A La-doped TiO2(La/TiO2) photocatalyst with optimum La/Ti molar ratio of 1.25% is prepared by ultrasound-assisted sol-gel method, followed by supercritical drying in ethanol fluid. During liquid phase photocatalytic degradation of phenol, the as-prepared La/TiO2 exhibits higher activity than the La/TiO2 obtained without ultrasonication. Meanwhile, the La/TiO2 obtained via supercritical treatment is more active than either the undoped TiO2 obtained under supercritical conditions or the La/TiO2 obtained via direct calcination instead of supercritical treatment. Based on various characterizations, the promoting effects of ultrasonication, supercritical treatment, and La-modification are discussed by considering the enhanced particle dispersion, the higher crystallization degree of anatase and the increase of the surface oxygen vacancies and/or defects, which facilitates the adsorption of phenol molecules and also inhibits the recombination between photoelectrons and holes, resulting in the higher quantum efficiency of photocatalysis. Meanwhile, the ultrasonication and supercritical treatment also strengthen the interaction between the La-dopants and the TiO2, which could enhance the light absorbance and thus, increase the photocatalytic activity. (c) 2007 Elsevier B.V. All rights reserved.