Photoassisted Fenton degradation of nonbiodegradable azo dye (Orange II) in Fe-free solutions mediated by cation transfer membranes

Photoassisted degradation of nonbiodegradable Orange II is shown to be cata lyzed by Nafion cation-transfer membranes exchanged with Fe ions in the pre sence of H2O2. The Nafion membranes in the oxidative media used degraded Or ange II with similar kinetics as found in the homogeneous Fe3+/H2O2 photoas sisted catalysis, avoiding the drawbacks of the homogeneous treatment. The treatment of this model textile dye is shown to proceed via a Fenton-like p rocess without sludge production because of the selective H2O2 decompositio n on the Fe ions exchanged on the membrane. The effect of the concentration of H2O2, solution pH, azo dye concentration, and light intensity (visible light) on the degradation of Orange is reported in detail. The activity of the membranes during the Orange II decomposition was tested for 1500 h and was observed to remain fairly stable within this period. The Fe/Nafion memb ranes consisted mainly of Fe2O3 (78%) before reaction and Fe2O3 (14%) after light irradiation during Orange II oxidation, as found by X-ray photoelect ron spectroscopy (XPS) and X-ray diffraction (XRD). The size of the Fe part icles in the Nafion was investigated by transmission electron microscopy (T EM) and turned out to be 37 +/- 4 Angstrom. These Q-sized Fe particles on t he Nafion absorbed directly the light energy, avoiding the losses due to ab sorption by the contaminants as it is the case in homogeneous photoassisted Fenton processes. A simplified reaction mechanism for Orange II decomposit ion is suggested that is consistent with the experimental findings for solu tions up to pH 4.8. The Fe redox reactions in the membranes under light wer e studied via XPS and spectrophotometric techniques. The effect of pretreat ment of the azo dye making possible subsequent biological degradation was t ested by BOD5. A drastic increase of the BOD5 values for the pretreated sol utions was found with respect to the zero BOD5 value observed for nonpretre ated Orange II.