pH-modulated oxidation of organic pollutants for water decontamination: A deep insight into reactivity and oxidation pathway

Solution pH is one of the primary factors affecting the efficiency of water decontamination. Although the influence of pH on oxidants activation, catalyst activity, and reactive oxygen species have been widely explored, there is still a scarcity of systemic studies on the changes in the oxidation behavior of organic pollutants at different pH levels. Herein, we report the influence laws of pH on the forms, reactivities, active sites, degradation pathways, and products toxicities of organic pollutants. Changes in pH cause the protonation or deprotonation of organic pollutants and further affect their forms and chemistry (e.g., electrostatic force, hydrophobicity, and oxidation potential). The oxidation potential of organic pollutants follows the order: protonated form > pristine form > deprotonated form. Moreover, protonation or deprotonation can modify the active sites and degradation pathways of organic pollutants, wherein deprotonation renders them more susceptible to electrophilic attack, while protonation reduces their activity against electrophilic and nucleophilic attacks. Additionally, pH adjustments can modify the degradation pathway and the toxicity of transformation products. Overall, pH changes can affect the oxidation fate of organic pollutants by altering their structure, which distinguishes it from the effect of pH on oxidants or oxidant activation processes. Environmental Implication This work revealed that the forms, oxidation potentials, active sites, degradation pathway, and transformation products toxicity of organic pollutants exhibit obvious pH-dependent behavior. Deprotonation endows organic pollutants enhanced reactivity in oxidation reactions, whereas protonation suppresses it. Moreover, deprotonation renders organic pollutants more susceptible to electrophilic attack, whereas protonation reduces their activity against electrophilic and nucleophilic attacks. Importantly, the degradation pathway and product toxicity of organic pollutants can be rationally designed by adjusting solution pH. These findings provide valuable insights into the oxidation behavior of organic pollutants under different pH conditions, and offer design guidance for effective water decontamination.