Degradation and mechanism of 2,4-dichlorophenoxyacetic acid (2,4-D) by thermally activated persulfate oxidation.

The chlorinated phenoxy herbicide of 2,4-dichlorophenoxyacetic acid (2,4-D) was oxidized by thermally activated persulfate (TAP). This herbicide was studied for different persulfate dosages (0.97-7.29 g L), for varying initial pH levels (3-12) and temperatures (25-70 °C). Compared with Fe/PS, TAP could achieve a higher total organic carbon (TOC) removal under wider pH ranges of 3-12. Increasing the mole ratio of PS to 2,4-D favored for the decay of 2,4-D and the best performance was achieved at the ratio of 50. The 2,4-D degradation rate constant highly depended on the initial pH and temperature, in accordance with the Arrhenius model, with an apparent activation energy of 135.24 kJ mol. The study of scavenging radicals and the EPR confirmed the presence of both SO and OH. However, SO was the predominant oxidation radical for 2,4-D decay. The presence of both Cl and CO inhibited the degradation of 2,4-D, whereas the effect of NO could be negligible. Verified by GC/MS, HPLC and ion chromatography, a possible degradation mechanism was proposed.