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In this work, we report a room-temperature approach to synthesizing reduced graphene oxide/NiO (RGO/NiO) nanocomposites. The chemical structure of RGO/NiO nanocomposites were investigated by Transmission Electron Microscope (TEM), X-ray photoelectron spectroscopy (XPS), and X-ray power diffraction (XRD). It is shown by the experiment that the RGO/NiO nanocomposites have strong capacity to absorb the hexavalent chromium ion (Cr (VI)), the maximum adsorption capacity of Cr (VI) on RGO/NiO nanocomposites at pH = 4 and T = 25 °C can reach 198 mg g −1 , higher than any other currently reported. The adsorption kinetic data were well described by a pseudo-second-order model. Both Freundlich and Langmuir isotherm models were applied to the experimental data analysis, and the latter proved to be a better fit. The pH value markedly affected the adsorption behavior of RGO/NiO nanocomposites, but the effect of temperature was insignificant. The probable mechanism of synergistic adsorption of Cr (VI) ions was considered. These results suggest that RGO/NiO nanocomposites have the potential to be applied in industrial wastewater treatment. [ABSTRACT FROM AUTHOR]