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

Abstract

The photocatalytic decomposition of octadecyltrichlorosilane (OTS) based self-assembled monolayer formed on TiO2 has been studied using atomic force microscopy(AFM), X-ray photoelectron spectroscopy (XPS), and contact angle analysis. The TiO2 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 SiO2 are formed on TiO2. It is found that the monolayers on TiO2 are decomposed much faster than those on SiO2 under UV irradiation of 254 nm in air. The OTS-based SAMs on TiO2 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 TiO2 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.

Electrochemical Monitoring of the Formation of Self Organized Monolayers: Octadecylphosphonic Acid on Anodically Grown Titanium Dioxide

“…Its intensity is slightly increased after UV exposure and the peak is shifted towards higher binding energies (132.9 eV). This implies a change of the binding state due to the absence of the carbon tail group as discussed also in previous works 1), 2), 28) . In contrast, the carbon peak shows a high intensity before UV irradiation which is indicating a relatively high amount of carbon on the surface and hence the present of a dense monolayer.…”

Photocatalytic oxidation of the organic monolayers on TiO2 surface investigated by in-situ sum frequency generation spectroscopy

“…In contrast, Lee et al studied the UV-induced decomposition of the OTS monolayer on the TiO 2 surface and demonstrated that a homogeneous reduction of the film thickness, implying that the immobilized OTS molecules were oxidized from the terminal CH 3 group to the other end of the molecule without formation of the ordered domains during the oxidation process. 7 In the present study, vibrational SFG spectroscopy was employed to study the UV-induced photocatalytic oxidation of two types of well-ordered monolayers on the TiO 2 surface. By monitoring the ordering of the monolayers during the photocatalytic oxidation, we could reveal the different reaction mechanisms for these monolayers; namely, a physisorbed AA monolayer maintains its ordered structure through the lateral diffusion, and a chemisorbed monolayer becomes more disordered during the reaction due to the limited mobility on the substrate surface.…”

“…[1][2][3] While most of the previous studies focused on small volatile molecules, there were only a very few studies on the photocatalytic reaction of long-chain organic molecules in a monolayer with well-defined structure. [5][6][7][8] As a model system for the photocatalytic reaction, the monolayers of long-chain organic molecules are both of practical and fundamental interests. 9 Understanding the photo-induced oxidation mechanism of organic thin-films is crucial for developing novel functional materials for environmental protection.…”

Preparation and gaseous photocatalytic activity of smooth potassium dititanate film

“…The water contact angle is sensitive to the type of organic substance on the material surface. It can affect indirectly the photocatalytic performance of film with OTS-based SAMs [18]. Generally, SAMs molecules link to the active site on film and decompose under irradiation.…”