A new anatase phase of photoactive Ti1-2XNbXScXO2 (X = 0-0.2) solid solutions was directly formed as nanoparticles from precursor solutions of TiOSO4, NbCl5, and Sc(NO3)(3) under mild hydrothermal conditions at 180 degrees C for 5 h using the hydrolysis of urea. With the increase of the content of niobium and scandium from X = 0 to 0.2, the lattice parameters a(0) and c(0), the crystallite size, and the optical band gap of anatase gradually increased. Their photocatalytic activity and adsorptivity were evaluated separately by the measurement of the concentration of methylene blue (MB) remained in the solution in the dark or under UV-light irradiation. The anatase-type Ti1-2XNbXScXO2 (X = 0.05) showed approximately two times and three times as high photocatalytic activity as those of the hydrothermal anatase-type pure TiO2 and commercially available reference pure TiO2 (ST-01), respectively. The anatase phase of Ti1-2XNbXScXO2(X = 0-0.2) existed stably up to 900 degrees C during heat treatment in air. New rutile-type Ti1-2XNbXScXO2 solid solutions are formed through the phase transformation. The starting temperature of anatase-to-rutile phase transformation for Ti1-2XNbXScXO2 (X = 0-0.2) solid solutions was delayed but its completing temperature was accelerated. (c) 2007 Elsevier Ltd. All rights reserved.