Surface Characterisation of Cerium-Doped Silica Coatings Obtained by Sol-Gel

The chemical composition of cerium-doped silica coatings prepared via sol-gel were studied using X-ray photoelectron spectroscopy (XPS) in conjunction with Ar⁺-ion sputtering, Rutherford back-scattering spectroscopy (RBS) and photoluminescence (PL) spectroscopy. XPS results showed that cerium was incorporated in the silica network as Ce(III). The absence of PL emissions from Ce(III) was explained by a clustering of the ions producing a quenching of the luminescence. XPS combined with Ar⁺ and RBS showed that the distribution of Ce is not uniform across the coating, showing a maximum concentration in an inner layer of the coating.     

New layered double hydroxides containing intercalated manganese oxide species: synthesis and characterization

Manganese oxide species (MnO(x)) have been intercalated within the gallery spaces of Mg-Al layered double hydroxides (LDHs). Synthesis of these materials was achieved by ion-exchange of the LDH-nitrate precursor with permanganate anion followed by reduction with organic reagents, such as glucose, ethanol, and ascorbic acid. Elemental analysis, X-ray diffraction, FT-IR spectroscopy, Raman spectroscopy, HR-TEM, and N(2) sorption analyses have been used to characterize these materials. TEM micrographs of LDH-MnO(x) materials revealed platelike morphology, characteristic of hydrotalcite-like compounds. Chemical analysis results showed that permanganate anions exchanged with nitrate anions. FT-IR and Raman spectroscopy confirmed the reduction of the permanganate anions after treatment with the organic reagents. The XRD diffraction patterns of LDH-MnO(x) revealed that the layer structure is maintained after all synthetic steps. The observed basal spacings of intercalates varied depending on the reducing agent; the largest expansion was 9.93A, corresponding to the use of ascorbic acid. The specific surface areas were also affected according to the organic reagent used, indicating that the structural modifications in the interlayer domain observed by X-ray diffraction also influence the microtextural properties.     

Classification and pattern recognition of acyclic octenes based on mass spectra

Two SIMCA models were developed for the classification of acyclic octene isomers, which only form a fraction of a very complex product mixture obtained, for example, from the transformation of 1-butene. The effects of spectral transformation, namely autocorrelation and logarithmic intensity ratios transforms, and (square-root) scaling of the octane isomers mass-spectral data were investigated. Both the spectral-features preprocessing methods and scaling were found to be vital for an adequate development and improvement of the classification models. The best SIMCA models were successfully applied on gas-chromatography-mass spectroscopy (GC-MS) analysis collected from the dimerization of 1-butene over heterogeneous catalysts in the liquid phase.     

Colorimetric determination of persulfate with alcian blue

Alcian blue buffered at pH 2.5 is oxidized by persulfate. The plot of optical density at 615 mμ vs. concentration of persulfate (within the range of 10 to 80 μg) is linear. The assay is not affected by bromate and iodate.     

Effects of Adsorbed Polyaniline on Redox Processes on As(2)O(3) Surfaces

Polyaniline deposited on As(2)O(3) surface resulted in a new material, which was characterized by infrared spectoscopy, thermogravimetry, differential scanning calorimetry, scanning electron microscopy, X-ray diffraction, and cyclic voltammetry. The mass percentage of polymer deposited on oxide surface is approximately 13%. The scanning electron microscopy images as well as the X-ray diffraction patterns provided conclusive evidence that the oxide surface is coated by the polymer. The cyclic voltammograms of the polyaniline adsorbed on As(2)O(3) surface showed that the adsorbate exerts remarkable effects on redox processes on this oxide. The pure oxide exhibited two oxidation/reduction peaks at 0.25/-0.06 and 0.47/-0.25 V attributed tentatively to the processes As(2)O(3)(s)+6H(+)+6e(-)=2As(s)+3H(2)O and As(s)+3H(+)+3e(-)=AsH(3)(g), respectively. The polyaniline-coated sample exhibited a better-defined voltammogram in which the first oxidation peak of the oxide had its intensity increased about four times. Copyright 2000 Academic Press.