Visible-light-responsive Fe-Based oxide nanomaterials for sustainable photo-Fenton degradation of hazardous phenols

Abstract Persistent pollutants like 2,4-dinitrophenol (2,4-DNP) pose serious risks to environmental and human health due to their toxicity and resistance to biodegradation. This study explores the degradation of 2,4-DNP using heterogeneous Fenton and photo-Fenton processes catalyzed by iron-based oxide nanomaterials synthesized hydrothermally. Four catalysts—Bi-Fe, Cu-Fe, Ag-Fe, and C/Ag-Fe, were prepared and characterized using XRD, SEM, and TEM to confirm their crystalline phases and nanostructures. Among them, Bi-Fe oxides exhibited the highest catalytic performance under visible light due to its porous morphology and mixed-phase composition. Under optimal photo-Fenton conditions (pH 3, 100 mg/L catalyst, 1000 mg/L H 2 O 2 ), Bi-Fe oxides achieved over 99.9% degradation of 10 mg/L 2,4-DNP within 240 min, with a rate constant of 0.024 min -1 . Cu-Fe demonstrated the best performance in conventional Fenton conditions, reaching 73.4% removal after 60 min. Ag-Fe and C/Ag-Fe showed moderate but consistent activity, with removal efficiencies up to 81.8% under photo-Fenton conditions. The impact of operational parameters—including catalyst dose, H 2 O 2 concentration, solution pH, and common anions—was systematically investigated. Sulfate and phosphate ions notably enhanced the photo-Fenton process. Zeta potential governs adsorption and stability of Bi–Fe, Cu–Fe oxides, and Fe 2 O 3 in Fenton systems, with all being strongly positive in acidic media but shifting negative at their respective isoelectric points (Cu–Fe ≈ 5.8, Bi–Fe ≈ 6.3, Fe 2 O 3 ≈ 7–7.8). Bi–Fe catalysts show higher stability under photo-Fenton (~ 92% activity, 0.7 mg/L leaching) than in dark Fenton (~ 82%, 1.2 mg/L), highlighting the role of light in reducing dissolution and sustaining long-term efficiency. Degradation pathways were elucidated using HPLC and IC, confirming the formation and subsequent breakdown of trihydroxybenzene and oxalic acid as intermediates. The results demonstrate that Bi-Fe system, driven by visible light, offers a sustainable and highly effective catalytic platform for degrading persistent phenolic pollutants. This study highlights the practical potential of photo-Fenton systems using iron-based nanomaterials for real-world wastewater treatment applications under mild and energy-efficient conditions.