The surface of TiO2 nanoparticles was modified by Samarium (Sm) and Gadolinium (Gd) doping to enhance their adsorption and photocatalytic performance. The undoped TiO2 and different (Sm or Gd)/Ti molar ratios of 0.9, 1.8 and 3.6 at.%, were prepared through a combined sol-gel milling method and sintered in two different temperatures of 550 and 700 degrees C. Scanning electron microscope (SEM) images of composite samples revealed a clear reduction in particle size compared to the undoped samples of the same temperature. Excellent adsorption and photodegradation of Congo red dye solution under ultraviolet (UV) irradiation were attained for Sm-TiO2 and Gd-TiO2 nanoparticles compared to the undoped samples sintered at the same temperature. The photocatalytic performance of composites was improved up to 1.8 at.% of Sm or Gd content. The results showed that the Gd-TiO2 composite nanoparticles had much. better performance compared to the Sm-TiO2 composite nanoparticles with the same molar ratio and the same sintering temperature. (C) 2017 Elsevier B.V. All rights reserved.