Organofunctionalization of TiO2(110):: (3,3,3-trifluoropropyl)trimethoxysilane adsorption

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.