Sonochemical degradation of azo dyes in aqueous solution

The sonochemical degradation of aqueous solutions of azobenzene (AB) and the related azo dyes methyl orange (MO), o-methyl red (p-MR) and p-methyl red (p-MR) was performed at 500 kHz and 50 W, under air, O-2 or Ar saturation at 288 K. Reaction products and intermediates were identified by HPLC-ES-MS. Total Organic Carbon was also determined as a function of reaction time. We propose a reaction mechanism based on the observed species and the extent and rate of TOC depletion. The effect of the dye structures and of the background gas on the sonochemical bleaching rates were investigated. The addition of Fe(II) increased the sonochemical bleaching rates, white O-3 Sparging increased considerably the mineralization extent.