Mechanistic investigations in sono-hybrid (ultrasound/Fe2+/UVC) techniques of persulfate activation for degradation of Azorubine.

Persulfate-based oxidation of recalcitrant pollutants has been investigated as an alternative to OH radical based advanced oxidation processes due to distinct merits such as greater stability and non-selective persistent reactivity of SO4- oxidant species. The present study has attempted to highlight mechanistic features of persulfate-based decolorization of textile dye (Azorubine) using sono-hybrid techniques of activation. Three activation techniques, viz. sonolysis, Fe2+ ions and UVC light and combinations thereof, have been examined. UVC is revealed to be the most efficient decolorization technique. The mechanism of sonolysis (i.e. thermal activation of persulfate in the bubble-bulk interfacial region) is revealed to be almost independent of the mechanism of UVC. Fe2+ activation is revealed to have an adverse interaction with UVC due to scavenging of sulfate radicals by Fe2+ ions. The best hybrid activation technique for persulfate-based degradation and mineralization of Azorubine is UVC+ultrasound. Due to independent mechanisms, degradation and mineralization of the dye obtained with simultaneous application of UVC and ultrasound is nearly equal to the sum of degradation and mineralization obtained using individual techniques.