Degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) using cobalt-peroxymonosulfate in Fenton-like process

2,4-Dichlorophenoxyacetic acid (2,4-D) was degraded using both Fenton reagent and cobalt-peroxymonosulfate (Co/PMS) advanced oxidation processes (AOPs) in the dark and under solar radiation as source of light in photo-assisted AOPs. Four different concentrations of the transition metal (cobalt or Fe(II)) were tested maintaining constant the initial oxidant agent (PMS or hydrogen peroxide) concentration. The effect of temperature was investigated in the dark for both processes and the activation energy was determined for each process. For the processes performed in the dark, the maximum degradation for 2,4-D (86%) was achieved using Co/PMS (0.25 mmol L−1 of cobalt) in 48 min, while the dark Fenton achieved a maximum degradation of 2,4-D (17%) using 0.1 mmol L−1 of Fe(II). Complete 2,4-D degradation was achieved when the samples were irradiated by the sun using the same conditions described for 5 min of reaction time. In the case of solar-driven Co/PMS, complete 2,4-D degradation was achieved after 40 min using 0.004 mmol L−1 of cobalt. Pseudo first order reaction rate constants determined in the dark for Fe/H2O2 and Co/PMS processes indicated that Co/PMS is able to perform the degradation of the pesticide at the same reaction rate as Fenton reagent, despite the fact that cobalt concentration is 100 times lower than Fe(II) concentration. Solar light increased the kinetic constant in the Co/PMS complex by 33 times compared with that obtained under dark conditions. Attempt to follow 2,4-D degradation using the photo-Fenton process was not possible since complete degradation occurred after the first 5 min of irradiation using [Fe] = 0.1 mmol L−1.