Study On Ozonation Degradation Mechanism Of Two Typical PPCPs In Water

Anti-inflammatory drugs and preservatives are important components of the emerging pollutants PPCPs.These two kinds of substances are relatively rich,and have a wide range of uses.Anti-inflammatory drugs are commonly used in painkillers,anti-inflammatory drugs and other important outpatient drugs.Preservatives are often used in combination as bactericidal preservatives in organic synthesis,food,cosmetics,medicine,and as feed preservatives.The main source of anti-inflammatory drugs and preservatives in the aquatic environment is anthropogenic discharges.The unsaturated bond in the structure makes its chemical properties very active,and can react with O3 molecules in water to generate a series of secondary organic pollutants.In order to explore the anti-inflammatory drugs and preservatives compounds in the reaction behavior of water environment,this paper uses the method of quantum chemistry on two typical anti-inflammatory drugs(diclofenac and ibuprofen)and two typical preservative(methylparabens and ethylparabens)of the liquid phase chemical reaction was studied,and reveals the liquid from the molecular level the degradation mechanism and dynamics properties,and the degradation products of aquatic toxicity is forecasted and evaluated.The results are summarized as follows1.Study on the mechanism,kinetics and ecotoxicity of liquid phase oxidative degradation of diclofenac initiated by O3 moleculeThe decomposition reaction of diclofenac with O3 molecule was calculated at M06-2X/6-311+G(3df,2p)//M06-2X/6-31+G(d,p)level.The decomposition reaction of diclofenac with O3 molecule mainly includes 13 primary reaction pathways of O3 addition and subsequent reaction of intermediate with H2O,NO and O3,etc.The ozone addition on benzene ring plays a dominant role.We used the gibbs free energy(reaction energy)ΔrGaq(kcal mol-1)and gibbs free energy of activation(energy barrier)ΔGaq≠;(kcal mol-1)to estimate the feasibility of the reaction.According to the thermodynamic data,the kinetic parameters were calculated by the transition state theory(TST).The total reaction rate constant(298 K,1 atm)of DCF induced by O3 is 2.57×103 s-1M-1,and the variation trend of reaction rate constant at 260～350 K has been calculated.The results show that the reaction rate constant has a good correlation with temperature.The ECOSAR program assesses the acute and chronic toxicity of DCF and its degradation products in three different aquatic organisms.Most products are converted into less toxic or harmless products.However,oxalaldehyde(P4)and N-(2,6-dichlorophenyl)-2-oxyacetamide(P7)still have certain hazards to these three aquatic organisms,which should be paid more attention in the future research and risk assessment.2.Study on the mechanism,kinetics and ecotoxicity of liquid phase oxidative degradation of methylparabens and ethylparabens initiated by O3The decomposition of methylparabens and ethylparabens with O3 at the M06-2X/6-311+G(3df,2p)//M06-2X/6-31+G(d,p)level has been calculated.The degradation process of the two substances includes 12 initial reaction channels and several subsequent reaction pathways containing Criegee radicals.The reaction rate constant was calculated by the transition state theory(TST)from thermodynamic data.At 298 K and 1 atm,the rate constants of MPB and EPB are 3.92 s-1M-1 and 3.94 s-1M-1,respectively.The rate constant increases with increasing temperature and increasing alkyl chain on the benzene ring.The ecotoxicity of benzoic acid esters and their degradation products were evaluated by ECOSAR procedure.Most of the degradation by-products or toxicity are greatly reduced or converted to non-toxic products.But some by-products are still harmful,such as oxalaldehyde(P2)and ethyl 2,3-dioxypropionate(P10).With the increase of alkyl chain on the benzene ring,the ecotoxicity of parabens is greater,The effect of increasing alkyl chain on benzene ring is not negligible.3.Study on the mechanism,kinetics and ecotoxicity of liquid phase oxidative degradation of ketoprofen initiated by O3 moleculeThe decomposition reaction of ketoprofen with O3 molecule was calculated at M06-2X/6-311+G(3df,2p)//M06-2X/6-31+G(d,p)level.It mainly includes 12 primary reaction paths of O3 addition with a total of 12 reaction sites on the two benzene rings in the compound structure,as well as subsequent reactions between intermediates and H2O,NO and O3.At 298 K and 1 atm,the reaction rate constant of ketoprofen was 1.99×10-2 s-1M-1,respectively.The rate constants increased with the increase of temperature.Ketoprofen was harmless to the three aquatic organisms by evaluating the aquatic toxicity,but some toxic by-products were produced during ozonation degradation.Attention should be paid to the toxicity of ozonation degradation products.