Activation of Peroxymonosulfate by Phosphate and Carbonate for the Abatement of Atrazine: Roles of Radical and Nonradical Species

While the activation mechanisms of peroxymonosulfate(PMS) by various homogeneous and heterogeneous catalysts have beenreported, the chemistry of PMS in a catalyst-free system and its interactionswith background oxyanions are still poorly understood. This paperdemonstrated the activation of PMS by two prevalent oxyanions (phosphateand carbonate) and revealed the mechanisms for the enhanced atrazine(ATZ) degradation by PMS at neutral pH. Both oxyanions activated PMS toproduce a sulfate radical (SO4 center dot-), which reacts with ATZ rapidly, butphosphate exhibited a stronger effect than carbonate. The reaction betweenSO(4)(center dot-) and ATZ produced other possible radicals in the presence of dissolvedoxygen (e.g., ATZ-O-O-center dot), which subsequently generated singlet oxygen(O-1(2)) with superoxide radical (O-2(center dot-)) as a precursor. However, their contributions to ATZ degradation were minimal. The formationof radical species in the PMS-ATZ-phosphate system was supported by selective quenching and electron paramagnetic resonancemeasurements under different conditions [oxic, anoxic, and different solvents (H2O and D2O)]. Direct oxidation of ATZ by PMSwas also observed. Overall, SO4 center dot- and direct oxidation by PMS accounted for 75-78% and 22-25% of ATZ degradation,respectively.