Insights into the generation of multiple reactive species in UV₂₅₄/PMS/I⁻ system and their roles for degradation of phenolic and non-phenolic pollutants

An innovative technology for the removal of phenolic and non-phenolic organic pollutants from aqueous solution was developed by combining UV₂₅₄ irradiation, peroxymonosulfate (PMS), and iodide ions (I⁻). Effects of pH, ratio of [I⁻]/[PMS], initial concentration of pollutant, dissolved organic matter (DOM) and typical inorganic constituents of environmental water on the degradation of studied pollutants with UV₂₅₄/PMS/I⁻ system were examined. The results showed that pH and [I⁻]/[PMS] exhibited significant impact on the degradation of pollutants during UV₂₅₄/PMS/I⁻ process. As the ratio of [I⁻]/[PMS] increased from 0.1 to 10.0, the removal efficiencies of phenolic pollutants remarkably increased, but those of non-phenolic pollutants decreased. The DOM at high concentration obviously inhibited the degradation of pollutants during UV₂₅₄/PMS/I⁻ process. Meanwhile, the occurrence of NO₃⁻ can slightly enhance the degradation of pollutants, and SO₄²⁻, Cl⁻, and HCO₄⁻ ions had no significant effects on UV₂₅₄/PMS/I⁻ system. The abundant reactive species including [rad]OH, SO₄[rad]⁻, and I[rad]/I₂[rad]⁻ during UV₂₅₄/PMS/I⁻ process were generated based on electron spin resonance, fluorescence spectroscopy and steady-state concentration analysis. Quenching experimental results indicated that I[rad]/I₂[rad]⁻ can selectively degrade phenolic pollutants via one-electron oxidation. This study provided a reference for the application of reactive radicals involved oxidative technique in water purification.