Efficiency and mechanism of 2,4-dichlorophenol degradation by the UV/IO₄^- process

This study explores the efficiency and kinetics of the photoactivated periodate process for the degradation of 2,4-dichlorophenol (2,4-DCP) in water. The obtained results show that the degradation rate was considerably higher for UV/IO₄^- compared to UV irradiation alone. Pseudo first-order reaction rate kinetics were obtained for all process conditions. The pH did not have a significant impact on the decomposition of 2,4-DCP using photoactivated periodate. Therefore, the applied method can be used to treat (waste)water at various pH. By raising the initial concentration of periodate to 5 mM, the degradation rate increased, while it decreased again at a concentration of 8 mM. As the 2,4-DCP concentration increased, the removal rate decreased. The extent of degradation was observed to be proportional with the UV intensity. A mechanistic study revealed that iodine radicals dominated the degradation of 2,4-DCP by photoactivated periodate, whereas OH and O(³P) only played a minor role. At pH 5.0, all chlorine atoms in 2,4-DCP were released as chloride ions in the UV/IO₄^- process, hence reaching a total dechlorination. Finally, the presence of inorganic salts, even at high levels, did not significantly impact the degradation. According to the results achieved in this study, the UV/IO₄^- system can be considered as a valuable alternative to treat effluents containing chlorinated organic compounds such as pulp and paper mill effluents and brine (waste)water.