Photodecomposition of a Langmuir−Blodgett Film of Stearic Acid on TiO 2 Film Observed by in Situ Atomic Force Microscopy and FT-IR

We have probed the TiO 2 -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 TiO 2 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 TiO 2 film and LB film disorganization phenomenon during the photodegradation process.