Quantum Chemical Studies On Ozonation Degradation For The Typical Unsaturated Volatile Organic Pollutants

Volatile organic compounds（VOCs）is an important class of air pollutants.A large number of VOCs are emitted into the atmosphere with the accelerated industrialization of human beings,which causes the significant impact on human health and the environment.These VOCs are the major contributors to the formation of photochemical smog,tropospheric ozone depletion and secondary organic aerosols.Their sources are wide,which mainly released into the troposphere through anthropogenic and natural sources.Among them,olefins and aldehydes unsaturated organic compounds are important components of volatile organic compounds in the atmosphere,and their ozonation is one of the major degradation pathways.With worsening atmospheric pollution,the degradation of organic pollutants through ozonation reactions is attracting more attention.However,complex and rapid degradation processes of a series of organic pollutants triggered by O₃make experimental studies for their degradation very difficult.Thus,in this paper,trans-2-pentenal,2-furancarboxylic acid,2,5-furandicarboxylic acid and methyl acrylate were selected as typical unsaturated VOCs,and their ozonation reaction mechanism,kinetics and ecotoxicity were studied by quantum chemical methods.The research contents are as follows:1.Quantum chemical study of trans-2-pentenal ozonation reaction in atmosphere.In this paper,the mechanism and kinetics of the ozonation reaction of trans-2-pentenal（T2P）in the atmosphere were investigated by quantum chemical methods.There were seven reaction channels for the reaction of T2P with O₃,mainly carbon addition reactions and hydrogen elimination reactions.Among them,the1,3-dipole cycloaddition reaction of O₃with C=C double bond was dominated.The dominant primary ozone compounds were firstly formed by 1,3-dipole cycloaddition reaction,and then Criegee intermediates that participate in the formation of secondary organic aerosols were formed by primary ozone compounds.The subsequent reactions of Criegee intermediates with common atmospheric species（NO,NO₂,SO₂,CH₂O,H₂O,and O₂）were investigated to state the atmospheric chemical behavior of Criegee intermediates.The total and branching reaction rate constants at 298 K and 1 atm were calculated by conventional transition state theory（CTST）and the Variflex program.At 298 K and 1 atm,the total reaction rate constant of T2P with O₃were9.13×10^-18cm³molecule^-1s^-1with atmospheric lifetime of 1.3 days.The branching reaction rates of the main reaction paths were 6.21×10^-18cm³molecule^-1s^-1and 2.92×10^-18cm³molecule^-1s^-1,respectively.The calculated rate constants is in general agreement with the available experimental data.This study is of importance in atmospheric chemistry of unsaturated aldehyde oxidation by ozone.2.Quantum chemical study of 2-furoic acid and furan-2,5-dicarboxylic acid ozonation reaction in wastewater.The furan-containing chemicals are an important intermediate for the synthesis of furan medicines,and their extensive uses make them likely contaminants in wastewater.Ozonation reaction is an effective removal route for furan derivatives in wastewater.In this paper,the mechanism,kinetics and ecotoxicity of the ozonation reaction of 2-furoic acid（FA）and furan-2,5 dicarboxylic acid（FDCA）in wastewater were investigated by quantum chemical methods.It was found that FA was structurally similar to FDCA,and the reactions with O₃had many similarities in reaction mechanism and kinetics.Among them,the 1,3-dipole cycloaddition reaction of O₃was dominated,and the electron withdrawing effect of the carboxyl group had an influence on the addition orientation of O₃.The primary ozone compounds with the central oxygen atom of O₃pointing to the furan ring were more stable.Moreover,the subsequent reaction mechanisms of the main Criegee intermediates formed by the primary ozone compounds were similar.The trends of the total and branching reaction rate constants of the reactions with temperature were calculated by transition state theory（TST）with the Kisthelp program.At 298 K and 1 atm,the total reaction rate constants were 1.22×10⁵M^-1s^-1and 2.22×10³M^-1s^-1,respectively.In addition,it was found that the half-life of FA and FDCA in water decreased with increasing concentration of O₃and temperature.At 298 K and 30μM[O₃],their half-life was only 0.19 and 10.39 s,respectively.The results showed that O₃can rapidly and effectively degrade FA and FDCA in wastewater.Meanwhile,the ozonation degradation of FA and FDCA were a process of decreasing toxicity.FA and most of their degradation products exhibited either positive mutagenicity or developmental toxicant.While,FDCA and its most of degradation products were developmental non-toxicant and showed negative mutagenicity.These results can provide a certain reference value for the ozonation degradation and toxicological study of furan derivatives in wastewater.3.Quantum chemical study for the ozonation reaction of methyl acrylate in the atmosphere and wastewater.Methyl acrylate（MA）is widely used in the production of acrylic resin materials.In order to discuss the degradation of MA,in this paper,the mechanism,kinetics and ecotoxicity of the ozonation reaction of methyl acrylate in atmosphere and wastewater were investigated by quantum chemical methods.It was found that the mechanism of the ozonation reaction of methyl acrylate in the atmosphere and wastewater was relatively close.The 1,3-dipole cycloaddition reaction of O₃with C=C double bond was dominated,and CH₂OO and CHOCOOCH₃were its most favorable degradation products.The trends of the total and branching reaction rate constants with temperatures for the reaction of MA with O₃in the gas and aqueous phases were calculated by using the conventional transition state theory（CTST）and the Variflex program.The total reaction rate constants in the gas and aqueous phase were 5.97×10^-18cm³molecule^-1s^-1and 3.91×10³M^-1s^-1at 298 K and 1 atm,respectively.The kinetic results showed that the reaction rate constant of MA was positive with temperature.The atmospheric lifetime of MA was relatively short,only 4.65 h.In the aqueous phase,the half-life was only 8.52 s at 298 K and 30μM[O₃].This paper also explores the influence of graphene adsorption on the reaction mechanism of methyl acrylate with O₃in atmosphere and in wastewater.The results showed that the adsorption process of graphene did not change the reaction mechanism of MA and O₃.However,it can effectively adsorbe MA and decrease the reaction energy barrier obviously.In addition,products formed by the decomposition of primary ozone compounds can continue to be adsorbed by graphene.The ecotoxicity of MA and its degradation products in the aqueous phase has been evaluated.The results showed that the aquatic toxicity of MA was high.However,the ecotoxicity of its ozonation degradation process were decreasing.Most of the degradation products were not harmful to the aquatic organisms.In addition,MA and most of its degradation products were developmental toxicants.