BACKGROUND Magnetic nanoparticles (MNPs) have recently gained importance for the treatment of water contaminated with heavy metal. However, conventional chemical synthesis of MNPs involves production of hazardous by-products. In the present study, starch (MNPST) and casein (MNPCS) functionalized MNPs were prepared via green synthesis and compared efficiency with bare MNPs. RESULTS Here, we prepared MNP, MNPST, and MNPCS with average sizes of 7.1, 9.0, and 9.7 nm, respectively. We conducted an adsorption study under optimized conditions such as temperature, pH, etc., and observed that the removal of lead(II) (Pb(II)) and chromium(VI) (Cr(IV)) follows the pseudo-second-order kinetic model for all MNPs. The experimental data fits better with Langmuir isotherm, and the maximal adsorption capacity (Q(m)) of MNPST was highest with 120.48 mg g(-1) for Pb(II) and 99.0 mg g(-1) for Cr(VI) compared to MNPCS [101.11 mg g(-1) for Pb(II) and 87.81 mg g(-1) for Cr(VI)] and MNP [74.07 mg g(-1) for Pb(II) and 68.96 mg g(-1) for Cr(VI)]. Furthermore, we also demonstrated that better regeneration capacity of MNPST was only 8.0% reduction of its removal efficiency, followed by MNPCS (12.1%) and MNP (14.8%). CONCLUSION Therefore, our findings revealed that starch capped magnetite nano-adsorbent could be used for the efficient removal of heavy metal from water with excellent regeneration efficiency. (c) 2019 Society of Chemical Industry