High temperature dependence of 2,4-dichlorophenoxyacetic acid degradation by Fe(3+)/H(2)O(2) system

Abstract

This study demonstrates the importance of reaction temperature on the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D). In addition, we provide a mechanistic explanation for the temperature dependence of 2,4-D degradation. Thermal enhancement of 2,4-D degradation and H2O2 decomposition was measured in the absence and in the presence of the .OH scavenger (t-butanol). The half-life for 2,4-D degradation was reduced by more than 70-fold in the absence of t-butanol, and by more than 700-fold, in the presence of t-butanol, when the reaction temperature was increased from 10 to 50 °C. In addition, similar temperature relationships were found for H2O2 decomposition. The major reason for the high temperature dependence of the Fe3+/H2O2 system in the case of 2,4-D degradation is due to the dependence of the initiation reaction of the Fe3+/H2O2 system (i.e., Fe3+ + H2O2 → Fe2+ + HO. 2 + H+ upon temperature), which is entirely consistent with the kinetics of the activation energy. In the presence of a .OH scavenger, the initiation reaction of the Fe3+/H2O2 system became a determining factor of this temperature dependence, whereas in the absence of .OH scavenger, several other radical reactions played a role and this result in an apparent decrease in the activation energy for 2,4-D degradation. Moreover, the enhanced 2,4-D removal at higher temperatures did not alter H2O2 utilization. The practical implications of the thermal enhancement of the Fe3+/H2O2 system are discussed.