Assessing the discrepant role of anions in the transformation of reactive oxygen species in H2O2 and PDS system: A comparative kinetic analysis

Clarifying reactive oxygen species (ROS) variation in the presence of co-existing anions is significant for understanding the catalytic effect of magnetite (Fe₃O₄)-induced advanced oxidation processes (AOPs) in natural environment, yet this remains controversial. Herein, we compare the specific impacts of NO₃^-, SO₄^2-, and Cl^- on ROS (^•OH, SO₄^•-, O₂^•-, and ¹O₂) exposure concentration in H₂O₂ and peroxydisulfate (PDS) systems, as well as how these variations affect the catalytic efficiency by developing kinetic model. In both two systems, NO₃^- demonstrates no discernible effect on ROS, whereas SO₄^2- inhibits the exposure of all ROS and thus micropollutants degradation. Through theoretical calculation, it is proposed that SO₄^2- primarily exerts its influence through affecting the electronic structure over catalyst surface. Regarding Cl^-, it affects ROS exposure mainly by reacting with ROS. It shows inhibitory effect on ¹O₂ in both systems, but its suppressive impact on ^•OH is markedly more pronounced in H₂O₂ system compared to PDS system, which may be related to its rapid reactivity with SO₄^•-. Besides, the chlorine radicals (mainly ClO^•) generated through the reaction of Cl^- may exert a selective influence on micropollutants degradation. This study can help to re-understand the influence behavior of co-existing anions during AOPs.