Surface and Electronic Features of Fluorinated TiO₂ and Their Influence on the Photocatalytic Degradation of 1‑Methylnaphthalene

Surface fluorination improves the photocatalytic activity of TiO₂, and the influences of various features of fluorinated TiO₂ (TiO₂–F) have often been discussed in the literature. The present paper addresses the changes induced by surface fluorination on the morphological, structural, surface, and electronic features of TiO₂. In particular, X-ray diffraction, specific surface area analysis, and transmission and scanning electron microscopy give evidence that surface fluorination does not affect the structural properties and the morphology of TiO₂ nanoparticles. In contrast, fluorination induces changes of surface and electronic properties. Chemical and thermogravimetric analyses show that surface fluorination can reach up to 50% of original Ti–OH surface sites. The surface charge of TiO₂ turns more negative upon fluorination, as shown by a shift of the point of zero charge toward lower pH. Electronic properties are deeply characterized by combining diffuse reflectance, X-ray, and UV photoelectron spectroscopies, as well as time-resolved fluorescence spectroscopy, and photoelectrochemical measurements. Results show the presence of intra-band-gap energy states induced by the local interaction of chemisorbed fluorine atoms. Such energy levels are close to the valence band. The unique surface and electronic properties of TiO₂–F make it a promising material for the photocatalytic degradation of poorly soluble emerging pollutants such as 1-methylnaphtalene. In particular, TiO₂–F demonstrates faster degradation kinetics with respect to both the pristine material and TiO₂ P25 used as a benchmark standard.