Design And Study Of Acid-responsive SiO₂-based Pesticide Controlled Release System

Root plays an important role in spatial survival and nutrient transport for plants.The chemical substances secreted by roots can not only complete the material commutation with the environment,but also stimulate the germination of pathogens that caused soil-borne diseases.The germination of pathogens is closely related to environmental conditions.plasmodiophora brassicae is harmful to cruciferous plants.The germination happens easily in weekly acidic soil（p H=4.0-6.5）.Based on the characteristics of soil-borne diseases,two kinds of acid-responsive pesticide controlled release nano-systems were designed and prepared here.First,MCM-41 was used as the carrier,the fungicide uniconazole（UNI）as the model drug,polyethylenimine（PEI）or layered double hydroxide（LDH）as the coating materials,and impregnation method was applied for drug loading.Second,acid stimulation-responsive drug-loaded microcapsules was prepared using microencapsulation method by in-situ loading dinazolol（DIN）.Specific study contents and results are as follows:1.Preparation and study of core-shell pesticide slow-controlled release system:In this paper,nano-MCM-41 was used to complete the loading of UNI by impregnation method.The optimized loading conditions were as follows:CH₂Cl₂as solvent,m（UNI）:m（MCM-41）=3:5,the concentration of mother solution was 1000 mg/L,impregnation for12 h.After drug loading,it was recorded as MCM-41-UNI,the drug loading was about150 mg/g,PEI or LDH coating was continued,and the optimized conditions were as follows:at room temperature,m（PEI/LDH）:m（MCM-41-UNI）was 1:2,impregnation for20 min,water as solvent.The obtained materials were recorded as PEI-MCM-41-UNI and LDH-MCM-41-UNI,and the adsorption quantity were about 147 mg/g and 84 mg/g,respectively.The results of FT-IR,N₂adsorption-desorption apparatus,Zeta potential,XRD and transmission electron microscopy showed that PEI and LDH coated the surface of mesoporous silica successfully,and the particle size distribution was uniform,about250 nm.The results of simulated release experiments of PEI-MCM-41-UNI and LDH-MCM-41-UNI showed that the release equilibrium was reached on the 28th and17th day,and the cumulative release rate was 75%and 55%,respectively.The cumulative release rate of PEI-MCM-41-UNI was higher.The two slow and controlled release preparations can be used selectively according to the cycle of disease occurrence.The fitting results of the kinetic release model showed that the release of both were consistent with the Ritger-Peppa release model.The rape seeds were treated with PEI-MCM-41-UNI suspension of different concentrations.The results showed that PEI-MCM-41-UNI could inhibit the seed germination in the early stage,and with the increase of the pesticide concentration,the germination rate gradually decreased,but did not affect the final germination rate.The germination rate reached 90%or more,and the biocompatibility of the material is good.2.Preparation of acid stimulation-responsive silica drug-carrying microcapsules:Using cetyltrimethylamine bromide（CTAB）dissolved in ultra-pure water as water phase and DIN dissolved in ethyl acetate as oil phase,acid stimulation-responsive silica drug-carrying microcapsules were synthesized by O/W microemulsion method.Through the optimization of experimental conditions,the optimal preparation conditions of silica drug-carrying microcapsules were obtained:V（water phase）:V（oil phase）=90 m L:18m L,an appropriate amount of concentrated ammonia（1-3 m L）.The adsorption quantity was about 142 mg/g-170 mg/g.The results of FT-IR,scanning electron microscopy and transmission electron microscopy showed that the particle size distribution of the silica drug-carrying microcapsules was uniform,about 100 nm.On the 35th day,the microcapsule sample reached a release equilibrium,and the cumulative release rate was80%.The release kinetics fitting results showed that the release curve of the microcapsule was more consistent with the Ritger-Peppa release model.