Abstract

This work investigates the photo-Fenton degradation of azo dyes in an aqueous medium rich in sodium dodecyl sulfate (SDS), using methyl orange (MO) as a model contaminant. Chemometric modeling was integrated with mechanistic analysis to elucidate the role of the micellar pseudophase in radical distribution, dye partitioning, and overall reaction efficiency. A sequential experimental design strategy was applied, combining fractional factorial design and response surface methodology (RSM) to evaluate the individual and interactive effects of key operational variables and determine the optimal operating conditions for maximum degradation efficiency. Under optimized conditions (pH 2.85, [H2O2] = 100 mM, [Fe2+] = 0.5 mM, [SDS] = 13 mM, [MO] = 0.01 mM), MO degradation reached 98.4% in 5 min. Spectroscopic and partitioning studies revealed a strong affinity of MO for the micellar interface, indicating preferential localization in a microheterogeneous environment. Radical scavenging experiments confirmed that hydroxyl radicals are the dominant oxidizing species in water, while the reduction observed in the presence of SDS suggested secondary radical pathways derived from the surfactant under micellar conditions. Kinetic analyses highlighted the role of intermolecular interactions and micellar compartmentalization in radical generation. The optimized system was successfully extended to other azo dyes, underscoring the potential of surfactant-rich organized media to enhance photo-Fenton reactions in complex aqueous environments.

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