Visible light-induced reduction of ferric iron and activation of persulfate in dissolved organic matter solutions: A green and efficient strategy to enhance fenton-like oxidation

The activation of persulfate (PS) in dissolved organic matter (DOM) solution using visible light has demonstrated potential for advanced wastewater treatment. This study presents a novel visible light-assisted homogeneous Fenton-like process (DOM-Fe³⁺-PS-Vis) for the efficient DOM degradation, based on the ligand-to-metal charge transfer (LMCT)-induced enhanced Fe³⁺ reduction and PS activation. The simultaneous addition of Fe³⁺ and PS to DOM-enriched solutions under visible light significantly improved PS activation, leading to the degradation of DOM and coexisting organic contaminants. The PS decomposition rate constant in the DOM-Fe³⁺-PS-Vis process was calculated to be 3.5–20.69 times higher than that of the DOM-PS-Vis, Fe³⁺-PS-Vis, and DOM-Fe³⁺-PS-Dark systems. Notably, over half of the decomposed PS in the DOM-Fe³⁺-PS-Vis process was activated by Fe²⁺ generated via the LMCT between DOM and Fe³⁺. SO₄[rad]⁻ and [rad]OH were identified as the dominant reactive species present in the DOM-Fe³⁺-PS-Vis process with the steady-state concentration of 1.63–4.11 × 10⁻¹³ M and 0.07 × 10⁻¹³ M, respectively, which were 2.4–81.5 and 0.5–7 times higher than those in the DOM-PS-Vis, Fe³⁺-PS-Vis, and DOM-Fe³⁺-PS-Dark systems. Additionally, hydrophobic components with more aromatic carbon in DOM were found to promote the catalytic performance of the DOM-Fe³⁺-PS-Vis process. This study highlights the efficiency and promise of LMCT-induced enhanced Fe³⁺ reduction and PS activation in DOM-enriched solutions under visible light for advanced wastewater treatment.