Abstract:
The interaction of (3,3,3-trifluoropropyl)trimethoxysilane (FPTS), or CF₃CH₂CH₂Si(OCH₃)(3), with TiO₂(110) has been studied using temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), and static secondary ion spectrometry (SSIMS). The FPTS dissociatively adsorbed on the TiO₂(110), forming adsorbed CF₃CH₂CH₂SiOCH₃ and -OCH₃ groups. An isotopically (O-18) enriched surface was used to show that the CF₃CH₂CH₂SiOCH₃ species was bound to the surface via two Si-O(surface) bonds, by using SSIMS to identify (SiO)-O-18 bond formation. The two -OCH₃ groups eliminated from the FPTS were bound to surface Ti4+ sites. When no surface hydroxyls were present, the -OCH₃ ligands, whether bound to Ti4+ or Si, decomposed at similar to 550-600 K to form methane, formaldehyde, and methanol gases. In the presence of water, the -OCH₃ bound to Ti4+ sites combined with the surface hydroxyls and desorbed as methanol at similar to 300K. The CF3CH2CH2-ligand decomposed at similar to 620 K via two elimination pathways. Either the H was eliminated from the beta-carbon to form CF3CH=CH2 gas or the CF3 group was eliminated to release CH2-CH2 gas. This methoxysilane was more reactive with TiO₂(110) than several ethoxysilanes previously studied.

Addresses:
Campbell CT, Univ Washington, Dept Chem, Seattle, WA 98195 USA.
Univ Washington, Dept Chem, Seattle, WA 98195 USA.
Pacific NW Natl Lab, Environm Mol Sci Lab, Richland, WA 99352 USA.

Publisher:
AMER CHEMICAL SOC, WASHINGTON

IDS Number:
ZU021

ISSN:
1089-5647