The sonochemical decolourisation of textile azo dye Orange II: effects of Fenton type reagents and UV light.

The removal of Orange II (O-II) from aqueous solution under irradiation at 850 kHz has been studied. The effects of both homogeneous (with FeSO4/H2O2), and heterogeneous (Fe containing ZSM-5 zeolite/H2O2) Fenton type reagents are reported together with the effect of UV irradiation in combination with ultrasound both alone and with homogeneous Fenton-type reagent. Degrees of decolourisation of 6.5% and 28.9% were observed using UV radiation and ultrasound, respectively, whereas under the simultaneous irradiation of ultrasound and UV light, the decolourisation degree reached 47.8%, indicating a synergetic effect of ultrasound and UV light. The decolourisation was increased with the addition of Fenton's reagent with an optimal Fenton molar reagent ratio, Fe(2+):H2O2 of 1:50. In the combined process of ultrasound and UV light with the homogeneous Fenton system 80.8% decolourisation could be achieved after 2h indicating that UV improves this type of Orange II degradation. The degree of decolourisation obtained using the heterogeneous sono-Fenton system (Fe containing ZSM-5 zeolite catalysts+H2O2+ultrasound) were consistently lower than the traditional homogeneous ultrasound Fenton system. This can be attributed to the greater difficulty of the reaction between Fe ions and hydrogen peroxide. In all cases the Orange II ultrasonic decolourisation was found to follow first order kinetics.