אסיף מאגר המחקר החקלאי

Determination of activation energy of entrance into micropores: Quenching of the fluorescence of pyrene-doped SiO2 sol-gel matrices by oxygen

Year:

1994

Source of publication :

Authors :

Volume :

6

Co-Authors:

Samuel, J., Institute of Chemistry, Hebrew University of Jerusalem, Jerusalem 91904, Israel
Polevaya, Y., Institute of Chemistry, Hebrew University of Jerusalem, Jerusalem 91904, Israel
Ottolenghi, M., Institute of Chemistry, Hebrew University of Jerusalem, Jerusalem 91904, Israel
Avnir, D., Institute of Chemistry, Hebrew University of Jerusalem, Jerusalem 91904, Israel

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Abstract:

Pyrene-doped xerogels were prepared by the sol-gel method from tetramethoxysilane (TMOS)/ water/methanol mixtures. N2 and CO2 adsorption isotherms were determined for the xerogels. The pyrene in acid-catalyzed low TMOS/water ratio xerogels was found to be nonleachable. Yet the excited-state dopant was observed to be completely reactive to O2 quenching in all samples. This finding is of general importance in relation to applications of sol-gel materials as reactive transparent supports for organic molecules. Penetration rates of oxygen into samples were determined by following the drop in pyrene fluorescence over time, after exposure of a precooled sample to the gas. From this data the activation energy for the penetration of oxygen into a xerogel was assessed and found to be 18 ± 1 kJ/mol. This long-range diffusion value is significantly higher than the activation energy for short-range diffusion of oxygen found previously on mesoporous silica. © 1994 American Chemical Society.

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