In this study, in order to overcome some common problems related to the application of nanoscale zerovalent iron (NZVI) in nitrate removal from drinking water, SiO2-FeOOH-Fe core-shell was synthesized. NZVI was immobilized on SiO2-FeOOH cores using reduction method with or without the presence of nitrogen gas. Nanostructures were characterized by FTIR, XRD, PSA, and SEM. The experiments revealed that using nitrogen gas leads to uniformity of size distribution and reduction of nanostructure size from 81 to 52 nm. Effects of different parameters such as amount of NZVI loading, pH, initial nitrate concentration, amount of nano SiO2-FeOOH-Fe core-shell, contact time, and sonication time were investigated. The NZVIs loading plays a significant role in nitrate removal. Actually, by doubling NZVI loading, removal of nitrate increases from 69% to 86%. The results show that nitrate removal increases with decrement of pH and increment of the rest of the parameters. The percentage removal of nitrate was 99.84% regarding the optimum conditions of pH 3, initial nitrate concentration of 64 mg/L, two-fold loading of Fe in nanostructures, sonication time of 3 min, and contact time of 120 min. (C) 2014 Elsevier B.V. All rights reserved.