Catalytic performance of Fe3O4-CoO/Al2O3 catalyst in ozonation of2-(2,4-dichlorophenoxy)propionic acid, nitrobenzene and oxalic acid in water

Fe₃O4-CoO/Al₂O3 catalyst was prepared by incipient wetness impregnation using Fe(NO₃)₃-9H₂O and Co(NO₃)2-6H₂O as the precursors, and its catalytic performance was investigated in ozonation of 2-(2,4-dichlorophenoxy)propionic acid (2,4-DP), nitrobenzene and oxalic acid. The experimental results indicated that Fe₃O₄-CoO/Al₂O₃ catalyst enabled an interesting improvement of ozonation efficiency during the degradation of each organic pollutant, and the Fe₃O₄-CoO/Al₂O₃ catalytic ozonation system followed a radical-type mechanism. The kinetics of ozonation alone and Fe₃O₄-CoO/Al₂O₃ catalytic ozonation of three organic pollutants in aqueous solution were discussed under the mere consideration of direct ozone reaction and OH radical reaction to well investigate its performance. In the catalytic ozonation of 2,4-DP, the apparent reaction rate constants (k) were determined to be 1.456 x 10⁻² min-¹ for ozonation alone and 4.740 x 10⁻² min ⁻¹ for O₃/Fe₃O₄-CoO/Al₂O₃. And O₃/Fe₃O₄-CoO/Al₂O₃ had a larger R_ct (6.614 x 10⁻⁹) calculated by the relative method than O₃ did (1.800 x 10-⁹), showing O₃/Fe₃O₄-CoO/Al₂O₃ generated more hydroxyl radical. Similar results were also obtained in the catalytic ozonation of nitrobenzene and oxalic acid. The above results demonstrated that the catalytic performance of Fe₃O₄-CoO/Al₂O₃ in ozonation of studied organic substance was universal to a certain degree.