We herein report a direct and facil sol–gel method for the preparation of porous silicon dioxide nanoparticles using dissolved silica gel and nitric acid. We prepared SiO nanoparticles at three diferent pH values: 6, 7, and 8. The washed and dried products were calcined at 800 °C for 2 h. The average crystallite size of the prepared SiO 2 nanoparticles was ca. 37.7 nm. The products were characterized by using FT-IR, TEM, FE-SEM, and XRD analyses. The as-prepared SiO showed high adsorption capacities; ca. 32.2 mg g −1 and 42.2 mg g −1 2 , for the removal of Pb(II) and Cd(II) ions, respectively, from aqueous media. The adsorption data followed well the pseudo-second-order and Langmuir isotherm models. The determined thermodynamic parameters: ΔG° (from − 5.026 to − 5.180 kJ/mol for Cd(II) ion adsorption and from − 5.528 to − 5.732 kJ/mol for Pb(II) ion adsorption) and ΔH° (− 7.00 and − 7.607 kJ/mol, respectively), indicate the spontaneous, exothermic, and physisorption nature of the adsorption process. Besides, the excellent reusability and adsorption capacity for SiO 2 nanoparticles revealed their good eiciency for the removal of Pb(II) and Cd(II) ions from aqueous media. 2 nanoparticles