Quantum Chemistry Study On Photocatalytic Degradation Of Typical Organic Pollutants In Aqueous System

Persistent organic pollutants to aqueous system and ecology environment was evoked widely attention by international community.photocatalytic technology was supposed to be a most effective way to remove antibiotics in aqueous system.However,it is impossible to comprehensively test the photo catalysis for all existing pollutants because of largeexpenditures of money and time.Since it has the characteristics of low cost and high efficiency,the quantum chemical theory is directly applied to the photocatalytic behavior of pollutant molecular simulation,which makes the calculation of chemical quantum theory has become an important tool in the field of environmental studies.In this thesis,6 Polycyclic Aromatic Hydrocarbons(PAHs)-naphthalene(NAP),fluorene(FL),phenanthrene(PHE),pyrene(PYR),benzo[a]pyrene(BaP),and dibenzo[a,h]anthracene(DahA)and 9 antibiotics-tetracycline(TC),oxytetracycline(OTC),sulfamethoxazole(SMZ),chlortetracycline(CTC),ofloxacin(OF),deme clocycline(DEM),doxycycline(DOX),minocycline(MIN)and methacycline(MET)and were choosing as model organic pollutants.Kinetic characteristics of TiO2 photocatalytic degradation of antibiotics and Pt/TiO2-SiO2 photocatalytic degradation of PAHs was studied.Based on the degradation mechanism and the regressionanalysis,Quantitative Structure Activity Relationship(QSAR)models were developed.In addition,the contribution experiments of various primary reactive species produced during the photocatalysis were investigated with the addition of different scavengers.Furthermore,the photocatalytic degradation ofrepresentative organic pollutants was compared and analyzed,Mainly includes two aspects:comparative analysis between PYR and TC under TiO2 photocatalytic degradation;conparative analysis for PYR between Pt/TiO2-SiO2 and TiO2 photocatalytic degradation.Photocatalytic degradation initial mechanism of TC and PYR were also proposed by theoretical data of frontier electron densities and point charges.1.The results of the study on the relationship between the photocatalytic degradation activity and the structural parameters of the antibiotics are as follows:(1)Nine tested antibiotics were demonstrated to be effectively degraded in TiO2 photocatalysis processes,the photocatalysis of antibiotics fit the pseudo-firstorder equation very well.(2)A QSPR model which relates to Alpha.Elumo?MW and Ehomo+Elumo for photo catalysis degradation rate constant of 9 antibiotics in aqueous solution under irradiation of a UV light source was developed.The model is as follows:K=-0.09988-0.02672xElumo-0.00045×MW-0.02192×(Ehomo+Elumo)+0.00033×Alpha?2.The results of the study on the relationship between the photocatalytic degradation activity and the structural parameters of the PAHs are as follows:(1)Six PAHs were experimentally tested in a Pt/TiO2-SiO2 suspension under UV irradiatioa The results show that the degradation of HMW PAHs,PYR,BaP,and DahA,was accelerated significantly in the presence of Pt/TiO2-SiO2,while the degradation efficiency of low molecular weight PAHs,NP,FL and PHE,was inhibited under the same experimental conditions.Both the photolysis and photocatalysis of PAHs fit the pseudo-firstorder equation very well,except FL.This might be attributed to FL's 5-carbon ring structure.(2)By comparing to the GAP of PAHs in this study,the photocatalytic degradability of 67 PAHs was predicted:46 PAHs were potentially photocatalytically degradable,4 PAHs were predicted to be not photocatalytically degradable,and 17 PAHs were predicted to exhibit indeterminate photocatalytic degradation.The experiments of photocatalytic degradation of ANand InP verified the above prediction.(3)A QSPR model which relates to Alpha?Elumo?TE and NRE for photocatalysis degradation rate constant IgK of PAHs in aqueous solution under irradiation of a UV light source was developed.The model is as follows:lgK=-11.274-0.03207×TE-0.01889xNRE-1.4649×Elumo +0.03379× Alpha?3.The results of comparative analysis and mechanism study of photocatalytic degradation of antibiotics and PAHs are as follows:(1)The contributions of active radicals during TiO2 photocatalytic degradation of different kinds of antibiotics vary respectively.During the photocatalytic degradation of TC and OF under UV,the hVB+ was the major reactive species.Photocatalytic degradation of CTC,DOX,OTCand MET,other reactive oxygen species(ROSs)plays the most important contribution The degradation rate of SMZ,the HO· radicals was the major reactive species.Photocatalytic degradation of DEM and MIN,both the hVB+ and HO·were the major reactive species.(2)The contributions of active radicals during pbotocatalytic degradation of different kinds of PAHs vary respectively.During the photocatalytic degradation of AN and PYR under UV,the hVB+ was the major reactive species.Photocatalytic degradation of BaP,DahA and InP,other reactive oxygen species(ROSs)plays the most important contribution.(3)PYR was accelerated significantly in the presence of both Pt/TiO2-SiO2 and TiO2,and the photocatalytic effect ofPt/TiO2-SiO2 is better than that of TiO2.In addition,the contribution of the reactive oxygen species in the two photocatalysis reaction system was similar.(4)The results of comparative analysis between PYR and TC under TiO2 photocatalytic degradation are as follbws:the degradation of TC is faster than PYR;During the photocatalytic degradation of PYR,the contributions of active radicals was hVB+>ROSs>HO·.During the photocatalytic degradation of PYR,the contributions of active radicals washyg>HOo>ROSs.(5)The initial HO· reaction sites for TC was C17 and C18,the initial HO· reaction sites for PYR was C7,C8,C10,C11 and C14.