Photocatalytic Decomposition of Alkylsiloxane Self-Assembled Monolayers on Titanium Oxide Surfaces

The photocatalytic decomposition of octadecyltrichlorosilane (OTS) based self-assembled monolayer formed on TiO 2 has been studied using atomic force microscopy(AFM), X-ray photoelectron spectroscopy (XPS), and contact angle analysis. The TiO 2 thin films were grown on Si(100) substrates by atomic layer deposition from titanium isopropoxide and water. Densely packed alkylsiloxane monolayers similar in quality to those on SiO 2 are formed on TiO 2 . It is found that the monolayers on TiO 2 are decomposed much faster than those on SiO 2 under UV irradiation of 254 nm in air. The OTS-based SAMs on TiO 2 are decomposed through the photocatalytic oxidation of the alkyl chains with a gradual and homogeneous reduction in chain length. After the complete photodecomposition of the OTS−SAMs, the siloxane headgroups remain on the TiO 2 surface. The observation indicates that the titanium oxide, a well-known photocatalyst for organic pollutant treatment, efficiently decomposes the alkylsiloxane monolayers under UV irradiation in air.