Far-UVC direct photolysis of iohexol and acetochlor: an experimental and mechanism study

Recently, the emission of 222 nm Far-UVC krypton chloride (KrCl*) excimer lamps, has gained widespread attention in the field of water treatment. This study compared the degradation kinetics of IOX and ACE under UV₂₂₂ and UV₂₅₄ irradiation. The results demonstrated that UV₂₂₂ irradiation exhibited higher efficiency, increasing the removal rates of IOX and ACE from 72.46% and 19.31% to 100%, respectively. Probe experiments and electron paramagnetic resonance (EPR) spectroscopy were used to identify the major active species generated during UV₂₂₂ irradiation ([HO•]_ss = 2.74 × 10^-13 M). In addition, the effect of pH, pollutant concentration, anions, and natural organic matter (NOM) on the photolysis of IOX and ACE was investigated. The results indicated that IOX and ACE exhibited minimal dependence on pH, and IOX showed low sensitivity to water matrix components. Finally, the electrical energy consumption of the IOX and ACE photolysis by UV₂₂₂ and UV₂₅₄ irradiation was evaluated. The results revealed that UV₂₂₂ irradiation demonstrated superior economic benefits (EE/O_UV222/IOX = 0.59951 KWh/L, EE/O_UV222/ACE = 0.25443 KWh/L), effectively reducing treatment costs. This study elucidated the photolysis characteristics of IOX and ACE under Far-UVC irradiation, providing a reference for the selection of process conditions in practical applications.