Single-layered graphene oxide (GO) prepared by the Hummers method was used to adsorb U(VI) ions from aqueous solutions. The U(VI) sorption was studied as a function of solution pH, ionic strength, and initial concentration of U(VI) using a batch method in air. It is found that the sorption is rapid, strongly dependent on pH, attaining a plateau at pH 4.0-7.5, and independent of the ionic strength. This suggests the formation of inner-sphere surface complexes of U(VI) on GO. The maximum sorption capacity of GO for U(VI) was evaluated to be 299 mg/g at pH 4.0, ranking it among the most effective sorbents reported for U(VI) so far. The abundant oxygen-containing functional groups of GO were demonstrated to play crucial roles in the sorption. Using the distribution coefficients obtained at different temperatures, thermodynamic parameters were also calculated, showing that the sorption is endothermic and spontaneous. GO could be a promising sorbent material applied in the environmental cleanup of uranium pollution and the enrichment of uranium from large volumes of solution. (C) 2012 Elsevier B.V. All rights reserved.