Operando FTIR study of the photocatalytic oxidation of acetone in air over TiO2–ZrO2 thin films

Operando FTIR spectroscopy has been used to study the photocatalytic oxidation of acetone vapors over semiconductors films containing TiO2 and ZrO2. Preparation of these coatings was carried out by dipping a silicon wafer in stable sols containing particles of TiO2, Ti1−xZrxO2, or a mixture of ZrO2 and TiO2. These differences in chemical composition and phase homogeneity were selected in order to determine their effect on the photocatalytic performance. A transmission cell specifically designed for in situ studies of photocatalytic coatings was utilized for the FTIR experiments under reaction conditions. In contrast with investigations with powdered photocatalysts, the use of thin films guarantees that the whole semiconductor is irradiated, and for that reason purely photochemical reactions are monitored. Acetone adsorption takes place molecularly and is higher on the Ti1−xZrxO2 coating. This fact is very likely related to the higher specific surface of the samples containing Zr. However, the maximum photocatalytic rate for acetone degradation corresponds to the films composed by a binary mixture of TiO2 and ZrO2. On the other hand, remarkable differences on the type and concentration of intermediates appearing as a result of the photocatalytic oxidation of acetone are found for the coatings studied. A simple kinetic model was applied to analyze the evolution of both gas phase and surface species. The parameters obtained indicate that each specific surface process is affected in a different way by the variation in the composition of the photoactive films.