Degradation Of Orange â…¡ By Heterogeneous Fenton Reactions

The textile effluents contain large quanties of orgainic dyes and strong alkaline substances. It is necessary to remove these toxic chemicals from the effluents before the disposal. Orange II is one of the widely used azo dyes in the textile industries, which is resistant to biological degradation, resulting in low efficiency of conventional biological treatment. The converntional methods, such as adsorption, membrane separation, electrochemical oxidation and flocculation have been studied to remove Orange II from aqueous solutions. However, these methods suffer some drawbacks such as low efficiency and high cost. As one of advanced oxidation processes(AOPs), the heterogeneous Fenton oxidation could be conducted in the circumnutral p H range with high efficiency and free of large volue of iron sludge. In this thesis, monodispersed α-Fe2O3 and Fe3O4 nanoparticles were synthesized using Fe Cl3·6H2O and Fe SO4 as precusors, respectively, via a facile hydrothermal method. The structural properties of α-Fe2O3 and Fe3O4 were charachertized by scaning electron microscopy and X-ray diffraction. It was found that the α-Fe2O3 exhibited a rod-like morphology with a lengthsof 70 nm and a width of 20 nm, and that the Fe3O4 showed a quasi-spherical morphology with a dimeter of 50 nm. The resulting α-Fe2O3 and Fe3O4 were utilized as catalysts for the heterogeneous Fenton-degradation of Orange II.It was found that the Fe2O3/H2O2 system showed outstanding performance for the Orange II degradation in the p H range of 3~10. With the optimized experimental condictions(initial p H = 3.0, substrate contrantion = 200 mg/L, H2O2 concentration = 1.5%, catalyst loading = 50 mg/L and reaction temperature = 30℃), the degradation rate of Orange II and COD were up to 98.74% and 73%, respectively, after 120 min. It was also confimed that the Fe2O3 exhibited excellent stability. No significant catalyst deactivation was noted in the five succeesive runs. The concentration of the dissolved iron ions was lower than 0.8 mg/L.The Fe3O4/H2O2 system showed good degradation performance in the p H range of 2-9. With the optimized experimental condictions(initial p H = 3.0, substrate contrantion = 400 mg/L, H2O2 concentration = 0.9%, catalyst loading = 400 mg/L and reaction temperature = 30℃), the degradation rate of Orange II and COD were up to 93.65% and 70%, respectively, after 150 min. It was indicated the Fe3O4 had poor stability. The activity of the catalyst decreased and significant leaching of iron occurred in the three successive runs.It was demonstrated that α-Fe2O3 and Fe3O4 showed superior catalytic performance for the degradation of Orange II. In comparison with the traditional iron ions, the exhibited distinct advantages in terms of p H range, iron leaching and facile separation. Thus, the α-Fe2O3 and Fe3O4 show great application potentials for the treatment of waste water.