Electrochemistry Of Metalloporphyrin-like Complexes And Catalytic Degradation Of DDT

DDT is a kind of excellent broad-spectrum organochlorine pesticide,but the study shows that it has teratogenic and carcinogenic effects,which can cause serious harm to human health.Therefore,since the late 1970 s,DDT has been gradually banned to be produced and used by many countries in the world.Because DDT is a persistent organic chlorine pollutant which is difficult to be degraded naturally,it cannot be completely eliminated from the environment in the short term.Therefore,it has a great academic and practical value to study new methods for rapid degradation of DDT.Methods that can be used for DDT degradation in present include physical degradation,biodegradation,chemical degradation and electrochemical degradation.Electrochemical degradation can be divided into electrocatalytic oxidation and electrocatalytic reduction.Electrocatalytic oxidation needs large energy consumption and high costs,but electrocatalytic reduction degradation is directed against the dechlorination of organic chlorine and only needs low energy consumption,thus make it worth to be further studied.The key technology of electrocatalytic reductive degradation of DDT is choice and use of electrocatalysts.It is shown that the metalloporphyrin macrocyclic complexes have a good catalytic performance on the degradation of organochlorine,but the most existing studies are limited to the water-soluble metalloporphyrins,and only a few water-insoluble metalloporphyrins were previously reported to use as electrocatalyst for reductive degradation of organic chlorine compounds.Therefore,on the basis of introducing the structures,properties and related applications of porphyrin complexes,the type,content and distribution of organochlorine pollutants in soil samples were studied by gas chromatography.The electrochemical properties of metalloporphyrin complexes with different macrocyclic structures and different central metal ions in nonaqueous media were examined in the fourth to eighth chapters respectively.Effects of macrocyclic structure,ring substituents and central metal ions on the catalytic performance of the porphyrin complexes for reductive degradation were emphatically examined,and the mechanism for DDT dechlorination under the given experimental conditions was also proposed and discussed.The main contents of the fourth to eighth chapters are described below.In the fourth chapter of the dissertation,cyclic voltammetry was used to determine the redox properties of cobalt octaethylporphyrin and cobalt tetraphenylporphyrin in DMF containing 0.1 mol/L n-tetrabutylammonium perchlorate(TBAP)as supporting electrolyte in the absence and presence of DDT.The reduced cobalt porphyrin,that is Co(I)species,has a good catalytic efficiency on DDT degradation.Significant different UV-vis spectra were obtained during the controlled potential reduction of cobalt porphyrin in the presence or absence of DDTwhich further proved that the one-electron reduced cobalt porphyrin could catalyze the degradation of DDT.After bulk electrolysis of a certain amount of cobalt porphyrin catalyst and a certain amount of DDT at applied potential in DMF for a different time,the degradation products of DDT were separated from the electrolyte by rotary evaporation and solvent leaching.Finally,the degradation products were identified by gas chromatography-mass spectrometry(GC-MS).The results indicate that the degradation efficiency of DDT increased with the increase of electrolysis time,and the reduction product of DDT was a mixture of various dechlorination products,mainly to be the 1,1-dichloro(4-chlorophenyl)-2,2(DDD)and 1,1-dichloro(4-chlorophenyl)-2,2-dichloroethylene(DDE)and 1,1-dichloro(4-chlorophenyl)-2-vinyl chloride(DDMU).In chapter 5,the catalytic properties of manganese octaethylporphyrin and manganese tetraphenylporphyrin for the reduction of DDT in DMF were studied.The results showed that the initial manganese porphyrin and its first reducted product cannot catalyze the degradation of DDT,but both the doubly and triply reduced manganese porphyrins have catalytic activity.After the reduction of DDT at applied potential in a certain time period in DMF,different degradation products can be separated.The GC-MS measurements indicated that the main products of DDT degradation were DDE and DDMU under the given experimental conditions.In Chapter 6,the properties of iron octaethylporphyrin and iron tetraphenylporphyrin for catalytic DDT reduction were examined in DMF containing 0.1 mol/L TBAP.The results showed that the two investigated iron porphyrins have three one-electron reduction processes.The first process is not affected by the presence of DDT in solution,indicating that the Fe(II)porphyrin generated by the first one-electron reduction cannot react with the DDT.However,the peak current of the second reduction of iron porphyrin improved obviously with the increase of DDT,indicating that the generated Fe(I)porphyrin after the second one-electron reduction can catalyze the degradation of DDT.The reductive degradation products of DDT are similar to use cobalt porphyrin or manganese porphyrins as the catalysts,but the iron tetraphenylporphyrin shows the highest efficiency under the same solution conditions.In Chapter 7,the degradation of DDT was studied by using iron(III)chloride phthalocyanine and iron(II)phthalocyanine as the electrocatalyst.It was found that the first oneelectron reduced iron(II)phthalocyanine or the second reduced Fe(III)phthalocyanine,that is,the generated Fe(I)phthalocyanine can catalyze the reductive degradation of DDT.The results show that Fe(II)phthalocyanine has better catalytic performance than Fe(III)phthalocyanine with the main degradation product being the DDE.Chapter 8 utilized the same electrochemical and spectroelectrochemical techniques forcharacterizing the properties of four substituted iron porphyrins and a series of metalloporphyrins containing different central metal ions,such as Sn,Ru,In,Ti and Nb.A preliminary study indicates that(OEP)Sn(OH)2,(OEP)Ru(CO)(THF)and(OEP)InCl have catalytic activity for reduction of DDT but(TPP)TiF2,(TPP)NbCl3 and(TPP)Ru(NO)showed inactive for catalytic reduction of DDT.The results indicate that both the porphyrin ring structure and the type of central metal ions have a great influence on the catalytic reductive degradation of DDT.