Sulfite activation using FeO as a source of ferrous ions for fluoxetine degradation: A collaborated experimental and DFT study

In this study, we constructed an advanced oxidation process using FeO for sulfite (S(IV)) activation. By selecting antidepressant fluoxetine (FLX) as the target, the FeO/S(IV) system's performance was investigated. Up to 84.4% of FLX could be rapidly eliminated in 17.5 min under optimal reaction conditions. The results confirmed that the S(IV) activation was dominantly attributed to the released Fe²⁺ from FeO, rather than an interface reaction, supported by theoretical calculations and electrochemical characterization. Besides, the Fe–S(IV) complex geometry was determined using density functional theory (DFT), indicating a Fe–O–S ligand form. Energy files demonstrate the decomposition of FeSO₃⁺ complex might be endothermic. These findings provide new insight into the Fe(II)/S(IV) mechanism. The generated SO₄^•− primarily caused FLX removal, where 23 product types were detected. The degradation pathway was proposed, mostly containing hydroxylation and ring-opening, which decreased the toxicity of FLX. Furthermore, the FeO/S(IV) system had good reusability and applicability, maintaining high efficiency in real water. Compared to peroxydisulfate and peroxymonosulfate, S(IV) had obvious advantages in FeO-induced activation. This research discloses a promising technology for the FeO/S(IV) water treatment system.