Composites of TiO2 and Ag nanoparticles were used to study photodegradation of aqueous Rhodamine B under natural sunlight exposure. The addition of Ag powder resulted in a similar to 45% increase of the photocatalytic activity of TiO2 after 30 mm, which is attributed to the suppression of the photo-generated electron-hole pair recombination. Electrokinetic studies on TiO2, Ag, and TiO2/Ag aqueous solutions address the question of how the electron transfer occurs. It was found that the TiO2 and TiO2/Ag zeta potential versus pH behavior is virtually identical which suggests that the Ag particles are encapsulated by the TiO2 particles, allowing the electron transfer across the 'static' semiconductor-metal interface. (C) 2013 Elsevier Ltd. All rights reserved.