DFT Study on the\nMechanism of As(III) Oxidation in\nthe Presence of Fe(II) and O<sub>2</sub>

In natural aquatic environments, the fate of arsenic\n(As) is significantly\ninfluenced by redox processes involving iron (Fe) species. Understanding\nthe mechanisms governing As transformation in the presence of Fe species\nis crucial for comprehending its environmental impact and advancing\nremediation strategies. In this work, the oxidation of As(III) in\noxygenated Fe(II) solutions was investigated. Density functional theory\n(DFT) methods were employed to explore the reaction of Fe(II) with <sup>3</sup>O<sub>2</sub> and subsequent As(III) oxidation by reactive\nspecies generated from Fe(II) oxidation. Electron paramagnetic resonance\nanalysis was utilized to confirm the formation of reactive species\nin the solution. Based on these results, it is concluded that <sup>1</sup>O<sub>2</sub>, ·O<sub>2</sub>H, and Fe(IV) are the critical\noxidants responsible for As(III) oxidation in oxygenated Fe(II) solutions\nunder circumneutral conditions. <sup>1</sup>O<sub>2</sub> readily\noxidizes As(III) by forming an arsenic superoxide AsO<sub>5</sub>H<sub>3</sub>. Interaction of As(III) with ·O<sub>2</sub>H or Fe(IV)\nleads to As(IV), which is further oxidized to As(V) by <sup>3</sup>O<sub>2</sub>, Fe(III), and Fe(IV).