The Preparation Of Fe₃O₄/MWCNTs And Degradation Of17α-methyltestosterone In Fenton-like System

In recent years, the environmental hormone pollution has attracted much attention among the people. The endangers of environmental hormones to the living things have become one of the most important environmental problems in the world at present. Nowadays, as an important advance oxidation processes (AOPs), heterogeneous Fenton method is being widely studied for the degradation of organic pollutants. To develop a heterogeneous Fenton catalyst which has good structural stability, little iron leaching, simple separation, stable catalytic activity in repetitive reaction cycle is an important trend in the Fenton catalysis.A novel Fenton oxidation catalyst, the ferroferric oxide nanoparticles decorated multiwalled carbon nanotubes (Fe3O4/MWCNTs) was successfully prepared. The widely used artificial hormone17a-methyltestosterone (MT) was chosen as a target contaminant. The adsorption capacity of the nanocomposites for trace MT in water was studied. The catalytic property of the catalyst in heterogeneous Fenton, UV-Fenton and MW-Fenton systems was investigated. The degradation mechanism and the reaction conditions that influence the MT degradation efficiency were discussed. (1) The surface of the MWCNTs was functionized by several oxidation methods. The regular growth of ferroferric oxide crystal on MWCNTs was achieved by in situ oxidation of Fe2+in hot alkaline solution. Inverse-spinel ferroferric oxide nanoparticles decorated MWCNTs (Fe3O4/MWCNTs) was obtained. The diameters of the loaded octahedron Fe3O4nanoparticles range from40to100nm. The specific surface area of the catalyst was20.58m2g-1. The catalyst has good dispersion property, strong magnetism and convenient recovery.(2) The adsorption capacity of Fe3O4/MWCNTs for trace MT in water was investigated. About90%MT was absorbed onto the catalyst when the conditions were [MT]=212μg L-1,[Fe3O4/MWCNTs]=2gL-1, pH=7.0and T=20℃, and just about10%of MT was absorbed by the same amount of Fe3O4. The adsorption of MT on Fe3O4/MWCNTs or Fe3O4in aqueous solution had no significant change when pH ranged from3-10. The degradation efficiency of MT in8h was85.9%for the first oxidation when the initial conditions were [MT]=212μg L-1,[Fe3O4/MWCNTs]=2g L-1, pH=5.0,[H2O2]=5.3mmol L-1under normal temperature and pressure. The change of pH has significant influence on the degradation efficiency of MT. The degradation efficiencies increased with the initial pH decreasing in the wide pH range of8.0-2.5. The nanocomposites displayed good catalytic stability. The leached iron concentration was lower than20mmol L-1in8h degradation time when the initial conditions were [MT]=212μg L-1,[Fe3O4/MWCNTs]=2g L-1, pH=3.5,[H2O2]=20mmol L-1. The MT degradation performance on the reused catalyst showed a slight difference with the first oxidation cycle. The degradation efficiency of MT was79.4%for the seventh oxidation cycle. The homogeneous reaction by the leached iron species from the catalyst just made a very small contribution to the MT degradation. The heterogeneous Fenton-like oxidation reaction occurred on the catalyst surface was the main pathway of the MT degradation.(3) The MT degradation and H2O2analysis approximately followed a pseudo-first-order reaction in kinetics under degradation conditions. The reaction-diffusion modulus implied that the average rate of the reaction of MT and H2O2on the catalyst surface was far slower than its diffusion rate to the surface through the external film. Therefore, the intrinsic reaction on the oxide surface was expected to be the rate-limiting step for the degradation process. The enriched MT in the very near vicinity of the catalyst surface might lead to a more efficient·OH scavenging action when competed with H2O2. The degradation mechanism of MT by Fe3O4/MWCNTs catalysis was discussed on the basis of analysis of the intermediates and the theoretical calculation of frontier electron densities and bond dissociation enthalpies of C-H and O-H of MT molecule. The estrogenic activity of the treated water was investigated during the catalytic reactions by human androgen ELISA test. The results showed that Fe3O4/MWCNTs-H2O2system could not only degrade MT but also remove its androgenic activity.(4) The MT degradation could be accelerated by the coupling of MW radiation with the heterogeneous Fenton reaction. The coupling of UV radiation could make MT transformed to be smaller compounds faster. The degradation efficiency increased with the rising of the UV irradiation intensity.