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 been reported, the chemistry of PMS in a catalyst-free system and its interactions with background oxyanions are still poorly understood. This paper demonstrated the activation of PMS by two prevalent oxyanions (phosphate and carbonate) and revealed the mechanisms for the enhanced atrazine (ATZ) degradation by PMS at neutral pH. Both oxyanions activated PMS to produce a sulfate radical (SO4•–), which reacts with ATZ rapidly, but phosphate exhibited a stronger effect than carbonate. The reaction between SO4•– and ATZ produced other possible radicals in the presence of dissolved oxygen (e.g., ATZ–O–O•), which subsequently generated singlet oxygen (1O2) with superoxide radical (O2•–) as a precursor. However, their contributions to ATZ degradation were minimal. The formation of radical species in the PMS–ATZ–phosphate system was supported by selective quenching and electron paramagnetic resonance measurements under different conditions [oxic, anoxic, and different solvents (H2O and D2O)]. Direct oxidation of ATZ by PMS was also observed. Overall, SO4•– and direct oxidation by PMS accounted for 75–78% and 22–25% of ATZ degradation, respectively.