A solvothermal method combining a calcination process was conducted to synthesize Fe3O4@NiO core–shell hierarchical nanostructures. First, Fe3O4 microspheres were synthesized through a solvothermal method by using ethylene glycol as solvent. Second, Fe3O4@Ni(OH)2 core–shell hierarchical nanostructures were prepared through an in situ growing procedure. Third, Fe3O4@NiO core–shell hierarchical nanostructures were obtained from the Fe3O4@Ni(OH)2 precursors by a simple calcination procedure. The results showed that the Fe3O4 core was about 250 nm in diameter and the NiO shell was around 30 nm in thickness. The Fe3O4@NiO core–shell nanostructures were used as a magnetically separable adsorbent for the removal of Congo red (CR) dye from aueous solution, which exhibited a high adsorption capacity of ~128.9 mg g−1. Moreover, the Fe3O4@NiO core–shell nanostructures displayed a superior catalytic property for the epoxidation of styrene with an extremely high selectivity (100%), conversion (99%) and yield (99%). Such Fe3O4@NiO catalyst could be conveniently recycled from the reaction system by using a magnet and without any noticeable catalytic deactivation even after five cycles. The results indicate that the as-prepared core–shell materials can be used as a recyclable catalyst for the epoxidation of styrene.