Graphene oxide (GO) supported uniform magnetite nanoparticle composites (M-GO) were prepared via in situ chemical precipitation method. The reaction mechanisms between M-GO and U(VI) under anoxic conditions were clarified based on macroscopic, spectroscopic, and theoretical techniques. Incorporation of magnetite nanoparticle into GO matrix facilitated removal rate and reduction of U(VI) to U(IV), as indicated by the kinetics model. According to XPS and XANES analysis, high efficient removal of U(VI) by M-GO was attributed to the abundant oxygen-containing groups of GO and reduction potential of magnetite dispersed on the GO surface uniformly. Based on DFT calculation, the high binding energy of [GO-O center dot center dot center dot UO2](+) (23.5 kcal/mol) and [GO-COO center dot center dot center dot UO2](+) (51.1 kcal/mol) (51.1 kcal/mol) revealed that the hydroxyl and carboxyl groups were responsible for the high removal of U(VI) on M-GO, which further facilitated the reduction of U(VI) to U(IV) due to the vicinity of structural Fe(II) of M-GO. (C) 2017 Elsevier B.V. All rights reserved.