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Kinetics of Fe₃O₄–CoO/Al₂O₃ catalytic ozonation of the herbicide 2-(2,4-dichlorophenoxy) propionic acid

Tong, Shao-Ping, Shi, Rui, Zhang, Hua, Ma, Chun-an
Journal of hazardous materials 2011 v.185 no.1 pp. 162-167
adsorption, aluminum oxide, catalysts, chemical degradation, herbicides, hydroxyl radicals, iron oxides, oxidation, ozonation, ozone, pH, propionic acid, reaction kinetics
The presence of Fe₃O₄–CoO/Al₂O₃ can improve degradation efficiency significantly during the ozonation of the herbicide 2-(2,4-dichlorophenoxy) propionic acid (2,4-DP). The main factors affecting degradation efficiency, such as pH, the catalyst concentration and addition of the scavenger, were investigated. The kinetics of the catalytic ozonation are also discussed. The results indicate that two factors, the oxidation after adsorption of 2,4-DP and the oxidation of hydroxyl radicals (OH), lead to a great enhancement in ozonation efficiency during the catalytic ozonation of 2,4-DP in the presence of Fe₃O₄–CoO/Al₂O₃, in which the oxidation of the OH plays an important role. Under controlled conditions, the apparent reaction rate constants for the degradation of 2,4-DP were determined to be 2.567×10⁻⁴s⁻¹ for O₃ and 1.840×10⁻³s⁻¹ for O₃/Fe₃O₄–CoO/Al₂O₃. The results from the analysis of the reaction kinetics using the relative method showed that O₃/Fe₃O₄–CoO/Al₂O₃ possessed a larger Rct (Rct is defined as the ratio of the OH exposure to the O₃ exposure, Rct=∫CO(1)OHt dt/∫CO(1) O₃ dt than O₃, indicating that O₃/Fe₃O₄–CoO/Al₂O₃ produced more hydroxyl radicals.