Sonochemical Degradation of Rhodamine B Using Oxidants, Hydrogen Peroxide/Peroxydisulfate/Peroxymonosulfate, with Fe2+ Ion: Proposed Pathway and Kinetics

This article addresses the sonochemical degradation of Rhodamine B (RB), a recalcitrant textile organic dye. The relative influence of extent of radical production by the cavitation bubbles and radical scavenging (or conservation) on the overall degradation of RB was assessed. Degradation of RB at different experimental conditions, such as pH, gases (air, argon [Ar], oxygen, and nitrogen), hydrogen peroxide (H2O2), peroxymonosulfate (PMS), peroxydisulfate (PDS), ferrous sulfate, and novel Fenton-like reagents (H2O2+ferrous sulfate, PDS+ferrous sulfate, and PMS+ferrous sulfate), was studied. Experimental results revealed that sonochemical degradation of RB is governed by the extent of utilization of HO center dot radicals. Ar-bubbled solution that produces higher HO center dot radicals gave a higher color-removal rate than other gases. Further, higher color removal was observed at solution pH of 3. Of all the experimental conditions studied, novel Fenton-like reagent, that is, PMS+ferrous sulfate-added solution, gave complete color removal. Mineralization study also revealed that higher removal of total organic carbon was attained at the condition of PMS with ferrous sulfate (pH 3) than with other experimental conditions. This result has been attributed to synergistic effects of HO center dot radicals and sulfate radicals providing effective interaction with the dye molecule. Degradation intermediates of RB through LCMS/GCMS analysis were also provided to support the degradation pathway.