New insights into stoichiometric efficiency and synergistic mechanism of persulfate activation by zero-valent bimetal (Iron/Copper) for organic pollutant degradation.

Extensive studies have been devoting to investigating the catalytic efficiency of zero-valent iron (Fe)-based bimetals with persulfate (PS), while little is known in the stoichiometric efficiency, underlying mechanisms and reaction center of zero-valent bimetallic catalysts in activating PS. Herein, nanoscale zero-valent Fe/Cu catalysts in decomposing 2,4-dichlorophenol (DCP) have been investigated. The results show that the increase of Cu ratio from 0 to 0.75 significantly enhances the DCP degradation with a rate constant of 0.025 min for Fe to 0.097 min for Fe/Cu(0.75) at pH ∼3.3, indicating Cu is likely the predominate reaction centers over Fe. The PS decomposition is reduced with the increase of Cu ratios, suggesting the stoichiometric efficiency of Fe/Cu in activating PS is notably enhanced from 0.024 for Fe to 0.11 for Fe/Cu(0.75). Analyses indicate Cu atoms are likely the predominant reaction site for DCP decomposition, and Fe atoms synergistically enhance the activity of Cu as indicated by DFT calculations. Both SO and ⦁OH radicals are responsible for reactions, and the contribution of SO is decreased at higher pH conditions. The findings of this work provide insight into the stoichiometric efficiency and the reaction center of Fe/Cu catalysts to activate PS for pollutant removals.