Herein, a facial stratagem for the large-scale synthesis of NiO/C nanosheets used as magnetic adsorbents is proposed by using nanoscale coordination polymers (nanoCPs) as precursors. The NiO nanoparticles (NPs) scattered on the NiO/C nanosheets have an untrasmall size (similar to 3 nm) as well as uniform dispersion, since the Ni2+ ions are preassembled into the nanoCPs precursors by coordination bonds and transformed to NiO NPs in situ under the restriction of carbon layers. Thanks to the small size and spatially uniform distribution of NiO NPs, fully exposed carbon matrix containing part of graphene structures, and the high specific surface area of the special nanosheet structure, the magnetic NiO/C nanosheets have an a great breakthrough in the adsorption performance toward Congo Red (CR) among many reported NiO-based materials. The maximum adsorption capacity for CR is up to 2000 mg/g, and the adsorption kinetics and thermodynamics are also systematically studied. Moreover, the NiO/C nanosheets can be separated from water and reused simply by an external magnetic field. The NiO/C nanosheets with low cost and extraordinary adsorption ability have great potential in water pollution treatment area. (C) 2019 Elsevier Inc. All rights reserved.