| As widely used from 1940s to 1960s,1,1, 1-Trichloro-2,2-bis (p-chlorophenyl) ethane (DDT) has improved the agricultural productivity remarkably and made a great contribution to preventing the spread of entomophilous diseases such like malaria and dengue, thus saving millions lives. However, due to its environmentally persistence, long-teme residual, bio-accumulation, semi-volatility, long-distance mobility and high bio-toxicity, DDT has already been banned worldwidely. Although forbidden for dozens of years, DDT has accumulated in ecosystem including water and soil as the result of the long-term and large-scale use in mid-20 century and would gather through the food chain and enter human body eventually. Since the threat of organochlorine pesticides (OCPs) like DDT on environment and human health has been increasingly severe, developing the remediation method toward OCPs has attracted researchers’attention.Advanced oxidation processes (AOPs) based on the hydroxyl radical (#OH) or sulfate radical (SR) (SO4-) toward the refractory organic pollutants has developed in recent years which is characterized as strong oxidative degradation ability and high mineralization. In the present thesis, our research is about the heterogeneous Fenton-like system and SR-AOP with the transition metal oxides-based catalysts. We have investigated on the DDT degradation performance, mainly focused on degradation kinetic, factors influencing the degradation reaction, and possible mechanisms and routes of degradation.(1) Fe2O3 nanoplate was synthesized via hydrothermal method as the precursor. Nickel loaded iron oxides (Ni@FeOx) were prepared as heterogeneous Fenton-like catalysts using Fe2O3 and NiCl2 as precursor and N2H4 as reductive agent. The phase and structure of the iron oxides in Ni@FeOx could be tuned via controlling the amount of nickel precursor. When the atomic ration between nickel and iron was over 20%, the iron oxides in the products would transfer from hexagonal Fe2O3 nanoplate to cubic Fe3o4 microcube. The catalyst sample 40%Ni@Fe3O4 exhibited the best DDT degradation performance within 8 h,90%DDT decompose. The superior degradation efficiency could be attributed to the synergistic effect between metallic Ni and Fe3O4, which could improve the utilization efficiency of H2O2 and therefore degrade DDT more completely.(2) CoFe2o4 catalyst was prepared via hydrothermal method using CoCI2 and FeCl3 as precursors, PVP as surfactant, which would be used to activate peroxymonosulfate (PMS) toward DDT degradation. BET results proved that CoFe2O4 has mesoporous structure and large specific surface area (132.6 m2/g), guaranteeing the sufficient contact between the CoFe2o4 catalyst and PMS and hence promoting the activation effect. The DDT degradation efficiency was 95.2%within 120 min. The quantitative GC results about the intermediates have revealed that DDE, rather than DDD, was the main product in the first degradation step. The qualitative GC-MS results on the products suggested that dechlorination and hydroxylation contributed to the degradation process of DDT, including the aliphatic chain cracking, the benzene ring cleavage, and final production of H2O2 and CO2.(3) Spinel ferrite catalysts (MFe2o4, M=Cu, Ni, Mn, Zn) were prepared via hydrothermal method. The samples were characterized via XRD, SEM, GC and GC-MS. All the ferrite catalysts showed the DDT degradation efficiency over 70%. Among them, CuFe2O4 displayed the superior DDT degradation efficiency to other ferrite catalysts with 82.6% DDT decomposed within 120 min. The operational stability of MFe2O4 catalysts were explored via testing the DDT degradation in consecutive runs and slight deactivation was observed after the third runs, which implies the MFe2o4 catalysts have good reaction stability and reusability. In addition, the MFe2O4 catalysts could be easily separated and recycled via external magnetic field... |
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