The Degradation Mechanism Of Antibiotics In Wastewater Studied By DFT Calculations

Due to the serious pollution caused by antibiotics to the environment and the huge potential threat to human beings caused by resistant bacteria,this paper uses density functional theory to study the degradation mechanism in detail.In this study,metronidazole,chloramphenicol and sulfadiazine were taken as the main research objects,and the degradation mechanism of antibiotics under the advanced oxidation method was analyzed in detail,and the differences of different degradation methods were compared.During the degradation of metronidazole,the possibility of nitro elimination reaction and hydroxyl oxidation to carboxylic acid is higher than that of other free radical elimination.The details of alcohol oxidation,addition elimination,methyl elimination,nitro elimination,and ethanol group separation of metronidazole were calculated using density functional theory.The molecular fragmentation of metronidazole was performed using statistical molecular fragmentation model.The consistency of the conclusions of the two methods indicates that the degradation of metronidazole occurs first at the nitro site,which requires lower activation energy and releases energy.In the study of the degradation mechanism of chloramphenicol,the structural properties and the Fukui function of chloramphenicol were deeply mined.In addition,the nitro elimination and hydrogen extraction reactions of chloramphenicol were calculated,and the two reaction paths were studied and compared.The results show that chiral carbon atoms in chloramphenicol are active sites for chemical reactions with hydroxyl radicals.The degradation reactions occurring at this position are mainly multi-step exothermic reactions such as hydrogen abstraction reactions,hydroxyl radical addition reactions,and bond cleavage.In addition,it is also found that the energy barrier of the nitro elimination reaction is much lower than that of the hydrogen abstraction reaction,which indicates that the nitro elimination reaction is most likely to occur during the degradation of chloramphenicol.In the study of the degradation mechanism of sulfadiazine,the bond dissociate energy information indicates that the single bond near the sulfur atom is unstable and it may be broken first in an advanced oxidizing environment.Density functional theory was used to study the five reaction modes of sulfadiazine and hydroxyl radicals,including the addition reaction,desulfurization reaction,hydrolysis reaction,hydrogen abstraction reaction and denitrification reaction.The results show that the denitrification reaction of sulfadiazine is most likely to occur.In the end,the hydroxyl radical replaces the amino group.Desulfurization and hydrolysis reactions have higher activation energy types,which are less likely to occur than other reactions.This study simulates the degradation reaction process of antibiotic molecules in water based on a theoretical basis.The structure and energy characteristics of the molecules in the reaction provide theoretical support to study the nature of the degradation reaction mechanism of antibiotics.It provides a new reference for improving the removal efficiency of antibiotics in the industrial process,which is of great significance.