A novel adsorbent Fe3O4/Ni/NixB nanocomposite was synthesized and used for the adsorption of copper. Moreover, natural adsorbents carob and grape seeds were used for this purpose. The surfaces and the elemental compositions of the adsorbents were characterized by SEM-EDX. The zero point charges of pH of Fe3O4/Ni/NixB nanocomposite, carob, and grape seeds were found as 8.4, 6.0, and 5.6, respectively. The Langmuir, Freundlich, and Dubinin-Radushkevich isotherm models were used for the identification of the mechanism of the adsorption. The adsorptions of Cu(II) on the three adsorbents were well fitted to the Langmuir isotherm. The maximum adsorption capacities obtained from the Langmuir isotherm were 106.4, 15.6, and 15.9 mg/g for Fe3O4/Ni/NixB nanocomposite, carob, and grape seeds, respectively. The equilibrium data of the isotherm models indicated that the Cu(II) adsorptions were favorable for all the adsorbents. The pseudo-first-order, pseudo-second-order, and Weber Morris intraparticle diffusion models were used for the validation of the adsorption kinetics. The kinetic data were better fitted to the pseudo-second-order kinetic model for all the adsorbents. Fe3O4/Ni/NixB nanocomposite, carob, and grape seeds are promising adsorbents for the adsorption of Cu(II) from water samples. The removal efficiencies were all about 100%.