| Recently,the feasibility of non-thermal atmospheric temperature plasma in the degradation of pesticides has been widely concerned by researchers.However,the current research has focused on the limited types of pesticides,excluding avermectin,and there are some gaps on the interaction mechanism between plasma and pesticides.In this paper,a degradation experimental platform of dielectric barrier discharge non-temperature plasma(DBD-NTP)is established.Based on the effects of different operating parameters(applied voltage,treatment time and gas flow rate)on the degradation of avermectin,the range of relevant parameters was determined to provide experimental basis for the degradation of avermectin by DBD-NTP.By means of Reactive Force Field Molecular Dynamic(ReaxFF-MD),the mechanisms of degradation between main reactive oxygen species(ROS)in plasma and avermectin are obtained at the micro level.The effects of ROS(OH·and O·)and particle number density on the breakage and formation of important chemical bonds are explored.In summary,the simulation provides theoretical support for DBD-NTP to degrade avermectin through the basic theoretical research.The specific work content and the results are as follows:(1)According to the research object,a DBD-NTP discharge device suitable for liquid treatment was designed to explore the electrical and spectrographic characteristics of DBD plasma.The results show that DBD used in the experiment is a resistance-capacitance discharge,and the discharge power increases with the increase of discharge voltage.The characteristic spectrum lines of OH·,O·and high energy metastable Ar atom are observed in the optical emission spectra(OES)results,which prove the application potential of plasma in the degradation of avermectin.(2)Based on the self-designed discharge device,an experimental platform for DBD-NTP degradation of avermectin was built,and the degradation effect of DBD-NTP on avermectin was investigated.The effects of treatment time,discharge voltage and gas flow rate on the degradation of avermectin were analysed by ultra-high performance liquid chromatography-tandem mass spectrometry(UPLC-MS/MS).The results testifies that the degradation efficiency of DBD-NTP increases with the increase of discharge voltage and treatment time.The degradation rate of DBD-NTP increases first and then decreases with the increase of gas flow rate.Comparing the properties of avermectin solution before and after treatment,it was found that the conductivity of the solution increases and the pH value decreases after DBD-NTP treatment.(3)The molecular structure was built in Materials Studio.The reaction molecular dynamics simulation platform of the reaction between ROS and avermectin was constructed to explore the possible destruction pathways of avermectin under the action of atomic oxygen O·and hydroxyl OH·.The results showed that ROS destroyed the structural integrity of avermectin by breaking the chemical bonds(C-O,C-C)in the molecular structure through hydrogen abstraction reaction.Among them,O·disintegrated the avermectin structure by destroying the glycoyl hexaheteron ring and the ester group structure,while OH·fractured the avermectin structure by destroying the ester group structure.As the number of OH·increases in the same size reaction space,the number of chemical bond types of avermectin destroyed by ROS increased,and the destruction rate of the dominant destruction path increased.In addition,when the number of OH·reaches 50,some new destruction pathways appeared in the simulation:the oleanolic fructose disaccharide will fall off in the presence of OH·.This study breaks through the limitations of traditional methods for the degradation of avermectin,which provides theoretical basis and technical support for the degradation of pesticide residues by plasma through the experimental research and simulation of the degradation of avermectin by DBD non-thermal atmospheric plasma. |
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