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To acquire a better understanding of the influence exerted by the presence of Cd2+ during the process of transforming ferrihydrite to goethite, the morphological and structural changes of several samples obtained by the addition of Cd2+ to a suspension of nascent goethite were explored, and their chemical reactivity in acid media assessed. The samples (series Gi) were obtained by adding, at different times during the synthesis process, Cd2+ ions to ferrihydrite (Fe5HO8.4H2O) formed in alkaline media. The suspensions were aged for 5 days at 70°C, and the amorphous materials were extracted using a HCl solution (series GHCl-i). The X-ray diffraction (XRD) patterns showed that a goethite-like phase was formed, and chemical analyses indicated that the Cd content, xCd, increased with the earlier addition of the Cd2+ ions to the Fe oxyhydroxide suspension. Lattice parameters and cell volume, obtained by the Rietveld simulation of XRD data, indicated an enlargement of the cell parameters of goethite in line with the Cd-for-Fe substitution. In order to determine the influence of oxalate ions on the non-extracted solids, a second set of samples was also prepared that was kept in contact with an ammonium oxalate solution for 4 h (series Gox-i). The dissolution behavior of two series of Cd goethites and of a third series, obtained from coprecipitation of Fe3+ and Cd2+ ions in alkaline media, was observed. Kinetics measurements in 4 M HCl showed that the initial dissolution rate of samples Gox-i decreased with aging time, while the opposite effect was observed for series GHCl-i. Dissolution–time curves were well described by the Kabai equation, and activation energies were calculated using the Arrhenius equation. The results indicate that the presence of Cd during the crystallization process of goethite leads to the formation of a Cd goethite with modified morphology, structural parameters, and chemical reactivity.

Polyethylene (PE)/clay nanocomposites were prepared by melt mixing using PE grafted with maleic anhydride (PEg) as compatibilizer. Concentrations between 2 and 15 wt% of an organophilic montmorillonite (MMT) and concentration ratios of 1:1, 2:1 and 3:1 of PEg/MMT were employed. The materials were characterized using X-ray diffraction, scanning electron microscopy (SEM) and thermogravimetry. The SEM images show that the presence of PEg results in a large degree of exfoliation at all clay concentrations. For 5 wt% MMT, the best degree of exfoliation is obtained for a 2:1 ratio of PEg/MMT. This ratio results in higher increase in the elastic modulus, mainly at low frequencies, with respect to that of the corresponding matrix. As the clay concentration increases, for a 2:1 ratio of PEg/MMT, the dynamic moduli increase showing pseudo solid-like behavior at clay concentrations higher than 8 wt%. Moreover, the nanocomposites show rheological properties that are affected by annealing at 200 C signaling further exfoliation or improved platelet and tactoid distributions. The oxygen permeability of PE decreases gradually with the clay concentration, reaching a maximum reduction of *30% for 15 wt% MMT.

The permeability and wear behavior of nanocomposites based on polypropylene (PP), polypropylene grafted with maleic anhydride (PPg), and montmorillonite (MMT) have been studied. Clay concentrations of 2-15 wt % and a constant PPg:MMT ratio of 3 : 1 were considered. The wear behavior of all materials was studied using the ''pin-on-disc'' technique. The results indicate that, for given clay concentration, the wear resistance decreases with applied load and that the composites are $ 20 times more resistant than their matrices. Moreover, the wear rate of the nanocomposites decreases as the clay concentration increases while that of the corresponding matrices increases. The PP, matrices, and composites display similar values of friction coefficient that neither changes with normal load. Additionally, the oxygen permeability of PP is gradually reduced by the increase of both clay and PPg concentration, being the effect of the filler tactoids much larger than that of the compatibilizer. V C 2012 Wiley Periodicals, Inc. J Appl Polym Sci 125: E495-E502, 2012

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This contribution provides insight on the elimination of heavy metals from water resources using magnetic separation. Nanocomposites based on magnetite and chitosan were prepared. An exhaustive characterization of the magnetic adsorbents was developed.Adsorption assays were performed in batch using Cu, Zn, Cd and Cr as model heavy metals. The efficiency of magnetic adsorbents followed the order: Cu  Cd  Zn  Cr, with maximum values of 188, 159, 72 and 46 mg of Me/g of nanocomposite, respectively. Kinetics and mechanistic issues were studied. The magnetic materials were efficient for five to eight cycles using Cu(II),Cd(II) and Cr(VI) .

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