Determination of the Orientation of Adsorbed Pyridine and γ-MPS on Alumina Surface by Photoacoustic FT-IR Spectroscopy

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Abstract
Fourier transform infrared photoacoustic spectroscopy has been applied to determine the structure and orientation of pyridine and γ-Metacryl-oxypropyltriethoxysilane (γ-MPS) on γ-Al2O3 surface. Adsorption of pyridine on activated γ-Al2O3 leads to formation of a pyridinium ion (pyN+-H) and pyridine N-oxide. The orientation of pyridinium ion on the alumina surface is random, whereas the pyridine N-oxide is parallel with respect to the surface. The adsorption of oligomers of γ-MPS gives parallel layers on the alumina surface. At low γ-MPS surface coverage, the carbonyl groups interact with the surface hydroxyl groups. Increasing surface coverage leads to an excess of the free C=O species.