Fe(II)/Cu(II) interaction on α-FeOOH, kaolin and TiO2 for interfacial reactions of 2-nitrophenol reductive transformation

• Interfacial reduction rates of 2-nitrophenol affected by Fe(II)/Cu(II) interaction.
• Fe(II)/Cu(II) interaction affect peak oxidation potential of active species.
• Fe(II)/Cu(II) molar ratio affect mineral-sorbed Fe(II) density.
• A lower peak oxidation potential indicates a higher reduction rates.
• A higher normalized sorbed Fe(II) density indicates a higher reduction rates.

Iron is the first abundant transition metal in the earth's crust. Meanwhile, copper is an essential trace element that can affect the reductive reactivity of sorbed Fe(II) species through Fe(II)/Cu(II) interaction. This study aims to elucidate the impact of the Fe(II)/Cu(II) interaction in 2-nitrophenol (2-NP) reductive transformation on kaolin, TiO2, and α-FeOOH. Kinetic measurements demonstrated that 2-NP reduction rates (k) by sorbed Fe(II) species can be promoted by adding Cu(II), whereas the impact of the Fe(II)/Cu(II) interaction on different minerals differed significantly with the k values. The increasing trend in the k values (kaolin < TiO2 < α-FeOOH) are consistent with the declining trend in the peak oxidation potential values (EP) of the active species obtained for the mineral-coated electrodes (kaolin/GC > TiO2/GC > α-FeOOH/GC), as well as with the increasing trend in the normalized sorbed Fe(II) density (kaolin < TiO2 < α-FeOOH). This study demonstrated that the enhanced interfacial reactions of 2-NP reduction on α-FeOOH are possibly attributed to the lower EP values and the higher k/sorbed Fe(II) values, thereby illustrating that 2-NP reduction on α-FeOOH is slightly more sensitive to the Fe(II)/Cu(II) interaction than the two other cases. These findings promote a general understanding of the Fe(II)/Cu(II) interaction and their impact on contaminant fate in actual subsurface environments.

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