A magnetic KMnO ₄ -treated graphene-oxide-based nanocomposite, Fe ₃ O ₄ @GO/MnO _x , was synthesized through a facile hydrothermal technique. The properties of the Fe ₃ O ₄ @GO/MnO _x nanocomposite were characterized by SEM, XRD and FTIR. Batch experiments showed that the maximum adsorption capacity calculated by the Langmuir model for Cu ²⁺ was 62.65 mg g ⁻¹ at T = 303.15 K. Kinetics and XPS analysis also revealed that the mechanism of Cu ²⁺ removal was mainly a chemical adsorption process involving both the MnO _x particles and oxygen functional groups. The prepared Fe ₃ O ₄ @GO/MnO _x was found to be an ideal adsorbent for the removal of Cu ²⁺ ions due to the MnO _x particle coating, and was easily separated using a magnetic field after utilization. Reusability studies imply that Fe ₃ O ₄ @GO/MnO _x is a suitable material for heavy metal ion removal from aqueous solutions in real applications.