Obtenção de nanocompositos de oxidos semicondutores inseridos em vidro poroso Vycor via decomposição de precursores metalorganicos

AUTOR(ES)
DATA DE PUBLICAÇÃO

2000

RESUMO

The aim of the present work was the preparation of nanocomposites containing semicondutor oxides such as Bi2O3, CeO2, CuO and Porous Vycor Glass (PVG). In the employed methodology, PVG plates were impregnated with metallorganic precursors which yield the desired oxides throught thermal decomposition. Bi(III), Ce(III) and Cu(II) 2-ethil hexanoates used as metalorganic precursors were dissolved in suitable solvents prior to the impregnation experiments. Higher impregnation amounts were observed when hexane was used as solvent instead of xylene. Investigation of the best impregnation and thermal treatment condictions is reported. PVG+metallorganic precursors and PVG+oxides samples were characterized by Fourier Transform Infrared Spectroscopy (FTIR), Spatial Resolution Raman Spectroscopy, UV/Visible Absorption Spectroscopy, Thermal Analysis (TGA and DTA), Solid State Nuclear Magnetic Resonance (Si-CP-MAS-NMR) and Powder X-ray Diffractometry, in order to characterize the phase composition of confined oxides. Carboxylate groups of the molecular precursors interact with the sylanol groups present in the porous surface according to Diffuse Reflectance Infrared Spectra results. Different steps of the pyrolisis process were studied by UV/Visible Absorption Spectroscopy. The amount of confiend oxides after a single impregantion step ranged from 9,34 to 21,96 mg oxide/g PVG, as calculated on the basis of TGA curves. Higher oxide amounts may be confined throught sucessive coimpregnation and pyrolysis procedures. X-ray diffraction measurements evidenced the presence of Ce(IV) and Cu(II) oxides in the pores of Vycor Glass. However, a rather different behavior was observed for the samples containing Bismuth. A mixture of two Bi2O3 crystalline phases was detected after a single impregnation step. After ten successive impregnation/pyrolysis steps, Bi2O3 probably reacts with PVG, yelding orthorhombic Bi2SiO5, according to XRD patterns.

ASSUNTO(S)

espectroscopia de infravermelho semicondutores oxidos

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