Enhanced photo-catalytic activity of TiO₂ films by removal of surface carbon impurities; the role of water vapor

Highlights: • Changes of TiO₂ surfaces during photo-catalysis were studied by XPS. • Role of humidity for photo-catalytic decomposition of acetaldehyde was studied. • Competitive adsorption of water and acetaldehyde resulted in the reduction of reaction rate. • Water vapor facilitated the photo-catalytic removal of carbon impurities from TiO₂. - Abstract: We have studied the photo-catalytic degradation of acetaldehyde over the surface of TiO₂ films under UV light (365 nm) irradiation both at dry and humid air conditions using a high vacuum chamber equipped with on-line gas-chromatography as a batch-type reactor. Changes of TiO₂ surfaces upon the photo-catalysis experiments were studied by X-ray photoelectron spectroscopy. The competitive adsorption of water and acetaldehyde resulted in the reduction of reaction rate of photo-catalytic degradation of acetaldehyde under the UV light irradiation. The photo-catalytic reaction rate of TiO₂ films towards acetaldehyde mineralization increased when the photo-catalysis experiments were performed repeatedly and it was much more pronounced under humid conditions. Our XPS analysis revealed that carbon impurities on the surface of TiO₂ films were removed by UV-light driven photo-catalytic mineralization under humid conditions. Water vapor facilitated the photo-catalytic removal of carbon impurities from TiO₂ surface generating additional active sites of TiO₂ which resulted in the enhanced photo-catalytic activity of TiO₂ films.