurement Take the controlled-release pesticide formulation powders prepared in Examples 1-4 respectively, dissolve them in 50 mL of deionized water, and stir thoroughly to disperse them evenly. Take 1 mL of the dispersion and place it in a petri dish, then let it air dry in the dark. Place the dried petri dish at a distance of about 30 cm from a UV lamp for irradiation. Remove the petri dish at set time intervals, and use 2 mL of methanol to ultrasonically extract the residual avermectin in the petri dish. After filtering the extract through a 0.22 μm organic filter membrane, use a UV spectrophotometer to detect the content of residual avermectin and analyze its photodegradation.

[0025] like Figure 5As shown, pure avermectin exhibits a degradation rate of approximately 90% after 10 hours of UV irradiation, demonstrating extremely poor photostability. Only the sample loaded on biochar showed a decrease in degradation rate. In contrast, the sustained-release formulation prepared in this invention significantly reduces the photodegradation rate of avermectin, with the degradation rate gradually decreasing as the number of coating layers increases. Specifically, the sample in Example 4 (7-layer deposition) showed an avermectin degradation rate of only about 13% after 10 hours of UV irradiation, exhibiting excellent photostability and effectively solving the technical challenges of avermectin's easy photodegradation and short duration of action.

[0026] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements 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 biomass-based avermectin sustained-release pesticide formulation, characterized in that, Includes the following steps: (1) Chitosan was added to formic acid solution and sodium lignosulfonate was added to deionized water. The mixture was then sonicated until completely dissolved to obtain chitosan solution and sodium lignosulfonate solution. (2) Add biochar to water and disperse it evenly by ultrasonication to obtain a biochar suspension; Add avermectin methanol solution to the biochar suspension, adjust the pH to 2-4 with sulfuric acid solution, centrifuge, discard the supernatant to remove unloaded avermectin, collect the precipitate, and obtain avermectin-loaded biochar. (3) Disperse the avermectin-loaded biochar in the chitosan solution and stir; centrifuge, discard the supernatant to remove unadsorbed chitosan, collect the precipitate, and obtain chitosan-coated biochar. (4) Disperse the chitosan-coated biochar in the sodium lignosulfonate solution and stir; centrifuge, discard the supernatant to remove unadsorbed sodium lignosulfonate, collect the precipitate, and complete the single deposition of chitosan and sodium lignosulfonate. (5) Repeat steps (3) to (4) to adjust the number of deposition layers, and finally vacuum dry to obtain the whole biomass-based abamectin slow-release pesticide formulation.

2. The preparation method according to claim 1, characterized in that, In step (1), the concentrations of the chitosan solution and the sodium lignosulfonate solution are both 2~6 mg / mL.

3. The preparation method according to claim 1, characterized in that, In step (1), the volume concentration of the formic acid solution is 0.5% to 1.5%.

4. The preparation method according to claim 1, characterized in that, In step (2), the concentration of the biochar suspension is 0.3g~0.6g / 100mL, the concentration of the avermectin methanol solution is 10~20mg / mL, and the mass ratio of avermectin to biochar is 1~2:

3.

5. The preparation method according to claim 1, characterized in that, In step (2), the concentration of the sulfuric acid solution is 2 mol / L.

6. The preparation method according to claim 1, characterized in that, In steps (2) to (4), the centrifugation speed is 7000-9000 rpm and the centrifugation time is 1-3 minutes.

7. The preparation method according to claim 1, characterized in that, In step (3), the stirring time is 1 to 3 hours and the stirring speed is 400 to 600 rpm.

8. The preparation method according to claim 1, characterized in that, In step (4), the stirring time is 1 to 3 hours and the stirring speed is 400 to 600 rpm.

9. A fully biomass-based avermectin sustained-release pesticide formulation prepared by the preparation method according to any one of claims 1 to 8.

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