DDT Degradation Performance Of Ferrous Oxides

Organic pesticides, DDT taken as an example, have played an important role in our pursuit of high production efficiency in agriculture. And DDT has also helped to control infectious diseases, such as malaria, spreaded by mosquitoes. However, DDT has accumulated in large amount in nature after large-scale use for about 30 years, because of DDT molecule’s stability. What’s more, because DDT has the character of lipotropy, gathering effect will occur to DDT’s transfer process in food chains, which means DDT can be harmful to mankind through food chains. Since DDT has put threat to our living environment, many researchers all over the world have put their focus on degradation method and mechanism of DDT. In the present thesis, we designed three ferrous compounds and their composites, and investigated their performance in DDT degradation and the mechanism of the degradation process. The main contents are listed as follows:(1) Fe3O4 micropheres were prepared via a hydrothermal method with FeCl3—6H2O as precursor, after which α-Fe2O3,γ-Fe2O3 and α-Fe2O3/γ-Fe2O3 nanocomposites were prepared through thermal treatment process. XRD and HRTEM results proved that the nanocomposites sample was composed of both a and y phase of iron oxides. Under similar degradation condition, single-phased iron oxide samples could only degrade about 20% of DDT pollutants while α-Fe2O3/y-Fe2O3 nanocomposites could reach about 65%. And the analysis of degradation product revealed that DDT degradation might be conducted by two pathways, i.e. dechlorination effect and dehydrochlorination effect. The outstanding performance of α-Fe2O3/γ-Fe2O3 nanocomposites in DDT degradation process was attributed to the nanocomposite structure of the α-Fe2O3/γ-Fe2O3 sample.(2) Ferrous alkoxide was prepared in a hydrothermal method, after which α-Fe2O3/γ-Fe2O3 nanocomposites were prepared by the thermal decomposition of ferrous alkoxide and FeOOH was prepared in a hydroxylation process, and by thermal treatment, the latter could be further transformed into γ-Fe2O3. The samples were characterized by SEM, XRD, TEM, BET and IR. By comparison of DDT degradation results of these samples, we investigated the influence of different factors on degradation efficiency. Under similar degradation condition, α-Fe2O3/γ-Fe2O3 nanocomposites degraded 70% of DDT because of the nanocomposite structure formed during the preparation process which was slightly above that of FeOOH (65%). γ-Fe2O3, with lower hydroxy on its surface, showed an efficiency of 15%. And the analysis of degradation product revealed that only dechlorination effect occurred to the DDT degradation process while the dehydrochlorination effect was inhibited in this case.(3) Through a solvent exchange method, CoFe2O4 gel with high specific area was prepared, after which Co was reduced through a liquid phase reduction process. The samples were characterized by SEM, XRD, TEM, BET and IR, and so on. Co/CoFe2O4 showed excellent performance in degrading DDT, and it was because Co was an active degradation agent for DDT and the high specific area of CoFe2O4 gel promoted this advantage. And the analysis of degradation product revealed that only dechlorination effect occurred to the DDT degradation process.