Kinetic modeling and mechanisms of parahalogenated phenols degradation by UV222/H2O2

Advanced oxidation technology of KrCl excimer lamp activated H2O2 (UV222/H2O2) have been received widespread attention in the field of water treatment recently, due to the higher radical yield and environmentally friendly nature compared to UV254/H2O2. In this investigation, four representative parahalogenated phenols (HPs) degradation kinetic and mechanisms by UV222 alone and UV222/H2O2 were studied, respectively. The results showed that the photolysis rate constants (kobs) under UV222 followed the order of p-Chlorophenol (p-CP) > p-Fluorophenol (p-FP) > p-Bromophenol (p-BP) > p-Iodophenol (p-IP), and the degradation rate constants (kobs) by UV222/H2O2 followed the order of p-FP > p-CP > p-BP > p-IP. The molar absorption coefficient (ε222nm) and quantum yield (Φ222nm) of HPs photolysis were measured. Kinetic model simulating results are in fair agreement with the experimental results. Through HPLC-MS analysis and DFT calculation, the impact of halogen ions on the degradation kinetics of HPS by UV222 and UV222/H2O2 was found, the possible reaction pathways and mechanisms were proposed. Compared with UV254/H2O2 for removing p-CP, UV222/H2O2 was much more energy efficient.