Transformation of 2,4-dichlorophenoxyethanoic acid (2,4-D) by a photoassisted ferrous oxalate/H₂O₂ system

The kinetics of the dependence of pH, oxalate, and hydrogen peroxide concentrations on the degradation performance of the herbicide 2,4-dichlorophenoxyethanoic acid (2,4-D) was studied in a novel ferrous oxalate/H2O2/UV system. The formation and destruction of the primary intermediate, 2,4-dichlorophenol (2,4-DCP), was also monitored in the study. A rate enhancement of about 2.9 times was found when 1.2 mM of oxalate was added to the conventional Fe2+ /H2O2/UV process. However, excess oxalate suppressed the reaction due to the scavenging and light attenuation effects. The 2,4-D transformation at a lower initial pH was faster than that at a higher pH, and the different reaction mechanisms were investigated. In addition to the decay rates, the yield of the intermediate 2,4-DCP was also affected by the initial solution pH. The increment of hydrogen peroxide concentration did not increase the initial decay rates of 2,4-D, yet it improved the overall removal of 2,4-D and elevated the formation of the corresponding intermediate (2,4-DCP).