Degradation Of Acid Azo Dyes Using Fenton And Persulfate Process Catalyzed By Magnetite Nano-sized Particles

Azo dyes are characterized by the bearing of azo-bonds（-N=N-） in association of aromatic rings, which are the major synthetic colorants used in printing and dying industries. Most azo dyes are refractory to biodegradation, the effluent containing azo dyes treated by conventional biological treatment process may no longer considered as a promising process. The commercially available magnetic nano particles（ MNP-Fe₃O₄） has advantages of fast-effective and ease of operation in removing dyes from aqueous solution. In this study, magnetic nano-sized particles（ MNP-Fe₃O₄） were used as catalyst to activate Fenton and persulfate reaction for degradation of an acid azo dye, New coccine（ NC）. At the same time, this paper was researched the reaction mechanism about these two processes, including adsorption and oxidation.Findings showed that the adsorption of NC onto MNP-Fe₃O₄ plays an important role in removal of dye from solution. Higher dye adsorbed at lower p H. The equilibrium adsorption of NC on MNP-Fe₃O₄ was 3.56×10-5 mol/g, and the degradation of NC was 90.29% in the optimum p H which the value is 2.5. Meanwhile, the adsorption was in line with the Langmuir isotherm, and it was chemical adsorption.Paper results indicated that the rate of removal NC was different in these two systems（ MNP-Fe₃O₄/Fenton and MNP-Fe₃O₄/PS）. Key factors affecting the performance of Fenton and PS systems, including dose of MNP-Fe₃O₄, p H, dosage of oxidizer, and temperature, were evaluated. Although high dose of MNP-Fe₃O₄ could accelerate the reaction in both two processes, the dye degradation efficiency was not equally proportional increase. The appropriate concentration of oxidizer also can enhance the decolorization of NC. In addition, experimental results showed that the rate of degradation increased with increasing temperature in MNP-Fe₃O₄/PS, which can be mainly ascribed to higher quantity of Fe2+ ions being released and higher amount of ·OH and SO4-· radicals were generated at higher temperature. When the temperature of system reach 60 oC, the concentration of NC（ 2x10-5M）drastically decreased to 95% within 20 min MNP-Fe₃O₄/PS reaction time. And the Arrhenius activation energy for the PS activated with MNP was 101.74 kcal/mol. In addition, findings indicated that the synergistic effect of ultrasound with these two systems（ MNP-Fe₃O₄/Fenton/US and MNP-Fe₃O₄/PS/US） can improved the dye degradation significantly, and MNP-Fe₃O₄/Fenton/US process is more effective than that of MNP-Fe₃O₄/PS/US. By using MNP-Fe₃O₄/Fenton, the addition of only 5 min ultrasound with US power density of 120W/L, up to 90% of NC could be removed within 15 min. In MNP-Fe₃O₄/PS, the concentration of NC decreased to 62.50%, 70.31%, 88.18% and 97.67% within 10 min, 20 min, 30 min and 45 min ultrasound reaction time, respectively, all of these were better than MNP-Fe₃O₄/PS which the rate of degradation was 50.32%.Addiction, finding from the experiments of the reaction mechanism showed that a positive synergistic effect was observed in MNP-Fe₃O₄/Fenton, including adsorption and oxidation, and the adsorption rate is much larger than oxidation. On the contrary, the main reaction in MNP-Fe₃O₄/PS is oxidation. Fenton reaction happened on the surface of MNP, PS was not, it happened in the solution mostly.