Construction,Characterization And Performance Study Of Micro/Nano Fungicide Controlled Release System

It is an inevitable requirement to achieve sustainable agricultural development to build a technical system that supports the green development of agriculture.In recent years,new materials and new technologies have made great strides in promoting the green development of agriculture.In particular,pesticide sustained/controlled release formulations prepared from degradable materials have the advantages of high application efficiency and environmental friendliness.After use,the carrier is easy to biodegrade and does not produce toxic by-products,which is of great significance to the reduction and efficiency of pesticides and the realization of sustainable agricultural development.Constructing nano-pesticide controlled release systems through nanotechnology can effectively improve the utilization rate of pesticides,achieve green prevention and control of pests and diseases,reduce environmental risks,and meet the needs of green development of agriculture and ecological environment.It is also an effective strategy to demonstrate ecological civilization.On account of this,in view of the needs of green disease prevention and control in different application scenarios,in this paper,difenoconazole,azoxystrobin and pyraclostrobin were taken as the research objects,high molecular biodegradable materials polylactic acid（PLA）and polybutylene succinate（PBS）,as well as carbon-based nanomaterials graphene oxide（GO）and multi-walled carbon nanotubes（MWCNT）were taken as the carrier.Three kinds of micro/nano fungicides-controlled release systems were constructed by optimizing the proportion of carrier materials by means of blending and doping.The physical and chemical properties,release behavior,biological activity,acute toxicity and crop safety of three micro/nano-controlled release systems were evaluated respectively,in order to provide technical support for the reduction of pesticide application and efficiency as well as the innovation of green nano pesticide dosage forms.The main research contents are as follows:1.Using fungicides azoxystrobin and difenoconazole with different action mechanisms as active ingredients,binary compound pesticide microspheres were prepared by solvent evaporation method.The degradable polymer PBS was used as the carrier,and it was modified by PLA to improve the molding stability and compatibility of the composite.When the addition amount of PLA was 30%,the thermal stability of PBS and PLA in the composite matrix was consistent,and the best encapsulation performance was obtained.The binary compound pesticide microspheres prepared with this carrier had smooth surface,uniform distribution,and average particle size of 7.20μm.The ratio of that release amount of the azoxystrobin and the difenoconazole in the binary compound pesticide microspheres was close to the design metering ratio during administration,so that the purpose of compounding and enhance efficiency could be achieved,the sustained release time was about 25 d,and the requirement on the critical period of disease prevention and control for crops such as fruits,vegetables and the like which have a short growth and harvesting period or are directly eaten could be met.In addition,compared with the commercial preparation 32.5%difenoconazole-azoxystrobin suspension,the safety of the binary compound pesticide microspheres to non-target organisms was also improved.2.The polylactic acid（PLA）and graphene oxide（GO）composite drug loading system was designed,and the polylactic acid-graphene oxide-based（PLA-GO）composites doped with different contents of graphene oxide were prepared.The polylactic acid-graphene oxide-based drug-loaded microspheres（PLA-GO-Pyr MS）were constructed by the solvent evaporation method to realize the coating of the methoxyacrylate fungicide pyraclostrobin.Scanning electron microscopy results showed that the introduction of GO-modified PLA could improve the crystallization defects of PLA crystals and endow the pesticide microspheres with higher drug loading.When the amount of GO added was 0.5%,the maximum drug loading of the prepared microspheres was about 40%.The release of pyraclostrobin in the drug-loaded microspheres gradually accelerated with the increase of temperature,and the drug release was dominated by the corrosion of the polymer matrix and accompanied by diffusion.Indoor toxicity testing confirmed the good inhibitory effect of PLA-GO-Pyr MS on Rhizoctonia solani(EC₅₀:1.268 mg/L),three times that of pyraclostrobin microcapsule suspension（Pyr CS）,which may be due to the synergistic effect of the carrier material and the active ingredient.In addition,the rice pot experiment proved that the composite material had no adverse effect on rice growth and had good crop safety.3.A multi-walled carbon nanotube delivery system（Pyr-loaded MWCNTs）was constructed,and the multi-walled carbon nanotubes were labeled with fluorescein isothiocyanate（MWCNTs-FITC）.The drug loading rate of the nano delivery system can reach16.64%,the sustained release time can reach more than 30 days,and the drug release is mainly controlled by diffusion.The indoor bioassay results showed that Pyr-loaded MWCNTs had excellent control effect on rice blast with EC₅₀ of 0.054 mg/L.This result of the pot experiment manifested that the nano-delivery system had a control effect of 86.16%against rice blast at a concentration of 300 mg/L,which was equivalent to a commercial preparation.The fluorescent-labeled nanoparticles could be transmitted on the surface of mycelium and the root of rice,which was conducive to the synergistic fungicidal activity,and were beneficial to exerting the synergistic fungicidal activity.Compared with the technical,the safety of Pyr-loaded MWCNTs to the zebra fish was improved by 80 times,and the acute toxicity to the zebra fish was remarkably reduced.In addition,MWCNTs were found to have no effect on rice seed germination and seedling growth and did not cause oxidative stress in rice plants within the concentration range of 40-500 mg/L.The research in this paper verified that the new dosage forms of three pesticides constructed with different carrier materials can not only improve the lasting period of three fungicides and their biological activities,but also reduce the acute toxicity of methoxyacrylate fungicides on non-target aquatic organisms,which is of great significance for the development of efficient,environmental-friendly and green agriculture.The development and application of MWCNT and GO provide a theoretical basis for the carbon-based nanomaterials to play a synergistic role of"pesticide+material"in the agricultural field.