Interactions of aminosilane with alumina and silica substrates deposited from nonaqueous and aqueous media

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Abstract
N-15 (Nitrogen-15) NMR studies of the widely-used coupling agent 3-aminopropyltriethoxysilane (APS) deposited onto native-oxide alumina and silica in submonolayers from nonaqueous and aqueous solutions reveal at least four different APS nitrogen environments. When APS is deposited on alumina from the nonaqueous solvents IPA (isopropanol) and NMP (N-methylpyrrolidone), three nitrogen environments, which are believed to be the amine, 'closed form' and unique form, are present. However, when APS is deposited on alumina from water, only two nitrogen environments, which are believed to be the amine cation and unique form, are seen. When aqueous APS is deposited on silica, the amine, amine cation and closed form are all present together, but low sensitivity makes it difficult to detect the unique form, if present. The unique nitrogen environment shows a nitrogen that appears to be a rigid and protonated form with considerable electronic deshielding relative to the amine/amine cation, possibly from an oxygen bon...

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