Preparation And Release Behavior Study Of Photo-responsive Paraquat Microspheres

Pesticide microspheres use carrier materials with controlled release properties to load active ingredients,which has certain targeting and slow release properties.While reducing the adverse effects of pesticides on the ecological environment and non-target organisms,it improves the utilization rate of pesticides.Pesticide microspheres has attracted more and more researchers’attention in the field of crop protection.The photo-responsive pesticide microspheres can respond to light stimulus from the external environment to release the active ingredients,thereby intelligently regulating harmful organisms and reducing the risk of exposure,so it has amazing potential for special compounds in specific control fields.Mesoporous silica nanoparticles（MSNs）has gradually become an important carrier in the field of drugs sustained and controlled releasedue to their excellent properties,such as high specific surface area,controllable particle size,uniform pores,easy modification of internal and external surfaces,low biological toxicity and good biocompatibility.This paper intends to construct paraquat-loaded microspheres with light-responsive mesoporous silica to express the herbicidal activity of paraquat under light conditions.When paraquat is swallowed by mistake,the release of paraquat will be inhibited,and the active ingredient will not be released or the active ingredient released will be below the safety threshold,thereby reducing the acute toxicity risk of paraquat and exerting its commercial value.In this paper,the photoreactive silane coupling agent,an azobenzene derivative,was used to modify mesoporous silica,and as a carrier to prepare paraquat microspheres,to explore the photo-responsive behavior and release of the microspheres mechanism.This research will provide new ideas for the efficient,low toxicity and safe use of pesticide formulations,provide a new way to reduce the risk of chemical pesticides on humans or non-target organisms,and help promote the application of MSNs in the field of pesticides.The main results achieved in this paper are as follows:Adopt soft template method,take ethyl orthosilicate（TEOS）as silicon source,and use cetyltrimethyl ammonium p-toluenesulfonate（CTATos）as template agent,react in alkaline ethanol aqueous solution,by optimizing the conditions,obtained MSNs with nanometer size and submicron size.Observation of microscopic morphology revealed that the obtained spherical particles had uniform particle size distribution,regular morphology and good dispersion.The best preparation conditions,submicron size:TEOS 1.56m L:CTATos 1.92g:ammonia 1.9m L:ethanol 42m L:deionized water 43.5m L;nano size:TEOS 1.56m L:CTATos 1.92g:TEOA 1.9m L:ethanol 10.5m L:deionized water 74.5 m L.Using para-aminoazobenzene（ABO）and silane coupling agent-isocyanate triethoxysilane（3-IPTS）as reactants,heating and refluxing under anhydrous conditions to obtain photoresponsive modified materials（AB-IPTS）.Photoresponsive mesoporous silica（AM）was obtained by functional modification of MSNs by grafting method,and photoresponsive pesticide microspheres（PQ@AM）were obtained by loading mode pesticide paraquat.The optimal drug loading time was 8 h,the best drug mass ratio（carrier:drug）was 1:8,and the maximum drug loading was about 11.8 wt%.The photo-response behavior of the controlled release system was explored.The general culture method was used to take samples at a set fixed time point.The drug concentration of the system was determined by a standard curve.The drug loaded controlled release system was plotted at T=25℃,p H=5;T=25℃,p H=6.9;T=35℃,p H=6.9 cumulative release curves.In general,under light conditions,about 80%of the active ingredients were released within 24 hours,while under dark conditions,only 20%of the active ingredients were released,and the microsphere system performed well controlled release performance.When the system p H=5.0,the release rate of the active ingredient was close to that of the system p H=6.9.When the system temperature increased from 25℃to 35℃,the cumulative release amount increased from 77.87%to 83.32%within 24 hours.Common drug sustained-release model equations were selected:Higuchi model,Rigter-Peppas model and Logistic model were used to fit and analyze the data obtained during the release of the prepared paraquat controlled release system.The fitting results showed that paraquat release process conforms to the Logistic model.Under the conditions of T=25℃,p H=6.9;T=25℃,p H=5;T=35℃,p H=6.9 the Logistic fitting equations of the controlled release system were Q₁=107.50-107.17/(1+（t/5.3905）^0.7528),Q₂=103.26-100.16/(1+（t/3.0985）^0.7729),Q₃=110.58-109.65/(1+（t/5.3929）^0.8484),and R²were all greater than 0.98.It shows that the release mechanism is in line with the complex coupling of disintegration and dissolution,and the release curve belongs to S-type.