Degradation of triclosan by UV/H₂O₂: Kinetics and reaction mechanism

The aim of this work is to investigate the transformation efficiency of triclosan (TCS) at the wavelength of 254 nm in the presence of H₂O₂. The effects of oxidant dosage, TCS concentration, NOM, and pH were evaluated. Most of these kinetic results could be described by a steady-state kinetic model. Increasing dosage of H₂O₂ increased the observed pseudo-first-order rate constant for TCS degradation (k_obs) when H₂O₂<1 mmol/L. However, when H₂O₂>1 mmol/L, k_obs decreased with H₂O₂ dosage increased due to the effects of radical scavenging by H₂O₂. Increasing concentration of TCS decreased the steady-state concentration of HO·. The presence of NOM significantly decreased k_obs due to the effects of UV absorption and radical scavenging. When pH=9, k_obs was higher than that when pH=5-7. This could be attributed that the deprotonated TCS was more reactive than protonated TCS. Six products were detected in TCS treated by UV/H₂O₂. A tentative pathway was proposed, where dechlorination and hydroxylation reaction were involved.