Quantifying Radical Pathways in a 425 kHz Sonoreactor: Coupled Calorimetric–Multidosimetric Assessment and Process Variable Impacts in Sunset Yellow FCF Degradation

This study quantifies radical pathways and the influence of process variables in a 425 kHz sonoreactor through a coupled calorimetric and multidosimetric approach during Sunset Yellow FCF degradation. Reactive oxygen species were mapped with four complementary dosimeters. Potassium iodide (KI) tracked interfacial hydroxyl radicals (^•OH). KI with ammonium heptamolybdate (AHM) captured ^•OH radicals together with hydrogen peroxide (H₂O₂). Bulk H₂O₂ accumulation integrated the recombination branch. Hydroxylation of 4-nitrophenol to 4-nitrocatechol acted as a selective near-interface ^•OH probe. Calorimetry showed that acoustic power density increased with set power and decreased with liquid height. All four dosimeters rose coherently with this variable, indicating that stronger driving elevated ^•OH generation while channeling a larger fraction into H₂O₂ through recombination. Process studies linked energy delivery to performance across operating conditions. Higher power accelerated pseudo-first order dye decay. Increasing initial dye concentration reduced fractional removal at fixed power, consistent with a radical-limited regime. Acidic media enhanced degradation by maintaining a stronger hydroxyl radical to water redox couple and by improving H₂O₂ persistence. Near neutral and alkaline media exhibited carbonate and bicarbonate scavenging of hydroxyl radicals and faster peroxide loss. Dissolved gas identity strongly modulated activity. Oxygen and argon outperformed air and carbon dioxide due to the combined thermophysical and chemical roles of the bubble gas. The calorimetry anchored and multidosimetric protocol provides a general route to compare reactors, optimize conditions, and support scale-up based on delivered energy density. Ultrasonication-driven degradation is a robust, practical technology for advanced treatment of dye-laden waters.