A fluorine doped TiO₂ sol (F-TiO₂) was prepared by a modified precipitation-sol-hydrothermal crystallization method using TiCl₄ as precursor．The influence of F doping, hydrothermal treating temperature and time, pH values of medium on the morphology and crystallization was studied. The structure of as-prepared F-TiO₂ sol was characterized by XRD, UV-Vis-DRS, TEM, TG-DTA, FTIR, XPS, and adsorption capacity determination and surface acidity determination. It was confirmed by XRD that F-TiO₂ sol particles had anatase crystalline structure; moreover, the addition of fluorine could decrease the temperature and shorten the time of process of hydrothermal crystallization, and improve the crystallization of particle significantly. The TEM images indicated that F-TiO₂ particles in sol were spherical, and the average particle size was ca. 6.5 nm. The XPS results showed that fluorine atoms were adopted by TiO₂ sol particles with two forms. One was physically adsorbed on the surface of TiO₂, and the other was embedded into TiO₂ crystal lattice. The experiments of the determination on interfacial adsorption capacity, surface acidity and the photocatalytic activity found that F-TiO₂ sol had stronger surface acidity, higher adsorption capability and good photocatalytic activity for decomposition of rhodamine B than pure TiO₂ sol and P25 TiO₂. Furthermore, the promotion mechanism of fluorine on the photocatalytic activities and structure of TiO₂ was discussed based on the separation efficiency theory of charge carrier.

Key words: precipitation-sol-hydrothermal method, preparation, characterization, fluorine, titanium dioxide sol