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Photoassisted degradation of nonbiodegradable Orange II is shown to be catalyzed by Nafion cation-transfer membranes exchanged with Fe ions in the presence of H2O2. The Nafion membranes in the oxidative media used degraded Orange II with similar kinetics as found in the homogeneous Fe3+/H2O2 photoassisted catalysis, avoiding the drawbacks of the homogeneous treatment. The treatment of this model textile dye is shown to proceed via a Fenton-like process without sludge production because of the selective H2O2 decomposition 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 membranes consisted mainly of Fe2O3 (78%) before reaction and Fe2O3 (14%) after light irradiation during Orange II oxidation, as found by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The size of the Fe particles in the Nafion was investigated by transmission electron microscopy (TEM) and turned out to be 37 ± 4 Å. These Q-sized Fe particles on the Nafion absorbed directly the light energy, avoiding the losses due to absorption by the contaminants as it is the case in homogeneous photoassisted Fenton processes. A simplified reaction mechanism for Orange II decomposition is suggested that is consistent with the experimental findings for solutions up to pH 4.8. The Fe redox reactions in the membranes under light were studied via XPS and spectrophotometric techniques. The effect of pretreatment of the azo dye making possible subsequent biological degradation was tested by BOD5. A drastic increase of the BOD5 values for the pretreated solutions was found with respect to the zero BOD5 value observed for nonpretreated Orange II.

Gold nanoparticles of 2-5 nm supported on woven fabrics of activated carbon fibers (ACF) were effective during CO oxidation at room temperature. To obtain a high metal dispersion, Au was deposited on ACF from aqueous solution of ethylenediamine complex [Au(en) 2 ]Cl 3 via ion exchange with protons of surface functional groups. The temperature-programmed decomposition method showed the presence of two main types of functional groups on the ACF surface: the first type was associated with carboxylic groups easily decomposing to CO 2 and the second one corresponded to more stable phenolic groups decomposing to CO. The concentration and the nature of surface functional groups was controlled using HNO 3 pretreatment followed by either calcination in He (300-1273 K) or by iron oxide deposition. The phenolic groups are able to attach Au 3+ ions, leading to the formation of small Au nanoparticles (< 5 nm) after reduction by H 2 . This was confirmed by high-resolution electron microscopy combined with X-ray energy-dispersive analysis. The catalyst with high Au dispersion demonstrated high activity in CO oxidation. The surface carboxylic groups decomposed during interaction with [Au(en) 2 ]Cl 3 solution and reduced Au 3+ to Au 0 , resulting in the formation of bigger (> 9 nm) Au agglomerates after reduction by H 2 . These catalysts demonstrated lower activity as compared to the ones containing mostly small Au nanoparticles. Complete removal of surface functional groups rendered an inert support that would not interact with the Au precursor. The oxidation state of gold in the Au/ACF catalysts was controlled by X-ray photoelectron spectroscopy before and after the reduction in H 2 . The high-temperature reduction in H 2 (673-773 K) was necessary to activate the catalyst, indicating that metallic gold nanoparticles are active during catalytic CO oxidation.  2004 Elsevier Inc. All rights reserved.