Photodegradation of red 40 via a manganese (II)-based photo-Fenton like process

Red 40 (R40) is an azo dye continuously discharged into wastewater effluents from the food, cosmetic, and textile industries. It is highly persistent, toxic, and potentially carcinogenic to aquatic organisms. Advanced oxidation processes (AOPs) of the Fenton type using manganese (II) represent a promising alternative for the degradation of dyes such as R40 through the generation of ●OH radicals under UV irradiation, without the operational pH limitations. In this study, the degradation of R40 was evaluated using a solar photo-Fenton like process with Mn 2+ , H₂O₂, and UV radiation from sunlight. Experiments were designed using a 3 3 factorial design to assess the effects of pH (4, 6, and 8), and the concentrations (mg L −1 ) of Mn 2+ (5, 7, and 10) and H₂O₂ (50, 100, and 150). Additionally, the influence of the initial dye concentration and the regeneration capacity of Mn 2+ compared to Fe 2+ over two cycles were investigated. Complete degradation of R40 (100%) was achieved. The degradation kinetics followed a pseudo-first-order model, with a rate constant of 60.9 × 10 −3 min −1 . R40 was mineralized to CO₂ with a yield of 0.34 ± 0.01. Mn 2+ showed a higher regeneration capacity than Fe 2+ . This study lays the groundwork for the use of manganese (II) catalysts in the degradation of organic pollutants in water, with superior regeneration capacity compared to iron (II). • Mn (II) catalyzes effective photo-Fenton degradation of R40 dye at pH 4. • Increasing H 2 O 2 boosts degradation efficiency and kinetic constants. • Higher initial dye concentrations reduce degradation rate and efficiency. • Mn (II) shows superior catalyst regeneration compared to Fe (II) over cycles. • Photo-Fenton with Mn (II) achieves R40 mineralization to CO 2 .