Abstract

Birnessite (MnO2) can mediate organic pollutant oxidation, which was often interfered by the coexisting dissolved organic matter (DOM). However, it is still arguable the role of soil-derived DOM in the MnO2-mediated oxidation of organic pollutants. Here, we used three types of well-characterized DOM derived from soil heated at 50, 250, and 400 °C (DOM_50, DOM_250, and DOM_400, respectively) to evaluate the impacts of DOM type, DOM concentration, and environmental pH on the MnO2-mediated oxidation of sulfamethoxazole (SMX), a widely detected emerging pollutant. The MnO2-mediated SMX degradation rate was possibly promoted by DOM_250 and generally inhibited by DOM_50 and DOM_400, first inhibited and then promoted with increasing DOM concentration, and consistently less inhibited at higher pH. The higher polyphenolic content in DOM_250 than DOM_50 and DOM_400 likely produced more reactive semiquinone radicals to further degrade SMX, while other components (including condensed aromatics) mainly block or consume the reaction sites on the surface of MnO2 and thus inhibit SMX degradation. Our results reconcile the debate on the role of DOM in MnO2-mediated SMX oxidation and highlight that the molecular composition and concentration of DOM as well as the reaction pH are decisive in the overall promoting or inhibiting role of DOM.

Reference

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