Degradation of PFOA by hydrogen peroxide and persulfate activated by iron-modified diatomite

Perfluorooctanoic acid (PFOA) is one of the most problematic perfluoroalkyl compounds widely used to make fluoropolymers. The exceptional strength of the carbon–fluorine (CF) bond in PFOA makes it extremely resistant to oxidative attack even by hydroxyl radicals, resulting in its persistence in the environment. As a result, this study investigated generation of superoxide radical anions to reductively decompose such a highly oxidized chemical, PFOA. Catalyzed hydrogen peroxide (CHP) propagations and activated persulfate systems for generating reductive species such as superoxide radical anions along with oxidizing hydroxyl and sulfate radicals were examined. Improved activation mechanism for hydrogen peroxide and persulfate by using iron-modified diatomite (MD), which favorably leads the reaction to generation of the reductive radicals, was proposed. Three comparative systems were efficient in order of CHP > hydrogen peroxide-activated persulfate > alkaline-activated persulfate at PFOA decomposition of 83%, 69% and 48%, respectively, under given conditions. The heterogeneous system employing MD was also compared with a homogeneous system employing dissolved Fe ions to evaluate the effectiveness of MD. All the results supported that MD has significant catalytic activity for the degradation of PFOA when used to activate hydrogen peroxide and persulfate for the generation of superoxide radical anions. The reductive systems coupled with MD exhibited high decompose efficiency for the most recalcitrant chemical, PFOA and thus high potential for the decomposition of other problematic halogenated compounds.