Mechanistic analysis of sono-photolysis degradation of carmoisine

•Identification of mechanistic interactions between sonolysis and photolysis.•Analysis of experimental results with simulations of cavitation bubble dynamics.•Degradation reactions initiated by oxidizing radicals generated by photolysis.•Sonolysis enhances kinetics of degradation and total mineralization.•Salt addition boosts effect of sonolysis by increasing ionic strength of solution.

The hybrid advanced oxidation process (AOP) of sono-photolysis, in which sonication and photolysis (UV-C/H2O2) are applied simultaneously, is known to give effective degradation of several bio-recalcitrant pollutants. This study has attempted to identify the links and interactions between the mechanisms of individual AOPs of sonolysis and photolysis, when applied simultaneously. Experimental results have been analyzed concurrently with the simulations of cavitation bubble dynamics. It is revealed that oxidizing (OH) radicals generated through photolysis contribute mostly to degradation reactions. Due to highly sporadic nature of transient cavitation, the contribution of sonolysis to degradation is rather subordinate as compared to photolysis. Nonetheless, faster degradation and higher mineralization in sono-photolysis, as compared to photolysis alone, essentially points at supportive role of ultrasound in the hybrid AOP. Addition of electrolytes (or salt) to the reaction mixture during sono-photolysis treatment causes effective partitioning of the pollutant molecules in the interfacial region of transient cavitation bubble, which results in further enhancement of degradation kinetics and mineralization. Although the present study has employed Carmoisine as model pollutant, the mechanistic principles identified in this study, and their manifestations in terms of degradation/mineralization of pollutants are applicable to any other bio-recalcitrant pollutant.

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