Size dependent photocatalytic activity of hydrothermally crystallized titania nanoparticles on poorly adsorbing phenol in absence and presence of fluoride ion

The photocatalytic degradation of phenol has been performed by adopting nanosized titanium dioxide, prepared with the sol–gel method, both in presence and absence of fluoride ions. Several catalyst treatments, that is hydrothermal heat treatment and calcination, have been applied in order to increase the crystallinity of the particles. A close relationship was found between the rate of phenol disappearance and the particle size, with an efficiency that becomes maximum when the combination of large particle size (7.8 nm) and surficial sites covered by fluoride is fulfilled. Intermediates profiles have been also evaluated, in order to verify if the surficial process occurring in the diverse materials still remains the same. It is accomplished in the case of the fluorinated titania, where both the rate of disappearance and the intermediates formation closely resemble those seen on Degussa P25, while a different formation ratio between catechol and hydroquinone was observed in the case of naked titania.