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

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.close384