We prepared novel Fe3O4 magnetic nanoparticles (MNPs) modified with 3-aminopropyltriethoxysilane CAPS) and copolymers of acrylic acid (AA) and crotonic acid (CA). The MNPs were characterized by transmission electron microscopy, X-ray diffraction, infra-red spectra and thermogravimetric analysis. We explored the ability of the MNPs for removing heavy metal ions (Cd2+, Zn2+, Pb2+ and Cu2+) from aqueous solution. We investigated the adsorption capacity of Fe3O4@APS@AA-co-CA at different pH in solution and metal ion uptake capacity as a function of contact time and metal ion concentration. Moreover, adsorption isotherms, kinetics and thermodynamics were studied to understand the mechanism of the synthesized MNPs adsorbing metal ions. In addition, we evaluated the effect of background electrolytes on the adsorption. Furthermore, we explored desorption and reuse of MNPs. Fe3O4@APS@AA-co-CA MNPs are excellent for removal of heavy metal ions such as Cd2+, Zn2+, Pb2+ and Cu2+ from aqueous solution. Furthermore, the MNPs could efficiently remove the metal ions with high maximum adsorption capacity at pH 5.5 and could be used as a reusable adsorbent with convenient conditions. (c) 2011 Elsevier B.V. All rights reserved.