ATR-IR spectroscopy was used to study the sorption of uranyl ions (10(-4) M) onto titanium oxide (mixture of rutile and anatase). A circulation setup, filled with a solution in D2O, allowed recording of the evolution of the antisyminetric O=U=O stretching of uranyl species onto titanium oxide particles deposited oil the ATR crystal. The band centered at 915 cm(-1) has been decomposed in two Gaussian peaks at 920 and 905 cm-1. From these values, and the observation that the ratio of the areas of the two peaks vs pH was constant, we have proposed that uranyl sorption on titanium oxide in the pH range 4-7 leads to the formation of one surface complex where uranium atoms have two different chemical environments. A trimer surface complex linked by two uranium atoms to the titanium oxide Surface would be consistent with this interpretation. (C) 2008 Elsevier Inc. All rights reserved.