Transformation of 2,4‐dichlorophenoxy‐ethanoic 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). Copyright © 2004 Society of Chemical Industry