Photodecomposition of a Langmuir−Blodgett Film of Stearic Acid on TiO₂ Film Observed by in Situ Atomic Force Microscopy and FT-IR

Abstract

We have probed the TiO2-mediated photomineralization of Langmuir−Blodgett (LB) films of stearic acid via atomic force microscopy (AFM) and FT-IR. In situ AFM images revealed that at the submicrometer level the photodecomposition process of stearic acid molecules on a polycrystalline anatase TiO2 film is inhomogeneous, with the various reaction initiation centers or nucleation regions being randomly distributed throughout the photocatalyst surface. Furthermore, parallel FT-IR results showed that the reaction follows pseudo-first-order kinetics. To rationalize the observed random LB film photoetching and buckling behavior, we invoked a simple reaction model that incorporates the reactivity of the TiO2 film and LB film disorganization phenomenon during the photodegradation process.

Preparation of TiO2 Thin Films Using Octadecylamine Langmuir-Blodgett Films and Evaluation of Their Photocatalytic Activity

“…The decomposition rate for the TiO 2 fi lm on irradiation with UV light was faster than that for a bare quartz plate. The photodecomposition of SA proceeded according to pseudo-first-order reaction kinetics, as previously observed for TiO 2 films deposited by a dipcoating technique 15 . Among the TiO 2 fi lms examined, the fi lms heat-treated at higher temperatures had lower photocatalytic activity.…”

Highly bioactive silver and silver/titania composite films grown by chemical vapour deposition

“…This has been discussed in various papers describing sol-gel Ag/TiO 2 films for which the amount of Ag is reported as critical [23,56,57] i.e. the photoactiv ity decreases above an optimum Ag level.…”

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

“…Fujishima and Hashimoto investigated the UV-induced oxidation of the LB-multilayer of stearic acid on the TiO 2 surface and reported that many island domain structures were formed during the photocatalytic decomposition process. 5 This indicates that the unoxidized fatty acid molecules are reconstructed to form stable domains on the TiO 2 surface during the photocatalytic process. 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.…”

“…[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.…”