Effect of TiO2 modification with fluorine on the physicochemical properties and activity in the photocatalytic oxidation of pollutants in air under UV irradiation

The influence of the modification of the TiO₂ surface with F^? ions on the physicochemical properties of the catalysts and efficiency in the photooxidation of gaseous molecules under atmospheric conditions and under UV irradiation was studied by IR spectroscopy. The fluorine-containing samples adsorb more water molecules than unmodified TiO₂. The amount of adsorbed water increases with increasing content of surface fluoride ions. The fluorination of the TiO₂ surface first leads to the substitution of the terminal OH groups by F^? ions and to an increase in acidity of the bridging acidic OH groups remained on the surface. The modification also results in the structural rearrangement of the surface involving defective and surface Ti⁴⁺ sites. Fluorine modification increases the activity of TiO₂ in the photocatalytic oxidation of ethanol, acetaldehyde, acetic acid, and acetone. At the same time, benzene and H₂S are oxidized more rapidly on unmodified TiO₂. The presence of fluorine on the TiO₂ surface exerts almost no effect on the oxidation rate of chlorine-containing substrates C₃H₇Cl and C₂H₄Cl₂.