Enhanced photo-fenton-like degradation of Orange II using iron-rich natural clay and oxalic acid under UVA-Vis irradiation

Abstract This study investigates the degradation of Orange II (ORII), a model azo dye, in water using a natural clay (NC)/Oxalate/UVA-Vis system via a heterogeneous photo-Fenton-like (HPF-like) process. Iron-rich natural clay acts as a sustainable photocatalyst in the presence of oxalic acid (OA) under UVA-Vis irradiation (366 nm) at free pH and ∼25 °C. Characterization (SEM-EDS, TEM, XRF, BET) confirmed 26.3 % iron content and a 52.66 m 2 g −1 surface area. ORII photodegradation (0.1 mM) in 1 g L −1 NC was enhanced by 5 mM oxalic acid, following first-order kinetics (t 1 / 2 ≈ 20 min) with 90 % removal after 2 h. The combined effect of UVA-Vis irradiation and the surface formation of ferrioxalate complexes facilitated the photoinduced reduction of iron, leading to its dissolution and the generation of hydroxyl radicals (HO · ) via a Fenton-like cycle, which were primarily responsible for ORII degradation. A synergistic effect was observed when H 2 O 2 was introduced further enhancing HO · radical formation. The NC/OA/UVA-Vis system exhibited degradation behavior similar to that of goethite and proved to be a cost-effective, eco-friendly method for pretreating water contaminated with azo dyes.