Research On The Design And Application Of Multifunctional Controlled-Release System Of Pesticide And Its Release Performance

Pesticides are an important material basis for ensuring food security and world peace and stability.Humankind's rigid demand for pesticides will exist for a long time.However,the current problems of large amounts of pesticides dosage and low utilization rate still exist objectively,leading to a series of problems such as waste of resources and environmental pollution.In order to realize the sustainable development of agriculture,the Chinese government has put forward the strategic requirement of"reducing pesticides application with increasing efficiency".In 2021,the No.1 document of the central government again emphasizes the green development of agriculture,and continued to promote the reduction of fertilizers and pesticides to increase efficiency.The use of functional material modification and loading technology to construct controlled-release formulations of pesticides for efficient target deposition and controlled release of active ingredient,showing a good application prospect in promoting pesticide dose reduction and efficiency enhancement.Based on the problem that large amounts of pesticides were used due to the mismatch of dosage between pesticide applied and actual dosage requirements for pest prevention and control,multifunctional controlled-release delivery systems(CRDS)of pesticides were designed and developed in this research.The high biocompatibility,cheap and easy-to-obtained polymer materials were selected as pesticide carriers.The pesticide loading method was innovated,and the preparation process of the multifunctional CRDS was optimized.Moreover,the release characteristics and biological activity were carried out.It is expected to provide theoretical guidance and technical support for the development of new pesticide formulations and strategy of reducing pesticides application with increasing efficiency.In this thesis,inorganic mesoporous silica and organic polymer polysaccharides were selected as carriers to develop multifunctional CRDS of pesticides,and the specific research results are as follows:(1)Design and performance study of multifunctional controlled-release delivery systems of pesticides based on mesoporous silica nanoparticles and surface modification:a)The carbon quantum dots-modified mesoporous silica nanoparticles(FL-MSN)were prepared and loaded with prothioconazole(Pro@FL-MSN).Pro@FL-MSN showed a slow and sustained-release pattern.The fluorescence of the nanoparticles imparted by the carbon quantum dots was helpful for the visual observation of pesticide-loaded nanoparticles in the plant and mycelium.This pesticide-loaded system shows potential application prospects for exploring the distribution and transmission of pesticides in crops;b)A novel strategy of emulsion-based synchronous azoxystrobin encapsulation and surface modification of MSN with CMCS was developed(AZOX@MSN-CMCS).Compared to the loading of AZOX into pre-modified MSN-CMCS with sharply decreased specific surface area and pore volume,this novel developed strategy can significantly increase the loading content about 6 times than the traditional loading content after pre-modification.The release of AZOX from CMCS-modified MSN was p H-sensitive.AZOX released slower in acidic solutions compared to that in basic and neutral media.The cumulative release amount reached 45%in a weakly acidic environment within 48 h,while 66%of AZOX released from the AZOX@MSN-CMCS in a neutral and alkaline conditions.The release mechanism is in accordance with the Korsmeyer-Peppas model.The carrier material has a certain antibacterial effect,so AZOX@MSN-CMCS exhibited better fungicidal activity against tomato late blight than AZOX technical under the same doses of active ingredient applied.The introduction of functional materials could increase the biological activity of the AZOX@MSN-CMCS about 17%,and nanoparticles can be transmitted in mycelium and plants;c)Copper ions chelated mesoporous silica nanoparticles(MSN)via dopamine chemistry(AZOX@MSN-PDA-Cu)for controlled azoxystrobin(AZOX)release have been developed.Metal copper ions with bactericidal activity can act as a"bridge"between pesticide molecules and carriers to regulate the release of pesticide molecules through metal coordination bonds.The release mechanism of the AZOX@MSN-PDA-Cu is the Korsmeyer-Peppas model,and the sustained-release performance is better after metal coordination.The accumulative release of AZOX within 24 h is 59.8%,45.5%,and56.1%,respectively.The carrier MSN-PDA-Cu not only have synergistic bactericidal activity,but also could improve the deposition of AZOX@MSN-PDA-Cu nanoparticles on target crops.(2)Design and performance study of multifunctional controlled-release delivery systems of pesticides based on natural polysaccharide chitosan:a)Chitosan copolymer(CS-g-PDMAEMA)was facilely prepared through free radical graft copolymerization with 2-(dimethylamino)ethyl 2-methacrylate(DMAEMA)as the vinyl monomer.An emulsion-based chemical cross-linking method was used to expediently fabricate pyraclostrobin microcapsules in situ entrapping the pesticide.The p H and temperature sensitive characteristics of the carrier material endow the microcapsules with environmental responsive release characteristics.The release of pyraclostrobin decreased with increasing p H and increased with increasing temperature.Microcapsulation could dramatically improve its photostability under ultraviolet light irradiation and reduce acute toxicity to non-target organism of zebrafish.b)Manganese-based carboxymethyl chitosan hydrogels were facilely prepared to encapsulate and release fungicide prothioconazole in a controllable manner.Prothioconazole was used as a model pesticide to verify the specificity of the metal ions selected when different pesticides were loaded.The optimal preparation conditions were screened out through single factor and orthogonal experiments as follows:the mass fraction of CMCS is 4%;the oil/water volume ratio is 1:10;the mass fraction of Tween-80 is 2.0%;the concentration of Mn²⁺is 0.2 M.The loading content and encapsulation efficiency are 22.17%±0.83%and 68.38%±2.56%respectively.The hydrogel granules showed p H-triggered release behavior of prothioconazole which was consistent with swelling behavior.The pesticide rapidly released in neutral and slightly alkaline solutions than in acidic conditions.Moreover,the prepared hydrogels showed enhanced fungicidal ability against wheat take-all pathogen compared to that of prothioconazole technical material.The hydrogels have nutritional functions for the growth of wheat,and it could promote the germination of seeds,and reduce the desulfurization metabolism of prothioconazole in the soil;c)Hydrogels were innovatively designed by using hymexazol-self as a gelling factor,and sodium alginate and carboxymethyl chitosan as carriers.Hydrogels with different rheological properties were prepared by electrostatic interaction.Hydrogels which suit for different application scenarios could be obtained by changing the ratio of materials.The swelling property of the hydrogel was sensitive to ions and p H value.The hydrogels suitable for soil application could reduce the leaching of hymexazol in the soil,and hydrogels suitable for stem and leaf spraying could improve the deposition performance on the target crops.The thesis takes the selection and design of the carrier material of the controlled-release systems of pesticides as an entry point to carry out the research.In addition to realizing the basic functional properties of loading and controlling the release of active ingredients,the carrier materials are endowed with additional functional properties such as fluorescence performance,nutritional function,targeted deposition and plant protection.For the inorganic carrier material of FL-MSN,in addition to enhance the transmission performance of pesticide-loaded nanoparticles,and its fluorescence performance can realize the visualization of the nanoparticles.The interface modification can improve the biological activity,and regulate the environmental responsive release characteristics of the active ingredients in pesticide-loaded nanoparticles.For the organic carrier material of chitosan-based pesticide-loaded systems,the carrier material could endow the active ingredients with temperature and p H-sensitive release characteristics.Moreover,the carrier material could also exert synergistic biological activity and nutritional functions,and improve the ability of targeted pesticide deposition and resistance to rain erosion.The research is fully centered on the concept of green development.Through interface modification methods and efficient preparation processes,the pesticide loading methods were innovated,and the multifunctional controlled release systems of pesticides were developed.This research provided new ideas and technical approaches for the development of strategy of reducing pesticides application with increasing efficiency,and preparation of sustained and controlled release formulations.Furthermore,it is of great significance for the upgrading and utilization efficiency enhancement of pesticide products.